Method for producing a high yield pulp and products based on high yield cellulose pulp

Abstract

Method for producing a high yield lignocellulose pulp, comprising the steps of i) providing lignocellulose material, ii) mixing the lignocellulose material with added alkali (6), wherein the alkali (6) is added at a weight ratio comprised in the range of 10 – 60 kg alkali / dry ton of lignocellulose material, a step iii) comprising treatment at high temperature, and further a subsequent step iv) comprising adding hydrogen peroxide (7), to the lignocellulose material at a weight ratio comprised in the range of 10 – 70 kg hydrogen peroxide / dry ton of lignocellulose material. There is also proposed a high yield cellulose pulp, a proposed a paper, a paperboard, a liner and a fluting produced from the high yield lignocellulose pulp.

Description

[0001] METHOD FOR PRODUCING A HIGH YIELD PULP AND PRODUCTS BASED ON HIGH YIELD CELLULOSE PULP

[0002] The present invention is related to a method for producing a high yield lignocellulose pulp according to claim 1.

[0003] BACKGROUND

[0004] The increasing demands for environmentally friendly products and the striving to use harvested biomass at a high yield, has put focus on the need to develop new and existing products for packaging. In the production of packaging papers based on virgin pulp (not based on recycled fibres), chemical pulp is often used which has a wood yield around 50%. Mechanical pulps, on the other hand, have much higher yield than chemical pulps, but generally have lower strength properties.

[0005] One way of increasing the strength of mechanical pulp, (high yield pulp) is to add chemicals. Addition of chemicals in the process of manufacturing High Yield Pulp (yield above 85%) has been used ever since the refiner process for fibre separation was developed by Asplund in the 1930' s, see Asplund, A. (1953) The origin and development of the Defibrator process. Svensk papperstidning, 56(14):550- 558. The two mostly used chemical systems are based on sulphite or alkaline peroxide. In most published work, the aim is to produce a pulp with high brightness, often above ISO 70% and low shives content.

[0006] It has been shown that a process using highly alkaline peroxide can be used to produce a strong pulp with high brightness see, Moldenius, S. (1988) Method of two-stage peroxide bleaching of mechanical pulp or semi-mechanical pulp. US pat. 4,734,160.

[0007] SHORT DESCRIPTION OF THE INVENTION

[0008] The prior art has not acknowledged the drawbacks related to packaging papers based on low yield pulp and environmental benefits from keeping the yield high. The increasing demands for environmentally friendly paper products and effective ways of using harvested biomass at a high yield have contributed to new applications for mechanical pulp, High Yield Pulp, HYP. However, HYPs, such as TMP and CTMP have been considered to have too low strength to be used for packaging paper.

[0009] The low strength of HYP can be overcome by producing a high yield lignocellulose pulp according to a method for producing a high yield lignocellulose pulp, comprising a first step / of providing lignocellulose material, preferably in the form of wood chips or fibre pulp. In an ensuing step ii there is a mixing the lignocellulose material with alkali. The alkali is added at a weight ratio comprised in the range of 10 kg - 60 kg alkal i / dry ton of lignocellulose material. The alkali may also be added in the range of 30 kg - 45 kg dry lignocellulose material. In a step Hi, there is provided a heating of the mixture of alkali and lignocellulose material to a temperature comprised in the range of 100°C - 200°C. The temperature range may also be in the range comprised in the range of 120°C - 160°C. In an ensuing step there is provided subsequent mixing of the lignocellulose material with hydrogen peroxide. The weight ratio is comprised in the range of 10 kg - 70 kg hydrogen peroxide / ton of dry lignocellulose material. The weight ratio may also be 20 kg - 40 kg of hydrogen peroxide / ton of dry lignocellulose material. The method resulting in that the lignocellulose material, after step iv comprises at least 85% by weight of dry solid lignocellulose material to the weight of the original dry lignocellulose material. The amount may also be above 90% by weight of the original lignocellulose material. The resulting lignocellulose material, after step iv, has an ISO brightness in the range of 10% - 50%. The brightness may also be 20% - 45% ISO brightness after step iv.

