Method for the production of cellulose and for obtaining lignin from a lignocellulose from raw material plants of the plant genus micanthus

Abstract

The invention relates to a process for producing pulp and for obtaining lignin from lignocellulose from raw material plants of the genus Miscanthus, wherein the raw material plants are crushed by means of a high-consistency pulper in at least a first mechanical processing stage and dissolved by the addition of water and an alkaline chemical, so that a lignocellulose-containing fiber slurry is obtained, wherein the cellulose from the fiber slurry is separated from a lignin-containing black liquor by means of a pressing device, so that pressed cellulose is obtained, which is washed by the addition of water and CO2, wherein enzymes or enzyme mixtures are added to the washed cellulose, and wherein the cellulose is dewatered, so that pulp suitable for further processing is obtained.The black liquor is concentrated to a TDS value between 15 and 45% and neutralized in a reactor, forming lignin particles, particularly lignin flakes, which are separated from the liquid. The separated lignin particles are washed and protonated in a further reactor, and the protonated lignin is separated and dried.

Description

[0001] The present invention relates to a process for the production of pulp and for the extraction of lignin from lignocellulose from raw material plants of the genus Miscanthus.

[0002] Pulp is used to manufacture paper, hygiene paper, and nonwoven materials, which are often also referred to as nonwovens. Pulp is a fibrous mass produced by the chemical pulping of plant fibers containing lignocellulose. Pulp consists predominantly of cellulose.

[0003] Lignocellulose contains lignin in addition to cellulose. This lignin is a waste product that must be extracted from the lignocellulose in a suitable manner so that the cellulose required for the production of pulp can be obtained in the highest possible purity.

[0004] To dissolve the lignin from lignocellulose for pulp production and obtain the purest possible cellulose, various fiber pulping processes are known from the prior art. An important, globally dominant process is the alkaline sulfate process, often also called the Kraft process, because it yields stronger pulp fibers. In this sulfate process, for example, wood chips are heated for several hours under elevated pressure of approximately 7 to 10 bar with sodium hydroxide, sodium sulfide, and sodium sulfate. Delignification of the lignocellulose typically occurs at temperatures of 170°C and above.

[0005] Other fiber digestion processes known from the prior art are the sulfite process, the soda process and the organosolv process.

[0006] Wood is very frequently used for pulp production. However, it is also possible to use non-woody raw material plants for pulp production. Examples of non-woody raw material plants are those of the genus Miscanthus. Exemplary plant species of the genus Miscanthus are Miscanthus sinensis, Miscanthus sacchariflorus, and Miscanthus × giganteus. Miscanthus × giganteus is a hybrid of Miscanthus sinensis and Miscanthus sacchariflorus. Raw material plants of the species Miscanthus × giganteus are characterized in particular by rapid growth and a favorable carbon dioxide balance, making them of great commercial importance.

[0007] Raw material plants of the species Miscanthus × giganteus can be cultivated locally and harvested between January and April. The harvested plants are typically pressed into bales and stored at a moisture content between 5 and 15%. These bales can be used immediately after harvesting or stored for later use. Miscanthus × giganteus plants are relatively robust against pests. Therefore, the use of pesticides during cultivation can be kept to a minimum to avoid ecological damage. Pesticides are only used in the first year after planting to prevent weeds from overgrowing the young plants. By the second year, when the first harvest takes place, no traces of the pesticides used are found in the raw material.Plants of the species Miscanthus × giganteus can be harvested every year for about 20 years without the need for additional pesticides or fertilizers.

[0008] WO 2017 / 178849 A1 discloses a continuous process for producing very high whiteness pulp from grass-like plant material suitable for papermaking. The process comprises the following steps: preparation of the grass-like plant material by shredding; dust removal; continuous digestion with optimized concentrations of NaOH and NaCl; dispersion; continuous bleaching with optimized concentrations of H₂O₂ and sodium silicate without the use of NaOH; optional dispersion; dewatering to remove black liquor; and washing to obtain very high whiteness pulp (>90%) suitable for papermaking. The process further includes the integrated electrolytic removal of lignin and other byproducts, accompanied by regeneration of the cooking chemical solution, thus enabling a completely closed-loop material cycle.

[0009] WO 2014 / 140643 A1 describes a process for treating lignocellulose biomass to dissolve the lignin it contains, while the cellulose remains intact. The resulting pulp can be used to produce glucose. Furthermore, the lignin can be isolated for subsequent use in the renewable chemicals industry as a source of aromatic platform chemicals.

