A device and method for preparing levulinic acid using continuous flow technology

Abstract

This invention provides an apparatus and method for preparing levulinic acid using continuous flow technology, relating to the field of chemical synthesis technology. The method includes: using furfuryl alcohol as a raw material, an organic solvent-water mixture as a two-way solvent system, and a composite system of inorganic protic acid and alkali metal halide as a catalyst, to achieve a one-step conversion of furfuryl alcohol to levulinic acid in a continuous flow microchannel reactor. The core advantages of this invention are: the yield of levulinic acid can reach 95.5%, and the purity of the product after separation and purification is higher than 99.9%; a cheap and readily available composite catalyst is used, and the raw material is renewable and widely available; the reaction apparatus is simple and efficient, improving heat and mass transfer performance, realizing continuous production, and effectively solving the drawbacks of traditional one-pot reactors.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis, specifically relating to an apparatus and method for preparing levulinic acid using continuous flow technology. Background Technology

[0002] With the increasing depletion of fossil resources, people are paying more and more attention to sustainable development. Biomass, as the only sustainable organic carbon source that can replace fossil resources, has become a research hotspot and urgent need in the chemical industry due to its efficient conversion and utilization. Furfuryl alcohol, as a key bio-based chemical, is mainly derived from the resource conversion of agricultural waste such as corn cobs, wheat straw, and sugarcane bagasse. It has the significant advantages of wide availability and renewability, providing high-quality raw materials for the synthesis of biomass-based chemicals.

[0003] Levulopyric acid (LA), as a multifunctional platform compound, is a core component in the production of diverse chemicals and biofuels. It is widely used in fuel additives, solvents, resin synthesis, polymer precursors, flavoring agents, pharmaceutical preparations, and chemical intermediates, and is listed as one of the 12 most valuable biomass-derived platform compounds, with broad market application prospects. Currently, the synthesis technology of levulopyric acid mainly focuses on two routes in domestic and international literature and patents: direct biomass hydrolysis and furfuryl alcohol-catalyzed hydrolysis. Among these, lignocellulosic biomass has a complex composition, containing a large amount of lignin and other impurities. These impurities inhibit the formation of levulopyric acid and its intermediate levulopyric acid ester, leading to numerous side reactions and difficulties in product separation during the direct alcoholysis or hydrolysis of biomass to prepare levulopyric acid ester. Ultimately, this results in a low yield of levulopyric acid, which is insufficient to meet the needs of industrial production.

[0004] Compared to direct biomass hydrolysis, furfuryl alcohol catalytic hydrolysis has advantages such as high raw material purity and a relatively clear reaction path. However, in existing technologies, this method usually requires a two-step synthesis of levulinic acid: the first step is to convert furfuryl alcohol into levulinic acid (ester) intermediates using a catalyst. For example, patent CN120079378A discloses a method for preparing alkyl levulinic acid esters from furfuryl alcohol, patent CN118307401A discloses a method for preparing ethyl levulinic acid esters from furfuryl alcohol using sulfonated activated carbon catalytic alcoholysis, patent CN118270838A discloses a method for converting furfuryl alcohol into ethyl levulinic acid esters based on ultrathin two-dimensional BiOCl nanosheets, and patent CN117229142A discloses a method for preparing ethyl levulinic acid esters from furfuryl alcohol using a supported non-precious metal catalyst. The second step requires an additional hydrolysis process to further hydrolyze the levulinic acid ester intermediates to obtain the levulinic acid product. This two-step synthetic route is lengthy, increasing reaction energy consumption and production time, as well as equipment investment and operating costs, thus hindering its industrial application. Therefore, developing a highly efficient synthetic technology that can convert furfuryl alcohol into levulinic acid in a single step with high concentration and high selectivity offers significant technological advantages and application value compared to the traditional two-step method.

