GB851026A - A process for the purification of solid materials - Google Patents

Abstract

Solid substances, e.g. disilylbenzene, are purified by a sublimation process wherein the substance is distilled in the presence of an inert carrier gas and the gaseous overheads are allowed to expand adiabatically into a region where the pressure is such that, as a result of the adiabatic expansion, the temperature falls to a value not higher than the temperature of solidification, Steam, nitrogen, hydrogen, and helium are p mentioned as suitable carrier gases.ALSO:Solid substances, e.g. phenthiazine, diphenylamine, p-hydroxy diphenylamine, acridine, anthracene, terphenyl (1 : 2 and 1 : 3 diphenyl benzene), naphthalene, 2,21-bis-(p-hydroxyphenyl propane), rosin acids such as abietic acid, high molecular weight coal tar products, and dicyclopentadienyl iron, are purified by subjecting the substance to distillation in the presence of an inert carrier gas, and allowing the gaseous overheads, comprising the normally solid substance in the gaseous state and the carrier gas, to expand substantially adiabatically into a region where the pressure is such that, as a result of adiabatic expansion, the temperature falls to a value not higher than the temperature at which the substance solidifies. Substantially adiabatic expansion comprises expansion which is at least 60% of the theoretical adiabatic expansion. Steam, nitrogen, hydrogen, helium, or alcohol vapour when appropriate may be used as the inert carrier gas. The adiabatic expansion may be attained by providing a constriction such as a converging-diverging nozzle between the heating vessel and the condensing chamber. The pressure in the heating vessel is generally above atmospheric but in some cases may be sub-atmospheric. A substance which removes chemically the impurities in the substance under treatment may be present, e.g. when treating phenothiazine about 1% of iron powder, based on the phenothiazine, may be added to the charge in order to remove iodine impurities. In an example, impure phenothiazine and a small proportion of iron powder are heated to 280 DEG C. and then superheated steam at 300 DEG C. is passed through the charge. A pressure in the vessel of 45 p.s.i.g. is maintained. The steam and distillate are cooled adiabatically by expanding through a nozzle into a condenser, maintained at atmospheric pressure. Solid phenothiazine is deposited.ALSO:Solid substances, e.g. selenium, are purified by a sublimation process in which the substance is distilled in the presence of an inert carrier gas such as steam, nitrogen, hydrogen, helium or alcohol vapour and the gaseous overheads comprising the said solid substance in the gaseous state and the carrier gas, allowed to expand adiabatically into a region where the pressure is such that, as a result of the adiabatic expansion, the temperature falls to a value not higher than the temperature at which the substance solidifies. The adiabatic expansion may be attained by providing a constriction such as a converging-diverging nozzle between the heating vessel and the condensing chamber. The pressure in the heating vessel may be above or below atmospheric.