FR2963338A1 - ELECTROLYSIS METHOD - Google Patents

Abstract

Electrolysis process in which the anode compartment of an electrolysis cell is fed with at least one brine which has been subjected to a stripping treatment in the presence of at least one stripping agent at a pH less than or equal to the pH of the anode compartment of the electrolysis cell, said brine comprising at least one organic compound before the treatment.

Description

The present invention relates to an electrolysis process. The present invention relates more specifically to a method of electrolysis of a brine contaminated with an organic compound and intended to supply an anode compartment of an electrolysis cell.

International Application WO 2008/152043 filed in the name of SOLVAY SA discloses the use of an aqueous composition containing a salt and at least one carboxylic acid as reagent in an electrolysis process. The presence of a carboxylic acid, however, remains a source of problems in the anode compartment of the electrolysis cell, such as troussage and temperature variations, for example. The present invention aims to remedy these problems by providing an electrolysis process that avoids the aforementioned disadvantages. For this purpose, the present invention firstly relates to an electrolysis process in which the anode compartment of an electrolysis cell is fed with at least one brine which has been subjected to a stripping treatment in the presence of at least one a stripping agent at a pH less than or equal to the pH of the anode compartment of the electrolysis cell, said brine comprising at least one organic compound before the treatment. In this case, the electrolysis process and the stripping treatment can be located on the same industrial site or on different industrial sites. In both cases, the electrolysis process and the stripping treatment can be operated by the same legal entity or by different legal entities. To this same effect, the present invention also relates to an electrolysis process comprising: (a) providing a brine comprising at least one organic compound; (b) at least one stripping treatment of the brine of (a) in the presence of at least one stripping agent to obtain a stripped brine; (c) feeding the anode compartment of an electrolysis cell with the brine stripped with (b); and wherein the stripping treatment of (b) is carried out at a pH less than or equal to the pH of the anode compartment of the electrolysis cell of (c).

One of the essential characteristics of the present invention lies in the value of the pH at which the stripping treatment is carried out. By feeding the anode compartment of an electrolysis cell with a brine which has been subjected to at least one stripping treatment carried out at a pH less than or equal to the pH of the anode compartment, no degradation in the performance of the anode compartment is observed. electrolysis cell. The cell voltage and the operating temperature thereof remain unchanged. This has the effect of keeping the cell's productivity constant and of avoiding losses of production capacity as well as of keeping current efficiency constant without generating additional anode overvoltages which are the source of an increase in the specific consumption of electricity. electricity. In the process according to the invention, the term brine means an aqueous composition containing at least one salt. The salt may be an organic salt, an inorganic salt, or a mixture of both. An inorganic salt is preferred. An inorganic salt is a salt whose anions and constituent cations do not contain a carbon-hydrogen bond. The inorganic salt may be selected from the group consisting of metal chlorides, metal sulfates, metal hydrogen sulphates, metal hydroxides, metal carbonates, metal hydrogen carbonates, metal phosphates, hydrogen phosphates of metals, metal borates and mixtures of two or more thereof. Alkaline and alkaline earth chlorides are preferred. Sodium and potassium chlorides are more particularly preferred and sodium chloride is very particularly preferred. The salt content of the brine is generally greater than or equal to 5 g of salt / kg of brine, often greater than or equal to 10 g / kg, frequently greater than or equal to 20 g / kg, commonly greater than or equal to 30 g / kg kg, preferably greater than or equal to 50 g / kg, more preferably greater than or equal to 100 g / kg, even more preferably greater than or equal to 140 g / kg, more preferably still greater than or equal to 160 g / kg, and very particularly preferably greater than or equal to 200 g / kg. This salt content is usually less than or equal to the value of the solubility of the salt expressed in g / kg at the operating temperature of the electrolysis process, in particular at the operating temperature of the anode compartment of the electrolysis cell, preferably less than or equal to the value of said salt solubility decreased by 20 g / kg, and more preferably less than or equal to the value of said salt solubility decreased by 50 g / kg. This salt content is usually less than or equal to 270 g of salt / kg of brine, preferably less than or equal to 250 g / kg and very particularly preferably less than or equal to 230 g / kg. A brine with a sodium chloride content greater than or equal to 140 g / kg and less than 210 g / kg is particularly suitable. A brine with a sodium chloride content greater than or equal to 220 g / kg is also particularly suitable. In the process according to the invention, the organic compound may be selected from the group consisting of aliphatic compounds, aromatic compounds or mixtures of at least two of them. These compounds may optionally contain at least one heteroatom selected from the group consisting of halogens, preferably fluorine, chlorine, bromine and iodine, chalcogens, preferably oxygen or sulfur, nitrogen, phosphorus and mixtures of at least two of them. The heteroatom is preferably oxygen. The organic compound may be as described in the application WO 2009/095429 in the name of SOLVAY (Société Anonyme), and more specifically, in the passage from page 2, line 16, to page 3, line 11. The organic compound is preferably a carboxylic acid. The carboxylic acid may be present in the brine before the stripping treatment in the acid form (protonated) or acid derivative. The carboxylic acid derivative is generally found in the group consisting of carboxylic acid salts, carboxylic acid esters, nitriles, amides, and mixtures of at least two of them. The carboxylic acid is preferably present in the acid form (protonated), a carboxylic acid salt or a mixture of both. The carboxylic acid may be a mono carboxylic acid or a polycarboxylic acid, and is preferably a mono carboxylic acid. The carboxylic acid is preferably a mono carboxylic acid whose number of carbon atoms is greater than or equal to 4 and less than or equal to 30, and in particular greater than or equal to 4 and less than or equal to 20. The acid The monocarboxylic acid is preferably selected from the group consisting of butyric acid, caproic acid, valeric acid, caprylic acid, enanthic acid, pelagornic acid, capric acid, undecanoic acid and the like. , lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nonadecanoic acid,

