Catalytic hydrolysis of hydrophobic esters on/in water by high-silica large pore zeolites

- High silica Hβ zeolite is an effective and reusable catalyst for hydrolysis of water-insoluble esters.
- It shows higher catalytic efficiency per catalyst weight than H2SO4.
- The high efficiency is due to preferential interaction of the hydrophobic zeolite pore with hydrophobic esters over polar molecules and transfer of the carboxylic acids to the oil phase.

Hydrolysis of water-insoluble esters is an industrially important but challenging reaction, because the esters are mostly present in oil droplets on water during the reaction. On the basis of the screening results for hydrolysis of a water-insoluble ester, 3-phenylpropionate, on/in water by 25 types of heterogeneous and homogenous catalysts, we have found that Hβ zeolite with a moderate Si/Al ratio (Si/Al = 75), Hβ-75, is an effective and reusable catalyst for hydrolysis of hydrophobic esters. The hydrolysis of esters with different sizes is studied by Hβ and HZSM5 zeolites with different Si/Al ratios, and the results show the hydrophobicity, pore size and number of Brønsted acid sites are critical factors affecting the catalytic activity for this system. Kinetic and adsorption studies show that the high yields by Hβ-75 are due to preferential interaction of the hydrophobic zeolite pore with hydrophobic esters over polar molecules (carboxylic acids, water, alcohols) and transfer of the carboxylic acids to the oil droplets on water, both of which inhibit the reverse reaction (esterification of the carboxylic acids).

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