Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CONTINUOUS PROCESS FOR PREPARING ETHYLBENZENE USING
LIQUID PHASE ALKYLATION AND VAPOR PHASE TRANSALKYLATION
The present invention relates to a process for
' preparing ethylbenzene using liquid phase alkylation and
vapor phase transalkylation.
Ethylbenzene is a valuable commodity chemical which is
currently used on a large scale industrially for the
production of styrene monomer. Ethylbenzene may be
produced by a number of different chemical processes but
one process which has achieved a significant degree of
commercial success is the vapor phase alkylation of benzene
with ethylene in the presence of a solid, acidic ZSM-5
zeolite catalyst. In the production of ethylbenzene by
this process, ethylene is used as the alkylating agent and
is reacted with benzene in the presence of the catalyst at
temperatures Which vary between the critical temperature of
benzene up to 900°F (480°C) at the reactor inlet. The
reactor bed temperature may be as much as 150°F (65°C)
above the reactor inlet temperature and typical
temperatures for the benzene/ ethylene reaction vary from
600° to 900°F (315° to 480°C), but are usually
maintained
above 700°F (370°C) in order to keep the content of the
more highly alkylated benzenes such as diethylbenzene at an
acceptably low level. Pressures typically vary from
atmospheric to 3000 prig (20785 kPa abs) with a molar ratio
of benzene to ethylene from 1:1 to 25:1, usually 5:1
(benzene:ethylene). Space velocity in the reaction is
high, usually in the range of 1 to 6, typically 2 to 5,
WHSV based on the ethylene flow, with the benzene space
velocity varying accordingly, in proportion to the ratio of
the reactants. The products of the reaction include
ethylbenzene which is obtained in increasing proportions as
temperature increases together with various
polyethylbenzenes, principally diethylbenzene (DIEB) which
also are produced in increasing amounts as reaction
temperature increases. Under favorable operating
conditions on the industrial scale, an ethylene conversion
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in excess of 99.8 weight percent may be obtained at the
start of the cycle.
In the commercial operation of this process, the
polyalkylated benzenes, including both polymethylated and
v
polyethylated benzenes are recycled to the alkylation
reactor in which the reaction between the benzene and the
ethylene takes place. By recycling the by-products to the
alkylation reaction, increased conversion is obtained as
the polyethylated benzenes (PEB) are converted to
ethylbenzene (EB). In addition, the presence of the PEB
during the alkylation reaction reduces formation of these
species through equilibration of the components because at
a given feed composition and under specific operating
conditions, the PEB recycle will reach equilibrium at a
certain level. This commercial process is known as the
Mobil/Badger process and is described in more detail in an
article by Francis G. Dwyer, entitled "Mobil/Badger
Ethylbenzene Process-Chemistry and Catalytic Implications",
appearing on pages 39-50 of a book entitled Catalysis of
Organic Reactions, edited by William R. Moser, Marcel
Dekker, Inc., 1981.
Ethylbenzene production processes are described in
U.S. Patents Nos. 3,751,504 4,547,605: and 4,016,218. The
process described in U.S. 3,751,504 is of particular note
since it includes a separate transalkylation step in the
recycle loop which is effective for converting a
significant proportion of the more highly alkylated
products to the desired ethylbenzene product. Other
processes for the production of ethylbenzene are disclosed
in U. S. Patents Nos. 4,169,111 and 4,459,426, in both of
which a preference for large-pore size zeolites such as
zeolite Y is expressed, in distinction to the intermediate-
pore size zeolites used in the processes described in U.S.
Patent Nos 3,751,504 4,547,605; and 4,016,218. U.S.
Patent No. 3,755,483 describes a process for the production
of ethylbenzene using zeolite ZSM-12 as the alkylation
catalyst.
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Ethylbenzene (EB) can be synthesized from benzene and
ethylene (C2=) over a variety of zeolitic catalysts in
either the liquid phase or in the vapor phase. An
advantage of a liquid phase process is its low operating
temperature and the resulting low content of by-products.
U.S. Patent No. 4,891,458 describes the liquid phase
synthesis of ethylbenzene with zeolite Beta.
U.S. Patent No. 5,149,894 describes the liquid phase
synthesis of ethylbenzene with a crystalline
aluminosilicate material designated SSZ-25.
U.S. Patent No. 5,334,795 describes the liquid phase
synthesis of ethylbenzene with a crystalline
aluminosilicate material designated MCM-22.
Current commercial processes for preparing
ethylbenzene (EB) conduct both alkylation and
transalkylation steps in the same phase, i.e., either both
steps in the vapor phase or both steps in the liquid phase.
In the vapor phase commercial process, higher temperatures
are required to maintain vapor phase conditions. At the
temperatures employed in these vapor phase conditions,
considerable quantities of xylene impurities are formed.
Since the boiling point for xylenes is very close to the
boiling point for ethylbenzene, the ethylbenzene product
from such an all vapor phase process exceeds 700 ppm of
xylene impurities. Eariler versions of the previously
mentioned Mobil/Badger process may produce an ethylbenzene
product having 1200-1600 ppm of xylene impurities. These
xylene impurities, which coboil with ethylbenzene, may
contaminate downstream products derived from ethylbenzene,
such as styrene and polystyrene.
