Catalyst for the accelerated establishment of the temperature-dependent equilibrium of ortho-para hydrogen mixtures

Abstract

The invention relates to a highly active iron-containing zeolite catalyst for accelerating the adjustment of the temperature-dependent ortho-para equilibrium of hydrogen, characterized in that the zeolite has a pore size between 4 and 8 angstroms, the formed Fe2O3 clusters have a maximum size equal to the zeolite pores, and in the manufacturing process, at least one combination of an oxidative temperature treatment followed by a reductive temperature treatment is carried out.

Description

[0001] The production of energy and chemical products from natural resources such as crude oil or natural gas will no longer be viable in the medium term due to limited reserves. In particular, this use results in high CO2 emissions, which contribute to global warming. While the potential consequences can only be estimated today, it is foreseeable that this will become a matter of existential concern for humanity. Furthermore, due to its composition and the multitude of basic molecules, crude oil is far too valuable to be burned by the chemical industry. Alternatives to fossil fuels are therefore extremely important for the long-term success of an energy transition and for global climate protection.

[0002] Hydrogen will play a key role in this, whether as an energy storage medium or as a material component for further material conversions. Climate-friendly hydrogen (green hydrogen) makes it possible to reduce CO2 emissions in mobile and stationary applications. This is especially true for applications where direct use of electricity from renewable energies is insufficient or not possible. Hydrogen production from renewable resources, as well as its transport and storage, are therefore key tasks at the global level.

[0003] For the storage and transport of hydrogen, liquefaction and subsequent storage in liquid form is often the most economical solution due to its significantly increased density. This is especially true when the geographical distance between the production site and the point of consumption is very large. Efficient transport via pipelines would require extremely high pressure, which would lead to embrittlement of the metal pipes under these conditions. Furthermore, numerous high-pressure compressors would be required, whose high energy requirements would ultimately make transport uneconomical. Therefore, hydrogen pipelines are only used locally, within chemical plants or integrated sites.

[0004] The hydrogen molecule can exist in two forms (allotropy), which differ in the arrangement of their H1 nuclear spin, thus exhibiting different rotational energies, which in turn lead to different physical properties. In the para form, the two nuclear spins are arranged antiparallel, while in the ortho form, they are arranged parallel. The allotropy of hydrogen was discovered in the 1920s during the development of quantum theory. Names associated with this include Bonhoeffer, Heisenberg, Eucken, Mecke, and Hund (U. Schindewolf, Bunsen-Magazin, 4th year, 6 / 2002, pp. 139-146).

[0005] The two allotropes exist side by side in a temperature-dependent equilibrium: above 250 K, the hydrogen allotropic mixture consists of 75% of the ortho form and 25% of the para form. A further increase in ambient temperature no longer changes this ratio. In this case, it is referred to as normal hydrogen. At low temperatures, such as those necessary for the liquefaction of hydrogen, the equilibrium shifts increasingly towards the para form. At temperatures below 20 K, almost exclusively the para form is present (DE 4403352 B4). However, the equilibrium transformation upon cooling from the ortho to the para form occurs only slowly because the interactions between the nuclei are very weak. The conversion of ortho-hydrogen to the para form is exothermic with a conversion energy of 527 kJ / kg. Conversely, the conversion from the para form to the ortho form is an exergonic reaction.

[0006] The rate of the ortho-para conversion and the resulting exothermic reaction play an important role in the liquefaction of hydrogen. Firstly, this necessarily increases the energy required for liquefaction because the energy released (527 kJ / kg) is higher than the evaporation enthalpy of para-hydrogen (446 kJ / kg). This means that with increasing ortho- to para-conversion, hydrogen evaporates, and further cooling is required, which requires a high energy expenditure, to ensure that the entire amount remains liquid. Secondly, due to the slow establishment of equilibrium, a certain proportion of the ortho-hydrogen is not immediately converted to para-hydrogen. During subsequent storage, the energy released during the self-conversion would lead to evaporation and thus to an undesirable loss of liquid hydrogen.For commercial liquid hydrogen, a parahydrogen content of at least 95% is therefore required, which ultimately significantly minimizes possible evaporation losses (storage time 14 days, hydrogen loss <1%). State of the art

[0007] To achieve the required low ortho-hydrogen contents, all industrial hydrogen liquefaction plants use catalysts that accelerate the establishment of equilibrium during the cooling process. If the establishment of the respective equilibrium is as fast as the cooling rate, no further energy is released at the triple point. In technology, a catalyst based on paramagnetic iron oxide (Fe2O3, IONEX) is almost exclusively used for this purpose. ® Type OP Catalyst, Molecular Products). This can already achieve significant energy savings (approximately 20%).

