The rate of oxidation of hydrogen sulphide by oxygen to elemental sulphur over NaX and NaY zeolites and the adsorption of sulphur

Applied Elsevier

Catalysis, 14 (1985) 185-206 Science Publishers B.V., Amsterdam

THE RATE OF OXIDATION OVER

OF HYDROGEN

NaX AND NaY ZEOLITES

A.5. VERVER

Department

VAN SWAAIJ

of Chemical

Technology,

(Received

Enschede,

16 June

in The Netherlands

SULPHIOE

BY OXYGEN

AND THE ADSORPTION

and W.P.M.

217, 7500 AE

185 - Printed

Twente

TO ELEMENTAL

SULPHUR

OF SULPHUR.

University

of Technology,

P.O.

Box

The Netherlands.

1984, accepted

22 November

1984)

ABSTRACT The rate of oxidation of H S by O2 over synthetic sodium faujasite zeolites to produce elemental su? phur has been studied at partial sulphur load of the zeolite using a gravimetric method. The rate of sulphur accumulation on a sample exposed to an atmosphere of about 1.0 vol % H2S and 0.5 vol % O2 in nitrogen has been measured. The rate of oxidation of H2S to sulphur has been derived for three different NaY type zeolites, i.e. with an Si/Al ratio at temperatures from about 120 to 200 of 1.70, 2.07 and 2.40 respectively, "C. The activation energy of the rate constant appears to be the same for these zeolites and amounts to about 53 kJ mol-I. The reaction rate increases substantially with a decreasing Si/Al ratio of the zeolite. So the NaX type zeolite is clearly more active in the H2S oxidation than the NaY type. The frequency factor of the rate constant is found to increase linearly with the number of H2S adsorption sites described previously by Karge and Rasko. This suggests that these sites act as reactive sites in the oxidation of H2S over sodium faujasite zeolites. By the same micro-weighing technique the rate of desorption of sulphur from sulphur loaded zeolites has been determined at a temperature of about 300 "C. The sulphur vapour pressure close to the zeolite surface has been derived from the rate of weight loss by mass transfer calculations. It appears to be slightly lower for NaX zeolite than for NaY zeolite. In general, the relative sulphur vapour pressure is well below 10e2 for all zeolites we tested, unless the maximum adsorption capacity has been approached closely. Because of the high activity and the low relative sulphur pressures observed for NaX type zeolite, this zeolite is preferable as a catalyst in the oxidation of H2S with O2 if sulphur should be recovered in an adsorbed state.

INTRODUCTION The oxidation the overall process

of hydrogen

reaction

with molecular

in the production

[I]. The primary

0166-9834/85/$03.30

sulphide

reaction

0 1985

of elemental

involved

Elsevier Science

is:

Publishers

B.V.

oxygen sulphur

is known

to be

in the Claus

186 H2S +;

Below

02 = S + H20

about 500 "C this oxidation

improvement quently

of reaction

mentioned

rate. Active

as useful

lites such as NaX exhibit sulphur

reaction

carbons,

catalysts.

superior

requires

Among

activity

the use of catalysts

aluminas

and zeolites

these catalysts, and selectivity

for

are fre-

synthetic towards

zeo-

elemental

[2,3].

In the Claus metric

process,

combustion

catalysts,

H2S is converted

and by reaction

according

with

to sulphur

vapour

the SO2 produced,

by substoichio-

over alumina-based

to the reaction:

2H2S + SO2 = 3s + H20

In processes

such as CBA [4,5] and Sulfreen

low-H2S

gases

Sulphur

condenses

by reaction

however,

deals with

2 at temperatures

on the catalyst

We are currently based,

(2)

investigating

on reaction

a similar

of the H2S

desulphurization paper

oxidation

and desorption

work a study has been initiated

modified

to the application

enabled.

On this subject

we shall

As a part of a larger investigated effect

of the sulphur

observed

a most

orders

report

signal

From kinetic

of sulphur

measurements

Oxidation

elsewhere

of H2S over synthetic

zeolites,

but gave no data on the reaction

The adsorption Whiteman

[IO] and by Steijns

high adsorption respectively

sorption

capacities

at relative

pour pressures sulphur.

