Method of catalytic hydrogenation by magnetic induction

Abstract

The present invention discloses the use of an innovative technology known as magnetic induction to carry out catalytic hydrogenation reactions using an unsupported multifunctional heterogeneous catalyst, such as Raney nickel, which can be heated in a controlled manner due to the action of an oscillating magnetic field. The invention relates to the use of Raney nickel as a bifunctional ferromagnetic material, which acts simultaneously as an active catalyst and a heating agent, offering an efficient, electrifiable and sustainable alternative to conventional thermal methods.

Description

[0001] Magnetic induction catalytic hydrogenation process

[0002] Field of invention

[0003] The present invention relates to the field of heterogeneous catalysis, in which it is required to employ an unsupported heterogeneous catalyst, mostly made of nickel, for application in hydrogenation reactions by magnetic induction heating, such as the methanation of CO2 to CH4.

[0004] Background of the invention

[0005] Heterogeneous catalysts are widely used in various sectors of the chemical industry, one of their main applications being hydrogenation reactions. They are fundamental in the fine chemical, pharmaceutical, and food industries, where advances in catalytic hydrogenation over the last century have provided significant economic and environmental benefits. Regarding the latter, it is well known that the excessive production and release of greenhouse gases (GHGs) is a global problem, with CO2 emissions being the main contributor. In order to limit global warming and reduce the carbon footprint, the scientific community is investigating the capture and subsequent use of CO2 as a raw material or chemical reagent, despite the catalytic challenges involved in its transformation.From this perspective, chemical energy storage through the methanation of carbon dioxide (Sabatier reaction, power-to-gas) is particularly promising. Specifically, methanation is a catalytic reaction that produces methane gas (CH4) from carbon dioxide (1), carbon monoxide (2), or a mixture of these, according to the following equations:

[0006] CO2+ 4H2O CH4+ 2H2O; AH= -165.1 kJ / mol (1)

[0007] CO + 3H2O CH4+ H2O; AH= -223.9 kJ / mol (2)

[0008] The limited availability of methane from natural sources, coupled with its immense utility as a clean, sulfur-free fuel, has created a significant demand for the production of synthetic natural gas. Methane produced by methanation is of great economic importance, as evidenced by the increasing number of biomethane plants in Europe. This increase stems from the fact that biomethane can be used as an alternative to natural gas, as it not only allows for a reduction in the EU's energy dependence but is also compatible with existing gas infrastructure. Current research is focused on improving efficiency and minimizing environmental impact by employing unconventional CO2 conversion technologies, rather than separation processes such as those described in Document EP1790614A1.

[0009] Among the emerging techniques is the biomethanation of CO2 using microorganisms as a catalyst (ES2871066T3), specifically the hydrogenotrophic methanogenic archaeon, whose working temperature is in the range of 55 to 65 °C. Some of the limitations of this technology are the low growth rate of the microorganisms and the consequent limited volumetric productivity of methane.

[0010] To overcome these production limitations, catalytic methanation is used, which, unlike biological methanation, employs a metallic catalyst at high temperatures and pressures instead of microorganisms. The most common catalysts for the methanation reaction of carbon dioxide or carbon monoxide are usually nickel-based, due to their high activity, excellent selectivity for methane, and lower cost compared to other noble metals. In this context, the Raney nickel catalyst is a very important industrial catalyst due to its high activity and selectivity, as well as its low production cost. This catalyst was discovered by Murray Raney and patented in 1925 (US1563587A). The catalyst contains mainly nickel and aluminum, and its total surface area is 50–130 m². 2CN104084219A describes the synthesis and application of Raney Nickel in a fixed bed for the methanation of CO, a less demanding process than the methanation of CO2, although it still requires temperatures in the range of 400-650 °C and pressures between 10 and 40 bar, which entails high energy consumption. Similarly, CN112138666A describes the use of the Raney Nickel catalyst for the methanation of CO, this time employing less severe temperatures (200 °C) but working with pressures of 30 bar H2. On the other hand, CN102942971 B also describes the use of Raney Nickel-based catalysts, but this time for the methanation of CO2 in a fixed-bed reactor, where its main limitation also lies in the need to apply pressures of 10 to 60 bar, with the associated hazards and high energy consumption.

[0011] Furthermore, Raney nickel has also been widely reported in the catalytic hydrogenation of organic compounds. For example, EP0934920A2 reports the use of Raney-type catalysts, specifically ruthenium-doped Raney nickel, for the selective hydrogenation of aromatic compounds with different functional groups. Although it is a very active and selective catalyst, it requires high temperatures (50 to 180 °C) and pressures (5 to 100 bar H2). ES2168244T3 refers to the use of various Raney nickel-based catalysts for the selective hydrogenation of nitrobenzene, requiring a temperature of 150 °C and an H2 pressure of 40 bar.

