Process for the conversion of ortho-hydrogen to para-hydrogen

Abstract

The subject of the present invention is a novel process for the conversion of ortho- to para-hydrogen. The invention also relates to the use of an iron-containing zeolite for the conversion of hydrogen isotopes, preferably further described herein.

Description

Technical Field

[0001] The present invention mainly relates to a process for the conversion of ortho-hydrogen to para-hydrogen, characterized in that an iron-containing zeolite is used as a catalyst. The present invention also relates to the use of an iron-containing zeolite for the conversion of hydrogen isotopes, preferably further described herein.

[0002] Further aspects of the present invention and their preferred embodiments will become apparent from the following description and the appended claims.

Background Art

[0003] The production of energy and chemical products from natural resources such as oil or natural gas is no longer sustainable in the medium term due to limited reserves. In particular, the use of natural resources results in high CO2 emissions leading to global warming. At present, the possible consequences from this can only be estimated, but it is foreseeable that this will become a survival problem for humanity. Furthermore, oil is too valuable for the chemical industry to burn due to its composition and the large number of basic molecules. For the long-term success of the energy transition and global climate protection, alternatives to fossil fuels are of utmost importance.

[0004] In this context, hydrogen plays an important role as an energy store or as a material element for further substance conversions. Climate-friendly hydrogen production (= green hydrogen) makes it possible to reduce CO2 emissions in mobile and stationary applications. This is particularly applicable to applications where the direct use of electricity from renewable resources is insufficient or not possible. Therefore, the production, transport and storage of hydrogen from renewable resources are important global issues.

[0005] For hydrogen storage and transportation, in many cases, liquefaction followed by storage in liquid form is the most economical solution due to the significantly increased density. This is especially true when the geographical distance between the production site and the consumption site is very large. Efficient transportation in pipelines requires extremely high pressures, which causes metal pipes to become brittle under these conditions. Furthermore, a large number of high-pressure compression devices are required, and as a result, due to their high energy requirements, it ultimately makes transportation uneconomical. Therefore, hydrogen pipelines are only used on a local scale within chemical factories or network facilities.

[0006] Hydrogen molecules can exist as two types of variant forms (allotropes), and these variant forms 1 differ in the orientation of their H nuclear spins and thus exhibit different rotational energies, which in turn give rise to different physical properties. The two nuclear spins are oriented antiparallel in the para form and parallel in the ortho form. The allotropy of hydrogen was discovered in the 1920s as part of the development of quantum theory. The names associated with this are, for example, Bonhoeffer, Heisenberg, Eucken, Mecke and Hund (Non-Patent Document 1).

[0007] These two types of allotropes coexist in an equilibrium state that depends on temperature. Above 250 K, the mixture of hydrogen allotropes consists of 75% ortho form and 25% para form. This ratio does not change even if the ambient temperature is higher. Here, standard hydrogen is being described. At the low temperatures required for hydrogen liquefaction, this equilibrium gradually shifts towards the para form. At temperatures below 20 K, almost only the para form exists (Patent Document 1). However, the equilibrium conversion from the ortho form to the para form occurs only slowly during cooling because the interaction between the nuclei is very weak. The conversion from ortho hydrogen to the para form is exothermic and has a conversion energy of 527 KJ / kg. Conversely, the conversion from the para form to the ortho form is an endoergic reaction.

[0008] The rate of ortho-para conversion and the exothermic nature of this reaction play an important role in the liquefaction of hydrogen. On the other hand, the energy required for liquefaction necessarily increases because the energy released (527 kJ / kg) is higher than the evaporation enthalpy of para-hydrogen (446 kJ / kg), i.e., hydrogen evaporates with the increase in the conversion from ortho to para and / or continuous cooling with high energy input is required to keep the whole amount in liquid state. On the other hand, due to the slow equilibration, a certain proportion of ortho-hydrogen is not converted to para-hydrogen. During subsequent storage, the energy released during self-conversion causes evaporation of liquid hydrogen and thus undesirable losses. Therefore, for industrial liquid hydrogen, a para-hydrogen content of at least 95% is required. In that case, ultimately, the possible evaporation losses are significantly minimized (storage period 14 days, hydrogen loss < 1%).

