Multi-stage gradient hemicellulose concentration and alkali recovery unit

Abstract

This utility model relates to the field of viscose fiber production technology, and is a multi-stage gradient hemicellulose concentration and alkali recovery device. It includes a membrane separation unit, a neutralization reaction tank, a ceramic membrane concentration unit, and a drying unit. A first material conveying pipeline connects the membrane separation unit and the neutralization reaction tank; a second material conveying pipeline connects the neutralization reaction tank and the ceramic membrane concentration unit; and a third material conveying pipeline connects the ceramic membrane concentration unit and the drying unit. The membrane separation unit employs a three-stage nanofiltration membrane system. The first and second stages of the nanofiltration membrane system use three-stage series nanofiltration membrane modules, while the third stage uses four-stage series nanofiltration membrane modules. This utility model has a reasonable and compact structure and is easy to use. Through multi-gradient concentration using the nanofiltration membrane system and deep purification by the ceramic membrane concentration unit, it gradually increases the hemicellulose concentration, reduces the inorganic salt content in the concentrate, and improves the quality of the hemicellulose product.

Description

Technical Field

[0001] This utility model relates to the field of viscose fiber production technology and is a multi-stage gradient hemicellulose concentration and alkali recovery device. Background Technology

[0002] Viscose fiber, also known as viscose yarn, is a type of man-made fiber. It has good moisture absorption, is easy to dye, does not easily generate static electricity, and has good spinnability, making it widely used in various textile and apparel industries. In the production process of viscose fiber, the recycling of liquid alkali (sodium hydroxide solution) and hemicellulose is a key step in achieving efficient resource utilization and green production.

[0003] Traditional methods for recovering liquid alkali and hemicellulose mainly rely on dialysis and membrane separation processes. Dialysis is gradually being phased out due to its low efficiency, high water consumption, and large footprint. While alkali-resistant nanofiltration membranes can separate hemicellulose from alkali solutions, current technologies face several bottlenecks: first, severe membrane fouling leads to rapid flux decline and frequent cleaning; second, the use of a two-stage nanofiltration system results in low hemicellulose concentration (≤100g / L in traditional processes), leading to high energy consumption in subsequent drying units; and third, the high sodium hydroxide content in the concentrate (≥35g / L in traditional processes) necessitates large amounts of sulfuric acid for neutralization, increasing operating costs and wastewater treatment burden.

[0004] Therefore, it is essential to invent a multi-stage gradient hemicellulose concentration and alkali recovery device. Summary of the Invention

[0005] This invention provides a multi-stage gradient hemicellulose concentration and alkali recovery device, which overcomes the shortcomings of the prior art and can effectively solve the problems of serious membrane fouling, low hemicellulose concentration, and high sodium hydroxide content in the concentrate in the existing hemicellulose concentration and alkali recovery process.

[0006] The technical solution of this utility model is achieved through the following measures: a multi-stage gradient hemicellulose concentration and alkali recovery device, including a membrane separation unit, a neutralization reaction tank, a ceramic membrane concentration unit, and a drying unit. A first material conveying pipeline is fixedly connected between the outlet of the membrane separation unit and the first inlet at the top of the neutralization reaction tank. A second material conveying pipeline is fixedly connected between the outlet at the bottom of the neutralization reaction tank and the inlet of the ceramic membrane concentration unit. A sulfuric acid conveying pipeline is fixedly connected to the second inlet at the top of the neutralization reaction tank. A third material conveying pipeline is fixedly connected between the outlet of the ceramic membrane concentration unit and the inlet of the drying unit. A hemicellulose conveying pipeline is fixedly connected to the outlet of the drying unit.

[0007] The following are further optimizations and / or improvements to the above-mentioned utility model technical solution: The membrane separation unit mentioned above includes a primary nanofiltration membrane system, a secondary nanofiltration membrane system, and a tertiary nanofiltration membrane system. The primary and secondary nanofiltration membrane systems are each configured as dual sets of three-stage series-connected nanofiltration membrane modules, while the tertiary nanofiltration membrane system is configured as a single set of four-stage series-connected nanofiltration membrane modules.

