Isomerization and disproportionation of trimethylbenzenes with LaY zeolite catalyst

Applied Catalysis,28 (1986) 35-55 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

ISOMERIZATION

AND DISPROPORTIONATION

OF TRIMETHYLBENZENES

Dermot J. COLLINS', Chris B. QUIREY' 1 Department of Chemical Engineering, 2

Kentucky

40292,

U.S.A.

Kentucky

Center

for Energy

13015,

Iron Works

(Received

University

Research

Pike, Lexington,

31 December

, John E.FERTIG'

1985, accepted

and Burtron

University

40412,

28 August

WITH LaY ZEOLITE

of Louisville,

Laboratory, Kentucky

35

CATALYST

H. DAVIS'

Louisville,

of Louisville,

P.O. Box

U.S.A.

1986)

ABSTRACT Trimethylbenzenes undergo both disproportionation and isomerization during conversion over LaY zeolite catalysts. Isomerization occurs primarily by a series of I,Z-methyl shifts. Disproportionation appears to occur by removal of a methyl group from one trimethylbenzene prior to its isomerization to other trimethylbenzenes; the methyl group is transferred to another trimethylbenzene as predicted for the ortho-para directing influence of the methyl groups already on the ring. A set of relative rate constants for isomerization, calculated using the Wei-Prater procedure, obtained for xylene and trimethylbenzene isomerization has a similar pattern.

INTRODUCTION Alkyl

aromatic

this reaction kinetics ranged

of interconversions

to high-temperature

silica-alumina

A number

consecutive, ortho

=

Dthers

used a triangular

example,

=

reference

because

a three-component

liquid-phase liquid-

of the importance

system.

homogeneous

or gas-phase

for example,

their xylene

reversible,

meta

within

studied

as well as the academic

interest

of

in the

The catalysts

acid catalysts, heterogeneous

e.g.,

have aluminum

catalysts,

or zeolite.

of investigators,

et al., 121, found

is widely

production

from low-temperature

chloride, e.g.,

isomerization

in aromatics

Chutoransky

isomerization

1,2-methyl

and Dwyer

data were

consistent

[I] and Collins with a simple

shift mechanism:

para reaction

scheme

to calculate

their

rate constants,

for

[2] and [3]:

ortho

para

v

meta

The Wei-Prater obtained

[4] technique

is especially

aging would

otherwise

where

applicable be a factor.

relative,

not absolute,

for heterogeneous

rate constants

reactions

are

since catalyst

38 In addition

to isomerization,

higher

and lower weight

xylene

isomerization

For xylene determining catalyst, relative of

occurs

isomerization

it appears

With silica-alumina [3] over

strongly

with larger

pare zeolites

ZSM-5 zeolite determined

the xylene

to extend

this study

catalyst

compare

isomerization

chloride

shift mechanism;

migration

This

the

rates

[6,7].

appears

trend continues

of the unallowed and, finally,

selectivity

conversion

increases

for the medium

appears

to

so that

pore sized

to be almost

completely

[X3.

the isomerization

[2]. This would

constants

reaction.

of pore diffusion

the isomerisation

same LaY zeolite

aluminum

of ortho = para conversion

silica-alumina

by pore diffusion

of interest

amount

isomerization

may play a role in

of ortho 1 para are about 4 orders

1,2-methyl

catalyzed

to

that

mechanism.

to a 1,2-methyl

conversions

[I,21 the amount

In view of the influence

study

adheres

the relative that of AlClS

disproportionation

[5] even proposed

With a homogeneous

than for the allowed

over that of the amorphous

undergo

and Bolton

that pore diffusion

rate constants.

rates for the unallowed smaller

aromatics

Lanawala

by a transalkylation

isomerization,

the relative

magnitude

increase

alkyl

aromatics.

on xylene

studies

isomerization

to other

of trimethylbenrenes

alkyl

was carried

as had been used for a previous

afford

the opportunity

for two reactants

to learn

for these

aromatics. out using

xylene

In the

isomerization

how the relative

as well as compare

and disproportionation

it was

the relative

rate

amount

of

reactants.

EXPERIMENTAL A commercial

NaY zeolite

solution.

The exchanged

activated

in sits

by heating

an air f7ow. The other activation

i7~ situ

The catalyst Glass

beads

was multiply

zeolite

exchanged

was stored

the wet cake

catalyst

lanthanum

in the reactor

was dried

as described

with

as a wet cake.

overnight

for 6 hours at 500°C

,puc~ was used. to

pressure.