[0009] To achieve the required low ortho-hydrogen content, all industrial hydrogen liquefaction plants use catalysts that accelerate the equilibration process during the cooling process. If the achievement of each equilibrium is as fast as the cooling rate, no further energy is released at the triple point. In practice, catalysts based on paramagnetic iron oxide (Fe2O3, IONEX (registered trademark) type O-P catalyst, Molecular Products) are almost exclusively used for this purpose. Thereby, a significant energy saving can already be achieved currently (about 20%).

[0010] The catalytic conversion by the interaction of hydrogen molecules with paramagnetic surfaces / species was discovered as early as the beginning of the 1930s by Farkas and Sachse (Non-Patent Document 2). Other paramagnetic catalysts, such as Ru / silicate, Ru / aluminate (Patent Document 2), Cr2O3 on Al2O3, CeO2, Ni / Al2O3, MnO2 on Al2O3 and unsupported (Non-Patent Document 3), Oxysorb (registered trademark), CrO3 on Apachi nickel-silica from SiO2 and Air Products (Non-Patent Document 4) have been described, but so far all candidates examined have been less effective than standard iron oxide catalysts.

[0011] However, the iron oxide catalysts commonly used today still have several disadvantages. The catalyst particles used are in the range of 0.3 - 0.6 mm and are very brittle. This means that they produce small particles (dust) that can lead to process problems. The available surface is basically the geometric surface of the particles, i.e., the central part inside the catalyst particles cannot come into contact with hydrogen. Furthermore, this material is highly hygroscopic, which hinders conversion even at low moisture concentrations and / or requires elaborate activation and regeneration, i.e., it has an adverse effect on the catalyst life. It should also be mentioned that due to the crystal shape and particle size, the design optimized for the application process (such as the cooling process etc.) is severely restricted.

[0012] It should also be mentioned that known iron oxide catalysts can only be used in the ortho-para conversion process below 80 K, i.e., they still cannot be used in conventional cooling processes at higher temperatures. This is mainly because known catalysts are hygroscopic and the initial mixture must have residual moisture removed in advance by a cooling process.

[0013] For potentially suitable catalysts, in order to achieve the overall optimal effect, it is necessary to consider and optimize multiple physical parameters. These are, in particular, 1. Diffusion through the fluid boundary layer to the catalyst surface, 2. Diffusion into the pores of the catalyst, 3. Adsorption on the surface of the catalyst center, 4. Surface reaction or interaction with paramagnetic centers or, if available, hydrogen exchange centers 5. Desorption from the catalyst center surface, 6. Diffusion of the product from the pores, and 7. Diffusion of the product through the fluid boundary layer, is.

[0014] An effective catalyst is a catalyst in which the entire process occurs at the desired rate. Thus, the slowest step in this process chain determines the overall rate of the desired reaction.

[0015] The conversion rate can be analyzed in various ways. In this specification, reference can be made to the method described in Patent Document 1 by Linde AG as a standard method. In this method, physical data such as temperature and pressure before conversion (before the catalyst) and after conversion (after the catalyst) are measured, and the para-ortho ratio is calculated using known physical data. This method is described in detail in Patent Document 1.

Prior Art Documents

Patent Documents

[0016]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0017]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Summary of the Invention

Means for Solving the Problems

[0018] The first object of the present invention is to provide a process for the conversion of ortho-hydrogen to para-hydrogen that overcomes the disadvantages described above. Preferably, a process that on the one hand avoids or reduces hydrogen loss due to evaporation during the production of liquid hydrogen and on the other hand minimizes or reduces the ortho-hydrogen ratio is provided, preferably in such a way that the adjustment of the thermodynamic ortho-para hydrogen equilibrium in the entire cooling process is linked to the adjustment of the cooling rate. This should advantageously lead to energy savings in the cooling process and generally also to cost savings. Furthermore, the present invention should result in higher quality industrially liquefied hydrogen that preferably meets the requirement of having a para-hydrogen content of at least 95%. Furthermore, a process is provided in which a preferred catalyst is used that does not require elaborate activation and regeneration treatments of the catalyst and has little or no reduction in efficiency. Above all, a process is provided in which the catalyst can be used over a significantly wider temperature range than the conventionally known iron oxide catalyst. Further objects underlying the present invention will become apparent from the following description and the appended claims.

