Process and system for comprehensive utilization of hemicellulose-containing waste alkali liquor

Abstract

This invention discloses a comprehensive utilization process and system for waste alkaline liquor containing hemicellulose, belonging to the technical field of waste liquor resource utilization in viscose fiber production. This invention achieves synergy between the resource utilization of hemicellulose and the optimization of viscose fiber production processes by pre-treating the waste alkaline liquor containing hemicellulose discharged from the pressing section of viscose fiber production (microfiltration and pressure filtration), nanofiltration, stainless steel membrane filtration, heat exchange and blending, xanthate esterification reaction, and reuse. Specifically, it treats the waste alkaline liquor containing hemicellulose to match existing large-scale production processes, reusing the recovered alkali in the impregnation section and the recovered hemicellulose in the xanthate treatment section, thereby achieving comprehensive resource utilization.

Description

Technical Field

[0001] This invention specifically relates to a comprehensive utilization process and system for waste alkaline solution containing hemicellulose. The process involves treating the waste alkaline solution containing hemicellulose, reusing the recovered alkali in the impregnation process, and using the recovered hemicellulose in the xanthation process to achieve comprehensive utilization of resources. This invention belongs to the field of waste liquid resource utilization technology in viscose fiber production. Background Technology

[0002] In the production of viscose fiber, pulps such as wood pulp and cotton pulp, which contain natural cellulose, are generally used as raw materials. The process involves mixing, feeding, impregnation, pressing, crushing, aging, weighing, xanthation and dissolution, maturation, filtration, and spinning. In the impregnation process, a high-concentration (approximately 20%) sodium hydroxide solution is added to the pulp. The cellulose reacts with the sodium hydroxide to form alkali cellulose, thus dissolving the hemicellulose. Simultaneously, the pulp expands, and hemicellulose and other impurities dissolve. In the pressing process, a plate and frame filter press is typically used to press and filter the alkali cellulose. The resulting solid alkali cellulose is used in the next production step, while the filtrate is an alkaline solution containing dissolved hemicellulose (sodium hydroxide content of 200–300 g / L and hemicellulose content of 40–50 g / L).

[0003] Currently, hemicellulose, after being dissolved in sodium hydroxide solution during the impregnation process, is typically treated as wastewater, increasing the wastewater treatment load and causing resource loss. Meanwhile, pulp consumption accounts for the highest proportion of the cost of raw material production, and reducing pulp consumption is a key factor in improving economic efficiency. Although existing technologies such as CN102643935A, CN116656883A, CN109112233A, and CN107572697A disclose the preparation of xylose from the pressing alkaline waste liquor containing hemicellulose generated during viscose fiber production, and existing technologies such as CN109021146A and CN113023996A recover the pressing alkaline waste liquor containing hemicellulose from viscose fiber production to prepare hemicellulose powder / solid hemicellulose, the relationship between the resource utilization of hemicellulose and the viscose fiber production process is almost entirely unaddressed, especially lacking low-cost, large-scale technological routes.

[0004] Furthermore, the prior art CN121853195A discloses "a method for preparing viscose fiber using alkali-impregnated hemicellulose," which involves directly xanthating a high-concentration hemicellulose alkali solution to generate hemicellulose xanthate; then, mixing it with the cellulose xanthate and adding a dilute alkali solution for dissolution, etc. However, the high-concentration hemicellulose alkali solution contains a certain amount of low molecular weight hemicellulose (such as xylan, glucomannan, etc.), whose molecular chains are short and have many branches (such as acetyl groups and arabinose side chains). During the xanthation stage, these low molecular weight hemicellulose molecules undergo side reactions with CS2, and the resulting by-products are more likely to precipitate in the spinning bath (containing acids, sulfates, etc.), forming tiny particles, gel-like precipitates, or oily viscous substances. This makes it impossible to form uniform and stable filaments, ultimately affecting the quality of the viscose fiber product (including low strength and easy breakage); it also reduces the efficiency of subsequent KKF filtration and increases the filtration pressure.

[0005] Therefore, there is a need for a comprehensive utilization process and system for semi-fiber-containing waste alkaline solution that can be matched with the existing large-scale production process of viscose fiber and can guarantee the quality of viscose fiber. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, a comprehensive utilization process and system for waste alkali liquor containing hemicellulose is proposed. In this invention, the resource utilization of hemicellulose is integrated with the viscose fiber production process. Specifically, the waste alkali liquor containing hemicellulose undergoes specific treatment to match the existing large-scale production process of viscose fiber. Then, the waste alkali liquor containing hemicellulose is comprehensively utilized in the viscose fiber production process. This includes: directly reusing the recovered alkali in the impregnation stage; and optimizing the viscose fiber production process to ensure that the recovered hemicellulose can be directly used in the xanthation stage, reducing pulp consumption per unit, thereby achieving comprehensive resource utilization.

