Molecular sieve abstract
Disclosed is a method of heat treating a molecular sieve. The method
comprises providing a template-containing molecular sieve, heating
the molecular sieve under conditions effective to remove a portion
of the template from the molecular sieve, and cooling the heated
molecular sieve to leave an amount of template effective to cover
catalytic sites within the molecular sieve. A catalyst composition
is also provided which comprises a molecular sieve having a microporous
structure and a binder, wherein between 10 and 90 vol % of the microporous
structure is occupied by a material, the material comprising a template
or a carbonaceous residue of a template, and the catalyst composition
exhibits a Davison Index of not greater than 30.
Molecular sieve claims
What is claimed is:
1. A catalyst composition comprising a molecular sieve having a
microporous structure and a binder, wherein between 10 and 90 vol
% of the microporous structure is occupied by a material, the material
comprising a template or a heat degraded product thereof, and the
catalyst composition exhibits a Davison Index of not greater than
30.
2. The catalyst composition of claim 1 wherein the Davison Index
is not greater than 20.
3. The catalyst composition of claim 2 wherein the Davison Index
is not greater than 10.
4. The catalyst of claim 1 wherein the molecular sieve is selected
from the group consisting of zeolites, tectosilicates, tetrahedral
aluminophosphates and tetrahedral silicoaluminophosphates.
5. The catalyst composition of claim 1 wherein between 20 and
80 vol % of the microporous structure is occupied by the material.
6. The catalyst composition of claim 5 wherein between 30 and
70 vol % of the microporous structure is occupied by the material.
7. The catalyst composition of claim 1 wherein the molecular sieve
is a tetrahedral silicoaluminophosphate molecular sieve 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 metal containing forms
thereof, and mixtures thereof.
8. The catalyst composition of claim 7 wherein the molecular sieve
is SAPCO-34.
9. The catalyst composition of claim 1 wherein the material is
a template selected from the group consisting of tetraethyl ammonium
salt, cyclopentylamine, aminomethyl cyclohexane, piperidine, triethylamine,
cyclohexylamine, tri-ethyl hydroxyethylamine, morpholine, dipropylamine,
pyridine, isopropylamine and mixtures thereof.
10. The catalyst composition of claim 1 wherein the material is
a heat degraded template, and the template is selected from the
group consisting of tetraethyl ammonium salt, cyclopentylamine,
aminomethyl cyclohexane, piperidine, triethylamine, cyclohexylamine,
tri-ethyl hydroxyethylamine, morpholine, dipropylamine, pyridine,
isopropylamine and mixtures thereof.
11. The catalyst composition of claim 7 wherein the molecular
sieve is selected from the group consisting of SAPO-34 SAPO-18
SAPO-11 SAPO-35 and SAPO-47.
12. Add The catalyst composition of claim 9 wherein the material
is selected from the group consisting of tetraethyl ammonium salt,
morpholine and mixtures thereof.
Molecular sieve description
FIELD OF THE INVENTION
This invention relates to a method of heat treating a molecular
sieve material and its corresponding catalyst composition. In particular,
this invention relates to a method of heat treating a crystalline
molecular sieve to provide hardness yet resist catalyst deactivation.
BACKGROUND OF THE INVENTION
A molecular sieve is generally a microporous structure composed
of either crystalline aluminosilicate, chemically similar to clays
and feldspars and belonging to a class of materials known as zeolites,
or crystalline aluminophosphates derived from mixtures containing
an organic amine or quaternary ammonium salt, or crystalline silicoaluminophosphates
which are made by hydrothermal crystallization from a reaction mixture
comprising reactive sources of silica, alumina and phosphate. Molecular
sieves have a variety of uses. They can be used to dry gases and
liquids; for selective molecular separation based on size and polar
properties; as ion-exchangers; as catalysts in cracking, hydrocracking,
disproportionation, alkylation, isomerization, oxidation, and conversion
of oxygenates to hydrocarbons; as chemical carriers; in gas chromatography;
and in the petroleum industry to remove normal paraffins from distillates.
Molecular sieves are manufactured by reacting a mixture of several
chemical components. One of the components used in the reaction
process is a template, although more than one template can be used.
The templates are used to form channels or tunnel like structures
(also called a microporous structure) within the composition. When
the template is removed, an open microporous structure is left behind
in which chemical composition can enter, as long as the chemical
compositions are small enough to be able to fit inside the tunnels.
Thus a molecular sieve acts to sieve or screen out large molecules
from entering a molecular pore structure.
Molecular sieves are particularly desirable for use as catalytic
agents. The molecular sieves that act as catalysts have catalytic
sites within their microporous structures. Once the template is
removed, a chemical feedstock that is small enough to enter into
the tunnels can come into contact with a catalytic site, react to
form a product, and the product can leave the molecular sieve through
any number of the tunnels or pores as long as the product has not
become too large to pass through the structure. The pore sizes typically
range from around 2 to 10 angstroms in many catalytic molecular
sieves.
