US3256164A - Electrolytic production of ozone - Google Patents

Electrolytic production of ozone Download PDF

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US3256164A
US3256164A US320057A US32005763A US3256164A US 3256164 A US3256164 A US 3256164A US 320057 A US320057 A US 320057A US 32005763 A US32005763 A US 32005763A US 3256164 A US3256164 A US 3256164A
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ozone
water
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liquid electrolyte
electrolyte
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John A Donohue
William A Wilson
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Standard Oil Co
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    • 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
    • C25B1/13—Ozone

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  • ozone is produced in high yield by carefully controlling the water concentration of the liquid electrolyte during electrolysis.
  • the liquid electrolyte consists essentially of HF and about 2-7 percent water, by weight. Maximum ozone yield is obtained when the HF electrolyte contains about 46% water.
  • anelectric current is passed through a liquid electrolyte consisting of hydrogen fluoride and not more than about weight percent of water to produce a mixture of gases containing ozone; oxygen difluoride, hydrogen and oxygen are also produced.
  • the amount of ozone produced is substantially greater than the amount of oxygen difluoride produced when the electrolysis is carried out at a temperature of not more than about 50 C., preferably 20 C. to +20C., with the electrolyte consisting of hydrogen fluoride and 4-6 percent of water.
  • the electrolytic method of the invention can be carried out in any electrolytic cell wherein a liquid electrolyte can be positioned in the cell and an electric current passed therethrough; more commonly, electrodes are immersed in the liquid electrolyte and provisions are made for maintaining liquid electrolyte at the desired temperature of operation.
  • Electrolytic cells suitable for the carrying out of a method of the invention include those now used for the electrolytic production of fluorine except that the carbon anode needs to be replaced by a metal anode. Illustrative descriptions of suitable cellsare given in Chapter 8, Flourine Chemistry, I. H. Simons, editor (Academic Press, 1950). It is to be understood that the cells will be modified by anyone of ordinary skill to mate-rials of construction suitable for use with HF solutions. It has been found that particularly suitable materials of construction for the electrodes are: anode formed of nickel and cathode formed of iron, specifically, black iron.
  • a liquid electrolyte consisting of an HP solution containing not more than about 10 weight percent of water
  • gases include hydrogen, molecular oxygen, oxygen difluoride (0P and ozone (0 content of the HF electrolyte is critical and must be carefully controlled.
  • Enough water must be present to perrnit passage of the electric current through the liquid HF positioned in the cell and to furnish the oxygen for the production of the O and 0P
  • at least about 1 weight percent of water is present; that is, the electrolyte consists of 99 percent of HF and 31 percent of water.
  • the electrolyte upon increasing the water content of the liquid electrolyte above about 1%, the-amount of ozone produced increases markedly and also increases with relative to the oxygen difluoride produced. Also, as the water content of the liquid electrolyte increases in the The water ice range of 4-6 weight percent, the yield of ozone passes through a maximum point. However, as the water content of the liquid electrolyte approaches toward 10 ,weight percent, the predominant position of ozone decreases and eventually the oxygen difluoride becomes predominant; so that the electrolyte used in the production of ozone as the desired product contains not more than about 10 weight percent of water; that is, the liquid electrolyte preferably consists of about 93-98 percent of HP and about 2-7 percent of water.
  • the hydrogen fluoride as used herein may include regular commercial grade acid as well as high purity hydrogen fluoride itself.
  • commercial grade acid the water content thereof will be calculated as part of the total desired water content of the particular liquid electrolyte present in the electrolytic cell.
  • the electrolyte must be in the liquid state and s'uflicient pressure must be maintained on the cell to keep the electrolyte in the liquid state at the particular temperature of operation. The temperature must not be so low that the electrolyte freezes.
  • the electrolytic cell is operated at any temperature which will permit the production of ozone.
