ABSTRACT

The spent IX resin wastes arising from nuclear power plants have high

radiation level due to fission product 137Cesium and activation product 60Cobalt. The

pyrolysis and oxidative pyrolysis processes have potential to minimise final waste form

volumes of these wastes .The major difficulty in deploying these processes for treatment

of spent IX resins is release of off-gases containing large quantities of aromatic

hydrocarbons, amines, sulphur dioxide, hydrogen sulphide, carbonyl sulphide etc. As an

alternative to high temperature incineration of the pyrolysis off gases, feasibility of using

catalytic combustion at moderate temperatures was investigated in the laboratory.

Copper Chromite, Copper Oxide- Ceric Oxide and Vanadium Pentaoxide

catalysts supported on alumina were prepared and tested for oxidation of styrene

monomer, toluene, ethyl benzene and trimethyl amine at 22500 hr-1 space velocity and

temperature range of 300 to 500oC. At temperatures over 475 oC, all three catalyst gave

oxidation efficiency of over 97 % for these compounds over concentration range of few

tens of ppm to few thousands ppm. A composite catalyst bed of three catalysts

comprising principally of Copper Chromite is proposed for treatment of IX resin

pyrolysis off-gases.

Keywords

Spent IX resins

Catalyst System

Transition Metal Oxide Catalysts

Styrene

Toluene

Ethyl Benzene

Trimethyl Amine

Oxidation Efficiency

CONTENTS

1. INTRODUCTION 1

2.0 TYPES OF IX RESINS USED IN NUCLEAR POWER PLANTS 1

3.0 CHEMICAL NATURE OF PYROLYSIS OFF GASES 2

3.1 Release of water vapour 2

3.2 Releases from Functional Groups of IX Resins 2

3.3 Releases of Hydrocarbons from Base Polymers 3

3.4 Release of Soot 3

4.0 CATALYST SYSTEM 4

4.1 Objective Of Using Catalytic Combustion 4

4.2 Requirements of Catalyst System 4

4.3 Catalyst Support 5

4.4 Washcoat On Support 5

4.5 Catalyst Impregnation 6

4.6 Metal Oxide catalysts of Interest 6

4.7 Operation of Catalyst bed 8

5.0 EXPERIMENTAL 9

5.1 Alumina Support 9

5.2 Wash coat of alumina 9

5.3 Copper Chromite Catalyst 9

5.4 Copper Oxide-Ceric Oxide Catalyst 10

5.5 Vanadium Pentoxide Catalyst 10

5.6 Evaluation of Catalysts 10

6.0 RESULTS AND DISCUSSIONS 18

7.0 CONCLUSIONS 19

ACKONWLEDGEMENTS 20

REFERENCES 20

Figures 6

Table 1

1.0 INTRODUCTION

Organic Ion Exchange (IX) resins are used [1] to purify primary coolant of

nuclear power plants. IX resin wastes have high radiation level arising from fission

product 137Cesium and activation product 60Cobalt.

Carbonisation [2,3], pyrolysis [4,5] and oxidative pyrolysis [6,7] of spent IX

resins have emerged as effective treatment methods for minimizing final waster form

volume. The major difficulty in deploying these processes for commercial applications is

release of off-gases containing large quantities of aromatic hydrocarbons, amines, sulphur

dioxide, hydrogen sulphide, carbonyl sulphide etc[8]. Uncatalysed incineration of the off

gases generates polyaromatic hydrocarbons(PAHs), soot, SOx and NOx [9,10] which are

toxic/corrosive to structural materials at high temperatures [>1000oC] encountered in

incinerators.

The chemical nature of the pyrolysis off gases is [11] similar to automobile

exhaust although the quantities of aromatic hydrocarbons, amines and sulphur dioxide

dominate the composition in a very large way. Transition and rare earth metal oxide

catalysts have been developed [12 to 14] for low temperature catalytic treatment of such

highly contaminated gas streams. Advantages of catalytic oxidation are low secondary

liquid waste generation, elimination of foul smell and prolonged life of high efficiency

particulate filters. The formation of NOx by oxidation of atmospheric nitrogen[9] at high

incinerator temperatures is avoided. Studies were taken up to explore feasibility of using

catalytic oxidation of IX resin pyrolysis off gases at moderately high temperatures. The

report describes requirements of the catalyst system, selection of low cost catalysts, their

preparation procedures and evaluations for aromatic hydrocarbons and amine oxidation.

