Group Title: kinetic study of the chlorination of unbleached kraft pulp
Title: A Kinetic study of the chlorination of unbleached kraft pulp
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Title: A Kinetic study of the chlorination of unbleached kraft pulp
Physical Description: viii, 148, 1 leaves : illus. ; 28 cm.
Language: English
Creator: Chapnerkar, Vasant Dinkarrao, 1932-
Publisher: University of Florida
Place of Publication: Gainesville, Fla
Publication Date: 1961
Copyright Date: 1961
 Subjects
Subject: Wood-pulp   ( lcsh )
Chlorination   ( lcsh )
Chemical Engineering thesis Ph. D
Dissertations, Academic -- Chemical Engineering -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: leaves 146-147.
Additional Physical Form: Also available on World Wide Web
General Note: Manuscript copy.
General Note: Thesis - University of FLorida.
General Note: Vita.
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Bibliographic ID: UF00097979
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000538007
oclc - 13026308
notis - ACW1213

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A KINETIC STUDY OF THE CHLORINATION

OF UNBLEACHED KRAFT PULP












By

VASANT DINKARRAO CHAPNERKAR


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY










UNIVERSITY OF FLORIDA
January, 1961














ACKNOWLEDGMENT


I wish to acknowledge my indebtedness to Dr.

William J. Nolan, Chairman of my Advisory Committee, to

whom I owe more than I can express for his stimulating

instruction, patient advice, academic and personal, with-

out which I couldn't have accomplished this piece of

work.

Sincere thanks are extended to Dr. A. J. Teller,

Dr. M. Tyner, Dr. P. M. Downey and Dr. D. E. South, mem-

bers of my Committee, for their wholehearted cooperation,

advice and assistance during the course of this research.

I would also like to thank very sincerely the Pulp

and Paper Laboratory, the Department of Chemical Engi-

neering and Dr. Felix Kiefer for all the help they have

extended to me during my stay at the University of Florida.

Deep appreciation and gratitude are extended to Mrs.

Ruth Pierce for typing the Dissertation and to the Graduate

School for answering all my queries.

I am deeply indebted to my wife, Sushila. Her

patience, assistance and support were a constant source

of encouragement during this study.















TABLE OF CONTENTS


ACKNOWLEDGMENT . . . . .

LIST OF TABLES . . . . . .

LIST OF FIGURES . . . . .

INTRODUCTION . . . . . .

Chapter


Page

. . ii

. . iv

. . vi

. . . . 1


I. LITERATURE REVIEW. . . . .

II. THEORETICAL CONSIDERATIONS . .

III. CHLORINATION EQUIPMENT . .

IV. METHOD OF PROCEDURE . . . .

V. DISCUSSION OF THE DATA AND RESULTS

SUMMARY AND CONCLUSIONS . . . . . .

TABLES . . . . . . . . .

FIGURES . . . . . . . . .

BIBLIOGRAPHY . . . . . . .

BIOGRAPHICAL ITEMS . . . . . .


. . 6

. . 14

. . 23

. . 32

. . 46

. . 83

. . 87

. . 108

. . 146

. . 148














LIST OF TABLES


Table Page

1. Effect of Chlorination Time on Chlorine Con-
sumption. . . .. . . . . 87

2. Effect of Chlorination Time on Chlorine Con-
sumption. . . . . . . . . . 88

3. Effect of Chlorination Time on Chlorine Con-
sumption . . . . . . . . . 89

4. Effect of Chlorine Concentration at 3 per cent
Consistency on Chlorine Consumption . . 90

5. Effect of Chlorination Time on Lignin Removal
and Degree of Polymerization Number of
Cellulose ... .......... . . 91

6. Effect of Chlorination Time on Lignin Removal
and Degree of Polymerization Number of
Cellulose . . . . . . . . 92

7. Effect of Chlorination Time on Lignin Removal
and Degree of Polymerization Number of
Cellulose . . . . . . . . . 93

8. Effect of Chlorine Concentration at 3 per cent
Consistency on Lignin Removal and Degree of
Polymerization Number of Cellulose. . . . 94

9. Amounts of Chlorine Consumed per gram of Total
Lignin Removed . . . ... ....... 95

10. Amounts of Chlorine Consumed by Substitution
and by Oxidation per Gram of Total Lignin
Removed .... . . . . . . . 96

11. Residual Chlorine Concentration in the Liquor 97

12. Effect of Chlorination Time on Lignin Removal
and Degree of Polymerization Number of the
Kraft Pulp. . . .. . . . . . .. 98











13. Effect of Chlorination Time on Lignin Removal
and Degree of Polymerization Number of the
Kraft Pulp. . . . . . . . .. 99

14. Effect of Chlorination Time on Lignin Removal
and Degree of Polymerization Number of the
Kraft Pulp .. ... . . . .... . 100

15. Effect of Chlorination Time on Lignin Removal
and Degree of Polymerization Number of the
Kraft Pulp. . . . . . . ... 101

16. Effect of Chlorination Time on Lignin Removal
and Degree of Polymerization Number of the
Kraft Pulp. .. . . . . . . . 102

17. Effect of Chlorination Time on Lignin Removal
and Degree of Polymerization Number of the
Kraft Pulp. . . . . . . . 103

18. Effect of Chlorination Time on Lignin Removal
From Pine . . . . . . . . .. 104

19. Effect of Chlorination Time on Lignin Removal
From Cold Soda Pulp . . . . . . 105

20. Effect of Chlorination Time on Lignin Removal
From Cold Soda Pulp ............. 106

21. Effect of Chlorination Time on Lignin Removal
From Cold Soda Pulp . . . . 107


Table


Page













LIST OF FIGURES


Figure Page

1. The Distribution of Chlorine among Elementary
Chlorine, Ilypochlorous Acid and IIypochlorite
Ion in a Solution of Chlorine in Water at
Various pHs . . . . . . . .. 17

2. Apparatus for Addition of Chlorine Water . . 25

3. Assembly for the Analysis of Liquor Samples. 27

4. Chlorination Tank. . . . . . . . 29

5. Solubility of Chlorine in Water. . . 35

6. Percent Residual Chlorine at Various Con-
sistencies versus Time . . . . . 108

7. Chlorine Consumed by Substitution and by
Oxidation versus Time for Kraft Pulp . .. 109

8. Percent Chlorine Consumed by Substitution
versus Time for Kraft Pulp at Various
Consistencies. ... . . . . . 110

9. Percent of Original Lignin Removed by Chlo-
rination versus Time for Kraft Pulp under
Various Conditions . . . . . .. . 111

10. Percent of Original Lignin Removed by Chlo-
rination and Alk. Extn. versus Time for
Kraft Pulp .................. 112

11. D. P. No. after Chlorination versus Time
for Kraft Pulp ......... . .. 113

12. D. P. No. after Chlorination and Alk, Extn.
versus Time for Kraft Pulp . . . . 114

13. Relation between Maximum Chlorine Applica-
tion versus Consistency at 760 mm Hlg and
Various Temperatures . . . . . . 115







Figure Page

14. Relation between Lignin Removal and Con-
sistency at 760 mm Hg and Various Tem-
peratures. ...... . . . . .... 116

15. Percent of Original Lignin Removed by Chlo-
rination versus Time for Kraft Pulp at 770F. 117

16. Percent of Original Lignin Removed by Chlo-
rination and Alk. Extn. for Kraft Pulp
at 770F. . . . . . . . .. 118

17. Percent of Original Lignin Removed from Kraft
Pulp versus Time at 0.57 g/l C12 Cone . .. 119

18. D. P. No. after Chlorination versus Time for
Kraft Pulp at 770F . . .. . 120

19. D. P. No. after Chlorination and Alk. Extn.
versus Time for Kraft Pulp at 77F . . .. 121

20, D. P. No. after Chlorination versus Time for
Kraft Pulp at 0.57 g/l C12 Cone. . ... 122

21. D. P. No. after Chlorination and Alk. Extn.
versus Time for Kraft Pulp at 0.57 g/l C12
Cone. . . . . . . . . . 123

22. Percent of Original Lignin Removed versus
Time for Ground Wood at 0.80 g/1 C12 Cone,
and 770F . . . . . 124

23. Percent of Original Lignin Removed by Chlo-
rination versus Time for Cold Soda Pulp at
770F . . . . ........... 125

24, Percent of Original Lignin Removed by Chlo-
rination and Alk. Extn. for Cold Soda Pulp
at 770F. . . . . . . 126

25. Log (-dL) versus Log L for Kraft Pulp at 770F. 127
aT
26. Log L after Chlorination versus Time for Kraft
Pulp at 770F and 0,36 g/l. ..... . 128

27. Log L after Chlorination versus Time for Kraft
Pulp at 770F and 0.57 g/l. . . . . 129

28. Log L after Chlorination versus Time for Kraft
Pulp at 770F; 0.90 and 1.63 g/l. ........ 130


vii









Figure Page

29. Log L after Chlorination and Alk. Extn. versus Time
for Kraft Pulp at 770F. . . 131

30. Log L' and L"after Chlorination and Alk. Extn.
versus Time for Kraft Pulp at 77 F. . . 132

31. Log L after Chlorination versus Time for
Kraft Pulp at 66F and 0.57 g/l ..... 133

32. Log L after Chlorination versus Time for
Kraft Pulp at 870F and 0.57 g/1 ....... 134

33. Reaction Velocity Constants, kI and k2, for
Chlorination at 0.57 g/l versus Reciprocal
of Absolute Temperature ...... 135

34. Log L after Chlorination and Alk. Extn,
versus Time for Kraft Pulp at 66F and 0,57
g/1 ....... . . . .... 136

35. Log L after Chlorination and Alk. Extn.
versus Time for Kraft Pulp at 870F and 0.57
g/1 . . . . . . . . . 137

36. Reaction Velocity Constants, k1 and k2, for
Chlorination and Alk. Extn, at 0.57 g/1
versus Reciprocal of Absolute Temperature 138

37. Log L after Chlorination versus Time for Cold
Soda Pulp at 770F and 0.80 g/1. . . . 139

38. Log L after Chlorination versus Time for Cold
Soda Pulp at 770F and 1.14 g/1 . .. .... 140

39. Log L after Chlorination versus Time for Cold
Soda Pulp at 770F and 1.50 g/1. .... .. 141

40. Log L after Chlorination and Alk. Extn. for
Cold Soda Pulp at 770F. ... ....... . 142

41. Log L' and L"after Chlorination and Alk. Extn.
for Cold Soda Pulp at 770F. .. . . . 143

42. Log k1 and k2 for Chlorination versus Log
C12 Conc. for Cold Soda Pulp. . . . .. 144

43, Log k1 and k2 for Chlorination and Alk.
Extn. versus Log C12 Cone. for Cold Soda
Pulp. . . . . . . . . . 145


viii











INTRODUCTION


The main object of bleaching pulp is to remove the

incrusting substances which cause discoloration and thus

obtain a white pulp. The sources of Kraft color are tan-

nins and phlobaphenes, sulfur dyes, lignin and its reac-

tion products, the carbohydrate degradation products and

the condensation product of tannins and alkali-labile car-

bohydrates. The color is mainly due to the oxidation or

condensation products of phlobatannin and lignin and its

derivatives. It has been shown that the brightness of the

pulp increases with decrease in lignin content of the pulp,

and the amount of bleach required by the pulp to attain a

fixed brightness is also a function of lignin content of

the pulp (1). In case of sulfite pulp, the colored impu-

rities appear to consist entirely of lignin compounds (2).

The bleaching process is really a continuation of

the pulping process in which it is a matter of converting

the lignin products into water soluble form. This process

must be carried out as gently as possible so that the carbo-

hydrate is not attacked; if it were, the strength would be

decreased in the case of paper pulp, while the rayon pulp

would show irregular decreases in viscosity and in C-

cellulose content (3), If an attempt is made to remove

most of the lignin in the pulping process, it has been









noticed that more and more holo-celluloses are hydrolyzed

and hence lower yields are obtained (4) and also the D. P.

(Degree of Polymerization) number is decreased. Hence,re-

cent trends in the development of the bleaching techniques

have therefore been to adapt the bleaching conditions in

such a way that the attack on cellulose constituents is

minimized, or to introduce new bleaching agents with such

properties that only the lignin compounds, and, if necessary,

the other discoloring matters, are attacked while the cellu-

losic material is left intact.

Chemical constituents of sulfate pulp indicate that

it is a pure form of wood cellulose (5) and capable of high

yields of white fibrous and resistant materials. Most of

the action of cooking is to reduce bleach consumption and

not to dissolve and degrade the cellulose. Modifications

in bleaching methods give promise of greater results than

modifying cooking methods. Modifications in which the

bleaching operation is two or three stages, with washing

between stages, can cut the bleach requirements consider-

ably. Pulps of better quality, both from physical and

chemical considerations, can be obtained by cooking the wood

as little as possible in isolating the fibers and by accom-

plishing as much of the burden of purification in the bleach-

ing and washing operations. The degree of purification is

however limited by economic considerations.










