Method for electrolyzing brominated hydrogen bromide

Abstract

A method of electrolyzing hydrogen bromide comprising the steps of: i) brominating a hydrocarbon such that hydrogen bromide is produced; ii) providing an electrolytic cell comprising an anode, a cathode, and a 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) operating the electrolytic cell to produce hydrogen at the cathode, wherein the hydrogen bromide fed in step iii) and / or the hydrogen bromide fed in step iv) is the hydrogen bromide produced in step i).

Description

Technical Field

[0001] The present disclosure relates to a method for electrolyzing brominated hydrogen bromide, the gas obtained by such a method, and corresponding uses. 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 relatively high energy to electrolyze water to produce H2. More specifically, following the reaction The electrolysis of water has a threshold voltage of 1.23 V. 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, the purpose of which is to store 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 usually not pure enough for the subsequent use of H2. In addition, in flow batteries, electrolysis is usually carried out in the liquid phase under mild conditions to avoid pressure increase and / or damage to the membrane, and is often operated at a limited conversion level 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 bromination of hydrogen sulfide. In addition, the concentrated HBr composition is only considered as a feed to the anode of the electrolytic cell, not to its cathode. In addition, the HBr electrolysis occurs in a biological waste treatment and collection (recovery) system, which requires additional bromine to be fed to the system, thereby increasing the operating cost of the system. Additionally, the system typically produces ash and greenhouse gas carbon dioxide (CO2). Ashes need to be removed, and CO2 needs to be captured or converted into urea to avoid its discharge into the environment, resulting in additional operating costs of the system.

[0006] In general, there remains a general desire for improved processes for the electrolysis of hydrogen bromide.

[0007] An object of the present disclosure is to provide a method for electrolyzing hydrogen bromide, which at least partially overcomes the shortcomings encountered in the art. Another object of the present disclosure is to provide a way to add value to HBr produced as a byproduct. Another object of the present disclosure is to provide a method for electrolyzing hydrogen bromide that makes HBr electrolysis more economical. In addition, an object of the present disclosure is to provide a method for electrolyzing hydrogen bromide in a safe manner. Another object of the present disclosure is to provide a method for electrolyzing hydrogen bromide, which helps alleviate global warming. In addition, an object of the present disclosure is to provide a method for electrolyzing hydrogen bromide, which helps to collect bromine. Another object of the present disclosure is to provide hydrogen, which at least partially overcomes the shortcomings encountered in the art. Another object of the present disclosure is to provide bromine, which at least partially overcomes the shortcomings encountered in the art. Another object of the present disclosure is to provide the use of an aqueous composition in the electrolysis of hydrogen bromide, 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 process, hydrogen, bromine and use according to the claims.Additional embodiments of the present disclosure are outlined throughout the specification.

[0009] According to a first aspect, the present disclosure provides a method for electrolyzing hydrogen bromide, comprising the following steps:

[0010] i) brominating a hydrocarbon to produce hydrogen bromide,

[0011] ii) providing an electrolytic cell comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode,

[0012] iii) feeding a first composition comprising hydrogen bromide and water to the anode,

[0013] iv) feeding a second composition comprising hydrogen bromide and water to the cathode, and

[0014] v) operating the electrolytic cell to produce hydrogen at the cathode,

[0015] The hydrogen bromide fed in step iii) and / or the hydrogen bromide fed in step iv) is the hydrogen bromide produced in step i).

[0016] More particularly, the present disclosure relates to a method for electrolyzing hydrogen bromide, comprising the steps of:

[0017] i) brominating a hydrocarbon to produce hydrogen bromide,

[0018] ii) providing an electrolytic cell comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode,

[0019] iii) feeding a first composition comprising hydrogen bromide and water to the anode,

[0020] iv) feeding a second composition comprising hydrogen bromide and water to the cathode, wherein the second composition has a hydrogen bromide concentration of at least 4 mol / kg, and

[0021] v) operating the electrolytic cell to produce hydrogen at the cathode,

[0022] 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).

