Method and system for preparing n-heptanoic acid by hydrolyzing methyl n-heptanoate

Abstract

The invention discloses a method and system for preparing n-heptanoic acid through hydrolysis of methyl n-heptanoate based on a reactive distillation technology, and belongs to the technical field of organic synthesis. The method comprises the following steps: continuously introducing methyl n-heptanoate and water into a reactive distillation tower filled with an H beta molecular sieve-sulfonated carbon-based composite solid acid catalyst, carrying out hydrolysis reaction at a reaction section temperature, and forming an incremental temperature gradient along the height direction of the reactive distillation tower to generate a reaction mixture containing n-heptanoic acid and methanol; the reaction mixture is subjected to rectification separation, and an n-heptanoic acid product is extracted from a tower kettle of the reactive distillation tower. The target product is high in selectivity, high in yield and high in purity (n-heptanoic acid with the purity larger than or equal to 99.5% can be obtained in a tower kettle); the catalyst is efficient and easy to separate and recover; the method is environment-friendly and less in'three wastes' emission, and accords with the green chemistry principle; the whole production cost is competitive, and industrial production is easy to realize.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic synthesis, and in particular to a method and system for preparing heptanoic acid based on reaction rectification technology, which is suitable for high-value utilization of fine chemical and biofuel downstream products. BACKGROUND

[0002] Heptanoic acid (CAS: 111-14-8), also known as heptylic acid, is an important saturated medium-chain fatty acid (C7); its molecular formula is CH3(CH2)5COOH. Heptanoic acid and its ester, salt and other derivatives have wide application value in the field of fine chemicals, mainly including: perfume and essence industry, lubricant and plasticizer, pharmaceutical and pesticide intermediates, and are used for synthesizing surfactants, preservatives, resin modifiers, etc. In view of its important application value, the development of efficient, economical and environmentally friendly heptanoic acid preparation method has been concerned by the industry and academia.

[0003] At present, the main preparation methods reported in the literature or industry are as follows: natural source extraction method, heptylaldehyde oxidation method, 1-hexene carbonyl synthesis method and biological fermentation method. In the biological fermentation method, specific microorganisms (such as yeast, bacteria) can be used to metabolize sugars or other carbon sources to produce heptanoic acid; this method has good environmental protection, but the yield needs to be improved.

[0004] In the commonly used synthesis method, the patent EP 0,789,081 B1 document introduces a method of using 1-hexene as raw material, using rhodium / biphosphine ligand catalyst for hydroformylation reaction to generate heptylaldehyde, which can be further oxidized by air to obtain heptylic acid. The straight-chain selectivity of the synthesized heptylaldehyde is >90%, but there are limitations such as high cost of catalyst, complex synthesis of ligand, large investment of high-pressure reaction equipment.

[0005] In summary, the existing heptanoic acid preparation methods generally have problems such as high cost of raw materials, complex process route, unsatisfactory reaction selectivity, and yield to be improved. Especially for the application scenarios that require high-purity, low-cost, green and sustainable production of heptanoic acid, such as high-end perfumes and pharmaceutical intermediates, the existing synthesis technology cannot fully meet the requirements. SUMMARY

[0006] In order to overcome the above-mentioned defects of the prior art, the present application provides a method and system for preparing heptanoic acid by hydrolysis of methyl heptanoate, which is a high-efficiency, environmentally-friendly heptanoic acid preparation method meeting the above-mentioned requirements, with high selectivity and high yield of target product, low cost, and easy to realize industrial production.

[0007] To achieve the above-mentioned purpose, the present application provides a method for preparing heptanoic acid by hydrolysis of methyl heptanoate, comprising the following steps:

[0008] In the reaction rectifying column filled with the Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst, the methyl n-heptanoate and water are continuously fed, and the hydrolysis reaction is carried out at the reaction section temperature, wherein an increasing temperature gradient is formed along the height direction of the reaction rectifying column, and a reaction mixture containing n-heptanoic acid and methanol is generated;

[0009] The reaction mixture is subjected to rectification separation, and the n-heptanoic acid product is taken out from the column bottom of the reaction rectifying column.

[0010] The Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst has a three-level pore structure of micropore-mesopore-macropore, and the mesopore volume accounts for ≥40%.

[0011] In particular, the Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst has sulfonic acid groups, carboxyl groups and hydroxyl groups on the surface, and the total acid density is ≥1.5 mmol / g.

[0012] The Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst is obtained by the following steps:

[0013] The Hβ molecular sieve is treated with a silanization reagent to obtain an amine-based molecular sieve;

[0014] The sulfonated carbon is subjected to oxidation-aldehyde group treatment to obtain an aldehyde group sulfonated carbon;

[0015] The amine-based molecular sieve and the aldehyde group sulfonated carbon are mixed and reacted, and the covalent bond catalyst is obtained by reduction;

[0016] The covalent bond catalyst is treated with a perfluorooctyltriethoxysilane solution under microwave irradiation to form a hydrophobic layer.

[0017] In particular, the Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst is filled on the reaction section tray of the reaction rectifying column, and the filling amount is 5-20 wt% of the liquid holdup of the reaction section.

[0018] In particular, the molar feeding ratio of water to methyl n-heptanoate is 2.5:1 to 4.0:1.

[0019] The reaction rectifying column has 15-25 theoretical plates; the reaction section temperature is 90-120°C; and the increasing temperature gradient includes 90-100°C for the 6th-8th plate, 100-105°C for the 9th-11th plate, and 105-118°C for the 12th-15th plate.

[0020] The reaction section of the reaction rectifying column accounts for 6-10 theoretical plates.

[0021] Particularly, the methyl n-heptanoate is fed from the 3rd to 8th theoretical plate of the column body, and the water is fed from the 10th to 18th theoretical plate; the reflux ratio of the reaction section of the reactive distillation column is controlled to be 0.5-2.0, the top temperature is 64-66℃, and the bottom temperature is 180-210℃.

[0022] The methanol-water azeotrope is taken out from the top of the reactive distillation column, and is also introduced into a membrane reforming reactor, under the action of a catalyst and a separation membrane, high-purity hydrogen is generated by reforming;

[0023] Particularly, under the action of a Cu / ZnO / Al2O3 catalyst and a PdAg separation membrane, high-purity hydrogen is generated by reforming at 250-280℃;

[0024] Particularly, the membrane reforming reactor generates carbon dioxide by reforming, and the carbon dioxide is injected into the reactive distillation column after being captured and compressed to strengthen heat transfer.

