Solid acid catalysts for use in a micro-packed bed reactor and methods of making the same

Abstract

This invention discloses a solid acid catalyst for a micro-packed bed reactor and its preparation method, relating to the field of catalysts. The preparation method of the solid acid catalyst includes the following steps: (1) providing a porous support, modifying the porous support with an acidic solution to load hydroxyl groups on the surface of the porous support, obtaining a modified support; (2) mixing the modified support with a solution containing silane, reacting at 50–200°C for 0.5–36 h, obtaining a first basic catalyst; wherein the silane is a silane with a carbon chain length greater than or equal to 3; (3) mixing the first basic catalyst with an oxidizing solution, reacting at 30–100°C for 0.5–36 h, obtaining a second basic catalyst; (4) mixing the second basic catalyst with a solution containing sulfonic acid groups, reacting at 30–100°C for 0.5–36 h, obtaining a finished reinforced solid acid catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalysts, and more particularly to a solid acid catalyst for a micro-packed bed reactor and a method for preparing the same. Background Technology

[0002] As a cornerstone compound for biomass value-added, 5-hydroxymethylfurfural (HMF) can be further processed through oxidation, hydrogenation, and hydration to produce 2,5-furandicarboxylic acid, 2,5-dimethylfuran, cyclohexanol, levulinic acid, sorbitol, and other substances, which is of great significance for the development of biomass resources. HMF is mainly derived from hexoses such as glucose and fructose. Among them, fructose is considered the most ideal substrate for HMF preparation due to its mild reaction conditions and short reaction pathway. Therefore, the efficient preparation of HMF from fructose, as well as the catalysts and process conditions involved, has become a focus of attention in the scientific and industrial communities. Currently, the preparation of HMF from fructose is usually carried out in batch reactors such as stirred tanks and three-necked flasks. Batch reactors are limited by mass and heat transfer and usually suffer from problems such as long reaction times, many by-products, low yield of target products, cumbersome batch operation, and complex scale-up. Furthermore, under high temperature and high pressure (100–200℃, 0–5 MPa) reaction conditions, batch reactors also pose potential safety risks. Micro-packed beds are widely used in catalytic conversion processes due to their advantages such as high mass and heat transfer efficiency, easy catalyst immobilization, plug flow characteristics, ease of automation and scale-up, and intrinsic safety. They also hold great potential in the preparation of 5-HMF.

[0003] On the other hand, the reaction for preparing HMF from fructose requires the presence of... Catalysts targeting acid sites are used to promote the dehydration of fructose to produce HMF. Early methods commonly used homogeneous catalysts, including inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid, but these suffer from problems such as reactor corrosion, catalyst separation and recycling difficulties, and environmental pollution. Currently, catalysts commonly used in batch reactors, such as zeolites, metal oxides, and functional organic frameworks, suffer from active site loss and poor stability. Furthermore, most are in powder form, and direct application to micro-packed bed reactors may lead to excessive pressure drop, resulting in reactor blockage and high energy consumption of the injection pump. Commercial ion exchange resin catalysts exhibit problems such as catalyst deformation and rapid performance degradation at high temperatures (above 120°C), as well as difficulties in catalyst recycling. Since the specific surface area decreases significantly with increasing catalyst particle size, directly applying powdered solid acid catalyst preparation processes to supports with particle sizes greater than 1 mm significantly reduces the active site loading density, leading to poor catalytic performance and insufficient stability in the prepared catalyst.

