Glycerol Vapor Adsorption on Clay Minerals and Montmorillonitic Soil Clays

Abstract

AbstractAdsorption isotherms of glycerol were obtained for clay fractions of montmorillonite, vermiculite, kaolinite, and eight soil clays at 80C in an evacuated system. The weight of glycerol required for monolayer formation was determined by application of the BET equation to adsorption data. Montmorillonite samples gave BET monolayer values from 211 to 230 mg glycerol/g of montmorillonite which is in the theoretical range. Monolayer values calculated for soil montmorillonites from BET monolayer values and corrected for impurities were 209 to 239 mg glycerol/g of montmorillonite in < 0.08µ soil clays. The surface area values estimated from these soil montmorillonite monolayer values range from 738 m2/g to 844 m2/g. Vermiculite gave BET monolayer values of 40 mg and 96 mg/g of clay for 2 to 0.2µ and 0.2 to 0.08µ samples, respectively. This method appears to effectively measure the sorption surface of montmorillonite and indicates lower sorption surface of vermiculite than is suggested by its structural similarity to montmorillonite. Glycerol monolayer values indicate only modest reduction of particle size in < 0.08µ compared to 0.2 to 0.08µ montmorillonite from soil clays and Wyoming bentonite. The success of glycerol adsorption on clays, in spite of a very low vapor pressure, suggests that more volatile polar organic molecules might effectively be studied by adsorption on clay surfaces.