Template material can be removed from the framework of a molecular
sieve by a variety of methods. A preferred method, however, is by
calcining or heat treating in an oxygen environment, since calcining
under appropriate conditions brings the additional advantage of
hardening the molecular sieve. Once the molecular sieve is hardened,
it can be more readily transported or more effectively blended with
other materials.
U.S. Pat. No. 5174976 discloses one method of calcining a molecular
sieve material in order to remove the template material. The method
includes the steps of heating a crystalline [metallo]aluminophosphate
composition to a calcination temperature at a rate no greater than
10.degree. C. per minute with a high flow rate of a non-oxidizing
gas, e.g., nitrogen, and thereafter with an oxygen-containing gas,
e.g. air, at high gas flow rates, e.g., 100 to 400 cc/minute/gram.
Calcination temperature is described as ranging from 100-600.degree.
C.
In U.S. Pat. No. 4681864 it is disclosed, however, that calcination
of SAPO-37 molecular sieve compositions to remove the template material
leaves a structure which is sensitive to contact with moisture.
A method of removing template in order to avoid the moisture problem
is suggested. Specifically, the method involves preparing a SAPO-37
molecular sieve with a template, and leaving the entire template
in place for storage purposes. The molecular sieve is stated to
contain an organic template in its pore structure in amounts ranging
from 1 to 50% by weight of the molecular sieve, with an inorganic
oxide matrix component such as silica, alumina, silica-alumina gels
and sols, clay, and mixtures thereof. The entire template is removed
by placing the molecular sieve in a catalytic cracking unit at 400-600.degree.
C.
Methods which are conventionally used to remove template material
either fail to provide adequate protection against contact with
moisture or fail to sufficiently harden the catalyst material so
that it can be transported from one location to another with little
physical damage. In general, it even appears that moisture damage
is not a generally recognized problem. This is suggested, for example,
by Hawley's Condensed Chemical Dictionary, Thirteenth Edition, Von
Nostrand Reinhold, 1997 where it is stated that one characteristic
of the molecular sieve materials is their ability to undergo dehydration
with little or no change in crystalline structure. Nevertheless,
even the few methods that have been suggested for providing protection
of specific molecular sieve compositions do not provide a product
that would be hard enough to withstand many of the physical tortures
encountered during transportation, much less the physical tortures
that would be encountered during actual use. Therefore, there is
a need to provide molecular sieves that are effectively protected
from damage due to contact with moisture and from damage due to
physical contact.
SUMMARY OF THE INVENTION
In order to overcome problems related to protecting molecular sieves
from damage due to contact with moisture and damage due to physical
contact, this invention provides a method of heat treating a molecular
sieve comprising providing a molecular sieve containing a template
within a micropotous structure, heating the molecular sieve under
conditions effective to remove a portion of the template from the
microporous structure, and cooling the heated molecular sieve to
leave an amount of template or degradation product thereof effective
to cover catalytic sites within the microporous structure. In another
embodiment there is provided a method of making an olefin product
from an oxygenate feedstock comprising, heating a molecular sieve
containing a template within a microporous structure under conditions
effective to remove a portion of the template from the microporous
structure, cooling the heated molecular sieve to leave an amount
of the template or degradation product thereof (i.e., a carbonaceous
residue of a template) effective to cover catalytic sites within
the molecular sieve, calcining the cooled molecular sieve, and contacting
the calcined molecular sieve with the oxygenate feedstock under
conditions effective to convert the oxygenate feedstock to an olefin
product. Preferably, the heated molecular sieve is cooled to below
100.degree. C., preferably, below 80.degree. C., preferably to ambient.
The molecular sieve or a catalyst containing the molecular sieve
can be stored or transported at the cooled conditions with relative
ease. Under the cooled conditions storage or maintenance can be
acceptably tolerated for at least 12 hours, preferably at least
2 weeks and most preferably at least 2 months. After storing or
transporting, the molecular sieve or catalyst can be calcined to
activate the catalytic sites prior to contact with the oxygenate
feedstock.
In a preferred embodiment, the crystalline molecular sieve is selected
from the group consisting of zeolites, tectosilicates, tetrahedral
aluminophosphates and tetrahedral silicoaluminophosphates. Preferably,
the crystalline molecular sieve is a crystalline silicoaluminophosphate
molecular sieve, and the silicoaluminophosphate molecular sieve
is preferably 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
metal containing forms thereof, and, mixtures thereof.
Preferably, the molecular sieve is mixed within a catalyst composition
comprising a binder. It is also preferred that heating is effective
to provide a catalyst composition having a Davison Index of not
greater than 30 more preferably not greater than 20 most preferably
not greater than 10.
