Selective deactivation of a bifunctional catalyst studied by alcohol decomposition

Applied Catalysis, 13 (1984) 39-48 Elsevier Science Publishers B.V., Amsterdam

SELECTIVE

J.C.

DEACTIVATION

LUY and

Santiago

CATALYST

STUDIEP

BY ALCOHOL

DECOf!POSITION

J.M. PARERA

de1 Ester0

(Received

in The Netherlands

OF A BIFUNCTIONAL

de Investigaciones

Instituto

39 -Printed

en Catdlisis

2654 - 3000 Santa

9 January

1984, accepted

y Petroquimica

-INCAPE-

Fe, Argentina,

21 September

1984)

ABSTRACT Methanol

and isopropanol

dehydration

reactions

to differentiate

influence

of coke deposition

The activities metallic

acidic

coke deposition

was affected

selectively

is immediately

affected

and metallic

functions

on the activities

and the poisoning

function

and dehydrogenation

deactivates

by coke,

and to study the

catalyst,

with H2S and NH3 were

Methylcyclopentane

the catalyst

whereas

of catalysts

of a bifunctional

of both functions

more severely.

were used as test

the acidic

studied;

the

was the coke former.

functions; function

Pt/A1203-Cl.

the metallic

is deactivated

The

function after

promotion. On the other does propylene

hand, coke formation

affects

diisopropyl

ether formation

more than

it

formation.

INTRODUCTION Bifunctional very important chemical

catalysts

techniques

interesting reactions

with a Group VIII metal

in industry.

Both catalyst

(gas chemisorption,

to simultaneously are simple

that allow:

in order to infer their nature; site when the catalyst

surface

differentiate

reactions

on an acid function

can be characterized

area, acidity,

both functions

etc.),

of the modifications

to treatment,

and

(c) choice

are

by physico-

but it is

by test reactions.

(a) the study of the catalyst

(b) the study

is submitted

supported

functions

Test

active

sites

of each type of of the best catalvst

from a group. In this paper the bifunctional the catalytic chosen

functions

as the test reaction.

(less than 3OO"C), different alcohol monoxide

alcohols,

Alcohol

and at higher methanol

(CO). Isopropanol

during

to dimethyl

0 1984 Elsevier

was studied

coking.

can be dehvdroqenated

temperatures

(iPrOH)

catalyst catalyst

and isopropanol,

that can be dehydrated

0166-9834/84/$03.00

Pt/A1203-Cl

are affected

carbon-carbon

ether

Science

Publishers

decomposition

or dehvdrated (MeOH)

(DME) and dehydrogenated alcohol

B.V.

was

at low temperatu

bonds can be broken.

were used. Methanol

is a secondary

in order to see how

Alcohol

Two

is a primary to carbon

that can be dehydrated

to

40

diisopropyl

ether(DIE)

Since dehydration metallic

literature

occur

respectively,

reaction

mainly

are typical

the selectivity

can give the relative

on these reactions

dehydration,

CC;), and dehydrogenated

and dehydrogenation

functions,

one or other

or propylene

simultaneously,

mainly

(l-5), and papers

on metal

reactions

of a metal

importance

is very extensive:

on alumina

oxides

to acetone

of the acid and the supported

on an acid to

of both functions.

there are many about

(ONE).

reviews

selectivity

The on alcohol

when

both reactions

(6-8).

EXPERIMENTAL Catalysts Several

acid

(alumina,

and bifunctional

chlorided

catalysts

A1203 was provided

alumina

(Pt on chlorided

by Cyanamid

Ketjen

and mordenite), alumina

(Amsterdam).

metallic

or on mordenite) A1203-Cl

HCl solution

to fill the pore volume

Pt/A1203-Cl

as described

in (9). Mordenite

was prepared

Co., and Pt/mordenite

solutions.

Pt/Si02

identified

as 27-Si02-Ion

was prepared

was provided

used. CK 300 by impregnatinc~

plus a 10% excess.

Zeolon

by impregnating

were

was prepared

CK 300 A1203 with enough

Norton

(Pt on silica),

900-H was provided

mordenite

by Prof. J. Butt from Northwestern

by

with Pt(NH3)4C12 University

and

X-S (10).

