One-step furfural preparation method using biomass as raw material

Abstract

The invention provides a one-step furfural preparation method taking biomass as a raw material, and relates to the technical field of resource utilization of agricultural and forestry wastes. The method comprises the steps of raw material pretreatment, catalytic liquid preparation, hydrolysis dehydration reaction, solid-liquid separation, washing liquid reuse, product purification, catalytic liquid recovery and the like. The reaction is completed by adopting a closed reactor under the condition of not introducing external steam, so that the energy consumption is obviously reduced; the catalytic liquid is formed by compounding sulfuric acid and Lewis acid, so that the reaction efficiency is high; closed circulation of the catalytic liquid and recycling of water resources are realized through rectification and ceramic membrane filtration. The method is simple in process flow, low in pollution emission and suitable for green and efficient bran preparation of various hemicellulose raw materials such as corncobs and straw, the purity of the obtained product can reach 99% or above, and the method has good industrial application prospects.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of biomass resources and preparation of bio-based chemicals, specifically to a one-step method for preparing furfural using biomass as raw material, which falls under the technical category of resource utilization and high-value-added transformation and application of agricultural and forestry waste. Background Technology

[0002] In the existing field of biomass resource utilization, furfural is a key bio-based platform compound with wide applications in multiple downstream industries such as fuel additives, pharmaceutical intermediates, and synthetic materials. It plays a significant role in replacing petrochemical resources and promoting the development of green chemistry. Currently, furfural production mainly relies on agricultural and forestry waste, particularly raw materials rich in hemicellulose such as corn cobs and straw, through acid-catalyzed hydrolysis and dehydration reactions to obtain the target product.

[0003] In existing technologies, the most common furfural production process is the acid-catalyzed steam stripping method. This method mainly consists of two steps: first, the pulverized and dried raw material is mixed with dilute sulfuric acid and hydrolyzed under heating and pressure to produce xylose; then, a large amount of high-temperature steam is introduced to dehydrate the xylose and produce furfural, which is then volatilized and separated using steam stripping. This type of method is relatively mature and has a certain industrialization foundation, but it also has many limitations.

[0004] For example, Chinese patent CN101302206A discloses a method for producing furfural from corn cobs. It uses dilute sulfuric acid to mix with the raw materials and then introduces steam to carry out a hydrolysis reaction. It relies on condensation and distillation columns for multiple purifications. Although the product purity is high, the entire reaction cycle is long (up to 4-6 hours) and requires a large amount of high-pressure steam, which not only consumes a lot of energy but also increases the difficulty of wastewater treatment.

[0005] Similarly, the method described in Chinese patent CN104557814A uses a lower concentration of sulfuric acid in the reaction, which reduces corrosivity to some extent, but it also has the problems of high energy consumption and high wastewater discharge, and does not clearly define the relationship between raw material particle size and furfural yield.

[0006] In addition, Chinese patent CN101914078A proposed a furfural preparation route using sugarcane bagasse as raw material. Although the reaction time is shortened (about 2 hours), it still uses steam-driven reaction separation, so the wastewater problem remains prominent, and the applicable range of its raw materials is limited.

[0007] Furthermore, Chinese patents CN110590718A and CN113861140A respectively attempted to optimize the yield by adding pretreatment steps or introducing an oil-water two-phase system, but their reaction process still requires a large amount of steam pressurization, the recovery system is complex, and the equipment requirements are high, failing to fundamentally solve the problem of "high energy consumption and high emissions" in furfural production.

[0008] In summary, existing furfural preparation technologies generally have the following common problems: (1) they rely on high-pressure steam to drive the reaction and separation, resulting in high energy consumption; (2) they generate a large amount of wastewater, which is difficult to treat; (3) the reaction process is long and the yield is easily affected by process control; (4) although some technologies introduce a recovery mechanism, the system is complex and economically inefficient.

[0009] Therefore, developing a furfural preparation process that does not require the introduction of large amounts of steam, has a short reaction time, high energy utilization, and enables the recycling of catalytic liquid is of great significance for reducing environmental pollution, improving economic feasibility, and promoting the green transformation of the furfural industry. Summary of the Invention

[0010] To address the problems commonly found in existing furfural production processes, such as high steam consumption, high energy consumption, high wastewater treatment pressure, and complex production processes, this invention provides a one-step furfural preparation method using biomass as raw material. This method significantly simplifies the furfural production process by optimizing raw material pretreatment, controlling raw material particle size, introducing a novel catalytic liquid ratio, and employing a closed reactor for hydrolysis, combined with a distillation and catalyst recovery system.

