Title: Autoxidation of industrial wastes with oxygen
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Title: Autoxidation of industrial wastes with oxygen
Physical Description: xi, 179 leaves. : illus. ; 28 cm.
Language: English
Creator: Riley, Boyd T., 1939-
Publication Date: 1966
Copyright Date: 1966
 Subjects
Subject: Factory and trade waste   ( lcsh )
Oxidation, Physiological   ( lcsh )
Distillation, Destructive   ( lcsh )
Pyrodigneous acid   ( lcsh )
Environmental Engineering Sciences thesis Ph. D
Dissertations, Academic -- Environmental Engineering Sciences -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis -- University of Florida.
Bibliography: Bibliography: leaves 171-178.
Additional Physical Form: Also available on World Wide Web
General Note: Manuscript copy.
General Note: Vita.
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Bibliographic ID: UF00097873
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 - 000559034
oclc - 13433356
notis - ACY4480

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AUTOXIDATION OF

WITH


INDUSTRIAL WASTES

OXYGEN


BOYD T. RILEY, JR.















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











UNIVERSITY OF FLORIDA


June, 1966












ACKNOWLEDGMENTS


For their guidance in the preparation of this disserta-

tion, the author wishes to express his sincere appreciation

to the members of his supervisory committees

Professor J. E. Kiker, Jr., chairman; Dr. C. I. Harding,

co-chairman; Dr. H. D. Putnam; and Dr. G. B. Butler.

The cooperation and advice extended by Dr. R. S. Sholtes,

Dr. W. H. Morgan, and Dr. H. A. Bevis greatly assisted

in preparing the experimental equipment. The aid of

Mr. H. McGraw in fabricating special fittings is noted in

a similar manner.

Finally, the author wishes to thank his wife for her

patience and encouragement, as well as her participation

in both the experimental work and manuscript preparation

for this dissertation.

The graduate training leading up to this study was

supported in part by U. S. Public Health Service Training

Grant 8T1-ES-11-04.

This study was supported financially by Cabot

Corporation.












TABLE OF CONTENTS


ACKNOWLEDGMENTS.... ............. ....... .... ..... .

LIST OF TABLES..................................

LIST OF FIGURES....................................

ABSTRACT...... .................... .. ...............

CHAPTER

I. INTRODUCTION ... ......... ............. ...

II. REVIEW OF THE ZIMPRO PROCESS..............

III. INTRODUCTION OF THE THEORY OF AUTOXIDATION
OF ORGANIC SUBSTANCES..........o......

IV. MATERIALS AND TECHNIQUES FOR THE
EVALUATION OF PARTIAL AUTOXIDATION OF
WOOD DISTILLATION AS PRETREATMENT
PROCESS. .... ...... .. .. ... .... .... ..

V. RESULTS OF THE INVESTIGATION OF PARTIAL
AUTOXIDATION AS A PRETREATMENT
PROCESS.. .. ... .. ........ ............

VI. CONCLUSIONS FROM THE STUDY OF PARTIAL
AUTOXIDATION AS A PRETREATMENT
PROCESS.... .. .. .... . ... .... ......

VII. EQUIPMENT FOR THE INVESTIGATION OF
COMPLETE AUTOXIDATION OF WASTES........

VIII. TECHNIQUES AND RESULTS OF THE STUDY OF
AUTOXIDATION OF WASTES...............

IX. CONCLUSIONS FROM THE STUDY OF AUTOXIDATION
OF WASTES... ...... ...... ......... ....


Page

ii

v

vi

ix



1

14


21




34



47



63


65


77


127


APPENDICES

1. CALIBRATION OF PRESSURE AND TEMPERATURE
SENSOR SYSTEMS......................... 131

iii






APPENDICES Page

2. COD TECHNIQUE.... ........ ................ 136

3. SOLUBILITY OF OXYGEN IN WATER............ 137

4. PARTIAL PRESSURE OF STEAM AS TEMPERATURE
VARIES............. .......... ......... 140

5. MAXIMUM THEORETICAL PARTIAL PRESSURE OF
CARBON DIOXIDE........................ 142

6. CALCULATION FOR COMPUTATION OF OXYGEN
PARTIAL PRESSURE IN AN EXPERIMENT..... 143

7. RESULTS OF TRIPLICATE COD DETERMINATIONS
ON RUN 7.............................. 144

8. TRACE ELEMENT FEED SCHEDULE FOR TRICKLING
FILTER........ ........... .... ... .... 145

9. CALIBRATION OF PRESSURE AND TEMPERATURE
SENSOR SYSTEMS FOR PARR REACTOR....... 146

10. INFORMATION ON GAS CHROMATOGRAPH
ANALYSES............ ..... ............. 149

11. STATISTICAL COMPARISON OF COD
DETERMINATIONS............ ............ 153

12. PRELIMINARY DESIGN AND ECONOMIC-
FEASIBILITY STUDY OF AUTOXIDATION AS A
WASTE TREATMENT PROCESS FOR
PYROLIGNEOUS ACID.................... 156

13. RECOMMENDATIONS FOR FUTURE RESEARCH...... 168

LIST OF REFERENCES................................ 171

BIOGRAPHICAL SKETCH............................... 179













LIST OF TABLES


Table Page

1. Summary of Acid Water Characteristics............ 4

2. Compounds Formed by Wood Carbonization............ 6

3. Autoxidation Properties of Several Materials..... 18












LIST OF FIGURES


Figure Page

1. Flow Diagram of Wood Distillation Process......... 2

2. Dilutions of Neutralized and Un-neutralized Acid
Water from Cabot Corporation .................. 5

3. Typical Zimpro Process........................... 15
4. Autoxidation Mechanisms....................... ... 23

5. Exterior View of 67-Liter Reactor ................ 36

6. Interior View of Reactor Top..................... 37

7. Trickling Filter................................. 44

8. COD vs. Time, Huns 2 and 3........................ 51

9. COD vs. Time, Run 4...................... ......... 52

10. COD vs. Time, Runs 5, 6, and 7.................... 53

11. COD vs. Time, Runs 8, 13, 14, and 15.............. 54

12. COD vs. Time, Runs 9, 16, and 17................ 56

13. COD vs. Time, Runs 10, 11, and 12................ 57

14. Typical Samples From Autoxidation Experiments..... 59

15. Trickling Filter Data............................ 61

16. Assembled Parr Reactor....................... ....... 70

17. Disassembled Parr Reactor....................... 71

18. Sampling Tube on Reactor.......................... 72

19. Experimental Equipment............................ 76

20. COD vs. Time, Runs 26, 32, and 38 ................ 80

21. COD vs. Time, Runs 44 and 49...................... 82






Figure Page

22. COD vs. Time, Runs 27, 33, and 39................ 83

23. COD vs. Time, Runs 45 and 50..................... 84

24. COD vs. Time, Runs 28, 34, and 40................ 85

25. COD vs. Time, Huns 46 and 51 .................... 86

26. COD vs. Time, Runs 29, 35, and 41................

27. COD vs. Time, Huns 30, 47, and 52................ 89

28. COD vs. ime, .uns 36, 42, and 48................ 90

29. COD vs. Time, Runs 31, 37, and 43................ 91

30. Samples from Autoxidation Reactions.............. 93

31. COD vs. Time, Run 54 ............................. 96

32. COD vs. Time, Run 55.............. ..... .......... 97

33. COD vs. Time, Run 57............................. 99

34. COD vs. Time, Run 5 .............. ... ......... .. 1 0

35. COD vs. Time, Run 59 ......................... ... 101

36. COD vs. Time, jun 69 ....................... 103

37. COD vs. Time, Run 70 .......................... ..1 4

38. COD vs. Time, Run 63............................. 1 6

39. COD vs. Time, .un 64 ............. ... ..... .... 107
40. COD vs. Time, Run 65............................. 1

41. COD vs. Time, Run 66.......................... 110

42. COD vs. Time, Run 67 ............................. 111

43. COD vs. Time, Run 6 .. ................ ........... . 112

44. COD vs. Time, Run 71............. .... ............. 13

45. COD vs. Time, Run 72............................ 116

46. COD vs. Time, Run 73.............................. 118

47. COD vs. Time, Run 74 .............................. 119

48. COD vs. Time, Run 75 ............................. 120

vil






Figure Page

49. COD vs. Time, Run 76 ............................ 122

50. COD vs. Time, Run 78............................123

51. COD vs. Time, Run 79................ ............124

52. COD vs. Time Run 77 ............................ 126

53. Circuit Diagram for Pressure-Sensing System....132

54. Calibration of Pressure Transducer-Recorder
System ...................................... 133

55. Circuit Diagram of Thermocouple-Aecorder
System.......................... ........ .. 134

56. Calibration of Thermocouple-Recorder System..... 135

57. Solubility of Oxygen in Water.................138

58. Solubility of Oxygen in Water...................139

59. Saturated Steam Partial Pressure vs.
Temperature... ................ ...... ......... 141

60. Calibration of Thermocouple-Recorder Against
Mercury Thermometer.......................... 147

61. Calibration of Pressure Transducer..............148

62. Typical Gas Peaks Obtained From An Analysis.....150

63. Calibration Curves for Oxygen, Nitrogen, and
Carbon Dioxide...............................151

64. F. & M. Model 720 Gas Chromatograph...............152

65. Extrapolation of Reaction Data................... 163

66. Flow Diagram of Autoxidation Waste Treatment
Process.............................. .......... 164

67. Schematic Plot Plan of Autoxidation Waste
Treatment Process.............................165

68. Schematic Profile of Autoxidation Waste
Treatment Process........................... .166

69. Design of Chemical Reactor......................167


viii













Abstract of Dissertation Presented to the Graduate
Council in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy


AUTOXIDATION OF INDUSTRIAL WASTE
WITH OXYGEN

By

Boyd T. Riley, Jr.

June, 1966

Chairman: Professor J. E. Kiker, Jr.
Co-Chairman: Dr. C. I. Harding
Major Department: Bioenvironmental Engineering

Destructive distillation of wood for charcoal manu-

facture produces a liquid waste known as pyroligneous acid,

which is driven out of the wood during the carbonizing

process. Pyroligneous acid is composed of many different

organic substances which are dissolved or dispersed in

the water. Pyroligneous acid has a Chemical Oxygen Demand

(COD) of about 100,000 mg/1, a pH of about 2.5; it is

amber in color, and toxic to microflora. A 1:100 dilution

of pyroligneous acid is necessary before it can be used

as a biological substrate. Such a high dilution makes

waste treatment by chemical rather than biological means a

desirable alternative. Many different chemical treatments,

among which are coagulation, chlorination, and pH adjust-

ment, have been attempted in the laboratory. These

experiments were completely unsuccessful.







After reviewing the information available on pyro-

ligneous acid, autoxidation as a treatment process was

considered. Many of the compounds found in this acid are

toxic to microflora and act as inhibitors of autoxidation

reactions. Pretreatment of the pyroligneous acid by partial

autoxidation might selectively reduce the toxicity of the

waste. If so, this pretreatment could be followed by

conventional biological treatment.

A 67-liter chemical reactor was used to autoxidize

partially the pyroligneous acid at about 1250C and the

equivalent of 100 psi at 0C oxygen partial pressure.

This type of treatment yielded about a 10 per cent COD

reduction in the waste during a 4-hour period. The toxicity

of the treated waste was measured by determining the loading

necessary for optimum response on a laboratory-scale

trickling filter. Results indicated that the toxic

compounds were not selectively oxidized.

