Previous work on vortex ring-induced extraction in a batch cell has fo
rmed the basis for design of a continuous multistage extractor. The un
it consists of a 3.0 m long rectangular tank divided into five compart
ments by four pneumatically driven reciprocating plate modules. The re
ciprocating plates generate a series of vortex rings which pump the li
quid phases countercurrently and provide interfacial contact. Baffles
in each module prevent backflow between the compartments. Stage effici
encies have been measured for the extraction of benzoic acid from kero
sene to water.