U.S. patent application number 14/921464 was filed with the patent office on 2016-02-11 for xylene isomerization process and catalyst therefor.
The applicant listed for this patent is ExxonMobil Chemical Patents Inc.. Invention is credited to Surbhi Jain, Shifang L. Luo, John Di-Yi Ou.
Application Number | 20160039727 14/921464 |
Document ID | / |
Family ID | 50184127 |
Filed Date | 2016-02-11 |
United States Patent
Application |
20160039727 |
Kind Code |
A1 |
Ou; John Di-Yi ; et
al. |
February 11, 2016 |
Xylene Isomerization Process and Catalyst Therefor
Abstract
The invention concerns a xylenes isomerization process for the
production of equilibrium or near-equilibrium xylenes from a
feedstream comprising phenol and/or styrene.
Inventors: |
Ou; John Di-Yi; (Houston,
TX) ; Luo; Shifang L.; (Annandale, NJ) ; Jain;
Surbhi; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Chemical Patents Inc. |
Baytown |
TX |
US |
|
|
Family ID: |
50184127 |
Appl. No.: |
14/921464 |
Filed: |
October 23, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13961530 |
Aug 7, 2013 |
9193645 |
|
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14921464 |
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61695439 |
Aug 31, 2012 |
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Current U.S.
Class: |
585/481 |
Current CPC
Class: |
C07C 2529/40 20130101;
C07C 5/2737 20130101; C07C 5/2737 20130101; Y02P 20/52 20151101;
C07C 15/08 20130101 |
International
Class: |
C07C 5/27 20060101
C07C005/27 |
Claims
1. A process for the isomerization of a paraxylene-depleted
aromatic hydrocarbon feedstream comprising styrene, wherein said
isomerization of a paraxylene-depleted feedstream is conducted in
the presence of a catalyst comprising HZSM-5, wherein said HZSM 5
is characterized by an average crystal size of <0.1 micron and a
SiO.sub.2/Al.sub.2O.sub.3 molar ratio in the range of about 20-100,
in a reactor at a temperature of less than 295.degree. C., and a
pressure sufficient to maintain the xylenes in liquid phase.
2-4. (canceled)
5. The process of claim 1, wherein said feedstream is characterized
as containing styrene in the amount of 100 ppm or less.
6. The process of claim 1, wherein said feedstream is characterized
as containing styrene in the amount of 50 ppm or less.
7. The process of claim 1, wherein said feedstream is characterized
as containing styrene in the amount of 20 ppm or less.
8. The process of claim 1, further characterized in that said
process is operated in a continuous mode with a feedstream
containing low ppm levels of dissolved H.sub.2 in the range of
about 4 to 100 ppm.
9. The process of claim 1, further characterized in that said
process is operated in a continuous mode with a feedstream
containing low ppm levels of dissolved H.sub.2 in the range of
about 4 to 20 ppm.
10. The process of claim 1, further characterized in that said
process is operated in a cyclic mode with an H.sub.2-free
feedstream, and further wherein said catalyst is periodically
regenerated by a step including contacting said catalyst with an
H.sub.2-containing feedstream, wherein said H.sub.2-free feedstream
is characterized as containing less than 4 ppm dissolved H.sub.2
and said H.sub.2-containing feedstream is characterized as
containing about 4 or more ppm dissolved H.sub.2.
11. The process of claim 1, wherein said reactor is at a
temperature of 260.degree. C. or less.
12. The process of claim 1, including a step of decreasing the
amount of phenol and/or styrene upstream of said isomerization.
13. The process of claim 1, wherein said paraxylene-depleted
feedstream is characterized as an aromatic hydrocarbon feedstream
consisting essentially of a xylenes wherein the concentration of
paraxylene is less than about 22 wt % relative to the total C8
aromatic hydrocarbons in said feedstream.
14. The process of claim 12, wherein said decreasing comprises:
treating a paraxylene-containing feedstream comprising styrene to
reduce the amount of said styrene, wherein said treating comprises
contact of said paraxylene-containing feedstream with a material
selective for the reduction of styrene relative to phenol and
paraxylene to produce a first product having a reduced
concentration of styrene.
15. The process of claim 14, wherein said paraxylene-containing
feedstream comprises paraxylene obtained from reformate, an
alkylation reaction, imported paraxylene, and mixtures thereof.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of
Provisional Application No. 61/695,493, filed on Aug. 31, 2012.
FIELD OF THE INVENTION
[0002] The invention relates to a xylene isomerization process and
catalyst therefor.
