WO2013004909A1 - Procédé d'élimination d'hémicelluloses dans une pâte - Google Patents

Procédé d'élimination d'hémicelluloses dans une pâte Download PDF

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Publication number
WO2013004909A1
WO2013004909A1 PCT/FI2012/050697 FI2012050697W WO2013004909A1 WO 2013004909 A1 WO2013004909 A1 WO 2013004909A1 FI 2012050697 W FI2012050697 W FI 2012050697W WO 2013004909 A1 WO2013004909 A1 WO 2013004909A1
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Prior art keywords
pulp
alkali
cellulose
cold
solution
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PCT/FI2012/050697
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English (en)
Inventor
Kari Kovasin
Esko Turunen
Ismo Reilama
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Metsä Fibre Oy
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Publication of WO2013004909A1 publication Critical patent/WO2013004909A1/fr

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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
    • 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
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
    • D21H11/16—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only modified by a particular after-treatment
    • D21H11/20—Chemically or biochemically modified fibres
    • 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
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/0007—Recovery of by-products, i.e. compounds other than those necessary for pulping, for multiple uses or not otherwise provided for

Definitions

  • the present invention relates to a method of producing dissolving pulp, wherein the raw- material is cellulose pulp which is subjected to a chemical treatment.
  • the method can also be applied in connection with dissolving pulping processes known in the art.
  • Dissolving pulp is normally used for the manufacture of viscose fibers and other fibers as well as for the production of processed products requiring high chemical purity. This kind of use requires an increase of the actual cellulose content (also known as alpha-cellulose) and reactivity towards various types of derivatization chemicals, such as carbon disulphide.
  • lignin and hemicellulose materials are removed from the cellulosic fibers. Removal of lignin is accomplished in a similar fashion as, generally, in the manufacture of chemical pulp, viz. by cooking of the lignocellulosic raw materials with chemicals which remove lignin at conditions typical for each process. The cooking methods may be subdivided, for example, into alkaline, acid and solvent (organosolv) cooking methods. It is also possible to combine a variety of cooking steps by which lignin is removed to provide a multi-step cook. Removal of lignin is complemented in downstream processing (oxygen
  • pulping methods wherein the target alpha-cellulose content can be achieved in connection with the cooking. Such methods are based on a multi-stage sulphite cooking or a prehydrolysis-kraft cooking.
  • the chemicals of the various cooking stages, and in particular the pH are varied suitably.
  • a specific acid hydrolysis step in which the pH of the chips is reduced with steam, water or an acid solution to a low level.
  • no separate removal step of hemicelluloses is necessarily needed at all.
  • the prehydrolysis- kraft cook is so close to the basic kraft process used for the production of paper pulp that its application does not require a radically different technology compared to that of the paper pulp production.
  • the prehydrolysis-kraft process has the disadvantage that when the intensity of the hydrolysis is increased, selectivity towards cellulose is jeopardized. This leads to the fact that the wood consumption per ton of dissolving pulp produced may be uneconomically high. Selectivity can be improved by selecting milder hydrolysis conditions, at which hydrolysis does not remove as much hemicelluloses as would be theoretically possible. A lower rate of removal of hemicelluloses, however, means that in order to reach the desired alpha-cellulose concentration the removal of hemi cello ses has to be continued for example, with a hot-alkali step connected to bleaching.
  • Xyrofin and Eastman Kodak WO 98/56958 and WO 98/16682 describe the production of xylose in connection with an alkaline treatment.
  • Xyrofin is the owner of a patent family (WO 01/04 362), which describes a solution in which xylan is removed from kraft pulp in one single step. This step is carried out at acidic conditions using hot formic acid.
  • Cold alkali extraction is a method which is highly effective and selective with regard to the removal of xylan-based hemicelluloses and, thus, for purification of cellulose.
  • hemicelluloses are dissolved in polymeric form in a concentrated alkaline solution at a low temperature.
  • the NaOH solution used in the processing should be clearly more concentrated than that used in a hot alkaline step.
  • the solubility of the hemicelluloses into such a solution is limited, and after a time they begin to re-precipitate on the surfaces of the fiber.
  • the other, mainly economic, limiting factor is associated with the closure of the alkali balance at a pulp mill.
  • a known method is to use oxidized white liquor, and to return from the cold alkali step the alkali recovered by washing and to recycle it in concentrated form to the recovery cycle of the white liquor of a pulp mill.