Chlorine had been found to be quite selective in

its action on lignin, and does not attack the cellulosic

matter in the pulp to any appreciable extent, But,the

main obstacle in the use of chlorination as a step in the

bleaching process was the difficulty, until recently, of

the handling of liquid chlorine. Moist chlorine is very

corrosive and hence ordinary materials of construction

could not be utilized to fabricate the chlorination equip-

ment. But,now with the help of the development of certain

alloys and various corrosion resistant coatings, it is pos-

sible to handle moist chlorine quite effectively. It was

only in 1909 that liquid chlorine in steel cylinders ap-

peared on the market. Hence,nowadays more and more Kraft

pulp is being bleached. Earlier,the main use of Kraft pulp

was to make unbleached paper or paperboard, as it was found

to be very difficult to bleach with hypochlorite without

severe degradation of the fiber.

Since chlorine was first used by A. Payen in 1839

(6) to delignify plant tissue, an enormous amount of ex-

perimental work has been carried out in an attempt to under-

stand better the mechanism of the reactions involved. Be-

cause of the lack of knowledge of the chemical structure of

lignin and its relationship to the carbohydrates in the

fiber, as well as the inherent complexity of aqueous solu-

tions of chlorine, progress has been slow.







In industry, chlorination of pulp is accomplished

at about 3 to 3 1/2 per cent consistency, with the addition

of chlorine amounting to 60 to 65 per cent of the test

bleachability. The chlorine is either added as a gas or

as solution in water. The time of reaction is usually one

hour and the temperature is usually the prevailing seasonal

temperature of the mill water. Chlorination is either car-

ried out batchwise or continuously. Continuous chlorina-

tion is carried out in a retention tower of sufficient ca-

pacity to allow about one hour of retention time. The

chlorinated pulp is washed with water in order to remove

the chlorinated products which have been rendered water sol-

uble. The washing is followed by hot alkaline extraction.

Alkaline extraction is carried out at 10 to 12 per cent

consistency for about one hour at about 600C. The amount

of sodium hydroxide added is about 1 to 2 per cent of the

weight of the pulp. The alkaline extracted pulp is later

washed with water and is further treated with either chlo-

rine, hypochlorite or chlorine dioxide, depending on the

end use of the pulp.

The purpose of this investigation is to study the

mechanism of the removal of lignin in the chlorination of

unbleached Kraft pulp. Although there are many variables

which could be considered, attention is mainly concentrated

on chlorine concentration, time and temperatures. An at-

tempt is also made to determine the effect of higher pulp






5



consistency on lignin removal and the degradation of the

cellulose, as well as the effect oi amounts of chlorine

consumed by substitution and oxidation on lignin removal

and the degradation of the cellulose.













CHAPTER I


LITERATURE REVIEW


A far reaching change in the character of the

bleaching industry commenced in the year 1787. In that year

chlorine, discovered by Schoele in 1773, was used in the

works of Macgregor, of Glasgow, where its application had

been suggested by James Watt. Watt had gained his informa-

tion about oxygenated muriatic acid, as chlorine was then

called, from Berthellot, who was the first to record the

effect of the gas in bleaching the natural color of linen.

In a paper read before the Academy of Sciences in Paris in

1875, Berthellot mentioned that he had found the gas to be

perfect in the bleaching of cloth. At this period, the

bleacher made his own chlorine and exposed the fabric in

chambers to the action of the gas, or steeped them in the

aqueous solution. The process was inconvenient, disagree-

able, and, worst of all, detrimental to the health of the

workers, so it was not surprising that in spite of the rapid

bleaching action the method did not gain great favor.

Chlorination as a step for the bleaching of wood

pulp had been first suggested by Watt and Burgess (7), who

obtained a United States patent in 1854, for a process in

which wood pulp produced by the soda process was first









chlorinated and subsequently bleached with hypochlorite.

But the chemistry of chlorination of the cellulosic mate-

rials was apparently investigated first by Cross and Bevan

(8) during the latter part of the nineteenth century.

There are no further references to the commercial

application of chlorination of pulp in the literature until

1913, when a patent was granted to deVains (9). This was

mainly due to the difficulty of handling chlorine. It was

only in 1909 that chlorine was available on the market in

steel cylinders. deVains' patent was for bleaching Kraft

pulp in two stages in which chlorination was the first

stage. Cataldi (10) obtained a patent in 1916 for the

bleaching of straws and grasses, the first stage of which

was chlorination. Drewson (11) obtained a patent in 1918

for the bleaching of pulp for nitration in which the first

step was chlorination.

E. Oppermann(12) had made laboratory study of the

method of deVains and Peterson in which the pulp was first

bleached with chlorine gas, washed with alkali, and then

bleached with bleaching powder. The cost varied, as com-

pared with the use of bleaching powder alone, but it averaged

60 to 70 per cent of the older method. The author was of

the opinion that the older method might be improved if the

process were carried out in steps and the products washed

with alkali as an intermediate step.









During the period from 1921 many attempts were

made to chlorinate the pulp continuously and at higher con-

sistencies. Hayward (13) bleached pulp at 20 per cent con-

sistency and showed that the pulp used 25 per cent less

bleach at 20 per cent consistency than that at 5 to 6 per

cent consistency. The failure of the commercial application

of this process was attributed to the fact that the chlorina-

tion reaction is very rapid. This rapidity of the reaction

presents the difficulty of proper control of overheating

caused by the heat of the reaction, and the action of hydro-

chloric acid formed on the cellulose. Hence,the cellulose

thus obtained would be degraded.

C. E. Curran and P. K. Baird (14) gave results of

their experiments which showed that the rate of bleach con-

sumption appeared as a linear function of the logarithm of

the time during the main course of the reaction and probably

within temperature limits of zero to 500C. Hibbert and

Taylor (15) found that between wide limits,the rate ol bleach-

ing was independent of the concentration of the hypochlorite.

They also described the chemistry of the reactions involved

in the chlorination of pulp. Hisey and Koon (16) studied

the bleaching action in solutions buffered at pH of

the solutions from 0.9 to 12.5 and found that the reaction

velocity was greatest in the strongly acid solutions, and

decreased steadily as the pH of the solutions was raised.

Carmody and Mears (17) bleached samples of pulp with









chlorine solution under conditions of constant hydrogen ion

concentration. Combining their data with that of Hisey and

Koon, they made an analysis of the mechanism of the reac-

tions involved. Two separate and distinguishable reactions

were noted, (a) a very fast reaction, the rate of which was

proportional to the first power of the "active lignin" con-

centration, and (b) a much slower reaction of the second

order involving "inactive lignin." In alkaline solution

both of these reactions were entirely oxidation, while in

acid solution they appeared to be mixtures of oxidation and

chlorination. Study of the amounts of the "active lignin"

for runs at several hydrogen ion concentrations indicated

that sixteen units or molecules of chlorine unite with one

unit or empirical molecular weight of lignin.

Arnold, Simmonds and Curran (18) determined that

chlorination of sulfate pulp was exothermic. Direct expo-

sure to sunlight or oven drying caused decomposition of

cellulose, but when air dried at room temperature out of di-

rect sunlight, no decomposition was noticed, They also in-

dicated the presence of carboxyl group in chlorinated lignin

and that part of the chlorine was lost upon treatment with

an alkaline solution,

Larson (19) in 1941, showed that chlorination of

pulps splits methoxyl groups from lignin; the greater the de-

gree of chlorination, the greater the loss of methoxyl group.

Caustic extraction of the residues from chlorination waste









liquors apparently had no effect on the methoxyl content,

but when chlorinated pulps were extracted, the lignin with

the lowest methoxyl content was removed.

About the same time, Hibbert, McCarthy and others

(5) concluded from kinetic measurements that the rate of

chlorination is similar with both soluble lignosulfonic acid

and insoluble lignin resided in the pulp, thus indicating

that diffusion of the halogenating reagent plays a minor

part in the actual chlorination and subsequent reactions.

However, the physical phenomena of diffusion and dissolution

are of considerable importance in the removal of potentially

soluble lignin from cellulose fibers. As evidence for this,

it was apparent that the amount of residual lignin depended

very markedly upon the temperature and time of alkaline wash-

ing.

Hedborg (20) studied the chlorination of sulfate

pulp and the succeeding treatment with alkali. The course

of different processes was followed by the determination of

permanganate consumption and the viscosity of the pulp. He

studied the effect of chlorine concentration and temperature

on the rate of lignin removal. Several other investigators

(21, 22) also studied the effect of temperature of chlorin-

ation on the extent of pulp degradation.

The reaction kinetics of chlorine cleavage from

chlorinated lignin in water and sodium carbonate solution










was studied by Jan Pokin (23). He found that the chlorine

is bound to aliphatic groups and its degree of reactivity

depends on the carbon to which it is bound and on the func-

tional side groups.

Grangaard (24) indicated that upon the addition of

an excess of chlorine to an unbleached pulp, the consumption

by the oxidation reaction amounted to 40 to 70 per cent of

the total chlorine consumption. In fact, for the pulps of

low permaangnate numbers, the consumption of chlorine might

be entirely by oxidation reaction. On chlorinating pulps

in 0.1 normal sulfuric acid, in contrast to a pulp where the

acidity was solely the result of the action of chlorine water,

a slight decrease in the consumption of chlorine by oxida-

tion, together with a slight increase in the consumption by

substitution, occurred. Lowering the temperature also de-

creased the consumption of chlorine by oxidation without

appreciable change in the consumption by substitution. It

was shown that the lignin solubilization which occurs as a

result of chlorination might be the result of the consump-

tion of chlorine by oxidation rather than by substitution.

It was indicated that, during the chlorination reaction, it

was not so much the question of getting the chlorine to the

lignin as it was of getting the chlorinated products out of

the pulp.

Kress and Davis (25) studied different chlorination,









alkali extraction and hypochlorite bleaching stages with dif-

ferent variations. They concluded that the resulting pulp

hydrates too rapidly and hence makes tinny sheets; alkali

extraction in between stages raises strength, and use of al-

kali in chlorination stage was not beneficial. Several in-

vestigators have studied the merits of combinations of dif-

ferent bleaching stages.

Sprout and Toovey (26) working with sulfate and sul-

fite pulps observed that these pulps were most effectively

and economically bleached when chlorinated to an optimum de-

gree which was characteristic of the pulp. They showed the

necessity of alkaline extraction between two chlorination

stages. It was also indicated that a three-stage chlorina-

tion procedure employing recycled chlorination liquors for

sulfate pulp bleaching had afforded reduction in operating

time as well as in cost of bleaching chemicals over a single

stage chlorination bleach and, to a lesser extent, over a

two-stage chlorination bleach when producing pulps of com-

parable brightness and physical properties. Rapson and

Anderson (27) proposed three stage bleachings. The first

stage was chlorination with addition of little chlorine di-

oxide, the second stage was sodium hydroxide extraction with

addition of a little of chlorine and the third stage was the

treatment with chlorine dioxide.

Due to the recent development of methods to regu-

late automatically the addition of chlorine to the pulp with





13



the help of oxidation-reduction potential cell, uniform

chlorination is accomplished (35). The automatic control

compensates for the variations in brown stock entering the

chlorination tower because of poor cooking, inefficient mix-

ing, poor blending, tower channeling, temperature, etc.,

(36).












CHAPTER II


THEORETICAL CONSIDERATIONS


Although a large amount of experimental work has

been done on the chlorination of pulp, in acid or alkaline

medium, no exact analysis of the chemical reactions involved

has been made. The problem is very complex, as there are

many variables involved The important variables in chlorin-

ation are:

1. The initial lignin content of the pulp.

2. Concentration of molecular chlorine in
the bleaching solution.

3. Hydrogen ion concentration.

4. Concentrations of Hypochlorous acid,
hypochlorite and chlorite ions. These
are dependent on 2 and 3.

5. Time of chlorination.

6. Temperature of chlorination.

7. Consistency of the reaction mixture.

8. The origin of the pulp.

There is also the possibility of numerous reactions

taking place simultaneously since each of chlorine, hypochlo-

rous acid and hypochlorite ion may react in more than one

way. The analysis of such a complex system of reactions

would demand the acquisition of exact data from a series of

experiments over a broad range in which each factor is

14









regulated or calculable from known relationships.

In commercial application, 5 to 8 are usually con-

stant Three and 4 are not controlled specifically, but are

dependent on the concentration of chlorine and the equilib-

rium between chlorine and water.

In order to understand the mechanism involved in

the reaction of chlorine in aqueous solution with pulp, con-

sideration must be given to what happens when chlorine gas

is dissolved in water. When chlorine gas is dissolved in

water, the following reversible hydrolysis occurs:


C12 H20 = HC1 + 1OC1 (I)


On the right hand side, there exists both hydrochlo-

ric acid and hypochlorous acid, one of which, namely, hydro-

chloric acid is strongly dissociated in dilute aqueous solu-

tion, while hypochlorous acid is comparatively little disso-

ciated. Equation (I) may therefore be written as follows:


C12 + H20 = H1f 4 Cl HOC1 (II)


The hydrolysis constant of this equilibrium was shown by

Jakowkin (28) to be represented as follows at 250C:


K = (H )(C1-)(HOC1) = (4.84)(10-4) (III)
(C12)

From this value it is possible to calculate the

amounts of the several constituents and the acidity of the









solution when increasing amounts of chlorine are dissolved

in water. It can be seen from equation (II) that,as dilu-

tion is increased, the equilibrium shifts more and more to

the right, and at very high dilution there can exist sub-

stantially no elemental chlorine in solution.