BACKGROUND OF THE INVENTION
[0003] An equilibrium mixture of xylenes contains about 24 wt %
paraxylene (PX), 56 wt % metaxylene (MX), and 20 wt % orthoxylene
(OX). PX is relatively high value as compared with MX and OX, since
it is a starting material for polyester fibers and resins.
Therefore it is advantageous to isomerize OX and/or MX to PX, such
as isomerizing a PX-lean stream (i.e., depleted from equilibrium
value) to equilibrium for PX recovery. It is an active area of
research.
[0004] Typically, xylene streams found in chemical or petrochemical
plants also contain ethylbenzene (EB). Conventional isomerization
technologies operating at high temperatures (e.g., 400.degree. C.)
in vapor phase isomerize the xylenes and dealkylate EB to benzene.
Other vapor-phase isomerization technologies convert EB to xylenes
in addition to xylenes isomerization. There are also liquid-phase
isomerization technologies. Conventional isomerization technologies
typically produce significant amounts (>0.5 mol %) of byproducts
such as benzene and A9+ (aromatic hydrocarbons having 9 or more
carbon atoms), and are also sensitive (e.g., the isomerization
catalyst deactivates) to impurities in the feedstream. Most
isomerization technologies also require high hydrogen partial
pressure to maintain the catalyst activity, which makes the process
arrangement complex and expensive.
[0005] U.S. Pat. No. 6,180,550 teaches ZSM-5 useful in the liquid
phase isomerization of xylene. The zeolite used has a
SiO.sub.2/Al.sub.2O.sub.3 ratio of less than 20.
[0006] U.S. Pat. No. 6,448,459 teaches isomerization without
hydrogen in a liquid phase diluted with toluene used as desorbent
in a simulated moving bed adsorptive separation unit. The catalyst
used in the liquid phase isomerization is said to be zeolitic, for
example ZSM-5, and in the example it is specified that there is no
hydrogen.
[0007] U.S. Pat. No. 6,872,866 teaches a two stage, liquid or
partially liquid phase isomerization process using a zeolitic-based
catalyst system preferably based on zeolite beta and on
pentasil-type zeolite. This patent also sets forth numerous
examples of prior art catalyst systems, including ZSM-5.
[0008] U.S. Pat. No. 7,244,409 teaches small crystallite ZSM-5
which may be used for isomerization reactions.
[0009] U.S. Pat. No. 7,371,913 teaches a ZSM-5 mole sieve further
comprising Ga used as an isomerization catalyst to provide an
increased amount of PX in the liquid phase in the substantial
absence of H.sub.2. The amount of H.sub.2 present is stated to be
less than 0.05, preferably less than 0.01, mole H.sub.2/mole
feed.
[0010] U.S. Pat. No. 7,495,137 teaches a two-stage isomerization
system, the first zone operating in the absence of hydrogen (as in
the above patent) using a platinum-free catalyst and the second
zone using a catalyst comprising a molecular sieve and a
platinum-group metal component. The catalyst in the first zone is
preferably a Ga-MFI-type zeolite and it is preferred that the
catalyst for the first zone has a Si:Al ratio greater than about
10.
[0011] U.S. Pat. No. 7,592,499 teaches a multi-stage process for
co-producing PX and styrene from a feed of hydrocarbons comprising
xylenes and EB. In the first stage, PX is separated from the feed
by means of a simulated moving bed adsorptive separation column to
produce a raffinate comprising EB, OX, and MX. Next, EB in the
raffinate is dehydrogenated to styrene. Eventually a stream
containing unconverted EB, MX, and OX is obtained and contacted
with an isomerization catalyst preferably in the liquid phase. The
catalyst is zeolitic, such as ZSM-5.
[0012] U.S. Pat. No. 7,932,426 teaches a two-stage isomerization
process, the first stage in the liquid phase in the substantial
absence of H.sub.2 to obtain an intermediate stream. In the second
stage, the intermediate stream is mixed with a stream rich in
naphthene, and contacted with an isomerization catalyst. By
"substantial absence of H.sub.2" is meant no free hydrogen is added
to a feed mixture and any dissolved hydrogen from prior processing
is substantially less than about 0.05 moles/mole of feed. The first
isomerization catalyst includes a molecular sieve, typically an
aluminosilicate having a Si:Al.sub.2 ratio greater than about 10.
In the example given, a Ga source is used to make the catalysts for
both the first and second isomerization steps.
[0013] U.S. Publication No. 2010-0152508 (U.S. application Ser. No.
