A method for co-producing furfural, 5-hydroxymethylfurfural and lignin from straw.

Abstract

This invention provides a method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw. The method includes: Step 1, mixing straw with acid solution A and heating the mixture to react, followed by solid-liquid separation to obtain cellulose solid and liquid phase one; Step 2, adding water to liquid phase one obtained in Step 1 to precipitate lignin, followed by solid-liquid separation to obtain lignin solid and liquid phase two, and heating liquid phase two to react to obtain a furfural-containing solution; Step 3, mixing the cellulose obtained in Step 1 with acid solution B and a catalyst and heating the mixture to react, followed by solid-liquid separation to obtain an undissolved straw solid phase and a liquid phase containing 5-hydroxymethylfurfural. The method provided by this invention produces few byproducts, and the obtained furfural and 5-hydroxymethylfurfural have good purity and conversion rates.

Description

Technical Field

[0001] This invention relates to the field of biomass energy utilization technology, and more specifically, to a method for preparing furfural, 5-hydroxymethylfurfural and lignin by co-producing them from straw. Background Technology

[0002] Furfural and 5-hydroxymethylfurfural are important bio-based platform compounds. Furfural is an intermediate raw material for the preparation of succinaldehyde, furanyl acrylate, furfurylamine fumarate, adipic acid, and furfuryl alcohol; it can also be used to synthesize fine chemicals such as pharmaceuticals, pesticides, veterinary drugs, dyes, fragrances, rubber additives, and preservatives. 5-hydroxymethylfurfural is an important furan compound with excellent chemical properties and is widely used in pharmaceuticals, chemicals, and energy fields. It is one of the ten most important platform chemicals listed by the U.S. Department of Energy. Its derivatives have significant application prospects in fine chemicals, pharmaceuticals, and biodegradable plastics. In particular, bio-based PEF polyesters based on furanyl dicarboxylic acid have demonstrated many properties superior to petroleum-based PET (polyethylene terephthalate).

[0003] The traditional petrochemical industry provides abundant petroleum-based products for all aspects of human life, including clothing, food, housing, transportation, and industrial production. While improving people's lives, it also generates large amounts of greenhouse gases and causes serious environmental pollution. Straw is a biomass resource with rapid regeneration and high yield, making it an ideal raw material for preparing bio-based platform compounds. High-value utilization of straw can not only alleviate the shortage of fossil fuels such as coal, oil, and natural gas, but also prevent environmental pollution caused by burning straw.

[0004] Straw is mainly composed of cellulose, hemicellulose, and lignin, possessing a natural anti-degradation barrier. The carbohydrate complex formed by hemicellulose and lignin tightly encapsulates crystalline cellulose, limiting the efficient hydrolysis and conversion of straw. Acid catalysts can promote the dissolution and degradation of cellulose and hemicellulose in lignocellulosic biomass. Hemicellulose can degrade to furfural under acidic conditions, and cellulose can degrade to 5-hydroxymethylfurfural (5-HMF) under acidic conditions. However, when hemicellulose degrades to furfural, it is easily further degraded to generate byproducts. Cellulose, due to its high crystallinity, requires stringent hydrolysis conditions; the process not only needs to break down the cellulose crystalline structure but also must prevent further degradation of 5-hydroxymethylfurfural. Currently, the preparation of furfural and 5-hydroxymethylfurfural from straw suffers from low product yield, poor selectivity, numerous byproducts, and difficulties in product separation. Furthermore, conventional strong acid and strong alkali treatment methods require large amounts of acid, alkali, and water, resulting in large volumes of post-treatment wastewater containing significant amounts of solid waste and high chemical oxygen demand (COD), thus greatly increasing treatment costs.

[0005] Traditional methods suffer from low yields, insufficient straw utilization, significant resource waste, the environmental impact of strong acids and alkalis, and the cost of catalysts or enzymes that restricts industrial-scale production and limits the comprehensive utilization of biomass resources. Therefore, developing a new method for the efficient preparation of furfural and 5-hydroxymethylfurfural from straw is an urgent problem to be solved. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw. This invention uses organic acids instead of inorganic acids and adds an aprotic polar solvent to the organic solvent, thereby better controlling the decomposition process of the raw materials, improving the conversion rate of furfural and 5-hydroxymethylfurfural, and resulting in fewer byproducts and higher product purity throughout the process.

