Method of producing cellulose carbamate filaments or fibres

Abstract

According to embodiments of the present invention, a method for manufacturing cellulose carbamate filaments or fibers is provided. The method comprises the following steps: providing a cellulose carbamate solution; feeding the cellulose carbamate solution into a spinning unit having an aqueous spinning bath containing sulfuric acid and a dissolved aluminum compound; coagulating the cellulose carbamate to form cellulose carbamate filaments; stretching the cellulose carbamate filaments; optionally cutting them to form fibers; and optionally washing. Additionally, the method includes chemical recycling, which involves extracting a portion of the spinning bath to regenerate it by removing at least a portion of sodium, water, and zinc ions; and recycling at least a portion of the regenerated aqueous spinning bath back to the spinning unit. Prior to regeneration, the extracted aqueous spinning bath preferably contains less than 20 g / L of dissolved ammonium nitrogen, for example, ammonium sulfate, at a temperature of at least 10°C.

Description

Technical Field

[0001] This invention relates to a method for manufacturing cellulose carbamate filaments or fibers, which includes the chemical recycling of chemicals. Prior Technology

[0002] Cellulose is the most widely used biopolymer in the world, and its fibers and derivatives (such as cellulose carbamate, cellulose acetate, ethers, and esters) are used in various industries, including paper and paperboard and textiles. However, the use of cellulose in these industries requires the dissolution of cellulose fibers to regenerate their structure. Cellulose is difficult to dissolve due to its semi-crystalline structure, strong hydrogen bonds in the polymer sheets, and the presence of hydrophilic and hydrophobic ends within the polymer. Therefore, cellulose needs to be modified in structure through derivatization, or its fibers need to be opened up to increase reactivity.

[0003] Various derivatization methods are known in the field to which this invention pertains, perhaps most notably the cellulose spinning process, in which cellulose is first treated with an alkali and then with carbon disulfide to produce cellulose xanthate. Due to the toxicity of carbon disulfide and the undesirable environmental impact of the cellulose spinning process, it is increasingly avoided. More and more are people turning to other derivatization methods, particularly those that are less expensive, do not have the toxicity and environmental problems of the cellulose spinning process, and can still be carried out using available infrastructure, such as in a cellulose spinning wet spinning mill.

[0004] The carbamate esterification method for manufacturing cellulose carbamates is a derivatization method. Cellulose carbamates are formed by reacting cellulose with urea. Methods for manufacturing cellulose carbamates are described, for example, in Finnish Patent Nos. 112869 and 112795.

[0005] After cellulose carbamate is dissolved in a mixture of an alkaline agent, such as sodium hydroxide and zinc oxide, the resulting cellulose carbamate solution is fed into a spinning bath to solidify the cellulose carbamate into filaments. In some embodiments, solidification is carried out in an acidic spinning bath containing sulfuric acid and aluminum sulfate. Such an acidic spinning bath typically contains a dissolved phase of zinc oxide (e.g., zinc ions) along with ammonium salts or ions (ammonium nitrogen), aluminum salts or ions, and sodium sulfate.

[0006] As is customary, spinning baths are equipped with chemical recycling facilities for dissolving and solidifying cellulose carbamates. Efficient chemical recycling remains a necessity. Summary of the Invention

[0007] The purpose of this method is to provide a way to produce high-quality cellulose carbamate filaments or fibers in a spinning cycle, wherein chemical recycling is optimized, preferably by crystallizing sodium sulfate as purely as possible (avoiding co-crystallization of zinc, aluminum, and nitrogen) and removing zinc as efficiently as possible by extraction (avoiding co-extraction of aluminum). Furthermore, the coagulation or spinning bath circulation system is kept as closed-loop as possible, i.e., semi-closed-loop, thus avoiding wastewater discharge. In addition, the water balance of the semi-closed-loop system is preferably maintained by removing water entering the system via the cellulose carbamate spinning solution (preferably by evaporation).

[0008] The first aspect of the present invention provides a method for manufacturing cellulose carbamate filaments or fibers, the method comprising the following steps: providing a cellulose carbamate solution containing cellulose carbamate dissolved in aqueous sodium hydroxide, the cellulose carbamate solution further containing a dissolved zinc compound; feeding the cellulose carbamate solution into a spinning unit having an aqueous spinning bath containing sulfuric acid and a dissolved aluminum compound; coagulating the cellulose carbamate from the cellulose carbamate solution into the aqueous spinning bath to form cellulose carbamate filaments; stretching and optionally washing the cellulose carbamate filaments, and optionally cutting the filaments into fibers; withdrawing a portion of the aqueous spinning bath containing sodium sulfate, water, and zinc ions; regenerating the withdrawn portion of the spinning bath by removing at least a portion of the sodium sulfate, water, and zinc ions; and recycling at least a portion of the regenerated aqueous spinning bath back to the spinning unit. Preferably, prior to regeneration, the extracted aqueous spinning bath contains less than 20 g / L of dissolved nitrogen in the form of ammonium nitrogen, such as ammonium sulfate, at a temperature of at least 10°C.

[0009] The extracted portion for regeneration may also include the extracted aqueous stretching bath and / or cleaning bath portions.

[0010] This invention is defined by the features of the independent items. Some specific embodiments are defined in the appendices.

[0011] The embodiments of the present invention enable the manufacture of high-quality cellulose carbamate filaments or fibers with efficient chemical recycling. Therefore, in the present invention, the spinning method achieves a high level of chemical recycling without impairing fiber properties. Simple Explanation of the Diagram

[0012] [Figure 1] illustrates a method for manufacturing cellulose carbamate filaments or fibers according to at least some embodiments of the present invention, the method further comprising a spinning bath regeneration method. Implementation

[0013] This technology provides an improved method for manufacturing cellulose carbamate filaments or fibers. The method includes chemical recycling. In various embodiments, the manufacturing method for cellulose carbamate filaments or fibers has been made sustainable by significantly improving the efficiency of chemical recycling in the spinning process.

[0014] The implementation provides cellulose carbamate filaments or fibers of good quality, with the aim of obtaining fibers that are as similar as possible to cotton fibers.

[0015] The embodiment includes: providing a cellulose carbamate solution, feeding the cellulose carbamate solution into a spinning unit having an aqueous spinning bath, causing the cellulose carbamate from the cellulose carbamate solution into the aqueous spinning bath to solidify to form cellulose carbamate filaments, subjecting the cellulose carbamate filaments to stretching in one or more stretching units and optionally cleaning in one or more cleaning units, and optionally cutting the filaments into fibers, thereby obtaining cellulose carbamate filaments or fibers. Additionally, the embodiment also includes chemical recycling. Therefore, a portion of the aqueous spinning bath containing sodium sulfate, water, and zinc ions is extracted from the spinning bath and regenerated by removing at least a portion of the sodium sulfate, water, and zinc ions.

[0016] Therefore, according to one embodiment, a method for manufacturing cellulose carbamate filaments or fibers includes the following steps: - A cellulose carbamate solution is provided, comprising a cellulose carbamate soluble in aqueous sodium hydroxide, the cellulose carbamate solution further comprising a zinc-dissolving compound; - The cellulose carbamate solution is fed into a spinning unit having an aqueous spinning bath containing sulfuric acid and aluminum sulfate; - The cellulose carbamate solution is transferred to the aqueous spinning bath and then solidified to form cellulose carbamate filaments; - The cellulose carbamate filament is stretched and optionally washed, and optionally cut into short fibers; - A portion of the aqueous spinning bath containing sodium sulfate, water, and zinc ions is extracted, the extracted aqueous spinning bath having a temperature of at least 10°C; - The extracted spinning bath portion is regenerated by removing at least a portion of the sodium sulfate, water, and zinc ions; and - Recycle at least a portion of the regenerated aqueous spinning bath to the spinning unit.