12/612,007, now allowed) teaches a process for isomerization that
is at least partially in the liquid phase and includes a step of
removal of C9 aromatic hydrocarbons from a feedstream including C8
and C9 aromatic hydrocarbons.
[0014] U.S. Publication No. 2011-0263918 teaches, in embodiments
the process takes a PX-lean feedstream to produce a product having
equilibrium or near equilibrium xylenes. In embodiments the process
produces very low levels of by-products (such as <0.3 wt. %).
Thus, there is no need for additional distillation columns.
Furthermore, the technology can operate without the presence of any
hydrogen or with only low ppm levels of dissolved hydrogen, making
it a simple and cost-effective process.
[0015] Other relevant documents include U.S. Pat. Nos. 7,439,412;
7,626,065; U.S. Publication Nos. 2011-0108867; 2012-0108868; and
U.S. patent application Ser. No. 13/861,473.
[0016] It has recently been discovered that paraxylene-enriched
streams from the alkylation of benzene and/or toluene with methanol
and/or dimethylether (DME) over acid-active catalysts such as
phosphorus-containing ZSM-5 contain oxygenates such as phenol and
olefins such as styrene, which are not easily removed from the
alkylation reactor feedstreams. The presence of such impurities are
believed to be detrimental to numerous downstream processing steps
in the conversion of paraxylene to polyester fibers and resins.
Methods of treating such phenol and styrene-containing product
streams from such sources as the aforementioned alkylation reaction
in the presence of acid-active catalyst, reformate streams,
imported streams (e.g., contamination by prior cargoes) are known;
see U.S. patent application Ser. Nos. 13/618,211; 13/557,605;
13/483,836; 13/487,651; and U.S. Publication Nos. 2011-0092755;
2011-0092756; and references cited therein.
[0017] The present inventors have discovered a catalyst system for
a liquid isomerization process that survives a low level of styrene
and phenols. In embodiments the process takes a PX-lean feedstream
comprising at least one of styrene and phenol to produce a product
having equilibrium or near equilibrium xylenes. Furthermore, the
technology can operate without the presence of any hydrogen or with
only low ppm levels of dissolved hydrogen, making it a simple and
cost-effective process.
SUMMARY OF THE INVENTION
[0018] The invention is directed to a xylenes isomerization
process, including a liquid phase isomerization, for the production
of equilibrium or near-equilibrium xylenes, comprising passing a
paraxylene-depleted aromatic hydrocarbon feedstream containing at
least one of phenol and styrene in the amount of about 10 ppm
phenol or less and/or 100 ppm styrene or less to a liquid
isomerization process in the presence of an appropriate catalyst
under suitable process conditions, including a temperature of less
than 295.degree. C., preferably less than 260.degree. C.
(500.degree. F.) and a pressure sufficient to maintain the xylenes
in liquid phase, to produce a product aromatic hydrocarbon process
stream having an increased amount of paraxylene relative to said
feedstream.
[0019] In embodiments the amount of phenol in said feedstream is 5
ppm or less, and in other embodiments the amount of phenol is 2 ppm
or less. In embodiments the amount of styrene in said feedstream is
50 ppm or less, and in other embodiments the amount of styrene in
said feedstream is 20 ppm or less.
[0020] In embodiments there is also at least one step of
purification of said feedstream upstream and/or downstream of said
liquid isomerization process, wherein said at least one step is
selected from removal of at least a portion of styrene in said
feedstream and/or removal of at least a portion of phenol in said
feedstream.
[0021] In embodiments, the liquid phase isomerization process
utilizes a catalyst comprising ZSM-5 and/or MCM-49.
[0022] In embodiments the catalyst comprises ZSM-5 crystals in the
protonated form (HZSM-5), and further characterized by a crystal
size of <0.1 micron and a SiO.sub.2/Al.sub.2O.sub.3 molar ratio
of about 20-100, preferably 20-50.
[0023] In embodiments, the process can be operated in a continuous
mode with low ppm levels of H.sub.2 in the feed and in other
embodiments in a cyclic mode without H.sub.2 in feed but with
periodic regenerations of the catalyst.
[0024] In embodiments, the process is operated in a continuous mode
with from 4 to 10 ppm H.sub.2 at a temperature of less than
295.degree. C. and total pressure sufficient to maintain the
xylenes in the liquid phase.
[0025] In embodiments, the process is operated in a cyclic mode
without H.sub.2 in the feed but with periodic regenerations using
greater than 5 ppm H.sub.2 in the feed, in embodiments at least 10
ppm H.sub.2 in the feed, in other embodiments at least 20 ppm
H.sub.2 in the feed.