2.0 TYPES OF IX RESINS USED IN NUCLEAR POWER PLANTS

The nuclear grade strongly acidic cationic (R-SO3-H+) and strongly basic anionic

(R-CH2-N[CH3]3+OH-) resins are used in the nuclear power plants. Base polymer of the

resins is polystyrene crosslinked by 8 to 10 mole % divinyl benzene.

In primary heat transport (PHT) systems of Pressurized Heavy Water Reactors

(PHWRs) mixed cationic and anionic IX resins in 30 : 70 weight ratio are used[1]. The

spent IX resins discharged from PHWRs are predominantly in H+ and OH- forms.

Moderator purification system of PHWRs uses anionic resins in borate form. The Russian

VVER reactors are pressurised water type reactors and use [15] cationic resins in K+

form and anionic resins in borate form. Spent cationic resins are partially loaded with

corrosion products of stainless steel, zircalloy and stilbite and the anionic resins with

carbonate, bicarbonate, chlorides and nitrates.

5.0 CHEMICAL NATURE OF PYROLYSIS OFF GASES

3.1 Release of water vapour

Spent IX resins are transferred by fluidisation with water to the pyrolyser. Excess

water is removed by applying vacuum . The water content of wet resins after this step is

around 72 weight percent. This water evaporates as steam during first step of pyrolysis at

the temperatures upto 130o C.

3.2 Releases from Functional Groups of IX Resins

Degradation of organic matter commences after the evaporation of water.

Pyrolysis of IX resins is carried out in presence of nitrogen to avoid unwanted exothermic

oxidation reactions and improve safety. It is reported that during decomposition of

sulphonic acid groups, 35 % sulphur is retained [16] in the polymer matrix. Sulphur has

capability to form –C=S=C- and –C-SO2-C-linkages with organic matter as observed in

vulcanization of rubber. During decomposition of sulphonic acid groups SO2 is released

[17] over temperature range of 250 to 1100 oC. Due to reducing conditions prevailing

during pyrolysis, part of sulphur is released as SO2, H2S, COS + and CS2 .

The quaternary ammonium hydroxide groups in the anionic resins decompose

giving amines. Trimethyl amine (TMA) is most dominant among them. The other

amines released from anionic resins are methylamine, dimethyl amine, methane diamine

1-3 butadyine.[8]. Oxidation of amines leads to formation of NOx. [9]

3.3 Releases of Hydrocarbons from Base Polymers

Styrene is monovinyl benzene. Hence off gas compositions of polystyrene and styrene–

divinyl benzene copolymer, which is IX resin base polymer, are similar. The pyrolysis of

polystyrene is widely studied [18 to 23] . Styrene, toluene and ethyl benzene constitute

major portion of aromatics released. Styrene contributes 75 to 90 % to total aromatics.

Polystyrene forms PAH during incomplete combustion[10]. Formation of polycyclic

structures during incomplete combustion is described by polyacetylene theory and ionic

theory . Free radical and ionic reactions lead to formation of PAHs. In pyrolysis under

nitrogen atmosphere, the C/O ratio of off gas is high and aromatics have high C/H ratios.

These two factors lead to formation of PAHs. Pyrolysis conditions especially temperature

and off gas stay time in hot zone influence the reactions between the aromatics. The

quantity of PAH formed [24,25] decreases with increasing combustion temperature from

800 to 950 oC. Styrene has tendency to polymerize. In pyrolysis of polystyrene at 540 oC

dimers and trimmers of styrene were also identified.. Some of the important PAHs

released [ 23,24] during pyrolysis of polystyrene are indene, naphthalene, biphenyl,

fluorine, and phenyl naphthalenes.

3.4 Release of Soot

Increase in molecular weight and free radical reactions lead [26,27] to formation

of species of 1 to 2 nm size. These species have tendency to form aggregates and

agglomerates by adsorption of hydrocarbons, water vapour and SOx which act as binder.

Their size increases to 10 to 20nm and behave like particulate matter called soot.

Styrene, toluene, ethyl benzene and TMA are major organics present in the IX

resin pyrolysis off gas. It will be sufficient to test the oxidation catalyst for these organic

compounds. The releases of higher homolog of styrene and PAHs are low and they are

expected to behave similarly under catalytic oxidation conditions.

