A chemical pretreatment method for reducing energy consumption of pulp refining by selectively breaking LCC ester bonds with hydroxylamine

Abstract

This invention discloses a pretreatment method for reducing energy consumption in chemimechanical pulping by selectively breaking LCC ester bonds with hydroxylamine. Specifically, hydroxylamine is used as a nucleophile to selectively hydroxylate LCC ester bonds under weakly alkaline conditions, directionally breaking the ester bond connections between lignin and hemicellulose while preserving the hemicellulose backbone structure. This significantly reduces energy consumption in subsequent disc milling by mitigating cell wall swelling and reducing the mechanical integrity of the wood. This belongs to the field of chemical pretreatment technology in pulping and papermaking. Its key feature is the treatment of hardwood raw materials using a hydroxylamine / sodium bicarbonate buffer system at 60°C and pH 8.5. Hydroxylamine molecules nucleophilically attack LCC ester bonds to generate isohydroxyxamic acid, releasing high-molecular-weight intact hemicellulose that can be recycled. The treated wood exhibits a reduction in elastic modulus of more than 20%, moderate cell wall swelling, and a reduction in milling energy consumption of approximately 16% compared to traditional hydrothermal pretreatment. If combined with a mild alkaline treatment to form a synergistic process, milling energy consumption can be reduced by more than 56%, and pulp yield can be increased by 5-8 percentage points compared to traditional alkaline pretreatment. This invention solves the technical problems of poor selectivity in existing alkali pretreatment, severe degradation of hemicellulose backbone, low pulp yield, and high waste liquor load, and provides a brand-new technical path for energy saving, consumption reduction and green production of chemimechanical pulp.

Description

Technical Field

[0001] This invention belongs to the field of pulp and paper technology, specifically relating to a pretreatment method for chemimechanical pulp, and more particularly to a chemical pretreatment method that utilizes hydroxylamine to selectively break LCC ester bonds to reduce pulping energy consumption. Background Technology

[0002] Chemi-mechanical pulp (CMP) and chemithermomechanical pulp (CTMP) are widely used in newsprint, printing and writing paper, paperboard, and high-value-added specialty paper industries due to their high yield, good bulk, and optical properties. However, the mechanical refining process is extremely energy-intensive, typically requiring 1200-2000 kWh / t, accounting for approximately 20-30% of the total pulping cost, and is one of the core bottlenecks restricting the development of chemi-mechanical pulp. To reduce refining energy consumption, chemical pretreatment methods are commonly used in industry. This involves treating wood chips with chemical agents before refining to soften cell walls and remove some lignin / hemicellulose, thereby reducing the mechanical energy input for subsequent refining. Currently, the mainstream pretreatment methods include alkali pretreatment, sulfite pretreatment, and hydrogen peroxide-enhanced alkali treatment (P-RC APMP process).

[0003] Alkali pretreatment (usually using NaOH) is currently the most widely used pretreatment method for chemimechanical pulping. NaOH breaks the ester bonds that connect lignin and hemicellulose, while simultaneously dissolving some lignin and hemicellulose, thus reducing the energy consumption for fiber separation. For example, researchers treated poplar chips with 1% NaOH at 50°C for 6 hours before disc milling, which significantly reduced milling energy consumption compared to untreated samples. Alkali-enzyme synergistic pretreatment technology has also been developed for the production of high-yield eucalyptus pulp. Under optimal pretreatment conditions (6% NaOH and 8 FPU / g cellulase), milling energy consumption was significantly reduced. Furthermore, the chemi-enzyme synergistic pretreatment system reduced refining energy consumption to 765.11 kWh / t, an energy saving of 40.99% compared to traditional mechanical pulping. However, existing chemimechanical pulping pretreatment technologies share the following common drawbacks: 1. Lack of selectivity: Existing pretreatment methods struggle to selectively break LCC ester bonds, often resulting in simultaneous degradation of the hemicellulose backbone or excessive lignin dissolution; 2. Insufficient understanding of mechanisms: There is currently a lack of mechanistic answers based on direct chemical evidence to the scientific question of "which chemical bonds break most effectively reduces pulping energy consumption"; 3. Difficulty in achieving "precise bond breaking": No pretreatment method can reduce pulping energy consumption solely by breaking LCC ester bonds without degrading the hemicellulose backbone, thus achieving the optimal balance between energy saving and fiber strength preservation. Therefore, developing a novel chemimechanical pulping pretreatment method that can selectively break LCC ester bonds, preserve the integrity of the hemicellulose backbone, consumes fewer chemicals, and is environmentally friendly has significant industrial value and scientific importance.