[0026] It is an object of the invention to provide a method of
processing paraxylene-depleted feedstreams containing at least one
of styrene and/or phenol, including a liquid phase isomerization
process which, compared to conventional xylenes isomerization
processes, provides at least one of the advantages selected from
low investment, low operating costs, low byproduct yields, and low
xylene loss.
[0027] These and other objects, features, and advantages will
become apparent as reference is made to the following detailed
description, preferred embodiments, examples, and appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 illustrates paraxylene yields for ZSM-5 crystals of
various sizes for embodiments of the liquid phase xylene
isomerization process according to the invention.
[0029] FIG. 2 is a comparison of liquid isomerization of different
feeds, illustrating at least one advantage of the present
invention.
DETAILED DESCRIPTION
[0030] According to the invention, there is provided a process for
the isomerization of a paraxylene-depleted aromatic hydrocarbon
feedstream comprising at least one of phenol, styrene, and mixtures
thereof, wherein phenol is present in the amount of 10 ppm or less,
such as 5 ppm or less, or 2 ppm or less, and/or styrene is present
in the amount of 100 ppm or less, such as 50 ppm or less, or 20 ppm
or less, wherein said isomerization of a paraxylene-depleted
feedstream is in the presence of a catalyst comprising MCM-49
and/or an HZSM-5 catalyst, wherein said HZSM-5 catalyst is
characterized in embodiments by a crystal size of <0.1 micron
and a SiO.sub.2/Al.sub.2O.sub.3 molar ratio of about 20-100,
preferably 20-50, in a reactor at a temperature of less than
295.degree. C., preferably 260.degree. C. or less, and a pressure
sufficient to maintain the xylenes in liquid phase.
[0031] The process may use low ppm levels of H.sub.2. Preferably,
the H.sub.2 concentration in the liquid phase in said reactor is
less than 100 ppm (wt % unless otherwise specified). In
embodiments, the process is operated in a continuous mode with from
4 to 10 ppm H.sub.2. In other embodiments the process is operated
in a cyclic mode without H.sub.2 in the feed but with periodic
regenerations using greater than 5 ppm H.sub.2 in the feed, in
embodiments at least 10 ppm H.sub.2 in the feed, in other
embodiments at least 20 ppm H.sub.2 in the feed. In still other
embodiments, a combination of the aforementioned continuous mode
and cyclic modes may be utilized.
[0032] In embodiments, the process utilizes a catalyst comprising
ZSM-5 crystals along with a binder or the ZSM-5 crystals may be
self-bound.
[0033] In preferred embodiments the ZSM-5 catalyst, if present, can
be characterized in any of the embodiments of the invention by one
or more of the following characteristics: [0034] the ZSM-5 is in
the proton form (HZSM-5); [0035] the ZSM-5 has a crystal size of
less than 0.1 microns; [0036] the ZSM-5 has a mesoporous surface
area (MSA) greater than 45 m.sup.2/g; [0037] the ZSM-5 has a
zeolite surface area (ZSA) to mesoporous surface area (MSA) ratio
of less than 9; and [0038] a silica to alumina weight ratio in the
range of 20 to 50.
[0039] As used herein, "crystal size" means average crystal size
and is conveniently determined by electron microscopy, as is
well-known per se in the art. The surface areas may also be
determined by methods well-known in the art.
[0040] The ZSM-5 catalyst can be formulated using various
techniques such as extrusion, pelletization, oil dropping, spray
drying, and the like, techniques which are per se well-known in the
art. Optionally, binder materials such as alumina, silica, clay,
aluminosilicate, may be used in the formulation. In preferred
embodiments, the catalyst is characterized by one or more of the
following properties with respect to the binder: [0041] the
zeolite:binder weight ratio is from 1:9 to 9:1; [0042] the binder
preferably comprises silica, alumina, and aluminosilicate; and
[0043] the catalyst is preferably extruded using acetic acid as
extrusion aid.
[0044] The preferred reactor is fixed bed and the flow may be up or
down.
[0045] In embodiments, the process can be operated in a continuous
mode with low ppm levels of H.sub.2 dissolved in the feed and in
other embodiments in a cyclic mode without the H.sub.2 in feed but
with periodic regenerations.
[0046] By "low ppm" is meant levels which one of ordinary skill in
the art would express as "ppm", generally below 100 ppm. The
expression "ppm" is weight ppm (wppm) unless otherwise
specified.
[0047] In embodiments, very low levels of by products are produced,
such as less than 1 wt % or preferably less than 0.5 wt % of by
products selected from non-aromatic compounds, benzene and
A9+(aromatic hydrocarbons having 9 or more carbon atoms), and
mixtures thereof.
