The Effects of Additives on the Cold Flow Properties of Biodiesel

Biodiesel is a viable alternative to petro-diesel and has a number of advantages over it, but biodiesel has poor cold flow properties, most notably its high cloud point. The purpose of this research was to analyze the effects of dimethyl azelate on various fatty acid methyl ester (biodiesel) blends. Dimethyl azelate was chosen as it is formed as a by-product in a particular mechanism to form biodiesel and it has a similar structure to fatty acid methyl esters. The research shows that dimethyl azelate improved cold flow properties by lowering the cloud point. As the amount of dimethyl azelate was increased, the cloud point further lowered. The research also showed interesting results such as lower cloud points for binary fatty acid methyl ester solutions than the single components. These results are attributed to co-crystallization of fatty acid methyl esters of similar chain length. The co-crystallization was proved by cooling a biodiesel sample at a slow rate and noticing that similar chain length fatty acid methyl esters did not have separate peaks, but instead crystallized together.

Further work was dedicated to fitting the cloud point data to ideal solution theory, which assumes that the components of the biodiesel will not interact with each other. The research indicates that biodiesel with similar chain length fatty acid methyl esters does not follow the ideal solution theory due to co-crystallization of the similar chain lengths. Furthermore, as higher mass percents of dimethyl azelate were added to the biodiesel, the actual cloud point deviated further from the predicted cloud point. This suggests that some interaction between the fatty acid methyl esters and dimethyl azelate is occurring, but future research is needed to explain why.