Method for converting orthohydrogen to parahydrogen

Abstract

The invention relates to a new method for converting orthohydrogen to parahydrogen. The present invention further relates to a use of an iron-containing zeolite, preferably according to a method as described herein, for converting hydrogen allotropes.

Description

[0001] Process for converting ortho-hydrogen to para-hydrogen

[0002] The present invention primarily relates to a process for converting ortho- to para-hydrogen, characterized in that an iron-containing zeolite is used as the catalyst. The present invention also relates to the use of an iron-containing zeolite for converting hydrogen allotropes, preferably as described in more detail herein.

[0003] Further aspects of the present invention and preferred embodiments thereof will become apparent from the following description and the appended claims.

[0004] 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 causes high CO2 emissions, which lead to global warming. While the potential consequences can only be estimated today, it is foreseeable that this will become a question of humanity's existential importance. Furthermore, crude oil, due to its composition and the multitude of basic molecules, is far too valuable to be burned in the chemical industry. Alternatives to fossil fuels are of paramount importance for the long-term success of an energy transition and for global climate protection. 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 carbon dioxide (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 on a global level. 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 and, under these conditions, would lead to embrittlement of the metal pipes.In addition, numerous high-pressure compressors would be required, which would ultimately make transportation uneconomical due to their high energy consumption. Therefore, hydrogen pipelines are only used locally, within chemical plants or integrated sites.

[0005] The hydrogen molecule can exist in two variants (allotropy), which differ in the arrangement of their 1 H nuclear spins differ, 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 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 (LJ. Schindewolf, Bunsen-Magazin, 4th year, 6 / 2002, pp. 139-146).

[0006] 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.

[0007] In the liquefaction of hydrogen, the rate of the ortho-para conversion as well as the resulting exothermicity play an important role. Firstly, this necessarily increases the energy required for liquefaction, as the energy released (527 kJ / kg) is higher than the enthalpy of vaporization 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 converted to para-hydrogen. During subsequent storage, the energy released during the self-conversion would cause evaporation and thus 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%).

[0008] To achieve the required low ortho-hydrogen contents, all industrial hydrogen liquefaction plants use catalysts that accelerate equilibrium establishment during the cooling process. If the establishment of the respective equilibrium is as rapid as the cooling rate, no further energy is released at the triple point. In practice, a catalyst based on paramagnetic iron oxide (Fe2C>3, IONEX® Type OP Catalyst, Molecular Products) is used almost exclusively. This can already achieve significant energy savings (approximately 20%).

[0009] The catalytic conversion by interaction of the hydrogen molecule via a paramagnetic surface / species was already discovered in the early 1930s by Farkas and Sachse (Farkas, A.; Sachse, H., On the homogeneous catalysis of the para-ortho-hydrogen conversion under the influence of paramagnetic ions II; Z. Physik. Chem. B23 (1933), pp. 19-27 25). Other paramagnetic catalysts have been described, such as Ru / silicate, Ru / aluminate (US 9,714,168 B1), CrOs on Al2O3, CeO2, Ni / AlCh, 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 CrOs 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 tested so far were less effective than the standard iron oxide catalyst.

[0010] However, the iron oxide catalyst commonly used today 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 processing difficulties. The available surface area is essentially the geometric surface of the particles, i.e., the centers within the catalyst grain are not accessible to hydrogen. In addition, the material is highly hygroscopic, which hinders conversion even at low water concentrations and / or necessitates complex activation and regeneration, i.e., negatively impacts the service life of the catalyst. Furthermore, the crystalline form and the grain size severely restrict the ability to optimize the shaping for the application process (e.g., cooling process).

[0011] It should also be noted that the known iron oxide catalysts can only be used in the ortho-para conversion process at temperatures below 80 K, meaning they cannot be used in the prior cooling process at higher temperatures. This is primarily due to the fact that the known catalysts are hygroscopic, and the starting mixture must be freed of residual water prior to the cooling process.

