Effect of contaminants on mass transfer coefficients in bubble column and airlift contactors |
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Authors: | J.M.T Vasconcelos S.C.P Orvalho R.L Mendes |
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Affiliation: | a Centro de Eng. Biologica e Quimica, Department of Chemical Engineering, Instituto Superior Técnico, Lisboa 1049-001, Portugal b Dep. Energias Renováveis, Instituto Nacional de Engenharia e Tecnologia Industrial, Edificio G, Lisboa 1649-038, Portugal |
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Abstract: | In this work, the effects of surface-active contaminants on mass transfer coefficients kLa and kL were studied in two different bubble contactors. The oxygen transfer coefficient, kL, was obtained from the volumetric oxygen transfer coefficient, kLa, since the specific interfacial area, a, could be determined from the fractional gas holdup, ε, and the average bubble diameter, d32. Water at different heights and antifoam solutions of 0.5- were used as working media, under varying gas sparging conditions, in small-scale bubble column and rectangular airlift contactors of 6.7 and capacity, respectively. Both the antifoam concentration and the bubble residence time were shown to control kLa and kL values over a span of almost 400%. A theoretical interpretation is proposed based on modelling the kinetics of single bubble contamination, followed by sudden surface transition from mobile to rigid condition, in accordance with the stagnant cap model. Model results match experimental kL data within ±30%. |
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Keywords: | Mass transfer Bubble Interface Surfactant Bubble column Airlift |
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