Molecular sieve abstract
The present invention provides a method for the conversion of oxygenates
to olefins comprising exposing said oxygenates to a catalytic coating
comprising a non-zeolitic molecular sieve catalyst coated on a support
comprising inorganic materials, wherein said catalyst comprises
in the range of from at least about 5 wt % of said support, under
conditions effective to convert said oxygenates to olefins.
Molecular sieve claims
We claim:
1. A method for the conversion of oxygenates to olefins comprising
exposing said oxygenates to a catalytic coating comprising a non-zeolitic
molecular sieve catalyst and an amount and distribution of a binder
which is effective to bind the non-zeolitic molecular sieve catalyst
to a support comprising inorganic materials, wherein said binder
comprises a material selected from the group consisting of colloidal
alumina, silica, and a combination thereof and wherein said catalyst
comprises between at least about 5 wt % of said support, under conditions
effective to convert said oxygenates to olefins.
2. The method of claim 1 wherein said conditions comprise
a temperature in the range of from about 200.degree. C. to 700.degree.
C.;
a pressure in the range of from about 0.1 kPa and about 100 MPa;
and
a weight hourly space velocity of in the range of from about 0.01
hr.sup.-1 to about 500 hr.sup.-1.
3. The method of claim 1 wherein said conditions comprise
a temperature in the range of from about 250.degree. C. to 600.degree.
C.;
a pressure in the range of from about 6.9 kPa to about 34 MPa;
and
a weight hourly space velocity of in the range of from about 0.1
hr.sup.-1 to about 200 hr.sup.-1.
4. The method of claim 1 wherein said conditions comprise
a temperature in the range of from about 300.degree. C. to 500.degree.
C.;
a pressure in the range of from about 48 kPa to about 0.34 MPa;
and
a weight hourly space velocity of in the range of from about 0.5
hr.sup.-1 to about 100 hr.sup.-1.
5. The method of claim 1 wherein said non-zeolitic molecular sieve
catalyst comprises a silicoaluminophosphate molecular sieve catalyst.
6. The method of claim 1 wherein said non-zeolitic molecular sieve
catalyst comprises a small pore non-zeolitic molecular sieve catalyst.
7. The method of claim 5 wherein said non-zeolitic molecular sieve
catalyst comprises a small pore silicoaluminophosphate molecular
sieve catalyst.
8. The method of claim 1 wherein said oxygenates are selected from
the group consisting of aliphatic alcohols, ethers, carbonyl compounds,
and compounds comprising hetero-atoms.
9. The method of claim 8 wherein said aliphatic alcohols comprise
an aliphatic moiety having in the range of from about 1-10 carbon
atoms.
10. The method of claim 8 wherein said aliphatic alcohols comprise
an aliphatic moiety having in the range of from about 1-4 carbon
atoms.
11. The method of claim 1 wherein said oxygenates are selected
from the group consisting of: lower straight chain and branched
aliphatic alcohols; unsaturated counterparts thereof; and, nitrogen,
halogen and sulfur analogues thereof.
12. The method of claim 1 wherein said oxygenates are selected
from the group consisting of: methanol; ethanol; n-propanol; isopropanol;
C.sub.4 -C.sub.10 alcohols; methyl ethyl ether; dimethyl ether;
diethyl ether; di-isopropyl ether; methyl mercaptan; methyl sulfide;
methyl amine; ethyl mercaptan; diethyl sulfide; diethyl amine; ethyl
chloride; formaldehyde; dimethyl carbonate; dimethyl ketone; acetic
acid; n-alkyl amines, n-alkyl halides, and n-alkyl sulfides comprising
n-alkyl groups having in the range of from about 3-10 carbon atoms;
and, mixtures thereof.
Molecular sieve description
FIELD OF THE INVENTION
The present invention relates to supports for non-zeolitic molecular
sieve catalysts, particularly monolithic supports for small pore
silicoaluminophosphate catalysts, and to methods of using such catalysts
to convert oxygenates to olefins.
