EP1061173A1 - Delignifizierung von lignocellulosischem Material mittels Sauerstoff - Google Patents

Delignifizierung von lignocellulosischem Material mittels Sauerstoff Download PDF

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Publication number
EP1061173A1
EP1061173A1 EP00111891A EP00111891A EP1061173A1 EP 1061173 A1 EP1061173 A1 EP 1061173A1 EP 00111891 A EP00111891 A EP 00111891A EP 00111891 A EP00111891 A EP 00111891A EP 1061173 A1 EP1061173 A1 EP 1061173A1
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Prior art keywords
pulp
stage
oxygen
soaking
alkali
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EP00111891A
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English (en)
French (fr)
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Jorge Luiz Colodette
Ana Sabina De Campos Henriques De Brito
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Praxair Technology Inc
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Praxair Technology Inc
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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
    • D21C9/10—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
    • 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

Definitions

  • This invention relates to oxygen delignification of pulp and, more particularly, to an improved oxygen delignification process that requires reduced amounts of capital equipment.
  • a minimum impact mill is one that generates minimum water and air emissions without negatively affecting wood and energy consumption or product quality.
  • the achievement of a MIM is a slow, stepwise process that requires many modifications and adjustments of current mill practices. These include: (1) minimization of spills; (2) closed water loops in the wood yard; (3) closed screen rooms; (4) efficient brown stock washing; (5) high yield and low energy intensive pulping processes; (6) extended oxygen delignification; and (7) partially closed bleach plants through reuse of some bleaching filtrate streams.
  • Lignocellulosic pulp originated from virgin or recycled fiber contains color-causing compounds, which must be removed during the bleaching operation in order to produce a bright and high quality pulp.
  • the removal of such compounds from virgin or recycled pulp fibers is usually done in a single stage but more commonly in a sequence of chemical treatments that may include two or more of the following chemicals: oxygen, ozone, chlorine, hypochlorite, chlorine dioxide, hydrogen peroxide, peracids, chelants, alkali, enzymes, etc.
  • An oxygen treatment is usually applied to the pulp in the beginning of the bleaching process to remove the bulk of the pulp colored materials such as lignin, extractives, dye, pigments, inks, etc.
  • the kappa number is defined as the number of milliliters of 0.1N potassium permanganate solution consumed by one gram of pulp and corrected for 50% consumption of the potassium permanganate initially added. The higher the kappa number, the more lignin is present in the pulp and vice-versa.
  • oxygen delignification is more selective than pulping, it is wise to stop the cooking at a higher kappa number and remove as much as possible of the lignin by oxygen delignification. This way, process yield and mill throughput are increased; wood consumption is decreased; causticizing and recovery loads are decreased; and pulp quality is maintained.
  • a bleach plant should produce low volume effluent, containing low concentrations of metals, chlorides and organic matter.
  • the initial stages of the bleaching sequence should generate filtrates, which are easily cycled back to the recovery system, i.e. they should contain low chloride and ideally be of an alkaline nature. This concept gave rise to the so-called elemental chlorine free (ECF) light bleaching processes, which necessarily require some form of extended oxygen delignification.
  • ECF elemental chlorine free
  • Double stage oxygen delignification requires high capital investment.
  • extended oxygen delignification which achieves the goal of ECF light bleaching, but at significantly decreased capital cost.
  • Double stage oxygen delignification can be practiced at medium consistency in a number of ways. Despite the high capital investment required to install this technology, most are suitable for combination with subsequent ECF light bleaching since they result in delignification rates in the range of 40-50% for hardwoods and 50-60% for softwoods.
  • these include: (1) two pressurized stages at high pressure, with and without intermediate washing; (2) two pressurized stages, the first being at high pressure and the second at low pressure, with and without intermediate washing; (3) two pressurized stages, the first being at low pressure and the second at high pressure, with and without intermediate washing; (4) two pressurized stages as in cases 1-3, but with a metals removal step in between, through chelation; (5) two pressurized stages as in cases 1-3 (with intermediate washing) with addition of hydrogen peroxide in the second stage; (6) two pressurized stages as in cases 1-3 with oxidative lignin activation in between; and (7) two pressurized stages as in cases 1-3 with mild acid hydrolysis in between to remove metals and hexene uronic acids, etc.
