Influence of sulfurization on coke formation over catalysts for naphtha reforming

Applied

Catalysis,

Elsevier

Science

INFLUENCE

-Printed

in The Netherlands

ON COKE FORMATION

R.J. VERDERONE,

OVER

CATALYSTS

FOR NAPHTHA

REFORMING

C.L. PIECK and E.M. TRAFFANO

de Investigaciones

Ester-o 2654 - 3000 Santa

(Received

15

15-22

B.V., Amsterdam

OF SULFURIZATION

J.M. PARERA, Instituto

23 (1986)

Publishers

en Catalisis

y Petroqufmica

- INCAPE

- Santiago

de1

Fe, Argentina.

7 May 1985, accepted

15 November

1985)

ABSTRACT The effect of sulfurization on coke deposition over Re/A1203, Pt/A1203 and Pt-Re/ A1203 was studied carrying out reforming of naphtha and pure compounds before and after sulfurization with H2S at 500°C. On all the catalysts sulfurization increases the total amount of coke. On the sulfurized ones the coke is localized mainly on the support and is less hydrogenated than that on the nonsulfurized catalysts. These results are explained in terms of of coke precursors a geometrical effect of the metal poisoning by S. Hydrogenolysis and their condensation on the metal are both demanding reactions greatly decreased by sulfurization. On the contrary, the formation of coke precursors by dehydrogenation is a non demanding reaction, and is decreased less. The coke precursors that can not condensate on the metal condensate on the support.

INTRODUCTION Catalysts functions Periodic alumina These

used

Table. whose

acidity

liquid yield.

function

During

are bifunctional,

is performed

may be improved

have an initial

exothermic

controllable

reforming

out by one or more metals,

The other

catalysts

highly

in naphtha

being carried

this period,

and produces

and dangerous

by adding

period with the main

halogens,

component

generally

gas production

reaction

of the

such as

chlorine

which

that may become

and the catalyst.

[I].

and a poor

is hydrogenolysis

in temperature

for the installation

from group VIII

by an acidic

a great

an increment

one of the catalytic

mainly

This

is un-

phenomenon

is known as run away hydrocracking. The initial and is more phenomenon practice

causes

a great

refers

reforming

hyperactivity

in some bimetallic

is to passivate

This paper naphtha

hydrogenolytic

important

initial catalysts

depends

catalysts

instability

on the metallic like Pt-Re/A1203

of the catalysts,

by sulfurization

to the influence

[2,3]. This

and an industrial

[4-61.

of sulfurization

using Pt, Re and Pt-Re supported

component,

on coke formation

during

catalysts.

EXPERIMENTAL The runs were performed commercial

bimetallic

0166-9834/86/$03.50

using catalysts

prepared

catalyst.

0 1986

Elsevier

Science

Publishers

B.V.

in the laboratory

and a

16 TABLE

1

Properties

of catalysts

prepared

in laboratory

Pt-Re/A1203

Pt/A1203

Re/A1203

'1Pt

0.3

0.37

0.0

%Re

0.3

0.0

0.3


0.01

0.01

0.01

'Xl

0.9

0.9

0.6

Sg,m 2 g -1

165

Vg, cm 3 g -1

Prepared

were prepared

was impregnated

HRe04)

and HCl, which

the catalyst ture. Table

0.49

accordinrl to [7] and [8]. A CK 300 alumina

with

a solution

was added

was calcined

on sulfurized

naphtha

tests

similar

as feed. Because

catalysts

- mainly

Table

2 shows

TABLE

2

Operating

Catalyst

catalysts

Monometallic

P=30

Bimetallic

T=480"C,

Also with cyclohexane

Pt/A1203

pressure

6h-'

H2:naphtha=8

were

with

and drying,

H2 at the same tempera-

-1

P=lO

I was

accelerated out using

of the nonsulfurized

lengthened

to 21 hours.

tests

II (15 h)

Period

kg cm -2, WHSV=Gh-'

T=480"C,

Idem I

Idem I

H2:naphtha=4

pure compounds

The operating

= 5 kg cm -2; WHSV = 4 h-'; molar

III (7 h)

H :naphtha=4

P=5 kg cm- K , WHSV=6h-'

runs using

performed.

and stability,

[9], were carried

in each case.

