Method for producing purified ionic liquid, method for producing cellulose solution and regenerated cellulose fiber, fiber composition and organic fiber cord

Abstract

To provide means capable of manufacturing a purified ion liquid capable of preventing a decrease of a molecular weight of a cellulose when dissolving the cellulose, that is, excellent in temporal storage stability and thermal stability.SOLUTION: At least one ionic liquid selected from the group consisting of imidazolium-based ionic liquids, pyridinium-based ionic liquids, ammonium-based ionic liquids, phosphonium-based ionic liquids, and cyclic amidinium-based ionic liquids is brought into contact with an inorganic adsorbent and purified under the conditions satisfying at least two of the following (1) to (3) to manufacture purified ion liquid; (1) an amount of the inorganic adsorbent is 0.5 to 20 pts.mass with respect to 100 pts.mass of the ionic liquid; (2) a contact temperature is 25 to 120°C; (3) a contact time is 10 minutes or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a purified ionic liquid, a method for producing a cellulose solution and a regenerated cellulose fiber, a fiber composition, and an organic fiber cord. [Background technology]

[0002] Cellulose is the most abundant organic compound in nature, accounting for one-third of all plant matter. Regenerated cellulose fiber, made from cellulose, a natural, non-petroleum-based material, not only utilizes cellulose, the most abundant biomass on Earth, but also has the advantage of placing less strain on the environment when disposed of.

[0003] However, because cellulose has very poor solubility in various solvents, it can only be dissolved and regenerated by limited methods, such as industrially produced rayon fibers. Moreover, all regenerated cellulose fibers are produced using methods that use solvents that are highly toxic or explosive. Therefore, there is a need for the development of solvents that are safe, highly productive, and capable of producing regenerated cellulose fibers with good spinnability.

[0004] In recent years, it has been reported that cellulose dissolves in ionic liquids (see Patent Document 1). In addition, methods for obtaining regenerated cellulose fibers with good spinnability have been disclosed, including dissolving cellulose in an ionic liquid to which an antioxidant has been added, and dissolving cellulose in an ionic liquid to which a basic compound has been added, and then using the resulting solution to spin regenerated cellulose fibers (see Patent Document 2 and Non-Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2005-506401 [Patent Document 2] International Publication No. 2006 / 000197 [Non-patent literature]

[0006] [Non-Patent Document 1] Lenzinger Berichte, 86 (2006) 154-161 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the inventors' investigations have revealed that when cellulose is dissolved using an ionic liquid prepared using the techniques described in the prior art documents, the molecular weight of the cellulose contained in the resulting cellulose solution may decrease if the ionic liquid is used after a certain amount of time has passed since its preparation or if the cellulose is heated to a temperature above a certain level during the dissolution process. When attempting to produce regenerated cellulose fibers using cellulose with such reduced molecular weight, the spinnability and mechanical properties of the resulting regenerated cellulose fibers are reduced. On the other hand, possible solutions to prevent this molecular weight decrease include dissolving the cellulose immediately after the preparation of the ionic liquid or setting an upper limit on the heating temperature during the dissolution process. However, both of these solutions result in reduced productivity, which is disadvantageous, particularly when considering industrial production.

[0008] Therefore, an object of the present invention is to provide a means for producing a purified ionic liquid that can prevent a decrease in the molecular weight of cellulose during the above-mentioned cellulose dissolution treatment, i.e., a purified ionic liquid that has excellent storage stability and thermal stability over time. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems, and as a result, have surprisingly found that the above problems can be solved by purifying an ionic liquid capable of dissolving cellulose by bringing it into contact with an inorganic adsorbent under specific conditions, thereby completing the present invention.

[0010] That is, according to a first aspect of the present invention, there is provided a method for producing a purified ionic liquid, which comprises purifying at least one ionic liquid selected from the group consisting of imidazolium-based ionic liquids, pyridinium-based ionic liquids, ammonium-based ionic liquids, phosphonium-based ionic liquids, and cyclic amidinium-based ionic liquids by contacting the liquid with an inorganic adsorbent under conditions that satisfy at least two of the following (1) to (3): (1) The amount of the inorganic adsorbent is 0.5 to 20 parts by mass relative to 100 parts by mass of the ionic liquid; (2) The temperature during contact is 25 to 120°C; (3) The contact time is 10 minutes or more.

[0011] Furthermore, according to a second aspect of the present invention, there is provided a method for producing a cellulose solution, which comprises dissolving cellulose in the purified ionic liquid obtained by the production method according to the first aspect of the present invention described above.

[0012] Furthermore, according to a third aspect of the present invention, there is provided a method for producing regenerated cellulose fibers, which comprises carrying out solution spinning using the cellulose solution obtained by the production method according to the second aspect of the present invention described above as a spinning solution.

[0013] Furthermore, according to a fourth aspect of the present invention, there is provided a fiber composition comprising regenerated cellulose fibers obtained by the production method according to the third aspect of the present invention described above.

[0014] Furthermore, according to a fifth aspect of the present invention, there is provided an organic fiber cord comprising the fiber composition according to the fourth aspect of the present invention described above. [Effects of the Invention]

[0015] According to the present invention, it is possible to produce a purified ionic liquid that can prevent a decrease in the molecular weight of cellulose during the dissolution treatment of cellulose, that is, that has excellent storage stability and thermal stability over time. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Method of producing purified ionic liquid> One aspect of the present invention is a method for producing a purified ionic liquid, comprising purifying at least one ionic liquid selected from the group consisting of imidazolium-based ionic liquids, pyridinium-based ionic liquids, ammonium-based ionic liquids, phosphonium-based ionic liquids, and cyclic amidinium-based ionic liquids by contacting the liquid with an inorganic adsorbent under conditions that satisfy at least two of the following (1) to (3): (1) The amount of the inorganic adsorbent is 0.5 to 20 parts by mass relative to 100 parts by mass of the ionic liquid; (2) The temperature during contact is 25 to 120°C; (3) The contact time is 10 minutes or more.

[0017] (ionic liquid) In this specification, "ionic liquid" refers to an ionic compound (ionically bonded salt) that is liquid at 100°C or below (having a melting point of 100°C or below) and that is composed of a cation moiety and an anion moiety.

[0018] In the present invention, the ionic liquid used is at least one selected from the group consisting of imidazolium-based ionic liquids, pyridinium-based ionic liquids, ammonium-based ionic liquids, phosphonium-based ionic liquids, and cyclic amidinium-based ionic liquids. These ionic liquids have an imidazolium cation, a pyridinium cation, an ammonium cation, a phosphonium cation, and a cyclic amidinium cation, respectively. All of these ionic liquids are known to dissolve cellulose and can be used in the method for producing a cellulose solution described below.