  • the most difficult practical problem related to the performance of the cold alkali step is to take care of the further treatment and recycling of NaOH back to the process.
  • a completely open process step in which NaOH is not recovered but drained, is a completely ⁇ unacceptable (economic) alternative as regards the operational economics of the process and processing of the waste water. If the pulp of the cold alkali stage is washed efficiently, almost all the NaOH can be transferred to the washing filtrate, whereby NaOH can in principle be returned to the feed of the cold alkali stage and re-used.
  • the washing step is never, however, 100% efficient, so that part of the NaOH will proceed forward along with the washed pulp through the process. This washing loss may be compensated by adding fresh NaOH to the filtrate recycle which is recirculated to the feed of the cold alkali stage.
  • the paper pulp can be used for other chemical processes, which aim may be to lower the degree of polymerization (DP) of the cellulose or at opening of the fiber or at increasing cellulose reactivity.
  • DP degree of polymerization
  • peroxide treatment and/or treatment with endoglucanase enzymes can be used, for example, peroxide treatment and/or treatment with endoglucanase enzymes.
  • the present invention aims at providing a novel method for treatment of bleached kraft pulp.
  • the present invention therefore relates to a method of manufacturing dissolving pulp, in which method the raw-material is bleached paper pulp obtained by the kraft method and for which material the present chemical treatment is carried out.
  • a cold alkali stage carried out in this way can be equally well be coupled to a prehydrolysis-kraft cooking method of a dissolving pulp mill and with some restrictions even to a dissolving pulp process equipped with a sulphite cooking step.
  • the present inventive method is characterized by what is set forth in the characterizing part of claim 1.
  • the present invention enables the production of modified cellulose, especially dissolving pulp, produced in any mill producing bleached kraft cellulose.
  • modified cellulose especially dissolving pulp
  • Membrane filtration and treatment of the filtrate by evaporation also allow for an increase of the alkali concentration of the cold alkali stage to a higher level than normal. By raising the concentration of the NaOH treatment it is possible to improve the selectivity of treatment with regard to cellulose.
  • the method according to the present invention for separating hemicellulose material from the filtrate of the cold alkali stage also makes it possible to recover the hemicellulose material dissolved during the alkali stage from the pulp and to exploit the material in the cellulose manufacturing process.
  • the hemicelluloses can be conducted for instance to cooking or to oxygen delignification, in which case a part of them can be precipitated on the fibers whereas the rest is taken to the production of energy by the recovery circulation.
  • Fig 1 shows one preferred embodiment of the method of the present invention. Detailed Description of Preferred Embodiments
  • the present invention relates to a method of manufacturing dissolving pulp or such modified pulp in which the raw material chosen is a normal hemicellulose containing bleached pulp, in particular paper pulp, cooked by the kraft method.
  • the method can also be applied to dried cellulose pulp.
  • the raw-material is preferably washed prior to the treatment, after cooking and bleaching, with water or with an aqueous solution, preferably with water. Washing can be carried out in one or more stages.
  • the present method is carried out by cold alkali treatment which is effected by mixing the raw-material mass into a concentrated alkali solution to give a mixture comprising 50-220 g/1, for example 50 to 120 g/1 of an alkali, and allowing the solution to be absorbed into the mass at a temperature of 20-50 °C, preferably 20-40 °C.
  • the alkali is allowed to act upon the pulp in order to dissolve the hemicelluloses into it, and the thus obtained hemicellulose containing alkali solution is separated from the thus treated pulp, i.e. dissolving pulp.
  • the hemicelluloses are separated from the alkali solution used for said treatment, and the solution is concentrated whereby a substantial part of the alkali solution is recycled, for example by recirculating it for the provision of a mixture of the raw-material and the alkali solution. In particular, at least 90% of the alkali solution is recycled.
  • the hemicellulose concentration of the mass is reduced by employing the cold alkali treatment in a novel way.
  • the cold alkali stage can be followed by further chemical processing to shorten the cellulose chains, for example in a peroxide step, or to improve the reactivity of cellulose using endoglucanase enzymes.
  • the cold alkali treatment carried out in a novel way also makes it possible efficiently to manufacture dissolving pulp also in dissolving pulp mills based on present process solutions.
  • the absorption of the cold alkali treatment is continued for at least 10 minutes, preferably for 30 minutes - 2 hours.