[0008] The aforementioned primary nanofiltration membrane system includes a primary feed tank, a first primary nanofiltration membrane module, a second primary nanofiltration membrane module, and a secondary feed tank. A fourth material conveying pipeline is fixedly connected between the lower outlet of the primary feed tank and the lower inlet of the first primary nanofiltration membrane module. A fifth material conveying pipeline is fixedly connected between the fourth material conveying pipeline and the lower inlet of the second primary nanofiltration membrane module. A sixth material conveying pipeline is fixedly connected between the upper outlet of the first primary nanofiltration membrane module and the first inlet at the top of the secondary feed tank. A seventh material conveying pipeline is fixedly connected between the upper outlet of the second primary nanofiltration membrane module and the second inlet at the top of the secondary feed tank. A first medium-concentration alkali solution conveying pipeline is fixedly connected to the top outlet of the first primary nanofiltration membrane module, and a second medium-concentration alkali solution conveying pipeline is fixedly connected between the top outlet of the second primary nanofiltration membrane module and the first medium-concentration alkali solution conveying pipeline.

[0009] The aforementioned two-stage nanofiltration membrane system includes a first-stage two-stage nanofiltration membrane module, a second-stage two-stage nanofiltration membrane module, and a third-stage feed tank. An eighth material conveying pipeline is fixedly connected between the lower outlet of the second-stage feed tank and the lower inlet of the first-stage two-stage nanofiltration membrane module. A ninth material conveying pipeline is fixedly connected between the eighth material conveying pipeline and the lower inlet of the second-stage two-stage nanofiltration membrane module. A tenth material conveying pipeline is fixedly connected between the upper outlet of the first-stage two-stage nanofiltration membrane module and the first inlet at the top of the third-stage feed tank. An eleventh material conveying pipeline is fixedly connected between the upper outlet of the second-stage two-stage nanofiltration membrane module and the second inlet at the top of the third-stage feed tank. A first low-concentration alkali solution conveying pipeline is fixedly connected to the top outlet of the first-stage two-stage nanofiltration membrane module. A second low-concentration alkali solution conveying pipeline is fixedly connected between the top outlet of the second-stage two-stage nanofiltration membrane module and the first low-concentration alkali solution conveying pipeline.

[0010] Each of the above-mentioned No. 1 primary nanofiltration membrane module, No. 2 primary nanofiltration membrane module, No. 1 secondary nanofiltration membrane module, and No. 2 secondary nanofiltration membrane module is equipped with six 4-core membrane tanks. The third-stage membrane modules of the No. 1 primary nanofiltration membrane module, No. 2 primary nanofiltration membrane module, No. 1 secondary nanofiltration membrane module, and No. 2 secondary nanofiltration membrane module all adopt a wide-channel structure membrane with a channel width of 46mil.

[0011] The aforementioned three-stage nanofiltration membrane system includes a three-stage nanofiltration membrane module. A twelfth material conveying pipeline is fixedly connected between the lower outlet of the three-stage feed tank and the lower inlet of the three-stage nanofiltration membrane module. A third low-concentration alkali conveying pipeline is fixedly connected between the top outlet of the three-stage nanofiltration membrane module and the first low-concentration alkali conveying pipeline between the outlet of the second low-concentration alkali conveying pipeline and the outlet of the first low-concentration alkali conveying pipeline. A first material conveying pipeline is fixedly connected between the upper outlet of the three-stage nanofiltration membrane module and the first inlet at the top of the neutralization reaction tank.

[0012] The first and second stages of the aforementioned three-stage nanofiltration membrane module each use twelve 4-core membrane tanks, the third stage uses ten 3-core membrane tanks, and the fourth stage uses ten 2-core membrane tanks. The first and second stages of the three-stage nanofiltration membrane module use narrow channel membrane structures with a channel width of 34 mil, while the third and fourth stages use wide channel membrane structures with a channel width of 46 mil.

