U.S. patent application number 13/652692 was filed with the patent office on 2013-04-25 for phosphorus modified zeolite catalysts.
This patent application is currently assigned to EXXONMOBIL RESEARCH AND ENGINEERING COMPANY. The applicant listed for this patent is EXXONMOBIL RESEARCH AND ENGINEERING. Invention is credited to TILMAN W. BEUTEL, MICHEL DAAGE, KARLTON J. HICKEY, STEPHEN J. McCARTHY, BEAU WALDRUP.
Application Number | 20130102825 13/652692 |
Document ID | / |
Family ID | 47089187 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130102825 |
Kind Code |
A1 |
BEUTEL; TILMAN W. ; et
al. |
April 25, 2013 |
PHOSPHORUS MODIFIED ZEOLITE CATALYSTS
Abstract
The invention relates to a bound phosphorus-modified catalyst
composition comprising a zeolite having a silica to alumina molar
ratio of at least 40 and a binder having a surface area less than
200 m.sup.2/g, wherein the bound catalyst composition exhibits a
mesopore size distribution with less than 20% of mesopores having a
size below 10 nm before steaming in approximately 100% steam for
about 96 hours at about 1000.degree. F. (about 538.degree. C.) and
with more than 60% of mesopores having a size at least 21 nm after
steaming in approximately 100% steam for about 96 hours at about
1000.degree. F. (about 538.degree. C.).
Inventors: |
BEUTEL; TILMAN W.; (Neshanic
Station, NJ) ; McCARTHY; STEPHEN J.; (Center Valley,
PA) ; DAAGE; MICHEL; (Hellertown, PA) ;
WALDRUP; BEAU; (Luberton, TX) ; HICKEY; KARLTON
J.; (Boothwyn, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EXXONMOBIL RESEARCH AND ENGINEERING; |
Annandale |
NJ |
US |
|
|
Assignee: |
EXXONMOBIL RESEARCH AND ENGINEERING
COMPANY
Annandale
NJ
|
Family ID: |
47089187 |
Appl. No.: |
13/652692 |
Filed: |
October 16, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61548057 |
Oct 17, 2011 |
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61548015 |
Oct 17, 2011 |
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61548038 |
Oct 17, 2011 |
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61548044 |
Oct 17, 2011 |
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61548052 |
Oct 17, 2011 |
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61548064 |
Oct 17, 2011 |
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Current U.S.
Class: |
585/407 ; 502/60;
502/64; 502/77; 585/467; 585/475; 585/899 |
Current CPC
Class: |
B01J 35/1004 20130101;
B01J 2229/42 20130101; B82Y 40/00 20130101; B01J 35/1019 20130101;
B01J 29/40 20130101; Y02P 30/20 20151101; B01J 37/0201 20130101;
B01J 37/04 20130101; B01J 35/1085 20130101; B01J 37/06 20130101;
Y02P 20/10 20151101; C01B 39/54 20130101; C07C 1/20 20130101; B01J
35/1038 20130101; B01J 2229/186 20130101; B01J 29/00 20130101; C10G
2400/02 20130101; B01J 2229/37 20130101; C07C 1/22 20130101; C07C
41/09 20130101; B01J 37/0009 20130101; C10G 3/49 20130101; B01J
29/83 20130101; B01J 2229/36 20130101; C07C 1/24 20130101; B01J
35/002 20130101; B01J 37/28 20130101; B82Y 30/00 20130101; B01J
35/1042 20130101; C10G 2400/04 20130101; B01J 35/1061 20130101;
B01J 35/1014 20130101; B01J 21/04 20130101; B01J 35/0026 20130101;
C07C 2/864 20130101; C07C 41/09 20130101; C07C 43/043 20130101 |
Class at
Publication: |
585/407 ;
585/475; 585/467; 585/899; 502/60; 502/77; 502/64 |
International
Class: |
B01J 29/83 20060101
B01J029/83; C07C 1/22 20060101 C07C001/22 |
Claims
1. A bound phosphorus-modified catalyst composition comprising a
zeolite having a silica to alumina molar ratio of at least 40 and a
binder having a surface area less than 200 m.sup.2/g, wherein the
bound catalyst composition exhibits a mesopore size distribution
with less than 20% of mesopores having a size below 10 nm before
steaming in approximately 100% steam for about 96 hours at about
1000.degree. F. (about 538.degree. C.) and with more than 60% of
mesopores having a size at least 21 nm after steaming in
approximately 100% steam for about 96 hours at about 1000.degree.
