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Beckman rearrangement of cyclohexanone-oxime on HNaY zeolites: kinetic and spectroscopic studies
187
Applied Catalysis, 22 (1986) 187-200 Elsevier Science Publishers B.V., Amsterdam -Printed
BECKMAN
REARRANGEMENT
SPECTROSCOPIC
OF CYCLOHEXANONE-OXIME
A. CORMAb
M.C. BURGUETa, Qufmica,
Facultad
(Valencia),
Spain.
Ingenierfa
50, Burjassot bInstituto
ON HNaY ZEOLITES:
KINETIC
AND
STUDIES
A. AUCEJOa, aDep.
in The Netherlands
de Catalisis
and V. FORNESC
Ciencias
Qufmicas
y Petroleoqufmica,
C.S.I.C.,
de Valencia,
Serrano,
C/Dr. Moliner,
119, 280064adrid,
Spain. 'Institute
de Ffsico-Qufmica
Mineral,
C.S.I.C.,
Serrano,
115 dup. 28006-Madrid,
Spain.
(Received
18 April
1985, accepted
9 December
1985)
ABSTRACT The cyclohexanone-oxime rearrangement catalysed by a series of HNaY zeolites was studied in a fixed-bed reactor with continuous plug flow at atmospheric pressure and 335°C. Selectivity curves for the different reaction products, viz, e-caprolactam,5-cyanopent-I-ene and cyclohexanone, were obtained and from them the reaction mechanism was established. The influence of the level of exchange of Na+ in the HNaY sample on the total conversion of cyclohexanone-oxime, the selectivity for the products and the decay of the catalyst are discussed. It has been found that the formation of E-caprolactam is catalysed by Brllnsted sites of strength pKa 5 1.5, and that 5-cyanopent-l-ene is formed mainly on the Na+ iOnS of the zeolite.
INTRODUCTION E-Caprolactam fibres.
as a catalyst. advantages amount
is important
Its production Although
related
caprolactam
selective,
sulphate.
Owing
in the manufacture
polar acids
investigated
the solid
this process
to these
most
and boron
such as the Beckman the catalytic
the rearrangement
0166-9834/86/$03.50
to their
rearrangement
activity
of various
of oximes
the production
of the operational
used were
silica
the success testing
[9-131. zeolites
to amides.
gel, alumina
and low selectivity.
phosphates
of a large of E-
parameters
Landis
and
Poles
0 1986 Elsevier Science Publishers B.V.
zeolites
acid-catalysed
(mordenite,
Butler
Other catalysts
[l-7].
of synthetic
in other
Thus,
and hetero-
have also been used for the re-
to give caprolactam
From the 1960s until the present, [8] has'led
from some dis-
of heat and the formation limitations,
show low activity
alumina
of cyclohexanone-oxime
lytic cracking
suffers
using oleum
[l-5].
catalysts
[6], but these
such as boron oxide,
of synthetic
out in the liquid phase
in the gas phase and the optimization being
Initially,
arrangement
highly
carried
to the rate of elimination
of ammonium
are still
as an intermediate
is normally
and Venuto
in cata-
reactions, [9] studied
NaX, Lax, HY, etc.,) [tOal used HY and Y
in
188 zeolites highly
containing
exchanged
rearrangement oxime These
to
conclusions
of nitrile
reaction, are also
However,
centration
to our knowledge,
of active
and the decay
TABLE
causes
with the work
showed
that
for the Beckman is responsible
the formation of Ward
for the
of nitriles.
[11,12] who,
verified
that the formation
Li>Na>K>Cs>H+.
a detailed
and selectivity
constants
results
of the catalyst
the metal
study of the cyclohexanone-oxime as a function
sites has not been reported.
of the adsorbed
Their
catalysts
doped with alkali metals,
in the order
of H+ exchange.
nature
whereas
on a series of HNaY zeolites
distribution
levels
of palladium.
and selective
in agreement
Y zeolites
decreases
arrangement
proportions
are active
and that the Brl)nsted acidity
lactam
using decationized
product
various
zeolites
catalysts
for the formation
have been related
re-
and con-
In this work we studied
of four zeolitic
The rate constants
of the nature
to the catalyst
the
with different
of the main
acidity
products
and to the
products.
1
Level of exchange
and unit cell dimensions
Catalyst
of the HNaY catalysts
% exchange
NaY
a/i
0.00
24.69
HNaY-1
23.50
24.67
H;;a'l-2
47.00
24.59
HFia'i3
87.50
24.50
Hfla'l-4
99.07
24.40
EXPERIMENTAL Materials An SK-40 NaY zeolite material.
The HNaY
of the NaY sample
with an Si/Al ratio of 2.4 was used as the starting
samples
The level of exchange the filtrate exchanged
using atomic
Uvasol)
was evaluated absorption
099.5%)
cyclohexanone-oxime and the solution
was dried
by repeated
NH4+ exchange
under vacuum
by determination
spectrometry.
and the unit cell dimensions
The reactant purity
were prepared
and calcination
at 550°C.
are given.
was dissolved
dried with anhydrous
and stored
in
In Table 1 the amount of Na+
of the samples
(Proquimed)
of the Na+ present
in benzene
Na2S04.
over 3fi molecular
Pyridine
sieve.
of high
(Merck,
189 PROCEDURE Catalytic
experiments
All experiments were
were carried
taken at different
the amount condensed
of catalyst
mesh Chromosorb
of a solution
measurements
adsorption
packed
by changing products
which
The reactor The reaction
in benzene
displacement
were
was connected O-ring.
was purged mixture
(17.4 %wt),
pump. The reactor
carried
which was
was glass
Pyrex
infrared
cell fitted
line by means
were evacuated
at room temperature
of a ground-
overnight
and after
at 673 K.
10 min desorbed
1 h at 150 and 350°C. The spectra were recorded at room temperature
by Benesi
tube
out using a grease-free Pyrex -5 Torr could be maintained. of 10
to the vacuum
The samples
(3 Torr) was adsorbed
580 B spectrophotometer
Titration
by
15% Ucon on 80-100-
of 20 mm.
experiments
glass joint with a Viton
Perkin-Elmer
were
and then analysed
with
with oxime.
system, in which a dynamic vacuum -2 were placed in a conventional
The pyridine
(W/F) and samples
Liquid
of experiments.
feeding
of 10 mg cm
with CaF2 windows,
for
constant.
on-stream,
of cyclohexanone-oxime
Catalyst
acidity
before
by a positive
diameter
glass vacuum
a 15 min period
in each series
heating
with an internal
Wafers
time
The W/F ratio was varied
the flow-rate
a 2 m x l/8 in. column
was used
fed into the reactor
Pyridine
contact
at 150-ZOO'C.
