WO2014161867A1 - Chlor-alkali electrolysis process - Google Patents

Chlor-alkali electrolysis process Download PDF

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Publication number
WO2014161867A1
WO2014161867A1 PCT/EP2014/056549 EP2014056549W WO2014161867A1 WO 2014161867 A1 WO2014161867 A1 WO 2014161867A1 EP 2014056549 W EP2014056549 W EP 2014056549W WO 2014161867 A1 WO2014161867 A1 WO 2014161867A1
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WO
WIPO (PCT)
Prior art keywords
brine
equal
depleted
vessel
treatment
Prior art date
Application number
PCT/EP2014/056549
Other languages
French (fr)
Inventor
Luca SAONER
Attilio BARGAGLI
Mauro Ricciardi
Original Assignee
Solvay Sa
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Solvay Sa filed Critical Solvay Sa
Publication of WO2014161867A1 publication Critical patent/WO2014161867A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
    • C25B1/46—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in diaphragm cells
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms

Definitions

  • the present invention relates to a chlor-alkali electrolysis process, more specifically a process for electrolysing a brine.
  • Electrolysis of brines is a well known process.
  • the brine used may be obtained by dissolving a salt, preferably rock salt, in water or may be a byproduct from a chemical process. Such process usually generates depleted brines that have to be disposed of or recycled to the electrolysis.
  • treatments for purifying such brines exist, their impact on the chlor-alkali electrolysis process remains often unpredictable because such processes are complex and extremely sensitive to even low amounts of impurities in the brine.
  • Assessing the suitability of brines for an industrial production of chlorine by electrolysis requires tests of brines in down-sized installations. However, down-sizing of all parts of the process is not always possible, in particular for long term continuous operation.
  • the object of the present invention is to provide an electrolysis process which does overcome these drawbacks.
  • the invention therefore relates in a first embodiment to a process for electrolyzing an entering brine into a depleted brine, comprising feeding at least one first vessel intermittently with a brine, subjecting this brine to at least one treatment in order to obtain the entering brine, feeding at least one electrolyser continuously with the entering brine in order to obtain the depleted brine, and withdrawing continuously the depleted brine from said electrolyser.
  • the chlor-alkali electrolysis process according to the invention is named indifferently chlor-alkali electrolysis process or electrolysis process or process in the text of the present application.
  • the electrolysis is carried out continuously, which allows evaluating the electrolysis performances over long periods of steady- state conditions of operation.
  • the electrolyser is fed from a vessel being intermittently supplied with the brine to be electrolysed. Such intermittent supply of the vessel has the advantage of allowing a down-sizing of the brine treatment equipment compatible with the down-sizing of the electrolyser and compatible with the brine treatment conditions of an industrial electrolysis process.
  • the chlor-alkali electrolysis process according to the invention is preferably a process for the production of chlorine and more preferably a chlor- alkali membrane electrolysis process for the production of chlorine.
  • brine By brine, one intends to denote any aqueous composition containing a metal chloride salt, which is to be submitted to the electrolysis in the electrolysis plant according to the invention.
  • the brine is preferably an alkaline metal chloride, an alkaline-earth metal chloride or any mixture thereof, more preferably an alkaline metal chloride, still more preferably sodium chloride, potassium chloride or any mixture thereof and most preferably sodium chloride.
  • the brine can originate from any source.
  • the brine is preferably selected from a brine from an industrial process for manufacturing chlorine, a brine from an epoxide manufacturing process, preferably ethylene oxide, propylene oxide, butylene oxide or epichlorohydrin, and more preferably epichlorohydrin, a brine from an epoxide derivative manufacturing process, preferably epoxy resin, a brine from a process for manufacturing a chlorinated organic product, preferably 1 ,2-dichloroethane or 1 ,2-dichloroethylene, and more preferably 1 ,2-dichloroethane, a brine from a process for manufacturing a monoisocyanate or a polyisocyanate, preferably 4,4'-methylenediphenyl diisocyanate (MDI), toluene diisocyanate (TDI) or hexamethylene-1,6
  • MDI 4,4'-methylenediphenyl diisocyanate
  • TDI tolu
  • depleted brine By depleted brine, one intends to denote a brine as described here above which has been depleted in salt after the electrolysis in the electrolysis process according to the invention.
  • the electrolysis process according to the invention preferably comprises feeding at least one second vessel continuously with the depleted brine from said electrolyser, withdrawing the depleted brine intermittently from said second vessel, and subjecting the depleted brine to at least one other treatment after withdrawal from the second vessel.
  • the electrolysis process according to the invention more preferably comprises feeding at least one third vessel continuously with the entering brine and feeding the at least one electrolyser continuously with the entering brine from said third vessel.
  • the electrolysis process according to the invention preferably comprises feeding the first vessel with the brine at a first flow rate, feeding the electrolyser with the entering brine at a second flow rate, withdrawing the depleted brine from said electrolyser at a third flow rate, and when the second and third flow rates are not zero, the first flow rate is occasionally zero.
  • the ratio between the duration when the first flow rate is zero and the duration when the second and third flow rates are not zero is higher than or equal to 0.1, preferably higher than or equal to 0.5 and most preferably higher than or equal to 0.9.
  • the electrolysis process according to the invention preferably comprises feeding the first vessel with the brine at a first flow rate, feeding the electrolyser with the entering brine at a second flow rate, withdrawing the depleted brine from said electrolyser at a third flow rate, withdrawing the depleted brine from the second vessel at a fourth flow rate, and when the second and third flow rates are not zero, the fourth flow is occasionally zero.
  • the ratio between the duration when the fourth flow is zero and the duration when the second and third flows are not zero is higher than or equal to 0.1, preferably higher than or equal to 0.5 and most preferably higher than or equal to 0.9.
  • the electrolysis process according to the invention preferably comprises feeding the first vessel with the brine at a first flow rate, feeding the electrolyser with the entering brine at a second flow rate, withdrawing the depleted brine from said electrolyser at a third flow rate, withdrawing the depleted brine from the second vessel at a fourth flow rate, and when the second and third flow rates are not zero, at least one of the first and the fourth flow rate is occasionally zero.
  • the second and third flow rates are not zero preferably between start-up and shut down of the electrolyzer.
  • the treatment of the brine and/or of the depleted brine is preferably selected from (A) an adjustment of the salt concentration of the brine, preferably by solid salt addition to the brine, (B) a removal of fine solid particles from the brine, preferably by filtration, (C) a removal of carbonate ions from the brine, preferably by acid addition followed by stripping, (D) a removal of iron and aluminium from the brine, preferably by filtration, (E) a removal of calcium and magnesium from the brine, preferably by ion-exchange, (F) a removal of iodide from the brine, preferably by oxidation and ion exchange, (G) a removal of bromide from the brine, preferably by oxidation, (H) a removal of silicon from the brine, preferably by precipitation and filtration, (I) a removal of chlorine from the brine preferably at least by acidification, stripping and adsorption, (J)
  • the treatment of the brine is more preferably selected from treatments (A) to (H) and (K) to (N), most preferably from treatments (A) to (E).
  • the units (A) to (E) are preferably connected according to the sequence (A) ⁇ (B) ⁇ (C) ⁇ (D) ⁇ (E).
  • the treatment of the depleted brine is more preferably selected from treatments (I) and (J).
  • the treatment of the brine is more preferably selected from treatments (A) to (H) and (K) to (N) and the treatment of the depleted brine is more preferably selected from treatments (I) and (J).
  • the electrolyser is preferably a diaphragm or a membrane electrolyser, and more preferably a membrane electrolyser.
  • the electrolyzer preferably contains at least two different separator-electrode assemblies.
  • the electrolyser is such as described in patent application filed the same day as the present application in the name of
  • the electrolysis of the the entering brine is preferably carried out under at least one of the following conditions:
  • a diaphragm or membrane active surface lower than or equal to 1 m 2 .
  • the electrical current intensity is preferably lower than or equal to 4 kA and more preferably lower than or equal to 2 kA. This electrical current intensity is usually higher than or equal to 0.5 kA, preferably higher than or equal to 0.75 kA and more preferably higher than or equal to 1 kA.
  • the entering brine flow rate is preferably lower than or equal to 400 1/h, more preferably lower than or equal to 300 1/h, yet more preferably lower than or equal to 200 1/h, still more preferably lower than or equal to 200 1/h, most preferably lower than or equal to 100 1/h, yet most preferably lower than or equal to 80 1/h and still most preferably lower than or equal to 70 1/h.
