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
  • D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
• • 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
  • D21C3/003—Pulping cellulose-containing materials with 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
  • D21C3/00—Pulping cellulose-containing materials
  • D21C3/04—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides
• • 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 invention concerns a method for preparation of a fibrous stock suitable for manufacture of paper out of herb-stemmed plants, in which method the fibrous raw- material is chipped, cooked, and bleached.
• herb-stemmed plants will be used to cover all those non-wood fibrous raw-materials that can be used for manufacture of fibrous pulp.
• the properties and the suitability of herb-stemmed plants for preparation of pulp vary. Generally speaking, they contain less lignin than wood raw-material does, but their contents of silicates and ashes can be remarkably high. This imposes specific requirements on the process of manufacture of pulp that is used.
• the object of the present invention is to provide a novel method for manufacture of fibrous pulp to be used for manufacture of paper out of herb-stemmed plants, by means of which method the drawbacks related to the prior- art methods are avoided.
• An object of the present invention is a pulp production process which is favourable in view of the environment and whose technical solutions are simple and which is economically profitable also when the unit is small.
• the method in accordance with the invention is characterized in that the cooking is carried out at a temperature of
• the cooking liquor that is used is water to which an acid has been added so that the ultimate pH of the cooking is lower than 7 but higher than 3.
• high-concentration chemical solutions and high cooking temperatures are employed.
• the loss of yield in the cooking is little, but the pulp can be bleached readily in the bleaching following after the cooking.
• the main part of the lignin, which is contained in the fibrous material and which binds the fibres together, is not dissolved until during the bleaching.
• the spent liquor from the cooking and the wash waters can be passed into the waste water cleaning plant to be processed by means of known biological cleaning processes. This is why the cost of investment and operation of the process is advantageous, for which reason it is also profitable in small units.
• the relatively simple pulp preparation process can be inte- grated readily in connection with a paper mill so as to produce, depending on the fibrous raw-material, either reinforcement stock or short- fibre stock for the paper machine. The process produces fibrous pulp of good quality, which is suitable for final products of many sorts. The yield of pulp is somewhat better than in the case of non-wood pulps prepared by means of conventional processes.
• the water cooking process in accordance with the present invention is suitable for delignification of many different herb-stemmed plants.
• the requirement of pre- treatment of the fibrous raw-material depends, among other things, on whether the whole plant can be utilized as such, or if it is necessary to separate the fibre fraction from the plant material mechanically.
• simple chipping of straw is sufficient as pre-treatment, whereas, for example, flax must be braked and scutched or fractioned mechanically in some other suitable way before the cooking in order that the fibrous material could be separated for cooking.
• the chips to be used for preparation of pulp must be relatively short in order that bundles of fibres should not be twisted with each other during cooking.
• a suitable chip length would seem to be 5...10 mm.
• the chip length can be up to 50 mm.
• the fibre chips are cooked in water into which an acid has been added to such an extent that the ultimate pH of the cook will be lower than 7 but higher than 3.
• the acid that is used can be any anorganic or organic acid whatsoever.
• organic acids are used, such as formic acid or acetic acid or a mixture of same.
• the addition of acid to be applied is so little that no "organosolv” cooking is concerned.
• the proportion of the organic solvent in the cooking liquor is, as a rule, 20...100 % .
• the addition of acid is always less than 2 % of the whole volume of the cooking liquor, preferably lower than 1 % . Good results have already been obtained even with an acid addition as low as about 0.06 % .
• the cooking is carried out at a temperature of 60...130 °C, preferably 70...100 °C. After cooking, the spent liquor is separated from the fibre chips and passed to waste water treatment.
• the loss of yield in acid water cooking is relatively little.
• a fibrous raw- material that has been cooked without mechanical pre-treatment is not necessarily defibrated after cooking as yet. Therefore, the water cooking is followed by bleaching, whose object is, besides increasing the brightness of the pulp, also to dissolve lignin and to provide defibration of the pulp.
• bleaching it is possible to use any prior-art bleaching process whatsoever.
• chlorine-free bleaching chemicals are used, such as peroxide.
• the fibre chips When peroxide bleaching is used, the fibre chips must be chelated before bleaching so as to stabilize the ions of heavy metals in order that these ions should not accelerate the decomposition of peroxide during bleaching.
• the pulp is treated, in a way in itself known, with a suitable chelating agent. Chelating can be carried out either as a separate step before bleaching or in connection with cooking so that a little dose of chelating agent is added to the cooking water.
• the bleaching is carried out in a conventional way while, however, using such dosages of chemicals and such conditions with which part of the lignin contained in the fibrous material can be dissolved.
• the unit that produces fibrous pulp out of herb-stemmed plants by means of the method in accordance with the present invention can be placed in connection with a paper mill so that it forms a part of the stock system of the paper machine.
