Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/02—Hydrogen or oxygen
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B17/00—Sulfur; Compounds thereof
  • C01B17/02—Preparation of sulfur; Purification
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B17/00—Sulfur; Compounds thereof
  • C01B17/69—Sulfur trioxide; Sulfuric acid
  • C01B17/74—Preparation
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/24—Halogens or compounds thereof
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
  • C25B15/081—Supplying products to non-electrochemical reactors that are combined with the electrochemical cell, e.g. Sabatier reactor

Definitions

• the invention relates to methods of hydrogen production by electrolysis of an aqueous solution of hydrobromic acid; as well as methods of hydrogen purification, separation, concentration and recovery of hydrogen, as well as methods of purifying flows from sulfur-containing and nitrogen-containing compounds.
• Hydrogen can be obtained from several sources, such as fossil fuels, biomass, water and even from H 2 S, or extracted from natural gas (natural hydrogen). Recent scientific and technical papers have highlighted the possibility that commercially valuable low-cost natural hydrogen may exist in many places of the world. The demand for hydrogen is expected to increase significantly in the upcoming decades. According to the Hydrogen Council (http://hydrogencouncil.com/wp- content/uploads/2017/11 /Hydrogen-scaling-up-Hy drogen-Council .pdf), considering hydrogen as one of the central pillars for the deep decarbonization of the transport, industry and energy sectors could potentially generate a tenfold increase in the demand for hydrogen, increasing from 8 EJ (2015) to almost 80 EJ by mid-century.
• the present technology consumes a huge amount of electricity per mol of hydrogen, requires significant water resources, does not use co-produced oxygen, and requires high capital investments (uses noble metal like iridium).
• the separation, purification, and compression of hydrogen is required.
• PSA pressure swing adsorption
• hydrogen-permeable membranes they fall generally into three classes: polymeric membranes, inorganic (non-metal porous or nonporous) membranes, and dense (nonporous) metal membranes;
• cryogenic or low temperature technologies for gas separation based on their difference in boiling points: the application of this technology for H 2 separation requires the cooling of the gas to cryogenic temperatures of - 200°C.
• the impurities (CH 4 , CO 2 , CO, H 2 O, etc.) in the gas flow are removed in adsorbent beds.
• the adsorbents are normally made of molecular sieves, activated alumina or silica gel, depending on the nature of the impurities.
• the impurities are adsorbed at higher partial pressure and desorbed at lower pressure. H 2 adsorption relative to other gases and light hydrocarbons is not very significant; therefore, it is obtained as highly purified.
• the adsorbent bed or beds are regenerated by reducing the pressure from feed to tail gas pressure and subsequently purging with a portion of the product H 2 .
• PSA Pressure Swing Adsorption
• the membrane flows can be used to recover hydrogen from highly concentrated flows with purity of more than 80%.
• the technology is very sensitive to contaminants, especially to the presence of H 2 S, H 2 O, C 3 + hydrocarbons. About 95% of H 2 is typically recovered with purity of above 90%. Membrane separation lacks efficiency and is not suitable for production of pure hydrogen. The presence of contaminants limits the lifetime thereof.
• the cryogenic method is a low-temperature separation method, which uses the difference in the boiling temperatures (relative volatilities) of feed components to carry out the separation.
• H 2 has a very high relative volatility compared to hydrocarbons. Therefore, cryogenic method has been used to recover H 2 from the refinery and petrochemical off gas for many years.
• the CH 4 wash column is used, which washes the impurities from the H 2 flow.
• CO 2 and water content should be reduced to less than 1 permille by passing the feed flow through a gas dehydration system.
• CO 2 is removed to 100 permille level in an amine treatment column.
• the cryogenic method is thermodynamically more efficient than the other H 2 upgrading methods. High recovery rate in the range of between 92 and 98% is easily achieved at 95%+ purity and the losses in recovery in case of increased hydrogen purity is less than for membrane systems.
• the main disadvantage of all the discussed methods is high cost, high energy requirement, moderate hydrogen recovery rate, and necessity to design for highly concentrated H 2 flows.
• Higher H 2 content of the feed promotes the PSA and membrane methods, and lower H 2 content promotes the cryogenic separation.
• Flows with 75-90 vol.% of H 2 are most economically purified by PSA or membrane methods with the selection being based on flow, pressure, and pretreatment requirements.
• Cryogenic separation technology is applicable to large flows with 30-75 vol.% of H 2 .
