Thin-film evaporator for the production of a transfer mixture and use of the device

Abstract

Thin-film evaporator (D) for producing a transfer mixture from a starting material of cellulose, water and a functional liquid of N-methylmorpholine N-oxide or an ionic liquid according to the direct dissolution process, comprising a feed (1), a housing (4) and an outlet (2), wherein an evaporator shaft (5) arranged in the housing (4) rotates and wipes the starting material over the heated interior of the housing (4), whereby the starting material heats up and some of the water evaporates, so that the transfer mixture is formed, which flows to the outlet (2) with a feed stream. characterized by the fact that the flow capacity of the outlet (2) is greater than the supply flow, wherein the flow capacity is defined as the flow rate at full supply, wherein the full supply is defined as the fully utilized flow rate at the currently set setting parameters of the outlet or a transfer element, wherein the outlet (2) leads into a downstream transfer element, wherein the flow capacity of the transfer element is greater than the supply flow.

Description

Technical area

[0001] The invention relates to a thin-film evaporator for producing a transfer mixture according to the preamble of claim 1 and to a use of the device according to claim 7. State of the art

[0002] Such thin-film evaporators are already known and in use in a wide variety of forms and designs. For example, WO 96 / 33302 A1 discloses a system for producing cellulosic films, fibers, and other molded articles using the amine oxide process. Two mixing devices with two different pulpers are preferably used.With the aid of these mixing devices, the pulp is to be first defibrated or ground, wherein a pump pumps a first suspension of pulp in an aqueous amine oxide solution with a dry matter density of not more than 10 mass% dry pulp into a device, wherein the device reduces the amount of water present until the suspension is converted into a concentrated pulp suspension, wherein the concentrated pulp suspension is transferred from the device to a further device, wherein the concentrated pulp suspension formed is converted into a moldable solution of cellulose.

[0003] A discharge pump is provided between the device and the additional device. Both devices can be designed as thin-film evaporators. However, the concentrated pulp suspension must be dammed up in the form of a liquid accumulation between the device and the additional device so that the discharge pump can operate.

[0004] For this purpose, the device has a truncated cone-shaped extension at the lower end of the container, which opens into a corresponding receiving chamber into which the concentrated pulp suspension is admitted. It is also taught that a stirrer with a rotor can be provided to stir the concentrated pulp suspension, and that radioactive level measurement is possible in this receiving chamber. This receiving chamber also has an opening provided for evacuating the container and removing water vapor. The disadvantage of this is that material accumulation can occur in the discharge area of ​​the receiving chamber, which can lead to decomposition of the amine oxide, which in turn can increase the risk of explosion. This is possible if more water evaporates unexpectedly, causing the suspension to concentrate to such an extent that the high heating temperatures typical in thin films trigger explosive decomposition of the amine oxide.

[0005] It is also disclosed that the further device carries out water evaporation under vacuum.

[0006] Furthermore, WO 2008 / 086550 A1 discloses a thin-film evaporator in which the starting mixture is pumped into the thin-film evaporator by means of a pressure-generating pump and is pumped out again as a solution at the end of the process by means of another pump. Due to the vacuum operation, this can only be done with a directly or indirectly connected pressure-building or pressure-blocking discharge device, such as a gear pump, or via a discharge device, such as a screw.

[0007] WO 2008 / 154668 A1 also discloses a thin-film evaporator for producing a lyocell spinning solution. The conveying elements on the shaft of the thin-film evaporator are steeply angled for rapid product transport, reducing the risk of overheating and, consequently, an exothermic reaction, even at high heating temperatures. The thin-film evaporator merges into a screw arranged at the end, which feeds a pump that pumps the spinning solution through pipes to spinnerets. This solution is only feasible if the spinning solution is backed upstream of the pump, because otherwise, the operation of the pressure-building pump and the operation of the thin-film evaporator under vacuum is not possible. Although the steeply angled conveying elements reduce the risk of explosion, the disadvantage of this process remains that the spinning solution that must be backed upstream of the pump still poses an explosion risk in the event of unplanned overheating.

