Preparation method for co-production of furfural, 5-hydroxymethylfurfural and lignin from straw

Abstract

The invention provides a preparation method for co-production of furfural, 5-hydroxymethylfurfural and lignin from straws, and the method comprises the following steps: step 1, mixing the straws and an acid solution A, carrying out a heating reaction, and then carrying out solid-liquid separation to obtain a cellulose solid and a liquid phase I; step 2, adding water into the liquid phase I obtained in the step 1 to precipitate lignin, then carrying out solid-liquid separation to obtain a lignin solid and a liquid phase II, and carrying out heating reaction on the liquid phase II to obtain a furfural-containing solution; and 3, mixing the cellulose obtained in the step 1 with an acid solution B and a catalyst, carrying out a heating reaction, and carrying out solid-liquid separation to obtain an undissolved straw solid phase and a liquid phase containing 5-hydroxymethylfurfural. The method provided by the invention has few by-products, and the obtained furfural and 5-hydroxymethylfurfural have good purity and conversion rate.

Description

Technical Field

[0001] The invention relates to the technical field of biomass energy utilization, and further to a method for preparing furfural, 5-hydroxymethylfurfural and lignin by co-producing furfural from straw. Background Art

[0002] Furfural and 5-hydroxymethylfurfural are important bio-based platform compounds. Among them, furfural is an intermediate raw material for the preparation of succinaldehyde, furan acrylic acid, furfurylamine fumaric acid, adipic acid, and furfuryl alcohol; it can also be used to synthesize fine chemicals such as medicines, pesticides, veterinary drugs, dyes, fragrances, rubber additives, and preservatives. 5-Hydroxymethylfurfural is an important furan compound with excellent chemical properties. It is widely used in medicine, chemistry, energy and other fields. It is one of the ten most important platform chemicals listed by the U.S. Department of Energy. Its derivatives have great application prospects in the fields of fine chemicals, medicine, and biodegradable plastics. In particular, bio-based PEF polyester based on furan dicarboxylic acid has shown many characteristics that are superior to petroleum-based PET (polyethylene terephthalate).

[0003] The traditional petrochemical industry provides a wealth of petroleum-based products for human food, clothing, housing, transportation and industrial production. While improving people's lives, it also produces a large amount of greenhouse gases and causes serious environmental pollution. Straw is a biomass resource with fast regeneration speed and high yield. It is an ideal raw material for preparing bio-based platform compounds. If straw can be used in a high-value way, it can not only alleviate the shortage of fossil energy such as coal, oil and natural gas, but also avoid environmental pollution caused by burning straw.

[0004] Straw is mainly composed of cellulose, hemicellulose and lignin, and has a natural anti-degradation barrier. The carbohydrate complex formed by hemicellulose and lignin tightly wraps the 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 be degraded to furfural under acidic conditions, and cellulose can be degraded to 5-hydroxymethylfurfural (5-HMF) under acidic conditions. When hemicellulose is degraded to furfural, it is easy to further degrade to form by-products; and cellulose has high crystallinity and harsh hydrolysis conditions. The process not only needs to be able to deconstruct the cellulose crystalline structure, but also must avoid further degradation of 5-hydroxymethylfurfural. At present, the preparation of furfural and 5-hydroxymethylfurfural from straw has problems such as low product yield, poor selectivity, many by-products, and difficult product separation. In addition, conventional strong acid and strong alkali treatment methods require the use of a large amount of acid, alkali and water, and the amount of wastewater in post-treatment is large. The wastewater contains a large amount of solid waste and has a large chemical oxygen demand, which greatly increases the treatment cost.

[0005] The traditional methods have low yields, insufficient straw utilization, large waste of resources, strong acids and alkalis that are not conducive to environmental protection, and the cost of catalysts or enzyme preparations that restrict the industrial production of the process and limit the comprehensive utilization of biomass resources. Therefore, developing a new method for efficiently preparing furfural and 5-hydroxymethylfurfural from straw is an urgent problem to be solved. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a method for preparing furfural, 5-hydroxymethylfurfural and lignin by co-producing furfural from straw. The present invention uses organic acid instead of inorganic acid, and adds a non-protonic polar solvent to the organic solvent, so as to better control the decomposition process of the raw materials, improve the conversion rate of furfural and 5-hydroxymethylfurfural, and the whole process has few by-products and high product purity.

