A method and application of superheated steam-assisted potassium sulfite treatment of biomass to prepare lignin soil conditioner and cellulose

Abstract

The application discloses a method for preparing lignin soil conditioner and cellulose by superheated steam assisted potassium sulfite treatment of biomass and application, and belongs to the field of solid waste resource utilization and soil conditioner processing. The application uniformly mixes agricultural and forestry residues and alkaline potassium sulfite solution into a slurry state, and then the slurry is put into a reactor, and superheated steam is introduced to perform lignin sulfonating reaction. In the reaction process, steam tail gas is returned to a steam heating device to improve heat energy recovery. After the reaction is completed, solid materials enter a percolation cleaning device to obtain lignin potassium sulfonate solution and cellulose solid product with degradable performance. After the lignin potassium sulfonate solution is mixed with xanthan gum, a trivalent iron ion salt solution is added to form lignin-based hydrogel as a soil conditioner. The application reduces a production process and reduces energy consumption by virtue of the high permeability of superheated steam. The lignin potassium sulfonate solution produced by using alkaline potassium sulfite is suitable for soil improvement, and can significantly improve the growth performance of crops in saline-alkali soil.

Description

Technical Field

[0001] The present invention belongs to the field of solid waste resource utilization and soil conditioner processing, and specifically relates to a method for preparing lignin soil conditioner and cellulose by treating biomass with superheated steam assisted by potassium sulfite, and its application. Background Art

[0002] Petrochemical-derived high-molecular-weight polymers such as acrylic acid and acrylamide have excellent water retention properties, but their degradation products pose potential biosafety concerns for soil and food security. For example, acrylamide is classified as a Group 2A carcinogen by the International Agency for Research on Cancer. The development of bio-based soil conditioners is currently a hot topic of research.

[0003] my country boasts abundant resources of agricultural and forestry residues. According to statistics, the total volume nationwide will exceed 1.3 billion tons by 2022. The comprehensive utilization rate of agricultural residues exceeds 88%, but the vast majority is simply mechanically returned to the fields, with only a small portion being utilized at a higher value through feed, base material, or material conversion. The main components of agricultural and forestry residue biomass are cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are divided into polymers of glucose and polymers of pentoses, primarily xylose. Microbial degradation during return to the fields releases significant amounts of greenhouse gases. In some regions, excessive return of agricultural residues to the fields, exceeding the upper limit of natural land degradation, not only impacts soil ecological balance but has even led to reports of severe insect infestations, severely impacting crop production, causing significant economic losses to farmers, and jeopardizing my country's food security. During natural degradation, high-polymer sugars such as cellulose and hemicellulose are more readily degraded than lignin. The degraded residues of straw are actually lignin components, which in turn contribute to soil organic matter, improving and regulating soil fertility. Therefore, by replacing the natural degradation of microorganisms in the process of returning to the field with industrial methods, agricultural and forestry residues can be efficiently and directionally depolymerized and separated, thereby obtaining high-value-added cellulose materials with high degradation performance and high purity and lignin soil conditioners with soil improvement and regulation value, which is of great significance to the high-value utilization of agricultural and forestry residue resources and the utilization of marginal land.

[0004] On the other hand, corn cobs and corn straw are most commonly used in industry to produce xylose and furfural. Generally, for every ton of xylose produced, about 4-6 tons of corn cobs or corn straw are consumed, and 3-5 tons of xylose residue waste are generated. For every ton of furfural produced, about 7-9 tons of corn cobs and corn straw are consumed, and about 5-8 tons of waste residue are generated. Currently, the commonly used method for treating waste residue is to mix it with coal and burn it, but the water content of the waste residue is about 60%. Burning it will cause unstable boiler operation, increase safety risks, and produce a large amount of waste gas. The efficient utilization of waste residue helps to reduce the production cost of xylose and furfural, and also reduces greenhouse gas emissions.

[0005] The sulfite process is a relatively mature method for removing lignin in the biomass pulping and papermaking industry. It primarily involves mixing acidic sodium sulfite with the raw material to form a slurry. The lignin is then sulfonated by high-temperature cooking to form soluble sodium lignin sulfonate. Repeated washing with large amounts of water removes the lignin and produces cellulose. The typical solid-to-liquid ratio of the mixed slurry is between 1:10 and 1:50, and the amount of sodium sulfite used is high. Furthermore, sodium cannot be absorbed as a nutrient during plant growth. When sodium lignin sulfonate is added to normal soil or saline-alkali soil, there is a potential risk of increasing soil salinity and impacting crop growth. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a lignin soil conditioner and high-purity cellulose by treating biomass with superheated steam assisted by potassium sulfite. The method proposes a novel normal-pressure superheated steam heating method, which reduces the potential danger of pressure vessels during the production process. Another technical problem to be solved by the present invention is to provide the application of the lignin soil conditioner, especially its application in saline-alkali soil.

