Isomerisation of 1-methylnaphthalene over Ω-zeolite

Ppplied Catalysis, 6 (1983) 171-177 ElsevierScientific PublishingCompany, Amhrdam - Printedin The Netherlands

171

ISOMERISATIONOF I-METHYLNAPHTHALENEOVER n-ZEOLITE V. SOLINAS, R. MONACI, B. MARONGIU and L. FORNIa Istituto di Chimica Fisica e Industriale, Universita di Cagliari, Via Ospedale, 72 09100 Cagliari, Italy. aIstituto di Chimica Fisica, Universita di Milano, Via C. Golgi, 19 20133 Milano, Italy. (Received 9 August 1982, accepted 5 October 1982).

ABSTRACT The title reaction was studied at 210-390°C over variously decationated nzeolite catalysts, prepared from the protonated form by ion-exchangewith aqueous NaCl. The catalysts were highly active and selective. However, the NaCl treatment proved unable to back-exchangemore than ~80% of the exchangeable ions, so that cracking reactions could not be completely stopped. A treatment with 0.02 M NaOH solution led to a fully inactive catalyst for both isomerisationand cracking. INTRODUCTION The isomerisationof I-methylnaphthalene(IMN) to P-methylnaphthalene(2MN) may represent an interesting upgrading process to provide a useful intermediate for several applications. The isomerisation reaction is promoted by acid catalysts [1,21. Among the few previous studies, a HF-BF3-based 131 and a Y-zeolite-based C41 catalytic system may be cited. When applicable, heterogeneous processes are usually preferred to homogeneous ones, due to significant practical and economic advantages. In the present work an attempt was made to employ large-pore n-zeolite at various degrees of decationation as a catalyst for 1MN + 2MN isomerisation. EXPERIMENTAL Materials IMN was Merck 99 mol % pure reagent. Gaschromatographic(GC) analysis revealed %l mol % 2MN as main impurity. Hydrogen was > 99.995 mol % pure. "Pro analysi" chemicals and bidistilled water were also used for the ion exchange process. Catalyst The fully decationated n-zeolite (ELZ-n-6) was purchased from Union Carbide as "cake," i.e. as crystalline, binderless powder. The residual Na content was 0.18 wt % and more than 90 wt % of the powder was made of ~15 Pm particles, as

2 -1 found by a Coulter Counter (Mod.ZB) determination (Figure 1). A value of ~350 m g

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172

1

FIGURE

1

Particle

Equivalent

size distribution

spherical

diameter

BET surface area was also measured, powder was pressed

to negative a muffle

and sieved,

collecting

on this granulated

concentrations,

similar

in a2 mm thick pellets

were gently crushed was performed

in the "as purchased"

ELZ-o-6 cake.

in abscissa.

at temperatures

to that referred

(maximum pressure

by others

the 40-60 mesh fraction.

solid with aqueous

C51. The

100-200 MPa), which

NaCl solutions

Ion exchange of various

ranging from ~25 to 90°C. After careful washing

AgCl test, the solid was dried in an oven at 120°C and calcined

furnace overnight

by atomic absorption concentration

at 500°C. The degree of ion exchange

spectrometry,

after dissolution

of Na+ ions, introduced

%30 mg Na/g of zeolite,

in

was determined

of the solid in acid. The

in such a way, reached a limiting

value of

after seven exchanges

with fresh saturated

NaCl solution

at 90°C. When referred

to a fully crystalline

form of Na-n-zeolite

(37 mg g-'1

C61, this corresponded

to a degree of back-exchange

ient to remove completely The remaining poisoned) washing

Na+ ions were introduced

by treatment

of the zeolite

(Table 1) was measured the presence

the stronger

of various

night in slowly flowing

from the catalyst

(and the residual

with 0.02 M NaOH aqueous

solution,

stronger followed

slurry to pH < 10, drying and calcination. by titration

with n-butylamine

indicators

[71, after heating

dry nitrogen.

surface acidity,

a titration

catalyst

(see Table

samples

acid centres

of over 80%, but was insuffic-

As an attempt

acidity by careful Surface acidity

in anhydrous

solvent

in

the solid at 500°C over-

to evaluate

was also made with tributylamine 1).

surface.

the "external"

[8,9] on two

173 TABLE

1

Surface acidity

(mmol/g cat.).

Pretreatment

temperature

5OO"C, titrating

base

n-butylamine.