[0019] Surprisingly, in the context of the present invention, it has been found that iron-doped hydrophobic zeolites, which advantageously have Bronsted centers, are ideally suitable for the conversion of ortho- to para-hydrogen. Zeolites rich in silicon with hydrophobic properties, a high internal surface area of several 100 m2 / g and proton-Bronsted centers have proven to be particularly suitable. Since the iron chemical species or clusters are preferably geometrically restricted in growth by the small pore sizes of 4 to 8 Å in the zeolite, such catalysts exhibit a high utilization rate of the intrinsic centers. Accessibility is ideally provided by the multidimensional pore system (three-dimensional pore system) in zeolites of the MFI, MOR, FAU or BEA type, for example. The further advantageously present proton-Bronsted centers are capable of proton exchange with hydrogen, thereby further accelerating (catalyzing) the overall conversion to para-hydrogen in a higher process temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0020]

Figure 1

Figure 2

DETAILED DESCRIPTION OF THE INVENTION

[0021] According to a first aspect, the present invention relates to a process for the conversion of ortho-hydrogen to para-hydrogen, comprising or consisting of the following plurality of steps: - providing a starting mixture comprising or consisting of ortho- and para-hydrogen; - cooling the starting mixture and converting ortho-hydrogen to para-hydrogen using a catalyst; characterized in that an iron-containing zeolite is used as the catalyst.

[0022] In a preferred embodiment, the cooling of the starting mixture and the conversion of ortho-hydrogen to para-hydrogen are carried out by one of the following plurality of steps: a) cooling the starting mixture and then converting ortho-hydrogen to para-hydrogen using a catalyst; or b) cooling the starting mixture and converting ortho-hydrogen to para-hydrogen using a catalyst simultaneously or partially simultaneously; or c) cooling the starting mixture and then reacting ortho-hydrogen using the catalyst to para-hydrogen, thereby further cooling the starting mixture during the conversion. This is the process according to the invention described herein, characterized in that it is carried out by one of the above.

[0023] In a particularly preferred embodiment, the process according to the invention is characterized in that liquid hydrogen or cryogenic hydrogen having a para-hydrogen content of at least 95% by weight based on the total hydrogen content is produced. Another preferred embodiment is the process according to the invention, characterized in that the iron-containing zeolite has Bronsted centers.

[0024] Catalysts particularly suitable for the processes described herein should have a high concentration of paramagnetic centers, or rather a high concentration of potential H + exchange centers, a high tendency to adsorb hydrogen and a high accessibility (porosity) that minimizes diffusion barriers. Most of the materials described and studied in the literature are hydrophilic and do not have acidic proton Bronsted centers.

[0025] In a particularly preferred embodiment, the iron species in the zeolite pores and / or pore intersections have a maximum diameter of 12 angstroms or less.

[0026] Another preferred embodiment of the process according to the invention is when the iron-containing zeolite has one of the following MFI structure, BEA structure, MOR structure, CHA structure, AEI structure, AFX structure, FAU structure.

[0027] Another preferred embodiment of the invention is a process in which the iron-containing zeolite used has an SiO2 / Al2O3 molar ratio between 2 and 1000, preferably between 5 and 200, particularly preferably between 10 and 100.

[0028] According to a preferred embodiment, the SiO2 / Al2O3 molar ratio of the iron-containing zeolite is adjusted or set such that it is hydrophobic.

[0029] Another preferred embodiment is the process according to the invention, in which the iron-containing zeolite has an Fe / Al atomic ratio between 0.1 and 2, preferably between 0.2 and 1.

[0030] Another preferred embodiment is the process according to the invention, in which the catalyst is present as a shaped body.

[0031] In this case, the shaped body preferably has one or more shapes selected from the group consisting of regular or irregular geometric shapes, such as spheres, pellets, perfect cylinders, such as extruded pellets or tablets, hollow cylinders such as rings, cylinders with several through internal perforations, tripods, crown rings, wheels, armchairs, granules, fragments of compressed masses, monoliths and cross-channel structures.