Hypochlorous acid also can ionize as follows:


HOC1 = H + OC1 (IV)


and numerous evaluations of this ionization constant have

been made. For example, Davidson (29) has found the follow-
0
ing value at 18 C:

-8
K = (H+)(OC1-) = (3.7)(10 ) (V)
(HOC1)


It is apparent that the relative amounts of molec-

ular chlorine, hypochlorous acid and hypochlorite ions exist-

ing in a given solution are markedly dependent upon the acid-

ity of the solution. The composition at various values of

hydrogen ion concentration of a solution is shown in Figure 1

(30). Below pH of the solution of 4.5, the hypochlorite

ion disappears and the available chlorine is present in

the form of molecular chlorine and hypochlorous acid. In this

range of pH of the solution between 4.5 and 9, the

activity of hypochlorite solutions of the same concentration













100 ------ 0


90 10


80 \ 20


70 30


60 40
0 \HOCI
S50 50


c 40 -60 "


a 30 70


8 20- 80
C12 C10
10 90

0 100
0 1 2 3 4 5 6 7 8 9
pH

Figure 1.-- The Distribution of Chlorine
among Elementary Chlorine, Hypochlorous Acid,
and Hypochlorite Ion in a Solution of Chlorine
in Water at Various pHs.









of available chlorine are definitely dependent on the hydro-

gen ion concentration. The higher the hydrogen ion concen-

tration of the liquor, the greater the activity, viz., con-

centration of molecular chlorine.

With this knowledge of the equilibrium of chlorine

and water, the reactions between chlorine and organic com-

pounds will be considered. It is known that chlorine reacts

in absence of water with saturated organic compounds by dir-

rect substitution as follows:


RH + CL2 = RC1 + HC1 (VI)


In this equation, R represents organic groups attached to the

hydrogen atom, which is replaced by chlorine atom with simul-

taneous formation of one molecule of hydrochloric acid. With

unsaturated compounds, two atoms of chlorine may enter the

molecule at the location of the double bond, thus forming a

saturated chlorine derivative according to the following

equation:


C12 + R2C:CR2 = R2ClC.CClR2 (VII)


It has been found in the chlorination of pulp that the amount

of chlorine used by addition should be neglected as there is

no evidence of double bonds in the lignin molecule (31) which

could be easily chlorinated.

Though equations (VI) and (VII) have been repre-

sented as applying in the absence of water, this is not









necessarily true (32). The hydrogen atoms located in read-

ily replaceable positions in the molecule can be substituted

by chlorine in the presence of water and, in many cases,

chlorine will add to the double bond in the presence of wa-

ter. In the presence of water, chlorine may also act as an

oxidizing agent according to the following reactions:


RH + C12 H H20 = ROH + 2 HCI (VIII)

RCH3 + 3 C12 2 H20 = RCOOH + 6 HC1 (IX)

RCHO + C12 + H20 = RCOOH + 2 HC1 (X)


In the chlorination of pulp, it had been found

earlier that 60 to 80 per cent of the chlorine reacts by sub-

stitution and the remainder by oxidation (30).


Possible Mechanisms and their Rate Equations:

Chlorination of pulp with chlorine water is an het-

ereogeneous reaction. The system can be considered as con-

sisting of fibers suspended in chlorine water, which is main-

tained at constant temperature. When the pulp is added to the

chlorine water, the lignin and the other coloring bodies at

the surface of the fiber react with the constituents of the

chlorine water. At the same time, chlorine water diffuses

and penetrates the inner layers and reacts with lignin in

the inner layers.

From the standpoint of kinetics, a reaction oc-

curring on a surface usually is regarded as involving the









following steps:

1. The transfer of the reactants and the
products to and from the surface of
the solid and main body of the fluid.

2. The diffusional and flow transfer of
the reactants and the products in and
out of the pore structure of the solid
when reaction takes place at interior
interfaces.

3. The activated adsorption of the reac-
tants and the activated desorption at
the solid-liquid interface.

4. The surface reaction of the adsorbed
reactants to form chemically adsorbed
products.

The rates of these four types of operations are

dependent on widely different factors in addition to concen-

trations or concentration gradients (33). The rate of the

overall reaction is dependent on the slowest step.

When temperature and all other conditions are

maintained constant, the rate equation can be supposed to

assume the following form:

a b
dL : r = k ( L L ) ( C ) (XI)
-a-
Where

r = instantaneous rate of lignin removal
expressed lignin still remaining after
a time, t, per unit time,

L = Original lignin content of the pulp,

L = Lignin remaining after time, t.

C = Concentration of elemental chlorine in
chlorine water,

k = Reaction velocity constant,
a and b are also constants.









If C were held constant throughout an experiment,

equation (XI) can be written as:


r a k ( Lo L ) (XII)


Taking logarithms of both sides of the equation (XII), we

get:


log r = log k a log ( Lo L ) (XIII)


According to equation (XIII), if r is plotted

against ( Lo L ), on log-log paper, then a straight line

should be obtained with slope equal to 'a' and intercept on

the x-axis equal to log k. It has to be assumed that 'a' is

constant and hence independent of the concentration of the

chlorine water. If it is not so, then this approach cannot

be applied.

From equations (XI) and (XII), it can be seen that


k k'( C )b (XIV)


Taking logarithm of equation (XIV), we get


log k = log k'+ b(log C) (XV)


Equation (XV), indicates that if k is obtained for

each corresponding value of C, then with the use of this equa-

tion values of k/ and'b can be evaluated. If k is plotted

against C on log-log paper, a straight line is obtained with

slope equal to 'b and intercept on the X-axis equal to log k.









The exponent b can also be evaluated with the use of ini-

tial rates.

Another possible mechanism may be one in which the

final reaction rate may be a combination of two or more si-

multaneous reaction rates. It is possible that two or more

different reaction rates exist due either to physical or

chemical factors, or to a combination of physical and chem-

ical phenomena. The concept of two delignification reactions

or steps has been applied to Sulfate (4) and Sulfite (34)

cooking.

The most widely used correlation between the tem-

perature and the reaction velocity constant is the empirical

Arrhenius equation, which is mathematically expressed as:


k = D e- LE/RT (XVI)

where

aE = energy of activation, calories per gram mole,

D = proportionality factor, characteristic of
-1
the system and termed frequency factor, Min. ,

R = gas constant, calories per gram mole, degree K.
-1
k = reaction velocity constant, Min. ,

T = absolute temperature, degree K.


As the temperature increases, the reaction rate

usually increases in accordance with the above equation.













CHAPTER III


CHLORINATION EQUIPMENT


This investigation is divided into two parts:

Part A: Chlorination of the unbleached pulp was carried out

with falling chlorine concentration.

Part B: Chlorination of the unbleached pulp was carried out

under constant chlorine concentration.


Requirements and Description of Equipment:

Part A: Chlorination with falling chlorine concentration:

In this part of the investigation, the concentra-

tion of the chlorine was not maintained constant. It was

allowed to fall with the consumption of chlorine by the un-

bleached pulp. The chief object of this part of the inves-

tigation was to determine the amount of chlorine being used

as substituting agent or as oxidizing agent. As discussed

earlier, chlorine in water can react as either a substitut-

ing agent or as an oxidizing agent.

Chlorination of the pulp was carried out in glass

bottles with airtight screw caps. The size of the bottles

used was dependent on the size of the pulp sample used. This

was because of the fact that air space in the bottle has to

be kept at a minimum. Otherwise, the chlorine losses in the









air space would be large, vapor pressure of chlorine being

quite high.

A water bath was provided in order to carry out

the experiments at constant temperature. The bath was

equipped with either heating or cooling coils, depending on

the room temperature with respect to the temperature speci-

fied for the experiment. The cooling coil was used when the

specified temperature was lower than the prevailing water

temperature and vice versa. The bath was also equipped with

thermostat accompanied by Fischer Unitized Bath Electronic

control unit and a stirrer.

Addition of the predetermined amount of chlorine

water was accomplished with the help of the apparatus shown

in Figure 2. The primary purpose of such a setup was to

eliminate the loss of chlorine from chlorine water by flash-

ing while the chlorine water was being added to the pulp.

The chlorine water from the polyethylene bottle was trans-

ferred to the graduated measuring cylinder with stopcocks

A, B and D open and stopcocks C, M and L closed. After the

graduated cylinder was filled with a sufficient amount of

chlorine water, stopcocks A, B and D were closed. Then,

with stopcocks C, D and L open, the predetermined amount

of chlorine water from the graduated cylinder was added to

the pulp in the glass bottle, after which stopcocks L, C and

D were closed. The tube passing through the opening N was















- Polyethylene Bottle


D




Graduated
_ Measuring
Cylinder


- Glass Bottle


Figure 2.-- Apparatus for Addition of Chlorine
Water.


I


iff


M C




t ,_
^Iii


4 '1


KI *
HAc









removed from the glass bottle and the opening closed with a

rubber stopper. The rubber tube connecting to stopcock L

and the conical flask, serving to trap any trace of escaping

chlorine gas, were also removed. Finally, the glass bottle

was placed in the water bath after thorough shaking.

The screw cap of the reaction glass bottle had to

have openings for adding chlorine water and also removing

samples of the liquor for analysis from the bottle. The

screw cap is shown in Figure 3. It was made of stainless

steel and had two stainless steel tubes and an opening N

with a rubber stopper. The lower end of the tube with stop-

cock M was covered with glass wool in order to filter out the

pulp when sampling the liquor.

As the vapor pressure of chlorine is very high,

the cap of the bottle could not be removed in order to re-

move the sample, otherwise, there would be an appreciable

loss of chlorine gas. Hence, a sample of the liquor was

forced out of the bottle with the help of a slight nitrogen

pressure. This was accomplished by connecting the tube

equipped with stopcock L (Figure 3) on the cap of the glass

bottle to the nitrogen cylinder. The tube with stopcock M

was then connected to the special pipets. These pipets, to

measure out the liquor samples, were specially designed to

suit the purpose. The stopcocks L, M, I, J and K were

opened so that the pipets E and F were filled with the



























0 o U



a -4
n 0 -



CC) U U)


C) 0 O 0
j2 m r












.00 -rC C

















4--
irr..' n


0
d


V)

0 0
0 a -0
+o 0



0

b0'






Ul
O

1:













.0

0-H
\ +I









Cn






^ ^-n.


- L~ ,Z
.-.J i.









liquor samples after a slight nitrogen pressure was applied.

Both the pipets E and F were calibrated. After the pipets

were filled, stopcocks I and J were reversed so that the

liquor samples from the pipets E and F emptied into the

flasks G and H. The samples were then analyzed for residual

chlorine and total chloride ion.


Part B: Chlorination with constant chlorine concentration:

The principle variables to be considered in this

study are chlorine concentration, temperature and the time

of chlorination. Hence, the chlorination equipment had to be

designed in such a way that proper control of chlorine con-

centration and temperature of chlorination could be obtained.

The chlorination of the pulp was carried out in a

chlorination tank, It consisted of a cylindrical pyrex glass

jar 11.25 inches in diameter and 23.4 inches high, having a

total capacity of 37.2 liters. On its front wall was marked

a vertical scale indicating the contents in liters correspond-

ing to the height. It had near its base an outlet which was

fitted with an outlet of a 5/8 inch rubber tube for sampling.

The complete assembly is shown in Figure 4,

Over the tank there was mounted a stirrer driven

by a 1/12 H. P. variable speed motor. The stirrer had short

stainless steel paddles with straight blades, four in number,

each 7 inches long, 5/8 inch wide and spaced 4 1/2 inches

apart. The lowest blade was 3 inches from the bottom of the















Cooling Coil


Cov


Rotameter

Chlorine
Gas
From
Cylinder
Gas
Dispersing
Tube


Baffles


o r


nnil

i i


Stirrer Rubber Stopper
/ ,


i1
^r
~nI


To Fischer
Electronic
Control Unit





Pyrex
Glass Jar

Vapor
Pressure
Thermoregulator



Opening for
-Pulp
Sampling


Figure 4.-- Chlorination Tank.









tank. The stirring paddles were set at right angles to each

other. Four stainless steel baffles were hung at the sides

of the tank to effect efficient mixing of the stock. Be-

cause of the severe corrosive action of moist chlorine, all

the stainless steel parts were coated with a corrosion re-

sistant film. Bitumastic super service black paint made by

Koppers was found to be very satisfactory. Because of the

high vapor pressure of chlorine, the tank was covered with

a wooden top in order to eliminate the loss of chlorine from

the chlorine water. An appropriate opening with stoppers

was provided in the cover so as to facilitate removal of

liquor samples from the tank for analysis. The cover was

sealed to the top of the tank with Permatex.

As the temperatures used in this investigation were

usually less than the room temperature, the stock in the tank

must be cooled. This was accomplished with the help of a

glass cooling coil provided in the tank. In order to maintain

the temperature constant, a Fischer Unitized Bath Electronic

Control unit accompanied with a Vapor Pressure Thermoregulator

was used. With the help of this setup, the pump circulating

the cold water through the cooling coil was automatically

operated so that a predetermined temperature was constantly

maintained. The sensitivity of this control was 0.10F.

