System and method for processing starting materials to obtain a forming solution according to the dry dissolution method - Patents.com

Abstract

The present invention relates to a method for producing a molding solution from a starting material consisting of cellulose, water and a functional medium, according to a dry dissolution method, in which the starting material is first fed to a high shear unit, in which a transfer mixture is obtained from the starting material, and then the transfer mixture is fed to a kneader-mixer for dissolution.

Description

[Technical field]

[0001] The invention relates to a method according to claim 1 and a system according to claim 11 for processing a starting material to obtain a forming solution according to the dry dissolution method. [Background technology]

[0002] Patent Document 1 describes, for example, that in a dry dissolution process in a twin-screw extruder, a molding solution is produced from fine fiber cellulose powder and liquid NMMO, but that this solution must be stabilized in a downstream storage vessel equipped with a pressure regulator.

[0003] Patent Document 2 describes a dry dissolution method, in which a swollen mixture is produced from subcooled liquid NMMO hydrate and cellulose powder in a twin-screw extruder, and the mixture is fed to a single-screw extruder, where it is subsequently dissolved. In particular, the problem is to produce starting materials that are melt-processed to form a solution.

[0004] Patent document 3 describes a method for mixing and homogenizing cellulose and aqueous NMMO in two shear zones of a first device to form a homogeneous suspension, where the amount of NMMO and the water content are adjusted to the possible water content of the cellulose so that the NMMO content in the liquid phase of the suspension formed is 70-80% by mass. Furthermore, a schematic system is shown consisting of a first device for producing a suspension and a second device connected to the first device as an evaporation stage. In view of the invention described below, patent document 3 therefore relates to the production of suspensions with such a high water content that the subsequent process stage for producing a spinning solution is characterized by the evaporation of water.

[0005] US Pat. No. 5,399,633 describes a process which involves mixing and subsequent dissolution of N-methylmorpholine N-oxide (NMMO) powder with ground cellulose, where both processes are carried out in a single twin-screw extruder.

[0006] Patent Document 5 describes dissolving a paste in an extruder to form a molding solution, where the paste is produced from an NMMO solution and ground cellulose in a preceding kneader-mixer, the NMMO solution consisting of NMMO and a small amount of cellulose powder. Thus, Patent Document 5 describes connecting a kneader-mixer upstream of an extruder so that the extruder can produce a molding solution.

[0007] All these dry dissolution methods use extruders for dissolving cellulose. They differ in that the preceding process steps are different. The reason is the high shear intensity of the extruder. However, the dry dissolution methods are not currently used on a large industrial scale. The reason is the limited capacity of the extruder. Extruders, which have a smaller diameter D, smaller clearances and faster shafts compared to kneader-mixers, are well suited to mixing two powders (frozen functional medium such as NMMO at room temperature and comminuted cellulose, where the frozen functional medium in powder form melts in the extruder by the introduction of shear energy to form a liquid functional medium) or to mixing cellulose powder with a functional medium in a liquid mass state, but at the same time, they have a shorter residence time of the product compared to kneader-mixers, because the extruders have a smaller clearance, which results in a significantly smaller processing volume than in the case of kneader-mixers, and at the same time, the residence time is limited due to the forced feeding of the product due to the higher shaft speed in contrast to the kneader-mixers. This limited residence time is further reinforced by the very high dynamic losses per processed volume.

[0008] Insufficient residence time (in the sense of being shorter than the dissolution time required for the specific mechanical action of the stirring elements) means that the homogeneity and dissolution state of the forming solution is insufficient, which can result in subsequent shaping, for example during spinning, in fiber splitting, clogging of spinning nozzles and reduced service life of filters.

[0009] Alternatively, with an increase in residence time (to reach the required dissolution time) or shaft speed (to achieve the required mechanical work) in the extruder, the mechanical energy input and therefore the risk of substantial overheating of the product or product components increases, which creates the risk of product damage and the risk of decomposition, which can result in significant costs due to the resulting price drop and, in the case of NMMO, especially IL, the replacement of the functional media, which is very expensive. Furthermore, in the extruder discharge area, in order to prevent overheating or substantial overheating, it is essential to dissipate heat from the product by cooling, which involves energy losses, increases energy costs and becomes increasingly difficult with increasing diameter due to the reduction in the extruder surface area / processing volume ratio, which ultimately limits the suitable extruder construction dimensions.

[0010] In the case of NMMO as functional medium, the risk of explosion is common to all the above-mentioned processes for producing molding solutions using extruders as well.Furthermore, due to the small non-agglomerated free volume in the process space of the extruder, there is also no easy way to monitor and mitigate the pressure increase that occurs throughout the process space as a result of the decomposition process of the functional medium.

[0011] In addition to the above-mentioned extruders, kneader mixers are also known to those skilled in the art. They preferably contain exactly one or exactly two kneader shafts, which are used to carry out high viscosity and crust forming processes, which can be operated under vacuum, atmospheric pressure or overpressure, and can be heated or cooled via heat exchange surfaces. Moreover, the kneader shafts and their shaft structure can heat the product very effectively by rotation and the resulting energy dissipation in the case of the product viscosities usually present.

[0012] If there is exactly one kneader shaft, this is a single-shaft kneader-mixer, as described, for example, in US Pat. No. 5,399,666. In this case, during operation, the shaft structure of the kneader shaft preferably meshes with a static structure of the housing, for example known as a mating hook. If there are exactly two kneader shafts, this is a twin-shaft kneader-mixer, as described, for example, in US Pat. No. 5,399,666. The shaft structures of the kneader shafts preferably mesh with each other during operation.

[0013] At least one kneader shaft comprises a shaft structure in the form of a disk and a bar fixed thereon, the shaft structure of the at least one kneader shaft being configured to mesh during operation with the shaft structure of a second kneader shaft or with fixed mating elements present in the kneader-mixer. Kneader-mixers with such mating elements are known and are called "self-cleaning", since the above-mentioned mating separates the accumulation of sediments from the mating elements.

[0014] The kneader-mixer comprises an opening to the process chamber (also called the input opening) for the input of the product to the process chamber of the kneader-mixer and a further opening to the process chamber of the kneader-mixer (also called the discharge opening) for the discharge of the product from the process chamber of the kneader-mixer. The input and discharge openings are typically located in areas of the kneader-mixer that face each other in the axial direction. The input openings can also consist of two or more openings distributed over the axially extending part of the length of the kneader-mixer. The further opening to the process chamber of the kneader-mixer is typically located in the upper half of the process chamber (also called the gas discharge opening) and allows the gas released in the kneader-mixer to be discharged to the process chamber through a separate opening, typically located between the input and discharge openings in the axial direction. If the kneader-mixer comprises a dome, the chamber defined by the inside of the dome (also called the dome gas chamber) is directly adjacent to the gas chamber of the process chamber, and these two form a common gas chamber. The dome is an attachment that extends vertically upwards, is in the form of a chimney, is placed directly on the gas discharge openings of the kneader-mixer, and in its upper region typically has openings (also called exhaust openings) for discharging gases (also called exhaust). Some of the inner surfaces of the dome can also be thermally heated or cooled. The kneader-mixer can also be equipped with two or more domes, which are sometimes collectively referred to as domes.

[0015] The abovementioned bar, interlocking hook and shaft structures are also collectively referred to as kneading elements. There are several methods for producing a forming solution from pulp (or cellulose). The difference between pulp and cellulose is irrelevant for the interpretation of this patent application, and the two terms can be used interchangeably. These may differ, among other things, depending on the water content in the starting material, which is excessive for a forming solution. The skilled person is further aware of methods for producing a forming solution from pulp by the dry dissolution method, using ionic liquids instead of NMMO as functional liquids. ILs (ionic liquids) relate to a group of organic compounds that, despite their ionic structure, have a low melting point (<100°C) and are therefore also called molten salts. The use of ILs as functional media therefore necessarily means an embodiment within the group of ionic liquids that is suitable for the dry dissolution method.

[0016] Those skilled in the art are aware that ILs are typically prone to thermal decomposition at elevated temperatures, and therefore, in processes involving heating ILs, the temperature of the IL must be kept below its decomposition temperature.