  • the alkali used in the actual cold alkali treatment is a strong base, which preferably is the NaOH or white liquor commonly used in the kraft cooking, preferably it is an aqueous NaOH solution, having a concentration of from 10 to 50 % by weight.
  • the alkali concentration is adjusted in the pulp suspension fed to the cold alkali stage to a level of 50 - 120 g NaOH/1.
  • the concentration of alkali may be increased if necessary to improve the selectivity of the method up to the concentration of mercerization liquor which usually is 180 - 220 gNaOH/l.
  • hemicelluloses are dissolved in polymeric form in the concentrated alkali solution used.
  • the temperature at this stage is from 20 - 40 ° C, preferably close to ambient temperature, that is, close to a value of 25 ° C, typically approximately 20-25° C.
  • the cold alkali stage in particular is carried out in such a way that the base used in the treatment or the liquor is recycled.
  • the base is preferably recovered by filtration, for example, with a semipermeable membrane, in particular by ultrafiltration. Recycling is preferably carried out while maintaining the necessary alkali concentration, for example, by evaporation of water and by removing dissolved organic matter (such as hemicelluloses) from the recycled liquor.
  • washing is however preferably carried out, whereby the pulp which has passed through the cold alkali stage is washed, for example, with water or aqueous solution, preferably water.
  • the base used is conducted into the washing filtrate which is then filtered to remove the organic material as described above. Washing can be carried out in one or more stages, preferably in 2 to 3 steps.
  • the performance of the cold alkali stage can be technically particularly meaningful and economical if the filtrate of the optional washing stage is fractionated by filtration such that the organic material, i.e. essentially the hemicelluloses dissolved in the cold alkali stage is enriched in the concentrate and the low molecular weight inorganic matter, i.e. in practice the alkali, is conducted according to the flow rate, through the membrane into the permeate. Washing losses can be, based on literature data, kept at a three-step washing at 20-50 kg NaOH / ton of pulp.
  • an ultrafiltering membrane having a cutoff values in the range of 1 - 10 kDa.
  • the filtering is executed so that the hemicellulose is concentrated in the input side of the membrane, in the so called concentration stream, and the alkali passes the membrane essentially without concentrating in the permeate stream.
  • the filtering is carried out in such a way that the hemicellulose content in the liquor, after filtering, remains in the reactor below the solubility limit, and by using a concentration rati o which enables total recycling of the concentrate as make-up alkali (generally 10 - 14 kg NaOH/ton of pulp, or less) for the cooking or oxygen delignifi cation.
  • a concentration rati o which enables total recycling of the concentrate as make-up alkali (generally 10 - 14 kg NaOH/ton of pulp, or less) for the cooking or oxygen delignifi cation.
  • the ultrafiltration membranes used are not capable of separating 100% of the organic matter and the NaOH from each other, whereby there will be present both NaOH and organic material in the permeate and in the concentrate.
  • the membrane filtration removes from the filtrate cycle to the pulping process 30 kg NaOH/ton of pulp, and if the washing loss of the washing following the cold alkali stage is 20 kg NaOH/ton of pulp, there is a need for fresh feed of NaOH for the cold alkali stage of 50 kg/ton of pulp.
  • the required dosage of NaOH per ton of pulp is as high as 900 - 1000 kg, expressed as pure NaOH. If the pulp of the cold alkali stage is efficiently washed almost all of the
  • NaOH can be transferred to the washing filtrate whereby this NaOH can be recycled to the feed of the cold alkali stage and re-used.
  • the washing step is never, however, 100 % efficient, so a part of the NaOH continues with the washed pulp further along the process. This washing loss can, however, be compensated by adding fresh NaOH to the filtrate recycle returned to the feed of the cold alkali stage.
  • the amount of NaOH exiting chemical circulation can amount to 10-100 kg of NaOH/ton of pulp. If it is desired to use fresh NaOH in the cold alkali stage, which is justified by processing efficiency and in order to avoid contaminants appearing in the white liquor, it is possible to recycle to the chemical circulation of the pulping process at the most 10 to 20 kg
  • the filtrate circulation of the cold alkali stage is almost completely closed.
  • diluting water along with the pulp stemming from an optional washing stage of the raw-material pulp together with excess water from an optional washing step which is carried out after the phase.
  • excess water from an optional washing step which is carried out after the phase.
