Preparation method, product and application of bimetallic MOF catalyst

Abstract

The invention relates to the technical field of preparation of high-added-value chemicals through chemical catalysis of catalysts, in particular to a preparation method, a product and application of a bimetallic MOF catalyst. The preparation method comprises the following steps: uniformly mixing zircon salt, tin salt, an organic ligand and an organic solvent to obtain a mixed solution; and heating the mixed solution for reaction to obtain a reaction solution, washing, carrying out solid-liquid separation, and drying the obtained solid to obtain the bimetallic MOF catalyst. The method is easy to operate and low in cost, is close to conditions of large-scale production and application, and has important practical value. The bimetallic MOF catalyst prepared by using the method disclosed by the invention enhances the Lewis acidity of the catalyst, effectively promotes isomerization conversion from xylose to xylulose and reverse aldol condensation from xylulose to a C3 intermediate product in a cascade reaction process, and improves the selectivity of a main reaction path for preparing lactic acid from biomass; and efficient catalytic conversion from biomass to lactic acid is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing high value-added chemicals by chemical catalysis of catalysts, and in particular to a preparation method, product and application of a bimetallic MOF catalyst. Background Art

[0002] Among various green and sustainable resources, biomass resources have attracted extensive attention from scholars due to their rich reserves, renewability, and carbon neutrality. At present, the main ways to utilize biomass are direct combustion for heating, anaerobic fermentation to synthesize biogas for power generation, and production of bio-liquid fuels. In recent years, the production of high-value-added chemicals using biomass as raw materials has become a hot topic of research and attention. Converting "carbon source material" biomass into high-value-added chemicals can not only get rid of excessive dependence on traditional fossil energy, but also reduce environmental pollution problems caused by fossil energy utilization and accumulation of waste biomass. It has huge market potential and has far-reaching significance for balancing the relationship between energy utilization and environmental pollution. It is an important direction for future global research.

[0003] Because biomass itself contains abundant oxygen-containing functional groups, directly converting it into oxygen-containing high-value-added chemicals has become one of the important research directions for biomass resource utilization, especially the production of high-value-added chemical lactic acid with 100% atom economy. At present, lactic acid has been widely used in food, cosmetics, chemical industry and other fields. One of the most important applications is the synthesis of biodegradable plastic polylactic acid. At present, the production of lactic acid is mainly based on microbial fermentation, but this technology has problems such as complex process, high cost, high energy consumption and production cannot meet demand continuously. The use of catalyst hydrothermal catalysis to prepare lactic acid from biomass has bottleneck problems such as difficulty in controlling the directional reaction path and low yield of the target product. Therefore, it is of great significance to develop specific catalysts to achieve efficient catalytic conversion of biomass to lactic acid.

[0004] Previous studies have shown that the design of specific catalysts can achieve the conversion of biomass into high-purity, high-value-added chemicals. Among them, the catalytic production of lactic acid from biomass is mainly carried out under the action of Lewis acidic catalysts. Lewis acids can promote the key reaction steps such as isomerization and retro-aldol condensation, thereby strengthening the main reaction path and achieving efficient conversion of biomass to lactic acid. Therefore, the development of Lewis acidic catalysts to control the reaction direction has become a key research issue. Summary of the invention

[0005] The purpose of the present invention is to provide a preparation method, product and application of a bimetallic MOF catalyst, aiming to improve the selectivity of the main reaction pathway for preparing lactic acid from biomass and achieve efficient conversion of biomass into lactic acid.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is a method for preparing a bimetallic MOF catalyst, comprising the following steps:

[0008] The zirconium salt, the tin salt, the organic ligand and the organic solvent are uniformly mixed to obtain a mixed solution;

[0009] The mixed solution is heated for reaction to obtain a reaction solution, which is then washed, solid-liquid separated, and the obtained solid is dried to obtain the bimetallic MOF catalyst.

[0010] The second technical solution of the present invention is to prepare a bimetallic MOF catalyst (UIO-66 (Zr x Sn 1-x )).

[0011] The third technical solution of the present invention is the use of the above-mentioned bimetallic MOF catalyst in catalyzing the preparation of lactic acid from biomass.

[0012] A fourth technical solution of the present invention is a method for catalyzing biomass to prepare lactic acid, comprising mixing the above-mentioned bimetallic MOF catalyst with biomass and water to carry out a hydrothermal reaction to produce lactic acid.

