Primary and secondary hydrogen conversion catalyst and method for preparing the same

Abstract

The application discloses a primary and secondary hydrogen conversion catalyst and a preparation method thereof. The catalyst comprises an active component of hydrated iron oxide. The hydrated iron oxide is in a weakly crystalline state, and the micro-particle size is 3-10 nm. The primary and secondary hydrogen conversion catalyst is in a granular form, the particle size is 20-80 mesh, the particle crushing strength is 5-13 N / particle, and the specific surface area is 160-300 m 2 / g. The preparation method is as follows: (1) under the simultaneous action of ultrasonic dispersion and physical dispersion, an iron salt solution is mixed with an inorganic lye to form a colloidal mixture, and then the colloidal mixture is left to stand for 0.5-5 hours; (2) the mixture in the step (1) is washed, separated, and then subjected to drying treatment, crushing and screening to obtain the primary and secondary hydrogen conversion catalyst. The primary and secondary hydrogen conversion catalyst has a large specific surface area and high physical strength, and has the advantages of simple preparation method, low reaction temperature, low energy consumption, high preparation efficiency and high catalytic activity for primary and secondary hydrogen conversion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ortho-para hydrogen catalytic conversion, and particularly relates to an ortho-para hydrogen conversion catalyst and a preparation method thereof. BACKGROUND

[0002] Liquid hydrogen is a high-efficiency liquid fuel and has a wide application prospect in the fields of chemical production, aerospace engineering, hydrogen energy automobile, etc. Liquid hydrogen has advantages such as convenient storage and metering, and becomes one of important ways for hydrogen energy use and storage and transportation.

[0003] A hydrogen molecule is composed of two hydrogen atoms with different nuclear spin directions, in which the nuclear spin symmetry is ortho-hydrogen, and the anti-symmetry is para-hydrogen. Ortho-hydrogen and para-hydrogen can stably exist in liquid and gaseous states, and the equilibrium concentration of the two is affected by temperature. At room temperature, the ortho-hydrogen content in hydrogen is 25%, and the para-hydrogen content is 75%, which is called normal hydrogen or standard hydrogen. When the temperature decreases, ortho-hydrogen will spontaneously convert into para-hydrogen. At the standard boiling point of liquid hydrogen, the para-hydrogen content can reach 99.8%. Without the action of an external catalyst, the spontaneous conversion of hydrogen from ortho-hydrogen to para-hydrogen is very slow, and the heat released during the conversion process is greater than the vaporization heat of liquid hydrogen, which will cause the vaporization loss of liquid hydrogen. In order to liquefy hydrogen while quickly completing the conversion of ortho-hydrogen to para-hydrogen, it is crucial to develop a high-performance ortho-para hydrogen conversion catalyst for the production of liquid hydrogen.

[0004] At present, amorphous hydrated iron oxide is mainly used as an ortho-para hydrogen conversion catalyst.

[0005] CN202210029537.5 provides a preparation method of nano hydrated iron oxide. The nano iron oxide with high crystallinity is obtained by a hydrothermal method, and the particle size is 15-25 nm. The product has a large particle size and a low specific surface area.

[0006] CN202111354244.6 discloses a preparation method of a doped ortho-para hydrogen conversion catalyst. An iron salt solution and a solution of metal ions to be doped are prepared respectively, the solution of metal ions to be doped is added into the iron salt solution in a certain proportion, and then an appropriate amount of lye is added. The precipitate obtained by the hydrothermal reaction of the mixed solution is washed, dried, and ground to obtain a hydrated iron oxide ortho-para hydrogen conversion catalyst. The doped iron oxide prepared by the high-temperature hydrothermal method has a large crystal grain size (300-1000 nm), a high crystallinity, and a small specific surface area. Meanwhile, the high-temperature reaction time is too long, the synthesis efficiency is low, and the energy consumption is high.

