Solid acid catalyst for hemicellulose depolymerization and preparation method thereof

Abstract

The invention relates to a solid acid catalyst for hemicellulose depolymerization and a preparation method thereof. The catalyst takes graphene as a carrier, is loaded with copper and nickel metals and sulfonate radicals as a catalytic activity center, and has the performance of efficiently catalyzing hemicellulose depolymerization. The preparation method comprises the following steps: dispersing graphene in ethylene glycol, adding copper chloride and nickel chloride as metal precursors, carrying out ultrasonic pretreatment, adjusting the pH value, adding a reducing agent to carry out a reduction reaction, and then carrying out a hydrothermal reaction and drying treatment. The obtained catalyst shows high catalytic activity and stability in the hemicellulose depolymerization reaction and is suitable for various biomass raw materials such as corn straw and corncob, and products are mainly xylose, furfural and the like. The catalyst disclosed by the invention is simple to prepare, low in cost and environment-friendly, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to a solid acid catalyst for hemicellulose depolymerization and a preparation method thereof. Background Art

[0002] Hemicellulose, an abundant, biodegradable, and renewable biomass polysaccharide resource, holds broad application prospects. Hemicellulose plays an indispensable role in numerous industries, including textiles, papermaking, cosmetics, and food packaging. However, efficiently depolymerizing hemicellulose into more valuable chemical products remains a research hotspot and a challenge.

[0003] At present, there are many methods for hemicellulose depolymerization, mainly including physical, chemical and biological methods. Physical methods, such as high-temperature hydrothermal treatment, can achieve hemicellulose depolymerization to a certain extent, but often produce degradation by-products such as hydroxymethylfurfural, which affect the purity and subsequent application of the product. Chemical methods, especially dilute acid hydrothermal treatment, are one of the most widely studied methods for hemicellulose depolymerization. However, this method has problems such as severe equipment corrosion, difficulty in recycling catalysts, and poor product selectivity, which greatly limit its prospects for industrial application. Alkali treatment may cause isomerization or degradation of sugars, which is also not conducive to the subsequent utilization of the product.

[0004] Biological methods, such as enzymatic hydrolysis, have the advantages of mild reaction conditions and low environmental pollution, but the cost of enzymes is high, the pretreatment process is complex, and the lignin barrier needs to be removed, which makes enzymatic hydrolysis face huge challenges in achieving industrial production.

[0005] Given the shortcomings of the above methods, solid acid catalysts have gradually attracted attention due to their unique advantages. Solid acid catalysts not only have high catalytic activity and mild reaction conditions, but are also resistant to high temperatures, have simple product separation processes, cause little environmental pollution, and are recyclable. However, existing solid acid catalysts still have many shortcomings in terms of preparation process, reaction conditions, catalytic activity, product yield, and catalyst stability, which to some extent limit their application in the field of hemicellulose depolymerization.

[0006] In order to solve the above problems, the applicant proposed a solid acid catalyst for hemicellulose depolymerization and a preparation method thereof. Summary of the Invention

[0007] The object of the present invention is to provide a solid acid catalyst for hemicellulose depolymerization and a preparation method thereof, so as to solve the problems in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a solid acid catalyst for hemicellulose depolymerization, wherein the catalyst uses graphene as a support carrier and is loaded with metallic copper, metallic nickel, and sulfonate groups as catalytic active centers, wherein the graphene ensures the uniform distribution of the metal components, the bimetallic copper and nickel can synergistically catalyze the depolymerization reaction, and the sulfonate groups can effectively activate the reaction raw materials.

[0009] Optionally, the preparation method of the catalyst includes: dispersing graphene in an ethylene glycol solution, adding copper chloride dihydrate and nickel chloride hexahydrate as metal precursors, and preparing a uniformly dispersed solution through ultrasonic pretreatment; then adjusting the pH value of the solution and adding a reducing agent to carry out a reduction reaction; finally, subjecting the reaction mixture to a hydrothermal reaction, and obtaining a bimetallic-loaded graphene solid acid catalyst after drying.

[0010] Optionally, the ultrasonic pretreatment time is 2-4 hours; the reducing agent is sodium borohydride; the hydrothermal reaction temperature is 200° C., and the time is 4 hours; the drying treatment temperature is 60° C., and the time is 24 hours.

[0011] Optionally, the use of the catalyst in a hemicellulose depolymerization reaction comprises adding a hemicellulose-containing biomass raw material and the catalyst into a reaction device, reacting at a temperature range of 100-160° C. for 0.5-2 hours to obtain products such as xylose and furfural.

