Method for removing sulfur-containing compounds from gas containing at least one sulfur-containing compound

Abstract

A process for removing at least one sulfur-containing compound from a gas containing at least one sulfur-containing compound wherein the process comprises the steps of: a) contacting a gas stream containing at least one sulfur-containing compound with a stream containing bromine and water to obtain a starting stream, b) reacting the starting stream provided in step a) to produce a reaction mixture effluent comprising sulfuric acid and hydrogen bromide, c) separating the reaction mixture effluent obtained in step b) into one or more hydrogen bromide-enriched compositions and one or more sulfuric acid-enriched compositions, d) subjecting at least a portion of the at least one hydrogen bromide-enriched composition obtained in step c) to a treatment wherein at least a portion of the hydrogen bromide-enriched composition is converted to bromine, e) recycling at least a portion of the bromine-containing composition obtained in step d) back to step a), and f) withdrawing a gas depleted of the at least one sulfur-containing compound, wherein step c) comprises at least one distillation step in which, if the reaction mixture is a single-phase liquid composition, the reaction mixture effluent or a mixture of the reaction mixture effluent and the sulfuric acid-enriched composition obtained in step c) is subjected as a feed to a first distillation step, or if the reaction mixture effluent is a two-phase gas / liquid composition, first separating the two-phase gas / liquid composition into a gaseous portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent, the liquid fraction of the reaction mixture effluent or a mixture of the liquid fraction of the reaction mixture effluent and the sulfuric acid-enriched composition obtained in step c) is then subjected to a first distillation step as a feed, where the feed is separated in the first distillation step into a mixture containing up to 1, 3, 4-trimethyl-1, 3-pentanediol. A gaseous overhead composition comprising a hydrogen bromide-enriched composition comprising more than 30% by weight of sulfuric acid and less than 1,000 ppm of hydrogen bromide, and a liquid bottoms composition comprising more than 30% by weight of sulfuric acid and less than 1,000 ppm of a sulfuric acid-enriched composition comprising hydrogen bromide, in which a) at least a portion of the hydrogen bromide-enriched gas composition obtained as overhead composition in the first distillation step is subjected to a water removal step, the invention relates to a method for separating a hydrogen bromide-enriched composition into a water-enriched composition and a hydrogen bromide-enriched, water-depleted gas composition comprising 90 to 99% by weight of hydrogen bromide and less than 10% by weight of water, in which at least a portion of the hydrogen bromide-enriched, water-depleted gas composition is subjected to an electrolysis or thermal oxidation step in step d), and / or beta) step c) comprises at least two distillation steps wherein the sulfuric acid-enriched composition obtained as the liquid bottoms composition of the first distillation step is subjected to a second distillation step to produce an overhead composition and a bottoms composition containing 60 to 95 wt% sulfuric acid and 5 to 40 wt% water, based on the total weight of the bottoms composition, wherein preferably at least a portion of the bottoms composition of the second distillation step is subjected to a third distillation step to produce an overhead composition containing at least 99.0% by weight of water and less than 10 ppm of hydrogen bromide and a bottoms composition containing at least 90% by weight of sulfuric acid and less than 10% by weight of water, based on the total weight of the bottoms composition, wherein a portion of the bottoms composition obtained in the second distillation step and / or a portion of the bottoms composition obtained in the third distillation step is recycled to the reaction mixture effluent or a liquid portion of the reaction mixture effluent and mixed with it as a sulfuric acid-enriched composition to obtain a mixture, the mixture contains at least 35% by weight of sulfuric acid, based on the total weight of the mixture, wherein the mixture is subjected to a first distillation step as a feed.

Description

[0001] The invention relates to a method and a device for removing at least one sulfur-containing compound from a gas containing the at least one sulfur-containing compound.

[0002] Removing non-hydrocarbon components and particularly sulfur-containing compounds from hydrocarbon-based gases, also known as gas desulfurization, is an important part of gas processing because such non-hydrocarbon components and particularly sulfur-containing compounds may seriously interfere with downstream applications. For example, natural gas must be purified before it is liquefied, sold or transported to commercial gas pipelines due to the toxicity of compounds (such as hydrogen sulfide) contained therein and due to the corrosion-forming components contained therein. Prominent examples of interfering non-hydrocarbon components and particularly sulfur-containing (non-hydrocarbon) compounds are acid gases, such as hydrogen sulfide and carbon dioxide, and other sulfur species such as mercaptans, organic sulfides and carbonyl sulfide. Hydrogen sulfide is highly toxic and forms weakly corrosive acids in the presence of a small amount of water, which can first cause corrosion in pipelines and then rupture and catch fire. The separation of methane from other major components helps to significantly save long-distance transportation of raw materials and avoid technical difficulties such as corrosion and potential pipeline ruptures. In addition, due to strict sales gas specifications and increasingly impure natural gas and the increasing demand for renewable natural gas, natural gas processing projects face increasing challenges. Many natural gas resources do not contain harmful large amounts of hydrogen sulfide, but contain significant amounts of carbon dioxide.

[0003] It is a challenge to remove carbon dioxide from natural gas in the presence of hydrogen sulfide, carbonyl sulfide and mercaptans. Conventional amine absorption methods are not suitable for natural gas containing large amounts of carbon dioxide in the presence of sulfides, carbonyl sulfide and mercaptans. It requires mixed solvents, such as, for example, a mixture of chemical and physical solvents, and increases energy consumption due to the higher temperatures used for amine regeneration. In addition, the extracted carbon dioxide stream may still need to respond to very strict specifications of up to 4ppm hydrogen sulfide, which is still generally challenging to achieve in a single step with membranes or amines, and may require a polishing adsorption step. On the other hand, the resulting hydrogen-rich carbon dioxide stream requires a further step of conversion to sulfur. This is usually carried out in a Claus unit. The use of Claus units has been well established, but is only feasible on a large scale. Most renewable gas projects cannot afford this type of treatment and require very expensive alternative sulfur removal technologies. These options can be based on adsorption on activated carbon, iron oxide, zinc oxide, etc. In addition, all methods for removing sulfur from biogas are hampered by extremely high costs and the resulting large amounts of waste. In addition, the presence of many forms of sulfur usually adds more challenges to the technology. Thereby, sometimes the whole gas treatment section becomes more expensive and depends largely on the amount of sulfur present at ppm level.

[0004] In summary, the known methods for removing sulfur-containing compounds from a gas containing at least one sulfur-containing compound are expensive and consume a large amount of energy, which leads to additional carbon dioxide emissions.

[0005] In view of the above, the basic object of the present invention is to provide a process for removing at least one sulfur-containing compound from a gas containing at least one sulfur-containing compound on an industrial scale, wherein the process can be carried out by separating and converting the sulfur-containing compound into a saleable sulfuric acid product stream in a single step, and wherein the process is cheaper, consumes less energy and causes less carbon dioxide emissions than known corresponding gas treatment processes.

[0006] According to the present invention, this object is solved by providing a method for removing at least one sulfur-containing compound from a gas containing at least one sulfur-containing compound, wherein the method comprises the following steps:

[0007] a) contacting a gas stream containing at least one sulfur-containing compound with a stream containing bromine and water to obtain a starting stream,

[0008] b) reacting the starting stream provided in step a) to produce a reaction mixture effluent comprising sulfuric acid and hydrogen bromide,

[0009] c) separating the reaction mixture effluent obtained in step b) into one or more compositions enriched in hydrogen bromide and one or more compositions enriched in sulfuric acid,

[0010] d) subjecting at least a portion of the at least one composition enriched in hydrogen bromide obtained in step c) to a treatment in which at least a portion of the composition enriched in hydrogen bromide is converted into bromine,

[0011] e) recycling at least a portion of the bromine-containing composition obtained in step d) back to step a), and

[0012] f) removing a gas depleted in at least one sulphur-containing compound,

[0013] wherein step c) comprises at least one distillation step, wherein in the case where the reaction mixture is a single-phase liquid composition, the reaction mixture effluent or a mixture of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) is subjected as feed to a first distillation step, or in the case where the reaction mixture effluent is a two-phase gas / liquid composition, the two-phase gas / liquid composition is first separated into a gaseous portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent, and then the liquid portion of the reaction mixture effluent or a mixture of the liquid portion of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) is subjected as feed to a first distillation step, wherein the feed is separated in the first distillation step into a gaseous overhead composition of a composition enriched in hydrogen bromide containing up to 1,000 ppm of sulfuric acid and a liquid bottom composition of a composition enriched in sulfuric acid containing more than 30% by weight of sulfuric acid and less than 1,000 ppm of hydrogen bromide, wherein

[0014] a) subjecting at least a portion of the hydrogen bromide-enriched gas composition obtained as an overhead composition in the first distillation step to a water removal step in order to separate the hydrogen bromide-enriched composition into a water-enriched composition and a hydrogen bromide-enriched, water-depleted gas composition comprising 90 to 99% by weight of hydrogen bromide and less than 10% by weight of water, wherein at least a portion of the hydrogen bromide-enriched, water-depleted gas composition is subjected in step d) to an electrolysis or thermal oxidation step, and / or

[0015] β) Step c) comprises at least two distillation steps, wherein the composition enriched in sulfuric acid obtained as the liquid bottoms composition of the first distillation step is subjected to a second distillation step to produce an overhead composition and a bottoms composition, the bottoms composition containing 60 to 95% by weight of sulfuric acid and 5 to 40% by weight of water, based on the total weight of the bottoms composition, wherein preferably at least a portion of the bottoms composition of the second distillation step is subjected to a third distillation step to produce an overhead composition containing at least 99.0% by weight of water and less than 10 ppm of hydrogen bromide and a bottoms composition containing at least 90% by weight of sulfuric acid and less than 10% by weight of water, based on the total weight of the bottoms composition, wherein a portion of the bottoms composition obtained in the second distillation step and / or a portion of the bottoms composition obtained in the third distillation step is recycled to the reaction mixture effluent or the liquid part of the reaction mixture effluent and mixed with the reaction mixture effluent or the liquid part of the reaction mixture effluent as a composition enriched in sulfuric acid to obtain a mixture containing at least 35% by weight of sulfuric acid, based on the total weight of the mixture, wherein this mixture is subjected to the first distillation step as feed.

[0016] The method is based on the following discovery: the reactive separation of sulfur-containing compounds from a gas stream via bromine-mediated oxidation in an aqueous medium allows the selective one-pot removal of all types of sulfur compounds from the gas stream, while additionally commercializing sulfur in the form of pure sulfuric acid (which is a very valuable chemical product). Thus, the method according to the present invention replaces the known methods of separating sulfur from gases (such as natural gas) and converting sulfur into sulfuric acid in a single step. In addition, the method according to the present invention causes a high degree of removal of sulfur-containing compounds from a gas containing at least one sulfur-containing compound reliably on an industrial scale in a cost-effective and energy-effective manner without generating any carbon dioxide emissions or at least not generating a significant amount of carbon dioxide emissions. More specifically, the reaction of bromine, water and sulfur-containing compounds (such as elemental sulfur or hydrogen sulfide) to sulfuric acid and hydrogen bromide in step b) is exothermic, and the energy thus obtained can be used to significantly reduce the amount of external energy required for the overall gas treatment process, which can be utilized in step d) to hydrogen bromide electrolysis or thermal oxidation of hydrogen bromide to bromine. In addition, the separation step c) separates the reaction mixture effluent containing hydrogen bromide and sulfuric acid and usually accompanied by unreacted water and bromine and other impurities resulting from the source of sulfur-containing gases into one or more compositions enriched in hydrogen bromide and one or more compositions enriched in sulfuric acid, wherein preferably at least one composition enriched in hydrogen bromide contains up to 1,000 ppm and most preferably up to 10 ppm of sulfuric acid, allowing such hydrogen bromide compositions depleted in sulfuric acid to be subjected to treatments, especially hydrogen bromide electrolysis, in step d), which reliably protect the electrolyzer (and especially the membranes and electrodes) from degradation, thereby resulting in a long life of the electrolyzer. Such degradation of the electrolyzer may be caused by the presence of sulfuric acid and products of the conversion of sulfuric acid in the electrolyzer (e.g., to elemental sulfur). Those products, such as, for example, elemental sulfur, may also be present due to incomplete oxidation of S species in the reaction mixture effluent in step b). Generally, the reaction of S-containing compounds may result in the presence of some individual sulfur impurities in step b), which is highly undesirable. Therefore, separation in step c) to significantly reduce the concentration of sulfuric acid in the HBr stream is important to protect the performance of the electrolyzer.

[0017] In addition, the generation of one or more sulfuric acid-enriched compositions in step c) allows the production of very pure sulfuric acid with a sulfuric acid concentration of up to 95% by weight in an easy and cost-effective manner, which can be sold commercially and thus further reduces the overall cost of the process according to the invention. In addition, the separation of the reaction mixture effluent containing hydrogen bromide and sulfuric acid and usually accompanied by unreacted water and bromine and other impurities produced by the source of sulfur-containing gases into one or more hydrogen bromide-enriched compositions and one or more sulfuric acid-enriched compositions concentrates water in the one or more sulfuric acid-enriched compositions and thus allows the easy removal of pure and particularly hydrogen bromide-free water from the one or more sulfuric acid-enriched compositions. Due to its purity, this pure and particularly hydrogen bromide-free water can be easily removed from the process, thus reliably and effectively allowing the avoidance of water accumulation in a continuous process. Avoidance of water accumulation in a continuous process is further ensured by carrying out a water removal step in step α) in order to separate the composition enriched in hydrogen bromide into a gaseous composition enriched in hydrogen bromide, depleted in water and a composition enriched in water which can be removed from the process, and / or by carrying out at least one further second distillation step and preferably even a third distillation step in step β), wherein a portion of the bottom composition obtained in the second distillation step and / or a portion of the bottom composition obtained in the third distillation step is recycled to the reaction mixture effluent or to the liquid part of the reaction mixture effluent and mixed therewith as a composition enriched in sulfuric acid to obtain a mixture which is subjected to the first distillation step as feed. By carrying out further distillation steps, a pure water stream is obtained which can be removed to avoid water accumulation, wherein recycling the bottom composition allows adjusting a sufficiently high amount of sulfuric acid in the mixture which breaks the hydrogen bromide-water azeotrope in the mixture. This allows to easily and effectively separate the gas composition of enriched hydrogen bromide with quite low water content from the liquid composition of enriched sulfuric acid and water by subsequent distillation steps, so that the gas composition of enriched hydrogen bromide can be directly used for step d) processing, such as electrolysis step or thermal oxidation step.For example, gas electrolysis is more energy efficient than aqueous solution electrolysis in which hydrogen bromide is dissolved in water.In addition, the reaction mixture effluent is separated into one or more compositions of enriched hydrogen bromide and one or more compositions of enriched sulfuric acid allowing a part of one or more compositions of enriched hydrogen bromide to be recycled back to the starting stream, thereby ensuring in a simple and effective manner that the starting stream is a single-phase liquid mixture comprising enough hydrogen bromide, so that in the reaction mixture, bromide and water are reliably avoided to be separated into two phases.In short, the method according to the present invention causes to reliably remove sulfur compounds from the gas containing at least one sulfur compound in a cost-effective and energy-effective manner on an industrial scale, without producing any carbon dioxide emissions or at least not producing a significant amount of carbon dioxide emissions, wherein the method can be carried out by separating the sulfur compounds in one step and converting them into a marketable sulfuric acid product stream.

