Molecular sieve abstract
Disclosed is a method of rejuvenating molecular sieve and molecular
sieve catalyst. The method includes freeze drying a molecular sieve
having a methanol conversion ratio of less than 1 or a catalyst
containing molecular sieve and a binder having a methanol conversion
ratio of less than 1. The rejuvenated molecular sieve or catalyst
is used to make an olefin product from an oxygenate. The olefin
product containing ethylene and propylene can then be used to make
polyethylene and polypropylene, respectively.
Molecular sieve claims
What is claimed is:
1. A method of making an olefin product from an oxygenate comprising:
providing molecular sieve containing catalyst having a methanol
uptake index of less than 1; freeze drying the molecular sieve containing
catalyst until the methanol uptake index is increased by at least
10%; and contacting the freeze dried molecular sieve containing
catalyst with an oxygenate to produce olefin product.
7. The method of claim 6 wherein the molecular sieve in the molecular
sieve containing catalyst is selected from the group consisting
of SAPO-17 SAPO-18 SAPO-34 SAPO-35 SAPO-44 SAPO-47 the metal
containing forms of each thereof, and mixtures thereof.
8. The method of claim 1 wherein freeze drying is carried out
at a pressure of 0.001 mtorr to 700 torr and a temperature of -200.degree.
C. to 0.degree. C.
9. The method of claim 1 wherein the freeze dried molecular sieve
containing catalyst is contacted with an oxygenate at a temperature
of 200.degree. C. to 700.degree. C.
10. The method of claim 1 wherein the olefin product comprises
ethylene and propylene.
11. The method of claim 1 further comprising separating the ethylene
and propylene into at least two separated product streams, and contacting
the separated ethylene and propylene with a polyolefin-forming catalyst
under conditions effective to form polyethylene and polypropylene,
Molecular sieve description
FIELD OF THE INVENTION
This invention is directed to a method of rejuvenating molecular
sieve or catalyst containing molecular sieve, and a method of using
the rejuvenated molecular sieve or catalyst to make an olefin product
from methanol. In particular, the invention is directed to rejuvenating
a silicoaluminophosphate (SAPO) molecular sieve or SAPO catalyst
by freeze drying the molecular sieve or catalyst prior to converting
the methanol feed.
BACKGROUND OF THE INVENTION
Silicoaluminophosphates (SAPOs) have been used as adsorbents and
catalysts. As catalysts, SAPOs have been used in processes such
as fluid catalytic cracking, hydrocracking, isomerization, oligomerization,
the conversion of alcohols or ethers, and the alkylation of aromatics.
In particular, the use of SAPOs in converting alcohols or ethers
to olefin products, particularly ethylene and propylene, is becoming
of greater interest for large scale, commercial production facilities.
As is known in the development of new large scale, commercial production
facilities in the commodity chemical business, many problems arise
in the scale up from laboratory and pilot plant operations. Scale
up problems arise in catalytic reaction systems in which large scale
operation will be several orders of magnitude larger than typical
pilot scale facilities. For example, conventional laboratory scale
processes of making olefin products from oxygenate feed are conducted
with catalyst loads of about 0.1 to 5 grams. Conventional large
pilot plant operations may utilize as much as 50 kg of catalyst,
making on the order of 20 kg/hr ethylene and propylene product,
but this is nevertheless minuscule in comparison to what a large
scale, commercial production facility would produce, if one were
in existence today. Large scale, commercial production facilities,
can require a catalyst loading of anywhere from 1000 kg to 700000
kg, producing anywhere from 600 to 400000 kg/hr of ethylene and
Operating large scale, commercial production facilities clearly
presents great challenges in the development of the catalyst production-to-use
chain. The term "production-to-use chain" refers to the
entire area of activities beginning with the production of molecular
sieve, including such activities as receipt of starting materials,
on through the crystallization process. Also included in the production-to-use
chain are intermediate activities which include formulation of the
sieve with binders and other materials, activation of the manufactured
sieve and finished catalyst; storage, transport, loading, unloading
of molecular sieve and finished catalyst; as well as other practices
associated with the handling and preparation of the sieve and finished
catalyst for its ultimate use. The production-to-use chain ends
at the point when the molecular sieve is introduced into the reaction
system. For purposes of this invention, the end of the production-to-use
chain does not necessarily mean the instant when the molecular sieve
is introduced into the reaction system, since large scale systems
are very large and instantaneous measurements are not practically
feasible. In large scale systems, the production-to-use chain may
be considered as completed some time within 12 hours of loading
catalyst into the reaction system.
Since information to date relating to production of olefin products
by catalytic conversion of oxygenate feedstock has been limited
to laboratory and small pilot plant activities, little if any attention
has been paid to the problems associated with the intermediate activities
in the production-to-use chain. For example, little attention has
been focused on the impact of storage, transport, etc. on catalyst
activity, since small scale activity is rather easily manageable.
While today only relatively small quantities of catalyst are prepared,
stored and transported, large quantities of materials will need
to be handled for commercial operations. Commercial operations may
be require that large quantities of molecular sieve catalysts be
stored for considerable periods of time and at multiple locations.
As the management of sieve and catalyst in the catalyst production-to-use
chain expands in volume and complexity, a likelihood exists that
millions of dollars will be tied up in catalyst inventory, and the
value of the sieve and catalyst will be lost if quality, as compared
to that of freshly prepared and calcined catalyst, is not maintained.
Loss of quality will necessarily translate to loss of product quality,
as well as loss of product quantity.
Although some work has been published relating to the intermediate
activities in the catalyst production-to-use chain, few of the problems
associated therewith have been addressed. For example, U.S. Pat.
No. 4681864 to Edwards et al. discuss the use of SAPO-37 molecular
sieve as a commercial cracking catalyst. It is disclosed that activated
SAPO-37 molecular sieve has poor stability, and that stability can
be improved by using a particular activation process. In this process,
organic template is removed from the core structure of the sieve
just prior to contacting with feed to be cracked. The process calls
for subjecting the sieve to a temperature of 400-800.degree. C.
within the catalytic cracking unit.
