Method for preparing furfural by using corncob as raw material

Abstract

The invention belongs to the technical field of furfural preparation, and particularly relates to a method for preparing furfural by taking corncob as a raw material, which comprises the following steps: raw material pretreatment: pretreating the corncob raw material; the method comprises the following steps: preparing a SO4 < 2-> / ZrO2-WO3 solid acid catalyst by a coprecipitation method; a reaction process: mixing the pretreated corncobs with a SO4 < 2-> / ZrO2-WO3 solid acid catalyst, and adding dilute sulphuric acid to carry out a hydrolysis reaction; and product separation: separating the product after the hydrolysis reaction to obtain the final product furfural. Through the self-made SO4 < 2-> / ZrO2-WO3 solid acid catalyst, the use amount of sulfuric acid is greatly reduced, the equipment cost is reduced, the service life of equipment is prolonged, the maintenance and replacement frequency of the equipment is reduced, and the production cost is further reduced; meanwhile, pollution to the environment is relieved, and the concept of green chemistry and sustainable development is met.

Description

Technical Field

[0001] The invention belongs to the technical field of furfural preparation, and specifically relates to a method for preparing furfural by taking corn cobs as raw materials. Background Art

[0002] Furfural, also known as furfural, is an extremely important organic chemical raw material with a wide range of applications. In the field of plastic production, furfural can be used to synthesize a variety of high-performance plastics, such as phenolic resins. These plastics have excellent mechanical properties, heat resistance, and insulation properties, and are widely used in the manufacturing of electrical appliances, automotive parts, and other fields. In the field of rubber production, furfural can be used as a raw material for rubber vulcanization accelerators, significantly improving the performance of rubber products and extending their service life. In the field of pharmaceutical research and development, furfural is an important intermediate in the synthesis of numerous drugs, providing a foundation for the development of therapeutic drugs for various diseases. In the field of pesticide production, pesticides synthesized using furfural as a raw material are characterized by high efficiency and low toxicity, playing an important role in ensuring the safety of agricultural production. Currently, the main raw material for the industrial production of furfural is agricultural and forestry waste rich in polysaccharides. Corncobs are the most commonly used raw material due to their wide availability and low price.

[0003] The traditional method of preparing furfural using corn cobs as raw materials is mainly the sulfuric acid-catalyzed hydrolysis method. This method mixes corn cobs with dilute sulfuric acid. Under high temperature and high pressure, the pentosan polysaccharides in the corn cobs are decomposed into pentoses, which are further dehydrated to produce furfural. However, this traditional preparation method has the following disadvantages. The strong corrosiveness of sulfuric acid places extremely high demands on the material of the reaction equipment. Special corrosion-resistant alloy materials must be used, which increases the cost of the equipment and shortens the service life of the equipment in a long-term corrosive environment. In addition, a large amount of sulfuric acid is used in the reaction process, and a large amount of alkaline substances are required for subsequent neutralization. This not only increases production costs, but also produces a large amount of saline wastewater. If it is directly discharged without effective treatment, it will cause serious pollution to the soil, water and other ecological environments, and destroy the ecological balance. Summary of the Invention

[0004] The present invention aims to provide a method for preparing furfural using corncobs as raw materials, thereby addressing the problems identified in the aforementioned background art. By comprehensively optimizing various aspects, including the raw material pretreatment method, catalyst system, reaction conditions, and product separation process, the method significantly improves the raw material conversion efficiency, reduces production costs, and achieves green, efficient, and sustainable production of furfural, providing a practical and feasible technical solution for the upgrading and development of the furfural industry.

[0005] To achieve the above object, the technical solution adopted by the present invention is to provide a method for preparing furfural using corn cobs as raw materials, comprising the following steps:

[0006] Raw material pretreatment: pretreatment of corn cob raw materials;

[0007] Catalyst preparation: Preparation of SO4 by co-precipitation 2- / ZrO2-WO3 solid acid catalyst;

[0008] Reaction process: pre-treated corn cobs and SO4 2- / ZrO2-WO3 solid acid catalyst is mixed and dilute sulfuric acid is added to carry out hydrolysis reaction;

[0009] Product separation: Separate the products after the hydrolysis reaction to obtain the final product furfural.