Using a bench-scale reactor, complete treatment of

pyroligneous acid by autoxidation was investigated and

found to be technically feasible. Minor variations in

experimental technique were found to cause large variations

in the rate and order of the reaction. The most rapid

reaction rates were obtained when undiluted pyroligneous

acid was rapidly mixed with high pressure oxygen at 1750C

and the equivalent of 150 psi at 0C oxygen partial pressure

Two rates were observable a very fast rate during the first

16 minutes of the experiment which resulted in an 80 per
cent reduction in the COD of the waste, and a slower rate

x






which lasted for the duration of the experiment (1 hour)

and resulted in a total COD reduction of 87 per cent. The

reaction was strongly exothermic during the first minutes

of the experiment, resulting in a 500C temperature rise

of the reactants. Changes in the temperature at which the

reactions were initiated caused large changes in the

reaction rates, with increases in temperature causing

greater than linear increases in reaction rates. The

reaction rates accelerated with increases of the oxygen

partial pressure at which the reactions were initiated.

Partial pressures of 50 psi and less reduced the reaction

rates. Complete mixing was necessary to maintain oxygen

in solution at any partial pressure.

Two other wastes and two pure compounds were also

investigated, but were not found to autoxidize as rapidly

as pyroligneous acid.

A preliminary design was proposed for a 15,000 gal/day

pyroligneous acid treatment plant. An economic-feasibility

study, based on this design yielded a cost of 1.4~/lb. of

COD removed.












CHAPTER I

INTRODUCTION

Description of the Waste


The development of a technically and economically

feasible process for the treatment of pyroligneous acid,

a waste product of the wood distillation industry poses

a challenging problem for the Environmental Engineer.

This dissertation suggests a solution to that problem.

The research conducted in the preparation of this disser-

tation was confined to the treatment of waste produced

by Cabot Corporation's Gainesville, Florida, plant. This

waste results from Cabot's use of the retort operation in

the processing of coniferous woods.

The retort operation is a batch process of destructive

distillation. (See Figure 1.) The stump wood is placed

into rectangular slat-sided iron crates which are mounted

on railcars. A train of several crates is assembled and

moved into a retort by a small engine. After the retort

is sealed, it is heated by oil burners to about 8000F, with

the atmosphere inside the retort kept under reducing

conditions. Essentially all of the liquids present in

the wood are driven out as the wood is carbonized. After

the wood has remained in the retort for 8 hours, the hot

retort is opened and the charcoal is moved to cooling

1


















Hot Charcoal




Cooling
Chamber



Cold Charcoal



Classification


Small Piece
of Charcoal


Liquids


Steam
Distillation


Oil
Sales


s


Sales of
Large Pieces
of Charcoal


Briquet
Sales


Flow Diagram of Wood Distillation Process


Figure 1.







chambers which are similar to retorts in construction;

the hot charcoal ignites as soon as it comes into contact

with oxygen. After the cooling chamber is sealed, the

enclosed oxygen is used up and the flames disappear. The

charcoal cools for 8 hours, after which it is removed from

the cooling chambers and stored. After size classification,

the large pieces are sold as raw material for the production

of activated carbon, and the small pieces are pulverized,

mixed with starch, and pressed into briquets.

The vapors pass out of the retort and through con-

densers. The liquids are pumped to unlined settling lagoons

where the heavy tars and oils are separated from the

aqueous portion of the liquid. The concentrated oils and

tars are pumped from the bottom of the settling lagoons

to a steam distillation column where they are further

fractionated, barreled, and sold. The aqueous portion,

known as acid water or pyroligneous acid by the industry,

seeps through the sandy walls of the lagoons and becomes

surface drainage.

Acid water is either bacteriostatic or toxic, depending

on the circumstances. Veijolo and Mustakallo (1) separated

wood tars into various gross fractions by solvent extractiorn

and tested the effects of these fractions on biological

systems. They concluded that the resin acid fraction was

primarily responsible for the bacteriostasis, and that

these resin acids were effective in either the acid or







salt form. The following table summarizes a few of the

characteristics of acid water as sampled at Cabot Corpora-

tion.


Table 1

Summary of Acid Water Characteristics

Color Dark Amber

COD 100,000 mg/l

Iron 73 mg/l

Orthophosphate 490 mg/1

Hardness 1,500 mg/1 as CaCO3

Phenol 750 mg/1

pH 2-3


Figure 2 shows dilutions of both neutralized and

un-neutralized acid water, also from Cabot Corporation.

Major quantitative differences have been reported

in the composition of acid water obtained from the

destructive distillation of coniferous woods as compared

with acid water obtained from the destructive distillation

of deciduous woods. The qualitative analyses of both

types of acid water are similar (2). Wise and Jahn (3)

have compiled a table from several sources listing 213

different organic compounds which have been isolated

from pyroligneous acid. The names of all the compounds

listed by Wise and Jahn are presented in Table 2.













































Figure 2.


Dilutions of Neutralized and Un-neutralized
Acid Water from Cabot Corporation






Table 2


Compounds Formed by Wood Carbonization


Ammonia Formaldehyde
Formic acid Methanol
Methylamine Glyoxal
Acetaldehyde Acetic acid
Methyl format Glycolaldehyde
Glycolic acid Trimethylamine
Ethyl alcohol Dimethylamine
Acrylic acid Acetone
Allyl alcohol Propionaldehyde
Methyl acetate Hydroxypropanone
Propionic acid Isopropyl alcohol
Propyl alcohol Methylal
Succinic anhydride Furan
Crotonaldehyde Biacetyl
3-Butenoic acid Butyrolactone
Crotonic acid Methacrylic acid
Methacrylic acid, polymer 2-Butanone
2-Buten-1-ol Butyric acid
Isobutyric acid Methyl Propionate
Isobutyl alcohol Acetaldehyde dimethyl acetal
1,2-Dimethoxyethane 2-Furfuraldehyde
2-Furoic acid Pyridine
2-Cyclopenten-1-one 2-Methylfuran
3-Methylfuran Furfuryl alcohol
Cyclopentanone Tiglaldehyde
Angelic acid Methyl crotonate
2,3-Pentanedione 2-Pentenoic acid
3-Pentenoic acid Tiglic acid
e-Hydroxyvalerolactone -Hydroxyvalerolactone
Levulinic acid Acetoxypropanone
ca-Hydroxy-y-hydroxyvalerolactone
Pentene 3-Methyl-2-butanone
Isovaleraldehyde 2-Pentanone
3-Pentanone Pivalaldehyde
Valeraldehyde c-Methylbutyric acid
Methyl butyrate 1,2-Cyclopentanediol
Methyl isobutyrate Isovaleric acid
4-Hydroxy-2-pentanone Valeric acid
Pentane Isoamyl alcohol
Propionaldehyde dimethyl acetal
Benzene Phenol
5-Methyl-2-furfuraldehyde 2-Furyl methyl ketone
Catechol 5-(Hydroxymethyl)-2-
furfuraldehyde
4-Methyl 2-furoic acid Methyl 2-furoate
Maltol Pyrocinchonic anhydride
Pyrogallol 2-Picolene
2-Methyl-2-cyclopenten-l-one 4-Methyl-2-cyclopenten-1-one






Table 2 (Continued)

2,5-Dimethylfuran 1-(3 or 4)-Cyclohexandione
2-Hydroxy-3-methyl-2-cyclopenten-l-one
Cyclohexanone 3-Hexen-2-one
Mesltyl oxide l-Hydroxy-2-butanone acetate
2,3-Hexanedione 4-Methyl-2-pentenolc acid
Hydroxy-2-propanone propionate Levoglucosan
Cyclohexanol Tetrahydro-2,5-dimethylfuran
3-Hexanone Butyl methyl ketone
2-Methyl-3-pentanone Caproic acid
Isocaprolc acid o-Methylvalerlc acid
Methyl valerate Toluene
o-Cresol m-Cresol
p-Cresol Gualacol
l-Methoxy-2,3-dlhydroxybenzene 5-Methyl pyrogallol
Lutidine l-Methyl-2-cyclohexen-5-one
Propylfuran 2,3,5-Trlmethylfuran
1-Heptyne Cyclohexanecarboxaldehyde
2-Ethyl-2,3-dihydro-5-methylfuran
Diemthylcyclopentanone 5-Heptenoic acid
Butyrone Enanthaldehyde
Methyl caproate Enanthic acid
Heptane Benzofuran
m-Xylene o-Ethylphenol
2,3-Xylenol 2,4-Xylenol
3,5-Xylenol Creosol
6-Methylgualacol 2,6-Dimethoxyphenol
Methoxy-4-homocatechol 2,4-Dimethyl-4-cyclohexene-
1-one
Methylcyclopentanone 3-Isopropyl-2-cyclopenten-
i-one
Trimethylcyclopentanone 3,6-Octanedione
Caprylic acid Methyl enanthate
Dihydroxycaprylic acid 4-Vinylguaiacol
Cumene Pseudocumene
3,5-Dimethylguaiacol 4-Ethylgualacol
Homoveratrole 2,6-Dimethoxy-4-methylphenol
5-propylpyrogallol Isophorone
Amylfuran 2,4,--Trimethylcyclohexanone
Cyclohexanepropionaldehyde 3,3,5-Trimethylcyclopentanone
Pelargonic acid Naphthalene
Estragole Eugenol
Isoeugenol Cymene
Durene Thymol
4-Propylgualacol 2,6-Dimethoxy-4-ethylpheno1
A5-propyl-monomethyl ether of pyrogallol
Camphene Limonene
Nopinene Pinene
Sylvestrene r-Terpinene
Terp nolene Camphor
Borneol Cineole
Fenchyl alcohol Isofencyl alcohol
r-Te rpineol Canric acid
1,3,3-Trimethylblcyclo(2.2.2)-5-o ten-2-one
5-Propyl-1,3-dimethyoxy-2-hydroxybenzene
2,5-Difurfuryledine-1-cyclopentanone
Cadinene Pentadecane






Palmitic acid Heptadecane
Chrysene Retene
Oleic acid Stearic acid
Octadecane Nonadecane
Abietic acid Pimaric acid
Arachidic acid Eicosane
Heneicosane Behenic acid
Do cosane Tricosane
Lignoceric acid Melene
c-Methyl-S-ethylacrolein

No single compound accounts for more than a few per

cent by weight of the organic material in the acid water.

Acetic acid is one of the more abundant compounds (2).

The preceding information suggests that either an

insensitive, broad-spectrum, efficient treatment process

must be devised or some use must be found either for the

acid water or for products made from the acid water which

would provide the industry with financial returns.


Review of Applications for Wood Tars and Pyroligneous Acid

Considerable work has been reported in the literature

concerning uses for wood tars, although little information

is available on acid water alone. Hedstrom and Ballin (4)

own a Swedish patent on a process for treating halogenated

wood tars with polysulfides under heat and pressure to

produce a product which resembles rubber. Lindhe (5)

developed and patented a process for oxidizing wood tars

after the light oil fractions had been removed. Air is

used as the oxidizing agent and the temperature of the

process may range from 1000C to 3000C. Pitch of any

desired melting point may be produced by controlling the

length of the oxidation as well as the temperature.

Jonsson (6) suggested that wood tars could be used as






a fuel in piston engines. A mixture of 75 to 80 per cent

pine stump resins and 20 to 25 per cent spruce resins

produces the best results. Eldus (7) proposed that wood

tars be used as motor oils and as motor oil additives. A

commercially owned French patent describes a process for

hydrogenating wood tars (8), which is carried out at from

3000C to 5000C and 20 to 80 kg/sq cm hydrogen pressure.