[0017] According to a preferred embodiment, the regeneration of the extracted spinning bath (and / or stretching bath and / or washing bath) portion includes at least one zinc removal step (preferably by zinc extraction) and a sodium sulfate removal step (preferably by sodium sulfate crystallization). Additionally, regeneration may include at least one separation step, such as filtration and / or water removal, for example by evaporation. Besides removing water by evaporation, it is preferred to remove at least a portion of the water from the spinning bath by sodium sulfate decahydrate crystals. Typically, at least a portion of the regenerated aqueous spinning bath is recycled back to the spinning unit.

[0018] According to one embodiment, a portion of the extracted spinning bath (and / or stretching bath and / or washing bath) undergoing regeneration can bypass one or more of the aforementioned regeneration cycle steps. For example, a portion of the filtered spinning bath can be recycled back to the spinning unit without performing zinc extraction, water evaporation, and / or sodium sulfate removal steps.

[0019] According to a preferred embodiment, the method of the present invention is a continuous process, namely, feeding a cellulose carbamate solution and continuously processing it in a spinning unit.

[0020] According to one embodiment, filaments or fibers are obtained by this method. According to a preferred embodiment, the filament product of this method is a continuous filament obtained after stretching and optionally washing the solidified filaments. The fiber product of this method is then obtained by producing filament bundles from the solidified filaments and stretching and cutting such filament bundles into fibers, particularly into short fibers or chopped fibers. Specifically, short fibers are obtained by cutting the filament bundles into short fibers, followed by washing, post-treatment, and drying. According to another embodiment, short fibers can be obtained by washing and post-treatment of the filament bundles themselves, and then cutting them into short fibers or chopped fibers in a wet or dry state.

[0021] In a first step of one embodiment, a cellulose carbamate solution is provided, comprising cellulose carbamate dissolved in aqueous sodium hydroxide.

[0022] In another embodiment, a cellulose carbamate solution is formed in the presence of zinc oxide and / or zinc hydroxide, preferably zinc oxide. Zinc oxide and / or zinc hydroxide may be added to the cellulose carbamate, to an alkaline aqueous solution, or to a mixture of the cellulose carbamate and an alkaline aqueous solution. Typically, the zinc oxide and / or zinc hydroxide are dissolved in an alkaline aqueous solution before being used as a dissolving alkali for the provided cellulose carbamate.

[0023] In one embodiment, the addition of zinc (e.g., zinc oxide dissolved in sodium hydroxide and / or zinc hydroxide) can partially enhance the solubility and filterability of the solution and partially extend the storage time before gelation begins. Typically, it also affects the viscosity of the cellulose carbamate solution and the yield strength of the resulting wet-spun cellulose carbamate fibers.

[0024] According to one embodiment, the aqueous alkali cellulose carbamate solution contains up to 10% by weight of cellulose carbamate. Additionally, it preferably contains less than 8% by weight of sodium hydroxide (especially free sodium hydroxide) and up to 2% by weight of Zn (calculated as ZnO), wherein the above percentages are based on the total weight of the solution. Preferably, the remainder of the cellulose carbamate solution is water; however, the aqueous cellulose carbamate solution may additionally contain small amounts of other substances, such as additives and / or auxiliaries.

[0025] In one embodiment, the cellulose carbamate solution has a zinc oxide content of 0.1 to 1.5% by weight, preferably up to 1.3% by weight, and most preferably up to 1.0% by weight, of the total weight of the cellulose carbamate solution. In one embodiment, the cellulose carbamate solution is defined at least in part by the ratio of cellulose carbamate to zinc oxide. Thus, in one embodiment, the cellulose carbamate solution has a cellulose carbamate:ZnO ratio of 6 to 10% by weight: 0.1 to 1.5% by weight. In practice, this means that for every 1 t of cellulose carbamate, there are 0.01 to 0.25 t of ZnO.

[0026] According to one specific embodiment, the aqueous alkali cellulose carbamate solution comprises: - 6 to 10% by weight, preferably 8 to 10% by weight, of cellulose carbamate (CCA) - 5 to 10% by weight, preferably 5 to 7% by weight, of sodium hydroxide (NaOH), and - 0.1 to 2% by weight, preferably 0.1 to 1.5% by weight of zinc oxide (ZnO). This percentage is based on the total weight of the cellulose carbamate solution.

[0027] Preferably, the cellulose carbamate solution is prepared and degassed at a temperature of about 10 to 30°C.

[0028] According to a preferred embodiment, a cellulose carbamate solution at a temperature of 10 to 30°C, preferably 10 to 20°C, such as about 15°C, is provided for optional filtration and curing. The cellulose carbamate solution is also fed into the spinning unit at such temperatures, particularly at 15 to 25°C. The temperature of the cellulose carbamate solution fed into the spinning unit affects, for example, the energy balance of the spinning bath recovery cycle.

[0029] According to one embodiment, based on the total weight of the cellulose carbamate solution, the cellulose carbamate solution has a maximum total dissolved nitrogen content of less than 0.2% by weight, preferably less than 0.15% by weight. The total dissolved nitrogen in the cellulose carbamate solution includes nitrogen chemically bound to cellulose (e.g., carbamate groups) and nitrogen released from the carbamate groups by alkaline hydrolysis.

[0030] The cellulose carbamate used in this invention can be obtained from any cellulose source.

[0031] Typically, cellulose carbamates are obtained from cellulose pulp (such as dissolving pulp). Chemical pulp or dissolving pulp can be prepared from wood species such as pine, spruce, birch, beech, poplar, maple, larch, acacia, eucalyptus, hemlock, purplewood, and oak, or from non-wood materials such as stalk fibers (wheat straw, rice straw, barley straw, bamboo, bagasse, and reeds). Feed sources can be in their original form as chemical pulp or dissolving pulp, or from recycled materials such as recycled paper and / or paperboard containing chemical pulp or dissolving pulp.

[0032] Natural plant fibers can be used on their own or in the form of chemical pulp or dissolving pulp. The source of natural plant fibers can be their raw form or textiles containing natural plant fibers or textiles containing recycled natural fibers. Natural plant fibers include seed fibers, such as cotton and kapok; bast fibers, such as hemp, jute, kenaf, ramie, Manila hemp, and flax; leaf fibers, such as Manila hemp, jute, pineapple, and banana; and fruit fibers, such as coconut fiber.

[0033] Therefore, in one embodiment, the recycled fiber feed is used as a raw material for manufacturing cellulose carbamate.

[0034] A cellulose carbamate solution (preferably continuously) is fed into a spinning unit having an aqueous spinning bath containing sulfuric acid and dissolved aluminum compounds. Preferably, the cellulose carbamate solution is fed into the spinning unit through one or more spinning nozzles. A spinning head may contain, for example, 45 nozzles, each having, for example, 2000 orifices. For example, a wet spinning production line for manufacturing short fibers may have at least 60 spinning heads coupled to the same spinning bath system. The cellulose carbamate solution is fed into the spinning unit at a suitable flow rate. According to one embodiment, once the cellulose carbamate solution is fed into the spinning unit, sulfuric acid reacts with sodium hydroxide and zinc oxide dissolved in sodium hydroxide to form sodium sulfate, zinc sulfate, and water, thereby the spinning bath containing (excess free) sulfuric acid, zinc sulfate, aluminum sulfate, sodium sulfate, and water. The cellulose carbamate solidifies and is formed into filaments when extruded through the spinning nozzles. Preferably, at least substantially all, i.e. at least 99% by weight, of the cellulose carbamate is solidified and formed into filaments.

