Thermogravimetric study of the desorption of cyclohexylamine and pyridine from an acid-treated Wyoming bentonite

Abstract

Four 15 g samples of an unsedimented Wyoming bentonite were treated with 200 cm³ of 0·025, 0·050, 0·100 and 0·250 mol dm⁻³ H₂SO₄ for 1 h at room temperature (samples I–IV, respectively). Three further 15 g samples were treated with 200 cm³ of 50% (v/v) H₂SO₄ for 1 h at 20°C (sample V), and 1 and 2 h under reflux (samples VI and VII, respectively). X-ray fluorescence and diffraction studies revealed that only samples VI and VII suffered any substantial structural attack. The resulting acidity of the clays, determined by cyclohexylamine desorption, indicated that sample V contained the largest number of protons at 0·59 mmol H⁺ (g clay)⁻¹. Sample V was also the most efficient catalyst for the dehydration and etherification of hexan-1-ol, giving a combined product yield of 17·0% after 2 h reflux in neat reactant. The parent bentonite and samples I and II showed no discernible catalytic activity despite measured acidities of 0·1, 0·24 and 0·34 mmol H⁺ (g clay)⁻¹. In contrast samples III and IV gave combined product yields of 4·5 and 11·0%, respectively, which correlated well with the measured acidities of 0·38 and 0·48 mmol H⁺ (g clay)⁻¹. Samples VI and VII, prepared by reflux in acid, contained 0·3 and 0·1 mmol H⁺ (g clay)⁻¹, respectively, and gave combined product yields of 13·0 and 6·0%.