AbstractThe mass transfer performance of 5 cm diameter reciprocating plate column has been measured with the systemn‐butyric acid/kerosene (dispersed)/water (continuous). In most of the tests, the reciprocating plate stack was made of stainless steel which was preferentially wet by the continuous phase. During the mass transfer process the holdup and in some cases the Sauter mean droplet diameter were measured.The mass transfer effectiveness, expressed as the height of a transfer unit (Hax) corrected for axial mixing, depended on the phase flow rates, the agitation rate and the direction of mass transfer. For continuous to dispersed phase mass transfer (c → d), the mass transfer was more effective, i.e.Haxwas lower than ford → cmass transfer under the same external conditions. Qualitative and quantitative observations indicated much larger drop sizes in thed → ccase due to enhanced coalescence. Although mass transfer was less effective underd → cconditions, the column capacity was increased. The same effects were also observed when the plate stack was modified by inserting some Teflon plates which were partly wet by the disper