[0013] The fourth, fifth, and twelfth material conveying pipelines between the fifth material conveying pipeline and the first primary nanofiltration membrane module, the eighth, ninth, and twelfth material conveying pipelines between the ninth material conveying pipeline and the first secondary nanofiltration membrane module, and the second material conveying pipeline are respectively equipped with a first conveying pump, a second conveying pump, a third conveying pump, a fourth conveying pump, a fifth conveying pump, and a sixth conveying pump.

[0014] The aforementioned ceramic membrane concentration unit employs a two-stage series alumina ceramic membrane module.

[0015] The aforementioned drying unit employs a hot air spray drying system.

[0016] This utility model has a reasonable and compact structure and is easy to use. It uses a multi-gradient concentration system of primary, secondary and tertiary nanofiltration membranes and a ceramic membrane concentration unit for deep purification. This gradually increases the concentration of hemicellulose, reduces the content of inorganic salts in the concentrate, and improves the quality of hemicellulose powder. At the same time, it reduces neutralization costs and sodium sulfate wastewater discharge, reduces sulfuric acid consumption by 140 kg per ton, and increases hemicellulose production by 20%. Attached Figure Description

[0017] Appendix Figure 1 This is a schematic diagram of the process flow of this utility model.

[0018] Appendix Figure 1The codes are as follows: 1 for neutralization reaction tank, 2 for first material conveying pipeline, 3 for second material conveying pipeline, 4 for third material conveying pipeline, 5 for sulfuric acid conveying pipeline, 6 for hemicellulose conveying pipeline, 7 for primary feed tank, 8 for first-stage nanofiltration membrane module 1, 9 for second-stage nanofiltration membrane module 2, 10 for secondary feed tank, 11 for fourth material conveying pipeline, 12 for fifth material conveying pipeline, 13 for sixth material conveying pipeline, 14 for seventh material conveying pipeline, 15 for first-stage medium-concentration alkali solution conveying pipeline, 16 for second-stage medium-concentration alkali solution conveying pipeline, 17 for first-stage secondary nanofiltration membrane module 1, and 18 for second-stage secondary nanofiltration membrane module 2. The system consists of: a secondary nanofiltration membrane module, a tertiary feed tank (19), an eighth material conveying line (20), a ninth material conveying line (21), a tenth material conveying line (22), an eleventh material conveying line (23), a first low-concentration alkali solution conveying line (24), a second low-concentration alkali solution conveying line (25), a tertiary nanofiltration membrane module (26), a twelfth material conveying line (27), a third low-concentration alkali solution conveying line (28), a first transfer pump (29), a second transfer pump (30), a third transfer pump (31), a fourth transfer pump (32), a fifth transfer pump (33), a sixth transfer pump (34), a ceramic membrane concentration unit (35), and a drying unit (36). Detailed Implementation

[0019] This utility model is not limited to the following embodiments, and the specific implementation method can be determined according to the technical solution of this utility model and the actual situation.

[0020] Unless otherwise specified, all equipment and devices used in this invention are existing, publicly known, and commonly used equipment and devices in the field.

[0021] In this utility model, for ease of description, the description of the relative positions of the components is based on the appendix to the specification. Figure 1 The layout is described using a diagrammatic method, such as the positional relationships of front, back, top, bottom, left, and right, which are based on the instructions attached. Figure 1 The orientation of the layout is determined by the direction of the map.

[0022] The present invention will be further described below with reference to the embodiments and accompanying drawings: Example 1: As shown in the attached document Figure 1 As shown, the multi-stage gradient hemicellulose concentration and alkali recovery device includes a membrane separation unit, a neutralization reaction tank 1, a ceramic membrane concentration unit 35, and a drying unit 36. A first material conveying pipeline 2 is fixedly connected between the outlet of the membrane separation unit and the first inlet at the top of the neutralization reaction tank 1. A second material conveying pipeline 3 is fixedly connected between the bottom outlet of the neutralization reaction tank 1 and the inlet of the ceramic membrane concentration unit 35. A third material conveying pipeline 4 is fixedly connected between the outlet of the ceramic membrane concentration unit 35 and the inlet of the drying unit 36. A hemicellulose conveying pipeline 5 is fixedly connected to the outlet of the drying unit 36. A sulfuric acid conveying pipeline 6 is fixedly connected to the second inlet at the top of the neutralization reaction tank 1.

