采用滴定沉淀法制备了系列稀土复合固体超强酸SO2-/ZrO - ZrO2/La3+,并用FTIR和SEM等手段表征了该固体超强酸的结构.表征结果显示,SO2-在ZnO和ZrO2表面是以螯合和桥式双配位两种形式与Zn和Zr结合的,SO2-4/ZnO - ZrO2/La3+中出现了棱柱形的ZnO晶体和ZrO2四方晶体,具有超强酸性.将SO2-/ZnO - ZrO2/La3+用于以D,L-乳酸为原料合成D,L-丙交酯的反应,考察了催化剂的原料配比和催化剂用量对催化活性的影响.实验结果表明,n( Zn2+)∶n(zr4+)=2∶1的SO2-4/ZnO - ZrO2/La3+催化活性最佳；适宜的反应条件为:D,L-乳酸用量60g、催化剂用量1.0％(相对于D,L-乳酸的质量分数)、脱水真空度0.050～0.060 MPa、脱水时间2.0h、脱水温度140℃、解聚真空度0.085～0.095 MPa、解聚温度200℃、解聚终止温度245℃.在此条件下,D,L-丙交酯粗产品的收率达82.7％.%A series of rare earth composite solid super acidic catalysts SO2-4/ZnO-ZrO2/La3+ were prepared by precipitation titration and characterized by means of FTIR and SEM. The results showed that the SO2-4 ions were bound with the Zr and Zn on the ZnO and ZrO2 crystal surfaces by either chelating or bidentate bridging. Prismatic ZnO and cubic ZrO2 crystals with superacidity were observed in the SO2-4/ZnO-ZrO2/La3+. The obtained SO2-4/ZnO-ZrO2/La3+ was used in synthesis of D,L-lactide from D,L-lactic acid. The effects of n (Zn2+ ) : n(Zr4+ ) in SO2-4VZnO-ZrO2/La3+ and thecatalyst dosage on the catalyst activity in the synthesis were investigated. Under the optimal conditions of n(Zn2+ ):n(Zr4+ ) 2 : 1 in S02VZn0-Zr02/La3+, D,L-lactic acid 60 g, catalyst dosage 1. 0% (based on the D,L-lactic acid mass), vacuum degree of dehydration 0.050 -0.060 Mpa, dehydration temperature 140 ℃, dehydration time 2.0 h, vacuum degree of depolymerization 0.085 -0.095 Mpa, depolymerization temperature 200℃ and termination temperature of the depolymerization 245 ℃, the crude D,L-lactide yield could reach 82.7%.
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