Ultrasonication for Improved Biodiesel Production

Alkali-catalyzed transesterification of triglycerides is the preferred commercial method for making biodiesel fuels in the United States. The economics of this process are sensitive mainly to feedstock price and conversion costs. The conversion costs relate to the feedstock purity, the reaction rate, the yield of alkyl esters, the efficiency of separating the esters from the glycerol, and the glycerol purity. Recent studies of biodiesel reactions, and a study of another two-phase natural oil reaction, have demonstrated that novel mixing technologies can make significant reductions in batch reaction times and product purities. This project will study the effects of ultrasound micromixing on the transesterification of soybean oil (SBO) with methanol under base catalysis. The primary hypothesis is that the increase in methyl ester formation rates is primarily dependent on the particle size distributions developed as a result of the ultrasonication. Measurements of the actual particle size distributions will be related to the ultrasonication power per unit volume. The transesterification kinetics will be interpreted in models that include the interfacial area between the oil-rich and alcohol-rich phases, and the partition coefficients for the various constituents. This model will be used, in part, to optimize product purities and yields for various feed compositions and conditions. Existing process design simulations of a biodiesel process will be updated based on our research to develop economic models comparing the new process to conventional technology. The work plan will generate the following deliverables: I) correlations of particle size distributions and interfacial area with energy per unit volume for ultrasound micromixing, 2) a kinetic model that includes interfacial area and predicts product purities and methyl ester yield, 3) phase equilibria models that correlate the partitioning of chemical components between the oil-rich and the alcohol-rich phases, and 4) a process design simulation suitable for economic evaluation of an ultrasonication process for biodiesel production from soybean oil. A successful project could result in new, low-cost reactor designs for biodiesel production and/or cost-saving modifications of existing reactors with appropriate technology. Many existing plants use waste oils and greases as triglyceride sources since the process feedstock is a major factor in the biodiesel price. While recycled triglycerides can have high free fatty acid levels and water contamination that will limit the improvements possible through improved mixing using sonication, it still is possible to retrofit existing plants for better performance. Soybean oil is good model system for this research as it has fairly uniform properties and is of interest to the co-sponsor.