U.S. patent application number 14/560113 was filed with the patent office on 2015-06-25 for catalyst for conversion of methanol to hydrocarbons.
This patent application is currently assigned to ExxonMobil Research and Engineering Company. The applicant listed for this patent is Christine N. Elia, Brett Loveless, Stephen J. McCarthy. Invention is credited to Christine N. Elia, Brett Loveless, Stephen J. McCarthy.
Application Number | 20150175897 14/560113 |
Document ID | / |
Family ID | 52134438 |
Filed Date | 2015-06-25 |
United States Patent
Application |
20150175897 |
Kind Code |
A1 |
Loveless; Brett ; et
al. |
June 25, 2015 |
CATALYST FOR CONVERSION OF METHANOL TO HYDROCARBONS
Abstract
Methods are provided for performing a conversion reaction using
a catalyst steamed under mild steaming conditions. Steaming a
conversion catalyst under mild steaming conditions can provide an
increased conversion activity and/or an increased run length for
the catalyst during conversion of an oxygenate feed to aromatic
hydrocarbons, such as benzene or xylene. Suitable conversion
catalysts can include alumina bound catalysts including a medium
pore molecular sieve.
Inventors: |
Loveless; Brett; (Maplewood,
NJ) ; Elia; Christine N.; (Bridgewater, NJ) ;
McCarthy; Stephen J.; (Center Valley, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Loveless; Brett
Elia; Christine N.
McCarthy; Stephen J. |
Maplewood
Bridgewater
Center Valley |
NJ
NJ
PA |
US
US
US |
|
|
Assignee: |
ExxonMobil Research and Engineering
Company
Annandale
NJ
|
Family ID: |
52134438 |
Appl. No.: |
14/560113 |
Filed: |
December 4, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61918984 |
Dec 20, 2013 |
|
|
|
61918994 |
Dec 20, 2013 |
|
|
|
61919013 |
Dec 20, 2013 |
|
|
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Current U.S.
Class: |
585/408 |
Current CPC
Class: |
B01J 37/0009 20130101;
C10L 2200/0423 20130101; C10L 2200/0469 20130101; C10G 3/45
20130101; B01J 35/1023 20130101; B01J 38/12 20130101; B01J 35/1038
20130101; B01J 35/1042 20130101; C10L 1/06 20130101; C07C 2529/70
20130101; B01J 37/0201 20130101; B01J 35/1019 20130101; B01J 35/108
20130101; C07C 2529/06 20130101; B01J 35/1057 20130101; B01J 27/14
20130101; B01J 29/061 20130101; C07C 2529/40 20130101; B01J 29/90
20130101; B01J 2229/186 20130101; Y02P 20/584 20151101; B01J 38/02
20130101; C07C 1/22 20130101; C10G 3/49 20130101; C10L 2270/023
20130101; B01J 29/40 20130101; B01J 29/7057 20130101; B01J 2229/20
20130101; C10G 3/55 20130101; B01J 2229/42 20130101; B01J 29/405
20130101; B01J 37/28 20130101; C07C 1/20 20130101; Y02P 30/40
20151101; B01J 23/06 20130101; B01J 35/10 20130101; B01J 21/04
20130101; B01J 29/7049 20130101; B01J 35/1014 20130101; B01J 35/109
20130101; Y02P 30/20 20151101; C07C 2523/06 20130101; C07C 1/20
20130101; C07C 11/02 20130101; C07C 1/20 20130101; C07C 15/02
20130101 |
International
Class: |
C10G 3/00 20060101
C10G003/00; C10L 1/06 20060101 C10L001/06; C07C 1/20 20060101
C07C001/20 |
Claims
1. A method of converting a feed to form olefins and aromatics,
comprising: steaming a catalyst in the presence of at least 0.01
atm (1 kPa) of water at a temperature of about 450.degree. F.
(about 221.degree. C.) to about 700.degree. F. (about 371.degree.
C.) for at least about 0.25 hours to form a steamed catalyst, 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; and subsequently exposing a feed comprising at least
about 30 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 at
least one aromatic, the effective conversion conditions including a
temperature of about 200.degree. C. to about 700.degree. C., the
steamed catalyst having a cycle length under the effective
conversion conditions that is at least about 15% greater than a
cycle length under the effective conversion conditions for the
catalyst prior to steaming, and/or the steamed catalyst having an
alpha value that is at least about 10 greater than an alpha value
for the catalyst prior to steaming.
2. The method of claim 1, wherein the catalyst further comprises
about 5 wt % to about 40 wt %, based on a total weight of the
catalyst, of a binder comprising alumina and/or silica.
3. The method of claim 1, wherein the catalyst is steamed for about
1 hour to about 16 hours.
4. The method of claim 1, wherein the catalyst has an alpha value
of at least about 200 prior to the steaming of the catalyst, the
steamed catalyst has an alpha value of at least about 300, or a
combination thereof.
5. The method of claim 4, wherein the steamed catalyst has an alpha
value that is greater than the alpha value of the catalyst prior to
the steaming of the catalyst by at least about 25.
6. The method of claim 1, wherein the steamed catalyst has an alpha
value that is greater than the alpha value of the catalyst prior to
the steaming of the catalyst by at least about 50.
7. 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, a moving bed reactor, or a riser reactor, or
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.
8. The method of claim 1, further comprising separating at least a
portion of the converted effluent to form a naphtha boiling range
product.
9. 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, butene, or a combination thereof
and a liquid effluent.
10. The method of claim 9, 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.
11. The method of claim 1, wherein the molecular sieve comprises
ZSM-5, ZSM-11, or a combination thereof.
12. The method of claim 11, wherein the molecular sieve has a
silicon to aluminum ratio of about 20 to about 100.
13. The method of claim 1, wherein the steamed catalyst further
comprises about 0.1 wt % to about 10 wt % of phosphorus, about 0.1
wt % to about 10 wt % of a transition metal, about 0.1 wt % to
about 10 wt % of a Group 13 metal or Group 14 metal, or a
combination thereof.
14. 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.
15. The method of claim 1, wherein the effective conversion
conditions comprise a temperature of about 450.degree. C. to about
550.degree. C.
16. The method of claim 1, wherein the feed substantially comprises
methanol, dimethyl ether, or a combination thereof.
17. The method of claim 1, wherein the catalyst is steamed at a
temperature of about 650.degree. F. or less.
18. The method of claim 17, wherein the catalyst is steamed in the
presence of at least about 1.0 atm (about 100 kPa) of water for
about 4.5 hours or less.
19. The method of claim 1, wherein the catalyst is steamed at a
temperature of about 600.degree. F. or less.
20. The method of claim 19, wherein the catalyst is steamed in the
presence of at least about 0.9 atm (about 90 kPa) of water for
about 15 hours or less.
21. A method of converting an oxygenate feed to form hydrocarbons,
comprising: steaming a catalyst in the presence of at least 0.9 atm
(90 kPa) of water at a temperature of about 450.degree. F. (about
221.degree. C.) to about 650.degree. F. (about 343.degree. C.) for
about 0.25 hours to about 16 hours to form a steamed catalyst, the
catalyst comprising a molecular sieve having at least one 8-member
ring channel, 10-member ring channel, or 12-member ring channel and
having no ring channels larger than a 12-member ring channel; and
subsequently 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 one or more hydrocarbons, the effective
conversion conditions including a temperature of about 200.degree.
C. to about 700.degree. C., the steamed catalyst having a cycle
length under the effective conversion conditions that is at least
about 15% greater than a cycle length under the effective
conversion conditions for the catalyst prior to steaming, and/or
the steamed catalyst having an alpha value that is at least about
10 greater than an alpha value for the catalyst prior to steaming.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Nos. 61/918,984, 61/918,994, and 61/919,013, each filed
on Dec. 20, 2013, the entire contents of each of which are hereby
incorporated by reference herein.