[0007] CN202210832769.4 provides an ortho-para hydrogen conversion catalyst and a preparation method thereof. The catalyst is a Fe atom-doped fibrous magnetic catalyst FeMnO x, with fibrous structure of diameter 2-5 nm and length 100 nm-500 nm, the product has large particle size and low specific surface area. The method needs hydrothermal reaction, which has high energy consumption, and needs to prepare manganese oxide precursor, so the preparation cost is also high.

[0008] CN201910782910.2 discloses a preparation method of hydrated iron oxide, a weakly basic compound is added to a ferric chloride complex solution, aged, filtered, and the filter cake is dispersed in an ammonium bicarbonate solution, filtered, dried, and hydrated iron oxide is obtained. The method uses a weak base as a precipitant, and the crystal phase of the product obtained at normal temperature and pressure is mainly amorphous. On the other hand, the filter cake is reacted with ammonium bicarbonate, and then ammonium bicarbonate is used to improve the specific surface area of the product by pyrolysis and pore-forming, but it will cause a significant decrease in the particle strength of the dried material. At the same time, the impurities introduced by the used ammonium bicarbonate are difficult to control, which is not conducive to the control of the catalyst index of the secondary hydrogen catalytic conversion.

[0009]

Fine Petroleum Chemical Industry Progress, 2010, 11 (7): 26-31

[0010] The specific surface area and particle strength are important control indicators of catalytic materials, and the specific surface area of the hydrated iron oxide used in the above primary and secondary hydrogen conversion catalyst is low, or the particle strength is weak, which is not conducive to the performance improvement of the primary and secondary hydrogen catalyst. SUMMARY

[0011] In view of the deficiencies of the prior art, the present application provides a primary and secondary hydrogen conversion catalyst and a preparation method thereof. The primary and secondary hydrogen conversion catalyst of the present application has large specific surface area and high physical strength, the preparation method is simple, the reaction temperature is low, the energy consumption is low, the preparation efficiency is high, and the primary and secondary hydrogen conversion catalyst has high catalytic activity.

[0012] The primary and secondary hydrogen conversion catalyst of the present application comprises an active component hydrated iron oxide, the hydrated iron oxide is weakly crystalline, and the micro-particle size is 3-10 nm; the primary and secondary hydrogen conversion catalyst is in the form of particles, the particle size is 20-80 mesh, the particle crushing strength is 5-13 N / particle, and the specific surface area is 160-300 m 2 / g.

[0013] In the positive and negative hydrogen conversion catalyst of the present invention, the weakly crystalline state has the following characteristics: (1) In the XRD pattern, the peak intensity of all characteristic diffraction peaks is not greater than 2 compared with the baseline intensity at the position (2θ) and the half width at half maximum of the diffraction angle 2θ is less than 2º; (2) There are distinguishable lattice fringes in high magnification (200,000 times and above) transmission electron microscopy images or distinguishable diffraction spots or diffraction rings in electron diffraction patterns.

[0014] The preparation method of the positive and negative hydrogen conversion catalyst of the present invention includes the following:

[0015] (1) Under the simultaneous action of ultrasonic dispersion and mechanical dispersion, the iron salt solution and inorganic alkali solution are mixed to form a colloidal mixture, and then the colloidal mixture is allowed to stand for 0.5-5 hours;

[0016] (2) Wash and separate the mixture from step (1), and then dry it. The drying process is as follows: First stage, drying temperature and time 40-100℃, drying time 6-96 hours; Second stage, drying temperature and time 100-200℃, drying time 1-48 hours, drying atmosphere is air.

[0017] (3) The dried material is crushed and screened to obtain the secondary hydrogen conversion catalyst.

[0018] In the method of the present invention, step (1) is generally carried out at room temperature, which is 10 to 45°C.

[0019] In the method of this invention, the iron salt in step (1) is ferric chloride and / or ferric sulfate; the iron salt solution in step (1) is in the form of Fe 3+ The concentration is 0.10–1.5 mol / L, preferably 0.15–1.0 mol / L.

