A method for recovering and reusing solvent from a regenerated cellulosic material production process

Abstract

The application provides a method for recycling and reusing solvents in a regenerated cellulose material production process, comprising: performing rough filtration on waste liquid generated in the regenerated cellulose material production process to obtain a rough filtrate; treating the rough filtrate with an anion ion exchange resin to obtain an eluate; passing the eluate through a multi-stage series membrane filtration platform to remove micro-nano impurities in the eluate, while separating tetrabutylammonium hydroxide, dimethyl sulfoxide and water, to obtain recovered tetrabutylammonium hydroxide, recovered dimethyl sulfoxide and recovered pure water; and mixing the recovered tetrabutylammonium hydroxide and the recovered dimethyl sulfoxide in a certain proportion and then using them for the production of regenerated cellulose fibers. The method is simple in operation, low in energy consumption and green in environment protection, and realizes efficient and low-cost recycling and reuse of tetrabutylammonium hydroxide solvent and dimethyl sulfoxide solvent.

Description

Technical Field

[0001] This invention belongs to the field of cellulose production and processing technology, and specifically relates to a method for recovering and reusing solvents from the production process of regenerated cellulose materials. Background Technology

[0002] Cellulose, a natural, green, and biodegradable environmentally friendly material, is made from inexhaustible agricultural and forestry biomass. It is primarily used in the production of textile fibers (regenerated cellulose materials), whose fabrics possess excellent abrasion resistance, moisture absorption, breathability, and antibacterial properties. However, traditional regenerated cellulose material production processes involve large quantities of hazardous chemicals such as caustic soda, sulfuric acid, and carbon disulfide, which severely corrode equipment and cause numerous production disruptions. Sulfur-containing toxic waste gases and large amounts of zinc-containing wastewater also pose a serious threat to the health of workers. Therefore, green, efficient, and environmentally friendly cellulose solvents, such as alkyl quaternary ammonium bases / water-dimethyl sulfoxide, ionic liquids, and N-methylmorpholine oxide, have been developed and their applications in cellulose spinning processes can effectively prevent the release of toxic substances during the production of regenerated cellulose materials.

[0003] Chinese patent CN104710627B discloses a process for improving the solubility of cellulose in tetrabutylammonium hydroxide aqueous solution, demonstrating that the tetrabutylammonium hydroxide-water solvent system can rapidly dissolve natural cellulose at room temperature. Chinese patent CN105801883B discloses a method for preparing cellulose solutions, which promotes the mild dissolution of cellulose at room temperature by adding co-solvents such as dimethyl sulfoxide to an organic base-water solvent system represented by tetrabutylammonium hydroxide. The resulting cellulose solution can be used to prepare regenerated cellulose fibers, regenerated cellulose membranes, cellulose-based composite materials, and other materials. The production process of regenerated cellulose materials generally uses water or dilute sulfuric acid as a coagulation bath. The coagulation bath waste liquid after producing regenerated cellulose materials according to this process contains cellulose residue, regenerated cellulose, hair, tetrabutylammonium hydroxide, water, dimethyl sulfoxide, acid radicals, colored impurities, and other components. For environmental protection and cost control considerations, it is necessary to recover and recycle the solvents generated during the production of regenerated cellulose fibers.

[0004] Solvent recovery rate not only determines the production cost of cellulose materials but also directly affects the environmental friendliness of the production process. Chinese patent CN108467347A discloses a method for recovering tetrabutylammonium hydroxide by electrolyzing a tetrabutylammonium sulfate solution, which involves bipolar membrane electrodialysis of the tetrabutylammonium sulfate aqueous solution in a four-compartment electrodialysis device. This process has high processing costs and energy consumption. Chinese patent CN117658874A discloses a method for recovering dimethyl sulfoxide from polyacrylonitrile waste slurry, which recovers dimethyl sulfoxide through filtration and double-effect high-temperature distillation. However, this method also has high processing costs and energy consumption. Cellulose spinning and membrane material forming based on a tetrabutylammonium hydroxide / water / dimethyl sulfoxide solvent system is a novel environmentally friendly process. The solvent recovery processes for tetrabutylammonium hydroxide and dimethyl sulfoxide reported in the aforementioned literature and patents are unsuitable for coagulation bath waste liquid systems containing complex components such as cellulose residue, regenerated cellulose, hair, tetrabutylammonium hydroxide, dimethyl sulfoxide, acid radicals, and colored impurities.

[0005] Therefore, there is an urgent need for a process to recover tetrabutylammonium hydroxide, dimethyl sulfoxide, and water from the coagulation bath waste liquid generated during the production of regenerated cellulose materials. Achieving low-energy consumption, low-cost, rapid, and efficient recovery of tetrabutylammonium hydroxide, dimethyl sulfoxide, and water is crucial for the industrialization of regenerated cellulose materials. Summary of the Invention

[0006] To address the issues of high energy consumption and high cost in existing tetrabutylammonium hydroxide and dimethyl sulfoxide recovery processes, this invention provides a method for recovering and reusing solvents from the production process of regenerated cellulose materials. This method is simple to operate, has low energy consumption, and is environmentally friendly, achieving efficient and low-cost recovery of tetrabutylammonium hydroxide and dimethyl sulfoxide.

[0007] This invention is achieved through the following technical solution:

[0008] This invention provides a method for recovering and reusing solvents from the production process of regenerated cellulose materials, the method comprising:

[0009] (1) The waste liquid generated during the production of regenerated cellulose materials is subjected to coarse filtration to remove micron-sized suspended impurities in the waste liquid and obtain coarse filtrate;

[0010] (2) The coarse filtrate is treated with an anion exchange resin to remove acid radicals and colored macromolecules from the coarse filtrate to obtain an eluent.

