PROCESS FOR BROMINE SEPARATION FROM AQUEOUS SOLUTIONS OF HBr

Abstract

The disclosure provides a process for separating bromine from an aqueous solution of hydrogen bromide, said process is remarkable in that it comprises the steps of (a) providing a first stream which is an aqueous solution of hydrogen bromide, said aqueous solution comprising bromine and wherein said aqueous solution is a single phase; (b) providing a second stream comprising water and / or an aqueous solution of one or more mineral acids; (c) mixing the first stream and the second stream so as to obtain a mixture; and (d) decanting the mixture obtained at step (c) so as to generate at least a third stream which is an aqueous solution of hydrogen bromide comprising bromine wherein the molar ratio between bromine and hydrogen bromide is less than in the mixture obtained at step (c).

Description

[0001] PROCESS FOR BROMINE SEPARATION FROM AQUEOUS SOLUTIONS OF HBr

[0002] TECHNICAL FIELD

[0003] The disclosure relates to a process for separating bromine from an aqueous solution of hydrogen bromide and to a process for bromine production, as well as to an installation for bromine production.

[0004] TECHNICAL BACKGROUND

[0005] Hydrogen bromide (HBr) is a colorless, corrosive, and non-flammable gas. HBr fumes strongly in moist air. It is one of the strongest mineral acids, extremely soluble in water, forming a strong acid that is available as 48% or 68% solutions. HBr is a severe irritant to the eyes, skin, and nasal passages; high concentrations may penetrate the lungs resulting in edema and hemorrhage.

[0006] There are many conventional industrial processes in which hydrogen bromide is produced as a by-product. However, hydrogen bromide by-products are not compatible with the environment, so, in most cases, they must first be neutralized to meet environmental regulations before being discharged into the environment.

[0007] Bromine is a compound used in different domains of the industry. For instance, it finds applications in the production of flame retardants or bromobutane rubbers, used in tires. Yet the production of bromine remains complex and costly.

[0008] By way of illustration, bromine may be obtained by electrolysis. Electrolysis of hydrogen bromide in the aqueous phase is generally applied for the production of hydrogen and / or recovery of bromine from streams comprising hydrogen bromide (HBr).

[0009] The reaction could be written in the following way:

[0010] 2HBr(aq) H2+ Br2

[0011] Bromine is almost insoluble in water. However, it could be dissolved in an HBr solution, as follows:

[0012] Br2+ HBr(aq) HBrs(aq)

[0013] Depending on the molar ratios, different anions are formed with a general formula [Br2n+i]’, where n = 1 ,2,3, etc. Therefore, in standard operating conditions, the liquid effluent will be a homogeneous solution of Br2in aqueous HBr. US5385650 discloses a process for recovering bromine from an acidic solution containing bromide ion comprising passing an electric current through said solution between an anode in contact with the said solution and a cathode in electrical communication with said solution, thereby generating bromine by electrolysis of said solution at the anode to produce an electrolyzate containing bromine; and separating bromine as a vapor from said electrolyzate under negative pressure.

[0014] US7341654 deals with the production of chlorine by electrolysis of aqueous HCI, in a membrane electrolyzer, using cathodic mediators such as Fe(lll) and / or Cu(ll) chlorides and a non-catalyzed three-dimensional cathode, with the real surface area at least ten times higher than its projected area. The HCI electrolysis section is combined with an oxidizer for regeneration of the mediator, product water removal step, and optional HCI recovery step. Under optimized conditions, chlorine can be produced at very high current densities of 30 kA / m2, without initiating an undesired H2 evolution reaction at the cathode.

[0015] There is a need for improvement in the process of recovery of the bromine present in hydrogen bromide solution and also of the bromine produced by electrolysis of hydrogen bromide in the aqueous phase. In particular, there is a need for a process that is highly efficient, simple, and easy to implement at an industrial scale and that is cheap.

[0016] SUMMARY

[0017] According to a first aspect, the disclosure provides a process for separating bromine from an aqueous solution of hydrogen bromide, the process is remarkable in that it comprises the following steps: a) providing a first stream which is an aqueous solution of hydrogen bromide, wherein the aqueous solution further comprises bromine and wherein said aqueous solution is a single phase; b) providing a second stream comprising water and / or an aqueous solution of one or more mineral acids; c) mixing the first stream and the second stream to obtain a mixture; d) decanting the mixture obtained at step (c) to generate at least a third stream which is an aqueous solution of hydrogen bromide comprising bromine wherein the molar ratio between bromine and hydrogen bromide is less than in the mixture obtained at step (c); e) optionally, recovering the third stream.

[0018] Advantageously, the step (d) of decanting the mixture obtained at step (c) further generates a fourth stream which comprises bromine. With preference, the process further comprises the step of recovering said fourth stream. For example, the process further comprises the step of drying said fourth stream.

[0019] For example, the molar ratio between bromine and hydrogen bromide in the mixture obtained at step (c) corresponds to the molar ratio between bromine and hydrogen bromide of the first stream provided at step (a).