[0010] US Patent 2010 / 269990 A1 discloses a process for separating the components of lignocellulosic biomass for the purpose of producing pure reactive cellulose. The process is two-stage. In the first stage, the lignocellulosic biomass is pretreated with steam, with or without an acid catalyst, and then pressed, with or without an eluent, to remove hemicellulose and other impurities. In the second stage, the pretreated biomass is extracted with a solvent such as ethanol, with or without acid catalysts, to remove lignin and release a purified cellulose stream. The extracted cellulose is then rapidly decompressed to break down the fiber structure. The process yields a purified cellulose stream that is relatively readily hydrolyzed with enzymes and fermented to produce biofuels and other chemicals such as ethanol.

[0011] DE 10 2016 225 827 A1 discloses a two-stage pulping process for the chemical fractionation of lignocellulose. In a first stage, the lignocellulose is pretreated with steam or water at temperatures above 100°C and elevated pressures. In a second stage, the pretreated lignocellulose is extracted with an extraction solution, whereby lignin is dissolved from the lignocellulose. The temperature is not reduced below 80°C between the two stages. The object of the present invention is to provide a process for the production of pulp and for the recovery of lignin from lignocellulose derived from raw material plants of the genus Miscanthus, by means of which pulp and lignin with particularly advantageous properties can be obtained.

[0012] The solution to this problem is provided by a process for producing pulp and for obtaining lignin from lignocellulose derived from raw material plants of the genus Miscanthus, comprising the features of claim 1. The dependent claims relate to advantageous embodiments of the invention. A process according to the invention for producing pulp and for obtaining lignin from lignocellulose derived from raw material plants of the genus Miscanthus comprises the steps: S1: Raw material plants of the genus Miscanthus are fed into a high-consistency pulper, S2: the raw material plants are crushed by means of the high-consistency pulper in at least a first mechanical processing stage and dissolved by the addition of water and an alkaline chemical, so that a lignocellulose-containing fiber slurry is obtained, wherein the reaction temperature in this process step is selected to be approximately 60°C to approximately 100°C, preferably 70°C to 90°C, S3: the cellulose is separated from the fiber slurry by means of a pressing device, in particular by means of a screw press, from a lignin-containing black liquor, so that pressed cellulose is obtained, S4: the pressed cellulose is washed by the addition of water and CO2, S5: enzymes or enzyme mixtures, in particular cellulose- and / or lignin-modifying enzymes or enzyme mixtures, are added to the washed cellulose,S6: The cellulose is dewatered by means of a pressing device, preferably a screw press, so that pulp suitable for further processing is obtained. S7: The black liquor is concentrated to a TDS value between 15 and 45%, preferably between 25 and 35%. S8: The black liquor is neutralized in a reactor, whereby lignin particles, in particular lignin flakes, are formed. S9: The lignin particles are separated from the liquid, preferably by means of a decanter separator. S10: The lignin particles separated in process step S9 are washed and protonated in a further reactor, using an acid as the washing chemical. S11: The protonated lignin is separated and dried, in particular by means of a rapid drying device.

[0013] Instead of a pulp boiler, which is very commonly used in prior art in pulp production, the process according to the invention uses a high-consistency pulper for pulp production from raw material plants of the genus Miscanthus. Advantageously, pretreatment of the raw material plants is not required.

[0014] The reaction temperature in process step S2 is selected to be approximately 60°C to approximately 100°C, preferably 70°C to 90°C. This means that the reaction temperature in process step S2 is considerably lower than in the prior art Kraft processes or soda processes.

[0015] It has been shown that, using the process according to the invention, a pulp with unbleached cellulose can be obtained from raw material plants of the genus Miscanthus, wherein the cellulose has a lighter color compared to conventional, unbleached celluloses. Preferably, raw material plants of the species Miscanthus x giganteus are used.

[0016] The finished cellulose fibers have a fiber length between 0.5 and 1.5 mm and an average thickness of approximately 15 to 25 micrometers. The TDS value specified in claim 1 is a chemical parameter and represents – as an abbreviation for the English expression " t total d issolved s Total solids (TDS) – the amount of all non-volatile substances contained in the solvent (water) of the black liquor. In the professional community, the TDS value is also frequently referred to as total dry residue.

