Investigation on feasibility of ionic liquids used in solar liquid desiccant air conditioning system

The corrosion problem of traditional liquid desiccants hinders the development of solar liquid desiccant air conditioning system. Ionic liquids (ILs) could be a possible substitute because of their low corrosion to metals. According to the characteristic of cation and anion, two ILs 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) and 1,3-dimethylimidazolium acetate ([Dmim]OAc) were selected for possibility investigation. The experimental results demonstrated that the surface vapor pressure of [Bmim]BF4 aqueous solution was so high that it was not suitable for dehumidification. With comparing the structure of [Bmim]BF4 and 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4), it was found that for imidazole salts with the same anion, as the alkyl chain of the cation becomes shorter, the surface vapor pressure of its aqueous solution would be lower. In addition, simulation model was used to compare the dehumidification performance of [Dmim]OAc and [Emim]BF4 with that of the traditional desiccants lithium Chloride (LiCl) and lithium bromide (LiBr). The results showed that in the same condition, [Dmim]OAc with an inlet mass concentration of 81.7% and [Emim]BF4 of 85.5% could reach the same dehumidification rate as LiCl of 40.9% and LiBr of 45.0% mass concentration. Better dehumidification performance of [Dmim]OAc than that of [Emim]BF4 was achieved, thus, like [Emim]BF4, [Dmim]OAc can also be a promising substitute for traditional desiccant.

► Liquid desiccant air conditioning system is efficient for solar thermal application. ► Ionic liquids are non-combustible, high stable, non or low corrosive to metals. ► [Dmim]OAc and [Emim]BF4 can achieve similar performance with LiCl and LiBr. ► [Dmim]OAc and [Emim]BF4 can be a possible substitute of current desiccant.