[0007] To achieve the above technical objectives, the following technical solution is proposed: The primary objective of this technical solution is to provide a comprehensive utilization process for waste alkaline solution containing hemicellulose, comprising the following steps: 1) Preprocessing Filtration: The semi-fiber-containing waste alkaline liquid discharged from the pressing section of viscose fiber production is passed into the plate and frame filter press system and filtered under a pressure of 6-8 MPa to remove large particulate impurities (the removal rate of large particulate impurities is 75-85%), and the pressed filtrate is obtained. The waste alkaline solution containing hemicellulose includes sodium hydroxide solution with a concentration of 200-230 g / L, hemicellulose with a concentration of 40-50 g / L, large particulate impurities (such as resin, pectin, etc.) and small particulate impurities (such as metal ions, pendimethalin, etc.). The press filtrate contains sodium hydroxide solution with a concentration of 200–230 g / L, hemicellulose with a concentration of 40–50 g / L, small particulate impurities, and a small amount of large particulate impurities. During the pressure filtration process, insufficient filtration pressure leads to reduced filtration accuracy and increased impurities; excessive filtration pressure reduces filtration efficiency and shortens membrane life. Therefore, filtration at 6–8 MPa is selected. The technical objective is to obtain a pressed filtrate with a concentration of 200–230 g / L sodium hydroxide solution, a concentration of 40–50 g / L hemicellulose, small particulate impurities, and a small amount of large particulate impurities, facilitating better integration with subsequent processes. If the filtration is not within this standard, the filtration ratio can be adjusted. Microfiltration: The pressed filtrate is passed into a microfiltration system and filtered at a pressure of 6-8 MPa and a temperature of 40-50°C to remove small particulate impurities (the removal rate of small particulate impurities is 75-85%), and microfiltration is obtained. The microporous filtration system uses a microporous filter element; the pore size of the microporous filter element is 5µm. The microporous filtrate contains sodium hydroxide solution with a concentration of 200–230 g / L, hemicellulose with a concentration of 40–50 g / L, a small amount of large particulate impurities, and a small amount of small particulate impurities. Among them, the plate and frame filter press system and the microporous filter system are used for pretreatment to remove most of the large and small particulate impurities in the semi-fiber waste alkaline liquid. Filtration at a pressure of 6–8 MPa and a temperature of 40–50°C not only effectively ensures impurity removal efficiency and quality (precision), but also extends the service life of the microporous filter element. Similarly, the technical objective is to obtain a microporous filtrate containing a sodium hydroxide solution with a concentration of 200–230 g / L, hemicellulose with a concentration of 40–50 g / L, a small portion of large particulate impurities, and a small portion of small particulate impurities, facilitating better integration with subsequent processes. If the filtration efficiency is not within this standard, it can be adjusted by changing the filtration ratio. 2) Nanofiltration The microporous filtrate obtained in step 1) is passed into a nanofiltration system and nanofiltration is performed at a pressure of 14-18 MPa and a temperature of 40-50°C to obtain a retentate and a permeate. In the nanofiltration system, hemicellulose is separated from sodium hydroxide, and low molecular weight hemicellulose, pigments, calcium ions, iron ions, magnesium ions and ash are removed; a nanofiltration membrane with a molecular weight cutoff of 200 to 2000 Da is selected. The retentate consists of a sodium hydroxide solution with a concentration of 13–130 g / L and hemicellulose with a concentration of 50–100 g / L; The permeate consists of a sodium hydroxide solution with a concentration of 13–130 g / L and a hemicellulose solution with a concentration of 3–10 g / L. The permeate is directly reused in the impregnation stage of viscose fiber production. Nanofiltration at a pressure of 14–18 MPa and a temperature of 40–50°C ensures filtration efficiency and quality (precision), while also extending the lifespan of the nanofiltration membrane. For example, if the pressure is too low, the filtration precision decreases and impurities increase; if the pressure is too high, the filtration effect decreases and the nanofiltration membrane lifespan decreases; if the temperature is too high, the filtration efficiency increases, but the lifespan of the nanofiltration membrane decreases and energy consumption increases; if the temperature is too low, the filtration efficiency decreases, and so on. Similarly, the technical objective is to obtain a retentate consisting of a sodium hydroxide solution with a concentration of 13–130 g / L and a hemicellulose concentration of 50–100 g / L, and a permeate consisting of a sodium hydroxide solution with a concentration of 13–130 g / L and a hemicellulose concentration of 3–10 g / L, to facilitate better integration with subsequent processes. If the result is not within this standard, the nanofiltration ratio can be adjusted. 3) Stainless steel membrane filtration The retentate obtained in step 2) is passed into a stainless steel membrane system and filtered at a pressure of 14–16 MPa and a temperature of 40–50 °C to remove low molecular weight hemicellulose (removal rate of 95%), resulting in stainless steel membrane retentate I with a sodium hydroxide solution concentration of 50–70 g / L and a high molecular weight hemicellulose concentration of 70–90 g / L; a stainless steel membrane permeate with a sodium hydroxide solution concentration of 50–70 g / L and a low molecular weight hemicellulose concentration of 2–3 g / L is also obtained (currently, the daily output is only 10 cubic meters). In the stainless steel membrane system, low molecular weight hemicellulose (HMW) is primarily separated from high molecular weight hemicellulose, and inorganic matter, calcium ions, iron ions, magnesium ions, ash, and small organic molecules are further removed. The stainless steel membrane has a pore size of 0.02 µm. The low molecular weight hemicellulose has a molecular weight below 10,000 (excluding 10,000), while the high molecular weight hemicellulose has a molecular weight above 10,000. Low molecular weight hemicellulose can react with CS2, affecting the quality of subsequent viscose and reducing KKF filtration efficiency. Furthermore, the proportion of usable high molecular weight hemicellulose is controlled to be above 50%, primarily concentrated in the molecular weight range of 3,000-8,000 (degree of polymerization 200-400) to ensure the efficiency and quality of subsequent xanthation and spinning reactions, reduce side reactions, and guarantee the quality of the resulting viscose fiber. Simultaneously, a process balance can be achieved between xanthation (reducing side reactions), spinning (controlling viscosity to prevent filtration difficulties), cost, and product quality (strength, etc.) to match existing large-scale viscose fiber production processes. Nanofiltration at a pressure of 14–18 MPa and a temperature of 40–50°C ensures filtration efficiency and quality (precision), while also extending the lifespan of the stainless steel membrane. For example, if the pressure is too low, the filtration precision decreases and impurities increase; if the pressure is too high, the filtration effect decreases and the lifespan of the stainless steel membrane decreases; if the temperature is too high, the filtration efficiency increases, but the lifespan of the stainless steel membrane decreases and energy consumption increases; if the temperature is too low, the filtration efficiency decreases, and so on. Similarly, the technical objective is to obtain "a stainless steel membrane retentate I with a controlled sodium hydroxide solution concentration of 50–70 g / L and a high molecular weight hemicellulose concentration of 70–90 g / L; and a stainless steel membrane permeate with a sodium hydroxide solution concentration of 50–70 g / L and a low molecular weight hemicellulose concentration of 2–3 g / L," to facilitate better integration with subsequent processes. If the results are not within this standard, the filtration ratio can be adjusted. The main objective of this technical solution is to separate and purify high molecular weight hemicellulose. In a subsequent process, the high molecular weight hemicellulose is subjected to a xanthate reaction with carbon disulfide to obtain hemicellulose xanthate, which replaces some of the alkali cellulose involved in the xanthation reaction and subsequent spinning process in the traditional xanthation process, ultimately yielding high-quality viscose fiber. For low molecular weight hemicellulose, due to its shorter molecular length, the quality of the resulting viscose fiber cannot be guaranteed (including low strength and brittleness). Therefore, this technical solution selectively separates it and then sells it directly or processes it in other ways. 4) Mixing Heat exchanger I is used to exchange heat with the stainless steel membrane retentate I obtained in step 3) to obtain stainless steel membrane retentate II with a temperature of 25-35℃. Then, stainless steel membrane retentate II is introduced into a mixing tank, water is added and mixed to obtain stainless steel membrane retentate III with a sodium hydroxide solution concentration of 5-15 g / L and a high molecular weight hemicellulose concentration of 2-6 g / L. Heat exchanger II is used to exchange heat with stainless steel membrane retentate III, and stainless steel membrane filtrate IV is obtained with a temperature of 3-8℃. The process involves two heat exchanges (first 25-35℃, then 3-8℃) to ensure orderly heat exchange, thus maintaining the stability of each process, reducing fluctuations, and better facilitating subsequent blending, xanthate esterification, and xanthation. It also reduces energy consumption. Temperature control serves two main purposes: First, it ensures the effective execution of the subsequent xanthate esterification reaction. Excessive temperature will lead to a more intense and uncontrollable reaction between high molecular weight hemicellulose and carbon disulfide; insufficient temperature will result in a slower reaction rate, impacting production efficiency. Second, it ensures the effective execution of the subsequent xanthation reaction. Excessive temperature will result in poor xanthate esterification; insufficient temperature will result in a slower reaction rate, also impacting production efficiency. Adjusting the concentration of sodium hydroxide solution can better facilitate subsequent xanthation processes. For example, if the concentration of sodium hydroxide solution is too high, it will cause fluctuations in subsequent processes and reduce spinnability; if the concentration of sodium hydroxide solution is too low, the filtration and backwashing interval of the matured KKF machine will be shortened, and the amount of waste rubber produced will increase. 5) Xanthate esterification reaction The stainless steel membrane filtrate IV obtained in step 4) is passed into the reaction vessel, carbon disulfide is introduced, and the mixture is stirred at 3-8°C for 60-120 min; xanthate esterification reaction is carried out to obtain a hemicellulose solution including hemicellulose xanthate with a concentration of 0.02-0.08% and sodium hydroxide with a concentration of 5-15 g / L. The amount of carbon disulfide added is 28-33% of the total amount of high molecular weight hemicellulose. This limitation can ensure that high molecular weight hemicellulose can react better with carbon disulfide, reduce side reactions, and improve the efficiency and quality of xanthate esterification reaction to meet actual production needs. 6) Reuse An alkali cellulose solution with a concentration of 28-35% and a sodium hydroxide concentration of 12-15% is introduced into a xanthation machine. Carbon disulfide is added, and xanthate reaction is carried out at 3-8°C and a vacuum degree of -400 to -10 Mbar to obtain a cellulose xanthate solution. Then, the hemicellulose solution obtained in step 5) is mixed with the cellulose xanthate solution to obtain a mixture. The mixture is then subjected to post-dissolution, mixing, filtration, degassing, and spinning in sequence to obtain viscose fiber.

