Esterification of citric acid with n-butanol over zirconium sulfate supported on molecular sieves

• TBC was produced by ZS catalyzed esterification of citric acid with n-butanol.
• 40 wt.% of ZS/HMS obtained 93% of citric acid conversion and 92% of TBC yield.
• ZS active species highly dispersed as monolayer on surface of HMS or MCM-41.
• ZS/HMS possessed Brønsted and Brønsted + Lewis acid sites for esterification.
• ZS catalyzed esterification obeyed Eley–Rideal mechanism.

Solid acid catalysts consisting of zirconium sulfate (ZS) supported on a series of molecular sieves including HZSM-5, HMS and MCM-41 were prepared and used in the esterification of citric acid with n-butanol to produce tributyl citrate (TBC). Highly dispersed ZS was supported on 40 wt.% ZS/HMS or ZS/MCM-41, whereas HZSM-5 loaded more bulk ZS species. The ZS loading and type of support showed obvious effect on thermal stability, acidity and type of acid sites. In the esterification of citric acid, 40 wt.% ZS/HMS or ZS/MCM-41 exhibited higher catalytic activity than pure ZS or 40 wt.% ZS/HZSM-5. An investigation focused on ZS/HMS showed that Brønsted and Brønsted + Lewis acid sites acted as the active center for the esterification reaction. 40 wt.% ZS/HMS calcined at 180 °C obtained the highest conversion of citric acid and TBC yield. The reaction was found to obey an Eley–Rideal mechanism.

40 wt.% zirconium sulfate supported on HMS was found to be an efficient catalyst for esterification of citric acid with n-butanol.Figure optionsDownload high-quality image (92 K)Download as PowerPoint slide