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CN-122003530-A - Drainage aid for bleaching of cellulosic fibres

CN122003530ACN 122003530 ACN122003530 ACN 122003530ACN-122003530-A

Abstract

A method for improving drainage in an acidic stage of a bleaching process of cellulosic fibers, followed by at least one scrubber stage, in which method a polymer comprising cationic functional groups is added to the acidic stage of the bleaching process, and the polymer comprising cationic functional groups has a mass average molecular weight of 4000000-17000000 g/mol, a cationic net charge and a total ionization degree of 5-mol-%.

Inventors

  • Marcus Aokoning

Assignees

  • 凯米拉公司

Dates

Publication Date
20260508
Application Date
20241010
Priority Date
20231012

Claims (20)

  1. 1. A method for improving drainage in an acidic stage of a bleaching process of cellulosic fibers, the method comprising Obtaining cellulose fibers from the pulping process and forming an aqueous cellulose fiber suspension, Bleaching said cellulosic fiber suspension in a bleaching process comprising at least one acidic stage, wherein the pH of said cellulosic fiber suspension is < 6, followed by at least one washer stage, Characterized in that the method further comprises -Adding a drainage aid to the cellulosic fiber suspension at least into the acidic stage of the bleaching process, wherein the drainage aid comprises a polymer comprising cationic functional groups and having a mass average molecular weight of 4000 000-17 000g/mol, a cationic net charge and a total ionization degree of 5-35 mol-% at pH 7.
  2. 2. The method according to claim 1, characterized in that said polymer comprising cationic functional groups comprises a cationic polyacrylamide obtained by copolymerization of (meth) acrylamide and at least one cationic monomer.
  3. 3. The method according to claim 1 or 2, characterized in that the polymer comprising cationic functional groups comprises an amphoteric polyacrylamide obtained by copolymerization of (meth) acrylamide with cationic and anionic monomers.
  4. 4. The method of any of the preceding claims, wherein the cationic functional group of the polymer is derived from a monomer selected from the group consisting of 2- (dimethylamino) ethyl acrylate (ADAM), [2- (acryloyloxy) ethyl ] trimethylammonium chloride (ADAM-Cl), 2- (dimethylamino) ethyl benzyl chloride, 2- (dimethylamino) ethyl acrylate dimethyl sulfate, 2-dimethylaminoethyl methacrylate (MADAM), [2- (methacryloyloxy) ethyl ] trimethylammonium chloride (MADAM-Cl), 2-dimethylaminoethyl methacrylate dimethyl sulfate, [3- (acrylamido) propyl ] trimethylammonium chloride (APTAC), and [3- (methacrylamido) propyl ] trimethylammonium chloride (MAPTAC), and any combination thereof.
  5. 5. The method according to any of the preceding claims, wherein the anionic functional groups of the amphoteric polyacrylamide are derived from monomers selected from the group consisting of unsaturated mono-or dicarboxylic acids such as acrylic acid, maleic acid, fumaric acid, itaconic acid, aconitic acid, mesaconic acid, citraconic acid, crotonic acid, isocrotonic acid, angelic acid and tiglic acid, and any combination thereof.
  6. 6. The method according to any of the preceding claims, characterized in that the polymer comprising cationic functional groups is added to the cellulosic fiber suspension in the acidic stage before an acidic stage scrubber.
  7. 7. A method according to any of the preceding claims, characterized in that the polymer comprising cationic functional groups is added to the cellulosic fibre suspension at least in the first acidic stage of the bleaching process.
  8. 8. The method according to any of the preceding claims, wherein the cellulose fibers are derived from hardwood, softwood or mixtures thereof.
  9. 9. A method according to any of the preceding claims, characterized in that the cellulose fibres originate from a chemical pulping process, such as a kraft pulping process.
  10. 10. The method according to any of the preceding claims, wherein the drainage aid is added in an amount of < 500 g/ton dry pulp, preferably < 300g polymer/ton dry pulp, more preferably < 200 g polymer/ton dry pulp or < 100 g polymer/ton dry pulp.
  11. 11. Use of a polymer comprising cationic functional groups as a drainage aid in a bleaching process of cellulose fibers, wherein the polymer is added to a cellulose fiber suspension in an acidic stage of the bleaching process, wherein the pH of the cellulose fiber suspension is < 6, and wherein the polymer comprising cationic functional groups has a mass average molecular weight of 4 000 000-17 000 g/mol, a cationic net charge and a total ionization degree of 5-35 mol-% at pH 7.
  12. 12. Use according to claim 11, characterized in that the polymer comprising cationic functional groups comprises a cationic polyacrylamide obtained by copolymerization of (meth) acrylamide and at least one cationic monomer.
  13. 13. Use according to claim 11 or 12, characterized in that the polymer comprising cationic functional groups comprises an amphoteric polyacrylamide obtained by copolymerization of (meth) acrylamide with cationic and anionic monomers.
  14. 14. The use according to any one of claims 11-13, wherein the cationic functional group of the polymer is derived from a monomer selected from the group consisting of 2- (dimethylamino) ethyl acrylate (ADAM), [2- (acryloyloxy) ethyl ] trimethylammonium chloride (ADAM-Cl), 2- (dimethylamino) ethyl benzyl chloride, 2- (dimethylamino) ethyl acrylate dimethyl sulfate, 2-dimethylaminoethyl methacrylate (MADAM), [2- (methacryloyloxy) ethyl ] trimethylammonium chloride (MADAM-Cl), 2-dimethylaminoethyl methacrylate dimethyl sulfate, [3- (acrylamido) propyl ] trimethylammonium chloride (APTAC), and [3- (methacrylamido) propyl ] trimethylammonium chloride (MAPTAC), and any combination thereof.
  15. 15. The use according to any one of claims 11-14, wherein the anionic functional group of the amphoteric polyacrylamide is derived from monomers selected from the group consisting of unsaturated mono-or dicarboxylic acids such as acrylic acid, maleic acid, fumaric acid, itaconic acid, aconitic acid, mesaconic acid, citraconic acid, crotonic acid, isocrotonic acid, angelic acid and tiglic acid, and any combination thereof.
  16. 16. Use according to any one of claims 11-15, characterized in that the polymer comprising cationic functional groups is added to the cellulosic fibre suspension in the acidic stage before an acidic stage scrubber.
  17. 17. Use according to any of claims 11-16, characterized in that the polymer comprising cationic functional groups is added to the cellulosic fibre suspension at least in the first acidic stage of the bleaching process.
  18. 18. Use according to any one of claims 11-17, characterized in that the cellulose fibres originate from hardwood, softwood or a mixture thereof.
  19. 19. Use according to any one of claims 11-18, characterized in that the cellulose fibres originate from a chemical pulping process, such as a kraft pulping process.
  20. 20. Use according to any of the preceding claims, characterized in that the drainage aid is added in an amount of < 500 g/ton dry pulp, preferably < 300g polymer/ton dry pulp, more preferably < 200 g polymer/ton dry pulp or < 100 g polymer/ton dry pulp.

