Method for comprehensive utilization of chemical pulp waste liquid

Abstract

The present application belongs to pulp wastewater treatment and comprehensive utilization of lignocellulosic biomass raw material technical field, specifically discloses a kind of method for comprehensive utilization of chemical pulp waste liquid.The method includes that the waste liquid generated in the process of chemical pulp is treated by microfiltration membrane to remove large particle impurities, then is treated by ultrafiltration membrane, and concentrated liquid rich in hemicellulose is obtained after separation;The concentrated liquid obtained is added to organic solvent as a transfer solvent under the condition of heating and stirring, then hydrophobic modification reagent benzyl chloride or epichlorohydrin is added drop by drop, and modified concentrated liquid is obtained;Modified concentrated liquid is obtained by centrifugation, washing and drying to obtain modified hemicellulose.The method provided by the present application directly completes modification in waste liquid, which is simple, rapid and fast;Hydrophobic hemicellulose precipitates in concentrated liquid, and crude product can be obtained by filtration separation, which saves a large amount of organic solvent consumed in traditional extraction method, simplifies process flow, avoids environmental pollution caused by organic solvent and reduces production cost.

Description

Technical Field

[0001] This invention relates to the field of pulping wastewater treatment and comprehensive utilization of woody biomass raw materials, and particularly to a method for comprehensive utilization of chemical pulping waste liquid. Background Technology

[0002] Lignocellulosic biomass is the most abundant renewable resource in nature, with approximately 100 million tons of lignocellulosic biomass used for pulping and papermaking globally each year. In the alkaline pulping process, chemimechanical pulp, rich in lignin and cellulose, is primarily used for papermaking, while a large amount of hemicellulose polysaccharides dissolve into the pulping waste liquor during the process. Currently, with the implementation of national energy conservation and emission reduction policies, the water consumption per ton of chemimechanical pulp in China has decreased from the previous 20 m³ / ton. 3 The above has been reduced to the current 10m 3 The COD concentration in wastewater has increased from 7000-9000 mg / L in the past to 12000-20000 mg / L now. The commonly used wastewater treatment method in domestic wood pulping enterprises is biological treatment technology centered on anaerobic / aerobic processes, including hydrolysis, anaerobic, aerobic, coagulation, and advanced treatment. This process is complex and difficult, costly, and ineffective for treating high-concentration pulping wastewater. Furthermore, while chemical alkali recovery methods can recover chemicals and heat from pulping wastewater, the organic matter is concentrated and burned to generate calorific value. However, hemicellulose has a low calorific value of only 35.12 MJ / kg, making high-value applications impossible and resulting in significant resource waste. Therefore, there is an urgent need to establish a comprehensive method for utilizing pulping wastewater, efficiently extracting hemicellulose products from the wastewater, and simultaneously recovering and reusing chemicals and water to improve the utilization rate and economic value of biomass resources in pulping wastewater.

[0003] Hemicellulose is a heteropolymer composed of several different types of monosaccharides. The hemicellulose of broadleaf and grass species is mainly composed of xylooligosaccharides, while that of coniferous trees is primarily composed of galacto-glucan polysaccharides. The hydrophilic properties and polysaccharide characteristics of hemicellulose give it significant advantages in food preservation, microbial culture, and biopharmaceuticals. However, the excessive hydrolysis of hemicellulose under high humidity conditions limits its applications. Modification of hemicellulose is key to overcoming these limitations. The conventional process flow is: membrane separation / alcohol precipitation separation – purification and drying – chemical modification.

[0004] Currently, the alcohol precipitation method for separating hemicellulose from pulping wastewater mainly involves acid neutralization followed by ethanol precipitation. This method requires a large amount of organic solvent. The precipitated hemicellulose is then dried to obtain commercial hemicellulose (Peng2009, DOI:10.1021 / jf900986b)(Journal of Chemical Engineering of Chinese Universities, 2019, 33(03):636-644.). Whether using membrane separation or alcohol precipitation, during the drying and dehydration process, hemicellulose undergoes irreversible crystallization due to hydrogen bonding between molecules. This reduces the number of reactive hydroxyl groups on the molecular chain surface to a certain extent, thus significantly reducing the degree of subsequent hemicellulose modification. Furthermore, this process is cumbersome, the wastewater contains a large amount of alkali, making processing difficult, causing severe pollution, and hindering large-scale production. To address this issue, patents CN 103613689B and CN 103613688B directly modify the hemicellulose in viscose fiber waste liquid with carboxylation and quaternization. However, even after modification, a large amount of ethanol organic solvent is still needed to precipitate and separate it from the waste liquid to obtain the product. This process merely postpones the separation step, without simplifying the process, and further increases the difficulty of separating the product from the aqueous system. Furthermore, the hydrophilic properties of the modified hemicellulose make it unsuitable for high-barrier packaging materials and biopharmaceutical applications requiring enhanced water repellency.