BACKGROUND OF THE INVENTION
Light olefins, such as ethylene, serve as feeds for the production
of numerous chemicals. Olefins traditionally are produced by petroleum
cracking. Because of the limited supply and/or the high cost of
petroleum sources, the cost of producing olefins from petroleum
sources has increased steadily.
Alternative feedstocks for the production of light olefins are
oxygenates, such as alcohols, particularly methanol, dimethyl ether,
and ethanol. Alcohols may be produced by fermentation, or from synthesis
gas derived from natural gas, petroleum liquids, carbonaceous materials,
including coal, recycled plastics, municipal wastes, or any organic
material. Because of the wide variety of sources, alcohol, alcohol
derivatives, and other oxygenates have promise as an economical,
non-petroleum source for olefin production.
Small pore molecular sieve catalysts, such as SAPO-34 are quite
successful in converting methanol and dimethyl ether to olefins.
However, methods are always needed for improving the performance
of such small pore molecular sieve catalysts.
Some have suggested using low surface area supports (hereinafter
"monolithic supports") containing zeolite catalysts. The
use of a monolithic support could produce a relatively low pressure
drop at low residence times and facilitate more uniform temperature
distribution in the catalyst bed. However, zeolites are relatively
hydrophilic and certain molecular sieves, particularly silicoaluminophosphate
(SAPO) molecular sieves, are relatively hydrophobic. Materials that
might be effective to bind a relatively hydrophilic zeolite catalyst
to a monolithic support would not necessarily be effective to bind
a relatively hydrophobic non-zeolitic catalyst to a monolithic support.
SUMMARY OF THE INVENTION
The present invention provides a method for the conversion of oxygenates
to olefins comprising exposing said oxygenates to a catalytic coating
comprising a non-zeolitic molecular sieve catalyst coated on a support
comprising inorganic materials, wherein said catalyst comprises
in the range of from at least about 5 wt % of said support, under
conditions effective to convert said oxygenates to olefins.
DETAILED DESCRIPTION OF THE INVENTION
The invention involves the conversion of oxygenates to olefins
using non-zeolitic molecular sieve catalysts carried on a monolithic
support. Suitable molecular sieve catalysts include, but are not
necessarily limited to, silicoaluminophosphates (SAPOs) and small
pore aluminophospho oxides (ALPO's). Examples of suitable small
pore ALPO's include, but are not necessarily limited to ALPO-20
and ALPO-25. Preferred molecular sieve catalysts are small pore
silicoaluminophosphates (SAPOs), such as SAPO-34 SAPO 17 SAPO-18
SAPO-43 and SAPO44 and others which may be synthesized according
to U.S. Pat. No. 4440871 incorporated herein by reference, and
Zeolites, Vol. 17 pp. 512-522 (1996), incorporated herein by reference.
Most preferred catalysts are SAPO-17 SAPO-18 and SAPO-34.
"Small pore" molecular sieve catalysts are defined as
catalysts with pores having a diameter or pore size of less than
about 5.0 Angstroms. Suitable catalysts have a pore size ranging
from about 3.5 to about 5.0 Angstroms, preferably from about 4.0
to about 5.0 Angstroms, and most preferably from about 4.3 to about
5.0 Angstroms.
SAPO's have a three-dimensional microporous crystal framework of
PO.sup.+, AlO.sub.2.sup.-, and SiO.sub.2 tetrahedral units. The
chemical composition (anhydrous) is:
wherein "R" represents at least one organic templating
agent present in the intracrystalline pore system: "m"
represents the moles of "R" present per mole of (Si.sub.x
Al.sub.y P.sub.z)O.sub.2 and has a value of from zero to 0.3 the
maximum value in each case depending upon the molecular dimensions
of the templating agent and the available void volume in the pore
system of the particular SAPO species involved, and "x",
"y", and "z" represent the mole fractions of
silicon, aluminum and phosphorus, respectively. "R" may
be removed at elevated temperatures.