[9]. They reported

of sulphur

On the other

Steijns

Steijns

and Mars

exposed

to H2S and

activities

was studied

also

for NaX and NaY

was studied authors

reaction

rate were

rate or the activation

[II]. These

[7]

et al. [8]

X and Y zeolites

different

is

and found an autocatalytic

of the reaction

on NaX zeolite

and Mars

catalyst

energy.

by Barrer

reported

and

remarkably

of about 0.35 and 0.30 kg sulphur per kg zeolite -2 pressures as low as 10 , i.e. sulphur va-

sulphur

of a factor

of sulphur

vapour

In that way the devel-

for NaX zeolite

and Ziolek

such as

catalysts,

up to 200 'C, they determined

by Dudzik

is

and

[6].

catalysts,

a few values

which

Based on the

on zeolite

over a moving

In ESR experiments

of H2S and O2 [8], but only

presented.

bed systems.

of H2S over NaX zeolite

adsorbed.

strong

of sulphur.

process

study on different

the oxidation

O2 mixtures.

behaviour

in fluidized

process

over zeolites

of the present

desulphurization

by heating.

is part of this study

NaX, and the adsorption

of a continuous

from

of sulphur.

periodically

findings

opment

is recovered

the dew point

bed and is removed

1. The present

the rate of reaction

[5] sulphur below

100 lower

hand,

than the equilibrium

no data are available

on NaY zeolites.

pressure

in literature

of liquid

on the ad-

187 In this study, sulphur

we focused

over various

determined dation

an the reaction

the rate of deposition

of H2S, on a catalyst

and 0.5 vol % 02. We looked ed sulphur

behaviour

the different

the influence

both

the maximum

NaX and NaY zeolites

caused

by the adsorb-

ratio of the zeolite

the adsorption Using

we

the rate of the oxi-

phenomena

we studied

of H2S to

method,

of about 1.0 vol % H2S

of the Si/Al

from the H2S oxidation.

we investigated

and hence

in an atmosphere

for autocatalytic

rate. Furthermore,

of sulphur

apparatus,

Using a gravimetric

of sulphur,

sample

and shall discuss

on the reaction

rate of the oxidation

NaX and NaY zeolites.

and desorption

the same micro-weighing

sulphur

adsorption

and the desorption

capacity

behaviour

of

of the sul-

phur adsorbed.

EXPERIMENTAL Experimental Sulphur

set-up adsorbed

slowly,

because

sulphur

load close

volatility

the relative

sulphur,

by measuring

The experimental

set-up

of a Sartorius

inserted

diameter

sample

pan (diameter

30 mm).

[lI]. Due to this low

the rate of the H2S oxidation accumulation

can be studied of a catalyst

atmosphere.

provided

with a quartz

mounted

tubular

furnace

samples

were contained

10 mm) in the middle

of the microbalance

was connected

(heated

1. It con-

hangdown

length

0.30 m, in-

in a shallow

quartz

of the oven. The electronic to a recorder

and the temperature

tube

con-

for continuous

regis-

of the gas in the vicinity

pan.

Reaction gas ___I_ A gaseous reaction was made

mixture

by adding

H2S. The composition and checked

capacity

Catalyst

of the sample weight

mixture

evaporates very -2 is below 10 even at a

used in this study is shown in Figure

troller

nitrogen

pressure

the rate of weight

tration

of the sample

vapour

4406 microbalance

in a vertically

ternal

of e.g. NaX zeolite

adsorption

in a H2S and O2 containing

sisted

m3s-I

sulphur

to the maximum

of adsorbed

gravimetrically sample

in the micropores

of about

together

1.0 vol % H2S and 0.5 vol % O2 in

flows of dry air and nitrogen

of the gas mixture

by chromatographic

was fed to the bottom

was adjusted

analysis

for each experiment.

of the hangdown

(at 20 "C and atmospheric

containing

by calibrated

florrmeters

The reaction

tube at a flowrate

of 3.3*10s6

pressure).

