Patent ID: 6949675

Claim:
A process for producing acrylic acid, comprising the step of subjecting acrolein or an acrolein-containing gas to catalytic gas phase oxidation with molecular oxygen or a molecular-oxygen-containing gas using a fixed-bed shell-and-tube reactor having a reaction tube packed with a catalyst, with the process being characterized in that: said catalyst is an oxide and/or a compound oxide having a metal element composition shown by the following general formula (1): Mo a V b A c B d C e O f (1) (wherein: Mo is molybdenum; V is vanadium; A is at least one element selected from the group consisting of niobium and tungsten; B is at least one element selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc, and bismuth; C is at least one element selected from the group consisting of phosphorus, tin, antimony, and tellurium; and O is oxygen; and wherein a is 12, and 1≦b≦14, 0<c≦12, 0<d≦10, 0≦e≦10; and f is a numerical value determined by the oxidation state of each element); and where said reactor has at least two reaction zones by dividing the inside of said reaction tube in a direction of an axis of the tube in the fixed-bed shell-and-tube reactor, and where each of said reaction zones are packed with the catalyst in such a manner that the activity of the catalyst in a first of said reaction zones is different from the activity of a second of said reaction zones by regulating the kind and/or amount of the A component and/or the kind and/or amount of the B component in the general formula (1).