Molecular sieve abstract
A molecular sieve and a molecular sieve catalyst containing a surface
heat impregnated with a metal. The molecular sieve is heated in
the presence of a metal containing solution at a temperature between
30.degree. C. and 400.degree. C. then separated from the metal containing
solution. The molecular sieve and molecular sieve catalyst is used
to make olefin from an oxygenate feedstock.
Molecular sieve claims
What is claimed is:
1. A method of making a molecular sieve comprising: a) mixing a
metal containing solution with a silicoaluminophosphate molecular
sieve, wherein the silicoaluminophosphate molecular sieve contains
a template; b) heating the mixture to a temperature between 30.degree.
C. and 400.degree. C. to obtain a silicoaluminophosphate molecular
sieve having a surface heat impregnated with a metal; c) separating
the heated silicoaluminophosphate molecular sieve from the heated
metal containing solution; and d) calcining the separated silicoaluminophosphate
molecular sieve.
2. The method of claim 1 wherein the silicoaluminophosphate molecular
sieve is selected from the group consisting of SAPO-5 SAPO-8 SAPO-11
SAPO-16 SAPO-17 SAPO-18 SAPO-20 SAPO-31 SAPO-34 SAPO-35 SAPO-36
SAPO-37 SAPO-40 SAPO-41 SAPO-42 SAPO-44 SAPO-47 SAPO-56 and
mixtures thereof.
3. The method catalyst of claim 1 wherein the silicoaluminophosphate
molecular sieve is selected from the group consisting of SAPO-18
SAPO-34 SAPO-35 SAPO-44 SAPO-47 and mixtures thereof.
4. The method of claim 3 wherein the silicoaluminophosphate molecular
sieve is selected from the group consisting of SAPO-34A, SAPO-34B,
and mixtures thereof.
5. The method of claim 1 wherein the calcined silicoaluminophosphate
molecular sieve comprises 0.5 to 40 percent by weight of the metal.
6. The method of claim 5 wherein the calcined silicoaluminophosphate
molecular sieve comprises 1 to 20 percent by weight of the metal.
7. The method of claim 6 wherein the calcined silicoaluminophosphate
molecular sieve comprises 1 to 10 percent by weight of the metal.
8. The method of claim 1 wherein the metal is selected from the
group consisting of Group IIA metals, Group IIIA metals, Group IB
metals, Group IIB metals, Group IIIB metals, Group VIB metals, Group
VB metals, Group VIB metals, Group VIIB metals, Group VIIIB metals,
and mixtures thereof.
9. The method of claim 1 wherein the metal is selected from the
group consisting of aluminum, magnesium, calcium, barium, lanthanum,
titanium, chromium, iron, cobalt, nickel, copper, zinc, and mixtures
thereof.
10. The method of claim 9 wherein the metal is copper, zinc, or
a mixture thereof.
11. The method of claim 1 wherein the metal is a heat decomposition
product of a metal acetate, metal nitrate, metal sulfate, or metal
halide.
12. The method of claim 11 wherein the surface is heat impregnated
with the metal at a temperature from 120.degree. C. to 260.degree.
C.
13. The method of claim 12 wherein the surface is heat impregnated
with the metal at a temperature from 160.degree. C. to 220.degree.
C.
14. The method of claim 1 wherein the mixture is heated at autogeneous
pressure.
15. The method of claim 1 wherein the metal containing solution
has a metal concentration between 0.01 M and 1.0 M.
16. The method of claim 15 wherein the metal containing solution
has a metal concentration between 0.05 M and 0.5 M.
17. The method of claim 16 wherein the metal containing solution
has a metal concentration between 0.08 M and 0.3 M.
18. The method of claim 1 wherein the metal containing solution
comprises metal salts selected from the group consisting of acetates,
nitrates, sulfates, halides, and mixtures thereof.
Molecular sieve description
FIELD OF THE INVENTION
The invention is directed to a method of making molecular sieve
that contain metals, catalysts containing molecular sieves that
contain metals, and a method for converting an oxygenate feedstock
to a product, including olefin. In particular, the invention is
directed to a silicoaluminophosphate catalyst with a molecular sieve
surface that is heat impregnated with a metal.
BACKGROUND OF THE INVENTION
Olefins, particularly light olefins, have been traditionally produced
from petroleum feedstocks by either catalytic or steam cracking.
Oxygenates, however, are becoming an alternative feedstock for making
light olefins, particularly ethylene and propylene. Promising oxygenate
feedstocks are alcohols, such as methanol and ethanol, dimethyl
ether, methyl ethyl ether, diethyl ether, dimethyl carbonate, and
methyl formate. Many of these oxygenates can be produced from a
variety of sources including synthesis gas derived from natural
gas; petroleum liquids; and carbonaceous materials, including coal.
Because of the relatively low-cost of these sources, alcohol, alcohol
derivatives, and other oxygenates have promise as an economical,
non-petroleum source for light olefin production.
One way of producing olefins is by the catalytic conversion of
methanol using a silicoaluminophosphate (SAPO) molecular sieve catalyst.
For example, U.S. Pat. No. 4499327 to Kaiser, discloses making
olefins from methanol using a variety of SAPO molecular sieve catalysts.
The process can be carried out at a temperature between 300.degree.
C. and 500.degree. C., a pressure between 0.1 atmosphere to 100
atmospheres, and a weight hourly space velocity (WHSV) of between
0.1 and 40 hr.sup.-1.
Inui has shown that nickel substitution into the SAPO-34 framework
results in an increase of ethylene selectivity relative to unsubstituted
SAPO-34. J Chemical Society Chem. Commun. p.205 1990. For example,
at 450.degree. C. the product stream comprised 88% ethylene and
5% propylene (100% methanol conversion).
In contrast to the work of Kaiser and Inui, metal incorporation
may also take place post-synthesis, that is, following the synthesis
of the molecular sieve framework. For example, U.S. Pat. No. 5962762
to Sun et al. teaches a process for converting methanol to light
olefins using a metal-incorporated SAPO catalyst. An aqueous metal
solution, preferably a nickel or cobalt containing solution, was
adsorbed onto the SAPO molecular sieve by allowing the solution
to remain in contact with the SAPO overnight at ambient conditions.
The treated molecular sieve was then separated from the solution
and dried. U. S. Pat. Nos. 5625104 and 5849968 to Beck at al.
teach a process of incorporating alkali earth and alkaline earth
metals into a zeolitic catalyst by pretreating the zeolite with
an organosilicon or poly-oxo silicon compound followed by the treatment
of a metal solution. U.S. Pat. No. 4692424 to Le Van Mao teaches
a process for the dry incorporation of manganese ions on the external
reactive sites of ZSM catalysts by adding a minimum amount of an
aqueous manganese solution to form a malleable paste and extruding
the paste under pressure.