• the larger the CH 4 content of a flow the more Joule-Thomson refrigeration is available to the cryogenic method.
• the reformer gas mainly consists of H 2 , CO, CO 2 and N 2 .
• the H 2 flow can be purified using a PSA system only, since it is the only method that can remove the above components easily and completely.
• H 2 flow is a refinery off gas
• the content of heavier hydrocarbons (C 5 +) is an important factor in the development of all three methods.
• Membrane systems will remove these components, but higher concentrations increase the condensation temperature of the retentate, which makes the reliability of the system more dependent on proper operation of the pretreatment system.
• PSA systems will remove heavier hydrocarbons, but increased concentrations result in larger systems with lower recovery due to difficulty in stripping of the mentioned impurities from the adsorbents.
• Heavier hydrocarbons concentrations in the feed for a cryogenic system must be limited in order to avoid freezing in the method, which makes this system also more dependent on the operation of the pretreatment systems. Benzene is of particular concern in the membrane and cryogenic methods due to its high boiling point.
• a gas flow contains H 2 S and NO x that must be removed, then the membrane method is not suitable, as H 2 S has a relatively high permeation rate, and will leave with the H 2 product. If H 2 S is present in concentrations exceeding a few hundred permille, then PSA method is advantageous, since the cryogenic method will require a separate H 2 S removal system.
• the PSA method is the most flexible method of the three methods under consideration in its ability to maintain H 2 purity and recovery under changing conditions. As the concentration of a feed impurity increases in the feed (at constant feed pressure), the partial pressure of the impurity also increases. An increase in the impurity partial pressure normally results in an increase in the amount of the impurity that would be adsorbed. Thus, the method is self-compensating to a large extent and even relatively large changes in feed impurity concentrations have little impact on hydrogen purity but would reduce the recovery rate.
• the cryogenic method is less flexible than the other two methods. Particular attention must be given to high freezing point constituents, which are removed in the pretreatment system, since failure to remove those contaminants can result in plugging of the heat exchangers. Changes in the concentration of the lower-boiling components of feed affect the product purity directly. Recovery is not strongly affected.
• reducing agent to re-obtain hydrobromic acid from bromine.
• One of the practically available reducing agents may be sulfur or sulfur-containing substances, hydrogen sulfide and sulfur-containing organics.
• the source of sulfur- containing reducing agents is, in particular, natural gas; biogas; exhaust gases from refineries, combustion plants, coal-fired power plants, metallurgical plants; flue gases, exhaust gases, etc.
• (1) amine washing followed by Claus method includes three steps: first, H 2 S present in the flows is being adsorbed in an amine or amine mixture and purified (“sweet”) gas flow is recovered from the unit; then, obtained saturated amine solution is directed to the desorption step, wherein H 2 S rich gaseous flow is obtained and unsaturated amine is returned to the first step; finally, H 2 S is reacted with air in Claus furnaces to obtain sulfur and water vapor;
• the amine washing/Claus method consumes a lot of energy, requires high capital investments and is economically advantageous only at high scale.
• the amine is an expensive consumable of the method, which needs to be gradually replaced due to thermal degradation.
• the presence of S-organic compounds reduces efficiency and increases purification costs.
• Resulting elemental sulfur is of low quality, which prevents sales opportunities thereof. It is worth mentioning that this solution is not economically justified for treatment of biogas, as the scale of biogas production is too small and its delivery to the treatment units demands either costly transportation or investments into entire pipeline network, which will significantly hinder opportunities for remote small-scale biogas producers.
• the adsorption by carbon filters will demand further infrastructure for treatment of waste filter material.
• the present invention is aimed at solving several problems, the main of which is the optimization of the electrolysis method of a solution of hydrobromic acid in water in the presence of bromine to produce hydrogen. Solving this problem leads to the development of an optimal method of hydrogen production by electrolysis of a solution of hydrobromic acid in water and the solution of related problems - providing optimal methods of concomitant disposal of more reducing agents, which in turn solves the problem of purification of various flows from the mentioned reducing agents and production of related products by oxidizing the mentioned reducing agents.
• the problem is solved by taking into account the unique discovery of the inventors, which became the basis of the present invention, in the electrolysis conditions. Namely, the discovery that the electrolysis of hydrobromic acid in the water/hydrobromic acid/bromine system is most effective in maintaining the single-phase nature of the system, i.e. that the resulting bromine does not form a separate fluid phase separated from water.
