Molecular sieve abstract
The present invention provides a process for making an olefin product
from an oxygenate-containing feedstock comprising: a) contacting
the feedstock in a reaction zone with catalyst particles comprising
a molecular sieve containing acid sites and having an average coke
loading of 1 to 10 carbon atoms per acid site of said molecular
sieve, under conditions effective to convert the feedstock into
an olefin product stream and to provide unregenerated catalyst particles,
b) removing a portion of said catalyst particles from said reaction
zone and contacting said portion with a regeneration medium in a
regeneration zone under conditions effective to obtain regenerated
catalyst particles which have an average coke loading of no greater
than 10 carbon atoms per acid site of said molecular sieve, and
c) introducing said regenerated catalyst particles into said reaction
zone to provide a catalyst mixture of unregenerated catalyst particles
and regenerated catalyst particles, in an amount sufficient to provide
an average coke loading on said catalyst mixture in an amount ranging
from 1 to 10 carbon atoms per acid site of said molecular sieve.
Molecular sieve claims
1. A process for making an olefin product from an oxygenate-containing
feedstock comprising: a) contacting the feedstock in a reaction
zone with catalyst particles comprising a molecular sieve containing
acid sites and having an average coke loading of 1 to 10 carbon
atoms per acid site of said molecular sieve, under conditions effective
to convert the feedstock into an olefin product stream and to provide
unregenerated catalyst particles, b) removing a portion of said
catalyst particles from said reaction zone and contacting said portion
with a regeneration medium in a regeneration zone under conditions
effective to obtain regenerated catalyst particles which have an
average coke loading of no greater than 10 carbon atoms per acid
site of said molecular sieve, and c) introducing said regenerated
catalyst particles into said reaction zone to provide a catalyst
mixture of unregenerated catalyst particles and regenerated catalyst
particles, in an amount sufficient to provide an average coke loading
on said catalyst mixture in an amount ranging from 1 to 10 carbon
atoms per acid site of said molecular sieve.
2. The process of claim 1 which further comprises d) repeating
steps a)-c)
3. The process of claim 1 wherein said carbon atoms per acid site
is measured using acid site density as determined by NMR.
4. The process of claim 1 wherein said oxygenate comprises methanol
and said average content of carbon on said catalyst mixture ranges
from 2 to 9 carbon atoms per acid site of said molecular sieve.
5. The process of claim 1 wherein said average content of carbon
on said catalyst mixture ranges from 4 to 7 carbon atoms per acid
site of said molecular sieve.
6. The process of claim 1 which is carried out in a circulating
fluid bed reactor.
7. The process of claim 1 which is carried out in a circulating
fluid bed reactor with continuous regeneration.
8. The process of claim 1 wherein said regenerated catalyst particles
have an average coke loading of at least 1 and no greater than 10
carbon atoms per acid site.
9. The process of claim 1 wherein said regenerated catalyst particles
have an average coke loading of no greater than 2 carbon atoms per
acid site.
10. The process of claim 6 wherein said circulating fluid bed reactor
is operated at at least 0.2 m/sec superficial gas velocity.
11. The process of claim 10 wherein said contacting is carried
out in a riser.
12. The process of claim 6 wherein said circulating fluid bed reactor
is operated at a feedstock conversion between 50% and 99%.
13. The process of claim 6 wherein said circulating fluid bed reactor
is operated at a feedstock conversion between 75% and 95%.
14. The process of claim 1 wherein at least a portion of said catalyst
mixture exits said reaction zone and is returned to said reaction
zone without regeneration.
15. The process of claim 1 wherein said molecular sieve has a pore
diameter of less than 5.0 Angstroms.
16. The process of claim 15 wherein said molecular sieve framework-type
is 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, and substituted groups thereof.
17. The process of claim 16 wherein said molecular sieve is selected
from the group consisting of ALPO-18 ALPO-34 SAPO-17 SAPO-18
and SAPO-34.
18. The process of claim 16 wherein said molecular sieve is SAPO-34.
19. The process of claim 1 wherein said molecular sieve has a
pore diameter of 5-10 Angstroms.
20. The process of claim 19 wherein said molecular sieve framework-type
is selected from the group consisting of MFI, MEL, MTW, EUO, MTT,
HEU, FER, AFO, AEL, TON, and substituted groups thereof.
21. A process for making an olefin product from an oxygenate-containing
feedstock comprising: i) providing an inventory of catalyst particles
comprising a molecular sieve containing acid sites, said catalyst
particles having an average coke loading of 1 to 10 carbon atoms
per acid site of said molecular sieve as measured using acid site
density as determined by NMR, ii) contacting the feedstock in a
reaction zone with said catalyst particles under conditions effective
to convert the feedstock into an olefin product stream to provide
unregenerated catalyst particles, iii) removing a portion of said
catalyst particles from said reaction zone and contacting said portion
with a regeneration medium in a regeneration zone under conditions
effective to obtain regenerated catalyst particles having an average
coke loading of no greater than 10 carbon atoms per acid site of
said molecular sieve, and iv) introducing said regenerated catalyst
particles into said reaction zone in an amount sufficient to provide
a catalyst mixture of unregenerated catalyst particles and regenerated
catalyst particles, said catalyst mixture having an average coke
loading of 1 to 10 carbon atoms per acid site on the molecular sieve
in said reaction zone.
22. The process of claim 21 which further comprises v) repeating
steps ii)-iv).
23. The process of claim 21 wherein said catalyst mixture has an
average coke loading of 3 to 9 carbon atoms per acid site on the
molecular sieve in said reaction zone, and said molecular sieve
has a framework-type of at least one 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,
and substituted groups thereof.
24. The process of claim 21 wherein said molecular sieve is selected
from ALPO 18 ALPO 34 SAPO 17 SAPO 18 SAPO-34 and substituted
groups thereof.
25. The process of claim 21 wherein said molecular sieve comprises
SAPO 34.
26. A process for making an olefin product from an oxygenate-containing
feedstock comprising: A) contacting the feedstock in a reaction
zone with catalyst particles comprising a molecular sieve containing
acid sites and having no greater than 10 carbon atoms per acid site,
under conditions effective to convert the feedstock into an olefin
product stream and to provide unregenerated catalyst particles,
B) analyzing a portion of said catalyst particles from said reaction
zone by measuring the number of carbon atoms per acid site of said
molecular sieve using acid site density as determined by NMR, to
provide a sample measurement value for said portion, C) contacting
a portion of said unregenerated catalyst particles with a regeneration
medium in a regeneration zone under conditions which are a function
of said sample measurement value, effective to obtain regenerated
catalyst particles which have an average coke loading of no greater
than 10 carbon atoms per acid site of said molecular sieve, and
D) introducing said regenerated catalyst particles into said reaction
zone to provide a catalyst mixture of unregenerated catalyst particles
and regenerated catalyst particles, in an amount sufficient to provide
an average coke loading on said catalyst mixture ranging from 1
to 10 carbon atoms per acid site of said molecular sieve.
Molecular sieve description
RELATED APPLICATIONS
[0001] This application is a non-provisional application claiming
priority from, and incorporating by reference in its entirety, provisional
U.S. Application Serial No. 60/345420 filed Dec. 31 2001.
FIELD OF THE INVENTION
[0002] The present invention relates to a method for converting
a feed including an oxygenate to a product including a light olefin.
BACKGROUND OF THE INVENTION
[0003] Light olefins, defined herein as ethylene, propylene, butylene
and mixtures thereof, serve as feeds for the production of numerous
important chemicals and polymers. Typically, light olefins are produced
by cracking petroleum feeds. Because of the limited supply of competitive
petroleum feeds, the opportunities to produce low cost light olefins
from petroleum feeds are limited. Efforts to develop light olefin
production technologies based on alternative feeds have increased.
[0004] An important type of alternate feed for the production of
light olefins is oxygenate, such as, for example, alcohols, particularly
methanol and ethanol, dimethyl ether, methyl ethyl ether, diethyl
ether, dimethyl carbonate, and methyl formate. Many of these oxygenates
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 light olefin production.
[0005] 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 life and selectivity
of the catalysts to ethylene and/or propylene.
[0006] The conversion of oxygenates to olefins generates and deposits
carbonaceous material (coke) on the molecular sieve catalysts used
to catalyze the conversion process. Over accumulation of these carbonaceous
deposits will interfere with the catalyst's ability to promote the
reaction. In order to avoid unwanted build-up of coke on the molecular
sieve catalyst, the oxygenate to olefin process incorporates a second
step comprising catalyst regeneration. During regeneration, the
coke is removed from the catalyst by combustion with oxygen, which
restores the catalytic activity of the catalyst. The regenerated
catalyst then may be reused to catalyze the conversion of oxygenates
to olefins.
[0007] Typically, oxygenate to olefin conversion and regeneration
are conducted in two separate vessels. The coked catalyst is continuously
withdrawn from the reaction vessel used for conversion to a regeneration
vessel and regenerated catalyst is continuously withdrawn from the
regeneration vessel and returned to the reaction vessel for conversion.
[0008] U.S. Pat. No. 4547616 to Avidan et al., incorporated herein
by reference, discloses a process for converting oxygenates to lower
olefins by operating a fluidized bed of zeolite catalyst, e.g. ZSM-5
whose activity is controlled to produce a product having propane:propene
molar ratio ranging from 0.04:1 to 0.1:1.
[0009] U.S. Pat. No. 4873390 to Lewis et al., incorporated herein
by reference, teaches conversion of a feedstock, e.g., alcohols,
to a product containing light olefins over a silicoaluminophosphate
having pores with diameters of less than 5 Angstroms, wherein carbonaceous
deposit material is formed on the catalyst. The catalyst is treated
to form a partially regenerated catalyst having from 2 to 30 wt.
% of the carbonaceous deposit material, with a preferred range between
4 and 20 wt. %.
[0010] U.S. Pat. No. 6137022 to Kuechler et al., incorporated
herein by reference, discloses a method of increasing selectivity
of a reaction to convert oxygenates to olefins by converting the
feedstock in a reaction zone containing 15 volume percent or less
of a catalyst comprising a silicoaluminophosphate molecular sieve
material, and maintaining conversion of the feedstock between 80%
and 99% under conditions effective to convert 100% of the feedstock
when the reaction zone contains at least 33 volume percent of the
molecular sieve material.
[0011] U.S. Pat. No. 6023005 to Lattner et al., incorporated
herein by reference, discloses a method of producing ethylene and
propylene by catalytic conversion of oxygenate in a fluidized bed
reaction process which utilizes catalyst regeneration. The process
maintains a portion of desired carbonaceous deposits on the catalyst
(wt. %) by removing only a portion of the total reaction volume
of coked molecular sieve catalyst and totally regenerating only
that portion of catalyst, which is then mixed back with the unregenerated
remainder of catalyst. The resulting catalyst mixture contains 2-30
wt % carbonaceous deposits.
[0012] S. Soundararajan et al., "Modeling of methanol to olefins
(MTO) process in a circulating fluidized bed reactor", Fuel
80 (2001), 1187-1197 at 1192-93 discuss the effect of coke content
(wt. %) on product selectivities from pure methanol using SAPO-34
catalyst. Although a relationship between wt. % carbon on catalyst
and selectivity for primary olefins has been observed, it can vary
considerably from one catalyst to another, even for molecular sieve
materials having the same structure.
