U.S. patent application number 11/812485 was filed with the patent office on 2008-02-07 for olefin upgrading process with guard bed regeneration.
This patent application is currently assigned to ExxonMobil Research and Engineering Company. Invention is credited to Michael C. Clark, Benjamin S. Umansky.
Application Number | 20080029437 11/812485 |
Document ID | / |
Family ID | 38997693 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080029437 |
Kind Code |
A1 |
Umansky; Benjamin S. ; et
al. |
February 7, 2008 |
Olefin upgrading process with guard bed regeneration
Abstract
A process for the regeneration of materials used in the guard
beds preceding the reactors used in an olefin conversion process
which converts olefinic refinery streams to higher boiling
hydrocarbon products by polymerization (oligomerization) or
alkylation of aromatics including benzene. Products of the process
may include olefin oligomers and alkylaromatics in the gasoline
boiling range as well as alkylaromatic petrochemicals such as
cumene and ethylbenzene. The process is integrated with the olefin
conversion process to ensure continuous operation of the olefin
conversion without sending the feedstock containing the
contaminant(s) to the reactor. The process uses reaction products
from the olefin conversion process to regenerate the guard bed
material and so is economically attractive since it does not
require the use of separate purge, regeneration feed and separation
systems. A plurality of guard beds is used, each containing a
material which removes catalyst poisons. The guard beds are
operated on a swing system in which one or more beds is kept on
stream to remove the contaminant(s) while one or more of the
remaining beds is being purged or regenerated. In this way,
continuity of operation is assured. The regeneration medium is a
product stream from the olefin conversion process.
Inventors: |
Umansky; Benjamin S.;
(Fairfax, VA) ; Clark; Michael C.; (Chantilly,
VA) |
Correspondence
Address: |
ExxonMobil Research & Engineering Company
P.O. Box 900, 1545 Route 22 East
Annandale
NJ
08801-0900
US
|
Assignee: |
ExxonMobil Research and Engineering
Company
Annandale
NJ
|
Family ID: |
38997693 |
Appl. No.: |
11/812485 |
Filed: |
June 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60834804 |
Aug 2, 2006 |
|
|
|
Current U.S.
Class: |
208/238 |
Current CPC
Class: |
B01J 29/7038 20130101;
C07C 7/13 20130101; B01J 20/3408 20130101; C10G 25/05 20130101;
C07C 7/13 20130101; C10G 2300/1096 20130101; C10G 11/00 20130101;
C10G 2300/1092 20130101; C10G 25/12 20130101; C10G 25/03 20130101;
C10G 2400/02 20130101; Y02P 20/52 20151101; C07C 11/02
20130101 |
Class at
Publication: |
208/238 |
International
Class: |
C10G 29/20 20060101
C10G029/20 |
Claims
1. A process for regenerating a guard bed of porous solid material
used for removing contaminants including sulfur compounds from a
feed stream comprising light refinery olefins passing to a reactor
containing a fixed bed of a solid, porous, molecular sieve catalyst
in which the feed stream is converted to a higher boiling range
hydrocarbon products, which comprises desorbing contaminants from
the feed which are present on the solid material by passing a
stream of hydrocarbon product from the reactor over the guard
bed.
2. A process according to claim 1 in which the feed stream is a
stream produced by catalytic cracking of a hydrocarbon feed and
comprising C3 to C4 olefins.
3. A process according to claim 1 in which the feed stream
comprises C3 to C4 olefins produced by catalytic cracking of a
hydrocarbon feed and aromatic compounds including benzene.
4. A process according to claim 1 in which the feed stream is
passed over a fixed bed of a catalyst comprising an MWW
zeolite.
5. A process according to claim 1 in which the guard bed material
comprises a molecular sieve capable of reacting with contaminants
in the feed stream.
6. A process according to claim 5 in which the guard bed material
comprises an MWW zeolite.
7. A process according to claim 1 in which the hydrocarbon from the
reactor passed over the guard bed material comprises a light
paraffin.
