One-step fabrication of polymeric self-solidifying ionic liquids as the efficient catalysts for biodiesel production

Polymeric self-solidifying ionic liquids (PSILs) were simply fabricated by the facile nucleophilic substitution reaction between polyethyleneimine (PEI) and 1,3-propanesultone (PS). Because of the presence of less-substituted amino groups in PEI chain, more than 1 equivalents of sulfonic groups (–SO 3 H) per amino group were grafted onto PEI chain. Part of –SO 3 H groups could be bonded with amino groups to form –SO 3 – …N + – zwitterions , the presence of zwitterion and the high molecular of PEI could make PSILs become solid, while the left free –SO 3 H groups played a role in the acid catalysis and therefore no additional acids were required. The final PSILs showed high catalytic activity , stability and generality as the heterogeneous catalysts for biodiesel production via the esterification of a variety of free fatty acids (FFAs), as well as the transesterification of waste cooking oil and palm oil. Moreover, the one-step fabrication process of PSILs is much simpler than the multi-step fabrication process of traditional ionic liquids, suggesting potential benefits.