Method for producing H2 and / or Br2 by electrolysis of HBr using fluoropolymer membranes

Abstract

A process for producing hydrogen and / or bromine by electrolyzing hydrogen bromide in the electrolysis of hydrogen bromide using a fluoropolymer membrane having a glass transition temperature Tg > = 110 DEG C, wherein the hydrogen bromide is derived from the bromination of hydrocarbons.

Description

Technical Field

[0001] The present disclosure relates to a method for producing hydrogen and / or bromine by electrolysis of hydrogen bromide. The present disclosure also relates to the use of fluoropolymer membranes in the electrolysis of brominated hydrogen bromide, and the gases obtained by such use and the corresponding method. Technical Background

[0002] The global demand for hydrogen (H2) and H2-derived fuels will increase significantly in the coming years. This is especially because H2 is expected to play a key role in mitigating global warming. In order to produce H2 in an environmentally friendly way, water electrolysis using renewable electricity is now a standard technology, and the hydrogen produced in this way is also called green hydrogen. There are basically three technologies to achieve water electrolysis, namely alkaline electrolysis (AEL), proton exchange membrane electrolysis (PEMEL) and solid oxide electrolysis (SOEL).

[0003] Different technologies have different operating ranges and different efficiencies. For example, SOEL technology is a high temperature solution that typically provides relatively high efficiency. However, SOEL solutions typically have a fairly limited service life and require relatively high capital expenditures (CAPEX) combined with a generally low level of technology readiness. AEL is the oldest technology, but is less flexible than PEMEL and does not allow power to be adjusted over a relatively wide range. In addition, AEL solutions typically suffer from unfavorable low current densities, which in turn increases CAPEX. In contrast, PEMEL solutions typically can be operated at higher current densities, which brings about a reduction in CAPEX. Therefore, PEMEL is generally beneficial to water electrolysis to produce green hydrogen.

[0004] However, liquid phase water electrolysis typically requires a fairly high threshold voltage and a relatively high amount of energy to electrolyze water to produce H2. More specifically, the electrolysis of water following the reaction 2H2O→O2+2H2 has a threshold voltage of 1.23V. Therefore, alternative electrolysis pathways for H2 have been considered. For example, the electrolysis of hydrogen halides may provide an alternative. Among the conceivable electrolysis, the electrolysis of HBr (or HBr electrolysis) rarely occurs and is much less common than the electrolysis of hydrogen chloride (HCl) or hydrogen fluoride (HF). At the industrial level, the only relevant practical application of HBr electrolysis is in flow batteries for the purpose of storing energy. However, such flow batteries produce neither H2 nor bromine (Br2) for their subsequent use, but use these compounds as energy carriers and often even store them in an unpurified form, which is sufficient for storage but is generally not pure enough for the subsequent use of H2. Additionally, in flow batteries, electrolysis is typically performed in the liquid phase under mild conditions to avoid pressure buildup and / or damage to the membranes, and is often operated at limited conversion levels to avoid the formation of multiple phases and any inhomogeneities in the system.

[0005] US 10,472,721 B1 describes HBr electrolysis under more severe conditions, but only in the context of the bromination of hydrogen sulfide. As equipment for such electrolysis, standard proton exchange membranes (PEM) or diaphragm cells are generally considered, wherein in the context of the former, the The glass transition temperature (T g ) characteristics, but reportedly T g Typically in the range of 98 to 109°C, depending on its hydration level (see, e.g., Jung et al., Int. J. Hydrogen Energy 37, 12580–12585, 2012). In addition, in long-term industrial operation, standard Membranes generally suffer from accelerated degradation at elevated temperatures like above 65° C., and they are generally unsuitable at temperatures above 100° C. due to irreversible structural changes in the polymers forming the membranes. Due to the lower operating temperatures required, such membranes have limited conductivity, can accommodate lower current densities, and require higher operating voltages, making electrolysis less economical.

[0006] Overall, there remains a general desire for improved HBr electrolysis.

[0007] An object of the present disclosure is to provide a method for improving HBr electrolysis, which at least partially overcomes the shortcomings encountered in the art. An object of the present disclosure is particularly to provide a method that allows HBr electrolysis to be performed at a higher current density and / or a lower operating voltage. Another object of the present disclosure is to provide a method that makes HBr electrolysis more economical. Another object of the present disclosure is to provide a method for improving HBr electrolysis, which helps alleviate global warming. In addition, an object of the present disclosure is to provide a method for adding value to HBr produced as a by-product. An object of the present disclosure is to provide hydrogen, which at least partially overcomes the shortcomings encountered in the art. An object of the present disclosure is also to provide bromine, which at least partially overcomes the shortcomings encountered in the art. An object of the present disclosure is also to provide a method for producing hydrogen and / or bromine, which at least partially overcomes the shortcomings encountered in the art. Summary of the invention

[0008] Surprisingly, it has been found that the problems underlying the present disclosure can be overcome by the use (as means), hydrogen, bromine and process according to the claims. Further embodiments of the present disclosure are outlined throughout the specification.

[0009] The subject of the present disclosure is a glass transition temperature T g ≥110℃, preferably T g ≥120℃, more preferably T g Use of fluoropolymer membranes at ≥ 125°C in the electrolysis of hydrogen bromide derived from the bromination of hydrocarbons.

[0010] As used herein, a (fluoropolymer) membrane is a sheet or layer that can be used as a proton exchange membrane in a standard electrolysis cell (or electrolytic cell). Thus, protons can migrate through such a membrane. Thus, the membrane used is a proton exchange fluoropolymer membrane.

[0011] The fluoropolymer membrane in the use according to the present disclosure comprises a fluoropolymer, and is therefore referred to as a fluoropolymer membrane.Preferably, the fluoropolymer membrane (in dry state) consists of a fluoropolymer, more preferably of a fluoropolymer in a chemically stable form.

[0012] As used herein, a fluoropolymer is a fluorocarbon-based polymer having multiple carbon-fluorine bonds. Such fluoropolymers typically do not contain silicon atoms. Such fluoropolymers may additionally contain no chlorine, bromine and / or iodine atoms.

[0013] As used herein, the glass transition temperature (or T g) is determined according to DIN EN ISO 11357-2:2020-08 (half-step-height method). Therefore, as used herein, the glass transition temperature of the fluoropolymer membrane is determined by differential scanning calorimetry (DSC) measurement, more specifically by the curve obtained by such DSC measurement. The glass transition temperature of the fluoropolymer membrane is determined on a sample of the fluoropolymer membrane, more specifically on a sample of the fluoropolymer membrane in a fully hydrated state. According to the present disclosure, a fluoropolymer membrane in a fully hydrated state is a fluoropolymer membrane that does not absorb any additional (deionized) water (deionized H2O, as described in the ASTM D5127-13 (2018) standard) after 24 hours at a temperature of 80°C, and is therefore a fully hydrated fluoropolymer membrane, or a fluoropolymer membrane saturated with water. Therefore, the water absorption of the fluoropolymer membrane has reached its maximum. A fully hydrated fluoropolymer membrane is obtained by immersing the fluoropolymer membrane in deionized water, which will result in an increase in weight of the fluoropolymer membrane, as can be measured by a balance. The fluoropolymer membrane is in a fully hydrated state when there is no more weight increase over time. A fully hydrated fluoropolymer membrane is typically obtained by immersing the fluoropolymer membrane in deionized water having a temperature of 80° C. for a period of 24 hours.

[0014] In some reports, the glass transition temperature of the dried membranes was reported (e.g., in Jung et al., Int. J. Hydrogen Energy 37, 12580–12585, 2012). However, in such a dry state, the membranes only show poor conductivity. During the hydration of the membranes, the T of the membranes decreases due to the plasticizer effect of water. g Typically, the T of the fluoropolymer membrane in accordance with the present disclosure is dependent on the fully hydrated state. g , because the T in the fully hydrated state g It best reflects the behavior of the membrane during electrolysis, especially during the electrolysis of hydrogen bromide.

[0015] In addition to the glass transition temperature (T g ), other characteristics of fluoropolymer membranes reported herein generally refer to the fluoropolymer membranes in the dry state.

