High yield cooking method

Abstract

A cooking method and digester system are disclosed wherein a partially digested cellulosic fiber source is compressed during the cooking process to provide high molecular weight xylan, high molecular weight lignin, and pulp.

Description

Field of the Invention

[0001] The present disclosure relates to a cooking process for the co-production of at least HMW lignin and pulp from a lignocellulosic feedstock by sulfite or organic acid. The pulp produced according to the process can be used to make paper grade pulp, dissolving cellulose products and cellulose derivatives. Background of the Invention

[0003] Organic acid, sulfite pulp and dissolving pulp, also known as pulp or dissolving cellulose, is a bleached wood pulp with a high cellulose content and is chemically produced from wood by using the sulfite process or the organic acid process. The sulfite process is a commonly used pulping process, and in the traditional sulfite process, wood is treated with an aqueous mixture of various sulfites to extract lignin from the wood chips. The salts used in the pulping process are sulfites (SO 3 2- ) or bisulfite (HSO 3 - ), depending on the pH. The counterion can be sodium (Na + ), calcium (Ca 2+ ), potassium (K + ), magnesium (Mg 2+ ) or ammonium (NH 4 + ). This treatment degrades and dissolves lignin, resulting in the defibration of wood fibers. The 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. An organic acid is an organic compound that has acidic properties. The most common organic acids are carboxylic acids, whose acidity is related to their carboxyl group –COOH. 2 Sulfonic acids with an OH group are relatively strong acids. Alcohols with a –OH group can act as acids, but they are usually very weak. The relative stability of the acid's conjugate base determines its acidity. Other groups can also impart acidity, usually weaker: thiol groups –SH, enol groups, and phenolic groups. In biological systems, organic compounds containing these groups are often called organic acids.

[0004] Typically, wood pulp contains high levels of alpha cellulose, which is used to make various cellulose derivatives for various end uses or products, known in the art as dissolving pulp. Other terms synonymous with dissolving pulp are chemical cellulose and special high alpha pulp. Dissolving pulp is usually made using two processes, namely:

[0005] 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

[0006] 2) Prehydrolysis - Kraft process, development of which began in 1929 (Rydholm, supra - p. 281)

[0007] The latter process utilizes an acid pretreatment ("prehydrolysis") step to remove hemicellulose prior to the alkaline pulping (delignification) step. South African Patent 88 / 4037 discloses a prehydrolysis-neutral sulfite-anthraquinone process (PH-NS-AO) for making "hemicellulose hydrolysate and special pulp" (high alpha grade). The prehydrolysis step performs essentially the same function as the prehydrolysis step prior to the Kraft (sulfate) pulping process for making dissolving grade pulp; although the neutral sulfite-anthraquinone delignification step is essentially the same as the process also known as the semi-alkaline sulfite-anthraquinone (SAS-AQ) process, which was first reported by Raubenheimer, S and Eggers, SH at a 1979 technical conference (both of whom were researchers employed by SAPPI LIMITED, the applicants herein), namely the 11th European ESPRA Conference held during May 1979, Maastricht, the Netherlands.

[0008] Furthermore, the yield of conventional papermaking and dissolving pulp by the sulfite process is low, as the hemicellulose and cellulose in the wood are degraded into low molecular weight hemicellulose, monosaccharides and hemicellulose degradation products in the process. The cooking time of the sulfite process is long, and as a result the hemicellulose and cellulose in the wood are degraded. Due to the difficulty in extracting these degradation products from the digester, the degraded material is preferably used for energy production by evaporating and burning the components, or simply discarded as waste.

[0009] A summary of the development of the acid sulfite pulping process for the preparation of semichemical pulps can be found in R. Runkel and KFPatt, "Halbzellstoffe" (Semichemical Pulps), Günther-Stalb Verlag, Biberach 1958, pages 35-37 and 95-96. The production of high-yield chemical pulps, semichemical pulps and chemimechanical pulps according to the sulfite process is also described in "SARydholm, Pulping Processes, Interscience Publishers, New York, London, Sydney, 1965, pages 418-420".