Various combinations of aliphatic and alicyclic compounds

may be produced by the proper selection of the reaction

conditions. The products can be used as lubricants,

solvents, and transformer oils. Bond (9) has developed a

process for "sweetening" hydrocarbon distillates containing

mercaptans. Wood tars are mixed with the petroleum dis-

tillates and air is bubbled into the mixture while the

temperature of the mixture is held at 540C. The wood

tars aid in the destruction of the mercaptans in the hydro-

carbon distillates. Uranov et al. (10) proposed that wood

tars be used as an adhesive in the manufacture of charcoal

briquets, rather than the commonly used starch.

Mukherjee and Srivostava (11) developed a process for

manufacturing crude plastics using sugar, molasses, phenol,

creosote, and wood tar as raw materials. A somewhat

similar process has been proposed by Lyass et al. (12)

for the production of bakelite-type plastics. The raw

materials for this process are: one part wood tar, three

to five parts formaldehyde, traces of hydrochloric acid,

one hundred parts sand, and 11 per cent acetone.







Kozlov et al. (13) have described a process incorporating

flotation agents made from pyroligneous acid and wood tars

for processing copper sulfide and zinc sulfide ores from

Ural mountains. Chertkov and Zrelov (14) stated that wood

tars were not adequate as antioxidant additives in hydro-

carbon motor fuels and that these additives should be

replaced with amino-phenols. This statement implies that

wood tars have been tried as antioxidants in hydrocarbon

fuels.

The preceding applications for wood tars or acid water

do not appear to offer adequate returns or a technically

feasible method of treating or disposing of pyroligneous

acid. Little work has been reported in the literature

concerning waste treatment processes which are capable of

handling pyroligneous acid in a suitable manner. Only

two references, discussed immediately below, were found

in the literature concerning waste treatment processes

for pyroligneous acid.


Review of Waste Treatment Processes for Pyroligneous Acid

Szulicka and Grendysz (15) reported the treatment of

waste waters from a wood distillation plant by dilution in

a lagoon. The primary waste effluent of the plant contained

2,500 mg/1 of methanol, 5.3 mg/1 of acetic acid, and

200 mg/1 of phenol at the entrance to the lagoon. This

effluent was found to be strongly bactericidal. Other

wastes entering the pond included ground water, cooling

water, and sanitary wastes from the plant. The effluent







from the pond contained 27 mg/1 of methanol and 42 mg/1 of

phenol, and supported a vigorous microflora believed to be

resistant to phenol and methanol. No data were given on

the overall dilution of the primary waste flow or on the

retention time through the lagoon.

Hickerson and McMahon (16) investigated spray irriga-

tion as a supplement to lagooning and dilution as treatment

methods for the wastes of a wood distillation plant which

used hardwoods as a raw material. They determined the

most suitable grasses for spray irrigation and then used

spray irrigation to supplement controlled discharge of

the lagooned wastes into an adjacent watercourse. They

also investigated other possible treatment processes

including pH adjustment, chemical precipitation, and autox-

idation. The results of these tests were not encouraging.

Their autoxidation study consisted of aerating the waste in

a chemical reactor at 1500C and 100 psi. This treatment

produced a black sludge which they believed would create

troublesome problems in any type of filtration process.

The Sanitary Engineering Section at the University of

Florida carried out extensive chemical and biological

investigations from 1949 to 1951 to develop a satisfactory

treatment process for the Cabot Corporation. While some

technological success was achieved, the cost of treatment

was extremely high. The best biological treatment system

involved neutralizing the waste and then treating it by high

rate trickling filtration. At a recirculation ratio of






100:1, the COD of the waste was reduced about 75 per cent.

Both the effluent and influent were highly colored.

Clarification of the effluent was obtained with large

quantities of powdered activated carbon. The chemical

treatments of the waste which were investigated are:

neutralization with lime, coagulation with iron compounds,

coagulation with alum, acidification, chlorination, chlorin-

ation followed by coagulation, and extraction with an

assortment of organic solvents. Direct application of the

waste to unpaved roads showed little promise (17).


Experimental Proposal

Two conclusions were suggested by the preceding

information. First of all, biological treatment of the

waste is unattractive because of the high dilutions

necessary to reduce the toxicity of the waste and because

the effluent from biological treatment requires rather

expensive processing for clarification. Secondly, chemical

treatments must utilize inexpensive chemicals or regenera-

tive processes to be economically feasible. Autoxidation

appears to fulfill best the requirements of either

pretreatment or complete treatment of the waste. As a

pretreatment, autoxidation of the waste might partially

oxidize many of the toxic compounds in the waste, with a

possible reduction in overall toxicity. Certain of the

known toxic compounds in the waste are similar to known

antioxidants in autoxidation reactions, e.g., phenol

(18,19). The waste may be amenable to complete oxidation






by autoxidation in a few hours if sufficiently rapid re-

action rates can be established and if there is no lengthy

induction time preceding the reaction. Either pure oxygen

or air with proportional pressure increases is an inexpen-

sive oxidizing agent. In addition, sufficient heat must

be generated by the reaction to make the process self-

sustaining. Only one autoxidation system is being used in

the sanitary engineering field at present on a significant

scale. The system is known as the Zimpro Process and is

briefly described in Chapter II of this dissertation.













CHAPTER II

REVIEW OF THE ZIMPRO PROCESS

Description of the Zimpro Process


The Zimpro Process is a continuous operation for the

autoxidatlon of wastes, which process was initially de-

veloped in 1944 by F. J. Zimmerman (20). The process

consists of mixing liquid wastes and air under pressures

of 1,000 psi to 2,200 psi, and at temperatures of 5000F

to 6000F. The carbonaceous matter in the wastes reacts

with oxygen, releasing heat for the process. The heat

and pressure of the process effluent are recovered and

transferred to the Influent. Under typical conditions, a

1-hour reactor retention time would allow for a 90 per cent

reduction in COD (20).

An autoxidatlon process similar to the Zimpro Process

could prove to be applicable to the waste of Cabot Corpora-

tion. Some modifications of the process would be necessary

since oxygen rather than air is the proposed oxidizing

agent; but basically, the processes would be quite similar.

Figure 3 is a schematic illustration of the flow through

a Zimpro Process (21).

The waste or aqueous fuel flows into a holding tank,

and is then conveyed to a high-pressure pump. The high-

pressure pump acts as the pressure source for the system,












































































32


ca
P <0
CO 0 (







and as the source of head which creates flow through the

system. The waste, now under high pressure, is mixed

with metered high-pressure air from an air compressor.

The mixture enters heat exchanger number 1, then is

discharged at an elevated temperature, though not suffi-

ciently elevated to cause the autoxidatlon reaction to

proceed. The waste passes through heat exchanger number 2,

in which it reaches the temperature necessary for the autox-

idation to occur at a rapid rate. The waste then enters

the reactor where it is retained long enough for the

reaction to be completed. Since heat is released during

the reaction, the effluent from the reactor is hotter than

the influent. The effluent passes countercurrently through

heat exchanger number 2, or if enough heat has been acquired

in the reactor a portion of the effluent may by-pass heat

exchanger number 2. The effluent stream, recombined with

the portion by-passing heat exchanger number 2, enters a

gas-liquid separator. The gas phase, including steam,

nitrogen, and carbon dioxide, passes through a pressure-

control valve and is expanded through a turbine to the

atmosphere. The turbine powers an air compressor and a

synchronous motor-generator. The power developed can be

estimated from the following expression: power developed

heat released by autoxidation minus heat losses in the

entire system. If heat losses are greater than the heat

from autoxidatlon, additional heat must be added to the

process. The aqueous portion of the reactor effluent is







withdrawn from the bottom of the gas-liquid separator and

passed countercurrently through heat exchanger number 1.

Finally, the effluent passes through a third heat exchanger

located in the aqueous-fuel storage tank. The effluent

then passes through a pressure-control valve and eventually

into a natural drainage channel (21).


Discussion of the Zimpro Process

The most important feature of the Zimpro Process is

the production of heat during the autoxidation of an other-

wise useless waste. Essentially the "waste" is no longer

wasted because it is used as a fuel. The Zimpro Process

must be self-sustaining once started to be economically

attractive. The use of the Zimpro Process offers two

advantages: first of all, it disposes of highly concen-

trated wastes, and secondly, it can produce quantities of

heat beyond the needs of the process, which may be used in

some other unit operation.

The Zimpro Process, however, does entail certain

problems. Oxidation occurs only in the liquid phase

(20,21,22). Thus, low molecular weight organic compounds

would pass through the process without being oxidized.

Since molecular stability increases as the number of carbon

atoms in the molecule decreases, economical operation of

a Zimpro Process dictates that the stable components,

e.g., methanol, methanoic acid, and acetic acid, leave the

reactor in both the liquid and gaseous effluents. The

liquid effluent would ordinarily have a high Biochemical







Oxygen Demand (BOD) (23). Zimmerman (20) suggests that

organic gases leaving the reactor can be oxidized by

passing them over a silver or platinum catalyst. The liquid

effluent contains insoluble inorganic ash and high BOD,

both of which should be treated by conventional biological

methods (21).

Zimmerman (20) stated that the COD of a waste is

approximately equal to the weight of oxygen necessary to

oxidize the waste. He also suggested the following

expression for predicting the heat value of a waste:

Heat value (BTU/gal) = 48.8 x COD (gm/1). Table 3 lists

some of the properties of selected materials which might

be oxidized by a Zimpro Process (20).


Hy
Et
Ca
Ac
Ox
Py
Fu
La
Ca


Table 3

Autoxidation Properties of Several Materials

Material BTU/lb. lb. of 02/lb. lb. of air/lb.
of material of material

drogen 61,000 7.937 34.34
hylene 21,460 3.420 14.80
rbon 14,093 2.660 11.53
etic Acid 6,270 1.070 4.60
alic Acid 1,203 0.178 0.77
ridine 14,950 2.530 10.90
el Oil 19,376 3.260 14.00
ctose 7,100 1.130 4.87
sein 10,550 1.750 7.55


Waste Sulfide
Liquor
Solids
Semichemical
Solids
Sewage Sludge
Primary
Sewage Sludee
Activated


7,900

5,812

7,820

6,540


1.320

0.955

1.334

1.191


5.70

4.13

5.75

5.14


BTU/lb.
of air

1,780
1,450
1,220
1,365
1,565
1,370
1, 380
1, 455
1,395



1,385
1,410

1,365

1,270







Jackson and Brown (24) made several observations

concerning the practical operation of a Zimpro Process for

the treatment and chemical recovery of spent semichemical

pulping liquors. Among the more important observations

were: (a) corrosion was non-existant; (b) 92 per cent of

the COD was removed; (c) 90 per cent of the sodium sulfate

was recovered; (d) the equipment was easy to operate and

the cost of maintenance was low; (e) steam was recovered

economically.

The Zimpro Process has been successfully used in both

treatment and chemical recovery of the following types of

pulp and paper liquors: magnesium-base spent sulfite

liquor; semichemical acid, neutral, and alkaline sodium

sulfite spent liquors; calcium-base spent sulfite liquor;

ammonium-base spent sulfite liquor; sodium-base spent liquor;

and kraft liquor (21).

Koenig (25) has presented a good summary of the

characteristics of wet oxidation of sewage sludge by the

Zimpro Process:

(1) Oxygen pressure has no effect on the rate or the
extent of the oxidation.

(2) The reaction produces C02 and H20 plus low
molecular weight acids, e.g., CH3COOH, HCOOC,
etc.

(3) The reaction has an initial extremely rapid rate
followed by a much slower rate.

(4) The reaction reaches a different ultimate fraction
converted at each temperature.

(5) The reaction reaches approximately the same
ultimate fraction regardless of initial con-
centration at low temperatures.







(6) The reaction shows a decrease of fraction converted
with increases of initial concentration at low
temperatures.

(7) The fraction converted is a probability function
of temperature.

