The design of extractive distillation for separating zeotropic mixture acetic acid (AA) -water with N-methyl acetamide (NMA) as entrainer was investigated. Although NMA was verified as a better entrainer by experimental data for AA dehydration, the challenge is that NMA forming another pinch point with AA, probably leading to energy cost and total annual cost (TAC) increase compared with the conventional distillation process. Through analyzing thermodynamic insight of the ternary residue curve map based onthe general feasibility rule, we found that the distillate product is an extractive stable node instead of an extractive saddle node, thuswe have proposed a new strategy: low recycling entrainer purity for the extractive distillation of class 0.0-1 with no univolatility line existing. The strategy enables to save energy cost by alleviating the approach of the pinch point between AA and NMA. The process flow sheet includes both the extractive distillation column and the entrainer regeneration column.We have run sequence iterative op-timization method for the process optimization. The total eleven variables wereoptimized. Results show that energy consumption and TAC are reduced by 50.6% and 52.1%, respectively. The results also reveal that shifting the feed tray locations could enhance the separation performance and a higher or lower efficiency indicator apart from the optimal efficiency indicator value implies an unreasonable design.
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