[0011] (3) The eluent is passed through a multi-stage series membrane filtration platform to remove micro- and nano-sized impurities in the eluent, while separating tetrabutylammonium hydroxide, dimethyl sulfoxide and water to obtain recovered tetrabutylammonium hydroxide, recovered dimethyl sulfoxide and recovered pure water;

[0012] (4) The recycled tetrabutylammonium hydroxide and the recycled dimethyl sulfoxide are mixed in proportion and used to dissolve plant cellulose to obtain a cellulose solution. After degassing, filtration and spinning, the solution is then subjected to multi-stage stretching and molding in a coagulation bath prepared by the recycled pure water and sulfuric acid. After oiling and drying, the solution is used for the production of regenerated cellulose fibers.

[0013] Furthermore, the coarse filtration treatment of the waste liquid generated during the production of regenerated cellulose materials to remove micron-sized suspended impurities and obtain coarse filtrate specifically includes:

[0014] The waste liquid generated during the production of regenerated cellulose materials is passed through a filter screen with a pore size of 300-800 mesh to remove micron-sized suspended impurities in the waste liquid and obtain coarse filtrate.

[0015] The waste liquid includes coagulation bath waste liquid and / or water bath waste liquid.

[0016] Furthermore, the step of subjecting the coarse filtrate to ion exchange treatment to remove acid radicals and colored macromolecules from the coarse filtrate to obtain an eluent specifically includes:

[0017] The coarse filtrate is subjected to ion exchange resin treatment to remove acid radicals and colored macromolecules from the coarse filtrate, thereby obtaining an eluent.

[0018] In the ion exchange treatment, the type of ion exchange resin includes at least one of styrene-based, acrylic-based, acetic acid-based, epoxy-based, and urea-formaldehyde-based resins.

[0019] The ion exchange resin carries at least one of the following groups: quaternary ammonium, primary ammonium, secondary ammonium, and tertiary ammonium.

[0020] The ion exchange resin has a particle size of 20-60 mesh and is packed in an amount of 0.3-0.9 times the volume of the exchange column.

[0021] In the ion exchange process, the flow rate of the coarse filtrate is 4 to 12 times the volume of the resin bed per hour.

[0022] Furthermore, the step of passing the eluent through a tandem membrane platform to remove micro- and nano-sized impurities from the eluent, while simultaneously separating tetrabutylammonium hydroxide, dimethyl sulfoxide, and water to obtain recovered tetrabutylammonium hydroxide, recovered dimethyl sulfoxide, and recovered pure water, specifically includes:

[0023] The eluent is passed through a series membrane platform at room temperature and a pressure of 0.2–1 MPa to remove micro- and nano-sized impurities from the eluent, while simultaneously separating tetrabutylammonium hydroxide, dimethyl sulfoxide, and water to obtain recovered tetrabutylammonium hydroxide, recovered dimethyl sulfoxide, and recovered pure water.

[0024] Furthermore, the tandem membrane platform includes any one of the following a) to f):

[0025] a) It is composed of microfiltration membrane, ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane connected in series in a membrane area ratio of 1:1:62:250;

[0026] b) It is composed of microfiltration membrane, nanofiltration membrane and reverse osmosis membrane connected in series with a membrane area ratio of 1:250:250;

[0027] c) It is composed of ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane connected in series with a membrane area ratio of 1:150:300;

[0028] d) It is composed of microfiltration membrane, ultrafiltration membrane and nanofiltration membrane connected in series in a membrane area ratio of 1:1:62;

[0029] e) It is composed of microfiltration membranes and nanofiltration membranes connected in series with a membrane area ratio of 1:250;

[0030] f) It is composed of ultrafiltration membranes and nanofiltration membranes connected in series with a membrane area ratio of 1:150;

[0031] The microfiltration membrane has a pore size of 0.1–10 μm, and the ultrafiltration membrane has a pore size of 0.001–0.1 μm.

[0032] The tandem membrane platforms are connected in series or parallel-series configurations according to the membrane area ratio.

[0033] Preferably, the series membrane platform is composed of microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes connected in series with a membrane area ratio of 1:1:62:250. Specifically, each series membrane consists of microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membrane modules connected in a 1:1:N1:N2 ratio with a membrane area ratio of 1:1:62:250. When N(1-2) = 1, the membrane area ratio of the microfiltration membrane, ultrafiltration membrane, nanofiltration membrane, and reverse osmosis membrane module is 1:1:62:250. When N(1-2) > 1, the membrane modules within the nanofiltration membrane and reverse osmosis membrane units are connected in parallel and then connected in series with the microfiltration membrane and ultrafiltration membrane to form a parallel-series integrated membrane platform. The total membrane area ratio of the microfiltration membrane unit, ultrafiltration membrane unit, nanofiltration membrane unit, and reverse osmosis membrane unit is 1:1:62:250.

[0034] Furthermore, when the tandem membrane platform includes any one of a) to b) or d) to e), the eluent first passes through the microfiltration membrane in a cross-flow filtration manner;

[0035] When the tandem membrane platform includes c) or f), the eluent first passes through the ultrafiltration membrane in a cross-flow filtration manner.

[0036] When the tandem membrane platform includes any one of a) to c), the nanofiltration membrane retrieval end yields tetrabutylammonium hydroxide, the reverse osmosis membrane retrieval end yields dimethyl sulfoxide, and the reverse osmosis membrane permeation end yields pure water.

[0037] When the tandem membrane platform includes any one of d) to f), the nanofiltration membrane retrieval end yields tetrabutylammonium hydroxide, and the nanofiltration membrane permeation end yields a dimethyl sulfoxide aqueous solution.

[0038] Furthermore, the material of the microfiltration membrane includes at least one of polypropylene, zirconium oxide ceramic, titanium oxide ceramic, alumina ceramic, zirconium oxide hybrid ceramic, titanium oxide hybrid ceramic, and alumina hybrid ceramic.

[0039] The material of the ultrafiltration membrane includes at least one of zirconia ceramic, titanium oxide ceramic, alumina ceramic, zirconia hybrid ceramic, titanium oxide hybrid ceramic, and alumina hybrid ceramic.