[0018] In principle, the present invention is not particularly limited to the type of sulfur-containing compound contained in the gas in step a), as long as it can react with bromine and optional water to form sulfuric acid. Therefore, it is not important whether the sulfur-containing compound contained in the gas is reacted into sulfuric acid in step b) by oxidizing sulfur atoms, by reducing sulfur atoms, or by not changing the oxidation state of sulfur atoms. According to an alternative, the sulfur-containing compound used in step a) can be oxidized into sulfuric acid. When the sulfur-containing compound is selected from any combination of sulfur, sulfur dioxide, sulfide, disulfide, thiophene, mercaptan and two or more of the aforementioned compounds, good results are particularly obtained. More preferably, the sulfur-containing compound is selected from any combination of hydrogen sulfide, sulfur, sulfur dioxide, carbonyl disulfide, carbonyl sulfide, methyl mercaptan and two or more of the aforementioned compounds. The particularly preferred example of the sulfur-containing compound contained in the gas used in step a) is hydrogen sulfide.

[0019] Illustratively, the reaction of some of the above sulfur-containing compounds with bromine and water in step b) is shown:

[0020] H2S+4Br2+4H2O→8HBr+H2SO4

[0021] S+3Br2+4H2O→6HBr+H2SO4

[0022] SO2+Br2+2H2O→2HBr+H2SO4

[0023] CS2+4Br2+10H2O→8HBr+2H2SO4+CO2

[0024] 2COS+4Br2+10H2O→8HBr+2H2SO4+2CO2

[0025] According to the present invention, the starting stream provided in step a) contains bromine, water and sulfur-containing compounds. Of course, the presence of other compounds is not excluded. On the contrary, it is preferred that the starting stream provided in step a) additionally contains hydrogen bromide. This is preferred, so as to achieve a single-phase liquid reaction mixture in step b). The binary system of bromine and water (except for very low bromine content) is a two-phase system, while the ternary mixture of bromine, water and hydrogen bromide is a single-phase liquid mixture at a hydrogen bromide concentration higher than a certain (e.g., 5 wt %), which depends on the relative amount of bromine and water. At a hydrogen bromide concentration equal to or higher than 11 wt % or 12 wt %, all ternary mixtures of bromine, hydrogen bromide and water are single-phase liquid mixtures. Therefore, it is preferred that the starting stream a) contains a correspondingly high amount of hydrogen bromide.

[0026] More specifically, if the starting stream is a gas-liquid mixture at the reaction temperature and reaction pressure of step b), preferably the starting stream contains at least 5% by weight, more preferably 11 to 46% by weight and most preferably 12 to 46% by weight of hydrogen bromide based on the total weight of bromine, hydrogen bromide and water in the liquid phase of the starting stream. If the starting stream is a liquid at the reaction temperature and reaction pressure of step b), preferably the starting stream contains at least 5% by weight, preferably 11 to 46% by weight and most preferably 12 to 46% by weight of hydrogen bromide based on the total weight of bromine, hydrogen bromide and water in the starting stream. A 5% by weight concentration of hydrogen bromide produces a single-phase liquid mixture at least for low and high bromine contents relative to water. However, as described above, a hydrogen bromide concentration of at least 11% by weight or at least 12% by weight produces a single-phase liquid mixture for each amount of bromine relative to water.

[0027] Preferably, if the starting stream is a gas-liquid mixture at the reaction temperature and reaction pressure, the starting stream comprises at least 5% by weight, preferably 11 to 46% by weight and most preferably 12 to 46% by weight of hydrogen bromide, at least 1% by weight and preferably 2 to 35% by weight of bromine and 40 to 75% by weight of water, based on the total weight of water, bromine and hydrogen bromide in the liquid phase of the starting stream. If the starting stream is a liquid at the reaction temperature and reaction pressure, preferably the starting stream comprises at least 5% by weight, preferably 11 to 46% by weight and most preferably 12 to 46% by weight of hydrogen bromide, at least 1% by weight and preferably 2 to 35% by weight of bromine and 30 to 75% by weight of water, based on the total weight of bromine, hydrogen bromide and water in the starting stream.

[0028] In order to achieve the addition of hydrogen bromide to the starting stream in an easy and cost-effective manner, it is proposed in a further development of the inventive concept that the process according to the invention further comprises a step of recycling at least a portion of the hydrogen bromide contained in one of the one or more compositions enriched in hydrogen bromide produced in step c) to step a), wherein the recycled hydrogen bromide is not subjected to the treatment of step d). Thus, it is not necessary to supply the starting stream in step a) with external hydrogen bromide, thereby further reducing the overall costs of the process and achieving a particularly efficient utilization of the hydrogen bromide formed in the reaction of step b). A further advantage of using recycled hydrogen bromide in the starting stream that has not been subjected to the treatment of step d), i.e. by using recycled hydrogen bromide in the starting stream that bypasses the treatment of step d), such as electrolysis or thermal oxidation, is that only a portion of the hydrogen bromide obtained in step b) needs to be sent to the treatment of step d) to produce bromine, and, for example in the case of aqueous hydrogen bromide electrolysis, is that the addition of more water to the electrolysis of step d) is avoided, both of which lead to significant energy savings in the process.

[0029] Under standard pressure and temperature conditions, hydrogen bromide forms a mixture with water in an azeotropic composition. Under those conditions, the relative amount of hydrogen bromide relative to the hydrogen bromide-water mixture is about 47% by weight. An important aspect of the process according to the invention is the ability to adjust the hydrogen bromide-water azeotrope composition or to completely break the azeotrope, if desired and depending on the embodiment. To this end, increasing amounts of sulfuric acid can be added to the hydrogen bromide-water mixture, which has the progressive effect of first reducing the hydrogen bromide fraction in the azeotropic composition and ultimately completely breaking the azeotrope, which occurs when the amount of sulfuric acid relative to the sum of hydrogen bromide and water is about 55% by weight.

[0030] Another important aspect of the present invention is that the optimum operating point of any embodiment can be that hydrogen bromide is present at the outlet of the reaction zone relative to the hydrogen bromide and water in the liquid portion at a near azeotropic composition. The reason for this is twofold: on the one hand, if hydrogen bromide is present at a concentration higher than the azeotropic composition in the reaction mixture effluent, then excess hydrogen bromide may also be contained in the gaseous portion of the reactor mixture effluent, and potentially, it may not only impair the operation of the subsequent gas scrubber described further below, but may also result in insufficient hydrogen bromide remaining in the liquid portion of the reaction mixture effluent, in which case, in the treatment of step d), such as in electrolysis (or other hydrogen bromide conversion methods), the conversion of hydrogen bromide to bromine will be insufficient. On the other hand, if hydrogen bromide is present at a concentration lower than the azeotropic composition in the reactor mixture effluent, then this means that excess water is present, which means that additional energy is consumed to evaporate this water in the subsequent hydrogen bromide recovery and sulfuric acid purification steps. In addition, this may also result in a sub-azeotropic hydrogen bromide solution entering the treatment of step d) (such as electrolysis), which is inefficient. Thus, as described further below, the optimum point can be directed by controlling the amount of additional water entering the gas scrubber.

[0031] As mentioned above, according to the present invention, in step a), use the gas containing at least one sulfur-containing compound as main component or at least as impurity, so that the gas desulfurization.Therefore, preferably in step a), the gas containing sulfur-containing compound is mixed with bromine, water and optional and preferred hydrogen bromide, the gas wherein containing at least one sulfur-containing compound is selected from biogas, natural gas, flue gas, from the combustion gas of sulfur compound, tail gas and two or more aforementioned gases in any combination.Based on the gross weight of gas, the concentration of sulfur-containing compound in gas can be 10ppm to 99 weight % and more preferably 1 to 40 weight %.Further preferably in this embodiment, the gas containing sulfur-containing compound contains by volume less than 500ppm, more preferably by volume less than 200ppm, even more preferably by volume less than 100ppm unsaturated compounds, and most preferably does not contain unsaturated compounds.This avoids the unnecessary consumption of bromine because of side reaction in the reaction of step b).

[0032] With regard to the reaction conditions of step b), i.e. with regard to the reaction temperature and the reaction pressure, the present invention is not particularly restricted. Good results are particularly obtained when the reaction in step b) is carried out at a temperature of at least 55° C. and preferably at a temperature of 60 to 200° C. Good results are also particularly obtained when the reaction in step b) is carried out at a pressure of at least 5 barg and preferably at a pressure of 6 to 15 barg.

[0033] This reaction does not require a catalyst.

[0034] The reaction mixture effluent formed during the reaction in step b) of the process according to the invention can in very rare cases (depending on the composition of the starting stream and on the reaction conditions) be a single-phase liquid, in particular if very high pressures are applied in step b).

[0035] However, in most cases, the reaction mixture effluent generated during the reaction of step b) will be a gas / liquid two-phase mixture. In this case, according to the present invention, the gas / liquid two-phase mixture is separated into a gas phase and a liquid phase, thereby allowing a certain amount of hydrogen bromide to be separated as a gas phase from the sulfuric acid generated in the reaction of step b) in an easy manner, as well as any non-reactive gas that may be present in the reactor feed mixture. When the gas-liquid mixture of the reaction mixture effluent is fed into a container in step c) and allowed to phase separate therein to separate the reaction mixture effluent into a gas portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent, good results are particularly obtained. Alternatively, phase separation can be achieved by subjecting the gas-liquid mixture of the reaction mixture effluent to at least one separation step selected from any combination of a stripping step, an absorption step, an extraction step, and two or more of the aforementioned separation steps, so as to separate the reaction mixture effluent into a gas portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent. Preferably, the aforementioned separation is carried out at the temperature and pressure when the reaction mixture effluent leaves the reactor (i.e., there is no active cooling, active heating, active pressurization, or active decompression between the reaction and the separation).

[0036] Preferably, a part of the liquid portion of the reaction mixture effluent is recycled to the reactor. If at least one sulfur-containing compound contained in the gas is hydrogen sulfide, this is particularly preferred. The hydrogen sulfide conversion reaction occurs in the liquid phase, and the reaction is irreversible and mass transfer limited. Therefore, it is advantageous to supply the reaction mixture with a liquid recirculation device, which helps to ensure that hydrogen sulfide and bromine are preferably maintained in the liquid phase. This also minimizes the amount of unreacted bromine. If at least one sulfur-containing compound is elemental sulfur, unreacted sulfur in the reaction mixture effluent should be filtered, and unreacted sulfur should be recycled to the reactor.

[0037] In a further development of the inventive concept, the oxidation of a portion of the S-containing compounds may stop at the elemental sulfur and not proceed to sulfuric acid. Such failures may be caused by different process upsets or occur during the start-up or shutdown of the operation (different transition stages). In this case, the reaction mixture effluent will also contain some elemental sulfur. The elemental sulfur impurities can be removed from the effluent by filtering, decantation or any other method known in the prior art and recycled back to the reactor.

[0038] In a further development of the inventive concept, it is proposed that the liquid portion of the reaction mixture effluent contains at least 20% by weight and preferably about 50% by weight of hydrogen bromide relative to the water content of the liquid portion of the reaction mixture effluent. Likewise, in the rare case that the reaction mixture effluent generated in step b) is a single-phase liquid, the liquid portion of the reaction mixture effluent corresponds to the total reaction mixture effluent. However, if the reaction mixture effluent generated in step b) is a gas-liquid two-phase mixture, the liquid portion of the reaction mixture effluent corresponds to the liquid phase obtained after the aforementioned separation step. It is particularly preferred that the liquid portion of the reaction mixture effluent contains hydrogen bromide and water in a concentration close to or in the hydrogen bromide-water azeotrope. For a binary mixture of water and hydrogen bromide at standard temperature and pressure, the azeotropic composition contains about 47% by weight of hydrogen bromide and about 53% by weight of water. However, the exact content of water and hydrogen bromide of the azeotropic composition also depends on the concentration of sulfuric acid in the case of the existing pressure conditions of the liquid portion of the reaction mixture effluent and the reactor outlet conditions. It is particularly advantageous to form such a hydrogen bromide-water azeotrope in the liquid portion of the reaction mixture effluent, especially since a sub-azeotropic composition may cause too much hydrogen bromide to be carried away by the gas leaving the gas-liquid reaction mixture effluent during the aforementioned separation into the gaseous portion of the reaction mixture effluent and the liquid portion of the reaction mixture effluent. In addition, a sub-azeotropic composition means, in the best case scenario, that too much water is circulated in the process, which needs to be removed by evaporation, which reduces the efficiency of the process, and in the worst case scenario, that if sulfuric acid is not added to the liquid portion of the reaction mixture effluent in the preferred subsequent distillation step further described below, the composition of the overhead stream will depend on whether the hydrogen bromide-water azeotrope is broken inside the distillation column. If the hydrogen bromide-water azeotrope is broken in the distillation step, hydrogen bromide with a relatively low water content can be removed in the overhead composition. However, if the hydrogen bromide-water azeotrope is not broken in the distillation step, a large amount of water will be contained in the overhead composition. On the other hand, assuming that the downstream unit for carrying out the treatment of step d), such as an electrolysis unit, can process up to 60% by mass aqueous hydrogen bromide solution, the target concentration in the liquid phase at the reactor outlet can be adjusted accordingly, but the same general principles as set out above still apply. The same principles apply whenever the azeotropic hydrogen bromide composition relative to water is changed due to the operating pressure in the reactor.