[0012] For potentially suitable catalysts, a number of physical parameters must be considered or optimized to achieve optimal overall performance. These are, in particular, the

[0013] 1. Diffusion through the flow boundary layer to the catalyst surface,

[0014] 2. Diffusion into the pores of the catalyst,

[0015] 3. Adsorption on the surface of the catalyst center,

[0016] 4. Surface reaction or interaction with paramagnetic centers or possibly with hydrogen exchange centers

[0017] 5. Desorption from the surface of the catalyst center,

[0018] 6. Diffusion of the products from the pores and

[0019] 7. Diffusion of the products through the flow boundary layer.

[0020] 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.

[0021] The conversion rate can be investigated using various methods. The process described in DE 4403352 B4 by Linde AG can be mentioned as a standard method here. In this process, 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 process is described in detail in DE 4403352 B4. The primary object of the present invention is to provide a process for converting ortho- to para-hydrogen which overcomes the disadvantages outlined above. The aim is preferably to provide a process which, on the one hand, avoids or reduces hydrogen losses during the production of liquid hydrogen by evaporation, and, on the other hand, minimizes or increases the content of ortho-hydrogen.reduced, preferably in such a way that the thermodynamic ortho-para-hydrogen equilibrium is adjusted to match the cooling rate throughout the entire cooling process. This should advantageously lead to energy savings in the cooling process and, in general, also to cost savings. Furthermore, the present invention should preferably produce higher-quality commercially liquefied hydrogen that meets the requirements of having a para-hydrogen content of at least 95%. Furthermore, a process should be provided in which a catalyst of such advantageous quality is used that complex activation and regeneration treatments of the catalyst are not necessary, while at the same time there is little or no loss of efficiency.Above all, a process is to be provided in which the catalyst can be used in a significantly broader temperature range than previously known iron oxide catalysts. Further objects underlying the present invention will become apparent from the following statements and the appended claims.

[0022] Surprisingly, it was found within the scope of the present invention that iron-doped hydrophobic zeolites, which advantageously contain Broenstedt centers, are ideally suited for the conversion of ortho- to para-hydrogen. Silicon-rich zeolites, which possess hydrophobic properties, a high internal surface area of ​​several hundred m, and a high ion exchange rate, were found to be particularly suitable. 2 / g and possess proton Broenstedt centers. Since iron species or clusters are geometrically limited in their growth by a preferably small pore size of 4 to 8 Angstroms in the zeolite, such catalysts exhibit a high intrinsic center utilization rate. Accessibility is ideally provided by the multidimensional pore system, e.g., in MFI, MOR, FAU, or BEA-type zeolites (three-dimensional pore system). The additionally advantageously present proton Broenstedt centers are capable of proton exchange with hydrogen and thereby additionally accelerate (catalyze) the overall conversion to para-hydrogen in the higher process temperature range. According to a primary aspect, the present invention relates to a process for converting ortho- to para-hydrogen, comprising or consisting of the following steps:

[0023] Providing a starting mixture of or comprising ortho- and para-hydrogen,

[0024] 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.

[0025] A preferred embodiment is a process according to the invention as described herein, characterized in that the cooling of the starting mixture and conversion of ortho-hydrogen to para-hydrogen is carried out according to one of the following steps: a) cooling the starting mixture and then conversion of ortho-hydrogen to para-hydrogen using the catalyst, or b) simultaneous or partially simultaneous cooling of the starting mixture and conversion of ortho-hydrogen to para-hydrogen using the catalyst, or c) cooling the starting mixture and then conversion of ortho-hydrogen to para-hydrogen using the catalyst, wherein the starting mixture is further cooled during the conversion.

[0026] In a particularly preferred embodiment, a process according to the invention is characterized in that a liquid or cryogenic hydrogen with a para-hydrogen content of at least 95 wt.%, based on the total hydrogen content, is produced.

[0027] A further preferred embodiment is a process according to the invention as described above, characterized in that the iron-containing zeolite has Broenstedt centers.

