Protective catalyst and preparation method thereof

Abstract

The invention discloses a protection catalyst and a preparation method thereof, and relates to the field of protection catalysts, and the preparation method comprises the following steps: taking aluminum hydroxide, nickel-loaded carbon nanotubes, nickel salt and a solvent, carrying out mixing extrusion molding, and then carrying out high-temperature calcination; the nickel-loaded carbon nano tube is obtained by performing plasma modification on a carbon nano tube to obtain a plasma modified carbon nano tube and loading a nickel element on the plasma modified carbon nano tube. According to the preparation method, part of nickel is loaded by adopting the carbon nanotubes subjected to plasma treatment, and then the aluminum hydroxide, the nickel-loaded carbon nanotubes and the nickel salt are mixed, extruded and calcined, so that on one hand, the combination effect of the carrier and the nickel active component is improved, and on the other hand, the specific surface area of the protection catalyst is increased; when the catalyst is matched with a main catalyst for use, the overall catalytic efficiency and catalytic stability are improved.

Description

Technical Field

[0001] The present application relates to the field of protecting catalysts, and in particular to a protecting catalyst and a preparation method thereof. Background Art

[0002] Protecting catalysts are commonly used in the secondary reforming furnace for converting gaseous hydrocarbons to protect the main catalyst, and at the same time catalyze the reaction of gaseous hydrocarbons and water to convert them into carbon dioxide and hydrogen. At the same time, it has good applications both in the recovery and utilization of gaseous hydrocarbons in production tail gas and in the production of hydrogen.

[0003] Currently, protecting catalysts include a carrier and an active metal component. The commonly used carrier is alumina, and the active metal components are nickel element and rare earth elements, etc. The active metal component is loaded on the carrier by impregnation or mixing extrusion. In the secondary reforming furnace, to improve the protection effect of the protecting catalyst on the main catalyst, the specific surface area of the protecting catalyst is controlled to be smaller than that of the main catalyst to cope with the gas flow erosion.

[0004] However, by using the mixing extrusion method, the specific surface area of the protecting catalyst will decrease under external pressure. If the specific surface area is too low, the catalytic effect of the protecting catalyst itself will be weakened. The content of the active metal component loaded by impregnation is limited, and the binding effect between the active metal component and the carrier is weak, which makes the active metal component easy to sinter and agglomerate, reducing the active sites and the catalytic effect of the protecting catalyst itself. Moreover, if the specific surface area of the protecting catalyst is too high, the anti-gas flow erosion ability will be reduced, resulting in a poor protection effect on the main catalyst. Summary of the Invention

[0005] In view of the above deficiencies in the related art, the purpose of the present application is to provide a protecting catalyst and a preparation method thereof. By using carbon nanotubes treated by plasma to load part of nickel, and then mixing and extruding aluminum hydroxide, nickel-loaded carbon nanotubes and nickel salt and calcining them, on the one hand, the binding effect between the carrier and the nickel active component is improved, and on the other hand, the specific surface area of the protecting catalyst is controlled to be of a suitable size, and when used in combination with the main catalyst, the overall catalytic efficiency and catalytic stability are improved.

[0006] In the first aspect, a preparation method of a protecting catalyst provided by the present application adopts the following technical solution: A preparation method of a protecting catalyst includes the following steps: taking aluminum hydroxide, nickel-loaded carbon nanotubes, nickel salt and a solvent, mixing and extruding them into a shape, and then calcining at a high temperature; the nickel-loaded carbon nanotubes are obtained by including subjecting carbon nanotubes to plasma modification to obtain plasma-modified carbon nanotubes, and loading nickel element on the plasma-modified carbon nanotubes.

[0007] Preferably, the plasma modification includes the following steps: subjecting the carbon nanotubes to alkali treatment, and then treating them in a plasma atmosphere obtained by ionizing an oxidizing gas to obtain plasma-modified carbon nanotubes.

[0008] Preferably, the oxidizing gas includes oxygen.

[0009] Preferably, the gas flow rate of the plasma modification is 6-9 mL / min, the ionization voltage is 90-110 V, and the treatment time is 15-25 min.

[0010] Preferably, the gas flow rate of the plasma modification is 8 mL / min, the ionization voltage is 100 V, and the treatment time is 20 min.

[0011] Preferably, loading nickel elements on the plasma-modified carbon nanotubes includes the following steps: mixing the plasma-modified carbon nanotubes, nickel chloride, and water evenly, and then performing evaporation and calcination to obtain nickel-loaded carbon nanotubes.