  • the entering brine flow rate is usually higher than or equal to 20 1/h, preferably higher than or equal to 40 1/h and more preferably higher than or equal to 50 1/h.
  • This depleted brine flow rate is preferably lower than or equal to 300 1/h, more preferably lower than or equal to 200 1/h, still more preferably lower than or equal to 100 1/h, yet more preferably lower than or equal to 70 1/h, yet more preferably lower than or equal to 60 1/h and most preferably lower than or equal to 50 1/h.
  • This depleted brine flow rate is usually higher than or equal to 10 1/h, preferably higher than or equal to 20 1/h and more preferably higher than or equal to30 1/h.
  • the treatment of the brine is particularly preferably carried out under at least one of the following conditions:
  • the treatment of the depleted brine is particularly preferably carried out under at least one of the following conditions:
  • the active surface of the membrane is usually lower than or equal to 1 m 2 , preferably lower than or equal to 0.5 m 2 , preferably lower than or equal to 0.4 m 2 and more preferably lower than or equal to 0.3 m 2 .
  • This active surface is usually higher than or equal to 0.05 m 2 , preferably higher than or equal to 0.075 m 2 and more preferably higher than or equal to 0.1 m 2 .
  • the electrolyser is more preferably a membrane electrolyser with a membrane exhibiting an active surface membrane as described here above.
  • electrolysis conditions are particularly well adapted to small size electrolysis processes, in particular to small size diaphragm or membrane electrolysis processes, in more particularly to small size membrane electrolysis processes, while still being representative of industrial brine electrolysis process conditions.
  • the treatment of the brine prior is advantageously carried out under at least one of the following conditions:
  • This brine flow rate is preferably lower than or equal to 500 1/h, preferably lower than or equal to 300 1/h and more preferably lower than or equal to 250 1/h.
  • This brine flow rate is usually higher than or equal to 20 1/h, preferably higher than or equal to 40 1/h and more preferably higher than or equal to 50 1/h.
  • This brine volume is preferably higher than or equal to 10 1, preferably higher than or equal to 30 1 and more preferably higher than or equal to 50 1.
  • This treated brine volume is usually lower than or equal to 500 1, preferably lower than or equal to 200 1 and more preferably lower than or equal to 100 1.
  • the treatment of the depleted brine is carried out under at least one of the following conditions:
  • This depleted brine flow rate is preferably lower than or equal to 300 1/h, preferably lower than or equal to 200 1/h and more preferably lower than or equal to 100 1/h.
  • This depleted brine flow rate is usually higher than or equal to 10 1/h, preferably higher than or equal to 20 1/h and more preferably higher than or equal to 30 1/h.
  • This depleted brine volume is preferably higher than or equal to 30 1, preferably higher than or equal to 50 1 and more preferably higher than or equal to 80 1.
  • This treated depleted brine volume is usually lower than or equal to 500 1, preferably lower than or equal to 250 1 and more preferably lower than or equal to 200 1.
  • Those brine and depleted brine treatment conditions are particularly well adapted to treatment ancillary to small size electrolysis processes, in particular to small size diaphragm or membrane electrolysis processes, in more particularly to small size membrane electrolysis processes, while still being representative of brine treatments for industrial brine electrolysis process conditions.
  • the invention in a second embodiment, relates to a movable chlor-alkali electrolysis plant for carrying out the chlor-alkali electrolysis process for electrolyzing an entering brine according to the invention, wherein the electro lyser is part of a chlor-alkali electrolysis module mounted on a first support which can be moved as a whole, and the brine and/or the depleted treatments are carried out in at least one treatment module mounted on a second support which can be moved as a whole.
  • the movable chlor-alkali electrolysis plant according to the invention is named indifferently movable chlor-alkali electrolysis plant or movable electrolysis plant or electrolysis plant or plant in the text of the present application.
  • electrolysis plant is mobile or expressed in a better way movable.
  • mobile/movable one intends to denote that the plant can be transported from one site to another one with minimal handling, i.e. minimal amount of dismantling/assembling operations.
  • minimal dismantling it is intended to mean that at most 10 % by weight, preferably at most 5 % by weight, more preferably at most 1 % by weight of the electrolysis module mounted on the first support or of the module for the treatment of the brine and/or depleted brine mounted on the second support, is dismantled before moving the plant.
  • first support and the second support can be distinct or can be the same. It is preferred that the first support and the second support are distinct.
  • the support can be of any type. This support must be resistant enough to accommodate the weight of the module. It must be rigid enough to be moved when moved with the module.
  • the support is preferably a metallic support.
  • the support is more preferably a container or a platform.
  • First and second supports are therefore more preferably a container or a platform. Examples of platforms are platforms constituted by a basis only or those comprising further a vertical axis on each of the four corner.
  • first support and the second support are distinct, one of them can be a container and the other a platform, both of them can be a container or both of them can be a platform.
  • the support mounted module is more preferably assembled in a container, preferably a standardized- size container, or on a platform, preferably a standard- size platform.
  • the support mounted module is most preferably assembled in a container, preferably a standardized-size container.
  • the module is therefore advantageously easily transported by transporting the container with its content or the platform with its content.
  • Transportation can be by road, by rail, by air, by sea, or by any
  • Transportation is preferably by road since industrial sites are more easily accessible by road than by any other transportation means.
  • the other means like by air, by sea or by rail, can however be envisioned at least for part of the transportation itinerary which is intermediate between the sites.
  • the movable electrolysis plant according to the invention can therefore be transported with a truck and discharged from the truck with usual mechanical means.
  • An example of usual mechanical means is a fork-lift truck.
  • Another example is a crane.
  • the support has advantageously dimensions adapted to transportation.
  • Standard-size containers can be of any type.
  • Standard-size platforms can be of any type. Such types are for example as disclosed in International Standard ISO 6346 managed by the International Container Bureau.
  • Standard-size containers are preferably selected from Standard 20', upgraded 20', Standard 40', High Cube 40', Open Top 20', Open Top 40', Reefer 20 ' , Reefer 40 ' , Reefer High Cube 40 ', Flat Rack 20 ', Flat Rack 40 ', Flat Rack Collapsible 20' or Flat rack Collapsible 40', which characteristics are disclosed in http://www.foreign-trade.conVreference/ocean.cfm.
  • Standard-size platforms are preferably selected from Platform 20', Platform 40', Chassis 23'6", Chassis 33' Tri-axle or Chassis 40' Gooseneck, which characteristics are disclosed at http ://www.foreign- trade . com/reference/ocean . cfm.
  • the movable electrolysis plant according to the invention is therefore advantageously not a plant deposited in a metallic frame or in a container or on a platform for transportation and separated from it for being used.
  • the support mounted electrolysis module usually exhibits an external envelope having a length lower than or equal to 12.50 m, a width lower than or equal to 2.50 m and a height lower than or equal to 3.50 m.
  • the support mounted electrolysis module has usually a weight lower than or equal to 40000 kg.
  • the support mounted module for a treatment of the brine and/or the depleted brine usually exhibits an external envelope having a length lower than or equal to 12.50 m, a width lower than or equal to 2.50 m and a height lower than or equal to 3.50 m.
  • the support mounted module for a treatment of the brine and/or depleted brine has usually a weight lower than or equal to 40000 kg.
  • external envelope one intends to mean the minimal parallelepiped volume which can contain the support mounted electrolysis module or the support mounted module for a treatment of the brine and/or depleted brine.
  • both the support mounted electrolysis module and the support mounted module for a treatment of the brine and/or depleted brine exhibit an external envelope as mentioned here above.
  • the support mounted electrolysis module and/or the support mounted module for a treatment of the brine and/or the depleted brine preferably exhibits at least one of the following features:
  • an external envelope having a length lower than or equal to 5.89 m, a width lower than or equal to 2.33 m, a height lower than or equal to 2.38 m, preferably lower than or equal to 2.28 m and a weight lower than or equal to 21727 kg;
  • an external envelope having a length lower than or equal to 5.89 m, a width lower than or equal to 2.31 m, preferably lower than or equal to 2.28 m, a height lower than or equal to 2.38 m, preferably lower than or equal to 2.28 m and a weight lower than or equal to 28120 kg.
