新型碳基固体酸SO_4~(2-)/Nd_2O_3/C制备及催化油酸与甲醇酯化反应合成生物柴油研究

在流化床管式炉中,通过对废山茶油壳进行高温炭化处理制备了一种碳基材料。以该碳基材料为载体,并对其进行稀土金属离子钕和硫酸磺化改性,合成了一种新型碳基固体酸催化剂SO_4~(2-)/Nd_2O_3/C。对制备而成的催化剂进行了多种物理化学表征分析,并以其为经甲醇和油酸酯化反应来合成生物柴油的催化剂,对其催化活性和稳定性进行了研究。结果表明,当甲醇和油酸物质的量比为2∶1,催化剂与反应物质量比为2%,反应时间为120 min,反应温度为90℃,油酸的转化率为96.70%。催化剂经循环使用三次后,油酸的转化率仍高达86.74%。高催化活性可归因如下:由于Nd、O、S元素的电负性分别为1.14、3.44和2.58,因而Nd易向O和S元素的2p空轨道提供孤对电子,使Nd~(3+)与SO_4~(2-)之间形成稳定的配位键。并且,由于S=O键具有强吸电子作用,而导致了与SO_4~(2-)配位的Nd~(3+)所产生的静电场增大,当有水(强配体)存在时,可使SO_4~(2-)/Nd_2O_3/C催化剂呈现出强Brnsted酸性。

Preparation of a novel solid acid catalyst SO42-/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.