8. A process according to claim 1 in which the hydrocarbon from the
reactor passed over the guard bed material comprises alkylaromatic
hydrocarbons.
9. A process according to claim 1 in which the hydrocarbon from the
reactor passed over the guard bed material comprises C4-C6
hydrocarbons.
10. A process according to claim 1 in which the stream of
hydrocarbon product from the reactor is passed over the guard bed
at a temperature of at least 100.degree. C.
11. In a process for converting a feed stream comprising light
refinery olefins and including sulfur compounds as contaminants to
a gasoline boiling range hydrocarbon product, by passing the feed
stream in a reactor over a fixed bed of a solid, porous, molecular
sieve catalyst at an elevated temperature, the improvement which
comprises the removal of contaminants from the feed stream by
passing the feed stream upstream of the reactor over a fixed guard
bed of solid, porous material and subsequently desorbing
contaminants from the feed which are present on the solid material
by passing a stream of hydrocarbon product from the reactor over
the guard bed.
12. A process according to claim 1 in which the feed stream is a
stream produced by catalytic cracking of a hydrocarbon feed and
comprising C3 to C4 olefins.
13. A process according to claim 1 in which the feed stream
comprises a stream produced by catalytic cracking of a hydrocarbon
feed and comprising C3 to C4 olefins and a reformate stream
comprising benzene.
14. A process according to claim 1 in which the feed stream is
passed over a fixed bed of a catalyst comprising an MWW
zeolite.
15. A process according to claim 1 in which the guard bed material
comprises a molecular sieve capable of reacting with contaminants
in the feed stream.
16. A process according to claim 5 in which the guard bed material
comprises an MWW zeolite.
17. A process according to claim 1 in which the stream of
hydrocarbon product from the reactor is passed over the guard bed
at a temperature of at least 100.degree. C.
18. A process according to claim 1 in which the stream of
hydrocarbon product from the reactor is passed over the guard bed
at a temperature of 200-300.degree. C.
19. A process according to claim 11 in which the contaminants are
removed feed stream by passing the feed stream upstream of the
reactor over a fixed guard bed of the solid, porous material in the
first of at least two guard bed vessels connected upstream of the
reactor and to an inlet of the reactor and the contaminants are
desorbed from the solid, porous material by passing a stream of
hydrocarbon product from the reactor over the guard bed material
contained in a second of the guard bed vessels.
20. A process according to claim 19 in which the first and second
guard beds are operate in a swing system in which the first guard
bed vessel is used to remove the contaminants from the feed stream
while the contaminants are removed from the guard bed material in
the second guard bed vessel by passing the stream of hydrocarbon
product from the reactor over the guard bed material contained in
the second guard bed vessel.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Patent Application Ser. No. 60/834,804, filed 2 Aug. 2006.
FIELD OF THE INVENTION
[0002] This invention relates to a method for the regeneration of
guard bed sorbents and catalysts used in light olefin
polymerization and alkylation processes for the production of
gasoline boiling range motor fuel.
[0003] The present application is related to the following
previously filed applications which describe related catalytic
processes used for making gasoline boiling range liquid hydrocarbon
products:
U.S. Ser. No. 11/362,257, filed 27 Feb. 2006, "Gasoline Production
by Olefin Polymerization". U.S. Ser. No. 11/362,128, filed 27 Feb.
2006, "Gasoline Production By Olefin Polymerization With Aromatics
Alkylation" U.S. Ser. No. 11/362,256, filed 27 Feb. 2006, "Process
for Making High Octane Gasoline with Reduced Benzene Content" U.S.
Ser. No. 11/362,255, filed 27 Feb. 2006, "Vapor Phase Aromatics
Alkylation Process" U.S. Ser. No. 11/362,139, filed 27 Feb. 2006,
"Liquid Phase Aromatics Alkylation Process"
[0004] The present rejuvenation process is intended for use with
manufacturing processes such as those described in these previous
applications; accordingly, reference is made to these prior
application for details of the processes and of the equipment used
for carrying them out.