Catalysta

pK,s -1.5

< 3.2

2 6.8

HNa-5b

0.067(0.018)c

0.113(0.036)

1.118(0.094)

HNa-16

0.050

0.084

0.460

HNa-34

0.040

0.076

0.320

HNa-68

0.014

0.056

0.116

HNa-81

0.012(<0.004)

0.033(0.017)

0.094(0.048)

Na-100d

0.000

0.022

0.038

aPercentage b

Original

of ion exchange

ELZ-n-6 Union Carbide

'In parentheses

from HNa-81

Apparatus

and procedure

The isomerisation glass microreactor,

referred

to the fully Na-form

zeolite.

data from titration

dObtained

in.situ,

(figure),

by exchange

with tributylamine.

with 0.02 M aqueous

runs were conducted on fresh catalyst

NaOH.

in a continuous,

samples

by heating at 500°C for 12 h in slowly flowing

the temperature

to the chosen value, a mixture

ratio RH = 5) was fed at time factor were collected

in traps, cooled

fixed-bed,

(% 1 g). The catalyst nitrogen.

of hydrogen

After lowering

and IMN (at a mole

'I = 5 (g cat.x h/ml liq.lMN).

in ice-salt mixture,

tubular was activated

The products

after 55, 170 and 330 min

time-on-stream.

Analysis Reactant

and products

were analysed

by GC, on a capillary

glass column,

25 m x 0.3 mn, coated with OV-1 and kept at 120°C.

RESULTS AND DISCUSSION The activity

comparison

ure. The catalyst

data were collected

performance

fed IMN) and selectivity

was expressed

S2MN to the desired

The results are shown in graphical All the catalysts, The equilibrium attained

except

conversion

or substantially

at 210-390°C

as overall product,

form in Figures

Na-100

(see Table),

conversion

press-

y (reacted/

both as molar fractions.

2-4.

proved to be highly active.

(0.62 to 0.60 at 210 to 4OO"C, approached

and atmospheric

respectively

with all fresh catalysts

ClOl),was

at any reaction

174

FIGURE 2

Conversion

RH = 5 (mol/mol),

vs. time-on-stream

catalyst

at various

temperatures.

-i = 5,

HNa-68.

1

Y

c .C

min

FIGURE 3

Conversion

The figures

vs. time-on-stream

refer to the percentage

for the variously

of exchanged

ion exchanged

Na+ (fully Na-form

catalysts.

= 100).

T = 270°C. .T = 5, RH = 5.

temperature,

even at relatively

low values of time factor.

than 0.7 and in some cases exceeded ed by GC in the effluent

0.9. Naphthalene

stream, denoting

a partial

SzMN was usually

was the only byproduct dealkylation

higher detect-

of both reactant

175

min FIGURE 4

Conversion

catalyst

vs. time-on-stream

for various

(ZMN), but simultaneous

cracking

(IMN) and product

also took place. As a consequence, was noticed at all reaction time-on-stream,

partial

pressure

surface

acidity

peratures ectivity

of the catalyst

and decreased

due to their apparent

to those

(pK,+1.5)

tribution

the substitution

and

activity,

cracking

sites are necessary

able by slurrying

in Figure

gives a catalyst

at lower tem-

conditions

of sel-

could not

may be classified

on the catalyst

require weaker

In addition,

to pKa<3.2

for isomerisation

In our case, the dis-

and its change with increasing

substantially

up to the maximum

For

with respect

it has been demonstrated

for transalkylation.

5. Moreover,

with

surface.

centres,

is required

of protons with Na+ ions, although

reactions,

after 55 min time-

but a clear correlation

reactions

for cracking.

corresponding

are summarized

lowered with increasing

when working

or reaction

present

and transalkylation

of acid sites concentration

ion exchange

(Figure

to hydrogen

randomness.

of acid centres,

required

[12,13] that a strength and even stronger

properties

temperature

proportional

respectively.

increased

that acid-catalysed

isomerisation

to reaction

was lowered by

values of 0.87, 0.81 and 0.74 were

catalysts,

S2MN usually

ring system

of the catalyst

conversion

3) and inversely

at higher temperatures,

to the strength

instance,

proportional

(e.g. average

data with either catalyst

It is known [11,12]

The overall

(Figure 4). S2MN generally

HNa-34 and HNa-81

At higher times,

be obtained,

overall

(Figure

in feed mixture

found for HNa-16, on-stream).

conditions.

surface acidity

of the naphthalene

a quite rapid deactivation

with a trend directly

2) and overall

respect

RH. T = ZlO"C, T = 5,

HNa-5.

the data of Figure reducing

degree of 3 show that

progressively

the

active for both isomerisation

degree of ion exchange

the zeolite with NaCl solutions.

Furthermore,

(~80%), attain-

the ratios between

176

e ;i;

o -1.5- 3.2

0 En . Z

0

3.2- 6.8

&5-

% Na+

FIGURE 5

Concentartion

exchange.

