High-yield cooking method

Abstract

The present invention discloses a cooking method and digestion system in which a partially digested cellulosic fiber source is compressed during cooking to provide high molecular weight xylan, high molecular weight lignin and pulp.

Description

[Technical Field]

[0001] The present disclosure relates to a cooking method for producing at least HMW (high molecular weight) lignin and pulp in combination from wood-based cellulosic feedstocks (wood-based cellulosic feedstocks) with sulfite or organic acids. The pulp produced according to this method is useful for producing paper-grade pulp, dissolving cellulose products, and cellulose derivatives. [Background technology]

[0002] Organic acid, sulfite pulp, and dissolving pulp, also known as paper pulp or dissolving cellulose, are bleached wood pulps with a high cellulose content that are chemically produced from wood using either the sulfite process or the organic acid process. The sulfite process is a commonly used pulping process. In the traditional sulfite process, lignin is extracted from wood chips by treating the wood with an aqueous mixture of various salts of sulfite. The salts used in the pulping process are sulfite (SO3), depending on the pH. 2- ) or bisulfite (HSO3 - ) The counter ion is either sodium (Na + ), calcium (Ca 2+ ), potassium (K + ), magnesium (Mg 2+ ), or ammonium (NH4 +), which decomposes and solubilizes lignin and defibrates wood fibers. Organic acids used in pulping can be, but are not limited to, lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid, and malic acid. Organic acids are organic compounds with acidic properties. The most common organic acids are carboxylic acids, whose acidity is related to the carboxyl group -COOH. Sulfonic acids, which contain the -SO2OH group, are relatively strong acids. Alcohols with -OH groups can act as acids, but are usually very weak. The relative stability of an acid's conjugate base determines its acidity. Other groups, such as thiol groups -SH, enol groups, and phenol groups, can also impart acidity, usually weakly. In biological systems, organic compounds containing these groups are commonly referred to as organic acids.

[0003] Wood pulp generally contains high levels of alpha cellulose and is used in the production of various cellulose derivatives and products for various end uses, and is known in the art as dissolving pulp. Other terms synonymous with dissolving pulp are chemical cellulose and special high alpha pulp. Two processes are commonly used to produce dissolving pulp: 1) The acid sulfite process, the development of which began around the beginning of this century (Rydholm, SA, Pulping Processes, p. 280, Interscience Publishers, New York-London-Sydney 1965); and 2) Preliminary hydrolysis - the Kraft process, the development of which began in 1929 (Rydholm, supra - p. 281).

[0004] The latter process utilizes an acidic pretreatment ("preliminary hydrolysis") step to remove hemicellulose before the alkaline pulping (delignification) step. South African Patent No. 88 / 4037 discloses a pre-hydrolysis - neutral sulfite - anthraquinone process (PH-NS-AO) for the production of "hemicellulose hydrolysate and special pulp" (high alpha grade). This pre-hydrolysis step essentially performs the same function as the pre-hydrolysis step that precedes the Kraft (sulfate) pulping process to produce dissolving-grade pulp. On the other hand, the neutral sulfite-anthraquinone delignification step is essentially the same as the process also known as the semi-alkaline sulfite-anthraquinone (SAS-AQ) method, which was first reported by Raubenheimer, S. and Eggers, S.H. (both researchers employed by SAPPI LIMITED, the applicant of this application) at a technical conference in 1979, namely the 11th European ESPRA Congress held in Maastricht, The Netherlands, in May 1979.

[0005] Furthermore, traditional production of paper pulp and dissolving pulp using the sulfite process suffers from the disadvantage of low yields due to the breakdown of hemicellulose and cellulose in wood into low molecular weight hemicellulose, monosaccharides, and hemicellulose degradation products during the process. The sulfite process also has the disadvantage of long cooking times, which decomposes the hemicellulose and cellulose in wood. Because these degradation products are difficult to extract from the digester, the decomposed material is often used for energy production by vaporizing and burning the components, or simply discarded as waste.

[0006] A summary of the development of the acid sulfite pulping process for preparing semi-chemical pulps can be found in R. Runkel and KF Att, "Halbzellstoffe" (Semichemical Pulps), Gunther-Stalb Verlag, Biberach, 1958, pp. 35-37 and 95-96. Also, the production of high-yield chemical, semi-chemical, and chemi-mechanical pulps by the sulfite process is described in S.A. Rydholm, Pulping Processes, Interscience Publishers, New York, London, Sydney, 1965, pages 418-420.

[0007] Furthermore, G. Jayme, L. Broschinksi, and W. Matzke (Das Papier 18, 1964, pp. 308-314) present a general survey of high-yield chemical pulping and also describe in detail rapid pulping in the gas phase with magnesium bisulfite for 8-20 minutes at temperatures up to 180°C.