The lower operating temperature required for the all
liquid phase process produces less than 100 ppm xylene
- byproducts, but it has now been discovered that certain
feed impurities in the form of benzene coboilers, when
~ present in the benzene feed, will tend to accumulate in the
all liquid phase system over time. It has further been
discovered that certain alkylation byproducts, particularly
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C~-benzenes and C,-benzenes, tend to accumulate over time in
the a17. liquid phase system.
Less expensive sources of benzene, which are
practicable for use as fresh feedstocks to the present
process, have considerable levels of impurities. These
impurities are difficult to separate from benzene by
distil7_ation, because they have boiling points close to the
boiling point of benzene. These difficultly separable
impurities are referred to herein as benzene coboilers.
These benzene coboilers include hydrocarbons having from 5
to 7 carbon atoms. These hydrocarbon impurities include
cycloaJ_iphatic, paraffinic, olefinic and aromatic
compounds. Particularly problematic benzene coboilers
include cyclohexane and methylcyclopentane. Toluene is
another particular example of a benzene coboiler which may
be present. Altogether, these benzene coboilers may be
present in 500-700 ppm levels in benzene sources suitable
for use as fresh feeds to the present process.
These benzene coboilers are largely inert under the
lower temperature liquid phase conditions. Expensive
separation procedures are required to satisfactorily remove
these coboilers from benzene. However, if these coboilers
are not removed, they will build up in the system, because
as benzene is reacted in the system it must be replaced by
fresh Need and each introduction of fresh feed introduces
more inert benzene coboilers to the all liquid phase
system.
In addition to the problem of benzene coboiler build-
up cawed by continuous introduction of these impurities
along with fresh benzene feed, a net production of such
coboilers can be realized in the all liquid phase process
as a result of ethylene oligomerization reactions in the
liquid phase alkylation reactor. More particularly, ,
ethylene may trimerize to form hexene, which, in turn may
undergo cyclization reactions to form cyclohexane and/or ,
methylcyclopentane. Ethylene oligomerization reactions in
the alkylation reactor can also be the root cause of the
generation of other problematic impurities in the all
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liquid phase system. These impurities comprise C9 and Clo
aromatics, especially propylbenzene and butylbenzene.
Butylbenzene may be formed in the alkylation reactor when
ethylene first dimerizes to form butene, which, in turn,
alkylates benzene. Each ethylene trimer (i.e., hexene) can
also exist in an equilibrium state with 2 molecules of
propylene, which, in turn, can also alkylate benzene to
form propylbenzene.
The C9 and Clo aromatic impurities tend to build-up
primarily in the polyethylbenzene recycle loop to the
transalkylation reactor of the all liquid phase system.
However, when these impurities are generated in sufficient
levels they can permeate the entire system. In the all
liquid phase system, the primary route for removal of the
C9 and Clo aromatic impurities is by further alkylation or
transalkylation with ethyl groups, followed by rejection
from the system as heavies. These side reactions result in
a net consumption of ethylene and can reduce overall liquid
yields by up to 2%.
As a result of the build-up of impurities in the all
liquid phase system, these impurities tend to be carried
over into the recovered ethylbenzene product. More
particularly, in a typical all liquid phase system, the
ethylbenzene product obtained from the all liquid phase
system may contain 600 ppm of benzene coboilers and 80o ppm
of C9 and Clo aromatics .
All vapor phase processes, such as the Mobil/Badger
process, produce an ethylbenzene product which contains
little or no (e.g., less than 50 ppm) benzene coboilers and
C9 and Clo aromatics. Under the high temperature operating
conditions of the all vapor phase process, benzene
coboilers and C9 and Clo aromatics are cracked and rejected
~ as lights. However, as mentioned previously, the
ethylbenzene product from the all vapor phase system will
- contain at least 700 ppm of xylene impurities. In summary,
a typical ethylbenzene product from an all vapor phase
system will contain at least 70o ppm xylene, no benzene
coboilers and no C9 and Clo aromatics, whereas a typical
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ethylbenzene product from an all liquid phase system will
contain at less than 100 ppm xylene, 600 ppm benzene
coboilers and 800 ppm C9 and Clo aromatics.
The present invention involves a liquid phase
alkylation step coupled with a vapor phase transalkylation
step. The present liquid phase alkylation/vapor phase
transal.kylation system achieves low levels of all of the
above-mentioned impurities (i.e., xylene, benzene coboilers
and Cs and Clo aromatics) in the ethylbenzene product
without: the need for prohibitively expensive separation
schemes. The separators employed in the present system may
be comparable in scale to those employed in the
Mobil/fiadger all vapor phase system.
The present invention resides in a process for
preparing ethylbenzene, said process comprising the steps
of
(a) contacting benzene and ethylene with a solid oxide
catalyst in a liquid phase alkylation reaction zone under
sufficient liquid phase conditions to generate ethylbenzene
product and byproducts comprising diethylbenzene; and
(b) contacting said diethylbenzene byproduct from step
(a) and benzene with a solid oxide catalyst in a vapor
phase transalkylation reaction zone under sufficient vapor
phase conditions to generate an effluent comprising another
ethylbenzene product,
wherein benzene feed which is introduced into said
vapor phase transalkylation zone of step (b) comprises
nonbenzene hydrocarbons having from 5 to 7 carbon atoms,
and wherein said nonbenzene hydrocarbons having from 5 to 7
carbon atoms are converted to hydrocarbons having a
different boiling point in said transalkylation zone, and
wherein unreacted benzene is recycled in said alkylation
zone and in said transalkylation zone.
