Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/001—Modification of pulp properties
  • D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/001—Modification of pulp properties
  • D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
  • D21C9/004—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives inorganic compounds
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/001—Modification of pulp properties
  • D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
  • D21C9/005—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives organic compounds
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/08—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/08—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching
  • D21C9/083—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching with inorganic compounds
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/08—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching
  • D21C9/086—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching with organic compounds or compositions comprising organic compounds
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/1073—Bleaching ; Apparatus therefor with O3
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
  • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone

Definitions

• the invention relates to the treatment of chemical papermaking pulps, in particular to the bleaching of chemical pulps, in particular kraft, soda or sulphite pulps.
• chemical paper pulp or chemical pulp are obtained after cooking the wood with reagents removing most of the lignin, such as sodium hydroxide possibly catalyzed by quinones (soda process to obtain the pasta soda), the combined sodium hydroxide sodium sulphide (kraft process for obtaining kraft pulps) or bisulphites (sulphite process to obtain sulphite pulps).
• reagents such as sodium hydroxide possibly catalyzed by quinones (soda process to obtain the pasta soda), the combined sodium hydroxide sodium sulphide (kraft process for obtaining kraft pulps) or bisulphites (sulphite process to obtain sulphite pulps).
• a first phase called delignification or pre-bleaching consists of removing about half of the lignin present in the pulp.
• This operation conventionally carried out by chemical oxygen treatment (O), is inherently accompanied by a whitening of the dough, due to the brown lignin depletion.
• O chemical oxygen treatment
• the next phase consists in completely eliminating the residual lignin, so as to keep only the fraction "carbohydrates" (cellulose and hemicelluloses) perfectly white.
• This treatment is based on the oxidation of the phenolic rings present in the lignin which, once converted into hydrophilic -COOH groups, can be removed by washing in solution, advantageously in an alkaline medium, which increases their solubilization.
• the bleaching of chemical pulps is carried out by means of a succession of treatments, called the bleaching sequence, using one or more oxidants, the most common of which are chlorine dioxide or ClO 2 (treatment denoted D).
• oxygen or O 2 treatment noted O
• oxygenated water or hydrogen peroxide or H 2 O 2 treatment noted P.
• Ozone treatment noted Z
• Ozone is a very promising oxidizing agent in this context in that its effectiveness in delignification surpasses that of chlorine dioxide, with the same amount of reagent applied.
• ozone Like chlorine dioxide (D), ozone works in an acidic environment. Thus and in the same way as for chlorine dioxide delignification, the delignification by ozone must be associated with an alkaline extraction (E) to be more complete.
• E alkaline extraction
• the ozone delignification process is generally denoted ZE, indicating that the oxidation by ozone in an acidic medium is followed by an alkaline extraction, advantageously in the presence of sodium hydroxide. It should be noted that these two steps can be separated by washing, generally carried out with water, which contributes to increasing the reaction pH. In the absence of washing, the treatment is then noted [ZE].
• the document WO 95/06773 describes a ZE treatment where the alkaline extraction following the ozone treatment is carried out, conventionally, using sodium hydroxide.
• an ozone treatment can be implemented upstream of the bleaching process in the case of mechanical pulps, as illustrated by the document WO 2010/046768 .
• the addition of magnesium hydroxide after the ozone treatment makes it possible to increase the pH, with a view to subsequent bleaching.
• OOZEP type bleaching sequences for example, for a complete replacement of chlorinated reagents, or OOZDEP, for example, for a partial replacement of chlorine dioxide.
• Another solution consists in carrying out the ZE treatment in two stages, according to the ZEZE sequence, by distributing the ozone load between the two Z treatments ( RW Allison, APPITA Journal, Vol 36 No. 1 pp. 42-46 (1982) )).
• the depolymerization of cellulose remains important in the absence of chemical action to stop depolymerization caused by ozonation followed by alkaline extraction.
• the present invention is therefore part of the search for technical solutions for preventing or reducing the depolymerization of cellulose pulps chemical pulp observed during their treatment with the ZE sequence.
• the present invention is based on the observation by the inventors that the degradation of cellulose in this context is certainly initiated during the treatment with ozone but is amplified in alkaline medium.
• the present invention provides a concrete technical solution, namely carrying out the alkaline extraction in the presence of specific ions, in this case magnesium (Mg 2+ ) cations, advantageously at a suitable concentration.
• specific ions in this case magnesium (Mg 2+ ) cations, advantageously at a suitable concentration.
• the magnesium ions are added to the pulp before the addition of the alkaline solution to the pulp, i.e. at a time when the pH of the pulp is alkaline, that is to say when the reaction medium has an acidic pH (pH less than 7) or even neutral (pH less than or equal to 7).