[0008] DE 10 2012 103 749 A1 shows a thin-film evaporator which has a rotor in the outlet area for mixing and discharging the product. The described residence time-extending mode of operation leads to an accumulation of product in the conical outlet area, which partially accumulates up to the level of the cylindrical part of the device. Despite the disclosed product-discharging properties of the thin-film evaporator, product accumulation therefore occurs. The residence time required for producing spinning solutions is usually achieved in thin-film evaporators using the method described above. The accumulation of product increases the risk of explosion caused by possible product overheating.

[0009] While thin-film evaporators are usually designed with a vertical orientation of the evaporator shaft, as described, for example, in WO 94 / 06530 A1, they can also be designed with a horizontal orientation of the evaporator shaft, as described, for example, in WO 2020 / 249705 A1.

[0010] The expert is also aware of the limited size of large-scale industrial thin-film heaters, whose maximum heating jacket area is typically approximately 50 m 2To prevent overheating of the amine oxide, the temperature of the heating jacket on the discharge side of the thin-film evaporator is significantly reduced, because the product is already heated there by friction due to increased viscosity. The purpose of reducing the heating jacket temperature is to compensate for this mechanical energy input. Consequently, heat is dissipated on the discharge side to prevent overheating of the spinning solution. This has the disadvantage that not the entire heating jacket surface, which, as mentioned above, is only available to a limited extent, can be used for thermal energy input.A further disadvantage is the resulting increase in energy costs, because firstly, instead of typically cost-effective thermal energy input via the heating jacket surface, a typically expensive electromechanical energy input takes place via energy dissipation of the rotating evaporator shaft of the thin-film device and secondly, because cooling means heat loss. Object of the invention

[0011] The object of the present invention is to overcome the disadvantages of the prior art. In particular, a thin-film evaporator and a use of the thin-film evaporator for evaporating water from a cellulose-water-functional fluid mixture are to be described, which can evaporate more water using thermal energy and, in the case of the amine oxide process, can be operated more safely. The thin-film evaporator is intended to produce a transfer mixture and not a spinning solution. This has the advantage that the product in the thin-film evaporator always has a sufficiently high water content, thus preventing overheating and the resulting potential risk of explosion. Furthermore, the device is intended to prevent a build-up of product within the thin-film evaporator, so that excessive energy input cannot result from energy dissipation in the accumulated product.This eliminates the need to reduce the heating jacket temperature, making the entire heating jacket surface available for more cost-effective thermal energy input, and minimizes the higher-cost electromechanical energy input. A further advantage is that this results in lower mechanical stress on the stirrer shaft, making it more cost-effective to implement. This increases the maximum amount of water evaporated per heating jacket surface of thin-film evaporators while simultaneously lowering energy costs and reducing construction costs, compared to using a thin-film evaporator for spinning solution production.

[0012] This task is not limited to the production of a spinning solution with amine oxide as the functional liquid, where overheating increases the risk of explosion, but also to spinning solution production with ionic liquids as the functional liquid, where overheating does not pose a risk of explosion but can lead to a loss of quality due to overdrying.

[0013] Since the transfer mixture is not yet a spinning solution but a mixture of partially dissolved and undissolved cellulose, water and functional solution, it can still be sensitive to compression, whereby pressure leads to dewatering of the mixture and / or to cellulose agglomerates that can no longer be dissolved.

[0014] The subject of the present invention is a thin-film evaporator which takes into account all the facts mentioned in the context of the task. Solution to the task

[0015] The features of claim 1 lead to the solution of the problem.

[0016] Advantageous embodiments are described in the subclaims.

[0017] A thin-film evaporator according to the invention is used to produce a transfer mixture by the direct dissolution process.

[0018] The thin-film evaporator has an inlet, a housing, and an outlet. A feed material consisting of cellulose, water, and a functional liquid in the form of N-methylmorpholine N-oxide or an ionic liquid is introduced into the housing through the inlet. A rotating evaporator shaft is arranged in the housing. The feed material is wiped across the heated interior of the housing by the evaporator shaft. This heats the feed material and evaporates some of the water, creating the transfer mixture, which flows to the outlet with a feed stream. The outlet is therefore designed so that the feed stream of the transfer mixture passes through the outlet without delay. The outlet can be an opening whose flow rate is determined and / or limited by its dimensions. The opening width can also be variable, i.e., openable or closable.