[0039] In addition to the aforementioned hydrogen bromide content, it is preferred that the liquid portion of the reaction mixture effluent comprises at least 0.1 wt % sulfuric acid, 20 to 70 wt % water, and up to 2 wt % bromine, based on the total weight of the liquid portion of the reaction mixture effluent. More preferably, the liquid portion of the reaction mixture effluent comprises 0.3 to 15 wt % sulfuric acid, 25 to 65 wt % water, and up to 0.5 wt % bromine, based on the total weight of the liquid portion of the reaction mixture effluent.

[0040] The gaseous portion of the reaction mixture effluent preferably comprises up to 50% by weight of hydrogen bromide, based on the total weight of the gaseous portion of the reaction mixture effluent.

[0041] The liquid portion of the reaction mixture effluent, i.e., the reaction mixture effluent in the rare case where the reaction mixture effluent is a single-phase liquid composition and in the usual case where the reaction mixture effluent is a gas / liquid two-phase composition, the liquid portion of the reaction mixture effluent, after separation from the gaseous portion of the reaction mixture effluent, is preferably separated by a further separation step into one or more additional compositions enriched in hydrogen bromide and one or more compositions enriched in sulfuric acid. To this end, step c) comprises, in addition to the aforementioned preferred gas-liquid separation step, at least one distillation step, preferably at least two distillation steps and more preferably three distillation steps.

[0042] Before being sent to the first distillation step, the pressure of the reaction mixture effluent or the liquid part of the reaction mixture effluent, respectively, is preferably reduced, for example by passing it through a throttling control valve.

[0043] In the case where the reaction mixture effluent is a single-phase liquid composition, the reaction mixture effluent or a mixture of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) is subjected to the first distillation step as feed. As further explained in detail below, if the treatment of step d) (such as thermal oxidation or electrolysis) is carried out with a gaseous composition enriched in hydrogen bromide, it is preferred to subject the reaction mixture effluent to the first distillation step as feed with a mixture of the composition enriched in sulfuric acid obtained in step c). This allows to increase the sulfuric acid concentration in the mixture of the reaction mixture effluent and the composition enriched in sulfuric acid, so that the hydrogen bromide-water azeotrope is destroyed in the mixture, or at least sufficiently modified, so that sufficient hydrogen bromide is ultimately available to undergo the treatment in step d), such as electrolysis, and thus regenerate the required amount of bromine under the reactor inlet conditions. As explained above, during the distillation step, a gaseous hydrogen bromide composition having a relatively low water content can be separated as a tower top composition from a liquid tower bottom composition comprising sulfuric acid and water. This is advantageous because the treatments of step d) using the gaseous hydrogen bromide-rich composition (such as thermal oxidation and electrolysis) do not tolerate excess water and therefore must only dry or partially condense the overhead composition having a relatively low water content to reduce the water content in the gaseous hydrogen bromide-rich composition to an amount acceptable for the treatment of step d). However, if the treatment of step d) (such as electrolysis) is carried out with a liquid (i.e., aqueous) hydrogen bromide composition, the reaction mixture effluent can be used without admixture with the sulfuric acid-enriched composition obtained in step c), because the higher water content in the overhead composition is not detrimental to the electrolysis due to the fact that the hydrogen bromide-water azeotrope is not broken during the distillation process. However, in this case, the reaction mixture effluent can also be mixed with the sulfuric acid-enriched composition obtained in step c) before using this mixture as a feed to the first distillation step. For example, this can be done to provide a liquid hydrogen bromide solution above the azeotropic composition to the electrolyzer.

[0044] In the aforementioned embodiment, the distillation step may also be settling the reaction mixture effluent or the mixture of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) in a container to separate the reaction mixture effluent or the mixture of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) into a gas composition enriched in hydrogen bromide and a liquid composition enriched in sulfuric acid. Settling in a container is considered to be a distillation step with one theoretical stage.

[0045] In the case where the reaction mixture effluent is a two-phase gas / liquid composition, the two-phase gas / liquid composition is first separated into a gaseous portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent as further described above, for example by feeding the reaction mixture effluent into a container and allowing it to phase separate therein or by subjecting it to at least one separation step selected from a stripping step, an absorption step, an extraction step and any combination of two or more of the aforementioned separation steps. Subsequently, the liquid portion of the reaction mixture effluent or a mixture of the liquid portion of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) is subjected as feed to a first distillation step. As described above, when the treatment in step d) is carried out with a gaseous composition enriched in hydrogen bromide, it is most preferred to mix the liquid portion of the reaction mixture effluent with the composition enriched in sulfuric acid obtained in step c) before subjecting the mixture to the first distillation step, however such a mixture may be used, but in the case where the treatment in step d) is carried out with a liquid (i.e., aqueous) composition enriched in hydrogen bromide, it is also suitable to use only the liquid portion of the reaction mixture effluent. Also in this embodiment, the distillation step may be settling of the reaction mixture effluent or a mixture of the reaction mixture effluent and the sulphuric acid-enriched composition obtained in step c) in a vessel.

[0046] As to the nature of the treatment carried out in step d), the invention is not particularly limited, provided that it is suitable for converting at least a portion of the hydrogen bromide contained in the composition enriched in hydrogen bromide into bromine. Good results are particularly obtained when the treatment in step d) is an electrolysis of hydrogen bromide producing hydrogen and bromine or a thermal oxidation of hydrogen bromide to bromine and water.

[0047] Hydrogen bromide electrolysis is preferred as a treatment step d), in particular when a significant amount of a gas stream containing at least one sulfur-containing compound (such as natural gas from a natural gas field) is subjected to the process in step a), or when a gas enriched in at least one sulfur-containing compound (such as a gas containing more than 1% by weight of at least one sulfur-containing compound) is subjected to the process in step a). Pure hydrogen produced in the electrolysis together with hydrogen bromide can improve the profitability of the process.

[0048] Thermal oxidation is preferred as a treatment step d), in particular when a limited amount of a gas stream containing at least one sulfur-containing compound (such as biogas) is subjected to the process in step a), or when a gas containing only a small amount of at least one sulfur-containing compound (such as a gas containing 5,000 ppm or less of at least one sulfur-containing compound) is subjected to the process in step a). Thermal oxidation is the preferred option in these cases, as the capital expenditure and operating expenditure of thermal oxidation are significantly lower compared to hydrogen bromide electrolysis.

[0049] Both the hydrogen bromide electrolysis or thermal oxidation can be carried out in the same plant in which process steps a), b), c), e) and f) are carried out, or off-site (i.e. in another plant), before the bromine thus produced is introduced back into the plant in which process steps a), b), c), e) and f) are carried out. Typically, the resulting composition enriched in hydrogen bromide will be transported to an external facility for bromine recovery.

[0050] Alternatively, the treatment of the composition enriched in hydrogen bromide in step d) can be carried out via another ex situ conversion step of converting at least a portion of the hydrogen bromide contained in the composition enriched in hydrogen bromide into bromine. An example of such another treatment is the recovery of bromine from a solution containing hydrogen bromide using chlorine displacement. This type of treatment can be used, for example, in mobile units to provide some temporary intervention, or can be used in sites where production is depleted.

[0051] If thermal oxidation is carried out in step d), at least a portion of the gas composition enriched in hydrogen bromide and depleted in water is preferably mixed with oxygen or an oxygen-containing gas such as air in the thermal oxidation step before the mixture thus obtained is reacted or "burned" into bromine and water, respectively, at a temperature of at least 700° C. according to 4HBr+O2→2Br2+2H2O. The reaction is exothermic and is completed at a conversion level of 50 to 95%. The reaction mixture obtained in the thermal oxidation process mainly comprises bromine and water, but in addition also comprises unreacted hydrogen bromide, nitrogen, small amounts of excess oxygen or excess air, respectively, and carbon dioxide from the oxidation of trace hydrocarbons contained in the reaction mixture. The hot effluent stream can be used for preheating any process stream, such as the feed stream entering the first distillation step, and / or for generating steam before recycling at least a portion of it to step a) of the process. Alternatively or in addition, the effluent stream of the thermal oxidation may be subjected to a scrubber step with water to remove its depleted air by quenching and washing with water, before optionally using at least a portion of the resulting hot aqueous effluent for preheating process streams and / or generating steam, and subsequently recycled to step a) of the process. Alternatively still, the hot effluent stream leaving the thermal oxidizer may be recycled directly to step a) of the process.

[0052] In most of the foregoing embodiments, in which a mixture of the reaction mixture effluent (in the case where the reaction mixture effluent is a single-phase liquid composition) or the liquid portion of the reaction mixture effluent (in the case where the reaction mixture effluent is a two-phase gas / liquid composition) with the composition enriched in sulfuric acid obtained in step c) is subjected as feed to the first distillation step, it is preferred, for the reasons previously mentioned, that the feed contains so much sulfuric acid that the hydrogen bromide-water azeotrope is broken during the distillation, or at least the azeotropic composition is changed so that sufficient hydrogen bromide will still be available for the treatment in step d), as explained above. Likewise, this allows efficient separation of hydrogen bromide in the gas phase from water in the liquid phase, so that an overhead composition having a fairly low water concentration of, for example, less than 30% by weight is obtained in the distillation, which water concentration can subsequently be further reduced by drying the overhead composition. The exact amount of sulfuric acid required to break the hydrogen bromide-water azeotrope depends on the concentration of sulfuric acid, but the hydrogen bromide-water azeotrope is reliably broken at a sulfuric acid concentration of at least 53% by weight relative to the water concentration. It is therefore particularly preferred that the feed in these embodiments comprises at least 53% by weight of sulfuric acid relative to the water content. For example, the feed comprises at least 40% by weight, more preferably at least 45% by weight and even more preferably at least 48% by weight of sulfuric acid and less than 38% by weight, more preferably at least 30% by weight and even more preferably at least 25% by weight of water, based on the total weight of the feed. Good results are obtained, for example, when the feed comprises 50 to 70% by weight of sulfuric acid, based on the total composition of the feed.

[0053] In the first distillation step, the feed is separated into an overhead composition of a gaseous composition enriched in hydrogen bromide and a bottom composition of a liquid composition enriched in sulfuric acid containing more than 30% by weight of sulfuric acid and preferably less than 1,000 ppm of hydrogen bromide, more preferably less than 100 ppm of hydrogen bromide and most preferably less than 5 ppm of hydrogen bromide. Preferably, the composition enriched in hydrogen bromide obtained in the first distillation step contains at most 1,000 ppm, more preferably at most 100 ppm, still more preferably at most 10 ppm and most preferably at most 1 ppm of sulfuric acid, 5 to 60% by weight of water and 40 to 95% by weight of hydrogen bromide, based on the total weight of the composition enriched in hydrogen bromide. On the other hand, the composition enriched in sulfuric acid obtained in the first distillation step preferably contains more than 50% by weight of sulfuric acid and less than 50% by weight of water, based on the total weight of the composition enriched in sulfuric acid. More preferably, the sulfuric acid-enriched composition obtained in the first distillation step contains 60 to 95% and even more preferably 70 to 80% sulfuric acid and 5 to 40% and even more preferably 20 to 30% water, based on the total weight of the sulfuric acid-enriched composition.

[0054] In a further development of the inventive concept, it is proposed to use the composition enriched in hydrogen bromide produced as a top composition in the first distillation step for the treatment in step d). As explained above, if the treatment in step d) is electrolysis, the electrolysis can be carried out with a gaseous hydrogen bromide-rich composition or with a liquid (i.e., aqueous) hydrogen bromide-rich composition. However, if the treatment in step d) is thermal oxidation, the thermal oxidation is preferably carried out with a gaseous hydrogen bromide-rich composition. In the case where electrolysis is carried out in step d), it is preferred that the composition enriched in hydrogen bromide produced as a top composition in the first distillation step contains at most 1,000 ppm, preferably at most 100 ppm, even more preferably at most 10 ppm and most preferably at most 1 ppm of sulfuric acid to protect the electrolytic cell and in particular the membrane from degradation. However, in the case where thermal oxidation is carried out in step d), such a low sulfuric acid content in the composition enriched in hydrogen bromide produced as a top composition in the first distillation step is possible, but not preferred.

[0055] In case the treatment and preferably electrolysis of step d) is carried out with a liquid hydrogen bromide-rich composition, it is preferred that the hydrogen bromide-rich composition produced as the overhead composition in the first distillation step is condensed in a condenser and all or part of it is fed to the electrolytic cell for electrolysis. In this case, the hydrogen bromide-rich liquid composition fed to the treatment unit or the electrolytic cell, respectively, has the same composition as the hydrogen bromide-rich composition produced as the overhead composition in the first distillation step, i.e., it preferably contains at most 1,000 ppm of sulfuric acid, more preferably at most 100 ppm, still more preferably at most 10 ppm and most preferably at most 1 ppm of sulfuric acid, 5 to 60 wt. % of water and 40 to 95 wt. % of hydrogen bromide, based on the total weight of the condensed hydrogen bromide-rich composition. In this embodiment, it is preferred that only a portion of the condensed composition enriched in hydrogen bromide is fed to the treatment unit or electrolyzer, respectively, while the remainder thereof bypasses the treatment unit or electrolyzer, respectively, and is recycled to the starting stream, i.e. is not fed to the treatment unit or electrolyzer, respectively, but is fed directly or indirectly by mixing it with other process streams into step a). Thus, it is not necessary to supply the starting stream in step a) with external hydrogen bromide, thereby further reducing the overall cost of the process and achieving a particularly efficient utilization of the hydrogen bromide formed in the reaction of step b). Another advantage of using hydrogen bromide in the starting stream that has not been subjected to electrolysis in step d) (i.e. by bypassing the treatment of step d) with a portion of the hydrogen bromide formed in the reaction of step b) is that only a portion of the hydrogen bromide obtained in step b) needs to be fed to the electrolysis of step d) to produce bromine, and in the case where the treatment of step d) is an aqueous hydrogen bromide electrolysis, the addition of more water to the electrolysis of step d) is avoided, both of which result in significant energy savings in the process.