[0020] In the method of this invention, the inorganic alkali in step (1) is one or more of sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, sodium carbonate, sodium bicarbonate, or ammonium bicarbonate, preferably one or more of sodium hydroxide, potassium hydroxide, rubidium hydroxide, or cesium hydroxide; the concentration of the inorganic alkali solution is expressed in OH⁻. - The concentration is calculated to be 0.5–2.0 mol / L, preferably 1.0–1.5 mol / L.

[0021] In the method of this invention, the iron salt solution in step (1) is Fe 3+ Calculated with inorganic alkaline solution as OH - Calculate, OH - / Fe 3+ The molar ratio is 3.0 to 4.5.

[0022] In the method, the ultrasonic dispersion condition in step (1) is that the ultrasonic frequency is 20-100 kHz, the ultrasonic power density acting on the reaction material is 10-1000 W / L, and the ultrasonic temperature is 10-45 ℃; the preferred ultrasonic dispersion condition is that the ultrasonic frequency is 40-80 kHz, the ultrasonic power density is 20-100 W / L, and the ultrasonic temperature is kept at 20-35 ℃.

[0023] In the method, the mechanical dispersion in step (1) includes but is not limited to mechanical stirring, magnetic stirring, shaking table, shear stirring and any mode and operation condition that is beneficial to rapid and uniform mixing of the material.

[0024] In the method, the order and mode of adding the material in step (1) are not particularly limited, and preferably, the lye is added to the iron salt solution, which can be added at one time or in batches, preferably in batches.

[0025] In the method, the separation in step (2) can separate the solid-liquid of the washed suspension by natural sedimentation, centrifugation, vacuum filtration or pressure filtration to obtain a solid phase material.

[0026] In the method, the degree of washing and filtering in step (2) needs to meet that the mass content of sodium element calculated as Na2O in the final obtained catalyst composition is less than 0.1%, and preferably, the content of Na2O is less than 0.01%; and deionized water is generally used for washing operation.

[0027] In the method, the drying treatment in step (2) is further preferably as follows: in the first stage, the drying temperature is 60-80 ℃, and the drying time is 12-24 hours; in the second stage, the drying temperature is 120-160 ℃, and the drying time is 6-24 hours.

[0028] In the method, the breaking in step (3) means that the large-sized dried filter cake is changed into small-sized particles by any mode such as knocking and rolling.

[0029] The screening in step (3) means that the small particles formed by breaking are screened out by a standard screen, and the particles with a mesh size of 20-80 are screened, and further preferably, the particles with a mesh size of 30-60 are used as the final use of the shaped particles, so that the high-strength, high-specific surface area primary / secondary hydrogen conversion catalyst is formed.

[0030] The application of the primary / secondary hydrogen conversion catalyst in the primary / secondary hydrogen conversion reaction.

[0031] The present application uses ultrasonic dispersion and physical dispersion to synergistically strengthen dispersion in the reaction process of preparing hydrated iron oxide, which can avoid the aggregation of colloids or precipitates to form larger particles, thereby maintaining a highly dispersed state, which is conducive to obtaining smaller reactant particles and improving the specific surface area of the product. The weakly crystalline hydrated iron oxide generated by the micro-shear and cavitation effect of ultrasonic waves at room temperature can improve the catalyst activity. The two-stage drying method can prevent secondary hydrothermal reaction of hydrated iron oxide in the filter cake caused by direct high-temperature drying and improve the strength of small particles obtained by crushing the dried filter cake. The present application does not use high-temperature hydrothermal synthesis, has low reaction temperature, low energy consumption, high efficiency, large specific surface area of the obtained hydrated iron oxide, high strength of the formed particles, and excellent activity for the catalytic conversion of primary and secondary hydrogen. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Transmission electron microscope image of the hydrated iron oxide prepared in Example 1.

[0033] Figure 2 X-ray diffraction spectrum of the hydrated iron oxide prepared in Example 1.

[0034] Figure 3 Electron diffraction spectrum of the hydrated iron oxide prepared in Example 1.

