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
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/22—Other features of pulping processes
  • D21C3/222—Use of compounds accelerating the pulping processes

Definitions

• the present invention relates to a process for the manufacture of chemothermal mechanical pulps and more particularly of chemothermal mechanical pulps having a high ability to be bleached using hydrogen peroxide in an alkaline aqueous medium.
• cellulosic material like wood in the form of chips, is subjected to separate or associated actions of mechanical, chemical or thermal origin.
• Mechanical type pulps or high yield pulps are produced by mechanical defibration of the lignocellulosic material, for example in a grindstone shredder or a disc shredder or refiner.
• the chemothermal-mechanical pastes whose manufacture is covered by the invention, designated in all that follows by CTMP pastes, are obtained by adding to the above process a non-destructive cooking of material carried out at a temperature equal to or greater than 100 ° C. under pressure saturated water vapor in the presence of sodium sulfite, or sodium bisulfite or more generally a mixture of sulfur dioxide SO2 and sodium hydroxide NaOH, indistinctly referred to in all that follows by sulfite, unless otherwise specified .
• CTMP pastes are of definite interest for the industry because they achieve a valid compromise between mechanical and chemical pulps themselves.
• the yield of CTMP pulp, weight of pulp in the dry state relative to the weight of starting material in the dry state is generally greater than 85% and most often at least equal to about 90%, this which makes them very close to the pastes of purely mechanical origin and which is translated here by the expression non-destructive cooking of the material.
• the present invention aims to obtain CTMP pastes which bleaching using hydrogen peroxide brings, except in special cases of interest understandable by those skilled in the art, to a degree of white generally greater than 80%, or 80 °, when it is measured in the usual way today at the wavelength of 457 nm with magnesium oxide as standard of reference using the spectrophotometer of the General Electric or Elrepho type.
• the French patent published under the number 1150451 recommends baking at a temperature of up to 150 ° C., using sulfite and hydrosulfite, in an acid medium. Any bleaching of the defibrated pulp would be facilitated, but no details are provided in this regard.
• the invention is first of all a process for manufacturing CTMP pastes in which sodium sulfite or sodium bisulfite or a mixture of sulfur dioxide and sodium hydroxide are involved, and a reducing agent which is more electronegative than ion.
• sulfite which consists in adding to a mechanical defibration of the cellulosic material a non-destructive cooking of said material at a temperature equal to or greater than 100 ° C.
• the reducing agent is most often chosen from thiourea dioxide or formamidinesulfinic acid, sodium borohydride and sodium hydrosulfite or sodium dithionite.
• the amount of reducing agent used can vary depending on the nature thereof. It is generally between 0.1 and 5% in the case of thiourea dioxide or dithionite. This quantity, like any quantity in all that follows, is expressed in percent by weight relative to the weight of lignocellulosic material in the dry state, unless indicated or evident.
• Sodium borohydride is used in an amount of about 0.01% to 0.5%.
• This reducing agent is conveniently used in the form of an aqueous solution such as for example the solution containing 12% by weight of sodium borohydride marketed under the name of BOROL® by the company VENTRON Corporation.
• the cooking temperature according to the invention can reach 200 ° C. It is most frequently chosen between around 120 ° C and 160 ° C.
• the pressure is practically equal to that corresponding to the pressure of the steam at the cooking temperature.
• the amount of molecular oxygen, such as oxygen in the air, especially that included in the lignocellulosic material must obviously be minimized. This is carried out in a known manner for example using steam or by compression as indicated inter alia the already cited work of James P. CASEY, p 213, which further describes, p 219 - 229 , equipment, in particular pressure resistant, suitable for the production of CTMP pastes.
• the committed amount of sulphite is that usually used in processes which do not incorporate the invention and which are known to be suitable for the preparation of CTMP pastes. It is therefore between approximately 0.1% and 10%, most often between 1% and 6% by expressing it in SO2.
• the cooking according to the invention can be carried out before, during or after a defibering or mechanical refining action.
