Microwave-mediated non-catalytic transesterification of algal biomass under supercritical ethanol conditions

A novel integrated approach has been proposed to convert lipid-rich, dry algae (Nannochloropsis salina) into fatty acid ethyl esters (FAEE) under microwave-mediated supercritical ethanol (MW-SCE) conditions with a non-catalytic transesterification approach. This process enables simultaneous extraction of lipids from algal biomass and conversion/transesterification of them into algal biodiesel in a relatively short reaction time, which may reduce energy consumption versus traditional processes due to simplified separation and purification steps. High conversion rates can be possible when the extractive-transesterification of algal biomass is performed near-critical or supercritical conditions. The use of passive heating elements made of silicon carbide (SiC) to aid the microwave-mediated heating process at higher temperatures is also described. Experimental runs were designed to optimize the process parameters to evaluate the effect on the algal biodiesel under controlled power conditions. The algal biomass characterization and algal biodiesel analysis were performed using various analytical instruments such as FTIR, SEM-EDS, TGA and GC–MS. It was demonstrated in this work that this direct conversion technique has the potential to provide an energy-efficient and economical route for algal biodiesel production.

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► Direct conversion of algal biomass to biodiesel under microwave-mediated supercritical ethanol conditions is demonstrated.
► The effects of algae to ethanol ratio and reaction time on algal biodiesel yield under controlled microwave power conditions are studied.
► The experiments are performed using passive heating elements (SiC) to aid the microwave at higher temperatures.
► In situ transesterification using a green solvent and catalyst-free approach can be a potentially efficient route for algal biodiesel.