[0019] Examples of imidazolium-based ionic liquids include those represented by the following chemical formula (1): Examples of pyridinium-based ionic liquids include those represented by the following chemical formula (2): Examples of ammonium-based ionic liquids include those represented by the following chemical formula (3): Examples of phosphonium-based ionic liquids include those represented by the following chemical formula (4): Examples of cyclic amidinium-based ionic liquids include those represented by the following chemical formula (5):

[0020] [ka]

[0021] In chemical formulas (1), (2), (3) and (4), R 1 ~R 19 are each independently a hydrogen atom, a substituted or unsubstituted linear or branched alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted linear or branched alkenyl group having 2 to 30 carbon atoms, a substituted or unsubstituted linear or branched alkynyl group having 2 to 30 carbon atoms, or a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms. 20 is a substituted or unsubstituted linear alkylene group having 1 to 3 carbon atoms. - are each independently a halogen ion, a phosphate ion, an alkyl phosphate ion, a hydroxide ion, a nitrate ion, a sulfate ion, a bisulfate ion, a sulfonate ion, a tosylate ion, a perchlorate ion, an aluminate ion, a dialuminate ion, a borate ion, an amide ion, a dicyanamide ion, a succinate ion, a thiocyanate ion, or a carboxylate ion.

[0022] Here, examples of the linear or branched alkyl group having 1 to 30 carbon atoms in the chemical formulae (1), (2), (3), and (4) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a tert-pentyl group, a neopentyl group, a 1,2-dimethylpropyl group, an n-hexyl group, an isohexyl group, a 1,3-dimethylbutyl group, a 1-isopropylpropyl group, a 1,2-dimethylbutyl group, an n-heptyl group, a 1,4-dimethylpentyl group, a 3-ethylpentyl group, a 2-methyl-1 Examples of groups include 1-isopropylpropyl group, 1-ethyl-3-methylbutyl group, n-octyl group, 2-ethylhexyl group, 3-methyl-1-isopropylbutyl group, 2-methyl-1-isopropyl group, 1-tert-butyl-2-methylpropyl group, n-nonyl group, 3,5,5-trimethylhexyl group, n-decyl group, isodecyl group, n-undecyl group, 1-methyldecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-eicosyl group, and n-triacontanyl group.

[0023] Examples of linear or branched alkenyl groups having 2 to 30 carbon atoms include vinyl, allyl, 2-butenyl, 3-pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl, nonadecenyl, eicosenyl, and triacontenyl groups.

[0024] Examples of the linear or branched alkynyl group having 2 to 30 carbon atoms include a 2-butynyl group, a 3-pentynyl group, and a hexynyl group.

[0025] Examples of cycloalkyl groups having 3 to 6 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, heptynyl, octynyl, nonynyl, decynyl, undecynyl, dodecynyl, tridecynyl, tetradecynyl, pentadecynyl, hexadecynyl, heptadecynyl, octadecynyl, nonadecynyl, eicosynyl, and triacontinyl groups.

[0026] Furthermore, examples of the linear alkylene group having 1 to 3 carbon atoms in chemical formula (5) include a methylene group, an ethylene group, and a trimethylene group.

[0027] Furthermore, when the above-mentioned alkyl group, alkenyl group, alkynyl group, cycloalkyl group or alkylene group is substituted, examples of the substituent substituting these groups include halogen atoms such as fluorine, chlorine, bromine and iodine, aryl groups such as phenyl group, p-tolyl group, xylyl group, cumenyl group, naphthyl group, anthryl group and phenanthryl group, alkoxy groups such as methoxy group, ethoxy group and tert-butoxy group, aryloxy groups such as phenoxy group and p-tolyloxy group, alkoxycarbonyl groups such as methoxycarbonyl group, butoxycarbonyl group, 2-ethylhexyloxycarbonyl group and phenoxycarbonyl group, acyloxy groups such as acetoxy group, propionyloxy group and benzoyloxy group, acetyl group, benzoyl group and isobutyryl group. Examples of suitable groups include acyl groups such as acryloyl, methacryloyl, and methoxalyl groups, alkylsulfanyl groups such as methylsulfanyl and tert-butylsulfanyl groups, arylsulfanyl groups such as phenylsulfanyl and p-tolylsulfanyl groups, alkylamino groups such as methylamino and cyclohexylamino groups, dialkylamino groups such as dimethylamino, diethylamino, morpholino, and piperidino groups, and arylamino groups such as phenylamino and p-tolylamino groups, as well as hydroxyl, carboxyl, formyl, mercapto, sulfo, mesyl, p-toluenesulfonyl, amino, nitro, cyano, trifluoromethyl, trichloromethyl, trimethylsilyl, phosphinico, and phosphono groups. Note that optional substituents may not be the same as the groups they replace. For example, alkyl groups are not substituted with alkyl groups.

[0028] In addition, in the chemical formulas (1), (2), (3), (4) and (5), X -represents an anion moiety, and each independently represents a halogen ion (fluoride ion, chloride ion, bromide ion, iodide ion (preferably chloride ion)), phosphate ion, alkyl phosphate ion (e.g., dimethyl phosphate ion, diethyl phosphate ion, etc.), hydroxide ion, nitrate ion, sulfate ion, bisulfate ion, sulfonate ion, tosylate ion, perchlorate ion, aluminate ion, dialuminate ion, borate ion, amide ion, dicyanamide ion, succinate ion, thiocyanate ion, or carboxylate ion (e.g., acetate ion, trifluoroacetate ion, etc.).

[0029] Specific examples of the cation moiety (imidazolium ion) of the imidazolium-based ionic liquid represented by chemical formula (1) include, for example, imidazolium ion, N-isobutylimidazolium ion, 2-methylimidazolium ion, 2-ethylimidazolium ion, 2-n-propylimidazolium ion, 2-isopropylimidazolium ion, 2-n-butylimidazolium ion, 4-methylimidazolium ion, 4-ethylimidazolium ion, 4,5-dimethylimidazolium ion, 1-butyl-3-methylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-isobutyl-2-methylimidazolium ion, 1-isobutyl-2,3-dimethylimidazolium ion, and 2,4,5-trimethylimidazolium ion. From the viewpoint of availability, 1-butyl-3-methylimidazolium, 1-isobutyl-2-methylimidazolium ion, and 1-isobutyl-2,3-methylimidazolium ion are preferred, and from the viewpoint of solubility in cellulose, 1-butyl-3-methylimidazolium ion or 1-ethyl-3-methylimidazolium ion is particularly preferred.

