Method for continuous purification of crude caprolactam obtained by the interaction of 6-aminocaproate with water

 

(57) Abstract:

The invention relates to a method for continuous purification of crude caprolactam obtained by the interaction of 6-aminocaproate with water. The process involves separating the low - and high-boiling components of the crude caprolactam, hydrogenation followed by treatment in an acidic environment and distillation in an alkaline environment. After separation of low - and high-boiling components of the crude caprolactam is treated with hydrogen at 50 to 150°C and 1.5 - 250,0 bar in the presence of a hydrogenation catalyst and optionally solvent. Thus obtained mixture A, which is passed in the solvent at 30 to 80°C. and 1 to 5 bar through the ion exchanger containing acidic groups, obtaining a mixture of B1 or distilled in the presence of sulfuric acid, and before adding sulfuric acid if necessary, remove the existing solvent to obtain a mixture of B2. As the solvent used water. A mixture of B1 or B2 is distilled in the presence of a base to obtain pure caprolactam. This results in improved yield and purity caprolactam. 1 C.p. f-crystals, 1 table.

The invention relates to the purification technology of cyclic lactams, and more particularly to a method of continuous clear the continuous purification of crude caprolactam, obtained by the interaction of 6-aminocaproate with water, including the separation of low-boiling and high-boiling components of the crude caprolactam, hydrogenation followed by treatment in an acidic environment and distillation in an alkaline environment. When this purified caprolactam is obtained in yields up to 76% (see U.S. patent N 2301964, CL 260-239, 17.11.1942 year).

The objective of the invention is to develop a method for continuous purification of crude caprolactam obtained by the interaction of 6 - aminocaproate with water, which allows you to get more pure caprolactam with a higher yield.

The problem is solved by the proposed method for continuous purification of crude caprolactam obtained by the interaction of 6-aminocaproate with water, due to the fact that

a) crude caprolactam after separation of low-boiling and high-boiling components is treated with hydrogen at 50 - 150oC and 1.5 - 250,0 bar in the presence of a hydrogenation catalyst and optionally a solvent to obtain A mixture,

b1pass the mixture in A solvent at 30 - 80oC and 1 - 5 bar through the ion exchanger containing acidic groups, obtaining a mixture of B1 or

b2) a mixture is distilled in the presence of sulfuric acid, and the PE the BR> C) a mixture of B1 or B2 is distilled in the presence of a base to obtain pure caprolactam.

Be cleaned crude caprolactam obtained by the interaction of 6-aminocaproate water in the well-known conditions, is a mixture consisting mainly of 50 to 98, preferably 80 to 95 wt.% water and from 2 to 50, preferably from 5 to 20 wt.% a mixture consisting of 50 to 90, preferably 65 to 85 wt.% caprolactam and from 10-50, preferably 15-35 wt.% the high-boiling fraction.

At the stage a) first, separate the low-boiling and high-boiling components by distillation. While it is preferable from the head of column to separate the ammonia present the above-mentioned solvents, in particular aliphatic alcohol, excess water and unreacted 6-aminocaproate, and low-boiling by-products, and then separated from the crude caprolactam by distillation, preferably from the head of the column from the high-boiling components such as oligomers of 6-aminocaproic acid. For the success of the invention is not crucial distilled whether low-boiling components before or after the high-boiling or simultaneously. Pre-cleared crude caprolactam is subjected to treatment with hydrogen in the form of rasps, is the quiet in the conditions of hydrogenation and processing of inert with respect to the ion exchanger; in particular, aliphatic alcohols with 1-3 carbon atoms, such as methanol, ethanol, n-propanol, ISO-propanol, preferably ethanol, and particularly preferably water.

According to a preferred form of carrying out the invention use solvents with the cyclization stage 6-aminocaproate, because it contains alcohol or water.

When the hydrogenation is usually used from 50 to 95, preferably from 70 to 95 weight. % solutions of crude caprolactam, counting on a solution. When the transfer of the solvent from the stage cyclization may be necessary to obtain a desired concentration addition or distillation of solvent.

The treatment with hydrogen is preferably carried out at a temperature from 60 to 95oWith, in particular from 70 to 90oC in the liquid phase. The pressure is selected depending on the temperature, therefore, to achieve the liquid phase. The pressure is preferably in the range from 5 to 100, in particular from 5 to 20 bar.

