The present invention relates to a process for producing ammonia and to the use of the process for removing at least nitrogen (N2) from air, i.e. atmosphere of Earth.
Nitrogen (N2) fixation is challenging because the bond energy of the nitrogen-nitrogen triple bond (941 KJ/mol) supplies an extremely high thermodynamic stability.
The Haber-Bosch process is an artificial nitrogen fixation, which produces ammonia from H2 and N2 gases in the presence of an active catalyst. Currently, this process produces more than 90% of ammonia (L. Wang, M. Xia, H. Wang, K. Huang, C. Qian, C. T. Maravelias and G. A. Onzin, Joule, 2018, 2, 1055-1074). However, the Haber-Bosch process is an energy-intensive process. Energy consumption is due to the extremely high pressures (100-300 bars) required to increase the equilibrium concentration of ammonia at the temperatures required by the current catalytic systems (375-500° C.) (C. Smith, A. K. Hill and L. Torrente-Murciano, Energy Environ. Sci., 2020, 13, 331-344; K. H. R. Rouwenhorst, Y. Engelmann, K-van't Veer, R. S. Postma, A. Bogaerts and L. Lefferts, Green Chem., 2020, 22, 6258-6287; J. Humphreys, R. Lan and S. Tao, Adv. Energy Sustainability Res. 2021, 2, 2000043; A. J. Martin, T. Shinagawa and J. Pérez-Ramirez, Chem, 2019, 5, 263-283).
Maintenance of the temperature and pressure required for the Haber-Bosch process worldwide consumes 1-2% of all energy generated by humans (E. Giamello, Nat. Chem., 2012, 4, 869-870). In addition, the Haber-Bosch process accounts for 1.4% of global CO2 emissions (M. Capdevila-Cortada, Nat Catal 2019, 2, 1055), and thus causes massive greenhouse gas release. A further detriment is the low conversion to ammonia (i.e. the single-pass yield is ˜15-20%, gas recycling steps being necessary).
In view of the foregoing, the object underlying the present invention is therefore to make available a process for producing ammonia which circumvents detriments, in particular as described above, in the context of conventional synthesis of ammonia, in particular in the context of the Haber-Bosch process.
The present invention relates to a process for producing or synthesizing ammonia (NH3). The process comprises the step of
Hereafter, the above step of the inventive process is denoted as “contacting step”.
The present invention rests on the surprising finding that production or synthesis of ammonia from nitrogen and water in the presence of permanently polarized hydroxyapatite as catalyst or a catalyst comprising permanently polarized hydroxyapatite is achievable under mild reaction conditions (particularly <10 bar pressure and <250° C. temperature). Thus, for example in comparison to the Haber-Bosch process, the energy consumption may be considerably reduced, thereby facilitating production of ammonia with (considerably) lower costs. In addition, the process according to the present invention does not or basically not cause any greenhouse gas release.
The term “permanently polarized hydroxyapatite” as used according to the present invention means a hydroxyapatite that has undergone a complete structural redistribution, in particular almost perfect, with a high crystallinity degree, i.e. particularly with a low amount of amorphous calcium phosphate and the presence of vacancies detected by increased electrochemical activity and the accumulation of charge per unit mass and surface. It has an electrochemical activity and ionic mobility which do not disappear over time. The corresponding 31P-NMR spectrum of the permanently polarized hydroxyapatite is as shown on
The term “thermally polarized hydroxyapatite” as used according to the present invention preferably means a permanently polarized hydroxyapatite obtained or obtainable by a process (thermal polarization process) comprising the steps of
The term “samples” as used according to the present invention may in particular mean one sample, i.e. only one sample (singular), or a plurality of samples, i.e. two or more samples.
The hydroxyapatite of the samples in step (a) may be a natural, i.e. naturally occurring, hydroxyapatite and/or a synthetic hydroxyapatite.
Further, the hydroxyapatite of the samples in step (a) may be a crystalline hydroxyapatite.
Further, the samples may comprise or consist of at least one further calcium phosphate material, i.e. at least one further material comprising or consisting of calcium cations and phosphate anions. In particular, the at least one further calcium phosphate material is in the form of a calcium phosphate salt or calcium phosphate mineral. Preferably, the at least one further calcium phosphate material is selected from the group consisting of brushite (CaHPO4·2H2O or Ca[PO3(OH)]·2H2O), brushite-like material, amorphous calcium phosphate, tricalcium phosphate, in particular β-tricalcium phosphate, and mixtures of at least two of the afore-said further calcium phosphate materials.
The term “brushite” as used according to the present invention means a calcium phosphate material, in particular a calcium phosphate salt or calcium phosphate mineral, preferably a synthetic calcium phosphate material, in particular synthetic calcium phosphate salt or calcium phosphate mineral, with the chemical formula CaHPO4·2H2O. In the WAXS (wide angle x-ray scattering) spectrum, the most representative peaks of brushite appear at 20=29°, 31°, 35°, 42°, and 51°, which have been attributed to the (141), (221), (121), (152) and (143) reflections, respectively (JCPDS card number 72-0713).