The experiments upon which this dissertation is based

were conducted using a process similar to the Zimpro Process,

differing only in the use of oxygen rather than air as the

oxidant. The use of oxygen in an industrial process appears

to offer two distinct advantages. First of all, the total

operating pressure of the system can be reduced, since no

nitrogen partial pressure contributes to the total pressure,

hence a lower equipment cost; secondly, since the oxygen

can be purchased under pressure, no compressor is necessary.

These advantages are at least partially offset by the cost

of the oxygen, although the results from experiments using

either air or oxygen as the oxidant should be comparable

if the partial pressures of oxygen are equivalent.














CHAPTER III

INTRODUCTION OF THE THEORY OF AUTOXIDATION
OF ORGANIC SUBSTANCES

General Description


Autoxidations are defined as oxidations which can be

brought about by oxygen gas at normal temperatures without

the intervention of a visible flame or an electric spark

(26). The preceding definition includes wet oxidation as

applied in the field of Sanitary Engineering. Bateman (27)

describes the complexities and vagaries of autoxidation

reactions very aptly. "The mechanisms (of autoxidations)

are complex and variable depending on constituent conditions

as well as trace impurities which may inhibit or initiate

the reaction." Since Bateman was speaking only of the study

of "pure" compounds, one can imagine the enormously complex

and dynamic reaction mechanisms which occur during the

autoxidation of a heterogeneous waste.

Ingold (28) describes the autoxidation of a pure

compound. "The normal curve for oxygen uptake during autox-

idation consists of an initial period where very little

oxidation occurs, known as the induction period. This is


"The succeeding discussion is taken largely from the
article cited in reference (28). The author has inserted
comments to aid in bridging the gap between theory and the
application of the autoxidation to heterogeneous wastes.







followed by a rapid increase in the rate due to autocatal-

ysis by chain-branching intermediates that build up during

the induction period. The rate soon reaches a maximum

value and then slowly starts to decrease." Figure 4 lists

the mechanisms which,in general, describe autoxidations.

RH represents the organic substrate, R02* is the correspond-

ing peroxy radical, and ROOH is the hydroperoxide.


Initiation

Reaction [il is a general expression for the initia-

tion process. The activation of organic species to the

free radical state is caused by heat, light, ionizing

radiation, or reaction with other free radicals. Hydrogen

atoms, or possibly protons, are preferentially attacked

in the following order: (1) hydrogens alpha to a double

bond or to a conjugated system, (2) tertiary hydrogens,

(3) secondary hydrogens, (4) primary hydrogens. Ingold (29)

has suggested that thermal initiation may involve the

reaction:

RH + 02 R* + H02'

since this reaction involves less energy than reaction [ .

Autoxidation of wastes, called wet oxidation by

Zimmerman and others, can be thermally initiated. Since

most wastes are heterogeneous mixtures, it is likely that

at least minute concentrations of hydroperoxide are present

in the waste. Ingold (28) states that in the presence of

minute traces of hydroperoxide, reaction 14] is the dominant

mode of initiation; and as the concentration of










Initiation:

RH activation> R- + (H.) [1]

Propagation:
R- + 02 R02* [2]

RO2* + RH ROOH + R* [3]

Decomposition of peroxide:
ROOH -RO* + .OH [4]

2ROOH RO + RO2. + H20 [5]


R02 + ROOH various products [6

ROOH -- -- nonradical products [7]

Induced decomposition of peroxide:
X + ROOH free radicals [8]

Y + ROOH ROH + YO [9]
Z + ROOH inactive products + Z 10o]

M + ROOH free radicals [ii]

Self-termination:

RO2. + RO2 --- inactive products [12]

Chain-breaking termination:

R02* + IH --- RO2H + I. [13]


Figure 4. Autoxidation Mechanisms







hydroperoxide increases, reaction 5] becomes increasingly

important as an initiation mechanism. Thermal initiation of

unsaturated substrates may occur as follows:
H H-O-
--C-C=C-? + 0=0 ----- -=-- (3 ,31,.
H H H H

-is represents the direct formation of a hydroperoxide

without free radical intermediates.


Propagation

Reaction I2] is extremely rapid except at very low

oxygen partial pressures. Consequently only peroxy radicals

are of importance in chain propagation and termination

(27,32).

In the absence of major steric effects, the rate of

reaction 3]1 depends on the carbon-hydrogen bond str-ngth

and on the availability of electrons at the carbon-hydrogen

bond being broken (33,34). Peroxy radicals can add to

olefinic double bonds (35), and tend to react more with the

oxygenated reaction products than with unoxidized species,

because the former frequently contain more reactive carbon-

hydrogen bonds (36).


Decomposition of Peroxide

The thermal decomposition of a hydroperoxide generally

yields several free radicals, which lead to chain branchin-

and account for the autocatalysis observed in many oxida-

tions. In addition, the solvent plays an important role in

the decomposition of hydroperoxide, causing the rate of






decomposition to change during an autoxidation as the
substrate is oxidized (37). At low hydroperoxide concen-
trations, the rate of hydroperoxide decomposition is first
order as exemplified by reaction [4] At higher hydro-
peroxide concentrations there are substantial deviations
from first order kinetics and apparent rate constant
increases (38,39). These phenomena are probably due to the
increasing importance of reactions [5] and [6] on the
overall autoxidation rate. The rate of decomposition of
hydroperoxides is accelerated by initiators which provide
an additional source of free radicals (40). The rate may
be retarded to a reproducible minimum value by the addition
of inhibitors of free radicals, which include polycyclic
aromatic hydrocarbons (41). The effects of reaction [5]
relative to reaction [4] decrease with increasing tempera-
ture (42). The following reaction represents a mechanism
which could be followed by the alkoxy radicals produced by
reactions [4] and [5] .
RO* + RH ROH + R*
Reactions [6] and [7? represent mechanisms which
terminate the chain reactions started by reactions 1
through [5] Reaction [7] may be considered as the reverse
of reactions [1] through [5] The products of reaction [7],
to be further oxidized, must again be activated to the free
radical state represented by reaction [i .






Induced Decomposition of Peroxide

Reactions [8] and [l1] represent catalysis of the
autoxidation while reactions [9] and [10] represent
inhibition. Reaction [8] shows the induced decomposition
of a hydroperoxide by substances not containing a heavy
metal. It results in the production of free radicals,
which accelerate the rate of the overall reaction. Alcohols

(43), ketones and ethers (44), fatty acids (45), and olefins
(46) are examples of this type of compound. A typical

mechanism for an olefin is as follows:

ROOH + R CH=CH2 -- R02. + R'HHCH3

Increasing the surface to volume ratio of the reaction
vessel or adding powdered solids may increase (47),
decrease (48), or have no effect (49) on the rate of
reaction [8] An increase in rate implies that reaction
[8] occurs only on a surface, whereas a decrease implies

that the surface promotes either reaction [o10 or the
destruction of free radicals without starting a chain
mechanism (28).

Reaction [9] describes a stoichiometric mechanism for

the inhibition of autoxidations by decomposing hydroper-

oxides to stable alcohols. Inhibition of an autoxidation

means the induced premature termination of free-radical-

forming chain reactions. Sulfur and selenium compounds
follow this inhibitory mechanism. Monosulfides which con-
tain at least one aliphatic or cycloaliphatic group attached
to the sulfur atom are more effective antioxidants than






mercaptans and disulfides, while diaryl sulfides and

sulfones are inactive (50). Inhibitors containing sulfur

are usually oxidized to strong acids which also act as

inhibitors, as shown in reaction 10o] Sulfur-containing

inhibitors also cause the production of resinous compounds

and sludges in a system undergoing autoxidatlon (51).

Selenides do not cause the formation of sludges and they

are more effective antioxidants than sulfur compounds (52).

As a rule, selenides are not found in wastes.

Reaction [o10 illustrates the mechanism by which

strong acids inhibit autoxidations. The acids are strong

in the Lewis sense (53). Although acids reduce the rate of

oxidation, they cause the production of resins, sludges,

and corrosive compounds (54). Bases are not as effective

as acids in reaction [0] but when used, resinous products

usually are not formed; when they are formed, these products

are selectively oxidized. Corrosive reaction products are

neutralized by the additives to form compounds with good

detergent properties (55).

Reaction [1i represents the induced decomposition of

hydroperoxides by a heavy metal. Metals which possess two

or more valency states with a suitable oxidation-reduction

potential between them can react with hydroperoxides to

form free radicals (56). Examples of suitable metals are

iron, cobalt, copper, manganese, add nickel. The metals

can act either as an oxidant or a reductant.

Oxidant Ce4 + ROOH -Ce3 + R02* + H






Reductant Fe2+ + ROOH Fe3+ + RO* + OH~

Certain metals, such as cobalt and manganese, can act both

as an oxidant and as a reductant. For these metals the

oxidant reaction may be rate-determining, since the metal is

found chiefly in its more highly oxidized state (57).

While ferric chloride acts as an inhibitor of the oxidation

of cumene and tetralin in aromatic solvents, it acts as an

initiator in polar solvents (58). Complexes of metal ions

and hydroperoxides are more active catalysts than metal

ions alone (59). The anion associated with the metal

can affect the catalytic activity of the metal either by

affecting its redox potential or by "blocking" the formation

of a catalyst-hydroperoxide complex. Anion effects are

specific for each metal and anion combination. The solvent

can affect the catalytic activity of the metal-anion

combination also (56).

Heavy metals act as powerful pro-oxidants of organic

autoxidations. Catalysis by metal surfaces is proportional

to their area and therefore is appreciable only in so far

as the metal is colloidally dispersed or dissolved (60).

The activity of the metal catalyst can be reduced by the

addition of corrosion inhibitors or metal passivators which

form a chemisorbed film on the surface of the metal (61).

Oxidation products form a non-corrosive substrate can also

laquer metal surfaces (62).

The catalytic effects of metal salts reach a constant

value at very low metal concentrations. This may be caused

by either chain termination by the catalyst (63) or by the







occurrence of a steady-state concentration of hydroperoxide,

as when reactions [3] and [l1i proceed at the same rate (64).

If reactions [3] and [11] proceed at the same rate, only one

new hydroperoxide is formed to replace each hydroperoxide

that decomposes. Consequently no chains can be started.

Metal catalysts can sometimes be completely precipitated

from solution shortly after the start of an autoxidation,

consequently such a catalyst could have no affect at all on

the rate of the reaction (65).

Metal ions and surfaces may be inactivated by chelating

agents such as ethylenediamine tetraacetic acid or

N,N -disalicylidene-1,2-propanediamine (66). Chelating

agents are effective because their stearic configuration

prevents the formation of metal ion-hydroperoxide complexes,

and also because they modify the redox potential of the

metal ions (58). The metal chelate may be oxidized during

an autoxidation, thus activating or releasing the metal

ion catalyst (67).


Self-termination

Reaction [12 represents the termination of a chain

by the interaction of two peroxy radicals. Primary and

secondary peroxy radicals terminate chains by way of a

cyclic transition state (68). Tertiary peroxy radicals

terminate reaction chains less readily since they lack a

hydrogen atom on thec<-carbon. These radicals are believed

to produce alkoxy radicals, which then dimerize (69). It

is possible to reduce the rate of autoxidation of a compound






which gives tertiary radicals by adding a compound which

produces primary or secondary radicals (34). Mixtures of

compounds can result in higher overall rates as compared

withthe sum of the rates of autoxidation of each of the

pure substituents.