In spite of the prior efforts to modify molecular sieve, the need
to find a molecular sieve or molecular sieve catalyst that exhibits
high ethylene and/or propylene selectivity still exists. Otherwise,
the use of crude oil feedstock to produce these olefins will continue
to be economically favored.
SUMMARY OF THE INVENTION
This invention provides various compositions of a molecular sieve
having a surface heat impregnated with one or more metals and of
a method of making the same. The metals are selected from Group
IIA metals, Group IHA metals, Group IB metals, Group 111 metals,
Group 111 metals, Group VIB metals, Group VB metals, Group VIIB
metals, Group VIIIB metals, Group VI11B metals, and mixtures thereof.
In one embodiment, the metals are selected from aluminum, magnesium,
calcium, barium, lanthanum, titanium, chromium, iron, cobalt, nickel,
copper, zinc, and mixtures thereof The silicoaluminophosphate (SAPO)
molecular sieve will contain about 0.5 to 40 percent by weight,
preferably about 1 to 20 percent by weight, most preferably 1 to
10 percent by weight, of the metal. In the preferred embodiment,
the SAPO molecular sieve will have a surface heat impregnated with
copper, zinc, or a mixture thereof, wherein the copper and/or zinc
will be present in about 1 to 20 percent by weight. The metal disposed
on the SAPO molecular sieve is a heat decomposition product of a
metal acetate, metal nitrate, metal sulfate, or metal halide. The
surface is heat impregnated with the metal at a temperature from
30.degree. C. to 400.degree. C., preferably from 120.degree. C.
to 260.degree. C., most preferably from 160.degree. C. to 220.degree.
C. The SAPO molecular sieve is selected from 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 SAP047 SAPO-56 the
metal containing forms thereof, and mixtures thereof, more preferably,
SAPO-18 SAPO-34 SAPO-35 SAPO-44 SAPO-47 and mixtures thereof,
most preferably, SAPO-34A, SAPO-34B, and mixtures thereof.
The invention is also directed to a SAPO molecular sieve catalyst
comprising: a surface heat impregnated with a metal selected from
the group consisting of Group IIA metals, Group IHA metals, Group
IB metals, Group IIB metals, Group IIIB metals, Group VIB metals,
Group VB metals, Group VIB metals, Group VIIB metals, Group VIIIB
metals, and mixtures thereof; and a binder. Generally, the binder
is selected from alumina, aluminum chlorhydrol, clay, and mixtures
thereof.
In one embodiment, the metals are selected from aluminum, magnesium,
calcium, barium, lanthanum, titanium, chromium, iron, cobalt, nickel,
copper, zinc, and mixtures thereof. The SAPO molecular sieve will
have about 0.5 to 40 percent by weight, preferably about 1 to 20
percent by weight, most preferably 1 to 10 percent by weight, of
the metal. In the preferred embodiment, the SAPO molecular sieve
will have a surface heat impregnated with copper, zinc, or a mixture
thereof, wherein the copper and/or zinc will be present in about
1 to 20 percent by weight. The metal disposed on the SAPO molecular
sieve is a heat decomposition product of a metal acetate, metal
nitrate, metal sulfate, or metal halide. The surface is heat impregnated
with the metal at a temperature from 30.degree. C. to 400.degree.
C., preferably from 120.degree. C. to 260.degree. C., most preferably
from 160.degree. C. to 220.degree. C. The SAPO molecular sieve is
selected from SAPO-5 SAPO-8 SAPO-11 SAPO-16 SAPO-17 SAPO-18
SAPO-20 SAPO-31 SAPO-34 SAPO-35 SAPO-36 SAPO-37 SAPO40 SAPO-41
SAPO-42 SAPO-44 SAPO-47 SAPO-56 the metal containing forms thereof,
and mixtures thereof, more preferably, SAPO-18 SAPO-34 SAPO-35
SAPO-44 SAPO-47 and mixtures thereof, most preferably, SAPO-34A,
SAPO-34B, and mixtures thereof.
The invention is also directed to a method of making a molecular
sieve comprising: mixing a metal containing solution with a SAPO
molecular sieve, wherein the SAPO molecular sieve contains a template;
heating the mixture to a temperature between 30.degree. C. and 400.degree.
C. to obtain a SAPO molecular sieve having a surface heat impregnated
with a metal; separating the heated SAPO molecular sieve from the
heated metal containing solution; and calcining the separated SAPO
molecular sieve. The metal is selected from the group consisting
of Group IIA metals, Group IIA metals, Group IB metals, Group IIB
metals, Group IIIB metals, Group VIB metals, Group VB metals, Group
VIB metals, Group VIIB metals, Group VIIIB metals, and mixtures
thereof In one embodiment, the metal is selected from aluminum,
magnesium, calcium, barium, lanthanum, titanium, chromium, iron,
cobalt, nickel, copper, zinc, and mixtures thereof, more preferably
copper, zinc, or a mixture thereof The source of the metal is the
heat decomposition product of the metal containing solution. In
one embodiment, selected metal salts include acetates, nitrates,
sulfates, halides, and mixtures thereof, more preferably nitrates.
The metal containing solution comprises a metal concentration between
0.01 M and 1.0 M, preferably between 0.05 M and 0.5 M, more preferably
between 0.08 M and 0.3 M. The surface heat impregnated with the
metal is heat impregnated at a temperature from 30.degree. C. to
400.degree. C., preferably from 120.degree. C. to 260.degree. C.,
more preferably from 160.degree. C. to 220.degree. C., at autogeneous
pressure.
The invention is also directed to a method of making an olefin
from an oxygenate feedstock comprising: providing a catalyst comprising
a SAPO molecular sieve having a surface heat impregnated with a
metal selected from the group consisting of Group IIA metals, Group
IHA metals, Group IB metals, Group IIB metals, Group IIIB metals,
Group VIB metals, Group VB metals, Group VIB metals, Group VIIB
metals, Group VIIIB metals, mixtures thereof, and a binder; and
contacting the oxygenate feedstock with the catalyst.
In one embodiment, the SAPO molecular sieve is selected from SAPO-18
SAPO-34 SAPO-35 SAPO-44 SAPO47 and mixtures thereof In the preferred
embodiment, the SAPO molecular sieve has a surface heat impregnated
with a metal comprising copper, zinc, or a mixture thereof. The
copper, zinc, or a mixture thereof is present in the molecular sieve
in about 1 to 20 percent by weight. The preferred oxygenate feedstock
will comprise methanol.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be better understood by reference to
the Detailed Description of the Invention when taken together with
the attached drawings, wherein:
FIG. 1 is a graphical representation of ethylene and propylene
selectivity of a heat impregnated metal SAPO-34A with a process
temperature of approximately 200.degree. C.;
FIG. 2 is a graphical representation of ethylene and propylene
selectivity of a heat impregnated metal SAPO-34A with a process
temperature approximately 180.degree. C.);
FIG. 3 is a graphical representation of ethylene and propylene
selectivity of a heat impregnated metal SAPO-34A with a process
temperature approximately 200.degree. C.);
FIG. 4 is a graphical representation of ethylene and propylene
selectivity of a heat impregnated metal SAPO-34A with a process
temperature approximately 180.degree. C.); and
FIG. 5 is a graphical representation of ethylene and propylene
selectivity of a heat impregnated metal SAPO-34A with a process
temperature approximately 160.degree. C.).