arachidic acid, heneicosanoic acid, behenic acid, tricosanoic acid, lignoceric acid, pentacosanoic acid, cerotic acid, heptacosanoic acid, montanic acid, nonacosanoic acid, melissic acid, hentriacontanoic acid, laceroic acid, 10-undecenoic acid, myristoleic acid, palmitoleic acid, petroselinic acid, petroselic acid, oleic acid, elaidic acid, gadoleic acid, erucic acid, brassidic acid, nervonic acid, linoleic acid, linolenidic acid, cis, cis, cis-9,12,15-octadecatrienoic acid, linolenic acid, α-eleostearic acid, 3-eleostearic acid, arachidonic acid, clupanodonic acid and mixtures of at least two of them. most preferred selected from the group consisting of butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelagornic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nonadecanoic acid, arachidic acid and mixtures of two or more thereof. The monocarboxylic acid is even more preferably selected from the group consisting of butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, acid and the like. myristic, palmitic acid, stearic acid and mixtures of at least two of them. The monocarboxylic acid is even more preferably selected from the group consisting of lauric acid, palmitic acid, stearic acid and mixtures of at least two of them. The monocarboxylic acid is most preferably selected from the group consisting of capric acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid , stearic acid and mixtures of at least two of them. In the process according to the invention the content of organic compound in the brine before the stripping treatment expressed in g of carbon per kg of brine is generally greater than or equal to 0.05 g / kg, preferably greater than or equal to 0 , 1 g / kg, more preferably greater than 0.5 g / kg and even more preferably greater than or equal to 1 g / kg. This content is generally less than or equal to 20 g / kg of brine, preferably less than or equal to 10 g / kg and more preferably less than or equal to 5 g / kg.

In the process according to the invention, the brine can come from any brine-generating process containing an organic compound. Examples of such processes are the processes for producing epoxides, in particular ethylene oxide, propylene oxide, butylene oxide or epichlorohydrin, processes for producing a derivative of a epoxide, in particular epoxy resins, processes for the production of chlorinated organic products, in particular 1,2-dichloroethane, processes for producing mono- and polyisocyanates, in particular 4,4'-methylenediphenyl diisocyanate (MDI), toluene diisocyanate (TDI) or hexamethylene-1,6-diisocyanate (HDI) and processes for producing the polycarbonates, in particular 2,2-bis (4-hydroxyphenyl) propane polycarbonate (bisphenol A polycarbonate). The brine can be a combination of brines from at least two of these processes. The derivatives of an epoxide, in particular epichlorohydrin, and epoxy resins, may be as described in the application WO 2008/152044 in the name of SOLVAY (Société Anonyme), and more specifically in the passage from page 13, line 22, at page 44, line 8. In the process according to the invention, the brine is preferably derived from a process for the manufacture of epichlorohydrin, a process for the manufacture of epoxy resins, a method of manufacturing 1,2-dichloroethane, a process for producing bisphenol A polycarbonate or a combination of at least two of these processes, and more preferably a process for producing epichlorohydrin, a process for producing epoxy resins, a process for producing 1,2-dichloroethane, or a combination of at least two of these methods.

In the process according to the invention, the brine is even more preferably derived from a process for producing epichlorohydrin, more preferably still, from a process for the manufacture of epichlorohydrin by dehydrochlorination of dichloropropanol, and in a completely particularly preferred for a process for producing epichlorohydrin by dehydrochlorination of dichloropropanol in which at least a part of the dichloropropanol was obtained from glycerol and at least a fraction of said glycerol is natural glycerol that is to say glycerol which was obtained from renewable raw materials. Natural glycerol is as described in the application WO 2006/1 003 1 2 in the name of SOLVAY (Société Anonyme), and more specifically, in the passage from page 4, 2963338 -6 line 22, to page 5, line 24 In this case, the organic compound present in the brine is preferably a mono carboxylic acid selected from the group consisting of butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelagornic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid , nondecanoic acid, arachidic acid, and mixtures of at least two of them. In this case, the brine may contain at least one other organic compound selected from the group consisting of acetone, acrolein, 2-butanone, isopropanol, 3-methoxy-1,2-epoxypropane, cyclopentanone, epichlorohydrin, chloroacetone, hydroxyacetone (acetal), the compound of formula C6H12O, 1,2,3-trichloropropane, 2,3-epoxy-1-propanol (glycido), 2-chloro -2-propen-1-ol, cis-3-chloro-2-propen-1-ol, 1-methoxy-3-chloropropan-2-ol, 3-chloro-1-propan-1-ol, 3 2-chloro-propen-1-ol trans, the compound of the empirical formula C6H8O2, the compound of the empirical formula C6H120Cl2, the compound of the empirical formula C6HI002Cl2, 1,3-dichloro-2-propanol, the compound of the empirical formula C9H10O2, 2,3-dichloro-1-propanol, phenol, glycerol, 1-chloro-2,3-propanediol, 2-chloro-1,3-propanediol, cyclic diglycerols, glyceraldehyde, fortnaldehyde acetaldehyde, propionaldehyde, butyraldehyde, acetic acid, acyl propionic acid, formic acid, glycolic acid, oxalic acid, lactic acid, and mixtures of two or more thereof. In the process according to the invention, stripping is understood to mean the separation of a substance by entrainment by means of a gas, of the vapor of a pure substance or of a mixture of the two (stripping agent) which dissolve or dissolve said substance. In the process according to the invention, said stripping agent may be chosen from the group consisting of air, oxygen-depleted air, nitrogen, oxygen, chlorine and hydrogen chloride. , water vapor, carbon dioxide, and mixtures of at least two of them. Water vapor, air and oxygen-depleted air are preferred stripping agents and water vapor is a more preferred stripping agent. A mixture of water vapor and oxygen-depleted air may also be suitable. When the stripping agent contains water vapor, it can be added to the brine during the stripping treatment or it can be generated from the brine, or it can be partly added to the brine when of the treatment of 2963338 -7

