DE102022102177A1 - Plant and method for processing a starting material into a form solution using the dry solution method - Google Patents

Abstract

The invention relates to a method for producing a mold solution from a starting material consisting of cellulose, water and a functional medium using the dry dissolving process, in which the starting material is first fed to a high-shear unit, with a transfer mixture being produced from the starting material in the high-shear unit and the transfer mixture then being fed to a mixing kneader for Dissolve is supplied.

Description

technical field

The invention relates to a method according to claim 1 and a plant according to claim 11 for processing a starting material into a molding solution using the dry dissolving method.

State of the art

In the EP 0 906 455 A1 it is described, for example, that a form solution is produced from fibrillar cellulose powder and liquid NMMO in a dry dissolving process in a twin-screw extruder, which must be stabilized in a downstream storage tank with a pressure regulator.

In the EP 1 191 038 A1 describes a dry dissolving process in which a swollen mixture is produced from supercooled liquid NMMO hydrate and cellulose powder in a twin-screw extruder and is fed to a single-screw extruder in order to then be dissolved in the single-screw extruder. In detail, it is about the production of a starting material, which is processed by melting it into a solution.

In the EP 1 144 455 B1 describes a method for mixing and homogenizing cellulose and water-containing NMMO in two shearing zones of a first apparatus to form a homogeneous suspension. Here, the amount and the water content of the NMMO is coordinated with the possible water content of the cellulose in such a way that the NMMO content in the liquid phase of the suspension formed is between 70 and 80% by mass. In addition, a schematic plant is shown consisting of a first apparatus for the production of the suspension and a second apparatus connected to the first as an evaporation stage. With regard to the invention described below, it is the EP 1 144 455 B1 i.e. the production of a suspension with such a large proportion of water that the subsequent process stage for the production of a spinning solution is characterized by the evaporation of water.

In the WO 2005/000945 A1 describes a process which involves mixing N-methylmorpholine-N-oxide (NMMO) powder with ground cellulose and subsequent dissolving, both processes taking place in a single twin-screw extruder.

The WO 2006/071 101 A1 describes dissolving a paste in an extruder to form a molding solution, the paste being produced in a preceding kneader from an NMMO solution and ground cellulose, the NMMO solution consisting of NMMO and a small proportion of cellulose powder. The WO 2006/071 101 A1 describes the upstream connection of a kneader to an extruder so that it can produce a mold solution.

All of these dry dissolving processes use an extruder to dissolve the cellulose. They differ in the various preceding process stages. The reason lies in the high shear intensity of extruders. However, dry dissolving processes are currently not used on an industrial scale for large capacities. The reason lies in the limited capacity of extruders. With their smaller diameters D compared to mixing kneaders, small clearances and high shaft speeds, extruders are well suited for mixing two powders (a frozen functional medium such as NMMO at room temperature and ground cellulose, with the frozen functional medium in powder form being introduced into the extruder by shear energy melts into a liquid functional medium), or a cellulose powder with a functional medium in the liquid state of aggregation, but at the same time only have a short residence time for the product compared to mixing kneaders, because the small clearances lead to significantly smaller process volumes than with mixing kneaders , and the high speeds of the shafts force the product at the same time - in contrast to mixing kneaders - and thus limit the residence time. This limited residence time is also reinforced by the very high mechanical dissipation per process volume.

An insufficient residence time (in the sense of shorter than the dissolving time required for the mechanical action specific to the agitating element) means insufficient homogeneity and dissolving conditions of the form solution, so that the subsequent shaping, e.g. during spinning, leads to fiber tears, spinneret clogging or short filter service lives.

On the other hand, with increasing dwell time (to achieve the necessary dissolving time) or speed of the shaft (to achieve the necessary mechanical action) in the extruder, the mechanical energy input increases and thus the risk of significant overheating of the product or product components, which can damage the product and Risk of decomposition, which can result in considerable costs due to product damage-related price reductions and the replacement of functional mediums, which are very expensive in the case of NMMO and especially IL. In addition, in the discharge area of the extruder, it may be necessary to remove heat from the product by cooling in order to avoid overheating or significant overheating, which means a loss of energy, which increases energy costs and with increasing throughput is becoming increasingly difficult due to the decreasing surface-to-process-volume ratio of extruders and ultimately also limits the size of suitable extruders.

In the case of NMMO as the functional medium, all the above-mentioned processes for preparing a molding solution, even with an extruder, have in common the risk of explosion. Due to the small, non-contiguous free volume in the processing space of extruders, there is also no easy way to monitor and relieve pressure build-up as a result of decomposition processes in the functional medium over the entire processing space.

In addition to the extruders described above, mixing kneaders are also known to those skilled in the art. They preferably have exactly one or exactly two kneader shafts, which are used to carry out highly viscous and crust-forming processes, which can be operated under vacuum, atmospheric or at overpressure and can be heated or cooled via thermal exchange surfaces. In addition, the kneader shaft and its shaft structures can very effectively heat the product with the typical product viscosities by rotation and the resulting energy dissipation.

If there is exactly one kneader shaft, then there is a single-shaft mixing kneader, which, for example, in CH 674 472 A5 is described. In this case, shaft structures of the kneader shaft mesh preferably during operation with static structures of the housing, for example so-called counter hooks. If there are exactly two kneader shafts, then there is a two-shaft mixing kneader, which is, for example, in DE 41 18 884 A1 is described. The shaft structures of the kneader shafts preferably mesh with one another during operation.

The at least one kneader shaft comprises shaft structures in the form of discs and bars attached thereto, the shaft structures of the at least one kneader shaft being set up to mesh with the shaft structures of a second kneader shaft or with stationary counter-elements present in the mixing kneader during operation. Mixing kneaders with such intermeshing elements are known and are referred to as <<self-cleaning>> because the combing described detaches any buildup from the intermeshing elements.

Mixing kneaders have an opening to the processing space for the entry of the product into the processing space of the mixing kneader (also called entry opening) and another opening to the processing space of the mixing kneader for discharging the product from the processing space of the mixing kneader (also called discharge opening). The input and output openings are typically located in the opposite areas of the mixing kneader—viewed axially. The feed opening can also consist of more than one opening distributed over an axially extending part of the length of the mixing kneader. Further openings to the process chamber of the mixing kneader can typically be arranged in the upper half of the processing chamber (also called gas discharge opening) in order to be able to discharge gases released in the mixing kneader to the processing chamber via separate openings, and which—viewed axially—typically are arranged between the entry and discharge opening are. If the mixing kneader has a dome, then the space delimited by the inside of the dome (also called the dome gas space) connects directly to the gas space of the process space, and these two form a common gas space. A dome is a chimney-like attachment that extends vertically upwards and is arranged directly on the gas discharge openings of the mixing kneader, in the upper area of which there is typically an opening for the discharge of gases (also called vapors) (also called vapor opening). A portion of the interior surfaces of the dome may also be thermally heated or cooled. Mixing kneaders can also be equipped with more than one dome, which are then also collectively referred to as domes.

The bars, counter hooks and shaft assemblies mentioned above are also summarized under the term kneading elements. There are several methods for producing a molding solution from pulp (or cellulose, the difference between pulp and cellulose being irrelevant for the interpretation of this patent application and the two terms can be used interchangeably). These can be distinguished, among other things, by the excess water content in the starting material for a mold solution.

The person skilled in the art is also aware of the method for producing a form solution from cellulose according to the dry dissolving method, in which an ionic liquid is used as the functional liquid instead of NMMO. IL (ionic liquids) or ionic liquids refers to a group of organic compounds which, despite their ionic structure, have a low melting point (<100°C) and are therefore also referred to as molten salts. The use of IL as a functional medium therefore always means an embodiment within the group of ionic liquids that is suitable for the dry dissolving process.

Those skilled in the art know that IL typically converts to a ther. at elevated temperatures mixing tend to decompose, so processes involving a heated IL must keep the temperature of the IL below its decomposition temperature.

The person skilled in the art is also aware that when the water content of an NMMO-water-cellulose mixture is reduced at elevated temperatures, decomposition of the NMMO begins. At temperatures typically above 140°C, there is an increasing risk of explosion as the water content decreases, for example due to explosive autocatalytic decomposition, which results in a further increase in temperature and thus an acute risk of explosion. Depending on the composition of the mixture, decomposition can already be observed at temperatures above 125°C, since the decomposition temperature can be reduced by the presence of reducing agents (e.g. cellulose) and heavy metal ions (e.g. iron ions).

