GB598532A - Improvements in or relating to apparatus for conducting reactions in liquid phase - Google Patents

Abstract

Apparatus for conducting chemical reactions under pressure in the liquid phase which reactions result in the production of a solid reaction product which comprises, connected together in the following sequence, a closed vessel provided with a pump for circulating liquid therethrough and means for admitting solid thereinto, a second pump for forcing liquid from the closed vessel and at the desired pressure through a closed reaction zone having associated means for maintaining the zone at a predetermined temperature and temperatures, heat exchange means for cooling the liquid, an enclosed filter for separating the solid reaction product from the attendant liquor, a conduit for returning the liquor to the closed vessel, and a reducing valve between the closed reaction zone and the return conduit. The apparatus may be employed in carrying out reactions in liquid ammonia, liquid sulphur dioxide or liquid carbon dioxide. As employed in the production of melamine by heating dicyandiamide dissolved in liquid ammonia, dicyandiamide is introduced into a vessel 2 through a cover 20, and after closing the cover and setting the valves, mother liquor or ammonia is circulated through the vessel from mother liquor tank 1 by a pump 46. When the solution reaches the required strength, by manipulating the valves the solution is pumped into the mother liquor tank and from thence to a storage tank 3. The solution is then withdrawn by a high pressure pump 4 and forced through steam-jacketed stainless-steel reaction tubes 6 heated to a temperature of 110-160 DEG F. The liquor is discharged into a water-cooler auto <PICT:0598532/III/1> clave 7 through a pressure reducing valve 70. The melamine crystals are removed by one or other of the alternately employed filters 8, 9, the mother liquor being returned through a line 14 to the tank 1. The melamine in the filter not in the circuit is washed with liquid ammonia, and discharged from the filter into water in a tank 120. After washing with water, the melamine slurry is forced by a pump 123 into a filter press 127. Deposition of melamine in the reaction tubes 6 brought about by a failure of the valve 70 to close and consequent reduction in pressure is prevented by the provision of a vessel 80 containing liquid ammonia under pressure and connected to the tubes 6 by a line 83.ALSO:In the production of melamine by heating dicyandiamide dissolved in liquid ammonia, the dicyandiamide is introduced into a vessel 2 through a cover 20, and after closing the cover and setting the valves mother liquor or ammonia is circulated through the vessel from a mother liquor tank 1 by a pump 46. When the solution reaches the required strength, by manipulating the valves the solution is pumped into the mother liquor tank and from thence to a storage tank 3. The solution is then withdrawn by a high pressure pump 4 and forced through steam-jacketed stainless-steel reaction tubes 6 heated to a temperature of 110-116 DEG C. The liquor is discharged into a water-cooled <PICT:0598532/IV/1> autoclave 7 through a pressure reducing valve 70. The melamine crystals are removed by one or other of the alternately employed filters 8, 9, the mother liquor being returned through a line 14 to the tank 1. The melamine in the filter not in the circuit is washed with liquid ammonia and discharged from the filter into water in a tank 120. After washing with water, the melamine slurry is forced by a pump 123 into a filter press 127. Deposition of melamine in the reaction tubes 6 brought about by a failure of the valve 70 to close and consequent reduction in pressure is prevented by the provision of a vessel 80 containing liquid ammonia under pressure and connected to the tubes 6 by a line 83. Such apparatus may also be used in the manufacture of guanidine nitrate by heating ammonium nitrate with dicyandiamide o cyanamide in water or aqueous ammonia.