A Detailed Reaction Study of Phosphorus Trichloride and Water

This paper reports on a comprehensive literature search and small scale experimental work on the reaction characteristics of phosphorous trichloride and water. More than 30 tests were conducted, including both closed and open test cells. The water to phosphorus trichloride molar ratio was varied form 1 to 25. When in contact, water and phosphorus trichloride will form two liquid layers with a reaction starting at the interface. The impact of variables on reaction rates (including the interface surface area, layer depth, and stirring were investigated experimentally. A reaction rate model that fits all the measured data is presented. Case studies illustrating the use of this data for emergency relief systems and vent containment design are presented in reference.

Background

The study reported in this paper was conducted in order to address safety and effluent handling issues with two reactor vessels where PCI₃ is used. Each reactor has a volume of 5,000 gallons and operates on a batch cycle. Each reactor is protected against overpressure by a rupture disc and a vent line which leads to an effluent handling system. A scenario was identified where it is possible for a heel of phosphorus trichloride to remain in either one of the reactors undetected (below detection level) at 40 C, and for an operator to attempt to flush the vessel with water. This can lead to the generation of gaseous hydrogen chloride and excessive system pressure.

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