US2921880A - Method of obtaining pulps usable in the paper-making or other industries, from wood or annual plants, and the pulps resulting therefrom - Google Patents

Method of obtaining pulps usable in the paper-making or other industries, from wood or annual plants, and the pulps resulting therefrom Download PDF

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Publication number
US2921880A
US2921880A US601623A US60162356A US2921880A US 2921880 A US2921880 A US 2921880A US 601623 A US601623 A US 601623A US 60162356 A US60162356 A US 60162356A US 2921880 A US2921880 A US 2921880A
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solution
chlorine
pulps
chlorinating
wood
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Grand Louis
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    • 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
    • D21C3/18—Pulping cellulose-containing materials with halogens or halogen-generating compounds

Definitions

  • the present invention relates to a method for totally chlorinating wood lignin with a view to obtaining pulps that can be used in paper-making, cardboard-making or other industries, from wood or annual plants.
  • this method enables operation at ambient temperature and at atmospheric pressure.
  • chlorination is done by nascent chlorine, set up by the chlorinating solution itself.
  • the method in question enables the treatment of all lignocellulosic materials, no matter where they come from, these materials being in a veryfinely divided state.
  • the method can also be applied to the mixture of these materials, which result could not be obtained with the other methods.
  • the method according to the invention is not a bleaching process, but a process for delignifying cellulosic raw materials, in order to convert them into pulps capable of being used in paper-making or the manufacture of artificial textiles, after having undergone a more or less complete bleaching treatment properly so called.
  • This bleaching operation may be of any known type having no connection with the present delignification process; it simply forms an extension thereof.
  • chlorine forms a very good reagent, for preparing pulps for use in paper-making or other industries, from various plants, by forming chlorolignins, which are soluble, as is known, in alkaline media.
  • the process according to the invention is a chlorination process for preparing pulps which eliminates the aforementioned primordial disadvantages, by limiting at any moment of the chlorination and at the temperature of use, the acidity, that is to say the concentration of 1-H ions to a value such that the degradation of the cellulose is made impossible.
  • chlorinating solutions which produce nascent chlorine are obtained that are practically free of hydrochloric acid; the hydrochloric acid that forms during chlorination is destroyed by the coexistence in the chlorine solution, of hypochlorous acid and a chloride, preferably a chloride of a weak base, the hypochlorous acid acting as a regulator of the pH, as will be seen farther on.
  • a solution of HOCl+CaCl were prepared by causing chlorine in the requisite quantity to pass into a suspension of CaCO to obtain exactly a solution of HOCl-l-CaCl and that to this solution a solution of chlorinated water were added, on the other hand, by causing chlorine to pass into water.
  • the pH of the adjusted mixture is a function of the quantity of the solution of HOCl+CaCl added.
  • the quantity of CaCO for obtaining preferably a pH comprised, according to the invention, between 3 and 3.5, corresponds to a starting aqueous suspension containing from 0.2 to 1 part of CaCO for 100 parts of water.
  • hydrochloric acid is still for-med, as shown by the equation mentioned above, namely:
  • the CaCOg has disappeared from the solution, the latter no longer intervenes and cannot neutralize the HCl.
  • the CaCO has thus only served to pre-form the hypochlorous acid solution (H001) and the calcium chloride (CaCl this solution playing the part of a buffer solution for the hydrochloric acid formed, and maintaining, according to its concentration, the pH of the final solution at suitable values.
  • the Ca Cl present in the solution ionises in the same way as the hydrochloric acid, HCl, and helps to provide the chlorine, C1 required for chlorination.
  • the equilibrium such as (C) thus enables chlorinating solutions to be obtained that are very rich in active chlorine, and whose pH has a value comprised in the zone which is favorable for cellulose, whereas in the ordinary chlorination formerly used, the hydrolysis of the chlorine causes the pH of the solution to drop to 1.5 and the chlorination reaction itself causes it to drop still further. This chlorination thus takes place in a strongly acid medium, which has the efiect of deteriorating the cellulose by hydrolysis.