[0004] Furthermore, the reaction process for preparing HMF from fructose mainly involves: (1) fructose adsorption on the catalyst surface, and (2) the fructose adsorbed on the catalyst surface. Dehydration occurs at acid sites to form HMF, and (3) HMF desorbs from the catalyst. Currently, there are catalysts for the preparation of HMF from fructose, even those containing... While possessing acidic sites, fructose adsorption capacity is weak, resulting in low efficiency and poor catalytic performance in fructose dehydration. Even when traditional catalysts are granulated using methods like tableting and placed in micro-packed bed reactors, low HMF yields persist. Furthermore, fructose loses three water molecules during HMF formation, and in the presence of water, HMF further binds with water on the catalyst surface to form the byproduct levulinic acid. Therefore, even in pure organic solvents, it is difficult to avoid byproduct formation during fructose dehydration to HMF. Especially in micro-packed reactors, mass transfer is significantly enhanced, meaning fructose readily dehydrates to form HMF, and HMF readily binds with water to form byproducts. Therefore, controlling the hydrophobic properties of the catalyst to prevent HMF on the catalyst surface from contacting water and continuing the reaction is an effective way to improve HMF yield. Thus, there is a need to develop a high-performance, stable, relatively hydrophobic solid acid catalyst that, when combined with a micro-packed bed reactor, can rapidly convert high-concentration fructose to HMF in a short time, bringing it closer to industrial production requirements. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a solid acid catalyst for a micro-packed bed reactor and its preparation method, which can improve catalytic efficiency and has strong stability.

[0006] The technical problem that this invention also aims to solve is to provide a method for preparing 5-hydroxymethylfurfural with high yield and high synthesis efficiency.

[0007] To address the aforementioned technical problems, this invention provides a method for preparing a solid acid catalyst for a micro-packed bed reactor, comprising the following steps:

[0008] (1) Provide a porous support, modify the porous support with an acidic solution to load hydroxyl groups on the surface of the porous support, and obtain a modified support;

[0009] The porous support can be activated carbon or molecular sieve, but is not limited to these. The acidic solution can be hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, or acetic acid, but is not limited to these. Modification with an acidic solution can not only increase the specific surface area of ​​the porous support, but also enhance its surface hydroxyl content, which can significantly strengthen the subsequent grafting of functional groups.

[0010] (2) The modified support is mixed with a solution containing silane and reacted at 50-200°C for 0.5-36 h to obtain the first basic catalyst; wherein the silane is a silane with a carbon chain length of 3 or more.

[0011] The silane can be mercaptosilane, methoxysilane, or ethoxysilane, but is not limited to these. The silane contains a carbon chain with at least three carbon molecules to impart a longer-chain modifying group to the first base catalyst. Specifically, mercaptosilane, for example, has the general formula HS-(CH2). n If the expression is -Si-X3, then n is greater than or equal to 3. In the above general formula, X is methoxy, ethoxy, methyl, or ethyl, but is not limited to these. By using a solution containing silane for modification, -Si bonds, mercapto groups, or methoxy, ethoxy, etc., can be loaded onto the surface of the modified support, laying a good foundation for improving the reaction activity. Furthermore, the grafting of long-chain active functional groups also improves the hydrophobicity of the catalyst.

[0012] (3) The first basic catalyst is mixed with an oxidizing solution and reacted at 30-100°C for 0.5-36 h to obtain the second basic catalyst;

[0013] The oxidizing solutions include, but are not limited to, hydrogen peroxide solution, sulfuric acid solution, or potassium permanganate solution. Treatment with oxidizing solutions can either further enhance the hydroxylation of the modified support surface or oxidize the previously loaded thiol groups to form sulfonic acid groups, thus creating acidic sites.

[0014] (4) The second basic catalyst is mixed with a solution containing sulfonic acid groups and reacted at 30-100°C for 0.5-36 hours to obtain the enhanced solid acid catalyst product.

[0015] The solution containing sulfonic acid groups is selected from chlorosulfonic acid or concentrated sulfuric acid, but is not limited to these. By treating the surface of the modified support with a solution containing sulfonic acid groups, sulfonic acid groups can be directly loaded onto the surface of the modified support, thereby forming modified groups with shorter chain lengths.

[0016] As an improvement to the above technical solution, in step (1), 1-10g of porous support is mixed with 10-200mL of acidic solution, stirred and refluxed at 30-150℃ for 0.5-36h, washed and dried to obtain modified support;

[0017] The acidic solution is selected from one or more of hydrochloric acid solution, nitric acid solution, sulfuric acid solution, and phosphoric acid solution, and the volume concentration of the acidic solution is 10 to 100% v / v.

[0018] As an improvement to the above technical solution, step (2) includes:

[0019] (2.1) Add the modified carrier obtained in step (1) to 50-200 mL of toluene, and then add 5-70 mL of silane;

[0020] (2.2) Stir and reflux at 80-200℃ for 10-36 h, then wash and dry to obtain the first basic catalyst;

[0021] The silane is selected from γ-mercaptopropyltrimethoxysilane and / or trimethoxy[3-(methylamino)propyl]silane.

