Thermomorphic behaviour intensifies the coproduction of glycerol carbonate and ethylene glycol

Glycerol carbonate is a chemical compound of high interest due to its unique properties that can be synthesized from glycerol, a byproduct of biodiesel, by transesterification with an organic carbonate. In this work, the transesterification of glycerol and ethylene carbonate has been conducted with the addition of low amounts of K₂CO₃ in a single-phase reaction system, at temperatures above 78 ºC – 80 ºC (glycerol - ethylene carbonate is a thermomorphic system with a biphasic-monophasic transition at that temperature range). Several runs have been carried out at diverse catalyst concentrations (20-500 ppm), EC to Gly molar ratios (1.5-2.5) and process temperature (80-120 ºC). Notably, as the system was solventless and glycerol conversion exceeded 96%, high concentrations of glycerol carbonate and monoethylene glycol (>3 mol/L) were reached with high selectivity (98%) in very short reaction times (40 minutes at 80 ºC) at low catalyst concentrations (100 ppm). Thus, turnover frequency is 4.37 h^-1, which compares well to hydrocalcite-NaAlO₂ catalyst (1.62 h^-1). Subsequently, a first-order (with respect every involved compound) multivariate kinetic model containing equations for both direct reverse reactions was successfully fitted to all data at the same time, showing higher equilibrium conversions at the lowest temperature tested (endothermic system). Finally, key green chemistry metrics highlight a potential low environmental impact: Atom economy was 64%, E-factor reached 0.62 at 96% yield to GC and 2:1 Gly:EC molar ratio and process mass intensity (PMI) of 2.27 if only GC is considered as reference, or 1.25 if monoethylene glycol is also accepted as a product of interest.