[0005] Continuous flow reactors, with their controllable residence time, large specific surface area, and minimal scale-up effect, have gained increasing attention and importance in the field of organic synthesis in recent years. In existing technologies, some researchers use high-pressure reactors for the conversion of furfuryl alcohol to levulinic acid. However, batch reactor reactions suffer from uneven temperature and concentration field distributions and poor process controllability, resulting in low selectivity for levulinic acid. Furthermore, the heating process easily leads to oligomerization of furfuryl alcohol, generating byproducts such as humin, which reduces raw material utilization and product yield. Using a continuous flow reactor for the furfuryl alcohol conversion effectively solves these technical problems. By precisely controlling reaction parameters to suppress side reactions, the selectivity of furfuryl alcohol conversion is significantly improved, achieving efficient synthesis of levulinic acid. Summary of the Invention

[0006] To address the problems of lengthy reaction processes, high energy consumption, low yield, poor selectivity, and numerous byproducts in existing levulinic acid synthesis technologies, this invention provides an apparatus and method for preparing levulinic acid using continuous flow technology. The aim is to achieve a one-step direct conversion of furfuryl alcohol to levulinic acid, effectively avoiding the cumbersome procedures of the traditional two-step method, while simultaneously improving product selectivity and yield. This provides a reliable solution for the efficient and low-cost industrial production of levulinic acid.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention first provides a continuous flow reaction apparatus for preparing levulinic acid, comprising: a high-pressure pump for continuously delivering the reaction liquid; a continuous reactor for converting furfuryl alcohol to levulinic acid; a back pressure valve located at the outlet end of the continuous reactor for maintaining the pressure of the reaction system; and a quenching reaction device located after the back pressure valve, employing an ice bath structure to rapidly terminate the reaction; the above components are connected in series via stainless steel pipes.

[0008] The present invention provides a method for preparing levulinic acid using continuous flow technology. This method uses furfuryl alcohol as a raw material, a mixture of organic solvent and water as the reaction medium, and a combination of inorganic protic acid and alkali metal halide as a catalyst. The reaction is completed using the aforementioned continuous flow preparation apparatus. Specifically, the method includes the following steps: Step 1: Mix furfuryl alcohol raw material, catalyst and solvent evenly to obtain reaction solution; Step 2: The reaction solution is continuously pumped into a continuous reactor using a high-pressure pump, and a hydrolysis reaction is carried out at a set temperature to achieve the conversion of furfuryl alcohol to levulinic acid. Step 3: After the hydrolysis reaction is completed, the reaction solution passes through the back pressure valve and the quenching reaction device in sequence to obtain the reaction product containing levulinic acid. Subsequently, it is separated and purified to obtain pure levulinic acid.

[0009] The technical solution of the present invention will be further described in detail below: In step 1: the purity of the furfuryl alcohol raw material is greater than 99%, and its concentration in the reaction solution is 0.1 mol / L to 3 mol / L. This concentration range can ensure the efficient conversion of the raw material, while avoiding the aggravation of side reactions caused by excessive concentration.

[0010] The catalyst is a combination of an inorganic protic acid and an alkali metal halide. The synergistic effect of the two ensures the efficient conversion of furfuryl alcohol to levulinic acid. The inorganic protic acid can be one or more of hydrochloric acid, sulfuric acid, or oxalic acid, accounting for 10% to 40% of the molar amount of furfuryl alcohol in the reaction solution. Its core function is to provide an acidic reaction environment, promote the ring-opening of furfuryl alcohol molecules, and induce hydrolysis. The alkali metal halide can be one or more of sodium chloride, potassium iodide, sodium iodide, or potassium bromide, accounting for 0% to 20% of the solvent mass in the reaction solution. Its function is to increase the boiling point of the reaction solvent and provide Lewis acid active sites, further enhancing the catalytic effect and improving product selectivity.

[0011] The inorganic protic acid is preferably hydrochloric acid accounting for 25 mol% of the molar amount of furfuryl alcohol, and the alkali metal halide is preferably sodium chloride with a concentration of 0.06 mol / L in the reaction solution.

[0012] The solvent is a mixture of an organic solvent and water in a volume ratio of 1 to 3:1. The organic solvent can be one or more of γ-valerol (GVL), tetrahydrofuran (THF), or butyronitrile, preferably a mixture of tetrahydrofuran and water in a volume ratio of 2:1. This two-way solvent system optimizes the solubility of the reaction system, ensures homogeneous reaction, and further improves furfuryl alcohol conversion efficiency and levulinic acid yield.

