Advancement in biodiesel production using ionic liquid as media and catalyst

Abstract

The swift depletion of fossil fuels and the growing desire to address the environmental impact of their use have caused the development of renewable energy sources. One of those renewable energy sources is biodiesel. However, the current methods for producing biodiesel rely heavily on using homogeneous catalysts (NaOH and H2SO4) that have created many problems related to soap formation, separation difficulties, and high energy requirements. As an alternative to conventional catalysts, ionic liquids (IL) possess a low volatility, can be reused, are thermally and chemically stable, and have an acidity or basicity that can be tailored for the various feedstocks. There are three categories of ILs: acidic ionic liquids (AILs), basic ionic liquids (BILs), and bifunctional ionic liquids (BILs) used for the esterification, transesterification, or both processes, respectively. ILs enhance the kinetics of the biodiesel formation reaction while improving the miscibility of the reactants and reducing the occurrence of undesired side reactions such as saponification. These ILs can also stabilise enzymes that are being used as biocatalysts in the production of biodiesel (i.e., lipases). Recent studies have focused on TSILs, attaching them to solid substrates (uses include microwave and ultrasonic waves). Although elevated yields and reuse capabilities exist, IL cost, viscosity, and recovery present challenges. This review paper will elucidate the current state of classification for ILs including uses in both catalytic and non-catalytic reaction systems. In addition, it will present new data that demonstrates how ILs have been employed to increase the efficiency, sustainability, and scalability of biodiesel production, as well as a focus on the development of cheaper and biodegradable ILs.