Method for preparing spinning-grade dissolving pulp and polysaccharide compound from straw

Abstract

The invention relates to the technical field of agricultural waste resource utilization, in particular to a process for preparing spinning-grade dissolving pulp and a polysaccharide complex from straw, which comprises the following steps: dipping crushed agricultural waste straw in hot water or a dilute acid solution, drying, secondarily crushing, and activating in an alkaline aqueous solution; the method comprises the following steps: carrying out freezing screw extrusion, carrying out high-pressure filtration treatment, and carrying out multi-stage bleaching, first-stage iron removal treatment and second-stage iron removal treatment on the obtained solid matter to obtain the pulp. The obtained filtrate is sequentially subjected to acid neutralization, flocculent precipitation and washing treatment, and the polysaccharide compound containing hemicellulose-lignin is obtained. The method has the beneficial effects that the agricultural waste resource dissolving pulp which is high in alpha-cellulose content, adjustable in polymerization degree and high in quality is prepared with lower production cost and higher universality, and meanwhile, a polysaccharide compound containing hemicellulose-lignin is extracted from the black liquor; and a practical and sustainable solution is provided for comprehensive utilization of agricultural wastes.

Description

Technical Field

[0001] The present invention relates to the technical field of utilization of agricultural waste resources, and particularly to a process for preparing spinning-grade dissolving pulp and polysaccharide complex from straw. Background Art

[0002] As a biomass resource with great potential, straw is widely distributed and has a rich yield in China. According to statistics, the annual straw yield in China has exceeded 200 million tons, making it one of the important renewable resources. At present, the utilization of straw mainly focuses on aspects such as fuelization, feedization, substrateization, silage, and straw returning to the field. However, these utilization methods generally have problems such as low industrial economic value, environmental pollution, and low resource utilization rate, and fail to fully exert the resource potential of straw. In addition, compared with traditional cellulose raw materials such as wood and cotton linter, straw has a higher content of miscellaneous cells and a lower fiber content, resulting in poor quality of the pulp obtained from pulping, which limits its application in high-value-added fields such as textiles and papermaking. From the perspective of chemical composition, the contents of cellulose, hemicellulose, and lignin in straw are 35 - 50%, 20 - 35%, and 10 - 25% respectively. Although its cellulose content is lower than that of wood, straw has advantages such as a short growth cycle and a large total amount, providing a basic condition for large-scale development and utilization.

[0003] To solve the technical problems of efficient utilization of straw resources, the inventor previously proposed a method for separating each component of straw by a low-temperature phase transformation method (Patent No.: CN110670397B). This method can conveniently and efficiently prepare straw cellulose microfibers, providing a new way for the high-value utilization of straw. However, in the actual pilot production process, it was found that the viscosity of the critical phase mixture obtained by this method is relatively large, and it is difficult for traditional mechanical stirring devices to effectively handle, which restricts its industrial application. In addition, although the cellulose content in the straw microfibers prepared by this method is as high as 81.8%, due to no further treatment, it cannot be directly used as dissolving pulp for spinning. At the same time, the black liquor generated during the separation of straw cellulose has not been effectively utilized, not only causing waste of resources, but also possibly causing secondary pollution to the environment.

[0004] Therefore, developing an efficient, clean, and low-energy-consuming straw pulping technology and realizing the high-value treatment of black liquor is of great significance for promoting the efficient utilization of straw resources, reducing environmental pollution, and promoting the sustainable development of the textile industry. Summary of the Invention

[0005] To overcome the defects of the existing technologies and achieve the high-value utilization of straw resources, the present invention discloses a process for preparing a spinning-grade dissolving pulp and a polysaccharide complex from straw. First, agricultural waste is activated, and then treated with the high shear force of a refrigerated screw under low-temperature conditions, changing the traditional high-temperature and high-pressure cooking and beating processes of pulp making. A dissolving pulp of agricultural waste resources with a high α-cellulose content and adjustable polymerization degree is prepared at a relatively low production cost and with high versatility.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A process for preparing a spinning-grade dissolving pulp and a polysaccharide complex from straw, specifically including the following steps:

[0008] Step 1: The dried or baked agricultural waste straw is crushed once, and then dedusted and sieved to obtain the first-crushed raw material. The agricultural waste straw is selected from rice straw, wheat straw, corn straw, soybean straw, etc., and dedusted using equipment such as a louver deduster.