N2 for 3 h with
consisted
during
using
Fresh catalyst with
times on-stream. and keeping
and collected
gas chromatography
out at a constant
with n-butylamine
equipped
was carried
in a
with a Data Station.
out following
the procedure
described
[14,15].
RESULTS Kinetic
and product
In preliminary particle
size
by external
distribution
experiments
that,
(0.5 - 1.0 mm) used in this work,
or internal
The chemical
for the flow-rates the process
and catalyst
is not controlled
diffusion.
species
are 5-cyanopent-I-ene,
detected
in a typical
cyclohexanone,
the first
three accounting
the curves
of the yields
version
data
it was found
for more
E-caprolactam,
of the reaction
aniline
than 99% of the total.
at constant
at 335°C are shown
analysis
in Figure
catalyst
to oxime
and methylpyridine,
For these
ratio versus
1 for HNaY zeolites
products
three products, total con-
with different
levels
of exchange. The lines called
in Figure
optimum
obtained
1, which
performance
at a constant
ratio was carried
enclose
envelopes
space velocity
out following
the catalyst/oxime
loops,
(OPE) [16]. The transformation to the data at a constant
a procedure
described
elsewhere
are the soof the results
catalyst [16,17].
to oxime
190
5-CYANO-1
CAPROLACTAM
0
10
CYCLOHEXANONE
FIGURE
1
Yields
were
primary
calculated
given
in Figure
The kinetic [I71 with
which
products
by measuring
30
LO
O-HNaY-1 O=HNaY-2 O-H NaY-3 @-HNaY -L
of the three main reaction
The types of products of the major
20
PENTENE
products
these OPEs represent are given
in Table
(Gi) versus
total conversion
and the initial
2. These
the slope of the tangent
selectivities
in tial selectivities
to the OPEs for the products
1 at zero conversion. rate and decay
the different
constants
catalyst
samples
for the total disappearance given
in Table
of reactant
3 were calculated
by fitting
the data from Figure 6 to the equation
x = 1 - exp
where global
-KT
[So]
(1 + Gt)-N P.b.tf
x is the instantaneous rate constant,
decay constant,
conversion
So is the initial
I
for the cyclohexanone-oxime, concentration
tf is the final time on-stream
ratio; G and N are the decay
parameters,
which
of active
and P is the catalyst take
into account
KT is the
sites,
Kd is the
to oxime
the decrease
in
193 TABLE
2
Initial
selectivities
S = secondary)
and behaviour
of the three main
(PS = primary
reaction
stable;
PI = primary
Initial
selectivity
Catalyst
Product
Type
HNaY-1 II
Caprolactam
PS + s
0.13
Cyanopentene
PI
0.53
Cyclohexanone
PI
0.29
Caprolactam
PS + s
0.58
Cyanopentene
PI
0.21
Cyclohexanone
PI
0.17
Caprolactam
PS
0.75
Cyanopentene
PS
0.07
Cyclohexanone
PI
0.16
Caprolactam
PS
0.77
Cyanopentene
PS + s
0.07
Cyclohexanone
PI
0.15
HNaY-2 II
HNaY-3 II II HNaY-4
TABLE
3
Kinetic
and decay
parameters
for the cyclohexanone-oxime
Catalyst
KT/min-'
G/min
HNaY-1
124.0
0.143
HNaY-2
125.0
HNaY-3
132.0
HNaY-4
139.5
0.050
conversion
with
-1
experimentally
m
Kd/min-'
1
2
0.143
0.114
1
2
0.114
0.081
1
2
0.081
1
2
0.050
time on-stream,
x = 1/t
is related
reaction
N
and are related
to the order
(Kd) by G = (m - 1) Kd and N = l/m-l. The average to the instantaneous
conversion,
conversion
(m) and decay constant x, measured
given
in equation
(I) by
tf f
x dt
(2)
s 0
With the global given
unstable;
products.
in Tables
rate constants
kinetic
rate constant
2 and 3, and taking for the formation
(Ki) can be calculated.
and initial
into account
E-caprolactam,
The results
are given
selectivity
(ISi) values
that ISi = Ki/KT, 5-cyanopent-I-ene
in Table
4.
the kinetic and cyclohexanone
192
TABLE
4
Rate constants
for the main reactions Ki/min -1
Catalyst E-Caprolactam
Cyclohexanone
5-Cyanopent-I-ene
HNaY-1
17.70
65.70
35.96
HNaY-2
72.50
26.00
21.00
HNaY-3
99.0
9.24
21.10
107.41
9.21
21.50
HNaY-4
I
i I
1500
1
I
1400
1600
I
I
1500
I
1400
2
IR spectra
of pyridine
1500
1400
HNaY-3
Wavenumber FIGURE
1600
HNaY-2
HNaY-1
I
I
I
1600
I
I
1500
1401
HNaY-4
(Cm-‘)
adsorbed
on the zeolite
catalysts
after
evacuation
at 150°C.
Catalyst
acidity
The infrared evacuation After
of pyridine
at 150°C are shown evacuation
characteristic entiated
data spectra
on the HNaY zeolites
at 20°C after
2.
at 150°C all the samples
exhibit
the band near 1545 cm-'
of the pyridinium ion (Brbnsted acidity) and two clearly differ-1 , which are associated with pyridine coordinated with
bands at 1455 cm
Na+ ion and true Lewis acid sites with Brbnsted in Table
adsorbed
in Figure
5.
and true Lewis
[11,18,19].
The intensity
acid sites were measured,
of the bands
and the values
associated
are given
193 TABLE
5
Pyridine
adsorption
IR associated
Intensity
experiments.
bands,
in arbitrary
units,
of Brllnsted (B) and Lewis acid
at 150°C.
Catalyst
B
L
HNaY-1
30
22
HNaY-2
66
54
HNaY-3
126
194
HNaY-4
123
148
TABLE
6
Acidity
of the catalysts
measured
by n-butylamine
titration.
m equiv. No.
Indicator
1
Anthraquinone
-8.2
2
Benzylacetophenone
-5.6
3
Dicinnamylacetone
-3.0
4
Benzeneazodiphenylamine
5
Butter yellow
6
Natural
In Table method
(L)
6 the acid strength
-1
cat
HNaY-2
HNaY-3
0.00
0.00
0.00
0.00
0.00
0.00
0.14
0.20
0.07
0.30
1.42
1.23
+1.5
0.18
0.86
1.23
1.23
+3.3
0.42
0.86
1.23
1.23
+6.8
1.25
1.75
1.57
1.40
pKa
red
HNaY-1
g
distributions
of the catalysts
measured
HNaY-4
by Benesi's
are reported.