[0008] DE-A-1-517219 relates to the production of (high-yield) sulfite chemical pulp. Wood raw materials are pulped in an aqueous solution containing sulfite and / or bisulfite ions, as well as sodium, potassium, magnesium, or ammonium ions. The pH of the solution at the start of pulping is 3.0 to 7.0, preferably 3.7 to 5.0. The maximum pulping temperature is 140°C to 190°C. The entire pulping process takes more than 400 minutes. The residence time at the maximum temperature is 30 to 200 minutes. Pulping is carried out to a final chemical pulp chlorine number in the range of 15 to 32. The pulped material then undergoes controlled defibration and / or defibration and refining. Fines, amounting to 0.2 to 7% of the chemical pulp volume, are then removed. The resulting material has a breaking length of 6.3 km in the unshredded state (freeness value °SR = 14.5 to 15). Chemical pulp is unbleached.

[0009] U.S. Patent Nos. 4,634,499 and 4,734,162 each relate to a method for producing chemical pulp from hardwood, which is particularly suitable for the production of tissue paper. Pulping is carried out using ammonium sulfite, initially at temperatures below 110°C, then at a maximum temperature of 140°C to 155°C, and at a pH of about 2 to 3. The chemical pulp is not subjected to an additional bleaching step.

[0010] EP 0287960A relates to a method for producing hemicellulose hydrolysates and specialty chemical pulps by a two-stage process, in which the first stage involves pre-hydrolysis of lignocellulosic material using, for example, water, mineral acid, sulfur dioxide, sulfite pulping liquor, and sulfite waste liquor at a temperature of 100°C to 180°C for a hydrolysis period of 10 to 200 minutes, and the second stage, in which the lignin contained in the pre-hydrolyzed material is dissolved, is carried out by neutral sulfite pulping with the addition of anthraquinone as a catalyst, with an initial pH of at least 10. The temperature is preferably 160°C to 180°C, and the treatment time is 100 to 200 minutes. Summary of the Invention [Problem to be solved by the invention]

[0011] It is therefore an object of the present disclosure to provide an improved industrial-scale cooking process for producing high-yield paper-grade pulp and dissolving pulp with low hemicellulose content that can be easily delignified and bleached to the required brightness and viscosity levels.

[0012] It is another object to provide a cooking system for wood cellulosic feedstocks that provides pulp, xylan and lignin with high productivity. [Means for solving the problem]

[0013] At least some of the above and other objects can be achieved by the present invention as defined in the independent claims. Additional advantages may be obtained when using the dependent claims and the embodiments described below. The present invention is advantageous in that it allows for the production of value-added products, such as at least one of HMW hemicellulose, HMW xylan, and HMW lignin, from woody cellulosic materials used in pulping. Furthermore, the present invention uses less energy in the production of dissolving pulp or paper-grade pulp than conventional pulping processes.

[0014] The present invention also allows for reduced processing / cooking times. A further advantage is that the overall yield of paper-grade pulp and dissolving pulp in the present process is higher than can be achieved using conventional sulfite processes when producing paper-grade pulp or dissolving-grade pulp.

[0015] Sulfite cooking liquor can be various salts of sulfite. Cooking liquor is used to extract lignin from wood-based cellulosic feedstocks such as wood chips. The salts used in sulfite cooking liquor range from sulfite (SO3 2- ) or bisulfite (HSO 3-) The counter ion is, for example, sodium (Na + ), calcium (Ca 2+ ), potassium (K + ), magnesium (Mg 2+ ) or ammonium (NH4 + ) or a combination thereof.

[0016] According to a first aspect, there is provided: 1. A cooking method comprising: a) providing a wood-based cellulose feedstock comprising chips, pin chips, shavings, sawdust, or a combination thereof; b) optionally pretreating the wood-based cellulose feedstock by exposure to steam at 80-120°C to provide a pretreated material comprising a solid fraction of cellulose; c) optionally pre-hydrolyzing the woody cellulose feedstock and / or the pre-treated material with steam or water to provide a pre-hydrolyzed material; d) cooking under cooking conditions including a cooking liquor containing an acid sulfite or an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid, and malic acid at a chemical loading selected from the range of 1 to 200 g / L to provide a cooked cellulosic material in spent cooking liquor; e) comminuting and compressing the cooked cellulosic material at cooking conditions to release HMW lignin from the cooked material into spent cooking liquor and provide a compressed cellulosic fraction; f) recovering HMW lignin from the spent cooking liquor; g) replacing the spent cooking liquor with a replacement liquor containing cooking liquor having 1 to 200 g / l of acid sulfite or organic acid; h) recovering HMW lignin from the displacement liquor; and i) recovering pulp from said compressed cellulose fraction. A cooking method comprising:

[0017] According to a second aspect, there is provided a HMW xylan fraction obtainable by using the method.

[0018] The method provides xylan with higher molecular weight, higher xylan yield, and higher xylan concentration in the HMW xylan fraction.