  • the double stage process is better fitted to oxygen delignification kinetics. It is well known that oxygen delignification reactions occur in two phases. A first phase is rapid and is controlled by diffusion. Most of the reaction occurs rapidly via electrophylic attack of the oxygen and other free radicals on residual lignin structures containing free phenolic units. The second phase is slow and is controlled by chemical reactions of types which include not only electrophylic attack of oxygen and other intermediate species to the lignin, but also nucleophylic attack of peroxides (organic and inorganic), which are produced in the first phase of the reaction. Thus, in the first phase of reaction, there occurs significant delignification and almost no pulp brightening, whereas both delignification and brightening occur in the second phase.
  • the oxygen delignification process is more suitable to the kinetics if performed as a double stage process. Since the first phase or reaction is fast, the first stage of the double stage process can be run for a shorter period of time than the second, and the remaining reaction takes place in the second stage reactor which is run for a longer period of time.
  • Fig. 1 shows a schematic of a prior art double stage oxygen delignification process, without inter-stage washing.
  • two high shear mixers 10 and 12 are required, one prior to first reactor 14; and the second prior to second reactor 16.
  • Oxygen and oxidized white liquor (OWL), a highly alkaline liquid, and/or caustic are added prior to first reactor 14; but provisions can be made to add these chemicals between reactors 14 and 16, if required.
  • a washing step between the two reactors is optional and is usually not required since its beneficial effects are questionable.
  • FIG. 2 A layout of the system containing intermediate washing stage 18 is shown in Fig. 2. However, since it is eventually needed to add hydrogen peroxide in a second reactor 16, the presence of intermediate washing stage 18 is desirable to avoid peroxide losses in reactions with partially oxidized organic carryover.
  • first oxygen reactor 14 must operate at low oxygen pressure and second oxygen reactor 16 at high oxygen pressure in order to maintain process selectivity.
  • the alkali charge must be kept high in first reactor 14 and low in second reactor 16, and the opposite is valid for the oxygen charge (partial pressure).
  • the oxygen should be split between the two reactors, with the larger fraction being applied in second reactor 16.
  • mixer 12 located between the two stages is the mixing of the oxygen added in the second stage and re-mixing the residual oxygen bubbles that eventually coalesced in the first reactor. Since the alkali readily mixes with the pulp, there is no need to re-mix it.
  • the desired rates of delignification are achieved using forms of the double stage oxygen delignification process depicted in Figs. 1 and 2.
  • the double stage processes are more expensive to install since they require heavy equipment.
  • an additional reactor and mixer are required.
  • an additional reactor, mixer and washer are required.
  • the invention configures a process for delignifying pulp wherein one stage of a two stage oxygen delignification plant is obviated.
  • a pulp soak stage enables a pulp stream to be mixed with an alkali feed and held in residence for a sufficient period of time to allow an alkali hydrolysis leaching of colored materials from the pulp and a swelling of the pulp fibers.
  • the pulp stream is combined with an oxygen feed and is processed through a mixer.
  • the output of the mixer is fed to a pressurized reactor where oxygen reacts with lignin of the pulp fibers.
  • the swelled pulp fibers facilitate the oxygen reaction with lignin and removal of additional colored materials.
  • a washing step is introduced between the soaking and the oxygen reaction stage to increase process efficiency, but at added capital cost.
  • the present invention is directed towards an improvement in the process of removing colored compounds from lignocellulosic material using alkali and oxygen.
  • the pulp is first treated with alkali and then further treated with oxygen.
  • a key feature of the present invention is the treatment of the pulp with alkali, prior to oxygen delignification.
  • the alkali soaking of the pulp fibers results in an alkali hydrolysis/leaching of easily accessible colored materials and also in the swelling of the pulp fibers, facilitating removal of the colored materials in the subsequent oxygen delignification stage.
  • a 5-10% improvement in the rate of removal of colored materials is achieved as compared to conventional oxygen delignification processes.
  • the invention allows for an achievement of the same rate of delignification as the prior art double stage oxygen delignification process (which requires much more capital investment).
  • the process of the invention is particularly efficient to delignify lignocellulosic material containing lignin contents higher than usual.
  • pulps having the following kappa numbers be subjected to the process of the present invention, that is: 30-40 for softwood kraft pulps, 17-25 for hardwood kraft pulps and 15-30 for recycled fibers. This specification expresses all compositions in weight percent, unless specifically expressed otherwise.
  • the present invention comprises the treatment of the lignocellulosic pulp with alkali in a vessel at atmospheric pressure.