DETAILED DESCRIPTION OF THE INVENTION
This invention is to a molecular sieve and a catalyst containing
the molecular sieve in which the surface of the molecular sieve
has been heat impregnated with a metal. The molecular sieve and
catalyst of the invention offer significant improvement in the amount
of ethylene produced from an oxygenate feedstock.
The molecular sieve of this invention is preferably a silicoaluminophosphate
(SAPO) molecular sieve. This type of molecular sieve comprises a
three-dimensional microporous crystal framework structure of [SiO.sub.2
], [AlO.sub.2 ] and [PO2) corner sharing tetrahedral units. The
way Si is incorporated into the structure can be determined by .sup.29
Si MAS NMR. See Blackwell and Patton, J. Phys. Chem., 92 3965 (1988).
The desired SAPO molecular sieves will exhibit one or more peaks
in the .sup.29 Si MAS NMR, with a chemical shift .delta.(Si) in
the range of -88 to -96 ppm and with a combined peak area in that
range of at least 20% of the total peak area of all peaks with a
chemical shift .delta.(Si) in the range of -88 ppm to -115 ppm,
where the .delta.(Si) chemical shifts refer to external tetramethylsilane
(TMS).
It is preferred that the SAPO molecular sieve used in this invention
have a relatively low Si/Al.sub.2 ratio. In general, the lower the
Si/Al.sub.2 ratio, the lower the C.sub.1 -C.sub.4 saturates selectivity,
particularly propane selectivity. A Si/Al.sub.2 ratio of less than
0.65 is desirable, with a Si/Al.sub.2 ratio of not greater than
0.40 being preferred, and a Si/Al.sub.2 ratio of not greater than
0.32 being particularly preferred. A Si/Al.sub.2 ratio of not greater
than 0.20 is most preferred.
SAPO molecular sieves are generally classified as being microporous
materials having 8 10 or 12 membered ring structures. These ring
structures can have an average pore size ranging from about 3.5-15
angstroms. Preferred are the small pore SAPO molecular sieves having
an average pore size of less than about 5 angstroms, preferably
an average pore size ranging from about 3.5 to 5 angstroms, more
preferably from 3.5 to 4.2 angstroms. These pore sizes are typical
of molecular sieves having 8 membered rings.
In general, SAPO molecular sieves comprise a molecular framework
of corner-sharing [SiO.sub.2 ], [AlO.sub.2 ], and [PO.sub.2 ] tetrahedral
units. This type of framework is effective in converting various
oxygenates into olefin products.
The [PO.sub.2 ] tetrahedral units within the framework structure
of the molecular sieve of this invention can be provided by a variety
of compositions. Examples of these phosphorus-containing compositions
include phosphoric acid, organic phosphates such as triethyl phosphate,
and aluminophosphates. The phosphorous-containing compositions are
mixed with reactive silicon and aluminum-containing compositions
under the appropriate conditions to form the molecular sieve.
The [AMO.sub.2 ] tetrahedral units within the framework structure
can be provided by a variety of compositions. Examples of these
aluminum-containing icompositions include aluminum alkoxides such
as aluminum isopropoxide, aluminum phosphates, aluminum hydroxide,
sodium aluminate, and pseudoboehmite. The aluminum-containing compositions
are mixed with reactive silicon and phosphorus-containing compositions
under the appropriate conditions to form the molecular sieve.
The [SiO.sub.2 ] tetrahedral units within the framework structure
can be provided by a variety of compositions. Examples of these
silicon-containing compositions include silica sols and silicium
alkoxides such as tetra ethyl orthosilicate. The silicon-containing
compositions are mixed with reactive aluminum and phosphorus-containing
compositions under the appropriate conditions to form the molecular
sieve.
Substituted SAPOs can also be used in this invention. These compounds
are generally known as MeSAPOs or metal-containing silicoaluminophosphates.
The metal can be alkali metal ions (Group IA), alkaline earth metal
ions (Group IIA), rare earth ions (Group IIB, including the lanthanoid
elements: lanthanum, cerium, praseodymium, neodymium, samarium,
europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,
ytterbium and lutetium; and scandium or yttrium) and the additional
transition metals of Groups IVB, VB, VIB, VIB, VIIIB, IB, and IB.
Preferably, the Me represents atoms such as Zn, Mg, Mn, Co, Ni,
Ga, Fe, Ti, Zr, Ge, Sn, and Cr. These atoms can be inserted into
the tetrahedral framework through a [MeO.sub.2 ] tetrahedral unit.
The [MeO.sub.2 ] tetrahedral unit carries a net electric charge
depending on the valence state of the metal substituent. When the
metal component has a valence state of +2 +3 +4 +5 or +6 the
net electric charge is between -2 and +2. Incorporation of the metal
component is typically accomplished adding the metal component during
synthesis of the molecular sieve.
Suitable SAPO molecular sieves include SAPO-5 SAPO-8 SAPO-11
SAPO-16 SAPO-17 SAPO-18 SAPO-20 SAPO-31 SAPO-34 SAPO-35 SAPO-36
SAPO-37 SAPO-40 SAPO-41 SAPO-42 SAPO-44 SAPO-47 SAPO-56 the
metal containing forms thereof, and mixtures thereof Preferred are
SAPO-18 SAPO-34 SAPO-35 SAPO-44 and SAPO-47 particularly SAPO-34
including the metal containing forms thereof, and mixtures thereof
As used herein, the term mixture is synonymous with combination
and is considered a composition of matter having two or more components
in varying proportions, regardless of their physical state.
An aluminophosphate (ALPO) molecular sieve can also be included
in the catalyst composition. Aluminophosphate molecular sieves are
crystalline microporous oxides which can have an AIP0.sub.4 framework.
They can have additional elements within the framework, typically
have uniform pore dimensions ranging from about 3 angstroms to about
10 angstroms, and are capable of making size selective separations
of molecular species. More than two dozen structure types have been
reported, including zeolite topological analogues. A more detailed
description of the background and synthesis of aluminophosphates
is found in U.S. Pat. No. 4310440 which is incorporated herein
by reference in its entirety. Preferred ALPO structures are ALPO-5
ALPO-11 ALPO-18 ALPO-31 ALPO-34 ALPO-36 ALPO-37 and ALPO-46.
The ALPOs can also include a metal substituent in its framework.