[0028] A catalyst particularly suitable for the process described herein should have a high concentration of paramagnetic centers or a high concentration of potential H +-exchange centers, a high propensity for hydrogen adsorption, and high accessibility (porosity) to minimize diffusion barriers. The majority of materials described and investigated in the literature are hydrophilic and lack acidic proton Broenstedt centers.

[0029] 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.

[0030] A further preferred embodiment is a process according to the invention, wherein the iron-containing zeolite has one of the following structures: MFI, BEA, MOR, CHA, AEI, AFX, FAU.

[0031] A further preferred embodiment is a process according to the invention, wherein the iron-containing zeolite used has a molar SiC^ / AFOs ratio between 2 and 1000, preferably between 5 and 200, particularly preferably between 10 and 100.

[0032] According to a preferred embodiment, the molar SiOVAbCh ratio of the iron-containing zeolite is adjusted or adjusted so that it is hydrophobic.

[0033] A further preferred embodiment is a process according to the invention, wherein the iron-containing zeolite has an atomic Fe / Al ratio between 0.1 and 2, preferably between 0.2 and 1.

[0034] A further preferred embodiment is a process according to the invention, wherein the catalyst is present as a shaped body.

[0035] It is preferred that the shaped body has a regular or irregular geometric shape, preferably one or more shapes selected from the group consisting of sphere, pellet, solid cylinder, such as extrusions or tablets, hollow cylinder such as ring, cylindrical shaped body with several through internal bores, trilope, crown ring, wheel, chair, granulate, fragment of compacted masses, monolith and cross-channel structure.

[0036] A further preferred embodiment is a process according to the invention, wherein the shaped body (preferably as described above) is or is produced by extrusion, granulation, tabletting or compaction.

[0037] A further preferred embodiment is a process according to the invention, wherein the catalyst is produced by coating a honeycomb or another geometrically shaped body. A further aspect of the present invention also relates to the use of an iron-containing zeolite (as described herein in the context of the process according to the invention) for converting hydrogen allotropes, preferably from ortho- to para-hydrogen, preferably in a process as described herein, particularly preferably in a preferred embodiment thereof (as described herein).

[0038] Also described herein is the product of a conversion of ortho- to para-hydrogen, prepared or preparable according to a process described herein, preferably as described herein as preferred, wherein the product preferably has a para-hydrogen content of at least 95%, based on the total amount of hydrogen.

[0039] A further preferred embodiment of a process according to the invention is a process as described above, wherein the temperature during the reaction is in a range from 150 to 20 K, preferably in a range from 120 to 20 K, particularly preferably in a range from 80 to 20 K.

[0040] A further preferred embodiment is a process according to the invention as described herein, wherein the pressure during the reaction is in a range from 50 to 5 bar, preferably in a range from 30 to 13 bar.

[0041] A preferred embodiment is a process according to the invention as described herein, wherein the iron-containing zeolite has pore openings with an average diameter in the range of 4 to 8 Angstroms.

[0042] Also disclosed herein is an iron-containing zeolite catalyst for converting ortho-hydrogen to para-hydrogen, characterized in that the iron-containing zeolite has pore openings with an average diameter in the range of 4 to 8 Angstroms. In general, and otherwise, what was stated above for the catalyst to be used according to the invention and its preferred embodiments, or what is specified in the appended claims, applies accordingly to this catalyst.

[0043] For example, it is therefore preferred that such an iron-containing zeolite catalyst is characterized in that the zeolite has Broenstedt centers.

[0044] For example, it is further preferred that an iron-containing zeolite catalyst is characterized in that the zeolite has one of the following structures: MFI, BEA, MOR, CHA, AEI, AFX, FAU. Furthermore, it is preferred that an iron-containing zeolite catalyst is characterized in that the molar SiO2 / Al2O3 ratio is between 2 and 1000, preferably between 5 and 200, particularly preferably between 10 and 100.

