Abstract: Vapor phase catalytic oxidation of propylene into acrolein in the first step and then into acrylic acid in the second step has been improved (1) by utilizing as a diluent for the oxidation in the first step the effluent gas from the second step after the acrylic acid produced has been recovered therefrom and after it has been catalytically combusted and (2) by specifying operation conditions set in view of the recycle of the combusted "waste" gas.The improved process, embodying the present invention, has made it possible to produce a high concentration of acrylic acid as both gas and condensation and also to prolong the catalytic activity of a Mo-Bi composite oxide catalyst used for the first oxidation reaction.

Abstract: Propylene in admixture with molecular oxygen and steam is subjected to a two-step, vapor-phase, catalytic oxidation to convert into acrolein and then into acrylic acid. At least the first-step reaction is conducted in tubes of an apparatus of a shell-and-tube heat-exchanger type structure, and the reaction product of the first-step reaction is quenched before it is subjected to the second-step reaction. Reaction conditions in both the steps are specified.

Abstract: Acrolein and acrylic acid are produced by vapor-phase catalytic oxidation of propylene in a multi-tubular, fixed-bed reaction vessel with the use of a composite oxide catalyst represented by the formula Mo.sub.a Bi.sub.b Fe.sub.c A.sub.d B.sub.e C.sub.f D.sub.g Si.sub.h O.sub.x, wherein A, B, C, and D represent components selectable from respective groups of elements, and the subscripts a through h and x are specific numbers of atoms of respective elements and groups of elements. This catalyst is adapted and packed in each reaction tube in a manner such that its activity is controlled to increase from the inlet toward the outlet of the tube.

Abstract: In the production of a Mo-Bi-Na composite oxide catalyst by the process comprising incorporating compounds as respective element sources into a composite and subjecting the composite to heating treatment in an aqueous system, bismuth oxide and/or bismuth subcarbonate are/is used as a Bi source copmpound and at least a part of the heat treatment is conducted at a temperature of 450.degree. to 600.degree. C. The activity of the catalyst is significantly improved by introducing Bi in the form of the specified water insoluble compound into the catalyst.

Abstract: In the production of a Mo-Bi-Na composite oxide catalyst by the process comprising incorporating compounds as respective element sources into a composite and subjecting the composite to heat treatment, a bismuth subcarbonate in which at least a part of required Na has been solid-dissolved is used as a Bi source compound. The activity of the catalyst is significantly improved by introducing Bi and Na in the form of the specified water insoluble compound into the catalyst.

Abstract: A process for regenerating a Mo.Bi-based multi-oxide catalyst the catalytic performance of which has deteriorated as a result of its use in vapor-phase catalytic oxidation of propylene or isobutene to prepare acrolein or methacrolein, respectively, which process comprises: heating the deteriorated Mo.Bi-based multi-oxide catalyst in an atmosphere consisting essentially of air at a temperature of 380.degree. C. to 540.degree. C., so as to attain at least partial restoration of the catalytic performance thereof.

Abstract: A method for producing an alkenylbenzene by catalytically dehydrogenating an alkylbenzene non-oxidatively in the presence of steam in the reaction zone comprising a fixed-bed of potassium-containing dehydrogenation catalyst particles, wherein the potassium-containing dehydrogenation catalyst particles are prevented from powdering by (a) using a fixed-bed comprising particles of at least two kinds of potassium-containing dehydrogenation catalyst with respectively different potassium contents and (b) arranging the catalyst particles so that those with higher potassium content are not disposed on the inlet side of said catalyst bed with respect to the reaction.

Abstract: In the production of acrylic acid by a two-stage, vapor-phase catalytic oxidation of propylene, a composite oxide catalyst expressed by the formula Mo.sub.a Bi.sub.b Ni.sub.c Co.sub.d Fe.sub.e Na.sub.f Mn.sub.g B.sub.h K.sub.i Si.sub.j O.sub.x is used in the first-stage reaction, which is carried out under specific reaction and operational conditions, and the second-stage reaction is carried under specific reaction and operational conditions while oxygen is supplied by a specific mode.

Abstract: In the production of a composite oxide catalyst containing at least Mo tegether with V and (or) Nb, the catalyst precursor is subjected to a thermal decomposition step in which: (1) the precursor is heated in a heat-exchanger type apparatus in which a first space accommodating the precursor and a second space through which a heating fluid flows are partitioned and separated from each other, the heating of the precursor being accomplished through the partitioning; (2) the thermal decomposition is carried out as an atmosphere gas of an oxygen concentration of 0.05 to 5 percent is caused to flow through the first space; and (3) the maximum temperature reached in the thermal decomposition is 300.degree. to 550.degree. C.