[0035] In this context, the term "steady state" is generally used to describe conditions, such as the concentration of a component, that do not change significantly over time. In a preferred embodiment, the steady-state conditions of the spinning bath correspond to the conditions of the extracted portion of the spinning bath before regeneration.

[0036] According to one embodiment, in a continuous spinning process where steady-state operating conditions have been reached, the spinning bath exiting the spinning unit has a pH (at 20°C) in the range of 0.2 to 0.9, preferably 0.7 to 0.9 or 0.5 to 0.8, and comprises: - Zinc, such as zinc sulfate (ZnSO4), in amounts of 10 to 50 g / L. - Dissolve ammonium nitrogen, such as ammonium sulfate ((NH4)2SO4), in amounts less than 20 g / L, preferably less than 15 g / L, and most preferably less than 10 g / L.

[0037] According to one embodiment, additives and / or auxiliaries present in the cellulose carbamate solution may also be included in the recycling of spinning bath chemicals. Alternatively, additives (i.e., spinning bath auxiliaries) may be added directly to the spinning bath, and the additives may also be present in the spinning cycle.

[0038] According to a preferred embodiment, the spinning bath exiting the spinning unit has a density of 1200 to 1330 kg / m³ (density measured at 20°C) and a Na₂SO₄ to Al₂(SO₄)₃ mass weight ratio of 1.0 to 3.0. The density of the spinning bath can be measured using a gas hydrometer or a liquid hydrometer (applicable to all densities in this application). In one embodiment, the density of the spinning bath exiting the spinning unit is generally related to the relative amounts of sodium sulfate and aluminum sulfate. In addition to sodium sulfate and aluminum sulfate, the spinning bath also contains sulfuric acid and other salts and compounds, but the sum of the concentrations of sodium sulfate and aluminum sulfate is the determining factor for density. Therefore, in one embodiment, the spinning bath conditions (e.g., the concentrations of each component) are selected in a manner appropriate to the use of these conditions.

[0039] According to one embodiment, the spinning bath exiting the spinning unit has a temperature of at least 10°C, preferably at least 15°C, for example in the range of 10 to 25°C, and most preferably in the range of 15 to 22°C.

[0040] Therefore, according to one embodiment, a method for manufacturing cellulose carbamate filaments or fibers includes the following steps: - A cellulose carbamate solution is provided, comprising a cellulose carbamate soluble in aqueous sodium hydroxide, the cellulose carbamate solution further comprising a zinc-dissolving compound; - The cellulose carbamate solution is fed into a spinning unit having an aqueous spinning bath containing sulfuric acid and aluminum sulfate; - The cellulose carbamate solution is transferred to the aqueous spinning bath and then solidified to form cellulose carbamate filaments; - The cellulose carbamate filament is stretched and optionally washed, and optionally cut into short fibers; - A portion of the aqueous spinning bath containing sodium sulfate, water, and zinc ions is extracted, the extracted aqueous spinning bath having a temperature of at least 10°C; - The extracted spinning bath portion is regenerated by removing at least a portion of the sodium sulfate, water, and zinc ions; and - At least a portion of the regenerated aqueous spinning bath is recycled to the spinning unit. The spinning bath conditions are selected such that the aqueous spinning bath portion extracted from the spinning unit has a density of 1200 to 1330 kg / m³ (density measured at 20°C) and a Na₂SO₄ to Al₂(SO₄)₃ mass weight ratio of 1:1 to 3:1.

[0041] According to one embodiment, the spinning bath exiting the spinning unit has a pH in the range of 0.2 to 0.9, preferably 0.7 to 0.9 (at 20°C).

[0042] The spinning bath of this invention is an acidic spinning bath containing sulfuric acid as a free acid. The amount of sulfuric acid is adjusted to maintain the pH of the spinning bath within the aforementioned range.

[0043] In this embodiment, the amount of soluble ammonium nitrogen, such as ammonium sulfate, is maintained generally at less than 20 g / L, preferably less than 15 g / L, and most preferably less than 10 g / L in the spinning bath and in the portion of the spinning bath removed from the spinning unit and recycled. Therefore, the formation of ammonium-aluminum double salts (i.e., ammonium sulfate) can be reduced or even substantially eliminated. The formation of ammonium sulfate as a sparingly soluble salt in the spinning bath causes at least a portion of the aluminum to precipitate.

[0044] The dissolved ammonium nitrogen content will be determined at least partially by the carbamate content of the cellulose carbamate material used to manufacture the cellulose carbamate solution and by the sustained conditions between the dissolution of the cellulose carbamate to form the cellulose carbamate solution and its feeding into the spinning unit. Therefore, the hydrolysis of cellulose carbamate during dissolution releases nitrogen compounds into the cellulose carbamate solution, primarily in the form of ammonium nitrogen compounds. The sustained temperature during dissolution and the delay time between the dissolution of the cellulose carbamate and the feeding of the formed cellulose carbamate solution into the spinning unit will affect the dissolved ammonium nitrogen content in the spinning bath composition.

[0045] Therefore, the hydrolysis of cellulose bound to carbamate groups releases ammonium nitrogen, most of which reaches the spinning bath as ammonium sulfate. However, cellulose carbamate may also contain other nitrogen compounds (such as urea and biuret), which do not reach the spinning bath as ammonium nitrogen and therefore do not form ammonium sulfate.

[0046] According to a preferred embodiment, a cellulose carbamate solution with a degree of hydrolysis of less than 70%, particularly less than 65%, and preferably less than 60%, is provided. This degree of hydrolysis is based on the difference in the percentage of cellulose-bound nitrogen between the cellulose carbamate before dissolution and the solidified cellulose carbamate.

[0047] According to one embodiment, if necessary, the amount of ammonium nitrogen can be maintained at a predetermined level by removing ammonium nitrogen from the spinning bath or from a portion of the spinning bath extracted during a regeneration cycle (e.g., a separation operation). According to one embodiment, if necessary, at least a portion of the ammonium nitrogen can be removed during the removal of sodium sulfate by crystallization. Therefore, in one embodiment, for processing the spinning bath, it is preferable to have a low content of soluble nitrogen (compounds), especially a low content of ammonium nitrogen.

[0048] In one embodiment, the amount of ammonium nitrogen in the spinning bath is at least 1 g / L of the total spinning bath volume. Therefore, in a preferred embodiment, the amount of ammonium nitrogen in the spinning bath and thus in the extracted aqueous spinning bath portion is in the range of 1 to 20 g / L, more preferably in the range of 1 to 15 g / L, for example in the range of 2 to 10 g / L.

[0049] According to a preferred embodiment, at least a majority of the soluble nitrogen content in the spinning bath is present in the coagulated filament, wherein the nitrogen does not need to be removed separately by other means. In one embodiment, at least 30% by weight, particularly at least 35% by weight, and preferably at least 40% by weight, of nitrogen in the form of nitrogen compounds (e.g., carbamate groups) from the cellulose carbamate solution is present in the coagulated filament or fiber.

[0050] Therefore, in one embodiment, the soluble nitrogen content in the spinning bath is determined and maintained at a suitable level by means of the combination of the above features.

