GB599252A - Improved process for the production of aromatic amines - Google Patents

Abstract

<PICT:0599252/III/1> Aromatic amines are obtained by continuously contacting a mixture of hydrogen and the corresponding nitro compound in the vapour phase with a fluidised mass of powdered solid hydrogenation catalyst (the contact time being controlled to give the required degree of conversion) and withdrawing the reaction products from the reaction zone. A suitable reaction temperature range is 400 DEG to 600 DEG and preferably 500 DEG to 550 DEG F. The nitro compound may enter the reaction zone as a liquid being then vaporised by the hot catalyst. Advantageously a portion of the products may be re-cycle to the reaction zone as a cooling medium and other liquids, e.g., water or oil may also be injected for cooling purposes. The catalyst itself may be recycled, e.g., by varying the amounts of a fluidising gas, e.g., hydrogen introduced at different parts of the circuit. A suitable catalyst size varies between 200 and 400 mesh. The catalyst is preferably sulphur activated, e.g., a metal sulphide such as molybdenum sulphide with or without an activated carbon base, tungsten sulphide, a mixture of nickel and tungsten sulphides, or a catalyst comprising the oxides of ferric iron, copper, potassium and magnesium. Activated sulphides of cobalt, cadmium, lead, silver and vanadium are also specified. The sulphides may be incorporated with a relatively inert support, e.g., magnesia, zinc oxide, or alumina, clay, synthetic gels of silica or alumina. Advantageousl the catalyst is activated continuously with a volatile sulphide, e.g., hydrogen sulphide or carbon disulphide. In examples (1) 2 nitro 1, 4 dimethyl benzene is reduced to the amine by excess hydrogen under pressure over a heated tungsten sulphide catalyst meta zylidene being used as a diluent; (2) as in (1) but under different conditions of temperature pressure and rate of flow; (3) nitro-toluene is reduced to the amine by excess hydrogen over a heated (a) molybdenum disulphide catalyst, activated by the passage of H2 S for half an hour at 600 DEG C., and (b) nickel sulphide tungsten sulphide catalyst activated by the passage of H2 S for half an hour at 610 DEG C; (c) nickel supported by HF treated clay; (4) nitro-toluene is reduced to the amine by excess hydrogen with a heated catalyst comprising 20 per cent. Fe2O3, 5 per cent. Cu O. 5 per cent. K2 O and 78.5 per cent. magnesium oxide. (5) A series of reductions of the following nitro compounds to the corresponding amines is effected by excess hydrogen and a heated tungsten sulphide catalyst; o nitro-toluene, the catalyst being reactivated after 26 hours by the addition of carbon disulphide to the feed stock; nitro p xylene initially diluted with xylidene; nitro m xylene followed by the re-activation of the catalyst by the passage of H2 S through the reactor; nitro o xylene followed by the re-activation of the catalyst by means of carbon disulphide, nitro ethyl benzene nitro xylenes containing dinitroxylenes with periodic or continuous H2 S activation. Dinitro compounds are also specified as starting materials. In carrying out the process of the invention the nitro compound and hydrogen are bubbled upwards through the finely divided catalyst at a velocity of from 0.5 to 4 ft. per second thereby fluidising the catalyst which may be withdrawn from the reactor as an aerated fluidised stream, cooled and re-cycled to withdraw more reaction heat. The catalyst may be activated by treating it with the sulphur-containing promoter during this circulation, and the promoter itself may be re-cycled together with excess hydrogen. An excess of H2 S is harmful to activity, and it should therefore be applied continuously in small amounts. In the apparatus of the diagram a reactor 14 is fed by a main pipe 12 into which ancilliary pipes bring 10 fresh nitro compound, 46 a portion of the amine product to act as diluent, 20 the excess hydrogen and the hydrogen sulphide or other catalyst activator, 18 fresh hydrogen. The catalyst passes through a heat-exchanger, and returns to the reactor by the pipe 12.ALSO:<PICT:0599252/IV/1> Aryl amines are obtained by continuously contacting a mixture of hydrogen and the corresponding nitro compound in the vapour phase with a fluidised mass of powdered solid hydrogenation catalyst (the contact time being controlled to give the required degree of conversion) and withdrawing the reaction products from the reaction zone. A suitable reaction temperature range is 400 DEG to 600 DEG and preferably 500 DEG to 550 DEG F. The nitro compound may enter the reaction zone as a liquid being then vaporised by the hot catalyst. Advantageously a portion of the products may be re-cycled to the reaction zone as a cooling medium and other liquids, e.g. water or oil may also be injected for cooling purposes. The catalyst itself may be recycled, e.g. by varying the amounts of a fluidising gas g. hydrogen introduced at different parts of the circuit. A suitable catalyst size varies between 200 and 400 mesh. The catalyst is preferably sulphur activated, e.g. a metal sulphide such as molybdenum sulphide with or without an activated carbon base, tungsten sulphide, a mixture of nickel and tungsten sulphides, or a catalyst comprising the oxides of ferric iron, copper, potassium and magnesium. Activated sulphides of cobalt, cadmium, lead, silver and vanadium are also specified. The sulphides may be incorporated with a relatively inert support, e.g. magnesia, zinc oxide, or alumina, clay, synthetic gels of silica or alumina. Advantageously the catalyst is activated continuously with a volatile sulphide g. hydrogen sulphide carbon disulphide. In examples: (1) 2-nitro-1,4-dimethyl-benzene is reduced to the amine by excess hydrogen under pressure over a heated tungsten sulphide catalyst meta xylidene being used as a diluent; (2) as in (1) but under different conditions of temperature pressure and rate of flow; (3) nitro-toluene is reduced to the amine by excess hydrogen over a heated (a) molybdenum disulphide catalyst, activated by the passage of H2S for half an hour at 600 DEG C., and (b) nickel sulphide tungsten sulphide catalyst activated by the passage of H2S for half an hour at 610 DEG C.; (c) nickel supported by HF treated clay; (4) nitrotoluene is reduced to the amine by excess hydrogen with a heated catalyst comprising 20 per cent Fe2O3, 5 per cent CuO, 5 per cent K2O and 78.5 per cent magnesium oxide; (5) a series of reductions of the following nitro compounds to the corresponding amines is effected by excess hydrogen and a heated tungsten sulphide catalyst; o-nitro-toluene the catalyst being reactivated after 26 hours by the addition of carbon disulphide to the feed stock; nitro p-xylene initially diluted with xylidene; nitro m-xylene followed by the re-activation of the catalyst by the passage of H2S through the reactor; nitro o-xylene followed by the reactivation of the catalyst by means of carbon disulphide; nitro ethyl benzene; nitro xylenes containing dinitroxylenes with periodic or continuous H2S activation. Dinitro compounds are also specified as starting material. In carrying out the process of the invention the nitro compound and hydrogen are bubbled upwards through the finely divided catalyst at a velocity of from 0.5 to 4 ft. per second thereby fluidising the catalyst which may be withdrawn from the reactor as an aerated fluidised stream, cooled and re-cycled to withdraw more reaction heat. The catalyst may be activated by treating it with the sulphur-containing promoter during this circulation, and the promoter itself may be recycled together with excess hydrogen. An excess of H2S is harmful to activity, and it should therefore be applied continuously in small amounts. In the apparatus of the diagram a reactor 14 is fed by a main pipe 12 into which ancilliary pipes bring 10 fresh nitro compound, 46 a portion of the amine product to act as diluent, 20 the excess hydrogen and the hydrogen sulphide or other catalyst activator, 18 fresh hydrogen. The catalyst passes through a heat-exchanger and returns to the reactor by the pipe 12.