[0009] Step 2: The first-crushed raw material obtained in Step 1 is placed in a reactor for impregnation treatment and washed with deionized water to obtain the impregnation treatment product.

[0010] Step 3: The obtained impregnation treatment product is dried and crushed twice to obtain the second-crushed product.

[0011] Step 4: The second-crushed product is placed in an alkaline aqueous solution, heated and stirred to obtain the activated product.

[0012] Step 5: The activated product is placed in a low-temperature reactor, stirred to present a viscous ice-water mixed phase, and then uniformly added to a refrigerated screw extruder through a metering pump to obtain the refrigerated screw extrusion product.

[0013] Step 6: The refrigerated screw extrusion product is subjected to high-pressure filtration treatment. The solid obtained after filtration is straw cellulose microfibrils, which are then subjected to multi-stage bleaching to obtain the bleached product, and the pH is adjusted; while the filtrate obtained after filtration is a mixture containing hemicellulose, lignin and alkali, which is neutralized to weakly alkaline with acid, and then a polymer flocculant is added for flocculation precipitation treatment, and the precipitate can be obtained after separation.

[0014] Step 7: The bleached product obtained in Step 6 is subjected to first-stage iron removal treatment and second-stage iron removal treatment in sequence to obtain a spinning-grade dissolving pulp, and the pulp sheet can be obtained after sheet forming.

[0015] Step 8: The precipitate obtained in Step 6 is washed successively with an acidic aqueous solution and an alcohol solution to obtain a polysaccharide complex containing hemicellulose-lignin.

[0016] Further, in step 2, hot water impregnation or dilute acid solution impregnation is selected for the impregnation treatment, the temperature is controlled at 20-100 °C, the impregnation time is 1-24 h. The impregnation treatment can remove most of the dust and water-soluble impurities, which can improve the efficiency of subsequent treatment. After the reaction, the raw materials are washed with deionized water.

[0017] Further, when dilute acid solution is used for impregnation, the acid selected is at least one of oxalic acid, citric acid, lactic acid, malic acid, maleic acid, itaconic acid, formic acid, acetic acid, oxalic acid, propionic acid, and the mass concentration of the acid is 0.1%-2.5%. Acid pre-hydrolysis can degrade the hemicellulose in the fiber, making the fiber structure more porous and improving the accessibility of chemical reagents in the subsequent alkali treatment and bleaching processes.

[0018] Further, in step 3, the drying temperature is controlled at 60-80 °C, and it is dried until the moisture content is less than 10%; the particle size of the secondary pulverized product is less than 32 mesh, and straws with different particle sizes can be treated simultaneously without particle size classification.

[0019] Further, in step 4, the solid-liquid ratio of the secondary pulverized product to the alkali solution is controlled at 1:15-1:30; the alkali solution selected is at least one of KOH, NaOH, LiOH, Na2CO3, NaHCO3, NH4OH, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and the mass fraction of the alkali solution is 1.5%-9.0%;

[0020] The heating temperature is controlled at 50-90 °C, and the stirring time is 0.5-2 h.

[0021] Further, in step 5, the temperature of the low-temperature reactor is controlled at -3 to -11 °C;

[0022] The freeze-screw extruder selects one of a twin-screw, a triple-screw, and a quadruple-screw extruder. The screw extruder has a horizontal shaft screw and a vertical shaft screw. The screw is a meshing co-rotating screw, a meshing non-phase parallel screw, and a conical screw. The screw diameter is one of 15 mm, 25 mm, 30 mm, 34 mm, 53 mm;

[0023] The length-diameter ratio of the screw of the screw extruder is 21-70, and the screw speed is 20-350 r / min;

[0024] The freeze-screw extruder uses a circulating cooling pump to cool the cavity, and controls the temperature of the freeze-screw cavity to be the same as or slightly lower than the temperature of the ice-water mixture by 2-3 °C.