Catalysts Small catalyst

amounts

was a commercial powder

of pure zeolite

powder,

and these were carefully

spread

grade Linde molecular

was supplied

by P.A. Jacobs

i.e. 1 to

10 mg, were

on the bottom

sieve,

(Katholieke

used

of the sample

type 13X. NaY(1.70, Universiteit

as a pan. NaX

see below)

Leuven,

Belgium).

-

air

3% H2S Q_ in N2

N2

I

FI

FI

Q

a--

J

reaction mixture

Q

vent

nitroger

%

m

vent

PU

Figure

4

I

I

Experimental

set-up.

2

3

ml

r-4

:I I

N2

FI

Furnace

Sample 7.

valve

controller switch pan

Gas flow 6.

5. Temperature

4.

Balance Recorder

2. 3.

controller

Microbalance

1.

189

The other NaY catalysts Amsterdam). resulting

Chemical Si/Al

NaX(1.151,

Before

bv (Research

were added

in parentheses

and NaY(2.40)

Centre

was performed

to the zeolite

and the

names:

respectively.

procedure the catalyst

rate about 0.2 'C s-l) up to 400 "C. temperature,

attained,

experiments.

sample was dried in a nitrogen -6 m3s-1 N2; flow rate 3.3*10 STPI at increasing

> 99.98%

(heating

the measurement were

by Akzo Chemie

of the Si and Al content

NaY(2.07)

the experiments,

(high purity, rature

ratios

NaY(1.701,

Experimental

were provided

analysis

nitrogen

both isothermal

was replaced

Unless mentioned

When,

conditions

by the reaction

otherwise,

flow tempe-

after cooling

and a constant

mixture

only fresh catalyst

to

weight

to start the samples

have

been used.

RESULTS Accumulation When

of sulphur

the reaction

was introduced was formed

gas mixture

to the hangdown

from the oxidation

on the catalyst.

Formation

reaction

was also

In the microbalance, colour

recorded.

Figure

2. Accumulation

A typical

of the experiment time in the tubing

a level others

roughly

corresponding

[lO,ll].

As a matter

decreases

when the maximum

available

surface

may also become sulphur

vapour

pressure

and the desorption

sulphur

sulphur

On account

load,

sulphur

In the course

of the deposition

of sulphur

owing

reported

by

to the decreasing

of the zeolite

of sulphur

pores

[lo]. As

from the H2S

as is shown

in Figure

(Cl stops the formation

the weight

of the catalyst

pressure

becomes

stable weight

of sulphur

at

of the relative

of sulphur

vapour

tube.

holds

rate of the H2S oxidation

increase

of sulphur

and an apparently

of the catalyst

is established,

by nitrogen

of the lower

by the

to this, desorption

filling

of sulphur,

the rate of desorption

a few minutes

uptake

the formation

of sulphur

after the

is caused

increase

of the rapid

mixture

and, due to desorption

decreases.

within

the reaction

between

time plot is given in

zone of the hangdown

load is reached,

at the maximum

oxidation

versus

of the sample

about 45 seconds

to the maximum

In addition

was apparent

increase

delay period

the weight

because

an equilibrium

2. Replacing

of a weight

sulphur

a result,

from the

of fact, the reaction

area [7, 121.

important

(see [6],

and in the preheating

time of reaction

of the H2S-O2

of sulphur

is observed

(A), which

sulphur

and deposited

with fluid bed reactors

and the sustained

example

residence

a certain

the presence

of weight

elemental sample

as the main product

in our experiments

beginning

After

tube of the microbalance,

of the zeolite

weight

1 ~01% H2S and 0.5 ~01% 02 in N2

of H2S over the catalyst

of sulphur

p. 151). yellowish

shown

of about

at slightly

negligibly

is observed

also water,

produced

of slowly lower

small (D). by the

190

0,6-

T

1

0

I

1

2

I

I

3

4

time (KP s) Figure 2 zeolite,

Typical

weight

registration

of sulphur

accumulation

NaY(2.40)

1.65 mg, 188 "C.