stripping and it can be for another part generated from the brine. The generation of this stripping agent from the brine is well suited. When this stripping agent is added partly or wholly to the brine, said part or all may have any origin. In particular, when the brine is derived at least in part from a process for the manufacture of epichlorohydrin, the stripping agent may come from any stage of the process for the manufacture of epichlorohydrin, in particular from the stage of producing dichloropropanol from glycerol. In this case, the steam is generated in the cooling and / or condensation stages of the dichloropropanol production plant streams. In the process according to the invention, the stripping treatment is carried out in a stripping zone. By stripping zone is meant the area where the brine and the stripping agent are in contact. In the process according to the invention, when the stripping agent is water vapor, the stripping treatment is carried out at a temperature generally greater than or equal to 10 ° C., often greater than or equal to 30 ° C. frequently greater than or equal to 40 ° C, more specifically greater than or equal to 60 ° C, in particular greater than or equal to 80 ° C and most preferably greater than or equal to 90 ° C. This temperature is generally less than or equal to 200 ° C., often less than or equal to 160 ° C., frequently less than or equal to 140 ° C., more specifically less than or equal to 120 ° C. and in particular less than or equal to 100 ° C. . In the process according to the invention, when the stripping agent is selected from the group consisting of air, oxygen-depleted air, nitrogen, oxygen, chlorine, chlorine, and the like. hydrogen, carbon dioxide, and mixtures of at least two of them, and in particular when the stripping agent is air or air depleted in oxygen, the temperature of the brine in the stripping zone is generally greater than or equal to 10 ° C, often greater than or equal to 30 ° C, frequently greater than or equal to 40 ° C and more specifically greater than or equal to 60 ° C. This temperature in the stripping zone is generally less than or equal to 100 ° C., often less than or equal to 90 ° C., frequently less than or equal to 85 ° C. and more specifically less than or equal to 80 ° C. In this case, the temperature of the brine in the stripping zone generally depends on the flow rate of the stripping agent, and a temperature range of between 15 ° C. and 35 ° C. may be suitable as long as the flow rate of the stripping agent stripper agent is sufficiently high.

In the process according to the invention, the temperature of the stripping treatment is often the temperature of the brine in the stripping zone. In the process according to the invention, the stripping treatment is generally carried out under a pressure greater than or equal to 50 mbar absolute, often greater than or equal to 100 mbar absolute, frequently greater than or equal to 200 mbar absolute, more specifically greater than or equal to 500 mbar absolute and in particular greater than or equal to 600 mbar absolute. This pressure is generally less than or equal to 5 bar absolute, often less than or equal to 3 bar absolute, frequently less than or equal to 2 bar absolute, more specifically less than or equal to 1.5 bar absolute and in particular less than or equal to 1, 3 absolute bar. A pressure greater than or equal to 0.7 bar absolute and less than or equal to 1.2 bar absolute is suitable. In the process according to the invention, the pH of the stripping treatment is preferably less than the pH of the anode compartment of the electrolysis cell of at least 0.1 pH unit, more preferably at least 0.5 pH unit, more preferably at least 1 pH unit, still more preferably at least 2 pH units, and more preferably at least 2.5 pH units. This pH is generally less than the pH of the anode compartment of the electrolysis cell of at most 5 pH units, and preferably of at most 4 pH units. In the process according to the invention, the pH of the anode compartment of the electrolysis cell is generally less than or equal to 7, often less than or equal to 6, frequently less than or equal to 5 and specifically less than or equal to 4.5. The pH of the anode compartment of the electrolysis cell is generally greater than or equal to 1, often greater than or equal to 2 and frequently greater than or equal to 2.5. A pH of 4.2 + 1- 0.5 is suitable. In the process according to the invention, the pH of the stripping treatment is generally less than or equal to 6.5, often less than or equal to 5, frequently less than or equal to 3 and specifically less than or equal to 2.5. The pH of the stripping treatment is generally greater than or equal to 0, often greater than or equal to 0.5, frequently greater than or equal to 1 and specifically greater than or equal to 1.5. In the process according to the invention, the pH of the stripping treatment is often the pH of the brine in the stripping zone. The measurement of the pH can be carried out by various means. A measurement using a pH sensitive electrode is suitable. Such an electrode should be stable in the brine before the stripping treatment and in the stripping medium under the stripping conditions and should not contaminate the brine. Glass electrodes for pH measurement are particularly suitable. Examples of such electrodes are given in Ullmann's Encyclopedia of Industrial Chemistry, © 2005, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 10.1002 / 14356007.e19_e01, pp. 8-15. Electrodes of the type 405-DPAS-SC-K85 supplied METTLER TOLEDO® or types Ceragel CPS7I and Orbisint CPS 11 supplied by ENDRESS + HAUSER® are examples of electrodes that can be used.