[0023] In this invention, after pretreatment by a front-end filtration system, the alkali liquid from the pressing waste liquor is adjusted to the required concentrations of alkali and hemicellulose before entering a primary nanofiltration membrane system to separate primary concentrate and primary purified liquor. The primary concentrate is diluted with water and then enters a secondary nanofiltration membrane system to separate secondary concentrate and secondary purified liquor. The secondary concentrate is diluted with water and then enters a tertiary nanofiltration membrane system to separate tertiary concentrate and tertiary purified liquor. All of the above-mentioned primary, secondary, and tertiary purified liquors are reused in the viscose fiber production system. The tertiary concentrate is neutralized with 93% sulfuric acid to a pH value of 5.5 to 6.5 and then enters a ceramic membrane concentration unit 35 to separate a concentrate with a hemicellulose concentration ≥200g / L. The concentrate is then dried by a drying unit 36 ​​to obtain hemicellulose particles.

[0024] By using multi-stage nanofiltration membrane gradient concentration and ceramic membrane purification, the efficient concentration of hemicellulose in the alkali liquor from pressing waste is achieved, along with alkali liquor reuse and wastewater reduction.

[0025] The above-mentioned multi-stage gradient hemicellulose concentration and alkali recovery device can be further optimized and / or improved according to actual needs: Example 2: Its difference from Example 1 is as follows: (See attached) Figure 1 As shown: The membrane separation unit includes a primary nanofiltration membrane system, a secondary nanofiltration membrane system, and a tertiary nanofiltration membrane system. The primary and secondary nanofiltration membrane systems are each configured as dual sets of three-stage series-connected nanofiltration membrane modules, while the tertiary nanofiltration membrane system is configured as a single set of four-stage series-connected nanofiltration membrane modules.

[0026] Example 3: Its difference from Examples 1 to 2 is as follows: (See attached) Figure 1 As shown, the primary nanofiltration membrane system includes a primary feed tank 7, a primary nanofiltration membrane module 8, a secondary nanofiltration membrane module 9, and a secondary feed tank 10. A fourth material conveying pipeline 11 is fixedly connected between the lower outlet of the primary feed tank 7 and the lower inlet of the primary nanofiltration membrane module 8. A fifth material conveying pipeline 12 is fixedly connected between the fourth material conveying pipeline 11 and the lower inlet of the secondary nanofiltration membrane module 9. A sixth material conveying pipeline 13 is fixedly connected between the upper outlet of the primary nanofiltration membrane module 8 and the first inlet at the top of the secondary feed tank 10. A seventh material conveying pipeline 14 is fixedly connected between the upper outlet of the secondary nanofiltration membrane module 9 and the second inlet at the top of the secondary feed tank 10. A first medium-concentration alkali solution conveying pipeline 15 is fixedly connected to the top outlet of the primary nanofiltration membrane module 8. A second medium-concentration alkali solution conveying pipeline 16 is fixedly connected between the top outlet of the secondary nanofiltration membrane module 9 and the first medium-concentration alkali solution conveying pipeline 15.