Reactants ~C. Erba RPE-grade

methanol,

were a pure grade provided

isopropanol,and

methylcyclopentane

were

used. The gases

by AGA.

Ecqament Runs were carried fed with

a syringe

out in a continuous

pump. The analysis

was a 3 m long, l/4 in.O.D., used catalysts

plug-flow

20% Carbowax

was determined

type reactor

was made chromatographically 20 M on Chromosorb

by combustion

volumetric

MeOH

system

2 CH30H CH30H -

CH30CH3 CO

+

+

(Dehydration)

H20

2 H2

(Dehydrogenation)

iPrOH system CH3-CHOH-CH3-

H2C=CH=CH3

CH CH I313 2 CH3-CHOH-CH3-H-F-D-f-H

+

H20 (Dehydration)

+

H20

CH3 CH3 CH3-CHOH-CH3----,

H3C-CO-CH3

+ H2

(Dehydrogenation)

on line. The column

W. Carbon

analysis.

Reactions

(1 atm, isothermal)

deposited

on the

41

Since the conversions independent.

are small,

The selectivity

it is possible

for each species

to consider

containing

carbon

the reactions atoms

as

is defined

as:

s. = Number of carbon atoms in species i = _Ji_ 1 c Number of carbon atoms in the feed "i i "i

= yi

NCi

yi being the molar effluent,

fractions

N the moles

of species

of alcohol

i, given

by the chromatographic

fed, and Ci the number

of carbon

analysis

of the

atoms of i.

For MeOH: NCCO = 1,

SC0 = yco

NCDME = 2,

NCMeOH

= l

yco + 2YDME + YMeOH 2YDME

'DME =

'CO ' 2YDME "MeOH

'MeOH = I - 'CO - 'DME Similarly

for iPrOH:

NCC= = 3, 3

NCDIE = 6,

NCONF

NC

= 3,

iPrOH = 3

YC= 3 "Cy = YC= + 2yDIE 3

' YONE

' YiPrOH

2YDIE

‘DIE = y = i- 2yDIE + yONE ’ YiPrOH c3

YONE 'ONE =

S

iPrOH

YC; ' 2YDIE ' YONE ' YiPrOH

= 1 - SC= - SDIE 3

- SONE

RESULTS Selectivity A1203, stream.

A1203-Cl,and

the temperature were

and bifunctional

Pt/A1203-Cl

rlordenite, Pt/mordenite

Afterward, alcohols

of acid, metallic,

introduced.

catalysts

were activated

and Pt/SiO,

was increased MeOH was first

and their poisoning

by heating

were similarly

to the reaction introduced

at 500°C for 2 h in a N2

activated

temperature

but in a H2 stream. (230°C)

and the

and then iPrOH, each over a period

42 of two hours. diluted Table

TABLE

In the case of mordenite,

Pt/mordenite

and Pt/SiO2,

the alcohol

was

in a H2 stream. 1 shows the selectivities

of acid, metallic,

and bifunctional

catalysts.

1

Selectivities

of acid, metallic,

Catalyst

Pt,

and bifunctional

Cl,

x

AJ203 (1) A1203-Cl

(1)

S

"C

0.79

iPrOH __~__________ SC= 'DIE _I

MeOH

Temp.,

%

catalysts

DME

SC0

'ONE

230

0.091

0

0.051

0.017

0.002

230

0.109

0

0.067

0.021

0.002

Pt/A1203-Cl

(1)

0.37

0.79

230

0.096

0.005

0.062

0.020

0.025

Pt/A1203-Cl

(1)

0.37

0.79

240

0.180

0.010

0.087

0.039

0.071

Pt/A1203-Cl

(1)

0.98

0.90

240

0.179

0.014

0.100

0.047

0.118

Mordenite

-

-

320

0.001

0

0.195

0.008

0

0.28

-

320

0.001

0.003

0.196

0.007

0.039

1.48

-

240

0

0.005

0.002

0.005

0.078

(2)

Pt/mordenite Pt/Si02

(2)

(2)

(1) Catalyst weight, 0.135 g; activation at 500°C in N2 flow; alcohol 13.5 ml h-1; without gas carrier (2) Catalyst weight, 0.150 g; activation at 500°C in H2 flow; alcohol 40 ml h-1; H2 carrier flow rate, 40 ml min-I

The acid catalysts negligible activity

(A1203, A1203-Cl,

dehydrogenation. and negligible

and the increase

The metallic

dehydration.

of Pt concentration

activity,

although

comparing

the metallic

Pt/A1203-Cl.

