Patent Application
20130161201
The present application claims benefit of French patent application No. 1056360 filed on Aug. 2, 2010, the content of which is incorporated herein by reference.
Should the disclosure of any of the patents, patent applications, and publications that are incorporated herein by reference conflict with the present specification to the extent that it might render a term unclear, the present specification shall take precedence.
The present invention relates to an electrolysis process. The present invention relates more specifically to a process for the electrolysis of a brine contaminated with an organic compound and intended to feed an anode compartment of an electrolytic cell.
International application WO 2008/152043 filed under the name of SOLVAY SA discloses the use of an aqueous composition containing a salt and at least one carboxylic acid as reactant in an electrolysis process. The presence of a carboxylic acid however remains a source of problems in the anode compartment of the electrolytic cell, such as foaming and temperature variations for example.
The present invention aims to overcome these problems by providing an electrolysis process that makes it possible to avoid the aforementioned disadvantages.
For this purpose, the present invention firstly relates to an electrolysis process in which the anode compartment of an electrolytic 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 electrolytic cell, said brine comprising at least one organic compound before the treatment.
In this case, the electrolysis process and the stripping treatment may be located at one and the same industrial site or at different industrial sites. In these two scenarios, the electrolysis process and the stripping treatment may be operated by one and the same legal entity or by two different legal entities.
For this same purpose, the present invention also relates to an electrolysis process comprising:
One of the essential features of the present invention lies in the pH value at which the stripping treatment is carried out.
By feeding the anode compartment of an electrolytic 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 of the performances of the electrolytic cell is observed. The cell voltage and the operating temperature of this cell remain unchanged. This has the effects of keeping the productivity of the cell constant and of preventing losses in production capacity and also of keeping the current efficiency constant without generating supplementary anode overvoltages which are a source of an increase in the specific electricity consumption.
In the process according to the invention, the term “brine” is understood to mean an aqueous composition containing at least one salt. The salt may be an organic salt, an inorganic salt or a mixture of the two. An inorganic salt is preferred. An inorganic salt is a salt whose constituent anions and cations do not contain a carbon-hydrogen bond. The inorganic salt may be chosen from the group consisting of metal chlorides, metal sulphates, metal hydrogen sulphates, metal hydroxides, metal carbonates, metal hydrogen carbonates, metal phosphates, metal hydrogen phosphates, metal borates and mixtures of at least two thereof. Alkali and alkaline-earth metal chlorides are preferred. Sodium and potassium chlorides are more 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, 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 customarily 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 electrolytic cell, preferably less than or equal to the value of said solubility of the salt decreased by 20 g/kg, and more preferably less than or equal to the value of said solubility of the salt decreased by 50 g/kg. This salt content is habitually 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 for which the sodium chloride content is greater than or equal to 140 g/kg of brine and less than 210 g/kg is very particularly suitable.
A brine for which the sodium chloride content is greater than or equal to 220 g/kg is also very particularly suitable.
In the process according to the invention, the organic compound may be chosen from the group consisting of aliphatic compounds, aromatic compounds or mixtures of at least two thereof. These compounds may optionally contain at least one heteroatom chosen from the group consisting of halogens, preferably fluorine, chlorine, bromine and iodine, chalcogens, preferably, oxygen or sulphur, nitrogen, phosphorus and mixtures of at least two thereof. The heteroatom is preferably oxygen.
The organic compound may be as described in application WO 2009/095429 in the name of SOLVAY (Société Anonyme), of which the content, and more specifically the passage from page 2, line 16, to page 3, line 11, is incorporated by reference.
