Application of Polymeric Ionic Liquids in the Catalytic Conversion of Fructose to Lactic Acid

Abstract

Preparation of lactic acid via chemical transformation of carbohydrates requires rigorous reaction conditions, such as high concentrations of alkali, high temperature, etc. This paper reports the use of polymeric ionic liquids ([IMEP]Cl) as catalyst for the hydrothermal conversion of fructose to lactic acid; the main variables of the reaction, temperature, substrate concentration, as well as the relative amount of [IMEP]Cl and NaOH were optimized. Results showed that, at 100 °C, substrate concentration of 25 mmol/L, reaction time of 30 min, the highest yield of lactic acid was 65% with [IMEP]Cl and NaOH concentrations of 100 and 50 mmol/L respectively. This method reduces the reaction temperature and alkali concentration compared to traditional hydrothermal method, additionally it was found that [IMEP]Cl can be used during 5 catalytic cycles without losing its catalytic effect with a lactic acid yield of 55% in the 5th reuse cycle. This demonstrates that the use of polymer ionic liquids as catalysts has a better prospect for future developments. A possible reaction mechanism has been proposed, but further investigation is required.