Acetalization of Heptanal over Al-SBA-1 molecular sieve

Al-SBA-1 (Si/Al = 40, 80 and 120) and Al,Mg-SBA-1 (Si/(Al + Mg) = 40 and 80) molecular sieves were synthesized and characterized. Acetalization of n-heptanal with methanol was studied under autogenous pressure between 80 and 150 °C. Since protonation of n-heptanal was fast, addition of methanol to the same formed hemiacetal slowly whereas conversion of hemiacetal to acetal was fast. The catalysts exhibited nearly similar conversion irrespective of their difference in acidity, and all of them showed more than 80% conversion either at 80 or 100 °C. Hence, it is evident that the difference in acidity is not so important in differentiating the activity of the catalysts. The large pore size and hydrophilic and hydrophobic properties are suggested to be the main factors that control acetalization.

Graphical AbstractAcetalization of n-heptanal with methanol was studied under autogenous pressures between 80 and 150°C over Al-SBA-1and Al,Mg-SBA-1. The catalysts exhibited nearly similar conversion irrespective of their difference in acidity.Figure optionsDownload as PowerPoint slideResearch Highlights
► Acetalization mainly controlled by hydrophilic-hydrophobic property of the catalyst.
► Conversion of n-heptanal takes place irrespective of Si/Al and Si/(Al + Mg) ratios.
► Diffusion problem greatly reduced by the mesoporous nature of catalyst.