Method and system for recovering hemicellulose from short fiber byproduct
By using concentrated sulfuric acid neutralization and multi-process linkage, the problem of low recycling rate of hemicellulose by-products was solved, achieving efficient separation and recycling, constructing a closed-loop green manufacturing system, and improving resource utilization and economic benefits.
Patent Information
- Application Number
- CN202511443815.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-10
- Publication Date
- 2026-01-23
AI Technical Summary
In existing technologies, the recycling rate of hemicellulose by-products is low, resulting in serious resource waste. Nanofiltration membrane dealkalization processes suffer from high water consumption, high energy consumption, and low dealkalization efficiency, leading to increased costs in subsequent processes and excessive wastewater treatment load.
By neutralizing the hemicellulose alkaline solution to a weakly acidic state with concentrated sulfuric acid, and combining plate and frame filtration, chromatographic separation, and MVR evaporation technology, efficient separation and recovery of hemicellulose and sodium sulfate can be achieved.
This improved the recovery rate of hemicellulose, reduced the sodium sulfate content, established a closed-loop green manufacturing system, reduced equipment corrosion and maintenance costs, and improved economic efficiency and resource utilization.
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Figure CN121372229A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of hemicellulose recovery, and particularly relates to a short fiber byproduct hemicellulose recovery method and system. BACKGROUND
[0002] In the two major pillar industries of the national economy, textiles and papermaking, the recycling of short fibers harbors great resource value, but also faces severe environmental challenges. When processing and extracting short fibers from cotton, hemp, wood pulp and other raw materials, a large amount of byproducts rich in hemicellulose is produced. As a key component of plant cell walls, this substance coexists with cellulose and lignin, and contains rich five-carbon and six-carbon sugar units in its molecular structure, making it a high-quality renewable resource for producing bio-based materials and high-value chemicals. However, for a long time, the industry has been trapped in the "resource waste and environmental pollution" dilemma: a large amount of hemicellulose is either directly burned, releasing carbon dioxide while producing volatile organic pollutants due to incomplete combustion, or is randomly buried, not only occupying land, but also continuously polluting the soil and groundwater with acidic substances during the degradation process. Currently, driven by the concept of circular economy, hemicellulose in the textile and papermaking industries has gradually achieved preliminary resource utilization, with the preparation of xylose being the main application direction. However, in the production of xylose from hemicellulose, the technical problem of high concentration of alkali in the hemicellulose solution is faced. If not properly addressed, it will directly affect the efficiency and product purity of the subsequent hydrolysis process, so removing excess alkali from the raw material has become an indispensable step in production. Currently, nanofiltration membrane technology is mainly used for alkali removal. However, nanofiltration membranes are sensitive to feed liquid concentration. To ensure operating efficiency and avoid flux decay caused by concentration polarization and membrane fouling, high-concentration hemicellulose alkali solution needs to be diluted to a lower concentration. This not only increases the volume of the liquid to be treated and the operating load of the membrane module, but also passively increases the processing capacity of the subsequent process. At the same time, a large amount of process water needs to be continuously introduced for washing during the filtration stage to improve the hemicellulose retention rate and reduce the residual pollutants on the membrane surface. The introduction of a large amount of additional water further exacerbates water consumption and energy consumption, and poses a hidden danger for subsequent wastewater treatment. Even after dilution and washing, the alkali removal rate of this process is only about 70%, with about 30% of the alkali remaining. To meet the requirements of the subsequent hydrolysis, a large amount of concentrated sulfuric acid needs to be added for neutralization, converting it into sodium sulfate. These salts will inhibit hydrolysis or mix salt impurities into the hydrolysis products, directly increasing the difficulty of subsequent refining processes (such as ion exchange and chromatographic separation). In addition, when nanofiltration membranes are used to retain hemicellulose, about 10% of the hemicellulose will be lost with the permeate (low-concentration alkali wastewater) due to the influence of membrane pore size distribution, operating pressure fluctuations, and washing methods. This not only directly wastes raw materials, but also increases the burden of wastewater treatment. In summary, the existing nanofiltration membrane dealkalization process has the problems of high water consumption and energy consumption, and due to the limited dealkalization efficiency and hemicellulose loss, it causes a chain reaction of increased neutralization cost, increased refining difficulty, and excessive wastewater treatment load. The current xylose market is highly competitive, and factors such as fluctuating raw material prices and severe product homogenization have compressed the profit margins of enterprises. Therefore, optimizing the hemicellulose pretreatment process, improving the recovery rate, and reducing the salt content and organic matter concentration in the filtrate have become important issues that need to be addressed. SUMMARY
[0003] The present application aims to solve the technical problems of low recovery rate of hemicellulose by-product and serious resource waste in the existing short fiber production, and proposes a short fiber by-product hemicellulose recovery method and system, which realizes the full-value utilization of by-products through multi-process coordinated linkage.