[0012] Optionally, the hemicellulose-containing biomass raw materials include corn stalks, corn cobs, walnut shells, sugarcane bagasse, etc.; and the reaction device is a sealed Teflon-lined autoclave.

[0013] Beneficial effects:

[0014] 1. High-efficiency catalytic performance: The graphene-based solid acid catalyst of the present invention exhibits excellent depolymerization universality and high-efficiency catalytic activity for a variety of biomass raw materials (such as corn straw, corn cobs, walnut shells, sugarcane bagasse, etc.), and can efficiently depolymerize hemicellulose into products such as xylose and furfural, with a substrate conversion rate of over 60%.

[0015] 2. Good stability and recyclability: The catalyst has good catalytic stability and maintains satisfactory catalytic activity after repeated use, effectively reducing production costs. At the same time, its solid acid properties make the catalyst easy to recycle and reuse, reducing environmental pollution.

[0016] 3. Green and environmentally friendly: Compared with the traditional dilute acid hydrothermal treatment method, the present invention avoids problems such as equipment corrosion and poor product selectivity. In addition, the catalyst preparation process is relatively simple, the reaction conditions are mild, and the environmental pollution is small. It is an environmentally friendly catalyst preparation method.

[0017] 4. Significant economic benefits: The catalyst of the present invention has low preparation cost and high catalytic efficiency, can significantly reduce the production cost of hemicellulose depolymerization, improve economic benefits, and has broad application prospects and market potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the process of an embodiment of the present invention; DETAILED DESCRIPTION

[0019] The following describes preferred embodiments of the present invention with reference to the accompanying drawings to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0020] This invention relates to a highly efficient catalyst for hemicellulose depolymerization and its preparation method. Specifically, it is a graphene-based solid acid catalyst, which uses graphene as a support and is loaded with metallic copper, metallic nickel, and sulfonate groups as catalytically active centers. This section will detail the technical solutions of the invention, including the catalyst's composition, preparation method, applications, advantages, specific implementation methods, and conclusions.

[0021] The core of this invention is the design of a novel graphene-based solid acid catalyst, which is composed of a graphene carrier, metallic copper, metallic nickel, and sulfonate. The functions of each component are as follows:

[0022] Graphene Support: Graphene, a two-dimensional carbon material, possesses an extremely high specific surface area and excellent electrical and thermal conductivity, effectively increasing the catalyst's active sites and electron transport capacity. In this invention, graphene serves as a support, capable of loading and evenly dispersing the metallic copper and nickel, ensuring high catalytic activity and stability during the reaction.

[0023] Copper and nickel: As bimetallic active components, copper and nickel synergistically catalyze the depolymerization of hemicellulose. The introduction of copper and nickel not only enhances the catalyst's activity but also broadens its applicability, enabling it to efficiently depolymerize hemicellulose from a wide variety of biomass feedstocks. Furthermore, the synergistic effect of the bimetallics improves product selectivity and yield.

[0024] Sulfonate: As an acidic functional group, sulfonate effectively activates the glycosidic bonds in hemicellulose molecules, promoting depolymerization. Furthermore, the introduction of sulfonate improves the stability and reusability of the catalyst, ensuring that the catalyst maintains high catalytic activity over extended periods of use. Furthermore, sulfonate forms stable catalytically active centers with copper and nickel, enhancing the catalyst's activity. Furthermore, repeated sulfonation of the catalyst allows for recyclability.

[0025] The preparation method of the graphene-based solid acid catalyst of the present invention comprises the following steps:

[0026] Graphene Dispersion: First, a certain amount of graphene oxide (GO) and reduced graphene oxide (rGO) is dispersed in ethylene glycol. Ethylene glycol, as an organic solvent, has excellent solubility and dispersibility, ensuring uniform dispersion of graphene in the solution. Ultrasonic pretreatment further promotes graphene dispersion, increasing the catalyst's specific surface area and the number of active sites. The duration of ultrasonic treatment can be adjusted as needed to ensure sufficient dispersion of the graphene.

[0027] Addition of Metal Precursors: Copper chloride dihydrate (CuCl2·2H2O) and nickel chloride hexahydrate (NiCl2·6H2O) are added to the dispersed graphene solution as metal precursors. Copper chloride and nickel chloride completely dissolve in water, forming a metal ion solution. Through stirring and reaction, the metal ions are evenly adsorbed on the graphene surface, laying the foundation for subsequent metal loading and the formation of catalytically active centers. The amount of metal precursor added can be adjusted according to the desired catalytic activity and product selectivity of the catalyst.

