Dilanthanum dioxymonosulfate as a recycle reagent and recycle substrate for the sulfur dioxide-iodine thermochemical hydrogen cycle

Abstract

Insoluble dilanthanum oxide-sulfite-sulfate-hydrates were prepared by reacting dilanthanum dioxymonosulfate with sulfur dioxide in aqueous media. These compositions reacted with iodine to yield sulfate in the solid phase and hydrogen iodide in the gas phase. Highest yields of hydrogen iodide were measured at 660 K for a reaction time of a few seconds. Yields also depended on the sulfite content of the hydrate compositions and were highest when the dilanthanum dioxymonosulfate was 60% neutralized. Higher yields of hydrogen iodide were obtained by a second iodine oxidation after separation of the first solid product. A water splitting thermochemical cycle using these reactions is described in which hydrogen is produced by catalytic decomposition of hydrogen iodide and oxygen results from thermal decomposition of the solid product.