Carry out of exothermic gas-phase reactions

A method for operating a tube bundle reactor for exothermic gas phase reactions, where an explosive gas mixture is fed into the tubes and a (possibly still explosive) gas mixture exits, involves: (i) providing a limit temperature (LT) in the tubes, above the maximum temperature in the hot zones of the tubes under normal conditions, but not more than the ignition temperature of the explosive gas mixture; and (ii) stopping non-operative hot zones (7), at a maximum temperature at least equal to LT and migrating longitudinally along the tube, within the tube, so that penetration of such hot zones into the inlet or outlet hood is inhibited. A method for operating a tube bundle reactor for exothermic gas phase reactions, consisting of a bundle of catalyst-filled reaction tubes (each having a hot zone), with a gas hood at one end, a gas outlet hood at the other end and heat carrier flowing around the exterior to abstract heat of reaction, where an explosive gas mixture is fed into the tubes via the inlet hood and a (possibly still explosive) gas mixture exits via the outlet hood, involves: (1) providing a limit temperature (LT) in the tubes (2), above the maximum temperature in the hot zones under normal conditions, but not more than the ignition temperature of the explosive gas mixture (G); and (2) stopping non-operative hot zones (7), at a maximum temperature at least equal to LT and migrating longitudinally along the tube, within the tube, so that penetration of such hot zones into the inlet or outlet hood is inhibited. Independent claims are included for: (A) apparatus (1, 300) for incorporation in the reactor operated as above, which is dimensioned to fit in a reaction tube (2) and creates a through-flow cross-section for obtaining the predetermined LT; (B) a reaction tube for a tube bundle reactor for exothermic gas phase reactions, including the above apparatus; and (C) a tube bundle reactor for exothermic gas phase reactions, including reaction tubes as above.