Similar

values

results

pulses

of poison

as a function

were found

the remaining

deactivated activity

dehydrogenation),

poisons

catalyst.

is reversibly promote

is promoted

the initial

poisoned.

and

in a H2 stream

conditions the runs.

for

iPrOH was Figures

l-3 show

and for an acid catalyst. amounts

of H2S or NH3

by H2S and reversibly function activity

In A1203-Cl

the acid activity,

for

functions,

on A1203-Cl

or bigger

The metallic

byH2S and by bases;

the dehydrogenation

to 500°C

during

of smaller

The acid function

both reactions

on both catalytic

Under these

injected

and

catalysts.

of time for a bifunctional

by the injection

H2S pulses

increases

catalyze

this test is a useful method

the catalyst

were

activity

shows dehydrogenation

iPrOH reactions

to 230°C.

flow rate,

dehydration

catalysts

of different

out by heating

of base in Pt/A1203-Cl

irreversibly

way. Thus,

of the classical

the temperature

and by using n-butylamine. by pulses

on the catalyst

and the acid function

Runs were carried

and several

selectivity

(Pt/SiC2)

and NH3 were used to poison

2 h and then decreasing introduced

exhibit

catalyst

The bifunctional

in a nonproportional

In order to see the effects H2S, n-butylamine,

mordenite)

flow rate,

is partially

poisoned and

is not recovered,

catalyst

(where there

but to a lesser

extent

and

is no

than in

43

2

0.10

> 5 Y g

0.05

0

FIG.

1.

Pt/Al203-Cl

3

2

1

0

poisoning

in H2 up to 500°C;

with

reaction

4 TIME, h

H2S. Selectivity temperature

as a function

= 230°C;

rate = 40 ml h-l; H2 flow rate = 40 ml min-I.

0

0

1

3

2

6

5

of time. Heating

W = O..l!iOg; iPrOH flow

1, SC;; 2, SDIEi

4

3, SONE.

5

TIME, h FIG.

2.

Pt/A1203-Cl

poisoning

conditions

and numbers

with NH3, Selectivity the same as Fig. 1.

as a function

of time.

Experiment

44

0.10 >

I-

L

s

0.05

ii 0

FIG.

Al,O,-Cl

3.

0

2 TIME,

1

poisoning

Experimental

and numbers

Selectivities Cl, 0.37%

of a hifunctional

of catalysts

Pt) catalyst

for A1203-Cl,

ta poisons

previously

o-xylene,

The three coked

in a N2 stream.

bed was cooled

the hydrocarbons

for 2 h without

results

thdi~ the acidic

and n-pentane samples

to 23O"C,

gas dilution.

and the selectivities

These

coked with hydrocarbons.

coked with cumene,

Then the catalyst

of time.

indicate

function,

catalyst

used in MeOH and iPrOH reactions.

were each introduced

as a function

the same as Fig. 1.

poisons

furrction is mure sensitive

Selectil0a deactivation

Selectivity

with ti,$ and NH3.

conditions

Pt./A1203-Cl; also bases are reversible that the meta?lic

3 h

to alcohol

were

A Pt/A1203-Cl

heated

for 2 h at 500°C

and MeOH and later iPrOH

The coke contents reaction

(0.9%

in runs at 500°C was

products

(% C) produced

by

are shown in

TabIe 2.

TABLE

2

Influence

of coke content

Catalyst,

Pt/A1203-Cl,

weight,

on catalyst

selectivity

0.79% Cl, 0.37% Pt; activation at 500°C in flowing -1 0.135 g; alcohol flow rate, 13.5 ml h without gas carrier

Coke former

Coke % C

rleOH

_ 'OME

iPrOH

____ sco

SC= I)

‘DIE

'ONE

0.067 0.090 0.057 0.061

0.021 0.039 0.019 0.020

0.025

3

None

0

0.096

Cumene o-Xylene n-Pentane

0.37 1.33 2.74

0.114 0.103 0.077

When the catalyst

0.005 0.001 0.001 0.001

had a small amount

practically

to zero and the dehydrating

was higher,

the dehydrating

Selective

deactivation

activity during

of coke,the activity

up on the catalyst.

dehydrogenating

increased.

