U.S. patent application number 12/021323 was filed with the patent office on 2008-05-22 for process and apparatus for alkylation of aromatic with olefin using impure aromatic recycle.
Invention is credited to Lance A. Baird, Michael R. Smith, Stephen W. Sohn.
Application Number | 20080119677 12/021323 |
Document ID | / |
Family ID | 39417153 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080119677 |
Kind Code |
A1 |
Sohn; Stephen W. ; et
al. |
May 22, 2008 |
Process and Apparatus for Alkylation of Aromatic with Olefin Using
Impure Aromatic Recycle
Abstract
Processes and apparatus for the alkylation of aromatic compound
with mono-olefin aliphatic compound in the presence of solid
alkylation catalyst use a lights distillation for obtaining desired
selectivities to arylalkane in a energy efficient manner. The
processes and apparatus offer the potential for debottlenecking
existing arylalkane production facilities and reducing the size and
energy requirements for a new arylalkane production facility.
Inventors: |
Sohn; Stephen W.; (Des
Planines, IL) ; Smith; Michael R.; (Des Plaines,
IL) ; Baird; Lance A.; (Des Plaines, IL) |
Correspondence
Address: |
HONEYWELL INTELLECTUAL PROPERTY INC;PATENT SERVICES
101 COLUMBIA DRIVE
P O BOX 2245 MAIL STOP AB/2B
MORRISTOWN
NJ
07962
US
|
Family ID: |
39417153 |
Appl. No.: |
12/021323 |
Filed: |
January 29, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11042587 |
Jan 25, 2005 |
|
|
|
12021323 |
Jan 29, 2008 |
|
|
|
Current U.S.
Class: |
585/470 |
Current CPC
Class: |
Y10S 585/903 20130101;
C07C 2/66 20130101; C07C 2/66 20130101; C07C 15/107 20130101 |
Class at
Publication: |
585/470 |
International
Class: |
C07C 4/00 20060101
C07C004/00; C07C 5/00 20060101 C07C005/00 |
Claims
1. A process for the alkylation of an aromatic compound having from
6 to 8 carbon atoms per molecule with an olefin-containing
aliphatic compound having from 8 to 18 carbon atoms per molecule,
the process comprising: a. co-currently passing the aromatic
compound and the olefin-containing aliphatic compound to an
alkylation zone containing solid alkylation catalyst and operating
under alkylation conditions to produce an effluent comprising an
arylalkane and the aromatic compound, wherein the alkylation
conditions comprise a liquid phase, an alkylation pressure, and a
molar ratio of the aromatic compound passed to the alkylation zone
to the olefin-containing aliphatic compound passed to the
alkylation zone of at least about 6:1; b. distilling at least a
portion of the effluent under flash distillation conditions
including a distillation pressure that is lower than the alkylation
pressure to provide at least an overhead and a bottoms stream, the
overhead comprising from about 20 to 98 weight percent of the
aromatic compound in the at least a portion of the effluent and
arylalkane, and the bottoms stream comprising at least about 80
weight percent of the arylalkane contained in the at least a
portion of the effluent; and c. recycling at least a portion of the
overhead to the alkylation zone.
2. The process of claim 1 wherein the aromatic compound is
benzene.
3. The process of claim 2 wherein the olefin-containing aliphatic
compound comprises an olefin having from 9 to 16 carbon atoms per
molecule.
4. The process of claim 3 further characterized in that a paraffin
having from 8 to 18 carbon atoms per molecule is co-currently
passed to the alkylation zone and wherein the overhead and the
bottoms stream contain the paraffin.
5. The process of claim 4 wherein the overhead contains between
about 5 and 30 weight percent of the paraffins in the at least a
portion of the effluent.
6. The process of claim 4 wherein the effluent has a concentration
of the paraffin of less than about 50 weight percent.
7. The process of claim 6 wherein the at least a portion of the
effluent comprises substantially all of the effluent.
8. The process of claim 7 wherein the distillation pressure is
between about 80 and 250 kPa absolute.
9. The process of claim 1 wherein the molar ratio of the aromatic
compound passed to the alkylation zone to the olefin-containing
aliphatic compound passed to the alkylation zone is at least about
10:1.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a Division of prior copending
application Ser. No. 11/042,587, filed Jan. 25, 2005, which is
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to processes and apparatus for the
alkylation of aromatic compound with aliphatic mono-olefin compound
in which the aromatic compound is provided in a stoichiometric
excess and unreacted aromatic compound is recycled.
BACKGROUND TO THE INVENTION
[0003] Alkylation of aromatic compounds produces arylalkanes that
may find various commercial uses, e.g., alkylbenzenes that can be
sulfonated to produce detergents. In the alkylation process,
aromatic compound is reacted with olefin of the desired molecular
weight to produce the sought arylalkane. The alkylation conditions
comprise a catalyst such as aluminum chloride, hydrogen fluoride,
or zeolitic catalysts and elevated temperature.