• cooking according to the invention of the starting lignocellulosic material can precede a mechanical defibration which continues the action started or which is carried out at low temperature at atmospheric pressure.
• wood shavings can be impregnated in a known manner when cold using an aqueous solution of the reagents necessary for carrying out the invention, then cooked according to the invention and finally defibrated as indicated in the preceding paragraph.
• cooking according to the invention begins in the mechanical defibrator or refiner which is fed by the starting lignocellulosic material, for example wood shavings, or said material already formed in the form of a paste by defibration, to be completed at- beyond if necessary.
• starting lignocellulosic material for example wood shavings, or said material already formed in the form of a paste by defibration
• the cooking according to the invention can be applied to a paste after defibering-refining of the starting lignocellulosic material, for example wood chips.
• the consistency, percentage by weight of lignocellulosic material counted in the dry state in the medium, is not a critical factor for the implementation of the invention. In practice, and depending on the methods of execution adopted, it is between approximately 5% and 50%, in general between 5% and 25% in the case of a material already defibrated.
• the duration of the cooking according to the invention depends on the other performance parameters including the type of equipment used. It usually does not exceed approximately 1 hour and is generally between a few tens of seconds and 30 minutes.
• the invention is also the bleaching of the pulp produced as described just above, which comprises washing said pulp in order to remove therefrom the sulphite ions and the reducing agent and the action on this washed pulp of peroxide. hydrogen in an alkaline aqueous medium.
• Washing is carried out in a known manner, for example in a repeated or non-repeated sequence of diluting the dough with water and reconcentrating the dough by pressing or filtration.
• Bleaching is for example carried out by using an amount of hydrogen peroxide of between approximately 0.5% and 10%, preferably between 2% and 6%, in the presence of approximately 1% to 6% of a solution of sodium silicate of density 1.33, at pH between about 9 and 11, at a temperature between 40 ° C and 100 ° C for about 0.5 hour to 2 hours, with a consistency between 10% and 30% .
• the bleaching solution may contain additives such as essentially one or more complexing or sequestering agents such as, for example, diethylenetriaminepentaacetic and ethylenediaminetetraacetic acids in the form of sodium salts in an amount generally between approximately 0.1% and 1%.
• the pulp to be bleached can also be subjected before bleaching to a treatment with, in kind and in quantity, the complexing or sequestering agents as above, at a temperature between 20 ° C and 100 ° C, preferably between 50 ° C and 100 ° C, preferably between 50 ° C and 95 ° C so as not to have to work under pressure while keeping a sufficiently rapid complexing or sequestration rate, at a consistency of between approximately 5% and 30% during periods of time can vary between about 5 minutes and 2 hours, and preferably followed by washing, for example by pressing.
• the cooking according to the invention can itself be preceded by a treatment of the lignocellulosic material using a complexing or sequestering agent, of the type described above.
• the consistency can then be between approximately 5% and 50% without generally being greater than approximately 25% to 30% when the treated material has previously been subjected to a mechanical defibration action.
• Such treatment contributes to further increasing the intrinsic effect of the invention on the degree of white after bleaching and on the action efficiency of hydrogen peroxide.
• the quantities are expressed in percent by weight relative to the lignocellulosic matter in the dry state, unless specified or evident, - when, before cooking, a treatment is applied using a complexing or sequestering agent, designated by sequestering treatment, it is carried out, unless otherwise specified, at 90 ° C for 15 minutes, at a consistency of 10%, at using 0.5% of an aqueous solution at 40% by weight of sodium salt of diethylenetriaminepentaacetic acid, designated by DTPA the initial pH of the cooking medium according to and, where appropriate, that of the aqueous impregnation solution containing the sulphite and the reducing agent, is between 7 and 12.5, - sodium borohydride is applied in the form of BOROL® and the quantity indicated is that of this presentation, - by silicate is designated an aqueous sodium dilicate solution with a density equal to 1.33, - the degree of white is measured (457 nm) using the ELREPHO type spectrophotometer
• Defibrated softwood shavings with a white degree of 53.7% are autoclaved under saturated steam pressure at 120 ° C for 0.5 hours at a consistency of 20% , in the presence, jointly, of 5.9% of sodium sulfite Na2SO3, 2.5% of sodium hydrosulfite and of 2% of sodium hydroxide.