  • an external envelope having a length lower than or equal to 12.01 m, a width lower than or equal to 2.33 m, preferably lower than or equal to 2.28 m, a height lower than or equal to 2.38 m, preferably lower than or equal to 2.28 m and a weight lower than or equal to 26780 kg.
  • an external envelope having a length lower than or equal to 12.01 m, a width lower than or equal to 2.33 m, a height lower than or equal to 2.69 m, preferably lower than or equal to 2.56 m and a weight lower than or equal to 26512 kg;
  • an external envelope having a length lower than or equal to 5.89 m, a width lower than or equal to 2.31 m, preferably lower than or equal to 2.28 m, a height lower than or equal to 2.33 m, preferably lower than or equal to 2.18 m and a weight lower than or equal to 21600 kg;
  • an external envelope having a length lower than or equal to 12.01 m, a width lower than or equal to 2.33 m, a height lower than or equal to 2.33 m, referably lower than or equal to 2.26 m and a weight lower than or equal to 26630 kg;
  • ⁇ an external envelope having a length lower than or equal to 5.38 m, a width lower than or equal to 2.26 m, a height lower than or equal to 2.26 m, preferably lower than or equal to 2.20 m and a weight lower than or equal to 20756 kg;
  • an external envelope having a length lower than or equal to 11.48 m, a width lower than or equal to 2.2.26 , a height lower than or equal to 2.18 m, preferably lower than or equal to 2.13 m and a weight lower than or equal to 25526 kg;
  • an external envelope having a length lower than or equal to 11.35 m, a width lower than or equal to 2.28 m, a height lower than or equal to 2.48 m, preferably lower than or equal to 2.43 m and a weight lower than or equal to 28120 kg;
  • the movable electrolysis plant according to the invention is
  • the support mounted electrolysis module and the support mounted module for a treatment of the brine and/or depleted brine are advantageouly assembled in the same container or in separate containers on a first site, and transported, preferably by road, to a second site.
  • the movable electrolysis plant according to the invention is preferably built as follows: the support mounted electrolysis module and the support mounted module for a treatment of the brine and/or depleted brine are preferably assembled in separate containers on a first site and transported, preferably by road, to a second site.
  • the chlor-alkali electrolysis module and the module for a treatment of the brine and/or of the depleted brine are equipped with one or more sensors for monitoring one or more parameters such as temperature, pressure, voltage, current, flow rate, electrolyte composition or fluid level.
  • Said sensors are preferably interconnected with one or more first computers.
  • Said first computers are preferably linked to one or more second computers in a control room via a communication network.
  • Said control room is preferably remote from the movable electrolysis unit.
  • the plant for electrolysis of an entering brine into a depleted brine preferably contains at least one chlor-alkali electrolysis module and at least two different support mounted modules for the treatment of the brine and/or of the depleted brine, and the electrolysis module and the treatment modules are connected to each other allowing that the operation of the plant can be started with only one treatment module or with any combination of two or more treatment modules, and that at any time one of the treatments can be switched off and/or an additional treatment can be added, and/or the order of the treatments can be modified.
  • Figure 1 is intended to illustrate the invention, without however limiting it.
  • Figure 1 is an example of a chlor-alkali electrolysis plant according to the invention.
  • a membrane bipolar electro lyzer (9) comprising three membranes each of which having an active surface of about 0.15 dm 2 is continuously fed with an entering brine (I) from a vessel (1) exhibiting a volume of about 0.15 m 3 containing initially a volume of 0.10 m 3 of brine, at a volumetric flow rate (Fl) of 50 1/h.
  • the electrolyser is supplied with a direct current of 6 KA/m 2 from an AC/DC rectifier.
  • a depleted brine (II) is withdrawn from electrolyser (9) at a volumetric flow rate (F2) of 40 1/h and feeds a vessel (2) exhibiting a volume of about 0.2 m 3 and containing initially a volume 0.05 m 3 of depleted brine.
  • Vessel (1) is continuously supplied with the brine (I) from a vessel (3) by passing a brine (III) from vessel (3) onto two consecutive ion-exchange columns (3') and through two Pall cartridge type filters (3") at a volumetric flow rate (F3) of 250 1/h until overflow, so that the initial volume of the brine in vessel (1) is continuously restored.
  • the overflow from vessel (1) returns back to vessel (3) at a volumetric flow rate (F3'), so that the net flowrate from vessel (3) to vessel (1) (F3-F3') is exactly equal to the entering brine flowrate which feeds the electrolyser (9).
  • Vessel (2) is then emptied of the depleted brine at a volumetric flow rate (F2') of 150 1/h until the initial volume of the depleted brine in vessel (2) is restored and the withdrawal of depleted brine from vessel (2) is stopped.
  • F2' volumetric flow rate
  • Vessel (3) exhibits a volume of about 0.15 m 3 and contains initially a volume of 0.06 m 3 of a brine (III).
  • the ion-exchange columns (3') have each of a volume of 0.04 m 3 .
  • the flow rate (F3) of brine (III), the ion exchange resin volume and the temperature of brine (III) ensure conditions, e.g. like a residence time of brine (III) on the ion-exchange resin, convenient to remove calcium and magnesium from brine (III) before entering vessel (1).
  • Brine (III) is a brine saturated in salt, removed from solid fine particles, from carbonates ions, from iron and aluminium, with a pH of about 9.
  • Brine (III) is obtained by addition in vessel (3) of sodium hydroxide to a brine (IV), brine (IV) having been saturated in salt, removed from solid fine particles and from carbonates ions. Stirring is ensured by external recirculation of brine (III) in vessel (3).
  • the dimensions of vessel (3) are convenient for accommodating the equipment to control operating conditions like temperature and pH probes and for adjusting pH like caustic soda addition and sampling devices.
  • the volume of brine (III) which is fed from vessel (3) to vessel (1) is replaced by transferring an equal volume of a brine (IV) from a vessel (4), via a filtration column (4') to vessel (3).
  • Vessel (4) exhibits a volume of about 0.15 m 3 and contains initially a volume of 0.06 m 3 of a brine (IV).
  • the filtration column (4') has a volume of 0.06 m 3 and contains an anthracite bed as filtration agent.
  • Brine (IV) is fed to vessel (3) at a volumetric flow rate (F4) of 0.15 m 3 /h until the initial volume of brine (III) in vessel (3) is restored, then stopped.
  • the flow rate (F4) of brine (IV), the anthracite bed (4') volume and the temperature ensure conditions e.g. like a residence time and a linear velocity of brine (IV) on the anthracite, convenient to remove aluminium and iron from brine (IV) before entering vessel (3).
  • Brine (IV) is a brine saturated in salt, removed from solid fine particles and from carbonates ions, with a pH of about 5.5.
  • Brine (IV) is obtained by addition in vessel (4) of sodium hydroxide to a brine (V), brine (V) having been saturated in salt, removed from solid fine particles and carbonates ions and with a pH of 2. Stirring is ensured by external recirculation of brine (IV) in vessel (4).
  • the dimensions of vessel (4) are convenient for accommodating the equipment to control operating conditions like temperature and pH probes and for adjusting pH like caustic soda addition and sampling devices.
  • the volume of brine (IV) which is fed to vessel (3) is replaced by transferring an equal volume of a brine (V) from a vessel (5) to vessel (4) and by adjusting pH in vessel (4).
  • Vessel (5) exhibits a volume of about 0.15 m 3 and contains initially a volume of 0.06 m 3 of a brine (V).
  • Brine (V) is fed to vessel (4) at a volumetric flow rate (F5) of 0.15 m 3 /h until the initial volume of brine (IV) in vessel (4) is restored, then stopped.
  • Brine (V) is a brine saturated in salt, removed from solid fine particles and from carbonates ions, with a pH of about 2 .
  • Brine (V) is obtained by addition of hydrochloric acid to a brine (VI), brine (VI) having been saturated in salt and removed from solid fine particles and with a pH of about 2 and by purging carbon dioxide with a nitrogen injection, in vessel (5). Stirring is ensured by external recirculation of brine (V) in vessel (5).
  • the dimensions of vessel (5) are convenient for accommodating the equipment to control operating conditions like temperature and pH probes and for adjusting pH like hydrochloric acid and nitrogen additions and sampling devices.
  • the volume of brine (V) which is fed to vessel (4) is replaced by transferring an equal volume of a brine (VI) from a vessel (6), via a filter (6') to vessel (5).
