U.S. patent application number 12/119171 was filed with the patent office on 2008-10-02 for alkylation process.
This patent application is currently assigned to FINA TECHNOLOGY, INC.. Invention is credited to James R. Butler, Kevin P. Kelly.
Application Number | 20080242906 12/119171 |
Document ID | / |
Family ID | 36932745 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080242906 |
Kind Code |
A1 |
Butler; James R. ; et
al. |
October 2, 2008 |
Alkylation Process
Abstract
A process for the production of ethylbenzene by the ethylation
of benzene in the critical phase in a reaction zone containing a
molecular sieve aromatic alkylation catalyst comprising
cerium-promoted zeolite beta. A polyethylbenzene is supplied into
the reaction zone and into contact with the cerium-promoted zeolite
beta having a silica/alumina mole ratio within the range of 20-500.
The reaction zone is operated at temperature and pressure
conditions in which benzene is in the supercritical phase to cause
ethylation of the benzene and the transalkylation of
polyethylbenzene and benzene in the presence of the zeolite beta
catalyst. An alkylation product is produced containing ethylbenzene
as a primary product with the attendant production of heavier
alkylated byproducts of no more than 60 wt. % of the ethylbenzene.
The alkylation reaction zone is operated under conditions providing
a composite byproduct yield of propyl benzene and butyl benzene
relative to ethylbenzene, which is no more than one half of the
corresponding yield byproduct for zeolite beta promoted with
lanthanum. The production of ethylbenzene in the critical phase
alkylation reaction zone is attended by recycle of a polyalkylated
aromatic component of the reaction product back to the reaction
zone.
Inventors: |
Butler; James R.; (League
City, TX) ; Kelly; Kevin P.; (Friendswood,
TX) |
Correspondence
Address: |
FINA TECHNOLOGY INC
PO BOX 674412
HOUSTON
TX
77267-4412
US
|
Assignee: |
FINA TECHNOLOGY, INC.
Houston
TX
|
Family ID: |
36932745 |
Appl. No.: |
12/119171 |
Filed: |
May 12, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11066951 |
Feb 25, 2005 |
7371911 |
|
|
12119171 |
|
|
|
|
Current U.S.
Class: |
585/323 |
Current CPC
Class: |
C07C 6/126 20130101;
Y02P 20/544 20151101; C07C 2/66 20130101; Y02P 20/54 20151101; C07C
2/66 20130101; C07C 15/073 20130101; C07C 6/126 20130101; C07C
15/073 20130101 |
Class at
Publication: |
585/323 |
International
Class: |
C07C 2/58 20060101
C07C002/58 |
Claims
1.-20. (canceled)
21. A process for the production of ethylbenzene comprising:
providing an alkylation reaction zone containing cerium-promoted
zeolite beta molecular sieve alkylation catalyst; introducing a
feed stock comprising an aromatic substrate and an alkylating agent
into an inlet of said alkylation reaction zone, and operating said
alkylation reaction zone at liquid phase conditions to cause
alkylation of said aromatic substrate in the presence of said
crystalline alkylation catalyst and to minimize the yield of
undesirable byproducts, thereby producing an alkylation product
comprising a mixture of said aromatic substrate and monoalkylated
and polyalkylated aromatic components; supplying the alkylation
product comprising a mixture of the aromatic substrate and
monoalkylated and polyalkylated aromatic components to a recovery
zone for separation of monoalkylated and polyalkylated aromatic
components from said unreacted aromatic substrate; supplying at
least a portion of the recovered polyalkylated aromatic component
including said dialkyl benzene to a transalkylation reaction zone
containing a cerium-promoted zeolite beta molecular sieve
transalkylation catalyst after using one or more intermediate
separation stages for the recovery of ethylene, ethylbenzene, and
polyethylbenzene; supplying benzene to said transalkylation zone;
and operating said transalkylation zone under liquid phase
temperature and pressure conditions to cause disproportionation of
said polyalkylated aromatic to produce a disproportionation
product.
22. The process of claim 21 wherein ethylene is supplied to said
reaction zone in an amount to provide a benzene/ethylene mole ratio
within the range of 1-15.
23. The process of claim 22 wherein the benzene to ethylene mole
ratio is less than 10.
24. The process of claim 22 wherein the benzene to ethylene mole
ratio is within the range of 2-5.
25. The method of claim 21 wherein said zeolite beta has a
silica/alumina mole ratio within the range of 50-150.
26. The process of claim 21 wherein said zeolite beta has a
cerium/aluminum atomic ratio within the range of 0.5-1.5.