[0013] Stephen Wilson et al., "The characteristics of SAPO-34
which influence the conversion of methanol to light olefins",
Microporous and Mesoporous Materials 29(1999) 117-126 describe
the relationship between acid-site strength and density on methanol
conversion to light olefins over chabazite structure types (SAPO-34
and SSZ-13) in terms of determining which catalyst was the most
resistant to coking at one acid-site per chabazite cage.
[0014] Ivar M. Dahl et al., "Structural and chemical influences
on the MTO reaction: a comparison of chabazite and SAPO-34 as MTO
catalysts", Microporous and Mesoporous Materials 29(1999) 185-190
describe the effect of relationship between acid-site strength and
susceptibility of chabazite and SAPO-34 to deactivation for oxygenate
conversion at high space velocities to avoid excess catalyst activity
causing undesired secondary reactions.
[0015] It would be desirable to provide a process for making olefins
from oxygenate which maximizes primary olefin yield, especially
light olefin yield (ethylene and propylene), for a wide variety
of catalysts.
SUMMARY OF THE INVENTION
[0016] The present invention relates to a process for making an
olefin product from an oxygenate-containing feedstock comprising:
[0017] a) contacting the feedstock in a reaction zone with catalyst
particles comprising a molecular sieve containing acid sites and
having an average coke loading of 1 to 10 carbon atoms per acid
site of said molecular sieve, under conditions effective to convert
the feedstock into an olefin product stream and to provide unregenerated
catalyst particles,
[0018] b) removing a portion of said catalyst particles from said
reaction zone and contacting said portion with a regeneration medium
in a regeneration zone under conditions effective to obtain regenerated
catalyst particles which have an average coke loading of no greater
than 10 carbon atoms per acid site of said molecular sieve, and
[0019] c) introducing said regenerated catalyst particles into
said reaction zone to provide a catalyst mixture of unregenerated
catalyst particles and regenerated catalyst particles, in an amount
sufficient to provide an average coke loading on said catalyst mixture
in an amount ranging from 1 to 10 carbon atoms per acid site of
said molecular sieve.
[0020] In another embodiment, the present invention relates to
the above process which further comprises d) repeating steps a)-c)
[0021] In yet another embodiment, the present invention relates
to the above process wherein said carbon atoms per acid site is
measured using acid site density as determined by NMR.
[0022] In still another embodiment, the present invention relates
to the above process wherein said oxygenate comprises methanol and
said average content of carbon on said catalyst mixture ranges from
1 to 9 carbon atoms per acid site, say, 4 to 7 carbon atoms, of
said molecular sieve.
[0023] In one embodiment, the present invention relates to the
above process wherein said regenerated catalyst particles have an
average coke loading of at least 1 and no greater than 10 carbon
atoms per acid site, say, an average coke loading of no greater
than 2 carbon atoms per acid site.
[0024] In yet still another embodiment of the present invention,
the above process is carried out in a circulating fluid bed reactor,
say, a circulating fluid bed reactor with continuous regeneration.
[0025] In still another embodiment of the present invention, the
process is carried out wherein the circulating fluid bed reactor
is operated at at least 0.2 m/sec superficial gas velocity.
[0026] In another embodiment of the above process, the circulating
fluid bed reactor is operated at a feedstock conversion between
50% and 99%, say, between 75% and 95%.
[0027] In still yet another embodiment of the process, at least
a portion of said catalyst mixture exits said reaction zone and
is returned to said reaction zone without regeneration.
[0028] In yet another embodiment, the present invention comprises
a contacting step carried out in a riser.
[0029] In another embodiment, the present invention employs a molecular
sieve which has a pore diameter of less than 5.0 Angstroms, e.g.,
a molecular sieve is of a molecular sieve framework-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, and substituted groups thereof. In
an alternative embodiment, the molecular sieve is selected from
the group consisting of ALPO-18 ALPO-34 SAPO-17 SAPO-18 and
SAPO-34.
[0030] In another embodiment, the present invention relates to
the above process wherein the molecular sieve has a pore diameter
of 5-10 Angstroms, e.g., a molecular sieve framework-type which
is selected from the group consisting of MFI, MEL, MTW, EUO, MTT,
HEU, FER, AFO, AEL, TON, and substituted groups thereof.
[0031] In another aspect, the present invention relates to a process
for making an olefin product from an oxygenate-containing feedstock
comprising:
[0032] i) providing an inventory of catalyst particles comprising
a molecular sieve containing acid sites, said catalyst particles
having an average coke loading of 1 to 10 carbon atoms per acid
site of said molecular sieve as measured using acid site density
as determined by NMR,
[0033] ii) contacting the feedstock in a reaction zone with said
catalyst particles under conditions effective to convert the feedstock
into an olefin product stream to provide unregenerated catalyst
particles,
[0034] iii) removing a portion of said catalyst particles from
said reaction zone and contacting said portion with a regeneration
medium in a regeneration zone under conditions effective to obtain
regenerated catalyst particles having an average coke loading of
no greater than 10 carbon atoms per acid site of said molecular
sieve, and
[0035] iv) introducing said regenerated catalyst particles into
said reaction zone in an amount sufficient to provide a catalyst
mixture of unregenerated catalyst particles and regenerated catalyst
particles, said catalyst mixture having an average coke loading
of 1 to 10 carbon atoms per acid site on the molecular sieve in
said reaction zone.
[0036] In one embodiment of this aspect, the process further comprises
v) repeating steps ii)-iv).
[0037] In another embodiment of this aspect, the catalyst mixture
has an average coke loading of 3 to 9 carbon atoms per acid site
on the molecular sieve in said reaction zone, and said molecular
sieve has a framework-type of at least one 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, and substituted groups thereof., e.g., the molecular
sieve is selected from ALPO 18 ALPO 34 SAPO 17 SAPO 18 SAPO-34
and substituted groups thereof, say, SAPO 34.
[0038] In another aspect, the present invention relates to a process
for making an olefin product from an oxygenate-containing feedstock
comprising:
[0039] A) contacting the feedstock in a reaction zone with catalyst
particles comprising a molecular sieve containing acid sites and
having no greater than 10 carbon atoms per acid site, under conditions
effective to convert the feedstock into an olefin product stream
and to provide unregenerated catalyst particles,
[0040] B) analyzing a portion of said catalyst particles from said
reaction zone by measuring the number of carbon atoms per acid site
of said molecular sieve using acid site density as determined by
NMR, to provide a sample measurement value for said portion,
[0041] C) contacting a portion of said unregenerated catalyst particles
with a regeneration medium in a regeneration zone under conditions,
which are a function of said sample measurement value, effective
to obtain regenerated catalyst particles which have an average coke
loading of no greater than 10 carbon atoms per acid site of said
molecular sieve, and
[0042] D) introducing said regenerated catalyst particles into
said reaction zone to provide a catalyst mixture of unregenerated
catalyst particles and regenerated catalyst particles, in an amount
sufficient to provide an average coke loading on said catalyst mixture
ranging from 1 to 10 carbon atoms per acid site of said molecular
sieve.
[0043] These and other advantages of the present invention shall
become apparent from the following detailed description, the attached
figure and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 provides a diagram of a reactor apparatus comprising
a high velocity fluid bed with catalyst recirculation, and a regenerator
suitable for use in accordance with a preferred embodiment of the
present invention.
[0045] FIG. 2 depicts prime olefin selectivity versus carbon on
catalyst by weight in a methanol to olefins conversion process of
a preferred embodiment of the present invention.
[0046] FIG. 3 depicts prime olefin selectivity versus carbon on
the molecular sieve by weight in a methanol to olefins conversion
process of a preferred embodiment of the present invention.
[0047] FIG. 4 depicts prime olefin selectivity versus carbon atoms
per acid site in a methanol to olefins conversion process of a preferred
embodiment of the present invention.
[0048] FIG. 5 depicts prime olefin selectivity, methane selectivity
and propane selectivity versus carbon atoms per acid site and shows
a well-defined maximum light olefin selectivity as a function of
average coke loading in a methanol to olefins conversion process
of a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0049] 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 production of methane, ethane,
propane, and C.sub.5+ materials. The present invention maintains
the average coke loading of the catalyst in a range particularly
selective for producing ethylene and propylene. Such range is based
on the acid site density of the molecular sieve component of the
catalyst.
[0050] Coke levels on the molecular sieve catalyst composition
are measured by withdrawing from the conversion process the molecular
sieve catalyst composition at a point in the process and determining
its carbon content. It is recognized that the molecular sieve catalyst
composition in the reaction zone is made up of a mixture of regenerated
catalyst and catalyst that has varying levels of carbonaceous deposits.
The measured coke level of carbonaceous deposits thus represents
an average of the levels of individual catalyst particles.
[0051] U.S. Pat. No. 6023005 incorporated herein by reference,
teaches the desirability of providing carbonaceous deposits, or
coke levels, for oxygenates to olefins conversion processes, in
the range of 2 wt. % to about 30 wt. % based on the total reaction
volume of coked catalyst to promote selectivity to light olefins.
However, the inventors have discovered that obtaining particularly
preferred results does not consistently depend on maintaining such
a coke level range alone, and certainly not over such a wide range
as has been previously disclosed. Rather, preferred results in an
oxygenate to olefins conversion reaction are in fact a consistent
function of the coke level correlated to the particular acidity
of the molecular sieve(s) in the catalyst utilized in the conversion
reaction. It has now been found that it is advantageous to maintain
a average coke loading of the catalyst in a range of 1 to 10 carbon
atoms per acid site of the molecular sieve component of the catalyst
utilized in an oxygenate to olefins conversion reaction to provide
superior prime olefin selectivity.
[0052] Molecular Sieves and Catalysts Thereof
[0053] Molecular sieves suited to use in the present invention
for converting oxygenates to olefins have various chemical and physical,
framework, characteristics. Molecular sieves have been well classified
by the Structure Commission of the International Zeolite Association
according to the rules of the IUPAC Commission on Zeolite Nomenclature.
A framework-type describes the connectivity, topology, of the tetrahedrally
coordinated atoms constituting the framework, and making an abstraction
of the specific properties for those materials. Framework-type zeolite
and zeolite-type molecular sieves for which a structure has been
established, are assigned a three letter code and are described
in the Atlas of Zeolite Framework Types, 5th edition, Elsevier,
London, England (2001), which is herein fully incorporated by reference.
[0054] Non-limiting examples of these molecular sieves are the
small pore molecular sieves of a framework-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, and substituted forms thereof; the medium pore
molecular sieves of a framework-type selected from the group consisting
of AFO, AEL, EUO, HEU, FER, MEL, MFI, MTW, MTT, TON, and substituted
forms thereof, and the large pore molecular sieves of a framework-type
selected from the group consisting of EMT, FAU, and substituted
forms thereof. Other molecular sieves have a framework-type selected
from the group consisting of ANA, BEA, CFI, CLO, DON, GIS, LTL,
MER, MOR, MWW and SOD. Non-limiting examples of the preferred molecular
sieves, particularly for converting an oxygenate containing feedstock
into olefin(s), include those having a framework-type selected from
the group consisting of AEL, AFY, BEA, CHA, EDI, FAU, FER, GIS,
LTA, LTL, MER, MFI, MOR, MTT, MWW, TAM and TON. In one preferred
embodiment, the molecular sieve of the invention has an AEI topology
or a CHA topology, or a combination thereof, most preferably a CHA
topology.
