Global multi-objective optimization of trimethyl orthoformate-acetic acid extractive distillation

The highest azeotrope exists between the reactant trimethyl orthoformate (TMOF) and the product acetic acid (HAc) in the production of 3- (methoxy methotenyl) - 2 (3H) benzofuranone, which leads to the accumulation of reactants and the loss of raw materials and is not conducive to the forward reaction. For TMOF-HAc system, vapor-liquid equilibrium was calculated and analyzed by Hayden-O'Connell's UNIFAC group contribution method with modified fugability coefficient. After error verification, NRTL-HOC model was used as the basis of simulation distillation. The azeotrope can be separated by empirical extractive distillation. The entrainment performance of HAc with N-methyl acetamide (NMA) and N-methyl pyrrolidone (NMP) was compared, and NMP was selected as the extractant. Conventional extractive distillation (CED), side-stream (liquid) extractive distillation (SED) and extractive dividing-wall column (EDWC) were designed with the objective of molar purity of system recovered components, reboiler thermal load (Q) and annual total cost (TAC). Sensitivity analysis was used to adjust the parameters of the three processes in advance. Based on the multi-objective constraints, the optimal parameter range was divided as the initial data of Box-Behnken response surface method (BBD-RSM) optimization, and then the global optimization of the three processes was further conducted by BBD within the specified range. The most economical scheme was formulated by optimizing the data regression multi-objective equation, and the mole purity was 99.8% HAc and 99.9% TMOF. The results show that EDWC and SED can save more economic input and reboiler heat load than CED under the same separation purity condition. SED can save 10.37% TAC and 6.88% heat load, and EDWC can save 10.65% TAC and 10.53% heat load. The results show that there is a good fitting relationship between the predicted value and the actual value, and the prediction errors of TAC and Q by CED, SED and EDWC are all less than 1%. All three process schemes can provide theoretical basis for actual chemical production. © 2022 Chemical Industry Press. All rights reserved.