6.0 CATALYST SYSTEM

4.1 Objective Of Using Catalytic Combustion

The catalyst consists of two components - the active catalyst and support

consisting of substrate and wash coat. The catalyst bed may be externally heated to

maintain at desired temperature. Premixed and preheated fuel-air mixture is passed

through catalytic combustor. Because of plug flow conditions provided by the catalyst

bed, thermal inertia of the catalyst bed and premixing of fuel and air, stable oxidation can

be sustained at low fuel concentrations. The activation energy for the heterogeneous

oxidation on the surface of a catalyst is much lower than that for purely homogeneous gas

phase oxidation reactions. Consequently appreciable heterogeneous oxidation rates can

be achieved for lower fuel concentrations and at lower temperatures compared to

homogeneous oxidation.

At lower catalyst bed temperatures, the reaction rate is determined by overall

intrinsic surface kinetics and .increases exponentially with bed temperature. At higher

catalyst bed temperature, reaction rates become so high that the overall process is limited

by rate of mass transport to the catalyst surface and reaction rates are insensitive to

temperature changes. At still higher temperatures, homogeneous combustion and

heterogeneous catalytic reactions occur simultaneously. Due to high combustion

efficiency, soot formation is almost completely eliminated.

4.2 Requirements of Catalyst System

The catalyst system should possess[28] the following properties-

i) Catalyst should be capable of igniting fuel-air mixture at lowest possible temperature

ii) Catalytic activity should be sufficiently high to maintain complete combustion at the

lowest preheat of fuel air mixture and highest values for mass throughput

iii) Support should have high surface area, low pressure drop, high thermal shock

resistance and high working temperature.

iv) Wash coated surface of support should be capable of maintaining high surface area

under combustion conditions

v) Catalyst should maintain high activity after prolonged use at elevated temperature.

4.3 Catalyst Support

Advantages of supported catalysts are high surface to volume ratio and high

thermal stability endowed by dispersion. They are prepared by impregnation on support.

The catalyst support serves[28] three important functions-

i) It increases the surface area of the metal oxide by providing dispersion

ii) It can reduce the sintering of the catalyst material and improve thermal stability

iii) It can enhance the activity of catalyst material.

The catalyst and support must have mutual insolubility. The melting points of

supports should be at least 1.5 times higher than maximum operating temperature of

catalyst. The catalyst supports should be resistant to thermal shock. Aluminas are less

expensive, reasonably resistant to thermal shock and can operate at high temperatures.

4.4 Washcoat On Support

The metal oxides may form aluminates at high temperature. The interactions of

catalyst and support can alter strength, decrease surface area and thermal shock

properties. Formation of lanthanum/cerium aluminates retards sintering of alumina and

minimises the transformations to low surface area alpha and delta forms. It is better to

start with low surface area wash coated catalysts since this would result in better

retention of strength and thermal shock properties as well as less change in catalyst

activity during operation.

La2O3 and CeO2 washcoats are most widely reported on alumina. La2O3 is[29]

valence invariant and more effective than ceria as wash coat. Ceria increases [30]

mechanical strength of alumina and stabilises against surface area loss by inhibiting

transformation of gamma alumina to high density alpha alumina.

4.5 Catalyst Impregnation

The impregnation and drying steps involve mass and heat transfer processes.

The impregnation profile means intra-pellet distribution of catalytic component.

Preparation of impregnated catalyst involves

i) contacting dry or wet support with an impregnating solution

ii) drying

iii) calcining.

The third step appears to have relatively small influence in determining

impregnation profiles. [31]

The impregnant solution is imbibed into pores due to capillary pressure. The flow

of solution inside pellet ceases after reaching centre of pellet and then only diffusion and

adsorption continue. Adsorption of metal ions on support is important in determining

impregnation profiles. The adsorption characteristics are dependent on pH of solution

and isoelectric point of support. At pH below isoelectric point, the support is positively

charged and adsorbs anions. At pH higher than isoelectric point, the surface is negatively

charged and adsorbs cations. Hydrolysis and/or precipitation of impregnant can change

the adosrptivity. Thus pH of solution, isoelectric point and nature of chemical species of

impregnant are important in impregnation. During drying step the evaporation of

solution redistributes the impregnant in pores. When heating rates are slow, the steady

state is established. The solution is drawn to evaporation zone and this results in

segregation of impregnant at pellet periphery. This is known as egg-white type

impregnation. At fast heating rate, the impregnant in pore volume solution increases its

concentration at menisci and deposits catalyst on pore walls. The fast drying leads to

distribution of impregnant towards centre. This egg yolk type impregnation is not of our

interest.

