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
  • D21C3/26—Multistage processes

Definitions

• the present invention relates to a process for the delignification of lignocellulosic materials for the preparation of pulps intended for the manufacture of paper. It relates more specifically to the field of chemical pulps obtained by cooking cellulosic materials in the presence of chemical reagents with delignifying properties.
• the invention remedies these drawbacks of known methods by providing a new method for delignifying cellulosic materials, which makes it possible to achieve high delignification rates while preserving the intrinsic quality of the cellulose and the weight yield of pulp produced.
• the invention relates to a process for the delignification of cellulosic materials according to which, in a first step, cellulosic materials are treated with an acid, in a second step, the cellulosic materials of the first step are treated with peroxide of hydrogen in an alkaline medium and, in a third step, the cellulosic materials of the second step are subjected to an alkaline cooking in the presence of at least one chemical reagent selected from the hydroxides of alkali or alkaline earth metals.
• cellulosic materials is intended to denote woody fragments of plants used as raw materials in the paper industry.
• examples of such materials are fragments of wood, annual herbaceous plants such as alfa, plants of the class of monocots such as cereal straws, bamboo, esparto, rushes and reeds as well as cane sugar, in particular its residue, bagasse, after sugar extraction.
• the invention applies very particularly to fragments of wood. All types of softwood or hardwood used in the paper industry are suitable for the process according to the invention. Softwood chips and sawmill waste are particularly suitable.
• the purpose of the treatment with an acid is to decontaminate the cellulosic materials of the metals which they generally contain.
• All inorganic acids or organic used in aqueous solution, alone or in mixture are suitable. Strong inorganic acids such as sulfuric acid or hydrochloric acid are well suited.
• the first step is carried out in the presence of an agent complexing metal ions.
• mixtures of the strong inorganic acids mentioned above with organic acids of the class of aminopolycarboxylic or amino polyphosphonic acids or their alkali metal salts are particularly suitable.
• suitable aminopolycarboxylic acids are diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, acid.
• Diethylenetriaminepentaacetic acid DTPA
• aminopolyphosphonic acids diethylenetriaminepentamethylenephosphonic acid, ethylenediaminetetra acid (methylenephosphonic) and nitrilotri acid (methylenephosphonic).
• Diethylene triaminepentamethylene phosphonic acid is preferred.
• the operating conditions of the first step of the process according to the invention are not critical. They must be determined in each particular case according to the type of cellulosic materials and the apparatus in which the treatment is carried out. In general, the choice of acid and the quantity used should be fixed to impose on the medium a pH of less than 7, for example between 0.5 and 6.5; especially advantageous pHs are those between 1.0 and 4.0.
• Temperature and pressure are not critical, with room temperature and atmospheric pressure generally suitable.
• the duration of the treatment can vary within wide limits depending on the type of equipment used, the choice of acid, the temperature and the pressure, for example from 30 minutes to several hours if the treatment is carried out by soaking the cellulosic materials in a vat, from 1 to 120 minutes if it is made by percolation in a column where the cellulosic materials to be treated are stacked.
• the cellulosic materials can be subjected, before the first step, to a treatment with water vapor.
• the purpose of this treatment is to facilitate the impregnation operations which will follow.
• the function of the hydrogen peroxide used in the second stage of the process according to the invention is to accelerate the delignification of the cellulosic materials in the subsequent cooking stage.
• the optimum amount of hydrogen peroxide to be used depends on the origin of the cellulosic materials. In general, it is necessary to use more than 0.1 g of hydrogen peroxide per 100 g of dry cellulosic materials. Amounts of hydrogen peroxide greater than 3 g / 100 g of dry cellulosic materials are rarely necessary to obtain rapid delignification. Usually, doses of hydrogen peroxide of between 0.5 and 2 g / 100 g of dry matter are used. Doses of peroxide between 0.7 and 1.5 g / 100 g of dry matter have given the best results.
• the hydrogen peroxide used can be anhydrous hydrogen peroxide or, preferably, an aqueous solution, for example a commercial aqueous solution of hydrogen peroxide whose content by weight is between 25 and 90 g of peroxide of pure hydrogen per 100 g of solution or alternatively a dilute alkaline aqueous solution of hydrogen peroxide produced by electrochemical reduction of oxygen.
• the treatment of cellulosic materials with alkaline hydrogen peroxide can be carried out in the presence of additives such as, for example, stabilizers and inhibitors of the decomposition of hydrogen peroxide.
• additives are, for example, sequestrants of inorganic or organic metal ions such as magnesium salts, aminopolycarboxylic acids or sodium silicate of soluble glass quality.
• Other additives which can also be used are surfactants, wetting agents, agents capable of protecting the cellulosic chains to prevent their depolymerization, activating agents or anti-corrosion agents.
• the amount of additive introduced is never greater than 1% of the weight of the cellulosic materials. It is most often between 0 and 0.5X of the weight of these materials.
• the alkaline medium is obtained by the addition of soluble materials of basic character.
• Ammonia, carbonates and inorganic hydroxides of alkali or alkaline earth metals such as sodium, potassium or calcium carbonate, sodium, potassium or calcium hydroxide are generally used.
• Oxides or peroxides of alkali or alkaline earth metals such as Na 2 0, Na 2 0 21 CaO and Ca0 2 , may also be suitable and in the case of peroxides supplement the supply of part of the hydrogen peroxide introduced in the second step of the process.
• Sodium hydroxide is usually preferred because of its high availability and low cost.
• the quantities of basic material to be used are chosen so as to adjust the pH of the peroxide solution between 11 and 13.5 and preferably between 12 and 13.
• the operating conditions of the second step of the process according to the invention can also vary within fairly wide limits depending, in particular, on the type of cellulosic materials and the type of equipment used.
