Method for preparing high-purity bleached broad bean by adopting agriculture and forestry three residues

Abstract

The invention discloses a method for preparing high-purity bleached broad beans from agriculture and forestry'three residues'. The method comprises the following operation steps: S1, raw material screening: selecting'three residues' meeting requirements; s2, chipping is conducted, specifically, after peeling, chipping and screening are conducted, sheets meeting the requirements are classified and piled up; s3, washing with water; s4, cooking: removing hemicelluloses and lignin in the sheets by adopting a vapor phase prehydrolysis sulfate cooking method; s5, pulp screening; s6, oxygen dealkalization: adding a certain amount of oxygen dealkalization into the collected material to carry out oxygen dealkalization reaction; s7, bleaching: bleaching the material obtained after the oxygen removal reaction; and S8, sheet making and whiteness and alpha cellulose detection: the product with the whiteness stabilized at 90% ISO or above and the alpha cellulose content controlled at 90% or above is the final product. According to the method disclosed by the invention, by carrying out physical property analysis and chemical component optimization on the cutting residues, the material-making residues and the processing residues, an efficient pulp screening, oxygen removal and multi-section bleaching process is developed, and the whiteness and the purity of the pulp are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of high-purity bleached fiber production and preparation technology, and in particular to a method for preparing high-purity bleached fiber using agricultural and forestry "three residues". Background Technology

[0002] Due to factors such as the shortage of hardwood resources and unstable raw material quality, traditional bleached hardwood pulp cannot meet the production requirements of high-purity specialty paper, exhibiting problems such as poor fiber uniformity, high resin content, and unstable whiteness. Because hardwood fiber has high yield and low cost, alternative hardwood resources need to be sought to meet market demands for high-purity bleached hardwood pulp and Lyocell. Agricultural and forestry "three residues" mainly refer to logging residues, timber processing residues, and processing residues. my country has abundant agricultural and forestry "three residues" resources, but their utilization rate is low, with most being discarded or incinerated, failing to be effectively transformed into high-value-added products. Existing technologies cannot fully process the complex components in agricultural and forestry "three residues," resulting in low pulp yield and high impurity content, limiting their application in high-purity bleached hardwood pulp. How to overcome the technological bottleneck of efficient utilization of agricultural and forestry "three residues" through process innovation and achieve large-scale production of high-yield, low-impurity high-purity bleached hardwood pulp has become a core issue that urgently needs to be addressed. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for preparing high-purity bleached pulp using agricultural and forestry "three residues". This method involves analyzing the physical properties and optimizing the chemical composition of logging residues, timber processing residues, and processing residues to develop an efficient pulp screening, oxygen desulfurization, and multi-stage bleaching process, which significantly improves the whiteness and purity of the pulp.

[0004] The technical solution provided by this invention is as follows: A method for preparing high-purity bleaching agents using agricultural and forestry residues includes the following steps: S1. Raw material screening: Select the "three residues" that meet the requirements; S2, Chipping: After peeling, chipping, and screening, the remaining materials that meet the requirements are directly stacked according to the tree species of the remaining materials. When producing high-purity bleached wood, the materials can be directly taken from the corresponding piles, ensuring the stability of the raw material characteristics and thus ensuring the continuity of product quality. S3. Washing: The sheet is washed with water or air-separated to remove foreign matter and wood chips from the sheet; S4. Cooking: The hemicellulose and lignin in the sheet are removed by vapor-phase pre-hydrolysis sulfate cooking. S5. Screening: Screen the pulp using a 0.15-0.25mm slotted screen and collect it using a mesh bag with a mesh size of not less than 350-500. The purpose of screening is to remove pulp agglomerates and pulp residue from the cooked pulp, leaving pulp for subsequent oxygen desulfurization and bleaching. S6, Oxygen De-alkali: A certain amount of oxygen de-alkali is added to the collected material to carry out the oxygen de-alkali reaction; S7. Bleaching: Bleaching the material obtained after the oxygen desulfurization reaction; S8. Forming and Whiteness / Fiber Residue Detection: The bleached material is formed into sheets (subsequent analysis uses a sheet forming device to obtain a quantitative sample of 200g / m³). 2 ±25 samples were dried at a low temperature of 40-60℃. The whiteness and fiber content of the dried material were tested. The product with a whiteness of 90% ISO or higher and a fiber content of 90% or higher was the final product.