[0007] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0008] A method for preparing a lignin soil conditioner and cellulose by treating biomass with superheated steam-assisted potassium sulfite comprises the following steps:

[0009] (1) After the agricultural and forestry residue biomass raw materials are mixed with alkaline potassium sulfite solution, they are put into the reactor and superheated steam is introduced to carry out directional depolymerization of lignin. During this period, the superheated steam is directly returned to the steam generator without condensation;

[0010] (2) The solid product after treatment in step (1) is subjected to diafiltration and washing, and the solid and liquid are separated, and the washing liquid is combined to form a potassium lignin sulfonate solution;

[0011] (3) The potassium lignin sulfonate solution obtained in step (2) is mixed with xanthan gum and stirred until a uniform colloid is formed, and then a trivalent iron ion salt solution is added. The mixture can be stirred or allowed to stand to form a lignin-based hydrogel, which is used as a soil conditioner;

[0012] (4) Drying the solid obtained in step (2) to obtain a biodegradable cellulose product.

[0013] Furthermore, the agricultural and forestry residue biomass raw material in step (1) is selected from corn straw, wood sugar residue, furfural residue, bamboo processing residue, rice straw, wheat straw, and bagasse.

[0014] Furthermore, in step (1), the water content of the reactants after the biomass raw material and the potassium sulfite solution are mixed is 65%-90%; the mass ratio of the absolutely dry agricultural and forestry residues to potassium sulfite is 1:5-30%; and the mass ratio of the absolutely dry agricultural and forestry residues to potassium hydroxide is 1:2-12%.

[0015] Furthermore, in step (1), the temperature of the superheated steam is 150-180°C, and the heating time of the superheated steam is 20-120 min; the heat energy of the superheated steam can be recovered and recycled, and the pressure of the reactor is atmospheric pressure.

[0016] Furthermore, the solid-liquid ratio of the diafiltration cleaning in step (2) is 1:10~50.

[0017] Furthermore, in the mixed colloidal solution of potassium ligninsulfonate and xanthan gum in step (3), the mass fraction of potassium ligninsulfonate is 0.5%-2.5%, and the mass fraction of xanthan gum is 1%-5%.

[0018] Furthermore, the molar concentration of the ferric ion in the ferric ion solution in step (3) is 5 mM.

[0019] Furthermore, the ferric ion salt solution in step (3) is a mixed solution of any one or more of ferric sulfate, ferric nitrate, and ferric chloride; and the volume ratio of the mixed colloidal solution to the ferric ion solution is 5:1.

[0020] Furthermore, any of the above methods for preparing lignin soil conditioner and cellulose by treating biomass with superheated steam assisted by potassium sulfite can prepare lignin soil conditioner and cellulose.

[0021] Furthermore, the lignin soil conditioner is used in saline-alkali soil.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The present invention proposes a new atmospheric pressure superheated steam heating method, which reduces the potential danger of pressure vessels in the production process.

[0024] (2) In the conventional sulfite pretreatment delignification method of the present invention, the high-water content pulp is heated to an appropriate temperature by steam to complete the sulfonation reaction. The product is separated into solid and liquid, washed multiple times, and then subjected to solid-liquid separation to obtain a cellulose solid product and a lignin sulfonate liquid. The method proposed in this application utilizes the high permeability of superheated steam to carry out the sulfonation reaction under low-water content conditions. The final product obtained is a solid (with a water content of about 5%). After diafiltration and washing, solid-liquid separation is performed to obtain a cellulose solid product and a potassium lignin sulfonate liquid, thereby reducing one production step and energy consumption.