[0016] As used herein, the glass transition temperature (T g ) refers to the lowest glass transition temperature of fluorinated polymers. Some polymers or films made of polymers, respectively, are known, for example, The type membrane may have multiple glass transition temperatures, in particular two glass transition temperatures. The first glass transition temperature is due to the mobility of the main chain in the polymer matrix, while the second glass transition temperature is due to side chain effects, in particular effects related to strong interactions of functional groups in such side chains, such as sulfonic acid groups. Once the first glass transition temperature is reached, the membrane undergoes irreversible changes and is in particular no longer usable in electrolysis processes. Therefore, in the context of the present disclosure, if a material (in particular a membrane or a membrane sample) exhibits multiple glass transition temperatures, only the lowest T g Compared with the T g Define related.

[0017] Any use according to the present disclosure may also be regarded as use of the corresponding method.

[0018] As used herein, electrolysis of hydrogen bromide (or electrolysis of HBr; or HBr electrolysis) refers to the electrolytic decomposition of HBr into hydrogen and bromine species (Br2 and / or Br3) by applying an external voltage to the electrodes of an electrolytic cell to which the HBr is fed, more specifically to the anode of such an electrolytic cell. - ).

[0019] The term "hydrocarbon" is used herein as generally understood in the art, and specifically encompasses unsubstituted or substituted, linear, branched or cyclic alkanes, alkenes or alkynes. A particularly preferred hydrocarbon is methane (CH4). As used herein, a hydrocarbon is not a carbon-free compound, and specifically is not hydrogen sulfide (H2S).

[0020] As used herein, "bromination of hydrocarbons" means that at least one hydrocarbon (hydrocarbon compound), in particular at least methane, is brominated. However, it is also contemplated that a mixture of two or more different hydrocarbon compounds is brominated to produce HBr for electrolysis. In this case, it may also be referred to as "bromination of hydrocarbons".

[0021] The term “OPEX” means “operating expenditure” and is expressed in units of surface power density (W / m 2 ). This is the operating voltage of the cell (in mV) multiplied by the applied current density (in kA / m 2 Count)(U op x J op ) results.

[0022] As used herein, hydrogen bromide derived from the bromination of a hydrocarbon can be the direct reaction product of such bromination, or can be formed after such bromination. In other words, hydrogen bromide is derived from the bromination of a hydrocarbon, i.e., it is produced directly in the bromination of a hydrocarbon, or is produced afterward.

[0023] Figure 5A preferred route for producing hydrogen bromide during the bromination of hydrocarbons is shown.

[0024] Thus, preferably, in the use according to the present disclosure, hydrogen bromide is produced during the bromination of hydrocarbons and / or the catalytic conversion of alkyl bromides. Bromination of hydrocarbons generally occurs according to the following reaction: x H y +Br2→C x H y-1 Br + HBr. The catalytic conversion or hydrolysis generally proceeds according to the following reaction: nC x H y-1 Br→mC z H h +nHBr.

[0025] In the bromination of hydrocarbons, at least one hydrogen atom of the hydrocarbon is replaced by a bromine atom (bromination or bromination reaction). However, multiple brominations at different sites of the hydrocarbon may also occur (multiple replacements of the hydrogen atoms of the hydrocarbon by bromine atoms). The products of such multiple brominations may be referred to as hydrocarbon polybromides, and in particular alkyl polybromides. Preferred alkyl polybromides are CH2Br2, CHBr3, C2H4Br2, C2H3Br3 and C3H6Br2, in particular CH2Br2. Such hydrocarbon polybromides may then be pyrolyzed. As an example, for CH2Br2, pyrolysis generally occurs according to the following reaction: CH2Br2→C+2HBr. Therefore, as used herein, hydrogen bromide derived from the bromination of hydrocarbons includes hydrogen bromide derived from the decomposition of at least one hydrocarbon polybromide and / or at least one carbon bromide (which itself is derived from the bromination of hydrocarbons).

[0026] As indicated above, HBr is a typical by-product of the bromination of hydrocarbons.

[0027] When step i) consists only of providing a stream containing hydrogen bromide obtained from the conversion of a hydrocarbon feedstock involving a bromination step, said stream will contain trace amounts of hydrocarbons and / or polybromides, such as CH4, C2H6, C3H8, CH2Br2, CHBr3, C2H4Br2, C2H3Br3, and C3H6Br2. The presence of hydrocarbons and / or polybromides in the stream containing hydrogen bromide obtained from the conversion of a hydrocarbon feedstock involving a bromination step can be determined by gas chromatography.

[0028] For example, a stream containing hydrogen bromide obtained from conversion of a hydrocarbon feedstock involving a bromination step includes at least 1 wt-ppm of at least one selected from CH4, C2H6, C3H8, CH2Br2, CHBr3, C2H4Br2, C2H3Br3, C3H6Br, and any mixture thereof, based on the total weight of the stream.

[0029] For example, a stream containing hydrogen bromide obtained from the conversion of a hydrocarbon feedstock involving a bromination step includes, based on the total weight of the stream, 1 wt ppm to 1 wt %, for example, 5 wt ppm to 0.5 wt %; or 10 wt ppm to 0.1 wt % of at least one selected from CH4, C2H6, C3H8, CH2Br2, CHBr3, C2H4Br2, C2H3Br3, C3H6Br, and any mixture thereof.

[0030] When the hydrocarbon is methane, the stream containing hydrogen bromide obtained from the conversion of the methane feedstock involving the bromination step includes at least 1 wtppm based on the total weight of the stream, for example, from 1 wtppm to 1 wt% based on the total weight of the stream, of at least one selected from CH4, CHBr3, and any mixture thereof.

[0031] One way to look at the HBr produced in this way is that HBr is a valuable resource that has the potential to collect both bromine and hydrogen. In particular, it is meaningful to close the bromine loop and recycle HBr back to Br2. However, this is typically done by thermal oxidation, where HBr is simply burned to form Br2 and water (H2O). Such a reaction is highly exothermic and therefore requires careful control. In addition, the hydrogen contained in the HBr will not be collected, but will be lost. Advantageously, by contrast, the purposes according to the present disclosure can be easily controlled and can allow the collection of H2 and Br2 in addition. In other words, the HBr produced as a by-product in the bromination of hydrocarbons (i.e., it is derived from the bromination of hydrocarbons) can be advantageously increased in value according to the purposes of the present disclosure.

[0032] Additionally, use according to the present disclosure may allow HBr electrolysis at higher temperatures and / or at higher pressures due to the greater elasticity of the fluoropolymer membrane. Without wishing to be bound by theory, it is postulated that the elasticity to HBr and, after electrolysis, to H2 and Br2 at higher temperatures and higher pressures is caused by having a T of equal to or greater than 110°C. g ≥110°C). In addition, especially higher temperatures can reduce the electrical resistance of the fluoropolymer membrane, which can allow higher proton conductivity. Higher proton conductivity can allow higher current density at lower operating voltage. Higher current density can help keep CAPEX low, while lower operating voltage leads to lower operating expenditure (OPEX), making the use according to the present disclosure particularly economical. Such use according to the present disclosure can also produce hydrogen in an eco-friendly manner, thereby contributing to mitigating global warming. When using a fluoropolymer membrane having a T g ≥115℃ or T g These effects can be even more pronounced when using fluoropolymer membranes with T gThese effects are even more pronounced when the fluoropolymer membrane is subjected to temperatures of ≥125°C.

[0033] The use according to the present disclosure can be used for the electrolysis of HBr which is carried out in the aqueous phase or in the gas phase, preferably in the aqueous phase, more preferably in the aqueous phase at an operating temperature above 60° C., and even more preferably in the aqueous phase at an operating temperature above 70° C. The solubility of Br2 in water is quite limited, but the compound is Br3 - As long as at least 33% of Br is present in the form of HBr, there is only one phase and no inhomogeneities in the electrochemical cell (electrolyzer). This is a typical situation for fuel cells for energy storage, and for safety reasons it is highly preferred to use B2 as Br3. - Br2 is stored in liquid solution. However, if the goal is Br2 harvesting and production of hydrogen, high conversion levels per pass are highly desired. Conversion levels of more than 67% per pass of HBr without any phase separation and instability in electrolyzer performance are typically not possible in aqueous phase at low temperatures, especially below the boiling point of Br2 (58.8°C). Preferably, above 60°C, more preferably above 70°C, Br2 evaporates fast enough to prevent the formation of a second liquid phase at high conversion levels. For the preferred electrolysis performed in aqueous phase at above 60°C, more preferably above 70°C, a catalyst with significantly higher T is used. g Fluoropolymer membranes of T are preferred, especially from the perspective of sustainable electrolysis. g At least 30° C. and more preferably at least 40° C. above the operating temperature of the electrolysis may result in a particularly sustainable electrolysis.

