Molecular sieve abstract
The present invention relates to new crystalline molecular sieve
SSZ-70 prepared using a N,N'-diisopropyl imidazolium cation as a
structure-directing agent, methods for synthesizing SSZ-70 and processes
employing SSZ-70 in a catalyst.
Molecular sieve claims
What is claimed is:
1. A process for oxidation of hydrocarbons comprising contacting
said hydrocarbon with an oxidizing agent in the presence of a catalytically
effective amount of a crystalline, titanium-containing molecular
sieve for a time and at a temperature effective to oxidize said
hydrocarbon, wherein the crystalline titanium-containing molecular
sieve is a molecular sieve having a mole ratio greater than about
15 of (1) silicon oxide to (2) titanium oxide, and having, after
calcination, the X-ray diffraction lines of Table II.
2. A process for epoxidation of an olefin comprising contacting
said olefin with hydrogen peroxide in the presence of a catalytically
effective amount of a crystalline, titanium-containing molecular
sieve for a time and at a temperature effective to epoxidize said
olefin, wherein the crystalline titanium-containing molecular sieve
is a molecular sieve having a mole ratio greater than about 15 of
(1) silicon oxide to (2) titanium oxide, and having, after calcination,
the X-ray diffraction lines of Table II.
3. A process for oxidizing cyclohexane comprising contacting said
cyclohexane with hydrogen peroxide in the presence of a catalytically
effective amount of a crystalline, titanium-containing molecular
sieve for a time and at a temperature effective to oxidize said
cyclohexane, wherein the crystalline titanium-containing molecular
sieve is a molecular sieve having a mole ratio greater than about
15 of (1) silicon oxide to (2) titanium oxide, and having, after
calcination, the X-ray diffraction lines of Table II.
4. A catalytic oxidation process comprising contacting under oxidation
conditions (1) a reactant which is catalytically oxidizable in the
presence of hydrogen peroxide, (2) aqueous hydrogen peroxide and
(3) a catalytically effective amount of an oxidation catalyst comprising
a molecular sieve having a mole ratio greater than about 15 of (1)
silicon oxide to (2) titanium oxide, and having, after calcination,
the X-ray diffraction lines of Table II.
5. The process of claim 4 wherein the elemental mole ratio of titanium
to silicon is about 0.005 to about 0.2.
6. The process of claim 4 wherein the elemental mole ratio of titanium
to silicon is about 0.01 to about 0.05.
7. The process of claim 4 wherein the oxidizable reactant is a
hydrocarbon.
8. A process for the epoxidation of an olefin comprising contacting
said olefin with hydrogen peroxide in the presence of a catalytically
effective amount of a catalyst comprising a molecular sieve having
a mole ratio greater than about of (1) silicon oxide to (2) titanium
oxide, and having, after calcination, the X-ray diffraction lines
of Table II.
9. The process of claim 8 wherein the elemental mole ratio of titanium
to silicon is about 0.005 to about 0.2.
10. The process of claim 8 wherein the elemental mole ratio of
titanium to silicon is about 0.01 to about 0.05.
Molecular sieve description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to new crystalline molecular sieve
SSZ-70 a method for preparing SSZ-70 using a N,N'-diisopropyl imidazolium
cation as a structure directing agent and the use of SSZ-70 in catalysts
for, e.g., hydrocarbon conversion reactions.
2. State of the Art
Because of their unique sieving characteristics, as well as their
catalytic properties, crystalline molecular sieves and zeolites
are especially useful in applications such as hydrocarbon conversion,
gas drying and separation. Although many different crystalline molecular
sieves have been disclosed, there is a continuing need for new zeolites
with desirable properties for gas separation and drying, hydrocarbon
and chemical conversions, and other applications. New zeolites may
contain novel internal pore architectures, providing enhanced selectivities
in these processes.
Crystalline aluminosilicates are usually prepared from aqueous
reaction mixtures containing alkali or alkaline earth metal oxides,
silica, and alumina. Crystalline borosilicates are usually prepared
under similar reaction conditions except that boron is used in place
of aluminum. By varying the synthesis conditions and the composition
of the reaction mixture, different zeolites can often be formed.