[0011] Compared with the traditional two-step acidolysis-steam extraction process, this invention has the advantages of simplified operation, significantly shortened reaction time, reduced steam consumption, lower energy consumption, and a substantial reduction in wastewater discharge. Furthermore, by recycling the catalytic liquid and utilizing byproducts, this invention improves the overall environmental friendliness and economy of the process, demonstrating promising prospects for industrial application.

[0012] According to one embodiment of the present invention, a one-step method for preparing furfural using biomass as raw material is provided, aiming to improve furfural yield, product purity, and comprehensive utilization efficiency of raw material resources through an integrated and efficient continuous process. The method includes the following steps:

[0013] (1) Raw material pretreatment: Select biomass raw materials rich in hemicellulose, such as corn cobs, corn stalks or tobacco stalks, etc., and first wash them to remove surface dust and impurities, and then crush them. By controlling the particle size to 0.1-10 mm, ensure that the raw materials have good reactivity and contact area in the subsequent hydrolysis reaction, which is conducive to the efficient release of furfural.

[0014] (2) Catalyst preparation: An acid catalytic system is used to achieve the hydrolysis of hemicellulose. The catalyst is prepared by mixing water and an acidic catalyst, wherein the catalyst can be sulfuric acid alone, or a complex Lewis acid system formed by sulfuric acid and one or more salts of ferric chloride, aluminum chloride, or zinc chloride. This combination helps to improve catalytic efficiency. The acid concentration (calculated as sulfuric acid) of the catalyst is controlled at 2% to 5% (w / w), which can effectively hydrolyze the raw materials and avoid side reactions. The catalyst can be freshly prepared or regenerated catalyst separated and recovered from the previous batch of production.

[0015] (3) Hydrolysis reaction: The pretreated biomass raw material from step (1) and the catalytic solution prepared in step (2) are added to a closed hydrolysis reactor at a solid-liquid mass ratio of 1:4 to 1:13. The reaction is carried out under stirring conditions of 150℃ to 180℃ and 0.6 to 1.0 MPa for 10 to 60 minutes. This integrated reaction system achieves efficient hydrolysis of hemicellulose and simultaneous generation of furfural, simplifies the multi-stage reaction and transfer steps in the traditional process, and improves the product yield.

[0016] (4) Solid-liquid separation: The above reaction mixture is filtered at 0.1-0.5 MPa to obtain a liquid product (containing furfural) and a solid residue (furfural residue). This step facilitates the subsequent purification of furfural and reduces the accumulation of impurities in the system.

[0017] (5) Washing and solid-liquid separation: The solid furfural residue is washed multiple times with recycled washing water at 25℃~80℃ to effectively recover furfural adsorbed on the surface and inside of the residue, while removing residual acidic substances. This not only improves the overall furfural yield but also reduces the corrosiveness and environmental burden of the waste residue.

[0018] (6) Washing liquid treatment: The washing liquid is introduced into the distillation column, and the top distillate containing furfural is recovered during the distillation process. The bottom liquid is filtered, and the resulting liquid is replenished with fresh water and reused as the washing water in step (5), thus constructing a recycling system for catalytic liquid and water.

[0019] (7) Product purification and catalyst recovery: The liquid product obtained in step (4) and the distillate from the top of the column in step (6) are combined into an integrated separation system. The system includes a phase separator and a distillation column combined unit. The furfural and water are separated by the density and volatility difference. Finally, furfural product with a purity of ≥99% is obtained. At the same time, the catalyst is separated and recovered for the next cycle reaction, which significantly reduces operating costs and environmental burden.

[0020] Furthermore, in step (1), the raw material crushing preferably adopts a graded crushing process to ensure that the particle size of the mixed particles meets the following requirements: the proportion of particles with a particle size ≤ 2 mm is ≥ 80%, or the proportion of particles with a particle size ≤ 4 mm is ≥ 80%. This measure enhances the uniformity and controllability of the material reaction interface.

[0021] Furthermore, the recovered catalyst in step (2) can be prepared by the following method: the residue in the distillation column in step (7) is filtered through a ceramic membrane with a molecular weight cutoff of 1000 Da to separate organic impurities and catalytic acid. The resulting filtrate is used as the base liquid for the recovered acid, and fresh sulfuric acid is added to adjust it to the target concentration to form a recyclable catalyst.

[0022] Furthermore, the hydrolysis reactor used in step (3) is preferably a vertical reactor with a spiral stirrer, and its stirring rate is controlled at 30 to 60 rpm to ensure that the reactants are fully mixed and the mass transfer efficiency is high under high temperature and high pressure conditions.

[0023] Furthermore, the solid-liquid separation equipment in steps (4) and (5) is preferably a compact two-in-one or three-in-one filter, which can perform continuous filtration and washing operations, is easy to maintain and control online, and is conducive to large-scale promotion.

