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
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
  • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone
• • 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 relates to the removal of lignin from lignocelluloses or pulp.
• "Lignocelluloses” are understood here to mean the macromolecular substances which, in addition to cellulose, also contain hemicelluloses and lignin, such as e.g. is the case with wood.
• the removal of lignin from cellulose or wood is also referred to as "delignification”.
• the raw material consisting of wood or woody annual plants, usually in a mechanically crushed state, is chemically digested.
• acetic acid is used instead of the conventional digestion chemicals based on sulfur compounds, which are problematic for disposal. This method, also known as the Acetosolv method, offers a significant reduction in environmental pollution compared to conventional methods.
• the pulps obtained from the Acetosolv digestion can still contain up to 4% residual lignin, which usually has to be removed by bleaching.
• hydrogen peroxide is added as the bleaching agent, which combines with the acetic acid to form peracetic acid, which is considered a selective lignin oxidizing agent.
• this bleaching has so far only led to satisfactory degrees of whiteness in hardwood pulp, and even then only with a relatively high consumption of hydrogen peroxide.
• ozone In addition to hydrogen peroxide and oxygen, ozone has also been proposed as a chlorine-free bleach. Despite great efforts, however, ozone has not yet been used technically as a bleaching agent because the reaction of ozone in water with hydroxyl ions generates hydroxyl radicals, which break down the cellulose molecules and thus lower the strength properties of the pulp and prejudice the use of ozone as Have established bleach in the pulp production.
• the inventive method for separating lignin from a cellulose mass is characterized in that the cellulose mass is exposed to the action of ozone in the gas phase in the presence of at least one C1 ⁇ 3 fatty acid in order to make the lignin contained in the cellulose mass more soluble by oxidative conversion into fatty acid close.
• ozone concentration is increased and, on the other hand, side reactions due to ozone decomposition products can be reduced.
• low fatty acids react as radical scavengers with OH radicals and can thus prevent these very unselective radicals from attacking cellulose.
• the ozone itself does not have a radical effect, but preferably electrophilic, as a result of which the lignin is selectively attacked and broken down into soluble products.
• ozone in low fatty acids increases its effectiveness as a bleaching agent and thus reduces ozone consumption, which is of fundamental importance for technical use.
• acetic acid is a better solvent for lignin than water, while the reverse is true for cellulose, which further increases the selectivity of ozone as a delignifying agent.
• cellulose mass in the claims and the description denotes all masses (including starting materials) which are suitable for the production of cellulose or cellulose and cellulose (here includes both ⁇ -cellulose and the hemicelluloses sometimes referred to as ⁇ - or ⁇ -cellulose). as well as lignin included.
• acetic acid and propionic acid are suitable as C1 ⁇ 3 fatty acids.
• Acetic acid is preferred.
• Mixtures of such acids with one another and / or with water in limited proportions are also suitable, the water content of the fatty acid, the fatty acid mixture or the preferred acetic acids generally being less than 50% by weight, in particular less than 30% by weight, and usually 1 to 10% by weight .% is.
• a low water content of e.g. 5 to 10% by weight, i.e. a 90 to 95% acetic acid is particularly preferred.
• Ozone obtainable with conventional generators is contained in the gas phase which surrounds the mixture combined with fatty acid, for example consisting of 2 to 50% by weight cellulose mass and 98 to 50% by weight fatty acid.
• the interaction between the cellulose mass / fatty acid mixture on the one hand and the gas phase or the ozone contained therein on the other hand can be influenced in particular by movement or / and the amount of ozone present and / or the temperature. Through movement, both the mixing intensity and the distribution of the solid and liquid phases can be influenced or varied and adapted. Conventional mixing devices that are sufficiently resistant to the components can be used for this purpose; Mixers with a pronounced shear effect on the mix are not preferred.
• the amount of ozone present in the gas phase can be influenced by the gas pressure and / or the ozone concentration in the gas phase.
• a gas phase which mainly consists of air.
• the ozone concentration of a gas phase suitable for the process and consisting predominantly of air or oxygen under normal or slight excess pressure is 0.1 to 10%, generally 1 to 3%. These values are based on the gas volume. Lower ozone concentration values are possible but are not preferred.
• amounts of ozone of 1 to 2% by weight, but also even higher concentrations, can be used without adverse effects for the pulp obtained when working at the preferred temperatures of 0 to 30 ° C. In general, the working temperature (measured in the cellulose mass or the gas phase) is below 100 ° C, in particular below 50 ° C.
