Preparation of a novel solid acid catalyst SO₄^2-/Nd₂O₃/C and study of its performance for the synthesis of biodiesel from esterification reaction of oleic acid and methanol

A carbon material was prepared from the high temperature carbonization of waste camellia seed shell in a fluidized bed tubular reactor.The carbon material was applied as the catalyst support to prepare a new catalyst SO₄^2-/Nd₂O₃/C after it was simultaneously modified by Nd³⁺ and sulfonated by concentrated sulfuric acid through impregnation method.The catalyst was characterized by several physical and chemical characterization methods.The catalytic activity and reusability of SO₄^2-/Nd₂O₃/C were evaluated using it to catalyze the esterification of methanol and oleic acid for the synthesis of biodiesel.Results showed that the conversion of oleic acid was 96.70% when the methanol/oleic acid molar ratio was 2:1, reaction temperature was 90℃, and catalyst/reactants was 2% under reflux condensation for 120 min.After recycling of three times, the conversion of oleic acid was still 86.74%.High activity can be explained as follows:the electro-negativity of Nd is 1.14, which is smaller than O (3.44) and S (2.58), so it will provide lone electron pair to the empty 2p orbit of O and S, resulting in the formation of a stable coordination bond between Nd³⁺ and SO₄^2-.In addition, S=O double bond can induce a strong electron withdrawing effect, which can increase the electrostatic field of Nd³⁺ when it was coordinated with SO₄^2-.And finally, it should be noticed that H₂O is a strong ligand.Hence, SO₄^2-/Nd₂O₃/C exhibited a strong Br nsted acidity when H₂O existed in the reaction medium.