[0040] The nanofiltration membrane includes an inorganic hybrid nanofiltration membrane with a molecular weight cutoff of 80–300 Da;

[0041] The reverse osmosis membrane includes an inorganic hybrid reverse osmosis membrane with a molecular weight cutoff of 40–70 Da.

[0042] Furthermore, the recovered tetrabutylammonium hydroxide and the new tetrabutylammonium hydroxide reagent are mixed at a mass ratio of 1:(0-30) to obtain a plant cellulose solvent with a tetrabutylammonium hydroxide concentration of 55±5wt%, which is used for dissolving plant cellulose and for spinning applications.

[0043] or

[0044] The recovered dimethyl sulfoxide is mixed with recovered tetrabutylammonium hydroxide (and / or neotetrabutylammonium hydroxide reagent) to obtain a plant cellulose solvent with a mass ratio of dimethyl sulfoxide:tetrabutylammonium hydroxide:water of (0.2-8):1:1, which is used for dissolving plant cellulose and for spinning applications.

[0045] The sulfuric acid and recycled pure water are mixed at a mass ratio of 1:(1.5-19) to obtain a 5wt%-40wt% H2SO4 coagulation bath, which is used for the spinning of plant cellulose.

[0046] The new tetrabutylammonium hydroxide reagent is an analytical grade tetrabutylammonium hydroxide aqueous solution with a concentration of 41-70 wt%.

[0047] The sulfuric acid is concentrated sulfuric acid with a concentration of 98 wt%.

[0048] Furthermore, after dissolving plant cellulose in the prepared cellulose solvent to obtain a cellulose solution, the solution is degassed, filtered, and spun. Then, it is subjected to multi-stage stretching and forming in a coagulation bath prepared with recycled pure water and sulfuric acid. After oiling and drying, it is used for the production of regenerated cellulose fibers.

[0049] Preferably, the components of the microfiltration membrane and the ultrafiltration membrane are tubular or plate and frame type, the microfiltration membrane has a filtration accuracy of 0.1 to 10 μm, and the ultrafiltration membrane has a filtration accuracy of 0.001 to 0.1 μm.

[0050] More preferably, the microfiltration membrane is a zirconia hybrid ceramic membrane, a titanium oxide hybrid ceramic membrane, or an alumina hybrid ceramic membrane, with a filtration accuracy of 1 to 5 μm, and the ultrafiltration membrane is a zirconia hybrid ceramic membrane, a titanium oxide hybrid ceramic membrane, or an alumina hybrid ceramic membrane, with a filtration accuracy of 0.01 to 0.1 μm.

[0051] Preferably, the microfiltration membrane, the ultrafiltration membrane, the nanofiltration membrane, and the reverse osmosis membrane all employ cross-flow filtration.

[0052] Based on the same inventive concept, the present invention provides a recovered tetrabutylammonium hydroxide and dimethyl sulfoxide, wherein the recovered tetrabutylammonium hydroxide and dimethyl sulfoxide are prepared by the above-mentioned method for recovering and reusing solvents from the production process of regenerated cellulose materials.

[0053] Based on the same inventive concept, the present invention also provides the use of recovered tetrabutylammonium hydroxide and dimethyl sulfoxide as solvents for the preparation of plant cellulose.

[0054] Optionally, the application includes:

[0055] The recovered tetrabutylammonium hydroxide and the new tetrabutylammonium hydroxide reagent were mixed at a mass ratio of 1:(0-30) to obtain a plant cellulose solvent with a tetrabutylammonium hydroxide concentration of 55±5wt%.

[0056] The recovered dimethyl sulfoxide was mixed with recovered tetrabutylammonium hydroxide (and / or neotetrabutylammonium hydroxide reagent) to obtain a plant cellulose solvent with a mass ratio of dimethyl sulfoxide:tetrabutylammonium hydroxide:water of (0.2-8):1:1.

[0057] The sulfuric acid and recycled pure water are mixed at a mass ratio of 1:(1.5-19) to obtain a 5wt%-40wt% H2SO4 coagulation bath;

[0058] The new tetrabutylammonium hydroxide reagent is an analytical grade tetrabutylammonium hydroxide aqueous solution with a concentration of 41-70 wt%.

[0059] The sulfuric acid is concentrated sulfuric acid with a concentration of 98 wt%.

[0060] The recovered tetrabutylammonium hydroxide and dimethyl sulfoxide are mixed in a certain proportion and used to dissolve plant cellulose (cellulose pulp) to obtain a cellulose solution. After degassing, filtration and spinning, the solution is then subjected to multi-stage stretching and molding in a coagulation bath made of recovered pure water and sulfuric acid. After oiling and drying, it is used for the production of regenerated cellulose fibers.

[0061] The plant cellulose includes any one of cotton cellulose, softwood cellulose, hardwood cellulose, and bamboo cellulose.

[0062] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0063] 1. This invention discloses a method for recovering and reusing solvents from the production process of regenerated cellulose materials. The method employs coarse filtration, ion exchange resin treatment, and tandem membrane treatment to sequentially remove visible suspended impurities (cellulose residues and hair, etc.), acid radicals, colored macromolecular impurities, and micro / nano-scale impurities from the waste liquid. This achieves the separation, purification, and concentration of tetrabutylammonium hydroxide, dimethyl sulfoxide, and water. Furthermore, the method uses a cross-flow filtration process to treat the waste liquid through tandem membranes, which improves the service life of the membrane materials and reduces the cost of waste liquid recovery. This method is simple to operate, has high recovery efficiency, low energy consumption, and is environmentally friendly, achieving efficient and low-cost recovery of tetrabutylammonium hydroxide, dimethyl sulfoxide, and water.

