Method for preparing lignin soil conditioner and cellulose by treating biomass with potassium sulfite under assistance of superheated steam and application of lignin soil conditioner and cellulose

Abstract

The invention discloses a method for preparing a lignin soil conditioner and cellulose by treating biomass with potassium sulfite under the assistance of superheated steam and application of the lignin soil conditioner and the cellulose, and belongs to the field of solid waste recycling and soil conditioner processing. The method comprises the following steps: uniformly mixing agriculture and forestry residues with an alkaline potassium sulfite solution to form slurry, putting the slurry into a reactor, introducing superheated steam to carry out lignosulphonation reaction, returning steam tail gas to a steam heating device in the reaction process to improve heat energy recovery, and after the reaction is finished, enabling a solid material to enter a percolation cleaning device; the preparation method comprises the following steps: preparing a potassium lignosulfonate solution and a degradable cellulose solid product, mixing the potassium lignosulfonate solution with xanthan gum, and adding a ferric ion salt solution to form the lignin-based hydrogel as the soil conditioner. By means of high permeability of the superheated steam, one production procedure is omitted, and energy consumption is reduced; the potassium lignosulfonate liquid produced by using the alkaline potassium sulfite is suitable for soil improvement, and the growth performance of crops in saline-alkali soil can be remarkably improved.

Description

Technical Field

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

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

[0003] my country has rich agricultural and forestry residue resources. According to statistics, the total amount of agricultural and forestry residues in China will exceed 1.3 billion tons by 2022. The comprehensive utilization rate of agricultural residues exceeds 88%, but most of them are returned to the fields through simple mechanical return, and only a small part is used for high-value utilization through feed, base material or material. 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 pentose mainly composed of xylose. In the process of returning to the fields, they will release a large amount of greenhouse gases through microbial degradation. In particular, excessive return of agricultural residues to the fields in some areas exceeds the upper limit of natural degradation of the land, which not only affects the ecological balance of the soil, but also has been reported to cause serious insect pests, which seriously affects crop planting, causes huge economic losses to farmers, and endangers my country's food security. In the process of natural degradation, high-polysaccharides such as cellulose and hemicellulose are easier to degrade than lignin. The residues of actual straw degradation are lignin components, which then form soil organic matter and achieve the improvement and regulation of soil fertility. Therefore, industrial methods are used to replace the natural degradation of microorganisms in the process of returning to the field, and agricultural and forestry residues are efficiently and directional depolymerized and separated, so as to obtain 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 stalks 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 stalks 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 stalks are consumed, and about 5-8 tons of waste residue are generated. At present, 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 hazards, 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 method is a relatively mature method for removing lignin in the biomass pulping and papermaking industry. It mainly forms a slurry by mixing acidic sodium sulfite with materials, and then sulfonates the lignin through high-temperature cooking to form soluble sodium lignin sulfonate. Then, a large amount of water is used to repeatedly wash and remove the lignin to obtain cellulose. The common solid-liquid ratio of the mixed slurry is 1:10-1:50, and the amount of sodium sulfite used is large. In addition, sodium cannot be used as a nutrient that can be absorbed by plants during growth. When sodium lignin sulfonate is added to normal soil or saline-alkali soil, there is a potential risk of increasing soil salinity and affecting 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 new normal-pressure superheated steam heating method, which reduces the potential danger of pressure vessels in the production process. Another technical problem to be solved by the present invention is to provide an application of the lignin soil conditioner, and its application in saline-alkali soil.

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

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

[0009] (1) The agricultural and forestry residue biomass raw materials are mixed with an alkaline potassium sulfite solution and then placed in a reactor, where superheated steam is introduced for directional depolymerization of lignin. During this process, the superheated steam is directly returned to the steam generator without condensation;

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

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

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

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

[0014] Furthermore, in the 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 absolute dry material of the agricultural and forestry residues to potassium sulfite is 1:5-30%; and the mass ratio of the absolute dry material of the 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 normal pressure.

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

[0017] Furthermore, in the step (3), 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%.

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

[0019] Furthermore, in step (3), the ferric ion salt solution is any one or more mixed solutions 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-mentioned 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 pulp with high water content is heated to a suitable temperature by steam to complete the sulfonation reaction, and the product is separated from the solid and liquid, washed several times, and then separated from the solid and liquid to obtain a cellulose solid product and a lignin sulfonate liquid. The method proposed in this application uses the high permeability of superheated steam to carry out the sulfonation reaction under low water content conditions. The final product is a solid (water content of about 5%). After diafiltration and washing, the solid-liquid separation can obtain a cellulose solid product and a lignin sulfonate potassium liquid, thereby reducing one production process and energy consumption.

