Catalyst layer-fixed reactor

A catalyst layer-fixed reactor for an exothermic reaction which comprises a plurality of reaction tube means disposed within a shell means, a first end of said reaction tube means being in flow communication with a first gas reactant inlet means and a second end of said reaction tube means being in flow communication with a gas exit means, said shell means having cooling medium inlet means and cooling medium outlet means positioned on said shell means for delivering a cooling medium flow therein to cool the gas in said reaction tube means, inner tube means disposed individually within said reaction tube means, catalyst layers individually packed in spaces inside said reaction tube means and outside said inner tube means, a first end of said inner tube means being adjacent to said first end of said reaction tube means and being in flow communication with a second gas reactant inlet means, a second end of said inner tube means being adjacent to said second end of said reaction tube means, a gas collecting tube means being positioned so as to provide flow communication between said second end of said inner tube means and said first gas reactant inlet means, so that an exothermic reaction is carried out by allowing a feed gas to flow in the inner tube means in cocurrent flow to a gas flowing in the catalyst layers after the gas has passed the inner tube means and the collecting tube means.