钙锌铝固体碱催化剂的制备及表征

Preparation and characterization of calcium-zinc-aluminum solid base catalyst

以硝酸钙、硝酸锌及硝酸铝为原料,碳酸钠为沉淀剂,采用共沉淀法制备了碳酸钙、碳酸锌及氢氧化铝。经陈化、抽滤、洗涤、干燥及焙烧得到钙锌铝固体碱催化剂。以蓖麻油甲醇解反应为模型反应,蓖麻油转化率为活性评价指标,采用正交实验考察了催化剂制备条件对其催化活性的影响。采用Hammett指示剂滴定法、TG、XRD、SEM及BET技术对催化剂及其前驱体进行了表征。结果表明:制备催化剂的优化条件为n(Ca)∶n(Zn)∶n(Al)=2.5∶0.5∶1、沉淀剂为碳酸钠、焙烧温度800℃、焙烧时间8 h,在优化条件下,蓖麻油转化率可达95.4%;催化剂前驱体在700~850℃温区有1个明显的失重台阶,在850℃以后质量基本不随温度变化;固体碱催化剂的碱强度在7.2~11.2之间,总碱位量为9.740 mmol/g,主要由Ca O、Zn O两种晶体构成,其形状为多孔的连续的不规则固体,其比表面积为30.75 m^2/g、孔容为0.051 64 cm^3/g。

Calcium carbonate, zinc carbonate and aluminum hydroxide were prepared by coprecipitation method using calcium nitrate, zinc nitrate and aluminum nitrate as raw materials and sodium carbonate as precipitant, then calcium-zinc-aluminum solid base catalyst was obtained by aging, filtration, washing, drying and roasting.The effects of catalyst preparation conditions on the catalytic activity were investigated by orthogonal experiment with methanolysis reaction of castor seed oil as model reaction and castor seed oil conversion rate as the activity evaluation index. The catalyst and its precursor were characterized by Hammett indicator method, TG, XRD, SEM and BET.The results showed that the optimal conditions for the preparation of the catalyst were obtained as follows：n（Ca）∶n（Zn）∶n（Al）=2.5∶0.5∶1, with sodium carbonate as precipitant, calcination temperature 800℃ and calcination time 8 h. Under the optimal conditions, the castor seed oil conversion rate was up to 95.4%. The catalyst precursor had a significant weight loss step at 700-850℃, and the mass did not change with temperature higher than 850℃. The alkali strength of the solid base catalyst was between 7.2 and 11.2, the total alkali amount was 9.740 mmol/g, mainly constituted by two kinds of crystals, CaO and ZnO.The shape of the solid base catalyst was porous continuous irregular solid, and the specific surface area was 30.75 m2/g, and the pore volume was 0.051 64 cm3/g.