U.S. Pat. No. 5185310 to Degnan et al. discloses a particular
method of calcining SAPO catalyst containing alumina as a binder.
The method calls for heating the catalyst to at least 425.degree.
C. in the presence of an oxygen depleted gas, and then in the presence
of an oxidizing gas. The object of the heating process is to maintain
the acid activity of the catalyst.
Briend et al., J Phys. Chem. 1995 99 8270-8276 teach that SAPO-34
loses its crystallinity when the template has been removed from
the sieve and the de-templated, activated sieve has been exposed
to air. Data is presented, however, which suggests that over at
least the short term, this crystallinity loss is reversible. Even
over a period of perhaps two years, the data suggest that crystallinity
loss is reversible when certain templates are used.
EP-A2-0 203 005 also discusses the use of SAPO-37 molecular sieve
in a zeolite catalyst composite as a commercial cracking catalyst.
According to the document, if the organic template is retained in
the SAPO-37 molecular sieve until a catalyst composite containing
zeolite and the SAPO-37 molecular sieve is activated during use,
and if thereafter the catalyst is maintained under conditions wherein
exposure to moisture is minimized, the crystalline structure of
the SAPO-37 zeolite composite remains stable.
Researchers at ExxonMobil Chemical Company has recently discovered
that activated SAPO molecular sieve will exhibit a loss of catalytic
activity when exposed to a moisture-containing environment. This
loss of activity can occur between the time the catalyst is activated
and even after as little as one day of storage. Although ways have
been found to inhibit loss of catalytic activity, it would be highly
beneficial to find a way to reverse the decrease of catalytic activity
in a molecular sieve exposed to a moisture-containing environment.
SUMMARY OF THE INVENTION
In order to overcome the various problems associated with decrease
of activity of a molecular sieve due to contact by moisture, this
invention provides a way to reverse such decrease, i.e., to rejuvenate
the molecular sieve. In general, this invention provides a process
for rejuvenating a molecular sieve which comprises providing molecular
sieve having a methanol uptake index of less than 1; and freeze
drying the molecular sieve until the methanol uptake index is increased
by at least 10%.
Preferably, the methanol uptake index is increased by at least
50%, more preferably the methanol uptake index is increased by at
least 100%, and most preferably the methanol uptake index is increased
by at least 500%. It is also preferred that the molecular sieve
be provided having a methanol uptake index of less than 0.5 more
preferably a methanol uptake index of less than 0.3 and most preferably,
a methanol uptake index of less than 0.15.
Desirably, the molecular sieve is selected from the group consisting
of SAPO-5 SAPO-8 SAPO-11 SAPO-16 SAPO-17 SAPO-18 SAPO-20
SAPO-31 SAPO-34 SAPO-35 SAPO-36 SAPO-37 SAPO-40 SAPO-41 SAPO-42
SAPO-44 SAPO47 SAPO-56 ALPO-5 ALPO-11 ALPO-18 ALPO-31 ALPO-34
ALPO-36 ALPO-37 ALPO-46 the metal containing forms of each thereof,
and mixtures thereof. Preferably, the molecular sieve is selected
from the group consisting of SAPO-17 SAPO-18 SAPO-34 SAPO-35
SAPO44 SAPO-47 the metal containing forms of each thereof, and
In a preferred embodiment, freeze drying is carried out at a pressure
of 0.001 mtorr to 700 torr. Preferably, freeze drying is also carried
out at a temperature of -200.degree. C. to 0.degree. C.
The invention also provides a method for rejuvenating molecular
sieve containing catalyst which comprises providing molecular sieve
containing catalyst having a methanol uptake index of less than
1; and freeze drying the molecular sieve containing catalyst until
the methanol uptake index is increased by at least 10%.
The invention is further to a method of making an olefin product
from an oxygenate which comprises providing molecular sieve containing
catalyst having a methanol uptake index of less than 1; freeze drying
the molecular sieve containing catalyst until the methanol uptake
index is increased by at least 10%; and contacting the freeze dried
molecular sieve containing catalyst with an oxygenate to produce
olefin product. In a preferred embodiment, the freeze dried molecular
sieve containing catalyst is contacted with an oxygenate at a temperature
of 200.degree. C. to 700.degree. C. Preferably, the olefin product
comprises ethylene and propylene. Desirably, the ethylene and propylene
are separated into at least two product streams. The separated ethylene
and propylene can then be contacted with a polyolefin-forming catalyst
to form polyethylene and polypropylene.
The invention will be better understood by reference to the Detailed
Description of the Invention when taken together with the attached
FIGURE and in association with the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The FIGURE shows methanol conversion for fresh, rejuvenated, and
moisture aged SAPO molecular sieve.
DETAILED DESCRIPTION OF THE INVENTION
Silicoaluminophosphate (SAPO) molecular sieves, in particular,
are susceptible to structural changes as a result of continued exposure
to even low levels of moisture. Such authorities as Paulitz et al.,
Microporous Materials, 2 223-228 (1994), however, have shown through
X-ray diffraction (XRD), nuclear magnetic resonance (NMR), infrared
(IR) and nitrogen (N.sub.2) adsorption analyses that the structural
change is largely reversible. These X-ray diffraction studies have,
nevertheless, been found to be unreliable in determining loss of
catalytic activity of these sieves. For example, Paulitz et al.
have shown that SAPO molecular sieve once structurally altered by
contact with moisture can be rejuvenated by calcination to exhibit
its typical X-ray diffraction pattern. However, the same procedure
has been shown not to rejuvenate catalytic activity of the molecular
sieve. See, for example, U.S. Ser. No. 09/391770 to ExxonMobil
The loss of catalytic activity as a result of contact of molecular
sieve with moisture presents a problem in the commercial production-to-use
chain where storage and transport of molecular sieve and catalyst
can occupy relatively long periods of time. For example, it is possible
that molecular sieve or catalyst containing molecular sieve can
be stored from 12 hours to many months, perhaps as long as one year
before its use in a catalytic process. This stored sieve or catalyst
is likely not to have a template within its internal pore structure
as a result of having been removed by calcination prior to storage.