Preferably, the metal is selected from the group consisting of magnesium,
manganese, zinc, cobalt, and mixtures thereof These materials preferably
exhibit adsorption, ion-exchange and/or catalytic properties similar
to aluminosilicate, aluminophosphate and silica aluminophosphate
molecular sieve compositions. Members of this class and their preparation
are described in U.S. Pat. No. 4567029 incorporated herein by
reference in its entirety.
The metal containing ALPOs have a three-dimensional microporous
crystal framework structure of MO.sub.2 AlO.sub.2 and PO.sub.2
tetrahedral units. These as manufactured structures (which contain
template prior to calcination) can be represented by empirical chemical
composition, on an anhydrous basis, as:
The metal containing ALPOs are sometimes referred to by the acronym
as MeAPO. Also in those cases where the metal "Me" in
the composition is magnesium, the acronym MAPO is applied to the
composition. Similarly ZAPO, MnAPO and CoAPO are applied to the
compositions which contain zinc, manganese and cobalt respectively.
To identify the various structural species which make up each of
the subgeneric classes MAPO, ZAPO, CoAPO and MnAPO, each species
is assigned a number and is identified, for example, as ZAPO-5
MAPO-11 CoAPO-34 and so forth.
The SAPO molecular sieves are synthesized by hydrothermal crystallization
methods generally known in the art. See, for example, U.S. Pat.
Nos. 4440871; 4861743; 5096684; and 5126308 the methods
of making of which are fully incorporated herein by reference. A
reaction mixture is formed by mixing together reactive silicon,
aluminum and phosphorus components, along with at least one template.
Generally the mixture is sealed and heated, preferably under autogenous
pressure, to a temperature of at least 100.degree. C., preferably
from 100-250.degree. C., until a crystalline product is formed.
Formation of the crystalline product can take anywhere from around
2 hours to as much as 2 weeks. In some cases, stirring or seeding
with crystalline material will facilitate the formation of the product.
Typically, the molecular sieve product is formed in solution. It
can be recovered by standard means, such as by centrifugation or
filtration. The product can also be washed, recovered by the same
means, and dried.
As a result of the crystallization process, the recovered sieve
contains within its pores at least a portion of the template used
in making the initial reaction mixture. The crystalline structure
essentially wraps around the template, and the template must be
partly or completely removed for the molecular sieve to exhibit
optimal catalytic activity. Once the template is removed or partially
removed, the crystalline structure that remains has what is typically
called an intracrystalline pore system.
In many cases, depending upon the nature of the final product formed,
the template may be too large to be eluted from the intracrystalline
pore system. In such a case, the template can be removed by a heat
treatment process. For example, the template can be calcined, or
essentially combusted, in the presence of an oxygen-containing gas,
by contacting the template-containing sieve in the presence of the
oxygen-containing gas and heating at temperatures from 200.degree.
C. to 900.degree. C. In some cases, it may be desirable to heat
in an environment having a low oxygen concentration. In these cases,
however, the result will typically be a breakdown of the template
into a smaller component, rather than by the combustion process.
This type of process can be used for partial or complete removal
of the template from the intracrystalline pore system. In other
cases, with smaller templates, complete or partial removal from
the sieve can be accomplished by conventional desorption processes
such as those used in making standard zeolites.
The reaction mixture can contain one or more templates. Templates
are structure directing or affecting agents, and typically contain
nitrogen, phosphorus, oxygen, carbon, hydrogen or a combination
thereof, and can also contain at least one alkyl or aryl group,
with 1 to 8 carbons being present in the alkyl or aryl group. Mixtures
of two or more templates can produce mixtures of different sieves
or predominantly one sieve where one template is more strongly directing
than another.
Representative templates include tetraethyl ammonium salts, cyclopentylamine,
aminomethyl cyclohexane, piperidine, triethylamine, cyclohexylamine,
tri-ethyl hydroxyethylamine, morpholine, dipropylamine (DPA), pyridine,
isopropylamine and combinations thereof Preferred templates are
triethylamine, cyclohexylamine, piperidine, pyridine, isopropylamine,
tetraethyl ammonium salts, dipropylamine, and mixtures thereof The
tetraethylammonium salts include tetraethyl ammonium hydroxide (TEAOH),
tetraethyl ammonium phosphate, tetraethyl ammonium fluoride, tetraethyl
ammonium bromide, tetraethyl ammonium chloride, tetraethyl ammonium
acetate. Preferred tetraethyl ammonium salts are tetraethyl ammonium
hydroxide and tetraethyl ammonium phosphate. Particularly preferred
templates are diethylamine (DEA) as used in the preparation of SAPO-34A
and triethylamine (TEA), as used in the preparation of SAPO-34B.
The SAPO molecular sieve structure can be effectively controlled
using combinations of templates. For example, in a particularly
preferred embodiment, the SAPO molecular sieve is manufactured using
a template combination of TEAOH and dipropylamine. This combination
results in a particularly desirable SAPO structure for the conversion
of oxygenates, particularly methanol and dimethyl ether, to light
olefins such as ethylene and propylene.
The SAPO molecular sieve of the invention can be admixed (i.e.,
blended, formulated) with other materials. Once prepared, the resulting
composition is typically referred to as a SAPO catalyst, with the
catalyst comprising the SAPO molecular sieve. Materials which can
be blended with the molecular sieve can be various inert or catalytically
active materials, or various binder materials. These materials include
compositions such as kaolin and other clays, various forms of rare
earth metals, metal oxides, other non-zeolite catalyst components,
zeolite catalyst components, alumina or alumina sol, aluminum chlorhydrol,
titania, zirconia, magnesia, thoria, beryllia, quartz, silica or
silica or silica sol, and mixtures thereof These components are
also effective in reducing, inter alia, overall catalyst cost, acting
as a thermal sink to assist in heat shielding the catalyst during
regeneration, densifying the catalyst and increasing catalyst strength.
It is particularly desirable that the inert materials that are used
in the catalyst to act as a thermal sink have a heat capacity of
from about 0.05 to about 1 cal/g-.degree. C., more preferably from
about 0.1 to about 0.8 cal/g-.degree. C., most preferably from about
0.1 to about 0.5 cal/g-.degree. C.
Preferably an alumina binder such as aluminum chlorhydrol, and/or
one or more clays, such as kaolin, is used in combination with the
molecular sieve of the invention. If the molecular sieve is in the
dry from, a fluid, such as water, is added to form a slurry. More
often, however, the catalyst is prepared following the preparation
of the molecular sieve which is maintained as a slurry from the
preceding crystallization step. The other components are then added
to the slurried molecular sieve as either dry solids and/or as slurries.
This final slurry having a specific solid content and particle size
is mixed until a relatively uniform distribution of all components
is obtained. The uniformly mixed slurry is then spray dried or extruded
to form the catalyst.
