Process for producing propylene oxide (Sumitomo Chemical)

PATENT
Process for producing propylene oxide (Sumitomo Chemical)
Publication number US8481764 B2
Application number US 11/997,965
Publication date Jul 9, 2013
Also published as CN101243059A
Inventors
Junpei Tsuji, Koji Shinohara
Original Assignee
Sumitomo Chemical Company, Limited
Abstract
A process for producing propylene oxide, which comprises supplying an organic peroxide and propylene to an epoxidation reactor in which a solid catalyst is packed thereby continuously producing propylene oxide through epoxidation reaction, wherein said process comprises cooling at least a part of the propylene before supplying to separate and remove water contained in the propylene, and supplying the propylene in which water has been separated and removed to the epoxidation reactor.
Description
TECHNICAL FIELD
The present invention relates to a process for producing propylene oxide.
BACKGROUND ART
For example, it is publicly known to continuously produce propylene oxide through epoxidation reaction by supplying an organic peroxide and propylene to an epoxidation reactor in which a solid catalyst such as titanium-containing silicon oxide is packed (e.g. EP 0345856 A). However, there were problems that a pressure loss of a solid catalyst layer increased with a continuous operation time and the catalyst was destroyed when the pressure loss was over the pressure resistant strength of the catalyst, and that the production amount had to be decreased through suppression of the amount to be supplied of the raw material for avoiding the destroy of the catalyst.
DISCLOSURE OF THE INVENTION
Under such situations, an object of the invention is to provide a process for continuously producing propylene oxide through epoxidation reaction by supplying an organic peroxide and propylene to an epoxidation reactor in which a solid catalyst is packed, the process being able to avoid the destroy of the solid catalyst generated by increase of a pressure loss of the catalyst layer and the situation that reduction of the production amount is forced.
Namely, the present invention relates to a process for producing propylene oxide, which comprises supplying an organic peroxide and propylene to an epoxidation reactor in which a solid catalyst is packed thereby continuously producing propylene oxide through epoxidation reaction, wherein said process comprises cooling at least a part of the propylene thereby separating and removing water contained in the propylene, and subsequently supplying the propylene to the epoxidation reactor.
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, propylene oxide is continuously produced through epoxidation reaction by supplying an organic peroxide and propylene to an epoxidation reactor in which a solid catalyst is packed
As a solid epoxidation catalyst, titanium-containing silicon oxide is used from the viewpoint of obtaining propylene oxide under high yield. As the catalyst, so-called Ti-silica catalysts containing titanium chemically bonded to silicon oxide, are preferable. For example, a catalyst prepared by supporting a Ti compound on a silica carrier, a catalyst prepared by combining a titanium compound with silicon oxide by a co-precipitation method or sol-gel method, zeolite compounds containing Ti, and the like, can be listed.
Specific examples of the present invention include a process for continuously producing propylene oxide through epoxidation reaction by supplying an organic peroxide to a fixed bed reactor in which a titanium-containing silicon oxide catalyst is packed.
Examples of the organic peroxide include cumene hydroperoxide, ethylbenzene hydroperoxide and tert-butyl hydroperoxide. The organic peroxide to be supplied to the epoxidation reactor can be synthesized by oxidation of a hydrocarbon corresponding to the peroxide. An organic acid generated in the oxidation, decreases the yield of epoxidation. Therefore, from viewpoints of removal of the organic acid, it is preferable to contact the organic peroxide to be supplied to the epoxidation reactor with an aqueous solution of an alkali metal compound during and/or after the oxidation. As the compound containing the alkali metal, sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate and the like are listed. Further, an aqueous solution of anyone of these compounds or a mixture thereof can be used. The concentration of the alkali metal of the aqueous solution is preferably 0.05 to 10% by weight.
When the concentration is lower than 0.05% by weight, the removal of the organic acid may become insufficient, and, on the other hand, when the concentration is higher than 10% by weight, the yield of the organic peroxide may be reduced by which decomposition of the formed organic peroxide is promoted. After contact with the aqueous solution containing the alkali metal compound, the resulting mixture is separated into an oil phase and an aqueous phase, the oil phase is contacted with water for removing the alkali metal compound remained in the oil phase, and then the resulted mixture is separated into an oil phase and an aqueous phase. These operations may be repeated if necessary.
The oil phase separated often contains a traced amount of water. This water is preferably removed as much as possible because the water also deteriorates the yield of epoxidation. Methods for removing water include publicly known methods such as a removing method using a separation membrane such as a corelesser, a method for removing by consuming water through a reaction, and a method for removing water by means of distillation. From the industrial viewpoint, it is preferable to remove water by means of distillation. A solution containing the organic peroxide thus obtained is supplied to the epoxidation reactor.
The epoxidation reaction is carried out in a liquid phase using a solvent. The solvent should be liquid under a temperature and a pressure during the reaction, and substantially inert to reactants and products. The solvent may be a substance present in a hydroperoxide solution to be used. For example, when cumene hydroperoxide is a mixture with cumene which is a raw material thereof, the cumene can be used as a substitute of a solvent without particularly adding a solvent. The epoxidation temperature is usually from 0 to 200° C., and preferably from 25 to 200° C. The pressure may be a pressure sufficient to keep the reaction mixture in a liquid condition. In general, the pressure is advantageously from 0.1 to 10 MPa.
A molar ratio of propylene to the organic peroxide compound to be supplied to the epoxidation reactor is preferably 2/1 to 50/1. When the ratio is lower than 2/1, the efficiency may be low because the reaction velocity decreases. In contrast, when the ratio is over 50/1, large energy may be required in a step for separating and recovering propylene from a reaction mixture obtained in the epoxidation step for recycling excess amount of unreacted propylene.
In general, a liquid linear velocity of the reaction mixture in the continuous method using a fixed bed reactor, is preferably properly determined in the range of 0.1 to 3 cm/sec since the appropriate velocity varies depending on conditions such as a composition of the mixture and a particle size of the solid catalyst.
The unreacted propylene contained in the reaction mixture after the epoxidation reaction, is recycled to the epoxidation reactor after separation and recovery. As a method for the separation and recovery of unreacted propylene, distillation can be used. In the distillation, it is preferable to use conditions under which propylene is easily evaporated. Though the conditions of distillation vary depending on the temperature and composition of the reaction mixture supplied to a distillation step, the pressure is usually 0 to 5 and preferably 0 to 3 MPa as a gauge pressure, the overhead temperature is usually −50 to 150° C., and the bottom temperature is usually 50 to 200° C., and preferably 80 to 200° C.
Further, a method for distilling propylene stepwise using a plurality of distillation columns, may be used.
Unreacted propylene thus separated and recovered can be supplied to the epoxidation reactor after mixing with fresh propylene.
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