27. The process of claim 21 wherein said reaction zone is operated
at temperature and pressure conditions in which ethylbenzene is in
the liquid phase.
28. The method of claim 1 wherein said alkylation reaction zone is
operated at temperature and pressure conditions to provide a
composite byproduct yield of propylbenzene and butylbenzene which
is less than the corresponding composite byproduct yield of
propylbenzene and butylbenzene for a zeolite beta promoted with
lanthanum at a lanthanum/aluminum atomic ratio at least equal to
the cerium-aluminum atomic ratio of said cerium-promoted zeolite
beta catalyst under the same temperature and pressure
conditions.
29. The method of claim 1 wherein said alkylation reaction zone is
operated at temperature and pressure conditions to provide a
composite byproduct yield of propyl benzene and butyl benzene which
is no more than one half of the corresponding byproduct yield of
propyl benzene and butyl benzene for a zeolite beta catalyst
promoted with lanthanum at a lanthanum/aluminum atomic ratio at
least equal to the cerium/aluminum atomic ratio of said catalyst
under the same temperature and pressure conditions.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the production of ethylbenzene and
more particularly to the ethylation of benzene and the
transalkylation of polyethylbenzene and benzene over a
cerium-promoted beta alkylation catalyst under conditions in which
the benzene is in the supercritical phase.
BACKGROUND OF THE INVENTION
[0002] The alkylation of benzene with ethylene over a molecular
sieve catalyst is a well known procedure for the production of
ethylbenzene. Typically, the alkylation reaction is carried out in
a multistage reactor involving the interstage injection of ethylene
and benzene to produce an output from the reactor that involves a
mixture of monoalkyl and polyalkylbenzenes. The principal
monoalkylbenzene is, of course, the desired ethylbenzene product.
Heavier byproducts, which are generally undesirable, include
polyalkylbenzenes such as diethylbenzene, triethylbenzene, xylenes
and diphenyl products such as 1,1 diphenyl ethane.
[0003] In many cases, it is desirable to operate the alkylation
reactor in conjunction with the operation of a transalkylation
reactor in order to produce additional ethylbenzene through the
transalkylation reaction of polyethylbenzene with benzene. The
alkylation reactor can be connected to the transalkylation reactor
in a flow scheme involving one or more intermediate separation
stages for the recovery of ethylene, ethylbenzene, and
polyethylbenzene.
[0004] Transalkylation may also occur in the initial alkylation
reactor. In this respect, the injection of ethylene and benzene
between stages in the alkylation reactor not only results in
additional ethylbenzene production, but also promotes
transalkylation within the alkylation reactor in which benzene and
diethylbenzene react through a disproportionation reaction to
produce ethylbenzene.
[0005] Various phase conditions may be employed in the alkylation
and transalkylation reactors. Typically, the transalkylation
reactor will be operated under liquid phase conditions, i.e.,
conditions in which the benzene and polyethylbenzene are in the
liquid phase, and the alkylation reactor is operated under gas
phase conditions, i.e., pressure and temperature conditions in
which the benzene is in the gas phase. However, liquid phase
conditions can be used where it is desired to minimize the yield of
undesirable byproducts from the alkylation reactor.
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention, there is provided
a process for the production of ethylbenzene by the ethylation of
benzene in the critical phase in a reaction zone containing a
molecular sieve aromatic alkylation catalyst comprising
cerium-promoted zeolite beta. In addition, a polyethylbenzene is
supplied into the reaction zone and into contact with the
cerium-promoted zeolite beta. Preferably, the zeolite beta has a
silica/alumina mole ratio within the range of 20-500 and more,
preferably within the range of 50-150. Ethylene is supplied to the
alkylation reaction zone in an amount to provide a benzene/ethylene
mole ratio of 1-15. The reaction zone is operated at temperature
and pressure conditions in which benzene is in the supercritical
phase to cause ethylation of the benzene and the transalkylation of
polyethylbenzene and benzene in the presence of the zeolite beta
catalyst. An alkylation product is produced containing ethylbenzene
as a primary product with the attendant production of heavier
alkylated byproducts. Such byproducts normally will be no more than
60 wt. % of the ethylbenzene. The alkylation product is recovered
from the reaction zone for further use or processing. Preferably,
the alkylation reaction zone is operated under temperature and
pressure conditions providing a composite byproduct yield of propyl
benzene and butyl benzene relative to ethylbenzene, which is no
more than one half of the corresponding yield byproduct for zeolite
beta promoted with lanthanum.