[0005] The article "Modification and Application of Hemicellulose in Reed Pre-hydrolysis Wastewater" describes the cationization modification of hemicellulose / xylan. By controlling the amount of alkali, reaction time, and reaction temperature, cationic hemicellulose with a degree of substitution of 0.0217 was finally obtained. However, the hemicellulose used in the literature was extracted from the hydrolysate by acid neutralization and alcohol precipitation, a method that still consumes a large amount of acid and organic solvents. In a patent for a modified hemicellulose-PVA composite film, its preparation method, and application, hemicellulose / xylan is silanized to give it hydrophobic properties, which can be used to prepare high-barrier membranes. Similarly, the hemicellulose used is also extracted from the hydrolysate by acid neutralization and alcohol precipitation.

[0006] The high-value treatment and utilization of hemicellulose in alkaline pulping waste liquor is a current technical challenge in the pulp and paper industry. The efficient recovery and high-value utilization of hemicellulose and alkali in the waste liquor is one of the important issues in solving waste liquor pollution and comprehensively utilizing hemicellulose plant resources. Summary of the Invention

[0007] The purpose of this invention is to address the aforementioned shortcomings of existing technologies by providing a method for the comprehensive utilization of chemimechanical pulp waste liquid. This method employs membrane separation to treat the waste liquid, concentrating it into a solution rich in hemicellulose and a certain amount of NaOH. Subsequently, a hydrophobic modifier is added to modify the hemicellulose. The organic matter in the waste liquid is then surface-modified and extracted using an in-situ method. This method simultaneously forms large-particle colloids and performs surface modification. Since the hemicellulose in the alkali-pre-impregnated chemimechanical pulp has not undergone ordinary separation and purification processes (meaning it has not been dried or cold-dried into commercial hemicellulose), the availability of hemicellulose chemicals is highest at this stage, making chemical modification easier and resulting in better grafting of hydrophobic groups.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] The first objective of this invention is to provide a method for the comprehensive utilization of chemical pulping waste liquid, comprising the following steps:

[0010] S1. The waste liquid generated during the chemimechanical pulping process is treated with microfiltration membrane to remove large particulate impurities, and then treated with ultrafiltration membrane. After separation, a concentrated liquid rich in hemicellulose is obtained.

[0011] S2. The concentrated solution obtained in step S1 is heated and stirred, and an organic solvent is added as a readily convertible solvent. Then, a hydrophobic modifying agent is added dropwise to obtain a modified concentrated solution. The hydrophobic modifying agent is benzyl chloride or epichlorohydrin.

[0012] S3. Centrifuge the modified concentrate from step S2, pour out the supernatant, and centrifuge and wash the remaining viscous colloid with water multiple times until it is neutral.

[0013] S4. The viscous colloid obtained in step S3 is dried in a vacuum drying oven to obtain modified hemicellulose.

[0014] Further, in step S1, the preparation process of the chemimechanical pulp waste liquid is as follows: the plant raw materials are soaked in a liquid ratio of 1:5, at 25℃~90℃, and with 2%~10% sodium hydroxide for 2h~8h, and then filtered to obtain the chemimechanical pulp waste liquid; the plant raw materials include any one or a combination of poplar, eucalyptus, pine, bamboo or moso bamboo; the pH of the chemimechanical pulp waste liquid is 13~14, and hemicellulose accounts for 30%~38% of the solids in the chemimechanical pulping waste liquid by mass fraction, with the hemicellulose percentage = total sugar in the waste liquid / total solids after drying × 100%; sodium hydroxide accounts for 4%~10% of the solids in the waste liquid by mass fraction, with the sodium hydroxide percentage = sodium hydroxide that can be titrated with hydrochloric acid in the waste liquid / total solids after drying × 100%.

[0015] Furthermore, in step S1, the pore size of the microfiltration membrane is 5-20 μm, and the temperature of the microfiltration treatment is not higher than 45°C.

