In-situ nitrogen-doped carbon-based loaded MOF (Metal Organic Framework) catalyst and preparation method and application thereof

Abstract

The invention discloses a preparation method of a two-enzyme method in-situ nitrogen-doped carbon-based loaded MOF (Metal Organic Framework) catalyst, which comprises the following steps: preparing starch into an aqueous solution, sequentially adding amylase and saccharifying enzyme, heating, keeping the temperature for a period of time to obtain enzyme-containing liquid glucose, and then carrying out hydrothermal treatment to prepare an in-situ nitrogen-doped carbon-based carrier; preparing an MOF catalyst precursor solution; carrying out hydrothermal treatment on the nitrogen-doped carbon-based carrier and the MOF catalyst precursor solution to prepare the nitrogen-doped carbon-based loaded MOF catalyst; and a good solution is provided for taking the low-cost modified hydrothermal carbon as a substitute of the carbon black.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical materials, and specifically relates to a dual-enzyme in-situ nitrogen-doped carbon-based supported MOF catalyst, its preparation method and application, mainly for modifying hydrothermal carbon as a carbon black substitute. Background Art

[0002] As an important industrial raw material, carbon black has good reinforcement, coloring and electrical conductivity properties, and is widely used in rubber and plastics and other applications. It is widely used for tire reinforcement in the rubber industry; while in plastics as a filler, it not only plays a role in coloring or color matching, but also has the functions of preventing ultraviolet aging, antistatic or conductive.

[0003] Currently, the conventional methods for producing carbon black in industry are furnace black, channel black, acetylene black and thermal black. These methods use synthetic hydrocarbons and natural gas as raw materials to produce carbon black by pyrolysis. However, this traditional production method requires a large amount of fossil fuels and large production equipment, and the carbon black raw materials account for nearly 60% of the total manufacturing cost. Therefore, the raw materials determine the market price of carbon black products. More than 90% of the world's carbon black is produced using fossil fuels as raw materials, either by furnace black production or by high-temperature pyrolysis of waste tires to produce high-quality carbon black.

[0004] Compared with traditional pyrolysis technology, hydrothermal carbonization has lower energy consumption and the raw materials do not need to be dried. Using biomass raw materials for hydrothermal carbonization can produce carbon black at low cost, which is the key link to reduce the production cost of carbon black. However, the hydrothermal carbon obtained by direct hydrothermal carbonization cannot meet the standards of commercial carbon black in terms of blackness, iodine adsorption value and oil absorption value, etc. (For example, the detection of Mitsubishi pigment carbon black #30 purchased: the blackness value is 42.00, the iodine adsorption value is 113.00 g / kg, and the oil absorption value is 103.00 cm 3 / 100 g), and further modification is required to be used as a carbon black substitute. Therefore, preparing a catalyst that can improve the yield, blackness, iodine adsorption value and oil absorption value of hydrothermal carbon is the focus of this field. Based on this, this application was developed. Summary of the Invention

[0005] Aiming at the deficiencies of the current hydrothermal carbon performance, in order to produce carbon black at low cost, the purpose of the present invention is to provide a dual-enzyme in-situ nitrogen-doped carbon-based supported MOF catalyst, which is a catalyst that can be used for preparing hydrothermal carbonization. Based on a large number of experiments and theoretical analyses, the present invention proposes a new type of in-situ nitrogen-doped carbon-based supported MOF catalyst, which uses the synergistic effect of metal active centers to improve the catalytic activity for hydrothermal carbon, and provides a solution for low-cost preparation of modified hydrothermal carbon as a carbon black substitute.

[0006] The present invention also provides a preparation method and application of the above-mentioned dual-enzyme in-situ nitrogen-doped carbon-based supported MOF catalyst.