[0051] Aluminum is therefore important because it improves the quality of the manufactured filaments or fibers, especially since the shape of the filaments or fibers is controlled by the amount of aluminum (aluminum sulfate) in the spinning bath and the controlled stretching. In particular, aluminum affects the cross-sectional shape of filaments and fibers that makes them more like cotton fibers (preferably). Additionally, aluminum inhibits the crystallization of cellulose during the coagulation process. Amphoteric aluminum compounds also affect the acid-base neutralization reaction during coagulation. Simultaneously, it improves the toughness yield of recycled filaments or fibers. A minimum amount of aluminum is required in acidic wet spinning to form general fibers in a controlled manner. However, aluminum also impairs the spinning bath regeneration process. Therefore, a balance between different components is necessary.

[0052] In one embodiment, the ratio of aluminum sulfate to sodium sulfate, calculated based on the mass weight ratio of Na₂SO₄ to Al₂(SO₄)₃, is 1:1 to 3:1. In one embodiment, the mass weight ratio of Na₂SO₄ to Al₂(SO₄)₃ in the spinning bath is maintained at 1:1 to 3:1 by regenerating and recycling the aqueous spinning bath. Therefore, in one embodiment, the mass weight ratio of Na₂SO₄ to Al₂(SO₄)₃ in the spinning bath is maintained at 1.0 to 3.0 by the following steps: - A portion of the spinning bath is withdrawn from the spinning unit for regeneration to reduce the sodium sulfate content of the withdrawn portion; and - Recycle at least a portion of the regenerated spinning bath to the spinning unit.

[0053] Therefore, according to one embodiment, a method for manufacturing cellulose carbamate filaments or fibers includes the following steps: - A cellulose carbamate solution is provided, comprising a cellulose carbamate soluble in aqueous sodium hydroxide, the cellulose carbamate solution further comprising a zinc-dissolving compound; - The cellulose carbamate solution is fed into a spinning unit having an aqueous spinning bath containing sulfuric acid and aluminum sulfate; - The cellulose carbamate is coagulated from the cellulose carbamate solution into the aqueous spinning bath to form cellulose carbamate filaments; - Stretch and optionally wash the cellulose carbamate filament, and optionally cut the filament into short fibers; The following steps are used to maintain the Na₂SO₄ to Al₂(SO₄)₃ mass-to-weight ratio in the spinning bath at 1.0 to 3.0: - A portion of the aqueous spinning bath is withdrawn from the spinning unit for regeneration to reduce the sodium sulfate content of the withdrawn portion; and - Recycle at least a portion of the regenerated aqueous spinning bath to the spinning unit.

[0054] In a preferred embodiment, the spinning bath has a density of 1200 to 1330 kg / m³.

[0055] According to one embodiment, the temperature of the spinning bath is at most 25°C, for example, 15 to 25°C, and most preferably in the range of 15 to 22°C. At too low a spinning bath temperature, salts will easily crystallize out from the aqueous spinning bath; however, the higher the spinning bath temperature, the higher the aluminum concentration is required to achieve the target toughness yield, because the solidification process is accelerated by the increase in temperature. Therefore, the spinning bath temperature is preferably within the above-mentioned range.

[0056] According to a preferred embodiment, the cellulose carbamate solution is coagulated in a spinning bath at a temperature of up to 23°C, most preferably at a temperature of up to 20°C.

[0057] In a spinning bath, cellulose carbamate is coagulated into cellulose carbamate filaments, preferably through one or more spinning nozzles. Such filaments are recovered from the spinning bath and subjected to stretching, optional cutting into fibers, and optional post-treatment, including washing, bleaching, and / or spinning finishing of the filaments or fibers.

[0058] According to one embodiment, a filament obtained from a spinning bath is stretched in a stretching unit. Cellulose carbamate filaments are stretched in one or at least two stretching units in a series.

[0059] According to one embodiment, the stretching unit comprises a stretching bath or air stretching. Typically, the stretching bath is an aqueous bath containing sulfuric acid, aluminum sulfate, zinc sulfate, and sodium sulfate, i.e., the same components as the spinning bath but at a lower concentration, because the coagulated filaments carry these components along with the stretching unit. The same components may also be carried by the filaments through one or more of the following steps (or carried by the fibers after cutting), i.e., the obtained product may still contain some components of the spinning bath. This is why, in some embodiments, the method of the present invention may comprise a semi-closed system. The stretching bath is particularly used when manufacturing cellulose carbamate staple fibers, i.e., when preferably stretching the fiber bundles.

[0060] According to one embodiment, the stretching bath is a hot stretching bath in which filaments or filament bundles are immersed in a stretching bath solution. The temperature of the stretching bath is typically in the range of 75 to 100°C, preferably in the range of 85 to 95°C, and more preferably in the range of about 90°C.

[0061] According to another embodiment, cellulose carbamate filaments are stretched in a stretching unit without a stretching bath, a process known as air stretching.

[0062] According to one embodiment, after stretching, the filament (especially the filament bundle) is cut into fibers of desired length in a cutting unit by a cutter. The cutting can be performed by any known filament cutting method.

[0063] Following stretching and optionally cutting, the filaments or fibers undergo post-processing in a post-processing unit. According to a preferred embodiment, post-processing includes washing, bleaching, spinning finishing, or any combination thereof. In one embodiment, washing is performed in the form of counter-current washing using water or effluent from preceding or following processing steps.

[0064] Finally, the obtained filaments or fibers are dried using any known drying method.

[0065] According to a preferred embodiment, cellulose carbamate filaments (especially cellulose carbamate filament bundles) are stretched, then cut to provide short fibers, and the obtained short fibers are then post-processed (especially washed) in a post-processing unit. Finally, the obtained fibers are dried.

[0066] According to another embodiment, cellulose carbamate filaments (especially cellulose carbamate filament bundles) are stretched, then post-treated (especially washed) in a post-treatment unit, and then the treated wet or dry filaments are cut into short fibers or chopped fibers.

[0067] According to another embodiment, the cellulose filaments are stretched, and then the obtained filaments are post-treated (especially washed) in a post-treatment cleaning unit.

[0068] The aforementioned spinning methods for manufacturing cellulose carbamate filaments or fibers involve several chemicals, among which chemical recyclability is crucial for the sustainability of the spinning process. Therefore, the method of the present invention further includes chemical recycling, wherein at least a portion of the spinning bath is regenerated and the solids are recovered.

[0069] According to a preferred embodiment, at least a portion of the stretching bath and / or washing bath is also regenerated and the solids are recovered. Therefore, the regeneration of the spinning bath described in this application is also applicable to the stretching bath and washing bath. In the same regeneration method, all the extracted portions can be regenerated simultaneously.

[0070] First, an aqueous spinning bath containing sodium sulfate, water, and zinc ions is extracted from the spinning unit (and / or stretching unit and / or cleaning unit), and this spinning bath (and / or stretching bath and / or cleaning bath) is regenerated by removing at least a portion of the sodium sulfate, water, and zinc ions. Regeneration of the acidic spinning bath requires the removal of these components to prevent their accumulation in the spinning bath due to the effect of the incoming cellulose carbamate solution. Before regeneration, the extracted aqueous spinning bath contains less than 20 g / L, preferably less than 15 g / L, and most preferably less than 10 g / L of dissolved ammonium nitrogen, such as ammonium sulfate, at a temperature of at least 10°C. Therefore, according to a preferred embodiment, the extracted aqueous spinning bath is at least substantially free of ammonium alum precipitates, and preferably does not contain any solid ammonium alum.

[0071] According to one embodiment, the aqueous spinning bath portion drawn from the spinning unit has a density of 1200 to 1330 kg / m³ (measured at 20°C) and a preferred mass-to-weight ratio of Na₂SO₄ to Al₂(SO₄)₃ of 1:1 to 3:1.