[0004] The alkylation, however, is not selective and can produce
dimers, dialkylaryl compounds and diaryl compounds ("heavies") and
can affect skeletal isomerization of the olefin, resulting in a
loss of selectivity to the sought arylalkane structure. The
formation of dialkylaryl compounds is particularly problematic as
the reaction approaches complete conversion of the olefin and the
greater concentration of the arylalkane since the likelihood has
increased that an olefin molecule will react with an arylalkane
molecule rather than a molecule of the aromatic compound in the
feed. Accordingly, typical processes use a large excess of aromatic
compound to enhance selectivity to arylalkane over dialkylaryl
compound. In many instances, the mole ratio of aromatic compound to
olefin is greater than 15:1.
[0005] In order to provide an economically viable process, the
unreacted aromatic compound must be recovered from the alkylation
product and recycled. Typical commercial processes recover the
aromatic compound during refining the alkylation product through
the use of several distillation steps. For instance, see Pujado,
Linear Alkylbenzene (LAB) Manufacture, Handbook of Petroleum
Refining Processes, Second Edition, pp 1.53 to 1.66 (1996),
especially pages 1.56 to 1.60, who discloses refining processes for
linear alkylbenzenes. In general, benzene and an olefin-containing
feedstock derived from a paraffin dehydrogenation are reacted to
produce an alkylation reaction product. The reaction product is
refined. A first distillation in a benzene column separates a
benzene stream as an overhead stream for recycling to the
alkylation reactor. The bottoms stream from the benzene column is
virtually free of benzene and is then subjected to a distillation
to separate paraffins and unreacted olefin in a paraffins column.
The paraffins-containing overhead is capable of being recycled to
the paraffin dehydrogenation unit while the bottoms stream is
passed to a heavy alkylate distillation column. In the heavy
alkylate distillation column, heavies are separated from the
lighter alkylbenzene, and a heavies-containing stream is withdrawn
as a bottoms stream. If desired, the bottoms stream can be
subjected to a further distillation to recover additional
alkylbenzene.
[0006] An important consideration for commercial-scale facilities
for production of arylalkanes, especially alkylbenzene, is energy
and equipment integration. For example, reboilers for distillation
columns are conventionally heated with a thermal stream, e.g., hot
oil or other thermally-stable liquid, derived from a central
heater. The capacity of a distillation column, at a given degree of
separation, can thus be limited by the availability of thermal
fluid. For an alkylbenzene process having a refining system
comprising a benzene column, paraffins column and heavy alkylate
column, the benzene column consumes the greatest portion of the
reboiler heat. Thus the heat demand or reboiler size for the
benzene distillation can provide a bottleneck to increased capacity
at a given benzene to olefin feed ratio to the alkylation reactor.
Similarly, the size of the benzene column itself can pose a
bottleneck.
[0007] Significant economic benefits can be achieved through even
slight improvements in efficiency or reductions in energy
consumption or increases in production capacity in a given existing
plant, e.g., through debottlenecking, provided that no undue
increase in the production of heavies occurs and the arylalkyl
meets specifications after refining.
[0008] Fritsch, et al., in U.S. Pat. No. 6,069,285 disclose the use
of a benzene rectifier and a benzene fractionation column to treat
effluent from an aromatic alkylation process using solid alkylation
catalyst. The rectifier provides an overhead containing feed
aromatics and a rectifier bottom stream comprising feed aromatics
and enriched in alkylaromatics. The overhead stream from the
rectifier is recycled to an on-stream alkylation reactor. The
benzene column produces higher purity benzene-containing overhead
stream that can be used to regenerate a sorption bed to treat the
olefin-containing feed prior to being passed to the alkylation
reactor and can be used to regenerate solid alkylation catalyst in
an off-stream alkylation reactor.
[0009] Processes and apparatus are sought to effect alkylation that
reduce the size and heat demand of the distillation system to
remove aromatics from the alkylation reaction product at a given
production rate. The processes and apparatus would thus allow the
debottlenecking of existing facilities and the design of new
facilities with a smaller aromatics removal column.
SUMMARY OF THE INVENTION
[0010] In accordance with this invention, it has been found that
viable aromatic alkylation processes can be provided wherein a
portion of the aromatic compound recycled is impure. In the
processes and apparatus of this invention, a lights distillation is
used to recover a portion of the unreacted aromatic compound
contained in the effluent from an alkylation reaction zone. The
aromatic compound recovered by the lights distillation is recycled
to the alkylation reaction zone, and the remaining portion of the
unreacted aromatic compound is recovered in a subsequent
distillation. The column size and energy requirements for the
subsequent distillation are thus reduced. Because the lights
distillation need not provide a relatively pure aromatic stream,
the energy requirements and size of the lights distillation can be
commercially viable. Often, the lights distillation is effected
using less than 5 theoretical distillation trays, especially a
flash distillation. Thus, the overhead can contain appreciable
amounts of arylalkane product as well as paraffins, if paraffins
are present in the alkylation reactor effluent. Although arylalkane
can be reacted to produce heavies under alkylation conditions, the
processes of this invention can still provide an alkylation
reaction effluent without an undue amount of heavies.
