Microwave-assisted preparation of a new esterification catalyst from wasted flint kaolin

Amazon flint kaolin, considered useless from an economic and industrial point of view, was calcined at 850 and 950 °C to obtain metakaolin samples. These samples were subsequently treated with sulfuric acid (4 M) by assisted heating with microwave radiation. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy and N2 physisorption; the surface acidity was determined by titration with 0.2 M KOH. The materials obtained were used as catalysts in the esterification of oleic acid with methanol. Metakaolin that was calcined at 850 °C and activated at 400 W for 15 min presented a surface area of 187 m2 g−1, yielding acidic sites with a concentration of 4.32 mmol g−1 and a conversion of 96.5% (115 °C, 40 min, molar ratio of oleic acid: methanol 1:60). In addition to a lower preparation time, the flint metakaolin activated by microwave radiation gave a catalytic performance equivalent or superior to the one prepared by reflux, as well as it showed considerably reduced reaction time and temperature.