Molecular sieve abstract
Olefins are selectively converted to epoxides by reacting with
an organic hydroperoxide in the presence of a heterogeneous catalyst
comprised of a carbon molecular sieve containing a Group IVA, VA,
VIA, or VIIA transition metal such as molybdenum.
Molecular sieve claims
We claim:
1. A process for producing an epoxide comprising contacting an
olefin with an organic hydroperoxide in the presence of a catalytic
amount of a carbon molecular sieve impregnated with a Group IVA,
VA, VIA, or VIIA transition metal for a time and at a temperature
effective to convert the olefin to the epoxide.
2. The process of claim 1 wherein the transition metal is molybdenum,
titanium, tungsten, or vanadium.
3. The process of claim 1 wherein said contacting is carried out
in a liquid phase.
4. The process of claim 1 wherein the temperature is from 50.degree.
C. to 150.degree. C.
5. The process of claim 1 wherein the organic hydroperoxide is
selected from tertiary butyl hydroperoxide, tertiary amyl hydroperoxide,
cumene hydroperoxide, ethyl benzene hydroperoxide, cyclohexyl hydroperoxide,
and methyl cyclohexyl hydroperoxide.
6. The process of claim 1 wherein the olefin is a C.sub.2 -C.sub.30
olefin having the general formula ##STR4## wherein R.sup.4R.sup.5R.sup.6
and R.sup.7 are the same or different and are selected from hydrogen,
C.sub.1 -C.sub.20 alkyl, C.sub.7 -C.sub.20 aryl alkyl, C.sub.5 -C.sub.20
alkyl cycloalkyl, and C.sub.6 -C.sub.20 aryl.
7. The process of claim 1 wherein the olefin is selected from the
group consisting of ethylene, propylene, 1-butene, 2-butene, 1-pentene,
2-pentene, 1-octene, allyl alcohol, allyl chloride, methallyl alcohol,
methallyl chloride, styrene, cyclohexane, cyclooctene, allyl phenyl
ether, norbornene, isoprene, butadiene, isobutylene, and vinyl cyclohexane.
8. The process of claim 1 wherein the carbon molecular sieve contains
from 0.01 to 25 percent by weight of the transition metal.
9. The process of claim 1 wherein the carbon molecular sieve has
an average pore radius of from 1 to 100 angstroms.
10. The process of claim 1 wherein the carbon molecular sieve has
a surface area of greater than 100 m.sup.2 /g.
11. The process of claim 1 wherein the molar ratio of olefin: organic
hydroperoxide is from 20:1 to 1:5.
12. The process of claim 1 wherein the carbon molecular sieve is
present at a concentration sufficient to provide from 10 to 10000
ppm transition metal based on the combined amount of olefin and
organic hydroperoxide.
13. The process of claim 1 wherein an organic solvent is additionally
present during said contacting.
14. The process of claim 13 wherein the organic solvent is an alcohol
or hydrocarbon corresponding in carbon skeleton to the organic hydroperoxide.
15. A process for producing an epoxide comprising contacting a
C.sub.2 -C.sub.10 olefin with an organic hydroperoxide having the
general structure ##STR5## wherein R.sup.1R.sup.2 and R.sup.3
are the same or different and are selected from hydrogen, C.sub.1
-C.sub.6 alkyl, and aryl provided that a maximum of one of R.sup.1
R.sup.2 and R.sup.3 is hydrogen, and a catalytic amount of a carbon
molecular sieve having an average pore radius of from 1 to 100 angstroms
and a surface area of at least 100 m.sup.2 /g and impregnated with
from 1 to 20 weight percent of molybdenum at a temperature of from
50.degree. to 150.degree. C. for a time effective to convert the
olefin to the epoxide.
16. The process of claim 15 wherein the olefin is selected from
ethylene, propylene, 1-butene, 2-butene, isobutylene, 1-pentene,
2-pentene, 1-octene, allyl alcohol, methallyl alcohol, styrene,
cyclohexene, cyclooctene, allyl phenyl ether, allyl ethyl ether,
norbornene, isoprene, butadiene, and vinyl cyclohexane.
