MXPA97003727A

MXPA97003727A - Caprolact preparation

Info

Publication number: MXPA97003727A
Application number: MXPA/A/1997/003727A
Authority: MX
Inventors: Fuchs Eberhard; Achhammer Gunther
Original assignee: Basf Ag 67063 Ludwigshafen De
Priority date: 1994-11-21
Filing date: 1997-05-21
Publication date: 1998-02-01

Abstract

The present invention relates to caprolactam which is prepared by reacting a solution of 6-aminocapronitrile with water in the liquid phase at temperatures eluted by a process in which (a) an aqueous solution of 6-aminocapronitrile in the liquid phase is heated without the addition of a catalyst in a reactor A to give a mixture I consisting essentially of water, caprolactam and a high-boiling fraction (high boiler), then (b) the water is removed from the resulting mixture I to give a mixture II consisting essentially of caprolactam and the high boilers, then (c) the caprolactam and the high boilers of the mixture II are removed by distillation, and then (d1) the high boilers of the step (c) are fed to the reactor A of step (a), or (d2) the high boilers are heated in the same manner as in step (a) in another reactor B and then processed in the same manner as steps (b) and (c) to produce m s caprolactam, or (d3) the high-boilers reduced in the presence of a base in a reactor C and the mixture pressure reaccionóse works by distillation to give heat caprolacta

Description

PREPARATION OF CAPROLACTAMA The present invention relates to a process for the preparation of caprolactam by reacting 6-α-incapronitrile with water at elevated temperatures. U.S. Patent 4,628,085 describes the reaction of 6-aminocapronitrile with water in the gas phase on a special acidic silica gel (Porasil® A) at 300 ° C. By diluting with water, ammonia and hydrogen / nitrogen it is possible to obtain caprolactam in a quantitative conversion and with a selectivity higher than 95%. However, due to the deactivation there is a notable decrease of at least 5% in the conversion and selectivity within the first 150 hours. A similar gas-phase process is described in U.S. Patent 4,625,023. In this patent, a highly diluted gas stream of 6-a-incapronitrile, adiponitrile, ammonia, water and the carrier gas is passed over a silica gel and a titanium-barium / chromium / copper oxide catalyst bed. The selectivity of caprolactam is 91% to 85% conversion. Both processes have the disadvantage that the heterogeneous catalyst used is rapidly deactivated. In addition, the highly diluted gas stream of 6- aminocapronitrile must be reacted with water on these heterogeneous catalysts, this leads to short energies for evaporation and large volumes in the reactor. U.S. Patent 2 245 129 describes the preparation of the linear polyamides by heating an aqueous solution of 6-aminocapronitrile at 50% by weight at 200 ° C. for 20 hours. In this patent, the caprolactam formation was not observed. An object of the present invention is to provide a process for the preparation of caprolactam from 6-aminocapronitrile, whose process is carried out with high selectivity in the liquid phase and without a catalyst, the intention being in particular to reduce the amount of the byproducts. We have found that this goal is achieved by a process of preparation of caprolactam by reacting 6-aminocapronitrile with water at elevated temperatures, where: (a) an aqueous solution of 6-aminocapronitrile in liquid phase is heated without the addition of a catalyst in a reactor A to give a mixture I consisting essentially of water, caprolactam and a high boiling fraction (boiling at high temperatures), then (b) the water is removed from the resulting mixture I to give a mixture II consisting essentially of caprolactam and the high boiling fractions, then (c) the caprolactam and the high boiling fractions of the mixture II are separated by distillation, and then (di) the high-boiling fractions of step (c) are fed into reactor A of stage (a) or (d2) The high-boiling fractions are also heated in the same manner as in step (a) in another reactor (b) and then worked in the same manner (c) and to give another caprolactam, or (d3) ) The high boiling fractions are heated under reduced pressure in the presence of a base in a C reactor and the reaction mixture is brought to distillation to give the caprolactam. The 6-aminocapronitrile which is used according to the invention as starting material is generally obtained by hydrogenation of adiponitrile by a known process, for example, that described in DE-A 836 938, DE-A 848 654, US Pat. 5 151 543. It is also possible to introduce into the reactor A mixtures which may contain essentially 6-aminocapronitrile and hexamethylenedia ina, adiponitrile and / or caprolactam, as well as high-boiling fractions (boilers). elevated) which are obtained when working the caprolactam prepared according to the invention. In addition, water is preferably used in excess; particularly, from 10 to 150, in particular from 20 to 100, moles of water is used per 6-aminocapronitrile template, to give a solution of 6-aminocapronitrile. In another preferred modality, from 5 to 25 moles of water are usually used by 6-aminocapronitrile mold, and the solution can usually be more diluted by 5-25% by weight of 6-aminocapronitrile by adding an organic solvent. Examples of suitable solvents are: Alkaloids of C1-C4, such as methanol, ethanol, n-propanol, isopropanol, and butanol, glycols such as ethylene glycol, diethylene glycol, triethylene glycol tetraethylene glycol, ethers such as methyl terbutilus ether and diethylene glycol diethyl ether, C6-C alkanes 0 as n-hexane, n-heptane, n-octane, n-nonane, n-decane, and cyclohexane, benzene, toluene, xylene, lactams, such as pyrrolidone, and caprolactam and N-C1-C4 alkylactams, such as N-methylpyrrolidone, N-methylcaprolactam and N-ethyl caprolactam. In another embodiment, from 0 to 5, preferably from 0.1 to 2% by weight of ammonia, hydrogen or nitrogen can be added to the reaction mixture.

