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The conversion of aromatics over dealuminised mordenites
321
Applied Catalysis, I (1983) 327-336 Elsevier Science Publishers B.V., Amsterdam -Printed
THE CONVERSION
OF AROMATICS
Duncan
SEDDON
I.C.I.
Petrochemicals
Present
address:
Laboratories,
(Received
in The Netherlands
OVER DEALUMINISED
and Plastics
Division,
The Broken Hill Proprietary
245 Wellington
18 February
P.O. Box 90, Wilton, Company,
Road, Mulgrave,
1983, accepted
MORDENITES
Melbourne
Melbourne,
Cleveland,
U.K.
Research
Australia.
20 May 1983)
ABSTRACT The effect of progressive removal of aluminium from mordenite on ethylbenzene transalkylation and xylene isomerization is described. Variation of xylene isomerization activity with silica-alumina ratio is discussed. Catalytic performance depended upon the method of aluminium removal.
INTRODUCTION The changes changes
of catalytic
Much of this interest be systematically
altered
the proximity
properties
of aluminium
isomerization.
a maximum
by progressively
deficient,
Catalytic
removing
breakdown
tetraacetic
that the former treatment of the zeolite,
interest. acidity
activity
for butene
(mole) of about
from the lattice and the
for cumene cracking
isomerization
was progress-
as X-ray analysis
ratio of 600 could be obtained
and
went through
26 as aluminium
collapse
can
without
demonstrated significant
[1,2].
Dwyer et al. [3] compared ethylenediamine
about by systematic
Zeolite
aluminium
large port mordenites
ratio
of silica-alumina
brought
is of considerable
Sand et al. [I] have described
This was not due to structure
that mordenites structure
catalysts
upon ZSM-5 and mordenite.
of acid sites.
at a silica-alumina
ively removed.
and selectivity
of zeolite
has centered
so change
butene
activity
to the acid strength
whereas
the effects
of aluminium
removal
acid (EDTA) and steam/acid
preferentially
removed
the latter removed
aluminium
aluminium
from zeolites
leaching,
using
and suggested
from the outer surface
more uniformly
throughout
the crystal. Recently, exchanged
Karge [4] has made a detailed
mordenites
transalkylation. to the acidity
for the catalysis
The work complemented of mordenites
aimed at rationalising
brought
0166-9834/83/$03.00
catalysts
of benzene earlier
alkylation
studies
about by metal
the high coking
Karge's work has now been extended of the mordenite
study of the properties
rate typical
and ethylbenzene
on the systematic
[5,6], and studies
of mordenite
catalysts
of partial
of ethylbenzene
0 1983 Elsevier Science Publishers B.V.
changes
ion exchange
to include the effects
on the transalkylation
of various metal
[7,&l].
dealumination
[9-111. The work
328 confirmed
the earlier observations
acid leaching
that catalyst
lifetimes
and that active centres were primarily
could be
associated
extended
by
with Bronsted
acid sites. This work describes steam/hydrochloric the infrared
the dealumination
of H-mordenite
by the action
acid and nitric acid. How these different
spectra of the products
and the activity
of EDTA,
treatments
for aromatic
affect
conversion
is
also described.
EXPERIMENTAL H-mordenite
used for this work was Zeolon
ratio (mole) of 14.8. The three methods
1OOH (Norton) with a silica-alumina
used for the removal are typically
as
follows.
Leaching with strong H-mordenite
nitric acid
(IO g) was refluxed
was then filtered
120°C. The silica-alumina
Leaching
(24 h) in nitric acid (100 ml, 6 M). The zeolite
from the nitric acid, washed with distilled
with EDTA
H-mordenite a soxlet
(20 g) was refluxed
thimble
into the mixture.
in water
(200 ml) so as to extract
was stopped and the mordenite
silica-alumina
ratio of the product was found to be 31.1.
Steaming
filtered,
washed
and dried.
(2.3 g). The
and acid leaching
H-mordenite
(30 g) was placed
in a tubular
passed at a known rate. The material
(4 h) with dilute
hydrochloric
It had a silica-alumina
Catalyst
furnace
was steamed
per hour. After 2 h the steam treatment
dried.
EDTA from
After three days little EDTA remlined
THe extraction
water
water and dried at
ratio of the product was found to be 65.6.
into which
steam could be
at 538°C in a flow of 18 g of
was stopped
and the product
acid (516 ml, 2 M), filtered
refluxed
and then washed
and
ratio of 68.8.
evaluation
Catalysts downflow
(5 g) as l/8 inch diameter
tubular
condensation
reactor
system.
over the catalyst
binder-free
fitted with reactant
Feeds
(ethylbenzene
at a weight
pellets were charged
vaporiser,
in xylene
hourly space velocity
thermocouples
or xylenes)
into a
and product
were then passed
of 5.0 h-l, at a bed temperature
of 450°C.
Analysis Aluminium alumina
contents
were determined
ratios are expressed
product crystallinity
by atomic
absorption
spectroscopy.
