SU784762A3 - Method of preparing adiponitrile - Google Patents

Abstract

Olefinic cpds. R2C=CR-X (where X = CN, CONR2 or COOR', R = H or R' and R' 1-4C alkyl), are hydrodimerised by electrolysing an aq. soln. contg. >=0.1 wt. % of the olefinic cpd. >=10-5 gmol/l quat. ammonium cations and >=0.1 wt. % of an alkali metal phosphate, borate or carbonate in a single compartment cell with an anode consisting primarily of carbon steel. Process is esp. useful for converting acrylonitrile into adiponitrile, a useful raw material for nylon 66 prodn. Process can be operated on commercial scale since no cell dividing membrane are necessary. Rate of anode corrosion is very low.

Description

(54) METHOD FOR OBTAINING ADIPONITRILE The invention relates to a process for the preparation of adiponitrile and widely used in the manufacture of synthetic fibers, in particular nylon. A known method for producing adiponitrile by electrolytic hydrodimerization, acrylonitrile in an aqueous solution of a quaternary ammonium salt at pH 6-10 and a temperature of 30-35 ° C. The anode is made of platinum or gel for, or nickel, the cathode is made of lead, alloy of mercury with lead, cadmium, alloy of thallium with lead, zinc or copper. Adiponitrile yield 83% fl. The disadvantage of this method is a significant anode corrosion rate of 17.8 mm per year in the case of a no keel anode (hydrodimerization conditions of acrylonitrile: time - 6 hours, current density 0.16 A / cm pH-8, concentration l. Wt.% , unsubstituted sodium phosphates and 10 g mol / l of ammonium base cations) and 48 mm per year in the case of using a thallium-lead alloy (conditions of hydro-dimization: time 24 h, current density - 0.16 A / cm 2, pH - 8) . The method of obtaining adiponitrile by electrolytic dimerization of acrylonitrile in a single-cell electrolyzer at a temperature of 0–40 s in the presence of additives of quaternary ammonium bases, phosphates and alkali metal borates and at pH 5–10 is also known to be closest in technical form to pre-cooked. The anode is made of iron or a cathode-graphite magnet, and the conversion of acrylonitrile is 20-70% 2. The disadvantage of this method is that the anode is corroded to 12 mm per year, even at a temperature of 20 ° C, which requires intensive cooling of the electrolysis medium and maintaining a sufficiently low current density (usually less than 0.1 A / cm). The purpose of the invention is to improve the process technology as a result of reducing the corrosion rate of the anode at relatively high temperature and current density. The goal is achieved by the method of obtaining adiponitrile by i electrolytic dimerization of acrylonitrile in a single-cell electrolyzer in the presence of additives — quaternary ammonium bases, phosphates and alkali metal borates, the distinguishing feature of which is that the electroconductor is made from carbon steel anode with SO. -SS C and current density 0.150, 27 A / cm. When using a carbon steel anode (0.1-1.5% carbon), the anode corrosion rate per year is 0.35-0.9 mm, and the process selectivity is 8.7.7%. The proposed method is carried out as follows. In the process of electrolytic hydrodimerization, the medium can be not only aqueous, but also the organic phase dispersed in an aqueous medium in any quantities at which the aqueous solution forms a continuous phase of the electrolysis medium. The quaternary ammonium cation concentration is from -10 g-mol / L. Such mohsho cations can be introduced into a hard solution in a known manner, for example, by dissolving hydroxide of even vertical ammonium or its salt in solution in an amount necessary to create a given concentration of cations, preferably tetralkyl ammonium ions. As phosphates and borates of alkaline metals, secondary or primary acidic phosphate or secondary acidic potassium borate can be used, usually in an amount of 0.5 weight.% The acidity of the solution is maintained so that the cathode should be neutral or alkaline, and around the anode equal to 7. In the process of single-cell electrolysis, the anode can be made in the form of a plate of a sheet element. The advantage of a carbon dioxide anode is also that it does not contain large amounts of metals which, as a result of entering the electrolysis medium, tend to be galvanically deposited on the cathode, thereby changing the nature of the cathode surface with the h, reducing the selectivity of the process. Example 1. In the course of a continuous process, an aqueous solution containing approximately 1.4% acrylonitrile, 1.2% adiponitrile, 0.2% acrylonitrile-UND by-products, b, 8 10 g-mol / l Unide ethyltribyl ethyl cations, 10% of a mixture of partially substituted sodium orthophosphates, which corresponds to pH of the solution equal to 9 (approximately. / 04) and 2% sodium pyroborate (N3-, 07.1 p, allowed at a temperature of 55 ° C and at a speed of 1.22 m / s an electrolytic bath not separated into sections with an anode made of carbon steel (0.2% C) separated by a gap of 2.36 mm from the cadmium cathode, the composition of which is described in Example 1. The solution, which also contains approximately 0.8% by weight of the organic phase, comprising approximately 58% adiponitrile, 25.5% acrylonitrile, 8.5% acrylonitrile-UND by-products, and 8% of water, is electrolyzed by passing it through a bath with an average voltage drop across 3.85 V across and a current density of 0.16 A / sq, see the anode (or cathode) surface in contact with the solution and then sent to a decanter to establish equilibrium with the resulting upper layer, the composition of which is approximately equal to the composition of the specified organic phase. Subsequently, the separated bottom layer (aqueous layer) is reclaimed for recirculation through the bath. After 62 hours of electrolysis, during which acrylonitrile and water are continuously added to the circulating aqueous solution and the equivalent amount of product is removed from the top layer of the decanter, it is established that the acrylo nitrile in the solution is converted to adiponitrile with an average molar selectivity of 87.7%, and the corrosion rate of the carbon steel anode is only 0.38 mm / year. Example 2. In the course of carrying out a continuous process, a liquid electrolytic medium consisting of a 99% aqueous solution containing, in a dissolved form, 0.6-0.9% acrylonitrile, 0.5-0.8% gishpinitryl, 21% mixture sodium orthophosphates, giving the solution a pH of 8.5, 0.7 1, 3x10 mol / l of ethyltributylammonium ions and borates, obtained by adding orthotoboric acid in an amount of approximately 2% solution, and from 1% dispersed, HC-30 undissolved organic phase containing 30- 32% acrylic nitrile, 54-56% adiponitrile, 7% acrylonitrile-EKD by-products and 6–7% of water is passed at a temperature of 55 s and at a speed of 1.2 m / s through an electrolytic bath, which is not divided into sections, with an anode of carbon steel, separated by a gap of 2.25 mm from a cadmium cathode whose composition (at least 99 , 9% cadmium) and subjected to electrolysis when it is passed through a bath with a current density of 0.185 A / cm of the cathode surface. Organic phase; the resulting adiononitrile, by-products, and unreacted acrylonitrile are separated — the electrolyzed medium before decantation, and acrylonitrile is added, after which the medium is recycled through the bath and electrolyzed again under the conditions described above. On kahsdy Faraday Current (96500

