Furfural production process

Abstract

The invention provides a furfural production process which comprises the following steps: step 1, preparing and pretreating raw materials, namely selecting corncobs, agricultural waste straws, rice hulls and cottonseed hulls in a specific proportion as mixed raw materials, and pretreating the raw materials through the steps of drying, crushing, steam explosion and the like; 2, adopting a mixed solvent composed of an ionic liquid and a low-boiling-point polar organic solvent, adding a specific proportion of a catalyst, carrying out a reaction in an electric heating reaction kettle, and controlling the reaction temperature, the reaction time and the stirring rate; and step 3, separating and purifying the product, and removing solid impurities and residual solvents in the reaction liquid through the steps of vacuum filtration, reduced pressure distillation, extraction, rectification and the like. The method is high in yield and low in impurity content.

Description

Technical Field

[0001] The invention relates to a method for processing chemical raw materials, and in particular to a furfural production process. Background Art

[0002] Furfural, also known as 2-furan carboxaldehyde, is an important organic chemical raw material, widely used in synthetic plastics, medicine, pesticides, spices and other fields. It is a colorless, transparent, oily liquid with a special smell similar to benzaldehyde. Melting point: -36℃ (some say -38.7℃). Boiling point: 161.7℃. Density: 1.16g / cm 3 . Flash point: 60℃. Solubility: slightly soluble in cold water, soluble in hot water, ethanol, ether, benzene and other organic solvents. Furfural contains aldehyde and diene ether functional groups in its molecular structure, so it has the properties of aldehyde, ether, diene and other compounds. It can undergo oxidation, hydrogenation, nitration, decarbonylation, condensation and other chemical reactions to produce a variety of derivatives.

[0003] The main raw materials of furfural are agricultural and sideline waste such as corn cobs, rice husks, and cottonseed hulls, which are rich in cellulose and hemicellulose. In order to increase the yield of furfural, the raw materials need to be pretreated, including crushing, drying, screening and other steps, so that the particle size and moisture content of the raw materials meet the reaction requirements. Acid hydrolysis and hydrolysis: Acid hydrolysis: The pretreated raw materials are mixed with dilute sulfuric acid and heated to a certain temperature to cause acid hydrolysis reaction of cellulose and hemicellulose in the raw materials to generate furfural and other by-products. Hydrolysis: The mixture after acid hydrolysis is diluted with water and heated to a certain temperature to separate furfural from other by-products to obtain crude furfural. Post-treatment: Crude furfural contains a large amount of impurities, such as acid, alcohol, aldehyde, etc., and post-treatment is required to obtain furfural with higher purity. Post-treatment methods include distillation, extraction, crystallization, etc. Among them, distillation is the most commonly used method. Impurities in crude furfural can be separated by distillation to obtain furfural with higher purity.

[0004] Furfural production can be divided into two types according to the hydrolysis process: direct one-step method and two-step method. Modern production almost exclusively adopts the one-step method, which has a relatively simple process flow and a high yield.

[0005] Furfural and its derivatives have a wide range of uses, including but not limited to the following: Raw materials for organic synthesis: Furfural can be used in synthetic resins, varnishes, pesticides, medicines, rubbers and coatings. Industrial solvent: Furfural is an excellent organic solvent that can be used to refine high-grade lubricants and diesel. Furfural can also be used to prepare furfuryl alcohol, furoic acid, tetrahydrofuran, γ-valerolactone, pyrrole, tetrahydropyrrole and other compounds, as well as as an analytical reagent and raw material for tanning leather.

[0006] Furfural production Due to improper reaction conditions and high impurity content of raw materials, crude furfural often contains a large amount of impurities, such as acid, alcohol, aldehyde, etc., and further refining is required to obtain furfural with higher purity. The existing furfural refining process is often complicated and requires a lot of energy and time. At the same time, the wastewater, waste gas and other pollutants generated during the refining process also need to be treated. Summary of the invention

[0007] Aiming at the deficiencies of the prior art, the present invention provides a furfural production process.