• the pressure prevailing during the second stage can thus be in the range from 2 kPa to 10 MPa and the temperature in the range from 290 K to 380 K.
• the treatment with hydrogen peroxide in an alkaline medium of the second stage is generally performed for a time greater than 2 minutes and not exceeding 180 minutes.
• the cellulosic materials to be treated are subjected to alkaline hydrogen peroxide in a liquor-to-wood weight ratio not exceeding 2.5: 1, and preferably ranging from 1: 1 to 2: 1.
• the cellulosic materials originating from the first stage are impregnated in a closed reactor with the alkaline liquor of hydrogen peroxide preheated, after which the excess liquor which has not impregnated the cellulosic materials. sics is drained from the reactor which is then heated to the reaction temperature.
• the soaking of the cellulosic materials in the hydrogen peroxide liquor, prior to the reaction generally does not require more than 5 minutes. However, it usually cannot be done in less than 30 seconds.
• the temperature of the peroxide liquor is most often chosen from 5 to 20 K higher than that which prevails in the reactor and which is maintained for 15 to 120 minutes by means of the heating mantle. A reaction temperature between 310 and 360 K is suitable. The best results were obtained with a temperature of 323 K and for a reaction time of 45 minutes.
• the third step of the process according to the invention consists in subjecting the cellulosic materials coming from the second step to a baking in the presence of at least one chemical reagent.
• the chemical reagent is chosen from hydroxides of alkali or alkaline earth metals. Examples of such chemical reagents which are especially suitable are sodium hydroxide and calcium hydroxide.
• delignifying additives can be added in the third step of the process according to the invention. These additives are generally used to increase delignification during alkaline cooking.
• Organic compounds are preferred, such as, for example: anthraquinone and its derivatives such as 1-methylanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-methoxyanthraquinone, 2,3-dimethylanthraquinone, 2, 7-dimethylanthraquinone, 1,4,4a, 5,8,8a, 9a, 10a-octahydroanthraquinone and 1,4,4a, 9a-tetrahydroanthraquinone; hydroquinones such as p-hydroquinone; certain anthracene derivatives such as 9-nitroanthracene, 9,10-dinitroanthracene and 9-nitro-10-chloro-9,10-dihydroanthracen
• inorganic compounds examples include hydrazine and the alkali metal borohydride. Anthraquinone and its derivatives are preferred. These additives are advantageously used in amounts not exceeding 2% of the weight of the dry cellulosic substances. Generally, their quantity is less than 1% of this weight.
• the optimum operating conditions for the third step of the process according to the invention depend on various parameters, in particular on the origin of the cellulosic materials and they can be easily determined in each particular case.
• a washing with water of the cellulosic materials is carried out between the second and the third stage.
• This embodiment is advantageous when the last step is carried out in the presence of additives comprising reducing substances.
• the purpose of this washing is to remove cellulosic materials, at least part of the water-soluble products generated in the second step and to extract the last traces of hydrogen peroxide still present, to avoid unnecessary oxidation of the reducing substances.
• the process according to the invention makes it possible to significantly speed up the delignification of the cellulosic materials treated, which has the effect of shortening the time required for the third stage of cooking with chemical reagents. This results in the significant advantage of a significant reduction in the size of the cooking equipment, which leads to savings in space and investment cost or, alternatively, increased capacity for a given cooking equipment.
• the invention also allows, at an equal delignification rate, a substantial reduction in the amount of chemical reagents in the cooking step, leading to substantial savings in chemical reagents.
• the invention also produces with better weight yields and therefore at lower cost, chemical pastes of higher viscosity than those obtained by the methods of the prior art.
• Tests 1 to 6R were carried out to demonstrate the improvement brought by the invention on the performance of the technique of cooking lignocellulosic materials.
• Test 1 (In accordance with the invention).
• the chips were then immersed at room temperature in a solution of Na 5 DTPA 0.003M and 0.1N H 2 SO 4 by drawing the solution into the reactor by means of the reduced pressure produced by the vacuum connection.
• the aqueous solution was used in an amount by weight equal to 8 times the weight of wood in the dry state.
• the shavings were then subjected to 3 washing cycles of 2 hours each with an amount of water equal to 8 times the weight of dry wood. The shavings were centrifuged between cycles.
• a 0.3 M aqueous solution of H 2 0 29 0.5 M in NaOH and 0.001 M in Mg ++ ions was preheated to 323 K and then introduced into the reactor in a quantity equal to 6 times the weight of dry wood. . After 2 minutes of impregnation, the excess liquor was drained out of the reactor by means of the tubular probe. The reaction was then allowed to proceed for 45 minutes by heating the reactor by circulating water thermostatically controlled at 323 K in the jacket.
• Wood chips as in test 1 subjected directly to the third stage of test 1 under the same conditions, failing to carry out the first and second stages.
• Test 6R (reference)
• the pasta obtained was analyzed under four aspects: kappa index, lignin content, total weight yield and viscosity.
• the methods used for these analyzes were the following standard methods:
• the total weight yield was determined gravimetrically by weighing the samples before and after the tests.
• the total carbohydrate content was also calculated by subtracting the lignin content from the total weight yield.
• a comparison of the results of test 1 with those of tests 2R, 3R and 5R demonstrates the synergistic effect of the combined implementation of the first and second stages of the process according to the invention on the delignification and the preservation of carbohydrates at l 'from the subsequent cooking step.
• the sequential implementation of the first two stages of the process according to the invention has made it possible to reduce the duration of the third cooking stage by at least 30 X, and consequently reduce simultaneously the size and cost of the cooking equipment.

