Method for co-producing furfural, polydextrose oligosaccharide and lignin by utilizing agricultural and forestry wastes

Abstract

The invention relates to the technical field of agricultural and forestry waste treatment and high-value utilization, in particular to a method for co-producing furfural, oligomeric dextrose and lignin by utilizing agricultural and forestry waste. Comprising the following steps: mixing the forestry and agricultural residues with a p-toluenesulfonic acid solution, carrying out first heat treatment, and carrying out solid-liquid separation after reaction to obtain a first filtrate and first residues; adding aluminum chloride and methyl isobutyl ketone into the first filtrate, carrying out second heat treatment, separating an organic phase and a water phase after the reaction is finished, collecting the organic phase, and distilling to obtain furfural; washing the first residue to be neutral, adding the first residue into a lithium chloride solution, adding an HZSM-5 molecular sieve, carrying out third heat treatment, and carrying out solid-liquid separation after reaction to obtain a second filtrate and a second residue; concentrating the second filtrate, adding methanol, and collecting the precipitate, namely the oligomeric dextrose; and adding acidic dioxane / water into the second residue, fully dissolving, carrying out solid-liquid separation, collecting a third filtrate, and removing the solvent dioxane to obtain lignin.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural and forestry waste treatment and high-value utilization, and in particular to a method for co-producing furfural, oligoglucose and lignin by utilizing agricultural and forestry waste. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Due to the limited storage of fossil fuels and the various environmental, economic, and political challenges associated with their widespread use, the search for alternatives to fossil fuels and the development of renewable energy have become key global energy development priorities. Biomass energy, due to its renewable and environmentally friendly nature, has become a crucial tool for addressing the dual challenges of energy security and climate change. Agricultural and forestry wastes, rich in a variety of bioresources such as cellulose and hemicellulose, are a valuable biomass resource. Utilizing agricultural and forestry wastes as energy sources is a research hotspot in the renewable energy field.

[0004] Agricultural and forestry wastes are rich in carbohydrates (cellulose and hemicellulose), which, after certain processing, can be converted into oligosaccharides or biomass monosaccharides (primarily glucose and xylose). Using biomass monosaccharide molecules as starting materials, under appropriate conditions, they can be converted into the important platform compound furfural. Furfural is an important precursor to furanic compounds and can be converted into widely used bulk chemicals such as furfuryl alcohol and tetrahydrofuran. As functional oligosaccharides with multiple physiological functions, oligosaccharides are increasingly in demand in the food and pharmaceutical industries. Agricultural and forestry wastes also contain significant amounts of lignin, which, with its rich aromatic ring structure, is an ideal renewable alternative to petroleum-based aromatic compounds (such as phenol, benzene, toluene, and xylene). Harvesting lignin from agricultural and forestry wastes can reduce dependence on fossil fuels and promote the development of green chemical industry.

[0005] Therefore, if oligosaccharides, furfural and lignin can be obtained from agricultural and forestry wastes, the resource utilization value of agricultural and forestry wastes can be significantly improved.

[0006] However, traditional furfural production often uses sulfuric acid to catalyze xylose dehydration. However, strong acids lead to increased side reactions, low furfural yields (usually <70%), and the generation of large amounts of acidic wastewater, resulting in high pollution control costs. Cellulose hydrolysis often relies on high temperature and pressure or strong acid / enzyme treatment, making it difficult to precisely control the degree of polymerization of the product, and prone to excessive degradation into glucose monomers (of low economic value) or residual fiber fragments that have not been fully depolymerized. Conventional organic solvent or alkaline lignin extraction processes are prone to condensation and denaturation, resulting in low yields (generally <80%) and insufficient purity (containing polysaccharides and ash impurities), making it difficult to meet the needs of material applications. Most current technologies only target a single component (such as furfural or ethanol alone), failing to achieve the integrated production of oligosaccharides, furfural, and lignin, resulting in resource fragmentation and the accumulation of secondary waste. Summary of the Invention

[0007] In order to overcome the above problems, the present invention provides a method for co-producing furfural, oligoglucose and lignin by utilizing agricultural and forestry wastes.