[0011] In one broad aspect of the processes of this invention, the
process for the alkylation of aromatic compound of 6 to 8 carbon
atoms with an aliphatic mono-olefin of 8 to 18 carbon atoms
comprises: [0012] a. co-currently passing said aromatic compound,
said aliphatic compound and paraffin of between 8 and 18 carbon
atoms to an alkylation zone comprising solid alkylation catalyst
under liquid phase alkylation conditions to produce an effluent
comprising arylalkane, aromatic compound and paraffin, the mole
ratio of said aromatic compound to said aliphatic compound passed
to the alkylation zone being at least about 6:1, preferably at
least about 10:1 or 15:1 and said paraffin passed to said
alkylation zone being in a mole ratio to said aliphatic compound of
between about 1:1 to 20:1, preferably 8:1 to 15:1; [0013] b.
distilling a distillation feed comprising at least a portion of the
effluent of step a, said distillation being conducted with less
than about 5, preferably less than 2, theoretical distillation
trays, and most preferably flash distillation, at a pressure of
less than about 500 kPa absolute with less than about 40 kcal,
preferably less than about 30 kcal, of heat being externally
supplied per kilogram of distillation feed so as to provide an
overhead comprising between about 20 and 98, frequently between
about 50 and 95, weight percent of the aromatic compound contained
in said at least a portion of the effluent and arylalkane, and a
bottoms stream comprising aromatic compound and at least about 80,
preferably at least about 90, weight percent of the arylalkane
contained in said at least a portion of the effluent, [0014] c.
recycling the overhead from step b to the alkylation zone of step
a, and [0015] d. distilling a second distillation feed comprising
bottoms stream from step b under distillation conditions sufficient
to provide an overhead comprising aromatic compound and a bottoms
stream comprising arylalkane having an essential absence of
aromatic compound. Often the overhead from step b contains at least
about 0.1 weight percent arylalkane, e.g., up to about 5 weight
percent arylalkane, for instance, 0.2 to 2, weight percent
arylalkane, based on the weight of the overhead. In a preferred
mode, at least a portion of the overhead from step d is recycled to
step a. Preferably the bottoms stream of step d contains less than
50 parts per million by weight aromatic compound.
[0016] In more preferred aspects of the processes of this
invention, the distillation of step b is conducted at a lower
pressure than the alkylation zone, and is often at between about 80
and 250 kPa absolute. Advantageously the pressure of the
distillation of step b is sufficiently lower than that of the
effluent from the alkylation zone that a significant portion of the
aromatic compound in the at least a portion of the effluent fed to
the first distillation zone, is vaporized.
[0017] In another broad aspect of the processes of this invention,
the processes for the alkylation of aromatic compound of 6 to 8
carbon atoms with an olefin-containing aliphatic compound of 8 to
18 carbon atoms comprise: [0018] a. co-currently passing said
aromatic compound and said aliphatic compound to an alkylation zone
comprising solid alkylation catalyst under liquid phase alkylation
conditions to produce an effluent comprising arylalkane and
aromatic compound, the mole ratio of said aromatic compound passed
to the alkylation zone to said aliphatic compound passed to the
alkylation zone being at least about 6:1, preferably at least about
10:1 or 15:1; [0019] b. distilling at least a portion of the
effluent of step a under flash distillation conditions including a
lower pressure than that of the alkylation zone to provide at least
an overhead and a bottoms stream, said overhead comprising about 20
to 98 weight percent of the aromatic compound in said at least a
portion of the effluent and arylalkane, and said bottoms stream
comprising at least about 80 weight percent of the arylalkane
contained in the at least a portion of the effluent, and [0020] c.
recycling the overhead of step b to the alkylation zone of step
a.
[0021] In yet another broad aspect of the processes of this
invention, the processes for the alkylation of aromatic compound of
6 to 8 carbon atoms with an olefin-containing aliphatic compound of
8 to 18 carbon atoms comprise: [0022] a. co-currently passing said
aromatic compound, said aliphatic compound and paraffin of between
8 and 18 carbon atoms to an alkylation zone comprising solid
alkylation catalyst under liquid phase alkylation conditions to
produce an effluent comprising arylalkane, aromatic compound and
paraffin, the mole ratio of said aromatic compound to said
aliphatic compound passed to the alkylation zone being at least
about 6:1 and preferably at least about 10:1 and said paraffin
passed to said alkylation zone being in a mole ratio to said
aliphatic compound of between about 1:1 to 20:1; [0023] b.
distilling a distillation feed comprising at least a portion of the
effluent of step a, said distillation being conducted with less
than about 5 theoretical distillation trays to provide an overhead
comprising between about 20 and 98 weight percent of the aromatic
compound contained in said at least a portion of the effluent and
arylalkane, and a bottoms stream comprising aromatic compound and
at least about 80 weight percent of the arylalkane contained in
said at least a portion of the effluent, [0024] c. recycling the
overhead from step b to the alkylation zone of step a, [0025] d.
distilling a second distillation feed comprising bottoms stream
from step b under distillation conditions sufficient to provide an
overhead comprising aromatic compound and a bottoms stream
comprising arylalkane having an essential absence of aromatic
compound, and [0026] e. withdrawing from at least one of steps a, b
and c, sufficient fluid to maintain the concentration of paraffin
in the effluent from the alkylation zone at less than about 50
weight percent and passing said fluid to the distilling of step
d.
