RU1806136C - Method for isolation and purification caprolactam of its mixture with water and impurities - Google Patents

Abstract

Usage: chemical technology, nitrogen-containing compounds, lactams, fertilizer component. SUMMARY OF THE INVENTION: Caprlactam acid ester is neutralized with ammonia, the reaction mixture is separated into lactam oil and a solution of ammonium sulfate, double extraction and distillation are carried out. The contaminated caprolactam-containing streams resulting from the evaporation and distillation of caprolactam are recycled. At the same time, mineral acid is added to the recirculated aqueous caprolactam-containing streams to a mixture pH of 2-5 and the mixture is treated with an aqueous solution of potassium permanganate at a temperature of 20-70 ° C for 30-60 minutes with a caprolactam-oxidizer mass ratio of 1000 : (1-3). The resulting aqueous solution of caprolactam was distilled in vacuo. 2 tab.

Description

The invention relates to methods for the isolation and purification of caprolactam and can be used in the chemical industry.

A known method of purification of caprolactam. obtained by neutralization of caprolactam acid ester with ammonia water, by separation of the reaction mixture into lactam oil and a solution of ammonium sulfate, purification of lactam oil by double extraction (in the first stage with an organic solvent, in the second stage with water), followed by isolation of the prepared caprolactam by evaporation and distillation (rectification ) In this case, along with marketable caprolactam, a series of concentrated caprolactam-containing streams (wastes) are formed that are heavily contaminated with impurities. The high cost of caprolactam forces the recycle of these contaminated streams in the process to recover the monomer. Naturally, in this case, impurities contained in the streams are returned to the cycle, which negatively affects the quality of intermediates and caprolactam. These caprolactam-containing streams include: aqueous solutions of caprolactam after micro-washing of the stage of extraction of caprolactam and regeneration of extractants, the main stage of evaporation and distillation (rectification) of caprolactam, distillation products of the stage of distillation (rectification) of caprolactam. Table 1 shows the qualitative and quantitative characteristics

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the above recyclable caprolactam-containing streams generated in the production of caprolactam with a capacity of 50 thousand tons per year.

From the data given in Table 1, it can be seen that the amount of waste returned to the cycle is about 20% of the volume of production of commodity monomer, which leads to the inevitable ingress of some impurities into caprol acts and to a decrease in quality indicators as an intermediate (lactam yes), and the final product is caprolactam.

Closest to the proposed method is a method for purifying caprolactam. According to this method, aqueous solutions of caprolactam are treated with a solution of potassium permanganate in an alkaline medium at pH 9-10 and room temperature for 4 hours. Under these conditions, partial impurities are oxidized to compounds removed in the subsequent technological stages of caprolactam production, and potassium permanganate reduced to colloidal manganese dioxide.

The disadvantage of this method is the insufficient cleaning efficiency of both the intermediate product (lactam-water) and commercial caprolactam, as well as the need to use bulky and expensive equipment (filters, centrifuges) to remove manganese dioxide formed from a colloidal solution. ;:

The proposed method is devoid of these disadvantages.

The purpose of the invention is to develop a method that provides more efficient cleaning of caprolactam and simplifies the hardware design of the cleaning stage.

This goal is achieved by treating the contaminated caprolactam-containing streams with solutions of potassium permanganate in an acidic medium at elevated temperature. For this, all contaminated caprolactam-containing wastes are combined into one stream, which in the reactor is acidified with sulfuric acid to a pH of 2-5. The resulting mixture is then treated with an aqueous solution of potassium permanganate at a temperature of 20-70 ° C for 30-60 minutes. With a mass ratio of caprolactam: oxidizing agent equal to 1000: 1 + 3. This effectively removes impurities from caprolactam, and potassium permanganate in an acidic environment turns into water-soluble sulfates of divalent manganese and potassium. The resulting homogeneous mixture is without further treatment directed to the step of neutralizing the caprolactam acid ester with ammonia water, where the excess sulfuric acid is neutralized to form ammonium sulfate. At this stage, the purified lactam passes into lactam oil, and the manganese and potassium sulfates are removed together with ammonium sulfate, enriching it with useful trace elements. Next, the lactam oil is processed according to the conventional technology (double extraction - evaporation - distillation).