T=480"C,

H2:naphtha=8

catalysts,

and benzene)

used

Period

WHSV=6h

After

instability

deactivation

I (21 h)

P=15 kg cmm2,

distribution.

0.03"g.

before

ones - period

kg cm -2, WHSV=

(H2PtC16

selectivity

initial

conditions

of accelerated

T=480"C,

was about

activity,

of the great

the bimetallic

Period

metal

(Cyanamid

precursors

of these catalysts.

to those described

the operating

conditions

uniform

in air at 500°C and reduced

In order to study the catalytic deactivation

of the metallic

to allow

1 shows the main properties

i #Ifur content

505°C;

164

0.48

catalysts

Catalysts Ketjen)

165

0.48

as feed

conditions

(n-hexane, were

temperature

ratio H2: HC = 4, length

= 7 h.

=

17 Commercial

catalysts

The chlorine the method

content

described

wtb were obtained.

of a commercial

in 181. Samples

Sulfur

Operating

with chlorine

content

periods

was regulated

percentages

ranging

following

0.15 - 1.3

conditions

temperature,

of the original catalyst were: 3 -1 0.46 cm g , and specific surface

of the sulfurized

for these catalysts

II, 17 h, 3.5 kg cm -'; Period

Period

catalyst

The main characteristics

0.01:; S, 0.3:L Pt, 0.967: Cl, pore volume

172m 2 g -I.

Pt-Re/A1203

catalysts were:

III, 10 h

WHSV and H2:naphtha

molar

0.3% Re, area

was about 0.03%.

Period

I, 16 h, P = 15 kg cm

-2

;

, P = 15 kg cm-'. During all the ratio were

4 h-' and

kept at 505"C,

4, respectively.

Feeds Accelerated naphtha

deactivation

containing

less than 1 ppm of sulfur.

0.736 g ml-'; mean molecular

were: density

147'C; Research hexane

tests were carried

Octane

and benzene,

Number

out using a commercial The main properties

weight

59. Pure compounds

109; boiling

of the naphtha

point range 65 -

were Carlo Erba n-hexane,

without

further

purification.

feeds were dried by passing

through

a bed of Molecular

Catalyst

hydrotreated

Before

cyclo-

being used, all the

Sieves

4 A.

sulfurization

Either

prepared

in Hp atmosphere

catalysts

at 500°C.

molar

? H2S in H2 during

After

sulfurization,

or commercial

Sulfurization

30 minutes

a H2 stream

ones were

was carried

sulfurized

after

out passing

a stream

at 500°C and under atmospheric

was passed

during

reduction of 0.06

pressure.

5 hours at 500°C

in order

to

eliminate any reversible sulfur adsorption. Analysis

of the carbonaceous

Carbon

content

H/C atomic

ratio.

Determined

on the rapid combustion into account

programmed

DT-30

without

coke)

oxidation

after

20 mg. The coked catalyst

are heated

in a dynamic

(aT) is plotted

versus

is produced

by the oxidation

selective

during

the reaction

amount

the H/C ratio

heats of combustion.

is based

of CO2 and HZ0 taking

trapping.

with a Shimadzu

Thermal

-1 , flow rate of oxygen: 50 ml min -1 , and the reference

oxygen

sample

to [IO], which

atmosphere,

temperature.

(same catalyst

and the difference Thus,

thermal

of coke and the area under the curve

to the heat evolved of coke when

similar

equipment.

measurement

(TPO). Performed

rate: 20°C min

temperature

have greater

in an equipment

in pressure

at a heating

and sample mass:

using a combustion-volumetry

of coke and the further

the difference

Temperature Analyzer

deposit

("i). Measured

[11]. The area

is greater,

because

is greater more

in

evolution

is proportional for the same

hydrogenated

hydrocarbons

18

01

CHLORINE

FIGURE

1

Carbon

catalysts:

percentage

1, Re/A1203;

1.0

ON CATALYST,

on the catalyst

2, Re-S/A1203;

Commercial

6, Pt-Re-S/A1203.

