Optimal Separation and Thermal Integration of NMP–CS ₂ –H ₂ O from Coal Extraction Solvent

Despite the huge scale of coal being employed, its efficiency and depth remain insufficient. The accurate analysis of the chemical composition of coal is the foundation for enhancing the utilization of its high-value resources. The coal extraction and back-extraction processes of coal enable the classification and separation of its organic matter, which has significant potential for structural research and resource utilization. However, this process generates an N -methyl-2-pyrrolidone (NMP), CS 2, and H 2 O mixture, whose effective separation is crucial for achieving process optimization and resource recovery. Developing energy-efficient and environmentally friendly separation technologies to unlock the full potential of coal-based extraction and back-extraction processes can promote the sustainability and energy efficiency of coal resources. This study employed a liquid–liquid separator combined with distillation to separate the NMP–CS 2 –H 2 O mixture. By analyzing the vapor–liquid equilibrium (VLE) of the mixture, a feasible separation process was determined, and the effect of pressure on relative volatility was investigated. Subsequently, based on sequential optimization results, a heat-integrated separation process coupled with heat pump distillation was designed. The molar purity of NMP, CS 2, and H 2 O reached over 99.9 mol % for both the sequential optimization and integrated processes. Compared with the sequential optimization process, the total cooling duty of the thermal integration process was reduced by 90.42%, and the exergy loss was reduced by 50.42%. This study presents an energy-integrated optimized process for the efficient separation of NMP–CS 2 –H 2 O mixtures generated during coal extraction and back-extraction, which provides valuable insights into coal structural research and the deepening of coal resource utilization.