Submitted to: Liquid Fuels from Renewable Resources Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/17/1996
Publication Date: N/A
Citation: Interpretive Summary: This work examines cold flow properties of diesel fuels derived from veg. oils. These fuels, called methyl esters, have cold flow problems that must be resolved before they can be marketed as alternative fuels in the North American transport industry. Filterability tests developed to predict operability limits of diesel fuels showed that cloud point, the highest temp. where crystals suspended in solution are visible, is linearly correlated with filterability. Thus, cloud points may be used to predict operability limits in place of more cumbersome, less "user friendly" filterability measurements. Mixing up to 30% methyl esters from animal fat (tallow) with methyl esters from veg. oil did not greatly affect the correlation between cloud point and filterability. However, treating methyl esters with additives marketed for petroleum diesel decreased the reliability of the correlation with cloud points. Thermal analysis showed that cloud points may be more accurately determined from melting peaks than standard methodology. This work demonstrates the importance of cloud point as well as thermal analysis in the evaluation of approaches for improving cold flow of methyl esters.
Technical Abstract: Methyl esters from vegetable oils have many characteristics that make them attractive as a fuel for diesel engines. Research has shown that cold flow properties should be resolved before methyl esters can be marketed in moderate temp. climates. In N. America, fuel systems powered by middle distillates develop operability problems when overnight temps. drop below -15C. Methyl esters from soybean oil develop similar problems at temps. near 0C. This work examines expected operability limits for methyl esters through evaluation of their low-temp. filterabil- ities. Low-temp. flow test (LTFT) and cold filter plugging point (CFPP) results showed nearly linear dependence with respect to cloud point (CP). Under most conditions, CFPP was nearly equivalent to LTFT as a predictor of operability limits for methyl esters. Slight improvement in filterability was observed when methyl esters were treated with "off-the-shelf" cold flow additives. Results from differential scanning calorimetry (DSC) melting curves also showed a correlation with CP. Finally, admixtures with up to 30 vol% methyl tallowate in methyl soyate showed no significant deviation with respect to cold flow properties.