Method for obtaining at least two cellulose pulps with different characteristics

Abstract

The subject of the invention is a method for obtaining at least two cellulose pulps, which comprises: - a step of mixing plant materials comprising at least 60% of lignocellulosic material having a lignin content greater than a given value, of the order of 10%, and also at least 2% of fibrous material having a lignin content less than the given value, - a step of cooking the mixture, - a step of removing the liquid phase in order to isolate a cellulose pulp, - a step of separating the cellulose pulp into at least two cellulose pulps, each having at least one characteristic different from each other. In contrast to the prior art, which selects a portion of a specific plant material to obtain a given cellulose pulp, the invention aims to transform a mixture of less selective plant materials to obtain a cellulose pulp and then to separate the latter in order to obtain two distinct cellulose pulps.

Description

[0001] Process for obtaining at least two cellulosic pulps having different characteristics

[0002] The present application relates to a process for obtaining at least two cellulosic pulps having different characteristics.

[0003] A hemp-based textile can be made from fibers derived from the bark of the hemp plant. To promote the quality of the so-called bast fibers, hemp is grown according to a so-called textile agricultural protocol, which involves harvesting the hemp before the seeds mature to prevent the fibers from thickening and stiffening. This textile agricultural protocol is characterized by a high seeding density, generally around 80 kg / ha.

[0004] According to one operating method, the mown plant material is subjected to a first retting stage, consisting of macerating it in a humid environment or leaving it to ret in the field after mowing, to facilitate the separation of the fibers from the heart of the stem (also called hemp shiv) then to a second scutching stage consisting of separating the fibers from the heart of the stems by crushing and beating. The tow thus obtained is relatively long, around 70 to 80 cm, and must be spun on specific tools to obtain thread for making fabric.

[0005] Alternatively, the hemp fibers from the defibering process are shortened and mixed with short fibers (such as cotton, for example) so that the resulting fibers can be spun on cotton spinning tools, which are widely used in the textile industry. However, in this second method, the resulting textile material contains at most 70% hemp, while being limited in fineness, which reduces the range of applications.

[0006] Regardless of the method of operation, hemp textiles are generally obtained from fibers from plants cut before the seeds have ripened, so the hemp is not used optimally, depriving farmers of income from harvesting the seeds. In addition, it is necessary to go through retting, scutching, or defibering stages to process this type of fiber, the retting stage degrading the hemp shiv, which can limit its use to low-value mulch. To overcome these disadvantages, according to another agricultural protocol called mixed, hemp is grown until the seeds have ripened. In this case, the entire plant can be used.However, hemp fibres from the mixed agricultural protocol are generally not used to obtain textile fibres for clothing given the low yields of sufficiently fine bast fibres and the difficulty of using them with textile industry tools or with specific tools for hemp from the textile agricultural protocol.

[0007] Documents FR31O66OO and W02021151904 propose a process for obtaining a hemp-based cellulosic pulp which, after dilution and / or dissolution and then regeneration steps, makes it possible to obtain a textile product such as a textile filament. This process uses a plant material comprising by weight at least 50% of hemp stalks harvested after flowering, said hemp stalks having a rate of at least 30% of hemp shiv and a length of less than 80 cm. This process comprises a step of cooking the plant material as well as at least one refining step aimed at reducing the length of the fibers and / or pieces contained in the cooked plant material.

[0008] According to another application, a cellulose pulp can be used for the production of paper pulp. According to a non-limiting procedure, this cellulose pulp is prepared from bast fibers originating from a plant material resulting from a specific agricultural protocol. This plant material is subjected to defibering-type pretreatment steps aimed at selecting a fraction of the plant material, namely the bast fibers, by removing in particular the core of the stem (or woody kernel) of the plant material. These bast fibers are then transformed into cellulose pulp by a transformation process comprising at least one cooking step.

