A non-grain biomass pulping process that can replace broadleaf pulp

Abstract

This invention discloses a non-grain biomass pulping process that can replace hardwood pulp, belonging to the field of pulping and papermaking engineering technology. The invention includes: deep magnetic sieve purification and ultrasonic washing for precise water control and material preparation; low-temperature circulating dilute alkali soaking for gentle fiber swelling; gradient heating cooking for selective delignification while retaining residual alkali; countercurrent vacuum washing for efficient black liquor separation while preserving heat and alkali; direct contact with residual heat for oxygen removal; composite additives to protect fibers; and finally, hydrogen peroxide bleaching to medical-grade high whiteness; black liquor concentration and combustion with an added silica removal process for complete heat and alkali recovery; two-stage fine screening; differentiated refining; and the addition of a wet strength agent to produce a special pulp for medical dressings. This invention, through the chemical potential connection and fiber differentiation treatment across cooking and bleaching processes, enables the same batch of pulp to simultaneously achieve both wet strength and absorbency without using chlorine-containing bleaching agents.

Description

Technical Field

[0001] This invention belongs to the field of pulp and paper engineering technology, and in particular relates to a non-grain biomass pulping process that can replace hardwood pulp. Background Technology

[0002] Non-grain biomass raw materials refer to agricultural and forestry waste fiber resources that are neither food crops nor traditional timber. Common examples include crop straw and husks from agricultural product processing. The fiber morphology and chemical composition of these raw materials differ from wood. While their cellulose content is suitable for papermaking, they typically contain lignin, hemicellulose, and some unique non-fiber components. In the pulping industry, using them to replace part of hardwood pulp is a technological approach to alleviate timber resource shortages and reduce raw material costs.

[0003] Chlorine-free bleaching technology, consisting of oxygen delignification and hydrogen peroxide bleaching, is a mature and widely used clean bleaching method in the current paper industry. This technology does not use chlorine gas, chlorine dioxide, or hypochlorite-containing bleaching agents throughout the entire process, thus avoiding the generation of adsorbable organic halides (AOX) during bleaching. AOX is a class of byproducts with potential bioaccumulation and toxicity, and its emission and control are among the core environmental issues facing the modern pulp industry. Although existing chlorine-free bleaching technologies have been applied on a large scale in wood pulp production, they often face problems such as excessive damage to fiber strength or difficulty in improving brightness when processing non-grain biomass raw materials.

[0004] Currently, the main problem facing the production of medical dressing-grade pulp using non-grain biomass raw materials is the difficulty in simultaneously achieving the three contradictory properties required for paper: wet strength, high absorbency, and soft hand feel, all while completely avoiding the generation of AOX (acid-free oxygen). Specifically, if bleaching or cooking conditions are intensified to ensure chemical purity, the fibers will undergo excessive degradation, resulting in soft and weak paper that is particularly prone to tearing when wet, failing to provide adequate support for the dressing. Conversely, if the fibers are retained to maintain strength, bleaching or cooking often needs to be weakened, inevitably leading to insufficient pulp brightness and cleanliness, making it unsafe for contact with wounds. Existing commercial pulp preparation technologies typically use uniform processing parameters for all fibers, without specific process design tailored to the differentiated fiber morphology requirements of medical dressings. Therefore, the following solutions are proposed to address these issues. Summary of the Invention

[0005] The purpose of this invention is to provide a non-grain biomass pulping process that can replace hardwood pulp. By linking the chemical potential energy of the cooking and bleaching processes and differentiating the fiber diversion, it is possible to achieve both wet strength and absorbency softness in the same batch of pulp without using chlorine-containing bleaching agents. This solves the problem that existing chlorine-free bleaching processes are unable to simultaneously meet the comprehensive requirements of medical dressing paper for wet strength, high absorbency, and soft hand feel when processing non-grain biomass raw materials.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: This invention provides a non-grain biomass pulping process that can replace hardwood pulp, comprising the following steps: Step S1, Raw material pretreatment: Select non-grain biomass raw materials, purify and wash them to obtain clean raw materials; Step S2, Pre-soaking and softening: The clean raw material is placed in a dilute alkaline solution and pre-soaked and softened under temperature control. Step S3, Cooking: Cook the pre-soaked material to obtain a coarse pulp; Step S4, Washing and Black Liquor Extraction: The crude pulp is washed countercurrently to extract black liquor; Step S5, Chlorine-free bleaching: The washed pulp is subjected to oxygen delignification treatment and hydrogen peroxide bleaching in sequence, without adding any chlorine-containing bleaching agent throughout the process; Step S6, Alkali Recovery and Recycling: The black liquor is evaporated, concentrated, and then burned. The resulting melt is dissolved to form green liquor. The green liquor is subjected to desiliconization treatment and then causticized to recover the alkali, which is then reused in step S2 and / or step S3. Step S7, Pulp Selection and Morphology Control: The bleached pulp is screened and purified. The purified pulp is then split into two streams for differentiated pulping, that is, it is processed separately according to different pulping methods and degrees. Finally, the two streams are mixed to obtain a pulp product that can replace hardwood pulp.

