Method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp

Abstract

The present invention relates to the technical field of preparing bamboo dissolving pulp for viscose fiber, and specifically to a method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp. The method uses commercially available natural KP bamboo pulp board as raw material, and performs bamboo pulp board crushing, low-temperature acid treatment, extrusion impurity removal, oxygen delignification, DOE OP D1 three-stage cleaning and bleaching, the bleached pulp is then treated with enzymatic pulping to prepare high value-added, low-pollution, high-quality viscose fiber dissolving pulp, which can also be used to produce cellulose derivative products.

Description

Technical Field

[0001] The invention relates to the technical field of preparing bamboo dissolving pulp for viscose fiber, in particular to a method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp. Background Art

[0002] With the rapid development of the global economy and the continuous improvement of people's living standards, the demand for dissolving pulp varieties is also increasing. The approximate proportion of global dissolving pulp demand is: viscose products account for about 60%, and others such as acetate fiber, cellulose ether, nitrocellulose, etc. account for about 40%. As the world's largest producer of textiles and raw materials, my country's domestic dissolving pulp market accounts for about 90% of the total demand for dissolving pulp, acetate fiber accounts for about 7%, and others account for about 3%.

[0003] It is reported that the annual demand for dissolving pulp in the global market is basically stable at 5-7.5 million tons, of which Asia accounts for the majority. my country's demand for dissolving pulp has increased year by year. According to statistics, from 2019 to 2021, my country's apparent consumption was 4.6 million tons, 4.45 million tons and 3.95 million tons respectively, while the total domestic pulp production from 2019 to 2021 was 1.6 million tons, 1.1 million tons and 500,000 tons respectively. During the same period, my country's pulp imports were 3 million tons, 3.35 million tons and 3.45 million tons respectively. In addition, data from my country's dependence on imports of dissolving pulp show that in 2016, the dependence on imports of dissolving pulp was 53.32%, and by 2021, the dependence on imports increased to 87.79%. It can be seen that the consumption of dissolving pulp in my country is increasing day by day, especially in the production fields of viscose in the textile industry, the consumption of raw materials is growing rapidly, but the expansion of production capacity is extremely limited, and the serious imbalance between demand and production has brought great production pressure to the domestic chemical fiber industry, making the sustainable development of related industries in my country very risky. Based on the above reasons, how to develop natural and renewable cellulose fibers suitable for my country's national conditions to make up for the shortage of raw materials; how to prepare high value-added bamboo dissolving pulp that meets the requirements through improvements in preparation processes, process technologies and equipment to meet market demand, reduce the dependence of related companies on imported dissolving pulp, and promote the healthy and sustainable development of the industry. Based on national conditions, the present invention uses commercially available natural sulfate (KP) bamboo pulp as raw material to prepare viscose-grade bamboo dissolving pulp through chemical modification.

[0004] my country is rich in bamboo raw materials, which are widely distributed, highly adaptable, fast growing, early mature, and biodegradable. The characteristics of bamboo fiber are between those of coniferous wood and broadleaved wood. The average fiber length is 1.5-2.0mm, which is between broadleaved wood (fiber length ≤ 1mm) and coniferous wood (3-5mm). The aspect ratio is 150-200 (the aspect ratio of coniferous wood is about 100-150), and the holocellulose content is as high as about 74% (about 65-73% in coniferous wood). In addition, from the perspective of the global bamboo pulp production layout, more than 80% of bamboo pulp is in China. Based on the above characteristics of bamboo raw materials, its fiber morphology and content are close to those of the most suitable wood raw materials for producing viscose fiber. Therefore, bamboo has the innate conditions for producing viscose fiber. However, studies have shown that bamboo has a dense tissue structure and contains more non-fibrous impurities such as lignin, pentose hemicellulose, organic solvent extracts, ash, and miscellaneous cells, which lead to problems such as increased chemical consumption, reduced yield, and unsatisfactory pulp reaction performance during the pulping process. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of insufficient raw materials for the existing viscose fiber production, the existing wood dissolving pulp mainly relying on imports, which is not conducive to the sustainable, stable and healthy development of related industries, and to provide a method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp suitable for my country's national conditions. The bamboo dissolving pulp prepared by this method has the following characteristics: yield 35-42% (for bamboo raw materials), α-cellulose content above 94%, cuprammonia polymerization degree 550-850, whiteness above 82% ISO, ash content below 0.1%, Fe ions below 10 mg / kg, Cu ions below 2 mg / kg, Mg ions below 300 mg / kg, Ca ions below 60 mg / kg, dichloromethane extract below 0.4%, polypentose below 5%, S 18 5% or less, S 10 6% or less, (S 10 -S 18 ) is less than 2%, and the Fock reaction performance is 79-88%.

[0006] In order to achieve the above invention object, the specific technical solution of the present invention is:

[0007] A method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp comprises the following steps:

[0008] (1) Crushing bamboo pulp board: crushing the commercially available natural KP bamboo pulp board into pulp;

[0009] (2) Acid treatment: the pulp after the crushing in step (1) is diluted and then enters a double-roll mixer, and acid and cold air are added, and then enters a bleaching tower for low-temperature acid treatment, and then is washed in a pulp washer after the acid treatment;

[0010] (3) Extrusion and impurity removal: the slurry obtained in step (2) is fed into a twin-roll press and treated by an integrated process of dilution, displacement and squeezing;

[0011] (4) Oxygen delignification: adding sodium hydroxide solution and magnesium salt protective agent to the pulp obtained in step (3), preheating through a double-roll mixer or directly entering the pulp pump riser, then entering a medium-consistency high-shear mixer and adding oxygen and medium-pressure steam, and then entering an upflow bleaching tower for oxygen bleaching;

[0012] (5)D0E OP D1 three-stage cleaning and bleaching:

[0013] (6) Enzymatic beating: OP After D1 three-stage cleaning and bleaching, the pulp is pulped and cellulase is added during pulping. After enzymatic pulping, it is washed in a pulp washer to obtain viscose grade bamboo dissolving pulp.

[0014] Furthermore, in step (1) of disintegrating bamboo pulp board, commercially available natural color KP bamboo pulp board is directly put into a high-consistency hydraulic pulper with a spiral drill-type rotor to disintegrate the pulp. The purpose of disintegration is to dissociate the bamboo pulp board and disperse the pulp board into a fiber suspension while maximally maintaining the original strength and length of the bamboo fibers in the pulp board.

[0015] The high-consistency hydraulic pulper with a spiral drill-type rotor uses a spiral or three-line conical rotor. Its movement mode is not impact pulping, but guiding the pulp flow from the bottom of the pulp tank to the periphery of the pulp tank and then falling back to the vicinity of the rotor; a large speed difference is maintained between the rotor and the pulp flow entering the rotor periphery, thereby generating a gentle hydraulic shearing effect between the fiber and the suspension, between the fiber and the fiber, and between the rotor and the fiber. Combined with the mechanical action of the rotor, the bamboo pulp fibers produce physical effects such as mutual friction, rubbing, twisting, and squeezing, which effectively reduces the cutting effect on the pulp fibers, and is conducive to the bamboo pulp board being dispersed into a fiber suspension while maintaining the original strength and length of the bamboo fibers in the pulp board; and the equipment The crushing concentration is 10-26%, which is a medium-high concentration. At this concentration (10-26%), the physical interaction between fibers is further promoted, the friction between fibers is enhanced, the heat generated is increased, and the fibers absorb heat and become soft and plastic, further reducing the tendency of fibers to be cut, reducing the amount of fiber fragments and fine fibers, and improving the purity. The crushed pulp develops in the direction of fibrillation and fine fiberization, so that a large amount of cellulose on the middle layer of the secondary wall (S2 layer) is fully exposed, increasing the specific surface area of ​​the fiber, creating favorable conditions for the excellent reaction performance, uniform fiber composition and uniform fiber morphology of the finished dissolving pulp; and the increase in crushing concentration can improve production capacity and save unit power consumption.

