A method for continuously preparing furoic acid by ozone oxidation of furfuryl alcohol

Abstract

The application belongs to the technical field of fine chemical industry, and particularly discloses a method for continuously preparing furoic acid by ozone oxidation of furfuryl alcohol. In view of the core defects of the traditional process, such as large wastewater discharge, inability to continuously produce, and dependence on organic solvents and ligands, the application innovatively adopts an integrated process of photocatalysis-ozone oxidation synergy of anatase titanium dioxide, ligand-free design, and continuous separation of a nanofiltration membrane; deionized water is used as a green solvent, and continuous reaction is realized at normal temperature and pressure under the assistance of ultraviolet light; the reaction solution is separated and purified through the nanofiltration membrane, and the filtered pure water can be recycled and reused, so that continuous production of furoic acid is realized. The method is suitable for large-scale production requirements, conforms to the green chemical industry policy, has low difficulty in industrialization reconstruction, and has environmental protection and economy.

Description

Technical Field

[0001] This invention belongs to the field of environmentally friendly continuous preparation technology of fine chemical materials, specifically involving a method for the continuous preparation of furoic acid by ozone oxidation of furfuryl alcohol based on the synergistic effect of anatase titanium dioxide photocatalysis-ozone oxidation, ligand-free design and continuous separation by nanofiltration membrane. Background Technology

[0002] Furoic acid, as an important fine chemical intermediate, is widely used in food additives, pharmaceutical synthesis, resin preparation, and other technical fields. Traditional furoic acid preparation processes mostly employ precious metal catalytic oxidation and organic solvents as reaction media, which have two major technical drawbacks: First, the process is batch production, resulting in low production efficiency and making it difficult to achieve large-scale mass production; second, the use of organic solvents and ligands in the reaction process generates a large amount of highly polluting wastewater in the subsequent separation and purification process, leading to high water consumption and wastewater treatment costs, which is inconsistent with current green chemical development policies.

[0003] Existing optimized processes have attempted to employ photocatalytic oxidation or membrane separation purification technologies, but these still fail to overcome the aforementioned core shortcomings. For example, existing patents disclose a method for preparing furoic acid through photocatalytic oxidation, but it uses a single photocatalytic system, resulting in low catalytic efficiency and requiring extended reaction time, thus failing to meet the demands of continuous production. Other existing patents utilize membrane separation to purify furoic acid, but this is still limited to intermittent production, suffering from severe membrane fouling, unstable separation efficiency, and the inability to achieve water resource recycling, leaving wastewater discharge problems unresolved. Furthermore, existing processes generally rely on ligands to enhance catalytic activity; the introduction of ligands not only increases production costs but also complicates subsequent impurity separation.

[0004] Therefore, developing a ligand-free, green solvent system, and integrated reaction-separation continuous production technology for furoic acid, achieving zero wastewater discharge and high-efficiency mass production, has become an urgent technological need in the field of fine chemicals. Based on this, this application was developed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and address the technical problems of large wastewater discharge, inability to achieve continuous production, and reliance on organic solvents and ligands in current furoic acid preparation processes. This invention provides a method for the continuous production of furoic acid from furfuryl alcohol via ozone oxidation. This method improves reaction efficiency by constructing an anatase titanium dioxide photocatalytic-ozone oxidation synergistic system, simplifies the process using a ligand-free design, and integrates purification and water resource recycling through continuous nanofiltration membrane separation. Ultimately, this achieves environmentally friendly continuous production of furoic acid, reaching the technical goals of zero wastewater discharge, high conversion rate, high yield, and low cost, thus complying with green chemical industry policies.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for the continuous preparation of furoic acid by ozone oxidation of furfuryl alcohol includes the following continuous steps: S1 Continuous photocatalytic ozone oxidation: furfuryl alcohol, deionized water and titanium dioxide photocatalyst are continuously added to the continuous photocatalytic reactor. Under stirring at room temperature, ultraviolet light is turned on and ozone is continuously introduced at the same time. The reaction residence time is controlled to continuously produce oxidized feed liquid. S2 Catalyst Continuous Recovery: The oxidized feed liquid produced by S1 is introduced into a ceramic membrane continuous filtration device for continuous filtration of ceramic membranes to recover the titanium dioxide photocatalyst and return it to S1 for recycling. After filtration, crude furoic acid solution is obtained. S3 Continuous nanofiltration membrane separation: The crude furoic acid solution obtained in S2 is continuously pumped into a nanofiltration membrane device for continuous nanofiltration membrane separation. Small molecule impurities are continuously removed by controlling the operating parameters to obtain pure furoic acid solution. S4 Continuous finished product preparation: The pure furoic acid solution obtained in S3 is sequentially fed into a continuous vacuum concentration device and a continuous vacuum drying device for continuous vacuum concentration and vacuum drying treatment to obtain the furoic acid finished product.