  • 0.05 molecule of C1 shall be released in a nascent state, at the same time as 0.05 molecule of HOCl disappears.
  • chlorination takes place by means of nascent chlorine, the latter being regenerated during chlorination by the disappearance of the HCl'resulting from the chlorinatioh itself.
  • hypochlorous acid-chlorine chloride of a weak base may be obtained:
  • the quantity of calcium carbonate required preferably applied in the process according to the invention, is put into suspension in water in a tank provided with a stirrer.
  • This suspension taken up by a pump, is poured at the top of a sandstone or protected steel absorption tower filled with Raschig rings.
  • the chlorine reaches the base of the tower. Absortion thus takes place by countercurrent and the solution flows continously to the base of the tower from whence it is directed towards a storage tank.
  • the regularity of the composition of the solution is automatically ensured by a pH meter, which regulator may operate according to circumstances, either on the input of the chlorine to the absorption tower, or on the rate of flow of the carbonate suspension. Labor is thus limited to supplying the CaQO which, moreover, only amounts to a small quantity (a few kilogrammes per cubic metre of solution).
  • the process according to the invention is especially applicable to materials already in a sufiiciently divided state. It is not applicable to the treatment of large wood chips, for, owing to the rapid attack (rapid chlorination), this attack would only be superficial, and delignification would not be complete even if the chlorinating solution were made to continue to act.
  • the fact of operating on finely divided material enables this material to be homogenised and, owing to this fact, enables woods as different as poplar, beech, oak, etc. to be treated together, especially if the material is divided down to a state of elementary fibre (Asplund fibre, for example) for there will only be ligno-cellulose fibres present having a chemical composition almost identical whatever their origin may be.
  • this finely divided material is first of all treated hot and in free air by an alkaline solution, for example, a 2% soda solution, to free it from resinous or waxy materials that it contains, and also to facilitate its ability to become wet; the matter thus treated is then subjected to one, two or three cycles, according to the raw material dealt with and the required quality of the pulp to be obtained.
  • an alkaline solution for example, a 2% soda solution
  • Chlorination takes place at ambient temperature and at atmospheric pressure and takes from 3 to 5 minutes according to cases, which is 'very rapid owing to the great activity of the chlorinating solution.
  • Straw, annual plants, hard or soft woods and their mixture can be delignified with success and provide, according to the number of cycles applied and the raw material treated, unbleached pulps or easily bleachable pulps.
  • paper pulps with raw materials as diverse as annual plants (straw, corn, sugar-cane, bagasse, alfa), resinous woods (pine, fir), leafy woods (poplar, eucalyptus), hard woods (oak, chestnut, beech).
  • raw materials may be treated mixed together provided the physical form under which the mixture is treated is homogeneous; in other words, a pulp obtained with a defibrator can be formed of a mixture of hard and soft woods; this mixture can be treated as easily as a pulp obtained from a single Wood, for as the matter is submitted in a homogeneous form, the chlorinating and dissolving reactions act in an identical manner on the fibres whatever be their origin.
  • the process according to the invention by enabling a mixture of the most diverse woods so treated, is suitable in all cases where the forest is not homogeneous, thus authorising the rational working of wooded clumps.
  • the delignified pulp can be subjected to bleaching operations in the usual manner.
  • the raw material is subjected to the action of the chlorinating solution in a sufliciently divided state.
  • the dryness of this material is preferably comprised between 3 and 4%.
  • Example 1 Chlorine is made to pass into a solution containing 0.16 mol of hypochlorous acid and 0.08 mol of CaCl which corresponds to an initial quantity of CaCO of 0.08 mol (being 0.8 part of CaCO for parts of water). The pH of the solution lowers progressively. If the passage of the chlorine is stopped at pH 3.5, a solution is obtained according to the equilibrium (C) which contains 0.168 mol of active chlorine per litre. If
