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
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/1005—Pretreatment of the pulp, e.g. degassing the pulp
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
  • D21B1/00—Fibrous raw materials or their mechanical treatment
  • D21B1/02—Pretreatment of the raw materials by chemical or physical means
  • D21B1/021—Pretreatment of the raw materials by chemical or physical means by chemical means
• • 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
  • D21C9/16—Bleaching ; Apparatus therefor with per compounds
  • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

• the present invention relates to a process for the production of high-yield, bleached paper pulps having good mechanical characteristics, particularly chemo-mechanical and chemo-thermal pulps.
• the wood chips are subjected to separate or associated actions of mechanical, chemical or thermal origin.
• Chemical pulps are obtained by chemical defibration of wood. Their yield is generally less than 50%.
• yield is meant the weight of dough in the dry state relative to the weight of starting material in the dry state.
• Mechanical type pulps, or high yield pulps are produced by mechanical defibration of wood chips, for example in a grindstone shredder or a disc shredder or refiner.
• the yield is generally greater than 85%.
• the mechanical characteristics, in particular the resistance to rupture, tearing and bursting, are poor.
• thermomechanical doughs TMP
• TMP thermomechanical doughs
• the wood chips were also treated with a sodium sulfite solution at acidic or basic pH depending on the nature of the wood.
• the pulps obtained also called chemical-mechanical pulps, have good mechanical characteristics.
• CMP chemothermal-mechanical pastes
• CTMP pastes are mechanical resistance and that the yield generally remains greater than 85% and, more often than not, at least equal to approximately 90% and therefore similar to that of purely mechanical origins.
• patent EP-A-239 583 describes a process in which the wood chips, before defibration, undergo three successive treatments, a treatment with a solution of agent complexing metal ions, a treatment with a solution of a stabilizing agent of hydrogen peroxide, such as sodium silicate and magnesium salts, and treatment with an alkaline solution of peroxide.
• the treatment, before defibration, with hydrogen peroxide, without treatment with sulphites also makes it possible to improve the mechanical strengths, but the properties are not yet high enough, in particular in the case of softwood.
• the subject of the present invention is therefore a process which makes it possible to obtain, after defibering, high-yielding pastes having both high mechanical properties (resistance to breakage, tearing, bursting), and a high degree whiteness, particularly above 80 ° ISO for softwoods, making them suitable for use in the manufacture of paper with a high whiteness level.
• an additional step of impregnating the chips with a solution containing a complexing or sequestering agent of metal ions can be provided before step (d), for example by using an aqueous solution at 40% of DTPA (sodium salt diethylenetriamine pentaacetic acid).
• DTPA sodium salt diethylenetriamine pentaacetic acid
• Lignocellulosic materials which can be treated by the process according to the invention include softwoods, such as fir, pine, spruce, etc., hardwoods, such as poplar, wood from eucalyptus, etc ... in the form of chips, as they are usually used in the pulp industry.
• softwoods such as fir, pine, spruce, etc.
• hardwoods such as poplar, wood from eucalyptus, etc ... in the form of chips, as they are usually used in the pulp industry.
• these chips are first treated with a solution of one or more reducing agents (step a). This treatment is done by impregnating the chips with the solution.
• the usual means of the paper industry can be used.
• these, previously softened by wetting and / or steaming with water vapor are compressed by means of a screw press, to remove a part of the gases and / or liquid present in the shavings.
• the chips are impregnated with the reducing solution.
• the PREX system from SUNDS-DEFIBRATOR
• the IMPRESSAFINER system from BAUER
• the HYMAC conical screw press and all the devices for obtaining one or more several com chip pressures and expansions in the presence of the impregnating solution with, preferably, the highest possible compression ratio.
• the expansion of the chips must be carried out in the presence of the smallest possible amount of solution with which the chips must be impregnated.
• the reducing solution used in the process according to the invention, contains one or more reducing agents which can be chosen from sulfite or bisulfite of alkali metal or a mixture of sulfur dioxide and an alkaline agent like hydroxide of sodium. It is also possible to use sodium borohydride (NaBH 4 ) pure or in alkaline solution.
• reducing agents which can be chosen from sulfite or bisulfite of alkali metal or a mixture of sulfur dioxide and an alkaline agent like hydroxide of sodium. It is also possible to use sodium borohydride (NaBH 4 ) pure or in alkaline solution.
• the reducing agent is chosen from alkali sulfites, such as sodium sulfite, sodium borohydride in alkaline solution, such as the product BOROL R , sold by the company MORTON International and comprising 12% by weight of sodium borohydride and 40% by weight of sodium hydroxide, the mixtures of sodium sulfite and alkaline solution of sodium borohydride BOROL R.
