U.S. patent application number 09/785122 was filed with the patent office on 2002-10-10 for method for converting an oxygenate feed to an olefin product.
Invention is credited to Cao, Chunshe, Fung, Shun C..
Application Number | 20020147376 09/785122 |
Document ID | / |
Family ID | 25134506 |
Filed Date | 2002-10-10 |
United States Patent
Application |
20020147376 |
Kind Code |
A1 |
Fung, Shun C. ; et
al. |
October 10, 2002 |
METHOD FOR CONVERTING AN OXYGENATE FEED TO AN OLEFIN PRODUCT
Abstract
The invention provides a method of making ethylene, propylene,
and butylene by contacting a molecular sieve catalyst with an
oxygenate to convert a portion of the oxygenate to a product
containing olefin; separating the catalyst from the olefin product
and directing a portion of the separated catalyst to a regenerator;
contacting, in an alcohol contact zone, the regenerated catalyst
with an alcohol selected from methanol, ethanol, 1-propanol,
1-butanol, or mixtures thereof; and directing the catalyst from the
alcohol contact zone to an oxygenate conversion zone. The relative
amounts of ethylene, proplyene, and butylene produced by the
process is in part dependant upon the composition of the alcohol
used to contact the regenerated catalyst.
Inventors: |
Fung, Shun C.; (Bridgewater,
NJ) ; Cao, Chunshe; (Kennewick, WA) |
Correspondence
Address: |
ExxonMobil Chemical Company
P.O. Box 2149
Baytown
TX
77522
US
|
Family ID: |
25134506 |
Appl. No.: |
09/785122 |
Filed: |
February 16, 2001 |
Current U.S.
Class: |
585/638 ;
585/639; 585/640 |
Current CPC
Class: |
C07C 1/20 20130101; Y02P
30/40 20151101; Y02P 30/42 20151101; C07C 2529/85 20130101; Y02P
30/20 20151101; Y02P 20/584 20151101; Y10S 585/904 20130101; C07C
1/20 20130101; C07C 11/04 20130101; C07C 1/20 20130101; C07C 11/06
20130101; C07C 1/20 20130101; C07C 11/08 20130101 |
Class at
Publication: |
585/638 ;
585/639; 585/640 |
International
Class: |
C07C 001/20 |
Claims
What is claimed is:
1. A method of making a product containing olefin comprising:
contacting, in an oxygenate conversion zone, a molecular sieve
catalyst with an oxygenate to convert a portion of the oxygenate to
an olefin product; separating the catalyst from the olefin product
and directing a portion of the separated catalyst to a regenerator;
contacting, in an alcohol contact zone, the regenerated catalyst
with an alcohol, selected from the group consisting of ethanol,
1-propanol, 1-butanol, and mixtures thereof; and directing the
alcohol contacted catalyst from the alcohol contact zone to the
oxygenate conversion zone.
2. The method of claim 1 wherein the alcohol further comprises
methanol.
3. The method of claim I wherein the alcohol comprises 1% to 99% by
weight ethanol.
4. The method of claim 2 wherein the alcohol comprises 1% to 60% by
weight methanol and 40% to 99% by weight ethanol.
5. The method of claim 1 wherein the alcohol comprises 1% to 99% by
weight 1-propanol.
6. The method of claim 2 wherein the alcohol comprises 1% to 60% by
weight methanol and 40% to 99% by weight 1-propanol.
7. The method of claim 1 wherein the alcohol comprises 1% to 99% by
weight 1-butanol.
8. The method of claim 2 wherein the alcohol comprises 1% to 60% by
weight methanol and 40% to 99% by weight 1-butanol.
9. The method of claim 1 wherein the alcohol comprises at least 20%
by weight ethanol, at least 10% by weight 1-propanol, and the
remaining percent by weight methanol.
10. The method of claim 9 wherein the alcohol comprises at least
40% by weight ethanol, at least 10% by weight 1-propanol, and the
remaining percent by weight methanol.
11. The method of claim 2 wherein the alcohol comprises at least
20% by weight ethanol, at least 20% by weight 1-propanol, at least
10% by weight butanol, and the remaining percent by weight
methanol.
12. The method of claim 2 wherein the alcohol comprises at least
20% by weight ethanol, at least 20% by weight 1-butanol, and the
remaining percent by weight methanol.
13. The method of claim 1 wherein the molecular sieve catalyst
contains SAPO molecular sieve selected from the group consisting of
SAPO-5, SAPO-17, SAPO-18, SAPO-20, SAPO-34, SAPO44, SAPO-56, the
metal containing forms of each thereof, or mixtures thereof.
14. The method of claim 1 wherein contacting the regenerated
catalyst with the alcohol comprises contacting the catalyst at a
temperature from 350.degree. C. to 550.degree. C.
15. The method of claim 1 further comprising directing fresh
catalyst to the alcohol contact zone, wherein the fresh catalyst
contacts the alcohol.
16. The method of claim 1 wherein the oxygenate comprises
methanol.
17. The method of claim 1 wherein the alcohol contact zone is an
auxiliary reactor.
18. The method of claim 1 further comprising separating hydrocarbon
produced in the alcohol contact zone from the alcohol contacted
catalyst.
19. The method of claim 1 wherein contacting the regenerated
catalyst with the alcohol comprises adding from about 2% to about
60% by weight CH.sub.2 per weight of catalyst.
20. The method of claim 19 wherein contacting the regenerated
catalyst with the alcohol comprises adding from about 2% to about
20% by weight CH.sub.2 per weight catalyst.
Description
FIELD OF THE INVENTION
[0001] This invention is directed to a method of converting an
oxygenate to an olefin product, particularly ethylene, propylene,
and butylene, using a silicoaluminophosphate molecular sieve
catalyst.
BACKGROUND OF THE INVENTION
[0002] Ethylene is an important petrochemical. In 1998 about 80
million tons of ethylene were produced, and demand is expected to
reach 100 million tons by 2003. The primary use for ethylene is as
a monomer for the production of low and high density polyethylene.