As the chlorination reaction proceeds, more and more

chlorine from the chlorine water in the tank was being con-

sumed and the concentration of the chlorine had decreased. In





31



order to maintain the chlorine concentration constant, chlo-

rine from a gas cylinder was added at the rate at which it

was consumed. The addition of the chlorine to the tank was

accomplished with a glass tube provided in the tank. This

glass tube had a fritted glass fitting attached to the end

which was immersed in the stock. The fritted glass fitting

dispersed the gas into small bubbles and hence facilitated

its uniform distribution throughout the stock. A Fischer and

Porter flowrator and a needle valve were provided in the gas

supply line in order to regulate exactly the flow of the

chlorine gas.













CHAPTER IV


METHOD OF PROCEDURE


1. Preparation of Samples for Chlorination:

The high lignin Kraft pulp used in this investi-

gation was prepared in the Pulp and Paper Laboratory at the

University of Florida. The slash pine mill chips were fed

to the Rotopulper set at a 15/16 inch opening. This shredding

of chips splits the chip along the grain, retaining the same

length of the shredded chip as the original chip. The

shredded chips were then screened by a gyratory screen, and

the fraction through 3 mesh on 8 mesh was used for cooking.

The shredded chips were cooked in a digester with cooking

liquor having 23.8 per cent sulfidity and 49.7 grams per

liter alkali as Na20. The liquor to wood ratio was 3.4 to

1.0. The cooking pressure was 115 psi gage and cooking time

was 90 minutes to bring to pressure and then 15 minutes at

the full pressure. The cooked wood was washed with hot water

and then screened through an 0.010 inch cut screen. Most of

the water from the screened pulp was squeezed out with the

help of an hydraulic press and then broken up in laboratory

shredder and air dried. The air-dried pulp was stored in

airtight cans, protecting it from sunlight, dust and moisture.

The air-dried pulp was 91.8 per cent dry. This pulp analyzed










11 50 per cent lignin and had a permangante number of

37.9.

The ground wood sample used in this investigation

was prepared by passing air-dried, shredded pine chips

through a Wiley mill provided with a 20 mesh screen. The

ground wood sample was screened and the fraction -20 + 35 was

then extracted with alcohol and benzene in order to remove

resins, gums, turpentine, etc., and later washed with hot

water and air dried. The cold soda pulp used for the exper-

iment was prepared by soaking air-dried, shredded pine chips

in sodium hydroxide liquor (63.9 grams Na20 per liter) and

raising the temperature of the mixture to 190 F. in a steam-

jacketed vessel. The steam was then cut off and the mixture

was allowed to stand over-night. Chips thus soaked were re-

fined in the Rotopulper set at an 0.16 inch opening. The re-

fined pulp was washed with hot water, screened through an

0.018 inch cut screen, squeezed and air dried.

For each experiment, a predetermined quantity of

air-dried pulp was taken from the storeroom. The quantity

of the pulp was based on oven dryness and hence the moisture

content of the pulp in the storeroom was periodically de-

termined. The weighed quantity of pulp was then soaked in
O
water at about 80 C for about 30 minutes. The purpose of

this treatment was twofold: first, it inactivated any cat-

alyse in the pulp; second, it returned the pulp to a uni-

formly wet condition and thus facilitated subsequent










disintegration in the laboratory disintegrator (Appendix A,

TAPPI Standard No. T-205). The weighed quantity was mixed in

the laboratory disintegrator for 300 revolutions of the agi-

tator per gram of dry sample. It was found that 300 revolu-

tions per gram of pulp gave reproducible results. Depending

on the consistency specified for the experiment, a definite

quantity of water is filtered from the pulp on a Buchner fun-

nel.


2. Preparation of Chlorine Water:

A two-gallon polyethylene bottle was filled with

distilled water at about 350 to 40 F. The bottle had a

screw cap at the top and an outlet with a valve at the bottom.

Chlorine gas from a gas cylinder was bubbled through the dis-

tilled water in the bottle with the help of a glass tube

having a fritted glass fitting for good dispersion. The sol-

ubility of the chlorine gas in water depends on the tempera-

ture. The relation between the solubility of chlorine gas

and water is shown in Figure 5. When the chlorine water

reached the desired concentration, the flow of chlorine gas

was cut off, The concentration was determined by volumetric

analysis of a sample. The chlorine water thus prepared was

placed in a water bath maintained at about 350F until it

was ready to be used.


3. Chlorination Procedure:

Part A: Chlorination with falling chlorine concentration:















15


14


13



12

oli
o 11



10
O

o
4 9
,-4


08
o

-' 7

06
-Eb


5


4



3


2


T r


0 10 20 30 40
Temperature ( OC )


Figure 5.--Solubility of Chlorine in Water


50


7-- T---- -


. \









-\


\\









The specified amount of disintegrated pulp was

placed in the proper glass bottle. A sufficient amount of

distilled water was added to the pulp so that after the ad-

dition of the calculated amount of chlorine water, the speci-

fied consistency was attained. The cap of the bottle was

then placed in position and the bottle made airtight. The

chlorine water from the polyethylene bottle was transformed

to the measuring cylinder. After a 25-milliliter sample of

the chlorine water in the measuring cylinder had been ana-

lyzed, the calculated amount of chlorine water was added to

the pulp. The amount of chlorine gas displaced when the

chlorine water was added to the pulp was trapped in the flask

which was provided with potassium iodide and acetic acid.

The amount of chlorine added to the pulp in the glass bottle

was later corrected for this loss. The temperature of the

mixture had been adjusted to the specified value with the

addition of hot or cold distilled water. The opening N

(Figure 3) for addition of chlorine water was closed with a

rubber stopper and the bottle was shaken vigorously and

placed in the water bath. This shaking was repeated at regu-

lar intervals of two minutes.

Just before the end of the specified time of chlo-

rination treatment, the tube with stoplock L on the cap of

the glass bottle was connected to the nitrogen cylinder. The

tube with stopcock M was connected to the special pipet. The

three-way stopcock K was opened in such a way that some of









the liquor could be drained out in the beaker P. This in-

sures a better sampling of the liquor for analysis. The

stopcock K was then opened in the direction permitting the

liquor to flow into the pipets. Then stopcocks I and J were

opened in such a way that under a slight pressure from the

nitrogen cylinder, the pipets E and F were filled with liquor.

Then stopcocks I and J were set so that the liquor from the

pipets dropped into the flasks G and H. G was filled with

potassium iodide and acetic acid and H was filled with sodium

pyrosulfite and sulfuric acid. The samples in flasks G and H

were then analyzed for residual chlorine and total chloride

ion, respectively.

Immediately after the liquor samples were removed,

the cap of the glass bottle was opened and the pulp poured

into a large beaker which had been filled with hot distilled

water. This terminated the chlorination reaction. The pulp

was filtered on a Buchner funnel and washed twice, each time

re-pulping in warm distilled water at a consistency of about

2 per cent and filtering. One quarter of the filtered chlo-

rinated pulp sample was air dried in a constant humidity room

and another quarter was treated with chlorine dioxide. The

other half of the pulp was immediately extracted with alkali.

The air-dried samples were later analyzed for lignin content

and viscosity.

When the time of chlorination was 15 minutes or

less, the analysis of the liquor and the subsequent treatment









of the chlorinated pulp could not be done on the same un-

bleached pulp sample, Hcnce,two separate but identical ex-

periments were performed: one in which the attention was

given to the analysis of the liquor; the other in which the

attention was given to the subsequent treatment and analysis

of the chlorinated pulp.


Part B: Chlorination with Constant Chlorine Concentration:

The glass jar was filled with distilled water at

the temperature specified for the experiment. The strong

chlorine water in the polyethylene bottle was analyzed and

the exact amount oi chlorine water needed was determined.

Then the calculated amount of chlorine water from the poly-

ethylene bottle was added to the water in the glass jar.

The total amount of water in the glass jar was adjusted so

that after the addition of the pulp suspension, the volume

of the stock was 33.0 liters. The chlorine water in the glass

jar was analyzed before addition of the pulp suspension and

adjustments in the chlorine concentration were made, if

necessary, with the addition of more chlorine water from the

bottle. The reason for analyzing each batch prior to chlo-

rination instead of the apparently much simpler method of

using a calculated amount of chlorine water of known strength

is because the analysis of chlorine water of high concentra-

tions is subject to inaccuracy, Either loss of vapor or the

slightest inconsistency in draining the sample pipet could

result in an appreciable error. The temperature of the










solution was adjusted and maintained with the help of the

temperature regulating system. The solution was agitated

with the stirrer in the tank.

After the chlorine water in the chlorination tank

had been adjusted to the required chlorine concentration and

temperature, the pulp suspension at approximately the same

temperature was poured in the tank, and the cover immediately

closed and the stop clock started. As an alternative proce-

dure, the calculated amount of chlorine might be added to

the tank containing the pulp suspended in solution which had

been adjusted to the specified temperature. However, this

alternative procedure was found to yield inconsistent re-

sults and abnormal chlorine consumption, presumably due to

the effect of localized high concentration before mixing is

complete.

As the reaction between chlorine and the unbleached

pulp proceeds, the chlorine concentration decreases. If the

exact rate of this concentration decrease is known, the

amount of addition of chlorine to maintain the chlorine con-

centration can be determined. It would seem that potentio-

metric measurement of the chlorine concentration would pro-

vide a means of indicating and thus controlling the chlorine

concentration. However, it was soon found that this method

was not accurate enough as the electromotive force measured

by the potentiometer is a logarithmic function of the chlo-

rine concentration. Hence trial runs were made under










identical conditions but without an attempt to maintain the

chlorine concentration constant in order to determine chlo-

rine consumption.

A trial batch,which was identical in composition

to the regular batch,was prepared and chlorination was car-

ried out under the same conditions as the regular run, ex-

cept that the chlorine concentration was not controlled. By

analyzing the samples of chlorine water at definite inter-

vals, the time rate of consumption of chlorine was calculated.

From these data a schedule of make-up additions of chlorine

as chlorine gas during the regular run was set up.

Pulp samples were withdrawn at fixed time intervals

through the outlet provided near the bottom of the tank.

When it was time for the sample to be withdrawn, the stop-

cock at the bottom was opened and a predetermined amount of

pulp suspension was allowed to flow into a laboratory cen-

trifuge. Some water for washing the sample was also added

in the centrifuge. This insured the instantaneous termi-

nation of the reaction. The centrifuged pulp was further

washed twice with hot water and filtered on a Buchner funnel

in order to remove the water soluble products. The chlorine

water in the tank was also analyzed at fixed intervals by

siphoning out a 25-milliliter sample with the help of a

pipet. The inlet of the pipet was covered with glass wool

to keep pulp out of the liquor sample. If these analyses

showed that chlorine concentration was not constant, tkn that










particular run was rejected. The chlorinated sample was

further treated in the same manner as explained in Part A.


4. Alkaline Extraction Procedure:

In this investigation, emphasis had been on the

chlorination reaction and hence a standard alkaline extrac- -

tion procedure was determined and used for all the experi-

ments. For determining this procedure, a sample of the un-

bleached pulp was chlorinated under the conditions of the

highest concentration used in this investigation. This chlo-

rinated sample was later alkali extracted at consistency of

10 per cent. The temperature of extraction was about 1300F.

The amount of alkali (sodium hydroxide) to be added was de-

termined with the help of pH determinations. The amount

which extracted most of the alkali soluble constituents of

the chlorinated sample was found to be 3 per cent sodium

hydroxide by weight of oven-dry pulp. The pH of the mixture

at the end of one hour was about 9.0.

The sample of chlorinated pulp to be extracted was

mixed in a 400-milliliter beaker with the predetermined

amount of alkali and sufficient water to result in a final

consistency of 10 per cent. Mixing was accomplished with the

help of a polyethylene spoon. The beaker was covered with a

watch glass and placed in a hastelloy pot in a water bath at

160-165 F. The mixture was mixed periodically with the help

of the spoon to insure uniform temperature and concentration









of alkali. At the end of extraction, the pulp was washed

in the same manner as after chlorination. Half of the ex-

tracted pulp was later air dried and analyzed for lignin

content and viscosity. The other half was treated with chlo-

rine dioxide and analyzed for viscosity


5. Chlorine Dioxide Treatment:

In order to evaluate the extent of degradation in

chlorination and alkali extraction, the chlorinated and al-

kali extracted samples of pulps were completely delignified

by chlorine dioxide treatment. The wet sample was mixed in

an airtight, small glass bottle with 50 per cent by weight of

sodium chlorite, 10 per cent by weight of glacial acetic acid

and sufficient water to result in a consistency of 5.0 per

cent. All percentages were based on the dry weight of pulp.

The mixture was well stirred and heated in a water bath at

150-160 F. for 30 minutes. The pulp was washed as before,

air dried and then analyzed for viscosity.


6. Analytical Procedure:

(a) Available chlorine in chlorine water.--TAPPI

standard T-611 was used. Accordingly, a 25-milliliter sample

of the chlorine water was pipeted into a 250-milliliter flask

containing approximately 25 milliliters of distilled water,

10 milliliters of 20 per cent acetic acid and 10 milliliters

of 20 per cent potassium iodide. The contents of the flask

were mixed by swirling and then titrated with 0.1 normal sodium









thiosulfate solution until the iodine color was almost dis-

charged, Then a starch indicator was added and titration

continued to the disappearance of blue color. A duplicate

sample was then analyzed using the same procedure. The anal-

ysis was reported as grams of chlorine per liter.