F. (about 538.degree. C.).
2. The catalyst composition of claim 1, wherein the silica to
alumina molar ratio of the zeolite is from about 40 to about
200.
3. The catalyst composition of claim 1, wherein said zeolite has a
constraint index from about 1 to about 12.
4. The catalyst composition of claim 1, wherein said zeolite
comprises ZSM-5.
5. The catalyst composition of claim 1, wherein the bound catalyst
composition exhibits an alpha value after steaming in approximately
100% steam for about 96 hours at about 1000.degree. F. (about
538.degree. C.) of at least 20.
6. The catalyst composition of claim 1, wherein the bound catalyst
composition exhibits an alpha value after steaming in approximately
100% steam for about 96 hours at about 1000.degree. F. (about
538.degree. C.) of at least 40.
7. The catalyst composition of claim 1, wherein the bound catalyst
composition exhibits a microporous surface area of at least 375
m.sup.2/g.
8. The catalyst composition of claim 1, further comprising
phosphorus in an amount between about 0.1 wt % and about 3 wt % of
the total catalyst composition.
9. The catalyst composition of claim 1, further comprising
phosphorus in an amount between about 0.5 wt % and about 2 wt % of
the total catalyst composition.
10. The eatalyyst composition of claim 1, wherein the binder has a
surface area less than 150 m.sup.2/g.
11. The catalyst composition of claim 1, wherein the binder has a
surface area less than or equal to 100 m.sup.2/g.
12. The catalyst composition of claim 1, wherein the binder is
present in an amount between about 1 wt % and about 50 wt % of the
total catalyst composition.
13. The catalyst composition of claim 1, wherein the binder is
present in an amount between about 5 wt % and about 40 wt % of the
total catalyst composition.
14. The catalyst composition of claim 1, wherein the binder
comprises alumina.
15. The catalyst composition of claim 1, wherein the zeolite has a
diffusivity for 2,2-dimethylbutane of greater than
1.2.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).
16. A process for organic compound conversion employing contacting
a feedstock with the bound catalyst composition of claim 1 under
organic compound conversion conditions.
17. The process of claim 16, wherein said organic compound
conversion comprises the conversion of methanol to hydrocarbons
boiling in the gasoline boiling range.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/548,057, filed on Oct. 17, 2011, the entire
contents of which are hereby incorporated by reference herein.
[0002] This application also claims the benefit of related U.S.
Provisional Application Nos. 61/548,015, 61/548,038, 61/548,044,
61/548,052, and 61/548,064, each filed on Oct. 17, 2011, the entire
contents of each of which are hereby also incorporated by reference
herein. This application is also related to five other co-pending
U.S. utility applications, each filed on even date herewith and
claiming the benefit to the aforementioned provisional patent
applications, and which are entitled "Process for Producing
Phosphorus Modified Zeolite Catalysts", "Process for Producing
Phosphorus Modified Zeolite Catalysts", "Phosphorus Modified
Zeolite Catalysts", "Phosphorus Modified Zeolite Catalysts", and
"Selective Dehydration of Alcohols to Dialkyl Ethers",
respectively, the entire contents of each of which utility patents
are hereby further incorporated by reference herein.
FIELD OF THE INVENTION
[0003] This disclosure relates to phosphorus modified zeolite
catalysts and their use in organic conversion reactions, such as
the conversion of methanol to gasoline and diesel boiling range
hydrocarbons.
BACKGROUND OF THE INVENTION
[0004] Phosphorus modification is a known method of improving the
performance of zeolite catalysts for a variety of chemical
processes including, for example, the conversion of methanol to
hydrocarbons and the methylation of toluene to produce xylenes. For
example, U.S. Pat. Nos. 4,590,321 and 4,665,251 disclose a process
for producing aromatic hydrocarbons by contacting one or more
non-aromatic compounds, such as propane, propylene, or methanol,
with a catalyst containing a zeolite, such as ZSM-5. The zeolite is
modified with phosphorus oxide by impregnating the zeolite with a
source of phosphate ions, such as an aqueous solution of an
ammonium phosphate, followed by calcination. The phosphorus oxide
modification is said to render the zeolite more active and/or
benzene selective in the aromatization reaction.