[0027] Thus, the processes of this invention can reduce the amount
of aromatic compound passing to a refining system for the
arylalkane. Therefore, for instance, the size of the aromatic
compound distillation for an existing facility can readily be
debottlenecked, and for a grass roots facility, the aromatic
compound distillation can be designed to be smaller and require
less reboiler demand. Advantageously the distillation of step b
does not need to achieve a high degree of separation of the
aromatic compound from the arylalkane to achieve these advantages
or to achieve desirable arylalkane product quality.
[0028] In the broad aspects of the apparatus of this invention for
alkylation of aromatic compound with olefin-containing aliphatic
compound, the apparatus comprises: [0029] a. an alkylation reactor
having an inlet portion in fluid communication with a supply of
olefin-containing aliphatic compound and an outlet portion, said
reactor having a chamber containing solid alkylation catalyst such
that fluid passing between the inlet portion and the outlet portion
contacts the catalyst; [0030] b. a first distillation column having
an inlet in fluid communication with the outlet of the reactor, an
overhead outlet in fluid communication with the inlet portion of
the reactor, and a bottoms stream outlet, said first distillation
column having less than 5 theoretical distillation plates; and
[0031] c. a second distillation column having an inlet in fluid
communication with the bottoms stream outlet of the first
distillation column, an overhead outlet in fluid communication with
the inlet portion of the reactor, and a bottoms stream outlet, in
which the second distillation column has greater than 5 theoretical
distillation plates.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a schematic representation of an apparatus adapted
to practice a process in accordance with this invention in which
two alkylation reactors are provided and the feed for the lights
distillation is obtained from the effluent from the first
reactor.
[0033] FIG. 2 is a schematic representation of an apparatus adapted
to practice a process in accordance with this invention having a
single alkylation reactor.
[0034] FIG. 3 is a schematic representation of another apparatus
adapted to practice a process in accordance with this invention in
which two alkylation reactors are provided and the feed for the
lights distillation is obtained from the effluent from the second
reactor and the overhead from the lights distillation is recycled
to the first reactor.
[0035] FIG. 4 is a schematic representation of still another
apparatus adapted to practice a process in accordance with this
invention in which a side stream cut is taken form the lights
distillation. This representation illustrates further distillations
to provide a purified arylalkane product.
DETAILED DISCUSSION
The Feed and Products:
[0036] Aliphatic mono-olefins and aromatic compounds are used for
the alkylation process. The selection of the olefin and aromatic
compounds is dependent upon the sought alkylation product.
[0037] The olefin-containing aliphatic compound is preferably of
about 8 to 18, often for detergent applications, 9 to 16, carbon
atoms. The positioning of the olefinic bond in the molecule is not
critical as most alkylation catalysts have been found to promote
migration of the olefinic bond. However, the branching of the
hydrocarbon backbone is often more of a concern as the structural
configuration of the alkyl group on the arylalkane product can
affect performance. For instance, where alkylbenzenes are
sulfonated to produce surfactants, undue branching can adversely
affect the biodegradability of the surfactant. On the other hand,
some branching may be desired such as the lightly branched modified
alkylbenzenes such as described in U.S. Pat. No. 6,187,981. The
olefin may be unbranched or lightly branched, which as used herein,
refers to an olefin having three or four primary carbon atoms and
for which none of the remaining carbon atoms are quaternary carbon
atoms. A primary carbon atom is a carbon atom which, although
perhaps bonded also to other atoms besides carbon, is bonded to
only one carbon atom. A quaternary carbon atom is a carbon atom
that is bonded to four other carbon atoms.
[0038] The olefin-containing aliphatic compound is usually a
mixture of two or more olefins. For commercial processes, other
components may be present with the olefin-containing aliphatic
compound. For instance, the olefin may be obtained by the
dehydrogenation of a paraffinic feedstock and unreacted paraffin,
which is difficult to separate from the olefin, is passed to the
alkylation reactor. See, for instance, U.S. Pat. No. 6,670,516,
herein incorporated by reference. Generally, where olefin is
obtained by the dehydrogenation of a paraffinic feedstock, the
molar ratio of olefin to paraffin is between about 1:12 to 1:8;
however, such amounts of paraffin are not critical to the processes
of this invention. Indeed, olefin-containing feedstocks having an
essential absence of paraffins are suitable. However, the processes
of this invention are particularly useful where paraffin is present
as a significant portion of the energy and size of the distillation
of step d is devoted to separating aromatic compound from paraffin.
The processes of this invention thus have a beneficial effect in
reducing the energy consumption and size of that distillation.
[0039] The source of the paraffinic feedstock for dehydrogenation
is not critical although certain sources of paraffinic feedstocks
will likely result in the impurities being present. Conventionally,
kerosene fractions produced in petroleum refineries either by crude
oil fractionation or by conversion processes therefore form
suitable feed mixture precursors. Fractions recovered from crude
oil by fractionation will typically require hydrotreating for
removal of sulfur and/or nitrogen prior to being fed to the subject
process. The boiling point range of the kerosene fraction can be
adjusted by prefractionation to adjust the carbon number range of
the paraffins. In an extreme case the boiling point range can be
limited such that only paraffins of a single carbon number
predominate. Kerosene fractions contain a very large number of
different hydrocarbons and the feed mixture to the subject process
can therefore contain 200 or more different compounds.