• the inventors have found that bromine is soluble in an aqueous solution of hydrobromic acid, without forming a separate fluid phase, in a molar ratio to hydrobromic acid not exceeding 1 (bromine : hydrobromic acid ⁇ 1). Carrying out electrolysis in the disclosed conditions, it is possible to use most easily more economically advantageous conditions of obtaining hydrogen, which is provided by the electrolysis of aqueous solution of hydrobromic acid in comparison with the electrolysis of water.
• the main technical result of the present invention is to provide a novel method of hydrogen production by the electrolysis of an aqueous solution of hydrobromic acid in a single-phase system.
• An additional useful result is the concomitant disposal of reducing agents required for the reduction of bromine and the formation of hydrobromic acid to close the reaction cycle on which the said method is based.
• the derived technical result from the disposal of reducing agents is the concomitant purification of flows (in particular, flows of saturated hydrocarbons and CO 2 ).
• one of the additional technical results of the present invention is the recovery of hydrogen from flows wherein hydrogen is present in small concentrations.
• one of the additional technical results is obtaining some oxidation products, which are themselves useful, in particular, sulfuric acid or sulfur (or its condensed forms).
• FIG. 1 shows a reactor which including a pyrex glass vessel equipped with a temperature regulator, a heating element, a Liebig refrigerator, and a mechanical stirrer coated with a layer of polytetrafluoroethylene (PTFE).
• PTFE polytetrafluoroethylene
• the technical solution of the present invention is a method of hydrogen production which includes:
• step (d) obtaining the fluid flow from step (b), wherein the said fluid flow contains essentially water, hydrobromic acid and residual bromine, and which is single-phase;
• step (e) directing the said fluid flow from step (d) to an electrolyser to convert at least a portion of the hydrobromic acid to bromine and hydrogen;
• step (f) obtaining the fluid flow from step (e) and redirecting thereof to step (a).
• the substance not oxidized by bromine, in step (c), is meant to be either the non- oxidizable component of the flow A, or the oxidation product of reducing agent from the flow A by bromine, which is incapable of further oxidation by bromine under the conditions of the method according to the invention, or both.
• the separation of the side flow in step (c) can occur, in particular, by decantation (when the fluid flows are not mixed), or the side flow is gaseous and thus facilitates its separation; also the side flow may be aqueous and require, in particular, the distillation for its separation.
• the side flow in step (c) is further washed and dried, and optionally at least one oxidation product of the reducing agent is separated from the flow A.
• the said flow A in the method according to the invention contains hydrogen as a reducing agent in the amount of at least 500 ppm.
• hydrogen in the flow A may be present in the amounts from 100 ppm up to 90% by weight.
• the said flow A may contain ammonia, nitrogen-containing organic compounds, amines and/or amides in the amount of at least 500 ppm as a reducing agent. Accordingly, the said side flow in step (c) may contain nitrogen. In a separate embodiment of the present invention, the above flow A contains carbon monoxide in the amount of at least 10 ppm as a reducing agent.
• the said flow A contains sulfur-containing compounds or sulfur in the concentration of not less than 1 ppm as a reducing agent.
• the sulfur-containing compound according to this embodiment may be CS 2 , H 2 S, SO 2 , COS, dimethyl sulfide, dimethyl disulfide, methyl mercaptan and/or ethyl mercaptan.
• At least one oxidation product of the reducing agent is separated from the fluid flow in step (d) from the flow A.
• the said separation from the fluid flow in step (d) can be carried out by distillation or extraction.
• the above said oxidation product of the reducing agent is sulfur and/or forms of condensed sulfur.
• the said oxidation product is sulfuric acid.
• the flow C containing water is additionally provided.
• the flow A is gaseous.
• the gaseous flow A can be provided at a pressure from 0.5 to 60 atmospheres.
• the gaseous flow after extraction in step (c) is additionally washed and dried by molecular sieve or distillation.
• the said gaseous flow contains essentially CO 2 .
• this gaseous flow contains essentially methane and/or other saturated hydrocarbons.
• the gaseous flow may contain nitrogen.
• the water is additionally added in step (d).
• the weight percent of hydrobromic acid in the flow B does not exceed 62% w/w. In more preferred embodiments of the present invention, the weight percent of hydrobromic acid in the flow B does not exceed 48% w/w.
• the molar ratio of bromine to hydrobromic acid in the flow B is less than or equal to 1.
• the potential in the electrolyser does not exceed 1.23 V relative to the standard hydrogen electrode.
• a water-miscible organic solvent and water-miscible compounds are added.