In particular, this process may be a continuous
process for preparing ethylbenzene, said process comprising _
the steps of:
(a) introducing benzene, benzene coboilers, and
ethylene into a liquid phase alkylation reaction zone,
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wherein said benzene and said ethylene are reacted in the
presence of an alkylation catalyst under sufficient liquid
phase conditions to generate an effluent comprising
ethylbenzene product, unreacted benzene, unreacted benzene
coboilers, and byproducts comprising diethylbenzene and
butylbenzene, said alkylation catalyst comprising an acidic
solid oxide selected from the group consisting of MCM-22,
MCM-49 and MCM-56;
(b) passing the effluent from said liquid phase
alkylation reaction zone of step (a) to a separation zone,
wherein said effluent is separated into separate streams
comprising (i) a light stream comprising benzene and
benzene coboilers, (ii) an intermediate product stream, and
(iii) a heavy stream comprising diethylbenzene and
butylbenzene:
(c) passing said heavy stream (iii) from step (b)
along with benzene and benzene coboilers to a vapor phase
transalkylation reaction zone, wherein said benzene and
diethylbenzene are reacted in the presence of a
transalkylation catalyst under sufficient vapor phase
conditions to generate an effluent comprising another
ethylbenzene product and unreacted benzene, said
transalkylation catalyst comprising a medium-pore size
zeolite:
(d) passing the effluent from said vapor phase
transalkylation reaction zone to the separation zone of
step (b), wherein said effluent is separated into separate
streams comprising (i) a light stream comprising unreacted
benzene, (ii) an intermediate product stream, and (iii) a
heavy stream comprising unreacted diethylbenzene:
(e) recycling unreacted benzene along with benzene
coboilers recovered in separation steps (b) and (d) in a
~ closed recycle loop to said alkylation reactor of step (a)
and to said transalkylation reactor of step (c):
- (f) introducing fresh benzene feed into said benzene
recycle loop at a rate sufficient to make up for benzene
converted in said alkylation zone and in said
transalkylation zone, wherein said fresh benzene comprises
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.g.
impurities comprising benzene coboiling nonbenzene
hydrocarbons having from 5 to 7 carbon atoms, said benzene
coboiling hydrocarbons being at least partially converted
to hydrocarbons having a different boiling point in said
. transalkylation zone of step (c), and butylbenzene being at
least partially converted to one or more different
hydrocarbons in said transalkylation zone of step (c): and
(g) recovering an ethylbenzene product from the
intermediate product stream of steps (b) and (d), the
recovered ethylbenzene product comprising less than 200 ppm
xylene, less than 100 ppm of hydrocarbons having 7 or less
carbon atoms and less than 100 ppm of hydrocarbons having 9
or more carbon atoms.
In the present liquid-vapor phase process, alkylation
takes place at low temperatures in the liquid phase,
thereby generating little or no xylene. In the vapor phase
transalkylation reaction, propylbenzene, butylbenzene and
benzene coboilers are converted to hydrocarbons having
different boiling points by a variety of reactions,
including cracking, dealkylation, alkylation (e. g., with
cracked fragments), and transalkylation. Benzene generated
by these reactions is recycled, whereas other conversion
products are rejected from the system as lights or heavies.
Only a small amount of xylene is produced in the
transalkylation reaction.
The recovered ethylbenzene product from the present
system may have less than 200 ppm xylene, less than 100 ppm
of hydrocarbons having 7 or less carbon atoms and less than
100 ppm of hydrocarbons having 9 or more carbon atoms.
The fresh benzene feed for the present system may
contain considerable amounts of impurities in the form of
benzene coboilers. More particularly, elemental analysis
of the benzene feed may reveal the presence of at least 500 ,
ppm of nonbenzene hydrocarbons having from 5 to 7 carbon
atoms. -
The present alkylation and transalkylation reaction
take place in separate zones. Each of these zones may
comprise a single reactor or more than one reactor
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connected in series. Preferably, these zones are each
encompassed within a single alkylation reactor and a single
transalkylation reactor.
The catalyst used in the present process comprises at
least one acidic solid oxide. Examples of such acidic
solid oxides include aluminosilicates and materials, such
as SAPO's, which contain oxides of elements other than
silicon and aluminum. These acidic solid oxides may be
amorphous or crystalline materials. The crystalline
materials may have non-layered, 3-dimensional framework
structures, or layered structures, such as the layered
structures of clays. Preferred acidic solid oxides are
zeolites, particularly medium-pore size and large-pore size
zeolites.
The catalyst for the present liquid phase alkylation
reaction may comprise a medium- or large-pore size zeolite.
Particular examples of acidic solid oxides which may be use
to catalyze the alkylation reaction include MCM-22, MCM-36,
MCM-49, MCM-56, zeolite Beta, zeolite X, zeolite Y, and
mordenite. Of these crystalline materials, MCM-22, MCM-49
and MCM-56 are particularly preferred.