Titrating

the acidities HNa-81,

Table

the a-zeolite 0.012

(0.018

back

of the various

between

strength

: 0.036 : 0.094 for HNa-5 and 0.004 : 0.017 : 0.048 for

1) obtained

by titration

with tributylamine,

pores [8,9], are comparable

that the centres

to the bulky

Table

of the latter react on the centres As for the relatively

by the particular

have practically coking-cracking

no connection

centres

sites are rapidly

the catalyst,

following

activity,

of 8-zeolite

of the channel.

the elimination

confirms

once again the carbonium

surface of the zeolite. it is generally

cracking

reactions.

recog-

the deactivation

is very likely

of the solid, whose main channels of polynuclear

blocks the access of reactant

As a result,

lost. Finally,

character

a large part of the

the complete

of the acidity

ion-based

part

are weak and this has been

at the pore mouths

to all the internal

running

[6], are not

to each other [63. The formation

potential

system,

These

they prove that an important

located on the external

pore structure

bulky byproducts

catalytic

the minor channel

Moreover,

also by us (see Figure 5). However,

accelerated

: 0.113 : 1.118 and

with n-butylamine.

cages in n-zeolite

rapid decay of catalyst

nised [14] that the acidic properties confirmed

1) obtained

located within

1MN molecules.

which hardly enters

with those (0.067

the major system of gmelinite-type

accessible

acid sites vs. degree of Na+ back-

base, n-butylamine.

: 0.033 : 0.094, respectively,

facts indicate

exch.

deactivation

by ion exchange

of

with NaOH,

of both isomerisation

and

CONCLUSIONS The main conclusions

which one may deduce from the present work are the following:

177 i) isomerisation acid sites;

of 1MN takes place easily on relatively

ii) cracking-coking

corresponding

reactions

of methylnaphthalene

of other aromatics,

(pK, $ -1.5) acid sites proved sufficient even at quite low temperature and good concentration

of intermediate

to be a highly active catalyst of higher strength

activity; zeolite

between

iii) due to its large-diameter strength

acid centres,

for IMN isomerisation;

of an essentially

HNa-n-zeolite

framework

monodimensional

channel

system,

v) the back-exchange

treatment

with NaCl of the protonated completely

a high activity

proved presence

of the zeolite,

so favouring

in neutralizing

rate,

pore system

iv) the simultaneous

channels,

while preserving

of stronger

them at substantial

adjacent

did not succeed

catalyst,

(-1.5 6 pKa 2 3.2)

since a small concentration

to promote

acid sites and the particular

erized by the presence any diffusion

(210°C);

weak

seem more facile than the

charact-

prevents

a rapid decay of the catalytic

the cracking

form of the

activity

of the

for IMN isomerisation.

ACKNOWLEDGEMENT This work was performed

within

the CNR Project

on Fine Chemistry.

REFERENCES 1

1: 13 14

M.L. Poutsma. in "Zeolite Chemistry and Catalysis", (J.A. Rabo, Ed.), ACS Monograph 17; (1976). Japan Kokai 74 49,945 May 1974; Chem. Abs., 81 (1974) 77737a. G. Suld and A.P. Stuart. J. Ors. Chem., 29 (1939) 2939. C. Dimitrov, Z. Popova and M. iuygn, React. Kinet. Catal. Lett., 8 (1978) 101. H.F. Leach and C.E. Marsden, in "Catalysis by Zeolites", (B. Imelik et al., Eds.), Elsevier, Amsterdam (1980) 141. J.F. Cole and H.W. Kouwenhoven, Adv. Chem. Ser., 121 (1973) 583. H.A. Benesi and B.H.C. Winquist, Advan. Catal., 27 (1978) 98. D. Barthomeuf, ACS Symp. Ser., 40 (1977) 453. 0. Barthomeuf, J. Phys. Chem., 83 (1979) 766. D.R. Stull, E.F. Westrum and G.C. Sinke, "The Chemical Thermodynamics of Organic Compounds", Wiley, New York, 1969. J.P. Damon, B. Delmon and J.M. Bonnier, J. Chem. Sot. Faraday I, 73 (1977) 372. P.A. Jacobs, "Carboniogenic Activity of Zeolites", Elsevier, Amsterdam, 1977. D. Atkinson and G. Curthoys, Chem. Sot. Rev., 8 (1979) 475. G.V. Tsitsishvili, V.I. Yakerson, Sh.L. Sidamoudze, 1.1. Iashvili and L.I. Lafer, Proc. V Inter. Conf. on Zeolites, Heyden, London, 1980.