17. The process of claim 15 wherein the organic hydroperoxide is
selected from tertiary butyl hydroperoxide, tertiary amyl hydroperoxide,
cumene hydroperoxide, ethyl benzene hydroperoxide, cyclohexyl hydroperoxide,
and methyl cyclohexyl hydroperoxide.
18. The process of claim 15 wherein the olefin is propylene and
the organic hydroperoxide is tertiary butyl hydroperoxide or ethyl
benzene hydroperoxide.
19. The process of claim 15 wherein the organic hydroperoxide is
generated by air oxidation of a hydrocarbon corresponding in carbon
skeleton to the organic hydroperoxide.
20. The process of claim 15 wherein the organic hydroperoxide is
converted to an alcohol corresponding in carbon skeleton to the
organic hydroperoxide during said contacting.
Molecular sieve description
FIELD OF THE INVENTION
This invention relates to methods wherein an olefin may be selectively
oxidized to an epoxide. More particularly, this invention pertains
to catalytic epoxidation processes employing certain transition
metals entrapped in a porous carbon matrix as catalyst and organic
hydroperoxides as oxidizing agent.
BACKGROUND OF THE INVENTION
Epoxides such as ethylene oxide, propylene oxide, 12-butene oxide
and the like are useful intermediates for the preparation of a wide
variety of products. The oxirane functionality in such compounds
is highly reactive and may be ring-opened with any number of nucleophilic
reactants. For example, epoxides may be hydrolyzed to yield glycols
useful as anti-freeze components, food additives, or reactive monomers
for the preparation of condensation polymers such as polyesters.
Polyether polyols generated by the ring-opening polymerization
of epoxides are widely utilized as intermediates in the preparation
of polyurethane foams, elastomers, sealants, coatings, and the like.
The reaction of epoxides with alcohols provides glycol ethers, which
may be used as polar solvents in a number of applications.
Many different methods for the preparation of epoxides have been
developed. One such method involves the epoxidation of an olefin
in a liquid phase reaction using an organic hydroperoxide as the
oxidizing agent and certain solubilized transition metal compounds
as catalyst. The early work in this field concluded that optimum
epoxidation rates and selectivity to epoxide generally are obtained
using metallic catalysts which are soluble in an organic reaction
medium. For example, U.S. Pat. No. 3350422 teaches in Example
6 that while vanadium naphthenate (a soluble catalyst) provided
72% hydroperoxide conversion and 38% selectivity to propylene oxide,
vanadium pentoxide (an insoluble species) gave only 34% hydroperoxide
conversion and 6% propylene oxide selectivity. Similarly, U.S. Pat.
No. 3351635 teaches that metals such as molybdenum, tungsten and
titanium are most effective as epoxidation catalysts when dissolved
in the epoxidation reaction mixture. Poorly soluble species such
as molybdenum trioxide thus are initially inactive and only become
suitable for use in such application when converted to a soluble
active form by reaction with alcohol, glycol, hydroperoxide or the
like (see, for example, the discussion in Sheldon, J. Mol. Cat.
7 pp. 107-126 (1980)).
A distinct disadvantage of an epoxidation process which utilizes
a soluble metallic compound as catalyst is the difficulty associated
with recovering the catalyst for reuse in subsequent runs. When
the other components of an epoxidation reaction mixture (typically,
epoxide, unreacted olefin, solvent, unreacted hydroperoxide, and
the alcohol derived from the reacted hydroperoxide) are relatively
volatile, these components may be separated from the soluble non-volatile
catalyst by distillation and the catalyst recovered in the form
of a bottoms stream. A problem associated with such a method, however,
is that the bottoms stream may tend to accumulate certain heavy
substances such as acids and polymers which may have a deleterious
effect on epoxide selectivity or olefin conversion when the stream
is reused. The catalyst may also have a tendency to precipitate
from solution if the bottoms stream is overly concentrated; recycle
of a relatively large bottoms stream may thus be required, which
will detrimentally affect the productivity of the epoxidation process.