Landscapes

• Polysaccharides And Polysaccharide Derivatives (AREA)
• Paper (AREA)
• Detergent Compositions (AREA)
• Materials For Medical Uses (AREA)
• Dental Preparations (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• External Artificial Organs (AREA)
• Ultra Sonic Daignosis Equipment (AREA)
• Chemical Or Physical Treatment Of Fibers (AREA)
• Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)
• Acyclic And Carbocyclic Compounds In Medicinal Compositions (AREA)
• Agricultural Chemicals And Associated Chemicals (AREA)

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Citations (5)

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• 1986
  • 1986-07-25 EP EP86110248A patent/EP0212329B1/de not_active Expired - Lifetime
  • 1986-07-25 AT AT86110248T patent/ATE57400T1/de not_active IP Right Cessation
  • 1986-07-25 AU AU60544/86A patent/AU591509B2/en not_active Ceased
  • 1986-07-25 DE DE8686110248T patent/DE3674859D1/de not_active Expired - Fee Related
  • 1986-07-28 NZ NZ217002A patent/NZ217002A/xx unknown
  • 1986-07-31 YU YU1369/86A patent/YU45351B/xx unknown
  • 1986-08-01 PT PT83118A patent/PT83118B/pt not_active IP Right Cessation
  • 1986-08-01 CA CA000515193A patent/CA1311093C/fr not_active Expired - Lifetime
  • 1986-08-04 JP JP61183262A patent/JPH0742670B2/ja not_active Expired - Lifetime
  • 1986-08-04 NO NO863133A patent/NO168490C/no not_active IP Right Cessation
  • 1986-08-04 ES ES8600840A patent/ES2000385A6/es not_active Expired
  • 1986-08-04 BR BR8603672A patent/BR8603672A/pt not_active IP Right Cessation
  • 1986-08-05 FI FI863194A patent/FI85726C/fi not_active IP Right Cessation

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Non-Patent Citations (3)

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