U.S. patent application number 15/637596 was filed with the patent office on 2017-10-19 for paraxylene separation process.
This patent application is currently assigned to ExxonMobil Chemical Patents Inc.. The applicant listed for this patent is ExxonMobil Chemical Patents Inc.. Invention is credited to Jeevan S. Abichandani, John Di-Yi Ou.
Application Number | 20170297976 15/637596 |
Document ID | / |
Family ID | 50685798 |
Filed Date | 2017-10-19 |
United States Patent
Application |
20170297976 |
Kind Code |
A1 |
Ou; John Di-Yi ; et
al. |
October 19, 2017 |
Paraxylene Separation Process
Abstract
The invention relates to a p-xylene separation process wherein
at least a portion of ethylbenzene present in an
aromatics-containing feed is removed prior to isomerization.
Aspects of the invention provide a process for producing p-xylene.
The process includes providing a first mixture comprising
.gtoreq.5.0 wt. % of aromatic C.sub.8 isomers, the C.sub.8 isomers
comprising p-xylene and ethylbenzene. A p-xylene-containing portion
and an ethylbenzene-containing portion are separated from the first
mixture in a first separation stage to form a p-xylene-depleted
raffinate. The first separation stage can include at least one
simulated moving-bed adsorptive separation stage. At least a
portion the p-xylene-depleted raffinate in the liquid phase is
reacted to produce a reactor effluent comprising aromatic C.sub.8
isomers. The first mixture can be combined with .gtoreq.50.0 wt. %
of the reactor effluent's aromatic C.sub.8 isomers. The combining
can be carried out before and/or during the separating of the
p-xylene and ethylbenzene portions.
Inventors: |
Ou; John Di-Yi; (Houston,
TX) ; Abichandani; Jeevan S.; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Chemical Patents Inc. |
Baytown |
TX |
US |
|
|
Assignee: |
ExxonMobil Chemical Patents
Inc.
Baytown
TX
|
Family ID: |
50685798 |
Appl. No.: |
15/637596 |
Filed: |
June 29, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14624861 |
Feb 18, 2015 |
9725378 |
|
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15637596 |
|
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61955907 |
Mar 20, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C07C 5/277 20130101;
C07C 5/277 20130101; C07C 2529/40 20130101; C07C 4/02 20130101;
C07C 6/06 20130101; C07C 15/08 20130101; C07C 5/222 20130101; C07C
15/08 20130101; C07C 7/12 20130101; C07C 5/2732 20130101; C07C 7/12
20130101 |
International
Class: |
C07C 5/27 20060101
C07C005/27; C07C 6/06 20060101 C07C006/06; C07C 5/27 20060101
C07C005/27 |
Foreign Application Data
Date |
Code |
Application Number |
May 12, 2014 |
EP |
14167834.2 |
Claims
1. A process for producing p-xylene, the process comprising: (a)
providing a first mixture comprising .gtoreq.5.0 wt. % of aromatic
C.sub.8 isomers, the C.sub.8 isomers comprising p-xylene and
ethylbenzene; (b) separating from the first mixture in a first
separation stage a p-xylene-containing portion and (i) an
ethylbenzene-containing portion and/or (ii) a non-aromatic
containing portion, to form a p-xylene-depleted raffinate; (c)
reacting at least a portion the p-xylene-depleted raffinate in the
liquid phase to produce a reactor effluent comprising aromatic
C.sub.8 isomers; (d) combining with the first mixture .gtoreq.50.0
wt. % of the reactor effluent's aromatic C.sub.8 isomers, the
combining being carried out before and/or during the separating of
(b), and (e) conducting away at least part of the separated
ethylbenzene-containing portion and/or conducting away at least
part of the separated non-aromatic containing portion.
2. The process of claim 1, wherein the separating step (b) includes
separating from the first mixture: i. the p-xylene-containing
portion comprising .gtoreq.10.0 wt. % of the first mixture's
p-xylene; and ii. the ethylbenzene-containing portion comprising
.gtoreq.10.0 wt. % of the first mixture's ethylbenzene.
3. The process of claim 1, further including conducting away at
least a portion of the separated p-xylene-containing portion.
4. The process of claim 1, further including conducting away
.gtoreq.50.0 wt. % of the separated ethylbenzene-containing
portion.
5. The process of claim 1, wherein the first mixture comprises
.gtoreq.50.0 wt. % of a mixture of p-xylene, ethylbenzene,
m-xylene, and o-xylene.
6. The process of claim 1, wherein the first mixture comprises 17
wt. % to 27 wt. % p-xylene, 40 wt. % to 50 wt. % m-xylene, 18 wt. %
to 28 wt. % o-xylene, and 5 wt. % to 15 wt. % ethylbenzene.
7. The process of claim 1, wherein the reacting at least a portion
the p-xylene-depleted raffinate in the liquid phase includes at
least one of (i) one or more reforming reactions, (ii) one or more
disproportionation reactions, (iii) one or more transalkylation
reactions, and (iv) one or more cracking reactions.
8. The process of claim 1, further comprising: (f) separating from
the reactor effluent in a second separation stage at least a
portion of any C.sub.1-C.sub.7 compounds produced during the
reacting step (c), the step (e) being carried out before the
combining step (d); and (g) conducting the separated
C.sub.1-C.sub.7 compounds away from the process.
9. The process claim 8, wherein the process further comprises: (h)
removing from the first mixture (1) at least a portion of any
o-xylene and/or (2) at least a portion of any C.sub.9+ aromatics;
and/or (i) separating from the reactor effluent in a third
separation stage one or more of toluene, o-xylene or C.sub.9+
aromatics, and conducting away at least a portion of one or more of
the separated toluene, the separated o-xylene, and the separated
C.sub.9+ aromatics.
10. The process of claim 1, further comprising conducting away
.gtoreq.50.0 wt. % of the non-aromatic containing portion separated
in step (b), based on the total weight of the separated
non-aromatic portion.
11. The process of claim 1, wherein the reacting of step (c)
includes liquid-phase isomerization, and wherein .ltoreq.10.0 wt. %
of the p-xylene-depleted raffinate is in the vapor phase during the
reacting.
12. The process of claim 1, wherein .ltoreq.1.0 wt. % of the
p-xylene-depleted raffinate is in the vapor phase during the
reacting.
13. The process of claim 1, wherein (i) .gtoreq.90.0 wt. % of the
first mixture's ethylbenzene is separated by chromatographic
separation in the first separation stage, (ii) .gtoreq.90.0 wt. %
of the separated ethylbenzene is conducted away from the process,
and (iii) .gtoreq.90.0 wt. % of the reactor effluent's aromatic
C.sub.8 isomers are combined with the first mixture in step
(d).
14. A process for producing p-xylene, the process comprising, (a)
providing a first mixture comprising .gtoreq.5.0 wt. % of aromatic
C.sub.8 isomers, said C.sub.8 isomers comprising p-xylene and
ethylbenzene; (b) separating from the first mixture in a first
separation stage wherein the first separation stage includes at
least one simulated moving-bed adsorptive separation stage: i. a
p-xylene-depleted raffinate; ii. a p-xylene-containing portion
comprising .gtoreq.10.0 wt. % of the first mixture's p-xylene; and
iii. an ethylbenzene-containing portion comprising .gtoreq.10.0 wt.
% of the first mixture's ethylbenzene; (c) conducting away at least
a portion of the p-xylene-containing portion; (d) conducting away
.gtoreq.50.0 wt. % of the ethylbenzene-containing portion; (e)
isomerizing at least a portion the p-xylene-depleted raffinate in
the liquid phase wherein .ltoreq.10.0 wt. %, e.g., .ltoreq.1.0 wt.
% or .ltoreq.0.1 wt. %, of the p-xylene-depleted raffinate is in
the vapor phase during the isomerizing, to produce a reactor
effluent comprising .gtoreq.90.0 wt. % p-xylene; and (f) combining
with the first mixture at least a portion of the reactor effluent,
the combining being carried out before and/or during the separating
of (b).