Hydrogen is usually introduced in a quantity of from 0.0001 to 5.0, preferably from 0.001 to 0.7, in particular from 0.03 to 0.3 mol per mole of caprolactam.

The reaction time is usually from 10 the tion from 1.5 to 10 kg of caprolactam per liter of catalyst per hour.

The hydrogenation can be conducted in suspension or in a fixed bed, and in the latter case, it is preferable to bring the solution of caprolactam together with hydrogen bottom-up or top-down through rigidly fixed to the tubular area of the catalyst.

As the hydrogenation catalyst, it is preferable to use those which are based on metal selected from the group consisting of iron, Nickel, cobalt, ruthenium, rhodium, palladium, osmium, iridium and platinum, particularly preferably cobalt, Nickel and palladium, more preferably palladium, in the form of solid catalysts or catalysts on a carrier, preferably in the form of a catalyst on the carrier.

According to a preferred form of execution of the invention using palladium catalysts on the media, which have a palladium content of from 0.01 to 10, preferably from 0.05 to 5, more preferably from 0.1 to 2 wt.%, counting on the catalyst. As the carrier used is preferably activated carbon, aluminum oxide, zinc oxide, silicon dioxide, titanium dioxide, lanthanum oxide or zirconium dioxide, or mixtures thereof.

According to another preferred form of the invention use the reading on the catalyst. In addition, the Nickel catalyst on a carrier may have additive on the basis of the elements: zirconium, manganese, copper or chromium, and these additives are in the range from 0.1 to 20, preferably from 1 to 5 wt.%, considering the number of entered Nickel, usually in the form of oxide.

As carriers are used preferably alumina, silica gel, alumina, activated carbon, silicates of magnesium, aluminum phosphate or boron phosphate, most preferably silicates of magnesium, aluminum phosphate, boron phosphate and aluminum oxide.

Evidence for this type of catalysts prepared by precipitation or impregnation can be found, for example, in Encyclopedia of Industrial Chemistry Ullman, T. A5, pages 348-350, 5th more. edition.

According to another preferred form of execution of the invention using the catalysts on a carrier, the surface of which is enriched with a catalytically active metal. Such catalysts usually get known methods by processing a pre-formed of the above substances of the medium in the form of tablets, pellets or rods, aqueous solution of metal salt, e.g. nitrate, then dried, calcined and then activate hydrogen.

According to the about feature in the tubular zone, for example, with a ratio of length to diameter of from 10:1 to 50:1, for example, in the form of dumping, and let a solution of crude caprolactam and hydrogen from the top or from the bottom through the fixed catalyst bed.

According to the observations in the processing of hydrogen primarily improves the UV number and the permanganate number, determined by titration, crude caprolactam.

After cooling and pressure relief get a mixture that consists mainly of caprolactam and solvent, if used. If you carry out the hydrogenation in the melt caprolactam obtained after hydrogenation of the product before processing the ion exchanger is dissolved in one of the above for the hydrogenation solvent, preferably in water.

Stage b1) is preferably carried out at a temperature from 50 to 60oC and at a pressure of from 1 to 2 bar. As the ion exchanger used is preferably strongly acidic, i.e., containing sulfopropyl, the ion exchanger in the H form. Suitable ion exchangers are, for example, Amberlite, Dowexor Lewatit (see Encyclopedia of Industrial Chemistry Ullman, T. A14, page 451, 5th more. edition).

The loading of the ion exchanger wybir the development of a cation-exchanger is even more improved UV number.

Regeneration of the loaded ion exchanger is possible by washing with an aqueous solution of mineral acid such as sulfuric or phosphoric, when this was recorded on an ion exchanger basic connectivity can be derived in the form of aqueous solutions of the corresponding salts.

According to the invention instead of processing the ion exchanger mixture A can distill in the presence of sulfuric acid (stage b2), before adding sulfuric acid to remove the solvent, if any.

According to a preferred form of execution of the invention the existing solvent is removed in a distillation column with two to four, particularly preferably two or three theoretical plates at a temperature of cube maximum 145oC. the Pressure is selected depending on the selected temperature. Usually it is chosen from 35 to 65 mbar, in particular from 40 to 60 mbar (measured in the column head), if the temperature of the cube is 145oC.

