This paper presents the liquid-liquid flow behaviour and the liquid-liquid mass transfer rates for a rotor-stator spinning disc reactor, with an axial disc spacing of 1 mm, a rotor radius of 0.066 m, and rotational disc speeds up to 1600 rpm. The liquid-liquid mass transfer rate is determined from extraction experiments of benzoic acid from n-heptane to water. For the calculation of the overall mass transfer rate the dimerization and acid dissociation equilibria are taken into account. Three flow patterns are characterized. Up to 100 rpm continuous radially inwards spiralling n-heptane patterns are observed. Between 100 rpm and 300 rpm this continuous spiral changes to spiralling n-heptane droplets. Above 300 rpm fully dispersed phase flow is observed. The overall mass transfer rate increases from 0.17 m(ORG)(3) m(R)(-3) s(-1) at 100 rpm and a water flow rate of 2.5 x 10(-6) m(AQ)(3) s(-1) (water: n-heptane = 1.1:1) to 51.47 m(ORG)(3) m(R)(-3) s(-1) at 1600 rpm and a water flow rate of 12.5 x 10(-6) m(AQ)(3) s(-1) (water: n-heptane = 5.6:1). These mass transfer rates are at least 25 times higher compared to those in packed columns, and at most 15 times higher compared to mass transfer rates in state of the art microchannels. (c) 2012 Elsevier B.V. All rights reserved.