15. The process of claim 14, further comprising: (g) removing from
the first mixture (1) at least a portion of any o-xylene and/or (2)
at least a portion of any C.sub.9+ aromatics; and/or (h) separating
from the reactor effluent in a third separation stage one or more
of toluene, o-xylene or C.sub.9+ aromatics, and conducting away at
least a portion of one or more of the separated toluene, the
separated o-xylene, and the separated C.sub.9+ aromatics; and
wherein the separating of step (b) further includes (iv) a
non-aromatic hydrocarbon portion, comprising .gtoreq.50.0 wt. %, of
the first mixture's non-aromatic hydrocarbon molecules.
Description
PRIORITY
[0001] This application is a divisional of U.S. patent application
Ser. No. 14/624,861, filed Feb. 18, 2015, which further claims
priority to U.S. Patent Application No. 61/955,907, filed Mar. 20,
2014, and EP 14167834.2 filed May 12, 2014, the disclosures of
which are incorporated in their entireties.
FIELD OF INVENTION
[0002] Aspects of the invention relate to para-xylene (p-xylene)
separation processes. In particular, aspects of the invention
relate to xylene loop processes.
BACKGROUND OF INVENTION
[0003] Aromatic hydrocarbons, such as benzene, toluene, xylene,
etc. are useful as fuels, solvents, and as feeds for various
chemical processes. Of the xylenes, para-xylene is particularly
useful for manufacturing phthalic acids such as terephthalic acid,
which is an intermediate in the manufacture of synthetic fibers
such as polyester fibers. Xylenes can be produced from naphtha,
e.g., by catalytic reforming, with the reformate product containing
a mixture of xylene isomers and ethylbenzene. Separating p-xylene
from the mixture generally requires stringent separations, e.g.,
separations utilizing superfractionation and multistage
refrigeration steps. Such separations are characterized by
complexity, high energy-usage, and high cost.
[0004] Chromatographic separation is an alternative to more
stringent separations, such as superfractionation, for removing
p-xylene from a mixture of aromatic C.sub.8 isomers.
Chromatographic separation involves simulating a moving bed of
selective adsorbent. Examples of commercial processes in which
p-xylene is separated from aromatic C.sub.8 isomers by simulated
moving-bed separation include PAREX, available from UOP, ELUXYL,
available from Axens, and AROMAX, available from Toray. Although a
raffinate depleted in p-xylene can be recycled as a feed component
to the p-xylene separation step, ethylbenzene will undesirably
accumulate in the recycle stream.
[0005] In order to overcome this difficulty, p-xylene is
conventionally produced in a continuous process (commonly referred
to as a xylene loop), in which p-xylene-depleted raffinate is
isomerized to reduce the amount of ethylbenzene therein. The
isomerization reduces the amount of ethylbenzene in the stream by
converting it into an equilibrium or near-equilibrium xylene
mixture, e.g., a mixture comprising xylene isomers; diethylbenzene;
benzene; and non-aromatics such as C.sub.2-C.sub.6 olefins and
C.sub.1-C.sub.6 paraffins. One such process involves (a) providing
a mixture of aromatic C.sub.8 isomers containing p-xylene, (b)
separating from the C.sub.8 isomers a high-purity p-xylene extract
and a p-xylene-depleted raffinate by simulated moving bed
adsorption, crystallization, or a combination thereof, (c)
catalytically isomerizing the p-xylene-depleted raffinate to
produce an isomerate, and (e) recycling the isomerate to step
(a).
[0006] Vapor-phase isomerization of the raffinate's ethylbenzene is
generally needed to achieve an ethylbenzene content of .ltoreq.10.0
mole % ethylbenzene per mole of isomerate. However, vapor-phase
isomerization has many disadvantages, including high energy
consumption, costly and complex process equipment, and high xylenes
loss due to conversion of the xylenes in the raffinate into
undesirable products such as light gases and heavy aromatics, e.g.,
by one or more side-reactions such as one or more of cracking,
transalkylation, or disproportionation. Attempts to overcome these
disadvantages include reducing the quantity of raffinate going to
the vapor-phase isomerization, e.g., removing ethylbenzene from the
raffinate by (i) superfractionation, as disclosed in French Patent
FR-A-2792632, or (ii) using chromatographic ethylbenzene separation
in the p-xylene separation stage, as disclosed in U.S. Pat. No.
7,915,471. The separated ethylbenzene is isomerized in a
vapor-phase isomerization stage, with the remainder of the
raffinate being isomerized in a liquid-phase isomerization stage.
The liquid-phase isomerization stage is operated under conditions
which lessen undesired cracking, transalkylation, and
disproportionation side-reactions. Isomerates from the vapor-phase
and liquid-phase isomerization stages are then combined and
recycled to stage (a) of the xylene loop.
[0007] Even when ethylbenzene is separated for vapor-phase
isomerization, with the remainder of the p-xylene-depleted
raffinate subjected to liquid-phase isomerization, the vapor-phase
isomerization stage contributes to xylene-loop inefficiencies. Some
of these inefficiencies result from one or more of (i) the need to
vaporize the separated ethylbenzene and then re-condense the
vapor-phase isomerate for combining with the isomerate derived from
the liquid-phase isomerization stage, (ii) the need to separate
unreacted molecular hydrogen vapor for re-use as an isomerization
treat gas, and (iii) the need for removing non-aromatics formed
during isomerization. Consequently, it is desired to further lessen
or even eliminate the need for vapor-phase isomerization.
SUMMARY OF INVENTION
[0008] It has been found that xylene loop efficiency is
unexpectedly improved by separating and removing from the loop at
least a portion of the ethylbenzene present in the feed to the
p-xylene separation stage and/or at least a portion of the
non-aromatics present in the feed to the p-xylene separation stage,
the ethylbenzene and/or non-aromatics removal being carried out
upstream of raffinate isomerization. Separating and conducting away
from the xylene loop at least a portion of the ethylbenzene
increases xylene loop energy efficiency, e.g., by lessening the
number of Joules consumed by the xylene loop to produce one
kilogram of p-xylene by .gtoreq.20%, e.g., .gtoreq.25% when
.gtoreq.90 wt. % of ethylbenzene present in the feed to the
p-xylene separation stage is removed upstream of the isomerization.
Moreover, removing at least a portion of the xylene loop's
ethylbenzene decreases the xylene loop's complexity, e.g., by
lessening or even eliminating the need for an energy-intensive and
complex vapor-phase isomerization downstream of p-xylene
separation. The ethylbenzene can be removed in the p-xylene
separation stage, e.g., as a component of a second raffinate that
is chromatographically separated in the p-xylene separation stage.
It is also advantageous to remove at least a portion of any
non-aromatics from the xylene loop, e.g., removing non-aromatics
upstream of raffinate isomerization. The advantages can be attained
even in aspects where ethylbenzene is not removed. Certain
advantages result from the relatively high-value of gasoline
boiling-range non-aromatics (e.g., those having an
atmospheric-pressure boiling point in the range of from 30.degree.
F. to 430.degree. F.), which can be removed from the loop for use
in higher-value uses, e.g., as a blendstock for transportation
fuels. Removing non-aromatics is also advantageous because doing so
lessens the amount of hydrogen utilized in the process, and the
associated compression costs.
[0009] In certain aspects, the invention relates to a process for
producing p-xylene, the process comprising, (a) providing a first
mixture comprising .gtoreq.5.0 wt. % of aromatic C.sub.8 isomers,
based on the weight of the first mixture, said aromatic C.sub.8
isomers comprising p-xylene and ethylbenzene; (b) separating a
p-xylene-containing portion and an ethylbenzene-containing portion
from the first mixture in a first separation stage to form a
p-xylene-depleted raffinate, wherein the first separation stage
optionally includes at least one simulated moving-bed adsorptive
separation stage; (c) reacting at least a portion the
p-xylene-depleted raffinate in the liquid phase to produce a
reactor effluent comprising aromatic C.sub.8 isomers; and (d)
combining with the first mixture .gtoreq.50.0 wt. %, preferably
.gtoreq.90.0 wt. %, of the reactor effluent's aromatic C.sub.8
isomers, preferably p-xylene, based on the weight of the reactor
effluent's aromatic C.sub.8 isomers, the combining being carried
out before and/or during the separating of (b). At least part of
the separated ethylbenzene-containing portion is conducted
away.