The person skilled in the art is also aware of the fact referred to as the problem of significant overheating within the scope of the invention, that great attention must be paid to controlling the temperature of the product (also referred to below as product temperature) in order to avoid decomposition of the functional medium. He therefore chooses a process in which the desired product temperature and the equilibrium temperature are below the decomposition temperature.

In the case of a multi-component mixture, as is the case with the cellulose-functional medium-water mixture, each composition of the mixture is assigned an equilibrium temperature under the prevailing process conditions (pressure) at which the mixture begins to boil. If energy is supplied to the multi-component mixture, some of the volatile components (here water) evaporate. At the same time, the composition of the mixture changes, which means that the equilibrium temperature also changes as a result. The mixture heats up when energy is supplied, while its composition changes along its equilibrium curve due to the evaporation of volatile components.

With NMMO as a functional medium, exothermic decomposition processes with existing transport limitations also lead to local material overheating (hotspots), from which the heat of reaction cannot be dissipated to a sufficient extent. This subsequently triggers further exothermic decomposition processes.

Significant overheating can, however, also affect the decomposition of the cellulose or the cellulose-functional medium-water mixture (or, according to the definition, the product), in that, at excessively high temperatures, possibly in conjunction with increased shearing action, which is typically the case with increased viscosities, leads to a reduction the degree of polymerization (known to those skilled in the art as DP) of the cellulose.

Those skilled in the art know that dissolving processes do not take place instantaneously but within a period of time with a dissolving speed and require a minimal dissolving time. The person skilled in the art is also aware that dissolution rates are influenced by various factors such as temperature, and that not only the temperature but also the concentration of the functional medium and the mechanical treatment of the mixture have an influence on the dissolution rate. With the same composition and the same temperature, different states of dissolution can occur as a result of different mechanical treatment of the material for the same treatment time.

The person skilled in the art is also familiar with methods for producing a form solution from cellulose using the direct dissolving process, the starting material of which has such a large water content compared to the water content in the form solution that a significant part of the process and the device is characterized by the evaporation of water (wet dissolving process). ), such as in the WO 1994/006530 A1 described, using NMMO as the functional medium and a thin-film evaporator for evaporating water. The disadvantage of the wet dissolving process is the high energy consumption caused by the evaporation of water.

Therefore, in addition to a suitable proportion of water, mechanical action on the product is also necessary for the production of a molding solution, which is achieved through the specifically selected geometry of a mixing element and which must take place over a certain period of time.

For example, methods are also known for the production of a mold solution which use more mechanical action on the product, which is achieved by the specifically selected geometry of a mixing element, and which, however, has to take place over a certain period of time.

Insides of process engineering apparatuses or machines such as mixer-kneader, extruder or thin-film evaporator housings, as well as kneader shaft(s) and discs of mixer-kneaders can be designed as thermal exchange surfaces that cannot be finally heated or cooled.

Discs of kneader shafts of mixing kneaders, which are designed as thermal exchange surfaces, have bores for electrical heating elements or cavities for a heat transfer medium or cooling medium, the latter having an inflow that is fed from the inflow in the kneader shaft and an outflow that leads to the reflux flows back in the kneader shaft. The cavities can typically be designed as double walls or bores and require greater wall thicknesses and larger dimensions of the shaft structures and kneader shafts with thicker walls and cause a significantly greater manufacturing effort compared to cavity-free (hereinafter also referred to as heating cavity-free) discs, which typically due to the omission of thermal exchange surfaces can be built smaller and easier.

Kneaders are known to those skilled in the art and, for example, in JP 1994 055267 B2 described. They differ from extruders in that they have a larger, free process volume and lower shearing action, and from mixing kneaders in particular in the one-dimensional combing and the associated absence of bars, which lead to the mixing effect typical of mixing kneaders. Kneaders can be operated continuously and discontinuously.

Z kneaders and sigma blade mixers are known to those skilled in the art and, for example, in DE 1 058 188 A1 described. They are characterized by two Z-shaped or multiple Z-shaped kneading arms, each rotating about a horizontal axis arranged parallel to the axis of the other kneading arm and interlocking or not interlocking in a large-volume - often trough-shaped - reactor space, and can only be operated in batches. Due to their large volume and batch operation, they are particularly suitable for mixing in a larger proportion of solids and for pre-mixing as well as in the DE 37 20 325 A1 described, in particular also because batchwise operation makes dosing much easier. However, due to the large free spaces and the lack of continuous operation, they are not suitable for sufficiently homogenizing and dissolving pulp on an industrial scale.

object of the invention

The object of the present invention is to overcome the disadvantages of the prior art.

In particular, a system and a method for processing a starting material into a form solution according to the dry dissolving process for processing a transfer mixture into a form solution are to be described, which primarily makes it possible to overcome the disadvantages of the dry-dissolving process of the prior art, in particular the Increasing product quality and being able to increase capacities at the same time.

solution of the task

The features according to claims 1 and 13 lead to the solution of the problem.

Advantageous configurations are described in the dependent claims.

The subject matter of the present invention is a method and a system which, among other things, shows a mixing kneader for processing a transfer mixture as the last process stage of an at least two-stage process according to the dry dissolving process in a mixing kneader, with all the facts mentioned in the context of the task being taken into account. A high-shear unit is connected upstream of the mixing kneader.

The mixing kneader is designed in such a way that, compared to extruders, it generally has a large volume and allows longer residence times relative to residence times, and has a lower shearing effect relative to a high-shear unit.

Compared to the mixing kneader, the high-shear unit is characterized by a high shearing action and, compared to the mixing kneader, shorter residence times.

The mixing, kneading and shearing effect on a product in a process element, such as in particular a high-shear unit or a mixing kneader, essentially results from the interaction of the product with the elements in the process element that move relative to one another as a result of the rotation of the shaft (also known as mixing-kneading called interaction) and depends on the process and product volume (degree of filling), the design of the geometry and surfaces of the elements in the process space, the rotational speed of at least one shaft, and the viscosity and the residence time of the product to be processed in the process organ.

In the context of the invention, the product is defined as any initial, intermediate or final state from the starting material to the solution.

The shearing action is the shear multiplied by the processing time during which the shearing occurs.

The highest possible shearing is achieved on the one hand by the largest possible shearing surface, which can extend both in the direction in which the two shearing surfaces move relative to one another and orthogonally thereto. In addition, a shearing gap that is as narrow as possible also increases the shearing, namely the distance between the two shearing surfaces measured orthogonally to the shearing surface. In addition, the highest possible relative speed of the two shearing surfaces also increases the shearing, as does the highest possible filling level of product in the shearing gap.

A high-shear unit is a processing element with at least one shaft, the speed of which is - typically significantly - higher than that of kneader shafts of mixing kneaders, and/or the clearances of the mixing or kneading elements in relation to the wall surfaces and the mixing or kneading elements of a second shaft are significantly smaller and/or or whose shearing area to process volume ratio is significantly greater than in mixing kneaders and/or whose exposure time - typically due to batchwise instead of continuous operation - is significantly longer than in mixing kneaders, so that the heavy impact resulting from the combination of these properties is significantly greater than that of mixing kneaders of comparable process volume. In terms of apparatus, the high shearing effect can be achieved with a high-speed high-shear unit, which is characterized by a small-volume process chamber compared to mixing kneaders with at least one shaft that rotates quickly compared to mixing kneaders with narrow gap dimensions compared to mixing kneaders and short residence times compared to mixing kneaders and like mixing kneaders continuous operation. A typical example of a high speed high shear unit is an extruder or a high speed mixer. High-speed mixers differ from extruders in that they achieve the high shearing effect through comparatively higher speeds at lower torques, such as an Ystral ^® mixer or solid-liquid mixer from IKA ^® or a so-called KRIMA ^® disperser from Cellwood Machinery ^® . Compared to extruders, high-speed mixers are distinguished in particular by higher speeds, shorter residence times and lower torques of the shaft. In terms of apparatus, a high shearing effect can also be achieved by a large-volume high-shear unit, which is achieved by shearing surfaces that are large compared to mixing kneaders with gap dimensions that are preferably adjustable compared to mixing kneaders in a large-volume process chamber with at least one shaft rotating at high speed similar to a kneader shaft with freely selectable lengths Distinguish residence times and, unlike industrially operated mixing kneaders, by operating exclusively in batches. A typical example of a large-volume high-shear unit is a Z-kneader or Sigmablade mixer. Typical residence times for high-speed mixers are a maximum of 10 seconds, for extruders a maximum of 5 minutes and for high-volume high-shear units at least 15 minutes.