[0024] Specifically, the product purification process in step (7) includes: a) introducing the mixed liquid phase into the first distillation column and operating at 0.02 MPa to atmospheric pressure, obtaining a recyclable catalyst liquid in the bottom of the column; b) condensing the top fraction of the first column and introducing it into a phase separator, separating the phases at 30℃~50℃ to obtain a furfural-rich organic phase and an aqueous phase; c) introducing the organic phase into the second distillation column and distilling it under similar pressure, obtaining a furfural product with a purity ≥99% in the bottom of the column; d) returning the aqueous phase as reflux material to the first column for recycling, achieving a highly efficient closed loop.

[0025] In particular, the distillation column can be operated in an intermittent or continuous manner to adapt to different production capacity scales and operating rhythms.

[0026] Based on the above technical solution, this invention provides a one-step furfural preparation method using biomass as raw material. By constructing a continuous process flow with "raw material pretreatment—acid-catalyzed reaction—solid-liquid separation—product purification—resource recycling" as the main line, it achieves efficient and direct extraction of furfural from agricultural and forestry waste. This method significantly simplifies the traditional multi-step furfural synthesis route, avoids energy consumption and material losses caused by intermediate product separation and tank-changing operations, and improves the overall efficiency and stability of the system operation.

[0027] This invention employs an integrated closed reactor. Under conditions of 150℃~180℃ and 6~10 bar pressure, a spiral stirring structure ensures uniform distribution of reactants within the reactor, enabling the hydrolysis dehydration reaction to proceed stably and efficiently. High conversion rates are achieved without introducing large amounts of steam, and the overall reaction time is significantly reduced to 10~60 minutes, substantially improving production pace and equipment utilization.

[0028] Furthermore, the solid-liquid separation and product purification system introduced in this invention adopts a process design combining a filter and a vacuum distillation column. This not only efficiently separates the reaction liquid from the solid residue but also reliably yields high-quality furfural products with a purity of ≥99%. Simultaneously, through the unified collection and distillation purification of the reaction residue and washing wastewater, the catalytic liquid is recovered and the water is recycled, thereby ensuring low energy consumption and minimal pollution emissions throughout the overall process, aligning with the concept of green manufacturing.

[0029] This invention constructs a low-energy-consumption, low-pollution, and high-efficiency one-step preparation route for furfural by controlling the particle size of raw materials, synergistic optimization of the catalytic system, integrated design of the reaction system, and efficient closed-loop control of the separation and purification process. It demonstrates excellent industrial feasibility and environmental adaptability and has broad prospects for promotion and application.

[0030] Compared to the traditional furfural production process that mainly uses steam stripping, this invention has significant advantages in the following aspects:

[0031] Significantly reduced energy consumption: This method completes the hydrolysis process in a closed reactor without the need for high-pressure steam, reducing steam consumption per unit output by more than 90%, which significantly reduces energy load and equipment complexity;

[0032] Shorter reaction time: The overall reaction time has been reduced from 4 to 6 hours required by traditional processes to less than 30 minutes, which greatly improves the turnover efficiency of production equipment and enhances the consistency of batch reactions;

[0033] Catalyst liquid can be recycled and reused: This invention introduces a catalyst liquid recycling mechanism, which realizes the efficient utilization of sulfuric acid catalyst liquid through fine filtration of ceramic membrane and recycling of residual liquid in distillation column. This reduces both the cost of catalyst and the environmental burden of waste acid emissions.

[0034] In summary, the one-step furfural preparation technology provided by this invention exhibits significant advantages in terms of energy efficiency, environmental protection, and industrial adaptability, and has considerable economic and social benefits. It is suitable for the large-scale preparation of sustainable bio-based chemicals. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the process flow for the one-step furfural preparation method of the present invention;

[0036] Figure 2 This is a schematic diagram of the catalyst recovery process of the present invention. Detailed Implementation

[0037] To better understand the present invention, the following detailed description of a one-step furfural preparation method using biomass as raw material, in conjunction with specific embodiments, is provided but should not be construed as a limitation on the scope of protection of the present invention.

[0038] Example 1:

[0039] like Figure 1 As shown, this embodiment uses corn cobs as biomass raw material to verify the operational feasibility of the method of the present invention under conditions without external steam and the furfural yield performance.

[0040] Step (1): Raw material pretreatment

[0041] Corn cobs, naturally air-dried to a moisture content of approximately 17%, are first washed and impurities removed, and then processed through a grading and crushing process.

[0042] Initially crushed into 5-10mm particles;

[0043] The material remaining on the sieve is then further crushed to 0.1–2 mm;

[0044] In the final mixed particles, the proportion of particles with a diameter ≤2mm is not less than 85%, which meets the particle distribution control requirements.

