A method for co-production of furfural, oligomeric glucose and lignin using agroforestry waste

Abstract

This invention relates to the field of agricultural and forestry waste treatment and high-value utilization technology, specifically to a method for co-producing furfural, oligodextrose, and lignin from agricultural and forestry waste. The method includes the following steps: mixing agricultural and forestry waste with a p-toluenesulfonic acid solution and performing a first heat treatment; after the reaction, solid-liquid separation is performed to obtain a first filtrate and a first residue; adding aluminum chloride and methyl isobutyl ketone to the first filtrate and performing a second heat treatment; after the reaction, separating the organic and aqueous phases, collecting the organic phase, and distilling to obtain furfural; washing the first residue to neutrality, adding it to a lithium chloride solution, and adding HZSM-5 molecular sieves for a third heat treatment; after the reaction, solid-liquid separation is performed to obtain a second filtrate and a second residue; concentrating the second filtrate and adding methanol, collecting the precipitate as oligodextrose; adding acidic dioxane / water to the second residue, dissolving it completely, performing solid-liquid separation, collecting the third filtrate, and removing the dioxane solvent to obtain lignin.

Description

Technical Field

[0001] This invention relates to the field of agricultural and forestry waste treatment and high-value utilization technology, specifically to a method for co-producing furfural, oligodextrose and lignin from agricultural and forestry waste. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Due to the limited storage of fossil fuels and the various environmental and economic problems caused by their extensive use, finding alternatives and developing renewable energy has become a crucial direction for global energy development. Biomass energy, with its advantages of renewability and environmental friendliness, has become an important means of addressing both energy security and climate change. Agricultural and forestry waste contains abundant cellulose and hemicellulose, among other usable substances, making it an important biomass resource. Utilizing agricultural and forestry waste as an energy source is one of the hot research topics in the field of renewable energy.

[0004] Agricultural and forestry wastes are rich in carbohydrates (cellulose and hemicellulose), which, after certain processing, can yield oligosaccharides or biomass monosaccharides (mainly glucose and xylose). Using biomass monosaccharide molecules as starting materials, under suitable conditions, they can be converted into furfural, an important platform compound. Furfural is an important precursor to furan compounds and can be converted into widely used bulk chemicals such as furfuryl alcohol and tetrahydrofuran. Oligosaccharides, as functional oligosaccharides with multiple physiological functions, are increasingly in demand in the food and pharmaceutical fields. Simultaneously, agricultural and forestry wastes also contain a large amount of lignin, which has abundant aromatic ring structures and is an ideal renewable alternative to petroleum-based aromatic compounds (such as phenol, benzene, toluene, xylene, etc.). Collecting 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 waste, the resource utilization value of agricultural and forestry waste can be significantly improved.

[0006] However, traditional furfural production often uses sulfuric acid to catalyze xylose dehydration, but the strong acid leads to increased side reactions, low furfural yield (usually <70%), and generates large amounts of acidic wastewater, resulting in high pollution treatment 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 it is easy to over-degrade into glucose monomers (with low economic value) or leave behind incompletely depolymerized fiber fragments. In conventional organic solvent or alkaline extraction processes for lignin, lignin is prone to condensation denaturation, resulting in low yield (generally <80%) and insufficient purity (containing polysaccharides and ash impurities), making it difficult to meet the needs of material applications. Currently, most technologies only target a single component (such as producing only furfural or ethanol), failing to achieve the integrated co-production of oligosaccharides, furfural, and lignin, resulting in resource fragmentation and the accumulation of secondary waste. Summary of the Invention

[0007] To overcome the above problems, the present invention provides a method for co-producing furfural, oligodextrose and lignin using agricultural and forestry waste.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for co-producing furfural, oligodextrose, and lignin from agricultural and forestry waste, comprising the following steps:

[0010] (1) After mixing agricultural and forestry waste with p-toluenesulfonic acid solution, a first heat treatment is performed. After the reaction is completed, solid and liquid are separated to obtain a first filtrate and a first residue; wherein the agricultural and forestry waste contains cellulose, hemicellulose and lignin.

[0011] (2) Add aluminum chloride and organic solvent methyl isobutyl ketone to the first filtrate, mix well and then perform a second heat treatment. After the reaction is completed, separate the organic phase and the aqueous phase, collect the organic phase and distill to obtain furfural.