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 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, sortie 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. U.S. Pat. Nos. 3,960,978 and 4,021,502 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. U.S. Pat. Nos. 4,150,062,
4,211,640 and 4,227,992 have also contributed improved processing
techniques to the MOGD system. 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, and 4,433,185, each of which is 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. Nos.
3,894,107, 3,928,483, 4,025,571, 4,423,274, and 4,433,189, each of
which are 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 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] U.S. Pat. No. 4,579,993 describes a method for treating
silica-bound catalysts for use in conversion of methanol to
hydrocarbon (or hydrocarbonaceous) products. The catalysts
correspond to molecular sieves bound in a silica matrix. The
treatment method includes a combination of steaming the catalyst
and performing an acid-extraction on the catalyst prior to use for
methanol conversion. The examples describe both alumina-bound and
silica-bound catalysts that, after steaming, have alpha values of
about 25 or less.
[0012] U.S. Pat. No. 6,372,949 describes methods for using
catalysts containing 10 member ring zeolites for conversion of
methanol to gasoline. The zeolite catalysts can be steamed prior to
use in the conversion reaction. The examples describe steaming of
the zeolite catalysts to produce steamed catalysts with alpha
values of about 100 or less.
[0013] U.S. Pat. No. 4,326,994 describes methods for enhancing
zeolite catalytic activity based on steaming a zeolite catalyst
under specific combinations of water partial pressure and steaming
temperature. The combinations of water partial pressure and
steaming temperature are defined by the formula
0.01*F.sub.T<(P*t)<10*F.sub.T, where P is the partial
pressure of water (in atmospheres) during steaming, t is the time
(in hours) of steaming, and F.sub.T is defined as
2.6.times.10.sup.-9e.sup.16000/T (T in Kelvin). The examples
provided include steaming at temperatures of 750.degree. F. or
higher.
SUMMARY OF THE INVENTION
[0014] In an aspect, a method of converting a feed to form olefins
and aromatics is provided, including steaming a catalyst in the
presence of at least 0.01 atm (1 kPa) of water at a temperature of
about 450.degree. F. (221.degree. C.) to about 700.degree. F.
(371.degree. C.) for at least about 0.25 hours to form a steamed
catalyst, 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; and exposing a feed comprising at least
about 30 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 at
least one aromatic (preferably para-xylene), the effective
conversion conditions including a temperature of about 200.degree.
C. to about 700.degree. C., or about 350.degree. C. to about
600.degree. C., or about 450.degree. C. to about 550.degree. C.
[0015] In some aspects, the catalyst can be an alumina-bound
catalyst that includes about 10 wt % to about 80 wt % of an alumina
binder. Optionally, the catalyst can have an alpha value of at
least about 200 prior to steaming and an alpha value that is at
least about 25 higher after steaming, such as an alpha value of at
least about 300. Optionally, the steaming conditions can include
one or more of, or two or more of, a) a partial pressure of steam
of at least about 0.5 atm (51 kPa), or at least about 0.9 atm (91
kPa); b) a steaming temperature of about 650.degree. F.
(343.degree. C.) or less, or about 625.degree. F. (329.degree. C.)
or less, or about 600.degree. F. (316.degree. C.) or less; and c) a
length of steaming of about 16 hours or less, or about 12 hours or
less, or about 8.5 hours or less, or about 4.5 hours or less.
[0016] In still another aspect, a method of converting an oxygenate
feed to form hydrocarbons is provided, the method including:
steaming a catalyst in the presence of at least 0.9 atm (91 kPa) of
water at a temperature of about 450.degree. F. (221.degree. C.) to
about 650.degree. F. (343.degree. C.) for at about 0.25 hours to
about 16 hours to form a steamed catalyst, the catalyst comprising
a molecular sieve having at least one 8-member ring channel,
10-member ring channel, or 12-member ring channel and having no
ring channels larger than a 12-member ring channel; 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 one
or more hydrocarbons, the effective conversion conditions including
a temperature of about 200.degree. C. to about 700.degree. C.
BRIEF DESCRIPTION OF THE FIGURES
[0017] FIG. 1 shows cracking activity for catalysts steamed under
various steaming conditions.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Overview
[0018] In various aspects, catalysts described herein can be used
to convert an oxygenate feed (such as methanol and/or dimethyl
ether) into aromatics and/or olefins with improved catalyst
lifetime and/or improved catalyst activity. One of the difficulties
in converting oxygenate feeds to products such as gasoline or other
aromatics can be that the conversion catalyst can have a strong
tendency to deactivate over time. For example, coke typically forms
as a side product during the conversion of an oxygenate feed to
gasoline or other aromatics. The coke can accumulate on the
conversion catalyst and can result in blocking of acidic sites on
the conversion catalyst. This can cause a corresponding loss of
catalyst activity. Such a loss in catalyst activity can become
apparent in a matter of a few days. This can pose challenges to
performing a methanol conversion process in a fixed bed reaction
system. Additionally, although methanol conversion catalysts can be
regenerated, the activity of the catalyst can be degraded with each
regeneration cycle, so that an increased frequency of regeneration
can lead to a more rapid need to entirely replace a catalyst.
[0019] Catalysts for conversion of methanol (and other oxygenates)
to gasoline and/or aromatics can be based on zeolites or other
molecular sieves. At least a portion of the activity of a
zeolite-based catalyst for conversion of methanol can be based on
the number of acidic sites on the catalyst. Increasing the number
of acidic sites, such as by reducing the ratio of silicon to
aluminum in the zeolite framework, can increase the activity of a
zeolite catalyst for methanol conversion. However, reducing the
silicon to aluminum ratio also has the potential to increase the
amount of coke formed during methanol conversion, at least for
sufficiently low silicon to aluminum ratios.
[0020] One option for reducing or minimizing coke formation can be
to reduce the number of acidic sites on the catalyst. For example,
a catalyst can be steamed under sufficiently severe conditions for
a period of time to decrease the number of acidic sites. However,
reducing the number of acidic sites can lead to a corresponding
reduction in catalyst activity for methanol conversion. The reduced
activity of a catalyst having a reduced number of acidic sites can
require operating a methanol conversion process at higher
temperatures and/or more severe operating conditions in order to
achieve full conversion of the methanol feed. Such higher severity
conditions can tend to reduce the yield of gasoline and/or
aromatics from a conversion process.
[0021] In various aspects, instead of steaming a catalyst under
conditions with sufficient severity to reduce the number of acidic
sites on a catalyst, the catalyst can be steamed under relatively
mild conditions. Without being bound by any particular theory, it
is believed that steaming under relatively mild conditions can make
more acidic sites available on a catalyst. However, this does not
necessarily correspond to an increase in the number of acidic
sites, as the mild steaming conditions may additionally or
alternatively make existing acidic sites more readily available for
reaction. Conventionally, increasing the number of acidic sites (or
number of "apparent" acidic sites) by any method would be believed
to cause increased coking with a corresponding decrease in run
length for a catalyst. It has been unexpectedly determined,
however, that using mild steaming conditions can provide improved
run length and/or improved catalyst activity. This can allow for
increased run lengths (and therefore reduced regeneration
frequency) for a conversion process. In some aspects, a catalyst
steamed under effective mild steaming conditions can be used for a
methanol conversion process that has an improved run (cycle) length
while allowing the conversion process to be performed at lower
conversion temperatures.
Catalyst Steaming Conditions
[0022] Prior to using a catalyst for conversion of oxygenates (such
as methanol) to gasoline, aromatics and/or olefins, the catalyst
can be steamed under effective steaming conditions. In various
aspects, the catalyst for conversion can be steamed under mild
steaming conditions, such as steaming conditions that can lead to
an increase in the number of apparent available acidic sites in the
catalyst. This can lead to an increase in catalyst activity and/or
lifetime for conversion of methanol and/or dimethyl ether to
gasoline or other aromatics and olefins. General examples of
effective steaming conditions including exposing a catalyst to an
atmosphere comprising steam at a temperature of about 450.degree.