[0007] Furthermore, in step S1, the non-grain biomass raw material is flax shavings or cotton stalk bark; the washing is carried out under ultrasonic assistance, and the moisture content of the raw material is controlled to be 45%-50% after washing.

[0008] Further, in step S2, the dilute alkaline solution is the dilute white solution recovered in step S6, with an effective alkali concentration of 8-12 g / L; the temperature control conditions are 48-52℃, and the residual alkali concentration of the leachate is controlled at 3-4 g / L and the pH value is 10.0-10.5 at the end of the pre-soaking, with the material liquid retention rate reaching 180%-200%.

[0009] Furthermore, in step S3, the cooking temperature is increased to 155°C at a rate of 0.8°C per minute and held for 20 minutes; after cooking, the kappa value of the pulp is 8-10 and the residual alkali concentration is 2-3 g / L.

[0010] Furthermore, in step S4, a multi-stage drum vacuum washer is used for countercurrent washing, with a vacuum degree of -30 to -40 kPa in the pulp formation zone and a vacuum degree of -50 to -60 kPa in the dewatering zone; the extracted black liquor has a solid content of ≥12% and a black liquor extraction rate of ≥95%.

[0011] Further, in step S5, the oxygen delignification treatment involves first adding 1.5%-2.0% NaOH (by weight of oven-dry pulp) to the washed pulp to adjust the initial pH to 11.0-11.2, then adding a composite additive composed of sodium dodecylbenzenesulfonate and magnesium sulfate in a mass ratio of 1:2, with a total dosage of 0.3% of the oven-dry pulp weight; and reacting for 40-50 minutes at a temperature of 95-100℃ and a pressure of 0.4-0.6MPa.

[0012] Further, in step S5, the hydrogen peroxide bleaching involves adding 2.5%-3.0% hydrogen peroxide, 3% sodium silicate, and 0.05% EDTA by weight of the oven-dry pulp, adjusting the initial pH to 10.8-11.2 with sodium hydroxide, and reacting at 85-90°C for 100-120 minutes.

[0013] Further, in step S6, the black liquor is evaporated and concentrated to a solid content of 60%-65% and then sent to the alkali recovery furnace, where the combustion zone temperature is controlled at 950-1050℃; the silicon removal treatment involves adding lime milk accounting for 1%-2% of the mass of the green liquor to the green liquor, causing the silicon to form calcium silicate precipitate and be separated and removed, and the clear liquor after silicon removal is then causticized.

[0014] Further, in step S7, the screening and purification adopts a two-stage pressure screen in series, with the first-stage screen having a mesh size of 0.2 mm and the second-stage screen having a mesh size of 0.1 mm; the differentiated refining process involves dividing the screened slurry into a first stream of 65%-70% by mass and a second stream of 30%-35% by mass. The first stream undergoes conventional refining to a freeness of 30-35°SR, while the second stream undergoes high-concentration microfibrillation refining with a concentration of 15%-20% and a grinding disc gap of 0.2-0.3 mm to a freeness of 32-35°SR. Finally, the two streams of slurry are mixed.