[0010] A particular aspect relates to a process for producing
p-xylene, the process comprising providing a first mixture
comprising >5.0 wt. % of aromatic C.sub.8 isomers, based on the
weight of the first mixture, said C.sub.8 isomers comprising
p-xylene and ethylbenzene. The following components of the first
mixture are separated in a first separation stage: (i) a
p-xylene-depleted raffinate; (ii) a p-xylene-containing portion
comprising .gtoreq.10.0 wt. % of the first mixture's p-xylene,
based on the weight of the first mixture's p-xylene; and (iii) an
ethylbenzene-containing portion comprising .gtoreq.10.0 wt. % of
the first mixture's ethylbenzene, based on the weight of the first
mixture's ethylbenzene. At least a portion of the
p-xylene-containing portion is conducted away from the process, as
is .gtoreq.50.0 wt. % of the ethylbenzene-containing portion, based
on the weight of the ethylbenzene-containing portion. The process
continues by isomerizing at least a portion the p-xylene-depleted
raffinate in the liquid phase wherein .ltoreq.10.0 wt. %, e.g.,
.ltoreq.1.0 wt. % or .ltoreq.0.1 wt. %, of the p-xylene-depleted
raffinate is in the vapor phase during the isomerizing, the weight
percent being based on the weight of the p-xylene-depleted
raffinate. The isomerizing produces a reactor effluent comprising
.gtoreq.90.0 wt. % p-xylene, based on the weight of the reactor
effluent's aromatic C.sub.8 isomers. At least a portion of the
reactor effluent is combined with the first mixture, the combining
being carried out before and/or during the separating in the first
separation stage.
[0011] In other aspects, the invention relates to an improved
xylene loop, wherein the xylene loop comprises (a) providing a
first mixture comprising aromatic C.sub.8 isomers; (b) separating
from the first mixture in a first stage: (i) a p-xylene-depleted
raffinate; (ii) a p-xylene-containing portion comprising
.gtoreq.10.0 wt. % of the mixture's p-xylene, based on the weight
of the mixture's p-xylene; and (iii) an ethylbenzene-containing
portion comprising .gtoreq.10.0 wt. % of the mixture's
ethylbenzene, based on the weight of the mixture's ethylbenzene;
wherein the first separation stage includes at least one simulated
moving-bed adsorption chromatographic separation; (c) conducting
away at least a portion of the separated p-xylene; (d) reacting at
least a portion the p-xylene-depleted raffinate in the liquid phase
to produce a reactor effluent comprising aromatic C.sub.8 isomers;
and (e) recycling to step (b) .gtoreq.50.0 wt. % of aromatic
C.sub.8 isomers of the reactor effluent, based on the weight of the
aromatic C.sub.8 isomers in the reactor effluent. The improvement
comprises: (f) conducting away from the xylene loop .gtoreq.50.0
wt. % of the ethylbenzene separated in step (c), based on the
weight of the separated ethylbenzene; and (g) exposing .ltoreq.10.0
wt. % of aromatic C.sub.8 isomers in the xylene loop to vapor-phase
isomerization, based on the weight of aromatic C.sub.8 isomers in
the xylene loop.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates a p-xylene separation process according
to an aspect of the invention.
[0013] FIG. 2 illustrates a p-xylene separation process according
to aspects of the invention including a second separation stage
wherein at least a portion of any C.sub.1-C.sub.7 compounds are
removed from the reactor effluent.
[0014] FIG. 3 illustrates a p-xylene separation process according
to aspects of the invention. The separation process includes
removing one or more by-products from the first mixture and/or
providing the C.sub.8+ hydrocarbons to a third separation stage
301.
[0015] FIG. 4 illustrates another aspect of a p-xylene separation
process according to the invention.
DETAILED DESCRIPTION
[0016] The following description relates to aspects of the
invention which include removing ethylbenzene from a xylene loop
upstream of isomerization. The invention is not limited to these
aspects, and is not meant to foreclose other aspects within the
broader scope of the invention, such as those which include
non-aromatics separation. FIG. 1 schematically illustrates a
process 100 which features certain aspects of the invention. First
mixture 101 is passed to first separation stage 102 where a
p-xylene-containing portion 103 and an ethylbenzene-containing
portion 104 are separated and conducted away, in order to produce a
p-xylene-depleted raffinate 105 for the isomerization. First
mixture 101 typically comprises .gtoreq.5.0 wt. % of aromatic
C.sub.8 isomers, based on the weight of the first mixture, said
aromatic C.sub.8 isomers comprising p-xylene and ethylbenzene.
Generally, the content of aromatic C.sub.8 isomers in first mixture
101 may range from 5.0 to 100.0 wt. %. The lower limit on the
content of aromatic C.sub.8 isomers in first mixture 101 may be 5.0
wt. %, 10.0 wt. %, 20.0 wt. %, 30.0 wt. %, 40.0 wt. %, 50.0 wt. %,
60.0 wt. %, 70.0 wt. %, 80.0 wt. %, 90.0 wt. %, 95.0 wt. %, 99.0
wt. %, or 100.0 wt. %. The upper limit on the content of aromatic
C.sub.8 isomers in first mixture 101 may be 5.0 wt. %, 10.0 wt. %,
20.0 wt. %, 30.0 wt. %, 40.0 wt. %, 50.0 wt. %, 60.0 wt. %, 70.0
wt. %, 80.0 wt. %, 90.0 wt. %, 95.0 wt. %, 99.0 wt. %, or 100.0 wt.
%. Aspects expressly described herein include those where any lower
limit is combined with any upper limit. In particular aspects,
first mixture 101 comprises .gtoreq.50.0 wt. %, e.g., .gtoreq.60.0
wt %, .gtoreq.65.0 wt. %, .gtoreq.70.0 wt. %. .gtoreq.75.0 wt. %,
.gtoreq.80.0 wt. % .gtoreq.85.0 wt. %, .gtoreq.90.0 wt. %,
.gtoreq.95.0 wt. %, .gtoreq.99.0 wt. %, of a mixture of p-xylene,
ethylbenzene, meta-xylene (m-xylene), and ortho-xylene (o-xylene),
based on the weight of the first mixture 101.
[0017] The first separation stage 102 is typically a simulated
moving bed absorptive separation unit having solvent (sometimes
referred to as "desorbant") circulating therethrough via line 106.
The circulation can be carried out using one or more pumps, such as
the pump shown schematically in FIG. 1 as a component of stage 102.
In particular aspects the first separation stage 102 is a
chromatographic separation stage. Solvent 106 should be selected to
separate under the separation conditions, e.g., solvent flow,
temperature, etc., the components of first mixture 101 as desired.
Typical solvents include hydrocarbon solvents, e.g., toluene.
Exemplary separation processes are described in U.S. Pat. No.
7,915,471, incorporated herein by reference in its entirety.
[0018] Separation stage 102 should be operated such that
p-xylene-containing portion 103 comprises .gtoreq.10.0 wt. % of the
first mixture's p-xylene, based on the weight of the first
mixture's p-xylene. Generally, the content of p-xylene in
p-xylene-containing portion 103 may range from 10.0 to 100.0 wt. %
of the first mixture's p-xylene. The lower limit on the content of
p-xylene in the p-xylene-containing portion 103 may be 10.0 wt. %,
20.0 wt. %, 30.0 wt. %, 40.0 wt. %, 50.0 wt. %, 60.0 wt. %, 70.0
wt. %, 80.0 wt. %, 90.0 wt. %, 95.0 wt. %, 99.0 wt. %, or 100.0 wt.