Liquid

products

pass

the

by glass wool

catdlys't'beb 'to act as a p&neater

reactant

were collected

was by gas chromatography

in

above.

on top o'f%he

A xyringe

was

in air at 120°C ,orior to

(1 g wet cake) was held in a plug flow reactor

were,dlaceo

nitrate

One catalyst

over

t’nc

catalyst

at intervals.

at

Analysis

plugs.

se&ion.

atmosdneric

of the aromatics

using a diisononylphthalate-Bentone-

column

with

1fiitia71y tk(e te??peraturE '&as h?ld a$ %."c, for 7 m,in, -1 dlK+ ^ h,e)ilat ",2D"C.?i,rttj1 a>> of Cc. ‘l/a Eem~@~UV!S to ?2C"C at ?D"l min

tempel-atU,-e piwgra~irrg. then raised had eluted. After

a run was completed,

was flushed

with nitrogen

fl"V iVah's fie1ac-d tut-e for

the catalyst

at the reaction

1 h; the temperature

After

was then incr-eased to 500°C

in an air flow and then flushed detailed

temperature.

First, 1 h,

the catalyst the nitrogen

at re?KtioD by an aSr $1&w. The a $r flow. Yas K ain,t,airred

air flow for at least 4 h. The catalyst

A more

was regenerated.

description

was then cooled

with nitrogen

of the procedure

prior

and held at 500°C with

to reaction

to starting

is given

+&!+era-

temperature

the reactant

in reference

[g].

flow.

37

0 FIGURE

1

transfer

Comparison

(0,1,3,5-TMB;a, equal amounts

15 Mole %

of the two disproportionation

of one methyl

25

20

10 Xylenes,

5

products

at 350°C from the

group for each of the three trimethylbenzene

1,2,4-TMB;D, of xylenes

1,2,3-TMB;

solid

(TMB) reactants

line is for the formation

of

and tetramethylbenzenes).

RESULTS

Disproportionation to equal amounts

of a trimethylbenzene

of xylene

and tetramethylbenzene

the case for each of the three slight

deviation

benzenes

(Figure

were varied

1). The conversions

by changing

to give LHSV's

initial

products

aromatic

result

could arise

methylbenzenes to transalkylate appears formed

is favored

conversions

isomers.

in Figure

conversions

if xylenes

undergo

that much more

that shape selectivity by transalkylation

(Figure

rapidly operates

to undergo

is a

over tetramethylfigures,

in the of these

2). The lower weight aromatics

(pentamethylbenrenes) reactions.

more

rapidly

used as reactants

than a trimethylbenzene so as to cause

further

there

of catalyst

disproportionation

when

leads

is very nearly

disproportionation

disproportionation

the xylenes,

group

1, and in succeeding

the amount

over the higher weight

for these secondary

do. However,

This

however,

curve to favor xylenes shown

liquid pump rate and/or

at higher

of one methyl

reactants;

of ca. 0.4 to ca. 100. Further

occurs

(toluene)

at higher

trimethylbenzene

from the theoretical

reactor

by transfer

reactions,

This than tetra-

[Z], do not appear does. Thus,

it

the pentamethylbenzenes such as coking

or de-

38

Toluene, Mole % FIGURE

2

Comparison

the transfer

of the disproportionation

of two methyl

groups

reactants

(0,1,3,5-TMB;n

, 1,2,4-TMB;

formation

of equal amounts

of toluene

10

20

0

3

Formation

30

of a primary

conversion

(isomerization

reactants

(0, 1,3,5-TMB;A,

, 1,2,3-TMB;

40

50 of

trimethylbenzene

from (TMB)

solid line is for the

plus disproportionation) 0

60

Reactant,

disproportionation

1,2,4-TMB;

at 3503C resulting

and pentamethylbenrenes).

Total Conversion FIGURE

products

for each of the three

70 Mole

product

60

90

%

(xylenes)

from the

of each of the trimethylbenzene

, 1,2,3-TMB)

at 35O'C.

39 40 -

36 -

32 -

28 E

4

8

12

Other FIGURE

4A

Relationship

1,2,4-TM6 at 350°C

methylation, lation

Trimethylbenzenes

(0

I

I

I

24

28

32

Formed, to xylenes

1

Mole % and the isomerization

, LaY predried at ~zo"c;~

of

Lay wet cake calcined

temperature).

more

products

diffusional

20

of disproportionation

to the other TMB's reaction

16

rapidly

(Figure

effect

than xylenes

do. The results

1) also provide

that slightly

favors

evidence

for the primary

that there

the formation

transalky-

is even a slight

of xylenes

over tetramethyl-

benzenes. Disproportionation benzenes.

proportionation

appears

of the conversion

trimethylbenzene

to be linearly

range studied.