Chain-breaking Termination

Reaction [13] describes the mechanism by which

inhibitors of free radicals reduce the oxidation rate of

organic compounds. Reaction [13] was first proposed to

cover phenolic inhibitors but was later extended to include

substituted analines. The free radical I* is stabilized by

resonance and sometimes by stearic interference by other

substituted groups. Thus I* does not initiate a new

oxidation chain (60). It will be destroyed by reacting

with another free radical. Other free radical inhibitory

reactions which have been identified are:

I. + R02 --- ROOI (70)

I. + R02* ------ ROOH + I (71)

Is + I --- .. ......... .---------- 12 (72)

Is + I. -- IH + I (73)

Many inhibitors whose active site is not protected by

bulky substituents can participate in the following

reactions:

I. + RH IH + R- (74)

102' + RH -- 100H + R" (74)

I. + 02 --- I02' (73)

I02* + I. --- 01 (73)







The inhibitor radical I* can react with hydroperoxides

and add to double bonds (75).

The rates of uninhibited oxidations are independent

of oxygen pressure, except at very low pressures (27). The

rates of inhibited reactions depend on oxygen pressure.

These data suggest that most Inhibitors react directly

with oxygen.

IH + 02 -- I + HO2. (76)

Oxidation of an inhibitor may either increase or decrease

the effectiveness of the inhibitor. The effect is dependent

on the specific conditions of a particular reaction.

Several qualitative comparisons of the effectiveness of

various Inhibitors have been compiled (77). The efficiency

of a given inhibitor type is increased by an increase in

the electron density at its reactive center, that is, by

a decrease in the redox potential of the inhibitor. If

the redox potential is too low, the efficiency of the

inhibitor is reduced because the inhibitor becomes suscep-

tible to direct oxidation (60).

While phenols and amines are the most effective Inhib-

itors known, other compounds such as quinones (78), ali-

phatic alcohols (79), and aromatic hydrocarbons, particu-

larly polycyclic aromatics (80), act as weak Inhibitors.

Two or more different inhibitors may act synergistic-

ally or antagonistically on the rate of an autoxidation.

Synergistic effects give an inhibited rate which is slower

than direct addition of the effects of the individual






Inhibitors might imply. Antagonistic effects give higher

reaction rates than would be reached if only one inhibitor

were present. Synergistic and antagonistic effects are

specific for each substrate and combination of Inhibitors

(28).


General Discussion

The preceding introduction to the theory of autox-

Idation is but a brief summary of volumes of material

available in the chemical literature. From an engineering

point of view, such theoretical explanations are valuable

for planning new research and improving the economic

operation of existing facilities. Each waste must be

studied separately to develop an optimum autoxidation

treatment process, because the reactions which can occur

simultaneously are so complex.

Three important areas of research for applied wet

oxidation processes are suggested by the theory discussed

in preceding portions of this chapter. Most important is

the development of techniques which tend to promote and

sustain autoxidation chain reactions. Since rapid reaction

rates are attained only when chain reactions are dominant,

reactors should be designed to promote and sustain chain

reactions. A faster reaction rate means smaller equipment

and a lower installation cost.

Other authors have pointed out that some autoxidation

reactions are surface reactions. For some wastes a packed

type of reactor might be best, while for others a tank-like





33

reactor would be as effective as one with a high surface

to volume ratio.

Catalysis of wet oxidation offers the promise of high

economic returns. Efficient catalysts should be discovered

for each waste. Furthermore, the most efficient method of

applying catalyst should be found. Some possibilities are:

dissolving or dispersing the catalyst in the waste, lining

the reactor walls with the catalyst, and making propellers

for mixing the reactants of a catalytic material.













CHAPTER IV

MATERIALS AND TECHNIQUES FOR THE EVALUATION OF PARTIAL
AUTOXIDATION OF WOOD DISTILLATION AS PRETREATMENT PROCESS

Introduction


The use of autoxidation as a pretreatment process

was investigated first since it promised to be more econom-

ical than complete autoxidation. In assessing the effects

of partial autoxidation on the waste, the experiments

were conducted on a pilot-plant scale. The kinetics of

the reaction were also studied while producing a substrate

to study biologically on a trickling filter. Considerable

equipment had to be collected and assembled to implement

the research.


Description of Reactor

A steam-heated chemical reactor of 67-liter volume

was obtained. The assembled reactor weighed 350 pounds

and was mounted on a four-wheel cart. The head of the

reactor could be removed by using a portable bomb hoist

mounted on a rotating T boom made of galvanized pipe.

The reaction chamber of the reactor and all fittings were

made of 316 stainless steel. The reactor was rated to

operate up to 250 psi and 1500C. The maximum temperature

which was attained in our laboratory was about 1300C

because of the inaccessibility of saturated steam at

34







pressures greater than 50 psi. The reactor was composed

of three primary sections. Figure 5 shows an overall view

of the assembled reactor.

The cylindrical base section of the reactor had a

dished bottom. The reaction chamber was surrounded by a

steam jacket. Condensate was removed from the bottom of

the steam jacket and water was circulated through the

steam jacket to cool the reactor. The reaction chamber

was sampled and drained through a 2-inch diameter threaded

opening located in the center of the dished bottom.

A 2-inch high pressure needle valve was attached to a

i-inch x i-inch bushing by a !-inch nipple. The female

half of a nut-union was attached to the outlet side of

the needle valve with a !-inch nipple. The male half of

the nut-union was attached to a !-inch pipe about 6 inches

long which served as a sample collector. The lower end

of the pipe was sealed with a -inch cap. The sample

volume was about 30 ml.

The liquids in the reaction chamber were mixed by a

four-bladed propeller, which was attached to a 1-inch

diameter stainless steel drive shaft. The drive shaft

entered the reaction chamber through the top of the reactor.

Figure 6 is an interior view of the top of the reactor

which shows the relative size of the propeller and drive

shaft. A standard asbestor-filled packing box was used

to maintain a pressure-tight seal around the drive shaft.

Silicone stopcock grease was used as a lubricant in the








Drive System
for Mixing
Reactants


Rupture
Disc
Assembly







Condensate
Drain Line


Steam Line
to Reactor


Gas Inlet
Valve,
Cross,
Pressure
Sensor
Fitting,
Gas Exhaust
Valve



Cooling
Water Line


Cart


Sampling Tube


Figure 5. Exterior View of 67-Liter Reactor












































Figure 6.


Interior View of Reactor Top






packing box rather than hydrocarbon grease, which can

react violently with high-pressure oxygen. An electric

motor attached to a speed-reducing gear box drives the shaft

at about 80 RPM. A 4-inch x 8-inch section of stainless

steel sheet metal was formed into a propeller and attached

to the top of the drive shaft, just inside the reactor.

This propeller was intended to mix the gases in the reaction

chamber.

Aside from the packing box and drive system, there

were two ports in the dished top. (See Figure 5.) A 2-inch

diameter port was fitted with a 2-inch, horizontally

oriented tube which was welded in place. The tube was

about 18 inches long and terminated in a machined flange.

This flange and a matching flange were used to hold a

nickel rupture disc, rated to burst at 350 psi and 720C,

to minimize the hazards of experimental explosions. The

atmosphere of the reactor was found to be highly corrosive

to the nickel discs. The corrosion rapidly reduced the

bursting strength of the discs. Coating the rupture discs

with silicone stopcock grease greatly retarded the corrosion.

A i-inch diameter cross was attached to a port in the

top of the reactor. A needle valve was attached to one

horizontal leg of the cross. Oxygen was fed into the

reactor through this valve from a standard high-pressure

oxygen cylinder. An Airco pressure-reducing valve was

used to control the oxygen pressure in the reactor.

The other horizontal leg of the cross was attached








to a tee. The 900 leg of the tee was fitted with a

1/16-inch tubing fitting which served as a connection for

a pressure-measuring device. The horizontal leg of the

tee was connected to a needle valve. This needle valve was

used to exhaust the gases in the reactor at the end of an

experiment or to decrease the pressure in the reactor during

an experiment. The vertical leg of the cross was fitted

with a thermocouple which extended about 12 inches into

the reaction chamber. The thermocouple was removed to

add waste to the reactor before starting a run.

The pressure and temperature inside the reactor were

measured continuously during an experiment. The readout

of the sensor signals was accomplished with a Brown Sixteen

Point Printing Recorder. All the even numbered recorder

inputs were wired together and connected to the pressure

transducer. Likewise all of the odd numbered recorder

inputs were wired together and connected to the thermo-

couple. The recorder read and printed, alternately,

pressure and temperature at 15 second intervals. Appendix 1

gives circuit diagrams and calibration curves for the

sensor systems.

The reactor was insulated with 1-inch thick fiberglass

insulation which was covered on both sides with aluminum

foil. The insulation helped maintain a constant reactor

temperature and prevented burns while working with the

reactor. Since samples had to be taken at known time

intervals, a stopwatch was used as a time monitor.








Experimental Technique for Reactor

The experimental technique is given in a step by step

manner as follows

1. A sample of waste was collected from the waste

lagoons at Cabot Corporation. (Grab samples were

taken.)

2. The dilution of the waste selected for any given

experiment was prepared with distilled water.

3. Twenty liters of the diluted waste were poured

into the reactor.

4. The waste and reactor atmosphere were purged with

nitrogen gas for 15 minutes. This created an

inert atmosphere in the reactor, which prevented

premature initiation of the autoxidation reactions.

5. The reactor was sealed by screwing the thermocouple

into place and closing all valves.

6. Mixing was begun.

7. The reactor was brought to the desired temperature

by opening the valve on the steam line and opening

the valve on the condensate drain line.

8. The temperature was held constant by adjusting the

condensate drain valve until the flow of steam

through the steam jacket gave the desired tempera-

ture. At temperatures around 1000C, it was neces-

sary to open and shut the steam-inlet valve rather

than use a continuous bleed system.

9. Oxygen was added to the reactor first by








pressurizing the oxygen feed line, then by opening

the reducing valve on the oxygen cylinder, and by

opening the needle valve attached to the cross

on the top of the reactor. The pressure in the

reactor was adjusted with the pressure-reducing

valve. If the pressure was accidently raised too

high, the exhaust valve could be opened briefly to

lower the reactor pressure.

10. The needle valve connected to the bottom of the

reactor was cracked open and any nonrepresentative

material was flushed out of the valve. This valve

was then closed. (This needle valve will be

called valve "A" in the rest of the procedure.)

11. The sampling tube was attached to the nut-union

and submerged in a liquid nitrogen bath.

12. Simultaneously, the stopwatch was started and valve

"A" was opened.

13. After the sampling tube was filled, valve "A"

was closed.

14. Within 40 seconds after having entered the

sampling tube, the sample was completely frozen.

The sampling tube was then disconnected from the

reactor.

15. The sample was thawed until it could be removed

from the sampling tube and transferred to a vial

for storage in a refrigerated area.

16. The sampling tube was washed, rinsed with distilled







water, and drained so that the next sample could

be collected.

17. Steps (10) through (16) were repeated for the

collection of successive samples, except that the

stopwatch was started only with the first sample

and let run continuously for the duration of the

experiment.

18. After the last sample was collected, the steam was

shut off. When the pressure in the steam jacket

had bled out through the condensate drain line,

cool water was flushed through the steam jacket

until the reactor returned to room temperature.

19. The pressure in the reactor was vented to the

atmosphere.

20. The partially oxidized waste was drained from the

reactor and stored in jugs to serve as substrate

for a trickling filter.

21. The reactor was washed and rinsed.


Samples were frozen as they were collected for two

reasons. First of all, chilling or freezing essentially

stops the oxidation, and secondly, freezing the sample

made it possible to remove the sampling tube from the

reactor without losing the sample through vaporization.