[0019] The flow rate of the outlet is greater than the feed flow. Flow rate is defined as the flow rate at full feed. Additionally, full feed is defined as the fully utilizing flow rate at the current setting parameters of the outlet or a transfer device, not at its maximum setting parameters.

[0020] The term "flow capacity" therefore aims to provide a functional description of what, for example, a transfer device would deliver more at existing settings if it were fed with a maximum of more material. This describes the effective operating mode, for example, the maximum flow rate at the effectively set speed of a pump, not the maximum flow rate at the maximum adjustable speed of the pump in question.

[0021] Analogously, a flow rate that is greater than the feed flow, in the case of a simple opening, describes that all material flowing in immediately falls out gravimetrically through a sufficiently large opening.

[0022] The advantage of the thin-film evaporator according to the invention is that, due to the composition of the starting material up to the transfer mixture, no potentially dangerous or product-damaging temperatures can be reached.

[0023] Furthermore, neither the starting material nor the transfer mixture are brought into a state of complete solution. This is the case when all essential cellulosic solid components of the starting material have completely dissolved in the functional liquid in the form of N-methylmorpholine N-oxide or an ionic liquid, resulting in a homogeneous, moldable mass.

[0024] This state, prior to the onset of complete solution, is defined as the transfer mixture state. In contrast to suspension, the cellulose in the transfer mixture is partially dissolved.

[0025] The starting material becomes a transfer mixture from the feed to the outlet.

[0026] The outlet leads into a downstream processing unit, which is preferably better suited than the thin-film evaporator for reliably transferring the transfer mixture into a spinning solution. Such a processing unit can be a mixing kneader, as described in WO 2013 / 156489 A1. Thanks to good high-viscosity mixing properties and effective mechanical energy input via the shaft, whose speed can be quickly adjusted and quickly reset to zero, this unit can regulate the temperature with high precision and reliably, generally avoiding cooling or heat dissipation. Thus, the increased energy efficiency and process reliability apply not only to the process step of producing the transfer mixture, but also, in combination with a suitable downstream processing unit, to the entire transfer of a starting material into a spinning solution.

[0027] A further thin-film evaporator can also be considered as a processing device – subject to the aforementioned disadvantages – whereby the thin-film evaporator's overall design can be tailored to reach the transfer mixture, and the further thin-film evaporator can be adapted to processing the transfer mixture through its overall design, such as overall length, angle of its wiper blades, or the like. The subsequent processing device is defined such that the processing device further processes the transfer mixture into a molding solution. The molding solution can then be used, for example, for spinning.

[0028] Additionally, it can be provided that the process chamber of the downstream process element and the process chamber of the housing form a common gas chamber. A common gas chamber in this context means that the housing and the downstream process element are pressure-equalized with each other, resulting in the same pressure conditions of a vacuum in a typical pressure range of 10-100 mbara, preferably 20-75 mbara, in the gas chamber. Equal pressure conditions also include pressure gradients across the gas chamber within the pressure range.

[0029] It is also possible for the outlet to flow into a downstream transfer device, with the flow rate of the transfer device being greater than the feed flow. The transfer device can be a pipe, a line, a screw, or a pump. A sufficiently large flow rate must be provided. In the case of a line or, for example, a pipe, this can mean providing a sufficiently large cross-section and / or a gradient. Ultimately, it is irrelevant how the specialist achieves the required flow rate. In the case of a screw or pump, the flow rate must also be designed to be sufficiently large. In the case of a screw, this can be achieved, for example, by an appropriate number of revolutions.

[0030] The transfer device is usually located between the thin-film evaporator and the downstream processing device. It therefore does not transfer a molding solution for spinning, but rather transfers the transfer mixture from the thin-film evaporator to the downstream processing device, which converts the transfer mixture into a spinnable solution. The advantage here is that the transfer device's design enables a continuous process.