The organic compound is preferably a carboxylic acid. The carboxylic acid may be present in the brine before the stripping treatment in the acid (protonated) form or in the form of a derivative of the acid. The derivative of the carboxylic acid is generally found in the group consisting of carboxylic acid salts, carboxylic acid esters, nitriles, amides, and mixtures of at least two thereof. The carboxylic acid is preferably present in the acid (protonated) form, in the form of a carboxylic acid salt or a mixture of the two. The carboxylic acid may be a monocarboxylic acid or a polycarboxylic acid, and is preferably a monocarboxylic acid. The carboxylic acid is preferably a monocarboxylic acid, the number of carbon atoms of which is greater than or equal to 4 and less than or equal to 32, conveniently greater than or equal to 4 and less than or equal to 30, in particular greater than or equal to 4 and less than or equal to 20 and specifically greater than 6 and less than or equal to 20. A monocarboxylic acid which molecule contains no more than two oxygen atoms is also suitable. The monocarboxylic acid is preferably a fatty acid. By fatty acid, one intends to denote an acid chosen from the group consisting of butyric acid, caproic acid, valeric acid, caprylic acid, enanthic acid, pelargonic acid, capric acid, undecanoic acid, 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, lacceroic acid, 10-undecenoic acid, myristoleic acid, palmitoleic acid, petroselinic acid, petroselaidic acid, oleic acid, elaidic acid, gadoleic acid, erucic acid, brassidic acid, nervonic acid, linoleic acid, linolelaidic acid, cis,cis,cis-9,12,15-octadecatrienoic acid, linolenic acid, α-eleostearic acid, β-eleostearic acid, arachidonic acid, clupanodonic acid and mixtures of at least two thereof.
The monocarboxylic acid is more preferably chosen from the group consisting of butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelagonic acid, capric acid, undecanoic acid, 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, lacceroic acid and mixtures of at least two thereof.
The monocarboxylic acid is more preferably chosen from the group consisting of butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelagonic 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 at least two thereof.
The monocarboxylic acid is more preferably still 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 at least two thereof.
The monocarboxylic acid is more preferably still chosen from the group consisting of lauric acid, palmitic acid, stearic acid and mixtures of at least two thereof.
The monocarboxylic acid is equally preferably chosen 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 thereof.
The monocarboxylic acid is equally preferably chosen from the group consisting of butyric acid, valeric acid and mixtures thereof.
A monocarboxylic acid chosen from the group consisting of 10-undecenoic acid, myristoleic acid, palmitoleic acid, petroselinic acid, petroselaidic acid, oleic acid, elaidic acid, gadoleic acid, erucic acid, brassidic acid, nervonic acid, linoleic acid, linolelaidic acid, cis,cis,cis-9,12,15-octadecatrienoic acid, linolenic acid, α-eleostearic acid, β-eleostearic acid, arachidonic acid, clupanodonic acid and mixtures of at least two thereof, is also convenient.
The monocarboxylic acid is most preferably chosen from the group consisting of butyric acid, valeric acid and mixtures thereof.
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 0.005 g/kg, preferably greater or equal to 0.01 g/kg, still preferably greater than or equal to 0.05 g/kg, yet preferably greater than or equal to 0.1 g/kg, more preferably greater than 0.5 g/kg, yet more preferably greater than or equal to 0.75 g/kg, more preferably still greater than or equal to 1 g/kg, and most preferably greater than or equal to 2.5 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 may originate from any process that generates a brine containing an organic compound. Examples of such processes are the processes for manufacturing epoxides, in particular ethylene oxide, propylene oxide, butylene oxide or epichlorohydrin, the processes for manufacturing a derivative of an epoxide, in particular epoxy resins, the processes for manufacturing chlorinated organic products, in particular 1,2-dichloroethane, the processes for manufacturing monoisocyanates and polyisocyanates, in particular 4,4′-methylenediphenyl diisocyanate (MDI), toluene diisocyanate (TDI) or hexamethylene-1,6-diisocyanate (HDI) and the processes for manufacturing polycarbonates, in particular 2,2-bis(4-hydroxyphenyl)propane polycarbonate (bisphenol A polycarbonate). The brine may be a combination of brines originating from at least two of these processes. The derivatives of an epoxide, in particular of epichlorohydrin, and the epoxy resins, may be as described in application WO 2008/152044 in the name of SOLVAY (Société Anonyme), of which the content, and more specifically the passage from page 13, line 22, to page 44, line 8, is incorporated herein by reference.
In the process according to the invention, the brine preferably originates from a process for manufacturing epichlorohydrin, from a process for manufacturing epoxy resins, from a process for manufacturing 1,2-dichloroethane, from a process for manufacturing bisphenol A polycarbonate or from a combination of at least two of these processes, and more preferably from a process for manufacturing epichlorohydrin, from a process for manufacturing epoxy resins, from a process for manufacturing 1,2-dichloroethane, or from a combination of at least two of these processes.