[0048] The process comprises contacting a feedstream comprising C8
aromatic hydrocarbons with a catalyst suitable for isomerization,
preferably a catalyst comprising MCM-49 and/or ZSM-5, preferably a
catalyst comprising ZSM-5 and more preferably having one or more of
the aforementioned properties and most preferably all of the
aforementioned properties, at a temperature below 295.degree. C.,
preferably below 280.degree. C., and at a pressure sufficiently to
keep the reactant in liquid phase. One of skill in the art in the
possession of the present disclosure would be able to determine
other operating characteristics, such as a lower temperature,
within which the present invention may be practiced. Lower limits
may be, for instance, above 180.degree. C. or 190.degree. C. or
200.degree. C., or 210.degree. C., and the like. The flow rate
(measured as wt-hourly space velocity, "WHSV") can be selected by
one of ordinary skill in the art in possession of the present
disclosure, but may advantageously be selected within the range
from 1 to 100 hr.sup.-1 (WHSV), preferably from 1 to 20 hr.sup.-1
(WHSV), and more preferably from 1 to 10 hr.sup.-1 (WHSV).
[0049] In embodiments, a process for the isomerization of an
aromatic hydrocarbon feedstream consisting essentially of a xylenes
wherein the concentration of paraxylene is less than about 22 wt %
relative to the total C8 aromatic hydrocarbons in said feedstream,
and at least one of phenol and styrene, said process
comprising:
[0050] (a) treating said feedstream to reduce the amount of at
least one of phenol and styrene relative to the amount of
paraxylene in said aromatic hydrocarbon feedstream, wherein said
treating comprises: (i) contact of said feedstream with a material
selective for the reduction of phenol relative to styrene and
paraxylene; and/or (ii) contact of said feedstream with a material
selective for the reduction of styrene relative to phenol and
paraxylene, to produce a first product having a reduced
concentration of phenol and/or styrene relative to said feedstream
in (a), and then
[0051] (b) isomerizing said first product in the liquid phase in
presence of an HZSM-5 catalyst, characterized in embodiments by a
crystal size of <0.1 micron and a SiO.sub.2/Al.sub.2O.sub.3
molar ratio of about 20-100, in a reactor at a temperature of less
than 295.degree. C., preferably 260.degree. C. or less, and a
pressure sufficient to maintain the xylenes in liquid phase, to
product a second product having an increased amount of paraxylene
relative to said feedstream in (a). In preferred embodiments, the
feedstream in (a) comprises paraxylene from reformate and/or
imported paraxylene. In a more preferred embodiment of the
aforementioned embodiment or preferred embodiment, said first
product comprises at least one of phenol and styrene, and wherein
the amount of phenol is less than 10 ppm, preferably less than 5
ppm, more preferably less than 2 ppm, and the amount of styrene is
less than 100 ppm, preferably less than 50 ppm, more preferably
less than 20 ppm. The term "selective for reduction of" with
respect to phenol and/or styrene means that the specified species
is removed or reduce, such as by adsorption, isomerization, and the
like, in an amount greater than the removal (again, such as by
adsorption, isomerization, and the like) of the other xylenes that
the feedstream. As used herein, when the term "consists essentially
of" (or similar language) means species which affect the basic and
novel features of the invention, e.g., styrene, phenol, and the
xylene isomers.
[0052] Other details of xylenes liquid phase isomerization are
available in U.S. Pat. Nos. 7,439,412; 7,626,065, U.S. application
Ser. No. 12/612,007, now allowed; and U.S. Publication No.
2011-0263918.
[0053] The following experiments are intended to illustrate a
process according to the present invention and should be taken as
representative thereof and not limiting.
Example 1
[0054] Three ZSM-5 crystals listed below in Table 1 were prepared
to investigate the effects of silica/alumina ratio and crystal size
in a process according to the present invention.
TABLE-US-00001 TABLE 1 Crystal Sizes, ZSM-5 Crystals
SiO.sub.2/Al.sub.2O.sub.3 Ratios micron I 25 0.5 II 60 <0.1 III
25 <0.1
[0055] The crystals were ion exchanged to proton form and extruded
into 1/20'' (about 0.127 cm) extrudates with an alumina binder. The
weight ratio of crystal to binder was 4. The extrudates were
calcined at 538.degree. C. The extrudates were evaluated using a
feed of 13.28 wt % para-xylene, 63.72 wt % meta-xylene, 17.94 wt %
ortho-xylene, 1.52 wt % ethylbenzene, 1.28 wt % toluene, and 2.25
wt % non-aromatics, and low levels of benzene and nine-carbon
aromatic compounds. The tests were performed in a 1/4'' (about
0.635 cm) stainless steel reactor with the feed going up flow
through the catalyst bed. Test conditions are listed below in Table
2.