DISCUSSION From the behaviour with all the catalysts 5-cyanopent-I-ene rearrangement, oxime.
of the OPE curves studied,
the three major
and cyclohexanone,
fragmentation
in the Figure
are primary
and hydrolysis,
1 it can be seen that
products, products,
respectively,
i.e., E-caprolactam, which
are produced
of cyclohexanone-
by
194
NOH
0 NH Beckman
rearrangement
’
CSN CH2 +H20
0
/
Fragmentation
E-caprolactam
G
I
0
5-cyanopentl-ene
+ NH20H Hydrolysis Nature
of the active
cyclohexanone
sites
We have seen that there are changes products
when
indicates
the level of exchange
that the active
rearrangement,
hydrolysis
In fragmentation selectivity decrease
sites
in the selectivity
of the zeolite
involved
when
in the three main
and fragmentation,
of cyclohexanone-oxime
and the kinetic rate constant the level of exchange
cannot
of the zeolite
the Briinsted or the total acidity
it is clear that the acid sites cannot in agreement
Na+ ions can also be active correlation
between
in the supercavity
with
in catalysing
i.e.,
with
the initial
of this product
catalyst
increases
Butler
increases increasing
(Table 2). level of
be the only ones responsible and Poles
such reaction,
the kinetic rate constant of the zeolite,
reactions,
This
be the same.
to give 5-cyanopent-I-ene,
exchange,
If,
is varied.
for the formation
As either
for this reaction.
of the three major
catalyst
[IO], we assume there should
and the amount
as can be observed
that
be a direct
of Na+ ions located
in Figure
3.
K2 (min-l)
‘O 60..
0' FIGURE
3
Rate constant
of the zeolites.
10
8
6
for the formation
4
2
0
5-cyanopent-I-ene
Na+ versus
Na+ content
195
Kl 160 (mine*)
t
12cb
FIGURE
4
Rate constant
Brt)nsted sites retaining
for the formation pyridine
after
of E-caprolactam
evacuation
vs. the intensity
of
at 150°C.
Kl 180 SO-
0
0 0
0.2
0.4
0.6
0.8
1.0
1.2
mequiv FIGURE
5
Rate constant
sites of different
In any case, total absence
for the formation
1.4
butylamine
of E-caprolactam
I 1.6 1.8 @.a] -1 cat. g vs. the amount
of acid
acid strength.
the existence
of 5-cyanopent-l-ene
of Na+ indicates
as a primary
that the acid centres
should
product
in the
also catalyse
this
reaction. In the case of the qualitatively E-caprolactam,
it is generally
Brt)nsted acid sites. rate constant medium
there
for this reaction
strength
of Figure
More specifically, rearrangement
C9,lOl
is a direct
and the amount
(those retaining
seen on inspection
Beckman
Indeed,
and quantitatively
accepted
pyridine
after
most
important
that the catalytic relationship
product,
sites are the
between
the kinetic
of BrClnsted sites of strong desorption
at 15O"C),
and
as can be
4.
if one tries to relate reaction
with
the kinetic
the amount
of acid
rate constant
for the
sites of different
acid
196 strength, (Figure
a straight
line is obtained
5). We can therefore
acid strength
Mechanistic
corresponding
The shape of the curves is a primary
level exchanged of exchange
Y zeolite,
e-caprolactam
zeolites,
exchanged
zeolites
These assume
results,
at high levels
of conversion stable
whereas
for those
which
appears
as a primary
by Na+ ions [lOa], which would the less exchanged
reversible
exchanged
cyanopent-I-ene as a primary
the opposite, although
would
product.
product
plus secondary
in Table
can be formed
low levels
On the other
on 23.5 and 47.0%
stable
product
when further
2, can be explained
in two possible
the e-caprolactam,
be responsible
intermediate
ways,
if we
one
and the other
for the high values
in the acid catalysis
5-cyanopent-I-ene
elsewhere
zeolites,
catalysed
obtained
with
[ZO,
product,
With a higher
5-cyanopent-I-ene
the small amount
proportion appearing
of transformed
the
This
73. high concentration
of E-caprolactam,
whereas
can explain
and E-caprolactam.
the relatively
cause the formation
plus secondary
product.
with
with 87.5 and 99.0%
stable
unstable
given
with
between
has been reported
In the less
zeolites
1) shows that
when working
zeolite.
of a common
transformation
possibility
unstable
E-caprolactam.
are used as catalysts. and also the values
by HC [9], competitive
The existence
(Figure
product
to be a primary
is a primary
that the 5-cyanopent-1-ene
catalysed
Brt)nsted sites with an
in producing
plus secondary
appears
5-cyanopent-I-ene,
exchanged
that only those
to pK, 2 1.5 are active
considerations
E-caprolactam
hand,
only when sites of pKa I 1.5 are considered
conclude
which would
5-cyanopent-l-ene
of e-caprolactam as a primary
E-caprolactam
of 5-
would
the process
plus secondary makes
appear
behave
as
can be
product,
this instability
negligible. The third major unstable explain traces
product.
compound,
cyclohexanone,
The presence
the primary
character
of water
of the cyclohexanone.
in the feed or as residual
possible
to explain
with nitrogenated
+
NH2R
water
the instability
bases
to give E-caprolactam
appears
adsorbed
unstable
media
This water
to
can be present
as
[21]. It is
by assuming
intermediate
as a primary,
is necessary
on the zeolite
of cyclohexanone
to give a highly
on all catalysts
in the reaction
that
it can react
that will decompose
[22]:
_
(3)
197 We checked by feeding
the possibility
cyclohexanone
HNaY zeolite were
take place
and cracked
and the formation
the instability
observed
under our experimental
with the ketoxime
temperature
of 335°C.
of 5-cyanopent-I-ene
for cyclohexanone
would
using an
products
reaction
Nevertheless,
conditions.
conditions
into the reactor,
The main reaction
Consequently,
products.
under our experimental
cyclohexanone with
together
at a reaction
5-cyanopent-I-ene
of such a reaction
detected
(3) does not
the disappearance
of
also be consistent
and the secondary
character
for the processes
taking
of
5-cyanopent-I-ene.
In conclusion, during
a possible
the Beckman
reaction
rearrangement
mechanism
on HNaY zeolites
place
is
Ni’H
3,3
Cyclohexanone
Pentametilw-
5-Cyanopent-l-ene
oxaziridine
Catalyst
decay
From Figure
6, where
seen that the activity
the conversion
vs. time on-stream
of the catalysts
decays
The decay may be due to the formation formation
during
methylpyridine
the reaction
and aniline.
the decay of the catalyst
products.