SUMMARY OF THE INVENTION
The present invention is directed to a family of crystalline molecular
sieves with unique properties, referred to herein as "molecular
sieve SSZ-70" or simply "SSZ-70". Preferably, SSZ-70
is obtained in its silicate, aluminosilicate, titanosilicate, vanadosilicate
or borosilicate form. The term "silicate" refers to a
molecular sieve having a high mole ratio of silicon oxide relative
to aluminum oxide, preferably a mole ratio greater than 100 including
molecular sieves comprised entirely of silicon oxide. As used herein,
the term "aluminosilicate" refers to a molecular sieve
containing both aluminum oxide and silicon oxide and the term "borosilicate"
refers to a molecular sieve containing oxides of both boron and
silicon.
In accordance with the present invention, there is provided a process
for oxidation of hydrocarbons comprising contacting said hydrocarbon
with an oxidizing agent in the presence of a catalytically effective
amount of a crystalline, titanium-containing molecular sieve for
a time and at a temperature effective to oxidize said hydrocarbon,
wherein the crystalline titanium-containing molecular sieve is a
molecular sieve having a mole ratio greater than about 15 of (1)
silicon oxide to (2) titanium oxide, and having, after calcination,
the X-ray diffraction lines of Table II.
There is further provided in accordance with this invention a process
for epoxidation of an olefin comprising contacting said olefin with
hydrogen peroxide in the presence of a catalytically effective amount
of a crystalline, titanium-containing molecular sieve for a time
and at a temperature effective to epoxidize said olefin, wherein
the crystalline titanium-containing molecular sieve is a molecular
sieve having a mole ratio greater than about 15 of (1) silicon oxide
to (2) titanium oxide, and having, after calcination, the X-ray
diffraction lines of Table II.
Further provided in accordance with the present invention is a
process for oxidizing cyclohexane comprising contacting said cyclohexane
with hydrogen peroxide in the presence of a catalytically effective
amount of a crystalline, titanium-containing molecular sieve for
a time and at a temperature effective to oxidize said cyclohexane,
wherein the crystalline titanium-containing molecular sieve is a
molecular sieve having a mole ratio greater than about 15 of (1)
silicon oxide to (2) titanium oxide, and having, after calcination,
the X-ray diffraction lines of Table II.
The present invention also provides a catalytic oxidation process
comprising contacting under oxidation conditions (1) a reactant
which is catalytically oxidizable in the presence of hydrogen peroxide,
(2) aqueous hydrogen peroxide and (3) a catalytically effective
amount of an oxidation catalyst comprising a molecular sieve having
a mole ratio greater than about 15 of (1) silicon oxide to (2) titanium
oxide, and having, after calcination, the X-ray diffraction lines
of Table II.
The present invention also provides a process for the epoxidation
of an olefin comprising contacting said olefin with hydrogen peroxide
in the presence of a catalytically effective amount of a catalyst
comprising a molecular sieve having a mole ratio greater than about
15 of (1) silicon oxide to (2) titanium oxide, and having, after
calcination, the X-ray diffraction lines of Table II.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an X-ray diffraction pattern of SSZ-70 after it has been
calcined.
FIG. 2 is an X-ray diffraction pattern of SSZ-70 in the as-synthesized
form, i.e., prior to calcination with the SDA still in the pores
of the SSZ-70.
DETAILED DESCRIPTION OF THE INVENTION
The present invention comprises a family of crystalline molecular
sieves designated herein "molecular sieve SSZ-70" or simply
"SSZ-70". In preparing SSZ-70 a N,N'-diisopropyl imidazolium
cation (referred to herein as "DIPI") is used as a structure
directing agent ("SDA"), also known as a crystallization
template. The SDA useful for making SSZ-70 has the following structure:
##STR00001##
The SDA cation is associated with an anion (X.sup.-) which may
be any anion that is not detrimental to the formation of the molecular
sieve. Representative anions include halogen, e.g., fluoride, chloride,
bromide and iodide, hydroxide, acetate, sulfate, tetrafluoroborate,
carboxylate, and the like. Hydroxide is the most preferred anion.
SSZ-70 is prepared from a reaction mixture having the composition
shown in Table A below.
