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  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/24—Halogens or compounds thereof
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
  • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
  • C02F1/46104—Devices therefor; Their operating or servicing
  • C02F1/46109—Electrodes
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
  • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
  • C02F1/467—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction
  • C02F1/4672—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction by electrooxydation
  • C02F1/4674—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction by electrooxydation with halogen or compound of halogens, e.g. chlorine, bromine
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
  • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
  • C02F1/46104—Devices therefor; Their operating or servicing
  • C02F1/46109—Electrodes
  • C02F2001/46133—Electrodes characterised by the material
  • C02F2001/46138—Electrodes comprising a substrate and a coating
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
  • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
  • C02F1/46104—Devices therefor; Their operating or servicing
  • C02F1/46109—Electrodes
  • C02F2001/46152—Electrodes characterised by the shape or form
  • C02F2001/46157—Perforated or foraminous electrodes
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/12—Halogens or halogen-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2201/00—Apparatus for treatment of water, waste water or sewage
  • C02F2201/46—Apparatus for electrochemical processes
  • C02F2201/461—Electrolysis apparatus
  • C02F2201/46105—Details relating to the electrolytic devices
  • C02F2201/4612—Controlling or monitoring
  • C02F2201/46125—Electrical variables
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2201/00—Apparatus for treatment of water, waste water or sewage
  • C02F2201/46—Apparatus for electrochemical processes
  • C02F2201/461—Electrolysis apparatus
  • C02F2201/46105—Details relating to the electrolytic devices
  • C02F2201/4612—Controlling or monitoring
  • C02F2201/46145—Fluid flow
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2201/00—Apparatus for treatment of water, waste water or sewage
  • C02F2201/46—Apparatus for electrochemical processes
  • C02F2201/461—Electrolysis apparatus
  • C02F2201/46105—Details relating to the electrolytic devices
  • C02F2201/46195—Cells containing solid electrolyte

Definitions

• the present invention relates to a process for electrochemical oxidation of bromide to bromine.
• the present invention more particularly relates to oxidation of bromide ions in brine, bittern and effluents using an indigenous cation exchange membrane flow cell.
• Oxidation of bromide in its source produces the elemental bromine, which is primarily used in the manufacture of both organic and inorganic bromo compounds.
• the compounds of bromine are well represented in many areas such as gasoline additives, agricultural chemicals, flame-retardants, dyes, photographic chemicals, pharmaceuticals etc.
• the high-density organo bromine compounds as hydraulic, gear/ore flotation fluids, the CaBr2-ZnBr2 composition as drilling fluid and the 1,2-dibromo ethylene as anti-knocking agent in gasoline are known to be useful.
• bromine is directly used as disinfectant in swimming pools, and as anti oxidant to control the growth of bacteria, algae and odor in cooling waters. It is also used for desizing of cotton, bleaching of pulp and paper, and in laboratories as a reagent.
• the source material is acidified to produce gaseous hydrobromic acid thereby oxidizing the bromide by oxygen over a metal oxide catalyst to produce a stream of bromine and water vapor.
• the drawbacks of this process are that it needs acidification and heating steps involving a catalyst, which adds to the production cost of bromine.
• the main object of the present invention is to provide a process for electrochemical oxidation of bromide to bromine in brine, bittern and effluents using a cation exchange membrane flow cell which obviates the drawbacks as detailed above.
• An object of the present invention is to use an indigenous cation ion-exchange membrane in a two compartmental solid polymer electrolyte flow cell.
• Yet another object of the present invention is to use precious triple metal oxide coated titanium as stable catalytic anode to oxidize bromide to bromine.
• Still another object of the present invention is to oxidize inorganic bromide present in non- acidified brine, bittern or enriched effluents to bromine.
• the present provides a process for electrochemical oxidation of bromide to bromine.
• the present invention more particularly relates to oxidation of bromide ions in brine, bittern and effluents using an indigenous cation exchange membrane flow cell.
• the present invention provides a process for electrochemical oxidation of bromide to bromine, said process comprising the steps of;
• Another embodiment of the present invention wherein a brine containing bromide in the range of 0.2 to 0.3% (w/v) is used. Still another embodiment of the present invention, wherein a bittern containing bromide in the range of 0.3 to 1.0% (w/v) is employed.
• bromide solution consisting of 0-20% (w/v) of sodium chloride, 0-2% (w/v) of calcium, 0-12% (w/v) of magnesium, 0- 3% (w/v) potassium chloride, 0-2% (w/v) sulfate, 0-40% (w/v) chloride and 0-0.01 M hydrochloric acid.
• Still another embodiment of the present invention wherein a solution of 0.1-0.3%o (w/v) sodium bromide having 5-15% (w/v) of sodium chloride, 0-5% (w/v) of calcium chloride, 0-3% (w/v) of magnesium chloride and 0-0.01 M hydrochloric acid is used.
