A bar-shaped primary and secondary hydrogen conversion catalyst and a method for preparing the same

Abstract

The application discloses a bar-shaped primary and secondary hydrogen conversion catalyst and a preparation method thereof. The primary and secondary hydrogen conversion catalyst comprises weakly crystallized hydrated iron oxide and clay, wherein the weakly crystallized hydrated iron oxide accounts for 80-95% and the clay accounts for 5-20% based on the total weight of the catalyst; the micro-particle size of the weakly crystallized hydrated iron oxide is 3-12 nm; the radial size of the catalyst particle is 1.0-1.5 mm, and the axial length is 1.5-4.5 mm; the radial crushing strength is 4.5-12.5 N / mm, and the abrasion is 0.10-0.25%; and the specific surface area is 150-285 m 2 / g. The preparation method is as follows: (1) mixing an iron salt solution and an inorganic alkali solution under the action of ultrasonic dispersion and mechanical dispersion to form a colloidal mixture, and then standing; (2) washing and separating the mixture in step (1) to obtain wet hydrated iron oxide; and (3) fully mixing the wet hydrated iron oxide obtained in step (2) with clay, and then mixing, kneading, extruding and drying to obtain the catalyst. The primary and secondary hydrogen conversion catalyst is suitable for primary and secondary hydrogen conversion reaction under high space velocity conditions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ortho-para hydrogen catalytic conversion, and relates to a strip-shaped 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, and 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 to para 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] CN202111354244.6 discloses a preparation method of a doped ortho-para hydrogen conversion catalyst. Iron salt solution and metal ion solution to be doped are prepared respectively, the metal ion solution 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 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 doped iron oxide prepared by the high-temperature hydrothermal method has a large grain size (300-1000 nm) and high crystallinity, and has a small specific surface area. Moreover, the high-temperature reaction time is too long, and the synthesis efficiency is low and the energy consumption is high.

[0006] CN202210832769.4 provides an ortho-para hydrogen conversion catalyst and a preparation method. The catalyst is a Fe atom-doped fibrous magnetic catalyst FeMnO x , which has a fibrous structure with a diameter of 2-5 nm and a length of 100 nm-500 nm. 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.

[0007] CN201910782910.2 discloses a preparation method of hydrated iron oxide, a weakly basic compound is added to a ferric chloride 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. The method uses ammonium bicarbonate to act on the filter cake, and then uses ammonium bicarbonate pyrolysis to increase the specific surface area of the product, but it will cause a large decrease in the particle strength of the dried material, and the particles have many corners, resulting in large abrasion.

[0008]

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

[0009]

Journal of Research of the National Bureau of Standards, 1958, 60 (3): 221-227

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

[0011] In view of the deficiencies of the prior art, the present application provides a strip-shaped primary and secondary hydrogen conversion catalyst and a preparation method thereof. The primary and secondary hydrogen conversion catalyst of the present application has a large specific surface area, high physical strength, simple preparation method, few catalyst particle corners, low energy consumption, high preparation efficiency, and is suitable for primary and secondary hydrogen conversion reaction under high space velocity conditions.

[0012] The bar-shaped primary and secondary hydrogen conversion catalyst of the present application comprises weakly crystalline hydrated iron oxide and clay, wherein the weakly crystalline hydrated iron oxide is 80% to 95% and the clay is 5% to 20% based on the total weight of the catalyst; the weakly crystalline hydrated iron oxide has a micro-particle size of 3 to 12 nm; and the weakly crystalline hydrated iron oxide has the following characteristics: (1) in the XRD spectrum, the peak intensity of all characteristic diffraction peaks and the baseline intensity at the position (2θ) do not have a ratio greater than 2 and a half-height width of diffraction angle 2θ less than 2º; and (2) in the high-magnification (200,000 times and above) 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.

[0013] In the catalyst, the radial size of the catalyst particles is 1.0 to 1.5 mm, the axial length is 1.5 to 4.5 mm, the radial crushing strength is 4.5 to 12.5 N / mm, the abrasion is 0.10 to 0.25%, and the specific surface area is 150 to 285 m 2 / g.