[0007] To achieve the above-mentioned invention object, the present invention provides the following technical solutions: A preparation method of an in-situ nitrogen-doped carbon-based supported MOF catalyst, which prepares an aqueous solution of starch, sequentially adds amylase and glucoamylase, heats up and keeps warm for a period of time to obtain an enzyme-containing sugar solution, and then performs hydrothermal treatment to prepare an in-situ nitrogen-doped carbon-based support; prepares an MOF catalyst precursor solution; performs hydrothermal treatment on the nitrogen-doped carbon-based support and the MOF catalyst precursor solution to prepare a nitrogen-doped carbon-based supported MOF catalyst; specifically includes the following steps: 1) Preparation of the in-situ nitrogen-doped carbon-based support: Mix starch and water evenly, add amylase, heat up to 35-100 °C and keep warm for 10-180 minutes for enzymatic hydrolysis; then adjust the temperature to 55-65 °C, add glucoamylase and keep warm for 30-240 minutes to obtain an enzyme-containing sugar solution, and then transfer it to a hydrothermal reaction kettle for hydrothermal treatment at 180-300 °C for 2-12 h, perform solid-liquid separation and drying to obtain the in-situ nitrogen-doped carbon-based support; 2) Preparation of the MOF catalyst precursor solution: According to the type of the selected MOF catalyst, prepare its corresponding precursor solution. On the basis of a large number of experiments, the present invention preferably selects an MIL-100(Fe-Ni) type MOF catalyst, and takes this catalyst as an example for description. Specifically: Mix trimesic acid, N,N-dimethylformamide, FeCl3, and Ni(NO3)2·6H2O evenly to obtain an MOF catalyst precursor solution; 3) Preparation of the in-situ nitrogen-doped carbon-based supported MOF catalyst: Mix the in-situ nitrogen-doped carbon-based support obtained in step 1) and the MOF catalyst precursor solution obtained in step 2) evenly, and then perform hydrothermal treatment at 160-300 °C for 2-12 h. After the hydrothermal treatment is completed, wash and dry to obtain the in-situ nitrogen-doped carbon-based supported MOF catalyst.

[0008] Specifically, in step 1), starch and water are mixed according to a solid-liquid ratio of 1 g: 5-30 mL. Further, the starch is a commercially available common starch, such as at least one of wheat starch, corn starch, potato starch, sweet potato starch, cassava starch, etc.

[0009] Specifically, in step 1), the dosage of amylase is 10-50 U / g of starch, and the dosage of glucoamylase is 100-500 U / g of starch. The amylase is preferably α-amylase. As a preference, in step 1), the heating temperature is 50-80 °C, and the heat preservation time is 40-90 min; continue to raise or lower the temperature to 60-65 °C, and the heat preservation time is 120-180 min; the hydrothermal treatment temperature is 180-240 °C, and the residence time is 6-10 h; the drying temperature is 105 °C.

[0010] Specifically, in step 2), the molar ratio of FeCl3, Ni(NO3)2·6H2O and trimesic acid is 1:1:1 - 2. Further, in step 2), 0.5 - 3 mL of N,N-dimethylformamide is added for every 0.02 mmol of FeCl3.

[0011] Specifically, in step 3), the in-situ nitrogen-doped carbon-based support obtained in step 1) and the MOF catalyst precursor solution obtained in step 2) are mixed evenly at a solid-liquid ratio of 1 g:1 - 3 mL.

[0012] Preferably, in steps 1), 2), and 3), the mixing and stirring method is magnetic stirring, the rotation speed of the magnetic stirring is 300 - 400 rpm, and the stirring time is 1 - 2 h.

[0013] Preferably, in step 3), the drying method is vacuum drying, the drying temperature is 60 °C, and the drying time is 1 h.

[0014] The present invention provides an in-situ nitrogen-doped carbon-based supported MOF catalyst prepared by the above preparation method.

[0015] The present invention also provides the application of the above in-situ nitrogen-doped carbon-based supported MOF catalyst in the preparation of hydrothermal carbon.

[0016] The present invention also provides a preparation method of modified hydrothermal carbon. After mixing xylose residue, the above in-situ nitrogen-doped carbon-based supported MOF catalyst and water evenly according to a mass ratio of 1:0.03 - 0.08:3 - 6, hydrothermal treatment is carried out at 250 - 350 °C for 3 - 8 h, followed by washing and drying to obtain the product.

[0017] The present invention also provides modified hydrothermal carbon prepared by the above preparation method.