In yet another preferred embodiment, the template is selected from
the group consisting of tetraethyl ammonium salt, cyclopentylamine,
aminomethyl cyclohexane, piperidine, triethylamine, cyclohexylamine,
tri-ethyl hydroxyethylamine, morpholine, dipropylamine, pyridine,
isopropylamine and mixtures thereof.
A catalyst composition is also provided which comprises a molecular
sieve having a microporous structure and a binder, wherein between
10 and 90 vol %, preferably between 20 and 80 vol %, more preferably
between 30 and 70 vol %, of the microporous structure is occupied
by a material, the material comprising a template or a or a heat
degraded product thereof. Preferably, the catalyst composition exhibits
a Davison Index of not greater than 30.
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 shows the temperature-programmed-oxidation (TIPO--1% O.sub.2
in helium) spectra of TEAOH, DPA, mixed TEAOH/DPA, and morpholine
deposited on high surface area silica;
FIG. 2 shows the TPO spectra of a SAPO-34 molecular sieve having
a mixed TEAOHA/PA template and a SAPO-34 molecular sieve having
a morpholine template;
FIG. 3 shows a comparison of the TPO (oxygen in helium) and the
TPO (no oxygen in helium) spectra of a SAPO-34 molecular sieve having
a mixed TEAOH/DPA template;
FIG. 4 shows a comparison of the TPO (oxygen in helium) and the
TPO (no oxygen in helium) spectra of SAPO-34 molecular sieves having
morpholine templates; and
FIG. 5 shows the TPO spectra of SAPO-34 molecular sieves having
a morpholine template in SAPO-34 one sample having been heat pretreated
at 450.degree. C. in helium for 1 hour, one sample having been heat
pretreated at 625.degree. C. in helium for 1 hour, and another sample
having no heat pretreatment.
DETAILED DESCRIPTION OF THE INVENTION
The molecular sieve of this invention is protected against possible
damage due to contact by moisture. In addition, the molecular sieve
is in a hardened form such that there is provided effective protection
against physical damage during transportation, shipping, storing
or subsequent use in an operating system.
In a preferred embodiment the molecular sieve is capable of functioning
as a catalyst. Preferably, the molecular sieve is selected from
the group consisting of zeolites, tectosilicates, tetrahedral aluminophosphates
(ALPOs) and tetrahedral silicoaluminophosphates (SAPOs). In a more
preferred embodiment, the molecular sieve is a silicoaluminophosphate.
Silicoaluminophosphate molecular sieves generally comprise a three-dimensional
microporous crystal framework structure of [SiO.sub.2 ], [AlO.sub.2
] and [PO.sub.2 ] tetrahedral units. The way Si is incorporated
into the structure can be determined by .sup.29 Si MAS NoM 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 [(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 [(Si) in the range
of -88 ppm to -115 ppm, where the [(Si) chemical shifts refer to
external tetramethylsilane (TMS).
Silicoaluminophosphate molecular sieves are generally classified
as being microporous materials having 8 10 or 12 membered ring
structures. These ring structures can have an average pore size
ranging from about 3.5-15 angstroms. Preferred are the small pore
SAPO molecular sieves having an average pore size ranging from about
3.5 to 5 angstroms, more preferably from 4.0 to 5.0 angstroms. These
pore sizes are typical of molecular sieves having 8 membered rings.
In genera, silicoaluminophosphate molecular sieves comprise a molecular
framework of corner-sharing [SiO.sub.2 ], [AlO.sub.2 ], and [PO.sub.2
] tetrahedral units. This type of framework is effective in converting
various oxygenates into olefin products.
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 [AlO.sub.2 tetrahedral units within the framework structure
can be provided by a variety of compositions. Examples of these
aluminum-containing compositions include aluminum alkoxides such
as aluminum isopropoxide, aluminum phosphates, aluminum hydroxide,
sodium ailuminate, 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 sots 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 MeAPSOs or metal-containing silicoaluminophosphates.
The metal can be alkali metal ions (Group IA), alkaline earth metal
ions (Group IIA), rare earth ions (Group IIIB, including the 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 cations of Groups IVB, VB, VIB, VIIB, VIIIB, 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 +3. Incorporation of the metal component is typically
accomplished adding the metal component during synthesis of the
molecular sieve, However, post-synthesis ion exchange can also be
used.
Suitable silicoaluminophosphate molecular sieves include SAPO-5
SAPO-8 SAPO-11 SAPO-16 SAPO-17 SAPO-18 SAPO-20 SAPO-31 SAPO-34
SAPO-35 SAPO-36 SAPO-37 SAPO-40 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 SAPO44 and SAPO-47 particularly
SAPO-18 and SAPO-34 including the metal containing forms thereof,
and mixtures thereof. As used herein, the term mixture is synonymous
with combination and is considered a composition of matter having
two or more components in varying proportions, regardless of their
physical state.
