Vapor-Liquid Equilibrium And Separation Of Multi-component Glycols

Glycols including 1,2-ethanediol,1,2-propanediol,1,3-propanediol,1,2-butanediol, 1,3-butanediol,2,3-butanediol,1,4-butanediol are promising bulk chemicals because they have extensive industrial applications, such as in the manufacture of printing inks, moistening and softening agents, explosives, plasticizers and pharmaceuticals.Recently, microbial production of glycols has attracted great attention worldwide, especially in China, as renewable biomass is a promising way to a more sustainable future. While due to the high similarities of their chemical structure, boiling point, polarities etc., the separation of these seven glycols is not an easy thing. In view of feasibility and economics for industrialization, a multi-column distillation process is considered for the separation of the mixture in this study.The VLE data are essential for the distillation design and hence have been studied carefully including measuring the VLE data of the three binary mixtures and the ternary system. The fugacity coefficients were calculated considering the non-ideality of the vapor phase by Hayden-O’Connell equation, and the non-ideality in liquid phase was described by NRTL, Wilson and UNIQUAC models. Both Van Ness point test and Herington test were used to confirm the accuracy of experimental data, which passed the thermodynamic consistency test. The corresponding binary interaction parameters of the three models were regressed and the optimum group were used to estimate the vapor composition of VLE data for ternary systems with a good consistency to experiment values, and then were used for the distillation process design.A feasible multi-column distillation process was designed with Aspen Plus based on thermodynamic study. The relationship between reflux ratio, total column stage, feed-stage and the purity of the products was investigated in details. At last, the purity of these glycols met the industrial requirements as expected, and the operation parameters were simulated and optimized. A reasonable and feasible technology has been presented to separate and purify the diols in this paper.