[0072] As described above, according to one embodiment, before regeneration, the portion of the spinning bath leaving the spinning unit, i.e., the extracted aqueous spinning bath portion having a pH (at 20°C) in the range of 0.2 to 0.9, preferably 0.5 to 0.8 or 0.7 to 0.9, comprises: - Zinc, such as ZnSO4, 10 to 50 g / l, and - Dissolved nitrogen, such as (NH4)2SO4, less than 20 g / L, preferably less than about 15 g / L, and most preferably less than 10 g / L.

[0073] According to one embodiment, the method includes continuously extracting a large volume of aqueous spinning bath from the spinning unit for regeneration. Similarly, according to one embodiment, the liquid phase portions of the stretching bath and the washing bath are continuously extracted for regeneration.

[0074] In one embodiment, by extracting the aqueous spinning bath and subjecting it to sodium sulfate and zinc recovery operations, for example, at least 70% by weight, preferably at least 80% by weight, and more preferably at least 90% by weight of sodium sulfate formed in the spinning bath (especially under steady-state conditions) is recovered in a crystallization step, and at least 80% by weight, preferably at least 85% by weight, and more preferably 90% by weight of zinc sulfate formed in the spinning bath (especially under steady-state conditions) is recovered in a zinc removal step.

[0075] According to one embodiment, a portion of the extracted aqueous spinning bath is first transferred to a tank called a "dilute bath," from which the aqueous spinning bath can be regenerated. According to one embodiment, an optional portion of the extracted aqueous stretching bath and / or cleaning bath can also be transferred to the same tank. In one embodiment, the water evaporation rate defines how much stretching bath and / or cleaning bath can be transferred to the spinning bath for recycling. In one embodiment, an optional portion of the extracted aqueous stretching bath and / or cleaning bath can also be directly transferred to a water removal feed (evaporation) to utilize the energy content of these high-temperature solution streams.

[0076] According to one embodiment, regeneration includes performing a separation step, a zinc removal step, a water removal step, or a sodium sulfate removal step, or any combination thereof, preferably all of them, on the extracted aqueous spinning bath portion.

[0077] In a preferred embodiment, the entire portion of the extracted aqueous spinning bath is filtered, but only a portion of the filtered spinning bath undergoes other separation steps.

[0078] According to a preferred embodiment, regeneration includes filtering the extracted aqueous spinning bath portion in a filtration unit, zinc extraction in an extraction unit, and sodium sulfate crystallization in a crystallization unit. According to another embodiment, regeneration may also include only one or two of these units; that is, regeneration may include filtration, zinc extraction, or sodium sulfate crystallization, or any combination thereof. Additionally, regeneration typically includes water evaporation.

[0079] According to one embodiment, the extracted aqueous spinning bath portion is preferably first separated, preferably filtered in a filtration unit to remove solids, such as any present ammonium aluminum sulfate and other solid materials. Optional separation can be carried out by any known separation method, such as filtration using diatomaceous earth or perlite, or, for example, centrifugation. Solids are recovered from the process. The filtrate (i.e., the extracted spinning bath portion without solids) is introduced into a regeneration process.

[0080] According to one embodiment, the method includes selectively removing zinc from a portion of the extracted aqueous spinning bath.

[0081] Therefore, according to a preferred embodiment, the extracted spinneret portion or at least a portion thereof is preferably subjected to selective zinc removal after separation, preferably zinc selective extraction. Prior to zinc removal, the extracted aqueous spinneret portion preferably has a pH higher than 0.2, more preferably higher than 0.5, and most preferably in the range of 0.7 to 0.9 or 0.5 to 0.75.

[0082] According to a preferred embodiment, the zinc concentrate recovered by zinc selective extraction contains preferably less than 10% by weight of aluminum ions (e.g., Al 3+), most preferably less than 5% by weight, such as less than 3% by weight, most preferably less than 2.5% by weight, such as less than 2.0% by weight, which is based on the zinc (e.g., Zn 2+) portion of the recovered zinc concentrate.

[0083] According to one embodiment, ferric iron (e.g., Fe³⁺) in the spinning bath, which is an impurity, is preferably reduced to ferrous iron (Fe²⁺) by using, for example, sulfur dioxide reduction before zinc extraction in the aqueous spinning bath. Ferric iron is then easily extracted with zinc by saturating the active extractant. If reduction treatment using sulfur dioxide is used, the individual iron removal step of purifying the saturated extractant can be avoided.

[0084] According to one embodiment, zinc can be removed by extraction, such as liquid-liquid phase extraction or solid phase extraction (SPE), particularly liquid-liquid phase extraction or ion exchange, in one or more stages. Preferably, zinc is removed selectively to avoid co-extraction with aluminum. It has been unexpectedly discovered in this invention that zinc can be selectively removed under the acidic conditions of this invention. In particular, the pH of the spinning bath is crucial during zinc extraction. Therefore, according to one embodiment, the above method comprises removing zinc from a portion of an extracted aqueous spinning bath having a pH higher than 0.2, preferably higher than 0.5, most preferably between 0.7 and 0.9 or 0.5 and 0.75.

[0085] According to one embodiment, the method comprises removing zinc from the extracted aqueous spinning bath portion by contacting it with an organic solvent containing an active extractant (especially an active extractant of an organophosphorus compound), particularly at least one of the following, either directly or in a carrier matrix: di-(2-ethylhexyl)phosphoric acid, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC-88A), bis-(2,4,4-trimethylpentyl)phosphonic acid, and bis-(2,4,4-trimethylpentyl)dithiophosphonic acid, or mixtures thereof, especially di-(2-ethylhexyl)phosphoric acid.

[0086] According to one embodiment, zinc removal can be performed at high temperature and the extracted aqueous spinning bath can be heated before zinc removal.

[0087] Therefore, according to one embodiment, the above method includes removing zinc by liquid-liquid phase extraction, particularly multi-stage liquid-liquid phase extraction, using an organic solvent and at high temperature from a portion of an extracted aqueous spinning bath having a pH of 0.7 to 0.9 or 0.5 to 0.75.

[0088] According to a preferred embodiment, zinc is removed from an organic active extractant / organic slightly water-soluble hydrocarbon solvent solution by liquid-liquid phase extraction (preferably multi-stage liquid-liquid phase extraction). According to one embodiment, the amount of active extractant in the extraction solvent is preferably 20 to 45% by volume, more preferably 40% by volume, where the volume percentage is based on the total volume of the extraction solvent, i.e., based on the total volume of the extractant and the hydrocarbon solvent. According to a most suitable embodiment, the organic solvent mixture for selective zinc extraction comprises di-(2-ethylhexyl)phosphoric acid as the active extractant and kerosene or a similar type of inert hydrocarbon solvent in the form of a slightly water-soluble hydrocarbon solvent as the carrier matrix.

[0089] The extracted zinc is typically recovered as a concentrated zinc sulfate solution containing sulfuric acid, and the remaining portion of the extracted spinning bath is transferred separately in a regeneration process.

[0090] In solid-phase extraction, zinc present in the liquid phase is adsorbed by the solid or stationary phase through which the liquid passes. The stationary phase may contain organophosphorus groups or compounds of the types mentioned above.

[0091] According to one embodiment, the recovered zinc is recycled back to the dissolution method and / or spinning method via zinc hydroxide precipitation to dissolve cellulose carbamate to form cellulose carbamate solution.