An aluminophosphate (ALPO) molecular sieve structure can also be
interspersed with the SAPO molecular sieves. Aluminophosphate molecular
sieves are crystalline microporous oxides which can have an AlPO.sub.4
framework. They can have additional elemens 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-31 ALPO-34 ALPO-36 ALPO-37 and ALPO-46.
The ALPOs can also include a metal subtituent 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, aliminophosphate and silica aluminophospate
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:
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 (M.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 of the pore
system of the particular metal aluminophosphate involved, "x",
"y", and "z" represent the mole fractions of
the metal "M", (i.e. magnesium, manganese, zinc and cobalt),
aluminum and phosphorus, respectively, present as tetrahedral oxides.
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 silicoaluminophosphate 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 will be formed in solution.
It can be recovered by standard means, such as by centrifugation
or filtration. The product can also be washed, recovered by 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
removed so that the molecular sieve can exhibit catalytic activity.
Once the template is removed, the crystalline structure that remains
has what is typically called an intracrystalline pore system.
The reaction mixture can contain one or more templates. Templates
are structure directing 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, 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.
Although not necessary, it is preferable that the templates of
this invention have a multimodal decomposition profile, meaning
that the decomposition of the template does not exhibit a single,
sharp peak as monitored by a flame ionization detector (FID). Examples
include templates which have more than one peak as monitored by
FID, as well as templates which have a more or less flat curve (i.e.,
not a single, sharp peak) as monitored by FID. The advantage of
a template having this type of decomposition profile is that the
"as manufactured" molecular sieve can be heated to harden
the material, yet heating can be safely stopped such that a portion
of the template, or at least the template's heat decomposed product,
can be left within the molecular sieve to protect the framework
from structural damage by moisture. The existence of a multimodal
decomposition profile can be determined by using a temperature-programmed-oxidation
(TPO) technique. The advantage of using a template or template mixture
having a multimodal decomposition profile is that heat treatment
can be controlled over a wider range of temperatures compared to
a template with a sharp decomposition profile. Nevertheless, a template
having a sharp decomposition profile can exhibit a flatter decomposition
profile when heat treated under appropriate conditions, preferably
under and oxygen depleted environment.
In the TPO technique, template-containing sieve or catalyst is
loaded into a quartz reactor, gas is injected into the reactor (preferably
1% O.sub.2 in helium or helium with essentially no O.sub.2), and
the reactor is heated at a constant rate of increase. The gas exiting
the quartz reactor is directed to a methanator, which contains a
ruthenium catalyst, and converts products, including CO and CO.sub.2
produced during template decomposition to CH.sub.4. The CH.sub.4
production rate is continuously monitored with a flame ionization
detector (FID). Details of this technique have been reported in
S. C. Fung an C. A. Querini, J. Cat., 138 240 (1992), and C. A.
Querini and S. C. Fung, J. Cat., 141 389 (1993), the descriptions
of each being fully incorporated herein by reference.
The multimodal decomposition profile can be essentially flat at
its maximum value or it can have two or more distinct peaks. A decomposition
profile having at least two distinct peaks is particularly preferred.
Preferably the profile at the approximate maximum value will extend
over at least about 200.degree. C. before the template is completely
removed, more preferably at least 250.degree. C. In other words,
the profile preferably will have a first peak followed by at least
one peak, and at least two of the peaks will occur over a range
of at least 200.degree. C., more preferably at least 250.degree.
C.
In this invention, it is important to heat the molecular sieve
or catalyst composition to sufficiently harden the material, yet
leave enough of the template or its residue within the framework
of the molecular sieve to cover internal catalytic sites. That is,
it is important to harden the molecular sieve or catalyst composition
and protect catalytic sites within the molecular sieve by leaving
sufficient template or carbonaceous material derived from the template
to block contact of the sites with water molecules. Preferably,
after heating the as manufactured molecular sieve, no more than
70 wt % of the template will be removed, preferably no more than
50 wt % will be removed, more preferably no more than 35 wt % of
the carbonaceous material of the template will be removed, and most
preferably nor more than 20 wt % of the carbonaceous material will
be removed.
Techniques for measuring the weight percent of template or a carbonaceous
heat degradation product of a template within the microporous structure
of a molecular sieve are known to those of ordinary skill in the
art. A preferred technique is temperature-programmed-oxidation (TPO).
In the preferred TPO technique, each material is evaluated by loading
0.005 gram of the template-containing silica material into a quartz
reactor. Helium containing 1%. O.sub.2 (partial pressure of 1 kPa)
is injected into a quartz reactor at a rate of 63 cc/min. Gas exiting
the quartz reactor is preferably directed to a methanator, containing
a ruthenium catalyst, to convert compositions produced during template
decomposition to CH.sub.4. The CH.sub.4 production rate can be continuously
monitored with a flame ionization detector (FID). To determine weight
percent carbon from the TPO spectra, a calibration should be carried
out. This is done by sending a known amount of CO.sub.2 gas as a
pulse to the methanator using the same carrier gas and carrier gas
flow rate as in the TPO experiment. This provides a peak in the
FID signal from which a calibration factor is determined, i.e.,
the amount of carbon per unit area. The weight percent of carbon,
i.e., the amount of template in the microporous structure, is calculated
by multiplying the spectral area from the helium step by the calibration
factor.
