Mechanism analysis of liquid-liquid extraction separation for dimethyl carbonate and methanol by choline-based DESs as extractants

Dimethyl carbonate (DMC) is a widely used chemical raw material and chemical product with excellent performance. In this manuscript, based on electrostatic potential (ESP), reduced density gradient (RDG) function, non-bond interaction energy, radial distribution function (RDF), spatial distribution function (SDF) and self-diffusion coefficient, the separation of DMC / methanol (MeOH) by four deep eutectic solvents (DESs) was studied. The results of ESP analysis showed that the hydrogen bond receptor played a leading role in the separation process, and the urea in the four hydrogen bond donors was more likely to form a stable structure with MeOH. The weak interaction region between different DESs and azeotropes was studied by RDG function. Based on the non-bond interaction energy, it can be seen that Cl− can form a very strong interaction with MeOH, and Electrostatic energy (Eelec) plays a leading role in the separation process. The charge density around the central atom can be observed by RDF and SDF, so as to determine the interaction between azeotrope and DESs. The diffusion rate of azeotrope in different DESs was studied by self-diffusion coefficient. The results showed that MeOH moved the slowest in the DES composed of urea and choline chloride (CHCl). The effect of DES structure on the liquid level of methanol dimethyl carbonate system was clarified by analyzing the experimental liquid-liquid equilibrium data. In this study, based on quantum chemistry (QC) calculation and molecular dynamics (MD) simulation, this study analyzed the liquid-liquid extraction and separation mechanism of DMC and MeOH. The extraction effect of DES composed of CHCl+urea is the best, which has certain theoretical guiding significance for liquid-liquid extraction to realize the green and efficient separation of DMC and MeOH.