4.6 Metal Oxide catalysts of Interest

Transition metal oxides are extensively used as catalyst in selective or complete

oxidation processes. The rate of catalytic oxidation depends on strength of metal-oxygen

bonds in their oxides. Noble metals having low bond strength are best catalysts. Copper,

chromium, vanadium, iron and nickel along with silver and cobalt fall in middle range.

Although noble metals are resistant to poisoning by H2S, SO2 etc, their high cost

demands recovery from spent catalyst making them unattractive for nuclear waste

management.

SO2 is one of the off gas component released from cationic resins. Sulphur

dioxide forms sulphites/sulphates with transition metal oxide catalysts. The sulphates of

transition metals have high decomposition temperatures which are generally above

operating range of transition metal oxide catalysts. Hence SO2 can cause irreversible

poisoning. Similarly H2S and COS can form sulphides with transition metal oxide

catalysts. Sulphide poisoned catalysts can however be regenerated by heating in air to

decompose them to oxides[32]. NaOH can react with SO2, H2S and COS. NaOH coated

alumina bed is preferred over NaOH scrubber at front end of transition metal oxide

catalysts since gases are at high temperatures and operation difficulties associated with

scrubbers.

Polystyrene along with ammonium perchlorate is used as solid Propellant in the

rockets. For efficient oxidation of polystyrene, copper chromite catalyst powder is used

as additive for increasing the burning rate of solid propellants[33,34]. Since styrene

vapours are most dominant component of IX resin pyrolysis off-gases, copper chromite

was selected as catalyst.

The incomplete oxidation of styrene, its higher homologues and PAH over copper

chromite catalyst can lead to formation of CO and soot. Hence it was decided to develop

catalysts which are reported to have high efficiency for CO and/or soot and also for

organic vapours. They are to be used as back up beds.

Ceric oxide in pure form or mixed with other oxides is [30,35] effective catalyst

to oxidise carbon monoxide to CO2 in temperature range of 100 to 200 oC. Addition of

some elements dramatically modifies behaviour of CeO2 towards oxidation of CO.

Addition of CuO to CeO2 lowers[30] the light off temperature (temperature of 50%

efficiency) by 200oC. Comparison of catalytic activity for CO oxidation over different

catalysts indicated [30] that Cu0.15Ce0.85O2+X gave high oxidation rates. Hence this

catalyst composition was selected as one of the back up bed to copper chromite catalyst

Since soot is particulate matter, its oxidation requires physical contact with

catalyst surface for achieving efficient oxidation. Surface temperature of carbon or soot

burning in air is high due to exothermic oxidations reactions. Vanadium pentaoxide and

alkali vanadates are [36 to 38] well known catalysts for oxidation reactions and have low

melting points. Molten V2O5 would have excellent contact with soot. Hence it was

selected as another back up bed for copper chromite catalyst.

4.7 Operation of Catalyst bed

As the pyrolysis is carried out in nitrogen atmosphere, The off -gases are mixed

with air to supply oxygen. While mixing of air with hot pyrolysis gases, the lower and

upper explosion limits of individual off gas components should be considered. These

limits are indicated[39] in Table 1. Computations of concentrations of components in the

off gases of IX resin pyrolysis pilot plant indicated that by maintaining air supply at 250

% of stoichiometric requirements, the lower explosion limits could be avoided safely.

Use of such high excess of air, leads to formation NOx from oxidation of TMA by

mechanism reported[9] elsewhere. Contribution of NOx from oxidations of atmospheric

nitrogen at catalytic oxidation operating temperatures is not significant due to kinetic

considerations..

Table 1

Physical Properties of Off-gas Components

Compound Melting

Point

( oC )

Boiling

Point

( oC )

Flash

Point ( oC )

Lower

explosion

limit

( % )

Upper

Explosion

limit

( % )

Auto

Ignition

temp.

( oC )

TMA -117 2.9 -6.6 2 11.6 190

Styrene -31 145 31.1 1.1 6.1 490

Toluene -93 110.6 4.4 1.4 6.7 536

Ethyl

benzene

-95 136 59F 1 6.7 432

5.0 EXPERIMENTAL

5.1 Alumina Support

Spherical pellets of gamma alumina having 6 to 8 mm diameter were procured from

indigenous source. They were crushed to -22,+50 mesh size, washed with demineralised

water and dried at 200 oC for storage.

