Reaction and Kinetic Studies of Lactic Acid Conversion over Alkali-Metal Salts

Abstract

Studies of lactic acid catalytic conversion over alkali salts and bases on silica demonstrate that the yield of 2,3-pentanedione (23P) increases with decreasing Lewis acidity of the alkali metal, from 15% for lithium hydroxide at 320 °C to 49% for cesium hydroxide at 280 °C. The rate of 23P formation varies linearly with alkali metal loading up to saturation at 2 mmol of catalyst/g of support. Experiments with different silica supports showed that acetaldehyde formation increases with support acidity, reducing 23P yield. Postreaction FTIR studies indicate the presence of alkali lactate as the dominant species on the support surface at reaction conditions. These results, along with the kinetic model developed, support the proposed mechanism of 23P formation as a condensation between lactic acid and alkali lactate.