[0005] The present application is also related to concurrently
filed application Ser. No. ______ (claiming priority of Provisional
application Ser. No. 60/834,805, Attorney Docket P2006EM056),
entitled "Rejuvenation Process for Olefin Polymerization and
Alkylation Catalyst
BACKGROUND OF THE INVENTION
[0006] Following the introduction of catalytic cracking processes
in petroleum refining in the early 1930s, large amounts of olefins,
particularly light olefins such as ethylene, propylene, butylene,
became available in copious quantities from catalytic cracking
plants in refineries. While these olefins may be used as
petrochemical feedstock, many conventional petroleum refineries
producing petroleum fuels and lubricants are not capable of
diverting these materials to petrochemical uses. Processes for
producing fuels from these cracking off gases are therefore
desirable and from the early days, a number of different processes
evolved. The early thermal polymerization process was rapidly
displaced by the superior catalytic processes of which there was a
number. The first catalytic polymerization process used a sulfuric
acid catalyst to polymerize isobutene selectively to dimers which
could then be hydrogenated to produce a branched chain octane for
blending into aviation fuels. Other processes polymerized
isobutylene with normal butylene to form a co-dimer which again
results in a high octane, branched chain product. An alternative
process uses phosphoric acid as the catalyst, on a solid support
and this process can be operated to convert all the C.sub.3 and
C.sub.4 olefins into high octane rating, branched chain polymers.
This process may also operate with a C.sub.4 olefin feed so as to
selectively convert only isobutene or both n-butene and isobutene.
This process has the advantage over the sulfuric acid process in
that propylene may be polymerized as well as the butenes and at the
present time, the solid phosphoric acid [SPA] polymerization
process remains the most important refinery polymerization process
for the production of motor gasoline.
[0007] In the SPA polymerization process, feeds are pretreated to
remove hydrogen sulfide and mercaptans which would otherwise enter
the product and be unacceptable, both from the view point of the
effect on octane and upon the ability of the product to conform to
environmental regulations. Typically, a feed is washed with caustic
to remove hydrogen sulfide and mercaptans, after which it is washed
with water to remove organic bases and any caustic carryover.
Because oxygen promotes the deposition of tarry materials on the
catalyst, both the feed and wash water are maintained at a low
oxygen level. Additional pre-treatments may also be used, depending
upon the presence of various contaminants in the feeds. With the
most common solid phosphoric acid catalyst, namely phosphoric acid
on kieselguhr, the water content of the feed needs to be controlled
carefully because if the water content is too high, the catalyst
softens and the reactor may plug. Conversely, if the feed is too
dry, coke tends to deposit on the catalyst, reducing its activity
and increasing the pressure drop across the reactor. As noted by
Henckstebeck, the distribution of water between the catalyst and
the reactants is a function of temperature and pressure which vary
from unit to unit, and for this reason different water
concentrations are required in the feeds to different units.
Petroleum Processing Principles And Applications, R. J.
Hencksterbeck McGraw-Hill, 1959. As described in the prior
applications cited above, there are two general types of units used
for the SPA process, based on the reactor type, the unit may be
classified as having chamber reactors or tubular reactors. The
chamber reactor contains a series of catalyst beds with bed volume
increasing from the inlet to the outlet of the reactor, with the
most common commercial design having five beds. The catalyst load
distribution is designed to control the heat of conversion.
[0008] For the production of motor gasoline only butene and lighter
olefins are employed as feeds to polymerization processes as
heavier olefins up to about C.sub.10 or C.sub.11 can be directly
incorporated into the gasoline. With the SPA process, propylene and
butylene are satisfactory feedstocks and ethylene may also be
included, to produce a copolymer product in the gasoline boiling
range. Limited amounts of butadiene may be permissible although
this diolefin is undesirable because of its tendency to produce
higher molecular weight polymers and to accelerate deposition of
coke on the catalyst. The process generally operates under
relatively mild conditions, typically between 150.degree. and
200.degree. C., usually at the lower end of this range between
150.degree. and 180.degree. C., when all butenes are polymerized.