[0055] Molecular sieve materials all have 3-dimensional, four-connected
framework structure of corner-sharing TO.sub.4 tetrahedra, where
T is any tetrahedrally coordinated cation. These molecular sieves
are typically described in terms of the size of the ring that defines
a pore, where the size is based on the number of T atoms in the
ring. Other framework-type characteristics include the arrangement
of rings that form a cage, and when present, the dimension of channels,
and the spaces between the cages. See van Bekkum, et al., Introduction
to Zeolite Science and Practice, Second Completely Revised and Expanded
Edition, Volume 137 pages 1-67 Elsevier Science, B.V., Amsterdam,
Netherlands (2001).
[0056] The small, medium and large pore molecular sieves have from
a 4-ring to a 12-ring or greater framework-type. In a preferred
embodiment, the zeolitic molecular sieves have 8-, 10- or 12-ring
structures or larger and an average pore size in the range of from
about 3 .ANG. to 15 .ANG.. In the most preferred embodiment, the
molecular sieves of the invention, preferably silicoaluminophosphate
molecular sieves have 8-rings and an average pore size less than
about 5 .ANG., preferably in the range of from 3 .ANG. to about
5 .ANG., more preferably from 3 .ANG. to about 4.5 .ANG., and most
preferably from 3.5 .ANG. to about 4.2 .ANG..
[0057] Molecular sieves, particularly zeolitic and zeolitic-type
molecular sieves, preferably have a molecular framework of one,
preferably two or more corner-sharing [TO.sub.4] tetrahedral units,
more preferably, two or more [SiO.sub.4], [AlO.sub.4] and/or [PO.sub.4]
tetrahedral units, and most preferably [SiO.sub.4], [AlO.sub.4]
and [PO.sub.4] tetrahedral units. These silicon, aluminum, and phosphorous
based molecular sieves and metal containing silicon, aluminum and
phosphorous based molecular sieves have been described in detail
in numerous publications including for example, U.S. Pat. No. 4567029
(MeAPO where Me is Mg, Mn, Zn, or Co), U.S. Pat. No. 4440871 (SAPO),
European Patent Application EP-A-0 159 624 (ELAPSO where El is As,
Be, B, Cr, Co, Ga, Ge, Fe, Li, Mg, Mn, Ti or Zn), U.S. Pat. No.
4554143 (FeAPO), U.S. Pat. Nos. 4822478 4683217 4744885
(FeAPSO), EP-A-0 158 975 and U.S. Pat. No. 4935216 (ZnAPSO, EP-A-0
161 489 (CoAPSO), EP-A-0 158 976 (ELAPO, where EL is Co, Fe, Mg,
Mn, Ti or Zn), U.S. Pat. No. 4310440 (AlPO.sub.4), EP-A-0 158
350 (SENAPSO), U.S. Pat. No. 4973460 (LiAPSO), U.S. Pat. No. 4789535
(LiAPO), U.S. Pat. No. 4992250 (GeAPSO), U.S. Pat. No. 4888167
(GeAPO), U.S. Pat. No. 5057295 (BAPSO), U.S. Pat. No. 4738837
(CrAPSO), U.S. Pat. Nos. 4759919 and 4851106 (CrAPO), U.S.
Pat. Nos. 4758419 4882038 5434326 and 5478787 (MgAPSO),
U.S. Pat. No. 4554143 (FeAPO), U.S. Pat. No. 4894213 (AsAPSO),
U.S. Pat. No. 4913888 (AsAPO), U.S. Pat. Nos. 4686092 4846956
and 4793833 (MnAPSO), U.S. Pat. Nos. 5345011 and 6156931 (MnAPO),
U.S. Pat. No. 4737353 (BeAPSO), U.S. Pat. No. 4940570 (BeAPO),
U.S. Pat. Nos. 4801309 4684617 and 4880520 (TiAPSO), U.S.
Pat. Nos. 4500651 4551236 and 4605492 (TiAPO), U.S. Pat.
No. 4824554 4744970 (CoAPSO), U.S. Pat. No. 4735806 (GaAPSO)
EP-A-0 293 937 (QAPSO, where Q is framework oxide unit [QO.sub.2]),
as well as U.S. Pat. Nos. 4567029 4686093 4781814 4793984
4801364 4853197 4917876 4952384 4956164 4956165
4973785 5241093 5493066 and 5675050 all of which are
herein fully incorporated by reference.
[0058] Other molecular sieves include those described in EP-0 888
187 B1 (microporous crystalline metallophosphates, SAPO.sub.4 (UIO-6)),
U.S. Pat. No. 6004898 (molecular sieve and an alkaline earth metal),
U.S. patent application Ser. No. 09/511943 filed Feb. 24 2000
(integrated hydrocarbon co-catalyst), PCT WO 01/64340 published
Sep. 7 2001(thorium containing molecular sieve), and R. Szostak,
Handbook of Molecular Sieves, Van Nostrand Reinhold, New York, N.Y.
(1992), which are all herein fully incorporated by reference.
[0059] The more preferred silicon, aluminum and/or phosphorous
containing molecular sieves, and aluminum, phosphorous, and optionally
silicon, containing molecular sieves include aluminophosphate (ALPO)
molecular sieves and silicoaluminophosphate (SAPO) molecular sieves
and substituted, preferably metal substituted, ALPO and SAPO molecular
sieves. The most preferred molecular sieves are SAPO molecular sieves,
and metal substituted SAPO molecular sieves. In an embodiment, the
metal is an alkali metal of Group IA of the Periodic Table of Elements,
an alkaline earth metal of Group IIA of the Periodic Table of Elements,
a rare earth metal of Group IIIB, including the Lanthanides: lanthanum,
cerium, praseodymium, neodymium, samarium, europium, gadolinium,
terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium;
and scandium or yttrium of the Periodic Table of Elements, a transition
metal of Groups IVB, VB, VIB, VIIB, VIIIB, and IB of the Periodic
Table of Elements, or mixtures of any of these metal species. In
one preferred embodiment, the metal is selected from the group consisting
of Co, Cr, Cu, Fe, Ga, Ge, Mg, Mn, Ni, Sn, Ti, Zn and Zr, and mixtures
thereof. In another preferred embodiment, these metal atoms discussed
above are inserted into the framework of a molecular sieve through
a tetrahedral unit, such as [MeO.sub.2], and carry a net charge
depending on the valence state of the metal substituent. For example,
in one embodiment, when the metal substituent has a valence state
of +2 +3 +4 +5 or +6 the net charge of the tetrahedral unit
is between -2 and +2.
[0060] In one embodiment, the molecular sieve, as described in
many of the U.S. Patents mentioned above, is represented by the
empirical formula, on an anhydrous basis:
mR:(M.sub.xAl.sub.yP.sub.z)O.sub.2
[0061] wherein R represents at least one templating agent, preferably
an organic templating agent; m is the number of moles of R per mole
of (M.sub.xAl.sub.yP.sub.z)O.sub.2 and m has a value from 0 to 1
preferably 0 to 0.5 and most preferably from 0 to 0.3; x, y, and
z represent the mole fraction of Al, P and M as tetrahedral oxides,
where M is a metal selected from one of Group IA, IIA, IB, IIIB,
IVB, VB, VIB, VIIB, VIIIB and Lanthanide's of the Periodic Table
of Elements, preferably M is selected from one of the group consisting
of Co, Cr, Cu, Fe, Ga, Ge, Mg, Mn, Ni, Sn, Ti, Zn and Zr. In an
embodiment, m is greater than or equal to 0.2 and x, y and z are
greater than or equal to 0.01.
[0062] In another embodiment, m is greater than 0.1 to about 1
x is greater than 0 to about 0.25 y is in the range of from 0.4
to 0.5 and z is in the range of from 0.25 to 0.5 more preferably
m is from 0.15 to 0.7 x is from 0.01 to 0.2 y is from 0.4 to 0.5
and z is from 0.3 to 0.5.
[0063] Non-limiting examples of SAPO and ALPO molecular sieves
of the invention include one or a combination of SAPO-5 SAPO-8
SAPO-11 SAPO-16 SAPO-17 SAPO-18 SAPO-20 SAPO-31 SAPO-34 SAPO-35
SAPO-36 SAPO-37 SAPO-40 SAPO-41 SAPO-42 SAPO-44 (U.S. Pat.
No. 6162415), SAPO-47 SAPO-56 ALPO-5 ALPO-11 ALPO-18 ALPO-31
ALPO-34 ALPO-36 ALPO-37 ALPO-46 and metal containing molecular
sieves thereof. The more preferred zeolite-type molecular sieves
include one or a combination of SAPO-18 SAPO-34 SAPO-35 SAPO-44
SAPO-56 ALPO-18 and ALPO-34 even more preferably one or a combination
of SAPO-18 SAPO-34 ALPO-34 and ALPO-18 and metal containing molecular
sieves thereof, and most preferably one or a combination of SAPO-34
and ALPO-18 and metal containing molecular sieves thereof.
[0064] In an embodiment, the molecular sieve is an intergrowth
material having two or more distinct phases of crystalline structures
within one molecular sieve composition. In particular, intergrowth
molecular sieves are described in the U.S. patent application Ser.
No. 09/924016 filed Aug. 7 2001 and PCT WO 98/15496 published
Apr. 16 1998 both of which are herein fully incorporated by reference.
In another embodiment, the molecular sieve comprises at least one
intergrown phase of AEI and CHA framework-types. For example, SAPO-18
ALPO-18 and RUW-18 have an AEI framework-type, and SAPO-34 has a
CHA framework-type.
[0065] Molecular Sieve Synthesis
[0066] The synthesis of molecular sieves is described in many of
the references discussed above. Generally, molecular sieves are
synthesized by the hydrothermal crystallization of one or more of
a source of aluminum, a source of phosphorous, a source of silicon,
a templating agent, and a metal containing compound. Typically,
a combination of sources of silicon, aluminum and phosphorous, optionally
with one or more templating agents and/or one or more metal containing
compounds are placed in a sealed pressure vessel, optionally lined
with an inert plastic such as polytetrafluoroethylene, and heated,
under a crystallization pressure and temperature, until a crystalline
material is formed, and then recovered by filtration, centrifugation
and/or decanting.
[0067] In a preferred embodiment the molecular sieves are synthesized
by forming a reaction product of a source of silicon, a source of
aluminum, a source of phosphorous, an organic templating agent,
preferably a nitrogen containing organic templating agent, and one
or more polymeric bases. This particularly preferred embodiment
results in the synthesis of a silicoaluminophosphate crystalline
material that is then isolated by filtration, centrifugation and/or
decanting.
[0068] Non-limiting examples of silicon sources include a silicates,
fumed silica, for example, Aerosil-200 available from Degussa Inc.,
New York, N.Y., and CAB-O-SIL M-5 silicon compounds such as tetraalkyl
orthosilicates, for example, tetramethyl orthosilicate (TMOS) and
tetraethylorthosilicate (TEOS), colloidal silicas or aqueous suspensions
thereof, for example Ludox-HS-40 sol available from E. I. du Pont
de Nemours, Wilmington, Del., silicic acid, alkali-metal silicate,
or any combination thereof. The preferred source of silicon is a
silica sol.