Silica-
on a molar basis. The extent of dealumination
was also monitored
by mid-range
infrared
spectroscopy.
and
329
0
FIGURE
1
Effectiveness
I 2 NO CF EXTRACTIONS
of multiple
moo
900
extractions.
800 WAVENUMBER
FIGURE 2
Infrared
and dealuminised
spectra
mordenite
3
700
600
SO0
cm-’
(1000 - 500 cm-') of H-mordenite (silica-alumina = 140).
(silica-alumina
= 14.6)
330
125 . IW
0(, 0
FIGURE 3
,
20
Correlation
‘0
of infrared
dealuminised
mordenites.
Compositions
of hydrocarbon
,
60 80 s,o? A'z'J,
ratio
100
120 lie
(R) with silica-alumina
feeds and products
were determined
ratio for
by gas chromatography.
RESULTS Efficacy
of aluminium
removal
The ease of aluminium silica-alumina
removal from mordenite
ratio of the dealuminised
three repeat dealuminations
is shown in Figure
product
is plotted
against
1, where the the number of
for each method.
As mordenite is dealuminised, the infrared spectrum in the region 1000 - 500 -1 cm changes; the peaks shift to higher frequencies and many broad bands become resolved. alumina
Figure 2 compares
ratio 140) obtained
Zeolon
100H with dealuminised
by multiple
mordenite
steam/hydrochloric
(of silica-
acid treatment.
The
difference
was quantified by comparison of the realtive intensities of the peak -1 at ca. 590 cm and the trough at ca. 575 cm-'. A ratio R was defined:
R=
where
1og(r'10)590
peak
1og(I'10)575
trough
Io is the baseline
for samples plot applies
produced
intensity.
R is plotted
by steam/hydrochloric
against
the silica-alumina
acid treatments
to nitric acid leached catalysts,
the slope of the line; EOTA leached mordenite
ratio
(Figure 3). A similar
but there was some difference did not fit the plot.
in
331 TABLE
1
Conversion
of an aromatic
mordenite
ratio of 83 (WHSV of 5.0 h-', 450°C).
Aromatic
On stream time /h
B
acid dealuminised
feed over a steam/hydrochloric
with a silica-alumina
0.09
EB
composition
/wt%
P-X
m-X
o-x
20.4
19.3
41.1
19.1
3.1
9.5
20.1
9.4
T
AEB/%
AX/%
23.6
84.8
40.3
C9+ 0.04
Feed
0.05
0.25
6.1
28.2
0.50
5.5
26.0
3.8
9.7
21.0
9.5
24.5
81.5
39.3
0.75
4.9
23.3
4.9
10.5
23.0
10.2
23.3
76.2
35.7
1.0
4.5
21.5
5.6
10.9
23.9
10.7
22.9
72.3
33.9
1.5
3.9
19.0
6.9
11.8
26.1
11.6
20.8
66.3
30.0
2.0
3.3
15.8
8.6
12.9
28.7
12.7
18.0
57.7
25.0
3.0
2.6
12.4
10.6
14.1
31.4
14.0
14.9
47.9
19.9
4.0
2.2
10.2
12.1
14.8
33.0
14.8
12.6
40.7
16.4
5.5
1.7
7.9
13.8
15.8
35.5
'5.7
9.6
42.2
12.4
6.0
1.2
5.5
15.5
16.6
37.5
16.6
7.1
24.0
8.7
(B,benzene; o-xylene;
T, toluene;
lost; AX, % of xylenes
Catalytic Table a typical
EB, ethylbenzene;
Cg+, aromatics
lost).
1 lists the product steam/hydrochloric
(of carbon
stability
of the mordenite
6.0 h. The rate of fouling is a function
conversion
as shown in Figure
The performance
materials
alumina
activity
ratio, as shown
The efficiency
demonstrate
the poor
and
(AEB) falls
acid dealuminised
time of mordenite
in Figure 4. The rate of fouling
thus, at a given on-stream
depends
on the method
against
but differently
is maintained
ratio
time, conversion
(e.g. 140) give low
of dealuminisation.
on-stream
In Figure
time for three catalysts
dealuminised.
for longer periods
with nitric acid. EDTA leached catalyst (the silica-alumina
toluene
5.
is plotted
content
ratio =83).
into benzene,
of ethylbenzene
with high silica-alumina
of mordenite
conversion
The conversion
feed over
(silica-alumina
time of 0.25 h to only 24% at an on-stream
dealumination,
However,
6, ethylbenzene
and xylenes
of the steam/hydrochloric
increases.
of an aromatic
mordenite
than 8). The results
catalyst.
of silica-alumina
falls with progressive
from conversion
ethylbenzene
number greater
from ca. 85% at an on-stream
of comparable
composition
acid dealuminised
disproportionates
aromatics
mordenite
m-X, m-xylene;' o-X,
9, IO and 11; AEB, % of ethylbenzene
performance
The catalyst
catalytic
p-X, p-xylene;
of carbon number
It appears
using mordenite
was of performance
similar
that
dealuminised to the starting
= 15 plot of Figure 4).
