Comparison of heterogeneous azeotropic distillation and energy-saving extractive distillation for separating the acetonitrile-water mixtures

摘要

The separation of acetonitrile-water mixtures is a challenging and significant task due to the presence of azeotrope, for which three separation alternatives are proposed, including an energy-efficient extractive distillation strategy (ED), an pressure-swing distillation strategy (PSD) and an novel azeotropic distillation strategy (EAD). Concept design based on ternary phase diagrams of various solvents demonstrates that benzene is a suitable solvent for the newly proposed EAD scheme. The separation sequence and operating parameters are optimized via using different sequential iterative procedures based on the minimal total annual cost (TAC). Under temperature-enthalpy (T-H) diagram guidance, heat integration applied to this three sequences significantly is completed, which reduces TAC by 27.45%, 30.42%, and 46.67%, respectively. Comprehensive evaluation of the three separation alternatives from the economic and environmental perspectives indicates that the heat-integrated EAD scheme is more attractive, since its TAC decreases by 52.03% and 55.30%, respectively, and CO2 emissions decreases by 56.63% and 61.63% compared with ED and PSD schemes. It is worth noting that the conceptual design of the EAD scheme also provides an energy efficient alternative for other systems that form azeotropes with water.