[0056] According to a particularly preferred embodiment of the present invention, the treatment of step d), i.e. thermal oxidation or electrolysis, is not carried out with a liquid hydrogen bromide-rich composition, but with a gaseous hydrogen bromide-rich composition. A particular advantage of carrying out the electrolysis of step d) with a gaseous hydrogen bromide-rich composition is that - compared with carrying out the electrolysis of step d) with a liquid hydrogen bromide-rich composition - the operating energy requirement in the electrolyzer is reduced by 10 to 15%. In the embodiment in which the treatment of step d) is carried out with a gaseous hydrogen bromide-rich composition, step α) is preferably carried out by subjecting at least a portion of the hydrogen bromide-rich composition obtained as a top composition in the first distillation step to a water removal step in order to separate the hydrogen bromide-rich composition into a water-rich composition and a hydrogen bromide-rich, water-depleted gaseous composition comprising 90 to 99% by weight of hydrogen bromide and less than 10% by weight, preferably less than 5% by weight, more preferably less than 2% by weight and most preferably less than 1% by weight of water. At least a portion of the hydrogen bromide-rich, water-depleted gaseous composition is subjected to the treatment of step d), i.e. thermal oxidation or electrolysis. In the case where the treatment in step d) is hydrogen bromide electrolysis, the gas composition enriched in hydrogen bromide and depleted in water preferably contains at most 1,000 ppm, preferably at most 100 ppm, more preferably at most 10 ppm and most preferably at most 1 ppm of sulfuric acid for the reasons mentioned above. The water removal step can be carried out by distillation, pervaporation or partial condensation. In the latter alternative, the gas composition enriched in hydrogen bromide obtained as the overhead composition in the first distillation step can be cooled and partially condensed and then separated into a liquid composition enriched in water and a gas composition enriched in hydrogen bromide and depleted in water. When the gaseous portion of the composition enriched in hydrogen bromide is fed to the treatment unit (i.e., thermal oxidation unit or electrolyzer) of step d) for the treatment of step d), it is preferred to allow the liquid portion of the composition enriched in hydrogen bromide to bypass the treatment of step d) and be recycled to the starting stream, i.e., not to the thermal oxidation unit or electrolyzer, but to enter step a) directly or indirectly by mixing it with other process streams.

[0057] Thus, the present invention comprises the following two particularly preferred embodiments. In the first of these two particularly preferred embodiments, at least a portion of the composition enriched in hydrogen bromide obtained as the overhead composition in the first distillation step is subjected to a water removal step to separate the composition enriched in hydrogen bromide into a composition enriched in water and a gas composition enriched in hydrogen bromide, depleted in water, comprising 90 to 99% by weight of hydrogen bromide and less than 10% by weight and preferably less than 1% by weight of water, wherein in step d) the gas composition enriched in hydrogen bromide, depleted in water is subjected to hydrogen bromide electrolysis.

[0058] In the second of these two particularly preferred embodiments, at least a portion of the composition enriched in hydrogen bromide obtained as a top composition in the first distillation step is subjected to a water removal step in order to separate the composition enriched in hydrogen bromide into a composition enriched in water and a gas composition enriched in hydrogen bromide, depleted in water, comprising 90 to 99% by weight of hydrogen bromide and less than 10% by weight and preferably less than 1% by weight of water, wherein at least a portion of the gas composition enriched in hydrogen bromide, depleted in water is subjected to thermal oxidation in step d). Preferably, at least a portion of the gas composition enriched in hydrogen bromide, depleted in water is mixed with oxygen or an oxygen-containing gas, such as air, in the thermal oxidation before reacting the mixture thus obtained to bromine and water at a temperature of at least 700° C.

[0059] Either of the above thermal oxidation or hydrogen bromide electrolysis can be carried out in an ex situ unit. In this case, at least a portion of the composition enriched in hydrogen bromide obtained in the first distillation step is directed to an ex situ unit comprising a thermal oxidation unit or an electrolysis cell for hydrogen bromide electrolysis, wherein at least a portion of the composition enriched in hydrogen bromide is converted into a bromine-containing composition by converting at least a portion of the hydrogen bromide into bromine, and subsequently at least a portion of the bromine-containing composition produced is recycled to step a) in step e). Alternatively, in step d), bromine is recovered from the solution containing hydrogen bromide by displacement with chlorine in an ex situ unit.

[0060] According to another particularly preferred embodiment of the present invention, the composition enriched in sulfuric acid obtained as the bottom composition of the first distillation step is further purified in one, two or more separation steps, and in particular in one, two or more distillation steps, to separate the composition enriched in sulfuric acid obtained as the bottom composition of the first distillation step into at least one composition of substantially pure water and at least one composition of concentrated sulfuric acid. Good results are particularly obtained when the composition enriched in sulfuric acid obtained as the bottom composition of the first distillation step is further purified in one or two further distillation steps, wherein if only one further distillation step is carried out, at least one composition enriched in substantially pure water is obtained as the top composition of the first further distillation step (which is the second distillation step as a whole), and if two further distillation steps are carried out, at least one composition enriched in substantially pure water is obtained as the top composition of the second further step (which is the third distillation step as a whole). The substantially pure water preferably contains at least 99.0% by weight, more preferably at least 99.5% by weight and even more preferably at least 99.9% by weight of water and preferably less than 10 ppm, more preferably less than 5 ppm and most preferably less than 1 ppm of bromine species, i.e. hydrogen bromide, bromine, etc. In order to obtain such pure water, it is preferred that the feed of the first additional (i.e. second) distillation step (if only one additional distillation step is performed) or the feed of the second additional (i.e. third) distillation step (if two additional distillation steps are performed) contains up to 1,000 ppm, more preferably up to 100 ppm and most preferably up to 5 ppm of hydrogen bromide. The aforementioned embodiments are particularly preferred because they reliably and effectively allow the avoidance of water accumulation in the continuous process, since pure water, and in particular water containing no hydrogen bromide, can be removed from the process as a purge. More specifically, it is particularly advantageous to control and minimize the amount of water in the process during the process. In order to control the amount of water in the system, water removal is preferably performed. This is particularly advantageous in the case of thermal oxidation in step d), because water is co-produced with bromine therein. In the case of not being removed from the process, the water so co-produced will remain in the system, resulting in the accumulation of water. However, considering operational flexibility, water control may also be relevant to other situations. Due to environmental restrictions, bromine-containing water cannot be removed to the environment, but needs to be purified in an additional water treatment facility to recover the remaining bromine species. The latter would result in a significant additional amount of energy and additional costs to the process. It is therefore preferred to separate the composition enriched in sulfuric acid obtained as the bottom composition of the first distillation step into at least one concentrated sulfuric acid composition and at least one substantially pure water composition, thereby allowing to remove from the plant at least one substantially pure and thus substantially free of bromine species water composition without the need for further purification thereof.

[0061] Thus, as explained above, in order to further purify and concentrate the composition enriched in sulfuric acid obtained as the bottom composition of the first distillation step, it is recommended in another preferred embodiment to subject it to a second distillation step to produce a top composition and a bottom composition containing 60 to 95% by weight and preferably 70 to 80% by weight of sulfuric acid and 5 to 40% by weight and preferably 20 to 30% by weight of water, based on the total weight of the bottom composition. It is further preferred that at least a portion of the bottom composition of the second distillation step is subjected to a third distillation step to produce a top composition and a bottom composition containing at least 90% by weight and preferably at least 94% by weight of sulfuric acid and less than 10% by weight and preferably less than 6% by weight of water, based on the total weight of the bottom composition. The top composition obtained in the third distillation step preferably contains at least 99.0% by weight, more preferably at least 99.5% by weight and even more preferably at least 99.9% by weight of water and less than 10 ppm, preferably less than 5 ppm and more preferably less than 1 ppm of bromine species, i.e. hydrogen bromide, bromine, etc. This pure water can be disposed of without any further required purification steps, thus reliably and efficiently allowing water accumulation in a continuous process to be avoided.

[0062] As explained above, in particular in the case of treatment with a gas composition enriched in hydrogen bromide by thermal oxidation or hydrogen bromide electrolysis in step d), it is preferred to adjust the concentration of sulfuric acid and water in the feed to the first distillation column so as to break the hydrogen bromide-water azeotrope during the distillation. Thus, hydrogen bromide in the gas phase is effectively separated from water. In order to appropriately adjust the concentration of sulfuric acid and water in the feed to the first distillation column, it is suggested in a further development of the inventive concept to carry out step β), i.e. to recycle a portion of the bottom composition obtained in the second distillation step and / or a portion of the bottom composition obtained in the third distillation step to the reaction mixture effluent (in the case where the reaction mixture effluent is a single-phase liquid composition) or to the liquid part of the reaction mixture effluent (in the case where the reaction mixture effluent is a gas / liquid two-phase composition) and to mix it as a composition enriched in sulfuric acid to obtain a mixture containing at least 35% by weight and preferably 50 to 70% by weight of sulfuric acid, based on the total weight of the mixture, and subjecting this mixture as feed to the first distillation step, before subjecting the thus obtained mixture as feed to the first distillation step.

[0063] According to another preferred embodiment of the invention, the gaseous part of the reaction mixture effluent or the mixture of the gaseous part of the reaction mixture effluent and the overhead composition of the second distillation step is subjected to a scrubbing step with water to obtain a gaseous composition containing less than 10 ppm of bromine and hydrogen bromide in total and an aqueous composition containing 5 to 40% by weight of hydrogen bromide, wherein the aqueous composition is recycled to step a). Thus, it is achieved to return the unreacted bromine that may be contained in the gaseous part of the reaction mixture effluent and subjected to the scrubbing step to the reactor, which allows a more efficient use of the bromine. The aqueous composition can be recycled directly to step a) or indirectly to step a) by mixing it with other process streams. At least part of the water required for the scrubbing step can be part or all of the overhead composition obtained in the third distillation step. For example, part of the overhead composition obtained in the third distillation step can be removed, while the other part can be used in the scrubbing step. The rest of the water required for the scrubbing step can be fresh water.

[0064] Alternatively, even though less preferred, the gaseous portion of the reaction mixture effluent or a mixture of the gaseous portion of the reaction mixture effluent and the overhead composition of the second distillation step can be recycled directly to step a), i.e. without being subjected to a scrubbing step. In this embodiment, part of the overhead composition obtained in the third distillation step can also be recycled directly to step a).

[0065] According to a particularly preferred embodiment of the present invention, in step d), electrolysis and / or thermal oxidation is carried out with a gaseous hydrogen bromide-rich composition, and step c) comprises the following steps:

[0066] i) feeding the reaction mixture effluent in step c) into a container and allowing it to phase separate therein to separate the reaction mixture effluent into a gaseous portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent,

[0067] ii) subjecting a mixture of the liquid portion of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) as feed to a first distillation step to separate the feed into an overhead composition of a composition enriched in hydrogen bromide containing at most 1,000 ppm of sulfuric acid and a bottom composition of a composition enriched in sulfuric acid containing more than 30% by weight of sulfuric acid and less than 1,000 ppm of hydrogen bromide, wherein the feed preferably contains at least 53% by weight of sulfuric acid relative to the water concentration,

[0068] iii) subjecting at least a portion of the composition enriched in hydrogen bromide obtained as the overhead composition in the first distillation step to a water removal step to separate the composition enriched in hydrogen bromide into a composition enriched in water and a gas composition enriched in hydrogen bromide, depleted in water, comprising 90 to 99% by weight of hydrogen bromide and less than 10% by weight and preferably less than 1% by weight of water, and subjecting at least a portion of the gas composition enriched in hydrogen bromide, depleted in water to the treatment in step d), preferably thermal oxidation or hydrogen bromide electrolysis,

[0069] iv) subjecting the composition enriched in sulfuric acid obtained as the bottom composition of the first distillation step to a second distillation step to produce an overhead composition and a bottom composition containing 60 to 95% by weight and preferably 70 to 80% by weight of sulfuric acid and 5 to 40% by weight and preferably 20 to 30% by weight of water, based on the total weight of the bottom composition, wherein preferably at least a portion of the bottom composition of the second distillation step is subjected to a third distillation step to produce an overhead composition and a bottom composition containing at least 90% by weight and preferably at least 94% by weight of sulfuric acid and less than 10% by weight and preferably less than 6% by weight of water, based on the total weight of the bottom composition,

[0070] v) recycling a portion of the bottom composition obtained in the second distillation step and / or a portion of the bottom composition obtained in the third distillation step as a composition enriched in sulphuric acid to and mixing it with the liquid part of the reaction mixture effluent to produce a mixture of the liquid part of the reaction mixture effluent and the composition enriched in sulphuric acid used in step ii),

[0071] vi) recycling at least a portion of the bromine-containing composition obtained in the electrolysis to step a), and

[0072] vii) optionally, recycling the gaseous portion of the reaction mixture effluent or the mixture of the gaseous portion of the reaction mixture effluent and the overhead composition of the second distillation step to step a) or subjecting the gaseous portion of the reaction mixture effluent or the mixture of the gaseous portion of the reaction mixture effluent and the overhead composition of the second distillation step to a scrubbing step with water to obtain a gaseous composition containing less than 10 ppm of bromine and hydrogen bromide in total and a liquid aqueous composition containing 5 to 40% by weight of hydrogen bromide, wherein the liquid aqueous composition is recycled to step a).

[0073] As an alternative to the aforementioned step i), separation can be achieved in step i) by subjecting the reaction mixture effluent to at least one separation step selected from a stripping step, an absorption step, an extraction step and any combination of two or more of the aforementioned separation steps.

[0074] Furthermore, the aforementioned method can be modified by replacing the first distillation step ii) with settling the reaction mixture effluent or the mixture of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) in a vessel to separate the reaction mixture effluent or the mixture of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) into a gas composition enriched in hydrogen bromide and a composition enriched in sulfuric acid. Settling in a vessel is considered as a distillation step with one theoretical stage.