[0012] Preferably, the weight ratio of the plasma-modified carbon nanotubes to the nickel chloride is 50:5-9.

[0013] Preferably, the weight ratio of the plasma-modified carbon nanotubes to the nickel chloride is 50:7.

[0014] Preferably, the temperature condition of the calcination is 300-330 °C, and the time is 2-4 h.

[0015] Preferably, the temperature condition of the calcination is 320 °C, and the time is 3 h.

[0016] Preferably, the weight ratio of the aluminum hydroxide, nickel-loaded carbon nanotubes, and nickel salt is 20:3-7:0.4-1.2.

[0017] Preferably, the weight ratio of the aluminum hydroxide, nickel-loaded carbon nanotubes, and nickel salt is 10:2.5:0.4.

[0018] Preferably, the temperature condition of the high-temperature calcination is 950-1000 °C, and the time is 4.5-6 h.

[0019] Preferably, the temperature condition of the high-temperature calcination is 980 °C, and the time is 5 h.

[0020] Preferably, the nickel salt includes one or more of nickel chloride, nickel nitrate, nickel sulfate, and nickel carbonate.

[0021] Preferably, the nickel salt is nickel carbonate.

[0022] On the other hand, the present application provides a catalyst protection method adopting the following technical solution: A protected catalyst is prepared by the above-mentioned method for preparing the protected catalyst.

[0023] In summary, the present application includes at least one of the following beneficial technical effects: 1. Part of the nickel is loaded by using carbon nanotubes treated with plasma, and then aluminum hydroxide, nickel-loaded carbon nanotubes and nickel salts are mixed, extruded and calcined. On the one hand, the tubular structure of nickel-loaded carbon nanotubes has a strong carrying capacity. The protected catalyst obtained after extrusion and calcination not only improves the carrying strength of the protected catalyst, but also improves the ability of the protected catalyst to resist airflow scouring, thereby protecting the main catalyst. On the basis of mixed extrusion, the specific surface area of the protected catalyst is appropriately increased, and the catalytic efficiency is improved. On the other hand, the combination effect of the carrier and the active metal nickel is improved, and the negative effect of reduced catalytic efficiency caused by the reduction of active sites due to the agglomeration of active metals is minimized. Under the combined effect, it is beneficial to improve the protection effect of the main catalyst, and improve the overall catalytic efficiency and catalytic stability when the main catalyst and the protective catalyst are used together; 2. The present application treats carbon nanotubes with alkali and then with oxygen plasma, which, on the one hand, increases the specific surface area of the carbon nanotubes, and on the other hand, forms oxygen-containing groups such as carboxyl groups on the surface of the carbon nanotubes, which are beneficial to the binding of the active metal component nickel ions. Under the combined effect, the content and adhesion effect of the active metal component nickel on the carbon nanotubes are increased, thereby increasing the content and stability of the active metal component nickel in the protected catalyst; 3. The nickel-loaded carbon nanotubes of the present application also act as a pore expander in the protective catalyst. When aluminum hydroxide, nickel-loaded carbon nanotubes and nickel salts are mixed and extruded, it is beneficial to appropriately increase the overall specific surface area of the protective catalyst. At the same time, the active metal nickel and nickel salts loaded on the carbon nanotubes are calcined at high temperature, and the active metal components exist in the carbon nanotubes and alumina structures respectively, thereby improving the uniformity and stability of the distribution of the active metal component nickel in the protective catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a comparison diagram of the conversion rate-time curve of methane conversion in Example 1 and Example 8 in combination with the main catalyst; Figure 2 This is a comparison chart of the conversion rate-time curves of methane converted by using the main catalyst in Examples 1-5. DETAILED DESCRIPTION

[0025] The present application will be further described in detail below in conjunction with embodiments. The following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those conditions not specified in the following embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. The methods used, unless otherwise specified, are all conventional methods well-known in the art, and the consumables and reagents used, unless otherwise specified, are all commercially available. Unless otherwise stated, the professional and scientific terms used herein have the same meaning as those familiar to skilled personnel in the art. In addition, any method or material similar or equivalent to the described content can also be applied to the present invention.

[0026] The raw materials used in the examples and comparative examples are all commercially available.