[0010] Optionally, the raw material pretreatment comprises the following steps:

[0011] Particle size control: Use a crushing device to crush the corn cobs to a particle size of 5-15mm;

[0012] Primary drying: Place the crushed corn cob particles in an environment with a temperature of 50-70°C and a relative humidity of 30%-50% for drying until the moisture content drops to 8%-12%;

[0013] Alkali solution soaking: soak the corn cob particles after primary drying in a sodium hydroxide solution with a mass fraction of 1% to 3% for 1 to 2 hours;

[0014] Cleaning and secondary drying: The soaked corn cob particles are repeatedly rinsed with clean water until the rinse liquid becomes neutral; then the corn cob particles are secondary dried to reduce the moisture content to 5%-8%.

[0015] Optionally, the catalyst preparation comprises the following steps:

[0016] Solution preparation: The solid acid catalyst was prepared by coprecipitation method. A certain amount of zirconium sulfate and ammonium metatungstate were weighed and dissolved in deionized water. The mixture was stirred thoroughly with a magnetic stirrer to ensure uniform mixing.

[0017] Precipitation formation: adding ammonia water dropwise to the above mixed solution under stirring, slowly adjusting the pH value of the solution to 8-9, so that a precipitate is formed in the mixed solution;

[0018] Post-treatment: Filter the generated precipitate to remove impurities in the solution, then wash the precipitate repeatedly with deionized water to clean the impurity ions remaining on the surface; dry the washed precipitate at 100-120℃ for 6-8 hours to remove moisture and make the precipitate initially formed; calcine the dried solid at 500-600℃ for 3-4 hours to cause the solid to undergo crystal phase transformation and structural reconstruction through high temperature calcination to form SO4 2- / ZrO2-WO3 solid acid catalyst.

[0019] Optionally, the reaction process comprises the following steps:

[0020] Material addition: Add the pretreated corn cob and the prepared catalyst to the reactor at a mass ratio of 10-15:1; then add a 5%-8% dilute sulfuric acid solution to the reactor, with a mass ratio of corn cob to dilute sulfuric acid solution of 1:8-10;

[0021] Reaction environment creation: After sealing the reactor, introduce nitrogen and use the inertness of nitrogen to replace the air in the reactor;

[0022] Reaction condition control: The internal temperature of the reactor is gradually raised to 160-180°C by a heating device. During the reaction, the materials are stirred and mixed by a stirring device, and the stirring speed is maintained at 200-300 r / min. The stirring time is 2-3 hours.

[0023] Optionally, the product separation comprises the following steps:

[0024] Solid-liquid separation: After the reaction is completed, the materials in the reactor are allowed to cool naturally to room temperature, and the solid residue is separated from the liquid product by filtration or centrifugation;

[0025] Vacuum distillation: The separated liquid portion is subjected to vacuum distillation. Under reduced pressure conditions, the boiling point of the liquid is lowered, allowing the unreacted sulfuric acid and water to be evaporated and separated at a lower temperature;

[0026] Extraction and separation: Use toluene to extract and separate the remaining crude furfural after vacuum distillation;

[0027] Distillation purification: After combining the extraction phases, a distillation operation is performed. Under the conditions of a pressure of 0.05-0.08 MPa and a temperature of 150-160°C, furfural and other impurities are separated by a distillation tower using the difference in boiling points. The fractions within a specific temperature range are collected to obtain the final product, furfural.

[0028] Optionally, the secondary drying method is vacuum drying, the drying temperature is 60-80° C., and the drying time is 4-6 hours.

[0029] Optionally, during the extraction and separation, the volume ratio of toluene to crude furfural is 1:2-3, and the number of extractions is 2-5 times.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention uses homemade SO4 2- / ZrO2-WO3 solid acid catalyst significantly reduces the amount of sulfuric acid used. Compared with the traditional preparation method that uses a large amount of highly corrosive sulfuric acid, the solid acid catalyst significantly reduces the degree of corrosion on the equipment, allowing the reaction equipment to use more conventional materials and reducing equipment costs. At the same time, it extends the service life of the equipment, reduces the frequency of equipment maintenance and replacement, and further reduces production costs. At the same time, the significant reduction in sulfuric acid consumption can significantly reduce the amount of salt-containing wastewater generated in the subsequent neutralization treatment process, reducing pollution to the environment, which is in line with the concepts of green chemistry and sustainable development.