disproportionation

reaction

accounts

in the conversion

related

The slopes

to the total

of the Figure

for about 46% of the total

the amount

(i.e., double

disproportionation-total

of trimethylbenzene

the amount conversion

of trimethyl-

and 1,3,5_trimethylbenzene,

and 37% for 1,3,5_trimethylbenzene.

disproportionation, products

is an important

For both 1,2,4_trimethylbenzene

of xylenes curve

dis-

conversion

3 curves

conversion

over most

show that for 1,2,4-

In this calculation converted

formed)

of

to disproportionation

is used. The slope of the

for 1,2,3-trimethylbenzene

does not

40

4

8

Other

FIGURE

48

Relationship

of 1,3-5-TMB 350°C

extrapolate

conversions

much more the amount

is a linear function tionation

probably

methylbenzene

This

rather,

rapidly

is also more

portion

and the isomerization calcined

wet cake

was dried

however,

was compared

different

initially

undergoes

At higher reactant

much of this dispropor-

reactions

of the other

batches

are consistent

tri-

calcined

was used to obtain

exhibited

a different

so that the batch (solid

appears

of LaY wet-cake,

of the other

4a, 4b and 4c. Furthermore,

of all three

to isomerization

in air at 12O"C, were

One of these preparations

batches

in Figures

with one reactant

for the disproportionation

Two portions

to the amount

catalyst

from the data

for disproportionation

activation.

isomer

of the 1,2,3-trimethylbenzene

for by secondary

formed

formed,

is apparent

active

that this

that are formed.

of xylenes

This ratio of disproportionation catalyst

%

it does disproportionation.

of disproportionation

the data for the two catalyst active

to xylenes

it appears

than

of the total conversion;

products

two trimethylbenzenes

more

28

Mole

, predried at 12O"C;o

can be accounted

When the amount

selectivity.

(0

24

temperature).

to the origin;

isomerization

20 Formed,

of disproportionation

to the other TMB's

reaction

16

12

Trimethylbenzenes

symbols

that is

in 4 a-c)

trimethylbenzenes.

to be sensitive

identical

except

in situ in two similar

the data represented

to

that one reactors.

by the open

24

4

Other

FIGURE

4C

Relationship

of disproportionation

of 1,2,3 TMB to the other 350°C

reaction

TMB's

(0

(0

,A)

5

Influence

of continuous

runs on the amount

to other TMB's

Mole

to xylenes

, predried

%

and the isomerization

at 12O"C;o

calcined

wet-cake

temperature).

Conversion FIGURE

Trimethylbsnzenes,

(0

,O)

of 1,2,3-Trimethylbenzene, aging

(a

,A)

and cyclic

of disproportionation

for 1,2,3-TMB

with the LaY

(A,A) (predried

Mole % aging

and regeneration

and isomerization at 120°C)

at 350°C.

42

40 30

';;>*e-::L

FIGURE

I 0 f--

1

0

2

6

Xylene

A

4

I

I

6

8

I

1

10 12 Mole%

isomer distribution

of 1,3,5-TMB

with

para-xylene;

equilibrium

predried

1

I

I

1

22

24

26

28

I

for increasing

LaY at 350°C

xylene

I

14 16 20 18 Xylenes Formed

amounts

(0, ortho-xylene;n

composition

:

of disproportionation

, meta-xylene;n,

shown at right of figure).

80

Equilibrium

0

L 2

I 4

I 8

I 8

0 10

I 12

Mole% FIGURE

7

Xylene

isomer distribution

of 1,2,4-TMB

with

para-xylene;

equilibrium

predried

1 14

I

I

I

18

20

22

I 24

26

28

30

Xylenes Formed for increasing

LaY at 350°C

xylene

L 16

amounts

(0, ortho-xylene;n,

composition

shown

of disproportionation meta-xylene;A,

at right of figure).

43

Mole

FIGURE

8

Xylene

of 1,2,3-TMB

isomer

with

distribution

predried

pat-a-xylene; equilibrium

circles;

% Xylenes

for increasing

LaY at 350°C

xylene

LaY produced

a catalyst

proportionation,

for a given amount

benzene

than the other

isomers,

amounts

of disproportionation

(0, ortho-xylene;n

composition

the other was used to obtain

the predried

Formed

, meta-xylene;A,

shown at right

of figure).

the data for the solid data points. that was 2 to 3 times as active

of isomerization

preparation

Thus,

for dis-

to the other two trimethyl-

which was calcined

by rapid

heating

of the wet cake. The initial

calcination

disproportionation

selectivity.