TABLE-US-00001 TABLE A Reaction Mixture Typical Preferred YO.sub.2/B.sub.2O.sub.3
5 60 10 60 OH--/YO.sub.2 0.10 0.50 0.20 0.30 Q/YO.sub.2 0.05 0.50
0.10 0.20 M.sub.2/n/YO.sub.2 0 0.40 0.10 0.25 H.sub.2O/YO.sub.2
30 80 35 45 F/YO.sub.2 0 0.50 0
where Y is silicon; M is an alkali metal cation, alkaline earth
metal cation or mixtures thereof; n is the valence of M (i.e., 1
or 2); F is fluorine and Q is a N,N'-diisopropyl imidazolium cation.
In practice, SSZ-70 is prepared by a process comprising:
(a) preparing an aqueous solution containing sources of at least
two oxides capable of forming a crystalline molecular sieve and
a DIPI cation having an anionic counterion which is not detrimental
to the formation of SSZ-70;
(b) maintaining the aqueous solution under conditions sufficient
to form crystals of SSZ-70; and
(c) recovering the crystals of SSZ-70.
Accordingly, SSZ-70 may comprise the crystalline material and the
SDA in combination with metallic and non-metallic oxides bonded
in tetrahedral coordination through shared oxygen atoms to form
a cross-linked three dimensional crystal structure. Typical sources
of silicon oxide include silicates, silica hydrogel, silicic acid,
fumed silica, colloidal silica, tetra-alkyl orthosilicates, and
silica hydroxides. Boron can be added in forms corresponding to
its silicon counterpart, such as boric acid.
A source zeolite reagent may provide a source of boron. In most
cases, the source zeolite also provides a source of silica. The
source zeolite in its deboronated form may also be used as a source
of silica, with additional silicon added using, for example, the
conventional sources listed above. Use of a source zeolite reagent
for the present process is more completely described in U.S. Pat.
No. 5225179 issued Jul. 6 1993 to Nakagawa entitled "Method
of Making Molecular Sieves", the disclosure of which is incorporated
herein by reference.
Typically, an alkali metal hydroxide and/or an alkaline earth metal
hydroxide, such as the hydroxide of sodium, potassium, lithium,
cesium, rubidium, calcium, and magnesium, is used in the reaction
mixture; however, this component can be omitted so long as the equivalent
basicity is maintained. The SDA may be used to provide hydroxide
ion. Thus, it may be beneficial to ion exchange, for example, the
halide to hydroxide ion, thereby reducing or eliminating the alkali
metal hydroxide quantity required. The alkali metal cation or alkaline
earth cation may be part of the as-synthesized crystalline oxide
material, in order to balance valence electron charges therein.
The reaction may also be carried out using HF to counterbalance
the OH-contribution from the SDA, and run the synthesis in the absence
of alkali cations. Running in the absence of alkali cations has
the advantage of being able to prepare a catalyst from the synthesis
product, by using calcination alone, i.e., no ion-exchange step
(to remove alkali or alkaline earth cations) is necessary. In using
HF, the reaction operates best when both the SDA and HF have mole
ratios of 0.50 relative to YO.sub.2 (e.g., silica).
The reaction mixture is maintained at an elevated temperature until
the crystals of the SSZ-70 are formed. The hydrothermal crystallization
is usually conducted under autogenous pressure, at a temperature
between 100.degree. C. and 200.degree. C., preferably between 135.degree.
C. and 160.degree. C. The crystallization period is typically greater
than 1 day and preferably from about 3 days to about 20 days.
Preferably, the molecular sieve is prepared using mild stirring
or agitation.
During the hydrothermal crystallization step, the SSZ-70 crystals
can be allowed to nucleate spontaneously from the reaction mixture.
The use of SSZ-70 crystals as seed material can be advantageous
in decreasing the time necessary for complete crystallization to
occur. In addition, seeding can lead to an increased purity of the
product obtained by promoting the nucleation and/or formation of
SSZ-70 over any undesired phases. When used as seeds, SSZ-70 crystals
are added in an amount between 0.1 and 10% of the weight of first
tetravalent element oxide, e.g. silica, used in the reaction mixture.
Once the molecular sieve crystals have formed, the solid product
is separated from the reaction mixture by standard mechanical separation
techniques such as filtration. The crystals are water-washed and
then dried, e.g., at 90.degree. C. to 150.degree. C. for from 8
to 24 hours, to obtain the as-synthesized SSZ-70 crystals. The drying
step can be performed at atmospheric pressure or under vacuum.