[0025] (3) The present invention uses alkaline potassium sulfite, and the resulting potassium lignin sulfonate liquid can be directly prepared into a gel-type lignin-based soil conditioner without drying. It can be applied on site to significantly improve the growth status of crops in highly saline-alkali soils. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the process of preparing potassium lignosulfonate liquid product and cellulose by treating biomass with superheated steam assisted by potassium sulfite according to the present invention;

[0027] Figure 2 The morphology of the lignin-based hydrogels S0-S4 of the present invention and the surface morphology of the S0, S2 and S4 gels after freeze-drying shown by scanning electron microscopy;

[0028] Figure 3 This is a diagram showing the application effect of the wood-based soil conditioner of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further illustrated below with reference to specific examples. The examples are implemented based on the technical solutions of the present invention. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0030] In the following examples, the alkaline potassium sulfite solution is a mixture of potassium sulfite, potassium hydroxide and water; the filtration device is a plate and frame filter or a centrifuge; and the saline-alkali soil is obtained from Ulanqab, Inner Mongolia, approximately at 107.6° east longitude and 39.5° north latitude.

[0031] In the following examples, the steps for acid-treating the raw materials are as follows: the raw materials are mixed with a 7% dilute sulfuric acid solution at a solid-to-liquid ratio of 1:10, the mixture is kept at 120°C for 1.5 hours, and the solid is filtered to obtain a solid. The solid is washed with water until the pH of the eluate is approximately 7.0. The washed solid is dried at 105°C to obtain the hemicellulose-free poplar wood chips.

[0032] Figure 1 Schematic diagram of the process flow for producing potassium lignosulfonate liquid product and cellulose for superheated steam-assisted potassium sulfite treatment of biomass

[0033] (1) After the agricultural and forestry residue biomass raw materials are mixed with alkaline potassium sulfite solution, they are put into the reactor and superheated steam is introduced to carry out directional depolymerization of lignin. During this period, the superheated steam is directly returned to the steam generator without condensation;

[0034] (2) The solid product after treatment in step (1) is subjected to diafiltration and washing, and the solid and liquid are separated, and the washing liquid is combined to form a potassium lignin sulfonate solution;

[0035] (3) The potassium lignin sulfonate solution obtained in step (2) is mixed with xanthan gum and stirred until a uniform colloid is formed, and then a trivalent iron ion salt solution is added and stirred to form a lignin-based hydrogel, which is a soil conditioner;

[0036] (4) Drying the solid obtained in step (2) to obtain a biodegradable cellulose product.

[0037] Example 1

[0038] Weigh 50 g of xylose residue, prepare potassium sulfite, potassium hydroxide, and water according to the conditions shown in Table 1 and mix them evenly. Place the materials in a superheated steam reactor and react at 170°C for 60 min. Take out the reaction product, place it in a percolation device, and wash it with water at a solid-liquid ratio of 1:40. After collecting the percolation liquid, perform solid-liquid separation, combine the washing liquid, and dry the solid product for enzymatic hydrolysis test analysis.

[0039] Table 1 Effects of xylose residue pretreatment conditions on product chemical composition and enzymatic hydrolysis rate

[0040]

[0041] The results are shown in Table 1. When the potassium sulfite concentration increased from 5% to 20%, the lignin removal rate increased from 27.7% to 68.3%, and the lignin removal rate and solid product enzymatic hydrolysis efficiency were significantly improved. When the potassium sulfite concentration increased from 20% to 30%, the lignin removal rate only increased from 68.4% to 77.3%. Therefore, a potassium sulfite addition of 20% was selected for subsequent analysis of influencing factors. When the moisture content of the material increased from 65% to 85%, the lignin removal rate increased to 68%. However, when the moisture content continued to increase, the lignin removal rate decreased to 50%. This may be because the concentration of potassium sulfite decreased after the moisture content increased, resulting in a decrease in reaction efficiency. Therefore, a moisture content of 85% was selected for subsequent analysis. When the alkali addition amount was only 2%, the lignin removal rate and cellulose purity could be significantly improved. When the alkali addition amount reached 12%, the lignin removal rate could reach 95.3%, and the cellulose purity could be increased to 90.2%. The possible reason is that under high temperature conditions, OH - The increased ion efficiency promotes the breakage of α-aryl ether bonds, α-alkyl ether bonds, β-aryl ether bonds, and ester bonds in the lignin macromolecules, improving the efficiency of the sulfonation reaction, indicating that alkaline sulfite has a synergistic effect on lignin removal. Therefore, the alkali addition level is 12%.

[0042] Example 2

[0043] 50 g of xylose residue was weighed, and potassium sulfite, potassium hydroxide, and water were prepared and mixed according to the conditions shown in Table 3. The materials were placed in a superheated steam reactor and reacted at 170 °C for 60 min. The reaction products were taken out and placed in a percolation device. Water was added at a solid-liquid ratio of 1:40 for washing. After collecting the percolation liquid, solid-liquid separation was performed, and the washing liquid was combined. The solid product was dried and used for enzymatic hydrolysis test analysis, as shown in Table 2.