[0016] Furthermore, in step S1, the molecular weight cutoff of the ultrafiltration membrane is 5000 to 20000, the inlet pressure of the ultrafiltration membrane is 5 bar to 30 bar, and the temperature of the ultrafiltration treatment is 25°C to 35°C.

[0017] Furthermore, the concentrated solution obtained in step S1 contains 8-10 g / L xylan and 20-30 g / L alkali.

[0018] Furthermore, in step S2, the organic solvent includes any one of ethanol, methanol, diethyl ether, dimethyl sulfoxide, or acetonitrile.

[0019] Furthermore, the process of adding the hydrophobic modifying agent dropwise is as follows: the stirring speed is 2000 rpm to 4000 rpm during the dropwise addition, and the stirring speed is 200 rpm to 500 rpm after all the reagent has been added, and the reaction time is 2 h to 8 h.

[0020] Furthermore, the molar ratio of the hydrophobic modifying agent to the hemicellulose hydroxyl groups in the waste liquid is 0.5:1 to 3:1, and the molar mass of hemicellulose is calculated as xylose = total sugar / 150.13.

[0021] Furthermore, the modified concentrate obtained in step S2 contains 2-4 g / L of alkali.

[0022] A second objective of this invention is to provide modified hemicellulose obtained by the above-described method for the comprehensive utilization of chemical pulp waste liquid.

[0023] A third objective of this invention is to provide the application of the above-described modified hemicellulose in the preparation of barrier membranes.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] (1) This invention provides a method for the comprehensive utilization of chemical pulp waste liquid. In the concentrate, the hydroxyl groups on hemicellulose are easily nucleophilically converted by alkali metal ions, and the resulting hemicellulose metal salt greatly enhances the reactivity. Based on this characteristic, the activated hemicellulose in the waste liquid is fully utilized, and it is directly hydrophobically modified and the product is collected by precipitation and filtration. This method simplifies the conventional process of "extracting hemicellulose with organic solvents - re-dissolving and then chemically modifying", reduces environmental pollution and lowers production costs;

[0026] (2) Traditional methods for separating and extracting hemicellulose require drying the hemicellulose before the modification reaction. This step causes partial crystallization of the hemicellulose, and subsequent chemical modification requires dissolution and activation again, which is a complex process and will affect the reaction efficiency of hemicellulose to a certain extent. This patent completes the chemical modification of hemicellulose directly in the waste liquid, ensuring the degree of modification and substitution, while making reasonable use of the alkali in the concentrate to solve the waste liquid pollution problem;

[0027] (3) Alkali-containing hemicellulose was extracted using membrane separation, which effectively recovered and rationally utilized hemicellulose and alkali in the chemical pulp waste liquid, solving the problems of waste liquid pollution and the reuse of hemicellulose plant resources. The modification process omitted the addition of organic solvents, simplifying the process flow, making it easy to operate and reducing processing costs. The resulting hydrophobic hemicellulose product not only maintains the biodegradability of hemicellulose but also endows the material with excellent water repellency and barrier properties. Attached Figure Description

[0028] Figure 1 A comparison of the thermogravimetric curves of the modified hemicellulose and natural xylan prepared in Example 1;

[0029] Figure 2 The image shows a comparison of the FTIR of hemicellulose prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments and accompanying drawings are described in further detail below. Where specific test methods, instruments, or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. All reagents and experimental materials used in this invention are commercially available.

[0031] In this embodiment, the content of hemicellulose was quantitatively analyzed using a two-step acid hydrolysis method proposed by the National Renewable Energy Laboratory (NREL) of the United States. Specifically, the chemical mechanical pulp waste liquid was adjusted to a sulfuric acid concentration of 4% with concentrated sulfuric acid, shaken in a water bath at 30°C for 60 min, and then autoclaved at 121°C for 60 min. Subsequently, it was analyzed by high performance liquid chromatography (HPLC) with 5 mmol / L sulfuric acid as the mobile phase and a flow rate of 0.6 ml / min. The obtained content was calculated according to the standard curve method.

[0032] In this embodiment, the molecular weight determination method for hemicellulose is gel permeation chromatography (GPC). The hemicellulose sample is dissolved in 0.3% sodium hydroxide solution with a concentration of approximately 2 mg / mL. 0.1 mol / L sodium nitrate solution is used as the eluent, and the flow rate is 0.8 mL / min. The obtained relative molecular weight is determined using polyethylene oxide standard.