SSZ-70 as prepared has a mole ratio of (1) silicon oxide to (2)
boron oxide greater than about 15; and has, after calcination, the
X-ray diffraction lines of Table II below. SSZ-70 further has a
composition, as synthesized (i.e., prior to removal of the SDA from
the SSZ-70) and in the anhydrous state, in terms of mole ratios,
shown in Table B below.
TABLE-US-00002 TABLE B As-Synthesized SSZ-70 YO.sub.2/B.sub.2O.sub.3
20 60 M.sub.2/n/YO.sub.2 0 0.03 Q/YO.sub.2 0.02 0.05 F/YO.sub.2
0 0.10
where Y, M, n, F is fluorine and Q are as defined above.
SSZ-70 can be an essentially all-silica material. As used herein,
"essentially all-silica" means that the molecular sieve
is comprised of only silicon oxide or is comprised of silicon oxide
and only trace amounts of other oxides, such as aluminum oxide,
which may be introduced as impurities in the source of silicon oxide.
Thus, in a typical case where oxides of silicon and boron are used,
SSZ-70 can be made essentially boron free, i.e., having a silica
to boron oxide mole ratio of .infin.. SSZ-70 is made as a borosilicate
and then the boron can then be removed, if desired, by treating
the borosilicate SSZ-70 with acetic acid at elevated temperature
(as described in Jones et al., Chem. Mater., 2001 13 1041 1050)
to produce an essentially all-silica version of SSZ-70.
If desired, SSZ-70 can be made as a borosilicate and then the boron
can be removed as described above and replaced with metal atoms
by techniques known in the art. Aluminum, gallium, iron, titanium,
vanadium and mixtures thereof can be added in this manner.
It is believed that SSZ-70 is comprised of a new framework structure
or topology which is characterized by its X-ray diffraction pattern.
SSZ-70 as-synthesized, has a crystalline structure whose X-ray
powder diffraction pattern exhibit the characteristic lines shown
in Table I and is thereby distinguished from other molecular sieves.
TABLE-US-00003 TABLE I As-Synthesized SSZ-70 2 Theta.sup.(a) d-spacing
(Angstroms) Relative Intensity (%).sup.(b) 3.32 26.6 VS 6.70 13.2
VS 7.26 12.2 S 8.78 10.1 S 13.34 6.64 M 20.02 4.44 S 22.54 3.94
M 22.88 3.89 M 26.36 3.38 S VS 26.88 3.32 M .sup.(a).+-.0.15 .sup.(b)The
X-ray patterns provided are based on a relative intensity scale
in which the strongest line in the X-ray pattern is assigned a value
of 100: W (weak) is less than 20; M (medium) is between 20 and 40;
S (strong) is between 40 and 60; VS (very strong) is greater than
60.
Table IA below shows the X-ray powder diffraction lines for as-synthesized
SSZ-70 including actual relative intensities.
TABLE-US-00004 TABLE IA 2 Theta.sup.(a) d-spacing (Angstroms) Relative
Intensity (%) 3.32 26.6 84 6.70 13.2 100 7.26 12.2 45 8.78 10.1
44 13.34 6.64 26 20.02 4.44 46 22.54 3.94 33 22.88 3.89 36 26.36
3.38 61 26.88 3.32 31 .sup.(a).+-.0.15
After calcination, the SSZ-70 molecular sieves have a crystalline
structure whose X-ray powder diffraction pattern include the characteristic
lines shown in Table II:
TABLE-US-00005 TABLE II Calcined SSZ-70 2 Theta.sup.(a) d-spacing
(Angstroms) Relative Intensity (%) 7.31 12.1 VS 7.75 11.4 VS 9.25
9.6 VS 14.56 6.08 VS 15.61 5.68 S 19.60 4.53 S 21.81 4.07 M 22.24
4.00 M S 26.30 3.39 VS 26.81 3.33 VS .sup.(a).+-.0.15
Table IIA below shows the X-ray powder diffraction lines for calcined
SSZ-70 including actual relative intensities.
TABLE-US-00006 TABLE IIA 2 Theta.sup.(a) d-spacing (Angstroms)
Relative Intensity (%) 7.31 12.1 67 7.75 11.4 93 9.25 9.6 79 14.56
6.08 68 15.61 5.68 49 19.60 4.53 58 21.81 4.07 38 22.24 4.00 41
26.30 3.39 99 26.81 3.33 80 .sup.(a).+-.0.15
The X-ray powder diffraction patterns were determined by standard
techniques. The radiation was the K-alpha/doublet of copper. The
peak heights and the positions, as a function of 2.theta. where
.theta. is the Bragg angle, were read from the relative intensities
of the peaks, and d, the interplanar spacing in Angstroms corresponding
to the recorded lines, can be calculated.