[0007] Specifically, in step S1, the titanium dioxide photocatalyst is anatase titanium dioxide, which is calcined and activated at 600±100℃ for 1-3 hours, and has a specific surface area ≥90m² / g. Preferably, the amount of titanium dioxide photocatalyst added is 4.3-4.6% of the mass of furfuryl alcohol, and it can be recycled ≥18 times with an activity decay ≤1%.

[0008] Furthermore, in step S1, the furfuryl alcohol has a purity of ≥99.5%, a feed rate of 1000±100g / h, a deionized water feed rate of 4000±500g / h, and a titanium dioxide photocatalyst feed rate of 45±10g / h.

[0009] Furthermore, in step S1, the ozone concentration is 58-62 mg / L, and the aeration rate is 1.6-2.0 L / min. Furthermore, in step S1, the UV light power is 240-260 W, the stirring rate is 220±20 r / min, and the reaction residence time is 0.6-0.8 h. These parameters synergistically ensure a furfuryl alcohol conversion rate ≥99.7%, with the stirring rate of 220±20 r / min balancing ozone dissolution efficiency and catalytic reaction uniformity, avoiding localized side reactions.

[0010] Specifically, in step S2, the ceramic membrane filtration accuracy is 0.1-0.2 μm.

[0011] Specifically, in step S3, the nanofiltration membrane operates at a pressure of 0.7-0.9 MPa and a temperature of 33-37°C, with a molecular weight cutoff of 180-220 Da. These parameters are suitable for separating furoic acid (molecular weight 112 Da) from small molecule impurities (molecular weight < 70 Da), achieving a membrane separation yield ≥ 98.8% and an impurity removal rate ≥ 99.2%. The filtrate from the nanofiltration membrane separation is pure water, which can be directly circulated back to step S1 as makeup water for the reaction via a reflux pump. Specifically, in step S4, the vacuum degree of continuous reduced pressure concentration is -0.07 ~ -0.09 MPa, and the temperature is 60-70℃. Furthermore, the vacuum drying temperature is 100-105℃.

[0012] The continuous furoic acid preparation method of the present invention is designed based on the concepts of continuous production and green environmental protection. The process parameters and equipment selection of each step have been precisely optimized, and it is feasible for industrialization. As a preferred technical solution, it specifically includes the following steps: S1 Continuous Photocatalytic Ozone Oxidation: In a continuous photocatalytic reactor made of 316L stainless steel, 99.5% pure furfuryl alcohol and deionized water are continuously added and stirred until homogeneous. Then, anatase titanium dioxide photocatalyst (calcined and activated at 600℃ for 2 hours, with a specific surface area ≥90 m²) is continuously added. 2 / g); A 380nm ultraviolet light source is installed in the reactor, the stirring rate is adjusted, and ultraviolet light irradiation and ozone introduction are simultaneously turned on at room temperature. The reaction residence time is controlled to continuously produce oxidized feed liquid. The core logic of this step is that anatase titanium dioxide, after high-temperature calcination, has abundant active centers. 380nm ultraviolet light can accurately excite them to generate electron-hole pairs, which, together with ozone, generate highly active hydroxyl radicals (·OH), significantly improving the rate and selectivity of furfuryl alcohol oxidation to furoic acid. This achieves a high-efficiency reaction at room temperature and pressure, without the need for high-temperature and high-pressure conditions, reducing industrial energy consumption and equipment requirements. The 316L stainless steel material can prevent equipment corrosion and the precipitation of impurities, ensuring product purity. The preferred stirring rate of 220r / min can balance ozone dissolution efficiency and reaction uniformity, reducing by-products. The preferred feed parameters are: furfuryl alcohol 1000g / h, deionized water 4000g / h, and titanium dioxide photocatalyst 45g / h; the preferred reaction parameters are: ultraviolet light power 250W, stirring rate 220r / min, ozone concentration 60mg / L, aeration rate 1.8L / min, and reaction residence time 0.7h.