[0009] According to one disadvantage, for bast fiber plants such as flax, hemp, kenaf and nettle, producing plant material according to specific specifications, which are restrictive for farmers, generally leads to limiting the resource and / or reducing biodiversity. According to another disadvantage, the pre-treatment steps (defibration, scutching, etc.) of the plant material prior to pulp production, aimed at fractionating the plant material to extract the bast fibers in particular, are generally energy-intensive, demanding in terms of the cleanliness of the products to be achieved, these pre-treatment steps being specific to agricultural protocols and / or to the plant. Finally, the steps of transformation into cellulosic pulp of the selected fraction of the selected plant material are specific to this fraction and result in a single type of cellulosic pulp.Thus, the same production of cellulosic pulp made from a specific fraction of a plant material produced according to specific specifications makes it possible to obtain a single cellulosic pulp with specific characteristics.

[0010] Document WO2017 / 035535 proposes a method for producing a nanocellulosic material comprising a step of selecting a biomass as well as a set of steps for transforming the selected biomass according to the nanocellulosic material to be obtained. According to the teaching of document WO2017 / 035535, the production of two cellulosic pulps consists of using two distinct production processes, one for each cellulosic pulp to be obtained, and comprises two steps of selecting distinct plant materials, one for each process, as well as two sets of distinct transformation steps, one for each process.

[0011] Having to process cellulosic pulps in parallel via two sets of processing steps leads to relatively high energy consumption. In addition, providing two stages of plant material selection leads to a large quantity of plant material not being used or being poorly used and / or imposes specific agricultural protocols that can be restrictive.

[0012] The present invention aims to remedy all or part of the drawbacks of the prior art.

[0013] To this end, the invention relates to a process for obtaining at least two cellulosic pulps each having at least one characteristic different from each other, characterized in that the process comprises:

[0014] At least one step of mixing plant materials comprising at least 60% of a first material, called lignocellulosic, having a lignin content greater than or equal to a given value, of the order of 10%, as well as at least 2% of a second material, called fibrous, having a lignin content less than or equal to the given value, at least one step of cooking the mixture of plant materials with a cooking liquid, at a temperature greater than or equal to 80°C, with, at least for part of the cooking time, at least one delignifying agent, at least one step of removing the liquid phase from the cooked mixture of plant materials in order to isolate a cellulosic pulp, at least one step of separating the cellulosic pulp into at least two cellulosic pulps each having at least one characteristic different from each other.

[0015] According to the invention, a less selective mixture of plant materials is used to obtain a cellulosic pulp which is then separated to isolate cellulosic pulps each having at least one given characteristic different from one pulp to another.

[0016] Therefore, unlike the prior art, the specifications of agricultural protocols are less restrictive, which helps to increase resources and promote biodiversity. The invention allows for greater versatility in the supply of agricultural materials.

[0017] As a further advantage, some steps of separation of plant material in order to isolate part of the raw plant material can be simplified or eliminated, thus helping to reduce energy consumption and facilitating the adoption of these plants as raw material for the production of cellulosic pulps.

[0018] Finally, the process of the invention makes it possible to obtain, from the same production, at least two distinct cellulosic pulps.

[0019] Other features and advantages will emerge from the detailed description of the invention which follows.

[0020] According to one operating mode, a process for obtaining cellulosic pulps comprises at least one step of mixing plant materials comprising at least 60% of a first material, called lignocellulosic, having a lignin content greater than or equal to a given value as well as at least 2% of a second material, called fibrous, having a lignin content less than or equal to the given value.

[0021] The value given for the lignin content is of the order of 10%. According to one example, the lignin content is greater than or equal to 12%, preferably 18% for the first material and less than or equal to 9%, preferably 7% for the second material.

[0022] Providing input plant materials with different lignin levels facilitates the separation of the two cellulosic pulps at the end of the process. This lignin level can be measured by chemical analysis using, for example, the Van Soest method or defined by so-called TAPPI standards formulated by the TAPPI association (Technical Association of the Pulp and Paper Industry).

[0023] For the present application, the percentages correspond to percentages by weight of dry matter.