[0010] In addition, G. Jayme, L. Broschinksi, W. Matzke (Das Papier 18, 1964, pp. 308-314) provide an overview of high-yield chemical pulping and give a detailed description of rapid pulping in the gas phase at a maximum temperature of 180° C. with magnesium bisulfite within a period of 8 to 20 minutes.

[0011] DE-A-1-517219 relates to the preparation of (high-yield) sulfite chemical pulp. The wood raw material is pulped with an aqueous solution containing sulfite and / or bisulfite ions and 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° 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 at a chlorine value of the finished chemical pulp in the range of 15 to 32, and the pulped material is then subjected to controlled fiber separation and / or fiber separation / refining. Thereafter, fines are removed in an amount of 0.2% to 7% of the amount of chemical pulp. In the uncomminuted form (freeness value °SR=14.5-15), the material obtained thereby has a breaking length of 6.3 km. The chemical pulp is unbleached.

[0012] U.S. Patent Nos. 4,634,499 and 4,734,162, respectively, relate to processes for preparing chemical pulp from hardwood, which is particularly suitable for preparing tissue paper. Pulping is first carried out at a temperature below 110°C, then at a maximum temperature of 140°C to 155°C, at a pH of about 2 to 3 using ammonium sulfite. The chemical pulp is not subjected to an additional bleaching step.

[0013] EP 0 287 960 A relates to a process for preparing hemicellulose hydrolysates and special chemical pulps by a two-step process, wherein the first step comprises prehydrolysis of lignocellulosic material, for example with water, mineral acids, sulfur dioxide, sulfite pulping liquors and sulfite waste liquors, at a temperature of 100° C. to 180° C. and for a hydrolysis period of 10 to 200 minutes, and a second step, wherein the dissolution of the lignin contained in the prehydrolyzed material is carried out by means of neutral sulfite pulping with addition of anthraquinone as catalyst, the initial pH being at least 10. The temperature is preferably 160° C. to 180° C. and the treatment time is 100 to 200 minutes.

[0014] It is therefore an object of the present disclosure to provide an improved industrial scale cooking process for producing high yield paper grade and dissolving pulps which have a low hemicellulose content and which can be easily delignified and bleached to desired brightness and viscosity levels.

[0015] Another object is to provide a cooking system for lignocellulosic raw materials which provides pulp, xylan and lignin at high productivity. SUMMARY OF THE INVENTION

[0017] At least some of the above objects and other objects can be obtained by the present invention as defined in the independent claims. Additional advantages can be obtained when using the dependent claims and the embodiments described below. The advantage of the present invention is that it can produce value-added products such as at least one of HMW hemicellulose, HMW xylan and HMW lignin from lignocellulosic material used for pulping. In addition, the present invention uses less energy in the production of dissolving pulp or paper grade pulp compared to conventional pulping processes.

[0018] The invention also allows to reduce the processing / cooking time.Another advantage is that in the present process the total yield of paper and dissolving pulp is higher than that achievable using conventional sulphite processes in the production of paper or dissolving grade pulp.

[0019] Sulfite cooking liquor can be any salt of sulfurous acid. Cooking liquor is used to extract lignin from lignocellulosic feedstocks such as wood chips. The salt used in sulfite cooking liquor is sulfite (SO 3 2- ) or bisulfite (HSO 3- ), depending on the pH. The counterion may be, for example, sodium (Na + ), calcium (Ca 2+ ), potassium (K + ), magnesium (Mg 2+ ) or ammonium (NH 4 + ) or a combination thereof.

[0020] According to a first aspect, there is provided a cooking method, comprising:

[0021] a) providing a lignocellulosic raw material, which comprises wood chips, pin chips, wood shavings, sawdust or a combination thereof;

[0022] b) pretreating the lignocellulosic feedstock, optionally by steam treatment at 80 to 120° C., to provide a pretreated material comprising a cellulosic solids fraction;

[0023] c) optionally prehydrolyzing the lignocellulosic feedstock and / or pretreated material with steam or water to provide a prehydrolyzed material;

[0024] d) cooking under cooking conditions comprising a cooking liquor comprising a chemical charge selected from 1-200 g / l of an acidic sulfite or an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid and malic acid to provide a cooked cellulosic material in a spent liquor;

[0025] e) grinding and compressing the cooked cellulosic material under cooking conditions to release HMW lignin from the cooked material into the spent cooking liquor and to provide a compressed cellulose fraction;

[0026] f) recovering HMW lignin from spent cooking liquor;

[0027] g) replacing the spent cooking liquor with a replacement liquor containing cooking liquor having 1-200 g / l of sulfite or an organic acid;

[0028] h) recovering the HMW lignin from the displacement liquid; and

[0029] i) recovering pulp from the compressed cellulose fraction.