[0017] Those skilled in the art also know that the decomposition of NMMO begins with a decrease in the water content of the NMMO / water / cellulose mixture at elevated temperatures. As the water content decreases, typically at temperatures above 140° C., the risk of explosion, for example due to explosive autocatalytic decomposition, increases, followed by a further increase in temperature and thus a sudden risk of explosion. Depending on the composition of the mixture, decomposition can already be observed from temperatures above 125° C., since the decomposition temperature can be reduced, for example, by the presence of reducing agents (such as cellulose) and heavy metal ions (such as iron ions).

[0018] The skilled person is further aware of situations in which substantial overheating is problematic within the context of the present invention, and in which great care must be taken in guiding the temperature of the product (hereinafter also referred to as the product temperature) in order to avoid decomposition of the functional medium. The skilled person will therefore select a process in which the required product and equilibrium temperatures are below the decomposition temperature.

[0019] In the case of a multicomponent mixture, as exists in the case of the cellulose / functional medium / water mixture, each component of the mixture is assigned an equilibrium temperature at the prevailing process conditions (pressure), at which the mixture starts to boil. When energy is supplied to the multicomponent mixture, some of the volatile components (here water) evaporate. At the same time, the composition of the mixture changes, and, as a result, the equilibrium temperature also changes. For example, the mixture is heated in the case of the supply of energy, while its composition changes along its equilibrium curve due to the evaporation of the volatile components.

[0020] In the case of NMMO as a functional medium, the transport limitations of the exothermic decomposition process can also result in localized material overheating (hot spots), from which the reaction heat cannot be dissipated to a sufficient extent, which then triggers further exothermic decomposition processes.

[0021] However, substantial overheating is also associated with the decomposition of the cellulose or cellulose / functional medium / water mixture (i.e., by definition, the product), which at too high a temperature leads to a decrease in the degree of polymerization of the cellulose (known to those skilled in the art as DP), possibly in conjunction with the increased shear action that is typically present with increased viscosity.

[0022] Those skilled in the art know that the dissolution process does not occur instantaneously, but rather within a period of time, at a dissolution rate, which requires a minimum dissolution time. Those skilled in the art further know that the dissolution rate is affected by various factors, such as temperature, and that in addition to temperature, the concentration of the functional medium and the mechanical treatment of the mixture also affect the dissolution rate. For example, different mechanical treatments of materials with the same composition and temperature at the same treatment period may result in different dissolution states.

[0023] The skilled person further knows a method for producing a forming solution of pulp according to the direct dissolution method, the starting material of which has a very high water content compared to the water content in the forming solution, so that a substantial part of the process and the equipment is effected by evaporation of the water content (wet dissolution method), as described, for example, in the example of US Pat. No. 5,399,433, where NMMO is used as functional medium, and thin film evaporators are used to evaporate the water. A disadvantage of the wet dissolution method is the high energy consumption, which is caused by the evaporation of water.

[0024] Thus, in addition to the appropriate water content to produce the molding solution, mechanical action on the product is also required, which is achieved by a deliberately selected geometry of the mixing elements and must be carried out over a certain period of time.

[0025] Methods are also known which use more mechanical action on the product, for example to produce a molding solution, but this action is achieved by a deliberately selected geometric shape of the mixing elements and must, however, be carried out over a certain period of time.

[0026] In a non-limiting manner, the heatable or coolable interiors of equipment or machines in process technology, such as kneader-mixers, extruder or thin-film evaporator housings, as well as the kneader shafts and discs of kneader-mixers, can be configured as heat exchange surfaces.

[0027] The disks of the kneader shaft of the kneader-mixer configured as heat exchange surfaces are provided with perforations for electric heating elements or cavities for heat transfer or cooling media, with an inlet supplied by the inflow in the kneader shaft and an outlet leading back to the return flow in the kneader shaft. The cavities can typically be configured as double-walled or perforated, but for this purpose a larger wall thickness and a larger dimensional shaft structure as well as a thicker-walled kneader shaft are required, which in turn results in significantly higher manufacturing costs compared to disks without cavities (hereinafter also referred to as without heating cavities). The disks are usually smaller and easier to build thanks to the omission of the heat exchange surface.

[0028] Kneaders are known to those skilled in the art and are described, for example, in US Pat. No. 5,399,363. Kneaders differ from extruders by a larger free processing volume and reduced shear action, and in particular from kneader-mixers by a one-dimensional intermeshing and the associated absence of bars that produce the mixing effect typical of kneader-mixers. Kneaders can be operated continuously and discontinuously.

[0029] Z-kneaders and sigma blade mixers are known to those skilled in the art and are described, for example, in US Pat. No. 5,399,663. They are characterized by two Z-shaped or multiple Z-shaped kneading arms, each arranged in a large-volume, often trough-shaped, reactor chamber, rotatably about a horizontal axis arranged parallel to the axis of the other kneading arm and either interlocked or non-interlocked with each other, and can only be operated batchwise. Due to their large volume and batchwise operation, they are particularly suitable for mixing and premixing at higher solids contents, as also described in US Pat. No. 5,399,663, in particular because dosing is also much easier due to the batchwise operation. However, due to the large free space and lack of a continuous operating mode, they are not suitable for sufficiently homogenizing and dissolving pulp on an industrial scale. [Prior art documents] [Patent documents]

[0030] [Patent Document 1] European Patent Application Publication No. 0906455A1 [Patent Document 2] European Patent Application Publication No. 1191038A1 [Patent Document 3] European Patent No. 1144455B1 [Patent Document 4] International Publication No. 2005 / 000945A1 Brochure [Patent Document 5] International Publication No. 2006 / 071101A1 Brochure [Patent Document 6] Swiss Patent No. 674472A5 [Patent Document 7] German Patent Application Publication No. 4118884A1 [Patent Document 8] International Publication No. 1994 / 006530A1 Brochure [Patent Document 9] Specification of Special Publication No. 6-55267 [Patent Document 10] DE 1058188 A1 [Patent Document 11] DE 3720325 A1 [Patent Document 12] Canadian Patent Application Publication No. 3020820A1 [Patent Document 13] International Publication No. 96 / 06207A1 Brochure [Patent Document 14] International Publication No. 96 / 06208A1 Brochure [Patent Document 15] US Patent Publication No. 4,196,282 Summary of the Invention [Problem to be solved by the invention]

[0031] The problem addressed by the present invention is to overcome the shortcomings of the prior art.

[0032] In particular, a system and method for processing a starting material to obtain a forming solution by a dry melting method should be described, which primarily makes it possible to overcome the shortcomings of the prior art dry melting methods, in particular to improve product quality and increase capacity in the process. [Means for solving the problem]

[0033] The features of claims 1 and 13 solve the problem. Advantageous embodiments are set forth in the dependent claims.

[0034] The invention relates in particular to a method and a system comprising a kneader-mixer for processing a transport mixture according to the dry dissolution method, as the final process stage of at least a two-stage process, in the kneader-mixer, taking into account all the facts mentioned in the scope of the description of the subject matter, in which case a high-shear unit is connected upstream of the kneader-mixer.

[0035] In this case, the kneader-mixer is generally configured to have a large volume compared to the extruder, in this case allowing a longer residence time compared to the residence time, and to have a smaller shear action compared to the high shear unit.

[0036] A high shear unit is characterised by a significant shear action compared to a kneader-mixer and by a shorter residence time compared to a kneader-mixer.

[0037] The mixing, kneading and shearing action on the product, especially in process elements such as high shear units or kneader-mixers, results substantially from the interaction of the product with the elements rotating relative to each other in the process element due to the rotation of the shafts (also called kneader-mixer interaction) and depends on the process, the product volume (filling level) in the process element, the geometrical shape and surface design of the elements in the process chamber, the rotation speed of at least one shaft, as well as the viscosity and residence time of the product to be processed in the process element.

[0038] In the context of the present invention, the starting, intermediate and final states from the starting materials to the solution are all referred to as products.

[0039] The shear effect results from the product of the shear and the processing time during which the shear occurs.

[0040] The maximum possible shear is achieved, on the one hand, by the largest possible shear plane, which can extend both in the direction in which the two shear planes move relative to each other and in the direction perpendicular thereto. Furthermore, the shear also increases if the shear gap, specifically the distance between the two shear planes measured perpendicular to the shear planes, is made as narrow as possible. Furthermore, the shear increases if the relative speed of the two shear planes is made as fast as possible, since the fill level of the product in the shear gap is as high as possible.

