| Solid acid catalysts are new and eco-friendly,which are expected to replace the industrial applications of traditional liquid acids in the future because of their unique advantages.However,some solid acid catalysts exhibit poor stability and are easy to deactivate.SO42-/MxOy is a kind of common solid acids,which comes from a wide range of sources and is simple to prepare,but it has some shortcomings,such as easy loss of active components,small specific surface area and so on.In this paper,the esterification of acetic acid and ethanol was used as the evaluation experiment for the catalytic performance of novel stable solid acids SO42-/MxOy to investigate the effects of different metal oxide carriers,different active component precursors and other solid acid preparation conditions on the catalytic activity;then,the effects of silane modification and lanthanum oxide modification on the performance of SO42-/MxOy were explored;finally,the performance of SO42-/MxOy in other condensation reactions was investigated.The main conclusions are as follows.First of all,nine kinds of metal oxides such as Al2O3 and ZrO2 were used as single oxide carrier or mixed oxide carrier to prepare solid acids.Cr2O3-Fe2O3 mixed metal oxide carrier with better catalytic effect was selected,and the better active component precursor was S2O82-,and the solid acid named S2-CrFe was finally obtained.Several solid acids were characterized by XRD,N2 adsorption-desorption isotherm,FTIR and NH3-TPD.The results showed that the mixing of the two metal oxides had no effect on the crystal phase structure,but had an effect on the surface area and acidity.The conditions for the preparation of solid acids were optimized,and the results were as follows:the mass ratio of CrO3 to Fe2O3 was 1:1,the concentration of ammonium persulfate impregnation solution was 1 mol/L,and the calcination temperature of solid acid was 550℃.Under these conditions,the yield of the esterification product was 91.2%.The stability of S2-CrFe was investigated and it was found that its catalytic activity decreased seriously after four cycles.Secondly,silane and lanthanum were used to modify S2-CrFe.In the experiment,S2-CrFe was impregnated in different volume fraction of TMCS cyclohexane solution,and the results showed that S2-CrFe modified with 15 V%TMCS had good catalytic activity and stability;then,S2-CrFe was doped with different mass fraction of lanthanum oxide,and the results showed that S2-CrFe modified with 3 wt%La2O3 had good catalytic activity and stability.XRD results revealed that silane or lanthanum oxide modification had no effect on the structure of S2-CrFe;FTIR and NH3-TPD results revealed that La could enhance the acidity of solid acids;CA results revealed that silane and La were able to increase the contact angle between S2-CrFe surface and pure water,that is,to enhance hydrophobicity,but the modification effect of La is not as good as silane.After four times of reuse,S2-CrFe-Si-15 and S2-CrFe-La-3 still had good catalytic performance,and the yield of ethyl acetate was higher than 60%.Finally,S2-CrFe,S2-CrFe-Si-15 and S2-CrFe-La-3 solid acids were applied to other condensation reactions.The reaction conditions for the synthesis of butyl acetate were optimized by orthogonal design method.Under the optimized conditions,the yield of butyl acetate was 78.8%by using S2-CrFe.The stability experimental results showed that the new solid acid performed relatively good stability in the reaction.The reaction conditions for the synthesis of ketal were optimized by single factor method.Under the optimized conditions,the yield of EMD was 60.2%catalyzed by S2-CrFe.After four times of reuse,the performance of S2-CrFe decreased,while S2-CrFe-Si-15 and S2-CrFe-La-3 generally maintained the same catalytic effect as fresh solid acids. |
PDF Full Text Request