[0069] Non-limiting examples of aluminum sources include aluminum-containing
compositions such as aluminum alkoxides, for example aluminum isopropoxide,
aluminum phosphate, aluminum hydroxide, sodium aluminate, pseudo-boehmite,
gibbsite and aluminum trichloride, or any combinations thereof.
A preferred source of aluminum is pseudo-boehmite, particularly
when producing a silicoaluminophosphate molecular sieve.
[0070] Non-limiting examples of phosphorous sources, which may
also include aluminum-containing phosphorous compositions, include
phosphorous-containing, inorganic or organic, compositions such
as phosphoric acid, organic phosphates such as triethyl phosphate,
and crystalline or amorphous aluminophosphates such as ALPO.sub.4
phosphorous salts, or combinations thereof. The preferred source
of phosphorous is phosphoric acid, particularly when producing a
silicoaluminophosphate.
[0071] Templating agents are generally compounds that contain elements
of Group VA of the Periodic Table of Elements, particularly nitrogen,
phosphorus, arsenic and antimony, more preferably nitrogen or phosphorous,
and most preferably nitrogen. Typical templating agents of Group
VA of the Periodic Table of elements also contain at least one alkyl
or aryl group, preferably an alkyl or aryl group having from 1 to
10 carbon atoms, and more preferably from 1 to 8 carbon atoms. The
preferred templating agents are nitrogen-containing compounds such
as amines and quaternary ammonium compounds.
[0072] The quaternary ammonium compounds, in one embodiment, are
represented by the general formula R.sub.4N.sup.+, where each R
is hydrogen or a hydrocarbyl or substituted hydrocarbyl group, preferably
an alkyl group or an aryl group having from 1 to 10 carbon atoms.
In one embodiment, the templating agents include a combination of
one or more quaternary ammonium compound(s) and one or more of a
mono-, di- or tri-amine.
[0073] Non-limiting examples of templating agents include tetraalkyl
ammonium compounds including salts thereof such as tetramethyl ammonium
compounds including salts thereof, tetraethyl ammonium compounds
including salts thereof, tetrapropyl ammonium including salts thereof,
and tetrabutylammonium including salts thereof, cyclohexylamine,
morpholine, di-n-propylamine (DPA), tripropylamine, triethylamine
(TEA), triethanolamine, piperidine, cyclohexylamine, 2-methylpyridine,
N,N-dimethylbenzylamine, N,N-diethylethanolamine, dicyclohexylamine,
N,N-dimethylethanolamine, choline, N,N'-dimethylpiperazine, 14-diazabicyclo(222)octane,
N', N',N,N-tetramethyl-(16)hexanediamine, N-methyldiethanolamine,
N-methyl-ethanolamine, N-methyl piperidine, 3-methyl-piperidine,
N-methylcyclohexylamine, 3-methylpyridine, 4-methyl-pyridine, quinuclidine,
N,N'-dimethyl-14-diazabicyclo(222) octane ion; di-n-butylamine,
neopentylamine, di-n-pentylamine, isopropylamine, t-butyl-amine,
ethylenediamine, pyrrolidine, and 2-imidazolidone.
[0074] The preferred templating agent or template is a tetraethylammonium
compound, such as tetraethyl ammonium hydroxide (TEAOH), tetraethyl
ammonium phosphate, tetraethyl ammonium fluoride, tetraethyl ammonium
bromide, tetraethyl ammonium chloride and tetraethyl ammonium acetate.
The most preferred templating agent is tetraethyl ammonium hydroxide
and salts thereof, particularly when producing a silicoaluminophosphate
molecular sieve. In one embodiment, a combination of two or more
of any of the above templating agents is used in combination with
one or more of a silicon-, aluminum-, and phosphorous-source, and
a polymeric base.
[0075] Polymeric bases, especially polymeric bases that are soluble
or non-ionic, useful in the invention, are those having a pH sufficient
to control the pH desired for synthesizing a given molecular sieve,
especially a SAPO molecular sieve. In a preferred embodiment, the
polymeric base is soluble or the polymeric base is non-ionic, preferably
the polymeric base is a non-ionic and soluble polymeric base, and
most preferably the polymeric base is a polymeric imine. In one
embodiment, the polymeric base of the invention has a pH in an aqueous
solution, preferably water, from greater than 7 to about 14 more
preferably from about 8 to about 14 most preferably from about
9 to 14.
[0076] In another embodiment, the non-volatile polymeric base is
represented by the formula: (R--NH).sub.x, where (R--NH) is a polymeric
or monomeric unit where R contains from 1 to 20 carbon atoms, preferably
from 1 to 10 carbon atoms, more preferably from 1 to 6 carbon atoms,
and most preferably from 1 to 4 carbon atoms; x is an integer from
1 to 500000. In one embodiment, R is a linear, branched, or cyclic
polymer, monomeric, chain, preferably a linear polymer chain having
from 1 to 20 carbon atoms.
[0077] In another embodiment, the polymeric base is a water miscible
polymeric base, preferably in an aqueous solution. In yet another
embodiment, the polymeric base is a polyethylenimine that is represented
by the following general formula: (--NHCH.sub.2CH.sub.2--).sub.m[--N(CH.s-
ub.2CH.sub.2NH.sub.2)CH.sub.2CH.sub.2--].sub.n), wherein m is from
10 to 20000 and n is from 0 to 2000 preferably from 1 to 2000.
[0078] In another embodiment, the polymeric base of the invention
has a average molecular weight from about 500 to about 1000000
preferably from about 2000 to about 800000 more preferably from
about 10000 to about 750000 and most preferably from about 50000
to about 750000.
[0079] In another embodiment, the mole ratio of the monomeric unit
of the polymeric base of the invention, containing one basic group,
to the templating agent(s) is less than 20 preferably less than
12 more preferably less than 10 even more preferably less than
8 still even more preferably less than 5 and most preferably less
than 4.
[0080] Non-limiting examples of polymer bases include: epichlorohydrin
modified polyethylenimine, ethoxylated polyethylenimine, polypropylenimine
diamine dendrimers (DAB-Am-n), poly(allylamine) [CH.sub.2CH(CH.sub.2NH.sub.2)].sub.n,
poly(12-dihydro-224-trimethylqui- noline), and poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine).
[0081] In another embodiment the invention is directed to a method
for synthesizing a molecular sieve utilizing a templating agent,
preferably an organic templating agent such as an organic amine,
an ammonium salt and/or an ammonium hydroxide, in combination with
a polymeric base such as polyethylenimine.
[0082] In a typical synthesis of the molecular sieve, the phosphorous-,
aluminum-, and/or silicon-containing components are mixed, preferably
while stirring and/or agitation and/or seeding with a crystalline
material, optionally with an alkali metal, in a solvent such as
water, and one or more templating agents and a polymeric base, to
form a synthesis mixture that is then heated under crystallization
conditions of pressure and temperature as described in U.S. Pat.
Nos. 4440871 4861743 5096684 and 5126308 which are all
herein fully incorporated by reference. The polymeric base is combined
with the at least one templating agent, and one or more of the aluminum
source, phosphorous source, and silicon source, in any order, for
example, simultaneously with one or more of the sources, premixed
with one or more of the sources and/or templating agent, after combining
the sources and the templating agent, and the like.
[0083] Generally, the synthesis mixture described above is sealed
in a vessel and heated, preferably under autogenous pressure, to
a temperature in the range of from about 80.degree. C. to about
250.degree. C., preferably from about 100.degree. C. to about 250.degree.
C., more preferably from about 125.degree. C. to about 225.degree.
C., even more preferably from about 150.degree. C. to about 180.degree.
C. In another embodiment, the hydrothermal crystallization temperature
is less than 225.degree. C., preferably less than 200.degree. C.
to about 80.degree. C., and more preferably less than 195.degree.
C. to about 100.degree. C.
[0084] In yet another embodiment, the crystallization temperature
is increased gradually or stepwise during synthesis, preferably
the crystallization temperature is maintained constant, for a period
of time effective to form a crystalline product. The time required
to form the crystalline product is typically from immediately up
to several weeks, the duration of which is usually dependent on
the temperature; the higher the temperature the shorter the duration.
In one embodiment, the crystalline product is formed under heating
from about 30 minutes to around 2 weeks, preferably from about 45
minutes to about 240 hours, and more preferably from about 1 hour
to about 120 hours.
[0085] In one embodiment, the synthesis of a molecular sieve is
aided by seeds from another or the same framework type molecular
sieve.
[0086] The hydrothermal crystallization is carried out with or
without agitation or stirring, for example stirring or tumbling.
The stirring or agitation during the crystallization period may
be continuous or intermittent, preferably continuous agitation.
Typically, the crystalline molecular sieve product is formed, usually
in a slurry state, and is recovered by any standard technique well
known in the art, for example centrifugation or filtration. The
isolated or separated crystalline product, in an embodiment, is
washed, typically, using a liquid such as water, from one to many
times. The washed crystalline product is then optionally dried,
preferably in air.
[0087] One method for crystallization involves subjecting an aqueous
reaction mixture containing an excess amount of a templating agent
and polymeric base, subjecting the mixture to crystallization under
hydrothermal conditions, establishing an equilibrium between molecular
sieve formation and dissolution, and then, removing some of the
excess templating agent and/or organic base to inhibit dissolution
of the molecular sieve. See for example U.S. Pat. No. 5296208
which is herein fully incorporated by reference.
[0088] Another method of crystallization is directed to not stirring
a reaction mixture, for example a reaction mixture containing at
a minimum, a silicon-, an aluminum-, and/or a phosphorous-composition,
with a templating agent and a polymeric base, for a period of time
during crystallization. See PCT WO 01/47810 published Jul. 5 2001
which is herein fully incorporated by reference.
[0089] Other methods for synthesizing molecular sieves or modifying
molecular sieves are described in U.S. Pat. No. 5879655 (controlling
the ratio of the templating agent to phosphorous), U.S. Pat. No.
6005155 (use of a modifier without a salt), U.S. Pat. No. 5475182
(acid extraction), U.S. Pat. No. 5962762 (treatment with transition
metal), U.S. Pat. Nos. 5925586 and 6153552 (phosphorous modified),
U.S. Pat. No. 5925800 (monolith supported), U.S. Pat. No. 5932512
(fluorine treated), U.S. Pat. No. 6046373 (electromagnetic wave
treated or modified), U.S. Pat. No. 6051746 (polynuclear aromatic
modifier), U.S. Pat. No. 6225254 (heating template), PCT WO 01/36329
published May 25 2001 (surfactant synthesis), PCT WO 01/25151 published
Apr. 12 2001 (staged acid addition), PCT WO 01/60746 published
Aug. 23 2001 (silicon oil), U.S. patent application Ser. No. 09/929949
filed Aug. 15 2001 (cooling molecular sieve), U.S. patent application
Ser. No. 09/615526 filed Jul. 13 2000 (metal impregnation including
copper), U.S. patent application Ser. No. 09/672469 filed Sep.
28 2000 (conductive microfilter), and U.S. patent application Ser.