[0032] 2. The present invention improves the structure and reaction activity of corn cobs by optimizing the raw material pretreatment process; adopts a high-efficiency solid acid catalyst to enhance the catalytic effect; and precisely controls the reaction conditions and product separation process to reduce the occurrence of side reactions, thereby increasing the yield of furfural. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 Flowchart of the present invention. DETAILED DESCRIPTION

[0035] Example 1

[0036] Raw material pretreatment:

[0037] The corn cobs were crushed to a particle size of 5 mm using a hammer mill.

[0038] The crushed corn cob particles are placed in a forced air drying oven, set at a temperature of 50°C and a relative humidity of 30%, and dried to a moisture content of 12%. A high-precision humidity sensor is used to monitor humidity changes in real time to ensure that the drying level meets the standard.

[0039] The corn cob particles are soaked in a 1% by mass sodium hydroxide solution for 1 hour, during which mechanical stirring is used to ensure full contact between the corn cob particles and the sodium hydroxide solution. After soaking, the corn cob particles are rinsed with deionized water until neutral, and then placed in a vacuum drying oven for secondary drying to reduce the moisture content to 8%.

[0040] Catalyst preparation:

[0041] Weigh 10 g of zirconium sulfate and 5 g of ammonium metatungstate, add them to 100 mL of deionized water, and stir with a magnetic stirrer for 2 hours to ensure full dissolution.

[0042] Ammonia water was added dropwise under stirring, and the pH value of the solution was monitored using a precision pH meter and adjusted to 8 to form a precipitate in the solution.

[0043] The generated precipitate was filtered with quantitative filter paper and washed 5 times with deionized water; then the precipitate was placed in an electric blast drying oven and dried at 100°C for 8 hours; then placed in a muffle furnace and calcined at 500°C for 4 hours to obtain SO4 2- / ZrO2-WO3 solid acid catalyst.

[0044] Reaction process:

[0045] 100 g of pretreated corn cobs and 10 g of catalyst were added to a stainless steel reactor.

[0046] 800 ml of 5% by mass dilute sulfuric acid solution was measured and added into a stainless steel reactor.

[0047] The reactor was sealed, and nitrogen was introduced through a nitrogen cylinder to replace the air in the reactor three times.

[0048] The reactor was heated to 160° C. using an electric heating mantle, and the magnetic stirrer was started, with the stirring speed maintained at 200 r / min, for 3 hours.

[0049] Product separation:

[0050] After the reaction is completed, the material in the reactor is cooled to room temperature and filtered using a Buchner funnel to achieve solid-liquid separation. The solid residue is washed and dried several times and then weighed.

[0051] The liquid portion was transferred to a rotary evaporator for vacuum distillation to recover unreacted sulfuric acid and water.

[0052] The remaining crude furfural was extracted and separated with toluene using a separatory funnel. The volume ratio of toluene to crude furfural was 1:2, and the extraction was performed twice.

[0053] The extract phases were combined and transferred to a distillation tower for distillation at a pressure of 0.05 MPa and a temperature of 150° C. The furfural fractions were collected, weighed, and the furfural yield was calculated.

[0054]

[0055] The solid residue was weighed to be 30 g, and the furfural yield was calculated to be 60%.

[0056] Example 2

[0057] Raw material pretreatment:

[0058] The corn cobs were crushed to a particle size of 10 mm using a hammer mill.

[0059] The crushed corn cob particles are placed in a forced air drying oven, set at a temperature of 60°C and a relative humidity of 40%, and dried to a moisture content of 10%. A high-precision humidity sensor is used to monitor humidity changes in real time to ensure that the drying level meets the standards.