[0033] This application addresses wastewater generated during the production of chemimechanical pulp, primarily including impregnation wastewater from chemical preimpregnation. The composition of the wastewater includes: alkali content (20%–30%), xylose (30%–60%), acetic acid (30%–60%), etc. The pH of the preimpregnation wastewater is 13–14, and the organic matter content is 1–100 g / L, as shown in Table 1.

[0034] Table 1. Composition of the concentrate after ultrafiltration membrane treatment

[0035]

[0036] The process of generating poplar wood pulp waste liquid in this application embodiment is as follows: (1) Poplar wood raw material pre-impregnation waste liquid: The process conditions are liquid ratio 1:5, 4% (W / V) NaOH, impregnation at room temperature for 8 hours (impregnation time and impregnation temperature can be adjusted as needed, impregnation time is generally 2 to 8 hours, impregnation temperature is generally room temperature to 100℃), after impregnation, the raw material is filtered and separated, the raw material is sent to the pulping section, and the waste liquid enters the treatment section; (2) Pulping, washing and screening wastewater: the impregnated poplar wood chips are sent to the pulping machine for pulping, and the wastewater generated is sent to the wastewater treatment section together with the subsequent washing and screening wastewater.

[0037] Example 1

[0038] This embodiment provides a method for the comprehensive utilization of chemical mechanical pulping waste liquid, the specific steps of which are as follows:

[0039] (1) Poplar chemimechanical pulp waste liquid was removed from large particles such as wood chips and sand by a 0.45μm microfiltration membrane at room temperature, and then separated by a 5000D hollow fiber spiral wound membrane to obtain concentrated waste liquid. The composition of the waste liquid was 23% (w / v) NaOH, 10% (w / v) xylan and 10% (w / v) acetic acid.

[0040] (2) Take 50 ml of the concentrated solution obtained in step (1) and add ethanol solution with a volume fraction of more than 95% as the transfer phase of the modifier at 80℃ and 500 rpm. After 10 min, add benzyl chloride as the in-situ reaction reagent. Stop the reaction after 4 h and let it stand at room temperature for 30 min.

[0041] (3) After the mixed solution in step (2) separates into solid and liquid phases, pour out the supernatant for later use. Wash the viscous gel at the bottom with deionized water until the center is reached. After centrifugation, dry in a vacuum drying oven at 45°C for 24 hours.

[0042] In step (2), the volume ratio of the added ethanol solution to the waste liquid is 1:50, and the volume ratio of the added benzyl chloride to the waste liquid is 1:10; the heating method is water bath heating.

[0043] In this application example, the hemicellulose recovered from 50ml of waste liquid using this treatment process was 0.43g (separated hemicellulose = hemicellulose in waste liquid - hemicellulose content in the modified supernatant), accounting for 87% of the hemicellulose in the waste liquid (separation rate = (hemicellulose in waste liquid - hemicellulose in supernatant) / hemicellulose in waste liquid × 100%). This indicates that the treatment process has a good separation effect. Furthermore, the separated hemicellulose was analyzed by thermogravimetric analysis (TGA). Figure 1 As shown, its thermogravimetric curve is compared with that of natural xylan. The rate of weight loss is smaller, indicating that it has good thermal stability. The contact angle increased from 43.33° to 83.57° by an optical contact angle tester (OCA), indicating that the process improved the hydrophobicity of hemicellulose.

[0044] Example 2

[0045] This embodiment provides a method for the comprehensive utilization of chemical mechanical pulping waste liquid, the specific steps of which are as follows:

[0046] (1) Poplar chemimechanical pulp waste liquid was removed from large particles such as wood chips and sand by a 0.45μm microfiltration membrane at room temperature, and then separated by a 5000D hollow fiber spiral wound membrane to obtain concentrated waste liquid. The composition of the waste liquid was 23% (w / v) NaOH, 10% (w / v) xylan and 10% (w / v) acetic acid.

[0047] (2) Take 50 ml of the concentrated solution obtained in step (1) and add ethanol solution with a volume fraction of more than 95% as the transfer phase of the modifier at 80℃ and 500 rpm. After 10 min, add epichlorohydrin as the in-situ reaction reagent. Stop the reaction after 4 h and let it stand at room temperature for 30 min.

