Claims
- 1. A process for peroxide bleaching of mechanical or high yield pulp, said process comprising:
adding to a pulp slurry at least one stabilizer for stabilizing transition metal ions in said slurry, said at least one stabilizer chosen from the group comprising silicate, MgSO4 in an amount not exceeding 0.2% by weight on dry pulp, and other stabilizers; subsequently adding hydrogen peroxide to said slurry at a preselected point; adding an alkali source to said slurry simultaneously with or subsequent to adding said at least one stabilizer; and subjecting said slurry to preselected conditions to complete said bleaching process, one of said preselected conditions comprising maintaining the pH of said slurry at not more than 11.5 at any point in said process.
- 2. The process of claim 1 wherein the pH of said slurry at the completion of said bleaching process is less than 9.5.
- 3. The process of claim 1 wherein said other stabilizers are chosen from DTPA, EDTA, or other chelants, or their salts.
- 4. The process of claim 1 wherein said stabilizer is a combination of sodium silicate, magnesium sulfate and DTPA.
- 5. The process of claim 1 wherein said alkali source is chosen from caustic soda, soda ash, magnesium oxide and magnesium hydroxide.
- 6. The process of claim 1 wherein said alkali source is caustic soda.
- 7. The process of claim 1 wherein said alkali source is magnesium hydroxide.
- 8. The process of claim 1 further comprising the pretreatment steps of adding a chelating agent to said slurry and subsequently removing chelated transition metal ions from said slurry.
- 9. The process of claim 8 wherein said chelating agent is DTPA, EDTA, or other chelants or their salts.
- 10. The process of claim 9 wherein said chelating agent is DTPA.
- 11. The process of claim 1 further comprising the pretreatment steps of adding a chelating agent and a reducing agent to said slurry and subsequently removing chelated transition metal ions from said slurry.
- 12. The process of claim 11 wherein said reducing agent is sodium hydrosulfite and said chelating agent is DTPA.
- 13. The process of claim 1 further comprising the step of thoroughly mixing said stabilizer with said slurry prior to adding said hydrogen peroxide.
- 14. The process of claim 1 further comprising the step of providing a predetermined time delay between the addition of said stabilizer and the addition of said hydrogen peroxide source.
- 15. A process for peroxide bleaching of mechanical or high yield pulp, said process comprising:
adding to a pulp slurry sodium hydrosulfite and DTPA; subsequently removing from said slurry chelated transition metal ions; adding to said slurry a stabilizer chosen from sodium silicate, magnesium sulfate, DTPA, EDTA and other chelants; subsequently adding hydrogen peroxide to said slurry at a preselected point in said process; adding caustic soda to said slurry simultaneously with or subsequent to adding said stabilizer; wherein the pH of said slurry at no time exceeds 11.5; and subjecting said slurry to preselected conditions to complete said bleaching process, such that the final pH of said slurry at completion of said bleaching process is less than 9.5.
- 16. A process for peroxide bleaching of mechanical or high yield pulp, said process comprising:
adding to a pulp slurry a stabilizer comprising DTPA; subsequently adding hydrogen peroxide to said slurry at a preselected point in said process; adding Mg(OH)2 to said slurry simultaneously with or subsequent to adding said stabilizer; wherein the pH of said slurry at no time exceeds 11.5; and subjecting said slurry to preselected conditions to complete said bleaching process, such that the final pH of said slurry at completion of said bleaching process is less than 9.5.
Parent Case Info
[0001] This is a Continuation-In-Part of U.S. patent application Ser. No. 09/564,853.
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
09564853 |
May 2000 |
US |
Child |
10251888 |
Sep 2002 |
US |