[0012] Most current research focuses on the development of catalysts and the replacement of thermal energy with more sustainable technologies. In this regard, magnetic induction heating has emerged as a promising alternative to conventional heating, as heat is distributed instantaneously and homogeneously within the catalyst without the need to heat the entire reactor, allowing the target temperature to be reached in just a few seconds. This makes the system suitable for the intermittent energy supply inherent in renewable sources. Thanks to the "hot spots" created around the ferromagnetic catalyst under the influence of the oscillating magnetic field, magnetic induction has been reported to be a technology capable of reducing the pressure required in this type of catalytic reaction (ACS Catalysis 2022, 12, 8462-8475).

[0013] Magnetic induction heating is based on the fact that nanometer-sized ferromagnetic materials, such as the active metals in CO2 methanation (Ni, Fe, and Co), release heat through hysteresis losses in the presence of a high-frequency alternating magnetic field. However, when an alternating magnetic field is applied to ferromagnetic materials with larger particles, above the nanoscale, they no longer heat up through hysteresis losses but instead heat up uncontrollably to incandescence due to eddy currents caused by the Joule effect. Therefore, being able to control the heating of micrometer-sized particles by eddy currents when applying a high-frequency alternating magnetic field is a major scientific challenge.

[0014] US9713809B2 proposes the use of catalysts based on ferromagnetic colloidal nanoparticles (Fe, FeC, Fe / FeC / Ru) for the methanation of CO₂ by magnetic induction heating. Specifically, it involves using a catalyst based on metallic nanoparticles composed of a catalytically active center (Ru) and a ferromagnetic center (Fe, FeC), which is heated by an oscillating magnetic field (heating agent). The problem with this document is that the catalyst, being based on unsupported colloidal nanoparticles, exhibits the typical problems associated with instability and sintering at high temperatures, which limits its viability for industrial applications. On the other hand, US2022370986A1 describes the application of heterogeneous catalysts based on ferromagnetic nickel nanoparticles on different supports (Al2O3, SiO2, TiO2, etc.).), with a metal content of less than 20% by weight, to carry out the methanation of CO2 by magnetic induction. In this case, the catalyst based on supported nickel nanoparticles has a limited heating capacity under the action of the alternating magnetic field (AMF), because nickel is a soft ferromagnetic material. Consequently, the design of the catalytic bed described in that document requires the incorporation of an external heating agent, such as iron wool or powder, which is the material that actually generates the heat necessary to activate the reaction under the oscillating magnetic field. Therefore, the system described in US2022370986A1 does not constitute a bifunctional material, since the catalytic and heating functions reside in different components. Furthermore, this methodology has a major limitation associated with the synthesis of the catalysts, which uses the organometallic approach.Specifically, an organometallic precursor, Ni(COD)2, is used, which is expensive and sensitive to air, complicating its industrial application. Furthermore, nickel nanoparticle-based catalysts present stability problems, with their catalytic activity decreasing after only 150 minutes of reaction. Recently, US202421789A1 also describes the use of magnetic induction for CO2 methanation, this time using a material consisting of Ni nanoparticles supported on uranium oxide (10-20 wt% Ni), achieving good CH4 yields in just 14 hours of reaction. In all cases reported to date, magnetic induction has been used as a novel technology for CO2 methanation, always employing ferromagnetic catalysts of nanometric size and a metal content of less than 20 wt%, generating heat through hysteresis losses.However, unsupported solid ferromagnetic catalysts with a micrometer particle size and a metal content exceeding 50% by weight have not yet been studied in this type of catalytic process due to the presumed uncontrolled heat generation from eddy currents, which would prevent control of the catalytic process. As we have seen, most of the technologies currently reported for CO2 methanation typically require high temperatures and, sometimes, high pressures, resulting in a very high energy input. In this context, magnetic induction catalysis using Raney Nickel allows for a significant reduction in the process temperature and pressure compared to conventional heating with the same catalyst. This is because Raney Nickel has a metal content exceeding 80% by weight, thus providing a large number of catalytic sites available for reaction.Furthermore, because nickel is a soft ferromagnetic material, it allows for precise temperature control during the process, even when heated by eddy currents, which are favored due to its high metal content and non-nanoparticle-based structure. Thus, the main innovation lies in the fact that Raney Nickel, due to its high metal content and differential particle size, is capable of acting multifunctionally, both as a heating agent and a catalyst, in the presence of a high-frequency oscillating magnetic field, achieving superior energy efficiency.

