Solution to the sorption hysteresis by novel compact composite multi-salt sorbents

Two novel types of consolidated composite sorbents of NH4Cl/CaCl2/MnCl2 and NH4Cl/CaCl2 are developed by the matrix of expanded natural graphite treated with sulfuric acid (ENG-TSA). The Clapeyron curves and sorption/desorption properties of different sorbents are tested and compared under non-equilibrium conditions. Compared with single-salt sorbent, the multi-salt/ENG-TSA sorbents show the combining properties of each kind of metal chloride they contain. One novel phenomenon is discovered in the study is that the sorption hysteresis of single salts, which is regarded as one common phenomenon for chemisorption, can be changed by the composite sorbents of multi-salt. For the composite bi-salt sorbent of NH4Cl/CaCl2 the sorption hysteresis is much less significant than the single metal chlorides of NH4Cl and CaCl2. For the tri-salt composite sorbent of NH4Cl/CaCl2/MnCl2 the sorption hysteresis disappears. The reason is analyzed and it may be related to the resorption between the metal chlorides they contain, which leads to a reduction of reaction heat that is believed to be a typical reason for sorption hysteresis.