The variation in the scattering angle (two theta) measurements,
due to instrument error and to differences between individual samples,
is estimated at .+-.0.15 degrees.
The X-ray diffraction pattern of Table I is representative of "as-synthesized"
or "as-made" SSZ-70 molecular sieves. Minor variations
in the diffraction pattern can result from variations in the silica-to-boron
mole ratio of the particular sample due to changes in lattice constants.
In addition, sufficiently small crystals will affect the shape and
intensity of peaks, leading to significant peak broadening.
Representative peaks from the X-ray diffraction pattern of calcined
SSZ-70 are shown in Table II. Calcination can also result in changes
in the intensities of the peaks as compared to patterns of the "as-made"
material, as well as minor shifts in the diffraction pattern. The
molecular sieve produced by exchanging the metal or other cations
present in the molecular sieve with various other cations (such
as H.sup.+ or NH.sub.4.sup.+) yields essentially the same diffraction
pattern, although again, there may be minor shifts in the interplanar
spacing and variations in the relative intensities of the peaks.
Notwithstanding these minor perturbations, the basic crystal lattice
remains unchanged by these treatments.
Crystalline SSZ-70 can be used as-synthesized, but preferably will
be thermally treated (calcined). Usually, it is desirable to remove
the alkali metal cation by ion exchange and replace it with hydrogen,
ammonium, or any desired metal ion. The molecular sieve can be leached
with chelating agents, e.g., EDTA or dilute acid solutions, to increase
the silica to alumina mole ratio. The molecular sieve can also be
steamed; steaming helps stabilize the crystalline lattice to attack
from acids.
The molecular sieve can be used in intimate combination with hydrogenating
components, such as tungsten, vanadium, molybdenum, rhenium, nickel,
cobalt, chromium, manganese, or a noble metal, such as palladium
or platinum, for those applications in which a hydrogenation-dehydrogenation
function is desired.
Metals may also be introduced into the molecular sieve by replacing
some of the cations in the molecular sieve with metal cations via
standard ion exchange techniques (see, for example, U.S. Pat. No.
3140249 issued Jul. 7 1964 to Plank et al.; U.S. Pat. No. 3140251
issued Jul. 7 1964 to Plank et al.; and U.S. Pat. No. 3140253
issued Jul. 7 1964 to Plank et al.). Typical replacing cations
can include metal cations, e.g., rare earth, Group IA, Group IIA
and Group VIII metals, as well as their mixtures. Of the replacing
metallic cations, cations of metals such as rare earth, Mn, Ca,
Mg, Zn, Cd, Pt, Pd, Ni, Co, Ti, Al, Sn, and Fe are particularly
preferred.
The hydrogen, ammonium, and metal components can be ion-exchanged
into the SSZ-70. The SSZ-70 can also be impregnated with the metals,
or the metals can be physically and intimately admixed with the
SSZ-70 using standard methods known to the art.
Typical ion-exchange techniques involve contacting the synthetic
molecular sieve with a solution containing a salt of the desired
replacing cation or cations. Although a wide variety of salts can
be employed, chlorides and other halides, acetates, nitrates, and
sulfates are particularly preferred. The molecular sieve is usually
calcined prior to the ion-exchange procedure to remove the organic
matter present in the channels and on the surface, since this results
in a more effective ion exchange. Representative ion exchange techniques
are disclosed in a wide variety of patents including U.S. Pat. No.
3140249 issued on Jul. 7 1964 to Plank et al.; U.S. Pat. No.
3140251 issued on Jul. 7 1964 to Plank et al.; and U.S. Pat.
No. 3140253 issued on Jul. 7 1964 to Plank et al.
Following contact with the salt solution of the desired replacing
cation, the molecular sieve is typically washed with water and dried
at temperatures ranging from 65.degree. C. to about 200.degree.
C. After washing, the molecular sieve can be calcined in air or
inert gas at temperatures ranging from about 200.degree. C. to about
800.degree. C. for periods of time ranging from 1 to 48 hours, or
more, to produce a catalytically active product especially useful
in hydrocarbon conversion processes.
