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

Preparation of a novel solid acid catalyst SO_4^(2-)/Nd_2O_3/C and study of its performance for the synthesis of biodiesel from esterification reaction of oleic acid and methanol

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。

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 newcatalyst 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 empty2 p 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.