Removal of cellulose-derived impurities from ionic liquid

Abstract

To provide a method for removing cellulose-derived impurities from an ionic liquid and effectively recovering the ionic liquid.SOLUTION: The present invention discloses a method for recovering a liquid comprising an ionic liquid and a cosolvent from an impurity-containing liquid comprising the ionic liquid, the cosolvent, and cellulose-derived impurities, the method including treating the impurity-containing liquid with an ultrafiltration membrane, thereby separating the liquid comprising the ionic liquid and the cosolvent from the cellulose-derived impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for removing cellulose-derived impurities from an ionic liquid. In particular, the present disclosure relates to a method for separating a liquid containing an ionic liquid and a co-solvent from the cellulose-derived impurities and recovering the liquid containing the ionic liquid and the co-solvent from an impurity-containing liquid containing the ionic liquid, a co-solvent, and the cellulose-derived impurities. The present disclosure also relates to a method for producing a cellulose ester, including the method. [Background technology]

[0002] Liquids containing ionic liquids have been used as solvents for synthesizing cellulose esters such as cellulose acetate. Ionic liquids have high solubility in cellulose, making it possible to synthesize cellulose esters uniformly. Liquids containing ionic liquids may contain cosolvents. The cosolvents reduce the viscosity of the liquid and can also reduce the amount of ionic liquid used.

[0003] Since ionic liquids are expensive, it is desirable to recycle the ionic liquid used in the synthesis of cellulose esters on an industrial scale by reusing the ionic liquid in the next synthesis. Cellulose esters synthesized in a liquid containing an ionic liquid can be recovered from the solid phase by precipitating the cellulose ester and performing solid-liquid separation. Meanwhile, the liquid containing the ionic liquid in the liquid phase contains impurities resulting from treatments during and after synthesis. These impurities include cellulose-derived impurities (e.g., unreacted cellulose, cellulose esters with a low degree of substitution, cellulose esters with a relatively low molecular weight, etc.) and coloring components resulting from heating the liquid after synthesis in processes such as distillation. To recycle ionic liquids, it is important to properly remove these impurities.

[0004] As methods for removing impurities and recycling ionic liquids, for example, Patent Document 1 discloses a method for removing impurities by extraction, Patent Document 2 discloses a method for removing impurities by recrystallization, and Patent Document 3 discloses a method for removing impurities using an ion exchange membrane. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-177324 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-144441 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-96255 Summary of the Invention [Problem to be solved by the invention]

[0006] When removing impurities from a liquid containing an ionic liquid and a co-solvent by extraction or recrystallization, problems generally arise, such as low recovery rates of the ionic liquid and co-solvent, and the need to add and recover additional substances for extraction or recrystallization. Furthermore, when removing impurities from a liquid containing an ionic liquid and a co-solvent using an ion exchange membrane, a problem arises: the membrane has low resistance to high-boiling polar solvents commonly used as co-solvents, such as dimethyl sulfoxide (DMSO), sulfolane, N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), and dimethylacetamide (DMAc). In view of these circumstances, an object of the present disclosure is to provide a method for effectively recovering an ionic liquid and a co-solvent by effectively removing impurities from a liquid containing an ionic liquid and a co-solvent. [Means for solving the problem]

[0007] The present disclosure discloses, for example, a method for recovering a liquid containing an ionic liquid and a co-solvent from an impurity-containing liquid containing an ionic liquid, a co-solvent, and cellulose-derived impurities, the method comprising subjecting the impurity-containing liquid to an ultrafiltration membrane to separate the liquid containing the ionic liquid and the co-solvent from the cellulose-derived impurities. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to effectively remove cellulose-derived impurities from a liquid containing an ionic liquid and a co-solvent, thereby enabling the ionic liquid and the co-solvent to be effectively recovered and reused. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 shows (1) the change in breaking strength over time, (2) the change in breaking elongation over time, and (3) the change in elastic modulus over time in the solvent resistance test of the ultrafiltration membrane used in Example 1. [Figure 2] FIG. 2 shows the ultraviolet / visible light spectrum of the feed solution containing an ionic liquid and a coloring component that was fed to the nanofiltration membrane of Example 8, and the permeate that passed through the nanofiltration membrane. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present disclosure will be described in detail below. However, the scope of the present disclosure is not limited to the embodiment described herein, and various modifications can be made without departing from the spirit of the present disclosure. Each aspect disclosed in this specification can be combined with any other feature disclosed in this specification. Furthermore, when multiple upper and lower limit values ​​are described for a specific parameter, any of these upper and lower limit values ​​can be combined to form a suitable numerical range. Furthermore, the lower and / or upper limit values ​​of a numerical range described in this disclosure are numerical values ​​within that numerical range and may be replaced with numerical values ​​shown in the examples. The expression "X to Y" indicating a numerical range means "X or more and Y or less." If a specific description described for one embodiment also applies to other embodiments, that description may be omitted in other embodiments.

[0011] <Method for recovering a liquid containing an ionic liquid and a co-solvent> In one embodiment, a method is disclosed for recovering a liquid comprising an ionic liquid and a co-solvent from an impurity-containing liquid comprising an ionic liquid, a co-solvent, and cellulose-derived impurities, the method comprising subjecting the impurity-containing liquid to an ultrafiltration membrane to separate the liquid comprising ionic liquid and co-solvent from the cellulose-derived impurities. This method allows for the effective recovery of ionic liquid and co-solvent. By reusing the recovered ionic liquid, costs associated with the use of expensive ionic liquid can be reduced. Furthermore, by reducing the amounts of ionic liquid and co-solvent used, the environmental impact can be reduced.

[0012] The impurity-containing liquid includes an ionic liquid, a cosolvent, and cellulose-derived impurities. In one embodiment, the impurity-containing liquid may be a reaction liquid obtained after the synthesis of a cellulose ester is completed and the cellulose ester is recovered as a product when esterifying cellulose. Specific examples of the ionic liquid, the cosolvent, and the cellulose-derived impurities will be described later.

[0013] In an impurity-containing liquid containing an ionic liquid, a cosolvent, and cellulose-derived impurities, and / or a liquid containing an ionic liquid and a cosolvent after removing cellulose-derived impurities using an ultrafiltration membrane, the content of the ionic liquid is preferably 20 to 99.9 wt %, more preferably 30 to 80 wt %, based on the total weight of the liquid.

[0014] In an impurity-containing liquid containing an ionic liquid, a cosolvent, and cellulose-derived impurities, and / or a liquid containing an ionic liquid and a cosolvent after removing cellulose-derived impurities with an ultrafiltration membrane, the content of the cosolvent is preferably 0.1 to 80 wt%, more preferably 20 to 70 wt%, based on the total weight of the liquid. The weight ratio of the ionic liquid to the cosolvent is preferably 20:80 to 99.9:0.1, more preferably 30:70 to 80:20.

[0015] In an impurity-containing liquid containing an ionic liquid, a cosolvent, and a cellulose ester, and / or a liquid containing an ionic liquid and a cosolvent after removing cellulose-derived impurities using an ultrafiltration membrane, the content of the ionic liquid relative to the total amount of the ionic liquid and the cosolvent is preferably 20 to 99.9 wt %, more preferably 30 to 80 wt %.