[0005] Preferably, the water used in the cooking, pulp screening, oxygen desulfurization, bleaching, and sheet forming processes mentioned above is deionized water.

[0006] Preferably, the "three residues" that meet the requirements in step S1 refer to "three residues" with a freshness of ≥95%, a pass rate of ≥75%, a decayed wood content of ≤5.0%, and a bark content of ≤2.0%.

[0007] Preferably, the sheet material that meets the requirements in step S2 refers to a sheet material with 4.8 ≤ L < 40 mm and H ≤ 8 mm; where L is the length of the sheet material, H is the thickness of the sheet material, and the width of the sheet material is not greater than the length of the sheet material.

[0008] Preferably, the vapor-phase pre-hydrolysis sulfate cooking method in step S4 is as follows: NaOH solution, Na2S liquid and water are mixed and cooked together with the sheet, the sheet accounts for 20±0.5% of the weight of the mixture, and the water, NaOH and Na2S liquid account for 80±0.5% of the weight of the mixture.

[0009] Preferably, in step S4, the concentration of the mixture formed by NaOH and Na2S is 22.5-24%, the heating time is 20-25 min, the cooking temperature is 162-164℃, the holding time is 80-95 min, and the cooling time is 20-25 min.

[0010] Preferably, in step S4, the kappa value at the end of the cooking process is controlled to be between 16 and 18, and the viscosity is maintained at 800 ml / g ± 30.

[0011] Preferably, in step S6, the oxygen dealkalization is performed using NaOH, and the amount of oxygen dealkalization accounts for 3.0 to 4.0% of the total mass of the material.

[0012] Preferably, in step S6, the oxygen removal reaction is carried out at a temperature of 95–105°C, a pressure of 0.65 ± 0.5 MPa, and a time of 60 ± 5 min, resulting in a viscosity reduction to 600 ± 30 ml / g after oxygen removal.

[0013] Preferably, step S7 employs a three-stage bleaching process: D0→EOP→D1. D0: ClO2 dosage 7-8 kg / ton, time 25-30 min, pH 1.5-2.5, temperature 80-90℃; EOP: Control the amount of H2O2 to 8-12 kg / ton, the time to 80-100 min, control the amount of NaOH to make the pH 11.8-12.8, the bleaching temperature to 85-90℃, and ensure the viscosity to be 530±30. D1: To supplement whiteness, use 3-5 kg / ton of ClO2, for 110-130 minutes, with a pH of 7-8 and a temperature of 80-90℃, to ensure a whiteness of 90% ISO or higher.

[0014] Preferably, in step S8, the ash content of the product is less than 0.1%, the iron content in the product is less than 10 ppm, and the viscosity of the product is 500 ± 30 ml / g.