[0028] pH adjustment and reduction reaction: Next, sodium hydroxide (NaOH) solution is used to adjust the pH value of the solution to about 10. Under alkaline conditions, metal ions can more easily bind to functional groups on the graphene surface. Then, sodium borohydride (NaBH4) is gradually added as a reducing agent to reduce the metal ions into metal nanoparticles and load them on the graphene surface. During the reduction reaction, the reaction temperature and stirring speed need to be controlled to ensure uniform growth and loading of metal nanoparticles. At the same time, attention should also be paid to the amount of reducing agent added to avoid excessive reduction leading to a decrease in catalyst activity.

[0029] Hydrothermal Reaction: The reaction mixture is transferred to a sealed, Teflon-lined autoclave for a hydrothermal reaction. This reaction, conducted under high temperature and pressure, promotes interaction and bonding between graphene and metal nanoparticles, forming stable catalytically active centers. The temperature and duration of the hydrothermal reaction can be optimized based on the desired catalyst performance.

[0030] Drying: Finally, the reaction product is repeatedly washed with distilled water and acetone to remove impurities and unreacted materials. It is then dried at 60°C for 24 hours to obtain the bimetallic graphene solid acid catalyst powder. During the drying process, the temperature and drying time must be controlled to prevent catalyst agglomeration and deactivation. The cleanliness of the drying environment must also be maintained to prevent catalyst contamination.

[0031] The graphene-based solid acid catalyst of the present invention has broad application prospects in hemicellulose depolymerization reactions. The following are the specific steps and conditions for catalyst application:

[0032] Raw material preparation: Biomass raw materials containing hemicellulose, such as corn stalks, corn cobs, walnut shells, and sugarcane bagasse, are used. These biomass raw materials are rich in hemicellulose and are ideal for producing valuable chemicals. The biomass raw materials are crushed and pretreated, such as through screening, washing, and drying, to improve their reactivity and accessibility.

[0033] Catalyst Addition: A certain amount of graphene-based solid acid catalyst is added to the hemicellulose-containing biomass feedstock. The catalyst dosage can be adjusted based on the properties of the feedstock and reaction conditions. Generally speaking, a higher catalyst dosage results in higher catalytic activity, but excessive dosages can lead to increased costs and decreased product selectivity. Therefore, it is important to select an appropriate catalyst dosage.

[0034] Controlling reaction conditions: The mixture is transferred to a sealed Teflon-lined autoclave and the reaction is carried out under a certain temperature and pressure. The reaction temperature is generally controlled between 100-160°C and the reaction time is controlled between 0.5-2 hours. By controlling the reaction temperature and time, the depolymerization efficiency of hemicellulose and the product distribution can be optimized. At the same time, the reaction system must be sealed and the stirring speed must be maintained to ensure a uniform reaction. Furthermore, the reaction conditions can be further optimized by adjusting the pH value of the reaction system and adding additives.

[0035] Product Separation and Purification: After the reaction is complete, the reaction products are separated and purified. The catalyst and product can be separated by filtration, centrifugation, washing, and other methods. The product is then further purified and processed, such as by distillation, crystallization, and extraction, to obtain high-purity valuable chemicals such as xylose and furfural.

[0036] Compared with existing hemicellulose depolymerization catalysts, the graphene-based solid acid catalyst of the present invention has the following significant advantages:

[0037] Highly efficient catalytic activity: Graphene's high specific surface area and excellent electrical and thermal conductivity, combined with the synergistic catalytic effects of copper and nickel, contribute to the catalyst's high catalytic activity. Under the same reaction conditions, the catalyst significantly improves hemicellulose depolymerization efficiency and product selectivity, thereby reducing production costs and improving economic benefits.

[0038] Excellent stability and reusability: Graphene serves as a carrier, effectively supporting the active components, including the bimetallic and sulfonate groups, significantly enhancing the catalyst's stability and reusability. The catalyst maintains high catalytic activity after repeated use, significantly reducing production costs and improving resource efficiency. Furthermore, the repeated sulfonation process significantly extends the catalyst's lifespan, helping to reduce waste and complying with environmental and sustainable development requirements.

[0039] Broad Applicability: The catalyst of this invention is suitable for depolymerizing hemicellulose from a variety of biomass feedstocks, such as corn straw, corn cobs, walnut shells, and sugarcane bagasse. This gives the catalyst broad application prospects in the development and utilization of biomass resources, helping to promote the industrialization of biomass energy and chemicals.

[0040] Environmentally friendly: Compared with traditional chemical methods, the catalyst preparation and use of this invention eliminates the need for large amounts of acid, base, and organic solvents, reducing environmental pollution and wastewater discharge. Furthermore, catalyst recovery and reuse align with the principles of green chemistry and the circular economy, contributing to the achievement of sustainable development goals.