[0016] [Ultrafiltration membrane] An ultrafiltration (UF) membrane is a membrane that can separate molecules having a molecular weight greater than a specific molecular weight cutoff from molecules having a molecular weight less than this. The molecular weight cutoff of the ultrafiltration membrane is preferably 1,000 to 1,000,000, more preferably 5,000 to 100,000, and even more preferably 10,000 to 30,000. Ultrafiltration membranes with a molecular weight cutoff within these ranges tend to be able to easily remove cellulose-derived impurities from an impurity-containing liquid that contains an ionic liquid, a cosolvent, and cellulose-derived impurities. The molecular weight cutoff of an ultrafiltration membrane can be determined, for example, by a constant-pressure cross-flow filtration test using an NMP solution of polyethylene glycol (PEG) having a predetermined molecular weight as the test solution. Specifically, the test can be performed, for example, as follows: PEGs with molecular weights of 3K, 8K, 12K, 35K, 100K, and 500K are each mixed and dissolved in NMP at 0.1%. This solution is passed through a hollow fiber membrane module composed of the ultrafiltration membrane to be tested at a flow rate of, for example, 9.9 ml / min. Furthermore, the test is performed under constant pressure conditions by setting the operating pressure to a predetermined pressure (e.g., 1 bar or 4 bar) using a pressure gauge installed near the inlet of the hollow fiber membrane and a pressure regulator installed near the outlet of the hollow fiber membrane. After the start of the flow (e.g., 6 hours), the feed solution and filtrate are collected. The collected feed solution and filtrate are then analyzed by liquid chromatography using a gel permeation chromatography (GPC) column and a differential refractive index (RI) detector. The strength of the feed solution (I) was calculated from the chromatogram of the RI peak intensity versus the molecular weight (calculated from the PEG calibration curve). feed ) and filtrate strength (I fill ) and calculate the rejection rate of PEG using the following formula 1 to plot a fractionation curve of the ultrafiltration membrane, and determine the molecular weight at which 90% rejection rate is achieved as the molecular weight cutoff. Formula 1: Inhibition rate (%) = (1-I fill / I feed ) x 100

[0017] The ultrafiltration membrane preferably has high resistance to high-boiling-point polar solvents, which allows the ultrafiltration membrane to be used stably even when the co-solvent is a high-boiling-point polar solvent.

[0018] The ultrafiltration membrane preferably has high hydrophilicity. The ionic liquid, cosolvent, and cellulose-derived impurities supplied to the ultrafiltration membrane are all highly hydrophilic. Therefore, when the ultrafiltration membrane has high hydrophilicity, adsorption of the ionic liquid, cosolvent, and cellulose-derived impurities to the ultrafiltration membrane is suppressed, thereby suppressing a decrease in permeation rate due to adsorption (membrane fouling), and the ultrafiltration membrane can easily be used stably for a long period of time.

[0019] The ultrafiltration membrane preferably contains a polyamide resin, which may be, for example, polyamide 6, polyamide 66, polyamide 46, polyamide 610, polyamide 612, polyamide 11, polyamide 1, polyamide MXD6, polyamide 4T, polyamide 6T, polyamide 9T, polyamide 10T, or a copolymer of these polyamides, or may contain a plurality of resins selected from these.

[0020] The NMP permeation rate of the ultrafiltration membrane is preferably 1 to 50 L / m 2 / h / bar, more preferably 10 to 20 L / m 2 It is / h / bar. The NMP permeation rate can be measured, for example, by a constant pressure cross-flow test. Specifically, it can be carried out, for example, as follows. NMP is passed through a hollow fiber membrane module composed of the ultrafiltration membrane to be tested, at a flow rate of, for example, 9.9 ml / min. Furthermore, the test is carried out under constant pressure conditions by setting the operating pressure to a predetermined pressure (for example, 1 bar or 4 bar) using a pressure gauge installed near the inlet of the hollow fiber membrane and a pressure regulator installed near the outlet of the hollow fiber membrane. At this time, the permeation rate of the filtrate discharged from the outlet of the hollow fiber membrane can be measured to determine the permeation rate per unit time (h) and per unit membrane area (m 2 ), permeation rate per unit pressure (bar) (L / m 2 / hr / bar) can be calculated.

[0021] The permeation rate of the impurity-containing liquid through the ultrafiltration membrane is preferably 0.1 to 10 L / m 2 / h / bar, more preferably 0.2 to 2 L / m 2 It is / h / bar. The permeation rate of the impurity-containing liquid through the ultrafiltration membrane can be measured in the same manner as the NMP permeation rate described above.

[0022] The rejection rate of the ultrafiltration membrane for impurities in an impurity-containing liquid is preferably 30 to 99%, and more preferably 70 to 99%. The impurity rejection rate of an ultrafiltration membrane can be measured, for example, by a constant pressure crossflow test. Specifically, this can be performed, for example, as follows: A liquid containing impurities is passed through a hollow fiber membrane module composed of the ultrafiltration membrane to be tested, at a flow rate of, for example, 9.9 ml / min. Furthermore, the test is performed under constant pressure conditions by setting the operating pressure to a predetermined pressure (e.g., 1 bar or 4 bar) using a pressure gauge installed near the inlet of the hollow fiber membrane and a pressure regulator installed near the outlet of the hollow fiber membrane. After the start of the liquid passage (e.g., 24 hours later), the feed liquid and filtrate are sampled. The cellulose acetate content of the sampled feed liquid and filtrate is quantified by sugar analysis using the phenol-sulfuric acid method. Considering the influence of the solvent on the measured value, the quantification is preferably performed using a calibration curve prepared using the same solvent system. The cellulose acetate content (C ) in the feed liquid is then measured. feed ), the content of cellulose acetate in the filtrate (C fill ) the rejection rate of impurities in the solvent can be calculated using the following formula 2. Formula 2: Rejection rate (%)=(1-C fill / C feed ) x 100

[0023] The ultrafiltration membrane may be used in the form of a membrane module housed in a container, and a plurality of such membranes may be used. In this case, the membrane area per membrane module may be any within the range in which the effects of the present invention can be obtained, but is preferably 1 to 200 m 2 and more preferably 10 to 100 m 2 The surface area of ​​the ultrafiltration membrane may be a value from a manufacturer's catalog or may be a value measured by a standard method. The number of membrane modules required is determined by the throughput and the membrane permeation rate.

[0024] The ultrafiltration membrane is resistant to a liquid containing an ionic liquid and a co-solvent for preferably 3 months, more preferably 6 months, and even more preferably 12 months.

[0025] The thickness of the ultrafiltration membrane is preferably 0.1 to 5 mm, more preferably 0.3 to 3 mm.

[0026] The ultrafiltration membrane may have any shape as long as the effects of the present invention can be obtained, and may be, for example, a hollow fiber membrane or a flat membrane.

[0027] As the ultrafiltration membrane, a commercially available ultrafiltration membrane can be used as long as the effects of the present invention can be obtained. Non-limiting examples of commercially available ultrafiltration membranes include UF50 and UF120 manufactured by Unitika. Alternatively, an ultrafiltration membrane manufactured by a known method can be used as the ultrafiltration membrane.

[0028] [Cellulose and cellulose esters] Cellulose has the molecular formula (C6H 10 O5) n Cellulose is a carbohydrate represented by the formula: Cellulose is the main component of plant cell walls and plant fibers. Cellulose esters are cellulose esters obtained by esterifying cellulose with an organic acid anhydride, for example, cellulose acetate is cellulose esterified with acetic anhydride. Cellulose ester is a biomass material and is important as a material with low environmental impact due to its high biodegradability.

[0029] [Cellulose-derived impurities] The cellulose-derived impurities are typically cellulose-derived impurities that are dissolved in or mixed into a reaction liquid after the synthesis is completed and the cellulose ester is recovered as a product when cellulose is esterified to produce a cellulose ester. The cellulose-derived impurities typically include one or more of unreacted cellulose, cellulose esters with a low degree of substitution, and cellulose esters with a relatively low molecular weight. The cellulose-derived impurities can become impurities when the liquid containing the ionic liquid and the co-solvent is reused in the next synthesis. The molecular weight of the cellulose-derived impurities is preferably 10,000 to 1,500,000, and more preferably 20,000 to 1,000,000. The molecular weight of the cellulose-derived impurities can be measured, for example, by gel permeation chromatography (GPC). The degree of substitution of cellulose esters contained as cellulose-derived impurities is preferably 3. The degree of substitution of the cellulose ester is preferably 0 or less, more preferably 2.9 or less, or is preferably 1.5 to 2.9, more preferably 2.0 to 2.9. The degree of substitution of the cellulose ester can be measured by a nuclear magnetic resonance analyzer (NMR). The cellulose ester contained as the cellulose-derived impurity is preferably cellulose acetate.

