metal catalysts in catalytic wet air oxidation -...

1November 2010, 16thMetal Kokkola 2010http://lacco.labo.univ-poitiers.fr

Sylvain KEAV, Jacques BARBIER Jr.

Catalysis by metals

Metal catalysts in Catalytic Wet Air Oxidation

energy energy –– environment environment –– fine chemistryfine chemistry

November 2010, 16th

Pollutant

O

O2

MSupport

CO2H2O

2November 2010, 16thMetal Kokkola 2010 22

CONTENTSA. Context

B. Water treatment

C. Water treatment processes

D. Wet Oxidation processes

E. Catalytic Wet Air Oxidation

F. Future of the process

3November 2010, 16thMetal Kokkola 2010

A. Context


• Problem: – Human activities (domestic or industrial) → contaminated waters,

– Environmental impact, – Decrease in the amount of drinking

water.

A. Context

• Water: A few data– 65 % of human body, – 70 % of the surface of the Earth, – 3 % under the form of fresh water, – Mean daily needs: 20-50 L/person/day.

→ Rare and precious resource to be protected


• Water availability forecast:– An unattractive future…– A world of thirst…

• Water pollution control laws

A. Context


B. Water treatment


• Water treatment: from polluted to fresh water– 4 steps:

Large objects (screening)(40 mm – 0.5 mm)

Sand and Grit (settling)(0.2-0.5 mm) Fats (skimmers)

B. Water treatment

• 1. Pretreatment: – Removal of all materials easily collectable from the raw wastewater and

which could damage the apparatus (pump, skimmer, etc.).



Raw water

Treated water

Sludge

Removal of:

- 60-65 % of suspended solids,

- 30-35 % of Chemical OxygenDemand (COD).

B. Water treatment

• 2. Primary treatment: – Physical separation: Flocculation/Sedimentation stage



• 3. Secondary treatment: Degradation of organic pollutants– Biological treatments, – Physico-chemical treatments.

• 4. Tertiary treatment (optional): Final raise of the effluent quality– Filtration, – Disinfection (ozonation, chlorination or UV treatment).


Discharge or reuse

B. Water treatment


• Biological treatment:– Digestion by microorganisms (bacteria,

fungi, protozoa), – Aerobic or anaerobic treatment.

• Incineration:– Combustion in specific oven at elevated

temperature (> 1000 °C).

• Physical processes:– Stripping, Adsorption, Membrane processes, etc. – Reduction of pollution to acceptable levels.



• Oxidation processes:

[O]Presence or absence

of a catalystCxHyOz

CO2, H2O


– Classic chemical processes: Cl2, ClO2, KMnO4, FeO42-,

– Advanced Oxidation Processes (Active species: HO•, HO2•, O2

•-): • Ozonation (O3), • Wet Peroxide Oxidation (H2O2), • Fenton (H2O2/Fe2+), • Photocatalysis (O2 activated by UV/TiO2),

– Wet Air Oxidation processes (pressurized O2). D. Wet Oxidation

processes


Process Advantages Drawbacks Limits Duration Cost (€/m3)

Biological treatment

Low cost, Easy to perform

Duration, Surface of the installation, Production of

sludge

Diluted, biodegradable and non toxic compounds

25-60 h < 1 to 25

Incineration Very fast, All kind of pollutants

Expensive, Production of ashes,

solid wastes and toxic fumes (HCl, NOx, SOx, dioxins)

Very concentrated effluents

A few seconds 50 to 200

Physical processes

Cheaper than incineration, All

kinds of pollutants

Limited yields, Pollution not destroyed but

displaced

Low concentrated effluents 1-30 min < 1 to 60

Oxidation processes

Cheaper than incineration, All

kinds of pollutantsOperating costs Refractory

compounds 10-120 min 5 to 35


• Comparison of water treatment processes:


• Fields of application1:


1G. Centi, Expert Group Meeting on "Cleaner Technologies for Sustainable Chemistry", International Center for Science and High Technology, 2002.


• Thermal Wet Air Oxidation (TWAO):

– Early 20th century,

– Principle: • Total oxidation: • Limited solubility of O2, • T = 125-450 °C, P = 5-200 bar,

– Field of application: • Intermediate pollution, • Toxic or non biodegradable compounds,

– Typical performances : • 80-99 % conversion after 10-120 min, • Incomplete mineralization ↔ formation of refractory intermediates.