[0035] Figure 4 X-ray diffraction spectrum of the iron oxide prepared in Comparative Example 1. DETAILED DESCRIPTION

[0036] The application is further described in detail below with reference to examples. The Na2O content in the catalyst is tested by XRF method; the specific surface area is tested by low-temperature nitrogen adsorption method, and the specific surface area value is calculated according to BET method; the crushing strength of the shaped particles is determined by a strength instrument, and the particles with a mesh size of 35-40 are screened, 50 particles are randomly selected to test the average strength as the crushing strength of the catalyst; the nanoparticle size and lattice image of the hydrated iron oxide are observed by transmission electron microscopy; and the determination method of the crystallization strength of the sample is defined as follows: (1) for a strong crystallization sample, in the XRD spectrum, at least one diffraction peak with a peak intensity to baseline intensity at the position (2θ) ratio greater than 2 exists, and the half-height width of the diffraction angle 2θ is less than 2°; (2) for a weak crystallization sample, no diffraction peak meeting the above strong crystallization determination condition exists in the XRD spectrum, but in the high-magnification transmission electron microscopy image, there should be distinguishable lattice stripe images, or in the electron diffraction spectrum, there should be distinguishable diffraction spots or diffraction rings. The content of normal and parahydrogen is calculated by gas chromatography, and the conversion rate of parahydrogen is calculated according to the formula: conversion rate = (parahydrogen content% - 25%) / 25.8%, wherein the contents of normal and parahydrogen in the raw hydrogen are calculated according to 75% and 25% respectively, and the equilibrium concentration of parahydrogen is calculated according to 50.8% at the liquid nitrogen temperature (77K). Example 1

[0037] A 1.0 mol / L sodium hydroxide solution and a 0.5 mol / L ferric chloride solution are prepared respectively, and under the condition of mechanical stirring and ultrasonic dispersion (40 kHz, 20 W / L) at room temperature (25°C), a certain amount of sodium hydroxide solution is added to the ferric chloride solution, so that the molar ratio of OH - / Fe 3+ is 3.5, a suspension is formed, and after standing for 2 hours, the sample is washed repeatedly with water and filtered to remove sodium ions in the sample to meet the index requirements. The washed material is dried in a forced air oven at 60°C for 12 hours, and then at 140°C for 12 hours to obtain the hydrated iron oxide, which is crushed and sieved to obtain particles of an appropriate size as a normal and parahydrogen conversion catalyst.

[0038] It is tested that no obvious diffraction peak exists in the X-ray diffraction spectrum, indicating that the crystallinity is not high, but in the transmission electron microscopy image with a magnification of 200,000 times, obvious lattice stripe images can be observed, and in the selected area electron diffraction spectrum, some diffraction spots also appear, indicating that the obtained hydrated iron oxide is in a weak crystalline state. The average particle size of the hydrated iron oxide is 5.9 nm. The specific surface area of the catalyst is 257 m 2 / g, and the average strength is 6.7 N / particle. The normal and parahydrogen conversion performance test is shown in Table 1. Example 2

[0039] A 1.5 mol / L sodium hydroxide solution and a 1.0 mol / L ferric chloride solution were prepared respectively. Under the condition of mechanical stirring (300 rpm) and ultrasonic dispersion (100 KHz, 100 W / L) acting together, a certain amount of ferric chloride solution was added to the sodium hydroxide solution at room temperature (30°C) to meet the molar ratio of OH - / Fe 3+ 3.5, and a suspension was formed. After standing for 4 hours, the precipitate was repeatedly washed and filtered with water to remove sodium ions in the sample to meet the index requirements. The washed product was dried in a forced air oven at 60°C for 12 hours and then at 160°C for 12 hours to obtain the hydrated iron oxide, which was crushed and sieved to obtain particles of appropriate size as a primary and secondary hydrogen conversion catalyst.