[0004] In order to achieve the above technical purpose, the technical scheme provided by the present application is: A short fiber by-product hemicellulose recovery method, comprising the following steps, Step 1: neutralization: neutralizing the hemicellulose lye with concentrated sulfuric acid to adjust the pH to weakly acidic to obtain a weakly acidic hemicellulose solution; Step 2: plate and frame pressure filtration: plate and frame pressure filtration of the weakly acidic hemicellulose solution of step 1 to obtain plate and frame filter cake and plate and frame filtrate; Step 3: chromatographic separation: chromatographic separation of the plate and frame filtrate of step 2 to obtain a hemicellulose solution and a sodium sulfate solution; Step 4: evaporation crystallization: evaporation and crystallization of the sodium sulfate solution to obtain sodium sulfate solid.
[0005] Further, in step 1, the hemicellulose lye includes 95-105 g / L of hemicellulose and 38-42 g / L of sodium hydroxide; the feed flow rate is 20-25 m³ / h.
[0006] Further, in step 1, the hemicellulose lye is adjusted to a pH of 4-6; the discharge flow rate is 20-25 m³ / h.
[0007] Specifically, the weakly acidic hemicellulose solution includes 95-105 g / L of hemicellulose and 67.5-74.5 g / L of sodium sulfate.
[0008] Further, in step 2, the plate and frame pressure filtration filter cloth material is polypropylene, and the air permeability is 2.5-3.5 m³ / (m²*h).
[0009] Further, the plate and frame pressure filtration operating conditions include an inlet temperature of 40-60°C, an operating pressure of <16 bar; a feed flow rate of 20-25 m³ / h; and a plate and frame filtrate discharge flow rate of 16-20 m³ / h.
[0010] Further, in step 2, the plate and frame filter cake has a water content of 60%, and the plate and frame filtrate contains 10-12 g / L of hemicellulose and 70-80 g / L of sodium sulfate.
[0011] Further, in step 3, the chromatographic separation uses a special resin, the feed flow rate is 16-20 m³ / h, and the operating temperature is 35-40℃.
[0012] Further, in step 3, the chromatographic separation needs to be separated multiple times by adding desalted water, the flow rate is 40-50 m³ / h; the hemicellulose solution has a discharge flow rate of 16-20 m³ / h, and the sodium sulfate solution has a discharge flow rate of 40-50 m³ / h.
[0013] The desalted water is water with extremely low salt content and organic matter content after reverse osmosis filtration, and the conductivity of the desalted water is 4-7 μS / cm; other water cannot be used, and water containing impurities will pollute the feed liquid and equipment.
[0014] Specifically, the hemicellulose solution and the plate and frame filter cake are mixed for hydrolysis to prepare xylose; the hemicellulose solution contains 10-12 g / L of hemicellulose and 0.5-1 g / L of sodium sulfate; and the sodium sulfate solution contains 0.5-1 g / L of hemicellulose and 28-32 g / L of sodium sulfate.
[0015] Further, in step 4, the evaporation temperature is 78-83℃, and the feed flow rate is 40-50 m³ / h.
[0016] Specifically, the evaporation uses an MVR (mechanical vapor recompression) evaporator, the sodium sulfate solution is concentrated to 40% (that is, 390-410 g / L) after MVR action, the 40% sodium sulfate is cooled to 10℃, and sodium sulfate solids are obtained by continuous centrifugation, the discharge amount is 0.95-1.05 t / h, and the evaporation condensate water discharge is 38-43 m³ / h; the mother liquor after centrifugation returns to the system for continuous evaporation.