[0012] (3) The first residue was repeatedly washed with deionized water until neutral, added to lithium chloride solution, and HZSM-5 molecular sieve was added. After mixing evenly, a third heat treatment was performed. After the reaction was completed, solid and liquid were separated to obtain the second filtrate and the second residue.

[0013] (4) After the second filtrate is concentrated, methanol is added, and the precipitate is collected to obtain solid oligosaccharides;

[0014] (5) Add a mixture of dioxane and water to the second residue, dissolve it completely, separate the solid and liquid, collect the third filtrate, remove the solvent dioxane to obtain lignin.

[0015] In one or more embodiments, the agricultural and forestry waste includes one or more of the following: corn stalks, corn cobs, rice stalks, sorghum stalks, sugarcane bagasse, wheat stalks, firewood, bark, bamboo, peanut shells, branches, wood shavings, and wood chips.

[0016] In one or more embodiments, agricultural and forestry waste is pretreated before reacting with p-toluenesulfonic acid solution. The pretreatment method includes pulverizing the agricultural and forestry waste to a particle size of 0.3-2 mm, followed by drying. Pulverizing the agricultural and forestry waste increases its specific surface area, thereby accelerating the subsequent reaction rate.

[0017] 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, the hemicellulose hydrolysis will be insufficient, affecting the yield of subsequent furfural production. Furthermore, in the subsequent production of oligosaccharides, the first residue will contain a large amount of hemicellulose hydrolysate in the hydrolysate due to insufficient hydrolysis of hemicellulose, affecting the cellulose hydrolysis efficiency and the yield of oligosaccharides. Conversely, if the concentration of the p-toluenesulfonic acid solution is too high, it will lead to further degradation of cellulose and lignin, resulting in a decrease in retention rate. The increase in glucose in the hydrolysate will affect the yield of furfural and will also lead to a decrease in the yield of subsequent oligosaccharides and lignin.

[0018] In one or more embodiments, in step (1), the solid-liquid ratio of agricultural and forestry waste to p-toluenesulfonic acid solution is 1:(5~15). Within this ratio range, the agricultural and forestry waste can react fully with the p-toluenesulfonic acid solution.

[0019] 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 h, and the mixture is continuously stirred 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.

[0020] 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 synergistically promotes the conversion of xylose to furfural with aluminum chloride, and under these conditions, the conversion rate of furfural is the highest.

[0021] 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 h. Under these conditions, the conversion rate of furfural is the highest.

[0022] In one or more embodiments, in step (3), the temperature of the lithium chloride solution is 120~150 ℃, and the concentration of lithium chloride in the lithium chloride solution is 45~55 wt%.

[0023] In one or more embodiments, in step (3), the solid-liquid ratio of the first residue to the lithium chloride solution is 1:(15~30). Under these conditions, the degradation of cellulose into controllable oligomers can be effectively regulated, avoiding excessive hydrolysis to generate monosaccharides.

[0024] 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 conditions, the degradation of cellulose into controllable oligomers can be effectively regulated, avoiding excessive hydrolysis to generate monosaccharides.

[0025] In one or more embodiments, in step (3), the temperature of the third heat treatment is 120~150 °C, and the reaction time is 10 min~3 h. Under these conditions, the degradation of cellulose into controllable oligomers can be effectively regulated, avoiding excessive hydrolysis to generate monosaccharides.

[0026] In one or more embodiments, in step (4), the degree of polymerization of solid oligosaccharides is 3 to 11, and the yield of solid oligosaccharides is 75-80 wt% (based on the mass of cellulose in the reaction raw materials).

[0027] In one or more embodiments, in step (5), the pH of the mixture of dioxane and water is 1.5 to 3, preferably 2.

[0028] 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.

[0029] In one or more embodiments, in step (5), the solid-liquid ratio of the second residue to the mixture of dioxane and water is 1:(19~21).

[0030] In one or more embodiments, in step (5), the method for removing the solvent dioxane is rotary evaporation.