In a preferred embodiment, the heat treated material will comprise
at least one molecular sieve having catalytic sites and the molecular
sieve is admixed (blended) with other materials. In this blended
form, the overall composition is typically referred to as a molecular
sieve catalyst.
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, other non-zeolite
catalyst components, zeolite catalyst components, alumina or alumina
sol, titania, zirconia, quartz, silica or silica or silica sol,
and mixtures thereof. These components are also effective in reducing
overall catalyst cost, acting as a thermal sink to assist in heat
shielding the catalyst during regeneration, densifying the catalyst
and increasing catalyst strength. The amount of molecular sieve
which is contained in the final molecular sieve catalyst product
ranges from 10 to 90 weight percent of the total catalyst, preferably
30 to 70 weight percent of the total catalyst.
In a preferred embodiment, the heat treated material is a molecular
sieve catalyst comprising a molecular sieve having a microporous
structure with catalyst sites therein and a binder. The microporous
structure is occupied by between 10 and 90 vol % of at least one
template or a heat degradation product thereof, preferably 20 and
80 vol % of at least one template or a heat degradation product
thereof, and more preferably between 30 and 70 vol % of at least
one template or a heat degradation product thereof.
One way in which the amount of template or degradation product
within the microporous structure of a molecular sieve can be determined
is by comparing the methanol adsorption capacity of the partially
detemplated molecular sieve to its fully detemplated counterpart.
The ratio of the methanol adsorption capacity of the partially detemplated
molecular sieve to the methanol adsorption capacity of the fully
detemplated counterpart will indicate the void space in the partially
detemplated template. Techniques for measuring methanol adsorption
capacity are known to those of ordinary skill in the art. In a preferred
technique, about 5 mg of sample is introduced into a thermogravimetric
analyzer (TGA). The sample is subjected to a heat treatment process,
which includes: (1) heating from room temperature to 150.degree.
C., with a heat up rate of 10.degree. C./min. in nitrogen; (2) holding
at 150.degree. C. for 60 min. (to remove any entrapped moisture,
but not degrade template further); and cooling to 30.degree. C.
in nitrogen. After the sample:has reached 30.degree. C., methanol
containing nitrogen is flowed into the TGA at methanol partial pressure
of 0.09 atm. The sample is contacted with this nitrogen/methanol
mixture for 180 minutes. The methanol adsorption capacity is the
weight percent weight increase after the 180 minutes contact with
the methanol vapor.
The hardness of the sieve composition can be determined by measuring
attrition resistance using the well known Jet Cup Attrition Method.
This is also commonly referred to as the Davison Attrition Index
or Davison Index (DI). See, e.g., U.S. Pat. Nos. 5547564 and 5364516.
The molecular sieve or catalyst composition of this invention is
desirably hard enough to provide protection against physical damage
during transportation or storing, preferably hard enough to be introduced
into a manufacturing unit to provide protection against physical
damage during operation. It is preferred in this invention that
the molecular sieve or catalyst composition exhibits a Davison Index
of not greater than 30 preferably not greater than 20 more preferably
not greater than 10. In general, the lower the Davison Index, the
harder the composition.
In this invention, the Davison Index is determined as follows:
A sample of molecular sieve with binder material is analyzed to
determine the 0 to 20 micron size content. The sample is then subjected
to a 20 minute test in a Fluid Catalyst Attrition Apparatus using
a hardened steel jet cup having a precision bored orifice. An air
flow of 18 liters per minute is used. The Davison Index is calculated
as ##EQU1##
It is preferred that the molecular sieve be mixed with at least
a binder material and heated under conditions effective to obtain
a Davison Index of not greater than 30 preferably not greater than
20 more preferably not greater than 10. This will provide sufficient
hardness so that the sieve or catalyst can be safely transported,
yet leave sufficient amount of template or template residue within
the microporous structure of the sieve to protect against degradation
of active sites by contact with moisture.
A preferred hardening temperature is in the range of between 200.degree.
C. and 800.degree. C., more preferably in the range of between 300.degree.
C. and 700.degree. C., most preferably in the range of between 400.degree.
C. and 650.degree. C. The upper temperature limit will be determined
by the amount of template or template residue that is to desirably
remain in the microporous structure after this initial heating.
Heat treatment can be carried out in an inert gas or an oxygen containing
gas (e.g., air) as long as these two conditions are satisfied.
Heat treatment is preferably carried out in an oxygen depleted
environment. An oxygen depleted environment is preferred, since
this type of environment will typically extend the decomposition
profile of the template. This means that an oxygen depleted environment
will extend the temperature range over which the template will be
fully decomposed. This will provide an advantage of being able to
increase the temperature at which the method can be carried out.