[0030] According to a second aspect, there is provided a HMW xylan fraction obtainable by using the present method.

[0031] The present method provides xylans with higher molecular weight, higher xylan yield and higher xyloglucan concentration in the HMW xylan fraction.

[0032] According to a third aspect, there is provided a HMW lignin fraction obtainable by using the present method.

[0033] With the process of the invention, a HMW lignin fraction with better lignin yield and higher consistency can be obtained. The HMW lignin also has an increased molecular weight compared to lignin produced according to prior art processes, such as the lignin disclosed in PCT / FI2011 / 050651.

[0034] According to a fourth aspect, there is provided a pulp, such as a dissolving pulp and / or a paper grade pulp, obtainable by using the present method. The pulp obtained according to the present method has a higher brightness and requires less wet pressing and lower steam consumption during drying than pulp produced according to conventional methods. The dissolving pulp has an additionally lower hemicellulose content than conventionally produced pulp.

[0035] Embodiments of the present disclosure provide certain benefits. Depending on the embodiment, one or more of the following benefits may be achieved: reduced consumption of chemicals, water, cellulose fiber sources, and energy; increased yield of cellulose, increased molecular weight of xylan and lignin.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematically shown is an embodiment of the process involving optional pre-steaming and optional pre-hydrolysis of a lignocellulosic feedstock and a digester system for grinding and / or compressing condensate from the wood chips after cooking. Figure 1 The process parameters mentioned in are exemplary only, and other process parameters may be used as described in the present disclosure.

[0038] Figure 2 An embodiment of a digester system for compressing cooking liquor from wood chips when using organic acid or sulfite cooking is schematically shown. Figure 2 The process parameters mentioned in are exemplary only, and other process parameters may be used as described in the present disclosure.

[0039] Figure 3 An embodiment of an illustrative process for compressing wood chips to press out cooking liquor is shown. Figure 3 The process parameters mentioned in are exemplary only, and other process parameters may be used as described in the present disclosure.

[0040] Figure 4 An embodiment of a process for displacing spent liquor from compressed wood chips is schematically shown. Figure 4 The process parameters mentioned in are exemplary only, and other process parameters may be used as described in the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0042] As used herein, the term "comprising" includes the broader meanings of "including," "containing," and "comprehending," as well as the narrower expressions "consisting of" and "consisting only of."

[0043] In one embodiment, the process steps are performed in the order identified in any aspect, embodiment or claim. In another embodiment, any process step specified to be performed on a product or intermediate obtained in a previous process step is performed directly on said product, i.e., without an additional, optional or auxiliary processing step between said two steps that chemically or physically changes the product.

[0044] In one embodiment, the lignocellulosic raw material used in the cooking method is in the form of wood chips, wood strands, wood shavings, sawdust or any combination thereof. Preferably, wood chips are used, more preferably softwood or hardwood chips, such as eucalyptus, pine or spruce chips. However, when wood chips are used as the main raw material, the raw material may contain smaller amounts of, for example, wood strands and / or sawdust.

[0045] Unless otherwise stated, all percentage values ​​refer to dry weight % and are expressed as wt %.

[0046] This process is suitable for a plant or mill, i.e. an industrial (large) scale process.

[0047] In one embodiment, the lignocellulosic feedstock has a xylan content of 4 wt% or more.In one embodiment, the lignocellulosic feedstock comprises wood chips.

[0048] The term high molecular weight xylan (HMW xylan) means xylan having an average molecular weight (Mw) of 45 000 g / mol or more.

[0049] The term high molecular weight lignin (HMW lignin) means a lignin having an average weight molecular weight (Mw) of 4500 g / mol or more for hardwoods and 4980 g / mol or more for softwoods.