[0023] According to a second aspect, the present disclosure provides a method for electrolyzing hydrogen bromide, comprising the following steps:

[0024] i) providing a stream containing hydrogen bromide obtained from the conversion of a hydrocarbon feedstock involving a bromination step,

[0025] ii) providing an electrolytic cell comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode,

[0026] iii) feeding a first composition comprising hydrogen bromide and water to the anode,

[0027] iv) feeding a second composition comprising hydrogen bromide and water to the cathode, and

[0028] v) operating the electrolytic cell to produce hydrogen at the cathode,

[0029] The hydrogen bromide fed in step iii) and / or the hydrogen bromide fed in step iv) is the hydrogen bromide provided in step i).

[0030] More particularly, the present disclosure relates to a method for electrolyzing hydrogen bromide, comprising the steps of:

[0031] i) providing a stream containing hydrogen bromide obtained from the conversion of a hydrocarbon feedstock involving a bromination step,

[0032] ii) providing an electrolytic cell comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode,

[0033] iii) feeding a first composition comprising hydrogen bromide and water to the anode,

[0034] iv) feeding a second composition comprising hydrogen bromide and water to the cathode, wherein the second composition has a hydrogen bromide concentration of at least 4 mol / kg, and

[0035] v) operating the electrolytic cell to produce hydrogen at the cathode,

[0036] wherein the hydrogen bromide-containing stream provided 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).

[0037] Surprisingly, in both the first and second aspects, it was found that increasing the HBr concentration at the cathode of the electrolytic cell reduces the operating voltage, with the result that OPEX is reduced.

[0038] For example, the hydrogen bromide concentration of the second composition ranges from 4 to 10 mol / kg; preferably 4 to 9 mol / kg, more preferably 4 to 8 mol / kg, or 4.5 to 8 mol / kg, or 5 to 8 mol / kg.

[0039] For example, in step v) the electrolytic cell is operated at a voltage of at most 1900 mV, preferably at most 1800 mV; more preferably at most 1700 mV; even more preferably at most 1600 mV, and most preferably at most 1500 mV. run.

[0040] For example, in step v), the electrolytic cell is operated at a voltage 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 ( )run.

[0041] For example, in step v) the electrolytic cell is operated at a current of at least 3 kA / m 2 The operating current density J op , preferably at least 5 kA / m2 , preferably at least 4 kA / m 2 ; More preferably at least 5 kA / m 2 , even more preferably at least 6 kA / m 2 ; Most preferably at least 7kA / m 2 ; even most preferably at least 8 kA / m; or at least 9 kA / m 2 ; or at least 10 kA / m 2 The operating current density J op run.

[0042] For example, in step v) the electrolytic cell is operated at a current of at most 12 kA / m 2 ; preferably up to 11 kA / m 2 , or up to 15 kA / m 2 The operating current density (J op )run.

[0043] For example, in step v) the electrolytic cell is operated at a current in the range of 3 kA / m 2 to 15 kA / m 2 ; preferably 4 kA / m 2 to 12 kA / m 2 , or 5 kA / m 2 to 12 kA / m 2 , or 6 kA / m 2 to 12 kA / m 2 The operating current density (J op )run.

[0044] For example, in step v) the electrolytic cell is operated at a temperature T of at least 70°C. op Run under, where T op Below the boiling point of the second composition, preferably at 75°C or higher, more preferably at 80°C or higher; even more preferably at 85°C or higher; and most preferably at 90°C or higher.

[0045] For example, in step v) the electrolytic cell is operated at an operating temperature T in the range of 70 to 122°C, preferably 70 to 120°C or lower, more preferably 75 to 115°C, even more preferably 80 to 110°C, most preferably 85 to 105°C, even most preferably 90 to 100°C, or 80 to 95°C, or 75 to 95°C. op Run below.

[0046] For example, both the first composition and the second composition are liquid compositions.

[0047] For example, the electrolytic cell is operated at the following pressure p opDown operation: It increases from the anode to the cathode.

[0048] For example, in step v), the electrolytic cell is at least partially operated at a pressure p above 0.1 MPa, preferably above 0.15 MPa; more preferably above 0.2 MPa. op Run below.

[0049] For example, the film is a fluoropolymer film having a glass transition temperature T of at least 110°C, preferably at least 112°C, more preferably at least 115°C, even more preferably at least 118°C, most preferably at least 120°C, even most preferably at least 122°C, or at least 125°C, as determined according to DIN EN ISO 11357-2:2020-08. g .