[0013] In step 2: a plunger pump can be used as the high-pressure infusion pump; the continuous reactor, as the core reaction unit, adopts a stainless steel tubular structure with an inner diameter of 1-2 mm, an outer diameter of 3 mm, and a tube length of 5-15 m, preferably with an inner diameter of 2 mm, an outer diameter of 3 mm, and a tube length of 10 m; this continuous reactor is uniformly placed in a temperature-controlled environment using dimethyl silicone oil as the heating medium, enabling precise control of the reaction temperature and uniform heat transfer. During the reaction, the reaction solution is continuously pumped into the continuous reactor via the high-pressure infusion pump, and the hydrolysis reaction is carried out at a temperature of 120-160℃. The reaction residence time is controlled at 10-30 min by adjusting the flow rate of the reaction solution, with the preferred reaction conditions being 20 min at 140℃. This range of process parameters maximizes the conversion of furfuryl alcohol to levulinic acid while effectively suppressing side reactions such as oligomerization and reducing the formation of byproducts such as humic acid.

[0014] In step 3: The quenching reaction device adopts an ice bath structure, which can quickly terminate the reaction and avoid secondary reactions in the reaction liquid that could affect the purity of the product. Specifically, the core of the quenching reaction device is the reaction vessel, which is equipped with a cooling jacket on its outer layer. The cooling jacket is used to introduce coolant to provide a continuous and uniform cooling environment. The coolant can be common low-temperature cooling media such as ice water, frozen brine, or ethylene glycol solution. At the same time, a cooling coil is installed inside the reaction vessel. The cooling coil is connected to the back pressure valve outlet through a stainless steel pipe. After the reaction is completed, the reaction liquid is pressurized by the back pressure valve and continuously flows into the cooling coil and along the coil. Through the dual cooling effect of the cooling jacket and the internal cooling coil, the reaction liquid can be quickly cooled down, achieving instantaneous quenching of the reaction.

[0015] The separation and purification method is as follows: the reaction product containing levulinic acid is mixed with an extractant and extracted to obtain an extract phase containing levulinic acid; the extract phase is back-extracted using water as the back-extractant to obtain an aqueous solution of levulinic acid; the aqueous solution of levulinic acid is post-treated (e.g., rotary evaporation or vacuum distillation) to obtain purified levulinic acid; wherein the extractant is selected from one or more of ethyl acetate, 2-octanol, dichloromethane, diethyl ether, and toluene.

[0016] After the reaction is completed, the reaction products are qualitatively and quantitatively analyzed by gas chromatography (GC) or nuclear magnetic resonance hydrogen spectroscopy to accurately detect the purity and yield of levulinic acid, providing data support for process optimization and industrial application.

[0017] Compared with existing technologies, the beneficial effects of this invention are reflected in: 1. This invention relies on continuous flow technology and specialized device design to achieve a one-step direct conversion of furfuryl alcohol to levulinic acid, significantly shortening the production process and reducing energy consumption and labor costs. At the same time, the eddy current effect and precise temperature and time control capability of the stainless steel microreactor improve the heat and mass transfer efficiency, significantly shortening the heating time. Combined with the synergistic effect of the composite catalyst and the two-way solvent system, it improves the conversion rate of furfuryl alcohol and the selectivity of levulinic acid, providing a new technical route for the efficient preparation of levulinic acid.

[0018] 2. The continuous flow preparation device of the present invention consists of a high-pressure infusion pump, a continuous reactor, a back pressure valve, and a quenching reaction device connected in series by stainless steel pipes. It has a simple structure, readily available parts, and is easy to assemble and maintain. Compared with traditional high-pressure reactors, this device has a smaller liquid holding capacity and more precise temperature and pressure control, which can effectively avoid safety risks such as local overheating and pressure fluctuations, and has higher operational safety. Moreover, the continuous flow mode can achieve linear capacity scaling up by connecting reactors in parallel or increasing the number of microchannels without the need for significant adjustments to core process parameters, providing reliable device support for the large-scale industrial production of levulinic acid.