The best technique for freezing the sample proved to be to

immerse the sampling tube in the liquid nitrogen bath

before the sample was collected. The reaction was stopped

as soon as the liquids contacted the cold tube, before the








sample was frozen. The container for the liquid nitrogen

bath was a wide-mouth vacuum-bottle liner. To reduce the

hazards of flying glass in the event of an accident, the

vacuum liner was wrapped with plastic tape.

The samples collected during the autoxidation were

analyzed by the Chemical Oxygen Demand test (COD) as

described in Standard Methods for the Examination of Water

and Waste Water (81). This test gave a measure of the

strength of the partially autoxidized waste relative to the

strength of the raw waste. Appendix 2 describes some minor

variations from the standard COD procedure which were used

throughout this research.


Description of Trickling Filter

A trickling filter using Dow-Pac medium was selected

because of its resistance to shock loads, as the best means

of evaluating the toxicity of the treated waste. The wall

of the filter consisted of three one-quarter sections of

8-inch diameter vitrified clay pipe. The pipe and medium

were supported by a wooden stand which allowed air to

circulate vertically through the filter. The base of the

stand was in a 67-liter tank. Substrate was cycled from the

tank through the filter and back into the tank. The tank

outlet was about 4 inches from its bottom, and consequently

acted as a sludge storage area. Flow through the filter

was maintained between 21 and 3 liters per minute and a

small centrifugal pump furnished the head necessary to

maintain flow through the system. Figure 7 shows the



















































Figure 7. Trickling Filter







trickling filter. The flow was distributed over the filter

surface with a horizontal section of pegboard. Substrate

flowed over the pegboard from the hose leading from the

pump. The edges of the pegboard were raised so that about

1 inch of head was developed above each of the perforations.

The flow passed equally through each perforation and into

the filter medium. The 1/8-inch diameter perforations in

the pegboard were arranged in a square pattern on 1-inch

centers. The studies were started using a batch process.

If the results had been encouraging, the trickling filter

could have been converted into a continuous system.


Experimental Technique for Trickling Filter

The primary problem to be solved by experiments with

the trickling filter was that of determining the effective-

ness of autoxidation on reducing the toxicity of the waste.

An experimental technique which provided the desired

information is given:

1. The contents of the tank were mixed.

2. A grab sample was collected and filtered, and its

COD determined.

3. Substrate was poured into the tank, and the tank's

contents were throughly mixed.

4. A grab sample was collected and filtered, and

its COD determined.

5. The procedure was repeated at the same time daily.


The samples were filtered through a fiberglass mat.








Filtration of the samples was necessary since, in an

industrial process, most of the suspended matter would be

removed by sedimentation, and only soluble material would

contribute significant amounts of COD to the filter. By

sampling the tank directly and determining the COD of the

sample, as well as the COD of raw Cabot waste, it was

possible to determine the dilutions of partially autox-

idized waste necessary to maintain an active filter relative

to the strength of the raw waste. This value, when compared

to dilution values for the raw waste, indicated the

effectiveness of partial autoxidation as a pretreatment.













CHAPTER V

RESULTS OF THE INVESTIGATION OF PARTIAL AUTOXIDATION
AS A PRETREATMENT PROCESS

Experimental Plan


Prior to this study, no information was available

concerning the autoxidation of pyroligneous acid. Since

explosions are not unexpected when dealing with high-

pressure oxygen systems, it was felt that a cautious

approach should be made in the experiments. The plan was

to start with mild oxidizing conditions and high dilutions

of the waste, and gradually to proceed to the maximum

oxidizing conditions and the highest concentrations of the

waste. Three factors affected the rate of the reactions:

concentration of the waste, temperature, and the partial

pressure of oxygen. The partial pressure of oxygen

determined how much oxygen dissolved in the waste at any

given temperature


Determination of Oxygen Partial Pressure

Appendix 3 gives data concerning the solubility of

oxygen in water at elevated temperatures and pressures.

The rate of mixing in the reactor affected the rate of

oxygen dissolution. This had an effect on the overall

rate of the autoxidation. Each experiment was started at

a different temperature, oxygen pressure, and concentration

47







of waste. The temperature and oxygen pressure were held

as constant as possible while the change in the COD of

the waste was measured.

The partial pressure of oxygen could not be measured

directly, so the total pressure was measured and the partial

pressure of each of the components deducted from the total

pressure. The result obtained was the partial pressure of

oxygen in the reactor at the temperature of the experiment.

The oxygen pressure was converted to a standard temperature

for comparative purposes. Steam pressure was taken from

readily available information on saturated steam pressures

at various temperatures. The assumption that saturated

steam rather than superheated steam was present in the

atmosphere of the reactor must be valid since there was

liquid water in the reactor during each run. The pyro-

ligneous acid was assumed to behave like water as far as

steam pressures were concerned. While the acid water

undoubtedly did not behave like pure water, the assumption

of equality between the two liquids was valid within the

anticipated limits of accuracy in the experiments. Appendix

4 gives the variation of saturated steam pressure with

temperature. The pressure monitoring system was sensitive

to a pressure change of 1 psi.

As autoxidation occurred in the reactor, some carbon

dioxide was produced as an end product of the reaction. The

carbon dioxide produced by the reaction in turn produced

partial pressures great enough to be measured by the







pressure sensing system. This resulted in a decrease in

the effective partial pressure of oxygen, directly propor-

tional to the increase in partial pressure of carbon dioxide.

The build-up of carbon dioxide was not rapid enough to

appreciably affect the oxygen partial pressure during any

experiment for two reasons. First of all, in most

experiments the dilution of the waste was great, and even if

all the carbon atoms had been converted to carbon dioxide,

there were not enough carbon molecules in the waste to

affect the pressure in the reactor to any measurable extent.

Secondly, the gas volume in the reactor was large, about

47 liters. To create a measurable carbon dioxide partial

pressure several grams of carbon dioxide would have to

have been released by the reaction. The only experiments

that might have been affected by carbon dioxide build-up

would have been those using undiluted waste under the most

extreme oxidizing conditions.

Appendix 5 shows a theoretical calculation of carbon

dioxide build-up as a result of autoxidation. If the

partial pressure of carbon dioxide was approximately zero,

then the partial pressure of oxygen was constant. Any

oxygen consumed by the waste was replaced from the oxygen

cylinder, since the cylinder remained open and connected

to the reactor during each run.

Appendix 6 shows a typical calculation for the com-

putation of an oxygen partial pressure in an experiment.

A similar procedure was used to compute oxygen partial







pressures in all other experiments.


Results of Autoxidations

Figure 8 compares the reaction rates with two 1:100

dilutions of acid water under different oxidizing conditions.

The average rates during the first hour of the reaction

indicated that temperature was important in determining the

rate of the reaction. Run 2 followed first order kinetics,

while Run 3 followed kinetics which were greater than first

order. If an 85 per cent COD reduction is considered

complete treatment of the waste, both rates are very

slow.

Figure 9 gives the rate with a 1:50 dilution of acid

water. The reaction followed two different first order

rates. The rate during the first hour of the reaction was

approximately the same as the rate of Run 3, even though

the initial waste concentration of Run 3 was about one-

half the initial waste concentration of Run 4.

Figure 10 compares the reaction rates of three

different dilutions of acid water. All three reactions

followed first order kinetics. Sensitivity to the partial

pressure of oxygen is shown by the reaction rate for

Run 6. Decreasing oxygen partial pressure appeared to

limit the reaction rate, but increasing the pressure of

oxygen did not promote proportional rate increases.

Figure 11 compares the reaction rates of four runs

on the same dilution of acid water. The initial concen-

trations were not identical because of differences in the









100


120


Time (min)

Figure 8. COD vs. Time


Run Symbol Avg.
Temp.
oC


2 (1- ) I10

3 (0-- ) 133


Avg.
PO2 @ 0C
(psi)


117


Waste
Dilution


2.5


1:100


Avg. Rate
For First
Hour
mg/1 min


2.5


1:100 6.0


89 2.5







300



200


100

80


60



40


Ir)


120


Time (min)


Figure 9. COD vs.


Run Symbol Avg.
Temp.
oC


4 (0--0) 132


Avg.
PO2 @ 00C
(psi)


113


pH



2.5


Waste
Dilution


1:50


Avg. Rate
For First
Hour
mg/1 min


6.6


180


240


I-Le


~


r


-=i;~_Q


(^








100

80


60


120


180


Time (min)

Figure 10. COD vs. Time


Run Symbol Avg.
Temp.
oC


5 (-- ) 127

6 (0--0) 129

7 (0----) 129


Avg.
P02 @ OOC
(psi)


116

47


Waste
Dilution


2.5

2.5


1:10

1:25


116 2.5 1:20


Avg. Rate
For First
Hour
mg/1 min


15.7

2.5

12.0


240




















~t+-

.1 <---;--- --- -


80 n-


60 L


120


Time (min)


Figure 11. COD vs. Time


Run Symbol Avg.
Temp.
oC


Avg.
P0 @ 0C
2(psi)


Waste
Dilution


Avg. iate
For First
Hour
mg/1 min


8 (0-0)

13 (----)
14 (0----0)


46 2.5 1:20


600


400


200


100


180


240


90
112

129


148

135
81


2.5

2.5
2.5


1:20
1:20
1:20


2.7
4.2

9.5
5.7


15 (0) 129







samples of acid water. The importance of temperature was

clearly shown. The data suggest that reaction rates were

primarily a function of temperature. A comparison of the

reaction rates for Runs 7, 14, and 15 supports the assump-

tion that, after a certain oxygen partial pressure is

attained, further increases in oxygen partial pressure

contribute little toward increasing the rate of the

autoxidation. The reactions followed first order kinetics.

Figure 12 gives the reaction rates of three runs at

higher concentrations. Run 9 represented a concentrated

sample, but because of dilution of the acid water in the

lagoon at the time the sample was collected, the COD of

the sample was about the same as that of a 1:1 dilution

of waste collected on another date. The reaction rate

followed first order kinetics. The rates of Runs 9 and

17 were substantially greater than any other runs. This

demonstrates that a significant increase in the concen-

tration of the waste results in an increase in the rate of

the reaction.

Figure 13 shows the effects of altering the pH of

the waste before the autoxidation is attempted. A cal-

careous sludge was used to adjust the pH of the acid water.

The sludge was obtained from the Gainesville water

softening plant. The rates of all three runs were inhibited

at a COD of about 2,100 mg/1. Run 12 showed an increase

in COD during the first 30 minutes of the experiment. The

data supplied no explanation for this phenomenon, although

such a phenomenon would not be desirable in a waste






600




400








200







100


120 240


Time (min)


Run Symbol Avg.
Temp.
OC


9 (0--- ) 133

16 (---A) 126

17 (E--- ) 125


Figure 12.

Avg.
PO @ OC
(psi)


93

101


COD vs.


Time


Waste
Dilution


2.5 none


2.5


1:5


81 2.5 1:1


Avg. Rate
For First
Hour
mg/1 min


25.0

11.7

45.0


360








500





400


/


4 + 4 4- -


---- I I--g


0 30 60 90


120


150 180


Time (min)


Run Symbol Avg.
Temp.
oC


Figure 13.


Avg.
P02 @ OOC
(psi)


COD vs. Time


Waste
Dilution


Avg. Rate
For First
Hour
mg/1 min


10 (0--0)

11 (---l)


108 8.0 1:20


]


300


200






100


210


127

125


92

110


6.5

6.5


1:20

1:20


8.8

10.8

2.2


i


I


I


i J


i-


I


)- - -


b


1---


12 (r---) 130







treatment process. Since neutralization of the acid

water prior to autoxidation did not accelerate the rate

of the reaction, no additional preneutralization experi-

ments were attempted.