[0008] Furthermore, the pressure filtration includes at least two stages of pressure filtration.

[0009] Furthermore, the nanofiltration includes 2 to 4 stages of nanofiltration.

[0010] The second objective of this technical solution is to provide: a comprehensive utilization system for hemicellulose-containing waste alkaline solution, installed in a viscose fiber production system, including a plate and frame filter press system for removing large particulate impurities, a microporous filtration system for removing small particulate impurities, a nanofiltration system for concentrating hemicellulose, a stainless steel membrane system for removing low molecular weight hemicellulose, heat exchanger I, a mixing tank for adjusting sodium hydroxide concentration, heat exchanger II, and a reaction vessel; wherein, The feed inlet of the plate and frame filter press system is connected to the outlet of the semi-fiber waste alkaline liquid on the press in the viscose fiber production system, and the outlet of the press filtrate of the plate and frame filter press system is connected to the feed inlet of the microporous filter system. The microfiltration liquid outlet of the microfiltration system is connected to the feed inlet of the nanofiltration system. The retentate outlet of the nanofiltration system is connected to the feed inlet of the stainless steel membrane system, and the permeate outlet of the nanofiltration system is connected to the impregnation tank or alkali preparation tank in the viscose fiber production system; the permeate outlet of the stainless steel membrane system is connected to the feed inlet of heat exchanger I. The discharge port of heat exchanger I is connected to the inlet of the mixing tank. The mixing tank is connected to a water inlet pipe. The discharge port of the mixing tank is connected to the inlet of heat exchanger II. The discharge port of heat exchanger II is connected to the inlet of the reactor. The reactor is connected to a carbon disulfide inlet pipe. The discharge port of the reactor is connected to the xanthation machine in the viscose fiber production system. The xanthation machine is also connected to the aging box in the viscose fiber production system. A continuous pathway for the separation, purification, and reuse of hemicellulose in waste alkaline solution containing hemicellulose is formed between the press, plate and frame filter press system, microfiltration system, nanofiltration system, stainless steel membrane system, heat exchanger I, mixing tank, heat exchanger II, reaction vessel, and xanthation machine. A continuous pathway is formed between the press, plate and frame filter press system, microfiltration system, nanofiltration system, and impregnation tank or alkali preparation tank for the separation, purification, and reuse of sodium hydroxide in semi-fiber waste alkali solution.

[0011] Furthermore, the plate and frame filter press system is equipped with a semi-fiber waste alkali liquid collection tank at the front of the workstation. The semi-fiber waste alkali liquid collection tank is connected to the semi-fiber waste alkali liquid outlet on the press. This setting can better connect with the subsequent work sections, that is, ensure the stable feeding of semi-fiber waste alkali liquid into the plate and frame filter press system.

[0012] Furthermore, the plate and frame filter press system includes at least two plate and frame filter press units, which are arranged in series; each plate and frame filter press unit is equipped with at least two plate and frame filters, which are arranged in parallel. This arrangement can better meet the requirements of filter press, such as achieving large-scale, batch, orderly, and controllable processing.

[0013] Furthermore, the microporous filtration system includes at least two microporous filtration devices, which are arranged in parallel.

[0014] Furthermore, the nanofiltration system includes 2 to 3 nanofiltration units, which are arranged in series; each nanofiltration unit is equipped with at least 2 nanofiltration membrane devices.

[0015] Furthermore, the stainless steel membrane system includes at least two stainless steel membrane devices.

[0016] Furthermore, a stainless steel membrane retentate I collection tank is provided between the stainless steel membrane system and heat exchanger I. This arrangement can better connect with subsequent processes, ensuring a stable feed of stainless steel membrane retentate I into heat exchanger I.

[0017] Furthermore, a stainless steel membrane filtrate IV collection tank is provided between the heat exchanger II and the reactor. This arrangement can better connect with subsequent processes, ensuring a stable feed of stainless steel membrane filtrate IV into the reactor.

[0018] The mechanisms underlying this technical solution include: 1. A stainless steel membrane system with selective filtration is adopted. When the waste alkaline liquid containing hemicellulose passes through the stainless steel membrane system, the high molecular weight hemicellulose is intercepted and enters the retentate. After process adjustment (heat exchange, water addition to adjust concentration, xanthate esterification reaction, etc.), it is transported to the xanthate section. The low molecular weight hemicellulose can directly pass through the stainless steel membrane into the filtrate, and is then sold or otherwise treated. II. Hemicellulose is a polysaccharide composed of various monosaccharides linked by glycosidic bonds, and its molecular chain contains a large number of hydroxyl groups (-OH). During the impregnation and alkalization process, hydroxide ions (OH-) in the sodium hydroxide solution... - It reacts with the hydroxyl groups on the hemicellulose molecule, causing the hydrogen atom in the hydroxyl group to be replaced by sodium ions (Na+). + The hydrogen atom replaces the hydroxyl group, forming sodium hemicellulose. This reaction increases the polarity of the hemicellulose molecule, improving its solubility in water. Simultaneously, it enhances the activity of the hydroxyl groups on the hemicellulose molecular chain, creating conditions for subsequent xanthate esterification. Essentially, the reaction involves the breaking of the covalent OH bond in the hydroxyl group of the hemicellulose molecule, allowing the hydrogen atom to react with the OH group. - Water is formed by the combination of oxygen atoms and Na. + Ionic bonds are formed, and finally, sodium hemicellulose is obtained. The reaction formula is as follows: Hemicellulose-(OH) n +nNaOH→hemicellulose-(O-Na) + ) n +nH2O (where n refers to the number of hydroxyl groups in the hemicellulose molecule); III. Inside the reaction vessel, the alkalized sodium hemicellulose salt undergoes a xanthate esterification reaction with free carbon disulfide (CS2). The oxygen anion (-O) in the sodium hemicellulose salt molecule... - Carbon disulfide (C2SNa) exhibits strong nucleophilicity, attacking carbon atoms in the carbon disulfide molecule to form an intermediate. This intermediate then undergoes intramolecular rearrangement, forming xanthate groups (-O-CS-SNa), which attach to the hemicellulose molecular chain. Since hemicellulose molecules contain multiple hydroxyl groups, each molecule can react with multiple C2S molecules to form hemicellulose xanthates containing multiple xanthate groups. These xanthates replace some of the cellulose in the xanthation reaction and subsequent spinning process. The chemical reaction formula is as follows: Step 1: Nucleophilic attack (forming intermediate products): Let one of the alkalized hydroxyl groups in the hemicellulose molecular chain be RO-Na. +(R represents a structural segment of the hemicellulose molecular chain), its oxygen anion -O - Nucleophilic attack on the carbon atom of carbon disulfide (CS2) forms an intermediate product: RO - Na + +CS2→RO-CS2-Na + ; Step 2: Intramolecular rearrangement (formation of xanthate groups): The intermediate product undergoes intramolecular rearrangement, in which one sulfur atom combines with a sodium ion to form a xanthate group: RO - CS2-Na + →RO-CS-SNa; The overall reaction formula (which involves multiple hydroxyl groups) is as follows: Because hemicellulose molecules contain n reactive hydroxyl groups (which become n -O groups after alkalization). - Na + Therefore, the overall reaction is: Hemicellulose-(O-Na) + ) n +nCS2→hemicellulose-(-O-CS-SNa) n ; Where n represents the number of hydroxyl groups (i.e. the number of xanthate groups) in the hemicellulose molecule that participate in the reaction. The above reaction is essentially a nucleophilic substitution and molecular rearrangement: the oxygen anion is nucleophilic and attacks the electron-deficient carbon of CS2, and then a stable xanthate structure is formed through rearrangement.