[0007] The production of ethylbenzene in the critical phase
alkylation reaction zone is attended by recycle of a polyalkylated
aromatic component of the reaction product back to the reaction
zone. The alkylation reaction zone is operated at temperature and
pressure conditions at which benzene is in the super critical phase
to cause ethylation of the benzene in the presence of the
cerium-promoted zeolite beta and to produce an alkylation product
comprising a mixture of benzene, ethylbenzene, and polyalkylated
aromatics, including diethylbenzene. The alkylation product is
recovered from the alkylation reaction zone and supplied to a
separation and recovery zone. In the recovery zone, ethylbenzene is
separated and recovered from the product. A polyalkylated component
including diethylbenzene is also separated from the product. At
least a portion of the polyalkylated aromatic component, including
diethylbenzene, is recycled to the critical phase reactor zone. In
one embodiment of the invention, another portion of the
polyalkylated product is supplied to a separate transalkylation
reaction zone containing a molecular sieve transalkylation
catalyst. Benzene is also supplied to the transalkylation reaction
zone, and the transalkylation reaction zone is operated under
temperature and pressure conditions to cause disproportionation of
the polyalkylated aromatic fraction to produce a disproportionation
product having a reduced diethylbenzene content and an enhanced
ethylbenzene content. Preferably, the transalkylation reaction zone
contains a zeolite Y catalyst and is operated under conditions to
maintain the polyalkylated aromatic component in the liquid phase.
Preferably, the cerium-promoted zeolite beta has a cerium/aluminum
ratio within the range of 0.25-5.0, more preferably 0.5-1.5.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is an idealized schematic block diagram of an
alkylation/transalkylation process embodying the present
invention.
[0009] FIG. 2 is a schematic illustration of a preferred embodiment
of the invention incorporating separate parallel-connected
alkylation and transalkylation reactors with an intermediate
multi-stage recovery zone for the separation and recycling of
components.
[0010] FIG. 3 is a schematic illustration of an alkylation reactor
comprising a plurality of series connected catalyst beds with the
interstate injection of feed components.
[0011] FIG. 4 is a schematic block diagram of another embodiment of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The present invention involves the critical phase alkylation
of benzene over a cerium-promoted zeolite beta alkylation catalyst
coupled with transalkylation of benzene and polyethylbenzene under
conditions to control and desirably minimize the yield of
byproducts in the reaction zone. The feedstock supplied to the
alkylation reaction zone comprises benzene and ethylene. Typically,
the benzene and ethylene streams will be combined to provide a
benzene-ethylene mixture into the reaction zone. The benzene
stream, which is mixed with the ethylene either before or after
introduction into the reaction zone, should be a relatively pure
stream containing only very small amounts of contaminants. The
benzene stream should contain at least 90 wt. % benzene.
Preferably, the benzene stream will be at least 95 wt. % benzene,
and more preferably at least 98 wt. % benzene, with only trace
amounts of such materials as toluene, ethylbenzene, and C.sub.7
aliphatic compounds that cannot readily be separated from benzene.
The alkylation/transalkylation reaction zone is operated under
supercritical conditions, that is, pressure and temperature
conditions which are above the critical pressure and critical
temperature of benzene. Specifically, the temperature in the
alkylation zone is at or above 300.degree. C., and the pressure is
at or above 715 psia. Preferably, the temperature in the alkylation
reactor will be maintained at an average value within the range of
275-350.degree. C. and a pressure within the range of 750-850 psia.
If desired higher alkylation temperatures can be employed since the
cerium-promoted zeolite beta retains its structural integrity at
temperatures of about 530-540.degree. C. Zeolite beta which has not
been promoted with cerium tends to lose its structural integrity as
the temperature reaches 500.degree. C. The critical phase
alkylation reaction is exothermic with a positive temperature
gradient from the inlet to the outlet of the reactor, providing a
temperature increment increase of about 40.degree..+-.10.degree.
C.
[0013] The operation of the alkylation reaction zone in the
supercritical region enables the alkylation zone to be operated
under conditions in which the benzene-ethylene mole ratio can be
maintained at relatively low levels, usually somewhat lower than
the benzene-ethylene mole ratio encountered when the alkylation
reaction zone is operated under liquid phase conditions. In most
cases, the benzene-ethylene mole ratio will be within the range of
1-15. Preferably, the benzene mole ratio will be maintained during
at least part of a cycle of operation at a level within the lower
end of this range, specifically, at a benzene-ethylene mole ratio
of less than 10. A benzene-ethylene mole ratio within the range of
2-8, and preferably 2-5, may be employed. Thus, operation in the
supercritical phase offers advantages similar to those achieved by
gas phase alkylation, in which the benzene-ethylene ratio can be
kept low, but without the problems associated with byproduct
formation, specifically xylene formation, often encountered in
gas-phase alkylation. At the same time, operation in the
supercritical phase offers the advantages accruing to liquid phase
alkylation in which the byproduct yield is controlled to low
levels. The pressures required for operation in the supercritical
phase are not substantially greater than those required in liquid
phase alkylation, and the benzene in the supercritical phase
functions as a solvent to keep the zeolite beta catalyst clean and
to retard coking leading to deactivation of the catalyst.