%. The upper limit on the content of p-xylene in
p-xylene-containing portion 103 may be 10.0 wt. %, 20.0 wt. %, 30.0
wt. %, 40.0 wt. %, 50.0 wt. %, 60.0 wt. %, 70.0 wt. %, 80.0 wt. %,
90.0 wt. %, 95.0 wt. %, 99.0 wt. %, or 100.0 wt. %. Aspects
expressly described herein include those where any lower limit is
combined with any upper limit. In particular aspects,
p-xylene-containing portion 103 comprises 10.0 to 75.0 wt %, 10.0
to 65.0 wt. %, 10.0 to 50.0 wt. %, 10.0 to 40.0 wt. %, 10.0 to 30.0
wt. %, or 10.0 to 20.0 wt. % of the first mixture's p-xylene. In
some aspects, p-xylene-containing portion 103 comprises 20.0 to
75.0 wt %, 30.0 to 75 wt. %, 40.0 to 75 wt %, 50.0 to 75.0 wt. %,
or 65.0 to 75.0 wt. % of the first mixture's p-xylene. In
particular aspects, least a portion of the p-xylene-containing
portion 103 is conducted away from the process 100. In certain
aspects, 10.0 to 100.0 wt. %, e.g., 40.0 to 100.0 wt. %, 50.0 to
100.0 wt. %, 60.0 to 100.0 wt. %, 70.0 to 100.0 wt. %, 80.0 to
100.0 wt. %, 80.0 to 100.0 wt. %, or 95.0 to 100.0 wt. %, of the
p-xylene portion is conducted away from the process.
[0019] Ethylbenzene is separated and removed from process 100 via
ethylbenzene-containing portion 104, which typically comprises
comprising .gtoreq.10.0 wt. % of the first mixture's ethylbenzene,
based on the weight of the first mixture's ethylbenzene. The lower
limit on the content of ethylbenzene in the ethylbenzene-containing
portion 104 may be 10.0 wt. %, 20.0 wt. %, 30.0 wt. %, 40.0 wt. %,
50.0 wt. %, 60.0 wt. %, 70.0 wt. %, 80.0 wt. %, 90.0 wt. %, 95.0
wt. %, 99.0 wt. %, or 100.0 wt. %. The upper limit on the content
of ethylbenzene in ethylbenzene-containing portion 104 may be 10.0
wt. %, 20.0 wt. %, 30.0 wt. %, 40.0 wt. %, 50.0 wt. %, 60.0 wt. %,
70.0 wt. %, 80.0 wt. %, 90.0 wt. %, 95.0 wt. %, 99.0 wt. %, or
100.0 wt. %. Aspects expressly described herein include those where
any lower limit is combined with any upper limit. Generally,
ethylbenzene-containing portion 104 comprises 10.0 to 75.0 wt. %,
10,0 to 65.0 wt. %, 10.0 to 500 wt. %, 10.0 to 40.0 wt. %, 10,0 to
30.0 wt %, or 10.0 to 20.0 wt. % of the first mixture's
ethylbenzene. In certain aspects, ethylbenzene-containing portion
104 comprises 20.0 to 75.0 wt. %, 30.0 to 75.0 wt. %, 40.0 to 75
wt. %, 50.0 to 75.0 wt. %, or 65.0 to 75.0 wt. % of the first
mixture's p-xylene. Removing at least a portion of the ethylbenzene
from the process decreases the xylene loop's complexity, e.g., by
lessening or even eliminating the need for an energy-intensive and
complex vapor-phase isomerization downstream of p-xylene
separation. The ethylbenzene can be removed in the p-xylene
separation stage, e.g., as a component of a second extract. The
second extract can be chromatographically separated in the p-xylene
separation stage, as disclosed in U.S. Pat. No. 7,915,471. In
particular aspects, at least a portion of the
ethylbenzene-containing portion 104 is conducted away from the
process 100, .gtoreq.10.0 wt. % of the ethylbenzene-containing
portion is conducted away, based on the weight of the
ethylbenzene-containing portion. In certain aspects, 10.0 to 100.0
wt. %, e.g., 40.0 to 100.0 wt. %, 50.0 to 100.0 wt. %, 60.0 to
100.0 wt. %, 70.0 to 100.0 wt. %, 80.0 to 100.0 wt. %, 80.0 to
100.0 wt. %, or 95.0 to 100.0 wt. %, of ethylbenzene-containing
portion 104 is conducted away from the process. Since at least part
of the first mixture's ethylbenzene is separated and conducted
away, the process generally includes isomerizing <90.0 wt. % of
the first mixture's ethylbenzene, e.g., .ltoreq.50.0 wt. %, such as
.ltoreq.25.0 wt. %. In certain aspects, the process includes
isornerizing .ltoreq.10.0 wt. % of the first mixture's
ethylbenzene, e.g., .ltoreq.5.0 wt. %, such as .ltoreq.1.0 wt.
%.
[0020] The process may include separating at least a portion of any
non-aromatic hydrocarbon molecules from the first mixture 101. This
can be done upstream of stage 107, e.g., in stage 102 (not shown).
First separation stage 102 may remove from 5.0 to 100 wt. % of any
non-aromatic hydrocarbons, based on the amount of such hydrocarbons
in the first mixture. In particular aspects, the first separation
stage 102 removes .gtoreq.50.0 wt. %, preferably .gtoreq.75.0 wt.
%, or .gtoreq.90.0 wt. % of the non-aromatic hydrocarbons. Certain
non-aromatic hydrocarbon molecules, e.g., C.sub.9 non-aromatic
molecules, have approximately the same volatility as p-xylene. It
is conventional to ameliorate problems associated with
non-aromatics separation from the xylene loop by cracking at least
a portion of the non-aromatics during xylene isomerization. This
approach lessens xylene loop efficiency (as a result of, e.g.,
bottlenecking of the isomerization stage), and leads to an increase
in separation complexity as a result of the need to remove the
cracked products. It has been found that this difficulty can be
overcome by removing at least a portion of the non-aromatics
upstream of the isomerization, e.g., by removing non-aromatics from
the first mixture in the first separation stage. As in the case of
ethylbenzene removal, separation of non-aromatics can be carried
out using at least one simulated moving-bed adsorption
chromatographic separation. Advantageously, non-aromatics
separation and ethylbenzene separation can be carried out in the
same simulated moving-bed adsorption chromatographic separation
using the same desorbent. The chromatographic separation can be
carried out using conventional methods, such as those described in
U.S. Pat. No. 3,662,020, which is incorporated by reference herein
in its entirety. One or more conventional desorbents can be used,
e.g., toluene. Conventional configurations can be utilized for the
simulated moving-bed adsorption chromatographic separation of the
first separation stage, e.g., stacked-bed mode and/or multiple bed
mode. Suitable configurations are disclosed in U.S. Pat. Nos.
2,985,589 and 3,310,486, which are incorporated by reference herein
in their entirety. In certain aspects, four streams are conducted
away from the first separation stage: (i) first and second extracts
and (ii) first and second raffinates. Referring again to FIG. 1,
the first extract corresponds to the p-xylene-containing portion
removed from stage 102. The second extract corresponds to the
ethylbenzene portion removed from stage 102. The first raffinate
comprises at least a portion of the first mixture's m-xylene and
o-xylene, e.g., .gtoreq.50.0 wt. % of the first mixture's m-xylene
and .gtoreq.50.0 wt. % of the first mixture's o-xylene. The second
raffinate comprises non-aromatics, e.g., .gtoreq.50.0 wt. % of the
first mixture's non-aromatics. Although it is not required, the
invention is compatible with removing at least a portion of any
desorbent from one or more of the first extract, second extract,
first raffinate, and second raffinate. For example, desorbent can
be removed from the first raffinate upstream of the isomerization
in order to further debottleneck the isomerizing. Since at least
part of the first mixture's non-aromatics can be separated and
conducted away, the process optionally includes subjecting to
isomerization conditions <90.0 wt % of the first mixture's
non-aromatics, e.g., .ltoreq.50.0 wt %, such as .ltoreq.25.0 wt. %.
In certain aspects, the process includes subjecting .ltoreq.10.0
wt. % of the first mixture's non-aromatics to isomerization
conditions, e.g., .ltoreq.5.0 wt. %, such as .ltoreq.1,0 wt. %.
[0021] The p-xylene-depleted raffinate 105 is provided to reactor
107 where raffinate 105 is reacted in the liquid phase to produce a
reactor effluent comprising aromatic C.sub.8 isomers. Reactor 107
may be any type of reactor or reactor process suitable for
increasing the amount of C.sub.8 isomers, relative to the amount of
aromatic C.sub.8 isomers in raffinate 105. Reactor 107 typically
performs at least one of (i) one or more reforming reactions, (ii)
one or more disproportionation reactions, (iii) one or more
transalkylation reactions, and (iv) one or more cracking reactions.