Indeed,
catalyst,
as is indicated
the increase
sample
in the reaction After
reaction, cm-').
work by elimination
centred
surface
with
several Because
infrared
bands appear
in HNaY-4
important
of basic
colour
factor
nitrogenated
level of exchange. after
on the and
Furthermore, being used
can be made.
catalyst
of interpreting
on hydrogen-Y
to the
of the catalyst
spectroscopy
possibilities.
adsorbed
and/or
of coke is deposited
observations
of the difficulty
of the different
white
increasing
by
it can be
such as hydroxylamine,
that the most
is the adsorption
7), the following
ClObJ, _":e cyclohexanone-oxime 3640 cm
indicate
by the still almost
is analysed
(Figure
of coke on the catalyst
a very small amount
of the decay constant
if the zeolite
(4000-1350
reaction
is plotted,
time on-stream.
of very basic products,
Two facts
producing
after
with
in the region the spectra
studied
we must
According
to Butler
and Poles
zeolite
interacts
with the
hydroxyl band of the zeolite, and its spectrum shows two bands -1 -1 at 1700 cm and 2700 cm assigned to v(C=N+) and v(N+-H), respectively.
.
,.
, _
~, ,_ ^
FIGURE 6
-
g
Total
0
, 60
_^
,
__.-
,
,
,
, T.0.S (min)
loo 120 140 160
-
(CT) vs. time on-stream
60
HNaY-3
conversion
,
40
,
20
(T.O.S.)
I
’
’
’
for the different
I
zeolite
Catalysts.
199
Wavenumber FIGURE 7
(Cm-l)
IR spectrum of HNaY-4 catalyst
after
reaction.
As both the 1700 and 2700 cm-' stretching
bands are absent
(Figure
oxime must
7), the presence
On the other hand, with
the presence
of cyclohexanone
of a band at about
[lob], and therefore
and water, at1650cm adsorbed
The v(NH)
it is masked
band at 1540 cm-'
by the v(CO)
(amide
and &(HOH)
II)
is very
of &-caprolactam
&-caprolactam. the band appearing
to NH stretching consequently
vibrations
The presence
at about
of amines
infer the probable
on the surface
in the spectrum Only a weak
3300, 3150 and 3050 cm
and u(=C-H)
presence
-1
can be assigned
of the aromatic
of aniline
ring. We can
and methylpyridine
adsorbed
of the zeolite. of 5-cyanopent-I-ene
ruled out, as the characteristic
band in this region
on the highly
band of nitriles
of 5-cyanopent-1-ene
adsorbed
is detected
exchanged at about
zeolites must be -1 2280 cm that appears
on HY zeolites
in the zeolites
[23] is not visible. with a high sodium
(Nay and HNaY-1).
On the other hand, (Table 3), decreases by considering nitroqenated amount
of E-caprolactam must be associated -1 [v(CO)] and a complex band centred 1650 cm
respectively. In the spectrum we observe a very strong band centred -1 -1 that may correspond to the , and a more complex band at 1450 cm
Finally,
content
be ruled out.
the IR absorption
at 1450 cm -' (uCH, CH2 scissor). weak
in the catalyst
the decay of the catalysts, with
compounds,
of these products
exchange
increasing
that aniline,
of the zeolite
level of exchange.
methylpyridine,
are responsible formed
measured
increases.
These
hydroxylamine
for the catalyst
per gram of catalyst
by their decay results
constants
are explained
and, in general, poisoning,
decreases
basic
and that the
when the level of
200 it can be said that the Beckman
In conclusion,
oxime on HNaY zeolites to this reaction, the active
5-cyanopent-l-ene
sites of this reaction
Na+ ions located is increased to primary
the behaviour
stable.
decay
(hydroxylamine,
is formed
which
is explained
aniline
coke on the catalyst
by fragmentation
changes
of the reactant, but also the of the zeolite
from primary
by considering
takes place at low levels
is due to poisoning
of cyclohexanone
When the level of exchange
of c-caprolactam
This result
rearrangement
by Brllnsted acid sites of pKa 5 1.5, Parallel
being not only the acid sites,
in the supercavity.
of 5-cyanopent-I-ene catalyst
is catalysed
plus secondary
a consecutive
of exchange.
reaction
Finally,
of the acid sites by the basic products
and methylpyridine),
rather
than to the deposition
the formed of
surface.
REFERENCES 1
9 10
1: 13 14 15 1; 18 :: 21 22 23
Badische Aniline und Soda Fabrik. Ger. Pat., 1.186.612 (Cl. c07d) Jan. 21 (1965). Farbenfabriken Bayer, Fr. Pat. 2.016.341 (1970). Mobil Oil Corporation, Neth. Pat. Appl. 6.514.009 (1966). Toray Industries, Japan Kokai 7633,914 (1976). British Petroleum Brit. Pat. 881.276 (1959). D. England, U.S. Pat. 2.634.269, April (1953). J. Garritsen and J. Ottenheim, U.S. Pat. 2,827,476 (1958). C.J. Planck, E.J. Rosinski and W.P. Wawthorne, Ind. Enq. Chem. Prod. Res. Dev., 3 (1964) 165. P.S. Landis and P.B. Venuto, J. Catal., 6 (1966) 245. a) J.D. Butler and T.C. Poles. J. Chem. Sot.. Perkin II (1973) 1,262. b) J. Chem. Sot. Perkin II (1973) 41. J.W. Ward, J. Catal., 10 (1968) 34. J.W. Ward, J. Catal., 13 (1969) 321. Mobil Oil Corporation, U.S. Pat. 225.157 (1981). H.A.Benesi, J. Amer. Chem. Sot., 78 (1956) 549. H.A. Benesi, J. Phys. Chem., 61 (1957) 970. D.R. Campbell and B.W. Wojciechowski, Cand. J. Chem. Eng., 48 (1970) 224. A. Corma, R. Cid and A. Lopez Agudo, Can. J. Chem. Eng., 57 (1979) 638. T.R. Hughes and H.M. White, J. Phys. Chem., 71 (1967) 2192. P.A. Jacobs "Carboniogenic Activity of Zeolites", Elsevier, Amsterdam (1977 1. A. Costa, P.M. Deya and J.V. Sinisterra, Can. J. Chem., 58 (1980) 1266. Rabo, Edit., (1976). J.W. Ward, "Zeolite Chemistry and Catalysis", J.A. Von E. Schmitz, R. Ohme, S. Schramm, H. Striegler, H.U. Heyne and J. Rusche Prakt. Chemie, 319 (1977) 195. J.D.Butler and T.C. Poles, 3. Chem. Sot., Perkin II (1973) 1976.