[0019] 3. This invention employs a composite catalytic system composed of inorganic protic acid and alkali metal halide, which synergistically enhances the effect, resulting in high catalytic activity. The raw materials are all inexpensive and readily available conventional chemicals, which significantly reduces catalyst costs compared to commonly used supported precious metal catalysts and special nanocatalysts in existing technologies. At the same time, the two-way solvent system composed of organic solvent and water ensures homogeneous reaction, improves reaction efficiency, and the solvent and catalyst are easy to recycle and process, which conforms to the concept of green chemical production and takes into account both economic efficiency and environmental friendliness.

[0020] 4. The entire reaction process of this invention is carried out continuously, and the feeding, reaction, quenching and other links are all automated and continuous, eliminating the need for intermittent feeding and discharging, which greatly improves production efficiency. At the same time, by precisely controlling parameters such as reaction temperature, residence time and raw material concentration, the stability and consistency of product quality can be guaranteed, reducing the risk of quality fluctuations during the production process. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0022] Figure 1This is a diagram of the continuous flow reaction apparatus for preparing levulinic acid according to the present invention; Figure 2 The image shows a gas chromatogram of levulinic acid, the reaction product prepared according to the technical solution of this invention. Detailed Implementation

[0023] To more clearly illustrate the present invention, the technical solution of the present invention will be clearly and completely described below with reference to embodiments. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0024] The reaction apparatus and process involved in the following embodiments are as follows: Figure 1 As shown, the continuous flow reaction apparatus includes a high-pressure delivery pump, a continuous reactor, a back pressure valve, and a quenching reaction device. These components are connected in series via stainless steel pipes to form a complete reaction system. Specifically: the high-pressure delivery pump can be a plunger pump; the continuous reactor adopts a stainless steel tubular disc structure, entirely placed inside an oil bath (using dimethyl silicone oil as the heating medium) for temperature control; the back pressure valve maintains the internal pressure of the reactor at the required process setting; the quenching reaction device is a closed reaction vessel with a cooling jacket and internal cooling coils. Coolant is circulated within the cooling jacket, and the reaction liquid flows through the cooling coils to achieve rapid cooling, thereby immediately terminating the reaction and ensuring product purity.

[0025] The general experimental steps for all embodiments of this invention are as follows: First, all reaction components are connected and assembled. Methanol and isopropanol are pumped in sequentially to clean the entire reaction system and remove impurities from the pipelines. After cleaning, the reaction solvent used in this experiment is pumped in to rinse the stainless steel microreactor pipeline to ensure that the reaction system and solvent are compatible. Subsequently, the prepared reaction solution is continuously pumped into the system. The reaction solution flows through a continuous reactor at a set temperature. After the hydrolysis reaction is completed according to the preset residence time, the reaction solution is recovered. The recovered reaction mixture is qualitatively and quantitatively analyzed using appropriate detection methods. Subsequently, levulinic acid product is obtained through separation and purification.

[0026] It should be noted that the listed embodiments are only some preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All other embodiments obtained by those skilled in the art based on the technical concept of the present invention without creative effort are within the scope of protection of the present invention.

[0027] Example 1 In this embodiment, an experiment was conducted to synthesize levulinic acid from furfuryl alcohol in the aforementioned continuous flow reactor. The specific steps are as follows: First, the raw material furfuryl alcohol was purified by vacuum distillation to obtain pure furfuryl alcohol with a purity of ≥99%. The reaction solution was prepared according to the experimental requirements: the furfuryl alcohol concentration was 1.00 mol / L, the molar amount of HCl catalyst was 25 mol of the molar amount of furfuryl alcohol, and the solvent was a tetrahydrofuran / water mixture (volume ratio of the two was 2:1).

[0028] After completing the connection, cleaning, and pipeline rinsing of the reaction apparatus according to the general experimental procedures, the above reaction solution is continuously pumped into the stainless steel continuous reactor through a high-pressure pump. The tube coil of the stainless steel continuous reactor has an inner diameter of 2.0 mm × an outer diameter of 3 mm × a tube length of 10 m. The oil bath temperature is controlled at 120℃, and the feed flow rate is adjusted to make the reaction residence time 20 min.