[0024] According to one configuration, the mixture of plant materials comprises at most 98% lignocellulosic material. Preferably, the mixture of plant materials comprises between 70 and 90% lignocellulosic material. Optimally, the mixture of plant materials comprises at least 80% lignocellulosic material. This percentage facilitates the step of separating the cellulosic pulps.

[0025] Lignocellulosic material means a lignocellulosic material or a mixture of lignocellulosic materials. The lignocellulosic material is selected from annual plants or parts of annual plants such as flax shives, hemp shives, kenaf woody kernel, nettle woody kernel, miscanthus, reed, bamboo, bagasse, certain cereal straws, pericarps or flower stems. This list is not exhaustive.

[0026] Lignocellulosic material comes in the form of chips that are less than 8 cm long, preferably less than 4 cm.

[0027] According to one configuration, the mixture of plant materials comprises at most 40% fibrous material. Preferably, the mixture of plant materials comprises between 10 and 30% fibrous material, and optimally between 5 and 20% fibrous material.

[0028] Fibrous material means a fibrous material or a mixture of fibrous materials. The fibrous material is chosen from bast fibers such as hemp fibers, flax fibers, jute fibers, kenaf fibers, nettle fibers or ramie fibers for example; pseudostem fibers such as banana fibers for example; leaf fibers such as abaca fibers or sisal fibers for example. This list is not exhaustive. Fibrous material is more flexible as opposed to a lignocellulosic material, which is more rigid and / or brittle.

[0029] The fibers of the fibrous material have a length of less than 80 cm, preferably less than or equal to 8 cm. According to another characteristic, 90% of the fibers of the fibrous material have a length greater than 5 mm. The mixture of plant materials comprises several different plant species and / or different fractions of the same plant species containing bast fibers.

[0030] The process for obtaining cellulosic pulps comprises at least one step of cooking the mixture of plant materials with a cooking liquid, at a temperature greater than or equal to 80°C, preferably greater than 140°C. According to one operating method, the cooking temperature is less than or equal to 190°C.

[0031] According to one configuration, the cooking liquid is water in liquid and / or gaseous form. The liquid / solid ratio is greater than or equal to 2, preferably greater than 3.5.

[0032] A cooking step is carried out for a duration, at maximum temperature, less than or equal to 480 min, preferably less than 300 min.

[0033] According to one operating method, the cooking step comprises at least first and second successive phases, the first phase consisting of cooking the mixture of plant materials with water, without delignifying agent, at a temperature greater than or equal to 80°C, optionally followed by removal of at least part of the liquid phase of the mixture of plant materials cooked at the end of the first phase of the cooking step, the second phase of the cooking step consisting of cooking the remainder of the mixture in the presence of at least one delignifying agent, at a temperature greater than or equal to 80°C.

[0034] During the first phase of the cooking step, the mixture gradually becomes acidic. As soon as the pH of the mixture is below a given threshold value corresponding to an acidic pH, preferably in the order of 3 to 5, the first phase is stopped. Thus, the first phase is stopped when the liquid phase contains at least 10% of the hemicelluloses present in the starting material. These hemicelluloses generally have a xylan content of at least 50%, the quantity of xylans being greater than that of mannans.

[0035] At the end of the first phase of the cooking step, the liquid phase, containing in particular hemicelluloses, polysaccharides or any other recoverable by-product such as furfural and acetic acid, can be separated from the solid phase of the mixture.

[0036] The second phase of the cooking step is carried out at a temperature greater than or equal to 80°C, the solid phase of the mixture resulting from the first phase of the cooking step being remixed with water and at least one delignifying agent.

[0037] In a simplified operating mode, cooking involves only one phase, with the cooking step being carried out from the beginning with at least one delignifying agent. However, carrying out the cooking step in two phases promotes delignification and makes it possible to obtain a purer cellulose pulp.

[0038] Delignifying agent means a delignifying agent or a mixture of delignifying agents.

