A process is provided which can effectively inhibit occurrence of hot spots
in reaction zones or heat accumulation at the hot spots, in the occasion
of producing acrolein and acrylic acid through vapor phase oxidation of
propylene in the presence of a catalyst using a fixed bed shell-and-tube
reactor, said catalyst having a composition represented by a general
formula (1):
Mo.sub.a W.sub.b Bi.sub.c Fe.sub.d A.sub.e B.sub.f C.sub.g D.sub.h E.sub.i
O.sub.x
(wherein A is at least an element selected from Co and Ni; B is at least an
element selected from P, Te, As, B, Sb, Sn, Ce, Nb, Pb, Cr, Mn and Zn; C
is alkali metal element; D is alkaline earth metal element; E is at least
an element selected from Si, Al, Ti and Zr; and O is oxygen; a, b, c, d,
e, f, g, h, i and x denote the atomic numbers of Mo, W, Bi, Fe, A, B, C,
D, E and O, respectively, and where a is 12, b is 0-5, c is 0.1-10, d is
0.1-10, e is 1-20, fis 0-5, g is 0.001-3, h is 0-3, i is 0-30, and x is a
numerical value which is determined depending on the extent of oxidation
of each of the elements).
Said process is characterized by preparing plural kinds of catalysts having
the above composition but differing from each other in (.alpha.) occupying
volume, (.beta.) calcining temperature and/or (.gamma.) kind and/or amount
of alkali metal element, and filling the reaction zones provided by
dividing the catalyst layer in each of the reaction tubes in the reactor
into at least two layers in the axial direction of the tube, sequentially
with said plural kinds of catalysts in such a manner that the catalytic
activity increases from the starting gas inlet side toward the outlet
side.
