U.S. patent application number 10/616058 was filed with the patent office on 2004-06-03 for process for converting oxygenates to olefins using molecular sieve catalysts comprising desirable carbonaceous deposits.
Invention is credited to Kuechler, Keith H., Lattner, James Richardson, Skouby, David C., Sun, Hsiang-Ning, Vaughn, Stephen Neil.
Application Number | 20040105787 10/616058 |
Document ID | / |
Family ID | 25391819 |
Filed Date | 2004-06-03 |
United States Patent
Application |
20040105787 |
Kind Code |
A1 |
Lattner, James Richardson ;
et al. |
June 3, 2004 |
Process for converting oxygenates to olefins using molecular sieve
catalysts comprising desirable carbonaceous deposits
Abstract
The present invention relates to methods for selectively
converting oxygenates to light olefins, preferably ethylene and
propylene, in which desirable carbonaceous deposits are maintained
on a total reaction volume of catalyst by totally regenerating only
a portion of the total reaction volume of catalyst and mixing the
regenerated portion with the unregenerated total reaction volume of
catalyst.
Inventors: |
Lattner, James Richardson;
(Seabrook, TX) ; Sun, Hsiang-Ning; (Houston,
TX) ; Vaughn, Stephen Neil; (Kingwood, TX) ;
Kuechler, Keith H.; (Friendswood, TX) ; Skouby, David
C.; (Flanders, NJ) |
Correspondence
Address: |
EXXONMOBIL CHEMICAL COMPANY
P O BOX 2149
BAYTOWN
TX
77522-2149
US
|
Family ID: |
25391819 |
Appl. No.: |
10/616058 |
Filed: |
July 9, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10616058 |
Jul 9, 2003 |
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09414002 |
Oct 7, 1999 |
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09414002 |
Oct 7, 1999 |
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08887766 |
Jul 3, 1997 |
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6023005 |
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Current U.S.
Class: |
422/129 |
Current CPC
Class: |
C07C 1/20 20130101; Y02P
20/584 20151101; B01J 29/90 20130101; C07C 2529/85 20130101; B01J
29/85 20130101; B01J 38/30 20130101; Y02P 30/42 20151101; Y02P
30/40 20151101; Y02P 30/20 20151101; C07C 1/20 20130101; C07C 11/02
20130101 |
Class at
Publication: |
422/129 |
International
Class: |
B01J 010/02 |
Claims
We claim:
1. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst under conditions effective to
produce a stream comprising C.sub.2-C.sub.3 olefins, wherein said
total reaction volume comprises desirable carbonaceous deposits
which render said catalyst more selective to C.sub.2-C.sub.3
olefins than in the absence of said desirable carbonaceous
deposits; and, wherein, upon accumulation of undesirable
carbonaceous deposits effective to interfere with catalyst
activity, said desirable carbonaceous deposits are maintained on
said molecular sieve catalyst by a process comprising: separating
said total reaction volume of molecular sieve catalyst into a
portion and a remainder; treating said portion with a regeneration
medium under conditions effective to remove said undesirable
carbonaceous deposits, forming a regenerated portion comprising in
the range of from about 0 wt % to a regenerated amount of
carbonaceous deposits; and, mixing said regenerated portion with
said remainder, wherein said regenerated amount of carbonaceous
deposits comprises an amount sufficient, upon said mixing, to
produce a regenerated total reaction volume comprising said
desirable carbonaceous deposits.
2. The method of claim 1 wherein said regenerated amount of
carbonaceous deposits comprises an amount of about 0.5 wt % or less
of said regenerated portion.
3. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst under conditions effective to
produce a stream comprising C.sub.2-C.sub.3 olefins, wherein said
total reaction volume comprises desirable carbonaceous deposits
which render said catalyst more selective to C.sub.2-C.sub.3
olefins than in the absence of said desirable carbonaceous
deposits; and, wherein, upon accumulation of greater than about 1.5
wt % carbonaceous deposits, said desirable carbonaceous deposits
are maintained on said molecular sieve catalyst by a process
comprising: separating said total reaction volume of molecular
sieve catalyst into a portion and a remainder; treating said
portion with a regeneration medium under conditions effective form
a regenerated portion comprising in the range of from about 0 wt %
to about 0.5 wt % carbonaceous deposits; and, mixing said
regenerated portion with said remainder) wherein said regenerated
amount of carbonaceous deposits comprises an amount sufficient,
upon said mixing, to produce a regenerated total reaction volume
comprising said desirable carbonaceous deposits.
4. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst under conditions effective to
produce a stream comprising C.sub.2-C.sub.3 olefins, wherein said
total reaction volume comprises desirable carbonaceous deposits
which render said catalyst more selective to C.sub.2-C.sub.3
olefins than in the absence of said desirable carbonaceous
deposits; and, wherein, upon accumulation of greater than about 1.5
wt % carbonaceous deposits, said desirable carbonaceous deposits
are maintained on said molecular sieve catalyst by a process
comprising: separating said total reaction volume of molecular
sieve catalyst into a portion and a remainder; treating said
portion with a regeneration medium under conditions effective to
form a regenerated portion comprising in the range of from about 0
wt % to a regenerated amount of carbonaceous deposits; and, mixing
said regenerated portion with said remainder, wherein said
regenerated amount of carbonaceous deposits comprise an amount
sufficient, upon said mixing, to produce a regenerated total
reaction volume comprising said desirable carbonaceous
deposits.
5. The method of claim 1 wherein said desirable carbonaceous
deposits comprise an amount in the range of from about 2 wt % to
about 30 wt % of said total reaction volume of molecular sieve
catalyst.