  • the treatment hereafter called pulp soaking, is carried out at a pH in the range about 9-14, advantageously about 11-12.
  • Preferred conditions for the pulp soaking are as follows: temperature 70-90°C, consistency 10-12%, retention time 0.5 to 1 hour and alkali dosage of 1-2% based on pulp dry weight.
  • the alkali dosage may vary substantially, depending upon the type of lignocellulosic material being treated.
  • the preferred way to control the pulp soaking is through monitoring of the pH of the slurry rather than the alkali dosage.
  • the lignin removal during the soaking is a function of the pulp's initial lignin content.
  • the pulp may go directly to a subsequent oxygen delignification stage or be washed in conventional washers or thickened to a consistency of about 30-35% in a wash press.
  • the soaked pulp is then treated with oxygen in a medium consistency oxygen delignification stage, hereafter designated as the O-stage.
  • This O-stage operates at 10-12% consistency, 11-12 pH, 60-95°C, 60-90 min reaction time, 400-600 kPa pressure and at a 1.2-2.5% oxygen dose.
  • a magnesium salt, magnesium sulfate or the like, at a dosage of 0.01-0.1 wt% Mg (based on dry pulp) and most advantageously about 0.02-0.03 of Mg, may be added to protect the pulp carbohydrates against alkali-induced degradation.
  • the magnesium salt should be added before the alkali addition in order to facilitate mixing of the salt with the pulp. Note that the dosage of alkali and of a magnesium salt will depend on whether or not there is a washing or pressing step in between pulp soaking and the O-stage.
  • Fig. 3 depicts the process of the invention wherein washing between pulp soaking and the O-stage is omitted.
  • the process comprises two separate stages, a pulp soak stage 50 and an O-stage 52, with no washing or pressing between them.
  • the pulp incoming from a brown stock washing operation receives both MgSO 4 via feed 51, and alkali (e.g., NaOH with oxidized white liquor or unoxidized white liquor) from a source 54 through pump 56.
  • alkali e.g., NaOH with oxidized white liquor or unoxidized white liquor
  • the pulp/alkali slurry then goes into a high density soak vessel 58 at atmospheric pressure, where it remains for a desired residence time.
  • the pulp slurry is then sent to O-stage 52 where additional alkali and a magnesium salt may be added (if necessary) in the suction of a pump 60. Thereafter, the slurry goes to a high shear mixer 62 where medium pressure steam and oxygen are added via feeds 64 and 66, respectively, to the pulp slurry. The pulp slurry is then pumped to pressurized reactor 68 where the slurry is maintained for a desired reaction time. After the reaction completes, the pulp is discharged into a blow tube and is pumped to post O-stage washers (not shown).
  • Fig. 4 shows a second embodiment of the invention wherein the pulp slurry is washed between pulp soak stage 50 and O-stage 52.
  • the pulp slurry is pumped by pump 70 to a washer 72 and is then conveyed to conventional O-stage 52, as previously described.
  • Fig. 5 shows a third embodiment wherein the pulp, after soaking in soak stage 50, is pumped to a wash press 80 instead of a regular washer.
  • the slurry is dewatered to a consistency between 35-40% and is then conveyed to a standpipe 82 where it is diluted to a consistency between 10-14% with filtrate from the subsequent O-stage.
  • the pub receives additional alkali and a magnesium salt via feed 84, and then goes to O-stage 52 for processing as above described.
  • FIG. 6 a pulp processing sequence is shown that comprises two separate stages, an alkaline soak stage 100 first and then an O-stage 102, with no washing or pressing between them.
  • the embodiment shown in Fig. 7 is similar except for the fact that pulp is washed or pressed between the alkaline soak and oxygen delignification stages.
  • the major difference between these processes, as compared to those described above with respect to Figs. 3-5 is that the oxygen treatment is effected at a lower reaction pressure (hydrostatic pressure), i.e., a mini-O.
  • This stage is carried out at 10-12% consistency, 11-12 pH, 70-80°C, 60-120 min reaction time, 150-300 kPa pressure (overpressure or head pressure), 0.5-1.05% oxygen dose.
  • a magnesium salt, magnesium sulfate or the like may be added to protect the pulp carbohydrates against alkali induced degradation.
  • the magnesium salt must be added before the alkali addition in order to facilitate mixing of the salt with the pulp. Note that the dosage of alkali and of a magnesium salt depends on whether or not there is a washing or pressing step between the pulp soaking and the O-stage.