[0013] S2 Catalyst Continuous Recovery: The oxidized feed liquid produced in S1 is introduced into a continuous ceramic membrane filtration device (filtration accuracy 0.1μm) for continuous filtration to recover the titanium dioxide photocatalyst. The recovered catalyst is directly recycled back to the continuous photocatalytic reactor of S1 for reuse. The filtrate is crude furoic acid solution. This step serves as an intermediate link in the continuous process. The ceramic membrane filter is selected with a filtration accuracy precisely matched to the titanium dioxide catalyst particles, enabling efficient catalyst retention (recovery rate ≥99.5%) and continuous recovery without complex regeneration treatment. Direct catalyst recycling simplifies the process, reduces consumption costs, avoids pollution caused by catalyst loss, ensures the continuity of material flow, and provides support for stable feeding of the subsequent S3 continuous nanofiltration membrane separation.

[0014] S3 Continuous Nanofiltration Membrane Separation: The crude furoic acid solution obtained in S2 is continuously pumped into a nanofiltration membrane unit via a booster pump for continuous nanofiltration membrane separation. The operating pressure, temperature, and molecular weight cutoff are controlled to continuously remove small molecule impurities (such as formic acid and acetic acid, with molecular weight <70 Da), yielding pure furoic acid solution. This step, as the core of the "purification-water resource recycling" process, features a molecular weight cutoff of 180-220 Da, precisely matching the retention requirements of furoic acid molecules (molecular weight 112 Da), achieving efficient purification. The optimized process parameters avoid membrane fouling, ensuring stable separation efficiency. Simultaneously, the membrane filtrate is pure water, which can be directly circulated back to S1 as reaction makeup water via a reflux pump, forming a closed-loop material flow of "reaction-separation-water reflux," achieving a water resource utilization rate of ≥98% and reaching the goal of zero wastewater discharge, thus meeting the resource-efficient utilization requirements of continuous production. The preferred nanofiltration membrane parameters are: operating pressure 0.8 MPa, temperature 35℃, and nanofiltration membrane molecular weight cutoff 200 Da.

[0015] S4 Continuous Finished Product Preparation: The pure furoic acid solution obtained in S3 is fed into a continuous vacuum concentration unit. Excess moisture is removed by concentration under set vacuum conditions (-0.09 MPa) and temperature (65℃). The concentrated material is then sent to a continuous vacuum drying unit (temperature 104℃) for drying, yielding an environmentally friendly, continuously produced furoic acid product. This step employs a low-temperature concentration design to avoid high-temperature deterioration of the furoic acid. The continuous vacuum drying parameters are precisely optimized to quickly remove residual trace amounts of moisture from the concentrated material, ensuring stable purity of the finished product. The entire finished product preparation process is connected in series with the upstream S3 nanofiltration membrane separation unit via sealed pipelines, forming a fully continuous production chain of "reaction-recovery-separation-finished product," significantly improving production efficiency. Under these parameters, the core indicators of continuous yield ≥93.0% and purity ≥99.5% can be stably achieved.

