Multifunctional performance of deep eutectic solvent (DES) K₂CO₃-glycerol in biodiesel synthesis and purification

Deep Eutectic Solvent K₂CO₃-Glycerol (DES K-G) was tested for its multiple roles in biodiesel production, serving as a catalyst, co-catalyst/reaction medium, and solvent in product purification. DES K-G was synthesised through a thermal mixing method at 80 °C with a molar ratio of K₂CO₃ : glycerol = 1 : 3.5. The catalyst performance in transesterification occurred at 65 °C, stirring at 450 rpm, with a methanol to oil weight ratio of 30 wt%. Under the same process conditions and catalyst ratio (1.2% w/w), the reaction performance with DES K-G was comparable with that of Sodium Methylate (SMO). The standard quality parameters used as benchmarks are total glycerol (<0.24%) and methyl ester content (>96.5%). To achieve the standards, the reaction with DES K-G requires a reaction time of 4 h, while with SMO it takes 1.5 h. Furthermore, biodiesel synthesis was tested using a dual catalyst system, with a combination of DES K-G and SMO, at a weight ratio of 1 : 3, which demonstrated the highest methyl ester content of 98.256% within 2 h. DES K-G also showed the best impurity removal performance in a 2-cycle washing treatment. The combination of extraction with DES K-G in the first cycle, followed by water washing in the second cycle, provided the best separation efficiency. There was an increase in methyl ester content of 5.1%, followed by changes in density, saponification value, and acid value, respectively, of 1.15%, 14.3%, and 47.6%. Thus, DES K-G demonstrates versatility and great potential for integrated biodiesel synthesis and purification.