Immobilised Lipase on Structured Supports Containing Covalently Attached Ionic Liquids for the Continuous Synthesis of Biodiesel in scCO2

Different nanostructured supports, based on 1-decyl-2-methyimidazolium cations covalently attached to a polystyrene divinylbenzene porous matrix, were used as carriers to immobilise Candida antarctica lipase B. The suitability of these immobilised lipase derivatives for the synthesis of biodiesel (methyl oleate) by the methanolysis of triolein has been tested in both tert-butanol and supercritical (sc)CO2 (18 MPa, 45 degrees C) as reaction media. The use of modified supports with low ionic-liquid loading covalently attached to the main polymeric backbone chains provide structured materials that led to the best biodiesel yields (up to 95%) and operational stability (85% biodiesel yield after 45 cycles of 84 h) in scCO(2) (45 degrees C, 18 MPa). The presence of tert-butanol as an inert cosolvent in the scCO(2) phase at the same concentration as triolein was key to avoid poisoning the biocatalyst through the blockage of its active sites by the polar byproduct (glycerol) produced in the biodiesel synthesis.