[0019] According to a third aspect, there is provided a HMW lignin fraction obtainable by using the present method.

[0020] Using this method, HMW lignin fractions can be obtained with better lignin yields and higher consistency. The HMW lignin also has an increased molecular weight compared to that produced according to conventional processes, such as that disclosed in PCT / FI2011 / 050651.

[0021] According to a fourth aspect, there is provided a pulp obtainable by using the present method, such as a dissolving pulp and / or a paper-grade pulp. The pulp obtained by the present method has higher brightness and requires less wet pressing and less steam consumption in drying compared to pulp produced by conventional methods. Furthermore, the dissolving pulp has a lower hemicellulose content compared to pulp produced by conventional methods.

[0022] Embodiments of the present disclosure offer certain advantages. Depending on the embodiment, one or several of the following advantages can be achieved: reduced consumption of chemicals, water, cellulose fiber sources, and energy; improved yield of cellulose, and increased molecular weight of xylan and lignin. [Brief explanation of the drawings]

[0023] [Figure 1]Figure 1 shows a schematic diagram of one embodiment of the present process, including optional preliminary steaming and optional preliminary hydrolysis of the wood cellulosic feedstock, and a digester (cooker) system for crushing and / or compressing the condensate from the wood chips after cooking. The process parameters mentioned in Figure 1 are exemplary only, and other process parameters can be used, as described in this disclosure.

[0024] [Figure 2] Figure 2 shows a schematic diagram of one embodiment of a digestion (cooking) system for compressing cooking liquor from wood chips when using organic acid or sulfite cooking. The process parameters mentioned in Figure 2 are exemplary only, and other process parameters can be used, as described in this disclosure.

[0025] [Figure 3] Figure 3 shows one embodiment of a general process for compressing wood chips and extruding cooking liquor. The process parameters mentioned in Figure 3 are exemplary only, and other process parameters can be used as described in this disclosure.

[0026] [Figure 4] Figure 4 shows a schematic representation of one embodiment of a process for displacing spent liquor from compressed wood chips. The process parameters mentioned in Figure 4 are exemplary only, and other process parameters can be used, as described in this disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0027] Detailed Description As used herein, the term "comprising" encompasses the broader terms "including," "containing," and "comprehending," as well as the narrower terms "consisting of" and "consisting only of."

[0028] In one embodiment, the process steps are performed in the order specified in any aspect, embodiment, or claim. In another embodiment, any process step specified to be performed on a product or intermediate obtained in a preceding process step is performed directly on said product, i.e., without additional, optional, or auxiliary processing steps that may chemically or physically alter the product between said two steps.

[0029] In one embodiment, the wood-based cellulose feedstock used in the present cooking process is in the form of chips, pin chips, shavings, sawdust, or any combination thereof. It is preferred to use wood chips, and more preferred to use softwood (coniferous) or hardwood (hardwood) chips, such as eucalyptus, pine, or spruce chips. However, when wood chips are used as the primary feedstock, the feedstock may contain lesser amounts of, for example, pin chips and / or sawdust.

[0030] Unless otherwise stated, all percentage values ​​refer to dry weight % expressed as weight % (wt-%).

[0031] The process is suitable for use in a plant or mill, i.e. industrial (large) scale process.

[0032] In one embodiment, the woody cellulose feedstock has a xylan content of 4% by weight or greater. In one embodiment, the woody cellulose feedstock comprises wood chips.

[0033] The term high molecular weight xylan (HMW xylan) means a xylan with a weight average molecular weight (Mw) of 45000 g / mol or greater.

[0034] The term high molecular weight lignin (HMW lignin) refers to lignin with a weight average molecular weight (Mw) of 4500 g / mol or more for hardwoods (broadleaf trees) and 4980 g / mol or more for softwoods (conifers).

[0035] In one embodiment, molecular weight is measured by size exclusion chromatography and is expressed as weight average molecular weight (MW).

[0036] Wood chips typically have a roughly rectangular shape with a height, length, and width. However, the geometry of a wood chip can vary, for example, depending on its manufacturing process. The length (longest dimension) and width (second-longest dimension) of the chip can be considered to determine the rough "flat side" of the chip, and the thickness is the smallest dimension of the chip. In the case of pin chips, the width and thickness can be close to each other, thereby forming an elongated object like a match. The exact dimensions of the chip can vary.

[0037] In one embodiment, the cellulose feedstock serving as the fiber source for the wood-based cellulose feedstock comprises or consists of wood chips, and grinding and compression is applied until the surface area of ​​the wood chips is maximized, preferably at a rate of 250 to 2000 kg / m to release at least HMW xylan and / or HMW lignin. 3 , preferably 350 to 1525 kg / m 3The grinding and compaction are performed to achieve a density of 0.01 mm. Grinding and compaction to a maximum surface area can be achieved by using a gap that allows the smallest dimension, or "side," of the chips to enter first. Devices used for this purpose can be segmented plates, feed screws with blades that decrease in distance, plug feed screws that feed against rotating segment plates, rotors and stators with segmented plates, modified pumps with segmented plates that allow the pump's stator and rotor to pressurize and feed, drum presses with gaps and segmented surfaces, and modified stator and rotor systems. The solution to the problem is not limited to the above and can be adapted by those skilled in the art.