• Such water- miscible organic solvents or compounds may be, in particular, methanol, acetone, acetic acid, nitromethane, sulfolene (butadiene sulfone), dimethyl sulfoxide, dimethyl formamide, acetonitrile, propionitrile, and/or ionic fluids, in particular, the imidazolium, pyrrolidinium, pyridinium salts, as, for example, bromides or sulfates.
• the concentration of unsaturated hydrocarbons in the flow A is lower than 100 ppm.
• a step of removing bromides and dibromides formed from olefins in such a reaction is performed.
• the disclosed removal is carried out by distillation and subsequent decomposition, in particular, thermal.
• the temperature at each step, in which bromine is present is maintained below 80 °C.
• the flow A is additionally concentrated before step (a).
• the said fluid flow from step (c) is concentrated, in particular by extractive distillation with, in particular, concentrated solutions of alkaline earth metal bromides or sulfuric acid, before being loaded to the electrolyser.
• the present invention is based on the features of the electrolysis of hydrogen bromide in aqueous solution, which were discovered by the inventors:
• the inventors of the present invention also found that there are some other limitations of single-phase nature and method efficiency: the weight percent of hydrobromic acid in water cannot exceed 62% (and the amount of bromine relative to water has no significance as it binds to hydrobromic acid).
• the most optimal value for the concentration of hydrobromic acid in water is 48 % w/w, which coincides with the concentration of azeotropic solution of hydrobromic acid.
• bromine begins to enter the gas phase at 60 °C, it is at a temperature of 80 °C, as found by the inventors, that a flow stratification and the bromine transition into the gas phase occur; starting from this temperature it is very difficult to control the method from a technical point of view.
• the concentration of unsaturated hydrocarbons in the flow A, which is reacted with bromine dissolved in aqueous hydrobromic acid must be lower than 100 ppm.
• Unsaturated hydrocarbons (olefins) in contact with bromine and hydrobromic acid form bromide and dibromide derivatives, which accumulate in the system and create problems with electrolysis, reducing its efficiency.
• the removal of bromides and dibromides formed from olefins in this reaction should be carried out.
• the disclosed removal can be performed before the electrolysis step; to remove these substances, in particular, distillation and subsequent decomposition, e.g. thermal, can be used.
• organic solvents or fluids that are miscible with water in particular methanol, acetone, acetic acid, nitromethane, sulfolene (butadiene sulfone), dimethyl sulfoxide, dimethyl formamide, acetonitrile, propionitrile, and/or ionic fluids, in particular, the imidazolium, pyrrolidinium, pyridinium salts, as, for example, bromides or sulfates.
• organic solvents or fluids that are miscible with water in particular methanol, acetone, acetic acid, nitromethane, sulfolene (butadiene sulfone), dimethyl sulfoxide, dimethyl formamide, acetonitrile, propionitrile, and/or ionic fluids, in particular, the imidazolium, pyrrolidinium, pyridinium salts, as, for example, bromides or sulfates.
• One of the main examples of use of the proposed invention is the method of recovering and separating hydrogen from gas flows.
• the method of the invention is a low-cost and low-carbon method of reduction and production of high purity hydrogen from flows, which may contain complex mixtures of hydrogen, CO, CO 2 , H 2 S, CS 2 , alkanes, nitrogen, nitrogen oxides, ammonia and noble gases, wherein hydrogen in the disclosed flows may be contained in amounts from 100 ppm up to 90% by weight.
• H 2 + Br 2 2HBr with the formation of hydrogen bromide, which is then reduced again to bromine by electrolysis with hydrogen obtaining captured from the flow of low concentration.
• hydrogen in this method is both a reducing agent and the product to the recovery of which this method is directed.
• the method according to the invention can also be used to purify flows of CO 2 for their subsequent transportation, as in many cases the amount of H 2 is a very critical parameter.
• Hydrogen reduction in this solution is close to 100%.
• the mentioned solution is not sensitive to changes in gas concentration and composition. This methodology is suitable even for the recovery of traces of hydrogen.
• This method can be used for:
• the reducing agent used to regenerate the hydrobromic acid spent on electrolysis is sulfur or sulfur-containing compounds, such as CS 2 , H 2 S, SO 2 , COS, dimethyl sulfide, dimethyl disulfide, methyl mercaptan and/or ethyl mercaptan.
• the sulfur source flow in step (1) may be a gaseous flow or a fluid flow containing at least one S-containing compound.