[0016] Addressing the core shortcomings of traditional processes—large wastewater discharge, inability to achieve continuous production, and reliance on organic solvents and ligands—this invention innovatively employs an integrated process combining anatase titanium dioxide photocatalysis and ozone oxidation, a ligand-free design, and continuous separation via nanofiltration membranes. Using deionized water as a green solvent, the reaction proceeds continuously at room temperature and pressure under UV light assistance. The reaction solution is purified via nanofiltration, and the filtered pure water can be recycled, enabling continuous production of furoic acid. This method is suitable for large-scale production, complies with green chemical policies, is easy to implement industrially, and is both environmentally friendly and economical.

[0017] Compared with the prior art, the advantages and beneficial effects of the method of the present invention are as follows: 1) Excellent environmental performance, in line with green chemical policy: This invention uses deionized water as a green solvent, eliminating the use of organic solvents and ligands from the source, reducing pollution sources; combined with nanofiltration membrane separation technology, the filtered pure water can be recycled as reaction water, achieving a water resource utilization rate of ≥98% and zero wastewater discharge, significantly reducing environmental treatment costs, and precisely meeting the requirements of green chemical development.

[0018] 2) Achieving continuous production and high efficiency: This invention adopts an integrated continuous process design of continuous reactor, continuous filtration, continuous nanofiltration membrane separation, and continuous concentration and drying. The various links are coordinated and connected, which can achieve continuous and stable production with a continuous operation time of ≥12h. Compared with the traditional intermittent process, the production efficiency is increased by more than 50%, which is suitable for the needs of large-scale mass production.

[0019] 3) Stable catalytic system and controllable cost: Anatase titanium dioxide photocatalyst can be recycled ≥18 times, with an activity decay of ≤1% and a catalyst recovery rate of ≥99.5%. It eliminates the need for frequent shutdowns to replace the catalyst, ensuring the stability of continuous production. Compared with traditional precious metal catalysts, it can significantly reduce catalyst consumption costs. The absence of ligand addition simplifies the process, reducing raw material costs and separation energy consumption. Water resource recycling further reduces production energy consumption. Multi-dimensional collaboration enables controllable production costs, providing economic feasibility for large-scale continuous mass production.

[0020] 4) Stable product quality and strong process adaptability: The process parameters of each step have been precisely optimized, and the fluctuation of parameters has minimal impact on product quality. The conversion rate of furfuryl alcohol is ≥99.7%, the purity of the finished product is ≥99.5%, and the impurity removal rate is ≥99.2%. The process can be adapted to industrial production of different scales, and the difficulty of industrialization transformation is low. Existing intermittent production equipment can be adapted to continuous production with simple modifications. Detailed Implementation

[0021] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0022] The technical solution of the present invention will be described in detail below with reference to three sets of parallel verification embodiments. Unless otherwise specified in the embodiments, all conditions are conventional experimental conditions for the preparation of environmentally friendly fine chemical materials (all reagents used are industrial-grade environmentally friendly). All equipment used has undergone sealing tests. The ceramic membrane continuous filtration device, nanofiltration membrane device, vacuum concentration device, and vacuum drying device used are mainly used to achieve the functions of ceramic membrane filtration, nanofiltration membrane separation, vacuum concentration, and vacuum drying, respectively. Their device structures can adopt conventional technologies in the field, and since their device structure is not the innovation or core of the present invention, it will not be described in detail here.

[0023] Example 1 is a benchmark verification of the preferred parameters of the technical solution, and Examples 2-3 are boundary verifications of the upper and lower limits of the parameters of the technical solution. The purpose is to comprehensively verify the stability of the technical effect of "environmentally friendly continuous, high yield, and zero emission" of the present invention, and at the same time to corroborate the rationality of the process parameter range, rather than to limit the scope of protection of the present invention.

[0024] In the following examples, all raw materials used are common commercially available products that can be purchased directly, or can be prepared using conventional techniques in the art. Example 1

[0025] Reference parameters.

