Process for producing propylene oxide

Abstract

The present invention relates to a process for producing propylene oxide comprising (I) reacting propene with hydrogen peroxide in the presence of a catalyst to give a mixture (GI) comprising propylene oxide, unreacted propene, and oxygen; (II) separating propylene oxide from mixture (GI) to give a mixture (GII) comprising propene and oxygen; (III) reducing the oxygen comprised in mixture (GII) at least partially by reaction with hydrogen in the presence of a catalyst comprising Sn and at least one noble metal.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a process for producing propylene oxide by epoxidation of propene with hydrogen peroxide in the presence of a catalyst, wherein a mixture (GII) obtained in the process which comprises propene and oxygen is subjected to a reduction reaction in which at least a portion of said oxygen comprised in (GII) is reacted with hydrogen in the presence of a specific catalyst, said catalyst comprising tin and at least one noble metal. BACKGROUND OF THE INVENTION [0002] DE 101 55 470 A1 describes a method for the synthesis of propylene oxide by epoxidation of propene with recovery of unreacted propene, in which propene is recovered from at least a portion of an off-stream of the propylene oxide synthesis by (i) addition of nitrogen to the off-gas stream, (ii) compression and (iii) condensation of the resulting stream, (iv) subjecting the stream to gas permeation and (v) separation. During condensation, a gas stream comprising propene,...

AI Technical Summary

Benefits of technology

[0093] According to an object of the present invention, heating up the product stream obtained from stage (i) is carried out using, at least partially, the bottoms stream of the distillation column of stage (ii). Thus, heat integration of the overall epoxidation process is improved. According to a preferred embodiment, of from 50 to 100%, more preferably of from 80 to 100% and especially preferably of from 90 to 100% of the bottoms stream obtained from the distillation column used in (ii) are used for heating up the product stream obtained from (i) from a temperature in the range of from 45 to 55° C. to a temperature in the range of from 65 to 70° C.

[0101] The dividing wall column used in the process of the present invention is preferably configured either as a packed column containing random packing or ordered packing or as a tray column. For example, it is possible to use sheet metal or mesh packing having a specific surface area of from 100 to 1000 m2 / m3, preferably from about 250 to 750 m2 / m3, as ordered packing. Such packing provides a high separation efficiency combined with a low pressure drop per theoretical stage.

[0216] It was surprisingly found that the energy comprised in the effluent, i.e. the product stream obtained from the last reactor of the cascade, preferably the second, the third, or the fourth reactor, more preferably the third or fourth reactor and still more preferably the third reactor, or the product stream obtained from the single reactor, can be effectively used to bring the mixture (GII) at least partially to the desired temperature of from 150 to 300° C., more preferably from 200 to 300° C. and still more preferably from 250 to 300° C., prior to the feeding into the first reactor.

[0217] Therefore, the present invention also provides an efficient heat integrated method in which the product stream obtained from (III) is effectively used for bringing the feed stream of (III) to a preferred temperature useful for conducting the reaction in (III).

[0243] Most preferably, the propene stream obtained from (IV) comprises at most 50 ppm, more preferably at most 40 ppm, more preferably at most 30 ppm, more preferably at most 20 ppm and still more preferably at most 10 ppm of oxygen. Yet more preferably, no traces of oxygen can be detected in the propene stream separated from (GIII). Since this propene stream is preferably recycled as feed stream into stage (I) of the inventive process, the present invention provides an integrated process in which propene is recycled and, simultaneously, the oxygen concentration of the reaction mixture in (I) is effectively prevented from increasing by substantially removing oxygen from the propene recycling stream.

[0244] Together with the heat integration method described above with regard to stage (III), the present invention thus provides a highly integrated process, in terms of heat integration as well as in terms of compound recycling.

Problems solved by technology

On the other hand, the prior art describes catalysts which do not meet the specific requirements of removing oxygen from gas mixtures obtained in epoxidation reactions such as epoxidation of propene.

Moreover, adsorption techniques described in the prior art have the major disadvantage that during adsorption, the explosive range of propene / oxygen mixtures is passed due to to the increasing concentration of absorbed oxygen.

Consequently, in order to avoid process risks, apparatuses used for adsorption techniques have to be constructed highly pressure resistant, thus causing high costs which in turn render the overall process economically undesirable.

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