[0030] Specific examples of the cation moiety (pyridinium ion) of the pyridinium-based ionic liquid represented by chemical formula (2) include, for example, a pyridinium ion, a 1-n-butyl-3-methylpyridinium ion, a 2-isobutylpyridinium ion, a 3-isobutylpyridinium ion, a 3-methylpyridinium ion, a 4-methylpyridinium ion, a 2-ethylpyridinium ion, a 3-ethylpyridinium ion, a 4-ethylpyridinium ion, a 4-propylpyridinium ion, a 2-n-hexylpyridinium ion, a 3-n-hexylpyridinium ion, a 3,5-dimethylpyridinium ion, a 3,5-diethylpyridinium ion, a 2,6-di-tert-butylpyridinium ion, and a 2-vinylpyridinium ion. Examples of suitable cations include 1-n-butyl-3-methylpyridinium ion, 2-methyl-5-ethylpyridinium ion, 4-methylpyridinium ion, 2-methyl-5-vinylpyridinium ion, 2-methyl-3-ethylpyridinium ion, 2-methyl-5-(iso)propylpyridinium ion, and 2,6-bis(hydroxymethyl)pyridinium ion. Among these, 1-n-butyl-3-methylpyridinium ion is particularly preferred from the viewpoint of solubility in cellulose.

[0031] Specific examples of the cation portion (ammonium ion) of the ammonium-based ionic liquid represented by chemical formula (3) include, for example, dimethylammonium ion, trimethylammonium ion, tetramethylammonium ion, diethylammonium ion, triethylammonium ion, tetraethylammonium ion, monopropylammonium ion, dipropylammonium ion, tripropylammonium ion, tetrapropylammonium ion, monobutylammonium ion, dibutylammonium ion, tributylammonium ion, tetrabutylammonium ion, monopentylammonium ion, dipentylammonium ion, tripentylammonium ion, tetrapentylammonium ion, monohexylammonium ion, dihexylammonium ion, methyl(ethyl)ammonium ion, methyl(propyl)ammonium ion, methyl(butyl)ammonium ion, methyl(pentyl)ammonium ion, methyl(hexyl)ammonium ion, ethyl(propyl)ammonium ion, ethyl(butyl)ammonium ion, ethyl(pent ... (butyl)ammonium ion, ethyl(hexyl)ammonium ion, dimethyl(ethyl)ammonium ion, dimethyl(propyl)ammonium ion, dimethyl(butyl)ammonium ion, trimethyl(ethyl)ammonium ion, trimethyl(propyl)ammonium ion, trimethyl(butyl)ammonium ion, trimethyl(pentyl)ammonium ion, trimethyl(hexyl)ammonium ion, monovinylammonium ion, divinylammonium ion, trivinylammonium ion, monopropenylammonium ion, dipropenylammonium ion, tripropenylammonium ion, monobutenylammonium ion, dibutenylammonium ion, tributenylammonium ion, monopentenylammonium ion, dipentenylammonium ion, tripentenylammonium ion, monohexenylammonium ion, dihexenylammonium ion, dimethyl(vinyl)ammonium ion, dimethyl(propenyl)ammonium ion, dimethyl(butenyl)ammonium ion, dimethyl(pentenyl)ammonium ion,Dimethyl(hexenyl)ammonium ion, bis(2-methoxyethyl)monoethylammonium ion, trimethyl(vinyl)ammonium ion, bis(2-methoxyethyl)monomethylammonium ion, monocyclopentylammonium ion, dicyclopentylammonium ion, tricyclopentylammonium ion, monocyclohexylammonium ion, dicyclohexylammonium ion, dimethyl(cyclopentyl)ammonium ion, dimethyl(cyclohexyl)ammonium ion, (methylcyclopentyl)ammonium ion, bis(methylcyclopentyl)ammonium ion, (dimethylcyclopentyl)ammonium ion, bis(dimethylcyclopentyl)ammonium ion, (ethylcyclopentyl)ammonium ion, bis(ethylcyclopentyl)ammonium ion, (methylethylcyclopentyl)ammonium ion, bis(methylethylcyclopentyl)ammonium ion, (diethylcyclopentyl)ammonium ion, (methylcyclohexyl)ammonium ion, bis(methylcyclohexyl)ammonium ion, (dimethyl (methylethylcyclohexyl)ammonium ion, bis(dimethylcyclohexyl)ammonium ion, (ethylcyclohexyl)ammonium ion, bis(ethylcyclohexyl)ammonium ion, (methylethylcyclohexyl)ammonium ion, (diethylcyclohexyl)ammonium ion, monomethanolammonium ion, dimethanolammonium ion, trimethanolammonium ion, monoethanolammonium ion, diethanolammonium ion, triethanolammonium ion, mono(n-propanol)ammonium ion, di(n-propanol)ammonium ion, tri(n-propanol)ammonium ion, monoisopropanolammonium ion, diisopropanolammonium ion, triisopropanolammonium ion, monobutanolammonium ion, dibutanolammonium ion, tributanolammonium ion, monopentanolammonium ion, dipentanolammonium ion, tripentanolammonium ion, monohexanolammonium ion, dihexanolammonium ion,Monomethyl monoethanol ammonium ion, monoethyl monoethanol ammonium ion, monoethyl monopropanol ammonium ion, monoethyl monobutanol ammonium ion, monoethyl monopentanol ammonium ion, monopropyl monoethanol ammonium ion, monopropyl monopropanol ammonium ion, monopropyl monobutanol ammonium ion, monopropyl monopentanol ammonium ion, monobutyl monoethanol ammonium ion, monobutyl monopropanol ammonium ion, monobutyl monobutanol ammonium ion, monobutyl monopentanol ammonium ion, dimethyl monoethanol ammonium ion, diethyl monoethanol ammonium ion, diethyl monopropanol ammonium ion, diethyl monobutanol ammonium ion, diethyl monopentanol ammonium ion, dipropyl monoethanol ammonium ion, dipropyl monopropanol ammonium ion, dipropyl monobutanol ammonium ion, dipropyl monopentanol ammonium ion, dibutyl monoethanol ammonium ion, dibutyl monopropanol ammonium ion, dibutyl monobutanol ammonium ion, dibutyl monopentanol ammonium ion, monomethyl diethanol ammonium ion, monomethyl dipropanol ammonium ion, monomethyl dibutanol ammonium ion, monomethyl dipentanol ammonium ion, monoethyl diethanol ammonium ion, monoethyl dipropanol ammonium ion, monoethyl dibutanol ammonium ion, monoethyl dipentanol ammonium ion, monopropyl diethanol ammonium ion, monopropyl dipropanol ammonium ion, monopropyl dibutanol ammonium ion, monopropyl dipentanol ammonium ion, monobutyl diethanol ammonium ion, monobutyl dipropanol ammonium ion, monobutyl dibutanol ammonium ion, monobutyl dipentanol ammonium ion, monocyclohexyl monoethanol ammonium ion, monocyclohexyl diethanol ammonium ion,Examples of the ammonium ion include monocyclohexylmonopropanolammonium ion, monocyclohexyldipropanolammonium ion, mono(β-aminoethyl)monoethanolammonium ion, monotert-butylmonoethanolammonium ion, monotert-butyldiethanolammonium ion, mono(β-aminoethyl)isopropanolammonium ion, diethylmonoisopropanolammonium ion, trimethylmonoethanolammonium ion (choline ion), triethylmonoethanolammonium ion, triethylmonopropanolammonium ion, triethylmonobutanolammonium ion, triethylmonopentanolammonium ion, tripropylmonoethanolammonium ion, tripropylmonopropanolammonium ion, tripropylmonobutanolammonium ion, tripropylmonopentanolammonium ion, diethylmonomethylethanolammonium ion, bis(2-methoxyethyl)monoethylmonomethylammonium ion, monoethylmonomethyldiethanolammonium ion, and diethylmonomethylmonoethanolammonium ion. Among these, trimethylmonoethanolammonium ion (choline ion) is particularly preferred from the viewpoint of solubility in cellulose.