[0008] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: The first aspect of the present invention provides a method for co-producing furfural, oligoglucose and lignin using agricultural and forestry wastes, comprising the following steps: (1) mixing agricultural and forestry waste with a p-toluenesulfonic acid solution and performing a first heat treatment, and performing solid-liquid separation after the reaction to obtain a first filtrate and a first residue; wherein the agricultural and forestry waste contains cellulose, hemicellulose, and lignin; (2) adding aluminum chloride and an organic solvent, methyl isobutyl ketone, to the first filtrate, mixing them evenly and then performing a second heat treatment. After the reaction is completed, the organic phase and the aqueous phase are separated, the organic phase is collected, and furfural is obtained by distillation; (3) The first residue is repeatedly washed with deionized water until neutral, added to a lithium chloride solution, and HZSM-5 molecular sieve is added. After mixing evenly, a third heat treatment is performed. After the reaction is completed, solid-liquid separation is performed to obtain a second filtrate and a second residue; (4) After the second filtrate is concentrated, methanol is added and the precipitate is collected to obtain solid oligosaccharide; (5) A mixture of dioxane and water is added to the second residue, and after it is fully dissolved, the solid and liquid are separated, and the third filtrate is collected. The solvent dioxane is removed to obtain lignin.

[0009] In one or more embodiments, the agricultural and forestry waste includes one or more of corn straw, corn cobs, rice straw, sorghum straw, bagasse, wheat straw, firewood, bark, bamboo, peanut shells, branches, wood curls and wood shavings.

[0010] In one or more embodiments, the agricultural and forestry waste is pretreated prior to reacting with the p-toluenesulfonic acid solution. The pretreatment method includes crushing the agricultural and forestry waste to a particle size of 0.3 to 2 mm and then drying it. Crushing the agricultural and forestry waste can increase the specific surface area, thereby accelerating the subsequent reaction rate.

[0011] In one or more embodiments, in step (1), the concentration of the p-toluenesulfonic acid solution is 0.5-1.5 wt%. If the concentration of the p-toluenesulfonic acid solution is too low, hemicellulose hydrolysis is insufficient, affecting the yield of subsequent furfural production. In addition, in the subsequent production of oligoglucose from the first residue, the hydrolyzate contains a large amount of hemicellulose hydrolysis products due to insufficient hemicellulose hydrolysis, affecting the cellulose hydrolysis efficiency and the yield of oligoglucose. Conversely, if the concentration of the p-toluenesulfonic acid solution is too high, it will lead to further degradation of cellulose and lignin, and the retention rate will be reduced. The increase in glucose in the hydrolyzate affects the yield of furfural and also leads to a decrease in the yield of oligoglucose and lignin.

[0012] In one or more embodiments, in step (1), the solid-to-liquid ratio of the agricultural and forestry waste to the p-toluenesulfonic acid solution is 1:(5-15). Within this ratio range, the agricultural and forestry waste can fully react with the p-toluenesulfonic acid solution.

[0013] In one or more embodiments, in step (1), the temperature of the first heat treatment is 140-190°C, the reaction time is 0.5-1.5 hours, and stirring is continued at a speed of 120-200 r / min during the reaction. Under these reaction conditions, most of the hemicellulose is hydrolyzed into xylose, while more cellulose and lignin are retained.

[0014] In one or more embodiments, in step (2), the concentration of aluminum chloride in the first filtrate is 5-10 mg / mL, and the volume ratio of the first filtrate to the organic solvent methyl isobutyl ketone is 1:(1-4). The p-toluenesulfonic acid solution in the first filtrate and the aluminum chloride synergistically promote the conversion of xylose to furfural. Under these limited conditions, the conversion rate of furfural is the highest.

[0015] In one or more embodiments, in step (2), the second heat treatment temperature is 140-190°C, and the reaction time is 0.5-2 hours. Under these conditions, the furfural conversion rate is the highest.

[0016] In one or more embodiments, in step (3), the temperature of the lithium chloride solution is 120-150° C., and the concentration of lithium chloride in the lithium chloride solution is 45-55 wt %.

[0017] In one or more embodiments, in step (3), the solid-to-liquid ratio of the first residue to the lithium chloride solution is 1:(15-30). Under this limited condition, the degradation of cellulose into controllable oligomers can be effectively regulated to avoid excessive hydrolysis to form monosaccharides.