[0030] [Ionic liquid] The ionic liquid is an ionic liquid that can dissolve cellulose. Ionic liquids include a cationic component and an anionic component.

[0031] (cationic component) The cationic component is preferably one or more cations selected from the group consisting of imidazolium cations, pyridinium cations, pyrrolidinium cations, piperidinium cations, quaternary ammonium cations, and quaternary phosphonium cations.

[0032] Non-limiting examples of imidazolium cations include cations represented by the following formula (1): The cation represented by formula (1) also includes its tautomers and cations represented by structural formulas that have a resonance relationship with formula (1). Formula (1): TIFF2025133235000001.tif27170 In formula (1), R 1 and R 3 are the same or different and are a substituted or unsubstituted alkyl group, alkenyl group, alkoxyalkyl group, or substituted or unsubstituted phenyl group, and R 2 , R 4 , and R 5are the same or different and are a hydrogen atom, a substituted or unsubstituted alkyl group, an alkenyl group, an alkoxyalkyl group, or a substituted or unsubstituted phenyl group. R 1 ~R 5 Examples of the substituted or unsubstituted alkyl group in the formula (I) include linear or branched alkyl groups having 1 to 20 (preferably 1 to 10, more preferably 2 to 6, and even more preferably 2 to 4) carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, butyl, hexyl, and octyl. A sulfo group may be bonded to the terminal of these alkyl groups. Examples of the alkenyl group include linear or branched alkenyl groups having 2 to 20 (preferably 2 to 10, more preferably 2 to 6, and even more preferably 2 to 4) carbon atoms, such as vinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 1-pentenyl, 2-pentenyl, 1-hexenyl, 2-hexenyl, and 1-octenyl. Examples of the alkoxyalkyl group include a linear or branched alkoxyalkyl group having 2 to 20 (preferably 2 to 10, more preferably 2 to 6, and even more preferably 2 to 4) carbon atoms, such as a methoxymethyl group, an ethoxymethyl group, a 1-methoxyethyl group, a 2-methoxyethyl group, a 1-ethoxyethyl group, and a 2-ethoxyethyl group. Examples of the substituted or unsubstituted phenyl group include a phenyl group optionally substituted with 1 to 2 groups selected from a hydroxyl group, a halogen atom, a lower alkoxy group, a lower alkenyl group, a methylsulfonyloxy group, a substituted or unsubstituted lower alkyl group, a substituted or unsubstituted amino group, a substituted or unsubstituted phenyl group, a substituted or unsubstituted phenoxy group, and a substituted or unsubstituted pyridyl group. R 1 and R 3 is preferably an alkyl group, an alkenyl group, or a substituted or unsubstituted phenyl group, and more preferably a linear alkyl group having 1 to 6 carbon atoms. 1 and R 3It is particularly preferred that one of R is a linear alkyl group having 1 to 4 carbon atoms and the other is a linear alkyl group having 2 to 6 carbon atoms, and that the numbers of carbon atoms of these alkyl groups are different. 2 , R 4 and R 5 is preferably a hydrogen atom, an alkyl group, an alkenyl group, or a substituted or unsubstituted phenyl group, and more preferably a hydrogen atom or an alkyl group. The imidazolium cation may be preferably one or more imidazolium cations selected from the group consisting of 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, 1-decyl-3-methylimidazolium, 1-tetradecyl-3-methylimidazolium, 1-hexadecyl-3-methylimidazolium, 1-octadecyl-3-methylimidazolium, 1-allyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-butyl-2,3-dimethylimidazolium, and 1-hexyl-2,3-dimethylimidazolium, and particularly preferably the cation of 1-ethyl-3-methylimidazolium (Emidazolium). + ) may be.

[0033] Non-limiting examples of pyridinium cations include cations represented by the following formula (2): The cation represented by formula (2) also includes its tautomers and cations represented by structural formulas that have a resonance relationship with formula (2). Formula (2): TIFF2025133235000002.tif27170 In formula (2), R 6 is an alkyl group, an alkenyl group, an alkoxyalkyl group, or a substituted or unsubstituted phenyl group, and R 7 ~R 11 are the same or different and are a hydrogen atom, an alkyl group, an alkenyl group, an alkoxyalkyl group, or a substituted or unsubstituted phenyl group. R 6 ~R 11The alkyl group, alkenyl group, alkoxyalkyl group, and substituted or unsubstituted phenyl group in the formula (1) are R 1 ~R 5 Examples of the same are as those described above. R 6 R is preferably an alkyl group, more preferably a linear alkyl group having 1 to 6 carbon atoms. 6 ~R 11 is preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom. The pyridinium cation may be preferably a pyridinium cation such as 1-ethylpyridinium, 1-butylpyridinium, 1-hexylpyridinium, 1-butyl-4-methylpyridinium, 1-butyl-3-methylpyridinium, 1-hexyl-4-methylpyridinium, 1-hexyl-3-methylpyridinium, 1-octyl-4-methylpyridinium, 1-octyl-3-methylpyridinium, 1-butyl-3,4-dimethylpyridinium, or 1-butyl-3,5-dimethylpyridinium, and is particularly preferably a 1-octyl-4-methylpyridinium cation.

[0034] Non-limiting examples of pyrrolidinium cations include cations represented by the following formula (3): The cation represented by formula (3) also includes its tautomers. Formula (3): TIFF2025133235000003.tif27170 In formula (3), R 12 and R 13 are the same or different and are an alkyl group, an alkenyl group, an alkoxyalkyl group, or a substituted or unsubstituted phenyl group; R 14 ~R 21 are the same or different and are a hydrogen atom, an alkyl group, an alkenyl group, an alkoxyalkyl group, or a substituted or unsubstituted phenyl group. R 12 ~R 21The alkyl group, alkenyl group, alkoxyalkyl group, and substituted or unsubstituted phenyl group in the formula (1) are R 1 ~R 5 Examples of the same are as those described above. R 12 and R 13 R is preferably an alkyl group, more preferably a linear alkyl group having 1 to 6 carbon atoms. 14 ~R 21 is preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom. The pyrrolidinium cation may preferably be the cation of 1-butyl-1-methylpyrrolidinium.

[0035] Non-limiting examples of piperidinium cations include cations represented by the following formula (4): The cation represented by formula (4) also includes its tautomers. Formula (4): TIFF2025133235000004.tif28170 In formula (4), R 22 and R 23 are the same or different and are an alkyl group, an alkenyl group, an alkoxyalkyl group, or a substituted or unsubstituted phenyl group; R 24 ~R 33 are the same or different and are a hydrogen atom, an alkyl group, an alkenyl group, an alkoxyalkyl group, or a substituted or unsubstituted phenyl group. R 22 ~R 33 The alkyl group, alkenyl group, alkoxyalkyl group, and substituted or unsubstituted phenyl group in the formula (1) are R 1 ~R 5 Examples of the same are as those described above. R 22 and R 23 R is preferably an alkyl group, more preferably a linear alkyl group having 1 to 6 carbon atoms. 24 ~R 33is preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom. The piperidinium cation may preferably be the cation of 1-butyl-1-methylpiperidinium.