The term “brushite-like material” as used according to the present invention refers to a calcium phosphate material that shows in the Raman spectrum peaks at 878, 848 and 794 cm−1, which correspond to the normal vibration mode of HPO42−, the POH deformation mode and the POH rotation mode, respectively.
The term “room temperature” as used according to the present invention means a temperature from 15° C. to 35° C., in particular 18° C. to 30° C., preferably 20° C. to 30° C., more preferably 20° C. to 28° C., particularly 20° C. to 25° C.
In an embodiment of the invention, the permanently polarized hydroxyapatite comprises or has
The term “bulk resistance” as used according to the present invention means resistance to the electron transfer and may be determined by means of electrochemical impedance spectroscopy.
Preferably, the bulk resistance increases by only 0.1% to 33%, in particular 4% to 63%, preferably by 4%, after 3 months.
The term “surface capacitance” as used according to the present invention means capacitance attributed to surface changes of hydroxyapatite induced by a thermal polarization process and may be determined by means of electrochemical impedance spectroscopy.
Especially preferably, the permanently polarized hydroxyapatite has a 31P-NMR spectrum showing a unique peak at 2.6 ppm or around 2.6 ppm, i.e. in the range of 2.5 ppm to 2.7 ppm, corresponding to phosphate groups of hydroxyapatite. Preferably, the 31P-NMR spectrum is carried out or obtained with solid permanently polarized hydroxyapatite at a temperature of 20° C. to 25° C. and using phosphoric acid (H3PO4) as a reference. A 31P-NMR spectrum of the permanently polarized hydroxyapatite is shown in
In a further embodiment of the invention, the catalyst, in particular the permanently polarized hydroxyapatite, is obtained or obtainable by a process comprising the steps of
The term “shaped bodies” as used according to the present invention may in particular mean one shaped body, i.e. only one shaped body (singular), or a plurality of shaped bodies, i.e. two or more shaped bodies.
The hydroxyapatite of the samples in step (a) may be a natural, i.e. naturally occurring, hydroxyapatite and/or a synthetic hydroxyapatite.
Further, the hydroxyapatite of the samples in step (a) may be a crystalline hydroxyapatite.
Further, the samples may comprise or consist of at least one further calcium phosphate material, i.e. at least one further material comprising or consisting of calcium cations and phosphate anions. In particular, the at least one further calcium phosphate material is in the form of a calcium phosphate salt or calcium phosphate mineral. Preferably, the at least one further calcium phosphate material is selected from the group consisting of brushite (CaHPO4·2H2O or Ca[PO3(OH)]·2H2O), brushite-like material, amorphous calcium phosphate, tricalcium phosphate, in particular β-tricalcium phosphate, and mixtures of at least two of the afore-said further calcium phosphate materials.
The shaped bodies as used according to the present invention may have a polygonal, for example triangular, quadratic or rectangular, pentagonal, hexagonal, heptagonal, octagonal or nonagonal, cross-section or a corner-less, in particular circular, oval-shaped or elliptical, cross-section. In particular, the shaped bodies may be in the form of a disc, plate, cone (conus) or cylinder. Further, the shaped bodies may have a thickness of >0 cm to 10 cm, in particular >0 cm to 1 cm, preferably >0 cm to 0.2 cm.
The aforementioned step (a) may be carried out by using ammonium phosphate dibasic (diammonium hydrogen phosphate, (NH4)2HPO4) and calcium nitrate (Ca(NO3)2) as reactants or starting materials. In particular, the step (a) may be carried out by
The step (a1) may be in particular carried out by using a mixture comprising or consisting of ammonium phosphate dibasic, calcium nitrate, water, in particular de-ionized water, ethanol, and optionally chelated calcium solutions. Advantageously, the pH value of the mixture and/or the pH value of an aqueous calcium nitrate solution applied for providing the mixture may be adjusted to 10-12, preferably 11. Thus, shapes and sizes of hydroxyapatite, in particular in the form of nanoparticles, can be controlled. Further, the step (a2) may be carried out under agitation, in particular gentle agitation, for example applying 150 rpm to 400 rpm. Further, the step (a2) may be carried out for 1 min to 12 h, in particular for 1 h. The step (a2) may also be termed as an aging step, according to the present invention. Further, the step (a3) may be carried out at a temperature of 60° C. to 240° C., preferably of 150° C. Further, the step (a3) may be carried out at a pressure of 1 bar to 250 bar, preferably of 20 bar. Further, the step (a3) may be carried out for 0.1 h to 72 h, preferably for 24 h. Further, the step (a4) may be carried out by cooling the mixture hydrothermally treated in step (a3) to a temperature of 0° C. to 90° C., in particular of 25° C. Further, the step (as) may be carried out by means of centrifugation and/or filtration. Further, the precipitates separated in step (as) may be washed, in particular using water and/or a mixture of ethanol and water, before the step (a6) is carried out. Further, the step (a6) may be carried out for 1 day to 4 days, in particular for 2 days to 3 days, preferably for 3 days.