[0031] The downstream processing element, the housing, and the transfer element can form another shared gas chamber. Thus, the transfer mixture from the housing, for example, to the downstream processing element is not exchanged through different pressure conditions, but rather by gravity or mechanically via a screw or pump.

[0032] With a specific composition, the functional fluid, water and cellulose, form a solution. N-methylmorpholine N-oxide (NMMO) or an ionic liquid can be used as the functional fluid. The parameters, such as cellulose content and water content, that lead to a solution, for example, a lyocell spinning solution, depend on the selected functional fluid.

[0033] The transfer mixture has the advantage that the product in the thin-film evaporator always has a sufficiently high water content, thus preventing significant overheating and, with NMMO as the functional fluid, the resulting potential explosion risk. Thus, the heating temperature towards the discharge side of the thin-film evaporator does not need to be reduced, or only slightly reduced. Instead, there is always a temperature difference necessary for thermal energy input—i.e., the difference between the heating temperature and the product temperature—of at least 20°C, preferably 50°C, and ideally 70°C. While avoiding significant overheating, the product temperature corresponds to the equilibrium temperature. A further advantage is that the lower viscosity results in lower mechanical stress on the evaporator shaft of the thin-film evaporator, allowing the thin-film evaporator to be implemented more cost-effectively.This increases the maximum amount of water evaporation per heating surface of thin-film evaporators while simultaneously lowering energy costs and reducing construction costs. The lower construction costs result, for example, from the fact that conventional thin-film evaporators can be made larger, allowing more material to be processed than previously possible. Thus, both the higher amount of water evaporation per heating surface and the larger construction sizes increase the production capacity per production line.

[0034] If the functional fluid is NMMO in the starting material, the material properties of the transfer mixture are in the general composition of maximum xH2O=−0.235 xCell+0.235 minimal xH2O=−0.59 xCell+0.2047 reached.

[0035] Even more preferred is the application of the transfer mixture with the preferred composition of maximum xH2O=0.2864 x2Cell−0.6786xCell+0.2288 minimal xH2O=0.2864 x2Cell−0.6786 xCell+0.2188 given.

[0036] With the general composition, discharging the transfer mixture is already advantageous because sufficient water has evaporated to create a transfer mixture, allowing further processing to form a solution in the subsequent processing element in a relatively short process time. With the preferred composition of the transfer mixture, the maximum water content is already closer to complete solution. On the other hand, the minimum water content is a greater distance from this complete solution. This allows further processing to be realized in a short process time, and at the same time, the risk of overdrying the material in the thin-film evaporator is further reduced. In both cases, however, the transfer mixture is removed from the more complex processing associated with the solution, so that the thin-film evaporator according to the invention can operate with the preferred operating characteristics described above.

[0037] Additionally, a use of the thin-film evaporator for producing a transfer mixture is disclosed. The use for production proceeds according to the direct dissolution process in a thin-film evaporator with an inlet, a housing, and an outlet. The inlet introduces a starting material consisting of cellulose, water, and a functional fluid into the housing. An evaporator shaft arranged in the housing rotates to sweep the starting material over the interior of the housing, causing the starting material to heat up and a portion of the water to evaporate, thus forming the transfer mixture. The transfer mixture flows to the outlet with a feed stream, wherein, according to the invention, the flow rate of the outlet is greater than the feed stream. The above-mentioned definition of flow rate also applies here.

[0038] The feed flow is a definable amount of the transfer mixture per unit of time, which can be calculated if a certain amount of feed material enters the housing through the inlet, and the evaporator shaft heats the feed material, and the water evaporates. By taking into account the thermal energy input over the processing period by the evaporator shaft, i.e., less the amount of evaporated water, the feed flow could be calculated and the outlet could be designed with a specific flow rate from the outset, or an adjustable flow rate could be specified, for example, by means of an expandable outlet, so that the transfer mixture could exit the housing or outlet without delay, thus ensuring a continuous process.