[0041] A high shear unit is a process element having at least one shaft, the rotation speed of which is typically significantly higher than that of the kneader shaft of a kneader-mixer, and / or the clearance between the wall and the mixing or kneading elements of the second shaft is significantly smaller, and / or the ratio of shear cross-section to processing volume is significantly higher than that of a kneader-mixer, and / or the exposure time is typically significantly higher than that of a kneader-mixer, since it is a batch-wise rather than a continuous procedure, and the heavy action resulting from the combination of these characteristics is significantly higher than that of a kneader-mixer of comparable processing volume. In terms of the equipment, the significant shear action can be achieved using a high-speed high-shear unit, which has a small volume compared to a kneader-mixer, is equipped with at least one shaft that rotates rapidly compared to a kneader-mixer, has a small gap size compared to a kneader-mixer, has a short residence time compared to a kneader-mixer, and is characterized by a process chamber that allows continuous operation, similar to a kneader-mixer. Typical examples of high-speed high-shear units are extruders or high-speed mixers. In this case, the high-speed mixer differs from extruders, such as those known as Ystral® mixers or solid-liquid mixers by IKA®, or KRIMA® dispersers by Cellwood Machinery®, in that they achieve significant shearing action at relatively high speeds with low torque. High-speed mixers are characterized in particular by higher shaft speeds, shorter residence times, and lower torques compared to extruders. Typical examples of large-volume high-shear units are Z-kneaders or Sigma Blade mixers. Typical residence times in high-speed mixers are up to 10 seconds, typical residence times in extruders are up to 5 minutes, and typical residence times in large-volume high-shear units are at least 15 minutes.

[0042] In the dry dissolution process and system, the arrangement of the kneader-mixer after the high shear unit allows the technical advantages of the kneader-mixer for the dry dissolution process to be particularly utilized. In this case, it has been found to be advantageous to connect the high shear unit upstream of the kneader-mixer. This is because, as a result, according to the present invention, the high shear unit complements the working mode of the kneader-mixer in that it utilizes the mixing capacity of the high shear unit to compensate for the disadvantages of the high shear unit, in particular the limited residence time of the high-speed high shear unit or the lack of continuous working mode of the large-volume high shear unit.

[0043] In the context of the present invention, the mixture of water, cellulose and functional medium introduced into the dry dissolution process is considered as starting material. In this case, the transfer mixture corresponds to an intermediate step in which the starting materials are mixed in a high shear unit but are not yet processed into a forming solution. In the context of the present invention, forming solution refers to one that is substantially suitable for subsequent transformation (also called extrusion), in particular spinning.

[0044] The product volume corresponds to the volume of the product to be processed contained in a process element such as a kneader-mixer according to the invention. The ratio of product volume to processing volume corresponds to the fill level.

[0045] The processing volume corresponds to the volume that a process element such as a kneader mixer according to the invention can contain the product to be processed. In the case of a rotor-stator system, this means in particular the stirred volume, and therefore the unstirred volume, for example in a connecting pipe, is not interpreted as the processing volume. This can be determined, for example, by "volume measurement in liters", in that the process chamber is completely filled with liquid and its volume is measured.

[0046] The two-dimensional (radial and axial) intermeshing typical of kneader-mixers constitutes a completely different mixing / kneading principle compared to extruders, where the mixing action typically only takes place in the radial direction and has regions that are always relatively small and spaced apart from one another in the axial direction by mixing / kneading blocks or by forced partial return flows.

[0047] Since kneader-mixers are typically operated at partial filling levels, the input flow rate and typically also the throughput of the discharge member can be selected virtually separately (in the sense of being independent of the speed of the kneader shaft) and, in contrast to extruders, the product in the kneader-mixer can easily avoid axial transport during the mixing-kneading interaction, so that in the case of kneader-mixers, the speed of the kneader shaft is only one of the variables that influences the throughput in coordination with the actual or desired filling level or its axial distribution, the input flow rate, the output flow rate and the throughput, and is not an influencing factor that builds up significant axial pressure, in comparison with extruders. The mixing effect of a kneader-mixer for a specific machine and a specific product depends not only on the speed, but also, in particular, on the freely selectable setting variables, the residence time and the filling level.

[0048] In contrast, in the case of an extruder, not only the mixing / kneading effect but also the product transport is practically directly dependent on the speed (forced transport), resulting in a rapid product transport due to the high speeds required for significant mixing, and therefore a shorter residence time compared to a kneader-mixer. This results in particular from the characteristic typical of extruders, that for a given extruder the residence time cannot be set independently of the speed. The mixing / kneading action of the extruder is therefore achieved only by the mutual engagement of the axially spaced rotating shafts and the product in the mixing / kneading zone. For a specific machine with a specific shaft configuration and for a specific product (with a specific product viscosity that is also temperature and speed or shear dependent), it basically depends only on the speed. Moreover, in order to achieve a constant residence time, the extruder must have a longer shaft length L compared to a kneader-mixer. The length / diameter ratio (L / D) of the extruder is significantly higher than in the case of a kneader-mixer, typically 24-48 compared to 3-6 for a typical kneader-mixer.

[0049] The traditional objective of both kneader-mixers and extruders is to process masses with a significantly increased viscosity in large volume tanks, which can no longer be stirred or mixed using conventional vertical stirring elements, typically mounted on the side, and where the process is determined by the mechanical energy input.

[0050] The term "dry dissolution method" is a general term for all methods that serve to produce a forming solution from a starting material, which in this case does not involve any or very little removal of water (especially evaporation of water). In this case, the starting material typically has a water content of 0% to 10% higher than the water content required for dissolving cellulose. Removing a large amount of water means that it determines the configuration in the sense that the system must be configured larger to remove the water or additional equipment or machines for processing the product must be added to the system (quite apart from the system for condensing the exhaust vapor stream generated by evaporation) to process the product. Dry dissolution methods include both the dry direct dissolution method with NMMO or IL as forming solution and the protolyte dissolution method with a forming solution based on a protolyte (acid or alkaline liquid), such as sodium hydroxide solution or phosphoric acid.

[0051] The final processing stage is defined by the fact that in this final processing stage a forming solution is produced from the transport mixture. Independently from this, but not included within the scope of the present invention, there are also process steps such as discharge elements and also intermediate pumps, filters and buffer tanks, which are still required up to the spinning / shaping stage and typically serve for transport or filtration of the forming solution, degassing or stabilization of pressure and mass flow rates.

[0052] In this case, the processing of the transfer mixture to form the forming solution consists of a dissolution process, also called dissolution. This requires a specific duration for a specific mixing intensity and kneading intensity (determined in particular by the type and proportion of cellulose and functional medium) for a specific product (determined in particular by the specific embodiment of the kneader-mixer and the rotation speed of the kneader shaft). This part of the process finally results in a forming solution flow, which can then be fed to the transformation. Since the design is determined by a specific mixing kneading intensity and time for a specific product, the throughput of the kneader-mixer is basically directly proportional to the volume of the forming solution flow (also called forming solution flow volume). This so-called volumetric scale-up is the opposite of the surface scale-up of the kneader-mixer for producing the forming solution, known to those skilled in the art, a process characterized by the evaporation of water, for which purpose the kneader-mixer must have a sufficient heating surface, determined by its size. Conversely, in the case of surface scale-up, the kneader-mixer can be miniaturized if the evaporation of water must be reduced or does not need to be evaporated.

[0053] This further shows the advantage that, whereas an increased mixing and kneading intensity in an extruder always leads to a shorter residence time of the product due to the forced conveying of the product, in a kneader-mixer the mixing and kneading intensity can be increased and the residence time can be freely selected (i.e. increased or decreased) independently. The kneader-mixer according to the invention is used to carry out the mixing and kneading of the product after its outlet as a transfer mixture from a high shear unit as a preceding process element. This mixing and kneading is necessary to achieve a forming solution. This makes it possible to exploit the strengths of the high shear unit, in particular to mix two powders or a powder in a liquid and then to further process the product in the kneader-mixer according to the invention. Due to the mixing and kneading action, the shear action on the product is much smaller than is typical in a high shear unit and therefore, in particular, more time is available for dissolution.