[0017] The pulp containing cellulose from raw material plants of the genus Miscanthus, in particular the species Miscanthus x giganteus, produced according to the invention, can advantageously be stored for extended periods without significant cellulose degradation. Furthermore, it has been shown that the pulp from raw material plants of the genus Miscanthus, in particular the species Miscanthus x giganteus, exhibits advantageous antimicrobial and antioxidant properties. These advantageous properties are very likely attributable to the residual lignin remaining in the cellulose (which is unavoidable due to the manufacturing process) and which possesses antimicrobial and antioxidant properties.

[0018] The pulp produced from raw material plants of the genus Miscanthus, in particular the species Miscanthus x giganteus, also possesses very good softness properties without losing strength. These are actually contradictory properties. Furthermore, the unbleached fibers have a very light color. The special enzyme treatment provided in the process according to the invention, which is not known in the prior art, advantageously ensures the strength, softness, and brightness of the pulp fibers. Enzymes or enzyme mixtures are used that improve the strength, softness, and brightness (i.e., the whiteness) of the pulp fibers.

[0019] The lignin recovery process yields a high quantity of lignin. Due to the low-energy pulping process, the lignin remains advantageously in its natural state. This has been shown to result in less intermolecular degradation of the lignin, which beneficially leads to a faint odor and lower glass transition temperatures. The gentle processing and the complete avoidance of sulfur-containing components in pulp production, as used particularly in prior art sulfate processes, result in a low-odor and light-colored lignin.

[0020] In one embodiment, the alkaline chemicals can be added to the raw material plants in process step S2 at a concentration of 1 to 10 mol [OH⁻] / kg of raw material plants, preferably 2 to 7 mol [OH⁻] / kg of raw material plants, and particularly 3 to 5 mol [OH⁻] / kg of raw material plants. For example, sodium hydroxide (NaOH) can be used. Alternatively, alkaline potassium hydroxides or calcium hydroxides can also be used, for example.

[0021] In an advantageous embodiment, process step S2 can be carried out under atmospheric pressure. This also means that the pressure is significantly lower than in the force processes or soda processes known from the prior art.

[0022] In a particularly advantageous embodiment, it is proposed that in process step S2, a second mechanical treatment is carried out in a second mechanical processing stage, in which additional mechanical energy is supplied to the fiber slurry, preferably by means of a milling pump. This advantageously achieves the comminution of any raw material plant pieces and shives that may still be contained in the fiber slurry, and allows the fibers to fibrillate into stronger and softer fibers. Preferably, an energy input of between 20 and 80 kWh / ton is introduced into the fiber slurry during the second mechanical treatment. Preferably, the energy input is between 40 and 60 kWh / ton.

[0023] In a preferred embodiment, it is proposed that between 70 and 140 g / ton, preferably between 80 and 100 g / ton, of enzymes or enzyme mixtures be added to the washed cellulose in process step S5.

[0024] Preferably, the enzymes or enzyme mixtures may be selected from a group consisting of cellulases, peroxidases, amylases, laccases or mixtures thereof.

[0025] In a preferred embodiment, the reaction temperature in process step S8 can be selected to be between 50°C and 100°C, preferably between 70°C and 90°C. During this chemical reaction in process step S8, the temperature is preferably maintained at this temperature for about one hour (primary reaction). The black liquor is preferably stirred in the reactor at a defined stirring speed to prevent rapid particle growth but to promote the formation of firmer, more compact particles. When a preset pH value, in particular a pH of 8, is reached, the stirring speed is reduced. The compact particles formed in this way can then grow into larger particles over a period of about one hour (secondary reaction), thereby forming flakes. The pressure during the entire reaction is between 1.0 and 3.0 bar, preferably between 1.5 and 2.0 bar.

[0026] In an advantageous embodiment, it is proposed that the reaction temperature during process step S10 is selected to be between 50° and 100°C, preferably between 70°C and 90°C.

[0027] In a particularly advantageous embodiment, ultrasonic defoaming can be performed during process step S10 of the lignin washing process. It has been shown that this ultrasonic defoaming can advantageously accelerate the lignin washing process.

[0028] Preferably, an optional further process step S12 may be provided, in which the liquid obtained in process step S11 is regenerated. The liquid is preferably mixed with calcium hydroxide. The carbonates combine with the [OH⁻] from the calcium hydroxide. This reaction forms a liquid alkaline chemical and solid calcium carbonate, which precipitates and can be easily separated from the liquid. The CO₂ is thus stored in the form of calcium carbonate. The reaction time is approximately 1 hour at a reaction temperature between 50 and 100°C, preferably between 70 and 90°C. The alkaline chemical recovered in this way can subsequently be reused for the fiber pulping of raw material plants of the genus Miscanthus, in particular the species Miscanthus x giganteus, according to the process described here.

