A standardised hydrocyclone is examined as an alternative reactor for the electrochemical processing of two-phase systems. Experimental measurements and computational predictions of residence time distributions demonstrate an appropriate hydrodynamics of the equipment. A main peak near the mean residence time was detected revealing that a fluid by-pass or dead regions are absent and the Peclet number, obtained by correlation of the experimental data, was higher than 9. Mass-transfer measurements made by using a segmented, or a grooved or a smooth cathode corroborate the good performance of the cylindrical body of the hydrocyclone. The presence of the gas phase has little influence on the residence time distribution as well as on the mass-transfer behaviour of this device. Sulphur dioxide reduction to colloidal sulphur was used as a test reaction to check the performance of the reactor. The best results were obtained at a cathodic potential of -0.5 V, against a saturated calomel electrode, where hydrogen evolution is not possible as a cathodic side reaction. Thus, a 56% current efficiency with a specific energy consumption of 20.4 kWh kg(-1) and a space time yield of 10.4 kg m(-3) h(-1) were attained under a two-phase flow of 5% SO2 in nitrogen. The sulphur particles obtained from the spigot present an average size of 6.7 mu m being those carried by the overflow stream smaller, both of them of high purity. (C) 2019 Elsevier Ltd. All rights reserved.