[0005] In addition, U.S. Patent Application Publication No.
2010/0168489 discloses a bound phosphorus-modified zeolite
catalyst, in which the binder material is treated with a mineral
acid prior to being bound with the phosphorus-modified zeolite.
Suitable binder materials are said to include inorganic oxides,
such as alumina, clay, aluminum phosphate and silica-alumina. In
the Examples, the binder material is a pseudobohemite-type alumina
available from Alcoa as HiQ.TM.-40 grade (with a surface area of
250 m.sup.2/g). After optional extrusion, the zeolite-binder
mixture is heated at a temperature of about 400.degree. C. or
higher to form a bound zeolite catalyst, typically from 0.01-0.15
gram of phosphorus per gram of zeolite. The catalyst is
particularly intended for use in the alkylation of toluene with
methanol to produce xylenes, but is also said to be useful in MTG
processes.
[0006] In the conversion of methanol to gasoline (MTG), the
reaction is believed to be catalyzed by acid sites generated by
framework aluminum inside the micropores of the zeolite catalyst.
The role of the phosphorus can be to stabilize the zeolite
framework aluminum against dealumination by the high temperature
steam generated as a by-product of the process. The role of the
binder material can be to assist in maintaining the integrity of
the catalyst particles in the catalyst bed. Surprisingly, however,
it has now been found that the activity of a bound
phosphorus-modified zeolite catalyst for the MTG reaction can be
enhanced by employing a binder with a relatively low surface area
(less than 200 m.sup.2/g) and a particular mesopore distribution.
This result is surprising, because binder particles can typically
be larger than the opening of the microchannels of the zeolite, and
hence penetration of binder into the zeolite micropores in such
situations was not anticipated. Moreover, blockage of zeolite
micropores by binder located at the pore mouth of the microchannels
was not expected to occlude zeolite micropore volume in a zeolite
with the three-dimensional pore structure favored for MTG
reactions, such as in MFI zeolites.
SUMMARY OF THE INVENTION
[0007] In one aspect, the invention resides in a bound
phosphorus-modified catalyst composition comprising a zeolite
having a silica to alumina molar ratio of at least 40, e.g., from
about 40 to about 200, and a binder having a surface area less than
200 m.sup.2/g, e.g., less than 150 m.sup.2/g or less than or equal
to 100 m.sup.2/g, wherein the bound catalyst composition exhibits a
mesopore size distribution with less than 20% of mesopores having a
size below 10 nm before steaming in approximately 100% steam for
about 96 hours at about 1000.degree. F. (about 538.degree. C.) and
with more than 60% of mesopores having a size at least 21 nm after
steaming in approximately 100% steam for about 96 hours at about
1000.degree. F. (about 538.degree. C.).
[0008] In some embodiments, the zeolite can have a constraint index
of about 1 to about 12 and/or can comprise ZSM-5.
[0009] Additionally or alternately, the catalyst composition has an
alpha value after steaming in .about.100% steam for .about.96 hours
at .about.1000.degree. F. (.about.538.degree. C.) of at least 20,
e.g. at least 40.
[0010] Additionally or alternately, the catalyst composition can
have a microporous surface area of at least 375 m.sup.2/g and/or
can contain phosphorus in an amount between about 0.1 wt % and
about 3 wt %, e.g., between about 0.5 wt % and about 2 wt %, of the
total catalyst composition.
[0011] Additionally or alternately, the binder can comprise alumina
and/or can be present in an amount between about 1 wt % and about
50 wt %, e.g., between about 5 wt % and about 40 wt %, of the total
catalyst composition.
[0012] Additionally or alternately, the catalyst can have a
diffusivity for 2,2-dimethylbutane of greater than
1.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).
[0013] In a further aspect, the invention can involve use of the
unbound catalyst composition described herein in organic conversion
reactions, such as the conversion of methanol to hydrocarbons
boiling in the gasoline boiling range.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 shows a graph comparing the normalized alpha values
of the catalysts of Examples 1-2 after steaming in .about.100%
steam for .about.96 hours at .about.1000.degree. F.
(.about.538.degree. C.).
[0015] FIG. 2 shows a graph comparing the microporous surface area
of the catalysts of Examples 1-2, normalized by zeolite
content.