[0034] Aqueous phase HBr electrolysis follows the reaction 2HBr+Br-→Br3-+H2, and has a threshold voltage of 1.10 V. Gas phase HBr electrolysis follows the reaction 2HBr→Br2+H2, and has a threshold voltage of 0.58 V. Considering equal losses during the electrolysis process, it can be seen that the production of hydrogen from HBr in both the aqueous and gas phases will be more energy efficient than the current state-of-the-art technology for producing green hydrogen by water electrolysis. In addition, although slightly inferior in terms of threshold voltage, HBr electrolysis in the aqueous phase can lead to safer production of hydrogen and bromine, because no dangerous gaseous HBr can escape the entire electrolysis process, and can lead to easier handling of the resulting bromine, because this is obtained in dissolved form.

[0035] Preferably, in the use according to the present disclosure, the fluoropolymer film has a glass transition temperature T in the range of 110 to 170° C., more preferably 120 to 170° C., and still more preferably 125 to 170° C. g. As discussed herein, HBr is a byproduct of the bromination of hydrocarbons. Such HBr is typically hot and will generally have to be cooled for its subsequent electrolysis. Conducting the electrolysis at elevated temperatures reduces the need for such cooling. Additionally, higher temperatures typically increase the proton conductivity of the fluoropolymer membrane, which may allow operation at higher current densities and / or lower voltages. Higher current densities help keep CAPEX low. In such context, it is preferred to conduct the electrolysis above 70°C. At such temperatures, liquid-liquid phase separation may be avoided. When the fluoropolymer membrane of the use of the present invention has a glass transition temperature T in the range of 110 to 170°C, more preferably in the range of 120 to 170°C, and still more preferably in the range of 125 to 170°C g When the operating temperature of the HBr electrolysis can be maintained at >70°C, more particularly at >90°C, especially at >100°C, which allows a good balance between the above advantages of higher operating temperatures on the one hand and lower operating temperatures on the other hand.

[0036] For the reasons stated above, it is also preferred that in the use according to the present disclosure, the HBr electrolysis is carried out at an operating temperature of >70° C., more preferably >90° C., and particularly preferably >110° C. Further preferably, in this context, T g At least 30° C. higher than the operating temperature of the electrolysis, more preferably at least 40° C. higher. By setting the temperature in this way, a sustainable process can be achieved.

[0037] Preferably, in the use according to the present disclosure, the fluoropolymer membrane, more particularly the fluoropolymer comprised by and preferably constituting the membrane, comprises -(CF2-CF2)- repeating units. Such -(CF2-CF2)- repeating units may increase the elasticity of the fluoropolymer membrane. The increased elasticity may allow HBr electrolysis at higher temperatures and at higher pressures, which may allow operation at higher current densities and / or at lower voltages, making the use of the present invention more economical.

[0038] Preferably, in the use according to the present disclosure, the fluoropolymer membrane, more particularly the fluoropolymer comprised by and preferably constituting said membrane, does not comprise a structural entity of the formula -O-CF2-CF(CF3)-O-. Such a structural entity is present in the fluoropolymers marketed under the trade name Commercial films sold, however, can result in films with lower rigidity, which are therefore more susceptible to degradation at higher temperatures and under higher pressures. Therefore, such films are disadvantageous in accordance with the present disclosure.

[0039] Preferably, in the use according to the present disclosure, the fluoropolymer membrane, more particularly the fluoropolymer comprised by and preferably constituting the membrane, comprises -CF3 chain ends. Such -CF3 chain ends may increase the elasticity of the fluoropolymer membrane. The increased elasticity may allow HBr electrolysis at higher temperatures and at higher pressures, which may allow operation at higher current densities and / or at lower voltages, making the use of the present invention more economical.

[0040] Preferably, in the use according to the present disclosure, the fluoropolymer membrane is a sulfonated fluoropolymer membrane. More specifically, the fluoropolymer comprised by and preferably constituting the membrane is a sulfonated fluoropolymer. As used herein, sulfonated means that the fluoropolymer of the fluoropolymer membrane carries -SO3H groups. Such -SO3H groups can increase the proton conductivity of the fluoropolymer membrane, which can allow operation at higher current densities and / or at lower voltages, making the use of the present invention more economical.

[0041] Preferably, in the use according to the present disclosure, the sulfonated fluoropolymer membrane, more particularly the fluoropolymer comprised by and preferably constituting said membrane, comprises -O(CF2) n -SO3H group, wherein n is an integer selected from 1, 2, 3, 4 and 5, preferably 2. Such -O(CF2) n The -SO3H group can help achieve an increased proton conductivity of the fluoropolymer membrane while increasing the elasticity of the fluoropolymer membrane. A favorable balance between these effects can be particularly achieved when n is selected from 1 to 5 and especially when n is 2. Without wishing to be bound by theory, it is assumed that -O-(CF2) n The relatively short chain length of the -SO3H group increases the glass transition temperature of the fluoropolymer membrane, making it more resilient at higher temperatures. Therefore, sulfonated fluoropolymer membranes are particularly advantageous from the perspective of HBr electrolysis at higher temperatures and / or at higher pressures, and thus at higher current densities and / or at lower voltages. Therefore, sulfonated fluoropolymer membranes can make the application of the present invention particularly economical.

[0042] Preferably, in the use according to the present disclosure, the sulfonated fluoropolymer membrane comprises a hydrolyzed copolymer of F2C=CF2 and CF2=CF-O(CF2)2-SO2F. Such a hydrolyzed copolymer may lead to an increased proton conductivity and / or increased elasticity of the fluoropolymer membrane. Therefore, the sulfonated fluoropolymer membrane is particularly advantageous from the point of view of HBr electrolysis at higher temperatures and / or at higher pressures, and thereby at higher current densities and / or at lower voltages. Therefore, the sulfonated fluoropolymer membrane may make the application of the present invention particularly economical.

[0043] Preferably, in the use according to the present disclosure, the fluoropolymer membrane has an acid capacity of ≥0.9meq / g, more preferably between 0.95 and 1.5meq / g, and particularly preferably between 1.0 and 1.2meq / g. As used herein, meq / g refers to milliequivalents per gram, where the equivalent is mol-H (i.e., the mole number of H-acidic sites), preferably mol-SO3H (i.e., the mole number of SO3H-groups). The acid capacity represents the total amount of active sites or functional groups responsible for the proton exchange of the fluoropolymer membrane. Such an acid capacity can increase proton conductivity, and thus can lead to increased HBr conversion in HBr electrolysis. The increased HBr conversion rate can reduce any need for separation and possible recycling of unconverted HBr, which can help maintain a low CAPEX for the use according to the present disclosure.

[0044] Preferably, in the use according to the present disclosure, the fluoropolymer film (in dry state) has a viscosity of ≥ 1.70 g / cm 3 , more preferably ≥1.80g / cm 3 , still more preferably ≥1.80 to ≤2.00 g / cm 3 , and particularly preferably ≥1.90 to ≤1.95 g / cm 3 The density of the fluoropolymer membrane can be determined in particular according to ASTM D792-20 for samples thereof. Such a density can increase the elasticity of the fluoropolymer membrane. The increased elasticity can allow HBr electrolysis at higher temperatures and higher pressures, which can allow operation at higher current densities and / or at lower voltages, making the use of the present invention more economical.

[0045] Preferably, in the use according to the present disclosure, the fluoropolymer membrane (in the dry state) has a thickness of 25 to 350 μm, more preferably 40 to 150 μm, still more preferably 45 to 130 μm, and particularly preferably 45 to 55 μm. Such a thickness allows a balance between sufficient elasticity on the one hand and CAPEX on the other hand. At lower thicknesses, there is a risk of undesired crossover of hydrogen / bromine through the fluoropolymer membrane. At higher thicknesses, an undesired reduction in proton conductivity may result.