[0014] The preparation method of the bar-shaped primary and secondary hydrogen conversion catalyst of the present application comprises the following contents:

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

[0016] (2) the mixture of step (1) is washed and separated to obtain wet hydrated iron oxide with a water content of 25 wt% to 50 wt%;

[0017] (3) the wet hydrated iron oxide obtained in step (2) is fully mixed with clay, and after mixing, kneading, extruding and drying, a bar-shaped primary and secondary hydrogen conversion catalyst is obtained.

[0018] In the method, step (1) is generally carried out at room temperature, and room temperature generally refers to a temperature of 10 to 45℃.

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

[0020] In the method, the inorganic base of step (1) is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate or ammonium bicarbonate, and preferably sodium hydroxide or potassium hydroxide; and the concentration of the inorganic alkali solution is 0.5 to 2.0 mol / L, preferably 1.0 to 1.5 mol / L. - ​​

[0021] In the method of the present application, the iron salt solution in step (1) is Fe 3+ counted in terms of OH - and the inorganic lye in terms of OH

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

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

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

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

[0026] In the method of the present application, the degree of washing and filtering in step (2) needs to meet the requirement that the mass content of sodium element in the final obtained catalyst composition is less than 0.2% in terms of Na2O, preferably less than 0.15% in terms of Na2O; and deionized water is used for washing operation.

[0027] In the method of the present application, the wet hydrated iron oxide with a certain water content in step (2) has the following water content: 1 gram of sample is placed in a 120℃ air oven for 12 hours, and the ratio of the mass difference before and after drying of the sample to the mass after drying is defined as the water content of the wet hydrated iron oxide.

[0028] In the method of the present application, the clay in step (3) includes kaolin, bentonite and their processed products.

[0029] In the method of the present application, the clay in step (3) is activated before use to remove part of the water: drying at 200-300℃ for 12-24 hours.

[0030] In the method of the present application, the kneading and extruding in step (3) are conventional operation processes.

[0031] In the method of the present application, the extruding in step (3) can be performed by using an extruder or other forming methods, and the shape of the obtained strip-shaped particles includes, but is not limited to, cylindrical shape, clover shape, four-leaf clover shape, and the like.

[0032] In the method of the present application, the drying condition in step (3) is drying at 130-250°C for 6-36 hours. The drying condition is further preferably drying at 140-220°C for 12-24 hours.

[0033] The application of the primary and secondary hydrogen conversion catalyst of the present application in the primary and secondary hydrogen conversion reaction, the reaction condition is: the activation condition is vacuum drying at 120-160°C for 12 hours, the evaluation temperature is 77K, the volume space velocity is 500-2000min -1 , preferably 800-1800min -1 .

[0034] In the preparation of hydrated iron oxide, the present application uses ultrasonic dispersion and physical dispersion together in the reaction process, which can synergistically strengthen the dispersion from macro and micro aspects, can avoid the aggregation of colloids or precipitates to form larger particles, and thus can maintain a highly dispersed state, which is beneficial to obtain smaller reactant particles and to improve the specific surface area of the product. In the present application, the weakly crystalline hydrated iron oxide can be generated by the micro-shear and cavitation effect of ultrasonic waves at room temperature. It has been found through experimental research that the weak crystallinity is beneficial to improve the catalyst activity. The weakly crystalline hydrated iron oxide in wet state is mixed with clay, at this time the clay can play a certain role as a binder, and also as a lubricant for extrusion molding, which is beneficial to obtain smooth strip-shaped particles with high strength after drying, and the particles have fewer edges and corners and low abrasion compared with irregular particles. The hydrated iron oxide in the present application is mixed with clay in wet state without drying, which can reduce energy consumption and improve the preparation efficiency. The strip-shaped particle catalyst of the present application can still maintain a high primary and secondary hydrogen conversion rate of 90-98% at high space velocity. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 XRD spectrum of the weakly crystalline hydrated iron oxide obtained in Example 1.

[0036] Figure 2 Transmission electron microscope image of the weakly crystalline hydrated iron oxide obtained in Example 1. IMPLEMENTATION

[0037] 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 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 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 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 hydrogen and parahydrogen in the raw material hydrogen are calculated according to 75% and 25% respectively, and the equilibrium concentration of parahydrogen is calculated according to 50.8% at liquid nitrogen temperature (77K). Example 1

[0038] A 1.2 mol / L sodium hydroxide solution and a 0.5 mol / L ferric chloride solution are respectively prepared, and under the condition of mechanical stirring and ultrasonic dispersion (40 kHz, 20 W / L) 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+ 3.5, and a suspension is formed. 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 requirements. The wet hydrated iron oxide (water content 40%) is mixed with kaolin activated at 200℃ for 12 hours, extruded, cut, and then dried at 160 o C for 12 hours, to obtain a cylindrical normal and parahydrogen conversion catalyst.

