Design and comprehensive analysis of a novel pressure-swing batch distillation process for the separation of a binary azeotrope with various boiling behaviors

Abstract

Batch distillation is widely employed in the fine chemical industry because of its operational flexibility. The mixture of n-heptane and isobutanol exhibits a special azeotropic phenomenon by which it changes from a minimum-boiling azeotrope to a maximum-boiling one with increasing pressure. However, the traditional double column batch rectifier and double column batch stripper processes cannot separate the mixture efficiently. Therefore, the double-column batch stripper–rectifier (DCBS-R) process was designed to obtain high-purity products, based on the azeotropic phenomenon. Further, control structures are explored to achieve stability, and the final purities of the separated products are over 99.9%. Each batch of raw materials is 100 kmol, and the expected annual production capacity is 800 batches. Additionally, a precooler of the low-pressure column (LPC) is introduced to reduce the exergy destruction by exergy analysis. The equipment cost and CO2 emissions are analyzed afterward to optimize the process, based on the multi-objective optimization method. Further, the number of stages and the pressure of the columns are optimized. The optimal obtained total annual cost (TAC) and CO2 emissions of the DCBS-R process are 2.26 × 105 $/y and 4.92 × 105 kg/y, respectively. The partial heat integration is studied to further improve the process performance, thus obtaining TAC and CO2 emissions of 2.22 × 105 $/y and 3.80 × 105 kg/y, which are 7.1% and 22.76% lower than the values obtained from the optimal process, respectively.