Abstract: A method for purifying methacrylic acid, including mixing raw material methacrylic acid and methanol; precipitating a crystal of methacrylic acid from the mixed solution; and separating the crystal and mother liquor, wherein the raw material methacrylic acid and methanol are mixed so that a concentration of methanol in the mixed liquid is 3.0 to 3.75% by mass, and the crystal of methacrylic acid is precipitated from the mixed solution in a cooling crystallization vessel.

Abstract: A method for purifying methacrylic acid, including mixing raw material methacrylic acid and methanol; precipitating a crystal of methacrylic acid from the mixed solution; and separating the crystal and mother liquor, wherein the raw material methacrylic acid and methanol are mixed so that a concentration of methanol in the mixed liquid is 3.0 to 3.75% by mass, and the crystal of methacrylic acid is precipitated from the mixed solution in a cooling crystallization vessel.

Abstract: Provided is a crystallization method by which a highly-pure methacrylic acid crystal can be produced with high productivity. The method for purifying methacrylic acid according to the present disclosure involves using crude methacrylic acid having a maleic acid concentration of 2000 ppm by mass or less and an acrylic acid concentration of 2000 ppm by mass or less and setting the slurry temperature to ?10 to 10° C. in order to crystallize methacrylic acid. A suspension-type jacket-cooling-system crystallization vessel is used as the crystallization apparatus, and an absolute value of the difference between a crystallization temperature and a temperature of a cooling medium in the jacket is preferably 15° C. or less.

Abstract: Provided is a crystallization method by which a highly-pure methacrylic acid crystal can be produced with high productivity. The method for purifying methacrylic acid according to the present disclosure involves using crude methacrylic acid having a maleic acid concentration of 2000 ppm by mass or less and an acrylic acid concentration of 2000 ppm by mass or less and setting the slurry temperature to ?10 to 10° C. in order to crystallize methacrylic acid. A suspension-type jacket-cooling-system crystallization vessel is used as the crystallization apparatus, and an absolute value of the difference between a crystallization temperature and a temperature of a cooling medium in the jacket is preferably 15° C. or less.

Abstract: The present invention provides a method for producing a catalyst for use in synthesizing methacrylic acid which can produce methacrylic acid in high yield, the catalyst for use in synthesizing methacrylic acid which can produce methacrylic acid in high yield and a method for producing methacrylic acid in high yield through gas-phase catalytic oxidation of methacrolein with molecular oxygen. The method for producing the catalyst containing molybdenum and phosphorus for use in synthesizing methacrylic acid is composed of the steps of: preparing a slurry containing at least molybdenum and phosphorus and having specific viscosity in the range of 2.5×10?4 to 7.0×10?4 m2/s, which is a value obtained by dividing viscosity (unit: kg/(m·s)) by specific gravity (unit: kg/m3); obtaining a dried material by drying the slurry; and calcining the dried material at 300 to 500° C.

Abstract: A vertical multitubular heat exchanger that can prevent clogging of a polymerized material and is continuously operable for an extended period of time is provided. The vertical multitubular heat exchanger (1) of the present invention introduces a process fluid containing an easily-polymerizable substance into heat exchanger tubes (28) to perform heat exchange. The vertical multitubular heat exchanger (1) includes a shell (2) extending in a vertical direction, an upper tube sheet (8) and a lower tube sheet (10) respectively disposed at the upper portion (4) and the lower portion (6) of the shell (2), and a plurality of heat exchanger tubes (28) whose outer circumferences (26) of both ends are respectively fixed to the upper tube sheet (8) and the lower tube sheet (10). An upper surface (34) of the upper tube sheet (8) is formed to be sloped and at least one of the heat exchanger tubes (28) is disposed in the vicinity of the lowest position of the upper surface (34) of the upper tube sheet (8).

Abstract: The present invention provides a method for producing methacrylic acid through gas-phase catalytic oxidation of methacrolein or a methacrolein-containing gas with molecular oxygen or a gas containing molecular oxygen by the use of a fixed-bed multitubular reactor comprising a plurality of reaction tubes each having a catalyst layer therein, wherein the above catalyst layer is divided in the direction of the tube axis of a reaction tube into two or more layers, to thereby provide a plurality of reaction zones, and the catalyst is caused to be present in the catalyst layer in such a way that a reaction load ratio CRc(i) per unit mass of the catalyst in each reaction zone becomes 0.8 to 1.0.

Abstract: The present invention provides a method for producing a catalyst for use in synthesizing methacrylic acid which can produce methacrylic acid in high yield, the catalyst for use in synthesizing methacrylic acid which can produce methacrylic acid in high yield and a method for producing methacrylic acid in high yield through gas-phase catalytic oxidation of methacrolein with molecular oxygen. The method for producing the catalyst containing molybdenum and phosphorus for use in synthesizing methacrylic acid is composed of the steps of: preparing a slurry containing at least molybdenum and phosphorus and having specific viscosity in the range of 2.5×10?4 to 7.0×10?4 m2/s, which is a value obtained by dividing viscosity (unit: kg/(m·s)) by specific gravity (unit: kg/m3); obtaining a dried material by drying the slurry; and calcining the dried material at 300 to 500° C.

Abstract: The present invention provides a method for producing methacrylic acid through gas-phase catalytic oxidation of methacrolein or a methacrolein-containing gas with molecular oxygen or a gas containing molecular oxygen by the use of a fixed-bed multitubular reactor comprising a plurality of reaction tubes each having a catalyst layer therein, wherein the above catalyst layer is divided in the direction of the tube axis of a reaction tube into two or more layers, to thereby provide a plurality of reaction zones, and the catalyst is caused to be present in the catalyst layer in such a way that a reaction load ratio CRc(i) per unit mass of the catalyst in each reaction zone becomes 0.8 to 1.0.

Abstract: A vertical multitubular heat exchanger that can prevent clogging of a polymerized material and is continuously operable for an extended period of time is provided. The vertical multitubular heat exchanger (1) of the present invention introduces a process fluid containing an easily-polymerizable substance into heat exchanger tubes (28) to perform heat exchange. The vertical multitubular heat exchanger (1) includes a shell (2) extending in a vertical direction, an upper tube sheet (8) and a lower tube sheet (10) respectively disposed at the upper portion (4) and the lower portion (6) of the shell (2), and a plurality of heat exchanger tubes (28) whose outer circumferences (26) of both ends are respectively fixed to the upper tube sheet (8) and the lower tube sheet (10). An upper surface (34) of the upper tube sheet (8) is formed to be sloped and at least one of the heat exchanger tubes (28) is disposed in the vicinity of the lowest position of the upper surface (34) of the upper tube sheet (8).