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

[0008] Step 1: mixing the straw with the acid solution A for heating reaction, and then performing solid-liquid separation to obtain cellulose solid and liquid phase 1; wherein the acid in the acid solution A includes at least one organic acid;

[0009] Step 2: adding water to the liquid phase 1 obtained in step 1 to precipitate lignin, and then performing solid-liquid separation to obtain lignin solid and liquid phase 2, and heating the liquid phase 2 to react to obtain a furfural-containing solution;

[0010] Step 3: Mix the cellulose obtained in step 1 with acid solution B and a catalyst for heating reaction, and then perform solid-liquid separation to obtain an undissolved straw solid phase and a 5-hydroxymethylfurfural-containing liquid phase; wherein the acid in the acid solution B includes at least one organic acid.

[0011] Furthermore, the organic acids are each independently selected from at least one of organic polyacids; preferably containing C2 to C 10 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 the acid solution A is a mixed solvent of an organic solvent and water; the solvent in the acid solution B is a mixed solvent of an 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., more preferably at least one of acetonitrile, tetrahydrofuran, acetone, dichloromethane and dioxane.

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

[0015] Further, in step 1, the conditions for the reaction of the straw and the acid solution A are:

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

[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 of the heating reaction is 50 to 200°C, preferably 100 to 120°C;

[0019] The reaction pressure is normal pressure;

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

[0021] After the reaction of step 1 is completed, a mixture of cellulose solid, C5 sugar solution and lignin solution is obtained, and a solid-liquid separation method is used to obtain a liquid phase 1 containing cellulose solid and C5 sugar solution and lignin solution.

[0022] It is worth mentioning that in the present invention, the raw materials come from the straws of various crops, such as common wheat, corn, and sugar cane. The straws need to be coarsely crushed to a length of 2 to 10 cm by a cutter, then conveyed to a straw impurity remover and an iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder.

[0023] Furthermore, in step 2, after water is added to the separated liquid phase 1, lignin will precipitate out, and then after solid-liquid separation, a lignin solid phase and a liquid phase 2 containing a C5 sugar solution are obtained, wherein the amount of water added for precipitating lignin is 1 to 5 times, preferably 3 to 4 times, the amount of organic solvent in the acid solution A added in step 1.

[0024] Further, in step 2, the furfural product is obtained by heating the liquid phase 2 containing C5 sugar separated in step 2, wherein the reaction conditions are:

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

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

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

[0028] After the liquid phase solution is heated and reacted, a furfural-containing solution is obtained, wherein the low-boiling-point organic solvent is recovered by fractionation through a distillation tower, and the furfural vapor is passed through a dehydration tower to obtain crude furfural, and the crude furfural can be purified and refined by secondary distillation in a distillation tower.

[0029] It is worth mentioning that when preparing furfural, the reaction temperature and reaction time need to be controlled. If the temperature is too high or the reaction time is too long, the obtained furfural will continue to degrade, the obtained product will be less, and the by-products will increase.

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

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

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

[0033] The temperature of the heating reaction is 160 to 250°C, preferably 180 to 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] Among them, 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 3 is completed, a solution containing 5-hydroxymethylfurfural is obtained, wherein the low-boiling organic solvent is recovered by a distillation tower, the bottom liquid of the tower is passed through a dehydration tower to obtain crude 5-HMF, and a catalyst solid is obtained at the bottom of the tower. The crude 5-HMF is purified and refined by column chromatography, and the organic solvent and catalyst can be recycled without purification after recovery.

[0038] It is worth mentioning that when preparing 5-hydroxymethylfurfural, the reaction temperature and reaction time need to be controlled. 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 present invention has the following beneficial effects:

[0040] 1. The present invention uses organic polyacids to separate cellulose, lignin and C5 sugar solution, which has better effect. The main reason is that organic polyacids 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 part can form hydrogen bonds with the hydroxyl groups on the sugar chain, stabilize the glycosidic bonds, inhibit the hydrolysis of cellulose and the degradation of hemicellulose, improve the separation efficiency, and make the preparation process more controllable. In addition, the organic polyacids are less corrosive than inorganic strong acids (sulfuric acid, hydrochloric acid), and are more friendly to equipment and processes.

