Towards energy saving and carbon reduction of pressure-swing distillation for separating the ternary azeotropic mixtures by thermodynamic insights and process intensification

Abstract

The recovery and separation of organic solvents such as tetrahydrofuran (THF), ethanol (EtOH), and methanol (MeOH) are important to protect the environment and save resources. Such ternary mixture has two azeotropes and one distillation boundary that makes separation difficult to be carried out using ordinary distillation technique. In this work, we developed a systematic approach for heat-integration (HI) and vapor recompression heat pump (VRHP) assisted triple-column pressure-swing distillation (TCPSD) for the recovery and separation of these valuable compounds. Firstly, the thermodynamics topological analysis is introduced to evaluate the feasibility of TCPSD for separating the ternary azeotropic mixture THF/EtOH/MeOH. Different separation sequence is determined via the combination of residue curve, component balance line, isovolatility curve, and distillation boundary. Subsequently, the potential application of HI and VRHP technologies is additionally explored for further minimizing the energy consumption and it is found that both process intensification technologies provide significant improvement in terms of economic, environmental impact, and energy efficiency. Relative to the traditional TCPSD, the application of VRHP technology to the TCPSD sequence B, in particular, provides 43.5% and 76.4% reduction in TAC and CO2 emission, respectively, while it improves the energy efficiency 100.4%.