Catalytic transalkylation of alkylphenol to phenol in supercritical benzene fluid over MFI type zeolite in a fixed-bed reactor: Diffusion and reaction limitations

The transalkylation reaction kinetics of 4-propylphenol (ppp) and supercritical benzene (11.0 MPa) over H-MFI-type zeolites, using different particle size and Si/Al ratios, in the temperature range of 623 K – 673 K, was studied in a fixed bed reactor. A 1st order parallel reaction kinetic model was evaluated for transalkylation of ppp and benzene, and ppp isomerization. High conversion of ppp and phenol production with low coke formation was obtained with nanometer-sized particles, transalkylation reaction proceeded under reaction control conditions. Thiele modulus was calculated to evaluate internal diffusion limitations, clearly observed when increasing the particle size (activation energies over micrometer- and nanometer- sized particles, 60.0 and 120 kJ mol−1, respectively). Nonetheless, decreasing the particle size (2.00 × 103 to 100 nm) successfully reduced the internal diffusion limitations and increased the selectivity of the reaction. The study showed that increasing Al sites in the framework not only increases the specific constant rate of the reaction, but also its selectivity, with a low impact on the effectiveness of the reaction according to the Thiele Modulus equation and the particle size obtained.