U.S. patent application number 14/560889 was filed with the patent office on 2015-06-25 for conversion of methanol to olefins and para-xylene.
The applicant listed for this patent is ExxonMobil Chemical Patents Inc.. Invention is credited to Samia Ilias, Helge Jaensch, Stephen J. McCarthy, John D. Ou, Mayank Shekhar, Nikolaos Soultanidis.
Application Number | 20150175499 14/560889 |
Document ID | / |
Family ID | 51062732 |
Filed Date | 2015-06-25 |
United States Patent
Application |
20150175499 |
Kind Code |
A1 |
Ou; John D. ; et
al. |
June 25, 2015 |
Conversion of Methanol to Olefins and Para-Xylene
Abstract
Methods are provided for conversion of methanol and/or dimethyl
ether to aromatics, such as a para-xylene, and olefins, such as
ethylene and propylene. The methods can be used in conjunction with
molecular sieve (zeolite) catalysts that are prepared for use in
conjunction with selected effective conversion conditions. The
combination of a catalyst and a corresponding effective conversion
condition can allow for improved yield aromatics and olefins
generally; improved yield of desired aromatics and olefins, such as
para-xylene, ethylene, and/or propylene; reduced production of less
desirable side products, such as methane, CO, CO.sub.2, and/or
coke; or a combination thereof. The preparation of the catalyst can
include modification of the catalyst with a transition metal, such
as Zn or Ga. The preparation of the catalyst can also include
steaming of the catalyst. In some aspects, the preparation of the
catalyst can further include modifying the catalyst with
phosphorous.
Inventors: |
Ou; John D.; (Houston,
TX) ; Soultanidis; Nikolaos; (Houston, TX) ;
Shekhar; Mayank; (Houston, TX) ; Ilias; Samia;
(Somerville, NJ) ; Jaensch; Helge; (Brussels,
BE) ; McCarthy; Stephen J.; (Center Valley,
PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Chemical Patents Inc. |
Baytown |
TX |
US |
|
|
Family ID: |
51062732 |
Appl. No.: |
14/560889 |
Filed: |
December 4, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62003290 |
May 27, 2014 |
|
|
|
61918984 |
Dec 20, 2013 |
|
|
|
61918994 |
Dec 20, 2013 |
|
|
|
61919013 |
Dec 20, 2013 |
|
|
|
Current U.S.
Class: |
585/408 ;
585/640 |
Current CPC
Class: |
C07C 1/22 20130101; C07C
2/64 20130101; C10G 2400/30 20130101; C10G 29/205 20130101; C07C
5/2729 20130101; Y02P 30/42 20151101; C10G 3/49 20130101; C07C 1/24
20130101; Y02P 30/20 20151101; C07C 2529/40 20130101; Y02P 30/40
20151101; C07C 6/06 20130101; C07C 6/00 20130101 |
International
Class: |
C07C 1/22 20060101
C07C001/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 7, 2014 |
EP |
14176022.3 |
Claims
1. A method of converting a feed to form olefins and aromatics,
comprising: steaming a catalyst in the presence of at least 1 vol %
water at a temperature of about 400.degree. C. to about 850.degree.
C. for at least about 0.25 hours, the catalyst comprising a
molecular sieve having at least one 10-member ring channel and
having no ring channels larger than a 10-member ring channel, the
catalyst further comprising about 0.1 wt % to about 10.0 wt % of a
metal from Groups 8-14; and exposing a feed comprising at least
about 50 wt % of methanol, dimethyl ether, or a combination thereof
to the steamed catalyst under effective conversion conditions to
form a conversion effluent comprising ethylene, propylene, and
para-xylene, the effective conversion conditions including a
temperature of about 350.degree. C. to about 600.degree. C.
2. The method of claim 1, wherein the effective conversion
conditions include a temperature of at least about 475.degree. C.
and a combined yield in the conversion effluent of CO and CO.sub.2
being about 5 wt % or less.
3. The method of claim 1, wherein exposing a feed to the steamed
catalyst comprises exposing the feed to the steamed catalyst in a
fluidized bed reactor or a riser reactor.
4. The method of claim 1, wherein the effective conversion
conditions include a temperature of at least about 500.degree.
C.
5. The method of claim 1, further comprising separating at least a
portion of the converted effluent to form a light ends product
comprising ethylene, propylene, or a combination thereof, and a
liquid effluent.
6. The method of claim 5, further comprising separating at least a
portion of the liquid effluent to form a C.sub.8 product stream and
one or more of a C.sub.7- stream and a C.sub.9+ stream.
7. The method of claim 6, wherein exposing a feed to the steamed
catalyst comprises exposing the feed to the steamed catalyst in the
presence of a hydrogen-lean stream, the method further comprising
recycling at least a portion of the C.sub.7- stream, the C.sub.9+
stream, or a combination thereof, to form the hydrogen-lean
stream.
8. The method of claim 6, further comprising separating the C.sub.8
product stream to form at least a para-xylene product stream, the
para-xylene product stream having a higher concentration of
para-xylene than the C.sub.8 product stream.
9. The method of claim 1, wherein the steamed catalyst further
comprises at least about 0.1 wt % of phosphorus, lanthanum, an
element from Groups 1 or 2, an element from Groups 13-16, or a
combination thereof.
10. The method of claim 1, wherein the steamed catalyst further
comprises at least about 0.1 wt % of phosphorus.
11. The method of claim 1, wherein the molecular sieve comprises
ZSM-5.
12. The method of claim 1, wherein the effective conversion
conditions comprise a pressure of about 100 kPaa to about 2500 kPaa
and a WHSV of about 0.1 hr.sup.-1 to about 20 hr.sup.-1.
13. The method of claim 1, wherein the feed substantially comprises
methanol, dimethyl ether, or a combination thereof.
14. The method of claim 1, wherein exposing a feed to the steamed
catalyst comprises exposing the feed to the steamed catalyst in the
presence of steam, a hydrogen-lean stream, or a combination
thereof.
15. A method of converting a feed to form olefins and aromatics,
comprising: steaming a catalyst in the presence of at least 1 vol %
water at a temperature of about 400.degree. C. to about 850.degree.
C. for at least about 0.25 hours, the catalyst comprising a
molecular sieve having at least one 10-member ring channel and
having no ring channels larger than a 10-member ring channel, the
catalyst further comprising about 0.1 wt % to about 10.0 wt % of
Zn, Ga, Ag, or a combination thereof; and exposing a feed
comprising at least about 50 wt % of methanol, dimethyl ether, or a
combination thereof to the steamed catalyst under effective
conversion conditions to form a conversion effluent comprising
ethylene, propylene, and para-xylene, the effective conversion
conditions including a temperature of about 425.degree. C. to about
600.degree. C.
16. The method of claim 15, wherein the effective conversion
conditions include a temperature of at least about 475.degree. C.
and a combined yield in the conversion effluent of CO and CO.sub.2
being about 5 wt % or less.
17. The method of claim 15, wherein the steamed catalyst further
comprises at least about 0.1 wt % of phosphorus, lanthanum, an
element from Groups 1 or 2, an element from Groups 13-16, or a
combination thereof.
18. The method of claim 15, wherein the steamed catalyst further
comprises at least about 0.1 wt % of phosphorus.
19. The method of claim 15, wherein the molecular sieve comprises
ZSM-5.
20. The method of claim 15, wherein the effective conversion
conditions comprise a pressure of about 100 kPaa to about 2500 kPaa
and a WHSV of about 0.1 hr.sup.-1 to about 20 hr.sup.-1.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Provisional U.S. patent
application Ser. No. 62/003,290 (Docket No. 2014EM128), filed May
27, 2014; Provisional U.S. Patent Application Ser. No. 61/918984
(Docket No. 2013EM376) filed Dec. 20, 2013; Provisional U.S. Patent
Application Ser. No. 61/918,994 (Docket No. 2013EM377) filed Dec.
20, 2013; Provisional U.S. Patent Application Ser. No. 61/919,013
(Docket No. 2013EM378) filed Dec. 20, 2013; and EP 14176022.3
(Docket No. 2014EM128) filed Jul. 7, 2014, the disclosures of which
are incorporated herein by reference in their entireties. Related
applications to which priority is not claimed are U.S. Patent
Application No. _____ (Docket No. 2014EM128/2US), filed Dec. 4,
2014; P.C.T. Patent Application No. _____ (Docket No.
2014EM128PCT), filed Dec. 4, 2014; P.C.T. Patent Application No.
_____ (Docket No. 2014EM360PCT), filed Dec. 4, 2014; U.S. Patent
Application No. _____ (Docket No. 2014EM359US) _____, filed Dec. 4,
2014; and P.C.T. Patent Application No. _____, (Docket No.
2014EM359PCT), filed Dec. 4, 2014.
FIELD OF THE INVENTION
[0002] Catalysts and methods are provided for manufacture of
olefins and aromatics from oxygenate feeds.