  • a small amount of water is transferred to the process.
  • the permeate of the membrane filtration is diluted because of these diluting water volumes, and in order to maintain the water balance and in order to achieve a sufficiently high concentration of alkali water needs to be evaporated from the permeate.
  • the evaporated water can be used for washing, for example in washing carried out after the stage or elsewhere in the pulp process.
  • Treatment of the washing filtrate or of a filtrate obtained without washing with membrane filtration and by evaporation also makes it possible to increase the alkali concentration of the cold alkali stage to a higher level than normal.
  • An increase of the concentration of the NaOH improves the selectivity of the treatment with respect to cellulose.
  • the NaOH concentration can to be increased to a concentration up to that of a mercerization liquor, which is generally at the level of 180 - 220 g NaOH/1.
  • a washing device or a washing system consisting of several washing stages from which the pulp is finally removed pressed to high consistency, for example at a consistency of more than 25 %, which is typical for a washing press. Consequently, after the cold alkali stage it is easy to adjust the pH to and/or temperature of the pulp. It becomes necessary to adjust the acidity for example when endoglucanase enzyme is being dosed in the next process step to increase the reactivity of the cellulose. pH adjustment may be needed also if the pulp is conducted to an acid bleaching reaction stage or to a dryer.
  • the alkali consumption of the entire mill can be reduced by improving the washing carried out after the cold alkali stage by neutralizing the pulp with S0 2 or with sulfuric acid, in particular to a pH of 5 to 7, prior to the last washing stage.
  • the thus obtained neutralized filtrate can be conducted for example to a washing of the raw-material pulp after bleaching, or to an endoglucanase treatment carried out for opening the fibre wall.
  • the raw-material which is a bleached hemicelluloses containing paper pulp produced by kraft pulping
  • - is subjected to a cold alkali treatment by mixing the raw-material pulp with a concentrated alkali solution such that the mixture formed by the pulp and the alkali solution contain 50 - 220 g/1 alkali, e.g. 50 - 120 g/1, and the solution is allowed to absorb into the pulp at a temperature of 20 - 50 °C, - then the alkali is allowed to act on the pulp for dissolving hemicelluloses from it,
  • the alkali solution which contains hemicelluloses and which is obtained from the cold alkali treatment is separated from the treated pulp, and then
  • the alkali solution which passes the ultrafiltration membrane is concentrated by evaporation in order to concentrate the alkali solution so that it has a greater concentration than in the cold alkali treatment;
  • the alkali solution obtained from separation is conducted to cellulose production by kraft pulping, for example to an oxygen delignification step.
  • the amount corresponding to the make up alkali need of the mill is conducted to the oxygen delignification.
  • At least a part ((typically 1 to 45 % by weight)) of the hemicellulose containing alkali solution is conducted in one preferred embodiment to the bleaching of a kraft pulping process to replace fresh alkali such that the amount of fresh alkali fed into the cold alkali stage can be kept at 40-90 kg NaOH/ton of pulp.
  • the large molecular hemicellulose of the concentrate stream is circulated to the production of paper pulp and precipitated on the surface of the cellulose fibres. Then at least a part of the circulated hemicellulose ends up in the recovery circulation of the kraft pulping process and is conducted further to combustion in a recovery boiler.
  • high molecular weight used in respect of hemicellulose means, in the present context, hemicellulose which does not significantly or at all pass an ultrafiltration membrane of the kind described herein.
  • xylan can also be separated by known methods (for example PCT application publication WO/2007/065969). This type of xylan can be used for example as a barrier material.
  • Figure 1 shows an apparatus suitabl e for use in a specific, preferred embodiment of the method according to the present invention.
  • the apparatus comprises the following parts:
  • the raw material pulp is conducted through the inlet 6 of the pulp into the cold alkali reactor 2.
  • the pulp can be obtained, for example, from an optional Prewasher 1 which preceeds the cold alkali stage and which has the task of not only reaching the desired washing result but also to regulate the temperature of the pulp suspension conducted to the cold alkali stage to a desired level.
  • Prewasher 1 which preceeds the cold alkali stage and which has the task of not only reaching the desired washing result but also to regulate the temperature of the pulp suspension conducted to the cold alkali stage to a desired level.
  • fresh alkali solution through the inlet 15 of this feed and via the alkali circulation line 13 of the recycled filtrate.