[0032] Another preferred embodiment is the process according to the invention, wherein the shaped body (preferably as described above) is produced by extrusion, granulation, tableting or compression.

[0033] Another preferred embodiment is the process according to the invention, wherein the catalyst is produced by coating a honeycomb or another geometric body.

[0034] Another aspect of the invention relates to the use of an iron-containing zeolite (described herein in the context of the process according to the invention) for the conversion of hydrogen isotopes, preferably from ortho-hydrogen to para-hydrogen, preferably in the process described herein, particularly preferably in its preferred embodiments (described herein).

[0035] Also described herein is a product of the conversion from ortho- to para-hydrogen, preferably obtained or obtainable by the process described herein, preferably described as preferred herein, and having a para-hydrogen content of at least 95% based on the total amount of hydrogen.

[0036] Another preferred embodiment of the process according to the invention is the process described above, wherein the temperature of the conversion is in the range of 150 to 20 K, preferably in the range of 120 to 20 K, most preferably in the range of 80 to 20 K.

[0037] A more preferred embodiment is the process according to the invention described herein, wherein the pressure during conversion is in the range of 50 to 5 bar, preferably in the range of 30 to 13 bar.

[0038] A preferred embodiment is the process according to the invention described herein, wherein the iron-containing zeolite has pore openings with an average diameter in the range of 4 to 8 angstroms.

[0039] Also disclosed herein is an iron-containing zeolite catalyst for the conversion of ortho-hydrogen to para-hydrogen, wherein the iron-containing zeolite is characterized by having pore openings with an average diameter in the range of 4 to 8 angstroms. In all other respects, the catalyst is as defined above for the catalysts used according to the invention and its preferred embodiments, or as specified in the appended claims.

[0040] Thus, for example, it is preferred that such an iron-containing zeolite catalyst is characterized in that the zeolite has Bronsted centers.

[0041] For example, it is more preferred that the iron-containing zeolite catalyst is characterized in that the zeolite has one of the following structures: MFI structure, BEA structure, MOR structure, CHA structure, AEI structure, AFX structure, FAU structure.

[0042] Furthermore, preferably, the iron-containing zeolite catalyst is characterized in that the SiO2 / Al2O3 molar ratio is between 2 and 1000, preferably between 5 and 200, more preferably between 10 and 100.

[0043] For example, it is also preferred that the iron-containing zeolite catalyst is characterized by the presence of an Fe / Al ratio between 0.1 and 2, preferably between 0.2 and 1.

[0044] Furthermore, it is particularly preferred that the iron-containing zeolite catalyst is characterized in that the catalyst exists as a shaped body.

[0045] Furthermore, it is particularly preferred that the iron-containing zeolite catalyst is prepared by extrusion, granulation, tableting or compression of the shaped body.

[0046] It is particularly preferred that the iron-containing zeolite catalyst is prepared / has been prepared by coating the catalyst on a honeycomb or another geometric shaped body.

[0047] Furthermore, in connection with the catalysts described herein, it is generally preferred that the catalyst is or can be obtained by iron exchange using solid phase ion exchange.

[0048] Furthermore, the preferred size of the iron species is generally in the range of 2 to 100 iron atoms, and particularly preferably in the range of 2 to 20 iron atoms. Iron clusters can be detected using known methods and thus the catalyst modification can be controlled for each intended application (for example, Sando Brandenberger, Oliver Kroecher, Arno Tissler and Roderik Althoff in Catalysis Reviews, Volume 50, pages 492 - 531 (2008), "State of the Art in Selective Catalytic Reduction of NO x by Ammonia Using Metal-Exchanged Zeolite Catalysts"). The method using ultraviolet-visible described in this citation is particularly suitable. x by Ammonia Using Metal-Exchanged Zeolite Catalysts)". The method using ultraviolet-visible described in this citation is particularly suitable.

[0049] The present invention will be described in more detail below with reference to selected examples. The examples are not intended to represent any limitation in the meaning of the present invention. The present invention can include any embodiments well-known to those having ordinary knowledge in the art.

