Catalytic wet air oxidationCatalytic wet air oxidation

The Budapest University of Technology and The Budapest University of Technology and EconomicsEconomics

Department of Chemical and Environmental Process Department of Chemical and Environmental Process EngineeringEngineering

Arezoo Mohammad HosseiniArezoo Mohammad HosseiniSupervisor: Prof. Tungler Antal Supervisor: Prof. Tungler Antal

20072007

Table of contentTable of content

IntroductionIntroduction Wet air oxidation (WAO)Wet air oxidation (WAO) Catalytic wet air oxidation (CWAO)Catalytic wet air oxidation (CWAO) ExperimentalExperimental ConclusionConclusion

IntroductionIntroduction

Industries generate large quantities of aqueous wastes containing Industries generate large quantities of aqueous wastes containing organic substances. Treatment of these waters has become a organic substances. Treatment of these waters has become a major social, technological, economical, and political problem. major social, technological, economical, and political problem.

Waste water treatment: physical, chemical, and biological.Waste water treatment: physical, chemical, and biological. Biological treatment: important for removal of organic pollutants, Biological treatment: important for removal of organic pollutants,

but often not suitable for waste streams originating from the but often not suitable for waste streams originating from the chemical industry since they may contain toxic, non-biodegradable chemical industry since they may contain toxic, non-biodegradable and hazardous pollutants. and hazardous pollutants.

One of the present technologies used for non-biodegradable waste One of the present technologies used for non-biodegradable waste treatment is wet air oxidation (WAO) treatment is wet air oxidation (WAO)

Heterogeneous catalysts used in wet air oxidationHeterogeneous catalysts used in wet air oxidation oxides of different transition metals such as Cu, Mn, Co, Cr, V, oxides of different transition metals such as Cu, Mn, Co, Cr, V,

Ti, Bi, Ti, Bi, noble metals (Ru, Pt and Pd)noble metals (Ru, Pt and Pd)

Copper oxide: the most active among oxides.Copper oxide: the most active among oxides. copper catalyst deactivate fast . This is because of formation of copper catalyst deactivate fast . This is because of formation of

polymeric substances which are deposited on catalyst particles polymeric substances which are deposited on catalyst particles and leaching of active ingredients to the reaction medium. and leaching of active ingredients to the reaction medium.

Carbon based materials are much more resistant to leaching in Carbon based materials are much more resistant to leaching in acidic solutions under WAO conditions than typical oxide supports acidic solutions under WAO conditions than typical oxide supports but they are oxidized to carbon dioxide and consumed slowly.but they are oxidized to carbon dioxide and consumed slowly.

0.01

1

100

10000

0 25 50 75 100

Flow Rate, m3/h

TO

C,

mg

C/l

Incineration Wet Air Oxidation (WAO)

RecoveryWAO & Incineration

Biological

WAO & BiologicalP

ho

toch

em

.

Ozone

AOP & Biological

H2O2

FentonFenton-likeD

O3/H2O2

h

0.01

1

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Flow Rate, m3/h

TO

C,

mg

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Incineration Wet Air Oxidation (WAO)

RecoveryWAO & Incineration

Biological

WAO & BiologicalP

ho

toch

em

.

Ozone

AOP & Biological

H2O2

FentonFenton-likeD

O3/H2O2

h

A

Wet air oxidationWet air oxidation

Breaking down biologically refractory compounds to Breaking down biologically refractory compounds to simpler, easily treatable materials. simpler, easily treatable materials.

Effective method forEffective method for The treatment of effluents containing a high organic matter The treatment of effluents containing a high organic matter

content (COD 10–100 g lcontent (COD 10–100 g l−1−1).). Toxic contaminants for which conventional biological Toxic contaminants for which conventional biological

treatment processes are inefficient.treatment processes are inefficient.

It is a liquid phase process that takes placeIt is a liquid phase process that takes place Elevated temperatures (200-300°C) Elevated temperatures (200-300°C) Pressures (50-175bar) Pressures (50-175bar) By means of active oxygen species, such as hydroxyl radicals .By means of active oxygen species, such as hydroxyl radicals . Under these conditions, complex organic compounds are Under these conditions, complex organic compounds are

mostly oxidized into:mostly oxidized into: innocuous inorganic compounds such as COinnocuous inorganic compounds such as CO22, H, H22O and hetero-atom O and hetero-atom

dissolved ions, along with simpler forms such as short-chain dissolved ions, along with simpler forms such as short-chain carboxylic acids. carboxylic acids.

..

Basic flow diagram of WAO plantBasic flow diagram of WAO plant

About 100 plants are at operation today.About 100 plants are at operation today.

Waste streams from petrochemical, chemical and pharmaceutical Waste streams from petrochemical, chemical and pharmaceutical industries as well as residual sludge from waste water streamsindustries as well as residual sludge from waste water streams..

Catalytic wet air oxidationCatalytic wet air oxidation

An alternative treatment technique to WAO.An alternative treatment technique to WAO. Use of suitable catalyst: Use of suitable catalyst:

Milder operation conditions and shorter residence timeMilder operation conditions and shorter residence time It might alter the selectivity of uncatalyzed oxidation towards It might alter the selectivity of uncatalyzed oxidation towards

the most readily biodegradable intermediates.the most readily biodegradable intermediates. Soluble metal salts (such as copper and iron salts) have been Soluble metal salts (such as copper and iron salts) have been

found to give significant enhancement of the reaction rate.found to give significant enhancement of the reaction rate. They suffer from the draw back that their use necessitates a They suffer from the draw back that their use necessitates a

separation step.separation step. Mixtures of metal oxides of Cu, Zn, Co, Mn, and BiMixtures of metal oxides of Cu, Zn, Co, Mn, and Bi

leaching of these catalysts was detected.leaching of these catalysts was detected. heterogeneous catalysts based on precious metals deposited on stable heterogeneous catalysts based on precious metals deposited on stable

supports are less prone to active ingredient leaching.supports are less prone to active ingredient leaching.