[0050] For example, the film is a fluoropolymer film having a glass transition temperature T of 170°C or less, preferably 168°C or less, more preferably 165°C or less, even more preferably 162°C or less, and most preferably 160°C or less, as determined according to DIN EN ISO 11357-2:2020-08. g .

[0051] For example, the film is a fluoropolymer film having a glass transition temperature T in the range of 110° C. to 170° C., or 120° C. to 165° C., determined according to DIN EN ISO 11357-2:2020-08. g .

[0052] For example, the film comprises Repeating unit of fluoropolymer film.

[0053] For example, the film is not including the formula A fluoropolymer film having a structural entity.

[0054] For example, the membrane is a sulfonated fluoropolymer membrane.

[0055] For example, the sulfonated fluoropolymer membrane comprises A group wherein n is an integer selected from 1, 2, 3, 4 and 5, preferably 2.

[0056] For example, the sulfonated fluoropolymer membrane comprises and of hydrolyzed copolymers.

[0057] For example, the membrane is a fluoropolymer membrane having 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.

[0058] For example, the membrane is a fluoropolymer membrane having an acid capacity in the range of 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; most preferably 1.0 to 1.2 meq / g. As used herein, meq / g refers to milliequivalents per gram, where an equivalent is mol-H (i.e., the number of moles of H-acid sites), preferably mol (Right now moles of groups).

[0059] For example, the hydrocarbon is an alkane, preferably selected from methane, ethane, propane and butane, more preferably methane.

[0060] For example, in step v), bromine is produced at the anode.

[0061] For example, the method is not performed in a flow battery.

[0062] For example, the process is carried out in the absence of hydrogen fluoride, hydrogen chloride and / or hydrogen iodide.

[0063] 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).

[0064] The term "hydrocarbon" is used herein in a manner 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).

[0065] 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) ( ) results.

[0066] As used herein, "bromination of hydrocarbons" means that at least one hydrocarbon (hydrocarbon compound) is brominated, in particular at least methane. This step may also be referred to as "bromination". However, it is also contemplated that a mixture of two or more different hydrocarbon compounds is brominated to produce hydrogen bromide in step i). In this case, it may also be referred to as "bromination of hydrocarbons".

[0067] As used herein, "so as to generate hydrogen bromide" means that hydrogen bromide is the direct reaction product of bromination, or that hydrogen bromide is formed after such bromination. In other words, the hydrogen bromide produced in step i) originates from the bromination of the hydrocarbon, that is, it is produced directly in the bromination of the hydrocarbon, or is produced afterward.

[0068] Figure 5 A preferred route for brominating hydrocarbons to produce hydrogen bromide is shown.

[0069] Therefore, preferably in step i) 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:

[0070] .

[0071] The catalytic conversion or hydrolysis generally occurs according to the following reaction:

[0072] .

[0073] When the hydrocarbon is brominated in step i), 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 , , , and ,in particular Such hydrocarbon polybrominates can then be pyrolyzed. As an example, for , pyrolysis generally occurs according to the following reactions: Thus, as used herein, hydrogen bromide produced in step i) includes hydrogen bromide produced from the decomposition of at least one hydrocarbon polybromide and / or at least one carbon bromide that is itself produced in the bromination of a hydrocarbon.

[0074] As indicated above, HBr is a typical by-product of the bromination of hydrocarbons.

[0075] When step i) consists only of providing a stream containing hydrogen bromide obtained from the conversion of the hydrocarbon feedstock involving a bromination step, said stream will contain traces of hydrocarbons and / or polybrominates, e.g. , , , , , , ,and The presence of hydrocarbons and / or polybrominates in the stream containing hydrogen bromide obtained from the conversion of the hydrocarbon feedstock involving the bromination step can be determined by gas chromatography.

[0076] For example, a stream containing hydrogen bromide obtained from the conversion of a hydrocarbon feedstock involving a bromination step comprises at least 1 ppm by weight, based on the total weight of the stream, of a compound selected from , , , , , , , , and at least one of any mixture thereof.

[0077] For example, a stream containing hydrogen bromide obtained from the conversion of a hydrocarbon feedstock involving a bromination step comprises, based on the total weight of the stream, from 1 wt ppm to 1 wt %, for example, from 5 wt ppm to 0.5 wt %; or from 10 ppm to 0.1 wt % of a selected , , , , , , , , and at least one of any mixture thereof.