[0025] In another aspect, the present application provides a system for preparing n-heptanoic acid by hydrolyzing methyl n-heptanoate, comprising a reactive distillation column with an ester feeding port and a water feeding port; a catalyst loading area is arranged in the reactive distillation column, and an Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst is loaded in the catalyst loading area for catalyzing the hydrolysis of methyl n-heptanoate at a reaction section temperature, and a temperature gradient is formed along the height direction of the reactive distillation column;

[0026] The bottom of the reactive distillation column is provided with an n-heptanoic acid outlet.

[0027] The catalyst loading area is located at the 5th to 15th theoretical plate, and a basket tray structure is adopted, and a corrosion-resistant metal wire mesh is wrapped around the Hβ molecular sieve-sulfonated carbon-based composite solid catalyst;

[0028] Particularly, the ester feeding port is located 1-3 plates above the catalyst loading area;

[0029] Particularly, the water feeding port is located 2-5 plates below the catalyst loading area; and the reactive distillation column is provided with a methanol-water azeotrope outlet at the top.

[0030] Compared with the prior art, the application is a method and system for preparing high-purity n-heptanoic acid by hydrolysis of methyl n-heptanoate based on reaction rectification technology. Through integrated design of hydrolysis reaction-rectification separation, under the action of Hbeta molecular sieve-sulfonated carbon-based composite solid acid catalyst, the hydrolysis reaction equilibrium breakthrough of methyl n-heptanoate and efficient separation of the product are realized. The method has the following advantages: relatively mild reaction conditions, easy to control; high selectivity, high yield and high purity of the target product (n-heptanoic acid with a purity of 99.5% or more can be obtained in the tower kettle); efficient and easy-to-separate catalyst; environmentally friendly, less "three wastes" discharge, in line with the principles of green chemistry; competitive overall production cost, easy to realize industrial production. Therefore, the application can improve the high cost, low reaction conversion rate, low selectivity, low yield and environmental unfriendliness in the preparation process of n-heptanoic acid.

[0031] In addition, the application further prepares high-purity n-heptanoic acid while improving economic benefits through superheated water feeding, basket-type catalyst tray, high-value utilization of byproduct methanol and other measures. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The DSC curve comparison chart of the specific composite catalyst in the embodiment of the application;

[0033] Figure 2 The TG and DTG curve comparison chart of the specific composite catalyst in the embodiment of the application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the application will be described below in a clear and complete manner. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0035] The application provides a method for preparing n-heptanoic acid by hydrolysis of methyl n-heptanoate, comprising the following steps:

[0036] In the reaction rectification tower filled with Hbeta molecular sieve-sulfonated carbon-based composite solid acid catalyst, methyl n-heptanoate and water are continuously fed in, and the hydrolysis reaction is carried out at the reaction section temperature, wherein an increasing temperature gradient is formed along the height direction of the reaction rectification tower, and a reaction mixture containing n-heptanoic acid and methanol is generated; the reaction mixture is subjected to rectification separation, and n-heptanoic acid product is collected from the tower kettle of the reaction rectification tower.

[0037] The present invention provides a system for the method described above, comprising a reactive distillation column having an ester inlet and a water inlet; the reactive distillation column is provided with a catalyst loading zone, which is filled with an Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst for catalyzing the hydrolysis of methyl heptanoate at the reaction section temperature, forming an increasing temperature gradient along the height of the reactive distillation column; the bottom of the reactive distillation column is provided with a heptanoic acid outlet.

[0038] This invention is mainly based on the hydrolysis reaction and distillation technology of methyl heptanoate, which can prepare high-purity heptanoic acid with high yield, low cost, and green sustainability.

[0039] The core of the embodiments of the present invention lies in:

[0040] (1) Reaction section: Methyl heptanoate hydrolyzes to produce heptanoic acid and methanol, as shown in the following reaction formula:

[0041] CH3(CH2)5COOCH3+H2O⇆CH3(CH2)5COOH+CH3OH;

[0042] (2) Separation section: The product is separated by utilizing the difference in boiling points (methanol 64.7℃, n-heptanoic acid 223℃).

[0043] In this embodiment of the invention, a reactive distillation column filled with a composite solid acid catalyst is used. The composite solid acid catalyst is an Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst, which has a three-level pore structure of micropore-mesopore-macropore, wherein the mesopore ratio is ≥40%, for example, 50~71%; the surface simultaneously contains -SO3H, -COOH, and -OH functional groups, and the total acid density is ≥1.5 mmol / g.

[0044] The preferred embodiment of the present invention prepares the Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst, and the preparation method specifically includes the following steps:

[0045] (1) By treating Hβ molecular sieves with silanizing reagents, amino-modified molecular sieves with an amino group density of 0.8-0.85 mmol / g can be obtained;

[0046] (2) Sulfonated carbon can be oxidized and aldehyde-treated to obtain aldehyde-treated sulfonated carbon with an aldehyde density of 0.65-0.70 mmol / g;

[0047] (3) In anhydrous ethanol, preferably the amination molecular sieve and aldehyde sulfonated carbon are mixed at a molar ratio of amination group: aldehyde group = 1:1.2, reacted at 60°C for 12 h, and reduced by sodium borohydride (NaBH4) to obtain a covalently bonded catalyst.

[0048] (4) Under microwave radiation, a hydrophobic layer is formed by treatment with perfluorooctyltriethoxysilane solution.

[0049] Conventional Hβ molecular sieves (H-Beta molecular sieves) are zeolite molecular sieves with a unique three-dimensional twelve-membered ring pore structure; sulfonated carbon is generally a solid sulfonic acid material prepared by sulfonating activated carbon. Its preparation method mainly uses concentrated sulfuric acid or chlorosulfonic acid as sulfonating agent and carries out sulfonation reaction under specific temperature conditions to generate porous carbon materials with sulfonic acid groups.

[0050] The above-mentioned silanization treatment involves forming a chemically bonded protective film on the surface of the molecular sieve material using an organosilane coupling agent, and mainly consists of the following steps:

[0051] ① Silane hydrolysis: Alkoxysilanes (general formula YR-Si(OR)3, where R represents alkyl and OR represents alkoxy) react with water in a solvent (such as ethanol) to generate active silanol groups (Si-OH), as shown in the following reaction formula. This reaction is affected by factors such as pH, temperature, and alcohol-to-water ratio. Acidic conditions (such as pH=4) can accelerate hydrolysis.

[0052] YR-Si(OR)3+ 3H2O → YR-Si(OH)3+ 3R2O.

