Liquid-phase mass transfer coefficient and gas holdup in a packed-bed cocurrent up-flow column.

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Packed-bed cocurrent up-flow reactors gave better results than conventional trickling flow reactors in hydrodesulfurization of heavy oil. To find the characteristics of this up-flow type reactor, liquid-phase mass transfer coefficient, gas-liquid interfacial area and gas holdup in a column packed with 0.1, 0.28 or 0.43 cm glass beads were studied using the oxidation reaction of sodium sulfite. Experiments were carried out at a reaction temperature of 20°C. Superficial liquid and gas velocities based on empty column, ul and ug, were 1-6 and 0.5-6cm/sec, respectively, for any size of glass beads. With the values of ul and ug, glass beads bed remained stationary, expanded or fluidized. Stagnant gas holdup was observed under the condition of ul<ulmf (minimum fluidization liquid velocity). It was found that the stagnant gas holdup was almost ineffective on mass transfer. Volumetric mass transfer coefficient, kLa, and gas-liquid interfacial area, ", were well correlated with dynamic gas holdup, εgd, which was a difference between total and stagnant gas holdups. When ul< uimf, the correlation was represented in a simple equation of kLa=fpεgd (fp: constant depending on particle size, dp). kLa was found to be mainly affected by gas-liquid interfacial area. Larger packing particles gave larger values of kLa. They were larger than those in bubble columns when dp≥0.28 cm and smaller when dp=0.1cm.
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