[0032] Specific examples of the cation moiety (phosphonium ion) of the phosphonium-based ionic liquid represented by chemical formula (4) include, for example, tetramethylphosphonium ion, ethyltrimethylphosphonium ion, diethyldimethylphosphonium ion, triethylmethylphosphonium ion, methyltripropylphosphonium ion, tributylmethylphosphonium ion, tetraethylphosphonium ion, trimethylpropylphosphonium ion, diallyldimethylphosphonium ion, tetra-n-propylphosphonium ion, and tetra-n-butylphosphonium ion. Among these, the tetra-n-butylphosphonium ion is particularly preferred from the viewpoint of solubility in cellulose.

[0033] Specific examples of the cation moiety (cyclic amidinium ion) of the cyclic amidinium ionic liquid represented by chemical formula (5) include, for example, a diazabicycloundecenium ion (a quaternary ammonium cation in which the nitrogen atom at position 1 of 1,8-diazabicyclo[5.4.0]undec-7-ene is protonated) and a diazabicyclononenium ion (a quaternary ammonium cation in which the nitrogen atom at position 1 of 1,5-diazabicyclo[4.3.0]non-5-ene is protonated).

[0034] In a preferred embodiment of the present invention, the ionic liquid is at least one selected from the group consisting of 1-butyl-3-methylimidazolium chloride (BmimCl), 1-ethyl-3-methylimidazolium acetate (EmimAc), 1-ethyl-3-methylimidazolium diethylphosphate (EmimDEP), 1-butyl-3-methylpyridinium chloride, choline acetate, and tetrabutylphosphonium chloride. In a more preferred embodiment of the present invention, the ionic liquid is 1-butyl-3-methylimidazolium chloride (BmimCl). These ionic liquids are particularly preferred from the viewpoint of cellulose solubility.

[0035] (inorganic adsorbent) In the method for producing a purified ionic liquid according to the present invention, the ionic liquid is purified by contacting it with an inorganic adsorbent. In this specification, the term "adsorbent" broadly refers to a substance that can adsorb components (impurities) other than the constituent components (i.e., cation moieties and anion moieties) of the ionic liquid contained in the ionic liquid to be purified by contact with the adsorbent, and can then remove the impurities from the ionic liquid by a subsequent separation operation.

[0036] Here, the inorganic adsorbent is an inorganic substance having the property of adsorbing metals. Specific examples of the inorganic adsorbent include, for example, hydrotalcite, aluminum silicate, activated carbon, activated alumina, zeolite, layered clay minerals, magnesium oxide, alumina, silica, lime, and the like. Here, the "hydrotalcite" in this specification refers to hydrotalcite compounds represented by the general formula: [(M 1 ) y-x (M 2 ) x (OH) 2y (A) x / k ·zH2O]. In the formula, M 1 represents a divalent metal ion, and M 2 represents a trivalent metal ion. A represents an interlayer anion, and k represents the valence of A. x, y, and z are natural numbers respectively, satisfying the conditions of x < y and 0 ≤ z < y. Examples of the divalent metal ions represented by M 1 include, for example, one selected from the group consisting of Mg, Fe, Zn, Ca, Li, Ni, Co, and Cu, or a plurality of divalent metal ions selected at any ratio. Examples of the trivalent metal ions represented by M 2 include, for example, one selected from the group consisting of Al, Fe, and Mn, or a plurality of trivalent metal ions selected at any ratio. Examples of the interlayer anions represented by A include, for example, one selected from the group consisting of carbonate ions, sulfate ions, fluoride ions, chloride ions, bromide ions, iodide ions, hydroxide ions, and acetate ions, or a plurality of anions selected at any ratio.

[0037] Examples of such inorganic adsorbents include, for example, Kyoward (registered trademark) 500 (hydrotalcite; Mg6Al2(OH) 16 CO3·mH2O), Kyoward (registered trademark) 1000 (hydrotalcite; Mg 4.5 Al2(OH) 13CO3·3.5H2O) and Kyoward® 700 (aluminum silicate; Al2O3·9SiO2·mH2O) (both manufactured by Kyowa Chemical Industry Co., Ltd.), and STABIACE® HT-6 (hydrotalcite; Mg6Al2(OH) 16 CO3·mH2O), STABIACE® HT-P(NC) (hydrotalcite; Mg 4.5 Al2(OH) 13 CO3·3.5H2O), STABIACE® HT-1 (NC) (hydrotalcite; Mg4Al2(OH) 12 CO3·3H2O), STABIACE® HT-7 (NC) (hydrotalcite; Mg 3.5 Zn 0.5 Al2(OH) 12 CO3·3H2O) (both manufactured by Sakai Chemical Industry Co., Ltd.), MA-OH (Mg4Al2(OH) 12 A mH2O (where A represents an anion other than CO3 (e.g., nitrate, chloride, or sulfate))) and MF-500 (Mg4Fe2(OH) 12 CO3·mH2O) (both manufactured by Kyoeisha Chemical Co., Ltd.).

[0038] According to one embodiment, the inorganic adsorbent preferably contains hydrotalcite, and more preferably is hydrotalcite. By contacting the ionic liquid with hydrotalcite under specific conditions, it is possible to further prevent the molecular weight of cellulose from decreasing during the dissolution treatment of cellulose. This is thought to be because hydrotalcite can remove a greater variety and / or amount of impurities during the purification treatment under specific conditions.