[0004] A review published by Zhu Yutong et al. systematically elucidated the structural characteristics of lignin-carbohydrate complex (LCC) chemical bonds in lignocellulose raw materials and their breakage mechanisms during various treatment processes. It pointed out that current technologies struggle to completely break LCC chemical bonds while preserving the structural integrity of lignin and hemicellulose. However, the review did not address specific methods for using hydroxylamine as a selective bond-breaking agent and its application in reducing the energy consumption of chemimechanical pulping. A series of studies published by Associate Professor Liu Yongzhuang's team performed structure-activity relationship analysis of the LCC structure at the molecular level, discovering that phenyl ester bonds (LCEs) possess unique reactivity and bonding positions, providing a possibility for precise bond cleavage to separate natural lignin. However, the review did not cover the selective cleavage of LCC ester bonds using the nucleophilic properties of hydroxylamine, nor the related research on the impact of this treatment on the mechanical properties of wood and pulping energy consumption. The literature published by Beata Doczekalska et al. describes thermochemical modification of beech wood using ammonium hydroxide. This involves treatment with hydroxylamine-related reagents and focuses primarily on improving the functional and visual properties of the modified wood. However, it does not address the selective cleavage of LCC ester bonds by hydroxylamine treatment or its application in reducing the energy consumption of chemimechanical pulping. A patent published by Li Qun et al. proposes a low-energy pulping method for rapid dissolution of hemicellulose. This method uses spiral extrusion tearing combined with caustic soda solution impregnation to treat wood chips. It increases the permeability of the treatment solution through physical tearing and utilizes the alkali solution to break LCC bonds. However, it does not address the use of hydroxylamine as a selective bond-breaking agent, nor does it solve the problem of hemicellulose backbone degradation caused by alkali treatment. Hans-Peter Kaul's published patent discloses a multi-component system for modifying, degrading, or bleaching lignin and lignin-containing materials. This system includes an oxidation catalyst, an oxidant, and compounds selected from hydroxylamine, hydroxylamine derivatives, and hydroxamic acid. Hydroxylamine is used as a component of this multi-component oxidation system for the oxidative degradation or bleaching of lignin. However, the patent does not address the selective cleavage of LCC ester bonds using hydroxylamine alone, nor does it address the impact of this treatment on wood mechanical properties and refining energy consumption. Existing research on reducing refining energy consumption in chemimechanical pulping has widely reported techniques such as alkali pretreatment and bioenzyme pretreatment. However, these techniques generally suffer from poor selectivity, hemicellulose backbone degradation, decreased pulp yield, and high wastewater treatment costs. Existing applications of hydroxylamine in the lignocellulose field have mainly focused on lignin modification or as a component of multi-component oxidation systems. There are no reports of using hydroxylamine alone as a selective bond-cleaving agent for LCC ester bond cleavage and systematically studying its effects on wood mechanical properties, cell wall swelling behavior, and refining energy consumption.Compared with existing research and technologies, the differences and advantages of this invention are as follows: Firstly, hydroxylamine is used alone as a highly selective chemical reagent, acting directly on the LCC ester bonds of wood under mild conditions (60℃, pH 8.5), achieving selective ester bond cleavage through hydroxylation while completely preserving the hemicellulose backbone structure. The effects of hydroxylamine treatment on wood mechanical properties (elastic modulus, static bending strength), cell wall swelling behavior (moisture adsorption, crystallinity changes), and refining energy consumption were systematically studied, establishing a complete correlation model of "chemical bond cleavage - mechanical properties - refining energy consumption." A two-step process of hydroxylamine pretreatment and hydroxylamine-alkali synergistic pretreatment was proposed, significantly reducing refining energy consumption while maintaining high pulp yield and fiber strength. This invention solves key technical problems in existing chemimechanical pulp pretreatment technologies, such as poor selectivity, large hemicellulose loss, and high wastewater treatment costs, providing a new technical path for energy saving, consumption reduction, and green production of chemimechanical pulp. Summary of the Invention

