Esterification of lower aliphatic alcohols with acetic acid in presence of different acid catalysts

Abstract

The preparation of sulfated zirconia (SZ-H) and silica supported sulfated zirconia (SZ/silica-H) catalysts using H₂SO₄as sulfating agent has been reported. These catalysts are then evaluated and compared with other acid catalysts, viz. para- toluene sulfonic acid (PTSA), Amberlyst-15, H-ZSM5 and γ-alumina for the esterification of ethanol and <i style="mso-bidi-font-style:normal">n</i>-butanol using acetic acid. Among the solid acid catalysts, SZ/silica-H shows superior esterification activity for both the alcohols. However, during the reusability of SZ/silica-H catalyst for 5 recycles, the observed gradual decrease in esterification activity (62.26 - 43.65%) is attributed to the partial leaching (35.9% after 5 cycles) of sulfated zirconia content from the silica support. To establish the leaching of sulfated zirconia, the fresh SZ/silica-H, SZ/silica-N and SZ/silica-Cl catalysts prepared by using different sulfating agents like H₂SO₄, (NH₄)₂SO₄ and ClSO₃H respectively have been given the water wash. The analysis of water washed catalysts shows the partial leaching (50-75% of the deposited quantity) of sulfated zirconia. The water washed catalysts containing the residual or trapped fraction of sulfated zirconia in the pores of silica show negligible esterification activity. These results indicate that the active sites on silica surface responsible for esterification activity are effectively leached out in aqueous medium.