[0022] As an improvement to the above technical solution, in step (3), the first basic catalyst obtained in step (2) is mixed with 100-300 mL of oxidizing solution, stirred and reacted at 30-60 °C for 10-36 h, washed and dried to obtain the second basic catalyst.

[0023] The oxidizing solution is selected from one or more of hydrogen peroxide solution, sulfuric acid solution, or potassium permanganate solution; the volume concentration of the oxidizing solution is 10-100% v / v.

[0024] As an improvement to the above technical solution, step (4) includes:

[0025] (4.1) Mix the second basic catalyst obtained in step (3) with 50-200 mL of organic solvent, and then add 5-70 mL of a solution containing sulfonic acid groups;

[0026] (4.2) React at 30-60℃ for 10-36 h, wash and dry to obtain the enhanced solid acid catalyst product;

[0027] The organic solvent is selected from one or more of dichloromethane, trichloromethane, dichloroethane, dichloropropane, and dibromomethane.

[0028] The solution containing sulfonic acid groups is selected from chlorosulfonic acid or concentrated sulfuric acid.

[0029] As an improvement to the above technical solution, the porous carrier is selected from one or more of alumina, zirconium oxide, silicon oxide, and activated carbon;

[0030] The porous carrier has a particle size of 20 nm to 1 mm.

[0031] As an improvement to the above technical solution, step (1) includes:

[0032] (1.1) Provide a porous support, heat it to 400-600℃ at a heating rate of 2-10℃ / min, and calcine it at that temperature for 2-5 hours;

[0033] (1.2) The calcined porous support is modified with an acidic solution to obtain a modified support.

[0034] Accordingly, the present invention also discloses a solid acid catalyst, which is prepared by the above-described method for preparing a solid acid catalyst for a micro-packed bed reactor.

[0035] Accordingly, the present invention also discloses a method for preparing 5-hydroxymethylfurfural, which includes: adding the above-mentioned solid acid catalyst into a micro-packed bed reactor, passing in a fructose aqueous solution with a concentration of 1-40 wt%, and reacting at 70-200°C and 0-3 MPa for 20-500 s.

[0036] As an improvement to the above technical solution, the micro-filled bed reactor has a long cylindrical structure with an aspect ratio greater than 30. Specifically, in some embodiments of the present invention, the filled bed reactor has a long cylindrical structure with a diameter of 2.38–6.4 mm, a length of 100–300 mm, and an aspect ratio of 30.5–35, but is not limited thereto.

[0037] Implementing this invention has the following beneficial effects:

[0038] 1. In one embodiment of the present invention, a method for preparing a solid acid catalyst for a micro-packed bed involves first loading hydroxyl groups onto the surface of a porous support using an acidic solution, then grafting silane groups onto the support using a silane solution, further enhancing surface hydroxylation with an oxidizing solution, and finally bonding sulfonic acid functional groups. Based on this technical solution, firstly, loading powdered solid acid onto the surface of a porous support solves problems such as reactor clogging and high injector energy consumption. Secondly, the porous support has a porous structure and adsorption capacity, which promotes the rapid binding of fructose at acid sites, synergistically enhancing the catalyst's performance. Thirdly, through a specific preparation process, two different types of catalysts with different volumes and chain lengths are bonded to the surface of the solid acid catalyst. The presence of acid sites not only enhances the acid density of the solid acid catalyst, but also allows both acid sites to simultaneously bind to a fructose molecule, synergistically promoting the rapid dehydration of fructose to prepare HMF. This means that while increasing the catalyst particle size, high catalytic efficiency is maintained. Fourthly, the active sites of this solid acid catalyst are chemically bonded to the porous support, resulting in high stability and long-term stable reaction, thus extending the catalyst's lifespan. Fifthly, the surface of the base catalyst in this embodiment is grafted with silanes with long carbon chains, effectively improving hydrophobic properties, reducing the contact between water molecules generated during the reaction and the catalyst, effectively preventing further reaction of HMF on the catalyst surface to form byproducts, and improving the yield of the target product HMF.