[0013] The present invention introduces metal substance Sn with Lewis acidity by element replacement method, so as to further enhance the Lewis acidity of the catalyst. x Sn 1-x ) bimetallic MOF catalyst is introduced into the catalytic reaction system, the UIO-66 (Zr x Sn 1-x ) Bimetallic MOF catalysts can effectively promote the isomerization of xylose to xylulose and the retro-aldol condensation of xylulose to C3 intermediates during the cascade reaction, improve the selectivity of the main reaction pathway for biomass preparation of lactic acid, and thus achieve efficient catalytic conversion of biomass to lactic acid.

[0014] The present invention discloses the following technical effects:

[0015] The present invention provides a heterogeneous catalyst——UIO-66(Zr x Sn 1-x ) A method for preparing a bimetallic MOF catalyst, which is easy to operate, low in cost, and close to the conditions for large-scale production applications, has important practical value.

[0016] UIO-66 (Zr x Sn 1-x) The bimetallic MOF catalyst enhances the Lewis acidity of the catalyst, effectively promotes the isomerization conversion of xylose to xylulose during the cascade reaction, improves the selectivity of the main reaction pathway for preparing lactic acid from biomass, and realizes the efficient catalytic conversion of biomass to lactic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 This is a process flow chart for preparing a bimetallic MOF catalyst according to Example 1 of the present invention.

[0019] Figure 2 UIO-66 catalyst and UIO-66(Zr 0.9 Sn 0.1 ) Py-IR pattern of the bimetallic MOF catalyst.

[0020] Figure 3 UIO-66 catalyst and UIO-66(Zr 0.9 Sn 0.1 ) The conversion of xylose into key intermediates catalyzed by the bimetallic MOF catalyst changes with reaction time.

[0021] Figure 4 UIO-66 catalyst and UIO-66(Zr 0.9 Sn 0.1 ) Graph showing the selectivity of bimetallic MOF catalysts in preparing lactic acid from different actual biomasses. DETAILED DESCRIPTION

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0024] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0025] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0026] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0027] The first aspect of the present invention provides a method for preparing a bimetallic MOF catalyst, comprising the following steps:

[0028] The zirconium salt, the tin salt, the organic ligand and the organic solvent are uniformly mixed to obtain a mixed solution;

[0029] The mixed solution is heated for reaction to obtain a reaction solution, which is then washed, solid-liquid separated, and the obtained solid is dried to obtain the bimetallic MOF catalyst.

[0030] The present invention also attempts to first prepare a metal organic framework Zr-MOF by combining zirconium salt with an organic ligand, and then coordinate Zr-MOF with tin to prepare a catalyst with two active centers. The results show that the catalyst prepared by this method is not suitable for efficient and directional production of lactic acid by hydrothermal catalysis of biomass, which is caused by the added form of Sn.

[0031] In a preferred embodiment of the present invention, the zirconium salt is zirconium tetrachloride; the tin salt is stannous chloride; and the organic ligand is terephthalic acid.

[0032] In a preferred embodiment of the present invention, the molar ratio of the zirconium salt to the tin salt is 1:(0.05-0.3).

[0033] In a further preferred embodiment of the present invention, the molar ratio of the zirconium salt to the tin salt is 1:(0.1-0.25).

[0034] The reason why the molar ratio of zirconium salt to tin salt is limited to the above ratio range is as follows: too much or too little tin salt will cause the molar ratio of zirconium salt to tin salt to exceed the above ratio range, which will lead to a significant decrease in the production rate of lactic acid.

[0035] In a preferred embodiment of the present invention, the molar mass ratio of the zirconium salt to the organic ligand is (0.5-1) mol: (80-120) g.

[0036] In a preferred embodiment of the present invention, the organic solvent is N,N-dimethylformamide and / or anhydrous ethanol.

[0037] The amount of the organic solvent used is sufficient to fully immerse the zirconium salt, the tin salt and the organic ligand to allow them to react fully.

[0038] In some specific embodiments of the present invention, the mixing is uniformly achieved by oscillation ultrasound, with an oscillation rate of 160r / min-200r / min and an oscillation ultrasound time of 15min-30min; other commonly used mixing methods in the art are also applicable to the present invention, as long as the zirconium salt, tin salt, organic ligand and organic solvent can be uniformly mixed.