[0019] In this technical solution, the positional relationships involved, such as "above", "middle", "between", and "front of the workstation", are defined according to the actual usage conditions and are conventional terms in this technical field, as well as conventional terms used by those skilled in the art in actual use.

[0020] In the description of this technical solution, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set up," "equipped with," and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this technical solution based on the specific circumstances.

[0021] The beneficial technical effects of adopting this technical solution are as follows: I. In this invention, the resource utilization of hemicellulose is combined with the optimization of viscose fiber production processes. Specifically, the waste alkaline solution containing hemicellulose is treated in a specific way to match the existing large-scale production process. This includes: directly reusing the recovered alkali (nanofiltration permeate) in the impregnation section; sequentially subjecting the recovered hemicellulose (nanofiltration retentate) to stainless steel membrane filtration, blending, xanthate esterification, etc., to ensure that the recovered hemicellulose (hemicellulose solution) can be directly used in the xanthation section. Then, the xanthation conditions are optimized (controlled by temperature 3-8℃ and vacuum degree -400 to -10Mbar) to ensure the efficiency and quality of the xanthation reaction, reduce side reactions, and thus achieve comprehensive utilization of resources. The process involves a series of steps, including pressure filtration, microfiltration, nanofiltration, stainless steel filtration, blending, reaction, and reuse. This process is well-suited for processing semi-fiber-containing alkaline waste liquor discharged from the pressing section of viscose fiber production (filtering substances of different precisions, with the precision of the filtered substances gradually decreasing). At the same time, it can be reused in the xanthation section. If the order of the processing steps is changed arbitrarily, it will affect the purification and separation effect, and may even lead to production stoppage and equipment scrapping. II. This invention establishes a new process for extracting high molecular weight hemicellulose and sodium hydroxide solution from hemicellulose-containing waste alkaline solution. This process combines pretreatment (impurity removal), purification and separation (removal of low molecular weight hemicellulose), blending (heat exchange, concentration adjustment), and pre-reaction (xanthate esterification reaction) with the xanthate stage, ensuring complete dissolution of hemicellulose xanthate and cellulose xanthate. This process is compatible with existing large-scale production processes and forms a utilization system for low-polymerization degree cellulose (i.e., unpurified hemicellulose). Furthermore, it reduces wastewater discharge, is environmentally friendly, and saves pulp raw materials (saving 5-10 kg of pulp raw materials per ton of viscose fiber produced). Attached Figure Description

[0022] Figure 1 This is a process flow diagram related to the present invention; Figure 2 This is a system block diagram related to the present invention; Figure 3 The GPC chart for the microporous filtrate in Example 3; Figure 4 The GPC calculation results are for the microporous filtrate in Example 3; Figure 5 The GPC chart for the secondary retentate in Example 6; Figure 6 The GPC calculation results are for the secondary retentate in Example 6; Figure 7 The GPC chart for the fourth-stage retentate in Example 6; Figure 8 The GPC calculation results are for the fourth-stage retentate in Example 6; Figure 9 The GPC chart for stainless steel membrane retentate I in Example 3; Figure 10 The GPC calculation results are for stainless steel membrane retentate I in Example 3; Figure 11 This is a schematic diagram of the separation and purification process involved in this invention; Figure 12 This is a schematic diagram of the mixing process involved in the present invention; Figure 13 This is a schematic diagram of the xanthate esterification reaction process involved in this invention; Figure 14 A photograph of the viscose fiber produced based on the present invention; Figure 15 This is a physical image of the intermediate (stainless steel membrane retentate I) involved in this invention; In the diagram, 0 is the viscose fiber production system, 01 is the alkali preparation tank, 02 is the impregnation tank, 03 is the press, 04 is the aging box, and 05 is the xanthation machine. 1. Collection tank for semi-fiber waste alkaline solution; 2. Plate and frame filter press system; 21. Plate and frame filter press unit; 211. Plate and frame filter press; 3. Microporous filtration system; 31. Microporous filtration device; 4. Nanofiltration system; 41. Nanofiltration unit; 410. Nanofiltration membrane device; 5. Stainless steel membrane system; 51. Stainless steel membrane device; 6. Heat exchanger I; 7. Mixing tank; 71. Water inlet pipe; 8. Heat exchanger II; 9. Reactor; 91. Carbon disulfide inlet pipe; 10. Stainless steel membrane retentate I collection tank; 11. Stainless steel membrane filtrate IV collection tank. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 This embodiment provides a comprehensive utilization process for waste alkaline solution containing hemicellulose, such as: Figure 1 As shown, it includes the following steps: 1) Preprocessing Filtration: The semi-fiber-containing waste alkaline liquid discharged from the pressing section of viscose fiber production is passed into plate and frame filter press system 2 and filtered under a pressure of 6MPa to obtain the pressed filtrate; wherein, two-stage filtration is performed. Microfiltration: The pressed filtrate is passed into the microfiltration system 3 and filtered at a pressure of 6 MPa and a temperature of 40°C to obtain microfiltration filtrate. 2) Nanofiltration The microporous filtrate obtained in step 1) is passed into nanofiltration system 4 and nanofiltration is performed at a pressure of 14 MPa and a temperature of 40 °C to obtain retentate and permeate. The permeate is directly reused in the impregnation section of viscose fiber production; wherein, two-stage nanofiltration is performed. 3) Stainless steel membrane filtration The retentate obtained in step 2) is passed into the stainless steel membrane system 5 to obtain stainless steel membrane retentate I with a sodium hydroxide solution concentration of 50-70 g / L and a high molecular weight hemicellulose concentration of 70-90 g / L. Stainless steel membrane permeate with a sodium hydroxide solution concentration of 50-70 g / L and a low molecular weight hemicellulose concentration of 2-3 g / L is also obtained; wherein, secondary stainless steel membrane filtration is performed. 4) Mixing Heat exchanger I6 is used to exchange heat with the stainless steel membrane retentate I obtained in step 3) to obtain stainless steel membrane retentate II with a temperature of 35℃. Then, it is introduced into the mixing tank 7, water is added and mixed to obtain stainless steel membrane retentate III with a sodium hydroxide solution concentration of 5-15 g / L and a high molecular weight hemicellulose concentration of 2-6 g / L; Heat exchanger II8 is used to exchange heat with stainless steel membrane retentate III, and stainless steel membrane filtrate IV is obtained at a temperature of 8℃. 5) Xanthate esterification reaction The stainless steel membrane filtrate IV obtained in step 4) is passed into the reaction vessel 9, carbon disulfide is introduced, and xanthate esterification reaction is carried out at 8°C to obtain a hemicellulose solution including hemicellulose xanthate with a concentration of 0.02-0.08% and sodium hydroxide with a concentration of 5-15 g / L. 6) Reuse The hemicellulose solution obtained in step 5) is mixed with the cellulose xanthate solution in xanthating machine 05 to obtain a mixture; the mixture is then subjected to post-dissolution, mixing, filtration, degassing and spinning in sequence to obtain viscose fiber.

