Solvent screening for the separation of ethylbenzene and p-xylene by extractive distillation

Extractive distillation is one of the most effective processes for the separation of ethylbenzene and p-xylene. The goal was to find single solvents or combinations of multi-solvents with good properties while minimizing the ratio of solvent to feed. The distillations were performed at equilibrium to determine the relative volatility of ethylbenzene to p-xylene with the extractive solvents under isothermal condition. For a single extraction solvent, 1,2,4-trichlorobenzene had the highest relative volatility at 1.123. In some cases, combinations of two or three solvents were used as well as different ratios of solvent to feed to investigate the synergy effect of the mixture solvents. The binary solvent mixture of 1,2,4-trichlorobenzene and maleic anhydride (2: 1) had the best performance with a relative volatility of 1.228 at the solvent/feed ratio of 1: 1. Some of the solvents were further studied at different solvent/feed (S/F) ratios. Selected solvents generally tended to have higher relative volatilities at high S/F ratios, but the operation cost will increase. Therefore, it is important to find the proper conditions to optimize the S/F ratio for extractive distillation from the industrial point of view.