No. 09/754812 filed Jan. 4 2001(freeze drying the molecular sieve),
which are all herein fully incorporated by reference.
[0090] In one preferred embodiment, when a templating agent is
used in the synthesis of a molecular sieve, it is preferred that
the templating agent is substantially, preferably completely, removed
after crystallization by numerous well known techniques, for example,
heat treatments such as calcination. Calcination involves contacting
the molecular sieve containing the templating agent with a gas,
preferably containing oxygen, at any desired concentration at an
elevated temperature sufficient to either partially or completely
decompose and oxidize the templating agent.
[0091] Molecular sieve have either a high silicon (Si) to aluminum
(Al) ratio or a low silicon to aluminum ratio, however, a low Si/Al
ratio is preferred for SAPO synthesis. In one embodiment, the molecular
sieve has a Si/Al ratio less than 0.65 preferably less than 0.40
more preferably less than 0.32 and most preferably less than 0.20.
In another embodiment the molecular sieve has a Si/Al ratio in the
range of from about 0.65 to about 0.10 preferably from about 0.40
to about 0.10 more preferably from about 0.32 to about 0.10 and
more preferably from about 0.32 to about 0.15.
[0092] The pH of a reaction mixture containing at a minimum a silicon-,
aluminum-, and/or phosphorous-composition, a templating agent, and
a polymeric base should be in the range of from 2 to 10 preferably
in the range of from 4 to 9 and most preferably in the range of
from 5 to 8. The pH can be controlled by the addition of basic or
acidic compounds as necessary to maintain the pH during the synthesis
in the preferred range of from 4 to 9. In another embodiment, the
templating agent and/or polymeric base is added to the reaction
mixture of the silicon source and phosphorous source such that the
pH of the reaction mixture does not exceed 10.
[0093] In one embodiment, the molecular sieves of the invention
are combined with one or more other molecular sieves. In another
embodiment, the preferred silicoaluminophosphate or aluminophosphate
molecular sieves, or a combination thereof, are combined with one
more of the following non-limiting examples of molecular sieves
described in the following: Beta (U.S. Pat. No. 3308069), ZSM-5
(U.S. Pat. Nos. 3702886 4797267 and 5783321), ZSM-11 (U.S.
Pat. No. 3709979), ZSM-12 (U.S. Pat. No. 3832449), ZSM-12 and
ZSM-38 (U.S. Pat. No. 3948758), ZSM-22 (U.S. Pat. No. 5336478),
ZSM-23 (U.S. Pat. No. 4076842), ZSM-34 (U.S. Pat. No. 4086186),
ZSM-35 (U.S. Pat. No. 4016245 ZSM-48 (U.S. Pat. No. 4397827),
ZSM-58 (U.S. Pat. No. 4698217), MCM-1 (U.S. Pat. No. 4639358),
MCM-2 (U.S. Pat. No. 4673559), MCM-3 (U.S. Pat. No. 4632811),
MCM-4 (U.S. Pat. No. 4664897), MCM-5 (U.S. Pat. No. 4639357),
MCM-9 (U.S. Pat. No. 4880611), MCM-10 (U.S. Pat. No. 4623527),
MCM-14 (U.S. Pat. No. 4619818), MCM-22 (U.S. Pat. No. 4954325),
MCM-41 (U.S. Pat. No. 5098684), M-41S (U.S. Pat. No. 5102643),
MCM-48 (U.S. Pat. No. 5198203), MCM-49 (U.S. Pat. No. 5236575),
MCM-56 (U.S. Pat. No. 5362697), ALPO-11 (U.S. Pat. No. 4310440),
titanium aluminosilicates (TASO), TASO-45 (EP-A-0 229-295), boron
silicates (U.S. Pat. No. 4254297), titanium aluminophosphates
(TAPO) (U.S. Pat. No. 4500651), mixtures of ZSM-5 and ZSM-11 (U.S.
Pat. No. 4229424), ECR-18 (U.S. Pat. No. 5278345), SAPO-34 bound
ALPO-5 (U.S. Pat. No. 5972203), PCT WO 98/57743 published Dec.
23 1988 (molecular sieve and Fischer-Tropsch), U.S. Pat. No. 6300535
(MFI-bound zeolites), and mesoporous molecular sieves (U.S. Pat.
Nos. 6284696 5098684 5102643 and 5108725), which are all
herein fully incorporated by reference.
[0094] Method for Making Molecular Sieve Catalyst Compositions
[0095] Once the molecular sieve is synthesized, depending on the
requirements of the particular conversion process, the molecular
sieve is then formulated into a molecular sieve catalyst composition,
particularly for commercial use. The molecular sieves synthesized
above are made or formulated into catalysts by combining the synthesized
molecular sieves with a binder and/or a matrix material to form
a molecular sieve catalyst composition or a formulated molecular
sieve catalyst composition. This formulated molecular sieve catalyst
composition is formed into useful shape and sized particles by well-known
techniques such as spray drying, pelletizing, extrusion, and the
like.
[0096] There are many different binders that are useful in forming
the molecular sieve catalyst composition. Non-limiting examples
of binders that are useful alone or in combination include various
types of hydrated alumina, silicas, and/or other inorganic oxide
sol. One preferred alumina containing sol is aluminum chlorhydrol.
The inorganic oxide sol acts like glue binding the synthesized molecular
sieves and other materials such as the matrix together, particularly
after thermal treatment. Upon heating, the inorganic oxide sol,
preferably having a low viscosity, is converted into an inorganic
oxide matrix component. For example, an alumina sol will convert
to an aluminum oxide matrix following heat treatment.
[0097] Aluminum chlorhydrol, a hydroxylated aluminum based sol
containing a chloride counter ion, has the general formula of Al.sub.mO.sub.n(OH).sub.oCl.sub.p.x(H.sub.2O)
wherein m is 1 to 20 n is 1 to 8 o is 5 to 40 p is 2 to 15 and
x is 0 to 30. In one embodiment, the binder is Al.sub.13O.sub.4(OH).sub.24Cl.sub.7.12(H.sub.2O)
as is described in G. M. Wolterman, et al., Stud. Surf. Sci. and
Catal., 76 pages 105-144 (1993), which is herein incorporated by
reference. In another embodiment, one or more binders are combined
with one or more other non-limiting examples of alumina materials
such as aluminum oxyhydroxide, .gamma.-alumina, boehmite, diaspore,
and transitional aluminas such as .alpha.-alumina, .beta.-alumina,
.gamma.-alumina, .delta.-alumina, .epsilon.-alumina, .kappa.-alumina,
and .rho.-alumina, aluminum trihydroxide, such as gibbsite, bayerite,
nordstrandite, doyelite, and mixtures thereof.
[0098] In another embodiment, the binders are alumina sols, predominantly
comprising aluminum oxide, optionally including some silicon. In
yet another embodiment, the binders are peptized alumina made by
treating alumina hydrates such as pseudobohemite, with an acid,
preferably an acid that does not contain a halogen, to prepare sols
or aluminum ion solutions. Non-limiting examples of commercially
available colloidal alumina sols include Nalco 8676 available from
Nalco Chemical Co., Naperville, Ill., and Nyacol available from
The PQ Corporation, Valley Forge, Pa.
[0099] The molecular sieve synthesized above, in a preferred embodiment,
is combined with one or more matrix material(s). Matrix materials
are typically effective in reducing overall catalyst cost, act as
thermal sinks assisting in shielding heat from the catalyst composition
for example during regeneration, densifying the catalyst composition,
increasing catalyst strength such as crush strength and attrition
resistance, and to control the rate of conversion in a particular
process.
[0100] Non-limiting examples of matrix materials include one or
more of: rare earth metals, metal oxides including titania, zirconia,
magnesia, thoria, beryllia, quartz, silica or sols, and mixtures
thereof, for example silica-magnesia, silica-zirconia, silica-titania,
silica-alumina and silica-alumina-thoria. In an embodiment, matrix
materials are natural clays such as those from the families of montmorillonite
and kaolin. These natural clays include subbentonites and those
kaolins known as, for example, Dixie, McNamee, Georgia and Florida
clays. Non-limiting examples of other matrix materials include:
haloysite, kaolinite, dickite, nacrite, or anauxite. In one embodiment,
the matrix material, preferably any of the clays, are subjected
to well known modification processes such as calcination and/or
acid treatment and/or chemical treatment.
[0101] In one preferred embodiment, the matrix material is a clay
or a clay-type composition, preferably the clay or clay-type composition
having a low iron or titania content, and most preferably the matrix
material is kaolin. Kaolin has been found to form a pumpable, high
solid content slurry, it has a low fresh surface area, and it packs
together easily due to its platelet structure. A preferred average
particle size of the matrix material, most preferably kaolin, is
from about 0.1 .mu.m to about 0.6 .mu.m with a D90 particle size
distribution of less than about 1 .mu.m.
[0102] In one embodiment, the binder, the molecular sieve and the
matrix material are combined in the presence of a liquid to form
a molecular sieve catalyst composition, where the amount of binder
is from about 2% by weight to about 30% by weight, preferably from
about 5% by weight to about 20% by weight, and more preferably from
about 7% by weight to about 15% by weight, based on the total weight
of the binder, the molecular sieve and matrix material, excluding
the liquid (after calcination).
[0103] In another embodiment, the weight ratio of the binder to
the matrix material used in the formation of the molecular sieve
catalyst composition is from 0:1 to 1:15 preferably 1:15 to 1:5
more preferably 1:10 to 1:4 and most preferably 1:6 to 1:5. It
has been found that a higher sieve content, lower matrix content,
increases the molecular sieve catalyst composition performance,
however, lower sieve content, higher matrix material, improves the
attrition resistance of the composition.
[0104] Upon combining the molecular sieve and the matrix material,
optionally with a binder, in a liquid to form a slurry, mixing,
preferably rigorous mixing is needed to produce a substantially
homogeneous mixture containing the molecular sieve. Non-limiting
examples of suitable liquids include one or a combination of water,
alcohol, ketones, aldehydes, and/or esters. The most preferred liquid
is water. In one embodiment, the slurry is colloid-milled for a
period of time sufficient to produce the desired slurry texture,
sub-particle size, and/or sub-particle size distribution.
[0105] The molecular sieve and matrix material, and the optional
binder, are in the same or different liquid, and are combined in
any order, together, simultaneously, sequentially, or a combination
thereof. In the preferred embodiment, the same liquid, preferably
water is used. The molecular sieve, matrix material, and optional
binder, are combined in a liquid as solids, substantially dry or
in a dried form, or as slurries, together or separately. If solids
are added together as dry or substantially dried solids, it is preferable
to add a limited and/or controlled amount of liquid.
[0106] In one embodiment, the slurry of the molecular sieve, binder
and matrix materials is mixed or milled to achieve a sufficiently
uniform slurry of sub-particles of the molecular sieve catalyst
composition that is then fed to a forming unit that produces the
molecular sieve catalyst composition. In a preferred embodiment,
the forming unit is spray dryer. Typically, the forming unit is
maintained at a temperature sufficient to remove most of the liquid
from the slurry, and from the resulting molecular sieve catalyst
composition. The resulting catalyst composition when formed in this
way takes the form of microspheres.