The benefit is that additional mechanical strength can be gained,
while keeping sufficient template within the molecular pore structure
to guard against structural damage by contact with water molecules.
The oxygen depleted environment can be provided by using a treat
gas having an oxygen partial pressure of less than 21 kPa, preferably
less than 1 kPa, more preferably less than 0.1 kPa and most preferably
less than 0.01 kPa. The treat gas is preferably selected from the
group consisting of nitrogen, helium, neon, argon, CO and CO.sub.2.
Although it is preferred to use a multimodal template in this invention
it is not necessary, since use of the TPO technique will enable
one to determine the temperature decomposition profile for any template
material. Even a template which exhibits a sharp peak in its temperature
decomposition profile can be used as long as the heat treatment
employs a temperature sufficiently high to harden the sieve material,
but sufficiently low to maintain a quantity of template or carbonaceous
material derived from the template in the microporous structure
effective to protect from structural damage as a result of contact
with water molecules. In the case where the temperature decomposition
profile has a single peak, it is preferable that the heat treatment
be between the peak decomposition temperature and 150.degree. C.
below the peak decomposition temperature, more preferably between
the peak decomposition temperature and 100.degree. C. below the
peak decomposition temperature, most preferably between the peak
decomposition temperature and 75.degree. C. below the peak decomposition
temperature.
The peak decomposition temperature is defined as the temperature
corresponding to the apex of the single peak temperature decomposition
profile.
Once the molecular sieve or the molecular sieve contained in a
binder material has been heat treated, the material is desirably
sufficiently hard to transport with ease. Because the sieve contains
an amount of template within the pore structure effective to protect
against contact with water molecules, the sieve can also be stored
for extended periods of time without undue concern for structural
damage.
When it is desired to fully activate the molecular sieve material
to its full catalytic state, this can be done by subjecting the
heat treated material to any known procedure for completely removing
the remaining template from the pore structure. For example, the
template can be calcined, or combusted, in the presence of an oxygen-containing
gas, such as air, to remove the remaining template. The calcining
step can be performed at any temperature sufficient to remove the
remaining template, preferably at least 300.degree. C. and up to
900.degree. C., with the lower limit being determined by the amount
of template or template residue that remains in the microporous
structure after the initial hardening step. In other words, calcining
the final template or residue removal will be accomplished by heating
at a temperature higher than that during hardening.
Calcining can be preformed in situ or ex situ. In situ calcining
means that complete removal of the remaining template or its decomposition
product can be removed inside a reactor unit when the molecular
sieve or catalyst is desired to be used as a catalyst. However,
in a preferred embodiment, the template or carbonaceous material
is removed ex situ. This means that it is preferred to activate
the catalytic sites of the molecular sieve outside of the reactor.
This is because there is less likelihood that the template material
will contaminate the reaction products. This is particularly beneficial
when the molecular sieve is used to convert oxygenate feed to olefin
product. In cases such as these the olefin product is typically
required to be very low in any nitrogen or sulfur-containing contaminants.
Since template likely will contain at least some nitrogen components,
it would be more desirable to remove remaining template outside
the reactor. Complete template removal in the regenerator or return
line from the regenerator to the reactor is acceptable.
The molecular sieve synthesized in accordance with the present
method can be used to dry gases and liquids; for selective molecular
separation based on size and polar properties; as an ion-exchanger;
as a catalyst in cracking, hydrocracking, disproportionation, alkylation,
isomerization, oxidation, and conversion of oxygenates to hydrocarbons;
as a chemical carrier, in gas chromatography; and in the petroleum
industry to remove normal paraffins from distillates. It is particularly
suited for use as a catalyst in cracking, hydrocracking, disproportionation,
alkylation, isomerization, oxidation, and conversion of oxygenates
to hydrocarbons. Most particularly, the molecular sieve is suited
for use as a catalyst in the conversion of oxygenates to hydrocarbons.
In its most preferred embodiment as a catalyst in the conversion
of oxygenates to hydrocarbons, a feed containing an oxygenate is
contacted in a reaction zone of a reactor apparatus with a molecular
sieve catalyst at process conditions effective to produce light
olefins, i.e., an effective temperature, pressure, WHSV (weight
hour space velocity) and, optionally, an effective amount of diluent,
correlated to produce light olefins. These conditions are described
in detail below. Usually, the oxygenate feed is contacted with the
catalyst when the oxygenate is in a vapor phase. Alternately, the
process may be it carried out in a liquid or a mixed vapor/liquid
phase. When the process is carried out in a liquid phase or a mixed
vapor/liquid phase, different conversions and selectivities of feed-to-product
may result depending upon the catalyst and reaction conditions.
As used herein, the term reactor includes not only commercial scale
reactors but also pilot sized reactor units and lab bench scale
reactor units.
