Kinetic and mechanistic studies on the synthesis of dimethyl carbonate reaction using deep eutectic solvents as catalysts

Dimethyl carbonate (DMC) is extensively utilized in various industries due to its exceptional physical and chemical properties, functioning as an additive in gasoline and an electrolyte solvent in lithium batteries. Among several production methods, the transesterification of propylene carbonate (PC) with methanol (MeOH) is the most efficient and environmentally friendly. This study synthesized various deep eutectic solvents (DESs) using choline chloride (ChCl) as the hydrogen bond acceptor (HBA) and monoethanolamine (MEA) as the hydrogen bond donor (HBD) in molar ratios of 1: n (n = 5, 6, 7, 8). The DESs' structures were analyzed using Fourier Transform Infrared (FT-IR) spectroscopy, and their melting points were determined via differential scanning calorimetry (DSC). The density, viscosity, and surface tension of the DESs were measured over a temperature range from 318.15 K to 358.15 K. The catalytic effects of four different DESs on PC transesterification with MeOH were investigated, revealing that ChCl-6MEA was the most effective catalyst, prompting its selection for further experiments. Subsequent investigations examined the effects of temperature, MeOH quantity, and catalyst dosage on PC conversion and DMC yield. Additionally, this study explored chemical equilibrium and reaction kinetics through experimental and theoretical approaches. Activity-based chemical equilibrium constants, derived from experimental data, and the van't Hoff equation elucidated their temperature dependency. A pseudo-homogeneous (PH) model characterized the non-ideal thermodynamic behavior of the liquid phase in reaction kinetics analysis. The Arrhenius equation was employed to delineate the impact of temperature variations on reaction rate constants. Finally, the proposed reaction mechanism for ChCl-6MEA catalyzed transesterification was elucidated and verified through quantum chemistry (QC) calculations.