[0107] When a spray drier is used as the forming unit, typically,
the slurry of the molecular sieve and matrix material, and optionally
a binder, is co-fed to the spray drying volume with a drying gas
with an average inlet temperature ranging from 200.degree. C. to
550.degree. C., and a combined outlet temperature ranging from 100.degree.
C. to about 225.degree. C. In an embodiment, the average diameter
of the spray dried formed catalyst composition is from about 40
.mu.m to about 300 .mu.m, preferably from about 50 .mu.m to about
250 .mu.m, more preferably from about 50 .mu.m to about 200 .mu.m,
and most preferably from about 65 .mu.m to about 90 .mu.m.
[0108] During spray drying, the slurry is passed through a nozzle
distributing the slurry into small droplets, resembling an aerosol
spray into a drying chamber. Atomization is achieved by forcing
the slurry through a single nozzle or multiple nozzles with a pressure
drop in the range of from 100 psia to 1000 psia (690 kPaa to 6895
kPaa). In another embodiment, the slurry is co-fed through a single
nozzle or multiple nozzles along with an atomization fluid such
as air, steam, flue gas, or any other suitable gas.
[0109] In yet another embodiment, the slurry described above is
directed to the perimeter of a spinning wheel that distributes the
slurry into small droplets, the size of which is controlled by many
factors including slurry viscosity, surface tension, flow rate,
pressure, and temperature of the slurry, the shape and dimension
of the nozzle(s), or the spinning rate of the wheel. These droplets
are then dried in a co-current or counter-current flow of air passing
through a spray drier to form a substantially dried or dried molecular
sieve catalyst composition, more specifically a molecular sieve
in powder form.
[0110] Generally, the size of the powder is controlled to some
extent by the solids content of the slurry. However, control of
the size of the catalyst composition and its spherical characteristics
are controllable by varying the slurry feed properties and conditions
of atomization.
[0111] Other methods for forming a molecular sieve catalyst composition
are described in U.S. patent application Ser. No. 09/617714 filed
Jul. 17 2000 (spray drying using a recycled molecular sieve catalyst
composition), which is herein incorporated by reference.
[0112] In another embodiment, the formulated molecular sieve catalyst
composition contains from about 1% to about 99%, more preferably
from about 5% to about 90%, and most preferably from about 10% to
about 80%, by weight of the molecular sieve based on the total weight
of the molecular sieve catalyst composition.
[0113] In another embodiment, the weight percent of binder in or
on the spray dried molecular sieve catalyst composition based on
the total weight of the binder, molecular sieve, and matrix material
is from about 2% by weight to about 30% by weight, preferably from
about 5% by weight to about 20% by weight, and more preferably from
about 7% by weight to about 15% by weight.
[0114] Once the molecular sieve catalyst composition is formed
in a substantially dry or dried state, to further harden and/or
activate the formed catalyst composition, a heat treatment such
as calcination, at an elevated temperature is usually performed.
A conventional calcination environment is air that typically includes
a small amount of water vapor. Typical calcination temperatures
are in the range from about 400.degree. C. to about 1000.degree.
C., preferably from about 500.degree. C. to about 800.degree. C.,
and most preferably from about 550.degree. C. to about 700.degree.
C., preferably in a calcination environment such as air, nitrogen,
helium, flue gas (combustion product lean in oxygen), or any combination
thereof.
[0115] In one embodiment, calcination of the formulated molecular
sieve catalyst composition is carried out in any number of well
known devices including rotary calciners, fluid bed calciners, batch
ovens, and the like. Calcination time is typically dependent on
the degree of hardening of the molecular sieve catalyst composition
and the temperature ranges from about 15 minutes to about 2 hours.
[0116] In a preferred embodiment, the molecular sieve catalyst
composition is heated in nitrogen at a temperature of from about
600.degree. C. to about 700.degree. C. Heating is carried out for
a period of time typically from 30 minutes to 15 hours, preferably
from 1 hour to about 10 hours, more preferably from about 1 hour
to about 5 hours, and most preferably from about 2 hours to about
4 hours.
[0117] Other methods for activating a molecular sieve catalyst
composition, in particular where the molecular sieve is a reaction
product of the combination of a silicon-, phosphorous-, and aluminum-sources,
a templating agent, and a polymeric base, more particularly a silicoaluminophosphate
catalyst composition (SAPO) are described in, for example, U.S.
Pat. No. 5185310 (heating molecular sieve of gel alumina and water
to 450.degree. C.), PCT WO 00/75072 published Dec. 14 2000 (heating
to leave an amount of template), and U.S. application Ser. No. 09/558774
filed Apr. 26 2000 (rejuvenation of molecular sieve), which are
all herein fully incorporated by reference.
[0118] Oxygenate to Olefins Process
[0119] In a preferred embodiment of the process of the invention,
the feedstock contains one or more oxygenates, more specifically,
one or more organic compound(s) containing at least one oxygen atom.
In the most preferred embodiment of the process of invention, the
oxygenate in the feedstock is one or more alcohol(s), preferably
aliphatic alcohol(s) where the aliphatic moiety of the alcohol(s)
has from 1 to 20 carbon atoms, preferably from 1 to 10 carbon atoms,
and most preferably from 1 to 4 carbon atoms. The alcohols useful
as feedstock in the process of the invention include lower straight
and branched chain aliphatic alcohols and their unsaturated counterparts.
Non-limiting examples of oxygenates include methanol, ethanol, n-propanol,
isopropanol, methyl ethyl ether, dimethyl ether, diethyl ether,
di-isopropyl ether, formaldehyde, dimethyl carbonate, dimethyl ketone,
acetic acid, and mixtures thereof.
[0120] In the most preferred embodiment, the feedstock is selected
from one or more of methanol, ethanol, dimethyl ether, diethyl ether
or a combination thereof, more preferably methanol and dimethyl
ether, and most preferably methanol.
[0121] The various feedstocks discussed above, particularly a feedstock
containing an oxygenate, more particularly a feedstock containing
an alcohol, is converted primarily into one or more olefin(s). The
olefin(s) or olefin monomer(s) produced from the feedstock typically
have from 2 to 30 carbon atoms, preferably 2 to 8 carbon atoms,
more preferably 2 to 6 carbon atoms, still more preferably 2 to
4 carbons atoms, and most preferably ethylene and/or propylene.
[0122] Non-limiting examples of olefin monomer(s) include ethylene,
propylene, butene-1 pentene-1 4-methyl-pentene-1 hexene-1 octene-1
and decene-1 preferably ethylene, propylene, butene-1 pentene-1
4-methyl-pentene-1 hexene-1 octene-1 and isomers thereof. Other
olefin monomer(s) include unsaturated monomers, diolefins having
4 to 18 carbon atoms, conjugated or nonconjugated dienes, polyenes,
vinyl monomers and cyclic olefins.
[0123] In the most preferred embodiment, the feedstock, preferably
of one or more oxygenates, is converted in the presence of a molecular
sieve catalyst composition into olefin(s) having 2 to 6 carbons
atoms, preferably 2 to 4 carbon atoms. Most preferably, the olefin(s),
alone or in combination, are converted from a feedstock containing
an oxygenate, preferably an alcohol, most preferably methanol, to
the preferred olefin(s) ethylene and/or propylene.
[0124] One process for converting feedstock into olefins is generally
referred to as methanol-to-olefins (MTO). In a MTO process, typically
an oxygenated feedstock, most preferably a methanol containing feedstock,
is converted in the presence of a molecular sieve catalyst composition
into one or more olefin(s), preferably and predominantly, ethylene
and/or propylene, often referred to as light olefin(s).
[0125] Increasing the selectivity of preferred hydrocarbon products
such as ethylene and/or propylene from the conversion of an oxygenate
using a molecular sieve catalyst composition is described in U.S.
Pat. No. 6137022 and PCT WO 00/74848 published Dec. 14 2000
which are all herein fully incorporated by reference.
[0126] The feedstock, in one embodiment, contains one or more diluent(s),
typically used to reduce the concentration of the feedstock, and
are generally non-reactive to the feedstock or molecular sieve catalyst
composition. Non-limiting examples of diluents include helium, argon,
nitrogen, carbon monoxide, carbon dioxide, water, essentially non-reactive
paraffins (especially alkanes such as methane, ethane, and propane),
essentially non-reactive aromatic compounds, and mixtures thereof.
The most preferred diluents are water and nitrogen, with water being
particularly preferred.
[0127] The diluent, water, is used either in a liquid or a vapor
form, or a combination thereof. The diluent is either added directly
to a feedstock entering into a reactor or added directly into a
reactor, or added with a molecular sieve catalyst composition. In
one embodiment, the amount of diluent in the feedstock is in the
range of from about 1 to about 99 mole percent based on the total
number of moles of the feedstock and diluent, preferably from about
1 to 80 mole percent, more preferably from about 5 to about 50
most preferably from about 5 to about 25. In one embodiment, other
hydrocarbons are added to a feedstock either directly or indirectly,
and include olefin(s), paraffin(s), aromatic(s) (see for example
U.S. Pat. No. 4677242) or mixtures thereof, preferably propylene,
butylene, pentylene, and other hydrocarbons having 4 or more carbon
atoms, or mixtures thereof.
[0128] The process for converting a feedstock, especially a feedstock
containing one or more oxygenates, in the presence of a molecular
sieve catalyst composition of the invention, is carried out in a
reaction process in a reactor, where the process is a fixed bed
process, or a fluidized bed process, preferably a continuous fluidized
bed process.
[0129] The reaction processes can take place in a variety of catalytic
reactors such as hybrid reactors that have a dense bed or fixed
bed zones and/or fast fluidized bed reaction zones coupled together,
circulating fluidized bed reactors, riser reactors, and the like.
Suitable conventional reactor types are described in, for example,
U.S. Pat. No. 4076796 U.S. Pat. No. 6287522 and Fluidization
Engineering, D. Kunii and O. Levenspiel, Robert E. Krieger Publishing
Company, New York, N.Y. 1977 which are all herein fully incorporated
by reference.
[0130] The preferred reactor type are riser reactors generally
described in Riser Reactor, Fluidization and Fluid-Particle Systems,
pages 48 to 59 F. A. Zenz and D. F. Othmo, Reinhold Publishing
Corporation, New York, 1960 and U.S. Pat. No. 6166282 and U.S.
patent application Ser. No. 09/564613 filed May 4 2000 which
are all herein fully incorporated by reference.
[0131] In the preferred embodiment, a fluidized bed process or
high velocity fluidized bed process includes a reactor apparatus,
a regeneration system and a recovery system.
[0132] The present invention solves the current needs in the art
by providing an improved method for converting a feed including
an oxygenate to a product including a light olefin. The method of
the present invention is conducted in a reactor apparatus. As used
herein, the term "reactor apparatus" refers to an apparatus
which includes at least a place in which an oxygenate to olefin
conversion reaction takes place. As further used herein, the term
"reaction zone" refers to the portion of a reactor apparatus
in which the oxygenate to olefin conversion reaction takes place
and is used synonymously with the term "reactor."Desirably,
the reactor apparatus includes a reaction zone, an inlet zone and
a disengaging zone. The "inlet zone" is the portion of
the reactor apparatus into which feed and catalyst are introduced.
