DE1926932A1 - Pure lactams, particularly epsilon-caprolactam, free of - basic and oxidizable impurities - Google Patents

Abstract

Impurities are removed by allowing the crude lactams at temp. 2-80 C, preferably at 5-30 C (above the m.pt. of the lactam), or the fresh, crude lactam distillate leaving the column to pass under exclusion of air, through pipes filled up with oxides of elements of gps. IIB, IIA, IVB, VA, IVA, VIB, or VIIIB, or with elementary metals of groups VIIIB of the periodical system and subsequently separating the pure lactams, and regenerating the purifying agents.

Description

Process for Purification of Lactams The invention relates to a process for the purification of lactams, especially caprolactam, in the molten state.

It is known to contaminate molten caprolactam by distillation with the addition of alkali or alkaline earth metal hydroxide or more acidic components to clean.

It is also known to use the) melted caprolactam for the purpose of transfer basic impurities in an undistillable form a mixture of acetic anhydride, Add acetic acid and solid sodium hydroxide and heat the mixture to 95 ° C and then to distill in vacuo. Additions of serve the same purpose Formaldehyde or oleum before distillation.

It is also known through additions of alkali or alkaline earth carbonates to caprolactam, which is then subjected to a hydration treatment and distillation is subjected to effect a purification of the caprolactam.

It is also known that contaminated lactams can be converted into rdin4 genes, that isocyanates are added to the lactam before the distillation.

It is also known to cause contaminated lactams to be hydrogenated clean, known hydrogenation catalysts are used.

It is also known to purify actatnen by adsorption the contamination of surface-active substances such as activated carbon, fuller's earth or Ion exchangers to make.

It is also known to purify by extracting the contaminated Lactams with various solvent mixtures, by heating the lactam with the passage of inert gases, by treatment with oxidizing agents such as potassium permanganate, Hydrogen peroxide, Ozone, or by recrystallization.

It is also known the basic impurities contained in raw lactam neutralize with carbon dioxide or sulfur dioxide and the resulting salty Disconnect connections.

It is also known that lactams are produced by photonitrification of cycloaliphatic ical hydrocarbons with nitrosyl chlorine: ld or nitrogen monoxide and chlorine and subsequent Beckmann rearrangement of the so-called photooximes were obtained, by adding catalytic amounts of magnesium, aluminum, copper, zinc, of Metals of the iron group of the periodic table, of chlorides of the metals of the groups II A and II B or of aluminum chloride, of carbonates of groups II A and II B or oxides of the elements of groups III A and II B, the iron group of the periodic table or to purify from copper and subsequent distillation.

After all, it is known to be a crude, already distilled pre-purified caprolactam by irradiation with ultra violet or even shorter cells Light and subsequent distillation with the addition of alkali to clean All described Require measures to improve the purity of molten caprolactam a high technological effort or are with a considerable need for additional Chemicals or auxiliary materials connected. In addition, the are constantly increasing Purity requirements for the lactams, especially for the caprolactam, which are in all analytical parameters of the product, but especially in the permanganate number, the pil value and the volatile base content, express with those proposed so far Measures not taken or only if additional cleaning processes are used in others Process stages of caprolactam synthesis met.

The purpose of the invention is to produce lactams, especially -caprolactam, all of the purity requirements that are made during further processing, is equivalent to.

The invention is based on the object of a method for cleaning of molten caprolactam, pre-purified by vacuum distillation, which still contains basic and oxidizable impurities, to find that technologically simple and not associated with high additional consumption of chemicals or auxiliary materials is.

This object is achieved in that the lactams in molten State according to the invention at a temperature above its melting point with oxides of the elements of groups II B, III A, IV A, IV B, V A, VI B or VIII B or with elementary metals of group VIII B of the periodic table, with their mixtures or with compounds of the oxides are brought into contact with one another, whereupon the lactams are separated from the detergents and the detergents if necessary can be regenerated again.

It is preferable to do the cleaning at temperatures that are 2 to 80 ° C, preferably 5 to 30 ° C, above the melting point of the lactams.

With the help of the cleaning method according to the invention, basic earths and oxidizable impurities of the lactam removed or significantly reduced, which can be found in the key figures of permanganate number, content of volatile bases and pH value to express. These key figures and the light adsorption, which according to the invention Process is also improved, characterize the quality of the end product.

