Synthesis of benzaldehyde glycol acetal catalyzed by co-doped TB0.5Zr0.5H0.5PW
A series of quaternary ammonium salts(benzyl triethyl ammonium chloride,tetrabutylammonium bromide and hexadecyl trimethyl ammonium bromide)and zirconium salt(ZrCl4)co-doped phosphotungstic acid catalysts were prepared by ion exchange method,characterized by SEM,FTIR,XRD,XPS,TGA-DTG,as well as n-butylamine potentiometric titration method,and evaluated on their catalytic performance for acetalization of benzaldehyde and glycol.The effects of catalyst amount(based on the mass of benzaldehyde,the same below),n(ethylene glycol)∶n(benzaldehyde),water carrying agent(cyclohexane)amount and reaction time on the yield of benzaldehyde glycol acetal(BEGA)were investigated through single factor and response surface experiments,the reusability of the catalyst was also explored.The results showed that the phosphotungstic acid catalyst TB0.5Zr0.5H0.5PW co-doped with tetrabutylammonium bromide(TB)and ZrCl4 exhibited the best catalytic performance,with its high catalytic activity attributed to the fact that the strong synergistic effect between Brønsted and Lewis acid centers,and"pseudo liquid phase"characteristics.Under the catalysis of TB0.5Zr0.5H0.5PW,the yield of BEGA could reach 94.6%under the optimized conditions via response surface experiments with n(glycol)∶n(benzaldehyde)of 1.5∶1,catalyst amount of 1.9%,reaction temperature of 110℃,reaction time of 3 h,and cyclohexane amount of 12.6 mL.The yield of BEGA was maintained at 91.9%with TB0.5Zr0.5H0.5PW recycled 6 times.
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