Process for the preparation of a catalyst for the conversion of primary and secondary hydrocarbons to hydrated iron oxides

Abstract

The application discloses a preparation method of hydrated ferric oxide primary and secondary hydrogen conversion catalyst, and comprises the following steps: (1) under the conditions of ultrasonic dispersion and stirring, alkaline solution is added dropwise into an aqueous solution of iron salt until the pH value of the system is 8.0-10.5, and then the first suspension is obtained by standing for 1-5 hours; (2) a certain amount of water is removed from the first suspension by evaporation to obtain the second suspension; (3) under the condition of high-speed dispersion, a modified metal salt solution is added into the second suspension, and then the mixture is obtained by standing for 1-5 hours; and (4) the mixture is washed, separated, dried and formed to obtain the hydrated ferric oxide primary and secondary hydrogen conversion catalyst. The hydrated ferric oxide primary and secondary hydrogen conversion catalyst prepared by the method has the advantages of small micro-particle size, low synthesis reaction temperature, small energy consumption, high preparation efficiency and high catalytic activity in a wide temperature range.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen energy, and specifically relates to a method for preparing a hydrated iron oxide secondary hydrogen conversion catalyst for hydrogen liquefaction. Background Technology

[0002] Liquid hydrogen has advantages such as ease of storage and high safety, making it one of the most important methods for hydrogen storage and transportation.

[0003] At room temperature, hydrogen gas consists of 75% orthohydrogen and 25% parahydrogen. As the temperature decreases, the proportion of orthohydrogen gradually decreases, while the proportion of parahydrogen gradually increases. When liquid hydrogen reaches its standard boiling point, the equilibrium concentration of parahydrogen is 99.8%. During hydrogen liquefaction, the heat released during the orthohydrogen-parahydrogen conversion exceeds the latent heat of vaporization of hydrogen, leading to significant losses of liquid hydrogen. Therefore, the parahydrogen content in liquid hydrogen products must be greater than 95%. The spontaneous orthohydrogen-parahydrogen conversion process is extremely slow; therefore, a catalyst must be added during hydrogen liquefaction to accelerate the conversion of orthohydrogen to parahydrogen.

[0004] The most commonly used catalyst for the conversion of n- and tertiary hydrogen is hydrated iron oxide. However, this type of catalyst generally has high catalytic activity in the temperature range of 70 to 80 K, while the catalytic conversion efficiency is relatively low in other temperature ranges.

[0005] To broaden the catalytic activity of catalysts for the conversion of ortho- and para-hydrogen in different temperature ranges, CN202111354244.6 discloses a method for preparing a single-element doped iron oxide ortho- and para-hydrogen conversion catalyst: An appropriate amount of alkaline solution is added to an iron salt solution containing the dopant element, and the mixture is hydrothermally treated. The resulting precipitate is washed, dried, and crushed to obtain a hydrated iron oxide ortho- and para-hydrogen conversion catalyst with high activity over a wide temperature range. However, this method uses a high-temperature hydrothermal approach to prepare doped iron oxide with relatively large grain size, which is not conducive to increasing the specific surface area of ​​the catalyst. Furthermore, the high-temperature reaction time is too long, resulting in low preparation efficiency and excessive energy consumption. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing a hydrated iron oxide secondary hydrogen conversion catalyst. The hydrated iron oxide secondary hydrogen conversion catalyst prepared by this method exhibits low synthesis reaction temperature, low energy consumption, high preparation efficiency, and high catalytic activity over a wide temperature range.

[0007] The preparation method of the hydrated iron oxide secondary hydrogen conversion catalyst of the present invention includes the following steps:

[0008] (1) At room temperature, under ultrasonic dispersion and stirring conditions, the alkali solution is added dropwise to the iron salt aqueous solution until the pH value of the system is 8.0 to 10.5, and the solution is allowed to stand for 1 to 5 hours to obtain the first suspension;

[0009] (2) Evaporate a certain amount of water from the first suspension to obtain the second suspension;

[0010] (3) Under high-speed dispersion conditions, the modified metal salt solution is added to the second suspension and allowed to stand for 1 to 5 hours to obtain a mixture;

[0011] (4) The mixture is washed, separated, dried and shaped to obtain hydrated iron-orthohydrogen conversion catalyst.

[0012] In the method of this invention, the iron salt in step (1) is one or more of ferric chloride, ferric nitrate, and ferric sulfate; the iron salt aqueous solution is Fe 3+ The concentration is 0.5–3 mol / L, preferably 1.0–2.5 mol / L.