[0015] The present invention has the following beneficial effects: This invention uses non-grain agricultural and forestry waste as raw materials, does not occupy arable land resources, and can partially replace hardwood pulp in the production of medical dressing paper. The entire process does not use chlorine bleaching agents, and the content of harmful halides in the produced pulp is below the national standard's lower limit, meeting the safety requirements for medical materials that come into contact with wounds. Through cooking and bleaching under medium-temperature conditions, fiber strength is well preserved, resulting in paper with both absorbency and a soft feel. Addressing the high silicon content of non-wood raw materials, a silicon removal process is added during alkali recovery, which helps reduce evaporator scaling and combustion furnace blockage, improving production continuity and operational stability. By diverting and differentiating fiber treatment, the paper achieves the required absorbency and tactile properties while maintaining sufficient wet strength. Furthermore, black liquor alkali recovery and heat energy recycling reduce chemical consumption and emissions, lowering the overall operating load.

[0016] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of a non-grain biomass pulping process that can replace hardwood pulp according to the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 Please see Figure 1 As shown, this invention is a non-grain biomass pulping process that can replace hardwood pulp, comprising the following steps: Step S1: Gradient purification of specific raw materials and ultrasonic-assisted critical point washing Non-grain, non-timber agricultural and forestry waste such as flax scraps or medical-grade cotton stalks are selected as single raw materials. The raw materials are first purified by a three-stage dry gradient method using a wind-magnetic screen: the first stage negative pressure air separation system removes light impurities such as husks and debris by utilizing density difference under a stable negative pressure of -500Pa; the second stage high gradient magnetic separator has a magnetic field strength set at 1.2T to capture metal particles that may be mixed in during sowing or field management; the third stage double-layer linear vibrating screen has a 6-mesh screen in the upper layer to intercept large foreign objects and a 20-mesh screen in the lower layer to remove fine dust and gravel. After purification, the raw materials enter the washing stage, which is carried out in a bubbling cleaning tank equipped with an ultrasonic vibrating plate using 35℃ process warm water. The ultrasonic frequency is 40kHz and the power density is 0.3. The cavitation effect is used to efficiently peel off and emulsify trace amounts of field pesticide residues or waxy layers adhering to the surface and crevices of raw materials. Food-grade alkyl glycosides, accounting for 0.03% of the water mass, are continuously injected into the water system as an surfactant. The washing continues until the readings of the online turbidity meter and conductivity meter show a change rate of less than 5% after three consecutive tests and tend to stabilize. At this point, it is determined that the raw materials have reached the initial medical cleanliness standard. After washing, the material is lightly dehydrated by a screw press under a pressure of 0.15 MPa, and the moisture content is controlled to be stable at about 47%. This moisture content can ensure rapid and uniform penetration of the pre-soaking alkali solution, and will not significantly dilute the concentration of the alkali solution due to excessive moisture content, thus ensuring the uniformity and repeatability of the pre-soaking process.

[0021] Step S2: Recover diluted white liquor, low-concentration alkali, temperature-controlled pre-soaking and softening. The material that meets the moisture content requirements in step S1 is fed into a vertical pre-impregnation tower. The impregnation medium is a recovered dilute white liquor from the alkali recovery causticizing section in step S6, which is precisely temperature-controlled to 50°C by a heat exchanger. Its effective alkali concentration is precisely adjusted to 10 g / L (calculated as NaOH). The core of the pre-impregnation process is to achieve gentle and uniform fiber softening and avoid damage. The system temperature is stabilized at the target value by circulating water in the tower jacket. At the same time, the internal circulation pump is started, so that the dilute white liquor permeates the material layer in a laminar flow uniformly from bottom to top at a constant flow rate of 0.6 m / s for 6-8 hours. Under this controlled temperature and alkali concentration combination, pectin, some low molecular weight lignin and soluble hemicellulose are selectively and gently hydrolyzed or dissolved, and microporous permeation channels are initially constructed between the fiber cell walls to achieve overall softening of the raw materials. The pre-soaking endpoint is determined by two parallel indicators: first, the residual alkali concentration in the leachate drops to 3 g / L, indicating that the active alkali has been effectively consumed; second, the pH value of the leachate stabilizes at 10.0, indicating that the buffer system has reached equilibrium. Pre-soaking ends when both conditions are met simultaneously. At this time, the fiber liquid holding rate naturally reaches 180%, ensuring that the fiber has been fully swollen and is in the best state for cooking.