[0016] This application further optimizes the scheme, and while the bamboo pulp board is being crushed, an alkaline substance, sodium hydroxide, is added. The amount of alkali is 0.2-3.5% relative to the absolute dry pulp mass, the time is 20-60min at room temperature, and the crushed pulp concentration is 10-26wt%. In addition, a surfactant is also added during the crushing, and the amount of surfactant is 0.1-6.5‰ relative to the absolute dry pulp mass. It is a compound of a nonionic surfactant and an anionic surfactant in a ratio of 1:2-4. The compounding can improve the surface activity of the system, change the interfacial properties of sodium hydroxide and fiber, significantly reduce the surface tension of the sodium hydroxide solution, and improve the penetration, wetting, dispersion, solubilization and other effects of alkali on the fiber, so that the fiber is fully swollen, the fiber is reduced from being cut, and it is beneficial for the fiber to be dissociated into a single fiber. Nonionic surfactants: lauryl alcohol polyoxyethylene ether, fatty acid methyl ester polyoxyethylene ether, Tween 80, glyceryl monostearate. Anionic surfactants: sodium dioctyl sulfosuccinate, sodium oleoylethanesulfonate, sodium N-oleoyl N-methyl taurate, sodium fatty alcohol sulfate.

[0017] The purpose of adding sodium hydroxide when the bamboo pulp board is broken down is to promote the dissolution of some alkali-soluble oligomers (such as uronic acid, low molecular chain lignin, ash, extracts, etc.) under the action of alkali, and form small "pores" on the surface of cell walls and intercellular layers to make it easier for water to enter the fiber tissue, promote fiber swelling, increase fiber softness, reduce fiber cutting, and facilitate the dissociation of raw materials into single fibers, maintaining fiber length and strength.

[0018] The high-consistency hydraulic pulper with a spiral drill-type rotor used in the present application is a prior art in the field of waste paper pulping, so its specific structure is not described in detail.

[0019] Furthermore, the acid treatment in step (2) can further destroy the tightly structured primary fiber wall (P) and the primary wall outer layer (S1), expose the secondary wall middle layer (S2), effectively remove impurities such as ash, metal ions, pentose hemicellulose and fine fibers in the pulp, overcome the weaknesses of the bamboo raw material itself, and achieve the effects of regulating the degree of polymerization or viscosity, purifying, astringing and depolymerizing the pulp, while reducing the ineffective decomposition of the subsequent bleaching agent by the presence of metal ions, improving the effectiveness of bleaching, and improving the whiteness, purity and whiteness stability of the pulp. In addition, low-temperature acid treatment can effectively avoid excessive acid hydrolysis and acid oxidation degradation of the fiber, avoid the generation of more small fibers and other oligomers in the pulp, and affect the pulp α-cellulose content and fiber polymerization degree distribution uniformity and dissolving pulp reaction performance.

[0020] Preferably, the mass concentration of the acid-treated pulp is 2-7%, the temperature is 1-10°C, the time is 20-180min, the acid dosage is 0.1-3.0% relative to the mass of the absolute dry pulp, and the pH value is 1.5-4.5; the acid is hydrochloric acid, sulfuric acid, sulfurous acid or a low molecular weight organic acid (formic acid, acetic acid, etc.).

[0021] The step (3) of extrusion removal is as follows: the pulp after acid treatment enters a double-roll pulping machine, and through the integrated treatment of dilution, displacement and squeezing, the impurity cells and other fine components in the pulp are effectively removed, the removal of the primary wall (P) and the primary wall outer layer (S1) is promoted, the fiber is further purified, and the uniformity of the polymerization degree distribution is improved.

[0022] The extrusion and impurity removal section uses a double-roll pulping machine with a displacement and washing function. The equipment consists of a pair of pressing rollers, a pulp tank, a feeding device, a screw conveying device and a transmission device. It has three displacement and washing zones: a dehydration zone, a displacement zone and a pressing zone. The working principle is: a slurry with a concentration of 2-5% is pumped into the pulp tank at a pressure of 0.02-0.06MPa. Under the action of the pulp inlet pressure and the liquid level pressure difference, it begins to enter the dehydration zone, and the waste liquid enters the roller through the filter holes on the roller surface and is discharged through the openings at both ends of the roller; the continuous pulp layer on the roller surface reaches the displacement zone with the rotation of the pressing roller, and the pulp concentration is about 10wt% at this time; the waste liquid in the pulp in the displacement zone is replaced by the washing liquid, and this displacement effect ends until the pulp enters the pressing zone; in the pressing zone, the pulp is squeezed to a concentration of 30-40wt% and is conveyed out by the upper screw.

[0023] The twin-roll pulping machine used in the present application is a prior art in the field of chemical pulp washing, so its specific structure will not be described in detail.

[0024] The step (4) oxygen delignification is as follows: sodium hydroxide solution and a magnesium salt protective agent are added to the pulp obtained in step (3), preheated in a double-roll mixer or directly entering the pulp pump riser, then entering a medium-consistency high-shear mixer and adding oxygen and medium-pressure steam, and then entering an upflow bleaching tower for oxygen bleaching, with a tower top pressure of 0.3-0.9 MPa, a pulp concentration of 7-18wt%, a temperature of 90-120°C, and a time of 60-90 min; the magnesium salt protective agent is magnesium carbonate, magnesium sulfate or magnesium oxide; relative to the mass of the absolute dry material, the amount of sodium hydroxide used is 1-5%, the amount of magnesium salt protective agent used is 0.1-3.5%, and the amount of oxygen used is 1.5-3.5%.

[0025] After oxygen delignification is completed, the material is pumped to the spray pot instead of the pressure spraying to the spray pot commonly used by technicians in this field. The reason is that when pressure spraying is used, the fibers are cut and damaged due to the shearing effect caused by turbulence and rapid evaporation of steam on the spray line and at the inlet of the spray pot during the spraying process, which will inevitably increase the content of fine components, reduce the purity of the pulp, and reduce the yield. However, after the oxygen delignification is completed, the present invention pumps the washing waste liquid of this section (i.e., the oxygen delignification section) into the tower from the bottom of the bleaching tower to replace the high-concentration hot bleaching waste liquid, and the bleaching waste liquid is used for washing the crude pulp after cooking, and the washing liquid can be sent to the alkali recovery system for treatment and combustion, thereby achieving no wastewater discharge. The pulp in the bleaching tower is mixed with the washing waste liquid of this section below 100°C and cooled, and at the same time plays a high-temperature washing role to improve the cleanliness of the pulp. When the pulp temperature in the tower drops below 100°C, it is pumped to the spray pot by a pump without rapid flash evaporation, which can effectively avoid the occurrence of the above situation.

[0026] Step (5) D0E OP D1 three-stage cleaning and bleaching:

[0027] D0E OP The three-stage cleaning and bleaching process conditions of D1 are the conventional process conditions used by those skilled in the art, and can achieve the technical effects of the present invention without any special requirements.

[0028] A. Chlorine dioxide primary bleaching: sodium hydroxide or sulfuric acid is added to the slurry obtained in step (4) to adjust the pH value, and the slurry is preheated in a double-roll mixer or directly enters the medium-consistency slurry pump riser, and then enters the medium-consistency high-shear mixer, and chlorine dioxide and steam are added to the medium-consistency high-shear mixer, and then enters the upflow or up-downflow bleaching tower for chlorine dioxide bleaching;

[0029] The chlorine dioxide bleaching process is: pulp concentration 7-16wt%, time 30-180min, temperature 50-95°C, relative to the absolute dry pulp mass, chlorine dioxide dosage 0.8-2.0%, sodium hydroxide or sulfuric acid dosage 0-0.5%, bleaching endpoint pH value 2-4.

[0030] B. EOP bleaching: After washing, the pulp obtained in step A is added with sodium hydroxide solution, preheated by a double-roll mixer or directly enters the medium-consistency pulp pump standpipe, then enters the medium-consistency high-shear mixer, and hydrogen peroxide, oxygen and medium-pressure steam are added, and then enters the ascending-descending flow bleaching tower for EOP bleaching;

[0031] The EOP bleaching process is: pulp concentration 7-16wt%, time 60-180min, temperature 50-95°C, oxygen pressure 0.1-0.3MPa, relative to the mass of absolute dry pulp, sodium hydroxide dosage 0.5-1.5%, oxygen dosage 0.2-1%, hydrogen peroxide dosage 0.1-1.0%.

