Double-column batch stripper process based on heterogeneous property and control strategy for the efficient separation of a ternary mixture containing two minimum boiling azeotropes

Abstract

Batch distillation is widely applied in the fine chemical industry due to the market demand for low-volume and high-value-added products. Heterogeneous ternary mixtures with two minimum boiling azeotropes, such as cyclohexane-acetonitrile-toluene, are common in production processes. However, the separation of a mixture based on batch distillation was rarely studied because of the complexity of the method. In this work, a double-column batch stripper (with a decanter) process with a processing capacity of 7200 kg was designed for the separation of a cyclohexane-acetonitrile-toluene ternary mixture by considering the heterogeneous properties of the components. The feasibility of the process was analyzed according to the phase diagram, and the production sequence was determined. The pressure of the columns and the decanter temperature were determined synthetically from the minimum total annual cost, operation time and recovery ratio. The production time of different components, which has significant impacts on the purity and yield, was determined. In view of the situation that two separated components would be successively obtained at the bottom of each column, a control strategy was designed which can switch the products vessels automatically and control the batch distillation process. The results show that the control structure exhibits a good controllability, and the purities of the separated products are all over 99.9 mol%. Based on the optimal batch distillation process, the environmental impacts of the process were calculated. The results of the environmental analysis show that the global warming potential (GWP), acid potential (AP) and human toxicity potential (HTP) are 8613.91 kg CO2 eq, 15.40 kg SO2 eq and 267.21 kg DCB eq, respectively.