Thermogravimetry–mass spectrometry investigations of benzoic acid interactions with sodium and calcium montmorillonites

• Strong interactions between benzoic acid and montmorillonites results in high thermal desorption temperatures.
• Benzoic acid more strongly adsorbs on calcium montmorillonite than on sodium montmorillonite.
• At high temperatures, adsorbed benzoic acid decomposes from montmorillonites into benzene and carbon dioxide.
• TG–MS results indicate that benzoic acid interacts with montmorillonites at multiple adsorption sites.

Results from thermal analyses of sodium and calcium montmorillonites containing adsorbed benzoic acid are described. Based on these results, adsorption sites and thermal desorption processes are elucidated. Desorption of interlayer water is affected by the presence of benzoic acid, which disrupts cation–water interactions. Multiple benzoic acid desorption sites are indicated, which have properties that depend on the clay interlayer cation. Benzoic acid desorption occurs at higher temperatures for clays containing calcium ions compared to those containing sodium ions, presumably due to stronger interactions between the adsorbate and calcium ions. Benzoic acid desorption profiles, as well as the detection of decomposition products, suggest that benzoic acid persists on clays to temperatures as high as 550 °C. Above 300 °C, benzoic acid decomposes, yielding benzene and carbon dioxide.