F. (about 232.degree. C.) to about 700.degree. F. (about
371.degree. C.), for example about 500.degree. F. (260.degree. C.)
to about 700.degree. F. (about 371.degree. C.), about 550.degree.
F. (about 288.degree. C.) to about 700.degree. F. (about
371.degree. C.), about 600.degree. F. (about 316.degree. C.) to
about 700.degree. F. (about 371.degree. C.), about 450.degree. F.
(about 232.degree. C.) to about 650.degree. F. (about 343.degree.
C.), about 500.degree. F. (about 260.degree. C.) to about
650.degree. F. (about 343.degree. C.), or about 550.degree. F.
(about 288.degree. C.) to about 650.degree. F. (about 343.degree.
C.). The atmosphere can include as little as 1 vol % water and up
to 100 vol % water. In various aspects, the partial pressure of
steam in the effective steaming conditions can be about 0.005 atm
(about 0.5 kPag) to about 5 atm (about 510 kPag), for example about
0.005 atm (about 0.5 kPag) to about 1 atm (about 100 kPag), about
0.005 atm (about 0.5 kPag) to about 2 atm (about 200 kPag), about
0.01 atm (about 1 kPag) to about 2 atm (about 200 kPag), about 0.01
atm (about 1 kPag) to about 1 atm (about 100 kPag), about 0.1 atm
(about 10 kPag) to about 2 atm (about 200 kPag), about 0.1 atm
(about 10 kPag) to about 1 atm (about 100 kPag), about 0.25 atm
(about 25 kPag) to about 2 atm (about 200 kPag), about 0.25 atm
(about 25 kPag) to about 1 atm (about 100 kPag), about 0.50 atm
(about 50 kPag to about 2 atm (about 200 kPag), about 0.50 atm
(about 50 kPag) to about 1 atm (about 100 kPag), about 0.75 atm
(about 76 kPag) to about 2 atm (about 200 kPag), about 0.75 atm
(about 76 kPag) to about 1 atm (about 100 kPag), about 0.90 atm
(about 90 kPag) to about 2 atm (about 200 kPag), or about 0.90 atm
(about 90 kPag) to about 1 atm (about 100 kPag). The catalyst can
be exposed to the steam for any convenient period of time, such as
about 10 minutes (about 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 48 hours, about
0.25 hours to about 24 hours, about 0.25 hours to about 16 hours,
about 0.25 hours to about 15 hours, about 0.25 hours to about 12
hours, about 0.25 hours to about 8 hours, about 0.25 hours to about
4 hours, about 0.25 hours to about 2 hours, about 0.5 hours to
about 24 hours, about 0.5 hours to about 16 hours, about 0.5 hours
to about 15 hours, about 0.5 hours to about 12 hours, about 0.5
hours to about 8 hours, about 0.5 hours to about 4 hours, about 0.5
hours to about 2 hours, about 0.75 hours to about 24 hours, about
0.75 hours to about 16 hours, about 0.75 hours to about 15 hours,
about 0.75 hours to about 12 hours, about 0.75 hours to about 8
hours, about 0.75 hours to about 4 hours, about 0.75 hours to about
2 hours, about 1 hour to about 24 hours, about 1 hour to about 16
hours, about 1 hour to about 15 hours, about 1 hour to about 12
hours, about 1 hour to about 8 hours, about 1 hour to about 4
hours, or about 1 hour to about 2 hours.
[0023] In some aspects, the effective steaming conditions can be
characterized based on a combination of the partial pressure of
water during steaming and a length of time for steaming. In such
aspects, a suitable combination of conditions can be determined by
multiplying the pressure, expressed in units of atmospheres, by the
length of steaming, expressed in units of hours. For example, for
effective steaming conditions based on a steaming temperature of
about 700.degree. F. (about 644.degree. K) or less, the product of
the pressure (in atmospheres) multiplied by the steaming time (in
hours) can be about 12.5 or less, for example about 4.5 or less or
about 1.5 or less, and optionally can be at least about 0.25. As
another example, for effective steaming conditions based on a
steaming temperature of about 650.degree. F. (about 617.degree. K),
the product of the pressure (in atmospheres) multiplied by the
steaming time (in hours) can be about 16.0 or less, for example
about 12.5 or less, about 8.5 or less, or about 4.5 or less, and
optionally can be at least about 0.25. As still another example,
for effective steaming conditions based on a steaming temperature
of about 625.degree. F. (about 603.degree. K), the product of the
pressure (in atmospheres) multiplied by the steaming time (in
hours) can be about 16.0 or less, for example about 12.5 or less,
about 8.5 or less, or about 4.5 or less, and optionally can be at
least about 0.25. As yet another example, for effective steaming
conditions based on a steaming temperature of about 600.degree. F.
(about 589.degree. K), the product of the pressure (in atmospheres)
multiplied by the steaming time (in hours) can be about 16.0 or
less, for example about 12.5 or less, about 8.5 or less, or about
4.5 or less, and optionally can be at least about 0.25.
[0024] In aspects involving steaming at a temperature of about
450.degree. F. (about 232.degree. C.) to about 700.degree. F.
(about 371.degree. C.) as described above, the alpha value of an
acidic molecular sieve (e.g., zeolite) catalyst can be increased.
Alpha value is a measure of the acid activity of a zeolite catalyst
as compared with a standard silica-alumina catalyst. The alpha test
gives the relative rate constant (rate of normal hexane conversion
per volume of catalyst per unit time) of the test catalyst relative
to the standard catalyst which is taken as an alpha of 1 (Rate
Constant.apprxeq.0.016 sec.sup.-1) The alpha test is described in
U.S. Pat. No. 3,354,078 and in the Journal of Catalysis, Vol. 4, p.
527 (1965); Vol. 6, p. 278 (1966); and Vol, 61, p. 395 (1980), each
incorporated herein by reference as to that description. The
experimental conditions of the test used herein include a constant
temperature of .about.538.degree. C. and a variable flow rate as
described in detail in the Journal of Catalysis, Vol. 61, p. 395.
The higher alpha values have been correlated to correspond with a
more active cracking catalyst.
[0025] For example, prior to steaming at a temperature of about
450.degree. F. (about 232.degree. C.) to about 700.degree. F.
(about 371.degree. C.) under effective steaming conditions as
described above, a suitable catalyst for conversion of methanol
and/or dimethyl ether can have an alpha value of at least about 20,
for example at least about 50, at least about 100, at least about
150, at least about 200, at least about 250, or at least about 300,
such as potentially up to about 1000 or more. After steaming, the
alpha value of the catalyst can increase by at least about 10, for
example at least about 25 or at least about 50. This can result in
a steamed catalyst with an alpha value of at least about 300, for
example at least about 350, at least about 375, or at least about
400, and potentially up to an alpha value of about 2000 or less,
for example about 1500 or less or about 1000 or less.
[0026] In other aspects, the steamed catalyst can have an increased
lifetime or cycle length for use in a reaction for conversion of
methanol to hydrocarbons, such as conversion of methanol to olefins
and aromatics or conversion of methanol to gasoline. In such
aspects, a cycle length for a catalyst can be measured based on any
convenient conditions that are effective for conversion of methanol
that also initially result in conversion of 99% of the methanol in
a feed. Under conditions that initially convert at least 99% of the
methanol in a feed, a cycle length can be defined based on the
amount of time a catalyst can be used for the methanol conversion
until the conversion drops below 99% of the methanol in the feed.
