Lowering the Glycerol Concentration in Biodiesel Using Choline Chloride-Gallic Acid Deep Eutectic Solvent: A Sustainable and Eco-Friendly Approach

Gallic acid (GA) (3,4,5-trihydroxybenzoic acid), which is a natural secondary metabolite and widely isolated from various plants, is for the first time employed as a hydrogen bond donor (HBD) for preparing a deep eutectic solvent (DES) with choline chloride (ChCl) as a hydrogen bond acceptor (HBA). This DES has been applied as an extractant to separate gycerol from biodiesel. The finding indicates that a DES could be formed at a molar ratio of ChCl to GA of 5 : 1, 6 : 1, and 7 : 1. The characterization of the synthesized DES shows its acidic polar property with a pH of lower than its constituents, density of lower than biodiesel, and the viscosity within the range reported for previously prepared DES. Functional groups analysis using FTIR indicated the presence of all functional groups from GA and ChCl in the DES structure, along with the absence of any new spectral peaks, suggesting that there was no chemical reaction involved in the DES formation. Its ability to reduce the glycerol concentration in the biodiesel in the range of 74.6 to 99.8 % denotes its capability as a potential extractant for separation of glycerol from biodiesel.