[0018] In one or more embodiments, in step (3), the mass ratio of the first residue to the HZSM-5 molecular sieve is 1:(2.5-4), preferably 1:3. Under these limited conditions, the degradation of cellulose into controllable oligomers can be effectively controlled to avoid excessive hydrolysis to form monosaccharides.

[0019] In one or more embodiments, in step (3), the third heat treatment temperature is 120-150°C, and the reaction time is 10 minutes to 3 hours. Under these limited conditions, the degradation of cellulose into controllable oligomers can be effectively regulated to avoid excessive hydrolysis to form monosaccharides.

[0020] In one or more embodiments, in step (4), the degree of polymerization of the solid oligoglucose obtained is 3-11, and the yield of the solid oligoglucose is 75-80 wt% (based on the mass of cellulose in the reaction raw materials).

[0021] In one or more embodiments, in step (5), the pH of the mixture of dioxane and water is 1.5 to 3, preferably 2.

[0022] In one or more embodiments, in step (5), the volume ratio of dioxane to water in the mixture of dioxane and water is (8.5-10):1, preferably 9:1.

[0023] In one or more embodiments, in step (5), the solid-to-liquid ratio of the second residue to the mixed solution of dioxane and water is 1:(19-21).

[0024] In one or more embodiments, in step (5), the method for removing the solvent dioxane is rotary evaporation.

[0025] The beneficial effects of the present invention are: (1) The present invention realizes the co-production of furfural, oligosaccharides and lignin from agricultural and forestry wastes. The specific process is as follows: agricultural and forestry wastes containing cellulose, hemicellulose and lignin are mixed with p-toluenesulfonic acid solution and then subjected to the first heat treatment. p-toluenesulfonic acid can catalyze the full hydrolysis of hemicellulose into xylose. By limiting the p-toluenesulfonic acid concentration and the temperature and time of the first heat treatment, the hemicellulose can be fully hydrolyzed into xylose while retaining most of the cellulose and lignin. The first filtrate contains xylose and p-toluenesulfonic acid, and most of the cellulose and lignin are retained in the first residue. The p-toluenesulfonic acid solution in the first filtrate and aluminum chloride synergistically promote the conversion of xylose into furfural. At the same time, an organic solvent, methyl isobutyl ketone, is added, and the furfural produced by the reaction enters the organic phase, promoting the forward reaction to increase the furfural yield and inhibiting the side reaction. The organic phase is collected and distilled to obtain furfural. Lithium chloride and HZSM-5 molecular sieve are added to the first residue that retains most of the cellulose and lignin. H in the molecular sieve in the solution system + Can be with Li + The method comprises the steps of: exchanging the cellulose and promoting the hydrolysis of cellulose, so that the combination of lithium chloride solution and HZSM-5 molecular sieve can efficiently depolymerize cellulose into controllable oligomers, filtering to obtain a second filtrate containing oligoglucose and a second residue containing lignin; utilizing the low solubility of oligoglucose in methanol, precipitating the oligoglucose, and obtaining solid oligoglucose through centrifugation, filtration, washing and drying; dissolving the lignin in the second residue in acidic dioxane / water, filtering and purifying again, collecting a third filtrate containing only lignin, and removing the solvent dioxane to obtain lignin.

[0026] (2) The combination of lithium chloride solution and HZSM-5 molecular sieve can efficiently depolymerize cellulose into controllable oligomers, while limiting the temperature and time of the second heat treatment to avoid excessive hydrolysis to form monosaccharides; the degree of polymerization of oligosaccharides can be controlled in the range of 3~11, with good functionality.

[0027] (3) The present invention realizes the separation and high-value utilization of hemicellulose, cellulose and lignin in agricultural and forestry wastes, converting them into furfural, oligosaccharides and lignin respectively, greatly improving the resource utilization rate of agricultural and forestry wastes and reducing resource waste.

[0028] (4) The reagents used in the present invention are environmentally friendly and reduce the generation of waste throughout the entire production process, thus avoiding the pollution to the environment caused by traditional agricultural and forestry waste treatment methods (such as incineration), which is in line with the concepts of green chemistry and sustainable development.

