| 摘要 |
PURPOSE:To produce phosphoric acid of high purity usable as a material for semiconductors, by decomposing crude phosphine thermally at the thermal decomposition temperature of the phosphine or above, and recovering the phosphine as elementary phosphorus. CONSTITUTION:Phosphine gas, obtained by gasifying crude elementary phosphorus into the gas, and filled in a gas cylinder 1 is introduced from the gas cylinder 1 quantitatively by a flowmeter 3 together with hydrogen gas as a carrier gas from a gas cylinder 2 into a thermal decomposition tube 5 replaced previously with air. The introduced phosphine gas is heated at a higher temperature than about 450 deg.C which is the thermal decomposition temperature of the phosphine by heating in a heating in a heating zone 6 and subjected to thermal decomposition. The average residence time within 3min at the higher temperature than the thermal decomposition temperature is sufficient. The phosphine is thermally decomposed to give gaseous elementary phosphorus, which is then colled and recovered as liquid in a yellow phosphorus collecting ampule 9. On other hand, nitrogen gas, gaseous carbon dioxide and hydrogen gas as the carrier gas, etc. are removed from an off-gas discharging outlet 10.
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