[0075] Furthermore, it is preferred in the aforementioned process that the overhead composition obtained in the third distillation, which consists essentially of water, is recycled to step a) or to the optional scrubber step.

[0076] According to an alternative particularly preferred embodiment of the present invention, in step d), the electrolysis is carried out with a liquid hydrogen bromide-rich composition, and step c) comprises the following steps:

[0077] i) feeding the reaction mixture effluent in step c) into a container and allowing it to phase separate therein to separate the reaction mixture effluent into a gaseous portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent,

[0078] ii) subjecting the liquid portion of the reaction mixture effluent or a mixture of the liquid portion of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) as feed to a first distillation step to separate the feed into an overhead composition of a composition enriched in hydrogen bromide containing up to 1,000 ppm of sulfuric acid and a bottom composition of a composition enriched in sulfuric acid containing more than 30% by weight of sulfuric acid and less than 1,000 ppm of hydrogen bromide,

[0079] iii) condensing at least part of the composition enriched in hydrogen bromide obtained as an overhead composition in the first distillation step and subjecting at least part of the condensed portion to the treatment in step d), which is preferably hydrogen bromide electrolysis,

[0080] iv) subjecting the composition enriched in sulfuric acid obtained as the bottom composition of the first distillation step to a second distillation step to produce an overhead composition and a bottom composition containing 60 to 95% by weight and preferably 70 to 80% by weight of sulfuric acid and 5 to 40% by weight and preferably 20 to 30% by weight of water, based on the total weight of the bottom composition, wherein preferably at least a portion of the bottom composition of the second distillation step is subjected to a third distillation step to produce an overhead composition and a bottom composition containing at least 90% by weight and preferably at least 94% by weight of sulfuric acid and less than 10% by weight and preferably less than 6% by weight of water, based on the total weight of the bottom composition,

[0081] v) recycling a portion of the bottom composition obtained in the second distillation step and / or a portion of the bottom composition obtained in the third distillation step as a composition enriched in sulphuric acid to the liquid part of the reaction mixture effluent and mixing it therewith to produce a mixture of the liquid part of the reaction mixture effluent and the composition enriched in sulphuric acid used in step ii),

[0082] vi) recycling at least a portion of the bromine-containing composition obtained in the electrolysis to step a),

[0083] vii) optionally, recycling the gaseous portion of the reaction mixture effluent to step a) or subjecting the gaseous portion of the reaction mixture effluent to a scrubbing step with water to obtain a gaseous composition containing less than 10 ppm of bromine and hydrogen bromide in total and a liquid aqueous composition containing from 5 to 40% by weight of hydrogen bromide, wherein the liquid aqueous composition is recycled to step a), and

[0084] viii) Optionally, a portion of the condensed fraction of the composition enriched in hydrogen bromide obtained in step iii) is recycled to step a) without subjecting it to the electrolysis in step d).

[0085] As an alternative to the aforementioned step i), the separation in step i) may be achieved by subjecting the reaction mixture effluent to at least one separation step selected from a stripping step, an absorption step, an extraction step and any combination of two or more of the aforementioned separation steps.

[0086] Furthermore, the aforementioned method can be modified by replacing the first distillation step ii) with settling the reaction mixture effluent or the mixture of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) in a vessel to separate the reaction mixture effluent or the mixture of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) into a gas composition enriched in hydrogen bromide and a composition enriched in sulfuric acid. Settling in a vessel is considered as a distillation step with one theoretical stage.

[0087] Furthermore, it is preferred in the aforementioned process that the overhead composition obtained in the third distillation, which consists essentially of water, is recycled to step a) or to the optional scrubber step.

[0088] In a further development of the inventive concept, it is proposed to carry out the treatment in step d) as hydrogen bromide electrolysis by using an electrolysis cell comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode, wherein an electric field can be applied between the anode and the cathode. The composition enriched in hydrogen bromide obtained in step c) and containing up to 1,000 ppm of sulfuric acid is fed to the anode, optionally a second composition comprising hydrogen bromide and water is fed to the cathode, and the electrolysis cell is operated to produce hydrogen at the cathode, wherein a bromine-containing composition is produced at the anode.

[0089] As explained in further detail below, the electrolysis in step d) is preferably carried out by using an electrolysis cell comprising a membrane made of a fluoropolymer membrane having a glass transition temperature of at least 110°C.

[0090] Furthermore, it is preferred that the electrolysis in step d) is carried out by operating the electrolysis cell at an operating temperature of at least 70°C, wherein the operating temperature is below the boiling point of the optional second composition fed to the cathode, and preferably at an operating temperature of 70 to 122°C.

[0091] Furthermore, it is preferred that the electrolysis is carried out in step d) by operating the electrolysis cell at an operating pressure which increases from the anode to the cathode.

[0092] Anode and cathode often comprise conductive materials, especially metal, coated metal, carbon cloth, graphite felt, carbon fiber composite material, carbon-loaded polymer or graphite, and are preferably made of carbon fiber composite material or coated metal. The membrane can be a sheet or layer that can be used in a standard electrolyzer, preferably as a proton exchange membrane. Therefore, preferably protons can migrate through such membranes.

[0093] As described above, electrolysis can be carried out with a gas composition enriched with hydrogen bromide or with a liquid (i.e., aqueous) composition enriched with hydrogen bromide. In an aqueous composition containing hydrogen bromide, hydrogen bromide is dissolved in water, wherein the hydrogen bromide dissolved in water will often dissociate in water, so that the composition will contain ionic species, especially protons, hydronium ions and bromine cations. At the anode of the feed hydrogen bromide, protons are generated during the electrolysis process, and the protons subsequently migrate to the cathode through the membrane. According to the present invention, the aqueous composition enriched with hydrogen bromide can also be fed to the cathode. This allows the electrolyzer to be operated at a lower operating voltage, which reduces operating costs. In addition, this allows the electrolyzer to be operated at a higher temperature, which reduces the cooling and / or heating requirements of the electrolyzer, which also reduces operating costs. In addition, this allows the electrolyzer to be operated at a higher current density, which reduces the capital expenditure of the electrolyzer. In addition, this can reduce the concentration gradient across the membrane, and thus reduce or even alleviate the undesirable transfer of hydrogen bromide and / or bromine and / or bromine cations from the anode to the cathode through the membrane. In addition, the presence of hydrogen bromide on the cathode side can allow hydrogen bromide to pass through the film from the cathode to the anode side. This causes an increase in the efficiency of the system, and allows to avoid any disturbance in the electrolytic process. Without wishing to be bound by theory, it is assumed that in this embodiment, there is actually hydrogen bromide passing through in the reverse direction, i.e. from the cathode to the anode. Such hydrogen bromide passing through in the reverse direction is considered to be one of the reasons that can improve the electrolysis efficiency of this embodiment. In this embodiment, preferably, the hydrogen bromide concentration of the composition fed to the cathode is at least 0.5mol / kg, more preferably at least 1mol / kg, more preferably at least 2mol / kg, even more preferably at least 3mol / kg, further preferably at least 4mol / kg, even further preferably at least 5mol / kg and most preferably at least 6mol / kg, wherein mol / kg refers to the mole number of hydrogen bromide per kilogram of corresponding composition.

[0094] Independently, whether or not the hydrogen bromide composition is directed to the cathode of the electrolysis cell, it is preferred that during the electrolysis of step d) at an operating voltage U of more than 0 mV to 1,900 mV and preferably more than 0 mV to 1,700 mV op Operating the electrolyzer at such an operating voltage improves the selectivity of the reaction to hydrogen bromide electrolysis and thereby reduces the operating costs of the electrolysis.

[0095] In a further development of the inventive concept, the electrolysis in step d) is preferably carried out by operating the electrolyser at an operating temperature of 70° C. to 122° C. Operating the electrolyser at such operating temperatures can reduce cooling and / or heating requirements. Such higher temperatures increase the proton conductivity of the membrane comprising the fluoropolymer, which allows operating the electrolyser at higher current densities and / or lower voltages. Higher current densities help to keep capital expenditures low. It is thus particularly preferred to keep the operating temperature above 70° C., more preferably above 90° C. and most preferably above 100° C.

[0096] It is further preferred that, during the electrolysis process in step d), the electrolyzer is operated at an operating pressure increased from the anode to the cathode. In other words, there is a pressure gradient increased from the anode to the cathode, wherein the corresponding pressures at the anode and the cathode have the same reference point, i.e., both are absolute pressures, or both are gauge pressures relative to the atmosphere around the electrolyzer. In such cases, electrolysis often occurs in the gas phase, i.e., by feeding the gas stream to the anode and the cathode. In such cases, the pressure at the cathode is higher than the pressure at the anode, preferably at least 0.01MPa (i.e., the difference between the pressure at the cathode and the pressure at the anode is 0.01MPa or more), more preferably at least 0.02MPa, more preferably at least 0.05MPa and most preferably at least 0.1MPa. For 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, more preferably 0.15 to 0.2MPa and most preferably 0.2MPa. However, an optional pressure at the cathode that is 1MPa, 2MPa, 3MPa, 4MPa or even 5MPa higher than the pressure at the anode is also envisioned. With such an increased pressure or pressure gradient, a reduced operating voltage of the electrolyzer can be achieved, which can cause reduced operating costs. In addition, the pressure gradient can allow hydrogen to be obtained at a higher pressure on the cathode side, so that subsequent compression may not be required or less compression is required to densify the hydrogen obtained. In addition, operation under a pressure differential improves operating parameters.

[0097] According to another preferred embodiment of the present invention, the membrane used for the electrolysis of step d) is a fluoropolymer membrane. When the glass transition temperature of the fluoropolymer membrane is at least 110°C, preferably at least 120°C and more preferably at least 125°C, good results are particularly obtained. Preferably, the fluoropolymer membrane (in a dry state) is composed of a fluoropolymer, and more preferably a fluoropolymer in a chemically stable form. As used herein, a fluoropolymer is a fluorine-carbon-based polymer with multiple carbon-fluorine bonds. Such fluoropolymers often do not contain silicon atoms. Such fluoropolymers may further be free of chlorine, bromine and / or iodine atoms. As used herein, the glass transition temperature of the fluoropolymer membrane is determined according to DIN EN ISO 11357-2:2020-08 (half-order height method). Therefore, as used herein, the glass transition temperature of the fluoropolymer membrane is measured by differential scanning calorimetry (DSC), 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 invention, 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) at a temperature of 80°C after 24 hours, 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 value. A fully hydrated fluoropolymer membrane is obtained by immersing the fluoropolymer membrane in deionized water (which will cause an increase in the weight of the fluoropolymer membrane measurable by a balance). When the weight no longer increases over time, the fluoropolymer membrane is in a fully hydrated state. A fluoropolymer membrane in a fully hydrated state is often obtained by immersing the fluoropolymer membrane in deionized water at a temperature of 80°C for a period of 24 hours. As used herein, glass transition temperature refers to the lowest glass transition temperature of a fluorinated polymer. It is known that certain polymers or films made of polymers, respectively, such as The type of film 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 associated with strong interactions of functional groups such as sulfonic acid groups in such side chains. Once the first glass transition temperature has been reached, the film undergoes irreversible changes and is particularly no longer usable for electrolysis processes. Therefore, in the context of the present invention, if a material, in particular a film or a film sample, exhibits multiple glass transition temperatures, only the lowest glass transition temperature is relevant to the definition of glass transition temperature provided herein.

[0098] Fluoropolymer membranes having a glass transition temperature of at least 110°C allow electrolysis to be performed at higher temperatures and / or higher pressures because the fluoropolymer membranes are more resilient. Without wishing to be bound by theory, it is believed that the resilience to hydrogen bromide and hydrogen and bromine after electrolysis at higher temperatures and at higher pressures is imparted by fluoropolymer membranes having a glass transition temperature of at least 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 voltages. Higher current density helps to keep capital expenditures low, while lower operating voltages result in lower operating costs.

[0099] Preferably, the fluoropolymer of the membrane comprises -(CF2-CF2)- repeating units. Such -(CF2-CF2)- repeating units increase the resilience of the fluoropolymer membrane. The increased resilience allows the electrolysis of hydrogen bromide to be carried out at higher temperatures and higher pressures, which allows operation at higher current densities and / or at lower voltages, thereby making the electrolysis more economical. Furthermore, preferably, the fluoropolymer of the membrane does not contain structural entities of the formula -O-CF2-CF(CF3)-O-. Such structural entities are found in the membranes marketed under the trade name In commercial films sold, however, this may result in a film with lower rigidity. The film is thus more susceptible to degradation at higher temperatures and higher pressures.

[0100] Preferably, the fluoropolymer film, more specifically the fluoropolymer that the film comprises and preferably constitutes the film, comprises -CF3 chain ends. Such -CF3 chain ends can improve the resilience of the fluoropolymer film. The improved resilience can allow HBr electrolysis to be carried out at higher temperatures and under higher pressures, and can allow operation at higher current densities and / or at lower voltages, making the method according to the present invention more economical thus.

[0101] According to a particularly preferred embodiment of the present invention, the fluoropolymer of the membrane is a sulfonated fluoropolymer. As used herein, sulfonation means that the fluoropolymer of the fluoropolymer membrane carries -SO3H groups. Such -SO3H groups increase the proton conductivity of the fluoropolymer membrane, which allows the electrolysis to be operated at higher current densities and / or at lower voltages, thereby making the electrolysis more economical. It is particularly preferred that the sulfonated fluoropolymer comprises -O-(CF2) n -SO3H group, wherein n is an integer selected from 1, 2, 3, 4 and 5, preferably 2. Such -O-(CF2) nThe -SO3H group contributes to achieving an increased proton conductivity of the fluoropolymer membrane while at the same time increasing the resilience of the fluoropolymer membrane. A favorable balance between these effects is 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 believed that -O-(CF2) n The relatively short chain length of the -S03H 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 point of view of hydrogen bromide electrolysis at higher temperatures and / or at higher pressures and therefore at higher current densities and / or at lower voltages. Therefore, sulfonated fluoropolymer membranes make electrolysis particularly economical.

[0102] It is preferred that 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 resilience of the fluoropolymer membrane. Therefore, from the point of view of hydrogen bromide electrolysis at higher temperatures and / or at higher pressures and therefore at higher current densities and / or at lower voltages, the sulfonated fluoropolymer membrane is particularly advantageous. Therefore, the sulfonated fluoropolymer membrane makes electrolysis particularly economical.