[0078] When the hydrocarbon is methane, the stream containing hydrogen bromide obtained from the conversion of the methane feedstock involving the bromination step comprises at least 1 ppm by weight, based on the total weight of the stream, for example from 1 ppm by weight to 1 % by weight, based on the total weight of the stream, of a compound selected from , , and at least one of any mixture thereof.

[0079] 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 method according to the present disclosure can be easily controlled and can allow the collection of H2 and Br2 in addition. In other words, the method according to the present disclosure can advantageously increase the value of HBr produced as a by-product in the bromination of hydrocarbons (i.e., it is produced when the hydrocarbons are brominated).

[0080] As used herein, an electrolytic cell comprises two electrodes, an anode and a cathode, between which an electric field can be applied. For this purpose, the anode and 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.

[0081] As used herein, a membrane is a sheet or layer that can be used as a proton exchange membrane in a standard electrolysis cell. Thus, protons can migrate through such a membrane.

[0082] As used herein, a membrane sandwiched between an anode and a 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.

[0083] As used herein, a 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 , and 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.

[0084] According to step v) of the 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 between the anode and the 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 for electrolyzing hydrogen bromide according to the present disclosure, which can alternatively be called electrolysis of hydrogen bromide or HBr electrolysis, refers to the electrolytic decomposition of HBr into hydrogen and bromine species (Br2 and / or Br3) by applying an electric field or operating voltage to the anode and the cathode. - ).

[0085] 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 membrane sandwiched in between to the cathode. According to the present disclosure, it is surprisingly advantageous to also feed HBr to the cathode, that is, to have a step iv) of feeding the second composition including hydrogen bromide and water to the cathode. 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 for electrolyzing hydrogen bromide, 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 for electrolyzing hydrogen bromide, and thus makes 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 for electrolyzing hydrogen bromide, and thus makes HBr electrolysis more economical. Furthermore, the method according to the present disclosure may also produce hydrogen in an eco-friendly manner, thereby contributing to the mitigation of global warming.

[0086] 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 preparing the electrolysis of the present invention. ...

[0087] Preferably, in the method for electrolyzing hydrogen bromide according to the present disclosure, the hydrogen bromide concentration of the second composition 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 become increasingly 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.

[0088] 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, is preferably ≥ 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.

[0089] Preferably, in the method for electrolyzing hydrogen bromide according to the present disclosure, in step v), the operating voltage is , preferably at operating voltage (But above 0 mV, that is ) 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.

[0090] Preferably, in the method for electrolyzing hydrogen bromide according to the present disclosure, in step v), the operating temperature is The electrolytic cell is operated at T op Below the boiling point of the second composition, preferably at the operating temperature Operating the electrolytic cell at such operating temperatures can reduce cooling and / or heating requirements. In particular, HBr is a byproduct of many chemical processes in which hydrocarbons are brominated. Such HBr is typically hot and must usually be cooled for its subsequent electrolysis. Performing electrolysis reduces the need for such cooling.

[0091] Additionally, higher temperatures typically increase the proton conductivity of the membrane comprising the fluoropolymer, which may allow operation at higher current densities and / or at lower voltages. Higher current densities help 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.

[0092] Additionally, But operating temperatures 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 voltages. Higher current density can help keep CAPEX low, while lower operating voltages can lead to lower OPEX, making the process for 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 process for electrolyzing hydrogen bromide in a safe manner.

[0093] When the operating temperature is All of these operating temperature-related effects can be even more pronounced when

[0094] Preferably, in the method for electrolyzing hydrogen bromide 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.

[0095] The electrolysis of HBr in water follows the reaction , and has a threshold voltage of 1.10 V. The electrolysis of HBr in the gas phase follows the reaction , 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 phase and the gas phase 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 and energy requirements, 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.

[0096] Preferably, in the method for electrolyzing hydrogen bromide according to the present disclosure, both the first composition and the second composition are liquid compositions having an operating temperature above 60°C, and 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. The solubility of Br2 in water is quite limited, but the compound is Br3 -As long as at least 33% of the 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. - 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 unstable performance of the electrolyzer 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.

