Understanding Hydrogen in Bayer Process Emissions. 2. Hydrogen Production during the Degradation of Unsaturated Carboxylic Acids in Sodium Hydroxide Solutions

Abstract

This is the second in a series of studies of the production of hydrogen from the degradation of organic compounds in sodium hydroxide solutions. Unsaturated carboxylates, which are intermediate products in the wet oxidation of the types of monoaromatic compounds typically present in Bayer process liquors, have been found to produce significant amounts of hydrogen during alkaline degradation. The alkaline degradation of nine unsaturated carboxylates was investigated under anaerobic conditions in an autoclave, and the effect of temperature (175–275 °C) and NaOH concentration (0–6 M) on the degradation of acrylate, 2-butenoate, maleate, and 2-hexenoate was studied in detail for reaction times up to 120 min. All of the compounds investigated decompose to produce about 1 mol of hydrogen gas per mole of organic compound consumed, as well as a range of low molecular weight (LMW) carboxylates. The stoichiometries of the formation of hydrogen and LMW carboxylates from the unsaturated carboxylates observed here are...