Molecular sieve abstract
The invention relates to a process for converting oxygenated organic
material, to olefins using small pore molecular sieve catalysts.
More particularly, the invention relates to a method for converting
oxygenated organic material to olefins with improved the olefin
yields and decreased yields of methane and other light saturate
byproducts. The improved yield slate is achieved by treating the
small pore molecular sieve catalyst with a modifier selected from
the group consisting of polynuclear aromatic heterocyclic compounds
with at least three interconnected ring structures having at least
one nitrogen atom as a ring substituent, each ring structure having
at least five ring members, decomposed derivatives of said polynuclear
aromatic heterocyclic compound, and mixtures thereof.
Molecular sieve claims
We claim:
1. A method for converting an organic starting material including
at least one oxygenate to olefins comprising:
contacting a feed comprising said organic starting material including
at least one oxygenate with a small pore molecular sieve catalyst
other than a zeolite under conditions effective to produce olefins,
wherein said catalyst comprises a framework of material selected
from the group consisting of silica, alumina, phosphate, and combinations
thereof, and a modifier selected from the group consisting of:
polynuclear aromatic heterocyclic compounds comprising at least
three interconnected ring structures comprising at least one nitrogen
atom as a ring substituent, each of said ring structures having
at least five ring members;
decomposed derivatives of said polynuclear aromatic heterocyclic
compounds; and
mixtures thereof.
2. The method of claim 1 wherein said polynuclear aromatic heterocyclic
compounds have the following general structure: ##STR3## wherein
at least one of R.sup.1 -R.sup.10 comprises nitrogen.
3. The method of claim 2 wherein at least two of R.sup.1 -R.sup.10
comprise nitrogen.
4. The method of claim 2 wherein said polynuclear aromatic heterocyclic
compounds comprise at least two nitrogen ring substituents at positions
selected from the group consisting of R.sup.1 and R.sup.10 R.sup.4
and R.sup.7 R.sup.1 and R.sup.7 and R.sup.5 and R.sup.6.
5. The method of claim 1 wherein said polynuclear aromatic heterocyclic
compound comprises 110-phenanthroline.
6. The method of claim 1 wherein said polynuclear aromatic heterocyclic
compounds have the following general structure: ##STR4## wherein
at least one of R.sup.1 -R.sup.10 is nitrogen.
7. The method of claim 6 wherein two of R.sup.1 -R.sup.10 are nitrogens.
8. The method of claim 6 wherein said polynuclear aromatic heterocyclic
compound comprises phenazine.
9. The method of claim 1 wherein said catalyst is a silicoaluminophosphate
catalyst comprising pores consisting essentially of a diameter less
than about 5.0 Angstroms.
10. The method of claim 2 wherein said catalyst is a silicoaluminophosphate
catalyst comprising pores consisting essentially of a diameter less
than about 5.0 Angstroms.
11. The method of claim 4 wherein said catalyst is a silicoaluminophosphate
catalyst comprising pores consisting essentially of a diameter less
than about 5.0 Angstroms.
12. The method of claim 5 wherein said catalyst is a silicoaluminophosphate
catalyst comprising pores consisting essentially of a diameter less
than about 5.0 Angstroms.
13. The method of claim 6 wherein said catalyst is a silicoaluminophosphate
catalyst comprising pores consisting essentially of a diameter less
than about 5.0 Angstroms.
14. The method of claim 7 wherein said catalyst is a silicoaluminophosphate
catalyst comprising pores consisting essentially of a diameter less
than about 5.0 Angstroms.
15. The method of claim 8 wherein said catalyst is a silicoaluminophosphate
catalyst comprising pores consisting essentially of a diameter less
than about 5.0 Angstroms.
16. The method of claim 1 wherein said organic starting material
is selected from the group consisting of methanol and dimethyl ether.
Molecular sieve description
FIELD OF THE INVENTION
The invention relates to a process for converting oxygenated organic
material to olefins using small pore molecular sieve catalysts.
More particularly, the invention relates to a method for converting
oxygenated organic material to olefins with improved the olefin
yields and decreased yields of methane and other light saturate
byproducts. The improved yield slate is achieved by treating the
small pore molecular sieve catalyst with a modifier selected from
the group consisting of polynuclear aromatic heterocyclic compounds
with at least three interconnected ring structures having at least
one nitrogen atom as a ring substituent, each ring structure having
at least five ring members, decomposed derivatives of said polynuclear
aromatic heterocyclic compound, and mixtures thereof.
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.
The total yield slate for a typical oxygenate to olefin process
includes (a) light saturates and oxygenates, i.e. methane, hydrogen,
carbon monoxide, carbon dioxide, and ethane, and (b) heavier by-products
with a molecular weight higher than propylene, i.e. C.sub.4 's and
C.sub.5 's. A typical oxygenate to olefin process has a methane
selectivity of no less than about 5 molar % or 2.5 wt %.
The literature related to oxygenate to olefin processes focuses
on maximizing ethylene and propylene product yields. Little attention
has been given to optimizing the total yield slate. One reason for
this lack of attention may be that the light saturate by-products
have no real fouling potential and also have some value--at least
as fuel. However, it is costly to separate the light saturate by-products
from the desired olefin products.