Further, the aforementioned step (b) may be carried out at a temperature between 700° C. and 1150° C., in particular between 800° C. and 1100° C., in particular at 1000° C.
Further, the process preferably comprises between the step (b) and the step (c) a further step (bc)
In particular, the step (bc) may be carried out under a pressure of 1 MPa to 1000 MPa, in particular 100 MPa to 800 MPa, preferably 600 MPa to 700 MPa. Further, the step (bc) may be carried out for 1 min to 90 min, in particular 5 min to 50 min, preferably 10 min to 30 min.
The shaped bodies may have a polygonal, for example triangular, quadratic or rectangular, pentagonal, hexagonal, heptagonal, octagonal or nonagonal, or a corner-less, in particular circular, oval-shaped or elliptical, cross-section. Further, the shaped bodies may have a thickness of >0 cm to 10 cm, in particular >0 cm to 5 cm, preferably >0 cm to 2 cm. In particular, the shaped bodies may have a thickness of 0.1 cm to 10 cm in particular 0.1 cm to 5 cm, preferably 0.5 cm to 2 cm.
Preferably, the shaped bodies are in the form of discs, plates, cones or cylinders.
Advantageously, by carrying out step (c), catalytic activation of the samples obtained in step (b) or the shaped bodies thereof may be accomplished. Preferably, step (c) is carried out by placing the samples obtained in step (b) or by placing the shaped bodies thereof between a positive electrode and a negative electrode, wherein the samples obtained in step (b) or the shaped bodies thereof are in contact with both electrodes. The positive electrode and negative electrode may, by way of example, be in the form of stainless steel plates, in particular stainless steel AISI 304 plates. Further, the positive electrode and negative electrode may have a mutual distance of 0.01 mm to 10 cm, in particular 0.01 mm to 5 cm, preferably 0.01 mm to 1 mm.
Further, the positive electrode and negative electrode can be of different shapes. The electrodes may have a polygonal cross-section, for example quadratic or rectangular, or a corner-less, in particular circular, oval-shaped or elliptical, cross-section. In particular, the electrodes may have a thickness of >0 cm to 10 cm, in particular >0 cm to 5 cm, preferably >0 cm to 1 mm. For example, the electrodes may be in the form of a disc, plate or a cylinder. Further, the constant or variable DC voltage or the equivalent electric field may be applied in the aforementioned step (c) for 1 h to 24 h, in particular 0.1 h to 10 h, in particular 1 h.
Further, the DC voltage applied in the aforementioned step (c) is preferably 500 V, which is equivalent to a constant electric field of 3 kV/cm.
Further, the equivalent electric field applied in the aforementioned step (c) is preferably 3 kV/cm.
Further, the temperature in the aforementioned step (c) is preferably at least 900° C., more preferably at least 1000° C. Preferably, the temperature in step (c) is 900° C. to 1200° C., in particular 1000° C. to 1200° C., particularly 1000° C.
Preferably, step (c) is carried out by applying a constant or variable DC voltage of 500 V at 1000° C. for 1 h to the samples obtained in step (b) or the shaped bodies, in particular discoidal shaped bodies, thereof.
Further, the aforementioned step (d) may be carried out by cooling the samples or shaped bodies obtained in step (c) to room temperature.
Further, the aforementioned step (d) may be carried out for 1 min to 72 h, in particular 15 min to 5 h, preferably 15 min to 2 h.
In a further embodiment of the invention, the catalyst, in particular the permanently polarized hydroxyapatite, is obtained or obtainable by a process comprising the steps of
With respect to further features and advantages of the steps (a)-(d), reference is made in its entirety to the previous description.
With respect to further features and advantages of the permanently polarized hydroxyapatite as used according to the present invention, it is referred to the PCT application WO 2018/024727 A1, the content of which is incorporated hereby by explicit reference.
Further, the catalyst may be in the form of a single-phase catalyst or in the form of a multi-phase (multiphasic) catalyst.
Further, the catalyst, in particular a phase or single phases thereof, may preferably (along the permanently polarized hydroxyapatite) comprise or consist of at least one further calcium phosphate material, i.e. at least one further material comprising or consisting of calcium cations and phosphate anions. In particular, the at least one further calcium phosphate material may be in the form of a calcium phosphate salt or calcium phosphate mineral. Preferably, the at least one further calcium phosphate material is selected from the group consisting of brushite (CaHPO4·2H2O or Ca[PO3(OH)]· 2H2O), brushite-like material, amorphous calcium phosphate, tricalcium phosphate, in particular β-tricalcium phosphate, and mixtures of at least two of the afore-said further calcium phosphate salts or minerals.