Approximately 60% of world ethylene consumption goes into making
polyethylene for such products as plastic films, containers, and
coatings. Other uses include the production of vinyl chloride,
ethylene oxide, ethylbenzene and alcohols.
[0003] Propylene is another important raw material. In 1998 about
46 million tons of propylene were produced, and demand is expected
to reach 60 million tons by 2003. About 55% of the world
consumption is directed to the production of polypropylene. Other
important end products include acrylonitrile for acrylic and nylon
fibers, and propylene oxide for polyurethane foams.
[0004] Butylenes are useful in preparing a wide variety of
derivative end products. Examples of such end products include
gasoline alkylate and ethylene-butylene (EB) copolymer. Butylenes
are also used as chemical building blocks for larger hydrocarbons.
These hydrocarbons find such applications in fuels, lubricants, and
specialty chemicals, e.g., plasticizers and solvents.
[0005] Ethylene, propylene, and butylene have been traditionally
produced by either catalytic or steam cracking of a petroleum
feedstock. As the cost of petroleum steadily increases it will be
important to find alternative feedstock sources for producing these
olefins. Oxygenates are a potential useful alternative to petroleum
for producing ethylene and propylene. A particularly promising
oxygenate is methanol. Methanol is readily produced from synthesis
gas, which is derived from the reforming of natural gas. Large
scale production of methanol from "stranded" natural gas could
provide methanol at a price that would allow methanol to be
economically competitive with petroleum feedstock for the
production of ethylene and propylene.
[0006] One way in which olefins can be made from an oxygenate
feedstock is by catalytic conversion. In U.S. Pat. No. 4,499,327 a
catalytic process for converting methanol to olefins is described.
The catalyst used in that process contains a silicoaluminophosphate
molecular sieve.
[0007] It is highly desirable to convert as much of the oxygenate
feedstock as possible into as much olefin product as possible.
Various methods of doing such have been suggested. For example,
U.S. Pat. No. 4,677,242 describes a method of increasing the amount
of ethylene and propylene produced from the catalytic conversion of
methanol by adding an aromatic diluent to the methanol. The
catalyst that is used in the process contains a
silicoaluminophosphate molecular sieve. The use of the diluent is
said to result in an increase ethylene selectivity.
[0008] U.S. Pat. No. 4,499,314 also discloses a catalytic process
for converting methanol to ethylene and para-xylene. The catalyst
that is used is a zeolitic molecular sieve, ZSM-5. Promoters are
used to promote either the formation of aromatic products or olefin
products. Benzene, toluene and para-xylene are preferred aromatic
promoters. Ethylene, propylene and butenes are preferred olefin
promoters.
[0009] Silicoaluminophosphate molecular sieve catalysts are
particularly useful catalysts for making olefins, such as ethylene
and propylene, from oxygenate compounds, such as methanol. However,
improved process conditions are needed to increase the production
of ethylene and/or propylene, as well as butylene if an oxygenate
feedstock is to replace or supplement petroleum feedstock for the
production of these olefins. Also, because of market demand
fluctuations for ethylene, propylene, and butylene, it would be
desirable to vary the production ratio of ethylene to propylene to
butylene without significant downtime in production.
SUMMARY OF THE INVENTION
[0010] The invention is directed to a method for increasing
ethylene, propylene, and/or butylene production in an oxygenate to
olefin process using molecular sieve catalysts. Catalyst from the
regeneration zone, and optionally fresh catalyst, is contacted with
an alcohol in an alcohol contact zone prior to contacting the
regenerated or fresh catalyst with the oxygenate feedstock. The
alcohol is selected from methanol, ethanol, 1-propanol, 1-butanol,
or a mixture thereof. The alcohol or mixture of alcohols used in
the alcohol contact zone will affect the production ratio of
ethylene to propylene to butylene in the olefin product.
[0011] The method for increasing ethylene, propylene, and/or
butylene production in an oxygenate to olefin process includes
contacting a molecular sieve catalyst with an oxygenate, preferably
methanol, to convert a portion of the oxygenate to an olefin
product; separating the catalyst from the olefin product and
directing a portion of the separated catalyst to a regenerator;
contacting, in an alcohol contact zone, the regenerated catalyst
with an alcohol, selected from the group consisting of ethanol,
1-propanol, 1-butanol and mixtures thereof; and directing the
alcohol contacted catalyst from the alcohol contact zone to an
oxygenate conversion zone. The method may further include
separating hydrocarbon produced in the alcohol contact zone from
the alcohol contacted catalyst, and adding fresh catalyst to the
alcohol contact zone.
[0012] The molecular sieve catalyst used in the invention contains
SAPO molecular sieve selected from SAPO-5, SAPO-17, SAPO-18,
SAPO-20, SAPO-34, SAPO-44, SAPO-56, the metal containing forms of
each thereof, or mixtures thereof. Desirably, the temperature of
the alcohol contact zone will be about 350.degree. C. to about
550.degree. C. Preferably, the alcohol contact zone is an auxiliary
reactor.
[0013] The present invention will be better understood by reference
to the Detailed Description of the Invention when taken together
with the attached drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a flow diagram of an embodiment of the process of
this invention; and
[0015] FIG. 2 is a graph of ethylene and propylene selectivity for
catalyst contacted with propanol.
DETAILED DESCRIPTION OF THE INVENTION
[0016] This invention is directed to method of making ethylene,
propylene, and butylene from an oxygenate feed. The invention
provides the ability to vary the production ratio of ethylene to
propylene to butylene in an oxygenate to olefin conversion process.
The ability to vary this production ratio is important given the
tight market dynamics of ethylene, propylene, and butylene demand.
For example, if the spot demand for propylene is high, the process
can be altered to produce additional propylene. Conversely, if the
spot demand for ethylene is high, additional ethylene can be
produced. The production ratio of ethylene to propylene to butylene
can be adjusted with little, if any, downtime in production. No
catalyst change is required and very little, if any, change in
operating conditions is required.
[0017] The invention provides a process for increasing the
production of ethylene, proplyene, and/or butylene by contacting
all or a portion of regenerated catalyst with an alcohol feed in an
alcohol contact zone prior to directing the regenerated catalyst to
an oxygenate conversion zone. Fresh catalyst may also be directed
to the alcohol contact zone prior to contacting the oxygenate feed.
