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
  • D21C9/1026—Other features in bleaching processes

Definitions

• the present invention relates to a method in processing, in particular the processing of cellulosic materials in a processing zone with a gas in a liquid, the gas being supplied to the liquid 5 and being conveyed together therewith to the processing zone.
• oxygen-enriched 0 alkali extraction implies that oxygen is added to and caused to react with paper pulp in the alkali extraction stage of the bleaching process, where the pulp concentration is normally between 8 and 12 per cent. Since that volume which is consumed both in oxygen bleaching and in oxygen-enriched alkali extraction 5 is considerably greater than that which would be possible to dissolve into the available volume of liquid, the greater part of the oxygen must be supplied in gas form and this oxygen volume must then be caused to remain in contact with the paper pulp for a sufficient time to allow for the necessary reactions. It is also important that the oxygen be distributed as uniformly as possible, in the form of minute gas bubbles, since this favours the reaction speed between oxygen and paper pulp.
• the desired effect is achieved by an intensive shearing of the paper pulp suspension, this suspension being subjected to a powerfully turbulent state.
• the paper fibres are released from one another and float freely in the suspension, and, in this state, the suspension assumes-, properties which very closely approximate those of a liquid.
• oxygen or other gas is supplied to a pulp suspension in this state, the gas will be distributed extremely uniformly throughout the suspension in the form of minute bubbles.
• the fibres attach to one another and create a relatively fixed network.
• This network is capable of retaining the " gas bubbles which were formed, until such time as the necessary reactions have taken place. Since its breakthrough roughly eight years ago, oxygen- enriched alkali extraction (which entails an oxygen addition in the alkali extraction stage of the bleaching plant) has developed apace. Considerable cost savings have been achieved at low investment costs. In so-called filter bleaching plants - in which the pulp is conveyed in conduits to the subsequent bleaching stage at a pulp concentration of between 8 and 12 per cent, it has become possible to apply this technique, since a high-intensity mixer may readily be installed in the conduits.
• the extraction liquid flows vertically downwardly in a central pipe from the top of the bleaching tower down to the distribution nozzles of the extraction stage.
• the extraction liquid is distributed from the nozzles into the paper pulp.
• One object of the present invention is to devize a method for increasing that volume of gas which may be retained in a liquid and be conveyed therewith.
• a further object of the present invention is to device a method for obtaining a finely-divided admixture of gas in a liquid which is stable for a relatively lengthy period of time. SOLUTION
• Fig. 1 shows the defoaming as a function of time for T-liquor and U-liquor before and after centrifuging in table centrifuge;
• Fig. 2 shows defoaming as a function of time for liquors from A, U and T;
• Fig. 3 shows defoaming as a function of time for the same liquors as in Fig. 2 with an addition of EDTA
• Fig. 4 shows defoaming as a function of time for T-liquor in different degrees of concentration
• Fig. 5 shows defoaming as a function of time for T-liquor, before and after pH adjustment and addition of EDTA
• Fig. 6 shows defoaming as a function of time for T-liquor and U-liquor before and after ultra-centrifuging.
• Fig. 1 shows a number of characteristic properties for extraction liquid from three mills, designated A, U and T.
• the liquor from mill T may only absorb relatively slight amounts of oxygen, while the liquors from mills A and U have a considerably greater capacity to absorb and transport oxygen.
• Extract content (%) of sample 0.013 0.010 0.006 Extract content ⁇ %) of dry content 1.2 0.8 0.7
• Fig. 1 shows the foam stability for liquors from plant T and from plant U.
• Liquor from the latter plant displays excellent foaming stability and is capable of absorbing a sufficient amount of oxygen for its purpose, while the liquor from plant T suffers from poor foam stability and displays an insufficient capacity to absorb and transport oxygen.
• One point of uncertainty was that the degree of acidity between the samples was extreme, i.e. pH 7 for liquor from plant U and pH 13 for liquor from plant T. A modification of the pH for the liquor from plant U to pH 13 did not, however, change the foam stability.
• Fig. 2 shows the foam degradation as a function of time for liquors from plants A, U and T.
• the l quor from plant T gives a less voluminous and stable foam than foam from either plant A or plant U.
• a complex foaming agent for int al calcium, EDTA the foam stability increases for liquors from all plants.
• the foam volume markedly increases for liquor from plant T, as will be apparent from Fig. 3. These results are reproduceable.
• liquor from plant T is evaporated to higher dry contents, both foam volume and foam stability increase, as is apparent from Fig. 4.
• the pH increases from 12.9 to 13.5 and the surface tension is reduced from 46.8 to 38.4 mN/m.
• Fig. 5 it has been shown that the foam increase and surface tension -reduction are not dependent upon any change of the degree of acidity of a liquor.
• the r ⁇ le played by the calcium soaps in the system is less clear.
• the calcium soaps act as anti-foaming agents. They do not form lamellar phases to the same extent as sodium soaps and are insoluble in their nature. In a system in which both lamellar phases and calcium soaps co-exist, it is possible that the foam-damping effect of the calcium soaps is "masked" by the stabilizing effect of the lamellar phase.
• the liquor from plant T contains, after ul ra-centrifuging, a minor amount of calcium soap and lamellar phase. Liquor from plant T reacts much more powerfully to an addition of complex-forming agents, for example EDTA, which are assumed to complex-bind calcium ions.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Chemical Or Physical Treatment Of Fibers (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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• 1987
  • 1987-03-13 SE SE8701042A patent/SE460202B/sv not_active IP Right Cessation
• 1988
  • 1988-03-09 WO PCT/SE1988/000117 patent/WO1988007102A1/en not_active Application Discontinuation
  • 1988-03-09 JP JP50259288A patent/JPH02502553A/ja active Pending
  • 1988-03-09 BR BR888807412A patent/BR8807412A/pt unknown
  • 1988-03-09 EP EP19880902602 patent/EP0342204A1/en not_active Ceased
• 1989
  • 1989-09-12 FI FI894312A patent/FI894312A0/fi not_active IP Right Cessation

Non-Patent Citations (1)

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