Higher temperatures may be used when propylene is included in the
feed. In a well established commercial SPA polymerization process,
the olefin feed together with paraffinic diluent, is fed to the
reactor after being preheated by exchange with the reaction
effluent.
[0009] The solid phosphoric acid catalyst used is non-corrosive,
which permits extensive use of carbon steel throughout the unit.
The highest octane product is obtained by using a butene feed, with
a product octane rating of [R+M]/2 of 89 to 91 being typical. With
a mixed propylene/butene feed, product octane is typically about 91
and with propylene as the primary feed component, product octane
drops to typically 87.
[0010] In spite of the advantages of the SPA polymerization
process, which have resulted in over 200 units being built since
1935 for the production of gasoline fuel, a number of disadvantages
are encountered, mainly from the nature of the catalyst. Although
the catalyst is non-corrosive, so that much of the equipment may be
made of carbon steel, it does lead it to a number of drawbacks in
operation. First, the catalyst life is relatively short as a result
of pellet disintegration which causes an increase in the reactor
pressure drop. Second, the spent catalyst encounters difficulties
in handling from the environmental point of view, being acidic in
nature. Third, operational and quality constraints limit flexible
feedstock utilization. Obviously, a catalyst which did not have
these disadvantages would offer considerable operating and economic
advantages.
[0011] In application Ser. No. 11/362,257, we have described the
production of gasoline boiling range hydrocarbons by a process
using solid, non-corrosive molecular sieve catalysts to polymerize
(oligomerize) light olefins in a refinery stream such as FCC
off-gas; this process can be operated in an existing Polygas.TM.
unit with relatively minor unit modifications and so, given the
advantages of the molecular sieve catalysts, the new process offers
and economically attractive way of improving existing refinery
units for gasoline production. A related aromatics alkylation
process is described in Ser. Nos. 11/362,256, 11/362,255 and
11/362,139; in the process set out in these applications, a
gasoline boiling range product of low benzene content is produced
using light refinery olefins to alkylate reformate streams
containing significant levels of benzene. Application Ser. No.
11/362,139 describes a number of integrated process schemes which
combine the polymerization process with the benzene alkylation
process.
[0012] The gasoline manufacturing processes described in these
patent application use feedstocks produced in the petroleum
refinery, usually a light olefinic stream form the FCCU as a source
of olefins, either alone or combined with a reformate stream in the
processes using aromatics alkylation. These olefinic streams from
the cracking unit usually contain significant levels of
contaminants, especially sulphur compounds including mercaptans,
thiophenes and substituted thiophenes, as well as compounds
containing other heteroatoms such as nitrogen. Many of these
contaminants will act as catalyst poisons for the molecular sieve
catalysts used in the olefin upgrading process. Since poisoning of
the catalyst results in decreased catalyst activity and possibly
also catalyst selectivity, it is desirable to keep these
contaminants from entering the catalyst bed. For this reason, guard
beds are frequently used, containing either a non-reactive sorbent
for the contaminants or a reactive material which undergoes a
reaction with the contaminant(s). Which ever, is used, the guard
bed material eventually requires regeneration itself when loaded
with the contaminant(s). Conventionally, a single guard bed is
used, making it necessary either to cease operation during
regeneration or to send the feed directly to the reactor without
separation of the contaminant(s), so shortening catalyst life
commensurately.
SUMMARY OF THE INVENTION
[0013] We have now devised a process for the regeneration of
materials used in the guard beds preceding the reactors used for
the light olefin conversion processes. Processes of this type
include the olefin conversion processes referred to above for the
manufacture of gasoline boiling range motor fuels, either using a
light olefin feed on its own or with a reformate co-feed to produce
a low-benzene alkylaromatic gasoline. Other olefin conversion
processes using refinery light olefin streams which may use these
guard bed regeneration techniques include the well-established
aromatics alkylation processes for making cumene or ethylbenzene.
According to the present invention, the guard bed regeneration step
is integrated with the olefin conversion to ensure continuous
operation of the olefin conversion without sending the feedstock
containing the contaminant(s) to the reactor. The process uses
reaction products from the olefin conversion process to regenerate
the guard bed material and so is economically attractive since it
does not require the use of separate purge, regeneration feed and
separation systems.