Fresh catalyst is defined as catalyst that has yet to contact
oxygenate in an oxygenate conversion reactor. Regenerated catalyst
is defined as catalyst that has contacted oxygenate in an oxygenate
conversion reactor and has passed through a regenerator to remove
carbonaceous material from the catalyst.
[0018] In the alcohol contact zone regenerated or fresh catalyst
contacts an alcohol feed. The alcohol feed contains one or more
alcohols selected from ethanol, 1-propanol, 1-butanol, or a mixture
thereof. The alcohol feed may also contain methanol. Preferably, to
optimize the production of ethylene, the alcohol feed will contain
greater than about 70% by weight ethanol. Other embodiments include
an alcohol feed that contains from about 1% to about 90% by weight
methanol and from about 1% to about 99% by weight ethanol.
Preferably, the alcohol feed will contain from about 1% to about
60% by weight methanol and from about 40% to about 99% by weight
ethanol, more preferably from about 1% to about 30% by weight
methanol and from about 70% to about 99% by weight ethanol.
[0019] A portion of the ethanol that contacts the catalyst is
converted to olefin, primarily to ethylene. In the alcohol contact
zone, greater than about 85%, preferably greater than about 95% of
the ethanol is converted to ethylene. As a result, the ethylene
produced in the alcohol contact zone adds to the overall ethylene
productivity. The alcohol-contacted catalyst is then directed to
the oxygenate conversion reactor. The olefin product produced in
the alcohol contact zone is also directed to the oxygenate
conversion reactor. Alternatively, a portion of the olefin product
produced in the alcohol contact zone may be separated from the
alcohol-contacted catalyst prior to the catalyst being fed into the
oxygenate conversion reactor.
[0020] Preferably, to optimize the production of propylene, the
alcohol feed to the alcohol contact zone will contain greater than
about 70% by weight 1-propanol. In other instances it may be
desirable to use a 1-propanol/methanol mixture as the alcohol feed.
The alcohol feed will contain from about 1% to about 90% by weight
methanol and from about 1% to about 99% by weight 1-propanol.
Preferably, the alcohol feed will contain from about 1% to about
60% by weight methanol and from about 40% to about 99% by weight
1-propanol, more preferably from about 1% to about 30% by weight
methanol and from about 70% to about 99% by weight 1-propanol. A
portion of the 1-propanol that contacts the catalyst is converted
to olefin, primarily to propylene. In the alcohol contact zone,
about 70% to about 85% of the 1-propanol is converted to propylene,
and about 10% to about 25% is converted to butenes and pentenes,
which are also commercially valued olefins.
[0021] Preferably, to optimize the production of butylene, the
alcohol feed to the alcohol contact zone will contain greater than
about 70% by weight 1-butanol. In other instances it may be
desirable to use a 1-butanol-methanol mixture as the alcohol feed.
The alcohol feed will contain from about 1% to about 90% by weight
methanol and from about 1% to about 99% by weight 1-butanol.
Preferably, the alcohol feed will contain from about 1% to about
60% by weight methanol and from about 40% to about 99% by weight
1-butanol, more preferably from about 1% to about 30% by weight
methanol and from about 70% to about 99% by weight 1-butanol. A
portion of the 1-butanol that contacts the catalyst is converted to
olefin, primarily to butylene. In the alcohol contact zone, about
40% to about 60% of the 1-butanol is converted to butylene, about
20% to about 30% is converted to propylene, and about 10% to about
20% is converted to pentenes, which are also commercially valued
olefins.
[0022] The alcohol feed to the alcohol contact zone may also
contain mixtures of methanol, ethanol, 1-propanol, and 1-butanol.
For example, the alcohol feed may contain from about 1% to about
90% by weight methanol, from about 5% to about 90% by weight
ethanol, from about 5% to about 90% by weight 1-propanol, and from
about 5% to about 90% by weight 1-butanol. The greater the
proportion of ethanol in the alcohol feed results in additional
ethylene in the olefin product. Conversely, a greater proportion of
1-propanol in the alcohol feed results in additional propylene in
the olefin product. It may also be desirable to feed a mixture of
ethanol and 1-propanol to the alcohol contact zone to increase the
overall production of both ethylene and propylene in the olefin
product. Likewise, greater amounts of 1-butanol and 1-propanol in
the alcohol feed will increase the overall production of propylene
and butylene in the olefin product.
[0023] The amount of alcohol feed added to the alcohol contact zone
can vary from about 2% to about 60% by weight CH.sub.2 per weight
of regenerated and fresh catalyst added to the alcohol contact
zone. Preferably the amount of alcohol feed added will vary from
about 2% to about 20% by weight CH.sub.2 per weight catalyst. More
preferably the amount of alcohol feed added will vary from about 4%
to about 12% by weight CH.sub.2 per weight catalyst. Methanol
contains one CH.sub.2 group or 44% by weight CH.sub.2. Ethanol
contains two CH.sub.2 groups or 61% by weight CH.sub.2. 1-propanol
contains three CH.sub.2 groups or 70% by weight CH.sub.2. 1-butanol
contains four CH.sub.2 groups or 76% by weight CH.sub.2.
Accordingly, the alcohol feed will contain sufficient amounts of
CH.sub.2 to satisfy the catalyst feed to the alcohol contact zone
for each of the stated ranges.
[0024] The alcohol feed in the alcohol contact zone may also
contain one or more inert diluents. As defined herein, diluents are
compositions which are essentially non-reactive across a molecular
sieve catalyst, and primarily function to make the alcohol feed
less concentrated. Typical diluents include, but are not
necessarily limited to, helium, argon, nitrogen, carbon monoxide,
carbon dioxide, water, paraffins (especially the alkanes such as
methane, ethane, and propane), aromatic compounds, and mixtures
thereof. The preferred diluents are water and nitrogen. Water can
be injected in either liquid or vapor form.