6. The method of claim 2 wherein said desirable carbonaceous
deposits comprise an amount in the range of from about 2 wt % to
about 30 wt % of said total reaction volume of molecular sieve
catalyst.
7. The method of claim 3 wherein said desirable carbonaceous
deposits comprise an amount in the range of from about 2 wt % to
about 30 wt % of said total reaction volume of molecular sieve
catalyst.
8. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst under conditions effective to
produce a stream comprising C.sub.2-C.sub.3 olefins, wherein said
total reaction volume comprises desirable carbonaceous deposits in
the range of from about 2 wt % to about 30 wt %; and, wherein, upon
accumulation of greater than about 1.5 wt/a carbonaceous deposits,
said desirable carbonaceous deposits are maintained on said
molecular sieve catalyst by a process comprising: separating said
total reaction volume of molecular sieve catalyst into a portion
and a remainder; treating said portion with a regeneration medium
under conditions effective form a regenerated portion comprising in
the range of from about 0 wt % to about 0.5 wt % carbonaceous
deposits; and, mixing said regenerated portion with said remainder
to produce a regenerated total reaction volume comprising said
desirable carbonaceous deposits in the range of from about 2 wt %
to about 30 wt %.
9. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst under conditions effective to
produce a stream comprising light olefins, wherein said total
reaction volume comprises desirable carbonaceous deposits which
render said catalyst more selective to light olefins than in the
absence of said desirable carbonaceous deposits, and wherein said
molecular sieve catalyst is selected from the group consisting of:
zeolites having a structural type selected from the group
consisting of AEI, AFT, APC, ATN, ATT, ATV, AWW, BIK, CAS, CHA,
CHI, DAC, DDR, EDI, ERI, GOO, KFI, LEV, LOV, LTA, MON, PAU, PHI,
RHO, ROG, THO, MFI, MEL, MTW, EUO, MTT, HEU, FER, AFO, AEL, TON,
and combinations thereof; and, silicoaluminophosphate catalysts
(SAPO's) selected from the group consisting of SAPO-34, SAPO-17,
SAPO-18, substituted SAPO's comprising MeAPSO's, and combinations
thereof; and, wherein, upon accumulation of undesirable
carbonaceous deposits effective to interfere with catalyst
activity, said desirable carbonaceous deposits are maintained on
said molecular sieve catalyst by a process comprising: separating
said total reaction volume of molecular sieve catalyst into a
portion and a remainder; treating said portion with a regeneration
medium under conditions effective to remove said undesirable
carbonaceous deposits, forming a regenerated portion comprising in
the range of from about 0 wt % to a regenerated amount of
carbonaceous deposits; and, mixing said regenerated portion with
said remainder, wherein said regenerated amount of carbonaceous
deposits comprises an amount sufficient, upon said mixing to
produce a regenerated total reaction volume comprising said
desirable carbonaceous deposits.
10. The method of claim 2 wherein said molecular sieve catalyst is
selected from the group consisting of: zeolites having a structural
type selected from the group consisting of AEL AFT, APC, ATN, ATT,
ATV, AWW, BIK, CAS, CHA, CHI, DAC, DDR, EDI, ERI, GOO, KFI, LEV,
LOV, LTA, MON, PAU, PHI, RHO, ROG, THO, MFI, MEL, MTW, EUO, MTT,
HEU, FER, AFO, AEL, TON, and combinations thereof; and,
silicoaluminophosphate catalysts (SAPO's) selected from the group
consisting of SAPO-34, SAPO-17, SAPO-18, substituted SAPO's
comprising MeAPSO's, and combinations thereof.
11. The method of claim 3 wherein said molecular sieve catalyst is
selected from the group consisting of: zeolites having a structural
type selected from the group consisting of AEI, AFT, APC, ATN, ATT,
ATV, AWW, BIK, CAS, CHA, CHI, DAC, DDR, EDI, ERI, GOO, KFI, LEV,
LOV, LTA, MON, PAU, PHI, RHO, ROG, THO, MFI, MEL, MTW, EUO, MTT,
HEU, FER, AFO, AEL, TON, and combinations thereof; and,
silicoaluminophosphate catalysts (SAPO's) selected from the group
consisting of SAPO-34, SAPO-17, SAPO-18, substituted SAPO's
comprising MeAPSO's, and combinations thereof.
12. The method of claim 4 wherein said molecular sieve catalyst is
selected from the group consisting of: zeolites having a structural
type selected from the group consisting of AEI, AFT, APC, ATN, ATT,
ATV, AWW, BIK, CAS, CHA, CHI, DAC, DDR, EDI, ERI, GOO, KFI, LEV,
LOV, LTA, MON, PAU, PHI, RHO, ROG, THO, MFI, MEL, MTW, EUO, MTT,
HEU, FER, AFO, AEL, TON, and combinations thereof; and,
silicoaluminophosphate catalysts (SAPO's) selected from the group
consisting of SAPO-34, SAPO-17, SAPO-18, substituted SAPO's
comprising MeAPSO's, and combinations thereof.
13. The method of claim 1 wherein said molecular sieve catalyst is
selected from the group consisting of ZSM-5, ZSM-34, erionite,
chabazite, and SAPO-34.
14. The method of claim 2 wherein said molecular sieve catalyst is
selected from the group consisting of ZSM-5, ZSM-34, erionite,
chabazite, and SAPO-34.
15. The method of claim 3 wherein said molecular sieve catalyst is
selected from the group consisting of ZSM-5, ZSM-34, erionite,
chabazite, and SAPO-34.
16. The method of claim 4 wherein said molecular sieve catalyst is
selected from the group consisting of ZSM-5, ZSM-34, erionite,
chabazite and SAPO-34.