Freed thus from the solvent or without a solvent, the crude caprolactam is mixed with sulfuric acid, usually taken in an amount of from 0.1 to 0.5, preferably from 0.2 to 0.3 wt.% (considered as 100% by weight sulfuric acid), based on capreolata preferred form of execution of the invention the distillation are in distillation columns with 12 - 18, preferably 14-16 theoretical plates when the pressure in the head of column 3 to 6, preferably from 3 to 4 mbar and the temperature of the cube maximum 145oC.

As the Foundation of the distillation of a mixture of B1 or B2 use usually compounds of alkali or alkaline earth metals, such as hydroxides or water-soluble carbonates, such as lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, sodium carbonate or mixtures thereof, especially preferred is sodium hydroxide in the form of sodium lye.

The amount of added base is chosen usually from 0.05 to 0.9, preferably from 0.1 to 0.8 mol.%, counting on caprolactam. According to a preferred form of execution of the invention add from 0.05 to 0.25, preferably from 0.1 to 0.15 wt.% sodium alkali (calculated as 100% by weight).

The distillation is carried out in a known manner, when it is separated from caprolactam solvent, low-boiling and high-boiling fractions.

According to a preferred form of execution of the invention is distilled from a mixed base mixture B1 or B2 first solvent, in particular water, from the head of the column, and the temperature of the pressure from 35 to 65, more preferably from 40 to 60 mbar (measured at the head of the column). CBM product is fed to the second perehodnoy column.

CBM product from the first distillation column is distilled in the second distillation column is typically at a pressure of from 4 to 6, preferably 4 mbar (measured at the head of the column) and the temperature of the cube maximum 145oC. At this stage distillation usually remove low-boiling components. Then CBM product is fed to the third distillation column.

CBM product from the second column serves normally to the next distillation column, and are usually at a pressure of from 4 to 6, preferably 4 mbar, and the temperature of the cube maximum 145oC. Head product consists of pure caprolactam, the relevant specifications.

According to another form of execution of the invention CBM product from the third column can be submitted to film evaporator, may be separated by an additional amount of caprolactam, which return the first perehodnoy column.

Further, the preferred option is, when the base used is sodium alkali. Here you sodium the product from the third column is e the split operation in the second and third columns to combine and use only one column. Usually divert low-boiling components from the head of the column, the high-boiling components from a bottom part and caprolactam from lateral release. It is reasonable to return a partial flow of the low-boiling components on stage) (hydrogen). According to available data processing by distillation in the presence of base further reduces UV number.

The proposed method allows to obtain pure caprolactam, which indicators permanganate number obtained by the titration method (EBB), permanganate number, obtained by the method of photometry (PCF), free base, volatile bases (LO) and ultraviolet (UV) fully complies with the specifications for pure caprolactam obtained by the method of Beckmann. The content defined chromatographic impurities is usually from 100 to 150 hours /million (counting on caprolactam). Since some impurities already at 10 o'clock /million and less make it impossible for compliance with performance requirements and structure of numerous impurities at a concentration of 10 hours/million and their chemical behavior during purification is unknown, the technical result of the method according to the invention it was impossible to predict.

The proposed method is illustrated by kalitala 10% ethanol solution of 6-aminocaproate (DCA) in the presence of two moles of water per mole of DCA:

In a heated tubular reactor with a capacity of 25 ml (diameter 6 mm, length 800 mm), which is filled with titanium dioxide (anatase) in the form of rods with a length of 1.5 mm, is passed at a pressure of 100 bar a solution of 6 - aminocaproate in water and ethanol (10 weight. % DCA, 6.4 wt.% water balance - ethanol), and the reaction temperature is 240oC and the reaction time is 30 minutes. Coming out of the reactor product is analyzed by gas chromatography and high performance liquid chromatography: conversion of 100%, the yield of 88%. The reaction product is separated by fractional distillation from the high-boiling and low-boiling components. Thus obtained crude caprolactam according to gas chromatographic analysis has a purity of 99.5%. 1000 g of the crude caprolactam is dissolved in 250 g of water. The aqueous solution is mixed in an autoclave with 3.5 g of 5 wt.%-aqueous palladium on charcoal as a carrier and hydronaut under stirring for 4 hours at 80oC and 5 bar. After cooling and removal of the pressure, the catalyst is filtered off. The filtrate is passed by method of irrigation at 50oC and normal pressure in 1 l of strongly acidic ion exchanger (AmberliteIR 120, H-form) in the course of 0.6 hours. The product after the ion exchanger is mixed with 4 g of a 25% aqueous solution of nolani 50 mbar and the temperature of the cube 135oC.

