A method for carrying out endothermic or exothermic gas phase reactions by
using a tube bundle reactor with a tube bundle of catalyst-filled
reaction tubes comprises the following steps: a) Introducing a reaction
gas mixture into the reaction tubes; b) Dividing-up of the reaction gas
mixture flow flowing through each of the reaction tubes into at least two
partial flows, each partial flow having the same composition; c)
Feeding-in of each partial flow at a different point along the catalyst
filling with an existing flow resistance; d) Determining the desired
partial flow volume for each partial flow (V.sub.1, V.sub.2, V.sub.3,
V.sub.4); e) Calculating the pressure at the point of the first division
of the reaction gas mixture (9); f) Calculating the pressure in the
catalyst filling (12) at the point of feeding-in of each partial flow
(V.sub.1, V.sub.2, V.sub.3, V.sub.4); and g) Setting of flow resistance
for each point of feeding-in in such a way that the flow resistance at
the desired partial flow volume corresponds to the pressure difference
between the pressures determined in steps e) and f).