酯交换法合成碳酸二苯酯用氧化铅-氧化锌催化剂的研究

Study on Pb-Zn Double Oxide for Synthesis of Diphenyl Carbonate by Transesterification

制备了一种用于苯酚与碳酸二甲酯酯交换合成碳酸二苯酯的新型氧化铅 氧化锌多相催化剂 .研究了制备方法、焙烧温度、不同母体和母体配比对催化剂催化性能的影响 .应用XRD ,TPR和原子吸收光谱对催化剂结构进行了表征 ,发现Pb3 O4是主活性物相 ,ZnO为助催化剂 ,并以非晶态或微晶态存在于催化剂体系中 .当焙烧温度为 5 0 0℃ ,n(Pb) /n(Zn) ≈ 2时 ,催化剂的活性最高 ,碳酸二苯酯产率可达 4 5 6 % .考察了催化剂的重复使用效果 。

A new heterogeneous catalyst, lead zinc double oxide, was prepared for the synthesis of diphenyl carbonate (DPC) by transesterification of dimethyl carbonate (DMC) and phenol. Usually, the reaction is carried out in the liquid phase using homogeneous catalysts such as organic Sn compound or Ti compound. Lead zinc double oxide can overcome the shortages of homogenous catalysts and it is an active and selective catalyst for the reaction. The catalyst samples were prepared by two methods of co precipitation and mechanical milling. In co precipitation, three aqueous solutions, Pb(NO 3) 2, Zn(NO 3) 2 and NH 3·H 2O, were added into a beaker simultaneously, then aged, filtrated, dried and calcined. In mechanical milling, lead hydrate and zinc hydrate were prepared separately, then mixed at some ration and calcined. The activity of single lead oxide or single zinc oxide was studied. The different conditions of preparation for lead zinc double oxide, for example, molar ratio of Pb/Zn, calcination temperature and precursor, were investigated. The catalyst sample prepared by co precipitation had high activity when n (Pb) / n (Zn) ratio was 2, Pb(NO 3) 2 and Zn(NO 3) 2 as precursors, and calcination temperature was 500 ℃, and DPC yield was 44 8%. DPC yield achieved 45 6% over the catalyst sample prepared by mechanical milling. XRD, TPR and atomic absorption spectroscopy were employed for catalyst characterization. Pb 3O 4 was found as the main active phase, and amorphous ZnO as promoter. The reusability of the catalyst and the reason of deactivation were also studied.