CS208772B2 - Method of removing the acids,esters from the liquid mixtures of the organic substances,released by the oxidation of the cyclohehexan and containing the cyclohexanone and/or cyclehoxanoee - Google Patents

Description

(54) A process for the removal of caustic and esters from liquid mixtures of organic substances which are lost during cyclohexane oxidation and which contain cyclohexanone and / or cyclohexanol

The invention relates to a process for the removal of acids and esters from liquid mixtures of organic substances which are lost during the oxidation of cyclohexane in the liquid phase by oxygen gases and containing cyclohexanone and / or cyclohexanol. In addition to cyclohexanone and / or cyclohexanol, said mixtures also contain unreacted cyclohexane, esters, acids and other oxygen-containing substances.

According to some known methods, acids are first removed from the crude cyclohexane oxidation product by treatment with alkali. In other techniques, excess cyclohexane is first distilled off from the crude product.

There are many modifications of the process for further processing of liquids obtained by said process, which usually contain up to 20% cyclohexane. They are mostly processed without prior distillation. In other methods, all nonvolatile by-products are first separated by evaporation of the desired products together with other volatile compounds.

Evaporation is normally carried out without steam or as steam distillation. The next step of working up the reaction mixtures is to remove the liquid acids and cyclohexyl esters of these acids. Said acids and their esters have an adverse effect on the quality of cyclohexanone. Either the crude product or the distillates obtained by one or both of these processes are subjected to this treatment step.

Acids and esters are removed chemically. Other physicochemical processes, such as distillation, extraction or crystallization, are unusable or uneconomical for removal.

A commonly used process for removing acids and esters from mixtures containing cyclohexanone and / or cyclohexanol is to treat the mixture at temperatures of 60-90 ° C with aqueous sodium hydroxide solution. The process is carried out in the liquid phase, with aqueous sodium hydroxide solutions being vigorously mixed with the organic liquid. Under these conditions, the saponification of the esters results in the sodium salts of the respective acids.

The saponification process has a number of drawbacks in the form used so far, the most important of which is that under the conditions used, side reactions occur, in particular the condensation of cyclohexanone to form cyclohexylidenecyclohexanone. The rate of the condensation reaction increases rapidly with increasing sodium hydroxide concentration. If a lower concentration of sodium hydroxide is used, the condensation is suppressed, but the saponification does not take place at a sufficient rate and the product obtained does not meet the requirements.

The prolongation of the reaction time leads to a decrease in the ester content, but on the other hand the amount of cyclohexylidene hexanone produced by the condensation reaction also increases.

In general, the saponification of cyclohexyl esters according to the described process causes great difficulties, in particular by the relatively slow diffusion in both. immiscible liquids.

Another drawback of the saponification processes used hitherto to remove esters from the liquid cyclohexane oxidation product is the difficulty of removing alkali from the saponification product. Generally, alkali is removed by extraction with water, but this procedure does not provide complete alkali removal.

As a result, residual amounts of alkali are generated into other processing equipment, where they cause a cyclohexanone condensation reaction and thus contribute to further losses of this compound. To avoid this, further distillation can be used, but this greatly increases operating costs.

A two-step process for the removal of esters and acids from the cyclohexane oxidation reaction products of brit. U.S. Pat. No. 890,137, in which, in the first step, an aqueous solution of alkali metal carbonates is used as reagents, and in the second stage an aqueous solution of hydroxides of these metals. The saponification of the esters in the presence of only the alkali metal carbonate is incomplete, and to the extent that the quality of the end product is insufficient, as determined by the authors of the process. Therefore, a two-step method is used. However, this is a complex and two-step process carried out in a complex reaction apparatus. In addition, the process has all the other drawbacks and inconveniences of the prior art processes for carrying out this liquid phase operation.

A considerably improved and simpler method is that described in PLR 70 457, wherein the removal of acids and esters from mixtures containing cyclohexanone and / or cyclohexanol is carried out in a paired phase. In this process, an aqueous sodium hydroxide solution is contacted with the vapors of the thickened cyclohexane oxidation product, most commonly in countercurrent.

The method makes it possible to simplify the apparatus and reduce, but not completely prevent, losses of products due to the condensation reaction, as well as less sodium hydroxide consumption, compared to the above methods. However, there are also drawbacks associated with the use of alkali metal hydroxides. The saponification reaction is carried out at a temperature of about 160 ° C in the presence of a 5% aqueous sodium hydroxide solution. Alkaline solutions used for. These conditions have corrosive properties, which makes it difficult to maintain the operability of the equipment.