[0039] 2. In the preparation method of the solid acid catalyst for micro-packed bed in one embodiment of the present invention, the porous support is pre-calcined, which effectively adjusts the pore structure of the porous support and increases the specific surface area. This not only enhances the adsorption of fructose on the catalyst surface, but also allows the HMF produced by the reaction to be desorbed in a timely manner through suitable pores, effectively reducing the generation of by-products and improving the reaction efficiency.

[0040] 3. In one embodiment of the present invention, the method for preparing 5-hydroxymethylfurfural (HMF) uses the aforementioned solid acid catalyst to catalyze the reaction of fructose. Firstly, this solid acid catalyst allows capillary forces to dominate within the reactor, significantly improving mass transfer capacity. Secondly, through the synergistic effect of the micro-packed bed and the solid acid catalyst, the reaction time is greatly shortened. Specifically, in this embodiment, the reaction time can be reduced from several hours to less than 1 minute, while still ensuring high conversion rates (≥92%, up to 99%) and high yields (≥86%, up to 97.5%). Thirdly, through the synergistic effect of the micro-packed bed and the solid acid catalyst, high-concentration fructose can be continuously converted to prepare HMF; in this embodiment, the fructose concentration can reach over 100 g / L. Attached Figure Description

[0041] Figure 1 It is the dual structure in Example 1 Electron micrographs and EDSMapping scans of activated carbon solid acid catalysts with acid sites;

[0042] Figure 2 It is the dual structure in Example 1 FT-IR spectra of activated carbon solid acid catalysts with acid sites. In the figures, the enhanced solid acid is the bi-structured catalyst prepared in this embodiment. The acid site activated carbon solid acid catalyst has an activated carbon support that has not been calcined or hydroxylated, a modified support that has been calcined or hydroxylated, and a base solid acid catalyst that has not been supported.

[0043] Figure 3 It is the dual structure in Example 1 XPS spectra of activated carbon solid acid catalysts at acid sites;

[0044] Figure 4 It is the dual structure in Example 1 NMR spectrum of activated carbon solid acid catalyst with acid sites;

[0045] Figure 5 It is the dual structure in Example 1 In the contact angle diagram of the acid site activated carbon solid acid catalyst, the support is an activated carbon support that has not undergone calcination and hydroxylation treatment, the modified support is an activated carbon support that has undergone calcination and hydroxylation treatment, the base solid acid is a base solid acid catalyst without support, and the enhanced solid acid is the dual-structure catalyst prepared in this embodiment. Acid site activated carbon solid acid catalyst. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0047] Example 1

[0048] (1) 5g of activated carbon carrier with a particle size of 0.8mm was heated to 500℃ in nitrogen at a rate of 2℃ / min for 2h and then added to 100mL of nitric acid aqueous solution with a concentration of 80% v / v. The mixture was stirred, refluxed and cooled at 80℃ for 24h, washed and dried to obtain surface-modified activated carbon carrier.

[0049] (2) The surface-modified activated carbon support obtained in step (1) was added to 100 mL of toluene solution, dispersed evenly, and then 50 mL of γ-mercaptopropyltrimethoxysilane was added. The mixture was stirred and refluxed at 120 °C for 24 h. After washing and drying, the basic activated carbon catalyst was obtained.

[0050] (3) Add the basic activated carbon catalyst obtained in step (2) to 200 mL of H2O2 aqueous solution with a volume concentration of 50% v / v, stir and reflux at 30 °C for 24 h to obtain a single structure. Acid site activated carbon solid acid catalyst;

[0051] (4) The single structure obtained in step (3) A solid acid catalyst with activated carbon at the acid site was added to 100 mL of dichloromethane and dispersed evenly. Then, 20 mL of chlorosulfonic acid was added, and the mixture was stirred and refluxed at 30 °C for 24 h. After washing and drying, a bi-structured catalyst was obtained. Acid site activated carbon solid acid catalyst.