[0031] The beneficial effects of this invention are as follows:

[0032] (1) In this invention, furfural, oligosaccharides and lignin are co-produced from agricultural and forestry waste. The specific process is as follows: Agricultural and forestry waste containing cellulose, hemicellulose and lignin is mixed with p-toluenesulfonic acid solution and subjected to a first heat treatment. P-toluenesulfonic acid can catalyze the complete hydrolysis of hemicellulose into xylose. By limiting the concentration of p-toluenesulfonic acid and the temperature and time of the first heat treatment, 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 the first residue retains most of the cellulose and lignin. The p-toluenesulfonic acid solution in the first filtrate and aluminum chloride synergistically promote the conversion of xylose into furfural. At the same time, the organic solvent methyl isobutyl ketone is added. The furfural produced by the reaction enters the organic phase, promotes the forward reaction, increases the furfural yield, and inhibits 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. In the solution system, the H in the molecular sieve + Can be with Li + The exchange process promotes cellulose hydrolysis. Therefore, the combination of lithium chloride solution and HZSM-5 molecular sieve can efficiently depolymerize cellulose into controllable oligomers. The second filtrate containing oligosaccharides and the second residue containing lignin are obtained by filtration. Taking advantage of the low solubility of oligosaccharides in methanol, the oligosaccharides are precipitated. After centrifugation, filtration, washing and drying, solid oligosaccharides are obtained. The lignin in the second residue is dissolved in acidic dioxane / water. After filtration and purification again, the third filtrate containing only lignin is collected. The solvent dioxane is removed to obtain lignin.

[0033] (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 and the generation of monosaccharides; the degree of polymerization of oligosaccharides can be controlled within the range of 3 to 11, and it has good functionality.

[0034] (3) This invention realizes the separation and high-value utilization of hemicellulose, cellulose and lignin in agricultural and forestry waste, which are converted into furfural, oligodextrose and lignin respectively, greatly improving the resource utilization rate of agricultural and forestry waste and reducing resource waste.

[0035] (4) The reagents used in this invention are environmentally friendly, and the entire production process reduces the generation of waste, avoiding the pollution caused to the environment by traditional agricultural and forestry waste treatment methods (such as incineration), which is in line with the concept of green chemistry and sustainable development.

[0036] (5) The process of this invention is relatively simple, easy to operate and control, and has low production cost. By converting agricultural and forestry waste into high value-added products, it can significantly improve the economic benefits of enterprises and has good market application prospects. Detailed Implementation

[0037] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0039] To enable those skilled in the art to better 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.

[0040] Example 1

[0041] (1) Crush the corn stalks to a particle size of 0.3~2mm, dry them at 100℃, and set aside for later use;

[0042] (2) The crushed corn stalks were put into a high-pressure reactor and 1 wt% p-toluenesulfonic acid solution was added. The solid-liquid ratio of corn stalks 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 200 r / min during the reaction. After the reaction, the solid and liquid were separated by filtration to obtain the first filtrate and the first residue. The xylose yield in the first filtrate was 91% (based on the hemicellulose in the raw material). The cellulose retention rate in the first residue was 95.5%, and the lignin retention rate was 97.1%.

[0043] (3) Add aluminum chloride and organic solvent methyl isobutyl ketone to the first filtrate. The concentration of aluminum chloride in the first filtrate is 5 mg / mL, and the volume ratio of the first filtrate to the organic solvent methyl isobutyl ketone is 1:1. React at 150 °C for 0.5 h. After the reaction is complete, separate the organic phase and the aqueous phase. Furfural is mainly present in the organic phase. Collect the organic phase and distill to obtain furfural. The yield of furfural was 82% by liquid chromatography (based on the xylose content in the first filtrate).

[0044] (4) The first residue was repeatedly washed with deionized water until neutral, added to lithium chloride solution, and HZSM-5 molecular sieve was added. The lithium chloride concentration in the lithium chloride solution (temperature 120 ℃) ​​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 ℃ for 30 min to catalyze the hydrolysis of cellulose to generate oligosaccharides and retain lignin. After the reaction was completed, the solid and liquid were separated to obtain the second filtrate containing oligosaccharides and the second residue containing lignin and HZSM-5 molecular sieve; the second filtrate was concentrated and methanol was added (the volume ratio of concentrated filtrate to methanol was 1:5), and oligosaccharides precipitated out. After centrifugation, filtration, washing and drying, solid oligosaccharides were obtained; the yield of oligosaccharides was 76.3%, and the degree of polymerization ranged from 3 to 11 as determined by ion chromatography, of which oligosaccharides with a degree of polymerization of 3 to 8 accounted for 64.5% of the total;

[0045] (5) Add a mixture of dioxane and water to the second residue (pH 2, volume ratio of dioxane to water 9:1), the solid-liquid ratio of the second residue to acidic dioxane / water is 1:20; after complete dissolution, separate the solid and liquid, collect the third filtrate containing lignin, remove the solvent dioxane by rotary evaporation to obtain lignin; the purity of lignin is 93%, and the yield of lignin is 91% (based on the lignin content in the raw material).

