Production process for water-absorbent resin

• US 6,927,268 B2
• Filed: 06/19/2001
• Issued: 08/09/2005
• Est. Priority Date: 06/21/2000
• Status: Active Grant

• Current Assignee: Nippon Shokubai Company Limited
• Original Assignee: Nippon Shokubai Company Limited
• Inventors: Ishizaki, Kunihiko, Matsumoto, Yukihiro, Kanto, Teruyuki
• Primary Examiner(s): Zalukaeva, Tatyana
• Application Number:
  US09/883,266
• Publication Number:
  US 20020120085A1
• Time in Patent Office: 1,512 Days
• Field of Search: 526/317.1, 526/77, 526/318.5, 526/88, 526/240, 562/600, 525/330.2, 524/556
• US Class Current: 526/317.1
• CPC Class Codes: C08F 20/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof

Abstract

The present invention provides a process for producing a water-absorbent resin of which the residual monomer content and the extractable content are low. The process for producing a water-absorbent resin comprises the step of polymerizing at least one monomer component including acrylic acid and/or its salt as major components to produce a water-absorbent resin that is a neutralized salt, and this process is characterized in that the acrylic acid is a product obtained by catalytic gas phase oxidation of propylene and/or propane and has a protoanemonin content of not more than 10 ppm, and in that the resultant water-absorbent resin has a neutralization ratio of not less than 50 mol %.

Claims

1. A process for producing a water-absorbent resin, which is a neutralized salt and is obtained by polymerizing at least one monomer component including acrylic acid and/cr its salt as major components,

wherein said acrylic acid aud/or its salt is produced by a process comprising the steps of

(i) obtaining acrylic acid by catalytic gas-base oxidation of propylene and/or propane, where the obtained acrylic acid contains impurities and/or byproducts and includes protoanemonin as an impurity or byproduct,

(ii) reducing a protoanemonin content of said acrylic acid to not more than 10 ppm, and then

(iii) subjecting at least 50 mol % of said acrylic acid and/or its salt obtained in step (ii) to alkali treatment, where the mixture of said acrylic acid and/or its salt and said alkali is a solution containing 0.5 to 20 ppm of oxygen.

2. A process according to claim, 1, wherein the acrylic acid has a furfural content of not more than 10 ppm.

3. A process according to according to claim 1, wherein the alkali treatment is a strong-alkali treatment with an excess of an alkali metal hydroxide.

4. A process according to claim 1, wherein the polymerization is aqueous solution polymerization.

5. A process according to claim 1, which further comprises the step of crosslinking the vicinity of the surface of the water-absorbent resin.

6. A process according to claim 1, further comprising distilling the acrylic acid in the presence of an aldehyde-treating agent to purify the acrylic acid.

7. A process according to claim 6, wherein the aldehyde-treating agent is a hydrazine compound.

12. A process according to claim 1, wherein said water-absorbent resin has a water absorption capacity of not less than 25 g/g under a load of about 1.96 kPa.

14. A process according to claim 1, wherein said water-absorbent resin has a liquid permeation quantity of not less than 100 g/g under a load of 0.3 psi over 10 minutes.

8. A process for producing a water-absorbent resin, which is a neutralized salt and is obtained by polymerizing at least one monomer component including acrylic acid and/or its salt as major components,

wherein said acrylic acid and/or its salt has a protoanemonin content of not more than 10 ppm and is produced by a process comprising the steps of

(i) obtaining acrylic acid by catalytic gas-phase oxidation of propylene and/or propane, where the obtained acrylic acid contains impurities and/or byproducts and contains not less than 10 ppm of an aldehyde as an impurity or a byproduct, and then

(ii) subjecting said acrylic acid and/or its salt to a strong alkali treatment with an alkali metal hydroxide, where the mixture of acrylic acid and/or its salt and alkali is a solution containing 0.5 to 20 ppm of oxygen, thus reducing an aldehyde content in said acrylic acid and/or its salt to not more than 10 ppm.

9. A process according to claim 8, wherein the strong-alkali treatment is carried out at a temperature of no lower than 40°

C.

10. A process according to claim 8, wherein the strong-alkali treatment comprises treating the raw acrylic acid with a molar excess of said strong alkali.

11. A process according to claim 8, further comprising the step of purifying the acrylic acid to reduce the protoanemonin content to not more than 10 ppm followed by the strong alkali treatment.

13. A process according to claim 8, wherein said water-absorbent resin has a water absorption capacity of not less than ²⁵ g/g under a load of about 1.96 kPa.

15. A process according to claim 8, wherein said water-absorbent resin has a liquid permeation quantity of not less than 100 g/g under a load of 0.3 psi over 10 minutes.