A method for preparing furfural from biomass sugars catalyzed by carboxyl-functionalized covalent organic framework materials.

Abstract

This invention belongs to the fields of biomass catalytic conversion technology and biomass energy chemical technology, specifically relating to a method for catalytically converting biomass into furfural using carboxyl-functionalized covalent organic framework (COF) materials. This invention uses carboxyl-functionalized monomers as raw materials and employs a solvothermal synthesis method to prepare carboxyl-functionalized COF materials via a Schiff base reaction. These materials can serve as highly efficient catalysts for the preparation of fine chemicals from biomass chemical components. This invention innovatively uses carboxyl-functionalized COFs to catalyze the production of furfural from biomass sugars. The prepared COFs exhibit high catalytic efficiency, good stability, and can be repeatedly used to catalyze furfural production. This solves the problems of poor environmental friendliness, difficulty in reusing, and equipment corrosion associated with liquid acid catalysts in furfural production, thus broadening a new sustainable path for the high-value utilization of biomass resources to produce fine chemicals.

Description

Technical Field

[0001] This invention belongs to the fields of biomass catalytic conversion technology and biomass energy chemical technology, specifically relating to a method for preparing furfural from biomass sugars using carboxyl-functionalized covalent organic framework materials. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] With the international community placing increasing emphasis on ensuring energy security, protecting the ecological environment, and addressing climate change, accelerating the development and utilization of renewable energy sources such as biomass feedstocks has become a global consensus. Biomass, a green and renewable organic resource, has received significant attention in today's rapidly industrializing world. As one of the most promising renewable resources, it has become the fourth largest energy source after coal, oil, and natural gas, with enormous development potential. Pretreated biomass feedstocks can be converted into platform compounds, leading to the derivation of various value-added chemicals, such as furfural, levulinic acid, and polyols. Among these, furfural, as an important platform compound, is considered a multifunctional bio-based C5 platform molecule with wide applications. It can be used to synthesize various chemical products, such as furfuryl alcohol, tetrahydrofurfuryl alcohol, furan, tetrahydrofuran, and furfurylamine, and can also be used as an extraction solvent in various chemical processes. The conversion process of biomass feedstocks to furfural mainly includes two steps: feedstock hydrolysis and sugar intermediate dehydration, with the acidity of the catalyst playing a decisive role.

[0004] Currently, acidic catalysts for the conversion of biomass sugars to furfural mainly include homogeneous and heterogeneous catalysts. Homogeneous catalysts are in the same phase as the reactants and have high mass transfer efficiency, enabling efficient furfural production. However, their corrosion of equipment and separation and recovery are key issues hindering their development. Heterogeneous catalysts are located at a heterogeneous interface with the substrate, making them easy to recover and reuse. However, they usually require pretreatment of the substrate to enhance the contact between the acidic sites of the catalyst and the substrate. Generally, the catalytic performance of this type of catalyst is lower than that of homogeneous catalysts. Therefore, developing novel heterogeneous catalysts with excellent catalytic performance and high stability is crucial for achieving efficient and sustainable development of the furfural industry.

[0005] Covalent organic frameworks (COFs) have significant potential applications in catalysis due to their outstanding advantages. COFs are a new class of crystalline porous polymer framework materials constructed through covalent bonds. Their unit organic building blocks contain light elements (C, H, O, B, N, etc.) and can extend in two or three dimensions to form robust organic frameworks with high designability. Their large surface area, abundant pore structure, and acidic sites provide sufficient prerequisites for the efficient preparation of furfural, making them the optimal choice for achieving efficient, stable, and continuous catalytic conversion of biomass to furfural. Summary of the Invention

[0006] To address the shortcomings of existing technologies, a method for catalytically converting biomass into furfural using carboxyl-functionalized covalent organic frameworks (COFs) is provided. Specifically, biomass sugar, carboxyl-functionalized COFs material, and solvent are sequentially added to a reaction vessel, which is then filled with an inert gas and reacted at a specific temperature to efficiently catalyze the conversion of biomass sugar into furfural.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] In one aspect, the present invention provides a method for catalytic conversion of biomass into furfural using carboxyl-functionalized covalent organic framework materials, comprising:

[0009] Carboxyl-functionalized COFs were prepared from structural monomers containing carboxyl functional groups using solvothermal or mechanical grinding methods.