[0027] Example 4: Its difference from Examples 1 to 3 is as follows: (See attached) Figure 1As shown, the secondary nanofiltration membrane system includes a primary secondary nanofiltration membrane module 17, a secondary secondary nanofiltration membrane module 18, and a tertiary feed tank 19. An eighth material conveying pipeline 20 is fixedly connected between the lower outlet of the secondary feed tank 10 and the lower inlet of the primary secondary nanofiltration membrane module 17. A ninth material conveying pipeline 21 is fixedly connected between the eighth material conveying pipeline 20 and the lower inlet of the secondary secondary nanofiltration membrane module 18. A tenth material conveying pipeline 22 is fixedly connected between the upper outlet of the primary secondary nanofiltration membrane module 17 and the first inlet at the top of the tertiary feed tank 19. An eleventh material conveying pipeline 23 is fixedly connected between the upper outlet of the secondary secondary nanofiltration membrane module 18 and the second inlet at the top of the tertiary feed tank 19. A first low-concentration alkali solution conveying pipeline 24 is fixedly connected to the top outlet of the primary secondary nanofiltration membrane module 17. A second low-concentration alkali solution conveying pipeline 25 is fixedly connected between the top outlet of the secondary secondary nanofiltration membrane module 18 and the first low-concentration alkali solution conveying pipeline 24.

[0028] Example 5: It differs from Examples 1 to 4 in that, as shown in the appendix... Figure 1 As shown, each of the first-stage nanofiltration membrane module 8, the second-stage nanofiltration membrane module 9, the first-stage nanofiltration membrane module 17, and the second-stage nanofiltration membrane module 18 is equipped with six 4-core membrane tanks. The third-stage membrane modules of the first-stage nanofiltration membrane module 8, the second-stage nanofiltration membrane module 9, the first-stage nanofiltration membrane module 17, and the second-stage nanofiltration membrane module 18 all adopt a wide-channel structure membrane with a channel width of 46mil.

[0029] As required, the first and second sections of the No. 1 primary nanofiltration membrane module 8, the No. 2 primary nanofiltration membrane module 9, the No. 1 secondary nanofiltration membrane module 17, and the No. 2 secondary nanofiltration membrane module 18 all adopt a narrow flow channel structure membrane with a flow channel width of 34mil.

[0030] When the hemicellulose and alkali solutions reach the third-stage membrane module, both the alkali concentration and hemicellulose solubility decrease, and the concentration factor increases. This places higher demands on the performance of the nanofiltration membrane module. Wide-channel membranes, with their lower flow rates, facilitate laminar flow, exhibit weaker shear forces, more pronounced concentration polarization, more uniform fluid distribution, lower flow resistance, lower pressure drop, and ample channel space, resulting in less particle retention and stronger antifouling capabilities. Therefore, the third-stage membrane modules of the No. 1 primary nanofiltration membrane module 8, No. 2 primary nanofiltration membrane module 9, No. 1 secondary nanofiltration membrane module 17, and No. 2 secondary nanofiltration membrane module 18 utilize wide-channel membranes, which are more conducive to the separation of alkali and hemicellulose.

[0031] Example 6: Its difference from Examples 1 to 5 is as follows: (See attached) Figure 1As shown, the three-stage nanofiltration membrane system includes a three-stage nanofiltration membrane module 26. A twelfth material conveying pipeline 27 is fixedly connected between the lower outlet of the three-stage feed tank 19 and the lower inlet of the three-stage nanofiltration membrane module 26. A third low-concentration alkali conveying pipeline 28 is fixedly connected between the top outlet of the three-stage nanofiltration membrane module 26 and the first low-concentration alkali conveying pipeline 24 between the outlets of the second low-concentration alkali conveying pipeline 25 and the first low-concentration alkali conveying pipeline 24. A first material conveying pipeline 2 is fixedly connected between the upper outlet of the three-stage nanofiltration membrane module 26 and the first inlet at the top of the neutralization reaction tank 1.

[0032] Example 7: Its difference from Examples 1 to 6 is as follows: (See attached) Figure 1 As shown, the first and second membrane modules of the three-stage nanofiltration membrane module 26 each use twelve 4-core membrane tanks, the third membrane module of the three-stage nanofiltration membrane module 26 uses ten 3-core membrane tanks, and the fourth membrane module of the three-stage nanofiltration membrane module 26 uses ten 2-core membrane tanks. The first and second membrane modules of the three-stage nanofiltration membrane module 26 use narrow channel structure membranes with a channel width of 34 mil, while the third and fourth membrane modules of the three-stage nanofiltration membrane module 26 use wide channel structure membranes with a channel width of 46 mil.