[0038] In one embodiment, the wood cellulosic feedstock is pretreated by steaming before cooking and / or pre-hydrolysis.

[0039] According to one embodiment, pretreatment by steaming is preferably carried out to achieve evacuation of air inside the wood chips to improve penetration of the liquid into the porous wood. Preliminary steaming can be carried out in a separate steaming vessel or chip silo. In one embodiment, steaming is carried out by using low-pressure steam having a pressure of about 3.5 bar for at least 10 minutes, preferably more than 20 minutes. In one embodiment, preliminarily steaming comprises pre-steaming with low-pressure steam at 1-4 bar for 1-100 minutes to provide a pretreated material. In one embodiment, the temperature is above 100°C, preferably above 120°C.

[0040] After optional pre-treatment, the feedstock may be subjected to an optional pre-hydrolysis step or directly to a cooking step.

[0041] In one embodiment, the optionally pretreated wood cellulosic feedstock is pre-hydrolyzed before cooking.

[0042] In one embodiment, the prehydrolysis is carried out with steam or water at a temperature selected from the range of 150-220° C. In one embodiment, the prehydrolysis step comprises prehydrolysis with steam at 8-15 bar for 1-150 minutes at a temperature selected from the range of 150-220° C.

[0043] In one embodiment, the grinding and compacting steps are performed by a plug feed screw in a separate screw with segmented plates, or the material is pressed through a rotating gap that allows the chips to enter shortest dimension first, but is not limited to these embodiments.

[0044] In a preferred embodiment, the chip is forced into the gap such that the flat side of the chip with the largest surface area does not enter the gap first, which can be achieved by pre-orienting the chip into the gap where it will not fit onto its flat side.

[0045] In one embodiment, the comminuting and compacting is carried out by drawing the material through a gap at cooking conditions and releasing the HMW lignin into the spent cooking liquor, thereby providing HMW lignin in the spent cooking liquor.

[0046] In one embodiment, the grinding and compaction is carried out to a consistency of more than 10% by weight, preferably more than 20%, or more preferably more than 30%, or preferably more than 65%. The consistency can be measured using the standard TAPPI T240 Consistency of a pulp suspension or the corresponding ISO 4119 standard.

[0047] In one embodiment, the grinding and compacting is carried out at cooking temperatures to a consistency of at least 10% by weight.

[0048] In one embodiment, the crushing and compacting is carried out by removing the wood chips through a gap in the range of 50 mm to 8 mm, resulting in a reduction in the porosity of the wood within the gap of at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, or more than 70% and release of at least the HMW lignin.

[0049] In one embodiment, grinding and compacting is performed by drawing pin tips through gaps ranging from 35 mm to 6 mm, resulting in a reduction in wood porosity by at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70% or more within the gaps and the release of at least HMW lignin.

[0050] In one embodiment, grinding and compacting is performed by drawing sawdust through a gap in the range of 20 mm to 4 mm, resulting in a reduction in wood porosity within the gap by at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, or more than 70% and release of at least HMW lignin.

[0051] In one embodiment, the grinding and compacting is carried out by pressing the optionally pre-hydrolyzed and / or cooked cellulosic material through a gap, and The size of this gap is chosen as follows: The gap between the wood chips is selected from the range of 50 mm to 8 mm. The gap for the pin tip is selected from the range of 35 mm to 6 mm, The gap for the sawdust is selected from the range of 20 mm to 4 mm.

[0052] The porosity of wood materials is expressed as 1 - the amount of wood in the pores (kg / m 3 ) / 1500kg / m3 It is calculated by:

[0053] Comminution and compression to the maximum surface area can be achieved by using a gap that allows the smallest dimension of the chips to enter first. Equipment used for this purpose can be segmented plates, screws, modified pumps, drum presses, modified screws, modified stators, and rotor systems.

[0054] According to one embodiment, the cooking liquor comprises sulfurous acid (acid sulfite) or an organic acid.

[0055] In one embodiment, the cooking method is a sulfite pulping process. The chemicals in the cooking liquor of a sulfite pulping process are sulfite (SO3 2- ) or bisulfite (HSO 3- ) The counter ion is either sodium (Na + ), calcium (Ca 2+ ), potassium (K + ), magnesium (Mg 2+ ), or ammonium (NH4 + ) may be.

[0056] In one embodiment, the cooking liquor comprises an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid, and malic acid. Organic acids are organic compounds with acidic properties.

[0057] In one embodiment, the cooking liquor has a chemical loading selected from the range of 1 to 200 g / l, preferably 1 to 100 g / l of an organic acid, or a sulfite, or a bisulfite, or an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid and malic acid.