of the catalysts
for isomerizing
xylenes was also determined
332
FIGURE 4 Variation of fouling rate with silica-alumina mordenite
(using a p-xylene Utilising
lean mixed xylenes
a computer
interconversion equilibrium
program,
feed (90% xylenes)
pseudo-first
of each xylene isomer by comparing
achieved
sion of m-xylene
WHSV = 5 h-l, at 45OY).
order constants
were predicted
the approach
by the reaction with the feed comoosition;
feed and oroduct was by g.1.c. A pseudo-first
plotted
ratio of dealuminised
(steam/HCl).
into p-xylene
against
in Figure 7. Dealuminised
rates. Again there appears
to be an optimum
alumina
ratio of 66. The starting
activity
and low rate of fouling.
material
to thermodynamic analysis
order rate constant
on-stream
mordenite
catalysts
show broadly
in activity
of the
for the conver-
time for several
catalysts
for
similar
is fouling
this time with silica-
(silica-alumina
= 15) showed low
DISCUSSION Mordenite
dealumination
Steam/hydrochloric procedure.
The extent of aluminium
time. A chosen progressively
procedure increased
a lesser extent) maximum
acid treatment
removal
gave reproducible dealumination.
by the EDTA treatment,
in the amount of aluminium
calcining
was found to be the most reliable
the product
between
varied with temperature results
Dealumination
and repeating
and steaming
the procedure
was also found
but the nitric acid appeared
removed;
dealuminising
(although
to
to reach a
this may be the result of not air
repeat nitric acid treatments
(see Sand et al. Cl]).
333
,, ,
20
LO
60
MO
120
IL0
S,LF.. ALUM/N/A
FIGURE 5
Variation
mordenite
(steam/HCl);
in conversion
with silica-alumina
8 = on-stream
o -LA--LA 0
FIGURE 6
Comparison
traetment
and EDTA leaching
benzene),
temperature
ratio of dealuminised
time.
l-. ?O
of mordenites
20
30 e hi ON -STREAM
aluminised
in the conversion
45O"C, WHSV = 5.
L.0
50
- TIM-
by nitric acid leaching, of an aromatics
feed
steam/HCl
(20% ethyl-
334
FIGURE 7 xylene
Effect of silica-alumina
isomerization
As aluminium change
is progressively
The spectral
is progressively these phenomena measured
infrared
removed from the mordenite spectrum.
and have been extensively
faujasites.
changes
large changes
studied,
integrity
remain obscure.
as aluminium
show the same variation
by Flanigen change
was progressively
removed.
the extent of dealumination However,
in infrared
that reported
in spectral
It was chosen
Infrared
catalysts
spectroscopy
can
the structural
do not seem to materials. the siliceous
content were observed
(similar
and (iii) multiple
to
due to removal of surface
present was found to be stable to (i)
action of fuming nitric acid (98%), (ii) steaming
It is not clear why these zeolites
to quantify
ratios of about 30, by the
for ZSM-5 by Dwyer et al. [33), presumably
but the bulk of the aluminium
was
to be undergoing
were made to dealuminise
in alumina
of
appearance
spectra as the other dealuminised
Slight changes
by HCl exchange,
as aluminium
[IZ] but the origins
and to confirm
EDTA dealuminised
Nu-I, Fu-I and ZSM-5, with silica-alumina
aluminium,
followed
in the use of dealuminised
spectrum which was observed
During the course of the work, attempts
described.
there is a steady
have been observed
especially
The progressive
portion of the mordenite
of the products.
procedures
on the rate of
and the shift to higher frequencies
removed has been reviewed
thus be used to monitor
prolonged
Such changes
by the ratio R, but its use is purely empirical.
a particular
zeolites
mordenite
(note log scales).
in the mid-range
previously
ratio of dealuminised
for 7 days at 550°C
EDTA extractions.
do not show the aluminium
lability
found
335 for mordenite.
Perhaps
they possess
Nu-1 and Fu-1 but unlikely more hydrophobic
than dealuminised
water to the channels
Catalytic In
which
mordenite
is necessary
mordenite,
ethylbenzene
at moderate
(toluene,
xylenes,
the occurrence
underwent
temperatures, styrenel
of cracking
be more prevalant The method
conversion
in fouling
possibly
to diethylbenzene >ca. 500 K cracked
The present
depends
of acidic
channel
Cracking
seems to
catalytic
in xylene
performance.
in ethylbenzene
isomerization
differs
from
(Figure 7). For both nitric acid and steam/hydro-
results
for ethylbenzene
from the starting
upon the presence
material.
conversion
in activity. of active
by steam/hydrochloric
at a sufficiently possibly
so that aromatic
isomer-
important
High fouling
rate
sites and the loss
acid or nitric acid is conversion
high silica-alumina
becomes
and xylene
This result could be due to a
of a high density
in acid strength
structure
products
(benzene plus toluene)
the performance
rate rather than to an increase
However,
and
(Table 1) also show
alone.