[0045] Step (2): Preparation of catalyst solution

[0046] A 5% (w / w) dilute sulfuric acid solution was prepared as a fresh catalyst solution. The catalyst (98 wt% concentrated sulfuric acid) was added to deionized water in a specific ratio and magnetically stirred until homogeneous, forming a catalyst solution with the target acid concentration. This was the first run of the experiment, and the recycled catalyst solution was not used.

[0047] Step (3): Hydrolysis reaction

[0048] Weigh 10g of pretreated corn cob raw material and mix it with 125g of dilute sulfuric acid catalyst solution (solid-liquid mass ratio of 1:12.5). Then, add the mixture to a vertical stainless steel sealed reactor equipped with a spiral stirrer. Set the reaction temperature to 160℃, the pressure to 0.8MPa, the stirring speed to 50rpm, and the reaction time to 30 minutes.

[0049] Step (4): Solid-liquid separation

[0050] After the reaction was completed, the mixture was subjected to solid-liquid separation through a three-in-one filter at 0.3 MPa to obtain the liquid phase and filter cake.

[0051] Step (5): Washing solid furfural residue

[0052] The solid furfural residue was washed twice with recycled hot washing water at 60°C, with the water volume being 12% of the residue mass each time. The resulting washing liquid was collected for later use.

[0053] Step (6): Washing liquid treatment

[0054] The washing liquid is introduced into the first distillation column at an operating pressure of 0.05 MPa. The top distillate is a mixture of furfural and water, which is condensed and filtered. The residual stream is replenished with fresh water and used as washing water for the next batch.

[0055] Step (7): Product purification and catalyst recovery

[0056] The liquid product obtained in step (4) is combined with the distillate obtained in step (6) and then fed into the distillation system:

[0057] The first distillation column operates at 0.05 MPa. The catalytic liquid is collected in the bottom of the column, and the top fraction is sent to the phase separator for phase separation at 40°C to obtain furfural organic phase and aqueous phase.

[0058] The furfural organic phase is introduced into the second distillation column for further purification, and furfural with a purity of ≥99% is obtained in the bottom of the column.

[0059] The aqueous phase is sent back to the first tower to participate in the next round of separation.

[0060] The resulting catalyst solution was filtered through a ceramic membrane with a molecular weight cut-off (MWCO) of 1000 Da and then acid was added for recycling.

[0061] Experimental results:

[0062] Finally, 0.92 g of furfural product was obtained, with stable yield and product purity (GC-MS analysis) ≥99%.

[0063] Example 2: Effect of different raw material particle sizes on furfural yield

[0064] This embodiment, while keeping other reaction conditions consistent, uses corn cob raw materials with different particle size ranges to verify the effect of raw material particle size on the hydrolysis reaction efficiency and furfural yield.

[0065] Step (1): Raw material pretreatment

[0066] Using corn cobs from the same source as in Example 1, dried to a moisture content of approximately 17%, two sets of raw materials were prepared:

[0067] Group A (larger particle size): After coarse crushing, the particles are directly passed through a 2-mesh sieve to obtain particles with a particle size range of 4.75 to 8 mm;

[0068] Group B (medium particle size): After crushing, the particle size is controlled within the range of 2.36-4 mm through a 6-mesh sieve;

[0069] No secondary fine grinding process was performed.

[0070] Step (2): Preparation of catalyst solution

[0071] The same catalyst solution as in Example 1 was used, namely a 5% sulfuric acid solution (without added recovery solution).

[0072] Step (3): Hydrolysis reaction

[0073] Weigh 10g of each raw material and mix it with 125g of catalyst solution at a solid-liquid mass ratio of 1:12.5. Then, add each mixture into a sealed reactor equipped with a spiral stirrer. The reaction temperature is set at 160℃, the pressure at 0.8MPa, the stirring speed at 50rpm, and the reaction time at 30 minutes.

[0074] Steps (4) to (7): Post-processing flow

[0075] Subsequent steps, including solid-liquid separation, slag washing, washing liquid separation, distillation purification, and catalytic liquid recovery, are the same as in Example 1.

[0076] Analysis of experimental results:

[0077] Raw material group Particle size range (mm) Furfural yield (g / 10g raw material) Group A 4.75～8 0.74 Group B 2.36～4 0.82

[0078] Analysis shows that:

[0079] Larger particle sizes (Group A) resulted in lower hydrolysis efficiency due to their smaller specific surface area and lower reaction mass transfer efficiency, leading to a significantly lower furfural yield compared to the medium particle size group (Group B). The filter cake also showed a higher residual sugar content, indicating incomplete reaction.