[0054] Thanks to the significant shearing action, the high shear unit creates a favorable starting state of the product, which is characterized by having the necessary homogeneity at least as a transfer mixture for processing in a kneader-mixer. When using a high-speed high shear unit as a high shear unit, under typical process conditions, it is possible to generate 10 to several hundred times more mechanical power (specific mechanical power input) per processing volume compared to a kneader-mixer. In the high-speed high shear unit, the much higher specific mechanical power input results in an intimate contact of the components of the starting material, thereby creating a favorable starting state for the subsequent dissolution process. This favorable starting state of the product, as a transfer mixture for processing in a kneader-mixer, is characterized by having the necessary homogeneity, as well as also containing a certain portion of dissolved cellulose. The continuous operation mode means that this is further processed directly in the kneader-mixer to form a forming solution before product decomposition occurs.

[0055] When using a large capacity high shear unit as the high shear unit, it is possible to functionally combine it with a long residence time so that the high shear action due to the large shear surface of the particularly long shear gap can be easily achieved in a batchwise operating mode.

[0056] When using a large-capacity high-shear device to produce a transport mixture, in batchwise operation mode, it is preferable to avoid that the transport mixture already contains a part of dissolved cellulose or dissolved pulp, because such direct further processing is not guaranteed in the kneader-mixer due to batchwise operation, which may lead to partial decomposition and inhomogeneous product quality.This also means that the transport mixture produced by the large-capacity high-shear device preferably has a certain storage stability.

[0057] By storage stability is meant that the product can be stored without its composition and its chemical and physical properties changing significantly to such an extent that it is no longer suitable for further processing without unacceptable deterioration of the product quality.

[0058] In this case, it is irrelevant whether the at least one high shear unit is connected directly to the kneader-mixer according to the invention or via an intermediate transfer member such as a gear pump, and whether it is operated batchwise or continuously.It is also conceivable that the high shear unit is not connected to the kneader-mixer according to the invention, and the transfer mixture is temporarily stored in a tank and fed to the kneader-mixer according to the invention in a manner of temporary and local transfer.

[0059] Even though the kneader-mixer according to the invention functions regardless of whether the high shear unit is operated batchwise or continuously, the operation mode of the kneader-mixer according to the invention is different. In the case of a continuously operated high shear unit, the residence time available in the continuously operated high shear unit is typically less than the required dissolution time, so the task of the kneader-mixer according to the invention is to extend the mixing and kneading time of the product until the dissolution time is reached. In the kneader-mixer according to the invention, the product is mixed and kneaded in a gentle manner compared to the high shear unit, so that the product does not overheat or does not overheat significantly due to the above-mentioned reduced shear action.

[0060] In the case of high shear units, typically operated batchwise, such as Z-kneader mixers, the transfer mixture is then discharged at the end of each batch (i.e. batchwise), preferably by a continuous discharge element, and fed to the kneader mixer according to the invention, which also ensures a continuous flow of the forming solution, in addition to additional kneading and mixing to form a homogeneous forming solution, with which the forming and spinning processes, which are also carried out continuously and are very sensitive to fluctuations, are fed. In this case, the sensitivity to fluctuations relates in particular to the continuity of the mass flow, as well as the continuity of the quality of the forming solution, in particular the homogeneity, viscosity and composition, and the influence of these properties by the degradation processes of the cellulose and functional media. The production of batchwise forming solutions is not suitable on an industrial scale due to the sensitivity of the forming and spinning processes to fluctuations. Moreover, process chambers which only discharge batchwise also do not have the self-cleaning property of the product by the downstream flow, as in continuous operation, which leads to time-consuming cleaning costs and product losses, in particular since the forming solution is typically much more viscous than the product before the dissolved state.

[0061] The transfer element may also include a conveying element, a tank or a combination of these elements. The conveying elements are known to those skilled in the art and include, in particular, non-compressed embodiments. The tank may be agitated or circulated, in particular to prevent separation.

[0062] Furthermore, during the process of processing the transfer mixture to form the forming solution, it is possible to reduce the water content remaining in the transfer mixture to the water content required for the dissolution process and the forming solution. In addition to the dissolution task of the kneader-mixer according to the invention, this evaporation task is firstly optional and secondly subordinate thereto and does not determine the installation size. For this evaporation, the kneader-mixer may require a heating surface for thermal energy input, which is arranged in the kneader-mixer, in addition to the mechanical energy input resulting from the viscosity in combination with the processing volume and at least one rotating kneader shaft, which is arranged in the kneader-mixer.

[0063] In the context of the present invention, the capacity of the kneader-mixer therefore means, on the one hand, the evaporation capacity and, on the other hand, the flow capacity of the forming solution.

[0064] In the direct dissolution method, the kneader-mixer according to the invention utilizes the hitherto unknown finding that below a certain water content in the transport mixture, it is no longer possible to configure the kneader-mixer to have a smaller processing volume without the flow capacity of the forming solution being reduced during processing. This is due to the fact that starting from this water content, the processing volume required for the dissolution time must necessarily be applied, and therefore the flow capacity of the forming solution determines the configuration. Conversely, this means that in the direct dissolution method, as the water content in the transport mixture increases from a certain water content, the kneader-mixer must be constructed larger than is required for the flow capacity of the forming solution, since the evaporation capacity requires a larger structure to arrange a corresponding heating surface in the kneader-mixer.

[0065] The kneader-mixer according to the invention therefore consists exclusively of a kneader-mixer whose size meets the requirements of the flow capacity of the forming solution.

[0066] Any evaporation capacity of the preceding process element to generate a transfer mixture by substantially evaporating water (hereinafter referred to as main evaporation) is adapted accordingly and results from the heating area of ​​the kneader-mixer and the mechanical energy input capacity depending on the viscosity and the kneader shaft speed. In the context of the present invention, it is also provided that the transfer mixture is generated from the starting material in a number of preceding process elements. In this case, in the present invention, said preceding process elements can be connected in series or in parallel and are associated with a high shear unit.

[0067] The kneader-mixer according to the present invention for treating a transport mixture by the dry dissolution method to form a forming solution is a kneader-mixer having a feed, a housing, at least one kneader shaft rotating in the housing and an outlet, the feed introduces a product in the form of a transport mixture consisting essentially of cellulose, water and a functional medium into the housing, the transport mixture is treated by stirring, as a result of which a forming solution is produced, the forming solution flows into the outlet together with the feed stream and is then fed to subsequent process elements, such as a discharge screw, a transfer pump, a filtering station, a buffer tank, a spinning pump and a spinning nozzle.

[0068] In one embodiment, mechanical and thermal energy inputs can also be used to evaporate some of the water until a forming solution is obtained, in case the water content in the starting material is higher than the amount required for the forming solution.

[0069] A further embodiment is characterized in that the excess water content in the starting material is deliberately selected, so that the mechanical energy introduced into the kneader-mixer by the mixing and kneading effect during a certain residence time is used firstly for the intended product heating and secondly for the evaporation of the water content, so that preferably overheating, at least significant overheating, of the product is prevented. This also has the advantage of pre-swelling compared to variants that perform pre-swelling without any evaporation at all, mitigating the recovery of the functional medium from the spinning bath or forming bath. In this case, a preferred embodiment consists in that the water content in the starting material or transport mixture is excessive compared to the forming solution, which is deliberately selected so that the energy required for its evaporation results from the mechanical energy input caused by dissipation, and no heat energy input via heated surfaces and, moreover, preferably, no heat energy release via cooled surfaces is required to prevent overheating or substantial overheating. The advantage of this embodiment is, on the one hand, a higher water content in the functional medium, which reduces the machine manufacturing costs and functional agent recovery costs, and, on the other hand, a faster production of the transfer mixture, since the water promotes the soaking of the cellulose and functional medium. The avoidance of heated or cooled surfaces relates in particular to the disks attached to the kneader shaft, but also preferably to the shaft and / or the inner housing surface. In terms of the device, the former means that the disks can be constructed simply without heating cavities or as supports with a purely minimized side surface, which reduces the load on the kneader shaft and simplifies its manufacture. Furthermore, this means that the kneader shaft is uniformly loaded, which, among other things, increases the service life of the kneader-mixer.