[0025] Further, in step 6, during the bleaching treatment of the solid matter, the oxidant selects one or more of hypochlorite, chlorite, hydrogen peroxide, peracetic acid, sodium perborate, sodium percarbonate, sodium dithionite, the oxidant concentration is 0.2-5.0%, and the temperature is 50-80 °C.

[0026] Further, in step 6, during the neutralization of the filtrate, the acid selected is at least one of hydrochloric acid, phosphoric acid, sulfuric acid, and acetic acid, and the flocculant selected is a cationic flocculant, which is at least one of polyacrylamide, poly(dimethyldiethylammonium methyl sulfate), and poly(methacryloyloxyethyltrimethylammonium chloride). After neutralization, stir and let stand for 30 min.

[0027] Further, in step 7, a dilute acid is used for the first-stage iron removal treatment, and then washed with distilled water. The dilute acid selected is dilute hydrochloric acid or dilute sulfuric acid, the pH of the solution is adjusted to 2 - 5, the solid-liquid ratio is 1:15 - 1:30, the treatment temperature is 40 - 80 °C, and the treatment time is 15 - 60 minutes. The first-stage iron removal treatment can dissolve the metal ions in it in the form of soluble salts and remove them in the subsequent washing. At the same time, the acid treatment can also reduce the ash content.

[0028] Further, in step 7, a chelating agent is used for the second-stage iron removal treatment, and then the complex impurities are washed away with distilled water. The chelating agent selected is one of ethylenediaminetetraacetic acid, diethylenetriamine, sodium hexametaphosphate, and sodium tripolyphosphate. The treatment temperature is 40 - 80 °C, and the treatment time is 15 - 60 min.

[0029] The beneficial effects of the present invention are as follows:

[0030] 1) The efficient separation and utilization of cellulose, hemicellulose, and lignin in agricultural waste resources are realized, and the comprehensive utilization rate of agricultural waste resources is improved.

[0031] 2) A new method for preparing dissolving pulp from agricultural waste resources is innovatively proposed. First, the agricultural waste is activated, and then treated with the high shear force of a screw under low-temperature conditions, changing the traditional high-temperature and high-pressure cooking and beating processes of pulp making. A dissolving pulp of agricultural waste resources with a high α-cellulose content and adjustable polymerization degree is prepared with low production costs and high versatility.

[0032] 3) The difficulty of waste liquid treatment is low, and a polysaccharide complex is obtained through the acid neutralization and flocculation treatment of black liquor for recovery.

[0033] The present invention can efficiently process different types of agricultural waste resources, without the need for strict particle size grading, simplifies the production process, and has good production practicability and industrial application prospects. Description of the Drawings

[0034] Figure 1 It is the infrared spectrum of the polysaccharide complex prepared in the embodiment of the present invention;

[0035] Figure 2 It is the X-ray diffraction pattern of the polysaccharide complex prepared in the embodiment of the present invention;

[0036] Figure 3 Schematic diagram of a flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0037] 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. 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.

[0038] The present invention solves the technical bottleneck in the prior art by improving the straw pulping technology and the black liquor treatment method, and promotes the green and efficient utilization of straw resources.

[0039] Example 1

[0040] A process for preparing spinning-grade dissolving pulp and polysaccharide complexes using straw, such as Figure 3 As shown, the specific process is:

[0041] The dried rice straw raw material is initially crushed, dusted by a cyclone dust collector, and passed through a vibrating screen.

[0042] The obtained raw material was placed in a reactor and impregnated with an acid solution. The conditions for the acid impregnation treatment were a solid-liquid ratio of 1:25, a propionic acid dosage of 0.5 wt.%, a temperature of 25° C., and a time of 18 hours.

