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

Abstract

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.