title: Efficient water removal in lipase-catalyzed esterifications using a low-boiling-point azeotrope.
abstract: High conversions in lipase-catalyzed syntheses of esters from free acyl donors and an alcohol requires efficient removal of water preferentially at temperatures compatible to enzyme activity. Using a lipase B from Candida antarctica (CAL-B)-mediated synthesis of sugar fatty-acid esters, we show that a mixture of ethyl methylketone (EMK) and hexane (best ratio: 4:1, vo/vo) allows efficient removal of water generated during esterification. Azeotropic distillation of the solvent mixture (composition: 26% EMK, 55% hexane, 19% water) takes place at 59 degrees C, which closely matches the optimum temperature reported for CAL-B. Water is then removed from the azeotrope by membrane vapor permeation. In case of glucose stearate, 93% yield was achieved after 48 h using an equimolar ratio of glucose and stearic acid. CAL-B could be reused for seven reaction cycles, with 86% residual activity after 14 d total reaction time at 59 degrees C. A decrease in fatty-acid chain length as well as increasing temperatures (75 degrees C) resulted in lower conversions. In addition, immobilization of CAL-B on a magnetic polypropylene carrier (EP 100) facilitated separation of the biocatalyst.
authors.affiliation: Institute of Technical Biochemistry, University of Stuttgart, Allmandring 31, D-70569 Stuttgart, Germany.
authors.forename: Youchun
authors.initials: Y
authors.lastname: Yan
authors.forename: Uwe T
authors.initials: UT
authors.lastname: Bornscheuer
authors.forename: Rolf D
authors.initials: RD
authors.lastname: Schmid
mesh_terms: D019149:Bioreactors; D002074:Butanones / Q000737:chemistry; D002241:Carbohydrates / Q000737:chemistry; D002384:Catalysis; D004951:Esterification; D004952:Esters / Q000138:chemical synthesis*; D005227:Fatty Acids / Q000737:chemistry; D005656:Fungal Proteins; D006586:Hexanes / Q000737:chemistry; D008049:Lipase / Q000737:chemistry* / Q000378:metabolism; D008567:Membranes, Artificial; D014867:Water / Q000032:analysis*
chemical_list: D002074:Butanones; D002241:Carbohydrates; D004952:Esters; D005227:Fatty Acids; D005656:Fungal Proteins; D006586:Hexanes; D008567:Membranes, Artificial; D014867:Water; C005222:methylethyl ketone; D008049:Lipase; C431349:lipase B, Candida antarctica