Applied Catalysis, 22 (1986) 187-200 Elsevier Science Publishers B.V., Amsterdam -Printed
BECKMAN
REARRANGEMENT
SPECTROSCOPIC
OF CYCLOHEXANONE-OXIME
A. CORMAb
M.C. BURGUETa, Qufmica,
Facultad
(Valencia),
Spain.
Ingenierfa
50, Burjassot bInstituto
ON HNaY ZEOLITES:
KINETIC
AND
STUDIES
A. AUCEJOa, aDep.
in The Netherlands
de Catalisis
and V. FORNESC
Ciencias
Qufmicas
y Petroleoqufmica,
C.S.I.C.,
de Valencia,
Serrano,
C/Dr. Moliner,
119, 280064adrid,
Spain. 'Institute
de Ffsico-Qufmica
Mineral,
C.S.I.C.,
Serrano,
115 dup. 28006-Madrid,
Spain.
(Received
18 April
1985, accepted
9 December
1985)
ABSTRACT The cyclohexanone-oxime rearrangement catalysed by a series of HNaY zeolites was studied in a fixed-bed reactor with continuous plug flow at atmospheric pressure and 335°C. Selectivity curves for the different reaction products, viz, e-caprolactam,5-cyanopent-I-ene and cyclohexanone, were obtained and from them the reaction mechanism was established. The influence of the level of exchange of Na+ in the HNaY sample on the total conversion of cyclohexanone-oxime, the selectivity for the products and the decay of the catalyst are discussed. It has been found that the formation of E-caprolactam is catalysed by Brllnsted sites of strength pKa 5 1.5, and that 5-cyanopent-l-ene is formed mainly on the Na+ iOnS of the zeolite.
INTRODUCTION E-Caprolactam fibres.
as a catalyst. advantages amount
is important
Its production Although
related
caprolactam
selective,
sulphate.
Owing
in the manufacture
polar acids
investigated
the solid
this process
to these
most
and boron
such as the Beckman the catalytic
the rearrangement
0166-9834/86/$03.50
to their
rearrangement
activity
of various
of oximes
the production
of the operational
used were
silica
the success testing
[9-131. zeolites
to amides.
gel, alumina
and low selectivity.
phosphates
of a large of E-
parameters
Landis
and
Poles
0 1986 Elsevier Science Publishers B.V.
zeolites
acid-catalysed
(mordenite,
Butler
Other catalysts
[l-7].
of synthetic
in other
Thus,
and hetero-
have also been used for the re-
to give caprolactam
From the 1960s until the present, [8] has'led
from some dis-
of heat and the formation limitations,
show low activity
alumina
of cyclohexanone-oxime
lytic cracking
suffers
using oleum
[l-5].
catalysts
[6], but these
such as boron oxide,
of synthetic
out in the liquid phase
in the gas phase and the optimization being
Initially,
arrangement
highly
carried
to the rate of elimination
of ammonium
are still
as an intermediate
is normally
and Venuto
in cata-
reactions, [9] studied
NaX, Lax, HY, etc.,) [tOal used HY and Y
in
188 zeolites highly
containing
exchanged
rearrangement oxime These
to
conclusions
of nitrile
reaction, are also
However,
centration
to our knowledge,
of active
and the decay
TABLE
causes
with the work
showed
that
for the Beckman is responsible
the formation of Ward
for the
of nitriles.
[11,12] who,
verified
that the formation
Li>Na>K>Cs>H+.
a detailed
and selectivity
constants
results
of the catalyst
the metal
study of the cyclohexanone-oxime as a function
sites has not been reported.
of the adsorbed
Their
catalysts
doped with alkali metals,
in the order
of H+ exchange.
nature
whereas
on a series of HNaY zeolites
distribution
levels
of palladium.
and selective
in agreement
Y zeolites
decreases
arrangement
proportions
are active
and that the Brl)nsted acidity
lactam
using decationized
product
various
zeolites
catalysts
for the formation
have been related
re-
and con-
In this work we studied
of four zeolitic
The rate constants
of the nature
to the catalyst
the
with different
of the main
acidity
products
and to the
products.
1
Level of exchange
and unit cell dimensions
Catalyst
of the HNaY catalysts
% exchange
NaY
a/i
0.00
24.69
HNaY-1
23.50
24.67
H;;a'l-2
47.00
24.59
HFia'i3
87.50
24.50
Hfla'l-4
99.07
24.40
EXPERIMENTAL Materials An SK-40 NaY zeolite material.
The HNaY
of the NaY sample
with an Si/Al ratio of 2.4 was used as the starting
samples
The level of exchange the filtrate exchanged
using atomic
Uvasol)
was evaluated absorption
099.5%)
cyclohexanone-oxime and the solution
was dried
by repeated
NH4+ exchange
under vacuum
by determination
spectrometry.
and the unit cell dimensions
The reactant purity
were prepared
and calcination
at 550°C.
are given.
was dissolved
dried with anhydrous
and stored
in
In Table 1 the amount of Na+
of the samples
(Proquimed)
of the Na+ present
in benzene
Na2S04.
over 3fi molecular
Pyridine
sieve.
of high
(Merck,
189 PROCEDURE Catalytic
experiments
All experiments were
were carried
taken at different
the amount condensed
of catalyst
mesh Chromosorb
of a solution
measurements
adsorption
packed
by changing products
which
The reactor The reaction
in benzene
displacement
were
was connected O-ring.
was purged mixture
(17.4 %wt),
pump. The reactor
carried
which was
was glass
Pyrex
infrared
cell fitted
line by means
were evacuated
at room temperature
of a ground-
overnight
and after
at 673 K.
10 min desorbed
1 h at 150 and 350°C. The spectra were recorded at room temperature
by Benesi
tube
out using a grease-free Pyrex -5 Torr could be maintained. of 10
to the vacuum
The samples
(3 Torr) was adsorbed
580 B spectrophotometer
Titration
by
15% Ucon on 80-100-
of 20 mm.
experiments
glass joint with a Viton
Perkin-Elmer
were
and then analysed
with
with oxime.
system, in which a dynamic vacuum -2 were placed in a conventional
The pyridine
(W/F) and samples
Liquid
of experiments.
feeding
of 10 mg cm
with CaF2 windows,
for
constant.
on-stream,
of cyclohexanone-oxime
Catalyst
acidity
before
by a positive
diameter
glass vacuum
a 15 min period
in each series
heating
with an internal
Wafers
time
The W/F ratio was varied
the flow-rate
a 2 m x l/8 in. column
was used
fed into the reactor
Pyridine
contact
at 150-ZOO'C.