Such a sieve or catalyst would be especially susceptible to damage
by contact with moisture. Even partial loss of catalytic activity
is of particular concern in a large scale catalytic process. As
defined herein, a large scale catalytic process is one having a
reactor loading in excess of 50 kg, particularly one having a reactor
system loading in excess of 500 kg, especially one having a reactor
loading in excess of 5000 kg.
The term "catalytic activity" used herein refers to the
conversion of oxygenate to total product, including olefin, based
upon the grams of methanol converted per gram of molecular sieve
for a given space velocity (residence time). Therefore, molecular
sieve having a higher conversion to total product (less oxygenate
in the product) for a given space velocity will have a greater catalytic
activity, regardless of the product selectivity. In the case of
molecular sieve catalyst, the weight of the molecular sieve in the
catalyst is used to determine catalytic activity.
SAPO molecular sieve, as well as catalyst containing SAPO molecular
sieve, which exhibits decreased catalytic activity as a result of
contact with moisture can be rejuvenated by freeze drying. The term
freeze drying as used herein describes a process in which a solid
or a slurry containing a solid is placed within a container and
cooled or frozen under vacuum. The container is connected to one
or more vacuum sources, and a vacuum (pressure less than 760 torr)
is applied. The container is then cooled to a temperature less than
0.degree. C., preferably between -200.degree. C. and 0.degree. C.
One method of cooling the container, which in turn cools the material
in the container, may include placing the container in a liquid
or gas coolant. Coolants that may be used include liquid nitrogen,
liquid or solid carbon dioxide, organic refrigerants, e.g., fluorocarbon
refrigerants. Water and/or other volatile components which may be
present within the sieve or catalyst will typically be removed as
a result of applying the vacuum conditions. The water, or other
volatile material which may be present, is then removed from the
container by way of the vacuum source.
In one embodiment, a molecular sieve or molecular sieve catalyst
that has been exposed to a moisture containing environment is added
to a container. A vacuum pump connected to the container creates
a vacuum in the container, i.e., a pressure of less than 760 torr.
Preferably, the pressure is between 0.001 mtorr and 700 torr, more
preferably between 0.01 mtorr and 4 torr, and most preferably between
0.02 mtorr and 0.1 torr. The sieve or catalyst is also cooled to
a temperature between -200.degree. C. and 0.degree. C., preferably
between -175.degree. C. and -25.degree. C., more preferably between
-150.degree. C. and -50.degree. C.
The sieve or catalyst is cooled under vacuum until the sieve or
catalyst has an increase in catalytic activity. Preferably, the
vacuum is removed and the sieve or catalyst is allowed to warm.
Heat can be applied if desired. Preferably, the sieve or catalyst
is heated to a temperature between 10.degree. C. and 200.degree.
C., more preferably, between 20.degree. C. and 100.degree. C. Gas,
e.g., air, that may be introduced to the container following removal
of the vacuum is preferably low in moisture content. Preferably,
the introduced gas will contain less than about 100 ppm water, more
preferably less than about 50 ppm water, and most preferably less
than about 10 ppm water.
The freeze dried sieve or catalyst can then be transferred to a
reactor, heated to a temperature between 400.degree. C. and 800.degree.
C., preferably between 450.degree. C. and 700.degree. C. Preferably,
heating is carried out under inert atmosphere, e.g., nitrogen, helium,
etc., for about 1 hour. Alternatively, an oxidizing atmosphere can
be used, e.g., air. The temperature of the reactor is desirably
set to a temperature that is optimized for the conversion of an
oxygenate to an olefin. Methanol is introduced to the reactor and
the products from the conversion of methanol determined.
It is to be understood in this invention that the freeze drying
process can be carried out in the reactor. As a result, the molecular
sieve or catalyst does not have to be transferred to another container.
Also, both the freeze drying process and the heating can be carried
out in one or more units separate from the reactor. For example,
a freeze drying unit can be connected to a heating unit which feeds
the reactor with catalyst. A freeze drying unit is the equipment
used in the freeze drying process. The freeze drying unit includes
a container to contain the sieve or catalyst, one or more evacuation
ports, and a coolant system.
SAPO molecular sieve, as well as catalyst containing SAPO molecular
sieve, which exhibits decreased catalytic activity as a result of
contact with moisture can be rejuvenated by freeze drying the sieve
or catalyst. According to this invention, rejuvenation of a molecular
sieve is determined using a methanol uptake index. A molecular sieve
having a methanol uptake index of less than 1 is capable of being
As used herein, methanol uptake index is defined as the methanol
adsorption capacity (wt. %) of a microporous SAPO molecular sieve
having been exposed to moisture, divided by the maximum methanol
adsorption capacity (wt. %) of a non-moisture exposed SAPO molecular
sieve (i.e., the initial or maximum methanol adsorption capacity
of a fresh, non-moisture exposed sieve). 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 450.degree. C., with a heat up rate of 20.degree.
C./min. in air; (2) holding at 450.degree. C. for 40 min. in air;
and cooling to 30.degree. C. in air. After the sample has reached
30.degree. C., the air flow in the TGA is switched to a methanol
containing nitrogen flow with a 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
In this invention, rejuvenation is considered to be demonstrated
when the rejuvenation process results in a relative increase in
the methanol uptake index of at least about 10%. Preferably, the
rejuvenation process will result in an increase in the methanol
uptake index of at least about 50%, more preferably at least about
100%, and most preferably at least about 500%, the increase being
calculated as the change before rejuvenation and after rejuvenation
on a percent basis.
The lower the methanol uptake index of a moisture exposed molecular
sieve, the more suitable the molecular sieve for rejuvenation. From
an efficiency standpoint, it is desirable to rejuvenate a molecular
sieve which has a methanol uptake index of less than about 0.5
preferably less than about 0.3 more preferably less than about
0.2 and most preferably less than about 0.15. Complete rejuvenation
results in a methanol uptake index of 1.