17. The method of claim 1 wherein said molecular sieve catalyst is
selected from the group consisting of small pore and medium pore
molecular sieve catalysts.
18. The method of claim 2 wherein said molecular sieve catalyst is
selected from the group consisting of small pore and medium pore
molecular sieve catalysts.
19. The method of claim 3 wherein said molecular sieve catalyst is
selected from the group consisting of small pore and medium pore
molecular sieve catalysts.
20. The method of claim 4 wherein said molecular sieve catalyst is
selected from the group consisting of small pore and medium pore
molecular sieve catalysts.
21. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst other than ZSM-5 under
conditions effective to produce a stream comprising light olefins,
wherein said total reaction volume comprises desirable carbonaceous
deposits which render said catalyst more selective to light olefins
than in the absence of said desirable carbonaceous deposits; and,
wherein upon accumulation of undesirable carbonaceous deposits
effective to interfere with catalyst activity, said desirable
carbonaceous deposits are maintained on said molecular sieve
catalyst by a process comprising: separating said total reaction
volume of molecular sieve catalyst into a portion and a remainder;
treating said portion with a regeneration medium under conditions
effective to remove said undesirable carbonaceous deposits, forming
a regenerated portion comprising in the range of from about 0 wt %
to a regenerated amount of carbonaceous deposits; and, mixing said
regenerated portion with said remainder, wherein said regenerated
amount of carbonaceous deposits comprises an amount sufficient,
upon said mixing, to produce a regenerated total reaction volume
comprising said desirable carbonaceous deposits.
22. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst comprising SAPO-34 under
conditions effective to produce a stream comprising C.sub.2-C.sub.3
olefins, wherein said total reaction volume comprises desirable
carbonaceous deposits which render said catalyst more selective to
C.sub.2-C.sub.3 olefins than in the absence of said desirable
carbonaceous deposits; and, wherein, upon accumulation of
undesirable carbonaceous deposits effective to interfere with
catalyst activity, said desirable carbonaceous deposits are
maintained on said molecular sieve catalyst by a process
comprising: separating said total reaction volume of molecular
sieve catalyst into a portion and a remainder; treating said
portion with a regeneration medium under conditions effective to
remove said undesirable carbonaceous deposits, forming a
regenerated portion comprising in the range of from about 0 wt % to
a regenerated amount of carbonaceous deposits; and, mixing said
regenerated portion with said remainder, wherein said regenerated
amount of carbonaceous deposits comprises an amount sufficient,
upon said mixing, to produce a regenerated total reaction volume
comprising said desirable carbonaceous deposits.
23. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst comprising SAPO-34 under
conditions effective to produce a stream comprising C.sub.2-C.sub.3
olefins, wherein said total reaction volume comprises desirable
carbonaceous deposits in the range of from about 2 wt % to about 30
wt %; and, wherein, upon accumulating greater than about 1.5 wt %
carbonaceous deposits, said desirable carbonaceous deposits are
maintained on said molecular sieve catalyst by a process
comprising: separating said total reaction volume of molecular
sieve catalyst into a portion and a remainder; treating said
portion with a regeneration medium under conditions effective form
a regenerated portion comprising in the range of from about 0 wt %
to about 0.5 wt % carbonaceous deposits; and, mixing said
regenerated portion with said remainder to produce a regenerated
total reaction volume comprising said desirable carbonaceous
deposits in the range of from about 2 wt % to about 30 wt %.
24. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst comprising SAPO-17 under
conditions effective to produce a stream comprising C.sub.2-C.sub.3
olefins, wherein said total reaction volume comprises desirable
carbonaceous deposits which render said catalyst more selective to
C.sub.2-C.sub.3 olefins than in the absence of said desirable
carbonaceous deposits; and, wherein, upon accumulating undesirable
carbonaceous deposits effective to interfere with catalyst
activity, said desirable carbonaceous deposits are maintained on
said molecular sieve catalyst by a process comprising: separating
said total reaction volume of molecular sieve catalyst into a
portion and a remainder; treating said portion with a regeneration
medium under conditions effective to remove said undesirable
carbonaceous deposits, forming a regenerated portion comprising in
the range of from about 0 wt % to a regenerated amount of
carbonaceous deposits; and, mixing said regenerated portion with
said remainder, wherein said regenerated amount of carbonaceous
deposits comprises an amount sufficient, upon said mixing, to
produce a regenerated total reaction volume comprising said
desirable carbonaceous deposits.
25. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst comprising SAPO-17 under
conditions effective to produce a stream comprising C.sub.2-C.sub.3
olefins, wherein said total reaction volume comprises desirable
carbonaceous deposits in the range of from about 2 wt % to about 30
wt %; and, wherein, upon accumulation of greater than about 1.5 wt
% carbonaceous deposits, said desirable carbonaceous deposits are
maintained on said molecular sieve catalyst by a process
comprising: separating said total reaction volume of molecular
sieve catalyst into a portion and a remainder; treating said
portion with a regeneration medium under conditions effective form
a regenerated portion comprising in the range of from about 0 wt %
to about 0.5 wt % carbonaceous deposits; and, mixing said
regenerated portion with said remainder to produce a regenerated
total reaction volume comprising said desirable carbonaceous
deposits in the range of from about 2 wt % to about 30 wt %.
26. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst comprising SAPO-18 under
conditions effective to produce a stream comprising C.sub.2-C.sub.3
olefins, wherein said total reaction volume comprises desirable
carbonaceous deposits which render said catalyst more selective to
C.sub.2-C.sub.3 olefins than in the absence of said desirable
carbonaceous deposits; and, wherein, upon accumulation of
undesirable carbonaceous deposits effective to interfere with
catalyst activity, said desirable carbonaceous deposits are
maintained on said molecular sieve catalyst by a process
comprising: separating said total reaction volume of molecular
sieve catalyst into a portion and a remainder; treating said
portion with a regeneration medium under conditions effective to
remove said undesirable carbonaceous deposits, forming a
regenerated portion comprising in the range of from about 0 wt % to
a regenerated amount of carbonaceous deposits; and, mixing said
regenerated portion with said remainder, wherein said regenerated
amount of carbonaceous deposits comprises an amount sufficient,
upon said mixing, to produce a regenerated total reaction volume
comprising said desirable carbonaceous deposits.
27. A method for treating a molecular sieve catalyst comprising:
contacting a feed comprising oxygenates with a total reaction
volume of a molecular sieve catalyst comprising SAPO-18 under
conditions effective to produce a stream comprising C.sub.2-C.sub.3
olefins, wherein said total reaction volume comprises desirable
carbonaceous deposits in the range of from about 2 wt % to about 30
wt %; and, wherein, upon accumulating greater than about 1.5 we/o
carbonaceous deposits, said desirable carbonaceous deposits are
maintained on said molecular sieve catalyst by a process
comprising: separating said total reaction volume of molecular
sieve catalyst into a portion and a remainder; treating said
portion with a regeneration medium under conditions effective form
a regenerated portion comprising in the range of from about 0 wt %
to about 0.5 wt % carbonaceous deposits; and, mixing said
regenerated portion with said remainder to produce a regenerated
total reaction volume comprising said desirable carbonaceous
deposits in the range of from about 2 wt % to about 30 wt %.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to methods for selectively
converting oxygenates to light olefins, preferably ethylene and
propylene, in which desired carbonaceous deposits are maintained on
a total reaction volume of catalyst by totally regenerating only a
portion of the total reaction volume of catalyst and mixing the
regenerated portion with the unregenerated total reaction volume of
catalyst.
BACKGROUND OF THE INVENTION
[0002] Light olefins (defined as "ethylene, propylene, and
butylene") serve as feeds for the production of numerous chemicals.
Light olefins traditionally are produced by petroleum cracking.
Because of the limited supply and/or the high cost of petroleum
sources, the cost of producing olefins from petroleum sources has
increased steadily.
[0003] Alternative feedstocks for the production of light olefins
are oxygenates, such as alcohols, particularly methanol, dimethyl
ether, and ethanol. Alcohols may be produced by fermentation, or
from synthesis gas derived from natural gas, petroleum liquids,
carbonaceous materials, including coal, recycled plastics,
municipal wastes, or any organic material. Because of the wide
variety of sources, alcohol, alcohol derivatives, and other
oxygenates have promise as an economical, non-petroleum source for
olefin production.
[0004] The catalysts used to promote the conversion of oxygenates
to olefins are molecular sieve catalysts. Because ethylene and
propylene are the most sought after products of such a reaction,
research has focused on what catalysts are most selective to
ethylene and/or propylene, and on methods for increasing the
selectivity of molecular sieve catalysts to ethylene and/or
propylene. The selectivity of molecular sieve catalysts to ethylene
and propylene is known to increase if the level of coke on the
total reaction volume of molecular sieve catalyst is maintained in
the range of from about 2 wt % to about 30 wt %. Some have
suggested maintaining this desired level of coke by removing all or
a portion of the total reaction volume of catalyst, partially
regenerating the catalyst so removed, and returning the partially
regenerated catalyst to the reactor. However, partial regeneration
may not result in maximum selectivity of the catalyst to light
olefins.
[0005] Methods are needed which will maintain a desired level of
coking on molecular sieve catalysts during the conversion of
oxygenates to olefins while maintaining maximum activity of the
catalyst.
SUMMARY OF THE INVENTION
[0006] The present invention provides a method for treating a
molecular sieve catalyst comprising: contacting a feed comprising
oxygenates with a total reaction volume of a molecular sieve
catalyst under conditions effective to produce a stream comprising
C.sub.2-C.sub.3 olefins, wherein said total reaction volume
comprises desirable carbonaceous deposits which render said
catalyst more selective to C.sub.2-C.sub.3 olefins than in the
absence of said desirable carbonaceous deposits; and wherein, upon
accumulation of undesirable carbonaceous deposits effective to
interfere with catalyst activity, said desirable carbonaceous
deposits are maintained on said molecular sieve catalyst by a
process comprising: separating said total reaction volume of
molecular sieve catalyst into a portion and a remainder; treating
said portion with a regeneration medium under conditions effective
to remove said undesirable carbonaceous deposits, forming a
regenerated portion comprising in the range of from about 0 wt % to
a regenerated amount of carbonaceous deposits; and, mixing said
regenerated portion with said remainder, wherein said regenerated
amount of carbonaceous deposits comprises an amount sufficient,
upon said mixing, to produce a regenerated total reaction volume
comprising said desirable carbonaceous deposits.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a diagram of a preferred embodiment of a high
velocity fluid bed reactor with catalyst recirculation for use in
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The conversion of oxygenates to light olefins is catalyzed
by various molecular sieve catalysts. Due to the high temperatures
required during the conversion process, carbonaceous deposits known
as "coke" unavoidably form on the surface of the molecular sieve
catalyst. In order to avoid a significant reduction in catalyst
activity, the catalyst must be regenerated by burning off coke
deposits.
