双模型介孔SiO_2负载磷钨酸催化剂催化废油脂酯化反应的失活研究

Deactivation of Bimodal Mesoporous SiO2Supported Phosphotungstic Acid in Esterification of Waste Oil

以双模型介孔SiO2(BMMs)为载体,采用浸渍法制备负载型磷钨酸催化剂(HPW/BMMs),借助XRD、FTIR、UV-Vis、N2吸附-脱附、31P NMR和XRF方法,重点研究了该催化剂在废油脂酯化反应过程中的重复使用性能、活性下降原因及反应前后催化剂的结构变化和化学组成。结果表明,HPW/BMMs催化剂重复使用4次后,酯化率由72.8%降至60.1%;反应前后催化剂中HPW的Keggin结构无明显变化,但其晶相结构发生了较大改变,同时载体BMMs的结构有序度有所下降,这是催化剂表面吸附了大量有机物所致;催化剂表面严重积炭和HPW的流失(重复使用4次后HPW质量分数由36%降至20%)可能是其活性下降的主要原因。

HPW/BMMs catalyst was prepared by supported phosphotungstic acid on bimodal mesoporous SiO2 via impregation method.The reusability and deactivation of HPW/BMMs catalyst during the esterification of waste oil with methanol were emphatically investigated.The structure derivation and physico-chemical properties were characterized by means of XRD,FT-IR,UV-Vis,N2 adsorption-desorption,31p NMR and XRF.The results showed that the conversion of esterification was decreased from 72.8 % to 60.1% after HPW/BMMs catalyst was reused 4 times.Meanwhile,the Keggin structure of HPW in HPW/BMMs catalysts did not change obviously,but the structure order degree of BMMs decreased remarkably,which stemmed from the influences of organic molecules on the mesoporous surface of BMMs.Furthermore,both the coke deposit on catalyst surface and the leaching of HPW （from 36% to 20% after 4 times recycle） might be the main reasons for the deactivation of HPW/BMMs catalyst during waste oil esterification.