[0092] According to one embodiment, the extracted spinning bath portion or at least a portion thereof is preferably subjected to water evaporation after filtration and / or zinc extraction. Therefore, according to one embodiment, the method includes removing water from the extracted spinning bath by evaporation before introducing the extracted spinning bath into the step of removing sodium sulfate. A cellulose carbamate solution introduces a large amount of water into the spinning unit, and in a preferred embodiment, the water is removed during a regeneration cycle. Preferably, the water is evaporated before sodium sulfate removal, as increasing the sodium sulfate concentration before sodium sulfate removal is suitable. According to one embodiment, the extracted aqueous spinning bath portion for sodium sulfate removal may comprise a combination of an evaporated aqueous spinning bath portion and an undevaporated aqueous spinning bath portion, provided the water volume is at an appropriate level for the following steps. In addition to removing water by evaporation, crystallizing sodium sulfate decahydrate also removes water from the spinning bath system by means of hydrated salt crystals.

[0093] According to a preferred embodiment, the extracted spinning bath is preferably subjected to sodium sulfate removal after separation, zinc removal, and / or water evaporation, preferably sodium sulfate crystallization (particularly in the form of sodium sulfate decahydrate), such as cold crystallization or vacuum crystallization. Therefore, according to one embodiment, the above method includes the partial removal of sodium sulfate from the extracted spinning bath by crystallization.

[0094] According to a preferred embodiment, the extracted aqueous spinning bath portion for sodium sulfate removal has a specific ratio of sodium sulfate to aluminum sulfate to avoid co-crystallization of aluminum sulfate, which would interfere with the crystallization of sodium sulfate to the purest possible concentration. Therefore, according to a preferred embodiment, the method includes providing a portion of the extracted aqueous spinning bath, preferably having a Na₂SO₄ to Al₂(SO₄)₃ mass weight ratio of 1.4:1 to 2.5:1, most preferably 1.5:1 to 2:1, and most preferably 1.6:1 to 1.9:1, and feeding this portion to the step for sodium sulfate removal. In one embodiment, the Na₂SO₄ to Al₂(SO₄)₃ ratio is adjusted, for example by adding sodium sulfate. Therefore, in one embodiment, a portion of the crystallized sodium sulfate is returned to the crystallization step to adjust the Na₂SO₄ to Al₂(SO₄)₃ ratio to promote crystallization. According to a preferred embodiment, a suitable mass weight ratio of Na₂SO₄ to Al₂(SO₄)₃ is controlled by adjusting the amount of crystallized sodium sulfate.

[0095] According to one embodiment, the extracted aqueous spinning bath portion for sodium sulfate removal has a pH in the range of 0.2 to 0.9 and a zinc concentration preferably of up to 60 g / l.

[0096] Therefore, according to one embodiment, there are several factors affecting the crystallization purity of sodium sulfate, one of the most important being the mass weight ratio of Na₂SO₄ to Al₂(SO₄)₃. If this ratio is not optimized, a large amount of aluminum sulfate may crystallize in the crystallized sodium sulfate. Furthermore, the concentrations of zinc and sulfuric acid affect the purity of the sodium sulfate crystals.

[0097] According to a preferred embodiment, aluminum sulfate remains essentially in the cycle, i.e., it does not participate in the crystallization of sodium sulfate. Therefore, the remainder of the spinning bath extracted from the crystallization preferably contains aluminum sulfate.

[0098] Preferably, external cooling is used to perform sodium sulfate cooling crystallization on the extracted aqueous spinning bath portion at a temperature of 1 to 10°C, for example, 4 to 8°C.

[0099] According to another embodiment, the extracted aqueous spinning bath portion is subjected to vacuum crystallization of sodium sulfate. During vacuum crystallization, the aqueous spinning bath is concentrated; for example, 4 to 8% by weight of water may be evaporated during vacuum crystallization.

[0100] Sodium sulfate crystals (especially in the form of sodium sulfate decahydrate) are recovered and optionally washed. The sodium sulfate decahydrate crystals are optionally calcined. The remaining portion of the spinning bath (i.e., the supernatant) extracted from crystallization is transferred to a "thick bath" tank.

[0101] According to one embodiment, the supernatant is separated from sodium sulfate and recycled to the spinning bath.

[0102] Therefore, according to one embodiment, the regenerated acidic spinning bath includes a portion of the extracted aqueous spinning bath that has been regenerated during the regeneration cycle, for example by extraction and crystallization, but it may also include a portion of the extracted spinning bath that has already undergone the regeneration step. Such regenerated spinning bath can be collected in a "concentrate" tank before being recycled back to the spinning unit bath.

[0103] According to one embodiment, the concentration of the spinning bath to be fed into the spinning unit is adjusted to an appropriate level by adding sulfuric acid and / or aluminum sulfate. According to another embodiment, the method includes feeding fresh sulfuric acid and / or aluminum sulfate into the spinning unit before recycling the regenerated spinning bath back to the spinning unit. Therefore, fresh raw materials of sulfuric acid, aluminum sulfate, aluminum hydroxide, or any mixture thereof are added to, for example, a "concentration bath". Optionally, fresh aluminum hydroxide may react with sulfuric acid to form aluminum sulfate.

[0104] According to one embodiment, if any aluminum sulfate reaches the effluent of a semi-closed-loop solidification or spinning bath circulation system, the aluminum will precipitate as aluminum hydroxide and optionally be returned to, for example, the spinning bath described above.

[0105] According to one embodiment, a method for manufacturing cellulose carbamate filaments or fibers includes the following steps: - A cellulose carbamate solution is provided, comprising cellulose carbamate dissolved in aqueous sodium hydroxide, the cellulose carbamate solution further comprising a dissolved zinc compound, wherein the solution comprises 6 to 10 wt% cellulose carbamate, 5 to 10 wt% sodium hydroxide and 0.1 to 2 wt% dissolved zinc compound, the wt% being based on the total weight of the cellulose carbamate solution; - The cellulose carbamate solution is fed into a spinning unit having an aqueous spinning bath containing sulfuric acid and aluminum sulfate, wherein the steady-state spinning bath has a pH in the range of 0.2 to 0.9 (at 20°C); - The cellulose carbamate solution is transferred to the aqueous spinning bath and then solidified to form cellulose carbamate filaments; - The cellulose carbamate filament is stretched and optionally washed, and optionally cut into short fibers; - A portion of the aqueous spinning bath containing sodium sulfate, water, and zinc ions is extracted, the extracted aqueous spinning bath having a temperature of at least 10°C; - The extracted spinning bath portion is regenerated by removing at least a portion of the sodium sulfate, water, and zinc ions; and - Recycle at least a portion of the regenerated aqueous spinning bath to the spinning unit.

[0106] According to one embodiment, the method includes a step of selectively removing zinc and a step of selectively recovering sodium sulfate and recycling the recovered aluminum sulfate to the spinning bath to recover aluminum sulfate.

[0107] The accompanying drawings illustrate the implementation method.

[0108] Figure 1 illustrates a method according to at least some embodiments of the present invention, wherein a cellulose carbamate solution is first fed into a spinning unit 1 having an aqueous spinning bath. In the spinning bath, the cellulose carbamate from the cellulose carbamate solution to the aqueous spinning bath is coagulated to form cellulose carbamate filaments or cellulose carbamate filament bundles, which are then stretched in one or more stretching units 2. The stretched filaments are then washed in a washing unit 3a. Alternatively, the stretched filament bundles are first cut into short fibers in a cutting unit 3b, and then washed in the washing unit 3a. After washing, cellulose carbamate filaments or short fibers are obtained.