5.2 Wash coat of alumina

LR grade La (NO3)3 6 H2O was used to give La2O3 washcoat and ceric

ammonium nitrate to give CeO2 wash coat to alumina. Lanthanum nitrate was estimated

by oxalate precipitation and titration of the precipitate with 0.1 N KMnO4. Ceric

ammonium nitrate solution was analysed by titration with ferrous ammonium sulphate.

The quantity of water required for incipient wetting was determined using 100 gm

alumina. It was 34 to 35 ml per 100gms. Quantity of La (NO3)3 6 H2O solution which can

give 10 grams of La2O3 after decomposition was taken and diluted to 350 ml. 1.0 kg of

alumina was added to lanthanum nitrate solution, mixed thoroughly and kept overnight

for equilibrium. The pellets were first dried under IR lamp followed by slow heating to

300 oC. Later alumina were sintered at 1100 o C for 2 hrs.

The same procedure was followed for giving CeO2 wash coat to other batch of alumina

using ceric ammonium nitrate solution.

5.3 Copper Chromite Catalyst

Copper chromite is generally obtained by calcinations of copper ammonium

chromate at temperatures between 300 and 500oC. Copper ammonium chromate was

precipitated on alumina pellets [40,41] by adding copper nitrate solution to ammoniacal

K2Cr2 O7 solution. To accurately weighed quantity of 18.913 grams of AR grade

K2Cr2 O7, 73 ml of ammonia was added. To this 14.6 ml of 1.84 M copper nitrate

solution was added with constant stirring. 250 grams of La2O3 wash coated alumina

pellets of -22,+50 mesh size were added to this copper ammonium chromate solution.

Alumina pellets were allowed to soak in this solution overnight. The alumina pellets

were separated and kept under IR lamp till the surface was completely dry. This allowed

slow evaporation of water from soaked pellets. The rest of water was evaporated by slow

heating to 200oC in a furnace. The temperature of furnace was raised to 500oC for 2

hours to decompose copper ammonium chromate and effect sintering of Copper

Chromite catalyst. Copper Chromite catalyst prepared thus have molar ratio of Cu : Cr as

1:1. The copper chromite catalyst loading on alumina was 8 wt %.

5.4 Copper Oxide-Ceric Oxide Catalyst

CeO2 wash coated alumina pellets of -22,+50 mesh size were used to prepare the

Cu 0.15Ce 0.85 O2 loaded catalyst. 58.9 gms of ceric ammonium nitrate were added to

10.3 ml of 1.84 M copper nitrate solution. The volume of the solution was made up to

87.5 ml and 250 gms of alumina pellets were added[42]. The contents of the flask were

allowed to soak in this solution overnight. The alumina pellets were separated. Drying

and sintering of the catalyst was carried out as indicated in section 5.3. Decomposition of

nitrates resulted in sintering of Cu 0.15Ce 0.85 catalyst. The copper oxide-ceric oxide

catalyst loading on alumina was 8 wt %.

5.5 Vanadium Pentoxide Catalyst

CeO2 wash coated alumina pellets of -22,+50 mesh size were used to prepare the

V2O5 loaded catalyst. 25.7 gms of NH4VO3 were added to 87.5 ml of deionised water.

After proper mixing, 250 gms of alumina pellets were added and allowed to soak for 2

days. The alumina pellets were separated. Drying and sintering of the catalyst was carried

out as indicated in section 5.3. Decomposition of ammonium vanadate resulted in

sintering of V2O5 catalyst. The Vanadium Pentoxide catalyst loading on alumina was 8

by wt %.

5.6 Evaluation of Catalysts

The catalysts were evaluated for their oxidation/destruction efficiency for styrene,

toluene, ethyl benzene and TMA. Stabilised monomer of LR grade styrene was used.

Toluene and ethyl benzene were of AR grade. TMA used was 40 % LR grade solution.

Stainless tubing having 6 mm outer diameter and 4.5 mm inner diameter was

shaped unto U tube for use as a catalyst bed. Quartz wool was introduced from one end of

the U tube to support the catalyst bed. 0.5 ml catalyst was transferred to the U tube arm

and it rested on vertical part of U tube. Another quartz wool plug was inserted in U tube

from top to keep the catalyst bed in place. For each experiment, a new U tube and new

catalyst bed were used. Ambient air flow was controlled at 375 ml. This provided the

space velocity of 22500 NTP hr -1 for the catalyst beds. It was passed through a scrubber

filled with desired organic liquid or its solution in Tri Butyl Phosphate(TBP). TBP has

very low vapour pressure and acted as diluent to reduce the volatility of organic liquid

being tested. This helped in evaluating the catalysts at different concentrations.