[0036] Non-limiting examples of quaternary ammonium cations include ammonium cations represented by the following formula (5): The cation represented by formula (5) also includes its tautomers. Formula (5): TIFF2025133235000005.tif20170 In formula (5), R 34 ~R 37 are the same or different and are an alkyl group, an alkenyl group, an alkoxyalkyl group, or a substituted or unsubstituted phenyl group. R 34 ~R 37Examples of the alkyl group in the formula (I) include linear or branched alkyl groups having 1 to 20 (preferably 1 to 10, more preferably 2 to 6, and even more preferably 2 to 4) carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, butyl, hexyl, and octyl. Examples of the alkenyl group include linear or branched alkenyl groups having 2 to 20 (preferably 2 to 10, more preferably 2 to 6, and even more preferably 2 to 4) carbon atoms, such as vinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 1-pentenyl, 2-pentenyl, 1-hexenyl, 2-hexenyl, and 1-octenyl. Examples of the alkoxyalkyl group include a linear or branched alkoxyalkyl group having 2 to 20 (preferably 2 to 10, more preferably 2 to 6, and even more preferably 2 to 4) carbon atoms, such as a methoxymethyl group, an ethoxymethyl group, a 1-methoxyethyl group, a 2-methoxyethyl group, a 1-ethoxyethyl group, and a 2-ethoxyethyl group. Examples of the substituted or unsubstituted phenyl group include a phenyl group optionally substituted with 1 to 2 groups selected from a hydroxyl group, a halogen atom, a lower alkoxy group, a lower alkenyl group, a methylsulfonyloxy group, a substituted or unsubstituted lower alkyl group, a substituted or unsubstituted amino group, a substituted or unsubstituted phenyl group, a substituted or unsubstituted phenoxy group, and a substituted or unsubstituted pyridyl group. R 34 ~R 37 is preferably an alkyl group, more preferably a linear alkyl group having 1 to 6 carbon atoms. The quaternary ammonium cation may preferably be one or more cations selected from the group consisting of trimethylpropylammonium, trimethylbutylammonium, triethylmethylammonium, trioctylmethylammonium, tetramethylammonium, tetraethylammonium, tetrabutylammonium, tetrapentylammonium, and tetrahexylammonium.

[0037] Non-limiting examples of quaternary phosphonium cations include phosphonium cations represented by the following formula (6): The cation represented by formula (6) also includes its tautomers. Formula (6): TIFF2025133235000006.tif20170 In formula (6), R 38 ~R 41 are the same or different and are an alkyl group, an alkenyl group, an alkoxyalkyl group, or a substituted or unsubstituted phenyl group. R 38 ~R 41 Examples of the alkyl group in the formula (I) include linear or branched alkyl groups having 1 to 20 (preferably 1 to 10, more preferably 2 to 6, and even more preferably 2 to 4) carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, butyl, hexyl, and octyl. Examples of the alkenyl group include linear or branched alkenyl groups having 2 to 20 (preferably 2 to 10, more preferably 2 to 6, and even more preferably 2 to 4) carbon atoms, such as vinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 1-pentenyl, 2-pentenyl, 1-hexenyl, 2-hexenyl, and 1-octenyl. Examples of the alkoxyalkyl group include a linear or branched alkoxyalkyl group having 2 to 20 (preferably 2 to 10, more preferably 2 to 6, and even more preferably 2 to 4) carbon atoms, such as a methoxymethyl group, an ethoxymethyl group, a 1-methoxyethyl group, a 2-methoxyethyl group, a 1-ethoxyethyl group, and a 2-ethoxyethyl group. Examples of the substituted or unsubstituted phenyl group include a phenyl group optionally substituted with 1 to 2 groups selected from a hydroxyl group, a halogen atom, a lower alkoxy group, a lower alkenyl group, a methylsulfonyloxy group, a substituted or unsubstituted lower alkyl group, a substituted or unsubstituted amino group, a substituted or unsubstituted phenyl group, a substituted or unsubstituted phenoxy group, and a substituted or unsubstituted pyridyl group. The quaternary phosphonium cation may preferably be one or more cations selected from the group consisting of tetramethylphosphonium, tetraethylphosphonium, tetrabutylphosphonium, tetrahexylphosphonium, tetraoctylphosphonium, triethylmethylphosphonium, and tributylethylphosphonium.

[0038] (anionic component) Non-limiting examples of anionic components include halogen anions, pseudohalogen anions, carboxylate anions, phosphate anions, amino acid anions, phenolates, pyrimidine olates, and tetrafluoroborate ions (BF 4- ), sulfomethyl ion (CH3SO3 - ), methylphosphonate, sulfate ion, PF6 - etc.

[0039] Non-limiting examples of halogen anions include fluoride ion (F - ), chloride ions (Cl - ), iodine ion (I - ), and bromide ion (Br - ) etc. Non-limiting examples of pseudohalogen anions include cyanide anion, thiocyanate anion, cyanate anion, fulminate anion, azide anion, and the like. Non-limiting examples of carboxylate anions include monocarboxylate anions or dicarboxylate anions having 1 to 18 carbon atoms. The carboxylate anion is preferably one or more selected from the group consisting of formate anion, acetate anion, propionate anion, butyrate anion, valerate anion, fumarate anion, oxalate anion, lactate anion, and pyruvate anion.

[0040] Non-limiting examples of phosphate anions include phosphate anion and phosphate ester anions having 1 to 40 carbon atoms. Non-limiting examples of phosphate ester anions include methyl phosphate monoester anion, octyl phosphate monoester anion, octyl phosphate diester anion, lauryl phosphate monoester anion, lauryl phosphate diester anion, stearyl phosphate monoester anion, stearyl phosphate diester anion, eicosyl phosphate monoester anion, eicosyl phosphate diester anion, etc.

[0041] (Combination of a cationic component and an anionic component) The ionic liquid is a combination of any of the above-mentioned cation components and anion components. For example, an ionic liquid containing an imidazolium cation or a quaternary ammonium cation as the cation component is preferred. Also, an ionic liquid containing a carboxylate anion as the anion component is preferred. More specifically, at least one selected from the group consisting of 1-ethyl-3-methylimidazolium acetate (EmimOAc), 1-ethyl-2,3-dimethylimidazolium acetate (EDmimOAc), 1-butyl-3-methylimidazolium acetate, 1-hexyl-3-methylimidazolium acetate, and tetrabutylammonium acetate is more preferred. The ionic liquid may be preferably at least one selected from the group consisting of 1-ethyl-3-methylimidazolium acetate (EmimOAc) and 1-ethyl-2,3-dimethylimidazolium acetate (EDmimOAc), and particularly preferably 1-ethyl-3-methylimidazolium acetate (EmimOAc). The ionic liquid may be a commercially available product or may be produced by a known technique.

[0042] [Co-solvent] The co-solvent is added to reduce the viscosity of the liquid containing the ionic liquid and to reduce the amount of the ionic liquid used. The co-solvent is preferably a high-boiling polar solvent. The high-boiling polar solvent is preferably a polar solvent having a boiling point higher than that of the organic acid. For example, when the organic acid is acetic acid, the boiling point is 117.9°C, so a polar solvent having a boiling point higher than that is preferred. The boiling point is preferably 120°C or higher, more preferably 150°C or higher. Non-limiting examples of co-solvents include, and may include, one or more co-solvents selected from the group consisting of dimethyl sulfoxide (DMSO), sulfolane, N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), and combinations thereof.

[0043] <Method of manufacturing cellulose ester> In one embodiment, A method for producing a cellulose ester, comprising: A first step of dissolving cellulose in a first liquid containing an ionic liquid and a co-solvent to obtain a second liquid; a second step of adding an organic acid anhydride to the second liquid to react the cellulose with the organic acid anhydride to produce a cellulose ester; a third step of adding a poor solvent to the second liquid to precipitate the cellulose ester; a fourth step following the third step, in which a solid phase containing the cellulose ester is separated from a liquid phase consisting of the ionic liquid, the cosolvent, and a third liquid containing cellulose-derived impurities, and the cellulose ester is recovered from the solid phase and the third liquid is recovered from the liquid phase; a fifth step of subjecting the third liquid to an ultrafiltration membrane to separate a fourth liquid containing the ionic liquid and the co-solvent from cellulose-derived impurities, and recovering the fourth liquid; Including, The first to fifth steps can be repeated by reusing all or part of the fourth liquid as all or part of the first liquid. A method of manufacture is disclosed. This method for producing a cellulose ester can effectively produce a cellulose ester by using a liquid containing an ionic liquid and a co-solvent as a reaction solvent. In addition, this method for producing cellulose ester can effectively recover the ionic liquid and co-solvent used in the cellulose ester synthesis reaction and reuse them in the next synthesis reaction, thereby reducing the cost associated with the use of expensive ionic liquid.In addition, by reducing the amount of ionic liquid and co-solvent used, the environmental load can be reduced.