  • the alkali requirement is minimum, only about 10-20% of the total amount required. This additional alkali is necessary to replenish the fraction consumed during the soaking stage.
  • additional alkali is required. An alkali dose of 1-1.5% should be added. Note that the alkali requirement varies substantially depending upon the type of lignocellulosic material.
  • the pulp slurry is conveyed directly to the O-stage where additional alkali and a magnesium salt are added in the suction of the pump; following the slurry goes to a high shear or static mixer where medium pressure steam and oxygen are added to the pulp.
  • the pulp is then pumped to a preretention tube 104 followed by a down-flow tower 106 (or directly to an up-flow tower) where it is maintained for the desired reaction time.
  • Preretention tube 104 is usually pressurized up to 200 kPa and down-flow tower 106 operates atmospherically.
  • the up-flow tower operates atmospherically but the head pressure of the column; the pressure in the bottom of the tower where the oxygen is injected depends upon the tower height.
  • the pulp is pumped to post stage washers (Fig. 6).
  • Fig. 7 illustrates the presence of an inter-stage washing system.
  • Figs. 3-7 The major advantages of the techniques described in regards to Figs. 3-7 are: (1) they are less capital intensive than double stage processes since they require one less pulp washer, high shear mixer and pressurized reactor, while maintaining pulp quality and process efficiency; (2) they are easily retrofitted to single stage oxygen delignification installations without major investment, with the advantage of enhancing delignification performance by 5-10%; and (3) they can also be applied to mini-O processes (low pressure oxygen delignification) enhancing rates also by 5-10% with minimal capital investment.
  • mini-O processes low pressure oxygen delignification
  • the difference between the process of the invention in relation to the prior art is a reduction in overall capital cost investment when compared to double stage oxygen delignification processes. Also, they can enhance delignification by 5-10% when applied in connection with both conventional single stage and mini-O oxygen delignification processes.
  • the invention treats lignocellulosic pulp with alkali at atmospheric conditions followed by a high or low-pressure exposure of the pulp to oxygen in pressurized vessels.
  • the invention is applicable to all kinds of fibrous raw material including pulps manufactured by processes such as kraft, soda, sulfite, magnefite, cold soda, NSSC and the like. These fibers may be obtained from hardwood, softwood, bamboo, bagasse, straw and other non-wood fiber supplies.
  • the process is also applied to de-inked recycled fibers and certain grades of brown recycled fibers.
  • the pulp alkali treatment can be performed in atmospheric and pressurized vessels, preferably in atmospheric ones.
  • the alkali used can be of several origins including plain NaOH, oxidized white liquor (OWL), unoxidized white liquor (WL) or the like. Most advantageously, the reaction occurs with 0.5-5 weight percent NaOH.
  • the vessel may be a dedicated one or the high-density tower already existing in most pulp mills.
  • the treatment called of pulp soaking (S) is carried out with a pulp consistency of about 6-14 weight percent.
  • a pH of at least 11 facilitates the alkali soaking. Most advantageously, the soak occurs at a pH between about 11 and 12. Elevating the soaking temperature to between 40 and 95°C accelerates swelling of the lignocellulosic pulp.
  • the soaking occurs at a temperature between 70 and 95°C to accelerate the reaction.
  • a soaking time of 15 to 240 minutes advantageously swells the fibers to facilitate the reaction between the oxygen and the lignin.
  • a soaking time between about 20 or 30 minutes and 60 minutes accomplishes the soaking.
  • the alkali dose consists about 0.5-5% NaOH, most advantageously, about 1-2% NaOH.
  • the alkali dosage may vary substantially, depending upon the type of lignocellulosic material being used.
  • the pulp may go directly to a subsequent oxygen treatment or be washed in conventional washers or thickened to a consistency of about 30-35% in a wash press.
  • the equipment required to wash or thicken the pulp is standard and available in the market. This operation affects the overall direct and indirect costs of this invention.
  • provisions can be made for additional pulp treatments such as chelation to remove metals and mild acid hydrolysis to remove hexene uronic acids and metals prior to the subsequent oxygen treatment.
  • the soaked pulp is then treated with oxygen three different ways: (1) at low pressure (mini-O), in a process hereafter designated as (EO); (2) in a conventional MC (medium consistency) single stage oxygen delignification process, hereafter designated as O; and (3) in a MC double stage oxygen process, hereafter designated as O/O or OO, depending on whether the pulp is washed between stages or not.