[0008] The catalytic conversion through interaction of the hydrogen molecule with a paramagnetic surface / species was discovered by Farkas and Sachse in the early 1930s (Farkas, A.; Sachse, H., On the homogeneous catalysis of para-ortho-hydrogen conversion under the influence of paramagnetic ions II; Z. Physik. Chem. B 23, (1933), pp. 19-27 25). Other paramagnetic catalysts have been described, such as Ru / silicate, Ru / aluminate (US 9,714,168 B1), Cr2O3 on Al2O3, CeO2, Ni / Al2O3, MnO2 on Al2O3 and unsupported (DH Weitzel, WV Loebenstein, JW Draper and OE Park, J. Of Research of National Bureau of Standards, Vol. 60, No. 3, 1958), Oxysorb ®, a CrO3 on SiO2, and Apachi nickel-silica from Air Products (Jürgen Essler, Dissertation: Physical and Technical Aspects of the Ortho-Para Conversion (2012), Chapter 5.5.3, p. 67 ff, Technical University of Dresden). All candidates investigated so far were less effective than the standard iron oxide catalyst.

[0009] Another hypothetical interaction of hydrogen atoms with metal hydride species has also been mentioned (Jürgen Essler, Dissertation: Physical and Technical Aspects of the Ortho-Para Conversion (2012), Chapter 5.5.3, p. 67 ff, Dresden University of Technology). However, a reaction involving strong Broenstedt (hydrogen) centers (splitting and recombination of hydrogen) is not yet known or investigated. Task

[0010] The iron oxide catalyst commonly used in hydrogen liquefaction today, however, still has a number of disadvantages. The catalyst grains used are in the range of 0.3 to 0.6 mm and are very brittle. This results in the formation of small particles (dust), which can lead to process difficulties. The available surface area is essentially the geometric surface of the particles, meaning that the centers within the catalyst grain are not or hardly accessible to hydrogen. Furthermore, the material is highly hygroscopic, which hinders conversion even at low water concentrations.

[0011] It is state of the art that the catalyst must be activated before commissioning. This is usually done by passing a dry hydrogen stream through the catalyst bed in the reactor at a temperature of 120–200°C. The lower the activation temperature and the time required, the greater the advantage of using a suitable catalyst (Jürgen Essler, Dissertation: Physical and Technical Aspects of Ortho-Para Conversion (2012), Chapter 7, p. 87 ff.). Furthermore, it should be noted that the crystalline form and grain size severely limit the ability to optimize the shape for the application (e.g., cooling process).

[0012] In order to make the production, storage and transport of liquid hydrogen more economical and energy-efficient, an improved catalyst should have the following property profile: - high activity: enables lower catalyst usage, smaller reactors, higher space velocities, higher productivity, - Activity at higher temperatures (> 80 K): a wider temperature range allows a continuous adjustment of the ortho-para equilibrium, which leads to lower cooling costs. - Variability in shape: enables catalysts with low pressure loss, adaptation to optimal reactor geometry, which significantly increases the range of applications. - Low hydrophilicity: resistant to water, reducing the activation and regeneration process. Subject of the invention

[0013] For potentially suitable catalysts, a number of physical parameters must be considered or optimized to achieve optimal overall performance. These are, in particular, the 1. Diffusion through the flow 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 possibly with hydrogen exchange centers 5. Desorption from the surface of the catalyst centers, 6. Diffusion of the products from the pores and 7. Diffusion of the products through the flow boundary layer.

[0014] An effective catalyst is characterized by the fact that the entire process proceeds at the desired rate. The slowest step in this process chain thus determines the overall rate of the desired reaction.