[0044] The above-mentioned fifth step is preferably carried out according to the above-mentioned method for recovering a liquid comprising an ionic liquid and a co-solvent.

[0045] The above-mentioned method for producing a cellulose ester may include a distillation step of distilling the third liquid to remove the poor solvent and / or organic acid derived from the organic acid anhydride in the third liquid prior to the fifth step. By including this distillation step, the method for producing a cellulose ester tends to be able to more effectively recover the fourth liquid in the fifth step.

[0046] In this embodiment, the ionic liquid, co-solvent, cellulose, cellulose ester, cellulose-derived impurities, etc. are the same as those described in the above-mentioned method for recovering a liquid containing an ionic liquid and a co-solvent. Furthermore, the composition of each liquid in this embodiment may be the same as that of the liquid described in the above-mentioned method for recovering a liquid containing an ionic liquid and a co-solvent.

[0047] [Organic acid anhydride] The organic acid anhydride can esterify cellulose to produce a cellulose ester. Non-limiting examples of the organic acid anhydride include an acid anhydride of preferably C1-18 carboxylic acid, more preferably C1-10 carboxylic acid, further preferably C1-6 carboxylic acid, particularly preferably C2-4 carboxylic acid, and also include an acid anhydride of carboxylic acid such as formic acid, acetic acid, propionic acid, trifluoroacetic acid, etc. The organic acid anhydride can be appropriately selected depending on the type of cellulose ester to be synthesized. For example, when the cellulose ester to be synthesized is cellulose acetate, acetic anhydride is preferably used as the organic acid anhydride.

[0048] [Organic acid] The organic acid is produced by hydrolysis of the organic acid anhydride. For example, the organic acid is produced as a by-product when cellulose is esterified by the organic acid anhydride in the above-mentioned reaction for producing cellulose ester. In addition, when the poor solvent described below contains water, the organic acid is also produced when the organic acid anhydride is hydrolyzed by water. When the organic acid anhydride is acetic anhydride, the organic acid produced is acetic acid.

[0049] [Poor solvent] The poor solvent is a solvent that has low solubility for cellulose ester. By adding the poor solvent to the second liquid in which the cellulose ester is dissolved, the cellulose ester can be precipitated from the second liquid. The poor solvent can also be used to wash the precipitated cellulose ester. In this case, the poor solvent used to wash the precipitated cellulose ester can be combined with the second liquid. Non-limiting examples of anti-solvents include water, alcohols such as methanol, ethanol, and 2-octanol, and ketones such as acetone. The second liquid or the third liquid excluding the precipitated cellulose ester in the second liquid may contain a poor solvent in an amount of preferably 30 to 90 wt %, more preferably 40 to 80 wt %, based on the total weight of the second liquid or the third liquid.

[0050] [distillation] Distillation is a process for purifying a liquid by evaporating and recondensing the impurity-containing liquid to remove impurities based on the difference in boiling points. The distillation temperature is appropriately set depending on the boiling points of the liquid and impurities. Furthermore, when a liquid contains multiple impurities, the liquid can be more effectively purified by sequentially performing multiple distillations at gradually increasing temperatures to sequentially remove the multiple impurities. For example, in the above-mentioned distillation process, distillation to remove the organic acid and distillation to remove the antisolvent can be performed sequentially.

[0051] [Additional process to remove coloring components] When the liquid containing the ionic liquid is heated in the distillation step, colored components may be generated in the liquid. The above-mentioned method for producing cellulose ester may include an additional step of removing coloring components formed by the distillation step. The additional step of removing coloring components formed by the distillation step is preferably carried out by subjecting the fourth liquid to a nanofiltration membrane or a reverse osmosis membrane after the above-mentioned fifth step. When the liquid containing the ionic liquid containing the coloring component generated by the distillation process is reused for the synthesis of cellulose ester, undesirable effects such as coloring of the synthesized cellulose ester may occur. Therefore, the method for producing cellulose ester includes an additional step of removing the coloring component generated by the distillation process, so that the ionic liquid can be recovered more effectively and reused more effectively.

[0052] (nanofiltration membrane or reverse osmosis membrane) A reverse osmosis membrane (RO membrane) is a membrane that allows water to pass through but does not allow impurities other than water, such as ions and salts, to pass through. Any reverse osmosis membrane can be used as the nanofiltration membrane according to the present disclosure as long as the effects of the present invention can be obtained. A nanofiltration (NF) membrane is a membrane with performance intermediate between a reverse osmosis membrane (RO membrane) and an ultrafiltration membrane (UF membrane), and typically allows particles or molecules of about 1 nm in size to pass through, but does not allow particles or molecules larger than this in size to pass through. Any nanofiltration membrane can be used as the nanofiltration membrane according to the present disclosure, as long as the effects of the present invention can be obtained.

[0053] A nanofiltration membrane or a reverse osmosis membrane can effectively remove coloring components contained in a liquid containing an ionic liquid.

[0054] The salt rejection of the nanofiltration membrane or reverse osmosis membrane when the liquid containing the ionic liquid does not contain methanol is preferably 95% or more, 96% or more, 97% or more, 98% or more, 98.5% or more, 99% or more, or 99.5% or more. When the liquid containing the ionic liquid contains methanol, the salt rejection of the nanofiltration membrane or reverse osmosis membrane is preferably 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, 98.5% or more, 99% or more, or 99.5% or more. Here, the salt rejection rate is Equation 3: Salt rejection rate (%) = (1 - C fill / C feed ) x 100 [In Equation 4, C feed is the NaCl concentration in the NaCl aqueous solution supplied to the nanofiltration membrane or the reverse osmosis membrane when the NaCl aqueous solution is passed through the nanofiltration membrane or the reverse osmosis membrane, and C fill is the NaCl concentration in the aqueous NaCl solution discharged from the nanofiltration membrane or the reverse osmosis membrane when the aqueous NaCl solution is passed through the nanofiltration membrane or the reverse osmosis membrane. It can be calculated as follows.

[0055] The nanofiltration membrane or reverse osmosis membrane preferably has a hydraulic conductivity of 1.0 L / m when the liquid containing the ionic liquid does not contain methanol. 2 / h / bar, more preferably 0.5 to 0.95 L / m 2 When the liquid containing the ionic liquid contains methanol, the permeability coefficient of the nanofiltration membrane or the reverse osmosis membrane is preferably 8.0 L / m 2 / h / bar, more preferably 1.0 to 8.0 L / m 2 It is / h / bar. The hydraulic conductivity can be defined as the permeation rate when a 1600 ppm NaCl aqueous solution passes through the nanofiltration membrane.

[0056] The nanofiltration membrane or reverse osmosis membrane preferably includes an active layer containing a crosslinked polyamide resin. The crosslinked polyamide resin is formed, for example, by interfacial polymerization of an aromatic or alicyclic polyfunctional amine with a polyfunctional acyl halide. The polyfunctional amine is selected from the diamine group consisting of m-phenylenediamine, p-phenylenediamine, xylylenediamine, 3,5-diaminobenzoic acid, 3-aminobenzylamine, 4-aminobenzylamine, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, 4-aminopiperidine, and piperazine. The polyfunctional acyl halide is selected from the trifunctional acyl halide group consisting of trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, and 1,2,4-cyclobutanetricarboxylic acid trichloride. The nanofiltration membrane or reverse osmosis membrane is more preferably a composite membrane in which an active layer containing a polyamide is formed on the surface of a membrane made of polyketone or polysulfone.