[0015] The present invention has the following advantages over the prior art: This invention utilizes agricultural and forestry byproducts as raw materials for producing high-purity bleached hardwood pulp. It fully leverages existing logging, timber processing, and finishing waste to produce high-purity bleached hardwood pulp, thus solving the problem of raw material availability for enterprise production. The raw material pretreatment stage employs an existing three-stage screening process (40mm sieve for the first layer, 20mm sieve for the second layer, and 5.0mm sieve for the third layer) to screen out qualified sheets, significantly improving the size qualification rate of the raw materials entering the cooking vessel and ensuring uniform cooking. By optimizing process parameters and using deionized water for washing throughout the process, the prepared high-purity bleached hardwood pulp meets superior standards, with key quality indicators showing a stable whiteness above 90% ISO and a methyl cellulose content controlled at an excellent level above 90%. This invention not only fully utilizes agricultural and forestry byproducts but also solves the technical problems of unstable raw material quality and poor product consistency in traditional bleached hardwood pulp production through refined process control, providing Lyocell with a high-quality raw material guarantee. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a process flow diagram of the method for preparing high-purity bleaching agents using agricultural and forestry "three residues" in an embodiment of the present invention. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0019] like Figure 1 As shown, this embodiment of the invention provides a method for preparing high-purity bleaching agents using agricultural and forestry "three residues", including the following steps: S1. Raw material screening: Select the "three residues" that meet the requirements; S2. Chipping: After peeling, chipping, and screening, the chips that meet the requirements are directly stacked according to the tree species of the "three residues". S3. Washing: The sheet is washed with water or air-separated to remove foreign matter and wood chips from the sheet; S4. Cooking: The hemicellulose and lignin in the sheet are removed by vapor-phase pre-hydrolysis sulfate cooking. S5. Slurry screening: Slurry screening is carried out using a 0.15-0.25mm slotted sieve, and collection is carried out using a mesh bag with a mesh size of not less than 350-500 mesh. S6, Oxygen De-alkali: A certain amount of oxygen de-alkali is added to the collected material to carry out the oxygen de-alkali reaction; S7. Bleaching: Bleaching the material obtained after the oxygen desulfurization reaction; S8. Flake making and whiteness and fiber content testing: The bleached material is folded into flakes, and the material after frying and drying is tested for whiteness and fiber content. The product with whiteness stable above 90% ISO and fiber content controlled above 90% is the final product.

[0020] In this embodiment, the water used in the cooking, pulp screening, oxygen desulfurization, bleaching, and sheet forming processes described above is all deionized water.

[0021] In this embodiment, the "three residues" that meet the requirements in step S1 refer to "three residues" with a freshness of ≥95%, a pass rate of ≥75%, a decayed wood content of ≤5.0%, and a bark content of ≤2.0%.

[0022] In this embodiment, the sheet material that meets the requirements in step S2 refers to a sheet material with 4.8 ≤ L < 40 mm and H ≤ 8 mm; where L is the length of the sheet material, H is the thickness of the sheet material, and the width of the sheet material is not greater than the length of the sheet material.

[0023] In this embodiment, the vapor phase pre-hydrolysis sulfate cooking method in step S4 is as follows: NaOH solution, Na2S liquid and water are mixed and cooked together with the sheet, the sheet accounts for 20±0.5% of the weight of the mixture, and the water, NaOH and Na2S liquid account for 80±0.5% of the weight of the mixture.

[0024] In this embodiment, the concentration of the mixture formed by NaOH and Na2S in step S4 is 22.5-24%, the heating time is 20-25 min, the cooking temperature is 162-164℃, the holding time is 80-95 min, and the cooling time is 20-25 min.

[0025] In this embodiment, in step S4, the kappa value at the end of the cooking process is controlled to be 16-18 (higher than the conventional 12-14), and the viscosity is maintained at 800 ml / g ± 30.

[0026] In this embodiment, the oxygen dealkali in step S6 is NaOH, and the amount of oxygen dealkali used accounts for 3.0 to 4.0% of the total mass of the material.

[0027] In this embodiment, the oxygen removal reaction in step S6 is carried out at a temperature of 95–105°C, a pressure of 0.65 ± 0.5 MPa, and a time of 60 ± 5 min. After oxygen removal, the viscosity is reduced to 600 ± 30 ml / g.

[0028] In this embodiment, step S7 employs a three-stage bleaching process: D0→EOP→D1. D0: ClO2 dosage 7-8 kg / ton, time 25-30 min, pH 1.5-2.5 (currently conventionally 3.0-4.0), temperature 80-90℃ (currently conventionally 70-75℃); EOP: Control the amount of H2O2 to 8-12 kg / ton, the time to 80-100 min, control the amount of NaOH to make the pH 11.8-12.8, the bleaching temperature to 85-90℃, and ensure the viscosity to be 530±30. D1: To supplement whiteness, use 3-5 kg / ton of ClO2, for 110-130 minutes, with a pH of 7-8 and a temperature of 80-90℃, to ensure a whiteness of 90% ISO or higher.