[0017] It is detected that, after the hemicellulose lye is neutralized, plate and frame pressure filtration, and chromatographic separation, the hemicellulose solution is diluted to 100 g / L, and the sodium sulfate content is less than 5 g / L; and the purity of the sodium sulfate solids is greater than 95%.
[0018] The application also provides a short fiber byproduct hemicellulose recovery system, which comprises an acid-base neutralization system for neutralizing hemicellulose lye; a plate and frame pressure filtration system for plate and frame pressure filtration of weakly acidic hemicellulose solution; a chromatographic separation system for chromatographic separation of plate and frame filtrate; an evaporation system for evaporation and concentration of sodium sulfate solution.
[0019] The application has the following beneficial effects: 1. Plate-and-frame filter + chromatographic separation technology to realize efficient alkali removal of hemicellulose alkali liquor: The present application uses sulfuric acid to neutralize the hemicellulose alkali liquor, which promotes the rapid precipitation of hemicellulose, and then plate-and-frame filtration is carried out for solid-liquid separation, efficiently completing the alkali removal process of hemicellulose alkali liquor. Compared with the traditional nanofiltration process, this technology has significant advantages in cost control, greatly improves the stability of operation, and can adapt to the needs of long-term continuous production. On this basis, chromatographic separation plays a key role: through precise separation mechanism, efficient separation of hemicellulose and sodium sulfate is realized, not only ensuring high recovery rate of hemicellulose and improving its resource utilization value, but also creating favorable conditions for subsequent purification and recovery of sodium sulfate, helping to form a circular economy model, and improving the resource utilization rate and economic benefit of the overall process.
[0020] 2. Closed-loop design of the whole process to build a green manufacturing system: As a key pre-technology for the production of xylose from hemicellulose hydrolysis, the present application realizes the high-value utilization of hemicellulose alkali liquor resources, significantly improving the economic benefits of the industry. The process design is based on the concept of circular economy, and a closed-loop production system with zero waste discharge is constructed, which meets the development requirements of modern green chemical industry.
[0021] 3. Mild process conditions improve equipment operation efficiency: The whole process runs in a near-neutral feed environment, with low temperature and low pressure process parameters, which greatly reduces the chemical corrosion and mechanical wear of the equipment. This mild operating condition not only prolongs the service life of various devices, but also improves the stability and reliability of the system operation, ensuring the long-term efficient operation of the process from the equipment level, and effectively reducing the operation and maintenance cost. BRIEF DESCRIPTION OF DRAWINGS
[0022] Figure 1 The logical connection diagram of the process system in the present application; Figure 2 The plate-and-frame filter process schematic diagram in the present application; Figure 3 The chromatographic separation process schematic diagram in the present application; Figure 4 The MVR evaporation working process schematic diagram in the present application.
[0023] In the figure: 1, neutralization tank, 2, weakly acidic hemicellulose solution temporary storage tank, 3, plate-and-frame filter device (the company's existing device can be realized), 4, plate-and-frame filter cake temporary storage area, 5, plate-and-frame filtrate temporary storage tank, 6, chromatographic separation device, 7, hemicellulose solution temporary storage tank, 8, sodium sulfate solution temporary storage tank, 9, MVR evaporation device, 10, sodium sulfate temporary storage area, 11, evaporation condensate temporary storage tank, 12, demineralized water tank. DETAILED DESCRIPTION
[0024] The technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of the present application.
[0025] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.
[0026] A short fiber byproduct hemicellulose recovery method, comprising the following steps, Step 1: Neutralization: the hemicellulose lye is neutralized with concentrated sulfuric acid to adjust the pH to weakly acidic to obtain a weakly acidic hemicellulose solution.
[0027] Specifically, the concentrated sulfuric acid is food-grade concentrated sulfuric acid, the hemicellulose lye includes 95-105 g / L of hemicellulose, 38-42 g / L of sodium hydroxide, and the feed flow rate is 20-25 m³ / h; the weakly acidic hemicellulose solution includes 95-105 g / L of hemicellulose, 67.5-74.5 g / L of sodium sulfate, as shown in Table 4.
