A process for the preparation of a primary-to-secondary hydrogen conversion catalyst

Abstract

The application discloses a preparation method of a primary and secondary hydrogen conversion catalyst, and comprises the following steps: (1) mixing an iron-containing solution with a precipitant under the simultaneous action of ultrasonic dispersion and mechanical dispersion to obtain a colloidal mixture, and then standing for a period of time; (2) washing and separating the material obtained in the step (1), and then performing drying treatment to obtain a weakly crystalline hydrated iron oxide material, crushing the material, and screening a powder with a mesh size of 500-1600; and (3) uniformly mixing the powder obtained in the step (2), clay and an organic acid solution, mixing, kneading, extruding, shortening, using a rolling machine to secondarily shape the strip-shaped material into spherical particles, and drying to obtain the catalyst. The primary and secondary hydrogen conversion catalyst has the advantages of large specific surface area, high physical strength, simple preparation method, few corners and edges of the catalyst particles, 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 catalyst preparation and relates to a preparation method of a primary-secular hydrogen conversion catalyst. BACKGROUND

[0002] Liquid hydrogen is an efficient 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, wherein the nuclear spin symmetry is primary hydrogen and the anti-symmetry is secular hydrogen. Primary hydrogen and secular hydrogen can stably exist in liquid and gaseous states, and the equilibrium concentration of the two is affected by temperature. At room temperature, the content of primary hydrogen in hydrogen gas is 25%, and the content of secular hydrogen is 75%, which is called normal hydrogen or standard hydrogen. When the temperature decreases, primary hydrogen will spontaneously convert to secular hydrogen. At the standard boiling point of liquid hydrogen, the content of secular hydrogen can reach 99.8%. Without the action of an external catalyst, the spontaneous conversion of hydrogen from primary to secular 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. To liquefy hydrogen while quickly completing the conversion of primary hydrogen to secular hydrogen, it is crucial to develop a high-performance primary-secular hydrogen conversion catalyst for the production of liquid hydrogen.

[0004] Currently, amorphous hydrated iron oxide is mainly used as a primary-secular hydrogen conversion catalyst. CN202111354244.6 discloses a preparation method of a doped primary-secular hydrogen conversion catalyst. An iron salt solution and a solution of metal ions to be doped are prepared, the solution of metal ions to be doped is added to the iron salt solution in a certain proportion, an appropriate amount of lye is added, the precipitate obtained by hydrothermal reaction of the mixed solution is washed, dried, and ground to obtain hydrated iron oxide particles with irregular shapes. The particles have many edges and corners and low strength, and have large abrasion when used as a catalyst. On the other hand, the method uses a high-temperature hydrothermal method to prepare doped iron oxide with a large grain size (300~1000nm) and high crystallinity, and the product has 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. CN202210832769.4 provides a primary-secular hydrogen conversion catalyst and a preparation method. The catalyst is a fiber magnetic catalyst FeMnO x doped with Fe atoms, has a fibrous structure with a diameter of 2~5nm and a length of 100nm~500nm, and the product has a large particle size and a low specific surface area. The method needs to use a hydrothermal reaction, has high energy consumption, and has high preparation cost due to the need to prepare a manganese oxide precursor.

[0005] CN201910782910.2 discloses a preparation method of hydrated iron oxide, a weakly basic compound is added to a ferric chloride solution, aging, filtering, and the filter cake is dispersed in an ammonium bicarbonate solution, filtering, drying, to obtain hydrated iron oxide. The method uses a weak base as a precipitant, and the crystal phase of the product obtained by reaction at normal temperature and pressure is mainly amorphous. In this method, the filter cake is reacted with ammonium bicarbonate, and then the ammonium bicarbonate is pyrolyzed to form pores to increase the specific surface area of the product, but this will cause a large decrease in the particle strength of the dried material, and the particles have many corners, resulting in large abrasion. SUMMARY

[0006] To overcome the shortcomings of the prior art, the present application provides a preparation method of primary and secondary hydrogen conversion catalyst. The primary and secondary hydrogen conversion catalyst has a large specific surface area, high physical strength, simple preparation method, few catalyst particle corners, low energy consumption, high preparation efficiency, and high catalytic activity for primary and secondary hydrogen conversion.

