Recovering acid-superbase conjugated ionic liquids by removing water in the lyocell fiber spinning process

Abstract

According to the present invention, a method for producing cellulose filaments or films is provided, the method comprising the following steps: dissolving a cellulose substrate in an ionic liquid composed of a superbase cation 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium [mTBDH]+ and an anion to produce a solution forming a spinning solution, wherein the anion is derived from an acid present in a stoichiometric excess relative to the superbase; extruding the spinning solution through a spinneret in a coagulation bath containing water to form filaments or films from the solution; extracting the extracted ionic liquid in the form of an aqueous mixture with water from the coagulation bath; recovering the ionic liquid [mTBDH][OAc] from the aqueous mixture by removing water; and selectively recycling the recovered ionic liquid to the dissolution step.

Description

Technical Field

[0001] The present invention relates to a method for producing an ionic liquid, in particular an acid-superbase conjugated ionic liquid, used as a cellulose solvent in a Lyocell process. In particular, the present invention relates to the recovery and recycling of the acid-superbase conjugated ionic liquid. Background Art

[0002] Ionic liquids (ILs) are molten salts with a melting point below 100 °C. Since their seminal discovery by Rogers and co-workers in 2002, ionic liquids have gained importance as high-performance cellulose solvents [2]. Alkylated imidazolium chlorides, acetates or diethylphosphate (DEP) are the most frequently studied powerful cellulose solvents. It has been shown that the direct dissolution of cellulose is easier to control than the NMMO process, the process is intrinsically safer and gives fibers with properties equivalent to those produced from NMMO solutions [3,4]. However, imidazolium-based ILs show no inertness towards cellulose [3,5]. Depending on the substituents on the cation and the chemical nature of the anion, cellulose is strongly degraded, also because higher temperatures are required to obtain good spinnability, which in turn requires the use of stabilizers. The first generation of ILs, which usually used chloride as anion, had the disadvantage that they required higher spinning temperatures due to the high viscosity of the resulting cellulose solution and also showed a high corrosion potential towards the materials used in the spinning equipment [6]. As shown by the example of [emim][OAc], chloride ions are quickly replaced by acetate, which greatly improves the solubility of cellulose and also greatly reduces the risk of corrosion. Nevertheless, the resulting cellulose solution shows insufficient spinning performance due to the delayed regeneration kinetics [7]. As an alternative to imidazolium-based ILs, superbase-based acetates have been shown to be excellent cellulose solvents, with comparable or even improved spinning performance compared to cellulose solutions in NMMO monohydrate. Among this class of base-conjugated ILs, 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (mTBD) all show excellent cellulose solubility and dry-jet / wet-spinning performance [1,8,9].

[0003] Subsequently, the air-gap spinning process based on the solvents [DBNH][OAc] and [mTBDH][OAc] was further developed and registered as Fiber technology. Cellulose solvent [DBUH] [OAc] also belongs to this class, but is no longer studied as a solvent because it does not offer convincing advantages over the other two ILs [9].

[0004] exist During process development, it was discovered that the guanidinium IL [mTBDH][OAc] was more suitable for fiber processing than the initially proposed amidinium IL [DBNH][OAc], primarily due to its higher hydrolytic stability in the presence of water [1]. This hydrolytic stability is critical for lossless water removal during recycling.

[0005] Both ionic liquids belong to Acidic ionic liquids (BAILs) are liquids in which a proton is transferred to a cation

[10] . The extent of the proton transfer can be estimated by the ΔpKa, which can be calculated as the difference between the pKa of the acid and the base. Protic ILs with ΔpKa values ​​above 8-10 are reported to have "ideal" ionicity

[11] . With the reported pKa of mTBD in water being 13.0 / 15.0 (experimental / calculated) and the pKa of acetic acid being 4.75, the ΔpKa of the BAIL [mTBDH][OAc] can be calculated to be 8.25 / 10.25, indicating high ionicity

[12] . Assuming that the pKa of DBN (pKa in water has not been published) is comparable to that of DBU, the ΔpKa can be estimated to be 6.75 / 8.75 [11.5 (experimental) - 4.75] / [13.5 (calculated) - 4.75]. This simplified approximation suggests that [mTBDH][OAc] can be assumed to be significantly more ionic than [DBNH][OAc]. Conjugated carboxylic acids of organic superbases can be distilled at relatively low temperatures and pressures to form neutral species in the gas phase via dynamic equilibrium according to:

[0006]

[0007] It has also been shown that the basicity of the anion (β value, empirical Kamlet-Taft (KT) parameter

[14] ) determines the volatility of the ionic liquid. For imidazolium-based ionic liquids, it was found that the stronger the ability to dissolve cellulose, the higher the thermal stability

[15] . Although the overall trend is comparable, this is not the case for DBN-based and mTBD-based ionic liquids. Although the KT parameter shows that [mTBD][OAc] has a slightly better ability to dissolve cellulose, the thermal stability of [mTBDH][OAc] is significantly higher than that of [DBNH][OAc] ( Figure 1 ).

[0008] The KT parameters of the two ionic liquids are summarized in Table 1.

[0009] Table 1: Kamlet-Taft parameters for anhydrous [mTBDH][OAc] and [DBNH][OAc]

[0010] parameter [mTBDH][OAc] [DBNH][OAc] ET(30) 48.96 49.88 π* 1.01 0.99 α 0.42 0.49 β 1.17 1.08 β-α 0.75 0.49

[0011] In the case of [mTBDH][OAc], the values ​​of β and β-α were higher, indicating that the solubilization ability of cellulose was slightly better than that of [DBNH][OAc]. Summary of the invention

[0012] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0013] According to one aspect of the present invention, a method for producing cellulose silk or film is provided. According to the method, a cellulose substrate is dissolved in an ionic liquid composed of a superbase cation 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium[mTBDH]+ and an anion to produce a solution forming a spinning solution, wherein the anion is derived from an acid that is present in excess relative to the superbase stoichiometric amount. The spinning solution is extruded through a spinneret in a coagulation bath containing water to form a silk or film from the solution. An ionic liquid in the form of an aqueous mixture with water is extracted from the coagulation bath. The ionic liquid [mTBDH][OAc] is recovered from the aqueous mixture by removing water and the recovered ionic liquid is selectively recycled to the dissolution step. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Thermogravimetric analysis (TGA) results of ionic liquids [DBNH][OAc] and [mTBDH][OAc] are shown. It is clearly confirmed that [DBNH][OAc] has higher volatility compared to [mTBDH][OAc].

[0015] Figure 2 The hydrolysis reaction of [DBNH][OAc] in the presence of water is shown, followed by irreversible formation of acetamide.

[0016] Figure 3 The hydrolysis reaction of [mTBDH][OAc] in the presence of water is shown, followed by irreversible formation of acetamide.

[0017] Figure 4 The kinetics of DBN degradation in ionic liquids with an acid-base ratio of 1:1 versus 5:3 (azeotropic mixture) are shown.

[0018] FIG. 5 shows the kinetics of (left) DBN hydrolysis and (right) mTBD hydrolysis at 85° C. in the presence of 10 wt % water at an acetic acid-base ratio of 1:1.

[0019] FIG6 shows the kinetics of hydrolysis of (left) DBN and (right) mTBD at 95° C. in the presence of 10 wt % water at an acetic acid-base ratio of 1:1.

[0020] Figure 7The kinetics of the formation and consumption of two isomeric H-mTBD forms at 95 °C and 10 wt% water are shown.

[0021] Figure 8 Shown is the disappearance of [mTBD] in the ionic liquid [mTBDH][OAc] over time at 95°C at different acetic acid-base molar ratios and in the presence of 10 wt% water.

[0022] Fig. 9 Shown is the percentage of mTBD degradation in PIL[mTBD][OAc] as a function of time at 95°C for various acid-base ratios 1 :1 (reference); 1.1 :1 and 1.2:1.

[0023] Fig.10 Shown are the amounts of hydrolysis products and any acetamide subsequently produced under equilibrium conditions (ΣmTBDdeg,equ) at 95°C, and the equilibrium constant Kc (A:B=1:1) as a function of the water content of [mTBD][OAc].

[0024] FIG. 11 shows the proportional area of ​​undissolved fiber elements in [mTBDH](1-x)[TBDH]x[OAc] based on a 13 wt% cellulose solution. Fig.11a (Left): 0 wt% TBD, Fig.11b (right): 30% by weight TBD.

[0025] Fig.12 The DSC and TGA graphs of [TBDH][OAc] are shown.

[0026] Fig.13 A laboratory-scale Simplified solution of the process.

[0027] Fig.14 Shown is a monofilament combined with ionic liquid recycling Simplified scheme of the fiber spinning process.

[0028] Fig.15 Shown are the histories of the acid-base ratio (A / B), residual water content and hydrolysis product concentration in the recycled ionic liquid during 20 cycles. DETAILED DESCRIPTION

[0029] definition

[0030] Unless otherwise stated herein or clearly indicated by the context, any percentages referred to herein are expressed as weight percentages based on the total weight of the respective composition.

[0031] Unless otherwise stated, the properties experimentally measured or determined herein are measured or determined at room temperature. Unless otherwise stated, room temperature is 25°C.

[0032] Unless otherwise stated, the properties experimentally measured or determined herein were measured or determined at atmospheric pressure.

[0033] It must also be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless otherwise indicated.

[0034] As used herein, the term "about" refers to the actual given value and also refers to the approximation to the given value that one skilled in the art could reasonably infer, including the approximation resulting from experimental and / or measurement conditions for the given value.

[0035] As used herein, unless otherwise indicated, the term "average molecular weight" refers to the weight average molecular weight (also abbreviated as "M W ” or “Mw”).