[0058] In one embodiment, the spent cooking liquor comprises spent sulfite liquor.

[0059] In one embodiment, the spent cooking liquor comprises spent organic acid liquor.

[0060] In one embodiment, cooking is carried out at a temperature of at least 120°C, preferably above 150°C, more preferably above 170°C.

[0061] In one embodiment, the woody cellulose feedstock has an alpha cellulose content of more than 60% by weight, preferably more than 70% by weight, more preferably more than 80% by weight, calculated on dry material.

[0062] The cooking time at the cooking temperature is 0 to 500 minutes, preferably 0 to 20 minutes. If the desired kappa number is reached quickly, short cooking times can be achieved even immediately after prehydrolysis, depending on the conditions, for example, the raw material, pretreatment, and prehydrolysis.

[0063] In one embodiment, the ratio of cooking liquor to wood cellulosic feedstock is selected from 2 to 10 by dry weight of wood cellulosic material.

[0064] In one embodiment, the grinding and compacting releases at least one of xylan and lignin into the cooking liquor, thereby forming a spent cooking liquor comprising at least one of HMW lignin and HMW xylan, and a solids fraction comprising the compacted material. The HMW xylan can be recovered from the spent liquor. The HMW lignin can be recovered from the spent liquor.

[0065] In one embodiment, grinding and compaction begins before the wood chips reach a porosity level of 0.35 to 0.9, preferably 0.35 to 0.85.

[0066] In one embodiment, during grinding and compression, particles of wood-based cellulose feedstock, such as wood chips, are directed through gaps, e.g., where the chips fit only on their flat surfaces. In one embodiment, this process results in a consistency of greater than 10%, preferably greater than 20%, more preferably greater than 30%, and even more preferably greater than 65%.

[0067] In one embodiment, the crushing and compression is performed by forcing the wood chips through a gap ranging from 50 mm to 8 mm, resulting in a reduction in the porosity of the wood within the gap of at least 20%, 30%, 40%, 50%, 60%, 70% or more. The increased porosity and pressure releases HMW lignin.

[0068] In one embodiment, the crushing and compression is performed by drawing pin tips through gaps ranging from 35 mm to 6 mm, resulting in a reduction in wood porosity within the gaps of at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, or more than 70%. The increased porosity and pressure releases HMW lignin.

[0069] In one embodiment, the crushing and compression is performed by forcing sawdust through gaps ranging from 20 mm to 4 mm, resulting in a reduction in wood porosity within the gaps of at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, or more than 70%. The increased porosity and pressure releases HMW lignin.

[0070] In one embodiment, the grinding and compacting is carried out by pressing the digested cellulosic material through a gap, and The size of this gap is chosen as follows: The gap between the wood chips is selected from the range of 50 mm to 8 mm. The gap for the pin tip is selected from the range of 35 mm to 6 mm, The gap for the sawdust is selected from the range of 20 mm to 4 mm.

[0071] The porosity of wood materials is expressed as 1 - the amount of wood in the pores (kg / m 3 ) / 1500kg / m 3 It is calculated by:

[0072] The term black liquor in the present invention means used cooking liquor, i.e., spent cooking liquor, or spent liquor.

[0073] In one embodiment, the recovered HMW lignin has an average weight molecular weight (MW) of greater than 4500 g / mol when using hardwood (broadleaf) feedstocks, and greater than 4580 g / mol when using softwood (conifer) feedstocks.

[0074] In one embodiment, the compressed cellulose fraction has an alpha cellulose content of greater than 65%, preferably greater than 85%, more preferably greater than 90%, even more preferably greater than 95%.

[0075] In one embodiment, the cooked material is compressed in spent liquor at a pressure selected from the range of 1 to 250 kPa to form a column of solids having a consistency of at least 5% by weight. After compression, the spent cooking liquor is replaced with a replacement liquor having a lower lignin content than the black liquor.

[0076] Non-limiting examples of suitable pressures to reach a selected target consistency value include 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa, 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, 100 kPa, 110 kPa, 120 kPa, 130 kPa, 140 kPa, 150 kPa, 160 kPa, 170 kPa, 180 kPa, 190 kPa, 200 kPa, 210 kPa, 220 kPa, 230 kPa, 240 kPa, and 250 kPa. Non-limiting examples of suitable consistency values ​​include 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, and 50% by weight on a dry matter basis.

[0077] The compacted column of material at the end of step e) may be diluted to a consistency selected from the range of 2 to 35% by weight, for example 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30% or 35% by weight on a dry matter basis.

[0078] In this embodiment, a HMW lignin fraction and / or a HMW xylan fraction is recovered from the spent cooking liquor. Optionally, lignin and / or xylan containing smaller molecular weight species are also recovered.