[0060] The corn cob particles were soaked in a 2% by mass sodium hydroxide solution for 1.5 hours, during which mechanical stirring was used to ensure full contact between the corn cob particles and the solution. After soaking, the corn cob particles were rinsed with deionized water until neutral, and then placed in a vacuum drying oven for secondary drying to reduce the moisture content to 6%.

[0061] Catalyst preparation:

[0062] Weigh 12 g of zirconium sulfate and 6 g of ammonium metatungstate, add them to 120 mL of deionized water, and stir them with a magnetic stirrer for 3 hours to ensure complete dissolution.

[0063] Ammonia water was added dropwise under stirring, and the pH value of the solution was monitored using a precision pH meter and adjusted to 8.5 to form a precipitate in the solution. The precipitate was filtered with quantitative filter paper and washed 5 times with deionized water. The precipitate was then placed in an electric blast drying oven and dried at 110°C for 7 hours. It was then placed in a muffle furnace and calcined at 550°C for 3.5 hours to obtain SO4 2- / ZrO2-WO3 solid acid catalyst.

[0064] Reaction process:

[0065] 120 g of pretreated corn cobs and 12 g of catalyst were added to a stainless steel reactor.

[0066] 960 ml of 6% by mass dilute sulfuric acid solution was measured and added into a stainless steel reactor.

[0067] The reactor was sealed, and nitrogen was introduced through a nitrogen cylinder to replace the air in the reactor three times.

[0068] The reactor was heated to 170° C. using an electric heating mantle, and the magnetic stirrer was started, with the stirring speed maintained at 250 r / min, for 2.5 hours.

[0069] Product separation:

[0070] After the reaction is completed, the materials in the reactor are cooled to room temperature, and then the solid and liquid are separated using a centrifuge. The solid residue is washed and dried several times and then weighed.

[0071] The liquid portion was transferred to a rotary evaporator for vacuum distillation to recover unreacted sulfuric acid and water.

[0072] The remaining crude furfural was extracted and separated with toluene using a separatory funnel. The volume ratio of toluene to crude furfural was 1:2.5, and the extraction was performed three times.

[0073] The extract phases were combined and transferred to a distillation tower for distillation at a pressure of 0.06 MPa and a temperature of 155° C. The furfural fractions were collected, weighed, and the furfural yield was calculated.

[0074]

[0075] The solid residue was weighed to be 28 g, and the furfural yield was calculated to be 65%.

[0076] Example 3

[0077] Raw material pretreatment:

[0078] The corn cobs were crushed to a particle size of 15 mm using a hammer mill.

[0079] The crushed corn cob particles are placed in a forced air drying oven, set at a temperature of 70°C and a relative humidity of 50%, and dried to a moisture content of 8%. A high-precision humidity sensor is used to monitor humidity changes in real time to ensure that the drying level meets the standards.

[0080] The corn cob particles were soaked in a 3% sodium hydroxide solution for 2 hours, during which mechanical stirring was used to ensure full contact between the corn cob particles and the solution. After soaking, the corn cob particles were rinsed with deionized water until neutral, and then placed in a vacuum drying oven for secondary drying to reduce the moisture content to 5%.

[0081] Catalyst preparation:

[0082] Weigh 15 g of zirconium sulfate and 8 g of ammonium metatungstate, add them to 150 mL of deionized water, and stir them with a magnetic stirrer for 4 hours to ensure complete dissolution.

[0083] Ammonia water was added dropwise under stirring, and the pH value of the solution was monitored using a precision pH meter and adjusted to 9 to form a precipitate in the solution.

[0084] The generated precipitate was filtered with quantitative filter paper and washed with deionized water 5 times; then the precipitate was placed in an electric blast drying oven and dried at 120°C for 6 hours; then placed in a muffle furnace and calcined at 600°C for 3 hours to obtain SO4 2- / ZrO2-WO3 solid acid catalyst.

[0085] Reaction process:

[0086] 150 g of pretreated corn cobs and 15 g of catalyst were added into a stainless steel reactor.

[0087] 1200 ml of 8% by mass dilute sulfuric acid solution was measured and added into a stainless steel reactor.

[0088] The reactor was sealed, and nitrogen was introduced through a nitrogen cylinder to replace the air in the reactor three times.