[0007] Specifically, the purpose of this invention is to provide a method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw, the method comprising the following steps:

[0008] Step 1: Mix straw with acid solution A and heat to react, then separate the solid and liquid phases to obtain cellulose solid and liquid phase 1; wherein, the acid in acid solution A includes at least one organic acid;

[0009] Step 2: Add water to the liquid phase 1 obtained in Step 1 to precipitate lignin, then perform solid-liquid separation to obtain lignin solid and liquid phase 2. Heat liquid phase 2 to react and obtain furfural-containing solution.

[0010] Step 3: The cellulose obtained in Step 1 is mixed with acid solution B and catalyst and heated to react, followed by solid-liquid separation to obtain an undissolved straw solid phase and a liquid phase containing 5-hydroxymethylfurfural; wherein the acid in acid solution B includes at least one organic acid.

[0011] Furthermore, each organic acid is independently selected from at least one of organic polybasic acids; preferably, it contains C2 to C3. 10 The organic polyacid; more preferably, at least one of oxalic acid, malic acid, maleic acid, tartaric acid, citric acid, fumaric acid, and ethylenediaminetetraacetic acid.

[0012] Furthermore, the solvent in acid solution A is a mixture of organic solvent and water; the solvent in acid solution B is a mixture of organic solvent and water.

[0013] Furthermore, the organic solvent is an aprotic organic solvent, preferably an aprotic polar organic solvent with a boiling point of 30 to 130°C, and more preferably at least one of acetonitrile, tetrahydrofuran, acetone, dichloromethane, and dioxane.

[0014] Furthermore, in acid solution A, the mass fraction of acid is 0.1–0.5%, preferably 0.35–0.5%; the volume of organic solvent accounts for 40–80% of the total volume of the mixed solvent, preferably 60–80%; in acid solution B, the mass fraction of acid is 0.5–2%, preferably 0.5–1%; the volume of organic solvent accounts for 20–60% of the total volume of the mixed solvent, preferably 20–40%.

[0015] Furthermore, in step one, the conditions for the reaction between the straw and acid solution A are as follows:

[0016] The straw is straw powder with a length of 1-5cm;

[0017] The mass ratio of straw to acid solution A is 1:5 to 1:20, preferably 1:8 to 1:10;

[0018] The temperature for the heating reaction is 50–200°C, preferably 100–120°C;

[0019] The reaction pressure is atmospheric pressure;

[0020] The reaction time is 30–120 min, preferably 90–120 min.

[0021] After the reaction in step one is completed, a mixture of cellulose solid, C5 sugar solution and lignin solution is obtained. Solid-liquid separation is used to separate the cellulose solid and the liquid phase containing C5 sugar solution and lignin solution.

[0022] It is worth mentioning that in this invention, the raw material comes from the straw of various crops, such as common wheat, corn, and sugarcane. The straw needs to be coarsely crushed to a length of 2-10cm using a cutting machine, then conveyed by belt to a straw impurity remover and an iron remover for stone and iron removal treatment, and finally conveyed to a hammer crusher to be crushed to a length of 1-5cm to obtain straw powder.

[0023] Furthermore, in step two, after adding water to the separated liquid phase one, lignin will precipitate out. After solid-liquid separation, a lignin solid phase and a liquid phase two containing C5 sugar solution are obtained. The amount of water added for precipitating lignin is 1 to 5 times, preferably 3 to 4 times, the amount of organic solvent in acid solution A added in step one.

[0024] Further, in step two, furfural product is obtained by heating the liquid phase containing C5 sugar separated in step two, wherein the reaction conditions are as follows:

[0025] The temperature for the heating reaction is 120–200°C, preferably 150–180°C;

[0026] The reaction pressure is 0.2–1.0 MPa, preferably 0.4–0.6 MPa;

[0027] The reaction time is 60–120 min, preferably 90–120 min.