The measurement of the pH of the anode compartment of the electrolysis cell can be conducted in the brine feeding the anode compartment or "in situ" in the brine in the anode compartment under the conditions of electrolysis or "ex situ" on a sample drawn off brine feeding the anode compartment or withdrawn from the anode compartment and brought to a temperature and pressure adequate to ensure a good longevity of the pH measuring equipment. The measurement of the pH of the anode compartment of the electrolysis cell is preferably conducted "in situ" in the anode compartment under the electrolysis conditions. The measurement of the pH of the stripping treatment can be carried out "in situ" in the brine before the stripping treatment or in the brine in the stripping medium under the conditions of stripping or "ex situ" on a sample drawn from the brine before the stripping treatment or on a brine sample withdrawn from the stripping medium and brought to a temperature and pressure adequate to ensure good longevity of the pH measuring equipment. For "ex situ" measurements, a temperature of 25 ° C and a pressure of 1 bar are examples of suitable temperature and pressure. The impact of temperature and pressure on the pH of the brine can be determined in order to establish a correlation between, for example, the pH of the brine at 25 ° C and 1 bar and that of the brine under the conditions of the brine. temperature and pressure in the stripping zone or in the anode compartment of the electrolysis cell. In general, the means for measuring the pH of the stripping treatment and the anode compartment of the electrolysis cell may be different. They are often identical. Frequently the same type of pH sensitive electrode is used. 2963338 -10-

In general, the conditions for measuring the pH of the stripping treatment and the anode compartment of the electrolysis cell may be different. Frequently the pH of the anode compartment of the electrolysis cell is that measured under the operating conditions of the anode compartment and the pH of the stripping treatment is that measured under the operating conditions of this treatment. In a first embodiment of the process according to the invention, the pH of the brine is brought to the desired value before the stripping treatment and it is naturally maintained at this value during the treatment. In a second embodiment of the process according to the invention, the pH of the brine is brought to the desired value before the stripping treatment and it evolves naturally during the treatment while remaining in the preferred pH range during the treatment. stripping. In a third embodiment of the process according to the invention, the pH of the brine is brought to the desired value before the stripping treatment and maintained at this value during the stripping treatment. In a fourth embodiment of the process according to the invention, the pH of the brine is brought to the desired value and maintained at this value during the stripping treatment. In a fifth embodiment of the process according to the invention, the pH of the brine is brought to the desired value and it evolves naturally during the stripping treatment while remaining in the preferred pH range during the stripping treatment. The first mode and the second embodiment are preferred. In the process according to the invention, the pH at which the stripping treatment is conducted is preferably controlled. In the process according to the invention, the pH can be controlled and maintained in the desired range. This procedure is more particularly used in the third and fourth embodiments of the method according to the invention. In order to maintain the pH in the desired range, the pH is measured and adjusted if necessary. The pH measurement can be done continuously or periodically. In the latter case, the measurement is generally made at a frequency sufficient to maintain the pH in the desired pH range for at least 80% of the duration of the stripping treatment, often for at least 90% of the time. 11-

frequently for at least 95% of the duration and in particular for at least 99% of the duration. The pH can be adjusted and / or maintained in the chosen range by addition of an acidic compound or addition of a basic compound. Inorganic acids and bases are preferred. Hydrogen chloride, gaseous and / or in aqueous solution, is a more preferred acidic compound. Solid sodium hydroxide and / or in aqueous solution and / or in aqueous suspension, is a more preferred basic compound, the aqueous solution of sodium hydroxide being very particularly preferred. The pH adjustment can be carried out in automated mode or in non-automated mode. It is preferred to use an automated mode in which pH control is performed in a closed circuit known as a control loop. Such control loops are described in Ullmann's Encyclopedia of Industrial Chemistry, © 2005, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 10.1002 / 14356007.e19_c0l, pp.24-27. A PROMINENT® DULCOMETERe system type PHD is an example of automated pH control and an adjustment instrument that can be used. In the method according to the invention, the stripping treatment can be carried out in continuous mode or in discontinuous mode. By continuous mode is meant a mode in which the brine and the stripping agent continuously feed a stripping zone over a period of time covering at least 50% of the duration of the stripping treatment, preferably at least 90 % of this duration and more preferably at least 95% of this duration. The duration of the stripping treatment is the time elapsed between the moment the brine and the stripping agent are contacted and the moment when this contacting is interrupted. Batch mode means any other mode of operation. The stripping treatment is preferably carried out in continuous mode. In the process according to the invention, when the stripping treatment is carried out continuously, the stripping agent and the brine can feed the stripping zone in co-currents or in counter currents or in cross currents. Feeding the countercurrent stripping zone is preferred. In the process according to the invention, when the stripping treatment is carried out continuously, the direction of flow of the stripping agent and brine flows can be vertical or horizontal or vertical for the brine flow and horizontal for the flow of the stripping agent or horizontal for the flow of 2963338 - 12 -

brine and vertical for the flow of the stripping agent A direction of vertical movement for the two streams is preferred. In the process according to the invention, the mass ratio between the total amount of stripping agent which is introduced during the stripping treatment and the amount of brine to be stripped is generally greater than or equal to 0.01, frequently higher or equal to 0.02, often greater than or equal to 0.05 and in particular greater than or equal to 0.07. This mass ratio is generally less than or equal to 50, frequently less than or equal to 10, often less than or equal to 1 and in particular less than or equal to 0.5. In the process according to the invention, when the stripping agent is water vapor, and the stripping treatment is carried out continuously in a stripping zone fed with brine and vertically circulating stripping agent and countercurrent, the ratio (ti) between the rising vapor flow rate (V) expressed in kg of steam per hour and that of the descending brine (W) expressed in kg of brine per hour preferably corresponds to the formula following: i a. [1 / (Kw-1)]. Wherein X is greater than or equal to 0.9, preferably greater than or equal to 0.95, and more preferably greater than or equal to 0. , 98 and is less than or equal to 5, preferably less than or equal to 4, more preferably less than or equal to 2.5 and most preferably less than or equal to 2, KW - (Porg / P) (1 / Sorg) td (Morg I Vsumure); q = 1 + [Cm- * tf-CPIF'tF)] / (AHvap) tf; Porg is the vapor pressure of the organic mixture; P is the total pressure of the system; Sorg is the solubility of organic compounds expressed in g of carbon / l; Morg is the molar mass of organics in g of carbon / mol; Vsaumre is the molar volume of the brine in 1 / mol; Xw is the organic compound content of the brine at the bottom of the stripping zone expressed in g of carbon / kg of brine; XF is the organic compound composition of the brine entering the stripping zone expressed in g of carbon / kg of brine; Crrf is the specific heat of the brine entering the stripping zone 35 at the incoming brine temperature tf, expressed in kJ / (kg brine.K); -13-