• 0-1 M hydrochloric acid is used as catholyte.
• anolyte and catholyte solutions are allowed to flow in the range of 2 to 15 ml/min under gravity.
• electrochemical oxidation of bromide ion is performed in a two-compartment electrochemical cell.
• a two-compartment rectangular cell of 18 cm x 15 cm x 5.5 cm consisting of a conventional cation exchange membrane of 80 - 180 cm2 area may be used.
• bromide ion is oxidized by the loss of one electron per atom at the anode producing elemental bromine and sodium ion in solution.
• the counter reaction at the cathode is the reduction of water or H+ in the case of H2SO4 as catholyte, liberating H2 gas with the release of OH- or C1-, respectively.
• the excess sodium (cation) ion liberated in the anode compartment migrates to the cathode compartment, for charge balancing by crossing over the ion-exchange membrane producing sodium hydroxide/corresponding metal hydroxide/chloride on the other side as the co- product.
• the overall cell reaction is then given as
• the reaction was conducted on a laboratory scale using a rectangular (18 cm xl 5 cm x 5.5 cm) teflon membrane cell consisting of a thin stainless steel plate, mesh or an expanded sheet as cathode and a special triple metal oxide coated titanium as anode having an effective surface area of 56 cm2, one on either side of the membrane.
• Double distilled water or 0.1 to 1.0 M hydrochloric acid was used as a common catholyte in all the experiments.
• An indigenous cation exchange membrane P. K. Narayanan et al. Indian Patent No. 160,880, 1987 was used in the cell to keep the electrode chambers separate.
• the cell temperature varied between 27 and 30 °C.
• the anolyte and catholyte solutions were allowed to flow at the rate in the range of 2 - 15 ml/min through the respective electrode chambers under gravitational force while the electrolysis was in progress.
• the bromide solutions When handling with dilute solutions or bittern, it is preferable to oxidize the bromide solutions at low current densities between 2 - 7 mA/cm2 to achieve maximum percentage of bromide conversion in a single pass at 10 - 15 ml/min flow rate to bromine with high coulombic efficiency. It is also advantageous to work with concentrated solutions of bromide at high current densities and flow rates for maximum yields of bromine and high coulombic efficiency. In the present invention the current density is varied in the range of 0.1 to 13 mA/cm2.
• the process according to the present invention is started at room temperature and maintained between 26 and 30 °C during the cell operation.
• the inorganic bromide converted to bromine with excellent yields. No appreciable loss was found in bromine content due to evaporation or by the reactions at both the electrodes.
• the bromide in the original solution or the oxidized bromine in the anode compartment was not transported to the cathode compartment through the membrane.
• the membrane and the cell body were also found to be intact even after carrying the experiments for several hours.
• a constant current ranging between 0.05 - 0.70 A is applied across the two working electrodes. In all cases, the cell potential across the two current carrying electrodes was measured in the range of 2 - 5 V.
• the anodized solutions in single pass conditions under the given set of experimental parameters were collected.
• the pH of these solutions was initially at 6.8 - 7.0 and it decreased to 2.60 - 1.48, depending on the magnitude of the current applied at the electrodes, while that of the water in cathode compartment was between 10 and 12.
• the catholyte solution water, 0.1 or 1 M hydrochloric acid
• Bromine in all the anodized solutions was estimated by the spectrophotometric method (K. Kumar and D. W. Margerum, Inorg. Chem. 1987, 26, 2706-2711) following the characteristic 390 nm band for bromine in acidic solution.
• the bittern 34 °Be' with 8.5 g/1 bromide, 18.5 g/1 sodium chloride, 2.7 g/1 potassium chloride, 108.5 magnesium, Mg (II), 3.2 g/1 calcium, Ca (II), 0.275 g/1 sulfate, 394.78 g/1 chloride at pH 3.9
• potash and magnesia chemicals was electrolyzed by passing it without any further treatment through the anode and 1 M hydrochloric acid through the cathode compartments at the current densities between 1.0 and 12.5 mA/cm2 and flow rates 2 to 15 ml/min.
• the present invention describes an improved electrochemical method of oxidation of inorganic bromide in bromide containing solutions to bromine employing a two- compartment electrochemical membrane cell.
• the process involves the passage of bromide containing solutions through the anode compartment while a solution of 0-1 M hydrochloric acid flows through the anode compartment, both at 2 to 15 ml/min under gravity.
• the membrane flow cell consists of an expanded precious triple metal oxide coated titanium anode and a thin stainless steel mesh, plate or expanded sheet as cathode.
• the electrodes are separated by placing a conventional cation-exchange membrane between them at a distance of 2 to 6 mm from each electrode to keep the products produced at the electrodes separated.
• This method is useful to oxidize the bromide ion at low current densities between 1.0 to 12.5 n A/cm2 against 2 to 15 V conveniently at ambient temperatures.