[0029] After the reaction was completed, the reaction solution was pressurized by a back pressure valve and then rapidly cooled and quenched in a quenching device. The reaction solution was then collected. Once the reaction solution returned to room temperature, it was extracted with ethyl acetate. A small amount of the extract was diluted with N,N-dimethylformamide, and levulinic acid was quantitatively detected using gas chromatography (GC). The remaining extract phase was back-extracted with water as the back-extraction agent to obtain an aqueous solution of levulinic acid. The solvent and water were then removed by rotary evaporation to finally obtain purified levulinic acid. The experimental results of this example are shown in Table 1.

[0030] Examples 2-5 Examples 2-5 all involved the synthesis of levulinic acid from furfuryl alcohol in the aforementioned continuous flow reactor. The experimental procedures were basically the same as in Example 1, except that an inorganic protic acid and alkali metal halide composite catalytic system was used, wherein the inorganic protic acid was HCl (accounting for 25 mol% of the molar amount of furfuryl alcohol), and the alkali metal halide was NaCl (with a concentration of 0.06 mol / L in the reaction solution). The reaction temperatures were set at 100℃, 120℃, 140℃, and 160℃ (corresponding to Examples 2-5, respectively), and all other experimental parameters were consistent with those in Example 1.

[0031] Each embodiment followed the same procedure as in Embodiment 1 to complete the device connection, cleaning, rinsing, reaction, post-treatment (quenching, extraction, dilution) and GC detection. The experimental results are shown in Table 1.

[0032] Examples 6-8 Examples 6-8 all involved the synthesis of levulinic acid from furfuryl alcohol in the aforementioned continuous flow reactor. The experimental procedures were basically the same as in Example 1, except that an inorganic protic acid and alkali metal halide composite catalytic system was used, wherein the inorganic protic acid was HCl (accounting for 25 mol% of the molar amount of furfuryl alcohol), and the alkali metal halide was NaCl (concentration of 0.06 mol / L in the reaction solution); the reaction temperature was set at 140℃, and the reaction residence times were 5 min, 10 min, and 30 min, respectively (corresponding to Examples 6-8). All other experimental parameters were consistent with those in Example 1.

[0033] Each embodiment followed the same procedure as in Embodiment 1 to complete the device connection, cleaning, rinsing, reaction, post-processing, and GC detection. The experimental results are shown in Table 1.

[0034] Examples 9-10 Examples 9-10 all involved the synthesis of levulinic acid from furfuryl alcohol in the aforementioned continuous flow reactor. The experimental procedures were basically the same as in Example 1, except that an inorganic protic acid and alkali metal halide composite catalytic system was used, wherein the inorganic protic acid was HCl and the alkali metal halide was NaCl (at a concentration of 0.06 mol / L in the reaction solution). The amount of HCl was adjusted to 10 mol% and 40 mol% of the molar amount of furfuryl alcohol, respectively (corresponding to Examples 9-10). The reaction temperature was set at 140℃, and all other experimental parameters were the same as in Example 1.

[0035] Each embodiment followed the same procedure as in Embodiment 1 to complete the device connection, cleaning, rinsing, reaction, post-processing, and GC detection. The experimental results are shown in Table 1.

[0036] Example 11 In this embodiment, the synthesis of levulinic acid from furfuryl alcohol was carried out in the above-mentioned continuous flow reactor. The experimental steps were basically the same as in Example 1, except that: an inorganic protic acid and alkali metal halide composite catalytic system was used, wherein the inorganic protic acid was HCl (accounting for 25 mol% of the molar amount of furfuryl alcohol), and the alkali metal halide was NaCl (with a concentration of 0.06 mol / L in the reaction solution); a tetrahydrofuran / water mixed system was used as the solvent, and the volume ratio of the two was adjusted to 5:1; the reaction temperature was set at 140℃, and all other experimental parameters were the same as in Example 1.

[0037] In this embodiment, the same process as in Embodiment 1 was followed to complete the device connection, cleaning, rinsing, reaction, post-processing and GC detection. The experimental results are shown in Table 1.

