Development of a Fatty Acid Esterification Catalytic Membrane Reactor

The use of Biodiesel in the U.S. is presently hampered by a lack of suitable feedstocks that do not compete with the food industry. The original biodiesel feedstock was food grade soybean oil, and became a significant problem: 1) politically, because of the impact on food pricing and 2) economically, because of pricing volatility due to world production and consumption fluctuations. This driving force motivated the biodiesel industry to shift to alternative feedstocks. Many of these alternatives have a problem of high Free Fatty Acid (FFA) which is typically corrected by an esterification reaction with methanol to convert the FFA to Fatty Acid Methyl Ester (FAME biodiesel) and water byproduct, using a liquid strong mineral acid as the catalyst. But unfortunately, both the acid and the water must be removed prior the transesterification of the triglyceride. The acid neutralization creates a solid which has to be removed in subsequent processing. The vaporization / distillation to remove the methanol water and dehydrate the methanol requires significant additional heat (and cost). Eagle Engineering and Testing Services is proposing to develop a solid catalytic membrane reactor to eliminate the acid neutralization requirement and the methanol vaporization / distillation steps before proceeding to the transesterification step. This will be accomplished by using a commercial solid Fatty Acid esterification catalyst coupled with a water selective membrane being developed by Pacific Northwest National Laboratory (PNNL). This novel membrane has unique properties (high water selectivity, high flux, and modest cost) that make it a superior choice to presently available membranes. Its this membrane that finally makes it possible the use of a membrane reactor for methanol esterification reactions. Once this technique is perfected and commercialized, it can significantly streamline the biodiesel process for high FFA feedstocks. It will be possible to build retrofits for previously virgin soybean oil plants which should make then profitable as compared to the liquid acid esterification technology. In addition to improving the economics, this technology will reduce the solids waste and its disposal. It should reduce the transesterification problems associated with water induced soap formation, and the subsequent need for extensive water washing. By reducing the washing load, the impact on the waste treatment plant that handles the wash will also be reduced. An additional advantage is the small size of this solid catalyst membrane reactor, when compared to the traditional liquid acid process. This will allow retrofits without increasing the processing facility significantly. In addition to commercial scale plant retrofits and new plant construction, this technology helps make small scale batch biodiesel processing of high FFA practical because of the significant simplification of the esterification. This type of processor is expected to fit into farming or coop type operations where the participants supply and/or buy feedstocks and make biodiesel for their own use. A rural farm based fuel supply network has significant advantages with respect to reducing fuel transportation and related costs.