LaY using a constant

reactant

that the total conversion Figure

5). Other

velocities,

with

this catalyst

Xylenes a methyl

altered

only meta-xylene.

reactant,

without While

products

there

that the xylene

(Figure

6). All three xylene

xylene

isomer

since steric

result;

however,

is formed effects

from

is some scatter approaches

isomers

1,2,4_trimethylbenzene.

experimental

in Figure

it appears

in preference

should make

reactions.

pure meta-xylene

to para-xylene.

it more difficult

data,

it is

of one methyl

7 show that this conversions,

This

of

produces

at low conversion

by the removal

that, at lower

aging

Removal

1,3,5_trimethylbenzene

in Figure

these

5. It is

nor catalyst

for the low conversion

can be formed

The data

space

selectivity.

of the disproportionation

composition

at various

in

in air separating

the regeneration

prior isomerization,

hours so

(solid symbols

time intervals,

are also plotted

neither

calcined

for several

48%

that had been regenerated

(open symbols)

evident

group from

from 86% to about

isomerization-

the pre-dried,

the isomerization-disproportionation

are primary

group,

the relative

the run was continued

runs were made for shorter

that, for a given

significantly

to determine

One run was made with flow;

decreased

runs. Some of these data evident

of LaY appears

is the

the ortho-

is also reasonable

to remove

the Z-methyl

group

44

r 2

0 l 1,2,4AA 1.3,50 w 1,2,3-

5 0.8 L zl

Reactant Reactant Reactant

l-

I

I

I

I

I

5 10 15 Tetramethylbenzenes FIGURE

9

Normalized

tetramethylbenzene

of disproportionation A

for predried

, 1,3,5-TMB; 0

,A

,m

to form para-xylene

than

1,2,4_trimethylbenzene. can be formed consistent

support

directly

the above

It is clear of the three

product

speculation,

o,@,

1,2,4-TMB;

symbols,

the 1 or 4 position

of

but not para-xylene,

since

basis,

hand, steric

it should

be more

should effects

difficult

Unfortunately,

groups.

they do not permit

be formed should

to remove

while

a conclusive

in

also the

the data do

distinction

between

in 1,2,3-trimethylbenzene.

trimethylbenzene

clear that the xylene

prior

distributions

are different a common reactants.

at low conversion

to trimethylbenzene

for each

intermediate It is also

show that the

isomerization

for each of the

reactants.

used in this study.

The ortho-para

compositions

This eliminates

reactants.

Two of the three tetramethylbenzene

in 1,2,4-trimethylbenzene

xylene

of the three trimethylbenzene

isomer

is removed

three trimethylbenzene

interest.

amounts

1,2,3,5_tetramethylbenzene).

at either

in a statistical

that the low-conversion

the g.c. columns

open

and meta-xylene,

On the other

the I- or 3-methyl

for the disproportionation

group

symbols:

symbols:

1,2,4,5-plus

the methyl

for increasing

1,2,3_trimethylbenzene;the data in Figure 8 is

from

of meta-xylene.

than either

these two effects

methyl

symbols,

to remove

(reactant

product

Both ortho-xylene

favor the ortho-xylene Z-methyl

solid

I

25 Mole %

distribution

LaY at 350°C

with this. Ortho-xylene,

twice the amount

isomer

, 1,2,3-TMB;

1,2,3,4_tetramethylbenzene;

20 Formed,

directing

isomers

eluted

together

Even so, the isomer

influence

of methyl

as one peak for

distributions

groups

are of

activates

that leads to all three tetramethylbenzene

positions

isomers;

45

I.0

0.9

A

l

Total

FIGURE 10

Fractional

approach

(I, 1,3,5-TMBq,2,3-TMB)

the products

obtained

are consistent conversions, formed more

from

Conversion,

to equilibrium

from 1,2,4-TMB

with

1,2,3,4-

1,2,3,4_tetramethylbenzene

methylbenzene;

however,

than the equilibrium influences,

even at very low conversion

is consistent

of the trimethylbenzenes

the xylene

where

xylene

and para-xylene

but an equilibrium In the following,

the initial

were

those expected

distribution

be

does yield

9). 1,3,5-

1,2,3,5-tetra-

that the product

composition.

products

from ortho-para

was obtained

isomerization

(Figure

form only

with a LaY catalyst

disproportionation

time and

would

this reactant

it appears

with an equilibrium

with

isomers

value

would

products LaY at 350°C.

even at low

distribution

at lower conversions

disproportionation isomers

predried

9) do not change

of an equilibrium

based on directing

isomer distribution

(Figure

with

and 1,2,3,5_tetramethylbenzenes

1,2,3-trimethylbenzene;

Trimethylbenzene,

for the isomerization

conversion

this reactant

with the formation Only

Mole %

In this respect

parallels

that of

from both ortho-

directing

influences

with meta-xylene.

of trimethylbenzenes

is first

considered

as

0.1

0.2

0.3

0.4

FiMRKE ‘II (0,

0,

Fractional

approach

1,2,4-TMB;a,

at 350°C.

the fractional

approach

Figure 1D show that methylbenzene, slightly more are

clearly

to equilibrium

to equiTibrium

with

1,2,4-trimethylbenzene

even at low conversions, rapidly.