[0029] Claim 13 proposes the use of a pulp produced according to a process according to any one of claims 1 to 12 for the manufacture of hygiene paper products, in particular tissue paper, or nonwoven fiber materials. The hygiene paper products or nonwoven fiber materials can be made from 100% fibers of the pulp produced by the process presented herein. In general, the hygiene paper products or nonwoven fiber materials can contain a proportion of > 0 wt.% to 100 wt.% of the pulp produced according to the process. The hygiene paper products or nonwoven fiber materials are characterized in particular by their softness, high strength, and light color.

[0030] In addition to fibers from the pulp produced using the process presented here from raw material plants of the genus Miscanthus, in particular the species Miscanthus x giganteus, further embodiments may also use pulp fibers of other origins, such as primary pulp fibers of wood origin or primary pulp fibers of non-wood origin and / or secondary pulp fibers obtained from recycled paper (deinking pulp, abbreviated: DIP), for the production of hygiene paper products, in particular tissue paper, or nonwoven fiber materials.

[0031] The antioxidant and antibacterial properties of cellulose make the pulp particularly suitable for use in the production of wet wipes made from a nonwoven fiber material and are also suitable for circular solutions, such as take-back programs for used products made from pulp containing this cellulose.

[0032] According to claim 14, the use of lignin obtained according to a method according to any one of claims 1 to 12 for the production of coating materials, adhesives, pigments, fillers or paints is proposed.

[0033] Further features and advantages of an embodiment of the invention are described with reference to Fig. 1 described below. Fig. 1is a schematic representation illustrating details of a process for the production of pulp and the extraction of lignin from lignocellulose from raw material plants of the genus Miscanthus.

[0034] The process described below uses Miscanthus x giganteus plants, belonging to the genus Miscanthus, for pulp production and lignin extraction. Miscanthus x giganteus plants have several advantages, including rapid growth and relative resistance to pests. Therefore, pesticide use can be minimized to avoid ecological damage during cultivation. Miscanthus x giganteus plants can be harvested annually for approximately 20 years without the need for additional pesticides or fertilizers.

[0035] The harvested raw materials can, for example, be pressed into bales and stored with a moisture content between 5 and 15%. These bales can contain the harvested raw materials completely or, for example, mechanically pre-treated raw materials, particularly chopped ones. The bales can be used immediately after harvesting or stored for later use.

[0036] To obtain lignin from lignocellulose from the raw material plants of the plant species Miscanthus x giganteus and to produce pulp, a process is explained in more detail below in which a combination of chemical, thermal, mechanical and enzymatic process steps is used to achieve a high quality of the unbleached pulp and also to obtain lignin with advantageous properties.

[0037] In the first process step S1, the raw material plants of the species Miscanthus x giganteus are fed into a high-consistency pulper. Such a high-consistency pulper is normally used for recycling and processing waste paper. The raw material plants of the species Miscanthus x giganteus can be fed into the high-consistency pulper, for example, in the form of the aforementioned plant bales, which may contain the harvested raw material plants completely or may contain already mechanically pre-treated, in particular shredded, raw material plants. Before being fed into the high-consistency pulper, a binding wire is removed from each of these plant bales, which ensures that the plant bales retain their shape.

[0038] In the next process step, S2, the raw material plants of the species Miscanthus x giganteus are mechanically shredded and dissolved using a high-consistency pulper. Recycled and / or fresh alkaline chemicals necessary for fiber extraction are added to the raw material plants. For example, sodium hydroxide (NaOH) can be used for this purpose. Alternatively, alkaline potassium hydroxide or calcium hydroxide can also be used.

[0039] The alkaline chemicals are added at a concentration of 1 to 10 mol [OH⁻] / kg of raw material (Miscanthus x giganteus), preferably at a concentration of 2 to 7 mol [OH⁻] / kg, and particularly at a concentration of 3 to 5 mol [OH⁻] / kg. Water at a temperature of approximately 60°C to 100°C is also added to the raw material along with the alkaline chemicals. The reaction temperature in this process step S2 is approximately 60°C to 100°C, preferably 70°C to 90°C. The total reaction time is approximately 30 to 120 minutes at atmospheric pressure. Preferably, the total reaction time is between 45 and 70 minutes. These measures ensure that the lignin is extracted and dissolved from the lignocellulose, advantageously without the need for additional heating.