The "monolithic supports" of the present invention preferably
are low surface area supports, or supports comprising materials
with very little surface porosity. Low surface area materials have
been difficult to coat with catalytic materials and have fewer sites
at which catalytic activity can take place. Such materials include,
but are not necessarily limited to glass, metals, and enamel, which
are substantially devoid of surface porosity. Monolithic supports
also may be made of materials which have minute surface porosity
but which are not impregnated in the usual sense by treatment, e.g.,
with silica sols. Such materials include, but are not necessarily
limited to porcelain, fused alumina, fused silica, mullite, beryl,
zirconia, dense sintered alumina, chromia, spinel, magnesia, fused
magnesia, and titania. The processes of the invention may be used
to apply catalytic coatings to porous catalyst supports, but the
real advantages are realized when the process is used to treat supports
having a low surface area.
The size or form of the support is not important, and the support
may be orientated or unorientated. The support may be in the shape
of a honeycomb, a sponge, pellets, granules, spheres, bars, rods,
tubes, rolls, spirals, screens, beads, coils, or any of the conventional
shapes in the art. Suitable supports include those described in
U.S. Pat. No. 3518206 incorporated herein by reference, either
coated or uncoated with colloidal amorphous silica spherulites.
The monolithic support preferably should be washcoated with a preparation
of alpha alumina, to smooth the surface and increase the surface
area. Suitable washcoating may be prepared using a known slip casting
process from an acid stabilized alpha-alumina, such as A16 SG, a
15 wt % acid stabilized alpha alumina available from Alcoa. The
washcoated samples should be dried and sintered, preferably at about
1200.degree. C. for about 24 hours.
A molecular-sieve containing slurry should be prepared by mixing
a desired amount of molecular sieve catalyst with a binder material
in a suitable solvent. Viscosifiers may be needed to prevent the
slurry from running off the surface of the monolith after application.
Any solvent may be used as long as the solvent does not adversely
affect the binder and/or the molecular sieves, maintains the binder
and molecular sieves in solution until after application to the
monolith, and thereafter evaporates at relatively low temperatures--on
the order of about 120.degree. C.--and after a relatively short
drying period--on the order of about 2 hours. A preferred solvent
is water.
Effective binder materials include, but are not necessarily limited
to colloidal alumina, (such as AL-20 available from Alcoa) and
silica (such as LUDOX AS-40). A preferred binder is silica.
Suitable viscosifiers include, but are not necessarily limited
to methyl cellulose (such as 20-213 a 20 wt % methyl cellulose)
and polyethylene glycol (such as a 20 wt % 2000 avg. MW PEG). Preferably,
a combination of methyl cellulose and PEG should be used in an amount
sufficient to raise the viscosity of the slurry to prevent runoff
after application. The slurry also should include a suitable grinding
media.
The mixture preferably should be milled and degassed to remove
air bubbles. The alpha-alumina coated monolithic support then may
be coated with the slurry, preferably using a known dip-coating
process. Where the monolithic support is a honeycomb or a sponge-type
structure, the excess slurry in the channels may be removed with
compressed air.
The coated samples should be dried, preferably at about 120.degree.
C. for about 2 hours. The coating procedure should be repeated until
a sufficient catalyst loading, preferably greater than about a 5
wt % catalyst loading, is achieved. Thereafter, the coated, dried
samples should be calcined. A preferred rate of calcination is about
20.degree. C. per hour for about 6 hours.