[0025] Example 2 This embodiment provides a comprehensive utilization process for waste alkaline solution containing hemicellulose, including the following steps: 1) Preprocessing Filtration: The semi-fiber-containing waste alkaline liquid discharged from the pressing section of viscose fiber production is passed into plate and frame filter press system 2 and filtered at a pressure of 8MPa to obtain the press filtrate; the process involves two-stage filtration. Microfiltration: The pressed filtrate is passed into the microfiltration system 3 and filtered under a pressure of 8 MPa and a temperature of 50°C to obtain microfiltration filtrate. 2) Nanofiltration The microporous filtrate obtained in step 1) is passed into nanofiltration system 4 and nanofiltration is performed at a pressure of 16 MPa and a temperature of 50°C to obtain retentate and permeate. The permeate is directly reused in the impregnation section of viscose fiber production; wherein, secondary nanofiltration is performed. 3) Stainless steel membrane filtration The retentate obtained in step 2) is passed into the stainless steel membrane system 5 to obtain stainless steel membrane retentate I with a sodium hydroxide solution concentration of 50-70 g / L and a high molecular weight hemicellulose concentration of 70-90 g / L. Stainless steel membrane permeate with a sodium hydroxide solution concentration of 50-70 g / L and a low molecular weight hemicellulose concentration of 2-3 g / L is also obtained; wherein, three-stage stainless steel membrane filtration is performed. 4) Mixing Heat exchanger I6 is used to exchange heat with the stainless steel membrane retentate I obtained in step 3) to obtain stainless steel membrane retentate II with a temperature of 25℃. Then, it is introduced into the mixing tank 7, water is added and mixed to obtain stainless steel membrane retentate III with a sodium hydroxide solution concentration of 5-15 g / L and a high molecular weight hemicellulose concentration of 2-6 g / L; Heat exchanger II8 is used to exchange heat with stainless steel membrane retentate III, and stainless steel membrane filtrate IV is obtained at a temperature of 3℃. 5) Xanthate esterification reaction The stainless steel membrane filtrate IV obtained in step 4) is passed into the reaction vessel 9, carbon disulfide is introduced, and xanthate esterification reaction is carried out at 3°C ​​to obtain a hemicellulose solution including hemicellulose xanthate with a concentration of 0.02-0.08% and sodium hydroxide with a concentration of 5-15 g / L. 6) Reuse The hemicellulose solution obtained in step 5) is mixed with the cellulose xanthate solution in xanthating machine 05 to obtain a mixture; the mixture is then subjected to post-dissolution, mixing, filtration, degassing and spinning in sequence to obtain viscose fiber.

[0026] Example 3 This embodiment provides a comprehensive utilization process for waste alkaline solution containing hemicellulose, including the following steps: 1) Preprocessing Filtration: The semi-fiber-containing waste alkaline liquid discharged from the pressing section of viscose fiber production is passed into plate and frame filter press system 2 and filtered under a pressure of 7MPa to obtain the press filtrate; wherein, three-stage filtration is performed. Microfiltration: The pressed filtrate is passed into the microfiltration system 3 and filtered under a pressure of 7 MPa and a temperature of 45°C to obtain microfiltration filtrate. 2) Nanofiltration The microporous filtrate obtained in step 1) is passed into nanofiltration system 4 and nanofiltration is performed at a pressure of 15 MPa and a temperature of 45 °C to obtain retentate and permeate. The permeate is directly reused in the impregnation section of viscose fiber production; wherein, four-stage nanofiltration is performed. 3) Stainless steel membrane filtration The retentate obtained in step 2) is passed into the stainless steel membrane system 5 to obtain stainless steel membrane retentate I with a sodium hydroxide solution concentration of 50-70 g / L and a high molecular weight hemicellulose concentration of 70-90 g / L. Stainless steel membrane permeate with a sodium hydroxide solution concentration of 50-70 g / L and a low molecular weight hemicellulose concentration of 2-3 g / L is also obtained; wherein, secondary stainless steel membrane filtration is performed. 4) Mixing Heat exchanger I6 is used to exchange heat with the stainless steel membrane retentate I obtained in step 3) to obtain stainless steel membrane retentate II with a temperature of 30℃. Then, it is introduced into the mixing tank 7, water is added and mixed to obtain stainless steel membrane retentate III with a sodium hydroxide solution concentration of 5-15 g / L and a high molecular weight hemicellulose concentration of 2-6 g / L; Heat exchanger II8 is used to exchange heat with stainless steel membrane retentate III, and stainless steel membrane filtrate IV is obtained at a temperature of 5℃. 5) Xanthate esterification reaction The stainless steel membrane filtrate IV obtained in step 4) is passed into the reaction vessel 9, carbon disulfide is introduced, and xanthate esterification reaction is carried out at 5°C to obtain a hemicellulose solution including hemicellulose xanthate with a concentration of 0.02-0.08% and sodium hydroxide with a concentration of 5-15 g / L. 6) Reuse The hemicellulose solution obtained in step 5) is mixed with the cellulose xanthate solution in xanthating machine 05 to obtain a mixture; the mixture is then subjected to post-dissolution, mixing, filtration, degassing and spinning in sequence to obtain viscose fiber.

[0027] Example 4 Based on Example 3, this example employs a two-stage nanofiltration process, specifically including: 2.1) First-stage nanofiltration The microporous filtrate obtained in step 1) is passed into the first-stage nanofiltration unit 41 and subjected to first-stage nanofiltration at a pressure of 18 MPa and a temperature of 50 °C to obtain a first-stage retentate and a first-stage permeate. The primary retentate consists of a sodium hydroxide solution with a concentration of 100 g / L and hemicellulose with a concentration of 80 g / L; The primary permeate consists of a sodium hydroxide solution with a concentration of 100 g / L and hemicellulose with a concentration of 4 g / L; 2.2) Secondary nanofiltration The primary retentate obtained in step 2.1) is passed into the secondary nanofiltration unit 41 and secondary nanofiltration is performed at a pressure of 18 MPa and a temperature of 50 °C to obtain secondary retentate and secondary permeate. The secondary retentate consists of a sodium hydroxide solution with a concentration of 80 g / L and a hemicellulose solution with a concentration of 80 g / L; The secondary permeate consists of a sodium hydroxide solution with a concentration of 80 g / L and a hemicellulose solution with a concentration of 4 g / L. Then, the resulting primary and secondary permeate solutions are directly recycled to the impregnation section of viscose fiber production. For the impregnation section, 40m³ of alkali solution can be saved. 3 / h.

[0028] Example 5 Based on Example 3, this example employs a three-stage nanofiltration process, specifically including: 2.1) First-stage nanofiltration The microporous filtrate obtained in step 1) is passed into the first-stage nanofiltration unit 41 and subjected to first-stage nanofiltration at a pressure of 16 MPa and a temperature of 50 °C to obtain a first-stage retentate and a first-stage permeate. The primary retentate consists of a sodium hydroxide solution with a concentration of 100 g / L and hemicellulose with a concentration of 80 g / L; The primary permeate consists of a sodium hydroxide solution with a concentration of 100 g / L and a hemicellulose solution with a concentration of 8 g / L. 2.2) Secondary nanofiltration The primary retentate obtained in step 2.1) is passed into the secondary nanofiltration unit 41 and secondary nanofiltration is performed at a pressure of 16 MPa and a temperature of 50 °C to obtain secondary retentate and secondary permeate. The secondary retentate consists of a sodium hydroxide solution with a concentration of 80 g / L and a hemicellulose solution with a concentration of 80 g / L; The secondary permeate consists of a sodium hydroxide solution with a concentration of 80 g / L and a hemicellulose solution with a concentration of 8 g / L. 2.3) Three-stage nanofiltration The tertiary retentate obtained in step 2.2) is passed into the tertiary nanofiltration unit 41 and subjected to tertiary nanofiltration at a pressure of 16 MPa and a temperature of 50 °C to obtain tertiary retentate and tertiary permeate. The tertiary retentate consists of a sodium hydroxide solution with a concentration of 40 g / L and a hemicellulose solution with a concentration of 100 g / L. The tertiary permeate consists of a sodium hydroxide solution with a concentration of 40 g / L and a hemicellulose solution with a concentration of 8 g / L. The primary, secondary, and tertiary permeate solutions can be collected and directly reused in the impregnation stage of viscose fiber production. For the impregnation stage, 55m³ of alkali solution can be saved.3 / h.