[0040] Throughout the entire reaction period, the high-consistency pulper exerts a shear stress on the fiber mass of the raw material plants. This shear stress constitutes an initial mechanical treatment and causes the raw material plants to be comminuted, resulting in a fiber slurry under mild ambient conditions (temperature and pressure) compared to prior art power processes or soda processes. The energy requirement of the high-consistency pulper for carrying out process step S2 is between 30 and 90 kWh / ton, preferably between 50 and 90 kWh / ton.

[0041] Furthermore, in this process step S2, a second mechanical treatment is carried out in which additional mechanical energy is supplied to the fiber slurry, preferably by means of a milling pump, under alkaline ambient conditions and mild temperature conditions, in order to break down any raw material plant pieces and shives that may still be contained in the fiber slurry and to fibrill the fibers into stronger and softer fibers. Energy for the mechanical post-treatment for this mechanical post-treatment is introduced into the fiber slurry by means of the milling pump at a rate of between 20 and 80 kWh / ton. Preferably, the energy input is between 40 and 60 kWh / ton.

[0042] In process step S3, the cellulose is separated from the lignin-rich alkaline water, hereinafter also referred to as black liquor, by means of a pressing device, in particular a screw press. In this process step S3, black liquor is thus obtained in addition to the pressed cellulose.

[0043] In process step S4, the pressed cellulose obtained in the previous process step is washed with water and CO2 to neutralize the pH value and remove any impurities.

[0044] Furthermore, in a subsequent process step S5, suitable enzymes or enzyme mixtures, in particular cellulose- and / or lignin-modifying enzymes or enzyme mixtures, are added to the washed cellulose to increase the softness, strength, and brightness (i.e., whiteness) of the cellulose fibers. The enzymes or enzyme mixtures are preferably selected from a group consisting of cellulases, peroxidases, amylases, laccases, or mixtures thereof.

[0045] In this process step S5, between 70 and 140 g / tonne, preferably between 80 and 100 g / tonne, of the enzyme or enzyme mixture is added to the washed cellulose. The enzyme reaction time is preferably at least one hour. The pH value after washing and during the enzymatic treatment is between 7 and 10, preferably between 8 and 9.

[0046] The finished pulp, suitable for further processing, is produced in process step S6 by dewatering the cellulose obtained as described above using a press, preferably a screw press. The pulp can then be stored for later processing or used immediately, for example, for the production of hygiene paper products, especially tissue paper, or nonwoven materials, which are often also referred to as nonwovens.

[0047] It has been shown that the process described here can be used to produce pulp with unbleached cellulose from the raw material plants of the Miscanthus x giganteus species, with the cellulose exhibiting a lighter color compared to conventional, unbleached cellulose. The finished cellulose fibers contained in the pulp have a typical fiber length of between 0.5 and 1.5 mm and an average thickness of approximately 15 to 25 micrometers.

[0048] The pulp containing cellulose from the raw material plants of the species Miscanthus x giganteus, produced in the manner described above, can be advantageously stored for extended periods without any noticeable degradation of the cellulose. This is likely due to the residual lignin remaining in the cellulose, which is unavoidable due to the manufacturing process and possesses antioxidant and antimicrobial properties. These properties make the cellulose particularly suitable for use in wet wipes made from nonwoven fabrics and also for circular economy solutions, such as take-back programs for used products made from pulp containing this cellulose.

[0049] The pulp containing cellulose produced from the raw material plants of the plant species Miscanthus x giganteus also has very good softness properties without losing any strength.

[0050] The following section will explain further process steps by which the lignin can be obtained from the black liquor, which leaves the press device, in particular the screw press, after the execution of process step S3.

[0051] The black liquor typically still contains a small amount of fiber from the raw material plants. These fibers are first removed from the black liquor in process step S7, for example, by one or more filtration stages or by centrifugation. The black liquor is then concentrated to a TDS value of approximately 30%. The concentrated black liquor contains the dissolved lignin. The TDS value is a chemical parameter and represents – as an abbreviation for the English expression " t total d issolved s Total solids (TDS) – the amount of all non-volatile substances contained in the solvent (water) of the black liquor. The TDS value is also frequently referred to as total dry residue in the industry. Generally, the TDS value of the black liquor in the process presented here can range between 15 and 45%, preferably between 25 and 35%.

