Preparation Method and Application of a Low-Cost and High-Activity Ortho-Para Hydrogen Conversion Catalyst

Abstract

The present invention relates to a preparation method and application of a low-cost and highly active ortho-para hydrogen conversion catalyst. The preparation method includes: preparing a mixed solution of an iron source and an aluminum source, adding a precipitating agent, and stirring and reacting to obtain the ortho-para hydrogen conversion catalyst. Compared with the prior art, the catalyst prepared by the present invention is amorphous, has the characteristics of small nanoparticle size, uniform particle distribution, small pores, magnetic disorder and high activity, which is beneficial to the catalytic conversion of hydrogen molecules. At the same time, this scheme is simple and convenient, with low cost. The prepared catalyst has high hardness and does not require secondary granulation, having the advantages of industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen liquefaction, and relates to a preparation method and application of a low-cost and highly active ortho-para hydrogen conversion catalyst. Background Art

[0002] Liquid hydrogen has become one of the important ways for large-scale transportation and application of hydrogen energy due to its high volume and mass storage density.

[0003] Standard hydrogen is a mixture of two hydrogen molecules, ortho-hydrogen (75%) and para-hydrogen (25%). The equilibrium percentage between the two is only related to temperature. When hydrogen is liquefied as the temperature decreases, the high-energy ortho-hydrogen will spontaneously and slowly convert into the low-energy para-hydrogen, releasing a large amount of conversion heat (706 kJ / Kg at 30 K). This part of the conversion heat is much greater than the latent heat of vaporization of liquid hydrogen (447 kJ / Kg at 30 K). Therefore, it will cause the vaporization of liquid hydrogen and result in a large loss of liquid hydrogen. Data shows that the conversion heat released by standard liquid hydrogen in one day can evaporate 18% of the liquid hydrogen without heat leakage, and the loss will exceed 40% after 100 h. Therefore, during the low-temperature liquefaction process, a specific ortho-para hydrogen conversion catalyst is required to achieve the rapid conversion of ortho-hydrogen to para-hydrogen.

[0004] An excellent ortho-para hydrogen conversion catalyst should have the conditions of high activity, high mechanical strength, low bed resistance, long service life, simple preparation, and low price. In terms of activity, doping with heteroelements can enhance the magnetic disorder inside the catalyst, which is beneficial to the improvement of activity. Since the ortho-para hydrogen conversion is related to the magnetic moment of the catalyst, for improving the activity of the catalyst material, adding transition metal elements containing unpaired electrons is an important means of catalyst modification. However, for some transition metal elements that can be uniformly doped into iron oxides, their high prices limit their industrial applications. At the same time, element doping often leads to a reduction in the strength of the material, causing it to break under the erosion of the hydrogen gas flow. On the one hand, it reduces the service life of the catalyst; on the other hand, the smaller debris of the catalyst flows into the hydrogen liquefaction device with the hydrogen gas, which has a greater impact on the equipment, especially devices such as throttling expansion.

[0005] Chinese Patent CN112844443A discloses a catalyst for ortho-para hydrogen conversion used in a liquid hydrogen production and storage device and a preparation method thereof. In particular, it relates to a supported ortho-para hydrogen conversion catalyst prepared by impregnating, roasting and then shaping using an ordered mesoporous material as a carrier and a chemical precipitation method. Using an ordered mesoporous material as a carrier can effectively reduce the ineffective path for hydrogen molecules to enter the carrier, improve the adsorption rate of hydrogen molecules on the inner surface of the carrier, help reduce the flow resistance of the device, and increase the para-hydrogen conversion rate of the ortho-para hydrogen catalytic conversion reaction at different space velocities. Compared with the method of shaping first and then impregnating, impregnating, roasting and then shaping can increase the contact area between the carrier and the active substance, thereby increasing the active sites of the catalytic reaction and improving the ortho-para hydrogen catalytic conversion activity of the catalyst. The invention adopts a loading method. Since the carrier does not have catalytic performance, the number of active sites per unit volume of the catalyst will be reduced, that is, a larger space is required to fill the catalyst, which is not conducive to the practical application of the catalyst. At the same time, the connection strength between the loading material and the carrier is not high, resulting in the situation that the loading material falls off with the gas flow. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method and application of a low-cost and high-activity ortho-para hydrogen conversion catalyst, which has the characteristics of simple synthesis, low cost, and high catalytic activity.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A preparation method of an ortho-para hydrogen conversion catalyst, comprising:

[0009] Prepare a mixed solution of an iron source and an aluminum source, add a precipitating agent, and stir and react to obtain an ortho-para hydrogen conversion catalyst.

[0010] Further, in the mixed solution, the molar ratio of iron element to aluminum element is (8~12):1.

[0011] Further, the concentration of the iron source is 0.01~1 moL / L.

[0012] Further, the iron source is one or more of ferric nitrate, ferric chloride, ferric sulfate or iron acetylacetonate.

