Water vapor adsorption of CaCl2-impregnated activated carbon

Activated carbons (AC) impregnated with the hygroscopic salt CaCl2 were synthesized to enhance the amount of water vapor adsorbed at low relative pressure (P/P0). Possible applications for these materials are in adsorption heat pumps and desiccant air conditioners. The ACs were synthesized from tissue paper by chemical activation with K2CO3 and the porous properties were investigated of a number of materials prepared under a variety of activation conditions. The highest specific surface area (SBET) (1820 m2/g) was obtained from the sample prepared with a K2CO3/sample ratio = 1/1 by mass, activated at 900 °C for 2 h under flowing N2 (2 L/min). Impregnation with CaCl2 was performed using 2.4–6.5 M CaCl2 solutions and a solution volume equal to the pore volume of the AC. XPS surface chemical analysis revealed that the impregnated CaCl2 was mostly successfully impregnated into the pores while the surface CaCl2 increased gradually with increasing amount of impregnation. The adsorption of water vapor in the P/P0 range 0.1–0.3 (ΔW0.1–0.3) was dramatically increased by CaCl2 impregnation, the ΔW0.1–0.3 value reaching 0.52 g/g in the sample impregnated with 70 mass% CaCl2; this value is much higher than previously reported ΔW0.1–0.3 values.