[0009] One goal during the conversion of oxygenates to olefins is
to maximize the production of light olefins, preferably ethylene
and propylene, and to minimize the product of methane, ethane,
propane, and C.sub.5+ materials. The present invention uses the
coke that unavoidably deposits on the catalyst to achieve this goal
by allowing "desirable carbonaceous deposits" to accumulate on the
molecular sieve catalyst while removing undesirable carbonaceous
deposits.
[0010] One method that has been suggested to maintain desirable
carbonaceous deposits on the catalyst is to only partially
regenerate some or all of the total reaction volume of molecular
sieve catalyst. Without limiting the present invention to a
particular theory, it is believed that only partially regenerating
a portion or only partially regenerating all of a total reaction
volume of coked molecular sieve catalyst has a serious drawback.
Coke that is produced during the conversion of oxygenates to
olefins is known to deposit both on the surface and in the
"micropores" of molecular sieve catalysts. The reactions that
selectively convert oxygenates to ethylene and propylene occur in
the micropores of the molecular sieve catalyst. It is relatively
difficult for a regeneration medium (usually oxygen) to access the
micropores. Because of this, coke that builds up in the micropores
is more difficult to remove during the regeneration process.
Partial regeneration most likely does not remove the coke from the
micropores of the catalyst, which result in an adverse impact on
the selectivity of the catalyst to ethylene and propylene.
[0011] The present invention maintains "desirable carbonaceous
deposits" on the catalyst by removing only a portion of the total
reaction volume of coked molecular sieve catalyst and totally
regenerating only that portion of catalyst. Total regeneration is
believed to remove coke from both the micropores and from the less
selective surface areas of the regenerated portion of the catalyst.
When the regenerated portion of catalyst is mixed with the
unregenerated remainder of the catalyst, the result is the
maintenance of desirable carbonaceous deposits blocking less
selective surface areas in the unregenerated portion of the
catalyst, and an increase in the sites available to selectively
convert oxygenates to light olefins (micropore surface area) in the
regenerated portion of the catalyst.
[0012] As used herein, the term "desirable carbonaceous deposits"
is defined to comprise an amount of at least about 2 wt %
carbonaceous deposits, preferably in the range of from about 2 wt %
to about 30 wt % carbonaceous deposits, based on the weight of the
total reaction volume of coked catalyst. "Desirable carbonaceous
deposits"--even if they comprise over 30 wt % of the total reaction
volume of molecular sieve catalyst--are carbonaceous deposits which
primarily block portions of the surface of the catalyst that are
not selective to the production of C.sub.2-C.sub.3 olefins.
[0013] Substantially any small or medium pore molecular sieve
catalysts and equivalents thereof may be used in to the present
invention. "Small pore molecular sieve" catalysts are deed as
catalysts with pores having a diameter of less than about 5.0
Angstroms. Medium pore molecular sieve catalysts are defined as
catalysts with pores having a diameter of in the range of from
about 5 and 10 Angstroms. "Equivalents thereof" is defined to refer
to catalysts having a pore size that performs substantially the
same function in substantially the same way to achieve
substantially the same result as catalysts having the foregoing
diameter or pore size.
[0014] One group of suitable molecular sieve catalysts is the
zeolite group. Several types of zeolites exist, each of which
exhibit different properties and different utilities. Structural
types of small pore zeolites that are suitable for use in the
present invention with varying levels of effectiveness include, but
are not necessarily limited to AEI, AFT, APC, ATN, AUT, ATV, AWW,
BIK, CAS, CHA, CHI, DAC, DDR, EDI, ERI, GOO, KFI, LEV, LOV, LTA,
MON, PAU, PHI, RHO, ROG, and THO and substituted examples of these
structural types, as described in W. M. Meier and D. H. Olsen,
Alias of Zeolite Structural Types (Butterworth Heineman-3rd ed.
1997), incorporated herein by reference. Preferred zeolite
catalysts include, but are not necessarily limited to, ZSM-5,
ZSM-34, erionite, and chabazite.
[0015] Silicoaluminophosphates ("SAPO's") are another group of
molecular sieve catalysts that are useful in the invention. SAPO's
have a three-dimensional microporous crystal framework of
PO.sub.2.sup.+, AlO.sub.2.sup.-, and SiO.sub.2 tetrahedral units.
Suitable SAPO's for use in the invention include, but are not
necessarily limited to SAPO-34, SAPO-17, and SAPO-18. A preferred
SAPO is SAPO-34, which may be synthesized according to U.S. Pat.
No. 4,440,871, incorporated herein by reference, and Zeolites, Vol.
17, pp. 512-522 (1996), incorporated herein by reference. SAPO's
with added substituents also may be useful in the present
invention. These substituted SAPO's form a class of molecular
sieves known as "MeAPSO's." Substituents may include, but are not
necessarily limited to nickel, cobalt, strontium, barium, and
calcium.
[0016] Structural types of medium pore molecular sieves useful in
the present invention include, but are not necessarily limited to,
MFI, MEL, MTW, EUO, MTT, HEU, FER, AFO, AEL, TON, and substituted
examples of these structural types, as described in the Atlas of
Zeolite Types, previously incorporated herein by reference.