[0025] It is to be understood that due to the hydroscopic nature of
methanol, ethanol, 1-propanol, and 1-butanol, water may be
contained within these alcohols without significantly affecting the
advantages of the invention. The amount of water or the diluents in
the alcohol feed is exclusive of the stated weight percent ranges
of the alcohols in the alcohol feed.
[0026] The oxygenate feedstock to the oxygenate conversion reactor
of this invention comprises at least one organic compound which
contains at least one oxygen atom, e.g., the lower alcohols,
ethers, ketone, and mixtures thereof. Examples of suitable
oxygenate compounds include, but are not limited to: methanol;
ethanol; 1-propanol; dimethylether; acetone; and mixtures thereof.
Preferred oxygenate compounds are methanol, dimethylether, or a
mixture thereof. The oxygenate, preferably methanol, is added at
one or more points to the oxygenate conversion reactor and/or to
the catalyst feed from the alcohol contact zone. The oxygenate is
converted to a product containing olefin.
[0027] One or more inert diluents and/or hydrocarbons may also be
present in the oxygenate feedstock. As defined herein, hydrocarbons
included with the feedstock are hydrocarbon compositions which are
converted to another chemical arrangement when contacted with
molecular sieve catalyst. These hydrocarbons can include olefins,
reactive paraffins, reactive alkylaromatics, reactive aromatics or
mixtures thereof. Preferred hydrocarbon co-feeds include,
propylene, butylene, pentylene, C.sub.4.sup.+ hydrocarbon mixtures,
C.sub.5.sup.+ hydrocarbon mixtures, and mixtures thereof. More
preferred as co-feeds are C.sub.4.sup.+ hydrocarbon mixtures, with
the most preferred being C.sub.4.sup.+ hydrocarbon mixtures which
are obtained from separation and recycle of reactor product.
[0028] In the preferred embodiment, an auxiliary reactor is used as
the alcohol contact zone. Preferably, the auxiliary reactor is
physically separated from the oxygenate conversion reactor.
Desirably, the auxiliary reactor is a fluidized bed reactor
operationally positioned between the oxygenate conversion reactor
and the regenerator. The auxiliary reactor is capable of
continuously receiving catalyst from the regenerator and
subsequently supplying the alcohol contacted catalyst to the
conversion reactor. The auxiliary reactor is also capable of
continuously receiving fresh catalyst.
[0029] Generally, when the alcohol contact zone is an auxiliary
reactor, the temperature of the auxiliary reactor will be less than
the temperature of the oxygenate conversion reactor. Preferably,
the temperature of the auxiliary reactor is 50.degree. C. less
than, more preferably 80.degree. C. less than, most preferably
100.degree. C. less than, the temperature of the oxygenate
conversion reactor. In a preferred embodiment, the temperature in
the alcohol contact zone is from about 150.degree. C. to about
500.degree. C., more preferably from about 200.degree. C. to about
400.degree. C., most preferably from about 250.degree. C. to about
350.degree. C.
[0030] Alternatively, an alcohol contact zone in the oxygenate
conversion reactor may substitute for the auxiliary reactor. The
oxygenate conversion reactor would then comprise an oxygenate
conversion zone and a contact zone. The function of the alcohol
contact zone in the oxygenate conversion reactor is nearly
identical to that of the auxiliary reactor. Generally, the
temperature of the alcohol contact zone is less than the
temperature in the oxygenate conversion zone of the reactor.
Preferably, the temperature of the alcohol contact zone is about
50.degree. C. less than, more preferably about 80.degree. C. less
than, most preferably about 100.degree. C. less than, the
temperature of the oxygenate conversion zone. In a preferred
embodiment, the temperature in the alcohol contact zone is from
about 150.degree. C. to about 500.degree. C., more preferably from
about 200.degree. C. to about 400.degree. C., most preferably from
about 250.degree. C. to about 350.degree. C.
[0031] The alcohol feed contacts regenerated catalyst, and
optionally fresh catalyst, in the contact zone at a pressure from
about 20 psia to about 1000 psia. Preferably, the alcohol feed
contacts the catalyst at a pressure from about 25 psia to about 500
psia, more preferably at a pressure from about 30 psia to about 200
psia.
[0032] The alcohol feed contacts regenerated catalyst, and
optionally fresh catalyst, at a weight hour space velocity (WHSV)
from about 1 hr.sup.-1 to about 500 hr.sup.-1. Preferably, the
alcohol feed contacts the catalyst at WHSV from about 1 hr.sup.-1
to about 100 hr.sup.-1, more preferably at a WHSV from about 1
hr.sup.-1 to about 50 hr.sup.-1. WHSV is defined herein as the
weight of oxygenate feed or alcohol feed, and/or hydrocarbon which
may optionally be in the feed, per hour per weight of the molecular
sieve content of the catalyst. Because the catalyst or the feed may
contain other materials which act as inerts or diluents, the WHSV
is calculated on the weight basis of the oxygenate or alcohol feed,
and any hydrocarbon which may be present, and the molecular sieve
contained in the catalyst.
[0033] The catalyst that is used in this invention is one that
incorporates a SAPO molecular sieve. The SAPO molecular sieve
contains a three-dimensional microporous crystal framework
structure of [SiO.sub.2], [AlO.sub.2] and [PO.sub.2] corner sharing
tetrahedral units. The way Si is incorporated into the structure
can be determined by .sup.29Si MAS NMR. See Blackwell and Patton,
J. Phys. Chem., 92, 3965 (1988). The desired SAPO molecular sieves
will exhibit one or more peaks in the .sup.29Si MAS NMR, with a
chemical shift .delta.(Si) in the range of -88 to -96 ppm and with
a combined peak area in that range of at least 20% of the total
peak area of all peaks with a chemical shift .delta.(Si) in the
range of -88 ppm to -115 ppm, where the .delta.(Si) chemical shifts
refer to external tetramethylsilane (TMS).
