GB722025A - Process and apparatus for the production of hydrogen cyanide - Google Patents

Abstract

<PICT:0722025/III/1> <PICT:0722025/III/2> <PICT:0722025/III/3> <PICT:0722025/III/4> In a process for the production of hydrogen cyanide by reacting ammonia with gaseous hydrocarbons such as methane, preferably in the presence of catalysts the hydrogen formed is employed in the production of methane and/or ammonia which products are recycled to the hydrogen cyanide production step. The ammonia may be synthesized from the hydrogen and elementary nitrogen whilst the methane may be prepared by means of the hydrogen from carbon monoxide or dioxide, or by hydrogenation of crude oil, petrol, coal, tar or carbon compounds, the hydrogenation producing products containing more than 2 carbon atoms which are separated, and methane-containing residual gases, which are recycled. In the figures, A indicates the hydrogen cyanide production, B, the methane synthesis, C the ammonia synthesis. In Fig. 1, recycled hydrogen and nitrogen are fed to C and part of the ammonia produced, together with added methane are fed to A. The hydrogen cyanide product is separated from the hydrogen which is recycled. If desired the necessary nitrogen may be added with the methane and recycled with the hydrogen to C, or another alternative (Fig. 3), part of the hydrogen produced is re-cycled and a part burned with air or an oxygen /nitrogen mixture to supply heat to the endothermic hydrogen cyanide reaction. The gases resulting from the combustion, after separation of the water formed are recycled to C to provide the necessary nitrogen, any surplus being withdrawn for use elsewhere. As shown in Fig. 6, a furnace gas containing carbon monoxide, hydrogen and nitrogen together with a recycled hydrogen/nitrogen mixture is fed to a methane synthesis B, after withdrawal of carbon dioxide the methane/nitrogen mixture is fed to A together with ammonia synthesized at C from the nitrogen/hydrogen mixture separated from the product. Further circuits illustrate the employment of the recycled hydrogen to hydrogenate a hydrocarbon mixture to produce hydrogenation products, which are separated, and methane which is fed to the hydrogen cyanide productions. Instead of methane, propylene, ethylene, butylene or acetylene may be employed. In such a case, employing propylene, only 3/4 of the hydrogen produced need be recycled to the ammonia synthesis, the remainder being withdrawn. In Figure 8 a calcium cynamide circuit is shown; ammonia synthesized at C and methane synthesized at B are fed to a reactor A. The hydrogen cyanide/hydrogen mixture is reacted at E with lime to produce calcium cyanamide which is recovered and a carbon monoxide/hydrogen mixture, the hydrogen component being in part separated and fed to C, whilst the remainder of the mixture passes to the methane synthesis at B, carbon dioxide product being removed before the methane formed is recycled. The methane synthesis may be carried out at 150-300 DEG C. preferably employing a catalyst containing aluminium, manganese and nickel, preferably prepared by decomposition of nitrates, formates or acetates. A silica gel carrier may be used. The hydrogen cyanide synthesis is carried out at 850-1350 DEG C. preferably in elongated reaction chambers such as tubes, the surfaces thereof consisting or containing catalysts which may be Ru, Rh, Pt, Os, Ir, Pd, Cu or alloys thereof with each other or with Au, Ag, Re, Nb, Ta, W, Mo or V, or oxides of Be, Al, Sc, Y, La, Mg, with or without the above metals. The catalysts may be employed as gauze or foils which may be electrically heated, or preferably as a coating deposited from a solution or dispersion on the inside or outside of heat-resistant metal tubes, reaction heat being supplied from the side not coated. A plurality of superposed coatings may be used. For example a sillimanite or corundum tube of 20-80 mm. diameter may be treated with a solution of a platinum metal in a mixture of concentrated nitric and hydrochloric acids, and the solvent evaporated while the tubes are rotated. After heating, if desired with a non-oxidizing gas, the catalyst coatings are p formed. The catalyst tubes may be placed in a heating chamber, either horizontally or vertically and are preferably fitted with lead-in pipes to direct the reaction gases to the hotter parts of the tube.