[0020] According to a second aspect, the disclosure provides a process for recovering bromine from a hydrogen bromide aqueous solution remarkable in that it comprises the following steps: i. providing one or more electrolytic cells each comprising an anode, a cathode, and an ion-exchange membrane placed between the anode and the cathode; ii. providing a first input flow at the anode of the one or more electrolytic cells that is or comprises a hydrogen bromide aqueous solution; and a second input flow at the cathode of the one or more electrolytic cells that is or comprises water or an aqueous solution; iii. performing an electrolysis to convert at least a part of the hydrogen bromide of the first input flow into bromine by operating the one or more electrolytic cells under electrolysis conditions; and iv. recovering from the anode a first stream which is an aqueous solution of unreacted hydrogen bromide, said aqueous solution comprising bromine and wherein said aqueous solution is a single phase; v. providing a second stream comprising water and / or an aqueous solution of one or more mineral acids; vi. mixing the first stream and the second stream to obtain a mixture; vii. decanting the mixture obtained at step (vi), comprising passing the mixture obtained at step (vi) in a decanter to obtain a first liquid phase comprising unreacted hydrogen bromide and bromine, wherein the molar ratio between bromine and unreacted hydrogen bromide is less than in the mixture obtained at step (vi); viii. optionally, recovering the first liquid phase.

[0021] Advantageously, the step (vii) of decanting the mixture obtained at step (vi) further generates a second liquid phase which comprises bromine. With preference, the process further comprises the step of recovering the second liquid phase. For example, the process further comprises the step of drying said second liquid phase. For example, the molar ratio between bromine and hydrogen bromide in the mixture obtained at step (vi) corresponds to the molar ratio between bromine and hydrogen bromide of the first stream recovered at step (iv).

[0022] According to another definition, the process of the second aspect is a process for bromine production remarkable in that it comprises the following steps:

[0023] A. providing one or more electrolytic cells each comprising an anode, a cathode, and an ion-exchange membrane placed between the anode and the cathode;

[0024] B. providing a first input flow at the anode of the one or more electrolytic cells that is or comprises a hydrogen bromide aqueous solution; and a second input flow at the cathode of the one or more electrolytic cells that is or comprises water or an aqueous solution;

[0025] C. performing an electrolysis to convert at least a part of the hydrogen bromide of the first input flow into bromine by operating the one or more electrolytic cells under electrolysis conditions; and

[0026] D. separating bromine from an aqueous solution of hydrogen bromide in accordance to the process of the first aspect wherein the first steam provided in step a) is the stream recovered from the anode after step C).

[0027] Surprisingly, it was found that the addition of a diluent, namely either water or an aqueous solution of one or more mineral acids, into a first stream being an aqueous solution of hydrogen bromide comprising bromine and forming a single phase considerably prevents the bromine from being dissolved by the hydrogen bromide. Indeed, the weaker the concentration of HBr is, the more difficult is for the bromine (Br2) to dissolve. This is because bromine is almost insoluble in water, and that reduction of the concentration of the other compounds that favors its solubility prevents its dissolution. Subsequently, performing a decanting step allows to recovery of a third stream and / or a first liquid phase which comprises a higher concentration of hydrogen bromide than the concentration of hydrogen bromide into the first stream.

[0028] Advantageously, the first stream, provided at step (a) or recovered at step (iv), which is an aqueous solution of hydrogen bromide, comprises at most 48.3 wt.% of hydrogen bromide based on the total weight of the first stream. For example, the first stream, provided at step (a) or recovered at step (iv), which is an aqueous solution of hydrogen bromide, comprises from 10 wt.% to 48.3 wt.% of hydrogen bromide based on the total weight of the first stream, preferably from 15 wt.% to 47.6 wt.%, more preferably from 17 wt.% to 46 wt.%, even more preferably from 19 wt.% to 45 wt.%, most preferably from 20 wt.% to 42 wt.%, or from 21 wt.% to 40 wt.%, or from 22 wt.% to 39 wt.%. Advantageously, the mixture obtained at step (c) or at step (vi) is an aqueous solution of hydrogen bromide with a concentration of hydrogen bromide lower than the concentration of hydrogen bromide presented by the first stream respectively provided at step (a) or recovered at step (iv).

[0029] For example, the amount of the second stream provided at step (b) or (v) ranges between 40 wt.% and 60 wt.% of the total weight of the first stream respectively provided at step (a) or recovered at step (iv), or between 45 wt.% and 55 wt.%.

[0030] For example, when the second stream provided at step (b) or (v) comprises an aqueous solution of one or more mineral acids, the aqueous solution of one or more mineral acids has a pH ranging from 0.1 to 5.0.

[0031] For example, when the second stream provided at step (b) or (v) comprises an aqueous solution of one or more mineral acids, said one or more mineral acids are selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid, hydroiodic acid or a mixture thereof. With preference, said mineral acid is sulfuric acid.

[0032] For example, step (d) or (vii) of decanting is performed during a time of at least 1 minute. With preference, step (d) or (vii) of decanting is performed during a time ranging between 2 minutes and 10 minutes.

[0033] For example, step (d) or (vii) of decanting is performed at a pressure of at least 0.12 MPa, preferably of at least 0.15 MPa, more preferably of at least 0.20 MPa, and / or of at most 0.50 MPa.

[0034] The second aspect is advantageously better described with one or more of the following features:

[0035] The electrolysis conditions of step (iii) comprise a voltage of at least 1.0 V, or of at least 1.5 V, or of at least 2.0 V, preferably of at least 2.5 V or of at least 3.0 V, more preferably of at least 3.5 V or of at least 4.0 V, even more preferably of at least 4.5 V, most preferably of at least 5.0 V, even most preferably of at least 5.2 V or of at least 5.5 V.

