Process and reactor for carrying out non-adiabatic catalytic reactions

Process for carrying out non-adiabatic reactions comprising the steps of: introducing in parallel a first stream of reactants into a first reaction space and a second stream of reactants into a second reaction space; at reaction conditions contacting the first reactant stream with a catalyst in the first reaction space in indirect heat exchange with a heat exchanging medium and contacting the second reactant stream with a catalyst in the second reaction space in indirect heat exchange with a heat ex- changing medium, and withdrawing a first and second steam reformed product gas; and the catalyst in the first reaction space being arranged within a tubular reactor in indirect heat exchanging rela- tionship with the heat exchanging medium by introducing the medium into tubular heat exchange space concentrically sur- rounding the tubular reactor with the first reaction space, the catalyst in the second reaction space being arranged on shell side of a heat exchange space in indirect heat ex- changing relationship with the heat exchanging medium.