0.7

0.8

for the isomerization

products

, 1,2,3-TMB; open symbols for predried Lay) from 1,3,5-

A

TNB conversion

0.8

0.5 Conversion

Total

These

those expected

results

increasing forms

both

conversion. 1,3,5-

and that the 1,3,5-isomer

for the conversion

for isomerization

by a series

The data

in

and 1,2,3-triis formed

of 1,2,4-trimethylbenzene reaction

mechanism.

Aor .1,~,,5-~f.rim~~h,v~~n7_~np .i_somP.r.i~&.i.na ,iF.Q.urp J,l,l.if .i_s .e.v.Gi.enf jAaf JJ,.Ptrimethylbenzene trimethylbenzene,

wears

is an initial an initial

product

product

and that the rate of formation

not allowed

+A approach, zero at law cmversims.

rate of formation

of the two isomerization

C,.r$~~;a<
6

5 ,Z ,G~s-ww

as shown i'n t7gut-e (I'; riowever, ttie generaf ty a series af <,Z-ii-metQt shifts

by a series methyl

of 1,7,3shift mec'nanism,

There are small differences products

from

in the

1,3,5_trimethylbenzene,

, SW Y+e +cm La%a'ly-f aCt-kat

k.tck,es. C&e data in Figure

I?

1.0

r

0.1

FIGURE

12

Fractional

(0, 1,2,4-TMB;

A

0.3 Total

0.2

approach

, 1,3,5-TMB)

0.5 0.4 Conversion,

0.7

0.6 Mole %

0.9

0.6

to equilibrium

for the isomerization

from

conversion

1,2,3-TMB

products

with predried

LaY at

350°C.

for 1,2,3_trimethylbenzene product

isomerization

is 1,2,4-trimethylbenzene;

clearly

the initial

show that the only

initial

rate of 1,3,5_trimethylbenzene

is zero. The Wei-Prater isomerization the three follow defined

technique

rate constants.

trimethylbenzenes

unimolecular,

correspondence

To perform

kinetics.

networks

study

a set of six relative

this calculation

fictitious reaction

rate constants

for xylene

were defined:

the concentration

to chemically

The triangular

so that the relative

to the previous reaction

to calculate

are transformed

uncoupled

for this study

the following

was employed

would

isomerization

species

network

of which

was

have a direct

with LaY 121; thus

48 TABLE 1 Relative

rate constants

calculated

from the curved

reaction

path starting

with

1,3,Strimethylbenzene

Reactant Trimethylbenzene

Xylene

Rate constant

1,3,5a

l,3,5b

XyleneC

k21

8.32

29.9

10.9

k31

1.0

k32

6.91

k12

11.2

k13

1.0

1.03

13.6

3.61

11.2

4.79

1.65

k23

1.65

30.4

aCalculated b Calculated

1.0

60.4

8.08

using

In 5, and In b2 from experimental

using

k,2. k3, and k,3 from (a)

data.

constant

and stepwise

increasing

k23 by 5.0. 'From reference

[Z].

k3,/4yO\k3)k;I;;\ k12

para

A

92

meta

1,2,3-TMB

,

'

k32

As a first step in the Wei-Prater determined;

the one chosen

and 1,2,4_trimethylbenzene characteristics

vectors

Xo, is the equilibrium vectors,

1,2,4-TMB

k32

needed

the orthogenality

a straight

line reaction

in this study was the one that axis. This

intercept,

Using

relations vector,

intercepts

calculations.

the 1,3,5-

A second

these two characteristic

given by Wei and Prater

X2, which

path is

X,, is one of the three

for the Wei-Prater

composition.

of a third characteristic

method,

should

also

permit

vector,

camposition a calculation

be a straight

line reaction

path. The experimentally transferred

observable

in the Wei-Prater

bo, b, and b2. In order reaction

trimethylbenzene

technique

to carry

isomer

out the calculation,

path data must be converted

concentrations

into a set of three

to the b-system.

are

characteristic

vectors:

only one of the curved

line

In this study the slope of

49

123 FIGURE

1.u 13

Fit of experimental

using the relative for constants

data

rate constants

with footnote

to the curved

obtained

a in Table

line reaction

with the Wei-Prater

1; -------

paths

calculated

method

for constants

with

(footnote

b in .Table1).