  • Sixth vessel (6) exhibits a volume of about 0.15 m 3 and contains initially a volume of 0.06 m 3 of a brine (VI).
  • the filter (6') is a Pall cartridge type filter (for example of PUY series).
  • Brine (VI) is fed to vessel (5) at a volumetric flow rate (F6) of 0.1 m 3 /h until the initial volume of brine (V) in vessel (5) is restored, then stopped.
  • the flow rate (F6) of brine (VI), the filter volume and the temperature ensure conditions e.g. like a superficial velocity of brine (VI) on the filter, convenient to remove fine solid particles from brine (VI) before entering vessel (5).
  • Brine (VI) is a brine saturated in salt.
  • Brine (VI) is obtained from a solid salt saturator (7').
  • the dimensions of vessel (6) are convenient for accommodating the equipment to control operating conditions.
  • the volume of brine (VI) which is fed to vessel (5) is replaced by transferring an equal volume of a brine (VII) from a vessel (7), via a solid salt saturator (7'), to vessel (6).
  • Vessel (7) exhibits a volume of about 0.15 m 3 and contains initially a volume of 0.06 m 3 of a brine (VII).
  • the saturator (7') is a conic type saturator, has a volume of 0.15 m 3 and contains a weight of salt of 0.04 t, continuously refilled by a salt charging device.
  • Brine (VII) is fed to vessel (6) at a volumetric flow rate (F7) of 0.1 m 3 /h, until the initial volume of brine (VI) in vessel (6) is restored, and then stopped.
  • the flow rate of brine (VII), the saturator volume and the temperature ensure conditions e.g. like a residence time of brine (VII) in the saturator long enough to saturate brine (VII) before entering vessel (6).
  • Brine (VII) is a brine not saturated in salt with a pH of about 9.
  • Brine (VII) is obtained by addition of caustic soda or hydrochloric acid to a brine (VIII). Stirring is ensured by external recirculation of brine (VII) in vessel (7).
  • the dimensions of vessel (7) give enough room for control probes like temperature and pH and addition and sampling devices.
  • the volume of brine (VII) which is fed to vessel (6) is replaced by transferring an equal volume of a brine (VIII) from a vessel (8).
  • Vessel (8) exhibits a volume of about 1 m 3 and contains initially a volume of 1 m 3 of a brine (VIII).
  • Brine (VIII) is fed to vessel (7) at a volumetric flow rate (F8) of 0.1 m 3 /h until the initial volume of brine (VII) in vessel (7) is restored, and then stopped.
  • Brine (VIII) is a brine not saturated in salt with a pH of about 10. It can be of any origin.
  • Vessel (2) exhibits a volume of 0.2 m 3 .
  • Brine (II) is a brine depleted in salt, containing chlorine and possibly chlorate with a pH of about 4.
  • vessel (2) hydrochloric acid is added to brine (II) until a pH of about 1.8 is obtained and the pH adjusted brine is stripped with air and circulated on an active coal containing column (2').
  • hydrochloric acid is added to brine (II) until a weight ratio HCl/NaC103 of about 130/100 g/g is obtained the brine is heated up, to convert chlorates into chlorine.
  • caustic soda is added until a pH of about 1.8 is obtained and the pH adjusted brine is stripped with air and circulated on an active coal containing column (2').
  • the dimensions of vessel (2) give enough room for control probes like temperature, pH and active chlorine content, and addition like hydrochloric acid, caustic soda and air, and sampling devices.
  • the resulting brine (IX) is withdrawn from vessel (2) at a flow rate (F9) and sent to storage and or disposal.

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Abstract

Chlor-alkali electrolysis process for electrolyzing an entering brine into a depleted brine, comprising feeding at least one first vessel intermittently with a brine, subjecting this brine to at least one treatment in order to obtain the entering brine, feeding at least one electrolyser continuously with the entering brine in order to obtain the depleted brine, and withdrawing continuously the depleted brine from said electrolyser.

Description

Chlor-alkali electrolysis process
This application claims priority to European application No. 13162064.3 filed on April 3, 2013, the whole content of this application being incorporated herein by reference for all purposes.
The present invention relates to a chlor-alkali electrolysis process, more specifically a process for electrolysing a brine.
Electrolysis of brines is a well known process. The brine used may be obtained by dissolving a salt, preferably rock salt, in water or may be a byproduct from a chemical process. Such process usually generates depleted brines that have to be disposed of or recycled to the electrolysis. Although treatments for purifying such brines exist, their impact on the chlor-alkali electrolysis process remains often unpredictable because such processes are complex and extremely sensitive to even low amounts of impurities in the brine. Assessing the suitability of brines for an industrial production of chlorine by electrolysis requires tests of brines in down-sized installations. However, down-sizing of all parts of the process is not always possible, in particular for long term continuous operation.
The object of the present invention is to provide an electrolysis process which does overcome these drawbacks.
The invention therefore relates in a first embodiment to a process for electrolyzing an entering brine into a depleted brine, comprising feeding at least one first vessel intermittently with a brine, subjecting this brine to at least one treatment in order to obtain the entering brine, feeding at least one electrolyser continuously with the entering brine in order to obtain the depleted brine, and withdrawing continuously the depleted brine from said electrolyser.
The chlor-alkali electrolysis process according to the invention is named indifferently chlor-alkali electrolysis process or electrolysis process or process in the text of the present application.
One of the important features of the process according to the invention is that the electrolysis is carried out continuously, which allows evaluating the electrolysis performances over long periods of steady- state conditions of operation. Another important feature of the process according to the invention is that the electrolyser is fed from a vessel being intermittently supplied with the brine to be electrolysed. Such intermittent supply of the vessel has the advantage of allowing a down-sizing of the brine treatment equipment compatible with the down-sizing of the electrolyser and compatible with the brine treatment conditions of an industrial electrolysis process. It has indeed been found that operating a small scale electrolyser leads to related brine treatment units with internal volumes incompatible with their necessarily associated process conditions like for example residence times and linear velocities, and also with their operating equipments like for instance, sampling probes, sensors, etc., which can not be miniaturized ad definition.
The combination of the above features allows evaluating the electrolysis performances over long periods of steady-state conditions of operation with associated brine treatment conditions of an industrial electrolysis process in a down-sized electrolysis process.
The chlor-alkali electrolysis process according to the invention is preferably a process for the production of chlorine and more preferably a chlor- alkali membrane electrolysis process for the production of chlorine.
By brine, one intends to denote any aqueous composition containing a metal chloride salt, which is to be submitted to the electrolysis in the electrolysis plant according to the invention.
The brine is preferably an alkaline metal chloride, an alkaline-earth metal chloride or any mixture thereof, more preferably an alkaline metal chloride, still more preferably sodium chloride, potassium chloride or any mixture thereof and most preferably sodium chloride.
When the brine is an aqueous composition containing sodium chloride, i.e. a sodium chloride brine, the brine can originate from any source. The brine is preferably selected from a brine from an industrial process for manufacturing chlorine, a brine from an epoxide manufacturing process, preferably ethylene oxide, propylene oxide, butylene oxide or epichlorohydrin, and more preferably epichlorohydrin, a brine from an epoxide derivative manufacturing process, preferably epoxy resin, a brine from a process for manufacturing a chlorinated organic product, preferably 1 ,2-dichloroethane or 1 ,2-dichloroethylene, and more preferably 1 ,2-dichloroethane, a brine from a process for manufacturing a monoisocyanate or a polyisocyanate, preferably 4,4'-methylenediphenyl diisocyanate (MDI), toluene diisocyanate (TDI) or hexamethylene-1,6- diisocyanate (HDI), a brine from a process for manufacturing a polycarbonate, preferably 2,2-bis(4-hydroxyphenyl)propane polycarbonate (bisphenol A polycarbonate), and any mixture thereof.
By depleted brine, one intends to denote a brine as described here above which has been depleted in salt after the electrolysis in the electrolysis process according to the invention.
The electrolysis process according to the invention preferably comprises feeding at least one second vessel continuously with the depleted brine from said electrolyser, withdrawing the depleted brine intermittently from said second vessel, and subjecting the depleted brine to at least one other treatment after withdrawal from the second vessel.
The electrolysis process according to the invention more preferably comprises feeding at least one third vessel continuously with the entering brine and feeding the at least one electrolyser continuously with the entering brine from said third vessel.