Preferably, the permanently polarized hydroxyapatite has a proportion which is larger than a proportion of the at least one further calcium phosphate salt or mineral, based on the total weight of the catalyst.
In particular, the permanently polarized hydroxyapatite may have a proportion of 50% by weight to 99.9% by weight, in particular 65% by weight to 99.9% by weight, in particular 75% by weight to 99% by weight, preferably 80% by weight to 95% by weight, in particular 85% by weight to 90% by weight, in particular 85% by weight to 88% by weight, based on the total weight of the catalyst.
Further, the brushite and/or the brushite-like material may have a proportion of >0% by weight to 50% by weight, in particular 0.1% by weight to 35% by weight, in particular 1% by weight to 25% by weight, preferably 5% by weight to 20% by weight, in particular 10% by weight to 15% by weight, in particular 12% by weight to 15% by weight, based on the total weight of the catalyst.
Further, the brushite and/or the brushite-like material may have a crystallinity, in particular determined by means of wide angle x-ray scattering (WAXS), from 65% to 99.9%, in particular 75% to 99%, preferably 80% to 95%. Further, crystallites of the brushite and/or the brushite-like material may have a size, in particular determined by means of wide angle x-ray scattering (WAXS), from 20 nm to 500 nm, in particular 50 nm to 200 nm, preferably 70 nm to 100 nm. Preferably, in this context, the term “size” refers to an average diameter of the crystallites of the brushite and/or the brushite-like material. Further, the amorphous calcium phosphate may have a proportion of <18% by weight, in particular from 0.1% by weight to 17% by weight or <9% by weight, preferably <5% by weight, in particular <0.1% by weight, or >0% by weight to 15% by weight, in particular from >0% by weight to 10% by weight, preferably >0% by weight to 5% by weight, based on the total weight of the catalyst.
Alternatively, the catalyst may be free of amorphous calcium phosphate.
Further, the tricalcium phosphate, in particular β-tricalcium phosphate, may have a proportion of <36% by weight, in particular from 0.1% by weight to 35% by weight or <12% by weight, preferably <5% by weight, in particular <0.5% by weight, or >0% by weight to 15% by weight, in particular >0% by weight to 10% by weight, preferably >0% by weight to 5% by weight, based on the total weight of the catalyst.
Alternatively, the catalyst may be free of tricalcium phosphate, in particular β-tricalcium phosphate.
Preferably, the catalyst further, i.e. along the permanently polarized hydroxyapatite, comprises or consists of brushite and/or brushite-like material. In this case, the catalyst has preferably a wide angle x-ray scattering (WAXS) pattern showing peaks, in particular representative or unique peaks, at 2θ=29°, 31°, 35°, 42°, and 51°, which have been attributed to the (141), (221), (121), (152) and (143) reflections, respectively (JCPDS card number 72-0713). Preferably, said pattern is carried out or obtained at room temperature, preferably at a temperature of 20° C. to 25° C. and/or under atmospheric conditions, in particular under atmospheric humidity and/or atmospheric pressure. A wide angle x-ray scattering (WAXS) pattern of the catalyst is shown in
Further, the catalyst as used according to the present invention may be in the form of particles. The particles may have a diameter, preferably mean diameter, in particular determined by means of wide angle x-ray scattering (WAXS), of 20 nm to 500 nm, in particular 50 nm to 200 nm, preferably 70 nm to 100 nm.
Further, the catalyst as used according to the present invention may be in the form of a powder, in particular having particles as mentioned in the preceding paragraph.
Further, the catalyst as used according to the present invention may be in the form of a shaped body. The shaped body may have a polygonal, for example triangular, quadratic or rectangular, pentagonal, hexagonal, heptagonal, octagonal or nonagonal, cross-section or a corner-less, in particular circular, oval-shaped or elliptical, cross-section.
In particular, the shaped body may be in the form of a disc, plate, cone (conus) or cylinder.
Further, the shaped body may have a thickness of >0 cm to 10 cm, in particular >0 cm to 1 cm, preferably >0 cm to 0.2 cm.
Further, the catalyst may be obtained or obtainable by a process comprising the steps of
Preferably, for performing step (c), the samples obtained in step (b) or the shaped bodies thereof are arranged between the positive electrode and the negative electrode, which are used for applying the constant or variable DC voltage, equivalent electric field or electrostatic discharge during step (c), such that the samples obtained in step (b) or the shaped bodies thereof are spaced only from one of the two electrodes, preferably only from the positive electrode, i.e. such that the samples obtained in step (b) or the shaped bodies thereof have a distance only to one of the two electrodes, preferably only to the positive electrode. In other words, the samples obtained in step (b) or the shaped bodies thereof are preferably left in contact with the other of the two electrodes, more preferably with the negative electrode.
Further, the samples obtained in step (b) or the shaped bodies thereof are spaced from the one of the two electrodes, preferably from the positive electrode, in a distance from >0 cm to 10 cm, in particular >0 cm to 5 cm, preferably >0 cm to 0.1 cm.
