Improved enantioselective esterification of dl-menthol catalyzed by immobilized TL 100L lipase

Lipozyme TL IM exhibits high enantioselectivity for the resolution of dl-menthol by the esterification of l-menthol. However, in this study, some factors such as protein loss, enzyme inactivation, and acetaldehyde damage greatly reduced the reaction conversion. For relieving the effects of these factors, macroporous resin that absorbs more protein was selected to immobilize Lipozyme TL 100L lipase with trehalose as the modifying agent. The immobilized lipases retained 37.2% of their initial activity after 8 times of repeated use. A packed-bed reaction system was designed to prevent the leaching of adsorbed lipase molecules out of the macroporous resin pore and to outflow acetaldehyde with the product. The immobilized lipase was continuously used with ee_p > 99.0%. Over 83.9% of the initial conversion remained after the reaction solution of 100 column volumes was pumped into the lipase column. The average volumetric productivity of l-menthyl acetate was 0.76 g/L/h. This process is readily applicable to large-scale preparation for optically active menthol.