[0014] The cerium-promoted beta enables super critical phase
alkylation to be carried out with byproducts that are substantially
less than the corresponding byproducts produced with super critical
phase alkylation employing lanthanum-promoted zeolite beta of
similar or greater metal content. Thus, the alkylation reaction
zone can be operated at supercritical phase temperature and
pressure conditions to provide a composite byproduct yield of
propylbenzene and butylbenzene which is less than the corresponding
composite byproduct yield of propylbenzene and butylbenzene for a
corresponding zeolite beta catalyst promoted with lanthanum at a
lanthanum/beta atomic ratio at least as great as the
cerium/aluminum atomic ratio of the cerium-promoted zeolite beta.
Preferably, the alkylation reaction zone is operated at temperature
and pressure conditions to provide a composite product yield of
propylbenzene and butylbenzene which is no more than one-half of
the corresponding composite byproduct yield of propylbenzene and
butylbenzene produced with the lanthanum-promoted zeolite beta.
[0015] Turning now to FIG. 1, there is illustrated a schematic
block diagram of an alkylation/transalkylation process employing
the present invention. As shown in FIG. 1, a product stream
comprising a mixture of ethylene and benzene in a mole ratio of
benzene to ethylene of about 1 to 15 is supplied via line 1 through
a heat exchanger 2 to an alkylation/transalkylation reaction zone
4. Reaction zone 4 preferably comprises one or more multi-stage
reactors having a plurality of series-connected catalyst beds
containing a cerium-promoted zeolite beta alkylation catalyst as
described herein. The alkylation zone 4 is operated at temperature
and pressure conditions to maintain the alkylation reaction in the
supercritical phase, i.e. the benzene is in the supercritical
state, and at a feed rate to provide a space velocity enhancing
ethylbenzene production while retarding byproducts production.
Preferably, the space velocity of the benzene feed stream will be
within the range of 10-150 hr..sup.-1 LHSV per bed.
[0016] The output from the alkylation reactor 4 is supplied via
line 5 to an intermediate benzene separation zone 6 that may take
the form of one or more distillation columns. Benzene is recovered
through line 8 and recycled through line 1 to the alkylation
reactor. The bottoms fraction from the benzene separation zone 6,
which includes ethylbenzene and polyalkylated benzenes including
polyethylbenzene, is supplied via line 9 to an ethylbenzene
separation zone 10. The ethylbenzene separation zone may likewise
comprise one or more sequentially connected distillation columns.
The ethylbenzene is recovered through line 12 and applied for any
suitable purpose, such as in the production of vinyl benzene. The
bottoms fraction from the ethylbenzene separation zone 10, which
comprises polyethylbenzene, principally diethylbenzene, is supplied
via line 14 for recycle to reactor 4 where it is employed in a
transalkylation reaction with benzene supplied to the reactor.
[0017] Upon recycle of the polyethylbenzene to the reactor, the
following concurrent reactions occur over the cerium-promoted
zeolite beta catalyst. Ethylene reacts with benzene to produce
ethylbenzene, usually accompanied by the production of smaller
amounts of diethyl benzene and even smaller amounts of
triethylbenzene. In addition, benzene reacts in a transalkylation
reaction with diethyl benzene, and possibly with smaller amounts of
triethylbenzene, in order to produce ethylbenzene. A side reaction
can involve the reaction of ethylene and benzene to produce
1,1-diphenylethane. The conditions are controlled in the reactor so
that the reactor temperature is above the critical temperature and
pressure of benzene so that the benzene is in the supercritical
phase. The ethylbenzene may be in either the liquid or
supercritical phase, but usually will be in the liquid phase. The
heavier aromatics such as polyethylbenzene will normally be in the
liquid phase, that is, the reactor temperature is below the
critical temperature for the diethylbenzene and other
polyethylbenzenes. Under severe reactor conditions, the temperature
may be sufficient to maintain the ethylbenzene in the critical
phase as well as maintaining the benzene in the critical phase. The
heavier polyethylbenzenes or polynuclear compounds such as
1,1-diphenylethane will, in any case, normally be in liquid
phase.