[0046] Preferably, in the use according to the present disclosure, the fluoropolymer film (in the dry state) has a tensile modulus of 100 to 500 MPa, more preferably 150 to 400 MPa, still more preferably 200 to 300 MPa, and particularly preferably 260 to 280 MPa. The tensile modulus of the fluoropolymer film can be determined in particular on a sample thereof according to ASTM D638-14. Such a tensile modulus can increase the elasticity of the fluoropolymer film. Increased elasticity can allow HBr electrolysis at higher temperatures and at higher pressures, which can allow operation at higher current densities and / or at lower voltages, making the use of the present invention more economical.

[0047] Preferably, in the use according to the present disclosure, the fluoropolymer film (in the dry state) has a tensile stress at break according to ASTM D882-18 in the machine direction (MD) of 10 to 70 MPa, more preferably 20 to 60 MPa, still more preferably 30 to 50 MPa, and particularly preferably 35 to 45 MPa. Such a tensile stress at break in MD can increase the elasticity of the fluoropolymer film. The increased elasticity can allow HBr electrolysis at higher temperatures and at higher pressures, which can allow operation at higher current densities and / or at lower voltages, making the use of the present invention more economical.

[0048] Preferably, in the use according to the present disclosure, the fluoropolymer film (in the dry state) has a tensile stress at break according to ASTM D882-18 in the cross direction (CD) of 5 to 60 MPa, more preferably 10 to 50 MPa, still more preferably 20 to 40 MPa, and particularly preferably 25 to 35 MPa. Such a tensile stress at break in CD may increase the elasticity of the fluoropolymer film. Increased elasticity may allow HBr electrolysis at higher temperatures and at higher pressures, which may allow operation at higher current densities and / or at lower voltages, making the use of the present invention more economical.

[0049] Preferably, in the use according to the present disclosure, the elongation at break according to ASTM D882-18 in the machine direction (MD) of the fluoropolymer film (in the dry state) is 100 to 200%, more preferably 120 to 180%, still more preferably 140 to 160%, and particularly preferably 145 to 155%. Such an elongation at break in MD can increase the elasticity of the fluoropolymer film. The increased elasticity can allow HBr electrolysis at higher temperatures and at higher pressures, which can allow operation at higher current densities and / or at lower voltages, making the use of the present invention more economical.

[0050] Preferably, in the use according to the present disclosure, the elongation at break of the fluoropolymer film (in the dry state) in the cross direction (CD) according to ASTM D882-18 is 100 to 350%, more preferably 120 to 300%, still more preferably 150 to 250%, and particularly preferably 190 to 210%. Such an elongation at break in CD can increase the elasticity of the fluoropolymer film. The increased elasticity can allow HBr electrolysis at higher temperatures and at higher pressures, which can allow operation at higher current densities and / or at lower voltages, making the use of the present invention more economical.

[0051] Preferably, in the use according to the present disclosure, the liquid phase is electrolyzed in the electrolysis. In such a case, the liquid stream is fed to both the anode and cathode of the electrolysis cell, wherein the liquid phase is electrolyzed. Electrolyzing the liquid phase can lead to a safer production of hydrogen and bromine, since no dangerous gaseous HBr can escape the electrolysis. In addition, electrolyzing the liquid phase can lead to easier handling of the resulting bromine, since this is obtained as dissolved bromine.

[0052] Preferably, in the use according to the present disclosure, an aqueous composition comprising hydrogen bromide is used as a feed to the cathode of an electrolytic cell in which electrolysis of hydrogen bromide occurs. Preferably, the hydrogen bromide is derived from the bromination of hydrocarbons, and hydrogen bromide derived from the bromination of hydrocarbons in addition is fed to the anode of the electrolytic cell. Preferably, the aqueous composition (or feed) comprises ≥0.5 mol / kg hydrogen bromide, more preferably ≥1 mol / kg hydrogen bromide, still more preferably ≥2 mol / kg hydrogen bromide, even more preferably ≥3 mol / kg hydrogen bromide, further preferably ≥4 mol / kg hydrogen bromide, even further preferably ≥5 mol / kg hydrogen bromide, and most preferably ≥6 mol / kg hydrogen bromide, wherein mol / kg refers to the number of moles of hydrogen bromide per kilogram of aqueous composition. Feeding an aqueous composition comprising hydrogen bromide, particularly a highly concentrated aqueous hydrogen bromide composition, to the cathode can reduce the operating voltage of the electrolytic cell, which can result in reduced OPEX.

[0053] In addition, in HBr electrolysis, HBr is first fed to the anode of the electrolyzer to achieve the desired electrolysis, wherein bromine is produced at the anode and protons are transferred to the cathode. Preferably, the hydrogen bromide fed to the anode is derived from the bromination of hydrocarbons, and in addition, the hydrogen bromide derived from the bromination of hydrocarbons is fed to the cathode of the electrolyzer. Most preferably, the hydrogen bromide fed to the anode and the hydrogen bromide fed to the cathode are both derived from the bromination of hydrocarbons. In either case, when HBr is also fed to the cathode of the electrolyzer, HBr is present on both sides of the electrolyzer, which can suppress unfavorable boiling. Additionally, feeding the above-mentioned highly concentrated aqueous hydrogen bromide composition to the cathode can also alleviate the interaction with bromine species (such as hydrogen bromide and / or Br and / or Br - Any problems related to the crossing of ions (Br(-I) ions) from the anode to the cathode.

[0054] Preferably, in the use according to the present disclosure, the electrolysis occurs at a temperature of 70° C. or higher (operating temperature) and / or at a pressure of greater than 0.1 MPa (operating pressure). More preferably, the electrolysis occurs at a temperature of 80° C. or higher and / or at a pressure of greater than 0.15 MPa, and still more preferably, the electrolysis occurs at a temperature of 90° C. or higher and / or at a pressure of greater than 0.2 MPa. Such electrolysis conditions may allow operation at higher current densities and / or at lower voltages, making the use of the present invention more economical.

[0055] When the electrolysis occurs in the liquid state, i.e., when the liquid phase is electrolyzed in the electrolysis, the azeotropic mixture of HBr / H2O is generally fed to the anode of the electrolysis cell in which the electrolysis occurs (the electrolysis is carried out). In such a case, it is preferred that the electrolysis occurs at a higher temperature, but below the boiling point of the HBr / H2O azeotropic mixture fed, more preferably at a temperature in the range of 70 to ≤122°C (the azeotropic HBr / H2O mixture of 48% HBr has a boiling point of about 122°C), which allows the use of higher temperatures with the advantages described herein while maintaining atmospheric pressure, so that the cost of increasing the pressure is avoided, which makes the use of the present invention more economical overall.

[0056] Preferably, in the purposes according to the present disclosure, pressure increases from the anode to the cathode of the electrolyzer where the electrolysis of hydrogen bromide occurs. Therefore, there is a pressure gradient increased from the anode to the cathode, wherein the corresponding pressure at the anode and cathode has the same reference point, that is, both are absolute pressures, or both are gauge pressures relative to the atmosphere around the electrolyzer. In such a case, electrolysis generally occurs in the gas phase, that is, gaseous streams are fed to the anode and cathode. In such a case, the pressure at the cathode is higher than the pressure at the anode, preferably high ≥ 0.01MPa (that is, the difference between the pressure at the cathode and the pressure at the anode is 0.01MPa or greater), more preferably high ≥ 0.02MPa, more preferably high ≥ 0.05MPa and most preferably high ≥ 0.1MPa. As a preferred example, when the absolute pressure at the anode is 0.1MPa, the absolute pressure at the cathode is 0.11 to 0.3MPa, more preferably 0.12 to 0.25MPa, still more preferably 0.15 to 0.2MPa, and most preferably 0.2MPa. However, an optional pressure at the cathode is also considered, which is 1MPa, 2MPa, 3MPa, 4MPa or even 5MPa higher than the pressure at the anode. By such an increased pressure or pressure gradient, a reduced operating voltage of the electrolytic cell can be achieved, which can lead to reduced OPEX. Additionally, the pressure gradient can allow H2 to be obtained at a higher pressure on the cathode side, so that there is no need or less compression to densify the obtained H2. Additionally, operating under a pressure difference (pressure increases from anode to cathode) can improve operating parameters.

