Mass transfer in a reciprocating plate extraction column - effects of mass transfer direction and plate material

The mass transfer performance of 5 cm diameter reciprocating plate column has been measured with the system n-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. Hax was lower than for d c mass transfer under the same external conditions. Qualitative and quantitative observations indicated much larger drop sizes in the d c case due to enhanced coalescence. Although mass transfer was less effective under d c conditions, 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 dispersed phase. On a mesure la performance au transfert de masse d'une colonne de 5 cm de diametre a plateaux alternants pour le systeme acide butyrique normal/kerosene (disperse)/eau (phase continue). Dans la plupart des essais, les plateaux alternants etaient faits d'acier inoxydable, qui est mouille de facon preferentielle par la phase continue. On a mesure, durant le procede de transfert de masse, la retention et, dans certains cas, le diamktre moyen de Sauter des gouttelettes. L'efficacite du transfert de masse, exprimee par la hauteur d'unite de transfert (Hox) corrigee pour le melange axial, depend des debits des phases, de la vitesse d'agitation et de la direction du transfert de masse. Dans le cas du transfert de masse a la phase continue a la phase dispersee ( cd), le transfert de rnasse s'est avere plus efficace, c'est-&hdire que Hox etait plus faible que dans le cas du transfert de masse de la phase dispersee & la phase continue (d c) dans les memes conditions externes. Des observations qualitatives et quantitatives ont indique la presence de gouttes de plus grandes dimensions dans le cas d c, par suite d'une augmentation de la coalescence. Bien que le transfert de masse ait ete moins efficace dans les conditions d c, la capacitC de la colonne s'est accrue. On a aussi observe les memes effets lorsqu'on a modifii le materiau des plateaux en y introduisant quelques plateaux de Teflon qui sont mouillks partiellernent par la phase dispersee.