[0010] In the disclosed process, lignocellulose material is mixed with alkali preferably at a consistency, dry content, above 25% and a temperature between 100°C - 200°C where after hydrogen peroxide is added to the alkali treated lignocellulose material. For the peroxide treatment, the process conditions (consistency, temperature) can be chosen more freely depending on the choice of process equipment.

[0011] An advantage of the disclosed process is that a pulp with low brightness and high strength, compared to normal mechanical pulps, can be achieved. This is unexpected since hydrogen peroxide is a known bleaching agent and thus low brightness is not expected. The separation of peroxide and alkali addition and the high temperature, 100°C - 200°C, at the alkali treatment results in the desired low brightness.

[0012] The disclosed process can be included in an existing process, which contains normal mechanical pulping equipment.

[0013] It is a major advantage that the yield of this lignocellulose pulp is much higher than in a traditional packaging pulp, such as a chemical pulp, e.g. KRAFT-pulp. In addition, as compared to recycled fibres, the high yield lignocellulose pulp is stronger, thus for example a packaging paper or paperboard can be produced at a lower grammage, which gives lighter packaging products.

[0014] In a further development there is proposed a method according wherein the consistency of the lignocellulose material in step ii, after addition of alkali, is controlled to be comprised in the range of 5% - 70% by dry weight of lignocellulose material. The consistency may also be 25% - 60% of lignocellulose material. The alkali treatment in step ii is preferably made at high consistency, >25%, since the required pH above 10, can be attained at a lower dose of alkali.

[0015] In a further development there is proposed a method wherein the heating of step iii) is performed to a predetermined time range comprised in the range of 1 second to 30 minutes depending on the treatment temperature.

[0016] Where the treatment time in step iii is adapted to the treatment temperature. If the treatment temperature is high, over 150°C only a very short retention time of 1 - 5 seconds is required, which is preferable since there is no need for large, pressurised reaction vessels at this high temperature. Thus, higher temperature gives faster reaction and a more efficient process.

[0017] In a further development there is proposed a method wherein the alkali is sodium hydroxide. The alkali may also be potassium hydroxide. The alkali may also be sodium carbonate. The alkali may also be oxidized white liquor. The alkali may also be an alkali which is a mixture of the mentioned alkalis in any ratio.

[0018] Sodium hydroxide is the preferred alkali since is gives a high pH and the cost is relatively low. However, other alkali sources are possible, for example potassium hydroxide and / or sodium carbonate and / or oxidized white liquor.

[0019] In a further development there is proposed a method wherein step ii is performed with a refiner. Step ii may also be made with a pump, or a mixer, or a compression screw, such as an extruder, etc., or any kind of equipment that gives the desired mixing.

[0020] The alkali addition can be accomplished with any kind of equipment that provides good mixing. However, the preferred equipment is a high consistency refiner since it gives good mixing and high temperature simultaneously, thus there is no need to separately add energy for heating. However, other equipment can be used such as a disc- or screw mixer or an MC pump combined with heating of the material.

[0021] In a further development there is proposed a method wherein step iv is performed with a refiner. Step iv may also be performed with a pump, or a mixer, or a compression screw, such as an extruder, etc., or any kind of equipment that gives the desired mixing.

[0022] Similar equipment can be used for the mixing of hydrogen peroxide as mentioned above for the alkali. Good mixing of the hydrogen peroxide is important for the strength development, but in this step, the temperature can be more freely chosen based on process considerations. In a further development there is proposed a method the refiner is a high consistency refiner, for example a single disc type refiner, or double disc type refiner.

[0023] High consistency refiners, normally used for TMP or CTMP production, provides a good combination of excellent mixing and a high temperature to achieve fast and homogenous chemical reactions.

[0024] In a further development there is proposed a method, wherein the method comprises a step between step / and / ' / , which comprises any pre-treatment of the lignocellulosic material such as preheating and / or refining, and / or chelation and / or pressing, e.g. dewatering, of the lignocellulosic material.

[0025] By applying treatment before step ii higher strength properties can be achieved since the content of disturbing extractives and metal ions can be reduced.

[0026] In a further development there is proposed a method wherein the method does not include a washing step between step ii and step iv.

[0027] The lignocellulose material is not washed between step ii and step iv since alkali should be present at the peroxide treatment.