[0057] For the case when the anode feed is gaseous HBr (with or without a pressure gradient), the aqueous composition (or feed) preferably sent to the cathode comprises ≤6 mol / kg hydrogen bromide, more preferably ≤5 mol / kg hydrogen bromide, particularly preferably ≤4 mol / kg hydrogen bromide, more particularly preferably ≤3 mol / kg hydrogen bromide, and most preferably ≤2 mol / kg hydrogen bromide. When the anode feed is gaseous, an increased HBr concentration on the cathode side may also produce a beneficial effect on the operating voltage. However, care must be taken because of the risk of membrane damage at higher concentrations and at the increased temperature required for the gas phase at the same time. In particular, at higher temperatures, thinner membranes may break easily. By the listed reduced HBr concentrations, a balance between the effects and risks mentioned can be achieved.

[0058] Preferably, in the use according to the present disclosure, the hydrocarbon is an alkane, preferably methane. In industry, there are various processes involving the bromination of alkanes, in particular methane. When the hydrocarbon is an alkane and in particular methane (CH4), the scope of use according to the present disclosure can be expanded, making the use particularly versatile.

[0059] Preferably, in the use according to the present disclosure, the electrolysis occurs in the absence of hydrogen fluoride, hydrogen chloride and / or hydrogen iodide. In the absence of hydrogen fluoride, hydrogen chloride and / or hydrogen iodide, the purity of the H2 and / or Br2 produced can be improved. In addition, fluctuations in the operating voltage can be avoided, which can reduce any need for adjusting the HBr electrolysis.

[0060] The subject of the present disclosure is also hydrogen obtained by the use of the present invention as described herein. In a similar manner, the preferred embodiments of the use described herein (including the claims) are also preferred for the hydrogen of the present invention. By such use of the present invention, pure hydrogen can be advantageously obtained by HBr electrolysis. By such use of the present invention, hydrogen that can be used for example for fuel synthesis can be obtained by HBr electrolysis, which can thus contribute to mitigating global warming.

[0061] The subject matter of the present disclosure also lies in the bromine obtained by the use of the invention described herein. In a similar manner, the preferred embodiments of the use described herein (including the claims) are also preferred for the bromine of the invention. By such use of the invention, pure bromine can advantageously be obtained by HBr electrolysis. By such use of the invention, bromine that can be used in subsequent chemical synthesis can be obtained by HBr electrolysis, which can thus contribute to closing the bromine loop.

[0062] The subject of the present disclosure is also to provide a method for preparing a crystalline solid having a glass transition temperature T g A method for producing hydrogen and / or bromine by electrolyzing hydrogen bromide with a fluorinated polymer membrane at ≥110°C, wherein the hydrogen bromide is derived from the bromination of hydrocarbons. In other words, the hydrogen bromide is pre-produced in the bromination of hydrocarbons, i.e., the method comprises a step of brominating hydrocarbons to produce hydrogen bromide, which step occurs before the electrolysis of hydrogen bromide. In a similar manner, the preferred embodiments of the use described herein (including the claims) are also preferred for the method of the present invention.

[0063] Preferably, according to the first aspect, the method for producing hydrogen and / or bromine by electrolysis of hydrogen bromide comprises the following steps:

[0064] i) brominating a hydrocarbon so as to produce hydrogen bromide,

[0065] ii) providing an electrolytic cell comprising an anode, a cathode and a glass transition temperature T of equal to or greater than 110° C., determined according to DIN EN ISO 11357-2:2020-08 g a fluoropolymer membrane sandwiched between an anode and a cathode,

[0066] iii) feeding a first composition comprising hydrogen bromide and water to the anode,

[0067] iv) feeding a second composition comprising hydrogen bromide and water to the cathode, and

[0068] v) operating the electrolytic cell to produce hydrogen at the cathode and / or bromine at the anode,

[0069] The hydrogen bromide fed in step iii) and / or the hydrogen bromide fed in step iv) is the hydrogen bromide produced in step i).

[0070] More particularly, the present disclosure relates to a method for producing hydrogen and / or bromine by electrolysis of hydrogen bromide comprising the steps of:

[0071] i) brominating a hydrocarbon so as to produce hydrogen bromide,

[0072] ii) providing an electrolytic cell comprising an anode, a cathode and a glass transition temperature T of equal to or greater than 110° C., determined according to DIN EN ISO 11357-2:2020-08 g a fluoropolymer membrane sandwiched between the anode and the cathode,

[0073] iii) feeding a first composition comprising hydrogen bromide and water to the anode,

[0074] iv) feeding a second composition comprising hydrogen bromide and water to the cathode, and

[0075] v) at operating voltages up to 1900mV (U op ) and at least 3kA / m 2 The operating current density (J op ) to produce hydrogen at the cathode and / or bromine at the anode,

[0076] The hydrogen bromide produced in step i) is used to prepare the first composition fed in step iii), or both the first composition and the second composition fed in steps iii) and iv).

[0077] In a second aspect, a method for producing hydrogen and / or bromine by electrolysis of hydrogen bromide comprises the following steps:

[0078] i) providing a stream containing hydrogen bromide obtained from the conversion of a hydrocarbon feedstock involving a bromination step,

[0079] ii) providing an electrolytic cell comprising an anode, a cathode and a glass transition temperature T of equal to or greater than 110° C., determined according to DIN EN ISO 11357-2:2020-08 g a fluoropolymer membrane sandwiched between an anode and a cathode,

[0080] iii) feeding a first composition comprising hydrogen bromide and water to the anode,

[0081] iv) feeding a second composition comprising hydrogen bromide and water to the cathode, and

[0082] v) operating the electrolytic cell to produce hydrogen at the cathode and / or bromine at the anode,

[0083] The hydrogen bromide-containing stream provided in step i) is used to prepare the first composition fed in step iii) and / or the second composition fed in step iv).

[0084] More particularly, the process for producing hydrogen and / or bromine by electrolysis of hydrogen bromide comprises the following steps:

[0085] i) providing a stream containing hydrogen bromide obtained from the conversion of a hydrocarbon feedstock involving a bromination step,

[0086] ii) providing an electrolytic cell comprising an anode, a cathode and a glass transition temperature T of equal to or greater than 110° C., determined according to DIN EN ISO 11357-2:2020-08 g a fluoropolymer membrane sandwiched between the anode and the cathode,

[0087] iii) feeding a first composition comprising hydrogen bromide and water to the anode,

[0088] iv) feeding a second composition comprising hydrogen bromide and water to the cathode, and

[0089] v) at operating voltages up to 1900mV (U op ) and at least 3kA / m 2 The operating current density (J op ) to produce hydrogen at the cathode and / or bromine at the anode,

[0090] The hydrogen bromide-containing stream provided in step i) is used to prepare the first composition fed in step iii) and / or the second composition fed in step iv).

[0091] Surprisingly, in both the first and second aspects, it was found that such a process for producing hydrogen and / or bromine by electrolysis of hydrogen bromide allows a significant reduction in energy consumption, thanks in particular to the use of specific fluoropolymer membranes and specific operating conditions. This is evidenced by an overall reduction in operating expenditures (OPEX).

[0092] For example, step v) of operating the electrolyte cell comprises an operating voltage (U ) of at most 1800 mV; preferably at most 1700 mV; more preferably at most 1600 mV, and even more preferably at most 1500 mV. op ).

[0093] For example, step v) of operating the electrolyte cell comprises an operating voltage (U ) of 400 to 1900 mV, preferably 500 to 1800 mV; more preferably 600 to 1700 mV; even more preferably 700 to 1600 mV, and most preferably 800 to 1500 mV. op ).

[0094] For example, step v) of operating the electrolyte bath comprises at least 4 kA / m 2 ; preferably at least 5kA / m 2 The operating current density (J op In an embodiment, step v) of operating the electrolyte cell comprises operating at least 6 kA / m 2 ; preferably at least 7kA / m 2 More preferably at least 8 kA / m 2 ; even more preferably at least 9 kA / m 2 ; and most preferably at least 10 kA / m 2 The operating current density (J op ).