BACKGROUND OF THE INVENTION
[0003] Conversion of methanol to olefins and other unsaturated
compounds is a commonly used reaction scheme for chemical
manufacture. Conventional methods can involve exposing a
methanol-containing feed to a molecular sieve, such as ZSM-5. In
addition to forming olefins, some desirable aromatic compounds can
also be formed, such as para-xylene.
[0004] U.S. Pat. Nos. 4,049,573 and 4,088,706 disclose conversion
of methanol to a hydrocarbon mixture rich in C.sub.2-C.sub.3
olefins and mononuclear aromatics, particularly p-xylene, by
contacting the methanol at a temperature of 250-700.degree. C. and
a pressure of 0.2 to 30 atmospheres with a crystalline
aluminosilicate zeolite catalyst which has a Constraint Index of
1-12 and which has been modified by the addition of an oxide of
boron or magnesium either alone or in combination or in further
combination with oxide of phosphorus. The above-identified
disclosures are incorporated herein by reference.
[0005] Methanol can be converted to gasoline employing the MTG
(methanol to gasoline) process. The MTG process is disclosed in the
patent art, including, for example, U.S. Pat. Nos. 3,894,103;
3,894,104; 3,894,107; 4,035,430 and 4,058,576. U.S. Pat. No.
3,894,102 discloses the conversion of synthesis gas to gasoline.
MTG processes provide a simple means of converting syngas to
high-quality gasoline. The ZSM-5 catalyst used is highly selective
to gasoline under methanol conversion conditions, and is not known
to produce distillate range fuels, because the C.sub.10+ olefin
precursors of the desired distillate are rapidly converted via
hydrogen transfer to heavy polymethylaromatics and C.sub.4 to
C.sub.8 isoparaffins under methanol conversion conditions.
[0006] Olefinic feedstocks can also be used for producing C.sub.5+
gasoline, diesel fuel, etc. In addition to the basic work derived
from ZSM-5 type zeolite catalysts, a number of discoveries
contributed to the development of the industrial process known as
Mobil Olefins to Gasoline/Distillate ("MOGD"). This process has
significance as a safe, environmentally acceptable technique for
utilizing feedstocks that contain lower olefins, especially C.sub.2
to C.sub.5 alkenes. In U.S. Pat. Nos. 3,960,978 and 4,021,502,
Plank, Rosinski and Givens disclose conversion of C.sub.2 to
C.sub.5 olefins alone or in admixture with paraffinic components,
into higher hydrocarbons over crystalline zeolites having
controlled acidity. Garwood et al have also contributed improved
processing techniques to the MOGD system, as in U.S. Pat. Nos.
4,150,062, 4,211,640 and 4,227,992. The above-identified
disclosures are incorporated herein by reference.
[0007] Conversion of lower olefins, especially propene and butenes,
over ZSM-5 is effective at moderately elevated temperatures and
pressures. The conversion products are sought as liquid fuels,
especially the C.sub.5+ aliphatic and aromatic hydrocarbons.
Olefinic gasoline is produced in good yield by the MOGD process and
may be recovered as a product or recycled to the reactor system for
further conversion to distillate-range products. Operating details
for typical MOGD units are disclosed in U.S. Pat. Nos. 4,445,031,
4,456,779, Owen et al, and U.S. Pat. No. 4,433,185, Tabak,
incorporated herein by reference.
[0008] In addition to their use as shape selective oligomerization
catalysts, the medium pore ZSM-5 type catalysts are useful for
converting methanol and other lower aliphatic alcohols or
corresponding ethers to olefins. Particular interest has been
directed to a catalytic process (MTO) for converting low cost
methanol to valuable hydrocarbons rich in ethene and C.sub.3+
alkenes. Various processes are described in U.S. Pat. No. 3,894,107
(Batter et al), U.S. Pat. No. 3,928,483 (Chang et al), U.S. Pat.
No. 4,025,571 (Lago), U.S. Pat. No. 4,423,274 (Daviduk et al) and
U.S. Pat. No. 4,433,189 (Young), incorporated herein by reference.
It is generally known that the MTO process can be optimized to
produce a major fraction of C.sub.2 to C.sub.4 olefins. Prior
process proposals have included a separation section to recover
ethene and other gases from by-product water and C.sub.5+
hydrocarbon liquids. The oligomerization process conditions which
favor the production of C.sub.10 to C.sub.20 and higher aliphatics
tend to convert only a small portion of ethene as compared to
C.sub.3+ olefins.
[0009] The methanol to olefin process (MTO) operates at high
temperature and near 30 psig in order to obtain efficient
conversion of the methanol to olefins. These process conditions,
however, produce an undesirable amount of aromatics and C.sub.2
olefins and require a large investment in plant equipment.
[0010] The olefins to gasoline and distillate process (MOGD)
operates at moderate temperatures and elevated pressures to produce
olefinic gasoline and distillate products. When the conventional
MTO process effluent is used as a feed to the MOGD process, the
aromatic hydrocarbons produced in the MTO unit are desirably
separated and a relatively large volume of MTO product effluent has
to be cooled and treated to separate a C.sub.2- light gas stream,
which is unreactive, except for ethene which is reactive to only a
small degree, in the MOGD reactor, and the remaining hydrocarbon
stream has to be pressurized to the substantially higher pressure
used in the MOGD reactor.
[0011] Chinese publications CN 101602648, CN 101602643, CN
101607864, and CN 101780417 describe use of selectivated catalysts
for conversion of methanol to para-xylene. In these publications,
zeolite catalysts are treated with silicate compounds, such as
tetraethylorthosilicate, to provide improved selectivity for
formation of olefins and para-xylene from methanol feeds. However,
silicon treatment introduces several undesired effects, it reduces
the per pass aromatic yield and promotes coke deposition that
limits the catalyst cycle length. Especially for metal promoted
zeolites, silicon treatment can promote metal migration and
sintering that results to shorter catalyst lifetime.
[0012] There is an ongoing need to provide improved catalysts and
methods for producing olefins and aromatics from oxygenated
feeds.
SUMMARY OF THE INVENTION
[0013] A method of converting a feed to form olefins and aromatics
is provided. The method includes steaming a catalyst in the
presence of at least 1 vol % water at a temperature of about
400.degree. C. to about 850.degree. C. for at least about 0.25
hours. The catalyst includes a molecular sieve having at least one
10-member ring channel and having no ring channels larger than a
10-member ring channel. The catalyst further includes about 0.1 wt
% to about 10.0 wt % of a metal from Groups 8-14. A feed comprising
at least about 50 wt % of methanol, dimethyl ether, or a
combination thereof is then exposed to the steamed catalyst under
effective conversion conditions to form a conversion effluent
comprising ethylene, propylene, and para-xylene. The effective
conversion conditions including a temperature of about 350.degree.
C. to about 600.degree. C. Optionally, the metal from Groups 8-14
can be Zn, Ga, Ag, or a combination thereof. Optionally, the
catalyst can further include about 0.1 wt % to about 10 wt % of
phosphorus, lanthanum, an element from Groups 1 or 2, an element
from Groups 13-16, or a combination thereof. Optionally, the method
can further include one or more separations to separate a stream
enriched in para-xylene from the conversion effluent.
BRIEF DESCRIPTION OF THE FIGURES
[0014] FIG. 1 schematically shows an example of a reaction system
for converting a feed to form olefins and aromatics.
[0015] FIG. 2 shows results from converting a feed in the presence
of various catalysts to form olefins and aromatics.
[0016] FIG. 3 shows results from converting a feed in the presence
of a catalyst at various temperatures to form olefins and
aromatics.
[0017] FIG. 4 shows results from converting a feed in the presence
of a catalyst at various temperatures to form olefins and
aromatics.
[0018] FIG. 5 shows results from converting a feed in the presence
of a catalyst to form olefins and aromatics.
[0019] FIG. 6 shows results from converting a feed in the presence
of various catalysts to form olefins and aromatics.
[0020] FIG. 7 schematically shows an alternative example of a
reaction system for converting a feed to form olefins and
aromatics.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Overview
[0021] In various aspects, methods are provided for conversion of
methanol and/or dimethyl ether to aromatics, such as a para-xylene,
and olefins, such as ethylene and propylene. The methods can be
used in conjunction with molecular sieve (zeolite) catalysts that
are prepared for use in conjunction with selected effective
conversion conditions. The combination of a catalyst and a
corresponding effective conversion condition can allow for improved
yield aromatics and olefins generally; improved yield of desired
aromatics and olefins, such as para-xylene, ethylene, and/or
propylene; reduced production of less desirable side products, such
as methane, CO, CO.sub.2, and/or coke; or a combination thereof.
