Chlorine adjustment in Al2O3 and naphtha reforming catalysts

341

Applied Cataysis, 6 (1983) 347-363 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

CHLORINE

IN A1203 AND NAPHTHA REFORMING

ADJUSTMENT

A.A. CASTRO, O.A. SCELZA, Instituto

C.T. BARONETTI,

de Investigaciones

en Catalisis

CATALYSTS

M.A. FRITZLER

and J.M. PARERA

y PetroquSmica,

Santiago

de1 Ester0 2654,

3000 Santa Fe, Argentina.

(Received

6 January

1983, accepted

27 March

1983)

ABSTRACT Chlorine concentration on Al2O3, Pt/A1203 a HCl-HpO-air mixture reaches an equilibrium molar ratio according to:

*

and Pt-Re/A1203 after treatment with value that depends on R = H2O/HCl

K L (l/R) 1 + K (l/R)

'Cl =

K and L were calculated at 400, 500 and 550°C. Chlorine retention on catalysts with low metal loadings is mainly given by the support retention capacity, which appears to be related to alumina acidity. Catalysts with high Pt loadings show a hiqher chlorine retention. This excess of chlorine is related to the metal and is eliminated when reducing the catalyst with hydrogen.

INTRODUCTION Alumina

is an active

and alcohol

dehydration,

strong acidity,

catalyst

for several

like hydrocarbon

cracking

has been treated with halogenated will catalyze

catalysts,

an acidic function,

[I], making

High chlorine

paraffins, Thus,

while

or catalyst

to study the method

However,

that require

alumina

that

acidity

0166-9&X34/83/$03.00

concentration

with an optimum

are controlled

with a H20-HCl-air

were studied,

stream

promotion

by the perfor-

the formation

of lower carbon

number

decreases

the catalytic

activity

with high activity formation.

level is needed,

and the influence

concentration.

provides In naphtha

in the catalyst

catalyst

chlorine

of its adjustment

alumina

addition.

parameter

for "dry gas" (C,-C4 paraffins)

In this paper, the acidic Al203 catalysts

promotes

catalyst,

by chlorine

reactions

it a very important

to have a reforming

the final chlorine

oxychlorination

reforming

enhanced

and hydrocracking

low chlorine

ization but low activity

regulate

isomerization

for reactions

(HCl, HF, etc.) to increase

such as naphtha

concentration

it is important

alumina

or cyclization.

compounds

and this is generally

the isomerization

acidic function mance.

such as olefin

these latter reactions.

In bifunctional

reforming

reactions,

but it has a much lower activity

An adequate

Hence, an

and it is important

of the parameters method

[Z].

for isomer-

which

to do this utilizes

[3,43.

of different

aluminas,

using the above-mentioned

0 1983 Elsevier Science Publishers B.V.

Pt/A1203

method.

and Pt-Re/

The effect of the

supported

metals

on the chlorine

adjustment

was also studied.

EXPERIMENTAL Acidic promotion (Cyanamid Davison

Ketjen),

A1203 Al 0104-T

Chemical),

bimetallic

was studied on A1203 CK 300 (Cyanamid

Pt/A1203

Pt-Re(0.3-0.3%)/A1203

support of catalyst

(Harshaw

catalysts

Chemical

prepared

catalysts

Ketjen),

A1203 OOO-3P

Co.), A1203 SMR 55 (Grace

in our laboratory

and two commercial

("A" and "8"). A1203 CK 300 is the

"B".

Before use, all the aluminas

were stabilized

by calcination

at 650°C

in a dry

air flow. Pt/A1203

catalysts

with an aqueous tration

were prepared

solution

according

to [5] impregnating

of H2PtC16 and HCl, using the necessary

A1203 CK 300 H2PtC16

to obtain 0.38, 1.6, 2.75 and 6 wt% Pt. The HCl concentration

0.6 mol 1-l. The samples were dried at 120°C for 12 h. More details elsewhere

[5]. Aluminas were impregnated

by the same procedure Impregnated

adjustment

as that used for the Pt/A1203

aluminas

room temperature

with HCl solution

and mono- and bimetallic

which was obtained

catalyst.

catalysts

pressure

by vaporizing

was always have been given

(0.6 mol 1-l) and dried

were heated

up to 400, 500 or 550°C. At these temperatures

was carried out at atmospheric

of HCl-H20-air

in air from

the chlorine

by passing a gaseous mixture

an aqueous HCl solution,

flow rate, in 1800 ml air h-' g-l. The H20/HC1 molar ratio was adjusted 20 and 200 by changing in air was between

the HCl concentration

in the solution.