[0053] ② Film-forming reaction: The silanol groups generated by hydrolysis dehydrate and condense with the hydroxyl groups on the surface of the molecular sieve material to form stable Si-OM (M is a metal) covalent bonds, thus constructing a dense protective film. Key conditions include: controlling the hydrolysis time (e.g., 5 hours for KH-550), silane concentration (volume ratio 1:6), and pH value (optimal pH=4).

[0054] Hydrophobic layer formation: Organic functional groups (Y) are arranged outward to impart hydrophobicity to the film (such as silanes containing long alkyl chains).

[0055] Elemental analysis (the most common and direct method): measures the weight percentage of nitrogen (N) in the product. Calculation: Amine density (mmol / g) = (N% / 14)*1000.

[0056] The above-described oxidation-aldehyde treatment process introduces aldehyde groups (-CHO) onto the material surface through an oxidation reaction, and consists of two steps:

[0057] ① Oxidation reaction: Using oxidizing agents (such as potassium permanganate KMnO4, chromium trioxide CrO3, or hydrogen peroxide H2O2), the hydroxyl (-OH) or olefin structures on the material surface are oxidized to aldehyde groups. Generally, the concentration of the oxidizing agent, temperature (room temperature to 80℃), and reaction time need to be controlled to avoid over-oxidation to carboxylic acids. Example reaction formula: R-CH2OH→R-CHO.

[0058] ② Aldehyde group activation: The carbonyl group of an aldehyde is highly reactive and can further participate in condensation, addition, and other reactions (such as forming an imine bond with amines). If it is necessary to retain the aldehyde group, a strong oxidizing environment should be avoided or acetalization protection should be used (such as reacting with alcohols to form an acetal).

[0059] The reduction reaction described above is mainly used to convert aldehyde groups to hydroxyl groups. In some embodiments, the aldehyde group is reduced to hydroxymethyl: NaBH4 or LiAlH4 is used as a reducing agent to reduce the aldehyde group (-CHO) to hydroxymethyl (-CH2OH). Conditions include: reaction at room temperature in an alcohol solvent for 1-2 hours. The reaction equation is, for example: R−CHO → R−CH2OH.

[0060] Finally, in this embodiment of the invention, the hydrophobic layer of the catalyst material is a silanized hydrophobic film. Based on the hydrolysis-condensation reaction of the silane coupling agent, a silane containing non-polar groups (perfluorooctyltriethoxysilane) is selected. The silicon wafer is hydroxylated with Piranha solution (H2SO4:H2O2=7:3), treated at 80°C for 1 hour, and then acid-washed (e.g., dilute HCl) or activated by plasma. The solution is selected as anhydrous ethanol or toluene (water content <0.1%) as solvent, with a concentration of 0.5~2 wt% (volume ratio 1:50~1:100). Acetic acid is used to adjust the pH to 5~6. The substrate is immersed or coated at room temperature to 40°C for 12~24 hours, rinsed three times with anhydrous ethanol to remove the physical adsorption layer, and then baked at 100~120°C for 5~10 hours to cure, forming a hydrophobic layer.

[0061] Constructing a PFOTS hydrophobic layer on the catalyst material gives its modified surface extremely low surface energy, exhibiting strong hydrophobicity and excellent oleophobicity. This effectively prevents the accumulation or blockage of high-surface-tension water or low-surface-tension organic reactants / products within the catalyst channels, maintaining the accessibility of active sites. Furthermore, it is not easily detached, dissolved, or degraded under the temperature, solvent environment, and mechanical stirring conditions of the catalytic reaction, resulting in a long lifespan without affecting the bulk properties of the catalyst. This reduces the oxidation, sintering, or irreversible adsorption of active components with impurities during use, thereby potentially improving reaction efficiency, selectivity, and catalyst stability in catalytic reactions.

[0062] The preparation of the composite solid acid catalyst is as follows:

[0063] (1) The Hβ molecular sieve was treated with a silanizing agent. First, the Hβ molecular sieve was calcined at 500~600℃ for 3h, and the concentration was optimized to be 10~40. One or more of anilinepropyltrimethoxysilane (PHAPTMS), aminosilane (such as KH550), and mercaptosilane (such as KH580) are used as silane reagents in wt%. Anhydrous ethanol or toluene is used as the solvent. The molecular sieve to silane reagent mass ratio is 1:2 to 1:20, and the solvent volume is 5 to 10 times the volume of the molecular sieve. The temperature is controlled at 80 to 120℃ (normal pressure reflux) or room temperature to 60℃ (mild conditions). The time is 6 to 24 hours (ultrasonic dispersion for 6 to 8 hours can improve uniformity). The pH is adjusted with acetic acid / water = 1:1 to maintain an acidic environment (pH = 4 to 6) to promote hydrolysis and condensation. The filtrate is then washed 3 to 5 times with anhydrous ethanol until the pH is neutral to remove physically adsorbed silane. The filtrate is then vacuum dried at 80 to 120℃ for 12 hours to obtain anamined molecular sieve with an amino group density of 0.8-0.85 mmol / g.

[0064] (2) Sulfonated carbon is subjected to oxidation-aldehyde treatment. First, the sulfonated carbon is pretreated by vacuum drying at 120℃ for 6 hours. Hydrogen peroxide (H2O2), potassium permanganate (KMnO4), and ozone (O3) with a concentration ≤30% are selected as oxidants and added to the solvent in 3-4 portions. The reaction temperature is 40-80℃ (controlled by water bath or oil bath), optimized to 60±5℃, and the reaction time is 1-4 hours (hydrogen peroxide system) or 2-6 hours (potassium permanganate system). 0.1-0.5 wt% Fe is added. 2+ / Cu 2+ Using ions (such as FeSO4) as catalysts, cetyltrimethylammonium bromide (CTAB, 0.5~2 g / L) is added as a phase transfer agent. After washing with deionized water / ethanol alternately, aldehyde-treated sulfonated carbon with an aldehyde group density of 0.65-0.70 mmol / g is obtained.

[0065] (3) In anhydrous ethanol, the amino-modified molecular sieve and the aldehyde-modified sulfonated carbon were mixed at a molar ratio of amino:aldehyde = 1:1.2 and reacted at 60°C for 12 h. The covalently bonded catalyst was obtained by reduction with NaBH4.

