Separation Of Ethanol-Dimethyl Carbonate By Extractive Distillation

Dimethyl carbonate (DMC), widely used in pesticides, pharmaceuticals, polymersynthesis, fuel additives and solvents, can react to make some important chemicalproducts, instead of the hyper toxic or carcinogenic substances like phosgene anddimethyl sulfate. Separation of ethanol and DMC will be inevitable in the synthesis ofdiethyl carbonate or methyl ethyl carbonate.Experimental and simulative researches on separation of ethanol-DMC usingextractive distillation were carried out in this work to obtain the products of ethanoland DMC with high purities and yields.Firstly, several solvents were picked out according to some empirical andqualitative rules. Furthermore, dimethyl benzene, furfural and chlorobenzene wereselected as appropriate solvents by UNIFAC group contribution method. And effectsof the three solvents on enlarging the relative volatility of ethanol and DMC were asfollowing: furfural> chlorobenzene> dimethyl benzene. To break the azeotrope, theminimum concentrations of furfural and chlorobenzene were0.25and0.35,respectively.Then, experiments of binary and ternary vapor-liquid equilibrium wereconducted based on the theoretical prediction. The experiment data were correlated bymeans of Wilson equation, in which the binary interaction parameters were alsoobtained. It was concluded that, the azeotrope disappeared when the mole fraction offurfural or chlorobenzene was0.5. And furfural was more effective on enlarging therelative volatility of ethanol and DMC than chlorobenzene. What’s more, thecalculation results of Wilson model matched well with the experiments.Finally, Aspen Plus software was used to simulate the continuous extractivedistillation processes of separating ethanol-DMC, and two operating modes ofdouble-column process and single-column with side-stream process were examined.For the double-column continuous extractive distillation, the purities of ethanol andDMC were99.60%and98.90%, whose yields were99.58%and99.55%, respectively.And for the single-column with side-stream continuous extractive distillation, thepurities of ethanol and DMC were99.60%and95.00%, whose yields were99.60%and95.13%, respectively. When both separation efficiency and cost were taken into consideration, the single-column continuous extractive distillation process waspreferred than the double-column process.