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United States Department of Agriculture

Agricultural Research Service

Title: Low-Temperature Phase Behavior of Vegetable Oil/co-Solvent Blends As Alternative Diesel Fuel

Authors
item Dunn, Robert
item Bagby, Marvin - RETIRED, NCAUR, USDA, ARS

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 31, 2000
Publication Date: N/A

Interpretive Summary: Vegetable oil co-solvent blends are legitimate candidates as alternative fuels for compression ignition (diesel) engines. In contrast to conversion to biodiesel, co-solvent blends require no chemical reactions because they are composed of an oil component (soybean oil) and a polar component (methanol or aqueous ethanol) mixed together by addition of the co-solvent (surfactant). This work addresses a crucial problem area for vegetable oil co-solvent blends, what happens to fuel formulations when ambient temperature decreases? Findings showed that the type of phase separation (formation of solid crystals or a separate liquid layer from the bulk liquid fuel) as well as the temperature where phase separation occurs both depend upon the nature and concentration of the co-solvent relative to soybean oil in the blend. As a result, soybean oil co-solvent blends can be formulated with significantly reduced cloud point as well as comparable viscosities with respect to biodiesel at lower temperatures. This work provides valuable information to development of viable and less costly conversion techniques for producing alternative making diesel fuels from renewable and environmentally friendly vegetable oils.

Technical Abstract: Veg. oils have many characteristics that make them attractive candidates as renewable alternative fuels for compression-ignition (diesel) engines. Unfortunately, veg. oils are too viscous to be compatible with modern direct-injection diesel fuel systems and engines. Co-solvent blending is an easy, flexible technique that reduces viscosity by mixing the oil with low-mol. wt. alcohol. The co-solvent (A) is necessary to solubilize the otherwise nearly immiscible mixture into an isotropic solution. This work examines anisotropic phase behavior of soybean oil (SBO) co-solvent blends at relatively low temperatures. Three SBO-methanol blends solubilized by A = unsaturated long-chain fatty alcohol or triethyl- ammonium linoleate mixed with a medium chain alkanol as well as one SBO-95 wt% ethanol blend solubilized by n-butanol were investigated. The latter blend was tested in mixtures with petroleum middle distillates. Two types of anisotropic phase behavior were observed, formation of a cloudy layer of solid crystals suspended in bulk solution and two immiscible liquid layers. The type of separation observed depended on the magnitude of the equilibrium phase separation temperature (Tp). When Tp < melting points of triglycerides and/or long chain co-solvent molecules present in solution, phase separation resulted in a cloudy layer; when Tp > the melting points, phase separation resulted in formation of two translucent liquid layers. Finally, Tp decreases as A/Oil mass ratio increases and increases with total alcohol content in solution. Therefore, SBO co-solvent blends can be formulated with significantly reduced cloud points and comparable kinematic viscosities relative to biodiesel (methyl soyate).

Last Modified: 7/31/2014
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