[0103] It is further preferred that the fluoropolymer membrane has an acid capacity of at least 0.9meq / g, more preferably 0.95 to 1.5meq / g and most preferably 1.0 to 1.2meq / g. As used herein, meq / g refers to milliequivalents / gram, wherein equivalents are mol-H (i.e., the moles of H acid sites), preferably mol-SO3H (i.e., the moles of SO3H groups). The acid capacity represents the sum of the active sites or functional groups responsible for the proton exchange of the fluoropolymer membrane. Such acid capacity can improve proton conductivity, and can thus cause the conversion rate of hydrogen bromide in electrolysis to increase. The improved hydrogen bromide conversion rate reduces the need for separation and possible recycling of unconverted hydrogen, which can help to maintain low capital expenditures.

[0104] It is further preferred that the fluoropolymer membrane (in dry state) has a thickness of 25 to 350 μm, more preferably 40 to 150 μm, even more preferably 45 to 130 μm and most preferably 45 to 55 μm. Such thickness achieves a good balance between sufficient resilience on the one hand and low capital expenditure on the other hand. At lower thicknesses, there is a risk of undesired crossover of hydrogen / bromine through the fluoropolymer membrane, and at higher thicknesses, an undesirable reduction in proton conductivity may result.

[0105] In a further development of the inventive concept, it is proposed that the fluoropolymer film (in the dry state) has a viscosity of at least 1.70 g / cm 3 , more preferably at least 1.80 g / cm3 , and more preferably 1.80 to 2.00 g / cm 3 and most preferably 1.90 to 1.95 g / cm 3 The density of the fluoropolymer film can be measured on its sample according to ASTM D792-20. It is further preferred that the fluoropolymer film (in a dry state) has a tensile modulus of 100 to 500 MPa, more preferably 150 to 400 MPa, more preferably 200 to 300 MPa and most preferably 260 to 280 MPa. The tensile modulus of the fluoropolymer film can be measured on its sample according to ASTM D638-14. In addition, it is preferred that the fluoropolymer film (in a dry state) has a tensile stress at break in the longitudinal direction (MD) according to ASTM D882-18 of 10 to 70 MPa, more preferably 20 to 60 MPa, more preferably 30 to 50 MPa and most preferably 35 to 45 MPa. In addition, it is preferred that the fluoropolymer film (in a dry state) has a tensile stress at break according to ASTM D882-18 in the transverse direction (CD) of 5 to 60 MPa, more preferably 10 to 50 MPa, even more preferably 20 to 40 MPa and most preferably 25 to 35 MPa. In addition, it is preferred that the fluoropolymer film (in a dry state) has an elongation at break according to ASTM D882-18 in the longitudinal direction (MD) of 100 to 200%, more preferably 120 to 180%, even more preferably 140 to 160% and most preferably 145 to 155%. Similarly, it is preferred that the fluoropolymer film (in a dry state) has an elongation at break according to ASTM D882-18 in the transverse direction (CD) of 100 to 350%, more preferably 120 to 300%, even more preferably 150 to 250% and most preferably 190 to 210%. The aforementioned properties improve the resilience of the fluoropolymer film. The increased resilience allows the hydrogen bromide electrolysis to be carried out at higher temperatures and at higher pressures. This can allow operation at higher current densities and / or at lower voltages, thereby making the electrolysis of step d) more economical.

[0106] According to a second aspect, the present invention relates to an apparatus for producing hydrogen, comprising:

[0107] a) a reactor comprising one or more inlet lines and an outlet line for the effluent of the reaction mixture,

[0108] b) a vessel comprising an inlet line connected to an outlet line for a reaction mixture effluent, wherein the vessel further comprises an outlet line for a gaseous portion of the reaction mixture effluent of the vessel and an outlet line for a liquid portion of the reaction mixture effluent of the vessel, wherein the outlet line for the gaseous portion of the reaction mixture effluent is directly or indirectly connected to the inlet line of the reactor,

[0109] c) a first distillation column comprising an inlet line connected to an outlet line for a liquid portion of the effluent of the reaction mixture, wherein the first distillation column comprises an overhead outlet line for a gaseous composition enriched in hydrogen bromide and a bottom outlet line for a composition enriched in sulfuric acid,

[0110] d1) an electrolyzer comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode, and an inlet line for a composition containing hydrogen bromide, an outlet line for hydrogen and an outlet line for a composition containing bromine, wherein the inlet line of the electrolyzer is connected to the outlet line of the first distillation column for a composition enriched in hydrogen bromide i) directly, or ii) via a condenser arranged therebetween, the condenser comprising an inlet line connected to the top outlet line of the first distillation column for a gas composition enriched in hydrogen bromide and comprising an outlet line connected to the inlet line for the composition containing hydrogen bromide of the electrolyzer, or iii) via a container arranged therebetween, the container comprising an inlet line connected to the top outlet line of the first distillation column for a gas composition enriched in hydrogen bromide, comprising a liquid outlet line and comprising a gas outlet line, wherein the gas outlet line is connected to the inlet line of the electrolyzer, and wherein the outlet line of the electrolyzer for the composition containing bromine is connected directly or indirectly to the inlet line of the reactor, or

[0111] d2) Thermal oxidizer, or

[0112] d3) an ex situ conversion unit for converting at least a portion of the hydrogen bromide contained in the composition enriched in hydrogen bromide into bromine,

[0113] e) a second distillation column comprising an inlet line connected to the bottom outlet line of the first distillation column for a composition enriched in sulfuric acid, wherein the second distillation column comprises a top outlet line for a composition enriched in hydrogen bromide and a bottom outlet line for a composition enriched in sulfuric acid, and

[0114] f) optionally, a third distillation column comprising an inlet line connected to the bottom outlet line of the second distillation column for a composition enriched in sulfuric acid, wherein the third distillation column comprises an overhead outlet line for a composition enriched in water and a bottom outlet line for a sulfuric acid product composition,

[0115] in

[0116] a) the electrolyzer or the thermal oxidizer is connected to the outlet line of the first distillation column for the composition enriched in hydrogen bromide via a condenser arranged therebetween, the condenser comprising an inlet line connected to the top outlet line of the gaseous composition enriched in hydrogen bromide of the first distillation column and comprising an outlet line connected to the inlet line of the composition containing hydrogen bromide of the electrolyzer or the thermal oxidizer,

[0117] and / or

[0118] β) The apparatus further comprises a recycle line introduced from a bottom outlet line of the second distillation column and / or from a bottom outlet line of the third distillation column to the inlet of the first distillation column.

[0119] The vessel b) can also be a stripping column, an absorption column, an extraction column or a distillation column.

[0120] Furthermore, it is preferred that the apparatus further comprises a scrubbing column comprising an inlet line connected to the outlet line of the vessel for the gaseous portion of the reaction mixture effluent, wherein preferably, the top outlet line of the second distillation column is connected to the outlet line of the vessel for the gaseous portion of the reaction mixture effluent, wherein the scrubbing column further comprises an inlet line for water, an outlet line for a gaseous composition containing less than 10 ppm of bromine and hydrogen bromide in total, and an outlet line for an aqueous composition containing 5 to 40% by weight of hydrogen bromide. Preferably, the inlet line for water of the scrubbing column is combined upstream of the scrubbing column with a recycle line from the top outlet line of the third distillation column for water produced as a top composition in the third distillation column.

[0121] Specific embodiments according to the present invention are described below by way of examples with reference to the accompanying drawings.

[0122] Figure 1 is a schematic diagram of an apparatus for removing at least one sulfur-containing compound from a gas containing at least one sulfur-containing compound using gas phase electrolysis according to one embodiment of the present invention.

[0123] Figure 2 is a schematic diagram of an apparatus for removing at least one sulfur-containing compound from a gas containing at least one sulfur-containing compound using gas-phase electrolysis according to another embodiment of the present invention.

[0124] Figure 3 is a schematic diagram of an apparatus for removing at least one sulfur-containing compound from a gas containing at least one sulfur-containing compound using liquid phase electrolysis according to one embodiment of the present invention.

[0125] Figure 4 is a schematic diagram of an apparatus for removing at least one sulfur-containing compound from a gas containing at least one sulfur-containing compound using liquid phase electrolysis according to another embodiment of the present invention.

[0126] Figure 5 is a schematic diagram of an apparatus for removing at least one sulfur-containing compound from a gas containing at least one sulfur-containing compound using a thermal oxidizer according to another embodiment of the present invention.

[0127] Figure 6is a schematic diagram of an apparatus for removing at least one sulfur-containing compound from a gas containing the at least one sulfur-containing compound using an off-site unit for recovering bromine using a thermal oxidizer according to one embodiment of the present invention.

[0128] Using gas phase electrolysis as a treatment for step d) Figure 1 The apparatus 10 shown in FIG. 1 comprises a reactor 12, a separation vessel 14, three distillation columns, namely a first distillation column 16, a second distillation column 18 and a third distillation column 20, and an electrolyzer 22. The reactor 12 comprises an inlet line 24 for natural gas, an inlet connected to a recycle line for a composition containing bromine, hydrogen bromide and water, an inlet connected to a recycle line 28 for a liquid portion of a reaction mixture effluent, and an outlet line 30 for the reaction mixture effluent. The outlet line 30 for the reaction mixture (from which the recycle line 28 branches off) leads to the vessel 14, which is further connected to an outlet line 32 for a gaseous portion of the reaction mixture effluent and an outlet line 34 for a liquid portion of the reaction mixture effluent. The outlet line 34 for the liquid portion of the reaction mixture effluent leads through a throttling valve 36, then combines with a recycle line 38 for a composition enriched in sulfuric acid and then leads to the inlet of the first distillation column 16. The first distillation column 16 comprises an overhead outlet line 40 and a bottom outlet line 42, which lead to the inlet of the second distillation column 18. Likewise, the second distillation column 18 comprises an overhead outlet line 44 and a bottom outlet line 46, which lead to the inlet of the third distillation column 20. Furthermore, the third distillation column comprises an overhead outlet line 48 and a bottom outlet line 50, which split into a recycle line 38 for the composition enriched with sulfuric acid and a sulfuric acid product outlet line 52.

[0129] The top outlet line 40 of the first distillation column 16 leads to a vessel 54, which is further connected to an outlet line 56 for liquid and to an outlet line 58 for gas. The outlet line 58 for gas leads to the electrolyzer 22, which further comprises an outlet line 60 for the bromine-containing composition and an outlet line 62 for hydrogen. The apparatus 10 further comprises a scrubbing column 64, which is connected to the outlet line 32 for the gaseous portion of the effluent of the reaction mixture, which is combined upstream of the scrubbing column 64 with the top outlet line 44 of the second distillation column 18. The scrubbing column 64 further comprises an inlet line 66 for water, which is combined upstream of the scrubbing column 64 with a recycle line 68 for the water produced as the top composition in the third distillation column 20. More specifically, the top outlet line 48 of the third distillation column 20 leads to a vessel 70, a liquid recycle line 72 leads from the vessel 70 back to the third distillation column 20, and a gas line 71 leads to a compressor 74, from the compressor 74 to a heat exchanger 76 and from the heat exchanger 76 to another vessel 78. The vessel 78 is connected to a gas outlet line 80 and a recycle line 68 for liquid water. The scrubber 64 is further connected to an outlet line 81 for a gas composition containing less than 10 ppm of bromine and hydrogen bromide in total and an outlet line 82 for an aqueous composition containing 5 to 40 wt.% hydrogen bromide. When the outlet line 81 leads to a vessel 84 containing a gas outlet line 86 and a recycle line 88 leading to the water inlet line 66 of the scrubber 64, the outlet line 82 of the scrubber 64 is combined with the outlet line 60 for the bromine-containing composition into a recycle line 26 leading to the reactor 12.

[0130] During operation of the apparatus 10, natural gas containing hydrogen sulfide as a sulfur-containing compound is fed via an inlet line 24, and a composition containing bromine, hydrogen bromide and water is fed into the reactor 12 via a recycle line 26 to form a starting stream therein, which reacts in the reactor 12 to form a reaction mixture effluent containing sulfuric acid, hydrogen bromide, unreacted bromine and water, and methane, ethane and carbon dioxide derived from the natural gas. The reaction mixture effluent is withdrawn from the reactor 12 via an outlet line 30, a portion of which is recycled to the reactor 12 via a line 28, and the remaining portion is fed into a separation vessel 14. The reaction mixture effluent is separated in the separation vessel 14 into a gaseous portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent. When the gaseous portion of the reaction mixture effluent leaves the separation vessel 14 via an outlet line 32, the liquid portion of the reaction mixture effluent leaves the separation vessel 14 via an outlet line 34. Prior to entering the first distillation column 16, the liquid portion of the reaction mixture effluent is combined with a composition enriched in sulfuric acid derived from a bottoms outlet line 50 of the third distillation column 20 and directed to line 34 via a recycle line 38 to increase the sulfuric acid concentration in the liquid portion of the reaction mixture effluent to a level high enough to break the hydrogen bromide-water azeotrope therein, thereby allowing efficient separation of hydrogen bromide in the vapor phase and water in the liquid phase in the first distillation column 16. The bottoms composition enriched in water and sulfuric acid produced in the first distillation column 16 is withdrawn from the first distillation column 16 via a bottoms outlet line 42 and introduced into the second distillation column 18, where the bottoms composition enriched in water and sulfuric acid of the first distillation column 16 is separated into a water-enriched overhead composition and a sulfuric acid-enriched bottoms composition. The bottom composition thus produced, enriched in sulfuric acid, is withdrawn from the second distillation column 20 via the bottom outlet line 46 and subsequently fed to the third distillation column 20 and separated therein into a pure water top composition comprising more than 99.9% by weight of water and a concentrated sulfuric acid bottom composition comprising at least 95% by weight of sulfuric acid. The concentrated sulfuric acid bottom composition thus produced is withdrawn from the third distillation column 20 via the outlet line 50. While a portion of the concentrated sulfuric acid composition is recycled into the liquid portion of the reaction mixture effluent directed through the line 34 via the recycle line 38, the remaining portion of the concentrated sulfuric acid composition is withdrawn from the apparatus 12 via the sulfuric acid product outlet line 52.