[0079] In one embodiment, the dissolving pulp is dewatered to remove 90% of the lignin, dissolved xylan, and other organic and inorganic material as a liquid stream from the pulp to provide a dewatered pulp.

[0080] In an embodiment of step e), the compression pressure is selected from the range of 35 kPa to 1000 kPa.

[0081] In this embodiment, the compression is 350 kg / m 3 ~2000kg / m 3 in the range of 350 kg / m 3 ~1525kg / m 3 The density can be selected from the range of

[0082] In this embodiment, step e) is carried out to increase the porosity of the cell walls of the fibers.

[0083] In this embodiment, step e) comprises pressing at a pressure selected from the range of 1 kPa to 250 kPa to form a column having a consistency of at least 5% by weight.

[0084] In this embodiment, the displacement liquor has an organic acid or acid sulfite cooking liquor with a chemical loading selected from the range of 1 to 200 g / l, preferably 1 to 100 g / l.

[0085] In this embodiment, the substitution is carried out at a temperature selected from the range of 70°C to 200°C.

[0086] In this embodiment, after step i), the pulp is dewatered to remove 90% or more of the sulfites, alkali, lignin, dissolved xylan, and other organic and inorganic materials from the pulp as a liquid stream to provide a dewatered pulp.

[0087] In this embodiment, the method includes delignifying the dewatered pulp with oxygen to provide a delignified pulp, optionally followed by washing and pressing.

[0088] In this embodiment, the temperature and alkali or acid sulfite cooking liquor loading are not changed between the cooking step and the milling and pressing step.

[0089] In one embodiment, the method includes a prehydrolysis step, wherein grinding and compacting is carried out at the prehydrolysis temperature to a consistency of at least 10% by weight.

[0090] In one embodiment, the method includes a prehydrolysis step, in which grinding and compacting is carried out to a consistency of at least 60% by weight.

[0091] In one embodiment, the method comprises a pre-hydrolysis step, where the cooking is continued at a cooking temperature selected from the range of 120-180°C until a kappa number selected from the range of 100-3 is reached.

[0092] In one embodiment, the method comprises a prehydrolysis step, wherein the prehydrolyzed material and / or the cooked cellulosic material is treated by grinding and compacting, preferably by applying pressure through a gap, and The size of this gap is chosen as follows: The gap between the wood chips is selected from the range of 50 mm to 8 mm. The gap for the pin tip is selected from the range of 35 mm to 6 mm, The gap for the sawdust is selected from the range of 20 mm to 4 mm.

[0093] In one embodiment, the grinding and compacting is carried out to a consistency of at least 10% by weight at the cooking temperature.

[0094] In one embodiment, in step e), the compression pressure is selected from the range of 35 kPa to 1000 kPa.

[0095] In one embodiment, the compression is 350 kg / m 3 ~2000kg / m 3 in the range of 350 kg / m 3 ~1525kg / m 3 The density can be selected from the range of

[0096] In one embodiment, step e) is performed in the method to increase the porosity of the cell walls of the fibers.

[0097] In one embodiment, step e) comprises pressing at a pressure selected from the range of 1 kPa to 250 kPa to form a column having a consistency of at least 5% by weight.

[0098] In one embodiment, the substitution is carried out at a temperature selected from the range of 70°C to 200°C.

[0099] In one embodiment, after step i), the pulp is dewatered to remove at least 90% of the sulfites, alkali, lignin and dissolved xylan and other organic and inorganic materials as a liquid stream from the pulp to provide a dewatered pulp.

[0100] In one embodiment, the method comprises delignifying the dewatered pulp with oxygen to provide a delignified pulp, optionally followed by washing and pressing. [Example]

[0101] The effects that can be obtained by embodiments of the method of the present invention are demonstrated by the following experiments, which should not be considered as limiting the scope of the present invention. The abbreviation REF (reference) refers to the prior art method, i.e., the cooking method without the compaction step according to the present invention. Cooking conditions can be selected by those skilled in the art to obtain a target kappa number at the end of the cooking stage.

[0102] Example 1 In this example, eucalyptus wood pulp was produced by cooking eucalyptus at 165°C with an acidic cooking liquor (MgSO3) containing 7.8% total SO2 and 0.71% active MgO, according to both the present invention and the Reference Method (REF). The wood chips were first impregnated at 9 bar by increasing the temperature from 50°C to 110°C in 90 minutes, with a liquor to wood ratio of 5. The liquor to wood ratio was then reduced to 3.8 during the cooking stage, and a cooking temperature of 151°C was reached after 2 hours and 10 minutes. At the end of the cooking according to the present invention, the chips were fed through a narrow gap, thereby causing pressure and shear, and the spent liquor containing HWM-lignin was replaced with wash filtrate.