According to the invention, the reaction in step (a) is carried out from 200 to 370 ° C, preferably from 220 to 350 ° C, particularly preferred from 240 to 320 ° C. The reaction in step (a) is usually carried out under super atmospheric pressure, the pressure that is chosen as a rule is from 0.1 to 50, preferably from 5 to 25, MPa, so that the reaction mixture of preference is present as a liquid phase. The reaction time in reactor A depends essentially on the parameters of the chosen process and is generally from 20 to 180, preferably from 20 to 90 minutes in a continuous process, as a rule, the conversion decreases in the case of times reaction times, while observations to date have shown that oligomers are formed that cause some problems during prolonged reaction times. The cyclization (step (a)) is preferably carried out continuously in a reactor A, preferably in a tube reactor in a stirred kettle or in a combination thereof. The cyclisation (step (a)) can be carried out in batch form. In this case, the reaction time is usually from 30 to 180 minutes. According to the invention, the discharge of the reactor A is a mixture I consisting essentially of 50 to 98, preferably from 80 to 95% by weight of water and 2 to 50, preferably from 5 to 20%, by weight of a mixture consisting essentially of 50 to 90, preferably 65 to 85% by weight of caprolactam and of 10 to 50 preferably 15 to 35% by weight of a high boiling fraction (hereinafter referred to as high boilers). According to the invention, the water contained in the mixture I is eliminated in step (b) by a conventional method, preferably by distillation to give a mixture II consisting essentially of caprolactam and the high boilers. In a preferred embodiment a distillation is carried out under reduced pressure from 10 to 500, preferably from 50 to 350 mbar (from 1 to 50, preferably from 5 to 35 MPa), the vacuum distillation column that is used is from 2 to 20, preferably from 4 to 10 theoretical plates. According to the invention, the mixture II obtained in step (d) is separated by distillation in step (c) in a fraction containing caprolactam (upper product) and a fraction containing the high boilers (lower product). The distillation in step (c) is preferably carried out from 0.1 to 100, preferably from 1 to 20 mbar (0.01 to 10, preferably from 0.1 to 2 MPa). Observations to date have shown that the yield of caprolactam after this distillation is 50 to 90, preferably 65 to 85% by weight based on the amount of 6-aminocapronitrile. According to the invention, the high boilers obtained in step (c) can be worked by three different methods. In stage (di) the high boilers of stage (c) are fed to reactor A of stage (a) or In (d2) the high boilers are heated in the same manner as in step (a) in another reactor B and then worked in the same manner as in steps (b) and (c) to give more caprolactam, the High boilers are preferably mixed with 5 to 25 times, preferably 10 to 15 times the weight of the water and then heated to 200 to 350 ° C, preferably from 280 to 320 ° C in a B reactor at a time of residence from 30 to 120, preferably from 45 to 90 minutes, or. In step (d3) the high boilers are heated under reduced pressure, in general from 1 to 50, preferably from 1 to 10 mbar (0.01 to 5, preferably 0.01 to MPa) in the presence of a base, as a rule from 1 to 10, preferably from 1 to 3% thereof, in a tube reactor, from 200 to 400 ° C, preferably from 280 to 320 ° C, and the reaction mixture is worked to give more caprolactam, preferably by distillation, preferably from 1 to 50, particularly preferred from 1 to 10 mbar (from 0.01 to 5, particularly from 0.01 to 1 MPa). In a preferred embodiment, a distillation column having from 2 to 20, particularly preferred from 5 to 10 theoretical plates is used. The base that is preferably used is an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide or a mixture thereof. The advantage of the novel process is that the caprolactam is obtained with a high selectivity and in a high yield starting from 6-aminocapronitrile in liquid phase without a catalyst in short reaction times.