[0070] The practical use of a kneader-mixer of the type previously used by the inventors for the forming solution process according to the invention by the direct dissolution method with NMMO as functional medium showed that the residence time in the kneader-mixer ranges from 2 to 15 minutes, whereby the residence time is highly dependent on the dissolution time of the cellulose, the exact dissolution time depending not only on the treatment in the high shear unit, but also, for example, on the cellulose concentration, the type of cellulose, its pretreatment and the type of functional medium, and can extend beyond these ranges. With a kneader-mixer volume of 2500 L, for example, an industrial production capacity of 6.4 kilotons of cellulose (or, in the case of further processing, cellulose fibers) per year can be achieved. In this case, if the product is introduced into the kneader-mixer in a concentration corresponding to 1.3 hydrate, the heating of the discs of the kneader shaft and the division into several temperature zones can be omitted. This corresponds to a residence time of about 12 minutes, which cannot be achieved with the prior art drying method using an extruder.

[0071] In particular, when using NMMO and IL as functional media, the transfer mixture is characterized by a product state that has not yet reached that of a forming solution, which is characterized by insufficient thermomechanical processing of the starting materials in the preceding process steps, in the sense that the dissolution time provided in the high shear unit for the current mixing and kneading action is too short or the water content is still too high due to insufficient or insufficient evaporation.

[0072] In the present invention, it is necessary to start the dissolution process in the kneader-mixer with the transfer mixture because the capacity of the kneader-mixer is insufficient to prevent or break up cellulose aggregates, due to the low shear, to the extent that the liquid is sufficiently stirred into a powdered solid and can be dissolved in the kneader-mixer by the functional medium. The production of the transfer mixture from the starting material therefore consists mainly of mechanical treatments, in particular mixing and shearing, so that the transfer mixture differs in particular by its improved homogeneity compared to the starting material, while the composition is not substantially changed and the dissolution process has not yet started or is only partially started. In this context, essentially unchanged refers in particular to the moisture content of the product, which may be reduced by evaporation or vaporization, in particular as a result of the input of dissipated energy, in particular to the high shear unit during the processing of the starting material for the transfer mixture.

[0073] The transfer mixture differs from the forming solution in that it corresponds to the product in its state before being transferred to the formable or spinnable solution, i.e., the forming solution. A formable or spinnable solution exists when all the essential cellulose components of the starting material have dissolved. In this context, "essential" means a very small amount of undissolved components, so that the so-called filter life reaches an economically acceptable level.

[0074] The filter service life usually concerns the filters used after the process step of producing the forming solution and before the process step of forming or spinning. The filter service life corresponds to the period or period of use until the filter needs to be replaced because the pressure drop across the filter is too high, which increases due to the accumulation of components that are undesirable for further processing. These components can, for example, consist of both undissolved cellulosic fibers and non-cellulosic impurities. The specific choice of the filter service life is therefore dependent on the overall economic cost and quality optimization aspects.

[0075] The transfer mixture furthermore differs from the starting material in that it has a higher homogeneity and is still preset as a suspension or partial solution due to the thermomechanical or exclusive mixing treatment in the preceding process element. In the embodiment with a higher water content in the starting material than is required for the forming solution, the kneader-mixer according to the invention for processing the transfer mixture is characterized in that the product in the kneader-mixer has a water content that corresponds to the water content that can still be evaporated during the dissolution time without increasing the processing volume of the kneader-mixer, as mentioned above, with the advantage that the kneader-mixer can be constructed as small as possible and ideally does not have to be heated on all surfaces.

[0076] This leads to optimal use of the kneader-mixer, with the advantage that it is possible to knead with a low mechanical input depending on the throughput compared to high-speed high-shear units, and the residence time during continuous operation for the complete dissolution of the cellulose can be freely selected. This is particularly advantageous since the strength of the high-shear unit is used at the same time, especially since mixing and kneading with a large amount of mechanical power input at relatively short residence times, typically between 0.2 seconds and 2 minutes, are used simultaneously to process the starting materials for the formation of the transport mixture.

[0077] When using a large volume high shear unit as a process step upstream of the kneader-mixer according to the invention, the optimal use of the kneader-mixer is in a continuous operation mode with essentially freely selectable residence time and input of mechanical energy, but also typically thermal energy, to completely dissolve the cellulose. The advantage of the above-mentioned continuous operation mode lies in the avoidance of time-consuming washing cycles and the minimization of quality fluctuations, which are very relevant for the forming solution and the forming quality. This is particularly advantageous, since it simultaneously utilizes the strength of the large volume high shear unit, in particular the ease of inputting large amounts of powder in batch mode into the liquid to process the starting material to form the transfer mixture, as well as mixing and kneading.

[0078] The mechanical power input based on the processing volume refers to the typical filling level, which is typically up to 100% for extruders and high speed mixers, but typically about 50% to 70% for kneader mixers and dry processes in Z kneaders or sigma blade mixers.

[0079] Since evaporation is not the strength of the high shear unit, on the contrary, using the preceding process components to their strength means that the input concentration of water in the transfer mixture substantially corresponds to that in the starting material, where "substantially" refers to correct operation with optimal settings of the high shear unit, excluding leaks, humidification or sampling.

[0080] For a certain filling level, the processing volume of the kneader-mixer is determined by the flow capacity of the required forming solution, which is determined by the dissolution time still required after the thermomechanical pretreatment in the preceding high shear unit and the possible residence time in the tank. This further depends on various factors such as the cellulose concentration, the particle size of the cellulose, the agglomeration state of the functional medium, the type of cellulose, its pretreatment, the functional medium and the kneading and mixing intensity of the kneader-mixer. The functional medium can be present as a liquid, but also in powder form, for example as granules or in the solid state of agglomeration. Thus, the skilled person knows that, for example, cellulose of different origin, for example different wood species, other plants such as cotton, or with different degrees of polymerization (known as DP) of cellulose, requires different dissolution times. The skilled person also knows that in different functional media, dissolution rates and therefore dissolution durations that deviate from each other can occur.

[0081] The functional medium is understood independently of the aggregation state in the starting material. Thus, for example, NMMO, which is mixed with cellulose powder as monohydrate in solid form at room temperature and becomes liquid only during further processing, is also called functional medium.

[0082] According to the invention, as an additional optimized method variant, the speed of the high shear unit is set so that for a safe and energy-efficient method, no mechanical power is introduced into the product, which must be dissipated again by contact cooling in the kneader-mixer according to the invention. This simplifies the process control and increases the process reliability of the method, especially when NMMO is used as a functional medium. Furthermore, the described method variant has the advantage that the heat load of the mixture in the kneader-mixer is minimal, which is beneficial for the product quality of the forming solution. From the point of view of the equipment, this means that the kneader shaft does not need to be equipped with multiple heating / cooling zones. In the case of the present invention, the shaft structure is preferably configured so that there are no heating cavities, and the mechanical energy input introduced by kneading is sufficient to generate the forming solution from the transported mixture. Ideally, preceding process elements, in the form of high shear units, already process the product during the production of the transport mixture to such an extent that the kneader-mixer according to the invention does not have to remove water from the transport mixture, and the dissipated energy only heats the product without overheating it or at least without substantially overheating it, so that condensation of the water evaporated in the kneader-mixer is not required, and the kneader-mixer is supplied with starting materials, the water content of which already corresponds to the water content of the forming solution.

[0083] In the case of NMMO as functional medium, a preferred embodiment that increases the process safety is characterized by a very high water content in the transport mixture, so that the water content in the high shear unit is sufficiently high that the risk of autocatalytic decomposition of NMMO is low. This applies if the water content of the transport mixture is within the following general ranges: min x H2O =-0.4525X Cell +0.1465 Max X H2O =0.2864X 2 Cell -0.6786X Cell +0.2288.

[0084] The water content of the transport mixture is preferably in the following preferred ranges: Max X H2O =0.2864X 2 CELL -0.6786X CELL +0.2288 min x H2O =-0.00022X 2 CELL -0.5317X CELL +0.1800.

[0085] In these two formulas for the general and preferred ranges of NMMO transport mixtures, X H2O represents the mass fraction of water based on the total mixture, and X CELL represents the corresponding fraction of cellulose. The energy input of the preceding process elements is therefore selected so that the process energy required for heating and possibly evaporating the mixture in the kneader-mixer preferably comes only from the mechanical power of the kneader-mixer. In this case, the specific water content is related to the range of cellulose content and cellulose quality (e.g., molar mass distribution) typical in the industry. This cellulose content and quality are known to those skilled in the art. For example, for a cellulose content of 0.110, a minimum water content of 0.097 is obtained for the typical transport range.