[0022] Step S3: Medium-temperature gradient cooking that balances delignification rate and fiber protection The pre-impregnated material, along with the leachate, is fed into a continuous cooking tube. The cooking tube is designed to have a pressure of no less than 0.7 MPa, and the entire process follows a precisely controlled temperature and pressure curve: first, the material is uniformly heated to 110°C within 25 minutes to homogenize the internal temperature; then, it is heated to the peak process temperature of 155°C within 50 minutes at a constant rate of 0.8°C per minute. In this slow heating phase, most of the lignin is efficiently and selectively removed under optimized reaction kinetics; after reaching 155°C, it enters the holding phase and is strictly held for 20 minutes to ensure uniform cooking. Then, the inter-tube cooling system is activated to reduce the material temperature to below 100°C within 20 minutes before unloading. The pressure throughout the process corresponds to the saturated vapor pressure at each temperature stage, which is formed naturally without the need for additional pressurization. The advantages of this cooking regime are: the maximum temperature of 155℃ is still below the critical temperature for significant degradation of hemicellulose, which can protect the fiber strength to the maximum extent, while being sufficient to reduce the kappa number of the pulp to 8, thus establishing a chemical basis for the next step of oxygen delignification to achieve the target whiteness; the residual alkali concentration of the pulp is controlled at 2g / L (calculated as NaOH) at the end of cooking, and the pH value is maintained at 10.5.

[0023] Step S4: Countercurrent displacement washing and high-concentration black liquor extraction based on a stable vacuum gradient The cooked pulp is directly fed into a four-stage drum vacuum washing unit at a high temperature of 85℃, where it undergoes multi-stage countercurrent displacement washing. The operation follows a truly industrially proven gradient vacuum distribution principle: in the pulp formation zone of each washing unit, a lower vacuum degree is used, set at -30kPa, to form a loose and uniform pulp layer, promoting the penetration and capillary displacement of black liquor within the fiber network; in the dewatering dryness enhancement zone, the vacuum degree smoothly transitions to -50kPa, efficiently extracting the displaced black liquor. Clean hot water is added from the fourth stage, and the filtrate is applied in reverse, stage by stage, so that the filtrate from the first stage is a high-temperature (85°C), high-concentration (solid content ≥12%) extraction black liquor. Under this controlled vacuum system, the black liquor extraction rate of the system can stably reach over 95%. After washing, the pulp is kept at the temperature and alkaline state, with a pH value of 10.5. The residual alkali is precisely retained rather than excessively removed, which can be seamlessly connected with the initial conditions of the next oxygen delignification process, requiring only a small amount of fresh alkali solution to be added.

[0024] Step S5: Oxygen-hydrogen peroxide combined chlorine-free bleaching based on cellulose protection and activation penetration Oxy-delignification stage: The 10% washed pulp does not need to be cooled. It is directly pumped into the oxygen delignification reaction tower using its own sensible heat of 85-90℃. Only a small amount of steam needs to be added to stably maintain the temperature inside the tower at 95℃. Add 1.8% NaOH by weight of oven-dry pulp to the pulp stream and precisely adjust the initial pH to 11.0 to meet the alkaline reaction conditions of oxygen delignification. Subsequently, 99.5% pure oxygen was introduced to maintain a pressure of 0.5 MPa inside the tower. Simultaneously, a composite protective agent was continuously injected at the oxygen addition point. This agent was prepared from sodium dodecylbenzenesulfonate and magnesium sulfate in a 1:2 mass ratio, with a total dosage of 0.3% of the oven-dry pulp. Sodium dodecylbenzenesulfonate, as an industrial standard penetrant, reduces the surface tension of the pulp, promotes the uniform diffusion of oxygen and alkali into the fiber interior, and ensures bleaching uniformity. Magnesium sulfate, as a cellulose protective agent, works by complexing harmful transition metal ions (mainly...) present in the pulp. , This process inhibits the oxidative degradation of cellulose molecular chains by oxygen catalyzed by these ions; after 45 minutes of this treatment, the slurry is thoroughly washed and cleaned before proceeding to the next step. Next, the pulp is fed into the second stage hydrogen peroxide bleaching tower. Based on the kappa number of the incoming pulp, 2.8% hydrogen peroxide and 3% sodium silicate are added as stabilizers, and an additional 0.05% EDTA is added to further control trace amounts of active metal ions. The initial pH is adjusted to 10.8 with sodium hydroxide, and the mixture is gently reacted at 90°C and normal pressure for 120 minutes to ensure the stable and efficient release of the bleaching active agent from the hydrogen peroxide. No chlorine-containing chemicals are used throughout the entire process.