[0039] Among hydrotalcites, Kyoward (registered trademark) 500 (Mg6Al2(OH) 16 CO3 mH2O), STABIACE(R) HT-6(Mg6Al2(OH) 16 CO3 mH2O), STABIACE (registered trademark) HT-P (NC) (Mg 4.5 Al2(OH) 13CO3·3.5H2O), STABIACE(R) HT-1(NC)(Mg4Al2(OH) 12 CO3·3H2O), STABIACE (registered trademark) HT-7 (NC) (Mg 3.5 Zn 0.5 Al2(OH) 12 CO3·3H2O), MA-OH(Mg4Al2(OH) 12 A mH2O (where A represents an anion other than CO3 (e.g., nitrate ion, chloride ion, sulfate ion) manufactured by Kyoeisha Chemical Co., Ltd.) and MF-500 (Mg4Fe2(OH) 12 CO₃·mH₂O, manufactured by Kyoeisha Chemical Co., Ltd.) is preferred, and Kyoward (registered trademark) 500 (Mg₆Al₂(OH) 16 CO3 mH2O), STABIACE(R) HT-6(Mg6Al2(OH) 16 CO3 mH2O), STABIACE (registered trademark) HT-P (NC) (Mg 4.5 Al2(OH) 13 CO3·3.5H2O), MA-OH(Mg4Al2(OH) 12 A mH2O (where A represents an anion other than CO3 (e.g., nitrate ion, chloride ion, sulfate ion) manufactured by Kyoeisha Chemical Co., Ltd.) and MF-500 (Mg4Fe2(OH) 12 CO₃·mH₂O, manufactured by Kyoeisha Chemical Co., Ltd.) is more preferred, and Kyoward (registered trademark) 500 (Mg₆Al₂(OH) 16 CO3 mH2O), STABIACE(R) HT-6(Mg6Al2(OH) 16 CO₃·mH₂O) and STABIACE® HT-P(NC) (Mg 4.5 Al2(OH) 13 CO3·3.5H2O) is even more preferred. By bringing an ionic liquid into contact with these hydrotalcites under specific conditions, the effect of the present invention, that is, preventing a decrease in the molecular weight of cellulose during the dissolution treatment of cellulose, is significantly achieved.

[0040] According to this embodiment, when the inorganic adsorbent is hydrotalcite, M contained in the hydrotalcite 2 M for 2O31 Molar ratio of O (M 1 O / M 2 2O3, M 1 represents a divalent metal ion, and M 2 represents a trivalent ion of a metal) is preferably 3.0 or more, more preferably 3.5 or more and 6.0 or less, even more preferably 4.0 or more and 6.0 or less, and particularly preferably 4.5 or more and 6.0 or less. M 1 O / M 2 By bringing hydrotalcite having a molar ratio of 2O3 within the above preferred range into contact with an ionic liquid, the effect of the present invention of preventing a decrease in the molecular weight of cellulose during the dissolution treatment of cellulose is significantly achieved.

[0041] In addition, the method for producing a purified ionic liquid of this embodiment may further include purifying the ionic liquid by contacting it with an adsorbent other than the inorganic adsorbent (e.g., an ion exchange material), so long as it includes purifying the ionic liquid by contacting it with an inorganic adsorbent under specific conditions. However, from the viewpoint of reducing production costs and simplifying the production process, it is preferable that the production method of this embodiment does not include purifying the ionic liquid by contacting it with another adsorbent.

[0042] A method for producing a purified ionic liquid according to one embodiment of the present invention is characterized in that the ionic liquid is purified by contacting the ionic liquid with an inorganic adsorbent under conditions that satisfy at least two of the following conditions (1) to (3): (1) The amount of the inorganic adsorbent is 0.5 to 20 parts by mass per 100 parts by mass of the ionic liquid (hereinafter also referred to as "condition (1)"); (2) The temperature during contact is 25 to 120°C (hereinafter also referred to as "condition (2)"); (3) The contact time is 10 minutes or longer (hereinafter also referred to as "condition (3)").

[0043] In this specification, the "treatment of bringing an ionic liquid into contact with an inorganic adsorbent" is also simply referred to as "inorganic adsorbent treatment."

[0044] In the present invention, it is essential to perform the inorganic adsorbent treatment under conditions that satisfy at least two of the above conditions (1) to (3). However, performing the inorganic adsorbent treatment under conditions that satisfy all three of the above conditions (1) to (3) is preferable because the effects of the present invention are more pronounced. On the other hand, if the inorganic adsorbent treatment is performed under conditions that satisfy only one of the conditions (1) to (3), it may not be possible to sufficiently prevent the molecular weight of cellulose from decreasing during the cellulose dissolution treatment. Each condition will be explained in more detail.

[0045] Condition (1) relates to the amount of inorganic adsorbent used when contacting the ionic liquid with the inorganic adsorbent. The amount of inorganic adsorbent is 0.5 to 20 parts by mass, preferably 1 to 15 parts by mass, more preferably 2 to 10 parts by mass, and even more preferably 2 to 5% by mass, per 100 parts by mass of the ionic liquid. By keeping the amount of inorganic adsorbent within the above preferred range, it is possible to further suppress the decrease in molecular weight of cellulose during the cellulose dissolution treatment. Note that when two or more inorganic adsorbents are used in the form of a mixture, the amount of the inorganic adsorbent refers to the total amount of each inorganic adsorbent.

[0046] Condition (2) relates to the temperature at which the ionic liquid is brought into contact with the inorganic adsorbent (hereinafter also referred to as the "contact temperature"). The contact temperature is 25 to 120°C, preferably 25 to 100°C, more preferably 30 to 90°C, and even more preferably 40 to 80°C. By setting the contact temperature within the above preferred range, it is possible to further suppress the decrease in the molecular weight of cellulose during the cellulose dissolution treatment. In this specification, the contact temperature refers to the temperature of the mixture containing the ionic liquid and the inorganic adsorbent during the inorganic adsorbent treatment.

[0047] Condition (3) relates to the time for which the ionic liquid is brought into contact with the inorganic adsorbent (hereinafter also referred to as "contact time"). The contact time is 10 minutes or more, preferably 20 minutes to 10 hours, and more preferably 0.5 to 3 hours. By keeping the contact time within the above preferred range, it is possible to further suppress the decrease in the molecular weight of cellulose during the cellulose dissolution treatment. In this specification, the contact time refers to the time from the time when the ionic liquid is brought into contact with the inorganic adsorbent (i.e., when the inorganic adsorbent is added to the ionic liquid) to the time when the ionic liquid and the inorganic adsorbent are separated (for example, when the inorganic adsorbent is removed by filtration).