[0005] The technical problem to be solved by this invention is: in the existing chemimechanical pulp pretreatment process, strong alkali causes hemicellulose degradation and excessive swelling causes energy dissipation in pulping. A pretreatment process using hydroxylamine as a selective bond-breaking agent is proposed. Through the directional breaking of LCC ester bonds, the mechanical softening of wood cell walls and the weakening of inter-fiber interfaces are achieved, which significantly reduces pulping energy consumption while maintaining high pulp yield and fiber strength.

[0006] To solve the above-mentioned technical problems, the present invention is implemented through the following technical solution: A chemical pretreatment method for reducing grinding energy consumption by selectively cleaving LCC ester bonds with hydroxylamine, comprising the following steps: (1) Preparation of wood raw materials: After peeling and chipping the wood raw materials, they are made into standard wood chips (20-40 mm in length and 2-5 mm in thickness), or crushed into 40-60 mesh wood powder and dried for later use; (2) Preparation of hydroxylamine working solution: Prepare an aqueous solution of hydroxylamine hydrochloride with a concentration of 0.5-2.0 mol / L. Add NaOH solution under ice bath and stirring conditions to adjust the pH value to 8.5±0.1. Then add NaHCO3 as a buffer and make up to volume to obtain a working solution with a final concentration of 0.3-1.0 mol / L hydroxylamine and 1.0 mol / L NaHCO3. Preheat to the reaction temperature. (3) Vacuum-assisted impregnation: Place the oven-dried wood raw material in a reaction vessel and add the preheated hydroxylamine working solution at a liquid-solid volume mass ratio of (5-20):1 (ml / g); perform vacuum-venting cycle treatment 2-4 times, with each vacuuming time being 3-10 minutes, so that the working solution penetrates into the wood chips. (4) Hydroxylamine selective bond breaking treatment: The impregnated wood samples were placed in a sealed reaction vessel and reacted at 60°C for 12-48 hours. In this system, hydroxylamine mainly exists in a neutral molecular form, with its nitrogen atom acting as the active center. Through an addition-elimination reaction mechanism, it launches a highly selective nucleophilic attack on the carbonyl carbon atom of the ester bond in LCC, ultimately breaking the ester bond and generating isohydroxamic acid. The pH value was maintained within the range of 8.0-9.0 throughout the reaction process; (5) Post-treatment and pulping: After the reaction is completed, the reaction liquid and the wood sample are separated. The wood sample is directly pulped by disc milling after dehydration until the pulp freeness reaches 300-400 CSF. The separated reaction liquid is recycled.

[0007] Furthermore, before the disc milling in step (5), a mild alkali treatment step can be introduced: after the hydroxylamine treatment is completed and the reaction solution is discharged, add a NaOH solution equivalent to 1% of the weight of the oven-dried wood chips to the wood sample and continue to treat it at 60°C for 30 minutes to synergistically dissolve hemicellulose and further soften the cell wall. Then, separate the alkali solution for milling. The advantages and effects of this invention are as follows:

[0008] High chemical selectivity: Unlike the indiscriminate degradation of traditional alkali treatment, this process utilizes the lone pair electrons of the nitrogen atom in the neutral hydroxylamine molecule to target the LCC ester bond through an addition-elimination reaction. This reaction has a weak effect on the glycosidic bonds of the hemicellulose backbone and the ether bonds of lignin, achieving structural dissociation while completely preserving the hemicellulose backbone structure, resulting in a significantly higher pulp yield than traditional alkali pretreatment processes.