[0026] The continuous feeding parameters are as follows: furfuryl alcohol 1000 g / h (purity 99.5%), deionized water 4000 g / h, titanium dioxide photocatalyst 45 g / h (anatase type, calcined and activated at 600℃ for 2 h, specific surface area 92 m²). 2 / g), 60mg / L ozone 1.8L / min.

[0027] The process steps and parameters are as follows: S1 Continuous Photocatalytic Ozone Oxidation: First, continuously add 1000 g / h of 99.5% pure furfuryl alcohol and 4000 g / h of deionized water to a continuous photocatalytic reactor (made of 316L stainless steel). After stirring and mixing evenly, continuously add 45 g / h of anatase titanium dioxide photocatalyst (calcined and activated at 600℃ for 2 hours, with a specific surface area of ​​92 m²). 2 / g); Install a 380nm ultraviolet light source (power 250W) in the reactor, adjust the stirring speed to 220r / min, turn on the ultraviolet light irradiation at room temperature, and simultaneously and continuously introduce 60mg / L ozone (air flow rate 1.8L / min), control the reaction residence time to 0.7h, and continuously produce oxidized feed liquid; S2 Catalyst Continuous Recovery: The oxidizing liquid is continuously filtered through a ceramic membrane continuous filtration device (filtration accuracy 0.1μm) to recover the titanium dioxide photocatalyst. The catalyst is recycled back to the photocatalytic reactor for reuse, and the filtrate is crude furoic acid solution. S3 Continuous Nanofiltration Membrane Separation: The crude product liquid is continuously pumped into the nanofiltration membrane device by a booster pump for continuous nanofiltration membrane separation. The operating pressure is controlled at 0.8MPa, the temperature at 35℃, and the molecular weight cutoff of the nanofiltration membrane is 200Da. Small molecule impurities are continuously removed. The retentate (pure furoic acid solution) is collected, and the filtrate (pure water) is collected in a collection tank and then returned to the photocatalytic reactor as makeup water by a reflux pump. S4 Continuous finished product preparation: The pure furoic acid solution is sent to a continuous vacuum concentration device (vacuum degree -0.09MPa, temperature 65℃) for continuous vacuum concentration, and then sent to a continuous vacuum drying device for vacuum drying at 104℃ to obtain environmentally friendly continuous furoic acid finished product.

[0028] Actual test data: furfuryl alcohol conversion rate 99.8%, furoic acid yield 93.5%, finished product purity 99.6%, membrane separation yield 99.1%, impurity removal rate 99.3%; continuous and stable operation for 15 hours without equipment blockage or efficiency reduction; water resource utilization rate 98.5%, zero wastewater discharge; after 18 catalyst cycles, activity decayed by 0.8%, and the reaction yield still reached 93.2%. Example 2

[0029] Lower limit of parameters.

[0030] The continuous feeding parameters are as follows: completely consistent with those in Example 1; The process steps and parameters are as follows: S1 Continuous Photocatalytic Ozone Oxidation: First, continuously add 1000 g / h of 99.5% pure furfuryl alcohol and 4000 g / h of deionized water to a continuous photocatalytic reactor (made of 316L stainless steel). After stirring and mixing evenly, continuously add 45 g / h of anatase titanium dioxide photocatalyst (calcined and activated at 600℃ for 2 hours, with a specific surface area of ​​92 m²). 2 / g); Install a 380nm ultraviolet light source (power 240W), stir at 220r / min, turn on ultraviolet light irradiation at room temperature, and simultaneously and continuously introduce 58mg / L ozone (air flow rate 1.6L / min), control the reaction residence time to 0.6h, and continuously produce oxidized feed liquid; S2 Continuous Catalyst Recovery: The parameters are the same as in Example 1, that is, the oxidizing liquid is continuously filtered by a ceramic membrane continuous filtration device (filtration accuracy 0.1μm) to recover the titanium dioxide photocatalyst. The catalyst is recycled back to the photocatalytic reactor for reuse, and the filtrate is crude furoic acid solution. S3 Continuous Nanofiltration Membrane Separation: The crude product liquid is continuously pumped into the nanofiltration membrane device by a booster pump for continuous nanofiltration membrane separation. The operating pressure is controlled at 0.7MPa, the temperature at 33℃, and the molecular weight cutoff at 180Da. Small molecule impurities are continuously removed, and the retentate (pure furoic acid solution) is collected. The filtrate (pure water) is collected in a collection tank and then returned to the reaction vessel by a reflux pump as makeup water. S4 Continuous finished product preparation: Same parameters as in Example 1.

