A recovery method and a recovery apparatus for a solvent used for producing regenerated cellulose material

Abstract

The present application belongs to the technical field of solvent recovery, and relates to a recovery method and a recovery device for a solvent used for preparing regenerated cellulose materials, wherein the method and the device adopt a multistage filtration recovery process, and a step of filtration is further designed after a step of reduced pressure distillation, and it is just the filtration in this step that leads to further improvement of the quality of the recovered solvent, so that the service life of a filter in a preparation process of the regenerated cellulose materials is prolonged by 5-10 times, which indicates that the recovery process plays a key role in the continuous stability of the subsequent preparation process of the regenerated cellulose materials.

Description

Technical Field

[0001] This invention belongs to the field of solvent recovery technology, and relates to a method and apparatus for recovering solvents used in the preparation of regenerated cellulose materials, specifically to a method and apparatus for recovering ionic liquids used in the large-scale preparation of regenerated cellulose materials. Background Technology

[0002] Ionic liquids are a green solvent for preparing regenerated cellulose materials. Cellulose is directly dissolved in an ionic liquid to obtain a cellulose ionic liquid solution, which is then solidified to produce the regenerated cellulose material. Compared to the traditional viscose process for producing regenerated cellulose materials, the ionic liquid method is more environmentally friendly. Furthermore, the ionic liquid can be repeatedly recycled during the preparation process. However, it is crucial to ensure the stability of the recycled ionic liquid and achieve a sufficiently high recovery rate to guarantee that the final regenerated cellulose material meets the requirements for widespread application in terms of quality and cost.

[0003] Due to the excellent dissolving power of ionic liquids, the large-scale investment and frequent recycling in actual large-scale production lead to a rapid accumulation of various impurities in the raw materials, equipment, and processes into the recycled ionic liquids. This results in a continuous decrease in the purity of the ionic liquids, which adversely affects subsequent production. For example, the continuously declining dissolving power of ionic liquids can cause unstable fluctuations in the large-scale dissolving process, make it impossible to achieve stable control of product performance indicators, result in a darker appearance of regenerated cellulose materials, and make it impossible to stably control fluctuations in the recycling process, seriously affecting normal production operations. Moreover, because ionic liquids are expensive, discarding these recycled ionic liquids or replacing them with new ionic liquids in batches would have a very negative impact on production costs and the environment. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a method and apparatus for recovering solvents used in the preparation of regenerated cellulose materials, specifically a method and apparatus for recovering ionic liquids used in the large-scale, continuous preparation of regenerated cellulose materials. The recovery method and apparatus enable low-cost, high-recovery-rate continuous recycling and reuse of solvents used in the preparation of regenerated cellulose materials, particularly ionic liquids used in the large-scale preparation of regenerated cellulose materials, with the solvent quality remaining stable even after 100 or even 800+ recycling cycles.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for recovering solvents used in the preparation of regenerated cellulose materials, the recovery method comprising the following steps:

[0007] 1) The aqueous solution containing the solvent for preparing regenerated cellulose material to be recycled is subjected to first-stage filtration;

[0008] 2) The aqueous solution after the first stage filtration in step 1) is treated with resin and then subjected to a second stage filtration;

[0009] 3) Perform membrane separation on the aqueous solution after the second-stage filtration in step 2);

[0010] 4) The aqueous solution after membrane separation in step 3) is evaporated under reduced pressure to obtain an aqueous solution containing concentrated solvent and evaporated condensate;

[0011] 5) The aqueous solution containing concentrated solvent from step 4) is subjected to a third-stage filtration, and the filtered aqueous solution is reused in the process of preparing regenerated cellulose materials.

[0012] Alternatively, the recycling method may include the following steps:

[0013] 1) The aqueous solution containing the solvent for preparing regenerated cellulose material to be recycled is subjected to first-stage filtration;

[0014] 2') Perform membrane separation on the aqueous solution after the first-stage filtration in step 1);

[0015] 3') The aqueous solution after membrane separation in step 2') is treated with resin and then subjected to a second-stage filtration;

[0016] 4') The aqueous solution after the second-stage filtration in step 3') is evaporated under reduced pressure to obtain an aqueous solution containing concentrated solvent and evaporated condensate;

[0017] 5) The aqueous solution containing concentrated solvent from step 4') is subjected to a third-stage filtration, and the filtered aqueous solution is reused in the process of preparing regenerated cellulose materials.

[0018] The present invention further provides a solvent recovery device for preparing regenerated cellulose materials. Specifically, the recovery device is used to implement the above-mentioned recovery method. The recovery device includes a first-stage filtration system, a resin system, a second-stage filtration system, a membrane separation system, a vacuum evaporation system, and a third-stage filtration system arranged in sequence. Alternatively, the recovery device includes a first-stage filtration system, a membrane separation system, a resin system, a second-stage filtration system, a vacuum evaporation system, and a third-stage filtration system arranged in sequence.

[0019] This invention addresses the large-scale batch production of solvents for preparing regenerated cellulose materials, emphasizing high efficiency, continuity, and stability. The beneficial effects of the above technical solution are as follows:

[0020] 1. This invention proposes a method and apparatus for the large-scale (solvent recovery capacity of over 10,000 tons), low-cost (e.g., recovery cost of AmimCl ionic liquid < 130 yuan / t), continuous and stable recovery with extremely high recovery rate (e.g., recovery rate of over 99.5%, and solvent quality still fully meets the requirements of process use after 100 or even 800 recycling cycles).

[0021] 2. This invention proposes a multi-stage filtration recovery process and apparatus. In particular, a filtration step is designed after the vacuum distillation step. It is this filtration step that leads to a further improvement in the quality of the recovered solvent, which extends the service life of the filter in the regenerated cellulose material preparation process by 5-10 times. This shows that the recovery process plays a key role in the continuous stability of the subsequent regenerated cellulose material preparation process.

[0022] 3. This invention also effectively improves the process conditions of the vacuum distillation step. Unexpectedly, when vacuum distillation is carried out using this invention, segmented vacuum distillation is performed according to the boiling points of solvent aqueous solutions of different concentrations, which greatly reduces the high energy consumption problem of single distillation method. Furthermore, by optimizing the vacuum distillation process conditions, the heating temperature of distillation is reduced, which greatly alleviates the problem of partial thermal decomposition of solvent caused by local heating, and ensures the purity and recovery rate of solvent.

[0023] 4. The stability issues of purity, appearance color, solubility, and other indicators of the solvent used for preparing regenerated cellulose materials after the present invention are effectively solved. The solvent used for preparing regenerated cellulose materials remains stable even after 100 or even 800 recycling cycles, which can fully meet the requirements of cellulose material preparation processes. It effectively solves the problems of poor stability of the dissolution process and poor quality and stability of finished products in existing cellulose material preparation processes, and significantly improves the continuous stability of the production process and the quality of products.

[0024] 5. By using the process and apparatus of the present invention, a closed-loop recycling of solvents and water for preparing regenerated cellulose materials is achieved, with 100% reuse of condensate and a solvent recovery rate of over 99.5% for preparing regenerated cellulose materials. Attached Figure Description

[0025] Figure 1 The present invention provides a preferred embodiment of the solvent recovery process for preparing regenerated cellulose materials.

[0026] Figure 2 This is an optical image of the mixed solution after the ionic liquid recovered from Example 1 dissolved cellulose.

[0027] Figure 3This is an optical image of the mixed solution after the ionic liquid recovered from Example 2 dissolved cellulose.

[0028] Figure 4 This is an optical image of the mixed solution after the ionic liquid recovered from Example 3 dissolved cellulose.

[0029] Figure 5 Optical image of the mixed solution after the ionic liquid recovered from Comparative Example 1 dissolves cellulose. Detailed Implementation

[0030] The inventors of this application, through large-scale production practice, have discovered that: First, the decisive factor affecting whether the solvent used in the preparation of regenerated cellulose materials meets the requirements for production use is the impurity content or purity of the solvent. Only solvents with impurity content within a certain range can meet the requirements for production use. Second, a solvent recovery rate of over 99.5% is necessary to ensure that the final product has a significant and outstanding cost advantage compared to products made using the viscose method. Third, controlling energy consumption during the recovery process is also crucial to ensuring the cost of the final product. Therefore, it is essential to purify the solvents used in the large-scale preparation of regenerated cellulose materials and to achieve efficient and comprehensive energy utilization to realize the continuous recycling and reuse of solvents with stable quality, low cost, and high recovery rate.

