EFFECTS OF MARANGONI SURFACE-TENSION FORCES ON MODERN DISTILLATION PACKINGS

New experimental data presented concern effects of Marangoni surface-t ension forces on the mass-transfer efficiency of packed distillation c olumns. Various random packings of sizes 6 and 25 mm, as well as struc tured 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 negative s ystem at high concentrations of n-propanol. It was confirmed that smal l packings show lower efficiencies for Marangoni negative systems, due to the breakup of the film of liquid on the packing surface. In the l arger column, however the situation is reversed with the negative mixt ures often showing better efficiencies, especially at heavier loadings . This is attributed to the observation that spray and droplet formati on are much more pronounced for the negative mixtures, providing extra surface for mass transfer and, hence, better mass-transfer efficiency . There are also some indications that the pressure drop is unexpected ly high for these conditions and that premature flooding can occur. Th is may have design implications for any mass-transfer device in which vapor and liquid phases are contacted in narrow passageways.