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

[Display omitted] ► Thermal activation at 850°C made the flint kaolin more reactive to acid leaching. ► Catalysts prepared using microwaves decreased time and temperature of reaction. ► Metakaolin activated at 400W by 15min presented better performance. ► A more efficient and eco-friendly catalyst for production of biodiesel. 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 (4M) 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 0.2M 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 400W for 15min presented a surface area of 187m2g−1, yielding acidic sites with a concentration of 4.32mmolg−1 and a conversion of 96.5% (115°C, 40min, 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.