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The less steep gradient could come from greater backmixing of the liquid or from channeling (radial velocity variations). The absence of any large effect of misalignment on the concentration drop at the feed inlet suggests that channeling in lower regions is the greater effect. This corresponds to the visual observations of channeling when KMn04 solution was added. CONCLUSIONSVertical misalignment of foam and bubble fractionation columns can strongly affect their performance, even for slight departures from the true vertical. The sensitivity to misalignment is probably affected by flow rates, bubble diameters, and length-to-diameter ratio of the column. These factors were not investigated explicitly. It would appear that a number of cases of nonreproducibility of bubble-column performances can be explained by slight departures from true vertical alignment of the contactor. Deckwer et al. (1973) reported experimentally derived backmixing coefficients for bubble columns, which varied abruptly at a certain point in the column. It may be that this phenomenon is also associated with effects of slight departures of the column from the vertical.

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