[0018] Referring now to FIG. 2, there is illustrated in greater
detail a suitable system incorporating a multi-stage intermediate
recovery zone for the separation and recycling of components
involved in the critical phase alkylation and transalkylation
process. As shown in FIG. 2, an input feed stream is supplied by
fresh ethylene through line 31 and fresh benzene through line 32.
As noted previously, the fresh benzene stream supplied via line 32
preferably is of high purity containing at least 98 wt. %,
preferably about 99 wt. % benzene with no more than 1 wt. % other
components. Preferably, the fresh benzene stream will contain about
99.5 wt. % benzene, less than 0.5% ethylbenzene, with only trace
amounts of non-aromatics and toluene. Line 32 is provided with a
preheater 34 to heat the benzene stream consisting of fresh and
recycled benzene to the desired temperature for the supercritical
alkylation reaction. The feed stream is supplied through a two-way,
three-position valve 36 and inlet line 30 to the top of one or both
parallel critical phase alkylation/transalkylation reactors 38 and
38a comprising a plurality of series connected catalyst beds each
of which contains the desired molecular sieve alkylation catalyst.
The reactors are operated at an average temperature, preferably
within the range of 275-350.degree. C. inlet temperature and at
pressure conditions of about 715 to 800 psia, to maintain the
benzene in the critical phase. As mentioned previously, because of
the high temperature structural integrity of cerium-promoted
zeolite beta, the alkylation reaction zone can be operated at
temperatures of up to about 500.degree. C. and even beyond that to
temperatures of about 540.degree. C.
[0019] In normal operation of the system depicted in FIG. 2, both
reaction zones 38 and 38a may, during most of a cycle of operation,
be operated in a parallel mode of operation in which they are both
in service at the same time. In this case, valve 36 is configured
so that the input stream in line 30 is roughly split in two to
provide flow to both reactors in approximately equal amounts.
Periodically, one reactor can be taken off-stream for regeneration
of the catalyst. Valve 36 is then configured so that all of the
feed stream from line 30 can be supplied to reactor 38 while the
catalyst beds in reactor 38a are regenerated and vise versa. The
regeneration procedure will normally take place over a relatively
short period of time relative to the operation of the reactor in
parallel alkylation mode. The regeneration procedure preferably is
carried out at temperatures substantially in excess of those
normally employed in the regeneration of zeolite beta-type
catalysts. When regeneration of the catalyst beds in reactor 38a is
completed, this catalyst can then be returned on-stream and at an
appropriate point, the reactor 38 can be taken off-stream for
regeneration. This mode of operation involves operation of the
individual reactors at relatively lower space velocities for
prolonged periods of time with periodic relatively short periods of
operation at enhanced, relatively higher space velocities when one
reactor is taken off-stream. By way of example, during normal
operation of the system with both reactors 38 and 38a on-stream,
the benzene in the feed stream is supplied to each reactor to
provide a space velocity of about 25-45 hr..sup.-1 LHSV. When
reactor 38a is taken off-stream and the feed rate continues
unabated, the space velocity for reactor 38 will approximately
double to 50-90 hr..sup.-1 LHSV. When the regeneration of reactor
38a is completed, it is placed back on-stream and again the feed
stream rate space velocity for each reactor will decrease to 25-45
hr..sup.-1 until such point as reactor 38 is taken off-stream, in
which case the flow rate to reactor 38a will, of course, increase,
resulting again in a transient space velocity in reactor 38 of
about 50-90 hr..sup.-1 LHSV.
[0020] A preferred reactor configuration is shown in detail in FIG.
3. As illustrated there, the reactor 38 comprises five series
connected catalyst beds designated as beds A, B, C, D and E. A
polyethylbenzene, benzene and ethylene feed stream is supplied to
the top of the reactor and into Bed A. An ethylene feed stream is
supplied via line 39 and proportionating valves 39a, 39b and 39c to
provide for the appropriate interstage injection of ethylene.
Benzene and diethylbenzene can also be introduced between the
catalyst stages by means of secondary benzene supply lines 41a, 41b
and 41c, respectively. As will be recognized, the parallel reactor
38a will be configured with similar manifolding as shown in FIG. 3
with respect to reactor 38.