[0015] The enormous potential of magnetic induction heating in terms of energy efficiency, thanks to the electrification of the process, and suitability to intermittency has driven the search for an unsupported, economical, readily available and stable solid ferromagnetic catalyst for use in hydrogenation reactions, such as the methanation of CO2.

[0016] Other documents related to the technology of the present invention are:

[0017] Pan Z et al. Integration of magnetically stabilized bed and amorphous nickel alloy catalyst for CO methanation. Chemical Engineering Science., 22 / 04 / 2007, Vol. 62, No. 10, Pages 2712-2717, ISSN 0009-2509, DOI: 10.1016 / j.ces.2007.02.007, which mentions an amorphous Ni-Al-Fe-Cr alloy in a magnetostabilized bed, but not in a direct inductive heating process; Abelló et al., High-loaded nickel-alumina catalyst for direct CO2 hydrogenation into synthetic natural gas (SNG). Fuel. AMSTERDAM, NL, 06 / 24 / 2013, Vol. 113, Pages 598-609, ISSN 0016-2361, DOI: 10.1016 / j.fuel.2013.06.012, which reports Ni—Al catalysts supported on Al₂O₃ for the methanation of CO₂ by conventional heating. Therefore, none of the aforementioned documents teaches or suggests the use of an unsupported Raney Nickel catalyst as a material susceptible to being heated by the application of a high-frequency oscillating magnetic field. Description of the invention

[0018] The present invention describes the use of Raney Nickel as an unsupported ferromagnetic catalyst capable of being heated and simultaneously catalyzing hydrogenation reactions, e.g., the methanation of CO2 or the valorization of biomass-derived products, by magnetic induction. This approach leads to significant savings in reaction costs due to the electrification of the process and the affordability of the catalyst.

[0019] Thus, the present invention relates to a catalytic hydrogenation process comprising at least the following steps: introducing a gas-phase feed stream into a reactor, contacting the feed stream with the unsupported Raney Nickel catalyst, heating the reaction mixture by magnetic induction using a high-frequency oscillating field to a temperature between 80 °C and 600 °C, preferably between 150 and 300 °C, and more preferably between 180 °C and 220 °C, increasing the pressure inside the reactor to between atmospheric pressure and 10 bar, preferably between atmospheric pressure and 2 bar, and using an feed stream flow rate inside the reactor between 1 mL min' 1 and 10 L-mirr 1 , preferably between 10 mL min' 1 and 1,000 mL-min' 1 .

[0020] The gas hourly space velocity (GHSV) per gram of nickel is between 0.1 and 500 L h'1 -gN¡' 1 , for example, 1 and 135 L h' 1 -gN¡' 1 .

[0021] The term "unsupported" in the present invention refers to the intrinsic structure of the catalytic material, not to the hardware elements of the reactor.

[0022] To carry out this procedure, different types of non-magnetic reactors can be used, such as quartz, fixed-bed, or fluidized-bed reactors, preferably fixed-bed reactors, in the gas phase (Figure 1 and Figure 2), employing Raney Nickel as a catalyst. Raney Nickel has the capacity to heat the reaction by magnetic induction within a specific temperature range. This novel catalytic application described in the present invention differs from the prior art because it has been demonstrated that Raney Nickel, even though it is a micrometer-sized material with a metal content exceeding 80% by weight, can be heated in a controlled manner by eddy currents, behaving as a multifunctional material by acting simultaneously as a heating agent and as a catalytically active species when exposed to a high-frequency oscillating magnetic field.

[0023] The use of a ferromagnetic catalyst with a high metal content, such as Raney Nickel, allows for the methanation of CO2 under milder reaction conditions (lower temperature and pressure) compared to conventional heating, potentially improving process efficiency. Furthermore, thanks to its soft ferromagnetic nature, it is possible to drastically reduce energy consumption in CO2 methanation compared to previous scientific studies.

[0024] According to a preferred embodiment, the inlet stream may consist of hydrogen-sustaining substrates and hydrogen. The hydrogen-sustaining substrates may be selected from, for example, CO2, CO, organic substrates with carbonyl (C=O), nitrile (CN), and nitro (NO2) groups circulated with an inert carrier gas, such as N2, and combinations thereof. Examples of these organic substrates include acetone, butanone, butanal, furfural, 5-hydroxymethylfurfural, vanillin, benzonitrile, and nitrobenzene. Preferably, these hydrogen-sustaining substrates are selected from CO2, CO, and combinations thereof.