[0066] (4) Under microwave radiation, the silicon wafer is treated with perfluorooctyltriethoxysilane solution, hydroxylated with Piranha solution (H2SO4:H2O2=7:3), treated at 80℃ for 1 hour, and then acid-washed (e.g., dilute HCl) or activated by plasma. The solution is selected as anhydrous ethanol or toluene (water content <0.1%) as solvent, with a concentration of 0.5~2 wt% (volume ratio 1:50~1:100). The pH is adjusted to 5~6 with acetic acid. The wafer is soaked or coated at room temperature~40℃ for 12~24 hours, rinsed 3 times with anhydrous ethanol to remove the physical adsorption layer, and then baked at 100~120℃ for 5~10 hours to cure and form a hydrophobic layer.

[0067] The aforementioned reactive distillation column couples reaction and distillation separation within the same column-type device, enabling timely separation of reaction products and achieving mutual promotion and continuous operation of reaction and separation. In this embodiment of the invention, the reactive distillation column is equipped with a catalyst loading zone, filled with the aforementioned Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst.

[0068] The reactive distillation column has an ester inlet and a water inlet. In this embodiment of the invention, methyl heptanoate and water are continuously introduced. Simultaneously, the hydrolysis reaction is specifically controlled at a reaction section temperature of 90-120°C, forming an increasing temperature gradient along the column height. Preferably, plates 6-8 are at 90-100°C, plates 9-11 at 100-105°C, and plates 12-15 at 105-118°C, generating a reaction mixture of heptanoic acid and methanol.

[0069] In an embodiment of the present invention, the reactive distillation column has 15-25 theoretical plates, of which the reaction section occupies 6-10 theoretical plates. Specifically, within the column, the catalyst loading zone is located on theoretical plates 5-15; the ester inlet is located 1-3 plates above the catalyst loading zone; the water inlet is located 2-5 plates below the catalyst loading zone; a methanol-water azeotrope outlet is provided at the top of the column, and a heptanoic acid outlet is provided at the bottom of the column.

[0070] The theoretical number of trays required for the gas and liquid phases to reach phase equilibrium in a distillation column is used to characterize the separation efficiency. The aforementioned composite solid acid catalyst is packed onto the reaction section trays of the reactive distillation column, preferably at a loading rate of 5-20 wt% of the liquid holdup in the reaction section. The catalyst loading zone preferably employs a basket-type tray structure, with a corrosion-resistant metal mesh inside to enclose the aforementioned composite solid acid catalyst.

[0071] In an embodiment of the present invention, methyl heptanoate is fed from theoretical plates 3-8 of the column, and water is fed from theoretical plates 10-18. Further, the molar feed ratio of water to methyl heptanoate is 2.5:1 to 4.0:1. Preferably, the reflux ratio of the reactive distillation column is controlled at 0.5-2.0, the top temperature is 64-66°C, and the bottom temperature is 180-210°C.

[0072] After forming a reaction mixture of n-heptanoic acid and methanol, the embodiments of the present invention are carried out by distillation separation through a reactive distillation column system. The methanol-water azeotrope is collected from the top of the column, and high-purity n-heptanoic acid product is continuously collected from the bottom of the column.

[0073] In addition, the embodiments of the present invention also carry out by-product conversion: the methanol-water azeotrope at the top of the tower is preferably passed into a membrane reforming reactor, where it can be reformed at 250-280°C to generate high-purity hydrogen under the action of Cu / ZnO / Al2O3 catalyst and PdAg separation membrane.

[0074] To address the problems of low conversion rate, severe equipment corrosion, and high separation energy consumption in existing technologies, the main concepts of this invention are reaction-separation coupling, innovation in the catalytic system, high-value utilization of by-products, and synergistic energy optimization, specifically including:

[0075] This method utilizes a reactive distillation column packed with an Hβ molecular sieve-sulfonated carbon-based composite catalyst (composite solid acid catalyst) at a loading of 5-20 wt%. The column is configured with 15-25 theoretical plates, with plates 6-10 designated as the catalyst reaction section. The temperature of the reaction section is controlled at 90-120℃. A continuous feed of water to methyl heptanoate at a molar ratio of 2.5:1-4.0:1 is employed, with optimized feed positions (ester: theoretical plates 3-8, water: theoretical plates 10-18). A reaction-separation coupling mechanism enables simultaneous separation of the hydrolysis reaction and the products. A methanol-water azeotrope is collected from the top of the column and simultaneously introduced into a membrane reactor for in-situ synthesis of high-purity hydrogen. The bottom of the column yields heptanoic acid with a purity ≥99.5%.

[0076] Traditional batch hydrolysis is limited by reaction equilibrium, resulting in a low conversion rate of methyl heptanoate. It requires excess water (water-to-ester ratio > 6:1) to drive the reaction, leading to high energy consumption. In this embodiment of the invention, a hydrolysis reaction section is integrated into a reactive distillation column. The methanol-water azeotrope is continuously removed from the top of the column, breaking the reaction equilibrium limitation and improving the reaction conversion rate. Furthermore, a segmented feeding strategy (ester to plate 5 / water to plate 15) optimizes the reactant concentration gradient, reducing backmixing losses.

[0077] Traditional liquid strong acid catalysts (such as H2SO4) are prone to causing equipment corrosion, requiring frequent material replacement and resulting in high maintenance costs. In embodiments of this invention, a composite solid acid catalyst is used to replace the liquid strong acid, thereby achieving efficient and green production.

[0078] To address the high energy consumption of traditional separation methods, this invention preferably employs a thermal integrated network (for preheated hot water feed) and a falling film reboiler (to suppress coking in the reboiler) to optimize the energy system. The CO2 generated during reforming is captured, compressed, and then injected into the reboiler to enhance heat transfer.

[0079] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention. The substances used in the embodiments of this invention can be purchased commercially or prepared; wherein, the synthesis method of the Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst is as follows:

[0080] (1) The Hβ molecular sieve was treated with a silanizing agent. First, the Hβ molecular sieve was calcined at 500~600℃ for 3h. After calcination, it was transferred to a desiccator and cooled to room temperature. A 20 wt% anilinepropyltrimethoxysilane (PHAPTMS) was selected as the silane reagent. Anhydrous toluene was used as the solvent, and the solid-liquid ratio was 1:5 between the molecular sieve and the silane reagent, and the volume of the solvent was 8 times the volume of the molecular sieve. Under nitrogen protection, the silane reagent was slowly added dropwise to the pre-dehydrated solvent. The calcined Hβ molecular sieve was added to the above silanizing solution and ultrasonically dispersed for 30 minutes (power 300W, intermittent pulse). Mild conditions were used: reaction at 50℃ for 18 hours. The pH was adjusted with acetic acid / water = 1:1 to maintain an acidic environment (pH=5) to promote hydrolysis and condensation. After the reaction, the solid was separated by vacuum filtration, washed five times with anhydrous ethanol until the filtrate was neutral in pH and free of silane reagent residue. The filtrate was then vacuum dried at 100°C for 12 hours to obtain anamined molecular sieves with anamine density of 0.8–0.85 mmol / g. The target value of 0.8–0.85 mmol / g corresponds to an N content of approximately 1.12–1.19 wt%.