[0013] In the method of the present invention, the modified metal in step (1) is any two of cobalt, nickel, lanthanum and cerium; the modified metal salt can be nitrate, chloride, etc., and the concentration of the modified metal salt solution as metal ions is 0.5 to 5 mol / L, preferably 1 to 4 mol / L.

[0014] The modified metal salt solutions described in step (1) can be prepared separately or in combination.

[0015] In the method of this invention, the alkaline solution in step (1) is an aqueous solution of sodium hydroxide and / or potassium hydroxide, wherein the alkaline solution is in the form of OH... — The concentration is 1–5 mol / L, preferably 1–4.5 mol / L.

[0016] In the method of the present invention, the room temperature in step (1) is 20 to 45°C.

[0017] In the method of the present invention, the conditions for ultrasonic dispersion in step (1) are: ultrasonic frequency 20-100kHz, ultrasonic power 40-1000W, and ultrasonic temperature 20-45℃.

[0018] In the method of the present invention, the stirring in step (1) includes, but is not limited to, any method that is conducive to uniform mixing of materials, such as mechanical stirring, magnetic stirring, shaking table, etc.

[0019] In the method of this invention, the evaporation in step (2) is atmospheric pressure evaporation or negative pressure evaporation, preferably rotary evaporation under negative pressure conditions. The operating conditions are: rotation speed 1-200 rpm, vacuum degree 0.05-200 Pa, and evaporation temperature 20-90℃. Preferably, the rotation speed is 20-100 rpm, the vacuum degree is 10-100 Pa, and the rotary evaporation temperature is 40-75℃.

[0020] In the method of the present invention, the degree of water removal in step (2) is 40% to 80% of the total water content in the iron salt aqueous solution and the alkaline solution, preferably 50% to 70%.

[0021] In the method of this invention, the high-speed dispersion mentioned in step (3) refers to the use of ordinary mechanical stirring, magnetic stirring, shear stirring, and other dispersion methods that can fully mix the materials. The rotation speed is not less than 1000 rpm, preferably 1500–30000 rpm. More preferably, shear stirring is used, with an operating condition of a shear speed of 5000–20000 rpm. The operating temperature is 20–45°C.

[0022] In the method of the present invention, the washing in step (4) can be done with water until the pH value of the washing solution is neutral or near neutral.

[0023] In the method of the present invention, the separation described in step (4) is a conventional process: the washed suspension is separated into solid and liquid phases by centrifugation, vacuum filtration or pressure filtration to obtain solid phase.

[0024] In the method of the present invention, the drying in step (4) is performed at 100-160°C for 2-48 hours, preferably at 130-150°C for 6-24 hours.

[0025] In the method of the present invention, the molding in step (4) involves crushing the dried product into granules and screening them to obtain granules of 30 to 60 mesh.

[0026] The hydrated iron oxide secondary hydrogen conversion catalyst prepared by the method of this invention has the following properties: based on the catalyst weight, the modified metal, calculated as oxide, is 0.5% to 15%; the catalyst particle size is 30 to 60 mesh; and the specific surface area is 150 to 250 m². 2 / g, crushing strength is 6-16N / particle, hydrated iron oxide microparticle size is 2-20nm, and the microparticle size of hydrated oxide formed by doping elements is 2-10nm.

[0027] This invention, in preparing dielement-doped hydrated iron oxide, does not employ co-precipitation. Instead, it first reacts an iron salt solution with an alkaline solution to form a suspension, which is then concentrated via rotary evaporation. The solution to be doped is then added to the concentrate, where it undergoes redeposition with the alkaline substances, ultimately forming dielement-doped hydrated iron oxide. Throughout the addition of the iron salt and alkaline solution, ultrasonic dispersion is used to prevent the suspension from agglomerating into large particles, thus maintaining a highly dispersed state. The rotary evaporation concentration method increases the concentration of alkaline substances in the suspension, while shear stirring further enhances the dispersion of the concentrate, facilitating good dispersion of the doped element and increasing the specific surface area of ​​the product. This invention features a low reaction temperature, low energy consumption, high efficiency, a large specific surface area of ​​the product, and high catalytic activity for the conversion of n- and para-hydrogen ions over a wide temperature range. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the embodiments. The size of the hydrated iron oxide nanoparticles was measured using transmission electron microscopy (TEM) in bright-field and scanning transmission dark-field modes. The size of the formed particles was determined by sieving using standard sieves. The crushing strength of the formed particles was measured using a strength tester. The specific surface area was measured using the low-temperature nitrogen adsorption method, and the specific surface area value was calculated according to the BET method. The mass content of doping elements was determined by X-ray fluorescence spectrometry (XRF). The secondary hydrogen content was detected by gas chromatography. The secondary hydrogen conversion rate at 77K was calculated as: Conversion rate = (Secondary hydrogen content % - 25%) / 25.6%. The secondary hydrogen conversion rate at 40K was calculated as: Conversion rate = (Secondary hydrogen content % - 25%) / 63.7%. The secondary hydrogen conversion rate at 20K was calculated as: Conversion rate = (Secondary hydrogen content % - 25%) / 74.6%. The equilibrium content of secondary hydrogen at room temperature was 25%. Example 1