[0089] The reactor was heated to 180°C using an electric heating mantle, and the magnetic stirrer was started, with the stirring speed maintained at 300 r / min, for 2 hours.

[0090] Product separation:

[0091] After the reaction is completed, the material in the reactor is cooled to room temperature and filtered using a Buchner funnel to achieve solid-liquid separation. The solid residue is washed and dried several times and then weighed.

[0092] The liquid portion was transferred to a rotary evaporator for vacuum distillation to recover unreacted sulfuric acid and water.

[0093] The remaining crude furfural was extracted and separated with toluene using a separatory funnel. The volume ratio of toluene to crude furfural was 1:3, and the extraction was performed three times.

[0094] The extract phases were combined and transferred to a distillation tower for distillation at a pressure of 0.08 MPa and a temperature of 160° C. The furfural fractions were collected, weighed, and the furfural yield was calculated.

[0095]

[0096] The solid residue was weighed to be 25 g, and the furfural yield was calculated to be 70%.

[0097] Comparative Example 1

[0098] Furfural was prepared using a conventional sulfuric acid-catalyzed hydrolysis method. Corncobs were crushed to a particle size of 5-15 mm and directly mixed with a 10% by mass dilute sulfuric acid solution, with a corncob to sulfuric acid ratio of 1:6. The reaction mixture was heated to 180°C in a reactor and reacted for 3 hours. The solid acid catalyst of the present invention was not used during the reaction. All other procedures were the same as in Example 1.

[0099] The solid residue was weighed to be 40 g, and the furfural yield was calculated to be 45%.

[0100] Comparative Example 2

[0101] No raw material pretreatment was performed, and other operations were the same as in Example 2.

[0102] The solid residue was weighed to be 35 g, and the furfural yield was calculated to be 55%.

[0103] By comparing the above examples with the comparative examples, it can be seen that:

[0104] The key role of raw material pretreatment: Comparative Example 2 was not pretreated, and the furfural yield was only 55%, significantly lower than the 65% in Example 2. This shows that soaking in sodium hydroxide solution can effectively remove lignin, destroy the dense structure of corn cobs, increase the accessibility of cellulose and hemicellulose, and make the hydrolysis reaction more complete. At the same time, secondary drying controls the moisture content of corn cob particles to 5%-8%, avoiding excessive moisture that reduces the acid concentration, or too little moisture that leads to poor fluidity of the reaction system, further verifying the necessity of the pretreatment process for improving yield.

[0105] Advantages of solid acid catalysts: In Examples 1 to 3, after the catalysts were reused three times, the furfural yield remained above 90% of the initial value (verified by cycle experiments), while the traditional method relied on a large amount of sulfuric acid, which not only corroded the equipment but also made it impossible to reuse the catalytic active components. The catalyst of the present invention is SO4 2- The / ZrO2-WO3 composite structure forms strong acidic sites, significantly reducing the reaction activation energy and improving the catalytic efficiency by about 30% compared with traditional sulfuric acid under the same conditions.

[0106] Synergistic effects of reaction parameters:

[0107] Temperature and Time: The yields of Example 1 (160°C, 3 h), Example 2 (170°C, 2.5 h), and Example 3 (180°C, 2 h) increased gradually, indicating that increasing the temperature can shorten the reaction time, but the reaction time must be below 180°C to avoid furfural decomposition. DSC thermal analysis showed that furfural began to significantly decompose above 190°C, so 160-180°C was the optimal temperature range.

[0108] Sulfuric acid concentration and dosage: The dilute sulfuric acid concentration in the examples is only 5%-8%, significantly lower than the 10% in the traditional method, and the mass ratio of corn cobs to acid solution is 1:8-10 (the traditional ratio is 1:6). This shows that the solid acid catalyst can significantly reduce the dependence on sulfuric acid and reduce the load of subsequent wastewater treatment.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing furfural using corncobs as raw materials, characterized in that: The following steps are involved: Raw material pretreatment: pretreatment of corn cob raw materials; Catalyst preparation: Preparation of SO4 by co-precipitation 2- / ZrO2-WO3 solid acid catalyst; Reaction process: pre-treated corn cobs and SO4 2- / ZrO2-WO3 solid acid catalyst is mixed and dilute sulfuric acid is added to carry out hydrolysis reaction; Product separation: Separate the products after the hydrolysis reaction to obtain the final product furfural.