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

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

[0027] Figure 2 The morphological diagrams of the lignin-based hydrogels S0-S4 of the present invention and the surface morphological diagrams 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 is further illustrated below in conjunction with 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 embodiments, 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 taken from Ulanqab City, Inner Mongolia, approximately at 107.6° east longitude and 39.5° north latitude.

[0031] In the following example, the steps of acid-treating the raw material are as follows: the raw material is mixed with a 7% dilute sulfuric acid solution at a solid-liquid ratio of 1:10, and after being kept at 120°C for 1.5 h, the solid is filtered to obtain the solid, and water is added to wash until the pH of the eluent is about 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) The agricultural and forestry residue biomass raw materials are mixed with an alkaline potassium sulfite solution and then placed in a reactor, where superheated steam is introduced for directional depolymerization of lignin. During this process, the superheated steam is directly returned to the steam generator without condensation;

[0034] (2) The solid product treated in step (1) is subjected to diafiltration and washing, and then 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 and mix potassium sulfite, potassium hydroxide and water according to the conditions shown in Table 1, place the materials in a superheated steam reactor, react at 170 °C for 60 min, take out the reaction product, place it in a percolation device, add water at a solid-liquid ratio of 1:40 for washing, collect the percolation liquid, separate the solid and liquid, combine the washing liquid, dry the solid product, and use it for enzyme 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 the efficiency of solid product enzymatic hydrolysis 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%. When the moisture content continued to increase, the lignin removal rate decreased to 50%. It may be that after the moisture content increased, the concentration of potassium sulfite decreased, resulting in a decrease in reaction efficiency. Therefore, a moisture content of 85% was selected for subsequent analysis. When the alkali addition was only 2%, the lignin removal rate and the purity of cellulose could be significantly improved. When the alkali addition 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 improvement of ion efficiency promoted the breakage of α-aryl ether bonds, α-alkyl ether bonds, β-aryl ether bonds and ester bonds in lignin macromolecules, and improved the efficiency of sulfonation reaction, indicating that alkaline sulfite has a synergistic effect on lignin removal. Therefore, the alkali addition amount was 12%.

[0042] Example 2

[0043] Weigh 50 g of xylose residue, prepare and mix potassium sulfite, potassium hydroxide and water according to the conditions shown in Table 3, place the materials in a superheated steam reactor, react at 170 °C for 60 min, take out the reaction product, place it in a percolation device, add water at a solid-liquid ratio of 1:40 for washing, collect the percolation liquid, separate the solid and liquid, combine the washing liquid, dry the solid product, and use it for enzyme 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 are shown in Table 2. As the reaction temperature increases, the lignin removal rate increases significantly, and the lignin content in the reaction product decreases gradually. When the reaction temperature increases from 170 °C to 180 °C, the cellulose content in the solid product only increases from 76.27% to 78.56%, indicating that a small amount of cellulose decomposes during the reaction. It may be that after the temperature increases, a small amount of low-crystallinity cellulose is hydrolyzed and dissolved at high temperature. Therefore, 170 °C is selected as the appropriate superheated steam pretreatment reaction temperature.

[0047] Example 3

[0048] Weigh 50 g of xylose residue, prepare and mix potassium sulfite, potassium hydroxide and water according to the conditions shown in Table 3, place the materials in a superheated steam reactor, react at 170 °C for 60 min, take out the reaction product, place it in a percolation device, add water at a solid-liquid ratio of 1:40 for washing, collect the percolation liquid, separate the solid and liquid, combine the washing liquid, dry the solid product, and use it for enzyme 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, the lignin removal rate can be improved by extending the reaction time, but the superheated steam has strong permeability and will gradually reduce the moisture content of the material during the reaction. Subsequently, the amount of sulfite ions and bisulfite ions released by sulfonate ionization will decrease, and the efficiency of the sulfonation reaction will decrease. When the reaction time exceeds 60 min, the delignification improvement is not significant. Therefore, the reaction time is selected as 60 min.

[0052] Example 4

[0053] Taking the sample treated with the d6 scheme 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), and the filtrate was collected to determine the content of potassium lignin sulfonate at 230 nm, and 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 lignin sulfonate is easily soluble in water, the greater the amount of water used in the washing process, the higher the dissolution rate of potassium lignin sulfonate, and the corresponding elution rate of lignin in the solid sample increases accordingly. When the solid-liquid ratio of the washing water is 1:40, the elution rate of lignin reaches 99.4%. Therefore, a solid-liquid ratio of 1:40 is selected to wash the reaction product.

