Microwave assisted biodiesel production using sulfonic acid-functionalized metal-organic frameworks UiO-66 as a heterogeneous catalyst

Abstract

Room temperature sulfonated UiO-66 (UiO-66-SO3H) was demonstrated to be an excellent catalyst in conversion of oleic acid, a commonly used test substrate for biodiesel synthesis, to methyl oleate under microwave irradiation. Owing to the high sulfonic acid density (1.25 mmol g−1) and surface area (735 m2 g−1), the catalyst showed excellent conversion of oleic acid to methyl oleate at 98.30 ± 0.8% under the optimized reaction of methanol to oleic acid ratio of 20: 1, catalyst loading of 8 wt %, reaction temperature of 100 °C and reaction time of 1 h in microwave irradiation. The morphology and chemical composition of the UiO-66-SO3H catalyst were exhaustively characterized using XRD, XPS, BET, SEM and TGA. In addition, the synthesized methyl oleate was characterized by GC-MS, 1H and 13C NMR. The catalyst reusability was investigated up to 5 successive cycles affording a high 82.12 ± 0.6% conversion of oleic acid to methyl oleate on the 5th catalytic cycle.