Disproportionation of isopropylnaphthalene on zeolite catalysts

Disproportionation of isopropylnaphthalene (IPN) was tested over H-mordenite, HY, H-beta zeolites and over amorphous aluminosilicate in the range of 150–300 °C. High β,β-selectivity in diisopropylnaphthalene (DIPN) product obtained over zeolites was observed. However, the 2,6-DIPN/2,7-DIPN mole ratio was dependent on the pore structure of the applied zeolite and on the temperature. Over H-mordenites 2,6-DIPN was the most preferred isomer, whereas 2,7-DIPN was favored over HY and H-beta zeolites. Such disproportion in isomer predominating in the DIPN product can be explained by a bimolecular mechanism of disproportionation. Due to the zeolite pore architecture the bent transition-state complex, leading to 2,7-DIPN (HY and H-beta) or more linear, leading to 2,6-DIPN (H-mordenite), was preferred. At high temperatures the monomolecular disproportionation mechanism (dealkylation realkylation) dominated and concealed (simultaneously with side reactions) the shape-selectivity effect. As a result the 2,6-DIPN/2,7-DIPN mole ratio in the product approached equilibrium value.