Experimental results of WAO of mildly concenrated chemical Experimental results of WAO of mildly concenrated chemical wastewaters indicated that over 50% reduction of the chemical wastewaters indicated that over 50% reduction of the chemical oxygen demand could be achieved in about an hour at oxygen demand could be achieved in about an hour at T>T>200°C 200°C and total operating pressure above 30bar. and total operating pressure above 30bar.

Table1. Summary of reported heterogeneous Table1. Summary of reported heterogeneous Catalytic WAO researchCatalytic WAO research

Cu alumina Phenol p-cresolCo none alcohols, amines , etc.Mn-Ce none poly(ethyleneglycol)Mn-Zn-Cr none industrial wastesFe Silica chlorophenolsRu-Rh alumina wet oxidizes sludgePt-Pd titania-zirconia industrial wastesRu titania-zirconia industrial wastes, sludge

Catalyst Application Active phase carrier

ExperimentalExperimental

Methods of operationMethods of operation Instrument: Instrument:

800 ml stainless steel high 800 ml stainless steel high pressure autoclave pressure autoclave

Experiments were carried outExperiments were carried out:: At 250˚C temperature and At 250˚C temperature and

50 bar pressure50 bar pressure Liquid sample analysis Liquid sample analysis

with respect to their with respect to their TOCTOC and and CODCOD content content

TOC: Shimadzu TOC TOC: Shimadzu TOC analyzer operation was analyzer operation was based on catalytic based on catalytic combustion and non combustion and non dispersive infrared dispersive infrared (NDIR)(NDIR) gas analysis gas analysis

COD: The dichromate COD: The dichromate methodmethod

Table2. Summary of some oxidation reactionsTable2. Summary of some oxidation reactions

COD decrease (%)

Final COD

Final TOC

CatalystStartingCOD

(mg/l)

Starting TOC

(mg/l)

Samplenumber

8344675060,6g Pdo/TiO2

243008450370

8394984823Net1218000344000373

18430460123200-525620134700600

593222421608-80236265805227

374998017000-80000250704695

3572412850-68000200904694

Table3. metal content of some samplesTable3. metal content of some samples

--10ppm50ppm150ppm100ppm0.1%0.1%4695

-5ppm--50ppm10ppm0.1%-5227

3ppm-30ppm200-250

ppm

5ppm300ppm-370

----20-50ppm

-0.03%-600

----400ppm300ppm0.5%0.5%4694

CrMoSrZnCuNiFekSAMPLE

ConclusionConclusion

Sample number 371 and 370Sample number 371 and 370 They were relatively easily oxidizable They were relatively easily oxidizable

(oxidized within 1-2 hours) (oxidized within 1-2 hours) With PdO/TiOWith PdO/TiO

2 2 higher reaction rate could be higher reaction rate could be achieved.achieved.

their final COD values went down almost to their final COD values went down almost to one-tenth of the starting values.one-tenth of the starting values.

Sample number 373Sample number 373 Highly concentrated acetic acid solutionHighly concentrated acetic acid solution

Mesh (Mesh (Titanium with a Ruthenium Mixed Titanium with a Ruthenium Mixed Metal Oxide coatingMetal Oxide coating)) proved to be the most proved to be the most efficient .efficient .

constant decrease in COD for example in constant decrease in COD for example in case of the catalyst Meshcase of the catalyst Mesh

In general we can see a following trend In general we can see a following trend in the effectivity of all catalysts used in in the effectivity of all catalysts used in this research work:this research work:

Mesh > RuOMesh > RuO22/TiO/TiO

2 2 > PtO2/TiO> PtO2/TiO2 2 > >

PdO/TiOPdO/TiO2 2

Sample371(100)

0100200

300400500600700

8009001000

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Time,min

TO

C (

mg

/ml)

Sample 373 (118)

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Time min

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C (

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//m

l)

Sample 373 (119)

020004000600080001000012000140001600018000

0 200 400 600Time,min

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C (

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/ml)

In generalIn general

-Some Metal content (e.g. Fe) of these waste waters act as catalyst -Some Metal content (e.g. Fe) of these waste waters act as catalyst and accelerates the oxidation processand accelerates the oxidation process-waste waters with high COD values (>100000 -waste waters with high COD values (>100000 (mg/l)(mg/l) ) were not easily ) were not easily oxidizableoxidizable

Sample 4694

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Sample 4695

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Sample number 4694Sample number 4694 The final COD value went down The final COD value went down

to half of the original value to half of the original value after almost 5 hours of after almost 5 hours of oxidation.oxidation.

Furhther oxidation was possible Furhther oxidation was possible in longer period (COD in longer period (COD reduction:66%) witout catalyst. reduction:66%) witout catalyst.

Sample number 4695Sample number 4695 Constant COD decreaseConstant COD decrease 68% COD reduction in almost 8 68% COD reduction in almost 8

hourshours

Thank you for your attentionThank you for your attention