Olefins can generally be produced at a wide range of temperatures.
An effective operating temperature range can be from about 200.degree.
C. to 700.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. An operating temperature
of at least 300.degree. C., and up to 500.degree. C. is preferred.
Owing to the nature of the process, it may be desirable to carry
out the process of the present invention by use of the molecular
sieve catalysts in a dynamic bed system or any system of a variety
of transport beds rather than in a fixed bed system. It is particularly
desirable to operate the reaction process at high space velocities.
The conversion of oxygenates to produce light olefins may be carried
out in a variety of large scale catalytic reactors, including, but
not limited to, 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 incorporated in its entirety herein by reference. Additionally,
countercurrent free fall reactors may be used in the conversion
process. See, for example, U.S. Pat. No. 4068136 and "Riser
Reactor", Fluidizatton and Fluid-Particle Systems, pages 48-59
F. A. Zenz and D. F. Othmo, Reinhold Publishing Corp., NY 1960
the descriptions of which are expressly incorporated herein by reference.
Any standard commercial scale reactor system can be used, including
fixed bed or moving bed systems. The commercial scale reactor systems
can be operated at a weight hourly'space velocity (WHSV) of from
1 hr.sup.-1 to 1000 hr.sup.-1. In the case of commercial scale reactors,
WHSV is defined as the weight of hydrocarbon in the feed per hour
per weight of silicoaluminophosphate molecular sieve content of
the catalyst. The hydrocarbon content will be oxygenate and any
hydrocarbon which may optionally be combined with the oxygenate.
The silicoaluminophosphate molecular sieve content is intended to
mean only the silicoaluminophosphate molecular sieve portion that
is contained within the catalyst. This excludes components such
as binders, diluents, inerts, rare earth components, etc.
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 preferably less than about 0.012
more preferably less than about 0.01. 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.: ##EQU2##
The pressure also may vary over a wide range, including autogenous
pressures. Preferred pressures are in the range of about 5 kPa to
about 5 MPa, with the most preferred range being of from about 50
kPa to about 0.5 MPa. The foregoing pressures are exclusive of any
oxygen depleted diluent, and thus, refer to the partial pressure
of the oxygenate compounds and/or mixtures thereof with feedstock.
One or more inert diluents 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). Typical diluents include, but are
not necessarily limited to helium, argon, nitrogen, carbon monoxide,
carbon dioxide, hydrogen, water, paraffins, alkanes (especially
methane, ethane, and propane), alkylenes, aromatic compounds, and
mixtures thereof. The preferred diluents are water and nitrogen.
Water can be injected in either liquid or vapor form.
The process may be carried out in a batch, semi-continuous or continuous
fashion. The process can be conducted in a single reaction zone
or a number of reaction zones arranged in series or in parallel.
The level of conversion of the oxygenates can be maintained to
reduce the level of unwanted by-products. Conversion can also be
maintained sufficiently high to avoid the need for commercially
undesirable levels of recycling of unreacted feeds. A reduction
in unwanted by-products is seen when conversion moves from 100 mol
% to about 98 mol % or less. Recycling up to as much as about 50
mol % of the feed is commercially acceptable. Therefore, conversions
levels which achieve both goals are from about 50 mol % to about
98 mol % and, desirably, from about 85 mol % to about 98 mol %.
However, it is also acceptable to achieve conversion between 98
mol % and 100 mol % in order to simplify the recycling process.
Oxygenate conversion may be maintained at this level using a number
of methods familiar to persons of ordinary skill in the art. Examples
include, but are not necessarily limited to, adjusting one or more
of the following: the reaction temperature; pressure; flow rate
(i.e., WHSV); level and degree of catalyst regeneration; amount
of catalyst re-circulation; the specific reactor configuration;
the feed composition; and other parameters which affect the conversion.
If regeneration is required, the molecular sieve catalyst can be
continuously introduced as a moving bed to a regeneration zone where
it can be regenerated, such as for example by removing carbonaceous
materials or by oxidation in an oxygen-containing atmosphere. In
a preferred embodiment, the catalyst is subject to a regeneration
step by burning off carbonaceous deposits accumulated during the
conversion reactions.
The oxygenate feedstock 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), and the feedstock may optionally
contain at least one compound containing a halide, mercaptan, sulfide,
or amine, as long as the optional components do not significantly
impede the performance of the catalyst. 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, their unsaturated
counterparts and the nitrogen, halogen and sulfur analogues of such.
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 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.
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
Four different templates (TEAOH, TEAOH/DPA, DPA, and morpholine)
were impregnated in silica powder by the following technique. A
solution containing a calculated amount of template was added to
silica powder in dropwise manner and mixed. After the desired amount
of template was added, the silica powder was dried in air, then
at 120.degree. C., to remove water and solvent. The following materials
were formed: (1) TEAOH/silica (containing 17.1 wt. % carbon); (2)
TEAOH/DPA/silica (containing 6.3 wt. % carbon); (3) morpholine/silica
(containing 4.1 wt. % carbon); and (4) DPA/silica (containing 2.1
wt. % carbon).