[0016] FIG. 3 shows a graph comparing the diffusivity for
2,2-dimethylbutane of the catalysts of Examples 1-2 at a
temperature of .about.120.degree. C. and a 2,2-dimethylbutane
pressure of .about.60 torr (.about.8 kPa).
[0017] FIG. 4 shows a graph comparing the mesopore size
distribution of the catalysts of Examples 1-2.
[0018] FIG. 5 shows a graph comparing the mesopore size
distribution of the catalysts of Examples 1-2 after steaming in
.about.100% steam for .about.96 hours at .about.1000.degree. F.
(.about.538.degree. C.).
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0019] Described herein is a bound phosphorus-stabilized zeolite
catalyst composition for use in any of a variety of organic
conversion reactions, particularly, but not exclusively, in the
conversion of methanol to hydrocarbons boiling in the gasoline
boiling range.
[0020] The zeolite employed in the present catalyst composition can
typically have a silica to alumina molar ratio of at least 40,
e.g., from about 40 to about 200. Generally, the zeolite can
comprise 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 can include, but are not necessarily limited to,
ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, and the
like, as well as combinations thereof. ZSM-5 is described in detail
in U.S. Pat. No. 3,702,886 and RE 29,948. ZSM-11 is described in
detail in U.S. Pat. No. 3,709,979. ZSM-12 is described in U.S. Pat.
No. 3,832,449. ZSM-22 is described in U.S. Pat. No. 4,556,477.
ZSM-23 is described in U.S. Pat. No. 4,076,842. ZSM-35 is described
in U.S. Pat. No. 4,016,245. ZSM-48 is more particularly described
in U.S. Pat. No. 4,234,231. In certain embodiments, the zeolite can
comprise, consist essentially of, or be ZSM-5.
[0021] When used in the present catalyst composition, the zeolite
can advantageously be present at least partly in the hydrogen form.
Depending on the conditions used to synthesize the zeolite, this
may implicate converting the zeolite from, for example, the alkali
(e.g., sodium) form. This can readily be achieved, e.g., by ion
exchange to convert the zeolite to the ammonium form, followed by
calcination in air or an inert atmosphere at a temperature from
about 400.degree. C. to about 700.degree. C. to convert the
ammonium form to the active hydrogen form. If an organic structure
directing agent is used in the synthesis of the zeolite, additional
calcination may be desirable to remove the organic structure
directing agent.
[0022] The zeolite can be combined with a binder, normally alumina,
silica, or silica-alumina, which can be selected so as to have a
surface area less than 200 m.sup.2/g, for example less than 150
m.sup.2/g or less than or equal to 100 m.sup.2/g. Suitable binders
can comprise or be Pural.TM. 200 and/or Versal.TM. 300 alumina.
Generally, the binder can be present in an amount between about 1
wt % and about 50 wt %, e.g., between about 5 wt % and about 40 wt
%, of the total catalyst composition.
[0023] To enhance the steam stability of the zeolite without
excessive loss of its initial acid activity, the present catalyst
composition can contain phosphorus in an amount between about 0.01
wt % and about 3 wt % elemental phosphorus, e.g., between about
0.05 wt % and about 2 wt %, of the total catalyst composition. The
phosphorus can be added to the catalyst composition at any stage
during synthesis of the zeolite and/or formulation of the zeolite
and binder into the catalyst composition. Generally, phosphorus
addition can be achieved by spraying and/or impregnating the final
catalyst composition (and/or a precursor thereto) with a solution
of a phosphorus compound. Suitable phosphorus compounds can
include, but are not limited to, phosphinic [H.sub.2PO(OH)],
phosphonic [HPO(OH).sub.2], and phosphoric [PO(OH).sub.3] acids,
salts and esters of such acids, phosphorus halides, and the like,
and combinations thereof. After phosphorus treatment, the catalyst
can generally be calcined, e.g., in air at a temperature from about
400.degree. C. to about 700.degree. C. to convert the phosphorus to
an oxide form.
[0024] The bound phosphorus-stabilized zeolite catalyst composition
employed herein can be characterized by at least one, and
preferably at least two, of the following properties: (a) a
microporous surface area of at least 375 m.sup.2/g; (b) a
diffusivity for 2,2-dimethylbutane of greater than
1.2.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); (c) an alpha value after steaming in
.about.100% steam for .about.96 hours at .about.1000.degree. F.