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

[0042] 3. The present invention adds a non-protonic polar organic solvent to the solvent. Cellulose has high crystallinity and harsh hydrolysis conditions, while polar organic solvents can destroy the crystalline structure of cellulose in an acidic environment, thereby promoting the separation and degradation of components in the straw. In addition, the non-protonic solvent can make the hydrolysis process of cellulose and hemicellulose moderately controllable, without the need to react at excessively high temperatures and in an overly acidic environment, thereby reducing further degradation of furfural and 5-HMF and generating by-products 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, the lignin in the straw is separated and collected, which increases the economy of the process.

[0044] 5. The method of the present invention has low straw processing temperature, low acid dosage, no corrosion to production equipment, and easy recovery of solvent, and is suitable for industrial application of straw biomass. DETAILED DESCRIPTION

[0045] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0046] The raw materials used in the examples and comparative examples, unless otherwise specified, are disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0047] The description of the test method in the present invention is as follows:

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

[0049] Among them, the determination method of C6 sugar and C5 sugar in straw comes from the standard method of the National Renewable Energy Laboratory (NREL). The test methods of furfural and 5-hydroxymethylfurfural refer to the national standards DB22 / T 247-2018 and DB61 / T 968-2015. Sampling is required during the experiment. The supernatant is collected after centrifugation. After the supernatant is filtered with a 0.45μm filter membrane, the sugar concentration in the sample is determined by high performance liquid chromatography (HPLC), so that the yield and purity of furfural and 5-hydroxymethylfurfural can be calculated.

[0050]

[0051]

[0052] Example 1

[0053] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Add straw powder and acetone / water / oxalic acid (i.e., acid solution A) into a reactor, wherein the mass fraction of acid in the acid solution A is 0.35%; in the mixed solvent of the acid solution A, the organic solvent accounts for 80% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 10. After reacting at 120° C. for 2 hours, cool down to room temperature, stand and filter to obtain cellulose solid and filtrate (separation liquid 1); add 3 times the volume of water to the filtrate (separation liquid 1), and then filter to obtain lignin solid and filtrate (separation liquid 2); concentrate the filtrate (separation liquid 2) to recover the organic solvent, and then filter, and continue to react at 150° C. and 0.4 MPa for 2 hours in the liquid phase to obtain a furfural solution, and recover the organic solvent through fractionation in a distillation tower, and obtain crude furfural through a dehydration tower. Cellulose solids are added to acetone / water / oxalic acid (i.e., acid solution B) and AlCl3 (3wt% of cellulose solids) for heating reaction, wherein the mass fraction of acid in acid solution B is 0.5%; in the mixed solvent of acid solution B, the organic solvent accounts for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B is 1 / 10; the reaction is carried out at 180°C and 0.8MPa for 20 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0054] Example 2

[0055] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Straw powder and acetone / water / oxalic acid (i.e., acid solution A) are added into a reactor, wherein the mass fraction of acid in the acid solution A is 0.35%; in the mixed solvent of the acid solution A, the organic solvent accounts for 80% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 10. After reacting at 120° C. for 2 hours, the mixture is cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid 1); 3 times the volume of water is added to the filtrate (separation liquid 1), and then filtered to obtain lignin solid and filtrate (separation liquid 2); the filtrate (separation liquid 2) is concentrated to recover the organic solvent, and then filtered, and the liquid phase continues to react at 150° C. and 0.6 MPa for 2 hours to obtain a furfural solution, and the low-boiling organic solvent is recovered by fractionation in a distillation tower, and the furfural vapor is passed through a dehydration tower to obtain crude furfural. Cellulose solids are added to acetone / water / oxalic acid (i.e., acid solution B) and CoCl2 (3wt% of cellulose solids) for heating reaction, wherein the mass fraction of acid in acid solution B is 0.5%; in the mixed solvent of acid solution B, the organic solvent accounts for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B is 1 / 10; the reaction is carried out at 180°C and 0.8MPa for 20 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0056] Example 3

