Substrate pretreatment can reduce the alcohol requirement during biodiesel production via in situ transesterification

Authors: Haas, Michael; Wagner, Karen

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2011
Publication Date: 5/1/2011
Citation: Haas, M.J., Wagner, K. 2011. Substrate pretreatment can reduce the alcohol requirement during biodiesel production via in situ transesterification. Journal of the American Oil Chemists' Society. 88:1203-1209.

Interpretive Summary: The ability of physical pretreatment of the feedstock to reduce the alcohol requirement for high yield fatty acid methyl ester (FAME) production during the in situ transesterification of soybeans was investigated. Soybeans were pretreated by (a) dehulling and flaking, (b) dehulling, flaking and passage through a twin screw extruder, (c) passage through an expander type extruder, or (d) conversion to a flour-like consistency via disruption in a Pulsewave disintegrator. Following drying, optimal reaction conditions for high yield, room temperature, in situ transesterification of the lipid-linked fatty acids resident in these materials were determined. Expander and Pulsewave pretreatment did not substantially reduce the amount of methanol required for high level FAME production below that required for flaked soybeans. However, the combination of flaking, extrusion and drying achieved a minimum nearly three-fold reduction in the methanol requirement compared with that for soybeans that had been only flaked and dried. The flaking/extrusion/drying regime resulted in a minimum optimal molar ratio for (methanol/substrate fatty acid) of 9 for effective in situ transesterification. This is a 20-fold reduction in methanol usage compared to the previously reported ratio of 181 for the use of flaked-only soybeans.

Technical Abstract: The development of new methods for biodiesel synthesis offers the possibility of reducing the production cost or expanding the range of materials that can serve as feedstocks for the synthesis of this renewable diesel fuel. We are developing such a new method, termed in situ transesterification, wherein it is not required to isolate the fat or oil from an agricultural material before converting it to biodiesel. By thereby simplifying the process technology required for biodiesel production this approach could reduce the overall cost of biodiesel. In previous work, however, we discovered that this new method requires nearly 100 times more alcohol, a co-reactant, than is required by conventional means of biodiesel production. Most of this alcohol is not consumed in the reaction and must be recovered. The substantial energy costs of this step threaten the overall economics of the process. In this paper we investigate the abilities of various physical pretreatments of the substrate to reduce the alcohol requirement during in situ transesterification of soybeans, identifying a simple and readily available pretreatment method that gives a very desirable 20-fold reduction in the methanol requirement.