Placing the mixing kneader after the high-shear unit in the dry dissolving process and in the system allows the technical advantages of the mixing kneader to be used specifically for the dry dissolving process. In this context, it has proven to be advantageous if the high-shear unit is installed upstream of the mixing kneader. This is because, according to the invention, the high-shear unit supplements the mode of action of the mixing kneader by using the mixing capability of the high-shear unit and compensating for the disadvantage of a high-shear unit, namely the limited residence time of the high-speed high-shear unit or the lack of continuous operation of the large-volume high-shear unit.

The mixture of water, cellulose and a functional medium introduced in the dry dissolving process is regarded as the starting material within the scope of the invention. The transfer mixture corresponds to an intermediate step in which the starting material has been mixed in the high-shear unit and has not yet been processed into a form solution. In the context of the invention, a form solution refers to what is subsequently essentially suitable for shaping, such as in particular for spinning—also called extrusion.

The product volume corresponds to the volume that a processing element such as the mixing kneader according to the invention contains of the product to be processed. The ratio of product volume and process volume corresponds to the degree of filling.

The process volume corresponds to the volume in which a process element, such as the mixing kneader according to the invention, can hold the product to be processed. In the case of rotor-stator systems, this means in particular the agitated volume, so that unagitated volumes in, for example, connection nozzles are not to be considered as process volumes. It can be determined, for example, by «measuring» by completely filling the process chamber with a liquid whose volume is measured.

The two-dimensional (radial and axial) combing typical of mixing kneading represents a fundamentally different mixing kneading principle than in extruders, in which the mixing effect is typically only radial and with zones arranged at an axial distance from one another by mixing kneading blocks or by forced partial reflux and always comparatively very small-scale.

Because mixing kneaders are typically operated with a partial filling level, the feed stream and typically also the throughput of the discharge element can be selected essentially separately (in the sense of being independent of the speed of the kneader shaft) and because the product in mixing kneaders in a mixing-kneading interaction in In contrast to extruders, an axial conveyance can simply be avoided, with mixing kneaders the speed of the kneader shaft is only one of the factors influencing the throughput, which is coordinated with the actual or desired degree of filling or its axial distribution, the input flow, the output flow and the throughput. and compared to extruders, no influencing factor that builds up significant axial pressure. The mixing kneading action of mixing kneaders for a given machine and a given product also depends not only on the speed, but in particular also on the freely selectable setting variables of residence time and degree of filling.

With extruders, on the other hand, not only the mixing kneading effect but also the product conveyance essentially depends directly on the speed (forced conveyance), which means that the product conveyance is fast due to the high speeds required for high mixing and the residence time is short compared to mixing kneaders is. This results in particular from the property typical of extruders that the dwell time for a given extruder cannot be set independently of the speed. The mixing kneading action of extruders is therefore only achieved through the mutual engagement of the rotating shafts and axially spaced mixing kneading zones in interaction with the product. For a given machine with a given shaft configuration and a given product (with the resultant given product viscosity, which in turn is also dependent on temperature and speed or shear), it essentially only depends on the speed. And to achieve a certain residence time, extruders must have a longer shaft length L than mixing kneaders: The length/diameter ratio L/D of extruders is significantly greater than that of mixing kneaders and is typically 24 to 48 compared to 3 to 6 for typical mixing kneaders.

Traditionally, both mixing kneaders and extruders aim to process masses with such a high viscosity that they can no longer be stirred or mixed by a classic, typically cantilevered vertical stirring element in a large-volume container, and that the mechanical energy input is process-determining .

Dry dissolving processes include all processes that are used to produce a form solution from a starting material and do not contain any or no significant water removal (in particular water evaporation). The starting material typically has a 0% to 10% higher water content than is necessary for dissolving the cellulose. Significant water removal means that this is design determinant in the sense that a facility must be designed larger or supplemented with additional product processing apparatus or machinery (apart from a facility for condensing from out vapor streams resulting from evaporation). Dry dissolution methods include both dry direct dissolution methods with NMMO or an IL as the form solution and protolyte dissolution methods with a form solution based on a protolyte (acid or base) such as sodium hydroxide or phosphoric acid.

A final process stage is defined by the fact that a mold solution is produced from the transfer mixture in this final process stage. Independent of this and not to be named as a process stage within the scope of the invention, a discharge element and other interposed pumps, filters and buffer containers or the like, which are still necessary up to spinning/shaping and typically transport or filtration, degassing or pressure and mass flow stability of the form solution.

The processing of the transfer mixture into a mold solution consists of a dissolving process, also known as dissolving. This requires a certain amount of time for a certain mixing and kneading intensity (determined in particular by the specific design of the kneader mixer and the rotational speed of the kneader shaft) for a specific product (determined in particular by the type and proportion of cellulose and functional medium). Ultimately, this part of the process results in a stream of mold solution—which can then be subjected to shaping. Since the design for a certain mixing and kneading intensity and a certain product is time-determined, the process volume of the mixing kneader is essentially directly proportional to the capacity of the form solution flow (also called form solution flow capacity). This so-called volume scale-up is in contrast to the surface scale-up of a mixing kneader known to those skilled in the art for the production of a mold solution, the process of which involves the evaporation of water is shaped, for which the mixing kneader must have sufficient heating surfaces, which determines the size. Conversely, with a surface scale-up, the mixing kneader could be smaller if it had to evaporate less or no water.

This also shows the advantage that increasing the mixing and kneading intensity in the extruder is always associated with a reduction in the residence time of the product due to the forced conveyance of the product, while the mixing and kneading intensity can be increased in the mixing kneader, and the Dwell time can be freely selected (i.e. also increased or reduced) independently of this. The mixing kneader according to the invention is used to carry out the mixing and kneading of the product required to achieve a form solution after it has exited as a transfer mixture from a high-shear unit as the preceding process element. This makes it possible to use the high-shear unit to its strengths, namely for mixing two powders or powder in a liquid, and then to further treat the product in the mixing kneader according to the invention with mixing and kneading action, the shearing action of which on the product is much lower, than is typical with high-shear units, and thus in particular more time is available for loosening.

Due to the high shearing effect, the high-shear unit produces an advantageous initial state of the product, which is characterized at least by the fact that this has the necessary homogeneity as a transfer mixture for processing in the mixing kneader.

When using a high-speed high-shear unit as a high-shear unit, it is possible under typical process conditions to generate tenfold to a hundredfold power input per process volume (specific mechanical power input) compared to mixing kneaders. The much higher specific mechanical power input creates close contact between the components of the starting material in the high-speed high-shear unit, thereby creating an initial state that is advantageous for the subsequent dissolving process. This advantageous initial state of the product is characterized by the fact that, as a transfer mixture for processing in the mixing kneader, it can also contain certain proportions of dissolved cellulose in addition to the necessary homogeneity. Due to the continuous mode of operation, these are further processed directly in the mixing kneader to form a form solution before the product can be decomposed.

When using a large-volume high-shear unit as a high-shear unit, it is possible to functionally combine the high shearing action, in particular due to large shearing surfaces or long shearing gaps in combination with long residence times, which can easily be achieved with batchwise operation.

Due to the batchwise mode of operation, when using a large-volume high-shear unit for the production of the transfer mixture, it is preferably avoided that the transfer mixture already contains parts of dissolved cellulose or dissolved pulp, since such direct further processing in the mixing kneader is not ensured due to the batchwise mode of operation, which partial decomposition and inconsistent product quality. This also means that the transfer mixture, which is produced by a large volume high shear unit, preferably has a certain storage stability.

Storage stability means that the product can be stored without changing its composition and chemical and physical properties to such an extent that it is no longer suitable for further processing without an unacceptable reduction in product quality.

It is irrelevant whether the at least one high-shear unit is connected to the mixing kneader according to the invention directly or via an intermediate transfer element such as a gear pump, and whether it is operated intermittently or continuously. In addition, it is also conceivable that the high-shear unit is not connected to the mixing kneader according to the invention and the transfer mixture is temporarily stored in a container and is fed to the mixing kneader according to the invention at different times or in different places.