(.about.538.degree. C.) of at least 20, e.g., at least 40; (d)
mesopore size distribution with less than 20% of mesopores having a
size below 10 nm; and (e) a mesopore size distribution with more
than 60% of mesopores having a size at least 21 nm after steaming
in approximately 100% steam for about 96 hours at about
1000.degree. F. (about 538.degree. C.). It should be appreciated by
one of ordinary skill in the art that properties (a), (b), and (d)
above, unlike properties (c) and (e), are measured before any
steaming of the catalyst composition.
[0025] Of these properties, micoporosity and diffusivity for
2,2-dimethylbutane can be determined by a number of factors,
including but not necessarily limited to the pore size and crystal
size of the zeolite and the availability of the zeolite pores at
the surfaces of the catalyst particles. Mesopore size distribution
can be determined mainly by the surface area of the binder. Given
the disclosure herein regarding the use of a relatively low surface
area binder, producing a zeolite catalyst with the desired mesopore
size distribution, microporous surface area, and 2,2-dimethylbutane
diffusivity should be well within the expertise of anyone of
ordinary skill in zeolite chemistry.
[0026] Alpha value can advantageously be a measure of the acid
activity of a zeolite catalyst, as compared with a standard
silica-alumina catalyst. The alpha test is described in U.S. Pat.
No. 3,354,078; in the Journal of Catalysis, v. 4, p. 527 (1965); v.
6, p. 278 (1966); and v. 61, p. 395 (1980), each incorporated
herein by reference as to that description. The experimental
conditions of the test used herein can include a constant
temperature of .about.538.degree. C. and a variable flow rate, as
described in detail in the Journal of Catalysis, v. 61, p. 395. The
higher alpha values can generally correspond to a more active
cracking catalyst. Since the present catalyst composition can be
intended for use in reactions such as MTG, where the zeolite can be
subject to hydrothermal dealumination of the zeolite, it can be
important for the catalyst composition to retain a significant
alpha value, namely at least 20, after steaming in .about.100%
steam for .about.96 hours at .about.1000.degree. F.
(.about.538.degree. C.).
[0027] The phosphorus-modified zeolite catalyst described herein
can be particularly useful in any organic conversion process where
the hydrothermal stability of the catalyst is important. Examples
of such processes can include, but are not necessarily limited to,
fluid catalytic cracking of heavy hydrocarbons to gasoline and
diesel boiling range hydrocarbons, methylation and
disproportionation of toluene to produce xylenes, n-paraffin (e.g.,
C.sub.6 and higher) cyclization, conversion of methanol to gasoline
and diesel boiling range hydrocarbons, and the like, and
combinations and/or integrations thereof.
[0028] The invention can additionally or alternately include one or
more of the following embodiments.
Embodiment 1
[0029] A bound phosphorus-modified catalyst composition comprising
a zeolite having a silica to alumina molar ratio of at least 40,
e.g., from about 40 to about 200, and a binder having a surface
area less than 200 m.sup.2/g, e.g., less than 150 m.sup.2/g or less
than or equal to 100 m.sup.2/g, wherein the bound catalyst
composition exhibits a mesopore size distribution with less than
20% of mesopores having a size below 10 nm before steaming in
approximately 100% steam for about 96 hours at about 1000.degree.
F. (about 538.degree. C.) and with more than 60% of mesopores
having a size at least 21 nm after steaming in approximately 100%
steam for about 96 hours at about 1000.degree. F. (about
538.degree. C.).
Embodiment 2
[0030] The catalyst composition of embodiment 1, wherein said
zeolite has a constraint index from about 1 to about 12.
Embodiment 3
[0031] The catalyst composition of any one of the previous
embodiments, wherein said zeolite comprises ZSM-5.
Embodiment 4
[0032] The catalyst composition of any one of the previous
embodiments, wherein the bound catalyst composition exhibits an
alpha value after steaming in approximately 100% steam for about 96
hours at about 1000.degree. F. (about 538.degree. C.) of at least
20, e.g., of at least 40.
Embodiment 5
[0033] The catalyst composition of any one of the previous
embodiments, wherein the bound catalyst composition exhibits a
macroporous surface area of at least 375 m.sup.2/g.
Embodiment 6
[0034] The catalyst composition of any one of the previous
embodiments, further comprising phosphorus in an amount between
about 0.1 wt % and about 3 wt %, e.g., between about 0.5 wt % and
about 2 wt %, of the total catalyst composition.