[0050] In one embodiment, the molecular weight is measured by size exclusion chromatography and is expressed as a weight average molecular weight (MW).

[0051] Wood chips generally have a generally rectangular shape, with a height, a length and a width. However, the geometry of the wood chips may vary, for example, depending on their manufacturing process. The length (longest dimension) and the width (second longest dimension) of the wood chip may be considered to determine the general "flat side" of the wood chip, and the thickness is the smallest dimension of the wood chip. For thin wood strips, the width and thickness may be close to each other, thereby forming a match-like elongated object. The exact dimensions of the wood chips may vary.

[0052] In one embodiment, the cellulosic raw material used as the fiber source of the lignocellulosic raw material comprises or consists of wood chips, and grinding and compression are applied to the largest area of ​​the surface of the wood chips. Preferably, grinding and compression are performed to obtain 250-2000 kg / m 3 Between, preferably 350-1525kg / m 3 to release at least HMW xylan and / or HMW lignin. Grinding and compression of the maximum surface area can be achieved by using gaps that allow the wood chips to enter their smallest size, or "one side" first. Equipment for this purpose can be equipment between segmented plates, feed screws with blades that reduce the distance, plug feed screws that feed by rotating segmented plates, rotors and stators with segmented plates, improved pumps in which the stator and rotor of the pump have segmented plates to achieve a pressing and feeding action, roller presses with gaps and segmented surfaces, improved stator and rotor systems. Solutions are not limited to those mentioned above and can be applied by a person skilled in the art.

[0053] In one embodiment, the lignocellulosic feedstock is pretreated with steam prior to cooking and / or prior to prehydrolysis.

[0054] According to one embodiment, pretreatment is preferably performed by steaming to achieve exhaust of air inside the wood chips, thereby increasing the liquid permeability of the porous wood raw material. Pre-steaming can be performed in a separate steaming tank or a wood chip silo. In one embodiment, steaming is performed by using low-pressure steam at a pressure of about 3.5 bar for at least 10 minutes, preferably more than 20 minutes. In one embodiment, pre-steaming includes pre-steaming with low-pressure steam at 1-4 bar for 1-100 minutes to provide a pretreated material. In one embodiment, the temperature exceeds 100°C, preferably exceeds 120°C.

[0055] After the optional pretreatment, the feedstock can be sent to an optional prehydrolysis step or directly to a cooking step.

[0056] In one embodiment, the optionally pretreated lignocellulosic feedstock is prehydrolyzed prior to cooking.

[0057] In one embodiment, the prehydrolysis is performed by steam or water at a temperature selected from the range of 150-220° C. In one embodiment, the prehydrolysis step comprises prehydrolysis with 8-15 bar steam at a temperature selected from the range of 150-220° C. for 1 to 150 min.

[0058] In one embodiment, the grinding and compression steps are performed by a plug feed screw in a single screw with segmented plates, or by pressing the material through a rotating gap. The gap allows the wood chips to enter so that the shortest size enters first, however not limited to these embodiments.

[0059] In a preferred embodiment, the wood chip is forced into the gap so that its flat side with the largest surface area does not enter the gap first. This can be achieved by guiding the wood chip to a gap where the wood chip does not fit into the flat side in front of it.

[0060] In one embodiment, the grinding and compression are performed by passing the material through a gap under cooking conditions to release the HMW lignin into the spent cooking liquor to provide the HMW lignin in the spent cooking liquor.

[0061] In one embodiment, grinding and compressing is performed to a consistency exceeding 10 wt%, preferably exceeding 20% ​​or more preferably exceeding 30%, preferably exceeding 65%.The consistency may be measured using the standard TAPPI T240 consistency (concentration) of pulp suspensions or the corresponding ISO 4119 standard.

[0062] In one embodiment, the grinding and compression is performed at cooking temperature and to a consistency of at least 10 wt%.

[0063] In one embodiment, the grinding and compression is performed by passing the wood chips through a gap in the range of 50mm-8mm, so that the wood porosity in the gap is reduced by at least 20%, 30%, 40%, 50%, 60%, 70% or more and at least HMW lignin is released.