[0017] The process for converting oxygenates to olefins employs an
organic starting material (feedstock) preferably comprising
"oxygenates." As used herein, the term "oxygenates" is defined to
include, but is not necessarily limited to aliphatic alcohols,
ethers, carbonyl compounds (aldehydes, ketones, carboxylic acids,
carbonates, and the like), and also compounds containing
hetero-atoms, such as, halides, mercaptans, sulfides, amines, and
mixtures thereof. The aliphatic moiety preferably should contain in
the range of from about 1-10 carbon atoms and more preferably in
the range of from about 14 carbon atoms. Representative oxygenates
include, but are not necessarily limited to, lower straight chain
or branched aliphatic alcohols, their unsaturated counterparts, and
their nitrogen, halogen and sulfur analogues. Examples of suitable
compounds include, but are not necessarily limited to: methanol;
ethanol; n-propanol; isopropanol; C.sub.4-C.sub.10 alcohols; methyl
ethyl ether; dimethyl ether; diethyl ether; di-isopropyl ether;
methyl mercaptan; methyl sulfide; methyl amine; ethyl mercaptan;
di-ethyl sulfide; di-ethyl amine; ethyl chloride; formaldehyde;
di-methyl carbonate; di-methyl ketone; acetic acid; n-alkyl amines,
n-alkyl halides, n-alkyl sulfides having n-alkyl groups of
comprising the range of from about 3 to about 10 carbon atoms; and
mixtures thereof. As used herein; the term "oxygenate" designates
only the organic material used as the feed. The total charge of
feed to the reaction zone may contain additional compounds, such as
diluents. Preferably, the oxygenate feedstock should be contacted
in the vapor phase in a reaction zone with the defined molecular
sieve catalyst at effective process conditions so as to produce the
desired olefins, i.e., an effective temperature, pressure, WHSV
(Weight Hourly Space Velocity) and, optionally, an effective amount
of diluent. Alternately, the process may be carried out in a liquid
or a mixed vapor/liquid phase. When the process is carried out in
the liquid phase or a mixed vapor/liquid phase, different
conversion rates and selectivities of feedstock-to-product may
result depending upon the catalyst and the reaction conditions.
[0018] The temperature employed in the conversion process may vary
over a wide range depending, at least in part, on the selected
catalyst. Although not limited to a particular temperature, best
results will be obtained if the process is conducted at
temperatures in the range of from about 200.degree. C. to about
700.degree. C., preferably in the range of from about 250.degree.
C. to about 600.degree. C., and most preferably in the range of
from about 300.degree. C. to about 500.degree. C. Lower
temperatures generally result in lower rates of reaction, and the
formation of the desired light olefin products may become markedly
slow. However, at higher temperatures, the process may not form an
optimum amount of light olefin products, and the coking rate may
become too high.
[0019] Light olefin products will form--although not necessarily in
optimum amounts--at a wide range of pressures, including but not
limited to autogeneous pressures and pressures in the range of from
about 0.1 kPa to about 100 MPa. A preferred pressure is in the
range of from about 6.9 kPa to about 34 MPA, most preferably in the
range of from about 48 kPa to about 0.34 MPA. The foregoing
pressures are exclusive of diluent, if any is present, and refer to
the partial pressure of the feedstock as it relates to oxygenate
compounds and/or mixtures thereof. Pressures outside of the stated
ranges may be used and are not excluded from the scope of the
invention. Lower and upper extremes of pressure may adversely
affect selectivity, conversion, coking rate, and/or reaction rate;
however, light olefins such as ethylene still may form.
[0020] The process should be continued for a period of time
sufficient to produce the desired olefin products. The reaction
time may vary from tenths of seconds to a number of hours. The
reaction time is largely determined by the reaction temperature,
the pressure, the catalyst selected, the weight hourly space
velocity, the phase (liquid or vapor), and the selected process
design characteristics.
[0021] A wide range of weight hourly space velocities (WHSV) for
the feedstock will function in the present invention. WHSV is
defined as weight feed (excluding diluent) per hour per weight of a
total reaction volume of molecular sieve catalyst (excluding inerts
and/or fillers). The WHSV generally should be in the range of from
about 0.01 hr.sup.-1 to about 500 hr.sup.-1, preferably in the
range of from about 0.5 hr.sup.-1 to about 300 hr.sup.-1, and most
preferably in the range of from about 0.1 hr.sup.-1 to about 200
hr.sup.-1.
[0022] One or more diluents may be fed to the reaction zone with
the oxygenates, such that the total feed mixture comprises diluent
in a range of from about 1 mol % to about 99 mol %. Diluents which
may be employed in the process include, but are not necessarily
limited to, helium, argon, nitrogen, carbon monoxide, carbon
dioxide, hydrogen, water, paraffins, other hydrocarbons (such as
methane), aromatic compounds, and mixtures thereof. Preferred
diluents are water and nitrogen.
[0023] A preferred embodiment of a reactor system for the present
invention is a circulating fluid bed reactor with continuous
regeneration, similar to a modern fluid catalytic cracker. Fixed
beds are not practical for the process because oxygenate to olefin
conversion is a highly exothermic process which requires several
stages with intercoolers or other cooling devices. The reaction
also results in a high pressure drop due to the production of low
pressure, low density gas.
[0024] Because the catalyst must be regenerated frequently, the
reactor should allow easy removal of a portion of the catalyst to a
regenerator, where the catalyst is subjected to a regeneration
medium, preferably a gas comprising oxygen, most preferably air, to
burn off coke from the catalyst, which restores the catalyst
activity. The conditions of temperature, oxygen partial pressure,
and residence time in the regenerator should be selected to achieve
a coke content on regenerated catalyst of less than about 0.5 wt %.
At least a portion of the regenerated catalyst should be returned
to the reactor.
[0025] It is important for the reactor to be designed such that a
relatively high average level of coke is maintained in the
reactor--an amount greater than about 1.5 wt %, preferably in the
range of from about 2 wt % to about 30 wt %, most preferably in the
range of from about 2 wt % to about 20 wt %. If the reactor is a
high velocity fluidized bed reactor (sometimes referred to as a
riser reactor), then a portion of the catalyst exiting the top of
the reactor must be returned to the reactor inlet. This is
different from a typical Fluid Catalytic Cracker (FCC) riser
reactor, where all or most of the catalyst exiting the top of the
reactor is sent to the regenerator. The return of coked catalyst
directly to the reactor, without regenerating the coked catalyst,
allows the average coke level in the reactor to build up to a
preferred level. By adjusting the ratio of the flow of the coked
catalyst between the regenerator and the reactor, a preferred level
of coking, or "desirable carbonaceous deposits," can be
maintained.