• CTMP paste obtained is then bleached at 90 ° C for 2 hours, at a consistency of 20%, using 5% hydrogen peroxide H2O2, 2% sodium hydroxide, 4% silicate and 0.5 % of DTPA.
• the degree of white thus obtained is equal to 82.8%.
• Example 1 The same starting lignocellulosic material as in Example 1 is subjected to the sequestering treatment and then to washing with water. It is then treated as in Example 1.
• the degree of white finally obtained is 83.3% when the cooking before blanching involves the joint action of the hydrosulfite with the sulfite. It is only 81% by adopting the cooking conditions defined for comparison in Example 1 with in addition a consumption of H2O2 being multiplied by 1.12.
• Example 2 is repeated in the case of the joint action of hydrosulfite with sulfite but with a cooking temperature of 140 ° C instead of 120 ° C.
• the degree of whiteness thus achieved is always high and equal to 82.6%.
• the lignocellulosic starting material of Example 1 is successively subjected to the sequestering treatment, to washing with water, to baking carried out under saturated steam pressure at 120 ° for 0.5 hour, the consistency being 20%, in the presence, jointly, of 1.5% of BOROL® and of 5.9% of sodium sulfite, finally to a washing with water to remove the sulfite and the reducing agent.
• the CTMP paste obtained is then bleached as after the joint action of the hydrosulfite with the sulfite in Example 1.
• the degree of white achieved then is equal to 84.5%.
• Example 4 is modified in that the amount of BOROL® goes from 1.5% to 1% and in that the sodium bisulfite, used at the rate of 5%, replaces the sodium sulfite.
• the CTMP paste obtained is bleached as after the joint action of the hydrosulfite with the sulfite in Example 1.
• the degree of white achieved after bleaching is equal to 82.7%.
• Example 5 is repeated but with 3% of BOROL® instead of 1%. The degree of white is then equal to 83.8%.
• the degree of whiteness is no longer equal to only 77%, yet engaging 5.4% of H2O2, and the rupture length only to 3,290 m.
• the starting chips have, after defibering-refining in the absence of any chemical reagent, a degree of whiteness equal to 55.5% and a rupture length equal to 2,755 m.
• the CTMP pulp bleached as in Example 7 but using only 4.7% of H2O2 has a degree of whiteness equal to 78.5% and a breaking length of 3,525 m.
• Example 2 The same starting lignocellulosic material as in Example 1 is subjected to the sequestering treatment and then to washing with water. It is then subjected to cooking according to the invention at 120 ° C. for 0.5 h, at a consistency of 20%, in the joint presence of 1% of thiourea dioxide and 5.9% of sodium sulfite.
• Cooking is followed by washing with water to remove the sulfite ions and the reducing agent.
• the washed paste obtained is then bleached as after the joint action of the hydrosulfite with the sulfite in Example 1, at 90 ° C for 2 hours, at a consistency of 20%, using 5% H deO2, 2% d sodium hydroxide, 4% silicate and 0.5% DTPA.
• the degree of white thus obtained is equal to 83.5%.
• Defibrated hardwood shavings with a whiteness level of 59.9% are subjected to autoclaving under saturated steam pressure at 120 ° C for 0.5 hours at a consistency of 20% , in the presence, jointly, of 1.5% of BOROL® and 5.9% of sodium sulfite, followed by washing with water to remove the sulfite and the reducing agent.
• the washed paste obtained is then bleached at 90 ° C for 2 hours, at a consistency of 20%, using 5% H2O2, 4% silicate and 0.5% DTPA.
• the degree of white achieved is equal to 86.6%.