[0027] Example 1

[0028] Example 1 of the present application provides a protective catalyst, which is prepared by the following steps: (1) Add 3.2 g of potassium hydroxide and 0.8 g of carbon nanotubes to 16 mL of ultrapure water, stir well, and then place it in a constant temperature oil bath at 120 °C to evaporate to dryness. Transfer the remaining solid to a tubular furnace, and under an argon atmosphere, heat it to 800 °C at a heating rate of 30 °C / min, keep the temperature constant and calcine for 1 h. Finally, add the calcined product to ultrapure water and dropwise add 1 mol / L hydrochloric acid to neutralize it. Rinse it repeatedly with ultrapure water until it is neutral, then dry and grind it to obtain alkali-treated carbon nanotubes. Take the alkali-treated carbon nanotubes and place them in a DBD discharge reactor, introduce oxygen at a flow rate of 8 mL / min, control the output voltage to 100 V, and the treatment time to 20 min. Stir the alkali-treated carbon nanotubes evenly three times during the reaction to obtain plasma-modified carbon nanotubes.

[0029] (2) Mix 5 g of plasma-modified carbon nanotubes, 100 mL of ammonia water (concentration 1 mol / L), and 7 mL of nickel chloride solution (concentration 0.1 g / mL), stir for 10 h, and then place it in a constant temperature oil bath at 60 °C to evaporate to dryness for 5 h. Then dry it in an oven at 80 °C to obtain a mixed powder. Put the mixed powder into a tubular furnace, and under an argon atmosphere, calcine it at 320 °C for 3 h to obtain nickel-loaded carbon nanotubes.

[0030] (3) Take 10 g of aluminum hydroxide, 2.5 g of nickel-loaded carbon nanotubes, 0.4 g of nickel carbonate, and 1 mL of acetic acid solution (4 wt%), mix them and extrude them into a cylindrical mixture. Dry it at 100 °C for 2 h, and then place it in a high-temperature furnace at 980 °C for 5 h to obtain a protective catalyst.

[0031] In this example, the carbon nanotubes are multi-walled carbon nanotubes with a length of 0.5 - 2 μm and a diameter of 30 - 50 nm.

[0032] Example 2

[0033] Example 2 of this application provides a protective catalyst. The difference between Example 2 and Example 1 is that in step (3) of Example 2, 1.5 g of nickel-loaded carbon nanotubes and 0.6 g of nickel carbonate are used.

[0034] Example 3

[0035] Example 3 of this application provides a protective catalyst. The difference between Example 3 and Example 1 is that in step (3) of Example 3, 3.5 g of nickel-loaded carbon nanotubes and 0.2 g of nickel carbonate are used.

[0036] Example 4

[0037] Example 4 of this application provides a protective catalyst. The difference between Example 4 and Example 1 is that in step (2) of Example 4, 5 mL of nickel chloride solution is used.

[0038] Example 5

[0039] Example 5 of this application provides a protective catalyst. The difference between Example 5 and Example 1 is that in step (2) of Example 5, 9 mL of nickel chloride solution is used.

[0040] Example 6

[0041] Example 6 of this application provides a protective catalyst. The difference between Example 6 and Example 1 is that in step (1) of Example 6, when plasma treatment is carried out, the treatment time is 25 min.

[0042] Example 7

[0043] Example 7 of this application provides a protective catalyst. The difference between Example 7 and Example 1 is that in step (1) of Example 7, when plasma treatment is carried out, the treatment time is 15 min.

[0044] Example 8

[0045] Example 8 of this application provides a protective catalyst. The difference between Example 8 and Example 1 is that in step (1) of Example 8, the carbon nanotubes are not subjected to alkali treatment. The carbon nanotubes are placed in a DBD discharge reactor, oxygen is introduced at a flow rate of 8 mL / min, the output voltage is controlled to be 100 V, the treatment time is 20 min, and the carbon nanotubes are stirred evenly three times during the reaction process to obtain plasma-modified carbon nanotubes.

[0046] Comparative Example 1

[0047] Comparative Example 1 provides a protective catalyst, which is prepared by the following steps: Take 10 g of aluminum hydroxide, 0.4 g of nickel carbonate and 10 mL of acetic acid solution (4 w%) and mix them, then extrude them into a cylindrical mixture, dry it at 100 °C for 2 h, and then place it at 980 °C for high-temperature calcination for 5 h to obtain the protective catalyst.

[0048] Comparative Example 2

[0049] Comparative Example 2 provides a protective catalyst, which is prepared by the following steps: Take 10 g of aluminum hydroxide, 2.5 g of carbon nanotubes, 0.4 g of nickel carbonate and 10 mL of acetic acid solution (4 w%) and mix them, then extrude them into a cylindrical mixture, dry it at 100 °C for 2 h, and then place it at 980 °C for high-temperature calcination for 5 h to obtain the protective catalyst.

