Continuous Production of Methyl Lactate from Hemicellulosic Sugars: Identifying and Sorting out Sn-USY-Based Catalyst Deactivation

Potassium-exchanged tin-functionalized USY zeolite ([K]-Sn-USY) has been studied in the continuous transformation of glucose, xylose, and their mixtures in a fixed-bed reactor for the production of methyl lactate at 150 °C. The catalyst efficiently drives the transformation of all the studied substrates, though it faces several deactivation mechanisms, especially in the case of hexoses. Potassium leaching from the catalyst and organic deposition adduced to furanics produced during the reaction were ascribed as the major deactivation causes. The addition of small amounts (10 mg/kg) of potassium (as KCl or KOH) alleviated the catalyst deactivation, allowing the latter stable methyl lactate production over 30% yield for over 140 h from individual carbohydrates and complex sugar mixtures like Scots Pine hemicellulose hydrolysates.