[0081] (2) Sulfonated carbon was subjected to oxidation-aldehyde treatment. First, the sulfonated carbon was pretreated by vacuum drying at 120℃ for 6 hours. Hydrogen peroxide (H2O2) with a concentration ≤30% was selected as the oxidant, and the reaction was carried out at 30-minute intervals. Ferrous sulfate heptahydrate (FeSO4·7H2O) with 0.2 wt% was used as the catalyst, and hexadecyltrimethylammonium bromide (CTAB) with 1.0 g / L was used as the phase transfer agent. The pretreated sulfonated carbon was dispersed in deionized water, and FeSO4 and CTAB were added. The water bath temperature was controlled at 60℃. Hydrogen peroxide was added dropwise in 4 equal amounts under stirring, and the total reaction time was 3 hours. After the reaction was complete, a small amount of Na₂SO₃ solution was immediately added to quench any residual hydrogen peroxide. The mixture was then washed alternately with deionized water and ethanol (first three times with water to remove inorganic salts, then twice with ethanol to dehydrate) until the filtrate was clear. Finally, it was vacuum dried overnight at 60°C to obtain aldehyde-treated sulfonated carbon with an aldehyde density of 0.65–0.70 mmol / g. The aldehyde density was determined by titration with hydroxylamine hydrochloride, and Fourier transform infrared spectroscopy (FT-IR) was performed at 1720–1740 cm⁻¹. -1 The C=O stretching vibration peak was observed to confirm the formation of aldehyde groups, and the changes in C=O bond content were analyzed by X-ray photoelectron spectroscopy (XPS).

[0082] (3) In anhydrous ethanol, the amino-modified molecular sieve and the aldehyde-modified sulfonated carbon were mixed at a molar ratio of amino group: aldehyde group = 1:1.2 and reacted at 60°C for 12 h. The covalently bonded catalyst was obtained by reduction with NaBH4.

[0083] (4) Under microwave irradiation, a fluorosilane solution with a concentration of 1.0 wt% and a volume ratio of approximately 1:80 was prepared using perfluorooctyltriethoxysilane (PFOTES) and anhydrous ethanol (water content <0.1%) as the solvent. The pH of the solution was adjusted to 5.5 with glacial acetic acid, and the mixture was magnetically stirred for 30 min for pre-hydrolysis. The catalyst particles were then immersed in the PFOTES solution and allowed to stand in a sealed container at 30°C for 18 h. After treatment, the particles were rinsed three times with anhydrous ethanol to remove physically adsorbed silane. The mixture was then heat-treated in an oven at 110°C for 8 h to form a hydrophobic layer.

[0084] The mass ratio of Hβ molecular sieve to sulfonated carbon is 3:1, and the catalyst is granular with a particle size of 2-3 mm.

[0085] Example 1

[0086] This embodiment provides a method for preparing high-purity n-heptanoic acid by hydrolyzing methyl n-heptanoate using reactive distillation technology, as detailed below:

[0087] (1) In a reactive distillation column packed with the Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst, methyl heptanoate and water are continuously fed in; the composite solid acid catalyst is packed at 5 wt% of the column volume, with a packing porosity of 40%. The reactive distillation column has a total of 15 theoretical plates, with 5, 6, and 9 theoretical plates distributed in the rectifying section, reaction section, and stripping section, respectively, wherein the reaction section is located between theoretical plates 6 and 10. Methyl heptanoate is fed from theoretical plate 5, and water is fed from theoretical plate 14; the molar feed ratio of water to methyl heptanoate is 2.5:1, the total feed rate is 120 kg / h, and the corresponding liquid hourly space velocity (LHSV) is 0.6 h⁻¹. -1 Before feeding, the aqueous phase is preheated to 80°C and the ester phase is preheated to 70°C, which is achieved through a plate heat exchanger.

[0088] (2) Catalytic reaction: The hydrolysis reaction is carried out at a reaction temperature of 90-120℃ (where an increasing temperature gradient is formed along the height of the tower: the 6th-8th plates are controlled at 95±2℃, heated by jacketed circulating heat transfer oil (flow rate 50 L / min); the 9th-11th plates are controlled at 102±2℃, heated by built-in coil steam (steam pressure 0.3 MPa); the 12th-15th plates are controlled at 112±3℃, using electric heating with zoned temperature control (power density 1.2 kW / m³). 2The reaction is carried out under atmospheric pressure, with an operating pressure of 0.1 MPa (absolute pressure) at the top of the column and 0.15 MPa at the bottom, producing a reaction mixture of n-heptanoic acid and methanol. The reflux ratio of the reactive distillation column is controlled at 0.8, and liquid phase separation is achieved by a total condenser at the top of the column. The temperature at the top of the column is maintained at 65±1℃, and the temperature at the bottom of the column is 190±5℃.

[0089] (3) Product Separation: The reaction and separation are coupled through a reactive distillation column. A methanol-water azeotrope (88-90 wt% methanol content) is continuously collected from the top of the column; after condensation, part of it is refluxed, and the remainder is used as reforming feedstock. High-purity n-heptanoic acid is continuously collected from the bottom of the column. The target product, n-heptanoic acid, has a purity ≥99.5%, an acid value ≥340 mg KOH / g, and a yield ≥92%. The energy consumption per unit product is 1.9 GJ / t, and the reboiler heat load is 340 kW.

[0090] (4) Byproduct conversion: This embodiment also provides a method for in-situ hydrogen production coupled with reactive distillation, the specific steps of which are as follows:

[0091] The methanol-water azeotrope collected from the top of the reactive distillation column was fed into a membrane reforming reactor. Steam reforming was carried out at 255±5℃ and 1.2 MPa under the action of a Cu / ZnO / Al2O3 catalyst (particle diameter 1-2 mm, loading 50 kg) and a PdAg separation membrane, with a gas hourly space velocity (GHSV) of 1200 h⁻¹. -1 High-purity hydrogen (purity ≥99.99%) is generated by reforming and analyzed online by a thermal conductivity detector. The CO2 generated by reforming is separated, captured and compressed, and then injected into the reboiler at a ratio of 5 wt% of the reboiler heat transfer medium flow rate to enhance heat transfer. The measured heat transfer coefficient of the reboiler is increased by 18%.

