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

Abstract

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 m2·g–1, a pore volume of 0.80 cm3·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 (−SO3H) 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.

Bentonites Modified with Phosphomolybdic Heteropolyacid (HPMo) for Biowaste to Biofuel Production

“…The values of the obtained Turnover Frequency (TOF) for these solids followed the same surface acidity trend. Since esterification requires catalysts with acidic sites [9,13,14,41,42,43], the results confirm that the acidity of the supports was a critical factor to maximize the catalytic activtity of the materials in the conversion of DDPO [9,39,49].…”

“…It is a relatively slow reaction and needs activation either by higher temperature or by a catalyst to achieve higher conversion [47]. Previous experiments [9,39,49] and preliminary experiments led us to use the considered optimum catalytic conditions, i.e., 25% HPMo, BLMW and BCMW to conduct the proposed esterifications (Table 3).…”

“…12-tungstophosphoric acid supported on metakaolin (25% HPW/MK700) [9] exhibited considerably high conversions at a high temperature (200 °C) despite the minor molar ratio of reactants. Comparatively, CrWO 2 and CrWTiO 2 catalysts required a temperature of 170 °C and a reaction time of 3 h to obtain high conversions (>80%), even though a small molar ratio of reagents is used [68,69], while a catalyst made of the kaolin residue functionalized with –SO 3 H groups) achieved excellent catalytic efficiency (98% conversion) [49] under similar reaction conditions to those employed in this work. Therefore, the present catalysts showed high DDPO conversions under comparatively more benign reaction conditions to most catalysts listed in Table 4.…”

“…At the end of the reactions, the catalyst was filtered off. The percent conversion of DDPO to the corresponding ester was estimated by an acid measure of the product by titration with 0.1 mol L −1 hydroxide according to the method described in the literature [9,39,49].…”

“…HPMo supported on natural bentonites was chosen because the reactions catalysed by that acid proved to be effective in the conversion of triacylglycerol and free fatty acids to alkyl esters [14,42,43]. This is an important topic, since distillate of deodorization of palm oil (DDPO) has a high content of free fatty acids (84%), besides being largely available at a low cost [9,39,48,49]. The esterification of DDPO was selected as a reaction to evaluate, for the first time, the catalytic performance of the catalysts obtained by the method adopted in this work.…”