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
  • 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
  • D21C9/1005—Pretreatment of the pulp, e.g. degassing the pulp
• • 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
  • 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
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
  • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone

Definitions

• the invention relates to a method for delignifying cellulose-containing raw materials with a digestion solution of concentrated aqueous acetic acid at elevated temperature and pressure.
• the digestion liquid contains, in addition to concentrated acetic acid, small amounts of a mineral acid used as a catalyst, e.g. B. hydrochloric acid. Furthermore, extraction with dilute aqueous sodium hydroxide solution is described, which would require technically complex alkali recovery. Furthermore, the continuous percolation of the wood provided in DE 34 45 132 A1 is associated with high acetic acid circulations, a weight ratio of wood to solvent of about 1 to 20 being typical.
• acetic acid is used both in the cooking stage for breaking up shredded wood or annual plants as a starting material and in a subsequent bleaching stage in the presence of hydrogen peroxide.
• ozone has also been used successfully as a bleaching agent in acetic acid, cf. EP-A-0 325 891.
• the catalytically active amounts of mineral acids from the waste water or the dissolved wood degradation products can hardly be recovered.
• these mineral acids are volatile, e.g. As hydrogen chloride or hydrogen bromide, which leads, among other things, to odor problems.
• salts would increase the wastewater load and, because of the halogen content, restrict the recycling or disposal of the separated lignin.
• the presence of hydrogen halide in the aqueous phase is known to be associated with considerable corrosion problems in the container materials.
• these processes are characterized by high consumption of bleaching chemicals with comparatively low whiteness.
• bleaching chemicals for conifers, for example, in the process according to DE 34 45 132 A1 with hydrogen peroxide consumption of about 5% by weight, based on cellulose, is absolutely dry (hereinafter dry), with a final whiteness of 48.6% ISO or in the process according to EP -A-0 325 891 with a consumption of about 2.6% by weight of ozone and 1.0% by weight of hydrogen peroxide, based on dry cellulose, with a final whiteness of 62% ISO.
• the task is derived, in order to obtain pulps suitable for paper production or also for the production of products from regenerated or chemically modified cellulose, to specify a sequence of process steps in a process of the type mentioned at the outset which completely delignify the wood in Allows connection with a bleaching sequence without the use of chlorine-containing chemicals.
• This object is achieved with a process for delignifying cellulose-containing raw materials with a weight ratio of the raw material to a digestion solution of aqueous acetic acid between 0.08 to 1 to 0.5 to 1, a water content in the Digestion solution of 5 to 50 wt .-%, a temperature between 140 and 230 ° C under a pressure of 3 to 30 bar and a residence time between 0.5 and 8 h in a first delignification stage, subsequent extraction or washing, characterized by treating the Acetic acid-moist pulp in the consistency range of 3 to 60 wt .-% in a liquid phase corresponding to the composition of the above-mentioned digestion solution with an ozone-containing gas at a pressure of 1 to 12 bar and a temperature of 15 to 50 ° C with an ozone amount of 0.1 to 2.5% by weight / atro raw material mass.
• the method according to the invention thus includes delignification in two successive delignification stages with ozone delignification as the second stage, it being possible to reduce the lignin content of the pulp to less than 1% by weight overall.
• lignin contents of about 1% by weight are also achieved, but with the acceptance of the presence of hydrogen halide and high bleach consumption.
• one or more bleaching stages using hydrogen peroxide, peracetic acid solutions, sodium borohydride or also chlorine dioxide can be connected to the delignification stages provided according to the invention.
• acetic acid provided according to the invention as the simplest (unsubstituted) representative of a C2-aliphatic monocarboxylic acid
• other C1-C4-aliphatic monocarboxylic acids preferably propionic acid, less preferably formic or butyric acid, can be used in the digestion of the cellulose-containing raw materials.
• the present two-stage process is advantageously carried out in such a way that first the mechanically chopped and used or raw materials crushed into chips e.g. B. brought to a desired water content by carefully carried out contact or convection drying processes and, if necessary, pre-impregnated, for example with acetic acid.
• Wood or other lignocellulose-containing, possibly pre-impregnated material is mixed with the solvent, consisting of the acetic acid / water mixture, the acetic acid content in the digestion solution including the water content contained in the raw material used being at least 50% by weight, and at a temperature between 140 and 230 ° C, preferably 170 to 200 ° C and an increased pressure between 3 to 30, preferably 5 to 12 bar.
• the reaction times are between 0.5 and 8, preferably 1 to 4, hours.
• the weight ratio of the dry to solvent feed during the reaction can be varied between 0.08 to 1 to 0.5 to 1, preferably 0.2 to 1 to 0.33 to 1.
• wood can be made into a solvent with higher proportions by weight. If fiber plants are used, this weight ratio can also be varied as necessary.
• the wood chips or the fiber plant sections are introduced by introducing mechanical energy, e.g. defibrated by means of stirring devices and freed from soluble degradation products with an aqueous acetic acid solution.
• the extracted pulp obtained from the first stage is then subjected to a further delignification by means of ozone-containing gases with an ozone content in the carrier gas of approximately 5 to 10% by weight.
• This reaction can be carried out in consistency ranges from only 3% by weight solids content up to over 60% by weight, preferably between 30 and 50% by weight solids content will.
• the pulp is pressed out or further acetic acid solution is added.
• the reaction is carried out at a pressure between 1 and 2 bar, but pressures of 1 to 12 bar can be used especially in the medium consistency range from 8 to 16% by weight solids content.
• the ozone treatment is expediently carried out at a temperature between 0 to 70 ° C., preferably 20 to 40 ° C.
• ozone carriers e.g. Air, nitrogen, oxygen or other carrier gases.
• the ozone-containing gases are produced in commercially available devices.
• the reaction times are 0.01 to 2, preferably 0.05 to 1 h.
• the ozone is transported to the cellulose fiber from the gas phase via diffusion through the liquid film attached to the fiber or, in the case of suspension of the cellulose, in a continuous liquid phase from the ozone fraction dissolved in the liquid phase by suitable distributing devices.
• the type of aftertreatment depends on the intended use of the pulp obtained and can consist in further extraction, bleaching or washing in the acidic, neutral or alkaline range. Both water and organic liquids can be used as solvents.
• the process according to the invention works without halogen-containing additives or bleaching agents and also leads to pulp with a residual lignin content of less than 1.0% by weight in the case of the softwood inputs which are difficult to delignify.
• the ozone is generated in a commercial generator from pure oxygen.
• the concentration is 105 g ozone / m3 of the gas mixture under normal conditions of 0 ° C and 1013 mbar.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Polysaccharides And Polysaccharide Derivatives (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=6426711

Family Applications (1)

Country Status (5)

Cited By (2)

Families Citing this family (1)

Citations (1)

Family Cites Families (6)

• 1991
  • 1991-03-08 DE DE19914107357 patent/DE4107357C1/de not_active Expired - Lifetime
• 1992
  • 1992-02-14 EP EP92102470A patent/EP0503304A1/de not_active Withdrawn
  • 1992-02-25 FI FI920831A patent/FI920831A/fi not_active Application Discontinuation
  • 1992-03-03 NO NO92920830A patent/NO920830L/no unknown
  • 1992-03-06 CA CA 2062475 patent/CA2062475A1/en not_active Abandoned

Patent Citations (1)

Non-Patent Citations (1)

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