[0046] Example 2

[0047] (1) Crush the wheat straw to a particle size of 0.3~2mm, dry it at 100℃, and set it aside for later use;

[0048] (2) Wheat straw was added to a high-pressure reactor, and 1 wt% p-toluenesulfonic acid solution was added. The solid-liquid ratio of wheat straw to p-toluenesulfonic acid solution was 1:10. The reaction was carried out at 140 °C for 1.5 h, and the mixture was continuously stirred at 200 r / min during the reaction. After the reaction, the solid and liquid were separated by filtration to obtain the first filtrate and the first residue. The xylose yield in the first filtrate was 92% (based on the hemicellulose in the raw material). The cellulose retention rate in the first residue was 94.2%, and the lignin retention rate was 96.2%.

[0049] (3) Add aluminum chloride and organic solvent methyl isobutyl ketone to the first filtrate. The concentration of aluminum chloride in the first filtrate is 7 mg / mL, and the volume ratio of the first filtrate to the organic solvent methyl isobutyl ketone is 1:2. React at 160 °C for 1 h. After the reaction is complete, separate the organic phase and the aqueous phase. Furfural is mainly present in the organic phase. Collect the organic phase and distill to obtain furfural. The yield of furfural was 83% by liquid chromatography (based on the xylose content in the first filtrate).

[0050] (4) The first residue was repeatedly washed with deionized water until neutral, added to lithium chloride solution, and HZSM-5 molecular sieve was added. The lithium chloride concentration in the lithium chloride solution (temperature 120 ℃) ​​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 ℃ for 20 min to catalyze the hydrolysis of cellulose to generate oligosaccharides and retain lignin. After the reaction was completed, the solid and liquid were separated to obtain the second filtrate containing oligosaccharides and the second residue containing lignin and HZSM-5 molecular sieve; the second filtrate was concentrated and methanol was added (the volume ratio of concentrated filtrate to methanol was 1:5), and oligosaccharides precipitated out. After centrifugation, filtration, washing and drying, solid oligosaccharides were obtained; the yield of oligosaccharides was 76.8%, and the degree of polymerization ranged from 3 to 11 as determined by ion chromatography, of which oligosaccharides with a degree of polymerization of 3 to 8 accounted for 65.6% of the total;

[0051] (5) Add a mixture of dioxane and water to the second residue (pH 2, volume ratio of dioxane to water 9:1), the solid-liquid ratio of the second residue to acidic dioxane / water is 1:20; after complete dissolution, separate the solid and liquid, collect the third filtrate containing lignin, remove the solvent dioxane by rotary evaporation to obtain lignin; the purity of lignin is 94%, and the yield of lignin is 90.5% (based on the lignin content in the raw material).

[0052] Example 3

[0053] (1) Crush the bamboo into particles with a diameter of 0.3~2mm and dry them at 100℃ for later use;

[0054] (2) The crushed bamboo was put into a high-pressure reactor and 1 wt% p-toluenesulfonic acid solution was added. The solid-liquid ratio of corn stalks to p-toluenesulfonic acid solution was 1:15. The reaction was carried out at 160 °C for 0.5 h, and the mixture was continuously stirred at 200 r / min during the reaction. After the reaction, the solid and liquid were separated by filtration to obtain the first filtrate and the first residue. The xylose yield in the first filtrate was 96% (based on the hemicellulose in the raw material). The cellulose retention rate in the first residue was 96.3%, and the lignin retention rate was 93.3%.

[0055] (3) Add aluminum chloride and organic solvent methyl isobutyl ketone to the first filtrate. The concentration of aluminum chloride in the first filtrate is 6 mg / mL, and the volume ratio of the first filtrate to the organic solvent methyl isobutyl ketone is 1:3. React at 170 °C for 1 h. After the reaction is complete, separate the organic phase and the aqueous phase. Furfural is mainly present in the organic phase. Collect the organic phase and distill to obtain furfural. The yield of furfural was 88% by liquid chromatography (based on the xylose content in the first filtrate).

