Green biocatalytic synthesis of biodiesel from microalgae in one-pot systems based on sponge-like ionic liquids

Abstract

Binary mixtures of ionic liquids (ILs) have been used for developing one-pot systems suitable for the direct extraction and biocatalytic transformation of algal oil to biodiesel without prior isolation. These mixtures were based on the combination of sponge-like ionic liquids (e.g. 1-hexadecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C16mim][NTf2]) with the IL 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]), taking into account the excellent suitability to carry out the biocatalytic synthesis of biodiesel of the first one, and the ability for dissolving cellulosic biomass of the second. The extraction of oils was carried out by incubating the dry microalgae (Chlorella vulgaris or Chlorella protothecoides) in the appropriated IL binary mixture at 110 °C, which after being cooled at 60 °C allowed to be transformed to biodiesel by an immobilized lipase. This resulted in a fast and efficient biodiesel synthesis, e.g. up to 100% yield in 2 h at 60 °C. The subsequent cooling until room temperature and the iterative centrifugation of the resulting semi-solid systems at 20 and 18 °C led to the separation of the liquid algae biodiesel from the solid IL mixture, which was recovered and reused for further operation cycles.