[0036] The present invention relates to the production of man-made cellulose fibers (MMCF) by the Lyocell process using ionic liquids as cellulose solvents. More specifically, the ionic liquids used belong to the group of acid-superbase conjugates, which have been described in earlier inventions as extremely powerful cellulose solvents, with which spinnable cellulose solutions can be produced, which can be spun into MMCF with very high strengths by a dry-wet spinning process [1]. The present invention shows that the solvent can be completely recovered under certain conditions by maintaining the level of degradation reactions of the superbase used at an acceptable level without affecting the solubility of the cellulose or the spinning properties of the resulting cellulose solution. Surprisingly, the unexpected composition containing [mTBDH][OAc] can, on the one hand, limit the degree of hydrolysis to a low level, and on the other hand, maintain the solubility characteristics of cellulose up to high concentrations, while maintaining the rheological properties at a level that allows excellent spinning properties. [DBNH][OAc] and [DBUH][OAc] do not allow similar uses associated with recycling by removing water.

[0037] Figure 1 TABLE 1 is a graph showing the results of thermogravimetric analysis (TGA) of ionic liquids [DBNH][OAc] and [mTBDH][OAc]. Although the KT parameters shown in Table 1 show that [mTBD][OAc] exhibits a slightly better ability to dissolve cellulose, [mTBD][OAc] has significantly higher thermal stability than [DBN][OAc].

[0038] Figure 2 The hydrolysis reaction of [DBNH][OAc] in the presence of water is shown, followed by irreversible formation of acetamide. The hydrolysis is an equilibrium reaction, so it can be transformed back to a superbase by appropriate reaction conditions (e.g., acid catalysis). However, in the presence of acetate anions in the ionic liquid, the hydrolysis product is converted to the corresponding acetamide. These consecutive reactions are irreversible, so it is impossible to recover the original superbase.

[0039] Figure 3 The hydrolysis reaction of [mTBDH][OAc] in the presence of water is shown, followed by irreversible formation of acetamide. Hydrolysis is an equilibrium reaction, so it can be transformed back to a superbase by appropriate reaction conditions (e.g., acid catalysis). However, in the presence of acetate anions in an ionic liquid, the hydrolysis product is converted to the corresponding acetamide. These sequential reactions are irreversible, so it is impossible to recover the original superbase.

[0040] Figure 4 The kinetics of DBN degradation in an ionic liquid with an acid-base ratio of 1:1 relative to an ionic liquid with an acetic acid superstoichiometric increase to 5:3 (azeotrope) are shown. The azeotrope has a higher acetic acid content due to its stronger ability to form hydrogen bonds with ion pairs. Despite such a high acid-base ratio of 5:3, especially in the first few hours, DBN degradation is hardly slowed down compared to an equimolar acid-base composition. In the composition of the azeotrope (A:B = 5:3), a slightly higher equilibrium concentration of DBN is achieved. However, this behavior is inconsistent with the Since acetic acid is a non-solvent, the ionic liquid is no longer a solvent for cellulose at an acid-base ratio of 5:3.

[0041] Figure 5 shows the kinetics of hydrolysis of (left) DBN and (right) mTBD at 85°C in the presence of 10 wt% water in an acetic acid-base ratio of 1:1. Figure 5 shows a significant difference in the hydrolytic stability of the two ILs, especially during the first 100 hours.

[0042] Figure 6 shows the kinetics of hydrolysis of (left) DBN and (right) mTBD at 95°C in the presence of 10 wt% water in an acetic acid-base ratio of 1:1. Figure 6 shows a significant difference in the hydrolytic stability of the two ILs, especially during the first 100 hours.

[0043] Figure 7 The kinetics of the formation and consumption of two isomeric H-mTBD forms at 95 °C and 10 wt% water are shown. Figure 7 As shown in , H-mTBD-1 is preferably formed.

[0044] Figure 8The disappearance of [mTBD] in the ionic liquid [mTBDH][OAc] over time is shown at different acetic acid-base molar ratios and in the presence of 10 wt% water at 95° C. In contrast to [DBNH][OAc], even a slight stoichiometric excess of acetic acid leads to a significant stabilization of the cation in the ionic liquid [mTBDH][OAc].

[0045] Fig. 9 The percentage of mTBD degradation in a protic ionic liquid (PIL) [mTBD][OAc] as a function of time at 95°C for various acid-base ratios 1:1 (reference); 1.1:1 and 1.2:1 is shown. The stabilizing effect of excess acetic acid is very evident in the first few hours. This is particularly relevant for the recovery of ionic liquids by thermal evaporation of water.

[0046] Fig.10 The amount of hydrolysis products and any acetamide subsequently produced under equilibrium conditions (∑mTBDdeg, equ) as a function of the water content of [mTBD][OAc] at 95°C, as well as the equilibrium constant Kc (A:B = 1:1) are shown. The water content of the ionic liquid significantly affects the hydrolysis behavior of the base in [mTBDH][OAc], as shown for equimolar acid-base mixtures.

[0047] FIG. 11 shows the proportional area of ​​undissolved fiber elements in [mTBDH](1-x)[TBDH]x[OAc] based on a 13 wt% cellulose solution: Fig.11a (Left): 0 wt% TBD, Fig.11b (right): 30% by weight TBD.

[0048] Fig.12 The DSC and TGA graphs of [TBDH][OAc] are shown. As can be seen from the DSC, the melting point of [TBDH][OAc] is 135°C and therefore does not belong to the class of ionic liquids.

[0049] Fig.13 A laboratory-scale Simplified scheme of the process. The slurry and the ionic liquid are fed into a kneader unit (1) to dissolve the slurry and provide a spinning solution, which is passed through a filter (2) to filter out impurities. The filtered spinning solution is then directed to a spinning unit (3) where the fibers are spun or a membrane is extruded into a spinning bath (4). After spinning or extrusion, the fibers or membrane are washed with water and stretched (5). The washed fibers are recovered and the washing filtrate from the washing and stretching unit (5) is disposed of. The spinning bath (4) solution is filtered and directed to the ionic liquid recovery. The spinning bath solution is first centrifuged or evaporated in a pre-concentration unit (6). The distillate from the pre-concentration unit (6) is processed. The pre-concentrate from the pre-concentration unit (6) is directed to a first thin film evaporation section (7). The distillate from the first thin film evaporation section (7) is directed to the spinning bath (4), and the residue from the first thin film evaporator section (7) is directed to a second thin film evaporation section (8). The distillate from the second thin-film evaporation section (8) is conducted to the spinning bath (4), and the recirculated ionic liquid is recovered from the second thin-film evaporator section (8) and conducted to the kneader (1) for dissolving further slurry.

[0050] Fig.14 Shown is a monofilament combined with ionic liquid recycling A simplified scheme of a fiber spinning process. The slurry and the ionic liquid are fed into a kneader unit (11) to dissolve the slurry and provide a spinning solution. The spinning solution is then directed to a spinning unit (13) where the fibers are spun or a film is extruded into a spinning bath (14). After spinning or extrusion, the fibers or film are washed with water and stretched (15). The washed fibers are recovered and the washing filtrate from the washing and stretching unit (15) is disposed of. The spinning bath (14) solution is filtered in a filtration unit (12) and directed to the ionic liquid recovery. The spinning bath solution is directed to a first thin film evaporation section (17). The distillate from the first thin film evaporation section (17) is directed to the spinning bath (14), and the residue from the first thin film evaporator section (17) is directed to a second thin film evaporation section (18). The distillate from the second thin-film evaporation section (8) is conducted to the spinning bath (14), and the recycled ionic liquid is recovered from the second thin-film evaporator section (18) and conducted to the kneader (11) for dissolving further slurry.

[0051] Fig.15 The history of residual water content, A / B ratio, and hydrolysis product concentration in recycled [mTBD][OAc] is summarized. It is very clearly shown that a slight increase in the A / B ratio results in a shift in the hydrolysis equilibrium toward the full superbase. Therefore, adjusting the A / B ratio is the best means to minimize the hydrolysis of the superbase in IL[mTBD][OAc].

[0052] As described above, the present invention relates to a method for producing cellulose filaments or films. In one embodiment, the method comprises the following steps: dissolving a cellulose substrate in an ionic liquid composed of a superbase cation 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium[mTBDH]+ and anions to produce a solution forming a spinning solution, wherein the anions are derived from an acid present in a stoichiometric excess relative to the superbase; extruding the spinning solution through a spinneret in a coagulation bath containing water to form filaments or films from the solution; extracting the ionic liquid in the form of an aqueous mixture with water from the coagulation bath; recovering the ionic liquid [mTBDH][OAc] from the aqueous mixture by removing water and selectively recycling the recovered ionic liquid to the dissolution step.

[0053] By way of embodiment, it was surprisingly found that the guanidinium IL, [mTBDH][OAc] (7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate) is highly tolerant to the presence of a large amount of non-methylated synthetic precursor TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene). Even a 30 wt % ratio of TBD in mTBD does not impair the excellent solubility of [mTBDH][OAc] relative to cellulose in a 13 wt % spinnable cellulose solution for making high-strength MMCF. This is an important discovery because the content of the residual concentration determines the price of mTBD. If there are no other impurities, benefits can be achieved by allowing a certain amount of residual water (in addition to the water in the slurry) of up to 7.5 wt % to be accommodated in the IL without affecting the solubility.