[0009] Energy dissipation control during pulping: This invention operates in a near-neutral or weakly alkaline (pH 8.5) system, effectively avoiding excessive fiber swelling and bloating caused by conventional strongly alkaline environments. Through precise cleavage of LCC ester bonds, mechanical softening of the cell wall and effective weakening of the interfiber interface are achieved without significant swelling. This avoids an increase in storage modulus caused by swelling, thereby significantly reducing the mechanical energy input during macroscopic fiber separation.

[0010] Synergistic effect: The two-step process of "hydroxylamine pretreatment + mild alkali treatment" proposed in this invention utilizes hydroxylamine pretreatment to selectively open LCC chemical bonds, creating a highly efficient penetration channel for subsequent mild alkali treatment. The synergistic effect of the two-step treatment can reduce pulping energy consumption to 60-70% of the traditional alkali treatment process while maintaining a high pulp yield of approximately 90%.

[0011] This process operates at a low reaction temperature (60℃), eliminating the need for the high-temperature, high-pressure equipment (above 100-120℃) required in traditional APMP pulping. The bond-breaking reaction produces isohydroxamic acid, with no toxic byproducts. The high molecular weight hemicellulose retained in the waste liquid is easily recovered, and the waste liquid load is significantly lower than that of traditional alkali pretreatment, meeting the green and clean production requirements of the pulp and paper industry. Furthermore, the characteristic groups constructed using this method can serve as chemical probes, providing a quantitative research basis for elucidating the chemical-mechanical synergistic mechanism in the pulping process. Detailed Implementation

[0012] The present invention will be further described in detail below through specific embodiments. The "wood / non-wood raw materials" mentioned in the present invention refer to any plant resource containing a lignin-carbohydrate complex (LCC) and wherein ester bonds are present. Wood raw materials include hardwoods (such as poplar, birch, eucalyptus, acacia, and other broadleaf woods) and coniferous woods; non-wood raw materials include gramineous plants (such as bamboo, rice straw, wheat straw, reeds, sugarcane bagasse, corn stalks, etc.).

[0013] The following examples are intended to demonstrate the applicability of the present invention to different typical raw materials and should not be construed as limiting the range of raw materials of the present invention.

[0014] A chemical pretreatment method for reducing grinding energy consumption by selectively cleaving LCC ester bonds using hydroxylamine is described below, along with the selected raw materials, chemicals, reaction equipment, and specific process parameters: (1) Raw material processing: Wood raw materials (such as poplar, eucalyptus and other broad-leaved wood) are peeled and shaved into standard wood chips (20-40 mm in length and 2-5 mm in thickness); Non-wood raw materials (such as bamboo and reeds) are washed and cut into bamboo strips or filaments 30-50 mm long.

[0015] (2) Preparation of hydroxylamine working solution: Prepare an aqueous solution of hydroxylamine hydrochloride with a concentration of 0.5-2.0 mol / L, adjust the pH to 8.5±0.1, and add 1.0 mol / L NaHCO3 as a buffer.

[0016] (3) Vacuum impregnation: liquid-solid ratio 10:1 (mL / g), vacuuming and degassing cycled 3 times to ensure that the drug solution enters the cell wall.

[0017] (4) Reaction process: The reaction was carried out at a constant temperature of 60°C for 24 hours. Hydroxylamine molecules weaken the interfibrillary interface and mechanically soften the cell wall by directionally attacking the LCC ester bond, while avoiding excessive swelling caused by strong alkali.

