Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-06-21
2002-08-06
Solola, T. A. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06429323
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of manufacturing oxides of alkenes and the generation of peroxides for use in such manufacture. More particularly, it relates to an integrated, continuous, liquid phase process in which a first reaction generates hydrogen peroxide in organic solution; this reaction mixture is used for epoxidation of an olefin, which is also maintained in organic solution. When hydrogen peroxide is generated under the conditions disclosed and the reactions are coupled according to the invention, the reaction mixture may be used directly as a reagent for the second reaction. Thus there is no requirement for extraction or separation of hydrogen peroxide after the first step nor for removal of products of this first reaction such as ketones. The second reaction is maintained in liquid phase by the use of an organic solvent in combination with appropriate temperature and pressure conditions. This epoxidation reaction also requires the presence of a titanium-impregnated, amorphous silica catalyst, which is described below as a part of the invention.
2. Background of the Invention
Olefinic epoxides, such as ethylene oxide and propylene oxide, are soluble in organic solvents but insoluble in aqueous solutions. The production of epoxides from olefins results in commercially valuable products that have multiple uses in the plastics and chemical industries. The broad range of olefinis available as starting material is capable of generating epoxides which serve as intermediates in the preparation of a vast spectrum of chemical compounds.
The industrial epoxidation of olefins is performed by the reaction of the olefin with a peroxide reagent. Either hydrogen peroxide or an organic peroxide may be used, although the appropriate reaction conditions, the attainable reaction efficiency and the stability of these reagents varies substantially. If the peroxide reagent is generated from organic precursors as part of an integrated process of olefin epoxidation, economies may be realised by reducing the handling and storage of these chemicals.
The integrated process must couple two reactions: a first reaction that would generate peroxide efficiently within a liquid organic medium and a second reaction that would introduce the peroxide product to an olefin maintained in liquid phase by solvent under pressure. Successful integration of the two reactions requires that the conditions of each should be selected so that the products of the first reaction are compatible with the physical and chemical conditions of the second. Besides balancing effects of temperature and polarity upon solubility and stability, the reaction conditions must minimise undesirable secondary reactions of the peroxide with the various organic substrates, products and solvents employed in an integrated process. This is a particular problem if hydrogen peroxide is used as an reagent or intermediate product, generally requiring that the hydrogen peroxide is isolated from reagents and co-products before it can be used in the epoxidation reaction. Previously, the practicality of combining and integrating these reactions has been compromised by the relatively low yields of hydrogen peroxide obtained from the organic reactions known in the art and by the violent oxidising properties of hydrogen peroxide: although commercially available in aqueous solutions of up to 70% by weight, hydrogen peroxide is unstable and is capable of reacting explosively with organic materials.
Hydrogen peroxide may nevertheless be used as an oxidising agent for the production of epoxides from olefins, but it is especially desirable to generate this reagent at the time and the location in which it is required, in order to minimise hazardous handling and storage operations. Moreover, if the kinetic advantages of the strongly oxidising properties of hydrogen peroxide are to be exploited by using this reagent in the epoxidation reaction, its capacity to undergo side reactions with other components of the reaction mixture must be limited. Thus substantial benefits may be gained by integrating into a combined reaction process the production of hydrogen peroxide and its utilisation for olefin epoxidation. Yet the detrimental complications that such a procedure would generate—such as the additional potential for side-reactions in which the hydrogen peroxide may participate—must also be addressed.
Further advantages are to be derived by generating the hydrogen peroxide from organic reagents in organic solution: the reagent may then be mixed rapidly and efficiently with the olefin and the solvent, permitting the epoxidation reaction rate to be controlled accurately. The ability to exercise fine control over the rate of this exothermic reaction is a prerequisite for the development of continuous methods of olefin epoxidation, which offer the potential for additional economic benefits through increased efficiency, particularly when associated with an integrated production process.
The nature of the epoxidation catalyst is also critical for the success of the integrated process. A solid catalyst provides advantages of simple recovery, for example by filtration, prior to regeneration. The supporting structure for transition metal catalysts of epoxidation reactions fall into two categories, possessing either a porous, crystalline zeolite or silicalite structure which possess the additional properties of a ‘molecular sieve’, or the structure of a solid, amorphous silica or alumina. Catalysts in the former group are expensive and limit the useful range of olefins with which they may be used because the diameter of the pores in the support limit access to the catalyst's active centres. Catalysts of the latter group have been used with less reactive organic peroxides as oxidising agents, but if hydrogen peroxide is the oxidant they lower selectivity by expanding the spectrum of significant side reactions that occur, especially if reactions are combined in series. Substantially reduced efficiency and contaminated products are the result.
3. Description of the Prior Art
Industrial epoxidation processes are generally performed by introducing hydrogen peroxide or an organic peroxide to the olefin while the latter is dissolved in an organic solvent. Development of integrated processes in which the peroxide reagent is produced in situ has been discouraged by the technical difficulties outlined above.
Nevertheless, there have been disclosures of industrial olefin epoxidation procedures in which the peroxide reagent is generated immediately prior to the epoxidation reaction as part of an integrated process. These processes lack either an adequate solution to one or more of the technical problems addressed by the present invention, or suffer from another disadvantage, as indicated in more detail below.
In U.S. Pat. No. 5,214,168 Zajacek and Crocco disclose an integrated process of air oxidation of an aryl-substituted secondary alcohol, followed by the use of the oxidation product for epoxidation of an olefin in the presence of a crystalline titanium silicalite catalyst.
European Patent No. EP 0 526 945 discloses an integrated method of olefin epoxidation utilising hydrogen peroxide that is generated in situ. The hydrogen peroxide is produced from a redox reaction between oxygen or air and an alkylanthrahydroquinone. It then reacts with the olefin in the presence of a titanium silicalite catalyst and a specific mixture of organic solvents, comprising one or more aromatic hydrocarbons, one or more polar organic compounds of high boiling point and an alcohol of low molecular weight (methanol). The precise reasons for using this complex mixture of solvents are not disclosed in the publication. Yet the rationale may be related to the low solubility exhibited by alkylanthroquinones and alkylanthrahydroquinones when dissolved together: this characteristic limits the maximum quantity of hydrogen peroxide that can be generated by any specified volume of reactor.
Clerici & Ingallina, European Patent No. 0 549 013, disc
De Frutos Escrig Ma Pilar
Martin Jose Migel Campos
Padilla Polo Ana
McMahon John C.
Repsol Quimica S.A.
Solola T. A.
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