For example, the steamed catalyst can have a cycle length that is
at least about 15% greater than the cycle length of the catalyst
prior to steaming, for example at least about 30% greater, for
example at least about 50% greater, at least about 75% greater, at
least about 90% greater, or at least about 100% greater, such as up
to about 300% greater. Additionally or alternately, the steamed
catalyst can have an n-hexane cracking activity that is at least
10% greater than the cracking activity of the catalyst prior to
steaming, for example at least about 20%, at least about 30%, at
least about 40%, at least about 50%, at least about 60%, at least
about 70%, at least about 80%, or at least about 90%.
[0027] In some alternative aspects, a catalyst can be steamed under
conditions suitable for preparing a catalyst for conversion of
methanol and/or dimethyl ether to aromatics (such as benzene,
toluene, and xylene) and olefins (such as ethylene and/or
propylene). This is in contrast to conversion of methanol to
gasoline. In this type of alternative aspect, instead of increasing
the number of acidic sites for reaction, the steaming can reduce
the overall number of acidic sites. As a result, the steaming in
this alternative aspect can reduce the alpha value of a steamed
catalyst relative to the unsteamed catalyst. This can produce a
catalyst with a reduced or minimized number of acidic reaction
sites that is suitable for conversion of methanol to olefins while
reducing or minimizing the amount of coke produced. In such
alternative aspects for production of olefins, examples of
effective steaming conditions including exposing a catalyst to an
atmosphere comprising steam at a temperature of at least about
375.degree. C., such as about 400.degree. C. to about 850.degree.
C., about 400.degree. C. to about 750.degree. C., about 400.degree.
C. to about 650.degree. C., about 500.degree. C. to about
850.degree. C., 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 1 hour to about 48 hours. In some aspects, the
time for exposure of the catalyst to steam can be at least about 1
hour, such as about 1.25 hours to about 8 hours, about 1.25 hours
to about 4 hours, about 1.25 hours to about 2 hours, about 1.5
hours to about 8 hours, or about 1.5 hours to about 4 hours. For
catalysts steamed according to the alternative steaming procedure,
after steaming, the alpha value of the catalyst can be about 100 or
less, for example about 75 or less, about 50 or less, or about 25
or less. Although this reduction in the number of acidic sites can
reduce catalyst activity, the reduced number of acidic sites can
also reduce the amount of coke formation. Such a reduction in the
amount of coke formation is an alternative option for increasing
catalyst lifetime.
Conversion Catalyst
[0028] In various aspects, a zeolite catalyst composition is
provided that is steamed to enhance the activity and/or lifetime of
the catalyst composition for conversion of methanol (or other
oxygenate feeds) to olefins. Optionally, the zeolite catalyst
composition can be a transition metal-enhanced zeolite catalyst
composition. In some alternative aspects, instead of an
aluminosilicate type molecular sieve, the catalyst composition can
use an alternative type of molecular sieve, such as a
silicoaluminophosphate molecular sieve or an aluminophosphate
molecular sieve.
[0029] The zeolite employed in the present catalyst composition
generally comprises at least one medium pore aluminosilicate
zeolite having a Constraint index of 1-12 (as defined in U.S. Pat.
No. 4,016,218). Suitable zeolites include zeolites having an MFI or
MEL framework, such as ZSM-5 or ZSM-11. ZSM-5 is described in
detail in U.S. Pat. Nos. 3,702,886 and RE29,948. ZSM-11 is
described in detail in U.S. Pat. No. 3,709,979. Preferably, the
zeolite is ZSM-5. Other useful molecular sieves can include 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).
Non-limiting examples of SAPO and AIPO molecular sieves can 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, AIPO-5,
AIPO-11, AIPO-18, AIPO-31, AIPO-34, AIPO-36, AIPO-37, and
AIPO-46.
[0030] 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 framework types.
[0031] In some alternative aspects, the molecular sieve can be a
molecular sieve that includes an 8-member ring channel (small pore
molecular sieves), a 10-member ring channel (as described above),
or a 12-member ring channel (large pore molecular sieves), but does
not have any ring channels based on a ring larger than a 12-member
ring. In such aspects, suitable large pore molecular sieves can
include those having AFI, AFS, ATO, ATS, *BEA, BEC, BOG, BPH, CAN,
CON, EMT, EON, EZT, FAU, GME, GON, IFR, ISV, -*ITN, IWR, IWW, LTL,
MAZ, MEI, MOR, MOZ, MSE, MTW, OFF, OKO, OSI, SAF, SAO, SEW, SFE,
SFO, SSF, SSY, and USI framework types. In such aspects, suitable
small pore molecular sieves can include those having the AEI, AFT,
AFX, ATT, DDR, EAB, EPI, ERI, KFI, LEV, LTA, MER, MON, MTF, PAU,
PHI, RHO, and SFW framework types.
[0032] Generally, a zeolite having the desired activity can have a
silicon to aluminum molar ratio of about 10 to about 300, for
example about 15 to about 100, about 20 to about 80, or about 20 to
about 40. In some embodiments, the silicon to aluminum ratio can be
at least about 10, for example at least about 20, at least about
30, at least about 40, at least about 50, or at least about 60.
Additionally, or alternately, the silicon to aluminum ratio can be
about 300 or less, for example about 200 or less, about 100 or
less, about 80 or less, about 60 or less, or about 50 or less.
[0033] In some preferred aspects, the silicon to aluminum ratio can
be at least about 20, for example at least about 30 or at least
about 40. In such embodiments, the silicon to aluminum ratio can
optionally be about 100 or less, for example about 80 or less,
about 60 or less, about 50 or less, or about 40 or less. Typically,
reducing the silicon to aluminum ratio in a zeolite can result in a
zeolite with a higher acidity, and therefore higher activity for
cracking of hydrocarbon or hydrocarbonaceous feeds, such as
petroleum feeds. However, with respect to conversion of oxygenates
to aromatics, such increased cracking activity due to a decrease in
the silicon to aluminum ratio may not be beneficial, and instead
may result in increased formation of residual carbon or coke during
the conversion reaction. Such residual carbon can deposit on the
zeolite catalyst, leading to deactivation of the catalyst over
time. Having a silicon to aluminum ratio of at least about 40, for
example at least about 50 or at least about 60, can reduce/minimize
the amount of additional residual carbon formed due to the acidic
or cracking activity of the catalyst.
[0034] It is noted that the molar ratio described herein is a ratio
of silicon to aluminum. If a corresponding ratio of silica to
alumina were described, the corresponding ratio of silica
(SiO.sub.2) to alumina (Al.sub.2O.sub.3) would be twice as large,
due to the presence of two aluminum atoms in each alumina
stoichiometric unit compare to only one silicon atom in the silica
stoichiometric unit. Thus, a silicon to aluminum ratio of 10
corresponds to a silica to alumina ratio of 20.
[0035] When used in the present catalyst composition, the zeolite
can be present at least partly in the hydrogen (active) form.
Depending on the conditions used to synthesize the zeolite, this
may correspond to converting the zeolite from, for example, the
sodium form. This can readily be achieved, for example, by ion
exchange to convert the zeolite to the ammonium form followed by
calcination in air or an inert atmosphere at a temperature of about
400.degree. C. to about 700.degree. C. to convert the ammonium form
to the active hydrogen form. Alternatively, methods for directly
converting a sodium form zeolite to a hydrogen form zeolite can
also be used.
[0036] Additionally, or alternately, the catalyst composition can
include and/or be enhanced by a transition metal. The transition
metal can be incorporated into the zeolite by any convenient
method, such as by impregnation or by ion exchange. After
impregnation or ion exchange, the transition metal-enhanced
catalyst can be treated in air or an inert atmosphere at a
temperature of about 400.degree. C. to about 700.degree. C. The
amount of transition metal can be related to the molar amount of
aluminum present in the zeolite. Preferably, the molar amount of
the transition metal can correspond to about 0.1 to about 1.3 times
the molar amount of aluminum in the zeolite. In some embodiments,
the molar amount of transition metal can be at least about 0.1
times the molar amount of aluminum in the zeolite, for example at
least about 0.2 times, at least about 0.3 times, or at least about
0.4 times. Additionally or alternately, the molar amount of
transition metal can be about 1.3 times or less relative to the
molar amount of aluminum in the zeolite, for example about 1.2
times or less, about 1.0 times or less, or about 0.8 times or less.