[0054] The main disadvantage of superbases in their practical application is that they are easily hydrolyzed to amines by ring-opening reactions (two isomers) even in the presence of small amounts of water. This leads to a weakening of the solubility of cellulose in the formed IL, which in turn can lead to solvent losses if these byproducts increase accordingly with increasing cycle number. This tendency is not as pronounced in guanidinium superbases as in amidinium superbases, but is still significant.

[0055] Surprisingly, it was shown that, at relatively low stoichiometric acetic acid excesses compared to [DBNH][OAc], the rate of hydrolysis of mTBD in IL[m TBDH][OAc] in the presence of varying amounts of water was significantly reduced, thereby reducing the concentration of the hydrolysate (which in any case had no cellulose solubility) to acceptable levels. Even more surprisingly, it was found that even in the presence of up to 30 mol % excess of acetic acid in IL[mTBDH][OAc], the solubility for cellulose was not affected. Thus, in one embodiment, the stoichiometric excess of acid is up to 30 mol %, for example 0.1-30 mol %, preferably 10-20 mol %.

[0056] The spinning properties of the resulting cellulose solution (spinning solution) are also not negatively affected. This high tolerance of IL[mTBDH][OAc] to residual water content (≤7.5 wt. % or ≤5 wt. %, in combination with other parameters), hydrolysis products (≤20 wt. %) and excess acid (≤30 mol %) provides the prerequisite for the almost loss-free recovery of IL by thermal and non-hot water removal processes.

[0057] Fiber formation during dry jet / wet spinning is carried out in a water bath (spinning bath), and the viscoelastic cellulose solution enters the water bath (spinning bath) in the form of filaments after passing through a short air gap (5-20 mm). At the same time, fiber formation requires stretching the filaments coming out of the spinneret to 5-15 times the extrusion speed to obtain fibers with high strength. In a closed-loop operation including a washing step, ionic liquids and degradation products from solvents and degradation solutes accumulate in the spinning bath. Under equilibrium conditions, the ionic liquid in the spinning bath can be increased to a concentration of 10-30 wt% without impairing the regeneration behavior of cellulose

[16] . Quantitative recovery of the ionic liquid requires purification of the ionic liquid and removal of water. Therefore, in one embodiment, the method also includes washing the short fibers, filaments or membranes obtained from the coagulation bath with water, and further extracting the ionic liquid in the form of an aqueous mixture with water from the washing step.

[0058] The conjugated carboxylic acid of the organic superbase may be distilled at relatively low temperature, particularly in the range 60 to 95°C, and low pressure, suitably in the range 10-30 mbar. In one embodiment, the anion is suitably a carboxylate, preferably acetate, formate or propionate.

[0059] As described above, it is shown that the guanidinium IL[mTBDH][OAc] is particularly suitable for fiber technology, mainly because of its hydrolytic stability in the presence of water. In a preferred embodiment, the ionic liquid is composed of 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-eneium[mTBDH]+ as a cation and acetate as an anion, and the stoichiometric excess of acetic acid relative to 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene in the ionic liquid is up to 30 mol%, preferably 10-20 mol%. As described, a stoichiometric excess of acetic acid is provided to reduce the concentration of mTBD hydrolysate to an acceptable level, which means that the solubility of the ionic liquid is not inhibited. In one embodiment, the level of hydrolysate is ≤20 wt%.

[0060] The method according to embodiments may be applied to dissolve a variety of different cellulosic substrates. In one embodiment, the cellulosic substrate is pulp, dissolving pulp, recycled cellulosic textile waste, recycled waste paper, most suitably bleached dissolving pulp.

[0061] In one embodiment, the superbase mTBD may contain 0-30 wt%, preferably 0-10 wt%, of superbase 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) residue as an impurity. Even if the proportion of TBD in mTBD is 30 wt%, it does not affect the excellent solubility of [mTBDH][OAc] relative to cellulose for making a 13 wt% spinnable cellulose solution for high-strength MMCF.

[0062] As mentioned earlier, the decomposition of amidines and guanidines in water occurs by hydrolysis rather than by elimination reactions. During hydrolysis, the hydroxide anion reacts with sp 2 Nucleophilic attack of the hybridized carbon atom

[12] , followed by cleavage of the carbon-nitrogen bond, forms a primary amine structure in the case of DBN (1-3-aminopropyl)-pyrrolidone = APP) and mTBD (two isomers: 1-[3-methylammonio)propyl]-1,3-diazocyclohexane-2-one] = [H-mTBD-1] and 1-(3-ammoniopropyl)-3-methyl-1,3-diazocyclohexane-2-one] = [H-mTBD-2]). Figure 2 and Figure 3 As shown in (Scheme), the hydrolysis is an equilibrium reaction and can therefore be converted back to a superbase by appropriate reaction conditions, such as acid catalysis. However, in the presence of acetate anions in the ionic liquid, the hydrolysis product is converted to the corresponding acetamide. These sequential reactions are irreversible and therefore it is impossible to recover the original superbase ( Figure 2 and Figure 3 ).

[0063] The guanidine structure of mTBD enables the formation of two isomeric hydrolysis products, followed by the formation of two isomeric acetamides. The disappearance of the superbase and the formation of the hydrolysis and acetamide products can be easily followed quantitatively over time using 1H-NMR spectroscopy. As we will see later, the formation and decomposition rates of the two hydrolysis isomers are significantly different.

[0064] It is reported that due to the presence of guanidine in sp 2 The higher electron density on the -hybridized carbon makes it more stable against hydrolysis than the amide structure. In the case of the amidine DBN, the release of the ring strain strongly promotes hydrolysis

[12] .

[0065] [DBNH][OAc] has to be recovered from the spinning bath after only one cycle, and it already contains too high a concentration of the hydrolysis product [APPH][OAc] to completely dissolve cellulose in the subsequent steps. This makes the ionic liquid [DBNH][OAc] unsuitable for Craftsmanship.

[0066] To verify this, kinetic studies were performed in which acetic acid was added superstoichiometrically in the ionic liquid up to a ratio of [HOAc]:[DBN] = 5:3, which corresponds to its azeotropic mixture

[26] . Figure 4 As shown in . Interestingly, the azeotrope is more acid-rich due to its stronger ability to form hydrogen bonds with ion pairs

[27] . Despite such a high acid-base ratio of 5:3, DBN degradation is hardly slowed down compared to the equimolar acid-base composition, especially in the first few hours. In the azeotrope composition (A:B = 5:3), the equilibrium concentration of DBN is slightly higher. However, this behavior is consistent with Since acetic acid is a non-solvent, the ionic liquid is no longer a solvent for cellulose at an acid-base ratio of 5:3.

[0067] Since the volatility of bases increases with concentration, the compositions of ILs showed higher acid contents after water evaporation. Together with the relatively high content of hydrolysis products ([APPH][OAc]), this means that [DBNH][OAc] lost its ability to dissolve cellulose after only one recycling cycle (Table 2).

[0068] Table 2: Composition of freshly prepared and once recycled [DBNH][OAc]. The latter was evaporated in a thin film evaporator.

[0069]

[0070] The ability of [DBNH][OAc] to dissolve cellulose at a concentration of 13 wt% ceases at a residual water content of 3%, an acid-base ratio of 1.05-1.10, and an [APPH] content of 10 mol%.

[0071] As can be understood from the above, the ability of the recovered ionic liquid [mTBDH][OAc] to dissolve cellulose is not impaired when its hydrolysis products are at the same content as the hydrolysis products of the DBN analog, but only when the content of hydrolysis products and acetamide is much higher. In one embodiment, the recovered ionic liquid [mTBDH][OAc] contains one or more of the following hydrolysis products in an amount ≤20 wt%, preferably ≤10 wt%, suitably ≤5 wt%, calculated based on the weight of the recovered ionic liquid: 1-[3-(methylammonio)propyl]-1,3-diazacyclohexane-2-one acetate ([H-mTBDH-1][OAc), 1-(3-ammoniopropyl)-3-methyl-1,3-diazacyclohexane-2-one acetate ([H-mTBDH-2][OAc]).

[0072] Evaporation is the most common process for removing water from the IL-water mixture produced by the combined spinning bath and water bath. Alternative processes such as membrane separation using pressure driven membrane technology, pervaporation, membrane distillation and electrodialysis have received attention but are too expensive based on the current state of development and do not show energy advantages over multi-stage evaporators.

[0073] A preferred method for removing water from the ionic liquid is a combination of a multi-stage falling film evaporator and a thin film evaporator, optionally combined with vapor recompression evaporation. In one embodiment, the ionic liquid [mTBDH][OAc] is recycled by removing water from an aqueous mixture of the ionic liquid in a series of water removal steps. In another embodiment, water is removed from the aqueous mixture by one or more evaporators selected from falling film evaporators, thin film evaporators and vapor recompression evaporators and combinations thereof. As already mentioned, the equilibrium concentration of the ionic liquid in the spinning bath and wash filtrate mixture ranges from 10% to 30%. As shown in detailed experiments, in order to achieve good dissolution and spinning performance of the cellulose solution in the next spinning cycle, it is not necessary to quantitatively remove water from the ionic liquid. A residual water concentration of ≤7.5 wt%, suitably 1-5%, preferably 3% is acceptable and allows stable process performance of the ionic liquid [mTBDH][OAc]. In a preferred embodiment, the amount of water present in the recovered ionic liquid is ≤7.5 wt%, preferably 3-5 wt%, most suitably ≤3 wt%, calculated based on the total weight of the recovered ionic liquid and water.

[0074] In one suitable embodiment, water is removed from the aqueous mixture in one or more multiple-effect evaporation devices comprising two or more evaporators selected from falling film evaporators, thin film evaporators, vapor recompression evaporators, and combinations thereof.

