Dicationic Ionic Liquids as Environmentally Benign Catalysts for Biodiesel Synthesis

Some dicationic ionic liquids, N,N,N′,N′-tetramethyl-N,N′-dipropanesulfonic acid ethylenediammonium hydrogen sulfate, N,N,N′,N′-tetramethyl-N,N′-dipropanesulfonic acid 1,3-propanediammonium hydrogen sulfate, N,N,N′,N′-tetramethyl-N,N′-dipropanesulfonic acid 1,6-hexanediammonium hydrogen sulfate, were prepared. These ionic liquids could be used as efficient and recyclable catalysts for the synthesis of biodiesel from free long-chain fatty acids or their mixtures with low-molecular-weight alcohols as substrates. the reaction was accomplished in a monophase at 70 °C for 6 h, while the products was separated from the catalyst system by liquid/liquid biphase separation at room temperature with good yields of 93−96%. The post processing was simple, and after removal of water, the catalysts could be reused at least six times and the decrease in the yield was 3%. The novel and clean procedure offers advantages including short reaction time, good yield, operational simplicity, and environmentally benign characteristics.