[0039] The obtained bar-shaped normal and parahydrogen conversion catalyst has a radial diameter of 1.0 mm, an axial length of 1.5-2.5 mm, and a radial crushing strength of 6.4 N / mm. The specific surface area is 233 m 2 / g. The mass content of the hydrated iron oxide is 85%, and the abrasion is 0.18%. The micro-particle size of the hydrated iron oxide is 6.8 nm, and the hydrated iron oxide has a weak crystalline state. The normal and parahydrogen conversion performance test is shown in Table 1. Example 2

[0040] 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) together, a certain amount of the ferric chloride solution was added into 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 3 hours, the precipitate was repeatedly washed and filtered with water to remove sodium ions in the sample to meet the index requirements. The wet state hydrated iron oxide (water content 30%) was mixed with kaolin activated at 300°C for 10 hours, extruded, cut, and then dried at 140 o C for 12 hours to obtain cylindrical primary and secondary hydrogen conversion catalysts.

[0041] The obtained strip-shaped primary and secondary hydrogen conversion catalyst had a radial size of 1.2 mm, an axial length of 1.5-3.0 mm, and a radial crushing strength of 5.8 N / mm. The specific surface area was 202 m 2 / g. The mass content of the hydrated iron oxide was 89%, and the abrasion was 0.18%. The hydrated iron oxide micro-particle size was 6.6 nm, and had a weak crystalline state. The primary and secondary hydrogen conversion performance test is shown in Table 1. Example 3

[0042] 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) together, a certain amount of the ferric chloride solution was added into 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 3 hours, the precipitate was repeatedly washed and filtered with water to remove sodium ions in the sample to meet the index requirements. The wet state hydrated iron oxide (water content 30%) was mixed with kaolin activated at 300°C for 10 hours, extruded, cut, and then dried at 140 o C for 12 hours to obtain cylindrical primary and secondary hydrogen conversion catalysts.

[0043] The obtained strip-shaped primary and secondary hydrogen conversion catalyst had a radial size of 1.2 mm, an axial length of 1.5-3.0 mm, and a radial crushing strength of 5.8 N / mm. The specific surface area was 202 m 2 / g. The mass content of the hydrated iron oxide was 89%, and the abrasion was 0.18%. The hydrated iron oxide micro-particle size was 6.6 nm, and had a weak crystalline state. The primary and secondary hydrogen conversion performance test is shown in Table 1. Example 4

[0044] The water content of the wet state hydrated iron oxide was changed as in Example 1. When the water content was adjusted to 20%, it was found that the material was too dry to achieve uniform mixing and extrusion molding. When the water content was adjusted to 60%, it was found that a large amount of clay needed to be additionally added to achieve uniform mixing and extrusion molding, and the active component content was too low at this time. Comparative Example 1

[0045] The catalyst was prepared according to the method provided in Example 1 without adding clay, and it was found that extrusion molding was relatively difficult and the strips were prone to breakage. The obtained product was broken into irregularly shaped particles with many corners after crushing, and the abrasion was 0.38%. The 30-40 mesh particles were selected for evaluation test. The primary and secondary hydrogen conversion performance test is shown in Table 1. Comparative Example 2

[0046] The iron oxide was prepared according to the method provided in CN202210029537.5 Example 1, the grain size of the iron oxide was 23 nm, the crystallinity was high, and the specific surface area was only 66 m 2 / g after test. It was pressed into 1mm thick tablets, and then slightly crushed. The primary and secondary hydrogen conversion performance test is shown in Table 1. Comparative Example 3

[0047] The iron oxide was prepared according to the method provided in CN202111354244.6 Example 1, the grain size of the doped iron oxide was 300-1000 nm, and the iron oxide showed strong crystallization, and the specific surface area was only 50 m 2 / g after test. It was pressed into 1mm thick tablets, and then slightly crushed. The primary and secondary hydrogen conversion performance test is shown in Table 1. Comparative Example 4

[0048] According to the research content of the literature

Journal of Research of the National Bureau of Standards, 1958, 60 (3): 221-227

[0049] Table 1 Secondary hydrogen conversion rate of catalyst

[0050]

[0051] Test conditions: The activation condition is vacuum drying at 130℃ for 12 hours, and the evaluation temperature is 77K.

