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Catalytic Wet Oxidation (CWO) in Waste Water Treatment

(Introduction of a new Technology).S. Tajammul HussainNational Centre for Physics /Chemistry DepartmentQuaid-i-Azam UniversityIslamabad, Pakistan

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CONTEXT OF CWO IN WASTE WATER TREATMENT

Problem: Treatment of waste water streams containing toxic & non-biodegradable organics at dilute concentrations.

•Phenols Chemical & petrochemical industries…•Chlorophenols pulp & paper industry (Cl bleach).

Proposed treatment method:Heterogeneous Catalytic Wet Oxidation (CWO) conducted at low severity (T, P)

•Catalyst (solid) recoverable & reusable.•Catalyst deactivation due to heavy polymeric deposits.•Low selectivity towards CO2.

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GENERAL OBJECTIVES

Development of:

Selective & cokeless industrial catalysts;

Trustful CWO kinetics accounting for deactivation.

Economically and process wise acceptable to industries.

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SPECIFIC OBJEVTIVESSPECIFIC OBJEVTIVESCWO of model phenol solution over MnO2/CeO2

•Pollutant and TOC removal,•Catalyst characterization, •Kinetic modeling,•Fate of removed C & catalyst selectivity,•MnO2/CeO2 noble metal promotion.

CWO of a model Chloroguaiacol solution•TOC & pollutant removal

•Effect of catalysts (noble metal; oxides),•Effect of temperature,•Intermediates identification.

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Range of operating conditions:Initial pollutant concentration 1-10 g/LCatalyst loading 1-5 g/LBET surface area

Mn/Ce 107 m2/gPt-Mn/Ce 102 #Pt/Al2O3 190 #Co/Bi 64 #CuO.ZnO/Al2O3 10 # Particle diameter <0.147 mmOxygen partial pressure 0.5-1.5 MPa

Temperature 80-200 oCStirrer speed 750 rpm

Analytical techniques:Liquid phase: GC-MSD, HPLC, TOC.Catalyst: BET, CHN, XPS, TPO-MS, TPR, SEM.

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A: Phenolic CarbonC: Total Inorganic Carbon

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Activation energies

Adsorption enthalpies

E (kJ/mol)

E (kJ/mol)

lnA

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TOC

, C s

olid

, C g

as (p

pm)

TOC

, C S

olid

, C g

as (p

pm)

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2

TOC

Con

vers

ion

(%)

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TOC

Con

vers

ion

(%)

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TOC

Con

vers

ion

(%)

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O

Cl4-C

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Catalyst Stability Increase.Catalyst Stability Increase.K doping and K doping and ZeoliteZeolite supportsupport

0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80 100 120

Time (min)

X/T

OC

1%3%8%0%

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Effect of Effect of ZeoliteZeolite addition on CWO addition on CWO reaction (catalyst Stability)reaction (catalyst Stability)

0

20

40

60

80

100

120

0 50 100 150 200 250 300

Time (min)

X/TO

C

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COCO22 yield (%) on yield (%) on ZeoliteZeolite supported supported and unsupported CWO catalystsand unsupported CWO catalysts

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60

Time (min)

CO

2 yi

eld

(%)

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TPO Study of CWO catalyst TPO Study of CWO catalyst

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XPS analysis of CWO CatalystsXPS analysis of CWO Catalysts

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CONCLUDING REMARKSCONCLUDING REMARKS

*Phenol & TOC removal is fast during CWO @ mild T & P over Mn/CeDeactivating carbonaceous deposits on catalyst surface.<< K >> addition drastically reduces the carbonaceous deposits.* Zeolite supportes CWO catalyst increases the catalyst life.* Phenol CWO kinetics treated using the LHHW approach for deactivating systems.*Successful description by LHHW approach of the 4 lumped species(CD;TIC; TOC; Solid C).*Enhanced selectivity to CO2 with M/zeolite-promoted Mn/Ce;*CWO effective removal Cl-guaiacol (Mn/Ce > Pt/Al2O3 > Co/Bi);*Fast destruction Cl-guaiacol & formation of recalcitrant interm. which can be used as polymers.