It would therefore be highly desirable to develop an insoluble (heterogeneous)
epoxidation catalyst which has high activity and selectivity and
which may be readily recovered in active form from an epoxidation
reaction mixture by filtration or similar separation techniques
or which may be utilized in the form of a fixed bed or the like.
SUMMARY OF THE INVENTION
This invention provides a process for producing an epoxide comprising
contacting an olefin with an organic hydroperoxide and a catalytic
amount of a carbon molecular sieve impregnated with a Group IVA,
VA, VIA, or VIIA transition metal such as titanium, tungsten, chromium,
vanadium, molybdenum, nickel, or rhenium for a time and at a temperature
effective to convert the olefin to the epoxide.
In a particular embodiment, the invention furnishes a method for
forming an epoxide comprising contacting a C.sub.2 -C.sub.10 olefin
with an organic hydroperoxide having the general structure ##STR1##
wherein R.sup.1 R.sup.2 R.sup.3 are the same or different and
are selected from hydrogen, C.sub.1 -C.sub.6 alkyl, and aryl provided
that a maximum of one of R.sup.1 R.sup.2 and R.sup.3 is hydrogen,
and a catalytic amount of a carbon molecular sieve having an average
pore radius of from 1 to 100 angstroms and a surface area of at
least 100 m.sup.2 /g and impregnated with from 1 to 20 weight percent
of molybdenum at a temperature of from 50.degree. C. to 150.degree.
C. for a time effective to convert the olefin to the epoxide.
A distinct advantage of the present invention is that the catalyst
employed is heterogeneous and thus may be readily recovered or separated
from an epoxidation reaction mixture and reused. Additionally, the
catalysts utilized in the process of this invention, despite their
insoluble character, have good activity and transform olefins into
epoxide in a highly selective manner.
DETAILED DESCRIPTION OF THE INVENTION
The catalyst used in the process of this invention is a carbon
molecular sieve containing transition metal atoms on its external
surface and/or within its pores. Although the precise mechanism
is not known, the transition metal atoms are apparently trapped
or immobilized inside the carbon molecular sieve matrix in a manner
such that the transition metal atoms are not readily solubilized
and yet are available for interaction with the olefin and the hydroperoxide,
thereby facilitating the catalytic transfer of oxygen from the hydroperoxide
to the olefin to form the desired epoxide.
Carbon molecular sieves suitable for use in preparing the metal-containing
catalysts are well known in the art and are amorphous materials
with average pore dimensions similar to the critical dimensions
of individual molecules. These carbon-based absorbents have also
been referred to as ultra microporous carbons and contain a large
specific pore volume primarily in pores of molecular dimensions.
They are generally obtained by the controlled pyrolysis of natural
and synthetic precursors, including coal, coconut shells, pitch,
phenolformaldehyde resins, styrene-vinyl benzene sulfonated resins,
polyfurfuryl alcohol, polyacrylonitrile, and polyvinylidene chloride.
Suitable precursors may be cross-linked and may contain a cation,
anion, strong base, weak base, sulfonic acid, carboxylic acid, halogen,
or alkyl amine functionality. The chemistry of such materials is
reviewed, for example, in Foley, "Carbon Molecular Sieves Properties
and Applications in Perspective", in Perspectives in Molecular
Sieve Science, Flank et al., Eds., American Chemical Society, pp.