[0086] This increases the maximum flow rate of the molding solution per kneader-mixer, which is the final step in the multi-stage dry dissolution process, and increases the overall maximum production capacity per production line.

[0087] According to the invention, preferably, but not necessarily, IL or NMMO or protolytes, i.e., acids or bases, as described, for example, in US Pat. No. 5,993,621 or US Pat. No. 5,399,663 and US Pat. No. 5,499,625, are added as functional media for the starting materials, which serve to dissolve cellulose under appropriate conditions.

[0088] In the above-mentioned combinations with the preceding process elements for producing a transfer mixture, a preferred embodiment of the kneader-mixer is characterized in that it is designed to process a transfer mixture in which the viscosity of the transfer mixture is not only sufficiently low so that significant overheating of the high-shear unit is prevented, but rather the mechanical energy input in the case of the kneader-mixer caused by friction is sufficiently high so that the need for thermal energy input to the kneader-mixer to supplement the mechanical energy input is very low, and the structure of the kneader shaft does not have to serve for heat exchange, but can be configured without a heating cavity. In this case, a further preferred embodiment is characterized in that the mechanical energy input is selected by the selection of the size and geometry of the kneader-mixer, the rotation speed of the kneader shaft, the viscosity of the product to be processed and the residence time of the product in the kneader-mixer, so that the kneader-mixer can be configured without a heat exchange surface of the kneader shaft or the housing, and the kneader shaft or the inner tube or the housing of the kneader-mixer is then equipped without a double outer shell. This allows a significantly easier, more cost-effective and faster construction method of the kneader shaft and the housing. In the preceding processing steps, the starting material is present as a mixture of cellulose, water and functional medium, the composition of which can vary significantly.

[0089] In this case, the starting material is made into a transfer mixture in a previous process step, which can preferably take place in one or more high shear units as the preceding process element or preceding process elements.

[0090] In the transport mixture according to the invention, the cellulose is present as a suspension or partially dissolved. In the case where water is evaporated in the kneader-mixer and NMMO is used as the functional medium, in an operating mode configured for process safety in the high shear unit, the minimum water content of the NMMO in the transport mixture can be determined by the formula:

[0091] All these cases share the basis of the inventive concept of using the kneader-mixer according to the invention for the production of dry or semi-dry forming solutions. In this context, semi-dry means that water has to be evaporated between the starting materials and the forming solution, but this process task does not determine the configuration of the high-shear unit according to the invention and the kneader-mixer according to the invention. From this, the flow rate of the forming solution determines what is meant by the minimum possible construction size of the kneader-mixer for a certain forming solution flow rate or the maximum forming solution flow rate for a certain kneader-mixer size.

[0092] Moreover, all cases have in common the concept of utilizing the advantages of the kneader-mixer according to the invention to compensate for the disadvantages of the high-shear unit, which at least consists in that the high-shear unit is suitable for mixing the components of the starting materials to form a transfer mixture, but not for further processing of this transfer mixture to a forming solution, in a given volume, and the kneader-mixer is suitable for further processing of the transfer mixture to a forming solution, but not for mixing the components of the starting materials to obtain a transfer mixture.

[0093] Due to technical characteristics such as low mechanical energy and dissipated energy input compared to high shear units, kneader mixers are particularly suitable for processing products from a transfer mixture into a forming solution by mixing and kneading without overheating or substantially overheating the product. In contrast, high shear units have a higher mechanical energy and dissipated energy input and are therefore suitable for processing starting materials to form a transfer mixture.

[0094] Compared to extruders, the kneader-mixer according to the present invention is characterized by a residence time that can be freely selected, largely independent of the speed of the kneader shaft and therefore independent of the mixing / kneading intensity.This is supported by the relatively small input of dissipated energy per processing volume in the kneader-mixer, and therefore the reduction of product heating, which is important due to the risk of overheating.The kneader-mixer therefore takes advantage of the intensive product contact in the extruder when mixing two powders or mixing one powder with a liquid, and compensates for the limited residence time in the extruder.

[0095] The kneader-mixer according to the invention is characterized in particular by its continuous operation mode, in comparison with the Z kneader-mixer or the Sigma blade mixer, which necessarily favors a homogeneous flow of the forming solution with less fluctuations, and takes advantage of the possibility that the Z kneader-mixer can meter powders in large quantities into the liquid in a simple manner and mix and knead it by means of intensive product contact.

[0096] The kneader-mixer according to the invention is characterized in particular by its freely selectable residence time and the high torque capacity of the kneader shaft, in comparison with high-speed mixers with residence times of less than 1 minute, preferably less than 30 seconds, in particular less than 10 seconds, and utilizes the ability of the high-speed mixer to meter powders into liquids in large quantities in a simple manner and to mix with high specific power. In comparison with all other high-shear units and kneader-mixers, high-speed mixers are typically characterized by applications with low product viscosities and therefore are not prior art for the forming solution method. The use of the kneader-mixer according to the invention as a prior process element in the dry dissolution method is based on the inventive concept that mixing is performed very quickly, so that no substantial increase in product viscosity occurs because the residence time is too short for this, and therefore the dissolution process cannot start or cannot progress to such an extent that it allows a significant increase in the product viscosity that exceeds the torque limit of the high-speed mixer.

[0097] The formula for describing the transport mixture with NMMO as functional medium relates to the generation of the transport mixture under thermomechanical conditions that allow low-risk operation of high-shear units and have been demonstrated in practice. However, due to the described influence on the dissolution rate of cellulose, this formula may predict a spinnable solution, but in reality, transport mixtures according to the invention still exist that contain undissolved cellulose components, despite the low water content, because of the special thermomechanical treatment selected, for example a very short treatment between the inlet and the outlet of the product. However, due to the low water content in the transport mixture, such a thermomechanical treatment is associated with an increased process risk at the same time due to substantial overheating in the event of explosive decomposition.

[0098] According to the present invention, this can also mean that the starting material, even if the composition is within the concentration range, is fed to a previous process stage describing a general transport mixture. This can also mean that, according to the present invention, the starting material, even if the composition is within the concentration range, is fed to a preceding processing step describing a general transport mixture. Typically, the transport mixture characterized by partial dissolution of the pulp results only from the process-specific thermomechanical treatment (elevated temperature and shear action) of the starting material.

[0099] Compared to processes in which a significant proportion of water is evaporated in the preceding process elements to produce the transport mixture, and which typically use thermal energy input via hot surfaces for the evaporation, high shear units and kneader-mixers, in particular thanks to their good mixing properties and the effective mechanical energy input via the rotating shaft, can set the speeds, and therefore the energy inputs, quickly and can also quickly counteract them. For this reason and also due to the high mixing intensity and the resulting low radial temperature gradients, high shear units and kneader-mixers are suitable for temperature control, generally cooling or heat dissipation, with high precision - and even more safely in the case of NMMO as functional medium - thus preventing overheating or substantial overheating.

[0100] In another embodiment, the transport mixture first passes through a high shear unit or multiple high shear units followed by a transport element or elements before being introduced into the kneading mixer.

[0101] Thus, the improvement in energy efficiency and process reliability applies not only to the process step of producing a forming solution from the transferred mixture in the kneader-mixer, but also to the entire transfer of starting materials into the forming solution in combination with suitable preceding process elements.

[0102] Material properties based on the above equations to describe the general transport range using NMMO as the functional medium are obtained from the following studies.

[0103] For the general transport ranges above, the minimum moisture content is X H2O describes, on the basis of US Pat. No. 5,399,433, a composition in which for the person skilled in the art, after visual inspection, crystals of NMMO can be observed for the first time in a cellulose / water / NMMO mixture, which thus separates from the crystalline phase a mixture capable of forming a complete forming solution upon corresponding thermomechanical treatment. What is described in US Pat. No. 5,999,633 regarding NMMO as a functional medium is confirmed by results and observations from industrial applications and tests by the inventors on a pilot plant scale. H2O The formula expressing the above formula is based on the knowledge of the industrial application of the direct dissolution process and on the data collected from a series of experiments carried out by the inventors on a pilot plant scale. It represents the upper limit of the transport range, which ensures optimal use of the kneader-mixer characteristics relevant to a particular process. The two formulas described herein therefore encompass the range of common transport mixtures.