I

0.5

0

%

after

the deactivation

3, Pt/A1203;

catalyst:

4, Pt-S/A1203;

A, Pt-Re/A1203;

test. Laboratory 5, Pt-Re/A1203;

B, Pt-Re-S/A1203.

RESULTS Prepared

catalysts

Figure

1 shows the carbon content of the catalysts

different together

run

conditions,

to compare

that on sulfurized ones. The smaller though

operated

produces

carbon

sulfurized catalysts

deposition

capacity

severe

but it is the least active

catalysts.

is higher

of Pt-Re

conditions

less coke than the Pt catalyst.

after the runs. Despite

of all the catalysts

with nonsulfurized carbon

coke formation

under more

contents

of all, producing

It can be observed

than on nonsulfurized

catalyst

is also seen since

(lower pressure)

Re catalyst more

are plotted

-

- this catalyst

has the smallest

hydrocracking

coke content,

than aromatization

121. TABLE

3

Analysis

of the carbonaceous

deposit Pt-S/A1203

Pt/A1203

CycloCyclohexane

n-Hexane

Benzene

hexane

0.20

0.32

0.97

0.78

0.60

1.01

0.87

0.75

0.68

0.54

0.55

0.62

Benzene Carbon

on catalyst,

Atomic

ratio H/C

Table

wt%

3 shows some results

pure compounds

polymerized

by analyzing

the coke on catalysts

when

were fed.

On Pt./Al203 catalyst 0.87, meanwhile

obtained

n-Hexane

benzene

produced

on Pt-S the amount

coke).

0.203; of carbon

of carbon

is higher

in a coke with

and the H/C ratio

ratio H/C = lower

(more

19

TEMPERATURE,

FIGURE

2

TPO of coked catalysts

“C

in runs with benzene.

TEMPERATURE, FIGURE

TPO of coked catalysts

3

A similar doubles

situation

the quantity

carbonaceous catalyst

deposit

is used;

occurs

lower temperatures coke is present, Section,

Figure commercial

are shown catalyst

modified

with results

the TPO curve

and a more hydrogenated

presents

in Table

of sulfur

The magnitude

of the

when a sulfurized

2-4. It can be seen

combustion

one because 3. As quoted

is proportional

peaks at

a less polymerized in the Experimental

to the heat released

coke - like that on the nonsulfurized

area for the same amount

2.

coke is produced, in Figures

than those of coke on a sulfurized in agreement

lysts - gives a larger

Commercial

a more polymerized

on a nonsulfurized

the area under

the reaction,

is smaller.

is only slightly

catalysts

1,2, same as Figure

is fed. The presence

and the H/C ratio

in this case,

TPO of the above mentioned that coke deposited

in runs with cyclohexane.

with n-hexane

2, Pt-S/A1203.

“c

when cyclohexane

of carbon

1, Pt/A1203;

in cata-

of carbon.

catalyst

1 shows the amount of coke deposited catalysts

as a function

on either

of the chlorine

sulfurized

concentration.

or nonsulfurized In these catalysts,

20

TEMPERATURE 1 “C

FIGURE

4

TPO of coked catalysts

the influence

of chlorine

in runs with n-hexane.

was found

Increasing

1,2, same as Figure

to be the same for both sulfurized

sulfurized

samples.

the concentration

deposition

decreasing

and a net increase

sulfurized

is clearly

seen.

of chlorine

in carbon

results

deposition

2.

and nonin the coke

when catalysts

are

DISCUSSION Unsaturated function

hydrocarbons

of the catalyst.

