Salting Effect of Sodium Hydroxide and Sodium Formate on the Liquid–Liquid Equilibrium of Polyoxymethylene Dimethyl Ethers in Aqueous Solution

In this work, the salting effect of sodium hydroxide (NaOH) and sodium formate (HCOONa) on the liquid–liquid equilibrium (LLE) of polyoxymethylene dimethyl ethers (DMMn) in aqueous solution was studied. The LLE data of the systems (DMM1 + water) and (DMM2 + water) and the system (DMM1 + water + DMM2) under different concentrations of NaOH and HCOONa at 293.15 and 308.15 K were measured. According to the verification with the Marcilla-modified Eisen–Joffe equation, the experimental data has a good consistency. Distribution coefficients were calculated and compared, and the results showed that NaOH and HCOONa have a significant salting-out effect on DMMn and water separation. Based on the experimental LLE data, the original nonrandom two liquid (NRTL) and the electrolyte NRTL activity coefficient models were correlated by the maximum-likelihood principle, which showed that the electrolyte NRTL model was more appropriate. The experimental data and the binary interaction parameters could provide a useful reference for DMMn product reaction extraction before rectification.