[0029] In this nanofiltration system 4, hemicellulose is separated from sodium hydroxide, and low molecular weight hemicellulose, pigments, calcium ions, iron ions, magnesium ions and ash are removed; each nanofiltration unit 41 uses a nanofiltration membrane with a molecular weight cutoff of 200 to 2000 Da.

[0030] Example 6 Based on Example 3, this example employs a four-stage nanofiltration process, specifically including: 2.1) First-stage nanofiltration The microporous filtrate obtained in step 1) is passed into the first-stage nanofiltration unit 41 and subjected to first-stage nanofiltration at a pressure of 14 MPa and a temperature of 50 °C to obtain a first-stage retentate and a first-stage permeate. The primary retentate consists of a sodium hydroxide solution with a concentration of 100 g / L and hemicellulose with a concentration of 80 g / L; The primary permeate consists of a sodium hydroxide solution with a concentration of 100 g / L and hemicellulose with a concentration of 3 g / L; 2.2) Secondary nanofiltration The primary retentate obtained in step 2.1) is passed into the secondary nanofiltration unit 41 and secondary nanofiltration is performed at a pressure of 14 MPa and a temperature of 50°C to obtain secondary retentate and secondary permeate. The secondary retentate consists of a sodium hydroxide solution with a concentration of 80 g / L and a hemicellulose solution with a concentration of 80 g / L; The secondary permeate consists of a sodium hydroxide solution with a concentration of 80 g / L and a hemicellulose solution with a concentration of 3 g / L. 2.3) Three-stage nanofiltration The secondary retentate obtained in step 2.2) is passed into the tertiary nanofiltration unit 41 and subjected to tertiary nanofiltration at a pressure of 14 MPa and a temperature of 50 °C to obtain tertiary retentate and tertiary permeate. The tertiary retentate consists of a sodium hydroxide solution with a concentration of 50 g / L and a hemicellulose solution with a concentration of 100 g / L. The tertiary permeate consists of a sodium hydroxide solution with a concentration of 50 g / L and a hemicellulose solution with a concentration of 3 g / L. 2.3) Four-stage nanofiltration The tertiary retentate obtained in step 2.2) is passed into the quaternary nanofiltration unit 41 and subjected to quaternary nanofiltration at a pressure of 14 MPa and a temperature of 50 °C to obtain quaternary retentate and quaternary permeate. The fourth stage retentate consists of a sodium hydroxide solution with a concentration of 13 g / L and hemicellulose with a concentration of 85 g / L; The fourth-stage permeate consists of a sodium hydroxide solution with a concentration of 13 g / L and a hemicellulose solution with a concentration of 6 g / L. The primary, secondary, tertiary, and quaternary permeates can be collected and directly reused in the impregnation process. In this nanofiltration system 4, hemicellulose is separated from sodium hydroxide, and low molecular weight hemicellulose, pigments, calcium ions, iron ions, magnesium ions, and ash are removed; each nanofiltration unit 41 uses a nanofiltration membrane with a molecular weight cutoff of 200–2000 Da.

[0031] The microfiltration solution obtained through microfiltration, the secondary retentate obtained through two-stage nanofiltration, the fourth-stage retentate obtained through four-stage nanofiltration, and the stainless steel membrane retentate I obtained through two-stage stainless steel membrane filtration were subjected to GPC analysis. The results are shown in Table 1 and 2. Figure 3-10 As shown.

[0032] Table 1

[0033] Depend on Figure 3-4 It can be seen that after microfiltration, the proportion of usable high molecular weight hemicellulose in the microfiltration liquid is 36.32%. Depend on Figure 5-6 It can be seen that after two-stage nanofiltration, the proportion of usable high molecular weight hemicellulose in the secondary retentate is 31.54%. Depend on Figure 7-8 It can be seen that after four-stage nanofiltration, the proportion of usable high molecular weight hemicellulose in the fourth-stage retentate is 30.88%. Depend on Figure 9-10 It can be seen that after filtration through a stainless steel membrane, the proportion of usable high molecular weight hemicellulose in the stainless steel membrane retentate I is 56.54%.

[0034] Example 7 A comprehensive utilization process for waste alkaline solution containing hemicellulose, such as Figure 11-13 As shown, it includes the following steps: 1) Preprocessing Filtration: The semi-fiber-containing waste alkaline liquid discharged from the pressing section is passed into the plate and frame filter press system 2 and filtered under a pressure of 6-8 MPa to remove large particulate impurities and obtain the pressed filtrate. The waste alkaline solution containing hemicellulose includes sodium hydroxide solution with a concentration of 200-230 g / L, hemicellulose with a concentration of 40-50 g / L, large particulate impurities (such as resin, pectin, etc.) and small particulate impurities (such as metal ions, pendimethalin, etc.). The press filtrate contains sodium hydroxide solution with a concentration of 200–230 g / L, hemicellulose with a concentration of 40–50 g / L, small particulate impurities, and a small amount of large particulate impurities. Microfiltration: The pressed filtrate is passed into the microfiltration system 3 and filtered at a pressure of 6-8 MPa and a temperature of 40-50°C to remove small particulate impurities (the removal rate of small particulate impurities is 75-85%), and microfiltration is obtained. In microporous filtration system 3, a microporous filter element is used; the pore size of the microporous filter element is 5µm; The microporous filtrate contains sodium hydroxide solution with a concentration of 200–230 g / L, hemicellulose with a concentration of 40–50 g / L, a small amount of large particulate impurities, and a small amount of small particulate impurities. The plate and frame filter press system 2 and the microporous filter system 3 are used for pretreatment to remove most of the large and small particulate impurities in the semi-fiber waste alkaline solution. 2) Nanofiltration The microporous filtrate obtained in step 1) is passed into nanofiltration system 4 and nanofiltration is performed at a pressure of 14-18 MPa and a temperature of 40-50°C to obtain retentate and permeate. In nanofiltration system 4, hemicellulose is separated from sodium hydroxide, and low molecular weight hemicellulose, pigments, calcium ions, iron ions, magnesium ions and ash are removed; a nanofiltration membrane with a molecular weight cutoff of 200 to 2000 Da is selected. The retentate consists of a sodium hydroxide solution with a concentration of 13–130 g / L and hemicellulose with a concentration of 50–100 g / L; The permeate consists of a sodium hydroxide solution with a concentration of 13–130 g / L and a hemicellulose solution with a concentration of 3–10 g / L. The permeate is directly reused in the impregnation stage of viscose fiber production. 3) Stainless steel membrane filtration The retentate obtained in step 2) is passed into the stainless steel membrane system 5 and filtered under controlled conditions of 14–16 MPa and 40–50 °C to remove low molecular weight hemicellulose (removal rate 95%), resulting in stainless steel membrane retentate I (e.g., sodium hydroxide solution concentration of 50–70 g / L and high molecular weight hemicellulose concentration of 70–90 g / L). Figure 15 (as shown); a stainless steel membrane permeate with a sodium hydroxide solution concentration of 50-70 g / L and a low molecular weight hemicellulose concentration of 2-3 g / L was also obtained (currently, the daily output is only 10 cubic meters). In the stainless steel membrane system 5, low molecular weight hemicellulose and high molecular weight hemicellulose are mainly separated, and inorganic matter, calcium ions, iron ions, magnesium ions, ash and small organic molecules are further removed; the pore size of the stainless steel membrane is 0.02µm; among them, the molecular weight of low molecular weight hemicellulose is less than 100,000 (excluding 100,000), and the molecular weight of high molecular weight hemicellulose is more than 100,000. The main objective of this technical solution is to separate and purify high molecular weight hemicellulose. In a subsequent process, the high molecular weight hemicellulose is subjected to a xanthate reaction with carbon disulfide to obtain hemicellulose xanthate, which replaces some of the alkali cellulose involved in the xanthation reaction and subsequent spinning process in the traditional xanthation process, ultimately yielding high-quality viscose fiber. For low molecular weight hemicellulose, due to its shorter molecular size, the quality of the resulting viscose fiber cannot be guaranteed. Therefore, this technical solution selectively separates it and then sells it directly or performs other treatments. 4) Mixing Heat exchanger I6 is used to exchange heat with the stainless steel membrane retentate I obtained in step 3) to obtain stainless steel membrane retentate II with a temperature of 25-35℃. Then, it is introduced into the mixing tank 7, water is added and mixed to obtain stainless steel membrane retentate III with a sodium hydroxide solution concentration of 5-15 g / L and a high molecular weight hemicellulose concentration of 2-6 g / L; Heat exchanger II8 is used to exchange heat with stainless steel membrane retentate III, and stainless steel membrane filtrate IV is obtained with a temperature of 3-8℃. The process involves two heat exchanges (first 25-35℃, then 3-8℃) to ensure orderly heat exchange, thus maintaining the stability of each process, reducing fluctuations, and better facilitating subsequent blending, xanthate esterification, and xanthation. It also reduces energy consumption. Temperature control serves two main purposes: First, it ensures the effective execution of the subsequent xanthate esterification reaction. Excessive temperature will lead to a more intense and uncontrollable reaction between high molecular weight hemicellulose and carbon disulfide; insufficient temperature will result in a slower reaction rate, impacting production efficiency. Second, it ensures the effective execution of the subsequent xanthation reaction. Excessive temperature will result in poor xanthate esterification; insufficient temperature will result in a slower reaction rate, also impacting production efficiency. Adjusting the concentration of sodium hydroxide solution can better facilitate subsequent xanthation processes. For example, if the concentration of sodium hydroxide solution is too high, it will cause fluctuations in subsequent processes and reduce spinnability; if the concentration of sodium hydroxide solution is too low, the filtration and backwashing interval of the matured KKF machine will be shortened, and the amount of waste rubber produced will increase. 5) Xanthate esterification reaction The stainless steel membrane filtrate IV obtained in step 4) is passed into the reaction vessel 9, carbon disulfide is introduced, and the mixture is stirred at 3-8°C for 60-120 min; the xanthate esterification reaction is carried out to obtain a hemicellulose solution including hemicellulose xanthate with a concentration of 0.02-0.08% and sodium hydroxide with a concentration of 5-15 g / L. The amount of carbon disulfide added is 28-33% of the total amount of high molecular weight hemicellulose; 6) Reuse An alkali cellulose solution with a concentration of 28-35% and a sodium hydroxide concentration of 12-15% is introduced into xanthation machine 05. Carbon disulfide is added, and xanthate esterification reaction is carried out at 3-8°C and a vacuum degree of -400 to -10 Mbar to obtain a cellulose xanthate solution. Then, the hemicellulose solution obtained in step 5) is mixed with the cellulose xanthate solution to obtain a mixture. The mixture is then subjected to dissolution, mixing, filtration, degassing, and spinning in sequence to obtain viscose fiber (e.g., ...). Figure 14 (As shown).

