Patent ID: 7045657

Claim:
A production process for an unsaturated aldehyde and/or an unsaturated carboxylic acid, which comprises the step of carrying out catalytic gas phase oxidation of at least one compound selected from the group consisting of propylene, isobutylene, t-butyl alcohol, and methyl t-butyl ether as a raw material with molecular oxygen or a molecular-oxygen-containing gas by using a fixed-bed multitubular reactor which is packed with catalysts, thereby producing the unsaturated aldehyde and/or the unsaturated carboxylic acid which correspond to the raw material; wherein: the catalysts include, as catalytic components, an oxide and/or a complex oxide including molybdenum, bismuth, and iron as essential components, and are particulate catalysts that have a hole; a catalyst-packed layer of each reaction tube of the fixedbed multitubular reactor is divided into at least two reaction zones in a tubular axial direction, wherein the packing of the catalysts is such that the diameters of the holes of the catalysts differ between at least two of the reaction zones; and wherein the catalyst-packed layer of each reaction tube is provided with three reaction zones consisting of a first reaction zone, a second reaction zone and a third reaction zone in order from the gas-inlet side, wherein: the diameter of the hole of the catalyst in the second reaction zone is smaller than that in the first reaction zone; and the outer diameter of the catalyst in the third reaction zone is smaller than that in the second reaction zone.