[0028] After the liquid phase solution has undergone heating and reaction, a furfural-containing solution is obtained. The low-boiling-point organic solvent is recovered by fractionation in a distillation column, and the furfural vapor is dehydrated in a dehydration column to obtain crude furfural. The crude furfural can be purified by secondary distillation in a rectification column.

[0029] It is worth mentioning that when preparing furfural, it is necessary to control the reaction temperature and reaction time. If the temperature is too high or the reaction time is too long, the obtained furfural will continue to undergo degradation reaction, resulting in less product and more by-products.

[0030] Further, in step three, cellulose reacts with acid solution B and a catalyst to obtain 5-hydroxymethylfurfural, wherein the reaction conditions are as follows:

[0031] The mass ratio of cellulose solids to acid solution B is 1:5 to 1:20; preferably 1:10 to 1:15.

[0032] The amount of catalyst used is 1 to 10% of the mass of cellulose solids, preferably 3 to 6%;

[0033] The temperature for the heating reaction is 160–250°C, preferably 180–220°C;

[0034] The reaction pressure is 0.4–1.0 MPa, preferably 0.8–1.0 MPa;

[0035] The reaction time is 5 to 30 minutes, preferably 10 to 20 minutes.

[0036] The catalyst is one or a combination of AlCl3, AlBr3, ZnCl2, ZnBr2, CoCl2, CoBr2, CrCl3, CrBr3, LiBr, and LiCl.

[0037] After the reaction in step three is completed, a solution containing 5-hydroxymethylfurfural is obtained. The low-boiling-point organic solvent is recovered by distillation, and the bottom liquid is dehydrated to obtain crude 5-HMF. Solid catalyst is obtained at the bottom of the distillation column. The crude 5-HMF is purified by column chromatography, and the recovered organic solvent and catalyst can be recycled without further purification.

[0038] It is worth mentioning that when preparing 5-hydroxymethylfurfural, it is necessary to control the reaction temperature and reaction time. If the temperature is too high or the reaction time is too long, the obtained 5-hydroxymethylfurfural will continue to undergo degradation reaction, resulting in less product and more by-products.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] 1. This invention uses organic polybasic acids to separate cellulose, lignin, and C5 sugar solutions, which yields better results. The main reason is that organic polybasic acids have the proton ionization ability of inorganic strong acids. The conjugate acid formed after primary ionization can buffer the pH of the solution. The unionized carboxylate group can form hydrogen bonds with the hydroxyl groups on the sugar chain, stabilizing the glycosidic bond and inhibiting the hydrolysis of cellulose and the degradation of hemicellulose, thereby improving the separation efficiency and making the preparation process more controllable. Furthermore, it is less corrosive than inorganic strong acids (sulfuric acid, hydrochloric acid), making it more friendly to equipment and processes.

[0041] 2. The organic polyacid used in this invention will donate hydrogen protons, which will accelerate the breaking of glycosidic bonds, causing cellulose and hemicellulose to degrade into sugars under acidic and high-temperature conditions. Metal chlorides, as Lewis acids, can catalyze the degradation of sugars to generate furfural derivatives.

[0042] 3. In this invention, an aprotic polar organic solvent is added to the solvent. Cellulose has a high degree of crystallinity and requires harsh hydrolysis conditions. The polar organic solvent can destroy the crystalline structure of cellulose in an acidic environment, promoting the separation and degradation of components in straw. Furthermore, the aprotic solvent can make the hydrolysis process of cellulose and hemicellulose moderately controllable, without requiring excessively high temperatures and strong acidic environments, thus reducing the further degradation of furfural and 5-HMF and the generation of byproducts such as lactic acid and levulinic acid.

[0043] 4. The method of the present invention is simple and easy to implement, increases the separation rate of straw components, and improves the yield of furfural and 5-HMF; at the same time, it separates and collects lignin from straw, increasing the economic efficiency of the process.