• alkali sulfites such as sodium sulfite, sodium borohydride in alkaline solution, such as the product BOROL R , sold by the company MORTON International and comprising 12% by weight of sodium borohydride and 40% by weight of sodium hydroxide, the mixtures of sodium sulfite and alkaline solution of sodium borohydride BOROL R.
• the reducing agent is used in an amount of 0.1 to 10% by weight relative to the weight of the chips in the dry state and, more particularly, in an amount of 0.5 to 6% for sodium sulfite, from 0 , 5 to 1.5% for the alkaline sodium borohydride solution BOROL R.
• the pH of the reducing solution is between a value greater than 7 and 13 depending on the nature of the lignocellulosic material of the shavings and, preferably, the pH is between 11 and 12.8 for the hardwood and between 9.5 and 11 for softwood.
• An alkaline agent such as NaOH, KOH, Na 2 CO 3 , K 2 CO 3 , MgO, CaO can be added, if necessary, to bring the pH of the reducing solution to the desired value.
• a complexing or chelating agent for metal ions can be added to the reducing solution.
• This agent can be, for example, sodium tripolyphosphate, sodium tetrapyrophosphate, sodium salts of nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriamine pentaacetic acid.
• the sodium salt of diethylenetriamine pentaacetic acid (DTPA) is preferably used in the form of a 40% aqueous solution, preferably in an amount of 0.2 to 0.5% of this solution.
• the temperature of the reducing solution during the impregnation can be between 10 and 100 ° C. depending on the stability of the reducing agent, a high temperature favoring the impregnation speed and a low temperature favoring the good conservation of the reducing properties of the solution.
• a temperature of 20 to 60 ° C is preferred and, in particular, a temperature of 20 to 40 ° C for the reducing solutions obtained by mixing Na 2 SO 3 and alkaline sodium borohydride solution BOROL R .
• the chips immediately after impregnation with the reducing solution, are heated to a temperature of 60 to 160 ° C and preferably from 75 to 120 ° C (step b).
• the duration of the heating depends on the temperature and the nature of the wood and varies from 1 minute to 3 hours.
• the preferred duration is 15 to 60 min at 90 ° C and 5 to 30 min at 120 ° C.
• the impregnated chips are transported and heated away from oxygen in the air, for example using an atmosphere of water vapor or an inert gas such as nitrogen or anhydride carbonic.
• the chips are subjected to this pressing because the efficiency of the process increases with the elimination of this solution. It is particularly desirable that at least 20% of the reducing solution is removed.
• the reducing solution can be removed in one or more pressing steps. You can also, after pressing, rinse the shavings with water.
• Pressing can be done at a temperature between 20 and 160 ° C.
• step (a) It is possible to recycle all or part of the reducing solution extracted during the pressing step to prepare the reducing solution useful in step (a).
• the chips after impregnation with the solution of reducing agent (s) and after pressing, are treated by impregnation (step d) with an alkaline solution of hydrogen peroxide.
• the oxidizing agent, hydrogen peroxide is used in an amount of 0.1 to 10% by weight relative to the weight of chips in the dry state to be treated, depending on the degree of whiteness sought; in general, the amount of hydrogen peroxide is between 1 and 5% by weight. More than 5% by weight is not generally used for economic reasons.
• alkaline agents such as NaOH, KOH, Na 2 CO 3 , K 2 CO 3 , MgO, CaO etc. are added to the H 2 O 2 solution so that the initial pH of this solution is understood between 8 and 12.5.
• the preferred agent is NaOH.
• the optimum amount of alkaline agent depends on the nature of the wood and is proportional to the amount of H 2 O 2 . This amount, expressed as NaOH, can vary from 0.5% to 10% and preferably from 0.5 to 6% by weight relative to the weight of chips in the dry state to be treated.
• One or more stabilizers of hydrogen peroxide in an alkaline medium can be added to the alkaline solution of H 2 O 2 to reduce the decomposition of this solution and thus increase the efficiency of the treatment.
• metal ions such as, for example, diethylenetriaminepentaacetic and ethylenediaminetetraacetic acids in the form of sodium salts. They are used in an amount of 0.1 to 1% by weight relative to the weight of chips in the dry state to be treated.
• the temperature of the alkaline solution of hydrogen peroxide during the impregnation is between 10 and 80 ° C and, preferably, at a temperature not exceeding 40 ° C to reduce the decomposition of the peroxide.
• the shavings are heated, during a step (e), to a temperature between 50 ° C. and 120 ° C. and preferably between 60 and 80 ° C for a period of 10 minutes to 5 hours depending on the nature of the wood, the temperature and the amount of hydrogen peroxide.
• the duration can reach 5 hours at 60 ° C, it is 2 to 3 hours at 70 ° C and 1 to 2 hours at 90 ° C.
• Heating is generally provided by steam in a saturated atmosphere.
• the chips are defibrated or refined, by passing through one or more refiners at atmospheric pressure or under the pressure of a few bars of water vapor.