The preparation of the catalyst can include modification of the
catalyst with a transition metal, such as Zn, Ga, or Ag. The
preparation of the catalyst can also include steaming of the
catalyst. In some aspects, the preparation of the catalyst can
further include modifying the catalyst with phosphorous. Use of
transition metal-modified molecular sieves can provide an improved
alternative pathway for synthesis of para-xylene. Such improved
alternatives are desirable in view of the increasing commercial
demand for para-xylene.
[0022] It has been unexpectedly found that various types of yield
improvements can be achieved during conversion of methanol and/or
dimethyl ether to olefins and aromatics (including para-xylene) by
using a combination of improved catalyst synthesis with
corresponding conversion conditions. The improved catalyst
synthesis techniques can provide a conversion catalyst that is
suitable for use in a commercial production environment. For
example, one improvement can be modification of a molecular sieve
or zeolite catalyst with a transition metal, such as Zn, Ga, or Ag.
Such a modified catalyst can then be steamed under effective
steaming conditions. Steaming of a catalyst can have various
impacts on the catalyst. Steaming a catalyst has an impact similar
to aging of the catalyst, so that changes in catalyst activity that
occur early during a processing run can be reduced or minimized
This includes reducing or minimizing the initial cracking activity
of a catalyst. Without being bound by any particular theory, it is
also believed that steaming of metal-modified conversion catalysts
can improve the dispersion of the modifying metals on the catalyst.
This improved dispersion can reduce or minimize the loss of reagent
to formation of side products, such as carbon oxides or coke. The
reduction of loss of reagent can be valuable, for example, for
allowing the conversion process to be performed at higher
temperatures. Higher temperatures are believed to be beneficial for
improving the yield of aromatics but higher temperatures also tend
to increase the yield of undesirable side products, such as carbon
oxides or coke. The improved dispersion of the modifying metal on
the catalyst can reduce or minimize such formation of the
undesirable side products at higher conversion temperatures.
[0023] Another type of improvement can be to further modify a
steamed, metal-modified catalyst with phosphorous. In some aspects,
in addition to providing an improved yield of aromatics, modifying
a catalyst with phosphorous can also improve the stability of a
catalyst over time during a processing run.
[0024] It is noted that various types of yield improvements can be
valuable in addition to a simple increase in the yield of
para-xylene. One type of yield improvement that can be valuable is
an improvement in the overall yield of aromatics. In some aspects,
a portion of the overall aromatics yield is due to the production
of other xylene isomers. Such xylene isomers can be isomerized in a
subsequent step to form para-xylene. Additionally or alternately, a
portion of the overall aromatics yield is due to production of
various aromatic compounds, such as benzene, toluene, or aromatics
with sufficient side chains to have a total of nine or more carbon
atoms. Such aromatics can be valuable as products, or such
aromatics can be recycled to the methanol conversion process to
enhance the overall yield.
[0025] Another type of valuable yield improvement can be an
improvement in the total yield of aromatics plus olefins. The
benefits of an improved yield of aromatics are noted above. Olefins
are valuable as a raw material for a variety of synthesis
processes, such as formation of aromatics or formation of
polymers.
[0026] Still another type of valuable yield improvement can be a
reduction in the yield of side products, such as carbon oxides,
methane, or coke. The formation of CO or CH.sub.4 can typically
represent conversion of methanol to a compound used for methanol
synthesis. Formation of CO.sub.2 and/or coke can be even less
favorable, as these products typically have little or no commercial
value or value as reagents. Because methanol conversion processes
are often run to achieve substantially complete conversion of
methanol (and/or dimethyl ether), avoiding formation of lower value
products can correspond to increased formation of higher value
products.
Conversion Catalyst
[0027] The catalyst used herein is a composition of matter
comprising a molecular sieve and a Group 8-14 element, or a
molecular sieve and a combination of metals from the same group of
the Periodic Table. The composition of matter can optionally
further comprise phosphorus and/or lanthanum and/or other elements
from Group 1-2 and/or Group 13-16 of the Periodic Table that
provide structural stabilization. In this sense, the term
"comprising" can also mean that the catalyst can comprise the
physical or chemical reaction product of the molecular sieve and
the Group 8-14 element or combination of elements from the same
group (and optionally phosphorus and/or lanthanum and/or other
elements from groups 1-2 and/or group 13-16). In this description,
reference to a group number for an element corresponds to the
current IUPAC numbering scheme for the periodic table. Optionally,
the catalyst may also include a filler or binder and may be
combined with a carrier to form slurry.
[0028] A catalyst comprising a molecular sieve can be modified by
the Group 8-14 metal(s) in any convenient manner. Typical methods
for modifying a catalyst with a metal include impregnation (such as
by incipient wetness), ion exchange, deposition by precipitation,
and any other convenient method for depositing a metal that is
supported by a catalyst and/or a catalyst support.
[0029] In various aspects, the molecular sieve comprises
.gtoreq.10.0 wt. % of the catalyst. The upper limit on the amount
of molecular sieve in the catalyst may be 10.0 wt. %, 12.5 wt. %,
15.0 wt. %, 20.0 wt. %, 25.0 wt. %, 30.0 wt. %, 35.0 wt. % 40.0 wt.
%, 45.0 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. %, 99.5 wt. %, or 100.0 wt. %. The lower limit on the
amount of molecular sieve in the catalyst may be 10.0 wt. %, 12.5
wt. %, 15.0 wt. %, 20.0 wt. %, 25.0 wt. %, 30.0 wt. %, 35.0 wt. %
40.0 wt. %, 45.0 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. %, 99.5 wt. %, or 100.0 wt. %. Ranges
expressly disclosed include combinations of any of the
above-enumerated upper and lower limits; e.g., 10.0 to 20.0 wt. %,
12.5 to 25.0 wt. %, 20.0 to 50.0, or 40.0 to 99.0 wt. %.
[0030] As used herein the term "molecular sieve" refers to
crystalline or non-crystalline materials having a porous structure.
Microporous molecular sieves typically have pores having a diameter
of .ltoreq. about 2.0 nm. Mesoporous molecular sieves typically
have pores with diameters of about 2 to about 50 nm. Macroporous
molecular sieves have pore diameters of >50.0 nm. The upper
limit on the pore diameter may be 1.00.times.10.sup.4 nm,
5.00.times.10.sup.3 nm, 2.50.times.10.sup.3 nm, 1.00.times.10.sup.3
nm, 5.00.times.10.sup.2 nm, 2.50.times.10.sup.2 nm,
1.25.times.10.sup.2 nm, 75.0 nm, 50.0 nm, 40.0 nm, 30.0 nm, 20.0
nm, 10.0 nm, or 5.0 nm. The lower limit on the pore diameter may be
5.00.times.10.sup.3 nm, 2.50.times.10.sup.3 nm, 1.00.times.10.sup.3
nm, 5.00.times.10.sup.2 nm, 2.50.times.10.sup.2 nm,
1.25.times.10.sup.2 nm, 75.0 nm, 50.0 nm, 40.0 nm, 30.0 nm, 20.0
nm, 10.0 nm, 5.0 nm, 4.0 nm, 3.0 nm, 2.0 nm, 1.0 nm or less. Ranges
of the pore diameters expressly disclosed include combinations of
any of the above-enumerated upper and lower limits. For example,
some molecular sieves may have pore diameters of about 1.0 to
>5.00.times.10.sup.3 nm, 2.0 to 5.00.times.10.sup.3 nm, 2.0 to
1.00.times.10.sup.3 nm, 2.0 to 5.00.times.10.sup.2 nm, 2.0 to
2.50.times.10.sup.2 nm, 2.0 to 1.25.times.10.sup.2 nm, 2.0 to 75.0
nm, 5.0 to 75.0 nm, 7.5 to 75.0 nm, 10.0 to 75.0 nm, 15.0 to 75.0
nm, 20.0 to 75.0 nm, 25.0 to 75.0 nm, 2.0 to 50.0 nm, 5.0 to 50.0
nm, 7.5 to 50.0 nm, 10.0 to 50.0 nm, 15.0 to 50.0 nm, 20.0 to 50.0
nm, or 25.0 to 50.0 nm, etc.
[0031] Additionally or alternatively, some molecular sieves useful
herein are described by a Constraint Index of about 1 to about 12.
The upper limit on the range of the Constraint Index may be about
12.0, 11.0, 10.0, 9.0, 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, or 2.0. The
lower limit on the range of the Constraint Index may be about 11.0,
10.0, 9.0, 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.0, or 1.0. Ranges of the
Constraint Indices expressly disclosed include combinations of any
of the above-enumerated upper and lower limits. For example, some
molecular sieves have a Constraint Index of 1.0 to about 10.0, 1.0
to about 8.0, 1 to about 6.0, 1 to about 5.0, 1 to about 3.0, 2.0
to about 11.0, 3.0 to 10.0, 4.0 to 9.0, or 6.0 to 9.0, etc.
Constraint Index is determined as described in U.S. Pat. No.
4,016,218, incorporated herein by reference for details of the
method.