It is also preferred in this invention that the freeze drying rejuvenation
process be carried out until a methanol uptake index of at least
0.4 is achieved, preferably until a methanol uptake index of at
least 0.6 is achieved, more preferably until a methanol uptake index
of at least 0.7 is achieved, and most preferably until a methanol
uptake index of at least 0.8 is achieved. Thus, in the more-practical
form of this invention, a molecular sieve having a methanol uptake
index of less than about 0.4 is a more likely candidate for rejuvenation,
although a molecular sieve having a methanol uptake index of less
than 1 is capable of being rejuvenated. It is preferred that rejuvenation,
or freeze drying, be carried out until a methanol uptake index of
at least 0.4 is achieved so that the sieve will of benefit in a
commercial scale system. Anything below 0.4 means that the catalytic
activity of the sieve would be less than 40%, which is extremely
low for a commercial process.
The catalyst that is used in this invention is one that incorporates
a silicoaluminophosphate (SAPO) molecular sieve. The molecular sieve
comprises 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 NMR. See Blackwell and Patton, J Phys. Chem.,
92 3965 (1988). The desired SAPO molecular sieves will exhibit
one or more peaks in the .sup.29 Si MAS NMR, with a chemical shift
.delta. (Si) in the range of -88 to -96 ppm and with a combined
peak area in that range of at least 20% of the total peak area of
all peaks with a chemical shift .delta. (Si) of -88 ppm to -115
ppm, when the .delta. (Si) chemical shifts refer to external tetramethylsilane
It is preferred that the silicoaluminophosphate molecular sieve
used in this invention have a relatively low Si/Al.sub.2 ratio.
In general, the lower the Si/Al.sub.2 ratio, the lower the C.sub.1
-C.sub.4 saturates selectivity, particularly propane selectivity.
A Si/Al.sub.2 ratio of less than 0.65 is desirable, with a Si/Al.sub.2
ratio of not greater than 0.40 being preferred, and a Si/Al.sub.2
ratio of not greater than 0.32 being particularly preferred. A Si/Al.sub.2
ratio of not greater than 0.20 is most preferred.
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
of about 3.5 angstroms to about 15 angstroms. Preferred are the
small pore SAPO molecular sieves having an average pore size of
less than about 5 angstroms, preferably an average pore size of
3.5 angstroms to 5 angstroms, more preferably from 3.5 angstroms
to 4.2 angstroms. These pore sizes are typical of molecular sieves
having 8 membered rings.
In general, 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 aluminate, and pseudoboehmite. The aluminum-containing compositions
are mixed with reactive silicon and phosphorus-containing compositions
under the appropriate conditions to form the molecular sieve.
The [SiO.sub.2 ] tetrahedral units within the framework structure
can be provided by a variety of compositions. Examples of these
silicon-containing compositions include silica sols and silicium
alkoxides such as tetra ethyl orthosilicate. The silicon-containing
compositions are mixed with reactive aluminum and phosphorus-containing
compositions under the appropriate conditions to form the molecular
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 IIB, including the lanthanoid
elements: lanthanum, cerium, praseodymium, neodymium, samarium,
europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,
ytterbium and lutetium; and scandium or yttrium) and the additional
transition cations of Groups IVB, VB, VIB, VIIB, VIIIB, IB, and
Preferably, the Me represents atoms such as Zn, Mg, Co, Ni, Ga,
Fe, Ti, Zr, Ge, Sn, and Cr. These atoms can be inserted into the
tetrahedral framework through a [MeO2] tetrahedral unit. The [MeO.sub.2
] tetrahedral unit carries a net electric charge depending on the
valence state of the metal substituent. When the metal component
has a valence state of +2 +3 +4 +5 or +6 the net electric charge
is between -2 and +2. Incorporation of the metal component is typically
accomplished adding the metal component during synthesis of the
molecular sieve. However, post-synthesis ion exchange can also be
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 SAPO1 SAPO42 SAPO-44 SAP047
SAPO-56 the metal containing forms thereof, and mixtures thereof.
Preferred are SAPO-17 SAPO-18 SAPO-34 SAPO-35 SAPO-44 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 can also be included
in the catalyst composition. Aluminophosphate molecular sieves are
crystalline microporous oxides which can have an AlPO.sub.4 framework.
They can have additional elements within the framework, typically
have uniform pore dimensions of about 3 angstroms to about 10 angstroms,
and are capable of making size selective separations of molecular
species. More than two dozen structure types have been reported,
including zeolite topological analogues. A. more detailed description
of the background and synthesis of aluminophosphates is found in
U.S. Pat. No. 4310440 which is incorporated herein by reference
in its entirety. Preferred ALPO structures are ALPO-5 ALPO-11
ALPO-18 ALPO-31 ALPO-34 ALPO-36 ALPO-37 and ALPO-46.
The ALPOs can also include a metal substituent in its framework.
Preferably, the metal is selected from the group consisting of magnesium,
manganese, zinc, cobalt, and mixtures thereof. These materials preferably
exhibit adsorption, ion-exchange and/or catalytic properties similar
to aluminosilicate, aluminophosphate and silica aluminophosphate
molecular sieve compositions. Members of this class and their preparation
are described in U.S. Pat. No. 4567029 incorporated herein by
reference in its entirety.
The metal containing ALPOs have a three-dimensional microporous
crystal framework structure of MO.sub.2 AlO.sub.2 and PO.sub.2
tetrahedral units. These as manufactured structures (which contain
template prior to calcination) can be represented by empirical chemical
composition, on an anhydrous basis, as:
The metal containing ALPOs are sometimes referred to by the acronym
as MeAPO. Also in those cases where the metal "Me" in
the composition is magnesium, the acronym MAPO is applied to the
composition. Similarly ZAPO, MnAPO and CoAPO are applied to the
compositions which contain zinc, manganese and cobalt respectively.
To identify the various structural species which make up each of
the subgeneric classes MAPO, ZAPO, CoAPO and MnAPO, each species
is assigned a number and is identified, for example, as ZAPO-5
MAPO-11 CoAPO-34 and so forth.
The 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.degree. C. to 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.
In many cases, depending upon the nature of the final product formed,
the template may be too large to be eluted from the intracrystalline
pore system. In such a case, the template can be removed by a heat
treatment process. For example, the template can be calcined, or
essentially combusted, in the presence of an oxygen-containing gas,
by contacting the template-containing sieve in the presence of the
oxygen-containing gas and heating at temperatures from 200.degree.