CpIF is the specific heat of the brine exiting at the bottom of the stripping zone at the temperature of the outgoing brine tF, expressed in kJ / (kg brine.K); and (AH ,, ap) tf is the latent heat of vaporization of the water at the incoming brine temperature tf, expressed in kJ / kg of steam. In the process according to the invention, the stripping treatment is generally carried out in a stripping zone and the stripping zone may comprise any type of apparatus or combination of apparatus such as those described for example in "Perry's". In a particular embodiment of the process according to the invention, the stripping zone comprises at least one stripping column. In a first aspect of this particular embodiment, the stripping zone comprises a single stripping column. In a second aspect of this particular embodiment, the stripping zone comprises more than one stripping column. In a first variant of this second aspect, the columns are fed in series by the brine, and by the stripping agent. In a second variant of this second aspect, the columns are fed in parallel by the brine, and in series by the stripping agent. In a third variant of this second aspect, the columns are supplied in parallel by the brine, and by the stripping agent. The formulas developed above are well suited when the stripping zone comprises a single stripping column. The apparatus in which the stripping process is conducted is generally made of or covered with a material which is resistant to stripping conditions. This material may be selected from the group consisting of carbon steels, stainless steels, enamelled steels, briquetted steels, titanium, titanium alloys and nickel alloys, polymers such as polyolefins such as polypropylene and the like. polyethylene, chlorinated polymers such as polyvinyl chloride and chlorinated polyvinyl chloride, fluorinated polymers such as perfluorinated polymers such as polytetrafluoroethylene, copolymers of tetrafluoroethylene and hexafluoropropylene, and poly (perfluoropropylvinylether), such as Partially fluorinated polymers such as polyvinylidene fluoride, copolymers of ethylene and chlorotrifluoroethylene, such as polymers

comprising sulfur, such as polysulphones and polysulfides, in particular aromatic, coatings using resins such as epoxy resins and phenolic resins, and combinations of at least two of them. The polymers can be used in bulk form, fretted or as a coating. The material is preferably selected from the group consisting of titanium and titanium alloys, and more preferably from the group consisting of titanium alloys. The titanium alloys are preferably selected from alloys comprising titanium and palladium, titanium and ruthenium, or titanium, nickel and molybdenum. Alloys comprising titanium and palladium or titanium and ruthenium are more particularly preferred and those comprising titanium and palladium are most preferred. In the process according to the invention, after the stripping treatment, at least two fractions are generally recovered. The first fraction comprises the stripping agent and a first portion of the organic compound initially present in the brine prior to the stripping treatment. The second fraction comprises brine and a second portion of the organic compound present in the brine prior to the stripping treatment. In the process according to the invention, the stripping treatment is carried out under conditions such that the amount of organic compound present in the first fraction obtained after the stripping treatment is generally greater than or equal to 90% of the amount of the organic compound. present in the brine before the stripping treatment, preferably greater than or equal to 95%, more preferably greater than or equal to 99%, more preferably greater than or equal to 99.9%, and most preferably greater than or equal to equal to 99.99%. In the process according to the invention, the content of organic compound in the second fraction expressed in g of carbon per kg of the second fraction is generally less than 5 g of carbon / kg of the second fraction, preferably less than or equal to 1 g. / kg, more preferably less than or equal to 0.5 g / kg, even more preferably less than or equal to 0.1 g / kg, more preferably less than or equal to 0.05 g / kg and still more preferably less than or equal to 0.01 g / kg. This content is generally greater than or equal to 0.0001 g of carbon per kg of second fraction. 2963338 - 15 -

In the process according to the invention, when the organic compound is a mono carboxylic acid whose number of carbon atoms is greater than or equal to 4 and less than or equal to 20, and preferably chosen from the group consisting of butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and mixtures of two or more of them, the content of acid in the second fraction expressed in g of carbon per kg of the second fraction is generally less than 5 g carbon / kg of the second fraction, preferably less than or equal to 1 g / kg, so more preferably less than or equal to 0.5 g / kg, more preferably still less than or equal to 0.1 g / kg, more preferably still less than or equal to 0.05 g / kg and still more preferred less than or equal to 0.01 g / kg. This content is generally greater than or equal to 0.0001 g of carbon per kg of the second fraction. In this case, the content of butyric acid in the second fraction expressed in g of carbon per kg of the second fraction is generally less than 0.5 g carbon / kg of the second fraction and preferably less than or equal to 0.1 g / kg. In this case, the content of valeric acid (pentanoic acid) in the second fraction expressed in g of carbon per kg of the second fraction is generally less than 0.1 g of carbon / kg of the second fraction, preferably less than or equal to 0 , 02 g / kg and more preferably less than or equal to 0.01 g / kg. In this case, the content of caproic acid (hexanoic acid) in the second fraction expressed in g of carbon per kg of the second fraction is generally less than 0.1 g carbon / kg of the second fraction, preferably less than or equal to 0 , 02 g / kg and more preferably less than or equal to 0.01 g / kg.