In the process according to the invention, the brine yet more preferably originates from a process for manufacturing epichlorohydrin, more preferably still from a process for manufacturing epichlorohydrin by dehydrochlorination of dichloropropanol, and very particularly preferably from a process for manufacturing epichlorohydrin by dehydrochlorination of dichloropropanol in which at least one portion of the dichloropropanol was obtained from glycerol and of which at least one fraction of said glycerol is natural glycerol, i.e. glycerol which has been obtained from renewable raw materials. The natural glycerol is as described in application WO 2006/100312 in the name of SOLVAY (Société Anonyme), of which the content, and more specifically the passage from page 4, line 22, to page 5, line 24, is incorporated herein by reference. In this case, the organic compound present in the brine is preferably a monocarboxylic acid chosen from the group consisting of butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelagonic 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 at least two thereof. In this case, the brine may contain at least one other organic compound chosen from the group consisting of acetone, acrolein, 2-butanone, isopropanol, 3-methoxy-1,2-epoxypropane, cyclopentanone, epichlorohydrin, chloroacetone, hydroxyacetone (acetol), the compound of empirical formula C6H12O, 1,2,3-trichloropropane, 2,3-epoxy-1-propanol (glycidol), 2-chloro-2-propen-1-ol, cis-3-chloro-2-propen-1-ol, 1-methoxy-3-chloropropane-2-ol, 3-chloro-1-propane-1-ol, trans-3-chloro-2-propen-1-ol, the compound of empirical formula C6H8O2, the compound of empirical formula C6H12OCl2, the compound of empirical formula C6H10O2Cl2, 1,3-dichloro-2-propanol, the compound of empirical formula C9H10O2, 2,3-dichloro-1-propanol, phenol, glycerol, 1-chloro-2,3-propanediol, 2-chloro-1,3-propanediol, cyclic diglycerols, glyceraldehyde, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, acetic acid, propionic acid, formic acid, glycolic acid, oxalic acid, lactic acid, and the mixtures of at least two thereof.
The processes for preparing epoxy resins, dichloropropanol and epichlorohdyrin can be such as disclosed in International applications WO2005/054167, WO2006/100311, WO2006/100312, WO2006/100313, WO2006/100314, WO2006/100315, WO2006/100316, WO2006/100317, WO2006/106153, WO2007/054505, WO 2006/100318, WO2006/100319, WO2006/100320, WO 2006/106154, WO2006/106155, WO 2007/144335, WO 2008/107468, WO 2008/101866, WO 2008/145729, WO 2008/110588, WO 2008/152045, WO 2008/152043, WO 2009/000773, WO 2009/043796, WO 2009/121853, WO 2008/152044, WO 2009/077528, WO 2010/066660, WO 2010/029039, WO 2010/029153, WO 2011/054769 and WO 2011/054770, filed in the name of SOLVAY, the contents of which are incorporated herein by reference. In the process according to the invention, the term “stripping” is understood to mean the separation of a substance by entrainment using a gas, the vapour of a pure material or a mixture thereof (stripping agent) which dissolves or does not 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, hydrogen chloride, steam, carbon dioxide and mixtures of at least two thereof. Steam, air and oxygen-depleted air are preferred stripping agents and steam is a more preferred stripping agent. A mixture of steam and oxygen-depleted air may also be suitable.
When the stripping agent contains steam, it may be added to the brine during the stripping treatment or it may be generated from the brine, or it may be, for one portion, added to the brine during the stripping treatment and it may be, for another portion, generated from the brine. Generating this stripping agent from the brine is very suitable. When this stripping agent is added as a portion or in its entirety to the brine, said portion or the entirety may have any origin. In particular, when the brine originates at least partly from a process for manufacturing epichlorohydrin, the stripping agent may originate from any step of the process for manufacturing epichlorohydrin, in particular from the step of producing dichloropropanol from glycerol. In this case, the vapour is generated in the steps of cooling and/or condensing the streams from the dichloropropanol production plant.
In the process according to the invention, the stripping treatment is carried out in a stripping zone. The expression “stripping zone” is understood to mean the zone where the brine and the stripping agent are in contact.
