Separation Of Multi-component Glycols

Ethanedio(EG),propanediol(PG)and butanediol(BD)are important compounds for raw materials.Fermentation is an important approach to produce diolsbecause of its sustainability with the itsrenewable materials.Mixtures of glycols obtained via fermentation are difficult to be applied and their separation is essential.However,they are homologs and their structures and properties are so similar that the separation is not easy.This is one of bottle necks which limits industrial production of bio-based glycols.A lot of relevant reseaches have been accomplished and technical pure products of diols have been obtained by multi-column sequence distillation in our lab.Tenary systems(1,2-EG +1,3-BD + 1,3-PG)and(1,2-PG + 1,3-BD + 1,4-BD)have been chosen as research objects and divided wall columns(DWC)has been appliedtoseparate themin order toincrease product purity and reduce separation costs.Vapor-liquid equilibrium(VLE)data of binary systems(1,2-EG +1,3-BD),(1,2-EG+1,3-PG),(1,2-PG + 1,3-BD),(1,2-PG + 1,4-BD),(1,3-BD + 1,4-BD)and tenary systems(1,2-EG+ 1,3-BD + 1,3-PG),(1,2-PG + 1,3-BD + 1,4-BD)were determined at normal pressure and were regressed withmodels of UNIQUAC,Wilson,NRTL to obtaintheir binary interaction parameters.The results have shown that:models of UNIQUAC,Wilson,NRTLcan be used to describe systems involved in this paper,but UNIFAC can not;there are no distillation boundaries in systems(1,2-EG + 1,3-BD+ 1,3-PG)and(1,2-PG+ 1,3-BD + 1,4-BD).Processes of two-column sequence distillation were designed and optimized at normal pressure for separation of the two ternay systems with Aspen Plus on the basis of thermodynamic studies.Design of DWC configurations was conducted to improve the purity of products,reduce energy consumption and capital costs.Initial values of related parameters in DWCs were obtained in the module ofDSTWU,and their optimizations were accomplishedin the Multifracmodule.Influences of the numbers of stages,length and location of divided wall,feed stage,location and flow rate of side product,connect streams l and v,reflux ratio on purity of products were studied for the DWC processes and their preliminarily optimal values were obtained.Response surface method(RSM)based on Box-Behnken design(BBD)has been applied to investigate the interactions of connect streams l and v.reflux ratio on purity of products and heat duties in reboilers inthe DWCprocesses for further optimization ofoperating parameters.And relations on response variables were also acquired.The results have shown that DWC can save 6 stages,reduce heat duty and cold duty up to 35%,32%,respectively,while the purity of products are the samefor the system(1,2-EG ?1,3-BD + 1,3-PG);DWC can save 5 stages,reduce heat duty and cold duty up to 50%,57%,respectively,while the purity of products are improved for the system(1,2-EG + 1,3-BD ?1,3-PG).