[0052] The black liquor is neutralized in a reactor during process step S8. In this neutralization process, compact lignin flakes are formed from the lignin particles, which can later be easily separated in a decanter separator. CO₂ is preferably used as the neutralizing agent, which is pumped into the reactor to chemically react with the alkaline salts in the black liquor. The CO₂ supply is preferably automatically stopped once the chemical reaction is complete.

[0053] In this chemical reaction, carbonates and water are formed, which lowers the pH of the black liquor. The lowered pH protonates the lignin, reducing the solubility of this large molecule. The lignin then leaches out of the solution, forming lignin flakes.

[0054] During this chemical reaction in process step S8, the temperature is maintained at approximately 80°C for one hour (primary reaction). The black liquor is stirred in the reactor at a defined speed to prevent rapid particle growth while promoting the formation of firmer, more compact particles. Once the set pH of 8 is reached, the stirring speed is reduced. The compact particles formed in this way can then grow into larger particles over a period of about one hour (secondary reaction), forming the flocs. Generally, the reaction temperature in process step S8 can be between 50°C and 100°C, preferably between 70°C and 90°C. The pressure during the reaction is between 1.0 and 3.0 bar, preferably between 1.5 and 2.0 bar. For the total reaction duration (approximately 2 hours), the primary reaction lasts about 1 hour, and the secondary reaction also lasts about 1 hour.

[0055] In process step S9, the lignin particles, which are present as lignin flakes, are separated from the liquid, preferably by means of a decanter separator.

[0056] The lignin solids, decanted in process step S9 and thus separated from the liquid, are subsequently dispersed in water in a further reactor for washing in a further process step S10. An acid is used as the washing chemical. This can be an organic or an inorganic acid. Sulfuric acid is preferably used. The pH value is lowered to 4 to further protonate the lignin and to remove silicates and other inorganic substances.

[0057] During this reaction, some residual carbonates are converted into other salts, releasing CO₂. The release of CO₂ causes foaming, which delays the addition of the acid. To accelerate the acid addition and thus also the lignin washing process, ultrasonic defoaming is preferably used. The reaction temperature during process step S10 is between 50° and 100°C, preferably between 70°C and 90°C. The reaction time is preferably about 1 hour.

[0058] In a subsequent step (process step S11), the protonated lignin is decanted, in particular by means of a solid decanter, and dried – preferably using a rapid drying unit. The moisture content of the lignin after drying is preferably 1 to 10%, particularly between 2 and 4%. The lignin purity is between 90 and 99.5%, particularly between 95 and 99%.

[0059] The liquid leaving the solid decanter in the previous step is used for chemical regeneration in an optional process step S12, which will be explained in more detail below.

[0060] The process presented here for the production of pulp from raw material plants of the plant species Miscanthus x giganteus in combination with the downstream black liquor process for obtaining lignin leads to a very native lignin with some special properties.

[0061] The mild process leads to less degradation of the lignin molecules due to the high proportion of β-O-4 linkages, as well as less oxidation and condensation of the lignin. The result is large lignin molecules with a high molecular weight.

[0062] Reduced molecular decomposition and the absence of sulfur-containing components during the pulping of the raw materials mean that fewer monomers and volatile organic compounds are formed, which could also explain the faint odor and light color of the lignin obtained using the process presented here. The gentle processing and the avoidance of sulfur-containing components in pulp production thus result in a low-odor lignin. The molecular weight of the lignin is between 6000 and 8000 g / mol with a polydispersity between 9 and 11. Further analyses have shown that the lignin has a relatively low glass transition temperature (Tg).

[0063] As mentioned above, lignin has a native structure. This native structure allows lignin to be used in a wider range of applications. Furthermore, it offers more possibilities for modifying lignin. Its light color and faint odor make lignin particularly advantageous for applications such as the production of coatings, adhesives, paints, fillers, pigments, and so on.

[0064] The decanter liquid obtained in process step S11 can be further processed after lignin neutralization in an optional process step S12 to regenerate the alkaline chemicals. The liquid is mixed with calcium hydroxide. The carbonates combine with the [OH⁻] from the calcium hydroxide. This reaction forms a liquid alkaline chemical and solid calcium carbonate, which precipitates and can be easily separated from the liquid. The CO₂ is thus stored in the form of calcium carbonate. The reaction time in this process step S12 is approximately 1 hour at a reaction temperature between 50 and 100°C, preferably between 70 and 90°C.