[0048] According to the method for producing a purified ionic liquid of this embodiment, by treating the ionic liquid under specific conditions using the inorganic adsorbent described above, it is possible to prevent the molecular weight of cellulose from decreasing during the cellulose dissolution treatment. In other words, it is possible to produce a purified ionic liquid that has excellent storage stability and thermal stability over time. The mechanism by which the configuration of this embodiment achieves the effects described above is not completely clear, but the following mechanism is presumed. That is, by treating the ionic liquid under specific conditions using an inorganic adsorbent, any impurities contained in the ionic liquid before treatment (such as salts other than the ionic liquid or acids or alkalis used in the production of the ionic liquid) and their decomposition products (such as free acids newly generated by dissociation of salts other than the ionic liquid) are adsorbed by the inorganic adsorbent. Then, the inorganic adsorbent that has adsorbed these impurities (decomposition products) is removed from the ionic liquid by a separation operation from the ionic liquid. In this way, components that would cause a decrease in the molecular weight of cellulose during cellulose dissolution treatment are removed by contact with the inorganic adsorbent, and as a result, it is thought that even if the ionic liquid is stored for a long period of time and then subjected to cellulose dissolution treatment, or if the cellulose is heated to a relatively high temperature during the cellulose dissolution treatment, a decrease in the molecular weight of cellulose contained in the resulting cellulose solution is prevented. However, this mechanism is merely based on speculation, and whether it is correct or incorrect does not affect the technical scope of the present invention.

[0049] In the method for producing a purified ionic liquid according to the present embodiment, the inorganic adsorbent treatment may be carried out in the form of a mixture consisting of only the ionic liquid and the inorganic adsorbent. However, from the viewpoint of facilitating the operation of the inorganic adsorbent treatment, the inorganic adsorbent treatment may be carried out in the presence of an appropriate amount of a solvent (e.g., water).

[0050] In the method for producing a purified ionic liquid according to this embodiment, an adsorbent other than the inorganic adsorbent (an organic adsorbent (e.g., an ion exchange resin)) may be used in combination. However, from the viewpoint of more effectively exerting the effects of the present invention, it is preferable not to include an adsorbent treatment using another adsorbent. For example, if an adsorbent treatment is performed using an ion exchange resin, ions originally present in the ion exchange resin may be discharged into the system. This is because these discharged ions may cause the ionic liquid or cellulose to decompose.

[0051] <Uses of purified ionic liquid> As described above, the purified ionic liquid produced by the production method according to one embodiment of the present invention has excellent storage stability and thermal stability over time, thereby preventing a decrease in the molecular weight of cellulose during the dissolution treatment of cellulose. Therefore, the purified ionic liquid is suitable for use as a solvent during the dissolution treatment of cellulose. A cellulose solution is obtained by such a cellulose dissolution treatment. Regenerated cellulose fibers are then produced by solution spinning using this cellulose solution as a spinning solution. The regenerated cellulose fibers produced in this manner can be used for organic fiber cords such as tire cords. Therefore, according to a second embodiment of the present invention, there is provided a method for producing a cellulose solution, which includes dissolving cellulose in the purified ionic liquid obtained by the production method according to the first embodiment of the present invention. Furthermore, according to a third embodiment of the present invention, there is provided a method for producing a regenerated cellulose fiber, which includes solution spinning using the cellulose solution obtained by the production method according to the second embodiment of the present invention as a spinning solution. Furthermore, according to a fourth embodiment of the present invention, there is provided a fiber composition comprising the regenerated cellulose fiber obtained by the production method according to the third embodiment of the present invention. Furthermore, according to a fifth embodiment of the present invention, there is provided an organic fiber cord comprising the fiber composition according to the fourth embodiment of the present invention. These forms will be described below.

[0052] <Method of manufacturing cellulose solution> According to a second aspect of the present invention, there is provided a method for producing a cellulose solution, which comprises dissolving cellulose in the purified ionic liquid obtained by the production method according to the first aspect of the present invention described above.

[0053] In the method for producing a cellulose solution according to the present embodiment, the cellulose used as a raw material is a natural polymer that is the main component of plant cell walls. The type of cellulose is not particularly limited, but examples include natural celluloses such as cotton, cotton linter, hemp, bamboo, abaca, and bacterial cellulose, as well as wood pulp, non-wood pulp, and paper refined from these. Regenerated celluloses such as rayon, cupra, and lyocell, as well as paper and clothing made from these materials, may also be reused. A high cellulose content in the cellulose used as a raw material reduces impurities such as oils and fats, lignin, and hemicellulose, which does not impair processability, solubility, or spinnability during grinding. Furthermore, the average degree of polymerization of the cellulose used as a raw material is preferably 500 or higher, and preferably 5000 or lower due to solubility. Within this range, the spun regenerated cellulose fibers have a tensile strength and elastic modulus suitable for processing.

[0054] In this embodiment, the method for dissolving cellulose in the purified ionic liquid is not particularly limited, and for example, a cellulose solution can be produced by contacting the purified ionic liquid with cellulose and, if necessary, heating or stirring. In some cases, the cellulose solution may also be produced by contacting a liquid containing the purified ionic liquid with cellulose and, if necessary, heating or stirring.

[0055] When a liquid containing a purified ionic liquid is used, a specific example of a liquid component other than the purified ionic liquid is an organic solvent. The organic solvent is not particularly limited as long as it is other than the purified ionic liquid, and can be appropriately selected taking into consideration compatibility with the purified ionic liquid, viscosity, etc. Among these, the organic solvent is preferably at least one selected from the group consisting of amide solvents, sulfoxide solvents, nitrile solvents, ether solvents, aromatic amine solvents, and ketone solvents.

[0056] Examples of amide solvents include N,N-dimethylformamide, N,N-dimethylacetamide, 1-methyl-2-pyrrolidone, and 1-vinyl-2-pyrrolidone. Examples of sulfoxide solvents include dimethyl sulfoxide and hexamethylene sulfoxide. Examples of nitrile solvents include acetonitrile, propionitrile, and benzonitrile. Examples of ether solvents include 1,3-dioxolane, tetrahydrofuran, tetrahydropyran, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, and ethyl acetate. Examples of aromatic amine solvents include pyridine. Examples of ketone solvents include acetone and methyl ethyl ketone.

[0057] When using these organic solvents, the blending ratio of the purified ionic liquid to the organic solvent is preferably 6:1 to 0.1:1, more preferably 5:1 to 0.2:1, and even more preferably 4:1 to 0.5:1. By using the organic solvent in this range, it is possible to obtain a solvent that easily swells the cellulose raw material. The amount of the organic solvent used is not particularly limited, but is preferably 100 to 3,000 parts by mass, more preferably 100 to 2,500 parts by mass, and more preferably 150 to 1,000 parts by mass per 100 parts by mass of cellulose. By using the organic solvent in this range, it is possible to obtain a cellulose solution with an appropriate viscosity. The use of such an organic solvent in combination with the purified ionic liquid is preferable because it further improves the solubility of the cellulose raw material. However, from the perspective of recovery and reuse of the ionic liquid, it is also preferable to treat cellulose using only the purified ionic liquid, rather than a liquid containing the purified ionic liquid.

