Thermal and Catalytic Amidation of Stearic Acid with Ethanolamine for Production of Pharmaceuticals and Surfactants

Thermal and catalytic amidation of stearic acid with ethanolamine in hexane was investigated using both microporous H-Beta and ZSM-5 zeolites, and mesoporous materials, H-MCM-36 and H-MCM-41, as catalysts in hexane. The main studied parameters were the catalyst structure and acidity, temperature and molar ratio of reactants. The results showed that thermal amidation of stearic acid with an equimolar ratio of ethanolamine was substantial giving 61 % conversion in 3 h. The highest conversion and selectivity to stearoylethanolamide, being 79 and 83 %, respectively, were achieved with microporous, relatively strongly acidic H-Beta-150 catalyst. Stearoylethanolamide and the corresponding esteramide were the main products. An optimum amount of Brønsted acid sites in the catalyst was required to achieve high yield and selectivity towards stearoylethanolamide. With increasing amount of Brønsted acid sites more esteramide was formed. Typically esteramide selectivity increased in the catalytic amidation of stearic acid with increasing conversion due to consecutive reactions. Low conversions were obtained, when increasing the molar ratio of stearic acid to ethanolamine. In addition, an excess of ethanolamine suppressed the reaction due to its strong adsorption on zeolite surface. An optimum reaction temperature was 180 °C. The mass transfer limitations were not fully absent in the reaction. A reaction mechanism, including both parallel and consecutive pathways was proposed.