C. to 900.degree. C. In some cases, it may be desirable to heat
in an environment having a low oxygen concentration. In these cases,
however, the result will typically be a breakdown of the template
into a smaller component, rather than by the combustion process.
This type of process can be used for partial or complete removal
of the template from the intracrystalline pore system. In other
cases, with smaller templates, complete or partial removal from
the sieve can-be accomplished by conventional desorption processes
such as those used in making standard zeolites.
The reaction mixture can contain one or more templates. Templates
are structure directing agents, and typically contain nitrogen,
phosphorus, oxygen, carbon, hydrogen or a combination thereof, and
can also contain at least one alkyl or aryl group, with 1 to 8 carbons
being present in the alkyl or aryl group. Mixtures of two or more
templates can produce mixtures of different sieves or predominantly
one sieve where one template is more strongly directing than another.
Representative templates include tetraethyl ammonium salts, cyclopentylamine,
aminomethyl cyclohexane, piperidine, triethylamine, cyclohexylamine,
tri-ethyl hydroxyethylamine, morpholine, dipropylamine (DPA), pyridine,
isopropylamine and combinations thereof. Preferred templates are
triethylamine, cyclohexylamine, piperidine, pyridine, isopropylamine,
tetraethyl ammonium salts, dipropylamine, and mixtures thereof.
The tetraethylammonium salts include tetraethyl ammonium hydroxide
(TEAOH), tetraethyl ammonium phosphate, tetraethyl ammonium fluoride,
tetraethyl ammonium bromide, tetraethyl ammonium chloride, tetraethyl
ammonium acetate. Preferred tetraethyl ammonium salts are tetraethyl
ammonium hydroxide and tetraethyl ammonium phosphate.
The SAPO molecular sieve structure can be effectively controlled
using combinations of templates. For example, in a particularly
preferred embodiment, the SAPO molecular sieve is manufactured using
a template combination of TEAOH and dipropylamine. This combination
results in a particularly desirable SAPO structure for the conversion
of oxygenates, particularly methanol and dimethyl ether, to light
olefins such as ethylene and propylene.
The silicoaluminophosphate molecular sieve is typically admixed
(i.e., blended) with other materials. When blended, the resulting
composition is typically referred to as a SAPO catalyst, with the
catalyst comprising the SAPO molecular sieve.
Materials which can be blended with the molecular sieve can be
various inert or catalytically active materials, or various binder
materials. These materials include compositions such as kaolin and
other clays, various forms of rare earth metals, metal oxides, other
non-zeolite catalyst components, zeolite catalyst components, alumina
or alumina sol, titania, zirconia, magnesia, thoria, beryllia, quartz,
silica or silica or silica sol, and mixtures thereof. These components
are also effective in reducing, inter alia, overall catalyst cost,
acting as a thermal sink to assist in heat shielding the catalyst
during regeneration, densifying the catalyst and increasing catalyst
strength. It is particularly desirable that the inert materials
that are used in the catalyst to act as a thermal sink have a heat
capacity of from about 0.05 cal/g-.degree. C. to about 1 cal/g-.degree.
C., more preferably from about 0.1 cal/g-.degree. C. to about 0.8
cal/g-.degree. C., most preferably from about 0.1 cal/g-.degree.
C. to about 0.5 cal/g-.degree. C.
Additional molecular sieve materials can be included as a part
of the SAPO catalyst composition or they can be used as separate
molecular sieve catalysts in admixture with the SAPO catalyst if
desired. Structural types of small pore molecular sieves that are
suitable for use in this invention include AEI, AFT, APC, ATN, ATT,
ATV, AWW, BIK, CAS, CHA, CHI, DAC, DDR, EDI, ERI, GOO, KFI, LEV,
LOV, LTA, MON, PAU, PHI, RHO, ROG, THO, and substituted forms thereof.
Structural types of medium pore molecular sieves that are suitable
for use in this invention include MFI, MEL, MTW, EUO, MIT, HEU,
FER, AFO, AEL, TON, and substituted forms thereof. Preferred molecular
sieves which can be combined with a silicoaluminophosphate catalyst
include ZSM-5 ZSM-34 erionite, and chabazite.
The catalyst composition preferably comprises about 1% to about
99%, more preferably about 5% to about 90%, and most preferably
about 10% to about 80%, by weight of molecular sieve. It is also
preferred that the catalyst composition have a particle size of
from about 20 .mu.m to 3000 .mu.m, more preferably about 30 .mu.m
to 200 .mu.m, most preferably about 50 .mu.m to 150 .mu.m.
The catalyst can be subjected to a variety of treatments to achieve
the desired physical and chemical characteristics. Such treatments
include, but are not necessarily limited to hydrothermal treatment,
calcination, acid treatment, base treatment, milling, ball milling,
grinding, spray drying, and combinations thereof.
It is particularly desirable that the rejuvenated molecular sieve
of this invention be used in the process of making olefin product
from an oxygenate-containing feedstock. In one embodiment of this
invention, a feed containing an oxygenate, and optionally a diluent
or a hydrocarbon added separately or mixed with the oxygenate, is
contacted with a catalyst containing a rejuvenated SAPO molecular
sieve in a reaction zone or volume. The volume in which such contact
takes place is herein termed the "reactor," which may
be a part of a "reactor apparatus" or "reaction system."
Another part of the reaction system may be a "regenerator,"
which comprises a volume wherein carbonaceous deposits (or coke)
on the catalyst resulting from the olefin conversion reaction are
removed by contacting the catalyst with regeneration medium.
The oxygenate feedstock of this invention comprises at least one
organic compound which contains at least one oxygen atom, such as
aliphatic alcohols, ethers, carbonyl compounds (aldehydes, ketones,
carboxylic acids, carbonates, esters and the like). When the oxygenate
is an alcohol, the alcohol can include an aliphatic moiety having
from 1 to 10 carbon atoms, more preferably from 1 to 4 carbon atoms.
