Synergistic Effect Of Mixed Entrainer And Process Integration And Control For Separating THF/ethanol/water Ternary Azeotropic Mixture

In this paper,the economy of the ternary extractive distillation processes for separating tetrahydrofuran?THF?/ethanol/water ternary azeotrope using single solvent and mixed solvent as entrainer was analyzed by Aspen Plus and Aspen Plus Dynamics.Dynamic control performances of ternary extractive distillation with different entrainer were explored.The economy,thermodynamic efficiency and environmental impact of different thermally coupled ternary extractive distillation sequences with different entrainer were studied.A qualitative screening was carried out in accordance with the polarity of the solvents and four solvents dimethyl sulfoxide?DMSO?,ethylene glycol?EG?,N,N-dimethylformamide?DMF?,and dimethylacetamide?DMAC?were selected as candidate entrainers.Two single entrainers of DMSO and EG were determine,and the mixed entrainer is mixed solvent of DMSO and EG.Taking the minimum annual total cost?TAC?as the objective function,the ternary extractive distillation processes with EG,DMSO,and mixed entrainer were optimized to obtain the optimal process parameters and minimal TAC by the sequential iterative optimization program.Compared with two single component entrainers DMSO and EG,the TAC of the extractive distillation process with mixed entrainer?60mol%DMSO+40mol%EG?decreases by 6.55%and 31.88%,respectively.Comparisons of the reboilers heat duties of two extractive distillation columns using mixed entrainer with two single component entrainers demonstrated that the tradeoff of entrainer performance between the two extractive distillation columns is the key element to reducing the energy consumption and TAC in the ternary extractive distillation process.Introduction of a mixed entrainer enhanced the flexibility of the tradeoff,which can be achieved simply by changing the composition of the mixed entrainer.Based on the optimal ternary extractive distillation process,the control structures of ternary extractive distillation using DMSO and the mixed solvent of DMSO and EG as entrainer were explored.The analysis of the±20%feed flow rate and feed composition disturbances demonstrates that the composition control structure with the ratio of reboiler duty to mole feed flow rate(Q_R/F)shows good disturbance rejection capability for the ternary extractive distillation processes with DMSO and mixed entrainer.Moreover,the dynamic performances of the ternary extractive distillation with DMSO and the mixed entrainer were compared.The result shows that the dynamic control performances of the extractive distillation process with mixed entrainer are better compared with the extractive distillation process with DMSO.Based on traditional ternary extractive distillation process,two thermally coupled ternary extractive distillation sequences,the combination of two extractive distillation columns?C1/C2?and the combination of extractive distillation column and entrainer-recovery column?C2/C3?,were explored.The thermodynamic efficiency,carbon dioxide emission and TAC of different thermal coupling ternary extractive distillation processes with different entrainer were studied.The result shows that C1/C2 thermal coupling ternary extractive distillation process with mixed entrainer has more advantages from the perspective of energy economy,environmental impact and economy.