• the magnesium ions are added between the step of treating the ozone paste and the alkaline extraction step.
• the present invention relates to a method of treating chemical papermaking pulp comprising treating the ozone pulp followed by alkaline extraction, wherein the alkaline extraction is carried out in the presence of magnesium ions (Mg 2+ ) and in the absence of hydrogen peroxide, the magnesium ions being present in an amount of 0.01 to 0.5% by weight relative to the dry weight of the dough.
• Mg 2+ magnesium ions
• treatment process can also be understood as “bleaching process”.
• the process according to the invention is particularly suitable for the treatment of chemical papermaking pastes such as, for example, soda pastes, kraft pastes or sulphite pastes, advantageously kraft or sulphite pastes.
• chemical papermaking pastes such as, for example, soda pastes, kraft pastes or sulphite pastes, advantageously kraft or sulphite pastes.
• the chemical papermaking pulps which are intended to be treated using the process according to the invention, are hardwood and resinous wood pulps, as well as the pasta of annual plants.
• the process according to the invention is defined by at least two specific steps, namely an ozonation phase and an alkaline extraction phase, advantageously with sodium hydroxide, the alkaline extraction phase being subsequent to the ozonation phase.
• the ozonation phase is directly followed by the alkaline extraction phase.
• the method according to the invention comprises the sequence [ZE].
• the ozonation phase and the alkaline extraction phase can be separated by a washing, advantageously carried out with water, resulting for example from the washing carried out after the subsequent complementary bleaching steps, the washing against the current being common practice in whitening pasta.
• the method according to the invention comprises the ZE sequence.
• the magnesium ions are added between the washing and the alkaline extraction step.
• another treatment step may be inserted between the ozonation and alkaline extraction phases, for example a chlorine dioxide treatment (D), optionally followed by a washing.
• the method according to the invention then comprises the ZDE sequence.
• a stage of treatment of heavy metals carried out at an acidic pH and in the presence of complexing agents such as EDTA, is not interposed between the ozonation phase and the alkaline extraction phase.
• complexing agents such as EDTA
• the treatment according to the invention has a more complex sequence, with treatments upstream and / or downstream of these at least two phases.
• the bleaching of chemical pulps begins with an oxygen treatment (O), or even a double treatment with oxygen (OO).
• This treatment is advantageously carried out in an alkaline medium, under oxygen gas pressure, at a temperature in the region of 100 ° C. It removes about half of the lignin from the pasta and causes pre-bleaching of the pasta.
• the two specific steps of the process according to the invention are advantageously carried out on a so-called pre-bleached pulp, treated with O or OO.
• the ZE sequence referred to in the invention is advantageously integrated in a more complex process, for example OOAZEP, OOAPZE, OOAZDEP, OOZEDD ...
• the beneficial effect of the magnesium ions on the depolymerization of the cellulose is observed irrespective of the positioning of the ZE sequence, and therefore regardless of the initial bleaching state of the pulp treated.
• the purpose of the present invention is to propose a process for bleaching chemical pulps comprising an ozonation phase followed by an alkaline extraction phase, preferably with sodium hydroxide, ZE, which is less degrading for cellulose. . It has been unexpectedly shown that when the E phase is carried out in the presence of small amounts of magnesium cations, the ZE process results in pastes whose degree of polymerization of the cellulose is increased significantly.
• the dough can undergo a hot acid treatment as described above, with the aim of at least partially removing the hexenuronic acids which constitute an annoying impurity in the pasta Hardwood kraft chemicals, as they consume bleaching reagents and impair whiteness stability of the dough.
• the paste is advantageously washed to remove the products of degradation of hexenuronic acids.
• alkaline extraction it is by definition at basic pH (greater than 7), in the presence of a base.
• a base is a strong base, even more preferably soda or sodium hydroxide (NaOH).
• Soda can be accompanied by another base of the same strength, such as sodium sulphide. This latter possibility may be advantageous in a kraft plant since the cooking reagent is a mixture of sodium hydroxide and sodium sulphide.
• magnesium salt any compound capable of releasing Mg ++ cations, such as, for example, magnesium sulfate (MgSO 4 ), magnesium carbonate (MgCO 3 ), magnesium hydroxide (Mg (OH ) 2 ), magnesium oxide (MgO or magnesia), magnesium gluconate (C 12 H 22 MgO 14 ). Mixtures of these salts can be used.
• the term "low amounts of magnesium ions" a mass proportion between 0.01 and 0.5%, preferably between 0.02 and 0.1%.
• the alkalinity of the E stage is advantageously related to the presence of the strong base, advantageously NaOH. which implies that the Mg ++ cations constitute an additive added in a small quantity.
