Hydrodynamics and mass transfer in a tubular reactor containing foam packings for intensification of G-L-S catalytic reactions in co-current up-flow configuration

Abstract

Stainless steel open-cell solid foams of various linear pore densities (20, 40, 60PPI) are wash-coated with a commercial catalyst and are evaluated as internals for G-L-S reactions in co-current up-flow configuration. Hydrodynamics parameters such as liquid mean residence time, axial dispersion and pressure drop have been determined for an air/water system with superficial velocities between 0.8mm/s and 25mm/s for liquid and between 100 and 900mm/s for gas. A generic piston-dispersion model represents well the liquid hydrodynamics and is used to estimate axial Péclet number and mean residence time for this phase. The Péclet number appears to increase with liquid velocity and foam linear pore density (5<Pe<60 for 20PPI, 10<Pe<140 for 40PPI and 60<Pe<200 for 60PPI). Determined liquid holdups (0.4<ɛL<0.8) are always higher than those encountered in conventional up-flow fixed beds under comparable flow conditions. Liquid superficial velocity and foam linear pore density appear to be the most influent parameters while the gas superficial velocity possesses a less pronounced impact. Pressure drop measurements may indicate the existence of two different flow regimes (bubbly and pulsed regime) and globally the total pressure drop remains low in the experimental domain tested with a maximum value of 0.2bar/m, comparable to literature data. The overall external mass transfer efficiency was determined through the gas/liquid/solid catalytic reaction of α-methylstyrene (AMS) hydrogenation and is compared to theoretical values obtained through correlations for conventional up-flow fixed beds. Very high mass transfer coefficients, in the range of 0.2–0.9s−1 were obtained at low Re numbers, which is one order of magnitude higher than in up-flow fixed beds. A set of correlations is derived for the calculation of the gas/liquid and liquid/solid contributions to external mass transfer and allows explaining the unique bell-shaped Re dependence displayed by the overall mass transfer coefficient.