[0131] The composition enriched in hydrogen bromide obtained as the overhead composition in the first distillation column 16 is fed via the overhead outlet line 40 of the first distillation column 16 to a vessel 54 where the composition enriched in hydrogen bromide is partially condensed and thereby separated into a water-enriched liquid composition withdrawn from the vessel via a liquid outlet line 56 and a hydrogen bromide-enriched, water-depleted gas composition containing less than 1% by weight of water withdrawn from the vessel via an outlet line 58. While the gaseous portion of the composition enriched in hydrogen bromide is fed via line 58 to the electrolysis cell 22 to be carried out therein in step d), the liquid portion of the composition enriched in hydrogen bromide is not subjected to any electrolysis and thereby bypasses the electrolysis cell 22 and is directed to the recycle line 26. Optionally, a portion of the water-enriched liquid composition leaving the vessel 54 is fed back to the top of the distillation column 16 as a liquid reflux. The composition enriched in hydrogen bromide is electrolyzed in the electrolysis cell 22 into hydrogen and a bromine-containing composition. While hydrogen is withdrawn from electrolyzer 22 via outlet line 62 and removed from the plant as a product, a bromine-containing composition is withdrawn from electrolyzer 22 via outlet line 60 and combined with an aqueous composition obtained as a bottom composition in scrubber 64. The combined stream thus obtained is directed to reactor 12 via recycle line 26, to which the liquid portion of the composition enriched in hydrogen bromide obtained in vessel 54, bypassing electrolyzer 22, is directed via line 56.

[0132] The gaseous portion of the reaction mixture effluent leaving the separation vessel 14 via the outlet line 32 is subjected to a scrubbing step with water in the scrubbing tower 64 to obtain a gaseous composition containing less than 10 ppm of bromine and hydrogen bromide in total, which is withdrawn from the scrubbing tower 64 via the gas outlet line 81, and an aqueous composition containing 5 to 40% by weight of hydrogen bromide, which is withdrawn from the scrubbing tower 64 via the liquid outlet line 82 and subsequently combined with the bromine-containing composition leaving the electrolyzer via the outlet line 60.

[0133] The top composition of the third distillation tower 20 taken out from the third distillation tower 20 via the outlet line 48 is degassed in the container 78, and the degassed pure water thus obtained is guided through the line 68 and combined with the water inlet line 66 leading to the scrubbing tower 64. Finally, the gas from which the sulfur-containing compounds are removed is taken out of the apparatus via the gas outlet line 86.

[0134] Figure 2 The device 10 shown in FIG. Figure 1 , except that the liquid portion of the reaction mixture effluent withdrawn from vessel 14 via outlet line 34 is not combined with the composition enriched in sulfuric acid obtained as a bottoms composition in third distillation column 20, but is combined with the composition enriched in sulfuric acid obtained as a bottoms composition in second distillation column 18 and directed to line 34 via recycle line 38.

[0135] and Figure 1 and Figure 2 The devices shown in 10 are different, Figure 3 The apparatus 10 shown in FIG. 1 uses liquid phase electrolysis. Figure 3 The device 10 shown in FIG. Figure 1 The apparatus shown in FIG. 1 differs in that the top outlet line 40 of the first distillation column 40 is not directed to the vessel 54 and is not separated therein into a liquid composition enriched in water and a gaseous composition enriched in hydrogen bromide and depleted in water. Instead, the top outlet line 40 of the first distillation column 40 is directed to a condenser 90 in which the top composition obtained in the first distillation column 16, which contains up to about 50% by weight of hydrogen bromide and up to 50% by weight of water, is condensed into a liquid. A portion of the liquid thus obtained is subsequently fed to the electrolysis cell 22 via the line 58, while the remainder of the liquid is directed via the bypass line 92 to the outlet line of the aqueous composition of the scrubbing column 64. Figure 1 Another difference of the device 10 shown in FIG. 1 is that Figure 3 The overhead outlet line 44 of the second distillation column 18 of the apparatus 10 shown in FIG. 1 is not combined with the line 32 for the gaseous portion of the effluent of the reaction mixture. Instead, Figure 3 The top outlet line 44 of the second distillation column 18 of the apparatus 10 shown in FIG. 1 is directed to a condenser 94, in which the water-enriched top composition obtained in the second distillation column 18 is condensed into a liquid, which is then directed via a liquid line 96 to a water inlet line 66 of a scrubbing column 64. Figure 1 Still another difference of the apparatus 10 shown in FIG. 1 is that the liquid portion obtained in the vessel 70 from the overhead composition withdrawn from the third distillation column 20 via the line 48 is not recycled to the third distillation column via the liquid recycle line 72. Instead, the liquid portion obtained in the vessel 70 from the overhead composition of the third distillation column 20 is conducted via the liquid line 98 and combined with the liquid portion of the water obtained in the vessel 78, wherein the pure water mixture thus obtained is directed via the recycle line 68 to the water inlet line 66 of the scrubbing column 64. Figure 1 In yet another difference of the apparatus 10 shown in , the gas composition obtained in the scrubbing tower 64 is not directed to the container 84. Instead, the gas composition obtained via line 81 and leaving the scrubbing tower 64 is withdrawn from the apparatus 10 via line 81.

[0136] Figure 4 The device 10 shown in FIG. Figure 31, except that the liquid portion of the reaction mixture effluent withdrawn from vessel 14 via outlet line 34 is not combined with the composition enriched in sulfuric acid obtained as a bottoms composition in third distillation column 20, but is combined with the composition enriched in sulfuric acid obtained as a bottoms composition in second distillation column 18 and directed to line 34 via recycle line 38.

[0137] Figure 5 The device 10 shown in FIG. Figure 1 The apparatus shown in is identical to that shown in , except that the treatment in step d) is not carried out as an electrolysis, but as a thermal oxidation. Thus, Figure 5 The plant 10 does not comprise an electrolytic cell 22, but rather it comprises a thermal oxidizer 100 connected to a line 82 for an aqueous phase from a scrubber 64, to a line 58 for a gaseous composition enriched in hydrogen bromide from a vessel 54, to an inlet line 102 for oxygen or air, to an outlet line 60 for a bromine-containing composition and to an exhaust gas outlet line 104. During operation of the plant 10, the composition enriched in hydrogen bromide from the vessel 54, the aqueous phase from the scrubber 64 and the air or oxygen react in the thermal oxidizer 100 to form a composition containing bromine and water, which is withdrawn from the thermal oxidizer 100 via the outlet line 60 and recycled to the reactor 12 via the recycle line 26. Figure 5 In the embodiment shown in FIG. 1 , the recycle line 38 leads from the bottom outlet line 50 of the third distillation column 20 to the outlet line 34 of the liquid portion of the reaction mixture effluent. However, alternatively, the recycle line 38 may lead from the bottom outlet line 46 of the second distillation column 18 to the outlet line 34 of the liquid portion of the reaction mixture effluent.

[0138] Figure 6 The device 10 shown in FIG. Figure 3 The apparatus shown in FIG. 1 is identical to that shown in FIG. 2 , except that the treatment in step d) is not carried out in the apparatus but in an external unit (such as, for example, an external electrolyzer). Thus, Figure 6 The plant 10 does not include an electrolytic cell 22. Instead, a line 58 for the condensed hydrogen bromide-enriched composition withdrawn from the first distillation column 16 as an overhead composition via line 40 leads to an external electrolytic cell, from which a line 60 for a bromine-containing composition returns to the plant 10 and leads to a recycle line 26. Figure 3 In another difference of the apparatus 10 shown in , the bypass line 92 leads to the recycle line 26 , and the outlet line 82 of the scrubber 26 also leads to the recycle line 26 .

[0139] Reference numerals list

[0140] 10. Equipment

[0141] 12 Reactor

[0142] 14 Separation Container

[0143] 16. First Distillation Column

[0144] 18 Second distillation tower

[0145] 20Third distillation tower

[0146] 22 Electrolyzer

[0147] 24 Inlet pipeline for natural gas

[0148] 26 Recycle line for a composition containing bromine, hydrogen bromide and water

[0149] 28 Recirculation line for the liquid portion of the effluent from the reaction mixture

[0150] 30 outlet pipeline for the outflow of the reaction mixture

[0151] 32 Outlet line for the gaseous portion of the effluent from the reaction mixture

[0152] 34 Outlet line for the liquid portion of the reaction mixture effluent

[0153] 36 throttle valve

[0154] 38 Recirculation line for composition enriched in sulfuric acid

[0155] 40Top outlet pipeline of the first distillation tower

[0156] 42 Bottom outlet pipeline of the first distillation tower

[0157] 44 The top outlet pipeline of the second distillation tower

[0158] 46 Bottom outlet pipeline of the second distillation tower

[0159] 48 The top outlet pipeline of the third distillation tower

[0160] 50 The bottom outlet pipeline of the third distillation tower

[0161] 52 Export pipeline for sulfuric acid product

[0162] 54 Container

[0163] 56 Liquid outlet pipeline

[0164] 58 Export pipeline

[0165] 60 Export pipeline for bromine-containing composition

[0166] 62 Export pipeline for hydrogen

[0167] 64 Scrubber

[0168] 66 Inlet line for water

[0169] 68 Recirculation line for water

[0170] 70 Containers

[0171] 71 Gas pipeline

[0172] 72 Liquid recirculation line

[0173] 74 Compressor

[0174] 76 Heat Exchanger

[0175] 78 Container

[0176] 80 Gas outlet pipeline

[0177] 81 Export pipeline for gas composition

[0178] 82 Outlet line for aqueous composition

[0179] 84 Container

[0180] 86 Gas export pipeline

[0181] 88 Recirculation line

[0182] 90 Condenser

[0183] 92 Bypass line

[0184] 94 Condenser

[0185] 96 Liquid pipeline

[0186] 98 Liquid pipeline

[0187] 100 Thermal Oxidizer

[0188] 102 Inlet line for air / oxygen

[0189] 104 Exhaust gas outlet pipeline

Claims

1. A method for removing at least one sulfur-containing compound from a gas containing at least one sulfur-containing compound, wherein the method comprises the following steps: a) contacting a gas stream containing at least one sulfur-containing compound with a stream containing bromine and water to obtain a starting stream, b) reacting the starting stream provided in step a) to produce a reaction mixture effluent comprising sulfuric acid and hydrogen bromide, c) separating the reaction mixture effluent obtained in step b) into one or more compositions enriched in hydrogen bromide and one or more compositions enriched in sulfuric acid, d) subjecting at least a portion of the at least one composition enriched in hydrogen bromide obtained in step c) to a treatment in which at least a portion of the composition enriched in hydrogen bromide is converted into bromine, e) recycling at least a portion of the bromine-containing composition obtained in step d) back to step a), and f) removing a gas depleted in at least one sulphur-containing compound, wherein step c) comprises at least one distillation step, wherein in the case where the reaction mixture is a single-phase liquid composition, the reaction mixture effluent or a mixture of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) is subjected as feed to a first distillation step, or in the case where the reaction mixture effluent is a two-phase gas / liquid composition, the two-phase gas / liquid composition is first separated into a gaseous portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent, and then the liquid portion of the reaction mixture effluent or a mixture of the liquid portion of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) is subjected as feed to a first distillation step, wherein the feed is separated in the first distillation step into a gaseous overhead composition of a composition enriched in hydrogen bromide containing up to 1,000 ppm of sulfuric acid and a liquid bottom composition of a composition enriched in sulfuric acid containing more than 30% by weight of sulfuric acid and less than 1,000 ppm of hydrogen bromide, wherein a) subjecting at least a portion of the gas composition enriched in hydrogen bromide obtained as an overhead composition in the first distillation step to a water removal step in order to separate the composition enriched in hydrogen bromide into a composition enriched in water and a gas composition enriched in hydrogen bromide, depleted in water, comprising 90 to 99% by weight of hydrogen bromide and less than 10% by weight of water, wherein at least a portion of the gas composition enriched in hydrogen bromide, depleted in water is subjected in step d) to an electrolysis or thermal oxidation step, and / or β) Step c) comprises at least two distillation steps, wherein the composition enriched in sulfuric acid obtained as the liquid bottoms composition of the first distillation step is subjected to a second distillation step to produce an overhead composition and a bottoms composition containing 60 to 95% by weight of sulfuric acid and 5 to 40% by weight of water, based on the total weight of the bottoms composition, wherein preferably at least a portion of the bottoms composition of the second distillation step is subjected to a third distillation step to produce an overhead composition containing at least 99.0% by weight of water and less than 10 ppm of hydrogen bromide and a bottoms composition containing at least 90% by weight of sulfuric acid and less than 10% by weight of water, based on the total weight of the bottoms composition, wherein a portion of the bottoms composition obtained in the second distillation step and / or a portion of the bottoms composition obtained in the third distillation step is recycled to the reaction mixture effluent or the liquid part of the reaction mixture effluent and mixed therewith as a composition enriched in sulfuric acid to obtain a mixture containing at least 35% by weight of sulfuric acid, based on the total weight of the mixture, wherein this mixture is subjected to the first distillation step as feed.

2. according to the method for claim 1, the sulfur-containing compound contained in the gas is selected from sulfur, sulfur dioxide, sulfide, disulfide, thiophene, mercaptan and any combination of two or more of the foregoing compounds, and is more preferably selected from hydrogen sulfide, sulfur, sulfur dioxide, carbon disulfide, carbonyl sulfide, methyl mercaptan, organic sulfide and any combination of two or more of the foregoing compounds.

3. The process according to claim 1 or 2, wherein the starting stream provided in step a) further contains hydrogen bromide, and wherein the process further comprises a step of recycling at least a portion of the hydrogen bromide contained in one of the one or more compositions enriched in hydrogen bromide produced in step c) to step a), wherein the recycled hydrogen bromide is not subjected to the treatment of step d).

4. according to any one of the preceding claims method, wherein in step a), the gas containing the sulfur-containing compounds is mixed with bromine, hydrogen bromide and water, wherein the gas containing the sulfur-containing compounds is preferably selected from biogas, natural gas, flue gas, from the combustion gas of the sulfur compounds, tail gas and any combination of two or more of the aforementioned gases.