With respect to further features and advantages of the electrodes, reference is made in its entirety to the previous description.
Further; the hydroxyapatite of the samples in step (a) may be a natural, i.e. naturally occurring, hydroxyapatite and/or a synthetic hydroxyapatite.
Further, the hydroxyapatite of the samples in step (a) may be a crystalline hydroxyapatite.
Further, the samples may comprise or consist of at least one further calcium phosphate material, i.e. at least one further material comprising or consisting of calcium cations and phosphate anions. In particular, the at least one further calcium phosphate material is in the form of a calcium phosphate salt or calcium phosphate mineral. Preferably, the at least one further calcium phosphate material is selected from the group consisting of brushite (CaHPO4·2H2O or Ca[PO3(OH)]·2H2O), brushite-like material, amorphous calcium phosphate, tricalcium phosphate, in particular β-tricalcium phosphate, and mixtures of at least two of the afore-said further calcium phosphate materials.
With respect to further features and advantages of the process, reference is made in its entirety to the previous description and to the applicants' non-published European patent application EP 20383003.9.
Preferably, the water or at least an amount or proportion of the water is in liquid form during the contacting step. Depending on the reaction conditions applied for carrying out the contacting step, in particular dependent on the applied pressure, in particular nitrogen pressure, and/or applied temperature, an amount or proportion of the water may be also in vapor form during the contacting step.
In a further embodiment of the invention, the contacting step is carried out with a volumetric ratio of the water to the catalyst of 10000:1 to 0.1:1, in particular 1000:1 to 0.1:1, preferably 1000:1 to 100:1.
Further, the contacting step may be carried out with a weight ratio of the water to the catalyst of 10000:3 to 0.1:3, in particular 1000:3 to 0.1:1, preferably 1000:3 to 100:3.
Further, the contacting step may be carried out by using a proportion of the water of 0.1% by weight to 99.97% by weight, in particular 0.1% by weight to 99.9% by weight, preferably 0.1% by weight to 99.7% by weight, more preferably 97% by weight to 99.7% by weight, based on a total weight of a mixture comprising or consisting of the water and the catalyst.
Preferably, the contacting step is carried out in a chamber, in particular inert chamber, of a reactor.
Further, the contacting step may be carried out by using a ratio of water volume to a volume of the chamber of 1 to 1000, in particular 1 to 100, preferably 1 to 10.
Further, the contacting step may be carried out by using a proportion of the catalyst of 0.03% by weight to 99.9% by weight, in particular 0.3% by weight to 99.9% by weight, preferably 0.3% by weight to 3% by weight, based on a total weight of a mixture comprising or consisting of the water and the catalyst.
In a further embodiment of the invention, the contacting step is carried out under a pressure, in particular under a pressure of nitrogen, of 0.01 bar to 20 bar, preferably 0.3 bar to 10 bar, more preferably 1 bar to 10 bar, in particular of 6 bar.
In a further embodiment of the invention, the contacting step is carried out with a molar ratio of nitrogen to the catalyst of 400 to 20, preferably 200 to 60, in particular 120.
In a further embodiment of the invention, the contacting step is carried out at a temperature of ≥95° C. to 140° C., preferably ≥95° C. to 120° C., more preferably 100° C. to 120° C., in particular of 120° C.
In a further embodiment of the invention, the contacting step is carried out for 0.0001 h to 120 h, in particular 0.1 h to 96 h, preferably 24 h to 72 h.
Further, the catalyst may be in the form of an uncoated catalyst, i.e. in the form of a catalyst lacking any coating.
Alternatively, the catalyst may be in the form of a coated catalyst. For example, the catalyst may be coated with a material, in particular a photocatalytic active material, such as TiO2, MgO2, MnO2 or combinations thereof. More specifically, the catalyst may be coated with a coating having a three-layer structure, in particular wherein the three-layer structure may be composed of two layers of aminotris (methylenephosphonic acid) and a layer of zirconium oxychloride (ZrOCl2) or zirconia (ZrO2), wherein the layer of zirconium oxychloride (ZrOCl2) or zirconia (ZrO2) is arranged or sandwiched between the two layers of aminotris (methylenephosphonic acid). By using a coated catalyst, the efficiency of the process according to the present invention may be additionally optimized.
Further, the catalyst may be doped with an additive. The additive may be in particular in the form of nanoparticles, i.e. of particles having a mean pore diameter of 1 nm to 100 nm. Further, the additive may be selected from the group consisting of a metal, a ceramic, an organic compound and combinations thereof. The metal may be selected from the group consisting of gold, silver, copper, zinc, titanium and combinations, in particular alloys, thereof. The ceramic may be selected from the group consisting of inorganic, non-metallic, often crystalline oxide, nitride, or carbide material, in particular phosphates, silicates and combinations thereof.