[0039] In a preferred embodiment of the present invention, the heating reaction temperature is 100°C-150°C, and the time is 18h-30h.

[0040] In a preferred embodiment of the present invention, the drying temperature is 60° C.-100° C., and the drying time is 8 h-15 h.

[0041] The washing is specifically performed by using the organic solvent for washing; the solid-liquid separation is specifically performed by using a centrifuge to centrifuge at a centrifugal speed of 6000r / min-10000r / min for 2min-15min to achieve solid-liquid separation.

[0042] The second aspect of the present invention provides a bimetallic MOF catalyst (UIO-66 (Zr x Sn 1-x )). (UIO-66(Zr x Sn 1-x ))The value range of x is 0.7-0.95.

[0043] A third aspect of the present invention provides an application of the bimetallic MOF catalyst in catalyzing the preparation of lactic acid from biomass.

[0044] A fourth aspect of the present invention provides a method for catalyzing biomass to prepare lactic acid, wherein the bimetallic MOF catalyst is mixed with biomass and water to undergo a hydrothermal reaction to produce lactic acid.

[0045] In some specific embodiments of the present invention, the mass ratio of the bimetallic MOF catalyst to the biomass is 1.5:1; the temperature of the hydrothermal reaction is 140-250°C, and the time is 0.5-5h. The biomass includes but is not limited to one or more of xylose, xylan, cellulose, reed, halophyte, cotton straw and tamarisk. The amount of water used is sufficient to fully immerse the bimetallic MOF catalyst and the biomass.

[0046] The present invention introduces Sn element by substitution method, enhances Lewis acidity of catalyst, effectively promotes xylose isomerization to xylulose and reverse aldol condensation of xylulose to C3 intermediate product in cascade reaction, improves selectivity of main reaction pathway for preparing lactic acid from biomass, and realizes efficient catalytic conversion of biomass to lactic acid. The method is easy to operate, low in cost, and close to conditions for large-scale production application, and has important practical value.

[0047] The process flow chart of preparing bimetallic MOF catalyst in Example 1 of the present invention is as follows Figure 1 shown.

[0048] The technical solutions described in the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0049] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0050] Example 1

[0051] A bimetallic MOF catalyst (UIO-66(Zr 0.9 Sn 0.1 )) preparation method, the steps are as follows:

[0052] Step 1: Weigh 0.612 mmol zirconium tetrachloride, 0.068 mmol stannous chloride and 102 mg terephthalic acid and measure 25 mL N,N-dimethylformamide solution, mix them and oscillate and ultrasonicate to form a uniform mixed solution.

[0053] Step 2: Place the above mixed solution in a hydrothermal reactor and heat at 120° C. for 24 h; after the reaction is completed, quickly cool to room temperature to obtain a reaction solution.

[0054] Step 3: Wash the reaction solution four times with N,N-dimethylformamide and anhydrous ethanol alternately, and centrifuge at 8000 r / min for 3 min to separate the solid and liquid.

[0055] Step 4: Dry the solid after solid-liquid separation at 80°C for 12 hours to obtain UIO-66(Zr0.9 Sn 0.1 ) Bimetallic MOF catalysts.

[0056] Example 2

[0057] UIO-66 (Zr) catalyst (abbreviated as: UiO-66 catalyst; preparation method: weigh 159 mg zirconium tetrachloride and 102 mg terephthalic acid, and 25 mL N, N-dimethylformamide solvent, put them into 100 mL polytetrafluoroethylene liner, install the hydrothermal reactor and place it in an oven to start heating, the reaction temperature is set to 120 ° C, constant temperature heating for 24 hours, after the reaction is completed, the hydrothermal reactor is naturally cooled to room temperature and then opened, the mixed solution is centrifuged at 8000 rpm for 3 minutes, the obtained white solid is washed with N, N-dimethylformamide and anhydrous ethanol for 3 times respectively, the solid is collected by centrifugation, and after washing, the solid is placed in an ordinary drying oven at 80 ° C for 12 hours to obtain a white solid UiO-66 catalyst) and UIO-66 (Zr 0.9 Sn 0.1 ) Changes in the reaction time of xylose conversion into key intermediates catalyzed by bimetallic MOF catalyst:

[0058] 150 mg of UIO-66 catalyst and UIO-66(Zr 0.9 Sn 0.1 ) The bimetallic MOF catalyst, 225 mg xylose and 10 mL deionized water were added into a 50 mL hydrothermal reactor and reacted at 190 °C for different time periods.