  • the concentrate 1 1 of the filtration 12 can be conducted to a pulp mill, e.g. to oxygen delignifi cation. Similarly, a part of the concentrated filtrate can be conducted 16 to a pulp mill, e.g. to bleaching.
  • the cold alkali treated pulp is drawn off the reactor 2 along outlet 7 and conducted to, for example, an optional postwasher 3.
  • a preselected amount of washing water is conducted along water inlet 8.
  • the temperature of the washing water can be adjusted as needed so that the cold alkali treated pulp that enters the next process step is at the desired temperature.
  • the pH of the discharge pulp can be adjusted to a level suitable for a next processing step.
  • the cold alkali treated and optionally washed pulp is conducted away from the cold alkali stage along the pulp discharge piping 9.
  • the efficiency of the optional washing stage carried out after the alkali treatment has to be selected such that the alkali and the organic substances dissolved by the alkali stage (mainly hemicellulose material) which are conducted along with the flow of the treated pulp can be transferred to the filtrate of the post washing stage, which filtrate preferably is further conducted to the feed piping 10 of the filtrate.
  • the recovery rate of this washing stage with respect to alkali and dissolved organic material is at least 95 %. The recovery rate can be even higher than that, even in excess of 98 %, if it is desired to recover the alkali as completely as possible or if the next processing step requires significant adjustment of pH.
  • the filtrate of the washing step is conducted preferably through said filter feed pipe 10 to the membrane filtration device 4, which can be an ultrafiltration device.
  • the membrane filtration device 4 a desired amount of water and filtrate is transferred through the membrane, which together form the so-called permeate.
  • the cutoff value of the membrane determines how small molecular weight materials will most likely be transferred to the permeate.
  • NaOH has so low molecular weight that its concentration in the permeate is essentially the same as that of the inlet filtration flow.
  • Material with a higher molecular weight in this case an organic material mainly consisting of dissolved hemicelluloses, is concentrated in the so-called concentrate.
  • concentration ratio is the flow ratio of the feed flow to the flow rate of the concentrate. For example, if the concentration ratio is 20, it means that the flow of the concentrate is 1/20 of the volume of the feed stream. Therefore, 19/20 of the feed stream is transferred to the permeate.
  • the mass flow of the NaOH is divided between the permeate and the concentrate in relation to their flow rates because sodium hydroxide has a molecular weight which is very small compared to the membrane's cutoff value.
  • a so-called retention value is generally defined for the high molecular material which is intended to be fractionated by the membrane separation.
  • concentrated is removed from the filtrate circulation and conducted preferably back to preceding steps of the cellulose process, for example to cooking, to washing of brown pulp, to oxygen delignification or to bleaching.
  • the permeate flow is preferably conducted to evaporation in an evaporator 5 which is suitable for that purpose in which the permeate can be concentrated to desired
  • Evaporation can be carried out by using different known technologies which are generally in use for aqueous NaOH containing solutions. Depending on the performance of the evaporation stage there may be a need for temperature regulation and heat recovery for adjusting the temperature of the circulating filtrate flow in order to maintain a desired temperature level of the cold alkali stage. For water economy of the process it is preferred to use the evaporated water in a second washing stage as washing water, depending on how that is made possible by the liquid balance. The evaporated water can also be used as washing water also elsewhere in the manufacturing process of cellulose, in washing stages where there is a need for clean washing water or, more generally, fresh water.
  • the concentrated permeate containing the desired amount of recyclable alkali at the desired concentration and with sufficiently low content of hemicellulose (so that no back- precipitation occurs), is preferably conducted to the pulp flow fed into the cold alkali stage, i.e. into the pulp feed 6.
  • the alkali and liquid balance is thus closed, and the concentration of the dissolved hemicelluloses (mainly xylan) is sufficiently low.
  • one or several chemical further processing steps are carried out after the cold alkali stage, whereby for example the length of the cellulose chains are shortened in a peroxide step or the reactivity of the cellulose is improved by using endoglucanase enzyme.
  • the peroxide solution is allowed to act for at least 10 minutes, especially at least 30 minutes, for example 45 minutes - 10 hours, preferably 1 - 5 hours, at a temperature which is 80 - 100 0 C, preferably about 90 ° C.
  • At treatment with endoglucanase enzyme preferably a neutral pH and a temperature range of 50 - 60 0 C is maintained.
  • the cold alkali extraction is suitable to use in combination with both the sulphite process and a prehydrolysis-kraft process.