[0026] If the fluidized bed reactor is designed with low gas
velocities, below about 2 m/sec, then cyclones may be used to
return catalyst fines to the fluidized bed reaction zone. Such
reactors generally have high recirculation rates of solids within
the fluidized bed, which allows the coke level on the catalyst to
build to a preferred level. Desirable carbonaceous deposits are
maintained by withdrawing catalyst from the bed and regenerating
the catalyst in the manner described above, and then returning at
least a portion of this regenerated catalyst to the reactor.
[0027] A preferred embodiment of a riser reactor configuration for
use in the present invention is depicted in FIG. 1. A methanol feed
12 is at least partially vaporized in a preheater (not shown). The
methanol feed is mixed with regenerated catalyst 28 and coked
catalyst 22 at the bottom of the riser reactor 14. An inert gas
and/or steam may be used to dilute the methanol, lift the catalyst
streams 22 and 28, and keep pressure instrument lines clear of
catalyst. This inert gas and/or steam mixes with the methanol and
catalyst in the reactor 14. The reaction is exothermic, and the
preferred reaction temperature, in the range of from about
300.degree. C. to about 500.degree. C., is maintained by removing
heat. Heat can be removed by any suitable means, including but not
necessarily limited to cooling the reactor with a catalyst cooler
(not shown), feeding some of the methanol as a liquid, cooling the
catalyst feed to the reactor, or any combination of these
methods.
[0028] The reactor effluent 16, containing products, coked
catalyst, diluents, and unconverted feed, should flow to a
disengaging zone 18. In the disengaging zone 18, coked catalyst is
separated from the gaseous materials by means of gravity and/or
cyclone separators. A portion of the coked catalyst 22 is returned
to the reactor inlet. The portion of coked catalyst 22 to be
regenerated is first sent to a stripping zone 29, where steam or
other inert gas is used to recover adsorbed hydrocarbons from the
catalyst. Stripped spent coked catalyst 23 should flow to the
regenerator 24. The portion of the catalyst sent to the regenerator
24 should be contacted with a regeneration medium, preferably a gas
comprising oxygen 30, at temperatures, pressures, and residence
times that are capable of burning coke off of the catalyst and down
to a level of less than about 0.5 wt %. The preferred temperature
in the regenerator is in the range of from about 550.degree. C. to
about 700.degree. C., the preferred oxygen concentration in the gas
leaving the regenerator is in the range of from about 0.1 vol % to
about 5 vol %, and the preferred residence time is in the range of
from about 1 to about 100 minutes.
[0029] The burning off of coke is exothermic. The temperature may
be maintained at a suitable level by any acceptable method,
including but not limited to feeding cooler gas, cooling the
catalyst in the regenerator with a cat cooler 26, or a combination
of these methods.
[0030] The regenerated catalyst 28 is sent to the reactor 14, where
it mixes with the recirculated coked catalyst 22 and the methanol
feed 12. The regenerated catalyst 28 may be lifted to the reactor
14 by means of an inert gas, steam, or methanol vapor (not shown).
The process should repeat itself in a continuous or semi-continuous
manner. The hot reactor product gases 20 should be cooled, the
water byproduct condensed and collected, and the desired olefin
product gases recovered for further processing.
[0031] In order to determine the level of coke in the reactor and
in the regenerator, small samples of catalyst periodically may be
withdrawn from various points in the recirculating system for
measurement of carbon content. The reaction parameters may be
adjusted accordingly.
[0032] The following examples illustrate, but do not limit, the
present invention.
EXAMPLE 1
[0033] A continuous circulating fluid bed reactor was charged with
3200 g of catalyst, which was spray dried from a mixture of SAPO-34
powder (obtained from UOP, Des Plaines, Ill.) with alumina and clay
binders having an average particle size of 90-100 microns. In three
different tests, neat methanol was charged at a rate of 900
grams/hour and vaporized in a preheater. The vaporized feed was
mixed with 20,000 to 25,000 grams/hour of catalyst, and fed to a
reactor with a 1.02 cm (0.4 inch) inner diameter and a length of
6.71 meters (22 feet). About 268.21 Liters/hr (7 scf/hr) of
nitrogen was used to lift the catalyst and keep pressure
instruments clear of catalyst fines. The nitrogen mixed with the
methanol and catalyst in the reactor. The temperature in the
reactor was maintained at 450.degree. C. by means of electric
heaters. The effluent from the reactor flowed to a stripper, where
the catalyst was removed from the product gas. The catalyst was
contacted with nitrogen in the bottom of the stripper to recover
volatile hydrocarbons from the catalyst. The stripped catalyst was
sent to a regenerator, where the catalyst was contacted with a
mixture of nitrogen and air. The temperature in the regenerator was
maintained at 620.degree. C. with electric heaters, and the air
rate could be varied to adjust the coke level on the regenerated
catalyst. The catalyst from the regenerator was returned to the
reactor, where it mixed with the methanol feed. The process
repeated itself in a continuous manner. The hot reactor product
gases were cooled, and the water byproduct condensed and collected.
