Experimental verification of kinetics and internal diffusion impact on low temperature steam reforming of a propane-methane mixture over Ni-based catalyst

Experiments were made on three fractions (0.5–1, 2–2.5 and 3–5 mm) of a Ni/Cr₂O₃/Al₂O₃ catalyst in order to verify the kinetics and influence of internal diffusion transport on the apparent reaction rate of low-temperature steam reforming of a propane-methane mixture. Feed gas composition was: C₃H₈ = 22.6%, CH₄ = 77.4%, H₂O/C = 0.51, GHSV = 11600 h⁻¹, temperature 300–370 °C. To analyze the experimental data, a plug-flow reactor model with fixed temperature profiles was used; the profiles were obtained by interpolating the measurements of a moving thermocouple placed along the axis of the catalyst bed. The global kinetic scheme included the parallel reactions of propane steam reforming and propane hydrogenolysis. The catalyst effectiveness factor was calculated with the effective diffusion coefficient based on the Wilke formula, Thiele modulus and experimental pore size distribution. Experimental data for all catalyst fractions are described well by the proposed model at a porous catalyst tortuosity factor 1.53 and permeability coefficient 0.26.