[0031] This embodiment provides a method for recovering solvents used in the preparation of regenerated cellulose materials, particularly a continuous method for recovering solvents used in the preparation of regenerated cellulose materials. The recovery method includes the following steps:

[0032] 1) The aqueous solution containing the solvent for preparing regenerated cellulose material to be recycled is subjected to first-stage filtration;

[0033] 2) The aqueous solution after the first stage filtration in step 1) is treated with resin and then subjected to a second stage filtration;

[0034] 3) Perform membrane separation on the aqueous solution after the second-stage filtration in step 2);

[0035] 4) The aqueous solution after membrane separation in step 3) is evaporated under reduced pressure to obtain an aqueous solution containing concentrated solvent and evaporated condensate;

[0036] 5) The aqueous solution containing concentrated solvent from step 4) is subjected to a third-stage filtration, and the filtered aqueous solution is reused in the process of preparing regenerated cellulose materials.

[0037] Alternatively, the recycling method may include the following steps:

[0038] 1) The aqueous solution containing the solvent for preparing regenerated cellulose material to be recycled is subjected to first-stage filtration;

[0039] 2') Perform membrane separation on the aqueous solution after the first-stage filtration in step 1);

[0040] 3') The aqueous solution after membrane separation in step 2') is treated with resin and then subjected to a second-stage filtration;

[0041] 4') The aqueous solution after the second-stage filtration in step 3') is evaporated under reduced pressure to obtain an aqueous solution containing concentrated solvent and evaporated condensate;

[0042] 5) The aqueous solution containing concentrated solvent from step 4') is subjected to a third-stage filtration, and the filtered aqueous solution is reused in the process of preparing regenerated cellulose materials.

[0043] In the above method, this invention employs a multi-stage filtration approach combined with a closed-loop circulation of solvent and water. This enables highly efficient solvent recovery, achieving a recovery rate of over 99.5%, and the solvent quality remains stable even after 100 or even 800 cycles. Furthermore, the closed-loop circulation of solvent and water effectively controls the production cost of regenerated cellulose materials; the recycling of water significantly reduces fresh water consumption during the regenerated cellulose material preparation process, lowering production costs (for example, traditional preparation methods consume 18m³ of fresh water per ton of regenerated cellulose membrane produced). 3 Fresh water is used, and by achieving a closed-loop water cycle, the fresh water consumption for producing one ton of regenerated cellulose membrane is reduced to 3m³. 3 ).

[0044] Specifically, the multi-stage filtration includes a first-stage filtration of an aqueous solution containing a solvent to be recycled for preparing regenerated cellulose materials, a second-stage filtration of an aqueous solution after resin treatment, and a third-stage filtration of an aqueous solution containing concentrated solvent after vacuum evaporation.

[0045] According to an embodiment of the present invention, the filter used in the first stage of filtration includes, but is not limited to, at least one of a quartz sand filter, a fiber bundle filter, a Y-type filter, a candle filter, and a bag filter. The first stage of filtration can ensure high-efficiency filtration and remove insoluble impurities such as mechanical impurities, grease, and suspended solids from the aqueous solution containing the solvent to be recovered, resulting in a clear aqueous solution containing the solvent to be recovered with a turbidity of <5 NTU. This ensures that the solution will not contaminate or clog the resin when it enters the resin treatment system, or that the solution will not damage or exacerbate membrane clogging when it enters the membrane separation system.

[0046] According to an embodiment of the present invention, the filter used in the second stage filtration includes, but is not limited to, at least one of a Y-type filter, a candle filter, and a bag filter. The second stage filtration can remove insoluble impurities, such as suspended solids and precipitates, from the resin-treated solution, ensuring that the solution does not damage the membrane or aggravate membrane blockage when it enters the membrane separation system, or ensuring that it does not adhere to the inner surface of the evaporation system and heat exchanger during the vacuum evaporation process, affecting evaporation efficiency or blocking the passage.

[0047] According to an embodiment of the present invention, the filter used in the third stage filtration includes, but is not limited to, at least one of a centrifuge, a plate and frame filter press, a closed plate filter, and a candle filter. The third stage filtration can remove suspended solids and impurity precipitates (including but not limited to small molecule polymers, colored impurities, and calcium and magnesium carbonate precipitates) enriched or precipitated during the concentration process, and at the same time decolorize the aqueous solution containing the concentrated solvent.

[0048] Unless otherwise specified, the term "aqueous solution" in this article refers to an aqueous solution containing a solvent.

[0049] According to an embodiment of the present invention, in step 1), the aqueous solution containing the solvent to be recovered comes from the preparation process of the regenerated cellulose material, such as any step in the preparation process of the regenerated cellulose material that can generate the aqueous solution containing the solvent to be recovered.

[0050] For example, the aqueous solution containing the solvent to be recovered comes from the coagulation and washing process of the regenerated cellulose material. In the preparation process of the regenerated cellulose material, the cellulose after spinning or extrusion molding needs to be coagulated in a coagulation bath and soaked and washed in a washing process, which will form a large amount of aqueous solution containing solvent.

[0051] For example, the aqueous solution containing the solvent to be recovered comes from the waste glue recycling process. The waste glue recycling process includes, for example, waste glue generated during the process adjustment or replacement of equipment spare parts or the shutdown and start-up process of cellulose dissolution, and waste containing more solvent generated during the process of breaking off regenerated cellulose materials. The waste glue or waste generated is sent to the waste glue recycling process for crushing, soaking and filtering. When the solvent in the waste glue or waste is recovered, an aqueous solution containing the solvent is generated.

[0052] For example, the aqueous solution containing the solvent to be recovered comes from a filtration system washing process, which includes, for example, wash water containing solvent after the filter has become clogged.

[0053] According to an embodiment of the present invention, the solvent components in the preparation process of regenerated cellulose materials are collected and processed to ensure the solvent recovery rate.

[0054] According to an embodiment of the present invention, in step 1), the aqueous solution containing the solvent to be recovered contains solvent, water, and impurities. The impurities include soluble and insoluble impurities. Exemplarily, the impurities include, but are not limited to, insoluble impurities such as mechanical impurities, greases, and suspended solids, as well as soluble impurities such as polymers, inorganic compounds, and organic compounds; for example, including but not limited to regenerated cellulose material fragments, rust and slag, dust particles, equipment lubricating oil, fine sealing materials, undissolved fibers, water-soluble compounds, or small molecule polymers. These impurity components can be effectively removed by the multi-stage filtration of the present invention, combined with resin treatment, membrane separation, and vacuum evaporation processes.

[0055] According to an embodiment of the present invention, in step 1), the aqueous solution containing the solvent to be recovered has a solvent mass percentage of 10-30 wt% (e.g., 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, or 30 wt%), a water mass percentage of 67.5-89.5 wt% (e.g., 67.5 wt%, 70 wt%, 72 wt%, 75 wt%, 78 wt%, 80 wt%, 82 wt%, 85 wt%, 88 wt%, or 89.5 wt%), and an impurity mass percentage of 0.5-2.5 wt% (e.g., 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, or 2.5 wt%). When the solvent concentration in the aqueous solution containing the solvent to be recovered is controlled at 10-30 wt%, high filtration and impurity removal efficiency can be achieved while also realizing low-cost solvent recovery. It is understandable that if the concentration of the solvent in the aqueous solution containing the solvent to be recovered is greater than 30 wt%, the solution of this application is also applicable. However, because the concentration is too high, it will affect the effect and efficiency of filtration and impurity removal, and will not be able to achieve the recovery capacity designed for the recovery equipment, thereby affecting the recovery efficiency, increasing the recovery cost, and further increasing the cost of preparing regenerated cellulose materials, thus weakening its promotion and application value. If the concentration of the solvent in the aqueous solution containing the solvent to be recovered is less than 10 wt%, the solution of this application is also applicable. However, because the concentration is too low, it will increase the energy consumption of concentration treatment (such as vacuum evaporation process), which will increase the recovery cost, and will also increase the cost of preparing regenerated cellulose materials, thus weakening its promotion and application value.

[0056] According to an embodiment of the present invention, in step 1), the solvent is an ionic liquid.

[0057] According to an embodiment of the present invention, the ionic liquid is selected from organic molten salts formed by cations and anions with a melting point below 100°C, and preferably molten salts capable of dissolving the cellulose.