TABLE-US-00002 TABLE 2 Flowrate, Weight Catalyst Reactor Reactor
Hourly Space Crystals loading, g temp., .degree. C. pressure, psig
Velocity (hr.sup.-1) I 0.4550 246 265 3.69 (1928 kPa) II 0.4545 246
265 3.69 III 0.4610 246 265 3.74
[0056] Test results are shown in FIG. 1. It is seen that all three
catalysts were able to isomerize meta- and ortho-xylene to
para-xylene. However, the paraxylene yield decreased in the order
of III>I>II and that the catalyst with crystal II delivered a
near-equilibrium para-xylene yield (97-98% equilibrium). A
comparison between Catalysts III and II shows that lowering
silica/alumina ratio from 60 to 25 raised para-xylene yield from
about 20.2% to about 22.2% and between Catalysts III and I shows
that reducing crystal size from 0.5 to <0.1 micron raised
para-xylene yield from an average of 21.6% to 22.2%.
Example 2
[0057] Two parallel runs were conducted to investigate the effect
of feed contaminants phenol and styrene on liquid phase
isomerization. Catalyst was 1/20'' (about 0.127 cm) catalyst
extrudates prepared from Catalyst III. Run #1 used Test Feeds and
Run #2 used Reference Feeds (free of styrene and phenol). Typical
compositions of the two feeds are 3.6-4.7 wt % paraxylene,
57.9-60.4 wt % metaxylene, 24.8-26.0 wt % orthoxylene, 8.7-9.5 wt %
ethylbenzene, 0.15-0.19 wt % toluene, 1.2-2.8 wt % non-aromatics,
and low levels of benzene and nine-carbon aromatic compounds. Test
Feeds contained 20 ppm styrene and 2 ppm phenol.
[0058] Performance tests were conducted in a 1/4'' (0.635 cm)
stainless steel reactor with the feed going up flow through a
catalyst bed. Test conditions are listed below in Table 3.
TABLE-US-00003 TABLE 3 Reactor Flowrate, Weight Catalyst Reactor
pressure, Hourly Space loading, g temp., .degree. C. psig Velocity
Run #1 with 0.5056 235, 255 265 1.5-2.6 Test Feed Run #2 with
0.5150 235, 255 265 1.8-2.5 Reference Feed
[0059] Test results are shown in FIG. 2. It is seen that both Run
#1 with Test Feeds and Run #2 with Reference Feeds achieved
near-equilibrium paraxylene yield (97-98% of equilibrium value).
Furthermore, a comparison between two runs shows that feed
contaminants such as 20 ppm styrene and 2 ppm phenol had no impact
on catalyst stability.
Example 3
[0060] The following experiments were run using the preferred
catalyst of the invention on various feedstreams (Table 4) at the
same conditions, including a temperature of 255.degree. C. and 2.1
hr.sup.-1 (WHSV). Experiments were run in a micro-unit; "PX
concentration decrease (%)" is paraxylene decrease relative to
other C8 aromatic hydrocarbons in the product versus feed, and are
extrapolations based on observed trends for six months (run 1 and
2), one week (run 3), and 2 weeks (2 weeks).
TABLE-US-00004 TABLE 4 Run Phenol, ppm Styrene, ppm PX
concentration decrease (%) 1 0 0 0 (i.e. no deactivation) 2 2 20 0
3 2 43 4.3 4 4 20 4.7
[0061] Two styrene concentrations studied were 20 and 43.2 wppm.
The temperature of testing was 255.degree. C. for both feeds.
Catalyst aging data showed that with 43.2 wpm styrene in the feed,
the LPI catalyst deactivated at a rate of 4.3% decrease in PX yield
per year (Table 1).
[0062] Two phenol concentrations studied were 2 and 4 wppm.
Temperatures of testing were 255 and 275.degree. C. for the 2 wppm
phenol feed, and 255, 265, and 275.degree. C. for the 4 wppm phenol
feed. With 2 wppm phenol in the feed, no catalyst aging was
observed at either temperature (Table 1). With the 4 wppm phenol in
the feed, however, catalyst aging was observed at 255 and
265.degree. C., but not at 275.degree. C.; the aging rates were
4.66% decrease in PX yield per year at 255.degree. C. and 0.88% at
265.degree. C. (Table 3).