[0064] 2. This invention discloses a method for recovering and reusing solvents from the production process of regenerated cellulose materials. The method is based on tandem integrated membrane technology to separate, purify, and concentrate tetrabutylammonium hydroxide, dimethyl sulfoxide, and water. The process includes coarse filtration, ion exchange resin exchange, and membrane treatment. The integrated membrane platform is preferably composed of microfiltration membrane, ultrafiltration membrane, nanofiltration membrane, and reverse osmosis membrane connected in series with a membrane area ratio of 1:1:62:250. This method overcomes the shortcomings of existing methods for recovering tetrabutylammonium hydroxide and dimethyl sulfoxide solvents, such as high energy consumption and low stability.

[0065] 3. This invention provides a method for recovering and reusing solvents from the production process of regenerated cellulose materials. After processing using this method, a 50wt% tetrabutylammonium hydroxide aqueous solution and a 94wt% dimethyl sulfoxide solution can be obtained. Both solutions, after reconfiguration, can dissolve various plant celluloses at room temperature. The resulting cellulose solution can be spun to obtain regenerated cellulose fibers with excellent mechanical properties, achieving closed-loop solvent utilization. Furthermore, this method can separate and purify 28–35wt% water from the waste liquid, which can be recycled for the coagulation regeneration and washing processes of regenerated cellulose materials, improving the utilization rate of water and chemical raw materials, and reducing chemical emissions and environmental pollution. Attached Figure Description

[0066] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0067] Figure 1 This is a process flow diagram for solvent recovery during the production of regenerated cellulose materials.

[0068] Figure 2 Comparative liquid chromatograms for the recovery of tetrabutylammonium hydroxide and dimethyl sulfoxide and their corresponding standard substances.

[0069] Figure 3 Optical images for the recovery of tetrabutylammonium hydroxide and dimethyl sulfoxide.

[0070] Figure 4 Infrared (FTIR) spectra for the recovery of tetrabutylammonium hydroxide and dimethyl sulfoxide.

[0071] Figure 5 Nuclear magnetic resonance (NMR) analysis for the recovery of tetrabutylammonium hydroxide and dimethyl sulfoxide 1 1H-NMR spectrum. Detailed Implementation

[0072] The present invention will be described in detail below with reference to specific embodiments and examples, thereby making the advantages and various effects of the present invention more clearly apparent. Those skilled in the art should understand that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the present invention.

[0073] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0074] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0075] The technical principle of this invention is as follows:

[0076] This invention discloses a method for recovering and reusing solvents from the production process of regenerated cellulose materials, the method comprising:

[0077] S1. The waste liquid generated during the production of regenerated cellulose materials is subjected to coarse filtration to remove micron-sized suspended impurities in the waste liquid and obtain coarse filtrate;

[0078] S2. The coarse filtrate is treated with an anion exchange resin to remove acid radicals and colored macromolecules from the coarse filtrate, thereby obtaining an eluent.

[0079] S3. The eluent is passed through a multi-stage tandem membrane filtration platform to remove micro- and nano-sized impurities from the eluent, while separating effective components such as tetrabutylammonium hydroxide, dimethyl sulfoxide, and water to obtain recovered tetrabutylammonium hydroxide, dimethyl sulfoxide, and pure water.

[0080] S4. The recovered tetrabutylammonium hydroxide and the recovered dimethyl sulfoxide are mixed in a certain proportion and used to dissolve plant cellulose (cellulose pulp) to obtain a cellulose solution. After degassing, filtration and spinning, the solution is then subjected to multi-stage stretching and forming in a coagulation bath prepared by the recovered pure water and sulfuric acid. After oiling and drying, the solution is used for the production of regenerated cellulose fibers.

[0081] Step S1 specifically includes:

[0082] The waste liquid generated during the production of regenerated cellulose materials is passed through a filter screen with a pore size of 300 to 800 mesh to remove micron-sized suspended impurities from the waste liquid and obtain coarse filtrate.

[0083] Optionally, the waste liquid includes coagulation bath waste liquid and / or water bath waste liquid.

[0084] In this invention, passing the waste liquid through a filter screen with a pore size of 300 to 800 mesh can remove micron-sized suspended impurities, such as cellulose residue and hair, from the waste liquid.

[0085] Step S2 specifically includes:

[0086] The coarse filtrate is treated with an anion exchange resin to remove acid radicals and colored macromolecules, thereby obtaining an eluent.

[0087] In the ion exchange treatment, the type of ion exchange resin includes at least one of styrene-based, acrylic-based, acetic acid-based, epoxy-based, and urea-formaldehyde-based resins.

[0088] The ion exchange resin carries at least one of the following groups: quaternary ammonium, primary ammonium, secondary ammonium, and tertiary ammonium.

[0089] The ion exchange resin has a particle size of 20-60 mesh and is packed in an amount of 0.3-0.9 times the volume of the exchange column.

[0090] In the ion exchange process, the flow rate of the coarse filtrate is 4 to 12 times the volume of the resin bed per hour.

[0091] In this invention, passing the coarse filtrate through an exchange column packed with the aforementioned ion exchange resin can remove acid radicals and colored macromolecules from the coarse filtrate.

[0092] In this invention, the ion exchange resin carries at least one of quaternary ammonium groups, primary ammonium groups, secondary ammonium groups, and tertiary ammonium groups, which provides the benefits of adsorbing acid radical ions and adjusting the pH value of the eluent.

[0093] Step S3 specifically includes:

[0094] The eluent is passed through a series membrane platform at room temperature and a pressure of 0.2–1 MPa to remove micro- and nano-sized impurities from the eluent, while simultaneously separating tetrabutylammonium hydroxide, dimethyl sulfoxide, and water to obtain recovered tetrabutylammonium hydroxide, recovered dimethyl sulfoxide, and pure water.

[0095] In this invention, the eluent is passed through a series membrane platform at room temperature and a pressure of 0.2–1 MPa to remove micro- and nano-sized impurities (including micron- and nano-sized regenerated cellulose impurities) from the eluent, and to separate effective components such as tetrabutylammonium hydroxide, dimethyl sulfoxide, and water, to obtain a tetrabutylammonium hydroxide solution with a concentration of 30–50 wt%, and recovered dimethyl sulfoxide and pure water with a concentration of 80–95 wt%.