Representative alcohols include but are not necessarily limited
to lower straight and branched chain aliphatic alcohols and their
unsaturated counterparts. Examples of suitable oxygenate compounds
include, but are not limited to: methanol; ethanol; n-propanol;
isopropanol; C.sub.4 -C.sub.20 alcohols; methyl ethyl ether; dimethyl
ether; diethyl ether; di-isopropyl ether; formaldehyde; dimethyl
carbonate; dimethyl ketone; acetic acid; and mixtures thereof. Preferred
oxygenate compounds are methanol, dimethyl ether, or a mixture thereof.
The method of making the preferred olefin product in this invention
can include the additional step of making these compositions from
hydrocarbons such as oil, coal, tar sand, shale, biomass and natural
gas. Methods for making the compositions are known in the art. These
methods include fermentation to alcohol or ether, making synthesis
gas, then converting the synthesis gas to alcohol or ether. Synthesis
gas can be produced by known processes such as steam reforming,
autothermal reforming and partial oxidization.
One or more inert 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). As defined herein, diluents are
compositions which are essentially non-reactive across a molecular
sieve catalyst, and primarily function to make the oxygenates in
the feedstock less concentrated. Typical diluents include, but are
not necessarily limited to helium, argon, nitrogen, carbon monoxide,
carbon dioxide, water, essentially non-reactive paraffins (especially
the alkanes such as methane, ethane, and propane), essentially non-reactive
alkylenes, essentially non-reactive aromatic compounds, and mixtures
thereof. The preferred diluents are water and nitrogen. Water can
be injected in either liquid or vapor form.
Hydrocarbons can also be included as part of the feedstock, i.e.,
as co-feed. As defined herein, hydrocarbons included with the feedstock
are hydrocarbon compositions which are converted to another chemical
arrangement when contacted with molecular sieve catalyst. These
hydrocarbons can include olefins, reactive paraffins, reactive alkylaromatics,
reactive aromatics or mixtures thereof. Preferred hydrocarbon co-feeds
include, propylene, butylene, pentylene, C.sub.4.sup.+ hydrocarbon
mixtures, C.sub.5.sup.+ hydrocarbon mixtures, and mixtures thereof.
More preferred as co-feeds are a C.sub.4.sup.+ hydrocarbon mixtures,
with the most preferred being C.sub.4.sup.+ hydrocarbon mixtures
which are obtained from separation and recycle of reactor product.
In the process of this invention, coked catalyst can be regenerated
by contacting the coked catalyst with a regeneration medium to remove
all or part of the coke deposits. This regeneration can occur periodically
within the reactor by ceasing the flow of feed to the reactor, introducing
a regeneration medium, ceasing flow of the regeneration medium,
and then reintroducing the feed to the fully or partially regenerated
catalyst. Regeneration may also occur periodically or continuously
outside the reactor by removing a portion of the deactivated catalyst
to a separate regenerator, regenerating the coked catalyst in the
regenerator, and subsequently reintroducing the regenerated catalyst
to the reactor. Regeneration can occur at times and conditions appropriate
to maintain a desired level of coke on the entire catalyst within
Catalyst that has been contacted with feed in a reactor is defined
herein as "feedstock exposed." Feedstock exposed catalyst
will provide olefin conversion reaction products having substantially
lower propane and coke content than a catalyst which is fresh and
regenerated. A catalyst will typically provide lower amounts of
propane as it is exposed to more feed, either through increasing
time at a given feed rate or increasing feed rate over a given time.
At any given instant in time, some of the catalyst in the reactor
will be fresh, some regenerated, and some coked or partially coked
as a result of having not yet been regenerated. Therefore, various
portions of the catalyst in the reactor will have been feedstock
exposed for different periods of time. Since the rate at which feed
flows to the reactor can vary, the amount of feed to which various
portions of the catalyst can also vary. To account for this variation,
the "average catalyst feedstock exposure index (ACFE index)"
is used to quantitatively define the extent to which the entire
catalyst in the reactor has been feedstock exposed.
As used herein, ACFE index is the total weight of feed divided
by the total weight of molecular sieve (i.e., excluding binder,
inerts, etc., of the catalyst composition) sent to the reactor.
The measurement should be made over an equivalent time interval,
and the time interval should be long enough to smooth out fluctuations
in catalyst or feedstock rates according to the reactor and regeneration
process step selected to allow the system to be viewed as essentially
continuous. In the case of reactor systems with periodic regenerations,
this can range from hours up to days or longer. In the case of reactor
systems with substantially constant regeneration, minutes or hours
may be sufficient.
Flow rate of catalyst can be measured in a variety of ways. In
the design of the equipment used to carry the catalyst between the
reactor and regenerator, the catalyst flow rate can be determined
given the coke production rate in the reactor, the average coke
level on catalyst leaving the reactor, and the average coke level
on catalyst leaving the regenerator. In an operating unit with continuous
catalyst flow, a variety of measurement techniques can be used.
Many such techniques are described, for example, by Michel Louge,
"Experimental Techniques," Circulating Fluidized Beds,
Grace, Avidan, & Knowlton, eds., Blackie, 1997 (336-337), the
descriptions of which are expressly incorporated herein by reference.
In this invention, only the molecular sieve in the catalyst sent
to the reactor may be used in the determination of ACFE index. The
catalyst sent to the reactor, however, can be either fresh or regenerated
or a combination of both. Molecular sieve which may be recirculated
to and from the reactor within the reactor apparatus (i.e., via
ducts, pipes or annular regions), and which has not been regenerated
or does not contain fresh catalyst, is not to be used in the determination
of ACFE index.
In a preferred embodiment of this invention, a feed containing
an oxygenate, and optionally a hydrocarbon, either separately or
mixed with the oxygenate, is contacted with a catalyst containing
a SAPO molecular sieve at process conditions effective to produce
olefins in a reactor where the catalyst has an ACFE index of at
least about 1.0 preferably at least 1.5. An ACFE index of about
1.0 to 20 is effective, with about 1.5 to about 15 being desirable.
An ACFE index of about 2 to about 12 is particularly preferred.
