EP0892107A1 - Herstellung von mechanischem Holzstoff mit reduziertem Energieverbrauch - Google Patents

Herstellung von mechanischem Holzstoff mit reduziertem Energieverbrauch Download PDF

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Publication number
EP0892107A1
EP0892107A1 EP98305702A EP98305702A EP0892107A1 EP 0892107 A1 EP0892107 A1 EP 0892107A1 EP 98305702 A EP98305702 A EP 98305702A EP 98305702 A EP98305702 A EP 98305702A EP 0892107 A1 EP0892107 A1 EP 0892107A1
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Prior art keywords
pulp
refining
sulfonation
energy
chemical
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EP98305702A
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English (en)
French (fr)
Inventor
Adrian J. Barnet
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Donohue Inc
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Donohue Inc
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Publication of EP0892107A1 publication Critical patent/EP0892107A1/de
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    • 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
    • D21C9/001—Modification of pulp properties
    • D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
    • D21C9/004—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives inorganic 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
    • D21C3/06—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides sulfur dioxide; sulfurous acid; bisulfites sulfites

Definitions

  • the present invention relates to the preparation of improved mechanical wood pulps with reduced refining energy useful in all papermaking applications.
  • mechanical pulp as used herein has its normal meaning in the art and refers to the product of disruption of a woody substance by mechanical action to yield a product consisting mainly of liberated and separated single woody fibres and their fragments and which is suitable for use in the manufacture of paper.
  • fibre as used herein also has its normal meaning in the art and refers to individual plant cells which make up the woody material and which, in softwoods, are known botanically as parenchyma cells and cracheids. These fibres inherently have diameters generally below 0.05 mm and in the case of wood species commonly used in pulp formation and paper making, such as, spruce, balsam, pine, aspen and poplar, considerably below 0.05 mm.
  • Refiner pulps are a class of mechanical pulps formed by passing particulated cellulosic fibrous material, usually wood chips through a small gap between two ribbed parallel plates rotating with respect to each other (known as a disc refiner). The procedure may be effected under pressure, typically about 1 to 2 atmospheres greater than atmospheric pressure, and at elevated temperature, such as, about 120°C, the product being known as “thermo mechanical pulp” (TMP).
  • TMP thermo mechanical pulp
  • the refining process usually is effected in two or more stages. In a first stage, the fibres are separated and liberated and in a second stage, additional refining energy is supplied to increase the fibre flexibility and conformability, fibrillation and bonding. Usually about half the overall refining energy used in the refining process of about 2.0 to about 2.4 MWh/odt or higher is applied to the fibre-liberation stage.
  • wood chips which have not been softened by chemical action, are subject to mechanical action in a disc refiner to form a pulp consisting mainly of single wood fibres and fragments thereof, the pulp is subjected to chemical reaction with a soluble salt of sulfurous acid under certain specific elevated temperature and pressure conditions, and the chemically-treated pulp is subjected to mechanical action to refine the same and improve pulp quality to provide a refined pulp having a Canadian Standard Freeness of about 50 to about 700.
  • the interstage chemical treatment is effected at an elevated temperature of above about 110°c and under a superatmospheric pressure with an aqueous solution of a soluble salt of sulfurous acid, usually sodium sulfite, containing sufficient alkali to maintain a pH greater than about 3 during the treatment.
  • the chemical treatment is effected at a temperature and for a time to enable reaction with the pulp to occur.
  • the chemical treatment also is effected at a temperature and for a time insufficient to result in a treated pulp yield below about 85% by weight, preferably to maintain the yield above about 90% by weight.
  • Fiber-to-fiber bonding within a dry paper sheet formed from the pulp produced by the procedure of CP 1,145,107 is improved, thereby resulting in the desirable properties of increased tensile and burst strength and increase sheet density.
  • a method of preparing a refiner mechanical pulp which comprises:
  • the maximum level of energy use in the primary stage of refining is about 0.75 MWh/odt (megawatt hours per oven dry tonne of pulp). This value compares with a minimum value of about 0.9 MWh/odt and a usual range of about 1.0 to about 1.2 MWh/odt as described in the aforementioned CP 1,145,107. Preferably, the energy level used is greater than about 0.4 MWh/odt.
  • the first stage of refining is then followed by the interstage chemical treatment and subsequent refining steps.
  • thermomechanical pulp TMP
  • the present invention employs the mechanical refining with interstage chemical treatment procedure of Canadian Patent No. 1,145,107 but in a manner which surprisingly leads to an overall energy saving for the same final pulp freeness of refiner mechanical pulp as compared to pulp produced by procedures described in the Canadian Patent.
  • the present invention enables there to be produced a pulp of paper-making properties similar to conventional thermomechanical pulp (TMP) of the same freeness at considerable energy savings in comparison to that required to produce TMP.
  • TMP thermomechanical pulp
  • the process of the invention comprises three steps, namely (a) subjecting particulated cellulosic fibrous material to mechanical action in a disc refiner under specific condition of energy application to form a pulp consisting mainly of single fibres and fragments thereof, (b) chemical reaction of the pulp with a soluble salt of sulfurous acid under certain precise elevated temperature and pressure conditions as detailed below, to produce a desired level of sulfonation and (c) subjecting the chemically-treated pulp to mechanical action to refine the same and improve the pulp quality.