[0014] According to the present invention, an olefin conversion
process which converts olefinic refinery streams to other, higher
boiling hydrocarbon products by polymerization (oligomerization) or
aromatics alkylation over a molecular sieve catalyst utilizes a
plurality of guard beds containing a material which removes
catalyst poisons. The guard beds are operated on a swing system in
which one or more beds is kept on stream to remove the
contaminant(s) while one or more of the remaining beds is being
purged or regenerated. In this way, continuity of operation is
assured. The regeneration medium is a product stream from the
olefin conversion process.
DRAWINGS
[0015] FIG. 1 shows a process schematic for the olefin
polymerization unit for converting light refinery olefins to motor
gasoline by the present process.
DETAILED DESCRIPTION
Olefin Conversion Process
[0016] The present process is for the conversion of light cracking
olefins or the alkylation of aromatics by light cracking olefins to
produce higher boiling liquid hydrocarbon products, for example,
motor gasoline and other motor fuels such as road diesel blend
stock as well as alkylaromatic petrochemical products such as
ethylbenzene and cumene. For convenience, the present guard bed
regeneration technique will be described below with reference to
the olefin polymerization process and the aromatics alkylation
processes described in the earlier filed applications cited above
but it is more generally applicable, to other similar processes
using molecular sieve catalysts and requiring a guard bed to remove
contaminants form the feed stream which would otherwise deactivate
the catalyst. As described in the previous applications cited
above, the olefin conversion process when used to produce gasoline
boiling range product, is intended to provide a replacement for the
SPA polymerization process, using a molecular sieve catalyst which
can be used as a direct replacement for SPA and so enables existing
SPA units to be used directly with the new catalyst, so allowing
the advantages of the new catalyst and process to be utilized while
retaining the economic benefit of existing refinery equipment. The
aromatic alkylation process is similar in operation and again, is
used to convert light refinery olefins to higher value, higher
boiling liquid products.
[0017] As described in prior application Ser. Nos. 11/362,257 and
11/362,139, the gasoline boiling range products can be produced by
the polymerization (oligomerization) of a light refinery olefin
stream. An alternative to the straightforward polymerization
process is an aromatics alkylation process of the type described in
Ser. Nos. 11/362,256, 11/362,255, 11/362,139, which may be combined
with the polymerization process as described in Ser. No.
11/362,139. Reference is made to these prior applications for
descriptions of the basic olefin upgrading processes.
[0018] The present guard bed regeneration technique is, as noted,
capable of use with other processes using molecular sieve catalysts
which are subject to poisoning by contaminants in the feed,
including processes for converting olefins into lubricants as
described in U.S. Pat. No. 4,956,514 which describes the use of
zeolite MCM-22 as an olefin oligomerization catalyst for making
lube range materials by the oligomerization of low molecular weight
olefins such as propylene and FCC off gas streams. Other processes
to which it can be applied are the well-established processes for
manufacturing aromatics such as ethylbenzene or cumene, using
reactions such as alkylation and transalkylation. The cumene
production (alkylation) process is described in U.S. Pat. No.
4,992,606 (Kushnerick et al). Ethylbenzene production processes are
described in U.S. Pat. Nos. 3,751,504 (Keown); 4,547,605 (Kresge);
and 4,016,218 (Haag); U.S. Pat. Nos. 4,962,256; 4,992,606;
4,954,663; 5,001,295; and 5,043,501 describe alkylation of aromatic
compounds with various alkylating agents over catalysts comprising
MWW zeolites such as PSH-3 or MCM-22. U.S. Pat. No. 5,334,795
describes the liquid phase synthesis of ethylbenzene with MCM-22.
The processes for cumene and ethylbenzene manufacture are
well-established commercially and are available under license from
vendors such as ExxonMobil Chemical Company and Polimeri
Europa.