Embodiment 7
[0035] The catalyst composition of any one of the previous
embodiments, wherein the binder is present in an amount between
about 1 wt % and about 50 wt %, e.g., between about 5 wt % and
about 40 wt %, of the total catalyst composition.
Embodiment 8
[0036] The catalyst composition of any one of the previous
embodiments, wherein the binder comprises alumina.
Embodiment 9
[0037] The catalyst composition of any one of the previous
embodiments, wherein the zeolite has a diffusivity for
2,2-dimethylbutane of greater than 1.2.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).
Embodiment 10
[0038] A process for organic compound conversion employing
contacting a feedstock with the bound catalyst composition of any
one of the previous embodiments under organic compound conversion
conditions.
Embodiment 11
[0039] The process of embodiment 10, wherein said organic compound
conversion comprises the conversion of methanol to hydrocarbons
boiling in the gasoline boiling range.
[0040] The invention will now be more particularly described with
reference to the Examples and the accompanying drawings.
EXAMPLES
Example 1
Preparation of ZSM-5/Versal.TM.-300 Alumina Catalyst
[0041] A mixture of .about.80 wt % of as-synthesized NaZSM-5
zeolite (containing the organic directing agent used in its
synthesis and having the properties summarized in Table 1 below)
was blended in a muller with .about.20 wt % of Versal.TM.-300
alumina binder. Versal.TM.-300 alumina used herein exhibited a
surface area of about 250-300 m.sup.2/g.
[0042] The blend was extruded, and the resultant extrudate sample
was calcined in nitrogen for .about.3 hours at .about.1000.degree.
F. (.about.538.degree. C.) to decompose the organic template into a
carbonaceous deposit. The calcined extrudate was then exchanged
with an ammonium nitrate solution to convert the zeolite from the
sodium to the ammonium form, whereafter the extrudate was calcined
in air for .about.3 hours at .about.1000.degree. F.
(.about.538.degree. C.) to convert the zeolite from the ammonium to
the hydrogen form. At the same time carbonaceous deposits were
removed by oxidation. The thus obtained H-ZSM-5-Al.sub.2O.sub.3
extrudate was then impregnated with phosphoric acid to a target
level of .about.0.96 wt % phosphorus via aqueous incipient wetness
impregnation. The sample was dried and then calcined in air for
.about.3 hours at .about.1000.degree. F. (.about.538.degree. C.).
The resultant product was labeled Catalyst A and had the properties
summarized in Table 1 below.
Example 2
Preparation of ZSM-5/Pural.TM. 200 Alumina Catalyst
[0043] The process of Example 1 was repeated, except that Pural.TM.
200 alumina was substituted as the alumina binder. Pural.TM. 200
alumina used herein exhibited a surface area of about 90 m.sup.2/g.
The resultant product was labeled Catalyst B and had the properties
summarized in Table 1 below.
TABLE-US-00001 TABLE 1 P (wt % microporous Alpha 2,2-DMB based
surface after Diffusiv. on Cat Si/Al.sub.2 area (m.sup.2/g) Alpha
steaming* (10.sup.-6 sec.sup.-1) zeolite) A 370 18 11,000 1.2 B 395
47 14,000 1.2 *Alpha value per gram of zeolite after steaming in
~100% steam for ~96 hours at ~1000.degree. F. (~538.degree. C.)
Example 3
Alpha Testing
[0044] MTG reactions are typically catalyzed over acid sites. The
acidity of the catalyst can tend to decrease with time on stream in
the MTG reactor, perhaps due to the effect of hydrothermal
dealumination of the zeolite. In order to assess the ability of the
catalyst to withstand the hydrothermal stress in the MTG reactor,
the steaming conditions in the MTG reactor were simulated by a
hydrothermal treatment in a laboratory reactor. The acidity of the
catalysts was then measured by its n-hexane cracking activity
(alpha test).
[0045] The n-hexane cracking activity, expressed as alpha value,
can be a measure for the acidity of the catalyst. Alpha value is
defined as the ratio of the first order rate constant for n-hexane
cracking, relative to a silica-alumina standard, and can be
determined using the following formula:
.alpha.=A*ln(1-X)/.tau.
where: [0046] A: includes the reference rate constant & unit
conversion.apprxeq.-1.043 [0047] X: fractional conversion [0048]
.tau.: residence time=wt/(.rho.*F) [0049] .rho.: packing density
[g/cm.sup.3] [0050] F: gas flow rate [cm.sup.3/min] [0051] wt:
catalyst weight [g]
[0052] The flow rate was adjusted to maintain a conversion between
5% and 25%. Four data points were measured at .about.4, .about.11,
.about.18, and .about.25 minutes. The alpha value was the relative
first order rate constant at .about.18 minutes.