The treatment of the lactam is preferably carried out so that the melted lactam with exclusion of air through filled with the detergent Pipes passed or in another technologically common type, z. B. in stirring or mixing equipment with which the cleaning agent is brought into close contact.

Appropriately, the flowing off from the deotization column, still liquid lactam distillate fed continuously into the cleaning apparatus.

The product flowing out of the cleaning apparatus shows the high Cleaning effect of the cleaning method according to the invention. at The permanganate numbers are given for the longest service life of the cleaning agents in seconds) at least doubles, the pH value reaches values around 7.0, the content of volatile bases is reduced and the light adsorption is 0 to 2%.

The duration of use of the cleaning agent depends on the content of the product used existing impurities and the amount of lactam penetrated per unit of time addicted.

The cleaning agents used are light and often brisk.

regenerable.

Compared to the prior art, the method according to the invention a technologically simple purification of lactams is achieved without a high consumption of auxiliary chemicals is associated.

Example 1 Liquid 2-caprolactam with a permanganate number of 8 000 sec.

and a pH of 7.5 was in a stirred vessel with 5 wt .-% Al2O3. based on the amount of caprolactam used, 20 minutes in a nitrogen atmosphere stirred at 80 ° C. After filtering off the aluminum oxide, it became a caprolactam with a per.

Manganate number of 17,400 sec. and a pH of 7.00 was obtained.

Examples 2 to 12 According to Example 1, liquid g-caprolactam with a per.

manganate number (PM number) of 8,000 sec. and a pH of 7.5 with in each case 5 Ge1, .-%, based on the amount of caprolactam used, that in the table listed catalysts ## i # in the following table contain: example Cleaning agent PM number pH value 2 ZnO 18,000 sec. 7.10 3 SiO2 13 200 "6.95 4 TiO2 14 500 "6.95 5 Sb2O3 17 100 7 05 7.05 6 Al2O3, SiO2 16 200" 7.00 7 Al2O3, MoO3 15 300 "6.95 8 Al2O3, MoO3, NiO 21 600" 7.05 9 Al2O3, Fe2O3 15 300 "7.15 10 Al2O3, Ni 16 200 "7.05 11 Al2O3, Pd 15 900" 7.05 12 Al2O3, Pt 16 500 "6.95 Example 13 Liquid @ -Caprolactam with a permanganate number of 8,000 sec., A content of volatile bases of 0.0 # ml nf10 HCl / 20 g caprolactam, a pH of 7.5 and a light adsorption of 5% at 75 oC through a filled with clay, pipe arranged vertically. The caprolactam flowing off showed a permanganate number of 17000 sec., a volatile base content of 0.04 ml n / 10 HCl / 20 g caprolactam, a pH of 7.0 and a light adsorption of 1%.

After giving up 200 times the amount of caprolactam - based on the Amount of @ alumina used - was not yet any deterioration in the cleaning effect to notice.

After the cleaning effect subsided, the clay was through each time Treatment with water or diluted acid and subsequent drying to full Activity regenerates.

Example 14 @ -Caprolactam with a permanganate number of 600 sec., a pH of 7.75 and a volatile base content of 0.1 ml n / 10 XC1 / 20 g caprolactam was passed through a tube filled with aluminosilicate at 80.degree. The purified product flowing out showed a permanganate number of 1330 sec., A pH 7.05 and a volatile base content of 0.05 ml n / 10 HCl / 20 g caprolactam.

Claims (2)

Claims 1. Process for the purification of lactams, the basic and oxidizable Contain impurities, especially # -caprolactam, in the molten state by adding detergents, characterized in that the lactams at a temperature above its melting point with oxides of the elements of the groups II R, III A, IV B, V, A, A, VI B or VIII B or with elemental metals of Group VIII B of the periodic table, with their mixtures or with compounds d [r Oxides are brought into contact with one another, whereupon the lactams from the detergents aboo separates and the cleaning agents are #generated again if necessary. 2. The method according to claim 1, characterized in that the cleaning at temperatures of 2 to 80 ° C, preferably 5 to 30 ° C, above the melting point of the lactam.