[0029] A 3.0 mol / L sodium hydroxide solution and a 1.0 mol / L ferric chloride solution were prepared, along with mixed solutions of lanthanum chloride and cobalt chloride with concentrations of 0.5 mol / L and 1.0 mol / L, respectively, to be doped. A certain amount of sodium hydroxide solution was added dropwise to the ferric chloride solution at room temperature (25℃), under mechanical stirring and ultrasonic dispersion (20 kHz, 100 W), forming a suspension, which was allowed to stand for 2 hours. Then, 50% of the water was evaporated by rotary evaporation at 100 Pa negative pressure and 45℃ to obtain a concentrate. Under high-speed shearing conditions of 10000 rpm, a certain amount of the element to be doped solution was added dropwise to the concentrate, and after standing for 2 hours, the precipitate was repeatedly washed and filtered with water until the pH of the washing solution was neutral. The washings were dried in a forced-air oven at 135℃ for 12 hours, and then crushed into 30–60 mesh particles to obtain the final product.

[0030] Tests showed that the product contained 6.1% lanthanum oxide and 2.7% cobalt oxide by mass, with a crushing strength of 8-15 N / particle and a specific surface area of ​​213 m². 2 / g, the microparticle size of hydrated iron oxide is 6.7nm, and the microparticle sizes of hydrated lanthanum oxide and cobalt oxide are 3.6nm and 3.2nm, respectively. The conversion performance of n- and para-hydrogen is shown in Table 1. Example 2

[0031] 3.5 mol / L sodium hydroxide solution and 2.0 mol / L ferric chloride solution were prepared, along with mixed solutions of lanthanum chloride and nickel chloride with concentrations of 1.5 mol / L and 1.0 mol / L, respectively, to be doped. A certain amount of sodium hydroxide solution was added dropwise to the ferric chloride solution at room temperature (30℃), under mechanical stirring and ultrasonic dispersion (20 kHz, 100 W), forming a suspension, which was allowed to stand for 3 hours. Then, 60% of the water was evaporated by rotary evaporation at 100 Pa negative pressure and 45℃ to obtain a concentrate. Under high-speed shearing conditions of 20,000 rpm, a certain amount of the dopant element solution was added dropwise to the concentrate, and after standing for 3 hours, the precipitate was repeatedly washed and filtered with water until the pH of the washing solution was neutral. The washings were dried in a forced-air oven at 135℃ for 12 hours, and then crushed into 30–60 mesh particles to obtain the final product.

[0032] Tests showed that the product contained 6.7% lanthanum oxide and 2.3% nickel oxide by mass, with a crushing strength of 8–17 N / piece and a specific surface area of ​​224 m². 2 / g, the microparticle size of hydrated iron oxide is 7.2nm, and the microparticle sizes of hydrated lanthanum oxide and nickel oxide are 2.8nm and 2.9nm, respectively. The n- and para-hydrogen conversion performance is shown in Table 1. Example 3

[0033] 4.5 mol / L sodium hydroxide solution and 2.5 mol / L ferric chloride solution were prepared, along with mixed solutions of cerium chloride and cobalt chloride with concentrations of 1.5 mol / L and 1.5 mol / L, respectively, to be doped. A certain amount of sodium hydroxide solution was added dropwise to the ferric chloride solution at room temperature (35℃), under mechanical stirring and ultrasonic dispersion (20 kHz, 100 W) to form a suspension, which was allowed to stand for 4 hours. Then, 70% of the water was evaporated by rotary evaporation at 100 Pa negative pressure and 45℃ to obtain a concentrate. Under high-speed shearing conditions of 40,000 rpm, a certain amount of the dopant element solution was added dropwise to the concentrate, and after standing for 4 hours, the precipitate was repeatedly washed and filtered with water until the pH of the washing solution was neutral. The washings were dried in a forced-air oven at 135℃ for 12 hours, and then crushed into 30–60 mesh particles to obtain the final product.

