Fiber-optic temperature measurement in a catalyst material

The invention relates to a tube reactor for carrying out heterogeneous catalyzed gas phase reactions comprising a thermal tube (2), which contains a catalyst material (3) and around which a fluid heat transfer medium (5) flows on the outer face (25) during operation, the catalyst material (3) consisting of particles (4). The tube reactor also comprises a temperature-sensitive optical waveguide (9) which is surrounded by a capillary tube (8), extends into the catalyst material (3) of the thermal tube (2), has measuring points (35) having a predetermined spacing (aM) between adjacent measurement points (35) in the axial direction of the thermal tube (2), and can be connected to a source for optical signals and to an evaluation unit (31) for optical signals reflected by the optical waveguide (9). At least in an axial thermal tube portion (34) of predetermined length containing at least a part of the catalyst material (3), the optical waveguide (9) has measuring points (35) having a spacing (aM) between adjacent