[0035] Comparative analysis showed that the appearance and properties of viscose fibers prepared by using hemicellulose xanthate and a mixture of hemicellulose xanthate (as described above) and cellulose xanthate respectively did not differ significantly.

[0036] Example 8 The embodiment provides: a comprehensive utilization system for waste alkaline solution containing hemicellulose, such as Figure 2 As shown, the viscose fiber production system 0 includes a plate and frame filter press system 2 for removing large particulate impurities, a microporous filtration system 3 for removing small particulate impurities, a nanofiltration system 4 for concentrating hemicellulose, a stainless steel membrane system 5 for removing low molecular weight hemicellulose, a heat exchanger I 6, a mixing tank 7 for adjusting the sodium hydroxide concentration, a heat exchanger II 8, and a reaction vessel 9; wherein, The feed inlet of the plate and frame filter press system 2 is connected to the outlet of the semi-fiber waste alkaline liquid on the press 03 in the viscose fiber production system 0, and the outlet of the pressed filtrate of the plate and frame filter press system 2 is connected to the feed inlet of the microporous filter system 3. The microfiltration liquid outlet of the microfiltration system 3 is connected to the feed inlet of the nanofiltration system 4. The retentate outlet of nanofiltration system 4 is connected to the feed inlet of stainless steel membrane system 5, and the permeate outlet of nanofiltration system 4 is connected to impregnation tank 02 or alkali preparation tank 01 in viscose fiber production system 0; the permeate outlet of stainless steel membrane system 5 is connected to the feed inlet of heat exchanger I6. The discharge port of heat exchanger I6 is connected to the inlet of mixing tank 7. Mixing tank 7 is connected to water inlet pipe 71. The discharge port of mixing tank 7 is connected to the inlet of heat exchanger II8. The discharge port of heat exchanger II8 is connected to the inlet of reactor 9. Reactor 9 is connected to carbon disulfide inlet pipe 91. The discharge port of reactor 9 is connected to xanthating machine 05 in viscose fiber production system 0. Xanthating machine 05 is also connected to aging box 04 in viscose fiber production system 0. A continuous pathway for the separation, purification, and reuse of hemicellulose in waste alkaline solution containing hemicellulose is formed between the press 03, plate and frame filter press system 2, microporous filter system 3, nanofiltration system 4, stainless steel membrane system 5, heat exchanger I 6, mixing tank 7, heat exchanger II 8, reaction vessel 9, and xanthation machine 05. A continuous pathway for the separation, purification, and reuse of sodium hydroxide in semi-fiber waste alkali solution is formed between the press 03, plate and frame filter press system 2, microporous filter system 3, nanofiltration system 4, and impregnation tank 02 or alkali solution preparation tank 01.

[0037] Example 9 Based on Example 8, this example further specifies the following to ensure stable, orderly, and controllable material transport: The plate and frame filter press system 2 is equipped with a semi-fiber waste alkali liquid collection tank 1 at the front of the station. The semi-fiber waste alkali liquid collection tank 1 is connected to the semi-fiber waste alkali liquid outlet on the press 03. This setting can better connect with the subsequent process section, that is, ensure the stable feeding of semi-fiber waste alkali liquid into the plate and frame filter press system 2.

[0038] In addition, a stainless steel membrane retentate I collection tank 10 is provided between the stainless steel membrane system 5 and the heat exchanger I 6. This setting can better connect with the subsequent process, that is, ensure the stable feeding of stainless steel membrane retentate I into the heat exchanger I 6. A stainless steel membrane filtrate IV collection tank 11 is provided between heat exchanger II8 and reactor 9. This arrangement can better connect with subsequent processes, ensuring a stable feed of stainless steel membrane retentate IV into reactor 9.

[0039] Example 10 Based on Examples 8-9, this example, in order to better match existing large-scale production processes and form a system for utilizing low-polymerization degree cellulose to meet the purification and separation requirements of high molecular weight hemicellulose, such as achieving large-scale, batch, ordered, and controllable processing, further specifies: The plate and frame filter press system 2 includes at least two plate and frame filter press units 21, which are arranged in series; each plate and frame filter press unit 21 is equipped with at least two plate and frame filters 211, which are arranged in parallel.

[0040] The microporous filtration system 3 includes at least two microporous filtration devices 31, which are arranged in parallel.

[0041] The nanofiltration system 4 includes 2 to 3 nanofiltration units 41, which are connected in series. Each nanofiltration unit 41 is equipped with at least 2 nanofiltration membrane devices 410, which are connected in series or in parallel, depending on the actual needs, by switching valves.