[0033] In this utility model, the first-stage nanofiltration membrane module 8, the second-stage nanofiltration membrane module 9, the first-stage nanofiltration membrane module 17, the second-stage nanofiltration membrane module 18, and the third-stage nanofiltration membrane module 26 are all acid and alkali resistant nanofiltration membranes, and the membrane structure adopts a spiral-wound FRP shell and a polysulfone permeate pipe.

[0034] As needed, the pressing waste alkaline liquor is pretreated by a plate and frame filter and a microfiltration system. After adjusting the alkaline concentration to 110 g / L and the hemicellulose concentration to 40 g / L, it enters a primary nanofiltration membrane system to separate a primary concentrate with a hemicellulose concentration ≥90 g / L and a primary purified liquor with an alkaline concentration ≥110 g / L. The primary concentrate is diluted with water and then enters a secondary nanofiltration membrane system to separate a secondary concentrate with a hemicellulose concentration ≥120 g / L and a secondary purified liquor with an alkaline concentration of 30 g / L to 40 g / L. The secondary concentrate is diluted with water and then enters a tertiary nanofiltration membrane system to separate a tertiary concentrate with a hemicellulose concentration ≥160 g / L and a tertiary purified liquor with an alkaline concentration of 15 g / L to 25 g / L.

[0035] Example 8: It differs from Examples 1 to 7 in that: as shown in the appendix Figure 1As shown, the fourth material conveying pipeline 11 between the fifth material conveying pipeline 12 and the first primary nanofiltration membrane module 8, the fifth material conveying pipeline 12, the eighth material conveying pipeline 20 between the ninth material conveying pipeline 21 and the first secondary nanofiltration membrane module 17, the ninth material conveying pipeline 21, the twelfth material conveying pipeline 27, and the second material conveying pipeline 3 are respectively fixedly installed with a first conveying pump 29, a second conveying pump 30, a third conveying pump 31, a fourth conveying pump 32, a fifth conveying pump 33, and a sixth conveying pump 34.

[0036] Example 9: It differs from Examples 1 to 8 in that: as shown in the appendix Figure 1 As shown, the ceramic membrane concentration unit 35 adopts a two-stage series alumina ceramic membrane module.

[0037] The separation precision of the alumina ceramic membrane module is 50 nm as required. Alumina ceramic membrane is an inorganic material thin film made of pure alumina, possessing excellent high-temperature resistance, corrosion resistance, high stability, and good chemical compatibility.

[0038] Example 10: It differs from Examples 1 to 9 in that, as shown in the appendix... Figure 1 As shown, the drying unit 36 ​​adopts a hot air spray drying system.

[0039] As needed, the hot air spray drying system is equipped with a sprayer, drying tower, exhaust fan, and cyclone separator, all of which are known and commonly used in the art. The concentrate from the outlet of the ceramic membrane concentration unit 35 is atomized by the sprayer and enters the drying tower. At the same time, hot air heated by steam and electricity enters the drying tower. The hot air heats and dries the atomized concentrate to remove moisture, resulting in hemicellulose particles and desalted filtrate. The desalted filtrate enters the wastewater treatment system. The dried hemicellulose particles exit the drying tower through the exhaust fan and enter the cyclone separator for gas-solid separation, and finally enter the silo.

[0040] Depending on the needs, the pipelines and equipment of this multi-stage gradient hemicellulose concentration and alkali recovery unit may also be equipped with conventional valves, thermometers, and pressure gauges known in the art, according to production requirements. The PLC controller can be a Siemens S7-1500, which is equipped with a Yokogawa CS3000 DCS control system.