the curve determined generated

using

The relative presented

data constants

in Table

with a similar

by plotting

LaY catalyst.

the rate constants line reaction to improve

for trimethylbenzene

calculated

with

held constant

of 5.0. One set of rate constants as 1,3,5 catalyst,

this data did not predict

(b). Describing

while

conversion

the relative

in the triangular

from the curved

conversion

rate constants, stable

the correct

path two constants

is listed

obtained isomer

with the LaY

number,

meta-xylene

or 1,2,4_trimethylbenzene,

that the same qualitative

pattern

is obtained

for the two reactants.

line reaction

paths calculated

using the

in Table

being designated

by the same rate constant

The curved

curved

In an attempt

from 30.4 in steps

by this procedure

plot with the most

As shown below,

very well.

k23 was incremented

obtained

LaY are

isomerization

for trimethylbenzene.

of 1,3,5_trimethylbenzene.

the fit to the 1,2,3-trimethylbenzene

with

for xylene

1,3,5 (a) were calculated

designated

path for 1,2,3_trimethylbenzene

(k13 and k12) were

isomerization

Two sets of rates are shown

path for the conversion

for the data

reactant.

1 together with the results obtained

The set of rate constants line reaction

In (b2) vs. In (b,) was obtained

the 1,3,5_trimethylbenzene

Wei-Prater

shows

relative

rate

1

50

1,2,3 FIGURE

1,2,4

14

Experimental

curved

with LaY (wet cake calcination)

constants data

from Table

fit either

of calculated appears a series

line reaction

paths

the calculated

rate constants

to overemphasize

lines reasonably

well.

However,

of these

two sets

the one that fits the 1,3,5_trimethylbenzene

the contribution

of the conversions

data

not permitted

by

reaction.

gave the curved

out at 275 and 35O'C.

reaction

paths shown

two sets of data are similar. for Wei-Prater

calculations

and this introduced The data

in Figures

However,

2 permit

in the calculated

a comparison

kinetic

and Wei-Prater

trends;

that is, the isomerization

1,2- methyl

the

was close

to the pure component

constants.

In general,

data obtained

both calculation

is predominately

a series

by methods of

group migrations.

Izepe and Levenspiel The equation

methods,

temperatures

at 275°C was not used

of the selectivity

the classical similar

at these

14 and 15. Qualitatively,

the data obtained

since the X, intercept

a large error

in Table

Data obtained

yield

l/(1

of TMB's

1 are shown as solid lines in Figure 13. The experimental

Runs were carried

$=

for the isomerization

at 275°C.

giving

+Bt)

[IO] list five equations

to describe

the best fit to the experimental

data

catalyst

(Figure

aging.

6) was:

51

123

1A4

FIGURE

15

Experimental

with LaY (predried)

TABLE

curved

line reaction

paths for the isomerization

of TMB's

at 350°C.

2

Comparison kinetic

of relative

conversions

and Wei-Prater

relative

calculated

as the ratio of the classical

rate constants.

A trimethylbenzene

to the other

two isomers Prater-Wei Approach Reactant

Ratio

1,3,5-

1,2,4-/1,2,3-

1,2,4-

1,3,5-/1,2,3-

1,2,3-

1,2,4-/1,3,5-

where

to

from

equilibrium

4 is the catalyst

constants

3.91

29.9

1.28

0.82

11.9

activity,

18.4

B is a constant

by separately

constant

flow rate of 6.5 x 10m4 cm3 s-' for 10 hours. ages the catalyst

(Table

3). It also appears

faster

than does

conversion

each reactant

2.4 g of fresh

rapidly

that 1,2,4_trimethylbenzene

1,2,3-trimethylbenzene.

since more

more

over

and t is time. Aging

effected

1,3,5_trimethylbenzene

passing

This aging

1,2,3_trimethylbenzene

1,3,5-rate

runs were

catalyst

at a

Under these conditions, than the other

two isomers

ages the catalyst

slightly

is not just due to total

molecules

are converted

during

a

52 1.0 0.9 0.8 0.7

0.0

1

1

I

I

I

1

1

1

I

1

0123458789

10 Time,

FIGURE

16

relative

TABLE

Catalyst

aging curves

conversion

for: @.

11

hrs.

calculated

, 1,3,5-TMB;

from a = l/(1

o, 1,2,4-TMB;

+Bt.) and experimental

0

, 1,2,3-TMB).