[0057] The nanofiltration membrane or reverse osmosis membrane may have any shape as long as the effects of the present invention can be obtained, and may be, for example, a hollow fiber membrane or a flat membrane.

[0058] As the nanofiltration membrane or reverse osmosis membrane, commercially available nanofiltration membranes or reverse osmosis membranes can be used as long as the effects of the present invention can be obtained. Non-limiting examples of commercially available nanofiltration membranes include TriSep TS80 manufactured by Aquqsource and NTR7250 manufactured by Nitto Denko Corporation. Non-limiting examples of commercially available reverse osmosis membranes include SWC4 manufactured by Nitto Denko Corporation.

[0059] (Coloring components and color removal rate) The coloring component is a component that is produced in a liquid containing an ionic liquid by a treatment involving heating, such as distillation. In a liquid containing an ionic liquid, coloring components generated by a heating process such as distillation have an absorption peak in the ultraviolet region and an absorption band extending into the visible light region (Figure 2). In this disclosure, the color removal rate is defined as the change in the average absorbance between 380 and 770 nm in a liquid containing an ionic liquid before and after passing through a nanofiltration membrane or reverse osmosis membrane. Therefore, the effectiveness of a nanofiltration membrane or reverse osmosis membrane in removing coloring components from a liquid containing an ionic liquid can be evaluated by the color removal rate of the nanofiltration membrane or reverse osmosis membrane. The color removal rate is Equation 4: Stain removal rate (%) = (1 - Abs fill / Abs feed ) x 100 [In Equation 4, Abs feed is the average absorbance at 380 to 770 nm of a liquid containing an ionic liquid supplied to a nanofiltration membrane or a reverse osmosis membrane when the liquid contains an ionic liquid and is passed through the nanofiltration membrane or the reverse osmosis membrane, and Abs fill is the average absorbance in the range of 380 to 770 nm of a liquid containing an ionic liquid that is discharged from a nanofiltration membrane or a reverse osmosis membrane when the liquid contains an ionic liquid and is passed through the nanofiltration membrane or the reverse osmosis membrane.] It can be calculated as follows. The color removal rate by the nanofiltration membrane or reverse osmosis membrane is preferably 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 90% or more.

[0060] [Additional Step of Adding and / or Removing Methanol] When the method for producing cellulose ester includes the additional step of removing the coloring components, the method may include adding methanol to the fifth liquid in an amount of preferably 30 to 70% by weight, more preferably 40 to 60% by weight, based on the total weight, prior to the additional step of removing the coloring components. In this case, the production method may further comprise, after the additional step of removing the coloring components, a step of removing methanol from the liquid containing the ionic liquid, for example by distillation or extraction.

[0061] A non-limiting list of exemplary embodiments and combinations of exemplary embodiments of the present disclosure are disclosed below. [1] A method for recovering a liquid containing an ionic liquid and a co-solvent from an impurity-containing liquid containing an ionic liquid, a co-solvent, and cellulose-derived impurities, the method comprising subjecting the impurity-containing liquid to an ultrafiltration membrane to separate the liquid containing the ionic liquid and the co-solvent from the cellulose-derived impurities. [2] The method according to [1], wherein the molecular weight cutoff of the ultrafiltration membrane is 1,000 to 1,000,000. [3] The method according to [1] or [2], wherein the ultrafiltration membrane comprises a polyamide resin. [4] The method according to any one of [1] to [3], wherein the cellulose-derived impurities include cellulose esters. [5] The method according to any one of [1] to [4], wherein the cellulose-derived impurities have a molecular weight of 10,000 to 1,500,000. [6] The method according to any one of [1] to [5], wherein the cellulose-derived impurities include a cellulose ester having a degree of substitution of 2.9 or less. [7] The method according to [1], wherein the ionic liquid contains an imidazolium cation or a quaternary ammonium cation as a cation component and a carboxylate anion as an anion component. [8] The method according to any one of [1] to [6], wherein the ionic liquid is selected from the group consisting of 1-ethyl-3-methylimidazolium acetate (EmimOAc), 1-ethyl-2,3-dimethylimidazolium acetate (EDmimOAc), 1-butyl-3-methylimidazolium acetate, 1-hexyl-3-methylimidazolium acetate, tetrabutylammonium acetate, and combinations thereof. [9] The method according to any one of [1] to [8], wherein the co-solvent is a high-boiling polar solvent.

[10] The method according to [9], wherein the high-boiling polar solvent is selected from the group consisting of dimethyl sulfoxide (DMSO), sulfolane, N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), and combinations thereof.

[11] The method according to any one of [1] to

[10] , wherein in the impurity-containing liquid and / or the liquid containing an ionic liquid and a co-solvent, the content of the ionic liquid relative to the total amount of the ionic liquid and the co-solvent is 20 to 99.9 wt %.

[12] A method for producing a cellulose ester, comprising: A first step of dissolving cellulose in a first liquid containing an ionic liquid and a co-solvent to obtain a second liquid; a second step of adding an organic acid anhydride to the second liquid to react the cellulose with the organic acid anhydride to produce a cellulose ester; a third step of adding a poor solvent to the second liquid to precipitate the cellulose ester; a fourth step following the third step, in which a solid phase containing the cellulose ester is separated from a liquid phase consisting of the ionic liquid, the cosolvent, and a third liquid containing cellulose-derived impurities, and the cellulose ester is recovered from the solid phase and the third liquid is recovered from the liquid phase; a fifth step of subjecting the third liquid to an ultrafiltration membrane to separate a fourth liquid containing the ionic liquid and the co-solvent from cellulose-derived impurities, and recovering the fourth liquid; Including, The first to fifth steps can be repeated by reusing all or part of the fourth liquid as all or part of the first liquid. Manufacturing method.

[13] The method according to

[12] , further comprising, prior to the fifth step, a distillation step of distilling the third liquid to remove the poor solvent and / or the organic acid derived from the organic acid anhydride in the third liquid.

[14] The method according to

[13] , further comprising the additional step of subjecting the fourth liquid to a nanofiltration membrane or a reverse osmosis membrane after the fifth step to remove colored components produced by the distillation step.

[15] A method for producing a cellulose ester, comprising: A first step of dissolving cellulose in a first liquid containing an ionic liquid and a co-solvent to obtain a second liquid; a second step of adding an organic acid anhydride to the second liquid to react the cellulose with the organic acid anhydride to produce a cellulose ester; a third step of adding a poor solvent to the second liquid to precipitate the cellulose ester; a fourth step following the third step, in which a solid phase containing the cellulose ester is separated from a liquid phase consisting of the ionic liquid, the cosolvent, and a third liquid containing cellulose-derived impurities, and the cellulose ester is recovered from the solid phase and the third liquid is recovered from the liquid phase; a fifth step of subjecting the third liquid to an ultrafiltration membrane according to the method of any one of [1] to

[11] to separate a fourth liquid containing the ionic liquid and the co-solvent from cellulose-derived impurities, and recovering the fourth liquid; Including, The first to fifth steps can be repeated by reusing all or part of the fourth liquid as all or part of the first liquid. Manufacturing method.

[16] The method according to

[15] , further comprising, prior to the fifth step, a distillation step of distilling the third liquid to remove the poor solvent and / or the organic acid derived from the organic acid anhydride in the third liquid.

[17] The method according to

[16] , further comprising the additional step of subjecting the fourth liquid to a nanofiltration membrane or a reverse osmosis membrane after the fifth step to remove colored components produced by the distillation step. The configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible as appropriate within the scope that does not deviate from the gist of this disclosure. [Example]

[0062] The present disclosure will be explained in more detail below by showing examples, but interpretation of the present disclosure is not limited to these examples.