[0109] The method of this invention further includes the chemical recovery and recycling of chemicals. Therefore, a portion of the aqueous spinning bath containing sodium sulfate, water, and zinc ions is preferably drawn from the spinning bath of spinning unit 1 into a "thin bath" tank 4. A portion of the aqueous stretching bath from stretching unit 2 is also drawn out and preferably introduced into the "thin bath" tank 4 along with the drawn-out spinning bath. The drawn-out spinning bath and stretching bath are partially regenerated by removing at least a portion of the sodium sulfate, water, and zinc ions. In the regeneration cycle, the drawn-out aqueous spinning bath and stretching bath are first filtered in filtration unit 5. After filtration, the filtrate is subjected to zinc selective extraction in extraction unit 6, but the residue (i.e., solids) is recovered from the method. At least a portion of the zinc ions are removed by zinc selective extraction, and preferably recovered as an acidic zinc sulfate concentrate. After zinc extraction, the remaining mixture of the extracted spinning and stretching baths is evaporated in evaporation unit 7, followed by sodium sulfate crystallization in crystallization unit 8. The crystallized sodium sulfate is recovered, and the remaining mixture of the extracted spinning and stretching baths is transferred to a "concentration bath" tank 9. Thus, the spinning bath collected in the "concentration bath" tank 9 is at least partially regenerated and then recycled back to spinning unit 1.

[0110] As described above, at least a portion of the regenerated aqueous spinning bath (preferably collected in the "concentrate bath" tank 9) is recycled back to the spinning unit 1. However, according to a preferred embodiment, the method further includes feeding fresh raw materials of sulfuric acid and aluminum sulfate into the spinning unit 1 before recycling the regenerated spinning bath back to the spinning unit 1. [Example]

[0111] The following non-limiting embodiments illustrate at least some implementations of the present invention: Example 1

[0112] Cellulose carbamate powder (having a nitrogen content of 1.6 wt% in dry cellulose carbamate) was dissolved in an alkaline aqueous solution to prepare a cellulose carbamate solution, yielding a composition comprising 8.5 wt% cellulose carbamate, 6.5 wt% sodium hydroxide, 1.3 wt% dissolved zinc oxide, and 0.085 wt% dissolved nitrogen. This composition (i.e., the cellulose carbamate solution) was fed into a spinning unit through a spinning nozzle, where the cellulose carbamate was solidified into cellulose carbamate fiber filaments. The filament bundles were formed and further stretched and cut into short fibers in a stretching bath, followed by washing the recovered short fibers in a post-treatment unit. The short fibers recovered from the post-treatment unit had a nitrogen content of 0.7 wt% in dry solids. The degree of hydrolysis of the cellulose carbamate was 56%.

[0113] A portion of the aqueous spinning bath was drawn from the spinning unit, having a pH of 0.75, a sodium sulfate to aluminum sulfate ratio of 1.63, a density of 1.300 kg / l, a temperature of 20°C, an ammonium sulfate content of 7.5 g / l, and a zinc sulfate content of 20.0 g / l. The density was measured using a liquid hydrometer / gas hydrometer.

[0114] The portion of the spinning bath that has been extracted is filtered.

[0115] A portion of a filtered aqueous spinning bath with a pH of 0.75 was subjected to a three-stage liquid-liquid phase extraction (Li-Li-PPE) process to remove a portion of the zinc. For Li-Li-PPE, two volumes of the aqueous spinning bath were efficiently mixed with one volume of an organic solvent mixture (containing 40% by volume di-(2-ethylhexyl)phosphoric acid in kerosene) for 3 minutes, followed by separation of the aqueous and organic solvent phases. The separated aqueous phase was then re-extracted with a portion of fresh organic solvent. The extraction process was repeated again with a portion of fresh organic solvent. The separated organic solvent phases from the three subsequent extraction steps were mixed together and zinc was released by back-extraction (removal) with a 100 g / L aqueous sulfuric acid solution. The zinc and aluminum content in the sulfuric acid solution obtained by removal was analyzed by selective titration with ethylenediaminetetraacetic acid (EDTA). Based on the analysis results, the total extraction yield was 87% by weight of zinc and 1.9% by weight of aluminum. Zinc was selectively extracted in the presence of aluminum. The zinc sulfate content in the water-based spinning bath was reduced from 20 g / l to 2.6 g / l.

[0116] A portion of the filtered and zinc-extracted aqueous spinning bath is evaporated: 21.5% by weight of water (based on the total volume of the aqueous spinning bath) is removed by evaporation, resulting in a concentrated aqueous spinning bath with a sodium sulfate to aluminum sulfate ratio of 1.63, a temperature of 50°C, and an ammonium sulfate content of 9.3 g / L (standard SFS 5505: 1988).

[0117] A portion of the concentrated aqueous spinning bath was cooled and crystallized. The temperature of the concentrate was reduced from 50°C to 8°C. The yield of sodium sulfate decahydrate containing salt crystals recovered by centrifugation was 29.4 wt%, and the supernatant was 70.6 wt%. The centrifuged crystals were washed with water to remove most of the supernatant residue from the crystal surface. The hydrated crystals were calcined at 130°C. Anhydrous crystal samples taken after calcination were dissolved in water, and the aluminum content was determined by selective titration with EDTA. The aluminum content of the recovered calcined sodium sulfate was 0.56 wt%, corresponding to aluminum sulfate in 3.5 wt% sodium sulfate. The sodium sulfate was selectively crystallized in the presence of aluminum sulfate. In contrast, when a sodium sulfate to aluminum sulfate ratio of 1.18 was used instead of 1.64, the aluminum content of the calcined sodium sulfate was 13 wt%, with other method conditions being the same. Therefore, the selectivity of crystallization was reduced when the sodium sulfate to aluminum sulfate ratio was not optimized.

[0118] The supernatant containing aluminum sulfate is recycled back to the spinning bath, which comprises regenerated and unregenerated aqueous spinning bath portions collected from different steps of the spinning bath regeneration process. Before recycling the mixture back to the spinning unit, some fresh sulfuric acid and aluminum sulfate are added.

[0119] It should be understood that the embodiments of the present invention disclosed herein are not limited to the specific structures, method steps, or materials disclosed herein, but extend to their equivalents, as would be understood by those skilled in the art related to the invention. It should also be understood that the terminology used herein is for describing specific embodiments only and is not intended to be limiting.

[0120] In this specification, an embodiment or implementation method refers to a specific feature, structure, or characteristic described in connection with an embodiment that is included in at least one embodiment of the invention. Therefore, the use of the terms "in one embodiment" or "in an embodiment" throughout this specification does not necessarily refer to the same embodiment. When terms such as approximately or substantially numerical values ​​are used, precise numerical values ​​are also disclosed.

[0121] As used herein, for convenience, multiple items, structural elements, constituent elements, and / or materials may be listed in a common list. However, these lists should be interpreted as each member of the list being interpreted as a separate and distinct member. Therefore, unless otherwise stated, an individual member on such a list should not be interpreted as a practical equivalent of any other member on the same list simply because such a member appears in a common group. Furthermore, various embodiments and examples of the invention, along with substitutions for their various components, may be mentioned herein. It should be understood that such embodiments, examples, and substitutions should not be construed as practical equivalents of each other, but should be regarded as separate and autonomous representations of the invention.

[0122] Furthermore, in one or more embodiments, the described features, structures, or characteristics may be combined in any suitable manner. In the following description, numerous specific details, such as examples of length, width, shape, etc., are provided to provide a thorough understanding of embodiments of the invention. However, those skilled in the art will recognize that the invention may be practiced without one or more specific details, or may be practiced with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring the nature of the invention.