The electrolysis process according to the invention preferably comprises feeding the first vessel with the brine at a first flow rate, feeding the electrolyser with the entering brine at a second flow rate, withdrawing the depleted brine from said electrolyser at a third flow rate, and when the second and third flow rates are not zero, the first flow rate is occasionally zero. By occasionally, one intends to denote that the ratio between the duration when the first flow rate is zero and the duration when the second and third flow rates are not zero, is higher than or equal to 0.1, preferably higher than or equal to 0.5 and most preferably higher than or equal to 0.9.
The electrolysis process according to the invention preferably comprises feeding the first vessel with the brine at a first flow rate, feeding the electrolyser with the entering brine at a second flow rate, withdrawing the depleted brine from said electrolyser at a third flow rate, withdrawing the depleted brine from the second vessel at a fourth flow rate, and when the second and third flow rates are not zero, the fourth flow is occasionally zero. By occasionally, one intends to denote that the ratio between the duration when the fourth flow is zero and the duration when the second and third flows are not zero, is higher than or equal to 0.1, preferably higher than or equal to 0.5 and most preferably higher than or equal to 0.9.
The electrolysis process according to the invention preferably comprises feeding the first vessel with the brine at a first flow rate, feeding the electrolyser with the entering brine at a second flow rate, withdrawing the depleted brine from said electrolyser at a third flow rate, withdrawing the depleted brine from the second vessel at a fourth flow rate, and when the second and third flow rates are not zero, at least one of the first and the fourth flow rate is occasionally zero.
The second and third flow rates are not zero preferably between start-up and shut down of the electrolyzer.
In the electrolysis process according to the invention, the treatment of the brine and/or of the depleted brine is preferably selected from (A) an adjustment of the salt concentration of the brine, preferably by solid salt addition to the brine, (B) a removal of fine solid particles from the brine, preferably by filtration, (C) a removal of carbonate ions from the brine, preferably by acid addition followed by stripping, (D) a removal of iron and aluminium from the brine, preferably by filtration, (E) a removal of calcium and magnesium from the brine, preferably by ion-exchange, (F) a removal of iodide from the brine, preferably by oxidation and ion exchange, (G) a removal of bromide from the brine, preferably by oxidation, (H) a removal of silicon from the brine, preferably by precipitation and filtration, (I) a removal of chlorine from the brine preferably at least by acidification, stripping and adsorption, (J) a removal of chlorate from the brine, preferably by acid addition followed by stripping and/or by catalytic hydrogenation, (K) a removal of sulphates from the brine by precipitation and filtration or nanofiltration by membranes, (L) a removal of organic compounds from the brine, preferably by oxidation, (M) a removal of mercury from the brine, preferably by precipitation, ion exchange or adsorption, and (N) a removal of ammonia from the brine, preferably by pH adjustment, oxidation and stripping.
Those treatments are such as described for units (A) to (N) in patent application filed the same day as the present application in the name of
SOLVAY S.A., entitled "Plant for chlor-alkali electrolysis and a process for using it", the entire content of which is herein incorporated by reference.
In the electrolysis process according to the invention, the treatment of the brine is more preferably selected from treatments (A) to (H) and (K) to (N), most preferably from treatments (A) to (E). The units (A) to (E) are preferably connected according to the sequence (A) < (B) < (C) < (D) < (E).
In the electrolysis process according to the invention, the treatment of the depleted brine is more preferably selected from treatments (I) and (J). In the electrolysis process according to the invention, the treatment of the brine is more preferably selected from treatments (A) to (H) and (K) to (N) and the treatment of the depleted brine is more preferably selected from treatments (I) and (J).
In the electrolysis process according to the invention, the electrolyser is preferably a diaphragm or a membrane electrolyser, and more preferably a membrane electrolyser. The electrolyzer preferably contains at least two different separator-electrode assemblies. The electrolyser is such as described in patent application filed the same day as the present application in the name of
SOLVAY S.A., entitled "chlor-alkali electrolysis plant and a process for using it", the entire content of which is herein incorporated by reference.
In the electrolysis process according to the invention, the electrolysis of the the entering brine is preferably carried out under at least one of the following conditions:
■ An electrical current intensity lower than or equal to 5 kA;
■ A, entering brine flow rate lower than or equal to 500 1/h;
■ A depleted brine flow rate lower than or equal to 400 1/h;
■ A diaphragm or membrane active surface lower than or equal to 1 m2.
The electrical current intensity is preferably lower than or equal to 4 kA and more preferably lower than or equal to 2 kA. This electrical current intensity is usually higher than or equal to 0.5 kA, preferably higher than or equal to 0.75 kA and more preferably higher than or equal to 1 kA.
The entering brine flow rate is preferably lower than or equal to 400 1/h, more preferably lower than or equal to 300 1/h, yet more preferably lower than or equal to 200 1/h, still more preferably lower than or equal to 200 1/h, most preferably lower than or equal to 100 1/h, yet most preferably lower than or equal to 80 1/h and still most preferably lower than or equal to 70 1/h. The entering brine flow rate is usually higher than or equal to 20 1/h, preferably higher than or equal to 40 1/h and more preferably higher than or equal to 50 1/h.
This depleted brine flow rate is preferably lower than or equal to 300 1/h, more preferably lower than or equal to 200 1/h, still more preferably lower than or equal to 100 1/h, yet more preferably lower than or equal to 70 1/h, yet more preferably lower than or equal to 60 1/h and most preferably lower than or equal to 50 1/h. This depleted brine flow rate is usually higher than or equal to 10 1/h, preferably higher than or equal to 20 1/h and more preferably higher than or equal to30 1/h. In the electrolysis process according to the invention, the treatment of the brine is particularly preferably carried out under at least one of the following conditions:
■ A brine flow rate higher than or equal to 20 1/h;
■ A brine volume higher than or equal to 50 1;
and the treatment of the depleted brine is particularly preferably carried out under at least one of the following conditions:
■ A depleted brine flow rate higher than or equal to 10 1/h;
■ A depleted brine volume higher than or equal to 100 1.
All those conditions are particularly well adapted to a small size electrolyser, in particular a small size diaphragm or membrane electrolyser.
Therefore, in the electrolysis process according to the invention, when the electrolyser is a membrane electrolyser, the active surface of the membrane is usually lower than or equal to 1 m2, preferably lower than or equal to 0.5 m2, preferably lower than or equal to 0.4 m2 and more preferably lower than or equal to 0.3 m2. This active surface is usually higher than or equal to 0.05 m2, preferably higher than or equal to 0.075 m2 and more preferably higher than or equal to 0.1 m2. The electrolyser is more preferably a membrane electrolyser with a membrane exhibiting an active surface membrane as described here above.
Those electrolysis conditions are particularly well adapted to small size electrolysis processes, in particular to small size diaphragm or membrane electrolysis processes, in more particularly to small size membrane electrolysis processes, while still being representative of industrial brine electrolysis process conditions.
In the electrolysis process according to the invention, the treatment of the brine prior is advantageously carried out under at least one of the following conditions:
■ A brine flow rate higher than or equal to 50 1/h;
- A brine volume higher than or equal to 50 1.
This brine flow rate is preferably lower than or equal to 500 1/h, preferably lower than or equal to 300 1/h and more preferably lower than or equal to 250 1/h. This brine flow rate is usually higher than or equal to 20 1/h, preferably higher than or equal to 40 1/h and more preferably higher than or equal to 50 1/h.
This brine volume is preferably higher than or equal to 10 1, preferably higher than or equal to 30 1 and more preferably higher than or equal to 50 1. This treated brine volume is usually lower than or equal to 500 1, preferably lower than or equal to 200 1 and more preferably lower than or equal to 100 1.
In the electrolysis process according to the invention, the treatment of the depleted brine is carried out under at least one of the following conditions:
■ A depleted brine flow rate higher than or equal to 40 1/h;
■ A depleted brine volume higher than or equal to 100 1.
This depleted brine flow rate is preferably lower than or equal to 300 1/h, preferably lower than or equal to 200 1/h and more preferably lower than or equal to 100 1/h. This depleted brine flow rate is usually higher than or equal to 10 1/h, preferably higher than or equal to 20 1/h and more preferably higher than or equal to 30 1/h.
This depleted brine volume is preferably higher than or equal to 30 1, preferably higher than or equal to 50 1 and more preferably higher than or equal to 80 1. This treated depleted brine volume is usually lower than or equal to 500 1, preferably lower than or equal to 250 1 and more preferably lower than or equal to 200 1.