[0044] 5. The method of the present invention has low straw processing temperature, low acid dosage which does not corrode production equipment, and easy solvent recovery, making it suitable for the biomass industrial application of straw. Detailed Implementation

[0045] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0046] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0047] The testing method in this invention is described in detail below:

[0048] The reaction yield was determined by measuring the concentrations of C6 sugars (including glucose and fructose) derived from the decomposition of cellulose, C5 sugars (including xylose and arabinose) derived from the decomposition of oligosaccharides and hemicellulose, as well as degradation byproducts such as furfural and 5-hydroxymethylfurfural in straw.

[0049] The methods for determining C6 and C5 sugars in straw are derived from the standard methods of the National Renewable Energy Laboratory (NREL) in the United States. The test methods for furfural and 5-hydroxymethylfurfural are found in national standards DB22 / T 247-2018 and DB61 / T 968-2015. Sampling is required during the experiment. After centrifugation, the supernatant is collected, filtered through a 0.45 μm filter membrane, and the sugar concentration in the sample is determined using high-performance liquid chromatography (HPLC). This allows for the calculation of the yield and purity of furfural and 5-hydroxymethylfurfural.

[0050]

[0051]

[0052] Example 1

[0053] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and acetone / water / oxalic acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid solution A was 0.35%. In the mixed solvent of acid solution A, organic solvent accounted for 80% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 10. After reacting at 120℃ for 2 hours, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). Three times the volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was further reacted at 150℃ and 0.4 MPa for 2 hours to obtain furfural solution. The organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were added to acetone / water / oxalic acid (i.e., acid solution B) and AlCl3 (3 wt% of cellulose solids) and heated to react. The mass fraction of acid in acid solution B was 0.5%. In the mixed solvent of acid solution B, organic solvent accounted for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 10. The reaction was carried out at 180℃ and 0.8 MPa for 20 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0054] Example 2

[0055] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and acetone / water / oxalic acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid in acid solution A was 0.35%. In the mixed solvent of acid solution A, organic solvent accounted for 80% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 10. After reacting at 120℃ for 2 hours, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). Three times the volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was further reacted at 150℃ and 0.6 MPa for 2 hours to obtain furfural solution. The low-boiling-point organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were added to acetone / water / oxalic acid (i.e., acid solution B) and CoCl2 (3 wt% of cellulose solids) and heated to react. The mass fraction of acid in acid solution B was 0.5%. In the mixed solvent of acid solution B, organic solvent accounted for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 10. The reaction was carried out at 180℃ and 0.8 MPa for 20 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0056] Example 3

[0057] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and acetone / water / oxalic acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid solution A was 0.35%. In the mixed solvent of acid solution A, organic solvent accounted for 80% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 10. After reacting at 120℃ for 2 hours, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). Three times the volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was further reacted at 150℃ and 0.6 MPa for 2 hours to obtain furfural solution. The low-boiling-point organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were added to acetone / water / oxalic acid (i.e., acid solution B) and ZnCl2 (3 wt% of cellulose solids) and heated to react. The mass fraction of acid in acid solution B was 0.5%. In the mixed solvent of acid solution B, organic solvent accounted for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 10. The reaction was carried out at 180℃ and 0.8 MPa for 20 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0058] Example 4

[0059] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and acetone / water / oxalic acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid solution A was 0.35%. In the mixed solvent of acid solution A, organic solvent accounted for 80% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 10. After reacting at 120℃ for 2 hours, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). Three times the volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was further reacted at 150℃ and 0.6 MPa for 2 hours to obtain furfural solution. The low-boiling-point organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were added to acetone / water / oxalic acid (i.e., acid solution B) and ZnBr2 (5 wt% of cellulose solids) and heated to react. The mass fraction of acid in acid solution B was 0.5%. In the mixed solvent of acid solution B, organic solvent accounted for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 10. The reaction was carried out at 180℃ and 1.0 MPa for 20 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0060] Example 5