(b) Permanganate number.--The permanganate number

of the pulp was determined according to TAPPI Standard T-214

m-42. The permanganate number of the pulp was reported as

milliliter of 0.1 N KMnO4 consumed per gram of moisture free

pulp.

(c) Lignin content.--TAPPI Standard Testing Pro-

cedure No. T-222 m-43 was used to analyze for lignin content

of the samples. As this is a standard procedure used in

every laboratory, it will not be elaborated on here other than

mentioning that the lignin referred to here is the fraction

which is not soluble in 72 per cent sulfuric acid at 200C

after two hours of treatment. The weight of lignin was re-

ported as percentage by weight of the moisture free sample.

(d) Degree of polymerization.--TAPPI Standard

No. T-230 using 0.5 molal cupriethylenediamine [Cu(En)2 was

used. Cu(En)2 solution was purchased from Ecusta Paper Com-

pany and adjusted to a molarity of 0.500 0.0025. Fesnke-

Ostwald viscosity pipets were used. Stirring of pulp and

Cu(En)2 solution was carried out with a copper stirrer under

an atmosphere of nitrogen in order to avoid oxidation and

consequent degradation of the cellulose. Degree of










polymerization (D. P. number) of the pulp was evaluated from

the viscosity measurements by means of Hercules Conversion

Chart for Cellulose Viscosities, Form 803, ZM 11-48, Hercules

Powder Company, Wilmington, Delaware.

(e) Residual chlorine.--Residual chlorine was de-

termined according to TAPPI Standard Testing Procedure No.

T-611. The liberated iodine was titrated against standard

sodium thiosulfate.

(f) Total chloride.--A measured quantity of liquor

sample was pipeted into a 250-milliliter flask which con-

tained 25 milliliters of 3 per cent sodium pyrosulfite and 10

milliliters of 10 per cent sulfuric acid. Pyrosulfite was

used to convert the residual chlorine to chloride according

to the following equation:


C12 + 2 Na2S205 = 2 NaC1 Na2SO4 + S02 (XVI)


The mixture was boiled for about one minute to remove the ex-

cess sulfur dioxide, then cooled and the chloride determined.

The determination of chloride by volumetric methods, by ti-

trating with silver nitrate using internal indicators,was

found to be quite difficult as the determination of the end

point was not distinct. Hence,potentiometric titration was

employed. The chloride was determined by titrating against

standard silver nitrate solution using silver and silver/

silver chloride electrodes in association with Beckman pH





45




Meter, Model G. The change in electromotive force across the

two electrodes with the addition of standard silver nitrate

was measured. When there was a sudden increase in the e.m.f.,

the quantity of silver nitrate added was noted. This value

was then converted to give the total chloride ion content of

the liquor sample.














CHAPTER V


DISCUSSION OF THE DATA AND RESULTS


Part A: Chlorination with Falling Chlorine Concentration:

The main purpose of this investigation was to de-

termine the effects of pulp consistency and of initial chlo-

rine concentration on the rates of lignin removal and the

degradation of the cellulose, and also to determine the

amounts of chlorine being used up in substitution and oxida-

tion. To achieve this, samples of high lignin Kraft pulp

were chlorinated at consistencies of 1, 2 and 3 per cent using

identical amounts of chlorine per gram of dry pulp. All of

the experiments were carried out at a constant temperature of

770F and varying chlorination time. The amount of chlorine

applied was determined from the chlorine number of the pulp.

The chlorine number represents the grams of chlorine absorbed

by 100 grams of moisture-free pulp at 20 C in 15 minutes. In

this investigation the chlorine number was calculated from

the permanganate number of the pulp and a relation between

the permanganate number and the chlorine number (TAPPI Stand-

art T-214 m-42).

Data from these experiments are recorded in Tables

1, 2 and 3 as amounts of chlorine used for substitution and










for oxidation, and percentage residual chlorine. The data

tabulated in Tables 5, 6 and 7 are the amounts of lignin re-

moved by chlorination and also by chlorination and alkali

extraction, and the degree of polymerization of the cellu-

lose.

As indicated earlier, chlorination of the pulp

occurs by two processes: one by substitution; the other by

oxidation, neglecting any possible addition process. From

equation (VI), it can be seen that in a substitution re-

action, for every mole of chlorine reacting, there is one

mole of hydrochloric acid formed. On the other hand,

equations (VIII), (IX) and (X) show that, for every mole of

chlorine reacting by oxidation, there are formed two moles

of hydrochloric acid. Thus, if one knows the amount of

total hydrochloric acid formed, the amounts of chlorine used

for substitution and for oxidation can be evaluated.

Suppose X = weight of total chlorine used, grams,

Y = weight of chlorine in the hydrochloric acid
formed, grams,

C = weight of chlorine used in substitution, grams,

D = weight of chlorine used in oxidation, grams,

then X = C + D.

As half of the chlorine used in substitution and all of the

chlorine used in oxidation appears as hydrochloric acid in

the liquor,

Y = C D









Solving the above equations for X and Y, one obtains:

C = 2(X-Y)

and D = Y (X-Y) = 2Y X.

For each experiment the exact amount of chlorine added to the

pulp was known and the residual chlorine and the total chlo-

ride ions in the liquor were determined analytically. If it

could be experimentally proved that there was no hydrochloric

acid adsorbed on the surface of the pulp, then all the hydro-

chloric acid formed must be in the liquor. Under such cir-

cumstances, the analysis of the liquor would give the correct

indication of the amount of hydrochloric acid formed.

In order to prove this absence of adsorption, a

sample of pulp was chlorinated at 3 per cent consistency for

15 minutes with the application of 10 per cent chlorine on

the basis of the pulp. Previous experiments had shown

that under these conditions all of the applied chlorine was

consumed. The complete reacted mixture containing both pulp

and liquor was analyzed for hydrochloric acid. In a dupli-

cate experiment, instead of analyzing the complete mixture,

a sample of the liquor was filtered from the pulp and ana-

lyzed for hydrochloric acid. The hydrochloric acid in the

complete reaction mixture determined by both methods was

found to be the same. This indicates that all of the hy-

drochloric acid formed was uniformly distributed in the

liquor and that there was no adsorption of hydrochloric










acid on the surface of the pulp.

Through the use of the above relations for de-

termining C and D, the actual weights of chlorine used in

substitution and oxidation of the pulp were calculated and

these values have been listed in Tables 1 to 4. The re-

sults in Tables 1, 2 and 3 were later calculated on the

basis of 100 grams of pulp and plotted in Figure 7, and the

percentages of residual chlorine were plotted in Figure 6.

The residual chlorine concentrations in the liquor in grams

per liter at different times are shown in Table 11.

Figure 6 indicates that increased chlorine con-

sumption occurs as the consistency of the reaction mixture

is increased. At first glance, it might be assumed that the

use of higher consistencies could reduce the reaction time

since the reaction rates would be increased. Actually, the

increased consumption of chlorine may be due either to the

increase in chlorine concentration or to the increase in the

pulp surface caused by the increase in pulp consistency. It

should be pointed out that pulp consistency, chlorine con-

centration and the weight of chlorine applied per gram of

pulp are three interdependent variables. By fixing the

value of any two of them, the value of the third becomes

automatically fixed.

From Figure 7, it can be seen that the higher the

consistency the larger is the amount of chlorine used by

substitution and the lower the amount of chlorine used by










oxidation. As discussed earlier, substitution is the de-

sired reaction. Increase in the pulp consistency would in-

crease the amount of chlorine used in substitution and de-

crease the amount of chlorine used for oxidation. Reduc-

tion in the amount of chlorine used by oxidation should

tend to decrease the degradation of the cellulose. However,

it has been found by earlier investigators (3) that some

slight degree of oxidation of the Kraft lignin is required,

because in sulfate cooking the lignin undergoes condensa-

tion to such an extent that a large part of it cannot be dis-

solved by alkaline treatment after chlorination.

Some authorities (3) have implied that upon the

addition of chlorine to the pulp, 40 to 20 per cent of the

chlorine is consumed by oxidation reaction, while 60 to 80

per cent of the chlorine is consumed by substitution re-

action. In Figure 8, the percentage of chlorine consumption

by substitution is plotted against time at various pulp

consistencies. It can be observed that the percentage of

chlorine consumption by substitution reaction ranges from

37 to 58 per cent, a range smaller than observed earlier.

The discrepancies in these observations can be attributed

to the inefficiency in analyzing the liquor samples since

any chlorine losses during the analysis show up as chlo-

rine consumption by substitution. In this investigation,

much care was taken in order to keep such chlorine losses to

a minimum and all the experiments had been duplicated.










Since the principle object of chlorination of the

pulp is to remove lignin without degradation of the cellu-

lose, the pulps were analyzed for the degree of polymeriza-

tion of the cellulose, as well as for lignin content. These

data, recorded in Tables 5, 6 and 7, have been plotted in

Figures 9, 10, 11 and 12. The Figures 9 and 10 show the

percentages of the original lignin removed by the chlorina-

tion treatment and by chlorination and alkali extraction,

respectively, as a function of time. Figures 11 and 12

show the degree of polymerization of the chlorinated, and

chlorinated and alkali extracted samples.

The lignin has not been removed completely from

the pulp in any of the experiments. Neither residual lignin

nor residual chlorinated lignin compounds are soluble in

cupriethylenediamine, which is used as a solvent for the de-

termination of the degree of polymerization of the cellulose

The presence of these residues tends to give erroneous re-

sults with the viscometer and hence should be removed before

viscosity determinations. This was done through the chlo-

rine dioxide treatment of the pulp. It has been found that

chlorine dioxide does not degrade the cellulose to any ap-

preciable extent, but removes all of the residual lignin

and thus makes it possible to find the true viscosity of

the pulp. Quantitative determination on the chlorine di-

oxide treatment showed that the loss in weight of the










chlorine-dioxide treated pulp corresponded exactly to the

amount of lignin removed. The amount of lignin remaining

after the treatment was practically zero.

From the results in Tables 1, 2, 3, 5, 6 and 7,

the consumption of chlorine per gram of lignin removed was

determined, basing the calculations on 100 grams of dry

pulp. These calculated values have been listed in Table 9.

It can be seen that the amount of chlorine consumed per

gram of lignin removed is approximately constant, indicat-

ing that about 1.30 grams of chlorine should be used to re-

move each gram of lignin. This quantity seems to be in-

dependent of the pulp consistency or initial chlorine con-

centration. Hence knowing the lignin content of the pulp,

one can determine the amount of chlorine actually needed

for removing the lignin from the pulp. A previous reference

(17) has noted that one unit of lignin reacts with 16 units

of chlorine. Taking the often reported value of the molec-

ular weight of lignin to be 840, the amount of chlorine re-

acting per gram of lignin is (16)(71) = 1.35 grams as com-
--4U
pared to 1.30 found in this investigation.

The amount of maximum chlorine which can be added

in a single chlorination stage is a function of the con-

sistency of the pulp and solubility of chlorine in water.

Basis: 100 grams of mixture of pulp and liquor.

Let X = percentage of pulp consistency = grams of pulp,









then (100-X) = milliliter of water.

Maximum weight of chlorine in (100-X) milliliter of water

= ST (100-X)


where ST = solubility of chlorine in water at tem-

perature of TC and 760 mm mercury pressure, in grams per

liter,

Hence,maximum chlorine applied per 100 grams of the pulp


(XVII)


SC = (ST)(100-X)
(10)(X)


This equation has been plotted in Figure 13 with C and X as

the ordinates and T as the parameter.

The low solubility of chlorine in water limits the

amount of lignin that can be removed for any particular con-

sistency. Therefore, the maximum amount of lignin which could

be removed for any consistency was determined in the follow-

ing manner:

The chlorine needed by the pulp = (X)(L) (1.30) grams,
100


where





The maximum


Equating the

rine availat


L = maximum lignin removed as percentage of
the pulp.

(1.30) = grams of chlorine required to remove
each gram of lignin.

chlorine available in chlorine water

SST (100-X)
1000

chlorine needed by the pulp to the maximum chlo-

,le in the chlorine water, one obtains:











L = (ST)(100-X) (XVIII)
(13.0) (X)


This equation has been plotted in Figure 14 with L and X as

the ordinates and T as the parameter. The figure gives an

approximation of the upper limits of consistency for pulp

with varying percentages of lignin removed. The curves do

not apply if higher vapor pressures of chlorine are used as

the above calculations have been based on a vapor pressure

of 760 mm mercury.

It has been discussed earlier that some portion of

the chlorinated lignin is soluble in the chlorine solution

itself and in wash water. About 55 to 60 per cent of the

total lignin is removed in the spent solution and subsequent

washings. The amount of this acid-soluble lignin is defi-

nitely dependent on the temperature of the wash water used.

Hence in all washings of chlorinated pulps, distilled water

at 50 to 600C. was used.