[0096] Furthermore, the tandem membrane platform includes any one of the following a) to f):

[0097] a) It is composed of microfiltration membrane, ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane connected in series in a membrane area ratio of 1:1:62:250;

[0098] b) It is composed of microfiltration membrane, nanofiltration membrane and reverse osmosis membrane connected in series with a membrane area ratio of 1:250:250;

[0099] c) It is composed of ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane connected in series with a membrane area ratio of 1:150:300;

[0100] d) It is composed of microfiltration membrane, ultrafiltration membrane and nanofiltration membrane connected in series in a membrane area ratio of 1:1:62;

[0101] e) It is composed of microfiltration membranes and nanofiltration membranes connected in series with a membrane area ratio of 1:250;

[0102] f) It is composed of ultrafiltration membranes and nanofiltration membranes connected in series with a membrane area ratio of 1:150;

[0103] The microfiltration membrane has a pore size of 0.1–10 μm, and the ultrafiltration membrane has a pore size of 0.001–0.1 μm.

[0104] In the process of processing the eluent, the present invention uses a microfiltration membrane to retain impurities larger than 0.1 μm; an ultrafiltration membrane to retain impurities larger than 0.01 μm; a nanofiltration membrane to separate tetrabutylammonium hydroxide from small molecules smaller than 80–300 Da (e.g., dimethyl sulfoxide, water) to obtain recovered tetrabutylammonium hydroxide; and a reverse osmosis membrane to separate dimethyl sulfoxide from small molecules smaller than 40–70 Da (e.g., water) to obtain recovered dimethyl sulfoxide and pure water.

[0105] In this invention, the advantage of connecting microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes in series or parallel-series configurations with a membrane area ratio of 1:1:62:250 ensures that the liquid flow rate through each membrane is comparable, guaranteeing the stable and reliable operation of the series membrane platform in optimal condition. This reduces membrane failures caused by flow fluctuations and improves the overall wastewater treatment efficiency of the series membrane platform. Appropriate flow rates also help reduce impurity accumulation on the membrane surface, prevent membrane pore blockage, reduce membrane wear and mechanical stress, and extend membrane lifespan.

[0106] Furthermore, the material of the microfiltration membrane includes at least one of polypropylene, zirconium oxide ceramic, titanium oxide ceramic, alumina ceramic, zirconium oxide hybrid ceramic, titanium oxide hybrid ceramic, and alumina hybrid ceramic.

[0107] The material of the ultrafiltration membrane includes at least one of zirconia ceramic, titanium oxide ceramic, alumina ceramic, zirconia hybrid ceramic, titanium oxide hybrid ceramic, and alumina hybrid ceramic.

[0108] The nanofiltration membrane includes an inorganic hybrid nanofiltration membrane with a molecular weight cutoff of 80–300 Da;

[0109] The reverse osmosis membrane includes an inorganic hybrid reverse osmosis membrane with a molecular weight cutoff of 40–70 Da.

[0110] In this invention, the nanofiltration membrane and reverse osmosis membrane are made of inorganic hybrid materials, which are resistant to alkalis and solvents, have higher stability, and better durability.

[0111] This invention discloses a method for recovering and reusing solvents from the production process of regenerated cellulose materials. The method employs three processes: coarse filtration, ion exchange resin exchange, and tandem membrane platform treatment. These processes sequentially remove visible suspended impurities (cellulose residues and hair, etc.), acid radicals, colored macromolecular impurities, and micron- and nano-sized regenerated cellulose impurities from the waste liquid. Simultaneously, by utilizing the difference between the pore size of nanofiltration membranes and reverse osmosis membranes and the size of solvent molecules in the solution, tetrabutylammonium hydroxide, dimethyl sulfoxide, and water are efficiently separated, achieving the purification and concentration of tetrabutylammonium hydroxide and dimethyl sulfoxide.

[0112] Step S4 specifically includes:

[0113] The recovered tetrabutylammonium hydroxide and dimethyl sulfoxide are mixed in a certain proportion to dissolve plant cellulose (cellulose pulp) to obtain a cellulose solution. After degassing, filtration and spinning, the solution is traction-formed in a 5wt% to 35wt% H2SO4 coagulation bath, oiled and dried, and then used for the production of regenerated cellulose fibers.

[0114] The process of this invention is simple to operate, has high recovery efficiency, low energy consumption, and the recovered solvent has good solubility for various plant celluloses, and realizes the spinning production of regenerated cellulose.

[0115] The following will describe in detail a method for recovering and reusing solvents from the production process of regenerated cellulose materials according to this application, in conjunction with embodiments and experimental data.

[0116] Example 1

[0117] This embodiment describes a method for recovering and reusing solvents from the production process of regenerated cellulose materials, including:

[0118] 1) The waste liquid consisting of coagulation bath and water washing bath generated during the production of 2L regenerated cellulose fiber (containing approximately 2wt% tetrabutylammonium hydroxide and 20wt% dimethyl sulfoxide) was filtered through an 800-mesh coarse filter for 0.2 hours to remove large suspended impurities.

[0119] 2) Pass the crude filtrate obtained in 1) into a quaternary ammonium styrene-divinylbenzene copolymer anion exchange (OH-). - A type (20-mesh) ion exchange resin with a particle size of 20 mesh was used. The resin content was 0.8 times the volume of the ion exchange column, and the feed flow rate was 5 times the volume of the resin bed per hour, resulting in a transparent eluent.

[0120] 3) The transparent eluent obtained in 2) was passed through a series membrane platform consisting of a 1μm zirconia hybrid ceramic microfiltration membrane, a 10nm zirconia hybrid ceramic ultrafiltration membrane, a 100Da inorganic hybrid nanofiltration membrane, and a 40Da inorganic hybrid reverse osmosis membrane in a membrane area ratio of 1:1:62:250 at a rate of 0.5L / h. Impurities larger than 10nm in the eluent were removed at room temperature and 1MPa to obtain a 50wt% tetrabutylammonium hydroxide solution, a 94wt% recovered dimethyl sulfoxide solution, and pure water.