From the cubic product of the first column is distilled in the second column with 15 theoretical plates of the low-boiling components when the pressure in the column head to 3.5 mbar and the temperature of the cube 140oC.

CBM product from the second column is distilled in the third column with 15 theoretical plates. When the pressure in the column head 4 mbar and the temperature of the cube 145oC distilled off from the head of column 990 g of caprolactam (99%, counting on the entered raw caprolactam).

Net caprolactam according to gas chromatography contains only 140 hours/million additives, compounds that would adversely affect the polymerization of caprolactam in nylon, were not detected. Indicators of caprolactam following:

PCF - 1,5; EBB - 1,2; free base < 0.05 mEq/kg; volatile base < 0.05 mEq/kg; UV - 2,5.

Thus, the obtained 6-aminocaproate caprolactam meets the specification requirements for caprolactam obtained by the method of Beckmann.

The table shows the improvement in UV and permanganate number (EBB) in the individual stages of cleanup.

Permanganate number titration method (FC)

The stability of caprolactam to VT is Araneta potassium in ml, per 1 kg of caprolactam, determined by titration with sulfuric acid solution.

Permanganate number by means of photometry (PCF)

The stability of caprolactam to the potassium permanganate is determined photometrically (see methods ISO 8660).

To do this, add the same amount of 0.01 n potassium permanganate solution to 3% (m/m) aqueous solution of caprolactam and a blank sample (diets. water). After 10 minutes, compare the extinction E at 420 nm caprolactamate sample and blank sample. Permanganate number is calculated as (E-E0)420 100:3.

Volatile bases (LO)

(Definition apparatus according to Parnas, see methods ISO 8661 "Caprolactam for industrial applications, determination of volatile compounds").

When distilled in the alkaline environment of the sample is separated volatile base (device, kildala), catch them 0,01 N. hydrochloric acid and determined by titration with a 0.01 N. sodium alkali, the addition of caprolactam(200,1) ,

< / BR>
A = flow rate of 0.01 N. caustic soda;

B = flow rate of 0.01 N. caustic soda idle for experience.

UV-number

The corresponding extinction of 50% (m/m) solution of caprolactam to determine 270, 280, 290, 300, 310, 320, 330, 340, 350 and 360 nm in 10-cm is x2">

Free base

To determine the free bases in 150 ml of distilled, free of carbon dioxide, saturated with nitrogen water was adjusted with the help of 0.01 N. caustic soda pH of exactly 7.0 and add 50 (+/-0,1) g of caprolactam. Then titrated at 25oC 0.01 N. hydrochloric acid to pH 7.0. Share free basis is calculated by using the equation below, where A (ml) mean flow rate of 0.01 N. hydrochloric acid:

free base = 0.01 A 1000/50 = 0.2 A mEq/kg

1. Method for continuous purification of crude caprolactam obtained by the interaction of 6-aminocaproate with water, including the separation of low - and high-boiling components of the crude caprolactam, hydrogenation followed by treatment in an acidic environment and distillation in an alkaline medium, characterized in that a) the crude caprolactam after separation of the low - and high-boiling components is treated with hydrogen at 50 - 150oC and 1.5 - 250,0 bar in the presence of a hydrogenation catalyst and optionally a solvent to obtain a mixture of A, B1) pass the mixture in the solvent at 30 - 80oC and 1 - 5 bar through the ion exchanger containing acidic groups, obtaining a mixture of B1 or B2) mixture And distilled in the presence of sulfuric acid, and before or B2 is distilled in the presence of a base to obtain pure caprolactam.

2. The method according to p. 1, characterized in that the solvent used water.

 

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