[0039] For example, the delignifying agent is chosen from the following non-exhaustive list: sulfites, deep eutectic solvents, Kraft liquors, ionic liquids, oxygen, ozone, hydrogen peroxide, acetic acid, peracetic acid, ethanol, methanol, acetone, dimethyl sulfoxide (DMSO), aldehydes, chlorine, sodium chlorite, chlorine dioxide, sodium hydroxide, sulfuric acid, acetic anhydride.

[0040] After the cooking step, the production process comprises at least one step of removing (or drawing off) the liquid phase of the cooked mixture of plant materials, also called liquor and which contains in particular lignins, in order to isolate a cellulosic pulp. This by-product containing lignins can be used, for example, to generate energy. These lignins can also be extracted from the liquor to obtain products in the fields of cosmetics, glues, resins or carbon fibers. For example, these lignins have a low mineral content, less than 10%, generally less than 5%; an EC50 value (antioxidant power) generally between 0.15 and 0.7 mg / mL as well as a carboxylic group content generally between 0.7 and 1.6 mmol / g.

[0041] At the end of this removal step, generally at least 80% by weight of the lignins contained in the initial mixture of plant materials have been removed.

[0042] Finally, the process for obtaining cellulosic pulps comprises at least one step of separating the cellulosic pulp into at least two cellulosic pulps, each having at least one characteristic different from the other.

[0043] Preferably, the separation step makes it possible to separate the cellulosic pulp resulting from cooking into at least two cellulosic pulps each having at least two characteristics different from each other, including in particular the length of the fibers, the degree of polymerization, the kappa index, the cellulose purity, the whiteness and the ash content, the cellulosic pulps being used for differentiated applications. The at least two different characteristics of the cellulosic pulps may relate to the characteristics of the fibers or particles of these cellulosic pulps.Thus, unlike the prior art which provides steps for separating a specific plant material prior to obtaining the cellulosic pulp to obtain a cellulosic pulp having fibers with given characteristics, the invention uses a less selective mixture of plant materials to obtain a cellulosic pulp which is then separated to isolate cellulosic pulps each having at least one given characteristic different from one pulp to another. Consequently, the specifications of the agricultural protocols are less restrictive, which contributes to increasing the resource and promoting biodiversity.

[0044] Being able to avoid or reduce pre-treatment steps such as retting, defibering, scutching, etc., which aim to select part of the plant material before obtaining cellulosic pulp, helps to facilitate the integration of agricultural biomass into cellulosic pulp and reduce the energy consumption of the process for obtaining cellulosic pulp.

[0045] Finally, selecting less plant material submitted to the cooking stage can allow the removal of larger volumes of by-products, promoting their recovery.

[0046] According to one procedure, the cellulosic pulp is separated so as to split it into a first cellulosic pulp having shorter fibers, of average length less than a given value, and a second cellulosic pulp having longer fibers of average length greater than or equal to the given value. According to one configuration, the given value is of the order of 300 to 800 pm, preferably of the order of 400 to 600 pm.

[0047] For example, to carry out this separation step, the cellulose pulp is separated by sieving by passing through a sieve with slits between 0.2 mm and 0.5 mm. The rate of passage of fibers or particles according to their length is closely linked to the dimensions of the sieve openings. The yield by type of cellulose pulp is in particular a function of the dimensions of the sieve openings as well as the initial rate of fibrous material.

[0048] Of course, the invention is not limited to this operating mode for the separation step. Thus, the cellulose pulp resulting from the cooking step can be separated using, for example, a centrifugation and / or decantation process. These processes can replace or complement the screening process. The first pulp consists of fibers or particles that have passed through the screen, which ensures a homogeneous quality of cellulose pulp in terms of fiber length (and width) and a lower degree of polymerization. This first cellulose pulp can be used as is or undergo additional treatments.