[0008] In order to achieve the above purpose, the present invention adopts the following scheme:

[0009] A furfural production process comprises the following steps:

[0010] Step 1, raw material preparation and pretreatment, selecting corn cobs, agricultural waste straw, rice husks and cottonseed husks in a specific proportion as mixed raw materials, and pretreating the raw materials through steps such as drying, crushing and steam explosion;

[0011] Step 2, using a mixed solvent consisting of an ionic liquid and a low-boiling point polar organic solvent, and adding a catalyst in a specific proportion, reacting in an electrically heated reactor, and controlling the reaction temperature, time and stirring rate;

[0012] Step 3, separating and purifying the product, removing solid impurities and residual solvent in the reaction solution through vacuum filtration, reduced pressure distillation, extraction and rectification.

[0013] In step 1, corn cobs (50-65% by weight), agricultural waste straw (15-25%), rice husks (8-15%) and cottonseed husks (8-15%) are specifically selected as mixed raw materials, with a total weight of 100%.

[0014] The drying condition in step 1 is drying at 80-100° C. for 2-4 hours; the crushing step uses a hammer mill to crush the dried raw material until it passes through a 20-mesh screen; the steam explosion step is kept warm at a steam pressure of 1.5-2.0 MPa for 5-10 minutes, and then the pressure is quickly released.

[0015] In step 2, a mixed solvent consisting of an ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and a low-boiling point polar organic solvent 1,4-dioxane is used, and the ionic liquid and 1,4-dioxane are evenly mixed in a volume ratio of 1:1.5-2 to obtain a mixed solvent; then the mixed solvent and water are mixed in a volume ratio of 1:45-50 to form a reaction solvent.

[0016] In step 2, a phosphotungstic acid-based phase transfer catalyst (HPW) is selected as the main catalyst, and betaine is added to the phosphotungstic acid at a mass ratio of 0.1:1 through an ion exchange reaction to modify the catalyst, thereby obtaining a modified catalyst.

[0017] The reaction conditions in step 2 are as follows: the reaction is carried out in an electrically heated reactor, the reaction temperature is controlled to be 120-140° C., the reaction time is 2-3 hours, the mass ratio of the raw material to the catalyst is 1:0.005-0.006, and the stirring rate is 600-800 r / min.

[0018] In step 3, a vacuum filtration device is used to remove solid impurities in the reaction solution; then, furfural is distilled out of the reaction solution by reduced pressure distillation at 80-90° C. and 0.1-0.2 MPa.

[0019] The furfural solution obtained by distillation is further subjected to extraction treatment using toluene as an extractant to remove impurities therein; the extracted furfural solution is further subjected to rectification treatment to further remove residual solvents and impurities.

[0020] The mass ratio of raw material to catalyst is 1:0.0055.

[0021] The vacuum distillation was carried out at 85°C and 0.15 MPa.

[0022] The invention has higher yield and less impurities. DETAILED DESCRIPTION

[0023] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention are further described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0024] The detailed steps of the present invention are specifically described below:

[0025] 1. Raw material preparation and pretreatment

[0026] Raw material selection: corn cobs (50-65% by weight), agricultural waste straw (15-25%), rice husks (8-15%), and cottonseed husks (8-15%) are selected as mixed raw materials; the total weight is 100%. These raw materials are rich in hemicellulose, low in cost, and easy to obtain.

[0027] Preprocessing steps:

[0028] Drying: Place the mixed raw materials in a hot air dryer and dry at 80-100℃ for 2-4 hours to remove moisture from the raw materials.

[0029] Crushing: Use a hammer mill to crush the dried raw materials until they pass through a 20-mesh sieve to ensure that the raw materials are uniform and fine.

[0030] Steam explosion: The crushed raw materials are placed in a steam explosion device, kept warm at a steam pressure of 1.5-2.0 MPa for 5-10 minutes, and then the pressure is quickly released to cause the raw materials to expand and explode instantly, destroying the cell wall structure and improving the accessibility of hemicellulose.