[0040] The paraffinic feedstock may alternatively be at least in
part derived from oligomerization or alkylation reactions. Such
feed mixture preparation methods are inherently imprecise and
produce a mixture of compounds. The feed mixtures to the process
may contain quantities of paraffins having multiple branches and
paraffins having multiple carbon atoms in the branches,
cycloparaffins, branched cycloparaffins, or other compounds having
boiling points relatively close to the desired compound isomer.
Thus, the feed mixtures to the process of this invention can also
contain sizable quantities of aromatic hydrocarbons.
[0041] Another source of paraffins is in condensate from gas wells.
Usually insufficient quantities of such condensate are available to
be the exclusive source of paraffinic feedstock. However, its use
to supplement other paraffinic feedstocks can be desirable.
Typically these condensates contain sulfur compounds, which have
restricted their use in the past. As this invention enables the use
of sulfur-containing feeds, these condensates can be used to supply
paraffins for alkylation.
[0042] Paraffins may also be produced from synthesis gas (Syngas),
hydrogen and carbon monoxide. This process is generally referred to
as the Fischer-Tropsch process. Syngas may be made from various raw
materials including natural gas and coal, thus making it an
attractive source of paraffinic feedstock where petroleum
distillates are not available.
[0043] The olefin-containing feed to the alkylation reactor should
be sufficiently free of impurities, such as water, nitrogen
compounds and sulfur compounds, that can unduly adversely affect
the life of the alkylation catalyst.
[0044] The aromatic-containing feedstock to the subject process
comprises a phenyl compound, which is benzene when the process is
detergent alkylation. In a more general case, the phenyl compound
of the aromatic feedstock may be alkylated or otherwise substituted
derivatives or of a higher molecular weight than benzene, including
toluene, ethylbenzene, xylene, etc., but the product of such an
alkylation may not be as suitable a detergent precursor as
alkylated benzenes.
Alkylation:
[0045] The olefin is reacted with aromatic compound to produce
arylalkane. Usually the aromatic compound is present in a
significant stoichiometric excess to the olefin, e.g., from about
6:1 or from about 10:1 or 15:1 up to about 50:1 and normally from
about 15:1 to about 30:1, on a molar basis.
[0046] The aromatic compound and the olefin are reacted under
alkylation conditions in the presence of a solid alkylation
catalyst. These alkylation conditions generally include a
temperature in the range between about 80.degree. C. and about
200.degree. C., most usually at a temperature not exceeding about
175.degree. C., say, about 125.degree. C. to 160.degree. C. Since
the alkylation is typically conducted in the presence of a liquid
phase, and preferably in either an all-liquid phase or at
supercritical conditions, pressures must be sufficient to maintain
reactants in the liquid phase. The requisite pressure necessarily
depends upon the olefin, the aryl compound, and temperature, but
normally is in the range of about 1300 to 7000 kPa(g), and most
usually between about 2000 and 3500 kPa(g). Preferably the
alkylation conditions do not substantially result in skeletal
isomerization of the olefin. For instance, less than 15 mole
percent, and preferably less than 10 mole percent, of the olefin,
the aliphatic alkyl chain, and any reaction intermediate undergoes
skeletal isomerization.
[0047] Alkylation of the aromatic compound by the olefins is
conducted in a continuous manner using one bed or two or more
catalyst beds in flow series. For purposes herein, a catalyst bed
is termed a reactor whether in the same or a separate vessel from
another bed. Each reactor has an inlet portion and an outlet
portion. The reactants may be in admixture prior to entering the
inlet portion of the reactor, or they may be individually
introduced and mixed in the reactor.
[0048] The catalyst may be used as a packed bed or a fluidized bed.
The feed to the reaction zone may be passed either upflow or
downflow, or even horizontally as in a radial bed reactor; however,
the flows of the aromatic compound and olefin-containing aliphatic
compound are co-current. In one desirable variant,
olefin-containing feedstock may be fed into several discrete points
within the reaction zone, and at each zone the aromatic compound to
olefin molar ratio may be greater than 50:1. The total feed
mixture, that is, aromatic compound plus olefin, is often passed
through the packed bed at a liquid hourly space velocity (LHSV)
between about 0.3 and about 6 or 10 hr-1 depending upon, e.g.,
alkylation temperature and the activity of the catalyst. Lower
values of LHSV within this range are preferred. It is usually
desired that sufficient residence time in the reaction zone be used
such that at least about 98, and often at least about 99.5, mole
percent of the olefin is reacted.
[0049] Any suitable alkylation catalyst may be used in the present
invention, provided that the requirements for conversion,
selectivity, and activity are met. Preferred alkylation catalysts
comprise zeolites having a zeolite structure type selected from the
group consisting of BEA, MOR, MTW, and NES. Such zeolites include
mordenite, ZSM4, ZSM-12, ZSM-20, offretite, gmelinite, beta, NU-87,
and gottardite. Clay or amorphous catalysts including
silica-alumina and fluorided silica-alumina may also find utility.