TABLE-US-00005 TABLE 5 Impact of Styrene and Phenol on LPI Catalyst
Aging Catalyst Aging Rate Phenol, Styrene, (Drop in absolute PX
Temp, .degree. C. WHSV, h-1 wppm wppm Yield per year) 255 2.1 2 20
0 255 2.1 4 20 4.66% 265 2.1 4 20 0.88% 275 2.1 4 20 0 255 2.1 2
43.2 4.30%
[0063] In an embodiment, a PX-lean xylenes feedstream is fed to at
least one reactor. "PX-lean", for the purposes of the present
invention, means less than equilibrium amount of paraxylene, i.e.,
less than 24 mol % PX, based on 100 mol % xylene feedstream. In
preferred embodiments, the feedstream will comprise from 2 to 18
mol % PX, based on 100 mol % xylene feedstream.
[0064] In preferred embodiments, there is no H.sub.2 in the xylene
feedstream. It is difficult to measure H.sub.2 in xylene
feedstreams with any accuracy at low ppm levels (which may be
attempted by such methods as GC techniques commonly known), and
therefore the expression "no H.sub.z" as used herein is meant no
H.sub.2 beyond inevitable impurities, and also that there is no
purposeful (intentional) addition of H.sub.2 in such feedstreams.
The feedstreams may also be purged with an inert gas, such as
N.sub.2, to reduce even "inevitable impurities" of H.sub.z, if so
desired. The expression "H.sub.z-free", also used herein, is
intended to mean the same thing as "no H.sub.2". In embodiments, it
will be sufficient for the purposes of the present invention that
the "H.sub.2-free" feedstream contain less than or equal to 4 ppm
H.sub.2. Low ppm amounts of H.sub.2 used in the continuous mode
will be, preferably, greater than 4 ppm to about 10 ppm (equivalent
to 0.00001 moles of H.sub.2 per mole of xylenes). However, the
amount of H.sub.2 may be higher, such as 50 or 100 ppm.
[0065] In practice, one way of accomplishing low ppm levels of
H.sub.2 is by controlling the quantity of H.sub.2 added to the
"H.sub.2-free stream". For instance, we may know that a stream is
H.sub.2 free because we know what upstream processing it has gone
through, such as distillation which would rid a stream of H2
easily. Then by carefully controlling how much H.sub.2 is added, we
would know the final H.sub.2 quantity.
[0066] The reactor may be of any type, such as a fixed bed reactor,
fluid bed reactor, dense bed reactor, and the like. For example,
the reactor could be a tubular fixed bed reactor packed with a
catalyst suitable for isomerization of C8 aromatic hydrocarbons,
more preferably a catalyst comprising HZSM-5 and/or MCM-49. The
feedstream can flow through the reactor in either up-flow or
down-flow mode. Such a reactor can be operated at a temperature
below 295.degree. C., a flow rate within the range of 0.1 to 100
hr.sup.-1 (WHSV), and a pressure sufficiently high to keep the
feedstream at liquid phase inside the reactor and advantageously
maintained so as to achieve the low byproducts yields. The person
of ordinary skill in the art, in possession of the present
disclosure, can achieve such conditions without more than routine
experimentation. Once temperature is set, those skilled in the art
can determine what pressure to use to keep it in liquid phase based
on xylenes VLE (vapor-liquid-equilibrium) data. By way of example,
without intending to be limiting, in embodiments the pressure may
be above 100 psia, or preferably above 150 psia.
[0067] Depending on the operating conditions, the catalyst may
exhibit a slow deactivation. Low ppm levels of dissolved hydrogen
in the xylenes feed can completely mitigate such deactivation.
Thus, one can run the reactor with a H.sub.z-free xylene feed for a
period of time, the length of which depends on the selection of
operating parameters of the operator, and at the end of the
operation, replace the H.sub.z-free xylene feed with a
H.sub.z-containing xylene feed at the same operating conditions.
Thus, in this embodiment, H.sub.2 is now purposefully added to the
feed. Only low ppm levels are necessary. Although, as mentioned
above, GC techniques are not particularly good at measuring H.sub.2
levels accurately at low ppm levels in a C8 aromatic hydrocarbon
feedstream, the presence of H.sub.2 at such levels can be estimated
based on H.sub.2-xylenes VLE. For the purposes of the present
invention, when the "H.sub.z-free" feedstream is defined as
containing 0.00005 moles H.sub.z/mole xylenes or less, or 0.00001
moles H.sub.z/mole xylenes or less, the H.sub.z-containing xylene
feed should have greater than 0.00005 moles H.sub.z/mole xylenes,
or greater than 0.00001 moles H.sub.z/mole xylenes,
respectively.