[0018] Metal-organic frameworks (MOFs) are porous materials formed by connecting organic ligands and metal atoms through coordination bonds, and they also have a high specific surface area and abundant active sites. Among them, metal centers such as Fe 3+ , Ni 2+ can promote the rearrangement and crystallization of carbon atoms, which is beneficial to the formation of graphite layered structures, improve the graphitization degree of hydrothermal carbon, and can effectively promote the hydrothermal carbonization reaction, thereby increasing the blackness, iodine adsorption value, and oil absorption value of hydrothermal carbon. The blackness value is measured using a blackness meter, and the measured blackness value is inversely proportional to the blackness, that is, the smaller the blackness value, the blacker the blackness. As important indicators for measuring the performance of traditional industrial carbon black, the iodine adsorption value and oil absorption value, the iodine adsorption value characterizes the specific surface area of carbon black and determines the reinforcing property and surface activity; the oil absorption value reflects the aggregate structure of carbon black and affects the processing performance and mechanical strength.

[0019] The preparation method of the modified hydrothermal carbon material of the present invention uses xylose residue as the raw material, adds the prepared nitrogen-doped carbon-based supported MOF catalyst, and realizes the low-energy consumption to obtain carbon black as its substitute by the hydrothermal carbonization method. The raw materials of this method are easily available, belonging to the high-value utilization of waste biomass, and the energy consumption is lower than that of traditional pyrolysis using the hydrothermal carbonization method. In addition, if the carbon black prepared after adding the MOF catalyst is used in the production of plastic films, the mechanical properties of the film can be improved and the service life of the film can be increased. Description of the Drawings

[0020] Figure 1 SEM image of the in-situ nitrogen-doped carbon-based support material prepared in Example 1; Figure 2 EDS image of the MIL-100(Fe-Ni) precursor solution prepared in Example 2; Figure 3 Thermogravimetric curve of the in-situ nitrogen-doped carbon-based supported MOF catalyst material prepared in Example 3; Figure 4 Infrared characterization image of the in-situ nitrogen-doped carbon-based supported MOF catalyst material prepared in Example 3. Detailed Description of the Invention

[0021] The technical solutions of the present invention will be further introduced in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

[0022] In the following embodiments, unless otherwise specified, the raw materials used are ordinary commercially available products that can be directly purchased, or can be prepared by conventional techniques in the art. For example, the enzyme activities of amylase and glucoamylase are 200,000 units and 100,000 units respectively, and both are purchased from Henan Tianguan Enterprise Group Co., Ltd.

[0023] Example 1: Preparation method of in-situ nitrogen-doped carbon-based support Weigh 2 g of wheat starch, add 12 mL of water, and magnetically stir at 400 rpm for 1.5 h to mix evenly to form a starch slurry; then add amylase according to the enzyme ratio activity of 20 U / g starch, stir evenly and heat to 50 °C and keep warm for 60 minutes; then add glucoamylase according to the enzyme ratio activity of 200 U / g starch, raise the temperature to 65 °C and keep warm for 180 minutes to form a uniform and transparent enzyme-containing sugar solution; then transfer it to a 150 mL hydrothermal reaction kettle and perform hydrothermal treatment at 200 °C for 10 h, filter and dry at 105 °C to obtain the in-situ nitrogen-doped carbon support.

[0024] Table 1 Elemental analysis data of the in-situ nitrogen-doped carbon-based support in Example 1 It can be seen from Table 1 that the N content of the in-situ nitrogen-doped carbon-based support prepared in Example 1 is 4.40%, indicating that the in-situ nitrogen-doped carbon-based support has been successfully prepared.

[0025] Figure 1 The SEM image of the in-situ nitrogen-doped carbon-based support material prepared in Example 1 is given. It can be seen from the figure that the pore structure of the in-situ nitrogen-doped carbon-based support material obtained in this invention is relatively developed and the particle size is relatively uniform.

[0026] Example 2: Preparation method of MIL-100(Fe-Ni) precursor.