Still further additionally or alternately, the amount of transition
metal can be expressed as a weight percentage of the bound zeolite
catalyst, such as having at least about 0.1 wt % of transition
metal, at least about 0.25 wt %, at least about 0.5 wt %, at least
about 0.75 wt %, or at least about 1.0 wt %. Additionally or
alternately, the amount of transition metal can be about 20 wt % or
less, for example about 10 wt % or less, about 5 wt % or less,
about 2.0 wt % or less, about 1.5 wt % or less, about 1.2 wt % or
less, about 1.1 wt % or less, or about 1.0 wt % or less.
[0037] In some aspects, the catalyst composition can be
substantially free of phosphorous. A catalyst composition that is
substantially free of phosphorous can contain no more than about
0.01 wt % of phosphorous, for example less than about 0.005 wt % of
phosphorous or less than about 0.001 wt % of phosphorous. A
catalyst composition that is substantially free of phosphorous can
be substantially free of intentionally added phosphorous or
substantially free of both intentionally added phosphorous as well
as phosphorous present as an impurity in a reagent for forming the
catalyst composition. In some aspects, the catalyst composition can
contain no added phosphorous, such as containing no intentionally
added phosphorous and/or containing no phosphorous impurities to
within the detection limits of standard methods for characterizing
a reagent and/or a resulting zeolite.
[0038] In other aspects, the catalyst composition can include
phosphorus. The total weight of the phosphorous can be from about
0.1 wt % to about 10.0 wt % based on the total weight of the
catalyst. Thus, the upper limit on the range of the phosphorous
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 %, or 1.0
wt %; and the lower limit on the range added to the molecular sieve
may be 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 shall not include amounts attributable to the
molecular sieve itself, if the molecular sieve contains any
phosphorus.
[0039] Additionally or alternatively, the catalyst composition can
include one or more Group 13 and/or Group 14 metals. Group 13 and
Group 14 refer to the group columns from the IUPAC periodic table,
and thus include the metals Ga, In, and Sn. The total weight of the
Group 13 and/or Group 14 metals can be about 0.1 wt % to about 10.0
wt % based on the total weight of the catalyst. Thus, the upper
limit on the range of the Group 13 and/or Group 14 metals 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 %, or 1.0 wt %; and
the lower limit on the range added to the molecular sieve may be
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
13 and/or Group 14 metals shall not include amounts attributable to
the molecular sieve itself, if the molecular sieve contains any
phosphorus.
[0040] In some optional aspects, the zeolite catalyst composition
employed herein can further be characterized by at least one, at
least two, or all three of the following properties: (a) a
mesoporosity of greater than about 20 m.sup.2/g, for example
greater than about 30 m.sup.2/g, and less than about 120 m.sup.2/g,
for example less than about 100 m.sup.2/g or less than about 85
m.sup.2/g; (b) a microporous surface area of at least about 290
m.sup.2/g, for example at least about 300 m.sup.2/g or at least
about 310 m.sup.2/g; and (c) a diffusivity for 2,2-dimethylbutane
of greater than about 1.0.times.10.sup.-2 sec.sup.-1, for example
greater than about 1.25.times.10.sup.-2 sec.sup.-1, when measured
at a temperature of about 120.degree. C. and a 2,2-dimethylbutane
pressure of about 60 torr (about 8 kPa). Additionally or
alternately, a bound catalyst composition can have a combined
micropore and mesopore surface area of at least about 380
m.sup.2/g, for example at least about 390 m.sup.2/g.
[0041] Of these properties, mesoporosity and diffusivity for
2,2-dimethylbutane can be determined by a number of factors for a
given zeolite, including the crystal size of the zeolite.
Microporous surface area is determined by the pore size of the
zeolite and the availability of the zeolite pores at the surfaces
of the catalyst particles. Producing a zeolite catalyst with the
desired minimum mesoporosity, microporous surface area and
2,2-dimethylbutane diffusivity should be well within the expertise
of anyone of ordinary skill in zeolite chemistry. It is noted that
mesopore or external surface area and micropore surface area can be
characterized, for example, using adsorption-desorption isotherm
techniques within the expertise of one of skill in the art, such as
the BET (Brunauer Emmett Teller) method.
[0042] It is noted that the micropore surface area can be
characterized for either zeolite crystals or a catalyst formed from
the zeolite crystals. In various aspects, the micropore surface
area of a self-bound catalyst or a catalyst formulated with a
separate binder can be at least about 340 m.sup.2/g, for example at
least about 350 m.sup.2/g, at least about 360 m.sup.2/g, at least
about 370 m.sup.2/g, or at least about 380 m.sup.2/g. Typically, a
formulation of zeolite crystals into catalyst particles (either
self-bound or with a separate binder) can result in some loss of
micropore surface area relative to the micropore surface area of
the zeolite crystals. Thus, in order to provide a catalyst having
the desired micropore surface area, the zeolite crystals can also
have a micropore surface area of at least about 340 m.sup.2/g, for
example at least about 350 m.sup.2/g, at least about 360 m.sup.2/g,
at least about 370 m.sup.2/g, or at least about 380 m.sup.2/g. As a
practical matter, the micropore surface area of a zeolite crystal
and/or a corresponding self-bound or bound catalyst as described
herein can be less than about 1000 m.sup.2/g, and typically less
than about 750 m.sup.2/g. Additionally or alternately, the
micropore surface area of a catalyst (self-bound or with a separate
binder) can be about 105% or less of the micropore surface area of
the zeolite crystals in the catalyst, and typically about 100% or
less of the micropore surface area of the zeolite crystals in the
catalyst, fir example from about 80% to 100% of the micropore
surface area of the zeolite crystals in the catalyst. In some
embodiments, the micropore surface area of a catalyst can be at
least about 80% of the micropore surface area of the zeolite
crystals in the catalyst, for example at least about 85%, at least
about 90%, at least about 95%, at least about 97%, or at least
about 98%, and/or about 100% or less, fir example about 99% or
less, about 98% or less, about 97% or less, or about 95% or
less.
[0043] Additionally or alternately, the diffusivity for
2,2-dimethylbutane of a catalyst (self-bound or with a separate
binder) can be about 105% or less of the diffusivity for
2,2-dimethylbutane of the zeolite crystals in the catalyst, and
typically about 100% or less of the diffusivity for
2,2-dimethylbutane of the zeolite crystals in the catalyst, for
example about 80% to 100% of the diffusivity for 2,2-dimethylbutane
of the zeolite crystals in the catalyst. In some embodiments, the
diffusivity for 2,2-dimethylbutane of a catalyst can be at least
about 80% of the diffusivity for 2,2-dimethylbutane of the zeolite
crystals in the catalyst, for example at least about 85%, at least
about 90%, at least about 95%, at least about 97%, or at least
about 98%, and/or about 100% or less, for example about 99% or
less, about 98% or less, about 97% or less, or about 95% or
less.
[0044] A catalyst composition as described herein can employ a
zeolite in its original crystalline form, or the crystals can be
formulated into catalyst particles, such as by extrusion. One
example of binding zeolite crystals to form catalyst particles is
to form a self-bound catalyst. A process for producing zeolite
extrudates in the absence of a binder is disclosed in, for example,
U.S. Pat. No. 4,582,815, the entire contents of which are
incorporated herein by reference.