[0018] (5) Grinding energy consumption measurement: After removing the reaction impregnation liquid, the wood chips / bamboo fibers are fed into the disc mill and ground to the target free degree (350±20 CSF), and the energy consumption is recorded.

[0019] Specific reaction process parameters: Hydroxylamine reaction tower: temperature 60℃, reaction time 24 h, hydroxylamine concentration 0.5 mol / L, NaHCO3 concentration 1 mol / L, pH 8.5±0.1, liquid-solid ratio 10:1.

[0020] Reactor: Vacuum degree -0.08 MPa, vacuuming-venting cycle 3 times, vacuuming for 5 minutes each time.

[0021] Disc milling: Pulp thickness 10%, mill to a freeness of 350±20 CSF. Example 1

[0022] This embodiment demonstrates the implementation method and effect of the synergistic effect of hydroxylamine pretreatment and mild alkali treatment, which achieves the best reduction in grinding energy consumption.

[0023] (1) After washing and screening, 1 kg of oven-dried poplar wood chips (20-40 mm in length and 2-5 mm in thickness) are placed in a reaction vessel.

[0024] (2) Prepare hydroxylamine working solution in the drug preparation container: Dissolve hydroxylamine hydrochloride in deionized water, slowly add sodium hydroxide solution while stirring to adjust the pH to 8.5±0.1, and add sodium bicarbonate as a buffer to make the final concentration of hydroxylamine 0.5mol / L and the concentration of sodium bicarbonate 1mol / L.

[0025] (3) Add the hydroxylamine working solution to the reaction vessel at a liquid-to-solid ratio of 10:1. Start the vacuum system and evacuate to -0.08 MPa. Maintain this for 5 minutes and then release the vacuum. Repeat this process 3 times to ensure that the solution fully penetrates into the wood chips.

[0026] (4) Turn off the vacuum system, heat the material in the reaction vessel to 60°C, and keep the reaction at this temperature for 24 hours. Keep the vessel sealed during the reaction, monitor the pH of the reaction solution regularly, and add sodium bicarbonate as needed to adjust it to 8.5±0.1.

[0027] (5) After the hydroxylamine reaction is complete, the reaction solution is drained. Then, 1% NaOH solution (relative to the weight of oven-dry wood chips) is added to the system and the system is treated at 60°C for 30 minutes to perform a mild alkali treatment to further dissolve some of the hemicellulose and soften the cell walls.

[0028] (6) After the alkali treatment is completed, the alkali solution is discharged. The separated wood chips are sent to a disc mill for pulping. The pulp concentration is 10%, and the gap between the discs is gradually reduced until the pulp freeness reaches 350±20 CSF. Record the pulping energy consumption.

[0029] The quality characteristics of the pulp obtained in this embodiment are as follows: Pulping energy consumption: 620 kWh / t (56.3% lower than the untreated blank group of Comparative Example 1, and 23.5% lower than the alkali-treated group of Comparative Example 4).

[0030] Pulp yield: approximately 90% (based on oven-dry wood).

[0031] Fiber morphology: The average fiber length is about 0.83 mm, the fiber length distribution is concentrated, and the degree of fine fiberization is moderate.

[0032] Hand-copied sheet quality: Hand-copied sheets were manufactured according to GB / T 24326-2009, with a basis weight of 60 g / m², whiteness of 65% ISO (without subsequent bleaching), tensile index of 41 N·m / g, and tear index of 6.3 mN·m² / g. After subsequent hydrogen peroxide bleaching (1.5% NaOH, 4% H₂O₂, 90℃, 90 min), the whiteness can reach 78% ISO.