The "reaction zone" is the portion of the reactor apparatus
in which the feed is contacted with the catalyst under conditions
effective to convert the oxygenate portion of the feed into a light
olefin product. The "disengaging zone" is the portion
of the reactor apparatus in which the catalyst and any additional
solids in the reactor are separated from the products. Typically,
the reaction zone is positioned between the inlet zone and the disengaging
zone.
[0133] In an embodiment, the amount of liquid feedstock fed separately
or jointly with a vapor feedstock, to a reactor system is in the
range of from 0.1 weight percent to about 85 weight percent, preferably
from about 1 weight percent to about 75 weight percent, more preferably
from about 5 weight percent to about 65 weight percent based on
the total weight of the feedstock including any diluent contained
therein. The liquid and vapor feedstocks are preferably of similar
composition, or contain varying proportions of the same or different
feedstock with the same or different diluent.
[0134] The feedstock entering the fluidized bed reactor apparatus
is preferably converted, partially or fully, in the reaction zone
into a gaseous effluent that enters the disengaging zone along with
a coked molecular sieve catalyst composition. In the preferred embodiment,
cyclone(s) within the disengaging vessel are designed to separate
the molecular sieve catalyst composition, preferably a coked molecular
sieve catalyst composition, from the gaseous effluent containing
one or more olefin(s) within the disengaging zone. Cyclones are
preferred, however, gravity effects within the disengaging vessel
will also separate the catalyst compositions from the gaseous effluent.
Other methods for separating the catalyst compositions from the
gaseous effluent include the use of plates, caps, elbows, and the
like.
[0135] In one embodiment of the disengaging zone, the disengaging
zone includes a disengaging vessel, typically a lower portion of
the disengaging vessel is a stripping zone. In the stripping zone
the coked molecular sieve catalyst composition is contacted with
a gas, preferably one or a combination of steam, methane, carbon
dioxide, carbon monoxide, hydrogen, or an inert gas such as argon,
preferably steam, to recover adsorbed hydrocarbons from the coked
molecular sieve catalyst composition that is then introduced to
the regeneration system. In another embodiment, the stripping zone
is in a separate vessel from the disengaging vessel and the gas
is passed at a gas hourly superficial velocity (GHSV) of from 1
hr.sup.-1 to about 20000 hr.sup.-1 based on the volume of gas to
volume of coked molecular sieve catalyst composition, preferably
at an elevated temperature from 250.degree. C. to about 750.degree.
C., preferably from about 350.degree. C. to 650.degree. C., over
the coked molecular sieve catalyst composition.
[0136] The conversion temperature employed in the conversion process,
specifically within the reactor system, is in the range of from
about 200.degree. C. to about 1000.degree. C., preferably from about
250.degree. C. to about 800.degree. C., more preferably from about
250.degree. C. to about 750.degree. C., yet more preferably from
about 300.degree. C. to about 650.degree. C., yet even more preferably
from about 350.degree. C. to about 600.degree. C. most preferably
from about 350.degree. C. to about 550.degree. C.
[0137] The conversion pressure employed in the conversion process,
specifically within the reactor system, varies over a wide range
including autogenous pressure. The conversion pressure is based
on the partial pressure of the feedstock exclusive of any diluent
therein. Typically the conversion pressure employed in the process
is in the range of from about 0.1 kPaa to about 5 MPaa, preferably
from about 5 kPaa to about 1 MPaa, and most preferably from about
20 kPaa to about 500 kPaa.
[0138] The weight hourly space velocity (WHSV), particularly in
a process for converting a feedstock containing one or more oxygenates
in the presence of a molecular sieve catalyst composition within
a reaction zone, is defined as the total weight of the feedstock
excluding any diluents to the reaction zone per hour per weight
of molecular sieve in the molecular sieve catalyst composition in
the reaction zone. The WHSV is maintained at a level sufficient
to keep the catalyst composition in a fluidized state within a reactor.
[0139] Typically, the WHSV ranges from about 1 hr.sup.-1 to about
5000 hr.sup.-1 preferably from about 2 hr.sup.-1 to about 3000
hr.sup.-1 more preferably from about 5 hr.sup.-1 to about 1500
hr.sup.-1 and most preferably from about 10 hr.sup.-1 to about
1000 hr.sup.-1. In one preferred embodiment, the WHSV is greater
than 20 hr.sup.-1 preferably the WHSV for conversion of a feedstock
containing methanol and dimethyl ether is in the range of from about
20 hr.sup.-1 to about 300 hr.sup.-1.
[0140] The superficial gas velocity (SGV) of the feedstock including
diluent and reaction products within the reactor system is preferably
sufficient to fluidize the molecular sieve catalyst composition
within a reaction zone in the reactor. The SGV in the process, particularly
within the reactor system, more particularly within the riser reactor(s),
is at least 0.1 meter per second (m/sec), preferably greater than
0.5 m/sec, more preferably greater than 1 m/sec, even more preferably
greater than 2 m/sec, yet even more preferably greater than 3 m/sec,
and most preferably greater than 4 m/sec. See for example U.S. patent
application Ser. No. 09/708753 filed Nov. 8 2000 which is herein
incorporated by reference.
[0141] In one preferred embodiment of the process for converting
an oxygenate to olefin(s) using a silicoaluminophosphate molecular
sieve catalyst composition, the process is operated at a WHSV of
at least 20 hr.sup.-1 and a Temperature Corrected Normalized Methane
Selectivity (TCNMS) of less than 0.016 preferably less than or
equal to 0.01. See, for example, U.S. Pat. No. 5952538 which
is herein fully incorporated by reference.
[0142] In another embodiment of the processes for converting an
oxygenate such as methanol to one or more olefin(s) using a molecular
sieve catalyst composition, the WHSV is from 0.01 hr.sup.-1 to about
100 hr.sup.-1 at a temperature of from about 350.degree. C. to
550.degree. C., and silica to Me.sub.2O.sub.3 (Me is a Group IIIA
or VIII element from the Periodic Table of Elements) molar ratio
of from 300 to 2500. See for example EP-0 642 485 B1 which is herein
fully incorporated by reference.
[0143] Other processes for converting an oxygenate such as methanol
to one or more olefin(s) using a molecular sieve catalyst composition
are described in PCT WO 01/23500 published Apr. 5 2001 which is
herein incorporated by reference.
[0144] The conversion of oxygenates to light olefins is catalyzed
by various molecular sieve catalysts. During conversion, carbonaceous
deposits known as "coke" unavoidably form on the surface
of or within the molecular sieve catalyst. In order to avoid a significant
reduction in catalyst activity, the catalyst must be regenerated
by burning off coke deposits.
[0145] In an embodiment, a portion of the coked molecular sieve
catalyst composition is withdrawn from the reactor apparatus and
introduced to the regeneration system. The regeneration system comprises
a regenerator where the coked catalyst composition is contacted
with a regeneration medium, preferably a gas containing oxygen,
under general regeneration conditions of temperature, pressure and
residence time.
[0146] Non-limiting examples of the regeneration medium include
one or more of oxygen, O.sub.3 SO.sub.3 N.sub.2O, NO, NO.sub.2
N.sub.2O.sub.5 air, air diluted with nitrogen or carbon dioxide,
oxygen and water (U.S. Pat. No. 6245703), carbon monoxide and/or
hydrogen. The regeneration conditions are those capable of burning
coke from the coked catalyst composition, preferably to a coke level
less than 0.5 weight percent based on the total weight of the coked
molecular sieve catalyst composition, to form a regenerated molecular
sieve catalyst composition.
[0147] The regeneration temperature is in the range of from about
200.degree. C. to about 1500.degree. C., preferably from about 300.degree.
C. to about 1000.degree. C., more preferably from about 450.degree.
C. to about 750.degree. C., and most preferably from about 550.degree.
C. to 700.degree. C. The regeneration pressure is in the range of
from about 15 psia (103 kPaa) to about 500 psia (3448 kPaa), preferably
from about 20 psia (138 kPaa) to about 250 psia (1724 kPaa), more
preferably from about 25 psia (172 kPaa) to about 150 psia (1034
kPaa), and most preferably from about 30 psia (207 kPaa) to about
60 psia (414 kPaa).
[0148] The preferred residence time of the molecular sieve catalyst
composition in the regenerator is in the range of from about one
minute to several hours, most preferably about one minute to 100
minutes, and the preferred volume of oxygen in the gas is in the
range of from about 0.01 mole percent to about 5 mole percent based
on the total volume of the gas.
[0149] In one embodiment, regeneration promoters, typically metal
containing compounds such as platinum, palladium and the like, are
added to the regenerator directly, or indirectly, for example with
the coked catalyst composition. Also, in another embodiment, a fresh
molecular sieve catalyst composition is added to the regenerator
containing a regeneration medium of oxygen and water as described
in U.S. Pat. No. 6245703 which is herein fully incorporated by
reference.
[0150] In an embodiment, a portion of the regenerated molecular
sieve catalyst composition from the regenerator is returned to the
reactor apparatus, or directly to the reaction zone, or indirectly,
by pre-contacting with the feedstock, or contacting with fresh molecular
sieve catalyst composition, or contacting with a regenerated molecular
sieve catalyst composition or a cooled regenerated molecular sieve
catalyst composition described below.
[0151] The burning of coke is an exothermic reaction, and in an
embodiment, the temperature within the regeneration system is controlled
by various techniques in the art including feeding a cooled gas
to the regenerator vessel, operated either in a batch, continuous,
or semi-continuous mode, or a combination thereof. A preferred technique
involves withdrawing the regenerated molecular sieve catalyst composition
from the regeneration system and passing the regenerated molecular
sieve catalyst composition through a catalyst cooler that forms
a cooled regenerated molecular sieve catalyst composition. The catalyst
cooler, in an embodiment, is a heat exchanger that is located either
internal or external to the regeneration system.
[0152] In one embodiment, the cooled regenerated molecular sieve
catalyst composition is returned to the regenerator in a continuous
cycle, alternatively, (see U.S. patent application Ser. No. 09/587766
filed Jun. 6 2000) a portion of the cooled regenerated molecular
sieve catalyst composition is returned to the regenerator vessel
in a continuous cycle, and another portion of the cooled molecular
sieve regenerated molecular sieve catalyst composition is returned
to the reaction zone, directly or indirectly, or a portion of the
regenerated molecular sieve catalyst composition or cooled regenerated
molecular sieve catalyst composition is contacted with by-products
within the gaseous effluent (PCT WO 00/49106 published Aug. 24
2000), which are all herein fully incorporated by reference. In
another embodiment, a regenerated molecular sieve catalyst composition
contacted with an alcohol, preferably ethanol, 1-propanol, 1-butanol
or mixture thereof, is introduced to the reactor system, as described
in U.S. patent application Ser. No. 09/785122 filed Feb. 16 2001
which is herein fully incorporated by reference.
[0153] Other methods for operating a regeneration system are disclosed
in U.S. Pat. No. 6290916 which is herein fully incorporated by
reference.
[0154] In one embodiment, the regenerated molecular sieve catalyst
composition withdrawn from the regeneration system, preferably from
the catalyst cooler, is combined with a fresh molecular sieve catalyst
composition and/or recirculated molecular sieve catalyst composition
and/or feedstock, and returned to the reactor apparatus. In another
embodiment, the regenerated molecular sieve catalyst composition
withdrawn from the regeneration system is returned to the reaction
zone, optionally after passing through a catalyst cooler. In one
embodiment, a carrier, such as an inert gas, feedstock vapor, steam
or the like, semi-continuously or continuously, facilitates the
introduction of the regenerated molecular sieve catalyst composition
to the reaction zone.