[0031] 2. Reaction system and reaction process

[0032] Selection and preparation of reaction solvent: A mixed solvent consisting of ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and low-boiling point polar organic solvent 1,4-dioxane is used; then mixed with water as a reaction solvent. The ionic liquid and 1,4-dioxane are mixed uniformly at a volume ratio of 1:1.5-2 to obtain a mixed solvent, and then the mixed solvent and water are mixed at a volume ratio of 1:45-50 to form a reaction solvent.

[0033] Selection and improvement of catalyst: A phosphotungstic acid-based phase transfer catalyst (HPW) was selected as the main catalyst, and betaine (a quaternary ammonium base / salt containing a hydrophilic functional group of a carboxyl group) was added to the phosphotungstic acid at a mass ratio of 0.1:1 through an ion exchange reaction to obtain a modified catalyst.

[0034] Reaction conditions: The reaction is carried out in an electrically heated reactor, the reaction temperature is controlled at 120-140°C, the reaction time is 2-3 hours, the mass ratio of raw materials to catalyst is 1:0.005-0.006, and the stirring rate is 600-800r / min. During the reaction, the temperature, pressure, stirring rate and other parameters are closely monitored, and the composition and furfural content of the reaction liquid are regularly sampled and analyzed.

[0035] 3. Product separation and purification

[0036] Product separation: After the reaction is completed, a vacuum filtration device is used to remove solid impurities in the reaction solution, and then furfural is distilled out of the reaction solution by reduced pressure distillation at 80-90°C and 0.1-0.2MPa.

[0037] Product purification: Toluene is used as the extractant to extract the furfural solution obtained by distillation to remove impurities. The extracted furfural solution is then distilled to further remove residual solvents and impurities to obtain a high-purity furfural product.

[0038] Embodiment 1

[0039] Raw material preparation and pretreatment: The raw materials were corn cobs (60%), agricultural waste straw (20%), rice husks (10%), and cottonseed husks (10%). The raw materials were dried at 90°C for 3 hours, crushed to pass through a 20-mesh screen, and steam exploded at 1.8 MPa for 7 minutes.

[0040] Reaction system and reaction process: Reaction solvent: ionic liquid [BMIM]Cl and 1,4-dioxane are mixed at a volume ratio of 1:1.7, and then mixed with water at a volume ratio of 1:47. The catalyst is HPW and betaine modified at a mass ratio of 0.1:1. Reaction conditions: 130°C, reaction time 2.5 hours, raw material to catalyst mass ratio 1:0.0055, stirring rate 700r / min.

[0041] Product separation and purification: Separation conditions: 85°C, 0.15MPa reduced pressure distillation. Furfural yield is 78.5%, purity is 99.6%. Impurity content: unreacted raw material residue 0.09%, total by-product 0.18%, including furfuryl alcohol 0.028%, 5-methylfurfural 0.019%, furoic acid 0.025%, 2-furfuryl alcohol 0.039%, cyclopentanone 0.039%, solvent residue 0.045%.

[0042] Embodiment 2

[0043] Raw material preparation and pretreatment: Raw materials: corn cobs (55%), agricultural waste straw (25%), rice husks (8%), cottonseed husks (12%). The raw materials were dried at 85°C for 4 hours, crushed to pass through a 20-mesh screen, and steam exploded at 1.6 MPa for 9 minutes.

[0044] Reaction system and reaction process: Reaction solvent: ionic liquid [BMIM]Cl and 1,4-dioxane are mixed in a volume ratio of 1:2, and then mixed with water in a volume ratio of 1:50. The catalyst is HPW and betaine modified in a mass ratio of 0.1:1. Reaction conditions: 125°C, reaction time 3 hours, raw material to catalyst mass ratio 1:0.006, stirring rate 650r / min.

[0045] Product separation and purification: Separation conditions: 80°C, 0.2MPa reduced pressure distillation. Purification results showed that the furfural yield was 79.2% and the purity was 99.7%. Impurity content: 0.08% of unreacted raw materials remained, and the total amount of by-products was 0.16%, including 0.025% furfuryl alcohol, 0.018% 5-methylfurfural, 0.027% furoic acid, 0.035% 2-furfuryl alcohol, 0.035% cyclopentanone, and 0.04% solvent residue.