The monolithic supported catalyst preferably is used in a process
for converting a starting material (feedstock) preferably comprising
"oxygenates" to olefins. As used herein, the term "oxygenates"
is defined to include, but is not necessarily limited to aliphatic
alcohols, ethers, carbonyl compounds (aldehydes, ketones, carboxylic
acids, carbonates, and the like), and also compounds containing
hetero-atoms, such as, halides, mercaptans, sulfides, amines, and
mixtures thereof. The aliphatic moiety preferably should contain
in the range of from about 1-10 carbon atoms and more preferably
in the range of from about 1-4 carbon atoms. Representative oxygenates
include, but are not necessarily limited to, lower straight chain
or branched aliphatic alcohols, their unsaturated counterparts,
and their nitrogen, halogen and sulfur analogues. Examples of suitable
compounds include, but are not necessarily limited to: methanol;
ethanol; n-propanol; isopropanol; C.sub.4 -C.sub.10 alcohols; methyl
ethyl ether; dimethyl ether; diethyl ether; di-isopropyl ether;
methyl mercaptan; methyl sulfide; methyl amine; ethyl mercaptan;
diethyl sulfide; diethyl amine; ethyl chloride; formaldehyde; dimethyl
carbonate; dimethyl ketone; acetic acid; n-alkyl amines, n-alkyl
halides, n-alkyl sulfides having n-alkyl groups of in the range
of from about 3-10 carbon atoms; and mixtures thereof. As used herein,
the term "oxygenate" designates only the organic material
used as the feed. The total charge of feed to the reaction zone
may contain additional compounds such as diluents.
The conversion of feed to olefins preferably should be carried
out in the vapor phase. Preferably, the feedstock should be contacted
in the vapor phase in a reaction zone with the defined monolithically
supported molecular sieve catalyst at effective process conditions
so as to produce the desired olefins, i.e., an effective temperature,
pressure, WHSV (Weight Hourly Space Velocity) and, optionally, an
effective amount of diluent, correlated to produce olefins. Alternately,
the process may be carried out in a liquid phase. When the process
is carried out in the liquid phase, different conversion rates and
selectivities of feedstock-to-product may result.
The temperature employed in the conversion process may vary over
a wide range depending, at least in part, on the selected catalyst.
Although not limited to a particular temperature, best results will
be obtained if the process is conducted at temperatures in the range
of from about 200.degree. C. to 700.degree. C., preferably in the
range of from about 250.degree. C. to 600.degree. C., and most preferably
in the range of from about 300.degree. C. to 500.degree. C. Lower
temperatures generally result in lower rates of reaction, and the
formation of the desired light olefin products may become markedly
slow. However, at higher temperatures, the process may not form
an optimum amount of light olefin products.
Light olefin products will form--although not necessarily in optimum
amounts--at a wide range of pressures, including but not limited
to autogeneous pressures and pressures in the range of from about
0.1 kPa to about 100 MPa. A preferred pressure is in the range of
from about 6.9 kPa to about 34 MPa, most preferably in the range
of from about 48 kPa to about 0.34 MPa. The foregoing pressures
are exclusive of inert diluent, if any is present, and refer to
the partial pressure of the feedstock as it relates to oxygenate
compounds and/or mixtures thereof. Pressures outside of the stated
ranges may operate and are not excluded from the scope of the invention.
Lower and upper extremes of pressure may adversely affect selectivity
and/or conversion rates.
The process should be continued for a period of time sufficient
to produce the desired olefin products. The reaction time may vary
from seconds to a number of hours. The reaction time is largely
determined by the reaction temperature, the pressure, the catalyst
selected, the weight hourly space velocity, the phase (liquid or
vapor), and the selected process design characteristics.
A wide range of weight hourly space velocity (WHSV) for the feedstock
will function in the present invention. The WHSV generally should
be in the range of from about 0.01 hr.sup.-1 to about 500 hr.sup.-1
preferably in the range of from about 0.1 hr.sup.-1 to about 200
hr.sup.-1 and most preferably in the range of from about 0.5 hr.sup.-1
to about 100 hr.sup.-1. The catalyst may contain other materials
which act as inerts; therefore, the WHSV is calculated on the weight
basis of methanol or dimethyl ether and catalyst.
The feed may contain one or more inert diluents in an amount in
the range of from about 1-99 molar percent, based on the total number
of moles of all feed and diluent components fed to the reaction
zone (or catalyst). Diluents which may be employed in the process
include, but are not necessarily limited to, helium, argon, nitrogen,
carbon monoxide, carbon dioxide, hydrogen, water, paraffins, other
hydrocarbons (such as methane), aromatic compounds, and mixtures
thereof. Preferred diluents are water and nitrogen.