Those brine and depleted brine treatment conditions are particularly well adapted to treatment ancillary to small size electrolysis processes, in particular to small size diaphragm or membrane electrolysis processes, in more particularly to small size membrane electrolysis processes, while still being representative of brine treatments for industrial brine electrolysis process conditions.
The other conditions for carrying out treatment (A) to (L), such as temperature, pressure, pH, residence time, etc. are as described for units (A) to (L) in patent application filed the same day as the present application in the name of SOL V AY S.A., entitled "Plant for chlor-alkali electrolysis and a process for using it", the entire content of which is herein incorporated by reference.
In a second embodiment, the invention relates to a movable chlor-alkali electrolysis plant for carrying out the chlor-alkali electrolysis process for electrolyzing an entering brine according to the invention, wherein the electro lyser is part of a chlor-alkali electrolysis module mounted on a first support which can be moved as a whole, and the brine and/or the depleted treatments are carried out in at least one treatment module mounted on a second support which can be moved as a whole.
The movable chlor-alkali electrolysis plant according to the invention is named indifferently movable chlor-alkali electrolysis plant or movable electrolysis plant or electrolysis plant or plant in the text of the present application.
One important feature of the electrolysis plant according to the invention is that it is mobile or expressed in a better way movable. By mobile/movable, one intends to denote that the plant can be transported from one site to another one with minimal handling, i.e. minimal amount of dismantling/assembling operations.
By as a whole, it is intended to mean that a minimal dismantling of the electrolysis module or of the treatment module is needed, before moving the electrolysis plant. By minimal dismantling, it is intended to mean that at most 10 % by weight, preferably at most 5 % by weight, more preferably at most 1 % by weight of the electrolysis module mounted on the first support or of the module for the treatment of the brine and/or depleted brine mounted on the second support, is dismantled before moving the plant.
In the movable electrolysis plant according to the invention, the first support and the second support can be distinct or can be the same. It is preferred that the first support and the second support are distinct.
In the movable electrolysis plant according to the invention, the support can be of any type. This support must be resistant enough to accommodate the weight of the module. It must be rigid enough to be moved when moved with the module. The support is preferably a metallic support. The support is more preferably a container or a platform. First and second supports are therefore more preferably a container or a platform. Examples of platforms are platforms constituted by a basis only or those comprising further a vertical axis on each of the four corner.
In case the first support and the second support are distinct, one of them can be a container and the other a platform, both of them can be a container or both of them can be a platform.
The support mounted module is more preferably assembled in a container, preferably a standardized- size container, or on a platform, preferably a standard- size platform. The support mounted module is most preferably assembled in a container, preferably a standardized-size container.
The module is therefore advantageously easily transported by transporting the container with its content or the platform with its content.
Transportation can be by road, by rail, by air, by sea, or by any
combination thereof. Transportation is preferably by road since industrial sites are more easily accessible by road than by any other transportation means. The other means like by air, by sea or by rail, can however be envisioned at least for part of the transportation itinerary which is intermediate between the sites.
The movable electrolysis plant according to the invention can therefore be transported with a truck and discharged from the truck with usual mechanical means. An example of usual mechanical means is a fork-lift truck. Another example is a crane.
In the movable electrolysis plant according to the invention, the support has advantageously dimensions adapted to transportation.
Standard-size containers can be of any type. Standard-size platforms can be of any type. Such types are for example as disclosed in International Standard ISO 6346 managed by the International Container Bureau.
Standard-size containers are preferably selected from Standard 20', upgraded 20', Standard 40', High Cube 40', Open Top 20', Open Top 40', Reefer 20 ' , Reefer 40 ' , Reefer High Cube 40 ', Flat Rack 20 ', Flat Rack 40 ', Flat Rack Collapsible 20' or Flat rack Collapsible 40', which characteristics are disclosed in http://www.foreign-trade.conVreference/ocean.cfm.
Standard-size platforms are preferably selected from Platform 20', Platform 40', Chassis 23'6", Chassis 33' Tri-axle or Chassis 40' Gooseneck, which characteristics are disclosed at http ://www.foreign- trade . com/reference/ocean . cfm.
The movable electrolysis plant according to the invention is therefore advantageously not a plant deposited in a metallic frame or in a container or on a platform for transportation and separated from it for being used.
In the movable electrolysis plant according to the invention, the support mounted electrolysis module usually exhibits an external envelope having a length lower than or equal to 12.50 m, a width lower than or equal to 2.50 m and a height lower than or equal to 3.50 m. The support mounted electrolysis module has usually a weight lower than or equal to 40000 kg.
In the movable electrolysis plant according to the invention, the support mounted module for a treatment of the brine and/or the depleted brine, usually exhibits an external envelope having a length lower than or equal to 12.50 m, a width lower than or equal to 2.50 m and a height lower than or equal to 3.50 m. The support mounted module for a treatment of the brine and/or depleted brine has usually a weight lower than or equal to 40000 kg. By external envelope, one intends to mean the minimal parallelepiped volume which can contain the support mounted electrolysis module or the support mounted module for a treatment of the brine and/or depleted brine.
In the movable electrolysis plant according to the invention, both the support mounted electrolysis module and the support mounted module for a treatment of the brine and/or depleted brine, exhibit an external envelope as mentioned here above.
The support mounted electrolysis module and/or the support mounted module for a treatment of the brine and/or the depleted brine preferably exhibits at least one of the following features:
■ an external envelope having a length lower than or equal to 5.89 m, a width lower than or equal to 2.33 m, a height lower than or equal to 2.38 m, preferably lower than or equal to 2.28 m and a weight lower than or equal to 21727 kg;
- an external envelope having a length lower than or equal to 5.89 m, a width lower than or equal to 2.31 m, preferably lower than or equal to 2.28 m, a height lower than or equal to 2.38 m, preferably lower than or equal to 2.28 m and a weight lower than or equal to 28120 kg.
■ an external envelope having a length lower than or equal to 12.01 m, a width lower than or equal to 2.33 m, preferably lower than or equal to 2.28 m, a height lower than or equal to 2.38 m, preferably lower than or equal to 2.28 m and a weight lower than or equal to 26780 kg.
■ an external envelope having a length lower than or equal to 12.01 m, a width lower than or equal to 2.33 m, a height lower than or equal to 2.69 m, preferably lower than or equal to 2.56 m and a weight lower than or equal to 26512 kg;
■ an external envelope having a length lower than or equal to 5.89 m, a width lower than or equal to 2.31 m, preferably lower than or equal to 2.28 m, a height lower than or equal to 2.33 m, preferably lower than or equal to 2.18 m and a weight lower than or equal to 21600 kg;
■ an external envelope having a length lower than or equal to 12.01 m, a width lower than or equal to 2.33 m, a height lower than or equal to 2.33 m, referably lower than or equal to 2.26 m and a weight lower than or equal to 26630 kg;
■ an external envelope having a length lower than or equal to 5.38 m, a width lower than or equal to 2.26 m, a height lower than or equal to 2.26 m, preferably lower than or equal to 2.20 m and a weight lower than or equal to 20756 kg;
■ an external envelope having a length lower than or equal to 11.48 m, a width lower than or equal to 2.2.26 , a height lower than or equal to 2.18 m, preferably lower than or equal to 2.13 m and a weight lower than or equal to 25526 kg;
■ an external envelope having a length lower than or equal to 11.35 m, a width lower than or equal to 2.28 m, a height lower than or equal to 2.48 m, preferably lower than or equal to 2.43 m and a weight lower than or equal to 28120 kg;
■ an external envelope having a length lower than or equal to 5.61 m, a width lower than or equal to 2.20 m, a height lower than or equal to 2.23 m and a weight lower than or equal to 27722 kg;
■ an external envelope having a length lower than or equal to 12.06 m, a width lower than or equal to 2.08 m, a height lower than or equal to 1.95 m and a weight lower than or equal to 38918 kg;
■ an external envelope having a length lower than or equal to 5.63 m, a width lower than or equal to 2.20 m, a height lower than or equal to 2.23 m and a weight lower than or equal to 27722 kg;
■ an external envelope having a length lower than or equal to 12.06 m, a width lower than or equal to 2.08 m, a height lower than or equal to 1.95 m and a weight lower than or equal to38918 kg;
■ an external envelope having a length lower than or equal to 6.07 m, a width lower than or equal to 2.43 m, a height lower than or equal to 2.23 m and a weight lower than or equal to 23993 kg;
■ an external envelope having a length lower than or equal to 12.19 m, a width lower than or equal to 2.43 m, a height lower than or equal to 1.95 m and a weight lower than or equal to 30117 kg;
■ an external envelope having a length lower than or equal to 8.25 m and a weight lower than or equal to 17955 kg;
■ an external envelope having a length lower than or equal to 12.7 m and a weight lower than or equal to 20227 kg;
■ an external envelope having a length lower than or equal to 9.97 m and a weight lower than or equal to 17955 kg;
- an external envelope having a length lower than or equal to 12 m and a weight lower than or equal to 20227 kg. The movable electrolysis plant according to the invention is
advantageously built as follows: the support mounted electrolysis module and the support mounted module for a treatment of the brine and/or depleted brine are advantageouly assembled in the same container or in separate containers on a first site, and transported, preferably by road, to a second site.