• This process can be carried out in the presence of other interfering ions such as calcium, magnesium, chloride etc with minimum problems caused by clogging and precipitation. It is highly useful for the oxidation of bromide ion in brine and bittern samples without involving corrosive and costly chemicals or the acidification step.
• the oxidation of bromide is effected by flowing the aqueous solution composed of 0.2% sodium bromide and 10% sodium chloride through the anode and distilled water through cathode compartments.
• a constant current of 6.25 mA cm2 is passed across the two electrodes while both of the solutions flew at 10-ml/min rate.
• the cell potential is dropped to 3 V, while the solution temperature is maintained at 28 °C.
• the percentage of bromide converted to bromine, in single pass is65.5 with 58.4% coulombic efficiency.
• the anolyte solution turned acidic to pH 1.73.
• Example 1 The solution described in example 1 is electrolyzed in the same cell at the current density 6.25 mA/cm2. The cell potential is dropped to 3 V while the solutions are set to flow at the rate of 15 ml/min. The temperature is maintained at 28 ⁇ 2 °C. The percentage of bromide converted to bromine under steady state conditions is 68.2%. The coulombic efficiency rose to 85% while the pH of the solution dropped to 1.75.
• a solution containing 0.2% sodium bromide, 10%) sodium chloride and 5% calcium chloride (3% magnesium chloride) is electrolyzed at the anode at a current density of 6.25 mA/cm2.
• a solution of 0.1 M hydrochloric acid is circulated through the cathode compartment to prevent the deposition of calcium (magnesium) hydroxide on the membrane surface facing towards the cathode by the reaction of them with hydroxyl ions produced in the cathode compartment.
• Both, the anolyte and catholyte solutions are set to flow at the rate 10 ml/min during the electrolysis.
• the cell potential in such conditions, varied between 3 and 4 V.
• the cell temperature remained at 28 °C.
• Bromine is also produced in the same cell as in example 1 by electrolyzing the under ground brine (26.8 °Be') having the composition of 1.8 g/1 bromide, 0.07 g/1 calcium, Ca(LT), 50.1 g/1 magnesium, Mg(U), 20.62 g/1 sodium, Na(I) 41 g/1 potassium, K(I) 202.31 g/1 chloride and 18.7 g/1 sulfate at pH 6.67, as collected from the experimental salt farm.
• the brine solution without any further treatment is run through the anolyte compartment at the rate of 10 ml/min.
• a solution of 0.1 M hydrochloric acid is run at the same rate through the cathode compartment to prevent the hydrolysis of Ca2+ and Mg2+ in the cathode compartment.
• Electrolysis is effected by applying a current density of 6.25 mA cm2 across the two electrodes. The cell potential is dropped to 3 V, while the solution temperature maintained at 28 °C The percentage of bromide converted to bromine in the single pass anodized solution is70.3 with about 65% coulombic efficiency.
• the pH of the anolyte solution is 1.73.
• Example 5 Bromide is also oxidized to bromine in the same cell as in example 1 by electrolyzing the end bittern (34 °Be') having the composition of 8.5 g/1 bromide 18.5 g/1 sodium chloride, 2.7 g/1 potassium chloride, 108.5 magnesium, Mg (JJ), 3.2 g/1 calcium, Ca (LI), 0.275 g/1 sulfate, 394.78 g/1 chloride at pH 3.9.
• the end bittern without any further treatment is run through the anolyte compartment at the rate 2 - 15 ml/min while varying the current density between 1 -13 mA/cm2.
• the end bittern described in example 6 is electrolyzed in the same cell at two current densities 4.5 and 8.0 mA/cm2 at two different flow rates 2 and 15 ml/min.
• the percentage of bromide converted to bromine at 4.5 mA/cm2, isl4.0 at 2 ml/min and 11.5 at 15 ml/min, while at 8.0 mA/cm2, it is30.8 at 2 ml/min and 11.9 at 15 ml/min flow rates.
• the coulombic efficiencies in these cases are 38.2 and 100% at 4.5 mA/cm2 and 46.8 and 100% at 8.0 mA/cm2 at 2 and 15 ml/min flow rates, respectively.
• the pH of the anolyte solutions varied between 3.0 and 3.9 while the cell temperature maintained at 28 °C. Advantages of the present invention
• Hydrogen is liberated as a byproduct, which can be recycled in a fuel cell, if desired.
• the process eliminates the problem of clogging. 8. It involves a compact cell conserving energy by avoiding steps like heating, acidification, separation and purification of hydrolysable materials from the medium.
• the method involves an inexpensive and easily moldable plastic cell with an inexpensive cathode and a non-polarizable anode for effecting the electrolysis.
• the membrane is easy to procure, install and durable.

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• 2003
  • 2003-03-31 AU AU2003226644A patent/AU2003226644B2/en not_active Ceased
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