[0068] It has been surprisingly found that the H.sub.z-containing
xylene feed will regenerate the catalyst to recover the lost
activity. The regeneration period can vary, such as from 1 day to a
few weeks. At the end of the regeneration, an operator can replace
the H.sub.z-containing feed with the H.sub.z-free feed and resume
the normal operation.
[0069] This regeneration technique has at least several advantages.
It is easy to implement and cost effective. Hydrogen can readily
dissolve in xylenes at the required level. By way of example, at
160 psia, 71 ppm H.sub.2 will be dissolved in xylenes at room
temperature.
[0070] It does not require such expensive and complex process
equipment as separator and recompressor that is required for the
high H.sub.2 partial pressure in conventional vapor-phase
isomerization technologies. The regeneration is done with a
H.sub.2-containing xylene feed at the same conditions as that for
the normal operation, which means that even during regeneration,
the reactor is still producing equilibrium or near equilibrium
xylenes; thus would be no productivity loss. In embodiments the
operator can increase the H.sub.2 concentration during the
regeneration to as high as 100% H.sub.2 and 0% xylenes and still
accomplish the objective.
[0071] In another embodiment, low ppm levels of H.sub.2 such as 4
to 100 ppm, preferably 4 to 10 ppm (within the standard sampling
error possible by current measurement techniques) are dissolved in
the xylene feed and fed to the reactor continuously throughout the
operation. The H.sub.2 at such levels will completely prevent the
catalyst deactivation. As a result, in this embodiment, there is
provided a process allowing for long, continuous operation without
any need to stop for regeneration. In addition to the advantages
listed above, in this embodiment a consistently high PX yield is
possible at all times.
[0072] Purification of the feedstream by removal of phenol and/or
styrene may be done by any method known in the art. Methods of
removal of phenol and/or styrene or other olefins have been
disclosed in U.S. Publication Nos. 2012-0048780; 2012-0316375; U.S.
patent application Ser. Nos. 13/618,211; 13/875,373; 13/875,402;
and references discussed therein. These processes are particularly
advantageously used when the source of phenols and/or styrene are
from an alkylation reactor process comprising the contact of
methanol and/or dimethylether with benzene and/or toluene in the
presence of an acid-active catalyst, particularly a
phosphorus-containing ZSM-5 catalyst that has been steamed at a
temperature on the order of 1000.degree. F. (538.degree. C.), such
as from about 500 to about 650.degree. C. Preferred materials to
remove at least a portion of phenol from the feedstream to the
isomerization process of the present invention include alumina,
silica, molecular sieves, zeolites, basic organic resins, and
mixtures thereof; preferred material to remove at least a portion
of styrene from the feedstream to the isomerization process of the
present invention include MWW molecular sieves, clay, and mixtures
thereof, such as at least one of MCM-22, MCM-36, MCM-49, MCM-56,
EMM-10 molecular sieves, and Engelhard F-24, Filtrol 24, Filtrol
25, and Filtrol 62 clays, Attapulgus clay and Tonsil clay.
[0073] One of skill in the art in possession of the present
disclosure can readily ascertain that phenol and/or styrene can be
present in numerous sources of paraxylene. By way of example, such
impurities may come from prior cargoes and may be present in
imported paraxylene, or it may come from other processes (other
than alkylation in the presence of an acid active catalyst) such as
reformate. Reformate may have, by way of example, on the order of
200-300 ppm styrene and on the order of 600-800 ppm styrenic
species (including dimethyl styrene). These are merely a few of the
many sources of paraxylene that need to be purified of phenol
and/or styrene in order to become suitable feedstreams for the
present process comprising liquid isomerization.
[0074] While the illustrative embodiments of the invention have
been described with particularity, it will be understood that
various other modifications will be apparent to and can be readily
made by those skilled in the art without departing from the spirit
and scope of the invention.
[0075] Trade names used herein are indicated by a .TM. symbol or
.RTM. symbol, indicating that the names may be protected by certain
trademark rights, e.g., they may be registered trademarks in
various jurisdictions. All patents and patent applications, test
procedures (such as ASTM methods, UL methods, and the like), and
other documents cited herein are fully incorporated by reference to
the extent such disclosure is not inconsistent with this invention
and for all jurisdictions in which such incorporation is permitted.
When numerical lower limits and numerical upper limits are listed
herein, ranges from any lower limit to any upper limit are
contemplated.
* * * * *