The portion of the chlorinated lignin insoluble

in the chlorine water is reacted and solubilized by alkaline

extraction. It is felt that this is not mere solubilization

of chlorinated compounds in alkali, since there is actual

consumption of alkali during alkaline treatment. It would

appear that sodium-salts are formed which are, themselves,

soluble in alkali.










The total amount of lignin removed increases with

increase in the pulp consistency and initial chlorine con-

centration. But,it has been found that at initial chlo-

rine concentrations of 3.30 and 5.00 grams per liter there

is no appreciable difference in the lignin removal. This may

be attributed to the fact that most of the accessible lignin

has been removed and hence further increase in the chlorine

concentration without any decrease in the chlorination time

would not be beneficial. It appears that as lignin concen-

tration decreases, concentration of chlorine is not the con-

trolling factor.

From Figure 12,it can be seen that increase in the

initial chlorine concentration has practically no effect on

the degree of polymerization of the cellulose for short

chlorination times. But,as the time of chlorination is

increased the degree of polymerization of the cellulose

drops considerably. This implies that use of higher initial

chlorine concentrations would not degrade the cellulose to

any appreciable extent provided the chlorination time is

less than 5 minutes.

Experiments were also carried out to determine the

effect ol initial chlorine concentration on chlorine consump-

tion at 3 per cent pulp consistency. The data are listed

in Tables 4 and 8. The data in Table 4 show the amounts of

chlorine consumed for substitution and also for oxidation.









In Table 8 is recorded the percentage of the original lignin

removed by the chlorination treatment and the chlorination

and alkali extraction for various initial chlorine concen-

trations. The data in Table 4 indicate that the amount of

chlorine used for substitution is fairly constant for chlo-

rine concentrations from 5.00 to 3.85 grams per liter but

it tends to drop below a chlorine concentration of 3.85

grams per liter. This implies that higher chlorine concen-

trations should be used in order to have more substitution

and less oxidation reaction. Tables 4 and 8 indicate that

at 3 per cent consistency and varying chlorine concentra-

tions approximately 1.30 grams of chlorine are also required

to remove one gram of lignin from the pulp.


Two Chlorination Stages:

In order to determine the effect of two chlorina-

tion stages, as opposed to one chlorination stage, a pulp

sample was chlorinated for 5 minutes at 3 per cent con-

sistency with an initial chlorine concentration of 5.00

grams per liter and subsequently alkali extracted (reference

Table 7). This pulp was given a second chlorination for 5

minutes at a consistency of 3 per cent with a chlorine con-

centration of 1.21 grams per liter. This chlorine concen-

tration was deliberately made equal to the concentration of

chlorine in the liquor at the end of the first chlorination

(reference Table 11). It was found that after the two









chlorinations and alkali extractions, 98 per cent of the

original lignin was removed. However, from Figure 10 it

can be seen that after a total of 10 minutes continuous

chlorination time, the percentage of the original lignin re-

moved would be only 88. This shows that two chlorinations

of short time duration are more effective in lignin removal

than a single stage chlorination at a time duration equal to

the sum of the time intervals used for the two chlorination

stages. This indicates that the chlorinated products might

have formed incrustations on the fiber walls which hinder

further reaction between pulp and chlorine.

The filtered spent liquor was found to contain

65.3 per cent of the original chlorine as unconsumed. This

liquor was found also to contain two moles of hydrochloric

acid for every mole of chlorine. This constitutes further

proof that all chlorine applied appears in the liquor as

residual chlorine and as chlorine in hydrochloric acid. It

would seem obvious that no hydrochloric acid is adsorbed on

the surface of the pulp and hence unaccounted for by liquor

analysis.


Heat of Reaction:

The chlorination of pulp is an exothermic reac-

tion and hence in the industry the generation of heat in the

chlorination stage should be taken into consideration, Al-

though the reaction rates would be higher at higher chlorina-

tion temperatures, the rate of degradation of the cellulose










increases likewise (21) due to the additional heat result-

ing from the reaction itself. The amount of temperature

rise depends on the heat of reaction, the heat capacity of

the system and radiation properties of the equipment. Hence,

in this investigation an attempt was made to determine the

heat of chlorination reaction.

In order to determine the heat of the chlorina-

tion reaction, the calorimetric method was used. The cal-

orimeter used was a Dewar flask which was provided with a

top made of 3/4 inch thick asbestos pad, a stirrer and a

thermometer which could be read exactly to the second

decimal place.

The standard reaction used to determine the water

equivalent of this calorimetric system was the neutraliza-

tion of an acid with an alkali, viz:


NaOH (Solution) + HC1 (Solution) =

NaCl (Solution) 1120 (XIX)


This is an exothermic reaction with the heat of reaction

equal to 2,490 BTU per pound mole. The water equivalent of

the calorimetric system was determined to be 4.07 pounds.

A 20 gram sample of the pulp was chlorinated in

the Dewar flask at 1.25 per cent consistency with the ap-

plication of 16.2 per cent chlorine, based on the pulp.

The initial temperature of both the pulp suspension and the









0
chlorine water was 77.90 F. The maximum rise in tempera-

ture of the reaction mixture was found to be 2,09 F. Using

this value of temperature rise and the water equivalent of

the calorimetric system, the heat of reaction of chlorina-

tion of the Kraft pulp was found to be 360 BTU per pound of

pulp treated. For the same pulp and with the same chlorine

concentration, the heat of reaction of sodium hypochlorite

and pulp was found to be 375 BTU per pound of pulp treated.

The heat of reaction of 360 BTU per pound of pulp

treated would give respective temperature rises for chlorina-

tions carried out at various consistencies. At a pulp con-

sistency of 3 per cent the temperature rise would b 5.10
and at a consistency of 3 per cent the temperature rise would be 5.10 F
and at a consistency of 9 per cent the temperature rise would

be 16.40 F. These magnitudes of temperature rises would not

cause serious pulp degradation in industrial operations,


part B: Chlorination with Constant Chlorine Concentration.

In studying the effects of C12 concentration,

chlorination time and temperature on the delignification of the

Kraft pulp, a pulp containing 11.50 per cent lignin was used.

It had been found in preliminary work with pulp containing

5 65 per cent lignin that the reaction rates for chlorina-

tion of the pulp were quite high. If this pulp of low

lignin content were used, practically all the lignin would

be removed in the first few minutes, making it impractical

to study the effect of chlorination time on the lignin re-

moval.









With the present available equipment in the lab-

oratory it took about one minute to withdraw the sample for

analysis. When attempts were made to study reaction times

of less than 5 minutes, the results could not be duplicated.

This was because the reaction rates were quite high in the

early stages, but after 5 minutes the reaction rates had de-

creased to such an extent that the results could be dupli-

cated with reasonable accuracy.

Chlorination experiments were conducted with Kraft

pulp under conditions of constant C12 concentration, con-

stant temperature and varying time. The experimental condi-

tions used were: C12 concentration from 0.36 to 1.63 grams
o o o
per liter; chlorination temperatures of 66 F, 77 F and 87 F;

chlorination times from 5 to 60 minutes. The data obtained

from these experiments are listed in Tables 12-17. The lig-

nin removal data from these tables are plotted versus time

in Figures 15-17. The data on D. P. number of the cellulose

are plotted versus time in Figures 18-21.

It has been discussed in Chapter II that if the

rates of delignification were to follow equation (XI), the

slopes, which are the instantaneous rates of delignifica-

tion (-dL) when plotted versus percent of lignin remaining
UT
(L), should give straight lines on log-log paper. Such

straight lines obtained for various constant C12 concentra-

ticns should be parallel to each other.

The curves of percent lignin removed versus time in











Figure 15 were graphically differentiated to determine

the value of slope (-dL). The graphical differentiation

was carried out with the help ox a mirror. Figure 25 shows

the log-log plot of (-dL) versus L. This plot gives ac-
UT
ceptable straight lines, but the lines are not parallel.

This means that the slopes of these lines vary with chlo-

rine concentration. Hence, as discussed in Chapter II,

equation (XI) could not be applied to the data.

An examination of the curves in Figure 15 indicates

that the curves approach straight lines at both ends. Thus,

there is a possibility that more than one reaction is taking

place. This would be quite plausible because of the complex

nature of the system. This complexity prohibits any attempt

at defining the exact mechanism of the reactions between

pulp and chlorine water. Therefore, an attempt was made to

find an empirical relation between rate of lignin removal,

chlorine concentration, chlorination time and temperature.

Under conditions of constant C12 concentration and

temperature, for a first order reaction, the quantity of a

component reacting in a definite time is proportional to

the quantity of unreacted component in the solid at that

time.

In the case of lignin removal,


-dL = k(L)
UT


(XX)









which becomes, on integration

-kt
L = Loe (XXa)

taking logarithm Log L = -kt + Log Lo (XXb)

where Lo = percent of the original lignin in
the pulp at the start of the reac-
tion,

L percent of the original lignin re-
maining after time, t,

k = reaction velocity constant.


Therefore,from equation (XXb), a first order reaction should

give a straight line when L is plotted versus time on semi-

logarithmic coordinates.

The percentages of the original lignin remaining alter

chlorination were plotted versus time on semi-logarithmic pa-

per as shown in Figures 26-28. All the lines were curves.

The shapes of these curves very early in the reaction indi-

cate, in all cases, that there is a certain percentage of

lignin removed extremely rapidly. In fact, it is this highly

reactive lignin which prevented accurate evaluation of re-

action rate in the first 5 minutes. If it can be assumed

for estimating purposes that this highly reactive lignin is

removed instantaneously, it might be possible to fit the re-

mainder of the data into the scheme involving two straight

line relationships.

The curve in Figure 26 where C12 concentration was

0.36 grams per liter was fitted with two straight lines










designated as A and B. First, line B was drawn so that it

was asymptotic with the data curve at longer chlorination

times. The equation of this line is

nI -k t
L = Be- 2 (XXc)

taking logarithm

Log L= -k2t + Log B (XXd)

where

L = percent of the original lignin remaining
from reaction B at time, t,

B intercept on the Y-axis = L o = 42

k2= apparent reaction velocity constant

= 0.00146.


The subscript 'O' indicates the value at the start of the re-

action.

For each value of time, the value of L" was obtained

and then subtracted from the experimental value of L at that

time. These differences when plotted on the same figure gave

a straight line, designated A. The equation of this line is

as follows:


= Ae-k 1t (XXe)

where L = per cent of the original lignin remaining
from reaction A, at time, t,

A = intercept of the Y-axis = L = 36,

kl= apparent reaction velocity constant,

= 0.0369,









The combination of equations (XXc) and (XXe) gives

the relationship between L for the chlorinated pulp and time.

The combined equation is as follows:


L = L L = Ae-kt + Be-kt (XXI)


Substituting the values of constants, the equation becomes

-0.0369t -0.00146t
L 36e 4 42e (XXIa)


At time zero, equation (XXIa) indicates that


L 36 42 78. However at the start of the re-

action, the value of Lo = 100. This Lo must be the sum

of Lo, L and the percent of lignin removed instantaneously.

Therefore percent of original lignin removed instantaneously
i / I
SLo Lo L

S100 36 42

22

i.e., L = 22 + Lo L,

or Lo = 22 + Ae-klt Be-k2t

This 22 per cent instantaneous removal is possibly

due to the fact that in the early part of chlorination, chlo-

rine reacts with the solid wall of lignin on the surface of

the fiber. It might also be that this 22 per cent is not

removed instantly, but is removed in the first 1-2 minutes.

This point can be clarified when equipment becomes available

so that chlorinations can be carried out accurately at very










short time intervals. As this 22 per cent of the original

lignin is removed instantaneously, it does not enter into

further consideration. It has similarly been found by

Findley (34) that in neutral sulfite pulping about 12.5 per

cent of the wood is removed very rapidly and hence does not

affect the kinetics.

Equation (XXI) indicates that there are two ap-

parent simultaneous or subsequent first order reactions in

chlorination in addition to the instantaneous reaction.

These two apparent reactions have different reaction rates

which can be seen from the difference in the apparent re-

action velocity constants k1 and k2.

The apparent reaction velocity constants k1 and k2

were similarly determined from Figures 27 and 28 for chlo-

rination experiments carried out at chlorine concentration

of 0.57,0.90 and 1.63 grams per liter. The values of k1 and

k2 are as follows:


A = intercept for line A = 36

B = intercept for line B = 42


-1 -1
C12 Cone. g/1. klmin k2, min


0.36 0.0369 0.00146
0.57 0.0791 0.00234
0 90 0.1316 0.00403
1.63 0.1316 0.00403










It can be seen from the above tabulation that k1

and k2 are functions of chlorine concentration. Hence, an

attempt was made to find a mathematical relationship be-

tween the C12 concentration and the apparent reaction ve-

locity constant. This attempt was not successful be-

cause the values of kI and k2 became constant at concen-

tration of 0.90 grams per liter or higher.

Some authorities have indicated that such a phe-

nomenon may be due to the fact that when chlorine concen-

tration is low, the lignin molecules are not surrounded by

a sufficiently large number of C12 molecules. Therefore,

reaction rate increases rapidly with increase in concentra-

tion. But, when the solution surrounding lignin has at-

tained saturation with respect to the chlorine demand of

lignin, then beyond this saturation further increase will

have no effect.