In this case, the content of caprylic acid (octanoic) in the second fraction expressed in g of carbon per kg of the second fraction is generally less than 0.01 g carbon / kg of the second fraction and preferably less than or equal to 0.005 g / kg. In this case, the content of capric acid (decanoic) in the second fraction expressed in g of carbon per kg of the second fraction is generally less than 0.015 g carbon / kg of the second fraction and preferably less than or equal to 0.010 g / kg . In this case, the content of lauric acid (dodecanoic) in the second fraction expressed in g of carbon per kg of the second fraction is generally less than 0.005 g of carbon / kg of the second fraction and preferably less than or equal to 0.002 g / kg. . 2963338 - 16-

In the process according to the invention, when the organic compound is a mono carboxylic acid whose number of carbon atoms is greater than or equal to 4 and less than or equal to 20, and preferably chosen from the group consisting of butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and mixtures of two or more among them, the treatment of the brine according to the invention makes it possible to reduce the content of said acids to such values that they do not disturb the electrolysis process in which the brine is engaged. This effect is unexpected. Indeed, whatever the distribution of the acids between their dissociated (basic) and undissociated (acid) form, and therefore the pH at which the stripping treatment is carried out, the elimination of the non-dissociated (acid) form by Stripping agent entrainment should cause displacement of the dissociation equilibrium of the acid towards the acidic fauna and thus its total elimination by the stripping agent. In the process according to the invention, the first fraction obtained after the stripping treatment may be subjected to any subsequent treatment. This treatment may be selected from the group consisting of distillation, evaporation, stripping, liquid-liquid extraction, liquid-liquid phase separation, liquid-solid phase separation, adsorption, deionization absorption, total or partial condensation, solidification and any combination of at least two of them. This subsequent treatment is generally intended to recover in a first part the majority of the organic compound present in the first fraction before the subsequent treatment and in a second part the majority of the stripping agent present in the first fraction before the subsequent treatment. The second part can be recycled in the stripping process or upstream of the stripping process. A first preferred aftertreatment is a liquid-liquid phase separation operation, particularly when the stripping agent 30 comprises water vapor. This separation generally leads to obtaining at least one organic phase which constitutes said first part and at least one aqueous phase which constitutes said second part. The phase separation operation may be a settling, coalescing or a combination thereof. When the organic compound is selected from the group consisting of butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, acid 2963338 -17-

palmitic acid, stearic acid and mixtures of at least two of them, an acidic inorganic compound may be advantageously added to the first fraction. The acidic compound may be added before and / or during the liquid-liquid phase separation operation. Inorganic acids are preferred inorganic acidic compounds. Hydrogen chloride, gaseous and / or in aqueous solution, is a more preferred acidic compound. The amount of acid added is such that the pH of the aqueous phase obtained at the end of the liquid-liquid phase separation operation is generally less than or equal to 4, preferably less than or equal to 3, and more This amount of added acid such as the pH of the aqueous phase obtained at the end of the liquid-liquid phase separation operation is generally greater than or equal to 0.5 and preferably less than or equal to 0.5. greater than or equal to 1. The settling and coalescing operations are carried out at a temperature generally less than or equal to 90 ° C, preferably less than or equal to 80 ° C and more preferably less than or equal to 70 ° C. The settling and coalescing operations are carried out at a temperature generally greater than or equal to 10 ° C, preferably greater than or equal to 25 ° C, more preferably greater than or equal to 35 ° C, most preferably greater than or equal to equal to 50 ° C. A second preferred subsequent treatment consists of a liquid / liquid extraction operation, in particular when the organic compound is selected from the group consisting of butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and mixtures of at least two of them. This separation generally leads to obtaining at least one organic phase which constitutes said first part and at least one aqueous phase which constitutes said second part. The organic phase resulting from the liquid-liquid extraction can be sent to a high temperature oxidation unit. The temperature and pH at which the liquid-liquid extraction operation is carried out are as described above for the liquid-liquid phase separation treatment. When the subsequent treatment is a liquid-liquid phase separation, liquid / liquid extraction or a combination thereof, at least a portion of the organic phase may be recycled upstream or downstream of the treatment. stripping. In particular, when the brine comes from a process for the manufacture of epichlorohydrin, more preferably, a process of - 18 -

production of epichlorohydrin by dehydrochlorination of dichloropropanol, and very particularly preferably a process for the manufacture of epichlorohydrin by dehydrochlorination of dichloropropanol in which at least a part of the dichloropropanol was obtained from glycerol and at least a fraction of which Glycerol is natural glycerol, said part of the organic phase can be recycled in any of these manufacturing processes, in particular in the process for producing dichloropropanol from glycerol. This case is well suited when the organic compound is selected from the group consisting of butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, acid myristic, palmitic acid, stearic acid and mixtures of at least two of them. In the process according to the invention, the first fraction obtained after the stripping treatment can be recycled upstream or downstream of the stripping treatment. It can for example be sent in a high temperature oxidation treatment. This last treatment is well suited in the case where the stripping agent is chosen from the group consisting of air, air depleted in oxygen, nitrogen, oxygen, chlorine, steam of water, carbon dioxide, and mixtures of at least two of them.