in determining
agent hardly affects
sites upon dealumination
unaffected.
over
times.
is important
material
by an increase
results
from transalkylation
(Figures 4 and 6) but performance
ization are different
of alkylaromatics
since more of the light products
acid dealumination,
zeolite
to proceed.
but at temperatures
at early on-stream
that of the starting
offset
for
they are
pure transalkylation
were formed.
of dealumination
Use of EDTA dealuminising
change
(possible
and so do not allow the access of
for the dealumination
study [9,10] of the conversion
are formed than would be expected
chloric
structure
ZSM-5), or perhaps
performance
Karge and Ladebeck's
benzene
too narrow a channel
for the IO-ring zeolite
is largely
ratio, collapse
of the
[1,2] and hence conversion
falls. The starting ization
Zeolon
IOOH shows a relatively
(Figure 7). It is possible
a high activity
for catalysing
also show a high fouling situated
rapidly.
more accessible the starting experiment However,
position,
the surface
activity
dealuminised
falls to the activity
channel
zeolite,
but
sites sites
and hence
It is postulated not observed
that in the
level of the surface.
are stripped
out by the
sites show high xylene
rates but, because
of the absence
loss is less rapid than in the starting
levels
mordenites
The remaining
and high fouling
activity
For EDTA treated
rate.
high initial activity,
sites and sites at the pore mouths
isomerization
blocking,
rapidly
described.
involves
block off the interior
show a much lower fouling
which
methods
to very low activity
rate possibly
isomer-
IOOH have
and isomerization
sites, because of their more exposed
Zeolon shows an extremely
described,
rate for xylene
sites of the Zeolon
transalkylation
of the zeolite which
The surface
dealumination
mouth
aromatic
rate. The high fouling
at the pore mouths
extremely
low fouling
that the channel
material.
of pore Decay
is observed. xylene
whereas
isomerization
ethylbenzene
activity
conversion
parallels
that of other
is very similar
to the
336 starting material. outside
It is probable
of the crystal.
This results
an interior of similar alumina is possible
It is suggested
the channels
increase
distribution conversion
behaviour
contains
isolated
conversion
However,
but
Hence,
it
few strong acid sites. remove aluminium
in a more
sites which are of enhanced rate. Thus the EDTA material, isomerization
the sites remaining
Zeolon and hence display
from the
aluminium,
material.
sites, shows similar xylene
materials.
as the starting
of low surface
of dealumination leaving
ethylbenzene
of surface and pore mouth
to the other dealuminised
removes aluminium
to the starting
material
that the other methods
throughout
strength which
denuded
in a crystal
distribution
that the EDTA dealuminised
random manner acidic
that EDTA primarily
activity
are of the same
the same ethylbenzene
as this latter material.
CONCLUSION The catalytic dealumination. whereas
performance
of dealuminised
EDTA treatment
is postulated
steam/hydrochloric
from within
the crystal
acid treatment
mordenite to affect
depends
upon the method
the removal
or nitric acid leaching
as well as denuding
of surface
of
alumina
removes aluminium
the surface of the zeolite
crystal.
ACKNOWLEDGEMENTS The author wishes and thanks
to acknowledge
ICI, PLC for permission
the experimental to publish
assistance
Dr. R.J. Sampson of ICI, PLC and Dr. T. Mole (C.S.I.R.O. Science)
for advice
in preparing
of Mrs. E. Kitching
this work. The author wishes Division
to thank
of Materials
the manuscript.
REFERENCES
1 2 3 4 5
1: 12
W.L. Kranich, Y.H. Ma, L.B. Sand, A.H. Weiss, I. Zwiebel, "Molecular Sieve Zeolites (I)", Advan. Chem. Ser., (1971) 101. N.Y. Chen and F.A. Smith, Inorg. Chem., (1976) 295. J. Dwyer, F.R. Fitch, F. Machado, G. Pin, S.M. Smyth and J.C. Vickerman, J.C.S. Chem. Comm., (1981) 422. H.G. Karge in "Molecular Sieves II", J.R. Katzer Ed., ACS Symp. Ser., 40 (1977) 548. Kh. Minachev, V. Garanin, T. Isakova, V. Kharlamov and V. Bogomolov, "Molecular Sieve Zeolites II”, Advan. Chem. Ser., (1971) 102. H. Itoh, T. Hattor and Y. Murakami, Applied Catal., 3 (1982) 19. E.A. Swabb, B.C. Gates, Ind. Eng. Chem. Fundam., (1972) 540. D.E. Walsh, L.D. Rollman, J. Catal., (1977) 367. H.G. Karge and J. Ladebeck, "Catalysis by Zeolites", Elsevier, Amsterdam, (1980) 151. H.G. Karge, J. Ladebeck, Z. Sorbak and K. Hatada, Zeolites, 2 (1982) 94. H.G. Karae. Z. Phvs. Chem. N.F.. 122 (1980) 103. J.A. Rabo Ed., ACS Monograph E.M. Flaiigen, "Zeolite Chemistry and‘catalysis", 171 (1976) 92.