[0050] Comparative Example 3

[0051] Comparative Example 3 provides a protective catalyst. The difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, only the carbon nanotubes are treated in step (1), the loading of the active metal nickel in step (2) is not carried out, and the obtained plasma-modified carbon nanotubes are used to replace the nickel-loaded carbon nanotubes in step (3).

[0052] Comparative Example 4

[0053] Comparative Example 4 provides a protective catalyst. The difference between Comparative Example 4 and Example 1 is that in step (1) of Comparative Example 4, argon is used instead of oxygen for plasma treatment.

[0054] Comparative Example 5

[0055] Comparative Example 5 provides a protective catalyst. The difference between Comparative Example 5 and Example 1 is that in step (1) of Comparative Example 5, hydrogen is used instead of oxygen for plasma treatment.

[0056] Test detection

[0057] (1) Respectively detect the specific surface area (m 2 / g) and pore volume (cm 3 / g) of the protective catalysts obtained in Examples 1-8 and Comparative Examples 1-5, as shown in Table 1 below.

[0058] Table 1: Data source <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Example 1 534.7 0.76 Example 2 513.4 0.74 Example 3 543.3 0.78 Example 4 526.9 0.74 Example 5 531.5 0.75 Example 6 528.1 0.73 Example 7 521.8 0.76 Example 8 506.6 0.71 Comparative Example 1 317.9 0.48 Comparative Example 2 486.2 0.65 Comparative Example 3 493.5 0.67 Comparative Example 4 508.4 0.71 Comparative Example 5 505.7 0.70 (2) Mix the protective catalysts of Examples 1-8 and Comparative Examples 1-5 with the main catalyst HZ204 type protective catalyst (Hubei Huihuang Technology Co., Ltd., specific surface area 573.5 m 2 / g) It is used in the top of the secondary methane reformer, with a pressure of 3.2 MPa, a controlled temperature of 850 - 960 °C, and a space velocity of 3000 h -1 , and the reaction lasts for 20 h. The conversion rate of methane is detected. The comparison graphs of the conversion rate - time change curves of Example 1 and Example 8 are as shown in Figure 1 , and the comparison graphs of the conversion rate - time change curves of Comparative Examples 1 - 5 are as shown in Figure 2 . After the reaction ends, the specific surface areas (m 2 / g) of the protective catalyst and the main catalyst of Examples 1 - 8 and Comparative Examples 1 - 5 are detected respectively, as shown in Table 2 below.

[0059] Table 2: Data source <![CDATA[Specific surface area of the protected catalyst (m 2 / g)]]> <![CDATA[Specific surface area of the main catalyst (m 2 / g)]]> Example 1 533.1 569.8 Example 2 511.5 567.5 Example 3 541.2 566.3 Example 4 525.1 567.8 Example 5 529.6 567.1 Example 6 525.7 566.7 Example 7 519.4 565.6 Example 8 503.2 561.4 Comparative Example 1 261.3 497.9 Comparative Example 2 452.6 522.4 Comparative Example 3 467.9 534.5 Comparative Example 4 489.4 541.7 Comparative Example 5 483.3 543.8 Result Analysis

[0060] The following will elaborate on this application in detail in combination with Figure 1-2 , the data results in Table 1 and Table 2.

[0061] Referring to Figure 1 and Figure 2 , when Example 1, Example 8, and Comparative Examples 1 - 5 are respectively combined with the main catalyst to convert methane, as the reaction time increases, the methane conversion rate in the systems using Comparative Examples 1 - 5 as the protective catalyst decreases significantly. The decrease ratio reaches 3.7 - 5.9% in 200 h, while the methane conversion rate in the systems using Example 1 and Example 8 as the protective catalyst only decreases by 0.9 - 1.2%, and the decrease amount of the conversion rate is less than one - third of that in the comparative example system. It shows that the protective catalysts of Examples 1 - 8 of this application are beneficial to improving the catalytic stability of the reaction system when combined with the main catalyst. The analysis is that, on the one hand, the addition of nickel - supported carbon nanotubes improves the uniform dispersion degree of the metal active components in the protective catalyst. At the same time, during the preparation process of the nickel - supported carbon nanotubes, amorphous carbon and impurities are removed through alkali treatment, increasing its specific surface area. Oxygen plasma treatment forms oxygen - containing functional groups on the surface of the carbon nanotubes, enhancing the interaction between the metal active component nickel and the carbon nanotubes. Under the combined action, the binding effect between the carbon nanotubes and the metal active component nickel is improved from both the binding strength and the binding range. On the other hand, while the nickel - supported carbon nanotubes play a role in pore expansion, they also play a role in strengthening the structure of the protective catalyst, improving the resistance to gas flow erosion during the reaction process, thereby protecting the main catalyst. Under the combined action, the loss of active sites caused by the agglomeration of active metal components in the reaction system is reduced, the service life of the main catalyst is extended, and the catalytic stability is improved. And the decrease amount of the conversion rate in the system when Example 1 is combined with the main catalyst is lower than that in the system when Example 8 is combined with the main catalyst, indicating that alkali treatment of the carbon nanotubes followed by oxygen plasma treatment is beneficial to further improving the catalytic stability of the reaction system.

