Patent ID: 8318978

Claim:
A process for producing acrylic acid by catalytic vapor-phase oxidation of acrolein or an acrolein-containing gas with molecular oxygen or a molecular oxygen-containing gas, using a fixed bed reactor which is loaded with the catalysts in such a manner that at least two layers of the reaction zones having different activity are formed in the axial direction of each of the reaction tubes, the process being characterized in that the acrolein supply rate is increased in the start-up stage of the reaction until the prescribed composition of the starting reactant gas and the flow rate of the starting reactant gas are obtained, while adjusting at least one of the reaction temperature, the composition of the starting reactant gas and the flow rate of the starting reactant gas, so as to maintain the acrolein conversion at not lower than 90 mol %, the maximum peak temperature of the catalyst layer in each reaction zone at no higher than 400° C., and the sum of each ΔT (maximum peak temperature of a catalyst layer—reaction temperature) at the catalyst layer in each of the reaction zones to be no more than 150° C., respectively.