Patent GB-400916-A (GB)
Title: Treatment of chemical compounds
Filed: 1932-01-30
Abstract: A chemical compound is separated from a second compound which dissolves endothermically by contacting a mixture of the two compounds with a quantity of solvent which dissolves the second compound and is thereby cooled to a temperature at which the first compound is relatively insoluble.  The process may be applied to the separation of a mixture of ammonium thiocyanate and thiourea by solution in water in which solvent the ammonium thiocyanate dissolves endothermically.  The process may also be applied to the recovery of ammonium thiocyanate prepared by heating carbon disulphide and ammonium carbonate under pressure and to the recovery of potassium thiocyanate made by heating potassium ferrocyanide with sulphur. Ammonium thiocyanate is melted, preferably under vacuum, and the molten mass is heated to above 140 DEG  C., say 160 DEG  C., to form thiourea.  The mass is then cooled slowly to near the melting point, solidified and further cooled. The solidification preferably takes place by pouring the melt on a cooled disc or roll.  The solidified mixture of thiourea and ammonium thiocyanate is contacted with a quantity of cold water which dissolves ammonium thiocyanate and is thereby cooled to a temperature at which a double salt of thiourea and ammonium thiocyanate according to the description, or thiourea according to the claims, is relatively insoluble.  The separated product is redissolved in hot water, decolorized with carbon or the like, filtered and cooled whereby thiourea separates.  The mother liquor from the thiourea or double salt separation is evaporated to dryness and the solids returned to the process.  The description also refers to the decomposition of thiourea by heat to produce cyanamide, the reaction of cyanamide with ammonium thiocyanate to produce guanidine thiocyanate and the reaction of ammonium thiocyanate with sulphuretted hydrogen to produce ammonium trithiocarbonate.ALSO:Ammonium thiocyanate is melted, preferably under vacuum, and the molten mass is heated to above 140 DEG  C., say 163 DEG  C., to form thiourea.  The mass is then cooled slowly to near the melting point, solidified and further cooled.  The solidification preferably takes place by pouring the melt on a cooled disc or roll.  The solidified mixture of thiourea and ammonium thiocyanate is contacted with a quantity of cold water which dissolves ammonium thiocyanate and is thereby cooled to a temperature at which a double salt of thiourea and ammonium thiocyanate according to the description, or thiourea according to the claims, is relatively insoluble.  The separated product is redissolved in hot water, decolorized with carbon or the like, filtered and cooled whereby thiourea separates.  The mother liquor from the thiourea or double salt separation is evaporated to dryness and the solids returned to the process.  The description also refers to the reaction of cyanamide with ammonium thiocyanate to produce guanidine thiocyanate.ALSO:A chemical compound is separated from a second compound which dissolves endothermically by contacting a mixture of the two compounds with a quantity of solvent which dissolves the second compound and is thereby cooled to a temperature at which the first compound is relatively insoluble.  The process may be applied to the separation of a mixture of ammonium thiocyanate and thiourea by solution in water in which solvent the ammonium thiocyanate dissolves endothermically.  The process may also be applied to the recovery of ammonium thiocyanate prepared by heating carbon disulphide and ammonium carbonate under pressure and to the recovery of potassium thiocyanate made by heating potassium ferrocyanide with sulphur.