[0095] For example, step v) of operating the electrolyte bath comprises operating at a current of at most 12 kA / m 2 ; preferably at most 11 kA / m 2 The operating current density (J op ).

[0096] For example, step v) of operating the electrolyte cell comprises operating the electrolyte cell at a range of 3 kA / m 2 Up to 15kA / m 2 ; 4kA / m is preferred 2 Up to 12kA / m 2 or 5kA / m 2 Up to 12kA / m 2 The operating current density (J op In an embodiment, step v) of operating the electrolyte cell comprises operating the electrolyte cell at a temperature in the range of 6 kA / m 2 Up to 12kA / m 2 The operating current density (J op ).

[0097] For example, the temperature of the first composition fed to the anode is at least 60°C or above, and the temperature of the second composition fed to the cathode is at least 60°C or above. Preferably, the temperature of the first composition fed to the anode is at least 65°C or above, and the temperature of the second composition fed to the cathode is at least 65°C or above. More preferably, the temperature of the first composition fed to the anode is at least 70°C or above, and the temperature of the second composition fed to the cathode is at least 70°C or above.

[0098] For example, the fluoropolymer film has a glass transition temperature T of equal to or greater than 112°C, preferably equal to or greater than 115°C, more preferably equal to or greater than 118°C, even more preferably equal to or greater than 120°C, most preferably equal to or greater than 122°C, and even most preferably equal to or greater than 125°C, as determined according to DIN EN ISO 11357-2:2020-08. g .

[0099] For example, the fluoropolymer film has a glass transition temperature T of equal to or lower than 170°C, preferably equal to or lower than 168°C, more preferably equal to or lower than 165°C, even more preferably equal to or lower than 162°C, and most preferably equal to or lower than 160°C, as determined according to DIN EN ISO 11357-2:2020-08. g .

[0100] For example, the fluoropolymer film has a glass transition temperature T in the range of 120 to 170° C., measured according to DIN EN ISO 11357-2:2020-08. g .

[0101] For example, the fluoropolymer film includes -(CF2-CF2)- repeating units.

[0102] For example, the fluoropolymer film does not include structural entities of the formula -O-CF2-CF(CF3)-O-.

[0103] For example, the fluorinated polymer membrane is a sulfonated fluorinated polymer membrane. For example, the sulfonated fluorinated polymer membrane includes -O-(CF2) n -SO3H group, wherein n is an integer selected from 1, 2, 3, 4 and 5, preferably 2. For example, the sulfonated fluoropolymer membrane includes a hydrolyzed copolymer of F2C=CF2 and CF2=CF-O(CF2)2-SO2F.

[0104] For example, the fluoropolymer membrane has an acid capacity equal to or greater than 0.9 meq / g; preferably, equal to or greater than 0.95 meq / g; more preferably, equal to or greater than 1.0 meq / g.

[0105] For example, the fluoropolymer membrane has an acid capacity ranging from 0.9 to 1.5 meq / g; preferably 0.95 to 1.5 meq / g; more preferably 1.0 to 1.4 meq / g; even more preferably 1.0 to 1.3 meq / g; and most preferably 1.0 to 1.2 meq / g. As used herein, meq / g refers to milliequivalents per gram, where equivalents are mol-H (i.e., moles of H-acidic sites), preferably mol-SO3H (i.e., moles of SO3H- groups).

[0106] For example, the electrolysis occurs at a temperature of 70°C or higher; preferably at a temperature of 75°C or higher, more preferably at a temperature of 80°C or higher; even more preferably at a temperature of 85°C or higher; and most preferably at a temperature of 90°C or higher.

[0107] For example, the electrolysis occurs at a temperature below 122°C; preferably at a temperature of 120°C or lower, more preferably at a temperature of 115°C or lower; even more preferably at a temperature of 110°C or lower; most preferably at a temperature of 105°C or lower; even most preferably at a temperature of 100°C or lower, or at a temperature of 95°C or lower.

[0108] For example, the electrolysis occurs at a temperature in the range of 70 to 122°C; preferably, 70°C to 120°C or lower; more preferably, 75°C to 115°C; even more preferably, 80°C to 110°C; most preferably, 85°C to 105°C; even most preferably, 90°C to 100°C; or 80°C to 95°C; or 75 to 95°C.

[0109] For example, the electrolysis occurs at a pressure greater than 0.1 MPa; preferably greater than 0.15 MPa; more preferably greater than 0.2 MPa.

[0110] For example, pressure increases from the anode to the cathode of an electrolytic cell in which electrolysis of hydrogen bromide occurs.

[0111] For example, the hydrocarbon is an alkane, preferably selected from methane, ethane, propane and butane, more preferably methane.

[0112] For example, the electrolysis is performed in the absence of hydrogen fluoride, hydrogen chloride and / or hydrogen iodide.

[0113] For example, the second composition comprises hydrogen bromide at a concentration of at least 0.5 mol / kg; preferably, at least 1 mol / kg; more preferably, at least 2 mol / kg; even more preferably, at least 3 mol / kg; most preferably, at least 4 mol / kg; even most preferably, at least 5 mol / kg or at least 6 mol / kg.

[0114] For example, the second composition comprises hydrogen bromide in a concentration of at most 12 mol / kg; preferably, at most 10 mol / kg; more preferably, at most 9 mol / kg; even more preferably, at most 8 mol / kg; and most preferably, at most 7 mol / kg.

[0115] For example, the second composition comprises hydrogen bromide in a concentration range of 0.5 to 12 mol / kg; preferably 0.5 to 10 mol / kg; more preferably 1 to 10 mol / kg; even more preferably 2 to 9 mol / kg; most preferably 3 to 9 mol / kg; even most preferably 4 to 9 mol / kg; or 5 to 8 mol / kg; or 3 to 7 mol / kg.

[0116] For example, the fluoropolymer membrane is selected to have a glass transition temperature that is at least 30°C higher; preferably greater than 35°C higher; and more preferably greater than 40°C higher than the operating temperature of the electrolysis.

[0117] Preferably, the hydrogen bromide produced in step i) is fed partly to the anode in step iii) and partly to the cathode in step iv).

[0118] In the method according to the present disclosure, the electrolytic cell comprises two electrodes, an anode and a cathode, between which an electric field can be applied. For this purpose, the anode and the cathode generally comprise a conductive material, in particular a metal, a coated metal, a carbon cloth, a graphite felt, a carbon fiber composite, a carbon-loaded polymer or graphite, and are preferably made of a carbon fiber composite or a coated metal. HBr forms a very corrosive environment, but the conductive materials mentioned can generally withstand such a corrosive environment and are therefore preferred.

[0119] In the method according to the present disclosure, the membrane sandwiched between the anode and the cathode is a membrane having two opposing surfaces, wherein the anode is disposed on one of the two opposing surfaces, and the cathode is disposed on the other of the two opposing surfaces.

[0120] In the method according to the present disclosure, the composition comprising hydrogen bromide and water is an aqueous composition in which HBr is dissolved in water. This is true for both the first composition and the second composition. HBr dissolved in water will generally dissociate in water, so that the (first, second) composition will generally include ionic species, especially HBr. + 、H3O+ and Br – The first and / or second composition may both be in liquid state, or both may be in gaseous state. Alternatively, the first composition may be in liquid state, while the second composition may be in gaseous state. Alternatively, the second composition may be in liquid state, while the first composition may be in gaseous state.

[0121] According to step v) of the preferred method according to the present disclosure, the electrolytic cell is operated to produce hydrogen at the cathode. Logically, this requires the application of an electric field to the anode and cathode. Alternatively, it can be said that an operating voltage must be applied to the electrolytic cell. It can therefore be said that the method according to the present disclosure, which may alternatively be referred to as electrolysis of hydrogen bromide or HBr electrolysis, refers to the electrolytic decomposition of HBr into hydrogen and bromine species by applying an electric field or operating voltage to the anode and cathode.