[0121] 4) Add 70g of cellulose to 791.49g of recycled dimethyl sulfoxide solution, soak for 30min, then add 138.81g of tetrabutylammonium hydroxide fresh solvent (concentration 67wt%), and magnetically stir for 1h at 500rpm / min in a 30℃ water bath to obtain a clear and transparent cellulose solution. Spin the solution using a spinning machine, and after degassing and filtration, extrude it through a metering pump. Draw and shape the fiber in a 25wt% H2SO4 coagulation bath (50℃), then draw the spun fiber onto a roller for primary drawing (7.5m / min) to make the internal crystal orientation of the cellulose fiber more uniform. At the same time, wash the cellulose solvent with a water bath (50℃), and draw the spun fiber onto the roller again for secondary drawing (10.5m / min). After passing through an oiling roller, draw the spun fiber to a heated roller for drying. Finally, collect the finished spun fiber by a take-up roller to obtain a smooth, glossy, silvery-white regenerated cellulose fiber.

[0122] Figure 2 The above is a comparison of liquid chromatography (LC) chromatograms of the tetrabutylammonium hydroxide and dimethyl sulfoxide (DMSO) recovered in Example 1 and their corresponding standard substances. Under the same conditions, the elution time of the recovered tetrabutylammonium hydroxide and the tetrabutylammonium hydroxide standard sample was 0.86 min, and the elution time of the recovered DMSO and the DMSO standard sample was 0.74 min.

[0123] like Figure 3 The images shown are optical images of the recovered tetrabutylammonium hydroxide and dimethyl sulfoxide. (a) is waste liquid from the production process of regenerated cellulose fiber; (b) is a new tetrabutylammonium hydroxide solution; (c) is the recovered tetrabutylammonium hydroxide; (d) is a new dimethyl sulfoxide solution; and (e) is the recovered dimethyl sulfoxide. It can be seen that the recovered tetrabutylammonium hydroxide and dimethyl sulfoxide obtained in this embodiment are colorless and clear, and their appearance is similar to that of the new tetrabutylammonium hydroxide solution and the new dimethyl sulfoxide solution.

[0124] Figure 4 The FTI R spectra of the tetrabutylammonium hydroxide and dimethyl sulfoxide recovered in this embodiment are shown below. Figure 5 The tetrabutylammonium hydroxide and dimethyl sulfoxide recovered in this embodiment 1 H-NMR spectrum, from Figure 4 , 5 It can be seen that the chemical composition of the recovered tetrabutylammonium hydroxide is the same as that of the new tetrabutylammonium hydroxide solution, and the chemical composition of the recovered dimethyl sulfoxide solvent is the same as that of the new dimethyl sulfoxide solution.

[0125] In this embodiment, the energy consumption for solvent recovery is only 0.44 kW / h (coarse filtration process time (0.2 h) × coarse filtration pump power (0.18 kW) + membrane technology process time (4 h) × membrane technology pump power (0.10 kW)

[0126] =0.44kW / h. Calculation formula: E = P × t, where, energy consumption E = power of the pump used for coarse filtration (circulating water pump P = 0.18kW) × coarse filtration process time + power of the pump used for membrane technology (self-priming pump 0.10kW) × membrane technology process time), and the separated water can be directly recycled for the regeneration and washing process of regenerated cellulose fibers (e.g. Figure 1 ).

[0127] Example 2

[0128] This embodiment describes a method for recovering and reusing solvents from the production process of regenerated cellulose materials, including:

[0129] 1) The waste liquid consisting of coagulation bath and water washing bath generated during the production of 2L regenerated cellulose fiber (containing approximately 2wt% tetrabutylammonium hydroxide and 20wt% dimethyl sulfoxide) was filtered through an 800-mesh coarse filter for 0.2 hours to remove large suspended impurities.

[0130] 2) Pass the crude filtrate obtained in 1) into a quaternary ammonium styrene-divinylbenzene copolymer anion exchange (OH-). - A type (20-mesh) ion exchange resin with a particle size of 20 mesh was used. The resin content was 0.8 times the volume of the ion exchange column, and the feed flow rate was 5 times the volume of the resin bed per hour, resulting in a transparent eluent.

[0131] 3) The transparent eluent obtained in 2) was passed through a series membrane platform consisting of a 1 μm zirconia hybrid ceramic microfiltration membrane, a 10 nm zirconia hybrid ceramic ultrafiltration membrane, and a 100 Da inorganic hybrid nanofiltration membrane at a rate of 1 L / h. Impurities larger than 10 nm in the eluent were removed at room temperature and 1 MPa. Tetrabutylammonium hydroxide and dimethyl sulfoxide were separated to obtain a recovered tetrabutylammonium hydroxide with a concentration of 34 wt% and a recovered dimethyl sulfoxide with a concentration of 21.25 wt%.

[0132] 4) Add 70g of cellulose to 744g of dimethyl sulfoxide in fresh solvent and soak for 30min. Then add 107.68g of recovered tetrabutylammonium hydroxide and 78.32g of tetrabutylammonium hydroxide in fresh solvent (concentration 72wt%). Stir magnetically at 500rpm / min for 1h in a 30℃ water bath to obtain a clear and transparent cellulose solution. Spin the solution using a spinning machine. After degassing and filtration, the solution is extruded through a metering pump and drawn into shape in a 25wt% H2SO4 coagulation bath (50℃). The spun fibers are then drawn onto rollers for primary drawing (7.5m / min) to make the internal crystal orientation of the cellulose fibers more uniform. At the same time, the cellulose solvent is washed off in a water bath (50℃). The spun fibers are then drawn onto rollers again for secondary drawing (10.5m / min). After passing through an oiling roller, the spun fibers are drawn to a heated roller for drying. Finally, the finished spun fiber is collected by a take-up roller.