[0039] During use, the transfer mixture can, for example, be passed on to a subsequent processing device. This subsequent processing device can be one of the previously described processing devices, such as a mixer-kneader or the additional thin-film evaporator. The subsequent processing device is intended to further process the transfer mixture into a molding solution.

[0040] N-methylmorpholine N-oxide (NMMO) or an ionic liquid can be added as the functional liquid for the starting material. These serve to dissolve the cellulose under appropriate conditions.

[0041] Furthermore, in a further embodiment, the transfer mixture can pass through a subsequent transfer element, wherein the flow rate of the transfer element is greater than the feed flow. The transfer element can be, for example, a pipe, a conduit, a screw, or a pump. A correspondingly large flow rate must be provided. This can be achieved in a conduit or, for example, a pipe, by providing a correspondingly large cross-section and / or a gradient. Ultimately, it is irrelevant how the expert achieves the required flow rate. In the case of a screw or pump, the flow rate must also be designed to be correspondingly large. In the case of a screw, this can be achieved, for example, by a corresponding speed.

[0042] The transfer element is located, for example, between the thin-film evaporator and the downstream processing element. It therefore does not transfer a solution for spinning, but rather transfers the transfer mixture from the thin-film evaporator to the downstream processing element, with the transfer mixture only becoming a spinnable solution in the processing element. The advantage here is that the transfer element's design enables a continuous process.

[0043] If the functional fluid added to the starting material is NMMO, the general material properties of the transfer mixture are in the general composition of maximum xH2O=−0.235 xCell+0.235 minimal xH2O=−0.59 xCell+0.2047 reached.

[0044] Even more preferred is the application of the transfer mixture with the preferred composition of maximum xH2O=0.2864 x2Cell−0.6786 xCell+0.2288 minimal xH2O=0.2864 x2Cell−0.6786 xCell+0.2188,

[0045] In the general composition and also the preferred composition, the transfer mixture is in a pre-dissolution state. This also ensures that the process for producing lyocell takes place under optimal operating parameters of the thin-film evaporator, avoiding the comparatively difficult material states of lyocell, for example, when incrustations, over-drying, or decomposition occur in the thin-film evaporator. These problematic material states can be relatively easily prevented in the downstream processing element because the downstream processing element is generally designed for lower rotational speeds and higher torques, for example. Character description

[0046] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings, which show: Fig. 1 a schematic view of a thin-film evaporator (D) according to the invention; Fig. 2 a diagram of the general and preferred material properties of a transfer mixture. Example

[0047] In Fig. Figure 1 shows a thin-film evaporator D according to the invention, which has an inlet 1, which in turn opens into a housing 4. A starting material consisting of cellulose, water, and a functional fluid enters the housing 4 through the inlet 1.

[0048] The housing 4 has an evaporator shaft 5 inside. The evaporator shaft 5 is rotated by a drive 3. The rotating evaporator shaft 5 sweeps the feed material across the heated interior of the housing 4, heating the feed material and evaporating a portion of the water, creating a transfer mixture that flows to the outlet 2 with a feed stream.

[0049] It is irrelevant whether the evaporator shaft 5 transports the starting material or, at a later stage of the process, the transfer mixture through its wipers attached to the evaporator shaft from the feed 1 to the outlet 2 and / or whether this process takes place gravimetrically.

[0050] The flow capacity of outlet 2 is designed to be larger than the feed flow.

[0051] The outlet 2 opens into a subsequent processing element 6. The outlet 2 is oriented at one end towards the housing 4 and the other end towards the subsequent processing element 6.

[0052] It is also shown that the housing 4 with the inlet 1 and the outlet 2, as well as the downstream process element 6, form a common gas space 7, so that a delay-free transition of the transfer mixture into the downstream process element 6 is possible.

[0053] In Fig. Figure 2 shows a diagram showing the general and preferred material composition of the transfer mixture. The general composition a has the following parameters of minimal xH2O=−0.235 xCell+0.235 minimal xH2O=−0.59 xCell+0.2047 and thus shows a greater scope than the preferred composition b, which has the following parameters of maximum xH2O=0.2864 x2Cell−0.6786 xCell+0.2288 minimal xH2O=0.2864 x2Cell−0.6786 xCell+0.2188 has.