Further discussion of alkylation catalysts can be found in U.S.
Pat. No. 5,196,574; U.S. Pat. No. 6,315,964 and U.S. Pat. No.
6,617,481.
The Lights Distillation Recycle:
[0050] In accordance with this invention at least a portion of an
alkylation reactor effluent is subjected to a lights distillation
to recover as overhead a fraction of the unreacted aromatic
compound. The recovered aromatic compound is recycled to the
alkylation reactor. Thus, the use of the lights distillation
reduces the amount of aromatic compound in the reaction product
passed to the refining system including a distillation assembly for
removing aromatic compound from the arylalkane.
[0051] In the processes of the invention, one or more alkylation
reactor beds may be used with the lights distillation overhead
being recycled to the inlet portion of the reactor from which the
effluent is obtained for the light distillation or of an upstream
alkylation reactor. The amount of the effluent directed to the
light distillation may be as little as 20 weight percent of the
total effluent or may comprise the entire effluent stream. Where it
is desired to debottleneck an existing manufacturing plant, even
directing a small amount of the effluent to the light distillation
can be beneficial. Often at least about 50, and sometimes at least
about 80, weight percent of the effluent is subjected to the light
distillation.
[0052] In any event, sufficient reaction product must be removed
from the alkylation reaction zone and the lights distillation loop
to prevent an undue build-up of paraffin or other inerts in the
loop. Typically the concentration of paraffin in the alkylation
zone or the alkylation zone effluent is less than about 50 weight
percent, and preferably less than about 40, e.g., less than about
35, weight percent. If more than one reactor is used, most
preferably it is the effluent from the first reactor that is
subjected to the lights distillation with the overhead from the
lights distillation being recycled to the inlet portion of that
reactor.
[0053] Only a portion of the aromatic compound contained in the
distillation feed to the lights distillation zone is intended to be
recovered in the overhead of the lights distillation. The amount of
the aromatic compound recovered in the overhead is often between
about 20 and 98, say, 60 or 75 to 98, weight percent of that in the
distillation feed. The overhead may also contain arylalkane,
unreacted olefin, aromatic by-products and paraffins, especially
where the olefin is supplied in combination with paraffins.
[0054] The recycling of paraffins, can lead to a higher
concentration of the paraffins in the alkylation reactor at steady
state conditions than in the olefin-containing feed to the
alkylation reactor which needs to be taken in account in reactor
sizing. Normally where paraffins are present, less than about 60,
preferably less than about 40, and often between about 5 and 30,
weight percent of the paraffins in the distillation feed is
contained in the overhead. Generally less than about 60, often
between about 5 and 30, weight percent of the unreacted
olefin-containing compound fed to the lights distillation will be
in the overhead.
[0055] Advantageously, the distillation equipment need not be
extensive to effect such recovery, e.g., the distillation may be
accomplished with less than about 5 theoretical distillation
plates. Moreover, the lights distillation is preferably conducted
without significant reboiler heat, and indeed, in some instances,
the sought recovery of aromatic compound may be accomplished by a
flash distillation due to a pressure drop of the effluent from
alkylation reaction conditions without the need for a heat source.
The feed to the lights distillation may be at any convenient
temperature. For instance, it may be at or close to the temperature
of the effluent from the alkylation reaction zone, or it may be
heated or cooled by indirect heat exchange. Generally the
temperature of the distillation feed is below about 300.degree. C.,
say 1000 to 275.degree. C. Where heat is externally supplied to the
lights distillation, e.g., to provide for internal reflux in a
fractionation column, it preferably is less than about 40, more
preferably less than about 30, kilocalories (kcal) per kilogram of
the feed to the lights distillation. As used herein, externally
supplied heat is heat supplied to the lights distillation,
excluding heat supplied with the lights distillation feed.
[0056] The bottoms temperature of the lights distillation zone is
usually in the range of about 80.degree. C. to 150.degree. C.,
preferably between about 90.degree. C. and 140.degree. C., and the
pressure in the lights distillation zone is typically between about
70 and 300, preferably between about 90 and 250, say, 100 and 200,
kPa absolute. Where a reflux is used, the rate of external reflux
(distillation feed to reflux, F/R) is preferably between about
0.1:1 to 5:1, more preferably between about 0.4:1 and 0.8:1,
kilogram per kilogram of effluent fed to the lights distillation
zone.
[0057] The lights distillation may be effected in an open vessel
for a flash distillation or may contain suitable trays or packing
for a fractionation. A flash distillation may contain a demister to
prevent liquid carryover in the overhead. Heat to the lights
distillation zone may be provided by indirect heat exchange at the
bottom of the zone, or by withdrawing, heating and recycling to the
base of the column a portion of the liquid contained at the bottom
of the lights distillation zone. Alternatively or additionally, the
distillation feed may be heated, but preferably not to a
temperature that may cause undue reaction or degradation of the
arylalkane, e.g., below about 300.degree. C.
