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Abstract

New experimental data presented concern effects of Marangoni surface-tension forces on the mass-transfer eficiency of packed distillation columns. Various random packings of sizes 6 and 25 mm, as well as structured packings of sizes 30 mm diameter and 150 mm, were used with the system n-propanol/water. This system can behave either as a Marangoni positive system at low concentrations of n-propanol or as a negatiue system at high concentrations of n-propanol. It was confirmed that small packings show lower eficiencies for Marangoni negative systems, due to the breakup of the film of liquid on the packing surface. In the larger column, howeuer, the situation is reversed with the negative mixtures often showing better eficiencies, especially at heauier loadings. This is attributed to the observation that spray and droplet formation are much more pronounced for the negative mixtures, providing extra surface for mass transfer and, hence, better mass-transfer eficiency. There are also some indications that the pressure drop is unexpectedly high for these conditions and that premature flooding can occur. This may haue design implications for any mass-transfer deuice in which vapor and liquid phases are contacted in narrow passageways.