[0028] In a further development there is proposed a method wherein the method comprises any further treatment of the lignocellulosic material, such as washing, and / or screening and / or cleaning, and / or refining, after step iv.

[0029] After the disclosed treatment of the lignocellulose material, it can be further treated depending on the application for the lignocellulose material, which means that it can be washed to remove dissolved substances, screened or cleaned to remove debris or further refined in subsequent refiners to attain higher strength properties.

[0030] In a further development there is proposed a method, wherein the pH of the lignocellulose material in step ii and / or step iii, and / or step iv is arranged to be at least 10, preferably at least 11, more preferred at least 12, even more preferred at least 13, or at least 14.

[0031] A pH at 10 or higher is helpful or sometimes necessary or efficient to achieve a maximal ISO brightness of 10 - 50 % or 20-45 %.

[0032] In a further development there is proposed a high yield lignocellulose pulp made according to any of the method steps including variations above. The high yield lignocellulose pulp is stronger at a given freeness (dewatering capability) than normal mechanical pulps, which is advantageous when paper or other products such as moulded packaging are formed from the pulp.

[0033] In a further development there is proposed a high yield cellulose paper made from the mentioned high yield lignocellulose pulp.

[0034] The alkali and peroxide treated lignocellulose material is used to produce any kind of paper for example, flexible packaging, sack paper, tissue or any other paper product.

[0035] In a further development there is proposed a paperboard made by the mentioned high yield lignocellulose pulp.

[0036] The advantages of the method is reflected in a paperboard made from pulp made from the method.

[0037] The paperboard may be used as is without any colouring and still provides a sufficiently strong paperboard for use in a packaging application. In addition, the paperboard provides for a particular good use of the raw material, as less original wood material is needed for a certain packaging size.

[0038] In a further development there is proposed a layered paperboard product wherein the paperboard is a layered paperboard product, comprising at least one ply with high yield lignocellulose pulp according to above. The said ply may be an outer ply of the layered paperboard product. The layered paperboard product may have both outer layers made from the high yield lignocellulose pulp.

[0039] Due to the high strength of the pulp from the disclosed process, it is suitable as outer plies in a multilayered paperboard with a bulky pulp, such as CTMP, in the middle layer(s).

[0040] In a further development there is proposed a Liner and / or fluting made from the mentioned high yield lignocellulose pulp.

[0041] Due to the high strength properties of the pulp produced according to the disclosed method, it can be used for both liner and fluting in corrugated board application.

[0042] LIST OF DRAWINGS

[0043] Fig. 1 discloses a general outline of the disclosed process.

[0044] Fig. 2 discloses an alternative in which the steps of the disclosed process are made in one device.

[0045] Fig. 5 discloses a general outline according to an extended process of Fig. 1

[0046] Fig. 3 discloses strength properties in relation to brightness of the pulp of the disclosure.

[0047] Fig. 4 discloses strength properties in relation to freeness of the pulp of the disclosure. Fig. 6 discloses the main method steps of the method of the disclosure.

[0048] Fig. 7 discloses the main method steps according to an alternative.

[0049] Fig. 8 discloses the main method steps according to an alternative.

[0050] Fig. 9 illustrates the set up for Example 1.

[0051] Fig. 10 illustrates the set up for Example 2.

[0052] DETAILED DESCRIPTION

[0053] The present disclosure relates to a method for producing a high yield lignocellulose pulp.

[0054] High yield pulp is to be defined as a pulp where, in comparison to the initial feed material, only a small amount is lost in the production of the pulp. I.e., yield is defined as the ratio, in percent, of the dry mass flow of final pulp exiting the process to the mass flow of dry incoming feed material, e.g. wood chips. In general, an amount of at least 80% by weight of the ingoing dry lignocellulose material is remaining in the high yield pulp, when it is ready for use for example on a board or paper machine. This should be compared with for example a KRAFT-pulp that may have 50% yield by weight, that is, around half of the initial content of the dry feed material by weight remains in the final pulp that is to be sent to a paper or board machine.

[0055] The doses of chemicals in the description are expressed as pure product, not the commodity used in the described process.