• this method can be used for producing hydrogen, splitting water to produce hydrogen, the conversion of sulfur- containing waste into sulfur or sulfuric acid, for desulfurization of gas flows (removal of CS 2 , H 2 S, SO 2 , COS) of different nature (natural gas; biogas; waste gases from refineries, combustion plants, coal power plants, metallurgical plants; flue gases, exhaust gases) on different scales.
• CS 2 , H 2 S, SO 2 , COS of different nature (natural gas; biogas; waste gases from refineries, combustion plants, coal power plants, metallurgical plants; flue gases, exhaust gases) on different scales.
• the method according to the invention is a simple and low-carbon method of purification of sulfur-containing flows (wherein sulfur is present in the form of H 2 S, CS 2 , COS, sulfur or S-organic) including in remote places with the joint production of high value products: hydrogen, sulfuric acid or sulfur; the invention provides a technology that can be easily presented on an enlarged or reduced scale, depending on specific requirements, and can be adjusted to produce sulfur or sulfuric acid when water is added.
• the methods of the present invention can be used to purify flows from carbon monoxide and ammonia and certain nitrogenous substances.
• the carbon dioxide is obtained, which can also be collected as a useful product, according to methods known to a person skilled in the art.
• the present invention it is possible to use the following substances as ammonia, nitrogen-containing organic compounds, amines and/or amides in the amount of at least 500 ppm as nitrogen-containing compounds as reducing agents in the flow A.
• Molecular nitrogen is formed as a product in reactions with the following reducing agents:
• the bromine-containing mixtures for Examples 1-3 were prepared using an azeotrope HBr (48 % w/w), fluid Br 2 and distilled water.
• Example 1 The gas mixture (1) containing 97 vol.% of CH 4 and 3 vol.% of H 2 S was used as a raw material for the reaction, and a single-phase solution containing water, HBr and Br 2 (52% w/w, 43 % w/w and 5% w/w, respectively) was used for the oxidation reaction of H 2 S to H 2 SO 4 .
• the applied reactor was a plant including a pyrex glass vessel (3) equipped with a temperature regulator, a heating element, a Liebig refrigerator, and a mechanical stirrer (4) coated with a layer of polytetrafluoroethylene (PTFE).
• the feed gas was fed through a PTFE tube connected to a Bronckhorst mass flow regulator (2), which was calibrated for the said gas mixture using an external flow meter.
• the reaction was carried out at the temperature of 55-60°C, the reactor was loaded with 1000 g of the single-phase solution, and the mechanical stirrer was maintained at 400 rpm throughout the experiment.
• the feed gas mixture flow was maintained for 10 hours at a flow rate of 2 1/h, and the Liebig refrigerator was constantly washed with water to avoid undesired loss of fluid products due to evaporation.
• the fluid in the reactor was cooled and analyzed by available analytical methods after completion of the reaction. According to the gravimetric analysis results, the total amount of H 2 SO 4 was 2.55 g, which indicated an almost complete conversion of H 2 S to H 2 SO 4 .
• the gas mixture containing 97 vol.% of CH 4 and 3 vol.% of H 2 S was used as a raw material for the reaction, and a single-phase solution containing water, HBr and Br 2 (53% w/w, 27% w/w and 20% w/w, respectively) was used for the oxidation reaction of H 2 S to H 2 SO 4 .
• the applied reactor was a plant including a pyrex glass vessel equipped with a temperature regulator, a heating element, a Liebig refrigerator, and a mechanical stirrer coated with a layer of PTFE.
• the feed gas was fed through a PTFE tube connected to a Bronckhorst mass flow regulator calibrated for the said gas mixture using an external flow meter.
• the reaction was carried out at the temperature of 55-60°C, the reactor was loaded with 1000 g of the single-phase solution, and the mechanical stirrer was maintained at 400 rpm throughout the experiment.
• the feed gas mixture flow was maintained for 10 hours at a flow rate of 10 1/h, and the Liebig refrigerator was constantly washed with water to avoid undesired loss of fluid products due to evaporation.
• the fluid in the reactor was cooled and analyzed by available analytical methods after completion of the reaction. According to the gravimetric analysis results, the total amount of H 2 SO 4 was 12.97 g, which indicated an almost complete conversion of H 2 S to H 2 SO 4 .
• the gas mixture containing 97 vol.% of CH 4 and 3 vol.% of H 2 S was used as a raw material for the reaction, and a single-phase solution containing water, HBr and Br 2 (52% w/w, 43 % w/w and 5 % w/w, respectively) was used for the oxidation reaction of H 2 S to H 2 SO 4 .