80 and 550 ppm. Afterwards,

at constant between

The HCl concentration

the mono- and bimetallic

were purged with 600 ml N2 h-' g-' and reduced

concen-

catalysts

at 500°C with 600 ml H2 h-' g-'

for 6 h. Unimpregnated to the chlorine

CK 300 alumina, adjustment

Pt and Cl contents as previously titration

RESULTS

previously

treatment

calcined

at 650°C in air, was subjected

at 500°C.

on the solid samples

and metallic

cited [5]. The total acidity was measured

method

dispersion

were determined

by the n-butylamine

[63.

AND DISCUSSION

Figure

1 shows the chlorine

and unimpregnated adjustment

alumina

treatment.

equilibrium concentration

value.

content on Pt(0.38%)/A1203,

samples as a function

The chlorine

concentration

HCl-impregnated

of time during

alumina

the chlorine

changes with time reaching

an

In a former paper [53 it was reported that the equilibrium

depends

on the H20/HCl molar ratio and the temperature.

a given R value, the particular no effect on the equilibrium

HCl concentration

chlorine

The results can be interpreted only involves the support

concentration

considering

Besides,

for

in air (from 80 to 550 ppm) has [5].

that the chlorine

by means of the reactions:

adjustment

treatment

349

4 TIME, FIGURE

1

Chlorine

as a function

content

ratio = 80. 0:

500°C and H20/HCl

molar

Al203 CK 300; fl:

unimpregnated

?H

PH

Al

Al

2

Al/'\Al

+

The overall

PH Al

+

HCl

2

HCl

F' Al

This reaction

* =

2

reaction

+

8

of time during Pt(0.38%)/A1203

adjustment CK 300; A

H20

OH

Cl

Al

Al

(2)

will be:

H20

(3)

equilibrium

as an exchange

concentration

between

OH and Cl surface

K L (l/R)

(4)

K the equilibrium

concentrations;

According

(4) for K(l/R) >> 1, Ct, = L. Hence,

Experimental

retention results

capacity

represented

K and L depend

constant

the OH and Cl surface to Equation

The results

1. These parameters show differences

and L the sum of

only on the temperature. it represents

the

of the support. as Ct, vs l/R for the different

shown in Figure 2. The K and L values calculated shown in Table

groups.

(C;,) is given by:

1 + K (l/RF

chlorine

at

(1)

where R is the H20/HCl molar ratio,

maximum

treatment

: HCl impregnated

A1203 CK 300.

can be considered

Hence, the chlorine

'Cl

+

Al"\Al

6 hour

by the least-squares

were used to draw the curves

in the chlorine

retention

supports

are

method

are

shown in Figure 2.

capacity

of the supports.

350

TABLE 1 K and L values of Equation

(4) for different

samples.

A1203 CK 300

165

400

321

1.46

0.99

A1203 CK 300a

165

500

207

1.10

0.87

A1203 CK 300

165

550

154

1.03

0.99

A1203 OOO-3P

206

500

154

1.22

0.99

A1203 Al 0104-T A1203 SMR 55

71

500

212

1.63

0.99

135

500

160

1.33

0.97

Pt-Re/A1203

"A"

172

500

305

0.98

0.90

Pt-Re/A1203

"6"

170

500

284

1.06

0.98

aData from [5] bAt the end of the adjustment reduction

treatment

for the aluminas

and at the end of the

for the catalysts.

80 60 40

*b 0

20 0

0.01

0

l/R) FIGURE 2

Equilibrium

different

supports

chlorine

Al 0104-T

HCl impregnated

at 500°C:

0.02 mol

concentration

(f)

aluminas

0.04

0.03 HCLI mol H20 (Cg,) as a function

CK 300, (U) and (a)

000-3P,

Pt-Re/A1203

(A) "A".

0.0:

of l/R for

SMR 55 and

(0)

351

1.8 1014 AL 0104-T

1 g

//

1014 -

1.4

Y

‘5

A ooo-3P __----

-7 1.0 10’4

-_H

/

/

&If? 55

,0’ ACK300

I

I

._ d4

2 1014

3 1014

n-BUTYLAMINE, mdec /cm2 FIGURE 3

Chlorine

of acidic

sites with pKa < +1.5.

retention

capacity

(L) at 500°C

as a function

of the density

@O.CK300

q 0 =

l/R, FIGURE 4

Equilibrium

with the same support. Equation from [5].

chlorine

Pt038'/.1/Al~O3

‘md HCl/mol

concentration

results

Hz0

(I$,) as a function

The curves are for the support,

(4). Experimental

CK300

for Pt(0.38%)/A1203

of l/R for samples

CK 300, calculated

with

CK 300 were extracted

352 Taking

into account

acidity,

retention

properties

the acidic acidic

(21, a higher number of exposed

would mean a higher chlorine

in the chlorine acidic

reaction

capacity

of the aluminas.

centers

The results

with pKa < +1.5, would

properties

CK 300 and supported

equilibrium

drawn.