[0063] <Removal of cellulose-derived impurities using ultrafiltration membranes> In order to investigate the removal of cellulose-derived impurities using the ultrafiltration membrane according to the present disclosure, the NMP permeation rate and molecular weight cutoff of the ultrafiltration membrane, as well as the permeation rate of an impurity-containing liquid and the rejection rate of impurities in the solvent were measured. As the ultrafiltration membranes, hollow fiber membranes made of nylon resin (UF50, UF120 manufactured by Unitika) and hollow fiber membranes made of polyethersulfone (PES) were used.

[0064] [NMP permeation rate] The NMP permeation rate is 2 The measurement was carried out by a constant pressure cross-flow test using a hollow fiber membrane. First, NMP was passed through the hollow fiber membrane at a flow rate of 9.9 ml / min. Furthermore, the operating pressure was set to 1 bar or 4 bar using a pressure gauge installed near the inlet of the hollow fiber membrane and a pressure regulator installed near the outlet of the hollow fiber membrane. At this time, the permeation rate of the filtrate discharged from the outlet of the hollow fiber membrane was measured, and the permeation rate per unit time (h) and unit membrane area (m 2 ), NMP permeation rate per unit pressure (bar) (L / m 2 / hr / bar (LMH / bar)) was calculated.

[0065] [Molecular weight cutoff] The molecular weight cutoff of the ultrafiltration membrane is 0.012 m 2 The measurements were performed using a constant-pressure cross-flow test using a hollow fiber membrane. Specifically, PEGs with molecular weights of 3K, 8K, 12K, 35K, 100K, and 500K were mixed and dissolved in NMP at 0.1% concentration, and this solution was first passed through the hollow fiber membrane at a flow rate of 9.9 mL / min. Furthermore, the test was performed under constant pressure conditions by setting the operating pressure to 1 bar using a pressure gauge installed near the inlet of the hollow fiber membrane and a pressure regulator installed near the outlet of the hollow fiber membrane. Six hours after the start of the flow, the feed solution and filtrate were collected. The collected feed solution and filtrate were analyzed by liquid chromatography using a gel permeation chromatography (GPC) column and a differential refractive index (RI) detector. The feed solution strength (RI) was determined from the chromatogram of RI peak intensity versus molecular weight (calculated from the PEG calibration curve). feed ) and filtrate strength (I fill ) was obtained, and the rejection rate of PEG was calculated using the following mathematical formula 1. A fractionation curve of the ultrafiltration membrane was plotted, and the molecular weight at which 90% rejection rate was obtained was determined as the molecular weight cutoff. Formula 1: Inhibition rate (%) = (1-I fill / I feed ) x 100

[0066] [Permeation rate of impurity-containing liquid and rejection rate of impurities in impurity-containing liquid] The impurity-containing liquid was an EmimOAc / NMP mixed solvent (weight ratio 50:50) containing 1000 ppm to 6400 ppm of cellulose acetate with a molecular weight of 50 kD or 700 kD. The molecular weight and content of cellulose acetate were determined by gel permeation chromatography (GPC). The permeation rate of the impurity-containing liquid and the rejection rate of the impurities in the solvent are 2 The measurement was performed by a constant pressure cross-flow test using a hollow fiber membrane. Specifically, the solvent was first passed through the hollow fiber membrane at a flow rate of 9.9 ml / min. Furthermore, the test was performed under constant pressure conditions by setting the operating pressure to 1 bar or 4 bar using a pressure gauge installed near the inlet of the hollow fiber membrane and a pressure regulator installed near the outlet of the hollow fiber membrane. 24 hours after the start of the liquid passage, the flow rate of the filtrate was measured. Furthermore, the feed liquid and the filtrate were sampled. The permeation rate of the impurity-containing liquid was calculated from the measured flow rate of the filtrate. The cellulose acetate content of the collected feed solution and filtrate was quantified by sugar analysis using the phenol-sulfuric acid method. The quantification was carried out using a calibration curve prepared using the same solvent system, taking into account the influence of the solvent on the measured value. The quantified cellulose acetate content (C feed ), the content of cellulose acetate in the filtrate (C fill) based on the above, the rejection rate of impurities in the impurity-containing liquid was calculated using the following formula 2. Formula 2: Rejection rate (%)=(1-C fill / C feed ) x 100

[0067] The results of the above measurements are shown in Table 1.

[0068] [Table 1]

[0069] As shown in Table 1, the ultrafiltration membranes of Examples 1 to 6 had appropriate molecular weight cutoffs and exhibited excellent permeation rates for impurity-containing liquids and excellent rejection rates for impurities in impurity-containing liquids. On the other hand, the ultrafiltration membrane of Comparative Example 1 was not resistant to the solvent and was unable to effectively remove impurities from the impurity-containing liquid. This result shows that the ultrafiltration membrane of the present invention can effectively remove impurities from impurity-containing liquids.

[0070] [Solvent resistance of ultrafiltration membranes] The resistance of the ultrafiltration membrane to solvents was examined by using the ultrafiltration membrane of Example 1 above and immersing it in a mixed solvent of EmimOAc / NMP (weight ratio 50:50) at room temperature. The hollow fiber membranes were removed immediately after immersion and after 1, 2, and 3 months, and the strength retention was evaluated. That is, after removing the hollow fiber membranes from the mixed solvent, the mixed solvent on the surface was gently removed with filter paper, and the hollow fiber membranes in the mixed solvent-impregnated state were used as samples, and the strength and elongation in a tensile test were measured using a benchtop testing machine. The measurement conditions were a sample length of 5 cm and a crosshead speed of 10 cm / min. The elastic modulus was estimated from the breaking strength, breaking elongation, and initial slope. The results are shown in Figure 1.

[0071] As shown in Figure 1, the hollow fiber membrane showed no significant changes over the three-month period of immersion in the mixed solvent in terms of (1) the change in breaking strength over time, (2) the change in breaking elongation over time, and (3) the change in elastic modulus over time. These results indicate that the ultrafiltration membrane of the present invention is resistant to a liquid containing an ionic liquid, a co-solvent, and a cellulose ester, and therefore can effectively recover the liquid containing the ionic liquid and the co-solvent from the liquid.

[0072] <Removal of colored components using nanofiltration membranes or reverse osmosis membranes> The removal of colored components using the nanofiltration membrane or reverse osmosis membrane according to the present disclosure was investigated. As nanofiltration or reverse osmosis membranes, polyketone-support interfacially polymerized composite membranes and polysulfone-support composite membranes were used. The polyketone-support interfacially polymerized composite membrane (IP-PK membrane) used was a membrane (IP-PK membrane) in which an active layer containing polyamide, composed of either m-phenylenediamine (MPD) or trimesoyl chloride (TMC) monomers, was polymerized by a known method on the surface of a substrate flat membrane made of polyketone (manufactured by Hyosung Co., Ltd.) prepared by a non-solvent phase separation method. The polysulfone-support composite membranes used were a commercially available reverse osmosis membrane, SWC4 manufactured by Nitto Denko Corporation, and commercially available nanofiltration membranes, TriSep TS80 manufactured by Aquqsource, and NTR7250 manufactured by Nitto Denko Corporation. SWC4 and TriSep TS80 are interfacially polymerized composite membranes (IP-PS membranes) whose separation active layer contains polyamide, while NTR7250 is a membrane (VA-PS membrane) whose separation active layer contains polyvinyl alcohol and polyamide. The liquids used for nanofiltration or reverse osmosis membranes were EmimOAc / NMP mixed liquids and mimOAc / NMP / methanol mixed liquids, which were heated at 120°C for 14 hours to produce colored components. The components of these liquids are expressed as the weight ratio of EmimOAc (ILq) to NMP, or the weight ratio of EmimOAc (ILq), NMP, and methanol (Me).

