Abstract: Multitube reactor for carrying out a process for catalytic conversion, comprising a normally substantially vertically extending vessel, a plurality of open-ended reactor tubes (2) arranged in the vessel parallel to its central longitudinal axis of which the upper ends are fixed to an upper tube plate (5) and in fluid communication with a fluid inlet chamber (8) above the upper tube plate (5) and of which the lower ends are fixed to a lower tube plate and in fluid communication with an effluent collecting chamber below the lower tube plate, an inlet (13) for supplying liquid to the fluid inlet chamber (8), inlet for supplying gas to the fluid inlet chamber (8), and an effluent outlet arranged in the effluent collecting chamber, wherein the upper end part of each reactor tube is provided with a cap (25) having a gas inlet opening (27), which defines a liquid inlet (28) and an outlet (30) in fluid communication with the upper end part of the reactor tube (2), and a liquid riser (33) extending between a level in