[0064] In one embodiment, the grinding and compression is performed by passing the wood strands through a gap in the range of 35mm-6mm, so that the wood porosity in the gap is reduced by at least 20%, 30%, 40%, 50%, 60%, 70% or more, and at least HMW lignin is released.

[0065] In one embodiment, the sawdust is ground and compressed by passing it through gaps in the range of 20mm-4mm, so that the wood porosity in the gaps is reduced by at least 20%, 30%, 40%, 50%, 60%, 70% or more and at least HMW lignin is released.

[0066] In one embodiment, the grinding and compression is performed by pressing the optionally pre-hydrolyzed material and / or the cooked cellulosic material through a gap, and the size of the gap is selected such that:

[0067] For wood chips, the gap is selected from the range of 50mm-8mm,

[0068] For thin wood strips, the gap is selected from the range of 35mm-6mm, and

[0069] For sawdust, the gap is selected from the range of 20 mm to 4 mm.

[0070] The porosity of wood materials is the amount of wood (kg / m 3 ) / 1500kg / m 3 calculate.

[0071] Grinding and compression of the maximum surface area can be achieved by using a gap that allows the wood chips to first come into their smallest size. Equipment used for this purpose can be segmented plates, screws, improved pumps, roller presses, improved screws, improved stator and rotor systems.

[0072] According to one embodiment, the cooking liquor comprises sulfurous acid (acidic sulfites) or an organic acid.

[0073] In one embodiment, the cooking method is a sulfite pulping process. The chemical in the cooking liquor of the sulfite pulping process is sulfite (SO 3 2- ) or bisulfite (HSO 3- ), depending on the pH. The counterion can be sodium (Na + ), calcium (Ca 2+ ), potassium (K+ ), magnesium (Mg 2+ ) or ammonium (NH 4 + ).

[0074] In one embodiment, the cooking liquor contains an organic acid selected from the group consisting of lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid and malic acid. An organic acid is an organic compound having acidic properties.

[0075] In one embodiment, the cooking liquor has a chemical charge of an organic acid or a sulfite or bisulfite in the range of 1-200 g / l, preferably 1-100 g / l, or an organic acid selected from lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid and malic acid.

[0076] In one embodiment, the spent cooking liquor comprises spent sulfite liquor.

[0077] In one embodiment, the spent cooking liquor comprises spent organic acid liquor.

[0078] In one embodiment, cooking is carried out at a temperature of at least 120°C, preferably above 150°C, more preferably above 170°C.

[0079] In one embodiment, the lignocellulosic feedstock has an alpha-cellulose content of more than 60 wt%, preferably more than 70 wt%, and more preferably more than 80 wt%, calculated on dry material.

[0080] The cooking time at the cooking temperature is between 0 and 500 min, preferably between 0 and 20. Short cooking times can be achieved when the desired kappa number is reached very quickly, even immediately after prehydrolysis, depending on, for example, the raw materials, pretreatment and prehydrolysis.

[0081] In one embodiment, the ratio of cooking liquor to lignocellulosic feedstock is selected from 2 to 10, as dry mass of lignocellulosic material.

[0082] In one embodiment, grinding and compressing releases at least one of xylan and lignin into the cooking liquor, thereby forming a spent cooking liquor containing at least one of HMW lignin and HMW xylan, and a solid fraction comprising compressed material. HMW xylan can be recovered from the spent liquor. HMW lignin can be recovered from the spent liquor.

[0083] In one embodiment, grinding and compression begins before the wood chips reach a porosity level of 0.35-0.9, preferably 0.35-0.85.

[0084] In one embodiment, during the grinding and compression process, the lignocellulosic raw material particles, such as wood chips, are guided through the gap, such as the wood chips only fit into the gap on their flat sides. In one embodiment, the treatment results in a consistency of more than 10%, preferably more than 20%, more preferably more than 30%, and even more preferably more than 65%.

[0085] In one embodiment, the wood chips are ground and compressed by passing them through gaps ranging from 50 mm to 8 mm, so that the porosity of the wood within the gaps is reduced by at least 20%, 30%, 40%, 50%, 60%, 70% or more. The increased porosity and pressure releases the HMW lignin.