[0049] According to one application, the first cellulosic pulp can be used as dissolving pulp. In this case, the cellulosic pulp is generally subjected to a bleaching and / or purification step in order to reduce the residual lignin content, adjust the degree of polymerization and / or reduce the ash content.

[0050] The second pulp consists of fibers or particles that do not pass through the sieve openings during the separation operation. This second cellulose pulp includes fibers with a higher average fiber length than the first cellulose pulp, which are more heterogeneous in terms of fiber length. This second pulp is different in terms of morphology compared to the first pulp. It generally has a higher degree of polymerization and the fibers present are more delignified. This second cellulose pulp is particularly suitable for packaging applications or for molding objects that have good strength, in particular due to the cohesion of its fibers. This second cellulose pulp can be used as is or undergo additional treatments.

[0051] Of course, the invention is not limited to fiber length as a characteristic for the cellulosic pulp separation step. Other characteristics are conceivable, such as fiber distribution, degree of polymerization, whiteness, kappa number, cellulose purity or ash content. This list is not exhaustive.

[0052] In addition, the process for obtaining cellulosic pulps can include several successive separation stages.

[0053] Each cellulosic pulp obtained from the process of the invention can be mixed with at least one other cellulosic pulp.

[0054] At least one of the cellulosic pulps obtained from the process of the invention can be used to obtain products, such as a dissolving pulp, a textile product (such as filaments obtained by dissolving then spinning for example), a membrane, a molded object, packaging or any other product obtained from the cellulosic pulp obtained alone according to the process of the invention or mixed with at least one other cellulosic pulp. The invention is now described by way of an example. The mixture of plant materials comprises 50% of fibrous hemp shiv (in which there remains

[0055] 20 to 40% bast fibers), 40% miscanthus and 10% flax shives.

[0056] Regarding hemp, it generally comprises 50% hemp shiv, 27% bast fibers and 23% dust. Hemp shiv has the following chemical composition: approximately 46% cellulose, 24% lignin and 18% hemicellulose. Bast fibers have the following chemical composition: more than 70% cellulose, approximately 5% lignin and 10 to 15% hemicellulose.

[0057] In this case, the hemp straw is dusted and shortened to a length of less than 10 cm and preferably less than 5 cm. The hemp does not undergo any defibration or scutching stage.

[0058] Regarding miscanthus, it has the following chemical composition: approximately 40 to 45% cellulose, 16 to 24% lignin and 25 to 28% hemicellulose.

[0059] Flax shives have the following chemical composition: approximately 43% cellulose, 25% lignin, and 27% hemicellulose. Flax shives can be obtained from flax scutching. This mixture of plant materials is introduced into a reactor to which water is added to obtain a liquid / solid ratio of around 3.5 to 7.5.

[0060] Next, this mixture of plant matter and water is subjected to a two-phase cooking step.

[0061] In the first phase, the mixture is heated to a temperature of around 120°C to 200°C for a maximum of 150 minutes. When the pH becomes acidic, the filtrate is extracted. The latter contains in particular a portion of the hemicelluloses (more than 10% by weight).

[0062] In the second phase, a delignifying agent and water are added to the hydrolyzed material in a reactor. For example, the delignifying agent is Kraft liquor or a deep eutectic solvent. The liquid / solid ratio is in the range of 3.5 to 7.5. The mixture is heated to a temperature in the range of 100°C to 170°C for a maximum duration of 60 to 300 min.

[0063] At the end of the second phase of the cooking stage, the cooking liquor is drawn off. This liquor notably includes a portion of the lignins (more than 60% by weight).

[0064] After the removal step, the cellulose pulp is rinsed, resuspended, and then passed through a sieve to perform the separation step. For example, the sieve has slits measuring 0.2 to 0.5 mm. The cellulose pulp passing through the sieve corresponds to the first cellulose pulp, and that remaining above the sieve or blocked by it corresponds to the second cellulose pulp. The second cellulose pulp represents 4 to 25%, generally 10 to 25%, of the total cellulose pulp before the separation step. Generally, the first cellulose pulp is the majority at the end of the separation step. Therefore, this first cellulose pulp is called the majority pulp, the second cellulose pulp being called the minority pulp.