[0080] Example 3: Verification of Catalytic Liquid Recovery and Recycling

[0081] This embodiment is based on the operation process of Example 1, and examines the stability of catalytic activity and changes in product yield after multiple rounds of continuous recycling of the recovered catalyst liquid, to verify the feasibility and industrial adaptability of the catalyst liquid recovery mechanism of the present invention.

[0082] First run (R1):

[0083] Following the operating steps of Example 1, 10g of corn cobs with a particle size ≤2mm were used as raw material and mixed with 125g of 5% (w / w) fresh sulfuric acid solution to form a catalytic solution. The reaction, separation, and distillation purification operations were completed to obtain 0.71g of furfural product. Subsequently, the residual acid liquid in the bottom of the distillation column was collected as the recovery base liquid.

[0084] Catalyst recovery process:

[0085] The acidic liquid remaining in the distillation column bottoms is filtered through a ceramic membrane with a molecular weight cutoff of 1000 Da to remove high-molecular-weight organic impurities and colloidal byproducts, yielding a clear and transparent acidic base liquid. The sulfuric acid concentration is adjusted to 5% (w / w) by adding an appropriate amount of 98wt% concentrated sulfuric acid, thus obtaining the second-stage catalytic solution.

[0086] Repeated cycle tests (R2~R5):

[0087] In the subsequent second to fifth rounds of experiments (R2 to R5), the recovered and acidified catalyst solution was reacted with corn cob raw material in the same manner. All reaction conditions (temperature, pressure, time, stirring speed) were the same as in R1, and the solid-liquid ratio was maintained at 1:12.5.

[0088] Experimental results statistics:

[0089]

[0090] Results analysis:

[0091] In five consecutive cycles of experiments, the furfural yield remained within ±5%, and the product purity (as determined by GC-MS) remained ≥99%. No significant discoloration, precipitation, or abnormal acid consumption was observed in the catalyst solution during any of the cycles, and the membrane filtration system showed no clogging and operated stably.

[0092] This embodiment fully demonstrates that the catalyst solution purified by ceramic membranes and appropriately supplemented with acid can be stably used in multiple rounds of reactions, exhibiting good reusability and catalytic activity retention. This recovery strategy significantly reduces sulfuric acid usage and waste acid emissions, validating the practicality and economic efficiency of the catalyst solution recovery mechanism.

[0093] Example 4: Effect of catalyst acid concentration on reaction efficiency

[0094] In this embodiment, under the premise of keeping the raw materials, temperature, pressure, reaction time, solid-liquid ratio and other conditions constant, the mass concentration (w / w) of sulfuric acid in the catalyst solution is adjusted, and the yield, liquid phase properties and by-product formation trend of furfural under different concentrations are compared.

[0095] The experimental conditions are uniformly set as follows:

[0096] Raw material: 10g of dried corn cobs with a particle size ≤2mm;

[0097] Solid-liquid ratio: 1:12.5;

[0098] Reaction temperature: 160℃;

[0099] Reaction pressure: 0.8 MPa;

[0100] Reaction time: 30 minutes;

[0101] Catalytic solution: Prepare sulfuric acid aqueous solutions of different acid concentrations without adding recovery solution.

[0102] Four sets of comparative experiments were set up:

[0103] Group Sulfuric acid concentration (w / w) Aldehyde yield (g / 10g raw material) A 2.0％ 0.80 B 3.5％ 0.68 C 5.0％ 0.92 D 6.0% (control group) 0.71

[0104] Results analysis:

[0105] When the acid concentration is 2.0%, the acidity of the system is low, the hemicellulose hydrolysis reaction is slow, and the furfural yield is low.

[0106] At concentrations of 3.5%–5.0%, the reaction exhibits good activity, ideal control of side reactions, and high yield, indicating a preferred reaction window.

[0107] When the acid concentration is increased to 6.0%, although it has a strong catalytic ability, it also induces further reactions in the product, reduces the final product yield, and decreases product stability.

[0108] This embodiment clearly verifies the significant impact of the concentration of the catalytic liquid acid on the yield of furfural and the stability of the system, proving that the concentration range of 2% to 5% (w / w) set in this invention is scientifically reasonable, with the preferred range being 3.5% to 5%. Within this range, the optimal balance between high yield and low by-products can be achieved, meeting the requirements of a green and efficient reaction system.

[0109] Example 5: Effect of sulfuric acid and Lewis acid combination on furfural yield

[0110] In this embodiment, under the same total acid concentration, the furfural yield and system stability of single sulfuric acid catalysis and sulfuric acid-Lewis acid complex system were compared, and the synergistic effect of different inorganic Lewis acids (FeCl3, ZnCl2, AlCl3) and sulfuric acid was explored.

