Zn-Mg复合氧化物催化大豆油甘油解合成单甘酯

Monoglyceride Synthesis by Glycerolysis of Soybean Oil over Zn-Mg Mixed Oxide Catalyst

摘要:

采用共沉淀法制备了一系列不同Zn/Mg摩尔比的Zn-Mg复合氧化物，并用其催化大豆油与甘油反应合成单甘酯。首先采用X射线衍射仪（XRD）、氮气吸附脱附仪、扫描电镜（SEM）等对Zn-Mg复合氧化物催化剂进行了表征，并采用Hammett指示剂法测定了催化剂的表面碱强和碱量。其次，优化了使用Zn-Mg复合氧化物催化合成单甘酯的工艺条件。最后考察了Zn-Mg复合氧化物的重复使用性能。结果表明，改变Zn/Mg摩尔比，不仅可以调控Zn-Mg复合氧化物的碱强与碱量，还可以调控其比表面积、孔容等结构参数。不同Zn/Mg摩尔比复合氧化物的催化活性变化趋势与其表面碱量、比表面积及孔容等结构参数的变化趋势一致。Zn/Mg摩尔比为0.1时，复合氧化物（ZM0.1）的催化甘油解反应活性最高。使用该催化剂合成单甘酯的适宜条件为，物料比n(甘油):n(大豆油)=3:1，反应温度210 ?C，反应时间2 h，催化剂添加量为大豆油质量的0.6%。在该适宜条件下，大豆油转化率达到95.6%，单甘酯收率为58.5%。ZM0.1催化剂稳定性好，重复使用5次时大豆油转化率仍高达80.9%。

Abstract:

A series of Zn-Mg mixed oxide catalysts with different Zn/Mg molar ratios were prepared by coprecipitation method for the glycerolysis of soybean oil to produce monoglyceride. These catalysts were firstly characterized by XRD, BET, SEM techniques, and the base strength and basicity of catalysts were determined by Hammett indicators. The reaction conditions were then optimized for the preparation of monoglyceride catalyzed by Zn-Mg mixed oxide catalyst. The reusability of Zn-Mg mixed oxide catalyst was studied finally. The results show that changing the Zn/Mg molar ratio can control the base strength, basicity, surface area and pore volume of Zn-Mg mixed oxide catalysts. The activities of Zn-Mg mixed oxide catalysts with different Zn/Mg molar ratio are consistent with the change of basicity, surface area and pore volume, and the maximum activity could be obtained when the Zn/Mg molar ratio reached 0.1. The optimum reaction conditions were as follows: n(glycerol):n(soybean oil)=3:1, reaction temperature 210?C, reaction time 2 h, and catalyst amount 0.6% (base on the mass of soybean oil). Under these conditions, the soybean oil conversion and monoglycerides yield can reach 95.6% and 58.5%, respectively. After recycling five times, the soybean oil conversion remains 80.9%, which means the ZM0.1 catalyst is stable.