[0103] In this example, pine wood pulp was also produced according to both the present invention and the reference method (REF). Sulfite cooking was performed using magnesium sulfite cooking. The active MgO content was 2%, the total SO2 was 7%, and the pH was 4%. Wood chips were initially impregnated at 9 bar by increasing the temperature from 50°C to 110°C in 90 minutes at a liquor-to-wood ratio of 5. The liquor-to-wood ratio was then reduced to 3.8 during the cooking stage, and a cooking temperature of 160°C was reached after 80 minutes. After cooking according to the present invention, the resulting chips were fed through a narrow gap, thereby causing pressure and shear, and the spent liquor containing HWM-lignin was replaced with wash filtrate.

[0104] The cooking results for sulfite cooking are shown in Table 1. [Table 1]

[0105] According to Table 1, the weight average molecular weight Mw of the lignin and the cooking yield are increased and the cooking time is reduced up to the target kappa number when cooking according to the present invention. The reduced cooking time increases the cooking plant capacity.

[0106] Table 2 shows the increase in pulp volume for the same drainage time. [Table 2]

[0107] These results confirm that the method also improves the drainage of the pulp and therefore increases the production capacity of the fiber line of the pulp mill.

[0108] The foregoing description provides a complete and informative description of the best modes presently contemplated by the inventors for carrying out the invention, as non-limiting examples of specific implementations and embodiments of the invention. However, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing embodiments, and that it may be practiced in other embodiments using equivalent means, or in different combinations of embodiments, without departing from the characteristics of the invention.

[0109] Moreover, some of the features of the above-described embodiments of the invention can be used to advantage without the corresponding use of other features. Accordingly, the foregoing description should be considered as merely illustrative of the principles of the invention, and not in limitation thereof. The scope of the invention is therefore limited only by the appended claims. Aspects or embodiments that may be included in the present invention are summarized as follows. [1]. 1. A cooking method comprising: a) providing a wood-based cellulose feedstock comprising chips, pin chips, shavings, sawdust, or a combination thereof; b) optionally pretreating the wood-based cellulose feedstock by exposure to steam at 80-120°C to provide a pretreated material comprising a solid fraction of cellulose; c) optionally pre-hydrolyzing the pre-treated material with steam or water to provide a pre-hydrolyzed material; d) cooking under cooking conditions including a cooking liquor containing an acid sulfite or an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid, and malic acid at a chemical loading selected from the range of 1 to 200 g / L to provide a cooked cellulosic material in spent cooking liquor; e) comminuting and compressing the cooked cellulosic material at cooking conditions to release HMW lignin from the cooked material into spent cooking liquor and provide a compressed cellulosic fraction; f) recovering HMW lignin from the spent cooking liquor; g) replacing the spent cooking liquor with a replacement liquor containing cooking liquor having 1 to 200 g / l of acid sulfite or organic acid; h) recovering HMW lignin from the displacement liquor; and i) recovering pulp from said compressed cellulose fraction. A cooking method comprising: [2]. 2. The method according to item 1, wherein the method comprises the prehydrolysis step, and the grinding and compacting is carried out at the temperature of the prehydrolysis to a consistency of at least 10% by weight. [3]. 3. The method according to item 1 or 2 above, wherein the method comprises said prehydrolysis step, and said grinding and compressing is carried out to a consistency of at least 60% by weight. [4]. The method according to any one of items 1 to 3, wherein the method comprises the pre-hydrolysis step, and the cooking is continued at a cooking temperature selected from the range of 120 to 180°C until a kappa number selected from the range of 100 to 3 is reached. [5]. The method comprises the prehydrolysis step, wherein the prehydrolyzed material and / or the digested cellulosic material is treated by grinding and compressing, preferably by grinding and compressing through a gap, and The size of this gap is chosen as follows: The gap between the wood chips is selected from the range of 50 mm to 8 mm. The gap for the pin tip is selected from the range of 35 mm to 6 mm, The gap for sawdust is selected from the range of 20 mm to 4 mm. The method according to any one of items 1 to 4 above. [6]. The method according to any one of the above items 1 to 5, wherein the grinding and compressing are carried out at the cooking temperature to a consistency of at least 10% by weight. [7]. 7. The method according to any one of items 1 to 6, wherein in step e), the compression pressure is selected from the range of 35 kPa to 1000 kPa. [8]. The compression is 350 kg / m 3 ~2000kg / m 3 a density selected from the range of 350 kg / m 3 ~1525kg / m 3 The method according to any one of items 1 to 7, wherein the method is carried out until the density is selected from the range of [9]. The method according to any one of items 1 to 8, wherein step e) is carried out to increase the porosity of the cell walls of the fibers.

[10] . The method according to any one of items 1 to 9, wherein step e) comprises applying a pressure selected from the range of 1 kPa to 250 kPa to form a column having a consistency of at least 5% by weight.

[11] . 11. The method according to any one of items 1 to 10, wherein the substitution is carried out at a temperature selected from the range of 70°C to 200°C.

