生物柴油催化剂——SO_4^(2-)/ZrO_2-TiO_2固体酸的制备及表征

Preparation and characterization of SO_4^(2-)/ZrO_2-TiO_2 solid acid catalyst for biodiesel synthesis

以ZrOCl2·8H2O和Ti(SO4)2为原料,以浓氨水为沉淀剂,以稀硫酸为浸渍剂,经高温焙烧制得SO24-/ZrO2-TiO2固体酸催化剂。采用正交试验考察了催化剂制备过程中各因素对其催化活性的影响,得到的优化条件为:焙烧温度723 K,焙烧时间4 h,n(Ti)/n(Zr)=6,浸渍液硫酸浓度1.50 mol/L。以优化工艺制备的SO24-/ZrO2-TiO2固体酸为催化剂,在n(醇)/n(油)=20,m(催化剂)/m(油)=0.03,反应温度423 K,反应时间5 h,搅拌速率370 r/min的条件下,蓖麻油平均转化率可达98.5%。采用Hammett指示剂法、XRD、SEM技术对正交试验条件下制得的SO24-/ZrO2-TiO2固体酸进行了表征。结果表明:其酸强度(H0)在0.8～6.8之间,催化剂活性随总酸量增加而增大;该固体酸催化剂骨架结构为TiO2锐钛矿型晶体且呈不规则微米块状结构。

SO4^2-/ZrO2-TiO2 solid acid catalyst was prepared by high temperature calcination, with ZrOC12 · 8HzO and Ti （SO4 ）2 as raw materials, concentrated ammonia solution as precipitation agent, and dilute sulfuric acid as impregnation agent. Effects of various factors during catalyst preparation process on the catalytic activity were investigated through orthogonal experiment. The optimal preparation conditions of the solid acid catalyst were obtained as follows：calcination temperature 723 K, calcination time 4 h, molar ratio of Ti to Zr 6：1 and impregnation solution concentration 1.50 mol/L. With the SO4^2-/ZrO2-TiO2 solid acid prepared under the optimal conditions being used as catalyst to converte castor seed oil to methyl esters, and under the conditions of molar ratio of methanol to oil 20： 1, mass ratio of catalyst to oil 0. 03： 1, reaction temperature 423 K, reaction time 5 h and stirring rate 370 r/min, the average conversion rate of castor seed oil could reach 98.5%. The SO4^2-/ZrO2-TiO2 solid acid was characterized by tech- niques of Hammett indicator method, XRD and SEM. The results showed that the acid strength （H0 ）was in the range of 0.8 - 6.8, the catalyst activity inc- reased with total acid amount increasing, and the skeleton structure of the solid acid catalyst was Ti02 anatase crystal with irregular micron bulk st- ructuFe.