The movable electrolysis plant according to the invention is preferably built as follows: the support mounted electrolysis module and the support mounted module for a treatment of the brine and/or depleted brine are preferably assembled in separate containers on a first site and transported, preferably by road, to a second site.
In the electrolysis plant according to the invention, the chlor-alkali electrolysis module and the module for a treatment of the brine and/or of the depleted brine are equipped with one or more sensors for monitoring one or more parameters such as temperature, pressure, voltage, current, flow rate, electrolyte composition or fluid level. Said sensors are preferably interconnected with one or more first computers. Said first computers are preferably linked to one or more second computers in a control room via a communication network. Said control room is preferably remote from the movable electrolysis unit.
In the chlor-alkali electrolysis plant of the second embodiment of the present invention, the plant for electrolysis of an entering brine into a depleted brine, preferably contains at least one chlor-alkali electrolysis module and at least two different support mounted modules for the treatment of the brine and/or of the depleted brine, and the electrolysis module and the treatment modules are connected to each other allowing that the operation of the plant can be started with only one treatment module or with any combination of two or more treatment modules, and that at any time one of the treatments can be switched off and/or an additional treatment can be added, and/or the order of the treatments can be modified.
Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.
Figure 1 is intended to illustrate the invention, without however limiting it. Figure 1 is an example of a chlor-alkali electrolysis plant according to the invention. A membrane bipolar electro lyzer (9) comprising three membranes each of which having an active surface of about 0.15 dm2 is continuously fed with an entering brine (I) from a vessel (1) exhibiting a volume of about 0.15 m3 containing initially a volume of 0.10 m3 of brine, at a volumetric flow rate (Fl) of 50 1/h. The electrolyser is supplied with a direct current of 6 KA/m2 from an AC/DC rectifier. A depleted brine (II) is withdrawn from electrolyser (9) at a volumetric flow rate (F2) of 40 1/h and feeds a vessel (2) exhibiting a volume of about 0.2 m3 and containing initially a volume 0.05 m3 of depleted brine.
Vessel (1) is continuously supplied with the brine (I) from a vessel (3) by passing a brine (III) from vessel (3) onto two consecutive ion-exchange columns (3') and through two Pall cartridge type filters (3") at a volumetric flow rate (F3) of 250 1/h until overflow, so that the initial volume of the brine in vessel (1) is continuously restored. The overflow from vessel (1) returns back to vessel (3) at a volumetric flow rate (F3'), so that the net flowrate from vessel (3) to vessel (1) (F3-F3') is exactly equal to the entering brine flowrate which feeds the electrolyser (9).
After 2 h, the depleted brine volume in vessel (2) has increased to 0.13 m3. Vessel (2) is then emptied of the depleted brine at a volumetric flow rate (F2') of 150 1/h until the initial volume of the depleted brine in vessel (2) is restored and the withdrawal of depleted brine from vessel (2) is stopped.
This operation of emptying vessel (2) is repeated after each 2 h.
Vessel (3) exhibits a volume of about 0.15 m3 and contains initially a volume of 0.06 m3 of a brine (III). The ion-exchange columns (3') have each of a volume of 0.04 m3.
The flow rate (F3) of brine (III), the ion exchange resin volume and the temperature of brine (III) ensure conditions, e.g. like a residence time of brine (III) on the ion-exchange resin, convenient to remove calcium and magnesium from brine (III) before entering vessel (1).
Brine (III) is a brine saturated in salt, removed from solid fine particles, from carbonates ions, from iron and aluminium, with a pH of about 9.
Brine (III) is obtained by addition in vessel (3) of sodium hydroxide to a brine (IV), brine (IV) having been saturated in salt, removed from solid fine particles and from carbonates ions. Stirring is ensured by external recirculation of brine (III) in vessel (3). The dimensions of vessel (3) are convenient for accommodating the equipment to control operating conditions like temperature and pH probes and for adjusting pH like caustic soda addition and sampling devices.
The volume of brine (III) which is fed from vessel (3) to vessel (1) is replaced by transferring an equal volume of a brine (IV) from a vessel (4), via a filtration column (4') to vessel (3).
Vessel (4) exhibits a volume of about 0.15 m3 and contains initially a volume of 0.06 m3 of a brine (IV). The filtration column (4') has a volume of 0.06 m3 and contains an anthracite bed as filtration agent.
Brine (IV) is fed to vessel (3) at a volumetric flow rate (F4) of 0.15 m3/h until the initial volume of brine (III) in vessel (3) is restored, then stopped. The flow rate (F4) of brine (IV), the anthracite bed (4') volume and the temperature ensure conditions e.g. like a residence time and a linear velocity of brine (IV) on the anthracite, convenient to remove aluminium and iron from brine (IV) before entering vessel (3).
Brine (IV) is a brine saturated in salt, removed from solid fine particles and from carbonates ions, with a pH of about 5.5.
Brine (IV) is obtained by addition in vessel (4) of sodium hydroxide to a brine (V), brine (V) having been saturated in salt, removed from solid fine particles and carbonates ions and with a pH of 2. Stirring is ensured by external recirculation of brine (IV) in vessel (4). The dimensions of vessel (4) are convenient for accommodating the equipment to control operating conditions like temperature and pH probes and for adjusting pH like caustic soda addition and sampling devices.
The volume of brine (IV) which is fed to vessel (3) is replaced by transferring an equal volume of a brine (V) from a vessel (5) to vessel (4) and by adjusting pH in vessel (4).
Vessel (5) exhibits a volume of about 0.15 m3 and contains initially a volume of 0.06 m3 of a brine (V).
Brine (V) is fed to vessel (4) at a volumetric flow rate (F5) of 0.15 m3/h until the initial volume of brine (IV) in vessel (4) is restored, then stopped.
Brine (V) is a brine saturated in salt, removed from solid fine particles and from carbonates ions, with a pH of about 2 .
Brine (V) is obtained by addition of hydrochloric acid to a brine (VI), brine (VI) having been saturated in salt and removed from solid fine particles and with a pH of about 2 and by purging carbon dioxide with a nitrogen injection, in vessel (5). Stirring is ensured by external recirculation of brine (V) in vessel (5). The dimensions of vessel (5) are convenient for accommodating the equipment to control operating conditions like temperature and pH probes and for adjusting pH like hydrochloric acid and nitrogen additions and sampling devices.
The volume of brine (V) which is fed to vessel (4) is replaced by transferring an equal volume of a brine (VI) from a vessel (6), via a filter (6') to vessel (5).
Sixth vessel (6) exhibits a volume of about 0.15 m3 and contains initially a volume of 0.06 m3 of a brine (VI). The filter (6') is a Pall cartridge type filter (for example of PUY series).
Brine (VI) is fed to vessel (5) at a volumetric flow rate (F6) of 0.1 m3/h until the initial volume of brine (V) in vessel (5) is restored, then stopped. The flow rate (F6) of brine (VI), the filter volume and the temperature ensure conditions e.g. like a superficial velocity of brine (VI) on the filter, convenient to remove fine solid particles from brine (VI) before entering vessel (5).
Brine (VI) is a brine saturated in salt.
Brine (VI) is obtained from a solid salt saturator (7'). The dimensions of vessel (6) are convenient for accommodating the equipment to control operating conditions.