[0056] In this application, consistency is defined as the ratio , in %,of the weight of oven dry lignocellulose material and the total weight of a solution i.e. the sum of oven dry weight of the lignocellulose material plus the weight of liquid.

[0057] Any given pressure in this application is given in absolute pressure. Thus, as an example a "pressure less" vessel thus has a pressure of approx, one Bar.

[0058] The method, see Fig. 1 and in particular Fig. 6, 7 and 8, according to the disclosure involves the step of: i, Providing lignocellulose material 5. Lignocellulose material is here primarily originating from softwoods such as pine or spruce. However, it is possible to use other softwood species or hardwoods or any other lignocellulose material that is possible to make a high yield pulp from.

[0059] The preferred forms of lignocellulose material are in the form of wood chips, as normally used for TMP production, or pulp i.e. a lignocellulose material mainly consisting of free fibres or fibre bundles. In an ensuing step, ii, of the method the lignocellulose material is mixed at 2 with alkali 6, at a predetermined ratio, kg alkali per dry ton of lignocellulose material.

[0060] The range of addition is in general 10 kg - 60 kg alkali per oven dry ton of lignocellulose material. A more preferred rate of addition is 30 kg - 45 kg of alkali per oven dry ton of lignocellulose material. Mixing ii of alkali with lignocellulose material can be performed at 5% - 70% consistency, preferably the consistency is 25% - 60% since less alkali is needed to reach the desired pH above 10 at higher consistency.

[0061] In relation to step ii of the process but also the process in general, it is a requirement of the present process to have a high pH. With high is meant as mentioned above at least 10. But specifically, the pH may be above 11, 12, 13 or 14 or any number in between, such as 10,5; 11,5; 12,5; 13,5. The high pH is necessary for the required low brightness. As can be seen in the description below, the desired ISO brightness is preferred to not be above 50 %. Thus, to the contrary of normal paper and pulping, no bleaching is desired. To achieve this result, it is necessary or helpful, to have a pH that is at least 10 but preferably higher. This may be achieved with tuning the alkali 6 concentration to the correct amount.

[0062] The alkali 6 is preferred to be in the form of sodium hydroxide. Other alkali is thinkable such as for example potassium hydroxide or sodium carbonate or oxidized white liquor, i.e. cooking chemicals in Kraft mills.

[0063] In an ensuing step, Hi, of the method the mixture of alkali and lignocellulose material is heated 3 to a temperature in the range 100°C - 200°C , preferably 120°C - 160°C.

[0064] Optionally the mixture is kept at the temperature for a predetermined time that preferably is <30 minutes. However, it is thinkable to have a predetermined time of 2 seconds to 20 minutes or even more preferred 2 seconds to 10 minutes. It may also be a very narrow predetermined time of 1 second to 3 seconds. Generally, shorter treatment time is required at higher temperature.

[0065] Step ii and Hi can be made simultaneously or in the opposite order, see in particular Fig. 2 and Fig. 8, that is, first heating the lignocellulose material and then adding the alkali and thereafter retaining the mixture at the high temperature for 1 second to 30 minutes, depending on the treatment temperature.

[0066] In the ensuing step, iv, the alkali-treated lignocellulose material is mixed 4 with hydrogen peroxide 7, wherein the hydrogen peroxide 7 is added at a weight ratio comprised in the range of 10 kg - 70 kg, preferably 20 kg - 40 kg, hydrogen peroxide per dry ton of lignocellulose material. In step iv, the pH may be a bit lower than in step ii, (and iii), but this still means that the pH is 10 or more.

[0067] The conditions, consistency, temperature and retention time, in stage iv can be chosen relatively freely, depending on the process design. For example, if the peroxide treatment is made in a HC refiner, the consistency is normally between 30% and 70% and the temperature is above 130°C which enables a very short retention time of 1 - 5 seconds, but it is also possible, as an example, to do the treatment atmospherically, below 100°C, in an MC dilution / mixing screw, at a consistency around 10%, and temperature 85°C ,see Example 2, then, the residence time is preferably around 15 minutes.

[0068] In the preferred embodiment of the process, all alkali is added in one step, step ii and all hydrogen peroxide is added in one step, step iv, however the additions can be made in several steps or positions of the process.