N2 for 3 h with
consisted
during
using
Fresh catalyst with
times on-stream. and keeping
and collected
gas chromatography
out at a constant
with n-butylamine
equipped
was carried
in a
with a Data Station.
out following
the procedure
described
[14,15].
RESULTS Kinetic
and product
In preliminary particle
size
by external
distribution
experiments
that,
(0.5 - 1.0 mm) used in this work,
or internal
The chemical
for the flow-rates the process
and catalyst
is not controlled
diffusion.
species
are 5-cyanopent-I-ene,
detected
in a typical
cyclohexanone,
the first
three accounting
the curves
of the yields
version
data
it was found
for more
E-caprolactam,
of the reaction
aniline
than 99% of the total.
at constant
at 335°C are shown
analysis
in Figure
catalyst
to oxime
and methylpyridine,
For these
ratio versus
1 for HNaY zeolites
products
three products, total con-
with different
levels
of exchange. The lines called
in Figure
optimum
obtained
1, which
performance
at a constant
ratio was carried
enclose
envelopes
space velocity
out following
the catalyst/oxime
loops,
(OPE) [16]. The transformation to the data at a constant
a procedure
described
elsewhere
are the soof the results
catalyst [16,17].
to oxime
190
5-CYANO-1
CAPROLACTAM
0
10
CYCLOHEXANONE
FIGURE
1
Yields
were
primary
calculated
given
in Figure
The kinetic [I71 with
which
products
by measuring
30
LO
O-HNaY-1 O=HNaY-2 O-H NaY-3 @-HNaY -L
of the three main reaction
The types of products of the major
20
PENTENE
products
these OPEs represent are given
in Table
(Gi) versus
total conversion
and the initial
2. These
the slope of the tangent
selectivities
in tial selectivities
to the OPEs for the products
1 at zero conversion. rate and decay
the different
constants
catalyst
samples
for the total disappearance given
in Table
of reactant
3 were calculated
by fitting
the data from Figure 6 to the equation
x = 1 - exp
where global
-KT
[So]
(1 + Gt)-N P.b.tf
x is the instantaneous rate constant,
decay constant,
conversion
So is the initial
I
for the cyclohexanone-oxime, concentration
tf is the final time on-stream
ratio; G and N are the decay
parameters,
which
of active
and P is the catalyst take
into account
KT is the
sites,
Kd is the
to oxime
the decrease
in
193 TABLE
2
Initial
selectivities
S = secondary)
and behaviour
of the three main
(PS = primary
reaction
stable;
PI = primary
Initial
selectivity
Catalyst
Product
Type
HNaY-1 II
Caprolactam
PS + s
0.13
Cyanopentene
PI
0.53
Cyclohexanone
PI
0.29
Caprolactam
PS + s
0.58
Cyanopentene
PI
0.21
Cyclohexanone
PI
0.17
Caprolactam
PS
0.75
Cyanopentene
PS
0.07
Cyclohexanone
PI
0.16
Caprolactam
PS
0.77
Cyanopentene
PS + s
0.07
Cyclohexanone
PI
0.15
HNaY-2 II
HNaY-3 II II HNaY-4
TABLE
3
Kinetic
and decay
parameters
for the cyclohexanone-oxime
Catalyst
KT/min-'
G/min
HNaY-1
124.0
0.143
HNaY-2
125.0
HNaY-3
132.0
HNaY-4
139.5
0.050
conversion
with
-1
experimentally
m
Kd/min-'
1
2
0.143
0.114
1
2
0.114
0.081
1
2
0.081
1
2
0.050
time on-stream,
x = 1/t
is related
reaction
N
and are related
to the order
(Kd) by G = (m - 1) Kd and N = l/m-l. The average to the instantaneous
conversion,
conversion
(m) and decay constant x, measured
given
in equation
(I) by
tf f
x dt
(2)
s 0
With the global given
unstable;
products.
in Tables
rate constants
kinetic
rate constant
2 and 3, and taking for the formation
(Ki) can be calculated.
and initial
into account
E-caprolactam,
The results
are given
selectivity
(ISi) values
that ISi = Ki/KT, 5-cyanopent-I-ene
in Table
4.
the kinetic and cyclohexanone
192
TABLE
4
Rate constants
for the main reactions Ki/min -1
Catalyst E-Caprolactam
Cyclohexanone
5-Cyanopent-I-ene
HNaY-1
17.70
65.70
35.96
HNaY-2
72.50
26.00
21.00
HNaY-3
99.0
9.24
21.10
107.41
9.21
21.50
HNaY-4
I
i I
1500
1
I
1400
1600
I
I
1500
I
1400
2
IR spectra
of pyridine
1500
1400
HNaY-3
Wavenumber FIGURE
1600
HNaY-2
HNaY-1
I
I
I
1600
I
I
1500
1401
HNaY-4
(Cm-‘)
adsorbed
on the zeolite
catalysts
after
evacuation
at 150°C.
Catalyst
acidity
The infrared evacuation After
of pyridine
at 150°C are shown evacuation
characteristic entiated
data spectra
on the HNaY zeolites
at 20°C after
2.
at 150°C all the samples
exhibit
the band near 1545 cm-'
of the pyridinium ion (Brbnsted acidity) and two clearly differ-1 , which are associated with pyridine coordinated with
bands at 1455 cm
Na+ ion and true Lewis acid sites with Brbnsted in Table
adsorbed
in Figure
5.
and true Lewis
[11,18,19].
The intensity
acid sites were measured,
of the bands
and the values
associated
are given
193 TABLE
5
Pyridine
adsorption
IR associated
Intensity
experiments.
bands,
in arbitrary
units,
of Brllnsted (B) and Lewis acid
at 150°C.
Catalyst
B
L
HNaY-1
30
22
HNaY-2
66
54
HNaY-3
126
194
HNaY-4
123
148
TABLE
6
Acidity
of the catalysts
measured
by n-butylamine
titration.
m equiv. No.
Indicator
1
Anthraquinone
-8.2
2
Benzylacetophenone
-5.6
3
Dicinnamylacetone
-3.0
4
Benzeneazodiphenylamine
5
Butter yellow
6
Natural
In Table method
(L)
6 the acid strength
-1
cat
HNaY-2
HNaY-3
0.00
0.00
0.00
0.00
0.00
0.00
0.14
0.20
0.07
0.30
1.42
1.23
+1.5
0.18
0.86
1.23
1.23
+3.3
0.42
0.86
1.23
1.23
+6.8
1.25
1.75
1.57
1.40
pKa
red
HNaY-1
g
distributions
of the catalysts
measured
HNaY-4
by Benesi's
are reported.