The catalyst for the present vapor phase
transalkylation reaction may comprise a medium- or large-
pore size zeolite. Particular examples of acidic solid
oxides which may be use to catalyze the transalkylation
reaction include MCM-22, ZSM-5, ZSM-11, ZSM-12, ZSM-22,
ZSM-23, ZSM-35, ZSM-48 and ZSM-50. Of these crystalline
materials, ZSM-5 is particularly preferred.
A convenient measure of the extent to which a zeolite
provides control of access to molecules of varying sizes to
its internal structure is the Constraint Index of the
zeolite. Zeolites which provide a highly restricted access
~ to and egress from its internal structure have a high value
for the Constraint Index, and zeolites of this kind usually
- have pores of small size, e.g., less than 5 Angstroms. On
the other hand, zeolites which provide relatively free
access to the internal zeolite structure have a low value
for the Constraint Index, and usually pores of large size,
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e.g., greater than 8 Angstroms. The method by which
Constraint Index is determined is described fully in U.S.
Patent No. 4,016,218.
A zeolite which may be used in the present reaction
may be a medium- or large-pore size zeolite. This zeolite
may have a Constraint Index of 12 or less. Zeo.lites having
a Constraint Index of 2-12 are generally regarded to be
medium-pore size zeolites. Zeolites having a Constraint
Index of less than 1 are generally regarded to be large-
pore s3_ze zeolites. Zeolites having a Constraint Index of
1-2 may be regarded as either medium- or large-pore size
zeolites.
Examples of zeolites having a Constraint Index of from
1 to 12 include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-
35, ZSM-38, and ZSM-48.
ZSM-5 is described in U.S. Patent Nos. 3,702,886 and
Re. 29,.948. ZSM-11 is described in U.S. Patent No.
3,709,979. ZSM-12 is described in U.S. Patent No.
3,832,449. ZSM-22 is described in U.S. Patent No.
4,556,477. ZSM-23 is described in U.S. Patent No.
4,076,842. ZSM-35 is described in U.S. Patent No.
4,016,245. ZSM-38 is described in U.S. Patent No.
4,406,859. ZSM-48 is described in U.S. Patent No.
4,234,231.
The large-pore zeolites, including those zeolites
having a Constraint Index less than 2, are well known to
the art and have a pore size sufficiently large to admit
the vast majority of components normally found in a feed
chargestock. The zeolites are generally stated to have a
pore size in excess of 7 Angstroms and are represented by
zeolites having the structure of, e.g., Zeolite Beta,
Zeolite Y, Ultrastable Y (USY), Dealuminized Y (Deal Y),
Mordenite, ZSM-3, ZSM-4, ZSM-18, and ZSM-20. A crystalline ,
silicate zeolite well known in the art and useful in the
present invention is faujasite. The ZSM-20 zeolite
resembles faujasite in certain aspects of structure, but
has a notably higher silica/alumina ratio than faujasite,
as does Deal Y.
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Zeolite ZSM-14 is described in U.S. Patent No.
3,923,636. Zeolite ZSM-20 is described in U.S. Patent No.
3,972,983. Zeolite Beta is described in U.S. Patent Nos.
3,308,069 and Re. No. 28,341. Low sodium Ultrastable Y
. molecular sieve (USY) is described in U.S. Patent Nos.
3,293,192 and 3,449,070. Dealuminized Y zeolite (Deal Y)
may be prepared by the method found in U.S. Patent No.
3,442,795. Zeolite UHP-Y is described in U.S. Patent No.
4,401,556.
A particular acidic solid oxide, which may be use to
catalyze either the present liquid phase alkylation
reaction or the present vapor phase transalkylation
reaction, is MCM-36. MCM-36 is a pillared layered material
having zeolitic layers. For the purposes of the present
disclosure, MCM-36 shall be considered to be a zeolite.
MCM-36 is described in U.S. Patent Nos. 5,250,277 and
5,292,698. U.S. Patent No. 5,258,565 describes the
synthesis of alkylaromatics, including ethylbenzene, using
a catalyst comprising MCM-36.
As mentioned hereinabove, MCM-22, MCM-49 and MCM-56
are particularly preferred acidic solid oxides for
catalyzing the present liquid phase alkylation reaction.
These crystalline oxides may also be used to catalyze the
present vapor phase transalkylation reaction. MCM-22 and
its use to catalyze the synthesis of alkylaromatics,
including ethylbenzene, is described in U.S. Patent Nos.
4,992,606: 5,077,445; and 5,334,795. MCM-49 is described
in U.S. Patent No. 5,236,575. The use of MCM-49 to
catalyze the synthesis of alkylaromatics, including
ethylbenzene, is described in U.S. Patent No. 5,371,310.
MCM-56 is described in U.S. Patent No. 5,362,697. The use
of MCM-56 to catalyze the synthesis of alkylaromatics,
including ethylbenzene, is described in U.S. Patent No.
5,453,554. MCM-56 is believed to be a layered material
- with zeolitic layers. For the purposes of the present
disclosure, MCM-56 shall be considered to be a zeolite.
