Aqueous-phase hydrogenation of lactic acid to propylene glycol

Abstract

The metal-catalyzed hydrogenation of lactic acid to propylene glycol (PG) in aqueous solution is investigated in a laboratory-scale stirred batch reactor. Ruthenium on activated carbon is identified as an active catalyst for the reaction, with nearly complete conversion achieved at reaction temperatures of 100–170°C and hydrogen pressures of 7–14 MPa. Selectivity to PG in excess of 90% at 95% lactic acid conversion has been obtained at optimal reaction conditions. Potassium and calcium lactate salts cannot be directly converted to PG, but simple addition of sulfuric acid suffices to convert the salt to free acid, which is then hydrogenated. The ready availability of low-cost lactic acid, produced via fermentation of corn-derived carbohydrates, makes this biomass-based route an attractive alternative to the traditional petroleum-based pathways to PG.