[0041] Industrial Production Potential: The catalyst preparation method of this invention is simple, easy to operate, and relatively low-cost. By optimizing the preparation process and reaction conditions, industrial production of the catalyst can be achieved, providing strong support for the development and utilization of biomass resources and the industrialization of hemicellulose depolymerization technology. Furthermore, large-scale production of the catalyst can help reduce production costs and improve market competitiveness.

[0042] In order to further illustrate the technical solutions and beneficial effects of the present invention, specific implementation methods are given below:

[0043] Example 1

[0044] Preparation of catalyst:

[0045] 300 mg of graphene oxide (GO) and reduced graphene oxide (rGO) were mixed in a ratio of 1:1 and dispersed in 50 ml of ethylene glycol.

[0046] Graphene was uniformly dispersed in ethylene glycol by ultrasonic pretreatment for 2-4 hours.

[0047] 0.02 M copper chloride dihydrate (CuCl2·2H2O) and 0.02 M nickel chloride hexahydrate (NiCl2·6H2O) were added, and the reaction mixture was vigorously stirred for 2 h to allow the metal ions to be uniformly adsorbed on the graphene surface.

[0048] The pH value of the mixed solution was adjusted to about 10 using 2 M sodium hydroxide solution.

[0049] 0.10 g of sodium borohydride (NaBH4) was gradually added as a reducing agent, and stirring was continued for 30 minutes to reduce the metal ions into metal nanoparticles and load them on the graphene surface.

[0050] The reaction mixture was transferred into a sealed Teflon-lined autoclave and maintained at 200 °C for 4 h for hydrothermal reaction.

[0051] After the reaction, the precipitate was repeatedly washed with distilled water and then with acetone to remove impurities and unreacted substances.

[0052] The mixture was dried at 60° C. for 24 hours to obtain bimetallic-loaded graphene solid acid catalyst powder.

[0053] Application of catalyst:

[0054] Take biomass raw materials containing hemicellulose (such as corn straw), crush them and sieve them to remove impurities.

[0055] Add a certain amount of catalyst to the biomass raw material and mix well.

[0056] The mixture was transferred into a sealed Teflon-lined autoclave and reacted at 120 °C for 1 h.

[0057] After the reaction is completed, the products are separated through filtration, washing and purification to obtain high-purity xylose and furfural.

[0058] Performance evaluation:

[0059] The catalytic activity of the prepared catalysts was tested to compare their hemicellulose depolymerization efficiency and product selectivity under different reaction conditions.

[0060] The stability and reusability of the catalyst were tested, and the changes in its catalytic activity after multiple uses were observed.

[0061] Catalytic activity and product analysis:

[0062] The reaction products are qualitatively and quantitatively analyzed by high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). The yield is much higher than that of traditional catalysts.

[0063] At the same time, the content of by-products in the product is low, indicating that the catalyst has high selectivity and can effectively promote the formation of the target product.

[0064] Catalyst stability and reusability test:

[0065] The used catalyst was recovered through simple filtration and washing steps and then reused and tested under the same reaction conditions.

[0066] The results showed that after five reuses, the catalytic activity of the catalyst decreased only slightly, while maintaining high hemicellulose depolymerization efficiency and product selectivity. This demonstrates that the catalyst of the present invention has good stability and reusability, and can significantly reduce production costs.

[0067] Characterization and analysis of catalysts:

[0068] The morphology and structure of the catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD).

[0069] SEM and TEM results show that metallic copper and nickel nanoparticles are evenly loaded on the graphene surface, and the particle size is small, which is conducive to providing more catalytic active sites.

[0070] XRD results showed that the crystal phase structure of metallic copper and nickel in the catalyst was clear, indicating that the metal ions had been successfully reduced into metal nanoparticles and formed stable catalytic active centers.

[0071] Example 2

[0072] In order to further verify the applicability of the catalyst of the present invention in different biomass raw materials, we selected another biomass raw material containing hemicellulose - sugarcane bagasse for experiment.

[0073] Preparation of catalyst:

[0074] The catalyst preparation method is the same as that in Example 1, and bimetallic-loaded graphene solid acid catalyst powder is obtained.

[0075] Application of catalyst:

[0076] Sugarcane bagasse is taken as the biomass raw material, which is crushed and sieved to remove impurities.

[0077] Add a certain amount of catalyst to the bagasse and mix well.

[0078] The mixture was transferred into a sealed Teflon-lined autoclave and reacted at 140 °C for 2 h.

[0079] After the reaction is completed, the products are separated through filtration, washing and purification to obtain high-purity xylose and furfural.