Additional molecular sieve materials can be included as a part
of the SAPO catalyst composition or they can be used as separate
molecular sieve catalysts in admixture with the SAPO catalyst if
desired. Structural types of small pore molecular sieves that are
suitable for use in this invention include AEI, AFT, APC, ATN, ATT,
ATV, AWW, BIK, CAS, CHA, CFH, DAC, DDR, EDI, ERI, GOO, KFI, LEV,
LOV, LTA, MON, PAU, PHI, RHO, ROG, THO, and substituted forms thereof
Structural types of medium pore molecular sieves that are suitable
for use in this invention include MFI, MEL, MTW, EUO, MTT, HEU,
FER, AFO, AEL, TON, and substituted forms thereof These small and
medium pore molecular sieves are described in greater detail in
the Alias of Zeolite Structural Types, W. M. Meier and D. H. Olsen,
Butterworth Heineman, 3rd ed., 1997 the detailed description of
which is explicitly incorporated herein by reference. Preferred
molecular sieves which can be combined with a silicoaluminophosphate
catalyst include ZSM-5 ZSM-34 erionite, and chabazite.
Incorporating the metal after the molecular sieve has been prepared
has some advantages over that of in-situ metal incorporation. The
physical characteristics of the molecular sieve, such as particle
and pore size, can be varied prior to metal incorporation. As a
result, post-synthesis techniques provide wider possibilities in
molecular sieve preparation and screening. For example, a particular
metal can be tested over a wide variety of molecular sieve, or a
particular molecular sieve can be tested over a wide range of metals.
The molecular sieve of the invention includes a surface heat impregnated
with a metal. The source of the metal is a solution of a metal complex.
Generally if the solution is aqueous, then the metal complex will
comprise metal acetates, nitrates, sulfates, and mixtures thereof.
Preferably, metal nitrates are used with the exception of titanium
where titanium sulfate is used. If the solution is nonaqueous, such
as an alcohol or a polar organic solvent, metal halides can be used.
The metal containing solution is then mixed with the molecular sieve
in a reaction vessel and heated to the selected temperature. Preferably,
the mixture is heated at autogeneous pressure. Typically, the mixture
is heated for about 12 hours. However, any period of time can be
used depending upon the process temperature, the type of metal complex
used, the concentration of the metal solution, and the type of molecular
sieve used. It is to be understood that one of ordinary still in
the art will know how to vary the amount of time the mixture is
heated depending upon each of these parameters.
Following heating of the mixture, the molecular sieve with the
surface heat impregnated with the metal is separated from the heated
solution. Often the relatively high process temperatures will cause
some decomposition of the metal complexes in solution resulting
in finely precipitated metals. The separated molecular sieve is
then washed with one or more fluids, typically water or an alcohol
to remove traces of the metal solution and loosely bound precipitated
metal. The washed molecular sieve is dried at 110.degree. C. preferably
overnight.
At this point the molecular sieve of the invention can be described
as having a surface heat impregnated with a metal. The metal can
be disposed on the external surface and/or within the pores of the
molecular sieve. Initially, the molecular sieve that is mixed with
the metal containing solution had its template positioned within
the pore structure. However, as the process temperature is raised
the template can exist the pore structure. The template may have
some solubility in the metal containing solution, thus enabling
the metal complex to replace the template in the pores. Often the
process temperature is above the boiling or melting point of the
template molecule even at the elevated pressures of the heating
process. Alternatively, the high process temperature can initiate
decomposition mechanisms of the template. For example during calcination
conditions, DEA and TEA are known to form ethylene and water as
they thermally decompose. The decomposed products can then exit
the pores. However, the pathway, usually some or all of the template
will exit the pore during heating and be replaced with the metal
and/or metal complex.
After the metal containing molecular sieve is washed and dried,
the molecular sieve can be calcined or partially calcined under
various conditions. Typically, the molecular sieve of the invention
is calcined at 550.degree. C. in air for about 2 to 5 hours prior
to use in a conversion reactor.
The surface of the molecular sieve can also be impregnated with
additional metals by adding a co-solution of the desired co-metal.
Alternatively, the surface of the molecular sieve can be impregnated
with the additional co-metal by following the first heat treatment
with one or more subsequent heat treatments. For example, proportional
amounts of cobalt and/or zinc can be added to SAPO with a surface
impregnated with copper according to the invention by adding a cobalt
and/or zinc solution to the Cu-SAPO and repeating the heating step.
The catalyst composition preferably comprises about 1% to about
99%, more preferably about 5% to about 90%, and most preferably
about 10% to about 80%, by weight of molecular sieve. It is also
preferred that the catalyst composition have a particle size of
from about 20 .mu. to 3000 .mu., more preferably about 30 .mu.
to 200 .mu., most preferably about 50 .mu. to 150 .mu..
The catalyst can be subjected to a variety of treatments to achieve
the desired physical and chemical characteristics. Such treatments
include, but are not necessarily limited to hydrothermal treatment,
calcination, acid treatment, base treatment, milling, ball milling,
grinding, spray drying, and combinations thereof
In this invention, a feed containing an oxygenate, and optionally
a diluent or a hydrocarbon added separately or mixed with the oxygenate,
is contacted with a catalyst containing a SAPO molecular sieve in
a reaction zone or volume. The volume in which such contact takes
place is herein termed the "reactor," which may be a part
of a "reactor apparatus" or "reaction system."
Another part of the reaction system may be a "regenerator,"
which comprises a volume wherein carbonaceous deposits (or coke)
on the catalyst resulting from the olefin conversion reaction are
removed by contacting the catalyst with regeneration medium.
The oxygenate feedstock of this invention comprises at least one
organic compound which contains at least one oxygen atom, such as
aliphatic alcohols, ethers, carbonyl compounds (aldehydes, ketones,
carboxylic acids, carbonates, esters and the like). When the oxygenate
is an alcohol, the alcohol can include an aliphatic moiety having
from 1 to 10 carbon atoms, more preferably from 1 to 4 carbon atoms.
Representative alcohols include but are not necessarily limited
to lower straight and branched chain aliphatic alcohols and their
unsaturated counterparts. Examples of suitable oxygenate compounds
include, but are not limited to: methanol; ethanol; n-propanol;
isopropanol; C.sub.4 -C.sub.20 alcohols; methyl ethyl ether; dimethyl
ether; diethyl ether; di-isopropyl ether; formaldehyde; dimethyl
carbonate; dimethyl ketone; acetic acid; and mixtures thereof Preferred
oxygenate compounds are methanol, dimethyl ether, or a mixture thereof.
The method of making the preferred olefin product in this invention
can include the additional step of making these compositions from
hydrocarbons such as oil, coal, tar sand, shale, biomass and natural
gas. Methods for making the compositions are known in the art. These
methods include fermentation to alcohol or ether, making synthesis
gas, then converting the synthesis gas to alcohol or ether. Synthesis
gas can be produced by known processes such as steam reforming,
autothermal reforming and partial oxidization.
