The large-scale enzymatic production of biodiesel suffers with technical problems such as enzyme inactivation by methanol and the immiscibility of methanol and oil. Ionic liquids (ILs) have the potential to solve these issues.

Xuebing Xu and colleagues, Aarhus University, Denmark, have evaluated several ILs as the reaction media for the enzymatic methanolysis of rapeseed oil and found the results were strongly dependent on the molecular structures of the ILs.

The IL Ammoeng 102, containing a tetraaminum cation with C₁₈ acyl and oligoethyleneglycol units, formed a suitable biphasic reaction system that allowed conversion of almost 100 % of the rapeseed oil, giving a biodiesel yield of 98 %. It also produced less mono- and diglyceride impurities than other ILs. Only small amount of IL was needed to host the reaction. The oil/Ammoeng 102 system also demonstrated a protective effect against enzyme deactivation and automatic phase separation, aiding biodiesel recovery.

• Characterization of ionic liquid-based biocatalytic two-phase reaction system for production of biodiesel
  B. L. A. P. Devi, Z. Guo, X. Xu,
  AIChE J. 2010.
  DOI: 10.1002/aic.12355