Patent ID: 7988927

Claim:
A method of varying the temperature of a tube bundle reactor for catalytic gas phase reactions upon start up and shut down, the tube bundle reactor comprising a major reactor portion which includes a bundle of vertically disposed reactor tubes, upper and lower tubesheets tightly connected to upper and lower ends, respectively, of the reactor tubes, and a reactor shell enclosing the tube bundle, a heat transfer medium having a melting temperature in the range of from 100° C. to 450° C. flowing around the outer surfaces of the reactor tubes during normal operation and being circulated in at least one circuit through the major reactor portion, the method comprising the following steps: (a) varying the heat transfer medium temperature by means of a heat exchanger during circulation of the heat transfer medium; and (b) passing a temperature gas through the reactor tubes for varying the temperature of the tube bundle reactor when the heat transfer medium is not circulated, wherein the temperature of the temperature gas, when entering the reactor tubes, is limited upwards during start up and downwards during shut down and/or the volume flow of the temperature gas is limited upwards such that, for any time period which begins with the first introduction of the temperature gas, the time average rate of change of the temperature of the temperature gas, when exiting the reactor tubes, does not exceed 30° C./hour, thereby limiting temperature differences occurring during start up or shut down such that inadmissible thermal stresses are widely avoided.