[0053] Prior to the alpha test, samples were steamed in .about.100%
H.sub.2O atmosphere for .about.96 hours at .about.1000.degree. F.
(.about.538.degree. C.). The alpha activity (value) was normalized
by the nominal amount of zeolite used in the preparation of the
extrudate. The results are shown in Table 1 above and FIG. 1 and
demonstrate that the reference catalyst containing alumina A
exhibited a relatively low alpha value (18), while the catalyst
extrudate containing alumina B exhibited a significantly higher
alpha value (47). It was surprising that the replacement of the
standard alumina binder with a different type of alumina binder
resulted in a dramatic increase in alpha activity (value) after
steaming.
Example 4
Microporous Surface Area
[0054] The MTG reaction can tend to take place inside the zeolite
micropores. It can, therefore, be beneficial to improve/maximize
the zeolitic micropore volume in order to achieve maximum MTG
activity. Samples selected of Catalysts A and B were heated under
vacuum (e.g., at most 10.sup.-4 atm, corresponding to at most 10
Pa, or alternately at most 10.sup.-5 atm, corresponding to at most
1 Pa) for .about.4 hours at .about.350.degree. C. prior to
measurement of the micropore surface are by N.sub.2-BET. The
micropore surface areas were normalized by the zeolite content
present in Catalysts A and B, and the results are shown in Table 1
above and FIG. 2. It can be seen that Catalyst B exhibited a higher
microporosity, compared with the reference Catalyst A containing a
standard alumina binder. Since the acid sites responsible for MTG
activity are believed to be located inside the zeolite micropores,
this result indicated an advantage of Catalyst B in an MTG
application, relative to the standard alumina binder in Catalyst A.
The result was surprising, because binder particles can typically
be larger than the opening of the microchannels of the zeolite, and
penetration of binder into the zeolite micropores was hence not
anticipated. Moreover, blockage of zeolite micropores by binder
located at the pore mouth of the microchannels was not expected to
occlude zeolite micropore volume in a zeolite with
three-dimensional pore structure, as in MFI. It was thus not
obvious that changing the type of alumina binder would result in an
increase in micropore surface area.
Example 5
Diffusivity for 2,2-Dimethylbutane
[0055] The porosity of a zeolite can play a role in product
selectivity and/or coke formation in reactions involving the
zeolite. Fast diffusion of reactants into and of products out of
zeolite micropores can be desirable to obtain the desired product
composition and/or to prevent coke formation. Samples of Catalysts
A and B were calcined in air for .about.6 hours at
.about.1000.degree. F. (.about.538.degree. C.) prior to measurement
of the diffusivity of 2,2-dimethylbutane (2,2-DMB). The diffusivity
was calculated from the rate of 2,2-DMB uptake and the amount of
hexane uptake using the following formula:
D/r.sup.2=k*(2,2-DMB uptake rate/hexane uptake)
where [0056] D/r.sup.2: diffusivity [10.sup.-6 sec.sup.-1] [0057]
2,2-DMB uptake rate: [mg/g/min.sup.0.5] [0058] Hexane uptake:
[mg/g] [0059] k: proportionality constant
[0060] Hexane and 2,2-DMB uptakes were measured in two separate
experiments using a microbalance. Prior to hydrocarbon adsorption,
about 50 mg of the particular catalyst sample was heated in air for
.about.30 minutes to .about.500.degree. C. in order to remove
moisture and hydrocarbon/coke impurities. For hexane adsorption,
the particular sample was cooled to .about.90.degree. C. and
subsequently exposed to a flow of .about.100 mbar hexane in
nitrogen at .about.90.degree. C. for .about.40 minutes. For 2,2-DMB
adsorption, the particular sample was cooled to .about.120.degree.
C. after the air calcination step and exposed to a
2,2-dimethylbutane pressure of .about.60 torr (.about.8 kPa) for
.about.30 minutes. The results are shown in Table 1 above and FIG.