[0045] For example, it is also preferred that an iron-containing zeolite catalyst is characterized by an Fe / Al ratio of between 0.1 and 2, preferably between 0.2 and 1.

[0046] Furthermore, it is particularly preferred that an iron-containing zeolite catalyst is characterized in that the catalyst is present as a shaped body.

[0047] Furthermore, it is particularly preferred that an iron-containing zeolite catalyst is characterized in that the shaped body is or is produced by extrusion, granulation, tabletting or compaction.

[0048] It is particularly preferred that an iron-containing zeolite catalyst is characterized in that the catalyst is produced by coating a honeycomb or other geometric shaped body.

[0049] Furthermore, in connection with the catalysts described herein, it is generally preferred that the catalyst is obtained by iron exchange by means of solid-state ion exchange.

[0050] 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. The iron clusters can be detected using known methods, allowing catalyst modification to be controlled for the respective intended applications (see, for example, 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.

[0051] The invention is explained in more detail below using selected examples. These examples do not represent limitations within the meaning of the present invention. The invention may encompass any embodiment familiar to a person skilled in the art.

[0052] Description of the images:

[0053] Fig. 1 shows a simplified model of a measuring cell for determining the temperature change during an adiabatic conversion. Fig. 2 illustrates the principle of measuring the ortho- and para-hydrogen fractions via the temperature difference during the adiabatic conversion.

[0054] Examples

[0055] 1) Preparation of an iron-containing zeolite catalyst

[0056] 1 A commercially available faujasite-type zeolite (zeolite Y) in the ammonium form with a SiO2 / Al2C>3 ratio of 12 was treated with an aqueous iron(II)SO4 solution by liquid-phase ion exchange. For this purpose, 140 g of Fe(II)SC>4 x 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 pH was 3.6. 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. 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 8 wt.%.

[0057] A commercially available faujasite-type zeolite in the ammonium form with a SiO2 / Al2O3 ratio of 12 according to a solid-state ion exchange process with

[0058] Fe(II)Cl2 x 4 H2O. For this purpose, 100 g of ammonium zeolite was mixed with 10 g of iron(II) chloride x 4 H2O (Merck) in a laboratory mortar and pestle, followed by grinding for 15 minutes. The resulting powder was then annealed in a laboratory furnace at 500 °C for 12 hours. The resulting powder quantity was 105 g. The average exchange ratio, defined as Fe / Al, calculated from the amounts used was 0.5, which corresponds to a weight fraction of Fe2Os in the exchanged zeolite of approximately 8 wt.%.

[0059] A commercially available BEA-type zeolite (zeolite beta) in the ammonium form with a SiO2 / Al2C>3 ratio of 10 was treated with an aqueous iron(II)SO4 solution by liquid-phase ion exchange. The procedure was analogous to that described in Example 1, except that 1 kg of the ammonium zeolite (BEA type) and 158 g of Fe(II)SO4 x 7 H2O (Roth) were used. The average exchange ratio calculated from the amounts used, defined as Fe / Al, was 0.5, which corresponds to a weight fraction of Fe2O5 in the exchanged zeolite of approximately 9 wt.%. The resulting powder quantity was 1020 g. A commercially available zeolite of the BEA type (zeolite beta) in the ammonium form with a SiO2 / Al2C>3 ratio of 10 was treated with Fe(II)Cl2 x 4 H2O according to a solid-state ion exchange process.The conditions described in Example 2 were analogous to those used, except that 100 g of ammonium zeolite (BEA type) and 11 g of iron(II) chloride x 4 H2O were used. This yielded 105 g of Fe zeolite with a calculated average exchange rate, defined as an Fe / Al ratio of 0.5, corresponding to a weight fraction of Fe2O3 in the exchanged zeolite of approximately 9 wt.%.