[0025] Step S6: Black liquor cogeneration and alkali closed-loop recovery using green liquor desiliconization process The high-concentration black liquor extracted in step S4 first enters a multi-effect falling film evaporator group, where it is concentrated to a solid content of 60% under progressively increasing vacuum. This is a feasible final concentration determined for the characteristics of non-wood raw material black liquor, which has high viscosity and is prone to scaling. The concentrated black liquor is then atomized and sent to the alkali recovery furnace. To ensure good fluidity and complete combustion of the high-silicon content non-grain raw material melt, the temperature in the combustion zone is controlled at 980℃. Organic matter in the furnace is fully combusted and releases heat. Its high-temperature flue gas is used to generate high-pressure steam through a waste heat boiler for power generation and steam supply for the whole plant. Inorganic sodium salts (mainly sodium carbonate) flow out from the bottom of the furnace in a molten state. After being dissolved in water, they form green liquid. Before entering the causticizing section, an additional desiliconization process is added: While stirring, 1.5% (by mass) of lime slurry is added to the green liquor. (Suspension), allowing for full reaction, causing a large amount of soluble silicate ions to precipitate out in the form of calcium silicate precipitate; The material is then fed into a clarifier, and the supernatant (purified green liquor) is transferred to a causticizer. Accurately measured amounts of quicklime (CaO) are added to carry out a causticizing reaction, regenerating the active alkali sodium hydroxide and by-product calcium carbonate required for cooking. After filtration to remove the white mud, a high-purity dilute white liquor is obtained. After concentration adjustment, it is precisely and quantitatively returned to the pre-soaking step S2 and the cooking step S3.

[0026] Step S7: Selection and Differentiated Morphology Control of Diversion Mode Slurry for Medical Performance The bleached clean slurry is first screened with a 0.2mm primary sieve to remove larger impurities, and then followed by a second-stage pressure sieve with a 0.1mm sieve to further remove any potential microfiber bundles and dust particles, ensuring that it meets the purity required for medical dressings. To address the contradictory requirements of high absorbency, soft feel and sufficient wet strength, a diversion-differentiated morphology control technology is introduced. The screened primary pulp is divided into two streams: the first stream, accounting for 65% of the total mass, is pumped into a conventional conical refiner and subjected to light cutting and fibrillation at a freeness target of 30°SR, forming a long fiber component that provides the skeleton for the paper's structural strength and wet strength; the second stream, accounting for 35% of the total mass, enters a high-consistency disc refiner, where it undergoes surface microfibrillation and low-intensity refining at a core control of 15% high concentration and a wide disc gap of 0.2mm, with a freeness target of 32°SR. This operation, while avoiding longitudinal fiber cutting, enriches the free hydroxyl groups on the fiber surface and fine fibrillates the fibers, giving the paper an ultra-high liquid absorption capacity and a soft, skin-like feel. The two differentiated fiber pulp streams were thoroughly mixed in the mixing tank according to the original ratio and concentrated to the specified concentration. Immediately, 0.25% of the oven-dry pulp mass of polyamide polyamine epichlorohydrin (PAE) wet strength agent was added. PAE is a widely validated permanent wet strength agent that meets medical contact safety requirements and can give the paper a necessary wet-to-dry strength ratio of not less than 15%. Finally, a wound absorbent dressing pulp product made entirely from non-grain biomass raw materials was prepared.

[0027] Comparative Example 2 The process is basically the same as in Example 1, except that in step S5, only NaOH is added to adjust the pH, and sodium dodecylbenzenesulfonate and magnesium sulfate are not added. That is, only traditional alkaline oxygen delignification is performed, and the other conditions are the same.

[0028] Main problems: The lack of penetrants leads to uneven distribution of oxygen and alkali, with some areas being over-bleached and some not, resulting in a decrease in whiteness uniformity; the lack of cellulose protectant allows transition metal ions to catalyze the attack of oxygen free radicals on cellulose, causing a decrease in fiber polymerization degree and a significant loss of wet strength of the pulp, making it difficult to meet the requirements for wet use of dressing paper.

[0029] Comparative Example 3 The process is basically the same as in Example 1, except that fiber separation is not performed in step S7. All the clean pulp after bleaching is fed into a conventional conical refiner and uniformly refined to 30-32°SR. Then, 0.25% PAE wet strength agent is added directly to form the pulp.