[0029] (5) The process of the present invention is relatively simple, easy to operate and control, and has low production costs. By converting agricultural and forestry waste into high-value-added products, it can significantly improve the economic benefits of the enterprise and has good market application prospects. DETAILED DESCRIPTION

[0030] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0031] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0032] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0033] Example 1 (1) Grind the corn stalks to a particle size of 0.3-2 mm, dry them at 100 °C, and set aside; (2) The crushed corn straw was placed in a high-pressure reactor, and 1 wt% p-toluenesulfonic acid solution was added. The solid-liquid ratio of corn straw to p-toluenesulfonic acid solution was 1:8. The reaction was carried out at 150 °C for 1 h, and the mixture was continuously stirred at a speed of 200 r / min during the reaction. After the reaction, solid-liquid separation was performed by filtration to obtain a first filtrate and a first residue. The yield of xylose in the first filtrate was 91% (based on the hemicellulose in the raw material). The retention rate of cellulose in the first residue was 95.5%, and the retention rate of lignin was 97.1%. (3) Aluminum chloride and an organic solvent, methyl isobutyl ketone, were added to the first filtrate. The concentration of aluminum chloride in the first filtrate was 5 mg / mL, and the volume ratio of the first filtrate to the organic solvent, methyl isobutyl ketone, was 1:1. The reaction was carried out at 150°C for 0.5 h. After the reaction was completed, the organic phase and the aqueous phase were separated. Furfural was mainly present in the organic phase. The organic phase was collected and distilled to obtain furfural. Liquid chromatography analysis showed that the yield of furfural was 82% (based on the xylose content in the first filtrate). (4) The first residue was repeatedly washed with deionized water until neutral, added to a lithium chloride solution, and HZSM-5 molecular sieve was added. The lithium chloride concentration in the lithium chloride solution (temperature was 120 °C) was 50 wt%, and the solid-liquid ratio of the first residue to the lithium chloride solution was 1:20; the mass ratio of the first residue to the HZSM-5 molecular sieve was 1:3; the reaction was carried out at 120 °C for 30 min to catalyze the hydrolysis of cellulose to generate oligosaccharides and retain lignin. After the reaction, the solid and liquid were separated to obtain a second filtrate containing oligosaccharides and a second residue containing lignin and HZSM-5 molecular sieve; the second filtrate was concentrated and methanol was added (the volume ratio of the concentrated filtrate to methanol was 1:5), and the oligosaccharides were precipitated. After centrifugation, filtration, washing and drying, solid oligosaccharides were obtained; the yield of oligosaccharides was 76.3%, and the degree of polymerization was found to range from 3 to 11 by ion chromatography, of which oligosaccharides with a degree of polymerization of 3 to 8 accounted for 64.5% of the total; (5) A mixture of dioxane and water (pH 2, volume ratio of dioxane to water 9:1) was added to the second residue, and the solid-liquid ratio of the second residue to the acidic dioxane / water was 1:20; after sufficient dissolution, the solid and liquid were separated, and the third filtrate containing lignin was collected, and the solvent dioxane was removed by rotary evaporation to obtain lignin; the purity of the lignin was 93%, and the yield of lignin was 91% (based on the content of lignin in the raw material).

