The Direct-contact Heat Transfer Reboiler For The Distillation Of Heat-sensitive Materials With Ionic Liquid As Heat Carrier

The purification of heat sensitive materials by distillation is a difficult problem in chemical separation engineering.The direct-contact heat transfer reboiler can greatly reduce the liquid holdup and heated time of the heat-sensitive materials,so the reboiler has good application prospect in the distillation of heat-sensitive materials.Ionic liquid is adopted as heat carrier in the direct-contact heat transfer process to overcome the disadvantages of conventional heat carrier,and a kind of direct-contact heat transfer reboiler with the ionic liquid as the heat carrier for the distillation of heat-sensitive materials is developed.The feasibility of using ionic liquid as the heat carrier in the direct-contact heat transfer reboiler was studied based on the properties of the ionic liquid.The heat sensitive materials diethyl phthalate(DEP),dicyclopentadiene(DCPD)and styrene were taken as example,and the ionic liquid 1-ethyl-3-methylimidazole acetate([Emim][OAc])was selected as the heat carrier.The liquid-liquid equilibrium of the binary systems [Emim][OAc] + diethyl phthalate(DEP),[Emim][OAc] + dicyclopentadiene(DCPD)and [Emim][OAc] + styrene were measured.The results show that [Emim][OAc] is almost insoluble in these three kinds of organic compounds,solubilities of DEP and DCPD in [Emim][OAc] increase with temperature but the solubility of styrene in [Emim][OAc] decreases with temperature.The ternary liquid-liquid equilibrium for the system of styrene + glycerol + [Emim][OAc] were also determined,the results indicate that the addition of glycerol can significantly reduce the solubility of styrene in [Emim][OAc].With the increase of the amount of glycerol,the solubility behavior of styrene with temperature was changed.The NRTL activity coefficient model was used to correlate the liquid-liquid equilibrium data,the binary interaction parameters of DEP-[Emim][OAc]?DCPD-[Emim][OAc]?styrene-[Emim][OAc]?styrene-glycerol?glycerol-[Emim][OAc] were obtained,and the correlation results agree well with the experimental data.The direct-contact heat transfer distillation experiments were carried out with the heat-sensitive material styrene as the dispersed phase and the ionic liquid [Emim][OAc] or the mixture of [Emim][OAc] + glycerol as the continuous phase.We found that the recovery of heat sensitive product obtained by distillation with the direct-contact heat transfer reboiler was greater than that obtained by conventional distillation.An improved expression of heat transfer rate is proposed,the effects of the feeding rate and the feeding tube diameter on the distillation efficiency were further investigated,the results show that a better distillation efficiency can be achieved by controlling the feeding rate and the feeding tube diameter.