Regardless of the cations present in the synthesized form of SSZ-70
the spatial arrangement of the atoms which form the basic crystal
lattice of the molecular sieve remains essentially unchanged.
SSZ-70 can be formed into a wide variety of physical shapes. Generally
speaking, the molecular sieve can be in the form of a powder, a
granule, or a molded product, such as extrudate having a particle
size sufficient to pass through a 2-mesh (Tyler) screen and be retained
on a 400-mesh (Tyler) screen. In cases where the catalyst is molded,
such as by extrusion with an organic binder, the SSZ-70 can be extruded
before drying, or, dried or partially dried and then extruded.
SSZ-70 can be composited with other materials resistant to the
temperatures and other conditions employed in organic conversion
processes. Such matrix materials include active and inactive materials
and synthetic or naturally occurring zeolites as well as inorganic
materials such as clays, silica and metal oxides. Examples of such
materials and the manner in which they can be used are disclosed
in U.S. Pat. No. 4910006 issued May 20 1990 to Zones et al.,
and U.S. Pat. No. 5316753 issued May 31 1994 to Nakagawa, both
of which are incorporated by reference herein in their entirety.
The partial oxidation of low value hydrocarbons such as alkanes
and alkenes into high value products such as alcohols and epoxides
is of great commercial interest. These oxidation products are not
only valuable as is, but also as intermediates for specialty chemicals
including pharmaceuticals and pesticides.
U.S. Pat. No. 4410501 issued Oct. 18 1983 to Esposito et al.,
discloses a titanium-containing analogue of the all-silica ZSM-5
molecular sieve. This material (known as "TS-1") has been
found to be useful in catalyzing a wide range of partial oxidation
chemistries, for example the production of catechol and hydroquinone
from phenol and hydrogen peroxide (H.sub.2O.sub.2) and the manufacture
of propylene oxide and cyclohexanone oxime from propylene and cyclohexanone,
respectively. In addition, TS-1 can be used to catalyze the reaction
of alkanes and aqueous H.sub.2O.sub.2 to form alcohols and ketones.
(See Huybrechts, D. R. C. et al., Nature 1990 345 240 242 and
Tatsumi, T. et al., J. C. S. Chem. Commun. 1990 476 477.)
TS-1 has many salient features, other than its catalytic abilities,
which make it attractive as a commercial catalyst. Most importantly,
it is a solid. This allows for easy separation from the reactants
and products (typically liquids) by simple, inexpensive filtration.
Moreover, this solid has high thermal stability and a very long
lifetime. Calcination in air at moderate temperatures (550.degree.
C.) restores the material to its original catalytic ability. TS-1
performs best at mild temperatures (<100.degree. C.) and pressures
(1 atm). The oxidant used for reactions catalyzed by TS-1 is aqueous
H.sub.2O.sub.2 which is important because aqueous H.sub.2O.sub.2
is relatively inexpensive and its by-product is water. Hence, the
choice of oxidant is favorable from both a commercial and environmental
point of view.
While a catalyst system based on TS-1 has many useful features,
it has one serious drawback. The zeolite structure of TS-1 includes
a regular system of pores which are formed by nearly circular rings
of ten silicon atoms (called 10-membered rings, or simply "10
rings") creating pore diameters of approximately 5.5 .ANG..
This small size results in the exclusion of molecules larger than
5.5 .ANG.. Because the catalytically active sites are located within
the pores of the zeolite, any exclusion of molecules from the pores
results in poor catalytic activity.
SSZ-70 containing titanium oxide (Ti-SSZ-70) is useful as a catalyst
in oxidation reactions, particularly in the oxidation of hydrocarbons.
Examples of such reactions include, but are not limited to, the
epoxidation of olefins, the oxidation of alkanes, and the oxidation
of sulfur-containing, nitrogen-containing or phosphorus-containing
compounds.
The amount of Ti-SSZ-70 catalyst employed is not critical, but
should be sufficient so as to substantially accomplish the desired
oxidation reaction in a practicably short period of time (i.e.,
a catalytically effective amount). The optimum quantity of catalyst
will depend upon a number of factors including reaction temperature,
the reactivity and concentration of the substrate, hydrogen peroxide
concentration, type and concentration of organic solvent, as well
as the activity of the catalyst. Typically, however, the amount
of catalyst will be from about 0.001 to 10 grams per mole of substrate.