[0058] The cation is selected from at least one of substituted or unsubstituted imidazole, pyridine, pyrrole, amine, phosphine, choline, diazabicyclic, and amino acid-type cations. For example, the substituent can be C. 1-12 Alkyl, C 2-12 alkenyl, C1-C 12 Alkoxy C1-C 12 Alkyl, hydroxyl, hydroxyl C 1-12 Alkyl, C 6-12 Aryl, C 6-12 Aryl C 1-12 Alkyl, C 6-12 Aryl C 1-12 At least one of alkoxy groups, etc.; preferably C 1-6 Alkyl, C 2-6 alkenyl, hydroxyl, hydroxyl C 1-6 Alkyl, phenyl, C 6-10 Aryl C 1-6 Alkyl, C 6-10 Aryl C 1-6At least one of the alkoxy groups, such as at least one of methyl, ethyl, butyl, pentyl, allyl, hydroxy, methoxymethyl, hydroxyethyl, phenyl, benzyl, m-methoxyphenyl, and m-methoxybenzyl. Exemplarily, the cation may be selected from: 1-ethyl-3-methylimidazolium cation ([EMIM]), 3-methylimidazolium cation ([MIM]), 1-propyl-3-methylimidazolium cation ([PMIM]), 1-allyl-3-methylimidazolium cation ([AMIM]), 1-butyl-3-methylimidazolium cation ([BMIM]), 1-butyl-2,3-dimethylimidazolium cation ([BMMIM]), 1,3-dimethylimidazolium cation ([MMIM]), 1-methoxyethyl-3-methylimidazolium cation ([MeOEMIM]), 1-methoxymethyl-3-methylimidazolium cation ([MeOMMIM]), 1-hydroxy-3-methylimidazolium cation ([HMIM]), 1-(2-hydroxyethyl)-3-methylimidazolium cation ([HOEMIM]), 1-methyl-3-benzylmethylimidazolium cation ([MBzIM]), 1-pentyl-3- The cation is selected from at least one of the following: methylimidazolium cation ([PeMIM]), 1-benzyl-3-methylimidazolium cation ([BzMIM]), 1-m-methoxybenzyl-3-methylimidazolium cation ([MeOBzMIM]), 1-m-methylbenzyl-3-methylimidazolium cation ([MeBzMIM]), N-methylpyridine cation ([MPyr]), N-ethylpyridine cation ([EPyr]), N-butylpyridine cation ([BPyr]), N-hexylpyridine cation ([HPyr]), 1-butyl-3-methylpyrrolidone ion ([BMPyrr]), tris(2-hydroxyethyl)methylamine ([THEMA]), tetrabutylamine ([TBA]), tetrabutylphosphine ([PBu4]), glycine cation ([Gly]), choline cation ([Ch]), and 1,5-diazazobicyclo[4.3.0]one-5-ene ([DBNH]). More preferably, the cation is selected from at least one of: 1-ethyl-3-methylimidazolium cation ([EMIM]), 1-allyl-3-methylimidazolium cation ([AMIM]), 1-butyl-3-methylimidazolium cation ([BMIM]), and choline cation ([Ch]).

[0059] The anion is selected from at least one of halogen anions, organic acid radicals, organic acid ester anions, and amino acid anions. For example, the anion is selected from: chloride ion ([Cl]), bromide ion ([Br]), fluoride ion ([F]), formate ion ([HCOO]), acetate ion ([CH3COO] or [Ac]), glycolate ion ([HOCH2COO]), propionate ion ([CH3CH2COO] or [OPr]), butyrate ion ([CH3CH2CH2COO] or [OBu]), octanoate ion ([Oct]), benzoate ion ([C6H5COO] or [PhCOO]), lactate ion ([CH3CH(OH)COO] or [Lac]), thioglycolate ion ([HSCH2COO]), and hexafluorophosphate ion. The anion is selected from at least one of the following: PF6, trifluoroborate (BF3), methyl phosphate (MeO)HPO2 or MP), dimethyl phosphate (MeO)2PO2 or DMP), diethyl phosphate (EtO)2PO2 or DEP), methanesulfonate anion (MeOSO3), trifluoromethanesulfonate anion (CF3SO3), glycine anion (Gly), lysine anion (Lys), valine anion (Val), dicyandiamide anion (N(CN)2 or DCA), and bis(trifluoromethanesulfonylimide) (Tf2N). More preferably, the anion is selected from at least one of the following: chloride ion ([Cl]), formate ion ([HCOO]), acetate ion ([Ac]), methyl phosphate ion ([(MeO)HPO2] or [MP]), dimethyl phosphate ion ([(MeO)2PO2] or [DMP]), and dicyandiamide anion ([N(CN)2] or [DCA]).

[0060] According to an embodiment of the present invention, the ionic liquid may be selected from: 1-ethyl-3-methylimidazolium chloride ionic liquid ([EMIM][Cl]), 1-ethyl-3-methylimidazolium bromide ionic liquid ([EMIM][Br]), 1-ethyl-3-methylimidazolium formate ionic liquid ([EMIM][HCOO]), 1-ethyl-3-methylimidazolium acetate ionic liquid ([EMIM][Ac]), 1-ethyl-3-methylimidazolium octanoate ionic liquid ([EMIM][Oct]), 1-ethyl-3-methylimidazolium methyl phosphate ionic liquid ([EMIM][MP]), 1-ethyl-3-methylimidazolium dimethyl phosphate ionic liquid ([EMIM][DMP]), 1- Ethyl-3-methylimidazolium diethyl phosphate ionic liquid ([EMIM][DEP]), 1-ethyl-3-methylimidazolium propionate ionic liquid ([EMIM][OPr]), 1-ethyl-3-methylimidazolium octate ionic liquid ([EMIM][OBu]), 1-ethyl-3-methylimidazolium glycinate ionic liquid ([EMIM][Gly]), 1-ethyl-3-methylimidazolium lysine ionic liquid ([EMIM][Lys]), 1-allyl-3-methylimidazolium chloride ionic liquid ([AMIM][Cl]), 1-allyl-3-methylimidazolium bromide ionic liquid ([AMIM][Br]), 1-allyl-3-methylimidazolium carbamate ionic liquid ([AMI]). 1-Butyl-3-methylimidazolium acetate ionic liquid ([AMIM][Ac]), 1-Butyl-3-methylimidazolium chloride ionic liquid ([BMIM][Cl]), 1-Butyl-3-methylimidazolium bromide ionic liquid ([BMIM][Br]), 1-Butyl-3-methylimidazolium formate ionic liquid ([BMIM][HCOO]), 1-Butyl-3-methylimidazolium acetate ionic liquid ([BMIM][Ac]), 1-Butyl-3-methylimidazolium hydroxyacetate ionic liquid ([BMIM][HOCH2COO]), 1-Butyl-3-methylimidazolium propionate ionic liquid ([BMIM][CH3CH2COO]), 1-Butyl-3- Methylimidazolium lactate ionic liquid [BMIM][Lac], 1-butyl-3-methylimidazolium butyrate ionic liquid ([BMIM][CH3CH2CH2COO]), 1-butyl-3-methylimidazolium benzoate ionic liquid ([BMIM][C6H5COO]), 1-butyl-3-methylimidazolium glycinate ionic liquid ([BMIM][H2NCH2COO]), 1-butyl-3-methylimidazolium dicyanamide ionic liquid ([BMIM][N(CN)2]), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquid ([BMIM][Tf2N]), 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid ([BMIM][PF6]).1-Butyl-3-methylimidazolium tetrafluoroborate ionic liquid ([BMIM][BF4]), 1-Butyl-3-methylimidazolium methanesulfonate ionic liquid ([BMIM][MeOSO3]), 1-Butyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid ([BMIM][CF3SO3]), 1-Butyl-2,3-dimethylimidazolium tetrafluoroborate ionic liquid ([BMMIM][BF4]), 3-methylimidazolium formate ionic liquid ([MIM][HCOO]), 1,3-dimethylimidazolium chloride ionic liquid ([MMIM][Cl]), 1,3-dimethylimidazolium methyl phosphate ionic liquid ([MMIM][MP]), 1,3-dimethylimidazolium dimethyl phosphate Ester salt ionic liquids ([MMIM][DMP]), 1,3-dimethylimidazolium methanesulfonate ionic liquids ([MMIM][MeOSO3]), 1-hydroxy-3-methylimidazolium chloride ionic liquids ([HMIM][Cl]), 1-hydroxy-3-methylimidazolium trifluoromethanesulfonate ionic liquids ([HMIM][CF3SO3]), 1-(2-hydroxyethyl)-3-methylimidazolium chloride ionic liquids ([HOEMIM][Cl]), 1-methoxymethyl-3-methylimidazolium bromide ionic liquids ([MeOMMIM][Br]), 1-methoxyethyl-3-methylimidazolium bromide ionic liquids ([MeOEMIM][Br]), N-ethylpyridine chloride ionic liquids ([E... Pyr][Cl]), N-ethylpyridine bromide ionic liquid ([EPyr][Br]), N-methylpyridine carboxylate ionic liquid ([MPyr][HCOO]), tris(2-hydroxyethyl)methylamine acetate ionic liquid ([THEMA][Ac]), tris(2-hydroxyethyl)methylamine methanesulfonate ionic liquid ([THEMA][MeOSO3]), tris(2-hydroxyethyl)methylamine trifluoromethanesulfonate ionic liquid [THEMA][CF3SO3], tetrabutylphosphine valine ionic liquid [PBu4][Val], tetrabutylphosphine lysine ionic liquid [PBu4][Lys], tetrabutylphosphine glycine ionic liquid [PBu4][Gly], 1-phenylmethyl- 3-Methylimidazolium chloride ionic liquid ([BzMIM][Cl]), 1-benzyl-3-methylimidazolium dicyandiamide ionic liquid ([BzMIM][DCA]), 1-m-methylbenzyl-3-methylimidazolium chloride ionic liquid ([MeBzMIM][Cl]), 1-m-methoxybenzyl-3-methylimidazolium chloride ionic liquid ([MeOBzMIM][Cl]), choline chloride ionic liquid ([Ch][Cl]), choline bromide ionic liquid (Ch][Br]), choline acetate ionic liquid ([Ch][CH3COO]), choline propionate ionic liquid ([Ch][CH3CH2COO]), choline butyrate ionic liquid ([Ch][CH3CH2CH2COO]).At least one of the following ionic liquids: glycine hydrochloride ionic liquid ([Gly][Cl]) and 1,5-diazabicyclo[4.3.0]ketone-5-ene acetate ionic liquid ([DBNH][Ac]).