[0057] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Add straw powder and acetone / water / oxalic acid (i.e., acid solution A) into a reactor, wherein the mass fraction of acid in the acid solution A is 0.35%; in the mixed solvent of the acid solution A, the organic solvent accounts for 80% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 10. After reacting at 120° C. for 2 hours, cool down to room temperature, stand and filter to obtain cellulose solid and filtrate (separation liquid 1); add 3 times the volume of water to the filtrate (separation liquid 1), and then filter to obtain lignin solid and filtrate (separation liquid 2); concentrate the filtrate (separation liquid 2) to recover the organic solvent, and then filter, and continue to react at 150° C. and 0.6 MPa for 2 hours in the liquid phase to obtain a furfural solution, and recover the low-boiling point organic solvent through fractionation in a distillation tower, and obtain crude furfural through a dehydration tower. Cellulose solids are added to acetone / water / oxalic acid (i.e., acid solution B) and ZnCl2 (3wt% of cellulose solids) for heating reaction, wherein the mass fraction of acid solution B is 0.5%; in the mixed solvent of acid solution B, the organic solvent accounts for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B is 1 / 10; the reaction is carried out at 180°C and 0.8MPa for 20 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0058] Example 4

[0059] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Add straw powder and acetone / water / oxalic acid (i.e., acid solution A) into a reactor, wherein the mass fraction of acid in the acid solution A is 0.35%; in the mixed solvent of the acid solution A, the organic solvent accounts for 80% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 10. After reacting at 120° C. for 2 hours, cool down to room temperature, stand and filter to obtain cellulose solid and filtrate (separation liquid 1); add 3 times the volume of water to the filtrate (separation liquid 1), and then filter to obtain lignin solid and filtrate (separation liquid 2); concentrate the filtrate (separation liquid 2) to recover the organic solvent, and then filter, and continue to react at 150° C. and 0.6 MPa for 2 hours in the liquid phase to obtain a furfural solution, and recover the low-boiling point organic solvent through fractionation in a distillation tower, and obtain crude furfural through a dehydration tower. Cellulose solids are added to acetone / water / oxalic acid (i.e., acid solution B) and ZnBr2 (5wt% of cellulose solids) for heating reaction, wherein the mass fraction of acid solution B is 0.5%; in the mixed solvent of acid solution B, the organic solvent accounts for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B is 1 / 10; the reaction is carried out at 180°C and 1.0MPa for 20 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0060] Example 5

[0061] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Add straw powder and tetrahydrofuran / water / maleic acid (i.e., acid solution A) into a reactor, wherein the mass fraction of the acid in the acid solution A is 0.1%; in the mixed solvent of the acid solution A, the organic solvent accounts for 40% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 5. After reacting at 150° C. for 1 hour, cool down to room temperature, stand and filter to obtain cellulose solid and filtrate (separation liquid 1); add 1 times the volume of water to the filtrate (separation liquid 1), and then filter to obtain lignin solid and filtrate (separation liquid 2); concentrate the filtrate (separation liquid 2) to recover the organic solvent, and then filter, and continue to react the liquid phase at 150° C. and 0.2 MPa for 1 hour to obtain a furfural solution, and recover the low-boiling organic solvent through fractionation in a distillation tower, and obtain crude furfural through a dehydration tower. Cellulose solids are added to tetrahydrofuran / water / maleic acid (i.e., acid solution B) and CoCl2 (2wt% of cellulose solids) for heating reaction, wherein the mass fraction of acid solution B is 0.6%; in the mixed solvent of acid solution B, the organic solvent accounts for 30% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B is 1 / 5; the reaction is carried out at 160°C and 0.4MPa for 5 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0062] Example 6

[0063] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Straw powder and acetonitrile / water / malic acid (i.e., acid solution A) are added into a reactor, wherein the mass fraction of acid in the acid solution A is 0.5%; in the mixed solvent of the acid solution A, the organic solvent accounts for 40% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 20. After reacting at 200° C. for 30 minutes, the mixture is cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid one); 5 times the volume of water is added to the filtrate (separation liquid one), and then filtered to obtain lignin solid and filtrate (separation liquid two); the filtrate (separation liquid two) is concentrated to recover the organic solvent, and then filtered, and the liquid phase continues to react at 200° C. and 1.0 MPa for 2 hours to obtain a furfural solution, and the low-boiling organic solvent is recovered by fractionation in a distillation tower, and the furfural vapor is passed through a dehydration tower to obtain crude furfural. Cellulose solid is added to acetonitrile / water / malic acid (i.e. acid solution B) and CoCl2 (3wt% of cellulose solid) for heating reaction, the mass fraction of acid solution B is 2%; in the mixed solvent of acid solution B, the organic solvent accounts for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solid to acid solution B is 1 / 20; the reaction is carried out at 220°C and 1.0MPa for 30 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0064] Example 7