[0046] Embodiment 3

[0047] Raw material preparation and pretreatment: Raw materials corn cob (65%), agricultural waste straw (15%), rice husk (15%), cottonseed husk (5%). The raw materials were dried at 100°C for 2 hours, crushed to pass through a 20-mesh screen, steam exploded at 2.0 MPa, and kept warm for 5 minutes.

[0048] Reaction system and reaction process: Reaction solvent: ionic liquid [BMIM]Cl and 1,4-dioxane are mixed at a volume ratio of 1:1.5, and then mixed with water at a volume ratio of 1:45. The catalyst is HPW and betaine modified at a mass ratio of 0.1:1. Reaction conditions: 140°C, reaction time 2 hours, raw material to catalyst mass ratio 1:0.005, stirring rate 800r / min.

[0049] Product separation and purification: Separation conditions: 90°C, 0.1MPa reduced pressure distillation. Purification results: furfural yield is 77.8%, purity is 99.5%. Impurity content: unreacted raw material residue 0.1%, total by-product 0.2%, including furfuryl alcohol 0.03%, 5-methylfurfural 0.02%, furoic acid 0.03%, 2-furfuryl alcohol 0.04%, cyclopentanone 0.04%, solvent residue 0.05%.

[0050] Embodiment 4

[0051] Raw material preparation and pretreatment: Raw materials corn cob (50%), agricultural waste straw (20%), rice husk (12%), cottonseed husk (18%). The raw materials were dried at 80°C for 4 hours, crushed to pass through a 20-mesh screen, steam exploded at 1.5 MPa, and kept warm for 10 minutes.

[0052] Reaction system and reaction process: Reaction solvent: ionic liquid [BMIM]Cl and 1,4-dioxane are mixed at a volume ratio of 1:1.8, and then mixed with water at a volume ratio of 1:48. The catalyst is HPW and betaine modified at a mass ratio of 0.1:1.

[0053] Reaction conditions: 135°C, reaction time 2.5 hours, raw material to catalyst mass ratio 1:0.0058, stirring rate 750 r / min.

[0054] Product separation and purification: Separation conditions: 88°C, 0.12MPa reduced pressure distillation. Purification results: furfural yield is 79.0%, purity is 99.65%. Impurity content: unreacted raw material residue is 0.095%, total by-products are 0.17%, including furfuryl alcohol 0.027%, 5-methylfurfural 0.019%, furoic acid 0.028%, 2-furfuryl alcohol 0.038%, cyclopentanone 0.038%, solvent residue 0.042%.

[0055] Comparative Example 5

[0056] Raw material preparation and pretreatment: Raw materials corn cobs (60%), agricultural waste straw (20%), rice husks (10%), and cottonseed husks (10%).

[0057] The raw materials were dried at 90°C for 3 hours, crushed to pass through a 20-mesh screen, and steam exploded at 1.8 MPa for 7 minutes.

[0058] Reaction system and reaction process:

[0059] Reaction solvent: A similar ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4) was selected and mixed with a low boiling point polar organic solvent dimethyl sulfoxide (DMSO) at a volume ratio of 1:1.7, and then mixed with water at a volume ratio of 1:50. The catalyst was a heteropolyacid catalyst silicotungstic acid (HSiW) and was modified by adding the same mass ratio of betaine. Reaction conditions: 130°C, reaction time 2.5 hours, raw material to catalyst mass ratio 1:0.0055, stirring rate 700r / min.

[0060] Product separation and purification: separation conditions: 85°C, 0.15MPa reduced pressure distillation. Purification results: furfural yield is 72.5%, purity is 98.0%. Impurity content: unreacted raw material residue is 0.35%, total by-products are 0.9%, including furfuryl alcohol 0.14%, 5-methylfurfural 0.1%, furoic acid 0.15%, 2-furfuryl alcohol 0.2%, cyclopentanone 0.21%, solvent residue 0.2%.