[0032] C. Chlorine dioxide secondary bleaching: After washing, the pulp obtained in step B is added with sodium hydroxide or sulfuric acid to adjust the pH value, preheated in a double-roll mixer or directly enters the medium-consistency pulp pump riser, and then enters a medium-consistency high-shear mixer, and chlorine dioxide and steam are added, and then enters an ascending-downflow bleaching tower for chlorine dioxide bleaching;

[0033] The chlorine dioxide bleaching process is: pulp concentration 7-16wt%, time 60-240min, temperature 70-80°C, relative to the absolute dry pulp mass, chlorine dioxide dosage 0.2-0.6%, sodium hydroxide or sulfuric acid dosage 0-0.5%, bleaching endpoint pH value 3.5-7.

[0034] The step (6) of enzymatic beating: the washed bleached pulp is treated by a pulping machine, and cellulase is added during beating. The amount of cellulase used is 0.02-0.5 IU / g based on the absolute dry pulp, the pulp concentration is 3-7 wt%, the environmental pH value is 3.5-6.8, the temperature is 25-85°C, and the action time is 20-180 min. After enzymatic beating, the pulp is washed clean by a pulp washer.

[0035] When beating the bleached pulp, cellulase is added, mainly to utilize the enzyme to act on the fiber, causing a series of physical and chemical changes such as amorphization, debonding, depolymerization, swelling and breaking of the cellulose crystal region, thereby destroying the fiber surface, generating micropores, improving the permeability of the fiber surface, and improving the accessibility of the fiber to the liquid medicine. Enzyme treatment combined with mechanical beating further breaks the primary wall (P layer) and the primary wall outer layer (S1 layer) outside the secondary wall middle layer (S2 layer), loosens the fibers in the S2 layer, improves the viscose liquid filtration performance, improves the reaction performance of dissolving pulp, and greatly improves its overall quality, ultimately ensuring that the quality of the end product is qualified and meets the production requirements of products such as viscose fiber. To this end, the action of enzymes and pulping treatment complement each other. After the action of enzymes on fibers, the tissue structure relaxes, the force between fine fibers weakens, and they slide against each other, creating favorable conditions for pulping and promoting the breaking of the P layer and the S1 layer. On the contrary, pulping treatment exposes S2 and loosens the fibers in the S2 layer, increasing the specific surface area of ​​the fibers, promoting the diffusion and penetration of enzyme molecules into the fibers, and making the action of enzymes on fibers more uniform and complete.

[0036] Cellulase is an amphiphilic molecule whose electrical properties change with the pH value of the environment. The pH value of the enzymatic pulping treatment environment of the present application is in the range of 3.5-6.8, which is higher than the isoelectric point (PI) of the cellulase protein molecule. Therefore, the cellulase molecule is negatively charged as a whole, and the fiber is also negatively charged. The two are in a state of repulsion. A mordant (such as cationic polyacrylamide) needs to be added to bring the two close to each other for reaction so that the cellulase can effectively play its catalytic role. The enzyme used is an exocellulase and / or an endocellulase.

[0037] The present application uses sodium bisulfite to adjust the pH value of enzymatic pulping, and the dosage is 0.1-2.5‰.

[0038] This application further optimizes the scheme, and adds a mordant, cationic polyacrylamide (CPAM), during enzymatic pulping. CPAM is a cationic polyelectrolyte polymer with high relative molecular mass and low charge density. The amount of CPAM added relative to the mass of the absolute dry pulp is 0.2-1.5‰, and its mechanism of action is mainly: cationic polyacrylamide (CPAM) exists in the form of a relatively curly, multi-chain tail in aqueous solution. When mixed with negatively charged pulp, CPAM is directly adsorbed on the surface of negatively charged pulp fibers in the form of chain tails. The adsorbed polymer chain tails can directly pass through the double electrical layer of the pulp fiber and adsorb to the surface of another particle (such as cellulase), bridging between the particles, so that the cellulase and the fiber are close to each other and react.

[0039] To further optimize the solution, cysteine ​​is also added. Cysteine ​​is a highly active and multifunctional amino acid. Each cysteine ​​molecule is linked by two cysteine ​​molecules, and its stability comes from an extremely strong disulfide bond. The most important function of cysteine ​​is to remove free radicals, antioxidants, and chelating agents for heavy metals such as copper and iron. For this reason, the addition of cysteine ​​to enzymatic pulping can stabilize the action environment of cellulase, further activate the activity of cellulase, and reduce the copper, iron and other ion content of the dissolving pulp. The amount of cysteine ​​added is 0.1-1.0‰ relative to the mass of the absolute dry pulp.

[0040] In the above steps, the water added to the slurry and the water used for washing are both distilled water or deionized water.

[0041] The method of obtaining dissolving pulp for viscose fiber by modifying and refining bamboo pulp can broaden the source of raw materials for dissolving pulp for viscose fiber production, laying a solid foundation for building a competitive industrial chain. At the same time, the implementation of the present invention has a positive effect on unblocking the innovation chain, industrial chain and supply chain of production links, and has practical significance for implementing the country's proposal of "promoting the formation of a new development pattern with the domestic circulation as the main body and the domestic and international circulations mutually promoting each other."

[0042] This application is based on the national conditions of "bamboo", takes natural sulfate bamboo pulp as raw material, and utilizes a treatment method that combines physical, chemical and biological methods, through acid treatment, double-roll pulping machine, oxygen delignification, and three-stage cleaning bleaching. The bleaching includes three stages: primary bleaching with chlorine dioxide (i.e., D0) - alkaline treatment with oxygen and hydrogen peroxide simultaneously enhanced (i.e., Eop) - secondary bleaching with chlorine dioxide (i.e., D1). The bleached pulp is then treated with enzymatic beating to prepare bamboo dissolving pulp for viscose fiber with high added value, low environmental pollution and quality that meets the requirements. It can also be used to produce cellulose derivative products.

[0043] The viscose-grade bamboo dissolving pulp is prepared by the method of this application. The chemicals used are clean and environmentally friendly, and the produced bamboo fiber dissolving pulp can fully meet the requirements of viscose fiber for dissolving pulp products, thereby achieving the sustainable development of viscose-grade bamboo dissolving pulp preparation in the textile industry in coordination with environmental protection. If this technology can be applied in production, it will bring good economic benefits, environmental benefits and social benefits. At the same time, this technology currently has outstanding innovation in the field of bamboo pulping. Once implemented, it will promote major changes in the field of bamboo pulp production technology, improve the level of clean production technology for bamboo dissolving pulp preparation, and at the same time promote employment and income growth for bamboo farmers, increase the social and economic contribution rate of the bamboo fiber industry, and help the vigorous development of bamboo fiber specialty industries.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (I) This application is a clean preparation method for preparing bamboo dissolving pulp by modifying commercially available natural KP bamboo pulp board:

[0046] First of all, based on my country's actual national conditions, using my country's abundant bamboo resources to replace or partially replace wood and cotton linter to produce bamboo dissolving pulp not only solves the problem of limited production of natural raw materials such as cotton linter and wood due to arable land, cost and ecological and environmental protection constraints, but also adds a new sustainable and renewable raw material to the dissolving pulp production field. At the same time, the production cost is greatly reduced, and the dependence on imported raw materials can be weakened, reducing the risks of sustainable development of related industries in my country and expanding the utilization value of KP bamboo pulp.