[0010] Furfural is prepared by uniformly mixing biomass sugars and carboxyl-functionalized COFs in a solvent and carrying out a catalytic reaction under an inert atmosphere.

[0011] In a second aspect, the present invention provides a method for preparing carboxyl-functionalized covalent organic framework materials, comprising: using 2,5-diaminobenzoic acid and trialdehyde m-phenyltrialdehyde as monomers, and performing a Schiff base reaction by solvothermal or mechanical grinding method to obtain carboxyl-functionalized COFs.

[0012] A third aspect of the present invention provides the application of the above-mentioned carboxyl-functionalized COFs in the catalytic preparation of furfural from biomass sugars.

[0013] This invention mainly includes the preparation of carboxyl-functionalized covalent organic frameworks and their catalytic conversion from biomass raw materials to furfural. Specifically, using structural monomers containing carboxyl functional groups as raw materials, imine-functionalized covalent organic frameworks (I-COFs) are prepared via a solvothermal synthesis method through a Schiff base reaction. The main characteristics of these materials are ease of synthesis, large specific surface area and porosity, high crystallinity, structural stability, and abundance of acidic sites, making them suitable as highly efficient catalysts for the preparation of fine chemicals from biomass chemical components. Furthermore, the carboxyl-functionalized COFs are used to catalyze the production of furfural from biomass sugars. The prepared carboxyl-functionalized COFs exhibit high catalytic efficiency, good stability, and can be repeatedly used to catalyze furfural production. This solves the problems of poor environmental friendliness, difficulty in reusing, and equipment corrosion associated with liquid acid catalysts in furfural production, thus broadening a new sustainable path for the high-value utilization of biomass resources to produce fine chemicals.

[0014] The beneficial effects of this invention are as follows:

[0015] 1. This invention applies acid-functionalized covalent organic framework materials to the catalytic production of furfural from biomass sugars, developing a novel catalyst for the efficient preparation of furfural and expanding the application scope of covalent organic framework materials.

[0016] 2. This invention uses structural monomers containing carboxyl functional groups as raw materials to synthesize imine-based functionalized covalent organic framework materials. These materials have a large specific surface area and a large number of uniformly distributed acidic sites, enabling them to efficiently catalyze the production of furfural from biomass sugars under milder conditions.

[0017] 3. The carboxyl-functionalized COFs prepared by this invention have high stability, can be reused multiple times, and have stable performance.

[0018] 4. The preparation method of this invention is simple, practical, and easy to promote. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 1 This is a process route diagram in an embodiment of the present invention;

[0021] Figure 2 The XRD pattern (A) and FTIR spectrum (B) of the carboxyl-functionalized COFs prepared in Example 1 of this invention are shown. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] A method for catalytic conversion of biomass to furfural using carboxyl-functionalized covalent organic framework materials includes:

[0024] Carboxyl-functionalized COFs were prepared from structural monomers containing carboxyl functional groups using solvothermal or mechanical grinding methods.

[0025] Furfural is prepared by uniformly mixing biomass sugars and carboxyl-functionalized COFs in a solvent and carrying out a catalytic reaction under an inert atmosphere.

[0026] In some embodiments, the biomass sugar includes, but is not limited to, xylan, xylose, arabinose, and biomass prehydrolysate. The biomass sugar serves as a substrate for a catalytic reaction.

[0027] In some embodiments, the solvent is one or more of water, tetrahydrofuran, 1,4-dioxane, dimethyl sulfoxide, and γ-valerolactone.

[0028] In some embodiments, the inert gas is selected from nitrogen, argon, and helium.

[0029] In some embodiments, the biomass sugar concentration is 10-50 g / L.

[0030] In some embodiments, the amount of carboxyl-functionalized COFs used is 5%-30% of the biomass sugar mass.

[0031] In some embodiments, the catalytic temperature is 140-180℃ and the catalytic time is 0.5-5h; preferably, the catalytic temperature is 150-170℃ and the catalytic time is 0.5-3h.

[0032] A method for preparing carboxyl-functionalized covalent organic framework materials includes: using 2,5-diaminobenzoic acid and trialdehyde m-phenyltrialdehyde as monomers, and performing a Schiff base reaction by solvothermal or mechanical grinding to obtain carboxyl-functionalized COFs.

