Catalytic wet air oxidation
The Budapest University of Technology and Economics
Department of Chemical and Environmental Process
Engineering
Arezoo Mohammad Hosseini
Supervisor: Prof. Tungler Antal
2007
Table of content
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Introduction
Wet air oxidation (WAO)
Catalytic wet air oxidation (CWAO)
Experimental
Conclusion
Introduction
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Industries generate large quantities of aqueous wastes containing organic
substances. Treatment of these waters has become a major social,
technological, economical, and political problem.
Waste water treatment: physical, chemical, and biological.
Biological treatment: important for removal of organic pollutants, but often
not suitable for waste streams originating from the chemical industry since
they may contain toxic, non-biodegradable and hazardous pollutants.
One of the present technologies used for non-biodegradable waste
treatment is wet air oxidation (WAO)
Heterogeneous catalysts used in wet air oxidation

oxides of different transition metals such as Cu, Mn, Co, Cr, V, Ti, Bi,
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noble metals (Ru, Pt and Pd)
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Copper oxide: the most active among oxides.
 copper catalyst deactivate fast . This is because of formation of
polymeric substances which are deposited on catalyst particles and
leaching of active ingredients to the reaction medium.
Carbon based materials are much more resistant to leaching in acidic
solutions under WAO conditions than typical oxide supports but they are
oxidized to carbon dioxide and consumed slowly.
A
10000
WAO & Incineration
Incineration
Recovery
Wet Air Oxidation (WAO)
100
H2O2
Fenton
Fenton-likeD
Biological
AOP & Biological
1
Photochem.
TOC, mg C/l
WAO & Biological
O3/H2O2
h
Ozone
0.01
0
25
50
75
3
Flow Rate, m /h
100
Wet air oxidation
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Breaking down biologically refractory compounds to simpler, easily
treatable materials.
Effective method for
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The treatment of effluents containing a high organic matter content
(COD 10–100 g l−1).
Toxic contaminants for which conventional biological treatment
processes are inefficient.
It is a liquid phase process that takes place
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Elevated temperatures (200-300°C)
Pressures (50-175bar)
By means of active oxygen species, such as hydroxyl radicals .
Under these conditions, complex organic compounds are mostly
oxidized into:

innocuous inorganic compounds such as CO2, H2O and hetero-atom
dissolved ions, along with simpler forms such as short-chain carboxylic acids.

Basic flow diagram of WAO plant
.
 About 100 plants are at operation today.
 Waste streams from petrochemical, chemical and pharmaceutical industries
as well as residual sludge from waste water streams.
Catalytic wet air oxidation
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An alternative treatment technique to WAO.
Use of suitable catalyst:
 Milder operation conditions and shorter residence time
 It might alter the selectivity of uncatalyzed oxidation towards the most
readily biodegradable intermediates.
Soluble metal salts (such as copper and iron salts) have been found to give
significant enhancement of the reaction rate.
 They suffer from the draw back that their use necessitates a separation
step.
Mixtures of metal oxides of Cu, Zn, Co, Mn, and Bi
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leaching of these catalysts was detected.
heterogeneous catalysts based on precious metals deposited on stable supports
are less prone to active ingredient leaching.
Experimental results of WAO of mildly concenrated chemical wastewaters
indicated that over 50% reduction of the chemical oxygen demand could be
achieved in about an hour at T>200°C and total operating pressure above
30bar.
Table1. Summary of reported heterogeneous Catalytic WAO
research
Catalyst
Active phase
Application
carrier
Cu
alumina
Co
Mn-Ce
Mn-Zn-Cr
Fe
Ru-Rh
Pt-Pd
Ru
none
none
none
Silica
alumina
titania-zirconia
titania-zirconia
Phenol
p-cresol
alcohols, amines , etc.
poly(ethyleneglycol)
industrial wastes
chlorophenols
wet oxidizes sludge
industrial wastes
industrial wastes, sludge
Experimental
Methods of operation
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Instrument:
 800 ml stainless steel high
pressure autoclave
Experiments were carried out:

At 250˚C temperature and 50
bar pressure
Liquid sample analysis
 with respect to their TOC and
COD content
 TOC: Shimadzu TOC analyzer
operation was based on
catalytic combustion and non
dispersive infrared (NDIR) gas
analysis
 COD: The dichromate method
Table2. Summary of some oxidation reactions
Sample
number
Starting
TOC
(mg/ml)
Starting
COD
(mg/ml)
Catalyst
Final
TOC
Final
COD
COD
decrease
(%)
4694
20090
68000
-
12850
35724
4695
25070
80000
-
17000
49980
37
5227
26580
80236
-
21608
32224
59
600
134700
525620
-
123200
430460
18
373
344000
1218000
Net
4823
9498
83
370
8450
24300
0,6g
Pdo/TiO2
506
4467
83
Table3. metal content of some samples
SAMPLE k
Fe
Ni
4694
0.5%
0.5%
4695
0.1%
5227
Cu
Zn
Sr
Mo
Cr
300ppm 400pp
m
-
-
-
-
0.1%
100ppm 150pp
m
50ppm
10ppm
-
-
-
0.1%
10ppm
50ppm
-
-
5ppm
-
600
-
0.03%
-
2050ppm
-
-
-
-
370
-
300ppm 5ppm
200250
30ppm
-
3ppm
ppm
Sample371(100)
Sample number 371 and 370
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They were relatively easily oxidizable (oxidized
within 1-2 hours)
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With PdO/TiO2 higher reaction rate could be
achieved.
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their final COD values went down almost to onetenth of the starting values.
TOC (mg/ml)
Conclusion
1000
900
800
700
600
500
400
300
200
100
0
0
50
100
150
Time,min
Sample 373 (118)
19500
19000
Sample number 373
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Highly concentrated acetic acid solution
TOC (mg//ml)
18500
18000
17500
17000
16500
16000
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Mesh (Titanium with a Ruthenium Mixed Metal
Oxide coating) proved to be the most efficient .
constant decrease in COD for example in case of
the catalyst Net
15500
In general we can see a following trend in the
effectivity of all catalysts used in this research
work:
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
Mesh > RuO2/TiO2 > PtO2/TiO2 > PdO/TiO2
0
50
100
150
200
250
300
Time min
Sample 373 (119)
TOC (mg/ml)

0
200
Time,min
400
600
Sample number 4694
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The final COD value went down to
half of the original value after
almost 5 hours of oxidation.
23000
21000
19000
TOC (mg/ml)

Sample 4694
Furhther oxidation was possible in
longer period (COD reduction:66%)
witout catalyst.
17000
15000
13000
11000
9000
7000
5000
0
100
500
30000
Constant COD decrease
68% COD reduction in almost 8
hours
400
Sample 4695
25000
TOC (mg/ml)

300
Time (min)
Sample number 4695
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200
20000
15000
10000
5000
0
100
200
300
400
500
600
Time (min)
In general
-Some Metal content (e.g. Fe) of these waste waters act as catalyst and
accelerates the oxidation process
-waste waters with high COD values(>100000 (mg/ml) )were not easily oxidizable
Thank you for your attention