Preparation Method and Application of a High-Efficiency Ortho-Hydrogen to Para-Hydrogen Conversion Catalyst

Abstract

The present invention relates to a preparation method and application of a highly efficient ortho-para hydrogen conversion catalyst. The preparation method includes: preparing a mixed solution containing an iron source and a cobalt source, adding a precipitant and stirring for reaction, and then aging to obtain the ortho-para hydrogen conversion catalyst. Compared with the prior art, the catalyst prepared by the present invention is a hetero-element doped catalyst prepared by the co-precipitation method, which has the characteristics of amorphous state, small pores, magnetic disorder and many active sites, and is beneficial to the catalytic conversion of hydrogen molecules; at the same time, the preparation method is simple and convenient, low in cost, and does not require secondary granulation, so it has 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 an efficient 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%), and the equilibrium percentage between them 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 (at 30 K, 706 kJ / Kg), and this part of the conversion heat is much greater than the latent heat of vaporization of liquid hydrogen (at 30 K, 447 kJ / Kg). 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 can evaporate 18% of the liquid hydrogen within one day 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] Chinese Patent CN113797928A provides an ortho-para hydrogen conversion catalyst for liquid hydrogen conversion and its preparation method, including: A) preparing an iron salt solution and a metal ion solution to be doped; B) preparing a doped iron salt solution: dropping the prepared metal ion solution to be doped into the iron salt solution according to a certain ratio, and magnetically stirring at room temperature to obtain a doped iron salt solution; C) preparing a precursor: dropping an appropriate amount of alkali solution into the doped iron salt solution obtained in step B) until the pH value of the mixed solution reaches 3-5; D) hydrothermal crystallization to obtain the finished product: placing the mixed solution obtained in step C) in a sealed reaction kettle, reacting at a certain temperature and pressure, then cooling, centrifuging, washing the obtained precipitate with water until the pH value is neutral; putting the above precipitate into a vacuum drying oven for drying and grinding to obtain the finished product. The ortho-para hydrogen conversion catalyst prepared by this invention can always maintain high activity throughout the temperature range of 20K - 80K, saving the dosage. At the same time, since this invention uses the method of high-temperature hydrothermal preparation of the catalyst, on the one hand, the high temperature causes an increase in the crystallinity of the catalyst, making the internal magnetic order of the catalyst, which is not conducive to the rapid occurrence of catalytic conversion. On the other hand, the production equipment is complex and the cost is high, which is not conducive to large-scale industrial production. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method and application of an efficient ortho-para hydrogen conversion catalyst, which has the advantages of simple preparation, low cost, and excellent catalytic performance.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A preparation method of a normal - para hydrogen conversion catalyst, comprising:

[0008] Preparing a mixed solution containing an iron source and a cobalt source, adding a precipitant and then stirring for reaction, and then aging to obtain the normal - para hydrogen conversion catalyst.

[0009] Further, in the mixed solution, the molar ratio of iron element to cobalt element is 10:(1 - 5).

[0010] Further, the concentration of the iron source is 0.01 - 1 moL / L.

[0011] Further, the iron source is one or more of iron nitrate, iron chloride, iron sulfate or iron acetylacetonate; the cobalt source is one or more of cobalt nitrate, cobalt chloride, cobalt sulfate or cobalt acetylacetonate.

[0012] Further, the precipitant is an alkaline solution.

[0013] Further, the precipitant is one or more of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate or sodium bicarbonate.

[0014] Further, the precipitant is added until the pH of the solution is 2.8 - 11.

[0015] Further, in the stirring reaction, the reaction temperature is room temperature and the reaction time is 1 - 5 h.

[0016] Further, in the aging process, the aging temperature is room temperature and the aging time is 0 - 15 h.

[0017] The application of the catalyst prepared by the above - mentioned method, including using the catalyst in the normal - para hydrogen conversion reaction.

[0018] Compared with the prior art, the present invention has the following characteristics:

[0019] 1) This catalyst is amorphous. Element doping leads to an increase in internal defects of the catalyst, an enhancement of magnetic disorder, and an increase in paramagnetic active sites, which is beneficial to catalytic conversion.

[0020] 2) Transition metal elements have an intrinsic spin magnetic moment due to unpaired electrons, which can create an internal magnetic field gradient in the catalyst, so it is beneficial to the progress of the conversion.

[0021] 3) The samples in the present invention have the advantages of uniform distribution of nanoparticles and small pores. The strong adsorption potential of small pores is conducive to the rapid and large - amount adsorption of hydrogen, and at the same time, it can shorten the distance between hydrogen molecules and the catalyst surface, which is beneficial to the improvement of catalytic efficiency.