[0025] Raney Nickel according to the procedure of the invention is a micromethco size material and with a nickel metallic content of 60 to 90%, preferably 85% by weight.

[0026] The Raney Nickel catalyst of the present invention, in all its variations, is preferably in the form of a micromethoc powder and composed of ferromagnetic particles with a size between 1 pm and 1000 pm, preferably between 250 pm and 600 pm. Since these ferromagnetic particles do not consist of supported metallic nanoparticles, they do not present the typical problems associated with high-temperature synthesization. This ferromagnetic material can be heated by magnetic induction using a high-frequency oscillating magnetic field with an amplitude between 0.1 mT and 200 mT and a frequency between 30 kHz and 500 kHz, preferably between 100 and 400 kHz.

[0027] The magnetic heating of Raney Nickel is governed by eddy currents through the Joule effect; however, even at high applied magnetic field strengths (mT), the temperature reached by the catalyst can be regulated without uncontrolled heating or incandescence of the multifunctional material. This makes the application of this technology with this material heated by eddy currents when a magnetic field is applied highly safe and controllable.

[0028] As previously mentioned, the implementation of magnetic induction heating allows for catalytic hydrogenation reactions to be carried out under much milder reaction conditions in terms of temperature and H2 pressure. Furthermore, thanks to the application of this new technology, it is possible to significantly reduce the temperature and hydrogen pressures typically used in these catalytic processes. For example, in the methanation of CO2, heating Raney Nickel with magnetic induction makes it possible to operate at atmospheric pressure and reduce the reaction temperature by more than 200 °C compared to traditional methods that use conventional heating. Moreover, thanks to the high activity and selectivity reported for Raney Nickel, the reaction conditions (temperature and pressure) for methanation can be reduced.

[0029] The Raney Nickel material used according to the present invention is easy to handle and has a very long service life. It is also easy to recover and does not contaminate the reactor.

[0030] According to a particular embodiment of the present invention, the process requires a maximum energy expenditure of 104 W h with efficiencies exceeding 90% during reaction times between 24 and 300 hours.

[0031] To carry out the procedure described in the present invention, the reactor used must preferably be composed of a non-magnetic material, preferably quartz, so that it does not heat up under the action of the applied magnetic field. This reactor may be selected from among fixed-bed, fluidized-bed, bubble, moving-bed, or membrane reactors.

[0032] According to a preferred embodiment, the reactor is a fixed-bed quartz reactor.

[0033] The term "conversion", as used in the context of the present invention, is expressed as a percentage and is understood as the fraction of carbon dioxide in the feed stream that is converted into other compounds in one pass through the reactor.

[0034] The term "selectivity", as used in the context of the present invention, is defined in percentage form and is understood as the ratio between the amount of product or reaction products, for example, methane in the effluent stream of the process reactor, and the total amount of reaction products in that stream.

[0035] The terms "process" and "procedure," as used interchangeably in the context of the present invention, are defined as the set of technical operations that involves the development of at least one chemical reaction, and which results in the deliberate modification of at least one chemical compound, which is part of a feed to the process, into at least one different chemical product.

[0036] Throughout the description and claims, the word "comprises" and its variations are not intended to exclude other technical features, additives, components, or steps. For those skilled in the art, other objects, advantages, and features of the invention will become apparent partly from the description and partly from the practice of the invention.

[0037] Brief description of the figures

[0038] Figure 1. Simplified schematic of a continuous fixed-bed reactor for carrying out selective methanation of CO2 by heterogeneous gas-solid catalysis according to the invention, with a downward-flowing gas inlet (10% N2, 18% CO2, and 72% H2) heated by magnetic induction by the ferromagnetic material. Legend: 1. Flow controller; 2. Calibrated gas mixture; 3. Manometer; 4. Pure H2; 5. Analysis; 6. Purge; 7. Porous frit; 8. Coil. Partial simplified schematic of a continuous fixed-bed reactor designed to carry out heterogeneous gas-solid reactions according to the invention, with a downward-flowing gas inlet (10% N2, 18% CO2, and 72% H2) heated by magnetic induction.The diagram shows the location of the catalyst on a porous frit inside a quartz tubular reactor, the placement of a type K thermocouple on the outside of the quartz tubular reactor, and the location of the coil for heating the ferromagnetic material, with the catalyst positioned at the same height on the vertical and horizontal axes. Legend: 1. Gas flow (H2 + CO2); 2. Non-thermal reactor; 3. Thermocouple; 4. Coil; 5. Catalyst; 6. Gas flow (post-reaction gases); 7. Porous frit.