[0043] After the impregnation, the raw materials are washed, dried at 60°C, and crushed for the second time to control the particle size after crushing to be less than 90 mesh.

[0044] The crushed rice straw raw material and a solution containing 2.5 wt.% sodium carbonate and 2 wt.% sodium bicarbonate at a solid-liquid ratio of 1:25 were heated to 60°C and reacted for 2 hours to obtain an activated product.

[0045] The activated product is placed in a low-temperature reactor and stirred at a constant temperature until the mixture presents a viscous ice-water mixed phase.

[0046] The obtained mixture is fed into a pre-cooled twin-screw extruder through a conveying system via a metering pump. The twin-screw diameter is 25 mm, the rotation speed is 280 r / min, and the screw cavity temperature is -5°C.

[0047] The mixture obtained after the treatment by the refrigerated screw extruder is filtered by a high-pressure filter to separate the rice straw cellulose microfibers and the filtrate containing hemicellulose, lignin and alkali, and the filtrate is collected for later use.

[0048] The filter cake was washed and mixed with a solution of 4wt.% hydrogen peroxide and 1wt.% sodium silicate at a solid-liquid ratio of 1:25, the pH was adjusted to 9.6 with sodium hydroxide, heated to 60°C, and bleached for 120 minutes.

[0049] The bleached product was filtered and washed and then subjected to two-stage iron removal treatment. The conditions for the dilute acid treatment were: adjusting the solution pH to 3.5 with dilute sulfuric acid, solid-liquid ratio of 1:25, temperature of 40°C, and reaction time of 60 minutes.

[0050] After filtering out the acid solution, chelating agent treatment was performed, and the reaction conditions were: adding 0.5wt.% disodium ethylenediaminetetraacetate, solid-liquid ratio 1:25, adjusting pH=4, and reacting at 40°C for 40 minutes.

[0051] The complex and other impurities were fully washed with distilled water. After washing, the pulp was neutral. After pulping, the rice straw dissolving pulp product was obtained. The performance parameters of the obtained dissolving pulp are shown in Table 1. The α-cellulose content can reach 92.6% and the degree of polymerization is 651.

[0052] The obtained filtrate was neutralized with sulfuric acid to a weak alkaline state, polyacrylamide flocculant was added, stirred and allowed to stand for 30 minutes, and a precipitate was separated and washed with an acetic acid aqueous solution and an ethanol solution in sequence to obtain a polysaccharide complex containing hemicellulose-lignin.

[0053] The composition of Example 1 analyzed by high performance liquid chromatography is shown in Table 2, which shows that arabinose is 6.36%, xylose is 34.05%, and a small amount of glucose is 2.13%. The relative molecular mass analyzed by GPC is shown in Table 3, which is 66211.

[0054] Example 2

[0055] A process for preparing spinning-grade dissolving pulp and polysaccharide complex using straw, the specific process is as follows:

[0056] The dried wheat straw raw material is initially crushed, dusted by a cyclone dust collector, and passed through a vibrating screen.

[0057] The obtained raw material was placed in a reactor and immersed in hot water. The conditions for the hot water immersion treatment were a solid-liquid ratio of 1:30, a temperature of 60° C., and a time of 24 hours.

[0058] After the impregnation, the raw materials are washed, dried at 80°C, and crushed for the second time, and the particle size after crushing is controlled to be less than 32 meshes.

[0059] The crushed wheat straw raw material and a KOH solution with a mass fraction of 7 wt.% were heated to 80°C at a solid-liquid ratio of 1:25 and reacted for 1 hour to obtain an activated product.

[0060] The activated product is placed in a low-temperature reactor and stirred at a constant temperature until the mixture presents a viscous ice-water mixed phase.

[0061] The obtained mixture is fed into a pre-cooled twin-screw extruder through a conveying system by a metering pump. The twin-screw has a diameter of 34 mm, a rotation speed of 180 r / min, and the temperature of the screw cavity is -8°C.