  • the cellulosic fibrous material species and refining conditions required to manufacture a usable mechanical pulp are well known to the art. For example, it is well known that most hardwoods cannot usefully be refined without a chemical pre-treatment to yield mechanical pulps with adequate strengths. Unlike the procedure described in CP 1,145,107, which is restricted to refiner pulps which are generated from softwoods, or other cellulosic fibrous material species which are recognized in the industry as being suitable for the preparation of refiner pulps.
  • the procedure of the present invention enables hardwoods to be used to produce mechanical pulps of adequate pulp properties. For example, this benefit can be realized by co-refining a mixture of softwood and hardwood chips and cotreating the resulting chips. Typical results are seen in Figures 9 to 13. The invention is described further with particular reference to wood species.
  • a wood fibre consists essentially of a cell wall, whose outer surface is made up of cellulose-rich fibrillar layers known as the S 1 and S 2 layers. In wood, the space between the fibres, known as the middle lamellae, is filled with a lignin-rich material.
  • the process of the invention requires that, in the initial liberation of the fibre from the wood in a disc refiner, the fracture occurs mainly in the S 1 and S 2 layers, thus exposing the cellulose-rich fibrillar material which is the source of the fibrillation characteristics of a good mechanical pulp. Since this fibre morphology is established at the moment of fibre liberation, it is necessary that the process of fibre liberation proceed largely to completion. Therefore, the product of the initial mechanical fibre separation step of the process of the invention must consist mainly of single wood fibres, which inherently have average diameters less than 0.05 mm.
  • the initial fibre separation step in this invention is effected at a temperature below the thermal softening point of lignin.
  • the latter temperature is variable with the wood species, duration of heating and refining conditions but is generally below 150°C.
  • the primary refining stage energy may be significantly decreased while maintaining the same level of interstage chemical treatment and subsequent refining energy while the freeness remains substantially unchanged.
  • the first stage of refining is affected at a maximum energy usage of about 0.75 MWh/odt, preferably greater than about 0.4 MWh/odt.
  • the effect of the decreased energy use in the first stage of refining on final freeness and overall energy may be seen in Figure 1.
  • the primary stage refining energy was varied while the interstage chemical treatment was maintained at a temperature of about 160°C for about 40 minutes at a chemical application of about 8 wt% sodium sulfite at about pH 8.7 under a pressure of about 75 psig at a pulp consistency of about 30% to provide a degree of sulfonation of 1.7 to 1.8%.
  • the second stage refining step which also included fibre rejected from screening stages was maintained at about 0.65 MWh/odt.
  • Primary stage refining is effected in the present invention at level below about 0.75 MWh/odt which is below any primary stage energy level contemplated in CP 1,145,107, wherein a minimum value of about 0.9 MWh/odt, usually about 1.0 to about 1.2 MWh/odt, is employed and leads to a significant overall energy requirement.
  • This phenomenon of decreased primary stage refining while maintaining substantially the same freeness can be achieved through high intensity refining in the primary stage and/or by making a higher freeness pulp in the primary stage of refining.
  • High intensity refining may be effected commercially in a number of ways, such as by increased refiner speed, increased throughput of the refiner or by manipulation of other refining parameters, such as consistency and plate pattern.
  • a higher freeness pulp may be achieved by directly decreasing the energy applied in the first stage of refining.
  • step (a) the chemical nature of the fibre is modified by reaction with an aqueous solution of a soluble salt of sulphurous acid, usually sodium sulphite, to sulfonate the fibers.
  • the reaction is effected at temperatures above about 110°C under a superatmospheric pressure for a time sufficient to yield a chemically-treated mechanical wood pulp capable of forming a paper web having improved wet stretch and stress-strain properties and exhibiting rapid drainage, but for a time insufficient to cause substantial dissolution of lignin with consequent loss of yield and generation of polluting effluents.
  • the exact nature of the chemical reactions involved in the chemical treatment effected in this invention are not fully understood, but involve sulfonation.
  • the alkali requirement may be met entirely with sodium sulphite. However, since only half of the sodium of sodium sulphite is available for neutralization, it is usually more economical to meet part of the alkali requirements by additions of sodium hydroxide or sodium carbonate.
  • the pH of the mixture is preferably kept below about 12 because hemicelluloses are dissolved from wood fibre by higher pH's, with consequent loss in yield.
  • the chemical reaction is effected in accordance with the present invention under reaction condition necessary to achieve levels of sulfonation of the pulp from about 0.3 to about 2 wt%, preferably about 0.4 to about 1.8 wt%.
  • levels of sulfonation may be achieved by utilizing selected combination of temperature, time and chemical concentration as the cooking conditions. As seen in Table 1 below, various levels of sulfonation may be achieved by varying these reaction conditions.
  • the amount of sodium sulphite used in the chemical treatment is in the range of about 1% to about 15% by weight based on mechanical wood pulp resulting from step (a), preferably about 2 to about 10% by weight.
