Abstract
The synthesis, characterization and catalytic performance of a conceptually simple, novel NbOx-SiO2 catalyst are here described. The niobium(V)-silica catalyst was prepared starting from cheap and viable reactants, by alkaline deposition of NH4Nb(C2O4)2·H2O in the presence of fructose as a stabilizer and subsequent calcination. The NbOx-SiO2 solid (0.95 Nb wt.%) was tested in the liquid-phase epoxidation with aqueous hydrogen peroxide of methyl oleate, as a model substrate. It was then tested in the epoxidation of a mixture of methyl esters (FAMEs) obtained by transesterification with methanol and purification of karanja oil, extracted from the autochthonous Indian variety of Millettia pinnata tree. The catalyst showed a promising performance in terms of methyl oleate conversion (up to 75%) and selectivity to epoxide (up to 82%). It was then tested on the FAME mixture from karanja oil, where interesting conversion values were attained (up to 70%), although with lower selectivities and yields to the mixture of desired epoxidized FAMEs. The solid withstood four catalytic cycles overall, during which a non-negligible surface reorganization of the Nb(V) sites was observed. However, this restructuring did not negatively affect the performance of the catalysts in terms of conversion or selectivity.
Highlights
Epoxide derivatives of fatty acid methyl esters (FAMEs) proved to be among the most versatile intermediates in oleochemistry, as they can be transformed into a broad series of key products through oxirane ring opening [1,2,3]
FAMEs obtained from karanja oil following an environmentally and economically sustainable approach, we focused our attention onto the use of aqueous hydrogen peroxide, as an oxidant, in the presence of a simple heterogeneous catalyst
Karanja FAME mixture was obtained by esterification with sodium methoxide and subsequent distillation under vacuum, according to an approach previously used with vegetable oils of different origin [45]
Summary
Epoxide derivatives of fatty acid methyl esters (FAMEs) proved to be among the most versatile intermediates in oleochemistry, as they can be transformed into a broad series of key products through oxirane ring opening [1,2,3]. In order to attain an appropriate degree of sustainability of the overall process and to properly tackle the fuel vs food/feed biomass dilemma, the scientific community is paying an ever-increasing attention to oleochemicals derived from either non-edible oils, extracted from land- or water-saving crops, or animal fats, obtained from food-processing waste [10,11,12] In this scenario, India possesses a broad variety of non-edible oil-bearing vegetable sources, such as jatropha (Jatropha curcas), neem (Azadirachta indica), mahua (Madhuca longifolia), castor Catalysts 2019, 9, 344 communis) and, in particular, karanja (Millettia pinnata) Triacylglycerols extracted from these species feature a high percentage of unsaturated fatty acids, which can be functionalised and converted into high added-values intermediates [10,13]
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