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
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
This study was supported financially by Cabot
TABLE OF CONTENTS
ACKNOWLEDGMENTS.... ............. ....... .... ..... .
LIST OF TABLES..................................
LIST OF FIGURES....................................
ABSTRACT...... .................... .. ...............
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... ...... ...... ......... ....
1. CALIBRATION OF PRESSURE AND TEMPERATURE
SENSOR SYSTEMS......................... 131
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
1. Summary of Acid Water Characteristics............ 4
2. Compounds Formed by Wood Carbonization............ 6
3. Autoxidation Properties of Several Materials..... 18
LIST OF FIGURES
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
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
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
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
68. Schematic Profile of Autoxidation Waste
Treatment Process........................... .166
69. Design of Chemical Reactor......................167
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
Boyd T. Riley, Jr.
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
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
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
Flow Diagram of Wood Distillation Process
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
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-
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
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.
Dilutions of Neutralized and Un-neutralized
Acid Water from Cabot Corporation
Compounds Formed by Wood Carbonization
Formic acid Methanol
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
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
2-Furoic acid Pyridine
3-Methylfuran Furfuryl alcohol
Angelic acid Methyl crotonate
2,3-Pentanedione 2-Pentenoic acid
3-Pentenoic acid Tiglic acid
Levulinic acid Acetoxypropanone
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
5-Methyl-2-furfuraldehyde 2-Furyl methyl ketone
4-Methyl 2-furoic acid Methyl 2-furoate
Maltol Pyrocinchonic anhydride
Table 2 (Continued)
2,5-Dimethylfuran 1-(3 or 4)-Cyclohexandione
Mesltyl oxide l-Hydroxy-2-butanone acetate
2,3-Hexanedione 4-Methyl-2-pentenolc acid
Hydroxy-2-propanone propionate Levoglucosan
3-Hexanone Butyl methyl ketone
2-Methyl-3-pentanone Caproic acid
Isocaprolc acid o-Methylvalerlc acid
Methyl valerate Toluene
l-Methoxy-2,3-dlhydroxybenzene 5-Methyl pyrogallol
Diemthylcyclopentanone 5-Heptenoic acid
Methyl caproate Enanthic acid
Caprylic acid Methyl enanthate
Dihydroxycaprylic acid 4-Vinylguaiacol
Pelargonic acid Naphthalene
A5-propyl-monomethyl ether of pyrogallol
Terp nolene Camphor
Fenchyl alcohol Isofencyl alcohol
r-Te rpineol Canric acid
Palmitic acid Heptadecane
Oleic acid Stearic acid
Abietic acid Pimaric acid
Arachidic acid Eicosane
Heneicosane Behenic acid
Do cosane Tricosane
Lignoceric acid Melene
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
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).
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.
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,
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
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).
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
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
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
(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,
(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
(7) The fraction converted is a probability function
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.
INTRODUCTION OF THE THEORY OF AUTOXIDATION
OF ORGANIC SUBSTANCES
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.
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
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
RH activation> R- + (H.) 
R- + 02 R02* 
RO2* + RH ROOH + R* 
Decomposition of peroxide:
ROOH -RO* + .OH 
2ROOH RO + RO2. + H20 
R02 + ROOH various products [6
ROOH -- -- nonradical products 
Induced decomposition of peroxide:
X + ROOH free radicals 
Y + ROOH ROH + YO 
Z + ROOH inactive products + Z 10o]
M + ROOH free radicals [ii]
RO2. + RO2 --- inactive products 
R02* + IH --- RO2H + I. 
Figure 4. Autoxidation Mechanisms
hydroperoxide increases, reaction 5] becomes increasingly
important as an initiation mechanism. Thermal initiation of
unsaturated substrates may occur as follows:
--C-C=C-? + 0=0 ----- -=-- (3 ,31,.
H H H H
-is represents the direct formation of a hydroperoxide
without free radical intermediates.
Reaction I2] is extremely rapid except at very low
oxygen partial pressures. Consequently only peroxy radicals
are of importance in chain propagation and termination
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  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  and  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 
relative to reaction  decrease with increasing tempera-
ture (42). The following reaction represents a mechanism
which could be followed by the alkoxy radicals produced by
reactions  and  .
RO* + RH ROH + R*
Reactions  and [7? represent mechanisms which
terminate the chain reactions started by reactions 1
through  Reaction  may be considered as the reverse
of reactions  through  The products of reaction ,
to be further oxidized, must again be activated to the free
radical state represented by reaction [i .
Induced Decomposition of Peroxide
Reactions  and [l1] represent catalysis of the
autoxidation while reactions  and  represent
inhibition. Reaction  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  An increase in rate implies that reaction
 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
Reaction  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  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  and [l1i proceed at the same rate (64).
If reactions  and  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).
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
Reaction  describes the mechanism by which
inhibitors of free radicals reduce the oxidation rate of
organic compounds. Reaction  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
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
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
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
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.
MATERIALS AND TECHNIQUES FOR THE EVALUATION OF PARTIAL
AUTOXIDATION OF WOOD DISTILLATION AS PRETREATMENT PROCESS
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
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
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
Figure 5. Exterior View of 67-Liter Reactor
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
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
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
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"
14. Within 40 seconds after having entered the
sampling tube, the sample was completely frozen.
The sampling tube was then disconnected from the
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
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
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
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
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.
RESULTS OF THE INVESTIGATION OF PARTIAL AUTOXIDATION
AS A PRETREATMENT PROCESS
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
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
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
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
Figure 8. COD vs. Time
Run Symbol Avg.
2 (1- ) I10
3 (0-- ) 133
PO2 @ 0C
Figure 9. COD vs.
Run Symbol Avg.
4 (0--0) 132
PO2 @ 00C
Figure 10. COD vs. Time
Run Symbol Avg.
5 (-- ) 127
6 (0--0) 129
7 (0----) 129
P02 @ OOC
116 2.5 1:20
.1 <---;--- --- -
Figure 11. COD vs. Time
Run Symbol Avg.
P0 @ 0C
46 2.5 1:20
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
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
Run Symbol Avg.
9 (0--- ) 133
16 (---A) 126
17 (E--- ) 125
PO @ OC
81 2.5 1:1
4 + 4 4- -
---- I I--g
0 30 60 90
Run Symbol Avg.
P02 @ OOC
COD vs. Time
108 8.0 1:20
)- - -
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 :
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
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
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.
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
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.
EQUIPMENT FOR THE INVESTIGATION OF COMPLETE
AUTOXIDATION OF WASTES
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
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
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-
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.
Figure 16. Assembled Parr Reactor
and Packing Box
Figure 17. Disassembled Parr Reactor
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.
i - -
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.
TECHNIQUES AND RESULTS OF THE STUDY OF
AUTOXIDATION OF WASTES
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
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
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
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.
0 30 60 90
COD vs. Time
PO2 @ 0C
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
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.
15 30 45
Figure 21. COD vs. Time
P02 @ 00C
226 79 300
3 40 60
Figure 22. COD vs. Time
PO @ OOC
33 (ED--- )
39 ( )
181 39 500
15 30 45 60 75
Figure 23. COD vs. Time
PO @ 0C
Figure 24. COD vs.
PO2 @ 00C
177 60 500
PO2 @ Ooc
226 59 350
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
0 20 40 60 80
Figure 26. COD vs. Time
PO @ 0C
c- - ---- -