335-360 (1988), Schmitt, "Carbon Molecular Sieves as Selective
Catalyst Supports-10 Years Later", Carbon, 29(6) pp. 743-745
(1991), and Walker, "Carbon-An Old But New Material Revisited",
Carbon, 28 (2/3), pp. 261-279 (1990). Certain carbon molecular sieves
are available from commercial sources and may also be utilized as
starting materials for the catalysts employed in the process described
herein. Such carbon molecular sieves include, for example, the Ambersorb
series of absorbent offered by the Rohm and Haas Company (e.g.,
"Ambersorb 563", "Ambersorb 564", "Ambersorb
572", "Ambersorb 575", "Ambersorb 348F")
as well as the carbon molecular sieve materials available from Anderson
Development Company ("Type AX21"), Calgon Carbon Corporation
("Calgon MSC-V"), Alltech Associates ("Carbosphere"),
and Takeda ("5A Carbon"). References describing methods
of preparing carbon molecular sieves include Lafyatis et al., Ind.
Eng. Chem. Res. 30 pp. 865-873 (1991), Japanese Kokai No. 61-191510
(abstracted in Chem. Abst. 105: 229264y), U.S. Pat. No. 4082694
(Wennerberg et al.), U.S. Pat. No. 4839331 (Maroldo et al.), U.S.
Pat. No. 4040990 (Neely), and U.S. Pat. No. 4528281 (Sutt) among
others; the teachings of these publications are incorporated herein
by reference in their entirety.
The Group IVA, VA, VIA, or VIIA transition metal entrapped in the
carbon molecular sieve may preferably be selected from titanium,
tungsten, chromium, vanadium, nickel, rhenium, or, most preferably,
molybdenum. Mixtures or combinations of different transition metals
may also be employed. The precise form of the transition metal present
in the carbon molecular sieve is not critical to the successful
operation of the process of this invention, but the oxidation state
of the metal and the substituents or ligands bound to or otherwise
associated with the transition metal should be such as to permit
the metal center to participate in the transfer of an oxygen atom
from the organic hydroperoxide to the olefin. Metal oxides represent
an exemplary class which may suitably be utilized. Transition metal-doped
carbon molecular sieves of this type are known in the art and may
be obtained by any of the synthetic procedures taught in the following
publications among others (all of which are incorporated by reference
in their entirety): European Pat. Pub Nos. 520779 and 525974
U.S. Pat. Nos. 4447665 (Wennerberg), 4482641 (Wennerberg), 4518488
(Wennerberg), 4569924 (Ozin et al.), 4591578 (Foley et al.),
4656153 (Wennerberg), 4970189 (Tachibana), 4992404 (Gruhl
et al.), and 5051389 (Lang et al.), Canadian Pat. Appl. No. 2047080
and Grunewald et al., "Carbon Molecular Sieves as Catalysts
and Catalyst Supports", J. Am. Chem. Soc. 113 pp. 1636-1639
(1991).
The physical and chemical characteristics of the carbon molecular
sieve may be manipulated as desired in order to favorably influence
the activity and selectivity of the resulting catalyst when utilized
to epoxidize olefins in the process of this invention. Such characteristics
include, for example, surface area, average pore radius, distribution
of pore sizes, pore volume (including the relative macropore, mesopore,
and micropore volumes), acidity/basicity, hydrophobicity/hydrophilicity,
and the like. The optimium type of carbon molecular sieve for a
particular epoxidation application will vary depending upon the
choice of olefin and organic hydroperoxide, transition metal, reaction
conditions, reaction medium (solvent), and so forth. For example,
the particular size and shape of the olefin to be epoxidized and
the organic hydroperoxide serving as the source of oxygen will affect
the selection of the carbon molecular sieve best suited for the
process of this invention. Such optimization may be readily performed
by the worker of ordinary skill in the art using routine experimental
methods.
Generally speaking, the transition metal content of the carbon
molecular sieve is not critical and may be varied within wide limits.