• 250 kg / h of defibered softwood chips are treated by impregnation with 0.5% DTPA at 90 ° C at a consistency of 20%, washed with diluted water tions and successive pressings, then subjected to cooking under saturated steam pressure at 120 ° C. during the stay of a duration of approximately 30 seconds in a mechanical defibrator at a consistency of 28% by joint action of 1, 5% BOROL® and 3% SO2 in a mixture of pH 8.4 with sodium hydroxide, extending at 100 ° C for 30 minutes.
• the dough washed with water after cooking by successive dilutions and pressings to remove the sulfite ions and the reducing agent, is finally bleached at 80 ° C for 2 hours at a consistency of 26.5% using 5.2% of H2O2, 2% NaOH, 4% silicate and 0.5% DTPA.
• the whiteness of the bleached washed pulp is 83.6%.
• the degree of whiteness of the bleached dough is only 80.1% by consuming 1.05 times more H2O2.
• Example 11 The procedure is as in Example 11, but starting from hardwood chips and cooking under saturated steam pressure with, together with BOROL®, 2.45% SO2 in a mixture of pH 11.5 with sodium hydroxide.
• the degree of white in the bleached pulp obtained is equal to 87.3%, the length of the break, in meters, equal to 3,235, and the tear index to 352.
• the degree of white is only 86%, the breaking length, in meters, is only 2,885 m and the tear index 310 , with identical degree of refinement.
• Example 4 is repeated on defibred softwood shavings with a degree of white equal to 62% except that the sequestering treatment is not carried out before cooking but that the latter is carried out in the presence, in addition to sulfite and BOROL ®, 0.5% DTPA.
• the degree of white of the bleached pulp obtained is equal to 86% while it is only 84% by operating as above but without using BOROL®.
• coniferous wood shavings are impregnated, by immersion and draining, simultaneously with 3% sodium sulfite, 3% sodium bisulfite, 1.5% BOROL®, 0.5 % of DTPA and are autoclaved under saturated steam pressure for 4 minutes at 190 ° C before undergoing mechanical defibration by sudden ejection from the autoclave through a die and refining in a disc refiner.
• the dough thus obtained is bleached, after washing to remove the sulphite and, at 90 ° C for 2 hours at a consistency of 20% using 5% H2O2, 2% sodium hydroxide, 4% silicate and 0 , 5% DTPA.
• the degree of whiteness of the paste thus finally obtained is equal to 71% while the refined starting chips had only a degree of whiteness equal to 56%.
• the invention makes it possible not only to manufacture CTMP bleached pulps of high white level from both softwood and hardwood with reduced consumption of H2O2 but also to conserve and even improve the mechanical properties of the pulps. usual bleached.

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• 1987
  • 1987-05-25 FR FR8707552A patent/FR2615874B1/fr not_active Expired - Lifetime
• 1988
  • 1988-05-17 DE DE198888420160T patent/DE293309T1/de active Pending
  • 1988-05-17 DE DE8888420160T patent/DE3861982D1/de not_active Expired - Fee Related
  • 1988-05-17 EP EP88420160A patent/EP0293309B1/de not_active Expired - Lifetime
  • 1988-05-17 ES ES88420160T patent/ES2004855B3/es not_active Expired - Lifetime
  • 1988-05-17 AT AT88420160T patent/ATE61639T1/de not_active IP Right Cessation
  • 1988-05-23 NZ NZ224749A patent/NZ224749A/xx unknown
  • 1988-05-24 CA CA000567547A patent/CA1310452C/fr not_active Expired - Lifetime
  • 1988-05-24 FI FI882448A patent/FI93746C/fi not_active IP Right Cessation
  • 1988-05-24 NO NO882263A patent/NO171801C/no not_active IP Right Cessation
  • 1988-05-24 PT PT87569A patent/PT87569B/pt not_active IP Right Cessation
  • 1988-05-25 AU AU16614/88A patent/AU609481B2/en not_active Ceased
  • 1988-05-25 JP JP63128124A patent/JPS63303189A/ja active Granted

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