One or more inert dilutents may be present in the feedstock, for
example, in an amount of from 1 to 99 molar percent, based on the
total number of moles of all feed and diluent components fed to
the reaction zone (or catalyst). As defined herein, diluents are
compositions which are essentially non-reactive across a molecular
sieve catalyst, and primarily function to make the oxygenates in
the feedstock less concentrated. Typical diluents include, but are
not necessarily limited to helium, argon, nitrogen, carbon monoxide,
carbon dioxide, water, essentially non-reactive paraffins (especially
the alkanes such as methane, ethane, and propane), essentially non-reactive
alkylenes, essentially non-reactive aromatic compounds, and mixtures
thereof. The preferred diluents are water and nitrogen. Water can
be injected in either liquid or vapor form.
Hydrocarbons can also be included as part of the feedstock, i.e.,
as co-feed. As defined herein, hydrocarbons included with the feedstock
are hydrocarbon compositions which are converted to another chemical
arrangement when contacted with molecular sieve catalyst. These
hydrocarbons can include olefins, reactive paraffins, reactive alkylaromatics,
reactive aromatics or mixtures thereof. Preferred hydrocarbon co-feeds
include, propylene, butylene, pentylene, C.sub.4.sup.+ hydrocarbon
mixtures, C.sub.5.sup.+ hydrocarbon mixtures, and mixtures thereof.
More preferred as co-feeds are a C.sub.4.sup.+ hydrocarbon mixtures,
with the most preferred being C.sub.4.sup.+ hydrocarbon mixtures
which are obtained from separation and recycle of reactor product.
In the process of this invention, coked catalyst can be regenerated
by contacting the coked catalyst with a regeneration medium to remove
all or part of the coke deposits. This regeneration can occur periodically
within the reactor by ceasing the flow of feed to the reactor, introducing
a regeneration medium, ceasing flow of the regeneration medium,
and then reintroducing the feed to the fully or partially regenerated
catalyst. Regeneration may also occur periodically or continuously
outside the reactor by removing a portion of the deactivated catalyst
to a separate regenerator, regenerating the coked catalyst in the
regenerator, and subsequently reintroducing the regenerated catalyst
to the reactor. Regeneration can occur at times and conditions appropriate
to maintain a desired level of coke on the entire catalyst within
the reactor.
Catalyst that has been contacted with feed in a reactor is defined
herein as "feedstock exposed." Feedstock exposed catalyst
will provide olefin conversion reaction products having substantially
lower propane and coke content than a catalyst which is fresh and
regenerated. A catalyst will typically provide lower amounts of
propane as it is exposed to more feed, either through increasing
time at a given feed rate or increasing feed rate over a given time.
At any given instant in time, some of the catalyst in the reactor
will be fresh, some regenerated, and some coked or partially coked
as a result of having not yet been regenerated. Therefore, various
portions of the catalyst in the reactor will have been feedstock
exposed for different periods of time. Since the rate at which feed
flows to the reactor can vary, the amount of feed to which various
portions of the catalyst can also vary. To account for this variation,
the "average catalyst feedstock exposure index (ACFE index)"
is used to quantitatively define the extent to which the entire
catalyst in the reactor has been feedstock exposed.
As used herein, ACFE index is the total weight of feed divided
by the total weight of molecular sieve (i.e., excluding binder,
inerts, etc., of the catalyst composition) sent to the reactor.
The measurement should be made over an equivalent time interval,
and the time interval should be long enough to smooth out fluctuations
in catalyst or feedstock rates according to the reactor and regeneration
process step selected to allow the system to be viewed as essentially
continuous. In the case of reactor systems with periodic regenerations,
this can range from hours up to days or longer. In the case of reactor
systems with substantially constant regeneration, minutes or hours
may be sufficient.
Flow rate of catalyst can be measured in a variety of ways. In
the design of the equipment used to carry the catalyst between the
reactor and regenerator, the catalyst flow rate can be determined
given the coke production rate in the reactor, the average coke
level on catalyst leaving the reactor, and the average coke level
on catalyst leaving the regenerator. In an operating unit with continuous
catalyst flow, a variety of measurement techniques can be used.
Many such techniques are described, for example, by Michel Louge,
"Experimental Techniques," Circulating Fluidized Beds,
Grace, Avidan, & Knowlton, eds., Blackie, 1997 (336-337), the
descriptions of which are expressly incorporated herein by reference.
In this invention, only the molecular sieve in the catalyst sent
to the reactor may be used in the determination of ACFE index. The
catalyst sent to the reactor, however, can be either fresh or regenerated
or a combination of both. Molecular sieve which may be recirculated
to and from the reactor within the reactor apparatus (i.e., via
ducts, pipes or annular regions), and which has not been regenerated
or does not contain fresh catalyst, is not to be used in the determination
of ACFE index.
In a preferred embodiment of this invention, a feed containing
an oxygenate, and optionally a hydrocarbon, either separately or
mixed with the oxygenate, is contacted with a catalyst containing
a SAPO molecular sieve at process conditions effective to produce
olefins in a reactor.
Any standard reactor system can be used, including fixed bed, fluid
bed or moving bed systems. Preferred reactors are co-current riser
reactors and short contact time, countercurrent free-fall reactors.
Desirably, the reactor is one in which an oxygenate feedstock can
be contacted with a molecular sieve catalyst at a weight hourly
space velocity (WHSV) of at least about 1 hr.sup.-1 preferably
in the range of from about 1 hr.sup.-1 to 1000 hr.sup.-1 more preferably
in the range of from about 20 hr.sup.-1 to 1000 hr.sup.-1 and most
preferably in the range of from about 20 hr.sup.-1 to 500 hr.sup.-1.
WHSV is defined herein as the weight of oxygenate, and hydrocarbon
which may optionally be in the feed, per hour per weight of the
molecular sieve content of the catalyst. Because the catalyst or
the feedstock may contain other materials which act as inerts or
diluents, the WHSV is calculated on the weight basis of the oxygenate
feed, and any hydrocarbon which may be present, and the molecular
sieve contained in the catalyst.
Preferably, the oxygenate feed is contacted with the catalyst when
the oxygenate is in a vapor phase. Alternately, the process may
be carried out in a liquid or a mixed vapor/liquid phase. When the
process is carried out in a liquid phase or a mixed vapor/liquid
phase, different conversions and selectivities of feed-toproduct
may result depending upon the catalyst and reaction conditions.
The process can generally be carried out at a wide range of temperatures.
An effective operating temperature range can be from about 200.degree.
C. to 700.degree. C., preferably from about 300.degree. C. to 600.degree.
C., more preferably from about 350.degree. C. to 550.degree. C.
At the lower end of the temperature range, the formation of the
desired olefin products may become markedly slow. At the upper end
of the temperature range, the process may not form an optimum amount
of product.