[0036] The electrolysis conditions of step (iii) comprise a voltage ranging between 1.0 V and 10.0 V, or between 1.5 V and 10.0 V, or between 2.0 V and 10.0 V, or between 2.5 V and 10.0 V, or between 3.0 V and 10.0 V, preferably between 3.5 V and 9.5 V, more preferably between 4.0 V and 9.0 V, even more preferably between 4.5 V and 8.5 V, most preferably between 5.0 V and 8.0 V; even most preferably between 5.2 V and 7.8 V or between 5.5 V and 7.5 V.

[0037] The electrolysis conditions of step (iii) comprise an anode current density of at least 1 .0 kA / m2, or of at least 2.0 kA / m2, or of at least 3.0 kA / m2, or of at least 4.0 kA / m2, preferably of at least 4.2 kA / m2or of at least 4.5 kA / m2, more preferably of at least 5.0 kA / m2or of at least 5.5 kA / m2, even more preferably of at least 6.0 kA / m2, most preferably of at least 6.2 kA / m2or of at least 6.5 kA / m2.

[0038] The electrolysis conditions of step (iii) comprise an anode current density ranging from 1.0 kA / m2to 10 kA / m2, or from 2.0 kA / m2to 10 kA / m2, or from 3.0 kA / m2to 10 kA / m2, or from 4.0 kA / m2to 9.5 kA / m2, preferably from 4.5 kA / m2to 9.0 kA / m2, more preferably from 5.0 kA / m2to 8.5 kA / m2, even more preferably from 6.0 kA / m2to 8.0 kA / m2, most preferably from 6.2 kA / m2to 7.8 kA / m2, or from 6.5 kA / m2to 7.5 kA / m2.

[0039] The electrolysis conditions of step (iii) comprise a temperature ranging from 20°C to 100°C, preferably from 40°C to 95°C, more preferably from 50°C to 90°C; even more preferably from 60°C to 85°C.

[0040] The step (iv) of recovering from the anode a first stream which is an aqueous solution of unreacted hydrogen bromide comprises cooling the first stream at a temperature ranging between 10°C and 40°C before the mixing step (vi).

[0041] The second input flow provided at step (ii) comprises an aqueous solution of one or more mineral acids. With preference, the aqueous solution of one or more mineral acids has a pH ranging from 0.1 to 5.0. With preference, the aqueous solution of one or more mineral acids comprises one or more selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid, hydroiodic acid or a mixture thereof, more preferably sulfuric acid.

[0042] The anode comprises an anode catalyst and the cathode comprises a cathode catalyst, and in that the anode catalyst and / or the cathode catalyst is or comprises one or more transition metal-based catalysts comprising ruthenium, rhodium, palladium, osmium, iridium, platinum, titanium, cobalt, iron, nickel, niobium, molybdenum, alloys of titanium, alloys of cobalt, alloys of iron, alloys of nickel, alloys of niobium, alloys of molybdenum, oxides of ruthenium, oxides of rhodium, oxides of palladium, oxides of osmium, oxides of iridium, and oxides of platinum and any mixtures thereof.

[0043] According to a third aspect, the disclosure provides an installation for recovering bromine from a hydrogen bromide aqueous solution according to the process defined by the second aspect; wherein the installation comprises at least one electrolytic cell with an anode, a cathode, an anode chamber, a cathode chamber, and an ion-exchange membrane separating the anode chamber from the cathode chamber; the installation further comprises at least one decanter with a top part and a bottom part, said top part of the decanter being downstream the anode chamber of said at least one electrolytic cell and in fluidic connection with the anode chamber; the installation is remarkable in that it further comprises dilution means placed between the anode chamber and the top part of said at least one decanter.

[0044] Advantageously, the installation further comprises a drying unit downstream of the bottom part of the decanter and in fluidic connection with the said bottom part of the decanter. With preference, the drying unit comprises one or more molecular sieves.

[0045] Advantageously, the ion-exchange membrane is a cation-exchange membrane. With preference, the cation-exchange membrane further comprises an ionomer comprising fluoropolymer having one or more sulfonic acid groups.

[0046] DESCRIPTION OF THE FIGURES

[0047] Figure 1 illustrates an installation according to the disclosure.

[0048] Figure 2 illustrates the electrolytic cell configurations.

[0049] Figure 3 illustrates a plot with the weight fraction of bromine at saturation in an aqueous solution of hydrogen bromide in function of the ratio of the weight fraction of hydrogen bromide to the weight fraction of water.

[0050] DETAILED DESCRIPTION

[0051] For the disclosure, the following definitions are given.

[0052] The terms "comprising", "comprises" and "comprised of' as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements, or method steps. The terms "comprising", "comprises" and "comprised of" also include the term “consisting of”.

[0053] The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g., 1 to 5 includes 1 , 2, 3, 4, 5 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of endpoints also includes the recited endpoint values themselves (e.g., from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein. The reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. The particular features, structures, characteristics, or embodiments may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the disclosure and form different embodiments, as would be understood by those in the art.

[0054] The term “alkali metal” refers to an element classified as an element from group 1 of the periodic table of elements, excluding hydrogen. According to this definition, the alkali metals are Li, Na, K, Rb, Cs, and Fr.

[0055] The term “alkaline earth metal” refers to an element classified as an element from group 2 of the periodic table of elements. According to this definition, the alkaline earth metals are Be, Mg, Ca, Sr, Ba, and Ra.