[0033] In some embodiments, the molar ratio of the mixture of 2,5-diaminobenzoic acid and trialdehyde m-phenyltrialdehyde is 3:2.

[0034] In some embodiments, the reaction is carried out using a solvothermal method, wherein the reaction is carried out at 90–120°C for 3–5 days. Preferably, the reaction is carried out at 120°C for 3 days.

[0035] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0036] Example 1

[0037] A method for preparing furfural from xylan catalyzed by carboxyl-functionalized covalent organic framework materials (1) Material preparation

[0038] In the preparation of carboxyl-functionalized COFs materials, the raw material components are mixed in the following proportions: 2,5-diaminobenzoic acid 23.11 mg, trialdehyde phloroglucinol 21.01 mg, 1,4-dioxane 4 mL, mesitylene 1 mL, and acetic acid 1.5 mL.

[0039] In the catalytic production of furfural, the raw material components of carboxyl-functionalized COFs materials are prepared according to the following proportions: xylan (10-50 g / L), solvent 30 ml, COFs (0.05-0.5 g). (2) Preparation of carboxyl-functionalized COFs materials

[0040] The prepared 2,5-diaminobenzoic acid (DAB), trialdehyde m-phenyltrialdehyde (TP), 1,4-dioxane, mesitylene, and 6M glacial acetic acid were sequentially added to a thick-walled pressure-resistant tube and mixed thoroughly. The pressure-resistant tube was then rapidly frozen at 77K in a liquid nitrogen bath. After three cycles of freezing-pumping-melting to remove gas, the tube was sealed under vacuum and reacted at 120℃ under a nitrogen atmosphere for 72 hours. After cooling, the tube was washed three times with N,N-dimethylformamide, o-dichlorobenzene, and ethanol, respectively. After drying for 12 hours, carboxyl-functionalized COFs material was obtained, namely TP-DAB material.

[0041] (3) Application of carboxyl-functionalized COFs materials in the preparation of furfural from xylan

[0042] The prepared xylan, solvent, and COFs materials were added sequentially to the reactor. The air inside the reactor was purged with nitrogen 3-4 times, and the stirring speed was set to 500 rpm. The solvent selection, reaction temperature, reaction time, and catalyst dosage are shown in Table 1. After the reaction was completed, the reactor was cooled to room temperature, and the liquid product was collected for qualitative and quantitative analysis. The results are shown in Table 1.

[0043] Table 1. Data on different reaction conditions and reaction results in Example 1

[0044]

[0045] ※: In the two-phase system composed of water and organic solvent, the ratio of water to organic solvent is (1:1).

[0046] Example 2

[0047] A method for preparing furfural from xylose catalyzed by carboxyl-functionalized covalent organic framework materials (1) Material preparation

[0048] In the preparation of carboxyl-functionalized COFs materials, the raw material components are mixed in the following proportions: 2,5-diaminobenzoic acid 23.11 mg, trialdehyde phloroglucinol 21.01 mg, 1,4-dioxane 4 mL, mesitylene 1 mL, and acetic acid 1.5 mL.

[0049] In the catalytic production of furfural, the raw material components of carboxyl-functionalized COFs materials are prepared according to the following proportions: xylose (10-50 g / L), solvent 30 ml, COF (0.05-0.5 g). (2) Preparation of carboxyl-functionalized COFs materials

[0050] The prepared 2,5-diaminobenzoic acid (DAB), trialdehyde m-phenyltrialdehyde (TP), 1,4-dioxane, mesitylene, and 6M glacial acetic acid were sequentially added to a thick-walled pressure-resistant tube and mixed thoroughly. The pressure-resistant tube was then rapidly frozen at 77K using a liquid nitrogen bath. After three cycles of freezing-pumping-melting to remove gas, the tube was sealed under vacuum and reacted at 120℃ under a nitrogen atmosphere for 72 hours. After cooling, the tube was washed three times with N,N-dimethylformamide, o-dichlorobenzene, and ethanol, respectively. After drying for 12 hours, the TP-DAB material was obtained.

[0051] (3) Application of carboxyl-functionalized COFs materials in the catalytic preparation of furfural from xylose

[0052] The prepared xylose, solvent, and COFs materials were added sequentially to the reactor. The air inside the reactor was purged with nitrogen 3-4 times, and the stirring speed was set to 500 rpm. The solvent selection, reaction temperature, reaction time, and catalyst dosage are shown in Table 2. After the reaction was completed, the reactor was cooled to room temperature, and the liquid product was collected for qualitative and quantitative analysis. The results are shown in Table 2.