[0034] It is preferred that the silicoaluminophosphate molecular
sieve used in this invention have a relatively low Si/Al.sub.2
ratio. In general, the lower the Si/Al.sub.2 ratio, the lower the
C.sub.1-C.sub.4 saturates selectivity, particularly propane
selectivity. A Si/Al.sub.2 ratio of less than 0.65 is desirable,
with a Si/Al.sub.2 ratio of not greater than 0.40 being preferred,
and a Si/Al.sub.2 ratio of not greater than 0.32 being particularly
preferred. A Si/Al.sub.2 ratio of not greater than 0.20 is most
preferred.
[0035] Silicoaluminophosphate molecular sieves are generally
classified as being microporous materials having 8, 10, or 12
membered ring structures. These ring structures can have an average
pore size ranging from about 3.5 angstroms to about 15 angstroms.
Preferred are the small pore SAPO molecular sieves having an
average pore size of less than about 5 angstroms, preferably an
average pore size ranging from about 3.5 angstroms to about 5
angstroms, more preferably from about 3.5 angstroms about to 4.2
angstroms. Particularly, the molecular sieve used in conjunction
with this invention will have 8 membered rings.
[0036] In general, silicoaluminophosphate molecular sieves comprise
a molecular framework of corner-sharing [SiO.sub.2], [AlO.sub.2],
and [PO.sub.2] tetrahedral units. This type of framework is
effective in converting various oxygenates into olefin
products.
[0037] The [PO.sub.2] tetrahedral units within the framework
structure of the molecular sieve of this invention can be provided
by a variety of compositions. Examples of these
phosphorus-containing compositions include phosphoric acid, organic
phosphates such as triethyl phosphate, and aluminophosphates. The
phosphorous-containing compositions are mixed with reactive silicon
and aluminum-containing compositions under the appropriate
conditions to form the molecular sieve.
[0038] The [AlO.sub.2] tetrahedral units within the framework
structure can be provided by a variety of compositions. Examples of
these aluminum-containing compositions include aluminum alkoxides
such as aluminum isopropoxide, aluminum phosphates, aluminum
hydroxide, sodium aluminate, and pseudoboehmite. The
aluminum-containing compositions are mixed with reactive silicon
and phosphorus-containing compositions under the appropriate
conditions to form the molecular sieve.
[0039] The [SiO.sub.2] tetrahedral units within the framework
structure can be provided by a variety of compositions. Examples of
these silicon-containing compositions include silica sols and
silicium alkoxides such as tetra ethyl orthosilicate. The
silicon-containing compositions are mixed with reactive aluminum
and phosphorus-containing compositions under the appropriate
conditions to form the molecular sieve.
[0040] Substituted SAPOs can also be used in this invention. These
compounds are generally known as MeAPSOs or metal-containing
silicoaluminophosphates. The metal can be alkali metal ions (Group
IA), alkaline earth metal ions (Group IIA), rare earth ions (Group
IIIB, including the lanthanide elements: lanthanum, cerium,
praseodymium, neodymium, samarium, europium, gadolinium, terbium,
dysprosium, holmium, erbium, thulium, ytterbium and lutetium; and
scandium or yttrium) and the additional transition cations of
Groups IVB, VB, VIB, VIIB, VIIIB, and IB.
[0041] Preferably, the Me represents atoms such as Zn, Mg, Mn, Co,
Ni, Ga, Fe, Ti, Zr, Ge, Sn, and Cr. These atoms can be inserted
into the tetrahedral framework through a [MeO.sub.2] tetrahedral
unit. The [MeO.sub.2] tetrahedral unit carries a net electric
charge depending on the valence state of the metal substituent.
When the metal component has a valence state of +2, +3, +4, +5, or
+6, the net electric charge is between -2 and +2. Incorporation of
the metal component is typically accomplished adding the metal
component during synthesis of the molecular sieve. However,
post-synthesis ion exchange can also be used.
[0042] Suitable silicoaluminophosphate molecular sieves include
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, SAPO41,
SAPO-42, SAPO-44, SAPO-47, SAPO-56, the metal containing forms
thereof, and mixtures thereof. Preferred are SAPO-17, SAPO-18,
SAPO-34, SAPO-44, SAPO-47, and SAPO-56, particularly SAPO-17,
SAPO-18 and SAPO-34, including the metal containing forms thereof,
and mixtures thereof. As used herein, the term mixture is
synonymous with combination and is considered a composition of
matter having two or more components in varying proportions,
regardless of their physical state.
[0043] The silicoaluminophosphate molecular sieves are synthesized
by hydrothermal crystallization methods generally known in the art.
See, for example, U.S. Pat. Nos. 4,440,871; 4,861,743; 5,096,684;
and 5,126,308. A reaction mixture is formed by mixing together
reactive silicon, aluminum and phosphorus components, along with at
least one template. Generally the mixture is sealed and heated,
preferably under autogenous pressure, to a temperature of at least
10.degree. C., preferably from 10.degree. C. to 250.degree. C.,
until a crystalline product is formed. Formation of the crystalline
product can take anywhere from around 2 hours to as much as 2
weeks. In some cases, stirring or seeding with crystalline material
will facilitate the formation of the product.
[0044] Typically, the molecular sieve product will be formed in
solution. It can be recovered by standard means, such as by
centrifugation or filtration. The product can also be washed,
recovered by standard means, and dried.
[0045] As a result of the crystallization process, the recovered
sieve contains within its pores at least a portion of the template
used in making the initial reaction mixture. The crystalline
structure essentially wraps around the template, and the template
must be removed so that the molecular sieve can exhibit catalytic
activity. Once the template is removed, the crystalline structure
that remains has what is typically called an intracrystalline pore
system.
[0046] In many cases, depending upon the nature of the final
product formed, the template may be too large to be eluted from the
intracrystalline pore system. In such a case, the template can be
removed by a heat treatment process. For example, the template can
be calcined, or essentially combusted, in the presence of an
oxygen-containing gas, by contacting the template-containing sieve
in the presence of the oxygen-containing gas and heating at
temperatures from 200.degree. C. to 900.degree. C. In some cases,
it may be desirable to heat in an environment having a low oxygen
concentration. In these cases, however, the result will typically
be a breakdown of the template into a smaller molecular fragments,
rather than by combustion. This type of process can be used for
partial or complete removal of the template from the
intracrystalline pore system. In other cases, with smaller
templates, complete or partial removal from the sieve can be
accomplished by conventional desorption processes such as those
used in making standard zeolites.