In the light of this particular system, the above

reasoning does not seem to apply. It seems more probable

that concentration of lignin remaining, rather than the con-

centration of chlorine, might be the controlling factor for

pulp containing about 10 per cent lignin. Under such cir-

cumstances, when lignin content of the pulp has decreased

to a certain extent, then further increases in concentra-

tion would not affect the rate of reaction.

The same mathematical analysis, using equation

(XXI), was applied to pulps which had been alkali extracted










after chlorination. The data listed in Tables 12-15, were

plotted in Figure 29 as logarithm of L versus time. Each

curve in Figure 29 for different C12 concentration was

fitted with two respective straight lines as shown in Figure

30.

The percent of original lignin instantly removed

was found to be 55. The values of constants determined from

Figure 30 are as follows:


A = intercept of line A = 29

B = intercept of line B = 16


-1 -1
Cl2 Cone. g/l. k1, min. k2, min.


0.36 0.0825 0.0135
0.57 0.1142 0.0153
0.90 0.1684 0.0181
1.63 00 0 0181


In this case, when the pulps had been alkali ex-

tracted after chlorination, the constancy of reaction con-

stant k2 occurs at high values of concentration just as

with chlorination. But, in the case of kl,however, Figure 30

shows that line A for C12 concentration of 1.63 grams per

liter, is a vertical straight line coinciding with the Y-axis.

This means that the value of kI increases without limits and

that the time interval is equal to zero. Therefore,accord-

ing to equation (XXe),









-k t -('o)(0)
L = Ae-kt = Ae-()() A 29

This indicates that at concentration of 1.63 grams

per liter, this 29 per cent is removed so rapidly as to be

considered as instantaneously removed. Therefore,this 29

per cent of the lignin falls in the same category as the

55 per cent which had already been assumed to be removed

instantaneously. This means that 84 per cent of the lig-

nin is removed instantaneously.

When the chlorinations and alkali extractions were

carried out under falling concentrations, it can be seen

from Figure 10, by extrapolation, that 83.0 per cent of the

lignin was removed instantaneously when the initial con-

centration was 1.63 grams per liter. For an initial con-

centration of 3.33, this value was 84.2 per cent and for

an initial concentration of 5.00, this value was 85.5 per

cent. These values of instantaneous removal of lignin

agree very well with that of 85 per cent, as found above.


Effect of Chlorine Concentration and Temperature on the
Degradation of the Cellulose:

Degree of polymerization numbers of cellulose after

chlorination treatment and chlorination followed by alkali

extraction are plotted in Figures 18-21 for various chlo-

rine concentrations and temperatures. These figures appear

to indicate that degradation of cellulose increases with

increase in chlorine concentration and chlorination tempera-

ture.








From Figures 16 and 19 it can be seen that for

85.6 per cent of original lignin removal at a C12 concen-

tration of 1.63 grams per liter, the degree of polymeriza-

tion number falls to 1454. For the same quantity of lignin

removed at 0.57 grams per liter, time of chlorination is

21.7 minutes and the degree of polymerization number is

1540. Extrapolation of the curves on Figure 16 can show

that a chlorination time of 2 minutes at 1.63 grams per

liter, the degree of polymerization number is about 1520.

But, for the same chlorination time at 0.57 grams per liter,

the degree of polymerization number is about 1555. There-

fore, it is quite possible that, at very short reaction times,

chlorinations may be carried out at relatively high chlorine

concentrations without extensive cellulose degradation.


Effect of Chlorination Temperature on the Delignification
of Kraft Pulp:

This set of experiments was conducted with the Kraft

pulp. The chlorine concentration of the liquor used in each

case was 0.57 grams per liter. The temperature was varied

from 660' to 870F. The data are shown in Tables 16, 17 and

plotted in Figure 17.

The data for chlorination at various temperatures

were plotted on semi-logarithmic paper in Figures 31 and 32,

with L and time as the coordinates. The curves obtained

were similarly fitted with two straight line relationships.

Then the values of constants kI and k2 were determined.

If the Arrhenius equation, which has been








mathematically explained as,

-AE/RT
k = De (XVI)

taking logarithm,

Log k = log D (AE)(1) (XVIa)


were to hold true for k1 and k2, straight lines should be ob-

tained when logarithms of k1 and k2 are plotted versus the

reciprocal of absolute temperature.

The values of k1 and k2 for chlorination at various

temperatures are as follows:


TF ToR (10+3)(1/T) kl,min.-1 k2,min.-1

66 526 1.90 0.0585 0.00061
77 537 1.86 0.0791 0.00234
87 547 1,83 0.0980 0.00464


These values of k1 and k2 were plotted versus 1/TR

on semi-logarithmic graph paper as shown in Figure 33. It

was found that acceptable straight lines were obtained, in-

dicating applicability of the Arrhenius equation.

Similarly data for chlorination at various tempera-

turesfollowed by alkali extraction were plotted on semi-

logarithm coordinates as shown in Figures 34 and 35. The

curves obtained were fitted with two straight line rela-

tionships. Then the values of constants k1 and k2 were de-

termined. These values are as follows:










TOF TR (10+3)(lT ) kl,min.-1 k2,min.-1


66 526 1.90 0.0223 0.0022
77 536 1.86 0,1142 0.0153
87 547 1.83 0.1840 0.0269


These values of k1 and k2 for chlorination followed

by alkali extraction were plotted versus (1/T R) on semi-

logarithm coordinates as shown in Figure 36. It was found

that acceptable straight lines were obtained.

The energies of activation for chlorination and for

chlorination followed by alkali extraction obtained from the

slopes of the straight lines in Figures 33 and 36 are as fol-

lows:


Energy of Activation Energy of Activation
for Reaction A for Reaction B
(l">^ >ool( )(cal/1n -J1 ) (0 ,r 1/4 -ole )(C J/, m_ l)

Chlorination 14,000 7,850 40,800 22,600

Chlorination followed
by Alkali Extraction 48,650 27,000 63,000 35,000


The values for constants D1 and D2 for chlorination are
12 32
1 12 x 10 and 1.72 x 10 respectively. For chlorination
40
followed by alkali extraction D1 and D2 are 1.70 x 10 and
55
1.18 x 10 respectively

The values of energy of activation indicate that re-

action A needs less energy for its activation and hence is

more rapid than reaction B.









In order to obtain relationship between L, tempera-

ture and time, equations(XVI) and XXI) were combined. The

combined equation is as follows:


L ee-dEl/RT- r 6E2/PRTJ
L = Ae Be 2 (XXII)




substituting the values of constants for chlorination car-

ried out at 0.57 grams per liter, equation (XXII) becomes

_(1.12 x 1012e-14,000/RT) t
L = 36e 10
-(3.32 x 10 e 40,800/RT)t (XXIIa)
-42e



Study of Rates of Delignification of Wood:

It has just been pointed out that there was no in-

crease of rate of delignification as chlorine concentration

increased above 0.90 grams per liter. This was attributed to

the decrease in lignin content to such an extent that it con-

trolled the delignification rates.

If a pulp of sufficiently high lignin content could

be used, the true effect of chlorine concentration might be

evaluated. It was felt that if ground wood, instead of a

pulp, were used, then a material containing 29.05 per cent

lignin could be obtained for experimentation. The Kraft

pulp which was used contained 11.50 per cent lignin.

In order to provide an extremely large surface, air-

dried wood was ground, screened and extracted as described










in Chapter III. This extracted wood fraction passing

through 28 mesh and retained by 35 mesh was used for chlo-

rination. The chlorination was carried out at constant con-
o
centration of 0.80 grams per liter and 77 F. The results

have been listed in Table 18 and plotted in Figure 22 as

percent lignin removed versus time.

From this figure it can be seen that after one

hour of chlorination followed by alkali extraction, the

percent of original lignin removed was 41.7. But, under the

same experimental conditions, the percent of original lig-

nin removed from Kraft pulp was 93.6 (reference Table 16).

This indicates that the reaction rate for chlorination ofthe

Kraft pulp was much higher than for chlorination of wood.

This is possible because of the nature of the surface ex-

posed for reaction.

The Kraft pulp is made of individual whole fibers

coated with lignin and hence presents a large lignin sur-

face. But, ground wood does not consist of individual

whole fibers. When the wood is ground in Wiley mill, most

of the fibers are cut in sections. As a fiber is made up

of cell walls with hollow lumens at the center, this cross-

cutting of fibers exposes the hollow lumens. And,as most

of the lignin is present in the outer cell wall, the actual

exposed lignin surface would be at the outer edge of the

cut.


The pine wood whole fibers are 2-3 mm long and










0.04 to 0.07 mm in diameter. Whereas, the ground wood

fraction used in this work consisted of spheres, cubes or

any other shapes between 0.4 and 0.6 mm in cross-section.

This seems to indicate that a cubical piece of ground wood

might consist of 30 to 150 sections of individual fibers.

These 30 to 150 fiber sections in a particle of

ground wood are cemented together by lignin. Thus, this

lignin surface between these fiber sections would not be

available for the reaction at the particle surface. Hence,

for ground wood the actual lignin surface exposed for re-

action at the surface would be quite small.


Effect of Change in Chlorine Concentration on the
Rates of Delignification of Cold Soda Pulp:

From this preliminary work on ground wood, it was

felt that material which would have a surface comparable to

that of Kraft pulp and having high lignin content should be

used. Such a type of material might be cold soda pulp.

In this cold soda process, wood chips are steeped

in alkali at temperatures below 100 C. This steeping in

alkali softens the wood chips without removing any of the

lignin. This softened wood is passed through an attrition

mill. The rubbing in the attrition mill separates the wood

into fibers or fiber bundles without extensive cutting of

the fibers. But, when the wood is ground in a Wiley mill,

the fibers, instead of being separated by rubbing, are cut

into sections of fiber bundles.










The cold soda pulp,prepared as described in Chapter

IV, was chlorinated at constant chlorine concentrations of
o
0.80, 1.14 and 1.50 grams per liter and 77 F. Half of the

chlorinated sample for all experiments was alkali extracted.

The data for chlorination and for chlorination followed by

alkali extraction are recorded in Tables 19-21 and plotted

in Figures 23 and 24.

The same method of attack was used as that de-

scribed for delignification of Kraft pulp. The data for

chlorination were plotted on semi-logarithmic coordinates

as shown in Figures 37-39. The data for chlorination fol-

lowed by alkali extraction were plotted on semi-logarithmic

coordinates in Figure 40.

The curves obtained in Figures 37-40 are similar

to those obtained for Kraft pulp. Hence,the curves in

Figures 37-40 were fitted with two straight line relation-

ships as shown in Figures 38-40 and 42.

It was found that the percent of original lignin

removed instantaneously was 22 for both chlorination and

chlorination followed by alkali extraction. The values

of constants A and B, and the apparent reaction velocity

constants kI and k2 determined from Figures 37-39 and 41,

are as follows:










Chlorination:

A 26 B = 51
-1 -1
C12 Cone. g/l kl,min. k2,min.


0.80 0.0785 0.0032
1.14 0.1121 0.0038
1.50 0.1566 0.0043

Chlorination and Alkali Extraction:

A -51 B 26

-1 -1
Cl2 Cone. g/l kl,min. k2,min.


0.80 0.0635 0.0006
1.14 0.1247 0.0031
1.50 0.2504 0.0097


It can be seen from the above tabulation that both

kI and k2 are functions of chlorine concentration. This

constitutes further proof that in the case of the Kraft pulp,

constancy of reaction rates at higher C12 concentrations

was not because of saturation of chlorine. Rather, it was

low lignin concentration which caused the constancy of re-

action rates.

An analysis was made of the variation of kI and k2

with chlorine concentration. It was found that a log-log

plot of k1 and k2 versus chlorine concentration, C, resulted

in acceptable straight lines for both chlorination and chlo-

rination followed by alkali extraction. The plots are shown

in Figures 42-43. This indicates the following relation-

ships:









k1 = oC"' (XXIII)

and k2 C^A (XXIIIa)


From Figures 42 and 43, the values of constants rC and P were

determined. These values are as follows:


c P, _C2 P

Chlorination 1.07 0.108 0.474 0.0037

Chlorination and
Alkali Extraction 2.18 0.103 3.09 0.0030



In order to find a mathematical relationship be-

tween L, chlorine concentration and time, equations (XXIII)

and (XXIIIa) were combined with equation (XXI). The re-

sulting combined equation is as follows:
_(e -(BIC l )t
L = Ae )t Be (XXIV)


Substituting the values of constants for chlorination re-

action in equation (XXIV), one obtains:
-474
.(o oac)t -(ooo0037 C 7 )t
L = 26e + 51e (XXIVa)


Through the use of equation (XXIV), one can determine

the values of L, if the values of C are known at a time, t.


Application of Equation (XXIV) to the Data in Part A:

When chlorination experiments on Kraft pulp were car-

ried out at a pulp consistency of 3 per cent and under falling









concentrations, chlorine concentration was a function of

time. The values of concentration at different times are

listed in Table 11.