[0040] Test results showed that the obtained hydrated iron oxide had a weak crystalline state, an average particle size of 7.3 nm, and a specific surface area of 239 m 2 / g. The average strength of the catalyst particles was 7.2 N / particle. The primary and secondary hydrogen conversion performance test results are shown in Table 1. Example 3

[0041] A 1.5 mol / L sodium hydroxide solution and a 1.0 mol / L ferric chloride solution were prepared respectively. Under the condition of mechanical stirring (300 rpm) and ultrasonic dispersion (100 KHz, 100 W / L) acting together, a certain amount of ferric chloride solution was added to the sodium hydroxide solution at room temperature (30°C) to meet the molar ratio of OH - / Fe 3+ 3.5, and a suspension was formed. After standing for 4 hours, the precipitate was repeatedly washed and filtered with water to remove sodium ions in the sample to meet the index requirements. The washed product was dried in a forced air oven at 60°C for 12 hours and then at 160°C for 12 hours to obtain the hydrated iron oxide, which was crushed and sieved to obtain particles of appropriate size as a primary and secondary hydrogen conversion catalyst.

[0042] Test results showed that the obtained hydrated iron oxide had a weak crystalline state, an average particle size of 7.3 nm, and a specific surface area of 239 m 2 / g. The average strength of the catalyst particles was 7.2 N / particle. The primary and secondary hydrogen conversion performance test results are shown in Table 1. Example 4

[0043] The sample was prepared according to the preparation method of Example 3 in CN201910782910.2, and other conditions were the same as those in Example 3.

[0044] Test results showed that the obtained hydrated iron oxide had a weak crystalline state, an average particle size of 7.3 nm, and a specific surface area of 239 m 2 / g. The crushed particles of appropriate size formed the normal-parahydrogen conversion catalyst. The normal-parahydrogen conversion performance test is shown in Table 1. Comparative Example 1

[0045] The preparation conditions were the same as in Example 1, except that only physical stirring was used without applying ultrasonic dispersion.

[0046] The resulting iron oxide was amorphous, and the average particle size of the hydrated iron oxide was 15.7 nm, and the specific surface area was 113 m 2 / g. The normal-parahydrogen conversion performance test is shown in Table 1. Comparative Example 2

[0047] The iron oxide was prepared according to the method provided in Example 1 of CN202210029537.5, and the grain size of the iron oxide was 24 nm, and the crystallinity was high. The specific surface area was only 64 m 2 / g. The normal-parahydrogen conversion performance test is shown in Table 1. Comparative Example 3

[0048] The iron oxide was prepared according to the method provided in Example 1 of CN202111354244.6, and the grain size of the resulting doped iron oxide was 300-1000 nm, and the iron oxide showed strong crystallization. The specific surface area was only 48 m 2 / g. The normal-parahydrogen conversion performance test is shown in Table 1. Comparative Example 4

[0049] The hydrated iron oxide was prepared according to the method of Example 3 of CN201910782910.2. The resulting hydrated iron oxide was amorphous, and the average particle size of the hydrated iron oxide was 5.8 nm, and the specific surface area was 251 m 2 / g, and the average strength of the particles was only 2.4 N / particle. The normal-parahydrogen conversion performance test is shown in Table 1.

[0050] Comparative Example 5

[0051] The sample was prepared according to the method of Example 1. The difference was that the drying stage was not staged drying, but was directly dried at 140°C for 12 hours. The resulting hydrated iron oxide had strong peaks in the XRD spectrum, indicating that the resulting hydrated iron oxide had high crystallinity. The normal-parahydrogen conversion performance test is shown in Table 1.

[0052] Table 1. Parahydrogen conversion rate of catalyst

[0053] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Secondary hydrogen conversion % 97.5 97.8 98.6 98.9 95.9 90.4 89.7 96.8 94.2

[0054] Test conditions: catalyst particle size 30-40 mesh, activation conditions 130°C vacuum drying for 12 hours, evaluation temperature 77K, volume space velocity 400 min -1 .

