Heats of immersion related to the extent of water loss and specific surface areas: SrCl2- and BaCl2-loaded aluminas as desiccant materials

Abstract

SrCl₂- and BaCl₂-loaded aluminas were thermally dehydrated in vacuo at various temperatures in the range 20–500 °C. The water loss, specific surface area for nitrogen adsorption and the integral heat of water immersion were determined for thermally treated samples. Possible changes in the porosity of the samples investigated were studied using the V₁-t method. The model-less method was used to determine the surface locations and the area fraction located in the mesopores was calculated. This fraction indicates the surface accessibility of various samples to nitrogen adsorbate molecules and to the smaller water molecules. The integral heats of water immersion normalized to nitrogen Brunauer-Emmett-Teller surface areas were studied over the entire temperature range. The samples with the highest surface accessibility to water molecules together with relatively high heats of immersion in water were assumed to be effective dehydrating materials. It was found that SrCl₂- and BaCl₂-loaded aluminas required heat treatment at 400 °C and 300 °C respectively to optimize their use as desiccant materials. Further detailed discussion is presented.