The excellent suitability of immobilized Candida antarctica lipase B (Novozym 435) catalyst to carry out the synthesis of methyl oleate (biodiesel) by methanolysis of triolein in ILs based on imidazolium cations with large alkyl side chain (from C(12) to C(18)) has been demonstrated at 60 and 85 degrees C. The phase behaviour of IL/triolein/methanol and IL/methyl oleate mixtures were studied at different concentrations and temperatures, the best results (up to 98.6% biodiesel yield after 6 h) being obtained for ILs able to provide monophasic reaction systems, i.e. 1-methyl-3-octadecylimidazolium bis(trifluoromethylsulfonyl)imide). A continuous enzymatic reactor, based on biocatalysts particles coated with hydrophobic ILs, for biodiesel synthesis in supercritical carbon dioxide was studied at 60 degrees C and 180 bar. The operational stability of the immobilized lipase was improved by its coating with ILs, i.e. 1-methyl-3-octadecylimidazolium hexafluorophosphate, leading to a two-phase systems with respect to the biodiesel product, which showed an excellent catalytic behaviour in continuous operation under supercritical conditions (up to 82% biodiesel yield after 12 cycles of 4 h). (C) 2011 Elsevier Ltd. All rights reserved.