The fundamental difference between the proposed method and the known one is that the treatment of contaminated aqueous solutions of caprolactam is carried out in an acidic environment

5 at a pH of 2-5, which improves the cleaning efficiency and further simplifies the technology by eliminating the separation of hard-to-filter colloidal manganese dioxide produced by the known method during the oxidation of impurities in an alkaline medium.

The isolation and purification process is carried out as follows.

Example (analog). 10 kg 27% aqueous

5 solution of caprolactam obtained by mixing recycled contaminated caprolactam-containing streams in the ratio according to table 1 (hereinafter the initial mixture) is mixed with 36 kg of acid

0 caprolactam ester (consists of 40% caprolactam and 60% sulfuric acid). The resulting mixture is neutralized with ammonia water to a pH of 5.5-6.0. After separation of the reaction mixture, an aqueous solution of ammonium sulfate 5 is sent to evaporation, drying and crystallization; and the resulting lactam. oil in the amount of 24 kg is first extracted with 115 kg of trichlorethylene, and then 51 kg of water is removed with caprolactam. Formed

0 25% aqueous solution of caprolactam in the amount of 68 kg after distillation of traces of the extractant has the following quality indicators: PI-38 D290-1.5; color - 49 ° X. After caprolactam allocated after 5 distillation of water and distillations in vacuo, it has the following qualitative indicators: PI 9.3; D290-0.060; chromaticity-7.0 ° X: volatile bases -0, 80 mmol / kg.

PRI me R 2 (prototype). K 10 kg of the original

To the mixture, 0.81 kg of a 1% aqueous solution of potassium permanganate was added and stirred in the reactor at a temperature of 20 ° C for 240 minutes. After separation of the resulting colloidal manganese dioxide by

5 filtration; the purified caprolactam solution is mixed with 36 kg of caprolactam acid ester and the resulting mixture is sent to neutralization with ammonia water to pH 5.5-6.0: Ammonium sulfate and caprolactam are isolated as in example 1. The resulting aqueous caprolactam solution has: PI-2 8 ; D290-0.8; chromaticity-33.0 ° X; and distilled caprolactam has: PI-5.8; Daeo - 0.047; chroma 3.0; Volatile bases - 0.55 mmol / kg.

Example 3 0.81 kg of a 1% aqueous solution of potassium permanganate and concentrated sulfuric acid were added to 10 kg of the starting mixture to pH 5.0. The resulting mixture was stirred at 20 ° C for 90 minutes. The resulting homogeneous mixture, together with 36 kg of caprolactam acid ester, is further processed as in Example 2. An aqueous solution of caprolactam with PI-20 is obtained; D290-0.5; chromaticity - 25 ° X and distilled caprolactam with PI-3.0; D290-0.026; chromaticity-1,0 ° X; volatile bases - 0.32 mmol / kg.

PRI me R 4. 10 kg of the initial mixture is treated with 0.81 kg of a 1% aqueous solution of potassium permanganate for 30 minutes as in example 3 at pH 2.0 and a temperature of 70 ° C. Get a solution of caprolactam with PI - 14; D290 - 0.4; chromaticity - 23 ° X and distilled caprolactam with PI-2,3; D290-0.016; chromaticity - 0.5 ° X; volatiles

0.22 mmol / kg.

PRI me R 5. 10 kg of the initial mixture is treated with 0.81 kg of a 1% aqueous solution of potassium permanganate for 60 minutes as in example 3 at pH 2.0 and a temperature of 40 ° C. Get a solution of caprolactam with PI - 15; D290-0.4: color - 24 ° X and distilled caprolactam with PI-2.2; D290-0.015; chromaticity - 0.5 ° X; volatiles

- 0.21 mmol / kg. PRI me R 6. 10 kg of the initial mixture is treated with 0.81 kg of a 1% aqueous solution of potassium permanganate for 90 min as in example 3 at pH 1.0 and a temperature of 80 ° C. Get a solution of caprolactam with PI - 12; D290 - 0.3; chromaticity. - 22 ° X and distilled caprolactam with PI - 2.1; Daeo - 0.012; chromaticity 0.5 ° X and volatile bases 0.20 mmol / kg.