[0075] The silk, film or staple fiber is formed in a coagulation bath or a spinning bath. In one embodiment, the coagulation bath or the spinning bath comprises an ionic liquid. In a preferred embodiment, the method comprises forming the silk or film or staple fiber in a coagulation bath or a spinning bath containing an ionic liquid at a concentration of 40 wt % or less.

[0076] Similarly, the washing step may involve water containing the ionic liquid. In one embodiment, the washing step comprises washing the silk or membrane or staple fiber with water having an ionic liquid concentration of 40 wt% or less.

[0077] In another embodiment, the aqueous mixture extracted from the coagulation bath or the washing step contains 40% or less ionic liquid.

[0078] Embodiments can be used to produce fibers with certain properties. In one embodiment, the process comprises producing cellulose fibers having a dry tenacity ≥ 35 cN / tex, a dry / wet tenacity > 0.80 and a modulus of tenacity ≥ 50 MPa, preferably a dry tenacity ≥ 40 cN / tex, a dry / wet tenacity > 0.85 and a modulus of tenacity ≥ 60 MPa. The tenacity (cN / tex), elongation at break (%) and linear density (dtex) were determined on a Favigraph apparatus (Textechno, Germany). Test parameters: 20 cN load cell, 10 mm gauge length, 10 mm min -1 Test speed, 100 mg pretension, fiber count 20. Measurements were performed under conditioning conditions: 20°C, 65% relative humidity and wet conditions, 10 s moistening before testing.

[0079] The toughness modulus is calculated as the integral of the stress-strain curve. The result (integral) is in J / g and multiplied by 1.5 of the cellulose density to give the unit MPa.

[0080] In another embodiment, the method is used to produce textile fibers, technical fibers or films.

[0081] The above-mentioned improved hydrolytic stability of mTBD relative to DBN in the presence of water was studied for the corresponding ionic liquids [mTBDH][OAc] and [DBNH][OAc] at consistent 95°C and 85°C temperatures and 10 wt% water content at equimolar acid-base compositions. Figures 5 and 6 show the significant difference in the hydrolytic stability of the two ILs, especially during the first 100 hours.

[0082] The most significant difference in hydrolysis performance between DBN and mTBD was evident within the first 5 h. While a substantial degradation of 37% of DBN occurred at 95 °C (29% at 85 °C), mTBD degradation was still very limited, at only 4% (1.5% at 85 °C). Acetamide formation from DBN started immediately after reaching the maximum APPH concentration after 5 h, and then rose sharply to a concentration of 38 mol% after 480 h. Thus, more than 77% of the original DBN amount was converted into acetamide, while only 6% remained as the hydrolysis product APP.

[0083] At 85 °C, acetamide derived from mTBD could only be detected after about 100 h of hydrolysis time and was still insignificant even after 300 h. Although two isomeric hydrolysis products were present in the case of mTBD, further reaction to the corresponding amide appeared to be significantly inhibited compared to the DBN analog. Figure 7 As shown in , the formation of H-mTBD-1 is preferred, followed by reaction to acetamide.

[0084] Overall, therefore, the question is whether the higher stability of mTBD is sufficient to allow for sustained recycling of the ionic liquid with minimal replenishment. At the same time, it must be ensured that the composition of the ionic liquid is in equilibrium, allowing for the desired spinning behavior.

[0085] Since [mTBDH][OAc] is more ionic than [DBNH][OAc] (see above), the acid-base composition of the azeotropic mixture is 3:2 and is therefore slightly lower than that of the latter

[28] . However, the recovered IL is expected to have a superstoichiometric acid-base ratio.

[0086] Since in the case of [DBNH][OAc] even a very small stoichiometric excess of acetic acid meant that cellulose was no longer completely soluble, we initially expected a similar reaction to occur with the ionic liquid [mTBDH][OAc] and did not intend to further investigate the effect of the stoichiometric excess of acid in the case of mTBD.

[0087] However, it was decided to investigate the influence of the acid / base molar ratio on the hydrolysis kinetics of [mTBDH][OAc]. Specifically, at a temperature of 95°C and a water content of 10 wt%, the acid / base molar ratio was gradually increased from 1:1 via 1.1:1 to 1.2:1, which could correspond to a possible equilibrium setting of the recycled ionic liquid. In order to be able to quantitatively evaluate possible differences, the results were modeled using a kinetic model, in which, for simplicity, the sum of the by-products was described as one species, [∑mTBDH deg ]:

[0088] [mTBD]+H2O[ΣH–mTBD]+ΣA–mTBD]=[ΣmTBD deg ] (1)

[0089] Both the forward (k1) and reverse (k2) reactions are pseudo-first order reactions. Therefore, the concentration of mTBD after time t [mTBD] t It can be calculated by equation (2):

[0090] [mTBD] t =[mTBD]0{(k2+k1e -(k1+k2)t ) / (k1+k2)} (2)

[0091] Equilibrium concentration of mTBD [mTBD] ∞ , estimated by equation (3),

[0092] [mTBD] ∞ =k2[mTBD]0 / (k1+k2) (3)

[0093] And the equilibrium constant Kc =d[mTBD] / dt=0→k1[mTBD]=k2[ΣmTBD deg ], we get equation (4)

[0094] K c =[ΣmTBD deg ] / [mTBD] ∞ =k1 / k2 (4)

[0095] In contrast to [DBNH][OAc], even a slight stoichiometric excess of acetic acid leads to a significant stabilization of the cation in the ionic liquid [mTBDH][OAc] ( Figure 8 This is also reflected by the kinetic coefficients (Table 3).

[0096] Table 3: Kinetic coefficients for the degradation of [mTBD] in the ionic liquid [mTBDH][OAc] at 99 °C and in the presence of 10 wt% water at different acid-base molar ratios

[0097]

[0098] Quite unexpectedly, this small acid excess of 20 mol % reduces the equilibrium constant by a factor of 3.3 and the reaction constant k1 by a factor of 2.5, whereas in the case of [DBNH][OAc], an excess of 66 mol % of acetic acid has almost no effect on the reaction coefficient k1. It is particularly noteworthy that the stabilizing effect of the excess acetic acid is very significant in the first few hours. This fact is particularly relevant for the recovery of IL by thermal evaporation of water ( Fig. 9 ).

[0099] At this point, we only know that a small excess of acetic acid in [mTBDH][OAc] has a very high impact on base stability. However, we do not yet know whether a 20 mol% excess of non-solvent will have a negative impact on the ability of the ionic liquid to dissolve cellulose, and if so, whether the resulting cellulose solution is spinnable.

[0100] As shown in the case of equimolar acid-base mixtures, the water content of the ionic liquid also significantly affects the base hydrolysis behavior of [mTBDH][OAc]. Fig.10 The characteristic values ​​in , the amount of decomposition products (sum of hydrolysis products and acetamide) and the equilibrium constant Kc are plotted against the water content.

[0101] Interestingly, the tendency of the superbase in the IL to hydrolyze is highest at a water content of 20 wt%. The reduction in the hydrolysis rate at lower water contents can be explained by the decrease in water activity with increasing salt concentration. Therefore, the available concentration of hydroxide anions increases up to a water content of 20 wt% and then decreases again by further dilution. A recent simulation study confirmed that the combined activity coefficient of water and mTBD is maximum at a water content of about 20 wt% in the IL. Interestingly, the superbase mTBD in the corresponding IL remains almost completely stable at water concentrations exceeding 60%, even at 95°C and hydrolysis times exceeding six weeks. Due to these unexpected results, it can be concluded that [mTBDH] is almost never hydrolyzed in the coagulation bath at low temperatures and in the wash water at high temperatures. Knowing that the highest hydrolysis rates occur between water contents of 10-40%, the hot water evaporation process can be designed to minimize the residence time in this water content range.

[0102] The last step in the synthesis of mTBD involves the methylation of TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene) by an alkylating agent such as dimethyl carbonate (DMC). The degree of residual contamination of TBD determines the price of the superbase. To this end, it was investigated which residual concentrations of TBD could be tolerated without affecting the solubility and spinning properties of [mTBDH][OAc]. In Example 1, the effects of different concentrations of TBDH in mTBDH were studied in IL[mTBDH](1-x)[TBDH]x[OAc].

[0103] Example

[0104] Embodiment 1:

[0105] In a first series of experiments, the extent of cellulose dissolution was monitored by optical microscopy using transverse polarization mode for the production of solutions with a cellulose content of 13 wt%. The image analysis method is based on the estimation of the white / colored surface ratio of the undissolved elements present in the total area of ​​the image. The method is described in detail in

[29] . The results presented in Table 4 show that the quality of the solution is hardly affected up to a TBD content of 30% in the IL.

[0106] Table 4: Dissolution testing in the presence of TBD in IL[mTDH][OAc]

[0107] TBD in solution Acid-total base Slurry* concentration Solubility** image weight% Mol / mol weight% ％ 0 1 13 99.6 Fig.11a 5 1 13 99.9 10 1 13 99.9 20 1 13 99.8 30 1 13 99.6 Fig.11b

[0108] *Pulp: Pre-hydrolyzed birch kraft pulp

[0109] **Optical microscopy: area of ​​dissolved fibers

[0110] Embodiment 2:

[0111] Based on these feasible dissolution results, a large number of cellulose solutions were prepared using 0 wt%, 5 wt% and 10 wt% TBD in IL at an acid / base ratio of 1:1. The results showed that when the TBD concentration reached 10 wt%, no effect on the rheology, spinning behavior or fiber properties of the prepared spinning solutions was observed. The results are summarized in Table 5.