Sufficient metal should be incorporated so as to avoid the need
to utilize an excessively large amount of the doped carbon molecular
sieve relative to the volume of organic reactants, but the metal
concentration should not be so high that leaching of the metal into
solution becomes a problem. Typically, the carbon molecular sieve
may contain from 0.01 to 25 percent by weight (preferably, from
1 to 20 percent by weight) of the transition metal. In general,
higher loadings of transition metal are possible by increasing the
surface area of the carbon molecular sieve. Sufficient metal-impregnated
carbon molecular sieve is present in the reaction zone together
with the olefin and organic hydroperoxide to attain a practically
rapid rate of epoxidation. The optimum amount of the catalyst will,
of course, depend on a number of variables including temperature,
the relative reactivities and concentrations of olefin and hydroperoxide,
the identity and activity of the transition metal selected, and
so forth, but generally the catalyst is present at a concentration
sufficient to provide from 10 to 10000 ppm transition metal based
on the combined weight of olefin and organic hydroperoxide.
The average pore radius of the carbon molecular sieve may be altered
as desired, but usually will advantageously be in the range of from
1 to 100 angstroms although larger average pore sizes may also be
useful under certain conditions. The relative proportions of macropores
(>500 angstroms), mesopores (20-500 angstroms), and micropores
(<20 angstroms) may be manipulated as needed to attain maximum
catalyst productivity with regard to the desired epoxide product.
The carbon molecular sieve can possess any surface area provided
the resulting doped catalyst is active in the epoxidation reaction.
Generally, the carbon molecular sieve possesses a surface area of
at least about 100 m.sup.2 /g with a surface area of at least 500
m.sup.2 /g being advantageous in certain epoxidation applications.
The surface area may be as high as the theoretical maximum possible
for such substances; the surface area thus, for example, may be
as high as 2000-3000 m.sup.2 /g. In order to avoid problems with
ring-opening reactions of the epoxide product, the carbon molecular
sieve containing the transition metal is preferably not highly acidic.
The transition metal-containing carbon molecular sieve may be employed
in any suitable physical form, including powders, particles, beads,
pellets, monoliths, spheres, granules, blocks, saddles, extrudates,
and the like. Preferably, the carbon molecular sieve is sufficiently
hard to resist attrition or other physical degradation during practice
of the instant process, particularly when the process is carried
out on a continuous basis for an extended period of time.
The organic hydroperoxide to be used as the oxidizing agent in
the process of this invention may be any organic compound having
at least one hydroperoxy functional group (-00H). Secondary and
tertiary hydroperoxides are preferred, however, owing to the higher
instability and greater safety hazards associated with primary hydroperoxides.
The organic hydroperoxide preferably has the general structure ##STR2##
wherein R.sup.1 R.sup.2 and R.sup.3 are the same or different
and are selected from the group consisting of hydrogen, C.sub.1
-C.sub.6 alkyl, and aryl. Preferably, the R groups are selected
from hydrogen, methyl, ethyl, and phenyl wherein a maximum of one
R group is hydrogen. The aforementioned R groups may each be a substituted
or unsubstituted alkyl, cycloalkyl, aralkyl, aralkenyl, hydroxyaralkyl,
cycloalkenyl, hydroxycycloalkyl and the like having from one to
10 carbon atoms. The hydroxy hydroperoxy species formed by the air
oxidation of alcohols such as cyclohexanol may also be employed.
Exemplary hydroperoxides include t-butyl hydroperoxide, t-amyl hydroperoxide,
cumene hydroperoxide, ethyl benzene hydroperoxide, cyclohexane hydroperoxide,
methyl cyclohexane hydroperoxide, tetralin hydroperoxide, isobutyl
benzene hydroperoxide, isopropyl hydroperoxide, ethyl naphthalene
hydroperoxide, tetralin hydroperoxide, and the like. Mixtures of
organic hydroperoxides may also be employed. The amount of organic
hydroperoxide is not critical, but most suitably the molar ratio
of olefin:organic hydroperoxide is from about 100:1 to 1:100 when
the olefin contains one ethylenically unsaturated group. The molar
ratio of ethylenically unsaturated groups in the olefin substrate
to organic hydroperoxide is more preferably in the range of from
20:1 to 1:5. One equivalent of hydroperoxide is theoretically required
to oxidize one equivalent of a mono-unsaturated olefin substrate,
but it may be desirable to employ an excess of one reactant to optimize
selectivity to the epoxide.