[0092] (5) Process Monitoring and Control: A DCS control system is configured to achieve fully automated operation of the entire process. Near-infrared spectroscopy (NIR, wavelength 1650 nm) combined with a PLS model is used to monitor methanol concentration online at the top of the column; an FTIR probe is installed at the bottom of the column to detect the carboxyl characteristic peak (1710 cm⁻¹) in real time. -1 To monitor the formation of n-heptanoic acid. A safety interlock mechanism is set up: the pressure relief valve automatically opens when the tower pressure difference > 0.05 MPa; the feed is cut off when the catalyst bed hot spot temperature > 130℃.

[0093] (6) Implementation Results: After 500 hours of continuous and stable operation, the catalyst showed no significant deactivation, the selectivity of n-heptanoic acid remained stable at over 95%, and XRD analysis showed no collapse of the catalyst crystal structure. By coupling hydrogen production and CO2 recycling, the cost of purchased hydrogen was reduced by 35%, steam consumption was reduced by 12%, and energy integration and green low-carbon operation were achieved.

[0094] Example 2

[0095] This embodiment provides a method for preparing high-purity n-heptanoic acid by hydrolyzing methyl n-heptanoate using reactive distillation technology, as detailed below:

[0096] (1) In a reactive distillation column packed with the Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst, methyl heptanoate and water are continuously fed in; the composite solid acid catalyst is packed at 20 wt% of the column volume, with a packing porosity of 40%. The reactive distillation column has a total of 24 theoretical plates, with 8, 11, and 16 theoretical plates distributed in the rectifying section, reaction section, and stripping section, respectively, wherein the reaction section is located between theoretical plates 6 and 16. Methyl heptanoate is fed from theoretical plate 6, and water is fed from theoretical plate 18; the molar feed ratio of water to methyl heptanoate is 4.0:1, the total feed rate is 150 kg / h, and the corresponding liquid hourly space velocity (LHSV) is 1.0 h⁻¹. -1 Before feeding, the aqueous phase is preheated to 80°C and the ester phase is preheated to 70°C, which is achieved through a plate heat exchanger.

[0097] (2) Catalytic reaction: The hydrolysis reaction is carried out at a reaction temperature of 90-120℃ (where an increasing temperature gradient is formed along the height of the tower: the 6th-8th plates are controlled at 100±2℃, using jacketed circulating heat transfer oil for heating (flow rate 50 L / min); the 9th-11th plates are controlled at 105±2℃, using built-in coil steam heating (steam pressure 0.3 MPa); the 12th-15th plates are controlled at 118±2℃, using electric heating with zoned temperature control (power density 1.2 kW / m³). 2 The reaction is carried out under atmospheric pressure, with an operating pressure of 0.1 MPa (absolute pressure) at the top of the column and 0.15 MPa at the bottom, producing a reaction mixture of n-heptanoic acid and methanol. The reflux ratio of the reactive distillation column is controlled at 2.0, and liquid phase separation is achieved by a total condenser at the top of the column. The temperature at the top of the column is maintained at 65±1℃, and the temperature at the bottom of the column is 205±5℃.

[0098] (3) Product separation: The reaction and separation are coupled through a reactive distillation column. A methanol-water azeotrope (88-90 wt% methanol content) is continuously collected from the top of the column; after condensation, part of it is refluxed, and the remainder is used as reforming feedstock. High-purity n-heptanoic acid is continuously collected from the bottom of the column. The target product, n-heptanoic acid, has a purity ≥99.5%, an acid value ≥340 mg KOH / g, and a yield ≥94%. The energy consumption per unit product is 2.1 GJ / t, and the reboiler heat load is 350 kW.

[0099] (4) Byproduct conversion: This embodiment also provides a method for in-situ hydrogen production coupled with reactive distillation, the steps of which are as follows:

[0100] The methanol-water azeotrope collected from the top of the reactive distillation column was fed into a membrane reforming reactor. Steam reforming was carried out at 275±5℃ and 1.2 MPa under the action of a Cu / ZnO / Al2O3 catalyst (particle diameter 1-2 mm, loading 70 kg) and a PdAg separation membrane, with a gas hourly space velocity (GHSV) of 1400 h⁻¹. -1 High-purity hydrogen (purity ≥99.99%) is generated by reforming and analyzed online by a thermal conductivity detector. The CO2 generated by reforming is separated, captured and compressed, and then injected into the reboiler at a ratio of 7 wt% of the reboiler heat transfer medium flow rate to enhance heat transfer. The measured heat transfer coefficient of the reboiler is increased by 20%.

[0101] The process monitoring and control in this embodiment are the same as in Embodiment 1.

[0102] Implementation Results: The catalyst operated continuously and stably for 600 hours, maintaining a stable structure. The conversion rate of methyl heptanoate was >99.5%, and the selectivity of heptanoic acid was ≥96%. By enhancing the reaction section configuration and improving separation precision and reforming intensity, both product purity and yield were simultaneously improved. This solution is suitable for industrial production with stringent quality requirements, pursuing high capacity and high added value. Its techno-economic advantages are reflected in product value enhancement and economies of scale.

[0103] Comparative Example 1

[0104] This comparative example verifies the necessity of the positive temperature gradient, and is basically the same as Example 1, except that the reactor temperature is kept constant at 90°C.

[0105] Comparative Example 2

[0106] This comparative example verifies the necessity of the positive temperature gradient, and is basically the same as Example 1, except that the reactor temperature is kept constant at 120°C.

[0107] Comparative Example 3

[0108] This comparative example verifies the necessity of the forward temperature gradient, and is basically the same as Example 1, except that the reactor temperature adopts a reverse gradient of 108→95℃.

[0109] Comparative Example 4

[0110] This comparative example verifies the performance of the bifunctional catalyst, and is basically the same as Example 2, except that the catalyst synthesis steps (1) and (3) are omitted.

[0111] Comparative Example 5

[0112] This comparative example verifies the performance of the bifunctional catalyst, and is basically the same as Example 2, except that the catalyst synthesis steps (2) and (3) are omitted.