[0155] In one embodiment, the gaseous effluent is withdrawn from
the disengaging zone and is passed through a recovery system. There
are many well known recovery systems, techniques and sequences that
are useful in separating olefin(s) and purifying olefin(s) from
the gaseous effluent. Recovery systems generally comprise one or
more or a combination of various separation, fractionation and/or
distillation towers, columns, and splitters, and other associated
equipment, for example, various condensers, heat exchangers, refrigeration
systems or chill trains, compressors, knock-out drums or pots, pumps,
and the like.
[0156] Non-limiting examples of these towers, columns, splitters
or trains used alone or in combination include one or more of a
demethanizer, preferably a high temperature demethanizer, a deethanizer,
a depropanizer, preferably a wet depropanizer, a wash tower often
referred to as a caustic wash tower and/or quench tower, absorbers,
adsorbers, membranes, ethylene (C2) splitter, propylene (C3) splitter,
butene (C4) splitter, and the like.
[0157] Various recovery systems useful for recovering predominately
olefin(s), preferably prime or light olefin(s) such as ethylene,
propylene and/or butene are described in U.S. Pat. No. 5960643
U.S. Pat. Nos. 5019143 5452581 and 5082481 U.S. Pat. No.
5672197 U.S. Pat. No. 6069288 U.S. Pat. No. 5904880 U.S.
Pat. No. 5927063 and U.S. Pat. No. 6121504 U.S. Pat. No. 6121503
and U.S. Pat. No. 6293998 which are all herein fully incorporated
by reference.
[0158] Generally accompanying most recovery systems is the production,
generation or accumulation of additional products, by-products and/or
contaminants along with the preferred prime products. The preferred
prime products, the light olefins, such as ethylene and propylene,
are typically purified for use in derivative manufacturing processes
such as polymerization processes. Therefore, in the most preferred
embodiment of the recovery system, the recovery system also includes
a purification system. For example, the light olefin(s) produced
particularly in a MTO process are passed through a purification
system that removes low levels of by-products or contaminants.
[0159] Non-limiting examples of contaminants and by-products include
generally polar compounds such as water, alcohols, carboxylic acids,
ethers, carbon oxides, sulfur compounds such as hydrogen sulfide,
carbonyl sulfides and mercaptans, ammonia and other nitrogen compounds,
arsine, phosphine and chlorides. Other contaminants or by-products
include hydrogen and hydrocarbons such as acetylene, methyl acetylene,
propadiene, butadiene and butyne.
[0160] Other recovery systems that include purification systems,
for example for the purification of olefin(s), are described in
Kirk-Othmer Encyclopedia of Chemical Technology, 4th Edition, Volume
9 John Wiley & Sons, 1996 pages 249-271 and 894-899 which
is herein incorporated by reference. Purification systems are also
described in for example, U.S. Pat. No. 6271428 U.S. Pat. No.
6293999 and U.S. patent application Ser. No. 09/689363 filed
Oct. 20 2000 which are herein incorporated by reference.
[0161] 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 production of methane, ethane,
propane, and C.sub.5+ materials. The present invention maintains
the average coke loading of the catalyst in a range particularly
selective for producing ethylene and propylene. Such range is based
on the acid site density of the molecular sieve component of the
catalyst.
[0162] Coke levels on the molecular sieve catalyst composition
are measured by withdrawing from the conversion process the molecular
sieve catalyst composition at a point in the process and determining
its carbon content. It is recognized that the molecular sieve catalyst
composition in the reaction zone is made up of a mixture of regenerated
catalyst and catalyst that has varying levels of carbonaceous deposits.
The measured coke level of carbonaceous deposits thus represents
an average of the levels of individual catalyst particles.
[0163] U.S. Pat. No. 6023005 incorporated herein by reference,
teaches the desirability of providing carbonaceous deposits, or
coke levels, for oxygenates to olefins conversion processes, in
the range of 2 wt. % to about 30 wt. % based on the total reaction
volume of coked catalyst to promote selectivity to light olefins.
It further teaches providing a regenerated catalyst having a coke
level of less than about 2 wt. % to provide such a total reaction
volume of coked catalyst. However, the inventors have discovered
that obtaining particularly preferred results does not consistently
depend on maintaining such a coke level range alone, and certainly
not over such a wide range as has been previously disclosed. It
has now been found that it is advantageous to maintain an average
coke loading of the catalyst in a range of 1 to 10 carbon atoms
per acid site of the molecular sieve component of the catalyst in
the reactor apparatus, or more particularly the reaction zone, to
provide superior prime olefin selectivity. In various embodiments,
the average coke loading on the molecular sieve-containing catalyst
utilized in an oxygenate to olefins reaction ranges from 2 to 9
or 3 to 8 or 4 to 7 carbon atoms per acid site of the molecular
sieve. A product containing at least about 67.0 wt. %, at least
about 70.0 wt. % prime olefins, at least about 72.0 wt. % prime
olefins, or even at least about 75.0 wt. % prime olefins can be
obtained from the present process. Preferably, a product containing
no greater than 4.0 wt. % methane, no greater than 3.0 wt. % methane,
or no greater than 2.0 wt. % methane can be obtained from the present
process. Additionally, a product containing no greater than 4.0
wt. % propane, preferably no greater than 3.0 wt. % propane, or
more preferably no greater than 2.0 wt. % propane can be obtained
from the present process.
[0164] In order to determine the carbon atoms per acid site of
the molecular sieve component of the catalyst it is first necessary
to determine the acid site density of the molecular sieve by a suitable
analytic method, e.g., by NMR, and then determine the coke content
of the catalyst by conventional methods, e.g., by burning off coke
to form oxides of carbon which are measured by a suitable analytic
method, e.g., IR.
[0165] The acid site density of the catalyst can range from 0.10
mmols/g to 0.40 mmols/g of formulated catalyst, e.g., from 0.13
mmols/g to 0.38 mmols/g of formulated catalyst, say, from 0.20 mmols/g
to 0.30 mmols/g of formulated catalyst.
[0166] The acidity desired for a specific commercial organic conversion
catalyst is based upon various factors including the type of the
reactor in which conversion takes place, intended operating conditions
for the reactor, and feedstock characteristics. Acidity of the catalyst
is of particular interest in oxygenates to olefins conversion, inasmuch
as excessive acidity can cause premature coking of the catalyst.
[0167] For silicoaluminophosphate molecular sieve materials, acidity
is typically directly related to the ratio of silicon atoms to aluminum
atoms in the framework. Acidity for aluminosilicate molecular sieve
materials, e.g, zeolites, is inversely related to the ratio of silicon
atoms to aluminum atoms. Thus the desired acidity can be varied
for molecular sieve materials by altering synthesis protocols, e.g.,
by adjusting the ratio of silicon atoms to aluminum atoms in the
synthesis mixture. Desired acid site densities for molecular sieve
materials can be achieved in other ways as well, including the substitution
of a hydrogen ion associated with an acid site with another ion,
e.g., metal ion.
[0168] A preferred embodiment of a reactor system for the present
invention is a circulating fluid bed reactor with continuous regeneration,
similar to a modem fluid catalytic cracker.
[0169] Because the catalyst must be regenerated frequently, the
reactor apparatus 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
an average coke loading on regenerated catalyst, in various embodiments,
of no greater than 10 carbon atoms per acid site, or no greater
than 9 carbon atoms per acid site, or no greater than 5 carbon atoms
per acid site, or no greater than 2 carbon atoms per acid site,
or no greater than 1 carbon atom per acid site of the molecular
sieve in the catalyst. At least a portion of the regenerated catalyst
should be returned to the reactor apparatus, or more particularly
the reaction zone, optionally through some portion of the reactor
apparatus or through combination with a recirculated catalyst, described
below. In various other embodiments, at least a portion of the regenerated
catalyst is returned to the reactor apparatus having an average
coke loading of at least 1 and no greater than 10 carbon atoms per
acid site, or at least 1 and no greater than 9 carbon atoms per
acid site, or at least 2 and no greater than 9 carbon atoms per
acid site, or at least 2 and no greater than 8 carbon atoms per
acid site.
[0170] In an embodiment of the present invention, the reactor apparatus
is operated such that a certain average coke loading on the catalyst,
comprising a mixture of both regenerated and unregenerated catalyst
particles, is maintained in the reactor apparatus, more particularly
the reaction zone--an amount such that the molecular sieve-containing
catalyst particles in the reactor apparatus or reaction zone have
an average coke loading of 1 to 10 carbon atoms per acid site of
the molecular sieve, or preferably 2 to 9 or more preferably 3
to 8 or most preferably 4 to 7 carbon atoms per acid site of the
molecular sieve.
[0171] In one embodiment, the desired average coke loading on the
molecular sieve catalyst composition in the reaction zone is maintained
by controlling the flow of the regenerated molecular sieve catalyst
composition or cooled regenerated molecular sieve catalyst composition
from the regeneration system to the reactor system, and regenerator
to reactor. Techniques for controlling the flow of a molecular sieve
catalyst composition are described in Michael Louge, Experimental
Techniques, Circulating Fluidized Beds, Grace, Avidan and Knowlton,
eds., Blackie, 1997 (336-337), which is herein incorporated by reference.
[0172] In one embodiment of the present invention, if the reactor
is a high velocity fluidized bed reactor (referred to herein as
a riser reactor), above about 2 meters per second gas superficial
velocity, then a portion of the catalyst exiting from the disengaging
zone is returned, or recirculated, to the reaction zone, becoming
recirculated catalyst. 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 and entering the disengaging zone is sent
to the regenerator. The return, or recirculation, 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
from the disengaging zone to the regenerator and the reactor, a
preferred level of carbon atoms per acid site of the molecular sieves
of the catalyst particles can be maintained in the reactor apparatus,
including on this recirculated catalyst.
[0173] In another embodiment of the present invention, if the fluidized
bed reactor is designed with low superficial 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 average coke loading can be 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.
[0174] A preferred embodiment of a reactor apparatus comprising
a riser for use in the present invention is depicted generally as
10 in FIG. 1. A methanol feed passed through line 12 is at least
partially vaporized in a preheater (not shown). The methanol feed
is mixed with regenerated catalyst from line 28 and coked catalyst
from line 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 in line 28 provide fluidization to the catalyst stream
in line 22 and keep pressure instrument lines clear of catalyst.
This inert gas and/or steam mixes with the methanol and catalyst
in the riser 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.
[0175] The reactor effluent flowing through the reactor exit 16
of riser reactor 14 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 in line 22 is recirculated to the reactor
inlet at the bottom of riser reactor 14. The portion of coked catalyst
from line 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 via line 23 flows
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 via line 30 introduced through regeneration
medium inlet 31 at temperatures, pressures, and residence times
that are capable of burning coke off of the molecular sieve-containing
catalyst and down to a level of no greater than 10 carbon atoms,
say less than 3 2 or even 1 carbon atom(s) per acid site of the
molecular sieve.
[0176] The preferred temperature in the reg |