The olefin substrate may be any organic compound having at least
one ethylenically unsaturated functional group (i.e., a carbon-carbon
double bond) and may be an aromatic, aliphatic, mixed aromatic-aliphatic
(e.g., aralkyl), cyclic, branched or straight chain olefin. Preferably,
the olefin contains from 2 to 30 carbon atoms (i.e., a C.sub.2 -C.sub.30
olefin). Olefins containing from two to ten carbon atoms are especially
preferred. The olefinic double bond may be in a terminal or internal
position on the olefin or may form part of a cyclic structure as
a cyclohexene. More than one carbon-carbon double bond may be present
in the olefin; dienes, trienes, and other polyunsaturated substrates
thus may be used. Other examples of suitable substrates include
unsaturated fatty acids or fatty acid derivatives such as esters
or glycerides and oligomeric or polymeric unsaturated compounds
such as polybutadiene.
In one embodiment, the olefin is a C.sub.2 -C.sub.30 olefin having
the general structure ##STR3## wherein R.sup.4 R.sup.5 R.sup.6
and R.sup.7 are the same or different and are selected from hydrogen,
C.sub.1 -C.sub.20 alkyl, C.sub.7 -C.sub.20 aryl alkyl, C.sub.5 -C.sub.20
alkyl cycloalkyl, and C.sub.6 -C.sub.20 aryl.
The olefin may contain substituents other than hydrocarbon substituents
such as halide, carboxylic acid, ether, hydroxy, thiol, nitro, cyano,
ketone, ester, anhydride, amino, and the like, provided such substituents
do not interfere with the desired epoxidation reaction.
Exemplary olefins suitable for use in the process of this invention
include ethylene, propylene, the butenes such as 1-butene, 2-butene
and isobutylene, butadiene, the pentenes such as 1-pentene and 2-pentene,
isoprene, 1-hexene, 1-octene, diisobutylene, 1-nonene, 1-tetradecene,
pentamyrcene, camphene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene,
1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene,
1-eicosene, the trimers and tetramers of propylene, polybutadiene,
polyisoprene, cyclopentene, cyclohexene, cycloheptene, cyclooctene,
cyclooctadiene, cyclododecene, cyclododecatriene, dicyclopentadiene,
methylenecyclopropane, methylenecyclopentane, styrene (and other
styrenic substrates), methylenecyclohexane, vinylcyclohexane, vinyl
cyclohexene, methallyl alcohol, allyl alcohol, allyl chloride, allyl
bromide, allyl phenyl ether, allyl ethyl ether, acrylic acid, methacrylic
acid, crotonic acid, vinyl acetic acid, crotyl chloride, methallyl
chloride, the dichlorobutenes, allyl carbonate, allyl acetate, allyl
acrylates and methacrylates, diallyl maleate, diallyl phthalate,
unsaturated triglycerides such as soybean oil, and unsaturated fatty
acids, such as oleic acid, linolenic acid, linoleic acid, erucic
acid, oleosteric acid, myristic acid, palmitic acid, and ricinoleic
acid and their esters.
An organic solvent or mixture of organic solvents may additionally
be present when the olefin is contacted with the hydroperoxide and
catalyst. Alternatively, the desired reaction may be conducted in
a neat state (without solvent) or using an excess of one reactant
such as the olefin as a diluent. The solvent may be used to dilute,
disperse, or dissolve the components of the reaction mixture, thus
providing better temperature control or faster reaction rates. The
identity of the solvent may advantageously be altered to control
the rate or selectivity of the epoxidation process. Examples of
suitable organic solvents include, but are not limited to, aliphatic
hydrocarbons (e.g., hexane, cyclohexane, petroleum ether), aromatic
hydrocarbons (e.g., benzene, toluene, xylene, ethyl benzene, napthalene,
cumene), and halogenated hydrocarbons (e.g., methylene chloride,
chloroform, carbon tetrachloride, trichloroethane, chlorobenzene).