Pendant) passed through the medium, discharging approximately 13 g of the solution from the system and replaced with water containing, in a dissolved form, ethyltributyl monibium ions and orthophosphates of sodium and borate in an amount that is sufficient to maintain the concentrations of these components of the solution at the above level and to keep the total The amount of medium is mostly constant. After 89 hours of electrolysis under these conditions, it is established that acrylonitrile is converted to adiponitrile with an average and final selectivities of 87.7 and 86.4%, respectively, and the corrosion rate of the anode surface is 0.35 mm / year.

Froze during the continuous process, a liquid electrolytic medium consisting of a 99% aqueous solution containing, in a dissolved form, 1.4-1.6% acrylonitrile, approximately 1.2% adiponitrile, 10% mixture of sodium orthophosphate, O, 2- 7.9 l10 mol / g hexamethylene bis (ethyl dibutylamlonium) ions and sodium borates, obtained by neutralizing orthoboric acid in an amount corresponding to approximately 2% of the solution to a pH of 8.5 and from approximately 1% dispersed, on an undissolved organic phase containing 27 -29% acrylon Itryl, 5458% adaponitrile, 7-9% acrylonitrile-UND by-products, and 8% water, are passed at 55 ° C and with a speed of L, 22 m / s through an electrolytic bath not divided into sections, with an anode of carbon steel separated by a gap 1, 76 N04 from the cadmium cathode, which mainly corresponds to hteHeHOMy in example 1 to the cathode, and is subjected to electrolysis when it is passed through the bath with a current density of 0.185 L / cm of the surface of the anode (or cathode.)

The organic phase containing the formed adiponitrile, acrylonitrile-UND by-products, and unreacted acrylonitrile are withdrawn from the electrolyzed medium and acrylonntrile is added, after which the medium is recycled through the bath and electrolyzed again under your conditions (under the conditions described above.) conditions establish that acrylonitrile is converted to adiponitrile with a selectivity of 87.8%, and the corrosion rate of the steel anode is less than 0.4 mm / g D,

0

Example 4. In the process, which basically corresponds to the process described in Example 3, except that instead of 0.25, 7.9 x 10 mol / l of hexixistetilenbis (ethyl dibutyleshmonium) ions are used in ka4ecTBe of quaternary cations in an aqueous solution of 0.4-2 , 6-10 mol / l tetramethylenebis (tributylammonium)

0 ions, installed after 85 hours of electrolysis, that acrylonitrile is converted to adiponitrile with an average selectivity of 87%, and the corrosion rate of the steel anode is less than 0.4 mm / year.

five

Claims (2)

1. US patent 3,611,765 cl. 204-222, publ. 1970. 2. US patent 3616321, cl. 204-73, publ. 1971.