[0059] After the reaction was completed and cooled to room temperature, the solid and liquid were separated by centrifugation, and the liquid was analyzed by liquid chromatography to obtain the yield of the key intermediate product xylulose under different time conditions. The results are as follows: Figure 3 shown.

[0060] from Figure 3 It can be seen that UIO-66(Zr 0.9 Sn 0.1 ) bimetallic MOF catalyst had higher yields of xylulose and C3 intermediates than UIO-66 catalyst, and with the extension of reaction time, the yields of xylulose and C3 intermediates showed a trend of increasing first and then decreasing. The yield of xylulose reached a maximum of 12.73% at 60 min, and the yield of C3 intermediate reached a maximum of 1.74% at 80 min. By comparing the UIO-66 catalyst with the UIO-66(Zr 0.9 Sn 0.1 ) Py-IR spectrum of bimetallic MOF catalyst, such as Figure 2 As shown, UIO-66(Zr 0.9 Sn 0.1)The introduction of Sn element in the bimetallic MOF catalyst enhances the Lewis acidity of the catalyst and effectively promotes the isomerization of xylose to xylulose and the retro-aldol condensation of xylulose to C3 intermediates during the cascade reaction.

[0061] Example 3

[0062] UIO-66 catalyst and UIO-66(Zr 0.9 Sn 0.1 ) The selectivity effect of bimetallic MOF catalysts on the preparation of lactic acid from different actual biomasses.

[0063] 150 mg of UIO-66 catalyst and UIO-66(Zr 0.9 Sn 0.1 ) The bimetallic MOF catalyst, 100 mg of different actual biomass and 10 mL of deionized water were added into a 50 mL hydrothermal reactor and reacted at 240 °C for 1 h.

[0064] According to the formula, lactic acid selectivity (%) = (carbon moles of lactic acid in the reaction solution / carbon moles of TOC in the reaction solution) × 100%, calculate UIO-66 (Zr 0.9 Sn 0.1 ) The selectivity of lactic acid in hydrothermal catalysis of different actual biomass by bimetallic MOF catalysts. Figure 4 shown. Figure 4 It shows that the introduction of Sn can improve the catalytic activity of the catalyst in the hydrothermal catalysis of actual biomass (cotton straw, reed, halophyte, and willow), promote the directional selection of the main reaction pathway for biomass preparation of lactic acid, and achieve efficient directional conversion of biomass to lactic acid.

[0065] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a bimetallic MOF catalyst, characterized in that: The following steps are involved: The zirconium salt, the tin salt, the organic ligand and the organic solvent are uniformly mixed to obtain a mixed solution; The mixed solution is heated for reaction to obtain a reaction solution, which is then washed, solid-liquid separated, and the obtained solid is dried to obtain the bimetallic MOF catalyst.

2. The method for preparing a bimetallic MOF catalyst according to claim 1, characterized in that: The zirconium salt is zirconium tetrachloride; the tin salt is stannous chloride; and the organic ligand is terephthalic acid.

3. The method for preparing a bimetallic MOF catalyst according to claim 1, characterized in that: The molar ratio of the zirconium salt to the tin salt is 1:(0.05-0.3).

4. The method for preparing a bimetallic MOF catalyst according to claim 1, characterized in that: The molar mass ratio of the zirconium salt to the organic ligand is (0.5-1) mol: (80-120) g.

5. The method for preparing a bimetallic MOF catalyst according to claim 1, characterized in that: The organic solvent is N,N-dimethylformamide and / or anhydrous ethanol.

6. The method for preparing a bimetallic MOF catalyst according to claim 1, characterized in that: The heating reaction is carried out at a temperature of 100°C-150°C and for a time of 18h-30h.

7. The method for preparing a bimetallic MOF catalyst according to claim 1, characterized in that: The drying temperature is 60°C-100°C, and the drying time is 8h-15h.

8. The bimetallic MOF catalyst prepared according to the preparation method according to any one of claims 1 to 7.

9. Use of the bimetallic MOF catalyst as claimed in claim 8 in catalyzing the production of lactic acid from biomass.

10. A method for catalyzing biomass to prepare lactic acid, characterized in that: The bimetallic MOF catalyst according to claim 8 is mixed with biomass and water to carry out a hydrothermal reaction to produce lactic acid.

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