[0032] Particular molecular sieves are zeolitic materials. Zeolitic
materials are crystalline or para-crystalline materials. Some
zeolites are aluminosilicates comprising [SiO.sub.4] and
[AlO.sub.4] units. Other zeolites are aluminophosphates (AlPO)
having structures comprising [AlO.sub.4] and [PO.sub.4] units.
Still other zeolites are silicoaluminophosphates (SAPO) comprising
[SiO.sub.4], [AlO.sub.4], and [PO.sub.4] units.
[0033] Non-limiting examples of SAPO and AlPO molecular sieves
useful herein include one or a combination of SAPO-5, SAPO-8,
SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34,
SAPO-35, SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44,
SAPO-47, SAPO-56, AlPO-5, AlPO-11, AlPO-18, AlPO-31, AlPO-34,
AlPO-36, AlPO-37, AlPO-46, and metal containing molecular sieves
thereof. Of these, particularly useful molecular sieves are one or
a combination of SAPO-18, SAPO-34, SAPO-35, SAPO-44, SAPO-56,
AlPO-18, AlPO-34 and metal containing derivatives thereof, such as
one or a combination of SAPO-18, SAPO-34, AlPO-34, AlPO-18, and
metal containing derivatives thereof, and especially one or a
combination of SAPO-34, AlPO-18, and metal containing derivatives
thereof.
[0034] Additionally or alternatively, the molecular sieves useful
herein may be characterized by a ratio of Si to Al. In particular
embodiments, the molecular sieves suitable herein include those
having a Si/Al ratio of about 10 to 100, preferably about 10 to 80,
more preferably about 20 to 60, and most preferably about 20 to
40.
[0035] In an embodiment, the molecular sieve is an intergrowth
material having two or more distinct crystalline phases within one
molecular sieve composition. In particular, intergrowth molecular
sieves are described in U.S. Patent Application Publication No.
2002-0165089 and International Publication No. WO 98/15496,
published Apr. 16, 1998, both of which are herein fully
incorporated by reference.
[0036] Particular molecular sieves useful in this invention include
ZSM-5 (U.S. Pat. No. 3,702,886 and Re. 29,948); ZSM-11 (U.S. Pat.
No. 3,709,979); ZSM-12 (U.S. Pat. No. 3,832,449); ZSM-22 (U.S. Pat.
No. 4,556,477); ZSM-23 (U.S. Pat. No. 4,076,842); ZSM-34 (U.S. Pat.
No. 4,079,095) ZSM-35 (U.S. Pat. No. 4,016,245); ZSM-48 (U.S. Pat.
No. 4,397,827); ZSM-57 (U.S. Pat. No. 4,046,685); and ZSM-58 (U.S.
Pat. No. 4,417,780). The entire contents of the above references
are incorporated by reference herein. Other useful molecular sieves
include MCM-22, PSH-3, SSZ-25, MCM-36, MCM-49 or MCM-56, with
MCM-22. Still other molecular sieves include Zeolite T, ZK5,
erionite, and chabazite.
[0037] Another option for characterizing a zeolite (or other
molecular sieve) is based on the nature of the ring channels in the
zeolite. The ring channels in a zeolite can be defined based on the
number of atoms including in the ring structure that forms the
channel. In some aspects, a zeolite can include at least one ring
channel based on a 10-member ring. In such aspects, the zeolite
preferably does not have any ring channels based on a ring larger
than a 10-member ring. Examples of suitable framework structures
having a 10-member ring channel but not having a larger size ring
channel include EUO, FER, IMF, LAU, MEL, MFI, MFS, MTT, MWW, NES,
PON, SFG, STF, STI, TON, TUN, MRE, and PON.
[0038] The catalyst also includes at least one metal selected from
Group 8-14 of the Periodic Table, such as at least two metals
(i.e., bimetallic) or at least three metals (i.e., trimetallic).
Typically, the total weight of the Group 8-14 elements is
.gtoreq.0.1 wt. % based on the total weight of the catalyst.
Typically, the total weight of the Group 8-14 element is
.ltoreq.about 10.0 wt. %, based on the total weight of the
catalyst. Thus, the upper limit on the range of the amount of the
Group 8-14 elements added to the molecular sieve may be 10.0 wt. %,
9.0 wt. %, 8.0 wt. %, 7.0 wt. %, 6.0 wt. %, 5.0 wt. %, 4.0 wt. %,
3.0 wt. %, 2.0 wt. %, 1.0 wt. %, or 0.1 wt. %. The lower limit on
the range of the amount of the Group 8-14 elements added to the
molecular sieve may be 10.0 wt. %, 9.0 wt. %, 8.0 wt. %, 7.0 wt. %,
6.0 wt. %, 5.0 wt. %, 4.0 wt. %, 3.0 wt. %, 2.0 wt. %, 1.0 wt. %,
or 0.1 wt. %. Ranges expressly disclosed include combinations of
any of the above-enumerated upper and lower limits; e.g., 0.1 to
10.0 wt. %, 0.1 to 8.0 wt. %, 0.1 to 6.0 wt. %, 0.1 to 5.0 wt. %,
0.1 to 4.0 wt. %, 0.1 to 3.0 wt. %, 0.1 to 2.0 wt. %, 0.1 to 1.0
wt. %, 1.0 to 10.0 wt. %, 1.0 to 9.0 wt. %, 1.0 to 8.0 wt. %, 1.0
to 7.0 wt. %, 1.0 to 6.0 wt. %, 1.0 to 5.0 wt. %, 1.0 to 4.0 wt. %,
1.0 to 3.0 wt. %, etc. Of course, the total weight of the Group
8-14 elements shall not include amounts attributable to the
molecular sieve itself.
[0039] Additionally or alternatively, in some aspects, the catalyst
can also include at least one of phosphorous and/or lanthanum
and/or other elements from groups 1-2 and/or group 13-16, such as
at least two such elements or at least three such elements.
Typically, the total weight of the phosphorous and/or lanthanum
and/or other elements from groups 1-2 and/or groups 13-16 is
.gtoreq.0.1 wt. % based on the total weight of the catalyst.
Typically, the total weight of the phosphorous and/or lanthanum
and/or other elements from groups 1-2 and/or groups 13-16 is
.ltoreq.about 10.0 wt. %, based on the total weight of the
catalyst. Thus, the upper limit on the range of the phosphorous
and/or lanthanum and/or other elements from groups 1-2 and/or
groups 13-16 added to the molecular sieve may be 10.0 wt. %, 9.0
wt. %, 8.0 wt. %, 7.0 wt. %, 6.0 wt. %, 5.0 wt. %, 4.0 wt. %, 3.0
wt. %, 2.0 wt. %, 1.0 wt. %, or 0.1 wt. %; and the lower limit on
the range added to the molecular sieve may be 10.0 wt. %, 9.0 wt.
%, 8.0 wt. %, 7.0 wt. %, 6.0 wt. %, 5.0 wt. %, 4.0 wt. %, 3.0 wt.
%, 2.0 wt. %, 1.0 wt. %, or 0.1 wt. %. Ranges expressly disclosed
include combinations of any of the above-enumerated upper and lower
limits; e.g., 0.1 to 10.0 wt. %, 0.1 to 8.0 wt. %, 0.1 to 6.0 wt.
%, 0.1 to 5.0 wt. %, 0.1 to 4.0 wt. %, 0.1 to 3.0 wt. %, 0.1 to 2.0
wt. %, 0.1 to 1.0 wt. %, 1.0 to 10.0 wt. %, 1.0 to 9.0 wt. %, 1.0
to 8.0 wt. %, 1.0 to 7.0 wt. %, 1.0 to 6.0 wt. %, 1.0 to 5.0 wt. %,
1.0 to 4.0 wt. %, 1.0 to 3.0 wt. %, etc. Of course, the total
weight of the phosphorous and/or lanthanum and/or other elements
from Groups 1-2 and/or Groups 13-16 shall not include amounts
attributable to the molecular sieve itself.
[0040] For the purposes of this description and claims, the
numbering scheme for the Periodic Table Groups corresponds to the
current IUPAC numbering scheme. Therefore, a "Group 4 metal" is an
element from Group 4 of the Periodic Table, e.g., Hf, Ti, or Zr.
The more preferred molecular sieves are SAPO molecular sieves, and
metal-substituted SAPO molecular sieves. In particular embodiments,
one or more Group 1 elements (e.g., Li, Na, K, Rb, Cs, Fr) and/or
Group 2 elements (e.g., Be, Mg, Ca, Sr, Ba, and Ra) and/or
phosphorous and/or Lanthanum may be used. One or more Group 7-9
element (e.g., Mn, Tc, Re, Fe, Ru, Os, Co, Rh, and Ir) may also be
used. Group 10 elements (Ni, Pd, and Pt) are less commonly used in
applications for forming olefins and aromatics, as the combination
of a Group 10 element in the presence of hydrogen can tend to
result in saturation of aromatics and/or olefins. In some
embodiments, one or more Group 11 and/or Group 12 elements (e.g.,
Cu, Ag, Au, Zn, and Cd) may be used. In still other embodiments,
one or more Group 13 elements (B, Al, Ga, In, and Tl) and/or Group
14 elements (Si, Ge, Sn, Pb) may be used. In a preferred
embodiment, the metal is selected from the group consisting of Zn,
Ga, Cd, Ag, Cu, P, La, or combinations thereof. In another
preferred embodiment, the metal is Zn, Ga, Ag, or a combination
thereof.