Even if the mixing kneader according to the invention functions independently of whether the high-shear unit is operated intermittently or continuously, the functioning of the mixing kneader according to the invention is different. In the case of a continuously operated high-shear unit, the object of the mixing kneader according to the invention is to extend the mixing and kneading time of the product until the dissolving time is reached, since the residence time available in a continuously operated high-shear unit is typically below the required dissolving time. In the mixing kneader according to the invention, the product is mixed and kneaded so gently in comparison to the high-shear unit because of the lower shearing effect mentioned that the product does not overheat, or only slightly so.

In the case of a batch-operated high-shear unit, such as typically a Z-kneader, of which the transfer mixture at the end of each paragraph (i.e. in batches) is preferably discharged by a continuous discharge device and fed to the mixing kneader according to the invention, the mixing kneader according to the invention, in addition to additional kneading and mixing to a homogeneous form solution, also ensures in particular a continuous flow of form solution, with which the shaping or shaping process, which also takes place continuously and is very sensitive to fluctuations, .Spinning process is fed. In addition to the continuity of the mass flow, the sensitivity to fluctuations relates in particular to the continuity of the quality of the form solution, in particular the homogeneity, viscosity and composition as well as the influence of these properties through degradation processes of the cellulose and the functional medium. Batch production of the form solution is not suitable on an industrial scale because of the sensitivity to fluctuations in the shaping or spinning process. In addition, a process chamber that only discharges intermittently does not have any self-cleaning through the product flowing in, as in continuous operation, which leads to time-consuming cleaning and product loss, especially since mold solutions are typically much more sticky than the product before it was dissolved.

A transfer element includes conveyor elements, containers or combinations of these elements. Conveying elements are known to the person skilled in the art and in particular include non-compressing designs. The container can be stirred or tumbled, in particular to counteract segregation.

In addition, there is the possibility of reducing the proportion of water remaining in the transfer mixture to the proportion required for the dissolving process and the form solution during the processing of the transfer mixture into a form solution. In addition to the dissolving task of the mixing kneader according to the invention, this evaporation task is firstly optional and secondly subordinate to it and does not determine its size. For this evaporation, in addition to the mechanical energy input resulting from viscosity in combination with a process volume and with at least one rotating kneader shaft, the mixing kneader can also require heating surfaces for thermal energy input, which are arranged in the mixing kneader.

Thus, in the context of this invention, the capacity of the mixing kneader means on the one hand an evaporation capacity and on the other hand a form solution flow capacity.

The mixing kneader according to the invention uses the hitherto unknown finding in the direct dissolving process that mixing kneaders below a certain water content in the transfer mixture can no longer be designed with a smaller process volume without the form solution flow capacity having to be reduced. This is due to the fact that from this water content onwards, the process volume required for the dissolving time must be applied - the form solution flow capacity is therefore decisive for the design. Conversely, this means that with the direct dissolving process, with increasing water content in the transfer mixture, the mixer kneader must be built larger than would be required for the mold solution flow capacity from a certain water content, because the evaporation capacity requires a larger design in order to arrange the corresponding heating surfaces in the mixer kneader.

The mixing kneader according to the invention therefore consists of a mixing kneader whose size only meets the requirements of a mold solution flow capacity.

The optional evaporation capacity of the preceding process element for producing the transfer mixture by evaporating essentially water (referred to below as main evaporation) is adjusted accordingly and results from the heating surfaces and the mechanical energy input capacity of the mixing kneader, which is dependent on viscosity and kneader shaft speed. It is also provided within the scope of the invention that the transfer mixture is produced from a starting material in a plurality of preceding process elements. These preceding processing elements within the scope of this invention can be connected in series or in parallel and relate to the high-shear unit.

The mixing kneader according to the invention for processing the transfer mixture into a form solution according to the dry dissolving process is a mixing kneader with a feed, a housing, at least one kneader shaft rotating in the housing and a discharge, the feed containing a product in the form of the transfer mixture consisting essentially of cellulose, water and the Brings the functional medium into the housing, with the transfer mixture being processed with stirring, so that the form solution is created, with the form solution flowing onto the discharge with a feed stream, and then the subsequent process element, such as the discharge screw, the transfer pump, a filter station, the buffer container, the spinning pump and fed to the spinneret.

Here, as an embodiment, the mechanical and thermal energy input can also be used to evaporate part of the water until a form solution is present. This is the case when the water content in the starting material rial is higher than is necessary for a mold solution.

A further embodiment is characterized in that an excess water content in the starting material is specifically selected in such a way that the mechanical energy introduced in the mixing kneader by the mixing and kneading effect during a specific residence time is used firstly for the intended product heating and secondly for the evaporation of the water content, so that preferably overheating but at least substantial overheating of the product is avoided. This also has the above-mentioned advantage of pre-swelling compared to the embodiment variants that do not require any evaporation at all and relieves the recovery of the functional medium from the spinning bath or shaping bath. A preferred embodiment consists in that a water content in the starting material or in the transfer mixture that is excess compared to a form solution is specifically selected such that the energy required for its evaporation comes from the mechanical energy input occurring through dissipation and no thermal energy input via heated surfaces and preferably also no thermal energy dissipation is required to avoid overheating or significant overheating via cooled surfaces. The advantage of this embodiment lies on the one hand in the higher water content in the functional medium, which reduces its machine production costs or functional agent recovery costs, and on the other hand in the shorter production of the transfer mixture, because the water promotes the penetration of cellulose and functional medium. The avoidance of heated or cooled surfaces relates in particular to the disks attached to the kneader shafts, but preferably also to the shafts and/or the inner housing surfaces. In terms of apparatus, the former means that the discs can only be designed without heating cavities or as pure supports with a minimized side surface, which relieves the kneader shaft and simplifies its production. In addition, this means an even load on the keter shaft, which, among other things, generally leads to a longer service life for the mixing kneader.

Practice with the types of mixing kneaders previously used by the inventors for the mold release process according to the direct dissolution process with NMMO as the functional medium has shown that the residence time in the mixing kneader is in a range between 2 and 15 minutes, with the residence time being largely determined by the dissolving time of the cellulose and the exact dissolving time not only depends on the treatment in the high-shear unit but also, for example, on the cellulose concentration, the cellulose type, its pre-treatment and the type of functional medium and can also go beyond these ranges. With a mixing kneader volume of 2500 L, an industrial production capacity of, for example, 6.4 kilotons per year of cellulose (or cellulose fibers in the case of further processing) can be achieved. There is no need to heat the discs of the kneader shaft or to divide the process into several temperature zones, provided the product is introduced into the mixing kneader with a concentration corresponding to a 1.3 hydrate. This corresponds to a residence time of about 12 minutes, which cannot be achieved in the prior art for a dry process using an extruder.

Especially when using NMMO and IL as a functional medium, the transfer mixture is characterized by the fact that the state of the product has not yet reached that of a mold solution. This can be characterized by the fact that the thermo-mechanical treatment of the starting material in the preceding process stage is insufficient, in the sense that the dissolving time provided in the high-shear unit is too short for the mixing and kneading action present, or that the water content is insufficient or lack of evaporation is still too high.

The need to start the dissolving process in the mixing kneader within the scope of the invention with a transfer mixture lies in the insufficient ability of mixing kneaders, due to low shear, to sufficiently mix liquids into a powdery solid and to avoid or crush cellulose agglomerates to the extent that they are in the mixing kneader can be detached from the functional medium. Thus, the production of a transfer mixture from a starting material mainly consists of mechanical processing, in particular mixing and shearing, so that the transfer mixture differs from the starting material in particular by its higher homogeneity, while the composition remains essentially unchanged and the dissolving process is not or only partly used. In this context, essentially unchanged refers in particular to the water content of the product, which can be reduced by evaporation or evaporation as a result of the input of, in particular, dissipation energy in the high-shear unit during the processing of the starting material to form the transfer mixture.

The transfer mixture differs from the form solution in that it corresponds to the product in a state before it is converted into a formable or spinnable solution, ie the form solution. A malleable or spinnable solution is present when all the essential cellulose cal components of the starting material have dissolved. In this context, essential means such a low proportion of undissolved components that the so-called filter service life reaches an economically acceptable level.