[0015] An improved catalyst should therefore exhibit a high concentration of paramagnetic centers or a high concentration of potential H+ exchange centers, a high propensity to adsorb hydrogen, and high accessibility (porosity) to minimize diffusion barriers. Studies on this conversion using microporous materials are known (US 20170065966).

[0016] The materials described and investigated in the literature are mostly hydrophilic but do not have acidic proton Broenstedt centers.

[0017] The conversion rate can be investigated using various methods. The Linde AG method described in DE 4403352 B4 is a standard method. Physical data such as temperature and pressure are measured before the conversion (before the catalyst) and after the conversion (after the catalyst), and the para-to-ortho ratio is calculated using the known physical data. This method is described in detail in DE 4403352 B4. Another method for determining the ortho-para composition of hydrogen is achieved with very high accuracy by measuring the speed of sound (M. Klaus, A. Schwab, Ch. Haberstroh, K. Eckhardt, Y. Beßler, J. Braggemann and T. Cronert; Materials Science and Engineering 502 (2019) 012161).

[0018] Surprisingly, it was found that iron-doped, hydrophobic zeolites that also contain Broenstedt centers are ideally suited for the conversion of ortho- to para-hydrogen when the hydrophobic Fe zeolites are subjected to a calcination step under oxidative conditions with an oxygen-containing gas mixture (e.g., air) followed by a reductive thermal treatment with a hydrogen-containing gas mixture (e.g., H2 / N2 mixtures). Catalysts produced in this way are highly active and open up significantly improved and more economical hydrogen liquefaction, as well as the storage and transport of liquid hydrogen.

[0019] Silicon-rich zeolites, which have hydrophobic properties and a high internal surface area of ​​several hundred m 2 / g and also possess proton Broenstedt centers. Since iron species or clusters are geometrically limited in their growth by the small pore size of 4 to 8 Angstroms in the zeolite, these catalysts exhibit a high intrinsic site utilization rate. Accessibility is ideally provided by the multidimensional pore system, for example, in MFI, MOR, or BEA-type zeolites (three-dimensional pore system). The additional proton Broenstedt centers are capable of proton exchange with hydrogen and thus further accelerate (catalyze) the overall conversion to para-hydrogen.

[0020] Hydrophobic zeolites loaded with iron cations and subsequently subjected to oxidative and reductive annealing have proven particularly suitable when the loading density (exchange rate) of iron cations is below 100%, i.e., sufficient Broenstedt centers are still present for proton exchange and the iron species are present at a maximum size in the zeolite pores. The iron species with optimal cluster size are in the range of 2 to 100 iron atoms, and especially in the range of 2 to 20 iron atoms. The iron clusters can be detected using known methods and thus a catalyst modification can be controlled for the respective intended applications (see e.g. Sando Brandenberger, Oliver Kröcher, Arno Tissler and Roderik Althoff “State of the Art in Selective Catalytic Reduction of NOx by Ammonia Using Metal-Exchanged Zeolite Catalysts” in Catalysis Reviews, Vol. 50 (2008) pp. 492 - 531).The UV-VIS method, as described in the literature cited here, is particularly suitable for characterization.

[0021] In principle, iron exchange can be carried out via liquid ion exchange, chemical vapor deposition, impregnation or similar processes.

[0022] Among the modification processes for iron introduction investigated, the so-called solid-state ion exchange (see EP0955080) has proven to be particularly advantageous, since it predominantly produces iron species in a suitable paramagnetic form.

[0023] A preferred embodiment is when the zeolite intended for ion exchange is subjected to calcination at 300 - 500 °C under oxygen-containing atmosphere (e.g. air) before the impregnation or exchange process in order to free the material from organic carbon-containing compounds / impurities.

[0024] A further preferred embodiment is when the oxidative calcination and the subsequent reductive temperature treatment of the Fe zeolite takes place after the catalyst forming process.