In the process according to the invention, when the stripping agent is steam, 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. and more specifically greater than or equal to 60° C., in particular greater than or equal to 80° C. and very particularly 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 chosen from the group consisting of air, oxygen-depleted air, nitrogen, oxygen, chlorine, hydrogen chloride, carbon dioxide and mixtures of at least two thereof, and in particular when the stripping agent is air or oxygen-depleted air, 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 between 15° C. and 35° C. may be suitable as long as the flow rate of the stripping agent is high enough.
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 bar absolute. A pressure greater than or equal to 0.7 bar absolute and less than or equal to 1.2 bar absolute is very suitable.
In the process according to the invention, the pH of the stripping treatment is preferably below the pH of the anode compartment of the electrolytic cell by at least 0.1 pH unit, more preferably by at least 0.5 pH unit, even more preferably by at least 1 pH unit, more preferably still by at least 2 pH units, and more particularly preferably by at least 2.5 pH units. This pH is generally below the pH of the anode compartment of the electrolytic cell by at most 5 pH units, and preferably by at most 4 pH units.
In the process according to the invention, the pH of the anode compartment of the electrolytic 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 electrolytic 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±0.5 is very 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 pH can be measured by various means. Measurement using a pH-sensitive electrode is very 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 the 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 405-DPAS-SC-K85 type supplied by METTLER TOLEDO® or of Ceragel CPS71 and Orbisint CPS11 types supplied by ENDRESS+HAUSER® are examples of electrodes that can be used.
The pH of the anode compartment of the electrolytic cell may be measured in the brine feeding the anode compartment or in situ in the brine in the anode compartment under the electrolysis conditions or ex situ on a sample withdrawn from the brine feeding the anode compartment or withdrawn from the anode compartment and brought to a temperature and to a pressure that are suitable for ensuring a good service life of the pH measurement equipment. The pH of the anode compartment of the electrolytic cell is preferably measured in situ in the anode compartment under the electrolysis conditions.
The pH of the stripping treatment may be measured in situ in the brine before the stripping treatment or in the brine in the stripping medium under the stripping conditions or ex situ on a sample withdrawn from the brine before the stripping treatment or on a sample of brine withdrawn from the stripping medium and brought to a temperature and to a pressure that are suitable for ensuring a good service life of the pH measurement equipment.
For the ex situ measurements, a temperature of 25° C. and a pressure of 1 bar are examples of suitable temperature and pressure. The impact of the temperature and of the pressure on the pH of the brine may be determined so as to establish a correlation between, for example, the pH of the brine at 25° C. and under 1 bar and that of the brine under the temperature and pressure conditions in the stripping zone or in the anode compartment of the electrolytic cell.
Generally, the means of measuring the pH of the stripping treatment and of the anode compartment of the electrolytic cell may be different. They are often identical. Frequently, the same type of pH-sensitive electrode is used.
Generally, the conditions for measuring the pH of the stripping treatment and of the anode compartment of the electrolytic cell may be different. Frequently, the pH of the anode compartment of the electrolytic 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 maintained naturally 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 changes naturally during the treatment while remaining in the preferred pH range during the stripping treatment.
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 is 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 is 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 changes naturally during the stripping treatment while remaining in the preferred pH range during the stripping treatment.
The first embodiment and second embodiment are preferred.
In the process according to the invention, the pH at which the stripping treatment is carried out is preferably controlled.
In the process according to the invention, the pH may be controlled and maintained within the desired range. This procedure is more particularly used in the third and fourth embodiments of the process according to the invention.
So as to maintain the pH in the desired range, the pH is measured and adjusted if necessary.
The pH may be measured continuously or periodically. In the latter case, the measurement is generally carried out at a sufficient frequency to maintain the pH within the desired pH range over at least 80% of the duration of the stripping treatment, often over at least 90% of the duration, frequently over at least 95% of the duration and in particular over at least 99% of the duration.