[0033] The advantage of this embodiment is that the hydroxylamine pretreatment selectively breaks the LCC ester bond, opening the penetration and reaction channels for subsequent alkali treatment. This allows for efficient dissolution of hemicellulose and further softening of the cell wall with mild alkali treatment. The two produce a significant synergistic effect, achieving a substantial reduction in pulping energy consumption while maintaining high pulp yield and fiber strength. Example 2

[0034] This embodiment demonstrates the implementation method and effect of using hydroxylamine alone for pretreatment.

[0035] (1) After washing and screening, 1 kg of oven-dried poplar wood chips (20-40 mm in length and 2-5 mm in thickness) are placed in a reaction vessel.

[0036] (2) Prepare hydroxylamine working solution in the drug preparation container: Dissolve hydroxylamine hydrochloride in deionized water, slowly add sodium hydroxide solution while stirring to adjust the pH to 8.5±0.1, and add sodium bicarbonate as a buffer to make the final concentration of hydroxylamine 0.5mol / L and the concentration of sodium bicarbonate 1mol / L.

[0037] (3) Add the hydroxylamine working solution to the reaction vessel at a liquid-to-solid ratio of 10:1 (volume:mass, mL / g). Start the vacuum system, evacuate to -0.08 MPa, maintain for 5 minutes, then release the vacuum. Repeat 3 times.

[0038] (4) Turn off the vacuum system, heat the material in the reaction vessel to 60°C, and keep the reaction at this temperature for 24 hours. Keep the vessel sealed during the reaction, monitor the pH of the reaction solution regularly, and add sodium bicarbonate as needed to adjust it to 8.5±0.1.

[0039] (5) After the reaction is complete, drain the reaction liquid. Send the separated wood chips into a disc mill for grinding. The pulp concentration is 10%, and the gap between the discs is gradually reduced until the pulp freeness reaches 350±20 CSF. Record the grinding energy consumption.

[0040] The quality characteristics of the pulp obtained in this embodiment are as follows: Grinding energy consumption: 880 kWh / t (38.0% lower than the untreated blank group).

[0041] Pulp yield: approximately 92% (based on oven-dry wood).

[0042] Fiber morphology: The average fiber length is about 0.85 mm, the fiber length distribution is concentrated, and the degree of fine fiberization is moderate, indicating that the hydroxylamine treatment did not cause excessive damage to the fiber.

[0043] Hand-copied sheet quality: Hand-copied sheets were manufactured according to GB / T 24326-2009, with a basis weight of 60 g / m², whiteness of 65% ISO (without subsequent bleaching), tensile index of 42 N·m / g, and tear index of 6.5 mN·m² / g. After subsequent hydrogen peroxide bleaching (1.5% NaOH, 4% H₂O₂, 90℃, 90 min), the whiteness can reach 78% ISO.

[0044] The advantages of this embodiment are as follows: hydroxylamine achieves mechanical softening of plant fiber cell walls by selectively cleaving LCC ester bonds without significantly degrading the cellulose and hemicellulose backbone. This results in a significant reduction in refining energy consumption compared to the untreated sample, while maintaining high pulp yield and fiber strength. Compared to the alkali pretreatment group in Comparative Example 4, although the refining energy consumption in this embodiment is slightly higher (880 kWh / t vs 810 kWh / t), the pulp yield is increased by approximately 7 percentage points (92% vs 85%), the average fiber length is increased by approximately 18%, and the tensile index and tear index are significantly better than the alkali pretreatment group, demonstrating superior overall performance. Comparative Example 1

[0045] This comparative example demonstrates the difference in performance between grinding directly without any chemical pretreatment, serving as a benchmark for calculating the energy savings of each pretreatment method.

[0046] One kg of oven-dried poplar chips (20-40 mm in length and 2-5 mm in thickness) were directly fed into a disc mill for pulping without any chemical pretreatment. The pulp concentration was 10%, and the gap between the discs was gradually reduced until the pulp freeness reached 350±20 CSF. The pulping energy consumption was recorded.