[0112] Table 5: Rheology of 13 wt% slurry* solutions prepared from [mTBDH][OAc], where different fractions of mTBD were replaced by TBD (dissolved at 80-85°C for 60-75 min). Properties of Ioncell fibers spun from the slurry solution by dry-jet wet spinning process at a draw ratio (DR) of 11.

[0113]

[0114] The results in Table 5 demonstrate that TBD at least up to a concentration of 10 wt. % in the IL has no negative effect on the spinning behavior (rheology) of the cellulose solution and on the fiber quality of the fibers spun therefrom.

[0115] Since the melting point of [TBDH][OAc] is 135 °C, it does not belong to the category of ionic liquids ( Fig.12 ), it is not so easy to expect that the ionic liquid [mTBDH][OAc] can tolerate TBD contents of up to 30 wt% without affecting the cellulose solubility.

[0116] Embodiment 3:

[0117] In addition to the TBD content, residual water and ∑H mTBD content ( Figure 3 ) and the acid-base ratio (A / B) also affect the dissolution behavior of [mTBDH][OAc], the rheological properties of the resulting cellulose solution, as well as the spinnability and fiber properties. The effects of individual and combined parameter deviations from the ideal [mTBDH][OAc] composition (water = 0%, ∑H mTBD = 0%, A / B = 1:1) were carefully investigated.

[0118] Solubility studies on birch prehydrolyzed kraft pulp at 13 wt% concentration at 80-85°C for 60-75 min showed that at ∑H mTBD of 0 wt% and water content of 1%, there was a considerable effect on alkaline hydrolysis without affecting cellulose solubility and fiber spinnability ( Figure 8) can be increased up to 1.3:1. When the A / B ratio is 1:1 and there is no ∑H mTBD, the water content can be increased up to 7.5%. It is worth noting that even at a residual water content of 3% and an A / B ratio of 1.2:1, the IL is very insensitive to the presence of up to 20 wt% ∑H mTBD. The results are summarized in Table 6.

[0119] Table 6: Effect of individual and combined deviations of water content, A / B ratio and ∑H mTBD parameters in the ideal composition of [mTBDH][OAc]. The quality of the solutions was determined by optical microscopy using transverse polarization mode

[29] . The composition of pure [mTBDH][OAc] was varied according to the information in the table. In all cases, birch PHK pulp was used to produce 13 wt% solutions.

[0120]

[0121] Dissolution levels above 99% can be rated as very good, values ​​below 95% are unacceptable for a uniform spinning process.

[0122] Fiber production using the recycled [mTBDH][OAc] according to the Ioncell process

[0123] Surprisingly, the experiments showed that the ionic liquid [mTBDH][OAc] (continuously recovered by thermal removal of water from spinning and washing water) did not lose its ability to dissolve cellulose, while the degree of hydrolysis by the superbase (∑H mTBD) was stabilized at a low level. Also surprisingly, the cellulose solution (10-17 wt%) produced from the recycled [mTBDH][OAc] could be spun into high-strength lyocell fibers with high uniformity and stability using the air-gap process. .

[0124] Hereinafter, an example is described in detail in which an ionic liquid [mTBDH][OAc] is used in a spinning process and the ionic liquid [mTBDH][OAc] is recovered from the spinning bath by a multi-stage evaporation process and reused in subsequent spinning experiments. These experiments are then repeated at different frequencies depending on the example.

[0125] Embodiment 4:

[0126] The ionic liquid (IL) [mTBDH] [OAc] was prepared by mixing the base and acid in an equimolar ratio by continuous stirring at a temperature below 70 °C for one hour. Using birch prehydrolyzed pulp (PHK) with an intrinsic viscosity of 494 mL / g, the mixture was stirred in a vertical kneader ( Fig.13, a cellulose solution (spinning solution) of 13 wt. % in [mTBDH][OAc] was produced in unit 1). Complete dissolution was achieved within 60-75 min at a temperature of 85°C and 15 mbar and a stirring speed of 30 rpm. The hot spinning solution was filtered through a metal fleece with a pore size of 5-6 μm using a hydraulic press. Since the rheological properties of the cellulose solution are decisive for the spinning behavior, these properties were measured using an Anton Paar MCR 300 rheometer with a plate and plate geometry (25 mm plate diameter, 1 mm gap size). A dynamic frequency scan in the angular frequency range of 0.01-100 s-1 was performed for each sample at a range of temperatures, including the required rheological parameters, where the complex viscosity was 25000-35000 Pas, the complex modulus at the crossover point (COP) was 3000-4500 Pa, and the angular frequency of the COP (ωCOP) was 0.5-1.5 s-1

[30] . 13 wt% cellulose solutions prepared from freshly synthesized IL showed desirable rheological properties at 85°C. The results of the rheological characterization are summarized in Table 7 along with the results for cellulose solutions produced from IL recycling.

[0127] Table 7: Rheological properties of fresh and recycled spinning dopes prepared from [mTBDH][OAc] and birch PHK slurry at 85°C at 13 wt% concentration.

[0128] cycle temperature Complex viscosity Angular frequency Composite modulus ℃ <![CDATA[η0 * [Pa.s]]> <![CDATA[ω[s at the COP -1 > G' = G" at COP [Pa] 1(Fresh) 85 28 953 0.78 3776 2 85 28 500 0.84 3996 3 85 31 200 0.74 3918 4 85 26 835 0.81 3630 5 85 32 890 0.76 4203 average value 85 29 676 0,79 3905 Standard Deviation 0 ±2 379 ±0.04 ±218

[0129] Fiber spinning was performed using a custom laboratory piston spinning device (Fourné Polymertechnik, Germany). The cylinder containing the cooled, solidified and formed [mTBDH][OAc]-slurry solution was heated to 85°C to form a bubble-free spinning solution. The temperature was maintained between 83-87°C while being extruded into a water coagulation bath through a 200-hole spinneret (capillary diameter 100 μm, L / D0.2) via an air gap of 1 cm. The temperature of the coagulation bath was maintained at 8-10°C. The extrusion rate was fixed at 3.5 m / min, while the winding speed was 42 m / min, resulting in a draw ratio (DR) of 12. The spun fibers were collected as headless filaments, cut into staple fibers, and thoroughly washed in demineralized water. The properties of the resulting regenerated cellulose fibers are summarized in Table 8. Fibers spun from a spinning solution made from a freshly prepared ionic liquid (cycle 1) had comparable properties to those spun from a spinning solution made from [DBNH][OAc] with the same DR. The overall orientation is very high, which explains the relatively low elongation. To develop the highest quality textile fibers, the overall orientation must be slightly reduced in favor of greater tenacity.

[0130] Table 8: Mechanical and structural properties of Ioncell-F fibers spun from birchwood PHK solutions in [mTBDH][OAc]

[0131]

[0132] Embodiment 5:

[0133] After spinning, the combined spinning bath ( Fig.13 The mixture of the distillates from the two thin film evaporator sections (TFE-1 and TFE-2) and the distillates from the two thin film evaporator sections (TFE-1 and TFE-2) is heated in a centrifugal evaporator ( Fig.13 After spinning, the mixture from the spinning bath is evaporating to two thin film evaporator sections (TFE-1 and TFE-2, Fig.13 The distillate from units (6) and (7) in the centrifugal evaporator was pre-concentrated in a centrifugal evaporator. Due to the high volume of distillate from the centrifugal evaporator, no distillate was recycled. Due to the low spinning bath temperature and the high dilution of IL during feeding and concentration during evaporation, the amount of hydrolysis products in the distillate was below the detection limit. Fig.13 As shown in , the residue from the centrifugal evaporator is fed to TFE-1 ( Fig.13 The distillation process is repeated for 1-2 hours and then the distillation is continued for 2 hours. The distillation process is repeated for 1-2 hours. The distillation process is repeated for 2 hours. The distillation process is repeated for 2 hours. The distillation process is repeated for 3 ...2 hours. The distillation process is repeated for 3 hours.

[0134] Table 9: Residual water concentration of the IL stream before and after the continuous evaporator unit measured by Karl-Fischer (KF) titration.

[0135]

[0136]

[0137] The IL concentration after spinning about 0.7-1.5 kg of cellulose solution into a coagulation bath with a volume of 120 L resulted in a very low IL concentration before evaporation. Only very old and unreliable centrifugal evaporators were available for preconcentration. Due to many technical problems, the IL concentration after preconcentration was generally low (especially after cycles 3-5) and had a large spread. However, the two subsequent thin film evaporators compensated well for the large variations in water content, so that the water content of the recovered IL (TFE-2, after unit (7)) was generally less than 3 wt. % and demonstrated little variation between cycles (Table 9). Therefore, despite the technical defects, the water content in the recovered IL can be adjusted very reliably, which is significantly below the limit value for cellulose solubility. If the acid-base ratio is close to 1:1, a water content of ≤7.5 wt. % in the IL is acceptable for complete dissolution of cellulose and the amount of hydrolysis products ∑H-mTBD is not significant (Table 6)

[29] .

[0138] In the presence of water, the superbase ionic liquid [mTBDH][OAc] undergoes hydrolysis to produce undesirable hydrolysis products, such as [H-mTBD-1][OAc] and [H-mTBD-2][OAc] ( Figure 3 Based on the results of the hydrolysis kinetics experiments, it can be concluded that low temperatures, very low (<5%) or high water contents (>40-60%), and higher acid-base ratios can delay hydrolysis (Figures 5, 5 and Table 3). The question is whether the concentration of hydrolysate in the recovered IL reaches an unacceptable level for reintroduction into the spinning process under the conditions of spinning, fiber washing, and subsequent evaporation of water from the collected IL stream. To our surprise, the concentration of hydrolysate in both the distillate and the centrate remained at a low level, well below the critical value for the solvency of the recovered IL (see Table 10).