[0097] For the preferred electrolysis in aqueous phase, i.e. when both the first composition and the second composition are fed as liquid compositions at above 60°C, more preferably above 70°C, the glass transition temperature (T g ) is preferred, especially from the perspective of sustainable electrolysis. Therefore, for such a case, the T of the fluoropolymer membrane is preferably 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.

[0098] Preferably, in the method for electrolyzing hydrogen bromide according to the present disclosure, the electrolytic cell is operated at an increasing pressure p from the anode to the cathode. opIn other words, there is a pressure gradient increased from the anode to the cathode, wherein the corresponding pressures at the anode and cathode have 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, a gaseous stream is 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 ≥ 0.01 MPa (that is, the difference between the pressure at the cathode and the pressure at the anode is 0.01 MPa or greater), more preferably high ≥ 0.02 MPa, more preferably high ≥ 0.05 MPa and most preferably high ≥ 0.1 MPa. As an example, when the absolute pressure at the anode is 0.1 MPa, the absolute pressure at the cathode is 0.11 to 0.3 MPa, more preferably 0.12 to 0.25 MPa, more preferably 0.15 to 0.2 MPa and most preferably 0.2 MPa. However, optional pressures at the cathode that are 1 MPa, 2 MPa, 3 MPa, 4 MPa, or even 5 MPa higher than the pressure at the anode are also contemplated. By such increased pressure or pressure gradient, a reduced operating voltage of the electrolytic cell can be achieved, which can result in reduced OPEX. Additionally, the pressure gradient can allow H2 to be obtained at a higher pressure on the cathode side, so that no or less compression is required to densify the obtained H2. Additionally, operating under a pressure differential (pressure increases from anode to cathode) can improve operating parameters.

[0099] For the case when the anode feed is gaseous HBr (with or without a pressure gradient), it is preferred that the second aqueous composition (or feed) 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 there is a pressure gradient from the anode to the cathode, a beneficial effect on the operating voltage can also be brought about. However, care must be taken because of the risk of membrane damage at higher pressures and at a simultaneously increased temperature. In particular, at higher temperatures, thinner membranes can easily break. By the listed reduced HBr concentrations, a balance between the effects and risks mentioned can be achieved.

[0100] Preferably, in the method for electrolyzing hydrogen bromide according to the present disclosure, the electrolytic cell is at least partially operated at an operating pressure p in step v). op >0.1 MPa operation. By such increased operating pressure, a reduced operating voltage of the electrolyzer 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.

[0101] Preferably, in the method for electrolyzing hydrogen bromide according to the present disclosure, the electrolytic cell is operated at a current density of , preferably at an operating current density 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.

[0102] Preferably, in the method for electrolyzing hydrogen bromide according to the present disclosure, the membrane is a fluorine-containing polymer membrane having a glass transition temperature T g ≥ 110°C, preferably with glass transition temperature T g ≥ 120°C, more preferably having a glass transition temperature T g ≥ 125°C. As used herein, the fluoropolymer membrane comprises a fluoropolymer, and is therefore referred to as a fluoropolymer membrane. Preferably, the fluoropolymer membrane (in a dry state) consists of a fluoropolymer, more preferably a fluoropolymer in a chemically stable form. As used herein, a fluoropolymer is a fluorocarbon-based polymer having a plurality of carbon-fluorine bonds. Such fluoropolymers are generally free of silicon atoms. Such fluoropolymers may additionally be free of chlorine, bromine and / or iodine atoms.

[0103] As used herein, the glass transition temperature (or T g ) is determined according to DIN EN ISO11357-2:2020-08 (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.

[0104] 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 showed poor conductivity. During the hydration of the membranes, the T of the membranes decreased 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.

[0105] In addition to the glass transition temperature (T g ), other characteristics of the fluoropolymer membranes reported herein refer to the fluoropolymer membranes in the dry state.

[0106] 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.

[0107] Due to the more resilient fluoropolymer film, the glass transition temperature T g Fluoropolymer membranes with a temperature of ≥ 110°C may allow the method of electrolyzing hydrogen bromide according to the present disclosure to be carried out at higher temperatures and / or at higher pressures. Without wishing to be bound by theory, it is hypothesized that the elasticity to HBr and, after electrolysis, to H2 and Br2 at higher temperatures and higher pressures is caused by having a fluoropolymer membrane at or above 110°C ( ) is imparted by a fluoropolymer membrane having a glass transition temperature of 100 Å. 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 voltages. Higher current density can help keep CAPEX low, while lower operating voltages lead to lower operating expenditures (OPEX), making the method according to the present disclosure particularly economical. Such a method 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 These effects can be even more pronounced when using fluoropolymer membranes with T g These effects are even more pronounced when the fluoropolymer membrane is subjected to temperatures of ≥125°C.