In a further embodiment of the invention, the contacting step is carried out under UV (ultraviolet) irradiation or UV-Vis (ultraviolet-visible) irradiation. In particular, the UV irradiation or UV-Vis irradiation may have a wavelength from 200 nm to 850 nm, in particular 240 nm to 400 nm, in particular 200 nm to 280 nm, preferably 240 nm to 270 nm, more preferably 250 nm to 260 nm, especially preferably of 253.7 nm. The UV irradiation or UV-Vis irradiation may be provided or generated by a suitable UV source or UV-Vis source, for example UV lamp or UV-Vis lamp.
In a further embodiment of the invention, the UV irradiation or UV-Vis irradiation has an irradiance from 0.1 W/m2 to 200 W/m2, in particular 1 W/m2 to 50 W/m2, preferably 2 W/m2 to 10 W/m2, more preferably of 3 W/m2.
In a further embodiment of the invention, a surface of the catalyst is exposed to the UV irradiation or UV-Vis irradiation, wherein the surface of the catalyst being exposed to the UV irradiation or UV-Vis irradiation is not covered by the water.
Further, the contacting step may be carried out in absence or basically in absence of carbon dioxide.
The term “basically in absence of carbon dioxide” as used according to the present invention means absence of free carbon dioxide (without considering the presence of physically and/or chemically absorbed carbon dioxide, in particular on inner walls of a reactor in which the contacting step may be carried out).
Further, the contacting step may be carried out in absence or basically in absence of methane.
The term “basically in absence of methane” as used according to the present invention means absence of free methane (without considering the presence of physically and/or chemically absorbed methane, in particular on inner walls of a reactor in which the contacting step may be carried out).
Further, the contacting step may be carried out in absence or basically in absence of carbon dioxide and methane.
In a further embodiment of the invention, the contacting step is carried under an atmosphere which is, apart from the nitrogen and optionally water vapor, free or basically free of any further gas. In other words, in a further embodiment of the invention, apart from nitrogen, no or basically no further gas is applied during the contacting step.
The term “basically free of any further gas” or “basically no further gas” as used according to the present invention means absence of free further gas (without considering the presence of physically and/or chemically absorbed further gas, in particular on inner walls of a reactor in which the contacting step may be carried out).
In a further embodiment of the invention, the contacting step is carried out by using air, in particular polluted air, preferably industrial and/or traffic polluted air, wherein the nitrogen is part of the air.
The term “air” as used according to the present invention means a layer of gases retained by Earth's gravity, surrounding the planet's Earth and forming its planetary atmosphere (so-called “atmosphere of Earth”).
The term “polluted air” as used according to the present invention means air comprising gaseous pollutants. The pollutants are preferably selected from the group consisting of carbon dioxide, methane, nitrogen dioxide, ozone, nitrogen oxides, sulfur dioxide, gases containing sulphur, cyanides, volatile organic carbon compounds (VOC) and mixtures of at least two of the afore-said gaseous pollutants.
The term “industrial and/or traffic polluted air” as used according to the present invention means air comprising gaseous pollutants, wherein the gaseous pollutants come from traffic, in particular motor vehicle traffic and/or rail transport and/or shipping and/or air traffic, and/or from industrial plants. As regards possible gaseous pollutants, reference is made in its entirety to the previous paragraph.
Further, the process, in particular the contacting step, according to the present invention may be carried out in continuous, semi-continuous or batch-like manner.
Preferably, the process comprises a further step
Further, the present invention relates to the use of the process according to the present invention for removing carbon dioxide and/or nitrogen, preferably carbon dioxide and nitrogen, from air, in particular polluted air, preferably industrial and/or traffic polluted air.
With respect to further features and advantages of the use, reference is made in its entirety to the previous description.
Further features and advantages of the invention will become clear from the following examples. The individual features can be realized either singularly or severally in combination in one embodiment of the invention. The preferred embodiments merely serve for illustration and better understanding of the invention and are not to be understood as in any way limiting the invention.
Further features and advantages of the invention will become clear from the following examples. The individual features can be realized either singularly or severally in combination in one embodiment of the invention. The preferred embodiments merely serve for illustration and better understanding of the invention and are not to be understood as in any way limiting the invention.
For a better understanding of what has been disclosed, some figures are attached which schematically or graphically and solely by way of non-limiting example show a practical case of embodiment of the present invention.
In the figures, the following is schematically displayed:
15 mL of 0.5 M of (NH4)2HPO4 in de-ionized water were added at a rate of 2 mL/min to 25 mL of 0.5 M of Ca(NO3)2 in ethanol (with pH previously adjusted to 11 using ammonium hydroxide solution) and left aging for 1 h. The whole process was performed under gentle agitation (150 rpm) and at room temperature. Hydrothermal treatment at 150° C. was applied using an autoclave marketed under the trademark DIGESTEC DAB-2™ for 24 h. The autoclave was allowed to cool down before opening. The precipitates were separated by centrifugation and washed with water and a 60/40 v/v mixture of ethanol-water (twice). After freeze-drying it for 3 days, the white powder obtained was sintered for 2 h at 1000° C. in air using a furnace marketed under the registered trademark CARBOLITE® ELF11/6B/301.