• refining is carried out with two stages of refining, the first stage being under pressure and the second atmospheric.
• the refining conditions depend on the characteristics required for the pulp.
• Refined pulp is generally neutralized by an acid to remove the alkalinity resulting from treatment with the alkaline solution of hydrogen peroxide.
• This neutralization is preferably carried out up to a pH of 5.5 to 6 using dilute sulfuric acid or alternatively SO 2 gas.
• the dough is then treated in the usual way (purification, classification, recycling of refusals, etc.).
• the amounts of reagents are expressed as a percentage by weight relative to the wood chips in the dry state.
• softwood (fir) or hardwood (poplar) wood chips are used.
• the shavings were taken from an industrial mechanical pulp manufacturing facility and meet industry standards.
• sheets of paper are produced with this pulp to measure the whiteness and the mechanical characteristics, according to ISO standards of the paper industry.
• the commercial sodium borohydride solution used comes from the company MORTON International and contains 12% NaBH 4 and 40% NaOH; it is designated under the name of BOROL R.
• the metal ion complexing agent used in the examples is DTPA (sodium salt of diethylenetriamine pentaacetic acid) in the form of a 40% aqueous solution.
• Softwood shavings (fir, spruce) are washed and steamed with water. These shavings are impregnated continuously with a reducing solution at 20 ° C. comprising 5.9% of sodium sulfite, 0.5% of DTPA solution at 40% and 1.5% of sodium borohydride solution BOROL R , the solution having a pH of 10.5.
• the chips are heated at 60 ° C for 30 min.
• the shavings are pressed at 60 ° C. to remove approximately 0.5 l of reducing solution per kg of (dry) shavings (ie approximately 50% removal). Rinse with 2 l of water per kg of dry chips.
• the chips are impregnated, continuously, with an oxidizing solution at 20 ° C., comprising 5% of hydrogen peroxide, 2% of sodium hydroxide, 4% of solution with 40% of sodium silicate and 0.5 % 40% DTPA solution.
• the oxidizing solution has a pH of 11.5.
• the impregnated chips are then heated at 90 ° C for 1 hour, then refined in a double disc refiner.
• the dough is then classified and the refusals are returned to the refiner.
• the refined dough has a drip index of 70 ° SR.
• the method according to the invention which comprises treatment with a reducing solution containing sodium sulfite and sodium borohydride and treatment with hydrogen peroxide makes it possible to obtain a pulp from softwood which, after defibration, has a high degree of whiteness, greater than 80 ° ISO.
• Example 2 The procedure is as for Example 1, but the duration of heating to 90 ° C. after impregnation with the oxidizing solution is 2 hours instead of 1 hour.
• a paste is obtained having the same mechanical characteristics and a whiteness of 83 ° ISO.
• Example 2 The procedure is as for Example 1, except that the reducing solution is composed of 5.9% Na 2 SO 3 and 0.5% of 40% DTPA solution and has a pH of 9.6 .
• a paste is obtained having the following characteristics: ISO whiteness 80 ° ISO Tear resistant : Break length 4400 m Burst resistance 2.2 KPa m 2 / g Tear resistance 5.4 mN m 2 / g.
• the procedure is as in Example 1, but the chips are not treated with a reducing solution.
• the first treatment consists of impregnating the chips with a solution containing only 0.5% of 40% DTPA solution.
• a paste is obtained having the following characteristics: ISO whiteness 78 ° ISO Tear resistant : Break length 3200 m Burst resistance 1.6 KPa m 2 / g Tear resistance 5.2 mN m 2 / g.
• Hardwood shavings (poplar, aspen), washed and steamed, are continuously impregnated with a reducing solution at 20 ° C, consisting of 5% Na 2 SO 3 , 1.5% sodium borohydride solution (BOROL R ) and 0.5% 40% DTPA solution and having a pH of 11.5.
• a reducing solution consisting of 5% Na 2 SO 3 , 1.5% sodium borohydride solution (BOROL R ) and 0.5% 40% DTPA solution and having a pH of 11.5.
• the impregnated shavings are heated at 100 ° C. for 30 min under an atmosphere of steam.
• the chips are then pressed at 60 ° C to remove more than 50% of reducing solution. Rinse with 2 1 of water per kg of dry chips.
• the shavings are then impregnated with an oxidizing solution at 20 ° C. comprising 5.2% of hydrogen peroxide, 4% of sodium hydroxide, 4% of solution with 40% of sodium silicate and 0.5% of solution at 40% DTPA, and having a pH of 11.4.
• the chips are then heated at 90 ° C for 2 hours and refined in a double disc refiner at atmospheric pressure.
• the refined dough After classification, the refined dough has a drip index of 56 ° SR.