Example

[0050] 1) Preparation of iron-containing zeolite catalyst

[0051] Example 1 A commercially available ammonium-type faujasite zeolite (zeolite Y) with a SiO2 / Al2O3 ratio of 12 was treated with an aqueous solution of iron(II) sulfate by liquid-phase ion exchange. For this purpose, 140 g of Fe(II)SO4·7H2O (Roth Company) was dissolved in 5 liters of distilled water at 80 °C in a 10-liter container equipped with a stirrer and a heating rod. Then, 1 kg of ammonium zeolite was added and stirred for 1 hour. The pH value was 3.6. Next, this mixture was filtered off, and the obtained hydrated powder was made into a flat layer and pre-dried at 120 °C, and then tempered at 500 °C for 6 hours in an oven. The result was 1020 g of Fe zeolite in powder form. Calculated from the amount used, the average degree of exchange defined as Fe / Al was 0.5, corresponding to about 8 wt% of the weight ratio of Fe2O3 in the zeolite after exchange.

[0052] Example 2 A commercially available ammonium-type faujasite-type zeolite with a SiO2 / Al2O3 ratio of 12 was treated with Fe(II)Cl2·4H2O using the solid-phase ion exchange method. To do this, 100 g of this ammonium zeolite was mixed with 10 g of iron(II) chloride·4H2O (Merck) in a laboratory mortar and then ground for 15 minutes. Next, the obtained powder was tempered at 500 °C for 12 hours in a laboratory oven. The amount of powder obtained as a result was 105 g. Calculated from the amount used, the average degree of exchange defined as Fe / Al was 0.5, corresponding to about 8 wt% of the weight ratio of Fe2O3 in the zeolite after exchange.

[0053] Example 3An ammonium-type BEA-type commercial zeolite (zeolite β) having a SiO2 / Al2O3 ratio of 10 was treated with an aqueous solution of iron(II) sulfate by the liquid-phase ion exchange method. The procedure was similar to the conditions described in Example 1, except that 1 kg of ammonium zeolite (BEA type) and 158 g of Fe(II)SO4·7H2O (Roth) were used. Calculated from the amounts used, the average exchange degree defined as Fe / Al was 0.5, corresponding to about 9 wt% of the weight ratio of Fe2O3 in the zeolite after exchange. The resulting powder amount was 1020 g.

[0054] Example 4 An ammonium-type BEA-type commercial zeolite (zeolite β) having a SiO2 / Al2O3 ratio of 10 was treated with Fe(II)Cl2·4H2O using a solid-phase ion exchange process. The procedure was similar to the conditions described in Example 2, except that 100 g of ammonium zeolite (BEA type) and 11 g of iron(II) chloride·4H2O were used. The result was 105 g of Fe zeolite, and the calculated average exchange degree defined as the Fe / Al ratio was 0.5, corresponding to about 9 wt% of the weight ratio of Fe2O3 in the zeolite after exchange.

[0055] 2) Molding the catalyst mass into a technically usable catalyst

[0056] Example 5The iron zeolite powder obtained in Examples 1 to 4 and dried, having an average particle size of less than 20 μm and a residual moisture content of less than 10% by weight, was filled into a press mold having a diameter of about 7.5 cm and subjected to a punch pressure of 90 bar for 1 minute. After removing from the mold, the obtained pellets were placed in the upper sieve of a two-stage sieving combination having a first sieve with a mesh size of 700 μm and a second sieve with a mesh size of 500 μm placed thereunder, and crushed with the aid of a mortar. The proportion of the obtained 500 - 700 μm sieved fraction was 55 - 60% by weight of the original pellets in each case. All the shaped catalyst samples thus produced showed no dust formation in the filling test and were technically usable in terms of shape stability. This example shows that shaping, such as tableting or compression compaction, can be carried out, whereby the shaping of the catalyst composition according to the invention can also be carried out without processing aids, thus avoiding possible disturbances in the catalytic activity.

[0057] Example 6 A suspension was prepared using a powerful stirrer from 1 kg of iron zeolite powder (iron zeolite type BEA produced by solid ion exchange) prepared by the process described in Example 4, 2.3 L of deionized water, and 120 g of Ludox 40 (SiO2 sol from Grace). The solid content of the suspension (washcoat) was 29.0% by weight. This washcoat was used to coat a cordierite ceramic honeycomb substrate having a cell density of 200 cpsi (cells per square inch) and dimensions of 10 cm × 10 cm × 10 cm using a conventional coating process known to those skilled in the art (dipping followed by blowing off the excess washcoat with air). The coated honeycomb was then dried in a circulating air drying cabinet (T = 130 °C, duration 5 hours) and then calcined at 500 °C for 3 hours. The coating rate of the iron zeolite powder was 130 g / l honeycomb.

