The present invention clarifies the characteristic of the hygroscopicity of the catalyst for producing acrylic acid and finds out a relationship between the water amount of the catalyst and the catalytic performance as the catalyst for producing acrylic acid, and provides an excellent catalyst. Provided is a catalyst for producing acrylic acid, which contains molybdenum and vanadium as essential active components, in which the amount of water contained in the catalyst is 0.01 mass % or more and 0.53 mass % or less.

The present invention clarifies the characteristic of the hygroscopicity of the catalyst for producing acrylic acid and finds out a relationship between the water amount of the catalyst and the catalytic performance as the catalyst for producing acrylic acid, and provides an excellent catalyst. Provided is a catalyst for producing acrylic acid, which contains molybdenum and vanadium as essential active components, in which the amount of water contained in the catalyst is 0.01 mass % or more and 0.53 mass % or less.

The present invention provides a method for producing an oxide catalyst containing antimony, comprising

a step (A) of obtaining the oxide catalyst using antimony particles containing a diantimony trioxide as a source of the antimony,

wherein an abundance of a pentavalent antimony in a surface layer of the antimony particle to be measured in XPS analysis is less than 70 atom %, and

the antimony particle has an average particle size of 1.2 m or less.

The present invention provides a method for producing an oxide catalyst containing antimony, comprising

a step (A) of obtaining the oxide catalyst using antimony particles containing a diantimony trioxide as a source of the antimony,

wherein an abundance of a pentavalent antimony in a surface layer of the antimony particle to be measured in XPS analysis is less than 70 atom %, and

the antimony particle has an average particle size of 1.2 m or less.

A method may load granules into reaction tubes of a vertical multitube reactor installed vertically by dropping the granules from above each of the reaction tubes whereby a linear member is inserted and suspended in the reaction tube. The reaction tube has an effective length of ?1000 mm. The linear member includes a small-diameter portion positioned on an upper side and large-diameter portion continuously extending from the small-diameter portion. The small-diameter portion has an outer diameter (Ra) of ?5.0 mm, and the large-diameter portion has an outer diameter (Rb) of 5.0 to 15.0 mm larger than Ra. A length of the small-diameter portion from reaction tube's upper end is 10.0 mm or more. A distance between an upper surface of a granule loaded layer formed inside the reaction tube and a lower end of the linear member inserted in the reaction tube is ?100 mm.

A method may load granules into reaction tubes of a vertical multitube reactor installed vertically by dropping the granules from above each of the reaction tubes whereby a linear member is inserted and suspended in the reaction tube. The reaction tube has an effective length of ?1000 mm. The linear member includes a small-diameter portion positioned on an upper side and large-diameter portion continuously extending from the small-diameter portion. The small-diameter portion has an outer diameter (Ra) of ?5.0 mm, and the large-diameter portion has an outer diameter (Rb) of 5.0 to 15.0 mm larger than Ra. A length of the small-diameter portion from reaction tube's upper end is 10.0 mm or more. A distance between an upper surface of a granule loaded layer formed inside the reaction tube and a lower end of the linear member inserted in the reaction tube is ?100 mm.

A method for producing an oxide catalyst according to the present invention is a method for producing an oxide catalyst containing Mo, V, Sb, and Nb, the method including: a raw material preparation step of obtaining an aqueous mixed liquid containing Mo, V, Sb, and Nb; an aging step of subjecting the aqueous mixed liquid to aging at more than 30 C.; a drying step of drying the aqueous mixed liquid, thereby obtaining a dried powder; and a calcination step of calcining the dried powder, thereby obtaining the oxide catalyst, wherein, in the raw material preparation step and/or the aging step, precipitation of Nb is facilitated by performing at least one operation selected from the group consisting of the following (I) to (III): (I) in the raw material preparation step, the aqueous mixed liquid is prepared by mixing a Nb raw material liquid containing Nb with a MoVSb raw material liquid containing Mo, V, and Sb, wherein ammonia is added to at least one of the MoVSb raw material liquid, the Nb raw material liquid, and the aqueous mixed liquid such that a molar ratio in terms of NH.sub.3/Nb in the aqueous mixed liquid is adjusted to be 0.7 or more, and in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 50 C.; (II) in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 65 C.; and (III) in the raw material preparation step, the aqueous mixed liquid is prepared by mixing a Nb raw material liquid containing Nb with a MoVSb raw material liquid containing Mo, V, and Sb, wherein a molar ratio in terms of H.sub.2O.sub.2/Nb in the Nb raw material liquid is adjusted to less than 0.2, and in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 50 C.

A method for producing an oxide catalyst according to the present invention is a method for producing an oxide catalyst containing Mo, V, Sb, and Nb, the method including: a raw material preparation step of obtaining an aqueous mixed liquid containing Mo, V, Sb, and Nb; an aging step of subjecting the aqueous mixed liquid to aging at more than 30 C.; a drying step of drying the aqueous mixed liquid, thereby obtaining a dried powder; and a calcination step of calcining the dried powder, thereby obtaining the oxide catalyst, wherein, in the raw material preparation step and/or the aging step, precipitation of Nb is facilitated by performing at least one operation selected from the group consisting of the following (I) to (III): (I) in the raw material preparation step, the aqueous mixed liquid is prepared by mixing a Nb raw material liquid containing Nb with a MoVSb raw material liquid containing Mo, V, and Sb, wherein ammonia is added to at least one of the MoVSb raw material liquid, the Nb raw material liquid, and the aqueous mixed liquid such that a molar ratio in terms of NH.sub.3/Nb in the aqueous mixed liquid is adjusted to be 0.7 or more, and in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 50 C.; (II) in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 65 C.; and (III) in the raw material preparation step, the aqueous mixed liquid is prepared by mixing a Nb raw material liquid containing Nb with a MoVSb raw material liquid containing Mo, V, and Sb, wherein a molar ratio in terms of H.sub.2O.sub.2/Nb in the Nb raw material liquid is adjusted to less than 0.2, and in the aging step, a temperature of the aqueous mixed liquid is adjusted to more than 50 C.

A process for producing unsaturated nitrile, using a fluidized bed reactor having an internal space having a catalyst capable of being fluidized therein, a feed opening to feed a starting material gas comprising hydrocarbon to the internal space, and a discharge port to discharge a reaction product gas from the internal space, the process comprising a reaction step of subjecting the hydrocarbon to a vapor phase catalytic ammoxidation reaction in the presence of the catalyst in the internal space to produce the corresponding unsaturated nitrile, wherein when in the internal space, a space where an existing amount of the catalyst per unit volume is 150 kg/m.sup.3 or more is defined as a dense zone and a space where an existing amount of the catalyst per unit volume is less than 150 kg/m.sup.3 is defined as a sparse zone in the reaction step, a gas residence time in the sparse zone is 5 to 50 sec.

A process for producing unsaturated nitrile, using a fluidized bed reactor having an internal space having a catalyst capable of being fluidized therein, a feed opening to feed a starting material gas comprising hydrocarbon to the internal space, and a discharge port to discharge a reaction product gas from the internal space, the process comprising a reaction step of subjecting the hydrocarbon to a vapor phase catalytic ammoxidation reaction in the presence of the catalyst in the internal space to produce the corresponding unsaturated nitrile, wherein when in the internal space, a space where an existing amount of the catalyst per unit volume is 150 kg/m.sup.3 or more is defined as a dense zone and a space where an existing amount of the catalyst per unit volume is less than 150 kg/m.sup.3 is defined as a sparse zone in the reaction step, a gas residence time in the sparse zone is 5 to 50 sec.