[0013] Further, the aluminum source is one or more of aluminum nitrate, aluminum chloride, aluminum sulfate or aluminum acetylacetonate.

[0014] Further, the precipitating agent is an alkaline solution.

[0015] Further, the precipitating agent is one or more of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate or sodium bicarbonate.

[0016] Further, add the precipitating agent until the pH of the solution is 2.8~11.

[0017] Further, in the stirring reaction, the reaction temperature is room temperature and the reaction time is 1 - 5 h.

[0018] The application of the catalyst prepared by the method as described above includes using the catalyst in the ortho - para hydrogen conversion reaction.

[0019] Compared with the prior art, the present invention has the following characteristics:

[0020] 1) The present invention uses iron and aluminum, which are rich in resources and low in price, as the main sources of the catalyst; a simple co - precipitation method is adopted to prepare a highly active catalyst. Its preparation process is simple, the yield is high, and the prepared catalyst is a hard block, and particles with a certain macroscopic size can be broken and screened according to the actual requirements of the device, which is simple and convenient and is conducive to industrial production.

[0021] 2) The present invention uses aluminum element, which has extremely low catalytic performance in the oxide state, as a doping element to prepare an amorphous aluminum - doped iron oxide catalyst. The aluminum element is directly doped into the iron oxide in the form of atoms, resulting in an increase in the paramagnetic defect active sites inside the catalyst, an enhancement of the magnetic disorder inside the catalyst, and an increase in activity; at the same time, the aluminum atom has an unpaired electron and has a certain magnetic moment, which is conducive to the occurrence of conversion.

[0022] 3) The catalyst prepared by the method adopted by the present invention has low nanoparticle size, small pores, a high degree of close packing between particles, and high mechanical strength, which is conducive to catalytic conversion. Description of the Drawings

[0023] Figure 1 XRD patterns of the ortho - para hydrogen conversion catalysts prepared in the examples and Comparative Examples 1 - 2;

[0024] Figure 2 XPS spectrum of Al 2p of the ortho - para hydrogen conversion catalyst Al - FO prepared in the example;

[0025] Figure 3 SEM images of the catalyst Al - FO (c, d) prepared in the example and the catalyst FO (a, b) prepared in Comparative Example 1;

[0026] Figure 4 Diagram of the para - hydrogen content after catalytic conversion of the catalyst Al - FO prepared in the example and the catalyst FO prepared in Comparative Example 1. Detailed Description of the Invention

[0027] The present invention will be described in detail below with reference to the drawings and specific examples.

[0028] A catalyst that can be used in the ortho - para hydrogen conversion reaction, and its preparation method includes:

[0029] Adding an iron source and an aluminum source into water, stirring for 10 - 30 min to mix them evenly, then adding a precipitant until the pH of the solution is 2.8 - 11, and then stirring and reacting at room temperature for 1 - 5 h to obtain an ortho - para hydrogen conversion catalyst;

[0030] Among them, in the mixed solution, the molar ratio of iron element to aluminum element is (8 - 12):1, preferably 10:1; the iron source concentration is 0.01 - 1 moL / L; the iron source is preferably one or more of iron nitrate, iron chloride, iron sulfate or iron acetylacetonate; the aluminum source is preferably one or more of aluminum nitrate, aluminum chloride, aluminum sulfate or aluminum acetylacetonate; the precipitant is an alkaline solution, and is preferably one or more of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate or sodium bicarbonate.

[0031] The catalyst prepared by the present invention is amorphous, having the characteristics of small nanoparticle size (10 - 30 nm), uniform particle distribution, small pores (pore size range is 0.5 - 5 nm), magnetic disorder and high activity, which is beneficial to the catalytic conversion of hydrogen molecules. At the same time, this scheme is simple and convenient, with low cost, the prepared catalyst has high hardness, does not require secondary granulation, and has the advantages of industrial production.

[0032] The following examples are implemented on the premise of the above technical solutions of the present invention, and give detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples.

[0033] Example 1

[0034] A highly efficient ortho - para hydrogen conversion catalyst of aluminum - iron oxide, and its preparation method includes:

[0035] Adding 8.08 g of ferric nitrate nonahydrate and 0.7502 g of aluminum nitrate nonahydrate into 500 mL of deionized water solvent, fully stirring for 20 min, then slowly dropping about 25 - 28% ammonia water (5 mL / min) until the pH value of the mixed solution is 10, and continuing to stir for 3 h. The obtained precipitate is filtered, washed and dried to finally obtain an Al - F2O3 highly efficient ortho - para hydrogen conversion catalyst, denoted as Al - FO.