[0065] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Straw powder and dioxane / water / citric acid (i.e., acid solution A) are added into a reaction kettle, wherein the mass fraction of acid in the acid solution A is 0.35%; in the mixed solvent of the acid solution A, the organic solvent accounts for 80% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 8. After reacting at 120° C. for 2 hours, the mixture is cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid 1); 3 times the volume of water is added to the filtrate (separation liquid 1), and then filtered to obtain lignin solid and filtrate (separation liquid 2); the filtrate (separation liquid 2) is concentrated to recover the organic solvent, and then filtered, and the liquid phase continues to react at 150° C. and 0.6 MPa for 2 hours to obtain a furfural solution, and the low-boiling organic solvent is recovered by fractionation in a distillation tower, and the furfural vapor is passed through a dehydration tower to obtain crude furfural. Cellulose solids are added to dioxane / water / citric acid (i.e., acid solution B) and CoCl2 (3wt% of cellulose solids) for heating reaction, wherein the mass fraction of acid solution B is 0.5%; in the mixed solvent of acid solution B, the organic solvent accounts for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B is 1 / 10; the reaction is carried out at 160°C and 0.8MPa for 20 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0066] Example 8

[0067] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Straw powder and dichloromethane / water / ethylenediaminetetraacetic acid (i.e., acid solution A) are added into a reaction kettle, wherein the mass fraction of acid in the acid solution A is 0.35%; in the mixed solvent of the acid solution A, the organic solvent accounts for 60% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 10. After reacting at 120° C. for 2 hours, the mixture is cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid 1); 3 times the volume of water is added to the filtrate (separation liquid 1), and then filtered to obtain lignin solid and filtrate (separation liquid 2); the filtrate (separation liquid 2) is concentrated to recover the organic solvent, and then filtered, and the liquid phase continues to react at 150° C. and 0.6 MPa for 2 hours to obtain a furfural solution, and the low-boiling organic solvent is recovered by fractionation in a distillation tower, and the furfural vapor is passed through a dehydration tower to obtain crude furfural. Cellulose solids are added to dichloromethane / water / ethylenediaminetetraacetic acid (i.e., acid solution B) and CoCl2 (5wt% of cellulose solids) for heating reaction, wherein the mass fraction of acid solution B is 0.5%; in the mixed solvent of acid solution B, the organic solvent accounts for 40% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B is 1 / 10; the reaction is carried out at 160°C and 0.8MPa for 20 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0068] Example 9

[0069] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Straw powder and acetonitrile / water / fumaric acid (i.e., acid solution A) are added into a reactor, wherein the mass fraction of acid in the acid solution A is 0.35%; in the mixed solvent of the acid solution A, the organic solvent accounts for 80% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 10. After reacting at 120° C. for 2 hours, the mixture is cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid 1); 3 times the volume of water is added to the filtrate (separation liquid 1), and then filtered to obtain lignin solid and filtrate (separation liquid 2); the filtrate (separation liquid 2) is concentrated to recover the organic solvent, and then filtered, and the liquid phase continues to react at 150° C. and 0.6 MPa for 2 hours to obtain a furfural solution, and the low-boiling point organic solvent is recovered by fractionation in a distillation tower, and the furfural vapor is passed through a dehydration tower to obtain crude furfural. The cellulose solid is heated to react with acetonitrile / water / fumaric acid (i.e., acid solution B) and CoCl2 (5wt% of the cellulose solid), wherein the mass fraction of the acid in the acid solution B is 0.5%; in the mixed solvent of the acid solution B, the organic solvent accounts for 60% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the cellulose solid to the acid solution B is 1 / 15; the reaction is carried out at 160°C and 0.8MPa for 20 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0070] Comparative Example 1