[0052] The dual structure obtained in this embodiment The activated carbon solid acid catalyst with acid sites was characterized, and the results are as follows: Figures 1-5 As shown. Among them, Figure 1 It is a dual structure Electron microscopy (EM) images and EDS mapping scans of the activated carbon solid acid catalyst at acid sites show that elements such as Si, S, and Cl are uniformly dispersed on the catalyst surface, proving that the active sites have been successfully grafted. Figure 2 It is a dual structure FT-IR spectra of activated carbon solid acid catalysts with acid sites. In the figures, the enhanced solid acid is the bi-structured catalyst prepared in this embodiment. The acid site activated carbon solid acid catalyst was prepared using an untreated activated carbon support and a modified activated carbon support that had undergone calcination and hydroxylation. The base solid acid was an unsupported base solid acid catalyst. As shown in the figure, the peak intensity of the hydroxyl groups on the catalyst surface significantly increased after surface modification and hydroxylation, proving the feasibility of the catalyst treatment method. Figure 3 It is a dual structure XPS spectra of the acid site activated carbon solid acid catalyst also proved that elements such as Si, S, C, and O were loaded on the support surface, indicating that the catalyst was successfully prepared. Figure 4 It is a dual structure The NMR spectrum of the activated carbon solid acid catalyst shows characteristic peaks for silanesulfonic acid and chlorosulfonic acid groups, respectively, indicating that the catalyst contains two structural groups. Acid sites. Figure 5 It is a dual structure The contact angle diagram of the acid site activated carbon solid acid catalyst is shown. In the diagram, the support is an activated carbon support that has not undergone calcination and hydroxylation treatment, the modified support is an activated carbon support that has undergone calcination and hydroxylation treatment, and the base solid acid is a base solid acid catalyst without loading. As can be seen from the diagram, the contact angle of the catalyst increases with the grafting of active functional groups, proving that its hydrophobicity is effectively improved.

[0053] The dual structure prepared in this embodiment Acid-containing activated carbon solid acid catalyst was packed into a micro-packed bed reactor (6.4 mm in diameter and 200 mm in length), and simultaneously 40 wt% fructose aqueous solution and 100% v / v dimethyl sulfoxide aqueous solution were introduced. The reaction was carried out at a flow rate of 0.1 mL / min at 150 °C and 0.5 MPa for 60 s, resulting in a fructose conversion rate of 99% and a HMF yield of 97.5%.

[0054] Example 2

[0055] (1) Add 5g of activated carbon carrier with a particle size of 0.8mm to 100mL of nitric acid aqueous solution with a concentration of 80v / v%, stir and reflux at 80℃ for 24h, wash and dry to obtain surface modified activated carbon carrier.

[0056] (2) The surface-modified activated carbon support obtained in step (1) was added to 100 mL of toluene solution, dispersed evenly, and then 50 mL of γ-mercaptopropyltrimethoxysilane was added. The mixture was stirred and refluxed at 120 °C for 24 h. After washing and drying, the basic activated carbon catalyst was obtained.

[0057] (3) Add the basic activated carbon catalyst obtained in step (2) to 200 mL of H2O2 aqueous solution with a volume concentration of 50% v / v, stir and reflux at 30 °C for 24 h to obtain a single structure. Acid site activated carbon solid acid catalyst;

[0058] (4) The single structure obtained in step (3) A solid acid catalyst with activated carbon at the acid site was added to 100 mL of dichloromethane and dispersed evenly. Then, 20 mL of chlorosulfonic acid was added, and the mixture was stirred and refluxed at 30 °C for 24 h. After washing and drying, a bi-structured catalyst was obtained. Acid site activated carbon solid acid catalyst.

[0059] The dual structure prepared in this embodiment Acid-containing activated carbon solid acid catalyst was packed into a micro-packed bed reactor (6.4 mm in diameter and 200 mm in length), and simultaneously 40 wt% fructose aqueous solution and 100% v / v dimethyl sulfoxide aqueous solution were introduced. The reaction was carried out at a flow rate of 0.1 mL / min at 150 °C and 0.5 MPa for 60 s, resulting in a fructose conversion rate of 96.8% and an HMF yield of 90.3%.

[0060] Example 3

[0061] (1) 5g of alumina support with a particle size of 20nm was heated to 500℃ in hydrogen at a rate of 2℃ / min and calcined for 2h. Then, 100mL of nitric acid solution with a volume concentration of 90% v / v was added and stirred, refluxed and cooled at 80℃ for 24h. After washing and drying, the surface-modified alumina support was obtained.