T("C)

Figure

3

(al fresh.

Thermoanalysis (b) containing

of NaY(2.40) 0.34

(1.65 mg, heating

kg sulphur

rate 0.17

per kg dry zeolite.

'C s-l).

191

reaction,

might

have been adsorbed

zeolites

are known

analysis

of a fresh NaY(2.40)

cant weight gradually

to strongly

sample,

loss due to dehydration

decreasing

shows a marked catalyst

simultaneously

adsorb

weight

At temperatures

(Figure

as given

below

is observed.

loss of weight

occurred

Similarly,

above 200 "C a second weight

caused

about 100 and 200 "C all the sulphur

by the desorption

is not likely obtained

to adsorb

eventually

sulphur

adsorption

Maximum

sulphur

adsorption

At temperatures

while

loaded

sample

of the fresh

is slightly

is observed,

adsorbed.

lower.

which

is ob-

Consequently,

on the catalyst,

while

And so the net increase

2 can be considered

of

the maximum

values

of the maximum

have been determined.

sulphur

The results

capaci-

are present-

NaX(1.15) zeolite appears to adsorb less sulphur than the

The adsorption

temperature,

a signifi-

uo to 2011 "C a

capacity

above 100 "C several

4. The

NaY zeolites.

because

of the zeolite.

ty of the NaX and NaY zeolites ed in Figure

loss

remains

substantially.

at D in Figure

capacity

dehydration

loss

of the sulphur

3a, shows even

a sulphur

this weight

viously

water

in Figure

in the range where

3b), although

the sulphur,

[13]. Thermogravimetric

100 "C, while

between

weight

with

water molecules

capacity

for NaY zeolites

of NaX(1.15)

is clearly

a slight decrease

independent

at increasing

of

tempe-

rature can be seen. Adsorption

of sulphur

ture, because passage atoms

the apertures

of most molecules

adsorbed

capacity.

takes

for NaX11.15) whereas

Seff [14]

the supercages

of NaA zeolite.

of NaX zeolite

and about

the presence

for

are too narrow

the maximum

zeolite

has studied

sulphur

S5 rings

in each

sulphur

adsorption

of about 14 sulphur adsorb

up to 21 sul-

adsorption

complexes

similar

By an X-ray

diffraction

supercage

adsorption

the

of sulphur

has supercages

ratio.

struc-

to allow

number

from the maximum a value

Such a zeolite

From the maximum

of the zeolite

the NaY zeolites

the same Si/Al

of two parallel

has been proven.

Consequently

can be calculated

per supercage,

phur atoms per cavity.

in the supercages

to the other cages [13].

in a supercaqe

We determined

atoms adsorbed

place

in

to those study

of the NaA zeolite

capacity

we calculated

NaX(1.15) zeolite about the same number of sulphur atoms per supercage,

namely

14. For NaY zeolites

observed. above,

This might

or it might

tion because zeolites

a higher amount of sulphur atoms per cavity is

indicate

be caused

of a lower

the absence by a larger

cation

volume

concentration

as will be substantiated

Steijns

of the sulphur

and Mars [II] reported

available

complexes

mentioned

for sulphur

in the supercages

adsorp-

of the NaY

below. a maximum

NaX zeolite

of about 0.30 kg sulphur

what higher

than we have found

sulphur

per kg zeolite

for the NaX(1.15)

adsorption

capacity

at 260 "C, which

zeolite.

of

is some-

This can be ex-

192

-

0

NaX

(1.15)

A Nay

-I

(170)

0

Nay

(2.07)

l

Nay

(2.40)

I

2jo

2bo

160

100

T("C) Figure

4

Maximum

sulphur

adsorption

capacity

of NaX and NaY zeolites

versus

ratio of their zeolite

sample

temperature.

plained, might

however,

have

by suggesting

that the Si/Al

been slightly higher. Unfortunately

the Si/Al

ratio was not stated

by them.