[0034] Tests showed that the product contained 7.0% cerium oxide and 3.1% cobalt oxide by mass, with a crushing strength of 9–18 N / particle and a specific surface area of ​​220 m². 2 / g, the microparticle size of hydrated iron oxide is 10.4nm, and the microparticle sizes of hydrated cerium oxide and cobalt oxide are 4.5nm and 3.8nm, respectively. The conversion performance of n- and para-hydrogen is shown in Table 1. Example 4

[0035] A 4.0 mol / L sodium hydroxide solution and a 1.0 mol / L ferric chloride solution were prepared, along with mixed solutions of lanthanum chloride and cobalt chloride with concentrations of 0.5 mol / L and 0.5 mol / L, respectively, to be doped. A certain amount of sodium hydroxide solution was added dropwise to the ferric chloride solution at room temperature (25℃), under mechanical stirring and ultrasonic dispersion (20 kHz, 100 W), forming a suspension, which was allowed to stand for 4 hours. Then, 50% of the water was evaporated by rotary evaporation at 100 Pa negative pressure and 45℃ to obtain a concentrate. Under high-speed shearing conditions of 30,000 rpm, a certain amount of the dopant element solution was added dropwise to the concentrate, and after standing for 4 hours, the precipitate was repeatedly washed and filtered with water until the pH of the washing solution was neutral. The washing solution was dried in a forced-air oven at 135℃ for 12 hours, and then crushed into 30–60 mesh particles to obtain the final product.

[0036] Tests showed that the product contained 6.3% lanthanum oxide and 2.4% cobalt oxide by mass, with a crushing strength of 7–16 N / particle and a specific surface area of ​​214 m². 2 / g, the microparticle size of hydrated iron oxide is 5.6nm, and the microparticle sizes of hydrated lanthanum oxide and cobalt oxide are 5.4nm and 4.9nm, respectively. The conversion performance of n- and para-hydrogen is shown in Table 1. Comparative Example 1

[0037] The preparation conditions were the same as in Example 1, except that the two-element doping was replaced with single-element doping, adding only cobalt while maintaining the final cobalt oxide content at 8.8%. The product was tested and found to have a crushing strength of 8–15 N / particle and a specific surface area of ​​225 m². 2 / g. The conversion performance of n- and para-hydrogen is shown in Table 1. The test results show that the performance of single-element doped catalysts is weaker than that of dual-element doped catalysts. Comparative Example 2

[0038] The sample was prepared according to the method and steps of Example 1 of CN202111354244.6, except that the same amount of nickel was introduced again. Testing showed that the obtained product had a nickel oxide content of 8.5% and a cobalt oxide content of 8.5%. The crushing strength of the product particles was 5–12 N / particle, and the specific surface area was 124 m². 2 / g. The microscopic particle size of hydrated iron oxide is approximately 760nm, while the microscopic particle sizes of hydrated lanthanum oxide and cobalt oxide are 50nm and 42nm, respectively. The n- and para-hydrogen conversion performance is shown in Table 1. Comparative Example 3

[0039] The preparation conditions were the same as in Example 1, except that the degree of water removal in step (2) was 90%, while other conditions remained unchanged. Testing showed that the mass content of lanthanum oxide and cobalt oxide in the product was 5.7% and 2.8%, respectively; the crushing strength of the product particles was 5–10 N / particle; and the specific surface area was 132 m². 2 The microparticle size of hydrated iron oxide is 6.9 nm, while the microparticle sizes of hydrated lanthanum oxide and cobalt oxide are 21.5 nm and 16.4 nm, respectively. Due to the high evaporation rate and excessively high alkali concentration, lanthanum and cobalt salts easily form large precipitates, which cannot form a uniform precipitate with hydrated iron oxide. This results in a decrease in the strength and specific surface area of ​​the final product, which is detrimental to improving catalytic performance. The n- and para-hydrogen conversion performance tests are shown in Table 1. Comparative Example 4

[0040] The preparation conditions were the same as in Example 1, except that the degree of water removal in step (2) was 30%, while other conditions remained unchanged. Testing showed that the mass content of lanthanum oxide and cobalt oxide in the product was 4.7% and 1.3%, respectively; the crushing strength of the product particles was 7–15 N / particle; and the specific surface area was 203 m². 2 / g. Due to the limited evaporation process and insufficient alkali concentration, lanthanum and cobalt salts could not precipitate sufficiently and were lost during washing, resulting in a decrease in the content of lanthanum oxide and cobalt oxide in the final product, which is detrimental to improving catalytic performance. The n- and para-hydrogen conversion performance tests are shown in Table 1. Comparative Example 5

