Phase equilibrium and evaporation process simulation for the lithium recovery from NaCl-LiCl-H2O system with high presence of organic NMP

In the production process of polyphenylene sulfide (PPS), there is a waste liquid with the main composition of NaCl-LiCl-NMP-H2O. For the recovery of LiCl, the phase equilibrium data of the NaCl-LiCl-H2O system at a temperature of 333.15 K and 348.15 K with the highest presence of 24 % NMP in the solvent was experimentally measured. The results show that the phase diagram has one invariant point, two univariant curves and two single-salt crystallization regions corresponding to NaCl and LiCl·H2O, respectively. Neither double salt nor solid solution is found in the system. Meanwhile, the Electrolyte NRTL model was successfully developed to reproduce the phase equilibrium of the systems. Finally, the evaporation crystallization process was developed for the lithium enrichment and sodium separation. The different process operations of multi-effect evaporation (MEE), mechanical vapor recompression (MVR), and hierarchical compression MVR were compared with the focus on the energy consumption. The results show that compared with the other two processes, for this high boiling point rise system, the total annual cost and exergy loss can be reduced by 53.57 % and 64.81 % to the maximum extent by using the hierarchical compression MVR system.