[0039] The porous frit has a purely mechanical function (particle retention and flow distribution) and does not participate in the surface chemistry of the catalyst.

[0040] Graph showing the methanation of CO2 with Raney Nickel according to the invention using magnetic induction as the heating method. The percentage (%) of CO2 conversion and selectivity to CH4 is shown as a function of time (>200 h). Applied field of 12 mT and flow rate of 32 mL / min. 1 (1:4, CÜ2:H2), which represents a GHSV of 4,780 mL h' 1 g N !' 1 .

[0041] Graph showing the methanation of CO2 with Raney Nickel according to the invention using a conventional furnace as the heating method. The percentage (%) of CO2 conversion and selectivity to CH4 is shown as a function of temperature (150-600 °C). Flow rate: 32 mL / min 1 (1:4, CÜ2:H2), which represents a GHSV of 4,780 mL h'

[0042] 1 gN¡' 1 .

[0043] Graph showing how flux variation affects the methanation of CO2 with Raney Nickel according to the invention using magnetic induction as the heating method. The percentage (%) of CO2 conversion and selectivity to CH4 is shown at a reaction time >200 h. Flux rate between 10 mL / min 1 and 100 mL min' 1 (1:4, CÜ2:H2), which implies a GHSV between 1,340 mL h' 1 gN¡' 1 and 13,400 mL h' 1 gN¡' 1 .

[0044] Graph showing the methanation of CO2 with Raney Nickel according to the invention, applying different magnetic field amplitudes. The percentage (%) of CO2 conversion and selectivity to CH4 is shown as a function of the applied magnetic field. The applied field ranges from 12 mT to 63 mT, and the flow rate is 32 mL / min. 1 (1:4, CÜ2:H2), which represents a GHSV of 4,780 mL h' 1 gN¡' 1 .

[0045] Graph showing how variations in the CO2:H2 ratio affect the methanation of CO2 with Raney Nickel according to the invention. The percentage (%) of CO2 conversion and selectivity to CH4 is shown as a function of the ratio.

[0046] C₂:H₂ used (1:1, 1:3, 1:4, 1:6). Applied field of 5 mT and inlet gas flow of 32 mL / min. 1 (10% N2, 18% CO2 and 72% H2), which represents a GHSV of 4,780 mL h' 1 gN¡' 1 .

[0047] Graph showing the methanation of a CO / CO2 mixture with Raney Nickel according to the invention using magnetic induction as the heating method. The percentage (%) of CO2 and CO conversion, and selectivity to CH4, are shown as a function of time (24 h). Applied field of 12 mT and inlet gas flow rate of 32 mL / min. 1 (1:4, CO / CO2:H2), which represents a GHSV of 4,780 mL h' 1 gN¡' 1 .

[0048] 9. Graph showing how the variation of flow affects (10% N2, 18% CO2, and 72%

[0049] H2) in the methanation of CO2 with Raney Nickel according to the invention using magnetic induction as the heating method. Inlet gas flow varies between 10 mL / min' 1 and 1,000 mL / min 1 (1:4, CÜ2:H2), which represents a GHSV between 1,340 mL (1.34 L)-h' 1 -g N Yo' 1 and 134,000 mL (134.0 L)- h' 1 ■ g N !' 1 -

[0050] DESCRIPTION OF REALIZATION MODES

[0051] Example 1. Methanation reaction: fixed bed reactor, calculation of conversion and selectivity, measurement of energy efficiency.

[0052] The methanation reaction (Equation 1) is carried out in a continuous fixed-bed quartz tube reactor (Figure 1) with an outer diameter of 12 mm and an inner diameter of 8 mm. Raney nickel is deposited onto a porous quartz frit within the tubular reactor itself (Figure 2). This reactor is positioned at the center of a coil connected to an alternating current magnetic induction device oscillating at a frequency of 320 kHz with a magnetic field amplitude ranging from 0.1 mT to 63 mT. The coil (manufactured by Ultraflex) consists of a copper solenoid with 6 turns, an inner diameter of 24 mm, and a height of 35 mm. The temperature is measured using a platinum thermocouple (type K temperature probe) located at the level of the catalytic bed outside the quartz reactor (Figure 2). Therefore, what is actually measured is the local system temperature (Tiocai).To avoid measurement errors, the thermocouple response was measured and corrected for different field amplitudes. Additionally, the Ti was verified. 0C Using an infrared pyrometer, no temperature differences greater than 5 °C were observed.