For evaluation of catalysts as prepared in sections 5.3 to 5.5, furnace with top lid

was used. A powdered alumina bed containing catalyst U tube was maintained at about

300oC initially and then its temperature was raised in steps to obtain the catalyst

efficiency data at higher temperature.

CHEMITO make Gas chromatograph (GC) fitted with automatic air

sampling valve, 3 mm diameter x 3 meter length SE-30 column and Flame Ionization

Detector was used for analysis. The injection port, column and detector base temperatures

were maintained at 200, 150 and 250 oC respectively. Injection port was used to

calibrate GC for styrene etc before start of each run by injecting 2 ìL of liquid samples.

Automatic gas sampling valve having 1 ml volume was used to analyse gas samples in air

streams on upstream and downstream sides of catalyst bed. The gas chromatographic

data was analysed by using CHEMITO 5000 data processor.

Based on calibration, gas stream samples were analysed. Initially catalyst bed

was bypassed to analyse the feed concentration of desired compound in air. Then the gas

stream was diverted through catalyst bed kept at 300oC. The feed compound peak areas

of the off-gas samples was used for computing the catalyst bed efficiency.

The results of evaluations of copper chromite catalyst for styrene, toluene, ethyl

benzene and TMA oxidation are presented in fig. 1 to 4.

300 325 350 375 400 425 450 475 500 52540

50

60

70

80

90

100

Fig. 1. Oxidation of Styrene on Copper Chromite

Catalyst at 22500 hr-1

Space Velocity

% R

emov

al

Catalyst Temperature (oC)

Styrene Concentration 10930 ppm 21 ppm 12 ppm

300 325 350 375 400 425 450 475 500 52570

75

80

85

90

95

100

105

Fig. 2. Oxidation of Toluene on Copper Chromite

Catalyst at 22500 hr-1 Space Velocity

% R

emov

al

Catalyst Temperature oC

Toluene Concentration 26760 ppm 121 ppm

300 325 350 375 400 425 450 475 500 52570

75

80

85

90

95

100

105

Fig. 3. Oxidation of Ethyl Benzene on Copper Chromite

Catalyst at 22500 hr-1 Space Velocity

% R

emov

al

Catalyst Temperature oC

Ethyl Benzene Concentration 4590 ppm 50 ppm

250 300 350 400 450 500 55050

55

60

65

70

75

80

85

90

95

100

105

Fig. 4. Oxidation of Trimethylamine on Copper Chromite Catalyst

at Different Concentrations and 22500hr-1 Space Velocity

% R

emov

al

Temperature ( oC )

Trimethyl Amine Concentration 1860 ppm 12 ppm

The results of evaluations of Copper Oxide-Ceric Oxide and Vanadium Pentoxide catalysts for these compounds are presented in Fig. 5 and 6 respectively.

300 325 350 375 400 425 450 475 500 52570

75

80

85

90

95

100

Fig. 5. Oxidation of Styrene,Toluene and Trimethyl amine

on Cu0.15

Ce0.85

O2+x

Catalyst at 45000 hr-1 Space Velocity

% R

emov

al

Temperature (oC )

Compound Concentration Styrene 37 ppm Toluene 10 ppm Trimethyl Amine 108 ppm

300 325 350 375 400 425 450 475 500 52530

40

50

60

70

80

90

100

110

Fig. 6. Oxidation of Styrene, Toluene and Trimethylamine

on V2O

5 Catalyst at 45000 hr-1 Space Velocity

% R

emov

al

Catalyst Temperature ( o C )

Compound Concentration Styrene 42 ppm Toluene 514 ppm Trimethyl Amine 77 ppm

6.0 RESULTS AND DISCUSSIONS

From Fig. 1 it is seen that the oxidation efficiency of copper chromite catalyst for

styrene improves with concentration in air and also with increasing temperature. At

350oC the efficiency was above 50 % for the styrene content of 7.5 to nearly 11000 ppm.