[0031] Actual measured data: furfuryl alcohol conversion rate 99.7%, furoic acid yield 93.0%, finished product purity 99.5%, membrane separation yield 98.8%, impurity removal rate 99.2%; continuous and stable operation for 12 hours, with stable equipment operation; water resource utilization rate 98.0%, zero wastewater discharge; catalyst activity decay of 1.0% after 18 reuses, meeting design requirements, verifying process stability under lower parameter limits. Example 3

[0032] Parameter upper limit.

[0033] The continuous feeding parameters are as follows: completely consistent with those in Example 1; The process steps and parameters are as follows: S1 Continuous Photocatalytic Ozone Oxidation: First, continuously add 1000 g / h of 99.5% pure furfuryl alcohol and 4000 g / h of deionized water to a continuous photocatalytic reactor (made of 316L stainless steel). After stirring and mixing evenly, continuously add 45 g / h of anatase titanium dioxide photocatalyst (calcined and activated at 600℃ for 2 hours, with a specific surface area of ​​92 m²). 2 / g); Install a 380nm ultraviolet light source (power 260W), stir at a speed of 220r / min, turn on ultraviolet light irradiation at room temperature, and simultaneously and continuously introduce 62mg / L ozone (air flow rate 2.0L / min), control the reaction residence time to 0.8h, and continuously produce oxidized feed liquid; S2 Continuous Catalyst Recovery: The parameters are the same as in Example 1, that is, the oxidizing liquid is continuously filtered by a ceramic membrane continuous filtration device (filtration accuracy 0.1μm) to recover the titanium dioxide photocatalyst. The catalyst is recycled back to the photocatalytic reactor for reuse, and the filtrate is crude furoic acid solution. S3 Continuous Nanofiltration Membrane Separation: The crude product liquid is continuously pumped into the nanofiltration membrane device by a booster pump for continuous nanofiltration membrane separation. The operating pressure is controlled at 0.9 MPa, the temperature at 37℃, and the molecular weight cutoff at 220 Da. Small molecule impurities are continuously removed, and the retentate (pure furoic acid solution) is collected. The filtrate (pure water) is collected in a collection tank and then returned to the reaction vessel by a reflux pump as makeup water. S4 Continuous finished product preparation: Same parameters as in Example 1.

[0034] Actual test data: furfuryl alcohol conversion rate 99.9%, furoic acid yield 93.8%, finished product purity 99.7%, membrane separation yield 99.3%, impurity removal rate 99.5%; continuous and stable operation for 18 hours with no decrease in equipment operating efficiency; water resource utilization rate 99.0%, zero wastewater discharge; catalyst activity decay of 0.7% after 18 reuses, reaction yield 93.6%. All indicators are better than the design requirements, further proving the rationality and superiority of the process parameter range of this invention.

[0035] Comparative test No ultraviolet light catalysis.

[0036] Experimental conditions: The feeding was the same as in Example 1, and the same continuous equipment and process parameters were used as in Example 1, except that the ultraviolet light source was turned off, and all other operations were the same.

[0037] Actual test data: furfuryl alcohol conversion rate was only 94.2%, and furoic acid yield was 86.7%. To achieve a similar conversion rate, the reaction residence time needs to be extended to 2.0 h. After only 6 hours of continuous operation, problems such as decreased catalyst activity and uneven mixing of materials in the reactor appeared, requiring shutdown to clean the catalyst and reactor. Membrane separation yield was 98.5%, but due to the increase in reaction byproducts, the impurity removal rate was only 97.3%, and the purity of the finished product was 98.2%, which did not meet the quality standards of this invention.