[0080] Performance evaluation:

[0081] At the same time, the stability and reusability of the catalyst were tested, and the results showed that after multiple uses, the catalyst still maintained a high catalytic activity.

[0082] Example 3

[0083] In order to explore the influence of various parameters in the catalyst preparation process on the catalytic performance, we conducted a series of comparative experiments.

[0084] Effect of different metal loadings:

[0085] Graphene-based solid acid catalysts with metal loadings of 1%, 3%, 5% and 7% were prepared, and hemicellulose depolymerization experiments were carried out under the same reaction conditions.

[0086] The results showed that the catalytic activity of the catalyst first increased and then decreased with increasing metal loading, reaching the optimal effect when the metal loading was 5%. This indicates that a moderate metal loading can provide sufficient catalytic active sites while avoiding metal particle agglomeration and reduced catalyst activity.

[0087] Effect of different hydrothermal reaction times:

[0088] Graphene-based solid acid catalysts with hydrothermal reaction times of 2 hours, 4 hours, 6 hours and 8 hours were prepared, and hemicellulose depolymerization experiments were carried out under the same reaction conditions.

[0089] The results showed that as the hydrothermal reaction time increased, the catalytic activity of the catalyst first increased and then stabilized, reaching its optimal effect when the hydrothermal reaction time was 4 hours. This indicates that a moderate hydrothermal reaction time can promote the interaction and bonding between graphene and metal nanoparticles, forming stable catalytic active centers.

[0090] Effect of different reaction temperatures:

[0091] Under the same catalyst and biomass raw material conditions, hemicellulose depolymerization experiments were carried out at different reaction temperatures (100℃, 120℃, 140℃, and 160℃).

[0092] The results showed that as the reaction temperature increased, the depolymerization efficiency and product selectivity of hemicellulose first increased and then decreased, reaching the optimal effect when the reaction temperature was 120°C. This indicates that a moderate reaction temperature can balance the reaction rate and product selectivity, thereby improving the catalytic performance of the catalyst.

[0093] The present invention successfully prepares an efficient, stable, and reusable graphene-based solid acid catalyst for the depolymerization reaction of hemicellulose. By optimizing the preparation method and reaction conditions of the catalyst, the depolymerization efficiency and product selectivity of hemicellulose are significantly improved. At the same time, the catalyst has good stability and reusability, which can greatly reduce production costs. In addition, the catalyst is also suitable for the depolymerization of hemicellulose in a variety of biomass raw materials and has a wide range of applicability. The catalyst of the present invention provides strong support for the development and utilization of biomass resources and the industrialization process of hemicellulose depolymerization technology, and has broad application prospects and market value.

[0094] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from all points of view, the embodiments should be regarded as illustrative and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and range of equivalents of the claims are included in the present invention. Any reference signs in the claims should not be construed as limiting the claim to which they relate.

[0095] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A solid acid catalyst for hemicellulose depolymerization, characterized in that: The catalyst uses graphene as a support carrier and is loaded with metallic copper, metallic nickel and sulfonate groups as catalytic active centers. Graphene ensures the uniform distribution of the metal components, bimetallic copper and nickel can synergistically catalyze the depolymerization reaction, and sulfonate groups can effectively activate the reaction raw materials.

2. The solid acid catalyst for hemicellulose depolymerization according to claim 1, characterized in that The catalyst preparation method comprises: dispersing graphene in an ethylene glycol solution, adding copper chloride dihydrate and nickel chloride hexahydrate as metal precursors, and preparing a uniformly dispersed solution through ultrasonic pretreatment; then adjusting the pH value of the solution and adding a reducing agent to carry out a reduction reaction; and finally subjecting the reaction mixture to a hydrothermal reaction, and obtaining a bimetallic-loaded graphene solid acid catalyst after drying.

3. The method for preparing a solid acid catalyst for hemicellulose depolymerization according to claim 2, wherein: The ultrasonic pretreatment time is 2-4 hours; the reducing agent is sodium borohydride; the hydrothermal reaction temperature is 200° C. and the time is 4 hours; the drying temperature is 60° C. and the time is 24 hours.

4. The solid acid catalyst for hemicellulose depolymerization according to claim 1, characterized in that The application of the catalyst in hemicellulose depolymerization reaction comprises adding hemicellulose-containing biomass raw materials and the catalyst into a reaction device, reacting at a temperature range of 100-160° C. for 0.5-2 hours to obtain products such as xylose and furfural.

5. The use of the solid acid catalyst for hemicellulose depolymerization according to claim 4, characterized in that: The biomass raw materials containing hemicellulose include corn stalks, corn cobs, walnut shells, sugarcane bagasse, etc.; the reaction device is a sealed Teflon-lined autoclave.

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