polymerize

on the metal

are produced These

accepted

of hydrocarbons

on Pt is a structure

[12], performed

on single metal

should

be a demanding

ensemble

[IZ]. Condensation on the metal. genolysis

On the other

sensitive

and hydrogenolysis produces

coke precursors

the carbonaceous

hand,

reaction

adsorb

polymeric

hydrocarbons

because

a typical effects

compounds

producing

lighter

deposit

in the sense of Boudart condensation

it requires

the condensing

have opposite

or

or dehydrogenation

reaction,

to that for hydrogenolysis,

The former

destroys

producing

insensitive

to fit and strongly

is similar

on the metallic

are able to condense

that the hydrogenation

atoms.

or structure

of many atoms

sensitivity

compounds

and on the support

It is generally

named coke.

by dehydrogenation

unsaturated

an

molecules.

demanding

This

reaction

on coke formation

leading and more

to coke, while

hydro-

hydrogenated

products. Studying

Pt/A1203

coke formation

catalyst,

on the metal

Barbier

occurs

both demanding

ensembles

metal

and their rates decrease

crystals

et al. [I31 showed

on the same active

of many Pt atoms.

Both reactions

when

crystal

that condensation

are produced

size decreases.

Cl31 found that very small Pt crystallites

do not have enough

the required

and they exhibit

when compared support

ensembles

[geometric

effect),

to large Pt crystallites

(electronic

effect).

because

or

sites as hydrogenolysis,

authors

Pt atoms to form

electronic

of an electronic

on large

These

defficiency

transfer

to the

21

When the catalyst number

of large ensembles.

hydrogenolysis demanding

zed metal.

amount

sulfurized amount

to the support

and the

of the hydrogenolysis

decrease

where

catalyst

that cannot

condense

they condensate

producing

coke

temperature

catalyst,

The comparison

[13]. Similarly

there are no large ensembles defficiency

higher

the catalyst in Table

The total

of Pt atoms

because

adsorption

function

of the Pt

of small and large Pt crystals on the sulfurized

(geometric

effect)

is sulfurized

[16-181.

metallic

to small crystals,

(electronic

peak

3). This can be

and the lower hydrogen

to the comparison

Produces

than the non

than that on the

out by many authors

and nonsulfurized

can be made analogously

made by Barbier

capacity

as pointed

of sulfurized

when

(lower H/C ratio

to the lower hydrogenating

of the sulfurized

is always

a larger

Catalyst

C14,15])

there

on the sulfuri-

1 and Table 3). The shift in the main combustion

to a higher

the

than the non

2-4 it can be seen that the sulfurized

a more polymerized

electronic

on the metal

(coke that burns at low temperature

one (Figure

(coke on the support)

catalyst

decreasing

one, and that the most part of the coke is on the support.

nonsulfurized

attributed

some Pt atoms,

are more decreased

hydrocarbons

of coke on the sulfurized

indicates

Because

reactions.

In Figures

less coke on the metal

blocks

coke precursors

of unsaturated

These migrate

of coke.

sulfur

In this way, the condensation

of unsaturated

dehydrogenation

is a larger

amount

is sulfurized,

effect)

Pt catalyst

and there

of an electronic

is an

transfer

from

Pt to s [19-j. With reference A1203

to Re/A1203

can be made,

the amount

of coke

catalysts,

sulfur

genOlYSis,

increasing

stated

a higher

first.

sulfurized

catalyst

metal,

of the sulfurized

activity

independently

for longer

function

Then, according

as shown

to that of Pt/

capacity

of Re and Pt-Re

in Figure

catalyst

of the fact that more

the catalyst

[XI]. Shum et al. ~211

the aromatization

suppression

in these

for hydro-

on the support.

is the stability,

time-on-streams

to our results,

1. Also

available

of coke precursors

controls

is due to a partial

analysis

of large ensembles

the concentration

that the metallic

deactivated

the amount

a similar

hydrogenolytic

is lower than on Pt/A1203, decreases

The great advantage maintaining

and Pt-Re/A1203

but due to the higher

reaction

the higher

of coke deposition

coke is produced

and is

stability

of the on the

on the support.

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