Catalytic isomerization of α-pinene and 3-carene in the presence of modified layered aluminosilicates

The catalytic properties of acid-modified montmorillonite, kaolinite (Mongolia) and illite (Belarus) clays, as well as a commercial aluminosilicate catalyst AS-36 were studied in the liquid-phase isomerization of α-pinene and 3-carene. The largest conversion of α-pinene (100% after 6 h) was observed in the presence of illite clay treated with 10% HCl at 90 °C. The presence of only weak and medium acidic sites in the clays resulted in the formation of camphene (50.1–54.3%) as the main reaction product. Conversion of 3-carene increases with an increase of the total catalyst acidity. The reaction products were 2-carene (11.9–15.0%), mentadienes (35.5–48.5%), menthenes (7.9–17.1%) and cymenes (10,1–20.4%). The amount of mentadienes in the reaction mixture decreased while the opposite was observed for menthenes and cymenes with increase of concentration and strength of the acid sites. The kinetic model for 3-carene transformations was developed.