[0139] Table 10: Composition of fresh and recycled IL and distillate stream recycled back to the spinning bath

[0140]

[0141]

[0142] As shown in Table 10, the concentration of hydrolyzate [∑H-mTBD] in the recovered IL is still far below the limit concentration allowed for complete dissolution of 13 wt% cellulose (Table 6)

[29] .

[0143] No real trend of increasing concentration of hydrolysate in each cycle was observed. However, it can be clearly seen that the acid-base ratio (A:B) in the recovered IL increased slightly to a value of 1.12 ± 0.03. In addition to the slight conversion of the superbase into its hydrolysate, the enrichment of the acid component of the recovered IL can be attributed to the preferential evaporation of the base due to the higher ability of the acid to form hydrogen bonds with ion pairs

[27] . The high volatility of the base in the PIL is reflected in the very low A:B ratio of the distillate (Table 10). The A:B ratio of the recovered [mTBDH][OAc] is still significantly lower than that of the recovered [DBNH][OAc], which has reached an A:B ratio of 1.27 after the first cycle. This difference also corresponds to the higher acid-base ratio of the azeotropic mixture of [DBNH][OAc] of 5:3, compared to the acid-base ratio of [mTBDH][OAc] of 3:2 (Tables 2 and 10).

[0144] The results of five complete recycling experiments of the cellulose solvent [mTBDH][OAc] show that, despite its tendency to hydrolysis reactions and the incomplete ionicity of the PIL, the properties of the recycled IL are almost indistinguishable from those of the freshly produced IL, so that the solubility for cellulose can be fully maintained. This is reflected in the almost constant rheological properties of the cellulose solution produced with the recycling of IL (Table 7) and the high quality of the fibers spun therein (Table 8). The slight decrease in the mechanical properties of the fibers of the 4th and 5th cycles (Table 8) can be explained by the very small amount of available cellulose solution and the associated reduced possibility of setting optimal spinning conditions. In addition, especially in cycle 4, the overall orientation of the fiber molecules is very high, indicating that the selected draft ratio is too high, so that some microfibers have been mechanically damaged.

[0145] Example 6: 20 recycling cycles of the used IL

[0146] In the new test series, a single-filament spinning system was used, which allowed a higher number of test cycles due to the small volume of the spinning bath. Fig.14 ) from the slurry dissolved in the kneader (unit 1), filament spinning (unit 2), spinning bath (unit 3), stretching and washing (unit 4), and IL recycling using a two-stage thin film evaporator (TFE-1: unit 5; TFE-2: unit 6).

[0147] Unlike Experiments 4 and 5, the IL recovered from the previous run was used to start a new series of 20 cycles. A spinning solution with a birch prehydrolyzed kraft pulp content of 13 wt% in [mTBDH][OAc] was produced in a vertical kneader (Scheme 4, Unit 1). The intrinsic viscosity of the pulp was 494 mL / g. Complete dissolution was achieved within 50 minutes at 80°C and 15 mbar and a stirring speed of 30 rpm. The hot spinning solution was spun into monofilaments without filtration. A single-hole nozzle with a diameter of 100 μm and a length-to-width ratio (L / D) of 2:1 was used. The extrusion speed varied from 1.3 to 1.9 m / min, while the temperature was adjusted between 80 and 87°C to obtain the best rheological properties for dry-jet wet spinning. As in Experiments 1 and 2, the viscoelastic properties of all cellulose solutions were measured on an Anton Paar MCR 300 rheometer with a plate and plate geometry (25 mm plate diameter, 1 mm gap size). A dynamic frequency sweep test was used to obtain the complex viscosity (η*) and the dynamic modulus (G', G") as a function of the angular frequency ω. Here, the dynamic modulus (G'=G") at the crossover point (COP) and the angular frequency (ω at the COP) are the decisive parameters describing the relevant viscoelastic properties of the spinning solution. The rheological properties results of the cellulose solution used for dry-jet wet spinning in 20 cycles are summarized in Table 11.

[0148] Table 11: Rheological properties of fresh and recycled spinning solutions prepared from [mTBDH][OAc] and birch PHK pulp at 13 wt% concentration at 85°C. The spinning solution in cycle 1 was prepared from IL recycled from the previous experiment with a water content of 3.7%, a H-mTBD content of 1.6% and an A / B ratio of 1.09.

[0149]

[0150]

[0151] The rheological parameters did not change much compared to the cellulose solutions prepared from fresh IL, except for the samples of cycle 12. Despite the high complex viscosity and dynamic modulus, the cellulose solutions of cycle 12 showed good spinnability (probably the samples were not measured when freshly prepared and already showed slight gel formation).

[0152] As described above, fiber spinning was performed using a custom-made single-filament laboratory piston spinning apparatus (Fourné Polymertechnik, Germany). The [mTBDH][OAc]-slurry solution, which had not been filtered, cooled, solidified, and formed, was charged into a cylinder and heated to 85°C to form a bubble-free spinning solution. A single-hole nozzle with a diameter of 100 μm and a length / width ratio (L / D) of 2:1 was used. The temperature was maintained at 80-87°C to accommodate the optimal rheological properties for dry-jet wet spinning.

[0153] In addition to spinning in pure water, the spinning behavior in a spinning bath enriched with (partially, 10 and) 20 wt % IL was also studied. The fiber property measurements of the individual spinning tests after maximum stretching in the spinning bath when spinning in pure water and at 20 wt % IL are given in Table 12.

[0154] Table 12: spun under conditioning conditions of birchwood PHK solutions in [mTBDH][OAc] in both pure water and water containing 10-30 wt% IL Mechanical properties of fibers

[0155]

[0156]

[0157]

[0158] At a spinning time of more than 300 (cycles 1-11) or 500 (cycles 12-20) seconds, the quality of the spinning behavior is determined according to the highest possible draw ratio. Due to time reasons, the draw ratio (DR) is not (always) increased by only 1 unit, but mainly in steps of 3 units, i.e. from DR 11 to 14. For this reason, the maximum DR is only possible to be 11, because at a DR of 15, the spinning time can only last about 200 seconds (lower draw ratios, about 13 or 14, were not tested for time reasons). Based on empirical data, the spinning behavior is classified as follows:

[0159] Unspinnable <3DR; 3 ≤ Poor <6; 6 ≤ Fair <8; 8 ≤ Good <12; 12 ≤ Very Good <15; Above 15 constitutes excellent spinnability.

[0160] According to the results shown in Table 12, the spinning performance of all spinning tests (cycle 1-cycle 20) can be rated as good to very good, even excellent in some cases. The fiber data obtained from all measurements of the fiber after the draft ratio is 11 clearly show that the fiber performance corresponds to the best available lyocell fiber. In addition, no change in the fiber data was observed throughout the 20 cycles. Considering the usual variation, the mechanical fiber properties remain stable at a high level. Surprisingly, when spinning in a spinning bath containing 10-20 wt % IL, a higher DR with high spinning stability is obtained compared to the case of using pure water as a spinning bath. As shown in Example 7 and Table 13, during the entire 20 cycles, the reason for the high spinning reliability under high DR is that the composition of the ionic liquid component is almost unchanged.

[0161] Embodiment 7:

[0162] The mixture of spinning bath and distillate from the previous run was filtered and fed directly to thin film evaporator TFE-1 for evaporation due to the small volume and high initial IL concentration ( Fig.14 ). All IL-containing streams, except the fiber wash filtrate, were combined and recycled.

[0163] Table 13: Evaporation of mixed stream containing IL by two-stage thin film evaporation (TFE-1: 60-62°C, 20 mbar, TFE-2: 80-82°C, 17 mbar). Characterization of the components of the TFE-1+2 residue and the distillate from TFE-2. (*) = AcOH / mTBD ratio

[0164]

[0165]

[0166]

[0167] After the first evaporation stage TFE-1, the average water content of the IL residue was about 14%, which is close to the maximum hydrolysis rate of mTBD ( Fig.10 ). Due to the short residence time in TFE-1, after 20 cycles, the amount of hydrolyzate produced remained at a low and safe level, averaging only 1.5%. The acid-base ratio increased only insignificantly to an average of 1.06:1.00.

[0168] After the second evaporation stage, the residual water content was adjusted to 3-4%, and the concentration of the hydrolyzate (only H-mTBD-1) even slightly decreased on average, probably due to a slight increase in the acid-base ratio.

[0169] Quite surprisingly and unexpectedly, during the twenty recycling cycles, neither the concentration nor the absolute amount of hydrolysis products in the ILs increased, but leveled off at a relatively low level. Not even trace amounts of acetamide were detected in all samples, indicating that the conditions applied during the 20 evaporation steps were relatively mild.

[0170] Since mTBD is highly excessive in the distillate of TFE-2, most of the superbase is converted to the hydrolysis product H-mTBD. The amount of hydrolysis product from the distillate is small compared to the total amount of ionic liquid, and does not increase the total amount of hydrolysis product after reintroduction into the spinning bath.

[0171] It should be understood that the disclosed embodiments of the present invention are not limited to the specific structures, process steps or materials disclosed herein, but are extended to equivalent schemes recognized by ordinary technicians in the relevant technical field. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not intended to be limiting.

[0172] Throughout this specification, reference to an embodiment or an implementation means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Therefore, throughout this specification, the phrases "in one embodiment" or "in an embodiment" appearing in various places do not necessarily refer to the same embodiment. If a value is referenced using terms such as, for example, "about" or "substantially", the exact value is also disclosed.