[0056] The term “transition metal” refers to an element whose atom has a partially filled d sub-shell, or which can give rise to cations with an incomplete d sub-shell (IIIPAC definition). According to this definition, the transition metals are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Ac, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, and Cn. The metals Ga, In, Sn, TI, Pb, and Bi are considered as “post-transition” metals.

[0057] Unless otherwise defined, all terms used in disclosing the disclosure, including technical and scientific terms, have the meaning as commonly understood by one skilled in the art to which this disclosure belongs. By means of further guidance, definitions for the terms used in the description are included to better appreciate the teaching of the present disclosure.

[0058] The particular features, structures, characteristics, or embodiments may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments.

[0059] The disclosure provides a process for separating bromine from an aqueous solution of hydrogen bromide, said process is remarkable in that it comprises a step (a) of providing a first stream which is an aqueous solution of hydrogen bromide further comprising bromine, wherein said aqueous solution is a single phase. A single phase aqueous solution corresponds to an homogeneous mixture at least two substances in water, in this case said two substances being bromine and hydrogen bromide. An homogenous mixture corresponds to a mixture in which all the properties are the same no matter where a sample is taken for analysis. For example, the molar ratio between bromine and hydrogen bromide in the first stream provided at step (a) is at most 1.5, preferably at most 1.3, more preferably at most 1.0, even more preferably lower than 1.0. The first stream provided at step (a) can therefore be an aqueous solution of hydrogen bromide further comprising bromine and which is preferably a lean-bromine stream. Step (b) consists of providing a second stream comprising water and / or an aqueous solution of one or more mineral acids. This second stream is used to dilute the first stream in a step (c), which is mixing the first stream and the second stream to obtain a mixture. The molar ratio between bromine and hydrogen bromide in the mixture obtained at step (c) corresponds to the molar ratio between bromine and hydrogen bromide of the first stream provided at step (a). Then a step (d) of decanting the mixture obtained at step (c) to generate at least a third stream is carried out. The third stream is an aqueous solution of hydrogen bromide comprising bromine wherein the molar ratio between bromine and hydrogen bromide is less than in the mixture obtained at step (c).

[0060] An optional step (e) of recovering the third stream can be carried out.

[0061] Advantageously, the step (d) of decanting the mixture obtained at step (c) further generates a fourth stream which comprises bromine. For example, the process further comprises the step of drying said fourth stream.

[0062] This process for separating bromine from an aqueous solution of hydrogen bromide comes within the scope of a process for recovering dry bromine from an aqueous hydrogen bromide solution after electrolysis, and / or for recovering bromine from a hydrogen bromide aqueous solution that has for example been used for working the electrolysis. Such a process can be carried out in an installation 1 as the one depicted in Figure 1. Therefore, the present disclosure also relates to a process for recovering bromine from a hydrogen bromide aqueous solution remarkable in that it comprises the following steps: i. providing one or more electrolytic cells 3 each comprising an anode, a cathode, and an ion-exchange membrane placed between the anode and the cathode; ii. providing a first input flow 5 at the anode of the one or more electrolytic cells 3 that is or comprises a hydrogen bromide aqueous solution; and a second input flow 7 at the cathode of the one or more electrolytic cells 3 that is or comprises water or an aqueous solution; iii. performing an electrolysis to convert at least a part of the hydrogen bromide of the first input flow 5 into bromine by operating the one or more electrolytic cells 3 under electrolysis conditions; and iv. recovering from the anode a first stream 9 which is an aqueous solution of unreacted hydrogen bromide, said aqueous solution comprising bromine and wherein said aqueous solution is a single phase; v. providing a second stream 11 comprising water and / or an aqueous solution of one or more mineral acids; vi. mixing the first stream 9 and the second stream 11 to obtain a mixture 13; vii. decanting the mixture 13 obtained at step (vi), comprising passing the mixture 13 obtained at step (vi) in a decanter 15 to obtain a first liquid phase 19 comprising unreacted hydrogen bromide and bromine, wherein the molar ratio between bromine and unreacted hydrogen bromide is less than in the mixture obtained at step (vi); viii. optionally, recovering the first liquid phase 19.

[0063] Advantageously, the step (vii) of decanting the mixture 13 obtained at step (vi) further generates a second liquid phase 17 which comprises bromine. With preference, the process further comprises the step of recovering the second liquid phase 17. For example, the process further comprises the step of drying said second liquid phase 17. Advantageously, this drying step can be carried out in a drying unit 21 downstream of the bottom part of the decanter 15 and in fluidic connection with said bottom part of the decanter 15. With preference, the drying unit 21 can comprise one or more molecular sieves. Said molecular sieves could be, for instance molecular sieves 3A, which is a commercial product used for drying (CAS 308080- 99-1). The drying step thus generates a stream of dry bromine 23.

[0064] For example, the molar ratio between bromine and hydrogen bromide in the first stream 9 recovered at step (iv) is at most 1.5, preferably at most 1.3, more preferably at most 1.0, even more preferably lower than 1 .0. The first stream 9 recovered at step (iv) can therefore be an aqueous solution of hydrogen bromide further comprising bromine and which is preferably a lean-bromine stream.

[0065] For example, the molar ratio between bromine and hydrogen bromide in the mixture 13 obtained at step (vi) corresponds to the molar ratio between bromine and hydrogen bromide of the first stream 9 recovered at step (iv).