[0062] (2) The surface-modified alumina support obtained in step (1) was added to 100 mL of toluene solution, dispersed evenly, and then 30 mL of trimethoxy[3-(methylamino)propyl]silane was added. The mixture was stirred and refluxed at 100 °C for 12 h, washed and dried to obtain the basic alumina catalyst.

[0063] (3) The basic alumina catalyst obtained in step (2) was added to 150 mL of sulfuric acid aqueous solution with a volume concentration of 10% v / v, and stirred and refluxed at 30 °C for 12 h to obtain a single-structure catalyst. Alumina solid acid catalyst with acid sites;

[0064] (4) The single structure obtained in step (3) Alumina solid acid catalyst with acid sites was added to 70 mL of chloroform and dispersed evenly. Then, 10 mL of chlorosulfonic acid was added, and the mixture was stirred and refluxed at 30 °C for 18 h. After washing and drying, a bi-structure was obtained. Alumina solid acid catalyst with acid sites;

[0065] The above-mentioned dual structure Alumina solid acid catalyst with acid sites was packed into a micro-packed bed reactor (6.4 mm in diameter and 200 mm in length), and simultaneously 40 wt% fructose aqueous solution and 100% v / v dimethyl sulfoxide aqueous solution were introduced. The reaction was carried out at 150 °C and 4 MPa for 60 s at a flow rate of 0.1 mL / min, resulting in a fructose conversion rate of 92.6% and an HMF yield of 86.5%.

[0066] Example 4

[0067] (1) 5g of silicon dioxide with a particle size of 0.5mm was heated to 500℃ in helium at a rate of 5℃ / min for 2h and then added to 150mL of nitric acid aqueous solution with a volume concentration of 70%. The mixture was stirred, refluxed and cooled at 120℃ for 12h, washed and dried to obtain surface-modified silicon dioxide support.

[0068] (2) The surface-modified silica support obtained in step (1) was added to 120 mL of toluene solution, dispersed evenly, and then 70 mL of γ-mercaptopropyltrimethoxysilane was added. The mixture was stirred and refluxed at 140 °C for 24 h. After washing and drying, the basic silica catalyst was obtained.

[0069] (3) The silica catalyst obtained in step (2) was added to 200 mL of sulfuric acid aqueous solution with a volume concentration of 80% v / v, and stirred and refluxed at 50 °C for 12 h to obtain a single-structure catalyst. Acid sites: silica solid acid catalyst;

[0070] (4) The single structure obtained in step (3) A silica solid acid catalyst with acidic sites was added to 120 mL of dibromomethane and dispersed evenly. Then, 40 mL of chlorosulfonic acid was added, and the mixture was stirred and refluxed at 50 °C for 12 h. After drying, a bi-structure was obtained. Acid sites: silica solid acid catalyst;

[0071] The above-mentioned dual structure A silica solid acid catalyst with acid sites was packed into a micro-packed bed reactor (6.4 mm in diameter and 200 mm in length), and simultaneously 40 wt% fructose aqueous solution and 100% v / v dimethyl sulfoxide aqueous solution were introduced. The reaction was carried out at a flow rate of 0.1 mL / min at 150 °C and 0.5 MPa for 84 s, resulting in a fructose conversion rate of 95.3% and a HMF yield of 88.6%.

[0072] Comparative Example 1

[0073] (1) 5g of activated carbon carrier with a particle size of 0.8mm was heated to 500℃ in nitrogen at a rate of 2℃ / min for 2h and then added to 100mL of nitric acid aqueous solution with a concentration of 80% v / v. The mixture was stirred, refluxed and cooled at 80℃ for 24h, washed and dried to obtain surface-modified activated carbon carrier.

[0074] (2) The surface-modified activated carbon support obtained in step (1) was added to 100 mL of toluene solution, dispersed evenly, and then 50 mL of γ-mercaptopropyltrimethoxysilane was added. The mixture was stirred and refluxed at 120 °C for 24 h. After washing and drying, the basic activated carbon catalyst was obtained.