[0071] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Add straw powder and acetone / water / sulfuric acid (i.e., acid solution A) into a reactor, wherein the mass fraction of acid in the acid solution A is 0.35%; in the mixed solvent of the acid solution A, the organic solvent accounts for 80% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 10. After reacting at 120° C. for 2 hours, cool down to room temperature, stand and filter to obtain cellulose solid and filtrate (separation liquid 1); add 3 times the volume of water to the filtrate (separation liquid 1), and then filter to obtain lignin solid and filtrate (separation liquid 2); concentrate the filtrate (separation liquid 2) to recover the organic solvent, and then filter, and continue to react the liquid phase at 150° C. and 0.4 MPa for 2 hours to obtain a furfural solution, and recover the low-boiling organic solvent through fractionation in a distillation tower, and obtain crude furfural through a dehydration tower. Cellulose solids are added to acetone / water / sulfuric acid (i.e., acid solution B) and AlCl3 (3wt% of cellulose solids) for heating reaction, wherein the mass fraction of acid solution B is 0.5%; in the mixed solvent of acid solution B, the organic solvent accounts for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B is 1 / 10; the reaction is carried out at 160°C and 0.8MPa for 20 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0072] Comparative Example 2

[0073] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Add straw powder and acetone / water / acetic acid (i.e., acid solution A) into a reactor, wherein the mass fraction of acid in the acid solution A is 0.35%; in the mixed solvent of the acid solution A, the organic solvent accounts for 80% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 10. After reacting at 120° C. for 2 hours, cool down to room temperature, stand and filter to obtain cellulose solid and filtrate (separation liquid 1); add 3 times the volume of water to the filtrate (separation liquid 1), and then filter to obtain lignin solid and filtrate (separation liquid 2); concentrate the filtrate (separation liquid 2) to recover the organic solvent, and then filter, and continue to react the liquid phase at 150° C. and 0.4 MPa for 2 hours to obtain a furfural solution, and recover the low-boiling organic solvent through fractionation in a distillation tower, and obtain crude furfural through a dehydration tower. Cellulose solids are added to acetone / water / acetic acid (i.e., acid solution B) and AlCl3 (3wt% of cellulose solids) for heating reaction, wherein the mass fraction of acid solution B is 0.5%; in the mixed solvent of acid solution B, the organic solvent accounts for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solids to acid solution B is 1 / 10; the reaction is carried out at 160°C and 0.8MPa for 20 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0074] Comparative Example 3

[0075] 1 kg of straw is roughly crushed to a length of 2 to 10 cm by a straw cutter, then conveyed to a straw impurity remover and iron remover by a belt to remove stones and iron, and finally conveyed to a hammer crusher to be crushed to a length of 1 to 5 cm to obtain straw powder. Straw powder and acetone / water / oxalic acid (i.e., acid solution A) are added into a reactor, wherein the mass fraction of acid in the acid solution A is 0.35%; in the mixed solvent of the acid solution A, the organic solvent accounts for 80% of the total volume of the mixed solvent, and the solid-liquid mass ratio of the straw to the acid solution A is 1 / 10. After reacting at 120° C. for 2 hours, the mixture is cooled to room temperature, allowed to stand, and then filtered to obtain cellulose solid and filtrate (separation liquid 1); 3 times the volume of water is added to the filtrate (separation liquid 1), and then filtered to obtain lignin solid and filtrate (separation liquid 2); the filtrate (separation liquid 2) is concentrated to recover the organic solvent, and then filtered, and the liquid phase continues to react at 150° C. and 0.4 MPa for 2 hours to obtain a furfural solution, and the low-boiling point organic solvent is recovered by fractionation in a distillation tower, and the furfural vapor is passed through a dehydration tower to obtain crude furfural. The cellulose solid is added to acetone / water / oxalic acid (i.e., acid solution B) for heating reaction, wherein the mass fraction of acid solution B is 0.5%; in the mixed solvent of acid solution B, the organic solvent accounts for 20% of the total volume of the mixed solvent, and the solid-liquid mass ratio of cellulose solid to acid solution B is 1 / 10; the reaction is carried out at 160° C. and 0.8 MPa for 30 minutes. The mixed solution is fractionated to recover the solvent, and the bottom liquid is passed through a dehydration tower to obtain crude 5-HMF.

[0076] The yields and purities of crude furfural and crude 5-HMF and the yield of lignin obtained in Examples 1 to 9 of the present invention and Comparative Examples 1 to 3 are specifically 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 method of using organic polyacid in Examples 1 to 9 are all good, and the purity of the obtained crude furfural and crude 5-HMF is above 84%.

[0080] In Comparative Examples 1 and 2, inorganic acid and monoacid were used respectively, and the yields of 5-HMF and lignin were not as good as those when organic polyacid was used. In addition, the sulfuric acid method was harmful to the equipment and a large amount of waste liquid was generated in the post-processing. In Comparative Example 3, when no catalyst was added, the yield of 5-HMF was low.