[0053] Table 2. Data on different reaction conditions and reaction results in Example 2

[0054]

[0055] ※: In the two-phase system composed of water and organic solvent, the ratio of water to organic solvent is (1:1).

[0056] Example 3

[0057] A method for preparing furfural from arabinose catalyzed by carboxyl-functionalized covalent organic framework materials.

[0058] (1) Material preparation

[0059] In the preparation of carboxyl-functionalized COFs materials, the raw materials are mixed in the following proportions: 23.11 mg of diaminobenzoic acid, 21.01 mg of trialdehyde phloroglucinol, 4 mL of 1,4-dioxane, 1 mL of mesitylene, and 1.5 mL of acetic acid.

[0060] In the catalytic production of furfural, the raw materials of carboxyl-functionalized COFs are prepared according to the following proportions: arabinose (10-50 g / L), solvent 30 ml, COFs (0.05-0.5 g). (2) Preparation of carboxyl-functionalized COFs materials

[0061] The prepared 2,5-diaminobenzoic acid, trialdehyde m-phenyltrialdehyde, 1,4-dioxane, mesitylene, and 6M glacial acetic acid were added sequentially to a glass bottle. The mixture was reacted at 120°C under a nitrogen atmosphere for 72 hours using a solvothermal method. After cooling, the mixture was washed three times with N,N-dimethylformamide, dichloromethane, and ethanol, respectively. After drying for 12 hours, the TP-DAB material was obtained.

[0062] (3) Application of carboxyl-functionalized COFs materials in the catalytic preparation of furfural from arabinose

[0063] The prepared arabinose, solvent, and COFs materials were added sequentially to the reactor. The air inside the reactor was purged with helium 3-4 times, and the stirring speed was set to 500 rpm. The solvent selection, reaction temperature, reaction time, and catalyst dosage are shown in Table 3. After the reaction was completed, the reactor was cooled to room temperature, and the liquid product was collected for qualitative and quantitative analysis. The results are shown in Table 3.

[0064] Table 3. Data on different reaction conditions and reaction results in Example 3

[0065]

[0066]

[0067] ※: In the two-phase system composed of water and organic solvent, the ratio of water to organic solvent is (1:1).

[0068] Depend on Figure 2 It can be seen that this invention successfully prepared carboxyl-functionalized COFs materials for use as catalysts. Specifically:

[0069] XRD pattern of catalyst TP-DAB ( Figure 2A) High-intensity diffraction was observed at a low angle of 4.50°, attributed to reflection from the original hexagonal lattice (100) plane, while the broader diffraction peak around 26.06° was attributed to reflection from the (001) plane. The PXRD diffraction peaks of all catalysts were in high agreement with the simulated XRD patterns and previously reported results, demonstrating the successful synthesis of the carboxyl-functionalized covalent organic framework TP-DAB.

[0070] FTIR spectrum of TP-DAB ( Figure 2 In B), the monomer TP has C=O (1640cm). -1 ) and NH (3305cm) on DAB -1 3415cm -1 The disappearance of the vibrational peak indicates that the monomer reaction is complete; 1701 cm⁻¹ -1 The vibrational peaks around the left and right originate from the C=O group in the carboxyl group, similar to those in the monomer DAB, proving the presence of a carboxyl group within the framework of TP-DAB. Furthermore, the 1560 cm⁻¹ peak on TP-DAB... -1 1213cm -1 The strong peak at the point corresponds to the stretching vibrations of the C=C and CN bonds present in the structure, indicating that TP-DAB was successfully synthesized.