[0111] General experimental conditions:

[0112] Raw material: 10g of dried corn cobs with a particle size ≤2mm;

[0113] Solid-liquid ratio: 1:12.5;

[0114] Total acid concentration: controlled at 5% (w / w);

[0115] Reaction temperature: 160℃;

[0116] Reaction pressure: 0.8 MPa;

[0117] Reaction time: 30 minutes;

[0118] The distillation and separation process is as described in Example 1.

[0119] The catalyst configuration groups are as follows:

[0120] Group Catalytic system Furfural yield (g / 10g raw material) A 5% sulfuric acid (single acid) 0.92 B <![CDATA[4% sulfuric acid + 1% FeCl3]]> 0.98 C <![CDATA[4% sulfuric acid + 1% ZnCl2]]> 0.96 D <![CDATA[4% sulfuric acid + 1% AlCl3]]> 0.91

[0121] Results analysis:

[0122] Group B (FeCl3) performed best, with a yield increase of approximately 5.6%, indicating that Fe... 3+ It has a synergistic catalytic effect that enhances the rate of xylose dehydration reaction, and the system is stable with no precipitation or abnormal color.

[0123] Group C (ZnCl2) also performed well, with a slightly lower yield than the FeCl3 group, but occasional white precipitates appeared in the liquid phase, presumably due to the presence of Zn. 2+ It is related to hydrolysis equilibrium.

[0124] Although the yield of group D (AlCl3) is close to that of the single sulfuric acid system, the system is slightly turbid, and there is a risk of forming colloids or complexes, which is not conducive to subsequent distillation and catalytic liquid recovery.

[0125] Control group A was used as a baseline to verify the potential of the compound system in terms of yield improvement and controllability.

[0126] Introducing appropriate amounts of FeCl3 or ZnCl2 as auxiliary catalysts can form a synergistic catalytic system with sulfuric acid, improving reaction efficiency and furfural yield without increasing the total acid concentration. The FeCl3 composite system is the most ideal and suitable for the industrial-grade catalyst formulation strategy described in this invention, which is beneficial for improving process performance and economy.

[0127] Example 6: Effect of reaction time on furfural yield

[0128] This embodiment, under the premise of keeping the raw material type, catalyst ratio, temperature and pressure constant, systematically examines the furfural formation efficiency and side reaction trend under different reaction times, verifying the necessity of the reaction time optimization of the present invention.

[0129] Uniform reaction conditions:

[0130] Raw material: 10g of corn cobs with a particle size ≤2mm;

[0131] Solid-liquid mass ratio: 1:12.5;

[0132] Catalyst solution: 5% (w / w) sulfuric acid solution;

[0133] Reaction temperature: 160℃;

[0134] Reaction pressure: 0.8 MPa;

[0135] Stirring speed: 50 rpm;

[0136] Other operating steps (solid-liquid separation, washing, distillation) are consistent with those in Example 1.

[0137] Set the reaction time gradient:

[0138] The reaction times were set to 10 min, 20 min, 30 min, 45 min, and 60 min, respectively, and the results are as follows:

[0139] Reaction time (min) Furfural yield (g / 10g raw material) 10 0.67 30 0.92 60 0.83

[0140] Analysis and Conclusion:

[0141] When the reaction time is 30 minutes, the furfural yield reaches its maximum value (0.92g / 10g raw material), the system is stable, and the product has high purity.

[0142] If the time is less than 10 minutes, the hydrolysis of raw materials and dehydration of xylose are insufficient, resulting in a low furfural formation rate.

[0143] After more than 60 minutes, although xylose is basically converted, furfural is prone to further degradation in an acidic and hot environment to generate impurities and pyrophoric substances, resulting in a decrease in yield, darkening of the liquid phase color, and deterioration of system stability.

[0144] In summary, the 10-60 minute reaction time range proposed in this invention has clear process boundaries and is reasonable. The preferred range is 25-35 minutes, which ensures the full generation of furfural while effectively suppressing side reactions, thus meeting the efficiency and quality requirements of continuous industrial production.

[0145] Example 7: Continuous one-step furfural preparation process and verification of high-efficiency recovery of catalyst solution

[0146] This embodiment, based on the technical solution proposed in this invention, further demonstrates its process feasibility under pilot-scale amplification conditions, its ability to control product purity, and its efficient recycling performance of the catalyst solution.