  • the passage of the chlorine is stopped at pH 3, the solution contains 0.193 'mol of active chlorine per litre.
  • the chlorine reacts first of all with the CaCO which the solution becomes limpid; it then contains 0.161 mol of HOCl and 0.08 of CaCl according to (A). The chlorine is further admitted and one gets back to the preceding case. The chlorine is stopped when the required pH has been reached.
  • the solution contains 0.193 mol of active chlorine and has necessitated the dissolving of the same quantity of gaseous chlorine, i.e. 13.7 gr. per litre of solution.
  • the solution will titrate at pH 3.5, 0.083 mol and at pH 3, 0.09 mol of active chlorine, i.e. 6.39 gr. per litre.
  • the concentration in active chlorine will be comprised, respectively between 0.043 and 0.25 mol per litre and between 0.040 and 0.25 mol per litre.
  • Example 2 The raw material formed by a single species of leafy wood or a mixture of woods of different species is first of all divided by any kind of means, the Asplund defibrator, for example.
  • the ligno-cellulose fibres obtained, containing all the original lignin, are treated for from half-an-hour to one hour by a weak sodium hydroxyde solution at atmospheric pressure (85 to 90); they are then washed.
  • the pulp is then subjected to the action of the chlorinating solution made up according to the equilibrium (C) containing, for example, 13.7 gr. of active chlorine per litre and at a pH of 3, at the rate of 7.5 kg. of active chlorine per 100 kg. of pulp, i.e. 547 litres of solution.
  • C the equilibrium
  • the dryness of the pulp should be about 5% before it is mixed with the chlorinating solution and the mixture should be made with vigorous stirring so that, in spite of its rapidity, the reaction is uniform.
  • the reaction is completed in from 5 to 7 minutes.
  • the pulp freed from the solution is washed and then subjected to the action of a weak alkaline solution to dissolve the chloro-lignins formed.
  • the washed pulp is again subjected to the same quantity (7.5%) of solution adjusted to pH 3 and containing 13.7 gr. of active chlorine per litre, is washed, alkalinised and washed. It can then be bleached by any of the known bleaching processes.
  • Example 3 The pulp composed of ligno-cellulose fibres, subjected, as above, to the action of a weak alkaline solution, is treated by achlorinating solution adjusted to pH 3 8 at the rate of 5 kg. of active chlorine per kg., i.e. 365 litres. After alkalinisation and washing as above, the second chlorination may be carried out with 10 kg. of active chlorine per 100 kg. of pulp, i.e. 730 litres of chlorinating solution.
  • This method which uses the same quantity of active chlorine as in the preceding example, is more efiicacious and provides highly delignified pulps which, during subsequent bleaching, reach a high degree of whiteness.
  • the chlorinating solution contains in equilibrium a mixture of chlorine, hypochlorous acid, a chloride of a weak base and a small amount of hydrochloric acid.
  • the chlorinating solution is prepared by dissolving chlorine in water containing calcium carbonate in suspension until the calcium carbonate has totally disappeared, the quantity of calcium carbonate utilized being between 0.2 and 1 part for 100 parts of water, and continuing to introduce the chlorine until a pH of between 3 and 3.5 is attained.

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US601623A 1951-04-12 1956-08-02 Method of obtaining pulps usable in the paper-making or other industries, from wood or annual plants, and the pulps resulting therefrom Expired - Lifetime US2921880A (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1970065A (en) * 1931-09-28 1934-08-14 George H Tomlinson Process of bleaching pulp and other lignified materials
US2021612A (en) * 1934-02-19 1935-11-19 Hooker Electrochemical Co Pulp treating process
US2049676A (en) * 1934-02-13 1936-08-04 George H Tomlinson Process of treating bleached pulp
US2070893A (en) * 1935-05-10 1937-02-16 Glass Hugh Bryson Process for improving the color of wood pulp

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1970065A (en) * 1931-09-28 1934-08-14 George H Tomlinson Process of bleaching pulp and other lignified materials
US2049676A (en) * 1934-02-13 1936-08-04 George H Tomlinson Process of treating bleached pulp
US2021612A (en) * 1934-02-19 1935-11-19 Hooker Electrochemical Co Pulp treating process
US2070893A (en) * 1935-05-10 1937-02-16 Glass Hugh Bryson Process for improving the color of wood pulp

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FR1109672A (fr) 1956-01-31

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