[0048] (3) After the mixed solution in step (2) separates into solid and liquid phases, pour out the supernatant for later use. Wash the viscous gel at the bottom with deionized water until the center is reached. After centrifugation, dry in a vacuum drying oven at 45°C for 24 hours.

[0049] In step (2), the volume ratio of the added ethanol solution to the waste liquid is 1:50, and the volume ratio of the added epichlorohydrin to the waste liquid is 1:10; the heating method is water bath heating.

[0050] In this application example, the hemicellulose recovered from 50ml of waste liquid using this treatment process was 0.35g (separated hemicellulose = hemicellulose in waste liquid - hemicellulose content in the modified supernatant), accounting for 71% of the hemicellulose in the waste liquid (separation rate = (hemicellulose in waste liquid - hemicellulose in supernatant) / hemicellulose in waste liquid × 100%), indicating that the treatment process has a good separation effect. Furthermore, the separated hemicellulose, when analyzed by thermogravimetric analysis (TGA), showed a smaller rate of weight decrease compared to the thermogravimetric curve of natural xylan, indicating good thermal stability. The contact angle increased from 43.33° to 79.43° using a dynamic contact angle tester (DCAT), demonstrating that this process improved the hydrophobicity of the hemicellulose.

[0051] Comparative Example 1

[0052] The process involves acid neutralization and alcohol precipitation of hemicellulose, with the following specific steps:

[0053] (1) Poplar chemimechanical pulp waste liquid was removed from large particles such as wood chips and sand by a 0.45μm microfiltration membrane at room temperature, and then separated by a 5000D hollow fiber spiral wound membrane to obtain concentrated waste liquid. The composition of the waste liquid was 23% (w / v) NaOH, 10% (w / v) xylan and 10% (w / v) acetic acid.

[0054] (2) Add 3 times the volume of ethanol solution to the concentrated solution obtained in step (1) while shaking at room temperature, and let stand for 12 hours;

[0055] (3) Centrifuge the solution obtained in step (2) at 4000 rpm / min for 10 minutes, and wash the precipitate with ethanol several times until neutral;

[0056] (4) The precipitate obtained in step (3) was freeze-dried at -50℃ for 24 hours to obtain crude hemicellulose.

[0057] The hemicellulose of Example 1 and Comparative Example 1 was detected by infrared spectroscopy (FIRT), and the results are as follows: Figure 1 As shown:

[0058] like Figure 2 As shown, alcohol-precipitated hemicellulose at 3426 cm⁻¹ -1 The peak for the stretching vibration of -OH is observed, but when benzyl chloride-modified hemicellulose reacts with benzyl chloride, the stretching vibration peak shifts to 3384 cm⁻¹. -1 Location; 2925cm -1 The peak at 1416 cm⁻¹ is the stretching vibration peak of C-H, while the characteristic absorption peaks of C-C and C=O appear at 1416 cm⁻¹. -1 With 1622cm -1 At this point, the stretching vibration peak of C—O—C appears at 1138 cm⁻¹. -1At the same time, the reaction between the -OH group of benzyl chloride-modified hemicellulose and benzyl chloride caused a significant shift in the C—O—C stretching vibration peaks. The benzyl chloride-modified hemicellulose exhibited peaks at 737 and 694 cm⁻¹. -1 The two characteristic peaks are caused by out-of-plane deformation of aromatic CH. These new and shifted bands confirm that hemicellulose was successfully benzylated in this application example, and also confirm that the surface modification of chemimechanical pulp waste liquor can be carried out in situ while separating hemicellulose.

[0059] Compared with the traditional ethanol precipitation process for hemicellulose, the process of separating hemicellulose by chemical modification with benzyl chloride in Example 1 of this application has the following advantages:

[0060] (1) Low chemical dosage and high economic benefits. The chemicals used in this application example are ethanol and benzyl chloride. The chemicals used in the traditional alcohol precipitation of hemicellulose are mainly ethanol. The dosage comparison is shown in Table 2 below:

[0061] Table 2. Comparison of Chemical Reagent Usage

[0062] ethanol 3 0.02 benzyl chloride 0 0.1

[0063] (2) The separated hemicellulose can be directly used in the preparation of biodegradable hydrophobic materials. It is well known that the difficulty in efficiently utilizing hemicellulose lies in its complex and diverse structure, leading to easy degradation, low yield, difficult purification, and high cost during extraction. Traditional alcohol precipitation separation of hemicellulose weakens the hydration layer of hemicellulose by adding ethanol, causing it to precipitate from the solution. After drying, commercial hemicellulose is obtained, which usually requires chemical modification to impart certain physicochemical properties such as hydrophobicity, thermal stability, air permeability, and thermoplasticity before it can be effectively applied in the industrial field. In this application example, hydrophobic groups are introduced into the hemicellulose molecular chain during separation, endowing the hemicellulose with hydrophobicity and better thermal stability, making it applicable to the plastics industry and reducing production processes.

