A reactor including a rotatable disc (3) having a surface (5) onto which reactant (15) is supplied by way of a feed (4). The disc (3) is rotated at high speed, and the reactant (15) spills over the surface (5) so as to form a film (17). The surface (5) is provided with features to enhance its surface area, such as a metal mesh (60), thereby helping to increase the residence time of the reactant (15) on the surface (5) and to help mixing.