[0027] Using trimesic acid as the organic ligand, N,N-dimethylformamide as the solvent, FeCl3 to provide Fe 3+ and Ni(NO3)2·6H2O to provide Ni. 2+ 0.24 mmol of FeCl3 (0.0389 g), 0.24 mmol of Ni(NO3)2·6H2O (0.0698 g) and 0.48 mmol of trimesic acid (0.1009 g) were added to 12 mL of N,N-dimethylformamide, and magnetically stirred at a rotation speed of 350 rpm for 1.5 h. The obtained light green solution is the MIL-100(Fe-Ni) precursor solution.

[0028] Figure 2 The EDS image of the MIL-100(Fe-Ni) precursor solution prepared in Example 2 is given. It can be seen from the figure that the actual Fe:Ni in the MIL-100(Fe-Ni) precursor solution prepared in Example 2 is 1:1, which is consistent with the target.

[0029] Example 3: Preparation method of in-situ nitrogen-doped carbon-based supported MOF catalyst.

[0030] The in-situ nitrogen-doped carbon support and the MIL-100(Fe-Ni) precursor solution were magnetically stirred at a rotation speed of 350 rpm for 1.5 h in a ratio of solid-liquid ratio of 1 g:2 mL to be mixed evenly, and then poured into a 150 mL hydrothermal reaction kettle and hydrothermally treated at 180 °C for 10 h to obtain the nitrogen-doped carbon-based supported MOF catalyst precursor; the hydrothermally treated solid was washed three times with deionized water and ethanol respectively, centrifuged, placed in a 60 °C vacuum drying oven and dried for 1 h, and ground into powder after natural cooling to obtain the in-situ nitrogen-doped carbon-based supported MOF catalyst.

[0031] Figure 3 The thermogravimetric curve of the in-situ nitrogen-doped carbon-based supported MOF catalyst material in Example 3 is given. It can be seen from the figure that the main decomposition peak of the prepared in-situ nitrogen-doped carbon-based supported MOF catalyst material is at 305 °C, indicating good thermal stability.

[0032] Figure 4 The infrared characterization diagram of the in-situ nitrogen-doped carbon-based supported MOF catalyst material in Example 3 is given. It can be seen from the figure that: a new functional group structure (Ni-O) is formed near 725 cm -1 and with the increase of the Ni doping ratio, the intensity gradually increases. This functional group structure will increase the structural stability of the material and improve the thermogravimetric characteristics.

[0033] Example 4: Preparation of modified hydrothermal carbon by in-situ nitrogen-doped carbon-based supported MOF catalyst.

[0034] Weigh 5.0 g of corncob residue (the corncob residue comes from Huakang Sugar Alcohol Technology Co., Ltd. in Jiaozuo City, which is the residue when producing xylose from corncob) and 0.25 g of in-situ nitrogen-doped carbon-based supported MOF catalyst, place them in 20 mL of deionized water and stir evenly. Pour the mixed solution into a hydrothermal autoclave, adjust the rotation speed of the magnetic stirrer to 270 rpm, and carry out hydrothermal treatment at a hydrothermal temperature of 300 °C for 6 h. After the reaction is completed, filter, wash the obtained solid with deionized water and ethanol three times each, filter, and dry in an oven at 105 °C for 12 h to obtain the modified hydrothermal carbon.

[0035] Comparative example: Preparation of hydrothermal carbon without adding in-situ nitrogen-doped carbon-based supported MOF catalyst.

[0036] Weigh 5.0 g of corncob residue, place it in 20 mL of deionized water and stir evenly. Pour the mixed solution into a hydrothermal autoclave, adjust the rotation speed of the magnetic stirrer to 270 rpm, and carry out hydrothermal treatment at a hydrothermal temperature of 300 °C for 6 h. After the reaction is completed, filter, wash the obtained solid with deionized water and ethanol three times each, and dry in an oven at 105 °C for 12 h to obtain the initial hydrothermal carbon.

[0037] Table 2 Data comparison of the prepared modified hydrothermal carbon and initial hydrothermal carbon The present invention respectively tested the yield, blackness value, iodine absorption value, oil absorption value and other related indexes of the modified hydrothermal carbon prepared in Example 4 and the initial hydrothermal carbon prepared in the comparative example. The results are shown in Table 2. The yield is used to evaluate the ability of the raw material corncob residue to produce hydrothermal carbon. In the application of carbon black coloring, choosing carbon black with high blackness can reduce the dosage and lower the cost. In rubber reinforcement, a high iodine absorption value can significantly improve the tensile strength and wear resistance of the material; a high oil absorption value indicates a complex aggregate structure and can increase the modulus in rubber.