[0047] The reaction mixture can contain one or more templates.
Templates are structure- directing or affecting agents, and
typically contain nitrogen, phosphorus, oxygen, carbon, hydrogen or
a combination thereof, and can also contain at least one alkyl or
aryl group, with 1 to 8 carbons being present in the alkyl or aryl
group. Mixtures of two or more templates can produce mixtures of
different sieves or predominantly one sieve where one template is
more strongly directing than another.
[0048] Representative templates include tetraethyl ammonium salts,
cyclopentylamine, aminomethyl cyclohexane, piperidine,
triethylamine, cyclohexylamine, tri-ethyl hydroxyethylamine,
morpholine, dipropylamine (DPA), pyridine, isopropylamine and
combinations thereof. Preferred templates are triethylamine,
cyclohexylamine, piperidine, pyridine, isopropylamine, tetraethyl
ammonium salts, dipropylamine, and mixtures thereof. The
tetraethylammonium salts include tetraethyl ammonium hydroxide
(TEAOH), tetraethyl ammonium phosphate, tetraethyl ammonium
fluoride, tetraethyl ammonium bromide, tetraethyl ammonium
chloride, tetraethyl ammonium acetate. Preferred tetraethyl
ammonium salts are tetraethyl ammonium hydroxide and tetraethyl
ammonium phosphate.
[0049] The SAPO molecular sieve structure can be effectively
controlled using combinations of templates. For example, in a
particularly preferred embodiment, the SAPO molecular sieve is
manufactured using a template combination of TEAOH and
dipropylamine. This combination results in a particularly desirable
SAPO structure for the conversion of oxygenates, particularly
methanol and dimethyl ether, to light olefins such as ethylene and
propylene.
[0050] The silicoaluminophosphate molecular sieve is typically
admixed (i.e., blended) with other materials. When blended, the
resulting composition is typically referred to as a SAPO catalyst,
with the catalyst comprising the SAPO molecular sieve.
[0051] Materials which can be blended with the molecular sieve can
be various inert or catalytically active materials, or various
binder materials. These materials include compositions such as
kaolin and other clays, various forms of rare earth metals, metal
oxides, other non-zeolite catalyst components, zeolite catalyst
components, alumina or alumina sol, titania, zirconia, magnesia,
thoria, beryllia, quartz, silica or silica or silica sol, and
mixtures thereof. These components are also effective in reducing,
inter alia, overall catalyst cost, acting as a thermal sink to
assist in heat shielding the catalyst during regeneration,
densifying the catalyst and increasing catalyst strength. It is
particularly desirable that the inert materials that are used in
the catalyst to act as a thermal sink have a heat capacity of from
about 0.05 cal/g-.degree. C. to about 1 cal/g-.degree. C., more
preferably from about 0.1 cal/g-.degree. C. to about 0.8
cal/g-.degree. C., most preferably from about 0.1 cal/g-.degree. C.
to about 0.5 cal/g-.degree. C.
[0052] Additional molecular sieve materials can be included as a
part of the SAPO catalyst composition or they can be used as
separate molecular sieve catalysts in admixture with the SAPO
catalyst if desired. Structural types of small pore molecular
sieves that are suitable for use in this invention include 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, and
substituted forms thereof. Structural types of medium pore
molecular sieves that are suitable for use in this invention
include MFI, MEL, MTW, EUO, MTT, HEU, FER, AFO, AEL, TON,.and
substituted forms thereof. These small and medium pore molecular
sieves are described in greater detail in the Atlas of Zeolite
Structural Types, W. M. Meier and D. H. Olsen, Butterworth
Heineman, 3rd ed., 1997. Preferred molecular sieves which can be
combined with a silicoaluminophosphate catalyst include ZSM-5,
ZSM-34, erionite, and chabazite.
[0053] The catalyst composition preferably comprises about 1% to
about 99%, more preferably about 5% to about 90%, and most
preferably about 10% to about 80%, by weight of molecular sieve. It
is also preferred that the catalyst composition have a particle
size of from about 20 .mu.m to about 3,000 .mu.m, more preferably
about 30 .mu.m to about 200 .mu.m, most preferably about 50 .mu.m
to about 150 .mu.m.
[0054] Olefin product can be separated from catalyst using
conventional means. For example, conventional cyclones or other
separation devices can be used to separate the olefin product from
the contacted catalyst. Following separation a portion of the
contacted catalyst is directed back to the methanol feed, and a
portion of the catalyst is directed to a regenerator for coke
removal.
[0055] As the catalyst is exposed to the oxygenate, carbonaceous
material known as coke accumulates within the pores of the
molecular sieve. This coke leads to a partial deactivation of the
catalyst. As a result, the coke must be removed by contacting the
catalyst with a regeneration medium. In the invention, a portion of
oxygenate exposed catalyst is regenerated by contacting the
oxygenate exposed catalyst with a regeneration medium to remove all
or part of the coke deposits that accumulate within the pores of
the molecular sieve.
[0056] Any standard oxygenate conversion reactor system can be
used, including fixed bed, fluid bed or moving bed systems.
Preferred reactors are co-current riser reactors and short contact
time, countercurrent free-fall reactors in which an oxygenate
feedstock can be contacted with a molecular sieve catalyst at a
WHSV of at least about 1 hr.sup.-1, preferably in the range of from
about 20 hr.sup.-1 to about 1000 hr.sup.-1, and most preferably in
the range of from about 20 hr.sup.-1 to about 500 hr.sup.-1.
[0057] Preferably, the oxygenate feed, as well as the alcohol feed,
contacts the catalyst in the vapor phase. Alternately, the process
may be carried out in a liquid or a mixed vapor/liquid phase. When
the process is carried out in a liquid phase or a mixed
vapor/liquid phase, different conversions and selectivities of
feed-to-product may result depending upon the catalyst and reaction
conditions.
