KR19980050084A - Purification Method of Low Purity Caprolactam - Google Patents

Abstract

In order to remove impurities contained in low-purity caprolactam, low-purity lactam is made into a 40-80% aqueous solution, and potassium permanganate with strong oxidizing power is added to the lactam solution before passing through the activated carbon tower, followed by adding lime or soda ash to inorganic salts. By adding (NaOH, KOH) and the like, various suspended solids or dissolved impurities are first removed, and impurities that are not removed are adsorbed and removed by activated carbon, followed by concentrating through a reverse osmosis membrane to obtain high purity caprolactam.

Description

Purification Method of Low Purity Caprolactam

The present invention relates to a purification method for producing high purity carrolactam by effectively removing various impurities remaining in low purity caprolactam, and more particularly, to oxidizing oxidizable impurities contained in low purity caprolactam to peroxides. The present invention relates to a purification method characterized by firstly removing impurities in caprolactam by alkali treatment, passing the same through activated carbon, and then concentrating caprolactam using a reverse osmosis membrane.

Generally, various impurities are present in carrolactam obtained by depolymerization of polycaprolactam under a phosphoric acid catalyst. These impurities are volatile substances flowing out of the reaction system, and compounds having a carboxyl group such as cyclopentanon, cyclohexane, and gamma-caprolactam in addition to lactams, oxidizable substances, and amines. Or formalin, formic acid, etc. are confirmed as a low boiling point impurity, In addition, the compound etc. which have a double bond between carbon exist. Due to the presence of a large amount of these impurities, deterioration and discoloration of lactams occur due to light, heat, air, etc., and various obstacles in the polymerization, which are the main factors that degrade the quality of the final product. Therefore, lactam as a polymerization raw material greatly affects the quality of the final product depending on the degree of removal of the impurities contained therein, so that high purity is required and the removal of impurities is particularly necessary.

Many studies have been conducted to remove such impurities, but prior art regarding the purification method of low purity caprolactam is a method of adding and refining alkali and peroxide (Japanese Patent Application No. 47-4190), and recrystallization from aqueous sulfuric acid solution. The method (Japanese Patent Laid-Open No. 47-24676) and the recrystallization method using an organic solvent (US Pat. No. 3,485,800) have been proposed in various ways, all using a concentration method through distillation. However, the distillation process is not expected to have an excellent quality effect due to the scattering of impurities and oxidation of caprolactam, there is a problem in terms of cost due to the need for a lot of energy.

The present invention, in order to remove the impurities contained in the low-purity lactam, which is a conventional problem, various kinds of suspended solids or dissolved by adding potassium permanganate with strong oxidizing power to the lactam aqueous solution before passing through the activated carbon tower, and then adding slaked lime or soda ash and adding alkali The impurities are first removed, and the impurities not removed are adsorbed on the activated carbon and then removed. The impurities are passed through a reverse osmosis membrane and concentrated to produce caprolactam of high purity.

More specifically, the low-purity lactam is made into a 40-80% aqueous solution, 0.3% potassium permanganate is added, and 0.5 weight equivalents of inorganic bases (NaOH, KOH) are added under 10 weight equivalents of hydrated lime or soda ash. The present invention provides a method for obtaining high purity lactam by passing through an activated carbon column and passing it through a reverse osmosis membrane.

The addition of hydrated lime or soda ash in the present invention is to remove various impurities and precipitates generated after treatment with potassium permanganate to extend the life of the activated carbon tower and to easily remove the various organic impurities reacted with potassium permanganate from the activated carbon tower. This is because it is effective to increase the removal rate of impurities.

In addition, by replacing the conventional distillation process with a reverse osmosis membrane permeation process of the aryl-alkyl polyetherurea material having a pore size of 5 to 20 kPa, it prevents oxidation of lactam and reduces energy cost, thereby solving the problems of the prior art. Improved.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the scope of the present invention is not limited by the following Examples.