[0047] Secondly, the raw material is traditional natural KP bamboo pulp, and the raw material preparation process is a common process used by technicians in this field. Therefore, the raw material is simple and easy to obtain, and the source is wide, which lays the material foundation for the production of bamboo dissolving pulp from the source. The commercially available natural bamboo pulp board has a copper ammonia polymerization degree of about 1200-1600, a kappa number of about 15-22, α-cellulose 84-89%, S18 8-12%, S1010-16%, ash content 1.5-2.5%, whiteness 28±2% ISO, and a yield of about 48-54% (for bamboo raw materials). The above indicators are not conducive to the production of dissolving pulp. Moreover, bamboo raw materials have inherent weaknesses such as high hemicellulose content, high ash content, and many miscellaneous cells. Therefore, commercially available natural KP bamboo pulp board is used as raw material, and a treatment method combining physical, chemical and biological methods is used, such as high-concentration hydraulic pulping with a spiral drill rotor, low-temperature acid treatment, double-roll pulping machine, oxygen delignification, pumping after oxygen delignification, and then DOE conventionally used by those skilled in the art OPD1 three-stage cleaning and bleaching treatment, the bleached pulp is then treated with enzymatic beating to effectively purify the fiber, converge the fiber, adjust the polymerization degree or viscosity of the dissolving pulp, so that the final product dissolving pulp has uniform polymerization degree distribution, uniform fiber length distribution, good pulp component uniformity, uniform fiber morphology structure, excellent reaction performance and good contact performance between cellulose and chemicals. The yield of bleached bamboo dissolving pulp is 35-42% (for bamboo raw materials), а-cellulose content is above 94%, copper ammonia polymerization degree is 550-850, whiteness is above 82% ISO, ash content is less than 0.1%, Fe ion is less than 10mg / kg, Cu ion is less than 2mg / kg, Mg ion is less than 300mg / kg, Ca ion is less than 60mg / kg, dichloromethane extract is less than 0.4%, polypentose is less than 5%, S 18 5% or less, S 10 6% or less, (S 10 -S 18 ) is less than 2%, and the Fock reaction performance is 79-88%.

[0048] (ii) The present application adopts a high-concentration hydraulic pulper with a spiral drill-type rotor to disintegrate the commercially available natural color KP bamboo pulp board, and produces a mild hydraulic shearing effect between the fibers and the suspension, between the fibers, and between the rotor and the fibers. At the same time, the addition of alkali and surfactant is more conducive to the bamboo pulp board being dispersed into a fiber suspension while maintaining the original strength and length of the bamboo fibers in the pulp board; in addition, the high-concentration pulping develops in the direction of fibrillation and fine fiberization, so that a large amount of cellulose on the middle layer (S2 layer) of the secondary wall is fully exposed, increasing the specific surface area of ​​the fiber, creating favorable conditions for the excellent reaction performance, uniform fiber composition and uniform fiber morphology structure of the finished dissolving pulp; and the increase in the disintegration concentration can improve the production capacity and save unit power consumption.

[0049] (III) The present application adopts low-temperature acid treatment, which can effectively remove impurities such as ash, metal ions, pentose hemicellulose and fine fibers in the pulp while destroying the tightly structured primary fiber wall (P) and the outer layer of the primary wall (S1). In addition, low-temperature acid treatment can effectively avoid excessive acid hydrolysis and acid oxidation degradation of the fiber, which will lead to the production of more fine fibers and other oligomers in the pulp, which is not worth the loss.

[0050] (iv) After the acid treatment, the present application uses a double-roll pulping machine to effectively remove solids such as foreign cells and other fine components in the pulp through integrated dilution, displacement and pressing, further purify the fibers, improve the uniformity of the polymerization degree distribution, and improve the filtration performance of the viscose liquid.

[0051] (V) The present application adopts a pump to pump the material to the spray pot after the oxygen delignification is completed, which effectively avoids the shearing effect caused by turbulence and rapid evaporation of steam on the spray line and at the inlet of the spray pot during the pressure spraying process, which causes the fibers to be cut and damaged, which is bound to increase the content of fine components and reduce the purity of the pulp.

[0052] (VI) The present application adds a mordant, cationic polyacrylamide, during enzymatic pulping, so that the negatively charged fibers and cellulase are brought into proximity with each other for reaction, thus giving full play to the catalytic effect of the enzyme.

[0053] (VII) The present application also adds cysteine ​​during enzymatic pulping to stabilize the action environment of cellulase, further activate the activity of cellulase, and at the same time reduce the copper, iron and other ion contents of the dissolving pulp, thereby improving the purity of the dissolving pulp. DETAILED DESCRIPTION

[0054] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0055] It should be noted that, in order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0056] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] The raw material used in the following implementation is a commercially available natural bamboo pulp board: its cuprammonia polymerization degree is about 1200-1600, the kappa number is about 15-22, the α-cellulose is 84-89%, S18 is 8-12%, S10 is 10-16%, the ash content is 1.5-2.5%, the whiteness is 28±2% ISO, and the yield is about 48-54% (for bamboo raw materials).

[0058] In this application, all reagents are commercially available, and all processes or devices not emphasized can be achieved by existing technologies.

[0059] Embodiment 1:

[0060] A method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp comprises the following steps:

[0061] (1) Bamboo pulp board disintegration: Under room temperature, commercially available natural color KP bamboo pulp board is directly put into a high-concentration hydraulic pulper with a spiral drill rotor to disintegrate the pulp. While the bamboo pulp board is disintegrating, an alkaline substance, sodium hydroxide, is added. The concentration of the disintegrated pulp is 20wt%. The amount of sodium hydroxide is 2.5% relative to the absolute dry pulp mass, and the pulping time is 40min. In addition, a surfactant is added during the disintegration process; the amount of the surfactant is 4.5‰ relative to the absolute dry pulp mass. Among them, the surfactant is a compound of lauryl alcohol polyoxyethylene ether and sodium diisooctyl sulfosuccinate in a mass ratio of 1:3. The compounded surfactant can improve the surface activity of the system, change the interfacial properties of sodium hydroxide and fiber, significantly reduce the surface tension of the sodium hydroxide solution, improve the penetration, wetting, dispersion, solubilization and other effects of alkali on the fiber, so that the fiber is fully swollen, reduce the fiber from being cut, and facilitate the fiber to be dissociated into single fibers.

[0062] (2) Acid treatment: The pulp after disintegration is diluted and enters a double-roll mixer, where acid and cold air are added. It is then transported by a screw conveyor and then enters a bleaching tower for low-temperature acid treatment. After acid treatment, it is washed by a pulp washer.

[0063] The mass concentration of the acid-treated pulp is 3wt%, the temperature is 6°C, the time is 100min, the acid dosage is 1.5% relative to the absolute dry pulp mass, the pH value is 3.2, and the acid is hydrochloric acid.

[0064] (3) Extrusion removal: The acid-treated pulp with a concentration of 3wt% is pumped into the pulp tank of the twin-roll pulping machine at a pressure of 0.04MPa. Through the integrated treatment of dilution, displacement and squeezing, the impurity cells and other fine components in the pulp are effectively removed, the removal of the primary wall (P) and the primary wall outer layer (S1) is promoted, the fiber is further purified, and the uniformity of the polymerization degree distribution is improved. Under the action of the pulp inlet pressure and the liquid level pressure difference, the impurities are removed by extrusion. After the impurities are removed, the deoxidation delignification treatment is carried out at a concentration of 35wt% by screw conveyor.

[0065] (4) Oxygen delignification: Add sodium hydroxide solution and magnesium salt protective agent (magnesium sulfate) to the pulp obtained in step (3). Relative to the absolute dry material mass, the addition amount of sodium hydroxide is 3%, and the addition amount of magnesium sulfate is 2%. The obtained material directly enters the pulp pump riser through a double-roll mixer, and then enters a medium-consistency high-shear mixer, and is added with 2.5% oxygen and medium-pressure steam (relative to the absolute dry material mass), and then enters an upflow bleaching tower for oxygen bleaching, wherein the tower top pressure is 0.5MPa, the pulp concentration is 10wt%, the temperature is 100°C, and the time is 80min. After the oxygen delignification is completed, the washing waste liquid (temperature below 100°C) of this section (i.e., the oxygen delignification section) is pumped into the tower from the bottom of the bleaching tower to replace the high-concentration thermal bleaching waste liquid, and this bleaching waste liquid is used for washing the raw pulp after cooking, and the washing liquid can be sent to the alkali recovery system for treatment and combustion, thereby achieving no wastewater discharge. The pulp in the bleaching tower is mixed with the washing waste liquid of this section below 100℃ and cooled, which plays a high-temperature washing role at the same time to improve the cleanliness of the pulp. When the pulp temperature in the tower drops below 100℃, it is pumped to the spray pot by a pump.