[0041] Before and after use: Before use: The concentration of the concentrated liquid in the ceramic membrane concentration unit 35 is ≤100g / L, requiring a large amount of sulfuric acid to neutralize the high-alkaline concentrated liquid. The flux recovery rate after the nanofiltration membrane module is fouled is <80%. The wastewater (sodium sulfate filtrate) discharge is 38m³ / h, and the annual hemicellulose production is 8000t to 9324t. After use: the concentration of the concentrate in the ceramic membrane concentration unit 35 is ≥160g / L, the annual sulfuric acid consumption is reduced by 6400t, the flux recovery rate of the nanofiltration membrane module after fouling is ≥90%, the wastewater (sodium sulfate filtrate) discharge is reduced by 23,000 tons / year, the annual carbon emission is reduced by about 13,800 tons (calculated based on steam calorific value), and the annual hemicellulose production is increased to 10,000t to 11,655t.

[0042] The above technical features constitute various embodiments of this utility model, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

[0043] The usage process of this utility model embodiment is as follows: First, the pretreated pressing waste alkaline liquid enters the first-stage nanofiltration membrane system to separate the first-stage concentrate and the first-stage purified liquid. The first-stage concentrate enters the second-stage nanofiltration membrane system to separate the second-stage concentrate and the second-stage purified liquid. The second-stage concentrate enters the third-stage nanofiltration membrane system to separate the third-stage concentrate. Next, the third-stage concentrate enters the neutralization reaction tank 1, and after adding sulfuric acid to adjust the pH value, it enters the ceramic membrane concentration unit 35 for concentration and purification to obtain a concentrated liquid. Finally, the concentrated liquid is dried by the drying unit 36 ​​to obtain hemicellulose particles.

Claims

1. A multi-stage gradient hemicellulose concentration and alkali recovery device, characterized in that... It includes a membrane separation unit, a neutralization reaction tank, a ceramic membrane concentration unit, and a drying unit. A first material conveying pipeline is fixedly connected between the outlet of the membrane separation unit and the first inlet at the top of the neutralization reaction tank. A second material conveying pipeline is fixedly connected between the bottom outlet of the neutralization reaction tank and the inlet of the ceramic membrane concentration unit. A third material conveying pipeline is fixedly connected between the outlet of the ceramic membrane concentration unit and the inlet of the drying unit. A hemicellulose conveying pipeline is fixedly connected to the outlet of the drying unit. A sulfuric acid conveying pipeline is fixedly connected to the second inlet at the top of the neutralization reaction tank.

2. The multi-stage gradient hemicellulose concentration and alkali recovery device according to claim 1, characterized in that... The membrane separation unit includes a primary nanofiltration membrane system, a secondary nanofiltration membrane system, and a tertiary nanofiltration membrane system. The primary and secondary nanofiltration membrane systems are each configured as dual sets of three-stage series-connected nanofiltration membrane modules, while the tertiary nanofiltration membrane system is configured as a single set of four-stage series-connected nanofiltration membrane modules.

3. The multi-stage gradient hemicellulose concentration and alkali recovery device according to claim 2, characterized in that... The primary nanofiltration membrane system includes a primary feed tank, a first primary nanofiltration membrane module, a second primary nanofiltration membrane module, and a secondary feed tank. A fourth material conveying pipeline is fixedly connected between the lower outlet of the primary feed tank and the lower inlet of the first primary nanofiltration membrane module. A fifth material conveying pipeline is fixedly connected between the fourth material conveying pipeline and the lower inlet of the second primary nanofiltration membrane module. A sixth material conveying pipeline is fixedly connected between the upper outlet of the first primary nanofiltration membrane module and the first inlet at the top of the secondary feed tank. A seventh material conveying pipeline is fixedly connected between the upper outlet of the second primary nanofiltration membrane module and the second inlet at the top of the secondary feed tank. A first medium-concentration alkali solution conveying pipeline is fixedly connected to the top outlet of the first primary nanofiltration membrane module, and a second medium-concentration alkali solution conveying pipeline is fixedly connected between the top outlet of the second primary nanofiltration membrane module and the first medium-concentration alkali solution conveying pipeline.