[0086] In one embodiment, the grinding and compression is performed by passing the wood strands through a gap ranging from 35 mm to 6 mm, so that the porosity of the wood within the gap is reduced by at least 20%, 30%, 40%, 50%, 60%, 70% or more. The increased porosity and pressure releases the HMW lignin.

[0087] In one embodiment, the sawdust is ground and compressed by passing it through gaps ranging from 20 mm to 4 mm, so that the porosity of the wood within the gaps is reduced by at least 20%, 30%, 40%, 50%, 60%, 70% or more. The increased porosity and pressure releases the HMW lignin.

[0088] In one embodiment, the grinding and compression is performed by pressing the cooked cellulosic material through a gap, and the size of the gap is selected such that:

[0089] For wood chips, the gap is selected from the range of 50mm-8mm,

[0090] For thin wood strips, the gap is selected from the range of 35mm-6mm, and

[0091] For sawdust, the gap is selected from the range of 20 mm to 4 mm.

[0092] The porosity of wood materials is the amount of wood (kg / m 3 ) / 1500kg / m 3 calculate.

[0093] The term black liquor in the present invention means spent cooking liquor, ie spent cooking liquor or spent liquor.

[0094] In one embodiment, the recovered HMW lignin has an average weight molecular weight (MW) exceeding 4500 g / mol when a hardwood feedstock is used, and exceeding 4580 g / mol when a softwood feedstock is used.

[0095] In one embodiment, the compressed cellulose fraction has an alpha cellulose content of more than 65%, preferably more than 85%, more preferably more than 90%, and even more preferably more than 95%.

[0096] In one embodiment, the cooking material is compressed in spent liquor with a pressure selected from the range between 1 and 250 kPa to form a column having a consistency of at least 5% solids by weight. After compression, the spent cooking liquor is replaced with a replacement liquor having a lower lignin content than the black liquor.

[0097] Non-limiting examples of suitable pressures to achieve a selected target consistency value are 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 ​​are 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% and 50% by weight on a dry matter basis.

[0098] At the end of step e), the compressed column of material may be diluted to a consistency selected from the range between 2% and 35% by weight, such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30% or 35% by weight based on dry matter.

[0099] 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.

[0100] In one embodiment, the dissolving pulp is dewatered to remove 90% of the lignin and dissolved xylan and other organic and inorganic materials from the pulp as a liquid stream and to provide a dewatered pulp.

[0101] In an embodiment of step e), the compression pressure is selected from the range between 35 kPa and 1000 kPa.

[0102] In this embodiment, compression is performed to a pressure selected from 350 kg / m 3 and 2000kg / m 3 Between, preferably 350kg / m 3 and 1525kg / m 3The density in the range between .

[0103] In an embodiment, step e) is performed to increase the porosity of the fiber cell walls.

[0104] In this embodiment, step e) comprises pressing with a pressure selected from the range between 1 kPa and 250 kPa to form a column having a consistency of at least 5% by weight.

[0105] In this embodiment, the replacement liquor has a chemical charge selected from an organic acid or acidic sulfite cooking liquor in the range between 1-200 g / l, preferably 1-100 g / l.

[0106] In this embodiment, the replacement is performed at a temperature selected from the range between 70°C and 200°C.

[0107] In an embodiment following step i), the pulp is dewatered to remove 90% or more of sulfites, alkalis, lignin, and dissolved xylan and other organic and inorganic materials from the pulp as a liquid stream and to provide a dewatered pulp.

[0108] In this embodiment, the method comprises delignifying a dewatered pulp by oxygen to provide a delignified pulp, optionally followed by washing and pressing.

[0109] In this embodiment, the temperature and alkaline or acidic sulfite cooking liquor charge are not changed between the cooking and milling and compression steps.

[0110] In one embodiment, the method comprises a prehydrolysis step, and wherein the grinding and compressing are performed at a prehydrolysis temperature and to a consistency of at least 10% by weight.

[0111] In one embodiment, the method comprises a pre-hydrolysis step, and wherein the grinding and compressing are performed to a consistency of at least 60% by weight.