[0034] Example 2 (1) Grind the wheat straw into a particle size of 0.3-2 mm, dry it at 100 °C, and set aside; (2) Wheat straw was placed in a high-pressure reactor, and 1 wt% p-toluenesulfonic acid solution was added, with a solid-liquid ratio of wheat straw to p-toluenesulfonic acid solution of 1:10; the reaction was carried out at 140 °C for 1.5 h, and stirring was continued at a speed of 200 r / min during the reaction; after the reaction, solid-liquid separation was performed by filtration to obtain a first filtrate and a first residue; the yield of xylose in the first filtrate was 92% (based on the hemicellulose in the raw material); the retention rate of cellulose in the first residue was 94.2%, and the retention rate of lignin was 96.2%; (3) Aluminum chloride and an organic solvent, methyl isobutyl ketone, were added to the first filtrate. The concentration of aluminum chloride in the first filtrate was 7 mg / mL, and the volume ratio of the first filtrate to the organic solvent, methyl isobutyl ketone, was 1:2. The reaction was carried out at 160°C for 1 hour. After the reaction, the organic phase and the aqueous phase were separated. Furfural was mainly present in the organic phase. The organic phase was collected and distilled to obtain furfural. Liquid chromatography analysis showed that the yield of furfural was 83% (based on the xylose content in the first filtrate). (4) The first residue was repeatedly washed with deionized water until neutral, added to a lithium chloride solution, and HZSM-5 molecular sieve was added. The lithium chloride concentration in the lithium chloride solution (temperature was 120 °C) was 52 wt%, and the solid-liquid ratio of the first residue to the lithium chloride solution was 1:25; the mass ratio of the first residue to the HZSM-5 molecular sieve was 1:3; the reaction was carried out at 130 °C for 20 min to catalyze the hydrolysis of cellulose to generate oligosaccharides and retain lignin. After the reaction, the solid and liquid were separated to obtain a second filtrate containing oligosaccharides and a second residue containing lignin and HZSM-5 molecular sieve; the second filtrate was concentrated and methanol was added (the volume ratio of the concentrated filtrate to methanol was 1:5), and the oligosaccharides were precipitated. After centrifugation, filtration, washing and drying, solid oligosaccharides were obtained; the yield of oligosaccharides was 76.8%, and the degree of polymerization was found to range from 3 to 11 by ion chromatography, of which oligosaccharides with a degree of polymerization of 3 to 8 accounted for 65.6% of the total; (5) A mixture of dioxane and water (pH 2, volume ratio of dioxane to water 9:1) was added to the second residue, and the solid-liquid ratio of the second residue to the acidic dioxane / water was 1:20; after sufficient dissolution, the solid and liquid were separated, and the third filtrate containing lignin was collected, and the solvent dioxane was removed by rotary evaporation to obtain lignin; the purity of the lignin was 94%, and the yield of lignin was 90.5% (based on the content of lignin in the raw material).

[0035] Example 3 (1) Crush the bamboo into particles with a size of 0.3-2 mm, dry them at 100 °C, and set aside; (2) The crushed bamboo was placed in a high-pressure reactor, and 1 wt% p-toluenesulfonic acid solution was added. The solid-liquid ratio of corn straw to p-toluenesulfonic acid solution was 1:15. The reaction was carried out at 160 °C for 0.5 h, and the mixture was stirred at a speed of 200 r / min during the reaction. After the reaction, solid-liquid separation was performed by filtration to obtain a first filtrate and a first residue. The yield of xylose in the first filtrate was 96% (based on the hemicellulose in the raw material). The retention rate of cellulose in the first residue was 96.3%, and the retention rate of lignin was 93.3%. (3) Aluminum chloride and an organic solvent, methyl isobutyl ketone, were added to the first filtrate. The concentration of aluminum chloride in the first filtrate was 6 mg / mL, and the volume ratio of the first filtrate to the organic solvent, methyl isobutyl ketone, was 1:3. The reaction was carried out at 170°C for 1 hour. After the reaction, the organic phase and the aqueous phase were separated. Furfural was mainly present in the organic phase. The organic phase was collected and distilled to obtain furfural. The yield of furfural was 88% (based on the xylose content in the first filtrate) as determined by liquid chromatography. (4) The first residue was repeatedly washed with deionized water until neutral, added to a lithium chloride solution, and HZSM-5 molecular sieve was added. The lithium chloride concentration in the lithium chloride solution (temperature was 120 °C) was 55 wt%, and the solid-liquid ratio of the first residue to the lithium chloride solution was 1:30; the mass ratio of the first residue to the HZSM-5 molecular sieve was 1:3; the reaction was carried out at 120 °C for 30 min to catalyze the hydrolysis of cellulose to generate oligosaccharides and retain lignin. After the reaction, the solid and liquid were separated to obtain a second filtrate containing oligosaccharides and a second residue containing lignin and HZSM-5 molecular sieve; the second filtrate was concentrated and methanol was added (the volume ratio of the concentrated filtrate to methanol was 1:5), and the oligosaccharides were precipitated. After centrifugation, filtration, washing and drying, solid oligosaccharides were obtained; the yield of oligosaccharides was 77.1%, and the degree of polymerization was found to range from 3 to 11 by ion chromatography, of which oligosaccharides with a degree of polymerization of 3 to 8 accounted for 68.3% of the total; (5) A mixture of dioxane and water (pH 2, volume ratio of dioxane to water 9:1) was added to the second residue, and the solid-liquid ratio of the second residue to the acidic dioxane / water was 1:20; after sufficient dissolution, the solid and liquid were separated, and the third filtrate containing lignin was collected, and the solvent dioxane was removed by rotary evaporation to obtain lignin; the purity of the lignin was 97%, and the yield of lignin was 90.7% (based on the content of lignin in the raw material).