[0061] According to an embodiment of the present invention, in step 1), after the first-stage filtration, insoluble impurity components (i.e. macroscopically visible impurity components) in the aqueous solution containing the solvent to be recovered can be effectively removed, such as mechanical impurities, grease and suspended matter, specifically regenerated cellulose material fragments, rust and slag, dust particles, equipment lubricating oil, fine sealing materials, undissolved fiber fibers, etc.

[0062] According to an embodiment of the present invention, in step 1), after the first-stage filtration, impurity components accounting for more than 99 wt% of the total insoluble impurity components in the aqueous solution containing the solvent to be recovered are removed.

[0063] According to an embodiment of the present invention, in step 1), the filtration is performed, for example, using a filter.

[0064] According to an embodiment of the present invention, in step 1), the filter includes, but is not limited to, at least one of a quartz sand filter, a fiber bundle filter, a Y-type filter, a candle filter, and a bag filter. If a multi-stage filter combination is used, the filtration accuracy of the multi-stage filters is set from low to high according to the material flow direction. For example, the material is sequentially passed through a polypropylene fiber bundle filter with an accuracy of 10 micrometers, a candle filter with an accuracy of 5 micrometers, and a bag filter with an accuracy of 0.5 micrometers.

[0065] According to an embodiment of the present invention, the quartz sand filter ensures that the effluent turbidity is ≤5 NTU; the fiber bundle filter is an acrylic fiber bundle filter or a modified fiber bundle filter with a precision of 0.1-10 micrometers (e.g., 0.1 micrometer, 0.5 micrometer, 1 micrometer, 2 micrometer, 3 micrometer, 4 micrometer, 5 micrometer, 8 micrometer or 10 micrometer); the Y-type filter uses an 80-120 mesh filter screen (e.g., 80 mesh, 100 mesh or 120 mesh); the candle filter has a precision of 0.1-10 micrometers (e.g., 0.1 micrometer, 0.5 micrometer, 1 micrometer, 2 micrometer, 3 micrometer, 4 micrometer, 5 micrometer, 8 micrometer or 10 micrometer); and the bag filter has a precision of 0.5-50 micrometers (e.g., 0.5 micrometer, 1 micrometer, 2 micrometer, 3 micrometer, 4 micrometer, 5 micrometer, 8 micrometer, 10 micrometer, 20 micrometer, 30 micrometer, 40 micrometer or 50 micrometer).

[0066] According to an embodiment of the present invention, in step 2) or step 3'), the resin is an ion exchange resin, for example, an anion exchange resin. Exemplarily, the resin includes a basic anion exchange resin, such as a strongly basic anion exchange resin or a weakly basic anion exchange resin.

[0067] According to an embodiment of the present invention, in step 2) or step 3'), after resin treatment, soluble impurity components (including but not limited to SO4) in the aqueous solution containing the solvent to be recovered can be effectively removed. 2- NO 3- HCO 3- Citrate, tartrate, oxalate, PO4 3- and NO 2- It contains impurities with larger molecular sizes, such as proteins, nucleic acids, and common colloids, and does not react chemically with the solvent to be recycled.

[0068] According to an embodiment of the present invention, in step 2) or step 3'), the mass ratio of the resin to the volume ratio of the solution to be treated is not specifically defined; it is sufficient to ensure that the resin can continuously adsorb soluble impurities in the aqueous solution. When the resin is saturated, it needs to be regenerated in a timely manner. If regeneration cannot restore the resin's exchange capacity, it needs to be replaced with new resin.

[0069] According to an embodiment of the present invention, in step 2) or step 3'), after resin treatment, impurity components accounting for 5-20 wt% of the total soluble impurity components in the aqueous solution containing the solvent to be recovered are removed.

[0070] According to an embodiment of the present invention, in step 2) or step 3'), after the second-stage filtration, insoluble impurities such as suspended matter and impurity precipitates in the resin-treated solution can be effectively removed, such as broken resin particles or powder, heavy metal salt precipitates generated by resin exchange, etc.

[0071] According to an embodiment of the present invention, in step 2) or step 3'), after the second-stage filtration, impurities accounting for more than 99% of the total insoluble impurity components in the resin-treated solution are removed.

[0072] According to an embodiment of the invention, in step 2) or step 3'), the filtration is performed, for example, using a filter.

[0073] According to an embodiment of the present invention, in step 2) or step 3'), the filter includes, but is not limited to, at least one of a Y-type filter, a candle filter, and a bag filter. If a multi-stage filter combination is used, the filtration accuracy of the multi-stage filters is set from low to high according to the material flow direction. For example, the material is sequentially passed through a bag filter with an accuracy of 50 μm, a candle filter with an accuracy of 5 micrometers; or through a 120-mesh Y-type filter, a bag filter with an accuracy of 50 μm, a candle filter with an accuracy of 5 micrometers, and a bag filter with an accuracy of 0.5 μm.

[0074] According to an embodiment of the present invention, the Y-type filter uses an 80-200 mesh filter screen, for example, 80 mesh, 100 mesh, 120 mesh, 150 mesh, 180 mesh, or 200 mesh.

[0075] According to an embodiment of the present invention, the accuracy of the candle filter is 0.1-5 micrometers, for example, 0.1 micrometer, 0.5 micrometer, 1 micrometer, 2 micrometer, 3 micrometer, 4 micrometer or 5 micrometer.

[0076] According to an embodiment of the present invention, the accuracy of the bag filter is 0.5-50 micrometers, for example, 0.5 micrometers, 1 micrometer, 2 micrometers, 3 micrometers, 4 micrometers, 5 micrometers, 10 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers or 50 micrometers.

[0077] According to an embodiment of the present invention, in step 3) or step 2'), after membrane separation treatment, soluble impurity components, such as polymers, in the aqueous solution containing the solvent to be recovered can be effectively removed.

[0078] According to an embodiment of the present invention, in step 3) or step 2'), after treatment by the membrane separator, 5-50 wt% of the total soluble impurity components in the aqueous solution containing the solvent to be recovered are removed.

[0079] According to an embodiment of the present invention, in step 3) or step 2'), the membrane separation is performed, for example, using a membrane separator.

[0080] According to embodiments of the present invention, the membrane separator includes, but is not limited to, at least one of reverse osmosis membranes, microfiltration membranes, ultrafiltration membranes, and nanofiltration membranes. When multiple membrane separators are used in combination, the separation precision of the multiple membrane separators is set from low to high according to the material flow direction, for example, through a ceramic membrane filter with a precision of 0.1 μm / 50 nm, a nanofiltration membrane filter with a precision of 3000 / 1500 / 400D, and a reverse osmosis membrane filter; or through a ceramic membrane filter with a precision of 50 / 25 nm, a nanofiltration membrane filter with a precision of 3000 / 1500 / 400D, and a reverse osmosis membrane filter.

[0081] According to an embodiment of the present invention, in step 4) or step 4'), the reduced pressure evaporation is carried out in an evaporator.

[0082] According to an embodiment of the present invention, in step 4) or step 4'), the evaporator includes, but is not limited to, at least one of a multi-effect evaporator, a rising film evaporator, a falling film evaporator, a vapor recompression evaporator, and a thin film evaporator.