[0022] 4) The experimental method of the present invention can directly synthesize large and hard particles, which can withstand the long-term impact of hydrogen gas flow. At the same time, according to the actual production needs, the particles can be directly crushed and screened into the required size without secondary granulation, which is simple and convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a scanning electron microscope image atlas of a highly efficient ortho-para hydrogen conversion catalyst of cobalt iron oxide prepared in the examples (A-C: Example 1, D-F: Example 2);

[0024] Figure 2 It is a VSM diagram of an ortho-para hydrogen conversion catalyst prepared in Examples 1-3 and the comparative example;

[0025] Figure 3 It is a diagram of the ortho-hydrogen content after catalytic conversion of an ortho-para hydrogen conversion catalyst prepared in Examples 1-3 and the comparative example. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] A catalyst that can be used in the ortho-para hydrogen conversion reaction, and its preparation method includes:

[0028] Adding an iron source and a cobalt source to water, stirring for 10-30 min to mix them evenly, then adding a precipitant and stirring and reacting at room temperature for 1-5 h, and then aging at room temperature for 0-15 h to obtain an ortho-para hydrogen conversion catalyst;

[0029] Among them, in the mixed solution, the molar ratio of iron element to cobalt element is preferably 10:(1-5); the iron source concentration is 0.01-1 moL / L; the iron source is one or more of iron nitrate, iron chloride, iron sulfate or iron acetylacetonate; the cobalt source is one or more of cobalt nitrate, cobalt chloride, cobalt sulfate or cobalt acetylacetonate; the precipitant is preferably an alkaline solution, and more preferably one or more of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate or sodium bicarbonate, and the dosage of the precipitant is: the pH of the solution after adding is 2.8-11.

[0030] The catalyst prepared by the present invention is a hetero-element doped catalyst prepared by the co-precipitation method, which has the characteristics of amorphous state, small pores, magnetic disorder and many active sites, which is beneficial to the catalytic conversion of hydrogen molecules; at the same time, the preparation method is simple and convenient, low in cost and does not require secondary granulation, so it has the advantages of industrial production.

[0031] 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.

[0032] Comparative Example 1:

[0033] An iron oxide ortho - para hydrogen conversion catalyst, and its preparation method includes:

[0034] At room temperature, 8.08 g of iron(III) nitrate nonahydrate was added to 500 mL of deionized water solvent. After stirring thoroughly for 20 min, ammonia water with a concentration of 25 - 28% (5 mL / min) was slowly added dropwise until the pH value of the mixed solution reached 10. After continuing to stir for 3 h, it was aged for 12 h. The obtained precipitate was filtered, washed, and dried to finally obtain an amorphous F2O3 (named FO) ortho - para hydrogen conversion catalyst.

[0035] Comparative Example 2:

[0036] A cobalt oxide ortho - para hydrogen conversion catalyst, and its preparation method includes:

[0037] At room temperature, 5.82 g of cobalt(II) nitrate hexahydrate was added to 500 mL of deionized water solvent. After stirring thoroughly for 20 min, ammonia water with a concentration of 25 - 28% (5 mL / min) was slowly added dropwise until the pH value of the mixed solution reached 10. After continuing to stir for 3 h, it was aged for 12 h. The obtained precipitate was filtered, washed, and dried to finally obtain an amorphous CoO (named CO) ortho - para hydrogen conversion catalyst.

[0038] Example 1

[0039] A cobalt - iron oxide high - efficiency ortho - para hydrogen conversion catalyst, and its preparation method includes:

[0040] At room temperature, 8.08 g of iron(III) nitrate nonahydrate and 0.582 g of cobalt(II) nitrate hexahydrate (the molar ratio of iron to cobalt is 10:1) were added to 500 mL of deionized water solvent. After stirring thoroughly for 20 min, 25 - 28% ammonia water (5 mL / min) was slowly added dropwise until the pH value of the mixed solution reached 10. After continuing to stir for 3 h, it was aged for 12 h. The obtained precipitate was filtered, washed, and dried to finally obtain a Co - F2O3 (named CFO - 1) high - efficiency ortho - para hydrogen conversion catalyst.

[0041] Example 2

[0042] A cobalt - iron oxide high - efficiency ortho - para hydrogen conversion catalyst, and its preparation method includes:

[0043] At room temperature, 8.08 g of iron(III) nitrate nonahydrate and 1.164 g of cobalt(II) nitrate hexahydrate (molar ratio of iron to cobalt is 10:3) were added to 500 mL of deionized water solvent. After stirring well for 20 min, 25 - 28% ammonia water (5 mL / min) was slowly added until the pH value of the mixed solution reached 10, and stirring was continued for 3 h followed by aging for 12 h. The resulting precipitate was filtered, washed, and dried to finally obtain a highly efficient Co-FO (CFO-3) ortho-para hydrogen conversion catalyst.