[0065] The alkaline chemical recovered in this way can subsequently be reused for the fiber pulping of raw material plants of the plant species Miscanthus x giganteus according to the method described here.

[0066] In the embodiment described here, the recovery of lignin (process steps S7 to S11 and S12, respectively) from the compressed cellulose obtained in process step S3 (process steps S4 to S6) is a subsequent step in pulp production. In principle, the reverse order is also possible, so that the lignin is recovered first and then the pulp is produced. The two branches of the process after process step S3 (i.e., pulp production on the one hand and lignin recovery on the other) can also be carried out in parallel or independently of each other.

Claims

1. Method for producing pulp and for obtaining lignin from a lignocellulose from raw material plants of the plant genus Miscanthus, which comprises the following steps: S1: raw material plants of the plant genus Miscanthus are fed to a high-consistency pulper, S2: the raw material plants are comminuted by means of the high-consistency pulper in at least one first mechanical processing stage and dissolved with addition of water and an alkaline chemical, so that a lignocellulose-containing fiber slurry is obtained, wherein the reaction temperature in this method step is selected so that it is about 60°C to about 100°C, preferably 70°C to 90°C, S3: the cellulose is separated from the fiber slurry by means of a pressing device, in particular by means of a screw press, from a lignin-containing black liquor, so that pressed cellulose is obtained, S4: the pressed cellulose is washed by addition of water and CO2, S5: enzymes or enzyme mixtures, in particular cellulose- and / or lignin-modifying enzymes or enzyme mixtures, are added to the washed cellulose, S6: the cellulose is dewatered by means of a pressing device, preferably by means of a screw press, so that pulp suitable for further processing is obtained, S7: the black liquor is concentrated to a TDS value between 15 and 45%, preferably between 25 and 35%, S8: the black liquor is neutralized in a reactor, wherein lignin particles, in particular lignin flakes, are formed, S9: the lignin particles are separated from the liquid, preferably by means of a decanter separator, S10: the lignin particles deposited in method step S9 are washed in a further reactor and protonated, wherein an acid is used as washing chemical, S11: the protonated lignin is deposited and dried, in particular by means of a rapid drying device.

2. Method according to claim 1, characterised in that raw material plants of the plant species Miscanthus x giganteus are used.

3. Method according to one of claims 1 or 2, characterised in that the alkaline chemicals are added to the raw material plants in method step S2 in a concentration range of 1 to 10 mol [OH-] / kg of raw material plants, preferably of 2 to 7 mol [OH-] / kg of raw material plants and in particular of 3 to 5 mol [OH-] / kg of raw material plants.

4. Method according to one of claims 1 to 3, characterised in that method step S2 is carried out under atmospheric pressure.

5. Method according to one of claims 1 to 4, characterised in that in method step S2 in a second mechanical processing stage a second mechanical treatment is carried out, in which additional mechanical energy is supplied to the fiber slurry.

6. Method according to claim 5, characterised in that in the second mechanical treatment an energy between 20 and 80 kWh / ton is introduced into the fiber slurry.

7. Method according to one of claims 1 to 6, characterised in that between 70 and 140 g / ton, preferably between 80 and 100 g / ton, of the enzymes or enzyme mixtures are added to the washed cellulose in method step S5.

8. Method according to one of claims 1 to 7, characterised in that the enzymes or enzyme mixtures are selected from a group consisting of cellulases, peroxidases, amylases, laccases or mixtures thereof.

9. Method according to one of claims 1 to 8, characterised in that the reaction temperature in method step S8 is selected so that it is between 50°C and 100°C, preferably between 70°C and 90°C.

10. Method according to one of claims 1 to 9, characterised in that the reaction temperature during method step S10 is selected so that it is between 50°C and 100°C, preferably between 70°C and 90°C.

11. Method according to one of claims 1 to 10, characterised in that during the lignin washing process in method step S10 an ultrasonic defoaming is carried out.

12. Method according to one of claims 1 to 11, characterised by a method step S12, in which the liquid obtained in method step S11 is regenerated.

13. Use of a pulp produced according to a method according to one of claims 1 to 12 for producing hygiene paper products, in particular tissue paper, or fibrous nonwoven materials.

14. Use of a lignin obtained according to a method according to one of claims 1 to 12 for producing coating materials, adhesives, fillers, pigments or paints.

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