Method and apparatus for carrying out exothermic gas phase reactions

With a method for operating a tube bundle reactor for exothermic gas phase reactions having a tube bundle with catalyst-filled reaction tubes ( 2 ), wherein the one ends of the reaction tubes are spanned by a gas inlet hood and the other ends are spanned by a gas outlet hood and wherein around the outside of the reaction tubes a heat transfer medium flows to carry off reaction heat. An explosive gas mixture (G) is introduced into the reaction tubes ( 2 ) via the gas inlet hood and after reaction the gas mixture (G), that may still be explosive, it is led off from the reaction tubes via the gas outlet hood. A limit temperature in the reaction tubes ( 2 ) is specified that lies above the normal operating temperatures in the reaction tubes ( 2 ) but at most equals the ignition temperature of the explosive gas mixture (G) Each non-operating high temperature region ( 7 ) forming in the reaction tubes ( 2 ) whose temperature is at least equal to the limit temperature and which migrates in the respective reaction tube ( 2 ) in the longitudinal direction thereof is stopped while still in the reaction tube ( 2 ) so that the high temperature region ( 7 ) is prevented from advancing into the gas inlet hood or the gas outlet hood.