[0036] Comparative Example 1 Compared with Example 3, the concentration of the toluenesulfonic acid solution in step (2) was reduced to 0.2 wt %, and the other conditions were exactly the same as those in Example 3.

[0037] The first filtrate and the first residue were tested, and the results showed that the yield of xylose was 65%, the cellulose retention rate was 99.1%, and the lignin retention rate was 98.6%, indicating that the hemicellulose hydrolysis was insufficient, affecting the yield of subsequent furfural production. In addition, in the subsequent production of oligosaccharides, the solid residue contained a large amount of hemicellulose hydrolysis products in the hydrolyzate due to insufficient hydrolysis of hemicellulose, affecting the cellulose hydrolysis efficiency and the yield of oligosaccharides.

[0038] Comparative Example 2 Compared with Example 3, the concentration of the toluenesulfonic acid solution in step (2) is increased to 10 wt %, and the other conditions are exactly the same as those in Example 3.

[0039] Testing of the first filtrate and first residue revealed xylose yields of 98% and glucose yields of 23%. Cellulose retention was 72.8%, and lignin retention was 86.5%. This indicates that higher p-toluenesulfonic acid concentrations can fully degrade hemicellulose, but also lead to further degradation of cellulose and lignin, resulting in reduced retention. Increased glucose in the hydrolyzate affects furfural yields and also reduces subsequent oligosaccharide and lignin yields.

[0040] Comparative Example 3 Compared with Example 3, this comparative example does not add HZSM-5 molecular sieve in step (4), and other conditions are exactly the same as those in Example 3.

[0041] The yield of oligosaccharide was 34.6%. This was mainly due to the lack of HZSM-5 molecular sieve. + , resulting in lower cellulose hydrolysis efficiency.

[0042] Comparative Example 4 Compared with Example 3, the temperature of the heat treatment in step (2) is reduced to 100°C, and the other conditions are exactly the same as those in Example 3.

[0043] Testing of the first filtrate and the first residue showed a xylose yield of 23%, a cellulose retention rate of 98.6%, and a lignin retention rate of 97.8%. This indicates that the low temperature and inadequate hemicellulose hydrolysis resulted in a low xylose yield.

[0044] Comparative Example 5 Compared with Example 3, the temperature of the heat treatment in step (2) is increased to 250°C, and the other conditions are exactly the same as those in Example 3.

[0045] Testing of the first filtrate and first residue revealed a xylose yield of 73%, a glucose yield of 62%, a cellulose retention rate of 32%, and a lignin retention rate of 65.7%. This indicates that the high temperature led to further conversion of the generated xylose, while also causing further degradation of cellulose into glucose and lignin, significantly reducing the retention rates of cellulose and lignin.

[0046] Comparative Example 6 Compared with Example 3, the temperature of the heat treatment in step (3) is reduced to 100°C, and the other conditions are exactly the same as those in Example 3.

[0047] The yield of furfural was 23.8%, indicating that the temperature was low, resulting in a low xylose conversion rate.

[0048] Comparative Example 7 Compared with Example 3, the temperature of the heat treatment in step (3) is increased to 250°C, and the other conditions are exactly the same as those in Example 3.

[0049] The yield of furfural was 61.8%, indicating that the high temperature caused side reactions, further degradation or polymerization of furfural, and reduced the yield of furfural.

[0050] Comparative Example 8 Compared with Example 3, in step (4), the concentration of lithium chloride was adjusted to 30 wt %, and the other conditions were exactly the same as those in Example 3.

[0051] The yield of oligosaccharides was 12%, indicating that the concentration of lithium chloride was low and the cellulose was not fully hydrolyzed.

[0052] Comparative Example 9 Compared with Example 3, in this comparative example, the temperature of the heat treatment in step (4) is reduced to 100°C, and the other conditions are exactly the same as those in Example 3.

