Limonene Epoxidation: Diffusion and Reaction over PW-Amberlite in a Triphasic System

The effect of several reaction parameters on limonene epoxidation and hydrogen peroxide decomposition over PW-Amberlite was studied. Parameters evaluated were as follows: amount of catalyst (8-28 g/L), average particle diameter (110-720 (mu)m), and concentrations of acetonitrile (7.4-15.7 mol/L), limonene (0.27-1.04 mol/L), hydrogen peroxide (0.73-1.92 mol/L), water (5.84-7.39 mol/L), and limonene epoxide (0-0.17 mol/L). The initial limonene reaction rate exhibits a maximum at 71 wt % acetonitrile (18 wt % hydrogen peroxide), 6.5 times higher than that obtained under biphasic conditions. According to Weisz-Prater criterion, mass transfer limitations were insignificant for catalyst particle sizes smaller than 425 (mu)m. External mass transfer limitations were avoided by using a stirring speed of 1000 rpm. The apparent activation energy of limonene epoxidation was 25 kJ/mol, three times lower than that previously found in a biphasic system. Empirical reaction rates of limonene epoxidation and hydrogen peroxide decomposition are proposed.