The amount of organic solvent is not critical, but typically will
be from about 5 to 95 weight % of the total reaction mixture. It
is generally desirable to carry out the process of this invention
under an inert atmosphere, that is, in the absence of oxygen.
In one embodiment of the invention, the solvent is a hydrocarbon
or alcohol which corresponds in carbon skeleton to the organic hydroperoxide
being used as the oxidant. For example, when tertiary butyl hydroperoxide
is employed as the organic hydroperoxide, tertiary butyl alcohol
may be used as solvent. Similarly, when ethyl benzene hydroperoxide
is the oxidant, the solvent may be ethyl benzene. Mixtures of hydroperoxides
and their corresponding alcohols or hydrocarbons may be readily
generated by air oxidation of a hydrocarbon such as isobutane or
ethyl benzene.
The reaction temperature is not critical, but should be sufficient
to accomplish substantial conversion of the olefin to epoxide within
a reasonably short period of time. It is generally advantageous
to carry out the reaction to achieve as high a hydroperoxide conversion
as possible, preferably at least 50% and desirably at least 90%,
consistent with reasonable selectivities. The optimum reaction temperature
will be influenced by catalyst activity, olefin reactivity, reactant
concentrations, and type of solvent employed, among other factors,
but typically will be in a range of from about 50.degree. C. to
150.degree. C. More preferably, the temperature will be from about
70.degree. C. to 125.degree. C. Reaction or residence times of from
about 1 minute to 48 hours (more preferably, 10 minutes to 3 hours)
will typically be appropriate, depending upon the above-identified
variables. Although sub-atmospheric pressures can be employed, the
reaction is preferably performed at atmospheric pressure or at elevated
pressure (typically, not greater than about 2000 psig). Generally,
it will be desirable to maintain the reaction components as a liquid
phase mixture.
The 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. The reactor advantageously may be a fluidized
bed, fixed bed, transport bed, moving bed, continuous stirred tank
(CSTR), or stirred slurry reactor. Known methods for conducting
transition metal catalyzed epoxidations of olefins using organic
hydroperoxides will generally also be suitable for use in this process.
Thus, the reactants may be combined all at once or sequentially.
For example, the organic hydroperoxide may be added incrementally
to the reaction zone. In one embodiment of the process, the olefin
and organic hydroperoxide are introduced separately or as a mixture
into a reaction zone wherein the catalyst is maintained in solid
form as a fixed, mobile, fluidized or moving bed. As the olefin
and hydroperoxide pass over and come into contact with the catalyst,
the desired epoxide product is formed and may be withdrawn from
the reaction zone as a liquid stream together with the alcohol derived
from the reacted hydroperoxide. Once the epoxidation has been carried
out to the desired degree of conversion, the desired epoxide 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. The co-product of the reaction will generally be the corresponding
alcohol derived from the organic hydroperoxide and may similarly
be separated and recovered for use as a valuable product in its
own right. For example, t-butyl alcohol will be produced if t-butyl
hydroperoxide is employed as the oxidant while methyl benzyl alcohol
is obtained using ethyl benzene hydroperoxide. The alcohol product
can in turn be readily dehydrated to a useful olefin such as isobutylene
or styrene. These olefins may, if desired, be hydrogenated and then
oxidized to the organic hydroperoxide. After separation from the
epoxidation reaction mixture, the recovered transition metal-doped
carbon molecular sieve catalyst may be economically re-used in subsequent
epoxidations. Periodic reactivation or regeneration of the catalyst
may be advantageous. Any unreacted olefin or organic hydroperoxide
may also be separated and recycled.
From the foregoing description, one skilled in the art can readily
ascertain the essential characteristics of this invention, and,
without departing from the spirit and scope thereof, can make various
changes and modifications of the invention to adapt it to various
usages, conditions, and embodiments. |