The acidic solid oxide crystals can be shaped into a
wide variety of particle sizes. Generally speaking, the
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particles can be in the form of a powder, a granule, or a
molded product such as an extrudate having a particle size
sufficient to pass through a 2 mesh (Tyler) screen and be
retained on a 400 mesh (Tyler) screen. In cases where the
catalyst is molded, such as by extrusion, the crystals can
be extruded before drying or partially dried and then
extruded.
The crystalline material may be composited with
another material which is resistant to the temperatures and
other conditions employed in the process of this invention.
Such materials include active and inactive materials and
synthetic or naturally occurring zeolites as well as
inorganic materials such as clays and/or oxides such as
alumina, silica, silica-alumina, zirconia, titania,
magnesia or mixtures of these and other oxides. The latter
may be either naturally occurring or in the form of
gelatinous precipitates or gels including mixtures of
silica and metal oxides. Clays may also be included with
the oxide type binders to modify the mechanical properties
of the catalyst or to assist in its manufacture. Use of a
material in conjunction with the solid crystal, i.e.,
combined therewith or present during its synthesis, which
itself is catalytically active may change the conversion
and/or selectivity of the catalyst. Inactive materials
suitably serve as diluents to control the amount of
conversion so that products can be obtained economically
and orderly without employing other means for controlling
the rate of reaction. These materials may be incorporated
into naturally occurring clays, e.g., bentonite and kaolin,
to improve the crush strength of the catalyst under
commercial operating conditions and function as binders or
matrices for the catalyst. The relative proportions of
finely divided crystalline material and inorganic oxide
matrix vary widely, with the crystal content ranging from 1
to 90 percent by weight and more usually, particularly when
the composite is prepared in the form of beads, in the
range of 2 to 80 weight percent of the composite.
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The alkylation reaction is carried out in the liquid
phase. Suitable conditions can be selected by reference to
the phase diagram for benzene.
In the liquid phase, the reaction is carried out with
the benzene feedstock in the liquid phase with the reaction
., conditions (temperature, pressure) appropriate to this end.
Liquid phase operation may be carried out at
temperatures between 300° and 552°F (150° to
289°C),
usually in the range of 400° to 500°F (205° to
260°C).
Pressures during the alkylation step may be as high as
3000 psig, (20875 kPa abs) and generally will not exceed
1000 psig (7000 kPa). The reaction may be carried out in
the absence of hydrogen and accordingly the prevailing
pressures are those of the reactant species. In a high
pressure liquid phase operation, the temperature may be
from 300° to 552°F (149°C to 289°C) with the
pressure in
the range of 2800 to 5600 kPa (400 to 800 psig). The space
velocity may be from 0.1 to 20 WHSV, based on the ethylene
feed, although lower space velocities are preferred for the
liquid phase reaction, for example, from 0.5 to 3 WHSV,
e.g., from 0.75 to 2.0 WHSV (ethylene). The ratio of the
benzene to the ethylene in the alkylation reactor may be
from 1:1 to 30:1 molar, normally 5:1 to 20:1 and in most
cases from 5:1 to 10:1 molar.
The alkylation process can be carried out as a
continuous operation utilizing a fixed, fluidized or moving
bed catalyst system.
Particular conditions for carrying out the liquid
phase alkylation step may include a temperature of from
150°C to 260°C, a pressure of 7000 kPa or less,~a WHSV
based on ethylene of from 0.5 to 2.0 hrl, and a mole ratio
of benzene to ethylene of from 1:1 to 30:1.
The vapor phase transalkylation step may be carried
out at a temperature of from 260°C to 482°C, a pressure of
from 450 to 3500 kPa (50 to 500 psig), a WHSV based on the
weight of the total vapor feed to the reaction zone of from
1 to 50 hrl, and a mole ratio of benzene to diethylbenzene
of from 1 to 50.
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The benzene feed to the transalkylation reactor may
comprise at least 100 ppm, e.g., at least 200 ppm, of
benzene coboilers, especially in the form of nonbenzene
hydrocarbons having from 5 to 7 carbon atoms per molecule.
In the present vapor phase transalkylation step,
ethylbenzene is believed to be produced by an actual
transal.kylation reaction involving both benzene and
polyethylbenzenes (e. g., diethylbenzene) as reactants.
However, it is also possible that at least some
ethylbenzene is generated by straight dealkylation of
polyethylbenzenes during this step.
When conducting alkylation, various types of reactors
can be used. Large scale industrial processes may employ a
fixed-bed reactor operating in an upflow or downflow mode
or a moving-bed reactor operating with concurrent or
countercurrent catalyst and hydrocarbon flows. These
reactors may contain a single catalyst bed or multiple beds
and may be equipped for the interstage addition of ethylene
and interstage cooling. Interstage ethylene addition and
more nearly isothermal operation enhance product quality
and catalyst life. A moving-bed reactor makes possible the
continuous removal of spent catalyst for regeneration and
replacement by fresh or regenerated catalysts.
In a particular embodiment of the present invention,
the alkylation process is carried out with addition of
ethylene in at least two stages. Preferably, there will be
two or more catalyst beds or reactors in series, wherein at
least a portion of the ethylene is added between the
catalyst beds or reactors. Interstage cooling can be
accomplished by the use of a cooling coil or heat
exchanger. Alternatively, interstage cooling can be
effected by staged addition of the benzene feedstock in at
least two stages. In this instance, at least a portion of
the benzene feedstock is added between the catalyst beds or
reactors, in similar fashion to the staged addition of _
ethylene described above. The staged addition of benzene
feedstock provides additional cooling to compensate for the
heat of reaction.