[0122] For the electrolysis of HBr, it is necessary to feed HBr to the anode of the electrolytic cell, where protons are produced. The protons then migrate to the cathode, in this case, through the sandwiched membrane to the cathode. For the method according to the present disclosure, it is surprisingly advantageous to also feed HBr to the cathode, i.e., a composition having a concentration of ≥1 mol / kg of hydrogen bromide. By feeding such HBr to the cathode, the electrolytic cell can be operated at a lower operating voltage. The lower operating voltage reduces the OPEX of the method, and thus makes HBr electrolysis more economical. In addition, by feeding such HBr to the cathode, the electrolytic cell can be operated at a higher temperature, which reduces cooling and / or heating requirements. The reduced cooling / heating requirements also reduce the OPEX of the method, and thus make HBr electrolysis more economical. Additionally, by feeding such HBr to the cathode, the electrolytic cell can be operated at a higher current density. The higher current density reduces the CAPEX of the method, and thus makes HBr electrolysis more economical. In addition, the method according to the present disclosure can also produce hydrogen in an eco-friendly manner, thereby helping to alleviate global warming.

[0123] In addition, feeding HBr on the cathode side can reduce the concentration gradient across the membrane and can reduce or even alleviate the concentration of HBr and / or Br2 and / or Br - The present invention relates to the method for the present invention. ...

[0124] Preferably, in the method according to the present disclosure, the hydrogen bromide concentration of the second composition fed to the cathode is ≥0.5 mol / kg, more preferably ≥1 mol / kg, still more preferably ≥2 mol / kg, even more preferably ≥3 mol / kg, further preferably ≥4 mol / kg, even further preferably ≥5 mol / kg, and most preferably ≥6 mol / kg, wherein mol / kg refers to the number of moles of hydrogen bromide per kilogram of the second composition. All the above effects of the second composition comprising hydrogen bromide and water fed to the cathode can be more and more significant as the hydrogen bromide concentration of the second composition becomes higher and higher, i.e., as the hydrogen bromide concentration of the second composition increases from a preferred concentration of ≥0.5 mol / kg to a most preferred concentration of up to ≥6 mol / kg.

[0125] Herein, the hydrogen bromide concentration is usually given in mol / kg, i.e., the number of moles of HBr per kg of the composition (or solution). HBr has a molecular weight of 80.91 g / mol. Thus, the hydrogen bromide concentration (c HBr) of the second composition, for example, ≥ 1 mol / kg HBr ) can alternatively be expressed as ≥ 80.91 g / kg, i.e. ≥ 80.91 g of HBr per kg of composition. The same conversion can be performed for any concentration mentioned herein.

[0126] Preferably, in the method according to the present disclosure, in step v) at an operating voltage U op ≤1900mV, preferably at operating voltage U op ≤1700mV (but above 0mV, that is, U op >0 mV). Operating the electrolysis cell at such an operating voltage can improve the selectivity of the reaction to HBr electrolysis and thereby reduce the OPEX of the process and thus can make HBr electrolysis more economical.

[0127] Preferably, in the method according to the present disclosure, in step v) at an operating temperature T op Operate the electrolytic cell at ≥70℃, where T op Below the boiling point of the second composition, preferably at an operating temperature of 70°C ≤ T op ≤122°C. Operating the electrolytic cell at such an operating temperature can reduce cooling and / or heating requirements. In particular, HBr is a byproduct of the bromination of hydrocarbons. Such HBr is typically hot and usually must be cooled for its subsequent electrolysis. At operating temperature T op Conducting the electrolysis at ≥70°C reduces the need for such cooling.

[0128] Additionally, higher temperatures typically increase the proton conductivity of the membrane comprising the fluoropolymer, which may allow operation at higher current density and / or at lower voltage. Higher current density helps keep CAPEX low. In this context, the electrolysis is preferably carried out at 70°C or above (≥70°C). At such temperatures, liquid-liquid phase separation may be avoided. Therefore, it is particularly preferred to set the operating temperature T op Maintained at >70°C, more specifically at >90°C, especially at >100°C.

[0129] Additionally, T op An operating temperature of ≥70°C but below the boiling point of the second composition can reduce the resistance of the membrane, which can allow higher proton conductivity. Higher proton conductivity can allow higher current density at lower operating voltage. Higher current density can help keep CAPEX low, while lower operating voltage can lead to lower OPEX, making the method of electrolyzing hydrogen bromide according to the present disclosure particularly economical. At the same time, boiling of the second composition can be prevented so that no gaseous HBr is formed, especially no gaseous HBr that can escape to the environment. This can help operate the method according to the present disclosure in a safe manner. When the operating temperature is 70°C≤T op All these operating temperature-related effects can be even more pronounced at ≤122°C.

[0130] Preferably, in the method according to the present disclosure, both the first composition and the second composition are liquid compositions. Such a method may also be referred to as electrolysis in an aqueous phase. In the case where both the first composition and the second composition are liquid compositions, the formation of gaseous HBr may be suppressed so that no such dangerous gaseous HBr may escape to the environment. This may help to operate the method for electrolyzing hydrogen bromide in a particularly safe manner.

[0131] Preferably, in the method according to the present disclosure, both the first composition and the second composition are liquid compositions having an operating temperature above 60°C, still more preferably above 70°C. That is, preferably, the temperature of the first composition fed to the anode is >60°C, and the temperature of the second composition fed to the cathode is >60°C, and more preferably, the temperature of the first composition fed to the anode is >70°C, and the temperature of the second composition fed to the cathode is >70°C. As mentioned above, the solubility of Br2 in water is quite limited, but Br2 is in the form of Br3 -of form perfectly dissolved in HBr, and as long as ≥33% of Br is present in the form of HBr, only one phase and no inhomogeneities are observed in the electrolytic cell. One of the purposes of the present disclosure is Br2 recovery, and a further purpose is H2 production, for which high conversion levels per pass are required. Conversion levels of more than 67% HBr per pass are typically not achievable in the aqueous phase at low temperatures without any phase separation and without adversely affecting the performance of the electrolytic cell, especially when not below the boiling point of Br2 (58.8°C). As previously mentioned, preferably above 60°C, more preferably above 70°C, Br2 evaporates quickly enough to prevent the formation of a second liquid phase at high conversion levels.

[0132] For the preferred electrolysis in aqueous phase, especially when both the first composition and the second composition are fed as liquid compositions at above 60°C, more preferably above 70°C, having a significantly higher T g Fluoropolymer membranes with a T of 0.0040 are preferred, especially from the perspective of sustainable electrolysis. Therefore, for such a case, a fluoropolymer membrane with a T of 0.0040 is preferred. g At least 30° C. and more preferably at least 40° C. higher than the operating temperature of the electrolysis (ie the temperature of the first and / or second composition, preferably the temperature of the first and the second composition). Such a temperature setting may lead to a particularly sustainable HBr electrolysis.

[0133] Preferably, the electrolysis cell is at least partially operated at an operating pressure p op >0.1 MPa operation. By such increased operating pressure, a reduced operating voltage of the electrolytic cell can be achieved, which can lead to reduced OPEX. Additionally, the increased operating pressure can allow H2 to be obtained at a higher pressure on the cathode side, so that no or less compression is subsequently required to densify the obtained H2.

[0134] Preferably, in the method according to the present disclosure, the electrolytic cell is operated at a current density J in step v). op ≥3kA / m 2 , preferably at an operating current density J op ≥4kA / m 2 More preferably, at an operating current density J op ≥5kA / m 2 By increasing the current density in this way, the CAPEX of the process for electrolyzing hydrogen bromide can be reduced, thereby making the process more economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0135] Figure 1 The general outline of an electrolytic cell suitable for use according to the present disclosure is shown.

[0136] Figure 2 The temperature dependence of the voltage for HBr electrolysis is shown.

[0137] Figure 3 Results of HBr electrolysis using different membranes are shown.

[0138] Figure 4 Results of additional HBr electrolysis using different membrane types are shown.

[0139] Figure 5 is a flow diagram of different routes for producing hydrogen bromide during the bromination of hydrocarbons.