: 0

activity

When the amount

decreased of coke

decreased.

the run with alcohol.

of SCG, iPrOH was used to study how the Pt/A1203-Cl is built

N2; catalyst

Because

functions

of the very small values are affected

when coke

45

In runs where cooled

the catalytic

to 230°C

dehydrogenation

activities,

that Pt was oxidized

to different

reaction)

it was decided

as follows:

space velocity.

different

amounts

and final

selectivities

hiqher

values

the temperature acidity,

SDIE follcws way. Figure formed

were measured.

with coke content

to 480°C

using

is

to reduce

that H2 would

increase which

to 480°C

is strongly

reduce

Pt

Afterward,

Figure

the E2 mechanism.

dependent

and methylcyclopentane in order to

to allow the deposition

of

the system was cooled

Metallic

whereas

to 230°C

of final

activity

(SON,-) was high

there was an increase

on pretreatment

coke contents.

temperature.

(much

Dehydrating

Even when coke content

was as high

activity,

to that of SC;, but SDIE

neighbor

It also indicates

were

MCP and H2 flow rates

is affected

of coke content.

it seems that coke deposition

and basic

and

activity

5 shows SDIE /S c3= ratio as a function

of acidic

selectivities

4 shows the correlation

on the catalyst.

the dehydrating

similar

(activation

(S = + SDIE)- It can be supposed that C3 (in order to feed MCP) would produce an increase in

for higher

not eliminate a behavior

the run

in a H2 stream

several

by H2 and fell sharply, in dehydrating

via an E2 mechanism,

possibility

indicate

H2 throughout

Feed times were also varied,

slowly decreased

as 17%, it could

was raised

was introduced

of the reduction

activity

The reason

was insufficient

for 1 h, and the initial

of coke on the catalyst.

at the outset)

support

the data.

than

bed was heated to 230°C for 2 h in a H2 streap,

introduced

Then the temperature

(MCP), the coke former,

because

values would

N2 for 2 h and then

were greater

to duplicate

by the reaction

to work with

the catalyst

and then iPrOH and H2 were

selectivity

in flowing

activities

extents.

For this reason

change

but it was difficult

and the H2 produced

The variation in selectivity

the metal.

measured.

bed was heated at 500°C

in order to feed iPrOH, dehydration

reduces

in a stronger

Assuming

that DIE is

considerably

the

sites being free and close enouqh to allow

that Ci can be formed

not only from DIE,

but in an

COKE, %

FIG. 4.

Selectivity as a function of coke content on the catalyst. Heating in H2 UP to 230°C. Experimental conditions and numbers, the same as Fig. 1.

46

0

k._-.

_.-

_;

~_A

10 COKE, %

FIG. 5. DIE/C; selectivity ratio as a function of coke content on the catalyst.

1 6

COKE,% FIG.

6.

Metallic/acid selectivity ratio as a function of coke content on the catalyst.

independent way, because when there is no ether, there is still a significant olefin value.

) ratio, i.e., the dehydrogenating,' Figure 6 shows the drop in SONE/(SC; + S DIE dehydrating activities ratio versus coke content. A 6% coke content on the catalysts produced a thousand-fold drop in the ratio. Figure 7 presents similar results to those of Fig, 4, but when the catalyst bed was heated in H2 to 5OO”C, it produced greater initial activity

ValUeS

as

expected.

Dehydrogenation activity also diminishes drastically with coke content, whereas, in th,. range we worked, dehydration activity increased to a certain value, which was almost constant. In this case it is not possible to assume an increase in activity as a resul 'ofheating for MCP addition because the preheating was at hioher temperature. The increment in dehydration activity at both activation temperatures (230 and 5009&$

47

COKE, "1.

Selectivity

FIG. 7.

to 500°C;

seems to indicate

when and

they

are

the ether.