  • the oxygen used in this treatment may be of purity varying from 80-100%, preferably 90-100%.
  • the low pressure oxygen treatment or mini-O (EO) may be carried out at a consistency of from 8-14 weight percent, preferably from 10-12 weight percent.
  • Preferred conditions for other parameters are: pH of from 10-14, preferably 11-12, alkali dose of 1-4% preferably 1-2%, temperature of 50-120°C, preferably 70-90°C, reaction time of from 30-180 min, preferably 60-90 min, reaction pressure of 100-600 kPa, preferably 150-300 kPa and oxygen dose of 0.2-2%, preferably 0.5-1%.
  • a magnesium salt, magnesium sulfate or the like may be added to protect the pulp carbohydrates against alkali induced degradation.
  • the magnesium salt can be added before or together with the alkali, but preferably before the alkali in order to facilitate mixing of the salt with the pulp.
  • the dose of the magnesium salt may be in the range of about 0.01-0.1% (as Mg) based on the pulp dry weight, preferably about 0.02-0.03%.
  • Hydrogen peroxide may also be added in the (EO) stage to boost delignification in the dose of 0.2-4%, preferably 0.5-1%. The addition of peroxide is feasible only when the pulp is washed after soaking.
  • the conventional single stage oxygen treatment, O may be carried out at a consistency of from 8-14%, preferably from 10-12%.
  • Preferred conditions for other parameters are: pH of from 10-14, preferably 11-12, alkali dose of 1-4% preferably 1-2%, temperature of 50-140°C, preferably 80-100°C, reaction time of from 30-180 min, preferably 60-90 min, reaction pressure of 100-800 kPa, preferably 400-600 kPa and oxygen dose of 0.5-4%, preferably 1-2%.
  • a magnesium salt, magnesium sulfate or the like may be added to protect the pulp carbohydrates against alkali induced degradation.
  • the magnesium salt can be added before or together with the alkali but preferably before the alkali in order to facilitate mixing of the salt with the pulp.
  • the dose of the magnesium salt may be in the range of 0.01-0.1% (as Mg) based on the pulp dry weight, preferably 0.02-0.03%.
  • Hydrogen peroxide may also be added in the (O) stage to boost delignification in the dose of 0.2-4%, preferably 0.5-1%; the addition of peroxide is feasible only when the pulp is washed after soaking.
  • the double stage oxygen treatment, O/O or OO may be carried out at a consistency of from 8-14%, preferably from 10-12%.
  • Preferred conditions for other parameters are: pH of from 10-14, preferably 11-12, alkali dose of 1-4% preferably (1.5/0.5%), temperature of 50-140°C, preferably (85/95)°C, reaction time of from 30-180 min, preferably (30/60) min, reaction pressure of 100-800 kPa, preferably 400-600 kPa and oxygen dose of 0.5-4%, preferably (1.5/0.5%).
  • a magnesium salt, magnesium sulfate or the like may be added to protect the pulp carbohydrates against alkali induced degradation.
  • the magnesium salt can be added before or together with the alkali but preferably before the alkali in order to facilitate mixing of the salt with the pulp.
  • the dose of the magnesium salt may be in the range of 0.01-0.1% (as Mg) based on the pulp dry weight, preferably (0.02/0.0%).
  • Hydrogen peroxide may also be added in the double stage oxygen treatment to boost delignification in the dose of 0.2-4%, preferably (0.0/0.5%); the addition of peroxide is feasible only when the pulp is washed after soaking.
  • the "/" divides the first stage addition or condition from the second stage addition or condition.
  • (0.03/0% Mg) indicates a 0.03% Mg addition to the first stage and a 0% Mg addition to the second stage.
  • the values of kappa number, viscosity, and brightness were measured according to the Technical Association of the Pulp and Paper Industry (Tappi) standard procedures. All experiments described were carried with two repetitions, being the results presented average values.
  • Pulp Alkali Soaking was effected at 12% consistency, 85°C, 30 min, with 1.5% alkali.
  • the reaction was carried out in a high shear mixer/reactor made of hasteloy having temperature and pressure controllers and devices for injection and relief of gases. The mixing was done intermittently every 1-min at 2000 rpm for 4 seconds. Variations in alkali dose, temperature and reaction time were practiced but they are described at the proper examples.