2. It can be seen that Catalyst B exhibited higher 2,2-DMB uptake
than Catalyst A. The formulation of a zeolite into an extrudate
with a binder can result in the blockage or narrowing of the pore
mouth. The higher diffusivity of the preferred catalyst B suggested
a larger degree of unobstructed zeolite channels and pore openings.
The preferred alumina binder B appeared to have less negative
interactions with the active zeolite component. It was inventive to
design an extrudate that would display these favorable properties
with an alumina binder.
Example 6
Mesoporosity
[0061] Mesoporosity is a property that can be beneficial to the
diffusion of reactants to the zeolite surface and to the release of
products away from the zeolite surface. Mesoporosity is defined
herein as pores having diameters between about 2 nm and about 50
nm, and can be measured from the hysteresis of the N.sub.2-BET.
Larger pores can allow faster transport of reactants and products
to and from the zeolite surface. FIG. 4 shows the pore size
distribution for the two Catalysts A and B after calcination for
.about.6 hours in air at .about.1000.degree. F. (.about.538.degree.
C.). Both samples, as calcined, displayed a maximum in the pore
size distribution curve at around 20-25 nm. However, Catalyst A
exhibited a pronounced shoulder extending from the maximum towards
narrower pores down to about 6 nm. Catalyst B displayed much less
porosity in the regime between 6 nm and the maximum of the pore
size distribution curve. From the N.sub.2-pore size distribution
curve, it was believed that Catalyst B might have slightly enhanced
diffusion properties relative to sample A.
[0062] Table 2 compares the mesopore volume in the pore size range
from 3-10 nm pore diameter with the total mesopore volume for the
two catalysts A and B after calcination for .about.6 hours in air
at .about.1000.degree. F. (.about.538.degree. C.). Mesopore volumes
were determined from the integrals of the PSD curve shown in FIG. 4
within the ranges indicated.
TABLE-US-00002 TABLE 2 Mesopore volumes for Catalysts A and B after
calcination Fraction of small mesopore volume (<10 nm), calcined
Small Total pore volume pore volume Fraction of (range in nm) Pore
volume (range in nm) mesopores Cat ml/g (range in nm) ml/g <10
nm A 0.164 (3-10) 0.265 (10-49) 0.429 (3-49) 0.38 B 0.036 (3-10)
0.230 (10-43) 0.266 (3-43) 0.14
[0063] From Table 2, it can be seen that the fraction of small
mesopores ranging from 3-10 nm relative to the total measured
mesopore volume was .about.14% for Catalyst B and .about.38% for
Catalyst A.
[0064] FIG. 5 shows the pore size distribution for Catalysts A and
B after steaming for .about.6 hours at .about.1000.degree. F.
(.about.538.degree. C.) in .about.100% H.sub.2O atmosphere.
Catalyst A showed a maximum around 21 nm in the pore size
distribution curve, while Catalyst B had its maximum shifted to
larger pore diameters at around 34 nm.
[0065] Table 3 compares the mesopore volumes in the pore size range
below and above 21 nm for Catalysts A and B after steaming for
.about.6 hours at .about.1000.degree. F. (.about.538.degree. C.) in
.about.100% H.sub.2O atmosphere. Mesopore volumes were determined
from the integrals of the PSD curve shown in FIG. 5 within the
ranges indicated.
TABLE-US-00003 TABLE 3 Mesopore volumes for Catalysts A and B after
steaming Fraction of large mesopore volume (>21 nm), steamed 96
h 1000 F. Total Pore volume Pore volume pore volume Fraction of
(range in nm) (range in nm) (range in nm) mesopores Cat ml/g ml/g
ml/g >21 nm A 0.274 (3-21) 0.142 (21-44) 0.416 (3-44) 0.34 B
0.091 (3-21) 0.345 (21-97) 0.436 (3-97) 0.79
[0066] From Table 3, it can be seen that Catalyst B displayed a
larger pore volume in the range above 21 nm than Catalyst B. The
fraction of relatively large mesopores (pore diameter above 21 nm)
was .about.79% for Catalyst B, compared to .about.34% for Catalyst
A.
[0067] While the present invention has been described and
illustrated by reference to particular embodiments, those of
ordinary skill in the art will appreciate that the invention lends
itself to variations not necessarily illustrated herein. For this
reason, then, reference should be made solely to the appended
claims for purposes of determining the true scope of the present
invention.
* * * * *