A significant drawback of the process is also associated with the fact that in the event of operating faults, the penetration of sodium hydroxide solution into other equipment, particularly in distillation column boilers, causes condensation of the product, which in extreme cases necessitates stopping the operation to clean the equipment.

Surprisingly, it has been found that, despite the general claim that an appropriate end product cannot be made using alkali metal carbonate solutions as a saponification agent, the product of the desired properties of the invention can be obtained by contacting the vapors of a mixture of cyclohexanone organic compounds with 1 to 20%, in particular 8 to 10 ·% aqueous solution and / or acidic sodium and / or potassium carbonate at temperatures of 100 to 200 ° C, in particular 155 to 165 ° C, and under a pressure of from 1 to 10 bar, especially 0.6 MPa.

There is no data in the literature on saponification of an ester with alkali metal carbonate solutions under the above conditions.

In the process of the invention, the amount of by-products produced by the undesired condensation reaction is three times less than in the process of Pat. PLR 70,457 and about the same as the amount of thermal condensation by-products. In addition, the operational difficulties and hazards caused by the use of alkali metal hydroxide solutions are reduced. In particular, alkali corrosion as well as condensation caused by the penetration of the saponification agent into other devices is reduced.

In many cases, the alkaline waste water resulting from the saponification process is incinerated in the furnace and aqueous solutions of sodium and / or potassium carbonate are obtained from the combustion product, the use of which is practically impossible. The process according to the invention allows a very favorable closed circulation of the saponification agent by returning said solutions to the process. The solutions often contain a certain amount, about a few percent of sodium and / or potassium sulfate. However, it has been found that the presence of these compounds does not adversely affect the ester saponification reaction.

According to the described process, the cost of the saponification agent used in the process is also reduced. The aqueous solutions present in the cyclohexane oxidizer can be used to prepare carbonate solutions. This recovers the organic compounds contained in the solutions and reduces the amount of waste water.

To determine the purity of the product, fractionation distillation of the samples saponified by both the process of the invention and the pat. PLR 70 457. In both cases a cyclohexanone fraction of the same satisfactory purity was obtained. The amount of cyclohexyl acetate was taken as a measure of cyclohexanone quality. Thus, the introduction of carbonate solutions into the process allows the above advantages to be achieved without adversely affecting the purity of the end product.

The saponification of the esters according to the process of the invention can be carried out in known types

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control, for example in a tray-type or packed-column type apparatus, but most preferably it is operated by pneumatic mixing (gas bubbling) in which the vapors of the compounds are distributed in the liquid by a set of suitable nozzles.

The following examples illustrate the process of the invention and the results obtained, but do not limit the process to the process parameters set forth in these examples.

Example 1. A 115 mm diameter pressure vessel was charged with 5 kg of a 7.4% aqueous sodium carbonate solution, and vapor of the starting mixture was passed through the aqueous layer at 160 ° C under a pressure of 0.65 MPa. Couples consist of

50.0 wt.%, Water, 28.0 wt.%, Cyclohexanol, 14.0 wt.%, Cyclohexanone, 2.8 wt. cyclohexane,

1.7% by weight of esters, calculated as cyclohexyl formate and

3.5% acids and unspecified compounds.

The flow rate is about 3 kg per hour. The vapors leaving the pressure vessel are condensed and the condensate is separated into two layers, aqueous and organic. Neither esters nor cyclohexanone are contained in the aqueous layer. The organic layer contains 400 ppm cyclohexyl acetate and below 50 ppm cyclohexylidenecyclohexanone. The organic layer was distilled in a laboratory distillation column to separate the cyclohexanone fraction. The distillation is carried out at a reflux of 20: 1 and at a pressure of 6.5 kPa. The cyclohexanone fraction contains about 100 ppm cyclohexyl acetate.

An analogous experiment was carried out with a 3.5% aqueous sodium hydroxide solution as the saponification agent and under the same process conditions as with the same starting product. The aqueous layer did not contain esters or cyclohexanone. The organic layer contained 400 ppm cyclohexyl acetate and 150 ppm cyclohexylidenecyclohexanone. The organic layer was distilled under the above conditions. The cyclohexanone fraction contained about 100 ppm cyclohexyl acetate.