2. The method for preparing furfural using corncobs as raw materials according to claim 1, wherein: The raw material pretreatment comprises the following steps: Particle size control: Use a crushing device to crush the corn cobs to a particle size of 5-15mm; Primary drying: Place the crushed corn cob particles in an environment with a temperature of 50-70°C and a relative humidity of 30%-50% for drying until the moisture content drops to 8%-12%; Alkali solution soaking: soak the corn cob particles after primary drying in a sodium hydroxide solution with a mass fraction of 1% to 3% for 1 to 2 hours; Cleaning and secondary drying: The soaked corn cob particles are repeatedly rinsed with clean water until the rinse liquid becomes neutral; then the corn cob particles are secondary dried to reduce the moisture content to 5%-8%.

3. The method for preparing furfural using corncobs as raw materials according to claim 1, wherein: The catalyst preparation comprises the following steps: Solution preparation: The solid acid catalyst was prepared by coprecipitation method. A certain amount of zirconium sulfate and ammonium metatungstate were weighed and dissolved in deionized water. The mixture was stirred thoroughly with a magnetic stirrer to ensure uniform mixing. Precipitation formation: adding ammonia water dropwise to the above mixed solution under stirring, slowly adjusting the pH value of the solution to 8-9, so that a precipitate is formed in the mixed solution; Post-treatment: Filter the generated precipitate to remove impurities in the solution, then wash the precipitate repeatedly with deionized water to clean the impurity ions remaining on the surface; dry the washed precipitate at 100-120℃ for 6-8 hours to remove moisture and make the precipitate initially formed; calcine the dried solid at 500-600℃ for 3-4 hours to cause the solid to undergo crystal phase transformation and structural reconstruction through high temperature calcination to form SO4 2- / ZrO2-WO3 solid acid catalyst.

4. The method for preparing furfural using corncobs as raw materials according to claim 1, wherein: The reaction process comprises the following steps: Material addition: Add the pretreated corn cob and the prepared catalyst to the reactor at a mass ratio of 10-15:1; then add a 5%-8% dilute sulfuric acid solution to the reactor, with a mass ratio of corn cob to dilute sulfuric acid solution of 1:8-10; Reaction environment creation: After sealing the reactor, introduce nitrogen and use the inertness of nitrogen to replace the air in the reactor; Reaction condition control: The internal temperature of the reactor is gradually raised to 160-180°C by a heating device. During the reaction, the materials are stirred and mixed by a stirring device, and the stirring speed is maintained at 200-300 r / min. The stirring time is 2-3 hours.

5. The method for preparing furfural using corncobs as raw materials according to claim 1, wherein: The product separation comprises the following steps: Solid-liquid separation: After the reaction is completed, the materials in the reactor are allowed to cool naturally to room temperature, and the solid residue is separated from the liquid product by filtration or centrifugation; Vacuum distillation: The separated liquid portion is subjected to vacuum distillation. Under reduced pressure conditions, the boiling point of the liquid is lowered, allowing the unreacted sulfuric acid and water to be evaporated and separated at a lower temperature; Extraction and separation: Use toluene to extract and separate the remaining crude furfural after vacuum distillation; Distillation purification: After combining the extraction phases, a distillation operation is performed. Under the conditions of a pressure of 0.05-0.08 MPa and a temperature of 150-160°C, furfural and other impurities are separated by a distillation tower using the difference in boiling points. The fractions within a specific temperature range are collected to obtain the final product, furfural.

6. The method for preparing furfural using corncobs as raw materials according to claim 2, wherein: The secondary drying method is vacuum drying, the drying temperature is 60-80°C, and the drying time is 4-6 hours.

7. The method for preparing furfural using corncobs as raw materials according to claim 5, wherein: During extraction and separation, the volume ratio of toluene to crude furfural is 1:2-3, and the number of extractions is 2-5 times.

Images