[0007] The preparation method of the primary and secondary hydrogen conversion catalyst of the present application includes the following contents:

[0008] (1) Under the simultaneous action of ultrasonic dispersion and mechanical dispersion, an iron-containing solution is mixed with a precipitant to obtain a colloidal mixture, which is then left to stand for a period of time;

[0009] (2) The material obtained in step (1) is washed, separated, and then dried to obtain a weakly crystalline hydrated iron oxide material, which is then crushed and sieved to obtain a powder with a particle size of 500-1600 mesh. The drying conditions are as follows: drying temperature 10-90℃, drying time 12-120 hours, and drying atmosphere air atmosphere;

[0010] (3) The powder obtained in step (2), clay, and an organic acid solution are thoroughly mixed and kneaded, extruded into strips, cut, and then formed into spherical particles using a rounder, and dried to obtain the catalyst.

[0011] In the method of the present application, the reaction temperature in step (1) is 10-45℃, and the standing time is 0.5-5 hours.

[0012] In the method of the present application, the iron-containing solution in step (1) is an aqueous solution of ferric chloride and / or ferric sulfate; the concentration of the iron-containing solution is 0.10-1.5 mol / L, preferably 0.15-1.0 mol / L. 3+

[0013] In the method of the present application, the precipitant in step (1) is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, or ammonium bicarbonate aqueous solution; the concentration of the precipitant is 0.10-1.5 mol / L, preferably 0.15-1.0 mol / L. - ​The concentration of the alkali solution is 0.5-2.0 mol / L, preferably 1.0-1.5 mol / L.

[0014] In the method, the iron-containing solution in step (1) has a concentration of Fe 3+ The molar ratio of the alkali solution to the precipitant is 3.0-4.5. -

[0015] In the method, the ultrasonic dispersion condition in step (1) is as follows: 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 as follows: 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 ℃.

[0016] In the method, the mechanical dispersion in step (1) includes but is not limited to mechanical stirring, magnetic stirring, a shaking table, shear stirring and any other mode and operation condition that is beneficial to the rapid and uniform mixing of the material.

[0017] In the method, the order and mode of adding the material in step (1) are not particularly limited, and the alkali solution is preferably added to the iron salt solution in one batch or in batches, preferably in batches.

[0018] In the method, the separation in step (2) can be performed by natural sedimentation, centrifugation, vacuum filtration or pressure filtration to separate the solid-liquid mixture after washing to obtain a solid phase material.

[0019] In the method, the degree of washing and filtering in step (2) needs to meet the following condition: the mass content of sodium element in the final obtained catalyst composition is less than 0.5% as Na2O, preferably less than 0.25% as Na2O; and deionized water is used for washing.

[0020] In the method, the drying treatment in step (2) is further preferred to be performed at a temperature of 40-80 ℃ for 12-24 hours.

[0021] In the method, the crushing in step (2) can be performed by various means such as rolling, ball milling and the like, and the crushing process should keep the powder from changing the crystal form.

[0022] In the method, the clay in step (3) includes kaolin, bentonite and processed products thereof.

[0023] In the method, the organic acid solution in step (3) is an aqueous solution of acetic acid, propionic acid, oxalic acid or citric acid, and the mass concentration is 2 wt%-10 wt%. ​

[0024] In the method, the amount of clay in step (3) is 5-25% by weight of the total amount of hydrated iron oxide and clay, and is further preferably 10-20%.

[0025] In the method, the amount of acid solution in step (3) is determined according to the amount of mixture added for suitable extrusion molding.

[0026] In the method, the material in step (3) further preferably includes 3-10% of organic additives, including amaranth powder and cellulose, by weight of the total amount of hydrated iron oxide and clay.

[0027] In the method, the kneading and extruding in step (3) are conventional operations. The obtained cylindrical particles have a radial dimension of 0.5-1.0 mm and an axial dimension of 0.5-1.0 mm in the wet state, and the ratio of the axial dimension to the radial dimension is 1: (1-2).

[0028] In the method, the drying condition in step (3) is a drying temperature of 140-300°C and a drying time of 6-36 hours.

[0029] In the method, the diameter of the spherical particles obtained after the rounding in step (3) is 0.3-0.6 mm after drying.

