Effect of liquid viscosity on liquid film mass transfer for packings
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The effect of liquid viscosity (μL) on liquid film mass transfer for packings was investigated in a pilot-scale column with 0.43 m (16.8 in) ID and 3 m (10 ft) maximum packing. Mass transfer area (ae) of three structured packings, one random packing, and one hybrid packings was measured by chemical absorption of CO2 into dilute (~ 0.1 mol/L) NaOH. Liquid film mass transfer coefficient (kL) of eight structured packings, one random packing, and one hybrid packing was measured by air stripping toluene from water. Liquid viscosity was varied 0.8-70 mPa·s by adding 0-89 wt % glycerol to water in one ae and nine kL experiments. In the experiments, the liquid load was varied 6-75 m3/m2·hr (2.5-30 gpm/ft2), and the gas rates were 0.6, 1, and 1.5 m/s (180, 300, and 450 ACFM). The models of ae,packing and kL were developed based on data for 39 packings from this work and the SRP air-water column database. The model of the gas film mass transfer coefficient, kG, was developed based on data for 20 packings in the SRP air-water database. The secondary (wall and end) effect of ae was corrected in the area model. A taller packing bed consistently gave smaller kL due to maldistribution. Liquid viscosity does not have a significant effect on ae. The kL depends on μL to the -0.75 power, in which the -0.4 is the direct influence on the liquid turbulence, and -0.35 is the indirect effect via diffusivity of the mass transfer species. The effect of μL on kL is the same for different packing geometry and types. To prepare for the pilot-scale area experiment with glycerol, reaction kinetic model of CO2 and hydroxide in aqueous glycerol was developed based on the wetted-wall column (WWC) experiments.