[0021] Returning to FIG. 2, the effluent stream from one or both of
the alkylation reactors 38 and 38a is supplied through a two-way,
three-position outlet valve 44 and outlet line 45 to a two-stage
benzene recovery zone which comprises as the first stage a
prefractionation column 47. Column 47 is operated to provide a
light overhead fraction including benzene which is supplied via
line 48 to the input side of heater 34 where it is mixed with
benzene in line 32 and then to the alkylation/transalkylation
reactor input line 30. A heavier liquid fraction containing
benzene, ethylbenzene and polyethylbenzene is supplied via line 50
to the second stage 52 of the benzene separation zone. Stages 47
and 52 may take the form of distillation columns of any suitable
type, typically columns having from about 20-60 trays. The overhead
fraction from column 52 contains the remaining benzene which is
recycled via line 54 to the alkylation reactor input. Thus, lines
48 and 54 correspond to the output line 8 of FIG. 1. The heavier
bottoms fraction from column 52 is supplied via line 56 to a
secondary separation zone 58 for the recovery of ethylbenzene. The
overhead fraction from column 58 comprises relatively pure
ethylbenzene which is supplied to storage or to any suitable
product destination by way of line 60. By way of example, the
ethylbenzene may be used as a feed stream to a styrene plant in
which styrene is produced by the dehydrogenation of ethylbenzene.
The bottoms fraction containing polyethylbenzenes, heavier
aromatics such as cumene and butyl benzene, and normally only a
small amount of ethylbenzene is supplied through line 61 to a
tertiary polyethylbenzene separation zone 62. As described below,
line 61 is provided with a proportioning valve 63 which can be used
to divert a portion of the bottoms fraction for recycling back
directly to the alkylation transalkylation reactor. The bottoms
fraction of column 62 comprises a residue, which can be withdrawn
from the process via line 64 for further use in any suitable
manner. The overhead fraction from column 62 comprises a
polyalkylated aromatic component containing diethylbenzene and a
smaller amount of triethylbenzene and a minor amount of
ethylbenzene is recycled to the alkylation/transalkylation reaction
zone. By minimizing the amount of ethylbenzene recovered from the
bottom of column 58, the ethylbenzene content of the
polyethylbenzene stream recycled to the critical phase reactor can
be kept small in order to drive the transalkylation reaction in the
critical phase reactor in the direction of ethylbenzene production.
The polyethylbenzene fraction withdrawn overhead from column 62 is
recycled back to the alkylation/transalkylation reactor via line
66. The weight ratio of benzene to polyethylbenzene should be at
least 1:1 and preferably is within the range of 1:1 to 4:1.
[0022] Returning to the operation of the separation system, in one
mode of operation the entire bottoms fraction from the ethylbenzene
separation column 58 is applied to the tertiary separation column
62 with overhead fractions from this zone then recycled to the
alkylation/transalkylation reactor. This mode of operation offers
the advantage of relatively long cycle lengths of the catalyst in
the reactor between regeneration of the catalyst to increase the
catalyst activity. Another mode of operation of the invention
achieves this advantage by supplying a portion of the output from
the ethylbenzene separation column 58 through valve 63 directly for
recycle to the alkylation/transalkylation reactor.
[0023] As shown in FIG. 2, a portion of the bottoms fraction from
the secondary separation zone 58 bypasses column 62 and is recycled
directly to the alkylation/transalkylation reactor via valve 63 and
line 88. A second portion of the bottoms fraction from the
ethylbenzene column is applied to the tertiary separation column 62
through valve 63 and line 90. The overhead fraction from column 62
is withdrawn via line 66 and commingled with the bypass effluent in
line 88 and the resulting mixture is fed to the alkylation
transalkylation reactor via line 67. In this mode of operation a
substantial amount of the bottoms product from column 58 can be
recycled directly to the alkylation transalkylation reactor,
bypassing the polyethylbenzene column 62. Normally, the weight
ratio of the first portion recycled via line 88 directly to the
alkylation transalkylation reactor to the second portion supplied
initially via line 90 to the polyethylbenzene column would be
within the range of about 1:2 to about 2:1. However, the relative
amounts may vary more widely to be within the range of a weight
ratio of the first portion to the second portion in a ratio of
about 1:3 to 3:1.
[0024] The molecular sieve catalyst employed in the critical phase
alkylation reactor is a zeolite beta catalyst that can be a
conventional zeolite beta modified by the inclusion of cerium as
described below. The cerium-promoted zeolite beta catalyst will
normally be formulated in extrudate pellets of a size of about 1/8
inch or less, employing a binder such as silica or alumina. A
preferred form of binder is silica, which results in catalysts
having somewhat enhanced deactivation and regeneration
characteristics than zeolite beta formulated with a conventional
alumina binder. Typical catalyst formulations may include about 20
wt. % binder and about 80 wt. % molecular sieve.