[0113] Comparative Example 6

[0114] This comparative example illustrates the original preparation method of n-heptanoic acid - the heptanal oxidation method. High-purity heptanal (purity >99%) is used as raw material, and homogeneous cobalt acetate is used as catalyst (2 wt%). The oxidation is carried out at 100℃ / atmospheric pressure with oxygen, and finally separated by vacuum distillation.

[0115] Comparative Example 7

[0116] This comparative example illustrates the original preparation method of n-heptanoic acid - the 1-hexene carbonyl synthesis method. High-purity 1-hexene (purity >99%) is used as raw material, and Rh / TPPTS (rhodium loading 0.1 wt%) is used as catalyst. The hydroformylation reaction is carried out at 90℃ / 3.0MPa, the oxidation reaction is carried out at 80℃ / air, and finally the separation is achieved by a two-stage distillation process.

[0117] Comparative Example 8

[0118] This comparative example illustrates the original preparation method of n-heptanoic acid - the bio-fermentation method. Genetically engineered Escherichia coli EC-7 is used as the strain, and 100 g / L glucose is used as the carbon source. Fermentation is carried out at 32℃ / pH 6.8 for 72 hours, and finally separated by ethyl acetate extraction + distillation.

[0119] Performance testing

[0120] 1. Characterization of catalyst specific surface area and pore structure (BET): The Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst was tested for adsorption-desorption under N2 (77K), and the specific surface area (SBET = 585 m²) was calculated. 2 / g), pore volume (0.18 cm³) 3 / g), mesoporous pore volume: 0.62 cm³ 3 / g (accounting for 71%), the high mesoporous content significantly promotes the improvement of mass transfer efficiency.

[0121] 2. TG and DSC Detection: Conventional sulfonated carbon-based catalysts and the catalyst obtained in Comparative Example 5 were tested using a NETZSCH STA 449F3 thermogravimetric analyzer and a NETZSCH DSC 204F1 DSC. The test results are shown in Table 1. Figure 1 , Figure 2 .

[0122] Table 1: Comparison of Key Thermal Analysis Data

[0123]

[0124] The results show that the glass transition temperature of the composite catalyst used in Example 1 is 24°C higher than that of the conventional sulfonated carbon-based catalyst. This indicates that by introducing Hβ molecular sieves, the structure of the composite catalyst's catalytic layer is strengthened, its glass transition temperature is significantly increased by 24°C, and the main thermal decomposition stage shifts to the high-temperature region, resulting in increased residual mass and improved thermal stability of the catalytic layer. All data consistently demonstrate that the heat resistance of this composite catalyst is superior to that of the conventional sulfonated carbon-based catalyst.

[0125] 3. Abrasion resistance test

[0126] A certain amount of conventional Hβ molecular sieve catalyst, as well as the catalysts obtained in Example 1 and Comparative Example 4, were weighed and placed into grinding jars using a YXQM planetary ball mill and grinding ceramic balls, respectively, and ground at a certain rate for the same amount of time. After removal, the resin grinding jar contained a large number of fine pulverized particles, which, when mixed with water, formed a thick, uniform suspension that slowly settled upon standing. In contrast, the grinding jar containing the material of Example 1 (sulfonated carbon-based composite catalyst) contained virtually no visible detached particles, the jar walls were smooth, and the liquid remained clear or only slightly turbid after the addition of water, mainly consisting of extremely fine debris. The grinding jar containing the catalyst of Comparative Example 4 contained a small amount of larger blocky or flaky detached material, and the turbidity of the suspension was between the two aforementioned examples; visible sediment was found at the bottom after standing. The pulverized particles were filtered, dried, and weighed. The test results are shown in Table 2.

[0127] Table 2 Abrasion resistance test results

[0128]

[0129] The results showed that the mass loss rate of the catalyst in Comparative Example 4 after grinding was 20-30% higher than that of the sulfonated carbon-based composite catalyst material in Example 1, and the mass loss rate of the catalyst in Comparative Example 4 was also 17% higher than that of the material in Example 1. The reason for this is that the addition of sulfonated carbon-based material as a toughening and binding phase improves the wear resistance of the material.

[0130] 4. Verification of reaction effect

[0131] The reaction conditions of Example 1 and Comparative Examples 1-3 were applied to the production of n-heptanoic acid by reactive distillation, and the reaction results are shown in Table 3. Data testing method for reaction results: Sampling was started after the system had been running continuously and stably for at least 24 hours. Sampling points were set at the top condensate outlet, the bottom product outlet, and the middle of the reaction section (near theoretical plates 8-10). Samples were collected every 4 hours for 5 consecutive times, and the average value was taken as the final data.

[0132] The content of methyl heptanoate in the feed and bottom product was analyzed by gas chromatography (GC, equipped with an FID detector), and the conversion rate was calculated.

[0133] The content of unreacted methyl heptanoate in the overhead condensate was analyzed by GC and expressed as a percentage by mass.

[0134] The product from the bottom of the column was analyzed by GC-MS to identify and quantify organic byproducts other than n-heptanoic acid. The results are expressed as mass percentages.

[0135] The DCS system is used to record real-time temperature, pressure, and flow data to ensure smooth operation.

[0136] Product purity and acid value: The content of n-heptanoic acid was determined by high performance liquid chromatography (HPLC) and quantified by external standard method; according to GB / T 5530-2005, the content was determined by potassium hydroxide ethanol solution titration method.

[0137] Table 3 shows the effect of the reaction conditions of Examples 1 and Comparative Examples 1-3 on the production of n-heptanoic acid by reactive distillation.

[0138]

[0139] As shown in Table 3, Example 1 exhibited the highest conversion rate and the lowest content of byproducts and top esters. The reason for this is likely that the gradient design spatially decouples the reaction and separation requirements, allowing the reaction to proceed at the optimal kinetic temperature. Simultaneously, it achieves a low-temperature reaction at the upper end to suppress feedstock volatilization and a high-temperature reaction at the lower end to enhance product separation, thus overcoming the inherent contradiction of mutual constraint between reaction and separation in isothermal operation. Maintaining a constant temperature of 120°C throughout the entire process leads to an accelerated reverse reaction rate and also easily promotes methanol dehydration to dimethyl ether, reducing reaction selectivity. Maintaining a constant temperature of 90°C throughout the entire process results in a decreased reaction rate, and insufficient gas phase load easily leads to tray leakage. The reverse gradient from 95°C to 108°C causes premature vaporization of the ester, which is collected at the top of the column before reacting, while the sudden change in gas phase load causes mist entrainment.