Example 1

The polyamide containing organic impurities is depolymerized with saturated steam at 350 ° C. under a phosphoric acid catalyst to obtain a low purity lactam. To 500 g of the obtained low-purity lactam was added 3 g of potassium permanganate (KMnO ₄ ) to 1,000 ml of a 60% aqueous solution prepared by adding water, followed by stirring for 1 hour to oxidize, followed by addition of 10 wt. Weight of soda ash (Na ₂ CO ₃ ). To the filtered lactam aqueous solution, 0.5 weight equivalent of sodium hydroxide (NaOH) is added and stirred. The lactam aqueous solution was passed through an activated carbon column, and concentrated through 50-60 atm of a spiral wound reverse osmosis membrane made of aryl-alkyl polyetherurea, having a pore size of 20 kPa, to prepare a high purity lactam. The results are shown in Table 1.

Example 2

Except for using slaked lime (Ca (OH) ₂ ), and in the same manner as in Example 1, the results are shown in Table 1.

Comparative Example 1

The polyamide containing organic impurities is depolymerized with saturated steam at 350 ° C. under a phosphate catalyst to obtain a low purity lactam. To 500 g of the low-purity lactam obtained by adding water, 1,000 g of potassium permanganate (KMnO ₄ ) 3g was added to 1,000 ml of an aqueous 60% aqueous solution, stirred for about 1 hour, and oxidized by adding 0.5 weight equivalent of soda ash (Na ₂ CO ₃ ). Stir. The lactam aqueous solution was passed through an activated carbon column, distilled to concentration, and the results are shown in Table 1.

Comparative Example 2

Except for using soda ash (Ca (OH) ₂ ) and in the same manner as in Comparative Example 1 shown in Table 1.

Comparative Example 3

Polyamide containing an organic impurity is obtained with a low purity lactam with saturated steam at 350 ° C. under a phosphoric acid catalyst. To 500 g of the lactam obtained, add 3 g of potassium permanganate (KMnO ₄ ) to 1,000 ml of a 50% aqueous solution prepared by adding water, stir and oxidize it for about 2 hours, and then pass the filtered lactam aqueous solution through an activated carbon column, distill and concentrate. The lactam was obtained and the results are shown in Table 1.

TABLE 1

[Measurement of physical properties]

(1) The volatile base was confirmed by distillation in a vessel containing 0.02N normal sulfuric acid from an aqueous solution obtained by dissolving 50 g of lactam in 100 ml of 20% NaOH, and quantitatively quantitatively. In addition, the above measurement was computed by the following formula.

V1: NaOH ml used for the sample

V2: Blank

F: NaOH and NH ₃ equivalent titers

(2) For PM No., add 1.0 ml of 0.01 N potassium permanganate (KMnO ₄ ) aqueous solution to 100 ml of lactam aqueous solution, and add ₂ g of standard solution (CaCl ₂ · 6H ₂ O, CuSO ₄ · 5H ₂ O) to 1 liter of water. It is the value which converted the time until it turns into the same color as the dissolved solution) in seconds.

According to the present invention, the lactam has a good colorlessness and prevents the scattering of impurities and the oxidation of the lactam generated in the conventional method, thereby obtaining a high purity pure lactam having a high PM value.

Claims (4)

In the method for purifying low-purity caprolactam, the low-purity lactam is made into a 40-80% aqueous solution, potassium permanganate is added, an inorganic base is added to the aqueous solution, and the liquid is passed through an activated carbon tower, which is then concentrated through a reverse osmosis membrane and concentrated. Purification method of low purity caprolactam, characterized in that the purification after. The method for purifying low purity caprolactam according to claim 1, wherein the potassium permanganate is added to the low purity lactam aqueous solution at 0.3%. The method for purifying low purity caprolactam according to claim 1, wherein the inorganic base is added with NaOH, KOH and the like in 0.5 weight equivalents of 10 weight equivalents of hydrated lime or soda ash. The method for purifying low purity caprolactam according to claim 1, wherein the reverse osmosis membrane uses a reverse osmosis membrane made of aryl-alkyl ployetherurea having a pore size of 5 to 20 kPa.