Various modifications have been made to molecular sieve catalysts
having intermediate sized pores to increase the selectivity of these
intermediate pore catalysts to olefins. However, little attention
has been given to treatments to increase the selectivity of small
pore catalysts to olefins.
Small pore zeolitic catalysts have a tendency to deactivate rapidly
during the conversion of oxygenates to olefins. A need exists for
methods to decrease the rate of deactivation of small pore zeolitic
catalysts during such conversions.
Small pore silicoaluminophosphate (SAPO) molecular sieve catalysts
have excellent selectivity in oxygenate to olefin reactions. However,
a continuing need exists for treatments which will maximize the
production of olefins and minimize the production of light saturate
byproducts using small pore molecular sieve catalysts, generally,
in order to reduce the cost of such processes and render them commercially
viable.
SUMMARY OF THE INVENTION
The present invention provides a method for increasing the selectivity
of a small pore molecular sieve catalyst to olefins comprising exposing
said small pore molecular sieve catalyst to a modifier under conditions
sufficient to produce a modified small pore molecular sieve catalyst
having improved selectivity to olefins, wherein the modifier is
selected from the group consisting of a polynuclear aromatic heterocyclic
compound comprising at least three interconnected ring structures
comprising at least one nitrogen atom as a ring substituent, each
of said ring structures having at least five ring members, decomposed
derivatives of said polynuclear aromatic heterocyclic compound,
and mixtures thereof.
DETAILED DESCRIPTION OF THE INVENTION
Substantially any small pore molecular sieve catalyst may be modified
according to the present invention. "Small pore" molecular
sieve catalysts are defined herein as catalysts with pores having
a diameter or pore size of less than about 5.0 Angstroms and equivalents
thereof. "Equivalents thereof" is defined to refer to
catalysts having a pore size that performs substantially the same
function in substantially the same way to achieve substantially
the same result as catalysts having a diameter or pore size of less
than about 5.0 Angstroms, exclusive of catalysts having a pore size
over about 5.2 Angstroms, or catalysts generally considered to be
"intermediate pore" or "large pore" molecular
sieve catalysts. Suitable catalysts include, but are not necessarily
limited to catalysts having a pore size in the range of from about
3.8 to about 5.0 Angstroms, preferably in the range of from about
4.1 to about 5.0 Angstroms, and most preferably in the range of
from about 4.3 to about 5.0 Angstroms.
Suitable small pore molecular sieve catalysts include, but are
not necessarily limited to zeolites, silicoaluminophosphates (SAPOs),
crystalline metal silico-aluminophosphates (MeAPSO's), crystalline
metal aluminophospho oxides (MeAPO's), and aluminophospho oxides
(ALPO's). Examples of suitable small pore zeolites include, but
are not necessarily limited to ZSM-34 erionite, and chabazite.
Examples of suitable small pore MeAPSOs and MeAPO'S include, but
are not necessarily limited to SAPO's and alumino phospho oxides
comprising preferably in the range of from about 0.005 to about
0.05 moles of a metal selected from the group consisting of magnesium,
zinc, iron, cobalt, nickel, manganese, chromium, and mixtures thereof.
Examples of suitable small pore ALPO's include, but are not necessarily
limited to ALPO-17 ALPO-20 and ALPO-25. The preparation of such
catalysts is well known in the art and is described in U.S. Pat.
Nos. 4554143; 4440871; 4853197; 4793984 4752651; and
4310440 all of which are incorporated herein by reference. Preferred
molecular sieve catalysts are SAPOs, such as SAPO-34 SAPO 17 SAPO-18
SAPO-43 and SAPO-44 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.
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 modifiers of the present invention comprise polynuclear aromatic
heterocyclic compounds with at least three interconnected ring structures
having at least one nitrogen atom as a ring substituent, each ring
structure having at least five ring members, and quaternary salts
thereof. Suitable modifiers include, but are not necessarily limited
to compositions having the following general structure: ##STR1##
wherein at least one of R.sup.1 -R.sup.10 is nitrogen. In a preferred
embodiment, two of R.sup.1 -R.sup.10 are nitrogens. In a most preferred
embodiment, two nitrogens are substituents on the ring at positions
selected from the group consisting of R.sup.1 and R.sup.10 R.sup.4
and R.sup.7 R.sup.1 and R.sup.7 and R.sup.5 and R.sup.6. Examples
include 110-phenanthroline, 47-phenanthroline, 17-phenanthroline,
and benzo(c)cinnoline. A preferred modifier having the foregoing
structure is 110-phenanthroline, in which R.sup.1 and R.sup.10
are nitrogens.
Suitable modifiers also include, but are not necessarily limited
to compositions having the following general structure, and quaternary
salts thereof: ##STR2## wherein at least one of R.sup.1 -R.sup.10
is nitrogen, preferably two of R.sup.1 -R.sup.10 are nitrogens.
In a most preferred embodiment, R.sup.1 and R.sup.6 are nitrogens,
resulting in phenazine.