[0028] The hemicellulose lye is adjusted to a pH of about 5, and the discharge flow rate is 20-25 m³ / h.
[0029] Step 2: Plate and frame filter pressing: the weakly acidic hemicellulose solution of step 1 is subjected to plate and frame filter pressing to obtain a plate and frame filter cake and a plate and frame filtrate.
[0030] Specifically, the filter cloth material for plate and frame filter pressing is polypropylene, and the air permeability is 3 m³ / (m²*h); as shown in Table 1, the plate and frame filter pressing operating conditions include an inlet temperature of 40-60°C, an operating pressure of <16 bar; a feed flow rate of 20-25 m³ / h; and a plate and frame filtrate discharge flow rate of 16-20 m³ / h.
[0031] As shown in Table 5, it is detected that the plate and frame filter cake has a moisture content of 60%, and the plate and frame filtrate includes 10-12 g / L of hemicellulose and 70-80 g / L of sodium sulfate.
[0032] Step 3: Chromatographic separation: the plate and frame filtrate of step 2 is subjected to chromatographic separation to obtain a hemicellulose solution and a sodium sulfate solution.
[0033] Specifically, the chromatographic separation uses a special resin, the feed flow rate is 16-20 m³ / h, as shown in Table 2, the operating temperature is 35-40°C, and the chromatographic separation requires the addition of process water for multiple separations, with a flow rate of 40-50 m³ / h; the hemicellulose solution has a discharge flow rate of 16-20 m³ / h, and the sodium sulfate solution has a discharge flow rate of 40-50 m³ / h.
[0034] The hemicellulose solution is mixed with the plate and frame filter cake to hydrolyze wood sugar; as shown in Table 6, the hemicellulose solution contains 10-12 g / L of hemicellulose and 0.5-1 g / L of sodium sulfate; the sodium sulfate solution contains 0.5-1 g / L of hemicellulose and 28-32 g / L of sodium sulfate.
[0035] Step 4: Evaporation crystallization: the sodium sulfate solution is concentrated and crystallized by evaporation to obtain sodium sulfate solids.
[0036] Further, in step 4, the evaporation temperature is 80°C and the feed flow rate is 40-50 m³ / h, as shown in Table 3.
[0037] Specifically, the evaporation uses an MVR (mechanical vapor recompression) evaporator. The core principle of the MVR evaporator is that the secondary steam generated during the evaporation process is compressed by a compressor to increase its temperature and pressure, so that it becomes higher quality steam (live steam), which is then reused as a heat source for the evaporator to heat the material to be evaporated. In this way, the system does not need or needs very little fresh steam from the outside (only when starting), and mainly relies on the work of the compressor to continuously operate, thereby greatly reducing energy consumption. The sodium sulfate solution is concentrated to 40% (i.e. 390-410 g / L) by MVR, and the 40% sodium sulfate is cooled to 10°C. Sodium sulfate solids are obtained by continuous centrifugation, with an output of 0.95-1.05 t / h, and an evaporation condensate output of 38-43 m³ / h. The mother liquor after centrifugation is returned to the system for continuous evaporation.
[0038] As shown in Table 7, after the hemicellulose lye is neutralized, plate and frame pressure filtration, and chromatographic separation, it is diluted to 100 g / L of hemicellulose solution, and the sodium sulfate content is <5 g / L; the purity of the sodium sulfate solids is >95%.
[0039] Table 1 Plate and frame pressure filtration control conditions Table 2 Chromatographic separation control conditions Table 3 Evaporation system control conditions Table 4 Detection indexes in the hemicellulose lye solution after neutralization Table 5 Detection indexes in the solution after plate and frame pressure filtration Table 6 Detection indexes in the solution after chromatographic separation Table 7 Detection index of sodium sulfate after evaporative crystallization As Figure 1 shown, the present application also provides a short fiber byproduct hemicellulose recovery system, comprising an acid-base neutralization system for neutralizing hemicellulose lye; a plate-and-frame filter pressing system for plate-and-frame filter pressing of weakly acidic hemicellulose solution; a chromatographic separation system for chromatographic separation of plate-and-frame filtrate; an evaporation system for evaporation and concentration crystallization of sodium sulfate solution.