[0025] The obtained and investigated iron-containing and hydrophobic zeolites exhibit a significantly higher conversion rate from ortho- to para-hydrogen than the standard Fe2O3 material. They are non-toxic and can be used as shaped catalyst bodies in the form of pellets, spheres, extrudates, or even on catalyst honeycombs. These catalysts can achieve significant energy savings and increased economic efficiency in the liquefaction of hydrogen through the catalyzed conversion of ortho- to para-hydrogen. Furthermore, the improved catalysts can be better adapted to the application process due to their freedom of shape. ExamplesExample 1) Preparation of an iron-containing zeolite material:

[0026] A commercially available BEA-type zeolite (zeolite beta) in the ammonium form with a SiO2 / Al2O3 ratio of 10 was treated with an aqueous iron(II)SO4 solution by liquid-phase ion exchange. For this purpose, 158 g of Fe(II)SO4 × 7 H2O (Roth) were dissolved in 5 liters of distilled water at 80 °C in a 10-liter container equipped with a stirrer and a heating element. Subsequently, 1 kg of the ammonium zeolite was added and stirred for one hour. The mixture was then filtered off, and the resulting moist powder was pre-dried in a flat bed at 120 °C and subsequently annealed in an oven at 500 °C for 6 hours in air. This yielded 1020 g of Fe zeolite in powder form. The average exchange ratio defined as Fe / Al calculated from the amounts used was 0.5, which corresponds to a weight fraction of Fe2O3 in the exchanged zeolite of approximately 9 wt.%. Example 2) Preparation of a particulate iron-containing zeolite material:

[0027] 150 g of the iron zeolite powder obtained in Example 1, with an average particle size of less than 20 µm, were filled into a mold with a diameter of approximately 7.5 cm in 15 g portions and subjected to a ram pressure of 100 bar for 1 minute. After demolding, the resulting compact was placed on the upper sieve of a two-stage sieve combination, with the first sieve having a mesh size of 700 µm and the second sieve below it having a mesh size of 500 µm, and crushed and sieved using a mortar and pestle. The resulting sieve fraction of 700-500 µm constituted 55-60 wt.% of the original compact. All catalyst samples produced in this way showed no dust generation during filling tests and are suitable for industrial use in terms of dimensional stability.The example shows that shaping, such as tabletting or compacting, can be carried out, whereby the shaping of the catalyst masses according to the invention can also be carried out without processing aids and thus a possible disturbance of the catalytic activity can be avoided. Example 3) Production of a monolithically structured Fe-zeolite molded body:

[0028] A suspension was prepared using an intensive stirrer from 500 g of the iron zeolite powder prepared in Example 1 (iron zeolite type BEA), 1.2 l of deionized water, and 60 g of Ludox 40 (SiO2 sol from Grace). The solids content of the suspension (washcoat) was approximately 29.0 wt.%. This washcoat was used to coat a ceramic cordierite support honeycomb with 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 (immersion followed by blowing out the excess washcoat with air). The coated honeycomb was then dried in a circulating air drying cabinet (T = 130 °C, duration 5 h) and then calcined at 500 °C for 3 h. The application rate of iron zeolite powder was 130 g / l honeycomb. Example 4) Preparation of a highly active catalyst for op-H2 conversion:

[0029] 20 g of the Fe-zeolite fraction obtained in Example 2, with a grain size of 700–500 µm, were placed in a quartz tube sealable at both ends and heated to 440 °C in a tube furnace under an air flow of 50 ml / min. The mixture was then cooled to 200 °C while maintaining the air flow, and the gas inlet was switched to forming gas (H2 / N2 mixture, hydrogen content 5 vol%). These conditions were maintained for 4 hours, and then cooled to RT while maintaining the forming gas flow. Approximately 19 g of black-colored material were obtained; the particle structure remained unchanged. A portion (approximately 3 g) of the catalyst thus obtained was tested for its ortho-para-hydrogen conversion activity at a temperature of 77 K using a standard method. The hydrophobic Fe zeolite catalyst showed a significantly higher conversion rate compared to the Fe2O3 standard material. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 4403352 B4 [0005, 0017] US 9,714,168 B1

[0008] US 20170065966

[0015] EP 0955080

[0022] Cited non-patent literature

[0000] Bonhoeffer, Heisenberg, Eucken, Mecke and Hund (U. Schindewolf, Bunsen Magazine, 4th year, 6 / 2002, pp. 139 - 146