[0062] The mixture obtained after being processed by the freezing twin-screw extruder is filtered by a high-pressure filtering device to separate wheat straw cellulose microfibers and a filtrate containing hemicellulose, lignin, and alkali. The filtrate is collected for later use.

[0063] The filter cake is washed and then mixed with a solution of sodium hypochlorite with a mass fraction of 1 wt.% at a solid-liquid ratio of 1:30. Sodium hydroxide is used to adjust the pH to 9.8, and it is heated to 70°C for bleaching treatment for 60 min. After filtering off the bleaching solution, the above steps are repeated for a second bleaching.

[0064] The bleached product is washed and subjected to two-stage iron removal treatment. The conditions for the dilute acid treatment are: adjusting the pH of the solution to 4 with dilute hydrochloric acid, a solid-liquid ratio of 1:20, a temperature of 60°C, and a reaction time of 20 min.

[0065] After filtering off the acid solution, chelating agent treatment is carried out. The reaction conditions are: adding 0.7 wt.% ethylenediaminetetraacetic acid, a solid-liquid ratio of 1:20, adjusting the pH to 4, and reacting at 60°C for 40 min.

[0066] It is washed thoroughly with distilled water to remove impurities such as complexes. After the washing is completed, the slurry is neutral. After making a pulp board, a rice straw dissolving pulp product is obtained. The performance parameters of the obtained dissolving pulp are shown in Table 1, and its α-cellulose content can reach 91.2%, and the degree of polymerization is 483.

[0067] The obtained filtrate is neutralized to weakly alkaline with hydrochloric acid, a flocculant of polydimethyldiethylammonium methyl sulfate is added, stirred and then left standing for 30 minutes to separate out a precipitate. The precipitate is washed successively with an acetic acid aqueous solution and an ethanol solution to obtain a polysaccharide complex containing hemicellulose-lignin.

[0068] The composition of Example 2 analyzed by high performance liquid chromatography is shown in Table 2. Arabinose is 2.20%, xylose is 34.57%, and there is a small amount of glucose at 3.77%. The relative molecular mass analyzed by GPC is shown in Table 3 and is 116082.

[0069] Example 3

[0070] A process for preparing a spinning-grade dissolving pulp and a polysaccharide complex from straw, the specific process:

[0071] The sun-dried corn stalk raw materials are preliminarily crushed, dusted by a cyclone dust collector, and passed through a vibrating screen.

[0072] The obtained raw materials are impregnated in an acidic solution in a reactor. The conditions for the acidic impregnation treatment are a solid-liquid ratio of 1:15, an oxalic acid dosage of 0.5 wt.%, a temperature of 90 °C, and a time of 2 hours.

[0073] After the impregnation is completed, wash them, dry the raw materials at 80 °C, and perform secondary pulverization, controlling the particle size after pulverization to be less than 100 mesh.

[0074] Mix the pulverized rice straw raw materials with a potassium hydroxide solution with a mass fraction of 5 wt.% at a solid-liquid ratio of 1:15, heat to 90 °C, and react for 1 h to obtain an activated product.

[0075] Place the above-mentioned activated product in a low-temperature reactor and stir at a constant temperature until the mixture presents a viscous ice-water mixed phase.

[0076] Feed the obtained mixture into a pre-cooled twin-screw extruder through a conveying system via a metering pump. The diameter of the twin-screws is 34 mm, the rotation speed is 160 r / min, and the temperature of the screw cavity is -6 °C.

[0077] The mixture obtained after being processed by the frozen screw extruder is filtered with a high-pressure filtration device to separate rice straw cellulose microfibers and a filtrate containing hemicellulose, lignin, and alkali, and collect the filtrate for later use.

[0078] Wash the filter cake and mix it with a sodium chlorite solution with a mass fraction of 1.5 wt.% at a solid-liquid ratio of 1:20. Adjust the pH = 3.7 with glacial acetic acid, heat to 75 °C, and perform bleaching treatment for 120 min. After filtering off the bleaching solution, repeat the above steps for the second-stage bleaching.

