Biodiesel production from algae by using heterogeneous catalysts: A critical review

The numerous challenges associated with declining fossil fuel reserves as energy sources, have accounted for a shift to biofuels as alternatives. However, transesterification of animal fats and edible vegetable oils using homogeneous acids and bases for biodiesel production is recently considered unsustainable by industries, particularly due to food versus fuel competition, and economic and environmental challenges associated with the feedstocks and catalyst systems, respectively. The paper therefore presents a critical review on the prospects of non-edible oil (i.e. algae oil) for biodiesel production via heterogeneous catalysis. It covers the advantages of algae oil exploitation over edible oil feedstocks, progress made in the oil extraction, available heterogeneous catalyst systems and reaction mechanisms, optimum transesterification conditions and the way forward. As the economic feasibility of biodiesel production from algae is supported by the valorization of glycerol as by-product, we have also highlighted key available heterogeneous catalysts to upgrade glycerol into more useful industrial products.