[0104] For a description of the material properties of the preferred transport range, with respect to the minimum water content, see in particular US Pat. No. 5,399,663. This formula combines the knowledge of the limit curves of the dissolution region described in US Pat. No. 5,399,663, with results from the industrial application of the direct dissolution method and data collection from a series of tests by the inventors on a pilot plant scale. The description of the maximum water content corresponds, in the preferred range, to the description of the general transport range.

[0105] The transfer mixture is in its general composition before dissolution and also in its preferred composition due to the selected thermomechanical treatment and treatment time in the high shear unit. This also results in the forming solution process being carried out under the optimal operating parameters of the high shear unit, and prevents relatively difficult material states of the forming solution, for example, when over-drying or decomposition occurs in the high shear unit due to excessively high shear action. These difficult material states do not lead to problematic process states in the subsequent kneader-mixer according to the invention, since this kneader-mixer is characterized by reduced shear action and residence times independent of mixing and kneading action.

[0106] In the case of the formula describing the general composition, if NMMO is used as the functional medium, it is advantageous to apply a transfer mixture that further contains an amount of water such that further processing for dissolution can take place in a relatively short processing time in the subsequent process elements, and further crystallization of the solvent is prevented.

[0107] In the formula describing the preferred composition of the transport mixture, the minimum content of water is further away from the crystalline phase compared to the definition of the general transport mixture. Therefore, the processing of the transport mixture to form the molding solution in the kneader mixer according to the present invention can be accomplished in a short time and at the same time the risk of overdrying of the material can be reduced.

[0108] In both cases, after a treatment time lasting from 2 to several minutes during which the product is homogenized in the kneader-mixer and possibly any remaining water is evaporated, the transfer mixture is removed from the moldable or spinnable solution.

[0109] The product, and thus also the starting material, essentially contains cellulose, water and a functional medium. In addition, the product contains further chemicals such as stabilizers, the detailed list of which can be omitted in the context of the present invention, since they are known to those skilled in the art and require adjustment for each individual application.

[0110] Moreover, the skilled person knows how to produce a forming solution from cellulose according to the dissolution method, where the functional medium essentially consists of a protolite, in particular a phosphoric acid or sodium hydroxide solution, where evaporation of water does not usually occur, but rather dissolution must occur, in particular at least partially near or below the freezing point, and where the forming solution is produced by a combination of mixing and shearing over a certain residence time. These dissolution methods (also called cold methods) are also characterized in the prior art by a limited capacity for the forming solution flow, when using high shear units, by a limited residence time or limited cooling capacity, typical of extruders, in particular when using extruders, and by a limited cooling surface, due to non-heatable or coolable shafts and shaft disks, in particular when using continuous mixers.

[0111] In one embodiment, the high shear unit consists of at least two large-capacity high shear units, for example in the form of a Z kneader mixer, i.e. a first Z kneader mixer and a further Z kneader mixer, which are connected upstream of the kneader mixer, one after the other or in parallel. The Z kneader mixer has the advantage that the starting materials are processed independently of the kneader mixer to form a transfer mixture, which is fed to the kneader mixer only when this is desired or a corresponding time frame exists. When using several Z kneader mixers arranged in parallel, for example when a transfer mixture is taken from the first Z kneader mixer to the kneader mixer, the further Z kneader mixer can independently generate a transfer mixture from the starting materials, and as soon as the transfer mixture is taken from the first Z kneader mixer, the further Z kneader mixer can be connected to the kneader mixer to take out the transfer mixture. This procedure can be carried out alternately.

[0112] A further embodiment consists in preparing the transfer mixture in a batch in a first Z-kneader mixer, which is fed in batches to a second Z-kneader mixer via a discharge screw, the capacity of which is selected so that it can converge the filling level fluctuations of the second Z-kneader resulting from the batch discharge from the first Z-kneader and feed the next kneader mixer continuously via the discharge screw. Also conceivable is a stirred tank equipped with a discharge screw instead of the second Z-kneader mixer.

[0113] The kneader-mixer according to the present invention and the method according to the present invention related thereto relate to a dry dissolution method, which is divided into a direct dissolution method without evaporating water, a direct dissolution method with evaporating water, and a protolite dissolution method.

[0114] The transfer mixture can also be prepared as a premix from the starting materials in a preceding process element, and then said premix is ​​introduced into the high shear unit as an agitated starting material.

[0115] The parameters of the high shear unit are also selected so that the composition of the transferred mixture and the starting material are substantially identical.

[0116] The kneader shaft of the kneader-mixer can rotate and the product can be wiped on the heated and / or cooled inner surface of the kneader-mixer. The shaft structure of the kneader shaft of the kneader-mixer can also be designed such that, for example, in the axial section of the kneader shaft, there is at least partially no heating cavity. Furthermore, the shaft structure of the kneader shaft of the kneader-mixer can also be configured such that, for example, in the axial section of the kneader shaft, there is at least partially no heating cavity.

[0117] Furthermore, the composition of the transfer mixture may be the same as that of the starting material, and the water content in the starting material may be selected such that a large amount of water in the transfer mixture is evaporated in the kneader-mixer by the mixing / kneading interactions and by the heated surfaces, and the evaporative cooling that occurs during processing results in a molding solution without substantially overheating the product during the process.

[0118] Evaporative cooling, aimed at preventing overheating or substantial overheating of the product, can be further achieved or enhanced in that water (also referred to in the present invention as evaporative cooling water) is added directly to the kneader-mixer. This water is heated to its boiling point at the surface of the product and instantly evaporates without being substantially mixed into the product and thus without substantially increasing the moisture content of the product, thereby drawing heat away from the product and thus cooling it.

[0119] The energy supply and dissipation of the thermally heatable or coolable inner surfaces (also called heat exchange surfaces) of the process chamber is generally carried out via a heating medium, typically a heat transfer medium such as water, steam or other, usually synthetic, liquid that flows through the heat exchange surfaces of the kneader-mixer and possibly through the associated dome, or a coil that is heated by an electric current that is installed near the heat exchange surface, thereby heating or cooling the surface of the kneader-mixer facing the process chamber in an energy supply manner.

[0120] The evaporative cooling water is added to the kneader-mixer directly and via a separate feed line, characterized in that it is not yet contained in the starting materials and does not enter the kneader-mixer as part of the transport mixture. The feed is typically carried out via a controllable valve so that the amount of water per time unit is deliberately matched to the evaporative cooling to be achieved. In this case, the temperature of the evaporative cooling water immediately before entering the process chamber of the kneader-mixer and the gas pressure in the process chamber of the kneader-mixer are selected so that the temperature of the evaporative cooling water is below the boiling point of water in the process chamber of the kneader-mixer, so that as little water as possible is evaporated by flashing as known to those skilled in the art, and so that as much water as possible reaches the surface of the product.

[0121] Evaporative cooling can also be achieved by evaporation of a liquid other than water, which is also an evaporative cooling medium. The evaporative cooling medium can be added together with the starting materials to the high shear unit or directly to the process chamber of the kneader-mixer instead of the evaporative cooling water. Evaporative cooling can also be achieved by partial evaporation of the functional medium, in which case the evaporated part of the functional medium is also called the evaporative cooling medium.

[0122] Cooling of the product for the purpose of preventing overheating or substantial overheating of the product can be further achieved or enhanced by wiping the product on at least partially cooled interior surfaces of the kneader-mixer.

[0123] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and on the basis of the drawings. [Brief description of the drawings]

[0124] [Figure 1] FIG. 1 shows diagrammatically a system containing a kneader-mixer 6 without evaporation. [Diagram 2] FIG. 2 shows diagrammatically a system containing a kneader-mixer 6 with evaporation. [Diagram 3] FIG. 3 shows diagrammatically a system containing a high speed high shear unit 5 and a kneader-mixer 6 . [Figure 4] FIG. 4 shows diagrammatically a system comprising two large volume high shear units 8 and a kneader-mixer 6 . [Diagram 5] FIG. 5 shows diagrammatically a further embodiment of the system according to the invention. [Figure 6] FIG. 6 is a first graph illustrating preferred material properties of the transport mixture. [Figure 7] FIG. 7 is a second graph showing typical material properties of the transport mixture. EXAMPLES

[0125] First, it should be noted that embodiments and features of individual components in the description of one figure are intended to apply to other figures as well, particularly when the same reference numerals are used for the same components in multiple figures.