[0057] Example 5

[0058] Weigh 50 g each of poplar sawdust, corn straw, wheat straw, rice straw, bamboo processing residues and bagasse from which hemicellulose was removed by acid treatment, mix 20% potassium sulfite, 12% potassium hydroxide and water to a moisture content of 85%, place the mixed materials in a superheated steam reactor, heat and react at 170 °C for 60 min, take out the reaction product, place it in a percolation device, add water at a solid-liquid ratio of 1:40 for washing, collect the percolate, perform solid-liquid separation, combine the washing liquid, and dry the solid product for enzyme 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 the present 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] The potassium lignin sulfonate washing solution (11.5 g / L) and xanthan gum were mixed in the proportions according to 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 concentration of potassium lignin sulfonate slightly affects the appearance of lignin-based hydrogels. Through scanning electron microscopy of standard freeze-dried gels S0, S2, and S4, it can be seen that regardless of whether potassium lignin sulfonate is added, the hydrogels are freeze-dried and the faults are multi-layered and lamellar, and the interior is loose. As the concentration of potassium lignin sulfonate increases, the surface of the gels S0-S4 after freeze-drying and dehydration is scanned by energy spectrum, showing that the potassium content is 0%, 0.16%, 0.33%, 0.79% and 1.66% respectively, and the potassium content shows a gradual increase trend, which is consistent with the increase in the concentration of potassium lignin sulfonate.

[0067] Example 7

[0068] Weigh saline-alkali soil with a salt content of 0.595%, about 200 g, weigh 50 g and 100 g of lignin soil conditioner gel S3-4 (xanthan gum mass fraction 1% on dry basis, potassium lignin sulfonate 0.4%), respectively, with dry basis weights of 0.7 g and 1.4 g, respectively, and mix with saline-alkali soil. Under constant temperature and light culture conditions (simulated daytime: light intensity 6500 lux, temperature 26 ℃, duration 10 hours; simulated night: light intensity 0, temperature 15 ℃, duration 14 hours), it was used for wheat cultivation. 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, the soil surface without the addition of the amendment was compacted and had poor water retention, the germination rate of wheat seeds was low, and some plants could not continue to grow even if they sprouted; in the improved saline-alkali soil with a dry base addition of 0.35%, the germination rate of wheat seeds increased, and the growth state of the plants improved; in the improved saline-alkali soil with a dry base addition of 0.7%, the germination rate of wheat seeds increased significantly, and the growth state of the plants was good. It can be seen from the preliminary evaluation of the use effect 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 principle of the present invention. These improvements and modifications should also be regarded as 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) The agricultural and forestry residue biomass raw materials are mixed with an alkaline potassium sulfite solution and then placed in a reactor, where superheated steam is introduced for directional depolymerization of lignin. During this process, the superheated steam is directly returned to the steam generator without condensation; (2) The solid product treated in step (1) is subjected to diafiltration and washing, and then the solid and liquid are separated, and the washing liquid is combined to form a potassium lignin sulfonate solution; (3) After the potassium lignin sulfonate solution obtained in step (2) is mixed with xanthan gum and stirred until a uniform colloid is formed, a trivalent iron ion salt solution is added, and the mixture is stirred or allowed to stand to form a lignin-based hydrogel as a soil conditioner; (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 by potassium sulfite according to claim 1, characterized in that: In the step (1), the agricultural and forestry residue biomass raw material is selected from corn straw, wood sugar residue, furfural residue, bamboo processing residue, rice straw, wheat straw, and bagasse.

3. The method for preparing lignin soil conditioner and high-purity cellulose by treating biomass with superheated steam assisted by potassium sulfite according to claim 1, characterized in that: In the 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 absolute dry material of the agricultural and forestry residues to the potassium sulfite is 1:5-30%; and the mass ratio of the absolute dry material of the agricultural and forestry residues to the potassium hydroxide is 1:2-12%.

4. The method for preparing lignin soil conditioner and cellulose by treating biomass with superheated steam assisted by potassium sulfite according to claim 1, characterized in that: In the 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 normal pressure.

5. The method for preparing lignin soil conditioner and cellulose by treating biomass with superheated steam assisted by potassium sulfite according to claim 1, characterized in that: The solid-to-liquid ratio of the diafiltration cleaning in step (2) is 1:10-50.

6. The method for preparing lignin soil conditioner and cellulose by treating biomass with superheated steam assisted by potassium sulfite according to claim 1, characterized in that: In the step (3), 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%.

7. The method for preparing lignin soil conditioner and cellulose by treating biomass with superheated steam assisted by potassium sulfite according to claim 1, characterized in that: The molar concentration of the trivalent iron ions in the trivalent iron ion solution in step (3) is 5 mM.

8. The method for preparing lignin soil conditioner and cellulose by treating biomass with superheated steam assisted by potassium sulfite according to claim 1, characterized in that: In step (3), the ferric ion salt solution is any one or more mixed solutions 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.

9. The method for preparing lignin soil conditioner and cellulose by treating biomass with potassium sulfite assisted by superheated steam according to any one of claims 1 to 9, wherein lignin soil conditioner and cellulose are prepared.

10. Use of the lignin soil conditioner according to claim 9 in saline-alkali soil.

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