Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Silicon containing or process of making
Reexamination Certificate
1999-12-09
2001-10-30
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Silicon containing or process of making
C502S060000, C502S064000, C502S071000, C502S077000, C502S232000, C502S240000, C502S243000
Reexamination Certificate
active
06309998
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention pertains to a process and catalyst for the direct oxidation of olefins, such as propylene, by oxygen to olefin oxides, such as propylene oxide.
Olefin oxides, such as propylene oxide, are used to alkoxylate alcohols to form polyether polyols, such as polypropylene polyether polyols, which find significant utility in the manufacture of polyurethanes and synthetic elastomers. Olefin oxides are also important intermediates in the manufacture of alkylene glycols, such as propylene glycol and dipropylene glycol, and alkanolamines, such as isopropanolamine, which are useful as solvents and surfactants.
Propylene oxide is produced commercially via the well-known chlorohydrin process wherein propylene is reacted with an aqueous solution of chlorine to produce a mixture of propylene chlorohydrins. The chlorohydrins are dehydrochlorinated with an excess of alkali to produce propylene oxide. This process suffers from the production of a low concentration salt stream. (See K. Weissermel and H. J. Arpe,
Industrial Organic Chemistry,
2
nd
ed., VCH Publishers, Inc., New York, N.Y., 1993, p. 264-265.)
Another well-known route to olefin oxides relies on the transfer of an oxygen atom from an organic hydroperoxide or peroxycarboxylic acid to an olefin. In the first step of this oxidation route, a peroxide generator, such as isobutane or acetaldehyde, is autoxidized with oxygen to form a peroxy compound, such as t-butyl hydroperoxide or peracetic acid. This compound is used to epoxidize the olefin, typically in the presence of a transition metal catalyst, including titanium, vanadium, molybdenum, and other heavy metal compounds or complexes. Along with the olefin oxide produced, this process disadvantageously produces equimolar amounts of a coproduct, for example an alcohol, such as t-butanol, or an acid, such as acetic acid, whose value must be captured in the market place. (See
Industrial Organic Chemistry,
ibid., p. 265-269.)
Although the direct oxidation of ethylene by molecular oxygen to ethylene oxide has been commercialized with a silver catalyst, it is known that the analogous direct oxidation of propylene exhibits a low selectivity to the olefin oxide. Disadvantageously large amounts of acrolein and oxygen-containing C
1-3
byproducts are produced, as taught in
Industrial Organic Chemistry,
ibid., p. 264. Some patents represented by U.S. Pat. Nos. 4,007,135 and 4,845,253, teach the use of metal-promoted silver catalysts for the oxidation of propylene with oxygen to propylene oxide. Among the metal promoters. disclosed are gold, beryllium, magnesium, calcium, barium, strontium, and the rare earth lanthanides. These promoted silver catalysts also exhibit low selectivities to the olefin oxide.
Alternatively, EP-A1-0,709,360 discloses a process of oxidizing an unsaturated hydrocarbon, such as propylene, with oxygen in the presence of hydrogen and a catalyst to form an epoxide, such as propylene oxide. Gold deposited on titanium dioxide, further immobilized on a carrier such as silica or alumina, is taught as the catalyst composition. The catalyst exhibits lower olefin oxide selectivity and less efficient hydrogen consumption when operated at higher temperatures. Additionally, the catalyst has a short run time.
PCT publication WO-A1-96/02323 discloses the oxidation of an olefin, including propylene, with oxygen in the presence of hydrogen and a catalyst to form an olefin oxide. The catalyst is a titanium or vanadium silicalite containing at least one platinum group metal, and optionally, an additional metal selected from gold, iron, cobalt, nickel, rhenium, and silver. The productivity of olefin oxide is low in this process.
In view of the above, a need continues to exist in the chemical industry for an efficient direct route to propylene oxide and higher olefin oxides from the reaction of oxygen with C
3
and higher olefins. The discovery of such a process which simultaneously achieves high selectivity to the olefin oxide at an economically advantageous conversion of the olefin would represent a significant achievement over the prior art. For commercial viability such a process would also require that the catalyst exhibit a long lifetime.
U.S. Pat. Nos. 4,839,327 and 4,937,219 represent additional art disclosing a composition comprising gold particles having a particle size smaller than about 500 Å immobilized on an alkaline earth oxide or titanium dioxide or a composite oxide of titanium dioxide with an alkaline earth oxide. A preparation of this composition involves deposition of a gold compound onto the alkaline earth oxide, titanium dioxide, or the composite oxide, followed by calcination so as to produce metallic gold of a particle size smaller than about 500 Å. This teaching is silent with respect to depositing the gold particles on a titanosilicate and to a process for producing olefin oxides.
SUMMARY OF THE INVENTION
This invention is a novel process of preparing an olefin oxide directly from an olefin and oxygen. The process comprises contacting an olefin having at least three carbon atoms with oxygen in the presence of hydrogen and in the presence of a catalyst under process conditions sufficient to produce the corresponding olefin oxide. The unique catalyst which is employed in the process of this invention comprises gold on a titanosilicate.
The novel process of this invention is useful for producing an olefin oxide directly from oxygen and an olefin having three or more carbon atoms. Unexpectedly, the process of this invention produces the olefin oxide in a remarkably high selectivity. Partial and complete combustion products, such as acrolein and carbon dioxide, which are found in large amounts in many prior art processes, are produced in lesser amounts in the process of this invention. Significantly, the process of this invention can be operated at a high temperature, specifically greater than about 120° C., while maintaining a high selectivity to olefin oxide. Operation at higher temperatures advantageously provides steam credits from the heat produced. Accordingly, the process of this invention can be integrated into a total plant design wherein the heat derived from the steam is used to drive additional processes, for example, the separation of the olefin oxide from water. Even more advantageously, since water is produced as a byproduct of this process, the hydrogen efficiency, as measured by the water to olefin oxide molar ratio, is good. Most advantageously, the process in its preferred embodiments exhibits an olefin conversion which is good.
In another aspect, this invention is a unique catalyst composition comprising gold on a titanosilicate.
The novel composition of this invention can be effectively used in the aforementioned direct oxidation of an olefin having three or more carbon atoms to the corresponding olefin oxide. Besides being active and highly selective for the olefin oxide, the catalyst exhibits evidence of a long lifetime. As a further advantage, when partially or completely spent, the catalyst is easy to regenerate. Accordingly, this unique catalyst exhibits highly desirable properties for the process of oxidizing propylene and higher olefins to their corresponding olefin oxides.
DETAILED DESCRIPTION OF THE INVENTION
The novel process of this invention comprises contacting an olefin having at least three carbon atoms with oxygen in the presence of hydrogen and an epoxidation catalyst under process conditions sufficient to prepare the corresponding olefin oxide. In one preferred embodiment, a diluent is employed with one or more of the reactants, as described in detail hereinafter. The relative molar quantities of olefin, oxygen, hydrogen, and optional diluent can be any which are sufficient to prepare the desired olefin oxide. In a preferred embodiment of this invention, the olefin employed is a C
3-12
olefin, and it is converted to the corresponding C
3-12
olefin oxide. In a more preferred embodiment, the olefin is a C
3-8
olefin, and it is converted to the corresponding C
3-8
olefin oxi
Bowman Robert G.
Clark Howard W.
Hartwell George E.
Maj Joseph J.
Womack Joseph L.
The Dow Chemical Company
Wood Elizabeth D.
Zuckerman Marie F.
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