[0066] (5)D0E OP D1 three-stage cleaning and bleaching.

[0067] D0E OP The three-stage cleaning and bleaching process conditions of D1 are the conventional process conditions used by those skilled in the art, and can achieve the technical effects of the present invention without any special requirements.

[0068] The first stage of chlorine dioxide (D0) bleaching: sulfuric acid is added to the pulp after oxygen delignification to adjust the pH value to 3, preheated by a double-roll mixer or directly enters the medium-consistency pulp pump riser, and then enters the medium-consistency high-shear mixer, where chlorine dioxide and steam are added, and then enters the upflow bleaching tower, the pulp concentration is 7wt%, the time is 90min, the temperature is 95℃, the chlorine dioxide dosage is 0.8% and the sulfuric acid dosage is 0.2% relative to the absolute dry pulp mass. After bleaching, the pulp is washed;

[0069] E OP Bleaching: Sodium hydroxide solution is added to the washed pulp, the pulp is preheated by a double-roll mixer or directly enters the medium-consistency pulp pump riser, and then enters the medium-consistency high shear mixer, and hydrogen peroxide, oxygen and steam are added to the medium-consistency high shear mixer, and then enters the up-down flow bleaching tower, the pulp concentration is 7wt%, the time is 120min, the temperature is 95°C, the oxygen pressure is 0.1MPa, and the amount of sodium hydroxide, oxygen and hydrogen peroxide is 0.8%, 0.2% and 0.5% relative to the mass of absolute dry pulp.

[0070] Second stage chlorine dioxide (D1) bleaching: E OPAfter washing, the bleached pulp is added with sulfuric acid to adjust the pH value to 3.5. The pulp is preheated by a double-roll mixer or directly enters the medium-consistency pulp pump riser, and then enters the medium-consistency high shear mixer, and chlorine dioxide and steam are added to the medium-consistency high shear mixer. Then it enters the up-down flow bleaching tower for chlorine dioxide bleaching, the pulp concentration is 16wt%, the time is 60min, the temperature is 70°C, and the amount of chlorine dioxide is 0.2% and the amount of sulfuric acid is 0.5% relative to the mass of the absolute dry pulp.

[0071] (6) Enzymatic pulping: The washed bleached pulp is treated in a pulping machine, and cellulase is added during the pulping process; sodium bisulfite is used to adjust the pH value of the enzymatic pulping process. During the enzymatic pulping process, a mordant, cationic polyacrylamide (CPAM), is added; in addition, cysteine ​​is also added during the enzymatic pulping process.

[0072] Relative to the absolute dry pulp mass, the dosage of endocellulase is 0.5 IU / g, the dosage of cationic polyacrylamide is 1.5‰, the dosage of cysteine ​​is 1.0‰, the dosage of sodium bisulfite is 1.5‰, the slurry concentration is 3wt%, the environmental pH value is 6.8, the temperature is 65°C, and the action time is 60min.

[0073] In the above steps, the water added to the slurry and the water used for washing are both distilled water or deionized water.

[0074] After testing, the performance indicators of the obtained bamboo dissolving pulp are: а-cellulose content 96.2%, cuprammonia polymerization degree 821, whiteness 88.5% ISO, ash content 0.05%, Fe ion 7mg / kg, Cu ion 1.1mg / kg, Mg ion 240mg / kg, Ca ion 48mg / kg, dichloromethane extract 0.28%, polypentose 4.1%, S183.4%, S10 4.9%, (S10-S18) 1.5%, Fock reaction performance 82%, and the yield of bleached bamboo dissolving pulp reaches 41.4% (for bamboo chip raw materials).

[0075] Comparative Example 1-1:

[0076] In the bamboo pulp board disintegration stage of the process, the anionic surfactant sodium dioctyl sulfosuccinate is eliminated and only the nonionic surfactant lauryl alcohol polyoxyethylene ether is used. The rest of the process and process are the same as in Example 1.

[0077] Comparative Example 1-2:

[0078] In the bamboo pulp board disintegration stage of the process, the nonionic surfactant lauryl alcohol polyoxyethylene ether is eliminated, and only the anionic surfactant sodium diisooctyl sulfosuccinate is used. The rest of the process and process are the same as in Example 1.

[0079] The performance indicators of Example 1 of the present application, i.e., the commercially available bamboo pulp board, which was only subjected to a crushing treatment, and the pulp after crushing (without subsequent acid treatment, extrusion and impurity removal, etc.) were compared with the results obtained in Comparative Examples 1-1 and 1-2, and the following comparative tests were conducted. After repeated experiments, the results are shown in Table 1.

[0080] Table 1 Comparison of the results obtained in Example 1, Comparative Example 1-1 and Comparative Example 1-2

[0081]

[0082] Note: Ash content is not important for bamboo raw materials.

[0083] As shown in Table 1, the compounding of nonionic surfactant and anionic surfactant (Example 1) has a synergistic effect, effectively improves the surface activity of the system, changes the interface properties of sodium hydroxide and fiber, significantly reduces the surface tension of sodium hydroxide solution, improves the penetration, wetting, dispersion and solubilization of alkali on fiber, makes fiber fully swelled, promotes the dissolution of some oligomers soluble in alkali (such as uronic acid, low molecular chain lignin, ash, extract, etc.), reduces the cutting of fiber, and improves the pulp purity, which is manifested in that the а-cellulose content is higher than that of Comparative Example 1-1 and Comparative Example 1-2, and the S10, S18, ash and Kappa value are reduced by 3.68%, 2.94%, 9.52% and 5.20% respectively compared with Comparative Example 1-1, and by 5.76%, 4.81%, 13.64% and 9.89% respectively compared with Comparative Example 1-2. Compared with Comparative Example 1-2, the former (Comparative Example 1-1) has an increased а-cellulose content, and S10, S18, ash content and Kappa value are reduced by 2.16%, 1.92%, 4.55% and 4.95% respectively compared with Comparative Example 1-2; the possible reasons are: the non-ionic surfactant is not affected by the hardness of the water used, and it is more prominent in changing the interfacial properties of sodium hydroxide and fiber, reducing the surface tension of sodium hydroxide solution, and improving the penetration, wetting, dispersion and solubilization of alkali on the fiber.

[0084] Comparative Example 2:

[0085] The low temperature process is eliminated in the acid treatment stage of the process. The remaining processes and procedures are the same as those in Example 1.

[0086] Comparative Example 3:

[0087] The extrusion and impurity removal section is eliminated in the process. The remaining processes and processes are the same as those in Example 1.

[0088] The performance indicators of the semi-slurry of Example 1 of the present application, i.e., commercially available bamboo pulp board after crushing, acid treatment, and extrusion to remove impurities, were compared with the results obtained in Comparative Examples 2 and 3. After repeated experiments, the results are shown in Table 2.

[0089] Table 2 Comparison of the results obtained in Example 1, Comparative Example 2 and Comparative Example 3

[0090]

[0091]

[0092] From Table 2, it can be seen that when the low temperature process is eliminated in the acid treatment stage (Comparative Example 2) compared with setting the low temperature (Example 1), the α-cellulose content in the semi-material pulp of the former (Comparative Example 2) is reduced by nearly 2 percentage points; the S10 content is increased by 5.21%; and the S18 content is increased by 3.80%. The possible reasons are: low temperature acid treatment can improve the selectivity of acid treatment to remove impurities such as ash, metal ions, pentose hemicellulose and fine fibers in the pulp, and effectively avoid the generation of more fine fibers and other oligomers in the pulp.

[0093] It can also be seen from Table 1 that when the extrusion impurity removal section (Comparative Example 3) is eliminated in the process, compared with the extrusion impurity removal section (Example 1) and Comparative Example 2, the purity of the semi-material pulp of the former (Comparative Example 3) decreases, which is manifested in that the α-cellulose content is nearly 3 percentage points lower than that of Example 1 and nearly 1 percentage point lower than that of Comparative Example 2; the S10 content is 28.13% higher than that of Example 1 and 21.78% higher than that of Comparative Example 2; the S18 content is 15.19% higher than that of Example 1 and 10.98% higher than that of Comparative Example 2. The possible reasons for this are: the extrusion impurity removal uses a double-roll pulping machine, which integrates dilution, displacement and squeezing, effectively removes impurity cells and other fine components in the pulp, and at the same time promotes the removal of the primary wall (P) and the primary wall outer layer (S1), further purifies the fiber, and improves the uniformity of the distribution of the degree of polymerization.