• these magnesium ions are added to the paste in the form of magnesium salts, advantageously by dissolving its salts in an aqueous solution, optionally water, having an acidic or neutral pH.
• aqueous solution optionally water, having an acidic or neutral pH.
• Such a solution can be prepared extemporaneously and added to the dough.
• the magnesium salt may be added directly to said solution.
• magnesium salts are also conventional in treatments of the chemical paper pulp with hydrogen peroxide or hydrogen peroxide in an alkaline medium ( The Ljugberg Textbook, Pulp Technology, Swiss KTH Editor, 2004, Chapter 27 page 25 ). More generally, it is well known that magnesium salts are stabilizing agents of hydrogen peroxide.
• the alkaline extraction step takes place in the presence of magnesium ions but in the absence of oxygen and / or hydrogen peroxide.
• the alkaline extraction step implemented in the context of the invention, there is no addition of oxygen or hydrogen peroxide.
• the alkaline extraction according to the invention is linked to the passage to an alkaline pH and not to the action of an oxidizing agent, in particular oxygen and / or hydrogen peroxide.
• the alkaline extraction is carried out in the presence of magnesium ions, advantageously a magnesium salt, but also in the presence of a strong alkaline agent, advantageously sodium hydroxide (NaOH) or a mixture of soda and sodium sulphide.
• a strong alkaline agent advantageously sodium hydroxide (NaOH) or a mixture of soda and sodium sulphide.
• the magnesium ions advantageously in the form of magnesium salts, are present in small amounts, preferably in a mass proportion of greater than or equal to 0.01%, or even greater than or equal to 0.02% and less than or equal to 0.5%, or even less than or equal to 0.1%, incompatible with an alkaline agent function.
• the dough can undergo other stages of bleaching to achieve the purity and whiteness required, including advantageously employing hydrogen peroxide.
• Magnesium cations are advantageously present in each of the extraction phases E of such a process. To ensure this, it is preferable to introduce each time according to the procedure described above, for example for the first phase E and then for the second phase E in the case of two stages ZE according to the invention.
• the advantage of the invention lies in the fact that the ZE process, in its various embodiments according to the invention, leads to a pulp whose cellulose is less depolymerized than after an unmodified ZE process (in the absence of magnesium ions).
• the degree of polymerization of the cellulose is for example measured by viscometry according to the ISO standard No. 5351/1-1981.
• the object of a ZE process applied to a chemical pulp is to reduce its residual lignin content, which is responsible for its coloration, and therefore to increase its whiteness. It is important to note that the ZE process according to the invention makes it possible, with equal performance of delignification and increase of whiteness, to obtain a paste of better degree of polymerization than after an unmodified ZE process.
• the pulp is then treated with ozone (Z) with a high consistency (40%) at 25 ° C, with a quantity of ozone corresponding to 0.6% of the weight of the dough counted in dryness at pH 2.5 during the time necessary for the introduction of the ozone (which reacts instantly), approximately 3 minutes.
• ozone (Z) with a high consistency (40%) at 25 ° C, with a quantity of ozone corresponding to 0.6% of the weight of the dough counted in dryness at pH 2.5 during the time necessary for the introduction of the ozone (which reacts instantly), approximately 3 minutes.
• the paste is thoroughly washed with pure water and then treated with sodium hydroxide (E) at 10% consistency, with a quantity of sodium hydroxide of 2% relative to the paste, at 70 ° C for 1 hour.
• the pH of the dough is then greater than 11.
• Example 2 The same sequence as that described in Example 1 is repeated, but this time by adding 0.3% by weight of MgSO 4 7H 2 O (ie approximately 0.03% of Mg) relative to the weight of dough counted in dry, after washing and before adding soda, that is to say at a time when the pH of the dough is not yet alkaline.
• 0.3% by weight of MgSO 4 7H 2 O ie approximately 0.03% of Mg
• the same paste as in Example 1, already treated OO is first treated with acidolysis (treatment A) at pH 3, for 3 hours at 90 ° C., and in the presence of EDTA, a conventional sequestering agent for the transition metal cations, so as to remove a part of the hexenuronic acids present.
• treatment A acidolysis
• EDTA a conventional sequestering agent for the transition metal cations
• the dough thus prepared undergoes the ZE treatment under the conventional conditions of Example 1, that is to say in particular with 0.6% of ozone by weight relative to the weight of dough counted in dry.
• the pulp of Example 1 is treated with ozone as indicated in Example 1, then without transition, the consistency of the pulp is reduced to 10% by the solution of sodium hydroxide and the alkaline extraction (E) is continued under the conditions of Example 1.

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• Wood Science & Technology (AREA)
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• General Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
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