[0058] There are no particular limitations on the method for contacting the purified ionic liquid (or a liquid containing the same) with cellulose. For example, the cellulose may be added to the purified ionic liquid (or a liquid containing the same), or the purified ionic liquid (or a liquid containing the same) may be added to the cellulose.

[0059] When heating is performed during dissolution, the heating temperature is preferably 30 to 200°C, and more preferably 70 to 180°C. Heating is preferred because it further improves the solubility of cellulose. The stirring method is also not particularly limited. For example, the purified ionic liquid (or a liquid containing the same) and cellulose may be mechanically stirred in a dissolution tank, sealed mixer, or extruder using a stirring blade, stirring rod, rotor, screw, or the like. Alternatively, the purified ionic liquid (or a liquid containing the same) and the cellulose raw material may be sealed in a sealed container and dissolved using microwaves. The stirring time is not particularly limited, and it is preferable to continue stirring until the cellulose is suitably dissolved.

[0060] Furthermore, when the liquid containing the purified ionic liquid contains an organic solvent in addition to the purified ionic liquid, the organic solvent and the purified ionic liquid may be mixed in advance, or the purified ionic liquid and cellulose may be mixed and then the organic solvent added to dissolve them, or the organic solvent and cellulose may be mixed and then the purified ionic liquid added to dissolve them.

[0061] The cellulose solution prepared using an ionic liquid as described above may contain, as necessary, fillers such as cellulose microcrystals and modified cellulose microcrystals, carbon nanotubes, clay, and silica, as well as additives such as surfactants, antioxidants, dispersants, viscosity modifiers, surface modifiers, plasticizers, pH adjusters, UV stabilizers, color inhibitors, matting agents, deodorizers, and flame retardants.

[0062] The cellulose solution obtained using the purified ionic liquid as described above may be subjected to filtration and degassing treatment as necessary, preferably while heating the cellulose solution to 30 to 180°C in order to reduce the viscosity of the solution.

[0063] <Method of manufacturing regenerated cellulose fiber> According to a third aspect of the present invention, there is provided a method for producing regenerated cellulose fibers, which comprises carrying out solution spinning using the cellulose solution obtained by the production method according to the second aspect of the present invention described above as a spinning solution.

[0064] In the method for producing regenerated cellulose fibers according to this embodiment, the cellulose solution obtained as described above is contacted with a coagulation liquid other than the cellulose solution to coagulate the cellulose, and regenerated cellulose fibers can be spun by known spinning methods such as dry-wet spinning and wet spinning. Here, dry-wet spinning generally refers to a method in which the cellulose solution, once discharged into the atmosphere from a spinneret, is introduced into a coagulation tank containing the coagulation liquid to spin the cellulose. Meanwhile, wet spinning refers to a method in which the cellulose discharged from a spinneret placed in a coagulation tank is spun. The coagulation tank refers to a bath containing the coagulation liquid for coagulating the cellulose. The coagulation liquid may be water or a polar solvent, either alone or in combination, and may further contain the ionic liquid described in the first embodiment of the present invention, if necessary. The ionic liquid may be treated with an adsorbent or may not be treated with an adsorbent.

[0065] Examples of polar solvents include tetrahydrofuran, acetone, acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, acetic acid, formic acid, 1-heptanol, 1-butanol, 2-propanol, 1-propanol, ethanol, and methanol.

[0066] The ionic liquid can be recovered and recycled from the coagulation liquid in the coagulation tank after spinning by known separation methods such as distillation, membrane separation, etc. Specific distillation methods include thin film distillation, reduced pressure distillation, atmospheric distillation, and molecular distillation. Specific membrane separation methods include ultrafiltration and reverse osmosis.

[0067] <Fiber composition and organic fiber cord> According to a fourth aspect of the present invention, there is provided a fiber composition comprising regenerated cellulose fibers obtained by the production method according to the third aspect of the present invention. Also, according to a fifth aspect of the present invention, there is provided an organic fiber cord comprising the fiber composition according to the fourth aspect of the present invention.

[0068] The fiber composition of this embodiment contains regenerated cellulose fibers obtained by the manufacturing method of the third embodiment of the present invention. The fiber composition may contain only the regenerated cellulose fibers, or may further contain other fibers. Examples of other fibers include organic fibers. As the constituent material of the organic fiber, for example, one or more selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, nylon 6, nylon 66, nylon 46, polyvinyl alcohol, rayon, and aramid are preferred from the viewpoints of versatility, durability, and industrial productivity.

[0069] The fiber composition according to this embodiment is preferably used as a raw material for an organic fiber cord. Here, "organic fiber cord" refers to a cord made of organic fibers, preferably a multifilament organic fiber cord. The organic fiber cord according to this embodiment can be used in various rubber components, including tires, belts, and hoses for automobiles, to contribute to reducing the weight and improving the durability of the rubber components. In particular, the organic fiber cord according to this embodiment is particularly preferably a tire cord used as a reinforcing material for pneumatic tires. Using the organic fiber cord according to this embodiment as a tire cord makes it possible to provide a tire cord with a low environmental impact, which uses a higher proportion of biomass materials. [Example]

[0070] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. In the following, the terms "parts" and "%" may be used, but they represent "parts by mass" or "% by mass" unless otherwise specified.

[0071] Treatment of ionic liquids using adsorbents First, 1-butyl-3-methylimidazolium chloride (BmimCl), an imidazolium-based ionic liquid, was prepared. Water was prepared as a solvent for the inorganic adsorbent treatment, and the following inorganic adsorbents were prepared.

[0072] [Table 1]

[0073] [Example 1] To 100 parts by mass of the ionic liquid prepared above, an appropriate amount of water and 1 part by mass of inorganic adsorbent A (Kyoward (registered trademark) 500-SN) were added, and the mixture was gently stirred at 25°C for 3 hours to treat the ionic liquid with the adsorbent. The resulting mixture was then filtered to remove the adsorbent, and the filtrate was dehydrated to obtain a purified ionic liquid.

[0074] [Example 2] A purified ionic liquid was obtained in the same manner as in Example 1 above, except that the amount of inorganic adsorbent A (Kyoward (registered trademark) 500-SN) added was changed to 2 parts by mass per 100 parts by mass of the ionic liquid.

[0075] [Example 3] A purified ionic liquid was obtained in the same manner as in Example 1 above, except that the amount of inorganic adsorbent A (Kyoward (registered trademark) 500-SN) added was changed to 3 parts by mass per 100 parts by mass of the ionic liquid.

[0076] [Example 4] A purified ionic liquid was obtained in the same manner as in Example 2 above, except that the treatment time was changed to 0.5 hours.

[0077] [Example 5] A purified ionic liquid was obtained in the same manner as in Example 4 above, except that the treatment temperature was changed to 40°C.

[0078] [Example 6] A purified ionic liquid was obtained in the same manner as in Example 4 above, except that the treatment temperature was changed to 70°C.