• the characteristics of this paste are as follows: ISO whiteness 87 ° ISO Tear resistant : Break length 3300 m Burst resistance 1.3 KPa m 2 / g Tear resistance 3.5 mN m 2 / g.
• hardwood shavings are treated which are relatively white.
• the method according to the invention makes it possible to obtain a paste, after defibering, the degree of white of which is very high.
• Example 5 The procedure is as for Example 5, but the reducing solution is composed of 5% Na 2 SO 3 and 0.5% of solution 40% DTPA and has a pH of 11.
• the dough obtained has the following characteristics: ISO whiteness 85.2 ° ISO Tear resistant : Break length 2900 m Burst resistance 1.20 KPa m 2 / g Tear resistance 3.1 mN m 2 / g.
• Example 5 The procedure is as in Example 5, but no reducing agent is added to the first treatment: the first impregnation is carried out with a solution containing only 0.5% of 40% DTPA solution.
• the dough obtained has the following characteristics: ISO whiteness 84 ° ISO Tear resistant : Break length 2300 m Burst resistance 0.9 KPa m 2 / g Tear resistance 2.9 mN m 2 / g.
• Hardwood (poplar) shavings are washed and dried at 90 ° C. They are impregnated, continuously, with a reducing solution at 20 ° C consisting of 1% sodium borohydride solution (BOROL R ) and 0.5% of 40% DTPA solution.
• the solution has a pH of 12.7.
• the chips are heated at 90 ° C for 15 min.
• the chips are pressed at a temperature of 60 ° C to eliminate approximately 0.5 l of reducing solution per kg of dry shavings (i.e. approximately 20% of reducing solution eliminated).
• the chips are then impregnated with an oxidizing solution at 20 ° C. comprising 4.25% of hydrogen peroxide and 3.8% of sodium hydroxide.
• the solution has a pH of 10.5.
• the shavings impregnated with oxidizing solution are heated at 85 ° C for 1 h. It is refined in a first double disc refiner at atmospheric pressure, then in a second single disc refiner also at atmospheric pressure.
• the refined paste after neutralization at pH 6 with SO 2 , has a drainage index of 62 ° SR and has the following characteristics: ISO whiteness 80.9 ° ISO Tear resistant : Break length 2800 m Burst resistance 1.25 KPa m 2 / g
• Example 8 The procedure is exactly as for Example 8, but a reducing solution composed of 1% Na 2 SO 3 , 1% sodium borohydride solution (BOROL R ) and 0.5% 40% DTPA solution is used. .
• the dough obtained has a drip index of 68 ° SR and has the following characteristics: ISO whiteness 81.1 ° ISO Tear resistant : Break length 3100 m Burst resistance 1.36 KPa m 2 / g
• Example 8 The procedure is exactly as for Example 8, but a reducing solution composed of 2% Na 2 SO 3 , 1% sodium borohydride solution (BOROL R ) and 0.5% 40% DTPA solution is used. .
• the dough obtained has a drip index of 65 ° SR and has the following characteristics: ISO whiteness 81.7 ° ISO Tear resistant : Break length 3320 m Burst resistance 1.38 KPa m 2 / g
• the procedure is as in Example 8, but without adding a reducing agent to the first treatment: the first impregnation is carried out with a solution composed only of 0.5% of 40% DTPA solution.
• the dough obtained has a drip index of 6 6 ° SR and has the following characteristics: ISO whiteness 79.8 ° ISO Tear resistant : Break length 2900 m Burst resistance 1.21 KPa m 2 / g
• Examples 8 to 11 hardwood (poplar) shavings with a lower initial whiteness are used than in Examples 5 to 7.
• the whiteness of the final pulp is therefore lower than that obtained in Examples 5 to 7 , but again, it can be seen that the treatment of the wood chips by a reducing treatment, then by an oxidizing treatment, makes it possible to obtain, after defibering the wood, a paste of very high level of whiteness and having reinforced mechanical characteristics. .

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• Engineering & Computer Science (AREA)
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• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
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• 1991
  • 1991-04-17 FR FR9104737A patent/FR2675518B1/fr not_active Expired - Fee Related
• 1992
  • 1992-04-06 NO NO921335A patent/NO300225B1/no not_active IP Right Cessation
  • 1992-04-13 IE IE921176A patent/IE75202B1/en not_active IP Right Cessation
  • 1992-04-14 AU AU14897/92A patent/AU650962B2/en not_active Ceased
  • 1992-04-14 DE DE69212051T patent/DE69212051T2/de not_active Expired - Fee Related
  • 1992-04-14 JP JP4120093A patent/JP2588495B2/ja not_active Expired - Lifetime
  • 1992-04-14 ES ES92401044T patent/ES2089436T3/es not_active Expired - Lifetime
  • 1992-04-14 EP EP92401044A patent/EP0509905B1/fr not_active Expired - Lifetime
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