[0030] The primary and secondary hydrogen conversion catalyst prepared by the method is a spherical particle with a diameter of 0.30-0.90 mm, a crushing strength of 5-12 N / particle, an abrasion of 0.05-0.20%, a specific surface area of 150-250 m 2 / g, and the catalyst includes hydrated iron oxide and clay, wherein the hydrated iron oxide accounts for 75-95% and the clay accounts for 5-25% by weight of the total catalyst, and the micro-particle size of the hydrated iron oxide is 3-12 nm.

[0031] In the primary and secondary hydrogen conversion catalyst, the hydrated iron oxide is in a weak crystalline state and has the following characteristics: (1) in the XRD spectrum, the peak intensity of all characteristic diffraction peaks does not have a ratio greater than 2 and a half-height width of diffraction angle 2θ less than 2º compared with the baseline intensity at the position (2θ); and (2) there are distinguishable lattice stripe images in the high-magnification (200,000 times and above) transmission electron microscope image or distinguishable diffraction spots or rings in the electron diffraction spectrum.

[0032] In the preparation of hydrated iron oxide, this invention utilizes both ultrasonic and physical dispersion throughout the reaction process. This synergistic effect enhances dispersion at both the macroscopic and microscopic levels, preventing the aggregation of colloids or precipitates into larger particles and maintaining a highly dispersed state. This results in smaller reactant particles and an increased specific surface area of ​​the product. At room temperature, the invention utilizes the micro-regional shearing and cavitation effects created by ultrasound to generate weakly crystalline hydrated iron oxide, which, according to experimental studies, enhances catalyst activity. This invention further refines the process by pulverizing the weakly crystalline hydrated iron oxide into fine particles, using clay as a binder and organic acid as a solvent. The particles are then extruded, re-sphericalized, and dried to obtain spherical catalyst particles. The internal distribution of hydrated iron oxide particles increases the catalyst's porosity, thereby improving the effective contact area between hydrogen molecules and the catalyst. The resulting spherical particles exhibit high strength, fewer sharp edges, and low wear. The spherical catalyst of this invention demonstrates excellent activity in the catalytic conversion of n- and para-hydrogen. The spherical shape of the catalyst helps reduce flow resistance in the device and also provides advantages such as convenient loading. Attached Figure Description

[0033] Figure 1 The image shows the XRD pattern of the weakly crystalline hydrated iron oxide obtained in Example 1.

[0034] Figure 2 The electron diffraction pattern of the weakly crystalline hydrated iron oxide obtained in Example 1 is shown. Detailed Implementation

[0035] The application is further described in detail below with reference to examples. The Na2O content in the catalyst is tested by XRF method; the hydrated iron oxide (calculated as Fe2O3) content in the catalyst is detected 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 the BET method; the nanoparticle size and lattice image of the iron oxide are observed by transmission electron microscopy. The radial crushing strength of the bar-shaped sample is detected according to the content of Chapter 5.11 in HG / T 3927-2007 method. The abrasion is tested according to HG / T 2976-1999. The judgment method of the crystallization strength of the sample is defined as follows: (1) for a strong crystallization sample, in the XRD spectrum of the sample, at least one diffraction peak with a ratio of peak intensity to baseline intensity at the position (2θ) greater than 2 exists, and the half-height width of the diffraction angle 2θ is less than 2º; (2) for a weak crystallization sample, no diffraction peak meeting the above strong crystallization judgment condition exists in the XRD spectrum of the sample, 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 method, 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). The application of the normal and parahydrogen conversion catalyst of the application in the normal and parahydrogen conversion reaction is under the following reaction conditions: the activation condition is vacuum drying at 120-160℃ for 6-12 hours, the evaluation temperature is 77K, the volume space velocity is 350min -1 . Example 1

[0036] A 1.2 mol / L sodium hydroxide solution and a 0.5 mol / L ferric chloride solution are respectively prepared, and under the condition that mechanical stirring and ultrasonic dispersion (40 kHz, 20 W / L) act together, a certain amount of the sodium hydroxide solution is added into the ferric chloride solution at room temperature (25℃), so as to meet the molar ratio of OH - / Fe 3+ in the system is 3.5, a suspension is formed, and after standing for 2 hours, the sample is repeatedly washed and filtered to remove sodium ions in the sample so as to meet the index requirement. The washed sample is dried in a blast drying oven at 50℃ for 12 hours to obtain hydrated iron oxide. The hydrated iron oxide is crushed by a pulverizer, and the powder with a particle size of 700-900 is mixed with clay, and a proper amount of 5% propionic acid solution is added, and after mixing, kneading, extruding, and shortening, the material is secondarily shaped into spherical particles by using a rolling machine. Then, the spherical particles are dried at 140 o C for 12 hours to obtain the spherical normal and parahydrogen conversion catalyst.

