Superiority of liquid membrane-based purification techniques in biodiesel downstream processing

Biodiesel, a biodegradable and non-toxic diesel alternative from the esterification and transesterification processes, is a viable bioenergy option. However, the presence of impurities in crude biodiesel necessitates purification to meet the standard specifications for high engine performance. Several techniques for biodiesel purification have been proposed, and they can be conveniently categorized based on the following: equilibrium, affinity, membrane, and reaction. Dry-washing methods have proven to be effective, though they generate a significant amount of waste. Additionally, water-based purification methods generate a large volume of wastewater with adverse environmental effects. The oxygen content in biodiesel has led to problems such as moisture absorption, corrosion and high viscosity. More recent research works focusing on membrane-based biodiesel purification techniques appear to be a promising alternative that offers high-quality fuel with lower volumes of wastewater discharges. This paper reviews the conventional and emerging liquid membrane technologies such as the emulsion liquid membranes and the bulk liquid membranes for biodiesel purification, highlighting their technical merits and environmental benefits. Over and above that, liquid membrane technology offers a promising solution for the efficient purification of crude biodiesel while minimizing the environmental impacts.