[0042] The stainless steel membrane system 5 includes at least two stainless steel membrane devices 51, which are connected in series or in parallel, depending on the actual needs, and the valves are switched.

[0043] Example 11 Based on Example 7, for the stainless steel membrane system, two sets of stainless steel membrane devices are arranged in series, and some field records are provided to show the equipment operation status and product status, as shown in Table 2 below. Table 2

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A comprehensive utilization process for waste alkaline solution containing hemicellulose, characterized in that, Includes the following steps: S1 Preprocessing The alkaline waste liquor containing hemicellulose discharged from the pressing section of viscose fiber production is subjected to pressure filtration, microfiltration and nanofiltration to obtain a retentate containing a sodium hydroxide solution with a concentration of 13-130 g / L and a hemicellulose concentration of 50-100 g / L. A permeate containing a sodium hydroxide solution with a concentration of 13-130 g / L and a hemicellulose concentration of 3-10 g / L is also obtained. The permeate is directly reused in the impregnation section of viscose fiber production. S2 stainless steel membrane filter The retentate obtained in step S1 is passed into the stainless steel membrane system to obtain stainless steel membrane retentate I with a sodium hydroxide solution concentration of 50-70 g / L and a high molecular weight hemicellulose concentration of 70-90 g / L. Stainless steel membrane permeate with a sodium hydroxide solution concentration of 50-70 g / L and a low molecular weight hemicellulose concentration of 2-3 g / L is also obtained. S3 blending Heat exchanger I is used to exchange heat with the stainless steel membrane retentate I obtained in step S2, and the temperature is controlled to obtain stainless steel membrane retentate II at 25-35℃. Then, stainless steel membrane retentate II is introduced into a mixing tank, water is added and mixed to obtain stainless steel membrane retentate III with a sodium hydroxide solution concentration of 5-15 g / L and a high molecular weight hemicellulose concentration of 2-6 g / L. Heat exchanger II is used to exchange heat with stainless steel membrane retentate III, and stainless steel membrane filtrate IV is obtained with a temperature of 3-8℃. S4 xanthate esterification reaction The stainless steel membrane filtrate IV obtained in step S3 is passed into the reaction vessel, carbon disulfide is introduced, and xanthate esterification reaction is carried out at 3-8°C to obtain a hemicellulose solution including hemicellulose xanthate with a concentration of 0.02-0.08% and sodium hydroxide with a concentration of 5-15 g / L. S5 reuse The hemicellulose solution obtained in step S4 is mixed with the cellulose xanthate solution in the xanthation machine to obtain a mixture; the mixture is then subjected to post-dissolution, mixing, filtration, degassing and spinning in sequence to obtain viscose fiber.

2. The comprehensive utilization process of hemicellulose-containing waste alkaline solution according to claim 1, characterized in that, In step S1, the hemicellulose-containing waste alkaline solution includes a sodium hydroxide solution with a concentration of 200-230 g / L, hemicellulose with a concentration of 40-50 g / L, large particulate impurities, and small particulate impurities.

3. The comprehensive utilization process of hemicellulose-containing waste alkaline solution according to claim 2, characterized in that, The pressure filtration is controlled at a pressure of 6-8 MPa; the pressure filtration includes at least two stages of pressure filtration.

4. The comprehensive utilization process of hemicellulose-containing waste alkaline solution according to claim 1, characterized in that, In the microporous filtration, the filtration is controlled at a pressure of 6-8 MPa and a temperature of 40-50°C; a microporous filter element with a pore size of 5 µm is used.

5. The comprehensive utilization process of hemicellulose-containing waste alkaline solution according to claim 4, characterized in that, The nanofiltration process is carried out at a pressure of 14–18 MPa and a temperature of 40–50 °C; a nanofiltration membrane with a molecular weight cutoff of 200–2000 Da is used; the nanofiltration includes 2–4 stages of nanofiltration.

6. The comprehensive utilization process of hemicellulose-containing waste alkaline solution according to claim 1, characterized in that, The stainless steel membrane system filters at a pressure of 14–16 MPa and a temperature of 40–50 °C.

7. The comprehensive utilization process of hemicellulose-containing waste alkaline solution according to claim 6, characterized in that, The stainless steel membrane system uses a stainless steel membrane with a pore size of 0.02µm; the stainless steel membrane filtration includes at least two stages of stainless steel membrane filtration.

8. The comprehensive utilization process of hemicellulose-containing waste alkaline solution according to claim 1, characterized in that, In the xanthate esterification reaction, the amount of carbon disulfide added is 28-33% of the total amount of high molecular weight hemicellulose; the xanthate esterification reaction is carried out by stirring at 3-8°C for 60-120 min.

9. A comprehensive utilization system for waste alkaline solution containing hemicellulose, characterized in that, The system used in the comprehensive utilization process of hemicellulose-containing waste alkaline liquid according to any one of claims 1-8 is set in the viscose fiber production system (0), and includes a plate and frame filter press system (2) for removing large particulate impurities, a microporous filtration system (3) for removing small particulate impurities, a nanofiltration system (4) for concentrating hemicellulose, a stainless steel membrane system (5) for removing low molecular weight hemicellulose, heat exchanger I (6), a mixing tank (7) for adjusting the sodium hydroxide concentration, heat exchanger II (8), and a reaction vessel (9); wherein, The feed inlet of the plate and frame filter press system (2) is connected to the outlet of the semi-fiber waste alkali liquid on the press (03) in the viscose fiber production system (0), and the outlet of the press filtrate of the plate and frame filter press system (2) is connected to the feed inlet of the microporous filter system (3). The microfiltration liquid outlet of the microfiltration system (3) is connected to the feed inlet of the nanofiltration system (4); The retentate outlet of the nanofiltration system (4) is connected to the feed inlet of the stainless steel membrane system (5), and the permeate outlet of the nanofiltration system (4) is connected to the impregnation tank (02) or the alkali preparation tank (01) in the viscose fiber production system (0); the permeate outlet of the stainless steel membrane system (5) is connected to the feed inlet of the heat exchanger I (6). The upper outlet of heat exchanger I (6) is connected to the upper inlet of mixing tank (7), and the mixing tank (7) is connected to a water inlet pipe (71). The upper outlet of mixing tank (7) is connected to the upper inlet of heat exchanger II (8). The outlet of heat exchanger II (8) is connected to the inlet of reactor (9). Reactor (9) is connected to carbon disulfide inlet pipe (91). The outlet of reactor (9) is connected to xanthation machine (05) in viscose fiber production system (0). Xanthation machine (05) is also connected to aging box (04) in viscose fiber production system (0). A continuous pathway for the separation, purification, and reuse of hemicellulose in waste alkaline liquid containing hemicellulose is formed between the press (03), plate and frame filter press system (2), microporous filter system (3), nanofiltration system (4), stainless steel membrane system (5), heat exchanger I (6), mixing tank (7), heat exchanger II (8), reaction vessel (9) and xanthation machine (05); A continuous pathway for the separation, purification, and reuse of sodium hydroxide in semi-fiber waste alkali solution is formed between the press (03), plate and frame filter press system (2), microfiltration system (3), nanofiltration system (4) and impregnation tank (02) or alkali preparation tank (01).

10. The comprehensive utilization system for hemicellulose-containing waste alkaline solution according to claim 9, characterized in that, The plate and frame filter press system (2) is provided with a semi-fiber waste alkali liquid collection tank (1) at the front of the work station, and the semi-fiber waste alkali liquid collection tank (1) is connected to the semi-fiber waste alkali liquid outlet on the press (03); A stainless steel membrane retentate collection tank (10) is provided between the stainless steel membrane system (5) and the heat exchanger I (6). A stainless steel membrane filtrate collection tank (11) is provided between the heat exchanger II (8) and the reactor (9).

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