CS256584B1 - The method of selectively oxidizing cyclohexane to cyclohexane and cyclohexanol - Google Patents

Abstract

The subject of the solution is a method of selective oxidation of cyclohexane to a mixture of cyclohexanone and cyclohexanol in the presence of catalysts, preferably cobalt and/or chromium compounds in a single or multi-stage reaction system, which is characterized by the fact that cyclohexane is dosed into the reaction system in a volume ratio of cyclohexane to the reaction volume of the reactor in the range of 0.667 to 1.8 h.-1. The process achieves an increase in the selectivity of the oxidation of cyclohexane to cyclohexanone and cyclohexanol by 2.5 to 4.5 »/o.

Description

The invention provides a process for the selective oxidation of cyclohexane to cyclohexanone and cyclohexanol in the liquid phase by oxygen or oxygen-containing gas.

The decisive element in the production of cyclohexanone or a mixture of cyclohexanone and cyclohexanol is the oxidation of cyclohexane. The selectivity of this reaction is influenced by several reaction parameters, of which the reaction temperature, the catalyst concentration, the ratio of the quantities of cyclohexane to oxygen dosed, the design of the reaction apparatus and the reaction time are significant.

Liquid phase oxidation of cyclohexane produces a significant amount of oxidation by-products in addition to the desired products. Although a number of processes for their economic use as secondary petrochemical raw materials are known, they currently greatly deteriorate the economics of production depending on the amount produced.

A multi-stage cyclohexane oxidation process is disclosed in which an increase in selectivity is achieved by feeding a certain amount of cyclohexane to each reaction stage. Cyclohexane and oxygen-containing gas are added to each stage in a constant volume ratio, the respective amount of cyclohexane being added being proportional to the heat released and reducing the amount of heat dissipated by cyclohexane evaporation (USSR Pat. 503,846). A similar process in which a mixture of cyclohexanone and cyclohexanol is obtained such that a portion of cyclohexane is dosed only to stages 2 and 3 in an amount of 5-20% of the amount of cyclohexane fed to stage 1, the temperature in each stage being constant or a downward trend in the flow direction of the reaction mixture. By using the process, the formation of organic acids and by-products is reduced (USSR Pat. 675,759). The cyclohexane oxidation process in three or more stages utilizes the addition of oxygen or oxygen-containing gas to each stage in an amount such that all of the oxygen has reacted or is dosed at a corresponding oxygen concentration of at least about 2% by volume. (BE patent 827,835).

Although the above inventions are characterized by an increase in selectivity, the known literature data as well as the production process of large capacity units indicate further possibilities for increasing the selectivity of cyclohexane oxidation and hence more economical use of raw materials and energies.

In a study of cyclohexane oxidation, it was found that the volumetric flow rate of cyclohexane to the reaction object significantly influenced the selectivity of the reaction,

The object of the present invention is a process for the selective oxidation of cyclohexane to cyclohexanone and cyclohexanol in liquid phase by oxygen or oxygen-containing gas in one or more reaction stages at temperatures of 130-220 ° C and pressures of 0.5-1.5 MPa in the presence of a catalyst, most commonly cobalt compounds. and / or chromium and / or lithium, characterized in that the cyclohexane to the reaction system consisting of the reactor and the scrubbers is metered in such an amount that the ratio of the cyclohexane volume flow rate to the effective reaction volume of the reactor is 0.667 to

1.8 h ^-1 . Moreover, the reaction parameters are maintained at values that guarantee efficient oxygen utilization and safe reactor operation. Unreacted cyclohexane is separated from the resulting reaction mixture, which is returned to the oxidation process together with fresh cyclohexane, and the resulting mixture is further worked up according to known methods.

The process of the present invention achieves a significant increase in the selectivity of cyclohexane oxidation to cyclohexanone and cyclohexanol, improving the quality of the final product due to lower byproduct formation. The process positively affects the further process of separating cyclohexanone and cyclohexanol from the reaction mixture. Its use will significantly reduce specific consumption of raw materials and energy. The advantage is also the simplicity of implementation and control of the oxidation process with the possibility of application in different types of reactors. The advantages of this procedure are illustrated by the following examples:

Example 1 (comparative)

Air and cyclohexane with a catalyst content of approx. 160 to 164 ° C and a pressure of 0.9 MPa are charged to the reaction system consisting of the reactor and the scrubbers.

2.5 ppm of cobalt in an amount such that the ratio of the volume flow rate of cyclohexane to the effective reaction volume of the reactor was 2.58 hours. ¹ . Under these conditions, a selectivity of 82 to 84% is achieved.

Example 2

Air and cyclohexane are metered into the reaction system and under the operating conditions of Example 1 in such an amount that the ratio of the cyclohexane volume flow to the effective reaction volume of the reactor is

1.6 h ^-1 . Under these conditions, a selectivity of 86-87.5% is achieved.

Example 3

Air and cyclohexane are metered in to the reaction system and under the conditions as in Example 1 in such an amount that the ratio of the cyclohexane volume flow to the effective reactor volume is 1.75 hours. ^-1 . Under these conditions, the cyclohexane oxidation process on the cyclohexanone and cyclohexanol takes place with a selectivity of 87-88%.

SUBJECT

Claims (1)

256584 SUBJECT Selective oxidation of cyclohexanone cyclohexanone and cyclohexanol in a liquid phase with oxygen or oxygen-containing gas in one or more reaction stages at temperatures of 130 to 220 ° C and pressures of 0.5 to 1.5 MPa in the presence of a catalyst, preferably cobalt and / or chromium and / or lithium compounds, characterized in that the cyclohexane is fed into the reaction system in a cyclohexane volume ratio to an effective reaction volume ranging from 0.667 to 1.8 hours. preferably 1.3 to 1.7 hours. "1.