Typically, the Ti-SSZ-70 is thermally treated (calcined) prior
to use as a catalyst.
The oxidizing agent employed in the oxidation processes of this
invention is a hydrogen peroxide source such as hydrogen peroxide
(H.sub.2O.sub.2) or a hydrogen peroxide precursor (i.e., a compound
which under the oxidation reaction conditions is capable of generating
or liberating hydrogen peroxide).
The amount of hydrogen peroxide relative to the amount of substrate
is not critical, but must be sufficient to cause oxidation of at
least some of the substrate. Typically, the molar ratio of hydrogen
peroxide to substrate is from about 100:1 to about 1:100 preferably
10:1 to about 1:10. When the substrate is an olefin containing more
than one carbon--carbon double bond, additional hydrogen peroxide
may be required. Theoretically, one equivalent of hydrogen peroxide
is required to oxidize one equivalent of a mono-unsaturated substrate,
but it may be desirable to employ an excess of one reactant to optimize
selectivity to the epoxide. In particular, the use of a moderate
to large excess (e.g., 50 to 200%) of olefin relative to hydrogen
peroxide may be advantageous for certain substrates.
If desired, a solvent may additionally be present during the oxidation
reaction in order to dissolve the reactants other than the Ti-SSZ-70
to provide better temperature control, or to favorably influence
the oxidation rates and selectivities. The solvent, if present,
may comprise from 1 to 99 weight percent of the total oxidation
reaction mixture and is preferably selected such that it is a liquid
at the oxidation reaction temperature. Organic compounds having
boiling points at atmospheric pressure of from about 50.degree.
C. to about 150.degree. C. are generally preferred for use. Excess
hydrocarbon may serve as a solvent or diluent. Illustrative examples
of other suitable solvents include, but are not limited to, ketones
(e.g., acetone, methyl ethyl ketone, acetophenone), ethers (e.g.,
tetrahydrofuran, butyl ether), nitrites (e.g., acetonitrile), aliphatic
and aromatic hydrocarbons, halogenated hydrocarbons, and alcohols
(e.g., methanol, ethanol, isopropyl alcohol, t-butyl alcohol, alpha-methyl
benzyl alcohol, cyclohexanol). More than one type of solvent may
be utilized. Water may also be employed as a solvent or diluent.
The reaction temperature is not critical, but should be sufficient
to accomplish substantial conversion of the substrate within a reasonably
short period of time. It is generally advantageous to carry out
the reaction to achieve as high a hydrogen peroxide conversion as
possible, preferably at least about 50%, more preferably at least
about 90%, most preferably at least about 95%, consistent with reasonable
selectivities. The optimum reaction temperature will be influenced
by catalyst activity, substrate reactivity, reactant concentrations,
and type of solvent employed, among other factors, but typically
will be in a range of from about 0.degree. C. to about 150.degree.
C. (more preferably from about 25.degree. C. to about 120.degree.
C.). Reaction or residence times from about one minute to about
48 hours (more desirably from about ten minutes to about eight hours)
will typically be appropriate, depending upon the above-identified
variables. Although subatmospheric pressures can be employed, the
reaction is preferably performed at atmospheric or at elevated pressure
(typically, between one and 100 atmospheres), especially when the
boiling point of the substrate is below the oxidation reaction temperature.
Generally, it is desirable to pressurize the reaction vessel sufficiently
to maintain the reaction components as a liquid phase mixture. Most
(over 50%) of the substrate should preferably be present in the
liquid phase.
The oxidation process of this invention may be carried out in a
batch, continuous, or semi-continuous manner using any appropriate
type of reaction vessel or apparatus such as a fixed bed, transport
bed, fluidized bed, stirred slurry, or CSTR reactor. The reactants
may be combined all at once or sequentially. For example, the hydrogen
peroxide or hydrogen peroxide precursor may be added incrementally
to the reaction zone. The hydrogen peroxide could also be generated
in situ within the same reactor zone where oxidation is taking place.
Once the oxidation has been carried out to the desired degree of
conversion, the oxidized product may be separated and recovered
from the reaction mixture using any appropriate technique such as
fractional distillation, extractive distillation, liquid-liquid
extraction, crystallization, or the like. |