[0173] Additional implementations are disclosed in the following numbered clauses:

[0174] 1. A method for producing cellulose fibers or films, comprising dissolving a cellulose substrate in a superbase cation 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium [mTBDH] + and an anion selected from an acid to form an ionic liquid to produce a spinning solution, wherein the acid is in a stoichiometric excess. The cation may contain a synthetic precursor 1,5,7-triazabicyclo[4.4.0]dec-5-enium [TBDH]+. The spinning solution is extruded through a spinneret to form a silk or film from the solution.

[0175] 2. The method according to clause 1, wherein the anion is a carboxylate, preferably acetate, formate or propionate.

[0176] 3. The process according to clause 1, wherein the stoichiometric excess of the acid is 0-30 mol %, preferably 10-20 mol %.

[0177] 4. The process according to clause 1, wherein the stoichiometric excess of acetic acid is 0-30 mol %, preferably 10-20 mol %.

[0178] 5. A method according to clause 1, wherein the cellulosic substrate is pulp, dissolving pulp, recycled cellulosic textile waste, recycled waste paper, most suitably bleached dissolving pulp.

[0179] 6. The method according to clause 1, wherein the superbase mTBD may contain 0-30 wt%, preferably 0-10 wt% TBD.

[0180] 7. A method according to clause 1, wherein the acceptable amount of the hydrolysis product 1-[3-(methylammonio)propyl]-1,3-diazocyclohexane-2-one acetate ([H-mTBDH-1][OAc]), 1-(3-ammoniopropyl)-3-methyl-1,3-diazocyclohexane-2-one acetate ([H-mTBDH-2][OAc]) is ≤20% by weight, preferably ≤10% by weight, and appropriately ≤5% by weight.

[0181] 8. The method according to clause 1, wherein the ionic liquid [mTBDH][OAc] is recycled in an infinite number of steps by removing water to an acceptable level.

[0182] 9. The method according to clause 1, wherein the water is removed by a multiple effect evaporation device, the multiple effect evaporation device comprising a falling film evaporator, a thin film evaporator and a vapor recompression evaporator.

[0183] 10. The method according to clause 1, wherein the acceptable amount of residual water comprises ≤ 7.5 wt%, preferably 3-5 wt%, most suitably ≤ 3 wt%.

[0184] 11. The process according to clause 1, wherein the solvent is completely stable when present in the coagulation bath and washing operations at a concentration of 40 wt% or less. This would affect the recovery of the distillate during the evaporation process.

[0185] 12. A method for producing cellulose fibers according to claim 1, wherein the cellulose fibers have a dry tenacity ≥35 cN / tex, a dry / wet tenacity >0.80 and a toughness modulus ≥50 MPa, preferably a dry tenacity ≥40 cN / tex, a dry / wet tenacity >0.85 and a toughness modulus ≥60 MPa.

[0186] 13. A method for producing textile fibers according to clause 1.

[0187] 14. A method for producing technical fibers according to clause 1.

[0188] 15. A method for producing a membrane according to clause 1.

[0189] As used herein, for convenience, multiple items, structural elements, constituent elements and / or materials can be presented in a general list. However, these lists should be interpreted as each member in the list being individually identified as a separate and unique member. Therefore, in the absence of contrary instructions, the members in the list should not be interpreted as being actually equivalent to any other member in the same list based solely on their presentation in a common group. In addition, various embodiments and embodiments of the present invention and alternatives to its various components may be mentioned in this article. It should be understood that such embodiments, embodiments and alternatives should not be interpreted as actually equivalent to each other, but should be regarded as separate and autonomous representations of the present invention.

[0190] In addition, in one or more embodiments, the described features, structures or characteristics may be combined in any appropriate manner. In the following description, many specific details, such as examples of length, width, shape, etc., are provided to provide a thorough understanding of embodiments of the present invention. However, those skilled in the relevant art will recognize that the present invention may be implemented without one or more of the specific details, and may also be implemented with other methods, components, materials, etc. In other cases, known structures, materials, or operations are not shown or described in detail to avoid obscuring various aspects of the present invention.

[0191] Although the above embodiments illustrate the principles of the present invention in one or more specific applications, it is obvious to those skilled in the art that many modifications can be made in details of form, use and implementation without using creativity and without departing from the principles and concepts of the present invention. Therefore, the present invention is not intended to be limited except as defined in the appended claims.

[0192] The verbs "comprise" and "include" are used in this document as open limitations, neither excluding nor requiring the presence of unrecited features. Unless explicitly stated otherwise, the features recited in the dependent claims may be freely combined with each other. Furthermore, it is to be understood that the singular forms "a" or "an" as used in this document do not exclude a plurality.

[0193] Industrial Applicability

[0194] At least some embodiments of the present invention are industrially applicable to the production of man-made cellulose fibers from a variety of cellulose substrates including pulp, dissolving pulp, recycled cellulose textile waste, recycled waste paper, and bleached dissolving pulp. The method can be used to produce textile fibers for clothing, soft furnishings, curtains, and upholstery, as well as for the production of technical fibers and for the production of films.

[0195] List of abbreviations

[0196] DSC = Differential Scanning Calorimetry

[0197] TGA = Thermogravimetric analysis

[0198] MMCF = Man-Made Cellulose Fiber

[0199] KT = Kamlet-Taft

[0200] A / B ratio = acid-base ratio

[0201] [APPH][OAc] = 1-(3-aminopropyl)-2-pyrrolidinium acetate

[0202] COP = Crossover Point

[0203] [emim][OAc] = 1-ethyl-3-methylimidazolium acetate

[0204] [DBNH][OAc]=1,5-diazabicyclo[4.3.0]non-5-enium acetate

[0205] [DBUH][OAc] = 1,8-diazabicyclo(5.4.0)undec-7-enium acetate

[0206] [H-mTBD-1][OAc] = 1-[3-(methylammonio)propyl]-1,3-diazolidin-2-one acetate

[0207] [H-mTBD-2][OAc]=1-(3-ammoniopropyl)-3-methyl-1,3-diazolidin-2-one acetate

[0208] [mTBDH][OAc] = 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate

[0209] [TBDH][OAc]=1,5,7-Triazabicyclo[4.4.0]dec-5-enium acetate

[0210] DBN = 1,5-diazabicyclo[4.3.0]non-5-ene

[0211] DBU=1,8-diazabicyclo(5.4.0)undec-7-ene

[0212] DMC = dimethyl carbonate

[0213] DR = Draft Ratio

[0214] IL = ionic liquid

[0215] PIL = Protic Ionic Liquid

[0216] Acidic ionic liquids

[0217] L / D aspect ratio

[0218] MMCF = Man-Made Cellulose Fiber

[0219] mTBD=7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene

[0220] NMMO = N-methylmorpholine N-oxide monohydrate

[0221] TBD = 1,5,7-triazabicyclo[4.4.0]dec-5-ene

[0222] TFE-1=First stage thin film evaporator

[0223] TFE-2=Second stage thin film evaporator

[0224] α = acidity

[0225] β = Alkalinity

[0226] β-α=net alkalinity

[0227] Δn = birefringence

[0228] η0*=complex viscosity

[0229] π*=solvent polarizability

[0230] ω = angular frequency

[0231] ω COP = angular frequency at the crossover point.

[0232] Reference numerals list

[0233] Kneading unit 1 Filters 2 Spinning unit 3 Spinning bath 4 Washing and stretching unit 5 Pre-concentration unit 6 The first thin film evaporation section 7 Second thin film evaporation section 8 Kneading unit 11 Filter unit 12 Spinning unit 13 Spinning bath 14 Washing and stretching unit 15 The first thin film evaporation section 17 Second thin film evaporation section 18

[0234] Citation List

[0235] 1. SIXTA, H. et al., A process for making a cellulose fiber or film, WO / 2018 / 138416, eds. 2018.

[0236] 2.Swatloski, RP et al., Dissolution of cellulose with ionicliquids. Journal of the American Chemical Society, 2002.124(18): pp. 4974-4975.

[0237] 3. Bentivoglio, G. et al., Cellulose processing with chloride-based ionic liquids. Lenzinger Ber., 2006.86 (Copyright (C) 2017 American Chemical Society (ACS). All rights reserved): pp. 154-161.

[0238] 4. Laus, G. et al., Ionic liquids: current developments, potential and drawbacks for industrial applications. Lenzinger Ber., 2005. 84 (Copyright (C) 2017 American Chemical Society (ACS). All rights reserved): pp. 71-85.

[0239] 5. Ebner, G. et al., Side reaction of cellulose with common 1-alkyl-3-methylimidazolium-based ionic liquids. Tetrahedron Lett., 2008.49 (Copyright (C) 2017 American Chemical Society (ACS). All rights reserved): pp. 7322-7324.

[0240] 6. Cai, T. et al., Structure and properties of cellulose fibers from ionic liquids. J. Appl. Polym. Sci., 2010. 115(2): pp. 1047-1053.

[0241] 7. Hauru, LKJ et al., Cellulose regeneration and spinnability from ionic liquids. Soft Matter, 2016.12 (Copyright (C) 2017 American Chemical Society (ACS). All rights reserved): pp. 1487-1495.

[0242] 8. Hummel, M. et al., Ionic liquids for the production of man-made cellulosic fibers: opportunities and challenges. Adv. Polym. Sci., 2016. 271 (Cellulose Chemistry and Properties: Fibers, Nanocelluloses and Advanced Materials): pp. 133-168.

[0243] 9. Elsayed, S., M. Hummel and H. Sixta, Comparative evaluation of the dry-jet wet spinning behaviour of three superbase-based ionic liquids in comparison to NMMO. Unpublished, 2020.