While the reaction processes in reactor 107 are conducted in the
liquid phase, some of raffinate 105 may be in the vapor phase.
Thus, in particular aspects, .ltoreq.10.0 wt. %, e.g., .ltoreq.7.5
wt. %, .ltoreq.5.0 wt. %, .ltoreq.2.5 wt. %, .ltoreq.1.0 wt. %,
.ltoreq.0.5 wt. %, .ltoreq.0.2 wt. %, .ltoreq.0.1 wt. %, of the
p-xylene-depleted raffinate 105 in reactor 107 is in the vapor
phase during the reacting, the weight percent being based on the
weight of the p-xylene-depleted raffinate 105.
[0022] Reactor effluent 108 generally comprises products formed in
reactor 107, and can also include unreacted raffinate. For example,
reactor effluent 108 can comprise C.sub.1-C.sub.7 compounds,
C.sub.8 aromatic isomers, and C.sub.9+ aromatics. In certain
aspects, the concentration of p-xylene in effluent 108 may be
suitable for use in other processes or it may be sent for further
purification and/or isolation of the p-xylene. In certain aspects,
at least a portion of the reactor effluent 108 is recycled through
line 109 to be combined with the first mixture 101. Any desirable
amount of reactor effluent may be recycled through line 109.
Typically, .gtoreq.50.0 wt. %, of the aromatic C.sub.8 isomers of
the reactor effluent 108, based on the total amount of aromatic
C.sub.8 isomers in reactor effluent 108, are recycled for combining
with the first mixture 101. The lower limit on the amount of
aromatic C.sub.8 isomers recycled for combining with the first
mixture 101 may be 50.0 wt. %, 55.0 wt. %, 60.0 wt. %, 65.0 wt. %,
70.0 wt. %, 75.0 wt. %, 80.0 wt. %, 85.0 wt. %, 90.0 wt. %, 95.0
wt. %, 99.0 wt. %, or 100.0 wt. %. The upper limit on the amount of
aromatic C.sub.8 isomers recycled for combining with the first
mixture 101 may be 50.0 wt. %, 55.0 wt. %, 60.0 wt. %, 65.0 wt. %,
70.0 wt. %, 75.0 wt. %, 80.0 wt. %, 85.0 wt. %, 90.0 wt. %, 95.0
wt. %, 99.0 wt. %, or 100.0 wt. %. Any combination of lower and
upper limits on the amount of aromatic C.sub.8 isomers recycled for
combining with the first mixture 101 is expressed disclosed. In
particular aspects, the aromatic C.sub.8 isomers recycled through
line 109 comprise .gtoreq.50.0 wt. % (e.g., .gtoreq.50.0 wt. %,
.gtoreq.55.0 wt. %, .gtoreq.60.0 wt. %, .gtoreq.65.0 wt. %,
.gtoreq.70.0 wt. %, .gtoreq.75.0 wt. %, .gtoreq.80.0 wt. %,
.gtoreq.85.0 wt. %, .gtoreq.90.0 wt. %, .gtoreq.95.0 wt. %,
.gtoreq.99.0 wt. %, xylene isomers (e.g., o-xylene, m-xylene,
p-xylene). In particular aspects, the xylene isomers comprise
.gtoreq.50.0 wt. %, .gtoreq.55.0 wt. %, .gtoreq.60.0 wt. %,
.gtoreq.65.0 wt. %, .gtoreq.70.0 wt. %, .gtoreq.75.0 wt. %,
.gtoreq.80.0 wt. %, .gtoreq.85.0 wt. %, .gtoreq.90.0 wt. %,
.gtoreq.95.0 wt. %, .gtoreq.99.0 wt. %, p-xylene. Line 109
typically provides the aromatic C.sub.8 isomers before and/or
during the separating of (b).
[0023] With continuing reference to FIG. 1, FIG. 2 illustrates
process 200. Process 200 includes providing the reactor effluent
108 to a second separation stage 201 wherein at least a portion of
one or more C.sub.1-C.sub.7 compounds in the reactor effluent 108
are separated via line 202. Particular aspects of process 200
include conducting the separated one or more C.sub.1-C.sub.7
compounds away from the process. Heavier compounds, including
aromatic C.sub.8 isomers and C.sub.9+ hydrocarbons, exit second
separation stage 201 via line 203. Separation stage 201 may be any
separation means suitable for separating C.sub.1-C.sub.7 compounds
from C.sub.8+ hydrocarbons. In particular aspects, separation stage
201 is a stabilization column or distillation column. Typically,
the C.sub.1-C.sub.7 compounds are separated in separation stage 201
before the reactor effluent 108 is recycled for combining with the
first mixture 101, as shown in FIG. 2. In other words, the
C.sub.1-C.sub.7 compounds are separated and at least a portion of
the C.sub.8+ hydrocarbons of line 203 are recycled through line 204
to be combined with first mixture 101. Any desirable amount of the
C.sub.8+ hydrocarbons exiting separation stage 201 via line 203 may
be recycled through line 204. Typically, .gtoreq.50.0 wt. %, of the
C.sub.8+ hydrocarbons of the separation stage 201, based on the
total amount of C.sub.8+ hydrocarbons exiting separation stage 201,
are recycled for combining with the first mixture 101. The lower
limit on the amount of C.sub.8+ hydrocarbons recycled for combining
with the first mixture 101 may be 10.0 wt. %, 20.0 wt. %, 30.0 wt.
%, 40.0 wt. %, 50.0 wt. %, 55.0 wt. %, 60.0 wt. %, 65.0 wt. %, 70.0
wt. %, 75.0 wt. %, 80.0 wt. %, 85.0 wt. %, 90.0 wt. %, 95.0 wt. %,
99.0 wt. %, or 100.0 wt. %. The upper limit on the amount of
C.sub.8+ hydrocarbons recycled for combining with the first mixture
101 may be 10.0 wt. %, 20.0 wt. %, 30.0 wt. %, 40.0 wt. %, 50.0 wt.
%, 55.0 wt. %, 60.0 wt. %, 65.0 wt. %, 70.0 wt. %, 75.0 wt. %, 80.0
wt. %, 85.0 wt. %, 90.0 wt. %, 95.0 wt. %, 99.0 wt. %, or 100.0 wt.
%. Any combination of lower and upper limits on the amount of
C.sub.8+ hydrocarbons recycled for combining with the first mixture
101 is expressed disclosed. In particular aspects, the C.sub.8+
hydrocarbons recycled through line 204 comprise .gtoreq.50.0 wt. %
(e.g., .gtoreq.50.0 wt. %, .gtoreq.55.0 wt. %, .gtoreq.60.0 wt. %,
.gtoreq.65.0 wt. %, .gtoreq.70.0 wt. %, .gtoreq.75.0 wt. %,
.gtoreq.80.0 wt. %, .gtoreq.85.0 wt. %, .gtoreq.90.0 wt. %,
.gtoreq.95.0 wt. %, .gtoreq.99.0 wt. %), C.sub.8+ aromatic
hydrocarbons (e.g., ethylbenzene, o-xylene, m-xylene, p-xylene). In
particular aspects, the aromatic C.sub.8+ hydrocarbons recycled via
line 204 comprise .gtoreq.50.0 wt. %, .gtoreq.55.0 wt. %,
.gtoreq.60.0 wt. %, .gtoreq.65.0 wt. %, .gtoreq.70.0 wt. %,
.gtoreq.75.0 wt. %, .gtoreq.80.0 wt. %, .gtoreq.85.0 wt. %,
.gtoreq.90.0 wt. %, .gtoreq.95.0 wt. %, .gtoreq.99.0 wt. %,
p-xylene.
[0024] With continuing reference to FIGS. 1 and 2, FIG. 3
illustrates an exemplary process 300. Optionally, process 100 or
process 200 may include removing one or more by-products from the
first mixture and/or providing at least a portion of any C.sub.8+
hydrocarbons exiting the separation stage 201 to a third separation
stage 301 via line 203. Optionally, the portion of C.sub.8+
hydrocarbon can be derived from a fourth separation stage 304.
