Molten Metaphosphate Electrolysis for Production of White Phosphorus

Technology

This invention uses molten salt electrolysis technology to promote white phosphorus collection by condensation and gas separation at a geometrically designed cathode. Oxidation on the counter electrode inside a tube submerged in the molten melt separates the cathodic and anodic gas streams, allowing evolution of reactive gases like oxygen or carbon dioxide, instead of carbon monoxide. Metaphosphate is utilized as an electrolyte for phosphate reduction. The use of metaphosphate salts is beneficial due to their low melting point of 625°C, their ease of synthesis, and their ability to accept or donate oxide ions via the breaking or formation of polyphosphate bonds. By specifically using carbon-platinum molten salt electrolysis the electrochemical products are phosphorus and oxygen.

The reactor consists of a sealed alumina tube containing a crucible, fitted at the top with a number of ports. By surrounding the counter electrode with a thermally resistant tube and submerging the assembly in molten metaphosphate salt, cathodic and anodic gases can be evolved with no crossover. The alumina tube can be replaced with a material less prone to corrosion, such as carbon or coated with gold/platinum.

Problem Addressed

Current methods of white phosphorus production in industry generate a significant amount of the unwanted byproducts carbon monoxide and carbon dioxide. These byproducts generate 3,250,000 tons of carbon dioxide annually, and decrease the sustainability of the phosphorus chemistry industry. Current methods also generate calcium silicate slag, a byproduct which must be removed from reactors. This invention circumvents carbon monoxide, carbon dioxide, and calcium silicate production in white phosphorus production by utilizing a molten salt electrolysis technology. This technology enables the carbon-free production of white phosphorus at temperatures lower than industry standard.

Advantages

• White phosphorus can be generated without the production of carbonaceous gases
• Electrolysis can be performed at much lower temperatures than industry standard (800°C vs. 1500°C)
• Process can be scaled down and performed on-site at companies that require white phosphorus