[0029] In this embodiment, the ash content of the product in step S8 is less than 0.1%, the iron content in the product is less than 10 ppm, and the viscosity of the product is 500 ± 30 ml / g.

[0030] In this embodiment, the residual alkali, pH value, solids content, coarse pulp yield, fine pulp yield, kappa value, and whiteness of the black liquor after cooking in step S4 were analyzed and tested. The results are shown in Tables 1 and 2.

[0031] Table 1 Results of Slurry Quality Testing

[0032] Table 2 Fiber Analysis Results

[0033] Table 1 shows that: the alkali dosage for cooking is 23%, the cooking H factor is 900, the pulp brightness is 44.48% ISO, the kappa number is 13.57, and the viscosity is 833, indicating that the pulp quality meets the requirements. Table 2 shows that:

[0034] Because the viscosity of the cooked product was 833, different processes were used for oxygen descaling and bleaching. The results are shown in Tables 3 and 4.

[0035] Table 3 Oxygen removal mass

[0036] Table 4 Bleaching Quality

[0037] As can be seen from Tables 3 and 4: 1) The whiteness after oxygen removal in stages 1-1 and 1-2 is relatively high, the chemical consumption for bleaching is not high, and the three-stage bleaching degree can reach more than 90% ISO; 2) The viscosity after bleaching in stage 1-1 is relatively high at 531 ml / g, and the viscosity of stage 1-2 is 477 ml / g, which can meet the requirements for high-purity bleaching; 3) After bleaching in stages 1-1 and 1-2, the ash content is not high at 0.05-0.07%, and the methyl cellulose is 90.4-91.7%, which can meet the requirements for high-purity bleaching.

[0038] The high-purity bleached hardwood pulp produced in this embodiment is manufactured from high-quality sulfate pulp and used in Lyocell production. The final product produced in this embodiment is cut-to-board pulp, with each small bag weighing 250±20 kg, packaged in sets of eight bags, or as specified in the order contract. The quality indicators of the high-purity bleached hardwood pulp developed using agricultural and forestry "three residues" in this application are shown in Table 5 below (mainly indicating that, through process adjustments, the hardwood residues can achieve the same level of pulp quality as eucalyptus log pulp): Table 5 Quality Indicators of High-Purity Bleached Hardwood Pulp

[0039] Compared with existing technologies, the method in this embodiment uses agricultural and forestry "residues" as raw materials for preparing high-purity bleached hardwood pulp. This fully utilizes existing logging, timber processing, and finishing waste to produce high-purity bleached hardwood pulp, solving the problem of timber raw material needs for enterprise production. The raw material pretreatment stage employs a three-stage screening process (first layer Φ40mm, second layer Φ20mm, third layer Φ5.0mm), significantly improving the size qualification rate of the raw materials entering the cooking pot and ensuring uniform cooking. Through optimized process parameters and the use of deionized water for washing throughout the process, the method in this embodiment produces high-purity bleached hardwood pulp that meets superior standards. Key quality indicators include a stable whiteness above 90% ISO, a methyl cellulose content above 90%, ash content less than 0.1%, and iron less than 10 ppm. The viscosity is an excellent level of 500±30. This method not only fully utilizes agricultural and forestry waste resources but also solves the technical problems of unstable raw material quality and poor product consistency in traditional bleached hardwood pulp production through refined process control, providing Lyocell with a high-quality raw material guarantee.