[0038] Through experimental tests, the yield, blackness value, iodine absorption value, and oil absorption value of the modified hydrothermal carbon prepared after adding the in-situ nitrogen-doped carbon-based supported MOF catalyst are 49.34%, 41.33, 113.64 g / kg, and 221 cm 3 / 100 g, which are increased by 7.28%, 103%, 62.54% and 52.38% respectively compared with the hydrothermal carbon without catalyst. Compared with the data indexes of Mitsubishi pigment carbon black #30, the blackness value and iodine adsorption value of the modified hydrothermal carbon of the present invention are comparable, but the oil absorption value is more than twice that of commercial #30 pigment carbon black.

Claims

1. A preparation method of an in-situ nitrogen-doped carbon-based supported MOF catalyst, characterized in that, It includes the following steps: 1) Mix starch and water evenly, add amylase, heat up to 35 - 100 °C and keep warm for 10 - 180 minutes for enzymatic hydrolysis; then adjust the temperature to 55 - 65 °C, add glucoamylase and keep warm for 30 - 240 minutes to obtain an enzyme-containing sugar solution, and then conduct hydrothermal treatment at 180 - 300 °C for 2 - 12 h, followed by solid-liquid separation and drying to obtain an in-situ nitrogen-doped carbon-based support; 2) Mix trimellitic acid, N,N-dimethylformamide, FeCl3, and Ni(NO3)2·6H2O evenly to obtain a MOF catalyst precursor solution; 3) Mix the in-situ nitrogen-doped carbon-based support obtained in step 1) and the MOF catalyst precursor solution obtained in step 2) evenly, and then conduct hydrothermal treatment at 160 - 300 °C for 2 - 12 h. After the hydrothermal treatment is completed, wash and dry to obtain the product.

2. The preparation method of the in-situ nitrogen-doped carbon-based supported MOF catalyst according to claim 1, characterized in that, In step 1), starch and water are mixed according to a solid-liquid ratio of 1 g : 5 - 30 mL.

3. The preparation method of the in-situ nitrogen-doped carbon-based supported MOF catalyst according to claim 2, characterized in that, The starch is at least one of wheat starch, corn starch, potato starch, sweet potato starch, and cassava starch.

4. The preparation method of the in-situ nitrogen-doped carbon-based supported MOF catalyst according to claim 1, wherein, In step 1), the dosage of amylase is 10 - 50 U / g starch, and the dosage of glucoamylase is 100 - 500 U / g starch.

5. The preparation method of the in-situ nitrogen-doped carbon-based supported MOF catalyst according to claim 1, wherein, In step 2), the molar ratio of FeCl3, Ni(NO3)2·6H2O, and trimellitic acid is 1 : 1 : 1 - 2; for every 0.02 mmol of FeCl3, 0.5 - 3 mL of N,N-dimethylformamide is added.

6. The preparation method of the in-situ nitrogen-doped carbon-based supported MOF catalyst according to claim 1, characterized in that, In step 3), the in-situ nitrogen-doped carbon-based support obtained in step 1) and the MOF catalyst precursor solution obtained in step 2) are mixed evenly according to a solid-liquid ratio of 1 g : 1 - 3 mL.

7. An in-situ nitrogen-doped carbon-based supported MOF catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the in-situ nitrogen-doped carbon-based supported MOF catalyst according to claim 7 in the preparation of hydrochar.

9. A preparation method of modified hydrothermal carbon, characterized in that, Mix xylose residue, the in-situ nitrogen-doped carbon-based supported MOF catalyst according to claim 8, and water evenly according to a mass ratio of 1 : 0.03 - 0.08 : 3 - 6, and then conduct hydrothermal treatment at 250 - 350 °C for 3 - 8 h, followed by washing and drying to obtain the product.

10. A modified hydrochar prepared by the preparation method according to claim 9.

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