The modifiers of the present invention may be adsorbed onto the
catalyst either prior to or simultaneous with the introduction of
the oxygenate feed.
The modifier may be adsorbed onto the catalyst prior to the introduction
of the feed using any suitable means. In one embodiment, a solution
of the desired modifier is first made by dissolving a desired amount
of the modifier in a solvent under mild conditions. Suitable solvents
are organic, inorganic, and aqueous. If water is used, the water
preferably should be de-ionized. Adjusting the pH to below 7.0 in
an aqueous system also helps the dissolution of the modifiers. The
temperature of mixing is dependent upon the solubility of the modifier
in the solvent selected. The process may be conducted under pressure,
at reduced pressure, or at atmospheric pressure.
After adequate mixing, the solution is added to a predetermined
amount of the catalyst. The resulting mixture is stirred as required.
In some cases, stirring is not required and the mixture may be left
undisturbed for a time adequate to permit the desired level of modifier
adsorption onto the catalyst. The catalyst product then is filtered
and dried. The catalyst preferably is then calcined to decompose
at least a portion of the modifier in an essentially non-oxidizing
atmosphere by methods well known to those skilled in the art. Suitable
non-oxidizing atmospheres include, but are not necessarily limited
to nitrogen, argon, helium, carbon dioxide, etc.
The amount of modifier adsorbed onto the catalyst may vary over
a wide range depending, at least in part, on the selected catalyst
and the incorporation method. Preferably, the amount of the modifier
adsorbed should be at least about 0.0001 wt. %, most preferably
in the range of from about 0.001 wt. % and about 5.0 wt. % nitrogen.
If the modifier is to be introduced with the oxygenate feed, the
modifier may be injected into the system in any suitable manner
as long as the conditions are such that the modifier is miscible
with the feed. For example, if the modifier has a low solubility
in alcohol, the solubility limits should not be exceeded. Or, if
the modifier has an exceptionally high melting or boiling point,
suitable adjustments should be made. If the reaction is carried
out in the vapor phase, a modifier with a boiling point below the
process temperature preferably should be used so that the modifier
may be carried into the reactor by entrainment, downflow, or other
methods known to those skilled in the art.
The conversion process employs an organic starting material (feedstock)
preferably comprising "oxygenates". As used herein, the
term "oxygenates" is defined to include, but is not necessarily
limited to aliphatic alcohols, ethers, carbonyl compounds (aldehydes,
ketones, carboxylic acids, carbonates, and the like), and also compounds
containing hetero-atoms, such as, halides, mercaptans, sulfides,
amines, and mixtures thereof. The aliphatic moiety preferably should
contain in the range of from about 1-10 carbon atoms and more preferably
in the range of from about 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 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 depending upon the composition
of the liquid.
The temperature employed in the conversion process may vary over
a wide range depending, at least in part, on the selected catalyst.
Although not limited to a particular temperature, best results will
be obtained if the process is conducted at temperatures in the range
of from about 200.degree. C. to about 700.degree. C., preferably
in the range of from about 250.degree. C. to about 600.degree. C.,
and most preferably in the range of from about 300.degree. C. to
about 500.degree. C. Lower temperatures generally result in lower
rates of reaction, and the formation of the desired light olefin
products may become markedly slow. However, at higher temperatures,
the process may not form an optimum amount of light olefin products,
and the coking rate may become too high.
Light olefin products will form--although not necessarily in optimum
amounts--at a wide range of pressures, including but not limited
to autogeneous pressures and pressures in the range of from about
0.1 kPa to about 100 MPa. A preferred pressure is in the range of
from about 6.9 kPa to about 34 MPa, most preferably in the range
of from about 48 kPa to about 0.34 MPa. The foregoing pressures
are exclusive of diluent, if any is present, and refer to the partial
pressure of the feedstock as it relates to oxygenate compounds and/or
mixtures thereof. Pressures outside of the stated ranges may operate
and are not excluded from the scope of the invention. Lower and
upper extremes of pressure may adversely affect selectivity, conversion,
coking rate, and/or reaction rate; however, light olefins such as
ethylene still may form.
The process should be continued for a period of time sufficient
to produce the desired olefin products. The reaction time may vary
from tenths of seconds to a number of hours. The reaction time is
largely determined by the reaction temperature, the pressure, the
catalyst selected, the weight hourly space velocity, the phase (liquid
or vapor), and the selected process design characteristics.
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, fillers, or binders; therefore, the WHSV is
calculated on the weight basis of methanol or dimethyl ether and
catalyst.
The feed may contain one or more diluents in an amount in the range
of from about 1 and 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 small pore catalysts advantageously may
be used in series to provide for a desired product mixture.
A dynamic bed system, or any system that includes a variety of
transport beds rather than fixed beds, may be desirable. If regeneration
of the catalyst is required, such a system would permit introduction
of the catalyst as a moving bed to a regeneration zone where, e.g.,
carbonaceous material could be removed or oxidized. Preferably,
the catalyst should be regenerated by burning off carbonaceous deposits
that accumulate during the process.
The following examples illustrate, but do not limit, the present
invention. |