JP4951975B2 - Propylene oxide production method - Google Patents

Description

  The present invention relates to a method for producing propylene oxide. More specifically, the present invention is a method for producing propylene oxide, in which an organic peroxide and propylene are supplied to an epoxidation reactor filled with an epoxidized solid catalyst, and propylene oxide is continuously produced by an epoxidation reaction.

  For example, a method for continuously producing propylene oxide by an epoxidation reaction by supplying an organic peroxide and propylene to an epoxidation reactor filled with an epoxidation solid catalyst such as titanium-containing silicon oxide is known (for example, patents). Reference 1).

  However, with continuous operation, the pressure loss of the solid catalyst layer increases, the problem that the catalyst breaks down beyond the crushing strength of the catalyst, and the supply of raw materials to avoid the destruction of the catalyst There was a problem that the production volume had to be reduced by reducing the flow rate.

JP-A-2-42072

  In such a situation, an object of the present invention is a method for producing propylene oxide, in which an organic peroxide and propylene are supplied to an epoxidation reactor filled with an epoxidized solid catalyst, and propylene oxide is continuously produced by an epoxidation reaction. A method for producing propylene oxide having an excellent effect of avoiding a situation in which the destruction of the catalyst due to the pressure loss of the solid catalyst layer that has risen with the production and the reduction of the production amount is unavoidable. It is to provide.

That is, the present invention is a method for producing propylene oxide in which an organic peroxide and propylene are supplied to an epoxidation reactor filled with an epoxidation solid catalyst, and propylene oxide is continuously produced by an epoxidation reaction. This relates to a method for producing propylene oxide having a propylene pretreatment step.
Propylene pretreatment step: a step of treating at least part of propylene supplied to the epoxidation reactor, and removing an oxygen-containing organic compound contained in propylene

  According to the present invention, there is provided a method for producing propylene oxide in which an organic peroxide and propylene are supplied to an epoxidation reactor filled with a solid catalyst, and propylene oxide is continuously produced by an epoxidation reaction. It is possible to provide a method for producing propylene oxide having an excellent effect that it is possible to avoid a situation in which the destruction of the catalyst due to the pressure loss of the raised solid catalyst layer and the reduction of the production amount are unavoidable.

  In the present invention, an organic peroxide and propylene are supplied to an epoxidation reactor filled with a solid catalyst for epoxidation, and propylene oxide is continuously produced by an epoxidation reaction.

  As the solid catalyst used in the epoxidation reaction, a titanium-containing silicon oxide catalyst is used from the viewpoint of obtaining the target product in a high yield. These catalysts are preferably so-called titanium-silica catalysts containing titanium chemically bonded to silicon oxide. For example, a titanium compound supported on a silica carrier, a compound compounded with silicon oxide by a coprecipitation method or a sol-gel method, a zeolite compound containing titanium, and the like can be given.

  The particle diameter of the titanium-containing silicon oxide catalyst charged in the epoxidation reactor is not particularly limited, and can be appropriately determined in consideration of the shape and size of the reactor, but is preferably 0.1 to 10 mm, more preferably 0.25 to 5 mm. If the particle size is too small, the pressure loss of the solid catalyst layer may increase, whereas if it is too large, the yield of propylene oxide may decrease.

  Examples of the organic peroxide include cumene hydroperoxide, ethylbenzene hydroperoxide, tert-butyl hydroperoxide, and the like. The organic peroxide supplied to the epoxidation reactor is synthesized by oxidation of a corresponding hydrocarbon compound (for example, cumene, ethylbenzene, isobutane, etc. in the above organic peroxide, respectively). The organic acid generated during the oxidation reaction also acts as a catalyst poison for the epoxidation catalyst. Therefore, as the organic peroxide supplied to the epoxidation reactor, it is preferable to use one from which the organic acid has been removed. As a method of removing, for example, it is preferable to contact with an aqueous solution of a compound containing an alkali metal during and / or after the oxidation reaction. Examples of the compound containing an alkali metal include sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate and the like, and any of these compounds or a mixed aqueous solution thereof can be used. The concentration of alkali metal in the aqueous solution is preferably 0.05 to 10% by weight. If the concentration is too low, the removal effect of the organic acid may be insufficient. On the other hand, if the concentration is excessive, the decomposition reaction of the generated organic peroxide may be promoted and the yield may be reduced. is there. After contact with an aqueous solution of a compound containing an alkali metal, it is usually separated into an oil phase / water phase, and the organic acid is removed from the oil phase. However, when the organic peroxide supplied to the epoxidation reactor is in contact with an aqueous solution of a compound containing an alkali metal, there arises a problem that the pressure loss of the solid catalyst layer of the epoxidation reactor increases. Sometimes. Therefore, it is usually preferable to separate the oil phase / water phase after contacting with water in order to remove the alkali metal-containing compound remaining in the oil phase. This operation is repeated if necessary.

