Study On Removing Thiopnene From Coking Benzene By Extractive Distillation With Salt

A extractive distillation with salt added to solvent was proposed to remove thiophene frombenzene, which is diffcult to sepratate because of their close boiling points. The method ofselecting salt and solvent,and the operate parameter were studied in this paper.DMF, which is a good solvent for many kinds of salt ,was choosen as the solvent forextractive distillation with salt,. and NaSCN, NaI, NaNO3, KI were selected as the adding salts .The effect of kinds of salt on the VLE of benzene and thiophene was studied, through mesuringthe VLE of benzene and thiophene contained solvent and different kinds of salt. The resultsshowed that the relactive volatility of benzene increase with adding salt selected in DMF. Asthe best effect of NaSCN, it was choosen as the salt for extractive distillation with salt .The influnce of NaSCN concentration and solvent ratio on the relative volatility of benzenewas studied, through mesuring the VLE of benzene and thiophene contained solvent and salt atdifferent fraction of salt and different solvent/feed volume ratio. The result showed that therelactive volatility of benzene increase with increasing of NaSCN concentration at lowconcentration, and reach a peak and then decrease at certain NaSCN concentration. The resultalso showed that the relative volatility of benzene will grow up as solvent ratio rise. The mostsuitable concentration of NaSCN in solvent is 10%~15%.,and the most suitable solvent/feedratio is 1~2.The continuous extractive distillation with salt added to solvent was carried out, and theeffect of reflux ratio on the composition of overhead was studied. The result showed that thefraction of thiophene in overhead will go down as the rise of reflux ratio , the most suitablereflux ratio is 5. The result proved that extractive distillation with salt can effectively removethiophene from benzene.