[0083] According to an embodiment of the present invention, the reduced-pressure evaporation can concentrate the solvent in the aqueous solution, i.e., obtain a solution system with a significantly increased solvent content. Evaporation is performed in stages according to the different water contents of the evaporating material to maximize recovery efficiency and save evaporation energy consumption. For aqueous solutions with a water content ≥40%, at least one of a multi-effect evaporator, a rising film evaporator, a falling film evaporator, and a vapor recompression evaporator can be used; for aqueous solutions with a water content <40%, at least one of a multi-effect evaporator, a rising film evaporator, a falling film evaporator, and a thin-film evaporator can be used.

[0084] According to an embodiment of the present invention, in step 4) or step 4'), the temperature of the reduced-pressure evaporation is 50-100°C (e.g., 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C). The vacuum degree of the reduced-pressure evaporation is 0.05-0.099 MPa (e.g., 0.05 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, or 0.09 MPa). Studies have found that the coordination of temperature and vacuum degree in this reduced-pressure evaporation process is very important. In particular, for aqueous solutions with a water content of <40%, if the vacuum degree is poor during the evaporation process, the evaporation temperature will rise significantly; that is, the lower the vacuum degree and the higher the evaporation temperature, the more likely it is to cause local thermal decomposition of the solvent, thereby affecting the purity and recovery rate of the solvent.

[0085] According to an embodiment of the present invention, in step 4) or step 4'), the aqueous solution containing the concentrated solvent contains solvent, water and impurities, the impurities including but not limited to suspended matter and impurity precipitates enriched or precipitated during the concentration process.

[0086] According to an embodiment of the present invention, in step 4) or step 4'), after vacuum evaporation, a concentrated aqueous solution of solvent with a water content of 5-25 wt% is obtained.

[0087] According to an embodiment of the present invention, in step 4) or step 4'), the aqueous solution containing concentrated solvent has a solvent content of 65-90 wt% by mass, a water content of 5-25 wt% by mass, and an impurity content of less than 10 wt% by mass.

[0088] According to an embodiment of the present invention, in step 4) or step 4'), the evaporated condensate is recycled into the preparation process of regenerated cellulose material. Exemplarily, it is recycled for use in the molding and washing process to wash regenerated cellulose material, in the waste glue recycling process to soak waste glue, in the membrane separation system to wash membrane elements, in the resin treatment system to clean resin, and in the filtration system to brush.

[0089] According to an embodiment of the present invention, in step 5), after the third-stage filtration, suspended solids, precipitates and colored substances enriched or precipitated during the concentration process can be effectively removed.

[0090] According to an embodiment of the present invention, in step 5), after the third-stage filtration, impurities accounting for 5-20 wt% of the total soluble impurities in the aqueous solution containing the solvent to be recovered are removed, and the solvent concentrate is simultaneously decolorized.

[0091] According to an embodiment of the present invention, in step 5), after the third-stage filtration, impurities accounting for more than 99 wt% of the total insoluble impurity components in the concentrated solvent aqueous solution are removed.

[0092] According to an embodiment of the present invention, in step 5), after the third-stage filtration, the total amount of soluble impurity components removed cumulatively accounts for 15-90 wt% of the total amount of soluble impurity components in the aqueous solution containing the solvent to be recovered.

[0093] According to an embodiment of the present invention, in step 5), after the third-stage filtration, the total amount of insoluble impurity components removed cumulatively accounts for more than 99 wt% of the total amount of insoluble impurity components in the aqueous solution containing the solvent to be recovered.

[0094] According to an embodiment of the present invention, in step 5), the filtration is performed using a filter.

[0095] According to an embodiment of the present invention, in step 5), the filter includes, but is not limited to, at least one of a centrifuge, a plate and frame filter press, a closed plate filter, and a candle filter. If a multi-stage filter combination is used, the filtration accuracy of the multi-stage filters is set from low to high according to the material flow direction; for example, the material sequentially passes through filters with an air permeability of 10-40 L / m³. 2 • S's polypropylene filter cloth plate and frame filter press, closed plate filter, candle filter with a precision of 30μm, or closed plate filter, candle filter with a precision of 10μm.

[0096] According to an embodiment of the present invention, the centrifuge separation factor is greater than 5000g, and the plate and frame filter press is selected with an air permeability of 10-40L / m³. 2 The polypropylene filter cloth of S is used in sealed plate filters, which use a blend of diatomaceous earth with a mesh size of 100-1000 mesh and decolorizing earth with a mesh size of 100-1000 mesh as filter media (such as a blend of 50wt% 200 mesh diatomaceous earth, 30wt% 500 mesh diatomaceous earth and 20wt% 200 mesh decolorizing earth, or a blend of 60wt% 200 mesh diatomaceous earth, 10wt% 500 mesh diatomaceous earth, 5wt% 1000 mesh diatomaceous earth and 25wt% 150 mesh decolorizing earth). The filter media of candle filters is 0.5-30 microns (e.g. 0.5 microns, 1 micron, 2 microns, 3 microns, 4 microns, 5 microns, 8 microns, 10 microns, 15 microns, 20 microns, 25 microns or 30 microns).

[0097] According to an embodiment of the present invention, in step 5), the filtered aqueous solution includes solvent, water and impurities. The impurities are soluble impurities that cannot be removed after three-stage filtration and are soluble in the concentrated solvent aqueous solution. The content of these soluble impurities is controlled within a certain range and does not affect the subsequent application in the preparation process of regenerated cellulose materials. This plays a key role in achieving low-cost preparation of regenerated cellulose materials, thereby ensuring the promotion and application value of regenerated cellulose materials.

[0098] According to an embodiment of the present invention, in step 5), the mass percentage of the solvent in the filtered aqueous solution is 70-93 wt%, the mass percentage of the water is 5-25 wt%, and the mass percentage of the impurities is less than 5 wt%.

[0099] According to an embodiment of the present invention, in step 5), the filtered aqueous solution is reused in the mixing process for preparing regenerated cellulose materials.

[0100] The present invention further provides a solvent recovery device for preparing regenerated cellulose materials. Specifically, the recovery device is used to implement the above-mentioned recovery method. The recovery device includes a first-stage filtration system, a resin system, a second-stage filtration system, a membrane separation system, a vacuum evaporation system, and a third-stage filtration system arranged in sequence, or includes a first-stage filtration system, a membrane separation system, a resin system, a second-stage filtration system, a vacuum evaporation system, and a third-stage filtration system arranged in sequence.

[0101] According to an embodiment of the present invention, the first-stage filtration system is connected to the second-stage filtration system via a resin system, the second-stage filtration system is connected to the vacuum evaporation system via a membrane separation system, and the vacuum evaporation system is connected to the third-stage filtration system; or the first-stage filtration system is connected to the second-stage filtration system via a membrane separation system and a resin system, the second-stage filtration system is connected to the vacuum evaporation system, and the vacuum evaporation system is connected to the third-stage filtration system.

[0102] According to an embodiment of the present invention, the first-stage filtration system includes a filter, which includes, but is not limited to, at least one of a quartz sand filter, a fiber bundle filter, a Y-type filter, a candle filter, and a bag filter.

[0103] According to an embodiment of the present invention, the resin system is an ion exchange resin, for example, an anion exchange resin.

[0104] According to an embodiment of the present invention, the second-stage filtration system includes a filter, which includes, but is not limited to, at least one of a Y-type filter, a candle filter, and a bag filter.

[0105] According to an embodiment of the present invention, the membrane separation system includes a membrane separator, which includes, but is not limited to, at least one of reverse osmosis membranes, microfiltration membranes, ultrafiltration membranes, and nanofiltration membranes.

[0106] According to an embodiment of the present invention, the third-stage filtration system includes a filter, which includes, but is not limited to, at least one of a centrifuge, a plate and frame filter press, a closed plate filter, and a candle filter.

[0107] The preparation method of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0108] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0109] In the description of this invention, it should be noted that the terms "first," "second," "third," etc., are used for descriptive purposes only and are not intended to indicate or imply relative importance.

[0110] The aqueous solution containing the solvent to be recovered used in the following embodiments comes from the coagulation and washing process of the regenerated cellulose material. The aforementioned aqueous solution containing the solvent to be recovered contains water, solvent, and impurity components. The impurity components include insoluble impurities such as mechanical impurities, grease, and suspended solids, and soluble impurities such as polymers, inorganic compounds, and organic compounds. Specifically, they include regenerated cellulose material fragments, rust and slag, dust particles, equipment lubricating oil, fine sealing materials, undissolved fiber fibers, water-soluble compounds, or small molecule polymers.

[0111] Use a turbidimeter or turbidimeter to measure the turbidity of the aqueous solution containing the solvent to be recovered.

[0112] The solvent concentration of the aqueous solution containing the solvent to be recovered was determined using the refractive index method.