[0038] Conclusion: This invention addresses the three core technical pain points of existing furoic acid production: large wastewater discharge, lack of continuous production, and reliance on organic solvents / ligands. It precisely designs a ligand-free green reaction system of "anatase titanium dioxide photocatalysis - ozone oxidation synergy," coupled with an integrated process of "continuous catalyst recovery via ceramic membrane - continuous separation via nanofiltration membrane - continuous concentration and drying," constructing a fully continuous production chain and forming a complete technical closed loop of "targeted pain points - solution adaptation - achieving target results." Specifically, the synergistic effect of photocatalysis and ozone can efficiently generate highly active hydroxyl radicals (·OH), fundamentally solving the industry pain point of low efficiency of single photocatalysis and ensuring the high efficiency of continuous reaction (residence time of only 0.6-0.8 h); nanofiltration membrane separation and water circulation design solve the wastewater discharge problem; the ligand-free and green solvent design controls pollution at the source, jointly achieving excellent environmental performance; the catalyst's continuous high recovery rate (≥99.5%) and stable reusability (≥18 times) ensure continuous production while reducing costs. Parallel verification in Examples 1-3 (covering upper and lower limits of parameters and benchmark values) shows that the core indicators of "conversion rate ≥99.7%, yield ≥93.0%, and purity ≥99.5%" can be stably achieved under all operating conditions, fully demonstrating the rationality of the process parameter range. Comparative experiments clearly show that ultraviolet light is the core of the synergistic system—without ultraviolet light, the furfuryl alcohol conversion rate drops sharply, and continuous operation stability fails. In summary, the technical solution of this invention precisely matches the invention's objective of "environmentally friendly continuous mass production of furfuryl acid," ultimately achieving a comprehensive beneficial effect of "zero emissions, high continuity, low cost, and high quality." The technical logic is rigorous and closed-loop, with significant creativity and practicality, and possesses broad prospects for industrial application.

[0039] Industrial Application Description: The preparation method of this invention can be directly adapted to the large-scale industrial production of furoic acid in an environmentally friendly and continuous manner. Its feasibility has been fully demonstrated through technical solution design and implementation examples. The core advantages are reflected in three dimensions: equipment compatibility, parameter controllability, and economic benefits. The core equipment used, such as the continuous photocatalytic reactor and the continuous ceramic membrane filtration device, are all existing mature equipment in environmentally friendly chemical production. They can be directly connected in series through sealed pipelines to form an integrated continuous production line without the need for customized development, thus reducing industrialization investment costs. Since furoic acid and reaction intermediates (such as furfural) are prone to oxidation reactions with oxygen in the air at room temperature, leading to a decrease in product purity and an increase in by-products, the entire production line is sealed and protected with inert gases (such as nitrogen, argon, etc., with nitrogen being preferred). This effectively prevents material oxidation and deterioration and the mixing of external impurities, achieving a fully enclosed flow of materials from reaction to finished product. The annual production capacity of a single production line can reach more than 5,000 tons. In terms of process parameter control, the high-precision automated control system enables precise control of the entire process: the reaction residence time is controlled by the linkage system between the feed rate and the reactor volume; the ozone concentration and aeration rate are regulated in tandem by the flow control system; and the nanofiltration membrane separation pressure and temperature are precisely controlled by the PID control system (pressure fluctuation ≤ ±0.005MPa, temperature fluctuation ≤ ±0.2℃), ensuring that each parameter remains stable within the range specified in the claims, with batch-to-batch purity fluctuation ≤ 0.1% and yield fluctuation ≤ 0.3%, thus guaranteeing product quality stability. This is consistent with the verification result of "continuous and stable operation for 12-18 hours" in the example. In terms of economic and social benefits, based on an annual production capacity of 5,000 tons of environmentally friendly continuous furoic acid, the raw material consumption (1.08 tons of furfuryl alcohol per ton of furoic acid), water consumption (0.02 tons per ton of furoic acid after recycling), and catalyst consumption (2.5 kg per ton of furoic acid after 18 reuses) of this process are all at the leading level in the industry. There is no consumption of organic solvents and ligands, zero wastewater discharge, and environmental protection treatment costs are reduced by more than 95%. The production cost is reduced by 25-30% compared with the traditional process, which can promote the transformation and upgrading of the furoic acid production industry from "intermittent high pollution" to "continuous green".