It is highly desirable to operate at a temperature of at least
300.degree. C. and a Temperature Corrected Normalized Methane Sensitivity
(TCNMS) of less than about 0.016. It is particularly preferred that
the reaction conditions for making olefin from oxygenate comprise
a WHSV of at least about 20 hr.sup.-1 producing olefins and a TCNMS
of less than about 0.016.
As used herein, TCNMS is defined as the Normalized Methane Selectivity
(NMS) when the temperature is less than 400.degree. C. The NMS is
defined as the methane product yield divided by the ethylene product
yield wherein each yield is measured on, or is converted to, a weight
% basis. When the temperature is 400.degree. C. or greater, the
TCNMS is defined by the following equation, in which T is the average
temperature within the reactor in .degree. C.: ##EQU1##
The pressure also may vary over a wide range, including autogenous
pressures. Effective pressures may be in, but are not necessarily
limited to, oxygenate partial pressures at least 1 psia, preferably
at least 5 psia. The process is particularly effective at higher
oxygenate partial pressures, such as an oxygenate partial pressure
of greater than 20 psia. Preferably, the oxygenate partial pressure
is at least about 25 psia, more preferably at least about 30 psia.
For practical design purposes it is desirable to operate at a methanol
partial pressure of not greater than about 500 psia, preferably
not greater than about 400 psia, most preferably not greater than
about 300 psia.
The conversion of oxygenates to produce light olefins may be carried
out in a variety of catalytic reactors. Reactor types include fixed
bed reactors, fluid bed reactors, and concurrent riser reactors
as described in "Free Fall Reactor," Fluidization Engineering,
D. Kunii and O. Levenspiel, Robert E. Krieger Publishing Co. NY,
1977 expressly incorporated herein by reference. Additionally,
countercurrent free fall reactors may be used in the conversion
process as described in U.S. Pat. No. 4068136 and "Riser
Reactor", Fluidization and Fluid-Particle Systems, pages 48-59
F. A. Zenz and D. F. Othmo, Reinhold Publishing Corp., NY 1960
the detailed descriptions of which are also expressly incorporated
herein by reference.
In a preferred embodiment of the continuous operation, only a portion
of the catalyst is removed from the reactor and sent to the regenerator
to remove the accumulated coke deposits that result during the catalytic
reaction. In the regenerator, the catalyst is contacted with a regeneration
medium containing oxygen or other oxidants. Examples of other oxidants
include O.sub.3 SO.sub.3 N.sub.2 O, NO, NO.sub.2 N.sub.2 O.sub.5
and mixtures thereof. It is preferred to supply O.sub.2 in the form
of air. The air can be diluted with nitrogen, CO.sub.2 or flue
gas, and steam may be added. Desirably, the O.sub.2 concentration
in the regenerator is reduced to a controlled level to minimize
overheating or the creation of hot spots in the spent or deactivated
catalyst. The deactivated catalyst also may be regenerated reductively
with H.sub.2 CO, mixtures thereof, or other suitable reducing agents.
A combination of oxidative regeneration and reductive regeneration
can also be employed.
In essence, the coke deposits are removed from the catalyst during
the regeneration process, forming a regenerated catalyst. The regenerated
catalyst is then returned to the reactor for further contact with
feed. Typical regeneration temperatures are in the range of 250-700.degree.
C., desirably in the range of 350-700.degree. C. Preferably, regeneration
is carried out at a temperature range of 450-700.degree. C.
In one embodiment, the reactor and regenerator are configured such
that the feed contacts the regenerated catalyst before it is returned
to the reactor. In an alternative embodiment, the reactor and regenerator
are configured such that the feed contacts the regenerated catalyst
after it is returned to the reactor. In yet another embodiment,
the feed stream can be split such that feed contacts regenerated
catalyst before it is returned to the reactor and after it has been
returned to the reactor.
It is preferred that the catalyst within the reactor have an average
level of coke effective for selectivity to ethylene and/or propylene.
Preferably, the average coke level on the catalyst will be from
about 2 wt. % to about 30 wt. %, more preferably from about 2 wt.
% to about 20 wt. %. In order to maintain this average level of
coke on catalyst, the entire volume of catalyst can be partially
regenerated under conditions effective to maintain the desired coke
content on catalyst. It is preferred, however, to recycle only a
portion of the coked catalyst for feed contact without regenerating.
This recycle can be performed either internal or external to the
reactor. The portion of coked catalyst to be regenerated is preferably
regenerated under conditions effective to obtain a regenerated catalyst
having a coke content of less than 2 wt. %, preferably less than
1.5 wt. %, and most preferably less than 1.0 wt. %.
In order to make up for any catalyst loss during the regeneration
or reaction process, fresh catalyst can be added. Preferably, the
fresh catalyst is added to the regenerated catalyst after it is
removed from the regenerator, and then both are added to the reactor.
However, the fresh catalyst can be added to the reactor independently
of the regenerated catalyst. Any amount of fresh catalyst can be
added, but it is preferred that an ACFE index of at least 1.5 be
maintained.
One skilled in the art will also appreciate that the olefins produced
by the oxygenate-to-olefin conversion reaction of the present invention
can be polymerized to form polyolefins, particularly polyethylene
and polypropylene. Processes for forming polyolefins from olefins
are known in the art. Catalytic processes are preferred. Particularly
preferred are metallocene, Ziegler/Natta and acid catalytic systems.
See, for example, U.S. Pat. Nos. 3258455; 3305538; 3364190;
5892079; 4659685; 4076698; 3645992; 4302565; and 4243691
the catalyst and process descriptions of each being expressly incorporated
herein by reference. In general, these methods involve contacting
the olefin product with a polyolefin-forming catalyst at a pressure
and temperature effective to form the polyolefin product.
A preferred polyolefin-forming catalyst is a metallocene catalyst.
The preferred temperature range of operation is between 50 and 240.degree.
C. and the reaction can be carried out at low, medium or high pressure,
being anywhere within the range of about 1 to 200 bars. For processes
carried out in solution, an inert diluent can be used, and the preferred
operating pressure range is between 10 and 150 bars, with a preferred
temperature range of between 120 and 230.degree. C. For gas phase
processes, it is preferred that the temperature generally be within
a range of 60 to 160.degree. C., and that the operating pressure
be between 5 and 50 bars.
In addition to polyolefins, numerous other olefin derivatives may
be formed from the olefins recovered therefrom. These include, but
are not limited to, aldehydes, alcohols, acetic acid, linear alpha
olefins, vinyl acetate, ethylene dicholoride and vinyl chloride,
ethylbenzene, ethylene oxide, cumene, isopropyl alcohol, acrolein,
allyl chloride, propylene oxide, acrylic acid, ethylene-propylene
rubbers, and acrylonitrile, and trimers and dimers of ethylene,
propylene or butylenes. The methods of manufacturing these derivatives
are well known in the art, and therefore, are not discussed herein.
