GB1036680A - Improvements in manufacture of boron-containing substances - Google Patents

Abstract

Diborane is produced by passing hydrogen, hydrogen chloride, and boron trichloride, together with boron or a boron compound, into a reaction zone maintained at 700-1500 DEG C. to form chlorinated boranes, disproportionating the chlorinated boranes to diborane and boron trichloride, separating diborane, and recycling the residual hydrogen, hydrogen chloride, and boron trichloride to the reaction zone together with fresh hydrogen. The boron compound used is boron carbide or an unsubstituted boron hydride with a hydrogen to boron ratio of less than 3: 1. The process operates continuously, hydrogen and boron or the boron compound being fed in amounts corresponding to the diborane withdrawn. The effluent from the reaction zone may be quenched in boron trichloride and then fractionated to form a stream containing hydrogen and hydrogen chloride, which is recycled direct, and a stream containing chlorinated borane and boron trichloride, which is disproportionated and fractionated into diborane product and boron trichloride which is recycled. A cyclone separator may be interposed between the quenching zone and the fractionation zone to remove contaminants. The solid boron or boron compound may form a fluidized, fixed, or moving bed in the reactor; when boron carbide is used, solid is continuously withdrawn to remove carbon by-product. Higher solid, liquid, or vaporous boron hydrides may be used as the feed with a bed of carbon or graphite particles and in this case the feed of hydrogen is reduced. In examples, a tubular reactor contains a bed of boron carbide or elemental boron; disproportionation is carried out at 65-80 DEG C. Other examples use a bed of granular coke or boron carbide to which is added solid boron hydride polymers or volatilized pentaborane or tetraborane.