[0040] Specifically, in the short fiber byproduct hemicellulose recovery system, various storage tanks such as acid liquid, lye, dilution liquid, process water, plate-and-frame filter pressing device, chromatographic separation device and MVR device are included.
[0041] As Figure 2 shown, the acid-base neutralization system comprises a neutralization tank 1 and a weakly acidic hemicellulose temporary storage tank 2 connected in sequence; the weakly acidic hemicellulose obtained after the hemicellulose lye enters the neutralization tank 1 enters the weakly acidic hemicellulose temporary storage tank 2; As Figure 3 shown, the plate-and-frame filter pressing system comprises a plate-and-frame filter pressing device 3, a plate-and-frame filter cake temporary storage area 4 and a plate-and-frame filtrate temporary storage tank 5; the weakly acidic hemicellulose solution in the weakly acidic hemicellulose temporary storage tank enters the plate-and-frame filter pressing device to obtain plate-and-frame filter cake and plate-and-frame filtrate, wherein the plate-and-frame filter cake enters the plate-and-frame filter cake temporary storage area and the plate-and-frame filtrate enters the plate-and-frame filtrate temporary storage tank; As Figure 4 shown, the chromatographic separation system comprises a chromatographic separation device 6, a sodium sulfate solution temporary storage tank 8, a hemicellulose solution temporary storage tank 7 and a desalted water tank 12; the plate-and-frame filtrate in the plate-and-frame filtrate temporary storage area enters the chromatographic separation device to obtain sodium sulfate solution and hemicellulose solution, the sodium sulfate solution enters the sodium sulfate solution temporary storage tank, the hemicellulose solution enters the hemicellulose solution temporary storage tank, and the desalted water in the desalted water tank enters the chromatographic separation device; The evaporation system comprises an MVR device 9, an evaporation condensate water temporary storage tank 11 and a sodium sulfate temporary storage area 10; the sodium sulfate solution in the sodium sulfate solution temporary storage tank enters the MVR device to obtain evaporation condensate water and sodium sulfate, the evaporation condensate water enters the evaporation condensate water temporary storage tank, and the sodium sulfate enters the sodium sulfate temporary storage area.
[0042] It should be noted that each device described above also includes a matching cleaning system, including a cleaning tank, various cleaning agent adding devices and matching pipelines, etc. According to actual needs, flow meters, control valves and automatic control devices are provided on each conveying pipe.
[0043] In the technical solution, the working principle is: In the pretreatment step, concentrated sulfuric acid is accurately added to neutralize the sodium hydroxide in the hemicellulose alkali solution. Given the solubility of hemicellulose in alkali, adjusting the pH can cause most of the hemicellulose to precipitate, which directly creates favorable conditions for the subsequent plate and frame filter pressing process.
[0044] The core of the plate and frame filter pressing system is the selective permeability of the filter cloth. In this system, sodium sulfate dissolved in water and a small amount of low molecular weight hemicellulose can pass through the filter cloth to form a plate and frame filtrate, while most of the hemicellulose and a small amount of sodium sulfate are intercepted by the filter cloth. Through this process, sodium sulfate can be effectively removed from the hemicellulose solution.
[0045] The separation principle of the chromatography system is based on the difference in the force between different solutes and the stationary phase and mobile phase. When the two phases move relative to each other, each solute will undergo multiple equilibria between the two phases, and then separate from each other, ultimately achieving the separation of hemicellulose and sodium sulfate.
[0046] The operation process of the MVR system is as follows: under the action of steam heating, the treated liquid is boiled, then the vacuum pump extracts the generated water vapor and liquefies it by cooling, and the compressor performs secondary compression and heating on the low-temperature steam. This process not only concentrates sodium sulfate, but also realizes the secondary utilization of heat. After the concentration of sodium sulfate is completed, a large amount of sodium sulfate crystals will be precipitated through cooling treatment, and then through centrifugal operation, a high-purity sodium sulfate solid can be obtained.