[0058] This example shows that a geometrically structured object or carrier material can be converted into an ortho-hydrogen - para-hydrogen conversion catalyst by means of a coating technique while maintaining the geometric shape of the carrier.

[0059] 3) Measuring the ortho-para hydrogen conversion catalyst properties

[0060] To measure the catalytic effect of the catalyst in the ortho-para hydrogen conversion, the standard method described in German Patent No. 4403352 is used. The basic principle of this method is based on the measurement of the enthalpy difference occurring during the exothermic ortho-para conversion in the form of the temperature change of a defined (pressure / temperature) ortho-para H2 mixture in the presence of the catalyst under adiabatic conditions, and the degree of conversion obtained as a result of the calculation.

[0061] For the principle of operation, see FIGS. 1 and 2 by way of example.

[0062] The advantageous measurement conditions / steps are as follows. - Catalyst: about 7 cm 3 , particle size 500 - 700 μm. - Activation / drying: At about 160 °C, use dried N2, H2 or He at T about 160 °C. - Reaction: Starting material, standard dried hydrogen, P about 3.5 bar, T 入り 77 K, corresponding to liquid nitrogen N2. - T measurement after the reactor. The measurement duration until T 出 is constant, about 30 - 60 minutes. - After the mass flow H2 reactor or measuring device, use volume flow measurement at room temperature.

[0063] To obtain a more accurate picture of the catalytic efficiency, further settings, for example other volume flows, can be obtained by varying the ratio of the mass fraction of the catalyst to the gas volume.

[0064] The iron zeolites prepared in Examples 1 to 4 with respect to the catalytic activity in the o-p conversion can be arranged in the following order.

[0065] BEA-10 (Solid-phase exchange, corresponding to Example 4) > FAU-12 (Solid-phase exchange, corresponding to Example 2) > BEA-10 (Liquid-phase exchange, corresponding to Example 3) > FAU-12 (Liquid-phase exchange, corresponding to Example 1).

Claims

1. The following plurality of steps, - providing a starting mixture comprising ortho- and para-hydrogen or consisting of ortho- and para-hydrogen, - cooling the starting mixture and converting ortho-hydrogen to para-hydrogen using a catalyst, A process for the conversion of ortho-hydrogen to para-hydrogen, comprising or consisting of, Characterized in that an iron-containing zeolite is used as said catalyst.

2. The process according to claim 1, characterized in that the iron-containing zeolite has Bronsted centers.

3. The process according to claim 1 or 2, characterized in that the iron species in the pores of the iron-containing zeolite and / or at the intersections of the pores of the iron-containing zeolite have a maximum diameter of 12 angstroms or less.

4. The process according to any one of claims 1 to 3, characterized in that the iron-containing zeolite has one of the following structures: MFI structure, BEA structure, MOR structure, CHA structure, AEI structure, AFX structure, FAU structure.

5. The iron-containing zeolite used has an SiO ２ / Al ２ O ３ molar ratio of 2 to 1000, preferably 5 to 200, particularly preferably 10 to 100, and is a process according to any one of claims 1 to 4.

6. The process according to any one of claims 1 to 5, characterized in that the iron-containing zeolite has an Fe / Al atomic ratio of 0.1 to 2, preferably 0.2 to 1.

7. The process according to any one of claims 1 to 6, characterized in that the catalyst is present as a shaped body.

8. The process according to any one of claims 1 to 7, characterized in that the shaped body is prepared by extrusion, granulation, tableting or compression.

9. The process according to any one of claims 1 to 8, characterized in that the catalyst is prepared by coating a honeycomb or another geometric shaped body.

10. Use of an iron-containing zeolite as defined in any one of claims 1 to 9, preferably in a process for the conversion of hydrogen isotopes, preferably from ortho-hydrogen to para-hydrogen, preferably according to any one of claims 1 to 9.

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