[0044] Table 2 Effect of reaction temperature on properties of xylose residue pretreatment products

[0045]

[0046] The results, as shown in Table 2, show that as the reaction temperature increased, the lignin removal rate significantly increased, while the lignin content in the reaction product gradually decreased. When the reaction temperature was increased from 170°C to 180°C, the cellulose content in the solid product only increased from 76.27% to 78.56%, indicating that a small amount of cellulose decomposed during the reaction. This may be due to the hydrolysis and dissolution of a small amount of low-crystalline cellulose at high temperatures. Therefore, 170°C was selected as the optimal reaction temperature for superheated steam pretreatment.

[0047] Example 3

[0048] 50 g of xylose residue was weighed, and potassium sulfite, potassium hydroxide, and water were prepared and mixed according to the conditions shown in Table 3. The materials were placed in a superheated steam reactor and reacted at 170 °C for 60 min. The reaction products were taken out and placed in a percolation device. Water was added at a solid-liquid ratio of 1:40 for washing. After collecting the percolation liquid, solid-liquid separation was performed, and the washing liquid was combined. The solid product was dried and used for enzymatic hydrolysis test analysis, as shown in Table 3.

[0049] Table 3 Effect of reaction time on properties of xylose residue pretreatment products

[0050]

[0051] As shown in Table 3, increasing the reaction time improves delignification efficiency. However, superheated steam has strong permeability, which gradually reduces the moisture content of the material during the reaction. Consequently, the amount of sulfite and bisulfite ions released by sulfonate ionization decreases, reducing the efficiency of the sulfonation reaction. When the reaction time exceeds 60 minutes, the delignification improvement is not significant. Therefore, a reaction time of 60 minutes was selected.

[0052] Example 4

[0053] Taking the sample treated with the D6 solution with the highest lignin removal rate as an example, it was washed under different solid-liquid ratios (1:10, 1:20, 1:30, 1:40 and 1:50). The filtrate was collected and the content of potassium lignin sulfonate was determined at 230 nm. The elution rate of potassium lignin sulfonate was analyzed. The results are shown in Table 4.

[0054] Table 4 Effect of different solid-liquid ratios of cleaning reaction products on lignin elution rate

[0055]

[0056] As shown in Table 4, although potassium ligninsulfonate is readily soluble in water, the greater the amount of water used during the cleaning process, the higher the dissolution rate of potassium ligninsulfonate, and the corresponding increase in the lignin elution rate from the solid sample. When the solid-to-liquid ratio of the cleaning water was 1:40, the lignin elution rate reached 99.4%. Therefore, a solid-to-liquid ratio of 1:40 was selected for cleaning the reaction product.

[0057] Example 5

[0058] Weigh 50 g each of acid-treated poplar sawdust, corn straw, wheat straw, rice straw, bamboo processing residues, and bagasse to remove hemicellulose. Mix 20% potassium sulfite, 12% potassium hydroxide, and water to a moisture content of 85%. Place the mixed materials in a superheated steam reactor and heat them at 170 °C for 60 min. Take out the reaction products, place them in a percolation device, and wash them with water at a solid-liquid ratio of 1:40. After collecting the percolation liquid, perform solid-liquid separation, combine the washing liquid, and dry the solid products for enzymatic hydrolysis test analysis, as shown in Table 5.

[0059] Table 5 Comparison of chemical composition and enzymatic hydrolysis efficiency of pretreatment products

[0060]

[0061] The results are shown in Table 5. The method proposed in this application has a high lignin removal rate for agricultural and forestry residues from different sources, such as poplar sawdust, corn straw and wheat straw, and the obtained cellulose raw materials have good enzymatic hydrolysis performance.

[0062] Example 6

[0063] Potassium lignin sulfonate washing solution (11.5 g / L) and xanthan gum were mixed according to the ratio in Table 6 to obtain colloidal solutions with different potassium lignin sulfonate contents. After adding 5 mM Fe(NO3)3 solution and letting it stand for a while, the lignin-based soil conditioner product was obtained. Figure 2 The morphology of lignin-based hydrogels S0-S4 and the surface morphology of S0, S2 and S4 gels after freeze-drying shown by scanning electron microscopy.