PRI me R 7. 10 kg of the initial mixture is treated with 0.81 kg of a 1% aqueous solution of potassium permanganate for 60 minutes as in example 3 at pH 5.0 and a temperature of 70 ° C. Get a solution of caprolactam with PI - 13; D290 - 0.4; chromaticity 22 ° X and distilled caprolactam with PI-2.2; D290 0.016; chromaticity-0.5 ° X and volatile bases of 0.20 mmol / kg.

An example. 10 kg of the initial mixture is treated with 1.08 kg of a 1% aqueous solution of potassium permanganate for 30 minutes as in example 3 at pH 5.0 and a temperature of 50 ° C. Get an aqueous solution of caprolactam with PI - 14; D290 - 0.3; chromaticity - 23 ° X and

distilled caprolactam with PI - 2.2; D290 - 0.013; chromaticity 0.5 ° X and volatile bases 0.23 mmol / kg.

PRI me R 9. 10 kg of the initial mixture is treated with 0.27 kg of a 1% aqueous solution of potassium permanganate for 30 minutes as in example 3 at pH 2.0 and a temperature of 70 ° C. Get a solution of caprolactam with PI - 16; D290 - 0.4; color - 24 ° X and distilled caprolactam with PI - 2.5; D290 - 0.019; chromaticity - 0.5 ° X and volatile bases

0.24 mmol / kg.

PRI me R 10. 10 kg of the initial mixture is treated with 0.81 kg of a 1% aqueous solution of potassium permanganate for 15 minutes as in example 3 at pH 4.0 and a temperature of 40 ° C. Get an aqueous solution of caprolactam with PI - 24; D290-0.6; chromaticity - 27 ° X and distilled caprolactam with PI - 5.1; D290 - 0.043; chromaticity 4.0 ° X and volatile bases 0.60 mmol / kg.

PRI me R 11. 10 kg of the initial mixture is treated with 0.40 kg of a 1% aqueous solution of potassium permanganate for 60 minutes as in example 3 at pH 5.0 and a temperature of 50 ° C. Get a solution of caprolactam with PI - 30; D290 - 1.0; chromaticity - 36 ° X and distilled caprolactam with PI -6.5; 058; chromaticity - 5.2 ° X and volatile bases

0.65 mmol / kg

From the above examples (Table 2) it follows that the optimal conditions for highly efficient purification are: a mass ratio of caprolactam and an oxidizing agent equal to 1000: 1-3, the pH of the mixture is 2-5, the temperature is 20-70 ° С and the oxidation time 30-60 minutes Reducing oxidizer consumption, temperature and processing time leads to a decrease in cleaning efficiency. A further increase in the consumption of oxidizing agent and sulfuric acid (decrease in pH) has practically no effect on the efficiency of the process, and an increase in temperature and processing time leads to the complication and enlargement of the used technological equipment. An increase in the pH of the mixture over 5.0 leads to the formation of an undesirable colloidal precipitate of manganese dioxide.

Claims (1)

SUMMARY OF THE INVENTION A method for isolating and purifying caprolactam from a mixture with water and impurities by neutralizing caprolactam acid ester with ammonia, separating the reaction mixture into lactam oil and an ammonium sulfate solution, purifying and isolating caprolactam by double extraction and distillation, recycling separated aqueous caprolactam-containing flows, characterized in that, in order to improve quality commercial caprolactam and simplification of the technological scheme of the purification stage, sulfuric acid is added to the processed recycle streams to a mixture pH of 2-5 and treated with an aqueous solution of potassium permanganate at a temperature of 20-70 ° C for 30-60 minutes with a mass ratio of caprolactam: potassium permanganate equal to 1000: (1 .- (- 3), then caprolactam is separated from water by distillation, Table 1 Absolute errors of quality indicators according to GOST 23743.1. 23743.3. 23743.7 and 23743.8 are equal: for PI - 0.6: D290 - 0.003: color - 0.5 ° X. volatile bases 0.05 mmol / kg at p-0.95. Table 2