Development of alternative methanol/dimethyl carbonate separation systems by extractive distillation — A holistic approach

Separation of dimethyl carbonate (DMC) with methanol (MeOH) is fundamentally difficult as DMC forms an azeotrope with MeOH. In this context, a holistic, three-tiered approach was undertaken to develop alternative MeOH/DMC separation systems by extractive distillation. To that end, a preliminary entrainer screening was conducted in the first tier using predictive UNIFAC-DMD and COSMO-SAC models. Based on calculated selectivities at infinite dilution (S_ij^∞), twelve potentially promising candidates were chosen out of 35 solvents. These mass separating agent (MSA) candidates were allowed to be advanced to the next level of screening in which the limiting activity coefficients of methanol as well as dimethyl carbonate in those selected solvents were experimentally measured by the technique of headspace gas chromatography. At this level of screening, a composite Z-score taking both selectivity and solvency factors into account was employed. Two solvents — methyl salicylate and ethyl benzoate with relatively high values of the composite Z-score were identified for further vapor ​– liquid equilibrium (VLE) experiment in the second tier where four sets of data were measured using a dynamic recirculation cell. The effectiveness of the two solvents acting as entrainers was further quantitatively assessed by simulation in the last tier, and compared with that of others being used industrially or proposed in the literature. Through a sequential iterative optimization scheme, extractive distillation system for each entrainer was optimized based on both conventional and heat-integrated schemes. The simulation results reveal that the effectiveness of methyl salicylate as an MSA outperforms all other entrainers.