[0108] Preferably, 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 many chemical processes in which hydrocarbons are brominated. 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 this context, it is preferred to conduct the HBr electrolysis above 70°C. At such temperatures, liquid-liquid phase separation may be avoided. When the fluoropolymer membrane 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, the HBr electrolysis may be performed at a temperature above 70°C. g When the operating temperature of HBr electrolysis can be maintained at >70°C, more particularly at >90°C, and especially at >100°C, which can lead to the advantages of higher operating temperatures as discussed herein.

[0109] Preferably, the fluoropolymer membrane, more particularly the fluoropolymer comprised by and preferably constituting said membrane, comprises Repeating unit. The repeating unit 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 process according to the present disclosure more economical.

[0110] Preferably, the fluoropolymer membrane, more particularly the fluoropolymer comprised by said membrane and preferably constituting said membrane, does not comprise a fluoropolymer of the formula Such structural entities exist in Commercial membranes sold, however, can result in membranes with lower rigidity, which are therefore more susceptible to degradation at higher temperatures and under higher pressures. Such membranes are therefore disadvantageous for the method according to the present disclosure.

[0111] Preferably, 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. 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 process according to the present disclosure more economical.

[0112] Preferably, 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 has 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, thereby making the process according to the present disclosure more economical.

[0113] Preferably, the sulfonated fluoropolymer membrane, more particularly the fluoropolymer comprised by said membrane and preferably constituting said membrane, comprises A group, wherein n is an integer selected from 1, 2, 3, 4 and 5, preferably 2. The 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 The relatively short chain length of the groups 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 process according to the present disclosure particularly economical.

[0114] Preferably, the sulfonated fluoropolymer membrane comprises and Such hydrolyzed copolymers may result in increased proton conductivity and / or increased elasticity of the fluoropolymer membrane. Therefore, sulfonated fluoropolymer membranes are particularly advantageous from the perspective of HBr electrolysis at higher temperatures and / or at higher pressures, and thereby at higher current densities and / or at lower voltages. Therefore, sulfonated fluoropolymer membranes may make the process according to the present disclosure particularly economical.

[0115] Preferably, the fluoropolymer membrane has an acid capacity of ≥ 0.9 meq / g, more preferably between 0.95 and 1.5 meq / g, and particularly preferably between 1.0 and 1.2 meq / g. As used herein, meq / g refers to milliequivalents per gram, where equivalents are mol-H (i.e., moles of H-acid sites), preferably mol (Right now The acid capacity represents the total amount of active sites or functional groups responsible for proton exchange of the fluoropolymer membrane. Such acid capacity can increase proton conductivity and thus can lead to increased HBr conversion in HBr electrolysis. Increased HBr conversion can reduce any need for separation and possible recycling of unconverted HBr, which can help maintain low CAPEX for the process according to the present disclosure.

[0116] Preferably, the fluoropolymer film (in dry state) has a viscosity of ≥ 1.70 g / cm 3 , more preferably ≥1.80 g / 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 process according to the present disclosure more economical.

[0117] Preferably, 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.

[0118] Preferably, the fluoropolymer membrane (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 membrane 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 membrane. 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, thereby making the process according to the present disclosure more economical.

[0119] Preferably, 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 the MD 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 process according to the present disclosure more economical.

[0120] Preferably, the fluoropolymer membrane (in the dry state) has a tensile stress at break in the cross direction (CD) according to ASTM D882-18 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 can increase the elasticity of the fluoropolymer membrane. 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 process according to the present disclosure more economical.

[0121] Preferably, the fluoropolymer film (in the dry state) has an elongation at break according to ASTM D882-18 in the machine direction (MD) of 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 the MD 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 process according to the present disclosure more economical.

[0122] Preferably, the fluoropolymer film (in the dry state) has an elongation at break according to ASTM D882-18 in the cross direction (CD) of 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. 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 process according to the present disclosure more economical.

