Investigation of a packed bed in a mini channel with a low channel-to-particle diameter ratio: Flow regimes and mass transfer in gas–liquid operation

• Flow regimes for a gas–liquid flow in a packed bed mini reactor were identified.
• Gas–liquid–solid mass transfer coefficients of this reactor were investigated.
• Mass transfer increased with raised superficial gas or liquid velocity.
• A correlation for the estimation of mass transfer coefficients was developed.

This work analyzes flow regimes and mass transfer in a miniaturized packed bed reactor under reacting conditions. The reactor consisted of a cylindrical channel with an inner diameter of 2 mm which was filled with spherical catalyst particles having an outer diameter of 0.8 mm. The liquid phase hydrogenation of α-methylstyrene over a Pd/γ-Al2O3 catalyst was employed as reaction system. Based on experimental reaction rates, overall (gas–liquid–solid) volumetric mass transfer coefficients of hydrogen, which were between 0.5 s−1 and 6.0 s−1, were computed. Detailed discussions focus on the impact of the flow regime, the gas and liquid superficial velocities and, consequently, their ratio, as well as system pressure on overall mass transfer rates.