[0047] Example 1 A short fiber byproduct hemicellulose recovery process, comprising the following steps: Neutralization: The hemicellulose alkali solution is neutralized with concentrated sulfuric acid to adjust the pH to weakly acidic; Plate and frame filter pressing: The weakly acidic hemicellulose solution after neutralization is introduced into the plate and frame filter pressing system to obtain plate and frame filter cake and plate and frame filtrate; Chromatographic separation: The plate and frame filtrate is introduced into the chromatographic separation system, and under the action of the chromatographic resin, a hemicellulose solution and a sodium sulfate solution are obtained; the hemicellulose solution is mixed with the plate and frame filter cake to hydrolyze and produce xylose; 4) Evaporation and crystallization: The sodium sulfate solution is introduced into the evaporation system, and sodium sulfate solid is obtained after concentration and crystallization.
[0048] Example 2 Based on Example 1, further improvements are made: The hemicellulose alkali solution refers to the hemicellulose alkali solution left after the alkali solution is used to extract cellulose and lignin from pulp in a chemical fiber factory and then filtered. The hemicellulose alkali solution includes 95-105 g / L of hemicellulose and 38-42 g / L of sodium hydroxide.
[0049] Example 3 Further to Example 2, further: Further, in the neutralization system of Step 1), the hemicellulose lye feed flow rate is 22 m3 / h, the weakly acidic hemicellulose lye after neutralization is 22 m3 / h, the pH of the feed liquid is automatically controlled by the regulating valve, and the pH is 5.1; Further, in the plate-and-frame filter system of Step 2), the plate-and-frame feed flow rate is 22 m3 / h, the feed liquid temperature is 51 °C, and the operating pressure is 12.5 bar; the plate-and-frame filtrate discharge flow rate is 17.6 m3 / h; the plate-and-frame filter cake moisture content is <60%, and the hemicellulose yield is >90%; Further, in the chromatographic separation system of Step 3), the chromatographic feed flow rate is 17.6 m3 / h (process water makeup flow rate is 43.25 m3 / h), and the feed liquid temperature is 39 °C; the hemicellulose solution discharge flow rate is 17.6 m3 / h, and the sodium sulfate solution discharge flow rate is 43.25 m3 / h; Further, in the evaporation system of Step 4), the feed flow rate is 43.25 m3 / h, the evaporation condensate water discharge flow rate is 39.5 m3 / h, and the concentrated liquid discharge flow rate is 3.75 m3 / h; the vacuum degree is 81 kpa, and the operating temperature is 80 °C.
[0050] Example 4 Further, in the neutralization system of Step 1), the hemicellulose lye feed flow rate is 24 m3 / h, the weakly acidic hemicellulose lye after neutralization is 24 m3 / h, the pH of the feed liquid is automatically controlled by the regulating valve, and the pH is 5.0; Further, in the plate-and-frame filter system of Step 2), the plate-and-frame feed flow rate is 24 m3 / h, the feed liquid temperature is 48 °C, and the operating pressure is 11.8 bar; the plate-and-frame filtrate discharge flow rate is 19.2 m3 / h; the plate-and-frame filter cake moisture content is <60%, and the hemicellulose yield is >90%; Further, in the chromatographic separation system of Step 3), the chromatographic feed flow rate is 19.2 m3 / h (process water makeup flow rate is 48 m3 / h), and the feed liquid temperature is 41 °C; the hemicellulose solution discharge flow rate is 19.2 m3 / h, and the sodium sulfate solution discharge flow rate is 48 m3 / h; Further, in the evaporation system of Step 4), the feed flow rate is 48 m3 / h, the evaporation condensate water discharge flow rate is 43.8 m3 / h, and the concentrated liquid discharge flow rate is 4.2 m3 / h; the vacuum degree is 80.9 kpa, and the operating temperature is 82 °C.
