PL213886B1 - Method for decomposition of cyclohexyl hydroperoxide in the process of cyclohexane oxidation - Google Patents

Description

The subject of the invention is a method of decomposing cyclohexyl hydroperoxide contained in the cyclohexane oxidation reaction product.

The industrial process of cyclohexane oxidation is carried out to obtain a mixture of cyclohexanol and cyclohexanone, from which cyclohexanone is obtained, an intermediate for the production of caprolactam, which is a monomer for the production of nylon 6 type polyamide fibers. The oxidation process is carried out in the liquid phase with oxygen-containing gases at a temperature of 140- 180 ° C, in a multistage reaction system in the presence of a catalyst consisting of a metal salt soluble in the reaction liquid with a variable valency, for example a Co, Cr, Fe, Ni, Mn salt or mixtures thereof. The products obtained as a result of the cyclohexane oxidation reaction - cyclohexanol and cyclohexanone - are the compounds with the lowest oxidation state and in the reaction medium they are easily further reacted to compounds with a higher oxidation state, mainly mono- and dicarboxylic acids, alcohols, aldehydes, as well as carbon monoxide and carbon dioxide. . The oxidation process is carried out at low degrees of cyclohexane conversion, amounting to 3-5%, so as to reduce the rate of side reactions. However, even with such low conversions, the selectivity of cyclohexane oxidation is 80-85%, which means that 15-20% of cyclohexane is converted to waste compounds, often of little use and burdensome for disposal. As a result of the reaction, more than a hundred compounds are formed, contained in the crude cyclohexane oxidation product in very different amounts.

Oxidation of cyclohexane in the liquid phase always leads to the formation of cyclohexyl hydroperoxide in the first stage, which undergoes thermal or catalytic decomposition to the desired products, i.e. cyclohexanol and cyclohexanone, but is more resistant to further oxidation than its decomposition products. Part of the cyclohexylhydroperoxide formed in the process is decomposed in the reaction system and the remainder is discharged in the crude cyclohexane oxidation product and decomposed outside the reaction system in a liquid not in contact with oxygen-containing gases.

The Polish cyclohexane oxidation process known as CYCLOPOL is carried out in a multi-stage horizontal reactor described e.g. in the patent description PL 64449. According to the patent description PL 71466, the crude product from the reactor, after expansion, is washed with water to remove water-soluble reaction products, which could form deposits in other devices. The reaction product remaining after washing with water is directed to a distillation column to distill off unreacted cyclohexane. A small part of cyclohexane is discharged from this column with cubic liquid and then recycled to it, after separation from the reaction products in further operations. In the distillation column, most of the cyclohexylhydroperoxide withdrawn from the reaction system is decomposed in the crude cyclohexane oxidation product. A small amount of cyclohexylhydroperoxide undecomposed in the column is discharged with the cubic liquid and decomposed in further steps.

The amount of cyclohexyl hydroperoxide in the crude product of cyclohexane oxidation depends on the conditions of the oxidation process and its content may be from several tenths to more than two percent by weight. After depressurization of the crude product and evaporation of a part of cyclohexane, the concentration of cyclohexyl hydroperoxide is about twofold increase.

One way to improve the selectivity of the cyclohexane oxidation process is the catalytic decomposition of cyclohexyl hydroperoxide outside the reaction system under milder conditions, i.e. at a lower temperature and without contact with oxygen-containing gases. For the catalytic decomposition of cyclohexylhydroperoxide, the same catalysts are used as in the cyclohexane oxidation process, ie single metal salts of variable valency or their mixtures.

An example of catalytic decomposition of cyclohexyl hydroperoxide outside the reaction system of the process is the solution presented in the patent specification PL 152388, in which the catalyst for decomposition of cyclohexyl hydroperoxide is introduced together with the crude oxidation product into a separate non-aerated apparatus or into a column in which unreacted cyclohexane is distilled off.

It turned out that the improvement of the selectivity of decomposition of cyclohexyl hydroperoxide in the cyclohexane distillation column is achieved by introducing to this column a catalyst, which is a salt or a mixture of organic variable metal salts, below the point of introducing the product from the cyclohexane oxidation reactor to the column, after depressurization and washing with water.

PL 213 886 B1

The method according to the invention produces a product in the cyclohexane oxidation plant which is a mixture with a more advantageous composition than in the case of the known methods, i.e. with a greater total content of target products: cyclohexanone and cyclohexanol, and with a higher content of cyclohexane, which is recycled to the oxidation process.

The method of decomposition of cyclohexyl hydroperoxide in the oxidation of cyclohexane in the liquid phase with oxygen-containing gases at a temperature of 140-180 ° C, in which the crude product of cyclohexane oxidation, containing cyclohexyl hydroperoxide, is expanded and washed with water, then the oxidation product to which it is added the cyclohexyl hydroperoxide decomposition catalyst is fed to the unreacted cyclohexane stripper, according to the invention the cyclohexyl hydroperoxide decomposition catalyst is fed to the unreacted cyclohexane stripper downstream of the oxidation product feed point.

Preferably, the decomposition catalyst is fed to the plate-shaped unreacted cyclohexane stripper at a height of 2-3 plates below the plate onto which the cyclohexane oxidation product is introduced.

Preferably, the cyclohexylhydroperoxide decomposition catalyst is fed to the unreacted cyclohexane stripping column in a mixture with its recycle unreacted cyclohexane contained in the vessel liquid from the column.

Preferably, the cyclohexylhydroperoxide decomposition catalyst is fed to the stripper of unreacted cyclohexane in admixture with fresh cyclohexane to be oxidized.

