The present invention provides a method for producing an oxide catalyst comprising Mo, V, Sb, and Nb for use in a gas-phase catalytic oxidation reaction or a gas-phase catalytic ammoxidation reaction of propane or isobutane, the method comprising: a preparation step of preparing a first aqueous mixed solution containing Mo, V, and Sb; a mixing step of mixing the first aqueous mixed solution with a support raw material comprising silica sol, and a Nb raw material to obtain a second aqueous mixed solution; a drying step of drying the second aqueous mixed solution to obtain a dry powder; and a calcination step of calcining the dry powder to obtain the oxide catalyst, wherein the support raw material comprises 25% by mass or more, based on SiO.sub.2, of the silica sol having an average primary particle size of 3.0 nm or larger and smaller than 11 nm based on a total amount of the support raw material, and the silica sol comprises 55% or more of silica sol particles having a primary particle size of smaller than 11 nm.

The present invention relates to the production of acrolein, acrylic acid or methacrylic acid by dehydration reaction of renewable raw material such as glycerin or hydroxycarboxylic acids, in the presence of a novel catalyst system supported on a carrier having a bimodal structure and a high pore volume and distribution. The dehydration reactions can be carried out for longer operation duration, so that acrolein, acrylic acid or methacrylic acid can be produced at higher productivity and for longer running time.

A method for producing a complex oxide catalyst containing a complex oxide represented by the formula:
Mo.sub.1V.sub.aSb.sub.bNb.sub.cW.sub.dZ.sub.eO.sub.n
(wherein a component Z represents an element such as La, Ce, Pr, Yb, Y, Sc, Sr, and Ba; a, b, c, d, e, and n each represent an atomic ratio of an element to one Mo atom; 0.1a0.4, 0.1b0.4, 0.01c0.3, 0d0.2, and 0e0.1; an atomic ratio a/b is 0.85a/b<1.0, and an atomic ratio a/c is 1.4<a/c<2.3.), the method including: a step of preparing a specific raw material-formulated solution containing Mo, V, Sb, Nb, W, and Z; a step of drying the raw material-formulated solution to obtain a dry powder; a step of pre-stage calcining the dry powder to obtain a pre-stage calcined product; a step of main-calcining the pre-stage calcined product to obtain a calcined product having a protrusion on the surface of the particle; and a step of removing the protrusion by an air stream, wherein the reduction rate of the pre-stage calcined product is 8 to 12%, and the specific surface area of the calcined product is 7 to 20 m.sup.2/g.

A method for producing a complex oxide catalyst containing a complex oxide represented by the formula:
Mo.sub.1V.sub.aSb.sub.bNb.sub.cW.sub.dZ.sub.eO.sub.n
(wherein a component Z represents an element such as La, Ce, Pr, Yb, Y, Sc, Sr, and Ba; a, b, c, d, e, and n each represent an atomic ratio of an element to one Mo atom; 0.1a0.4, 0.1b0.4, 0.01c0.3, 0d0.2, and 0e0.1; an atomic ratio a/b is 0.85a/b<1.0, and an atomic ratio a/c is 1.4<a/c<2.3.), the method including: a step of preparing a specific raw material-formulated solution containing Mo, V, Sb, Nb, W, and Z; a step of drying the raw material-formulated solution to obtain a dry powder; a step of pre-stage calcining the dry powder to obtain a pre-stage calcined product; a step of main-calcining the pre-stage calcined product to obtain a calcined product having a protrusion on the surface of the particle; and a step of removing the protrusion by an air stream, wherein the reduction rate of the pre-stage calcined product is 8 to 12%, and the specific surface area of the calcined product is 7 to 20 m.sup.2/g.

