The desorption of benzoic acid and stearic acid from sodium and calcium montmorillonites has been studied using thermogravimetric and differential thermogravimetric analysis. Desorption of benzoic acid from sodium montmorillonites occurs at 140 °C and from calcium montmorillonites at 179 °C. This increase in temperature is attributed to the benzoic acid bonding to the calcium in the interlayer. A lowering of the dehydroxylation temperature of montmorillonites is observed with acid adsorption. Stearic acid desorbs at 218 °C as observed by the DTG curves. The desorption pattern differs between the sodium montmorillonites and the calcium montmorillonites.
Thermal analysis and differential thermal analysis offers a novel means of studying the desorption of acids such as stearic
acid from clay surfaces. Both adsorption and chemisorption can be distinguished through the differences in the temperature
of mass losses. Increased adsorption is achievable by adsorbing onto a surfactant adsorbed montmorillonite. Stearic acid sublimes
at 179 °C but when adsorbed upon montmorillonite sublimes at 207 and 248 °C. These mass loss steps are ascribed to the desorption
of the stearic acid on the external surfaces of the organoclays and from the de-chemisorption from the surfactant held in
the interlayer of the montmorillonite.