• the process according to the invention offers particular advantages when it is used as a delignification stage for pulp bleaching, in which the starting material, in particular wood, is mixed with acetic acid, e.g. is broken down by the process described in DE-A-3 445 132.
• the starting material in particular wood
• acetic acid e.g. is broken down by the process described in DE-A-3 445 132.
• coniferous wood e.g. spruce wood
• kappa values or kappa numbers given here were determined using the method described in Leaflet IV / 37/80 of the Technical Committee for Chemical Pulp and Paper Testing in the Association of Pulp and Paper Chemists and Engineers (BR Germany).
• kappa values or kappa numbers given here were determined using the method described in Leaflet IV / 37/80 of the Technical Committee for Chemical Pulp and Paper Testing in the Association of Pulp and Paper Chemists and Engineers (BR Germany).
• Whiteness levels in the range just mentioned can also be achieved if bleaching is carried out first with peracetic acid and then with ozone. According to the prior art, whitenesses of over 70% ISO after digestion of acetic acid could only be achieved with relatively large amounts of peroxide. According to the invention, degrees of whiteness of over 80% ISO can be achieved if the pulp is first bleached with ozone in a three-stage bleach (Z), then treated with H2O2 (P) and finally again with ozone (Z) or with a PZP bleaching sequence in the same solvent, ie C1 ⁇ 3 fatty acid or acetic acid.
• the process according to the invention is particularly advantageous as a process stage in a "countercurrent process" which e.g. with known carousel extractors according to the information in the magazine "Wood as raw and material", 44 (1986) 207-212, can be carried out;
• acetic acid with or without ozone is used not only for the final extraction, but as the only lignin solvent.
• operation with a low consistency, preferably 2 to 10% pulp, and ozone concentrations below 2%, preferably 0.5 to 1.5%, is possible.
• the acetic acid should contain less than 50% by weight of water, preferably less than 30% by weight and in particular less than 10% by weight of water.
• an addition of another substance, in particular another C1 ⁇ 3 fatty acid, can also be used, i.e. it can also be used with acetic acid, e.g. Contains 1 to 50 wt.% Propionic and / or formic acid.
• devices which are known per se and which have at least one chamber or zone for receiving the cellulose mass containing the fatty or acetic acid are suitable for carrying out the process according to the invention as a separate treatment or as a step in a sequence of treatments or processing operations in the production of cellulose, if these devices have devices known per se for treatment with a gas phase containing ozone.
• the parts of the device which come into contact with the mass or the gas phase consist of correspondingly resistant work materials, preferably steel alloys.
• the properties e.g. the characteristic values of the pulp obtained, such as tear length, rupture area and tear resistance, were not significantly changed by the treatment with ozone by the process according to the invention; the process according to the invention enables pulp products to be obtained, the quality of which corresponds to that of the conventional pulps obtainable by the sulfate process and is considerably better than that of the products obtained by the sulfite process.
• the ozone treatment can drastically reduce peroxide consumption and still achieve a whiteness of over 70% without the mechanical product properties suffering.
• the fatty acid used for the process according to the invention can be worked up and recirculated in an environmentally friendly manner in a manner known per se, for example by azeotropic distillation.
• the distillation residue containing the lignin can also be worked up in an environmentally friendly manner, for example burned.
• C1 ⁇ 3 fatty acid mixtures which, for example, are available in the hydrolysis of plant waste and consist of mixtures of acetic acid, propionic acid and formic acid.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Compounds Of Unknown Constitution (AREA)
• Polysaccharides And Polysaccharide Derivatives (AREA)
• Silicates, Zeolites, And Molecular Sieves (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Citations (4)

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• 1988
  • 1988-01-25 AT AT88810034T patent/ATE90404T1/de not_active IP Right Cessation
  • 1988-01-25 ES ES198888810034T patent/ES2041828T3/es not_active Expired - Lifetime
  • 1988-01-25 EP EP88810034A patent/EP0325890B1/fr not_active Expired - Lifetime
  • 1988-01-25 DE DE8888810034T patent/DE3881676D1/de not_active Expired - Fee Related
• 1989
  • 1989-01-23 CA CA000588913A patent/CA1319472C/fr not_active Expired - Fee Related
  • 1989-01-25 JP JP1017414A patent/JPH01221587A/ja active Pending
  • 1989-01-25 BR BR898900299A patent/BR8900299A/pt not_active Application Discontinuation
• 1990
  • 1990-10-31 US US07/606,595 patent/US5074960A/en not_active Expired - Fee Related

Patent Citations (4)

Non-Patent Citations (6)

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