[0037] The obtained spherical primary and secondary hydrogen conversion catalyst particles have a diameter of 0.5 mm, a radial crushing strength of 6.4 N / particle, a specific surface area of 215 m 2 / g. The hydrated iron oxide has a mass content of 86%, an abrasion of 0.12%, a micro-particle size of 6.6 nm, and a weak crystalline state. The primary and secondary hydrogen conversion performance test is shown in Table 1. Example 2

[0038] A 1.5 mol / L sodium hydroxide solution and a 1.0 mol / L ferric chloride solution were prepared respectively, and a certain amount of the ferric chloride solution was added into the sodium hydroxide solution at room temperature (30°C) under the combined action of mechanical stirring (300 rpm) and ultrasonic dispersion (100 KHz, 100 W / L) 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 material was dried in a blast drying oven at 60°C for 12 hours and then at 160°C for 12 hours to obtain the hydrated iron oxide. The hydrated iron oxide was crushed by a pulverizer, and the powder with a mesh size of 800-1000 was mixed with bentonite. An appropriate amount of 5% acetic acid solution was added, and after mixing, extruding, and shortening, the material was secondarily shaped into spherical particles by a spheroidizing machine. Then, the spherical particles were dried at 160 o C for 10 hours to obtain the spherical primary and secondary hydrogen conversion catalyst of the present application.

[0039] The obtained spherical primary and secondary hydrogen conversion catalyst particles have a diameter of 0.4 mm, a radial crushing strength of 5.5 N / particle, a specific surface area of 233 m 2 / g. The hydrated iron oxide has a mass content of 90%, an abrasion of 0.10%, a micro-particle size of 6.2 nm, and a weak crystalline state. The primary and secondary hydrogen conversion performance test is shown in Table 1. Example 3

[0040] A 1.5 mol / L sodium hydroxide solution and a 1.0 mol / L ferric chloride solution were prepared respectively, and a certain amount of the ferric chloride solution was added into the sodium hydroxide solution at room temperature (30°C) under the combined action of mechanical stirring (300 rpm) and ultrasonic dispersion (100 KHz, 100 W / L) to meet the molar ratio of OH - / Fe 3+The molar ratio is 3.5, a suspension is formed, and after standing for 0.5 hours, the precipitate is repeatedly washed and filtered with water to remove sodium ions in the sample to meet the index requirements. The washed material is dried in a forced air oven at 80°C for 10 hours and then at 105°C for 12 hours to obtain the hydrated iron oxide. A pulverizer is used to crush it, and the 1200-1400 mesh powder is screened and mixed uniformly with bentonite. An appropriate amount of 3% propionic acid solution is added, and after mixing, extruding, and shortening, the material is again shaped into spherical particles using a spheroidizing machine. Then, the spherical particles are dried at 130 o C for 15 hours to obtain the spherical primary and secondary hydrogen conversion catalyst described in the application.

[0041] The obtained spherical primary and secondary hydrogen conversion catalyst particles have a diameter of 0.9 mm, a radial crushing strength of 8.8 N / mm, a specific surface area of 248 m 2 / g. The mass content of hydrated iron oxide is 75%, the abrasion is 0.18%, the micro-particle size is 6.5 nm, and it has a weak crystalline state. The primary and secondary hydrogen conversion performance test is shown in Table 1. Comparative Example 1

[0042] Iron oxide is prepared according to the method provided in CN202111354244.6 Example 1, and the obtained doped iron oxide has a grain size of 300-1000 nm. The iron oxide is strongly crystalline, and the specific surface area is only 50 m 2 / g after testing. The obtained irregular particles have many edges and corners, and the abrasion is 0.43%. The primary and secondary hydrogen conversion performance test is shown in Table 1. Comparative Example 2

[0043] Iron oxide is prepared according to the method provided in CN202210029537.5 Example 1, and the iron oxide has a grain size of 23 nm and high crystallinity. The specific surface area is only 66 m 2 / g after testing. The primary and secondary hydrogen conversion performance test is shown in Table 1. Comparative Example 3

[0044] Hydrated iron oxide is prepared according to the method provided in Example 1, but no clay is added for shaping. It can be extruded into a strip shape, but when the spheroidizing machine is used to make balls, the small balls are easily scattered and broken, and the abrasion is 0.38%.