The autoxidation experiments at a pH of about 2.5

all followed a pattern of changes which were visually

perceptible in samples removed during a run. The 1:20

dilutions of the waste resulted in the most clearly

perceptible of these typical visual changes in the waste,

as seen in Figure 14. Sample 1 was collected just before

oxygen was added to the reactor, while sample 2 was

collected just after oxygen was added to the reactor. The

remainder of the samples were collected at thirty minute

intervals. The first visual change in the waste appeared

as the waste was heated prior to the addition of oxygen.

Heating partially broke the emulsion of tars in the waste

and caused these tars to adhere to the walls of the reactor.

This effect caused the COD of the waste to drop slightly

before any oxidation occurred. As soon as oxygen was added

to the reactor, the oils and tars in the acid water under-

went an extremely rapid polymerization reaction. The

particulate polymers which were formed caused the waste to

appear to be very dark in color. In addition, the waste

acquired strong surfactant characteristics which resulted

in stable foams. As the autoxidation continued, the waste

gradually acquired a yellow color. The polymers which

were formed at the start of the reaction were oxidized,

















1 5 q 7 q
S11 1'if N1o a1 I* Iv :

iIIufl"E


I


Figure 14. Typical Samples From Autoxidation Experiments






and the waste gradually lost its surfactant properties.

The presence of solids and stable foams in the samples

caused some difficulty in obtaining reproducible COD

values.

Appendix 7 gives triplicate COD values on Run 7.

The samples in which the initial COD was above 10,000 mg/1

did not become clear during the experiment.


Results of Trickling Filter Experiments

The substrate for the toxicity experiments was the

final reactor effluent in the autoxidation experiments.

In addition to the carbonaceous substrate (acid water),

several salts were added to the filter daily. These

salts were added because they are generally acknowledged

to be essential to bacteriological growth. The trace

elements insured that the toxicity of the acid water, and

not the lack of some essential element, would limit the

response of the trickling filter. Appendix 8 lists the

salts used and the amounts which were fed.

The trickling filter was acclimated to the partially

oxidized acid water for about one month prior to collection

of any data. Figure 15 gives the results of feeding the

partially oxidized acid water to the trickling filter.

The vertical lines on the graph represent the COD increases

in the substrate which resulted from the addition of acid

water. The diagonal lines represent the response of the

filter during a 24-hour period. The dashed line indicates

that the filter was still "alive" ten days after the last








O
14


/
/

/

/

/
/
/


J















I _
~^_







f7


I








04-) 0
o o



r-





-4
b3 'd



H -
C) r-4
SGO
iD CC)









-r4
1 II
oC


(t/2") GOD




62

daily feeding, on day thirty. The optimum response of the

filter occurred at a COD of about 1,000 mg/1. Since a 1:100

dilution is required to treat raw acid water by trickling

filtration, and the ratio of the partially oxidized acid

water is 1,000:90,000 or 1:90, no substantial reduction

in toxicity has been attained by partial autoxidation of

the pyroligneous acid.













CHAPTER VI

CONCLUSIONS FROM THE STUDY OF PARTIAL AUTOXIDATION
AS A PRETREATMENT PROCESS


The experiments already described in this disserta-

tion provide considerable information on the relationships

of pyroligneous acid to autoxidation. The main purpose

of this phase of the research was to determine if partial

autoxidation of pyroligneous acid would greatly reduce the

toxicity of the waste so that complete treatment of the

waste could be effected by conventional biological methods.

The data indicate that the toxicity of the waste was not

reduced any more than the COD of the waste was reduced.

Consequently, partial autoxidation of the waste does not

appear to be effective or desirable as a pretreatment for

pyroligneous acid. Either the toxic components of the

waste are not oxidized or they are partially oxidized to

other compounds which are equally as toxic as their

predecessors.

The data show that the acid water is autoxidized

during all experiments, although the reaction rates were

slow compared to the strength of the waste. The data

imply that if the proper conditions were discovered,

complete autoxidation would be possible. Succeeding

chapters of this dissertation support this contention.






No induction period was observed at the start of the

experiments. Consequently, the absence of an induction

period caused the complete oxidation of pyroligneous acid

to appear feasible by autoxidation techniques.

These data suggest that the reaction rates are

dependent primarily on temperature, although the partial

pressure of oxygen also affects the rate at any given

temperature. The reaction rates increased directly with

the temperature and oxygen partial pressure, although the

increases do not appear to be linear with either of these

variables. An increase in the concentration of the waste

caused a relatively large increase in the reaction rate.

The increase in rate was considerably less than the increase

in the concentration. The rate of oxygen transfer from the

gas phase into solution limited the increase of the reaction

rate as the COD or concentration of the waste was increased.

Neutralizing or raising the pH of the waste did not appear

to be desirable.

The preceding conclusions resulted in the study of

autoxidation as a technique for the complete oxidation of

the wood distillation waste. The following chapters of

this dissertation explain the study in detail.












CHAPTER VII

EQUIPMENT FOR THE INVESTIGATION OF COMPLETE
AUTOXIDATION OF WASTES

Introduction


The reaction rates obtained in the 67-liter reactor

under the most extreme oxidizing conditions possible with

the reactor, were not rapid enough to be used for the

complete autoxidatlon of the waste in an industrial

process. The data suggested that the reaction rates

could be accelerated greatly by increasing the temperature

at which the reaction was carried out and by increasing

the rate of oxygen transfer from the gas phase to the

liquid phase during the reaction. Since pressure is

dependent on the temperature, an increase in the temperature

capabilities of the reactor necessitated the use of a

high pressure reactor.


Description of Reactor and Heater

A 2-liter, electrically heated Parr reactor, capable

of operating at temperatures up to 3500C and pressures up

to 1,000 psi, was obtained. The aparatus consisted of

two sections, a 220-volt heater and controls, and the

reaction chamber, or bomb, and controls.

The 220-volt heater was composed of two concentric

cylinders. The opening between them was enclosed on both

65







ends with annular aluminum plates and was filled with

vermiculite insulation. Heat was supplied by six 250-watt

strip heaters, and the heat output was controlled by a

General Radio Co. Type W2HM Autotransformer.

A Sargent Model T Thermomonitor was included in the

heater circuit to obtain automatic temperature control.

The thermomonitor used a thermistor sensor which was

sensitive to 1/10 of 10C temperature change between 110C

and 2350C. Since the thermomonitor operated on 110 volt

AC, a relay was used in the heater circuit rather than a

direct electrical connection through the thermomonitor.

In addition, a switch was included so that the thermomonitor

might be shorted out of the heater circuit, and detached

and used elsewhere without rewiring the heater circuit.

The reaction chamber was composed essentially of two

sections, a cylinder with one end closed, and a top for

sealing the other end of the cylinder. The two pieces

together, which will be referred to as the reaction chamber,

or bomb, were constructed of 316 stainless steel. The

top was fitted with a teflon gasket to provide a pressure

tight seal when the bomb was assembled. The center of the

top housed the drive mechanism and packing box. The drive

mechanism consisted of a V-belt-powered hub which was

mounted on needle bearings. The drive shaft passed through

the packing box and attached to a lower drive shaft on

which two six-blade propellers were mounted. The propellers

were moved up and down on the drive shaft, which rotated








at 600 RPM. A pressure tight seal was maintained around

the rotating drive shaft with two "Rulon" cones. The

hollow cones were mounted back to back on the drive shaft

through openings in the narrow ends of the cones. The

space inside the cones was filled with silicone stopcock

grease. The grease acted as a lubricant and aided in

forming a tight seal around the drive shaft.

The life of the "iulon" cones -as about 40 operating

hours when the silicone grease was replaced at the start

of each experiment. Pressure was placed on the packing

cones before the bomb was pressurized. If this had not

been done, the lubricant would have been forced out of the

cones, resulting in the deterioration of the cones in 1 or

2 operating hours. The packing box was cooled during an

experiment by circulating tap water around the outside of

the box. The packing system of the reactor performed very

satisfactorily.

The gas exhaust for the bomb, a needle valve fitted

into a 1/8-inch diameter opening in the top of the bomb,

was used to lower the pressure in the bomb during an

experiment if by accident the reactor was over pressurized,

and to vent the gases in the reactor at the end of an

experiment. The same pressure transducer used with the

67-liter reactor was attached to a 1/8-inch opening in

the reactor top. The temperature sensor was the same

thermocouple arrangement used with the 67-liter reactor,

with the exception that the functions of the two junctions






were reversed. The sensing thermocouple was inserted into

a thermowell through the top of the reactor and extended

to the bottom of the reactor. Both pressure and temperature

were continuously recorded as in the earlier research.

Appendix 9 gives the calibration curves and other pertinent

information concerning the calibration of the pressure and

temperature sensing systems.

A silver rupture disc was used to minimize the danger

of an explosion during the course of an experiment.

Galvanized pipe was connected to the exhaust side of the

rupture-disc fitting to convey the reactants out the nearest

window. The first experiment conducted in the reactor with

pyroligneous acid demonstrated that silver was as sensitive

to the corrosive properties of the waste as nickel. A

teflon sheet was placed on the reaction-chamber side of the

rupture disc to minimize the corrosion of the rupture disc

and thus prevent premature breakage. The bursting pressure

of the rupture disc was rated as 1,800 psi at room tempera-

ture.

Oxygen was added to the reactor from a standard

cylinder and reducing valve. The oxygen line from the

cylinder attached to a needle valve, called the gas-inlet

valve, which connected to the top of the reactor by a tee.

The long axis of the tee joined the needle valve to the top

of the reactor. A second valve, the liquid-sampling valve,

was mounted on the 900 leg of the tee. A tube inside of the

reaction chamber led from these valves almost to the bottom







of the bomb. This arrangement made it possible to withdraw

liquid samples from the reactor by closing the gas inlet

valve and opening the liquid sampling valve. The tube was

then purged by oxygen when the gas inlet valve was reopened

after the liquid sampling valve was closed.


Collection of Liquid Samples

A coiled tube with outlets through the top of the

reactor was used to cool the reactants during the reaction

or at the end of an experiment. Both air and water were

used as coolants. The cooling coil reduced the volume of

the reactor from 2 liters to 1.362 liters. The top was

held on the cylindrical portion of the reactor by a split-

ring closure mechanism. Figure 16 shows the reactor

completely assembled and placed in the heater. Figure 17

shows the disassembled reactor with the lower drive shaft

disengaged so that the mixing propeller may be seen.

Liquid samples were collected by a technique similar

to that used in earlier research; that is, the sample

filled a sample-collection tube and was frozen with liquid

nitrogen. The sampling tube was made of 3/16-inch tubing

formed into a coil. Figure 18 shows the sampling tube

connected to the reactor just after the liquid nitrogen

bath has been removed. The lower end of the sampling tube

was closed with a Swagelock cap fitting, while the other

end was attached to the liquid sampling valve on the reactor.

The sample volume was approximately 7 ml.









Pressure
Transducer


Mixing
Drive
Motor



Brine Bath


Rupture
Disc Vent
Pipe







Oxygen
Inlet and
Liquid
Sampling
Valve





Heater
Casing


Auto-
transformer


Figure 16. Assembled Parr Reactor











Ru
Di
As


Oxygen Inlet
Valve


Drive Mechanism
and Packing Box

ipture Pressl
*sc Trans(
1sembly Conne



\/


ure
ducer
action


Cylindrical
Portion of
Reactor


Cooling
Coil






Mixing
Propeller


Closure Rings
(Foreground)


Figure 17. Disassembled Parr Reactor












AtSL


Figure 18. Sampling Tube on Reactor







Temperature Control During Experiments

Precise and automatic control of the temperature of

the reactor proved to be difficult to attain for a number

of reasons. First, the thermowell in the reactor was not

large enough to accommodate both the thermistor and

thermocouple sensors. Since the thermocouple gave a direct

measure of the temperature of the reactants, it was used

in the more desirable thermowell position. The thermistor

sensor was located beneath the reactor and held against the

bottom and side of the reactor by fiberglass insulation.

