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
  • D21C11/00—Regeneration of pulp liquors or effluent waste waters
  • D21C11/04—Regeneration of pulp liquors or effluent waste waters of alkali lye
• • 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
  • D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
  • D21C3/026—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes in presence of O2, e.g. air
• • 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
  • D21C9/1073—Bleaching ; Apparatus therefor with O3

Definitions

• This invention refers to a process to produce pulps from vegetable, lignocellulose-containing fibrous material, e.g. coniferous wood, straw and bagasse.
• the mentioned drawbacks involve also high energy consumption due to the plants for impregnation of the raw material with cooking chemicals, for pulp bleaching, for recovery of chemicals and for environment protection.
• the main object of the invention is to provide a process for production of pulps wherein the handling of the chemicals is simplified so that the aforestated drawbacks are avoided.
• a second object of the invention is by the simplified handling of chemicals to obtain lower investment costs which results in that minor plants also become profitable, which permits the installation of plants nearer the raw material sources with consequent reduction of transport costs, which also involves a generally widened range of raw or starting materials.
• a third object of the invention is to render possible in this connection a widened utilization of non-traditional raw materials for production of pulps such as green chips, i.e. twigs, branches, bushes and shrubs and low-grade timber especially from coniferous wood as result from various thinning and cleaning operations, furthermore agricultural wastes like wheat, rice straw and bagasse, but also e.g.
• banana stems, soybeans and coconut shells furthermore also from other annual vegetables cultivated for their fibre content more than with regard to their nutritive value, such as cotton, flax, kenaf, but also wild annual vegetables such as certain kinds of grass and reeds, and finally also wastes from tradiational woodworking industry in the shape of sawmill waste and especially waste from tropical kinds of wood possessing very high density and therefore difficult to treat with conventional processes of pulp production, and waste from traditional pulp industry in the shape of knot catcher rejects and some kind of fibre sludge.
• other annual vegetables cultivated for their fibre content more than with regard to their nutritive value such as cotton, flax, kenaf, but also wild annual vegetables such as certain kinds of grass and reeds
• the fibrous material is subjected to a sequence of treatment stages, of which in stage 1 the fibrous material is impregnated with a solution of sodium hydroxide in which the material is soaked during a time of from 15 to 45 minutes at a temperature of between 50° and 110°C, and simultaneously partially disintegrated by mechanical working, that in stage 2 the excess of alkaline solution is squeezed out from the fibrous material until the dry content of the treated material amounts to 20-55% and its content of sodium hydroxide amounts to at least 15 kgs per ton of treated material calculated as dry substance (BD ton of treated material), that in stage 3 the fibrous material is subjected to additional disintegration under supply of a solution of sodium carbonate .
• stage 1 the fibrous material is impregnated with a solution of sodium hydroxide in which the material is soaked during a time of from 15 to 45 minutes at a temperature of between 50° and 110°C, and simultaneously partially disintegrated by mechanical working, that in stage 2 the excess of alkaline solution is squeezed out from the fibr
• stage 4 the treated material suspension is subjected in a pressurized reactor to a cooking process at a temperature of at least 110°C during 1-4 hours and under stirring and supply of oxygen, whereafter the cooked pulp is washed.
• the fibrous material Prior to the impregnation with sodium hydroxide, the fibrous material can be washed and simultaneously pre-disintegrated.
• the finally treated pulp can be bleached in known manner by means of-ozone, the ozone (0 3 ) being produced from oxygen gas (0 2 ) in ozonisers, and after the bleaching the oxygen gas is purified from remainders of ozone by being passed through a coal bed in the presence of water and thereafter returned into the process.
• sodium carbonate is used as a reactant.
• the reactivity of the mentioned salt is known to be low towards lignine but also towards the cellulosic components and the cellulose and in any case inferior to the reactivity of the correspondent hydrate. Therefore the carbonate is activated, in stage 3 after a first delignification has been accomplished by means of sodium hydrate in stage 1, where chips imbibition takes place, in quantities corresponding to the necessary ones to make up the loss of process reactants.
• the quantity varies, according to raw materials and final products, between 15 and 30 kg of hydrate per BDT (bone dry ton) of processed fibrous material.
• stage 3 For the activation 0 2 also and possibly other oxidative agents (peroxides) are used in stage 3 where working pressure, temperature and amount of O2 are varied within very wide limits (10-20 Bar, 110 ⁇ 150°C and 6-14% of 0 2 ) according to raw material and desired final products.
• the process according to the invention is therefore characterized by the use of carbonate as alkaline salt directly in the process of delignification (stage 3).
• Very good delignification (kappa no between 15 and 8) has been obtained with the aforedescribed process simultaneously with viscosity levels high enough after the subsequent bleaching process to ensure good characteristics of resistance of the paper puIp together with a brightness of about 50% Scan, impossible to be obtained by any known alkaline process.
• Characteristic for the process according to the invention is also that it yields pulps with low extractive content and with high cleanliness in spite of utilization of low quality raw material containing bark, for example. This is due to the fact that oxygen gas in alkaline medium reacts specifically with bark and fibre bundles which are difficult to become delignified by usual processes.
• pulps produced according to the invention are highly bleachable by ozone which affords a number of advantages.
• Ozone bleaching is carried out in a single stage at atmospheric pressure. Investment and energy costs of the ozone bleaching are lower than for other comparable processes.
• the production costs for ozone and chlorine dioxide are on the same level with today's technology, the energy consumption is 10 kWh per kg ozone, provided that ozonisers are fed with oxygen, in comparison to 12-14 kWh per kg of chlorine dioxide starting from sodium chlorate.
• the effluent from the ozone bleaching stage can be conveyed to black liquor evaporation and combustion, for which reason environmental pollution is reduced to a minimum.
• the process according to the invention is characterized also by the possibility of utilizing O2 (moist and not pure) resulting from the ozone bleaching treatment.
• Industrial ozonisers when fed with oxygen yield a gas mixture where the ozone content is 2.5-2.7 vol %, the rest being oxygen.
• oxygen may be recycled to stage 3.
• the gas mixture coming from the bleaching stage is here passed through an ozone purifier in the shape of a coal bed in the presence of water in order to prevent carbohydrate degradation which is particularly severe at the used high reactor temperature even when traces only of ozone are present.
• Black liquors contain those inorganic chemicals which have been used for the delignification, chemicals to a small extent as free reactants and for the most part in combination with salts of organic acids, alkali lignine and other compounds of sometimes very complex structure and forming non-cullulosic wood components.

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• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

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Publications (2)

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ID=11214834

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• 1980
  • 1980-09-22 IT IT8024818A patent/IT1209352B/it active
• 1981
  • 1981-09-21 BR BR8108805A patent/BR8108805A/pt unknown
  • 1981-09-21 EP EP81902585A patent/EP0060277B1/en not_active Expired
  • 1981-09-21 WO PCT/SE1981/000273 patent/WO1982001019A1/en not_active Ceased
• 1982
  • 1982-05-21 DK DK231182A patent/DK155192C/da active

Patent Citations (1)

Non-Patent Citations (1)

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