[0030] Main problems: The fiber processing lacks specificity, the long fiber skeleton is over-cut, and the short fiber components are not sufficiently microfibrilized. The resulting paper structure is dense but lacks open capillary channels, significantly reducing the liquid absorption rate; at the same time, the paper surface feels stiff, and the softness index deteriorates, failing to meet the dual requirements of absorption rate and tactile comfort for medical dressings.

[0031] Comparative Example 4 The process is basically the same as in Example 1, except that in step S3 the temperature is raised to 165°C and kept warm for 20 minutes, while the other cooking conditions and subsequent steps remain unchanged.

[0032] Main problems: The cooking temperature has entered the range of drastic hemicellulose degradation. Although the kappa number can be reduced to 6-7, the pulp yield decreases by 3-5 percentage points. The large amount of hemicellulose dissolution leads to a decrease in the rigidity of the fiber cell walls and an increase in the freeness of the pulp. Although the brightness is easy to meet the standard, the intrinsic strength of the fiber is damaged, the wet-dry strength ratio of the paper drops to 10-12%, the softness is too high and there is a lack of resilience, it is easy to collapse during use, and the necessary wet integrity of the dressing is lost.

[0033] Comparative Example 5 The process is basically the same as in Example 1, except that step S5 is completely replaced by the traditional CEH three-stage bleaching: the chlorination stage ( Dosage 3%, pH 2-3, room temperature 60 min), alkali treatment section (NaOH 2%, 60℃, 60 min), hypochlorite bleaching section ( Use 4% (38-40℃, 120 min), bleach thoroughly, then wash thoroughly. Repeat steps S1.

[0034] Key issues: The product contains up to 2-5 mg / L of adsorbable organic halides (AOX), far exceeding the safety limits for medical contact materials. Trace amounts of residual chlorine organics in the pulp can cause cytotoxic reactions and skin irritation, making it completely unsuitable for wound dressings. Furthermore, the chlorination process also oxidatively degrades cellulose, resulting in pulp strength inferior to that of Example 1.

[0035] Comparative Example 6 The process is basically the same as in Example 1, except that the pre-soaking and softening process in step S2 does not involve temperature control. Instead, the same concentration of recycled diluted white liquor is used for soaking for the same duration at room temperature, and the endpoint is determined based on residual alkali and pH.

[0036] Main problems: At low temperatures, the diffusion rate of alkali solution into the fiber core and the rate of chemical reaction slow down significantly, resulting in uneven pre-impregnation and insufficient softening in the central area of ​​the raw material. This leads to significant differences in delignification during subsequent cooking, with some fibers being over-cooked and others under-cooked, resulting in uneven overall pulp brightness and large fluctuations in fiber strength. Ultimately, the final product exhibits poor consistency in liquid absorbency and softness.

[0037] For a detailed performance comparison, please refer to the table below: Table 1. Comparison of key processes and product performance in each embodiment / comparative example Comparative Analysis: Example 1 achieves the best balance in cleanliness, mechanical properties, absorbency, and production continuity through synergistic optimization of each process. While Comparative Example 1 has acceptable product quality, the lack of silica removal severely restricts industrial continuity; Comparative Examples 2 and 4 both result in a collapse in wet strength; Comparative Example 3 loses its core functions of liquid absorption and softness; Comparative Example 5 violates medical safety principles; and Comparative Example 6 suffers from poor uniformity, making stable mass production difficult. This demonstrates that the various technical features of this invention are interdependent, collectively constituting a complete solution for medical dressing paper pulping.

[0038] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A non-grain biomass pulping process that can replace hardwood pulp, characterized in that, The pulping process includes the following steps: Step S1, Raw material pretreatment: Select non-grain biomass raw materials, purify and wash them to obtain clean raw materials; Step S2, Pre-soaking and softening: The clean raw material is placed in a dilute alkaline solution and pre-soaked and softened under temperature control. Step S3, Cooking: Cook the pre-soaked material to obtain a coarse pulp; Step S4, Washing and Black Liquor Extraction: The crude pulp is washed countercurrently to extract black liquor; Step S5, Chlorine-free bleaching: The washed pulp is subjected to oxygen delignification treatment and hydrogen peroxide bleaching in sequence, without adding any chlorine-containing bleaching agent throughout the process; Step S6, Alkali Recovery and Recycling: The black liquor is evaporated, concentrated, and then burned. The resulting melt is dissolved to form green liquor. The green liquor is subjected to desiliconization treatment and then causticized to recover the alkali, which is then reused in step S2 and / or step S3. Step S7, Pulp Selection and Morphology Control: The bleached pulp is screened and purified. The purified pulp is then split into two streams for differentiated pulping, that is, it is processed separately according to different pulping methods and degrees. Finally, the two streams are mixed to obtain a pulp product that can replace hardwood pulp.

