Comparison of direct transesterification of algal biomass under supercritical methanol and microwave irradiation conditions

In this comparative study, the direct conversion of algal biomass to biodiesel using the supercritical methanol and the microwave-assisted transesterification methods was investigated. Wet algal biomass was used as feedstock in the supercritical methanol process and dry algal biomass for the microwave-assisted transesterification. Experimental runs were designed using a response surface methodology and the process parameters such as wet/dry algae to methanol ratio, reaction temperature, reaction time and catalyst concentrations were optimized for both processes. It was observed that both conversion techniques have the potential to provide energy-efficient routes for biodiesel production from algal biomass. In comparison, the microwave-assisted approach was more successful in extracting majority of the polyunsaturated fatty acids and other valuable byproducts from the algal biomass in a short period of reaction time; and the non-catalytic supercritical methanol process may reduce the energy consumption due to easier separation and purification steps. The algal biomass characterization and algal biodiesel analysis using ATR-FTIR and GC-MS methods are reported. The transmission electron microscopy (TEM) analysis, fatty acid composition and energy requirements for the two processes are also presented.