[0047] The results obtained from this comparative example are as follows: the energy consumption for pulping is 1420 kWh / t. This set of data serves as a baseline for calculating the energy savings of each pretreatment method. Comparative Example 2

[0048] This comparative example demonstrates the difference in effects when using only deionized water for immersion treatment.

[0049] (1) Place 1 kg of oven-dried poplar wood chips (20-40 mm in length and 2-5 mm in thickness) in a reaction vessel and add deionized water at a liquid-to-solid ratio of 10:1.

[0050] (2) Evacuate to -0.08 MPa, maintain for 5 minutes and then release. Repeat 3 times.

[0051] (3) Heat the container to 60°C and keep it warm for 24 hours.

[0052] (4) After the reaction is complete, drain the water and send the wood chips into a disc mill for grinding. The pulp concentration is 10%, and the gap between the discs is gradually reduced until the pulp freeness reaches 350±20 CSF. Record the grinding energy consumption.

[0053] The results obtained in this comparative example are as follows: the grinding energy consumption is 1050 kWh / t. In comparison, the grinding energy consumption of the hydroxylamine pretreated group in Example 2 was reduced by 16.2% compared to this comparative example, indicating that the chemical bond-breaking effect of hydroxylamine has a substantial contribution to reducing grinding energy consumption, rather than being solely due to the physical swelling effect of water. Comparative Example 3

[0054] This comparative example demonstrates the effect of impregnation treatment using only sodium bicarbonate buffer (without hydroxylamine).

[0055] (1) Preparation of sodium bicarbonate buffer: Dissolve sodium bicarbonate in deionized water to a concentration of 1 mol / L, and adjust the pH to 8.5±0.1 with sodium hydroxide solution.

[0056] (2) Place 1 kg of oven-dried poplar wood chips (20-40 mm in length and 2-5 mm in thickness) in a reaction vessel and add the above buffer solution at a liquid-to-solid ratio of 10:1.

[0057] (3) Evacuate to -0.08 MPa, maintain for 5 minutes and then release. Repeat 3 times.

[0058] (4) Heat the container to 60°C and keep it warm for 24 hours. During this period, check the pH regularly and add sodium bicarbonate if necessary to maintain the pH at 8.5±0.1.

[0059] (5) After the reaction is complete, drain the buffer solution and send the wood chips into a disc mill for grinding. The pulp concentration is 10%, and the gap between the discs is gradually reduced until the pulp freeness reaches 350±20 CSF. Record the grinding energy consumption.

[0060] The results obtained in this comparative example are as follows: the grinding energy consumption is 1030 kWh / t. In comparison, the grinding energy consumption of the hydroxylamine pretreatment group (880 kWh / t) in Example 2 is 14.6% lower than that of this comparative example. This difference clearly reflects the core role of hydroxylamine in selectively breaking the LCC ester bond in reducing grinding energy consumption, rather than the non-specific effect caused by the weakly alkaline conditions of the buffer solution. Comparative Example 4

[0061] This comparative example demonstrates the effects of using the traditional sodium hydroxide alkali pretreatment method.

[0062] (1) Place 1 kg of oven-dried poplar wood chips (20-40 mm in length and 2-5 mm in thickness) in a reaction vessel and add 1% NaOH solution (relative to the mass of oven-dried wood chips) at a liquid-to-solid ratio of 10:1.

[0063] (2) Evacuate to -0.08 MPa, maintain for 5 minutes and then release. Repeat 3 times.

[0064] (3) Heat the container to 80°C and keep it warm for 2 hours.

[0065] (4) After the reaction is complete, drain the alkaline solution. Feed the wood chips into a disc mill for grinding. The pulp concentration is 10%. Gradually reduce the gap between the discs until the pulp freeness reaches 350±20 CSF. Record the grinding energy consumption.

[0066] The results obtained from this comparative example are as follows: Energy consumption for grinding: 810 kWh / t.

[0067] Pulp yield: approximately 85% (based on oven-dry wood).