[0045] As another example of forming a self-bound catalyst, the
following procedure describes a representative method for forming
self-bound ZSM-5 catalyst particles. It is noted that the absolute
values in grams provided below should be considered as
representative of using an appropriate ratio of the various
components. ZSM-5 crystal (such as about 1,400 grams on a solids
basis) can be added to a mixer and dry mulled. Then, approximately
190 grams of deionized water can be added during mulling. After
about 10 minutes, about 28 grams of about 50 wt % caustic solution
mixed with about 450 grams of deionized water can be added to the
mixture and mulled for an additional 5 minutes. The mixture can
then be extruded into 1/10'' quadrulobes. The extrudates can be
dried overnight (.about.8-16 hours) at about 250.degree. F. (about
121.degree. C.) and then calcined in nitrogen for about 3 hours at
about 1000.degree. F. (about 538.degree. C.). The extrudates can
then be exchanged twice with an .about.1N solution of ammonium
nitrate. The exchanged crystal can be dried overnight (.about.8-16
hours) at about 250.degree. F. (about 121.degree. C.) and then
calcined in air for about 3 hours at about 1000.degree. F. (about
538.degree. C.). This can result in a self-bound catalyst. Based on
the exchange with ammonium nitrate and subsequent calcinations in
air, the ZSM-5 crystals in such a self-hound catalyst can
correspond to ZSM-5 with primarily hydrogen atoms at the ion
exchange sites in the zeolite. Thus, such a self-bound catalyst can
sometimes be described as being a self-bound catalyst that includes
H-ZSM-5.
[0046] As an alternative to forming self-bound catalysts, zeolite
crystals can be combined with an alumina binder to form bound
catalysts. Generally, a binder can be present in an amount between
about 1 wt % and about 90 wt %, for example between about 3 wt %
and about 90 wt % of a catalyst composition, about 3 wt % to about
80 wt %, about 5 wt % to about 90 wt %, about 5 wt % to about 80 wt
%, about 5 wt % to about 40 wt %, or about 10 wt % to about 40 wt
%. In some aspects, the catalyst can include at least about 5 wt %
binder, for example at least about 10 wt %, or at least about 20 wt
%. Additionally or alternately, the catalyst can include about 90
wt % or less of binder, for example about 80 wt % or less, about 50
wt % or less, about 40 wt % or less, or about 35 wt % or less.
Combining the zeolite and the binder can generally be achieved, for
example, by mulling a mixture of the zeolite and binder (optionally
an aqueous mixture) and then extruding the mixture into catalyst
pellets.
[0047] In some aspects, a binder for formulating a catalyst can be
selected so that the resulting bound catalyst has a micropore
surface area of at least about 290 m.sup.2/g, for example at least
about 300 m.sup.2/g or at least about 310 m.sup.2/g. Optionally but
preferably, a suitable binder can be a binder with a surface area
of about 200 m.sup.2/g or less, for example about 175 m.sup.2/g or
less or about 150 m.sup.2/g or less. Unless otherwise specified,
the surface area of the binder is defined herein as the combined
micropore surface area and mesopore surface area of the binder.
[0048] As an example of forming a bound catalyst, the following
procedure describes a representative method for forming alumina
bound ZSM-5 catalyst particles. ZSM-5 crystal and an alumina
binder, such as an alumina binder having a surface area of about
200 m.sup.2/g or less, can be added to a mixer and mulled.
Additional deionized water can be added during mulling to achieve a
desired solids content for extrusion. Optionally, a caustic
solution can also be added to the mixture and mulled. The mixture
can then be extruded into a desired shape, such as .about. 1/10''
quadrulobes. The extrudates can be dried overnight (.about.8-16
hours) at about 250.degree. F. (about 121.degree. C.) and then
calcined in nitrogen for about 3 hours at about 1000.degree. F.
(about 538.degree. C.). The extrudates can then be exchanged twice
with an .about.1N solution of ammonium nitrate. The exchanged
crystal can be dried overnight (.about.8-16 hours) at about
250.degree. F. (about 121.degree. C.) and then calcined in air for
about 3 hours at about 1000.degree. F. (about 538.degree. C.). This
can result in an alumina bound catalyst. Based on the exchange with
ammonium nitrate and subsequent calcinations in air, the ZSM-5
crystals in such a bound catalyst can correspond to ZSM-5 with
primarily hydrogen atoms at the ion exchange sites in the zeolite.
Thus, such a bound catalyst can sometimes be described as being a
bound catalyst that includes H-ZSM-5.
[0049] To form a transition metal-enhanced catalyst, a bound (or
self-bound) catalyst can be impregnated via incipient wetness with
a solution containing the desired metal for impregnation, such as
Zn and/or Cd. The impregnated crystal can then be dried overnight
at about 250.degree. F. (about 121.degree. C.), followed by
calcination in air for about 3 hours at about 11000.degree. F.
(about 538.degree. C.). More generally, a transition metal can be
incorporated into the ZSM-5 crystals and/or catalyst at any
convenient time, such as before or after ion exchange to form
H-ZSM-5 crystals, or before or after formation of a bound
extrudate. In some aspects that are preferred from a standpoint of
facilitating manufacture of a bound zeolite catalyst, the
transition metal can be incorporated into the bound catalyst (such
as by impregnation or ion exchange) after formation of the bound
catalyst by extrusion or another convenient method.
Conversion Conditions
[0050] In various aspects, catalysts described herein can be used
for conversion of oxygenate feeds to aromatics and/or olefins
products, such as oxygenates containing at least one
C.sub.1-C.sub.4 alkyl group and/or oxygenate. Examples of suitable
oxygenates include feeds containing methanol, dimethyl ether,
C.sub.1-C.sub.4 alcohols, ethers with C.sub.1-C.sub.4 alkyl chains,
including both asymmetric ethers containing C.sub.1-C.sub.4 alkyl
chains (such as methyl ethyl ether, propyl butyl ether, or methyl
propyl ether) and symmetric ethers (such as diethyl ether, dipropyl
ether, or dibutyl ether), or combinations thereof. It is noted that
oxygenates containing at least one C.sub.1-C.sub.4 alkyl group are
intended to explicitly identify oxygenates having alkyl groups
containing about 4 carbons or less. Preferably the oxygenate feed
can include at least about 50 wt % of one or more suitable
oxygenates, for example at least about 75 wt %, at least about 90
wt %, or at least about 95 wt %. Additionally or alternately, the
oxygenate feed can include at least about 50 wt % methanol, for
example at least about 75 wt % methanol, at least about 90 wt %
methanol, or at least about 95 wt % methanol. The oxygenate feed
can be derived from any convenient source. For example, the
oxygenate feed can be for by reforming of hydrocarbons in a natural
gas feed to form synthesis gas (H.sub.2, CO, CO.sub.2), and then
using the synthesis gas to form alcohols.
[0051] In some aspects, the feedstock 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 liquid water and/or steam at any convenient time, such
as prior to entering a conversion reactor or after entering a
conversion reactor. Examples of suitable feeds (excluding the
presence of water and/or 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 30 wt % of methanol
and/or dimethyl ether, or at least about 50 wt %, or at least about
60 wt %, or at least about 75 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), for example at least 95 wt %
of the compound, at least 98 wt % of the compound, or at least 99
wt % of the compound, on a water-/steam-free basis. For a feed that
is less than 100 wt % methanol and/or dimethyl ether (excluding the
presence of water and/or any optional dilution with steam), other
hydrocarbon compounds (and/or hydrocarbonaceous compounds) in the
feed can include paraffins, olefins, aromatics, and mixtures
thereof.
[0052] The feed can be exposed to the conversion catalyst in any
convenient type of reactor. Suitable reactor configurations include
fixed bed reactors, moving 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.
