The flow and mass transfer in a discontinuous reactor configuration consisting of a pair of corotating enclosed disks with a chemical reaction taking place at the disk surfaces have been analyzed. The calculated mass-transfer efficiencies do not follow the expected Sh=Sh(Re,Sc) dependence because the overall mass-transfer process is not boundary-layer controlled, especially at high Schmidt numbers. It has been found in all of the cases investigated that despite the fact that the reactant concentration is continuously dropping with time its spatial distribution, relative to the volume-averaged value, becomes stationary after a short initial transient. This result implies that the mass-transfer efficiency in the discontinuous reactor also becomes stationary and the resulting time-independent value, Sh, obtained either directly from calculation or from the fit of the collected results, provides a fairly good estimate of the reactor operation time needed to achieve the target reactant conversion. (c) 2014 American Institute of Chemical Engineers AIChE J, 61: 1015-1031, 2015