Berezin

et al.

one controlled

by coke,

The acidic

(11)

(in coking

Cl/C3

TABLE

in H2 up

as Fig. 1.

sites

in Table

an increase

function

catalyst

to acid function)

alone

in Table

and by Parera

during

Table

in dehydration

naphtha

catalyst

than the

et al. (12)

reforming.

activities

(points

selectivities

3 shows that on A1203-Cl

activities,

by

two runs were made with

3. Only dehydration

1 it was shown that acid

Of coke iS high. was cited

is more affected

has the same behavior,

than in Pt/A1203-Cl

Oldin

the.v found that aromatization

or cyclohexane)

(methylcyclopentane)),

(metallic

higher

when the amount

the

as observed

at origin

could

be

of Figures

of A1203-Cl

are

low coke contents

using

Pt/A1203-Cl.

3

Selectivities Catalyst carrier

as a function

weight,

of coke content

0.150 g; activation -1

on A1203-Cl

in H2 flow; alcohol

catalyst

(0.79% Cl)

flow rate: 40 ml h-l; R2

rate, 40 ml min

Initial

Activation temperature

230°C 500°C

Heating

sites to produce

on the metallic

(n-hcxane

than those of Pt/A1203-Cl.

also produced

(and basic)

a Pt-Re/A1203-Cl

sites

0.79% Cl. Data are reported and they were

4 and 7). Similarly higher

on the acidic

coke deposition

by the acidic

the ratio

A1203-Cl,

and numbers

sites are also deactivated

of initial

To see if the acid function

observed

conditions

on the catalyst.

that alcohol reacts in a preferential way on the metallic sites. and

by the metallic

measuring

of coke content

other experimental

blocked

The property

controlled

as a function

selectivities

SC5

‘DIE

%NE

0.033 0.055

0.009 0.016

i

Coke %C

1.29 1.61

Final selectivities

s= C3

‘DIE

‘ONE

0.059 0.061

0.016 0.021

:

48 Consequently presence

the increase

in activity

is produced

by the coke,

independently of the

of Pt.

CONCLUSIONS The study metallic

of the dehydrogenation-dehydration

and acidic

The metallic deposition, by higher

functions

function

whereas

of bifunctional

of the Pt/A1203-Cl

the acidic

function

of iPrOH gives

information

about the

catalysts. catalyst

is promoted

is initially at low carbon

affected values

during

car

and deactiva

coke depositions.

REFERENCES

11

ME. Winfield, in "Catalysis" (P.H. Emmett, ed.) Vol. 7, Reinhold, New York, 1960 p. 93 H. Pines and J. Manassen, Adv. Catal., 16 (1966) 49. H. Knezinger and P. Ratnasamy, Catal. Rev. Science Eng., 17 (1978) 31. C.S. John and M.S. Seursell, in "Catalysis" (Specialist Periodical Reports, C. Kemball, ed.), The Chemical Society, London 1977, vol. 1, p. 136. J.M. Winterbottom, in "Catalysis" (Specialist Periodical Reports, C. Kemball, ed. The Chemical Society, London 1931, vol. 4, p. 141. K. Hauffe, Adv. Catal., 7 (1955) 213. O.V. Krylov, "Catalysis by Nonmetals", Academic Press, New York 1970, p, 116. J. Cunningham, B.K. Hodnett, M. Ilyas, J. Tobin, E.L. Leahy and J.L.G. Fierro, Far. Discuss. Chem. Sot., 72 (1981) 282. A.A. Castro, O.A. Scelza, E.R. Benvenuto, G.T. Baronetti and J.M. Parera, J. Cata 69 (1981) 222. T. Uchijima, J.M. Herrmann, Y. Inoue, R.L. Burwell, J.B. Butt and J.B. Cohen, J. Catal., 50 (1977) 464. V.A. Berezin, L.I. iabotin, M.Ye. Levinter and S.N. Ul'yanova, Neftekhimiya, 21

12

(1981) 212. J.M. Parera, N.S. Figoli, E.M. Traffano,

1 2 : 5 6 ; 9 10

Appl.

Catal.,

5 (1983) 33.

J.N. Beltramini

and E.E. Martinelli,