[0112] In one embodiment, the method comprises a pre-hydrolysis step and continues cooking at a cooking temperature selected in the range between 120 and 180°C to a kappa number selected in the range between 100 and 3.

[0113] In one embodiment, the method comprises a prehydrolysis step, and the prehydrolyzed material and / or the cooked cellulosic material is processed by grinding and compression, preferably by pressing through a gap, and the size of the gap is selected such that:

[0114] For wood chips, the gap is selected from the range of 50mm-8mm,

[0115] For thin wood strips, the gap is selected from the range of 35mm-6mm, and

[0116] For sawdust, the gap is selected from the range of 20 mm to 4 mm.

[0117] In one embodiment, the grinding and compression is performed at cooking temperature and to a consistency of at least 10% by weight.

[0118] In an embodiment of step e), the compression pressure is selected from the range between 35 kPa and 1000 kPa.

[0119] In this embodiment, compression is performed to a pressure selected from 350 kg / m 3 and 2000kg / m 3 Between, preferably 350kg / m 3 and 1525kg / m 3 The density in the range between .

[0120] In one embodiment, method step e) is performed to increase the porosity of the fiber cell walls.

[0121] In one embodiment, step e) comprises pressing with a pressure selected from the range between 1 kPa and 250 kPa to form a column having a consistency of at least 5% by weight.

[0122] In one embodiment, the substitution is performed at a temperature selected from the range between 70°C and 200°C.

[0123] In one embodiment, step i) is followed by dewatering the pulp to remove 90% or more of sulfites, alkalis, lignin and dissolved xylan and other organic and inorganic materials from the pulp as a liquid stream and to provide a dewatered pulp.

[0124] In one embodiment, the method comprises delignifying a dewatered pulp by oxygen to provide a delignified pulp, optionally followed by washing and pressing. Example

[0125] The effects obtainable 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 refers to the prior art method, i.e. the cooking method according to the present invention without a compression step. A person skilled in the art can select the cooking conditions to obtain the target kappa number at the end of the cooking stage.

[0126] Example 1

[0127] In this example, the total SO was digested at 165 °C according to the present invention and according to the reference method (REF). 2 Eucalyptus acid cooking liquor (MgSO 3), to produce eucalyptus pulp. The chips are first impregnated at 9 bar, by increasing the temperature from 50°C to 110°C in 90 minutes, with a liquid to wood ratio of 5. Afterwards, in the cooking stage, the liquid to wood ratio is reduced to 3.8, and the cooking temperature of 151°C is reached after 2 hours and 10 minutes. At the end of the cooking according to the invention, the chips are fed through a narrow gap, causing pressing and shearing, and the spent liquor containing HWM lignin is replaced with a washing filtrate.

[0128] In this example, pine pulp was also produced according to the invention and the reference method (REF). Sulfite cooking was carried out using magnesium sulfite cooking. The active MgO content was 2% and the total SO 2 The wood chips were first impregnated at 9 bar with a liquid to wood ratio of 5 by increasing the temperature from 50°C to 110°C in 90 minutes. Afterwards, in the cooking stage, the liquid to wood ratio was reduced to 3.8 and a cooking temperature of 160°C was reached after 80 minutes. After cooking according to the invention, the obtained wood chips were fed through a narrow gap, causing pressing and shearing, and the spent liquor containing HWM lignin was replaced with a washing filtrate.

[0129] The cooking results for sulfite cooking are provided in Table 1.

[0130] Table 1

[0131]

[0132] According to Table 1, when cooking is performed according to the present invention, the lignin weight average Mw molecular weight cooking yield increases and the cooking time is reduced to the target Kappa number. Due to the reduction in cooking time, the cooking plant production capacity increases.

[0133] The increase in slurry volume for the same discharge time is provided in Table 2.

[0134] Table 2. Slurry charges for the same discharge time.

[0135] sample REF Sulphite Eucalyptus 1000g / m2 REF Sulphite Pine 1000g / m2 Sulfite Eucalyptus 1550g / m2 Sulfite Pine 1750g / m2

[0136] As the results demonstrate, the method also improves pulp discharge and thus increases the production capacity of the pulp mill fiber line.