[0069] There is no washing, by washing is meant dilution of the lignocellulose material followed by pressing to remove dissolved substances, between additions of alkali, step ii and addition of peroxide, step iv. It is important to have a high pH of the lignocellulose material when peroxide is added to achieve high strength and low brightness.

[0070] The yield of the disclosed method is at least 85% by weight, i.e. the ratio of lignocellulose material after step iv, to the lignocellulose feed material to the process. The yield can be even higher, for example above 90% by weight, or over 92% by weight.

[0071] The ISO brightness of the lignocellulose material after step iv is in the range of 10% - 50% ISO brightness, even more preferred in the range of 20% - 45% ISO brightness. But also, ISO brightness of 0-20 % is thinkable, individual numbers of ISO-brightness is of course thinkable as for example 10, 15, 20, 25, 30, 35, 40, 45, 50 % or any number in between.

[0072] The mixing of alkali and peroxide with the lignocellulose material can be made with several different devices that provide good mixing. The treatment can be made in batch or continuous devices. Pressurized high consistency, HC, refiners are excellent mixers and provide the high temperature, i.e. combining step ii and iii and the high pH needed to achieve low brightness without a long retention time. The preferred consistency in a HC refiner is 25% - 60% dry weight lignocellulose material to the total mixture weight. The flexibility is larger for the addition of peroxide iv, which can be added to a second pressurized HC refiner which provides fast chemical reactions due to the high temperature. However, the peroxide can also be added in other types of equipment such as atmospheric HC refiners, MC refiners, mixers, screw mixers, MC pumps or similar equipment. If the peroxide 9 optionally is added in an atmospheric device, longer retention time is required for chemical reactions, up to 30 min depending on the temperature. In order to keep the reaction time low, it is preferable to perform the peroxide treatment at a temperature above 50°C.

[0073] The alkali 6 and peroxide 7 are preferably separately mixed with the lignocellulose material, which can be achieved in two subsequent devices 2, 4, Fig. 1 or in one device 23, Fig 2, with separate mixing zones, 23a, 23b and 23c. One example of a two-stage equipment is a conical disc, CD, refiner, in which the alkali 6 can be added before or in the flat zone and the peroxide 7 in or right before the conical zone.

[0074] After the disclosed process 1 the treated lignocellulose material 5a can be further treated in any kind of equipment or process, including washing to remove dissolved substances, further refining at low to high consistency, screening or cleaning to remove impurities such as shives or bark, or other processes. One such example is disclosed in Fig 3. In this alternative, the process is altered by adding a mixing stage 2a, a pressing stage 2b and a washing stage 4a + 4b, see Fig. 5.

[0075] Remaining alkali 6a from a washing stage at the end section of the process, 4b, is added to the mixing device 2a. After the mixing of recycled alkali 6a there is a pressing stage 2b, where a stream 2c comprising water and dissolved substances leaves the process. In the ensuing step 2 the addition and mixing of alkali according to step ii is performed. After step ii there is a heating stage Hi followed by stage iv in which hydrogen peroxide 7 is added. Water can be added in the stage iv device 4 or separately in an optional device 4a. Thereafter the pulp is pressed, 4b. The liquid filtrate 6a of this pressing, containing recyclable alkali solution, is as said sent to the mixing stage 2a. In addition, this modified version of the process has no washing between step ii and step iv. The advantage of the modified process is a reduction of the total alkali, in kg / ton, needed to reach a given strength and also lower pH of the filtrate 2c leaving the process.

[0076] Optionally, lignocellulose material 5 can be pre-treated in optional ways such as in the positions 2a, 2b, including pre-heating, washing, addition of chelation agents, such as EDTA or DTPA, refining or other chemical or mechanical treatments.

[0077] By adjusting the conditions of steps ii, Hi and iv, the strength properties of the lignocellulose pulp are set, but also the visual appearance is set by achieving a low brightness.

[0078] The lignocellulose material produced according to the disclosed process is used to produce paper on a paper machine, but may be used in any application where fibre pulp material is used. It is advantageous to make packaging paper from the high yield lignocellulose pulp of the described method. It is easy to achieve the desired ISO brightness and also achieve good strength properties, with considerably higher yield than for normal chemical pulps used for the same purpose.