EXAMPLES Example 1 A solution of 10% by weight of 6-aminocapronitrile (ACN) in water is heated to 300 ° C in a reactor tube (volume 300 ml), the average residence time is one hour. No ACN sample was detected in the download. The product mixture (mixture I) contained 90% by weight of water and 10% by weight of a mixture containing 76% by weight of caprolactam and 24% by weight of high boilers. The mixture I was then distilled from 100 to 300 mbar (10 to 30 MPa) in a vacuum distillation column with 5 theoretical plates, water containing ammonia was obtained as the superior products and caprolactam and the high boilers were obtained in the lower part of the column (mixture II). The mixture II was separated in another column of vacuum distillation (pressure of 3 to 10 bar) in a caprolactam fraction (upper product) and a high boiling fraction (lower products). The yield of caprolactam was obtained 74%, since 2% by additional weight of the amount of caprolactam obtained in the above was converted into high boilers (essentially oligomeric lactams) during the process.

EXAMPLE 2 The high boiling fraction of Example 1 was mixed with 10 times the weight of water and heated in a separating reactor for one hour at 300 ° C. The mixture of the separated product was worked in the same manner as described in Example 1, with 74% by weight of the obtained caprolactam, so that the total yield of caprolactam was 93% by weight, based on the amount of the ACN that was used.

Example 3 Example 1 was repeated, and then the high boilers were recycled to the cyclization reactor (reactor A). The process was carried out as established in the example 1, the total yield of caprolactam is 93% by weight.

Example 4 Repeated as in Example 1, 1% by weight of solid sodium hydroxide was added to the high boilers obtained, and the mixture was heated at 300 ° C under reduced pressure to 5 mbar (0.5 MPa) (reactor C). At the same time, the formed caprolactam was continuously removed from equilibrium by means of a distillation column having five theoretical plates. The yield of caprolactam was 74% based on the high boilers, so that the total yield of caprolactam was 93% based on 6-aminocapronitrile that was used. 1Q

Claims

1. A process for the preparation of caprolactam by reacting a solution of 6-aminocapronitrile with water in a liquid base at elevated temperatures, wherein (a) an aqueous solution of 6-aminocapronitrile in the liquid phase is heated without the addition of catalyst in a reactor A to give a mixture I consisting essentially of water, caprolactam and a high boiling fraction (high boilers), then (b) the water is removed from the resulting mixture I to give a mixture II consisting essentially of caprolactam and the boilers high, then (c) The caprolactara and the high boilers of the mixture II are separated by distillation, and then (di) the high boilers of the step (c) are fed to the reactor A of stage (a), or (d2) ) the high boilers are heated in the same manner as in step (a) in another reactor B and then processed in the same manner as in steps (b) and (c) to give more caprolactam, or (d3) boiler are elevated are heated under reduced pressure in the presence of a base in a reactor C and the mixture that reacted is processed by distillation to give caprolactam

2. The process, according to claim 1, wherein from 10 to 150 mol of water are used per mole of 6-aminocapronitrile.

3. The process according to claim 1 or 2, wherein an organic solvent is added to the reaction mixture in step (a).

4. The process according to any of claims 1 to 3. , wherein the reaction in reactor A is carried out from 200 to 370 ° C. The process, according to any of claims 1 to 4, wherein the reaction in reactor A is carried out from 0.1 to 50 Mpa 6. The process, according to any of claims 1 to 5, wherein the residence time is from 20 to 180 minutes in which they are kept in reactor A. SUMMARY OF THE INVENTION The present invention relates to caprolactam which is prepared by reacting a solution of 6-aminocapronitrile with water in the liquid phase at elevated temperatures by a process in which (a) an aqueous solution of 6-aminocapronitrile in the liquid phase is heated without the addition of a catalyst in a reactor A to give a mixture I consisting essentially of water, caprolactam and a high-boiling fraction (high boiler), then (b) the water is removed from the resulting mixture I to give a mixture II consisting essentially of caprolactam and the high boilers, then (c) the caprolactam and the high boilers of the mixture II are removed by distillation, and then (di) the high boilers of the step (c) are fed to the reactor A of step (a), or (d2) the high boilers are heated in the same manner as in step (a) in another reactor B and then processed in the same manner as steps (b) and (c) to produc go more caprolactam, or (d3) the high boilers are heated under reduced pressure in the presence of a base in a C reactor and the The mixture that reacted is worked by distillation to give caprolactam.