[0133] In this embodiment, the energy consumption for solvent recovery is only 0.236 kW / h (calculation process: coarse filtration process time (0.2h) × coarse filtration pump power (0.18kW) + membrane technology process time (2h) × membrane technology pump power (0.1kW) = 0.236 kW / h. Calculation formula: E = P × t, where, energy consumption E = coarse filtration pump power (circulating water pump P = 0.18kW) × coarse filtration process time + membrane technology pump power (self-priming pump 0.1kW) × membrane technology process time).

[0134] Comparative Example 1

[0135] This comparative example describes a method for recovering and reusing solvents from the production process of regenerated cellulose materials. In contrast, this comparative example does not use an ion exchange process and includes:

[0136] 1) The waste liquid consisting of coagulation bath and water washing bath generated during the production of 2L regenerated cellulose fiber (containing approximately 2wt% tetrabutylammonium hydroxide and 20wt% dimethyl sulfoxide) was filtered through an 800-mesh coarse filter for 0.2 hours to remove large suspended impurities.

[0137] 2) The coarse filtrate obtained in 1) was passed through a series membrane platform consisting of a 1 μm zirconia hybrid ceramic microfiltration membrane, a 10 nm zirconia hybrid ceramic ultrafiltration membrane, and a 100 Da inorganic hybrid nanofiltration membrane at a rate of 1 L / h. Impurities larger than 10 nm in the eluent were removed at room temperature and 1 MPa. Tetrabutylammonium hydroxide and dimethyl sulfoxide were separated to obtain a recovered tetrabutylammonium hydroxide with a concentration of 30 wt% and a recovered dimethyl sulfoxide with a concentration of 21.42 wt%.

[0138] 3) Add 70g of cellulose to 744g of dimethyl sulfoxide in fresh solvent and soak for 30min. Then add 97.43g of recovered tetrabutylammonium hydroxide and 88.57g of tetrabutylammonium hydroxide in fresh solvent (concentration 72wt%). Stir magnetically at 500rpm / min for 1h in a 30℃ water bath to obtain a clear and transparent cellulose solution. Spin the solution using a spinning machine. After degassing and filtration, the solution is extruded through a metering pump and drawn into shape in a 25wt% H2SO4 coagulation bath (50℃). The spun fibers are then drawn onto rollers for primary drawing (7.5m / min) to make the internal crystal orientation of the cellulose fibers more uniform. At the same time, the cellulose solvent is washed off in a water bath (50℃). The spun fibers are then drawn onto rollers again for secondary drawing (10.5m / min). After passing through an oiling roller, the spun fibers are drawn to a heated roller for drying. Finally, the finished spun fiber is collected by a take-up roller.

[0139] The energy consumption for solvent recovery in this comparative example is only 0.236 kW / h (coarse filtration process time (0.2h) × coarse filtration pump power (0.18 kW) + membrane technology process time (2h) × membrane technology pump power (0.1 kW) = 0.236 kW / h. Calculation formula: E = P × t, where energy consumption E = coarse filtration pump power (circulating water pump P = 0.18 kW) × coarse filtration process time + membrane technology pump power (self-priming pump 0.1 kW) × membrane technology process time).

[0140] Finally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0141] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0142] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for recovering and reusing solvents from the production process of regenerated cellulose materials, characterized in that, The method includes: (1) The waste liquid generated during the production of regenerated cellulose materials is subjected to coarse filtration to remove micron-sized suspended impurities in the waste liquid and obtain coarse filtrate; (2) The coarse filtrate is treated with an anion exchange resin to remove acid radicals and colored macromolecules from the coarse filtrate to obtain an eluent. (3) The eluent is passed through a multi-stage series membrane filtration platform to remove micro- and nano-sized impurities in the eluent, while separating tetrabutylammonium hydroxide, dimethyl sulfoxide and water to obtain recovered tetrabutylammonium hydroxide, recovered dimethyl sulfoxide and recovered pure water; (4) The recycled tetrabutylammonium hydroxide and the recycled dimethyl sulfoxide are mixed in proportion and used to dissolve plant cellulose to obtain a cellulose solution. After degassing, filtration and spinning, the solution is then subjected to multi-stage stretching and molding in a coagulation bath prepared by the recycled pure water and sulfuric acid. After oiling and drying, it is used for the production of regenerated cellulose fibers. Step (3) specifically includes: The eluent is passed through the multi-stage tandem membrane filtration platform at room temperature and pressure of 0.2–1 MPa to remove micro- and nano-sized impurities from the eluent, while separating tetrabutylammonium hydroxide, dimethyl sulfoxide, and water to obtain recovered tetrabutylammonium hydroxide, recovered dimethyl sulfoxide, and recovered pure water. The multi-stage tandem membrane filtration platform includes any one of the following a) to f): a) It is composed of microfiltration membrane, ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane connected in series in a membrane area ratio of 1:1:62:250; b) It is composed of microfiltration membrane, nanofiltration membrane and reverse osmosis membrane connected in series with a membrane area ratio of 1:250:250; c) It is composed of ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane connected in series with a membrane area ratio of 1:150:300; d) It is composed of microfiltration membrane, ultrafiltration membrane and nanofiltration membrane connected in series in a membrane area ratio of 1:1:62; e) It is composed of microfiltration membranes and nanofiltration membranes connected in series with a membrane area ratio of 1:250; f) It is composed of ultrafiltration membranes and nanofiltration membranes connected in series with a membrane area ratio of 1:150; The microfiltration membrane has a pore size of 0.1–10 μm, and the ultrafiltration membrane has a pore size of 0.001–0.1 μm.