[0123] While the above embodiments illustrate the principles of the invention in one or more specific applications, it will be apparent to those skilled in the art that many modifications can be made to the form, usage, and details of the implementation without employing inventive capabilities and without departing from the principles and concepts of the invention. Therefore, the invention is not intended to be limited except as set forth in the claims below.

[0124] In this text, the verbs "contain" and "include" are used as open restrictions, neither excluding nor requiring the existence of unlisted features. Unless otherwise expressly stated, the features listed in the appendix can be freely combined. Furthermore, it should be understood that the use of the singular forms "a" or "an" in this text does not preclude the plural. [Industrial Utilization]

[0125] At least some embodiments of the present invention have industrial applications in the production of cellulose carbamate filaments or fibers from cellulose carbamate solutions.

[0126] 1: Spinning unit 2: Tensioning Unit 3a: Cleaning unit 3b: Cutting unit 4: "Diluted Bath" Tank 5: Filtering unit 6: Extraction Unit 7: Evaporation Unit 8: Crystallization unit 9: "Concentrated Bath" Tub

Claims

1. A method for manufacturing cellulose carbamate filaments or fibers, comprising the following steps: providing a cellulose carbamate solution comprising cellulose carbamate dissolved in aqueous sodium hydroxide, the cellulose carbamate solution further comprising a dissolved zinc compound; feeding the cellulose carbamate solution into a spinning unit having an aqueous spinning bath comprising sulfuric acid and aluminum sulfate; coagulating the cellulose carbamate from the cellulose carbamate solution into the aqueous spinning bath to form cellulose carbamate filaments; stretching the cellulose carbamate filaments; extracting a portion of the aqueous spinning bath comprising sodium sulfate, water, and zinc ions, the extracted aqueous spinning bath having a temperature of at least 10°C, wherein the extracted aqueous spinning bath portion contains dissolved nitrogen in the form of ammonium nitrogen of less than 20 g / L; regenerating the extracted spinning bath portion by removing at least a portion of the sodium sulfate, water, and zinc ions; and recycling at least a portion of the regenerated aqueous spinning bath back to the spinning unit.

2. The method of claim 1, wherein prior to the regeneration, the extracted aqueous spinning bath portion contains dissolved nitrogen in the form of ammonium nitrogen at a temperature of at least 10°C.

3. The method of claim 1 or 2, wherein the mass weight ratio of Na2SO4 to Al2(SO4)3 in the spinning bath is maintained at 1:1 to 3:1 by regenerating and recycling the aqueous spinning bath.

4. The method of claim 1 or 2, wherein the aqueous spinning bath portion drawn from the spinning unit has a density of 1200 to 1330 kg / m3 and a Na2SO4 to Al2(SO4)3 mass weight ratio of 1:1 to 3:

1.

5. The method of claim 1 or 2, wherein, prior to regeneration, the extracted aqueous spinning bath portion having a pH in the range of 0.2 to 0.9 (at 20°C) comprises: - zinc, 10 to 50 g / l, and - dissolved nitrogen, less than 20 g / l.

6. The method of claim 1 or 2, comprising separating the extracted aqueous spinning bath portion to remove solids.

7. The method of claim 1 or 2, comprising selectively removing zinc from the extracted portion of the aqueous spinning bath.

8. The method of claim 1 or 2, comprising removing zinc from the portion by contacting the extracted aqueous spinning bath portion having a pH higher than 0.2 with at least one of the following, either alone or in a carrier matrix: di-(2-ethylhexyl)phosphoric acid, mono-2-ethylhexyl 2-ethylhexylphosphonate (PC-88A), bis-(2,4,4-trimethylpentyl)phosphonic acid, and bis-(2,4,4-trimethylpentyl)dithiophosphonic acid, or mixtures thereof.

9. The method of claim 1 or 2, which includes the removal of zinc by extraction or ion exchange in one or more stages.

10. The method of claim 7, wherein zinc is removed by liquid-liquid phase extraction or solid phase extraction.

11. The method of claim 1 or 2, comprising removing water from the extracted aqueous spinning bath portion by evaporation before subjecting the extracted aqueous spinning bath portion to the step of removing sodium sulfate.

12. The method of claim 1 or 2, comprising removing sodium sulfate from the extracted aqueous spinning bath portion having a Na2SO4 to Al2(SO4)3 mass weight ratio of 1.4:1 to 2.5:1 before crystallizing the extracted aqueous spinning bath portion for removing sodium sulfate.

13. The method of claim 12, wherein the ratio of Na2SO4 to Al2(SO4)3 is adjusted by adding sodium sulfate before the sodium sulfate is removed from the extracted aqueous spinning bath portion.

14. The method of claim 1 or 2, comprising removing sodium sulfate from the extracted aqueous spinning bath portion by crystallization.

15. The method of claim 1 or 2, wherein the extracted aqueous spinning bath portion is subjected to cooling crystallization of sodium sulfate at a temperature of 1 to 10°C.

16. The method of claim 1 or 2, wherein the extracted aqueous spinning bath portion is subjected to vacuum crystallization of sodium sulfate.

17. The method of claim 11, wherein the recovered sodium sulfate is in the form of sodium sulfate decahydrate.

18. The method of claim 1 or 2, wherein the extracted aqueous spinning bath portion is substantially free of solid ammonium alum precipitate.

19. The method of claim 1 or 2, comprising feeding the fresh raw material into a regenerated acid spinning bath before recycling the fresh raw material of sulfuric acid, aluminum sulfate, aluminum hydroxide or any mixture thereof into the spinning unit.

20. The method of claim 1 or 2, comprising recovering aluminum sulfate from the steps of selectively removing zinc and selectively removing sodium sulfate, and recycling the recovered aluminum sulfate to the spinning bath.

21. The method of claim 1 or 2, wherein the aqueous alkaline cellulose carbamate solution comprises up to 10% by weight of cellulose carbamate, less than 8% by weight of sodium hydroxide and up to 1.5% by weight of Zn (calculated as ZnO), wherein the percentages are based on the total weight of the cellulose carbamate solution.

22. The method of claim 1 or 2, wherein the cellulose carbamate solution has a maximum dissolved nitrogen content of less than 0.2% by weight, based on the weight of the cellulose carbamate solution.

23. The method of claim 1 or 2, wherein the cellulose carbamate solution is provided to the spinning unit at a temperature of 10 to 30°C.

24. The method of claim 1 or 2, wherein the cellulose carbamate solution is coagulated in the spinning bath at a temperature of up to 25°C.

25. The method of claim 1 or 2, wherein the cellulose carbamate in the cellulose carbamate solution is provided with a degree of hydrolysis of less than 70%, the degree of hydrolysis being based on the difference in the percentage of cellulose-bound carbamate nitrogen between the cellulose carbamate before dissolution and the cellulose carbamate after coagulation.

26. The method of claim 1 or 2, wherein the coagulated cellulose carbamate filament is stretched in one or more stretching units, then cut to provide short fibers, and the recovered filament or short fibers are washed in a washing unit.

27. The method of claim 1 or 2, comprising feeding a spinning solution into the spinning unit and withdrawing an aqueous spinning bath from the spinning unit, such that at least 70% by weight of the sodium sulfate formed in the spinning bath is removed in a crystallization step for removing sodium sulfate, and at least 80% by weight of the zinc formed in the spinning bath is removed in a zinc removal step.

28. The method of claim 1 or 2, comprising further extracting a portion of the aqueous stretching and / or washing bath containing sodium sulfate, water and zinc ions together with the extracted portion of the spinning bath to the regeneration.

Images