CS269535B1 - A method for oxidizing cyclohexane - Google Patents

Abstract

The method solves the problem of removing the water of reaction formed during the oxidation of cyclohexane to cyclohexanol and cyclohexanone. Operating the oxidation reactor according to the solution reduces the amount of water in the reaction mixture and thus the probability of its clogging. The procedure according to this solution increases the selectivity of the oxidation process.

Description

The invention relates to a method for oxidizing cyclohexane to cyclohexanol and cyclohexanone in the presence of an oxidation catalyst.

The oxidation of cyclohexane to cyclohexanone and cyclohexanol with oxygen from the air in the presence of a catalyst at a temperature of 100 to 200 °C and a pressure of 0.5 to 1.5 MPa takes place in a cylindrical, horizontal six-chamber reactor, with the individual chambers of the reactor representing oxidation stages. The catalyst - cobalt naphthenate and the oxidizing gas - air, which simultaneously mixes the reaction mixture, are fed to the 1st to 5th oxidation stages. The oxidation of cyclohexane is an exothermic reaction with a significant thermal effect, with the excess reaction heat evaporating part of the reaction solution. The vapors, together with the used air, pass through a series of cooling and separation devices, where they are freed from condensable vapors. The non-condensable residue is discharged into the atmosphere. A significant portion of the reaction water, which adversely affects the oxidation of cyclohexane to cyclohexanol and cyclohexanone, is also discharged with the off-gas from the reactor. The disadvantage of the described method of cyclohexane oxidation is the limited amount of air supplied to the individual oxidation stages, which depends on the degree of cyclohexane conversion. U.S. patent 3,530,185 from 1970 describes a vertical multi-section reactor, where the liquid contacts the gas countercurrently. The reactor is divided into four zones: oxidation, concentration, heating and stripping-cooling. Air for oxidation is supplied to the 1st to 10th floors, the 11th to 14th floors serve as the heating zone of the reactor. Floors 15 to 18 determine the stripping-cooling zone of the reactor. An inert gas is supplied below the 18th floor of the reactor. The advantage of the described solution is the continuous dilution of the oxidation gas supplied to the higher floors with the used air from the lower floors. The disadvantage is the method of cooling the reaction mixture in the reactor itself.

U.S. patent 2,557,281 recommends continuous distillation of the water formed during oxidation to enable the separation of isolated oxidation products and subsequent extraction of acids with water. However, even with this technology, more than 20% of the reacted cyclohexane is converted into undesirable by-products. According to NSR patent 1,047,778, the formation of high-molecular compounds during oxidation, which deposit on the walls of the reactor and slow down the reaction, can be prevented by washing the cyclohexane with acidic water before oxidation, but this method does not achieve an increase in the yield of cyclohexanone and cyclohexanol.

The essence of the method of oxidation of cyclohexane to cyclohexanol and cyclohexanone according to the present invention is the oxidation of cyclohexane in one to nine oxidation stages of a horizontal oxidation reactor at a temperature of 100 to 200 ° C and a pressure of 0.5 and 1.5 MPa. In this case, for the oxidation of cyclohexane, preferably in the fourth and fifth oxidation stages, a mixture of air and inert gas is used, preferably nitrogen in the ratio air:nitrogen = 1:0.001, preferably 1:0.15. The amount of inert gas fed to the individual oxidation stages increases in the direction of increasing conversion and proportionally to the amount of water in the reaction product in the ratio mass % water:Nm ³ /h inert = 1; 100 to 100,000.

The advantage of the method of operating the oxidation reactor according to the present invention is the possibility of continuous removal of reaction water in individual oxidation stages independently of the amount of oxidizing gas. By reducing the amount of water in the oxidation of cyclohexane to cyclohexanone and cyclohexanol, the probability of clogging of the oxidation reactor is reduced, and increasing the amount of inert depending on the degree of conversion and the amount of reaction water has a positive effect on the selectivity of the oxidation of cyclohexane to cyclohexanone and cyclohexanone.

The way of operating a horizontal oxidation reactor is obvious from Example 1

The current state of cyclohexane oxidation to cyclohexanone and cyclohexanol takes place in a six-chamber horizontal cylindrical reactor. The first chamber of the reactor is fed with 600 m ³ /h of cyclohexane, 5600 Nm ³ /h of air and 0.060 m ³ /h of catalyst, the second, third and fourth chambers are fed with 2900 m ³ /h of air and 0.005 m ³ /h of catalyst. The fifth chamber of the reactor is fed with 2500 Nm ³ /h of air and 0.005 m ³ /h of catalyst. The sixth chamber is fed with 0.010 m ³ /h of catalyst, no air is fed. The reaction proceeds

CS 269535 B1 at a temperature of 160 °C and a pressure of 0.9 MPa with 3.5% conversion and 80% selectivity to cyclohexanone and cyclohexanol. water content in individual chambers;

1st chamber 0.0318% by mass*, 2. chamber 0.0481 wt%, 3rd chamber 0.0665 wt%, 4th chamber 0.0726 wt%, 5th chamber 0.082 wt%, and in the 6th chamber 0.0686 wt%. .

example 2

The process described in Example 1, where 500 Nm ³ /h of nitrogen is fed into the fourth and fifth chambers of the oxidation reactor, the content of reaction water in the fourth and fifth reaction chambers drops to 0.05% by weight.

Example 3: The process described in Example 1, whereby 100 ^Nm3 /h is fed to the first chamber of the oxidation reactor, 200 ^Nm3 /h to the second chamber, 300 ^Nm3 /h to the third, 400 ^Nm3 /h to the fourth, 500 Nm3/h to the fifth and 300 Nm3/h to the sixth of nitrogen. The amount of water produced is reduced and the selectivity of oxidation is increased by approximately 2%.

Claims (2)

SUBJECT OF THE INVENTION 1. A method for oxidizing cyclohexane to cyclohexanol and cyclohexanone in one to nine oxidation stages at a temperature of 100 to 200 °C and a pressure of 0.5 to 1.5 MPa, characterized in that for the oxidation of cyclohexane, preferably in the fourth and fifth oxidation stages, air is used in a mixture with an inert gas, preferably with nitrogen in an air:nitrogen ratio equal to 1:0.001 to 1, preferably 1:0.15. 2. The method according to item 1, characterized in that the amount of inert gas in a mixture with air fed to the individual oxidation stages increases in the direction of increasing conversion and proportionally to the amount of water in the reaction solution in a ratio by weight of water: Nm ³ /h of inert equal to 1: 100 to 100,000.