[0041] Particular molecular sieves and metal-containing derivatives
thereof have been described in detail in numerous publications
including for example, U.S. Pat. No. 4,567,029 (MeAPO where Me is
Mg, Mn, Zn, or Co), U.S. Pat. No. 4,440,871 (SAPO), European Patent
Application EP-A-0 159 624 (E1APSO where El is Be, B, Cr, Co, Ga,
Fe, Mg, Mn, Ti, or Zn), U.S. Pat. No. 4,554,143 (FeAPO), U.S. Pat.
Nos. 4,822,478, 4,683,217, 4,744,885 (FeAPSO), EP-A-0 158 975 and
U.S. Pat. No. 4,935,216 (ZnAPSO, EP-A-0 161 489 (CoAPSO), EP-A-0
158 976 (ELAPO, where EL is Co, Fe, Mg, Mn, Ti, or Zn), U.S. Pat.
No. 4,310,440 (A1PO4), U.S. Pat. No. 5,057,295 (BAPSO), U.S. Pat.
No. 4,738,837 (CrAPSO), U.S. Pat. Nos. 4,759,919, and 4,851,106
(CrAPO), U.S. Pat. Nos. 4,758,419, 4,882,038, 5,434,326, and
5,478,787 (MgAPSO), U.S. Pat. No. 4,554,143 (FeAPO), U.S. Pat. Nos.
4,686,092, 4,846,956, and 4,793,833 (MnAPSO), U.S. Pat. Nos.
5,345,011 and 6,156,931 (MnAPO), U.S. Pat. No. 4,737,353 (BeAPSO),
U.S. Pat. No. 4,940,570 (BeAPO), U.S. Pat. Nos. 4,801,309,
4,684,617, and 4,880,520 (TiAPSO), U.S. Pat. Nos. 4,500,651,
4,551,236, and 4,605,492 (TiAPO), U.S. Pat. Nos. 4,824,554,
4,744,970 (CoAPSO), U.S. Pat. No. 4,735,806 (GaAPSO) EP-A-0 293 937
(QAPSO, where Q is framework oxide unit [QO2]), as well as U.S.
Pat. Nos. 4,567,029, 4,686,093, 4,781,814, 4,793,984, 4,801,364,
4,853,197, 4,917,876, 4,952,384, 4,956,164, 4,956,165, 4,973,785,
5,241,093, 5,493,066, and 5,675,050, all of which are herein fully
incorporated by reference. Other molecular sieves include those
described in R. Szostak, Handbook of Molecular Sieves, Van Nostrand
Reinhold, New York, N.Y. (1992), which is herein fully incorporated
by reference.
[0042] In some aspects, a catalyst comprising a molecular sieve as
modified by the Group 8-14 element and/or a Group 1-2, Group 13-16,
lanthanum, and/or phosphorous is a ZSM-5 based molecular sieve. In
some preferred aspects, the Group 8-14 element can be selected from
Groups 11-13, such as Zn, Ga, Ag, or combinations thereof. In other
aspects, the Group 8-14 element can be two or more elements from
Groups 11-13, such as two or more elements from the same group in
Groups 11-13. In still other aspects, the molecular sieve can be
modified with at least one element from Groups 8-14, such as at
least two elements or at least three elements from Groups 8-14, the
at least two elements or at least three elements optionally being
from the same group in Groups 8-14. In any of the above aspects, a
catalyst comprising a molecular sieve can be further modified by an
element from Groups 1-2, Groups 13-16, lanthanum, and/or
phosphorus.
[0043] Various methods for synthesizing molecular sieves or
modifying molecular sieves are described in U.S. Pat. No. 5,879,655
(controlling the ratio of the templating agent to phosphorus), U.S.
Pat. No. 6,005,155 (use of a modifier without a salt), U.S. Pat.
No. 5,475,182 (acid extraction), U.S. Pat. No. 5,962,762 (treatment
with transition metal), U.S. Pat. Nos. 5,925,586 and 6,153,552
(phosphorus modified), U.S. Pat. No. 5,925,800 (monolith
supported), U.S. Pat. No. 5,932,512 (fluorine treated), U.S. Pat.
No. 6,046,373 (electromagnetic wave treated or modified), U.S. Pat.
No. 6,051,746 (polynuclear aromatic modifier), U.S. Pat. No.
6,225,254 (heating template), International Patent Application WO
01/36329 published May 25, 2001 (surfactant synthesis),
International Patent Application WO 01/25151 published Apr. 12,
2001 (staged acid addition), International Patent Application WO
01/60746 published Aug. 23, 2001 (silicon oil), U.S. Patent
Application Publication No. 2002-0055433 published May 9, 2002
(cooling molecular sieve), U.S. Pat. No. 6,448,197 (metal
impregnation including copper), U.S. Pat. No. 6,521,562 (conductive
microfilter), and U.S. Patent Application Publication No.
2002-0115897 published Aug. 22, 2002 (freeze drying the molecular
sieve), which are all herein incorporated by reference in their
entirety.
Conversion Conditions
[0044] The feedstock for forming aromatics (such as para-xylene)
and olefins can be a feed that includes methanol, dimethyl ether,
or a combination thereof. The feed may also include other
hydrocarbons or hydrocarbonaceous compounds (i.e., compounds
similar to hydrocarbons that also contain one or more heteroatoms).
Additionally or alternately, the feed can be diluted with steam at
any convenient time, such as prior to entering a conversion reactor
or after entering a conversion reactor. Examples of suitable feeds
(excluding any optional dilution with steam) include feeds that are
substantially methanol, feeds that are substantially dimethyl
ether, feeds that are substantially methanol and dimethyl ether, or
feeds that include at least about 50 wt % of methanol and/or
dimethyl ether, such as at least about 60 wt % or at least about 70
wt %. A feed that is substantially composed of a compound (or
compounds) is a feed that is at least 90% wt % of the compound (or
compounds), or at least 95 wt % of the compound, or at least 98 wt
% of the compound, or at least 99 wt % of the compound. For a feed
that is less than 100 wt % methanol and/or dimethyl ether
(excluding any optional dilution with steam), other hydrocarbon
compounds (and/or hydrocarbonaceous compounds) in the feed can
include paraffins, olefins, aromatics, and mixtures thereof
[0045] The feed can be exposed to the conversion catalyst in any
convenient type of reactor. Suitable reactor configurations include
fixed bed reactors, fluidized bed reactors (such as ebullating bed
reactors), riser reactors, and other types of reactors where the
feed can be exposed to the catalyst in a controlled manner.
[0046] Prior to using a catalyst for conversion of methanol and/or
dimethyl ether to aromatics and olefins, the catalyst can be
steamed under effective steaming conditions. General examples of
effective steaming conditions including exposing a catalyst to an
atmosphere comprising steam at a temperature of about 400.degree.
C. to about 850.degree. C., or about 400.degree. C. to about
750.degree. C., or about 400.degree. C. to about 650.degree. C., or
about 500.degree. C. to about 850.degree. C., or about 500.degree.
C. to about 750.degree. C., or about 500.degree. C. to about
650.degree. C. The atmosphere can include as little as 1 vol %
water and up to 100 vol % water. The catalyst can be exposed to the
steam for any convenient period of time, such as about 10 minutes
(0.15 hours) to about 48 hours. In some aspects, the time for
exposure of the catalyst to steam is at least about 0.25 hours,
such as about 0.25 hours to about 8 hours, or about 0.25 hours to
about 4 hours, or about 0.25 hours to about 2 hours, or about 0.5
hours to about 8 hours, or about 0.5 hours to about 4 hours, or
about 0.5 hours to about 2 hours, or about 1 hour to about 8 hours,
or about 1 hour to about 4 hours, or about 1 hour to about 2
hours.
[0047] A suitable feed can be converted to aromatics (including
para-xylene) and olefins by exposing the feed to a conversion
catalyst under effective conversion conditions. General conversion
conditions for conversion of methanol and/or dimethyl ether to
aromatics and olefins include a pressure of about 100 kPaa to about
2500 kPaa, or about 100 kPaa to about 2000 kPaa, or about 100 kPaa
to about 1500 kPaa, or about 100 kPaa to about 1200 kPaa. The
amount of feed (weight) relative to the amount of catalyst (weight)
can be expressed as a weight hourly space velocity (WHSV). Suitable
weight hourly space velocities include a WHSV of about 0.1
hr.sup.-1 to about 20 hr.sup.-1, or about 1.0 hr.sup.-1 to about 10
hr.sup.-1.
