Sulfonated magnetic nanobiochar as heterogeneous acid catalyst for esterification reaction

Abstract

In this work, heterogeneous magnetic acid catalyst were prepared through the pyrolysis-carbonization process of Indonesia’s indigenous biomass, oil palm empty fruit bunches. The process, which followed the pretreatment of biomass with FeCl3, generated the magnetic biochar (MBC). The carbonization temperature were varied which resulted in an optimum surface area of the sample MBC02 of 53.77 m2/g exhibiting mesoporous structure at 500 °C. The MBC02 samples were further treated via sulfonation to increase the acidic properties obtaining the heterogenous acid catalyst, MBC02-SO3H in which the surface consists of strong (SO3H and COOH) and weak (OH) acid sites with total acidity of 0.28 mmol/g. The carbon nanomaterials were observed to be in its amorphous phase with crystallite Fe3O4 which corroborates the ‘soft’ ferromagnetic properties of the samples. The activity of sample MBC02-SO3H as an acid catalyst was evaluated via esterification reaction of oleic acid and methanol. The effect of catalyst loading, reaction time and temperature were investigated. At optimum reaction condition with 5.0 % (w/w) catalyst loading, with an oleic acid: methanol volume ratio of 1:8 at 150 °C and 90 min, the esterification using MBC02-SO3H gave a methyl oleic ester yield of 97.6 %. The catalyst activity was superior compared to commercial solid acid and homogenous acid catalyst confirming the excellent performance of MBC02-SO3H as a magnetic solid acid catalyst for esterification.