[0061] Comparative Example 6

[0062] Raw material preparation and pretreatment: Raw materials corn cob (55%), agricultural waste straw (25%), rice husk (8%), cottonseed husk (12%). The raw materials were dried at 85°C for 4 hours, crushed to pass through a 20-mesh screen, steam exploded at 1.6 MPa, and kept warm for 9 minutes.

[0063] Reaction system and reaction process:

[0064] The reaction solvent is a mixture of a similar ionic liquid 1-octyl-3-methylimidazolium chloride ([OMIM]Cl) and a low-boiling polar organic solvent acetonitrile (ACN) at a volume ratio of 1:2, and then mixed with water at a volume ratio of 1:55. The catalyst is a solid acid catalyst niobate (HNbO3) and is modified by adding the same mass ratio of betaine. The reaction conditions are 125°C, the reaction time is 3 hours, the mass ratio of raw materials to catalyst is 1:0.006, and the stirring rate is 650r / min.

[0065] Product separation and purification: Separation conditions: 80°C, 0.2MPa vacuum distillation. Purification results: furfural yield is 73.2%, purity is 97.8%. Impurity content: 0.5% of unreacted raw materials remain, total by-products are 1.0%, each component has increased significantly, and solvent remains 0.25%.

[0066]

[0067] The technical advantages of the present invention are:

[0068] High yield. The production process of the present invention can achieve a furfural yield of 79%, significantly improving the yield of furfural. This is mainly due to the optimized raw material pretreatment steps, the efficient reaction system and the effective product separation and purification method.

[0069] High purity: Through distillation and purification, the purity of the furfural product can reach more than 99.5%. This is mainly due to the application of the two-liquid phase reaction system and the purification method combining extraction and distillation, which can effectively remove low-boiling point and high-boiling point impurities.

[0070] Low impurity content: After testing, the main impurities in the furfural product produced by this method include unreacted raw material residues, by-products and solvent residues. Among them, the unreacted raw material residues are less than 0.1%, the by-product content is less than 0.2%, among which furfuryl alcohol is less than 0.03%, 5-Methylfurfural is less than 0.02%, furoic acid is less than 0.03%, 2-furylmethanol is less than 0.04%, cyclopentanone is less than 0.04%, and the solvent residue is less than 0.05%. These low impurity contents ensure the high quality and wide applicability of furfural products.

[0071] In the present invention, the phosphotungstic acid-based phase transfer catalyst (HPW) selected has been significantly improved in catalytic activity after being modified with betaine, and exhibits a good directional catalytic effect. Specifically, the modified catalyst can more efficiently promote the reaction path of hemicellulose conversion to furfural, while inhibiting the occurrence of other side reactions. This is mainly due to the optimized interaction between the active sites on the catalyst surface and the reactant molecules, making it easier for the reactant molecules to be converted according to the target reaction path.

[0072] Since the catalyst has a directional catalytic effect, it can more efficiently promote the conversion of hemicellulose into furfural, thereby significantly improving the yield of furfural. This not only reduces production costs, but also improves production efficiency. The directional catalytic effect can inhibit non-target reaction paths, thereby reducing the generation of by-products. In this technical solution, through the directional catalytic effect, the content of by-products such as furfuryl alcohol, 5-methylfurfural, furoic acid, 2-furfuryl methanol and cyclopentanone is significantly reduced, ensuring the high purity of the furfural product.

[0073] The modified catalyst not only has higher catalytic activity, but also shows better stability and recyclability, which means that the catalyst can be reused multiple times while maintaining its catalytic performance, further reducing production costs and environmental pollution.

[0074] Through directional catalysis, furfural products with higher purity can be obtained to meet the demand for high-quality raw materials in the fields of medicine, pesticides, dyes, fragrances and resin synthesis.

[0075] Due to the high efficiency and recyclability of the catalyst, production costs can be reduced and production efficiency can be improved. At the same time, reducing the generation of by-products also helps to reduce subsequent processing costs. Directed catalysis reduces the generation of by-products and the content of impurities such as solvent residues, thereby reducing environmental pollution during the production process.