[0048] The temperature for the conversion reaction can vary
depending on the nature of the catalyst used for the conversion.
Suitable reaction temperatures include a temperature of about
350.degree. C. to about 600.degree. C., or about 400.degree. C. to
about 600.degree. C., or about 400.degree. C. to about 575.degree.
C., or about 425.degree. C. to about 600.degree. C., or about
425.degree. C. to about 575.degree. C., or about 450.degree. C. to
600.degree. C., or about 450.degree. C. to about 575.degree. C., or
about 475.degree. C. to about 600.degree. C., or about 475.degree.
C. to about 575.degree. C., or about 500.degree. C. to about
600.degree. C., or about 500.degree. C. to about 575.degree. C., or
about 525.degree. C. to about 575.degree. C.
[0049] In some aspects, a metal-modified and steamed catalyst can
be used at any of the temperatures described above. Converting a
methanol and/or dimethyl ether feed using a metal-modified and
steamed catalyst can allow for an improved yield of aromatics
and/or olefins; or a decreased yield of undesirable side products;
or a combination thereof
[0050] In other aspects, a temperature of at least 475.degree. C.
can be used for conversion of a methanol and/or dimethyl ether feed
in the presence of a metal-modified and steamed catalyst. Steaming
of the catalyst can reduce or minimize the yield of undesirable
side products when the conversion is performed at higher
temperature while also increasing the aromatics yield.
[0051] In still other aspects, a temperature of at least
525.degree. C. can be used for conversion of a methanol and/or
dimethyl ether feed in the presence of a metal-modified and steamed
catalyst. In this type of aspect, steaming of a metal-modified
catalyst can provide a catalyst with an initially favorable yield
profile. In a reaction system where catalyst can be exchanged
and/or regenerated, such as an ebullating bed or fluidized bed
reactor, the metal-modified and steamed catalyst can be used for
conversion at high temperature by taking advantage of the initially
favorable yield profile. The catalyst can then be withdrawn from
the system to reduce or minimize the amount of conversion performed
after the catalyst has been degraded to a less favorable yield
profile.
[0052] During a conversion process, a feed comprising methanol,
dimethyl ether, or a combination thereof can be introduced into a
reactor containing a conversion catalyst. Steam can optionally also
be introduced into the reactor. After performing the conversion
reaction, the reactor effluent can be quenched to facilitate
separation of the effluent. The quench can be sufficient to allow
removal of water from the effluent as a liquid. Light organics
containing 4 carbons or less are removed as a gas phase stream.
Ethylene and propylene can subsequently be separated from this
light ends stream. The remaining portion of the effluent can
substantially correspond to hydrocarbons that are liquids at
standard temperature and pressure. A series of separations can then
be performed to separate out desired products. For example, a first
separation on the liquid effluent can separate C.sub.7- (lower
boiling) compounds from C.sub.8+ (higher boiling) compounds. In the
first separation, para-xylene and other C.sub.8+molecules are
included in the higher boiling fraction, while C.sub.7- compounds
(benzene, toluene) and other lower boiling compounds such as
oxygenates form the lower boiling fraction. In this discussion, a
C.sub.7- product stream is defined as a product stream where at
least 50 wt % of the hydrocarbons correspond to hydrocarbons having
7 carbons or less. Similarly, a C.sub.8+ product stream is defined
as a product stream where at least 50 wt % of the hydrocarbons
correspond to hydrocarbons having at least 8 carbons. This lower
boiling fraction may also contain a variety of non-aromatic
compounds. The lower boiling compounds from this first separation
are one suitable source, if desired, for a recycle stream to
provide hydrogen-lean molecules to the conversion reaction.
[0053] The C.sub.8+ fraction can then be further separated into a
C.sub.8 fraction and a C.sub.9+ fraction.
[0054] The C.sub.9+ fraction will typically be primarily aromatics
and is another suitable fraction for recycle, if desired. In this
discussion, a C.sub.8 product stream is defined as a product stream
where at least 50 wt % of the hydrocarbons correspond to
hydrocarbons having 8 carbons. Similarly, a C.sub.9+ product stream
is defined as a product stream where at least 50 wt % of the
hydrocarbons correspond to hydrocarbons having at least 9 carbons.
In some aspects, if a distillation column is used, the first
separation and second separation can be combined to form the
C.sub.7-, C.sub.8, and C.sub.9+ fractions in a single distillation
or fractionation process. In some aspects, the separations to form
the C.sub.7-, C.sub.8, and C.sub.9+ fractions can correspond to any
convenient number of distillation steps in order to improve
recovery of the desired C.sub.8 fraction.
[0055] The C.sub.8 fraction of the liquid effluent from conversion
will typically include at least a portion of xylene isomers other
than para-xylene. The ortho- and meta-xylene isomers can be
separated from the para-xylene isomers by any convenient method,
such as by using crystallization to separate the isomers or by
selective adsorption. Optionally, the C.sub.8 fraction can be
treated in a xylene isomerization unit prior to recovery of the
para-xylene. This can increase the concentration of para-xylene in
the C.sub.8 fraction relative to the concentration prior to the
xylene isomerization. Optionally, the separated ortho- and
meta-xylenes can be recycled back to the distillation step(s) for
further recovery of any remaining para-xylene and/or for further
isomerization to form more para-xylene.
[0056] FIG. 1 shows an example of a reaction system for converting
a methanol/dimethyl ether feed to aromatics and olefins. In FIG. 1,
a methanol (and/or dimethyl ether) feed 105 is introduced into a
conversion reactor 110. The reactor 110 can be a fixed bed reactor,
a fluidized bed reactor, a riser reactor, or another convenient
type of reactor. The total effluent 115 from the conversion reactor
110 can then be passed into a quench stage 120 for separation based
on phases of the effluent. Water 124 can be separated out as one
liquid phase, while a liquid hydrocarbon effluent 122 can
correspond to a second liquid phase. Lower boiling hydrocarbons are
removed as a gas phase or light ends stream 126. The light ends
stream 126 typically includes ethylene and/or propylene, which can
be recovered 160 in one or more recovery processes.
[0057] The liquid hydrocarbon effluent 122 is then separated in one
or more distillation steps to recover a C.sub.8 portion of the
effluent (i.e., a C.sub.8 product stream). Any convenient number of
distillations may be performed. In FIG. 1, the distillation(s) are
schematically represented as corresponding to two distillation
steps for ease of understanding. A first distillation stage 130 can
form a C.sub.7- stream 132 and a C.sub.8+ stream 134. The C.sub.8+
stream 134 is then separated in a second distillation stage 140 to
form a C.sub.9+ stream 142 and a C.sub.8 stream 144. The C.sub.8
stream 144 can then be separated 150, such as by crystallization or
selective adsorption, to separate para-xylene stream 154 from the
other xylene isomers 152.
[0058] In some alternative aspects, a stream of hydrogen-lean
molecules can also be introduced into the conversion reactor. For
example, during a conversion process, a feed comprising methanol,
dimethyl ether, or a combination thereof can be introduced into a
reactor containing a conversion catalyst. Steam can optionally also
be introduced into the reactor. Optionally, a stream of
hydrogen-lean molecules can also be introduced.
[0059] Compounds can be considered `hydrogen-lean` based on the
molecules containing one or more degrees of unsaturation and/or one
or more heteroatoms. Examples of hydrogen-lean molecules include
aromatics such as benzene, toluene and aromatics containing 9 or
more carbons, olefins containing 4 or more carbons (C.sub.4+
olefins), steam cracked naphtha or other refinery streams
containing a mixture of compounds that include hydrogen-lean
molecules, and oxygenates such as alcohols. Without being bound by
any particular theory, it is believed that introduction of hydrogen
lean molecules into the reaction environment can allow excess
hydrogen in the reaction environment to be consumed while reducing
or minimizing saturation of the desired para-xylene, ethylene, and
propylene products. In some aspects, the stream of hydrogen-lean
molecules is based at least in part on one or more recycled output
streams from the conversion process.
[0060] FIG. 7 shows an example of another reaction system for
converting a methanol/dimethyl ether feed to aromatics and olefins.
In FIG. 7, a methanol (and/or dimethyl ether) feed 705 is
introduced into a conversion reactor 710. The reactor 710 can be a
fixed bed reactor, a fluidized bed reactor, a riser reactor, or
another convenient type of reactor. An optional stream of
hydrogen-lean molecules 707 is also shown in FIG. 7 as being
introduced into the reactor. FIG. 7 shows the hydrogen-lean
molecules 707 as including at least a portion 737 of a recycled
C.sub.7- stream 732, but in other aspects a recycled portion of
C.sub.9+ stream 742 could be used instead of or in addition to the
C.sub.7- stream. Optionally, a recycled portion 728 of the C.sub.4-
stream can also be included in the hydrogen-lean molecules, if it
is desired to include ethylene and/or propylene as part of the
reactants in the conversion reactor.