[0004] DH Weitzel, WV Loebenstein, JW Draper and OE Park, J. Of Research of National Bureau of Standards, Vol. 60, No. 3, 1958

[0008] Jürgen Essler, Dissertation: Physical and technical aspects of ortho-para conversion (2012), Chapter 5.5.3, p. 67 ff, Technical University of Dresden

[0008] M. Klaus, A. Schwab, Ch. Haberstroh, K. Eckhardt, Y. Beßler, J. Braggemann and T. Cronert; Materials Science and Engineering 502 (2019) 012161

[0017] Sando Brandenberger, Oliver Kröcher, Arno Tissler and Roderik Althoff “State of the Art in Selective Catalytic Reduction of NOx by Ammonia Using Metal-Exchanged Zeolite Catalysts” in Catalysis Reviews, Vol. 50 (2008) pp. 492 - 531

[0020]

Claims

[1] The invention relates to an iron-containing zeolite catalyst for the accelerated adjustment of the temperature-dependent equilibrium of ortho-para hydrogen mixtures, characterized by that the zeolite has a pore size between 4 and 8 Angstroms, the Fe2O3 clusters formed have a maximum size equal to the size of the zeolite pores and that during its production process a combination of an oxidative temperature treatment followed by a reductive temperature treatment is carried out at least once. [2] Iron-containing zeolite catalyst for the accelerated adjustment of the temperature-dependent equilibrium of ortho-para hydrogen mixtures according to claim 1, characterized by that the zeolite has Broenstedt centers. [3] Iron-containing zeolite catalyst for the accelerated adjustment of the temperature-dependent equilibrium of ortho-para hydrogen mixtures according to claims 1 and 2, characterized bythat the iron exchange is carried out by solid-state ion exchange. [4] Iron-containing zeolite catalyst for the accelerated adjustment of the temperature-dependent equilibrium of ortho-para hydrogen mixtures according to claims 1-3 characterized by that the zeolite has one of the following structures: MFI, BEA, MOR, CHA, AEI, AFX, FAU, [5] Iron-containing zeolite catalyst for the accelerated adjustment of the temperature-dependent equilibrium of ortho-para hydrogen mixtures according to claims 1 to 4, characterized by that the iron-containing zeolite used has a molar SiO2 / Al2O3 ratio between 2 and 1000, preferably between 5 and 200, particularly preferably between 10 and 100. [6] Iron-containing zeolite catalyst for the accelerated adjustment of the temperature-dependent equilibrium of ortho-para hydrogen mixtures according to claims 1 to 5, characterized by that the Fe / Al ratio is between 0.1 and 2. [7] Iron-containing zeolite catalyst for the accelerated adjustment of the temperature-dependent equilibrium of ortho-para hydrogen mixtures according to claim 6, characterized by that the oxidative temperature treatment required in the manufacturing process is carried out at temperatures of 200 to 600°C, preferably at 300 - 500°C and the subsequent reductive temperature treatment is carried out at temperatures of 50 to 400°C, preferably at temperatures of 100 to 300°C, particularly preferably at temperatures of 120 - 200°C. [8] Iron-containing zeolite catalyst for the accelerated adjustment of the temperature-dependent equilibrium of ortho-para hydrogen mixtures according to claim 7, characterized bythat the oxidative temperature treatment is carried out with oxygen / inert gas mixtures, preferably air, the subsequent reductive temperature treatment is carried out with hydrogen / inert gas mixtures, preferably hydrogen / nitrogen mixtures, and the previously set gas mixtures are maintained during the cooling steps. [9] Iron-containing zeolite catalyst for the accelerated adjustment of the temperature-dependent equilibrium of ortho-para hydrogen mixtures according to claim 8, characterized by that the combination of oxidative / reductive temperature treatment takes place after the catalyst has been formed. [10] Iron-containing zeolite catalyst for the accelerated adjustment of the temperature-dependent equilibrium of ortho-para hydrogen mixtures according to claims 1-9, characterized bythat the catalyst is used as a shaped body, produced by shaping processes such as compacting, tabletting, granulation, extrusion or coating of geometric structures in the production of liquid hydrogen, its storage and transport.