Claims

1. A primary-to-secondary hydrogen conversion catalyst characterized by: The active component is hydrated iron oxide, and the hydrated iron oxide is in a weakly crystalline state; the weakly crystalline state has the following characteristics: (1) in an XRD spectrum, the peak intensity of all characteristic diffraction peaks does not have a ratio greater than 2 compared with the baseline intensity at the position 2θ, and the half-height width of the diffraction angle 2θ is less than 2º; (2) in a 20 million times transmission electron microscope image, there are distinguishable crystal lattice stripe images or in an electron diffraction spectrum, there are distinguishable diffraction spots or diffraction rings; the preparation method of the primary and secondary hydrogen conversion catalyst comprises the following steps: (1) under the simultaneous action of ultrasonic dispersion and mechanical dispersion, an iron salt solution is mixed with an inorganic lye to form a colloidal mixture, and then the mixture is left to stand for a period of time; (2) the mixture obtained in step (1) is washed, separated, and then dried; the drying process comprises the following steps: in the first stage, the drying temperature is 40-100 ℃, and the drying time is 6-96 hours; in the second stage, the drying temperature is 100-200 ℃, and the drying time is 1-48 hours, and the drying atmosphere is air; (3) the dried material is crushed and sieved to obtain the primary and secondary hydrogen conversion catalyst.

2. The catalyst of claim 1, wherein: The hydrated iron oxide micro-particle size is 3-10 nm.

3. The catalyst of claim 1, wherein: The primary / secondary hydrogen conversion catalyst is in the form of particles having a particle size of 20-80 mesh and a particle crushing strength of 5-13 N / particle, and a specific surface area of 160-300 m 2 / g.

4. A process for the preparation of a primary-to-secondary hydrogen conversion catalyst as claimed in any one of claims 1 to 3, characterized in that The preparation method comprises the following steps: (1) under the simultaneous action of ultrasonic dispersion and mechanical dispersion, an iron salt solution is mixed with an inorganic lye to form a colloidal mixture, and then the mixture is left to stand for a period of time; (2) the mixture obtained in step (1) is washed, separated, and then dried; the drying process comprises the following steps: in the first stage, the drying temperature is 40-100 ℃, and the drying time is 6-96 hours; in the second stage, the drying temperature is 100-200 ℃, and the drying time is 1-48 hours, and the drying atmosphere is air; (3) the dried material is crushed and sieved to obtain the primary and secondary hydrogen conversion catalyst.

5. The method of claim 4, wherein: The iron salt in step (1) is ferric chloride and / or ferric sulfate; the iron salt solution in step (1) has a Fe 3+ concentration of 0.10-1.5 mol / L.

6. The method of claim 4, wherein: The inorganic base in step (1) is one or more of sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, sodium carbonate, sodium bicarbonate or ammonium bicarbonate; the concentration of the inorganic base solution is 0.5-2.0 mol / L as OH - .

7. The method of claim 4, wherein: The iron salt solution in step (1) is in a molar ratio of Fe 3+ to OH - in terms of OH - / Fe 3+ of 3.0 to 4.

5.

8. The method of claim 4, wherein: The ultrasonic dispersion condition in step (1) is that the ultrasonic frequency is 20-100 kHz, the ultrasonic power density acting on the reaction material is 10-1000 W / L, and the ultrasonic temperature is 10-45 ℃.

9. The method of claim 4, wherein: The mechanical dispersion in step (1) is one or more of mechanical stirring, magnetic stirring, shaking table or shearing stirring.

10. The method of claim 4, wherein: The colloidal mixture in step (1) is left to stand for 0.5-5 hours.

11. The method of claim 4, wherein: The drying process in step (2) comprises the following steps: in the first stage, the drying temperature is 60-80 ℃, and the drying time is 12-24 hours; in the second stage, the drying temperature is 120-160 ℃, and the drying time is 6-24 hours.

12. The method of claim 4, wherein: The sieving in step (3) refers to sieving out small particles formed by crushing through a standard sieve, and the sieved particles are 20-80 mesh.

13. Application of the primary and secondary hydrogen conversion catalyst as claimed in any one of claims 1-3 in a primary and secondary hydrogen conversion reaction.

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