[0094] Comparative Example 4:

[0095] In the process, the pumping to the spray pot after the oxygen delignification stage is cancelled, and instead the pressure spraying to the spray pot is adopted, which is customary for those skilled in the art. The rest of the processes and procedures are the same as those in Example 1.

[0096] The following comparative test was conducted on the performance indicators of the natural color (before bleaching) pulp of Example 1 of the present application, i.e., commercially available bamboo pulp board after crushing, acid treatment, extrusion removal of impurities, and oxygen delignification, with the results obtained in Comparative Example 4. After repeated experiments, the results are shown in Table 3.

[0097] Table 3 Comparison of the results obtained in Example 1 and Comparative Example 4

[0098]

[0099] The yields in the table are for bamboo chips.

[0100] As shown in Table 3, the yield, purity and whiteness of the natural color pulp produced by the pumping after oxygen delignification (Comparative Example 4) are reduced compared with the pumping (Example 1), as shown in that the yield is reduced by 1.1%; the whiteness is reduced by nearly 2 percentage points; the α-cellulose content is reduced by 2.1 percentage points compared with Example 1, the S10 content is increased by 14.81% compared with Example 1, and the S18 content is increased by 5.88% compared with Example 1. The possible reasons are: the pressure spraying is used, and the shearing effect caused by the turbulence and the rapid evaporation of steam on the spraying line and the inlet of the spraying pot causes the fibers to be cut and damaged, increasing the content of fine components in the system, reducing the pulp yield and purity.

[0101] Comparative Example 5-1:

[0102] In the enzymatic pulping, only the addition of cationic polyacrylamide is eliminated, and the rest of the processes and procedures are the same as those in Example 1.

[0103] Comparative Example 5-2:

[0104] Only the addition of cysteine ​​was eliminated during enzymatic beating, and the rest of the processes and procedures were the same as those in Example 1.

[0105] The following comparative test was conducted on the performance indicators of bamboo dissolving pulp of Example 1 of the present invention, i.e. commercially available bamboo pulp board after crushing, acid treatment, extrusion removal of impurities, oxygen delignification, three-stage bleaching, and enzymatic beating, with the results obtained in Comparative Examples 5-1 and 5-2. After repeated experiments, the results are shown in Table 4.

[0106] Table 4 Comparison of the results obtained in Example 1, Comparative Example 5-1 and Comparative Example 5-2

[0107]

[0108]

[0109] As shown in Table 4, the purity of the bleached bamboo dissolving pulp produced by the cancellation of the addition of cationic polyacrylamide in the enzymatic pulping (Comparative Example 5-1) is reduced compared with the setting of adding this drug (Example 1), which is manifested in that the Fe ion content is increased by 71.43%, the copper ion content is increased by nearly 3 times, the α-cellulose content is reduced by nearly 5 percentage points, S10 and S18 are increased by 59.18% and 73.53% respectively, the Fock reaction performance is reduced by 9 percentage points, and the copper ammonia polymerization degree is increased by 979. The analysis reason may be: although cellulase is added in the enzymatic pulping stage, cellulase is an amphiphilic molecule, and its electrical properties change with the change of the pH value of the environment. The pH value of the enzymatic pulping treatment environment of the present application is in the range of 3.5-6.8, which is higher than the isoelectric point (PI) of the cellulase protein molecule. Therefore, the cellulase molecule is negatively charged as a whole, and the fiber is also negatively charged. The two are in a state of repulsion, and the cellulase does not play an effective catalytic role, and the mutual promotion effect with pulping is not good.

[0110] It can also be seen from Table 4 that the purity of the bleached bamboo dissolving pulp produced by the former (Comparative Example 5-2) is reduced compared with the setting of adding this drug (Example 1), which is manifested in that the Fe ion content is increased by 42.86%, the copper ion content is increased by 2.5 times, the α-cellulose content is reduced by nearly 4 percentage points, S10 and S18 are increased by 24.49% and 38.24% respectively, the Fock reaction performance is reduced by 6 percentage points, and the copper ammonia polymerization degree is increased by 885. And compared with Comparative Example 5-1, it is concluded that the purity and Fock reactivity of the bamboo dissolving pulp obtained by eliminating cationic polyacrylamide in the enzymatic pulping stage are lower than that of eliminating cysteine. The analysis reason may be: cationic polyacrylamide, as a mordant, connects the negatively charged fiber and cellulase, so that the two react, and cysteine ​​is a stabilizer for cellulase, which stabilizes the action environment of cellulase, further activates the activity of cellulase, and at the same time reduces the copper, iron and other ion content of the dissolving pulp, purifies the pulp.

[0111] Embodiment 2:

[0112] A method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp comprises the following steps:

[0113] (1) Disintegration of bamboo pulp board: The commercially available natural color KP bamboo pulp board is directly put into a high-concentration hydraulic pulper with a spiral drill head rotor to disintegrate the pulp. While the bamboo pulp board is being disintegrated, an alkaline substance, sodium hydroxide, is added. The disintegration concentration is 10wt%, the amount of sodium hydroxide is 0.2% relative to the absolute dry pulp mass, and the time is 60min. In addition, a surfactant is also added in the disintegration step, and the amount of surfactant is 0.1‰ relative to the absolute dry pulp mass. The surfactant is a compound of glyceryl monostearate and sodium N-oleoyl N-methyl taurate in a ratio of 1:2.

[0114] (2) Acid treatment: The pulp after disintegration is diluted and enters a double-roll mixer, where acid and cold air are added. It is then transported by a screw conveyor and then enters a bleaching tower for low-temperature acid treatment. After acid treatment, it is washed by a pulp washer.

[0115] The mass concentration of the acid-treated pulp is 2wt%, the temperature is 10°C, the time is 20min, the acid dosage is 3.0% relative to the absolute dry pulp mass, the pH value is 1.5, and the acid is acetic acid.

[0116] (3) Extrusion removal: The acid-treated pulp with a concentration of 2wt% is pumped into the pulp tank of the twin-roll pulping machine at a pressure of 0.06MPa. Through the integrated treatment of dilution, displacement and squeezing, the impurity cells and other fine components in the pulp are effectively removed, the removal of the primary wall (P) and the primary wall outer layer (S1) is promoted, the fiber is further purified, and the uniformity of the polymerization degree distribution is improved. Under the action of the pulp inlet pressure and the liquid level pressure difference, the impurities are removed by extrusion. After the impurities are removed, the deoxidation delignification treatment is carried out at a concentration of 30wt% by screw conveying.

[0117] (4) Oxygen delignification: Add sodium hydroxide solution and magnesium salt protective agent (magnesium carbonate) to the pulp obtained in step (3). Relative to the absolute dry material mass, the addition amount of sodium hydroxide is 1%; the addition amount of magnesium carbonate is 0.1%. The obtained material directly enters the pulp pump riser through a double-roll mixer, then enters a medium-consistency high-shear mixer and adds 1.5% oxygen and medium-pressure steam (relative to the absolute dry material mass), and then enters an upflow bleaching tower for oxygen bleaching. The tower top pressure is 0.3MPa, the pulp concentration is 18wt%, the temperature is 90°C, and the time is 90min. After the oxygen delignification is completed, the washing waste liquid (temperature below 100°C) of this section (i.e., the oxygen delignification section) is pumped into the tower from the bottom of the bleaching tower to replace the high-concentration thermal bleaching waste liquid, and this bleaching waste liquid is used for washing the raw pulp after cooking, and the washing liquid can be sent to the alkali recovery system for treatment and combustion, thereby achieving no wastewater discharge. The pulp in the bleaching tower is mixed with the washing waste liquid of this section below 100℃ and cooled, which plays a high-temperature washing role at the same time to improve the cleanliness of the pulp. When the pulp temperature in the tower drops below 100℃, it is pumped to the spray pot by a pump.

