SK283710B6 - Process for decomposition of distillation residuals from the cyclohexanone production - Google Patents

Abstract

Process for decomposition of distillation residuals from the cyclohexanone production comprising heating and mixing these residuals with the aqueous solution of weak acids sodium salts, dissociation constant of which is less than 1 x 10exp(-4), under the temperatures 200 to 250 °C and the pressure, which is equal at least to the pressure of the saturated vapours under the system temperatures.

Description

Technical field

The present invention relates to a process for decomposing residues from a cyclohexanone distillation process, specifically residues from a cyclohexanone process based on liquid-phase oxidation of cyclohexane.

BACKGROUND OF THE INVENTION

Cyclohexanone, a major intermediate used in the manufacture of polyamides, is produced annually in quantities of several million tones worldwide. The compound is produced predominantly by air-liquid oxidation of cyclohexane. The production reaction provides cyclohexanol and cyclohexanone; cyclohexanol is dehydrogenated to give cyclohexanone.

Another large scale production process is the hydrogenation of phenol.

In each process, the reaction media are subjected to many operations to form condensation products, specifically cyclohexylidenecyclohexanone. The boiling points of these condensation products are higher than the boiling points of cyclohexanol and cyclohexanone. Distillation residues remain in the distillation stages. Generally, the weight of these residues is only a few percent of the cyclohexanone mass produced, but the cyclohexylidenecyclohexanone content can be as high as 50% by weight.

It is well known that cyclohexylidenecyclohexanone can be decomposed to cyclohexanone by treatment with alkali metal hydroxides, preferably sodium hydroxide, in the presence of water. The literature discloses sodium hydroxide used at varying concentrations starting from a very low concentration, for example 1% by weight and ending in high concentrations.

Czech patent 273820 discloses a method of heating distillation residues with sodium alkali and steam bubbling superheated to 260 ° C with liquid.

Heating distillation residues from the treatment of cyclohexanone with sodium alkali at varying concentrations up to temperatures above 200 ° C has many disadvantages. The main disadvantage of this method is that, under such drastic conditions, unidentified reaction products are formed to give solid or semi-solid substances that clog the tubes and make the process impossible. This disadvantage can be partially eliminated when a dilute solution of sodium alkali is used in large amounts. However, this process does not exclude the use of bulky streams of process medium and makes the method unsuitable.

Many problems arise in connection with the corrosive properties of sodium hydroxide.

SUMMARY OF THE INVENTION

Surprisingly, it has been found that the decomposition reaction of the residue from the distillation treatment of cyclohexanone can be carried out in a manner which completely eliminates the above disadvantages. It has been found that residues can decompose in the presence of aqueous solutions of weak acid sodium salts. The decomposition proceeds similarly as observed in the presence of sodium alkali; but neither solid nor semi-solid substances are formed and there are little corrosion problems.

The present invention essentially comprises heating distillation residues from cyclohexanone production at temperatures

200 ° C to 250 ° C with an aqueous solution of weak acid sodium salts whose dissociation constant is less than 1 x 10 ^-4 at a concentration of 10 to 50% by mass with vigorous stirring sufficient to assist the development of the interface between the residue and sodium salt solutions which are immiscible with each other. The system pressure is equal to the saturated steam pressure at the system temperature.

The sodium salts used may include sodium salts of organic acids, which by their very nature are very weak acids and also sodium salts of weak inorganic acids, specifically sodium carbonate. Most preferred is the use of sodium salts of those organic acids which are formed in the process of oxidation of cyclohexane by air and are neutralized by sodium hydroxide during the process: these are therefore the salts which appear in the cyclohexanone production plant in the form of aqueous solutions. The advantage is that their use does not require any new media being fed into the device.

The technical embodiments of the present invention may vary. There are two basic procedures that give good results.

One way is to carry out the reaction in a closed system and to strip off the volatile compounds, specifically cyclohexanone, after the chemical reaction has ended.

Another way is to remove the resulting cyclohexanone from the system while the chemical reaction is in progress. Although more complicated equipment is required in this process, the resulting cyclohexanone yields are much higher.

Each method allows various process modifications. For example, the process may be carried out in a series of reactors equipped with mechanical stirrers. It can also be carried out by allowing two liquids to flow through the oven under conditions such that stratification into water and the organic phase does not occur.

This modification requires the application of turbulent flow.

The quantitative ratio of the organic phase (distillation residue) to the aqueous phase (sodium salt solution) is irrelevant to the process.