[0058] The oxygenate conversion process can generally be carried
out at a wide range of temperatures. An effective operating
temperature range can be from about 200.degree. C. to about
700.degree. C., preferably from about 300.degree. C. to about
600.degree. C., more preferably from about 350.degree. C. to about
550.degree. C. At the lower end of the temperature range, the
formation of the desired olefin products may become markedly slow.
At the upper end of the temperature range, the process may not form
an optimum amount of product.
[0059] The pressure throughout the system also may vary over a wide
range, including autogenous pressures. Effective pressures may be
in, but are not necessarily limited to, oxygenate partial pressures
at least 1 psia, preferably at least 5 psia. The process is
particularly effective at higher oxygenate partial pressures, such
as an oxygenate partial pressure of greater than 20 psia.
Preferably, the oxygenate partial pressure is at least about 25
psia, more preferably at least about 30 psia. For practical design
purposes it is desirable to operate at a methanol partial pressure
of not greater than about 500 psia, preferably not greater than
about 400 psia, most preferably not greater than about 300
psia.
[0060] It is desirable to strip at least some of the volatile
organic components which may be adsorbed onto the catalyst or
located within its microporous structure prior to entering the
regenerator. This can be accomplished by passing a stripping gas
over the catalyst in a stripper or stripping chamber, which can be
located within the reactor or in a separate vessel. The stripping
gas can be any substantially inert medium that is commonly used.
Examples of stripping gas are steam, nitrogen, helium, argon,
methane, CO.sub.2, CO, flue gas, and hydrogen.
[0061] It is desirable in this invention that the catalyst within
the conversion reactor be maintained at a condition optimized for
the selectivity to ethylene and/or propylene. It is desirable to
maintain the catalyst within the reactor at an average carbon
content of from about 1.0% to about 25% by weight, more preferably
from about 2% to about 15% by weight. In order to maintain this
average level of carbon on catalyst, a portion of the catalyst that
has been separated from the olefin product is directed to a
regenerator. The portion of catalyst to be regenerated is
preferably regenerated under conditions effective to obtain a
regenerated catalyst having a carbon content of less than 2 wt. %,
preferably less than 1.5 wt. %, and most preferably less than 1.0
wt. %.
[0062] In the regenerator, the catalyst is contacted with a
regeneration medium containing oxygen or other oxidants. Examples
of other oxidants include O.sub.3, SO.sub.3, N.sub.2O, NO,
NO.sub.2, N.sub.2O.sub.5, and mixtures thereof. It is preferred to
supply O.sub.2 in the form of air. The air can be diluted with
nitrogen, CO.sub.2, or flue gas, and steam may be added. Desirably,
the O.sub.2 concentration in the regenerator is reduced to a
controlled level to minimize overheating or the creation of hot
spots in the spent or deactivated catalyst. The deactivated
catalyst also may be regenerated reductively with H.sub.2, CO,
mixtures thereof, or other suitable reducing agents. A combination
of oxidative regeneration and reductive regeneration can also be
employed.
[0063] The coke deposits are removed from the catalyst during the
regeneration process, forming a regenerated catalyst. Typical
regeneration temperatures are from 250.degree. C. to 700.degree.
C., desirably from 350.degree. C. to 700.degree. C. Preferably,
regeneration is carried out at a temperature of 450.degree. C. to
700.degree. C. It may be desirable to cool at least a portion of
the regenerated catalyst to a lower temperature before it is
directed to the alcohol contact zone. A heat exchanger located
externally to the regenerator may be used to remove some heat from
the catalyst after it has been withdrawn from the regenerator.
[0064] A preferred embodiment of the oxygenate to olefin conversion
process is shown in FIG. 1, with the reaction being carried out in
an oxygenate conversion reactor 10. Oxygenate is introduced into
the process through line 11. The oxygenate contacts catalyst from
the alcohol contact zone 12, which is shown in FIG. 1 as an
auxiliary reactor. The mix of catalyst from the alcohol contact
zone 12 and oxygenate enters reactor 10 where the oxygenate is
converted to olefin product. Catalyst that has bypassed the
regenerator 16 is also added to the oxygenate via line 19. Some
conversion to olefin may also occur prior to entering the reactor
10 because the catalyst from the auxiliary reactor is at an
elevated temperature when it contacts the oxygenate from line
11.
[0065] Any unreacted feed and/or product formed is separated from
the catalyst in separator 14 by a appropriate filtering or
separation means. Any conventional separation means, e.g., cyclone
separators or filters, can be used. Cyclone separators are
preferred. The catalyst preferably flows downward from separator
14, forming a dense, fluidized bed. The catalyst is then removed
through line 13. Hydrocarbon product from separator 14 is removed
through line 15. Conventional separation means 18, such as ethylene
and propylene fractionation units, are used to separate the desired
olefins from the hydrocarbon product. Additional separation units
may be utilized to remove various oxygenates, e.g., dimethyl ether,
from the hydrocarbon product.
[0066] A portion of the catalyst from separator 14 is sent to
regenerator 16 via line 17, where oxidation of the coke takes
place. Any conventional regeneration means can be used. Once
oxidation is sufficiently complete, the regenerated catalyst is
directed to the alcohol contact zone 12. In the auxiliary reactor
the regenerated catalyst contacts the alcohol feed 20. Fresh
catalyst 22 may also be introduced to the alcohol contact zone
12.
[0067] One skilled in the art will also appreciate that the olefins
produced by the oxygenate-to-olefin conversion reaction of the
present invention can be polymerized to form polyolefins,
particularly polyethylene and polypropylene. Processes for forming
polyolefins from olefins are known in the art. Catalytic processes
are preferred. Particularly preferred are metallocene,
Ziegler/Natta and acid catalytic systems. See, for example, U.S.
Pat. Nos. 3,258,455; 3,305,538; 3,364,190; 5,892,079; 4,659,685;
4,076,698; 3,645,992; 4,302,565; and 4,243,691. In general, these
methods involve contacting the olefin product with a
polyolefin-forming catalyst at a pressure and temperature effective
to form the polyolefin product.