The rate of oxidation The increase of oxidation influenced dation.

by simultaneous

According

within which served

might

concentration the catalyst causes

under

of water

analysis

curve

weight,

completely

might

be

also by the H2S oxi-

(cf. Figure

3) relatively

of the H2S oxidation, because

water

at B) that this amount

change

to be present

of the H2S - 02 feed,

adsorbed,

if the temperature

higher

a substantial

is likely

interruption

the weight

on the rate

increase

above 100 'C if the atmos-

on the catalyst,

of any possible

these conditions

almost

produced

from the H2S oxidation,

By intermediate

2, dotted

depends

the rate of weight

are to be expected

be present

layer.

2 obviously

But in the course

resulting

per cent of the catalyst

corresponds

water

the desorption

(cf. Figure

Therefore,

However,

adsorption

of nitrogen.

of water

in Figure

to the thermogravimetric

of adsorbed

phere consists amounts

observed

of H2S to sulphur.

low amounts

water

of Ii22

of weight

it could is less

is above

about

of the catalyst

to the rate of the deposition

be ob-

than one 120 'C. sample

of sulphur

and

193

hence to the rate of the oxidation the H2S oxidation plot according

From these

=>=dLp MS

x

results,

can be evaluated

only

to the known

data on the reaction

in the Appendix.

the mass

the concentration

zeolite.

was measured,

for the NaY zeolites

The rate of oxidation described typical

above,

example

I

gradientless

5

Reaction

(zeolite

I

versus

I

150

could

temperature

increase

transfer

rise of

for the ex-

was always

limitations.

be determined

in the that But

satisfactorily,

from the weight

the sulphur

1

1

I

0.3

(kgS/kgzeolite)

signal

load. Figure

to be poorly

0.2

“C)(a)

experi-

conditions.

rate of the oxidation

NaY(1.70),

mass

a). The rate data appear

0.1

as is de-

in this case an activity

of H2S was calculated

Xs

Figure

by serious

are

is at least 80 per

has to be made

the rate of the weight

and was plotted (curve

0

load

Although

the rate of reaction

approximately

in detail

and that the ultimate

are

effects

that in most

at the catalyst

bed is less than 4 "C. An exception

high that it has been influenced

i.e. under

phenomena

we have estimated

of both reactants

on the NaX(1.15)

at the catalyst

and if temperature

and heat transfer

Accordingly,

cent of the feed gas concentration

H2S oxidation

time

rate of the H2S oxidation

if the H2S and O2 concentration

We studied

periments

versus

(3)

feed gas concentrations

absent.

the catalyst

of fact, the rate of

to the weight

W,MS

useful

scribed ments

of H2S. As a matter

from the tangent

to:

'H2S = 2 * '02

close

then follows

as

5 shows a

reproducible

I

r

0.4

-

of H2S with

first experiment

O2 versus

the sulphur

(b) fourth experiment.

194 below

a sulphur

load of about 5 wt %, whereas

load are significant era1 cycles sequent

with

and, for example,

regeneration

accumulation

(see Figure

of the high activity

%, is not very clear.

We looked

on the fresh catalyst,

amounts,

load contributes

catalyst,

TABLE

but as is shown

considerably

more

to describe

Weight increase (wt %1

At high sulphur

load a maximum

to an NaX catalyst

peratures

between

phenomena

are generally

assumed kinetics

tained, from which -1 is derived.

an activation This

energy

of the reaction -1 about 55 kJ mol . Based

agrees

adsorbed

in H2S. energy

effect

-0.02 0.03 0.05 0.08

obtained

This

[7] with

regard effect

6.

Autocatalytic

are given

rate equation

and 13X molsieve

that the

lines

are ob-

of about 53 kJ

of the activation

reported

by Steijns,

viz.

adsorbed

on purified

active

mechanism [7,8].

in the

has been

are approximately

parallel

of the rate constant

of sulphur

tem-

at a sulphur

et al. [R] who have found

Reasonably

a general

in porous materials

at different

respectively

fairly well with values

et al. derived

Iron content, dry base (wt %l

in Figure

rate over a 13X catalyst

on the autocatalytic Steijns

over sulphur

on aluminas

in O2 and zero order

of the zeolites

and Mars

7. A first order

data of Steijns

of the H2S oxidation

mol

carbons,

with

2

rates observed

0.03 and 0.05 kg S per kg zeolite

in accordance

of the

extensively.

by them as the autocatalytic

The reaction

in Figure

activity

activity

of the catalyst.