Applied Catalysis, I (1983) 327-336 Elsevier Science Publishers B.V., Amsterdam -Printed
THE CONVERSION
OF AROMATICS
Duncan
SEDDON
I.C.I.
Petrochemicals
Present
address:
Laboratories,
(Received
in The Netherlands
OVER DEALUMINISED
and Plastics
Division,
The Broken Hill Proprietary
245 Wellington
18 February
P.O. Box 90, Wilton, Company,
Road, Mulgrave,
1983, accepted
MORDENITES
Melbourne
Melbourne,
Cleveland,
U.K.
Research
Australia.
20 May 1983)
ABSTRACT The effect of progressive removal of aluminium from mordenite on ethylbenzene transalkylation and xylene isomerization is described. Variation of xylene isomerization activity with silica-alumina ratio is discussed. Catalytic performance depended upon the method of aluminium removal.
INTRODUCTION The changes changes
of catalytic
Much of this interest be systematically
altered
the proximity
properties
of aluminium
isomerization.
a maximum
by progressively
deficient,
Catalytic
removing
breakdown
tetraacetic
that the former treatment of the zeolite,
interest. acidity
activity
for butene
(mole) of about
from the lattice and the
for cumene cracking
isomerization
was progress-
as X-ray analysis
ratio of 600 could be obtained
and
went through
26 as aluminium
collapse
can
without
demonstrated significant
[1,2].
Dwyer et al. [3] compared ethylenediamine
about by systematic
Zeolite
aluminium
large port mordenites
ratio
of silica-alumina
brought
is of considerable
Sand et al. [I] have described
This was not due to structure
that mordenites structure
catalysts
upon ZSM-5 and mordenite.
of acid sites.
at a silica-alumina
ively removed.
and selectivity
of zeolite
has centered
so change
butene
activity
to the acid strength
whereas
the effects
of aluminium
removal
acid (EDTA) and steam/acid
preferentially
removed
the latter removed
aluminium
aluminium
from zeolites
leaching,
using
and suggested
from the outer surface
more uniformly
throughout
the crystal. Recently, exchanged
Karge [4] has made a detailed
mordenites
transalkylation. to the acidity
for the catalysis
The work complemented of mordenites
aimed at rationalising
brought
0166-9834/83/$03.00
catalysts
of benzene earlier
alkylation
studies
about by metal
the high coking
Karge's work has now been extended of the mordenite
study of the properties
rate typical
and ethylbenzene
on the systematic
[5,6], and studies
of mordenite
catalysts
of partial
of ethylbenzene
0 1983 Elsevier Science Publishers B.V.
changes
ion exchange
to include the effects
on the transalkylation
of various metal
[7,&l].
dealumination
[9-111. The work
328 confirmed
the earlier observations
acid leaching
that catalyst
lifetimes
and that active centres were primarily
could be
associated
extended
by
with Bronsted
acid sites. This work describes steam/hydrochloric the infrared
the dealumination
of H-mordenite
by the action
acid and nitric acid. How these different
spectra of the products
and the activity
of EDTA,
treatments
for aromatic
affect
conversion
is
also described.
EXPERIMENTAL H-mordenite
used for this work was Zeolon
ratio (mole) of 14.8. The three methods
1OOH (Norton) with a silica-alumina
used for the removal are typically
as
follows.
Leaching with strong H-mordenite
nitric acid
(IO g) was refluxed
was then filtered
120°C. The silica-alumina
Leaching
(24 h) in nitric acid (100 ml, 6 M). The zeolite
from the nitric acid, washed with distilled
with EDTA
H-mordenite a soxlet
(20 g) was refluxed
thimble
into the mixture.
in water
(200 ml) so as to extract
was stopped and the mordenite
silica-alumina
ratio of the product was found to be 31.1.
Steaming
filtered,
washed
and dried.
(2.3 g). The
and acid leaching
H-mordenite
(30 g) was placed
in a tubular
passed at a known rate. The material
(4 h) with dilute
hydrochloric
It had a silica-alumina
Catalyst
furnace
was steamed
per hour. After 2 h the steam treatment
dried.
EDTA from
After three days little EDTA remlined
THe extraction
water
water and dried at
ratio of the product was found to be 65.6.
into which
steam could be
at 538°C in a flow of 18 g of
was stopped
and the product
acid (516 ml, 2 M), filtered
refluxed
and then washed
and
ratio of 68.8.
evaluation
Catalysts downflow
(5 g) as l/8 inch diameter
tubular
condensation
reactor
system.
over the catalyst
binder-free
fitted with reactant
Feeds
(ethylbenzene
at a weight
pellets were charged
vaporiser,
in xylene
hourly space velocity
thermocouples
or xylenes)
into a
and product
were then passed
of 5.0 h-l, at a bed temperature
of 450°C.
Analysis Aluminium alumina
contents
were determined
ratios are expressed
product crystallinity
by atomic
absorption
spectroscopy.