[0068] A preferred polyolefin-forming catalyst is a metallocene
catalyst. The preferred temperature range of operation is from
50.degree. C. to 240.degree. C. and the reaction can be carried out
at low, medium or high pressure, being anywhere from about 1 bar to
200 bars. For processes carried out in solution, an inert diluent
can be used, and the preferred operating pressure is from 10 bars
to 150 bars, with a preferred temperature from 120.degree. C. to
230.degree. C. For gas phase processes, it is preferred that the
temperature generally be within a temperature of 60.degree. C. to
160.degree. C., and that the operating pressure be from 5 bars to
50 bars.
[0069] In addition to polyolefins, numerous other olefin
derivatives may be formed from the olefins recovered therefrom.
These include, but are not limited to, aldehydes, alcohols, acetic
acid, linear alpha olefins, vinyl acetate, ethylene dicholoride and
vinyl chloride, ethylbenzene, ethylene oxide, cumene, isopropyl
alcohol, acrolein, allyl chloride, propylene oxide, acrylic acid,
ethylene-propylene rubbers, and acrylonitrile, and trimers and
dimers of ethylene, propylene or butylenes. The methods of
manufacturing these derivatives are well known in the art, and
therefore, are not discussed herein.
[0070] This invention will be better understood with reference to
the following examples, which are intended to illustrate specific
embodiments within the overall scope of the invention as
claimed.
EXAMPLE 1
[0071] SAPO-34 catalyst, 0.3 g, 50% SAPO-34/50% binder, was added
to a fluidized-batch-recirculating (FBR) reactor at a
gas-recirculating rate of about 10 circulations per second. The
catalyst was placed in a basket bound by two sintered-porous metal
disks. An impeller rotating at 6000-7000 rpm circulated the gas in
the reactor from the top of the basket through the annulus space to
the bottom of the basket. The gas entered the bottom of the basket
at a speed sufficient to fluidize the catalyst particles. Catalyst
particles were in turbulent fluidization condition with very
limited amount of gas bubbles in the suspension. Gas residence time
was controlled by time-programmed valves that emptied the reactor
gas to a large vacuum vessel. A gas chromatograph (GC) sampling
valve was used to collect a gas sample for product composition
analysis.
[0072] The reactor was maintained at a temperature of about
450.degree. C. A pressure of about 60 psia was maintained by adding
sufficient quantities of argon. This was to ensure that the
circulation of the argon gas by the fast rotation of the impeller
can fluidize the catalyst particles before the injection of 0.07
cm.sup.3 methanol so that there are good contacts of the oxygenates
with the fluidized catalyst particles. The 0.07 cm.sup.3 methanol
provides a feed to catalyst ratio (based on CH.sub.2 content in the
oxygenate) of 0.08/1. The reaction time was controlled by venting
the reactor gas, via an automated valve, passing a GC sampling
valve to a vacuum vessel at a preset time of one minute. The gas
composition was determined by GC analysis and is shown in Table 1
which provides conversion and selectivity data.
EXAMPLE 2
[0073] An experiment identical to Example 1 was conducted using
0.05 cm.sup.3 of ethanol instead of methanol. The lower amount of
ethanol used as compared with methanol is to account for their
density difference and molecular weight difference. They both give
a feed to catalyst ratio (based on CH.sub.2 content in the
oxygenates) of 0.08/1. Table 1 shows the conversion and selectivity
data for ethanol conversion.
EXAMPLE 3
[0074] An experiment identical to Example 1 was conducted using
0.043 cm.sup.3 of 1-propanol instead of methanol. The lower amount
of 1-propanol used as compared with methanol is to account for
their density difference and molecular weight difference. They both
give a feed to catalyst ratio (based on CH.sub.2 content in the
oxygenates) of 0.08/1. Table 1 shows the conversion and selectivity
data for 1-propanol conversion. FIG. 2 shows the higher ethylene
and propylene selectivity for fresh catalyst contacted with
propanol.
EXAMPLE 4
[0075] An experiment identical to Example I was conducted using
0.04 cm.sup.3 of 1-butanol instead of methanol. The lower amount of
1-butanol used as compared with methanol is to account for their
density difference and molecular weight difference. They both give
a feed to catalyst ratio (based on CH.sub.2 content in the
oxygenates) of 0.08/1. Table 1 shows the conversion and selectivity
data for 1-butanol conversion.
[0076] Table 1 indicates that fresh SAPO catalyst contacted with
ethanol, 1-propanol, or 1-butanol in an alcohol contact zone
possess relatively higher rates of methanol conversion and higher
ethylene, propylene, and butylene selectivity, respectively, than
SAPO catalyst contacted with methanol under similar reaction
conditions. Ethanol and 1-propanol produce much higher
C.sub.2.sup.= plus C.sub.3.sup.= selectivities, 99% by weight and
80% by weight, respectively, compared to 66.5% by weight for
methanol when fresh catalyst is used. 1-butanol provides much
higher butylene selectivities. A significant amount of propylene is
also produced. The alcohol contacted catalyst is then directed to
the methanol conversion reactor resulting in improved methanol
conversion and greater ethylene, propylene, and/or butylene
productivity.
1 TABLE 1 Methanol Ethanol 1-propanol 1-butanol Conversion 98.2 100
99.03 99.31 Methane selectivity, C 1.43 0.04 0.03 0.03 Ethylene
selectivity, C.sub.2.sup.= 25.32 99.0 1.47 119 Ethane selectivity,
C.sub.2 0.23 0.12 0.02 0.02 Propylene selectivity, C.sub.3.sup.=
41.18 0.22 78.70 23.64 Propane selectivity, C.sub.3 0 0 0 0 Butanes
selectivity, C.sub.4 0.65 0.05 0.18 1.03 Butylenes selectivity,
C.sub.4.sup.= 15.53 0.44 11.06 55.84 C.sub.5.sup.= selectivity
15.66 0.13 8.44 18.25 C.sub.2.sup.= plus C.sub.3.sup.= selectivity
66.50 99.22 80.26 24.83
[0077] Having now fully described this invention, it will be
appreciated by those skilled in the art that the invention can be
performed within a wide range of parameters within what is claimed,
without departing from the spirit and scope of the invention.
* * * * *