[0061] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and tetrahydrofuran / water / maleic acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid in acid solution A was 0.1%. In the mixed solvent of acid solution A, organic solvent accounted for 40% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 5. After reacting at 150℃ for 1 hour, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). One volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was further reacted at 150℃ and 0.2 MPa for 1 hour to obtain furfural solution. The low-boiling-point organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were added to tetrahydrofuran / water / maleic acid (i.e., acid solution B) and CoCl2 (2 wt% of cellulose solids) and heated to react. The mass fraction of acid in acid solution B was 0.6%. In the mixed solvent of acid solution B, organic solvent accounted for 30% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 5. The reaction was carried out at 160℃ and 0.4 MPa for 5 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0062] Example 6

[0063] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and acetonitrile / water / malic acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid in acid solution A was 0.5%. In the mixed solvent of acid solution A, organic solvent accounted for 40% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 20. After reacting at 200℃ for 30 min, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). Five times the volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was continued to react at 200℃ and 1.0 MPa for 2 h to obtain furfural solution. The low-boiling-point organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were added to acetonitrile / water / malic acid (i.e., acid solution B) and CoCl2 (3 wt% of cellulose solids) and heated to react. The mass fraction of acid in acid solution B was 2%. In the mixed solvent of acid solution B, organic solvent accounted for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 20. The reaction was carried out at 220℃ and 1.0 MPa for 30 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0064] Example 7

[0065] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and dioxane / water / citric acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid solution A was 0.35%. In the mixed solvent of acid solution A, organic solvent accounted for 80% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 8. After reacting at 120℃ for 2 hours, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). Three times the volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was further reacted at 150℃ and 0.6 MPa for 2 hours to obtain furfural solution. The low-boiling-point organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were added to a mixture of dioxane / water / citric acid (i.e., acid solution B) and CoCl2 (3 wt% of cellulose solids) and heated to react. The mass fraction of acid solution B was 0.5%. In the mixed solvent of acid solution B, organic solvent accounted for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 10. The reaction was carried out at 160℃ and 0.8 MPa for 20 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0066] Example 8

[0067] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and dichloromethane / water / ethylenediaminetetraacetic acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid solution A was 0.35%. In the mixed solvent of acid solution A, organic solvent accounted for 60% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 10. After reacting at 120℃ for 2 hours, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). Three times the volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was further reacted at 150℃ and 0.6 MPa for 2 hours to obtain furfural solution. The low-boiling-point organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were added to dichloromethane / water / ethylenediaminetetraacetic acid (i.e., acid solution B) and CoCl2 (5 wt% of cellulose solids) and heated to react. The mass fraction of acid solution B was 0.5%. In the mixed solvent of acid solution B, organic solvent accounted for 40% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 10. The reaction was carried out at 160℃ and 0.8 MPa for 20 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0068] Example 9

[0069] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and acetonitrile / water / fumaric acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid in acid solution A was 0.35%. In the mixed solvent of acid solution A, organic solvent accounted for 80% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 10. After reacting at 120℃ for 2 hours, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). Three times the volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was further reacted at 150℃ and 0.6 MPa for 2 hours to obtain furfural solution. The low-boiling-point organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were reacted with acetonitrile / water / fumaric acid (i.e., acid solution B) and CoCl2 (5 wt% of cellulose solids) by heating. The mass fraction of acid solution B was 0.5%. In the mixed solvent of acid solution B, organic solvent accounted for 60% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 15. The reaction was carried out at 160℃ and 0.8 MPa for 20 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0070] Comparative Example 1

[0071] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and acetone / water / sulfuric acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid in acid solution A was 0.35%. In the mixed solvent of acid solution A, organic solvent accounted for 80% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 10. After reacting at 120℃ for 2 hours, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). Three times the volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was further reacted at 150℃ and 0.4 MPa for 2 hours to obtain furfural solution. The low-boiling-point organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were added to acetone / water / sulfuric acid (i.e., acid solution B) and AlCl3 (3 wt% of cellulose solids) and heated to react. The mass fraction of acid in acid solution B was 0.5%. In the mixed solvent of acid solution B, organic solvent accounted for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 10. The reaction was carried out at 160℃ and 0.8 MPa for 20 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0072] Comparative Example 2