[0019] FIG. 1 shows a simplified illustrative configuration for an
olefin upgrading unit operating on the principle of aromatics
alkylation. In FIG. 1 the dotted lines show the needed
modifications to a conventional Polygas unit but in this case using
the zeolite molecular sieve catalyst to catalyze the olefin
oligomerization. The unit which is used for the aromatics
alkylation process would be similar but would utilize the
additional piping and equipment for the aromatic co-feed as
described in Ser. Nos. 11/362,139, 11/362,256, 11/362,255 and
11/362,139. The quench circuit used in the olefins polymerization
version of the process is omitted for clarity. The reactors can be
tubular or chamber type. The number of reactors changes from unit
to unit, in this example the configuration has three reactors and
this potentially enables the rejuvenation can be practiced in one
of the reactors while keeping the others in operation. The feed to
be used as the rejuvenation stream is the olefin-depleted stream
from the overhead of the fractionation tower. In this
configuration, some piping is needed, and an additional pump to
boost the recycle stream to the reactor operating pressure; this
pump is needed in any event if the recycle is used as quench as
described in Ser. No. 11/362,257.
[0020] A mixed light olefin feed from a catalytic cracking unit is
introduced through line 10 and passes through guard bed 11 which
operates on a swing reactor system with a matching guard bed 12.
The feed then passes to feed drum 13 and on through line 14 to
reactors 15A, 15B, 15C. The olefins in the feed are polymerized in
reactors 15A, 15B and 15C. The effluent from the reactors passes to
fractionator 20 by way of line 16. The reactor effluent is
fractionated in the fractionator to produce the desired product
fractions. The heavy product fraction leaves fractionator 20
through line 26 as product. A portion of the light product fraction
with unreactive paraffins from the feed is removed from the top of
the fractionator and passed by way of line 21, pump 22, line 23,
pump 24 and line 25 to second guard bed 12 which is in the
regeneration phase, desorbing the contaminants which have been
removed from the feed. The guard bed vessels are switched
alternately between feed treatment and regeneration by means of
conventional valving (not shown) which may also direct effluent
from the guard bed during the regeneration portion of the cycle to
recovery facilities by way of line 27 so as to permit removal of
the desorbed contaminants. When desorption of the contaminants from
the guard bed in the regeneration phase is complete, the beds can
be switched so that bed 11 is in the regeneration phase, receiving
product from fractionator 20 to desorb contaminants and bed 12 is
put into the feed treatment phase with the feed passing from bed 12
to reactors 15A, 15B and 15C. If the reaction in reactors 15 is the
olefin/aromatics alkylation reaction, using a mixed refinery
olefin/reformate stream as the feed, the contaminant desorption
stream will usually be a light stream with a heavier alkylaromatic
fraction going to recovered product.
[0021] The guard beds may be operated on the swing cycle with two
beds, 11 and 12 as described above. If desired, a purge phase may
be added before a regenerated bed is returned to feed treatment
although this will not always be necessary since the bed contains
at that point only innocuous reaction products which can be
recycled to the reaction. A three-bed guard bed system may be used
with the two beds used in series for contaminant removal and the
third bed on regeneration. With a three guard system used to
achieve low contaminant levels by the two-stage series sorption,
the beds will pass sequentially through a three-phase cycle of:
regeneration, second bed sorption, first bed sorption.
[0022] The compressed fraction from pump 24 may also be sent
through branch lines 29A, 29B and 29C to the reactors to rejuvenate
the catalysts, as described in co-pending patent application Ser.
No. ______ (claiming priority from Provisional Application No.
60/834,805, filed 2 Aug. 2006).
Olefin and Aromatic Feeds, Reaction Conditions
[0023] The light olefins and aromatic feeds as well as the actual
conditions used for converting them to gasoline boiling range
products and the products themselves will be as described in the
prior applications referred to above. The conditions used in other
alkylaromatics processes will be those appropriate to the selected
process and therefore chosen according to conventional criteria.