The volume of brine (VI) which is fed to vessel (5) is replaced by transferring an equal volume of a brine (VII) from a vessel (7), via a solid salt saturator (7'), to vessel (6).
Vessel (7) exhibits a volume of about 0.15 m3 and contains initially a volume of 0.06 m3 of a brine (VII). The saturator (7') is a conic type saturator, has a volume of 0.15 m3 and contains a weight of salt of 0.04 t, continuously refilled by a salt charging device.
Brine (VII) is fed to vessel (6) at a volumetric flow rate (F7) of 0.1 m3/h, until the initial volume of brine (VI) in vessel (6) is restored, and then stopped. The flow rate of brine (VII), the saturator volume and the temperature ensure conditions e.g. like a residence time of brine (VII) in the saturator long enough to saturate brine (VII) before entering vessel (6).
Brine (VII) is a brine not saturated in salt with a pH of about 9.
Brine (VII) is obtained by addition of caustic soda or hydrochloric acid to a brine (VIII). Stirring is ensured by external recirculation of brine (VII) in vessel (7). The dimensions of vessel (7) give enough room for control probes like temperature and pH and addition and sampling devices. The volume of brine (VII) which is fed to vessel (6) is replaced by transferring an equal volume of a brine (VIII) from a vessel (8).
Vessel (8) exhibits a volume of about 1 m3 and contains initially a volume of 1 m3 of a brine (VIII).
Brine (VIII) is fed to vessel (7) at a volumetric flow rate (F8) of 0.1 m3/h until the initial volume of brine (VII) in vessel (7) is restored, and then stopped.
Brine (VIII) is a brine not saturated in salt with a pH of about 10. It can be of any origin.
The transfer in cascade of the various brines (IV) to (VIII) between the various vessels is triggered by the emptying of vessel (3).
Vessel (2) exhibits a volume of 0.2 m3.
Brine (II) is a brine depleted in salt, containing chlorine and possibly chlorate with a pH of about 4.
In vessel (2), hydrochloric acid is added to brine (II) until a pH of about 1.8 is obtained and the pH adjusted brine is stripped with air and circulated on an active coal containing column (2'). When chlorates are present, hydrochloric acid is added to brine (II) until a weight ratio HCl/NaC103 of about 130/100 g/g is obtained the brine is heated up, to convert chlorates into chlorine. After a residence time of 0.5 h at least, caustic soda is added until a pH of about 1.8 is obtained and the pH adjusted brine is stripped with air and circulated on an active coal containing column (2'). The dimensions of vessel (2) give enough room for control probes like temperature, pH and active chlorine content, and addition like hydrochloric acid, caustic soda and air, and sampling devices.
The resulting brine (IX) is withdrawn from vessel (2) at a flow rate (F9) and sent to storage and or disposal.

Claims

C L A I M S
1. Chlor-alkali electrolysis process for electrolyzing an entering brine into a depleted brine, comprising feeding at least one first vessel intermittently with a brine, subjecting this brine to at least one treatment in order to obtain the entering brine, feeding at least one electrolyser continuously with the entering brine in order to obtain the depleted brine, and withdrawing continuously the depleted brine from said electrolyser.
2. Process according to claim 1, comprising feeding at least one second vessel continuously with the depleted brine from said electrolyser, withdrawing the depleted brine intermittently from said second vessel, and subjecting the depleted brine to at least one other treatment after withdrawal from the second vessel.
3. Process according to either claim 1 or 2, comprising feeding at least one third vessel continuously with the entering brine and feeding the at least one electrolyser continuously with the entering brine from said third vessel.
4. Process according to any one of claims 1 to 3, comprising feeding the first vessel with the brine at a first flow rate, feeding the electrolyser with the entering brine at a second flow rate, withdrawing the depleted brine from said electrolyser at a third flow rate, withdrawing the depleted brine from the second vessel at a fourth flow rate, wherein when the second and third flow rates are not zero, at least one of the first and the fourth flow rate is occasionally zero.
5. Process according to any one of claims 1 to 4, wherein the treatment of the brine and/or of the depleted brine is selected from (A) an adjustment of the salt concentration of the brine, preferably by solid salt addition to the brine, (B) a removal of fine solid particles from the brine, preferably by filtration, (C) a removal of carbonate ions from the brine, preferably by acid addition followed by stripping, (D) a removal of iron and aluminium from the brine, preferably by filtration, (E) a removal of calcium and magnesium from the brine, preferably by ion-exchange, (F) a removal of iodide from the brine, preferably by oxidation and ion exchange, (G) a removal of bromide from the brine, preferably by oxidation, (H) a removal of silicon from the brine, preferably by precipitation and filtration, (I) a removal of chlorine from the brine preferably at least by acidification, stripping and adsorption, (J) a removal of chlorate from the brine, preferably by acid addition followed by stripping and/or by catalytic
hydrogenation, (K) a removal of sulphates from the brine by precipitation and filtration or nanofiltration by membranes, (L) a removal of organic compounds from the brine, preferably by oxidation, (M) a removal of mercury from the brine, preferably by precipitation, ion exchange or adsorption, and (N) a removal of ammonia from the brine, preferably by pH adjustment, oxidation and stripping.
6. Process according to claim 5, wherein the treatment of the brine is selected from treatments (A) to (H) and (K) to (N) and the treatment of the depleted brine is selected from treatments (I) and (J).
7. Process according to any one of claims 1 to 6 wherein the electro lyser is a membrane electrolyser.
8. Process according to claim 7, wherein the electrolysis of the entering brine is carried out under at least one of the following conditions:
■ An electrical current intensity lower than or equal to 5 kA;
■ A brine flow rate lower than or equal to 500 1/h;
■ A depleted brine flow rate lower than or equal to 400 1/h;
■ A diaphragm or membrane active surface lower than or equal to 1 m2.
9. Process according to either claim 7 or 8, wherein the treatment of the brine is carried out under at least one of the following conditions:
■ A brine flow rate higher than or equal to 20 1/h;
■ A brine volume higher than or equal to 50 1; and the treatment of the depleted brine is carried out under at least one of the following conditions:
■ A depleted brine flow rate higher than or equal to 10 1/h;
■ A depleted brine volume higher than or equal to 100 1.
10. Process according to any one of claims 1 to 9, wherein the brine is selected from a brine from n industrial process for manufacturing chlorine, a brine from an epoxide manufacturing process, preferably ethylene oxide, propylene oxide, butylene oxide or epichlorohydrin, and more preferably epichlorohydrin, a brine from an epoxide derivative manufacturing process, preferably epoxy resin, a brine from a process for manufacturing a chlorinated organic product, preferably 1 ,2-dichloroethane or 1 ,2-dichloroethylene, and more preferably 1 ,2-dichloroethane, a brine from a process for manufacturing a monoisocyanate or a polyisocyanate, preferably 4,4'-methylenediphenyl diisocyanate (MDI), toluene diisocyanate (TDI) or hexamethylene-1,6- diisocyanate (HDI), a brine from a process for manufacturing a polycarbonate, preferably 2,2-bis(4-hydroxyphenyl)propane polycarbonate (bisphenol A polycarbonate), and any mixture thereof.
11. Process according to any one of claims 1 to 10 for the production of chlorine.
12. Movable chlor-alkali electrolysis plant for carrying out the process according to any one of claims 1 to 11 , wherein the electro lyser is part of a chlor- alkali electrolysis module mounted on a first support which can be moved as a whole, and the brine and/or depleted brine treatments are carried out in at least one treatment module mounted on a second support which can be moved as a whole.
13. Chlor-alkali electrolysis plant according to claim 12, wherein the first and second supports are a container or a platform..
14. Electrolysis plant according to either claim 12 or 13, wherein the chlor- alkali electrolysis module and the module for the treatment of the brine and/or of the depleted brine are equipped with one or more sensors for monitoring one or more parameters such as temperature, pressure, voltage, current, flow rate, electrolyte composition or fluid level.
15. Electrolysis plant according to any one of claims 12 to 14, for electrolysis of an entering brine into a depleted brine, containing at least one chlor-alkali electrolysis module and at least two different support mounted modules for the treatment of the brine and/or of the depleted brine, wherein the chlor-alkali electrolysis module and the treatment modules are connected to each other allowing that the operation of the plant can be started with only one treatment module or with any combination of two or more treatment modules, and that at any time one of the treatments can be switched off and/or an additional treatment can be added, and/or the order of the treatments can be modified.
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