Mechanical consistent discs of ˜1.5 mm of thickness and 1.766 mm of diameter were obtained by pressing 150 mg of HAp powder at 620 MPa for 10 min in a mold. Thermal polarization was done placing the HAp discs between two stainless steel (AISI 304) and applying a constant DC voltage conducted by Pt cables of 500 V for 1 h with a GAMMA power supply, while temperature was kept at 1000° C. during such a period using the same laboratory furnace. The discs were allowed to cool down maintaining the applied electric potential for 30 minutes, and finally, all the system was powered off and left to cool overnight.
A high pressure stainless steel reactor was employed to perform the catalytic reactions. The reactor had an inert reaction chamber coated with a perfluorinated polymer (120 mL) where both the catalyst and water were incorporated. The reactor was equipped with an inlet valve for the entrance of gases (i.e. N2) and an outlet valve to recover the gaseous reaction products. A UV lamp (GPH265T5L/4, 253.7 nm) was also placed in the middle of the reactor to irradiate the catalyst directly, the lamp being protected by a UV transparent quartz tube. All surfaces were coated with a thin film of a perfluorinated polymer in order to avoid any contact between the reaction medium and the reactor surfaces, in this way discarding other catalyst effects.
Catalyst samples, weighting approximately 150 mg, and de-ionized liquid water were initially incorporated into the reaction chamber. The chamber was extensively purged with N2 in order to eliminate the initial air content. After this, N2 gas was introduced to increase the reaction chamber pressure (measured at room temperature) to the target pressure.
The reaction products were analyzed by 1H NMR spectroscopy. All 1H NMR spectra were acquired with a Bruker Avance-II+ spectrometer operating at 600 MHz. The chemical shift was calibrated using tetramethylsilane (TMS) internal standard. 512 scans were recorded in all cases. In order to remove the reaction products from the catalyst, 10 mg of the reacted catalyst were dissolved in 15 mL of water with pH adjusted to 2.1±0.2 using 7.6 mM H2SO4, to promote the conversion of ammonia in NH4+, and applying 4 cycles that involved sonication (5 min) and stirring (1 min) steps. Then, for the 1H NMR sample preparation, 500 μL of the reacted catalyst solution were mixed with 100 μL of DMSO-d6 instead of solvents with labile deuterons (i.e. D20) to avoid the formation of ammonium deuterated analogues, not desired for quantitative analysis. The same treatment was applied to the water supernatant.
The p-HAp electrocatalyst was prepared as described in previous work (J. Sans, E. Armelin, V. Sanz, J. Puiggali, P. Turon and C. Alemán, J. Catal., 2020, 389, 646-656; J. Sans, V. Sanz, J. Puiggali and P. Turon, Cryst. Growth Des. 2021, 21, 748-756). In brief, after hydrothermal synthesis of HAp using a recently proposed procedure to control the anisotropic growth, the resulting powder was sintered at 1000° C. Then, discs of ˜1.5 mm thickness and 1.766 mm diameter were obtained by pressing in a mold. Then, the discs were polarized applying a DC voltage of 500 V for 1 h at 1000° C.
In order to investigate the electrocatalytic synthesis of ammonia over p-HAp, a reaction was performed at 120° C. in a stainless steel reactor with an inert reaction chamber (i.e. a chamber coated with a perfluorinated polymer) illuminated with UV light. In order to eliminate the initial air content, the chamber was firstly purged with the N2 and, subsequently, filled with N2 (6 bar). A volume of 20 mL of de-ionized water was introduced in the reactor and put in contact with the non-irradiated side of the p-HAp disk, as is sketched in
The products generated on the surface of the p-HAp disk after 96 h of reaction were identified adapting a procedure for rapid NH4+ analyses using 1H NMR spectroscopy (R. Y. Hodgetts, A. S. Kiryutin, P. Nichols, H.-L. Du, J. M. Bakker, D. R. Macfarlane and A. N. Simonov, ACS Energy Lett., 2020, 5, 736-741). More specifically, 10 mg of the reacted catalyst were dissolved in 15 mL of water with pH adjusted to 2.1±0.2 using 7.6 mM H2SO4, to promote the conversion of ammonia in NH4, and applying 4 cycles that involved sonication (5 min) and stirring (1 min) steps. Then, for the 1H NMR sample preparation, 500 μL of the reacted catalyst solution were mixed with 100 μL of DMSO-d6. As is illustrated in
Other products coming from CO2 fixation were also identified in the 1H NMR spectrum: formic acid (8.07 ppm), acetone (2.06 ppm) and acetic acid (1.92 ppm). Although p-HAp was found to catalyze the electroreduction of CO2, the source of such gas in the reaction chamber was initially uncertain. After different tests aimed at having an exhaustive purge of the reactor chamber, ensuring the elimination of gases other than N2, and several blank and control reactions, it was concluded that the CO2 adsorbed by the perfluorinated polymer, which coated all surfaces of the reaction chamber, was the source for the carbon-fixation reaction. Thus, although the yield of NH4+ was null in absence of catalyst (blank reaction) and very low (1.3±0.5 μmol/g) when the p-HAp was not irradiated with UV light (control reaction), weak signals associated to formic acid, acetone and acetic acid were still detectable in the former case while they were not detected in the latter one (