Any standard reactor system can be used, including fixed bed, fluid
bed or moving bed systems. Preferred reactors are co-current riser
reactors and short contact time, countercurrent free-fall reactors.
Desirably, the reactor is one in which an oxygenate feedstock can
be contacted with a molecular sieve catalyst at a WHSV of at least
about 1 hr.sup.-1 preferably in the range of from about 1 hr.sup.-1
to about 1000 hr.sup.-1 more preferably in the range of from about
20 hr.sup.-1 to about 1000 hr.sup.-1 and most preferably in the
range of from about 20 hr.sup.-1 to about 500 hr.sup.-1. WHSV is
defined herein as the weight of oxygenate, and hydrocarbon which
may optionally be in the feed, per hour per weight of the molecular
sieve content of the catalyst. Because the catalyst or the feedstock
may contain other materials which act as inerts or diluents, the
WHSV is calculated on the weight basis of the oxygenate feed, and
any hydrocarbon which may be present, and the molecular sieve contained
in the catalyst.
Preferably, the oxygenate feed is contacted with the rejuvenated
catalyst when the oxygenate is in a vapor phase. Alternately, the
process may be carried out in a liquid or a mixed vapor/liquid phase.
When the process is carried out in a liquid phase or a mixed vapor/liquid
phase, different conversions and selectivities of feed-to-product
may result depending upon the catalyst and reaction conditions.
The process can generally be carried out at a wide range of temperatures.
An effective operating temperature range can be from about 200.degree.
C. to about 700.degree. C., preferably from about 300.degree. C.
to about 600.degree. C., more preferably from about 350.degree.
C. to about 550.degree. C. At the lower end of the temperature range,
the formation of the desired olefin products may become markedly
slow. At the upper end of the temperature range, the process may
not form an optimum amount of product.
It is highly desirable to operate at a temperature of at least
300.degree. C. and a Temperature Corrected Normalized Methane Sensitivity
(TCNMS) of less than about 0.016. It is particularly preferred that
the reaction conditions for making olefin from oxygenate comprise
a WHSV of at least about 20 hr.sup.-1 producing olefins and a TCNMS
of less than about 0.016.
As used herein, TCNMS is defined as the Normalized Methane Selectivity
(NMS) when the temperature is less than 400.degree. C. The NMS is
defined as the methane product yield divided by the ethylene product
yield wherein each yield is measured on, or is converted to, a weight
% basis. When the temperature is 400.degree. C. or greater, the
TCNMS is defined by the following equation, in which T is the average
temperature within-the reactor in .degree. C.: ##EQU1##
The pressure also may vary over a wide range, including autogenous
pressures. Effective pressures may be in, but are not necessarily
limited to, oxygenate partial pressures at least 1 psia, preferably
at least 5 psia. The process is particularly effective at higher
oxygenate partial pressures, such as an oxygenate partial pressure
of greater than 20 psia. Preferably, the oxygenate partial pressure
is at least about 25 psia, more preferably at least about 30 psia.
For practical design purposes it is desirable to operate at a methanol
partial pressure of not greater than about 500 psia, preferably
not greater than about 400 psia, most preferably not greater than
about 300 psia.
The conversion of oxygenates to produce light olefins may be carried
out in a variety of catalytic reactors. Reactor types include fixed
bed reactors, fluid bed reactors, and concurrent riser reactors.
Additionally, counter current free fall reactors may be used in
the conversion process as described in U.S. Pat. No. 4068136
the detailed description of which is also expressly incorporated
herein by reference.
In a preferred embodiment of the continuous operation, only a portion
of the catalyst is removed from the reactor and sent to the regenerator
to remove the accumulated coke deposits that result during the catalytic
reaction. In the regenerator, the catalyst is contacted with a regeneration
medium containing oxygen or other oxidants. Examples of other oxidants
include O.sub.3 SO.sub.3 N.sub.2 O, NO, NO.sub.2 N.sub.2 O.sub.5
and mixtures thereof. It is preferred to supply O.sub.2 in the form
of air. The air can be diluted with nitrogen, CO.sub.2 or flue
gas, and steam may be added. Desirably, the O.sub.2 concentration
in the regenerator is reduced to a controlled level to minimize
overheating or the creation of hot spots in the spent or deactivated
catalyst. The deactivated catalyst also may be regenerated reductively
with H.sub.2 CO, mixtures thereof, or other suitable reducing agents.
A combination of oxidative regeneration and reductive regeneration
can also be employed.
In essence, the coke deposits are removed from the catalyst during
the regeneration process, forming a regenerated catalyst. The regenerated
catalyst is then returned to the reactor for further contact with
feed. Typical regeneration temperatures are in the range of 250.degree.
C. to 700.degree. C., desirably in the range of 350.degree. C. to
700.degree. C. Preferably, regeneration is carried out at a temperature
range of 450.degree. C. to 700.degree. C.
It is desirable to strip at least some of the volatile organic
components which may be adsorbed onto the catalyst or located within
its microporous structure prior to entering the regenerator. This
can be accomplished by passing a stripping gas over the catalyst
in a stripper or stripping chamber, which can be located within
the reactor or in a separate vessel. The stripping gas can be any
substantially inert medium that is commonly used. Examples of stripping
gas are steam, nitrogen, helium, argon, methane, CO.sub.2 CO, flue
gas, and hydrogen.
It may be desirable to cool at least a portion of the regenerated
catalyst to a lower temperature before it is sent back to the reactor.
A heat exchanger located externally to the regenerator may be used
to remove some heat from the catalyst after it has been withdrawn
from the regenerator. When the regenerated catalyst is cooled, it
is desirable to cool it to a temperature which is from about 200.degree.
C. higher to about 200.degree. C. lower than the temperature of
the catalyst withdrawn from the reactor. More desirably, it is cooled
to a temperature from about 10-200.degree. C. lower than the temperature
of the catalyst withdrawn from the reactor. This cooled catalyst
then may be returned to either some portion of the reactor, the
regenerator, or both. When the regenerated catalyst from the regenerator
is returned to the reactor, it may be returned to the reactor's
catalyst disengaging zone, the reaction zone, and/or the inlet zone.