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In a fixed-bed re~rctor or moving-bed reactor,
alkylation is completed in a relatively short reaction zone
following the introduction of ethylene. Ten to thirty
percent of the reacting benzene molecules may be alkylated
. more than once. Transalkylation is a slower reaction which
occurs in the alkylation zone. If transalkylation proceeds
to equilibrium, better than 90 wt.~ selectivity to
monoalkylated product is generally achieved. Thus,
transalkylation increases the yield of monoalkylated
product by reacting the polyalkylated products with
additional benzene.
The alkylation reactor effluent contains the excess
benzene feed, monoalkylated product, polyalkylated
products, and various impurities. The benzene feed is
recovered by distillation and recycled to the alkylation
and transalkylation reactors. A small bleed may be taken
from the recycle stream if needed to eliminate unreactive
impurities from the loop. However, since benzene coboilers
are eliminated via the present vapor phase transalkylation
step, this bleeding process is substantially less needed
than in an all liquid phase alkylation/transalkylation
process. Since little or no benzene needs to be bled out
of the present benzene recycle loop, benzene can be
essentially recycled to extinction in the present process.
The percentage of ethylene converted in the liquid
phase alkylation step may be at least 950, e.g., at least
97~. The weight ratio of ethylbenzene to diethylbenzene
produced in the liquid phase alkylation step may be from 2
to 30.
When MCM-22, MCM-49 or MCM-56 is chosen as the acidic
solid oxide to catalyze the present liquid phase alkylation
reaction, the reaction is highly selective for the
production of ethylbenzene. More particularly, this
alkylation product may comprise at least 92 wt~ of
- ethylbenzene, with less than 7 wt% of diethylbenzene and
less than 1 wt~, e.g., less than 0.5 wt~, of
triethylbenzene. In the present liquid phase alkylation
step, MCM-22, MCM-49 and MCM-56 are believed to be
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substantially more active than zeolite Y. Therefore, the
MCM-22, MCM-49 or MCM-56 catalyzed reaction requires less
catalyst and a smaller alkylation reactor for a given level
of throughput than a zeolite Y catalyzed reaction. ,
Furthermore, at the end of a reaction cycle, the catalyst
containing MCM-22, MCM-49 or MCM-56 can be regenerated in
to in the alkylation reactor, whereas other catalysts may
require removal from the reactor for regeneration, due to
the large catalyst inventory and possible local overheat
during the regeneration process.
Th.e.medium-pore size zeolites, especially ZSM-5, used
in the present vapor phase transalkylation step, are more
shape selective than large-pore size zeolites, such as USY,
used as. catalysts for liquid phase transalkylations.
Consequently, the present vapor phase transalkylation step,
catalyzed by medium-pore size zeolites, produces less
heavies (e. g., C11+ hydrocarbons) than liquid phase
transalkylations catalyzed with large-pore size zeolites.
The present liquid-vapor phase reaction system may
comprise one or more separation zones situated downstream
from the reaction zones. Preferably, the products from
both the liquid phase alkylation zone and the vapor phase
transal.kylation zone are passed into a single separation
zone. This separation zone may comprise a series of three
distillation columns. In a first distillation column, the
products from the alkylation zone and the transalkylation
zone are introduced as a feed and benzene is recovered as
an overhead stream. The recovered benzene overhead stream
is recycled as a reactant to both the liquid phase
alkylat:ion zone and the vapor phase transalkylation zone.
The bottoms from the first distillation column are passed
as a feed to a second distillation column. Ethylbenzene
product is recovered as an overhead stream, and the bottoms
from the second distillation column are passed as a feed
stream to a third distillation column. Diethylbenzenes and _
triethylbenzenes are recovered as an overhead stream from
the third distillation column, and this stream comprising
diethylbenzene may be passed as a reactant stream to the
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transalkylation zone. The bottoms from the third
distillation column are rejected from the system as
heavies.
The separation zone for the present liquid-vapor phase
system may be essentially the same as those illustrated in
the art for all liquid phase or all vapor phase systems.
Such a separation zone for an all liquid phase system is
illustrated in U.S. Patent No. 4,169,111, and such a
separation zone for an all vapor phase is illustrated in
Figure 3 on page 45 of the article by Francis G. Dwyer,
entitled °'Mobil/Badger Ethylbenzene Process-Chemistry and
Catalytic Implications'°, appearing on pages 39-50 of a book
entitled Catalysis of Orctanic Reactions, edited by William
R. Moser, Marcel Dekker, Inc., 1981.
Fresh benzene feed is preferably introduced into the
present system directly into the separation zone or at a
point immediately upstream from the separation zone. When
fresh benzene is introduced into the system in this manner,
the benzene, which is introduced into both the liquid phase
alkylation zone and the vapor phase transalkylation zone,
is essentially a mixture of recycled benzene and fresh fed
benzene.
Figure 1 is a graph showing a comparison of the
activity of MCM-22, MCM-49, MCM-56 and zeolite Beta for
catalyzing the liquid phase synthesis of ethylbenzene.