This invention will be better understood with reference to the
following examples, which are intended to illustrate specific embodiments
within the overall scope of the invention as claimed.
EXAMPLE 1.
SAPO-34A was made hydrothermally using diethylamine (DEA) as the
templating agent. SAPO-34A, 10 grams, was added to an aqueous zinc
nitrate solution, 100 ml, 0.1 M. This mixture was stirred in a 200
ml stainless steel vessel. The vessel was closed and heated in an
oven at 180.degree. C. at autogeneous pressure for 12 hours. The
molecular sieve was recovered by filtration, washed with water,
and dried at 110.degree. C. overnight. The molecular sieve was then
calcined by heating in air to 550.degree. C. for two to five hours.
This prepared molecular sieve is labeled as Zn-SAPO-34A-180.
EXAMPLE 2.
The procedure of Example 1 was repeated with the exception that
the processing temperature was 200.degree. C. This prepared molecular
sieve is labeled as Zn-SAPO-34A-200.
EXAMPLE 3.
The procedure of Example 1 was repeated for the other metals listed
in Tables 1-5 at the stated processing temperatures and molecular
sieve type. In all cases metal nitrates were used, except for M=Ti,
where titaniuim sulfate was used.
EXAMPLE 4.
Conversion reactions in which methanol (MeOH) was converted to
olefin product was carried out in a fixed bed reactor (ID=1/2"
quartz) with continuous flow of MeOH vapor (WHSV=2hr.sup.1) diluted
with nitrogen (60 ml/min) at 450.degree. C. The molecular sieve
as prepared in Examples 1-3 were pressed into tablets. The prepared
tablets were then crushed to a powder with 20-40 mesh size. 1.28
g of the powdered molecular sieve was placed in the reactor and
activated at 500.degree. C. in flowing N.sub.2 (60 ml/min) for one
hour prior to initiating the MeOH feed. The reaction products were
analyzed using an on-line gas chromatograph equipped with a Paropak-QS.RTM.
column and a thermalcouple detector. The test results shown in Tables
1-5 summarize the initial performance of the molecular sieve of
the invention approximately two minutes after MeOH was introduced.
The relative crystallinity of a given sample was determined using
x-ray diffraction, with the non-metal SAPO-34A as the reference
sample. The lifetime (min.) is defined as the time-on-stream when
MeOH conversion dropped below 100%.
As shown by the product selectivities summarized in Tables 1-5
and depicted graphically in the corresponding FIGS. 1-5 the temperature
at which the mixture is heated affects the surface properties, and
hence the surface composition of the molecular sieve or at least
the way in which the metal is disposed on the molecular sieve surface.
Tables 1 and 2 summarize the methanol-to-olefin (MTO) selectivity
to light olefins and other conversion products for the molecular
sieve SAPO-34A having a surface heat impregnated with a selected
metal. FIGS. 1 and 2 depict a graphical representation of the ethylene
and propylene data of Tables 1 and 20 respectively. SAPO-34A without
metal present was used as a control for the experiments. As shown,
some of the metal molecular sieve of the invention prepared at a
temperature of 180.degree. C. exhibited less light olefin selectivity
than the control. However, if the process temperature of the invention
is increased from 180.degree. C. to 200.degree. C. many of the metal
molecular sieve of the invention exhibit higher selectivities than
the control. For example, SAPO-34A with a surface heat impregnated
with aluminum, cobalt, and chromium exhibits approximately a 15%
increase in C.sub.2 -C.sub.3 (ethylene/propylene) olefin selectivity
as the processing temperature is increased from 180.degree. C. to
200.degree. C. In contrast, other metals, such as zinc and titanium,
exhibit substantially lower levels of C.sub.2 -C.sub.3 selectivity
as the temperature is increased. In particular, zinc exhibits decreased
levels of approximately 50% and titanium of approximately 90%. At
a processing temperature of 180.degree. C. copper and zinc SAPO-34A
exhibit very similar C.sub.2 -C.sub.3 selectivities, 81.7% and 81.2%,
respectively, though the relative ethylene to propylene ratios are
significantly different in the two samples. The Zn-SAPO-34A-180
exhibits a greater selectivity for ethylene, than that of Cu-SAPO-34A-180.
However, Cu-SAPO-34A-200 exhibits the highest light olefin selectivity
(86%) of any of the molecular sieve of the invention tested to date.
Tables 3-5 summarize the MTO selectivity to light olefins and other
products for SAPO-34B having a surface heat impregnated with a metal
at 200.degree. C., 180.degree. C. and 160.degree. C., respectively.
FIGS. 3-5 depict a graphical representation of the ethylene and
propylene data of Tables 3-5 respectively. As shown in Table 5
and the corresponding FIG. 5 the SAPO-34B of the invention prepared
at a processing temperature of 160.degree. C. exhibit very little
change from the unmodified catalyst with the exception of copper
and zinc. However, as the process temperature is increased many
of the SAPO-34B of the invention exhibit an increase in ethylene
selectivity. Generally, more pronounced increases in ethylene selectivities
(3-7%) are observed for SAPO-34B than the corresponding SAPO-34A
of the invention. As shown, SAPO-34B with a surface heat impregnated
with copper and zinc exhibit the highest degree of light olefin
selectivity, particularly ethylene selectivity. One interesting
exception to the series SAPO-34B of the invention is barium and
calcium SAPO-34B. The SAPO-34B with these two metals exhibit a slight
preference for propylene over ethylene.
Depending upon the process temperature Cu-SAPO-34A-T exhibited
on average a 20% to 30% increase in ethylene selectivity compared
to the control with the added ethylene selectivity coming at the
expense of the amount of propylene produced. Also, it is important
that the Cu-SAPO-34B-T produces 8 to 10% less C.sub.3 -C.sub.5 paraffin
product. Therefore, about two-thirds of the increase in ethylene
selectivity comes at the expense of propylene, and the remaining
10% at the expense of undesirable parafin product. The Zn-SAPO-34B-T
catalyst exhibited a 10% to 25% increase in ethylene with less of
a decrease in propylene. Also, Zn-SAPO-34B-T produced less C.sub.4.sup.+
hydrocarbon. Particularly, Zn-SAPO-34B180 exhibits a 24% increase
in ethylene selectivity compared to the control. Again, the higher
ethylene selectivity comes at the expense of propylene (about 13%),
propane (6%) and C.sub.5.sub.+ (4%). As shown in FIGS. 3 and 5 SAPO-34B
having a surface heat impregnated with zinc tends to be more dependant
upon the process temperature than the corresponding copper molecular
sieve of the invention. For example, Zn-SAPO-34B-160 exhibits a
15% increase in ethylene and only a 5% decrease in propylene, while
Zn-SAPO-34B-200 exhibits a 10% increase in ethylene with no appreciable
loss of propylene selectivity. |