[0076] This technical solution uses a mixed solvent consisting of ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and low-boiling point polar organic solvent 1,4-dioxane, which is then mixed with water as a reaction solvent. This solvent system has unique advantages: ionic liquids have strong dissolving power and high stability, and can effectively dissolve and catalyze the conversion of hemicellulose in the raw material into furfural; low-boiling point polar organic solvents help to form a two-liquid phase reaction system, which is beneficial to the separation and purification of furfural; the addition of water further promotes the reaction and helps to reduce solvent residues. This optimized solvent system not only improves the yield and purity of furfural, but also effectively reduces the content of impurities such as solvent residues.

[0077] In summary, this technical solution ensures low impurity content and high quality of furfural products through various measures such as refined raw material pretreatment, optimized reaction solvent system, efficient catalyst selection and improvement, strict reaction condition control, and efficient separation and purification process. These advantages make the furfural products produced by this technical solution have broad application prospects in the fields of medicine, pesticides, dyes, fragrances, and resin synthesis.

[0078] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A furfural production process, characterized in that The following steps are involved: Step 1, raw material preparation and pretreatment, selecting corn cobs, agricultural waste straw, rice husks and cottonseed husks in a specific proportion as mixed raw materials, and pretreating the raw materials through steps such as drying, crushing and steam explosion; Step 2, using a mixed solvent consisting of an ionic liquid and a low-boiling point polar organic solvent, and adding a catalyst in a specific proportion, reacting in an electrically heated reactor, and controlling the reaction temperature, time and stirring rate; Step 3, separating and purifying the product, removing solid impurities and residual solvent in the reaction solution through vacuum filtration, reduced pressure distillation, extraction and rectification.

2. The furfural production process according to claim 1, characterized in that In step 1, corn cobs (50-65% by weight), agricultural waste straw (15-25%), rice husks (8-15%) and cottonseed husks (8-15%) are specifically selected as mixed raw materials, with a total weight of 100%.

3. The furfural production process according to claim 1, characterized in that The drying condition in step 1 is drying at 80-100° C. for 2-4 hours; the crushing step uses a hammer mill to crush the dried raw material until it passes through a 20-mesh screen; the steam explosion step is kept warm at a steam pressure of 1.5-2.0 MPa for 5-10 minutes, and then the pressure is quickly released.

4. The furfural production process according to claim 1, characterized in that In step 2, a mixed solvent consisting of an ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and a low-boiling point polar organic solvent 1,4-dioxane is used, and the ionic liquid and 1,4-dioxane are evenly mixed at a volume ratio of 1:1.5-2 to obtain a mixed solvent; then the mixed solvent is mixed with water at a volume ratio of 1:45-50 to form a reaction solvent.

5. The furfural production process according to claim 1, characterized in that In step 2, a phosphotungstic acid-based phase transfer catalyst (HPW) is selected as the main catalyst, and betaine is added to the phosphotungstic acid at a mass ratio of 0.1:1 through an ion exchange reaction for modification to obtain a modified catalyst.

6. The furfural production process according to claim 1, characterized in that The reaction conditions in step 2 are to carry out the reaction in an electrically heated reactor, control the reaction temperature to be 120-140° C., the reaction time to be 2-3 hours, the mass ratio of the raw material to the catalyst to be 1:0.005-0.006, and the stirring rate to be 600-800 r / min.

7. The furfural production process according to claim 1, characterized in that In step 3, a vacuum filtration device is used to remove solid impurities in the reaction solution; then the reaction solution is distilled under reduced pressure at 80-90°C. Furfural is distilled out from the reaction solution under the condition of 0.1-0.2MPa.

8. The furfural production process according to claim 7, characterized in that The furfural solution obtained by distillation is further subjected to extraction treatment using toluene as an extractant to remove impurities therein; the extracted furfural solution is further subjected to rectification treatment to further remove residual solvents and impurities.

9. The furfural production process according to claim 6, characterized in that The mass ratio of raw material to catalyst is 1:0.0055.

10. The furfural production process according to claim 7, characterized in that The distillation was carried out under reduced pressure at 85°C and 0.15 MPa.

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