[0073] [Membrane salt rejection and hydraulic conductivity] The salt rejection rate and hydraulic conductivity of nanofiltration or reverse osmosis membranes were measured using a surface area of ​​0.0008 m 2The measurements were carried out by a constant pressure cross-flow test using a flat nanofiltration membrane or reverse osmosis membrane. Specifically, a solution of 1600 ppm NaCl dissolved in pure water was passed through the nanofiltration membrane or reverse osmosis membrane at a flow rate of 9.9 ml / min. Furthermore, the test was carried out under constant pressure conditions by setting the operating pressure to 10 bar using a pressure gauge installed near the inlet of the nanofiltration membrane or reverse osmosis membrane and a pressure regulator installed near the outlet of the nanofiltration membrane or reverse osmosis membrane. One hour after the start of the liquid passage, the feed liquid and the filtrate were sampled. The NaCl concentration (C) in the feed liquid was measured using an electrical conductivity meter. feed ) and NaCl concentration in the filtrate (C fill ) was measured. The salt rejection rate is Equation 3: Salt rejection rate (%) = (1 - C fill / C feed ) x 100 [In Equation 3, C feed is the NaCl concentration in the aqueous NaCl solution supplied to the nanofiltration membrane or the reverse osmosis membrane when the aqueous NaCl solution is passed through the nanofiltration membrane or the reverse osmosis membrane, and C fill is the NaCl concentration in the aqueous NaCl solution discharged from the nanofiltration membrane or the reverse osmosis membrane when the aqueous NaCl solution is passed through the nanofiltration membrane or the reverse osmosis membrane. It was calculated by: The hydraulic conductivity was determined as the permeation rate when an aqueous NaCl solution was passed through a nanofiltration membrane or a reverse osmosis membrane. [Color removal rate] A constant pressure cross-flow test was carried out for each liquid in the same manner as above. The resulting feed liquid and filtrate were used as samples, and these were diluted 20 times with acetonitrile. The average absorbance of the feed liquid (Abs fill ) and the average absorbance of the filtrate (Abs fill ) was sought. The color removal rate is Equation 4: Stain removal rate (%) = (1 - Abs fill / Abs feed ) x 100 [In Equation 4, Abs feedis the average absorbance at 380 to 770 nm of a liquid containing an ionic liquid supplied to a nanofiltration membrane or a reverse osmosis membrane when the liquid contains an ionic liquid and is passed through the nanofiltration membrane or the reverse osmosis membrane, and Abs fill is the average absorbance in the range of 380 to 770 nm of a liquid containing an ionic liquid that is discharged from a nanofiltration membrane or a reverse osmosis membrane when the liquid contains an ionic liquid and is passed through the nanofiltration membrane or the reverse osmosis membrane.] Calculated from. As shown in Figure 2, the coloring components generated in a liquid containing an ionic liquid by a heating process such as distillation have an absorption peak in the ultraviolet region and an absorption band extending into the visible light region. Therefore, as described above, the color removal rate can be appropriately evaluated based on the average absorbance in the range of 380 to 770 nm. [Recovery rate of ionic liquid] The recovery rate of the entire ionic liquid was evaluated as follows. The liquid before and after the operation to remove the colored components was evaporated to dryness under reduced pressure (140°C, 5 hours) to remove the volatile solvent (NMP, methanol) from the liquid. The weight of the ionic liquid residue was measured before and after the operation to remove the colored components. The weight of the ionic liquid after the operation to remove the colored components was divided by the weight of the ionic liquid before the operation to remove the colored components, and multiplied by 100 to calculate the recovery rate (%).

[0074] [Removal of coloring components using activated carbon] As a comparative example for the removal of coloring components, the removal of coloring components using activated carbon was evaluated. Commercially available activated carbons, Shirasagi A, Shirasagi ANOX-1, and Carborafine, manufactured by Osaka Gas Chemicals Co., Ltd., were used as activated carbon. The decolorization test using activated carbon was carried out by adding 1.0 g of activated carbon to 50 g of liquid (bath ratio 50), stirring the mixture in a vortex mixer for 1 minute, leaving it to stand for 5 minutes, then centrifuging it (3000 rpm x 10 minutes), and filtering the supernatant through filter paper. The liquid was compared with a liquid to which activated carbon had not been added, and each parameter was determined in the same manner as described above.

[0075] A comparison of the color removal rates of nanofiltration membranes or reverse osmosis membranes with those of activated carbon is shown in Table 2.

[0076] [Table 2]

[0077] As shown in Table 2, the nanofiltration membrane or reverse osmosis membrane showed good color removal rates, while the activated carbon did not.

[0078] The parameters of the nanofiltration or reverse osmosis membranes are shown in Table 3.

[0079] [Table 3]

[0080] As shown in Table 3, the nanofiltration membranes or reverse osmosis membranes of the examples showed good color removal rates, while the nanofiltration membranes or reverse osmosis membranes of the comparative examples did not show good color removal rates.

Claims

1. A method for recovering a liquid containing an ionic liquid and a co-solvent from an impurity-containing liquid containing an ionic liquid, a co-solvent, and cellulose-derived impurities, the method comprising subjecting the impurity-containing liquid to an ultrafiltration membrane to separate the liquid containing the ionic liquid and the co-solvent from the cellulose-derived impurities.

2. 2. The method according to claim 1, wherein the molecular weight cutoff of the ultrafiltration membrane is 1,000 to 1,000,000.

3. The method of claim 1 , wherein the ultrafiltration membrane comprises a polyamide resin.

4. The method of claim 1 , wherein the cellulose-derived impurities comprise cellulose esters.

5. 2. The method of claim 1, wherein the cellulose-derived impurities have a molecular weight of 10,000 to 1,500,000.

6. 2. The method of claim 1, wherein the cellulose-derived impurities comprise cellulose esters having a degree of substitution of 2.9 or less.

7. The method according to claim 1 , wherein the ionic liquid comprises an imidazolium cation or a quaternary ammonium cation as a cation component and a carboxylate anion as an anion component.

8. 2. The method of claim 1, wherein the ionic liquid is selected from the group consisting of 1-ethyl-3-methylimidazolium acetate (EmimOAc), 1-ethyl-2,3-dimethylimidazolium acetate (EDmimOAc), 1-butyl-3-methylimidazolium acetate, 1-hexyl-3-methylimidazolium acetate, tetrabutylammonium acetate, and combinations thereof.

9. The method of claim 1 , wherein the co-solvent is a high boiling polar solvent.

10. 10. The method of claim 9, wherein the high boiling point polar solvent is selected from the group consisting of dimethyl sulfoxide (DMSO), sulfolane, N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), and combinations thereof.

11. 2. The method according to claim 1, wherein in the impurity-containing liquid and / or the liquid containing an ionic liquid and a cosolvent, the content of the ionic liquid relative to the total amount of the ionic liquid and the cosolvent is 20 to 99.9% by weight.

12. A method for producing a cellulose ester, comprising: A first step of dissolving cellulose in a first liquid containing an ionic liquid and a co-solvent to obtain a second liquid; a second step of adding an organic acid anhydride to the second liquid to react the cellulose with the organic acid anhydride to produce a cellulose ester; a third step of adding a poor solvent to the second liquid to precipitate the cellulose ester; a fourth step following the third step, in which a solid phase containing the cellulose ester is separated from a liquid phase consisting of the ionic liquid, the cosolvent, and a third liquid containing cellulose-derived impurities, and the cellulose ester is recovered from the solid phase and the third liquid is recovered from the liquid phase; a fifth step of subjecting the third liquid to an ultrafiltration membrane to separate a fourth liquid containing the ionic liquid and the co-solvent from cellulose-derived impurities, and recovering the fourth liquid; Including, The first to fifth steps can be repeated by reusing all or a part of the fourth liquid as all or a part of the first liquid. Manufacturing method.

13. The method according to claim 12, further comprising, prior to the fifth step, a distillation step of distilling the third liquid to remove the poor solvent and / or the organic acid derived from the organic acid anhydride in the third liquid.

Images