350oC temperature can be taken as light off temperature for the Copper Chromite

catalyst developed. Above 475oC, the styrene oxidation efficiency was over 90 % for

the concentration range studied and at 500oC, the efficiency approached 100 %. For

11000 ppm styrene concentration, the oxidation efficiency was above 95 % for the

temperature range studied. The GCs of the off gas samples taken at catalyst bed

temperatures upto 350oC indicated presence of small quantities of decomposition

products of styrene indicating incomplete oxidation. The presence of incomplete

oxidation products gradually disappeared with increase in catalyst bed temperature

indicating complete oxidation.

Form fig 2, it is seen that oxidation of toluene followed near same pattern as

styrene on Copper Chromite catalyst. For oxidation of toluene at 26700 ppm

concentration the Copper Chromite catalyst was over 97% efficient at the temperature

range of 300 to 500oC. For toluene concentration of 121 ppm, oxidation efficiency on the

copper Chromite catalyst rose with temperature. The light off temperatures for toluene

appears to be below 300oC at which the catalyst had over 70 % efficiency.

Form Fig 3, it is seen that for ethyl benzene, oxidation efficiency on the copper

Chromite catalyst rose with temperature. The light off temperatures for toluene appears to

be below 300oC at which the catalyst had over 70 % efficiency. The light off

temperatures for toluene appears to be below 300oC at which the catalyst had over 70 %

efficiency.

From Fig. 4 it is observed that for TMA oxidation on copper chromite catalyst

followed same pattern as aromatic compound studied above. At high TMA concentration

of 1860 ppm the efficiency of catalyst was over 97 % and at lower concentration of 12

ppm it increased linearly with temperature. Again at 500 oC temperature the copper

chromite catalyst is equally efficient for TMA oxidation.

As seen in Fig. 5, the Copper Oxide-Ceric Oxide catalyst had efficiency of over

98 % for styrene for temperature range of 300 to 500oC. The oxidation efficiency rose

with temperature for toluene and TMA. The rise was steeper for TMA as compared to

that for toluene. The catalyst bed temperature of 500oC is sufficient to oxidise the

styrene, and TMA with over 98 % efficiency. But efficiency for toluene was only 90 %

at 500 oC.

As seen in Fig. 6, the pattern of oxidation efficiency for styrene, toluene and

TMA on Vanadium Pentaoxide catalyst was similar to that found for Copper oxide-Ceric

oxide catalyst. The rise in efficiency for TMA oxidation temperature was steeper than

that of toluene. The catalyst bed temperature of 500oC is sufficient to oxidise the styrene,

toluene and TMA with over 95 % efficiency.

Based on these results the operating temperature of 500oC was selected for

experiments in resin pyrolysis pilot plant. The Space Velocity of 22500 hr -1is sufficient

to achieve over 95 % efficiency. Since copper chromite was efficient in oxidising

important components of resin pyrolysis off gases, it is selected as primary catalyst. The

Copper Oxide-Ceric oxide and V2O5 catalyst are to be used as back up beds in smaller

proportions. As indicated in section 4.6, NaOH coated alumina is to be used at the front

end of catalyst bed to absorb SO2 and H2S which have potential to poison the prinicipal

catalysts.

These catalysts need to be evaluated for prolonged time to oxidise organic

vapours/gases from cationic resins pyrolysis set up to estimate their service life and

poisoning characteristics.

7.0 CONCLUSIONS

Copper Chromite, Copper Oxide- Ceric Oxide and Vanadium pentaoxide catalysts

supported on alumina were prepared and tested for oxidation of styrene monomer,

toluene, ethyl benzene and trimethyl amine at 22500 hr -1 space velocity and

temperature range of 300 to 500oC. At temperatures over 475 oC, Copper chromite

catalyst gave oxidation efficiency of over 97 % for these compounds over concentration

range of few tens of ppm to few thousands ppm. Copper Oxide- Ceric Oxide catalyst

gave 97 % efficiency for toluene and styrene and 90 % for TMA under same

conditions.V2O5 catalyst gave oxidation efficiency of 95 % for all the three compounds.

A composite catalyst bed of 3 catalyst composing principally of Copper Chromite is

proposed for treatment of IX resin pyrolysis off-gases.

ACKNOWLEDGEMENT

The authors thank Shri. K. K. Prasad Head, Back-End Technology Development

Division for his guidance and interest in the course of this work.

REFERENCES

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Proceedings of Nuclear and Radiochemistry Symposium NUCAR-2003, pp 271-272.

(2003)

2. Sathi Sasidharan, N., Deshingkar, D.S., Wattal, P.K., Cementation of secondary

wastes generated from carbonisation of spent organic ion exchange resins from

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