Description

Drainage aid for bleaching of cellulosic fibres Technical Field The present invention relates to the use of a polymer comprising cationic functional groups as a drainage aid (DRAINAGE AID) in the bleaching of cellulose fibres, and to a method for improving drainage in the acidic phase of the bleaching of cellulose fibres according to the independent claims presented below. Background Cellulose fibers obtained from chemical pulping processes are bleached in a bleaching process wherein residual lignin is removed from the fibers to increase the brightness of the fibers. Bleaching is a staged process in which various bleaching chemicals are typically used in different successive stages to break down lignin into smaller structures. The lignin decomposition structure is water soluble, especially at pH > 7, and is removed from the fiber and bleaching process in an alkaline extraction (alkaline extraction) stage located after or between bleaching stages. Thus, the bleaching process of cellulosic fibers typically comprises a plurality of bleaching stages with a wash stage in between. Multi-stage bleaching produces quality-optimized and cost-effective results. However, bleach plants may experience drainage and dewatering problems in the scrubber connected to each bleaching stage. In bleaching processes where an acidic bleaching stage is followed by an alkaline washing stage, the washing efficiency of the alkaline stage may be lower if the previous acidic stage scrubber has drainage problems. Poor drainage reduces the consistency of the pulp in the next stage, which results in a lower bleaching efficiency and thus higher chemical consumption. In addition, chemicals and poorly washed impurities in the acidic stage may enter the subsequent alkaline stage, also resulting in higher consumption of chemicals. The increased consumption of chemicals results in higher costs in the bleaching plant and also has an environmental impact. Furthermore, the deposition of inorganic impurities throughout the bleaching process may lead to runnability problems. Disclosure of Invention The object of the present invention is to reduce or even eliminate the above mentioned problems occurring in the prior art. The object of the present invention is to reduce drainage and dewatering problems in a scrubber connected to an acidic bleaching stage in a bleaching process, thereby improving the runnability of a bleaching plant. The object of the present invention is also to improve the quality of the filtrate obtained from the scrubber of the bleaching stage. Improved removal of water and impurities reduces the consumption of chemicals in the subsequent stages of the bleaching process, and the present invention therefore also provides a more cost-effective bleaching process. Furthermore, the environmental load of the bleaching process is reduced due to the reduced consumption of chemicals. To achieve the object presented above, the invention is characterized by what is presented in the appended independent claims. Some preferred embodiments of the invention will be described in the other claims. The embodiments and advantages mentioned herein relate to all aspects of the invention where applicable, even if not always specifically mentioned. An exemplary method for improving drainage in the acidic stage of a bleaching process of cellulosic fibers according to the present invention comprises Obtaining cellulose fibers from the pulping process and forming an aqueous cellulose fiber suspension, -Bleaching the cellulosic fibre suspension in a bleaching process comprising at least one acidic stage, wherein the pH of the cellulosic fibre suspension is < 6, followed by at least one washer stage, and -Adding a drainage aid to the cellulosic fiber suspension entering the acidic stage of the bleaching process, wherein the drainage aid comprises a polymer comprising cationic functional groups and having a mass average molecular weight of 4 000 000-17 000 g/mol, a cationic net charge and a total ionization degree of 5-35 mol-% at pH 7. A typical use of the polymer comprising cationic functional groups according to the invention is as a drainage aid in a bleaching process of cellulose fibers, wherein the polymer is added to a cellulose fiber suspension in an acidic stage of the bleaching process, wherein the pH of the cellulose fiber suspension is < 6, and wherein the polymer comprising cationic functional groups has a mass average molecular weight of 4 000 000-17 000 g/mol, a cationic net charge and a total ionization degree of 5-35 mol-% at pH 7. It has now been found that the use of a polymer comprising cationic functional groups and having a mass average molecular weight of 4 000 000-17,000 g/mol, a cationic net charge and a total ionization degree of 5-35 mol-% as a drainage aid improves drainage in the scrubber in the acidic stage. The polymer comprising cationic functional groups used as a drainage aid in the present invention is added to the acidic stage