[0058] The composition of the overhead from the lights distillation
is primarily dependent upon the composition of the distillation
feed, the temperature and pressure for the lights distillation, the
reflux ratio and the practical distillation plates contained in the
lights distillation zone. The practical distillation plates are
determined from the actual performance of the distillation
column.
[0059] The overhead form the lights distillation may be cooled to
cause condensation and then the liquid pumped to the inlet portion
of the designated alkylation reactor. If desired, a portion of the
condensed liquid may be used as reflux for the lights
distillation.
[0060] The lights distillation will provide at least a bottoms
stream containing arylalkane. When the lights distillation is other
than a flash distillation, one or more midcuts can also be taken.
If no midcuts are taken, the composition of the bottoms stream will
simply be the balance of the feed to the lights distillation
column. If one or more midcuts are taken, the composition of the
bottoms stream would differ. Usually the bottoms stream will
contain at least about 80, and often at least about 90 or even 95
or more, weight percent of the arylalkane in the effluent fed to
the lights distillation column. The bottoms stream will also
contain aromatic compound, e.g., at least about 0.5, say, 1 to 80,
weight percent of the aromatic compound in the distillation feed.
Where no midcut is taken and paraffin is present, the bottoms
stream will contain paraffin, usually in an amount of at least 40,
say 45 to 95, weight percent of the paraffin contained in the
distillation feed.
[0061] The processes of this invention provide not only for energy
efficient recycling of large amounts of aromatic compound to the
alkylation reactor to provide for desired selectivities to the
sought arylalkane product and for debottlenecking of existing
arylalkane production facilities, but also they enable flexibility
in the manner in which the arylalkane is purified. See, for
instance, the discussion of FIG. 4 below.
[0062] In common commercial configurations, the alkylation reactor
effluent would be passed to a distillation assembly that separates
as a relatively pure stream the aromatic compound contained in the
effluent. The bottoms stream from this distillation assembly would
then be passed to a distillation assembly to separate as the
overhead, paraffins and unreacted olefins, and the bottoms from
this second distillation assembly would be fed to a heavies
distillation assembly where the arylalkane product is contained in
the overhead. If desired, a finishing column may be used to further
purify the arylalkane, especially after a clay treatment to remove
color formers. In this type of distillation train, the bottoms
stream of the lights distillation is normally fed to the
distillation assembly for separating the aromatic compound.
[0063] For purposes of illustration only, the following disclosure
references the production of alkylbenzene. In an alkylbenzene
refining system, the benzene distillation is generally conducted
with a bottoms temperature of less than about 300.degree. C.,
preferably less than about 275.degree. C., usually between about
230.degree. and 270.degree. C., and at a pressure at which the
overhead is provided of between about 5 and 300, preferably between
about 35 and 70, kPa gauge. The overhead generally contains less
than about 2, preferably less than about 1.5, weight percent
paraffins. The benzene distillation assembly may comprise one or
more distillation columns. More than one overhead may be obtained
from the benzene distillation assembly. For instance, a highly pure
stream may be obtained for process needs such as regenerating
catalysts or sorbents, e.g., having a paraffin concentration less
than about 1, preferably less than about 0.1, weight percent. A
lesser purity overhead may be obtained from the benzene
distillation assembly, e.g., as a side draw, for use as a recycle
to the alkylation reaction.
[0064] Each column in the benzene distillation assembly may contain
any convenient packing or distillation trays, but most often trays
such as sieve and bubble trays, are used. Often the assembly
provides at least about 5, say 6 to 70, and preferably 20 to 50,
theoretical distillation plates. The reflux ratio (herein defined
as the distillate to reflux weight ratio) is often in the range of
about 2:1 to 1:10, preferably about 1.5:1 to 1:5. The bottoms
stream from the benzene distillation generally contains less than
about 1000 ppmw, preferably less than about 50 ppmw, and sometimes
less than about 5 ppmw, benzene. The benzene distillation may occur
in a single column or two or more distinct columns may be used. For
instance, a stripping column may be used to remove a portion, e.g.,
20 to 50 percent, of the benzene and then the bottoms from the
stripping column would be subjected to rectification in a
subsequent column to obtain the desired separation.
[0065] The paraffin distillation is generally conducted with a
bottoms temperature of less than about 300.degree. C., preferably
less than about 275.degree. C., usually between about 250.degree.
C. and 275.degree. C., and at a pressure at which overhead is
provided of between about 5 and 110, preferably between about 10
and 50, kPa absolute. The column may contain any convenient packing
or distillation trays, but most often sieve trays are used. Often
the paraffins distillation assembly provides at least about 5, say
7 to 20, theoretical distillation plates. The reflux ratio is often
in the range of about 3:1 to 1:10, preferably about 1:1 to 1:3. The
bottoms stream from the paraffins distillation generally contains
less than about 5000, preferably less than about 500, parts by
million by weight (ppmw) paraffins and preferably less than about
10, often less than about 1, ppmw benzene. The paraffins
distillation may occur in a single column or two or more distinct
columns may be used.
[0066] The heavy alkylate distillation is generally conducted with
a bottoms temperature of less than about 300.degree. C., preferably
less than about 275.degree. C., usually between about 250.degree.