Filter life refers to filters that are typically used after the forming solution preparation stage and before the forming/spinning stage. The filter service life corresponds to the length of time or the period of use until a filter has to be replaced because the pressure drop across the filter becomes too high, which increases due to the accumulation of components undesirable for further processing. These components can represent, for example, undissolved cellulosic fibers as well as non-cellulosic contaminants. The concrete choice of a filter service life is therefore subject to macroeconomic costs and quality-optimizing aspects.

The transfer mixture also differs from the starting material in that the transfer mixture has a higher degree of homogeneity due to thermo-mechanical or exclusively mixing treatment in the preceding process element and is still present as a suspension or as a partial solution. In the embodiment with a water content in the starting material that is higher than is necessary for a mold solution, the mixing kneader according to the invention for processing the transfer mixture is, as mentioned, characterized in that the product in the mixing kneader has a water content that corresponds to the water content that occurs during the dissolving time must and can still be evaporated without increasing the process volume of the mixing kneader, which has the advantage that the mixing kneader can be built as small as possible and ideally not all surfaces have to be heated.

This leads to optimal use of the mixing kneader, since its strength is kneading with a low mechanical power input in relation to the process volume compared to high-speed high-shear units, as well as a freely selectable residence time in continuous operation for the complete dissolution of the cellulose. This is also particularly advantageous since the strength of the high-shear unit, namely mixing and kneading with high volume-related mechanical power input with comparatively short residence times of typically 0.2 seconds to 2 minutes, is used to process the starting material into a transfer mixture.

When using large-volume high-shear units as the process stage upstream of the mixing kneader according to the invention, the optimal use of the mixing kneader is in continuous operation with essentially freely selectable residence time and not only mechanical but typically also thermal energy input for the complete dissolving of the cellulose. The advantage of the continuous mode of operation mentioned lies in the avoidance of time-consuming cleaning cycles and the minimization of quality fluctuations, which are very relevant for the mold solution and molding quality. This is also particularly advantageous since the strength of the large-volume high-shear unit, namely the simple metering and mixing and kneading of large quantities of powders in a liquid for processing the starting material into a transfer mixture because of the batchwise operation, is used at the same time.

The mechanical power input related to the process volume refers to a typical fill level. While this is typically up to 100% for extruders and high-speed mixers, it is typically up to approx. 50% to 70% for dry processes for mixing kneaders and Z-kneaders or Sigmablade mixers.

Conversely, since evaporation is not a strength of high-shear aggregates, a preceding process element used to its strengths means that the initial concentration of water in the transfer mixture essentially corresponds to that in the starting material. "Essentially" refers to the proper operation with optimal setting of the high-shear unit with the exception of leaks, evaporation or sampling.

The process volume of the mixing kneader results for a specific filling level from the required form solution flow capacity, which results from the dissolving time still required after the thermo-mechanical pretreatment in the preceding high-shear unit and the residence time in any container. This in turn depends on various factors, such as the cellulose concentration, the particle size of the cellulose, the state of aggregation of the functional medium, the cellulose type, its pretreatment, the functional medium and the kneading and mixing intensity of the mixing kneader. The functional medium can be a liquid, but also, for example, granules or a powder in a solid aggregate state. For example, the person skilled in the art knows that cellulose of different origins requires different dissolving times, such as different types of wood, other plants such as cotton or different degrees of polymerization (so-called DP) of the cellulose. It is also known to those skilled in the art that in under different functional media, different dissolving speeds and consequently dissolving times can occur.

The functional medium is understood to be independent of its aggregate state in the starting material. For example, NMMO is also referred to as a functional medium if it is mixed in solid form as a monohydrate with a cellulose powder at room temperature and only becomes liquid during further processing.

As an additional optimized process variant, the speed of the high-shear unit is set according to the invention in such a way that no mechanical power is introduced into the product, which must be dissipated again by contact cooling in the mixing kneader according to the invention for a safe and energy-efficient process. This simplifies the process control and increases the process reliability of the method, especially when using NMMO as the functional medium. In addition, the process variant described has the advantage of minimal thermal stress on the mixture in the mixing kneader, which is beneficial to the product quality of the molding solution. In terms of apparatus, this means that the kneader shaft does not have to have several heating/cooling zones. In the case of the present invention, the shaft structures can preferably be designed without heating cavities and the input of mechanical energy introduced by kneading is sufficient to produce a molding solution from the transfer mixture. Ideally, the preceding processing element in the form of a high-shear unit during the production of the transfer mixture according to the invention already processes the product to such an extent that the mixing kneader according to the invention does not have to remove any water from the transfer mixture, and the dissipation energy only leads to heating of the product without overheating it or at least without it not to be overheated significantly, so that no condensation of water evaporated in the mixing kneader is necessary, and it is charged with a starting material whose water content already corresponds to that of a molding solution.

$${\text{maximal x}}_{\text{H2O}}=-\mathrm{0,2864}{\text{ x}}^{\text{2}}{}_{\text{Cell}}-\mathrm{0,6786}{\text{ x}}_{\text{Cell}}+\mathrm{0,2288.}$$

In the case of NMMO as the functional medium, a preferred embodiment that increases process reliability is characterized in that the proportion of water in the transfer mixture is so large that the proportion of water in the high-shear unit is sufficiently high that the risk of autocatalytic decomposition of the NMMO is low. This is the case provided that the water content of the transfer mixture is within the following general range: $${\text{minimum x}}_{\text{H2O}}=-0.4525{\text{x}}_{\text{Cell}}+0.1465$$

$${\text{maximum x}}_{\text{H2O}}=-0.2864{\text{x}}^{\text{2}}{}_{\text{Cell}}-0.6786{\text{x}}_{\text{Cell}}+\mathrm{0.2288.}$$

$${\text{minimal x}}_{\text{H2O}}=-\mathrm{0,00022}{\text{ x}}^{\text{2}}{}_{\text{Cell}}-\mathrm{0,5317}{\text{ x}}_{\text{Cell}}+\mathrm{0,1800}$$

The water content of the transfer mixture is preferably in the following preferred range: $${\text{maximum x}}_{\text{H2O}}=0.2864{\text{x}}^{\text{2}}{}_{\text{Cell}}-0.6786{\text{x}}_{\text{Cell}}+0.2288$$

$${\text{minimum x}}_{\text{H2O}}=-0.00022{\text{x}}^{\text{2}}{}_{\text{Cell}}-0.5317{\text{x}}_{\text{Cell}}+0.1800$$

In these two equations for a general and preferred range of an NMMO transfer mixture, x _H2O describes the mass fraction of water in relation to the total mixture and x _Cell describes the corresponding fraction of cellulose. The energy input of the preceding process element is thus selected such that the process energy required for heating and optionally evaporating the mixture in the mixing kneader preferably results only from the mechanical output of the mixing kneader. The water contents given here relate to a range of cellulose contents and cellulose qualities (eg molar mass distribution) which are typical in the industry and are known to the person skilled in the art. For example, a cellulose content of 0.110 results in a minimum water content of 0.097 for the general transfer area.

This increases the maximum mold solution flow capacity per mixing kneader as the last process element in a multi-stage dry solution process and thus the maximum production capacity per production line overall.

According to the invention, a functional medium for the starting material is preferably and not exclusively an IL or NMMO or a protolyte, ie an acid or a base, such as, for example CA 3 020 820 A1 or WO 96/06207 A1 and the WO 96/06208 A1 described containing mixture added. The functional medium serves to dissolve the cellulose under the right conditions.

In the mentioned combination with a preceding process element for the production of a transfer mixture, a preferred embodiment of the mixing kneader is characterized in that it is designed for the processing of a transfer mixture, which is selected so that the viscosity of the transfer mixture is not only low enough that a significant Overheating in the high-shear unit is avoided, but also large enough that the mechanical energy input caused by friction in the mixing kneader is so high that the need for thermal energy input in the mixing kneader - supplementing the mechanical energy input - is so low that the structures of the kneader shaft do not must serve thermal heat exchange, but can be designed without heating cavity. A further preferred embodiment is characterized in that the mechanical energy input is selected by selecting the size and geometry of the mixing kneader, the rotational speed of the kneader shaft, the viscosity of the product to be processed and the residence time of the product in the mixing kneader so that the mixing kneader without thermal Exchange surfaces of the kneader shaft or the housing can be designed by equipping the kneader shaft without an inner tube or the housing of the mixing kneader without a jacket. This enables a significantly simpler, cheaper and faster construction of the kneader shaft and the housing.

In a preceding process step, the starting material is a mixture of cellulose, water and functional medium, the composition of which can vary greatly.