[0045] Table 1 Secondary hydrogen conversion rate of catalyst

[0046] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Parahydrogen conversion % 97.5 97.6 98.2 88.6 90.1

Claims

1. A process for the preparation of a primary-to-secondary hydrogen conversion catalyst, characterized in that The method comprises the following steps: (1) mixing and reacting an iron-containing solution and a precipitant under the simultaneous action of ultrasonic dispersion and mechanical dispersion to obtain a colloidal mixture, and then standing for a period of time; (2) washing, separating and drying the material obtained in step (1) to obtain weakly crystalline hydrated iron oxide material, and then crushing and screening the material to obtain a powder with a particle size of 500-1600; the drying treatment is performed at a drying temperature of 10-90°C for 12-120 hours in an air atmosphere; (3) mixing the powder obtained in step (2), clay and an organic acid solution uniformly, and then mixing, kneading, extruding, shortening, and using a rolling machine to reshape the strip-shaped material into spherical particles, and then drying to obtain a catalyst; the reaction temperature in step (1) is 10-45°C, and the standing time is 0.5-5 hours; the precipitant in step (1) is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate or ammonium bicarbonate solution; the concentration of the precipitant is 0.5-2.0 mol / L in terms of OH - ; the ultrasonic dispersion conditions in step (1) are as follows: an ultrasonic frequency of 20-100 kHz, an ultrasonic power density of 10-1000 W / L acting on the reaction material, and an ultrasonic temperature of 10-45°C; the molar ratio of the precipitant in step (1) to the iron-containing solution in terms of OH - to Fe 3+ is 3.5; the organic acid solution in step (3) is one or more of acetic acid, propionic acid, oxalic acid and citric acid solution, and the concentration of the organic acid solution is 2wt%-10wt%; the amount of the clay in step (3) accounts for 5%-25% of the total amount of the hydrated iron oxide and the clay in terms of weight.

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

3. The method of claim 1, wherein: The concentration of the precipitant in step (1) is 1.0 to 1.5 mol / L in terms of OH - .

4. The method of claim 1, wherein: The ultrasonic dispersion conditions of step (1) are as follows: ultrasonic frequency 40-80 kHz, ultrasonic power density 20-100 W / L, and ultrasonic temperature 20-35℃.

5. The method of claim 1, wherein: The drying conditions of step (2) are as follows: drying temperature 40-80℃, and drying time 12-24 hours.

6. The method of claim 1, wherein: The amount of clay used in step (3) is 10%-20% by weight of the total amount of hydrated iron oxide and clay.

7. The method of claim 1, wherein: The drying conditions of step (3) are as follows: drying temperature 140-300℃, and drying time 6-36 hours.

8. A primary-secondary hydrogen conversion catalyst prepared according to the method of any one of claims 1 to 7, characterized by: The catalyst is in the form of spherical particles having a diameter of 0.30 to 0.90 mm, a crushing strength of 5 to 12 N / particle, an attrition of 0.05 to 0.20%, and a specific surface area of 150 to 250 m 2 / g.

9. The catalyst of claim 8, wherein: The catalyst comprises hydrated iron oxide and clay, wherein the amount of hydrated iron oxide is 75%-95% and the amount of clay is 5%-25% based on the total weight of the catalyst, the micro-particle size of the hydrated iron oxide is 3-12 nm, the hydrated iron oxide is weakly crystalline, and has the following characteristics: (1) in the XRD spectrum, the peak intensity of all characteristic diffraction peaks is not greater than 2 times the baseline intensity at the position 2θ, and the half-height width of the diffraction angle 2θ is less than 2º; (2) in the 200,000 times or more transmission electron microscope image, there are distinguishable crystal lattice stripe images or in the electron diffraction spectrum, there are distinguishable diffraction spots or diffraction rings.

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