[0062] Referring to Table 1 and Table 2, it can be seen that the specific surface areas of the protective catalysts in Examples 1-8 are slightly smaller than those of the main catalysts used in combination, which is beneficial to maintaining the stability of the specific surface area of the protective catalyst in a high-temperature environment and protecting the main catalyst. At the same time, compared with the protective catalysts in Comparative Examples 1-5, the specific surface area has increased, thereby improving the catalytic efficiency of the protective catalyst itself. The decrease in the specific surface area after the conversion of methane by the combination of the main catalyst in Examples 1-8 is much lower than that in Comparative Examples 1-5. Moreover, the decrease ratio of the specific surface area of the main catalyst combined with Examples 1-8 is only 0.41%-1.58%, which is much lower than the 3.52%-7.39% of the decrease ratio of the specific surface area of the main catalyst combined with Comparative Examples 1-5, indicating that when Examples 1-8 are used in combination with the main catalyst, it is beneficial to maintain the stability of the specific surface area of the main catalyst, extend the service life of the main catalyst, and improve the catalytic efficiency. In addition, the change in the specific surface area of the protective catalyst in Examples 1-8 is smaller than that of the protective catalyst in Comparative Examples 1-5, and the degree of carbon deposition of the protective catalyst in Examples 1-8 of the present application is low. The protective catalyst in Examples 1-8 of the present application is also beneficial to reducing the degree of carbon deposition of itself and the main catalyst.

[0063] This specific embodiment is only an interpretation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A preparation method of a catalyst protector, characterized in that: It includes the following steps: Take aluminum hydroxide, nickel-loaded carbon nanotubes, nickel salt and a solvent, mix and extrude them into a mold, and then calcine at a high temperature; the nickel-loaded carbon nanotubes are obtained by including plasma modification of carbon nanotubes to obtain plasma-modified carbon nanotubes, and loading nickel elements on the plasma-modified carbon nanotubes; The plasma modification includes the following steps: subject the carbon nanotubes to alkali treatment, and then place them in a plasma atmosphere obtained by ionizing an oxidizing gas for treatment to obtain plasma-modified carbon nanotubes.

2. The preparation method of a catalyst protection according to claim 1, characterized in that: The gas flow rate of the plasma modification is 6 - 9 mL / min, the ionization voltage is 90 - 110 V, and the treatment time is 15 - 25 min.

3. The preparation method of a catalyst protection according to claim 1, characterized in that: The step of loading nickel elements on the plasma-modified carbon nanotubes includes the following steps: uniformly mix the plasma-modified carbon nanotubes, nickel chloride and water, and then evaporate and calcine to obtain nickel-loaded carbon nanotubes.

4. The preparation method of a catalyst protection according to claim 3, characterized in that: The weight ratio of the plasma-modified carbon nanotubes to the nickel chloride is 50:5 - 9.

5. The preparation method of a catalyst protection according to claim 3, characterized in that: The temperature condition of the calcination is 300 - 330 °C, and the time is 2 - 4 h.

6. The preparation method of a catalyst protection according to claim 1, characterized in that: The weight ratio of the aluminum hydroxide, nickel-loaded carbon nanotubes and nickel salt is 20:3 - 7:0.4 - 1.

2.

7. The preparation method of a catalyst protection according to claim 1, characterized in that: The temperature condition of the high-temperature calcination is 950 - 1000 °C, and the time is 4.5 - 6 h.

8. A method for preparing a catalyst protection according to claim 1, characterized in that: The nickel salt includes one or more of nickel chloride, nickel nitrate, nickel sulfate and nickel carbonate.

9. A catalyst protection, characterized in that: It is prepared by the method for preparing a protective catalyst according to any one of claims 1 - 8.

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