120 and 200 "C, are summarized apparent.

the ini-

at higher

rate is observed.

by Steijns

rate of the H2S oxidation

plot presented

order

in the reaction

reported

in the micropores

on the reaction

explain

the activity

NaX(1.15) NaY(1.70) NaY(2.07) NaY(2.401

and has been described

adsorbed

load of 0.01,

been

about 5 wt

1, only small

cannot

Iron content -Catalyst

I:! 108 133

has previously

i.e. below

to the overall

Temperature ("Cl

1.0 0.4 0.4 0.3

of sulphur

again

temperature

H2S from an 02-free

in Table

the initial

data for H2S (1.0 vol.%)

phenomenon

Arrhenius

of

TABLE

NaX(1.151 NaY(1.70) NaY(2.071 NaY(2.401

Data

load,

Because

1

Catalyst

first

at low sulphur

for the adsorption

satisfactorily.

we did not attempt

Adsorption

to about 400 "C and sub-

reaction

i.e. less than 1.0 wt %, were found, which

tial peak in the activity sulphur

in nitrogen

at the original

of sev-

in the course

5, curve bl.

The nature

mixture

by heating

of sulphur

at a higher

the data obtained

also persistent

for the oxidation

They showed

of H2S

that the oxida-

0

-

load.

Reaction

0.4

01 x5 (kgS/

02 03 __

0.4

of H2S with O2 versus

kg NaY(207))

rate of the oxidation

0

1

(a) NaY(1.70).(b) NaY(2.07).(c) NaY(2.40).

Figure 6

03

02

01

X,(kgS/kgNaY(170))

006 004

the sulphur

OA Xs

(kgS/kgNaY

(240))

-

196

E=

53

kJ mol-'

NaY

(I.701

NaY

(2.071

NaY (240)

220 I I

I

100 I I

1

2.0

T("C)

140 I

I I

2.2

103 r

I

I

2.4

2.6

IO3 / T ( K-l> Figure

7

Arrhenius

plot of reaction

tion rate over an NaX zeolite [IZ], which

clearly

reflects

is related

with

sulphur

tial differences similarity

in the reaction

area are unlikely Q/Al

ratio

might

be causing

iron content

Obviously,

more

Dudzik

zeolite

active.

activity

is attended

parameters

which

surface

discussed comprises

We have found

differences adsorbed

Steijns

[7,12].

(see Table

by Steijns

an interaction

[9]. The chemisorption

in

of the

surface

with

a low

that iron impurities

analysis

of the zeolites

2) and, additionally, activity

in the oxidation

a mechanism

area

substan-

Because

in sulphur

on zeolites

suggested

Chemical

by a decreasing

are involved

than those considered

and Ziolek

NaY zeolites,

sulphur

shown low iron contents

increasing

NaY zeolites

large

surface

On the other

on a 13X zeolite,

catalyst.

rate over the NaY zeolites.

and, therefore,

a higher

sulphur

role of sulphur.

adsorbed

carbon

structure,

seems to be more

has, however,

of sulphur

on an active

of the zeolite

to the specific

the autocatalytic

hand, they found a high activity comparison

rate constants.

an

of the catalyst.

of H2S over NaX and

[15].

of the H2S oxidation of adsorbed

over NaX and

reactants

of H2S is suggested

and the

as an essential

197

step, at least during

the initial

on NaX and NaY zeolites spectroscopy

of zeolites

Rasko [17] determined na-rich

zeolites,

ally on unlocated tration

unit cell, inside

with

and suggested Na+ cations

remaining

cations

oxidation

of H2S is likely

cationic equal

n

near the walls depends

is equal

occupy

ratio.