Preferably, the cyclohexylhydroperoxide decomposition catalyst is introduced to the unreacted cyclohexane stripping column at multiple points below the point of introduction of the cyclohexane oxidation product, in a manner ensuring that the catalyst is evenly dispersed in the liquid on the tray.

The solution according to the invention does not require the introduction of new apparatuses and does not increase the energy consumption in the reaction node. In addition, the use of the solution according to the invention reduces energy consumption in the cyclohexanol dehydrogenation plant due to the increase in the content of cyclohexanone in the product of the cyclohexane oxidation plant, i.e. in the mixture of cyclohexanone and cyclohexanol. It also makes it possible to increase the load on the cyclohexanol dehydrogenation reactors without the need for additional expenditure.

The process of the invention is illustrated in the Examples and comparative examples are provided to compare the result.

P r z k ł a d I

The cyclohexane oxidation process is carried out continuously in a multi-section industrial reactor with oxygen-containing gases in the presence of a catalyst. The crude product leaving the reactor is depressurized, washed with water, and directed to an unreacted cyclohexane stripper containing 22 hood plates. In the stream entering the column on the 16th plate (numbering of the plates from the top of the column) there is 2.1 wt.%. % of cyclohexanone, 3.8 wt.% % of cyclohexanol and 1.7 wt.%. cyclohexyl hydroperoxide. A solution of the cyclohexylhydroperoxide decomposition catalyst, which is cobalt ethyl hexanoate, in an amount corresponding to a metal concentration of 0.2 ppm in relation to the amount of reactor product directed to the column, is introduced to the column on the tray located two trays below the feed point of the reactor product.

The end product of the cyclohexane oxidation plant, i.e. a mixture of cyclohexanone and cyclohexanol, contains 38.5% by weight. % of cyclohexanone, 58.8 wt. % of cyclohexanol and 2.7 wt.%. other relationships.

P r z x l a d II

The cyclohexane oxidation process is carried out continuously in a multi-section industrial reactor with oxygen-containing gases in the presence of a catalyst. The crude product leaving the reactor is depressurized, washed with water, and directed to an unreacted cyclohexane stripper containing 22 hood plates. In the stream entering the column, the 16th plate (plate numbering from the top of the column) is 2.0 wt.%. % of cyclohexanone, 3.9 wt.% % of cyclohexanol and 1.8 wt.%. cyclohexyl hydroperoxide. A solution of the catalyst for decomposition of cyclohexyl hydroperoxide, which is a mixture of cobalt ethyl hexanoate and iron ethyl hexanoate in a 1: 1 ratio by weight, in an amount corresponding to a total metal concentration of 0.2 ppm, is introduced into the column, located two shelves below the place of feeding the product from the reactor, relative to the amount of product from the reactor going to the column.

PL 213 886 B1

The end product of the cyclohexane oxidation plant, i.e. a mixture of cyclohexanone and cyclohexanol, contains 40.3 wt.%. % of cyclohexanone, 57.2 wt. % of cyclohexanol and 2.5 wt.%. other relationships.

Comparative example I

The process of oxidizing cyclohexane with oxygen-containing gases in the presence of a catalyst was carried out continuously in an apparatus as in Example 1, illustrating the method of the invention. The composition of the stream entering the unreacted cyclohexane stripper was the same as in Example 1. A catalyst solution of the same composition and in the same amount as in Example 1 was directed to this stream, before entering the column.

In the mixture of cyclohexanone and cyclohexanol, ie in the final product, 35.8 wt.% Was obtained. % of cyclohexanone, 61.0 wt. % of cyclohexanol and 3.2 wt. other relationships.

Comparative example II

The process of oxidizing cyclohexane with oxygen-containing gases in the presence of a catalyst was carried out continuously in an apparatus as in Example 1, illustrating the process of the invention. The composition of the stream entering the unreacted cyclohexane stripper was the same as in Example 2. Into this stream, before entering the column, a catalyst solution of the same composition and in the same amount as in Example 2 was directed.

In the mixture of cyclohexanone and cyclohexanol, i.e. in the final product of the oxidation plant, 37.5 wt.% Was obtained. % of cyclohexanone, 59.4 wt. % of cyclohexanol and 3.1 wt.%. other relationships.

Claims (5)

The method of decomposition of cyclohexyl hydroperoxide in the process of cyclohexane oxidation in the liquid phase with oxygen-containing gases at a temperature of 140-180 ° C, in which the crude product of cyclohexane oxidation, containing cyclohexyl hydroperoxide, is expanded and washed with water, and then the oxidation product to the cyclohexylhydroperoxide decomposition catalyst is added to the unreacted cyclohexane stripper, characterized in that the cyclohexylhydroperoxide decomposition catalyst is fed to the unreacted cyclohexane stripper downstream of the oxidation product introduction point. A method according to claim 1, characterized in that the decomposition catalyst is introduced into a plate stripper of unreacted cyclohexane at a height of 2 or 3 plates below the plate on which the cyclohexane oxidation product is introduced. 3. The method according to p. The process of claim 1, wherein the cyclohexylhydroperoxide decomposition catalyst is fed to the unreacted cyclohexane stripper in a mixture with its recycle unreacted cyclohexane contained in the column fluid. 4. The method according to p. The process of claim 1, wherein the cyclohexyl hydroperoxide decomposition catalyst is fed to the stripper of unreacted cyclohexane in a mixture with fresh, oxidized cyclohexane. 5. The method according to p. The process of claim 1, wherein the cyclohexyl hydroperoxide decomposition catalyst is introduced into the unreacted cyclohexane stripper multiple points downstream of the cyclohexane oxidation product introduction point in a manner ensuring that the catalyst is uniformly dispersed in the liquid on the tray.