[0073] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and acetone / water / acetic acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid in acid solution A was 0.35%. In the mixed solvent of acid solution A, organic solvent accounted for 80% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 10. After reacting at 120℃ for 2 hours, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). Three times the volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was further reacted at 150℃ and 0.4 MPa for 2 hours to obtain furfural solution. The low-boiling-point organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were added to acetone / water / acetic acid (i.e., acid solution B) and AlCl3 (3 wt% of cellulose solids) and heated to react. The mass fraction of acid in acid solution B was 0.5%. In the mixed solvent of acid solution B, organic solvent accounted for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 10. The reaction was carried out at 160℃ and 0.8 MPa for 20 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0074] Comparative Example 3

[0075] 1 kg of straw is coarsely crushed to a length of 2-10 cm by a straw cutter, then conveyed by belt to a straw impurity remover and iron remover for stone and iron removal, and finally conveyed to a hammer crusher to be crushed to a length of 1-5 cm to obtain straw powder. Straw powder and acetone / water / oxalic acid (i.e., acid solution A) were added to a reaction vessel. The mass fraction of acid solution A was 0.35%. In the mixed solvent of acid solution A, organic solvent accounted for 80% of the total volume of the mixed solvent. The solid-liquid mass ratio of straw to acid solution A was 1 / 10. After reacting at 120℃ for 2 hours, the mixture was cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one). Three times the volume of water was added to the filtrate (separation liquid one), and then the mixture was filtered to obtain lignin solid and filtrate (separation liquid two). The organic solvent was recovered from the concentrated filtrate (separation liquid two), and then the mixture was filtered. The liquid phase was further reacted at 150℃ and 0.4 MPa for 2 hours to obtain furfural solution. The low-boiling-point organic solvent was recovered by fractionation in a distillation column, and the furfural vapor was passed through a dehydration column to obtain crude furfural. Cellulose solids were added to acetone / water / oxalic acid (i.e., acid solution B) and heated to react. The mass fraction of acid solution B was 0.5%. In the mixed solvent of acid solution B, organic solvent accounted for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B was 1 / 10. The reaction was carried out at 160℃ and 0.8MPa for 30 min. The mixed solution was fractionated to recover the solvent, and the bottom liquid was passed through a dehydration tower to obtain crude 5-HMF.

[0076] The yields and purities of crude furfural and crude 5-HMF, as well as the yield of lignin, obtained in Examples 1-9 and Comparative Examples 1-3 of this invention are shown in Table 1 below.

[0077] Table 1

[0078]

[0079] As shown in Table 1, the yields of furfural, 5-HMF, and lignin obtained by the organic polyacid method in Examples 1-9 were all good, and the purity of crude furfural and crude 5-HMF was above 84%.

[0080] Comparative Examples 1 and 2 used inorganic acids and monocarboxylic acids, respectively. The yields of 5-HMF and lignin were lower than those obtained when organic polycarboxylic acids were used. Furthermore, the sulfuric acid process was highly hazardous to the equipment, and the post-treatment process generated a large amount of waste liquid. In Comparative Example 3, the yield of 5-HMF was lower when no catalyst was added.

[0081] In summary, this invention provides a method for the co-production of furfural, 5-HMF, and lignin from straw, resulting in crude furfural, crude 5-HMF, and lignin with good yields and high purity.