Silica-
on a molar basis. The extent of dealumination
was also monitored
by mid-range
infrared
spectroscopy.
and
329
0
FIGURE
1
Effectiveness
I 2 NO CF EXTRACTIONS
of multiple
moo
900
extractions.
800 WAVENUMBER
FIGURE 2
Infrared
and dealuminised
spectra
mordenite
3
700
600
SO0
cm-’
(1000 - 500 cm-') of H-mordenite (silica-alumina = 140).
(silica-alumina
= 14.6)
330
125 . IW
0(, 0
FIGURE 3
,
20
Correlation
‘0
of infrared
dealuminised
mordenites.
Compositions
of hydrocarbon
,
60 80 s,o? A'z'J,
ratio
100
120 lie
(R) with silica-alumina
feeds and products
were determined
ratio for
by gas chromatography.
RESULTS Efficacy
of aluminium
removal
The ease of aluminium silica-alumina
removal from mordenite
ratio of the dealuminised
three repeat dealuminations
is shown in Figure
product
is plotted
against
1, where the the number of
for each method.
As mordenite is dealuminised, the infrared spectrum in the region 1000 - 500 -1 cm changes; the peaks shift to higher frequencies and many broad bands become resolved. alumina
Figure 2 compares
ratio 140) obtained
Zeolon
100H with dealuminised
by multiple
mordenite
steam/hydrochloric
(of silica-
acid treatment.
The
difference
was quantified by comparison of the realtive intensities of the peak -1 at ca. 590 cm and the trough at ca. 575 cm-'. A ratio R was defined:
R=
where
1og(r'10)590
peak
1og(I'10)575
trough
Io is the baseline
for samples plot applies
produced
intensity.
R is plotted
by steam/hydrochloric
against
the silica-alumina
acid treatments
to nitric acid leached catalysts,
the slope of the line; EOTA leached mordenite
ratio
(Figure 3). A similar
but there was some difference did not fit the plot.
in
331 TABLE
1
Conversion
of an aromatic
mordenite
ratio of 83 (WHSV of 5.0 h-', 450°C).
Aromatic
On stream time /h
B
acid dealuminised
feed over a steam/hydrochloric
with a silica-alumina
0.09
EB
composition
/wt%
P-X
m-X
o-x
20.4
19.3
41.1
19.1
3.1
9.5
20.1
9.4
T
AEB/%
AX/%
23.6
84.8
40.3
C9+ 0.04
Feed
0.05
0.25
6.1
28.2
0.50
5.5
26.0
3.8
9.7
21.0
9.5
24.5
81.5
39.3
0.75
4.9
23.3
4.9
10.5
23.0
10.2
23.3
76.2
35.7
1.0
4.5
21.5
5.6
10.9
23.9
10.7
22.9
72.3
33.9
1.5
3.9
19.0
6.9
11.8
26.1
11.6
20.8
66.3
30.0
2.0
3.3
15.8
8.6
12.9
28.7
12.7
18.0
57.7
25.0
3.0
2.6
12.4
10.6
14.1
31.4
14.0
14.9
47.9
19.9
4.0
2.2
10.2
12.1
14.8
33.0
14.8
12.6
40.7
16.4
5.5
1.7
7.9
13.8
15.8
35.5
'5.7
9.6
42.2
12.4
6.0
1.2
5.5
15.5
16.6
37.5
16.6
7.1
24.0
8.7
(B,benzene; o-xylene;
T, toluene;
lost; AX, % of xylenes
Catalytic Table a typical
EB, ethylbenzene;
Cg+, aromatics
lost).
1 lists the product steam/hydrochloric
(of carbon
stability
of the mordenite
6.0 h. The rate of fouling is a function
conversion
as shown in Figure
The performance
materials
alumina
activity
ratio, as shown
The efficiency
demonstrate
the poor
and
(AEB) falls
acid dealuminised
time of mordenite
in Figure 4. The rate of fouling
thus, at a given on-stream
depends
on the method
against
but differently
is maintained
ratio
time, conversion
(e.g. 140) give low
of dealuminisation.
on-stream
In Figure
time for three catalysts
dealuminised.
for longer periods
with nitric acid. EDTA leached catalyst (the silica-alumina
toluene
5.
is plotted
content
ratio =83).
into benzene,
of ethylbenzene
with high silica-alumina
of mordenite
conversion
The conversion
feed over
(silica-alumina
time of 0.25 h to only 24% at an on-stream
dealumination,
However,
6, ethylbenzene
and xylenes
of the steam/hydrochloric
increases.
of an aromatic
mordenite
than 8). The results
catalyst.
of silica-alumina
falls with progressive
from conversion
ethylbenzene
number greater
from ca. 85% at an on-stream
of comparable
composition
acid dealuminised
disproportionates
aromatics
mordenite
m-X, m-xylene;' o-X,
9, IO and 11; AEB, % of ethylbenzene
performance
The catalyst
catalytic
p-X, p-xylene;
of carbon number
It appears
using mordenite
was of performance
similar
that
dealuminised to the starting
= 15 plot of Figure 4).