The pH may be adjusted and/or maintained within the chosen range by addition of an acid compound or by addition of a basic compound. Inorganic acids and bases are preferred. Hydrogen chloride, gaseous and/or in aqueous solution, is a more preferred acid compound. Sodium hydroxide, solid 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 may be adjusted in automated mode or in non-automated mode. It is preferred to use an automated mode in which the control of the pH is carried out in a closed circuit known under the name of a control loop. Such control loops are described in Ullmann's Encyclopedia of Industrial Chemistry,© 2005, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
In the process according to the invention, the stripping treatment may be carried out in continuous mode or in batch mode. The expression “continuous mode” is understood to mean a mode in which the brine and the stripping agent feed a stripping zone in an uninterrupted manner 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 when the brine and the stripping agent are brought into contact and the moment when this contact is interrupted. The expression “batch mode” is understood to mean any other operating mode. 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 may feed the stripping zone cocurrently or countercurrently or crosscurrently. Countercurrent feeding of the stripping zone is preferred.
In the process according to the invention, when the stripping treatment is carried out continuously, the direction of movement of the streams of stripping agent and of brine may be vertical or horizontal, or vertical for the stream of brine and horizontal for the stream of stripping agent or horizontal for the stream of brine and vertical for the stream of stripping agent. A vertical direction of movement for both streams is preferred.
In the process according to the invention, the weight ratio between the total amount of stripping agent that is introduced during the stripping treatment and the amount of brine to be stripped is generally greater than or equal to 0.01, frequently greater than or equal to 0.02, often greater than or equal to 0.05 and in particular greater than or equal to 0.07. This weight 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 steam, and when the stripping treatment is carried out in continuous mode in a stripping zone fed with brine and with stripping agent circulating vertically and countercurrently, the ratio (τ) between the flow rate of ascending steam (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 following formula:
τ=α.[1/(KW−1)].{1+(XW/XF)[KW(q−1)−]}
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 equipment or combination of equipment such as those, for example, described in “Perry's Chemical Engineers' Handbook” in the 14th section of the 7th Edition, 1997.
In one particular embodiment of the process of 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 a single 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 fed in parallel by the brine, and by the stripping agent.
The formulae developed above are very suitable when the stripping zone comprises a single stripping column.
The equipment in which the stripping treatment is carried out is generally made of or covered with a material that withstands the stripping conditions. This material may be chosen from the group consisting of carbon steels, stainless steels, enamelled steels, compressed steels, titanium, titanium alloys and nickel alloys, polymers, coatings using resins such as epoxy resins and phenolic resins, and combinations of at least two thereof. Polymers can be for instance, polyolefins, such as polypropylene and polyethylene, chlorinated polymers, such as polyvinyl chloride and chlorinated polyvinyl chloride, fluorinated polymers, such as perfluorinated polymers, like for example polytetrafluoroethylene, copolymers of tetrafluorethylene and hexafluoropropylene, and poly(perfluoropropyl vinyl ether), such as partially fluorinated polymers, like for example polyvinylidene fluoride and copolymers of ethylene and chlorotrifluoroethylene, sulphur-containing polymers, such as polysulphones and polysulphides, in particular that are aromatic. The polymers may be used in bulk or shrunk-fit form or as a coating. The material is preferably chosen from the group consisting of titanium and titanium alloys and more preferably from the group consisting of titanium alloys. The titanium alloys are preferably chosen from the 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 very particularly preferred.
In the process according to the invention, after the stripping treatment, in general at least two fractions are recovered. The first fraction comprises the stripping agent and a first portion of the organic compound initially present in the brine before the stripping treatment. The second fraction comprises the brine and a second portion of the organic compound present in the brine before 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 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 still greater than or equal to 99.9% and very particularly preferably greater than or 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 second fraction is generally less than 5 g of carbon/kg of 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 still less than or equal to 0.05 g/kg and more preferably still 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.
In the process according to the invention, when the organic compound is a monocarboxylic acid, the number of carbon atoms of which is greater than or equal to 4 and less than or equal to 20, 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 at least two thereof, the content of acid in the second fraction expressed in g of carbon par kg of second fraction is generally less than 5 g of carbon/kg of 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 still less than or equal to 0.05 g/kg and more preferably still 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. In this case, the content of butyric acid in the second fraction expressed in g of carbon per kg of second fraction is generally less than 0.5 g of carbon/kg of 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 second fraction is generally less than 0.1 g of carbon/kg of 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 second fraction is generally less than 0.1 g of carbon/kg of 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 acid) in the second fraction expressed in g of carbon per kg of second fraction is generally less than 0.01 g of carbon/kg of second fraction and preferably less than or equal to 0.005 g/kg. In this case, the content of capric acid (decanoic acid) in the second fraction expressed in g of carbon per kg of second fraction is generally less than 0.015 g of carbon/kg of second fraction and preferably less than or equal to 0.010 g/kg. In this case, the content of lauric acid (dodecanoic acid) in the second fraction expressed in g of carbon per kg of second fraction is generally less than 0.005 g of carbon/kg of second fraction and preferably less than or equal to 0.002 g/kg.