[0053] 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 fir conversion of methanol and/or dimethyl ether (and/or
other oxygenates) to aromatics and olefins include a pressure of
about 100 kPaa to about 3000 kPaa, for example about 100 kPaa to
about 2500 kPaa, about 100 kPaa to about 2000 kPaa, 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 can include a WHSV of about 0.1
hr.sup.-1 to about 20 hr.sup.-1, for example about 1.0 hr.sup.-1 to
about 10 hr.sup.-1.
[0054] The temperature for the conversion reaction can vary
depending on the nature of the catalyst used for the conversion
and/or the desired type of conversion reaction. Suitable reaction
temperatures for conversion of methanol to gasoline or other
aromatics and olefins can include a temperature of about
200.degree. C. to about 450.degree. C., for example about
200.degree. C. to about 400.degree. C., about 200.degree. C. to
about 375.degree. C., about 200.degree. C. to about 350.degree. C.,
about 250.degree. C. to about 450.degree. C., about 250.degree. C.
to about 400.degree. C., about 250.degree. C. to 375.degree. C.,
about 250.degree. C. to about 350.degree. C., about 275.degree. C.
to about 450.degree. C., about 275.degree. C. to about 400.degree.
C., about 275.degree. C. to about 375.degree. C., or about
300.degree. C. to about 450.degree. C.
[0055] In some alternative aspects, the reaction conditions can be
selected for conversion of methanol and/or dimethyl ether to
aromatics (such as benzene, toluene, and/or xylene and olefins.
Suitable reaction temperatures include a temperature of about
350.degree. C. to about 700.degree. C., for example about
350.degree. C. to about 600.degree. C., about 350.degree. C. to
about 550.degree. C., about 350.degree. C. to about 500.degree. C.,
about 375.degree. C. to about 600.degree. C., about 375.degree. C.
to about 550.degree. C., about 375.degree. C. to about 500.degree.
C., about 400.degree. C. to about 600.degree. C., about 400.degree.
C. to about 550.degree. C., about 400.degree. C. to about
500.degree. C., about 425.degree. C. to about 600.degree. C., about
425.degree. C. to about 550.degree. C., about 450.degree. C. to
600.degree. C., about 450.degree. C. to about 550.degree. C., about
475.degree. C. to about 600.degree. C., or about 475.degree. C. to
about 550.degree. C., about 500.degree. C. to about 600.degree. C.,
or about 500.degree. C. to about 550.degree. C.
[0056] In still other alternative aspects, suitable reaction
temperatures can include a temperature of about 200.degree. C. to
about 700.degree. C., for example about 450.degree. C. to about
700.degree. C., about 450.degree. C. to about 650.degree. C., about
450.degree. C. to about 600.degree. C., about 475.degree. C. to
about 700.degree. C. about 475.degree. C. to about 650.degree. C.,
about 475.degree. C. to 600.degree. C., about 500.degree. C. to
about 700.degree. C., about 500.degree. C. to about 650.degree. C.,
about 500.degree. C. to about 600.degree. C., about 525.degree. C.
to about 700.degree. C., about 525.degree. C. to about 650.degree.
C., or about 550.degree. C. to about 700.degree. C.
[0057] As an 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.
Alternatively, other oxygenates can be used in addition to or in
place of the methanol and/or dimethyl ether. Liquid water and/or
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 4-5 carbons or less can be
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.
In some aspects, at least a portion of the liquid product (i.e.,
liquid at standard temperature and pressure) can correspond to a
naphtha boiling range product (gasoline).
[0058] Alternatively, if individual aromatic products are desired,
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.
[0059] The C.sub.8+ fraction can then be further separated into a
C.sub.8 fraction and a C.sub.9+ fraction. 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.
[0060] 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.
ADDITIONAL EMBODIMENTS
Embodiment 1
[0061] A method of converting a feed to form olefins and aromatics,
comprising: steaming a catalyst in the presence of at least 0.01
atm (1 kPa) of water at a temperature of about 450.degree. F.
(about 221.degree. C.) to about 700.degree. F. (about 371.degree.
C.) for at least about 0.25 hours to form a steamed catalyst, 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; and subsequently exposing a feed comprising at least
about 30 wt % (for example at least about 50 wt %, at least about
75 wt %, or at least about 90 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 at least one aromatic (preferably
para-xylene), the effective conversion conditions including a
temperature of about 200.degree. C. to about 700.degree. C., for
example about 350.degree. C. to about 600.degree. C. or about
450.degree. C. to about 550.degree. C., the steamed catalyst having
a cycle length under the effective conversion conditions that is at
least about 15% greater than a cycle length under the effective
conversion conditions for the catalyst prior to steaming, and/or
the steamed catalyst having an alpha value that is at least about
10 greater than an alpha value for the catalyst prior to
steaming.
Embodiment 2
[0062] A method of converting an oxygenate feed to form
hydrocarbons, comprising: steaming a catalyst in the presence of at
least 0.9 atm (91 kPa) of water at a temperature of about
450.degree. F. (about 221.degree. C.) to about 650.degree. F.
(about 343.degree. C.) for at about 0.25 hours to about 16 hours to
form a steamed catalyst, the catalyst comprising a molecular sieve
having at least one 8-member ring channel, 10-member ring channel,
or 12-member ring channel and having no ring channels larger than a
12-member ring channel; and subsequently 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 one
or more hydrocarbons, the effective conversion conditions including
a temperature of about 200.degree. C. to about 700.degree. C., the
steamed catalyst having a cycle length under the effective
conversion conditions that is at least about 15% greater than a
cycle length under the effective conversion conditions for the
catalyst prior to steaming, and/or the steamed catalyst having an
alpha value that is at least about 10 greater than an alpha value
for the catalyst prior to steaming.
Embodiment 3
[0063] The method of any one of the previous embodiments, wherein
the catalyst further comprises about 3 wt % to about 90 wt %, based
on a total weight of the catalyst, for example about 3 wt % to
about 80 wt %, about 5 wt % to about 90 wt %, about 5 wt % to about
80 wt %, about 5 wt % to about 40 wt %, about 10 wt % to about 90
wt %, about 10 wt % to about 80 wt %, or about 10 wt % to about 40
wt %, of a binder comprising alumina and/or silica.
Embodiment 4
[0064] The method of any of the above embodiments, wherein the
catalyst is steamed at a temperature of about 650.degree. F. (about
343.degree. C.) or less, for example about 625.degree. F. (about
329.degree. C.) or less or about 600.degree. F. (316.degree. C.) or
less; wherein the catalyst is steamed in the presence of partial
pressure of at least about 0.5 atm (about 50 kPag) of water, for
example at least about 0.9 atm (about 90 kPag) of water, the
catalyst optionally being steamed in the presence of about 5 atm
(about 510 kPag) of water or less, for example about 2 atm (about
200 kPag) of water or less; wherein the catalyst is steamed for
about 16 hours or less, for example about 8.5 hours or less or
about 4.5 hours or less, the catalyst optionally being steamed for
at least about 0.75 hours; or a combination thereof.
Embodiment 5
[0065] The method of any one of the previous embodiments, wherein
the catalyst has an alpha value of at least about 20, at least
about 50, or at least about 200 prior to the steaming of the
catalyst and optionally an alpha value prior to the steaming of the
catalyst of about 1000 or less.
Embodiment 6
[0066] The method of any one of the previous embodiments, wherein
the steamed catalyst has an alpha value that is greater than the
alpha value of the catalyst prior to the steaming of the catalyst
by at least about 10, at least about 25, or at least about 50.
Embodiment 7
[0067] The method of any one of the previous embodiments, wherein
the steamed catalyst has an alpha value of at least about 250, at
least about 300, or at least about 350, and optionally an alpha
value of about 2000 or less.
