A novel deep eutectic solvent-based liquid membrane for the extraction of glycerol from crude biodiesel

This study used deep eutectic solvent (DES) as the liquid membrane in a bulk liquid membrane system (BLM) to remove glycerol from waste cooking oil-based biodiesel. The DES was prepared from choline chloride and tetraethylene glycol at a molar ratio of 1:5. Diethyl ether was employed as a novel strip phase for the glycerol in BLM. The effects of the DES: biodiesel ratio, stirring speed, and extraction time on the extraction and stripping efficiencies were investigated. The results showed that BLM could give better glycerol removal from biodiesel than mechanical shaking. Increasing the DES: biodiesel ratio, stirring speed, and extraction time can enhance glycerol removal from the feed phase, achieving purified biodiesel that complies with biodiesel international standards. The purified biodiesel met the ASTM D6751 and EN 14214 international standards requirement for glycerol content of less than 0.24% under the following conditions of DES: biodiesel ratio of 1:1, stirring speed of 200 rpm, and extraction time of 240 min. The transport mechanisms of glycerol in the system were postulated based on two consecutive irreversible first-order extraction and stripping. The kinetic study shows that the extraction and stripping processes in this system could be explained by a first-order kinetic model, as the experimental results fitted into the model showed R² values of 0.98, 0.97, and 0.97 for the feed phase, membrane phase, and strip phase, respectively. The extraction and stripping rate constants (k₁ and k₂) were 0.0031 and 0.0019 min⁻¹, respectively.