In the preceding process step, the starting material becomes a transfer mixture. This process step can preferably take place in one or more high-shear units as the preceding processing element or preceding processing elements.

In the transfer mixture according to the invention, the cellulose is present as a suspension or partially dissolved. In the case of water evaporation in the mixing kneader and NMMO as the functional medium, the minimum water content in the NMMO of the transfer mixture can be taken from the mathematical formula if the operating mode is designed for process reliability in the high-shear unit.

Common to all cases is the inventive concept of using the mixing kneader according to the invention for dry or semi-dry mold solution production. In this context, semi-dry means that although water has to be evaporated between the starting material and the form solution, this process task is not decisive for the design of the high-shear unit according to the invention and the mixing kneader according to the invention. This entails that the mixing kneader determines through the form solution flow capacity what the smallest possible size of the mixing kneader means for a specific form solution flow capacity or the maximum form solution flow capacity for a specific mixing kneader size.

In addition, all cases have in common the idea of using the strengths of the mixing kneader according to the invention to compensate for the deficits of high-shear units, which consists at least of the fact that the high-shear unit according to the invention is indeed suitable for mixing the components of the starting material to form a transfer mixture at a given capacity, but that it is not suitable for further processing this transfer mixture into a form solution, and that the mixing kneader is suitable for further processing the transfer mixture into a form solution and is not suitable for mixing the components of the starting material into a transfer mixture.

Due to its technical properties, such as a low input of mechanical energy and dissipation energy compared to a high-shear unit, the mixing kneader is particularly suitable for processing the product by mixing and kneading from a transfer mixture to a form solution without the product overheating or not significantly is overheated. The high-shear unit, on the other hand, has a higher input of mechanical energy and dissipation energy and is therefore suitable for processing the starting material into the transfer mixture.

The mixing kneaders according to the invention are distinguished from extruders by a residence time that can be freely selected largely independently of the speed of the kneader shaft and thus independently of the mixing kneading intensity. This is supported by the comparably lower input of dissipation energy per process volume in the mixing kneader and consequently a lower heating of the product - which is significant because of the risk of overheating. The mixing kneader therefore uses the intensive product contact in extruders when mixing two powders or one powder into a liquid and compensates for the limited residence time of extruders.

Compared to Z-kneaders or Sigmablade mixers, the mixing kneader according to the invention is characterized in particular by its continuous mode of operation, which is advantageous for a necessarily low-fluctuation, homogeneous mold solution flow and uses the possibility of Z-kneaders to meter powder into a liquid easily and in large quantities and with intensive product contact to mix and knead.

The mixing kneader according to the invention is distinguished from high-speed mixers whose residence time is less than 1 minute, preferably less than 30 seconds and preferably in particular less than 10 seconds, in particular by its freely selectable residence time and the high torque possibilities of the kneader shaft, and uses the ability of high-speed mixers Powder can be dosed easily and in large quantities into a liquid and mixed with a high specific power input. Compared to all other high-shear units and mixing kneaders, high-speed mixers are usually characterized by applications with low product viscosity cosmetics, which is why they are not state of the art for shape solution processes. Its use as a preceding process element of the mixing kneader according to the invention in the dry dissolving process is based on the inventive idea that the mixing in takes place so quickly that there is also no significant increase in the viscosity of the product, because the residence time is too short for this, so that the dissolving process does not start or does not get far can develop to increase the viscosity of the product so much that it exceeds the torque limit of the high speed mixer.

The formulas for describing the transfer mixture with NMMO as the functional medium refer to the production of a transfer mixture under thermo-mechanical conditions that allow low-risk operation of a high-shear unit and have proven themselves in practice. Due to the explained influences on the rate of dissolution of the cellulose, however, it is possible that the formula predicts a spinnable solution, while in practice, despite low water content, there is still a transfer mixture according to the invention with undissolved cellulose components, since a special thermo-mechanical treatment was chosen, such as for example very short times of the product between feed and outlet. Due to the associated lower water content in the transfer mixture, such thermo-mechanical treatments are associated with an increased process risk due to significant overheating and explosive decomposition.

According to the invention, this can also mean that the starting material, even if the composition is within the concentration range, is fed to the preceding process step, which describes the general transfer mixture. A transfer mixture, which is characterized by a partial dissolution of the cellulose, is usually only created through the process-specific thermo-mechanical treatment of the starting material (increased temperature and shearing effect).

Compared to processes with a significant amount of water to be evaporated in the preceding process element for the production of a transfer mixture, which typically use thermal energy input via hot surfaces for evaporation, high-shear units and mixing kneaders can, in particular thanks to good mixing properties and effective mechanical energy input via the rotating shaft, reduce the speed and thus also adjust the energy input quickly and also quickly withdraw it again. For this reason and because of their high mixing intensity and consequently their low radial temperature gradient, high-shear units and mixing kneaders are suitable for controlling the temperature and, as a rule, cooling or heat dissipation and thus also overheating with great accuracy - and in the case of NMMO as a functional medium also reliably or to avoid significant overheating.

In another exemplary embodiment, the transfer mixture firstly passes through a transfer element or elements downstream of the high-shear unit or several high-shear units, before it is fed into the mixing kneader.

Thus, the increased energy efficiency and process reliability not only applies to the process step of producing the mold solution from the transfer mixture in the mixing kneader, but also in combination with a suitable upstream processing element for the entire conversion of a starting material into a mold solution.

The material properties using the formulas listed above to describe the general transfer range with NMMO as the functional medium result from the following investigations.

For the general transfer range shown above, the minimum water content x _H2O describes for the expert based on the US 4,196,282A the composition in which, after visual inspection, crystals of the NMMO could be observed for the first time in the cellulose-water-NMMO mixture. It thus delimits from the crystalline phase the mixtures capable of forming complete form solutions under appropriate thermo-mechanical treatment. The one in the US 4,196,282A Statements made in relation to NMMO as a functional medium are confirmed by results and observations from industrial applications and experiments by the inventors on a pilot plant scale. The formula for describing the maximum water content x _H2O of the general transfer area is based on results from industrial applications of the direct dissolving process and data collection from the inventors' test series on a pilot plant scale. It marks the upper limit of the transfer range, within which optimal utilization of the specific, process-relevant mixing kneader characteristics is guaranteed. The two formulas presented consequently enclose the range of the general transfer mixture.

In order to describe the material properties of the preferred transfer area, reference is made, among other things, to the minimum water content US 4,196,282A to refer. The formula combines insights from in the US 4,196,282A described n limit curves of the solution range with results from industrial applications of the direct solution process and data collection from test series by the inventors on a technical scale.

In the preferred range, the description of the maximum water content corresponds to that of the general transfer range.

In its general composition and also in its preferred composition, the transfer mixture is in a pre-dissolution state also due to the thermo-mechanical treatment and treatment duration selected in the high-shear unit. This also means that the mold release process takes place under optimal operating parameters of the high-shear unit and the comparatively difficult material conditions of the mold release are avoided if, for example, overdrying or decomposition occurs in the high-shear unit due to excessive shearing. These difficult material states do not lead to problematic process states in the subsequent mixing kneader according to the invention, because this is characterized by a lower shearing action and a residence time that is independent of the mixing and kneading action.

With the formula that describes the general composition, and provided that NMMO is used as the functional medium, it is advantageous to apply the transfer mixture that contains just enough water to allow further processing to the solution in the downstream process element in a relatively short time Process time can take place and on the other hand crystallization of the solvent is prevented.

In the formula describing the preferred composition of the transfer mixture, the minimum proportion of water is further from the crystal phase compared to the definition of the general transfer mixture. In this way, the processing of the transfer mixture into a form solution in the mixing kneader according to the invention can be realized in a short process time and at the same time the risk of overdrying of the material can be reduced.

In both cases of the formula, however, the transfer mixture is removed from a moldable or spinnable solution after a processing time of two to several minutes, during which the product is homogenized in the mixing kneader and any residual water is evaporated.

The product and thus also the starting material essentially contain cellulose, water and a functional medium. In addition, the product contains other chemicals such as stabilizers, etc., which need not be listed in detail within the scope of the invention, since they are known to the person skilled in the art and require adaptation for each individual case of use.