In the process according to the invention, the second fraction obtained after the stripping treatment may be subjected to any subsequent treatment before feeding the anode compartment of an electrolysis cell. This treatment can be chosen from the group consisting of thermal conditioning, dilution, concentration, distillation, evaporation, decantation, coalescence, liquid / liquid extraction, filtration, crystallization and adsorption operations. , oxidation, reduction, neutralization, complexation, precipitation, salt addition and combinations of at least two thereof. These treatments are as described in the application WO 2008/152043 of SOLVAY (Société Anonyme) and more specifically in the passage from page II, line 13 to page 29, line 7, and in the application WO 2009/095429 of SOLVAY ( Company Anonymous) and more specifically to the passage from page 1, line 24 to page 27, line 26. The process according to the invention generally comprises at least one operation other than the stripping treatment and chosen from the group consisting of the dilution , concentration, distillation, evaporation, liquid / liquid extraction, filtration, crystallization, adsorption, oxidation, reduction, neutralization, complexation, precipitation, bacterial treatment aerobic, anaerobic bacterial treatment, and combinations of at least two of them.

In the process according to the invention, the brine can therefore be subjected to at least one operation before the stripping treatment at a pH less than or equal to the pH of the anode compartment of the electrolysis cell. This treatment may be chosen from the group consisting of dilution, concentration, distillation, evaporation, decantation, coalescence, liquid / liquid extraction, filtration, crystallization, adsorption and oxidation operations. , reduction, neutralization, complexation, precipitation, and combinations of at least two thereof. These treatments are as described in the application WO 2008/152043 of SOLVAY (Société Anonyme) and more specifically in the passage from page 11, line 13 to page 29, line 7, and in the application WO 2009/095429 of SOLVAY ( Société Anonyme) and more specifically to the passage from page 1, line 24 to page 27, line 26. In another particular embodiment of the process according to the invention, the brine comes from a process for the manufacture of a derivative. epichlorohydrin, in particular an epoxy resin, by reaction between epichlorohydrin and a monohydric alcohol and / or a polyol, in which the epichlorohydrin has been obtained by dehydrochlorination of dichloropropanol at least a part of which has been obtained from glycerol and at least a fraction of said glycerol is natural glycerol. In this embodiment, the brine contains epichlorohydrin and / or dichloropropanol and said brine is subjected to a treatment intended to recover on the one hand most of the epichlorohydrin and / or dichloropropanol contained in the brine, and on the other hand a brine depleted in epichlorohydrin, prior to the stripping treatment of the process according to the invention. In yet another particular embodiment of the process according to the invention, the brine comes from a process for producing an epoxy resin by reaction between dichloropropanol and a monoalcohol and / or a polyol, in which at least a part dichloropropanol was obtained from glycerol and at least a fraction of said glycerol is natural glycerol. In this embodiment, the brine contains epichlorohydrin and / or dichloropropanol and said brine is subjected to a treatment for

recovering on the one hand most of the epichlorohydrin and / or dichloropropanol contained in the brine, and on the other hand a brine depleted in epichlorohydrin, prior to the stripping treatment of the process according to the invention.

In these three embodiments above, the brine generally contains at least one organic compound, other than epichlorohydrin or dichloropropanol. This organic compound is often a monocarboxylic acid, and frequently a carboxylic acid selected from the group consisting of butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and mixtures of at least two of them. In a first variant of these embodiments, the brine depleted in epichlorohydrin and / or dichloropropanol is then subjected to an oxidation treatment prior to the stripping treatment of the process according to the invention. In a second variant of these embodiments, the brine depleted of epichlorohydrin and / or dichloropropanol is subjected to the stripping treatment of the process according to the invention, and the brine resulting from said stripping treatment is then subjected to an oxidation treatment. before feeding the anode compartment of an electrolysis cell. In a third variant of these embodiments, the brine depleted of epichlorohydrin and / or dichloropropanol is acidified and then subjected to a decantation operation. This operation makes it possible to separate at least a portion of the acids contained in the brine before the stripping treatment according to the invention. In the process according to the invention, the electrolysis cell can be a mercury cell or a diaphragm cell or a membrane cell of a chlor-alkali electrolysis. This type of electrolysis can be as described in application WO 2008/152043 in the name of SOLVAY (Société Anonyme) and more specifically the passage from page 31, line 18, to page 37, line 13. The cell of Electrolysis is preferably a membrane cell of a chlor-alkali electrolysis. In the process according to the invention, the electrolysis cell is preferably a mercury cell or a diaphragm cell or a membrane cell of a chlor-alkali electrolysis, and the brine comes from a process chosen from the group consisting of the manufacture of epichlorohydrin, the manufacture of a 2963338 -21-

derived from epichlorohydrin, the manufacture of 1,2-dichloroethane, the manufacture of polycarbonates and combinations of at least two of them. The following examples intend to illustrate the invention without limiting it. Example 1 (according to the invention) (a) 500.4 g of an aqueous brine containing 17% g / g of NaCl and caproic acid corresponding to 69 mg / l of TOC (Total Organic Carbon) was placed in a one-liter flask surmounted by a glass distillation head connected to an oblique cooler for the evacuation and condensation of the vapor emitted during the test. The flask and the distillation head were equipped with a thermowell with a thermocouple. The pH of the brine was adjusted to a value of 2.0 measured at 25 ° C by addition of concentrated hydrochloric acid. The brine was heated to about boiling at atmospheric pressure (105 ° C.) and water vapor was introduced at a constant rate via a capillary tube immersed in the brine. After injection of 50 g of water vapor in 26 min, the brine contained 17 mg / l of TOC and its pH measured at room temperature was 2.11 (b) The electrolysis test was carried out in a cell electrolysis device of 0.6 1, comprising an anode compartment with an anode and a cathode compartment with a cathode separated by a membrane. The anode consisted of titanium coated with an electrochemical coating. The cathode was nickel coated with electrochemical coating. The membrane was an Asahi Glas Company - Flemion F8020 membrane. The cathode compartment was continuously fed with an aqueous composition containing 32% g / g NaOH. The anode compartment was fed with an aqueous composition containing 18% of NaCl and caproic acid corresponding to 18 mg / l of TOC. The pH of the anode compartment was 4. A current density of 4 kA per m 2 of electrode was applied between the anode and the cathode. The cell was maintained at 85 ° C and operated at a pressure of 1 bar absolute. The measured cell voltage was nearly identical to that measured in a reference test performed under the same conditions but with an aqueous composition feeding the anode compartment which contained 18% NaCl and no caproic acid. 2963338 - 22 -