[0140] The catalysts of Example 1 and Comparative Examples 4 and 5 were applied to reactive distillation to produce n-heptanoic acid, and the reaction results are shown in Table 4.

[0141] Table 4 shows the reaction effects of the catalysts in Examples 1 and Comparative Examples 4 and 5 on the production of n-heptanoic acid by reactive distillation.

[0142]

[0143] As shown in the table above, Example 1 exhibited the best catalytic effect, indicating a significant synergistic effect of the bifunctional compounds. In Comparative Example 4, the diffusion limitation within the micropores led to easy blockage of acid sites by the products, and the high water-to-ester ratio operation easily caused the framework to collapse, resulting in poor reaction performance. In Comparative Example 5, the carbon framework was easily oxidized at high temperatures, significantly reducing the catalytic effect.

[0144] The reaction results of Example 1 and the conventional n-heptanoic acid production method (Comparative Examples 6-8) are shown in Table 5.

[0145] Table 5. Reaction effects of Example 1 and conventional methods for producing n-heptanoic acid (Comparative Examples 6-8)

[0146]

[0147] As shown in the table above, this method significantly improves both yield and product purity compared to the three previous methods for producing n-heptanoic acid.

[0148] In summary, the representative embodiments of the present invention have the following advantages compared with traditional preparation methods: Compared with traditional methods, the embodiments of the present invention utilize reactive distillation to break the equilibrium limitation, and the removal of methanol-water azeotrope at the top of the column greatly promotes the forward reaction and improves the reaction conversion rate.

[0149] Compared to traditional methods, this invention uses solid acid instead of liquid sulfuric acid, reducing equipment maintenance costs. Simultaneously, the removal of methanol-water azeotrope directly converts it into high-value hydrogen, creating greater economic benefits.

[0150] Compared to traditional single catalysts, the embodiments of the present invention employ bifunctional catalysts, which achieve longer service life and better catalytic performance through the synergistic effect of pore regulation and geometric constraints.

[0151] Compared to traditional separation technologies, the waste heat recovery from the top of the column is used directly for distillation. At the same time, compared with the traditional method of incinerating methanol by-products, carbon emissions are only 1 / 4 of those of traditional processes, which meets the policy orientation of "dual carbon".

[0152] Compared to traditional production methods, products produced using this method can be applied to high-value-added fields, such as fragrance-grade n-heptanoic acid (purity >99%), pharmaceutical intermediates, etc. Traditional methods require secondary purification due to metal residues.

[0153] The method of the representative embodiment of the present invention has the following advantages when used for the production of n-heptanoic acid: high raw material utilization rate, high single-pass conversion rate, few by-products, simple separation, and high purity of n-heptanoic acid.

[0154] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0155] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A method for preparing n-heptanoic acid by hydrolysis of methyl n-heptanoate, characterized in that, Includes the following steps: In a reactive distillation column packed with Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst, methyl heptanoate and water are continuously introduced and hydrolyzed at the reaction section temperature, wherein an increasing temperature gradient is formed along the height of the reactive distillation column, and a reaction mixture containing heptanoic acid and methanol is generated. The reaction mixture is then subjected to distillation, and the bottom of the reactive distillation column yields heptanoic acid.

2. The method according to claim 1, characterized in that, The Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst has a three-level pore structure of micropore-mesopore-macropore, wherein the mesopore volume accounts for ≥40%; the surface of the Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst simultaneously contains sulfonic acid groups, carboxyl groups and hydroxyl groups, and the total acid density is ≥1.5mmol / g.

3. The method according to claim 1, characterized in that, The Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst was obtained according to the following steps: Hβ molecular sieves were treated with silanizing reagents to obtain amination-modified molecular sieves; Sulfonated carbon is subjected to oxidation-aldehyde oxidization treatment to obtain aldehyde-oxidized sulfonated carbon; The amino-modified molecular sieve and aldehyde-modified sulfonated carbon were mixed and reacted, and then reduced to obtain a covalently bonded catalyst. The covalently bonded catalyst is treated with a perfluorooctyltriethoxysilane solution under microwave irradiation to form a hydrophobic layer, thus obtaining the catalyst.

4. The method according to claim 1, characterized in that, The Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst is packed on the reaction section tray of the reactive distillation column, with a packing amount of 5-20 wt% of the liquid holdup in the reaction section.

5. The method according to any one of claims 1-4, characterized in that, The molar feed ratio of water to methyl heptanoate is 2.5:1 to 4.0:

1.

6. The method according to any one of claims 1-4, characterized in that, The theoretical number of plates in the reactive distillation column is 15-25; the temperature of the reaction section is 90-120℃; the increasing temperature gradient includes: 90-100℃ for plates 6-8, 100-105℃ for plates 9-11, and 105-118℃ for plates 12-15.

7. The method according to claim 6, characterized in that, The reaction section of the reactive distillation column occupies 6-10 theoretical plates; the methyl heptanoate is fed from theoretical plates 3-8 of the column, and the water is fed from theoretical plates 10-18; the reflux ratio of the reaction section of the reactive distillation column is controlled at 0.5-2.0, the top temperature is 64-66℃, and the bottom temperature is 180-210℃.

8. The method according to any one of claims 1-4, characterized in that, The methanol-water azeotrope is collected from the top of the reactive distillation column and then fed into a membrane reforming reactor, where it is reformed to produce high-purity hydrogen under the action of a catalyst and a separation membrane. The membrane reformer produces carbon dioxide, which is then captured, compressed, and injected into a reactive distillation column to enhance heat transfer.

9. A system using the method according to any one of claims 1-8, characterized in that, The reactive distillation column includes an ester feed inlet and a water inlet; the reactive distillation column is provided with a catalyst loading zone, which is filled with an Hβ molecular sieve-sulfonated carbon-based composite solid acid catalyst to catalyze the hydrolysis of methyl heptanoate at the temperature of the reaction section, forming an increasing temperature gradient along the height of the reactive distillation column. The bottom of the reactive distillation column is equipped with an outlet for n-heptanoic acid.

10. The system according to claim 9, characterized in that, The catalyst loading zone is located on theoretical plates 5-15, and adopts a basket-type tower plate structure, with Hβ molecular sieve-sulfonated carbon-based composite solid catalyst wrapped in corrosion-resistant metal wire mesh. The ester inlet is located 1-3 trays above the catalyst loading zone; the water inlet is located 2-5 trays below the catalyst loading zone; and the top of the reactive distillation column is equipped with a methanol-water azeotrope outlet.

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