[0056] (4) The first residue was repeatedly washed with deionized water until neutral, added to lithium chloride solution, and HZSM-5 molecular sieve was added. The lithium chloride concentration in the lithium chloride solution (temperature 120 ℃) ​​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 ℃ for 30 min, catalyzing the hydrolysis of cellulose to generate oligosaccharides and retaining lignin. After the reaction was completed, 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 concentrated filtrate to methanol was 1:5), and oligosaccharides precipitated out. After centrifugation, filtration, washing and drying, solid oligosaccharides were obtained; the yield of oligosaccharides was 77.1%, and the degree of polymerization ranged from 3 to 11 as determined by ion chromatography, of which oligosaccharides with a degree of polymerization of 3 to 8 accounted for 68.3% of the total;

[0057] (5) Add a mixture of dioxane and water to the second residue (pH 2, volume ratio of dioxane to water 9:1), the solid-liquid ratio of the second residue to acidic dioxane / water is 1:20; after complete dissolution, separate the solid and liquid, collect the third filtrate containing lignin, remove the solvent dioxane by rotary evaporation to obtain lignin; the purity of lignin is 97%, and the yield of lignin is 90.7% (based on the lignin content in the raw material).

[0058] Comparative Example 1

[0059] Compared with Example 3, the concentration of toluenesulfonic acid solution in step (2) of this comparative example is reduced to 0.2 wt%, while other conditions are exactly the same as in Example 3.

[0060] The first filtrate and the first residue were tested, and the results showed that the xylose yield was 65%, the cellulose retention rate was 99.1%, and the lignin retention rate was 98.6%. This indicates that the hemicellulose hydrolysis was insufficient, which affected the yield of subsequent furfural production. Furthermore, due to the insufficient hydrolysis of hemicellulose, the solid residue contained a large amount of hemicellulose hydrolysis products in the hydrolysate during the subsequent production of oligosaccharides, which affected the cellulose hydrolysis efficiency and the oligosaccharide yield.

[0061] Comparative Example 2

[0062] Compared with Example 3, the concentration of toluenesulfonic acid solution in step (2) of this comparative example is increased to 10 wt%, while other conditions are exactly the same as in Example 3.

[0063] Analysis of the first filtrate and the first residue revealed a xylose yield of 98% and a glucose yield of 23%; cellulose retention was 72.8%, and lignin retention was 86.5%. This indicates that a higher concentration of p-toluenesulfonic acid can adequately degrade hemicellulose, but it also leads to further degradation of cellulose and lignin, resulting in lower retention rates. Increased glucose in the hydrolysate affects the furfural yield and also reduces the yields of subsequent oligosaccharides and lignin.

[0064] Comparative Example 3

[0065] Compared with Example 3, this comparative example does not include HZSM-5 molecular sieve in step (4), but the other conditions are exactly the same as in Example 3.

[0066] The yield of oligosaccharides was tested to be 34.6%. This is mainly due to the absence of HZSM-5 molecular sieves, resulting in a lack of H+. + This results in low cellulose hydrolysis efficiency.

[0067] Comparative Example 4

[0068] Compared with Example 3, the temperature of the heat treatment in step (2) of this comparative example is reduced to 100 °C, while the other conditions are exactly the same as those in Example 3.

[0069] The first filtrate and the first residue were tested, and the xylose yield was 23%, the cellulose retention rate was 98.6%, and the lignin retention rate was 97.8%. This indicates that the low temperature resulted in incomplete hydrolysis of hemicellulose, leading to a low xylose yield.

[0070] Comparative Example 5

[0071] Compared with Example 3, the temperature of the heat treatment in step (2) of this comparative example is increased to 250 °C, while the other conditions are exactly the same as those in Example 3.

[0072] The first filtrate and the first residue were tested, and the yield of xylose was 73%, the yield of glucose was 62%, the retention rate of cellulose was 32%, and the retention rate of lignin was 65.7%. This indicates that excessively high temperature leads to further conversion of the generated xylose, and at the same time, high temperature also leads to further degradation of cellulose into glucose and degradation of lignin, resulting in a significant decrease in the retention rates of cellulose and lignin.

[0073] Comparative Example 6

[0074] Compared with Example 3, the temperature of the heat treatment in step (3) of this comparative example is reduced to 100 °C, while the other conditions are exactly the same as those in Example 3.

[0075] The yield of furfural was 23.8%, indicating that the low temperature led to a low xylose conversion rate.

[0076] Comparative Example 7

[0077] Compared with Example 3, the temperature of the heat treatment in step (3) of this comparative example is increased to 250 °C, while the other conditions are exactly the same as those in Example 3.