[0041] The preparation conditions were the same as in Example 1, except that high-speed stirring was not used throughout the process; instead, a conventional 200 rpm stirring rate was employed. Testing revealed that the product contained 6.5% lanthanum oxide and 2.4% cobalt oxide by mass, respectively. The crushing strength of the product particles was 7–15 N / particle, and the specific surface area was 185 m². 2 / g. Due to the lack of high-speed stirring, larger precipitate particles will be generated, which is not conducive to increasing the specific surface area. The n- and para-hydrogen conversion performance tests are shown in Table 1.

[0042] Table 1. Secondary hydrogen conversion rate (%) of catalysts at different temperatures.

[0043] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 77K 96.9 97.4 96.1 97.8 94.8 90.6 93.0 93.4 94.2 40K 96.8 97.9 96.6 98.4 94.3 91.2 92.7 93.2 93.5 20K 97.0 96.9 96.8 98.1 94.6 90.8 93.2 93.1 93.6

[0044] Test conditions: catalyst particle size 30-40 mesh, activation conditions: vacuum drying at 130℃ for 12 hours, volume hourly space velocity 200 min. -1 .

Claims

1. A method for preparing a hydrated iron oxide secondary hydrogen conversion catalyst, characterized in that... The process includes the following steps: (1) Under ultrasonic dispersion and stirring conditions, alkali solution is added dropwise to an iron salt aqueous solution until the pH of the system is 8.0-10.5, and the solution is allowed to stand for 1-5 hours to obtain a first suspension; (2) A certain amount of water is removed by evaporation of the first suspension to obtain a second suspension; (3) Under high-speed dispersion conditions, a modified metal salt solution is added to the second suspension and allowed to stand for 1-5 hours to obtain a mixture; (4) The mixture is washed, separated, dried, and shaped to obtain a hydrated iron-to-hydrogen conversion catalyst; The iron salt mentioned in step (1) is one or more of ferric chloride, ferric nitrate, and ferric sulfate, and the iron salt aqueous solution is prepared with Fe 3+ The concentration is 0.5–3 mol / L; the modified metal in step (1) is any two of cobalt, nickel, lanthanum, and cerium, and the concentration of the modified metal salt solution as metal ions is 0.5–5 mol / L; the alkali solution is OH- — The concentration is 1-5 mol / L; the evaporation in step (2) is negative pressure evaporation, and the evaporation temperature is 20-90℃; the degree of water removal in step (2) is 40%-80% of the total water in the iron salt solution and alkali solution; the high-speed dispersion in step (3) has a rotation speed of not less than 1000 rpm.

2. The method according to claim 1, characterized in that: The alkaline solution mentioned in step (1) is an aqueous solution of sodium hydroxide and / or potassium hydroxide.

3. The method according to claim 1, characterized in that: The conditions for ultrasonic dispersion in step (1) are: ultrasonic frequency 20-100kHz, ultrasonic power 40-1000W, and ultrasonic temperature 20-45℃.

4. The method according to claim 1, characterized in that: The evaporation described in step (2) is rotary evaporation under negative pressure conditions. The operating conditions are: rotation speed 1 to 200 rpm, vacuum degree 0.05 to 200 Pa.

5. The method according to claim 1, characterized in that: The degree of water removal in step (2) is to remove 50% to 70% of the total water in the iron salt solution and alkali solution.

6. The method according to claim 1, characterized in that: The high-speed dispersion speed mentioned in step (3) is 1500 to 30000 rpm.

7. The method according to claim 1, characterized in that: The washing described in step (4) is done with water until the pH of the washing solution is neutral or near neutral.

8. The method according to claim 1, characterized in that: The drying process described in step (4) is carried out at 100-160°C for 2-48 hours.

9. The method according to claim 1, characterized in that: The molding process described in step (4) involves crushing the dried product into granules and then screening them to obtain granules with a mesh size of 30 to 60.

10. A hydrated iron oxide secondary hydrogen conversion catalyst prepared by the method according to any one of claims 1 to 9, characterized in that... It possesses the following properties: based on the catalyst's weight, the modified metal, calculated as oxides, comprises 0.5%–15%; the catalyst particle size is 30–60 mesh; and the specific surface area is 150–250 m². 2 / g, crushing strength is 6-16N / particle, hydrated iron oxide microparticle size is 2-20nm, and the microparticle size of hydrated oxide formed by doping elements is 2-10nm.