Selective water sorbents for multiple applications, 1. CaCl₂ confined in mesopores of silica gel: Sorption properties

Abstract

This paper presents sorption properties of a selective water sorbent based on mesoporous KSKG silica gel as a host matrix and calcium chloride as a hygroscopic salt. Sorption isobars, isochores and isotherms at T=20–150°C and vapor partial pressures of 8–133 mbar clearly showed two types of water sorption: 1) the formation of solid crystal hydrates at low amounts N of sorbed water, and 2) vapor absorption mainly by the salt solution at higher N. Sorption properties of CaCl₂ crystal hydrates were found to change strongly due to their impregnation into mesoporous silica gel, whereas the solution confinement to the mesopores did not change its water sorption properties with respect to the bulk solution. Isosteric sorption heat was measured to depend on water sorption and to change from 62.5 kJ/mol for solid hydrates to 42.2–45.6 kJ/mol for solution.