[0064] Comparative Example 2

[0065] The steps for cationizing hemicellulose using CHPTMAC (3-chloro-2-hydroxypropyltrimethylammonium chloride) are as follows:

[0066] (1) Extract hemicellulose from chemical pulp waste liquid by alcohol precipitation to obtain dried finished hemicellulose;

[0067] (2) Dissolve the hemicellulose obtained in step (1) in an appropriate amount of hot water. After complete dissolution, add an appropriate amount of anhydrous ethanol. The volume ratio of the added ethanol solution to the waste liquid is 1:50.

[0068] (3) Add an appropriate amount of NaOH dropwise to the mixed solution obtained in step (2) at 30℃ and 500rpm, and stir thoroughly for 20min to activate; the ratio of the volume of NaOH solution added to the volume of waste liquid is 3:1000;

[0069] (4) Add 100% cationic etherifying agent (CHPTMAC) and 3% NaOH dropwise to the mixed solution obtained in step (3) at 65°C and 500 rpm, and stir for 4 hours; the ratio of the volume of NaOH solution added to the volume of waste liquid is 3:1000, and the ratio of the volume of the etherifying agent solution added to the volume of waste liquid is 1:1.

[0070] (5) After the solution obtained in step (3) is cooled to room temperature, hydrochloric acid is added to neutralize it, then 3 times the volume of ethanol is added to precipitate it. After filtration and washing, it is vacuum dried at 55°C for 24 hours to obtain cationic hemicellulose.

[0071] The epichlorohydrin-modified hemicellulose process of Example 2 of this application has the following advantages compared with the CHPTMAC cationic hemicellulose process of Comparative Example 2:

[0072] (1) Low chemical dosage and high economic benefits. The chemical used in Example 2 was epichlorohydrin, while the main chemicals used in Comparative Example 2 were ethanol and CHPTMAC. The comparison of chemical dosages is shown in Table 3 below:

[0073] Table 3. Comparison of Chemical Reagent Usage

[0074] (ton) (ton) ethanol 0 3 epichlorohydrin 0.1 0 CHPTMAC 0 1

[0075] (2) Compared with Example 2, the hemicellulose used in Comparative Example 2 was also extracted by traditional acid neutralization and alcohol precipitation. The process is complicated and lengthy. After drying, some of the crystal structures of the hemicellulose undergo irreversible changes, and some hydroxyl groups are difficult to be activated by alkali, resulting in a low degree of cationization substitution. In contrast, Example 2 directly modifies the chemical pulp waste liquid, and the hydroxyl groups on the hemicellulose are activated to the maximum extent, making the cationization reaction easier to occur, and its degree of modification substitution is correspondingly higher.

[0076] Example 3

[0077] The benzyl hemicellulose ether obtained in Example 1 was used to prepare a biodegradable barrier membrane, and the preparation steps are as follows:

[0078] (1) The mixed solution obtained in step (1) and (2) of Example 1 was separated by centrifugation to obtain undried benzyl hemicellulose ether;

[0079] (2) The benzyl hemicellulose ether obtained in step (1) was slowly poured into a polytetrafluoroethylene mold by casting method. After being smoothed with a scraper, it was vacuum dried at 40°C for 4 hours to obtain a benzyl hemicellulose ether film.

[0080] It was discovered that grafting benzyl groups onto hemicellulose imparts film-forming properties, allowing for the direct preparation of a slightly yellow, transparent film using the above steps. The resulting benzyl hemicellulose ether film was analyzed by infrared spectroscopy (ATR) at 734 cm⁻¹. -1 696cm -1 The presence of a CH vibration peak in the aromatic ring indicates successful grafting of benzyl groups. Thermogravimetric analysis (TGA) at 10℃ / min was used to detect its thermogravimetric curves compared to those of natural hemicellulose at temperatures ranging from 18℃ to 600℃, revealing that it exhibits better thermal stability than pure natural hemicellulose membranes. Dynamic contact angle testing (DCAT) was used to measure its water contact angle, finding that its water contact angle was twice that of natural hemicellulose tablets, indicating that the benzyl groups impart better hydrophobic properties to the hemicellulose.

