Selective water sorbents for multiple applications.: 11.: CaCl2 confined to expanded vermiculite

This paper presents the water sorption properties of a new selective water sorbent based on expanded vermiculite as a host matrix and calcium chloride as a hygroscopic salt. Sorption isobars, isosters and isotherms at T = 30-150 degreesC and vapor partial pressure 8.2-42.0 mbar clearly show that at low water contents crystalline hydrates with 0.33, 1 and 2 molecules of water per 1 molecule of CaCl2 are formed in the pores. These hydrates are stable over a temperature change of 20-30 degreesC and exhibit kinetically slow transformations. At higher water uptake, the vapor absorption leads to the formation of a CaCl2 aqueous solution inside the pores, which properties are close to those in the bulk. Isosteric sorption heat was found to depend on water sorption and change from 76.3 kJ/mol for solid hydrates to 39.1-46.6 kJ/mol.