[0079] It is also advantageous to use the high yield lignocellulose pulp for a ply in a layered paperboard. Most advantageous is to use the pulp in the two outer fibre layers of a multi-layered product, which may for example have a bulky CTMP pulp in the middle layer(s).

[0080] It is also possible to make a liner product of the high yield lignocellulose pulp, which may be used in producing a corrugated board.

[0081] It is also possible to make a fluting product of the high yield lignocellulose pulp, which may be used in producing a corrugated board.

[0082] It is also possible to produce a full corrugated board product using both the mentioned liner product and the mentioned fluting product.

[0083] Example 1

[0084] In a two-stage TMP line, Fig. 9 operating at 7 ton dry pulp / h production rate using spruce wood chips as raw material, the following trial was made.

[0085] Preheated and washed wood chips 9 were fed through a plug screw 10 to a ,CD70 HC, refiner 11 operating at 4 bars housing pressure and a blow line pulp consistency of 50% by weight. Sodium hydroxide, NaOH, 6 at a concentration of 25% by weight, was added at two dosing levels, 25 and 30 kg / ton dry pulp together with 3 kg / ton dry pulp EDTA to the CD zone dilution water. The refined pulp was separated from steam in a steam separating device 12 and fed to a second stage HC refiner 13, RGP262, operating at 4 bars housing pressure and 40% pulp consistency. In the second stage HC refiner 13, hydrogen peroxide 7 was added directly into the refining zone at a dosing level of 25 kg / ton dry pulp. The refiner loads were 8 MW in the primary refiner 11 (CD70), and 4 MW in the second refiner 13. Pulp samples 14 were taken from the blow line from the second stage refiner and diluted with fresh water to 4% consistency and thoroughly agitated before dewatering with Buchner funnels to 25% consistency. Pulp properties were measured after hot disintegration of the pulp samples.

[0086] In figure 4, brightness is shown versus burst index for normal TMP without any chemicals and for the trial with two levels of sodium hydroxide. With 25 kg / ton NaOH, high burst index and brightness level was reached, 35% ISO. As clearly can be seen in in Fig. 3, the burst index is considerably higher than the normal reference TMP and the brightness is at a desired low level. When the strength of the pulp is compared at a given freeness (150 ml), Fig. 4, the burst index is 20% higher for the treated pulps compared to the TMP.

[0087] Example 2

[0088] Application of the invention for production of high yield fluting

[0089] A mill trial was performed with the aim to produce a fluting for corrugated board. Virgin pulp based fluting is normally made from hardwood NSSC pulp with a yield around 80% which requires sulphite doses around 100-150 kg / ton of wood.

[0090] For the present example, Fig. 10, a trial was performed with a single stage double disc refiner 16 (RGP68DD), which normally produces pulp with a relative low fibre length, similar to hardwood NSSC pulp.

[0091] The refiner 16 was fed through a plug screw 10 with preheated and washed Norway spruce wood chips 9 at a production rate of 17 adt / h. The refining pressure was 6.5 bars and the blow line consistency was 35%. 40 kg / adt sodium hydroxide 6 was dosed to the blow-line from the DD refiner, where the temperature was 165°C - 170°C. After the blow-line, pulp and steam was separated 12 and the pulp was discharged through a plug-screw 15 to a dilution screw 17. The residence time for the sodium hydroxide at 150°C was only a few seconds. In the dilution screw 17, white water 8 was added to a consistency of 9% and 30 kg / adt hydrogen peroxide 7 was added to the dilution screw 17 Pulp samples were taken after the dilution screw 17 and retained for 10 min at 85°C before washing (dilution to 4% consistency and subsequent pressing). The properties of the produced pulp is shown in Table 1. Notably, the SCT index, which is an important pulp property for fluting, of the pulp from the new process was very high. For a normal TMP this level of SCT index is only possible to reach at around 80 ml CSF.