The process may be carried out in a batch, semi-continuous, or
continuous fashion. The process may use a single reaction zone or
a number of reaction zones arranged in series or in parallel. The
process may be intermittent or continuous in an elongated tubular
zone or a number of such zones. When multiple reaction zones are
used, one or more of the monolithically supported catalysts advantageously
may be used in series to provide for a desired product mixture.
The following examples illustrate, but do not limit, the present
invention.
EXAMPLE 1
SAPO-34 molecular sieve catalyst was obtained from UOP, Des Plaines,
Ill., disclosed in U.S. Pat. No. 4440871 incorporated herein
by reference.
EXAMPLE 2
Standard cordierite honeycombs (#9475) with 400 channels/m.sup.2
a 1/3 inch outside diameter, and a length of 9 inches, were obtained.
The honeycombs first were washcoated with alpha alumina, to smooth
the surface and increase the surface area. The washcoating was prepared
from an acid stabilized alpha-alumina (A16 SG, obtained from Alcoa)
using a slip casting process. The washcoated samples were dried
and sintered at 1200.degree. C. for 24 hours.
A molecular-sieve containing slurry was prepared by adding to a
500 ml polyethylene bottle the following: 9 g of the SAPO-34 molecular
sieve catalyst obtained in Example 1; 60 g water; 30 g colloidal
alumina (AL-20 obtained from Alcoa); 45 g of methyl cellulose (20-213
2 wt %); 2 ml of PEG (MW=2000 20 wt %); and, grinding media.
The mixture was milled overnight and degassed to remove air bubbles.
The alpha-alumina coated honeycombs then were coated with the slurry
using a dip-coating process. The excess slurry in the channels of
the honeycombs was removed with compressed air. The coated samples
then were dried at about 120.degree. C. for 2 hours. The coating
procedure was repeated two or three times, until greater than 5
wt % loading of catalyst was achieved. After all of the coating
and drying steps were completed, the samples were calcined at a
rate of 20.degree. C. per hour for 6 hours.
A 1:1 mixture of methanol and water is contacted with the catalyst
in a catalytic zone at a temperature of about 350.degree. C., at
a pressure of about 34 kPa (5 psia), and at a weight hourly space
velocity of about 1.3 hr.sup.-1. The conversion of methanol to carbon
dioxide and hydrogen is approximately 30%. Only small amounts of
methane, CO, and dimethyl ether are found in the product.
EXAMPLE 3
The procedures of Example 2 were repeated substituting the colloidal
alumina in the slurry with 15 g of LUDOX AS-40.
A 1:1 mixture of methanol and water is contacted with the catalyst
in a catalytic zone at a temperature of about 350.degree. C., at
a pressure of about 34 kPa (5 psia), and at a weight hourly space
velocity of about 1.3 hr.sup.-1. The conversion of methanol to carbon
dioxide and hydrogen is approximately 30%. Only small amounts of
methane, CO, and dimethyl ether are found in the product.
EXAMPLE 4
The procedures of Example 2 were repeated substituting the honeycomb
monolithic support with alumina form support called RETICEL, obtained
from Hi-Tech Ceramics.
A 1:1 mixture of methanol and water is contacted with the catalyst
in a catalytic zone at a temperature of about 350.degree. C., at
a pressure of about 34 kPa (5 psia), and at a weight hourly space
velocity of about 1.3 hr.sup.-1. The conversion of methanol to carbon
dioxide and hydrogen is approximately 30%. Only small amounts of
methane, CO, and dimethyl ether are found in the product.
Persons of ordinary skill in the art will recognize that many modifications
may be made to the present invention without departing from the
spirit and scope of the present invention. The embodiments described
herein are meant to be illustrative only and should not be taken
as limiting the invention, which is defined in the following claims. |