Karge

of alumina

The concen-

tetrahedra

and hexagonal

per

where

the number

by Karge

of

positions

prisms.

of the supercages,

sites per unit cell has been proposed

and

on alumi-

The number

the well-coordinated

Consequently,

By IR

preferenti-

of the supercages.

cages

near the walls

to proceed.

ratios,

takes place

on the Si/Al

i.e. sodalite

are located

Si/Al

of H2S

[16,17,18].

of the H2S adsorption

to the number

preferentially

the small cages [lg],

varied

nature

Adsorption

authors

that this adsorption

strongly

per unit cell but cations

by many

systematically

the dissociative

of these cations

Na+ cations

stage of the reaction.

has been described

The the

of these

and Rasko

as being

to: 192 + Sl/Al - 56

=1 Na+

(4)

They have found a good correlation ly adsorbed equation sites

H2S molecules

above.

zeolite. calculated Figure

8 as a function

concentration

8

factor

from the reaction

4. The value

Figure

reaction,

in the supercages

The frequency

k. of the Arrhenius

to increase

Frequency

factors

equation, in Figure

concentration rather

of the Arrhenius

to the

sites act as reactive to the number

on the Si/Al ratio of the

with

equation

which

can be

7, is plotted

calculated

linearly

sites in accordance

in the supercages.

of dissociative-

sites according

rate is related

and thus depends

rate data presented

of H2S adsorption

Na+ concentration

the reaction

of the Na+ cation

of k. is found

the concentration

of cationic

if the H2S adsorption

Consequently,

in the oxidation

of Na+ cations

between

and the number

with

an increasing

the suggested

versus

in

by equation

reac-

the calculated

198

tive sites model.

Figure

Na+ cations,

would

However,

which

8 predicts

this can also be explained

56 in equation cations

Ziolek

ratio [ZO]. They suggested (A104-)

cations

is located

heating

H2S oxidation,

which

of

by other workers

the catalytic and the Si/Al

with the number

of alumina

the total number

of Na+ ca-

because

only a fraction

sites and are thus likely

to about 300 "C, sulphur

desorbs

this treatment.

slowly

of Na+

to participate

accumulated

during

in detail

Barrer of sulphur

in

at each

and Whiteman

desorbs

be removed

by

in subsequent

from the zeolite

some irreversibly

adsorbed

the main part of the sulphur

at moderate

in the Appendix,

heating.

the sulphur

bed can be determined

sulphur

vapour

pressure

at

from the rate of the weight

loss as a function

and as a result,

of the sulphur

data on the vapour

load were obtained.

[lo] have investigated

and phosphorus

on different

of sulphur

concentration

very small bed heights

These

pres-

data are presented

gradients

and Mars

ate-adsorbate

[ll],

interaction

pressure ratio,

vapour

pressure

inside

the catalyst

sorption

bed.

S-shaped

isotherms

on the adsorbing of sulphur

might

more

we used

be consider-

determined an adsorb-

The sulphur

material. rapidly,

sul-

load.

indicating

molecules.

no

fluxes

the minimum

on NaX zeolite

zeolite

proceeds

Moreover,

sulphur

are found

sulphur

expect

and the mass

at the interface

isotherms

a relativ-

we might

to reach

at the actual

of the adsorbed

also depends

the desorption

pressure

and desorption

and have mentioned Therefore,

two to six hours

of sulphur

with the sulphur

In agreement

zeolites

of less than half a millimeter,

phur load, So the sulphur ed the equilibrium

the adsorption

from NaX zeolite.

were very low, i.e. it took about

by Steijns

while

the

over 90 per

9.

ely rapid release important

are formed,

experiments

could

adsorbed

could be removed obviously,

during

Eventually

the H2S oxidation

the rate of the weight

load in the desorption

in Figure

species

of the catalyst

loss. We measured

sure of sulphur

cycles,

the H2S oxidation

As is described the surface

during

On the fresh zeolite,

sulphur

was accumulated bed.

is the fact that sulphur

accumulationdesorption

or chemisorbed

which

from the catalyst

accumulated

Noteworthy

about completely.

