Ce改性硅钨酸催化制备月桂酸单甘酯

Catalytic Properties of Ce Exchanged Tungstosilicic Acid on the Esterification to Glycerol Monolaurate

摘要:

采用离子交换法合成多种稀土改性硅钨酸催化剂MxH4–3xSiW12O40 (M = La, Ce, Pr, Nd, Sm; x = 1/3, 2/3, 1, 4/3)，并利用FTIR，XRD，TGA-DTG，固体核磁共振结合探针分子技术(31P-TMPO MAS-NMR)对CexH4–3xSiW12O40 催化剂结构、稳定性及酸性进行了表征；结果表明，Ce1/3H3SiW12O40催化剂在月桂酸单甘酯制备中显示出最好的催化性能。稀土Ce有效结合到硅钨酸上，制备的催化剂保持了完整的Keggin结构。与纯硅钨酸相比，CexH4–3xSiW12O40 的酸强度有所减弱，但由于该类催化剂较强的Brønsted酸性及Brønsted-Lewis酸性位间的协同效应，使CexH4–3xSiW12O40 在月桂酸单甘酯的制备中具有良好的催化性能。以Ce1/3H3SiW12O40为催化剂，在甘油/月桂酸物质的量比为4/1，催化剂用量为月桂酸质量的4%，反应温度423K，反应时间120 min下，月桂酸单甘酯产率为78.4%；动力学研究表明，该反应活化能为42.37 kJ/mol；Ce1/3H3SiW12O40催化剂经5次回收利用，月桂酸单甘酯的产率为71.4%，具有较好的重复使用性能。

Abstract:

A series of rare earth modified tungstosilicic acid catalysts MxH4–3xSiW12O40 (M = La, Ce, Pr, Nd, Sm; x = 1/3, 2/3, 1, 4/3) were prepared by ion exchange method. The structure, stability and acidity of the catalysts (CexH4–3xSiW12O40 ) were characterized by different analytical and spectroscopic techniques such as FT-IR, XRD, TGA-DTG and 31P MAS-NMR, and their catalytic properties were investigated on the esterification of lauric acid (LA) and glycerol (GL) to glycerol monolaurate (GML). Results showed that Ce1/3H3.0SiW12O40 catalyst had the best catalytic activity in the synthesis of GML. The rare earth metal cation (Ce) had been effectively combined to tungstosilicic acid, and the catalysts maintained the complete Keggin structure. Compared with tungstosilicic acid, the acidity of CexH4–3xSiW12O40 catalysts decreased, but the catalysts had good catalytic performance during the esterification for strong Brønsted acidity and Brønsted-Lewis acid synergy. The Ce1/3H3.0SiW12O40 was utilized to optimize the reaction conditions with 78.4% GML yield under GL/LA molar ratio of 4.0, catalyst amount (relative to LA mass) 4%, reaction temperature 423 K and reaction time 120 min. Kinetic studies revealed that the Ce1/3H3.0SiW12O40 for synthesis of GML with an apparent activation energy of 42.37 kJ/mol. The GML yield decreased to 71.4% after five consecutive, the catalyst still had superior reusability in the reaction system.