[0053] The methanation reaction of CO2 takes place at atmospheric pressure and at a Ti 0C The temperature varies between 100 and 250 °C. Between 100 and 500 mg of Raney Nickel are introduced into the reactor, which is fed with H2 and CO2 from a bag of known composition (17.90% CO2, 72.12% H2 and 9.98% N2, ratio 1:4 CO2:H2), controlling the dosed flow rate using a flow meter (Iberfluid Instruments) within a range of 8 mL / min. 1 and 100 mL min' 1The inlet gas stream (10% N2, 18% CO2, and 72% H2) flows downwards (Figure 2), where the feed gas (CO2 and H2) is circulated over the catalytic bed, selectively generating methane. The methane formed and the remaining gases (CO2, H2, and also CO, from any possible side reaction) are analyzed sequentially by gas chromatography (Agilent 8890 GC). The gas injection calibration and the GC analysis method were performed using pure gases. The analyte response factor (FRi) was determined by injecting known quantities of each analyte i into the chromatograph, using N2 as the internal standard.

[0054] »»2%■

[0055] The peak area of ​​species i in the chromatogram (A¡) allowed the determination of the CO2 conversion (Xco2) and the selectivity to CH4 (SCH4) based on the following calculations: where %CÜ2 is the known percentage of CO2 in the inlet stream, Aco2 is the chromatographic area of ​​the analyzed CO2 in the outlet stream, FRco2 is the calculated response factor for CO2, and S%X is the sum of the percentages of all analyzed species derived from the CO2 transformation. The energy efficiency of the process is calculated by considering the energy consumption (in percentage, %) when applying magnetic induction as the heating method and comparing it with the same process heated conventionally to achieve a specific methane yield. Thus, the energy efficiency is calculated as follows: 100 where W ra m P a,iM and W ra m Pa,conv. are the energy consumptions calculated during the heating ramp for a given CH4 yield for magnetic induction and conventional heating, respectively. Westationary.lM and VVstationary.conv. are the consumption calculated for one hour of reaction at the same yield considered.

[0056] Example 2. Methanation of CO2 using the Raney Nickel ferromagnetic catalyst by magnetic induction heating.

[0057] The catalytic bed consists of 500 mg of Raney Nickel (Ni Raney®2800) with a particle size between 400 µm and 600 µm, occupying a height of 7 mm in the catalytic bed. The Raney Nickel is pre-activated at 400 °C under a flow of H2 (25 mL min' 1 ) to ensure it is completely reduced. The gas flow introduced into the continuous reactor is downward, with a constant flow rate of 32 mL / min' 1of CÜ2:H2 (4:1) at atmospheric pressure (1 bar), which represents a GHSV of 4.288 mL h' 1 gN¡' 1 .

[0058] The CO2 conversion and CH4 selectivity results are shown in Figure 3. With a field amplitude of 15 mT, equivalent to an energy consumption of 104 W h, Raney Nickel demonstrates complete selectivity to CH4, achieving yields exceeding 90% for over 200 h of reaction without catalyst reactivation. To carry out the reaction, the ferromagnetic catalyst, under the influence of the magnetic field (15 mT), reaches a Ti 0C ai of 190 °C being stable throughout the process.

[0059] Example 3. Methanation of CO2 using the ferromagnetic catalyst Raney Nickel by conventional heating. The catalytic bed consists of 500 mg of Raney Nickel (Ni Raney®2800) with a particle size between 400 pm and 600 pm, occupying a height of 7 mm in the catalytic bed. The Raney Nickel is pre-activated at 400 °C under a flow of H2 (25 mL min' 1 ) to ensure it is completely reduced. The gas flow introduced into the continuous reactor is downward, with a constant flow rate of 32 mL / min' 1 of CÜ2:H2 (4:1) at atmospheric pressure (1 bar), which represents a GHSV of 4.288 mL h' 1 gN¡' 1 .

[0060] The CO2 conversion and CH4 selectivity results are shown in Figure 4. Instead of heating by magnetic induction, the quartz reactor is covered with a heating oven with an energy consumption of 500 W h. To achieve the same CH4 efficiency, a temperature of 350 °C is required.

[0061] Example 4. Methanation of CO2 with different GHSVs using the Raney Nickel ferromagnetic catalyst by magnetic induction heating.

[0062] The catalytic bed consists of 500 mg of Raney Nickel (Ni Raney®2800) with a particle size between 400 µm and 600 µm, occupying a height of 7 mm in the catalytic bed. The Raney Nickel is pre-activated at 400 °C under a flow of H2 (25 mL min' 1 ) to ensure it is completely reduced. The gas flow introduced into the continuous reactor is downward, with a variable flow rate between 10 mL / min' 1 and 1,000 mL min' 1of CÜ2:H2 (4:1) at atmospheric pressure (1 bar), which implies a GHSV between 1,340 mL h' 1 gN¡' 1 and 134,000 mL h' 1 g N !' 1 .