[0075] (3) Add the basic activated carbon catalyst obtained in step (2) to 200 mL of H2O2 aqueous solution with a volume concentration of 50% v / v, stir and reflux at 30 °C for 24 h to obtain a single structure. Acid site activated carbon solid acid catalyst.

[0076] The single structure prepared in this comparative example Acid-containing activated carbon solid acid catalyst was packed into a micro-packed bed reactor (6.4 mm in diameter and 200 mm in length), and simultaneously 40 wt% fructose aqueous solution and 100% v / v dimethyl sulfoxide aqueous solution were introduced. The reaction was carried out at a flow rate of 0.1 mL / min at 150 °C and 0.5 MPa for 60 s, resulting in a fructose conversion rate of 82% and a HMF yield of 72.3%.

[0077] Comparative Example 2

[0078] (1) 5g of activated carbon carrier with a particle size of 0.8mm was heated to 500℃ for 2h in nitrogen at a rate of 2℃ / min, and then 100mL of nitric acid aqueous solution with a concentration of 80 / 20v / v% was added. The mixture was stirred, refluxed and cooled at 80℃ for 24h, washed and dried to obtain surface-modified activated carbon carrier.

[0079] (3) Add the single activated carbon support obtained in step (1) to 100 mL of dichloromethane, disperse it evenly, add 20 mL of chlorosulfonic acid, stir and reflux at 30 °C for 24 h, and then wash and dry to obtain the activated carbon solid acid catalyst.

[0080] The activated carbon solid acid catalyst prepared in this comparative example was packed into a micro-packed bed reactor (6.4 mm in diameter and 200 mm in length), and simultaneously 40 wt% fructose aqueous solution and 100% v / v dimethyl sulfoxide aqueous solution were introduced. The reaction was carried out at 150 °C and 0.5 MPa for 60 s at a flow rate of 0.1 mL / min, resulting in a fructose conversion rate of 79% and an HMF yield of 53%.

[0081] Comparative Example 3

[0082] (1) 5g of activated carbon carrier with a particle size of 0.8mm was heated to 500℃ in nitrogen at a rate of 2℃ / min for 2h and then added to 100mL of nitric acid aqueous solution with a concentration of 80% v / v. The mixture was stirred, refluxed and cooled at 80℃ for 24h, washed and dried to obtain surface-modified activated carbon carrier.

[0083] (2) The surface-modified activated carbon support obtained in step (1) was added to 100 mL of toluene solution, dispersed evenly, and then 50 mL of mercaptomethyltriethoxysilane was added. The mixture was stirred and refluxed at 120 °C for 24 h. After washing and drying, the basic activated carbon catalyst was obtained.

[0084] (3) Add the basic activated carbon catalyst obtained in step (2) to 200 mL of H2O2 aqueous solution with a volume concentration of 50% v / v, stir and reflux at 30 °C for 24 h to obtain a single structure. Acid site activated carbon solid acid catalyst;

[0085] (4) The single structure obtained in step (3) A solid acid catalyst with activated carbon at the acid site was added to 100 mL of dichloromethane and dispersed evenly. Then, 20 mL of chlorosulfonic acid was added, and the mixture was stirred and refluxed at 30 °C for 24 h. After washing and drying, a bi-structured catalyst was obtained. Acid site activated carbon solid acid catalyst.

[0086] The bistructure prepared in this comparative example Acid-containing activated carbon solid acid catalyst was packed into a micro-packed bed reactor (6.4 mm in diameter and 200 mm in length), and simultaneously 40 wt% fructose aqueous solution and 100% v / v dimethyl sulfoxide aqueous solution were introduced. The reaction was carried out at a flow rate of 0.1 mL / min at 150 °C and 0.5 MPa for 60 s, resulting in a fructose conversion rate of 94.3% and an HMF yield of 61.8%.

[0087] Comparative Example 4

[0088] Commercial solid acid HND8 particles (average particle size 50 μm) were packed into a micro packed bed reactor (diameter 6.4 mm, length 200 mm), and simultaneously 10 wt% fructose aqueous solution and 100% v / v dimethyl sulfoxide aqueous solution were introduced. The reaction was carried out at 150 °C and 5 MPa for 60 s at a flow rate of 0.1 mL / min, resulting in a fructose conversion rate of 83% and an HMF yield of 62%.