[0066] As regards the dilution of the first stream 9 by the second stream 11

[0067] The addition of a diluent, namely either water or an aqueous solution of one or more mineral acids, into a first stream 9 which is an aqueous solution of unreacted hydrogen bromide comprising bromine and wherein said aqueous solution is a single phase considerably prevents the bromine from being dissolved by the hydrogen bromide. Indeed, the weaker the concentration of HBr is, thanks to its high dilution level, the more difficult is for the bromine (Br2) to dissolve since less dissolving HBr is available for the bromine. This is because bromine is almost insoluble in water, and reduction of the concentration of the other compounds favors its solubility, in other words, the scarcity of the HBr due to its high dilution level, prevents the dissolution of bromine. Subsequently, performing a decanting step allows to recovery of a third stream or a first liquid phase 19 which comprises a higher concentration of hydrogen bromide than the concentration of hydrogen bromide into the first stream 9.

[0068] For example, when the second stream 11 provided at step (b) or (v) comprises an aqueous solution of one or more mineral acids, the aqueous solution of one or more mineral acids has a pH ranging from 0.1 to 5.0. For example, the one or more mineral acids can be selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid, hydroiodic acid or a mixture thereof. With preference, said mineral acid is sulfuric acid.

[0069] Advantageously, the first input flow 5 that is or comprises a hydrogen bromide aqueous solution and / or the first stream 9, provided at step (a) or recovered at step (iv), which is an aqueous solution of hydrogen bromide, comprises at most 48.3 wt.% of hydrogen bromide based on the total weight respectively of the hydrogen bromide aqueous solution and / or of the first stream 9. For example, the first input flow 5 that is or comprises a hydrogen bromide aqueous solution and / or the first stream 9, provided at step (a) or recovered at step (iv), which is an aqueous solution of hydrogen bromide, comprises from 10 wt.% to 48.3 wt.% of hydrogen bromide based on the total weight respectively of the hydrogen bromide aqueous solution and / or of the first stream 9, preferably from 15 wt.% to 47.6 wt.%, more preferably from 17 wt.% to 46 wt.%, even more preferably from 19 wt.% to 45 wt.%, most preferably from 20 wt.% to 42 wt.%, or from 21 wt.% to 40 wt.%, or from 22 wt.% to 39 wt.%.

[0070] Advantageously, the mixture 13 obtained at step (c) or at step (vi), namely that is obtained after a step of dilution of the first stream 9 with the second stream 11 , is an aqueous solution of hydrogen bromide with a concentration of hydrogen bromide lower than the concentration of hydrogen bromide presented by the first stream 9 respectively provided at step (a) or recovered at step (iv).

[0071] For example, the mixture 13 is an aqueous solution of hydrogen bromide with a concentration of hydrogen bromide that is at most 40%, or at most 45%, or at most 50%, or at most 55%, or at most 60% the concentration of the hydrogen bromide presented by the first stream 9 provided at step (a) or recovered at step (iv). For example, the amount of the second stream 11 provided at step (b) or (v) ranges between 30 wt.% and 70 wt.% of the total weight of the first stream 9 respectively provided at step (a) or recovered at step (iv), or between 35 wt.% and 65 wt.%, or between 40 wt.% and 60 wt.%, or between 45 wt.% and 55 wt.%.

[0072] As regard to the decanting step (d) or (vii)

[0073] The decanting step (d) or (vii) is performed in a decanter 15. The first liguid phase 19 comprising unreacted hydrogen bromide (HBr) and bromine with a molar ratio between bromine and unreacted hydrogen bromide being less than in the mixture 13 obtained at step (c) or (vi) and / or in the first stream 9 provided at step (a) or recovered at step (iv) is a supernatant that is over the second liguid phase 17 comprising bromine (Br2).

[0074] For example, the step (d) or (vii) of decanting can be performed during a time of at least 10 minutes. With preference, the steps (d) or (vii) of decanting can be performed during a time ranging between 10 minutes and 60 minutes.

[0075] As the pressure into the decanter 15 can be elevated due to the continuous incoming flow of the mixture 13, the decanter 15 can further comprise a degassing outlet (not shown) that can be useful for removing the vapours, such as oxygen and / or air. In an embodiment, the decanting step (e) can be performed at a pressure of at least 0.12 MPa to avoid vapor formation so that the bromine is kept in a liguid phase.

[0076] For example, the step (d) or (vii) of decanting can be performed at a pressure of at least 0.12 MPa, preferably of at least 0.15 MPa, more preferably of at least 0.20 MPa and / or of at most 0.50 MPa.

[0077] As regards the electrolysis of the hydrogen bromide

[0078] According to the disclosure, in the process for process for bromine production, the one or more electrolytic cells 3 can be selected from zero-gap electrolytic cells, two-gap electrolytic cells, or one-gap electrolytic, which could be catholyte-free one-gap electrolytic cells. Preferably the one or more electrolytic cells are zero-gap electrolytic cells, such as membrane electrode assembly (MEA). The different configurations are illustrated in Figure 2.

[0079] In the cases where the electrolytic cell is a zero-gap electrolytic cell (Figure 2A) or a one-gap electrolytic cell (figure 2C and figure 2D), the cathode catalyst layer is in contact with the ionexchange membrane. In the cases where the electrolytic cell is a zero-gap electrolytic cell (Figure 2A) or a one-gap electrolytic cell (figure 2B), the anode catalyst layer is in contact with the ion-exchange membrane.