  • the process is flexible: it can be placed in connection with oxygen delignification, inside bleaching or after bleaching.
  • Implementing the cold alkali stage as a step which is carried out after bleaching for example before a dryer which is operated at a temperature which is significantly lower than that of the bleaching is more advantageous from the point of view of heat economy than the placing of it in the middle of the process.
  • the prepared dissolving pulp can be used, for example, in viscose manufacture, or in speciality papers, in pressing products or tissue products, in particular in products, such as a plastic laminates, photo papers, filter papers, blotting and absorption papers, egg cartons, or baby diapers or disposable medical supplies, or, after further processing,
  • microcrystalline cellulose microcrystalline cellulose
  • Example 1 The following calculations are based on an example of a preferred embodiment of the method according to the invention and carried out with an apparatus as shown in Figure 1, wherein (X is for xylan, "tp" for tons of pulp):
  • the reactor feed comprises a pulp which comes from a first washer (wash press or equivalent) at a 30 % consistency;
  • test conditions were as follows: temperature 20-25 °C (room temperature) and pressure 0.8-1.2 bar overpressure.
  • the composition of the filtrate before ultrafiltration was:
  • carbohydrate composition xylan 67 % and glucomannan 33 %
  • the filtrate was concentrated on the ultrafiltration device at a concentration ratio of 6.9. This means that the portion which passes the membrane in ultrafiltration (permeate) was 58.7 litre and the concentrate was correspondingly 9.8 litre.
  • composition of the concentrate was:
  • carbohydrate composition xylan 67 %, glucomannan 30 %, glucose 3 % (glucose is apparently derived from partially hydrolyzed glucomannan)
  • the composition of the permeate was:
  • NaOH is divided in the relationship between the flows, this means that retention of NaOH is in practice zero. Some minor dilution takes place in the system because of leakage of condensation water to the apparatus.
  • the test arrangements were not of a kind which allowed further concentration to be carried out. However, it is evident based on the results already obtained that by further concentrating the streams, a concentration ratio of 10 to 20 could have been attained.
  • test results show that an ultrafiltration membrane having a nominal cutoff value of 10 kDa in the present method makes it possible selectively to separate dissolved carbohydrate. Selectivity can be further improved by lowering the cutoff value of the membrane to, for example, a value of about 5 kDa.

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Abstract

La présente invention concerne un procédé de production de pâte dissolvante, une pâte à papier blanchie produite par un procédé de fabrication de pâte kraft étant utilisée en tant que pâte de matière première, le procédé étant réalisé par un traitement avec base froide en mélangeant la pâte de matière première avec une solution de base concentrée de telle façon que le mélange de la pâte et de la solution de base contienne 50 à 220 g/l de base et que la solution puisse être absorbée dans la pâte à une température de 20 à 50°C. L'étape suivante consiste à laisser la base agir sur la pâte afin de dissoudre les hémicelluloses dans celle-ci, et la solution de base contenant les hémicelluloses est séparée de la pâte, c'est-à-dire de la pâte dissolvante de cellulose. Enfin, la solution de base séparée est concentrée et recyclée vers l'alimentation de l'étage avec base froide.
PCT/FI2012/050697 2011-07-01 2012-07-02 Procédé d'élimination d'hémicelluloses dans une pâte WO2013004909A1 (fr)

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FI20115711A FI20115711L (fi) 2011-07-01 2011-07-01 Menetelmä hemiselluloosien poistamiseksi sellusta

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CN105544310A (zh) * 2015-12-03 2016-05-04 高大元 一种改性竹浆纤维壁纸的制备方法
WO2018073177A1 (fr) 2016-10-19 2018-04-26 Re:Newcell Ab Recyclage de textiles cellulosiques
WO2018104330A1 (fr) 2016-12-06 2018-06-14 Re:Newcell Ab Fibres de cellulose
WO2018115290A1 (fr) * 2016-12-23 2018-06-28 Södra Skogsägarna Ekonomisk Förening Procédé de fabrication de pâte à dissoudre
US11332883B2 (en) 2013-12-31 2022-05-17 International Paper Company Treated Kraft pulp compositions and methods of making the same
CN115075033A (zh) * 2022-05-31 2022-09-20 中国制浆造纸研究院有限公司 一种预水解硫酸盐浆制备浆粕的方法

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