[0036] Comparative Example 1:

[0037] A highly efficient ortho - para hydrogen conversion catalyst of iron oxide, and its preparation method includes:

[0038] 8.08 g of iron(III) nitrate nonahydrate was added to 500 mL of deionized water as a solvent. After stirring well for 20 min, approximately 25 - 28% ammonia water (5 mL / min) was slowly added dropwise until the pH value of the mixed solution reached 10. Stirring was continued for 3 h. The resulting precipitate was filtered, washed, and dried to finally obtain an F2O3 high-efficiency ortho-para hydrogen conversion catalyst, denoted as FO.

[0039] Comparative Example 2:

[0040] A manganese iron oxide ortho-para hydrogen conversion catalyst, and its preparation method includes:

[0041] 8.08 g of iron(III) nitrate nonahydrate and 0.3939 g of manganese(II) nitrate nonahydrate were added to 500 mL of deionized water as a solvent. After stirring well for 20 min, approximately 25 - 28% ammonia water (5 mL / min) was slowly added dropwise until the pH value of the mixed solution reached 10, and stirring was continued for 3 h. The resulting precipitate was filtered, washed, and dried to finally obtain a Mn-F2O3 high-efficiency ortho-para hydrogen conversion catalyst, denoted as Mn-FO.

[0042] Application Example:

[0043] The catalyst was sieved to obtain catalyst particles with a particle size of 55 - 40 mesh. 0.2 g of the activated (in vacuum, 140 °C, 24 h) catalyst was filled into the conversion device. Through a gas chromatograph, the catalytic performance of the catalyst at different hydrogen flow rates was tested at a temperature of 77 K. The results are as Figure 4 shown. After analysis, the catalytic performance of the Al-FO sample is higher than that of FO.

[0044] The pore size of the above catalysts was characterized, and the results are shown in Table 1. The average pore size of the catalyst FO before aluminum doping was 3.04 nm, and the average pore size of the doped catalyst was 2.73 nm. The above catalysts were tested by XRD, and the results are as Figure 1 shown. After doping with elements, the crystallinity of the Al-FO catalyst decreased, and the intensity of the XRD diffraction peaks was lower than that of the sample Mn-FO. Combining with the XPS data analysis, as Figure 2 shown, the Al element was mainly doped into iron oxide in atomic form and did not form chemical bonds with other elements. Therefore, compared with other elements that can replace the iron element position in iron oxide, such as manganese, the internal lattice disorder of the Al-FO sample is higher, resulting in more point defects and a higher degree of magnetic disorder. Since the vast majority of defects have paramagnetic characteristics, the number of active sites of the Al-FO catalyst is higher. Through SEM testing, it was found that as Figure 3As shown, compared with other samples, the nanoparticles in the Al-FO sample are smaller, the particle distribution is uniform, the close packing between particles is better, and there is no inter-particle aggregation or large pores. Therefore, for this catalyst: firstly, the reduction of the nanoparticle size can increase the specific surface area of the catalyst; secondly, the reduction of pores can increase the adsorption potential, which is beneficial to the rapid adsorption of hydrogen; thirdly, small pores can reduce the distance between the adsorbed hydrogen and the inner surface of the pores, which is beneficial to the conversion of hydrogen; finally, the dense packing between particles enhances the mechanical strength of the particles, which is beneficial to the improvement of the service life of the catalyst.

[0045] Table 1

[0046] FO Al-FO Pore Size(nm) 3.04 2.73

[0047] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. Application of a catalyst for ortho-para hydrogen conversion, characterized in that the preparation method of the catalyst comprises: preparing a mixed solution of an iron source and an aluminum source, adding a precipitating agent, and stirring and reacting to obtain the catalyst; in the mixed solution, the molar ratio of iron element to aluminum element is (8-12):1; the catalyst is used for ortho-para hydrogen conversion reaction.

2. The application of a normal para-hydrogen conversion catalyst according to claim 1, characterized in that, The concentration of the iron source is 0.01-1 moL / L.

3. Use of a catalyst for ortho-para hydrogen conversion according to claim 1, characterized in that, The iron source is one or more of iron nitrate, iron chloride, iron sulfate or iron acetylacetonate.

4. Use of a catalyst for converting ortho-hydrogen to para-hydrogen according to claim 1, characterized in that, The aluminum source is one or more of aluminum nitrate, aluminum chloride, aluminum sulfate or aluminum acetylacetonate.

5. Use of a catalyst for converting ortho-hydrogen to para-hydrogen according to claim 1, characterized in that, The precipitating agent is an alkaline solution.

6. The application of a normal para-hydrogen conversion catalyst according to claim 5, characterized in that, The precipitating agent is one or more of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate or sodium bicarbonate.

7. Use of a catalyst for converting ortho-hydrogen to para-hydrogen according to claim 6, characterized in that, The precipitating agent is added until the pH of the solution is 2.8-11.

8. Use of a catalyst for converting ortho-hydrogen to para-hydrogen according to claim 1, characterized in that, In the stirring reaction, the reaction temperature is room temperature and the reaction time is 1-5 h.

Images