[0053] The yield of oligosaccharides was 38%, indicating that the temperature was low, the degree of cellulose hydrolysis was insufficient, and the yield of oligosaccharides was reduced.

[0054] Comparative Example 10 Compared with Example 3, in this comparative example, the temperature of the heat treatment in step (4) is increased by 250°C, and the other conditions are exactly the same as those in Example 3.

[0055] No oligosaccharides were detected in the hydrolyzate, and the product was mainly glucose, indicating that the temperature was too high, resulting in sufficient hydrolysis of cellulose, and the oligosaccharides produced during the reaction were further degraded into glucose.

[0056] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for co-producing furfural, oligoglucose and lignin using agricultural and forestry wastes, characterized in that: The steps include: (1) mixing agricultural and forestry waste with a p-toluenesulfonic acid solution and performing a first heat treatment, and performing solid-liquid separation after the reaction to obtain a first filtrate and a first residue; wherein the agricultural and forestry waste contains cellulose, hemicellulose, and lignin; (2) adding aluminum chloride and an organic solvent, methyl isobutyl ketone, to the first filtrate, mixing them evenly and then performing a second heat treatment. After the reaction is completed, the organic phase and the aqueous phase are separated, the organic phase is collected, and furfural is obtained by distillation; (3) The first residue is repeatedly washed with deionized water until neutral, added to a lithium chloride solution, and HZSM-5 molecular sieve is added. After mixing evenly, a third heat treatment is performed. After the reaction is completed, solid-liquid separation is performed to obtain a second filtrate and a second residue; (4) After the second filtrate is concentrated, methanol is added and the precipitate is collected to obtain solid oligosaccharide; (5) A mixture of dioxane and water is added to the second residue, and after it is fully dissolved, the solid and liquid are separated, and the third filtrate is collected. The solvent dioxane is removed to obtain lignin.

2. The method according to claim 1, wherein The agricultural and forestry wastes include one or more of corn stalks, corn cobs, rice straw, sorghum straw, bagasse, wheat straw, firewood, bark, bamboo, peanut shells, branches, wood curls and wood shavings; Alternatively, the agricultural and forestry waste is pretreated before reacting with the p-toluenesulfonic acid solution, and the pretreatment method includes: crushing the agricultural and forestry waste to a particle size of 0.3-2 mm, and then drying it.

3. The method according to claim 1, wherein In step (1), the concentration of the p-toluenesulfonic acid solution is 0.5-1.5 wt%; Alternatively, in step (1), the solid-liquid ratio of the agricultural and forestry waste to the p-toluenesulfonic acid solution is 1:(5-15).

4. The method according to claim 1, wherein In step (1), the temperature of the first heat treatment is 140-190° C., the reaction time is 0.5-1.5 h, and stirring is continued at a speed of 120-200 r / min during the reaction.

5. The method according to claim 1, wherein In step (2), the concentration of aluminum chloride in the first filtrate is 5-10 mg / mL, and the volume ratio of the first filtrate to the organic solvent methyl isobutyl ketone is 1:(1-4); Alternatively, in step (2), the second heat treatment temperature is 140-190°C, and the reaction time is 0.5-2 h.

6. The method according to claim 1, wherein In step (3), the temperature of the lithium chloride solution is 120-150°C, and the concentration of lithium chloride in the lithium chloride solution is 45-55 wt%; Alternatively, in step (3), the solid-liquid ratio of the first residue to the lithium chloride solution is 1:(15-30).

7. The method according to claim 1, wherein In step (3), the mass ratio of the first residue to the HZSM-5 molecular sieve is 1:(2.5-4), preferably 1:

3.

8. The method according to claim 1, wherein In step (3), the third heat treatment temperature is 120-150°C, and the reaction time is 10 min-3 h.

9. The method according to claim 1, wherein In step (4), the degree of polymerization of the obtained solid oligoglucose is 3 to 11.

10. The method according to claim 1, wherein In step (5), the pH of the mixture of dioxane and water is 1.5 to 3, preferably 2; Alternatively, in step (5), the volume ratio of dioxane to water in the mixture of dioxane and water is (8.5-10):1, preferably 9:1; In step (5), the solid-liquid ratio of the second residue to the mixed solution of dioxane and water is 1:(19-21).