A method for producing a complex oxide catalyst containing a complex oxide represented by the formula:
Mo.sub.1V.sub.aSb.sub.bNb.sub.cW.sub.dZ.sub.eO.sub.n
(wherein a component Z represents an element such as La, Ce, Pr, Yb, Y, Sc, Sr, and Ba; a, b, c, d, e, and n each represent an atomic ratio of an element to one Mo atom; 0.1a0.4, 0.1b0.4, 0.01c0.3, 0d0.2, and 0e0.1; an atomic ratio a/b is 0.85a/b<1.0, and an atomic ratio a/c is 1.4<a/c<2.3.), the method including: a step of preparing a specific raw material-formulated solution containing Mo, V, Sb, Nb, W, and Z; a step of drying the raw material-formulated solution to obtain a dry powder; a step of pre-stage calcining the dry powder to obtain a pre-stage calcined product; a step of main-calcining the pre-stage calcined product to obtain a calcined product having a protrusion on the surface of the particle; and a step of removing the protrusion by an air stream, wherein the reduction rate of the pre-stage calcined product is 8 to 12%, and the specific surface area of the calcined product is 7 to 20 m.sup.2/g.

An apparatus for producing a mixed solution, comprising a mixing vessel for preparing an aqueous mixed solution containing a dicarboxylic acid and an Nb compound and a filter for the aqueous mixed solution connected to the mixing vessel via a pipe, the mixing vessel being anticorrosive and equipped with a stirring unit, a heating unit and a cooling unit for the aqueous mixed solution, wherein the aqueous mixed solution prepared in the mixing vessel is fed to the filter via the pipe and filtered in the filter under increased pressure.

An apparatus for producing a mixed solution, comprising a mixing vessel for preparing an aqueous mixed solution containing a dicarboxylic acid and an Nb compound and a filter for the aqueous mixed solution connected to the mixing vessel via a pipe, the mixing vessel being anticorrosive and equipped with a stirring unit, a heating unit and a cooling unit for the aqueous mixed solution, wherein the aqueous mixed solution prepared in the mixing vessel is fed to the filter via the pipe and filtered in the filter under increased pressure.

An apparatus for producing a mixed solution, comprising a mixing vessel for preparing an aqueous mixed solution containing a dicarboxylic acid and an Nb compound and a filter for the aqueous mixed solution connected to the mixing vessel via a pipe, the mixing vessel being anticorrosive and equipped with a stirring unit, a heating unit and a cooling unit for the aqueous mixed solution, wherein the aqueous mixed solution prepared in the mixing vessel is fed to the filter via the pipe and filtered in the filter under increased pressure.

The object is to prevent deterioration and loss of dicyanobenzene in producing dicyanobenzene by ammoxidation of xylene to thereby achieve industrial and economical advantage in producing of dicyanobenzene. The method for producing dicyanobenzene of the present invention includes: contacting a xylene-ammoxidation reaction gas containing dicyanobenzene in ammoxidation of xylene with an organic solvent so as to obtain a dicyanobenzene-absorbing solution; contacting the dicyanobenzene-absorbing solution with a basic aqueous solution containing a salt such as ammonium carbonate so as to extract a water-soluble salt formed by neutralization reaction between carboxylic acid in the dicyanobenzene-absorbing solution and a base in the basic aqueous solution into an aqueous phase; separating the mixture of the dicyanobenzene-absorbing solution and the basic aqueous solution into an organic phase and an aqueous phase; decomposing the salt such as ammonium carbonate contained in the organic phase for separation of the salt from the organic phase; and distilling the organic phase to separate low boiling point compounds contained in the organic phase from the organic phase so as to obtain dicyanobenzene.

The object is to prevent deterioration and loss of dicyanobenzene in producing dicyanobenzene by ammoxidation of xylene to thereby achieve industrial and economical advantage in producing of dicyanobenzene. The method for producing dicyanobenzene of the present invention includes: contacting a xylene-ammoxidation reaction gas containing dicyanobenzene in ammoxidation of xylene with an organic solvent so as to obtain a dicyanobenzene-absorbing solution; contacting the dicyanobenzene-absorbing solution with a basic aqueous solution containing a salt such as ammonium carbonate so as to extract a water-soluble salt formed by neutralization reaction between carboxylic acid in the dicyanobenzene-absorbing solution and a base in the basic aqueous solution into an aqueous phase; separating the mixture of the dicyanobenzene-absorbing solution and the basic aqueous solution into an organic phase and an aqueous phase; decomposing the salt such as ammonium carbonate contained in the organic phase for separation of the salt from the organic phase; and distilling the organic phase to separate low boiling point compounds contained in the organic phase from the organic phase so as to obtain dicyanobenzene.