Figure 2 is a graph showing a comparison of the
selectivity of MCM-22, MCM-49, MCM-56 and zeolite Beta for
catalyzing the liquid phase synthesis of ethylbenzene.
Example 1
2.0 g of an MCM-22 catalyst (~4 cc 1/16°' extrudate,
sized to 1/16°° length, 35% alumina binder, 620 alpha value,
' 25 Si02/A1203) was mixed with ~20 cc of 20-40 mesh quartz
chips, and then charged to an isothermal, down-flow, fixed-
bed reactor. The catalyst was dried at 125°C and 1 atm
with 50 cc/min of flowing N2 for 2 hours. NZ was turned
off. Benzene was fed into the reactor at 16.7 WHSV for 1
hour and then at 8.35 WHSV while the reactor temperature
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and pressure were increased to 150°C and 500 psig,
respectively. After the desired temperature and pressure
were reached, ethylene was introduced from a mass flow
controller at 0.55 WHSV (5.5 benzene/ethylene molar ratio). ,
After lining out, liquid products were collected in a cold-
trap and analyzed off-line with a Varian 3700 GC. Offgas .
was analyzed with an on-line Carle refinery gas analyzer.
Ethylene conversion was determined by measuring unreacted
ethylene in the offgas relative to feed ethylene. Total
material balances were 100~2%. During the 18 day
experiment, the effects of temperature (200-320°C),
ethylene WHSV (1.1 to 2.2 h-1) and benzene/ethylene molar
ratio (4.5-6.5) were studied all at 3550 kPa (500 psig).
The catalyst activity and selectivity for liquid phase
ethylbenzene synthesis are compared with those of MCM-49,
MCM-56,. and zeolite Beta in Example 7. At the end of the
run, no activity loss was observed.
Example 2
4.0 g of the same MCM-22 catalyst (-8 cc, mixed with
--16 cc of 20-40 mesh quartz chips) was used for this run
also at 3550 kPa (500 psig). The reaction was brought on
stream similarly to what was described in Example 1. The
initial conditions were 182°C, 0.55 ethylene WHSV, and 5.5
benzene/ethylene molar ratio. Ethylene conversion
decreased from 94 to 82% over 5 days at 182°C. Increasing
reactor temperature did not yield stable ethylene
conversion until 210°C. At 220°C, the ethylene conversion
stabilized at 97-98% for 18 days without aging. Liquid
products obtained at 220°C and 97-98% ethylene conversion
were nearly identical to what was observed from Example 1
at similar conditions.
Example 3
Although no aging was observed at 220°C in Example 2,
the catalyst was subjected to a regeneration procedure at
the end of the stability study to assess its robustness.
The catalyst was regenerated in situ at 100 kPa (1 atm) in
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a mixture of air and NZ (total flow of 200 cc/min): 25% of
air for 30 minutes at 400°C; 50%, 75% and 100% of air for
30 minutes each at 450°C; then 100% air at 538°C far 2
hours. The temperature was decreased to 220°C. The
regenerated catalyst was then tested for 5 days under
conditions identical to those before regeneration: 220°C,
3550 kPa (500 psig), 0.55 ethylene WHSV, and 5.5
benzene/ethylene molar ratio. The regenerated catalyst was
slightly more active reaching 98-99% ethylene conversion
(97-98% before regeneration). The DEB/EB molar ratio also
increased slightly after regeneration from 0.05 to 0.07.
Example 4
2.0 g of an MCM-49 catalyst (-4 cc 1/16" extrudate,
sized to 1/16'° length, 35% alumina binder, 910 alpha value,
18 SiOz/A120" mixed with 20 cc of 20-40 mesh quartz chips)
was tested similarly to what was described for MCM-22 in
Example 1. Benzene was fed into the reactor at 30 WHSV for
1 hour and then at 16.7 WHSV while the reactor temperature
and pressure were increased to 220°C and 3550 kPa (500
psig), respectively. After reaching 220°C and 3550 kPa
(500 psig), ethylene was introduced at 1.1 WHSV (5.5
benzene/ethylene molar ratio). During the 25 day
experiment, the effects of temperature (200-320°C),
ethylene WHSV (1.1 to 2.2 h-1) and benzene/ethylene molar
ratio (4.5-6.5) were studied all at 3550 kPa (500 psig).
The catalyst activity and selectivity for liquid phase
ethylbenzene synthesis are compared with those of MCM-22,
MCM-56, and zeolite Beta in Example 7. At the end of the
run, the catalyst was tested again at conditions identical
to those used at the beginning of the run. No activity
loss was observed.
Example 5
- 1.0 g of an MCM-56 catalyst (2 cc 1/16" extrudate,
sized to 1/16", 35% alumina binder, 400 alpha value, 18
Si02/A1203, mixed with ~10 cc of 20-40 mesh quartz chips)
was tested similarly to what was described for MCM-22 in
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Example 1. Benzene was fed into the reactor at 45 WHSV for
1 hour and then at 16.7 WHSV while the reactor temperature
and pressure were increased to 220°C and 3550 kPa (500
psig), respectively. After reaching 220°C and 3550 kPa
(500 psig), ethylene was introduced at 1.1 WHSV (5.5
benzene/ethylene molar ratio). During the 13 day ,
experiment, the effects of temperature (200-320°C) and
ethylene WHSV (1.1 to 2.8 h-1) were studied at 3550 kPa (500
psig) and ~5.5 benzene/ethylene molar ratio. The catalyst
activity and selectivity for liquid phase ethylbenzene
synthesis are compared with those of MCM-22, MCM-49, and
zeolite Beta in Example 7. At the end of the run, the
catalyst was tested again at conditions identical to those
used at the beginning of the run. No activity loss was
observed.