[0061] The total effluent 715 from the conversion reactor 710 can
then be passed into a quench stage 720 for separation based on
phases of the effluent. Water 724 can be separated out as one
liquid phase, while a liquid hydrocarbon effluent 722 can
correspond to a second liquid phase. Lower boiling hydrocarbons are
removed as a gas phase or light ends stream 726. The light ends
stream 726 typically includes ethylene and/or propylene, which can
be recovered 760 in one or more recovery processes.
[0062] The liquid hydrocarbon effluent 722 is then separated in one
or more distillation steps to recover a C.sub.8 portion of the
effluent (i.e., a C.sub.8 product stream). Any convenient number of
distillations may be performed. In FIG. 7, the distillation(s) are
schematically represented as corresponding to two distillation
steps for ease of understanding. A first distillation stage 730 can
form a C.sub.7- stream 732 and a C.sub.8+ stream 734. The C.sub.8+
stream 734 is then separated in a second distillation stage 740 to
form a C.sub.9+ stream 742 and a C.sub.8 stream 744. The C.sub.8
stream 744 can then be separated 750, such as by crystallization or
selective adsorption, to separate para-xylene stream 754 from the
other xylene isomers 752.
EXAMPLE 1
Selectivity of Steamed Conversion Catalyst
[0063] One benefit of steaming a conversion catalyst prior to use
can be an improvement in the selectivity or yield of the desired
products (aromatics, olefins) from the conversion reaction. When a
conversion catalyst is newly synthesized or "fresh", the catalyst
may have a relatively high cracking activity due to the presence of
additional acidic sites on the catalyst. Steaming the catalyst for
a period of time prior to use in a conversion reaction can reduce
the number of acidic sites, leading to increased production of
desired products at the expense of side products such as carbon
oxides and coke.
[0064] FIG. 2 shows results from conversion reactions performed on
several catalysts with different amounts of initial steaming For
the results shown in FIG. 2 (and also in FIGS. 3-5), the conversion
reactions were performed to achieve 100% conversion of a methanol
feed. The catalyst used for the conversion reactions in FIG. 2 was
bound ZSM-5 catalyst modified to include 1 wt % Zn. Catalyst A in
FIG. 2 corresponds to the as-is or "fresh" catalyst. Catalyst B was
steamed for 1 hour prior to use in the conversion reaction,
while
[0065] Catalyst C was steamed for 24 hours and Catalyst D was
steamed for 72 hours. Steaming was used as a means to simulate
catalyst aging. For instance, steaming Catalyst C for 24 hours
prior to use is believed to represent the effect on the catalyst of
being used in a conversion reaction for 1 year under effective
conditions for converting methanol to aromatics and olefins. In
FIG. 2, the results are displayed as a grouping of bar graphs for
each product type, with the bars shown in the order A-B-C-D, as
indicated for the first data set (paraffins) and the last data set
(coke).
[0066] FIG. 2 shows the average product distribution in the
conversion effluent for the fresh and steamed 1% Zn-ZSM-5
catalysts. The conversion reactions for the results in FIG. 2 were
performed at 450.degree. C., 15 psig and 2 hr.sup.-1. Steaming the
1% Zn-ZSM-5 catalyst for 1 hour
[0067] (Catalyst B) caused a decrease in the unwanted side products
(methane, CO, CO.sub.2 and coke) and a corresponding increase in
the paraffins, olefins and olefins+aromatics selectivity compared
to the fresh catalyst (Catalyst A). It is noted that the amount of
coke shown in FIG. 2 represents the amount of coke measured on the
catalyst after the end of the process run. As shown in FIG. 2, the
aromatics selectivity was .about.55% for both Catalyst A and
Catalyst B. Further steaming of the catalyst for 24 and 72 hours
(Catalysts C and D) resulted in a lower aromatics selectivity of
about 39% and about 32% aromatics, respectively. This decrease in
aromatics selectivity, however, was accompanied by an increase in
olefins and paraffins selectivity. As a result, the combined
olefins+aromatics yield was found to be greater for steamed
catalysts, but substantially independent of the time for which the
catalyst was steamed. It is also noted that Catalyst B (1 hour of
steaming) produced substantially reduced amounts of methane, CO,
CO.sub.2, and coke, while Catalyst C (24 hours steamed) and
Catalyst D (72 hours steamed) produced negligible amounts of
methane, CO, CO.sub.2 and coke. These results are consistent with
the hypothesis that steaming reduced the acidity of the zeolite
material.
EXAMPLE 2
Impact of Reaction Temperature with Steamed Catalysts
[0068] As shown above, steaming of a conversion catalyst can reduce
or minimize the yield of side products, such as carbon oxides and
coke, during a conversion reaction. The results shown in FIG. 2
corresponded to conversion reactions performed at 450.degree. C. As
the reaction temperature is increased, the benefits of using a
steamed catalyst can increase.
[0069] FIG. 3 shows results from converting methanol to aromatics
and olefins at reaction temperatures of 450.degree. C., 500.degree.
C., and 550.degree. C. using a catalyst corresponding to Catalyst A
(fresh 1% Zn-ZSM-5) as described above. In FIG. 3, the results are
displayed as a grouping of bar graphs for each product type, with
the bars shown in the order 450.degree. C.-500.degree.
C.-550.degree. C., as indicated for the first data set (paraffins).
The pressure during the conversion reactions was 15 psig and the
WHSV was 2 hr.sup.-1. Again, the conversion reaction was performed
to achieve 100% conversion of the methanol feed. As the temperature
is increased above 450.degree. C., Catalyst A (fresh 1% Zn-ZSM-5)
showed a significant reduction in the yields of aromatics (by
.about.10% at 500.degree. C., .about.30% at 550.degree. C.),
olefins (by .about.5% at 550.degree. C.) and paraffins (by
.about.20% at both 500.degree. C. and 550.degree. C.). The increase
also resulted in a corresponding increase in coke formation on the
catalyst, methane, CO and CO.sub.2 formation. The results in FIG. 3
show that the production of the undesired side products can be a
substantial difficulty at temperatures above 450.degree. C. when
using a fresh catalyst.
[0070] FIG. 4 shows results from converting methanol to aromatics
and olefins at 450.degree. C. and 500.degree. C. using Catalyst C
(1% Zn-ZSM-5 steamed for 24 hours) as described above. In FIG. 4,
the results are displayed as a grouping of bar graphs for each
product type, with the bars shown in the order 450.degree.
C.-500.degree. C., as indicated for the first data set (paraffins).
The pressure during the conversion reactions was 15 psig and the
WHSV was 2 hr.sup.-1. As shown in
[0071] FIG. 4, performing the conversion reaction with Catalyst C
at 500.degree. C. did not result in the substantial decrease in
aromatics selectivity and increases in side product yield that were
observed for Catalyst A in FIG. 3. Instead, using a steamed
catalyst for the conversion reaction resulted in only minimal
production of CO, CO.sub.2, CH.sub.4, and coke on catalyst at the
higher reaction temperature. For example, the combined amount of CO
and CO.sub.2 produced was less than about 5 wt %, or less than
about 3 wt %. In addition to reducing or minimizing the yield of
side products, performing the conversion reaction with a steamed
catalyst at 500.degree. C. also increased the selectivity for
aromatics formation (by about 10%) as well as the yield or
selectivity for combined olefins plus aromatics (by about 7%).
Without being bound by any particular theory, it appears that
steaming the catalyst to reduce formation of side products allowed
the conversion reaction to be performed under reaction conditions
that were more favorable for production of aromatics while still
maintaining high overall yields.
[0072] FIG. 5 shows results from performing the conversion reaction
in the presence of Catalyst C at 550.degree. C. The pressure during
the conversion reaction was 15 psig and the WHSV was 2 hr.sup.-1
for the 1.sup.st Cycle. FIG. 5 shows the change in selectivity for
forming various products over the course of a processing run. In
FIG. 5, the diamond symbols correspond to the amount of methanol
conversion (left axis); the triangles correspond to olefin
selectivity (left axis); the asterisk symbols correspond to
aromatics selectivity (left axis); the open squares correspond to
paraffin selectivity (left axis); and the filled circles correspond
to the amount of end of cycle coke formed (right axis). As shown in
FIG. 5, performing the reaction at 550.degree. C. with a steamed
catalyst resulted in a yield of about 62% aromatics during the
early portions of the processing run. This is substantially higher
than the yield at either 450.degree. C. (about 39%) or 500.degree.