[0137] The above description provides a complete and informative description of the best mode currently contemplated by the inventor for carrying out the present invention by way of non-limiting examples of specific embodiments and embodiments of the present invention. However, it will be clear to those skilled in the art that the present invention is not limited to the details of the embodiments set forth above, but may be implemented in other embodiments using different combinations of equivalents or embodiments without departing from the features of the present invention.

[0138] In addition, some features of the above disclosed embodiments of the present invention can be advantageously used without corresponding use of other features. Therefore, the above description should be regarded as merely illustrating the principles of the present invention and is not limited thereto. Therefore, the scope of the present invention is only limited by the attached patent claims.

Claims

1. A cooking method, include: a) providing a lignocellulosic raw material, which includes wood chips, wood strands, wood shavings, sawdust or a combination thereof; b) pretreating the lignocellulosic feedstock by steam treatment at 80-120° C. to provide a pretreated material comprising a cellulose solid fraction; c) prehydrolyzing the pretreated material with steam or water to provide a prehydrolyzed material; d) cooking under cooking conditions comprising a cooking liquor comprising a chemical charge selected from the group consisting of acidic sulfites in the range of 1-200 g / l or organic acids selected from the group consisting of lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid and malic acid to provide a cooked cellulosic material in a spent liquor; e) grinding and compressing the cooked cellulosic material under the cooking conditions to release HMW lignin from the cooked material into spent cooking liquor and to provide a compressed cellulose fraction; f) recovering the HMW lignin from the spent cooking liquor; g) replacing the spent cooking liquor with a replacement liquor containing cooking liquor having 1-200 g / l of acidic sulfite or organic acid; h) recovering said HMW lignin from said displacement liquid; and i) recovering pulp from said compressed cellulose fraction.

2. The process of claim 1, wherein the process comprises the prehydrolysis step, and wherein the grinding and compressing are carried out at the prehydrolysis temperature and to a consistency of at least 10% by weight.

3. The process of claim 1, wherein the process comprises the pre-hydrolysis step and wherein the grinding and compression are carried out to a consistency of at least 60% by weight.

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

5. The method of any one of claims 1 to 3, wherein the method comprises the prehydrolysis step, and the prehydrolyzed material and / or the cooked cellulosic material is processed through a gap by grinding and compression, and the size of the gap is selected such that: For wood chips, the gap is selected from the range of 50mm-8mm, For thin wood strips, the gap is selected from the range of 35mm-6mm, and For sawdust, the gap is selected from the range of 20 mm to 4 mm.

6. The method of claim 1, wherein grinding and compression are performed at said cooking temperature and to a consistency of at least 10% by weight.

7. The method of claim 1, wherein in step e), the compression pressure is selected from the range between 35 kPa and 1000 kPa.

8. The method of claim 1, wherein the compression is performed to a pressure selected from 350 kg / m 3 and 2000kg / m 3 The density of the range between.

9. The method of claim 1, wherein step e) is performed to increase the porosity of the fiber cell wall.

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

11. The method of claim 1, wherein the replacing is performed at a temperature selected from the range between 70°C and 200°C.

12. The method of claim 1, wherein after step i), the pulp is dewatered to remove 90% or more of sulfites, alkalis, lignin and dissolved xylan and other organic and inorganic materials from the pulp as a liquid stream and provide a dewatered pulp.

13. A method as claimed in claim 12 comprising delignifying the dewatered pulp by oxygen to provide a delignified pulp followed by washing and pressing.

14. The method of claim 1, wherein the temperature and cooking liquor chemical charge are not changed between the cooking and grinding compression steps.

15. The method of claim 1, wherein the compression is performed to a temperature selected from 350 kg / m 3 and 1525kg / m 3 The density of the range between.

16. A high molecular weight lignin fraction obtained from hardwood and by using the method of any one of claims 1 to 15, and wherein the lignin has an average molecular weight of 4500 g / mol or more.

17. A high molecular weight lignin fraction obtained from softwood and by using the method of any one of claims 1 to 15, and wherein the lignin has an average molecular weight of 4980 g / mol or more.

18. A pulp product obtainable using the method of any one of claims 1-15.

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