The person skilled in the art is also aware of methods for producing a form solution from cellulose according to a dissolving method, in which the functional media essentially consist of a protolyte such as, for example, in particular a phosphoric acid or a sodium hydroxide solution, and in which typically no evaporation of water takes place, but dissolving in particular at least partially must take place at or below freezing point and mold release occurs through a combination of mixing and shearing over a period of dwell time. These dissolving processes (also called cold processes) are also characterized in the prior art by a limited capacity of the form solution flow when using a high-shear unit, namely when using an extruder because of the limited residence time typical of extruders, or by limited cooling capacity, namely when Use of a continuous mixer due to the limited cooling surfaces due to the shafts and shaft washers that cannot be heated or cooled.

In one exemplary embodiment, the high-shear unit consists of at least two large-volume high-shear units, such as in the form of Z-kneaders, ie a first Z-kneader and a further Z-kneader, which are connected one behind the other or next to the mixing kneader. The Z kneaders have the advantage that the starting material is processed into the transfer mixture independently of the mixing kneader and is only fed to the mixing kneader when this is required or when there is a corresponding time window. When using several Z kneaders arranged side by side, for example, when discharging the transfer mixture from the first Z kneader into the mixing kneader, the further Z kneader can independently produce a transfer mixture from the starting material, and as soon as the first Z kneader is discharged, the further Z kneaders are fed to the mixing kneader for unloading. This process can take place alternately.

A further embodiment consists in producing the transfer mixture batchwise in a first Z-kneader, which is fed batchwise via a discharge screw into a second Z-kneader whose capacity is selected such that this level fluctuations resulting from batchwise discharge from the first Z-kneader of the second Z kneader and continue the subsequent mixing kneader Lich can be fed via a discharge screw. Instead of the second Z-kneader, a mixing container equipped with a discharge screw is also conceivable.

The mixing kneader according to the invention and the associated methods according to the invention in this invention relate to dry dissolving methods which differ between a direct dissolving method without evaporation of water, a direct dissolving method with evaporation of water and a protolyte dissolving method.

Provision can also be made for the transfer mixture to be produced from the starting material as a premix (also called premix) in a preceding process unit, and for this premix then to be brought into the high-shear unit as stirred starting material.

The parameters of the high-shear unit are also chosen in such a way that the composition of the transfer mixture and the composition of the starting material are essentially identical.

It can also be provided that the kneader shaft of the mixing kneader rotates and wipes the product over heated and/or cooled inner surfaces of the mixing kneader. Furthermore, it can also be provided that shaft structures of the kneader shaft of the mixing kneader are at least partially designed without heating cavities, for example in axial sections of the kneader shaft.

Furthermore, the composition of the transfer mixture can be identical to the composition of the starting material, and the water content in the starting material can be selected in such a way that so much water in the transfer mixture evaporates in the mixing kneader through the mixing-kneading interaction and through heated surfaces that the resulting evaporative cooling Mold release occurs without significantly overheating the product.

Evaporative cooling for the purpose of avoiding overheating or substantial overheating of the product can also be achieved or increased by adding water (in the context of this invention also called evaporative cooling water) directly to the mixing kneader. This is heated to its boiling temperature on the surface of the product, so that it vaporizes immediately without being mixed into the product significantly and consequently without significantly increasing the water content of the product. This removes heat from the product and thus cools it.

The energy supply or energy dissipation of the thermally heatable or coolable inner surfaces, also called thermal exchange surfaces, of the process space usually takes place via a heating medium. Typical heating media are heat carriers such as water, steam or other, mostly synthetic liquids, which flow through the thermal exchange surfaces of the mixing kneader and possibly an associated dome, or coils built into thermal exchange surfaces, through which electric current flows and which are thereby heated, around the process chamber-side surfaces of the mixing kneader to provide energy for heating or cooling.

Evaporative cooling water is characterized in that it is added directly to the mixing kneader via a separate feed and is not already contained in the starting material and does not enter the mixing kneader as part of the transfer mixture. Typically, the supply takes place via a controllable valve, so that the amount of water per unit of time is specifically tailored to the evaporative cooling to be achieved. The temperature of the evaporative cooling water immediately before it enters the processing space of the mixing kneader and the gas pressure in the processing space of the mixing kneader are selected in such a way that the temperature of the evaporating cooling water is below the boiling point of water in the processing space of the mixing kneader, so that as little water as possible can escape through a Flash known to those skilled in the art evaporates and as much water as possible reaches the surface of the product.

Evaporative cooling can also be achieved by evaporating a liquid (also known as an evaporative cooling medium) other than water. The evaporation cooling medium can be added to the high-shear unit together with the starting material or added directly to the process space of the mixing kneader instead of the evaporation cooling water. Evaporative cooling can also take place by partially evaporating the functional medium, with the evaporating portion of the functional medium also being referred to as the evaporative cooling medium.

Cooling of the product in order to avoid overheating or significant overheating of the product can also be achieved or increased by wiping the product over the at least partially cooled inner surfaces of the mixing kneader.

character list

• 1 schematisch eine Anlage mit einem Mischkneter 6 ohne Verdampfung;
• 2 schematisch eine Anlage mit dem Mischkneter 6 mit Verdampfung;
• 3 schematisch eine Anlage mit einem Hochdrehzahl-Hochscheraggregat 5 und dem Mischkneter 6;
• 4 schematisch eine Anlage mit zwei Grossvolumen-Hochscheraggregaten 8 und dem Mischkneter 6;
• 5 schematisch ein weiteres Ausführungsbeispiel einer erfindungsgemässen Anlage;
• 6 ein erstes Schaubild über die bevorzugten Materialeigenschaften eines Transfergemisches;
• 7 ein zweites Schaubild über die allgemeinen Materialeigenschaften des Transfergemisches.

Further advantages, features and details of the invention result from the following Description of preferred embodiments and based on the drawings; these show in:

• 1 schematically a system with a mixing kneader 6 without evaporation;
• 2 schematically a system with the mixing kneader 6 with evaporation;
• 3 schematically a system with a high-speed high-shear unit 5 and the mixing kneader 6;
• 4 schematically a system with two large-volume high-shear units 8 and the mixing kneader 6;
• 5 schematically another embodiment of a system according to the invention;
• 6 a first diagram of the preferred material properties of a transfer mixture;
• 7 a second diagram of the general material properties of the transfer mixture.

example

First of all, it is pointed out that explanations and features of individual components should also apply to the other figures when they are explained for one figure. This applies in particular if the same reference numbers are used for the same components in different figures.

In the 1 a mixing kneader 6 is shown. The processing chamber 12 is located inside the mixing kneader 6. The processing chamber 12 is fed at one end by a continuous stream of transfer mixture 2 and at the other end a form solution or a form solution stream 3 leaves the mixing kneader 6. In the exemplary embodiment shown here, the mixing kneader 6 is operated without evaporation .

In the 2 a plant is shown in which the mixing kneader 6 is operated with evaporation. For this purpose, the mixing kneader 6 again has the continuous stream of transfer mixture 2 at one end and the form solution or the form solution stream 3 at the other end. In addition, the addition of evaporative cooling water 13 is shown schematically by an arrow. In addition, the processing space 12 or the mixing kneader 6 includes a dome 7 . A second arrow for a vapor flow 4 is again shown schematically pointing away from the dome 7 .

In the 3 the mixing kneader 6 is partially shown. It can also be seen how the continuous stream of transfer mixture 2 is delivered from a high-speed high-shear unit 5 to the mixing kneader 6 . It can also be seen how, schematically with a third arrow, a continuous addition of the components of a starting material 1 is introduced into the high-speed high-shear unit 5 .

In the 4 shows how two large-volume high-shear units 8 arranged next to one another are operated in alternation in batches and in each case give a batchwise flow of transfer mixture 11 into the mixing kneader 6 . For this purpose, the large-volume high-shear units 8 in turn each have a discharge element 9 that is operated intermittently. In addition, it can be seen how a fourth arrow in each case represents a batchwise addition of the components of the starting material 10 into the large-volume high-shear units 8 .

In the 5 a further exemplary embodiment of a system according to the invention is shown schematically. An additional operating part is shown there between the mixing kneader 6 and the large-volume high-shear unit 8 . This additional operating part is either a further large-volume high-shear unit or a stirred container 14. It is therefore possible to provide either the further large-volume high-shear unit or the stirred container 14. The requirement that the additional operating part has a continuously operated discharge element 15 and thus enables the continuous flow of transfer mixture 2 into the mixing kneader 6 is important when making the selection. The large-volume high-shear unit 8 has a discontinuous feeding of the further large-volume high-shear unit or the agitated container 14 in the form of the intermittent stream of transfer mixture 11 . Whereas the further high volume high shear aggregate or agitated vessel 14 feeds the mixing neter 6 with a continuous flow of transfer mixture 2 . With regard to the large-volume high-shear unit 8, the comments on one of the large-volume high-shear units 8 from FIG 4 .

