Study On Salt Effect And Its Application In Separation Process

Several fields of salt effect was studied by theoretical analysis and experiment to meet the need of separation task in chemical engineering process. They are: Salt selection; Salt effect on VLE and LLE; "Salt Distillation-Salt Extraction" combined separation process.Since general interaction between a salt and a solvent was expressed by the product of the effect force ksi between the salt and the solvent, which comes from the correlation of the experiment data of depressing of vapor pressure of solution with salt, and the solubility of the salt in the solvent-"s", so for a binary solution the criteria of salt selection was described as the difference of the general interaction between a salt and two solvents in the solution, that is: . Two kinds of models in correlation of VLE and LLE data in a binary solution under salt effect were offered. As for VLE, the first kind of model was based on Furter equation. The T-Wilson equation was introduced and modified to describe binary system VLE theoretically, which belongs to the second kind of model. As for LLE, the first kind of model is: the difference of the distribution coefficient before and after adding salt to the solution was correlated with salt concentration in water layer. The second kind of model is: electrolyte NRTL (MNRTL) model was used to calculate LLE data theoretically. In general, the first kind methods were simple and meaningful, and the second kind models were more accurate and useful in process simulation.A new process combining azeotrope distillation and salt extraction that purifies the organic solvent from their azeotropes with water was preceded. A novel tower with a salt extractor and a middle vessel was proposed. Water can be got away from bottom and overhead of tower at the same time, and the organic solvent was concentrated in the tower and accumulated in the middle vessel at last. So the progress is time-shorted and energy-saved. The concentration of product is up to 99.9% and the product yield 99.5%.The new process was studied experimentally and simulated by constant molar holdup method. At last, recovery of salt from its aqueous was studied by "extractive crystallization" process.In conclusion, salt separation process is promised.