Brown researchers develop single-vessel catalyst method for WVO conversion

By Luke Geiver | September 20, 2010
Posted Oct. 13, 2010

Two chemists from Brown University have found a way to convert both triacylglycerols and free fatty acids found in waste vegetable oils using a single catalyst vessel. While the common method for converting waste vegetable oils requires two separate reactions, the chemists, Aaron Socha and Jason Sello, used Lewis acidic metal catalysts scandium triflate and bismuth triflate in a single reaction to create the methyl esters. In a paper titled, "Efficient conversion of triacylglycerols and fatty acids to biodiesel in a microwave reactor using metal triflate catalysts," the two said, "Our objective was to identify catalysts that could be used in an industrial context for the conversion of fatty acids and tricylglycerols into biodiesel." Based on their objectives, the two looked to acidic metal catalysts used in organic chemistry.

The metal catalysts did not initially perform using standard transesterification methods. "As was the case for transesterification reactions, the metal catalysts did not catalyze the desired reaction in refluxing methanol," the two said. "However, in a microwave reactor, both scandium triflate and bismuth triflate were remarkably effective catalysts for the conversion of fatty acids." Using a microwave reactor that reached 150 degrees Celsius versus the standard 60 degree temperatures under current methods, the reactions occurred in roughly 20 minutes. They used a Biotage Initiator microwave reactor using 0.2-0.5 mL and 0.5-2.0 mL microwave reaction vials equipped with magnetic stirring bars.

According to Socha, microwave irridation is an under-examined component of biodiesel research and the fact that microwave irridation works with these catalysts while conventional reflux does not, illustrates that point.

"Remarkably," they said, "the recovered scandium triflate did not lose any catalytic activity," which allowed for the recycling of the catalysts up to five times at a 97 percent efficiency rate. Although the energy required to run the microwave reactor is greater than typical methods, the overall energy usage is less because of the shorter time required for the reaction, according to the chemists. "Our findings suggest that both scandium and bismuth triflates have utility in the industrial production of biodiesel from components of plant and animal derived oils and fats."

The chemists used reagent grade FFAs and TAGs and have not at this point attempted any reactions with low-grade grease. According to Socha, they have not been able to recover reusable catalyst from transesterification reactions, only FFA esterifications, Socha said. The team has, however, spoken with a biotech venture based in Texas on a scale-up process for esterification using the bismuth triflate.
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