  The oil phase after separation from the aqueous phase often contains a trace amount of water. Since this water reduces the yield of the epoxidation reaction and also acts as a catalyst poison, it is preferably removed as much as possible. Examples of the method for removing water include a method for removing using a separation membrane such as a coalescer, a method for consuming and removing by a reaction, a method for removing by distillation, etc., but using distillation from an industrial viewpoint. It is preferable to remove. The solution containing the organic peroxide thus obtained is fed to the epoxidation reactor.

  The epoxidation reaction is performed in a liquid phase using a solvent. The solvent must be liquid at the temperature and pressure during the reaction and be substantially inert to the reactants and products. The solvent may consist of substances present in the organic peroxide solution used. For example, when cumene hydroperoxide is a mixture with cumene as its raw material, when ethylbenzene hydroperoxide is a mixture with ethylbenzene as its raw material, or isobutane with tert-butyl hydroperoxide as its raw material. In the case of the mixture, it is also possible to substitute the solvent without adding a solvent.

  The epoxidation reaction temperature is generally 0 to 200 ° C, but a temperature of 25 to 200 ° C is preferable. The pressure may be sufficient to keep the reaction mixture in a liquid state. In general, the pressure is advantageously from 0.1 to 10 MPa.

  The molar ratio of propylene / organic peroxide fed to the epoxidation reactor is preferably 2/1 to 50/1. If the ratio is less than the range, the reaction rate is lowered and the efficiency is poor. On the other hand, if the ratio is more than the range, it is separated from the epoxidation reaction solution to recycle excess unreacted propylene.・ A large amount of energy is required in the recovery process.

  The liquid linear velocity of the reaction liquid (mixture) in the fixed bed continuous method of the present invention varies depending on the composition of the mixture and the particle size of the solid catalyst, but is generally preferably 0.1 to 3 cm / sec. If the liquid line speed falls below that range, drift may occur in the solid catalyst layer in the reactor, while if it exceeds this range, the pressure loss of the solid catalyst layer may increase.

  Unreacted propylene contained in the mixed solution after the epoxidation reaction is separated and recovered and recycled to the epoxidation reactor. Distillation can be used as a method for separating and recovering unreacted propylene. Distillation usually uses conditions where propylene is easily vaporized from the reaction solution. The distillation conditions vary depending on the temperature and composition of the reaction solution supplied to the distillation step, but usually the pressure is 0 to 5 MPa in gauge pressure, preferably 0 to 3 MPa, the top temperature is −50 to 150 ° C., The tower bottom temperature is 50 to 200 ° C, preferably 80 to 200 ° C. Moreover, you may use the method of distilling propylene in steps using a some distillation column.

  The unreacted propylene separated and recovered in this way can be mixed with newly supplied propylene and supplied to the epoxidation reactor.

  However, according to the study by the present inventors, when the propylene supplied to the epoxidation reactor contains unreacted propylene after the epoxidation reaction, the pressure loss of the solid catalyst layer of the epoxidation reactor The problem of increasing. Further, the organic peroxide supplied to the epoxidation reactor is in contact with an aqueous solution of a compound containing an alkali metal, and the propylene supplied to the epoxidation reactor is an unreacted propylene after the epoxidation reaction. When it was contained, there was a problem that the increase in pressure loss of the solid catalyst layer of the epoxidation reactor was particularly remarkable.

  In this invention, the said subject was able to be solved by performing the following pre-processing process to propylene.

  The propylene pretreatment step is a step of treating at least a part of propylene supplied to the epoxidation reactor, and is a step of removing oxygen-containing organic compounds contained in propylene.

  Examples of the oxygen-containing organic compound include formaldehyde, acetaldehyde, formic acid, methanol and the like.

  Oxygen-containing organic compounds are often generated in the epoxidation reactor. The oxygenated organic compound generated in the epoxidation reactor is contained in unreacted propylene separated and recovered from the mixed solution after the epoxidation reaction, and as the propylene is recycled and supplied to the epoxidation reactor, Supplied into the epoxidation reactor.

  Examples of the method for removing the oxygen-containing organic compound contained in propylene include a method of removing by washing with water, a method of removing by distillation, and / or a method of removing with an adsorbent. Among these, the method of washing propylene with water is preferable because the oxygen-containing organic compound contained in propylene can be efficiently removed. Specific examples of washing propylene with water are as follows.