[0118] (5)D0E OP D1 three-stage cleaning and bleaching

[0119] D0E OP The D1 three-stage cleaning and bleaching process conditions are conventional techniques for those skilled in the art.

[0120] D0E OP Technical process conditions of D1 three-stage cleaning and bleaching:

[0121] Technical conditions for D0 bleaching: pulp concentration 16wt%, time 30min, temperature 95°C, relative to the mass of absolute dry pulp, chlorine dioxide dosage 1.2%, sulfuric acid dosage 0.5%. After bleaching, the pulp is washed.

[0122] E OP Bleaching: After washing, the pulp is added with sodium hydroxide solution. OP Bleaching, the pulp is preheated by a double-roll mixer or directly enters the medium-consistency pulp pump riser, then enters the medium-consistency high-shear mixer, and hydrogen peroxide, oxygen and steam are added to the medium-consistency high-shear mixer, and then enters the ascending and descending flow bleaching tower, the pulp concentration is 16wt%, the time is 60min, the temperature is 70℃, the oxygen pressure is 0.3MPa, and the sodium hydroxide dosage is 0.5%, the oxygen dosage is 1.0%, and the hydrogen peroxide dosage is 1.0% relative to the absolute dry pulp mass. E OP The bleached pulp was washed and then sulfuric acid was added to adjust the pH value to 3.5, and D1 bleaching was performed.

[0123] D1 bleaching: The pulp is preheated by a double-roll mixer or directly enters the medium-consistency pulp pump riser, and then enters the medium-consistency high-shear mixer, and chlorine dioxide and steam are added to the medium-consistency high-shear mixer, and then enters the up-down flow bleaching tower for chlorine dioxide bleaching, the pulp concentration is 8wt%, the time is 100min, the temperature is 80°C, the amount of chlorine dioxide is 0.4% and the amount of sulfuric acid is 0.2% relative to the mass of absolute dry pulp.

[0124] (6) Enzymatic pulping: The washed bleached pulp is treated in a pulping machine, and cellulase is added during pulping. Sodium bisulfite is used to adjust the pH value of the enzymatic pulping. During the enzymatic pulping, a mordant, cationic polyacrylamide (CPAM), is added. In addition, cysteine ​​is also added during the enzymatic pulping process.

[0125] Relative to the absolute dry pulp mass, the dosage of exocellulase is 0.02IU / g, the dosage of cationic polyacrylamide is 0.2‰, the dosage of cysteine ​​is 0.1‰, the dosage of sodium bisulfite is 2.5‰, the pulp concentration is 7wt%, the environmental pH value is 3.5, the temperature is 25℃, and the action time is 180min.

[0126] In the above steps, the water added to the slurry and the water used for washing are both distilled water or deionized water.

[0127] After measurement, the performance indicators of the obtained bamboo dissolving pulp are: а-cellulose content 94.8%, cuprammonia polymerization degree 673, whiteness 86.1% ISO, ash content 0.08%, Fe ion 9 mg / kg, Cu ion 1.6 mg / kg, Mg ion 259 mg / kg, Ca ion 51 mg / kg, dichloromethane extract 0.33%, polypentose 4.6%, S18 4.5%, S10 5.6%, (S10-S18) 1.1%, Fock reaction performance 88%, and the yield of bleached bamboo dissolving pulp reaches 35.7% (for bamboo chip raw materials).

[0128] Embodiment 3:

[0129] A method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp comprises the following steps:

[0130] (1) Bamboo pulp board disintegration: The commercially available natural color KP bamboo pulp board is directly put into a high-concentration hydraulic pulper with a spiral drill-type rotor to disintegrate the pulp. While the bamboo pulp board is being disintegrated, an alkaline substance, sodium hydroxide, is added. The disintegration concentration is 26wt%, and the amount of sodium hydroxide is 3.5% relative to the absolute dry pulp mass, and the time is 20min. In addition, a surfactant is also added during the disintegration, and the amount of surfactant is 6.5‰ relative to the absolute dry pulp mass. It is a compound of fatty acid methyl ester polyoxyethylene ether and fatty alcohol sodium sulfate in a ratio of 1:4.

[0131] (2) Acid treatment: The pulp after disintegration is diluted and enters a double-roll mixer, where acid and cold air are added. It is then transported by a screw conveyor and then enters a bleaching tower for low-temperature acid treatment. After acid treatment, it is washed by a pulp washer.

[0132] The mass concentration of the acid-treated pulp is 7wt%, the temperature is 1°C, the time is 180min, the acid dosage is 0.1% relative to the absolute dry pulp mass, the pH value is 4.5, and the acid is sulfuric acid.

[0133] (3) Extrusion removal: The acid-treated pulp with a concentration of 5wt% is pumped into the pulp tank of the twin-roll pulping machine at a pressure of 0.02MPa. Through the integrated treatment of dilution, displacement and squeezing, the impurity cells and other fine components in the pulp are effectively removed, the removal of the primary wall (P) and the primary wall outer layer (S1) is promoted, the fiber is further purified, and the uniformity of the polymerization degree distribution is improved. Under the action of the pulp inlet pressure and the liquid level pressure difference, the impurities are removed by extrusion. After the impurities are removed, the deoxidation delignification treatment is carried out at a concentration of 40wt% by screw conveying.

[0134] (4) Oxygen delignification: Add sodium hydroxide solution and magnesium salt protective agent (magnesium oxide) to the pulp obtained in step (3). Relative to the absolute dry material mass, the addition amount of sodium hydroxide is 5%; the addition amount of magnesium oxide is 3.5%. The obtained material directly enters the pulp pump riser through a double-roll mixer, then enters a medium-consistency high-shear mixer and adds 3.5% oxygen and medium-pressure steam, and then enters an upflow bleaching tower for oxygen bleaching, with a tower top pressure of 0.9 MPa, a pulp concentration of 7wt%, a temperature of 120°C, and a time of 60 minutes. After the oxygen delignification is completed, the washing waste liquid (temperature below 100°C) of this section (i.e., the oxygen delignification section) is pumped into the tower from the bottom of the bleaching tower to replace the high-concentration thermal bleaching waste liquid, and this bleaching waste liquid is used for washing the crude pulp after cooking, and the washing liquid can be sent to the alkali recovery system for treatment and combustion, thereby achieving no wastewater discharge. The pulp in the bleaching tower is mixed with the washing waste liquid of this section below 100℃ and cooled, which plays a high-temperature washing role at the same time to improve the cleanliness of the pulp. When the pulp temperature in the tower drops below 100℃, it is pumped to the spray pot by a pump.

[0135] (5)D0E OP D1 three-stage cleaning and bleaching.

[0136] D0E OP D1 three-stage cleaning and bleaching is a conventional technology in this field.

[0137] D0E OP The process conditions of D1 three-stage cleaning and bleaching are:

[0138] Technical conditions for D0 bleaching: pulp concentration 12wt%, time 180min, temperature 70°C, relative to the mass of absolute dry pulp, chlorine dioxide dosage 2.0%, sulfuric acid dosage 0.2%.

[0139] E OP Bleaching technical conditions: pulp concentration 10wt%, time 180min, temperature 85°C, oxygen pressure 0.2MPa, relative to the mass of absolute dry pulp, sodium hydroxide dosage 1.5%, oxygen dosage 1.0%, hydrogen peroxide dosage 0.1%.

[0140] D1 bleaching technical conditions: pulp concentration 10wt%, time 240min, temperature 70℃, relative to the absolute dry pulp mass, chlorine dioxide dosage 0.6%, sodium hydroxide dosage 0.5%.

[0141] (6) Enzymatic pulping: The washed bleached pulp is treated in a pulping machine, and cellulase is added during the pulping process; sodium bisulfite is used to adjust the pH value of the enzymatic pulping process. During the enzymatic pulping process, a mordant, cationic polyacrylamide (CPAM), is added; in addition, cysteine ​​is also added during the enzymatic pulping process.

[0142] Relative to the absolute dry pulp mass, the dosage of exocellulase is 0.15 IU / g, the dosage of cationic polyacrylamide is 1.0‰, the dosage of cysteine ​​is 0.5‰, the dosage of sodium bisulfite is 0.1‰, the pulp concentration is 5wt%, the environmental pH value is 5.5, the temperature is 85℃, and the action time is 20min.