( ) ( ) ( ) ( )l2g2aq2aqzyx OH2yCOxO

2z

4yxOHC +⎯→⎯⎟

⎠⎞

⎜⎝⎛ −++


• Oxidability scale1:

0.6

0.0

0.2

0.4

1.0

0.8

Oxidability

Acetic acidPropionic acid

n-butanoic acid

Paper industry effluent

Sewage slugeDye industry effluent

Oxalic acid

Isobutanol

1H. Debellefontaine et al., Environ. Pollut., 92, 154-164, 1996

Carboxylic acids :– Refractory to oxidation,– Easily biodegradable

→ Biological treatment.



• Wet Oxidation process objective?


Total degradation:

One-step treatment

Partial degradation:

Two-step treatment

High temperature and pressure

Moderate temperature and pressure

Main reaction products: CO2, H2O

Main reaction products: Carboxylic acids, CO2, H2O

Reuse or discharge

Biological treatment


Elevated costs

Pollutant

O

O2

MSupport

CO2H2O


• TWAO drawbacks: – Severe operating conditions, – Acidic/Corrosive medium → Resistant reactors,– Refractory intermediates.

• Improvement of efficiency, • Milder operating conditions:

– T ≤ 200 °C, P ≤ 30 bar,

• Better elimination of refractory organic compounds better mineralization,

• Decrease in operating costs.

→ Catalytic system


• Commercial applications: – Complete oxidation or conditioning of sewage sludge, – Treatment of industrial wastewaters:

• Paper, dye, detergent, food, sugar (etc.) industries, • Alcohol distillery waste, • Chemical, petrochemical, pharmaceutical industries,

– Treatment of polluted waters: • Pesticides,

– Spent activated carbon regeneration.

• Fundamental research: – Model molecules:

• phenol and derivatives, carboxylic acids, nitrogen containing organic compounds, ammonia,

– Real industrial wastewaters.




I. Wet Air Oxidation catalystsII. Deactivation of WAO catalystsIII. CWAO reactors and processes


I. Wet Air Oxidation catalystsE. Catalytic Wet Air Oxidation

• Homogeneous catalysts: – Metallic salts:

• Copper and Iron salts,

– Advantages: • Very active,

– Drawbacks: • Precipitation/Separation step: Cu2+

(aq) → Cu(OH)2(s) or CuS(s), • Loss of catalyst, • Increase in operating time and costs.



1R.P. Kochetkova et al., Khim. Tekhnol. Topl. Masel, 4, 31, 1992.

• Heterogeneous catalysts: – Transition metals and oxides of transition metals:

• Examples: – Al, Bi, Ce, Cd, Co, Cr, Cu, Fe, Mn, Ni, Ti, V, Y, Zn, Zr, etc., – Simple oxides1: CuO > CoO > Cr2O3 > NiO, – Mixed oxides: Combinations of simple oxides (MnO2-CeO2, ZrxCe1-xO2,etc.)

• Advantages: – Cheap,

• Drawbacks: – Less active than metal salts (75-90 % mineralization), – Limited stability.



• Heterogeneous catalysts: – Carbon based catalysts:

• Examples: – Activated carbon, – Carbon Black Composite (CBC), – Carbon nanotubes,

• Advantages: – High adsorptive properties, – Resistant to acidic conditions, – Cheap,

• Drawbacks: – Combustion of the catalyst.



• Heterogeneous catalysts: – Supported noble metal catalysts:

• Examples: – Active phase: 0.1-5.0 wt-% Ir, Pd, Pt, Rh, Ru, – Typical supports: γ-Al2O3, CeO2, TiO2, ZrO2, SiO2, Activated carbon, – Ranking depends on support phase and on oxidized compounds1,2,3,

• Advantages: – Very active (85-98 % mineralization), – Very stable,

• Drawbacks: – Very expensive.

1S. Imamura et al. Ind. Eng. Chem. Res., 27, 718-721, 1988. 2J. Trawczynski et al., Carbon, 41, 1515-1523, 2003. 3J. Barbier Jr., Top. Catal., 33, 77-86, 2005.



0 60 120 1800

20

40

60

80

100

ΔTO

C (%

)

t (min)

Blank Ce PtCe RuCe ZrCePr PtZrCePr RuZrCePr

1S. Keav et al., Catal. Today, 151, 143-147, 2010.

• Example: – Activity of Pt and Ru catalysts supported on CeO2, Zr0.1Ce0.9O2 and

Zr0.1(Ce0.75Pr0.25)0.9O2 oxides1:

– CWAO of phenol in a batch reactor:

• Significant increase in activity, • Pt > Ru.


II. Deactivation of WAO catalysts

SupportM0 M0M0M0

SupportM0 M0M0M0

Mx+(aq)

Mx+(aq)

Mx+(aq)

Mx+(aq)

– Loss of active species, – Secondary pollution.