[0054] As the water content decreases, the solution range L is reached first and as the water content decreases further, crystallization K is reached. List of reference symbols 1 feed-in 2 outlet 3 Drive 4 housings 5 Evaporator shaft 6 Subsequent procedural body 7 Gas room 8 9 A General composition of the transfer mixture B Preferred composition of the transfer mixture K Crystallization L Solution D Thin film evaporator

Claims

[1] Thin-film evaporator (D) for producing a transfer mixture from a starting material of cellulose, water and a functional liquid of N-methylmorphloin-N-oxide or an ionic liquid according to the direct dissolution process with an inlet (1), a housing (4) and an outlet (2), wherein an evaporator shaft (5) arranged in the housing (4) rotates and wipes the starting material over the heated interior of the housing (4), whereby the starting material is heated and part of the water evaporates, so that the transfer mixture is formed, which flows to the outlet (2) with a feed stream, characterized by , that the flow capacity of the outlet (2) is greater than the feed flow, wherein the flow capacity is defined as the flow rate at full feed, wherein the full feed is represented as the fully utilizing flow rate with the currently set setting parameters of the outlet or a transfer element, wherein the outlet (2) opens into a subsequent transfer element, wherein the flow capacity of the transfer element is greater than the feed flow. [2] Thin film evaporator (D) according to claim 1, characterized by that the outlet (2) opens into a subsequent processing element (6). [3] Thin film evaporator (D) according to claim 1, characterized by that the transfer element is arranged between the thin-film evaporator (D) and the subsequent processing element (6). [4] Thin-film evaporator (D) according to one of claims 1 to 3, characterized bythat the subsequent processing element (6) is a processing processing element which further processes the transfer mixture into a molding solution. [5] Thin-film evaporator (D) according to one of the preceding claims 2 to 4, characterized by that the subsequent processing element (6) and the housing (4) form a common gas space (7). [6] Thin-film evaporator (D) according to one of the preceding claims 1 to 5, characterized by that the subsequent processing element (6) and the housing (4) and the transfer element form a further common gas space. [7] Use of the device according to claims 1 to 6 for producing a transfer mixture according to the direct dissolution process with a feed (1), a housing (4) and an outlet (2), wherein the feed (1) introduces a starting material consisting of cellulose, water and a functional liquid into the housing (4), wherein an evaporator shaft (5) arranged in the housing (4) rotates and wipes the starting material over the interior of the housing (4), wherein the starting material is heated and part of the water evaporates, so that the transfer mixture is formed, wherein the transfer mixture flows to the outlet (2) with a feed stream, characterized by , that the flow capacity of the outlet (2) is greater than the feed flow, where the flow capacity is defined as the flow rate at full feed, where the full feed is the fully utilizing flow rate at the currently set setting parameters of the outlet or a transfer device and not at its maximizing setting parameters. [8] Use according to claim 7, characterized by that the transfer mixture passes through a subsequent transfer element, whereby the flow capacity of the transfer element is greater than the feed flow. [9] Use according to claim 8, characterized by that the transfer mixture is passed on to a subsequent processing element (6). [10] Use according to claim 9, characterized by that the transfer mixture first passes through the transfer organ and then enters the subsequent processing organ (6). [11] Use according to claim 9 or 10, characterized bythat the subsequent processing element (6) further processes the transfer mixture into a molding solution. [12] Use according to claims 7 to 11, characterized by that when using NMMO as functional fluid, the transfer mixture in the general composition of maximum xH2O=−0.235 xCell+0.235 minimal xH2O=−0.59 xCell+0.2047 is output as feed stream into the outlet (2). [13] Use according to claim 12, characterized by that when using NMMO as functional fluid, the transfer mixture at the preferred composition of maximum xH2O=0.2864 x2Cell−0.6786 xCell+0.2288 minimal xH2O=0.2864 x2Cell−0.6786 xCell+0.2188 is output as feed stream into the outlet (2).

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