[0071] Furthermore, as shown in Tables 1-3, carboxyl-functionalized COFs materials exhibit high catalytic activity in the preparation of furfural from biomass sugars, especially in a two-phase solvent system of water and tetrahydrofuran. In addition, the furfural yield is also affected by reaction temperature, reaction time, and catalyst dosage. After optimizing the reaction conditions, the results show that in the process of preparing biomass sugars (xylan, xylose, arabinose) catalyzed by the TP-DAB catalyst, the reaction temperature should not be too high, preferably 160℃, because lower temperatures cannot completely convert the biomass sugars; while excessively high temperatures may increase other side reactions, such as furfural enrichment and subsequent degradation into small molecules (humic substances, humin, etc.). Secondly, the effect of reaction time on furfural yield is similar to that of temperature; longer reaction times may lead to furfural decomposition or aggregation, hindering the catalytic reaction; shorter reaction times are insufficient to catalyze the conversion of biomass sugars to furfural, resulting in a lower yield. In addition, the amount of substrate (biomass sugar) and catalyst has a similar effect on the catalytic effect. The amount of substrate and catalyst should be matched with each other. Otherwise, it will lead to competition for active reaction sites or saturation of catalytic sites, resulting in low catalytic efficiency and low furfural yield.

[0072] Example 4:

[0073] This embodiment will test the reusability of the carboxyl-functionalized COFs materials described in Examples 1-3. The COFs materials involved in the catalytic preparation of furfural from biomass sugars in Examples 1-3 were filtered and recovered, washed, and then dried in an oven for 12 hours.

[0074] 0.1 g of COFs material, dried to constant weight, was mixed with 0.8 g xylan / 1.2 g xylose / 1.2 g arabinose and 30 ml of water-tetrahydrofuran solution, and then added to a reaction vessel. The air inside the vessel was purged with nitrogen 3-4 times. The reaction temperature was set at 160℃, the reaction time at 3 h, and the stirring speed at 500 rpm. After the reaction was completed, the vessel was cooled to room temperature, and the liquid product was collected for qualitative and quantitative analysis. The above process was repeated 4 times. The results are shown in Table 4.

[0075] Table 4. Data on different reaction conditions and reaction results in Example 4

[0076]

[0077]

[0078] ※: In the two-phase system composed of water and organic solvent, the ratio of water to organic solvent is (1:1).

[0079] Note: Numbers 1-4 are the reusability tests of TP-DAB material in Example 1; Numbers 5-8 are the reusability tests of TP-DAB material in Example 2; Numbers 9-12 are the reusability tests of TP-DAB material in Example 3.

[0080] As shown in Table 4, carboxyl-functionalized COFs materials exhibit excellent recyclability and reusability in the catalytic production of furfural from biomass. After four uses, the furfural yield did not decrease significantly.

[0081] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for catalytic conversion of biomass into furfural using carboxyl-functionalized covalent organic framework materials, characterized in that, include: Using 2,5-diaminobenzoic acid and trialdehyde m-benzyltrialdehyde as monomers, Schiff base reaction was carried out by solvothermal or mechanical grinding to prepare carboxyl-functionalized COFs. Furfural is prepared by uniformly mixing biomass sugars and carboxyl-functionalized COFs in a solvent and carrying out a catalytic reaction under a protective gas. The biomass sugar is one or more of xylan, xylose, arabinose, and biomass prehydrolysate.

2. The method for catalytic conversion of biomass into furfural using carboxyl-functionalized covalent organic framework materials according to claim 1, characterized in that, The solvent is one or more of water, tetrahydrofuran, 1,4-dioxane, dimethyl sulfoxide, and γ-valerolactone.

3. The method for catalytic conversion of biomass into furfural using carboxyl-functionalized covalent organic framework materials according to claim 1, characterized in that, The protective gas is selected from nitrogen, argon, and helium.

4. The method for catalytic conversion of biomass into furfural using carboxyl-functionalized covalent organic framework materials according to claim 1, characterized in that, The biomass sugar concentration is 10-50 g / L.

5. The method for catalytic conversion of biomass into furfural using carboxyl-functionalized covalent organic framework materials according to claim 1, characterized in that, The amount of carboxyl-functionalized COFs used is 5%-30% of the biomass sugar mass.

6. The method for catalytic conversion of biomass into furfural using carboxyl-functionalized covalent organic framework materials according to claim 1, characterized in that, The catalytic temperature is 140-180℃, and the catalytic time is 0.5-5h.

7. The method for catalytic conversion of biomass into furfural using carboxyl-functionalized covalent organic framework materials according to claim 6, characterized in that, The catalytic temperature is 150-170℃, and the catalytic time is 0.5-3h.

8. The application of the carboxyl-functionalized COFs of claim 1 in the catalytic preparation of furfural from biomass sugars.

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