An important aspect to be considered is the transfer of the ammonia molecules formed on the surface of the catalyst to the water medium, which is in contact with the p-HAp disk (
Analyses of the supernatants have been also used to study the influence of the reaction time in the yield of products coming from desorbed CO2 fixation. Results are displayed in
The influence of different factors on the yield of ammonia is described in
Another important factor that deserves consideration is the reaction temperature. This was varied from 95 to 140° C. (
The volume of water introduced in the reactor, which is the source of protons for NH4 production, is a key parameter that deserves consideration. Reactions were conducted considering 0, 10, 20 and 40 mL of water in contact with the p-HAp catalyst (see
The influence of the time on the yield of NH4+ was examined considering reactions of 24 h, 48 h and 96 h while the N2 pressure, the temperature and the initial content of water were kept at 6 bar, 120° C. and 20 ml, respectively (
As a proof of concept, the performance of the catalyst was explored with polluted air at atmospheric pressure. More specifically, air polluted by the combustion of fossil carburant was captured from a road with a large volume of traffic of cars and trucks and transferred to the reaction chamber. In addition of N2 and O2, the content of CO2, CH4 and other pollutants was significantly higher than the average of the ambient air. Therefore, the valuable products coming from both CO2-, CH4- and N2-fixation were expected to be obtained by exposing the polluted air to the optimized reaction conditions. The reaction was conducted using p-HAp in contact with 20 ml of water at 120° C. and under UV radiation. Representative 1H NMR spectra of the catalyst solution and the supernatant after 96 h reactions are shown in
As it can be seen, NH4+ was observed in both the catalyst and the supernatant, even though the amount detected in the last was four times greater than in the first. The total yield of ammonium was of 20.7±4.7 μmol/g of catalyst. Although this value was lower than the one observed using 6 bar of N2 and 96 h at 120° C. (27.3±2.8 μmol/g of catalyst), the difference was less than expected, suggesting that other components and/or pollutants of air, as for example Oz and NO, could affect favorably to nitrogen fixation.
Valuable products coming from carbon fixation were also detected. In addition of formic acid, acetone and acetic acid, which were previously detected as a consequence of the CO2 desorption from the perfluorinated coating, ethanol was also identified. This was not a surprising result since previous studies proved that p-HAp catalyzes the formation of ethanol by carbon fixation from mixtures of CO2 and CH4, the latter among the common urban volatile organic compound emissions. Overall, these results demonstrate that the p-HAp catalyst cleans polluted air producing valuable compounds using mild reaction condition that can be employed as raw material for manufacturing fertilizers and other chemicals. It is worth noting that the simultaneous fixation of N2 and CO2 is a paradox since the CO2 emitted by conventional production of ammonia using N2 and H2 causes massive greenhouse effect. Within this context, the p-HAp appears to be a step in the right direction to fight anthropogenic climate change without detriment in the production of fertilizers.
The electrosynthesis of ammonia from N2 and water with p-HAp has been demonstrated using mild reaction conditions. The yield of the reaction has been optimized by considering the temperature, the N2 pressure, the volume of water and the reaction time. The main part of the produced ammonia migrates from the catalyst to the water supernatant, which is in contact with the surface of the catalyst, facilitating its recovery and avoiding the catalyst saturation. On the other hand, this catalyst is also able to convert CO2 into valuable chemical products, such as formic acid, ethanol and acetone. The coexistence of nitrogen- and carbon-fixation processes and the migration of the products to the liquid phase suggest that p-HAp is particularly suitable for the catalytic cleaning of polluted air. Within this context, the reaction produced using 1 bar of air in polluted by vehicle emissions resulted in the formation of 138.4±23.8 μmol of valuable chemicals/g of catalyst (i.e. 118.7±19.8 and 20.7±4.7 μmol/g from carbon- and nitrogen-fixation processes).
Number | Date | Country | Kind |
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21382671.2 | Jul 2021 | EP | regional |
This application is the United States national stage entry of International Application No. PCT/EP2022/070577, filed on Jul. 22, 2022, and claims priority to European Application No. 21382671.2, filed on Jul. 22, 2021. The contents of International Application No. PCT/EP2022/070577 and European Application No. 21382671.2 are incorporated by reference herein in their entireties.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2022/070577 | 7/22/2022 | WO |