Stage 304 can be located downstream of stage 201, as shown in the
figure. For example, in process 300, first mixture 101 may be
passed to third separation stage 301, wherein at least a portion of
a by-product, e.g., o-xylene and/or any C.sub.9+ aromatics in the
first mixture are removed via line 303. The remainder is passed to
the first separation stage 102. The amount of the one or more
by-products removed in the separation stage 301 may be 5.0 to 100.0
wt. %, based on the amount of the by-product in the first mixture
101. The lower limit on the amount of by-product removed from the
first mixture 101 may be 5.0 wt. %, 10.0 wt. %, 20.0 wt. %, 30.0
wt. %, 40.0 wt. %, 50.0 wt. %, 55.0 wt. %, 60.0 wt. %, 65.0 wt. %,
70.0 wt. %, 75.0 wt. %, 80.0 wt. %, 85.0 wt. %, 90.0 wt. %, 95.0
wt. %, 99.0 wt. %, or 100.0 wt. %. The upper limit on the amount of
by-product removed from the first mixture 101 may be 5.0 wt. %,
10.0 wt. %, 20.0 wt. %, 30.0 wt. %, 40.0 wt. %, 50.0 wt. %, 55.0
wt. %, 60.0 wt. %, 65.0 wt. %, 70.0 wt. %, 75.0 wt. %, 80.0 wt. %,
85.0 wt. %, 90.0 wt. %, 95.0 wt. %, 99.0 wt. %, or 100.0 wt. %. Any
combination of lower and upper limits on the amount of by-product
removed from the first mixture 101 is expressed disclosed. In
particular aspects, the by-product removed via line 303 is
o-xylene. In another aspect, the by-product comprises one or more
C.sub.9+ aromatic compounds. In particular aspects, the portion of
the C.sub.8+ hydrocarbons provided to stage 301, e.g., via line
204, comprises .gtoreq.50.0 wt. %, .gtoreq.55.0 wt. %, .gtoreq.60.0
wt. %, .gtoreq.65.0 wt. %, .gtoreq.70.0 wt. %, .gtoreq.75.0 wt. %,
.gtoreq.80.0 wt. %, .gtoreq.85.0 wt. %, .gtoreq.90.0 wt. %,
.gtoreq.95.0 wt. %, .gtoreq.99.0 wt. %, p-xylene. Optional fourth
separation stage will now be described in more detail.
[0025] Fourth separation stage 304 may be any suitable separation
means, e.g., distillation tower, stabilization tower, flash drum,
etc. At least a portion of the reactor effluent comprising the
C.sub.8+ hydrocarbons separated in second separation stage 201 via
line 203 may be provided to fourth separation stage 304, for
removing and conducting away from the process at least a portion of
one or more of toluene, o-xylene or C.sub.9+ aromatics. A p-xylene
containing portion exits third separation stage 304 via a stream
306, which may be further processed or purified. In particular
aspects at least a portion of p-xylene containing stream 306 may be
recycled as described for streams 203 and 204.
[0026] FIG. 4 illustrates a process 400 encompassing aspects of the
invention. First mixture 401, comprising ethylbenzene, p-xylene,
m-xylene, and o-xylene may be provided to optional distillation
column 402. Optional distillation column 402 separates an
ethylbenzene containing distillate 403 comprising p-xylene and
m-xylene and a residue 404 comprising xylenes and a minor amount of
ethylbenzene. In particular aspects, however, distillation tower
402 may be absent. In certain aspects where distillation column 402
is absent, first mixture 401 may be provided directly to
distillation tower 409 or to first simulated moving bed absorptive
separation column 418.
[0027] In aspects utilizing distillation tower 402, residue 404 is
provided to distillation tower 409. Optional distillation tower 409
may be any separation means suitable for at least partially
separating o-xylene from the residue 404. In particular aspects,
distillation tower 409 may be a xylene splitter. Optionally,
residue 404 may be combined with isomerate from isomerization
reactor 427 described below.
[0028] Distillation tower 409 delivers a distillate through a line
410 comprising an increased concentration of the m-xylene and
p-xylene, based on the concentration of these compounds as provided
to the distillation tower 409. A residue comprising o-xylene exits
the distillation tower 409 via line 411.
[0029] The o-xylene in line 411 is further isolated in a
distillation column 412 from which o-xylene-containing distillate
is removed from line 413. At least a portion of the o-xylene
exiting the distillation tower 412 via line 413 may be recycled to
an isomerization reactor 427 or carried away from the process for
further isolation or processing. A residue containing C.sub.9+
hydrocarbons exits distillation tower 409 via line 415.
[0030] Distillate is provided to a first simulated moving bed
absorptive separation column 418 having a desorbent, e.g., toluene,
introduced therein from an external source (not shown) and recycled
through column 418 via line 418a. A p-xylene containing portion is
typically withdrawn along with desorbent via line 419. The p-xylene
in line 419 may be directed to a distillation column 421 to
separate the desorbent as a distillate fraction which is combined
via line 421a with the desorbent in line 423 for recycle to stage
418. The p-xylene recovered as residue by line 422 generally has a
high purity, e.g., 99.8%, or otherwise purified in at least one
crystallization zone 417 at high temperature, as described European
Patent EP-B-531 191, incorporated herein by reference in its
entirety. The p-xylene conducted away via line 424 generally has a
purity greater than 99.9%, for example. A liquid stream obtained
from crystallization zone 417 can be withdrawn via line 416,
combined the xylene-containing distillate in line 410 and provided
to the first simulated moving bed absorptive separation stage
418.
[0031] An ethylbenzene-containing portion as described above is
withdrawn from the column 418 via line 420, and is preferably
removed from the process. Non-aromatics can be removed in stage 418
and conducted away (not shown).
[0032] A p-xylene depleted raffinate as described above is
withdrawn from the column 418 via line 425. This raffinate
typically comprises toluene and m-xylene. The raffinate of line 425
is combined with the o-xylene-rich line 413, and introduced into
isomerization reactor 427 via line 426. In particular aspects the
p-xylene depleted raffinate in line 426 comprises <10 wt. %
ethylbenzene and >10 wt. % toluene, based on the total weight of
the components in line 426.
[0033] Isomerization reactor 427 may be any suitable reactor for
isomerizing xylene/ethylbenzene mixtures. In particular aspects,
the reactor 427 comprises a liquid phase isomerization process
including a fixed bed of a zeolitic catalyst such as ZSM-5, under
isomerization conditions the increase the content of p-xylene
therein, preferably operated in the absence of hydrogen at a space
velocity of 3 hr.sup.-1, for example, at a temperature of about
260.degree. C. and a pressure <30 bar.
[0034] This reactor effluent exits the reactor 427 and is
introduced into a distillation column 428 (for example a
distillation column comprising about 30 plates). Distillation
column 428 separates the reactor effluent into a light fraction
(e.g., C.sub.1-C.sub.7 hydrocarbon, particularly C.sub.1-C.sub.7
non-aromatic hydrocarbon) recovered by a line 429, a toluene
fraction recycled by a line 430 to the adsorption column 418, and a
xylene-enriched raffinate that is provided to distillation tower
409 via line 431. Optionally, residue 404 may be combined with
distilled isomerate from the isomerization reactor 427.
[0035] Typically, the xylene-enriched raffinate 431 comprises
p-xylene as the major isomer. A typical concentration of xylene
isomers corresponding comprises 15 to 30 wt. % p-xylene, 10 to 30
wt. % o-xylene and 40 to 60 wt. % m-xylene. Typically, ethylbenzine
comprises about 10 wt. % of the xylene-enriched raffinate.
