Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2002
Publication Date: 7/20/2002
Citation: DUNN, R.O. LOW-TEMPERATURE FLOW PROPERTIES OF VEGETABLE OIL/CO-SOLVENT BLEND DIESEL FUELS. JOURNAL OF THE AMERICAN OIL CHEMISTS' SOCIETY. 2002. Interpretive Summary: Vegetable oils are an attractive and renewable source for alternative diesel fuels. Unlike conversion to biodiesel, blending vegetable oils such as soybean oil with co-solvents and methanol or ethanol is a less costly and easier to adapt technology that requires no time-consuming chemical reactions or separation of products. This work addresses the crucial problem of how decreasing ambient temperatures affect cold flow behavior of soybean oil/co-solvent/alcohol blends in modern diesel engines and fuel systems. Results showed the following: 1) cloud point is an important parameter for predicting the cold flow behavior of co- solvent blends; 2) at equilibrium, the temperature that produces phase separation in co-solvent blends may be used to infer cloud point and other cold flow properties; and 3) laboratory thermal analysis of co-solvent blends can predict in minutes what otherwise would take hours or days to determine from equilibrium phase separation or cold flow property studies. This work provides essential information on development of a low-cost technique to convert vegetable oils such as soybean oil into alternative diesel fuels.
Technical Abstract: Veg oils are an attractive renewable source for alternative diesel fuels. However, the relatively high kinematic viscosity of veg oils must be reduced to make them more compatible with conventional compression-ignition engines and fuel systems. Co-solvent blending is a low-cost technology that reduces viscosity by diluting the veg oil with a low-mol wt alcohol (methanol or ethanol). The co-solvent (A), which consists of one or more amphiphilic compounds, is added to solubilize the otherwise nearly immiscible oil-alcohol mixture. This work investigates cold flow properties and phase equilibrium behavior associated with soybean oil (SBO)-methanol stabilized by three different binary co-solvent admixtures (n-butanol/oleyl alcohol, 2-octanol/ triethylammonium linoleate, 2-octanol/SBO fatty alcohols) and with a SBO-ethanol (95 %) blend stabilized by n butanol and mixed 50:50 (v/v) with No. 2 diesel fuel. Cloud point (CP), pour point (PP) and cold filterability data were compared with equilibrium phase separation temps (Tf). Although CP data were measured under non-steady state experimental conditions, a nearly linear correlation was found between Tf and CP. Stat anal showed that Tf may also be correlated with cold filterability parameters. Anal of heating and cooling differential scanning calorimetry curves indicated that peak temps may be employed to predict the cold flow properties and Tf behavior of SBO/co-solvent blends. Cooling curve parameters correlated more readily than heating curve parameters. Relatively low quantities of heat evolved during cooling showed that crystallization in the SBO/co-solvent blends studied in this work occurs quickly.