The hydrocarbon gases were separated from the water and analyzed by
GC. The flue gas from the regenerator was analyzed for oxygen,
carbon monoxide, and carbon dioxide, and the rate was measured in a
dry test meter. Small samples of catalyst were periodically
withdrawn from both the stripper and the regenerator for
measurement of carbon content. Based on these measurements, the
yield of products, including coke, were calculated.
[0034] In test 1, the air rate was set so that nearly all of the
carbon on the catalyst was removed during each pass through the
regenerator. The carbon content on the catalyst leaving the reactor
was 0.5 wt %, and the regenerator removed all but 0.2 wt % of this
carbon. The selectivity to ethylene was 10.8 wt % and the
selectivity to heavies and coke was 34.9 wt % and 14.3 wt %,
respectively.
[0035] In test 2, the air rate to the regenerator was reduced so
that all of the catalyst was only partially regenerated at each
pass. The carbon on the circulating catalyst increased, eventually
reaching a steady state such that carbon was removed at the same
rate that it was deposited. At this point, the carbon on catalyst
to the regenerator was 5.5%, and the carbon content of the catalyst
leaving the regenerator was 4.9%. The selectivity to ethylene
improved to 26.7%, and the selectivity to undesirable heavies
decreased to 17.90%. The coke yield remained relatively unchanged
at 13.6%. The methanol conversion was 91.3%, showing a decline in
the catalyst activity due to the coke on the catalyst.
[0036] In test 3, the methanol feed was stopped and the circulating
catalyst was allowed to be fully regenerated (down to 0.15 w/o
carbon). Then the air to the regenerator was stopped, the methanol
feed was reintroduced and coke was allowed to build up on the
catalyst without regeneration for about 5 hours. The carbon content
on the circulating catalyst after 5 hours was 5.8%. At this point,
the selectivity to ethylene had improved to 35.0%, the heavies
selectivity was further reduced to 13.4%, and the selectivity to
coke was reduced to 4.1%. The coke yield was calculated from
measurements of the carbon accumulation on the catalyst over the
previous hour on oil. The conversion at this point was 89.9%,
showing that the catalyst had roughly the same activity as the
catalyst in test 2.
[0037] Following test 3, the reactor was returned to the same
operating conditions as in test 1, and then test 2. The methanol
conversions and product yields essentially were the same as the
original yields in test 1 and 2 after a total of 150 hours on oil,
showing that the results were not simply the effect of catalyst
aging.
[0038] Column 4 represents a calculated product selectivity for a
commercial reactor using the present invention, based on the data
from Tests 1 and 3. Column 4 assumes that 10% of the methanol is
converted over freshly regenerated catalyst (selectivities
according to test I), and the remaining 90% of the methanol is
converted over coked catalyst (selectivities according to test 3).
The calculated selectivities are slightly worse than the results of
test 3, but still are significantly better than would be obtained
if the catalyst was only partially regenerated, as in test 2:
1 Test No. 1 2 3 4(calculated) Regeneration Complete Partial None
Complete Mode regeneration regeneration regeneration of all of the
of all of the of a portion catalyst catalyst of catalyst Carbon on
0.5% 5.5% 5.8% 5.3% catalyst leaving reactor Carbon on 0.2% 4.9%
5.8% 0.2% catalyst leaving regenerator Methanol 97.8% 91.3% 89.9%
90.7% conversion Selectivities*: Hydrogen 0.1 0.2 0.1 0.1 Methane
3.1 2.1 4.0 3.9 Ethane 0.4 0.5 0.9 0.9 Ethylene 10.8 26.7 35.0 32.6
Propane 5.1 0.7 0.2 0.7 Propylene 16.0 24.4 27.5 26.4 Butenes 14.9
14.0 14.1 14.2 Heavies 34.9 17.9 13.4 15.6 CO.sub.2 0.3 0.1 0.6 0.6
Coke 14.3 13.6 4.1 5.1 *"Selectivities" are on a water-free
basis
[0039] The foregoing results demonstrated that coked catalysts
(.about.5% on catalyst) achieved higher selectivities to ethylene
and propylene than catalysts having coke levels less than 1%. The
results also showed that totally regenerated catalyst which was
allowed to accumulate coke achieved higher selectivities than
catalyst that was partially regenerated to reduce the same coke to
the same level. These results are consistent with the theory that
partial regeneration of coke selectively removes coke that is
blocking undesirable surface reactions that form propane and
C.sub.5+ materials. The reactions that selectively make ethylene
and propylene occur in the small pores, and the coke that
accumulates in these pores is more difficult to remove than the
outer surface (macropore) coke. When a "clean" catalyst is allowed
to coke, the coke deposits faster on the macropore surfaces than in
the micropores, slowing the non-selective surface reactions, thus
accounting for the improved selectivities for "coked" versus
"clean" catalyst. As more and more coke accumulates, however, the
catalyst eventually becomes inactive. The activity is restored by
regeneration with air, but it is important that the catalyst be
fully burned to remove as much carbon as possible, and then allowed
to coke up again in the reactor. Partial regeneration of the
catalyst, as taught in U.S. Pat. No. 4,873,390 to Lewis, was not
nearly as effective at maintaining ethylene and propylene
selectivity in the reactor.
[0040] Based on the foregoing, it was concluded that better
selectivity to light olefins can be achieved in an oxygenate to
olefin conversion if desirable coke is maintained on a total
reaction volume of molecular sieve catalyst by totally regenerating
only a portion of the catalyst and returning at least a part of the
regenerated portion to the total reaction volume.
[0041] Persons of ordinary skill in the art will recognize that
many modifications may be made to the present invention without
departing from the spirit and scope of the present invention. The
embodiment described herein is meant to be illustrative only and
should not be taken as limiting the invention, which is defined in
the following claims.
* * * * *