2. The method for recovering and reusing solvents from the production process of regenerated cellulose materials according to claim 1, characterized in that, The process of coarsely filtering the wastewater generated during the production of regenerated cellulose materials to remove micron-sized suspended impurities and obtain coarse filtrate specifically includes: The waste liquid generated during the production of regenerated cellulose materials is passed through a filter screen with a pore size of 300-800 mesh to remove micron-sized suspended impurities in the waste liquid and obtain coarse filtrate. The waste liquid includes coagulation bath waste liquid and / or water bath waste liquid; The step of subjecting the coarse filtrate to ion exchange resin treatment to remove acid radicals and colored macromolecules from the coarse filtrate to obtain an eluent specifically includes: The coarse filtrate is subjected to ion exchange resin treatment to remove acid radicals and colored macromolecules from the coarse filtrate, thereby obtaining an eluent. In the ion exchange treatment, the type of ion exchange resin includes at least one of styrene-based, acrylic-based, acetic acid-based, epoxy-based, and urea-formaldehyde-based resins. The ion exchange resin carries at least one of the following groups: quaternary ammonium, primary ammonium, secondary ammonium, and tertiary ammonium. The ion exchange resin has a particle size of 20-60 mesh and is packed in an amount of 0.3-0.9 times the volume of the exchange column. In the ion exchange process, the flow rate of the coarse filtrate is 4 to 12 times the volume of the resin bed per hour.

3. The method for recovering and reusing solvents from the production process of regenerated cellulose materials according to claim 1, characterized in that, Multi-stage series membrane filtration platforms are connected in series or parallel-series configurations according to membrane area ratio; The multi-stage series membrane filtration platform is composed of microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes connected in series with a membrane area ratio of 1:1:62:

250. Each series membrane is composed of microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membrane modules connected in a 1:1:N1:N2 ratio with a membrane area ratio of 1:1:62:

250. When N(1~2)=1, the membrane area ratio of the microfiltration membrane, ultrafiltration membrane, nanofiltration membrane, and reverse osmosis membrane module is 1:1:62:

250. When N(1~2)>1, the membrane modules within the nanofiltration membrane and reverse osmosis membrane units are connected in parallel and then connected in series with the microfiltration membrane and ultrafiltration membrane to form a parallel-series integrated membrane platform. The total membrane area ratio of the microfiltration membrane unit, ultrafiltration membrane unit, nanofiltration membrane unit, and reverse osmosis membrane unit is 1:1:62:

250. Furthermore, when the multi-stage tandem membrane filtration platform includes any one of a) to b) or d) to e), the eluent first passes through the microfiltration membrane in a cross-flow filtration manner; When the multi-stage tandem membrane filtration platform includes c) or f), the eluent first passes through the ultrafiltration membrane in a cross-flow filtration manner.

4. The method for recovering and reusing solvents from the production process of regenerated cellulose materials according to claim 1, characterized in that, When the multi-stage tandem membrane filtration platform includes any one of a) to c), the nanofiltration membrane retrieval end yields tetrabutylammonium hydroxide, the reverse osmosis membrane retrieval end yields dimethyl sulfoxide, and the reverse osmosis membrane permeation end yields pure water. When the multi-stage tandem membrane filtration platform includes any one of d) to f), the nanofiltration membrane retrieval end yields tetrabutylammonium hydroxide, and the nanofiltration membrane permeation end yields a dimethyl sulfoxide aqueous solution.

5. The method for recovering and reusing solvents from the production process of regenerated cellulose materials according to claim 1, characterized in that, The material of the microfiltration membrane includes at least one of polypropylene, zirconium oxide ceramic, titanium oxide ceramic, alumina ceramic, zirconium oxide hybrid ceramic, titanium oxide hybrid ceramic, and alumina hybrid ceramic. The material of the ultrafiltration membrane includes at least one of zirconia ceramic, titanium oxide ceramic, alumina ceramic, zirconia hybrid ceramic, titanium oxide hybrid ceramic, and alumina hybrid ceramic. The nanofiltration membrane includes an inorganic hybrid nanofiltration membrane with a molecular weight cutoff of 80–300 Da; The reverse osmosis membrane includes an inorganic hybrid reverse osmosis membrane with a molecular weight cutoff of 40–70 Da.

6. The method for recovering and reusing solvents from the production process of regenerated cellulose materials according to claim 1, characterized in that, The recycled tetrabutylammonium hydroxide and the new tetrabutylammonium hydroxide reagent are mixed at a mass ratio of 1:(0-30) to obtain a plant cellulose solvent with a tetrabutylammonium hydroxide concentration of 55±5 wt%, which is used for dissolving plant cellulose and for spinning applications. or The recovered dimethyl sulfoxide is mixed with recovered tetrabutylammonium hydroxide (and / or neotetrabutylammonium hydroxide reagent) to obtain a plant cellulose solvent with a mass ratio of dimethyl sulfoxide:tetrabutylammonium hydroxide:water of (0.2-8):1:1, which is used for dissolving plant cellulose and for spinning applications. The sulfuric acid and recycled pure water are mixed at a mass ratio of 1:(1.5-19) to obtain a 5 wt%-40 wt% H2SO4 coagulation bath, which is used for the spinning of plant cellulose. The new tetrabutylammonium hydroxide reagent is an analytical grade tetrabutylammonium hydroxide aqueous solution with a concentration of 41-70 wt%. The sulfuric acid is concentrated sulfuric acid with a concentration of 98 wt%.

7. The method for recovering and reusing solvents from the production process of regenerated cellulose materials according to claim 1, characterized in that, The cellulose solution obtained by dissolving plant cellulose in the cellulose solvent prepared in claim 6 is then degassed, filtered, and spun into a cellulose solution. After degassing, filtration, and spinning, the solution is subjected to multi-stage stretching and forming in a coagulation bath prepared with recycled pure water and sulfuric acid. After oiling and drying, the solution is used for the production of regenerated cellulose fibers. The plant cellulose includes any one of cotton cellulose, softwood cellulose, hardwood cellulose, and bamboo cellulose.

8. A method for recovering tetrabutylammonium hydroxide, dimethyl sulfoxide, and pure water, characterized in that, The recovered tetrabutylammonium hydroxide, dimethyl sulfoxide, and pure water are obtained by a method according to any one of claims 1-7 for recovering and reusing solvents from the production process of regenerated cellulose materials.

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