[0051] Example 5 Further, in the neutralization system of Step 1), the hemicellulose lye feed flow rate is 23.4 m3 / h, the weakly acidic hemicellulose lye after neutralization is 23.4 m3 / h, the pH of the feed liquid is automatically controlled by the regulating valve, and the pH is 4.9; Further, in the plate-and-frame filter system of step 2), the plate-and-frame feed flow rate is 23.4 m3 / h, the feed temperature is 50℃, the operation pressure is 12.2 bar; the plate-and-frame filtrate flow rate is 18.72 m3 / h; the plate-and-frame filter cake moisture content is < 60%, and the hemicellulose yield is > 90%; Further, in the chromatographic separation system of step 3), the chromatographic feed flow rate is 18.72 m3 / h (the process water make-up flow rate is 46.8 m3 / h), the feed temperature is 40℃; the hemicellulose solution flow rate is 18.72 m3 / h, and the sodium sulfate solution flow rate is 46.8 m3 / h; Further, in the evaporation system of step 4), the feed flow rate is 46.8 m3 / h, the evaporation condensate flow rate is 42.8 m3 / h, and the concentrated liquid flow rate is 4.0 m3 / h; the vacuum degree is 81.2 kpa, and the operation temperature is 81℃.
[0052] Example 6 Based on the examples 3-5, further: In step 1), the weakly acidic hemicellulose-containing alkali liquor includes 101.3 g / L of hemicellulose and 71.7 g / L of sodium sulfate; In step 2), the plate-and-frame filtrate includes 10.5 g / L of hemicellulose and 76.4 g / L of sodium sulfate; In step 3), the hemicellulose solution includes 10.2 g / L of hemicellulose and 0.5 g / L of sodium sulfate; and the sodium sulfate solution includes 0.6 g / L of hemicellulose and 31.8 g / L of sodium sulfate; In step 4), the sodium sulfate concentrated liquid includes 405 g / L of sodium sulfate.
[0053] Example 7 Based on the example 6, the difference of the present example is: In step 1), the weakly acidic hemicellulose-containing alkali liquor includes 99.6 g / L of hemicellulose and 69.4 g / L of sodium sulfate; In step 2), the plate-and-frame filtrate includes 10.1 g / L of hemicellulose and 72.3 g / L of sodium sulfate; In step 3), the hemicellulose solution includes 10.0 g / L of hemicellulose and 0.6 g / L of sodium sulfate; and the sodium sulfate solution includes 0.7 g / L of hemicellulose and 28.8 g / L of sodium sulfate; In step 4), the sodium sulfate concentrated liquid includes 397 g / L of sodium sulfate.
[0054] Example 8 Based on the examples 6-7, the difference of the present example is: In step 1), the weakly acidic hemicellulose-containing alkaline liquor includes 104.1 g / L of hemicellulose and 71.8 g / L of sodium sulfate; In step 2), the plate-and-frame filtrate includes 11.2 g / L of hemicellulose and 73.4 g / L of sodium sulfate; In step 3), the hemicellulose solution includes 10.7 g / L of hemicellulose and 0.6 g / L of sodium sulfate; and the sodium sulfate solution includes 0.6 g / L of hemicellulose and 30.9 g / L of sodium sulfate; In step 4), the sodium sulfate concentrated solution includes 400 g / L of sodium sulfate.
[0055] Therefore, the present application accurately neutralizes the hemicellulose alkaline liquor, adjusts the system pH value to the optimal range of about 5, and lays a foundation for subsequent separation and purification processes. This step avoids the degradation of hemicellulose caused by excessive acid conditions and the corrosion of subsequent filter pressing equipment by optimizing the acid-base ratio, thereby significantly improving the stability of the process. The core separation stage adopts the combined technology of plate-and-frame filter pressing and chromatographic separation. The plate-and-frame filter pressing process can directionally intercept about 90% of the hemicellulose components through the design of the selection permeability of the customized filter cloth, while reducing the moisture content of the hemicellulose filter cake to below 60%. This process can simultaneously remove 85% of the sodium sulfate in the hemicellulose, significantly reducing the salt content in the hemicellulose, creating favorable conditions for the subsequent hydrolysis process, and finally stabilizing the hemicellulose yield at about 90%. The filtrate generated by the plate-and-frame filter pressing is immediately subjected to chromatographic separation, which utilizes the selective adsorption characteristics of special resins for organic and inorganic substances to achieve efficient separation of hemicellulose and sodium sulfate. This step not only avoids the loss of hemicellulose, but also successfully solves the technical problem of the difficulty in separating the hemicellulose and sodium sulfate mixture in traditional processes. The recovered hemicellulose can be directly returned to the plate-and-frame filter cake and enter the hydrolysis process together to prepare xylose.
