Interesterification of Vegetable Oils Using Ferric Sulfate: Biodiesel Yield and Cloud Point Analysis.

The combustion of biodiesel emits significantly fewer toxic pollutants and greenhouse gases than fossil fuels, and the feedstocks used to create biodiesel can be sustainably sourced. Despite these advantages, biodiesel tends to have poor cold flow properties, challenging the ability for it to be widely implemented. Cold flow properties are typically characterized by the temperature at which the fluid begins to crystalize (the cloud point). Currently, biodiesel is typically created using a transesterification reaction with methanol and homogeneous catalysts forming glycerol as a low-value by-product that must be removed prior to use as a fuel. The novel interesterification reaction has promising fatty acid methyl ester (FAME) yields when used to synthesize biodiesel, and it creates a co-product, triacetin, that may be beneficial for the fuel’s cloud point. Interesterification is a promising alternative to the common transesterification reaction, but its reaction kinetics are slow, so additional catalysts are being studied to improve reaction rates and conversions. In this work ferric sulfate, a heterogeneous acid catalyst, is being further explored due to its relatively high interesterification reaction yields.

The goal of this project is to optimize the interesterification of vegetable oils using ferric sulfate as a catalyst and to determine how the conversion and composition of the resulting biodiesels affects the fuels’ cloud points. Reactions were carried out for 48 hours at 100℃ with 7.5wt% ferric sulfate and a 20:1 methyl acetate to oil molar ratio using palm, soybean, coconut, canola, rapeseed, and cottonseed oil feedstocks. These oils contain diverse compositions of fatty acids, ranging from short alkyl chain, saturated fatty acids to long chain, unsaturated fatty acids. Generally, biodiesels with high concentrations of short chained FAMEs had low cloud points, while biodiesels with high concentrations of unsaturated FAMEs had the lowest cloud points. Interesterification biodiesel products have lower cloud points than those for transesterification, likely due to the presence of triacetin in the product. These trends can be used to help predict the cloud points of complex biodiesel mixtures and illustrate the benefit of using interesterification for biodiesel conversion.