[0079] Perform two-stage iron removal treatment on the bleached product. The conditions for the dilute acid treatment are: adjust the pH of the solution to 3.6 with dilute sulfuric acid, a solid-liquid ratio of 1:25, a temperature of 60 °C, and react for 35 min.

[0080] After filtering off the solution, perform chelating agent treatment. The reaction conditions are: add 0.6 wt.% sodium tripolyphosphate, a solid-liquid ratio of 1:20, adjust the pH = 9, and react at 60 °C for 35 min.

[0081] Wash it thoroughly with distilled water to remove impurities such as complexes. After the washing is completed, the slurry is neutral. After making a pulp board, a rice straw dissolving pulp product is obtained.

[0082] The key performance parameters of the straw dissolving pulp prepared in Examples 1-3 are shown in Table 1 below. Its α-cellulose content can reach 94.2%, and the degree of polymerization is 833.

[0083] The obtained filtrate is neutralized to weakly alkaline with acetic acid, a polyacrylamide flocculant is added, stirred and then left to stand for 30 minutes, the precipitate is separated, and the precipitate is washed successively with an acetic acid aqueous solution and an ethanol solution to obtain a polysaccharide complex containing hemicellulose-lignin.

[0084] The composition of Example 3 analyzed by high performance liquid chromatography is shown in Table 2. Arabinose is 1.51%, xylose is 27.61%, and there is a small amount of glucose which is 6.20%. The relative molecular mass analyzed by GPC is shown in Table 3 and is 177942.

[0085] Table 1

[0086]

[0087] The composition of the polysaccharide complexes prepared in Examples 1 - 3 is shown in Table 2 below.

[0088] Table 2

[0089]

[0090] The molecular weights of the polysaccharide complexes prepared in Examples 1 - 3 are shown in Table 3 below.

[0091] Table 3

[0092] Sample Mn (g / mol) Mw (g / mol) PDI Example 1 66211 98212 1.48 Example 2 116082 195603 1.69 Example 3 177942 2389703 13.43

[0093] The infrared spectra of the polysaccharide complexes prepared in Examples 1 - 3 of the present invention are as Figure 1 shown; the X - ray diffraction patterns of the polysaccharide complexes prepared in Examples 1 - 3 of the present invention are as Figure 2 shown. The analysis results of the infrared spectra and XRD of the polysaccharide complexes prove that Example 3 is an amorphous powder.

[0094] Certainly, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the scope of the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A process for preparing a spinning-grade dissolving pulp and a polysaccharide complex from straw, characterized in that, Specifically, it includes the following steps: Step 1: Crush the dried or baked agricultural waste straw once, then perform dust removal and screening to obtain the primary crushed raw material; Step 2: Place the primary crushed raw material obtained in Step 1 in a reactor for impregnation treatment, and wash it with deionized water to obtain the impregnation treatment product; Step 3: Dry the obtained impregnation treatment product and crush it a second time to obtain the second crushed product; Step 4: Place the second crushed product in an alkaline aqueous solution, heat and stir to obtain the activated product; Step 5: Place the activated product in a low-temperature reactor, stir to present a viscous ice-water mixed phase, and then uniformly add it to a frozen screw extruder through a metering pump to obtain the frozen screw extrusion product; Step 6: Perform high-pressure filtration on the frozen screw extrusion product. The solid obtained after filtration is straw cellulose microfiber, and after multi-stage bleaching, the bleached product is obtained and the pH is adjusted; the filtrate obtained after filtration is neutralized to weakly alkaline with acid, then a polymer flocculant is added for flocculation precipitation treatment, and the precipitate can be obtained after separation; Step 7: Perform first-stage iron removal treatment and second-stage iron removal treatment on the bleached product obtained in Step 6 in sequence to obtain the spinning-grade dissolving pulp, and the pulp sheet can be obtained after sheet forming; Step 8: Wash the precipitate obtained in Step 6 with acetic acid aqueous solution and ethanol solution in sequence to obtain the polysaccharide complex containing hemicellulose-lignin.