[0081] In summary, it can be seen that the present invention provides a method for co-producing furfural, 5-HMF and lignin from straw, and the obtained crude furfural, crude 5-HMF and lignin have good yield and high purity.

[0082] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to 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: mixing the straw with acid solution A for heating reaction, and then performing solid-liquid separation to obtain cellulose solid and liquid phase 1; the acid in the acid solution A includes at least one organic acid; Step 2: adding water to the liquid phase 1 obtained in step 1 to precipitate lignin, and then performing solid-liquid separation to obtain lignin solid and liquid phase 2, and heating the liquid phase 2 to react to obtain a furfural-containing solution; Step 3: Mix the cellulose obtained in step 1 with acid solution B and a catalyst for heating reaction, and then perform solid-liquid separation to obtain an undissolved straw solid phase and a 5-hydroxymethylfurfural-containing liquid phase; the acid in the acid solution B includes at least one organic acid.

2. The method for preparing furfural, 5-hydroxymethylfurfural and lignin from straw according to claim 1, characterized in that: In the step 1 or the step 3, The organic acids are each independently selected from at least one of organic polyacids; Preferably, the organic polyacid is selected from C2 to C 10 At least one of the organic polyacids; More preferably, 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; and / or, The solvent in the acid solution A is a mixed solvent of an organic solvent and water; and / or, The solvent in the acid solution B is a mixed solvent of an organic solvent and water.

3. The method for preparing 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 to 0.5%, preferably 0.35 to 0.5%; and / or; In the acid solution B, the mass fraction of the acid is 0.5-2%, preferably 0.5-1%.

4. The method for preparing furfural, 5-hydroxymethylfurfural and lignin from straw according to claim 2, characterized in that: The organic solvent is an aprotic organic solvent; Preferably, the organic solvent is at least one of aprotic polar organic solvents having a boiling point of 30 to 130°C; More preferably, the organic solvent is at least one of acetonitrile, tetrahydrofuran, acetone, dichloromethane and dioxane.

5. The method for preparing furfural, 5-hydroxymethylfurfural and lignin from straw according to claim 2, characterized in that: In the acid solution A, the volume of the organic solvent accounts for 40 to 80% of the total volume of the mixed solvent; preferably 60 to 80%; 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; preferably 20-40%.

6. 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 to 5 cm; and / or, The mass ratio of the straw to the acid solution A is 1:5 to 1:20; preferably 1:8 to 1:10; and / or, The temperature of the heating reaction is 50-200°C, preferably 100-120°C; and / or, The reaction pressure is normal pressure; and / or, The reaction time is 30 to 120 minutes, preferably 90 to 120 minutes.

7. The method for preparing furfural, 5-hydroxymethylfurfural and lignin from straw according to claim 1, characterized in that: In the step 2, the amount of water added is 1 to 5 times, preferably 3 to 4 times, the amount of the organic solvent in the acid solution A in the step 1.

8. The method for preparing furfural, 5-hydroxymethylfurfural and lignin from straw according to claim 1, characterized in that: In the step 2, the heating reaction conditions of the liquid phase 2 are: The temperature of the heating reaction is 120-200° C., preferably 150-180° C.; and / or, The reaction pressure is 0.2-1.0 MPa, preferably 0.4-0.6 MPa; and / or, The reaction time is 60 to 120 minutes, preferably 90 to 120 minutes.

9. 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 the acid solution B is 1:5 to 1:20; preferably 1:10 to 1:15; and / or, The amount of the catalyst is 1-10% of the mass of the cellulose solids, preferably 3-6%; and / or, The temperature of the heating reaction is 160-250° C., preferably 180-220° C.; and / or, The reaction pressure is 0.4-1.0 MPa, preferably 0.8-1.0 MPa; and / or, The reaction time is 5 to 30 minutes, preferably 10 to 20 minutes.

10. The method for preparing furfural, 5-hydroxymethylfurfural and lignin from straw according to claim 1, characterized in that: In step three, the catalyst is one or a combination of AlCl3, AlBr3, ZnCl2, ZnBr2, CoCl2, CoBr2, CrCl3, CrBr3, LiBr, and LiCl.

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