[0079] [Example 7] A purified ionic liquid was obtained in the same manner as in Example 4 above, except that the treatment temperature was changed to 90°C.

[0080] [Example 8] A purified ionic liquid was obtained in the same manner as in Example 6, except that the amount of inorganic adsorbent A (Kyoward (registered trademark) 500-SN) added was changed to 0.5 parts by mass per 100 parts by mass of ionic liquid and the treatment time was changed to 10 hours.

[0081] [Example 9] A purified ionic liquid was obtained in the same manner as in Example 8 above, except that the amount of inorganic adsorbent A (Kyoward (registered trademark) 500-SN) added was changed to 2 parts by mass per 100 parts by mass of the ionic liquid.

[0082] [Example 10] A purified ionic liquid was obtained in the same manner as in Example 6 above, except that the amount of inorganic adsorbent A (Kyoward (registered trademark) 500-SN) added was changed to 3 parts by mass per 100 parts by mass of the ionic liquid.

[0083] [Example 11] A purified ionic liquid was obtained in the same manner as in Example 6 above, except that inorganic adsorbent B (MA-OH) was used instead of inorganic adsorbent A.

[0084] [Example 12] A purified ionic liquid was obtained in the same manner as in Example 6 above, except that inorganic adsorbent C (MF-500) was used instead of inorganic adsorbent A.

[0085] [Example 13] A purified ionic liquid was obtained in the same manner as in Example 6 above, except that inorganic adsorbent C (STABIACE (registered trademark) HT-6) was used instead of inorganic adsorbent A.

[0086] [Comparative Example 1] A comparative ionic liquid was obtained in the same manner as in Example 1 described above, except that the amount of inorganic adsorbent A (Kyoward (registered trademark) 500-SN) added was changed to 0.4 parts by mass per 100 parts by mass of ionic liquid, and the treatment temperature was changed to 20°C.

[0087] Comparative Example 2 A comparative ionic liquid was obtained in the same manner as in Comparative Example 1 above, except that the treatment temperature was changed to 70° C. and the treatment time was changed to 0.1 hours.

[0088] Comparative Example 3 The comparative ionic liquid of Comparative Example 3 was an ionic liquid that had not been treated with an inorganic adsorbent.

[0089] <<Dissolution treatment of cellulose using purified ionic liquid>> Dissolving pulp (degree of polymerization 1200) was placed in a stainless steel can, and then the purified ionic liquid obtained in each of the above-mentioned Examples or the comparative ionic liquid in each of the Comparative Examples was poured into the can to obtain a mixture adjusted to a cellulose concentration of 9% by mass. The mixture was then heated to 100°C and stirred for 2 minutes and 30 seconds at 2000 rpm and 0.2 kPa using a vacuum planetary centrifugal mixer (Thinky ARV-310) and allowed to stand at 100°C for 15 minutes. The mixture was then stirred again at 2000 rpm and 0.2 kPa for 2 minutes and 30 seconds using a vacuum planetary centrifugal mixer. The dissolution state was confirmed using a polarizing microscope. Once dissolution was confirmed, the viscosity was measured after standing at 100°C for 5 or 24 hours, with the time immediately after preparation being set as time 0. Viscosity measurements were performed using a Malvern Kinexus Pro+ rheometer under parallel plate conditions at 100°C and steady flow conditions. The viscosity was measured at a shear rate of 0.1 s. -1 The viscosity was read at 100°C, and this value was used as the viscosity value. The results are shown in Tables 2 and 3 below.

[0090] [Table 2]

[0091] [Table 3]

[0092] The above results demonstrate that the production method of the present invention can prevent a decrease in the molecular weight of cellulose during the dissolution treatment of cellulose, i.e., can produce a purified ionic liquid that has excellent storage stability and thermal stability over time.

Claims

1. purifying at least one ionic liquid selected from the group consisting of imidazolium-based ionic liquids, pyridinium-based ionic liquids, ammonium-based ionic liquids, phosphonium-based ionic liquids, and cyclic amidinium-based ionic liquids by contacting the liquid with an inorganic adsorbent under conditions that satisfy at least two of the following (1) to (3), thereby obtaining a purified ionic liquid; dissolving cellulose in the purified ionic liquid; Including, A method for producing a cellulose dissolved solution, wherein the inorganic adsorbent contains hydrotalcite; (1) The amount of the inorganic adsorbent is 0.5 to 20 parts by mass per 100 parts by mass of the ionic liquid; (2) The temperature during contact is 25 to 120°C; (3) The contact time is 10 minutes or more.

2. M contained in the hydrotalcite ２ ２ O ３ M against １ Molar ratio of O (M １ represents a divalent metal ion, M ２ The method for producing a cellulose dissolved solution according to claim 1, wherein the ion concentration (I) is 3.0 or more.

3. 3. The method for producing a cellulose dissolving solution according to claim 1 or 2, wherein the ionic liquid is at least one selected from the group consisting of an imidazolium-based ionic liquid represented by the following chemical formula (1), a pyridinium-based ionic liquid represented by the following chemical formula (2), an ammonium-based ionic liquid represented by the following chemical formula (3), a phosphonium-based ionic liquid represented by the following chemical formula (4), and a cyclic amidinium-based ionic liquid represented by the following chemical formula (5): 【Chemical 1】 In the chemical formulas (1), (2), (3) and (4), R １ ~R １９ each independently represents a hydrogen atom, a substituted or unsubstituted linear or branched alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted linear or branched alkenyl group having 2 to 6 carbon atoms, a substituted or unsubstituted linear or branched alkynyl group having 2 to 6 carbon atoms, or a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms; In chemical formula (5), R ２０ is a substituted or unsubstituted linear alkylene group having 1 to 3 carbon atoms, In the chemical formulas (1), (2), (3), (4) and (5), X － are each independently a halogen ion, a phosphate ion, an alkyl phosphate ion, a hydroxide ion, a nitrate ion, a sulfate ion, a bisulfate ion, a sulfonate ion, a tosylate ion, a perchlorate ion, an aluminate ion, a dialuminate ion, a borate ion, an amide ion, a dicyanamide ion, a succinate ion, a thiocyanate ion, or a carboxylate ion.

4. The method for producing a cellulose dissolving solution according to any one of claims 1 to 3, wherein the ionic liquid is 1-butyl-3-methylimidazolium chloride (BmimCl).

5. A method for producing regenerated cellulose fibers, comprising carrying out solution spinning using the cellulose solution obtained by the production method according to any one of claims 1 to 4 as a spinning solution.

6. A method for producing a fiber composition, comprising obtaining regenerated cellulose fibers by the method according to claim 5.

7. A method for producing an organic fiber cord, comprising obtaining a fiber composition by the method according to claim 6.

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