of the catalysts
for isomerizing
xylenes was also determined
332
FIGURE 4 Variation of fouling rate with silica-alumina mordenite
(using a p-xylene Utilising
lean mixed xylenes
a computer
interconversion equilibrium
program,
feed (90% xylenes)
pseudo-first
of each xylene isomer by comparing
achieved
sion of m-xylene
WHSV = 5 h-l, at 45OY).
order constants
were predicted
the approach
by the reaction with the feed comoosition;
feed and oroduct was by g.1.c. A pseudo-first
plotted
ratio of dealuminised
(steam/HCl).
into p-xylene
against
in Figure 7. Dealuminised
rates. Again there appears
to be an optimum
alumina
ratio of 66. The starting
activity
and low rate of fouling.
material
to thermodynamic analysis
order rate constant
on-stream
mordenite
catalysts
show broadly
in activity
of the
for the conver-
time for several
catalysts
for
similar
is fouling
this time with silica-
(silica-alumina
= 15) showed low
DISCUSSION Mordenite
dealumination
Steam/hydrochloric procedure.
The extent of aluminium
time. A chosen progressively
procedure increased
a lesser extent) maximum
acid treatment
removal
gave reproducible dealumination.
by the EDTA treatment,
in the amount of aluminium
calcining
was found to be the most reliable
the product
between
varied with temperature results
Dealumination
and repeating
and steaming
the procedure
was also found
but the nitric acid appeared
removed;
dealuminising
(although
to
to reach a
this may be the result of not air
repeat nitric acid treatments
(see Sand et al. Cl]).
333
,, ,
20
LO
60
MO
120
IL0
S,LF.. ALUM/N/A
FIGURE 5
Variation
mordenite
(steam/HCl);
in conversion
with silica-alumina
8 = on-stream
o -LA--LA 0
FIGURE 6
Comparison
traetment
and EDTA leaching
benzene),
temperature
ratio of dealuminised
time.
l-. ?O
of mordenites
20
30 e hi ON -STREAM
aluminised
in the conversion
45O"C, WHSV = 5.
L.0
50
- TIM-
by nitric acid leaching, of an aromatics
feed
steam/HCl
(20% ethyl-
334
FIGURE 7 xylene
Effect of silica-alumina
isomerization
As aluminium change
is progressively
The spectral
is progressively these phenomena measured
infrared
removed from the mordenite spectrum.
and have been extensively
faujasites.
changes
large changes
studied,
integrity
remain obscure.
as aluminium
show the same variation
by Flanigen change
was progressively
removed.
the extent of dealumination However,
in infrared
that reported
in spectral
It was chosen
Infrared
catalysts
spectroscopy
can
the structural
do not seem to materials. the siliceous
content were observed
(similar
and (iii) multiple
to
due to removal of surface
present was found to be stable to (i)
action of fuming nitric acid (98%), (ii) steaming
It is not clear why these zeolites
to quantify
ratios of about 30, by the
for ZSM-5 by Dwyer et al. [33), presumably
but the bulk of the aluminium
was
to be undergoing
were made to dealuminise
in alumina
of
appearance
spectra as the other dealuminised
Slight changes
by HCl exchange,
as aluminium
[IZ] but the origins
and to confirm
EDTA dealuminised
Nu-I, Fu-I and ZSM-5, with silica-alumina
aluminium,
followed
in the use of dealuminised
spectrum which was observed
During the course of the work, attempts
described.
there is a steady
have been observed
especially
The progressive
portion of the mordenite
of the products.
procedures
on the rate of
and the shift to higher frequencies
removed has been reviewed
thus be used to monitor
prolonged
Such changes
by the ratio R, but its use is purely empirical.
a particular
zeolites
mordenite
(note log scales).
in the mid-range
previously
ratio of dealuminised
for 7 days at 550°C
EDTA extractions.
do not show the aluminium
lability
found
335 for mordenite.
Perhaps
they possess
Nu-1 and Fu-1 but unlikely more hydrophobic
than dealuminised
water to the channels
Catalytic In
which
mordenite
is necessary
mordenite,
ethylbenzene
at moderate
(toluene,
xylenes,
the occurrence
underwent
temperatures, styrenel
of cracking
be more prevalant The method
conversion
in fouling
possibly
to diethylbenzene >ca. 500 K cracked
The present
depends
of acidic
channel
Cracking
seems to
catalytic
in xylene
performance.
in ethylbenzene
isomerization
differs
from
(Figure 7). For both nitric acid and steam/hydro-
results
for ethylbenzene
from the starting
upon the presence
material.
conversion
in activity. of active
by steam/hydrochloric
at a sufficiently possibly
so that aromatic
isomer-
important
High fouling
rate
sites and the loss
acid or nitric acid is conversion
high silica-alumina
becomes
and xylene
This result could be due to a
of a high density
in acid strength
structure
products
(benzene plus toluene)
the performance
rate rather than to an increase
However,
and
(Table 1) also show
alone.
in determining
agent hardly affects
sites upon dealumination
unaffected.