[0064] Table 6 Raw material ratio

[0065]

[0066] like Figure 2 As shown, the addition of potassium lignosulfonate slightly affects the appearance of the lignin-based hydrogels. Scanning electron microscopy of standard freeze-dried gels S0, S2, and S4 reveals that regardless of whether potassium lignosulfonate was added, the hydrogels exhibited a multilayered, lamellar structure at the fracture surface after freeze-drying, with a loose interior. As the potassium lignosulfonate concentration increased, energy spectrum scanning of the surfaces of freeze-dried and dehydrated gels S0-S4 revealed potassium contents of 0%, 0.16%, 0.33%, 0.79%, and 1.66%, respectively. This gradual increase in potassium content is consistent with the increase in potassium lignosulfonate concentration.

[0067] Example 7

[0068] Approximately 200 g of saline-alkali soil with a salt content of 0.595% was weighed. 50 g and 100 g of the lignin soil conditioner gel S3-4 (xanthan gum, potassium lignin sulfonate, 1% dry weight, 0.7 g and 1.4 g dry weight, respectively) were mixed with the saline-alkali soil. Wheat was cultivated under constant light and temperature conditions (simulated daytime: 6500 lux, 26°C, 10 hours; simulated nighttime: 0 light intensity, 15°C, 14 hours). Figure 3 This is a diagram showing the effect of applying wood-based soil conditioner.

[0069] The culture results are as follows Figure 3 As shown in the results, the soil surface without the addition of the amendment was compacted and had poor water retention, resulting in a low wheat seed germination rate, and some plants could not continue to grow even if they germinated. In the improved saline-alkali soil with an addition of 0.35% on a dry basis, the wheat seed germination rate increased, and the plant growth condition improved. In the improved saline-alkali soil with an addition of 0.7% on a dry basis, the wheat seed germination rate increased significantly, and the plant growth condition was good. Therefore, through preliminary evaluation of the use effect, it can be seen that the addition of high-water-retention soil amendments significantly improved the growth performance of wheat in moderate saline-alkali soil.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing lignin soil conditioner and cellulose by treating biomass with superheated steam assisted by potassium sulfite, characterized in that: The following steps are involved: (1) After the agricultural and forestry residue biomass raw materials are mixed with alkaline potassium sulfite solution, they are put into the reactor and superheated steam is introduced to carry out directional depolymerization of lignin. During this period, the superheated steam is directly returned to the steam generator without condensation; the agricultural and forestry residue biomass raw materials are selected from corn straw, wood sugar, furfural residue, bamboo processing residue, rice straw, wheat straw, and bagasse; the water content of the reactants after the biomass raw materials are mixed with the potassium sulfite solution is 65%-90%; the mass ratio of the agricultural and forestry residue absolute dry material to potassium sulfite is 1:5-30%; the mass ratio of the agricultural and forestry residue absolute dry material to potassium hydroxide is 1:2-12%; the temperature of the superheated steam is 150-180 °C, and the heating time of the superheated steam is 20-120 min; the heat energy of the superheated steam can be recovered and recycled, and the pressure of the reactor is atmospheric pressure; (2) The solid product after treatment in step (1) is subjected to diafiltration washing, and the solid-liquid separation is performed, and the washing liquid is combined to form a potassium lignin sulfonate solution; the solid-liquid ratio of the diafiltration washing is 1:10~50; (3) The potassium lignin sulfonate solution, a liquid product obtained in step (2), is mixed with xanthan gum and stirred until a uniform colloid is formed, and then a trivalent iron ion salt solution is added. Stirring or standing can form a lignin-based hydrogel as a soil conditioner; the mass fraction of potassium lignin sulfonate in the mixed colloidal solution of potassium lignin sulfonate and xanthan gum is 0.5%-2.5%, and the mass fraction of xanthan gum is 1%-5%; the molar concentration of trivalent iron ions in the trivalent iron ion solution is 5 mM; the trivalent iron ion salt solution is a mixed solution of any one or more of ferric sulfate, ferric nitrate, and ferric chloride; the volume ratio of the mixed colloidal solution to the trivalent iron ion solution is 5:1; (4) Drying the solid obtained in step (2) to obtain a biodegradable cellulose product.

2. The method for preparing lignin soil conditioner and cellulose by treating biomass with superheated steam assisted potassium sulfite according to claim 1, wherein lignin soil conditioner and cellulose are prepared.

3. Application of the lignin soil conditioner according to claim 2 in saline-alkali soil.

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