The use of the aqueous phase in a large excess is not desirable because the volume of the flow that passes through the apparatus is undesirably increased. However, even a large excess of the aqueous phase does not adversely affect cyclohexanone precipitations. Good results are obtained when two phases are used in a 1: 1 weight ratio.

DETAILED DESCRIPTION OF THE INVENTION

The following examples illustrate the various ways in which the present invention may be practiced, but these examples have not been construed to limit the scope of the invention. In each example, the distillation residue from cyclohexanone production had the following composition:

cyclohexanone <0.5 wt. cyclohexanol <0.5 wt. cyklohexylidencyklohexanón 37% by weight, cyklohexylcyklohexanón 3 wt. dicyclohexyl 2 wt. dicyklohexyléter 8 wt.

The remaining components were not identified.

Example I

The distillation residue, 400 g, was heated with an aqueous solution of 600 g, a mixture of sodium salts of monocarboxylic acids forming waste water from a cyclohexanone production plant for 2 hours at 200 ° C in a 2 L autoclave, with stirring by a mechanical mixer rotating at 600 rpm. min ¹ . The waste water contains about 30 wt. dry residue. The alkanoic acids were present in the following ratios: capric (hexanoic) 25 wt.

% valeric (pentanoic acid) 60 wt.

% lower acid 15 wt.

Cyclohexanone and cyclohexanol were obtained in a total amount of 96 g, i. in 24.0% yield based on the weight of the distillation residue used. The reaction mixture contains no semi-solid components.

Example II

The procedure was identical to that of Example I, except that the temperature used was 220 ° C.

Cyclohexanone and cyclohexanol were obtained in a total amount of 124 g, i. in a yield of 31% by weight, based on the distillation residue used. The product contains no semi-solid ingredients.

Example III

The procedure was identical to that of Example II except that the aqueous solution of sodium alkanoates was replaced with 600 g of aqueous 20% Na ₂ CO ₃ .

Cyclohexanone and cyclohexanol were obtained in a total amount of 122 g, i. in a yield of 30.5%, based on the weight of the distillation residue used. The product contains no semi-solid ingredients.

Example IV

A 5-stage column, 80 mm in diameter, containing 1 L of liquid in each stage and one ascending type overflow was fed on top with a solution of 1.4 kg / h of sodium alkanoates of the composition given in Example I. Stage no. 3, numbered from above, was fed about 1.14 kg / h of distillation residue. The steam was introduced to the bottom of the column, 0.78 kg / h. The temperature and pressure prevailing in the column were 220 ° C and 2.1 MPa. The upper vapors were collected and condensed. The obtained condensed product finally made 0.78 kg / h of the aqueous phase and 0.35 kg / h of the organic phase. The bottom product was removed at a rate allowing a constant liquid level to be kept at the lowest level.

On steady-state conditions, the material balance is performed at two hourly intervals. The average result was 35.9 wt. of the combined cyclohexanone and cyclohexanol product, based on the weight of the distillation residue used.

Example V (comparative)

The procedure was as described in Example IV, except that the sodium alkanoate solution was replaced with aqueous 20% NaOH. After about 3 hours the overflow was blocked and the course was interrupted.

The procedure was repeated at 200 ° C; after a few hours the runoff was again clogged. The liquid collected from the bottom of the column contained pieces of semi-solid substances.

Example VI (comparative)

The distillation residue, 400 g aqueous 20% NaOH, 600 g, were heated together in a 2 1 autoclave, equipped with a mechanical mixer, which was rotated at 660 rpm with ¹ to 200 C for 2 hours. The liquid, unless removed from the autoclave, was distilled with water vapor to remove volatiles and the aqueous distillate was recycled to the distillation vessel. The organic phase of the distillate contained 128 g of cyclohexanone + cyclohexanol; 32.0% by weight based on the distillation residue used. The reaction mixture contained pieces of semi-solid substances.

Claims (5)

CLAIMS 1. A process for decomposing distillation residues from the production of cyclohexanone, comprising heating and mixing these residues with an aqueous alkaline solution at temperatures of 200 to 250 ° C and a pressure equal to at least saturated vapor pressure at system temperatures, characterized in that it is an alkaline solution. use an aqueous solution of weak acid sodium salts whose dissociation constant is less than 1 x 10 ^-4 . The process according to claim 1, characterized in that the weak acids are organic carboxylic acids. Process according to claim 1, characterized in that carbonic acid is used as the weak acid. The process according to claim 1, characterized in that in periodic operation the process is carried out in a closed system and the resulting volatile products are removed after the reaction is completed. The method of claim 1, wherein in continuous operation the resulting volatile products are removed during the chemical reaction.