[0036] Optionally, distillate 403 comprising p-xylene and m-xylene
from the distillation column 402 may be fed, optionally in
combination with ethylbenzene provided via line 420, to a catalytic
vapor-phase isomerization reactor 432 of operating e.g., at a
temperature of about 370-400.degree. C. In aspects utilizing line
420, ethylbenzene conveyed via line 420 can be obtained from an
external source (not shown). Typically, the distillate 403
comprises .ltoreq.10.0 wt. %, e.g., .ltoreq.7.5.0 wt. %,
.ltoreq.5.0 wt. %, .ltoreq.2.5 wt. %, .ltoreq.1.0 wt. %, of the
aromatic C.sub.8 isomers in the xylene loop, based on the weight of
aromatic C.sub.8 isomers in the xylene loop. The resulting
isomerate conducted away from stage 432 is enriched in xylene, and
may be passed to separation stage 405. Light hydrocarbons i.e.,
C.sub.1-C.sub.7 hydrocarbons are separated and carried away form
the process via line 407, optionally combined with the light
hydrocarbons of line 429. Benzene and toluene may be separated from
the isomerate, and optionally carried away from the process, via
line 406. Isomerization effluent exits the separation stage 405 may
be combined with the first mixture 401 and provided to the
distillation column 402.
Particular Aspects
[0037] Additionally or alternately, the present invention can
include one or more of the following embodiments. The invention is
not limited to these embodiments, and this description is not meant
to foreclose other embodiments within the broader scope of the
invention.
[0038] Embodiment 1. A process for producing p-xylene, the process
comprising, (a) providing a first mixture comprising .gtoreq.5.0
wt. % of aromatic C.sub.8 isomers, based on the weight of the first
mixture, said C.sub.8 isomers comprising p-xylene and ethylbenzene;
(b) separating from the first mixture in a first separation stage
one or more of (i) a p-xylene-containing portion, (ii) a
non-aromatics containing portion, and (iii) an
ethylbenzene-containing portion, to form a p-xylene-depleted
raffinate, wherein the first separation stage includes at least one
simulated moving-bed adsorptive separation stage; (c) reacting at
least a portion the p-xylene-depleted raffinate in the liquid phase
to produce a reactor effluent comprising aromatic C.sub.8 isomers;
and (d) combining with the first mixture .gtoreq.50.0 wt. %,
preferably .gtoreq.90.0 wt. %, of the reactor effluent's aromatic
C.sub.8 isomers, preferably p-xylene, based on the weight of the
reactor effluent's aromatic C.sub.8 isomers, the combining being
carried out before and/or during the separating of (b).
[0039] Embodiment 2. The process of Embodiment 1, wherein the
separating step (b) includes separating from the first mixture: (A)
the p-xylene-depleted raffinate; (B) the p-xylene-containing
portion comprising .gtoreq.10.0 wt. % of the first mixture's
p-xylene, based on the weight of the first mixture's p-xylene; and
(C) the ethylbenzene-containing portion comprising .gtoreq.10.0 wt.
% of the first mixture's ethylbenzene, based on the weight of the
first mixture's ethylbenzene.
[0040] Embodiment 3. The process of Embodiment 1 or 2, further
including conducting away at least a portion of the
p-xylene-containing portion.
[0041] Embodiment 4. The process of any of Embodiments 1 to 3,
further including conducting away .gtoreq.50.0 wt. % of the
ethylbenzene-containing portion, based on the weight of the
separated ethylbenzene.
[0042] Embodiment 5. The process of any of Embodiments 1 to 4,
wherein the first mixture comprises .gtoreq.50.0 wt. % of a mixture
of p-xylene, ethylbenzene, m-xylene, and o-xylene, based on the
weight of the first mixture.
[0043] Embodiment 6. The process of any of Embodiments 1 to 5,
wherein the first mixture comprises about 12 wt. % to 32 wt. %,
particularly 17 wt. % to 27 wt. % or 20.0 wt. % to 25.0 wt. %,
p-xylene; 35 wt. % to 55 wt. %, particularly 40 wt. % to 50 wt. %
or 42.5 wt. % to 47.7 wt. %, m-xylene; 13 wt. % to 33 wt. %,
particularly 18 wt. % to 28 wt. % or 20.0 wt. % to 25.0 wt. %
o-xylene; and 1.0 wt. % to 20.0 wt. %, particularly 5.0 wt. % to
15.0 wt. % or 7.5 wt. % to 12.5 wt. %, ethylbenzene.
[0044] Embodiment 7. The process of any of Embodiments 1 to 6,
wherein reacting at least a portion the p-xylene-depleted raffinate
in the liquid phase includes at least one of (i) one or more
reforming reactions, (ii) one or more disproportionation reactions,
(iii) one or more transalkylation reactions, and (iv) one or more
cracking reactions.
[0045] Embodiment 8. The process of any of the Embodiments
encompassed by Embodiment 7, further comprising: (e) separating
from the reactor effluent in a second separation stage at least a
portion of any C.sub.1-C.sub.7 compounds produced during the
reacting step (c), the step (e) being carried out before the
combining step (d); and (f) conducting the separated C.sub.7
compounds away from the process.
[0046] Embodiment 9. The process of any of Embodiments 1 to 8,
wherein the process further comprises: (g) removing a by-product
from the first mixture, the by-product comprising (1) at least a
portion of the first mixture's o-xylene and/or (2) at least a
portion of any C.sub.9+ aromatics in the first mixture; and/or (h)
separating from the reactor effluent in a third separation stage
one or more of toluene, o-xylene or C.sub.9+ aromatics, and
conducting away at least a portion of one or more of the separated
toluene, the separated o-xylene, and the separated C.sub.9+
aromatics.
[0047] Embodiment 10. The process of any of the Embodiments
encompassed by Embodiment 9, further comprising separating from the
first mixture in the first separation stage .gtoreq.50.0 wt. %,
preferably .gtoreq.75.0 wt. %, or .gtoreq.90.0 wt. %, of any
non-aromatic hydrocarbon molecules.
[0048] Embodiment 11. The process of any of Embodiments 1-10,
wherein the reacting of step (c) includes liquid-phase
isomerization, and wherein .ltoreq.10.0 wt. % of the
p-xylene-depleted raffinate is in the vapor phase during the
reacting, the weight percent being based on the weight of the
p-xylene-depleted raffinate.
[0049] Embodiment 12. The process of Embodiment 11, wherein
.ltoreq.1.0 wt. %, preferably .ltoreq.0.1 wt. %, of the
p-xylene-depleted raffinate is in the vapor phase during the
reacting.
[0050] Embodiment 13. The process of any of Embodiments 1-12,
wherein (i) .gtoreq.90.0 wt. % of the first mixture's ethylbenzene
is separated by chromatographic separation in the first separation
stage, (ii) .gtoreq.90.0 wt. % of the separated ethylbenzene is
conducted away from the process, and (iii) .gtoreq.90.0 wt. % of
the reactor effluent's aromatic C.sub.8 isomers are combined with
the first mixture in step (d).
[0051] Embodiment 14. In a xylene loop, wherein the xylene loop
comprises (a) providing a first mixture comprising aromatic C.sub.8
isomers; (b) separating from the first mixture in a first stage:
(i) a p-xylene-depleted raffinate; (ii) a p-xylene-containing
portion comprising .gtoreq.10.0 wt. % of the mixture's p-xylene,
based on the weight of the mixture's p-xylene; and at least one of
(iii) an ethylbenzene-containing portion comprising .gtoreq.10.0
wt. % of the first mixture's ethylbenzene, based on the weight of
the first mixture's ethylbenzene; or (iv) .gtoreq.10.0 wt. % of any
non-aromatics in the first mixture; wherein the first separation
stage includes at least one simulated moving-bed adsorption
chromatographic separation; (c) conducting away at least a portion
of the separated p-xylene; (d) reacting at least a portion the
p-xylene-depleted raffinate in the liquid phase to produce a
reactor effluent comprising aromatic C.sub.8 isomers; and (e)
recycling to step (b) .gtoreq.50.0 wt. % of aromatic C.sub.8
isomers of the reactor effluent, based on the weight of the
aromatic C.sub.8 isomers in the reactor effluent; the improvement
comprising: (f) conducting away from the xylene loop (i)
.gtoreq.50.0 wt. % of the ethylbenzene separated in step (c), based
on the weight of the separated ethylbenzene, and/or (ii)
.gtoreq.50.0 wt. % of any non-aromatics separated in step (c); and
(g) exposing .ltoreq.10.0 wt. % of aromatic C.sub.8 isomers in the
xylene loop to vapor-phase isomerization, based on the weight of
aromatic C.sub.8 isomers in the xylene loop.