[0063] The results of CO2 conversion and selectivity to CH4 are shown in Figures 5 and 9. Raney Nickel is completely selective to methane production up to 150 mL min' 1 (10% N2, 18% CO2 and 72% H2), with a progressive loss of selectivity down to 91% with an inlet gas flow of 1,000 mL min' 1 It is worth noting that even at 150 mL / min 1 It is capable of achieving a CH4 yield of over 85%. At higher flow rates, such as 1,000 mL min' 1 , the performance decreases to 70% with an applied magnetic field of only 15 mT (104 W h).

[0064] Example 5. Methanation of CO2 with different values ​​of applied magnetic field using the Raney Nickel ferromagnetic catalyst.

[0065] The catalytic bed consists of 500 mg of Raney Nickel (Ni Raney®2800) with a particle size between 400 µm and 600 µm, occupying a height of 7 mm in the catalytic bed. The Raney Nickel is pre-activated at 400 °C under a flow of H2 (25 mL min' 1 ) to ensure it is completely reduced. The gas flow introduced into the continuous reactor is downward, with a constant flow rate of 32 mL / min' 1 of CÜ2:H2 (4:1) at atmospheric pressure (1 bar), which represents a GHSV of 4.288 mL h' 1 gN¡' 1 .

[0066] The CO2 conversion and CH4 selectivity results are shown in Figure 6. Raney Nickel is completely selective across the entire range of applied field amplitudes; only the conversion, and therefore the yield to CH4, is affected. As the applied magnetic field amplitude changes, the Ti 0Cobserved ai and, consequently, the conversion of CO2. As can be seen in Figure 6, at a field of 12 mT (62 W h) the Ti 0C The achieved temperature is 122 °C, which represents a conversion of only 2%. With a field of 15 mT (104 W h) the Ti 0C The temperature rises to 190 °C, but the conversion reaches a value of 90%. As we increase the field to larger amplitudes, for example, 17 mT (148 W h), 20 mT (207 W h), or even 63 mT (2,000 W h), the temperature does not increase considerably, nor does the conversion, reaching conversions close to 91% in all cases. Therefore, we set 15 mT (104 W h) as the optimal field amplitude for the application of this technological process.

[0067] Example 6. Methanation of CO2 with different CO2:H2 ratios using the Raney Nickel ferromagnetic catalyst by magnetic induction heating.

[0068] The catalytic bed consists of 500 mg of Raney Nickel (Ni Raney®2800) with a particle size between 400 µm and 600 µm, occupying a height of 7 mm in the catalytic bed. The Raney Nickel is pre-activated at 400 °C under a flow of H2 (25 mL min' 1 ) to ensure it is completely reduced. The gas flow introduced into the continuous reactor is downward, with a constant flow rate of 32 mL / min' 1 with different proportions of C₂:H₂ (1:1, 1:3, 1:4 and 1:6) at atmospheric pressure (1 bar), which implies a GHSV between 4,780 mL h' 1 gN¡' 1 .

[0069] The CO2 conversion and CH4 selectivity results are shown in Figure 7. As can be seen, Raney Nickel is completely selective regardless of the C₂:H₂ ratio used, always >99%. The CO2 conversion varies depending on the amount of H₂. As a general rule, the higher the amount of H₂, the greater the observed conversion, with total conversion reached when the C₂:H₂ ratio is 1:6. Therefore, the 92% conversion observed with a C₂:H₂ ratio of 1:4 is solely due to a lack of hydrogen in the catalytic reaction, not to the ferromagnetic catalyst.

[0070] Example 7. Methanation of a CO / CO2 mixture using the Raney Nickel ferromagnetic catalyst by magnetic induction heating.

[0071] The catalytic bed consists of 500 mg of Raney Nickel (Ni Raney®2800) with a particle size between 400 µm and 600 µm, occupying a height of 7 mm in the catalytic bed. The Raney Nickel is pre-activated at 400 °C under a flow of H2 (25 mL min' 1 ) to ensure it is completely reduced. The gas flow introduced into the continuous reactor is downward, with a constant flow rate of 32 mL / min' 1 of CO / CO2:H2 (4:1) at atmospheric pressure (1 bar), which represents a GHSV of 4,780 mL h' 1 gN¡' 1 .