[0143] In the above steps, the water added to the slurry and the water used for washing are both distilled water or deionized water.

[0144] After measurement, the performance indicators of the obtained bamboo dissolving pulp are: а-cellulose content 95.3%, cuprammonia polymerization degree 725, whiteness 85.4% ISO, ash content 0.07%, Fe ion 8 mg / kg, Cu ion 1.4 mg / kg, Mg ion 247 mg / kg, Ca ion 49 mg / kg, dichloromethane extract 0.30%, polypentose 4.4%, S18 3.8%, S10 5.1%, (S10-S18) 1.3%, Fock reaction performance 84%, bleached bamboo dissolving pulp yield 38.6% (for bamboo chip raw materials).

[0145] The above-mentioned examples are only preferred implementations of this patent, but the protection scope of this patent is not limited thereto. It should be pointed out that, for ordinary technicians in this technical field, without departing from the principle of this patent, according to the technical solution and patent concept of this patent, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of this patent.

Claims

1. A method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp, characterized in that The following steps are involved: (1) Crushing bamboo pulp board: crushing the commercially available natural KP bamboo pulp board into pulp; (2) Acid treatment: the pulp after the crushing in step (1) is diluted and then enters a double-roll mixer, and acid and cold air are added, and then enters a bleaching tower for low-temperature acid treatment, and then washed in a pulp washer after the acid treatment; the treatment temperature of the acid treatment is 1-10°C; (3) Extrusion and impurity removal: the slurry obtained in step (2) is fed into a double-roll press and treated by an integrated process of dilution, displacement and squeezing; (4) Oxygen delignification: adding sodium hydroxide solution and magnesium salt protective agent to the pulp obtained in step (3), preheating through a double-roll mixer or directly entering the pulp pump riser, then entering a medium-consistency high-shear mixer and adding oxygen and medium-pressure steam, and then entering an upflow bleaching tower for oxygen bleaching; (5)D0E OP D1 three-stage cleaning and bleaching: (6) Enzymatic beating: OP D1 After three-stage cleaning and bleaching, the pulp is beaten, and cellulase is added during beating; after enzymatic beating, it is washed in a pulp washer to obtain viscose-grade bamboo dissolving pulp; In the step (1), alkaline substances sodium hydroxide and surfactants are also added during the crushing process. Relative to the mass of the absolute dry pulp, the amount of alkali is 0.2-3.5%, and the amount of surfactant is 0.1-6.5‰; the crushing temperature is room temperature, and the time is 20-60min; the crushing pulp concentration is 10-26wt%; the surfactant is a non-ionic surfactant and an anionic surfactant compounded in a ratio of 1:2-4; the non-ionic surfactant is selected from any one or a mixture of lauryl alcohol polyoxyethylene ether, fatty acid methyl ester polyoxyethylene ether, Tween 80 or monostearate glycerol; the anionic surfactant is selected from any one or a mixture of diethylhexyl succinate sodium, sodium oleoylethanesulfonate, sodium N-oleoyl N-methyl taurate or sodium fatty alcohol sulfate.

2. The method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp according to claim 1, characterized in that: The mass concentration of the pulp after acid treatment in step (2) is 2-7%; the treatment time is 20-180 min; the acid dosage is 0.1-3.0% relative to the absolute dry pulp mass, and the pH value is 1.5-4.5; the acid is any one of hydrochloric acid, sulfuric acid, sulfurous acid or a mixture of low molecular weight organic acids.

3. The method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp according to claim 1, characterized in that: In the step (4), an upflow bleaching tower is used for oxygen bleaching, and the tower top pressure is 0.3-0.9 MPa, the pulp concentration is 7-18wt%, the temperature is 90-120°C, and the time is 60-90min; the amount of sodium hydroxide used is 1-5% relative to the mass of the absolute dry material, and the amount of oxygen used is 1.5-3.5%; after the oxygen delignification is completed, the bleaching tower is pumped into the blowdown pot.

4. The method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp according to claim 1, characterized in that: The magnesium salt protective agent described in step (4) is magnesium carbonate, magnesium sulfate or magnesium oxide, and the amount of the magnesium salt protective agent is 0.1-3.5%.

5. The method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp according to claim 1, characterized in that: Step (5) DOE OP The specific steps of D1 three-stage cleaning and bleaching are as follows: A. Chlorine dioxide primary bleaching: sodium hydroxide or sulfuric acid is added to the pulp obtained in step (4) to adjust the pH value, the pulp is preheated in a double-roll mixer or directly enters the medium-consistency pulp pump riser, and then enters the medium-consistency high-shear mixer, and chlorine dioxide and steam are added to the medium-consistency high-shear mixer, and then enters the upflow or up-downflow bleaching tower for chlorine dioxide bleaching; the chlorine dioxide bleaching process is as follows: the pulp concentration is 7-16wt%, the time is 30-180min, the temperature is 50-95°C, the amount of chlorine dioxide is 0.8-2.0% relative to the mass of the absolute dry pulp, the amount of sodium hydroxide or sulfuric acid is 0-0.5%, and the pH value at the bleaching end point is 2-4; B. EOP bleaching: the pulp obtained in step A is washed and then added with sodium hydroxide solution, preheated by a double-roll mixer or directly enters the medium-consistency pulp pump riser, then enters the medium-consistency high-shear mixer, and hydrogen peroxide, oxygen and medium-pressure steam are added, and then enters the ascending-descending flow bleaching tower for EOP bleaching; the EOP bleaching process is as follows: pulp concentration is 7-16wt%, time is 60-180min, temperature is 50-95°C, oxygen pressure is 0.1-0.3MPa, relative to the mass of absolute dry pulp, sodium hydroxide dosage is 0.5-1.5%, oxygen dosage is 0.2-1%, and hydrogen peroxide dosage is 0.1-1.0%; C. Secondary bleaching with chlorine dioxide: After washing, the pulp obtained in step B is added with sodium hydroxide or sulfuric acid to adjust the pH value, preheated in a double-roll mixer or directly enters the medium-consistency pulp pump riser, and then enters a medium-consistency high-shear mixer, and chlorine dioxide and steam are added, and then enters an ascending-downflow bleaching tower for chlorine dioxide bleaching; the chlorine dioxide bleaching process is as follows: the pulp concentration is 7-16wt%, the time is 60-240min, the temperature is 70-80°C, the amount of chlorine dioxide is 0.2-0.6% relative to the mass of the absolute dry pulp, the amount of sodium hydroxide or sulfuric acid is 0-0.5%, and the pH value at the bleaching end point is 3.5-7.

6. The method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp according to claim 1, characterized in that: The cellulase described in step (6) is used in an amount of 0.02-0.5 IU / g based on the absolute dry pulp, the pulp concentration is 3-7wt%, the environmental pH value is 3.5-6.8, the temperature is 25-85°C, and the action time is 20-180min.

7. The method for preparing viscose-grade bamboo dissolving pulp by modifying bamboo chemical pulp as claimed in claim 1, characterized in that: In step (6), sodium bisulfite is used to adjust the pH value of enzymatic pulping, and its dosage is 0.1-2.5‰; cationic polyacrylamide and cysteine ​​are also added during the enzymatic pulping process; relative to the mass of the absolute dry pulp, the amount of cationic polyacrylamide added is 0.2-1.5‰; the amount of cysteine ​​added is 0.1-1.0‰.

8. The viscose grade bamboo dissolving pulp obtained by the method according to any one of claims 1 to 7, characterized in that: The viscose-grade bamboo dissolving pulp has an а-cellulose content of more than 94%, a cuprammonia polymerization degree of 550-850, a whiteness of more than 82% ISO, an ash content of less than 0.1%, Fe ions of less than 10 mg / kg, Cu ions of less than 2 mg / kg, Mg ions of less than 300 mg / kg, Ca ions of less than 60 mg / kg, a dichloromethane extract of less than 0.4%, polypentose of less than 5%, S18 of less than 5%, S10 of less than 6%, S10-S18 of less than 2%, and a Fock reaction performance of 79-88%.

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