[0113] The moisture content of the concentrated solvent was determined using a fully automated Karl Fischer moisture analyzer.

[0114] Ion chromatography was used to determine the purity of concentrated ionic liquids.

[0115] The color of a solvent aqueous solution of a certain concentration was determined using the platinum-cobalt color number method.

[0116] Example 1

[0117] An aqueous solution of AMIMCl ionic liquid (recovery number 150) from the regenerated cellulose material preparation process, with an ionic liquid concentration of 15 wt% and a turbidity of 12.5 NTU, was prepared at a concentration of 5.8 m... 3 The flow rate, at a rate of [value] / h, passes through a quartz sand filter and then through a 10-micron polypropylene fiber tow filter and a 5-micron candle filter for the first stage of filtration. This first-stage filtration removes macroscopically visible impurities from the aqueous solution containing the ionic liquid to be recovered, such as mechanical impurities, grease, and suspended solids. Specifically, this includes fragments of regenerated cellulose material, rust and slag, dust particles, equipment lubricating oil, fine sealing materials, and undissolved fibers. After the first stage of filtration, 99% of the insoluble impurities in the aqueous solution containing the ionic liquid to be recovered are removed; the turbidity of the resulting ionic liquid aqueous solution is reduced to 3 NTU.

[0118] The ionic liquid aqueous solution after the first stage filtration was then distilled at 5.8 m... 3 A flow rate of [flow rate] / h is introduced into a strongly basic anion exchange resin to remove soluble impurities, including SO42-, from the aqueous solution containing the ionic liquid to be recovered. 2- HCO 3- After resin treatment, 10 wt% of the total soluble impurity components, such as citrate and oxalate, are removed from the aqueous solution containing the ionic liquid to be recovered.

[0119] The resin-treated aqueous solution was sequentially passed through a bag filter with a precision of 50 μm and a candle filter with a precision of 5 microns for secondary filtration. After secondary filtration, suspended solids and impurities in the resin-treated solution were removed, specifically broken resin particles or powder, heavy metal salt precipitates generated by resin exchange, etc. After secondary filtration, 99 wt% of the total insoluble impurities in the resin-treated solution were removed.

[0120] The aqueous solution after the second stage filtration is sequentially passed through a ceramic membrane filter with a precision of 50 / 25 nm, a nanofiltration membrane filter with a precision of 3000 / 1500 / 400D, and a reverse osmosis membrane filter for membrane separation. After membrane separation, most of the high molecular weight substances, including polymers, are removed from the aqueous solution containing the ionic liquid to be recovered. After the membrane separator treatment, 40 wt% of the total soluble impurities in the aqueous solution containing the solvent to be recovered are removed.

[0121] The aqueous solution after membrane separation was subjected to vacuum evaporation using a vapor recompression evaporator. The vacuum evaporation temperature was 92℃, the vacuum degree was 0.08MPa, and the feed flow rate was 5.8m³ / h. 3 / h, discharge flow rate is 1.9m 3 / h, a preliminary concentrated ionic liquid aqueous solution and evaporation condensate are obtained. The concentration of the ionic liquid in the preliminary concentrated ionic liquid aqueous solution is 45wt%, and the water content is 51wt%. It enters the intermediate storage tank and then enters the next reduced pressure evaporation process. The evaporation condensate enters the condensate collection tank and is sent to the regenerated cellulose material washing process for washing the regenerated cellulose materials. It can also be used for soaking waste glue in the waste glue recycling process and for washing equipment containing ionic liquid.

[0122] The pre-concentrated ionic liquid aqueous solution was subjected to reduced-pressure evaporation sequentially using a multi-effect evaporator and a thin-film evaporator. The evaporation temperature in the multi-effect evaporator was 50-100℃, and the vacuum degree was 0.095MPa. The evaporation temperature in the thin-film evaporator was 80-100℃, and the vacuum degree was 0.098MPa. The feed flow rate was 1.9m³ / h. 3 / h, discharge flow rate is 0.95m³ / h. 3 / h, a high-concentration ionic liquid aqueous solution and evaporated condensate are obtained; the high-concentration ionic liquid aqueous solution has an ionic liquid concentration of 90wt% and a water content of 5.0wt%, and enters the pre-filter tank; the evaporated condensate enters the condensate collection tank.

[0123] The high-concentration ionic liquid aqueous solution in the pre-filter tank is sequentially passed through a permeability of 20 L / m³. 2 The polypropylene filter cloth plate and frame filter press of S uses a compound material of 50wt% 200-mesh diatomaceous earth, 30wt% 500-mesh diatomaceous earth and 20wt% 200-mesh decolorizing earth as the filter media in a closed plate filter. A candle filter with a precision of 30μm is used for the third stage of filtration to remove suspended solids and impurities that have been enriched or precipitated during the concentration process and to decolorize the ionic liquid aqueous solution. The resulting ionic liquid has a water content of 5.2wt% and an ionic liquid concentration of 91wt%.

[0124] After the third stage of filtration, impurities accounting for 16 wt% of the total soluble impurities in the aqueous solution containing the solvent to be recovered were removed, and the solvent concentrate was decolorized at the same time; insoluble impurities accounting for more than 99 wt% of the total insoluble impurities in the concentrated solvent aqueous solution were removed.

[0125] The total amount of soluble impurities removed cumulatively accounted for 66 wt% of the total soluble impurities in the aqueous solution containing the solvent to be recovered, and the total amount of insoluble impurities removed cumulatively accounted for 99 wt% of the total insoluble impurities in the aqueous solution containing the solvent to be recovered. A high-concentration ionic liquid aqueous solution meeting the quality requirements was obtained. After being adjusted to the required water content in a mixing tank, it was transported to the mixing process for the preparation of regenerated cellulose materials. The quality indicators of the recovered solvent are shown in Table 1.

[0126] Calculations show that the ionic liquid recovery rate was 99.62%, and the recovery cost was 128 yuan / ton of ionic liquid (referring to the cost of removing water by converting it to the mass of the recovered high-concentration ionic liquid aqueous solution).

[0127] Example 2

[0128] An aqueous solution of AMIMCl ionic liquid (recovery number 805) from the regenerated cellulose material preparation process, with an ionic liquid concentration of 22 wt% and a turbidity of 11 NTU, was prepared at a concentration of 6.9 m... 3 The flow rate, at a rate of [value] / h, passes through a quartz sand filter, then through a 10-micron polypropylene fiber tow filter, a 5-micron candle filter, and a 0.5-micron bag filter for first-stage filtration. This first-stage filtration removes macroscopically visible impurities from the aqueous solution containing the ionic liquid to be recovered, such as mechanical impurities, grease, and suspended solids. Specifically, this includes fragments of regenerated cellulose material, rust and slag, dust particles, equipment lubricating oil, fine sealing materials, and undissolved fibers. After the first-stage filtration, 99 wt% of the insoluble impurities in the aqueous solution containing the solvent to be recovered are removed; at this point, the turbidity of the resulting ionic liquid aqueous solution is reduced to 1.26 NTU.

[0129] The ionic liquid aqueous solution after the first stage filtration was then distilled at 6.9 m... 3 A flow rate of [flow rate] / h is introduced into a strongly basic anion exchange resin to remove soluble impurities, including SO42-, from the aqueous solution containing the ionic liquid to be recovered. 2- HCO 3- After resin treatment, 15 wt% of the total soluble impurities, such as citrate and oxalate, are removed from the aqueous solution containing the solvent to be recovered.

[0130] The resin-treated aqueous solution was sequentially passed through a 120-mesh Y-type filter, a 50μm bag filter, a 5-micron candle filter, and a 0.5μm bag filter for secondary filtration. After secondary filtration, suspended solids and impurities were removed from the resin-treated solution, specifically broken resin particles or powder, and heavy metal salt precipitates generated by resin exchange. After secondary filtration, 99% of the insoluble impurities in the resin-treated solution were removed.

[0131] The aqueous solution after the second stage filtration is sequentially passed through a ceramic membrane filter with a precision of 0.1μm / 50nm, a nanofiltration membrane filter with a precision of 3000 / 1500 / 400D, and a reverse osmosis membrane filter for membrane separation. After membrane separation, most of the high molecular weight substances, including polymers, are removed from the aqueous solution containing the ionic liquid to be recovered. After the membrane separator treatment, impurities accounting for 30wt% of the total soluble impurities in the aqueous solution containing the solvent to be recovered are removed.

