Novel Reactor Design for Conversion of Waste Oils to Biodiesel

Biodiesel is a renewable, carbon-neutral fuel that can ease pressure on the world’s dwindling supply of oil and petroleum diesel. This research explores production of biodiesel from alternative low-value feedstocks such as waste oils. Traditional biodiesel reactions mix an alcohol and a refined triglyceride (TAG) are mixed with an alkaline catalyst to create Fatty Acid Alkyl Esters. At Drexel University, a novel method is being developed for the production of biodiesel using an acid catalyst to esterify low-value natural oil and grease feedstocks that contain TAG and high concentrations of free-fatty acids (FFA). This method uses a novel column reactor, in which an alcohol vapor bubbles through the oil at temperatures in excess of 110°C. This method effectively produces biodiesel from unrefined waste oils, which have FFA contents in excess of 50% and are much cheaper than refined vegetable oils. The current reactor method has also shown that a water-diluted alcohol may be nearly as effective as a pure alcohol feed. Because the bubble reactor system is more robust for unrefined waste oils and impure alcohol feedstocks than traditional biodiesel reactors, this reactor could operate at a much lower cost than traditional biofuel processes. This talk analyzes performance of a bubble column reactor using mixed oil feedstocks containing both FFA and TAG which traditionally are reacted in two separate steps with different catalysts. Experimental data shows that in the bubble reactor with an acid catalyst, the FFA reacts quickly to biodiesel in less than 90 minutes and the TAG reacts more slowly. There are two chemical pathways for converting TAG to biodiesel, (1) direct transesterification of TAG and (2) hydrolysis to FFA followed by esterification of FFA; this talk explores the relative importance of these reactions within a bubble reactor.