Biodiesel production could become more environmentally friendly thanks to researchers in the UK who are using non-toxic ionic liquids to remove unwanted by-products.

The main by-product in the production of biodiesel from vegetable oils is glycerol. This syrupy sugar alcohol must be removed from the biodiesel as it can damage engines. Andrew Abbott and colleagues from the University of Leicester have developed a simple new approach to this sticky problem: they use green ionic liquids called deep eutectic solvents to just wash the glycerol out of the biodiesel.

Deep eutectic solvents are two or more substances mixed in a ratio that has a melting point much lower than any of the constituents. These are generally made from an organic halide salt that is complexed with something that will form a hydrogen bond. Abbott's team used quaternary ammonium salts complexed with glycerol as the washing liquid. This green washing liquid has many advantages including its low cost and toxicity; in fact, one salt used is choline chloride - vitamin B₄.

This procedure not only has potential as a greener method of cleaning up biodiesel, but also as a method of producing pure glycerol. Alexei Lapkin of the University of Bath commented that the work 'is a very interesting development for downstream glycerol treatment and utilisation'.

Abbott hopes that 'further research will reveal a better method for recycling the salt and recovering the glycerol'. He added that the team want 'to collaborate with a biodiesel producer to test this technology on a practical scale'.

Wendy Crocker