Si/Al

equals

number

process.

cent of the sulphur

vapour

between

correlation

of the constant

higher

suggested

of

sites.

desorption

After

sulphur

a relation

is not very likely,

on supercage

the H2S adsorption

Sulphur

a direct

This

lower value

over NaX and NaY zeolites

per unit cell,

tions per unit cell.

in the absence

of e.g. other

the apparently

H,S adsorption

have elaborated

of the H2S oxidation

tetrahedra

with

for dissociative

and Dudzik

activity

activity

activity

by a possibly

4, in correspondence

available

a residual

imply an additional

At increasing

which

might

be

202 gas velocity

Ills

V

volume

m3

W

weight

V

wO

weight

ng h

kg of dry catalyst

sulphur

xS a

sample

load

heat transfer viscosity thermal

-1

coefficient

of gas conductivity

of gas

kg kg Slkg zeolite)-1 W m-2 .C-1 -2 Nsm W m-1 .C_l

4;;

heat flux

kW m

4;

mass

molm

d

Thiele

pg P

flux

-2 -2

s

-1

modulus

density

of gas

density

of zeolite

kg m particle

-3

kg me3

Subscripts eff

effective

i

at the interface

REFERENCES

5 6 7 8 ?O

11 12 13 14 15 16 :‘B 19 20 21 22 23 24 25 2’;

B.W. Gamson and R.H. Elkins, Chem. Eng.Prog. 49, (1953) 203. G.T. Kerr and G.C. Johnson, J. Phys. Chem., 64 (1960) 381. M. Steijns and P. Mars, Ind. Eng. Chem. Prod. Res. Dev., 16 (1977) 35. J.E. Nobles, J.W. Palm and U.K. Knudtson, Hydrocarbon Process., 56 (1977) 7 143. A.L. Kohl and F.C. Riesenfeld, Gas Purification, Gulf Publishing Co., Houston, 1979. A.B. Verver, Thesis, Twente University of Technology, The Netherlands,1984. M. Steijns and P. Mars, J. Catal., 35 (1974) 11. M. Steijns, F. Derks, A. Verloop and P. Mars, J. Catal., 42 (1976) 96. Z. Dudzik and M. Ziolek, J. Catal., 51 (1978) 345. R.M. Barrer and J.L. Whiteman, J. Chem. Sot. A, (1967) 13. M. Steijns and P. Mars, J. Colloid Interface Sci., 57 (1967) 175. M. Steijns, A. Peppelenbos and P. Mars, J. Colloid Interface Sci., 57 (1967) 181. D.W. Breck, Zeolite Molecular Sieves, John Wiley & Sons, 1974. K. Seff, J. Phys. Chem., 76 (1972) 2601. M. Steijns, Thesis, Twente University of Technolagy, The Netherlands,1976. A.V. Deo, I.G. Dalla Lana and H.W. Habgood, J. Catal., 21 (1971) 270. H.G. Karge and G. Rasko, J. Colloid Interface Sci., 64 (1978) 522. R.W. Tower, Z.M. George and H.G. Karge, Preprints 6th Can. Symp. on Catalysis, August 19-21, 1979, Ottawa, Ontario. J.V. Smith, in: Zeolite Chemistry and Catalysis, Ed.: J.A. Rabo, ACS Monograph 171, 1976. M. Ziolek and Z. Dudzik, Zeolites, 1 (1981) 117. R.B. Bird, W.E. Stewart and E.N. Lightfoot, Transport Phenomena, John Wiley & Sons, 1960. W.E. Resnick and R.R. White, Chem. Eng. Progr., 45 (1949) 377. T. Wigmans, H. van Cranenburgh, R. Elfring and J.A. Moulijn, Carbon, 21 (1983) 23. C.N. Satterfield, Mass Transfer in Heterogeneous Catalysis, M.I.T. Press,1970. A. Meisen and H.A. Bennett, Hydrocarbon Process., 58 (1979), 12 131. International Critical Tables, McGraw-Hill, New York, 1929. A.B. Verver and W.P.M. van Swaaij, to be published.