The Determination of the Surface Area of Sepiolite From Carbon Dioxide Adsorption Isotherms

Abstract

Sepiolite has a microporous structure the pores of which may be Renetrated to differing extents by molecules of different gases. A study has been made of the adsorption of CO, on outgassed sepiolite (from Amboseli, Tanzania) at I93O, 209.7~~ 273.*2:, and 298.2 OK using a gravimetric method. Values of the surface area of sepiolite were calculated from BET (Brunauer, Emmett, and Teller) andKaganer plots of results, assuming molecular areas for CO, based on extrapolated liquid densities. There were only relatively small deviations from a mean value of 279 m'/g. However, the values were much lower than those previously determined by adsorption of Ns and of other gases.It is suggested that COI adsorbed at these temperatures should be assumed to be in the liquid state, but that the usual method of calculating the molecular areas of adsorbed CO, from the liquid densities at these temperatures yields values which are too low. Molecular areas of 20.8 A' at 193 O K and 23.4 A' at 209.7 OK are preferred.Isosteric heats of adsorption at different coverages were calculated from the isotherms. The results indicated heterogeneity of the surface, with decreases in the values of the heat of adsorption occurring at low coverages and in the 'monolayer region'. They compare well with values calculated from the BET equation.

Particle Size Analysis

“…Experimental techniques for B.E.T. analysis were proposed by Takagi (180), Rawson (147), Watanabe and Yamashina (192), Dandy (34), Walker and Patel (190), and Granville et al (54). Rawson described a new method for soils using ethylene glycol vapor.…”

Surface Properties of Sepiolite from Amboseli, Tanzania, and Its Catalytic Activity for Ethanol Decomposition

“…On heating the structure loses water, resulting in a decrease in the surface area and micropore accessibility (Hayashi et al, 1969;Martin Vivaldi and Fenoll Hach-Ali, 1969;Nagata et al, 1974;Dandy and Nadiye-Tabbiruka, 1975;Fernandez-Alvarez, 1978;Serratosa, 1979). Sepiolite has a high adsorptive capacity for many gases and vapors (Barrer et al, 1954;Dandy, 1968Dandy, , 1969Dandy, , 1971Fenoll Hach-Ali and Martin Vivaldi, 1970;Serna and Fernandez-Alvarez, 1975;Serna and Vanscoyoc, 1979). Lopez-Gonzalez et al (1978) studied the adsorption of aminobutane (n-butylamine) on acid-activated sepiolite as an indicator of surface acidity.…”