[12] . 12. The method according to any one of items 1 to 11, wherein after step i), the pulp is dewatered to remove 90% or more of the sulfite, alkali, lignin and dissolved xylan and other organic and inorganic materials as a liquid stream from the pulp to provide a dewatered pulp.

[13] . 13. The method according to claim 12, comprising delignifying the dewatered pulp with oxygen to provide a delignified pulp, optionally followed by washing and pressing.

[14] . 14. The method according to any one of the above items 1 to 13, wherein the temperature and chemical loading of the cooking liquor do not change between the cooking step and the grinding and compacting steps.

[15] . A high-molecular-weight xylan fraction obtained by the method according to any one of items 1 to 14 above.

[16] . A high-molecular-weight lignin fraction obtained by the method according to any one of items 1 to 14 above.

[17] . Pulp obtained by the method according to any one of items 1 to 14 above.

Claims

1. 1. A cooking method comprising: a) providing a woody cellulose feedstock comprising chips, pin chips, shavings, sawdust, or a combination thereof; b) optionally pretreating said woody cellulose feedstock by exposure to steam at 80-120°C to provide a pretreated material comprising a solid fraction of cellulose; c) optionally pre-hydrolyzing the pre-treated material with steam or water to provide a pre-hydrolyzed material; d) cooking under cooking conditions comprising a cooking liquor comprising an acid sulfite or an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid, and malic acid at a chemical loading selected from the range of 1 to 200 g / l to provide a cooked cellulosic material in spent cooking liquor; e) comminuting and compressing the cooked cellulosic material at cooking conditions to release HMW lignin from the cooked material into the spent cooking liquor and provide a compressed cellulosic fraction; f) recovering HMW lignin from the spent cooking liquor; g) replacing the spent cooking liquor with a replacement liquor containing cooking liquor having 1 to 200 g / l of acid sulfite or organic acid; h) recovering HMW lignin from the displacement liquor; and i) recovering pulp from said compressed cellulose fraction. A cooking method comprising:

2. 10. The method of claim 1, wherein the method includes said prehydrolysis step, and wherein said grinding and compacting is carried out at the prehydrolysis temperature to a consistency of at least 10% by weight.

3. 3. The method according to claim 1 or 2, wherein the method comprises said prehydrolysis step, and wherein said grinding and compacting is carried out to a consistency of at least 60% by weight.

4. 4. The method according to any one of claims 1 to 3, wherein the method comprises said prehydrolysis step, and wherein said cooking is continued at a cooking temperature selected from the range of 120 to 180°C to a kappa number selected from the range of 100 to 3.

5. The method comprises the prehydrolysis step, wherein the prehydrolyzed material and / or the digested cellulosic material is treated by grinding and compressing, preferably by grinding and compressing through a gap, and The size of this gap is chosen as follows: The gap between the wood chips is selected from the range of 50 mm to 8 mm; The gap for the pin tip is selected from the range of 35 mm to 6 mm; The gap for sawdust is selected from the range of 20 mm to 4 mm; The method according to any one of claims 1 to 4.

6. 6. The method according to any one of claims 1 to 5, wherein the grinding and compacting is carried out at said cooking temperature to a consistency of at least 10% by weight.

7. 7. The method according to any one of claims 1 to 6, wherein in step e) the compression pressure is selected from the range of 35 kPa to 1000 kPa.

8. The compression is 350 kg / m ３ ~2000 kg / m ３ a density selected from the range of 350 kg / m ３ ~1525 kg / m ３ The method according to any one of claims 1 to 7, wherein the method is carried out to a density selected from the range of

9. The method according to any one of claims 1 to 8, wherein step e) is carried out to increase the porosity of the cell walls of the fibres.

10. 10. The method of claim 1, wherein step e) comprises pressing at a pressure selected from the range of 1 kPa to 250 kPa to form a column having a consistency of at least 5% by weight.

11. The method according to any one of claims 1 to 10, wherein the substitution is carried out at a temperature selected from the range of 70°C to 200°C.

12. 12. The method of any one of claims 1 to 11, wherein after step i), the pulp is dewatered to remove at least 90% of the sulfites, alkali, lignin and dissolved xylan and other organic and inorganic materials as a liquid stream from the pulp to provide a dewatered pulp.

13. 13. The method of claim 12, comprising delignifying the dewatered pulp with oxygen to provide a delignified pulp, optionally followed by washing and pressing.

14. A method according to any one of the preceding claims, wherein the temperature and chemical loading of the cooking liquor do not change between the cooking step and the grinding and pressing steps.

15. A high molecular weight lignin fraction obtained from hardwood using the method of any one of claims 1 to 14, having a weight average molecular weight (Mw) of 4500 g / mol or more.

16. A high molecular weight lignin fraction obtained from softwood using the method of any one of claims 1 to 14, and having a weight average molecular weight (Mw) of 4580 g / mol or more.

17. A pulp product obtainable using the method according to any one of claims 1 to 14.

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