[0068] Fiber morphology: The average fiber length is about 0.72 mm, the fiber length distribution is relatively dispersed, and the content of fine particles is high, indicating that the alkali treatment caused a certain degree of damage to the fiber.

[0069] Quality of hand-copied sheets: tensile index 35 N·m / g, tear index 5.2 mN·m² / g.

[0070] A comparison of this comparative example with the various embodiments shows that the hydroxylamine-alkali synergistic pretreatment group in Example 1 is significantly superior to this comparative example in terms of refining energy consumption (620 kWh / t) and pulp yield (approximately 90%), fully demonstrating the advanced nature and comprehensive advantages of the technical approach of this invention. Although the hydroxylamine-only pretreatment group in Example 2 has slightly higher refining energy consumption (880 kWh / t) than this comparative example, its pulp yield is increased by approximately 7 percentage points, its average fiber length is increased by approximately 18%, and its tensile index and tear index are significantly superior to those of this comparative example, indicating that this invention has a clear advantage in maintaining fiber strength.

[0071] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A pretreatment method for reducing the energy consumption of chemimechanical pulping by selectively breaking LCC ester bonds in wood using hydroxylamine, characterized in that: Hydroxylamine is used as a nucleophile in a weakly alkaline buffer system to selectively hydroxylate LCC ester bonds in wood under liquid-solid two-phase reaction conditions. This directionally breaks the ester bonds and releases intact hemicellulose, while avoiding cell wall swelling to a certain extent, thereby reducing the mechanical properties of wood and the energy consumption of subsequent disc milling and pulping.

2. The preprocessing method according to claim 1 specifically includes the following steps: (1) Preparation of wood raw materials: After peeling and chipping the hardwood raw materials, they are made into standard wood chips (20-40 mm in length and 2-5 mm in thickness), or crushed into 40-60 mesh wood powder and dried to constant weight for later use; (2) Preparation of hydroxylamine working solution: Weigh hydroxylamine hydrochloride and dissolve it in deionized water. Under ice bath cooling and stirring conditions, add alkaline solution to adjust the pH to 8.0-9.

0. Add sodium bicarbonate as a buffer and make up to volume to obtain a working solution with hydroxylamine concentration of 0.3-1.0 mol / L and sodium bicarbonate concentration of 0.5-2.0 mol / L. Preheat to the reaction temperature. (3) Vacuum-assisted impregnation: Place the wood raw material from step (1) into a reaction vessel, add the hydroxylamine working solution from step (2) at a liquid-solid ratio of (5-20):1, and perform vacuum-venting cycle treatment 2-4 times, with each vacuuming lasting 3-10 minutes; (4) Hydroxylamine reaction treatment: The mixture from step (3) is reacted at a constant temperature of 50-80°C for 12-48 hours, and the pH is maintained at 8.0-9.0 during the reaction. (5) Post-treatment and grinding: After the reaction is completed, the solid and liquid are separated and then sent to a disc mill for grinding. The grinding energy consumption is recorded.

3. The pretreatment method according to claim 2, characterized in that: The preferred conditions for the hydroxylamine working solution in step (2) are: hydroxylamine concentration 0.5 mol / L, sodium bicarbonate concentration 1 mol / L, pH 8.5±0.1; the preferred reaction temperature in step (4) is 60°C, and the preferred reaction time is 24 hours; the preferred liquid-to-solid ratio in step (3) is 10:

1.

4. The pretreatment method according to claim 2, characterized in that: The final freeness of the pulp described in step (5) is 300-400 CSF.

5. The pretreatment method according to claim 1 or 2, characterized in that: It also includes a hydroxylamine-base synergistic pretreatment step, in which, after the hydroxylamine reaction treatment, the solid residue is not washed, but a 1%-3% sodium hydroxide solution is directly added, and the mixture is treated at 40-60°C for 4-8 hours, then washed until neutral and then ground.