[0147] Raw material pretreatment:

[0148] Naturally air-dried corn cobs were selected as the starting material, with a moisture content controlled at ≤17% and a hemicellulose content of 35±2%. After washing to remove surface impurities, the raw material was fed into a FS-850 classifying pulverizer (55kW power) for crushing, equipped with a screen aperture adjustable range of 0.5-10mm. Laser particle size analysis showed that the resulting mixed particles exhibited a bimodal particle size distribution: the main peak was located at 0.8-2.0mm, accounting for 86±3%; the secondary peak was located at 2.1-7.5mm, accounting for 14±3%. This particle size design balances reaction mass transfer efficiency with the operability of subsequent solid-liquid separation.

[0149] Catalyst preparation:

[0150] In a 316L stainless steel preparation tank, 98% concentrated sulfuric acid and ferric chloride hexahydrate (FeCl3·6H2O, purity ≥99%) were mixed at a mass ratio of 4:1. Deionized water was then slowly injected at a flow rate of 0.5 L / min, controlling the system temperature to ≤40℃ to prevent ferric salt hydrolysis. The final catalytic solution had a density of 1.18 g / cm³. 3 (25℃), pH value 0.7, sulfuric acid concentration 3.2±0.1% (w / w), Fe 3+ The concentration is 0.45 mol / L. This catalytic system is composed of a protic acid and a Lewis acid, and has both hydrolysis and dehydration promoting effects.

[0151] Hydrolysis reaction:

[0152] The pretreated raw materials and catalyst solution were mixed at a solid-liquid mass ratio of 1:10 (error ≤ ±2%) and then added to a vertical closed reactor for reaction. The reactor was equipped with a spiral stirrer with a stirring speed set at 50 rpm. The reaction temperature was 170℃, the pressure was controlled at 0.9 MPa, and the reaction time was 25 minutes. Real-time online HPLC monitoring was used during the reaction. The results showed that the xylose conversion rate reached 98.7% and the furfural selectivity was 81.3% after 25 ± 1 minutes. The reaction system maintained stable self-generated pressure, and the condenser reflux device enabled steam condensation and circulation within the closed system.

[0153] Solid-liquid separation and washing:

[0154] After the reaction was completed, the mixture was passed through a three-in-one filter (filtration area 12m²) under a pressure of 0.2±0.02MPa. 2 Solid-liquid separation was performed using a 316L stainless steel sintered filter element (5μm pore size) to obtain a liquid product and solid furfural residue. The solid residue was further fed into a three-stage countercurrent scrubbing tower (6m high, 4.5m packing height) and washed with recycled wash water at 70±2℃ at a liquid-to-solid ratio of 1:3. After washing, GC testing showed that the residual furfural content was no higher than 0.5%, and the wash liquid was collected for subsequent processing.

[0155] Washing solution is distilled and reused:

[0156] The washing liquid is introduced into a plate distillation column with a diameter of 1.2m (theoretical plate number 25, reflux ratio 1.5:1) and operated under atmospheric pressure. The distillate with a furfural mass fraction of 25±0.5% is obtained at the top of the column. The residue in the bottom of the column is finely filtered and then replenished with fresh deionized water, thus forming a closed-loop washing water reuse system, which significantly reduces the discharge of process wastewater.

[0157] Product purification and catalyst recovery:

[0158] The liquid product obtained from solid-liquid separation and the overhead distillate obtained from washing liquid distillation are combined and sequentially fed into a two-stage distillation system for purification:

[0159] The first-stage distillation column operates at a pressure of 0.05 MPa. The bottom of the column yields a catalytic liquid recovery solution containing sulfuric acid. The top fraction is condensed and sent to a phase separator at 45°C to separate an organic phase with a furfural mass fraction of 91% and a recyclable aqueous phase.

[0160] The organic phase is further fed into a second-stage atmospheric distillation column, and furfural product with a purity of 99.52±0.03% is obtained from the bottom of the column. The product meets the national standard GB / T 1926.1-2009 after GC-FID testing.

[0161] Catalyst regeneration and recycling:

[0162] like Figure 2 As shown, the catalytic liquid recovery solution is fed into a cross-flow ceramic membrane filtration system (19-channel tubular membrane, MWCO 1000Da, membrane area 8m²). 2 The process is carried out under a transmembrane pressure difference of 0.8 MPa. The sulfuric acid recovery rate after filtration is not less than 92%. Adding an appropriate amount of 98% concentrated sulfuric acid to adjust the acid concentration to 4.2 ± 0.1% (w / w) allows it to be used as a regenerated catalyst solution for the next batch of reactions, forming a highly efficient closed-loop catalyst solution circulation system.

[0163] In summary, the one-step furfural preparation method using biomass as raw material proposed in this invention, through reasonable control of raw material particle size, optimization of catalyst system, improvement of reaction process parameters, and introduction of a highly efficient separation and recovery system, not only effectively improves the yield and purity of furfural but also significantly reduces energy consumption and wastewater discharge, achieving a green, efficient, and low-cost furfural production pathway. This method is applicable to various agricultural and forestry waste raw materials rich in hemicellulose, exhibiting good raw material adaptability and promising industrial application prospects, and can provide strong support for the transformation, upgrading, and sustainable development of the furfural industry.