Example 2 (not according to the invention) (a) 496.7 g of an aqueous brine containing 17% g / g of NaCl and caproic acid corresponding to 82 mg / 1 of TOC (Total Organic Carbon) was placed in a 1-liter flask surmounted by a glass distillation head 5 connected to an oblique refrigerant for the evacuation and condensation of the vapor emitted during the test. The flask and the distillation head were equipped with a thermowell with a thermocouple. The pH of the brine was adjusted to a value of 5.5 measured at 25 ° C, by addition of 1N hydrochloric acid. The brine was heated to about boiling at atmospheric pressure (105 ° C.) and water vapor was introduced at a constant rate via a capillary tube immersed in the brine. The pH of the brine was maintained at its starting value by regular addition of 1N hydrochloric acid. After injecting 50 g of steam in 26 min, the brine contained 54 mg / I of TOC and its pH was 5.4. (B) An electrolysis test was carried out according to the conditions described in test 1 at point b differed by the aqueous composition feeding the anode compartment consisting of 18% g / g of NaCl and containing 55 mg / l of TOC. . The pH of the anode compartment was 4. The measured cell voltage was 20 mV higher than the voltage measured in a reference test carried out under the same conditions but with an aqueous composition supplying the anode compartment which contained 18% g / g. g NaCl and no caproic acid.

Claims (10)

CLAIMS 1. A chlor-alkali electrolysis process in which the anode compartment of a chlor-alkali electrolysis cell is fed with at least one brine which has been stripped in the presence of at least one agent stripping at a pH less than or equal to the pH of the anode compartment of the electrolysis cell, said brine comprising at least one organic compound before the treatment. 2. A chlor-alkali electrolysis process comprising: (a) providing a brine comprising at least one organic compound; (b) at least one stripping treatment of the brine of (a) in the presence of at least one stripping agent to obtain a stripped brine; (e) feeding the anode compartment of a chlorealkali electrolysis cell with the brine stripped with (b); and wherein the stripping treatment of (b) is carried out at a pH lower than or equal to the pH of the anode compartment of the electrolysis cell of (c). 3. Method according to claim 1 or 2 wherein the brine before the stripping treatment contains at least sodium chloride in a content greater than or equal to 140 g of NaCl per kg of brine. 4. Process according to any one of claims 1 to 3 wherein the organic compound is a monocarboxylic acid whose carbon number is greater than or equal to 4 and less than or equal to 20. The process according to claim 4 wherein the monocarboxylic acid is selected from the group consisting of butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and mixtures of two or more thereof. 6. Process according to any one of claims 1 to 5 wherein the pH of the stripping treatment is less than the pH of the anode compartment of the electrolysis cell of at least 0.1 pH unit. 7. Method according to any one of claims 1 to 6 wherein the stripping agent selected from the group consisting of air, air depleted in oxygen, nitrogen, oxygen, chlorine , hydrogen chloride, water vapor, carbon dioxide, and mixtures of two or more thereof. 8. The method of claim 7 wherein the stripping agent is water vapor, and the stripping treatment is conducted continuously in a stripping zone fed with brine and vertically circulating stripping agent and countercurrent, the ratio (r) between the rising vapor flow rate (V) expressed in kg of steam per hour and that of the descending brine (W) expressed in kg of brine per hour, corresponds to the following formula: T> at. [1 / (Kw-1)]. {1 + (Xw / XF) [Kw (q-1) -1] 1 where a is greater than or equal to 0.9 and less than or equal to 5; Kw = (Porg / P) (1 / Sorg) td (Morg / Vsumure); q = 1 + [Cplf * tf - CPIF * tF)] / (OHvap) tf; Porg is the vapor pressure of the organic mixture; P is the total pressure of the system; Sorg is the solubility of organic compounds expressed in g of carbon / l; Morg is the molar mass of organics in g of carbon / mol; Vsaumure is the molar volume of the brine in 1 / mol; Xw is the organic compound content of the brine at the bottom of the stripping zone expressed in g of carbon / kg of brine; XF is the organic compound composition of the brine entering the stripping zone expressed in g of carbon / kg of brine; CPIf is the specific heat of the brine entering the stripping zone at the incoming brine temperature tf, expressed in kJ / (kg brine.K); Cp ~ F is the specific heat of the brine exiting at the bottom of the stripping zone at the temperature of the outgoing brine tF, expressed in kJ / (kg brine.K); and (AH'ap) tf is the latent heat of vaporization of the water at the incoming brine temperature tf, expressed in kJ / kg of steam. 9. Process according to any one of claims 1 to 8 comprising at least one operation other than the stripping operation and selected from the group consisting of dilution, concentration, distillation, evaporation, liquid extraction. liquid filtration, crystallization, adsorption, oxidation, reduction, neutralization, complexation, precipitation, aerobic bacterial treatment, anaerobic bacterial treatment, salt addition and combinations of at least two of them. The process according to any one of claims 1 to 9 wherein the chlor-alkali electrolysis cell is a mercury cell or a diaphragm cell or membrane cell of a chlor-alkali electrolysis, and wherein the brine comes from a process selected from the group consisting of the manufacture of epichlorohydrin, the manufacture of a derivative of epichlorohydrin, the manufacture of 1,2-dichloroethane, the manufacture of polycarbonates and combinations of at least two of them.