[0244] 10. Amarasekara, A. S., Acidic Ionic Liquids. Chem. Rev. (Washington, DC, U.S.), 2016. 116 (Copyright (C) 2016 American Chemical Society (ACS). All rights reserved): pp. 6133-6183.

[0245] 11. Angell, C. A., N. Byrne and J.-P. Belières, Parallel Developments in Aprotic and Protic Ionic Liquids: Physical Chemistry and Applications. Accounts of Chemical Research, 2007. 40(11): pp. 1228-1236.

[0246] 12. Hyde, A. M. et al., Investigating the Underappreciated Hydrolytic Instability of 1,8-Diazabicyclo[9.4.0]undec-7-ene and Related Unsaturated Nitrogenous Bases. Org. Process Res. Dev., 2019. 23(9): pp. 1860-1871.

[0247] 13. Earle, MJ et al., The distillation and volatility of ionic liquids. Nature (London, UK), 2006. 439(7078): pp. 831-834.

[0248] 14. Hauru, LKJ et al., Role of Solvent Parameters in the Regeneration of Cellulose from Ionic Liquid Solutions. Biomacromol., 2012. 13(9): pp. 2896-2905.

[0249] 15. King, AWT et al., Relative and inherent reactivities of imidazolium-based ionic liquids: the implications for lignocellulose processingapplications. RSC Adv., 2012.2 (Copyright (C) 2016 American Chemical Society (ACS). All rights reserved): pp. 8020-8026.

[0250] 16. Guizani, C. et al., Air gap spinning of a cellulose solution in anionic liquid with a novel vertically arranged spinning bath to simulate aclosed loop operation Cellulose submitted, 2020.

[0251] 17. Zhou, J. et al., Recovery and purification of ionic liquids from solutions: a review. RSC Adv., 2018. 8(57): pp. 32832-32864.

[0252] 18. H. et al., Cellulose, in Ullmann's Encyclopedia of Industrial Chemistry. 2004.

[0253] 19. Michud, A., Development of a novel process for the production of man-made cellulosic fibers from ionic liquid solution, in Department of Forest Products Technology. 2016, Thesis, Aalto University: Espoo. p. 71.

[0254] 20. Lewis, C.A. and R. Wolfenden, The Nonenzymatic Decomposition of Guanidines and Amidines. J. Am. Chem. Soc., 2014. 136(1): pp. 130 - 136.

[0255] 21. Carafa, M., E. Mesto and E. Quaranta, DBU-Promoted Nucleophilic Activation of Carbonic Acid Diesters. European Journal of Organic Chemistry, 2011. 2011(13): pp. 2458 - 2465.

[0256] 22. Mayr, H. et al., Scales of Lewis Basicities toward C-Centered Lewis Acids (Carbocations). Journal of the American Chemical Society, 2015. 137(7): pp. 2580 - 2599.

[0257] 23. Wolfe, R.H.d., Kinetics and mechanisms of reactions of amidines, in Amidines and Imidates (1979), S. Patai ed. 1975, John Wiley & Sons. pp. 349 - 384.

[0258] 24. Heidelberger, C. et al., Amidine as Intermediates in Transamidation Reactions. 9th Communication on Transamidation Reactions. Helvetica Chimica Acta, 1981, 64(2): pp. 399 - 406.

[0259] 25. Oediger, H. et al., 1,9 - Diazabicyclo[4.3.0]nonene-(9). A New Reagent for the Introduction of Double Bonds. Chemische Berichte, 1966, 99(6): pp. 2012 - 2016.

[0260] 26. Ostonen, A., Thermodynamic study of protic ionic liquids, in Department of Biotechnology and Chemical Technology. 2017, Aalto University: Espoo.

[0261] 27. Ribeiro, F.M.S. et al., Experimental Evidence for Azeotrope Formation from Protic Ionic Liquids. ChemPhysChem, 2018: pp. Ahead of Print.

[0262] 28. Baird, Z.S. et al., Vapor - liquid equilibrium of the ionic liquid 7 - methyl - 1,9,7 - triazabicyclo[4.4.0]dec - 9 - enium acetate and its mixtures with water. Journal of Chemical & Engineering Data, 2020. Accepted. Vol. 65, No. 5, 2405 - 2421

[0263] 29. Benjamin, V., Effect of some Ioncell-F process parameters on the cellulose dissolution and dope spinnability, in Bioproducts and Biosystems. 2019, Aalto University: Espoo, Finland。

[0264] 30. Michud, A., M. Hummel and H. Sixta, Influence of molar mass distribution on the final properties of fibers regenerated from cellulose dissolved in ionic liquid by dry-jet wet spinning. Polymer, 2015. 75: pp. 1-9.

Claims

1. A method for producing cellulose filaments or films, comprising the following steps: - dissolving a cellulose substrate in an ionic liquid consisting of a superbase cation 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium [mTBDH]+ and an anion derived from an acid present in a stoichiometric excess relative to the superbase; the stoichiometric excess of the acid being at most 30 mol%; and the anion being acetate to produce a solution forming a spinning solution; - extruding the spinning solution through a spinneret in a coagulation bath containing water to form filaments or films from the solution; - extracting the ionic liquid in the form of an aqueous mixture with water from the coagulation bath; - recovering the ionic liquid from the aqueous mixture by removing water; the amount of water present in the recovered ionic liquid is ≤ 7.5% by weight, calculated based on the total weight of the recovered ionic liquid and the water; and - optionally recycling the recovered ionic liquid to the dissolution step.

2. The method according to claim 1 further comprises the steps of washing the short fibers, silk or membrane obtained from the coagulation bath with water, and further extracting the ionic liquid in the form of an aqueous mixture with water from the washing step.

3. The process according to claim 1, wherein the stoichiometric excess of the acid is 10-20 mol%.

4. The method according to claim 1, wherein the cellulosic substrate is pulp, dissolving pulp, recycled cellulosic textile waste, recycled waste paper.

5. The method of claim 1, wherein the cellulosic substrate is bleached dissolving pulp. 6 . The method according to claim 1 , wherein the superbase mTBD contains 0-30 wt % of residues of the superbase 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as an impurity. 7 . The method according to claim 1 , wherein the superbase mTBD contains 0-10 wt % of residues of the superbase 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as an impurity.

8. The method of claim 1, wherein the recovered ionic liquid [mTBDH][OAc] contains one or more of the following hydrolyzates in an amount ≤20 wt% calculated based on the weight of the recovered ionic liquid: 1-[3-(methylammonio)propyl]-1,3-diazacyclohexane-2-one acetate ([H-mTBDH-1][OAc]), 1-(3-ammoniopropyl)-3-methyl-1,3-diazacyclohexane-2-one acetate ([H-mTBDH-2][OAc]).

9. The method of claim 1, wherein the recovered ionic liquid [mTBDH][OAc] contains one or more of the following hydrolyzates in an amount of ≤10 wt % calculated based on the weight of the recovered ionic liquid: 1-[3-(methylammonio)propyl]-1,3-diazacyclohexane-2-one acetate ([H-mTBDH-1][OAc]), 1-(3-ammoniopropyl)-3-methyl-1,3-diazacyclohexane-2-one acetate ([H-mTBDH-2][OAc]).

10. The method of claim 1, wherein the recovered ionic liquid [mTBDH][OAc] contains one or more of the following hydrolyzates in an amount of ≤5 wt% calculated based on the weight of the recovered ionic liquid: 1-[3-(methylammonio)propyl]-1,3-diazacyclohexane-2-one acetate ([H-mTBDH-1][OAc]), 1-(3-ammoniopropyl)-3-methyl-1,3-diazacyclohexane-2-one acetate ([H-mTBDH-2][OAc]).

11. The process of claim 1 , wherein the ionic liquid [mTBDH][OAc] is recycled by removing water from the aqueous mixture of the ionic liquid in a series of dehydration steps.

12. The process of claim 1, wherein water is removed from the aqueous mixture by one or more evaporators selected from the group consisting of falling film evaporators, thin film evaporators, and vapor recompression evaporators, and combinations thereof.

13. The method of claim 12, wherein water is removed from the aqueous mixture in one or more multiple-effect evaporation devices comprising two or more evaporators selected from falling film evaporators, thin film evaporators, and vapor recompression evaporators, and combinations thereof.

14. The method according to claim 1, wherein the amount of water present in the recovered ionic liquid is 3-5 wt%, calculated based on the total weight of the recovered ionic liquid and the water.

15. The method of claim 1, wherein the amount of water present in the recovered ionic liquid is ≤ 3 wt%, calculated based on the total weight of the recovered ionic liquid and the water.

16. The method of claim 1, comprising forming the filament or film in a coagulation bath containing the ionic liquid at a concentration of 40 wt% or less.

17. The method of claim 16, wherein the aqueous mixture extracted from the coagulation bath step contains 40% or less of ionic liquid.

18. The method according to claim 2, comprising washing the silk or membrane with water having an ionic liquid concentration of 40 wt% or less in the washing step.

19. The method of claim 18, wherein the aqueous mixture extracted from the washing step contains 40% or less of ionic liquid.

20. The method according to any one of claims 1 to 19, comprising producing cellulose fibers having a dry tenacity ≥ 35 cN / tex, a dry / wet tenacity > 0.80 and a modulus of tenacity ≥ 50 MPa.

21. The method according to any one of claims 1 to 19, comprising producing cellulose fibers having a dry tenacity ≥ 40 cN / tex, a wet / dry tenacity > 0.85 and a modulus of tenacity ≥ 60 MPa.

22. Use of the method of any one of claims 1 to 21 for producing textile fibers or films.

23. Use of the method according to any one of claims 1 to 21 for producing technical fibers.

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