The organic layer of the product saponified with sodium carbonate is washed twice with an equal amount of distilled water. Three equal 400 ml samples are taken from the product thus obtained. To the first sample, add 100 ml of distilled water, to the second 100 ml of a 7.4% sodium carbonate solution and to the third 100 ml of a 3.5% sodium hydroxide solution. Then all the samples were shaken and the aqueous layers were separated. Heat the organic layers in an oil bath to boil in a flask with an azeotropic extender for 10 hours. Cyclohexylidenecyclohexanone content is determined in samples taken after 5 and 10 hours.

The results of the analyzes are shown in the following table.

Heating time hours

Saponifying agent

Cyclohexylidenecyclohexanone content, ppm

0 Soap-free 50 5 ňovacího 900 10 reagents 1100 5 ' 7.4% solution 1100 10 sodium carbonate 1300 5 3.5% solution 2800 10 sodium hydroxide 3400

Example 2

Example 3

5 kg of a 7.4% solution of sodium bicarbonate are introduced into a 115 mm diameter pressure vessel and the aqueous saponification product vapors of the same composition as in Example 1 are passed through this aqueous layer at a temperature of 160 ° C and under a pressure of 0.65 MPa. 3 kg per hour. The vapors leaving the pressure vessel are condensed and the condensate is separated into two layers, aqueous and organic. The aqueous layer contains neither esters nor cyclohexylidene hexanone. The organic layer contained 500 ppm cyclohexyl acetate and below 50 ppm cyclohexylidenecyclohexanone.

5 kg of an aqueous solution containing 7.4% w / w sodium carbonate and 7.4% w / w sodium sulphate are introduced into a 115 mm diameter pressure vessel and the saponification product vapors of the same composition as in Example 1 are passed through this aqueous layer. , at a temperature of 160 ° C and under a pressure of 0.65 MPa at a rate of about 3 kg per hour. The vapors leaving the pressure vessel are condensed and the condensate is separated into two layers, aqueous and organic. The aqueous layer contains neither esters nor cyclohexylidene hexanone. The organic layer contains 400 ppm cyclohexyl acetate and below 50 ppm cyclohexylidene hexanone.

Example 4

A 115 mm diameter pressure vessel was charged with 5 kg of a 7.4% aqueous solution of sodium bicarbonate and passed through the aqueous layer to a vaponable product of the same composition as in Example 1 at 135 ° C and below. at a pressure of 0.35 MPa at a rate of about 3 kg per hour.

The vapors leaving the pressure vessel are condensed and the condensate is separated into two layers, aqueous and organic. The aqueous layer contains neither esters nor cyclohexylidene hexanone. The organic layer contains 600 ppm of cyclohexyl acetate. The distillate thus obtained is then passed through a layer of 4 kg of a 7.4% sodium bicarbonate solution under the same conditions. The vapors leaving the pressure vessel are condensed and separated into two layers, aqueous and organic. The aqueous layer contains neither esters nor cyclohexylidene hexanone; The organic layer contains 450 ppm of cyclohexyl acetate and below 50. ppm cyclohexylidene hexanone.

Example. 5

6 kg of a 8.9% aqueous potassium bicarbonate solution are introduced into a 115 mm diameter pressure vessel. and the saponification product vapors of the same composition as in Example 1 are passed through this aqueous layer at a temperature of 135 ° C and under a pressure of 0.35 MPa at a rate of about 3 kg per hour. The vapors leaving the pressure vessel are condensed and divided into two layers, aqueous and organic. The aqueous layer contains neither esters nor cyclo-hexylidene hexanone. The organic layer contains 500 ppm cyclohexyl acetate and below 50 ppm cyclohexylidenecyclohexanone,

Claims (3)

SUBJECT A method for removing acids and esters from. liquid mixtures of organic substances which are lost during the oxidation of cyclohexane and containing cyclohexanone and / or cyclohexanol, by alkaline saponification of the esters, characterized in that the vapors of the mixture are brought into contact. with 1 to 20 ° C, in particular 8 to 10 ° C, with an aqueous solution of carbonate and / or sodium and / or potassium carbonate at temperatures of 100 to 200 ° C, in particular 155 to 165 ° C, and under a pressure of 0 1 to 1 MPa, in particular 0.6 MPa. 2. The method according to claim 1, INVENTION that a saponification agent used is a solution of a mixture of carbonate and / or sodium and / or potassium carbonate, which is omitted in the cyclohexane oxidation. 3. A method according to claim 1 or 2, characterized in that the vapors of the mixture are contacted with aqueous solutions. containing, in addition to 1 to 20% by weight, in particular 8 to 10% by weight, of sodium and / or potassium carbonate and / or acidic carbonate, also 0.1 to 15% by weight, of sodium and / or potassium sulphate.