  • the chemical charge preferably has a pH between about 7 to about 12, and contains sodium sulphite and sufficient alkali to maintain a pH greater than 3 throughout the reaction.
  • step (c) the maximum improvement, namely, maximum increase in wet stretch, maximum improvement in stress-strain, maximum increase in strength characteristics, and maximum decrease in refiner power requirements for the second stage (step (c) discussed below), is obtained from the process of the invention when the mechanical pulp from step (a) with added chemical is heated at about 160°C for 30 minutes.
  • the temperature can be lowered if the reaction time is increased. Below about 120°C, reaction time becomes impractically long, and below 110°C, the required reactions effectively cease.
  • the reaction temperature can be increased if the reaction time is shortened.
  • the practical upper limit of temperature appears to be about 200°C with reaction times of 1 to 2 minutes. We prefer not to operate under these extreme conditions because the precise control of conditions and reaction times needed to achieve an optimum product and difficult to secure.
  • reaction time is shorter than optimum, the improvements in wet stretch, stress-strain and strength properties and energy requirements are less than may be otherwise obtained by operating under optimum conditions. If the reaction time is too long, substantial dissolution of the lignin from the pulp, in the treating chemical occurs, with consequent loss of yield and formation of polluting effluent. While the process is still operable to produce property improvements under these conditions some of the advantages of wood economy and low pollution are lost and generally are avoided.
  • the chemical treatment is operable over a time-temperature range from about 110°C for about 12 hours to about 200°C for about 1 minute. It is understood that an increase in temperature must be accompanied by a concomittant decrease in reaction time.
  • the temperature of the reaction varies from about 130° to about 160°C with reaction times from about 20 to 60 minutes.
  • temperature/time profiles are employed in conjunction with chemical concentration to achieve the desired degree of sulfonation between about 0.3 to about 2 wt%, preferably about 0.4 to about 1.8 wt%.
  • step (b) is subjected to further refining action, following the usual practice of the industry for subsequent refining of a mechanical wood pulp.
  • Such subsequent refining may include a separate refining step.
  • the results of this further refining action differ from those obtained with an ordinary mechanical wood pulp because the application of steps (a) and (b) in accordance with this invention places the pulp in the required physical and chemical configuration to utilize further refining energy efficiently and economically.
  • the product of step (b) may be refined to equivalent quality with significantly less energy, while achieving a faster drainage, as compared to mechanical pulp from step (a) which has not been subjected to step (b).
  • the same overall freeness and pulp quality of the three-stage process of CP 1,145,107 can be achieved herein at a reduced overall energy saving, as a result of the reduced application of energy in the first stage refining.
  • a lesser quality pulp comparable to conventional TMP is desired, such a product can be achieved with a considerably decreased overall energy usage as compared to the processes of TMP.
  • the amount of energy applied in step (c) may be varied according to the desired properties of the product and the intended end use.
  • the degree of refining to which the pulp is subjected to usually controlled by the freeness of the finished pulp. For most applications, this freeness should fall within the range of about 50 to about 700 C.S.F.
  • boxboard stock is typically of higher freeness than magazine grade paper stock.
  • This Example illustrates the effect of interstage cooking condition on the degree of sulfonation.
  • Wood chips were subjected to primary stage refining at an energy level of 0.7 MWh/odt at various temperatures, times and sodium sulfite solution concentration at about pH 8.7 under a suitable superatmospheric pressure at a pulp consistency of about 35%. The results obtained are shown in Table 1 below.
  • Table 1 shows the impact of the variation in the time, temperature and amount of chemical added on the degree of sulfonation, illustrating that the severity of the cook may be manipulated to achieve a desired degree of sulfonation to the pulp.
  • This Example illustrates the effect of degree of sulfonation on wet web properties and the energy savings resulting therefrom.
  • Figure 3 shows that the same wet web tensile strength can be achieved by combining both the refining energy as measured by a drop in freeness and the degree of sulfonation.
  • the reference TMP sample in these Figures is given by the legend "0% sulfonation”.
  • Figure 4 shows that the same bulk value can be reached by combining both the refining energy as measured by a drop in freeness and the degree of sulfonation.
  • Figure 5 shows that the same breaking strength can be obtained by combining the refining energy as measured by the drop in freeness and by the degree of sulfonation.
  • This Example illustrates the savings in energy achieved using a combination of hardwood and softwood to form the pulp.
  • the wet web properties of paper sheets were determined for a mixture of 50:50 hardwood/softwood pulp produced under the condition of sulfonation to provide 0.8 wt% sulfonation.
  • Figures 9 to 12 show the improvement in pulp properties due to the interstage treatment which can be obtained with a combination of hardwood/softwood pulps for a given level of sulfonation.
  • Figure 13 shows the decrease in overall energy saving which is achieved according to the invention. As seen therein, to achieve the same freeness level as the reference TMP, substantially less refining time and hence refining energy, is required after cooking the pulp.
  • the present invention provides novel procedure for producing pulps of paper-making properties the same as the superior to conventional TMP at an overall energy saving. Modifications are possible within the scope of the present invention. Impact of Cooking Conditions on Degree of Sulfonation COOK NO.