5. The process according to claim 1 , wherein if the starting stream is a gas-liquid mixture at the reaction temperature and the reaction pressure, the starting stream comprises at least 5% by weight, preferably 11 to 46% by weight and more preferably 12 to 46% by weight of hydrogen bromide, at least 1% by weight and preferably 2 to 35% by weight of bromine and 40 to 75% by weight of water, based on the total weight of water, bromine and hydrogen bromide in the liquid phase of the starting stream, and wherein if the starting stream is a liquid at the reaction temperature and the reaction pressure, the starting stream comprises at least 5% by weight, preferably 11 to 46% by weight and more preferably 12 to 46% by weight of hydrogen bromide, at least 1% by weight and preferably 2 to 35% by weight of bromine and 30 to 75% by weight of water, based on the total weight of the starting stream.

6. A process according to any one of the preceding claims, wherein the reaction mixture effluent is a gas-liquid mixture and in step c) is fed to a vessel and allowed to phase separate therein, or is subjected to at least one separation step selected from a stripping step, an absorption step, an extraction step and any combination of two or more of the preceding separation steps, to separate the reaction mixture effluent into a gaseous portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent, wherein the liquid portion of the reaction mixture effluent comprises at least 20% by weight and preferably from 25 to 50% by weight of hydrogen bromide relative to the water content of the liquid portion of the reaction mixture effluent, and wherein the liquid portion of the reaction mixture effluent comprises at least 0.1% by weight and preferably from 0.3 to 15% by weight of sulfuric acid, 20 to 70% by weight and preferably from 25 to 65% by weight of water and at most 2% by weight and preferably at most 0.5% by weight of bromine, based on the total weight of the liquid portion of the reaction mixture effluent.

7. The process according to any one of the preceding claims, wherein the treatment of step d) is electrolysis, thermal oxidation or another conversion step carried out ex situ which converts at least part of the hydrogen bromide contained in the composition enriched in hydrogen bromide into bromine.

8. The process according to any one of the preceding claims, wherein the reaction mixture effluent is fed in step c) into a container and allowed to phase separate therein or is subjected to at least one separation step selected from a stripping step, an absorption step, an extraction step and any combination of two or more of the preceding separation steps to separate the reaction mixture effluent into a gaseous portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent, and then the liquid portion of the reaction mixture effluent or a mixture of the liquid portion of the reaction mixture effluent and the sulfuric acid-enriched composition obtained in step c) is subjected as feed to a first distillation step.

9. The process according to claim 8, wherein at least a portion of the gas composition enriched in hydrogen bromide obtained as the overhead composition in the first distillation step is i) condensed and subjected to electrolysis in step d), or ii) subjected to a water removal step a) to separate the composition enriched in hydrogen bromide into a composition enriched in water and a gas composition enriched in hydrogen bromide, depleted in water, comprising 90 to 99% by weight of hydrogen bromide and less than 10% by weight and preferably less than 1% by weight of water, wherein at least a portion of the gas composition enriched in hydrogen bromide, depleted in water is subjected to electrolysis in step d) and ... or iii) directed to an off-site unit preferably comprising a thermal oxidation unit or an electrolytic cell for the electrolysis of hydrogen bromide, wherein at least a portion of the composition enriched in hydrogen bromide is converted into a bromine-containing composition by converting at least a portion of the hydrogen bromide into bromine, before at least a portion of the bromine-containing composition produced is recycled in step e) to step a).

10. The process according to any one of claims 8 or 9, wherein the composition enriched in sulfuric acid obtained as the liquid bottoms composition of the first distillation step is subjected to a second distillation step to produce an overhead composition and a bottoms composition containing 60 to 95% by weight and preferably 70 to 80% by weight of sulfuric acid and 5 to 40% by weight and preferably 20 to 30% by weight of water, based on the total weight of the bottoms composition, wherein preferably at least a portion of the bottoms composition of the second distillation step is subjected to a third distillation step to produce an overhead composition containing at least 99.0% by weight, more preferably at least 99.5% by weight and even more preferably at least 99.9% by weight of water and less than 10 ppm, preferably less than 5 ppm and more preferably less than 1 ppm. % and preferably less than 6% by weight of water, wherein preferably a portion of the bottoms composition obtained in the second distillation step and / or a portion of the bottoms composition obtained in the third distillation step is recycled to the reaction mixture effluent or the liquid part of the reaction mixture effluent and mixed therewith as a composition enriched in sulfuric acid to obtain a mixture containing at least 35% by weight and preferably from 50 to 70% by weight of sulfuric acid, based on the total weight of the mixture, and the mixture is subjected to the first distillation step as feed.

11. A method according to any one of the preceding claims, comprising: i) feeding the reaction mixture effluent from step c) as a two-phase gas / liquid composition into a vessel and allowing it to phase separate therein, to separate the reaction mixture effluent into a gaseous portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent, ii) subjecting the mixture of the liquid portion of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) as feed to a first distillation step in order to separate the feed into an overhead composition and a bottom composition of a composition enriched in hydrogen bromide, wherein the feed preferably contains at least 53% by weight of sulfuric acid relative to the water concentration, iii) subjecting at least a portion of the composition enriched in hydrogen bromide obtained as the overhead composition in the first distillation step to a water removal step in order to separate the composition enriched in hydrogen bromide into a composition enriched in water and a gas composition enriched in hydrogen bromide, depleted in water, comprising 90 to 99% by weight of hydrogen bromide and less than 10% by weight and preferably less than 1% by weight of water, and subjecting at least a portion of the gas composition enriched in hydrogen bromide, depleted in water to electrolysis or thermal oxidation in step d), iv) subjecting the composition enriched in sulfuric acid obtained as the bottom composition of the first distillation step to a second distillation step to produce an overhead composition and a bottom composition containing 60 to 95% by weight and preferably 70 to 80% by weight of sulfuric acid and 5 to 40% by weight and preferably 20 to 30% by weight of water, based on the total weight of the bottom composition, wherein preferably at least a portion of the bottom composition of the second distillation step is subjected to a third distillation step to produce an overhead composition and a bottom composition containing at least 90% by weight and preferably at least 94% by weight of sulfuric acid and less than 10% by weight and preferably less than 6% by weight of water, based on the total weight of the bottom composition, v) recycling a portion of the bottom composition obtained in the second distillation step and / or a portion of the bottom composition obtained in the third distillation step as a composition enriched in sulphuric acid to and mixing it with the liquid part of the reaction mixture effluent to produce a mixture of the liquid part of the reaction mixture effluent and the composition enriched in sulphuric acid used in step ii), vi) recycling at least a portion of the bromine-containing composition obtained in the electrolysis to step a), and vii) optionally, recycling the gaseous portion of the reaction mixture effluent or the mixture of the gaseous portion of the reaction mixture effluent and the overhead composition of the second distillation step to step a) or subjecting the gaseous portion of the reaction mixture effluent or the mixture of the gaseous portion of the reaction mixture effluent and the overhead composition of the second distillation step to a scrubbing step with water to obtain a gaseous composition containing less than 10 ppm of bromine and hydrogen bromide in total and a liquid aqueous composition containing 5 to 40% by weight of hydrogen bromide, wherein the liquid aqueous composition is recycled to step a).

12. A method according to any one of claims 1 to 11, comprising: i) feeding the reaction mixture effluent in step c) into a container and allowing it to phase separate therein to separate the reaction mixture effluent into a gaseous portion of the reaction mixture effluent and a liquid portion of the reaction mixture effluent, ii) subjecting the liquid portion of the reaction mixture effluent or a mixture of the liquid portion of the reaction mixture effluent and the composition enriched in sulfuric acid obtained in step c) as feed to a first distillation step to separate the feed into an overhead composition of a composition enriched in hydrogen bromide containing at most 1,000 ppm of sulfuric acid and a bottom composition of a composition enriched in sulfuric acid containing more than 30% by weight of sulfuric acid and less than 1,000 ppm of hydrogen bromide, iii) condensing at least a portion of the composition enriched in hydrogen bromide obtained as an overhead composition in the first distillation step and subjecting at least a portion of the condensed portion to electrolysis in step d), iv) subjecting the composition enriched in sulfuric acid obtained as the bottom composition of the first distillation step to a second distillation step to produce an overhead composition and a bottom composition containing 60 to 95% by weight and preferably 70 to 80% by weight of sulfuric acid and 5 to 40% by weight and preferably 20 to 30% by weight of water, based on the total weight of the bottom composition, wherein preferably at least a portion of the bottom composition of the second distillation step is subjected to a third distillation step to produce an overhead composition and a bottom composition containing at least 90% by weight and preferably at least 94% by weight of sulfuric acid and less than 10% by weight and preferably less than 6% by weight of water, based on the total weight of the bottom composition, v) recycling a portion of the bottom composition obtained in the second distillation step and / or a portion of the bottom composition obtained in the third distillation step as a composition enriched in sulphuric acid to the liquid part of the reaction mixture effluent and mixing it therewith to produce a mixture of the liquid part of the reaction mixture effluent and the composition enriched in sulphuric acid used in step ii), vi) recycling at least a portion of the bromine-containing composition obtained in the electrolysis to step a), vii) optionally, recycling the gaseous portion of the reaction mixture effluent to step a) or subjecting the gaseous portion of the reaction mixture effluent to a scrubbing step with water to obtain a gaseous composition containing less than 10 ppm of bromine and hydrogen bromide in total and a liquid aqueous composition containing from 5 to 40% by weight of hydrogen bromide, wherein the liquid aqueous composition is recycled to step a), and viii) Optionally, a portion of the condensed fraction of the composition enriched in hydrogen bromide obtained in step iii) is recycled to step a) without subjecting it to the electrolysis in step d).

13. The process according to any one of the preceding claims, wherein in step d), the electrolysis is carried out by using an electrolysis cell comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode, wherein the composition enriched in hydrogen bromide containing up to 1,000 ppm of sulfuric acid obtained in step c) is fed to the anode, optionally a second composition comprising hydrogen bromide and water is fed to the cathode, and the electrolysis cell is operated to produce hydrogen at the cathode, wherein a bromine-containing composition is produced at the anode, wherein the membrane is made of a fluoropolymer having a glass transition temperature of at least 110°C.

14. The process according to claim 13, wherein the electrolysis cell is operated at an operating temperature of at least 70°C and preferably at an operating temperature of 70°C to 122°C, wherein preferably the electrolysis cell is operated at an operating pressure that increases from the anode to the cathode.

15. An apparatus for producing hydrogen, comprising: a) a reactor comprising one or more inlet lines and an outlet line for the effluent of the reaction mixture, b) a vessel comprising an inlet line connected to an outlet line for an effluent of the reaction mixture, wherein the vessel further comprises an outlet line for a gaseous portion of the effluent of the reaction mixture and an outlet line for a liquid portion of the effluent of the reaction mixture, wherein the outlet line for the gaseous portion of the effluent of the reaction mixture is directly or indirectly connected to the inlet line of the reactor, c) a first distillation column comprising an inlet line connected to an outlet line for a liquid portion of the reaction mixture effluent from the vessel, wherein the first distillation column comprises an overhead outlet line for a gaseous composition enriched in hydrogen bromide and a bottom outlet line for a composition enriched in sulfuric acid, d1) an electrolyzer comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode, and an inlet line for a composition containing hydrogen bromide, an outlet line for hydrogen and an outlet line for a composition containing bromine, wherein the inlet line of the electrolyzer is connected to the outlet line of the first distillation column for a composition enriched in hydrogen bromide i) directly, or ii) via a condenser arranged therebetween, the condenser comprising an inlet line connected to the top outlet line of the first distillation column for a gas composition enriched in hydrogen bromide and comprising an outlet line connected to the inlet line of the electrolyzer containing a composition containing hydrogen bromide, or iii) via a container arranged therebetween, the container comprising an inlet line connected to the top outlet line of the first distillation column for a gas composition enriched in hydrogen bromide, comprising a liquid outlet line and comprising a gas outlet line, wherein the gas outlet line is connected to the inlet line of the electrolyzer, and wherein the outlet line of the electrolyzer for a composition containing bromine is connected directly or indirectly to the inlet line of the reactor, or d2) Thermal oxidizer, or d3) an ex situ conversion unit for converting at least a portion of the hydrogen bromide contained in the composition enriched in hydrogen bromide into bromine, e) a second distillation column comprising an inlet line connected to the bottom outlet line of the first distillation column for a composition enriched in sulfuric acid, wherein the second distillation column comprises a top outlet line for a composition enriched in hydrogen bromide and a bottom outlet line for a composition enriched in sulfuric acid, and f) optionally, a third distillation column comprising an inlet line connected to the bottom outlet line of the second distillation column for a composition enriched in sulfuric acid, wherein the third distillation column comprises an overhead outlet line for a composition enriched in water and a bottom outlet line for a sulfuric acid product composition, in a) the electrolyzer or the thermal oxidizer is connected to the outlet line of the first distillation column for the composition enriched in hydrogen bromide via a condenser arranged therebetween, the condenser comprising an inlet line connected to the top outlet line of the gaseous composition enriched in hydrogen bromide of the first distillation column and comprising an outlet line connected to the inlet line of the composition containing hydrogen bromide of the electrolyzer or the thermal oxidizer, and / or β) The apparatus further comprises a recycle line introduced from a bottom outlet line of the second distillation column and / or from a bottom outlet line of the third distillation column to an inlet of the first distillation column.

16. The apparatus according to claim 15, wherein the apparatus further comprises a scrubbing column comprising an inlet line connected to the outlet line of the vessel for the gaseous portion of the reaction mixture effluent, wherein preferably the top outlet line of the second distillation column is connected to the outlet line of the vessel for the gaseous portion of the reaction mixture effluent, wherein the scrubbing column further comprises an inlet line for water, an outlet line for a gaseous composition containing less than 10 ppm of bromine and hydrogen bromide in total, and an outlet line for an aqueous composition containing 5 to 40 wt.% of hydrogen bromide.

17. The apparatus according to claim 16, wherein the outlet line of the scrubbing column for the aqueous composition containing 5 to 40% by weight of hydrogen bromide is connected to the recirculation line leading to the reactor.

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