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
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摘要: 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SO42-/Nd2O3/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Nd3+与SO42-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SO42-配位的Nd3+所产生的静电场增大, 当有水 (强配体) 存在时, 可使SO42-/Nd2O3/C催化剂呈现出强Br nsted酸性。Abstract: 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 SO42-/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 SO42-/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 SO42-.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 SO42-.And finally, it should be noticed that H2O is a strong ligand.Hence, SO42-/Nd2O3/C exhibited a strong Br nsted acidity when H2O existed in the reaction medium.
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图 5 SO42-/Nd2O3/C催化剂的Raman谱图
Figure 5 Raman patterns of SO42-/Nd2O3/C catalyst
a: carbon; b: SO42-/Nd2O3/C
图 7 反应温度对油酸转化率的影响
Figure 7 Influence of reaction temperature on the conversion of oleic acid
图 9 甲醇与油酸的物质的量比对油酸转化率的影响
Figure 9 Influence of molar ratio of methanol/oleic acid on the conversion of oleic acid
图 10 催化剂用量对油酸转化率的影响
Figure 10 Influence of catalyst loading on the conversion of oleic acid
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