[0078] The yield of furfural was 61.8%, indicating that excessively high temperature caused side reactions, leading to further degradation or polymerization of furfural and a decrease in the yield.

[0079] Comparative Example 8

[0080] Compared with Example 3, in step (4), the concentration of lithium chloride was adjusted to 30 wt%, while other conditions were exactly the same as in Example 3.

[0081] The yield of oligosaccharides was 12%, indicating that the concentration of lithium chloride was low and the hydrolysis of cellulose was incomplete.

[0082] Comparative Example 9

[0083] Compared with Example 3, in step (4), the heat treatment temperature in this comparative example is reduced to 100 °C, while the other conditions are exactly the same as in Example 3.

[0084] The yield of oligosaccharides was 38%, indicating that the temperature was too low, the degree of cellulose hydrolysis was insufficient, and the yield of oligosaccharides was reduced.

[0085] Comparative Example 10

[0086] Compared with Example 3, in step (4), the temperature of the heat treatment was increased by 250 °C, while the other conditions were exactly the same as in Example 3.

[0087] No oligosaccharides were detected in the hydrolysate, and the main product was glucose, indicating that the high temperature led to complete hydrolysis of cellulose, and the oligosaccharides produced during the reaction were further degraded into glucose.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for co-producing furfural, oligosaccharides, and lignin from agricultural and forestry waste, characterized in that, Includes the following steps: (1) After mixing agricultural and forestry waste with p-toluenesulfonic acid solution, a first heat treatment is performed. After the reaction is completed, solid and liquid are separated to obtain a first filtrate and a first residue; wherein the agricultural and forestry waste contains cellulose, hemicellulose and lignin. (2) Add aluminum chloride and organic solvent methyl isobutyl ketone to the first filtrate, mix well and then perform a second heat treatment. After the reaction is completed, separate the organic phase and the aqueous phase, collect the organic phase and distill to obtain furfural. (3) The first residue was repeatedly washed with deionized water until neutral, added to lithium chloride solution, and HZSM-5 molecular sieve was added. After mixing evenly, a third heat treatment was performed. After the reaction was completed, solid and liquid were separated to obtain the second filtrate and the second residue. (4) After the second filtrate is concentrated, methanol is added, and the precipitate is collected to obtain solid oligosaccharides; (5) Add a mixture of dioxane and water to the second residue, dissolve it completely, separate the solid and liquid, collect the third filtrate, remove the solvent dioxane to obtain lignin; 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 agricultural and forestry waste to p-toluenesulfonic acid solution is 1:(5~15). 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 ℃, and the reaction time is 0.5~2 h; In step (1), the temperature of the first heat treatment is 140~190 ℃, the reaction time is 0.5~1.5 h, and the reaction is continuously stirred at a speed of 120~200 r / min. In step (3), the temperature of the lithium chloride solution is 120~150 ℃, and the lithium chloride concentration 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).

2. The method as described in claim 1, characterized in that, The agricultural and forestry wastes include one or more of the following: corn stalks, corn cobs, rice stalks, sorghum stalks, sugarcane bagasse, wheat stalks, firewood, bark, bamboo, peanut shells, branches, wood shavings, and wood chips. Alternatively, agricultural and forestry waste may be pretreated before reacting with p-toluenesulfonic acid solution. 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 as described in claim 1, characterized in that, In step (3), the mass ratio of the first residue to the HZSM-5 molecular sieve is 1:(2.5~4).

4. The method as described in claim 3, characterized in that, In step (3), the mass ratio of the first residue to the HZSM-5 molecular sieve is 1:

3.

5. The method as described in claim 1, characterized in that, In step (3), the temperature of the third heat treatment is 120~150℃, and the reaction time is 10min~3h.

6. The method as described in claim 1, characterized in that, In step (4), the degree of polymerization of the obtained solid oligosaccharide is 3 to 11.

7. The method as described in claim 1, characterized in that, In step (5), the pH of the mixture of dioxane and water is 1.5~3; Alternatively, in step (5), the volume ratio of dioxane to water in the mixture of dioxane and water is (8.5~10):1; In step (5), the solid-liquid ratio of the second residue to the mixture of dioxane and water is 1:(19~21).

8. The method as described in claim 7, characterized in that, In step (5), the pH of the mixture of dioxane and water is 2; or, in step (5), the volume ratio of dioxane to water in the mixture of dioxane and water is 9:1.