[0080] In the case wherein the electrolytic cell is a two-gap electrolytic cell (Figure 2E) none of the cathode catalyst layer and anode catalyst layer is in contact with the ion-exchange membrane. This is due to the presence of both a catholyte and an anolyte.

[0081] In Figure 2, DL is for the diffusion layer, which is a porous medium that enables uniform distribution of reactive liquids of gases on the surface of the electrodes and transports of electrons. For example, the zero-gap cell and the one-gap cell comprise at least one diffusion layer as illustrated in Figure 2. Suitable materials for the diffusion layer are known to the person skilled in the art. It is preferred that the diffusion layer is a conductive material. For example, the diffusion layer is a composite material comprising polytetrafluoroethylene (PTFE) and a conductive material such as carbon particles.

[0082] The anode catalyst and the cathode catalyst may be any suitable catalyst known from the art. The anode catalyst and the cathode catalyst can be the same or different.

[0083] For example, the anode catalyst and / or the cathode catalyst are or comprise one or more transition metal-based catalysts comprising ruthenium, rhodium, palladium, osmium, iridium, platinum, titanium, cobalt, iron, nickel, niobium, molybdenum, alloys of titanium, alloys of cobalt, alloys of iron, alloys of nickel, alloys of niobium, alloys of molybdenum, oxides of ruthenium, oxides of rhodium, oxides of palladium, oxides of osmium, oxides of iridium, and oxides of platinum and any mixtures thereof.

[0084] For example, the anode catalyst comprises platinum; with preference the anode catalyst comprises at least 0.5 wt.% of platinum based on the total weight of the anode catalyst. However, it was reported that at high bromine concentrations platinum losses could occur due to dissolution and poisoning (Kyu Taek Cho, Michael C. Tucker, Adam Z. Weber, Energy Technology, Volume 4, Issue 6, 2016, Pages 655-678).

[0085] Alternatively, DSA® brand anode catalysts produced by the De Nora company could be applied. This type of anode uses mixed metal oxide (MMO) coating which allows a long and stable operation.

[0086] Also, Lead Dioxide Titanium Electrode (Ti / PbCh) anode could be used. The lead dioxide coating on titanium substrate has strong corrosion resistance and is suitable for the media. Mentioned anodes could be further modified by doping Ce or Bi metals to the anode catalyst using the techniques known in the art (Pengfei Xu, Xiaohong He, Junwei Mao, and Yongming Tang, Journal of The Electrochemical Society, Volume 166, Number 13, 2019, 638).

[0087] For example, the cathode catalyst comprises platinum; with preference the cathode catalyst comprises 0.5 wt.% of platinum based on the total weight of the cathode catalyst.

[0088] The ion exchange membrane is a cation-exchange membrane (CEM), preferably a protonexchange membrane (PEM). Both types of membranes are well-known by the person skilled in the art. Typical cation exchange membranes include proton conducting membranes, such as the perfluorosulfonic acid polymer available under the trade designation Nation® from E. I. du Pont de Nemours and Company (DuPont) of Wilmington, Del. A proton-exchange membrane, or polymer-electrolyte membrane, is a semipermeable membrane generally made from ionomers and designed to conduct protons while acting as an electronic insulator and reactant barrier, e.g., to oxygen and hydrogen gas.

[0089] Another example is commercial PEM membranes is Aquivion membranes developed by Solvay company.

[0090] Thus, the cation-exchange membrane can further comprise an ionomer, more particularly an ionomer comprising fluoropolymer having one or more sulfonic acid groups or one or more pendant sulfonic acid groups. For example, the cation-exchange membrane can comprise one or more layers, wherein the layer or at least one of the layers comprises an ionomer, more particularly an ionomer comprising fluoropolymer having one or more sulfonic acid groups or one or more pendant sulfonic acid groups.

[0091] For example, the ionomer comprises a perfluorinated sulfonic acid ionomer. For example, said perfluorinated sulfonic acid ionomer comprises sulfonated tetrafluoroethylene based fluoropolymer-copolymer (such as Nation® or 1 ,1 ,2,2-Tetrafluoroethene;1 ,1 ,2,2-tetrafluoro-2- [1 ,1 ,1 ,2,3,3-hexafluoro-3-(1 ,2,2-trifluoroethenoxy)propan-2-yl]oxyethanesulfonic acid), SSC, Aciplex, Flemion, 3M-perfluorinated sulfonic acid ionomer, Aquivion, an ionene, or a combination thereof.

[0092] Thus, in an embodiment, the ion-exchange membrane is a proton exchange membrane comprising one or more layers, wherein the layer or at least one of the layers comprises an ionomer comprising a fluoropolymer having one or more pendant sulfonic acid groups.

[0093] The electrolysis conditions of step (iii) advantageously comprise a voltage of at least 1 .0 V, or of at least 1.5 V, or of at least 2.0 V, preferably of at least 2.5 V or of at least 3.0 V, more preferably of at least 3.5 V or of at least 4.0 V, even more preferably of at least 4.5 V, most preferably of at least 5.0 V, even most preferably of at least 5.2 V or of at least 5.5 V. For example, the electrolysis conditions of step (iii) comprise a voltage ranging between 1.0 V and 10.0 V, or between 1.5 V and 10.0 V, or between 2.0 V and 10.0 V, or between 2.5 V and 10.0 V, or between 3.0 V and 10.0 V, preferably between 3.5 V and 9.5 V, more preferably between 4.0 V and 9.0 V, even more preferably between 4.5 V and 8.5 V, most preferably between 5.0 V and 8.0 V; even most preferably between 5.2 V and 7.8 V or between 5.5 V and 7.5 V.