2. The non-grain biomass pulping process that can replace hardwood pulp according to claim 1, characterized in that, In step S1, the non-grain biomass raw material is flax shavings or cotton stalk bark; the washing is carried out under ultrasonic assistance, and the moisture content of the raw material is controlled to be 45%-50% after washing.

3. The non-grain biomass pulping process that can replace hardwood pulp according to claim 1, characterized in that, In step S2, the dilute alkaline solution is the dilute white solution recovered in step S6, with an effective alkali concentration of 8-12 g / L; the temperature control conditions are 48-52℃, and the residual alkali concentration of the leachate is controlled at 3-4 g / L and the pH value is 10.0-10.5 at the end of the pre-soaking, with the material liquid retention rate reaching 180%-200%.

4. The non-grain biomass pulping process that can replace hardwood pulp according to claim 1, characterized in that, In step S3, the cooking temperature is increased to 155°C at a rate of 0.8°C per minute and held for 20 minutes; after cooking, the kappa value of the pulp is 8-10 and the residual alkali concentration is 2-3 g / L.

5. A non-grain biomass pulping process that can replace hardwood pulp according to claim 1, characterized in that, In step S4, a multi-stage drum vacuum washer is used for countercurrent washing. The vacuum degree in the pulp formation zone is -30 to -40 kPa, and the vacuum degree in the dewatering zone is -50 to -60 kPa. The extracted black liquor has a solid content of ≥12% and a black liquor extraction rate of ≥95%.

6. A non-grain biomass pulping process that can replace hardwood pulp according to claim 1, characterized in that, In step S5, the oxygen delignification treatment involves first adding 1.5%-2.0% NaOH (by weight of oven-dry pulp) to the washed pulp to adjust the initial pH to 11.0-11.2, then adding a composite additive composed of sodium dodecylbenzenesulfonate and magnesium sulfate in a mass ratio of 1:2, with a total dosage of 0.3% of the oven-dry pulp weight; and reacting for 40-50 minutes at a temperature of 95-100℃ and a pressure of 0.4-0.6MPa.

7. A non-grain biomass pulping process that can replace hardwood pulp according to claim 1, characterized in that, In step S5, the hydrogen peroxide bleaching involves adding 2.5%-3.0% hydrogen peroxide, 3% sodium silicate, and 0.05% EDTA by weight of oven-dry pulp, adjusting the initial pH to 10.8-11.2 with sodium hydroxide, and reacting at 85-90°C for 100-120 minutes.

8. A non-grain biomass pulping process that can replace hardwood pulp according to claim 1, characterized in that, In step S6, the black liquor is evaporated and concentrated to a solid content of 60%-65% and then sent to the alkali recovery furnace, where the combustion zone temperature is controlled at 950-1050℃. The silicon removal process involves adding lime milk accounting for 1%-2% of the mass of the green liquor to the green liquor, causing the silicon to form calcium silicate precipitate and be separated and removed. The clear liquor after silicon removal is then causticized.

9. A non-grain biomass pulping process that can replace hardwood pulp according to claim 1, characterized in that, In step S7, the screening and purification process uses a two-stage pressure screen connected in series, with the first-stage screen having a mesh size of 0.2 mm and the second-stage screen having a mesh size of 0.1 mm. The differentiated refining process involves dividing the screened slurry into a first stream (65%-70% by mass) and a second stream (30%-35% by mass). The first stream undergoes conventional refining to a freeness of 30-35°SR, while the second stream undergoes high-concentration microfibrillation refining with a concentration of 15%-20% and a grinding disc gap of 0.2-0.3 mm to a freeness of 32-35°SR. Finally, the two streams of slurry are mixed.

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