[0164] It should be noted that the specific embodiments described in this specification are only for the purpose of helping to understand the principles and core concepts of the present invention. For those skilled in the art, various modifications or equivalent substitutions can be made to the embodiments of the present invention without departing from the spirit and essence of the invention, and all such modifications or substitutions should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A one-step method for preparing furfural using biomass as raw material, characterized in that, Includes the following steps: (1) Raw material pretreatment: The biomass raw material rich in hemicellulose is washed and crushed, and the particle size of the raw material is controlled within the range of 0.1 to 10 mm; (2) Catalytic solution preparation: The catalytic solution is prepared by mixing the catalyst with water; the catalyst is sulfuric acid, or a mixture of sulfuric acid and at least one Lewis acid salt selected from ferric chloride, aluminum chloride or zinc chloride; the acid concentration of the catalytic solution is controlled at 2% to 5% (w / w) based on sulfuric acid; the catalytic solution includes freshly prepared catalytic solution or recycled catalytic solution from the previous batch. (3) Hydrolysis reaction: The raw material obtained in step (1) and the catalyst obtained in step (2) are added to a closed hydrolysis reaction reactor at a solid-liquid mass ratio of 1:4 to 1:

13. The reaction is carried out at a temperature of 150℃ to 180℃ and a pressure of 0.6 to 1.0 MPa for 10 to 60 minutes with stirring to obtain a reaction mixture containing furfural. (4) Solid-liquid separation: The reaction mixture obtained in step (3) is filtered under a pressure of 0.1 to 0.5 MPa to separate the liquid product and the solid furfural residue; (5) Washing solid-liquid separation: The solid furfural residue from step (4) is washed with recycled washing water at a temperature of 25℃~80℃ to obtain washing liquid and waste residue. (6) Washing liquid treatment: The washing liquid obtained in step (5) is sent to a distillation column for separation. A distillate containing furfural and water is obtained at the top of the column. The bottom stream is replenished with fresh water and used as the recycled washing water in step (5). (7) Product purification and catalyst recovery: The liquid product from step (4) and the distillate from the top of the column obtained in step (6) are introduced into a separation system consisting of a phase separator and a distillation unit for separation and purification. After separation, furfural product with a purity of ≥99% is obtained, and the catalyst is recovered from the system.

2. The method according to claim 1, characterized in that, The biomass raw material is agricultural and forestry waste rich in hemicellulose, selected from corn cobs, corn stalks, or tobacco stalks.

3. The method according to claim 1, characterized in that, The raw material crushing in step (1) adopts a graded crushing process to control the particle size distribution of the mixed particles to meet the following requirements: the proportion of particles with a particle size ≤ 2 mm is ≥ 80%, or the proportion of particles with a particle size ≤ 4 mm is ≥ 80%.

4. The method according to claim 1, characterized in that, The recovered catalyst solution in step (2) is prepared by the following method: the residual acid solution in the distillation column bottom in step (7) is filtered through a ceramic membrane with a molecular weight cutoff of 1000 Da, and the resulting filtrate is collected as the base solution for the recovered acid solution; fresh sulfuric acid is added to the base solution for the recovered acid solution to an acid concentration of 2% to 5% (w / w) to obtain the recovered catalyst solution.

5. The method according to claim 1, characterized in that, The reactor in step (3) is a vertical reactor equipped with a spiral stirring device, with a stirring speed of 30 to 60 rpm.

6. The method according to claim 1, characterized in that, The solid-liquid separation in steps (4) and (5) uses a two-in-one filter, a three-in-one filter, or other types of solid-liquid separation devices.

7. The method according to claim 1, characterized in that, The product purification process in step (7) is as follows: a) The liquid product is introduced into the first distillation column and operated under conditions of 0.02 MPa to atmospheric pressure, and a recyclable acidic catalyst liquid is obtained in the bottom of the column; b) The overhead fraction of the first distillation column is condensed and introduced into a phase separator for phase separation at 30℃~50℃ to obtain an organic phase rich in furfural and an aqueous phase rich in water; wherein the mass fraction of furfural in the overhead fraction is >20%; c) The organic phase is introduced into a second distillation column and operated under pressure conditions from 0.02 MPa to atmospheric pressure. The bottom of the column yields furfural product with a purity of ≥99%. d) The aqueous phase is returned as feed to the first distillation column for further separation and purification.

8. The method according to claim 7, characterized in that, The first and second distillation columns are operated in either batch or continuous distillation mode.

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