Design and optimization of energy-saving heterogeneous azeotropic distillation processes for the separation of ternary mixture of ethyl acetate/n-propanol/water

Heterogeneous azeotropic distillation (HAD) is expected to be an effective process for separating the ternary mixtures of ethyl acetate (EtAc)/n-propanol (NPA)/water, which have a heterogeneous liquid–liquid equilibrium region across the distillation boundary in the thermodynamic diagram. In the present study, a HAD process is designed based on the thermodynamic insights including the thermodynamic diagrams, residual curve maps and lever rule, and then simulated in Aspen Plus and optimized in MATLAB with the minimum total annual cost (TAC) as the objective function. Subsequently, two process intensification technologies, i.e., the heat-integrated and heat-pump technologies, are introduced into the original HAD process to develop two energy-saving processes, including the heat-integrated HAD (HI-HAD) process and vapor recompression heat pump-assisted HAD (VRHP-HAD) processes. The economic, environmental, energy consumption and efficiency performance of the three HAD processes are evaluated and compared in terms of the indicators of TAC, gas emissions, total energy consumption and exergy efficiency. The results demonstrate that the employment of HI and VRHP technologies can significantly reduce the energy consumption of the HAD process, leading to reductions by 13.16 % and 2.36 % in TAC with a three-year payback period, 26.84 % and 28.66 % in gas emissions and an improvement by 36.59 % and 64.35 % in exergy efficiency for the HI-HAD and VRHP-HAD processes, respectively. Although with a higher capital cost, the VRHP-HAD process exhibits obvious long-term advantages over the HI-HAD process due to its lower energy consumption and higher exergy efficiency.