– Irreversible, – Optimization of

synthesis protocols, – Operating conditions.

Lixiviation


• Homogeneous catalysts:– Precipitation or complexation of metal ions,

• Heterogeneous catalysts: – Several deactivation phenomena:



SupportM0 M0M0M0

Support

M0 M0

– Irreversible, – Optimization of

synthesis protocols, – Operating conditions.

– Decrease in active surface, – Rare in CWAO.

Sintering


• Example: – CWAO of succinic acid on 2.2 wt-% Au/TiO2

1:

9.71.7Initial2.34.2After sintering

TOF (molSucc.molAu-1.h-1)dp (nm)

1M. Besson et al., Catal. Commun., 4, 471-476, 2003.



SupportM0 M0M0M0

– Reversible, – Operating conditions.

– Blocking of active sites, – Favoured if unsaturated

molecule.

Deposition of strongly adsorbed organic

species (poisoning or fouling)

SupportM0 M0M0M0


– Reactivation by combustion, cracking or extraction.



Deposit

Before CWAO After CWAO


1S. Keav et al., C. R. Chimie, 13, 508-514, 2010

• Transmission Electron Microscopy images: – 2.5 wt-% Pt/CeO2 tested in CWAO of phenol1


II. Deactivation of WAO catalystsE. Catalytic Wet Air Oxidation

• Catalyst reactivation:

0 60 120 1800

20

40

60

80

100Δ

TOC

(%)

t (min)

Fresh Deactivated Reactivated


III. CWAO reactors and processes• More than 200 WAO plants in operation in the world1, • Several industrial technologies with different catalysts, • Difference between research and commercial reactors:

– Batch reactor:

1V.S. Mishra et al., Ind. Eng. Chem. Res., 34, 2-48, 1995.


O2(g) P

T

..

. .. ..

. ..

.. • Most of fundamental studies, • Easy to perform, • Continuous reactors favoured

for commercial applications.


III. CWAO reactors and processes– Continuous stirred-tank reactor:

• Laboratory-scale pilot reactor

Gasoutlet

Outlet tank

T

O2

Inlet tank

P

F Gasoutlet

Outlet tank

TT

O2

Inlet tankInlet tank

PP

FF



III. CWAO reactors and processes• BAYER LOPROX® (Low-pressure Wet Oxidation):

– Bubble column reactor,– Mild conditions → Pretreatment prior to biological

treatment.

Fe2+

+ co-catalyst

Catalyst

7-30120-2003-20

Capacity (m3.h-1)T (°C)P (bar)

1O. Horek et al. Bayer AG, Swedish patent SE 7 613 832 A, 1977.



III. CWAO reactors and processes

• CIBA-GEIGY® process1: – Reactor divided into individual tube sections, – Mobile installation.

1F. Yoahimu et al., Ciba Geigy AG, Japanese patent JP 4 227 100 A, 1992.


Cu2+≈ 300≈ 150CatalystT (°C)P (bar)


III. CWAO reactors and processes• ATHOS® process1:

– Sludge treatment, – 12 m X 6 m X 10 m installation.

1F. Luck, Catal. Today, 53, 81-91, 1999.


Cu2+ or CuO220-23540CatalystT (°C)P (bar)



• NIPPON SHOKUBAI KAGAKU® process1: – Trickle-bed reactor.

1T. Ishii et al., Nippon Shokubai Kagaku Kogyo Co. Ltd., European patent EP 0 431 932 A1, 1990.


Metal/TiO2 + Oxide of a lanthanide element

(Monoliths)< 3709-80

CatalystT (°C)P (bar)



• OSAKA GAS® process1: – Bubble column reactor,

1N. Okada, Osaka Gas Co. Ltd., Japanese Patent, JP 53 020 663 A, 1976.


Metal/ZrO2 or Metal/ZrO2-TiO2

250-32070

CatalystT (°C)P (bar)


• One of the most efficient processes for intermediate pollution, • Applicable to continuous technologies, • Powder catalysts for bubble column reactors,• For other continuous reactors → shaped catalysts:

– Pellets, – Beads, – Rings, – Foams, Monoliths.



• Foam and monolithic catalysts:– Catalyst deposited on a ceramic foam or honeycomb structure,– Advantages:

• Large variety of channel shape and size, • No risk of reactor clogging due to solid particles, • High mass transfer rates,

– Widely used in various gas phase applications (VOC oxidation, catalytic converter, etc.),

– Challenge: • Active phase resistant to aqueous medium.


Ceramic support

Deposited active phase


Thank you for your attention…

metal catalysts in catalytic wet air oxidation -...

Documents