• the applied reactor was a plant including a pyrex glass vessel equipped with a temperature regulator, a heating element, a Liebig refrigerator, and a mechanical stirrer coated with a layer of PTFE.
• the feed gas was fed through a PTFE tube connected to a Bronckhorst mass flow regulator calibrated for the said gas mixture using an external flow meter.
• the reaction was carried out at the temperature of 55-60°C, the reactor was loaded with 1000 g of the single-phase solution, and the mechanical stirrer was maintained at 400 rpm throughout the experiment.
• the feed gas mixture flow was maintained for 10 hours at a flow rate of 6 1/h, and the Liebig refrigerator was constantly washed with water to avoid undesired loss of fluid products due to evaporation.
• Example 3 The fluid product obtained in Example 3 was placed in a distillation unit with a round bottom flask, reflux condenser and refrigerator.
• the fluid was diluted with 100 ml of distilled water, as some of the water was consumed during the reaction with H 2 S and distilled at 124-127 °C for 6 hours in a well- ventilated exhaust hood.
• the total amount of almost colorless fluid collected in the receiver flask was 1072 g, and the amount of fluid residue with a higher boiling point in the round bottom flask was 33 g.
• This residue was analyzed for sulfuric acid content using gravimetric analysis. It was found that the total amount of H 2 SO 4 was 7.63 g, which indicated an almost complete conversion of H 2 S to H 2 SO 4 during Example 3.
• the analysis of this distillate showed that it was an 8.2 M HBr solution close to an azeotrope (8.89 M).
• a specially designed electrolysis unit was used to decompose HBr into H 2 and Br 2 .
• 600 ml of a solution containing 48% w/w of HBr in water was passed through an electrolysis unit using a peristaltic pump with a PTFE surface.
• the fluid yield from the electrolysis unit was collected in a glass vessel; the gaseous yield was released into the exhaust hood.
• the total duration of electrolysis was ⁇ 7 minutes, the average voltage during the run ⁇ 1.02 V, the average current ⁇ 82 A.
• the voltage during the experiment was stable.
• Liquid products were analyzed for Br 2 and HBr by titration and gravimetric analysis. The analysis showed a final content of HBr and Br 2 44% w/w and 4% w/w, respectively.
• An individually designed electrolysis unit containing a nation membrane was used as the reactor.
• the gas mixture (CH 4 /H 2 95/5 vol.) and a single-phase solution comprising water, HBr and Br 2 (52% w/w, 43 % w/w and 5 % w/w, respectively) were used as raw material.
• the feed gas was fed through a PTFE tube connected to a Bronckhorst mass flow regulator calibrated for the said gas mixture using an external flow meter.
• the supply of the fluid phase was carried out by a syringe pump.
• the flow of this gas mixture was set at 5 1/h, the experiment was performed for 2 hours.
• the average cell voltage was 0.96 V, and the average current was 0.6 A.
• a specially designed electrolysis unit was used to decompose the model mixture, including water, HBr and Br 2 (35% w/w, 28% w/w and 36% w/w, respectively). 100 g of this solution was combined in a closed circuit with an electrolysis cell and recycled through the mentioned cell with an average flow rate of 15 ml/min. The average voltage during the run was approx. 1.03 V, the average current was approx. 39 A. After approximately 5 minutes of the experiment, a clear formation of a second layer at the flask bottom was observed, corresponding to a conversion of approximately 35 mol. % of HBr, i.e. the molar ratio of HBr/Br 2 is less than 1.
• the voltage began to rise and reached a value of 1.34V at the point of 6.5 min; after all, the 1.34 V cell potential was accompanied by the formation of bubbles at the anode, which, as expected, were oxygen, formed due to the water decomposition.
• the total bromine content was analyzed using gravimetric analysis.
• This method is based on the HBr neutralization by adding excess sodium carbonate followed by the addition of silver nitrate and the sedimentation of AgBr. All manipulations were performed at the temperature of 40 °C and with vigorous stirring to ensure the completion of the reaction. Then the solid sediment of AgBr was filtered off, dried in air and calcinated at the temperature of 400 °C for 6 hours for providing the purity of the sample.
• the molecular bromine content which may be present in the form of polybromides, [Br 2n +1 ]-, was analyzed using iodometric titration.
• the polybromides were reacted with an excess solution of potassium iodide with obtaining molecular iodine.
• the formed iodine was titrated with a solution of sodium thiosulfate with colloidal starch as an indicator.

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