DE2641478A1 - CLEANING CAPROLACTAM - Google Patents

Description

Bayer Aktiengesellschaft 264η? Δ

Central area of patents, trademarks and licenses

5090 Leverkusen, Bayerwerk

^G ~ ^by U, Sep. 197 ©

Purification of caprolactam

E-caprolactam is used to cleanse and improve the color treated with potassium permanganate. In general, the permanganate is added as an aqueous solution to an aqueous solution of the Caprolactams, so that a dilute, aqueous solution is present during the oxidative cleaning. The presence of Great importance is attached to water in sufficient quantities. One has even with the treatment less water-insoluble Lactams Added water-soluble lactams to create an aqueous medium.

However, a yellow coloration occurs when the dilute aqueous caprolactam solutions are treated with potassium permanganate which can no longer be eliminated by crystallization from the specified solvents. The result is general color numbers in the order of magnitude of 250. The yellow coloration is achieved by the process according to the invention avoided. This is a method of purifying ^ -Caprolactam by treating it with potassium

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permanganate and crystallization, which is characterized in that one ε-caprolactam in the presence of 0.01 to 5 wt .-%. Water, based on caprolactam, treated with potassium permanganate and then crystallized from toluene, benzene, ethylbenzene or xylene. In general, the caprolactam to be purified, which may have already undergone an extraction and / or crystallization, is first dehydrated, then potassium permanganate is added, preferably as a concentrated aqueous solution, the water content of the mixture being 0.01 to 5 wt. % and the amount of potassium permahganate is such that it is completely reduced in 5 minutes at 80 ° C. In general, amounts of 0.05 to 0.1% by weight, based on caprolactam, are required for this if benzene, ethylbenzene or xylene is added, but preferably toluene, the ε-caprolactam is dissolved in it and crystallized out. After washing and drying, the crystallized product is generally pure enough for the subsequent polymerization. It has a solidification point above 69 °, a color number around 5, a volatile base content of 0.3 meq (garbage equivalents per kilogram) or less, a UV count of 95, and a permanganate count of> 40,000 e is how the color number shows completely £ Colorless. ^: . ^: . ■ "■ -

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example 1

200 g of caprolactam crystals, obtained from raw caprolactam the gas phase rearrangement of cyclohexanone oxime by extraction with toluene and crystallization from toluene, were melted and then for 30 minutes at 80 ° C. with 2 g of 10% strength aqueous potassium permanganate solution touched. Then 86 g of toluene were added, filtered and crystallized by slowly cooling to 20 ° C. The obtained crystal slurry was filtered with toluene mashed and centrifuged. The key figures of the E-caprolactams after drying were as follows:

Freezing point 69.10 ⁰ C Hazen color number 5
Volatile content
Bases (can be driven off with NaOH; amines) 0.15 meq UV number 9 5 ^kg permanganate number l x 40,000

Example 2

200 g of caprolactam crystals, obtained by crystallizing E-caprolactam with cleavage of polyamide the following key figures:

He s disguise points 69.0O ⁰ C - 3 - Color number 200 fl. bases 2.0 meq UV number 10 ^k p P eranganate count 600 Le A 17 381

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were treated and worked up according to Example 1. the Kenh numbers were thereafter:

Freezing point 69 , 10 ⁰ C .000 Color number ■; '.; ".- ..; 5 f1. Bases O , 25 mlq UV number · ■ ;. "; 95 kg Permanganate number) k 40 Example 3 "/

Caprolactam produced by Beckmann storage was extracted with toluene. 2000 g toluene / caprolactam extract (80 wt% toluene) was concentrated to 600 g. These The solution was stirred for 30 minutes at 80 ° C. with 1 g of 10% strength aqueous potassium permangant solution. The other Working up according to Example 1 yielded the following key figures: V

Freezing point 69 , 10 ⁰ C .000 Color number ■ 5 fl. bases 0 , 10 mEq UV number 98 kg Permanganate number > 40 Example 4

200 g of pure caprolactam was dehydrated with 100 ppm Caprolactam added. The mixture had a permanganate number of 1000. It was treated according to Example 1 and

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worked up. The following key figures were obtained:

Freezing point 69 , 10 ⁰ C .000 Color number 5 fl. bases O , 15 mEq UV number 98 kg Permangana t - number > 40

Comparative example 1

As comparative example 1, 200 g of caprolactam from the crude crystallization stage of the catalytic rearrangement were dissolved in 298 g of water and then stirred with 2 g of 10% strength aqueous potassium permanganate solution at 80 ° C. for 30 minutes. The caprolactam solution was then filtered and distilled anhydrous. The thus isolated caprolactam was added with 86 g of toluene and slowly cooled from 60 ⁰ C to 20 ° C. The crystal slurry was then processed further as in Example 1. The following key figures for caprolactam were obtained:

Freezing point 69.0O ⁰ C
Color number 250

Comparative example · 2

The procedure according to Comparative Example 1 was followed up to the dehydration of the caprolactam. The anhydrous CaprolactaIn 86 g of toluene and 2 g of activated charcoal were added

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and stirred at 60 ° C for 10 minutes. After that the activated carbon filtered off and the caprolactam crystallized from the filtrate. The crystal slurry was worked up as in Example 1. Caprolactam was obtained with the following key figures:

Freezing point 69.10 ° C, color number 50

Comparative example 3

200 g of pure caprolactam was dehydrated with 100 ppm Lactam is added and, as a comparison to Example 4, oxidized and purified according to Comparative Example 1. It was Get caprolactam with the following metrics:

Freezing point 69 , 06 ⁰ C .000 Color number 10 fl. bases 0 , 3 mEq UV numbers 86 kg Permanganate number 30th

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Claims (1)

Claim Process for purifying C-caprolactam by treatment with potassium permanganate and crystallization, characterized in that that one £ I-Caprolact; afii! in the presence of 0.01 to 5% by weight of water, based on caprolactam, treated with potassium permanganate and then made from toluene, Benzene, ethylbenzene or xylene crystallizes. Le A 17 381 - 7 - 809812/0 098 ^0F ^ INAL INSPECTED