C. (about 48%). The combined olefins plus aromatics selectivity was
similarly high during the initial 4 hours (about 80%). However,
this increased aromatics selectivity began to decay rapidly after 4
hours, with a corresponding increase in formation of methane, CO,
CO.sub.2 and coke. Despite the rapid deactivation, the results in
FIG. 5 show that processing at 550.degree. C. could be effective
for a fluidized bed reactor application. In a fluidized bed reactor
or riser reactor, the nature of the reaction system can allow for
withdraw and/or regeneration of the catalyst during a processing
run. As a result, the catalyst in the fluidized bed or riser could
be maintained in a condition of only being exposed to a few hours
or less of conversion processing during the course of a longer
processing run. This could allow the high initial selectivity for
aromatics formation to be used in a commercial scale process.
EXAMPLE 3
Modification with Phosphorus
[0073] In addition to the benefits provided by steaming a
metal-modified conversion catalyst, phosphorus can also be added to
the catalyst. FIG. 6 shows the average product distributions for
performing a conversion reaction using a catalyst corresponding to
Catalyst C (24 hours steamed 1% Zn-ZSM-5) and a catalyst that also
included phosphorous (1% P and 1% Zn-ZSM-5), which can be referred
to as Catalyst E. FIG. 6 shows results from performing conversion
reactions using Catalyst C and Catalyst E at temperatures of
450.degree. C. and 500.degree. C., a pressure of 15 psig, and a
WHSV of 2 hr.sup.-1 for the 1.sup.st Cycle. In FIG. 6, the results
are displayed as a grouping of bar graphs for each product type,
with the bars shown in the order C 450.degree. C.-E 450.degree.
C.-C 500.degree. C.-E 500.degree. C., as indicated for the first
data set (paraffins).
[0074] In FIG. 6, for Catalyst E, the carbon selectivity towards
aromatics increased by 8% and .about.6% at 450.degree. C. and
500.degree. C., respectively. However, the olefins selectivity
decreased by .about.20% and .about.15% at 450.degree. C. and
500.degree. C. respectively. The addition of 1% phosphorous also
lead to decreased coke and hydrogen formation. Further, the
stability of the catalyst including 1% P and 1% Zn-ZSM-5 was better
compared to the 1% Zn-ZSM-5 catalyst when compared at the same
conditions and the same level of steaming.
ADDITIONAL EMBODIMENTS
Embodiment 1
[0075] A method of converting a feed to form olefins and aromatics,
comprising: steaming a catalyst in the presence of at least 1 vol %
water at a temperature of about 400.degree. C. to about 850.degree.
C. for at least about 0.25 hours, the catalyst comprising a
molecular sieve having at least one 10-member ring channel and
having no ring channels larger than a 10-member ring channel, the
catalyst further comprising about 0.1 wt % to about 10.0 wt % of a
metal from Groups 8-14; and exposing a feed comprising at least
about 50 wt % of methanol, dimethyl ether, or a combination thereof
to the steamed catalyst under effective conversion conditions to
form a conversion effluent comprising ethylene, propylene, and
para-xylene, the effective conversion conditions including a
temperature of about 350.degree. C. to about 600.degree. C.
Embodiment 2
[0076] A method of converting a feed to form olefins and aromatics,
comprising: steaming a catalyst in the presence of at least 1 vol %
water at a temperature of about 400.degree. C. to about 850.degree.
C. for at least about 0.25 hours, the catalyst comprising a
molecular sieve having at least one 10-member ring channel and
having no ring channels larger than a 10-member ring channel, the
catalyst further comprising about 0.1 wt % to about 10.0 wt % of
Zn, Ga, Ag, or a combination thereof; and exposing a feed
comprising at least about 50 wt % of methanol, dimethyl ether, or a
combination thereof to the steamed catalyst under effective
conversion conditions to form a conversion effluent comprising
ethylene, propylene, and para-xylene, the effective conversion
conditions including a temperature of about 425.degree. C. to about
600.degree. C.
Embodiment 3
[0077] The method of Embodiment 1 or 2, wherein the effective
conversion conditions include a temperature of at least about
475.degree. C., a combined yield in the conversion effluent of CO
and CO.sub.2 being about 5 wt % or less, or about 3 wt % or
less.
Embodiment 4
[0078] The method of any of the above embodiments, wherein the
effective conversion conditions include a temperature of at least
about 500.degree. C.
Embodiment 5
[0079] The method of any of the above embodiments, wherein exposing
a feed to the steamed catalyst comprises exposing the feed to the
steamed catalyst in a fluidized bed reactor or a riser reactor.
Embodiment 6
[0080] The method of any of the above embodiments, further
comprising separating at least a portion of the converted effluent
to form a light ends product comprising ethylene, propylene, or a
combination thereof and a liquid effluent.
Embodiment 7
[0081] The method of Embodiment 6, further comprising separating at
least a portion of the liquid effluent to form a C.sub.8 product
stream and one or more of a C.sub.7- stream and a C.sub.9+ stream,
wherein exposing a feed to the steamed catalyst optionally
comprises exposing the feed to the steamed catalyst in the presence
of a hydrogen-lean stream, the method optionally further comprising
recycling at least a portion of the C.sub.7- stream, the C.sub.9+
stream, or a combination thereof to form the hydrogen-lean
stream.
Embodiment 8
[0082] The method of Embodiment 7, further comprising separating
the C.sub.8 product stream to form at least a para-xylene product
stream, the para-xylene product stream having a higher
concentration of para-xylene than the C.sub.8 product stream.
Embodiment 9
[0083] The method of any of the above embodiments, wherein the
steamed catalyst further comprises about 0.1 wt % to about 10 wt %
of phosphorus, lanthanum, an element from Groups 1 or 2, an element
from Groups 13-16, or a combination thereof, or 0.1 wt % to about
10 wt % of each of two or more of the above.
Embodiment 10
[0084] The method of Embodiment 9, wherein the steamed catalyst
further comprises at least about 1 wt %, or at least about 2 wt %,
or at least about 3 wt %, or at least about 4 wt %, or at least
about 5 wt %, or at least about 6 wt %, or at least about 7 wt %,
or at least about 8 wt %, or at least about 9 wt % of phosphorus,
lanthanum, an element from Groups 1 or 2, an element from Groups
13-16, or a combination thereof, or of each of two or more of the
above, and/or about 10 wt % or less, or about 9 wt % or less, or
about 8 wt % or less, or about 7 wt % or less, or about 6 wt % or
less, or about 5 wt % or less, or about 4 wt % or less, or about 3
wt % or less, or about 2 wt % or less.
Embodiment 11
[0085] The method of any of the above embodiments, wherein the
steamed catalyst comprises at least about 1 wt %, or at least about
2 wt %, or at least about 3 wt %, or at least about 4 wt %, or at
least about 5 wt %, or at least about 6 wt %, or at least about 7
wt %, or at least about 8 wt %, or at least about 9 wt % of the
metal from Groups 8-14 and/or about 10 wt % or less, or about 9 wt
% or less, or about 8 wt % or less, or about 7 wt % or less, or
about 6 wt % or less, or about 5 wt % or less, or about 4 wt % or
less, or about 3 wt % or less, or about 2 wt % or less.
Embodiment 12
[0086] The method of any of the above embodiments, wherein the
molecular sieve comprises ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23,
ZSM-34, ZSM-35, ZSM-48, ZSM-57, or ZSM-58, or wherein the molecular
sieve comprises ZSM-5, ZSM-11, ZSM-23, ZSM-35 or ZSM-48, or wherein
the molecular sieve comprises ZSM-5.
Embodiment 13
[0087] The method of any of the above embodiments, wherein the
effective conversion conditions comprise a pressure of about 100
kPaa to about 2500 kPaa, or about 100 kPaa to about 1200 kPaa; and
a WHSV of about 0.1 hr.sup.-1 to about 20 hr.sup.-1, or about 1.0
hr.sup.-1 to about 10 hr.sup.-1.
Embodiment 14
[0088] The method of any of the above embodiments, wherein the feed
substantially comprises methanol, dimethyl ether, or a combination
thereof.
Embodiment 15
[0089] The method of any of the above embodiments, wherein exposing
a feed to the steamed catalyst comprises exposing the feed to the
steamed catalyst in the presence of steam, a hydrogen-lean stream,
or a combination thereof.
Embodiment 16
[0090] The method of any of the above embodiments, wherein the
catalyst is steamed in the presence of 1 vol % to 100 vol % water
for 0.25 hours to 48 hours, or for 0.25 hours to 8 hours, or for
0.5 hours to 8 hours, or for 0.5 hours to 4 hours, the steaming
optionally being at a temperature of at least about 500.degree. C.,
or about 750.degree. C. or less, or about 650.degree. C. or
less.
[0091] Although the present invention has been described in terms
of specific embodiments, it is not so limited. Suitable
alterations/modifications for operation under specific conditions
should be apparent to those skilled in the art. It is therefore
intended that the following claims be interpreted as covering all
such alterations/modifications as fall within the true spirit/scope
of the invention.
* * * * *