C. and 275.degree. C., and at a pressure of between about 0.5 and
30, preferably between about 1 and 5, kPa absolute. The column may
contain any convenient packing or distillation trays, but most
often structured packing is used. Often the heavy alkylate
distillation assembly provides at least about 5, say 10 to 30, and
preferably 10 to 20, theoretical distillation plates. The reflux
ratio is often in the range of about 2:1 to 1:5, preferably about
0.2:1 to 1:1. The overhead from the heavy alkylate distillation
generally contains less than about 1000, preferably less than about
100 ppmw, and sometimes less than about 50 ppmw, total heavies.
[0067] The refining system may contain additional distillation
zones, e.g., to recover additional arylalkane from heavies.
[0068] The invention will be further illustrated by reference to
the drawings, which are not in limitation of the scope of the
invention. The drawings will be discussed in terms of the
production of alkylbenzene from benzene and an olefin-containing
feed which is a dehydrogenated paraffin feedstock for the sake of
ease of reference; however, the broad aspects of the invention are
not limited to such feedstocks.
[0069] With reference to FIG. 1, an olefin-containing feedstock is
supplied via line 102 to a first alkylation reactor 104. Effluent
from alkylation reactor 104 passes via line 106 to a second
alkylation reactor 120. Under normal operation, at least about 90
percent by weight of the olefin fed to reactor 104 is consumed in
reactor 104. Accordingly, an additional supply of olefin feedstock
is introduced from line 102 through line 118 into line 106 for feed
to reactor 120.
[0070] A portion of the effluent in line 106 is withdrawn via line
108 and is fed to lights distillation column 110. The overhead from
column 110, which is primarily benzene, passes via line 112 through
condenser 114 to line 104 were it is admixed with the olefin feed
and a portion of the overhead of benzene column 130. Column 110 is
a flash column and no reflux is used. A bottoms stream is withdrawn
via line 124 from column 110. A portion of the bottoms stream is
passed via line 126 through heat exchanger 128 and back to the
lower portion of column 110.
[0071] Returning to the second alkylation reactor 120, effluent is
withdrawn from the reactor via line 122 and passed to benzene
column 130. The bottoms stream from column 110 is passed via line
124 to line 122 and is also sent to column 130. A benzene overhead
is withdrawn from column 130 via line 132 and condensed in
condenser 134. A portion of the overhead is sent back to the top of
column 130 and the remaining portion is passed via line 136 to line
102. A bottoms stream is withdrawn from column 130 via line 138. A
portion of this bottoms stream is passed via line 140 through heat
exchanger 142 and returned to column 130 to supply heat for the
distillation.
[0072] In FIG. 2, the same numerical indicators indicate the same
components as are identified for FIG. 1. The apparatus depicted in
FIG. 2 differs from that in FIG. 1 in that no second alkylation
reactor 120 is used and the bottoms stream from column 110 is
passed via line 124 to benzene distillation column 130. Thus, the
entire effluent from alkylation reactor 104 is passed via line 106
to lights distillation column 110. Also, a portion of the condensed
liquid in line 112 is returned via line 202 to the top of column
110 as reflux. Column 110 contains structured packing.
[0073] In FIG. 3, the same numerical indicators indicate the same
components as are identified for FIGS. 1 and 2. The apparatus
depicted in FIG. 3 differs from that in FIG. 1 in that line 108
withdraws a portion of the reaction effluent not from reactor 104
but from reactor 120. A portion of the overhead from lights
distillation column 110 is recycled to alkylation reactor 104.
Also, a portion of the condensed liquid in line 112 is returned via
line 202 to the top of column 110 as reflux. Column 110 contains
packing.
[0074] In FIG. 4, the same numerical indicators indicate the same
components as are identified for FIG. 2. The apparatus depicted in
FIG. 4 differs from that in FIG. 2 in that column 110 is a trayed,
dividing wall column having partition 400. On the opposite side of
column 110 from the point of introduction of the alkylation reactor
effluent, a midcut is removed via line 402. This midcut contains
benzene and paraffin and is passed to benzene column 130. The
bottoms stream from column 130 will contain little alkylbenzene and
will be rich in paraffin. Thus a portion of the bottoms stream in
line 138 can be returned to a paraffin dehydrogenation unit.
[0075] The bottoms stream from lights distillation column 110 is
passed via line 124 to heavies column 404. Heavies column 404
provides an overhead containing benzene and paraffin which is
withdrawn via line 408, condensed in condenser 410 and a portion is
returned via line 412 to column 404 as reflux and the remaining
portion is passed via line 408 to benzene column 130. The bottoms
stream from column 404 contains heavies such as dialkyl benzene and
is withdrawn via line 414. A portion of the bottoms stream is
passed via line 416, heated in heat exchanger 418, and returned to
the bottom portion of column 404. Column 404 is also provided with
partition 406, which defines a zone 426. Zone 426 can perform as a
column within column 404. An alkylbenzene stream is withdrawn via
line 420 from the bottom of zone 426. A portion of this
alkylbenzene stream in line 420 is returned to the lower portion of
the partitioned zone 426 via line 422 having heat exchanger 424.
The remaining portion of the stream in line 420 is product.
* * * * *