Patent GB-727571-A (GB)
Title: Manufacture of acrylonitrile
Filed: 1951-07-18
Abstract: In the production of acrylonitrile by the additive combination of hydrocyanic acid and acetylene in the presence of an aqueous acid cuprous salt catalyst the hydrocyanic acid is used in a dilute gaseous form, i.e. in the form of a gas which contains less than 20 per cent by volume and usually only about 0.3 to 5 per cent by volume of hydrocyanic acid, and is absorbed in a first stage of the process in the cuprous salt catalyst at a temperature not substantially exceeding 60 DEG  C. and the absorbed hydrocyanic acid is reacted with the acetylene in a second stage of the process at a temperature of about 70-100 DEG  C., which temperature is favourable to the formation of acrylonitrile.  The process may be carried out continuously or discontinuously and it is preferred to use a cuprous chloride catalyst, e.g. a Nieuwland catalyst consisting of a mixture of cuprous chloride, <PICT:0727571/IV (b)/1> ammonium chloride, concentrated hydrochloric acid and water and to carry out the synthesis in an oxygen-free atmosphere.  In the discontinuous process the dilute gaseous hydrocyanic acid is introduced into the cuprous chloride catalyst, preferably at room temperature, and advantageously until about 30 grams of material have been absorbed per litre of catalyst, the gas stream is then shut off and the reaction mixture heated to about 70-100 DEG  C. and acetylene introduced into the heated mixture.  The acetylene leaving the mixture carries away the acrylonitrile formed and the flow of acetylene is stopped when no more acrylonitrile is formed. In the continuous process the gas containing hydrocyanic acid may be introduced into an absorption vessel through at least a part of the aqueous cuprous chloride catalyst preferably at below 40 DEG  C., e.g. at room temperature, and the catalyst is led out of the absorption vessel into a reaction tower heated to 70-100 DEG  C., preferably to 80-90 DEG  C., and through which is passed a stream of acetylene which may be diluted with an inert gas.  The acrylonitrile formed is removed with the gas stream and absorbed in water or condensed by cooling and then purified by distillation.  The excess of acetylene is reintroduced into the reaction tower and at least a part of the used catalyst, after cooling e.g. to be low 40 DEG  C., is recycled to the absorption vessel where it is recharged with hydrocyanic acid.  The acetylene used in the synthesis may be in concentrated form or may be diluted with an inert gas such as nitrogen.  Acetylene from an electric arc is suitable.  The hydrocyanic acid may be used in the form of the gaseous mixture containing hydrocyanic acid and acetylene obtained by the synthesis of hydrocyanic acid in an electric arc by the method of Andriessen, see Specification 296,355, [Class 2 (i)], or it may be used in the form of the gas obtained by the synthesis of hydrocyanic acid by the method of Andrussow, see Specification 361,004, [Group III], or in the form of the gas resulting from the distillation of molasses residues. When the hydrocyanic acid is used in the form of the gaseous mixture obtained by synthesis in the electric arc, the acetylene present may be utilized in various ways, e.g. by passing the gaseous mixture into the catalyst so that initially both the hydrocyanic acid and the acetylene are absorbed, the absorbed acetylene being driven out as the concentration of the combined hydrocyanic acid increases, and being then used for the reaction in the second stage of the process.  The acetylene and hydrocyanic acid may also be absorbed simultaneously in the catalyst by adjusting the ratio of the amount of gas to be absorbed and the speed of re-circulation of the catalyst.  The gas containing hydrocyanic acid and acetylene may also be passed through two absorption vessels arranged in series so as to absorb the two gases separately and the catalyst charged with hydrocyanic acid and acetylene passed into a reaction tower where it is heated to effect the synthesis of acrylonitrile.  In another arrangement two gases are used, one containing hydrocyanic acid and the other containing dilute acetylene, e.g. acetylene produced in an electric arc from hydrocarbons, each gas being passed into the catalyst in an absorption vessel and the catalyst charged with hydrocyanic acid and acetylene passed from the respective absorption vessels into the reaction tower which is heated to effect the acrylonitrile synthesis. It is desirable to free the catalyst issuing from the reaction tower from volatile compounds dissolved therein before returning it to the absorption vessel. In examples: (1) the apparatus shown in Fig. 3 is used.  It consists essentially of a reaction tower R, an absorption vessel A and a washing device W.  The reaction tower R which can be heated has a branch pipe r and is connected to the absorption vessel by a system of pipes and cooling vessel a1, a2 and a3 in which the catalyst is cooled.  The catalyst passes to the tower by the system a4, a5 and a6 and is slowly heated in the pipe a6.  The reaction tower is connected with the washing device W for the acrylonitrile and by cooling the gases issuing from the top end of the tower part of the acrylonitrile separates and is collected in liquid form in the vessel W2.  The uncondensed acrylonitrile vapour is dissolved out of the gaseous mixture by the water in the washing device W and the pipe 5 serves to introduce fresh acetylene, the circulation of which is maintained by the pump Pa whilst a part of the recirculated acetylene is removed through pipe 7 together with impurities.  The dilute hydrocyanic acid gas is introduced into the absorption vessel through the pipe 1 and the waste gases removed through pipe 2.  In operation the reaction tower, absorption vessel and connecting system are charged with Nieuwland catalyst, some hydrocyanic acid being added to the catalyst to reduce its tendency to crystallization, and the temperature in the reaction tower is brought to 85-90 DEG  C. while the catalyst enters the absorption vessel at 30-40 DEG  C. and leaves it at 20-25 DEG  C.  Nitrogen is passed through the system for the circulation of the acetylene whilst a gas containing hydrocyanic acid is passed through the absorption vessel.  The catalyst charged with hydrocyanic acid is pumped into the reaction tower where it mixes with the catalyst present and is thus heated to 85-90 DEG  C. and as soon as the current of nitrogen leaving the tower contains about 0.5 gram hydrocyanic acid per 100 litres it is replaced by acetylene. The acrylonitrile formed is recovered in part in the receiver W2 and in part by absorption in the water in the washing device W; (2) the apparatus used is the same as in (1) except that the pipe for the supply of fresh acetylene is closed so that only the acetylene in circulation is used.  In this case a gaseous mixture containing hydrocyanic acid, crude acetylene and nitrogen is introduced into the absorption vessel and the catalyst which becomes charged with both hydrocyanic acid and acetylene is passed, together with some of the gas in contact with the catalyst in the absorption vessel, into the reaction tower where it is heated to 85-90 DEG  C. and in which a part of the absorbed acetylene reacts while the remainder passes into the system for the circulation of acetylene.  The acrylonitrile is recovered as in (1); (3) as in (2) except that purified acetylene is used in admixture with hydrocyanic acid and nitrogen.