Equation (XXIVa) was applied to the chlorination

data at 3 per cent consistency. The calculated values of

L for chlorination are shown in the following tabulation

along with the observed value. Similarly equation (XXIV)

with appropriate values of constants was used to calculate

the values of L for chlorination followed by alkali extrac-

tion. These calculated values of L, along with the ob-

served values, are also shown in the following tabulation:




Time C12 Cone. L Calculated from L Observed
min. g/1. Eq. (XXIV) from Table 7


Chlorination


5 1.192 64.4 51.6
20 0.815 53.1 47.3
40 0.550 49.0 43.1
60 0.457 45.9 40.2


Chlorination and Alkali Extraction


5 1.192 50.9 13.0
20 0.815 41.9 10.0
40 0.550 39.0 6.5
60 0.457 38.6 4.5



The above tabulation indicates that the residual lig-

nins,calculated by the equation,are much higher than those









actually observed. This indicates that the constants and

exponents derived for the cold soda pulp do not apply to

the Kraft pulp. The most logical explanation of this fact

would be that the ratio of surface to weight for the cold

soda pulp is much less than that for the Kraft pulp.

A comparison of Figure 16, the lignin removal

curves for Kraft pulp, and Figure 23, a similar plot for

cold soda pulp, show a similar discrepancy for rates of

lignin removal for the two materials. For example, Figure

16 shows that for 20 minutes chlorination time, 84.5 per

cent of the total lignin is removed at a concentration of

0.90 grams per liter. But, Figure 23 shows that chlorina-

tion of cold soda pulp at considerably higher C12 concen-

tration of 1.63 grams per liter removed only 45.8 per cent

of the total lignin after 20 minutes. If cold soda pulp

and Kraft pulp were exactly the same material, the lignin

removed under the same conditions should be higher for cold

soda pulp than for Kraft pulp.

The lignin in the cold soda pulp is uniformly dis-

tributed on the surface of the fibers. In the Kraft pulp

60 per cent of the lignin has been removed in cooking, and

distribution of the lignin on the fibers is not known. But,

at any rate, the lignin surface exposed cannot be greater

than that of the cold soda pulp Under such circumstances,

the rate of delignification for the cold soda pulp should

be as high or higher than for Kraft pulp, However,the data









prove that this is not true. Therefore,there must be some

explanation for this fact that the rate of delignification

of cold soda pulp is slow.

Two possible explanations become immediately ap-

parent. On the one hand, it is possible that the alkali

used to soften the lignin may have brought about a chemical

change, making it less reactive to chlorination. On the

other hand, lignin may have remained unaltered, as generally

considered, and the discrepancy will have to be explained

by physical difference. The only way this is possible

is that cold soda pulp is not made of 100 per cent indi-

vidual discrete fibers.

It has been a long-known fact that cold soda pulp

is a mixture of individual fibers and fiber bundles. The

relative proportion of individual fibers to fiber bundles

depends on the degree of the softening of the lignin and

on the degree of refining. Usually a rather high per-

centage of fiber bundles are tolerated in order that the

energy of refining be kept at a minimum and that fiber

cutting be minimized.

In making cold soda pulp for the experiments, it

was noticed that after steeping in alkali the shredded wood

chips were not nearly as flexible as might be desired. This

would indicate that the cementing lignin had not been suf-

ficiently softened to bring about complete fiber separa-

tion during refining.









A microscopic examination of the Kraft and cold soda

pulps showed that there were some fiber bundles in the cold

soda pulp, while the Kraft pulp had all individual fibers.

The diameters of the cold soda fibers appear to be about one

and one-half times the diameter of Kraft fibers. The Kraft

fibers were quite uniform in length, while the cold soda

contained some short fibers caused by fiber cutting. There

were also some fibers in the cold soda pulp, which were about

twice as long as the Kraft fibers. These long fibers were

probably made up of more than one individual fiber.

All these observations from the microscopic study

indicate that the lignin surface in the cold soda pulp was

considerably less than that in the Kraft pulp, Reaction rate

equation with values of constants and exponents derived from

this cold soda pulp with low lignin surface to weight ratio

would naturally give higher values of L, as was found to be

true,

This would appear to open an entirely new approach

to the problem. The shredded wood should be steeped in al-

kali under various conditions of concentration of alkali,

steeping time and temperature. These different steeped-wood

samples should later be refined in an attrition mill. These

refined samples may have different proportions of individual

fibers and degrees of fiber cutting, depending on the con-

ditions of steeping,

Each of these samples should be later chlorinated









at constant chlorine concentrations for various time in-

tervals and the values of L determined. The values of con-

stants in equation (XXIV) should be determined for each

sample. Through the use of these constants and equation

(XXIV), the values of L under conditions of falling concen-

tration for the Kraft pulp should be calculated.

The sample for which the calculated values of L were

equal to or possibly even less than those observed for the

Kraft pulp would seem to have lignin surface similar to

that of the Kraft pulp. Thus, this sample can be used to

determine the mechanism of chlorination.

It may be concluded that lignin surface might be an

important variable just as has been found in delignification

by chemical pulping. This surface variable should be in-

corporated in equation (XXIV). In such a case, constants

(~1 and ]2 may possibly, in reality, be a combination of

another constant and the surface variable.













SUMMARY AND CONCLUSIONS


An investigation was made of the chlorination of

pulps with a view to study the mechanism of lignin removal

and the pulp degradation. The individual effects of chlo-

rine concentration, chlorination time and temperature on

the rate of delignification were also evaluated.

1. When the pulp was chlorinated under conditions

of falling concentration, increases in pulp consistency and

initial chlorine concentration increased the total chlo-

rine consumption, as well as the consumption of chlorine

by substitution.

2. Above a certain initial chlorine concentra-

tion there was no change in the rate of lignin removal with

increase in initial chlorine concentration. At short-time

intervals the degradation of the cellulose was independent

of the initial chlorine concentration.

3. For the Kraft pulp used it was found that, for

every gram of lignin removal, the pulp consumed about 1.30

grams of chlorine.

4. Two chlorination stages of short-time duration

with immediate alkali extraction removed more lignin than

a single chlorination stage of a time equal to the two

chlorination stages. This indicated that the incrustations









of chlorinated products formed on the fiber hinder further

reaction and hence should be removed.

5. The heat of reaction between the Kraft pulp and

chlorine was found to be 360 BTU/# of pulp treated and cor-
0
responds to a temperature rise of 16.4 F at a pulp con-

sistency of 9 per cent. The heat of reaction of sodium hy-

pochlorite and pulp was found to be 375 BTU/# of pulp treated.

6. When the Kraft pulp was chlorinated under con-

ditions of constant chlorine concentration and temperature,

it was found that constancy of reaction rates was attained

at higher chlorine concentrations.

7. The delignification data for the Kraft pulp

after chlorination and for chlorination followed by alkali

extraction fit very well an equation based on two apparent

simultaneous or consecutive first order reactions. In ad-

dition to the lignin removed by these two apparent reactions,

a certain percentage of the original lignin was assumed to

be removed instantaneously.

8. The reaction velocity constants for both the

apparent first order reactions have been shown to vary with

chlorination temperature in accordance with the Arrhenius

equation.

9. For the same quantity of lignin removed at dif-

ferent concentration levels, it was found that the degree

of polymerization number of the cellulose was lower at










higher concentrations. However, it was also indicated that

at very short-tine intervals the decrease in the degree of

polymerization number at higher concentration levels was

not appreciable.

10. It was found that rates of delignification of

the ground wood were slower as compared to those for the

Kraft pulp. This might have been due to the small area

of lignin surface exposed for reaction in the ground wood.

11. The rate of delignification of cold soda pulp

was a function of chlorine concentration and no constancy

of reaction rates was found. This substantiated the fact

that for the Kraft pulp the constancy of the apparent re-

action velocity constants at higher chlorine concentrations

was possibly due to the low lignin concentration. Thus, it

was the concentration of lignin and not the concentration

of chlorine which was the controlling factor.

12. An equation similar to that derived from

the Kraft pulp seemed to apply well to the delignification

data for the cold soda pulp. The apparent reaction velocity

constants for both the reactions were logaritnhic functions

of chlorine concentration. Hence the equation was developed

which correlated L, chlorine concentration and chlorination

time.

13. It was found that the values of L calculated

for the Kraft pulp through the use of equation derived for






86



the cold soda pulp were much higher than those observed.

14. A microscopic study of both the cold soda pulp

and the Kraft pulp indicated that the ratio of surface to

weight for the cold soda pulp was considerably less than

the Kraft pulp.

15. It was concluded that in chlorination of

pulps, the exposed surface is an important variable. There-

fore, an attempt should be made to incorporate this variable

in the general equation derived for delignification by

chlorination.














TABLE 1

EFFECT OF CHLORINATION TIME ON
CHLORINE CONSUMPTION


Weight of oven-dry sample 16.5 gm.

Pulp consistency = 1.0 %

Initial C12 concentration in liquor = 1.63 g/1

Total volume of liquor = 1635 ml.

Temperature = 770F.


Total C12 C12 used C12 used
Time Res. C12 % Res. C12 used by Subs. by Oxid.
min. gm. gm. gm. gm.


3 0.897 33.6 1.77 0.92 0.85

5 0.839 31.4 1.83 0.90 0.93

10 0.669 25.0 2.00 0.90 1.10

20 0.572 21 4 2.20 0.89 1.31

40 0.357 13 3 2.31 0.87 1.44

60 0.312 11.6 2.36 0.87 1.49














TABLE 2

EFFECT OF CHLORINATION TIME ON
CHLORINE CONSUMPTION


Weight of oven-dry sample

Pulp consistency

Initial C12 concentration in liquor

Total volume of liquor

Temperature


= 16.5 gm.

S 2.0 %

= 3.33 g/1.

: 810 ml.

= 770F.


Total C12 C12 used C12 used
Time Res. C12 % Res. C12 used by Subs. by Oxid.
min. gm. gm. gm. gm.


3 0.784 29.4 1.89 0.94 0,95

5 0.660 24.7 2.01 0.92 1.09

10 0.553 20.7 2.12 0.93 1.19

20 0.460 17.2 2.21 0.94 1.27

40 0.320 12.0 2.35 0.93 1.42

60 0.273 10.2 2.40 0.93 1.47














TABLE 3

EFFECT OF CHLORINATION TIME ON
CHLORINE CONSUMPTION


Weight of oven-dry sample = 25.0 gm.

Pulp consistency 3.0 %

Initial C12 concentration in liquor a 5.00 g/l.

Total volume of liquor 810 ml.

Temperature = 770F.



Total C12 Cl2 used C12 used
Time Res. C12 % Res. C12 used by Subs. by Oxid.
min. gm. gm. gm. gm.


1.134

0.967

0.788

0.660

0.446

0.371


27.7

23.9

19.4

16,2

11.0

9.2


2.92

3.08

3.26

3.39

3.60

3.68


1.70

1.74

1.76

1.77

1.82

1.84


1.22

1.34

1.50

1.62

1.78

1.84













TABLE 4

EFFECT OF CHLORINE CONCENTRATION AT 3.0%
CONSISTENCY ON CHLORINE CONSUMPTION


Weight of oven-dry sample

Pulp consistency

Total volume of liquor

Temperature

Chlorination time


= 25.0 gm.

: 3.0 %

= 810 ml.

S7701.

= 5 min.


Init.C12 Total Cl2 Cl2 used C12 used
No. Cone. Res.C12 % Res.C12 used by Subs. by Oxid.
gm. gm. gm. gm. gn.


1 5.00 0.967 23.9 3.08 1.74 1.34

2 4.62 0.666 17.8 3.07 1.76 1.31

3 4.23 0.432 12.6 3.00 1.73 1.26

4 3.85 0.291 9,3 2.84 1.64 1.20

5 3.08 0.025 1.0 2,46 1,36 1.10














TABLE 5

EFFECT OF CHLORINATION TIME ON LIGNIN REMOVAL AND
DEGREE OF POLYMERIZATION NUMBER OF CELLULOSE


The experimental conditions are same as listed in

Table 1.



Time % Pulp Re- % L in % of Orig. % of Orig.
min. maining Pulp L Removed L Remaining D.P. No.


Chlorination


0 100.0 11.50 0.0 100.0 1715
5 95.2 7.40 37,4 62.6 1690
20 94.0 6.25 47.8 52.2 1630
40 93.1 6.05 50.0 50.0 1603
60 92.2 5.81 52.4 47.6 1576


Chlorination and Alkali Extraction


0 88.5 1.92 84.5 15.5 1660
20 87.3 1 52 88,2 11 8 1625
40 87 0 1 35 91.3 8 7 1580
60 86.8 0.86 93.8 6.2 1535













TABLE 6

EFFECT OF CHLORINATION TIME ON LIGNIN REMOVAL AND
DEGREE OF POLYMERIZATION NUMBER OF CELLULOSE


The experimental conditions are same as listed in

Table 2.



Time % Pulp Re- % L in % of Orig. % of Orig.
min. maining Pulp L Removed L Remaining D.P. No.


Chlorination


5 94.3 6.54 45.0 55.0 1675
20 93.1 5.98 50.4 49.6 1632
40 92.2 5.63 54.0 46.0 1600
60 91.5 5.20 58.9 41.1 1578


Chlorination and Alkali Extraction


5 86.7 1.76 86.0 13.0 1659
20 86.0 1.27 89.8 10.2 1605
40 85.3 1,15 93.5 6.5 1568
60 84.9 0,65 95.5 4.5 1540




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