Characterization of MgCl2/AC composite adsorbent and its water vapor adsorption for solar drying system application

In order to realize dehumidification and heat recovery from solar drying system, a fresh walnut-shell activated carbon (AC0) was prepared by KOH chemical activation method and used as a novel host matrix for hygroscopic salt MgCl2 impregnation. The effects of MgCl2 loading amounts and cerium (Ce) addition on water vapor adsorption performance of the composite adsorbents were investigated. N2 adsorption-desorption isotherm and scanning electron microscope were employed to characterize pore development and morphology of the composite adsorbents. Finally, regenerabilities and stabilities of AC0, AC40 (theoretical MgCl2 loading amount 40 wt%), and AC404 (theoretical MgCl2 loading amount 40 wt% and theoretical Ce addition amount 4 wt%) were studied. The results show that water vapor adsorption amount of the composite adsorbents decreases slightly and then increases significantly with the increase of the MgCl2 loading amount. Under the 70% relative humidity and the adsorption temperature of 298 K, water vapor adsorption amounts of AC0, AC40, and AC404 are 0.6022 g/g, 0.9410 g/g and 1.0502 g/g, respectively. AC0 does well in excellent reversibility of water vapor adsorption. Ce addition slightly promotes uniform distribution of MgCl2 within the composite adsorbent, prevents the conversion from MgCl2·6H2O to Mg2CO3Cl(OH)·3H2O, and improves adsorption-regeneration performance. The present study confirms that the composite adsorbent would be one of the potential candidates for dehumidification and heat recovery in solar drying system.