[0123] Preferably, in the method for electrolyzing hydrogen bromide 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 of the method according to the present disclosure can be expanded, making the method particularly versatile.

[0124] Preferably, in the method for electrolyzing hydrogen bromide according to the present disclosure, bromine is produced at the anode in step v). As previously mentioned, HBr is a typical byproduct of the chemical industry, especially a typical byproduct of hydrocarbon bromination, after which HBr often undergoes thermal oxidation. That is, HBr is burned to produce Br2 and H2O in a highly exothermic reaction that requires careful control, while H2 is lost. Advantageously, in contrast, the method for electrolyzing hydrogen bromide according to the present disclosure can be easily controlled and can additionally allow the recovery of both H2 and Br2.

[0125] Preferably, the method of electrolyzing hydrogen bromide according to the present disclosure does not occur in a flow battery. When the method occurs or is performed in a flow battery, the advantages brought by the method of the present invention are generally not observed.

[0126] Preferably, the process according to the present disclosure occurs in the absence of hydrogen fluoride, hydrogen chloride and / or hydrogen iodide or is carried out 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.

[0127] The subject of the present disclosure is also hydrogen obtained by the method described herein. In a similar manner, the preferred embodiments (including claims) of the method described herein are also preferred for the hydrogen of the present invention. In this way, pure hydrogen can be advantageously obtained by HBr electrolysis. In addition, hydrogen that can be used, for example, for fuel synthesis can be obtained by HBr electrolysis, which can thus contribute to mitigating global warming.

[0128] The subject matter of the present disclosure also lies in the bromine obtained by the method described herein. In a similar manner, the preferred embodiments (including the claims) of the method described herein are also preferred for the bromine of the present invention. In this way, pure bromine can be advantageously obtained by HBr electrolysis. In addition, bromine that can be used in subsequent chemical synthesis can be obtained by HBr electrolysis, which can thus help to close the bromine loop.

[0129] The subject of the present disclosure is also the use of an aqueous composition comprising hydrogen bromide as a cathode feed in the electrolysis of hydrogen bromide, wherein the hydrogen bromide is derived from the bromination of hydrocarbons. In a similar manner, the preferred embodiments (including claims) of the method described herein are also preferred for the use of the present invention. Particularly preferably, in the use of an aqueous composition comprising hydrogen bromide according to the present disclosure, the hydrogen bromide concentration of the aqueous composition 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 mole number of hydrogen bromide of the second composition per kilogram. The beneficial effects of such hydrogen bromide concentrations are the same as those discussed herein for the method according to the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0130] Figure 1 The general outline of an electrolytic cell suitable for use in the process according to the present disclosure is shown.

[0131] Figure 2 Results of HBr electrolysis feeding different HBr concentrations are shown.

[0132] Figure 3 Results of additional HBr electrolysis at different HBr concentrations are shown.

[0133] Figure 4 Results for HBr electrolysis in the gas phase are shown.

[0134] Figure 5 is a flow diagram of different routes for producing hydrogen bromide during the bromination of hydrocarbons.

[0135] Experimental Section

[0136] Figure 1 2 are a general overview of an exemplary electrolysis cell and an exemplary electrolysis procedure, respectively, which illustrate how a method of electrolyzing hydrogen bromide according to the present disclosure may be implemented. Figure 1 The proton exchange membrane depicted in is, for example, a membrane having a glass transition temperature A fully hydrated fluoropolymer membrane, such as Membrane or fully hydrated 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 are produced in the bromination of methane, following the reaction Applying an electric field to the electrolytic cell causes 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.

[0137] Figure 2 The results of actual electrolysis of HBr are shown with different HBr concentrations fed to the cathode of the electrolytic cell used. The electrolysis was carried out at 5 kA / m 2 of constant current density and at a constant temperature of 95 °C using a commercial proton exchange membrane ( ). It can be seen that an increase in the HBr concentration from 0 mol / kg (deionized water) to 6 mol / kg leads to a continuously reduced operating voltage. In particular, already at a HBr concentration of 1 mol / kg fed to the cathode, a practically relevant reduction in the operating voltage can be inferred from the experimental results. When a HBr concentration of 2 mol / kg, better 3 mol / kg, even better 4 mol / kg, still better 5 mol / kg and particularly better 6 mol / kg is fed to the cathode, a significant further reduction in the operating voltage can be achieved. It can be seen from this that, although it is not necessary to feed HBr to the cathode for HBr electrolysis at all, the operating voltage is significantly reduced when HBr is fed to the cathode of the electrolysis cell in which HBr electrolysis occurs. The reduced operating voltage in turn leads to an advantageously reduced OPEX.