[0094] The electrolysis conditions of step (iii) advantageously comprise an anode current density of at least 1.0 kA / m2, or of at least 2.0 kA / m2, or of at least 3.0 kA / m2, or of at least 4.0 kA / m2, preferably of at least 4.2 kA / m2or of at least 4.5 kA / m2, more preferably of at least 5.0 kA / m2or of at least 5.5 kA / m2, even more preferably of at least 6.0 kA / m2, most preferably of at least 6.2 kA / m2or of at least 6.5 kA / m2. For example, the electrolysis conditions of step (iii) comprise an anode current density ranging from 1.0 kA / m2to 10 kA / m2, or from 2.0 kA / m2to 10 kA / m2, or from 3.0 kA / m2to 10 kA / m2, or from 4.0 kA / m2to 9.5 kA / m2, preferably from 4.5 kA / m2to 9.0 kA / m2, more preferably from 5.0 kA / m2to 8.5 kA / m2, even more preferably from 6.0 kA / m2to 8.0 kA / m2, most preferably from 6.2 kA / m2to 7.8 kA / m2, or from 6.5 kA / m2to 7.5 kA / m2.

[0095] The electrolysis conditions of step (iii) advantageously comprise a temperature ranging from 20°C to 100°C, preferably from 40°C to 95°C, more preferably from 50°C to 90°C; even more preferably from 60°C to 85°C.

[0096] The step (iv) of recovering from the anode a first stream which is an aqueous solution of unreacted hydrogen bromide advantageously comprises cooling the first stream at a temperature ranging between 10°C and 40°C before the mixing step (vi).

[0097] The second input flow provided at step (ii) advantageously comprises an aqueous solution of one or more mineral acids. With preference, the aqueous solution of one or more mineral acids has a pH ranging from 0.1 to 5.0. With preference, the aqueous solution of one or more mineral acids comprises one or more selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid, hydroiodic acid or a mixture thereof, more preferably sulfuric acid.

[0098] Example

[0099] The following non-limiting example illustrates the disclosure:

[0100] A mixture of HBr (9.0g), H2O (53.0g), Br2 (30.6g) was used for analysis of bromine separation using dilution. As-made mixture is a single-phase solution and no bromine separation occurs under normal conditions. The mixture was diluted with 50 g of demineralized water, stirred for 3 min and left undisturbed in a separation funnel. Second phase of pure bromine has appeared at the bottom. Bromine was removed from the funnel. Total mass of separated bromine was 3.03 g, which corresponds to -10% of overall bromine amount.

[0101] Figure 3 is a plot showing the weight fraction of bromine at saturation in an aqueous solution of hydrogen bromide in function of the ratio of weight fraction of hydrogen bromide to weight fraction of water, namely in function of the quantity of water. Smaller the ratio of weight fraction of hydrogen bromide to weight fraction of water is, higher is the water concentration. It can be seen that a high dilution, namely at high water concentration or at a low ratio of the weight fraction of hydrogen bromide to the weight fraction of water, the weight fraction of bromine at saturation in an aqueous solution of hydrogen bromide is low, thus exacerbating its separation from the hydrogen bromide. This plot is obtained from data found in M.A. Menkovskii, N.A.

[0102] Petrou, K.L. Litvin, J. of Inorganic Chemistry, USSR, Vol. 1 , No. 7, 1956, pp. 1658-1664 and in R. Benizri, P. Lessart, P. Courvoisier, Study of the Liquid-Vapor Equilibrium in the Bromine- Hydrobromic Acid-Water System, Nasa Technical Memorandum, NASA TM-77787, 1984.

Claims

CLAIMS1. A process for separating bromine from an aqueous solution of hydrogen bromide, the process is characterized in that it comprises the following steps: a) providing a first stream which is an aqueous solution of hydrogen bromide, wherein the aqueous solution further comprises bromine and wherein said aqueous solution is a single phase; b) providing a second stream comprising water and / or an aqueous solution of one or more mineral acids; c) mixing the first stream and the second stream so as to obtain a mixture; d) decanting the mixture obtained at step (c) so as to generate at least a third stream which is an aqueous solution of hydrogen bromide comprising bromine wherein the molar ratio between bromine and hydrogen bromide is less than in the mixture obtained at step (c); e) optionally, recovering the third stream.

2. A process for recovering bromine from a hydrogen bromide aqueous solution characterized in that it comprises the following steps: i. providing one or more electrolytic cells (3) each comprising an anode, a cathode, and an ion-exchange membrane placed between the anode and the cathode; ii. providing a first input flow (5) at the anode of the one or more electrolytic cells (3) that is or comprises a hydrogen bromide aqueous solution; and a second input flow (7) at the cathode of the one or more electrolytic cells (3) that is or comprises water or an aqueous solution; iii. performing an electrolysis to convert at least a part of the hydrogen bromide of the first input flow (5) into bromine by operating the one or more electrolytic cells (3) under electrolysis conditions; and iv. recovering from the anode a first stream (9) which is an aqueous solution of unreacted hydrogen bromide, said aqueous solution comprising bromine and wherein said aqueous solution is a single phase; v. providing a second stream (11) comprising water and / or an aqueous solution of one or more mineral acids; vi. mixing the first stream (9) and the second stream (11) so as to obtain a mixture (13); vii. decanting the mixture obtained at step (vi), comprising passing the mixture (13) obtained at step (vi) in a decanter (15) to obtain a first liquid phase (19) comprisingunreacted hydrogen bromide and bromine, wherein the molar ratio between bromine and unreacted hydrogen bromide is less than in the mixture (13) obtained at step (vi); viii. optionally, recovering the first liquid phase (19).