It can be seen that, for these low metal the Ci, values for the catalysts

Figure 5 shows the results end of the adjustment

chlorine

and reduction

where

indicate

atmosphere

there are no differences

chlorine

concentration

of a complex

has been previously

at the

with different

at the end of the adjustment to hydrogen

Pt

reduced

concentration

on the catalysts

to Pt', the chlorine

phase retains

chlorine

among Pt ions, chlorine,

mentioned

treatment

reduction.

is close to that on the support without

that the metallic

step. The existence

loadings,

and those of the support.

step is higher than that on the support.

Pt is completely

catalysts

vs l/R for

Using K and L

(41, the curves of Figure 4 were

in Figure 5 that the chlorine

at the end of the adjustment

results

of

L and the

to A1203 CK 300. It was found that the

on A1203 CK 300 samples

It can be observed

on the Pt/A1203

in the

concentration

steps vs l/R for catalysts

does not change when they are subjected

after reduction,

the difference

between

CK 300 catalysts.

of the equilibrium

the solid line corresponding content

a relation

chlorine

Pt and Pt-Re on A1203

for A1203 CK 300 (Table 1) and Equation

loadings,

Therefore,

to differences

shown in Figure 3, L vs density

indicate

values

between

capacity.

or Lewis

of the aluminas.

Figure 4 shows the experimental A1203

retention

could be attributed

Al atoms,

during

metal.

These

the adjustment

and A1203

[71. The differences

However, concentration

in an oxidant

between

the molar

_____-------* A ATTHE

ENDOF REDUCTIDN

ADJUSTMENT

5

Equilibrium

chlorine

at the end of the adjustment different

Pt loadings.

line. The numbers

A

Pt 1.6"1. 173)

g Pt 2.76'1.

V

pt 275.10 (70)

0 Pt 6e/o

APt60/0

I I 0.01 0.02 01)3 QO4 l/R, mol HCII md Hz0

0

FIGURE

0 Pt 1.6'1.

concentration

L 0.05

as a function

and at the end of the reduction

The chlorine

between

(($1

parentheses

retention

(561

of l/R at 5OO"C,

for samples with

on A1203 CK 300 is drawn as a solid

are the metallic

dispersion

percentages.

353 Cl content

at the end of the adjustment

the fraction fraction

of halogen

ranged

Therefore, samples capacity

retained

between

retention

the adjustment

of the support.

participation

the chlorine

0.5 and 1 mol Cl per mol of exposed

the maximum

during

and that at the end of the reduction

by the metal during

of chlorine

of the metal

in the chlorine

naphtha

adjustment

This

Pt.

by the metal

in Pt(0.38%)/A1203

will be less than 5% of the chlorine

Thus, for commercial

gives

adjustment.

reforming

retention

catalysts

the

is negligible.

CONCLUSIONS The chlorine

content

on aluminas,

value when they are subjected is given by Equation

Pt/A1203

to a treatment

(4) which

and Pt-Re/A1203

reaches an equilibrium

with a H20-HCl-air

is based on a reaction

between

mixture.

Such value

the support

and the

H20-HCl mixture. The chlorine related

retention

to the acidity

The Pt deposited treatment.

on the alumina

The chlorine

For low metal

capacity

loadings,

the amount of chlorine

is different

for each alumina

and seems to be

of the support. also retains

on the metal

chlorine

is eliminated

upon reduction

like those of the commercial retained

by the metal

during the adjustment with hydrogen.

naphtha reforming

is negligible

catalysts,

in comparison

with

that of the support.

ACKNOWLEDGEMENTS The authors Subsecretarfa

thank Juan C. Yori for experimental de Estado de Ciencia y

Tecnologfa

help. Financial -SUBCYT-

support

(Argentina)

from

is also

acknowledged.

REFERENCES B.C. Gates, J.R. Katzer and G.C.A. Schuit, "Chemistry of Catalytic Processes", McGraw-Hill, N. York, 1979, p. 275. N.S. Ffgoli, M.R. Sad, J.N. Beltramini, E.L. Jablonski and J.M. Parera, Ind. Eng. Chem. Prod. Res. Dev., 19 (1980) 545. F.C. Wilhem, U.S. Patent 1,366,344 (1971). R.E. Rausch, U.S. Patent 1,293,247 (1970). A.A. Castro, O.A. Scelza, E.R. Benvenuto, G.T. Baronetti and J.M. Parera, J. Catal., 69 (1981) 222. J.M. Parera and N.S. Ffgoli, J. Catal., 14 (1969) 303. K.W. McHenry, R.J. Bertolacini, H.M. Brennan, J.L. Wilson and H.S. Seelig, Peme Cong. Int. Catal., Paris 1960, (Editions Technip), Vol. 2, P. 2295.