[0040] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing high-purity bleaching agents using agricultural and forestry "three residues", characterized in that, The following steps are included: S1. Raw material screening: Select the "three residues" that meet the requirements; S2. Chips: After peeling, chipping, and screening, the chips that meet the requirements are directly stacked according to the tree species of the "three residues". S3. Washing: The sheet is washed with water or air-separated to remove foreign matter and wood chips from the sheet; S4. Cooking: The hemicellulose and lignin in the sheet are removed by vapor-phase pre-hydrolysis sulfate cooking. S5. Slurry screening: Slurry screening is carried out using a 0.15-0.25mm slotted sieve, and collection is carried out using a mesh bag with a mesh size of not less than 350-500 mesh. S6, Oxygen De-alkali: A certain amount of oxygen de-alkali is added to the collected material to carry out the oxygen de-alkali reaction; S7. Bleaching: Bleaching the material obtained after the oxygen desulfurization reaction; S8. Flake making and whiteness and fiber content testing: The bleached material is folded into flakes, and the material after frying and drying is tested for whiteness and fiber content. The product with whiteness stable above 90% ISO and fiber content controlled above 90% is the final product.

2. The method for preparing high-purity bleaching agents using agricultural and forestry "three residues" according to claim 1, characterized in that, The "three residues" that meet the requirements in step S1 refer to "residues" with a freshness of ≥95%, a pass rate of ≥75%, a decayed wood content of ≤5.0%, and a bark content of ≤2.0%.

3. The method for preparing high-purity bleaching agents using agricultural and forestry "three residues" according to claim 1, characterized in that, In step S2, the sheet material that meets the requirements refers to a sheet material with 4.8 ≤ L < 40 mm and H ≤ 8 mm; where L is the length of the sheet material, H is the thickness of the sheet material, and the width of the sheet material is not greater than the length of the sheet material.

4. The method for preparing high-purity bleaching agents using agricultural and forestry "three residues" according to claim 1, characterized in that, The vapor-phase pre-hydrolysis sulfate cooking method in step S4 is as follows: NaOH solution, Na2S liquid and water are mixed and cooked together with the sheet. The sheet accounts for 20±0.5% of the weight of the mixture, and the water, NaOH and Na2S liquid account for 80±0.5% of the weight of the mixture.

5. The method for preparing high-purity bleaching agents using agricultural and forestry "three residues" according to claim 4, characterized in that, In step S4, the concentration of the mixture formed by NaOH and Na2S is 22.5-24%, the heating time is 20-25 min, the cooking temperature is 162-164℃, the holding time is 80-95 min, and the cooling time is 20-25 min.

6. The method for preparing high-purity bleaching agents using agricultural and forestry "three residues" according to claim 1, characterized in that, In step S4, the kappa value at the end of the cooking process is controlled to be between 16 and 18, and the viscosity is maintained at 800 ml / g ± 30.

7. The method for preparing high-purity bleaching agents using agricultural and forestry residues according to any one of claims 1-6, characterized in that, In step S6, the oxygen dealkali is NaOH, and the amount of oxygen dealkali used accounts for 3.0 to 4.0% of the total mass of the material.

8. The method for preparing high-purity bleaching agents using agricultural and forestry "three residues" according to claim 7, characterized in that, In step S6, the oxygen removal reaction is carried out at a temperature of 95–105°C, a pressure of 0.65 ± 0.5 MPa, and a time of 60 ± 5 min. After oxygen removal, the viscosity is reduced to 600 ± 30 ml / g.

9. The method for preparing high-purity bleaching agents using agricultural and forestry "three residues" according to any one of claims 1-6, characterized in that, Step S7 employs a three-stage bleaching process: D0→EOP→D1. D0: ClO2 dosage 7-8 kg / ton, time 25-30 min, pH 1.5-2.5, temperature 80-90℃; EOP: Control the amount of H2O2 to 8-12 kg / ton, the time to 80-100 min, control the amount of NaOH to make the pH 11.8-12.8, the bleaching temperature to 85-90℃, and ensure the viscosity to be 530±30. D1: To supplement whiteness, use 3-5 kg / ton of ClO2, for 110-130 minutes, with a pH of 7-8 and a temperature of 80-90℃, to ensure a whiteness of 90% ISO or higher.

10. The method for preparing high-purity bleaching agents using agricultural and forestry "three residues" according to any one of claims 1-6, characterized in that, In step S8, the ash content of the product is less than 0.1%, the iron content is less than 10 ppm, and the viscosity is 500 ± 30 ml / g.

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