The olefinic feeds are generally obtained from a catalytic cracking
unit operating on a hydrocarbon feed such as vacuum gas oil or a
resid fraction. The olefins will normally be the light olefins in
the FCC off-gas in the range C2 to C.sup.4 as the higher olefins
will be removed by the fractionation for separate use directly as
gasoline. The aromatics will normally be derived from a reformate
stream. More extended descriptions of both streams in their
application to the production of olefin polymer and alkylaromatic
fuels are given in the prior applications such as those
described.
[0024] A light olefin stream such as ethylene, propylene,
optionally with butylene and possibly other light olefins, is
polymerized or reacted with an aromatic compound or compounds to
form a gasoline boiling range [C.sub.5+-200.degree. C.]
[C.sub.5+-400.degree. F.] product. The process is carried out in
the presence of a molecular sieve catalyst which is usually a
member of the MWW family of zeolites, a family which includes
zeolites PSH 3, MCM-22, MCM-49, MCM-56, SSZ 25, ERB-1 and ITQ-1
although other sieves such as ZSM-5 or ZSM-11 may be used,
especially in the vapor phase alkylation process described in Ser.
No. 11/362,255. The term "polymerized" is used here consistent with
the petroleum refinery usage although, in fact, the process is one
of oligomerization (which term will be used in this specification
interchangeably with the conventional term) in which a low
molecular weight polymer is the desired product. The process is
carried out in a fixed bed of the catalyst, in the case of the
straightforward polymerization process, with feed dilution,
normally a hydrocarbon diluent, or added quench to control the heat
release which takes place.
[0025] The preferred catalysts used in the present process contain,
as their essential catalytic component, a molecular sieve of the
MWW type, as described in the prior applications referred to above.
In addition, a matrix material or binder in order to give adequate
strength to the catalyst as well as to provide the desired porosity
characteristics in the catalyst. High activity catalysts may,
however, be formulated in the binder-free form by the use of
suitable extrusion techniques, for example, as described in U.S.
Pat. No. 4,908,120. When used, matrix materials suitably include
alumina, silica, silica alumina, titania, zirconia, and other
inorganic oxide materials commonly used in the formulation of
molecular sieve catalysts. For use in the present process, the
level of MCM-22 in a finished matrixed catalyst of the preferred
type will be typically from 20 to 70% by weight, and in most cases
from 25 to 65% by weight. Catalyst formulation techniques are
described in the prior applications, to which reference is made for
a description of them.
Guard Bed
[0026] The catalyst used in the guard bed may be a reactive
material, that is one, which undergoes a surface reaction with the
contaminants in the feed stream so as to hold the contaminants on
the exterior or interior surfaces of the material. Materials of
this kind may conveniently be the same catalyst used in the
polymerization or alkylation reactor as a matter of operating
convenience but this is not required: if desired another catalyst
or sorbent to remove contaminants from the feed may used, typically
a cheaper guard bed sorbent, e.g a used catalyst from another
process. Alternatively, a non-reactive sorbent such as alumina or
silica-alumina may be used. The objective of the guard bed is to
remove the contaminants from the feed before the feed comes to the
reaction catalyst and provided that this is achieved, there is wide
variety of choice as to guard bed catalysts and conditions useful
to this end. The contaminants which are normally encountered are
sulfur compounds such as thiols, sulfides, thiophenes and
disulfides; in processing light aromatics stream, nitrogen
contaminants may also be encountered, for example, nitrogen-based
organic species derived from aromatics extraction operations using
solvents such as N-methylpyrrolidone (NMP), dimethylformamide
(DMF), N-formyl morpholine (NFM) and similar materials. These
contaminants may adversely affect catalyst performance and
accordingly, should be removed from the feedstream before it
encounters the catalyst in the main reactor. The volume of the
guard bed will normally not exceed about 20% of the total catalyst
bed volume of the unit.
Guard Bed Regeneration
[0027] The guard bed is regenerated at periodic intervals when
necessary by switching the on-line bed in the feed treatment phase
to regeneration. This can be done by valving in the conventional
manner for swing reactor operation. Because the regeneration is
carried out using a portion of the product stream, no purging of
the feed is necessary before switching to the regeneration phase
nor is purging of the regeneration stream necessary before
reverting to the feed treatment phase although, if purging is not
carried out, care should be taken to see that the contaminants are
substantially completely removed from the bed prior to the bed
switching.