2. The process for preparing a spinning-grade dissolving pulp and a polysaccharide complex using straw according to claim 1, characterized in that, In Step 2, the impregnation treatment is selected from hot water impregnation or dilute acid solution impregnation, the temperature is controlled at 20-100°C, and the impregnation time is 1-24 h.

3. The process for preparing a spinning-grade dissolving pulp and a polysaccharide complex using straw as claimed in claim 2, wherein, When dilute acid solution is used for impregnation, the acid selected is at least one of oxalic acid, citric acid, lactic acid, malic acid, maleic acid, itaconic acid, formic acid, acetic acid, oxalic acid, propionic acid, and the mass concentration of the acid is 0.1%-2.5%.

4. The process for preparing a spinning-grade dissolving pulp and a polysaccharide complex using straw as claimed in claim 3, characterized in that, In Step 3, the drying temperature is controlled at 60-80°C, and it is dried until the moisture content is less than 10%; the particle size of the second crushed product is less than 32 mesh.

5. The process for preparing a spinning-grade dissolving pulp and a polysaccharide complex using straw as claimed in claim 4, wherein In Step 4, the solid-liquid ratio of the second crushed product to the alkali solution is controlled at 1:15-1:30; the alkali solution is selected from at least one of KOH, NaOH, LiOH, Na2CO3, NaHCO3, NH4OH, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and the mass fraction of the alkali solution is 1.5%-9.0%; The heating temperature is controlled at 50-90°C, and the stirring time is 0.5-2 h.

6. The process for preparing a spinning-grade dissolving pulp and a polysaccharide complex using straw as claimed in claim 5, characterized in that, In Step 5, the temperature of the low-temperature reactor is controlled at -3 to -11°C; The screw extruder is selected from one of the twin-screw, triple-screw, and quadruple-screw extruders, and the screw diameter is one of 15 mm, 25 mm, 30 mm, 34 mm, 53 mm; The length-diameter ratio of the screw of the screw extruder is 21-70, and the screw speed is 20-350 r / min.

7. A process for preparing a spinning-grade dissolving pulp and a polysaccharide complex using straw, as claimed in claim 6, wherein In Step 6, during the bleaching treatment of the solid, the oxidant is selected from one or more of hypochlorite, chlorite, hydrogen peroxide, peracetic acid, sodium perborate, sodium percarbonate, sodium dithionite, the oxidant concentration is 0.2-5.0%, and the temperature is 50-80°C.

8. A process for preparing a spinning-grade dissolving pulp and a polysaccharide complex using straw as claimed in claim 7, characterized in that, In step 6, during the neutralization of the filtrate, the acid selected is at least one of hydrochloric acid, phosphoric acid, sulfuric acid, and acetic acid, and the flocculant is at least one of polyacrylamide, poly(dimethyl diethyl ammonium methyl sulfate), and poly(methacryloyloxyethyl trimethyl ammonium chloride).

9. The process for preparing a spinning-grade dissolving pulp and a polysaccharide complex using straw as claimed in claim 8, wherein, In step 7, one-stage iron removal treatment is carried out with dilute acid, and then washed with distilled water. The dilute acid selected is dilute hydrochloric acid or dilute sulfuric acid, the pH of the solution is adjusted to 2 - 5, the solid-liquid ratio is 1:15 - 1:30, the treatment temperature is 40 - 80 °C, and the treatment time is 15 - 60 minutes.

10. The process for preparing a spinning-grade dissolving pulp and a polysaccharide complex using straw as claimed in claim 9, characterized in that, In step 7, a chelating agent is used for two-stage iron removal treatment, and then the complex impurities are washed away with distilled water. The chelating agent selected is one of ethylenediaminetetraacetic acid, diethylenetriamine, sodium hexametaphosphate, and sodium tripolyphosphate, the treatment temperature is 40 - 80 °C, and the treatment time is 15 - 60 min.

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