Valorization of Mining Waste in the Synthesis of Organofunctionalized Aluminosilicates for the Esterification of Waste from Palm Oil Deodorization

The synthesis of aluminosilicate Al-MCM-41 was performed using mining kaolin waste as an alternative source of silicon and aluminum to add value to this waste. In a preliminary stage, acid leaching was carried out with the kaolin residue with three different durations (1, 1.5 and 2 h) to evaluate the leaching time that provided the highest amounts of silicon and aluminum in the tailings. Molecular sieves were synthesized by the hydrothermal method and calcined at 550 °C to eliminate the surfactant. X-ray diffractograms of the synthesized samples revealed that the sample AM41-2H, obtained from kaolin leached for 2 h (MC7-2H), presented the best structural arrangement due to the presence of 2θ angles close to 2.32°, a specific surface area of 1016 m 2 ·g -1 , a pore volume of 0.80 cm 3 ·g -1 , and a pore diameter of 3.14 nm, which are characteristic of Al-MCM-41. A sample of AM41-2H was functionalized with 3-mercaptopropyltrimethoxysilane (MTPS) (5 mmol MTPS/g AM41-2H). To eliminate excess unaltered MTPS on the surface of the material, the functionalized aluminosilicate (AM41-2H-F) was subjected to a purification step. The organic functional group that remained in the molecular sieve (-SH) was then oxidized to its corresponding acid group (-SO 3 H) to form stronger acid sites. Then, the heterogeneous catalyst obtained (AM41-2H-O) was tested in an esterification reaction of oleic acid with methanol and in an esterification reaction of an industrial waste from palm oil refinement (DDPO), which is generated during the deodorization process of palm oil. Both reactions were carried out for 2 h at 130 °C, with a fatty acid/methanol molar ratio of 1:30 and addition of 5% catalyst to the mass of fatty acid. The results obtained revealed that the conversion to esters from oleic acid and DDPO was 99% and 98%, respectively, in contrast to the uncatalyzed reaction, which achieved only 15% conversion. The catalysts used in the reactions were recovered and reused in the same conditions as the initial reactions, which showed conversions in this first cycle of catalyst reuse of 98% for oleic acid and 81% for DDPO, proving the efficiency of the catalyst synthesized from industrial kaolin waste. © Copyright 2019 American Chemical Society.