[0056] In terms of resource recycling, the separated sodium sulfate solution is concentrated to 33% concentration by multi-effect evaporation, and high-purity sodium sulfate products can be prepared through a cooling crystallization process, realizing the resource utilization of waste. The entire process efficiently connects each link, improves the quality of xylose and sodium sulfate products, realizes the full recovery and recycling of short fiber by-products, significantly reduces the solid waste discharge during production, fully implements the green production concept, and provides a referenceable technical paradigm for clean production in the textile and chemical industry.
[0057] Although embodiments of the present application have been shown and described, it will be understood by those having ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.
[0058] The above detailed description is a detailed description of the application, and cannot be considered as limiting the specific embodiments of the application to these descriptions. For those skilled in the art, without departing from the concept of the application, a number of simple deductions and substitutions can be made, which should be considered as falling within the scope of protection of the application.
Claims
1. A method for recovering hemicellulose, a short fiber byproduct, characterized in that, Includes the following steps, Step 1: Neutralization: Neutralize the hemicellulose alkaline solution with concentrated sulfuric acid and adjust the pH to weakly acidic to obtain a weakly acidic hemicellulose solution; Step 2: Plate and frame filtration: The weakly acidic hemicellulose solution from Step 1 is subjected to plate and frame filtration to obtain plate and frame filter cake and plate and frame filtrate; Step 3: Chromatographic separation: The plate and frame filter filtrate from Step 2 is subjected to chromatographic separation to obtain a hemicellulose solution and a sodium sulfate solution; Step 4: Evaporation and crystallization: The sodium sulfate solution is evaporated, concentrated, and crystallized to obtain solid sodium sulfate.
2. The method for recovering hemicellulose, a short fiber byproduct, according to claim 1, is characterized in that, In step 1, the hemicellulose alkali solution comprises 95-105 g / L of hemicellulose and 38-42 g / L of sodium hydroxide; the feed flow rate is 20-25 m³ / h.
3. The method for recovering hemicellulose, a short fiber byproduct, according to claim 1, is characterized in that, In step 1, the pH of the hemicellulose alkali solution is adjusted to around 5; the discharge flow rate is 20-25 m³ / h.
4. The method for recovering hemicellulose, a short fiber byproduct, according to claim 1, is characterized in that, In step 2, the filter cloth of the plate and frame filter press is made of polypropylene with an air permeability of 3 m³ / (㎡*h).
5. The method for recovering hemicellulose, a short fiber byproduct, according to claim 1, is characterized in that, The operating conditions for plate and frame filter press include a feed temperature of 40-60℃, an operating pressure of <16 bar, a feed flow rate of 20-25 m³ / h, and a filtrate discharge flow rate of 16-20 m³ / h.
6. The method for recovering hemicellulose, a short fiber byproduct, according to claim 1, is characterized in that, In step 2, the moisture content of the plate and frame filter cake is 60%, and the plate and frame filtrate includes 10-12 g / L of hemicellulose and 70-80 g / L of sodium sulfate.
7. The method for recovering hemicellulose, a short fiber byproduct, according to claim 1, is characterized in that, In step 3, the resin is a special resin with a feed flow rate of 16-20 m³ / h and an operating temperature of 35-40℃.
8. The method for recovering hemicellulose, a short fiber byproduct, according to claim 1, is characterized in that, In step 3, the chromatographic separation requires the addition of process water for multiple separations at a flow rate of 40-50 m³ / h; the hemicellulose solution discharge flow rate is 16-20 m³ / h, and the sodium sulfate solution discharge flow rate is 40-50 m³ / h.
9. The method for recovering hemicellulose, a short fiber byproduct, according to claim 1, is characterized in that, In step 4, the evaporation temperature is 80℃ and the feed flow rate is 40-50 m³ / h.
10. A short fiber byproduct hemicellulose recovery system, characterized in that, include An acid-base neutralization system is used to neutralize alkaline solutions containing hemicellulose. Plate and frame filtration system for filtration of weakly acidic hemicellulose solutions; A chromatographic separation system for the chromatographic separation of plate and frame filtrates; An evaporation system is used to evaporate, concentrate, and crystallize sodium sulfate solution.