In the process according to the invention, when the organic compound is a monocarboxylic acid, the number of carbon atoms of which is greater than or equal to 4 and less than or equal to 20, 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 at least two thereof, the treatment of the brine according to the invention makes it possible to reduce the content of said acids to values such that they do not disrupt the electrolysis process in which the brine is engaged. This effect is unexpected. Indeed, irrespective of the distribution of the acids between the dissociated (basic) and undissociated (acid) form thereof, and therefore of the pH at which the stripping treatment is carried out, the removal of the undissociated (acid) form via entrainment by the stripping agent should shift the acid dissociation equilibrium towards the acid form and should therefore give rise to the complete removal thereof 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 chosen from the group consisting of distillation, evaporation, stripping, liquid-liquid extraction, liquid-liquid phase separation, liquid-solid phase separation, adsorption, absorption, complete or partial condensation, solidification and any combination of at least two thereof. This subsequent treatment is generally intended to recover, in a first portion, the majority of the organic compound present in the first fraction before the subsequent treatment and, in a second portion, the majority of the stripping agent present in the first fraction before the subsequent treatment. The second portion may be recycled to the stripping treatment or upstream of the stripping treatment.
A first preferred subsequent treatment consists of a liquid-liquid phase separation operation, in particular when the stripping agent comprises steam. This separation generally results in at least one organic phase, which constitutes said first portion, and at least one aqueous phase, which constitutes said second portion, being obtained. The phase separation operation may be a settling operation, a coalescence operation or a combination thereof. When the organic compound is 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 at least two thereof, an acid inorganic compound may advantageously be added to the first fraction. The acid compound may be added before and/or during the liquid-liquid phase separation operation. Inorganic acids are preferred acid inorganic compounds. Hydrogen chloride, gaseous and/or in aqueous solution, is a more preferred acid 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 preferably less than or equal to 2. This amount of acid added so that 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 greater than or equal to 1. The settling and coalescence 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 coalescence 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. and very particularly preferably greater than or equal to 50° C.
A second preferred subsequent treatment consists of a liquid-liquid extraction operation, in particular when the organic compound is 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 the mixtures of at least two thereof. This separation generally results in at least one organic phase, which constitutes said first portion, and at least one aqueous phase, which constitutes said second portion, being obtained.
The organic phase resulting from the liquid-liquid extraction may be sent to a high-temperature oxidation unit. The temperature and the 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 operation, liquid-liquid extraction operation, or a combination thereof, at least one portion of the organic phase may be recycled upstream or downstream of the stripping treatment. In particular, when the brine originates from a process for manufacturing epichlorohydrin, preferably from a process for manufacturing epichlorohydrin by dehydrochlorination of dichloropropanol, and very particularly preferably from a process for manufacturing epichlorohydrin by dehydrochlorination of dichloropropanol in which at least one portion of the dichloropropanol was obtained from glycerol and of which at least one fraction of said glycerol is natural glycerol, said portion of the organic phase may be recycled to any of these manufacturing processes, in particular to the process for manufacturing dichloropropanol from glycerol. This scenario is very suitable when the organic compound is 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 the mixtures of at least two thereof.
In the process according to the invention, the first fraction obtained after the stripping treatment may be recycled upstream or downstream of the stripping treatment. It may for example be sent to a high-temperature oxidation treatment. The latter treatment is very suitable in the case where the stripping agent is chosen from the group consisting of air, oxygen-depleted air, nitrogen, oxygen, chlorine, steam, carbon dioxide and mixtures of at least two thereof.