[0082] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw, the method comprising the following steps: Step 1: Mix straw with acid solution A and heat to react, then perform solid-liquid separation to obtain cellulose solid and liquid phase 1; the acid in acid solution A includes at least one organic acid; the heating reaction temperature is 50~200℃; the reaction pressure is atmospheric pressure; Step 2: Add water to the liquid phase I obtained in Step 1 to precipitate lignin, then perform solid-liquid separation to obtain lignin solid and liquid phase II. Heat liquid phase II to obtain a furfural-containing solution; the heating reaction temperature is 120~200℃; the reaction pressure is 0.2~1.0 MPa. Step 3: The cellulose obtained in Step 1 is mixed with acid solution B and catalyst and heated to react, followed by solid-liquid separation to obtain an undissolved straw solid phase and a liquid phase containing 5-hydroxymethylfurfural; the acid in acid solution B includes at least one organic acid; the heating reaction temperature is 160~250℃; the reaction pressure is 0.4~1.0 MPa; Each of the organic acids is independently selected from at least one of organic polybasic acids; The solvents in acid solution A and acid solution B are both independently a mixture of organic solvent and water; The catalyst is one or a combination of AlCl3, AlBr3, ZnCl2, ZnBr2, CoCl2, CoBr2, CrCl3, CrBr3, LiBr, and LiCl.

2. The preparation method for the co-production of furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 1, characterized in that, In step one or step three, the organic polyacid is selected from those containing C2~C3. 10 At least one of the organic polyacids.

3. The preparation method for the co-production of furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 2, characterized in that, The organic polyacid is selected from at least one of oxalic acid, malic acid, maleic acid, tartaric acid, citric acid, fumaric acid, and ethylenediaminetetraacetic acid.

4. The preparation method for the co-production of furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 1, characterized in that, In the acid solution A, the mass fraction of the acid is 0.1~0.5%; and / or; In the acid solution B, the mass fraction of the acid is 0.5-2%.

5. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 4, characterized in that, In the acid solution A, the mass fraction of the acid is 0.35~0.5%; and / or; In the acid solution B, the mass fraction of the acid is 0.5-1%.

6. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 1, characterized in that, The organic solvent is an aprotic organic solvent.

7. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 6, characterized in that, The organic solvent is at least one of the aprotic polar organic solvents with a boiling point of 30~130℃.

8. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 6, characterized in that, The organic solvent is at least one of acetonitrile, tetrahydrofuran, acetone, dichloromethane, and dioxane.

9. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 1, characterized in that, In the acid solution A, the volume of the organic solvent accounts for 40-80% of the total volume of the mixed solvent; and / or, In the acid solution B, the volume of the organic solvent accounts for 20-60% of the total volume of the mixed solvent.

10. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 9, characterized in that, In the acid solution A, the volume of the organic solvent accounts for 60-80% of the total volume of the mixed solvent; and / or, In the acid solution B, the volume of the organic solvent accounts for 20-40% of the total volume of the mixed solvent.

11. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 1, characterized in that, In step one: The straw is straw powder with a length of 1-5 cm; and / or, The mass ratio of the straw to acid solution A is 1:5 to 1:20; and / or, The heating reaction temperature is 100~120℃; and / or, The reaction time is 30~120 min.

12. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 11, characterized in that, In step one: The mass ratio of the straw to acid solution A is 1:8 to 1:10; and / or, The reaction time is 90-120 min.

13. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 1, characterized in that, In step two, the amount of water added is 1 to 5 times the amount of organic solvent used in acid solution A in step one.

14. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 13, characterized in that, In step two, the amount of water added is 3 to 4 times the amount of organic solvent used in acid solution A in step one.

15. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 1, characterized in that, In step two, the heating reaction conditions for liquid phase two are as follows: The heating reaction temperature is 150~180℃; and / or, The reaction pressure is 0.4~0.6 MPa; and / or, The reaction time is 60-120 min.

16. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 15, characterized in that, In step two, the reaction time is 90-120 min.

17. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 1, characterized in that, In step three: The mass ratio of the cellulose solid to acid solution B is 1:5 to 1:20; and / or, The amount of catalyst used is 1-10% of the cellulose solids mass; and / or, The heating reaction temperature is 180~220℃; and / or, The reaction pressure is 0.8~1.0 MPa; and / or, The reaction time is 5 to 30 minutes.

18. The method for preparing furfural, 5-hydroxymethylfurfural, and lignin from straw according to claim 17, characterized in that, In step three: The mass ratio of the cellulose solid to acid solution B is 1:10 to 1:15; and / or, The amount of catalyst used is 3-6% of the cellulose solids mass; and / or, The reaction time is 10-20 min.

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