[0038] Examples 12-13 Examples 12-13 were all conducted in the above-mentioned continuous flow reactor to synthesize levulinic acid from furfuryl alcohol. The experimental procedures were basically the same as in Example 1, with the key difference being: an inorganic protic acid and alkali metal halide composite catalytic system was used, wherein the inorganic protic acid was HCl (accounting for 25 mol% of the molar amount of furfuryl alcohol), and the alkali metal halide was NaCl (concentration of 0.06 mol / L in the reaction solution); the solvent was adjusted to an acetonitrile / water (volume ratio 2:1) mixture and a γ-valerolactone (GVL) / water (volume ratio 2:1) mixture (corresponding to Examples 12-13 respectively); the reaction temperature was set at 140℃, and all other experimental parameters were the same as in Example 1.

[0039] Each embodiment followed the same procedure as in Embodiment 1 to complete the device connection, cleaning, rinsing, reaction, post-processing, and GC detection. The experimental results are shown in Table 1.

[0040] Example 14 In this embodiment, the synthesis of levulinic acid from furfuryl alcohol was carried out in the above-mentioned continuous flow reactor. The experimental steps were basically the same as in Example 1. The core difference was that an inorganic protic acid and alkali metal halide composite catalytic system was used, wherein the inorganic protic acid was H2SO4 (accounting for 12 mol% of the molar amount of furfuryl alcohol), and the alkali metal halide was NaCl (with a concentration of 0.06 mol / L in the reaction solution); the reaction temperature was set at 140℃, and all other experimental parameters were the same as in Example 1.

[0041] In this embodiment, the same process as in Embodiment 1 was followed to complete the device connection, cleaning, rinsing, reaction, post-processing and GC detection. The experimental results are shown in Table 1.

[0042] Example 15 In this embodiment, the synthesis of levulinic acid from furfuryl alcohol was carried out in the above-mentioned continuous flow reactor. The experimental steps were basically the same as in Example 1, with the key difference being: an inorganic protic acid and alkali metal halide composite catalytic system was used, wherein the inorganic protic acid was HCl (accounting for 25 mol% of the molar amount of furfuryl alcohol), and the alkali metal halide was NaCl (with a concentration of 0.06 mol / L in the reaction solution); the dimensions of the stainless steel microreactor were adjusted to an inner diameter of 1.5 mm × an outer diameter of 3 mm × a tube length of 10 m; the reaction temperature was set to 140℃, and all other experimental parameters were consistent with those in Example 1.

[0043] In this embodiment, the same process as in Embodiment 1 was followed to complete the device connection, cleaning, rinsing, reaction, post-processing and GC detection. The experimental results are shown in Table 1.

[0044] Table 1 As shown in Table 1, the method of this invention can convert furfuryl alcohol to levulinic acid in a short time, reducing side reactions and saving a significant amount of time. Levulinic acid was prepared by homogeneous catalysis with an acid catalyst in a mixed solvent of organic solvent and water, achieving a yield as high as 95.5%. The catalyst is inexpensive and readily available.

[0045] Comparative Example 1 This comparative example demonstrates the synthesis of levulinic acid from furfuryl alcohol in a conventional batch reactor. 30 mmol of pre-prepared furfuryl alcohol, 7.5 mmol of HCl catalyst, 105 mg of NaCl, and 30 mL of tetrahydrofuran / water mixed solvent (volume ratio 2:1) were added to a 50 mL reactor. Nitrogen gas was purged into the reactor three times to eliminate oxygen interference. The reactor was sealed and stirred at 140 °C for 4 h. After the reaction, the reaction system was cooled to room temperature, and the reaction solution was extracted with ethyl acetate. The extracted sample was diluted with N,N-dimethylformamide, and the yield of levulinic acid was determined by gas chromatography (GC). The results are shown in Table 2.

[0046] Comparative Example 2 The experimental procedure for this comparative example was exactly the same as that for Comparative Example 1, except that the solvent system was changed to a γ-valerolactone / water mixed solvent (volume ratio 2:1). After the reaction, the same procedure was followed for post-processing and detection. The results are shown in Table 2.

[0047] Comparative Example 3 The experimental procedure for this comparative example was exactly the same as that for Comparative Example 1, except that the 7.5 mmol HCl catalyst was replaced with a 3.7 mmol H2SO4 catalyst. After the reaction was completed, the same procedure was followed for post-processing and detection. The results are shown in Table 2.