  The propylene supplied to the epoxidation reactor is usually a mixture of unreacted propylene separated and recovered from the mixed solution after the epoxidation reaction and newly supplied propylene. Examples of the method for washing propylene with water include a method for washing gaseous propylene with water and a method for bringing liquid propylene into contact with water. In consideration of the fact that propylene supplied to the epoxidation reactor is usually in a liquid state, contact efficiency, volume necessary for contact, and the like, a method of bringing liquid propylene into contact with water is preferable. Liquid propylene is washed by contacting part or all of it with water before being fed to the epoxidation reactor. As a contact method with water, a method of simply cutting water into the pipe to mix and contact in the pipe, or a method of increasing the contact efficiency with a mixer or the like can be used. As an example of the mixer, a stirrer / mixer comprising a stirrer and a container can be mentioned. However, if the contact efficiency is sufficient, a pipe scale such as a static mixer can be used. As a contact condition, any condition may be used as long as it is sufficiently washed. Preferred examples include a propylene / water weight ratio of 0.1 to 200, a contact temperature of 4 to 120 ° C., and a contact time. 1 to 1800 seconds (excluding standing and separation time). Propylene mixed and contacted with water is separated into an oil phase and an aqueous phase by standing. As preferable conditions for standing and separation, the standing and separating time can be 1 to 300 minutes, and the temperature can be 4 to 120 ° C. The concentration of the oxygen-containing organic compound in propylene after washing, standing, and separation is preferably 200 ppm by weight or less as the concentration of each component. Washing, standing, and separation conditions are selected so that such propylene is obtained. Since the separated aqueous phase contains an oxygen-containing organic compound, it is discarded out of the system or used in other processes if possible. Also, some of them may be recycled and used again for washing propylene. The separated oil phase may be supplied to the epoxidation reactor as it is, but the remaining water lowers the yield of the epoxidation reaction and also acts as a catalyst poison. Therefore, it is preferable to remove as much as possible. Examples of the method for removing water include a method for removing using a separation membrane such as a coalescer, a method for consuming and removing by a reaction, a method for removing by adsorption with an adsorbent, a method for removing by distillation, and the like. By supplying the pretreated propylene as described above to the epoxidation reactor, an increase in pressure loss of the solid catalyst layer can be suppressed.

  As described above, according to the present invention, propylene oxide can be efficiently produced from an organic peroxide and propylene.

The following examples illustrate the invention.
Example 1
The Ti-containing silicon oxide catalyst prepared according to Example 1 of JP-A No. 2004-195379 was sieved to a particle size of 0.25 to 0.5 mm and packed in a SUS fixed bed flow reactor. A solution containing 25% by weight cumene hydroperoxide and propylene (formaldehyde concentration less than 10 ppm by weight) obtained in the following propylene pretreatment step are continuously fed at a weight ratio of 1: 1 and a liquid line speed of 2 cm / sec. Then, the epoxidation reaction was performed, and at the same time, the pressure change at the inlet and outlet of the reactor was observed. The reaction temperature was 80 ° C., and the reaction pressure was 4.2 MPa as a gauge pressure on the outlet side of the reactor. FIG. 1 shows the change over time in the pressure difference between the inlet and outlet of the reactor corresponding to the pressure loss of the solid catalyst layer in this experiment.
The solution containing 25% by weight cumene hydroperoxide used above was prepared as follows.
The oxidation reaction solution obtained by air oxidation of cumene is brought into contact with an aqueous solution of a compound containing 2% by weight of alkali metal, then separated into an oil phase / water phase, and then the obtained oil phase is brought into contact with water. Then, the oil phase / water phase was separated, and a trace amount of water remaining in the obtained oil phase was removed by distillation to obtain a solution containing 25 wt% cumene hydroperoxide.

Propylene pretreatment step Propylene (containing 50 ppm by weight of formaldehyde) 300 g / hr and 30 g / hr of water separated and recovered from the mixed solution after the epoxidation reaction, each with a static mixer (contact time: about 5 seconds) The propylene was washed with water. At this time, the contact temperature was room temperature, the system pressure was 2 MPa, liquid propylene and water were brought into contact with each other, washed with water, and then allowed to stand to separate into propylene and an aqueous phase. The formaldehyde concentration in the obtained propylene was less than 10 ppm by weight.

3 is a graph showing the transition (change over time) in the pressure difference between the inlet and outlet of the reactor corresponding to the pressure loss of the solid catalyst layer in Example 1. FIG.

Claims (5)

A method for producing propylene oxide in which an organic peroxide and propylene are supplied to an epoxidation reactor filled with a solid catalyst and propylene oxide is continuously produced by an epoxidation reaction, the propylene having the following propylene pretreatment step Production method of oxide.
Propylene pretreatment step: a step of washing at least a part of propylene supplied to the epoxidation reactor with water , and removing an oxygen-containing organic compound contained in propylene 2. The production method according to claim 1, wherein the propylene supplied to the propylene pretreatment step contains unreacted propylene recovered from the mixed solution after the epoxidation reaction. The process according to claim 1, wherein the solid catalyst is a titanium-containing silicon oxide catalyst. The production method according to claim 1, wherein the organic peroxide supplied to the epoxidation reactor is one obtained by removing the organic acid. The process according to claim 1, wherein the liquid linear velocity of the reaction liquid in the epoxidation reactor is 0.1 to 3 cm / sec.

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