3

Constant

for the deactivation

trimethylbenzene

equation

for LaY catalyst

Reactant

Constant

1,3,5_trimethylbenzene

0.830

1,2,4_trimethylbenzene

0.284

1,2,3-trimethylbenzene

0.177

standard

for each of the three

reactants

time interval

only the total moles

than are converted

converted

1,2,3_trimethylbenzene

should

to other cause

for the other

products

the most

two isomers.

was the most

rapid catalyst

Thus,

important

if

factor,

aging.

DISCUSSION For a LaY catalyst, reaction

disproportionation

just as it was with xylene

to that of isomerization and trimethylbenzene and TMB's.

crowded

most closely

isomerization.

to the other

reactants.

xylenes

two isomers

In general,

With both xylenes (o-xylene

of trimethylbenzene

The ratio of disproportionation is shown

a similar

in Table

pattern

and TMB, the reactant

or 1,2,3-TMB)

is an important

isomerizes

is obtained

with

more

4 for xylene for the

the substituents

rapidly,

for a given

53 TABLE

4

Ratio of disproportionation/isomerization (predried)

at 350°C and AlC13

for xylene

and TMB conversion

with LaY

at 60°C.

Reactant

Xylenea,

A1C13

Xyleneb,

LaY

TMB,

LaY

o-xylene

(or 1,2,3-TMB)

0.023

0.34

m-xylene

(or 1,2,4-TMB)

0.023

0.59

1.7(1.0)c

p-xylene

(or 1,3,5-TMB)

0.037

0.63

0.88

aCalculated orthob

from the data

and meta-xylene

Calculated

in Figure

from slopes

in Figure

for wet cake calcination.

amount

of disproportionation, selectivity

two isomers,

3, reference

and 1,2,3_trimethylbenzene,

diameter

than the other

using the "homogeneous"

was 10 to 20 times smaller

three xylenes

and the para-xylene

that of the ortho-xylene

determining

cycles

(metal or proton)

Diffusion

location

factor

aromatic,

amount

(Figure

1). Thus,

undergo

further

methyl product amount

it appears

run. This

group

reactions

group. should

With

from pores

slightly

and directs

(Figure

1,3,5_trimethylbenzene

calcination,

since the higher

aromatic

is formed

is much more pronounced

weight

aromatics

aromatics

in

product.

to position

however,

either

or to form coke

ring for electrophilic

the only initial

be 1,2,3,5_tetramethylbenzene;

is present

for a given

2) than for tetramethylbenzene

a reaction

an aromatic

the substituent

of 1,2,3,4_tetramethylbenzene

selectivity

higher molecular

to become

aging

selectivity.

or pentamethylbenzene,

lower weight

in

that the cation

by the initial

to lower weight

activates

factor

Repeated

suggests

1 and 2). This effect

that these

disproportionation

to diffusing

The methyl

(Figures

was about

in the disproportionation

the disproportionation

pentamethylbenzene

for all

(0.037)

selectivity.

tetramethylbenzene

reaction

fraction

a change

determined

than the corresponding

for the larger aromatic,

stitution

or number,

in determining

from

(0.023).

to produce

long aging

or larger,

disproportionation/

the LaY catalyst

of LaY is an important

may play a role in disproportionation

weight

disproportionation

addition

do not appear

from that of a single

is an important

in smaller

calcination

since these

The LaY data differ

disproportionation

the disproportionation/isomerization

selectivity

molecular

than with

This greater

control

With the A1C13

A1C13.

or meta-xylene

that the initial

and regeneration

of 44% for

have as large,

two isomers.

isomerization

It appears

two isomers.

not be due to diffusional

that obtained

twice

for conversion

[Z].

than do the other

should

ortho-xylene

cross-sectional

[6]

and 27% for para-xylene.

'Value

isomerization

11, reference

ca. 0

sub-

ortho or para to a tetramethylbenzene

a nearly

equilibrium

from this reactant

even at very

54 low conversion.

For the other

benzene

is an allowed

benzene

reactant

conversions. stitution

product

and is formed;

it is formed

Thus,

in greater

to make

by the methyl

a final decision

reactants

compositions

substituents

Xylenes

are also products

of the primary

6,7 and 8 clearly

show that equilibrium

conversions. products

but that kinetically

For each of the three

are comprised

isomerization

tion results

in (a) removal

of that reactant appears

prior

which

to desorption

require,

mechanism

methyl

group

to an adsorbed

would

require

the bulkier

so that they undergo

products

Thus,

at low

disproportiona-

tetramethylbenzenes

with,

An equally

encounter

disproportionations

without

of a tetramethyl-

trimethylbenzene

cation.

xylene

of a methyl

an equilibrium

are consistent

a gas phase

The data

the initial

by removal

reactant.