DISCUSSION From the behaviour with all the catalysts 5-cyanopent-I-ene rearrangement, oxime.
of the OPE curves studied,
the three major
and cyclohexanone,
fragmentation
in the Figure
are primary
and hydrolysis,
1 it can be seen that
products, products,
respectively,
i.e., E-caprolactam, which
are produced
of cyclohexanone-
by
194
NOH
0 NH Beckman
rearrangement
’
CSN CH2 +H20
0
/
Fragmentation
E-caprolactam
G
I
0
5-cyanopentl-ene
+ NH20H Hydrolysis Nature
of the active
cyclohexanone
sites
We have seen that there are changes products
when
indicates
the level of exchange
that the active
rearrangement,
hydrolysis
In fragmentation selectivity decrease
sites
in the selectivity
of the zeolite
involved
when
in the three main
and fragmentation,
of cyclohexanone-oxime
and the kinetic rate constant the level of exchange
cannot
of the zeolite
the Briinsted or the total acidity
it is clear that the acid sites cannot in agreement
Na+ ions can also be active correlation
between
in the supercavity
with
in catalysing
i.e.,
with
the initial
of this product
catalyst
increases
Butler
increases increasing
(Table 2). level of
be the only ones responsible and Poles
such reaction,
the kinetic rate constant of the zeolite,
reactions,
This
be the same.
to give 5-cyanopent-I-ene,
exchange,
If,
is varied.
for the formation
As either
for this reaction.
of the three major
catalyst
[IO], we assume there should
and the amount
as can be observed
that
be a direct
of Na+ ions located
in Figure
3.
K2 (min-l)
‘O 60..
0' FIGURE
3
Rate constant
of the zeolites.
10
8
6
for the formation
4
2
0
5-cyanopent-I-ene
Na+ versus
Na+ content
195
Kl 160 (mine*)
t
12cb
FIGURE
4
Rate constant
Brt)nsted sites retaining
for the formation pyridine
after
of E-caprolactam
evacuation
vs. the intensity
of
at 150°C.
Kl 180 SO-
0
0 0
0.2
0.4
0.6
0.8
1.0
1.2
mequiv FIGURE
5
Rate constant
sites of different
In any case, total absence
for the formation
1.4
butylamine
of E-caprolactam
I 1.6 1.8 @.a] -1 cat. g vs. the amount
of acid
acid strength.
the existence
of 5-cyanopent-l-ene
of Na+ indicates
as a primary
that the acid centres
should
product
in the
also catalyse
this
reaction. In the case of the qualitatively E-caprolactam,
it is generally
Brt)nsted acid sites. rate constant medium
there
for this reaction
strength
of Figure
More specifically, rearrangement
C9,lOl
is a direct
and the amount
(those retaining
seen on inspection
Beckman
Indeed,
and quantitatively
accepted
pyridine
after
most
important
that the catalytic relationship
product,
sites are the
between
the kinetic
of BrClnsted sites of strong desorption
at 15O"C),
and
as can be
4.
if one tries to relate reaction
with
the kinetic
the amount
of acid
rate constant
for the
sites of different
acid
196 strength, (Figure
a straight
line is obtained
5). We can therefore
acid strength
Mechanistic
corresponding
The shape of the curves is a primary
level exchanged of exchange
Y zeolite,
e-caprolactam
zeolites,
exchanged
zeolites
These assume
results,
at high levels
of conversion stable
whereas
for those
which
appears
as a primary
by Na+ ions [lOa], which would the less exchanged
reversible
exchanged
cyanopent-I-ene as a primary
the opposite, although
would
product.
product
plus secondary
in Table
can be formed
low levels
On the other
on 23.5 and 47.0%
stable
product
when further
2, can be explained
in two possible
the e-caprolactam,
be responsible
intermediate
ways,
if we
one
and the other
for the high values
in the acid catalysis
5-cyanopent-I-ene
elsewhere
zeolites,
catalysed
obtained
with
[ZO,
product,
With a higher
5-cyanopent-I-ene
the small amount
proportion appearing
of transformed
the
This
73. high concentration
of E-caprolactam,
whereas
can explain
and E-caprolactam.
the relatively
cause the formation
plus secondary
product.
with
with 87.5 and 99.0%
stable
unstable
given
with
between
has been reported
In the less
zeolites
1) shows that
when working
zeolite.
of a common
transformation
possibility
unstable
E-caprolactam.
are used as catalysts. and also the values
by HC [9], competitive
The existence
(Figure
product
to be a primary
is a primary
that the 5-cyanopent-1-ene
catalysed
Brt)nsted sites with an
in producing
plus secondary
appears
5-cyanopent-I-ene,
exchanged
that only those
to pK, 2 1.5 are active
considerations
E-caprolactam
hand,
only when sites of pKa I 1.5 are considered
conclude
which would
5-cyanopent-l-ene
of e-caprolactam as a primary
E-caprolactam
of 5-
would
the process
plus secondary makes
appear
behave
as
can be
product,
this instability
negligible. The third major unstable explain traces
product.
compound,
cyclohexanone,
The presence
the primary
character
of water
of the cyclohexanone.
in the feed or as residual
possible
to explain
with nitrogenated
+
NH2R
water
the instability
bases
to give E-caprolactam
appears
adsorbed
unstable
media
This water
to
can be present
as
[21]. It is
by assuming
intermediate
as a primary,
is necessary
on the zeolite
of cyclohexanone
to give a highly
on all catalysts
in the reaction
that
it can react
that will decompose
[22]:
_
(3)
197 We checked by feeding
the possibility
cyclohexanone
HNaY zeolite were
take place
and cracked
and the formation
the instability
observed
under our experimental
with the ketoxime
temperature
of 335°C.
of 5-cyanopent-I-ene
for cyclohexanone
would
using an
products
reaction
Nevertheless,
conditions.
conditions
into the reactor,
The main reaction
Consequently,
products.
under our experimental
cyclohexanone with
together
at a reaction
5-cyanopent-I-ene
of such a reaction
detected
(3) does not
the disappearance
of
also be consistent
and the secondary
character
for the processes
taking
of
5-cyanopent-I-ene.
In conclusion, during
a possible
the Beckman
reaction
rearrangement
mechanism
on HNaY zeolites
place
is
Ni’H
3,3
Cyclohexanone
Pentametilw-
5-Cyanopent-l-ene
oxaziridine
Catalyst
decay
From Figure
6, where
seen that the activity
the conversion
vs. time on-stream
of the catalysts
decays
The decay may be due to the formation formation
during
methylpyridine
the reaction
and aniline.
the decay of the catalyst
products.
