Optimisation of enzymatic synthesis of diacylglycerols in binary medium systems containing ionic liquids

Two different approaches, namely the n-hexane/ionic liquid (IL) system and the binary IL system, were optimised as a reaction medium for selective production of diacylglycerols (DGs) by lipase-catalysed glycerolysis of triolein. ILs used are [BMIM]·[BF₄], [BMIM].[PF₆], [OMIM]·[PF₆], [TOMA]·[TFA], [TOMA]·[Tf₂N], and Ammoeng 120. The effect of mixing n-hexane with IL in different ratios and at different temperatures was found to depend on the polarity of the IL used. In general, the addition of n-hexane resulted in improvement of triacylglycerol (TG) conversion and DG yield. The enhancement of mass transfer due to the decrease of viscosity is a major reason. The binary IL systems were evaluated with the aim of increasing DG yield and TG conversion while decreasing monoacylglycerol (MG) content. The reaction conditions of glycerolysis in the binary IL system consisting of [TOMA]·[Tf₂N]/Ammoeng 102 were optimised by response surface methodology (RSM). Optimal conditions were recommended as temperature between 55-60 °C, glycerol/oil amount between 1.8-2 mmol/2 mmol, [TOMA]·[Tf₂N] concentration less than 10%, reaction time 24 h, and lipase amount 15 wt.% based on oil mass. Under these conditions, the glycerolysis reaction resulted in reasonably high DG yield (∼70%) and TG conversion (∼90%).