Embodiment 8
[0068] The method of any one of the previous embodiments, wherein
exposing a feed to the steamed catalyst comprises exposing the feed
to the steamed catalyst in a fixed bed reactor, a fluidized bed
reactor, a moving bed reactor, or a riser reactor; wherein exposing
a feed to the steamed catalyst comprises exposing the feed to the
steamed catalyst in the presence of steam and/or a hydrogen-lean
stream; or a combination thereof.
Embodiment 9
[0069] The method of any of the above embodiments, further
comprising separating at least a portion of the converted effluent
to form a naphtha boiling range product.
Embodiment 10
[0070] 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 11
[0071] The method of any of the above embodiments, 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.
Embodiment 12
[0072] The method of any of the above embodiments, therein the
catalyst is steamed for about 1 hour to about 16 hours.
Embodiment 13
[0073] The method of any of the above embodiments, wherein the
molecular sieve comprises ZSM-5, ZSM-11, or a combination thereof,
preferably ZSM-5.
Embodiment 14
[0074] The method of any of the above embodiments, wherein the
molecular sieve has a silicon to aluminum ratio of about 20 to
about 100, for example about 20 to about 80.
Embodiment 15
[0075] The method of any of the above embodiments, wherein the
steamed catalyst further comprises about 0.1 wt % to about 10 wt of
phosphorus, about 0.1 wt % to about 10 wt % of a transition metal,
about 0.1 wt % to about 10 wt % of a Group 13 metal or Group 14
metal, or a combination thereof.
Embodiment 16
[0076] The method of any of the above embodiments, wherein a) the
effective conversion conditions comprise a pressure of about 100
kPaa to about 2500 kPaa, for example about 100 kPaa to about 1200
kPaa; and a WHSV of about 0.1 hr to about 2.0 hr, for example about
1.0 hr.sup.-1 to about 10 hr.sup.-1; b) the feed substantially
comprises methanol, dimethyl ether, or a combination thereof; or c)
a combination thereof.
EXAMPLE
Example 1
Cracking Activity of Steamed Conversion Catalyst
[0077] A series of steamed and unsteamed catalysts were
investigated to determine the n-hexane cracking activity of the
catalysts. The catalysts were bound ZSM-5 catalysts composed of
.about.65 wt % ZSM-5 (in the H+ form) and .about.35 wt % of a
binder. The catalysts were bound with either an alumina binder or a
silica binder. The steamed catalysts were generated by one of two
types of steam treatments. Some catalysts were steamed by treating
the catalyst in .about.1 atm (.about.100 kPa) of flowing steam at
.about.650.degree. F. (.about.343.degree. C.) for about 12 hours.
This is referred to as "Steaming method 1" in Table 1. Other
catalysts were steamed by treating the catalyst in .about.1 atm
(.about.100 kPa) of flowing steam at .about.650.degree. F.
(.about.343.degree. C.) for about 4.5 hours. This is referred to as
"Steaming method 2" in Table 1. The ZSM-5 crystals used in the
silica-bound sample were made using n-propylamine as the organic
template. The alumina-bound samples were made using
tetrapropylammonium bromide as the organic template.
[0078] After forming the bound catalysts, the catalysts were used
for conversion of a substantially pure methanol feed to form
products. During conversion, the space velocity of the methanol
feed, defined as grams of methanol per gram of catalyst per hour,
was maintained at a constant value. The bound catalysts were
contacted with the substantially pure methanol feed in an
isothermal (.about.440.degree. C.), fixed-bed reactor at about 30
psig (about 210 kPag) and a weight hourly space velocity of about 6
(grams methanol/grams catalyst/hour). The conversion temperature
and pressure were selected so that at least 99% of the feed was
converted. The conversion process was then performed until the
methanol conversion dropped below 99%. The cycle length for the
catalyst for the conversion process was measured based on the time
from the start of the conversion process until the conversion
dropped below 99%.
[0079] Table 1 below shows representative examples of the cycle
length for steamed and unsteamed versions of bound ZSM-5 catalysts.
Catalysts A and B correspond to alumina bound ZSM-5 catalysts,
while Catalyst C is a silica bound catalyst. In Table 1, the
reactivity of each steamed catalyst is expressed as a relative
value in comparison with the unsteamed version of the catalyst. As
shown in Table 1, for the two different types of alumina bound
ZSM-5 catalysts, steaming of the catalyst provided a cycle length
that was at least about twice as long as the cycle length for the
corresponding unsteamed catalyst. This is in contrast to silica
bound Catalyst C, which had roughly the same cycle length for the
steamed and unsteamed versions of the catalyst.
[0080] Table 1 also shows the relative activities of the steamed
and unsteamed catalysts, based on the activity of the catalysts for
cracking of n-hexane. The n-hexane activities were measured using a
method similar to the alpha test method described above. It is
believed that n-hexane cracking activity can be an indicator of
activity for methanol conversion. As shown in Table 1, steaming of
all of the catalysts resulted in an increase in the n-hexane
cracking activity, although the amount of increase varied. It is
noted that the shorter steaming time period resulted in an increase
of about 90% in n-hexane cracking activity, while the longer
protocol provided increases in activity from about 10% to about
50%.
TABLE-US-00001 TABLE 1 Catalyst Cycle Length and Cracking Activity
% Relative Cycle improvement n-hexane Length in cycle cracking
Binder (days) length activity Catalyst A Al.sub.2O.sub.3 2.6 1
Steamed Catalyst A Al.sub.2O.sub.3 5.5 112 1.3 (Steaming method 1)
Steamed Catalyst A Al.sub.2O.sub.3 4.2 61 1.9 (Steaming method 2)
Catalyst B Al.sub.2O.sub.3 3.8 1 Steamed Catalyst B Al.sub.2O.sub.3
8.0 111 1.1 (Steaming method 1) Catalyst C SiO.sub.2 3.2 1 Steamed
Catalyst C SiO.sub.2 3.1 <none> 1.5 (Steaming method 1)
[0081] It is noted that for the catalyst steamed according to
"Steaming method 2", the pressure (in atm) multiplied by the time
hours) results in a value of .about.4.5. It is also noted that
0.01*F.sub.T, where F.sub.T is defined as
2.6.times.10.sup.-9e.sup.16000/T, results in a value of .about.4.65
using "Steaming method 2".
[0082] FIG. 1 shows additional investigation of the n-hexane
cracking activity for alumina bound ZSM-5 catalyst samples that
were steamed at various temperatures in .about.1 atm (.about.100
kPa) of steam tier about 12 hours. The alpha value for the "fresh"
ZSM-5 prior to steaming was about 400. FIG. 1 shows the relative
n-hexane cracking activity in comparison with an unsteamed sample
of the catalyst. As shown in FIG. 1, tier temperatures less than
about 700.degree. F. (about 371.degree. C.) steaming of the
catalyst appeared to result in an increase in the relative n-hexane
cracking activity. It is noted that the samples showing improved
activity in FIG. 1 had conditions roughly overlapping with the
conditions shown in Table 1 for providing improved catalyst cycle
length. It is also noted that, for a temperature of
.about.600.degree. F. (.about.589.degree. K), the value of
0.01*F.sub.T, where F.sub.T is defined as
2.6.times.10.sup.-9e.sup.16000/T, resulted in a value of 16.5. For
steaming at temperatures of about 700.degree. F. (about 371.degree.
C.) or greater, such as about 800.degree. F. (about 427.degree. C.)
or about 900.degree. F. (about 482.degree. C.), the relative
II-hexane activity appeared to decrease below the activity of the
corresponding unsteamed catalyst. It is believed that these lower
activity samples did not have the increased catalyst lifetime
benefit, as the steaming conditions at temperatures greater than
about 700.degree. F. (about 371.degree. C.) can correspond to
conventional steaming conditions that result in a reduced number of
acidic sites on the catalyst.
[0083] 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.
* * * * *