[0140] Experimental Section

[0141] Figure 1 A general overview of an exemplary electrolytic cell and an exemplary electrolysis procedure, respectively, that may be employed in use according to the present disclosure. Figure 1 The proton exchange membrane depicted in FIG. 1 has a glass transition temperature T g Fully hydrated fluoropolymer membranes at ≥110°C, such as fully hydrated E98-05S membrane or fully hydrated E87-05S membrane. The membrane is sandwiched between two catalytic layers. The catalytic layers themselves are sandwiched between two gas diffusion layers. On the left, the anode is arranged on the first gas diffusion layer, i.e. on the surface opposite to the surface on which the first catalytic layer is arranged. On the right, the cathode is arranged on the second gas diffusion layer, i.e. on the surface opposite to the surface on which the second catalytic layer is arranged. A first mixture comprising HBr and H2O is fed to the anode, while a second mixture also comprising HBr and H2O is fed to the cathode. The HBr fed to the anode and the HBr fed to the cathode originate from the bromination of methane, following the reaction CH4+Br2→CH3Br+HBr. An electric field is applied to the electrolytic cell so that the electrons (e - ) is transferred from the anode to the cathode. At the anode, HBr migrates through the anode gas diffusion layer to the anode catalyst layer, where it is electro-oxidized, so that Br2 is formed and protons are left behind. Protons migrate from the anode catalyst layer through the membrane to the cathode catalyst layer. At the cathode catalyst layer, protons recombine with electrons to form H2. The formed H2 migrates through the cathode gas diffusion layer. As electrolysis products, a stream including Br2 and H2O is extracted from the anode, and a stream including H2, H2O and HBr is extracted from the cathode. The stream extracted from the anode may additionally include unconverted HBr.

[0142] Figure 2 Shows the use at different temperatures Results of practical electrolysis of HBr with E98-05S membrane. Despite the use of highly concentrated HBr feed with a HBr concentration of 6 mol / kg as anode feed, successful electrolysis was performed at elevated temperatures from 75°C up to 95°C without any indication of membrane degradation. The operating voltage was reduced from 1301 mV at a temperature of 75°C to 1230 mV at a temperature of 95°C, maintaining 3 kA / m 2 Therefore, at 3kA / m 2 At a constant high current density, increasing to a higher temperature results in an advantageous reduction in the required input voltage, which in turn results in an advantageous reduction in OPEX.

[0143] Figure 3 The results of practical electrolysis of HBr using two different membranes and current densities are shown, namely at 10 kA / m 2 At a current density of E98-05S membrane and at 5kA / m 2 At a current density of E98-05S membrane. In addition, the HBr concentration of the aqueous HBr solution fed to the cathode of the electrolytic cell was increased from 0 mol / kg (deionized water) to 2 mol / kg, and another 4 mol / kg up to 6 mol / kg. It can be seen that at an elevated temperature of 95°C and at 5 kA / m 2 And even 10kA / m 2 Successful electrolysis was performed at high current densities without any signs of membrane degradation. Furthermore, feeding the cathode with a highly concentrated aqueous HBr solution did not impair membrane performance. On the contrary, except for With the exception of a small outlier at 2 mol / kg for the E98-05S membrane, increasing the HBr concentration surprisingly leads to a significant reduction in the operating voltage, which in turn leads to a beneficially reduced OPEX.

[0144] Figure 4 Results of actual electrolysis of HBr using different current densities and different membranes are shown. Comparing the results obtained with 2 NAFION membranes at 5kA / m2 and 95°C with an Aquivion membrane under the same conditions, it can be seen that the Aquivion operates at a lower voltage, resulting in lower OPEX.

Claims

1. A method for producing hydrogen and / or bromine by electrolysis of hydrogen bromide, comprising the following steps: i) brominating a hydrocarbon so as to produce hydrogen bromide, ii) providing an electrolytic cell comprising an anode, a cathode and a glass transition temperature T of equal to or greater than 110° C., determined according to DIN EN ISO 11357-2:2020-08 g a fluoropolymer membrane sandwiched between the anode and the cathode, iii) feeding a first composition comprising hydrogen bromide and water to the anode, iv) feeding a second composition comprising hydrogen bromide and water to the cathode, and v) at an operating voltage of up to 1900 mV and at least 3 kA / m 2 operating the electrolytic cell at an operating current density of 100 to produce hydrogen at the cathode and / or bromine at the anode, The hydrogen bromide produced in step i) is used to prepare the first composition fed in step iii), or both the first composition and the second composition fed in steps iii) and iv).

2. A method for producing hydrogen and / or bromine by electrolysis of hydrogen bromide, comprising the following steps: i) providing a stream containing hydrogen bromide obtained from the conversion of a hydrocarbon feedstock involving a bromination step, ii) providing an electrolytic cell comprising an anode, a cathode and a fluoropolymer membrane having a glass transition temperature Tg equal to or greater than 110° C., determined according to DIN EN ISO 11357-2:2020-08, the fluoropolymer membrane being sandwiched between the anode and the cathode, iii) feeding a first composition comprising hydrogen bromide and water to the anode, iv) feeding a second composition comprising hydrogen bromide and water to the cathode, and v) at an operating voltage (Uop) of up to 1900 mV and at least 3 kA / m 2 operating the electrolytic cell at an operating current density (Jop) of 100 Å to produce hydrogen at the cathode and / or bromine at the anode, The hydrogen bromide-containing stream provided in step i) is used to prepare the first composition fed in step iii) and / or the second composition fed in step iv).

3. The method according to claim 1 or 2, characterized in that: Step v) of operating the electrolyte cell comprises an operating voltage of at most 1500 mV; or from 800 to 1500 mV.

4. The method according to any one of claims 1 to 3, characterized in that Step v) of operating the electrolyte cell comprises at least 4 kA / m 2 , or 4kA / m 2 Up to 12kA / m 2 The operating current density.

5. The method according to any one of claims 1 to 4, characterized in that The temperature of the first composition fed to the anode is at least 60°C or higher, and simultaneously the temperature of the second composition fed to the cathode is at least 60°C or higher.

6. The method according to any one of claims 1 to 5, characterized in that The fluoropolymer film has a glass transition temperature T in the range of 120 to 170° C., determined according to DIN EN ISO 11357-2:2020-08. g .

7. The method according to any one of claims 1 to 6, characterized in that The fluoropolymer film includes -(CF2-CF2)- repeating units.

8. The method according to any one of claims 1 to 7, characterized in that The fluoropolymer film does not include structural entities of the formula -O-CF2-CF(CF3)-O-.

9. The method according to any one of claims 1 to 8, characterized in that The fluoropolymer membrane is a sulfonated fluoropolymer membrane.

10. The method according to claim 9, characterized in that The sulfonated fluoropolymer membrane comprises -O-(CF2) n -SO3H group, wherein n is an integer selected from 1, 2, 3, 4 and 5, preferably 2.

11. The method according to claim 10, characterized in that The sulfonated fluoropolymer membrane includes a hydrolyzed copolymer of F2C=CF2 and CF2=CF-O-(CF2)2-SO2F.

12. The method according to any one of claims 1 to 11, characterized in that The fluoropolymer membrane has an acid capacity equal to or greater than 0.9 meq / g.

13. The method according to any one of claims 1 to 12, characterized in that The electrolysis occurs at a temperature of 70°C or higher and / or the electrolysis occurs at a temperature of less than 100°C.

14. The method according to any one of claims 1 to 13, characterized in that The electrolysis takes place at a temperature ranging from 75 to 95°C.

15. The method according to any one of claims 1 to 14, characterized in that The electrolysis takes place at a pressure greater than 0.1 MPa.

16. The method according to any one of claims 1 to 15, characterized in that The pressure increases from the anode to the cathode of the electrolytic cell where the electrolysis of hydrogen bromide occurs.

17. The method according to any one of claims 1 to 16, characterized in that The hydrocarbon is an alkane, preferably methane.

18. The method according to any one of claims 1 to 17, characterized in that The electrolysis takes place in the absence of hydrogen fluoride, hydrogen chloride and / or hydrogen iodide.

19. The method according to any one of claims 1 to 18, characterized in that The second composition comprises a hydrogen bromide concentration of at least 0.5 mol / kg, preferably at least 3 mol / kg.

20. The method according to any one of claims 1 to 19, characterized in that The second composition comprises a hydrogen bromide concentration ranging from 0.5 to 10 mol / kg; preferably 3 to 7 mol / kg.

21. The method according to any one of claims 1 to 20, characterized in that The fluoropolymer membrane is selected to have a glass transition temperature that is at least 30°C higher than the operating temperature of the electrolysis; preferably more than 40°C higher.

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