Claims

1. A strip-shaped catalyst for the conversion of n- and secondary hydrogen, characterized in that: The catalyst comprises weakly crystalline hydrated iron oxide and clay. Based on the total weight of the catalyst, the weakly crystalline hydrated iron oxide accounts for 80%–95%, and the clay accounts for 5%–20%. The radial size of the catalyst particles is 1.0–1.5 mm, and the axial length is 1.5–4.5 mm. The microscopic particle size of the weakly crystalline hydrated iron oxide is 3–12 nm. The weakly crystalline hydrated iron oxide has the following characteristics: (1) In the XRD pattern, there is no diffraction peak with a ratio greater than 2 and a half-width at half-maximum of less than 2º compared with the baseline intensity at position 2θ of all characteristic diffraction peaks; (2) There are identifiable lattice fringes in the transmission electron microscope image at 200,000 times magnification or above, or identifiable diffraction spots or diffraction rings in the electron diffraction spectrum; the radial crushing strength of the catalyst is 4.5–12.5 N / mm, the wear is 0.10–0.25%, and the specific surface area is 150–285 m². 2 / g.

2. A method for preparing the strip-shaped n-parahydrogen conversion catalyst according to claim 1, characterized in that... The process includes the following: (1) Under the combined action of ultrasonic dispersion and mechanical dispersion, 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; (2) The mixture from step (1) is washed and separated to obtain wet hydrated iron oxide with a water content of 25wt%~50wt%; (3) The wet hydrated iron oxide obtained in step (2) is thoroughly mixed with clay, and after kneading, extrusion and drying, strip-shaped positive secondary hydrogen conversion catalyst is obtained.

3. The method according to claim 2, characterized in that: The iron salt mentioned in step (1) is ferric chloride and / or ferric sulfate; the iron salt solution is in the form of Fe 3+ The concentration ranges from 0.10 to 1.5 mol / L.

4. The method according to claim 2, characterized in that: The inorganic alkali mentioned in step (1) is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, or ammonium bicarbonate; the concentration of the inorganic alkali solution is expressed in terms of OH... - The concentration is calculated to be 0.5–2.0 mol / L.

5. The method according to claim 2, characterized in that: The inorganic alkaline solution described in step (1) is in the form of OH - Calculated with iron salt solution in Fe 3+ The molar ratio is 3.0 to 4.

5.

6. The method according to claim 2, characterized in that: The ultrasonic dispersion conditions in step (1) are: ultrasonic frequency 20-100kHz, ultrasonic power density acting on the reactant 10-1000W / L, and ultrasonic temperature 10-45℃.

7. The method according to claim 2, characterized in that: The ultrasonic dispersion conditions in step (1) are: ultrasonic frequency 40-80kHz, ultrasonic power density 20-100W / L, and ultrasonic temperature maintained at 20-35℃.

8. The method according to claim 2, characterized in that: The separation described in step (2) involves natural sedimentation, centrifugation, vacuum filtration, or pressure filtration to separate the solid and liquid phases of the washed suspension, thereby obtaining the solid phase.

9. The method according to claim 2, characterized in that: The degree of washing and filtration described in step (2) is such that the sodium content in the final catalyst composition, calculated as Na2O, is less than 0.2% by mass.

10. The method according to claim 2, characterized in that: The clay described in step (3) is activated before use to remove some of the moisture: it is dried at 200-300℃ for 12-24 hours.

11. The method according to claim 2, characterized in that: The extrusion process described in step (3) is carried out using a forming method such as an extrusion machine, and the resulting strip particles are cylindrical, clover-shaped, or four-leaf clover-shaped.

12. The method according to claim 2, characterized in that: The drying conditions for step (3) are to dry at 130-250°C for 6-36 hours.

13. The application of the strip-shaped n-parahydroconversion catalyst according to claim 1 in the n-parahydroconversion reaction, characterized in that: The reaction conditions for the conversion of n- and secondary hydrogen are: volume hourly space velocity (VHSV) of 500–2000 min. -1 .

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