[0052] Embodiment 15. The process of Embodiment 14, wherein the
first mixture comprises .gtoreq.50.0 wt. % of a mixture of
p-xylene, ethylbenzene, m-xylene, and o-xylene, based on the weight
of the first mixture.
[0053] Embodiment 16. The process of Embodiment 14 or 15, wherein
the first mixture comprises about 12 wt. % to 32 wt. %,
particularly 17 wt. % to 27 wt. % or 20.0 wt. % to 25.0 wt. %,
p-xylene; 35 wt. % to 55 wt. %, particularly 40 wt. % to50 wt. % or
42.5 wt. % to 47.7 wt. %, m-xylene; 13 wt. % to 33 wt. %,
particularly 18 wt. % 28 wt. %, or 20.0 wt. % to 25.0 wt. %
o-xylene; and 1.0 wt. % to 20.0 wt. %, particularly 5.0 wt. % to
15.0 wt. % or 7.5 wt. % to 12.5 wt. %, ethylbenzene.
[0054] Embodiment 17. The process of any of Embodiments 14 to 16,
wherein reacting at least a portion the p-xylene-depleted raffinate
in the liquid phase includes at least one of (i) one or more
reforming reactions, (ii) one or more disproportionation reactions,
(iii) one or more transalkylation reactions, and (iv) one or more
cracking reactions.
[0055] Embodiment 18. The process of any of Embodiments 14 to 17,
further comprising: (h) separating from the reactor effluent in a
second separation stage at least a portion of any C.sub.1-C.sub.7
compounds produced during the reacting step (c), the step (e) being
carried out before the combining step (d); and (i) conducting the
separated C.sub.1-C.sub.7 compounds away from the process.
[0056] Embodiment 19. The process of any of Embodiments 14 to 18,
wherein the process further comprises: (j) removing a by-product
from the first mixture, the by-product comprising (1) at least a
portion of the first mixture's o-xylene and/or (2) at least a
portion of any C.sub.9+ aromatics in the first mixture; and/or (k)
separating from the reactor effluent in a third separation stage
one or more of toluene, o-xylene or C.sub.9+ aromatics, and
conducting away at least a portion of one or more of the separated
toluene, the separated o-xylene, and the separated C.sub.9+
aromatics.
[0057] Embodiment 20. The process of any embodiment encompassed by
Embodiment 19, further comprising separating from the first mixture
in the first separation stage .gtoreq.50.0 wt. %, preferably
.gtoreq.75.0 wt. %, or .gtoreq.90.0 wt. %, of any non-aromatic
hydrocarbon molecules.
[0058] Embodiment 21. The process of any of Embodiments 14 to 20,
wherein the reacting of step (d) includes liquid-phase
isomerization, and wherein .ltoreq.10.0 wt. % of the
p-xylene-depleted raffinate is in the vapor phase during the
reacting, the weight percent being based on the weight of the
p-xylene-depleted raffinate.
[0059] Embodiment 22. The process of any embodiment encompassed by
Embodiment 20, wherein .ltoreq.1.0 wt. %, preferably .ltoreq.0.1
wt. %, of the p-xylene-depleted raffinate is in the vapor phase
during the reacting.
[0060] Embodiment 23. The process of any of Embodiments 14 to 22,
wherein (i) .gtoreq.90.0 wt. % of the first mixture's ethylbenzene
is separated by chromatographic separation in the first separation
stage, (ii) .gtoreq.90.0 wt. % of the separated ethylbenzene is
conducted away from the process, and (iii) .gtoreq.90.0 wt. % of
the reactor effluent's aromatic C.sub.8 isomers are combined with
the first mixture in step (d).
[0061] Embodiment 24. A process for producing p-xylene, the process
comprising, (a) providing a first mixture comprising .gtoreq.5.0
wt. % of aromatic C.sub.8 isomers, based on the weight of the first
mixture, said C.sub.8 isomers comprising p-xylene and ethylbenzene;
(b) separating from the first mixture in a first separation stage
wherein the first separation stage includes at least one simulated
moving-bed adsorptive separation stage: (i) a p-xylene-depleted
raffinate; (ii) a p-xylene-containing portion comprising
.gtoreq.10.0 wt. % of the first mixture's p-xylene, based on the
weight of the first mixture's p-xylene; and (iii) an
ethylbenzene-containing portion comprising .gtoreq.10.0 wt. % of
the first mixture's ethylbenzene, based on the weight of the first
mixture's ethylbenzene; (c) conducting away at least a portion of
the p-xylene-containing portion; (d) conducting away .gtoreq.50.0
wt. % of the ethylbenzene-containing portion, based on the weight
of the ethylbenzene-containing portion; (e) isomerizing at least a
portion the p-xylene-depleted raffinate in the liquid phase wherein
.ltoreq.10.0 wt. %, e.g., .ltoreq.1.0 wt. % or .ltoreq.0.1 wt. %,
of the p-xylene-depleted raffinate is in the vapor phase during the
isomerizing, the weight percent being based on the weight of the
p-xylene-depleted raffinate, to produce a reactor effluent
comprising .gtoreq.90.0 wt. % p-xylene, based on the weight of the
reactor effluent's aromatic C.sub.8 isomers; and (f) combining with
the first mixture at least a portion of the reactor effluent, the
combining being carried out before and/or during the separating of
(b).
[0062] Embodiment 25. The process of Embodiment 24, further
comprising: (g) removing a by-product from the first mixture, the
by-product comprising (1) at least a portion of the first mixture's
o-xylene and/or (2) at least a portion of any C.sub.9+ aromatics in
the first mixture; and/or (h) separating from the reactor effluent
in a third separation stage one or more of toluene, o-xylene or
C.sub.9+ aromatics, and conducting away at least a portion of one
or more of the separated toluene, the separated o-xylene, and the
separated C.sub.9+ aromatics; and wherein step (b) further includes
(iv) a non-aromatic hydrocarbon portion, comprising .gtoreq.50.0
wt. %, preferably .gtoreq.75.0 wt. %, or .gtoreq.90.0 wt. %, of the
first mixture's non-aromatic hydrocarbon molecules.
[0063] While the present invention has been described and
illustrated by reference to particular embodiments, those of
ordinary skill in the art will appreciate that the invention lends
itself to variations not necessarily illustrated herein. For this
reason, then, reference should be made solely to the appended
claims for purposes of determining the enforceable scope of the
present invention.
[0064] As demonstrated above, aspects of the invention provide
methods of making p-xylene, particularly in a xylene loop. The new
methods have one or more of the following advantages. For example,
the vapor-phase isomerization stage may be further reduced in size
when non-aromatics are separated and conducted away from the xylene
loop upstream of isomerization. Vapor-phase isomerization stage(s)
can be eliminated altogether when substantially all of the
non-aromatics and substantially all of the ethylbenzene are
separated and conducted away from the xylene loop upstream of
isomerization. An advantage of some aspects is that the same type
of chromatographic separation as is used for p-xylene and
ethylbenzene separation from a mixture of aromatic C.sub.8 isomers
can also be utilized for separating and removing non-aromatics from
the loop, e.g., as a component of a third raffinate, upstream of
the isomerization stage. In the conventional process, vapor-phase
isomerization is needed for cracking these molecules into lower
molecular weight fragments. The invention overcomes this difficulty
because the sufficient non-aromatics are conducted away from the
xylene loop as a component of the third raffinate. Other
characteristics and additional advantages are apparent to those
skilled in the art.
[0065] All documents described herein are incorporated by reference
herein for purposes of all jurisdictions where such practice is
allowed, including any priority documents and/or testing procedures
to the extent they are not inconsistent with this text. As is
apparent from the foregoing general description and the specific
embodiments, while forms of the invention have been illustrated and
described, various modifications can be made without departing from
the spirit and scope of the invention. Accordingly, it is not
intended that the invention be limited thereby. Likewise, the term
"comprising" is considered synonymous with the term "including".
Likewise whenever a composition, an element or a group of elements
is preceded with the transitional phrase "comprising," it is
understood that we also contemplate the same composition or group
of elements with transitional phrases "consisting essentially of,"
"consisting of," "selected from the group of consisting of," or
"is" preceding the recitation of the composition, element, or
elements and vice versa.
* * * * *