Hydrodynamics and Axial Dispersion Effects in Toluene Hydrogenation over Pt/Al₂O₃ in a Trickle-Bed Reactor

Toluene hydrogenation to methylcyclohexane over 5 wt% Pt/Al₂O₃ was studied in a laboratory trickle bed reactor (TBR) by systematically varying liquid flow rate (0.8–1.4 mL/min) and temperature (80–120°C). Residence time distribution (RTD) analysis using NaCl tracer revealed strong deviation from plug flow, with Peclet numbers Pe = 6, 7, and 9, axial dispersion coefficients Dz = 1.67–1.85 × 10⁻⁵ m²/s, and mean liquid holdup εL = 0.26 ± 0.01. Conversion increased with temperature and decreased with flow rate, with 100% selectivity to methylcyclohexane and stable catalyst performance over 50 h. A Langmuir–Hinshelwood kinetic model fitted to batch data captures the temperature-dependent shift in apparent reaction order. A one-dimensional axial dispersion model implemented in gPROMS, with hydrodynamic parameters fixed from RTD, is under experimental validation and will provide a predictive tool for TBR scale-up.