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 electrolytic cell. This treatment may be chosen from the group consisting of thermal conditioning, dilution, concentration, distillation, evaporation, settling, coalescence, liquid-liquid extraction, filtration, crystallization, adsorption, oxidation, reduction, neutralization, complexation, precipitation and salt addition operations and combinations of at least two thereof. These treatments are as described in application WO 2008/152043 by SOLVAY (Société Anonyme), of which the content, and more specifically the passage from page 11, line 13 to page 29, line 7, is incorporated herein by reference and in application WO 2009/095429 by SOLVAY (Société Anonyme), of which the content, and more specifically the passage from page 1, line 24 to page 27, line 26 is incorporated herein by reference.
The process according to the invention generally comprises at least one operation other than the stripping treatment, chosen from the group consisting of dilution, concentration, distillation, evaporation, liquid/liquid extraction, filtration, crystallization, adsorption, oxidation, reduction, neutralization, complexation, precipitation, aerobic bacterial treatment, anaerobic bacterial treatment, and combinations of at least two thereof.
In the process according to the invention, the brine may 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 electrolytic cell. This treatment may be chosen from the group consisting of dilution, concentration, distillation, evaporation, settling, coalescence, liquid-liquid extraction, filtration, crystallization, adsorption, oxidation, reduction, neutralization, complexation and precipitation operations and combinations of at least two thereof. These treatments are as described in application WO 2008/152043 by SOLVAY (Société Anonyme), of which the content, and more specifically the passage from page 11, line 13 to page 29, line 7, is incorporated herein by reference and in application WO 2009/095429 by SOLVAY (Société Anonyme), of which the content, and more specifically the passage from page 1, line 24 to page 27, line 26 is incorporated herein by reference.
In another particular embodiment of the process according to the invention, the brine originates from a process for manufacturing a derivative of epichlorohydrin, in particular an epoxy resin, by reaction between epichlorohydrin and a monoalcohol and/or a polyol, in which the epichlorohydrin was obtained by dehydrochlorination of dichloropropanol, of which at least one portion was obtained from glycerol, and of which at least one 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 that is 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 originates from a process for manufacturing an epoxy resin by reaction between dichloropropanol and a monoalcohol and/or a polyol, in which at least one portion of the dichloropropanol was obtained from glycerol, and of which at least one 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, an epichlorohydrin-depleted brine, prior to the stripping treatment of the process according to the invention.
In these preceding three embodiments, 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 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 the mixtures of at least two thereof.
In a first variant of these embodiments, the brine that is depleted in epichlorohydrin and/or in 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 that is depleted in epichlorohydrin and/or in 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 electrolytic cell.
In a third variant of these embodiments, the brine that is depleted in epichlorohydrin and/or in dichloropropanol is acidified and then subjected to a settling operation. This operation makes it possible to separate at least one portion of the acids contained in the brine before the stripping treatment according to the invention.
In the process according to the invention, the electrolytic cell may be a mercury cell or a diaphragm cell or a membrane cell of a chlor-alkali electrolysis. This type of electrolysis may be as described in application WO 2008/152043 in the name of SOLVAY (Société Anonyme), of which the content, and more specifically the passage from page 31, line 18, to page 37, line 13, is incorporated herein by reference. The electrolytic cell is preferably a membrane cell of a chlor-alkali electrolysis.
In the process according to the invention, the electrolytic cell is preferably a membrane cell of a chlor-alkali electrolysis, and the brine originates from a process for the manufacture of epichlorohydrin, still more preferably from a process for manufacturing epichlorohydrin by dehydrochlorination of dichloropropanol in which at least one portion of the dichloropropanol has obtained from glycerol and of which at least one fraction of said glycerol has been obtained from renewable raw materials.
In the process according to the invention, the electrolytic cell is preferably a mercury cell or a diaphragm cell or a membrane cell of a chlor-alkali electrolysis, and the brine originates from a process chosen from the group consisting of the manufacture of epichlorohydrin, the manufacture of an epichlorohydrin derivative, the manufacture of 1,2-dichloroethane, the manufacture of polycarbonates and combinations of at least two thereof.
The examples below are intended to illustrate the invention without, however, limiting it.
The cell voltage measured was 20 mV higher than the voltage measured in a reference test carried out under the same conditions but with an aqueous composition feeding the anode compartment that contains 18% g/g of NaCl and no caproic acid.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10.56360 | Aug 2010 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP11/62711 | 7/25/2011 | WO | 00 | 1/30/2013 |