[0081] In summary, the modified hemicellulose extracted from chemical pulp waste liquid can be used in high-barrier membrane applications, or it can be compounded with other polymer materials to make barrier membranes, which can improve the biodegradability of polymer barrier membranes.

[0082] For any points not covered above, existing technologies shall apply.

[0083] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Those skilled in the art can make modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the direction of the present invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for comprehensive utilization of chemical pulping waste liquid, characterized in that, Includes the following steps: S1. The waste liquid generated during the chemimechanical pulping process is treated with a microfiltration membrane to remove large particulate impurities, followed by ultrafiltration membrane treatment. After separation, a concentrated liquid rich in hemicellulose is obtained. Specifically, the waste liquid is prepared by soaking plant materials in a liquid-to-liquid ratio of 1:5, at 25℃~90℃, with 2%~10% sodium hydroxide for 2h~8h, and then filtering to obtain chemimechanical pulp waste liquid. The plant materials include any one or a combination of poplar, eucalyptus, pine, bamboo, or moso bamboo. The pH of the chemimechanical pulp waste liquid is 13~14, and the hemicellulose accounts for 30%~38% of the solids in the chemimechanical pulp waste liquid by mass fraction. The hemicellulose percentage is calculated as: total sugar in the waste liquid / total solids after drying × 100%. The sodium hydroxide accounts for 4%~10% of the solids in the waste liquid by mass fraction. The sodium hydroxide percentage is calculated as: sodium hydroxide that can be titrated with hydrochloric acid in the waste liquid / total solids after drying × 100%. S2. The concentrated solution obtained in step S1 is heated and stirred, and an organic solvent is added as a readily convertible solvent. Then, a hydrophobic modifying agent is added dropwise to obtain a modified concentrated solution. The hydrophobic modifying agent is benzyl chloride or epichlorohydrin. S3. Centrifuge the modified concentrate from step S2, pour out the supernatant, and centrifuge and wash the remaining viscous colloid with water multiple times until it is neutral. S4. The viscous colloid obtained in step S3 is dried in a vacuum drying oven for 24 hours to obtain modified hemicellulose.

2. The method for comprehensive utilization of chemical pulping waste liquid as described in claim 1, characterized in that, In step S1, the pore size of the microfiltration membrane is 5~20μm, and the temperature of the microfiltration membrane treatment is not higher than 45℃; the molecular weight cutoff of the ultrafiltration membrane is 5000~20000, the inlet pressure of the ultrafiltration membrane is 5 bar~30 bar, and the temperature of the ultrafiltration membrane treatment is 25℃~35℃.

3. The method for comprehensive utilization of chemical pulping waste liquid as described in claim 1, characterized in that, The concentrated solution obtained in step S1 contains 8-10 g / L xylan and 20-30 g / L alkali.

4. The method for comprehensive utilization of chemical pulping waste liquid as described in claim 1, characterized in that, In step S2, the organic solvent includes any one of ethanol, methanol, diethyl ether, dimethyl sulfoxide, or acetonitrile.

5. A method for comprehensive utilization of chemical pulping waste liquid as described in claim 4, characterized in that, The process of adding the hydrophobic modifying agent dropwise is as follows: the stirring speed is 2000 rpm to 4000 rpm during the dropwise addition, and the stirring speed is 200 rpm to 500 rpm after all the reagent has been added. The reaction time is 2 h to 8 h.

6. The method for comprehensive utilization of chemical pulping waste liquid as described in claim 4, characterized in that, The molar ratio of the hydrophobic modifying agent to hemicellulose in the waste liquid is 0.5:1 to 3:1, and the molar mass of hemicellulose is calculated as xylose = total sugar / 150.

13.

7. A method for comprehensive utilization of chemical pulping waste liquid as described in claim 5, characterized in that, The modified concentrate obtained in step S2 contains 2-4 g / L of alkali.

8. A modified hemicellulose obtained by a method for comprehensively utilizing chemical pulp waste liquid as described in any one of claims 1-7.

9. The application of the modified hemicellulose as described in claim 8 in the preparation of barrier membranes.

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