[0048] Table 2 A comparative analysis of the experimental results in Tables 1 and 2 clearly reveals that the continuous flow microreactor technology of this invention exhibits significant technical advantages over the traditional batch reactor process in the preparation of levulinic acid: the reaction residence time of the continuous flow process is only 20 minutes, far shorter than the 4 hours required by the reactor, significantly shortening the production cycle and reducing energy consumption; simultaneously, under optimal process conditions, the yield of levulinic acid in the continuous flow process can reach 95.5%, while the highest yield of the traditional reactor process is only 37.9%, representing an increase in product yield of over 150%. This result fully demonstrates that the continuous flow technology of this invention, by enhancing heat and mass transfer and precisely controlling reaction parameters, can effectively suppress side reactions, significantly improve reaction efficiency and product selectivity, and provide a superior technical path for the industrial-scale, efficient production of levulinic acid.

Claims

1. A continuous flow reaction device for the production of levulinic acid, characterized in that, include: High-pressure infusion pumps are used for the continuous delivery of reaction solutions; A continuous reactor is used to convert furfuryl alcohol to levulinic acid; A back pressure valve, located at the outlet end of a continuous reactor, is used to maintain the pressure of the reaction system. The quenching reaction device is located after the back pressure valve and uses an ice bath structure to quickly terminate the reaction; The above components are connected in series via stainless steel pipes.

2. The continuous flow reaction apparatus of claim 1, wherein, The continuous reactor is placed in a temperature-controlled environment with dimethyl silicone oil as the heating medium.

3. The continuous flow reaction apparatus of claim 1, wherein, The continuous reactor adopts a stainless steel tube disc structure with an inner diameter of 1~2 mm, an outer diameter of 3 mm, and a tube length of 5~15 m.

4. A method for producing levulinic acid using a continuous flow technique, characterized by, Using the continuous flow reaction apparatus according to any one of claims 1 to 3, the following steps are performed: Step 1: Mix furfuryl alcohol raw material, catalyst and solvent evenly to obtain reaction solution; Step 2: The reaction solution is continuously pumped into a continuous reactor through a high-pressure pump to carry out a hydrolysis reaction, thereby converting furfuryl alcohol into levulinic acid. Step 3: After the hydrolysis reaction is completed, the reaction solution passes through the back pressure valve and the quenching reaction device in sequence to obtain the reaction product containing levulinic acid. Subsequently, it is separated and purified to obtain pure levulinic acid.

5. The method of claim 4, wherein: The concentration of the furalcohol raw material in the reaction solution of Step 1 is 0.1 mol / L -1 3 mol / L -1 .

6. The method of claim 4, wherein: The catalyst is a combination of an inorganic protic acid and an alkali metal halide, wherein the inorganic protic acid accounts for 10% to 40% of the molar amount of furfuryl alcohol in the reaction solution, and the alkali metal halide accounts for 0% to 20% of the solvent mass in the reaction solution.

7. The method according to claim 6, characterized in that: The inorganic protic acid is one or more of hydrochloric acid, sulfuric acid, or oxalic acid; the alkali metal halide is one or more of sodium chloride, potassium iodide, sodium iodide, or potassium bromide.

8. The method according to claim 6, characterized in that: The solvent is a mixture of organic solvent and water, with a volume ratio of organic solvent to water of 1 to 3:1; the organic solvent is selected from one or more of γ-valerol, tetrahydrofuran, or butyronitrile.

9. The method according to claim 6, characterized in that: In step 2, the hydrolysis reaction is carried out at a temperature of 120~160℃ and the reaction residence time is 10~30 min.

10. The method according to claim 6, characterized in that, In step 3, the separation and purification method is as follows: the reaction product containing levulinic acid is mixed with an extractant and extracted to obtain an extract phase containing levulinic acid; the extract phase is back-extracted using water as the back-extractant to obtain an aqueous solution of levulinic acid; the aqueous solution of levulinic acid is post-treated to obtain purified levulinic acid; wherein the extractant is selected from one or more of ethyl acetate, 2-octanol, dichloromethane, diethyl ether, and toluene.

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