[0044] Example 3

[0045] A highly efficient ortho-para hydrogen conversion catalyst of cobalt iron oxide, and its preparation method includes:

[0046] At room temperature, 8.08 g of iron(III) nitrate nonahydrate and 1.746 g of cobalt(II) nitrate hexahydrate (molar ratio of iron to cobalt is 10:5) were added to 500 mL of deionized water solvent. After stirring well for 20 min, 25 - 28% ammonia water (10 mL / min) was slowly added until the pH value of the mixed solution reached 10, and stirring was continued for 3 h followed by aging for 12 h. The resulting precipitate was filtered, washed, and dried to finally obtain a highly efficient Co-FO (CFO-5) ortho-para hydrogen conversion catalyst.

[0047] Since the catalyst material was not calcined at high temperature, it was amorphous. After doping with cobalt element, due to the existence of defects, the crystallinity of the sample was lower, increasing the degree of magnetic disorder inside the catalyst. As Figure 1 shown, through SEM testing, after doping, the nanoparticle size of the catalyst decreased, with a particle size range of 10 - 30 nm, the particle distribution was significantly more uniform, the packing between particles was denser, and the pore diameter decreased. As shown in Table 1, the pore size range after doping was 0.5 - 5 nm, which was beneficial to the increase of the specific surface area of the catalyst and the improvement of hydrogen adsorption kinetics. At the same time, small pores were beneficial to reducing the distance between hydrogen molecules and the catalyst surface, facilitating the rapid occurrence of conversion.

[0048] Table 1

[0049] FO CFO-1 CFO-3 CFO-5 Pore Size(nm) 3.46 3.13 2.59 2.90

[0050] The close packing between nanoparticles was beneficial to improving the hardness of the catalyst, increasing the service life of the catalyst, and reducing the damage to hydrogen liquefaction devices caused by the catalyst powder entering the hydrogen liquefaction device with hydrogen. Doping led to an increase in the magnetization intensity of the catalyst, especially CFO-3, indicating that the magnetic moment of the sample increased after doping, providing a greater acting force for ortho-para hydrogen conversion and facilitating the rapid occurrence of catalytic conversion.

[0051] Application example:

[0052] The catalyst particles with a particle size of 40 - 55 mesh were obtained by sieving the catalysts prepared in Examples 1 - 3 and the comparative examples. 0.2 g of the activated (under vacuum, 140 °C, 24 h) catalyst was filled into the conversion device, and the catalytic performance of the catalyst at different hydrogen flow rates was tested at a temperature of 77 K by a gas chromatograph.

[0053] After analysis, as Figure 3 shown, the catalytic performance of the doped samples was higher than that of FO. Therefore, doping with heteroelements is beneficial to the ortho - para hydrogen conversion of iron - based catalysts. Among them, the synergistic effect of the excellent small pore diameter and high magnetization intensity of sample CFO - 3 makes it have better catalytic activity.

[0054] 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 the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a catalyst for ortho-para hydrogen conversion, characterized in that, The supported components of the ortho-para hydrogen conversion catalyst are iron and cobalt; The preparation method includes: Preparing a mixed solution containing an iron source and a cobalt source, adding a precipitant and then stirring and reacting, and then aging to obtain the ortho-para hydrogen conversion catalyst; In the said mixed solution, the molar ratio of iron element to cobalt element is 10:

3.

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

3. The preparation method of a normal para-hydrogen conversion catalyst according to claim 1, characterized in that, The said iron source is one or more of iron nitrate, iron chloride, iron sulfate or iron acetylacetonate; the said cobalt source is one or more of cobalt nitrate, cobalt chloride, cobalt sulfate or cobalt acetylacetonate.

4. The preparation method of a normal para-hydrogen conversion catalyst according to claim 1, characterized in that, The said precipitant is an alkaline solution.

5. The preparation method of a normal para-hydrogen conversion catalyst according to claim 4, characterized in that, The said precipitant is one or more of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate or sodium bicarbonate.

6. The preparation method of a normal para-hydrogen conversion catalyst according to claim 5, characterized in that, Adding the precipitant until the pH of the solution is 2.8 - 11.

7. The preparation method of a normal para-hydrogen conversion catalyst according to claim 1, characterized in that, In the said stirring reaction, the reaction temperature is room temperature and the reaction time is 1 - 5 h.

8. The preparation method of a normal para-hydrogen conversion catalyst according to claim 1, characterized in that, In the said aging process, the aging temperature is room temperature and the aging time is 0 - 15 h.

9. Use of the catalyst prepared by the method according to any one of claims 1 to 8, characterized in that, The said catalyst is used for the ortho-para hydrogen conversion reaction.

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