[0126] Figure 1 shows a kneader-mixer 6. A process chamber 12 is arranged inside the kneader-mixer 6. The process chamber 12 is fed at one end with a continuous flow of the transfer mixture 2 and at the other end with the forming solution or forming solution stream 3 leaving the kneader-mixer 6. In the embodiment shown here, the kneader-mixer 6 is operated without evaporation.

[0127] Figure 2 shows a system in which the kneader-mixer 6 is operated with evaporation. For this purpose, the kneader-mixer 6 again has a continuous flow of the transport mixture 2 at one end and again a forming solution or forming solution flow 3 at the other end. Also, the supply of evaporative cooling water 13 is shown diagrammatically by an arrow. In addition, the process chamber 12 or kneader-mixer 6 comprises a dome 7. Then, pointing away from the dome 7, a second arrow showing a steam flow 4 is shown diagrammatically.

[0128] In figure 3 the kneader-mixer 6 is partially shown. Furthermore it is shown how a continuous flow of the transport mixture 2 is fed from the high speed high shear unit 5 to the kneader-mixer 6. The way in which a continuous feed of the components of the starting material 1 is introduced into the high speed high shear unit 5 is indicated diagrammatically by the third arrow.

[0129] 4 shows how two large-capacity high-shear units 8 arranged side by side are operated batchwise in an alternating manner and in the process in each case supply a batchwise flow of the transfer mixture 11 to the kneader-mixer 6. For this purpose, the large-capacity high-shear units 8 are each equipped with a discharge member 9 which is operated batchwise. In addition, the batchwise supply of the components of the starting material 10 to the large-capacity high-shear units 8 is in each case indicated diagrammatically by a fourth arrow.

[0130] FIG. 5 shows a schematic representation of a further embodiment of the system according to the invention. Here, an additional operation is shown between the kneader-mixer 6 and the high-volume high-shear unit 8. Said additional operation is either a further high-volume high-shear unit or a stirring vessel 14. Thus, in this case, either a further high-volume high-shear unit or a stirring vessel 14 can be provided. What is important in the selection is the requirement that the additional operation is equipped with a continuously operated discharge member 15, thus allowing a continuous flow of the transfer mixture 2 to the kneader-mixer 6. In this case, the high-volume high-shear unit 8 has a discontinuous feed to the further high-volume high-shear unit or a stirring vessel 14 in the form of a batchwise flow of the transfer mixture 11. In contrast, the further high-volume high-shear unit or a stirring vessel 14 supplies a continuous flow of the transfer mixture 2 to the kneader-mixer 6. For the high-volume high-shear unit 8, the statements made with respect to one of the high-volume high-shear units 8 in FIG. 4 apply.

[0131] Combinations of the systems of Figures 1 to 5 should also be considered as disclosed in the context of the present invention, if the combinations are not mutually exclusive in each case.

[0132] 6 and 7 show schematic equations for the general and preferred ranges of NMMO transport mixtures.

[0133] Here, a general composition a has the following parameters: Max X H2O =0.2864X 2 CELL -0.6786X CELL +0.2288 min x H2O =-0.4525X CELL +0.1465 For this reason, the general composition a has a larger range than the preferred composition b, which has the following parameters: Max X H2O =0.2864X 2 CELL -0.6786X CELL +0.2288 min xH2O =-0.00022X 2 CELL -0.5317X CELL +0.1800

[0134] When the water content is decreased, first the range of solution L is reached, and when the water content is further decreased, crystallization K of NMMO occurs.

[0135] Using the equations for the general and preferred ranges of NMMO transport mixtures, an example is given below of the production of a casting solution with a cellulose content of 12% by weight, for example, with the aid of the direct dissolution method using NMMO as a functional example, without significant evaporation of water during processing.

[0136] All content specifications below are with respect to the total mass of the cellulose / NMMO / water mixture. A starting material with a cellulose content of about 12.0% by weight was produced from cellulose and NMMO monohydrate, resulting in a NMMO content of about 77.4% by weight.

[0137] This starting material is introduced into the high shear unit at a flow rate of about 217 kg / h where it is processed to form a transport mixture, in this example the high shear unit is operated at atmospheric pressure.

[0138] In this example, the heating temperature of the high shear unit is 90° C., thus avoiding overheating of the product. The transfer of the mixture takes place at a product temperature of about 105° C. after the thermomechanical treatment in the high shear device.

[0139] The ratio of water to NMMO remained constant compared to the beginning of the process. The transport mixture provided by the high shear unit subsequently enters the kneader mixer at a flow rate of about 217 kg / h.

[0140] There, complete dissolution of the cellulose and homogenization of the mixture by kneading and mixing effect occurs, as a result of which a complete molding solution is obtained. The residence time of the mixture in the kneader mixer is 8.5 minutes.

[0141] The processing volume of the kneader-mixer is therefore about 70 L. The forming solution leaves the kneader-mixer at a flow rate of about 217 kg / h, having a cellulose content of 12.0 wt.%, an NMMO content of about 77.4 wt.% and a temperature of about 107°C. [Explanation of symbols]

[0142] [Table 1]

Claims

1. 1. A method for producing a molding solution from a starting material consisting of cellulose, water and a functional medium according to a dry dissolution method, characterized in that the starting material is first fed to a high shear unit (5, 8), in which a transfer mixture (A, B) is obtained from the starting material in the high shear unit (5, 8), and then the transfer mixture (A, B) is fed to a kneader-mixer (6) for dissolution.

2. 2. The method according to claim 1, characterized in that the composition of the starting material and the composition of the transfer mixture (A, B) are substantially identical.

3. 3. The method according to claim 1 or 2, characterized in that the machine controller monitors and controls or adjusts via sensors the content of water, cellulose and functional medium in the composition of the product from the starting material to the forming solution, the product temperature, the product viscosity, the pressure or temperature of the heating medium, the pressure in the process chamber (12) or the rotation speed or torque of the kneader shaft.

4. The method according to any one of claims 1 to 3, characterized in that at least a part of the inner surface of the kneader-mixer (6) is heated and / or cooled.

5. 5. The method according to claim 1, wherein the water content in the transfer mixture (A, B) is greater than the water content in the forming solution, and the water is evaporated in the kneader-mixer (6).

6. 6. The method according to claim 5, characterized in that the energy required for the evaporation of the water occurs substantially only through dissipation due to the interaction of the kneading elements which mesh with the product due to the rotation of the kneader shaft.

7. 6. The method according to claim 5, characterized in that the energy required for the evaporation of the water occurs essentially only through dissipation and heated heat exchange surfaces resulting from the interaction of the kneading elements which mesh with the product due to the rotation of the kneader shaft.

8. Method according to any one of claims 5 to 7, characterised in that the shaft structure of the kneader shaft is configured at least partially free of heating cavities.

9. A method according to any one of claims 5 to 8, characterized in that evaporative cooling resulting from the evaporation of water at the surface of the product dissipates energy for cooling the product.

10. The method according to any one of claims 1 to 8, characterized in that evaporative cooling water (13) is supplied to the kneader-mixer (6), and the evaporative cooling resulting from the evaporation of the evaporative cooling water (13) on the product surface dissipates energy for cooling the product.

11. 11. The method according to claim 5, characterized in that for the purpose of evaporative cooling, an evaporative cooling medium is evaporated instead of or in addition to water, said evaporative cooling medium being fed together with the starting material to the high shear unit (5, 8) or fed directly to the process chamber (12) of the kneader-mixer (6) instead of the evaporative cooling water (13).

12. A method according to any one of the preceding claims, characterised in that a cooled heat exchange surface dissipates energy for cooling the product.

13. A system for producing a molding solution by a dry dissolution method from starting materials consisting of cellulose, water and a functional medium, comprising a kneader-mixer (6) and a high shear unit (5, 8), characterized in that the high shear unit (5, 8) is connected directly or indirectly upstream of the kneader-mixer (6).

14. 14. The system according to claim 13, characterized in that the processing volume of the kneader-mixer (6) is configured for a capacity corresponding only to the flow rate of the forming solution.

15. 15. The system according to claim 13 or 14, characterized in that the high shear units (5, 8) consist of a first large capacity high shear unit (8) and a further large capacity high shear unit (8) connected upstream of the kneader-mixer (6), either one behind the other or in tandem.

16. 15. The system according to claim 13 or 14, characterized in that the high shear unit is configured as a continuously operating high speed high shear unit (5).

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