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
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EP98305702A 1997-07-17 1998-07-16 Herstellung von mechanischem Holzstoff mit reduziertem Energieverbrauch Withdrawn EP0892107A1 (de)

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US5292497P 1997-07-17 1997-07-17
US52924P 1997-07-17

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003002813A3 (de) * 2001-06-29 2003-03-20 Voith Paper Fiber Systems Gmbh Verfahren zum delignifizieren lignocellulosischer rohstoffe
WO2004104293A1 (de) * 2003-05-21 2004-12-02 Voith Paper Fiber Systems Gmbh & Co. Kg Verfahren zum delignifizieren lignocellulosischer rohstoffe

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4145246A (en) * 1976-07-19 1979-03-20 Crown Zellerbach Corporation Process for making high-strength, high-yield sulfite-modified thermomechanical pulp and a linerboard composition produced therefrom
EP0030778A1 (de) * 1979-12-17 1981-06-24 Q.N.S. Paper Company Limited Verfahren zur Herstellung raffinierter Pulpe

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4145246A (en) * 1976-07-19 1979-03-20 Crown Zellerbach Corporation Process for making high-strength, high-yield sulfite-modified thermomechanical pulp and a linerboard composition produced therefrom
EP0030778A1 (de) * 1979-12-17 1981-06-24 Q.N.S. Paper Company Limited Verfahren zur Herstellung raffinierter Pulpe

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
HAYNES J B ET AL: "IMPROVING TMP PULP PROPERTIES BY SULFONATION", TAPPI JOURNAL, vol. 71, no. 10, October 1988 (1988-10-01), pages 123 - 127, XP000025617 *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003002813A3 (de) * 2001-06-29 2003-03-20 Voith Paper Fiber Systems Gmbh Verfahren zum delignifizieren lignocellulosischer rohstoffe
US7182836B2 (en) * 2001-06-29 2007-02-27 Voith Paper Fiber Systems Gmbh Kg Method for delignifying lignocellulosic raw materials
WO2004104293A1 (de) * 2003-05-21 2004-12-02 Voith Paper Fiber Systems Gmbh & Co. Kg Verfahren zum delignifizieren lignocellulosischer rohstoffe

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Publication number Publication date
CA2243228A1 (en) 1999-01-17
NO983302L (no) 1999-01-18
NO983302D0 (no) 1998-07-16

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