  • Press washing between stages was effected by diluting the pulp after the stage to a consistency of 4% and then pressing it to a consistency of about 35%. This corresponds to a washing efficiency of about 80%, considering for example the pulp entering the washing stage at 10% consistency. Note that washing between stages has no representation whereas no washing is usually represented by a slash symbol (/).
  • the kraft pulp sample employed in this example was obtained in the laboratory from eucalyptus wood. After pulping, the brown pulp had a initial kappa number of 19.6, a viscosity of 58.7 mPa.s and a brightness of 28.9% ISO. The soaking was carried out at, 65, 75 and 85°C for periods of time of 15, 30, 60 and 180 min. Other conditions were maintained constant as described in previous sections. After soaking, the pulp was thoroughly washed and then analyzed for kappa number, viscosity and brightness. The results shown in Table 1 indicate that soaking efficiency as measured by kappa drop is positively influenced by both time and temperature. However, the benefits of the soaking somewhat decrease after 30-min reaction, particularly at the 85°C temperature.
  • Example 2 The same kraft pulp sample employed in Example 1 was soaked with alkali doses of 0.5, 1.0, 1.5, 2.5 and 4% NaOH. Other soaking conditions were maintained constant as described above. After soaking, the pulp was thoroughly washed with distilled water and the values of kappa number, viscosity and brightness measured. The results in Table 2 denote that increasing soaking pH above 12 produces only slight benefits in terms of kappa drop but penalizes somewhat pulp viscosity. Thus the pH 12, which for this pulp sample is equivalent to an alkali charge of 1.5%, was considered to be the most satisfactory.
  • the various hardwood kraft pulp samples employed in this Example were obtained from eucalyptus wood. Pulping conditions were adjusted in order to produce low, medium and high degree of delignification pulps, for hardwood standards. After pulping, the sample of low degree of delignification had 14.3 kappa, 35.7 mPa.s viscosity and 34.9% ISO brightness; the medium degree of delignification sample had 16.8 kappa, 47.5 mPa.s viscosity and 32.3% ISO brightness; the high degree of delignification sample had 19.6 kappa, 58.7 mPa.s viscosity and 28.9% ISO brightness. The soaking was carried out under the conditions previously described. After soaking, the pulp was thoroughly washed with distilled water and the values of kappa, viscosity and brightness measured.
  • the hardwood kraft pulp sample employed in this example was the same described in Example 1.
  • the soaking was carried out at fixed conditions as described in the above sections.
  • the subsequent oxygen delignification treatments were carried out as described above, under the following conditions: O: 10% consistency, 95°C, 60 min, 600 kPa overpressure, 1.5% NaOH, 1.5% O 2 , 0.03% Mg; (EO): 10% consistency, 85°C, 60 min, 200 kPa pressure, 1.5% NaOH, 0.8% O 2 , (0.03 Mg); O/O: 10% consistency, (85/95°C), (30/60 min), 600 kPa pressure, (1.5/0% NaOH), (1.5/0.5% O 2 ), (0.03/0% Mg); OO: 10% consistency, (85/95°C), (30/60 min), 600 kPa pressure, (1.5/1.0% NaOH), (1.5/0.5% O 2 ) and (0.02/0.02% Mg).
  • the insertion of the washing step between these treatments still was not enough to make additive the benefits of the treatments.
  • the soaking treatment removes lignin fractions that would otherwise be removed in the subsequent oxygen treatments.
  • additive benefits are not to be expected, there is still an advantage of applying the soaking since overall delignification can still be increased by up to 7.4% with this technique.
  • Table 5 Another interesting aspect shown in Table 5 is with regard to the soaking plus low pressure (mini-O) oxygen delignification, S/(EO) and S(EO) processes.
  • the soaking treatment adds an extra 5-7% kappa reduction to a (EO) stage.
  • This benefit is rather significant given the fact that the EO (oxygen extraction) operation is designed to achieve lower delignification levels than conventional O-stages.
  • a 5% improvement in the (EO)-stage, which gives 20-25% delignification rate, is more significant than a 8% improvement in the O-stage that gives 35-40% delignification rate. Note that this benefit is obtained with no penalty to pulp quality and with very low capital investment.
  • the softwood kraft pulp sample employed in this example was obtained from a Western North American pulp mill and was made from Spruce. After pulping, the brown pulp had a 32.2 kappa number, a 42.7 mPa.s viscosity and a 26.4% ISO brightness. The soaking was carried at fixed conditions as described in previous sections.