3. Process according to claim 1 or 2, respectively characterized in that the step (d) of decanting the mixture obtained at step (c) or the step (vii) of decanting the mixture (13) obtained at step (vi), further respectively generates a fourth stream which comprises bromine, or a second liquid phase (17) which comprises bromine.

4. Process according to claim 1 or 2, characterized in that, the process further comprises the step of drying respectively said fourth stream or said second liquid phase (17).

5. Process according to any one of claims 1 to 4, characterized in that the first stream, provided at step (a) or recovered at step (iv), which is an aqueous solution of hydrogen bromide, comprises at most 48.3 wt.% of hydrogen bromide based on the total weight of the first stream.

6. Process according to any one of claims 1 to 5, characterized in that the mixture obtained at step (c) or at step (vi) is an aqueous solution of hydrogen bromide with a concentration of hydrogen bromide lower than the concentration of hydrogen bromide presented by the first stream respectively provided at step (a) or recovered at step (iv).

7. Process according to any one of claims 1 to 6, characterized in that the amount of the second stream provided at step (b) or (v) is ranging between 30 wt.% and 70 wt.% of the total weight of the first stream respectively provided at step (a) or recovered at step (iv).

8. Process according to any one of claims 1 to 7, characterized in that when the second stream provided at step (b) or (v) comprises an aqueous solution of one or more mineral acids, the aqueous solution of one or more mineral acids has a pH ranging from 0.1 to 5.0.

9. Process according to any one of claims 1 to 8, characterized in that said one or more mineral acids are selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid, hydroiodic acid or a mixture thereof.

10. Process according to claim 9, characterized in that said mineral acid is sulfuric acid.

11. Process according to any one of claims 1 to 10, characterized in that the step (d) or (vii) of decanting is performed during a time of at least 10 minutes.

12. Process according to any one of claims 1 to 11 , characterized in that the step (d) or (vii) of decanting is performed at a pressure of at least 0.15 MPa.

13. Process according to any one of claims 2 to 12, characterized in that the electrolysis conditions of step (iii) comprise a voltage of at least 1.0 V.

14. Process according to any one claims 2 to 13, characterized in the that the electrolysis conditions of step (iii) comprise an anode current density ranging from 1.0 kA / m2to 10 kA / m2.

15. Process according to any one of claims 2 to 14, characterized in that the electrolysis conditions of step (iii) comprise a temperature ranging from 20°C to 100°C.

16. Process according to claim 15, characterized in that the electrolysis conditions of step (iii) comprise a temperature ranging from 60°C to 85°C.

17. Process according to any one of claims 2 to 16, characterized in that the step (iv) of recovering from the anode a first stream (9) which is an aqueous solution of unreacted hydrogen bromide comprises cooling the first stream (9) at a temperature ranging between 10°C and 40°C before the mixing step (vi).

18. Process according to any one of claims 2 to 17, characterized in that the second input flow (7) provided at step (ii) comprises an aqueous solution of one or more mineral acids.

19. Process according to claim 18, characterized in that the aqueous solution of one or more mineral acids has a pH ranging from 0.1 to 5.0.

20. Process according to claim 18 or 19, characterized in that the aqueous solution of one or more mineral acids comprises one or more selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid, hydroiodic acid or a mixture thereof.21 . Process according to any one of claims 2 to 20, characterized in that the anode comprises an anode catalyst and the cathode comprises a cathode catalyst, and in that the anode catalyst and / or the cathode catalyst is or comprises one or more transition metal-based catalysts comprising ruthenium, rhodium, palladium, osmium, iridium, platinum, titanium,cobalt, iron, nickel, niobium, molybdenum, alloys of titanium, alloys of cobalt, alloys of iron, alloys of nickel, alloys of niobium, alloys of molybdenum, oxides of ruthenium, oxides of rhodium, oxides of palladium, oxides of osmium, oxides of iridium, and oxides of platinum and any mixtures thereof.

22. An installation for recovering bromine from a hydrogen bromide aqueous solution according to the process of any one of claims 2 to 21 ; wherein the installation comprises at least one electrolytic cell (3) with an anode, a cathode, an anode chamber, a cathode chamber, and an ion-exchange membrane separating the anode chamber from the cathode chamber; the installation further comprises at least one decanter (15) with a top part and a bottom part, said top part of the decanter being downstream the anode chamber of said at least one electrolytic cell and in fluidic connection with the anode chamber; the installation is characterized in that it further comprises dilution means placed between the anode chamber and the top part of said at least one decanter.

23. Installation according to claim 22, characterized in that the installation further comprises a drying unit (21) downstream of the bottom part of the decanter and in fluidic connection with said bottom part of the decanter.

24. Installation according to claim 23, characterized in that the drying unit comprises one or more molecular sieves.

25. Installation according to any one of claims 22 to 24, characterized in that the ion-exchange membrane is a cation-exchange membrane.

26. Installation according to claim 25, characterized in that the cation-exchange membrane further comprises an ionomer comprising fluoropolymer having one or more sulfonic acid groups.

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