[0025] The cerium-promoted zeolite beta employed in the critical
phase alkylation transalkylation reactor can be a zeolite beta of
the type described in U.S. Pat. No. 3,308,069 to Wadlinger or U.S.
Pat. No. 4,642,226 to Calvert, which has been modified by the
inclusion of cerium in the crystalline framework. The
cerium-promoted zeolite beta employed in the present invention can
be based on a high silica/alumina ratio zeolite beta or a ZSM-12
modified zeolite beta as described in U.S. Pat. No. 5,907,073 to
Ghosh, the entire disclosure of which is incorporated herein by
reference.
[0026] Basic procedures for the preparation of zeolite beta are
well known to those skilled in the art. Such procedures are
disclosed in the aforementioned U.S. Pat. Nos. 3,308,069 to
Wadlinger et al and 4,642,226 to Calvert et al. and European Patent
Publication No. 159,846 to Reuben, the entire disclosure of which
are incorporated herein by reference. The zeolite beta can be
prepared to have a low sodium content, i.e. less than 0.2 wt. %
expressed as Na.sub.2O and the sodium content can be further
reduced to a value of about 0.02 wt. % by an ion exchange
treatment.
[0027] As disclosed in the above-referenced U.S. patents to
Wadlinger et al., and Calvert et al., zeolite beta can be produced
by the hydrothermal digestion of a reaction mixture comprising
silica, alumina, sodium or other alkyl metal oxide, and an organic
templating agent. Typical digestion conditions include temperatures
ranging from slightly below the boiling point of water at
atmospheric pressure to about 170.degree. C. at pressures equal to
or greater than the vapor pressure of water at the temperature
involved. The reaction mixture is subjected to mild agitation for
periods ranging from about one day to several months to achieve the
desired degree of crystallization to form the zeolite beta. Unless
steps are taken to minimize the alumina content, the resulting
zeolite beta is normally characterized by a silica to alumina molar
ratio (expressed as SiO.sub.2/Al.sub.2O.sub.3) of between about 20
and 50.
[0028] The zeolite beta is then subjected to ion exchange with
ammonium ions at uncontrolled pH. It is preferred that an aqueous
solution of an inorganic ammonium salt, e.g., ammonium nitrate, be
employed as the ion-exchange medium. Following the ammonium
ion-exchange treatment, the zeolite beta is filtered, washed and
dried, and then calcined at a temperature between about 530.degree.
C. and 580.degree. C. for a period of two or more hours.
[0029] Zeolite beta can be characterized by its crystal structure
symmetry and by its x-ray diffraction patterns. Zeolite beta is a
molecular sieve of medium pore size, about 5-6 angstroms, and
contains 12-ring channel systems. Zeolite beta is of tetragonal
symmetry P4.sub.122, a=12.7, c=26.4 .ANG. (W. M. Meier and D. H.
Olson Butterworth, Atlas of Zeolite Structure Types, Heinemann,
1992, p. 58); ZSM-12 is generally characterized by monoclinic
symmetry. The pores of zeolite beta are generally circular along
the 001 plane with a diameter of about 5.5 angstroms and are
elliptical along the 100 plane with diameters of about 6.5 and 7.6
angstroms. Zeolite beta is further described in Higgins et al, "The
framework topology of zeolite beta," Zeolites, 1988, Vol. 8,
November, pp. 446-452, the entire disclosure of which is
incorporated herein by reference.
[0030] The cerium-promoted zeolite beta employed in carrying out
the present invention may be based upon conventional zeolite beta,
such as disclosed in the aforementioned patent to Calvert et al.
For a further description of procedures for producing zeolite beta
useful in accordance with the present invention, reference is made
to the aforementioned U.S. Pat. Nos. 3,308,069 to Wadlinger,
4,642,226 to Calvert, and 5,907,073 to Ghosh and EPA Publication
No. 507,761 to Shamshoum, the entire disclosures of which are
incorporated herein by reference.
[0031] The invention can also be carried out with a zeolite beta
having a higher silica/alumina ratio than that normally
encountered. For example, as disclosed in EPA Publication No.