• the fibrous stock produced by the process can be utilized directly in the paper machine as mixed with normal wood pulp.
• Pulps prepared out of herb-stemmed plants do, as a rule, not require highly intensive grinding, but a treatment of defibration type or pulpering can be sufficient.
• Pulp of short fibres can be used, among other things, for intermediate layers in multi-layer board to replace recycled fibre or wood fibre.
• Long-fibre pulp (flax, hemp, kenaf) can be substituted for wood fibre, for example, in the manufacture of recycled paper.
• the method in accordance with the invention requires low investments, because it is unnecessary to provide for recovery of chemicals.
• the consumption of chemicals in the cooking is little, but in bleaching, on the contrary, it is necessary to use more chemicals if a fully bleached pulp is aimed at.
• the method is also favourable in view of the environment, because no sulphur compounds are used in cooking, and preferably no chlorine compounds are used in bleaching.
• Example 1 Cooking and bleaching of wheat straw
• Wheat straw was subjected to water cooking and to peroxide/peracetic-acid bleaching under laboratory conditions.
• the straw was initially chipped to lengths of about 50 mm, and the chips were cooked in revolving electrically heated cookers of 15 litres.
• the conditions and yields of two cookings performed at different temperatures are given in Table 1.
• the cooking liquor that was used was water which had been made acid by to it adding a little amount of an acid solution, which had been prepared by mixing concentrated formic acid and concentrated acetic acid at a ratio of 1:3.
• the necessary amount of water was added to the cooker in order to reach the desired liquid-to-straw ratio 10: 1.
• the addition of acid was 0.064 % of the volume of the cooking liquor.
• the acid solution contained concentrated formic acid and concentrated acetic acid at a ratio of 1 :3.
• the straw chips were washed and chelated for an hour with an EDTA dose of 0.3 % at a consistency of 3 % and at a temperature of 70 °C.
• the straw chips still non-defibrated were bleached under the conditions given in Table 2.
• the bleaching comprised two peroxide stages, a peracetic-acid stage, and a third peroxide stage.
• the results of the bleachings are given in Table 3.
• the bleached pulps were ground, and the paper-technical properties were determined from them.
• the raw-material was still in straw form, but it was defiberized during the second peroxide stage. Based on the yield figures, the loss of material in cooking was about 10 % and in bleaching about 40 % of the weight of the original raw- material.
• flax pulp As the raw-material, flax was used which had been partly soaked on the field, braked and scutched and which was cut off to a length of about 12 mm. The function of the mechanical pre-treatment was to separate the fibre fraction from the rest of the plant material. The flax with long fibres was chipped in order that the fibre bundles should not be twisted together during cooking and during the further treatment of the pulp.
• the flax pulp was bleached in three stages with a sequence peroxide - peracetic acid - peroxide.
• the bleaching conditions are given in Table 4.
• the flax pulp was ground as mixed with birch pulp.
• the yield of bleached flax pulp was 75.0 % of the original fibrous raw-material.
• the brightness of the pulp was 86.9 , i.e. clearly better than with the straw pulps of Example 1. In order that this level of brightness could be achieved, less bleaching chemicals were needed than with straw pulps.
• the total consumption of peroxide was 4.25 %, and the consumption of peracetic acid 0.81 % , calculated from the dry solids of the water-cooked flax.
• a mixed pulp was prepared from wheat straw and flax by cooking them together at a relatively low temperature in the presence of chelate. 645 grams of chipped wheat straw (length 50 mm) and 100 grams of partly soaked, braked, scutched, and chipped fibre fraction of flax (length 12 mm) were cooked over a period of 60 minutes at 70 °C. To the cooking water, for chelating, 0.3 % of EDTA, calculated from the weight of the fibrous raw-material, was added, and for regulation of pH, 6.4 ml of a mixture of concentrated formic acid and concentrated acetic acid (1:3) was added, in which case the concentration of the acid in the cooking liquor was 0.086 % by volume. The ultimate pH of the cook was 4.9.
• the mixed pulp of flax and straw was bleached by means of the same four-stage sequence and under the same conditions as pure straw pulp was bleached, see Table 2. Owing to different yields of flax and wheat, the ultimate mixing ratio in the bleached pulp was about 20:80. The yield of bleached pulp was 62.7 % of the original raw-material, and the brightness was 84.6 % . The consumption of peroxide in bleaching was 7.2 %, and the consumption of peracetic acid was 0.9 % .
• the bleachability of the pulp did not have any detrimental effect from the fact that the cooking was carried out at a lower temperature and with a shorter duration than in Examples 1 and 2. Chelating can already be carried out very well in connection with cooking. The test also proved that different fibrous raw-materials can be cooked and bleached together, provided that the requirements of the raw-material whose bleaching is more difficult are taken into account in the choice of the bleaching conditions.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

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Cited By (6)

Citations (4)

• 1998
  • 1998-08-27 FI FI981836A patent/FI109545B/fi active
• 1999
  • 1999-08-24 WO PCT/FI1999/000697 patent/WO2000012810A1/en not_active Application Discontinuation
  • 1999-08-24 AU AU53761/99A patent/AU5376199A/en not_active Abandoned
  • 1999-08-24 JP JP2000567785A patent/JP2002523650A/ja active Pending
  • 1999-08-24 EP EP99939478A patent/EP1115944A1/de not_active Withdrawn

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