[0089] The above description is a preferred embodiment of the invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the invention, and these improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. A process for the preparation of a solid acid catalyst for use in a micro packed bed reactor, characterized in that, Includes the following steps: (1) Provide a porous carrier, modify the porous carrier with an acidic solution to load hydroxyl groups on the surface of the porous carrier to obtain a modified carrier; the porous carrier is selected from one or more of alumina, zirconium oxide, silicon oxide, and activated carbon; the particle size of the porous carrier is 0.5 mm to 1 mm. (2) The modified support is mixed with a solution containing silane and reacted at 50~200℃ for 0.5~36h to obtain the first basic catalyst; wherein the silane is γ-mercaptopropyltrimethoxysilane; (3) The first basic catalyst is mixed with an oxidizing solution and reacted at 30~100℃ for 0.5~36h to obtain the second basic catalyst; (4) The second basic catalyst is mixed with a solution containing sulfonic acid groups and reacted at 30~100℃ for 0.5~36h to obtain the enhanced solid acid catalyst product; wherein, the solution containing sulfonic acid groups is chlorosulfonic acid.

2. The method for preparing a solid acid catalyst for a micro-packed bed reactor as described in claim 1, characterized in that, In step (1), 1~10g of porous support is mixed with 10~200mL of acidic solution, stirred and refluxed at 30~150℃ for 0.5~36h, washed and dried to obtain modified support; The acidic solution is selected from one or more of hydrochloric acid solution, nitric acid solution, sulfuric acid solution, and phosphoric acid solution, and the volume concentration of the acidic solution is 10~100%v / v.

3. The method for preparing a solid acid catalyst for a micro-packed bed reactor as described in claim 1, characterized in that, Step (2) includes: (2.1) Add the modified carrier obtained in step (1) to 50~200mL of toluene, and then add 5~70mL of silane; (2.2) Stir and reflux at 80~200℃ for 10~36h, then wash and dry to obtain the first basic catalyst; The silane is selected from γ-mercaptopropyltrimethoxysilane.

4. The method for preparing a solid acid catalyst for a micro packed bed reactor according to claim 1, wherein In step (3), the first basic catalyst obtained in step (2) is mixed with 100~300mL of oxidizing solution, stirred and reacted at 30~60℃ for 10~36h, washed and dried to obtain the second basic catalyst; The oxidizing solution is selected from one or more of hydrogen peroxide solution, sulfuric acid solution or potassium permanganate solution; the volume concentration of the oxidizing solution is 10~100% v / v.

5. The method for preparing a solid acid catalyst for a micro-packed bed reactor as described in claim 1, characterized in that, Step (4) includes: (4.1) Mix the second basic catalyst obtained in step (3) with 50~200mL of organic solvent, and then add 5~70mL of a solution containing sulfonic acid groups; (4.2) React at 30~60℃ for 10~36h, wash and dry to obtain the enhanced solid acid catalyst product; The organic solvent is selected from one or more of dichloromethane, trichloromethane, dichloroethane, dichloropropane, and dibromomethane.

6. The method for preparing a solid acid catalyst for a micro-packed bed reactor as described in claim 1, characterized in that, Step (1) includes: (1.1) Provide a porous carrier, heat it to 400-600℃ at a heating rate of 2-10℃ / min, and calcine it at that temperature for 2-5 hours; (1.2) The calcined porous support is modified with an acidic solution to obtain a modified support.

7. A solid acid catalyst characterized by, It is prepared by the method for preparing a solid acid catalyst for a micro-packed bed reactor as described in any one of claims 1 to 6.

8. A method for preparing 5-hydroxymethylfurfural, characterized by, The solid acid catalyst as described in claim 7 is added to a micro-packed bed reactor, and a fructose aqueous solution with a concentration of 1-40 wt% is introduced. The reaction is carried out at 70-200°C and 0-3 MPa for 20-500 s.

9. The method for preparing 5-hydroxymethylfurfural as described in claim 8, characterized in that, The micro-filled bed reactor has a long cylindrical structure with a length-to-diameter ratio greater than 30.

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