Combinations of the systems from the 1 until 5 are to be regarded as co-published within the scope of the invention if the combination is not mutually exclusive.

In the 6 and 7 Graphs the equations for the general and preferred range of an NMMO transfer mixture.

$${\text{minimal x}}_{\text{H2O}}=-\mathrm{0,4525}{\text{ x}}_{\text{Cell}}+\mathrm{0,1465}$$

auf und zeigt damit einen grösseren Spielraum als die bevorzugte Zusammensetzung b, welche folgende Parameter von $${\text{maximal x}}_{\text{H2O}}=\mathrm{0,2864}{\text{ x}}^{\text{2}}{}_{\text{Cell}}-\mathrm{0,6786}{\text{ x}}_{\text{Cell}}+\mathrm{0,2288}$$

$${\text{minimal x}}_{\text{H2O}}=-\mathrm{0,00022}{\text{ x}}^{\text{2}}{}_{\text{Cell}}-\mathrm{0,5317}{\text{ x}}_{\text{Cell}}+\mathrm{0,1800}$$

aufweist.The general composition a has the following parameters $${\text{maximum x}}_{\text{H2O}}=0.2864{\text{x}}^{\text{2}}{}_{\text{Cell}}-0.6786{\text{x}}_{\text{Cell}}+0.2288$$

$${\text{minimum x}}_{\text{H2O}}=-0.4525{\text{x}}_{\text{Cell}}+0.1465$$

on and thus shows a greater scope than the preferred composition b, which has the following parameters of $${\text{maximum x}}_{\text{H2O}}=0.2864{\text{x}}^{\text{2}}{}_{\text{Cell}}-0.6786{\text{x}}_{\text{Cell}}+0.2288$$

$${\text{minimum x}}_{\text{H2O}}=-0.00022{\text{x}}^{\text{2}}{}_{\text{Cell}}-0.5317{\text{x}}_{\text{Cell}}+0.1800$$

having.

With a decreasing water content, the range of the solution L is first reached and with a further decrease in the water content, the crystallization K of the NMMO takes place.

Applying the equations for the general and preferred range of an NMMO transfer mixture, the example below shows the preparation of a molding solution with a cellulose content of 12 wt% using the direct dissolving process with NMMO as a working example and without significant evaporation of water during the process.

All of the following proportions refer to the total mass of the cellulose-NMMO-water mixture. A starting material with a cellulose content of approx. 12.0 wt% is produced from cellulose and NMMO monohydrate, resulting in an NMMO content of approx. 77.4 wt%.

This starting material is introduced into a high-shear unit at a flow rate of approx. 217 kg/h and processed there into a transfer mixture. In the example, the high-shear unit is operated at atmospheric pressure.

In the present example, the heating temperature of the high-shear unit is 90°C, so that overheating of the product is avoided. The mixture is transferred after thermo-mechanical treatment in the high-shear unit at a product temperature of approx. 105°C.

The ratio of water and NMMO has remained constant compared to the beginning of the process. The transfer mixture provided by the high-shear unit is then fed into the mixing kneader at a flow rate of approx. 217 kg/h.

There, the cellulose is completely dissolved and the mixture is homogenized by kneading and mixing, resulting in a complete mold solution. The residence time of the mixture in the mixing kneader is 8.5 minutes.

The process volume of the kneader is therefore approx. 70 L. The form solution leaves the mixing kneader at a flow rate of approx. 217 kg/h with a cellulose content of 12.0 wt%, an NMMO content of approx. 77.4 wt% and a temperature of approx. 107 °C.

Reference List

1

Continuous addition of the raw material components

2

Continuous flow of transfer mixture

3

Form solution or form solution stream

4

vapor flow

5

High-speed high-shear unit

6

mixing kneader

7

Dom

8th

Large-volume high-shear unit

9

Discharge unit operated intermittently

10

Gradual addition of the components of the starting material

11

Intermittent flow of transfer mixture

12

process room

13

evaporative cooling water

14

Large volume high shear unit or stirred tank

15

Continuously operated discharge device

A

general Composition of the transfer mixture

B

Preferred transfer mix composition

K

crystallization

L

Solution

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 0906455 A1 [0002]
• EP 1191038 A1 [0003]
• EP 1144455 B1 [0004]
• WO 2005/000945 A1 [0005]
• WO 2006/071101 A1 [0006]
• CH 674472 A5 [0012]
• DE 4118884 A1 [0012]
• WO 1994/006530 A1
• JP 6055267 B2 [0029]
• DE 1058188 A1 [0030]
• DE 3720325 A1 [0030]
• CA 3020820 A1 [0089]
• WO 9606207 A1 [0089]
• WO 9606208 A1 [0089]
• US4196282A[0106, 0107]

Claims (16)

Method for producing a form solution from a starting material made of cellulose, water and a functional medium according to the dry dissolving process, the starting material first being fed to a high-shear unit (5, 8), characterized in that a transfer mixture is produced from the starting material in the high-shear unit (5, 8). (A, B) is formed and the transfer mixture (A, B) is then fed to a mixing kneader (6) for dissolving. procedure after claim 1 , characterized in that the composition of the starting material and the composition of the transfer mixture (A, B) are essentially identical. Method according to one of the preceding claims, characterized in that a machine control the proportion of water, cellulose and functional medium in the composition of the product from the starting material to the mold solution, the product temperature, the viscosity of the product, the pressure or the temperature of the heating medium, the pressure in the process space (12), monitors and controls or regulates the rotational speed or the torque of a kneader shaft via sensors. Method according to one of the preceding claims, characterized in that at least part of an inner surface of the mixing kneader (6) is heated and/or cooled. Process according to one of the preceding claims, characterized in that the proportion of water in the transfer mixture (A, B) is greater than in the form solution and water is evaporated in the mixing kneader (6). procedure after claim 5 , characterized in that the energy required for the evaporation of the water occurs essentially or exclusively via dissipation as a result of the interaction of the kneading elements meshing with the product as a result of the rotation of the kneader shaft. procedure after claim 5 , characterized in that the energy required for the evaporation of the water occurs essentially or exclusively via dissipation as a result of the interaction of the kneading elements meshing with the product as a result of the rotation of the kneader shaft and through heated thermal exchange surfaces. Procedure according to one of Claims 5 until 7 , characterized in that the shaft structures of the kneader shaft are designed at least partially free of heating cavities. Procedure according to one of Claims 5 until 8th , characterized in that the evaporative cooling resulting from the evaporation of water on the product surface dissipates energy for cooling the product. Method according to one of the preceding claims, characterized in that evaporation cooling water (13) is added to the mixing kneader (6) and the evaporation cooling resulting from the evaporation of the evaporation cooling water (13) on the product surface dissipates energy for cooling the product. Procedure according to one of Claims 5 until 10 characterized in that for the purpose of evaporative cooling, instead of the water or in addition to the water, an evaporative cooling medium is evaporated, which is either fed to the high-shear unit (5, 8) together with the starting material or instead of the evaporative cooling water (13) directly into the process space (12) of the mixing kneader ( 6) is added. Method according to one of the preceding claims, characterized in that cooled thermal exchange surfaces dissipate energy for cooling the product. Plant for the production of a form solution from a starting material of cellulose, water and a functional medium according to the dry dissolving process, consisting of a mixing kneader (6) and a high-shear unit (5, 8), characterized in that the high-shear unit (5, 8) is connected to the mixing kneader (6 ) is connected directly or indirectly upstream. plant after Claim 13 , characterized in that the process volume of the mixing kneader (6) is designed for a capacity which corresponds exclusively to the mold solution flow capacity. plant after Claim 13 or 14 , characterized in that the high-shear unit (5, 8) consists of a first large-volume high-shear unit (8) and a further large-volume high-shear unit (8), which are arranged one behind the other or next to one another upstream of the mixing kneader (6). Plant after one of Claims 13 and 14 , characterized in that the high shearing unit is designed as a continuously operated high-speed high-shearing unit (5).

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