[0132] The aqueous solution after membrane separation was subjected to vacuum evaporation using a vapor recompression evaporator. The vacuum evaporation temperature was 78℃, the vacuum degree was 0.088MPa, and the feed flow rate was 6.9m³ / h. 3 / h, discharge flow rate is 2.3m³ / h. 3 / h, a preliminary concentrated ionic liquid aqueous solution and evaporation condensate are obtained. The concentration of the ionic liquid in the preliminary concentrated ionic liquid aqueous solution is 60wt% and the water content is 35wt%. It enters the intermediate storage tank and then enters the next reduced pressure evaporation process. The evaporation condensate enters the condensate collection tank and is sent to the regenerated cellulose material washing process for washing the regenerated cellulose materials. It can also be used for soaking waste glue in the waste glue recycling process and for washing equipment containing ionic liquid.

[0133] The pre-concentrated ionic liquid aqueous solution was subjected to reduced-pressure evaporation using a multi-effect evaporator. The evaporation temperature was 50-100℃, the vacuum degree was 0.098MPa, and the feed flow rate was 2.3m³ / h. 3 / h, discharge flow rate is 1.74m³ / h. 3 / h, a high-concentration ionic liquid aqueous solution and evaporated condensate are obtained; the high-concentration ionic liquid aqueous solution has an ionic liquid concentration of 80wt% and a water content of 14.2wt%, and enters the pre-filter tank; the evaporated condensate enters the condensate collection tank.

[0134] The high-concentration ionic liquid aqueous solution in the pre-filter tank was sequentially passed through a closed plate filter with a composite material of 60wt% 200-mesh diatomaceous earth, 10wt% 500-mesh diatomaceous earth, 5wt% 1000-mesh diatomaceous earth, and 25wt% 150-mesh decolorizing earth as the filter media, and then through a candle filter with a precision of 10μm for third-stage filtration. This process removed suspended solids and impurities that had accumulated or precipitated during the concentration process and decolorized the ionic liquid aqueous solution. The resulting ionic liquid had a water content of 14.6wt% and an ionic liquid concentration of 81.3wt%.

[0135] After the third stage of filtration, impurities accounting for 10 wt% of the total soluble impurities in the aqueous solution containing the solvent to be recovered are removed, and the solvent concentrate is decolorized at the same time; insoluble impurities accounting for more than 99 wt% of the total insoluble impurities in the concentrated solvent aqueous solution are removed.

[0136] The total amount of soluble impurities removed cumulatively accounts for 55 wt% of the total soluble impurities in the aqueous solution containing the solvent to be recovered, and the total amount of insoluble impurities removed cumulatively accounts for 99 wt% of the total insoluble impurities in the aqueous solution containing the solvent to be recovered. A high-concentration ionic liquid aqueous solution meeting the quality requirements is obtained. After being adjusted to the required water content in a mixing tank, it is then transported to the mixing process for the preparation of regenerated cellulose materials. The quality indicators of the recovered solvent are shown in Table 1.

[0137] Calculations show that the ionic liquid recovery rate was 99.59%, and the recovery cost was 119 yuan / ton of ionic liquid (referring to the cost of removing water by converting it to the mass of the recovered high-concentration ionic liquid aqueous solution).

[0138] Example 3

[0139] An aqueous solution of AMIMCl ionic liquid (recovery number 822) from the regenerated cellulose material preparation process, with an ionic liquid concentration of 20 wt% and a turbidity of 14 NTU, was prepared at 7.2 m... 3 The flow rate, at a rate of [value] / h, passes through a quartz sand filter, then through a 5-micron polypropylene fiber tow filter, a 1-micron candle filter, and a 0.5-micron bag filter for the first stage of filtration. This first-stage filtration removes macroscopically visible impurities from the aqueous solution containing the ionic liquid to be recovered, such as mechanical impurities, grease, and suspended solids. Specifically, this includes fragments of regenerated cellulose material, rust and slag, dust particles, equipment lubricating oil, fine sealing materials, and undissolved fibers. After the first stage of filtration, 99 wt% of the insoluble impurities in the aqueous solution containing the solvent to be recovered are removed; at this point, the turbidity of the resulting ionic liquid aqueous solution is reduced to 0.95 NTU.

[0140] The ionic liquid aqueous solution after the first stage filtration was then distilled at 7.2 m... 3 The flow rate is sequentially passed through a ceramic membrane filter with a precision of 50 / 25nm, a nanofiltration membrane filter with a precision of 3000 / 1500 / 400D, and a reverse osmosis membrane filter for membrane separation. After membrane separation, most of the high molecular weight substances, including polymers, are removed from the aqueous solution containing the ionic liquid to be recovered. After the membrane separator treatment, 44wt% of the total soluble impurities in the aqueous solution containing the solvent to be recovered are removed.

[0141] The aqueous solution of the ionic liquid after membrane separation is passed through a weakly basic anion exchange resin to remove soluble impurities, including SO4, from the aqueous solution containing the ionic liquid to be recovered. 2- HCO 3-After resin treatment, 18 wt% of the total soluble impurity components, including citrate and oxalate, are removed from the aqueous solution containing the solvent to be recovered.

[0142] The resin-treated aqueous solution was sequentially passed through a 200-mesh Y-type filter, a candle filter with a precision of 5 micrometers, and a bag filter with a precision of 0.5 μm for secondary filtration. After secondary filtration, suspended solids and impurities in the resin-treated solution were removed, specifically broken resin particles or powder, and heavy metal salt precipitates generated by resin exchange. After secondary filtration, 99% of the insoluble impurities in the resin-treated solution were removed.

[0143] The aqueous solution after the second-stage filtration was subjected to vacuum evaporation using a vapor recompression evaporator. The vacuum evaporation temperature was 85℃, the vacuum degree was 0.084MPa, and the feed flow rate was 7.2m³ / h. 3 / h, discharge flow rate is 2.36m³ / h. 3 / h, a preliminary concentrated ionic liquid aqueous solution and evaporation condensate are obtained. The concentration of the ionic liquid in the preliminary concentrated ionic liquid aqueous solution is 55wt%, and the water content is 39wt%. It enters the intermediate storage tank and then enters the next reduced pressure evaporation process. The evaporation condensate enters the condensate collection tank and is sent to the regenerated cellulose material washing process for washing the regenerated cellulose materials. It can also be used for soaking waste glue in the waste glue recycling process and for washing equipment containing ionic liquid.

[0144] The pre-concentrated ionic liquid aqueous solution was subjected to reduced-pressure evaporation using a multi-effect evaporator. The evaporation temperature was 50-100℃, the vacuum degree was 0.098MPa, and the feed flow rate was 2.36m³ / h. 3 / h, discharge flow rate is 1.6m 3 / h, a high-concentration ionic liquid aqueous solution and evaporated condensate are obtained; the high-concentration ionic liquid aqueous solution has an ionic liquid concentration of 84wt% and a water content of 10.5wt%, and enters the pre-filter tank; the evaporated condensate enters the condensate collection tank.

[0145] The high-concentration ionic liquid aqueous solution in the pre-filter tank was sequentially passed through a closed plate filter with a composite material of 60wt% 200-mesh diatomaceous earth, 10wt% 500-mesh diatomaceous earth, 5wt% 1000-mesh diatomaceous earth, and 25wt% 150-mesh decolorizing earth as filter media, and then through a candle filter with a precision of 10μm for third-stage filtration. This process removed suspended solids and impurities that were enriched or precipitated during the concentration process and decolorized the ionic liquid aqueous solution. The resulting ionic liquid had a water content of 11.1wt% and an ionic liquid concentration of 85wt%.

[0146] After the third stage of filtration, impurities accounting for 8 wt% of the total soluble impurities in the aqueous solution containing the solvent to be recovered were removed, and the solvent concentrate was decolorized at the same time; insoluble impurities accounting for more than 99 wt% of the total insoluble impurities in the concentrated solvent aqueous solution were removed.

[0147] The total amount of soluble impurities removed cumulatively accounts for 70 wt% of the total soluble impurities in the aqueous solution containing the solvent to be recovered, and the total amount of insoluble impurities removed cumulatively accounts for 99 wt% of the total insoluble impurities in the aqueous solution containing the solvent to be recovered. A high-concentration ionic liquid aqueous solution meeting the quality requirements is obtained. After being adjusted to the required water content in a mixing tank, it is then transported to the mixing process for the preparation of regenerated cellulose materials. The quality indicators of the recovered solvent are shown in Table 1.

[0148] Calculations show that the ionic liquid recovery rate was 99.75%, and the recovery cost was 121 yuan / ton of ionic liquid (referring to the cost converted to the mass of water removed by the recovered high-concentration ionic liquid aqueous solution).

[0149] Comparative Example 1

[0150] The other operations are the same as in Example 1, except that the high-concentration ionic liquid aqueous solution (ionic liquid concentration of 90 wt% and water content of 5.0 wt%) that has not undergone third-stage filtration is directly injected into the mixing tank and mixed to the required water content before being transported to the mixing process for the preparation of regenerated cellulose materials. The quality indicators of the recovered solvent are shown in Table 1.