4. The multi-stage gradient hemicellulose concentration and alkali recovery device according to claim 3, characterized in that... The two-stage nanofiltration membrane system includes a first-stage two-stage nanofiltration membrane module, a second-stage two-stage nanofiltration membrane module, and a third-stage feed tank. An eighth material conveying pipeline is fixedly connected between the lower outlet of the second-stage feed tank and the lower inlet of the first-stage two-stage nanofiltration membrane module. A ninth material conveying pipeline is fixedly connected between the eighth material conveying pipeline and the lower inlet of the second-stage two-stage nanofiltration membrane module. A tenth material conveying pipeline is fixedly connected between the upper outlet of the first-stage two-stage nanofiltration membrane module and the first inlet at the top of the third-stage feed tank. An eleventh material conveying pipeline is fixedly connected between the upper outlet of the second-stage two-stage nanofiltration membrane module and the second inlet at the top of the third-stage feed tank. A first low-concentration alkali solution conveying pipeline is fixedly connected to the top outlet of the first-stage two-stage nanofiltration membrane module. A second low-concentration alkali solution conveying pipeline is fixedly connected between the top outlet of the second-stage two-stage nanofiltration membrane module and the first low-concentration alkali solution conveying pipeline.

5. The multi-stage gradient hemicellulose concentration and alkali recovery device according to claim 4, characterized in that... Each of the No. 1 primary nanofiltration membrane module, No. 2 primary nanofiltration membrane module, No. 1 secondary nanofiltration membrane module, and No. 2 secondary nanofiltration membrane module is equipped with six 4-core membrane tanks. The third-stage membrane modules of each of the No. 1 primary nanofiltration membrane module, No. 2 primary nanofiltration membrane module, No. 1 secondary nanofiltration membrane module, and No. 2 secondary nanofiltration membrane module all adopt a wide-channel structure membrane with a channel width of 46mil.

6. The multi-stage gradient hemicellulose concentration and alkali recovery device according to claim 2, 3, 4, or 5, characterized in that... The three-stage nanofiltration membrane system includes a three-stage nanofiltration membrane module. A twelfth material conveying pipeline is fixedly connected between the lower outlet of the three-stage feed tank and the lower inlet of the three-stage nanofiltration membrane module. A third low-concentration alkali conveying pipeline is fixedly connected between the top outlet of the three-stage nanofiltration membrane module and the first low-concentration alkali conveying pipeline between the outlet of the second low-concentration alkali conveying pipeline and the outlet of the first low-concentration alkali conveying pipeline. A first material conveying pipeline is fixedly connected between the upper outlet of the three-stage nanofiltration membrane module and the first inlet at the top of the neutralization reaction tank.

7. The multi-stage gradient hemicellulose concentration and alkali recovery device according to claim 6, characterized in that... The first and second stages of the three-stage nanofiltration membrane module each use twelve 4-core membrane tanks. The third stage of the three-stage nanofiltration membrane module uses ten 3-core membrane tanks, and the fourth stage of the three-stage nanofiltration membrane module uses ten 2-core membrane tanks. The first and second stages of the three-stage nanofiltration membrane module use narrow channel membrane structures with a channel width of 34 mil, while the third and fourth stages of the three-stage nanofiltration membrane module use wide channel membrane structures with a channel width of 46 mil.

8. The multi-stage gradient hemicellulose concentration and alkali recovery device according to claim 7, characterized in that... The fourth material conveying pipeline between the fifth material conveying pipeline and the first primary nanofiltration membrane module, the eighth material conveying pipeline between the ninth material conveying pipeline and the first secondary nanofiltration membrane module, the ninth material conveying pipeline, the twelfth material conveying pipeline, and the second material conveying pipeline are respectively fixedly installed with the first conveying pump, the second conveying pump, the third conveying pump, the fourth conveying pump, the fifth conveying pump, and the sixth conveying pump.

9. The multi-stage gradient hemicellulose concentration and alkali recovery device according to claim 1, 2, 3, 4, 5, 7, or 8, characterized in that... The ceramic membrane concentration unit uses a two-stage series alumina ceramic membrane module.

10. The multi-stage gradient hemicellulose concentration and alkali recovery device according to claim 9, characterized in that... The drying unit uses a hot air spray drying system.

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