Example 6
2.0 g of a zeolite-Beta catalyst (-4 cc 1/16"
extrudate, sized to 1/16" length, 35~ alumina binder, 690
alpha value, 43 Si02/A1203, mixed with 20 cc of 20-40 mesh
quartz chips) was tested similarly to what was described
for MCM-22 in Example 1. Benzene was fed into the reactor
at 30 WHSV for 1 hour and then at 25 WHSV while the reactor
temperature and pressure were increased to 160°C and 3550
(500 psig), respectively. After reaching 160°C and
3550 kPa (500 psig), ethylene was introduced at 1.65 WHSV
(5.5 benzene/ethylene molar ratio). At 160°C, ethylene
conversion declined from 97 to 74~ in 4 days and continued
to dec7_ine thereafter. Increasing temperature to 180°C did
not recover catalyst activity. The catalyst was air
regenerated using procedures described in Example 3 and was
brought: on stream again at 220°C, 3550 kPa (500 psig), 1.65
ethylene WHSV, and 5.5 benzene/ethylene molar ratio. The
catalyst was then tested under various conditions to study
the effects of temperature (180-320°C), ethylene WHSV (1.1 .
to 3.3 h-1), and benzene/ethylene molar ratio (4.5-6.5) at
3550 kPa (500 psig). Stable and 97+~ ethylene conversion
was achieved at 180°C, 1.1 ethylene WHSV, and 5.5
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benzene/ethylene molar ratio. The catalyst activity and
selectivity for liquid phase ethylbenzene synthesis are
compared with those ~of MCM-22,y MCl~-49, ~ and MCM-56 in
t Example 7. At the end of the run, the catalyst was tested
.again at conditions identical to those used at the
beginning of the run. No activity loss was observed.
Example 7
Figure 1 compares catalyst activity at 220°C, 3550 kPa
(500 psig), and 5.5 benzene/ethylene molar ratio. At
constant ethylene conversion (e. g., 95%), the relative
catalyst activity is:
MCM-22: MCM-49: MCM-56: zeolite Beta = 1.0: 1.2: 1.6: 2.2
Table 1 indicates that at 96+% CZ= conversion, MCM-22,
MCM-49, and MCM-56's overall alkylation selectivities to EB
and polyethylbenzene (99.9 mol%) are all higher than that
of zeolite Beta. The EB selectivities of MCM-22, MCM-49,
and MCM-56 (93-95 mol%) are 5-7 mol$ higher than zeolite
Beta. MCM-22, MCM-49, and MCM-56 made less
polyethylbenzene and less non-EB by-products than zeolite
Beta.
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Table :L. Ethylbenzene Synthesis - Selectivity Comparison
Cataly:~t/ MCM-22 MCM-49 MCM-56 Zeolite
I 35% A1203
Beta
C2' WHS'V 1.1 1.1 1.65 2.2
CZ- Conversion,% 96.6 97.1 96.2 97.0
Product distr.
(mol % )
EB 94.0 95.3 93.7 88.0
DEB 5.7 4.5 6.0 10.6
TEB+ 0.2 0.1 0.2 1.1
99.9 99.9 99.9 99.7
xylenes 0.00 0.00 0.00 0.00
n-C3-Bz+cumene o.00 0.00 0.00 0.00
sec-C,~-Bz 0.07 0.06 0.04 0.13
aromatics 0.02 0.02 0.02 _0.14
other C
9
E (by products) 0.09 0.09 0.06 0.27
220 ° C, 3550 KYa, aria 5 . 5 nenzene/ w2= llLUld1 lat.lv
Catalyst selectivities (further represented as DEB/EB
molar ratio) at other temperatures are compared in Figure
2. In the liquid phase (<260°C at 3550 kPa), MCM-22, MCM-
49, and MCM-56 catalysts made less DEB than zeolite Beta.
At 220°C, MCM-22, MCM-49, and MCM-56 made -50% less DEB
than zeolite Beta.
Example 8
After distillation, the polyethylbenzene (PEB) rich
bottoms product is mixed with benzene (recovered by a prior
distillation step) and processed in the transalkylation
reactor in the vapor phase over a medium pore zeolite such "
as ZSM-5. Transalkylation conditions are typically 335-
350°C (635-662°F), 930 kPa (120 psig), 40 total WHSV
(benzene and PEB), and 3:1 benzene/PEB weight ratio. Under
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these conditions, DEB conversion per pass is >_45~. The
products are sent to the distillation section for benzene
and incremental EB recovery, and PEB is recycled to the
transalkylator. The resultant EB quality from the overall
process is excellent (<200 ppm xylenes, no benzene
coboilers, and no C9 and Clo aromatics).