[0151] Calculations show that the recovery rate of this portion of ionic liquid is 99.65%, and the recovery cost is 127.8 yuan / ton of ionic liquid (referring to the cost converted to the mass of water removed by the recovered high-concentration ionic liquid aqueous solution).

[0152] When this batch of ionic liquid was used in the preparation of regenerated cellulose materials, the pressure difference of the sol filter increased rapidly, indicating that the sol filter was clogged. The service life of this filter was only 3.5 days. Similarly, under the operation of Examples 1 and 2, the service life of the sol filter in the preparation of regenerated cellulose materials was 42 days and 45 days, respectively.

[0153] Table 1: Detection Indicators of Ionic Liquids in Examples and Comparative Examples

[0154]

[0155] Figure 2 This is an optical image of the mixed solution after the ionic liquid recovered from Example 1 dissolved cellulose. Figure 3 This is an optical image of the mixed solution after the ionic liquid recovered from Example 2 dissolved cellulose. Figure 4This is an optical image of the mixed solution after the ionic liquid recovered from Example 3 dissolved cellulose. Figure 5 The image shows an optical image of the mixed solution after cellulose was dissolved by the ionic liquid recovered in Comparative Example 1. It can be seen that the ionic liquid recovered in Comparative Example 1 showed poorer solubility of cellulose, while the ionic liquids recovered in Examples 1, 2, and 3 showed normal solubility of cellulose.

[0156] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering solvents used in the preparation of regenerated cellulose materials, characterized in that, The recycling method includes the following steps: 1) The aqueous solution containing the solvent for preparing regenerated cellulose material to be recycled is subjected to first-stage filtration; 2) The aqueous solution after the first stage filtration in step 1) is treated with resin and then subjected to a second stage filtration; 3) Perform membrane separation on the aqueous solution after the second-stage filtration in step 2); 4) The aqueous solution after membrane separation in step 3) is evaporated under reduced pressure to obtain an aqueous solution containing concentrated solvent and evaporated condensate; 5) The aqueous solution containing concentrated solvent from step 4) is subjected to a third-stage filtration, and the filtered aqueous solution is reused in the process of preparing regenerated cellulose materials. Alternatively, the recycling method may include the following steps: 1) The aqueous solution containing the solvent for preparing regenerated cellulose material to be recycled is subjected to first-stage filtration; 2') Perform membrane separation on the aqueous solution after the first-stage filtration in step 1); 3') The aqueous solution after membrane separation in step 2') is treated with resin and then subjected to a second-stage filtration; 4') The aqueous solution after the second-stage filtration in step 3') is evaporated under reduced pressure to obtain an aqueous solution containing concentrated solvent and evaporated condensate; 5) The aqueous solution containing concentrated solvent from step 4') is subjected to a third-stage filtration, and the filtered aqueous solution is reused in the process of preparing regenerated cellulose materials. The filters used in the third stage of filtration include at least one of centrifuges, plate and frame filter presses, closed plate filters, and candle filters; The first stage of filtration is a combination of multiple filters. The filtration accuracy of the multiple filters is set from low to high according to the material flow direction. The material is passed in sequence into a polypropylene fiber tow filter with an accuracy of 10 microns, a candle filter with an accuracy of 5 microns, and a bag filter with an accuracy of 0.5 microns. The second stage of filtration uses a combination of multi-stage filters. The filtration accuracy of the multi-stage filters is set from low to high according to the material flow direction. The material is passed through a bag filter with an accuracy of 50μm and a candle filter with an accuracy of 5 microns in sequence; or through a Y-type filter with a 120-mesh filter, a bag filter with an accuracy of 50μm, a candle filter with an accuracy of 5 microns, and a bag filter with an accuracy of 0.5μm. The third stage of filtration involves a combination of multiple filters. The filtration precision of the multiple filters is set from low to high according to the material flow direction, and the air permeability is 10-40 L / m³ for each stage. 2 • S's polypropylene filter cloth plate and frame filter press, closed plate filter, candle filter with a precision of 30μm, or closed plate filter, candle filter with a precision of 10μm; The reduced pressure evaporation is carried out in an evaporator, which includes at least one of a multi-effect evaporator, a rising film evaporator, a falling film evaporator, a vapor recompression evaporator, and a thin film evaporator; for aqueous solutions with a water content ≥40%, at least one of a multi-effect evaporator, a rising film evaporator, a falling film evaporator, and a vapor recompression evaporator is used; for aqueous solutions with a water content <40%, at least one of a multi-effect evaporator, a rising film evaporator, a falling film evaporator, and a thin film evaporator is used. The temperature of the vacuum evaporation is 50-100℃; the vacuum degree of the vacuum evaporation is 0.05-0.099MPa. In step 5), the filtered aqueous solution contains 70-93 wt% solvent, 5-25 wt% water, and less than 5 wt% impurities.

2. The recycling method according to claim 1, characterized in that, In step 2) or step 3'), the resin is an ion exchange resin.

3. The recycling method according to claim 1, characterized in that, In step 3) or step 2'), the membrane separation is performed using a membrane separator, which includes at least one of reverse osmosis membrane, microfiltration membrane, ultrafiltration membrane and nanofiltration membrane.

4. The recycling method according to any one of claims 1-3, characterized in that, The membrane separation is achieved through a ceramic membrane filter with a precision of 0.1 μm / 50 nm, a nanofiltration membrane filter with a precision of 3000 / 1500 / 400D, or a reverse osmosis membrane filter; or through a ceramic membrane filter with a precision of 50 / 25 nm, a nanofiltration membrane filter with a precision of 3000 / 1500 / 400D, or a reverse osmosis membrane filter.

5. A solvent recovery device for preparing regenerated cellulose materials, the recovery device being used to implement the recovery method according to any one of claims 1-4, the recovery device comprising a first-stage filtration system, a resin system, a second-stage filtration system, a membrane separation system, a vacuum evaporation system, and a third-stage filtration system arranged in sequence, or the recovery device comprising a first-stage filtration system, a membrane separation system, a resin system, a second-stage filtration system, a vacuum evaporation system, and a third-stage filtration system arranged in sequence; The first-stage filtration system uses a combination of multi-stage filters. The filtration accuracy of the multi-stage filters is set from low to high according to the material flow direction. The material is sequentially passed through a polypropylene fiber tow filter with an accuracy of 10 microns, a candle filter with an accuracy of 5 microns, and a bag filter with an accuracy of 0.5 microns. The second-stage filtration system uses a combination of multi-stage filters. The filtration accuracy of the multi-stage filters is set from low to high according to the material flow direction. The material is passed through a bag filter with an accuracy of 50μm and a candle filter with an accuracy of 5 microns in sequence; or through a Y-type filter with a 120-mesh filter, a bag filter with an accuracy of 50μm, a candle filter with an accuracy of 5 microns, and a bag filter with an accuracy of 0.5μm. The third-stage filtration system uses a combination of multi-stage filters. The filtration precision of the multi-stage filters is set from low to high according to the material flow direction, and the air permeability of the material is sequentially introduced at 10-40 L / m³. 2 • S's polypropylene filter cloth plate and frame filter press, closed plate filter, candle filter with a precision of 30μm, or closed plate filter, candle filter with a precision of 10μm.

6. The recycling device according to claim 5, characterized in that, The first-stage filtration system is connected to the second-stage filtration system via a resin system, the second-stage filtration system is connected to the vacuum evaporation system via a membrane separation system, and the vacuum evaporation system is connected to the third-stage filtration system. Alternatively, the first-stage filtration system is connected to the second-stage filtration system via a membrane separation system and a resin system, the second-stage filtration system is connected to a reduced-pressure evaporation system, and the reduced-pressure evaporation system is connected to the third-stage filtration system.

7. The recycling device according to claim 5 or 6, characterized in that, The resin system is an ion exchange resin.

8. The recycling device according to claim 5 or 6, characterized in that, The membrane separation system includes a membrane separator, which includes at least one of reverse osmosis membrane, microfiltration membrane, ultrafiltration membrane and nanofiltration membrane.

9. The recycling device according to claim 8, characterized in that, The membrane separation is achieved through a ceramic membrane filter with a precision of 0.1 μm / 50 nm, a nanofiltration membrane filter with a precision of 3000 / 1500 / 400D, or a reverse osmosis membrane filter; or through a ceramic membrane filter with a precision of 50 / 25 nm, a nanofiltration membrane filter with a precision of 3000 / 1500 / 400D, or a reverse osmosis membrane filter.

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