over
times.
is important
material
by an increase
results
from transalkylation
(Figures 4 and 6) but performance
ization are different
of alkylaromatics
since more of the light products
acid dealumination,
zeolite
to proceed.
but at temperatures
at early on-stream
that of the starting
offset
for
they are
pure transalkylation
were formed.
of dealumination
Use of EDTA dealuminising
change
(possible
and so do not allow the access of
for the dealumination
study [9,10] of the conversion
are formed than would be expected
chloric
structure
ZSM-5), or perhaps
performance
Karge and Ladebeck's
benzene
too narrow a channel
for the IO-ring zeolite
is largely
ratio, collapse
of the
[1,2] and hence conversion
falls. The starting ization
Zeolon
IOOH shows a relatively
(Figure 7). It is possible
a high activity
for catalysing
also show a high fouling situated
rapidly.
more accessible the starting experiment However,
position,
the surface
activity
dealuminised
falls to the activity
channel
zeolite,
but
sites sites
and hence
It is postulated not observed
that in the
level of the surface.
are stripped
out by the
sites show high xylene
rates but, because
of the absence
loss is less rapid than in the starting
levels
mordenites
The remaining
and high fouling
activity
For EDTA treated
rate.
high initial activity,
sites and sites at the pore mouths
isomerization
blocking,
rapidly
described.
involves
block off the interior
show a much lower fouling
which
methods
to very low activity
rate possibly
isomer-
IOOH have
and isomerization
sites, because of their more exposed
Zeolon shows an extremely
described,
rate for xylene
sites of the Zeolon
transalkylation
of the zeolite which
The surface
dealumination
mouth
aromatic
rate. The high fouling
at the pore mouths
extremely
low fouling
that the channel
material.
of pore Decay
is observed. xylene
whereas
isomerization
ethylbenzene
activity
conversion
parallels
that of other
is very similar
to the
336 starting material. outside
It is probable
of the crystal.
This results
an interior of similar alumina is possible
It is suggested
the channels
increase
distribution conversion
behaviour
contains
isolated
conversion
However,
but
Hence,
it
few strong acid sites. remove aluminium
in a more
sites which are of enhanced rate. Thus the EDTA material, isomerization
the sites remaining
Zeolon and hence display
from the
aluminium,
material.
sites, shows similar xylene
materials.
as the starting
of low surface
of dealumination leaving
ethylbenzene
of surface and pore mouth
to the other dealuminised
removes aluminium
to the starting
material
that the other methods
throughout
strength which
denuded
in a crystal
distribution
that the EDTA dealuminised
random manner acidic
that EDTA primarily
activity
are of the same
the same ethylbenzene
as this latter material.
CONCLUSION The catalytic dealumination. whereas
performance
of dealuminised
EDTA treatment
is postulated
steam/hydrochloric
from within
the crystal
acid treatment
mordenite to affect
depends
upon the method
the removal
or nitric acid leaching
as well as denuding
of surface
of
alumina
removes aluminium
the surface of the zeolite
crystal.
ACKNOWLEDGEMENTS The author wishes and thanks
to acknowledge
ICI, PLC for permission
the experimental to publish
assistance
Dr. R.J. Sampson of ICI, PLC and Dr. T. Mole (C.S.I.R.O. Science)
for advice
in preparing
of Mrs. E. Kitching
this work. The author wishes Division
to thank
of Materials
the manuscript.
REFERENCES
1 2 3 4 5
1: 12
W.L. Kranich, Y.H. Ma, L.B. Sand, A.H. Weiss, I. Zwiebel, "Molecular Sieve Zeolites (I)", Advan. Chem. Ser., (1971) 101. N.Y. Chen and F.A. Smith, Inorg. Chem., (1976) 295. J. Dwyer, F.R. Fitch, F. Machado, G. Pin, S.M. Smyth and J.C. Vickerman, J.C.S. Chem. Comm., (1981) 422. H.G. Karge in "Molecular Sieves II", J.R. Katzer Ed., ACS Symp. Ser., 40 (1977) 548. Kh. Minachev, V. Garanin, T. Isakova, V. Kharlamov and V. Bogomolov, "Molecular Sieve Zeolites II”, Advan. Chem. Ser., (1971) 102. H. Itoh, T. Hattor and Y. Murakami, Applied Catal., 3 (1982) 19. E.A. Swabb, B.C. Gates, Ind. Eng. Chem. Fundam., (1972) 540. D.E. Walsh, L.D. Rollman, J. Catal., (1977) 367. H.G. Karge and J. Ladebeck, "Catalysis by Zeolites", Elsevier, Amsterdam, (1980) 151. H.G. Karge, J. Ladebeck, Z. Sorbak and K. Hatada, Zeolites, 2 (1982) 94. H.G. Karae. Z. Phvs. Chem. N.F.. 122 (1980) 103. J.A. Rabo Ed., ACS Monograph E.M. Flaiigen, "Zeolite Chemistry and‘catalysis", 171 (1976) 92.