[0040] This specification discloses the technical solution of the present invention in detail, aiming to enable those skilled in the art to understand and implement the present invention. The specific embodiments described herein do not constitute a limitation on the scope of protection of the present invention, which is determined by the claims.

Claims

1. A method for the continuous preparation of furoic acid by ozone oxidation of furfuryl alcohol, characterized in that, Includes the following steps: S1 Continuous photocatalytic ozone oxidation: furfuryl alcohol, deionized water and titanium dioxide photocatalyst are continuously added to the photocatalytic reactor. Under stirring at room temperature, ultraviolet light is turned on and ozone is continuously introduced at the same time. The reaction residence time is controlled to continuously produce oxidized feed liquid. S2 Catalyst Continuous Recovery: The oxidized feed liquid produced by S1 is continuously filtered through a ceramic membrane to recover the titanium dioxide photocatalyst and return it to S1 for recycling. After filtration, crude furoic acid solution is obtained. S3 Continuous nanofiltration membrane separation: The crude furoic acid solution obtained in S2 is subjected to continuous nanofiltration membrane separation to obtain pure furoic acid solution; S4 Continuous finished product preparation: The pure furoic acid solution obtained in S3 is continuously concentrated under reduced pressure and dried under vacuum to obtain the finished furoic acid product.

2. The method for continuous ozone oxidation of furfuryl alcohol to prepare furoic acid according to claim 1, characterized in that, In step S1, the titanium dioxide photocatalyst is anatase titanium dioxide, which is activated by calcination at 600±100℃ for 1-3 hours and has a specific surface area ≥90m² / g.

3. The method for continuous ozone oxidation of furfuryl alcohol to prepare furoic acid according to claim 1, characterized in that, In step S1, the purity of furfuryl alcohol is ≥99.5%, the feed rate is 1000±100g / h, the feed rate of deionized water is 4000±500g / h, and the feed rate of titanium dioxide photocatalyst is 45±10g / h.

4. The method for continuous ozone oxidation of furfuryl alcohol to prepare furoic acid according to claim 1, characterized in that, In step S1, the ozone concentration is 58-62 mg / L and the ventilation rate is 1.6-2.0 L / min.

5. The method for continuous ozone oxidation of furfuryl alcohol to prepare furoic acid according to claim 1, characterized in that, In step S1, the ultraviolet light power is 240-260W, the stirring rate is 220±20r / min, and the reaction residence time is 0.6-0.8h.

6. The method for continuous ozone oxidation of furfuryl alcohol to prepare furoic acid according to claim 1, characterized in that, In step S2, the ceramic membrane filtration accuracy is 0.1-0.2 μm.

7. The method for continuous ozone oxidation of furfuryl alcohol to prepare furoic acid according to claim 1, characterized in that, In step S3, the nanofiltration membrane operates at a pressure of 0.7-0.9 MPa and a temperature of 33-37°C, and the nanofiltration membrane retains a molecular weight of 180-220 Da. The filtrate separated by the nanofiltration membrane is pure water, which is circulated back to step S1 as reaction makeup water via a reflux pump.

8. The method for continuous ozone oxidation of furfuryl alcohol to prepare furoic acid according to claim 1, characterized in that, In step S4, the vacuum degree of continuous decompression concentration is -0.07 ~ -0.09 MPa and the temperature is 60-70℃.

9. The method for continuous ozone oxidation of furfuryl alcohol to prepare furoic acid according to claim 1, characterized in that, In step S4, the vacuum drying temperature is 100-105℃.