[0072] The CO2 conversion and CH4 selectivity results are shown in Figure 8, where Raney Nickel demonstrates almost complete yield (>96%) to methane during the 24-hour reaction. To carry out the reaction, the ferromagnetic catalyst, under the influence of a magnetic field (15 mT), reaches a Ti 0C ai of 200 °C being stable throughout the process.

[0073] Example 8. Energy efficiency.

[0074] Energy efficiency calculations were performed by comparing the consumption produced during heating by magnetic induction and by the heating blanket (example 2 and 3, respectively).

[0075] The great advantage of using the Raney Nickel ferromagnetic catalyst is its ability to reach high temperatures in just a few seconds, resulting in significant energy savings during the heating ramp. For example, to achieve 90% CH4 efficiencies, the heating mantle requires temperatures of 400 °C (25 °C min'). 1 ), which implies a time of 16 minutes to reach that temperature. If the heating blanket consumes 500 W, it is estimated that 133.3 W / h is consumed during the heating ramp. However, through magnetic induction heating, Raney Nickel is able to achieve the same performance at CH4 with a Ti 0CRaney Nickel reaches a temperature of only 190 °C when a magnetic field of 15 mT (104 W h) is applied. This temperature is reached in less than 1 minute, resulting in an energy cost of 1.7 W h during the heating ramp. Therefore, during the heating ramp alone, thanks to the ferromagnetic nature and high activity of Raney Nickel, magnetic induction is 78 times more energy-efficient than conventional heating.

[0076] Furthermore, considering the energy consumed during one hour of reaction to achieve the same methane yield (~90%), we can also observe that magnetic induction is a more energy-efficient process than conventional heating. This represents an energy saving of 83%. Electrifying the process facilitates its direct coupling to intermittent renewable energy sources, resulting in minimal environmental impact. Consequently, magnetic induction, and specifically the use of Raney Nickel as a bifunctional electromagnetic catalyst, meets the stability, dynamic response, and energy efficiency requirements necessary for its effective integration into sustainable energy conversion systems.

Claims

CLAIMS 1. A catalytic hydrogenation process characterized in that it comprises at least the following steps: introducing a gas-phase inlet stream into a reactor, contacting the inlet stream with the unsupported Raney Nickel catalyst, heating the reaction mixture by magnetic induction using a high-frequency oscillating field to a temperature between 80 °C and 600 °C, increasing the pressure inside the reactor to between atmospheric pressure and 10 bar, and circulating a gas flow inside the reactor at a gas inlet flow rate between 1 mL min' 1 up to 10 L-min' 1 .

2. Catalytic hydrogenation process according to claim 1, characterized in that the inlet stream is composed of substrates susceptible to hydrogenation and hydrogen.

3. Catalytic hydrogenation process according to claim 2, characterized in that the hydrogenation-susceptible substrates of the inlet stream are selected from CO2, CO, organic substrates with carbonyl (C=O), nitrile (CN), nitro (NO2) groups, and combinations thereof.

4. Catalytic hydrogenation process according to claim 3, characterized in that said hydrogenation-capable substrates are selected from CO2, CO, and combinations thereof.

5. Catalytic hydrogenation process according to any of the preceding claims, characterized in that the Raney Nickel catalyst, in all its variations, is in the form of a micrometric powder and composed of ferromagnetic particles with a size between 1 pm and 1,000 pm.

6. Catalytic hydrogenation process according to any of the preceding claims, characterized in that the temperature to which the reactor mixture is heated by magnetic induction is between 150 and 300 °C.

7. Catalytic hydrogenation process according to any of the preceding claims, characterized in that the pressure inside the reactor is between atmospheric pressure and 2 bar.

8. Catalytic hydrogenation process according to any of the preceding claims, characterized in that the flow (of inlet gases inside the reactor is between 10 mL min' 1 up to 1,000 mL-min' 1 .

9. Catalytic hydrogenation process according to any of the preceding claims, characterized in that the reactor mixture is heated by magnetic induction using a high-frequency oscillating magnetic field with an amplitude between 0.1 mT and 200 mT and a frequency between 30 kHz and 500 kHz.

10. Catalytic hydrogenation process according to claim 9, characterized in that the oscillating magnetic field has a frequency between 100 and 400 kHz.

11. Catalytic hydrogenation process according to any of the preceding claims, characterized in that the reactor is a reactor made of a non-magnetic material selected from a fixed bed reactor, fluidized bed reactor, bubble reactor, moving bed reactor or membrane reactor.

12. Catalytic hydrogenation process according to claim 11, characterized in that the reactor is made of quartz.

13. Catalytic hydrogenation process according to claim 12, characterized in that the reactor is a fixed bed quartz reactor.

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