[0065] The first cellulosic pulp is homogeneous and has a kappa number of the order of 10 to 30, generally 12 to 25, as well as a degree of polymerization of between 800 and 1300. This first cellulosic pulp can be subjected to at least one additional step such as bleaching to adjust its degree of polymerization and / or increase its purity. According to one application, this first cellulosic pulp can be used as dissolving pulp after a purification step.

[0066] The second cellulose pulp is more heterogeneous in terms of fiber length and has a kappa number at least 2 points lower than that of the first pulp. This second cellulose pulp can be used as molding pulp and / or specialty papers. It can also be used for the production of textile fibers, for example after a microfibrillation step.

Claims

CLAIMS 1. Process for obtaining at least two cellulosic pulps each having at least one characteristic different from each other, characterized in that the process comprises: at least one step of mixing plant materials comprising at least 60% of a first material, called lignocellulosic, having a lignin content greater than or equal to a given value, of the order of 10%, as well as at least 2% of a second material, called fibrous, having a lignin content less than or equal to the given value, at least one step of cooking the mixture of plant materials with a cooking liquid, at a temperature greater than or equal to 80°C with, at least for part of the cooking time, at least one delignifying agent, at least one step of removing the liquid phase from the cooked mixture of plant materials in order to isolate a cellulosic pulp,at least one step of separating the cellulosic pulp into at least two cellulosic pulps each having at least one characteristic different from each other., 2. Method according to the preceding claim, characterized in that the separation step is configured to allow the cellulosic pulp resulting from cooking to be separated into at least two cellulosic pulps each having at least two characteristics different from each other, including in particular the length of the fibers, the distribution of the fibers, the degree of polymerization, the kappa index, the cellulose purity, the whiteness and the ash content.

3. Method according to claim 1 or 2, characterized in that the cooking step comprises first and second successive phases, the first phase consisting of cooking the mixture of plant materials without delignifying agent after removal of at least part of the liquid phase of the mixture of plant materials cooked at the end of the first phase of the cooking step, the second phase of the cooking step consisting of cooking the remainder of the mixture in the presence of at least one delignifying agent.

4. Method according to one of the preceding claims, characterized in that the mixture of plant materials comprises between 70 and 90% lignocellulosic material and between 10 and 30% fibrous material.

5. Method according to one of the preceding claims, characterized in that the lignocellulosic material is in the form of chips which have a length of less than 8 cm, preferably less than 4 cm.

6. Method according to one of the preceding claims, characterized in that the fibers of the fibrous material have a length of less than 80 cm, preferably less than 8 cm.

7. Method according to one of the preceding claims, characterized in that the cellulosic pulp is separated so as to split it into a first cellulosic pulp having shorter fibers, of average length less than a given value, and a second cellulosic pulp having longer fibers, of average length greater than or equal to the given value.

8. Method according to one of the preceding claims, characterized in that the cellulosic pulps are separated by sieving, centrifugation and / or decantation.

9. Method according to the preceding claim, characterized in that the cellulosic pulp is separated by passing it through a sieve having slots between 0.2 mm and 0.5 mm, the cellulosic pulp passing through the sieve corresponding to the first cellulosic pulp, that remaining above the sieve or blocked by the latter corresponding to the second cellulosic pulp.

10. Cellulosic pulp obtained from the process according to one of the preceding claims, having short fibers, of average length less than a given value of the order of 300 to 800 pm.

11. Cellulosic pulp obtained from the process according to one of claims 1 to 10, having long fibers, of average length greater than a given value of the order of 300 to 800 pm.

12. Product obtained from at least one cellulose pulp according to claim 11 or 12.

13. Lignins obtained during a removal step of a process according to one of claims 1 to 10.

14. Hemicelluloses obtained during a cooking step of a process according to one of claims 1 to 10.

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