[0092] Table 1

[0093] Ref. TMP New process

[0094] CSF ml 162 153

[0095] Fibre length mm 0.96 0.96

[0096] Tensile index Nm / g 39.0 45.6

[0097] TEA J / m2 32.0 39.9

[0098] Density kg / m3 447 500

[0099] Tensile Stiffness kN / m 285 339

[0100] Burst Index kPa.m2 / g 2.03 2.22

[0101] SCT index Nm / g 21.8 26.6

Claims

CLAIMS1. Method for producing a high yield lignocellulose pulp, comprising the steps of: / providing lignocellulose material (5), preferably in the form of wood chips or fibre pulp, / ■ / mixing the lignocellulose material with alkali (6), wherein the alkali (6) is added at a weight ratio comprised in the range of 10 kg - 60 kg alkali / dry ton of lignocellulose material, preferably 30 kg - 45 kg dry lignocellulose material,Hi Heating (3) the mixture of alkali and lignocellulose material to a temperature comprised in the range of 100°C - 200°C, wherein the temperature range is preferred to be comprised in the range of 120°C - 160°C, iv subsequently mixing (4) the lignocellulose material with hydrogen peroxide (7), at a weight ratio comprised in the range of 10 kg - 70 kg hydrogen peroxide / ton of dry lignocellulose material, preferably 20 kg - 40 kg, hydrogen peroxide / ton of dry lignocellulose material, wherein the method resulting in that the lignocellulose material, after step iv), comprises at least 85% by weight of dry solid lignocellulose material to the weight of the original dry lignocellulose material, preferably above 90% of the original lignocellulose material, -and resulting in that the lignocellulose material after step iv), has an ISO brightness in the range of 10% - 50%, even more preferred 20% - 45% ISO brightness.

2. Method for producing a lignocellulose pulp according to claim 1, wherein the consistency of the lignocellulose material in step ii, after addition of alkali, is controlled to be comprised in the range of 5% - 70% by dry weight of lignocellulose material, preferably 25% - 60% of lignocellulose material.

3. Method for producing a lignocellulose pulp according to claim 1 or 2, wherein the heating of step Hi is performed to a predetermined time range comprised in the range of 1 second to 30 minutes depending on the treatment temperature.

4. Method according to any of the claims above, wherein the alkali is sodium hydroxide, and / or potassium hydroxide, and / or sodium carbonate, and / or oxidized white liquor.

5. Method according to any of the claims above, wherein step ii is performed with a refiner, or a pump, or a mixer, or a compression screw, such as an extruder, etc., or any kind of equipment that gives the desired mixing.

6. Method according to any of the claims above, wherein step iv is performed with a refiner, or a pump, or a mixer, or a compression screw, such as an extruder, etc., or any kind of equipment that gives the desired mixing.

7. Method according to any of the claims 5 or 6, wherein the refiner is a high consistency refiner, for example a single disc type refiner, or double disc type refiner.

8. Method according to any of the claims above, wherein the method comprises a step between step / and / ' / , which comprises any pre-treatment of the lignocellulosic material such as preheating and / or refining, and / or chelation and / or pressing, e.g. dewatering, of the lignocellulosic material.

9. Method according to any of the claims above, wherein the method does not include a washing step between step ii and step iv.

10. Method according to any of the steps above, wherein the method comprises any further treatment of the lignocellulosic material, such as washing, and / or screening and / or cleaning, and / or refining, after step iv.

11. Method according to any of the steps above, wherein the pH of the lignocellulose material in step ii and / or step iii, and / or step iv is arranged to be at least 10, preferably at least 11, more preferred at least 12, even more preferred at least 13, or at least 14.

12. High yield lignocellulose pulp produced according to the method of any of the claims 1-11.

13. Paper made from high yield lignocellulose pulp according to claim 12.

14. Paperboard made from high yield lignocellulose pulp according to claim 12.

15. Paperboard according to claim 14, wherein the paperboard is a layered paperboard product, comprising at least one ply with high yield lignocellulose pulp according to claim 12, preferably said ply is an outer ply of the layered paperboard product, more preferred said layered paperboard product has both outer layers made from the high yield lignocellulose pulp.

16. Liner and / or fluting for producing a corrugated board, wherein the liner and / or fluting is made from the high yield lignocellulose pulp according to claim 12.

Images