Method for producing acrylic acid
A method for producing acrylic acid, comprising (a) a absorption step of absorbing acrylic acid-containing gas obtained by oxidizing raw material gas in gas phase as crude acrylic acid-containing solution, (b 1 ) a step of separating high boiling point components that separates the crude high boiling point components at a distillation column as (b) a step of purifying the acrylic acid-containing solution, and further, (c) a decomposition step of decomposing Michael adducts contained in the high boiling point components to prepare acrylic acid and (d) a collection step of collecting acrylic acid generated in the decomposition step (c), whereby the proportion of the amount of maleic acid to a sum of the sum of the maleic acid and maleic anhydride in the high boiling point components that are fed from the high boiling point component separation step (b 1 ) to the decomposition step (c) satisfies a equation below: [ Equation 1 ] ` [ Maleic acid ( mass ) ] [ Maleic acid ( mass ) ] + [ Maleic anhydride ( mass ) ] × 100 ≦ 70 % . ( 1 )
1. A method for producing acrylic acid, comprising
(a) an absorption step of absorbing an acrylic acid-containing gas obtained by oxidizing a raw material gas in gas phase as a crude acrylic acid-containing solution;
(b 1 ) a high boiling point component separation step of separating high boiling point components at a distillation column as (b) a step of purifying the crude acrylic acid-containing solution;
(c) a decomposition step of decomposing Michael adducts contained in the high boiling point components to generate acrylic acid; and
(d) a collection step of collecting the acrylic acid generated in the decomposition step (c), wherein a column bottom of the distillation column at the high boiling point component separation step (b 1 ) has a temperature of 90 to 130° C., a residence time of a column bottom solution is 2 to 30 hours, and a ratio of a mass of solution fed to the distillation column to a mass of extraction solution from the column bottom of the distillation column is 5 to 20, and
a proportion of an amount of maleic acid to a sum of maleic acid and maleic anhydride in the high boiling point components fed from the high boiling point component separation step (b 1 ) to the decomposition step (c) satisfies equation (1) below:
[
Maleic
acid
(
mass
)
]
[
Maleic
acid
(
mass
)
]
+
[
Maleic
anhydride
(
mass
)
]
×
100
≦
70
%
.
(
1
)
2. A method for producing acrylic acid according to claim 1 , further comprising (b 2 ) a crystallization purification step of separating crystals obtained by crystallizing acrylic acid in the crude acrylic acid-containing solution from residual mother liquid as an additional step of purifying the acrylic acid-containing solution (b), wherein at least one portion of the residual mother liquid obtained in the crystallization purification step (b 2 ) is fed to the high boiling point component separation step (b 1 ).
3. A method for producing acrylic acid according to claim 2 , wherein a column bottom solution obtained in the high boiling point component separation step (b 1 ) is fed to the decomposition step (c), a portion of a distillate obtained in the decomposition step (c) is fed to the high boiling point component separation step (b 1 ), and a distillate obtained in the high boiling point component separation step (b 1 ) and/or the distillate obtained in the decomposition step (c) are fed to the absorption step (a).
4. A method for producing acrylic acid according to claim 1 , wherein a concentration of the Michael adducts in the high boiling point components fed to the decomposition step (c) is 20 to 60% by mass.
5. A method for producing acrylic acid according to claim 1 , wherein the decomposition step (c) is carried out by a reaction-distillation process.
6. A method for producing acrylic acid according to claim 5 , wherein the decomposition step (c) according to the reaction-distillation process is carried out at a reflux ratio of 0.5 to 6 using a shelf plate distillation column.
7. A method for producing acrylic acid according to claim 6 , wherein the shelf plate distillation column has 3 or more of theoretical stages, and the position of 70 to 100% of total theoretical stages setting a column top side of the shelf plate distillation column as a base point is heated at 125° C. or less.
8. A method for producing acrylic acid according to claim 6 , wherein the shelf plate distillation column is equipped with a tray having opening with a hole diameter of 10 to 50 mm.
9. A method for producing acrylic acid according to claim 1 , wherein the decomposition step (c) uses a forced circulation type heat exchanger, heats the high boiling point components fed to the decomposition step (c) to 155 to 220° C., and controls temperature difference between a heat source of the forced circulation type heat exchanger and the high boiling point components heated by the forced circulation type heat exchanger at 15 to 80° C.
10. A method for producing acrylic acid according to claim 1 , whereby the decomposition step (c) is carried out in a presence of an N-oxyl compound.
11. A method for producing acrylic acid according to claim 1 , wherein all of a distillate obtained in the decomposition step (c) is fed to the high boiling point component separation step (b 1 ) and fed to the absorption step (a) through the high boiling point component separation step (b 1 ).
12. A method for producing acrylic acid according to claim 11 , wherein a concentration of maleic acid in the distillate fed to the absorption step (a) is 2% by mass or less.