This technique gave a temperature variation of about 150C

after the system had stabilized. The thermistor was

inserted into the vermiculite insulation inside the heater

casing through an opening in the lower annular aluminum

plate. The sensor element was placed at various positions

relative to the strip heaters. However, the temperature

differential between the heater and the bomb was considera-

bly larger than anticipated. The large temperature

differential was caused by a 1/8-inch air gap between the

wall of the bomb and the heater. This air gap provided

very good insulation for the reactor. Consequently, the

temperature inside the vermiculite insulation in the heater

casing was considerably greater than the temperature of the

reactor. The strip heaters were capable of heating the

vermiculite insulation much more rapidly than they heated

the reactor. Because of these factors the temperature

fluctuation in the reactor was about t30C when the







temperature was controlled only by the thermomonitor.

The temperature could have been held closer to a constant

value manually if it had not been necessary to perform

other tasks during an experiment.


Collection of Gas Samples

During the studies that were conducted with the Parr

reactor, it became apparent that some information on the

composition of gases in the reactor was needed. The gas

samples were collected by bleeding a sample from the gas

exhaust valve on the reactor, through a brine bath to

dry the gases, and into a balloon. The moisture trap in

the brine bath was made of a capped section of galvanized

pipe about 8 inches long. The gases entered the trap

through a section of i-inch copper tubing which was soldered

into a hole drilled into the galvanized cap. This section

of the copper tubing which acted as the gas inlet extended

almost to the bottom of the trap. The gases then passed

vertically through coarse brass wool filtering material and

out of the trap through a second section of copper tubing.

The gaseous sample was collected in a rubber balloon which

was attached to one leg of a !-inch stainless steel cross.

The two legs of the cross, which formed 900 angles with the

leg to which the balloon was attached, were used for

evacuating the sampling train and for conveying the gases

from the reactor into the balloon. Tubing and pinch clamps

were arranged on these two legs so that the cross and

balloon were detached from the sampling train without loss








of the sample. The fourth leg of the cross was fitted with

a rubber septum so that portions of the sample were with-

drawn with a hypodermic syringe. Figure 19 shows all of

the equipment used to conduct the autoxidation experiments.

The gases were analyzed for oxygen and other components

on an F. and M. Model 720 thermal conductivity gas chromato-

graph. Appendix 10 describes the conditions used for the

analyses and shows typical peaks and calibration curves.

Several different experimental techniques were used

in the course of the research. The following chapter

presents each technique and the results obtained.
















W-
_ _=
i - -
S


Figure 19. Experimental Equipment


The equipment shown in the above figure is from left
to right as follows: the Sargent Thermomonitor, gas sampling
balloon (on top of the Thermomonitor), brine bath moisture
trap and gas sampling line, the Thermomonitor shorting
switch, autotransformer, heater with reactor in place,
stirrer motor, liquid nitrogen storage dewar, liquid
nitrogen bath dewar, recorder, ice water thermocouple
reference bath (on top of recorder), and pressure reducing
valve attached to the oxygen cylinder.













CHAPTER VIII

TECHNIQUES AND RESULTS OF THE STUDY OF
AUTOXIDATION OF WASTES

Introduction


The purpose of the following research was to investi-

gate the complete oxidation of wood distillation waste

by autoxidation techniques. The variables which were

expected to exert the greatest effect on the reaction

were temperature and oxygen partial pressure. During the

experimentation, it became obvious that minor changes in

experimental technique had profound effects on the rate of

the reaction. Consequently, the final experimental

technique was the result of an evolutionary process.


Source of Waste

Only the undiluted waste was used, to simulate most

realistically an industrial process. One problem already

described was the collection of reproducible samples from

the lagoons at the Cabot plant. To overcome this difficulty,

Cabot Corporation collected all the liquors from one day's

retort operation in a single tank. The settlable oils

were separated and a portion of the acid water was stored

in wooden barrels. The pyroligneous acid thus collected

gave satisfactory reproducibility during the remainder of

the study. The COD of the acid water was about 99,100 mg/1

77







when originally collected and about 90,000 mg/1 after three

months of storage. This loss of COD was probably a result

of the formation by the suspended tars of a coating on the

inside of the barrels.


First Experimental Technique

The experiments were planned to start with the study

of the reactions at a low temperature (1250C) and a low

partial pressure of oxygen (25 psi at 0C), and to proceed

stepwise by increasing the oxygen partial pressure up to

400 psi at 0C. The temperature was increased in 250C

steps up to 2250C, and a range of partial pressures was

investigated. This process was continued until the maximum

temperature and pressure capabilities of the system were

reached. During each experiment the temperature and oxygen

partial pressure were held as constant as possible.

The experimental techniques were similar to, but not

identical with, those used with the 67-liter reactor. The

technique used is given:

1. 1 liter of waste was poured into the reaction

chamber.

2. The reactor was assembled and placed in the heater.

3. Mixing was begun.

4. The gases in the reactor were evacuated and the

reactor was sealed.

5. The reactor was heated to the selected temperature

and the temperature was stabilized.

6. oxygen was gradually added to the reactor over a







period of approximately 3 minutes until the desired

partial pressure was reached.

7. The first sample was forced into the sampling

tube and a stopwatch was started simultaneously.

8. The sample was frozen in the sampling tube with

a bath of liquid nitrogen.

9. The sampling tube was disconnected from the reactor

and the sample was gradually thawed. As the sample

thawed, the expansion of the entrained gases forced

the liquid and particles of ice out of the sampling

tube. They were collected in a vial and analyzed

for COD determination (See Appendix 2).

10. Steps (7), (8), and (9) were repeated for the

collection of the succeeding samples. The stop-

watch ran continuously for the duration of the

experiment.

11. After the final sample was collected, the oxygen

cylinder was closed and the reactor was cooled

by passing water through the cooling ooil.

12. After the reactor was cooled to 500C or less, the

gases were vented to the atmosphere. The reactor

was disassembled and washed.


Results of the First Experimental Technique

The data shown in Figure 20 compare the reaction rates

at three different temperatures and approximately the same

very low partial pressure of oxygen. The rates of all three

reactions were quite slow and were approximately first order.







100


0 30 60 90


Time (min)


Figure 20.


COD vs. Time


Run Symbol


Avg.
Initial
Temp.
oC


Avg.
Initial
PO2 @ 0C
(psi)


Initial
Vol. of
Waste
(ml)


Avg. Rate
For First
Hour
mg/1 min


26 (0--O)

32 (E--])

38 (A--)


132

154


1000

1000


97

150


500 228


120


150


177 21







The rates during the first 20 minutes of the reaction were

substantially greater than the rates for the remainder of

the experiment. This was probably caused by the polymeri-

zation of the oils in the acid water, which occurred as

soon as the oxygen entered the reactor. The solid polymers

stuck to the walls of the reactor and were not measured by

the liquid sampling technique. The initial COD decreased

as the initiation temperature of the reaction was increased.

Heating the acid water partially broke the emulsion of

tars present in the acid water, and these particles adhered

to the walls of the reactor.

The information shown in Figure 21 compares the

reaction rates of two experiments at temperatures and

partial pressures higher than those presented in Figure 20.

A considerable increase in the reaction rate was readily

apparent. As a result of this faster rate, the COD was

reduced to a much lower value than in previous experiments.

Run 49 represented a 75 per cent reduction in the COD of

the waste in 75 minutes. Both reactions followed first

order kinetics.

The reaction rates shown in Figures 22 and 23 compare

the effects of five different initiation temperatures at

low oxygen partial pressures. The kinetics of all the

experiments were first order, and the rates of the two

experiments initiated at temperatures above 2000C were

considerably faster than those from experiments initiated

below 2000C. The results given in Figures 24 and 25

corroborate the results presented in Figures 22 and 23.







100


80


60


15 30 45

Time (min)

Figure 21. COD vs. Time


Run Symbol


Avg.
Initial
Temp.
oc


Avg.
Initial
P02 @ 00C
(psi)


Initial
Vol. of
Waste
(ml)


Avg. date
For First
Hour
mg/l min


44 (--O)

49 (0---GC)


203


400


226 79 300


400

903
































3 40 60
Time (min)
Figure 22. COD vs. Time


Run Symbol


Avg.
Initial
Temp.
oC


Avg.
Initial
PO @ OOC
(psi)


Initial
Vol. of
Waste
(ml)


Avg. Rate
For First
Hour
mg/1 min


27 (0-0)
33 (ED--- )
39 ( )


141
151


1000
500


181 39 500


100

80


60


I
o

r-


0


20






10
0


100


178
334
292


ii


I






100


15 30 45 60 75


Time (min)

Figure 23. COD vs. Time


Run Symbol


Avg.
Initial
Temp.
OC


Avg.
Initial
PO @ 0C
(psi)


Initial
Vol. of
Waste
(ml)


Avg. late
For First
Hour
mg/1 min


45 (0--0)

50 ([D---0)


207


400


455


350 692


I I


227 26







100


80


60




40







20







i_-


100


Time (min)


Figure 24. COD vs.


Run Symbol


Avg.
Initial
Temp.
OC


Avg.
Initial
PO2 @ 00C
(psi)


Initial
Vol. of
Waste
(ml)


Avg. Rate
For First
Hour
mg/l min


28 (0---0)

34 (0--0)
40 (--a)


136

160


52

112


1000

500


177 60 500


Time


110

365

392






100

80


60


Time (min)


Figure 25.


COD vs.


Run Symbol


Avg.
Initial
Temp.
OC


Avg.
Initial
PO2 @ Ooc
(psi)


Initial
Vol. of
Waste
(ml)


Avg. Rate
For First
Hour
mg/1 min


46 (0--0)

51 (E---)


205


400


226 59 350


Time


445

678


I







The data shown in Figures 26 and 27 compare the rates

of reactions initiated at higher partial pressures of

oxygen. Runs 41, 47, and 52 suggest that two first order

reaction rates were followed by the reaction at temperatures

above 1750C and partial pressures of about 100 psi. Run 30,

as shown on Figure 27, illustrates the importance of tem-

perature in achieving rapid reaction rates.

Support for the statements concerning the data shown

in Figures 26 and 27 is given by the data shown in Figure 28.

Higher temperatures affected the reactions in two different

ways. First of all, the higher temperatures caused more

rapid reaction rates, because the percentage of molecules

which reacted with oxygen was greater. This implies that

the rate of oxygen dissolution becomes rate-limiting as

the temperature of the reaction is increased. Secondly,

higher temperatures made a greater portion of the molecules

susceptible to oxidation; hence, a greater percentage of

the COD can be satisfied by the autoxidation.

Data comparing the rates of three experiments carried

out at intermediate temperatures and very high oxygen

partial pressures are given in Figure 29. Only Run 43

exhibits a very rapid rate.

Autoxidation of the waste caused several characteristic

changes to occur in the waste, which could be observed

visually during an experiment. These changes were similar

to those observed during experiments with the 67-liter

reactor. First of all, oils which were emulsified in the

acid water were polymerized into solid particles as soon as






100

80


60


I --


I+


100


0 20 40 60 80

Time (min)
Figure 26. COD vs. Time


Run Symbol


Avg.
Initial
T8mp.
C


Avg.
Initial
PO @ 0C
2(psi)


Initial
Vol. of
Waste
(ml)


Avg. Rate
For First
Hour
mg/1 min


(0--0)

(O---)


C---~

c- - ---- -


126

151

186


120

120

97


1000

500

500


280

275

490


I


1




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