Indeed,
catalyst,
as is indicated
the increase
sample
in the reaction After
reaction, cm-').
work by elimination
centred
surface
with
several Because
infrared
bands appear
in HNaY-4
important
of basic
colour
factor
nitrogenated
level of exchange. after
on the and
Furthermore, being used
can be made.
catalyst
of interpreting
on hydrogen-Y
to the
of the catalyst
spectroscopy
possibilities.
adsorbed
and/or
of coke is deposited
observations
of the difficulty
of the different
white
increasing
by
it can be
such as hydroxylamine,
that the most
is the adsorption
7), the following
ClObJ, _":e cyclohexanone-oxime 3640 cm
indicate
by the still almost
is analysed
(Figure
of coke on the catalyst
a very small amount
of the decay constant
if the zeolite
(4000-1350
reaction
is plotted,
time on-stream.
of very basic products,
Two facts
producing
after
with
in the region the spectra
studied
we must
According
to Butler
and Poles
zeolite
interacts
with the
hydroxyl band of the zeolite, and its spectrum shows two bands -1 -1 at 1700 cm and 2700 cm assigned to v(C=N+) and v(N+-H), respectively.
.
,.
, _
~, ,_ ^
FIGURE 6
-
g
Total
0
, 60
_^
,
__.-
,
,
,
, T.0.S (min)
loo 120 140 160
-
(CT) vs. time on-stream
60
HNaY-3
conversion
,
40
,
20
(T.O.S.)
I
’
’
’
for the different
I
zeolite
Catalysts.
199
Wavenumber FIGURE 7
(Cm-l)
IR spectrum of HNaY-4 catalyst
after
reaction.
As both the 1700 and 2700 cm-' stretching
bands are absent
(Figure
oxime must
7), the presence
On the other hand, with
the presence
of cyclohexanone
of a band at about
[lob], and therefore
and water, at1650cm adsorbed
The v(NH)
it is masked
band at 1540 cm-'
by the v(CO)
(amide
and &(HOH)
II)
is very
of &-caprolactam
&-caprolactam. the band appearing
to NH stretching consequently
vibrations
The presence
at about
of amines
infer the probable
on the surface
in the spectrum Only a weak
3300, 3150 and 3050 cm
and u(=C-H)
presence
-1
can be assigned
of the aromatic
of aniline
ring. We can
and methylpyridine
adsorbed
of the zeolite. of 5-cyanopent-I-ene
ruled out, as the characteristic
band in this region
on the highly
band of nitriles
of 5-cyanopent-1-ene
adsorbed
is detected
exchanged at about
zeolites must be -1 2280 cm that appears
on HY zeolites
in the zeolites
[23] is not visible. with a high sodium
(Nay and HNaY-1).
On the other hand, (Table 3), decreases by considering nitroqenated amount
of E-caprolactam must be associated -1 [v(CO)] and a complex band centred 1650 cm
respectively. In the spectrum we observe a very strong band centred -1 -1 that may correspond to the , and a more complex band at 1450 cm
Finally,
content
be ruled out.
the IR absorption
at 1450 cm -' (uCH, CH2 scissor). weak
in the catalyst
the decay of the catalysts, with
compounds,
of these products
exchange
increasing
that aniline,
of the zeolite
level of exchange.
methylpyridine,
are responsible formed
measured
increases.
These
hydroxylamine
for the catalyst
per gram of catalyst
by their decay results
constants
are explained
and, in general, poisoning,
decreases
basic
and that the
when the level of
200 it can be said that the Beckman
In conclusion,
oxime on HNaY zeolites to this reaction, the active
5-cyanopent-l-ene
sites of this reaction
Na+ ions located is increased to primary
the behaviour
stable.
decay
(hydroxylamine,
is formed
which
is explained
aniline
coke on the catalyst
by fragmentation
changes
of the reactant, but also the of the zeolite
from primary
by considering
takes place at low levels
is due to poisoning
of cyclohexanone
When the level of exchange
of c-caprolactam
This result
rearrangement
by Brllnsted acid sites of pKa 5 1.5, Parallel
being not only the acid sites,
in the supercavity.
of 5-cyanopent-I-ene catalyst
is catalysed
plus secondary
a consecutive
of exchange.
reaction
Finally,
of the acid sites by the basic products
and methylpyridine),
rather
than to the deposition
the formed of
surface.
REFERENCES 1
9 10
1: 13 14 15 1; 18 :: 21 22 23
Badische Aniline und Soda Fabrik. Ger. Pat., 1.186.612 (Cl. c07d) Jan. 21 (1965). Farbenfabriken Bayer, Fr. Pat. 2.016.341 (1970). Mobil Oil Corporation, Neth. Pat. Appl. 6.514.009 (1966). Toray Industries, Japan Kokai 7633,914 (1976). British Petroleum Brit. Pat. 881.276 (1959). D. England, U.S. Pat. 2.634.269, April (1953). J. Garritsen and J. Ottenheim, U.S. Pat. 2,827,476 (1958). C.J. Planck, E.J. Rosinski and W.P. Wawthorne, Ind. Enq. Chem. Prod. Res. Dev., 3 (1964) 165. P.S. Landis and P.B. Venuto, J. Catal., 6 (1966) 245. a) J.D. Butler and T.C. Poles. J. Chem. Sot.. Perkin II (1973) 1,262. b) J. Chem. Sot. Perkin II (1973) 41. J.W. Ward, J. Catal., 10 (1968) 34. J.W. Ward, J. Catal., 13 (1969) 321. Mobil Oil Corporation, U.S. Pat. 225.157 (1981). H.A.Benesi, J. Amer. Chem. Sot., 78 (1956) 549. H.A. Benesi, J. Phys. Chem., 61 (1957) 970. D.R. Campbell and B.W. Wojciechowski, Cand. J. Chem. Eng., 48 (1970) 224. A. Corma, R. Cid and A. Lopez Agudo, Can. J. Chem. Eng., 57 (1979) 638. T.R. Hughes and H.M. White, J. Phys. Chem., 71 (1967) 2192. P.A. Jacobs "Carboniogenic Activity of Zeolites", Elsevier, Amsterdam (1977 1. A. Costa, P.M. Deya and J.V. Sinisterra, Can. J. Chem., 58 (1980) 1266. Rabo, Edit., (1976). J.W. Ward, "Zeolite Chemistry and Catalysis", J.A. Von E. Schmitz, R. Ohme, S. Schramm, H. Striegler, H.U. Heyne and J. Rusche Prakt. Chemie, 319 (1977) 195. J.D.Butler and T.C. Poles, 3. Chem. Sot., Perkin II (1973) 1976.