  • the subsequent oxygen delignification treatments were carried out under the following conditions: O: 10% consistency, 95°C, 60 min, 600 kPa pressure, 2.0% NaOH, 2.0% O 2 , 0.03% Mg; (EO): 10% consistency, 85°C, 60 min, 200 kPa pressure, 2.0% NaOH, 1.0% O 2 , 0.03% Mg; O/O: 10% consistency, (85/95°C), (30/60 min), 600 kPa pressure, (2.0/0% NaOH), (1.5/0.5% O 2 ), (0.03/0% Mg); OO: 10% consistency, (85/95°C), (30/60 min), 600 kPa pressure, (1.5/1.0% NaOH), (1.5/0.5% O 2 ) and (0.02/0.02% Mg).
  • the D(EOP)D designation represents a sequence which comprises three separate stages, the first D-stage, an (EOP) stage and then another D-stage, with a washing or pressing step between these stages.
  • first D-stage 10% consistency, 75°C, 60 min, 3.0 final pH and a kappa factor of 0.24
  • (EOP) 10% consistency, 85°C, (15/75) min, 200 kPa pressure, 10.5 final pH, 1.4% NaOH, 0.5% O 2 , 0.5% H 2 O 2 , 0.03% Mg
  • second D-stage 10% consistency, 75°C, 240 min, 3.8 final pH and variable amounts of ClO 2 depending upon pulp previous treatment and type.
  • the control of pH in the first and second D-stages was achieved through small additions of NaOH or H 2 SO 4 in the stages as required.

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EP00111891A 1999-06-14 2000-06-13 Delignifizierung von lignocellulosischem Material mittels Sauerstoff Withdrawn EP1061173A1 (de)

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RU2233926C1 (ru) * 2003-06-30 2004-08-10 Алтайский государственный университет Способ делигнификации растительного сырья
EP3380667A4 (de) * 2015-11-27 2019-04-17 Valmet Ab Verfahren und vorrichtung zur sauerstoffdelignifizierung von zellstoff
CN112778539A (zh) * 2021-01-04 2021-05-11 中国林业科学研究院林产化学工业研究所 一种从纤维原料中制备高羧基含量的氧化木质素的方法
EP3682056A4 (de) * 2017-09-11 2021-06-09 Solenis Technologies, L.P. Verfahren zur verbesserten sauerstoffdelignifizierung von chemischen holzzellstoffen
SE2250793A1 (en) * 2022-06-27 2023-12-28 Valmet Oy Method for processing cellulose pulp obtained from a kraft process

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CN112342816B (zh) * 2020-11-02 2022-08-09 天津科技大学 一种氧脱木素中纸浆的保护技术
CN115417931B (zh) * 2022-09-22 2024-03-22 上海同化益生纤生物科技有限公司 一种耐温型纤维素的制备方法与应用

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2233926C1 (ru) * 2003-06-30 2004-08-10 Алтайский государственный университет Способ делигнификации растительного сырья
EP3380667A4 (de) * 2015-11-27 2019-04-17 Valmet Ab Verfahren und vorrichtung zur sauerstoffdelignifizierung von zellstoff
EP3682056A4 (de) * 2017-09-11 2021-06-09 Solenis Technologies, L.P. Verfahren zur verbesserten sauerstoffdelignifizierung von chemischen holzzellstoffen
US11193237B2 (en) 2017-09-11 2021-12-07 Solenis Technologies, L.P. Method for enhanced oxygen delignification of chemical wood pulps
CN112778539A (zh) * 2021-01-04 2021-05-11 中国林业科学研究院林产化学工业研究所 一种从纤维原料中制备高羧基含量的氧化木质素的方法
SE2250793A1 (en) * 2022-06-27 2023-12-28 Valmet Oy Method for processing cellulose pulp obtained from a kraft process
SE546238C2 (en) * 2022-06-27 2024-07-23 Valmet Oy Method for processing cellulose pulp obtained from a kraft process

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CN1277283A (zh) 2000-12-20
JP2001003287A (ja) 2001-01-09
BR0002634A (pt) 2001-01-02
CA2311718A1 (en) 2000-12-14
KR100538083B1 (ko) 2005-12-22
KR20010049536A (ko) 2001-06-15
NO20003014D0 (no) 2000-06-13
NO20003014L (no) 2000-12-15

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