[0060] 2) Shaping the catalyst masses into technically usable catalysts

[0061] 5 Of the iron zeolite obtained and dried in Examples 1 to 4,

[0062] A 15 g portion of powders with an average particle size of less than 20 pm and a residual moisture content of less than 10 wt.% were filled into a mold with a diameter of approximately 7.5 cm and subjected to a ram pressure of 90 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 pm and the second sieve below it having a mesh size of 500 pm, and crushed using a mortar. The proportion of the resulting sieve fraction of 500 - 700 pm was 55 - 60 wt.% of the original compact. All molded catalyst samples produced in this way showed no dust development in filling tests and are technically usable 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.

[0063] A suspension was prepared using an intensive stirrer from 1 kg of iron zeolite powder (iron zeolite type BEA produced via solid-state ion exchange), prepared according to the method described in Example 4, 2.3 l of deionized water, and 120 g of Ludox 40 (SiO2 sol from Grace). The solids content of the suspension (washcoat) was 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 x 10 cm x 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 of honeycomb. This example shows that geometrically structured objects, orSupport materials can be converted into ortho-para-hydrogen rearrangement catalysts by coating techniques, while preserving the geometry of the support.

[0064] 3) Conversion of ortho- to para-hydrogen: Measurement of the catalytic properties. To measure the catalytic effect of catalysts in ortho-para-hydrogen conversion, a method described in DE 4403352 is used as standard. The basic principle of the 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-FF mixture in the presence of a catalyst under adiabatic conditions and the resulting calculated degree of conversion.

[0065] For the functional principle, see Fig. 1 and Fig. 2 as examples.

[0066] Advantageous measurement conditionsZ-steps are:

[0067] - Catalyst: approx. 7 cm 3 , grain size 500 - 700 pm.

[0068] - Activation / Drying: approx. 160 °C, with dried N2, H2 or He at T approx. 160 °C.

[0069] - Reaction: Output normal hydrogen dry, P approx. 3.5 bar, Tein: 77 K, corresponding to liquid N2.

[0070] - T-measurement after reactor, measurement time until Taus = constant, approx. 30 - 60 min.

[0071] - Mass flow H2: after reactor or measuring apparatus, at room temperature by volume flow measurement.

[0072] Further settings can be made, e.g. different volume flows in order to obtain a more accurate picture of the catalyst efficiency by changing the ratio of catalyst mass to gas volume.

[0073] With regard to the catalytic activity in the op conversion, the iron zeolites prepared in Examples 1 - 4 can be arranged in the following order:

[0074] BEA-10 (solid phase exchange; corresponds to example 4) > FAU-12 (solid phase exchange; corresponds to example 2) > BEA-10 (liquid phase exchange; corresponds to example 3) > FAU 12 (liquid phase exchange; corresponds to example 1).

Claims

Patent claims 1 . A process for converting ortho- to para-hydrogen, comprising or consisting of the following steps: Providing a starting mixture of or comprising 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.

2. Process according to claim 1, characterized in that the iron-containing zeolite has Broenstedt centers.

3. The process of claim 1 or 2, wherein the iron species in the zeolite pores and / or pore intersections have a maximum diameter of 12 Angstroms or less.

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

5. Process according to one of claims 1 to 4, characterized in that the iron-containing zeolite used has a molar SiOVAhCh ratio between 2 and 1000, preferably between 5 and 200, particularly preferably between 10 and 100.

6. Process according to claims 1 to 5, characterized in that the iron-containing zeolite has an atomic Fe / Al ratio between 0.1 and 2, preferably between 0.2 and 1.

7. Process according to one of claims 1 to 6, characterized in that the catalyst is in the form of a shaped body.

8. Process according to one of claims 1 to 7, characterized in that the shaped body is or is produced by extrusion, granulation, tabletting or compaction. Process according to one of claims 1 to 8, characterized in that the catalyst is produced by coating a honeycomb or another geometrically shaped body. Use of an iron-containing zeolite as defined in one of claims 1 to 9 for converting hydrogen allotropes, preferably from ortho- to para-hydrogen, preferably in a process according to one of claims 1 to 9.

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