[0138] Figure 3 Results from practical electrolysis of HBr using different current densities and different membranes are shown. Figure 2The experimental results reported in are again included. Also in these experiments, 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 further 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 Up to 16 kA / m 2 It is also found that for various membranes and current densities, except for Apart from a small outlier at 2 mol / kg for the membrane, increasing the HBr concentration surprisingly leads to a significant reduction in the operating voltage, which in turn leads to a beneficially reduced OPEX.

[0139] Figure 4 shows that on the cathode side, at increasing pressures, using the same commercial proton exchange membrane ( ) Results for the practical electrolysis of HBr in the gas phase. The pressure difference between the anode and cathode was varied from 0 through 0.2, 0.4, 0.6 and 0.8 to 1 barg (gauge pressure; corresponding to pressure differences of 0, 20, 40, 60, 80 and 100 kPa). It can be seen that the current density increases from 4 (two data points) to 4.66 kA / m 2 (six data points), which has a positive impact on CAPEX at the expense of increased operating voltage, which has a negative impact on OPEX. It is further seen that increasing the voltage differential between the anode and cathode again results in a beneficially reduced operating voltage. Thus, the applied voltage differential allows a balance between the undesirable OPEX effects of higher operating voltages and the beneficial CAPEX effects of increased operating current density.

Claims

1. A method for electrolyzing hydrogen bromide, comprising the following steps: i) brominating a hydrocarbon to produce hydrogen bromide, ii) providing an electrolytic cell comprising an anode, a cathode and a 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, wherein the second composition has a hydrogen bromide concentration of at least 4 mol / kg, and v) operating the electrolytic cell to produce hydrogen at the cathode, 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 electrolyzing 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 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, wherein the second composition has a hydrogen bromide concentration of at least 4 mol / kg, and v) operating the electrolytic cell to produce hydrogen at the cathode, Therein, the hydrogen bromide-containing stream provided 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).

3. The method according to claim 1 or 2, wherein the hydrogen bromide concentration of the second composition ranges from 4 to 10 mol / kg; preferably from 4 to 8 mol / kg.

4. The method according to claim 1 , wherein the electrolytic cell is operated at a voltage of at most 1900 mV in step v). , preferably at an operating voltage of up to 1700 mV Run below.

5. The method according to claim 1, wherein the electrolytic cell is operated at a temperature of at least 70° C. in step v). , preferably in the range of 70°C to 122°C operating temperature Conduct, among which Below the boiling point of the second composition.

6. The method according to at least one of the preceding claims, wherein both the first composition and the second composition are liquid compositions.

7. The method according to claim 1, wherein the electrolytic cell is operated at an increasing pressure from the anode to the cathode. Run below.

8. The method according to claim 1 , wherein the electrolysis cell is operated at least partially in step v) at an operating pressure above 0.1 MPa. run.

9. The method according to at least one of the preceding claims, wherein the electrolytic cell in step v) is heated at a current of at least 3 kA / m 2 The operating current density , preferably at least 5 kA / m 2 The operating current density run.

10. The method according to at least one of the preceding claims, wherein the film has a glass transition temperature of at least 110° C., determined according to DIN EN ISO 11357-2:2020-08. , preferably having a glass transition temperature of at least 120°C of fluoropolymer membranes.

11. The process according to at least one of the preceding claims, wherein the hydrocarbon is an alkane, preferably methane.

12. The process according to at least one of the preceding claims, wherein bromine is produced at the anode in step v).

13. The method according to at least one of the preceding claims, which does not take place in a flow battery.

14. The process according to claim 1, which is carried out in the absence of hydrogen fluoride, hydrogen chloride and / or hydrogen iodide.

15. The method according to at least one of the preceding claims, characterized in that The film comprises Repeating unit of fluoropolymer film.

16. The method according to at least one of the preceding claims, characterized in that The membrane is a sulfonated fluoropolymer membrane.

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