[0028] The guard bed regeneration is carried out using product from
the reactor. Normally, it will be adequate to divert only a portion
of the product volume to the guard bed in order to regenerate the
bed over an acceptable period of time and so the regeneration gas
can be taken as a slip stream from the product stream. A fraction
of the product stream will normally be used, selecting the fraction
with the most favorable desorption characteristics for the
contaminants which actually become sorbed onto the guard bed
material. When the reaction is one of olefin polymerization,
without using a reformate co-feed, the regeneration is preferably
carried out using a light hydrocarbon fraction (C4-C8, preferably
C4-C6) from the product fractionator since this fraction is
reasonably inert and has good desorption characteristics for the
most common contaminants sorbed onto zeolite guard beds, e.g.
MCM-22 or MCM-49. If the reaction is the aromatic alkylation
reaction, the regeneration can be carried out with a light
alkylaromatic fraction, for example, the C8-C10 fraction. In both
cases, the regeneration stream will typically include light
paraffins, normally in the C4-C8 range, from any feed components
which have passed unchanged through the oligomerization or
alkylation steps, in addition to the lighter fractions resulting
from the processing. The nature of the light paraffins from the
process feed will be dependent on the composition of the feed
stream(s): reformate streams, for example, may often include C6 and
C7 paraffins, the amounts depending on reforming conditions and
product cut points. In the case of the olefin oligomerization
process, the light fraction used to regenerate the guard bed may
include the monolefinic oligomerization products, such as the
di-branched octenes from a C4 olefin feed; with other olefin feeds,
including mixed olefin feeds, other oligomerization products will
be obtained and may also be used for the regeneration of the guard
bed.
[0029] The regeneration is carried out an elevated temperature,
typically above ambient with a temperature of at least 100.degree.
C. being customary and usually in the range of 150-300.degree. C.,
preferably 150-250.degree. C. High pressures are not necessary and,
in fact relatively low pressures may assist desorption. Pressure
will therefore normally be in the range of 1000 kPag to 4000 kPag
(about 145 to 580 psig) with pressures of 1000 to 2000 kPag (about
145 to 290 psig) being preferred, although in many cases, the
pressures imposed by existing equipment will dictate as a practical
matter the pressure actually used.
[0030] Space velocity through the bed is not an important factor
provided that the regeneration phase is continued long enough to
secure the desired degree of contaminant desorption. Normally, the
space velocity of the regeneration gas will be in the range of 0.1
to 10 LHSV (hr.sup.-1) relative to the volume of the guard bed
material and in most cases from 0.5 to 5 LHSV, with velocities of
about 0.5 to 2.0 LHSV representing typical operation.
EXAMPLE
[0031] The efficacy of the contaminant desorption treatment for the
guard bed material was demonstrated using a reactive guard bed
contained in a 10 mm diameter microunit containing 2 g of an MCM-49
catalyst packed with sand to make up the reactor volume. A feed
mixture of benzene and propylene (2.8:1 molar ration benzene:
propylene) was passed through the tube held at a temperature of
120.degree. C. and a pressure of 2400 kPag (350 psig), using a
space velocity of 1.25 WHSV of propylene. From day 1 until day 20,
the feed included 200 ppm water and the propylene conversion was at
or close to 100% during this time. At day 20, 25 ppmw sulfur was
added to the feed as iso-propyl sulfide and in the course of five
days, the conversion dropped to about 23-47 percent. On reverting
to a clean feed (200 ppmw water), the propylene conversion reverted
over about five days to essentially 100 percent. After about 32
days on stream, the feed was changed to a dry feed (less than 10
ppmw water) containing 25 ppmw sulfur as iso-propyl sulfide. The
propylene conversion again decreased, to a level of about 31-50%.
On removal of the sulfur from the feed at about day 43, the
propylene conversion reverted once more to essentially 100
percent.
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