Introducing the cooled catalyst into the reactor or regenerator
serves to reduce the average temperature in the reactor or regenerator.
In one embodiment, the reactor and regenerator are configured such
that the feed contacts the regenerated catalyst before it is returned
to the reactor. In an alternative embodiment, the reactor and regenerator
are configured such that the feed contacts the regenerated catalyst
after it is returned to the reactor. In yet another embodiment,
the feed stream can be split such that feed contacts regenerated
catalyst before it is returned to the reactor and after it has been
returned to the reactor.
It is preferred the catalyst within the reactor have an average
level of coke effective for selectivity to ethylene and/or propylene.
Preferably, the average coke level on the catalyst will be from
about 2 wt. % to about 30 wt. %, more preferably from about 2 wt.
% to about 20 wt. %. In order to maintain this average level of
coke on catalyst, the entire volume of catalyst can be partially
regenerated under conditions effective to maintain the desired coke
content on catalyst. It is preferred, however, to recycle only a
portion of the coked catalyst for feed contact without regenerating.
This recycle can be performed either internal or external to the
reactor. The portion of coked catalyst to be regenerated is preferably
regenerated under conditions effective to obtain a regenerated catalyst
having a coke content of less than 2 wt. %, preferably less than
1.5 wt. %, and most preferably less than 1.0 wt. %.
In order to make up for any catalyst loss during the regeneration
or reaction process, fresh catalyst can be added. Preferably, the
fresh catalyst is added to the regenerated catalyst after it is
removed from the regenerator, and then both are added to the reactor.
However, the fresh catalyst can be added to the reactor independently
of the regenerated catalyst. Any amount of fresh catalyst can be
added, but it is preferred that an ACFE index of at least 1.5 be
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. The ethylene and propylene can be separated from
the oxygenate conversion product by conventional processes. For
example, the product stream can be directed to a C.sub.1 separation
unit, followed by C.sub.2 and C.sub.3 separation units. The separated
C.sub.2 and C.sub.3 streams can be further separated if desired
to give an ethylene and propylene stream containing little ethane
and propane, respectively. The separated ethylene and propylene
can then be used to make 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.degree.
C. 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 bar to 200 bars. For processes carried out in solution, an inert
diluent can be used, and the preferred operating pressure range
is between 10 bars and 150 bars, with a preferred temperature range
of between 120.degree. C. and 230.degree. C. For gas phase processes,
it is preferred that the temperature generally be within a range
of 60.degree. C. to 160.degree. C., and that the operating pressure
be between 5 bars and 50 bars.
In addition to polyolefins, numerous other olefin derivatives may
be formed from the olefins recovered therefrom. These include, but
are not limited to, aldehydes, alcohols, acetic acid, linear alpha
olefins, vinyl acetate, ethylene dichloride and vinyl chloride,
ethylbenzene, ethylene oxide, cumene, isopropyl alcohol, acrolein,
allyl chloride, propylene oxide, acrylic acid, ethylene-propylene
rubbers, and acrylonitrile, and trimers and dimers of ethylene,
propylene or butylenes. The methods of manufacturing these derivatives
are well known in the art, and therefore, are not discussed herein.
This invention will be better understood with reference to the
following examples, which are intended to illustrate specific embodiments
within the overall scope of the invention as claimed.
A sample of SAPO-34 molecular sieve synthesized with morpholine
as the template was heated under nitrogen at 650.degree. C. for
5 hours, followed by heating under dry air at 650.degree. C. for
3 hours, to remove the morpholine template. The sample of SAPO was
cooled to 150.degree. C. under dry air. A portion of this sample
(0.3 g) was placed in a tubular, fixed bed reactor, to which an
on-line GC equipped with a FID and TCD detector was connected for
product analysis. This portion of the sample is referred to as "fresh"
sample. The remainder of the SAPO-34 sample was placed in an environment
with a relative humidity of 90% (saturated KNO.sub.3 solution).
This portion of the sample is referred to as "aged" sample.
Fresh sample in the reactor was heated under nitrogen for 1 hour
at 625.degree. C. (heat up 5.degree. C./min.) prior the introduction
of the methanol. The reactor conditions were maintained at 450.degree.
C. and 25 psig with a WHSV of 25 hr.sup.-1. Methanol conversion
was calculated as: 100 wt % --(wt % methanol left in product +dimethyl
ether left in product). Methanol conversion as a function of the
amount of methanol fed/gram of molecular sieve in the reactor is
shown in the FIGURE, with the label "fresh" (solid circles).
A sample of aged (3 days) SAPO-34 molecular sieve was added to
a reactor and heated under nitrogen for 1 hour at 625.degree. C.
(heat up 5.degree. C./min.) prior to the introduction of methanol.
Using the same reaction conditions as in Example 1 methanol conversion
was calculated. Methanol conversion as a function of the amount
of methanol fed/gram of molecular sieve in the reactor is shown
in the FIGURE with the label "3 days aged" (solid triangles).
A sample of aged (3 days) SAPO-34 molecular sieve was added to
a round bottom flask which was connected to a vacuum pump. The sample
was evacuated at room temperature to a pressure of about 20 mtorr,
while the round bottom was continually rotated. The round bottom
flask containing the molecular sieve was cooled with liquid nitrogen
while the flask remained under vacuum. After about 30 minutes, the
dewer containing the liquid nitrogen was removed, and the sample
warmed under a continuous vacuum until a free flowing catalyst was
observed in the flask as the flask rotated. Dry air was introduced
into the evacuated flask and the flask heated to 150.degree. C.
The sample was then transferred to the reactor and evaluated for
methanol conversion as in Example 1. Methanol conversion as a function
of the amount of methanol fed/gram of molecular sieve in the reactor
is shown in the FIGURE with the label "3 days aged+freeze dried"
The FIGURE shows that a SAPO molecular sieve aged for 3 days has
almost no catalytic activity. However, a SAPO molecular sieve aged
for 3 days and freeze dried exhibited catalytic activity very similar
to that of a fresh or non-aged molecular sieve.
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.