The dried materials were then subjected to temperature-programmed-oxidation
(TPO). In the TPO technique, each material was evaluated by loading
0.005 gram of the template-containing silica material into a quartz
reactor. Helium containing 1% O.sub.2 (i.e., oxygen partial pressure
of 1 kPa) was injected into the reactor at a rate of 63 cc/min.
The gas exiting the quartz reactor was directed to a methanator,
containing a ruthenium catalyst, to convert compositions produced
during template decomposition to CH.sub.4. The CH.sub.4 production
rate was continuously monitored with a flame ionization detector
(FID). FIG. 1 shows the decomposition spectra of each sample. The
figure indicates that templates deposited on high surface area silica
give similar peak decomposition temperatures, with all peak decomposition
temperatures below about 300.degree. C.
EXAMPLE 2
A sample of SAPO-34 containing TEAOH/DPA as template material (13.8
wt. % carbon in the templated material), and a sample of SAPO-34
containing morpholine as a template (9.82 wt. % carbon in the templated
material) were subjected to decomposition analysis as in Example
1. FIG. 2 shows the decomposition spectra of each sample. The figure
indicates that morpholine template has a multimodal decomposition
profile, whereas TEAOH/DPA has a single composition peak. It is
unexpected that the template decomposition temperatures of the microporous
molecular sieves of this Example are substantially higher than the
template decomposition temperatures of Example 1.
EXAMPLE 3
A first sample of SAPO-34 containing TEAOH/DPA as template material
was subjected to decomposition analysis as in Example 1. A second
sample of SAPO-34 containing TEAOH/DPA as template material was
subjected to decomposition analysis as in Example 1 except that
the helium injected into the reactor contained essentially no oxygen.
FIG. 3 shows the decomposition spectra of each sample. In this particular
example, the reduction in oxygen content had little if any effect
on extending the decomposition profile.
EXAMPLE 4
A first sample of SAPO-34 containing morpholine as template material
(9.82 wt. % carbon in the templated material) was subjected to decomposition
analysis as in Example 1. A second sample of SAPO-34 containing
morpholine as template material (9.5 wt. % carbon in the templated
material) was subjected to decomposition analysis as in Example
1 except that the helium injected into the reactor contained essentially
no oxygen. FIG. 4 shows the decomposition spectra of each sample.
In this particular example, the two samples contained essentially
the same amount of template material and the reduction in oxygen
content significantly extended the decomposition profile.
EXAMPLE 5
Three samples of SAPO-34 containing morpholine as a template material
were evaluated. A first sample (containing 9.82 wt. % carbon) was
subjected to decomposition analysis as in Example 1. FIG. 5 shows
the decomposition profile of the sample.
A second sample was heat pretreated by heating in helium for 1
hour at 450.degree. C. to density the material. Following heat pretreatment,
the sample was subjected to decomposition analysis as in Example
1. FIG. 5 shows the decomposition profile of the sample. This profile
shows that following heat pretreatment, the sample contained 8.99
wt. % carbon in the sample (about 92% of the total carbonaceous
material, based on a total of 8.99 out of a total of 9.82).
A third sample was heat pretreated by heating in helium for 1 hour
at 625.degree. C. to density the material. Following heat pretreatment,
the sample was subjected to decomposition analysis as in Example
1. FIG. 5 shows the decomposition profile of the sample. This profile
shows that following heat pretreatment, the sample contained 8.20
wt. % carbon in the sample (about 84 wt. % of the total carbonaceous
material, based on 8.2 out of a total of 9.82).
EXAMPLE 6
A catalyst composition comprising about 50% SAPO-34 the remainder
being binder material, was spray dried and analyzed for hardness
using the well known Jet Cup Attrition Method, i.e., the Davison
Attrition Index or Davison Index (DI) method. The catalyst composition
was analyzed to determine the 0 to 20 micron size content. The composition
was then subjected to a 20 minute test in a Fluid Catalyst Attrition
Apparatus using a hardened steel jet cup having a precision bored
orifice. An air flow of 18 liters per minute was used. The Davison
Index was calculated to be 65.4 (percent loss to <20 microns
in 20 minutes).
EXAMPLE 7
A catalyst composition comprising about 50% SAPO-34 the remainder
being binder material, was spray dried and calcined for 2 hours
at 550.degree. C. The calcined composition was analyzed for hardness
using the well known Jet Cup Attrition Method as in Example 6. The
Davison Index was calculated to be 7.5 (percent loss to <20 microns
in 20 minutes).
Having now fully described this invention, it will be appreciated
by those skilled in the art that the invention can be performed
within a wide range of parameters within what is claimed, without
departing from the spirit and scope of the invention. |