to nearly

results

trimethylbenzene

secondary

analysis

are obtained

are formed

reactants

and (b) the formation

These where

reaction.

compositions

that are formed

isomerization

as a product,

with sub-

isomer

group from one trimethylbenzene

molecule

to undergo

a Rideal-Eley

xylene

controlled

of a methyl

isomerization

are consistent

disproportionation

of the trimethylbenzene

benzene

at lower

but a complete

trimethylbenrene

of those isomer(s)

group without

amounts

on this point.

in Figures

at high conversions

1,2,3,4_tetramethyl-

in the case of the 1,2,3-trimethyl-

than equilibrium

the tetramethylbenzene

being directed

is required

two trimethylbenzene

composition

but do not transfers

likely

diffusional

a

explanation

resistance

to form lower carbon

number

aromatics. A relative

rate constant

each of the curved-line appropriate

straight-line

rate constants

was calculated

reaction

reaction

have a similar

path.

pattern;

reactant

and largest

rate constant.

In addition,

curved-line

reaction

benzene

for xylene

isomerization

benzene

calculated

to equilibrium

for

the smallest

obtained

obtained

with the

the 1,3,5-trimethyl-

to the ones calculated conversion

data as well as from

2) calculated

data are very similar

between

using

[2]. The ratio of some relative

(Table

for

and the

calculated

1 rate constants

using the Table

that is very similar

the ratios

rate constants

procedure

data fit the three

data than for the constants

from the approach

rate constants;

range

the experimental

the rate constants

data have a pattern

be calculated method

Also,

the constants

have the greatest

paths calculated

with the 1,3,Strimethylbenzene two reactants.

the Wei-Prater

Each of the three sets of six relative

however,

the 1,3,Strimethylbenzene

other

using

paths for each of the three reactants

previously

rates can the Wei-Prater

from the 1,3,5-trimethyl-

to those obtained

from the classical

kinetic method. The Wei-Prater method

since

especially

important

aging makes generated

technique

absolute

has a distinct

reaction

consideration

it very difficult

for heterogeneous

to obtain

in this study emphasize

When the straight-line

advantage

over the classical

rates do not need to be measured;

reaction

absolute

a difficulty

path intercepts

catalysis

rate data.

in using

kinetic

this is an

where

catalyst

However,

the data

the Wei-Prater

the composition

technique.

axis near to a

55 pure reactant

composition

of the intercept

value.

it becomes

This uncertainty

the calculated

rate constants

run, prohibit

one from making

The LaY catalyst vity and activity migration

produced

is the predominate

proportionation

occurs

by methyl

on primary

product

as the homogeneous

similar

to produce

products

composition,

the 1,2-methyl

product

a large error

in

the data for the 275°C

and isomerization reactants.

compositions

for 1,2-methyl it appears

also

the LaY product

group

Dis-

are primarily is not, based only

shift

isomerization

that secondary

The smaller

selecti-

1,2-Methyl

for both reactants.

The LaY catalyst

shift mechanism.

disproportionation

some role in determining

whose

effects.

is; thus,

tend to disguise

playing

mechanism

as selective

catalyst

measure

of the rate constants.

disproportionation

isomerization

an accurate

introduce

and trimethylbenrene

molecular

weight

in X, may

a calculation

group directing

AlC13

to obtain

and, as was the case with

for both xylene

determined

difficult

amount

is indicative

reactions

of the higher

of pore diffusion

selectivity.

ACKNOWLEDGEMENT Funding ment,

was provided

Kentucky

Energy

by the Kentucky

Department

of Energy

Research

and Develop-

Cabinet.

REFERENCES

1 P. Chutoransky 2 3 4 5 6 7 8 9 10

and F.G. Dwyer, Advan. Chem. Ser., 121 (1973) 540. D.J. Collins, K.J. Mulrooney, _ R.J. Medina and B.H. Davis, J. Catal., 75 (1982) 291. A.J. Silvestri and C.D. Prater, J. Phys. Chem., 68 (1964) 3268. J. Wei and C.D. Prater, Advan. Catal., 13 (1962) 203. M.A. Lanawala and A.P. Bolton, J. Org. Chem., 34 (1969) 3107. D.J. Collins, R.P. Scharff and B.H. Davis, Appl. Catal., 8 (1983) 273. R.H. Allen and L.D. Yates, J. Amer. Chem. Sot., 81 (1959) 5289. 0-J. Collins, R.J. Medina and B.H. Davis, Canadian J. Chem. Eng., 61 (1983) 29. C.B. Quirey, M. Eng. Thesis, University of Louisville, 1982. S. Szepe and 0, Levenspiel, Chem. Eng. Sci., 23 (1968) 881.