186,447 to Kennedy, a calcined zeolite beta can be dealuminated by
a steaming procedure in order to enhance the silica/alumina ratio
of the zeolite. Thus, as disclosed in Kennedy, a calcined zeolite
beta having a silica/alumina ratio of 30:1 was subjected to steam
treatment at 650.degree. C. and 100% steam for 24 hours at
atmospheric pressure. The result was a catalyst having a
silica/alumina ratio of about 228:1, which was then subjected to an
acid washing process to produce a zeolite beta of 250:1. Various
zeolite betas, such as described above, can be subject to
extraction procedures in order to extract aluminum from the zeolite
beta framework by extraction with nitric acid. Acid washing of the
zeolite beta is carried out initially to arrive at a high
silica/alumina ratio zeolite beta. This is followed by
ion-exchanging cerium into the zeolite framework. There should be
no subsequent acid washing in order to avoid removing cerium from
the zeolite.
[0032] The procedure disclosed in EP 507,761 to Shamshoum, et al.
for incorporation of lanthanum into zeolite beta can be employed to
produce the cerium-promoted zeolite beta used in the present
invention. Thus cerium nitrate may be dissolved in deionized water
and then added to a suspension of zeolite beta in deionized water
following the protocol disclosed in EP 507,761 for the
incorporation of lanthanum into zeolite beta by ion exchange.
Following the ion exchange procedure, the cerium exchanged zeolite
beta can then be filtered from solution washed with deionized water
and then dried at a temperature of 110.degree. C. The powdered
cerium exchanged zeolite beta can then be molded with an aluminum
or silicon binding agent followed by extrusion into pellet
form.
[0033] In experimental work carried out respecting the present
invention alkylation/transalkylation was carried out employing a
single stage alkylation reactor. The reactor operated as a
laboratory simulation of the single stage of a multiple stage
reactor of the type illustrated in FIG. 3. In carrying out the
experimental work, a cerium-promoted zeolite beta having a silica
alumina ratio of 150 and a cerium/aluminum atomic ratio of 0.75 was
employed. This catalyst was formed employing a silica binder.
[0034] The single stage reactor was operated at a temperature
within the range of 315-325.degree. C. and at a pressure of about
750 psia. Benzene was supplied to the top of the reactor and a
product stream including unreacted benzene, ethylbenzene and
polyethylbenzene were recovered from the bottom of the reactor. The
product recovered from the reactor was split into two fractions,
one fraction being employed in an internal recycle to the reactor
and the other fraction subjected to downstream separation
procedures to recover benzene, ethylbenzene, polyethylbenzene and a
heavy residue component, which was withdrawn from the process. The
weight ratio of product fraction of ethylbenzene and
polyethylbenzenes recycled to the reactor in the internal recycle
to the fraction passed to the separation system was within the
range of 3:1 to 6:1. The separation system was operated to separate
ethyl benzene, which was withdrawn from the process, benzene and
polyethylbenzene, which were recycled to the inlet side of the
reactor. Fresh benzene and ethylene were, of course, supplied to
the top of the reactor. In operation of the experimental reactor,
the polyethylbenzene produced was monitored, and with continued
operation, approached an equilibrium condition in which no
additional polyethylbenzene was produced. Since polyethylbenzene as
well as ethylbenzene was continually produced by the alkylation
reactor with only ethylbenzene being withdrawn from the system, the
equilibration condition reached by the polyethylbenzene content
confirmed that some of the polyethylbenzene was being eliminated by
the system by a transalkylation reaction carried on concurrently
with the alkylation reaction.
[0035] While the present invention can be carried out with
transalkylation occurring only in the alkylation/transalkylation
reactor, in a further embodiment of the invention, a separate
transalkylation reactor can be employed to provide a secondary
transalkylation function. A schematic illustration of this
embodiment of the invention is illustrated in FIG. 4. In FIG. 4,
like components as shown in FIG. 1 are indicated by the same
reference numerals as employed in FIG. 1. In operation of the
system shown in FIG. 4, a first portion of the polyethylbenzene
fraction is supplied via line 14 for recycle to reactor 4 as
described previously. A second portion is split off from the
recycle line and applied via line 15 to a secondary transalkylation
reactor 16. Benzene is also supplied to the transalkylation reactor
through line 18. The transalkylation reactor, which normally will
be operated under liquid phase conditions, contains a molecular
sieve catalyst, preferably zeolite Y, which has a somewhat larger
pore size than the cerium-modified zeolite beta used in the initial
alkylation/transalkylation reaction zone. The output from the
transalkylation reactor 16, which contains the ethylbenzene product
as well as some unreacted benzene and polyethylbenzene, is recycled
via line 20 to the downstream separation system 6.
[0036] Having described specific embodiments of the present
invention, it will be understood that modifications thereof may be
suggested to those skilled in the art, and it is intended to cover
all such modifications as fall within the scope of the appended
claims.
* * * * *