  • the cell is operated at a temperature of not more than about C. and desirably at a temperature below about 50 C.
  • the cell is operated at a temperature between about 20 C. to +20 C.
  • the product of the electrolysis comprises a mixture of hydrogen, oxygen, oxygen difluoride and ozone.
  • the hydrogen may be readily separated from the other gaseous products by condensing these three.
  • the oxygen may be removed by low temperature distillation from the ozone and the oxygen difluoride.
  • the ozone and the oxygen difluoride may be separated by low temperature distillation. It has been discovered that silica gel adsorbs ozone in preference to oxygen difluoride and essentially pure ozone may be recovered from the silica gel adsorbent.
  • FIGURE 1 The cell used in this work is shown schematically in, FIGURE 1. It is composed of a Kel-F cup covered by a stainless steel cap. The use of Kel-F allows the contents of the cell to be observed during the electrolysis. The cup was approximately 2" in diameter and 4 high. The diaphragm made from $5 Kel-F sheet, was solid above the liquid level to prevent mixing of anode and cathode gaseous products, but perforated below the liquid level to allow free flow of the electrolyte. The nickel anode x 1%" x 2%”) and the black iron cathode (%2" x 1'78 x 3") were held in place by slots in the cup wall and a Kel-F spacer. The electrode separation was inch.
  • Nichrome wire leads were welded to each electrode and insulated from the steel cap with Teflon.
  • the steel cap was provided with two openings on each side of the diaphragm.
  • the anode inlet was connected, via a calibrated Kel-F transfer buret, to an HP cylinder.
  • the fittings were of Monel, and the gas (nitrogen or helium) used to transfer the HF was also used as anode flush gas.
  • a copper tube conducted the flush gas to the cathode inlet. This could be easily removed and water or other materials inserted.
  • the vents on both sides of the cell were connected separately, via copper tubing, to a reflux condenser filled with Dry Ice-acetone (78 C.). Any HF which passed the condenser was absorbed in sodium fluoride packed tubes. The HF free gases could then be passed into glass bubblers for analysis.
  • Voltages in tests 4, 7 and 8 are averages over the time.
  • Ozone itself has a considerable use in the purification of drinking water, the treatment of industrial wastes and the deodorization of air and sewage gases.
  • the compositions containing ozone and oxygen difluoride are useful where oxidizing power is desired and there is no problem of effect on animal life.
  • the mixed composition of the invention may be used in the treatment of industrial wastes which are not disposed of directly in sources of drinking water.
  • the mixed compositions may be used in chemical reactions where the presence of combined fluorine is not detrimental to the quality of the final product; for example, in ozonolysis reactions with olefins.
  • a method of electrolytically generating ozone which method comprises passing an electrical current at a voltage in the range of about 6.0 v. to about 11.0 v. through a liquid electrolyte positioned in an electrolytic cell said liquid electrolyte being maintained at a temperature in the range of about 20 C. to about +20 C., said liquid electrolyte consisting of hydrogen fluoride and about 2-7 weight percent of Water, and withdrawing fro said cell gases containing ozone.
  • a method of electrolytically generating ozone and oxygen difluoride, with the ozone being in the greater amount comprises passing an electrical current at a voltage in the range of about 6.0 v. to about 11.0 v. between the electrodes of an electrolytic cell, said cell containing a liquid electrolyte into which said electrodes are immersed said liquid electrolyte being maintained at a temperature in the range'of about ,20 C. to about +20 C., said liquid electrolyte consisting of hydrogen fluoride and about 4-6 weight percent of Water, and withdrawing from said cell gases containing ozone and oxygen difiuoride, the amount of ozone being substantially greater than the amount of oxygen diflouride.

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Description

June 1966 J. A. DONOHUE ETAL 3,256, 64
ELECTROLYTIC PRODUCTION OF OZONE Filed Oct. 30, 1965 3 Sheets-Sheet 1 NICKEL ANODE IRON CATHODE VENT VIA REFLUX COND. VENT VIA REFLUX COND. (-78 C)NOF ABSORBER AND (-78C)NOF ADSORBER AND KI BUBBLER KI BUBBLER INLET FOR HF 8 INLET FOR ANODE FLUSH GAS T CATHODE FLUSH GAS AND WATER x STAINLESS STEEL HEAD TEFLON INSULATION I KEL'F CUP I E & I I
I ANODE i IRON CATHODE 5 t I I 5 I i L KEL-F DIAPHRAM Fig 1 3 (PERFORATED) 5 I i I i I I l n i i 7 I E I i I i N KEL-F ELECTRODE INVENTORS:
SPACER John A. Dona/we BY Willie/I A. Wilson ATTORNEY June 14, 1966 J. A. DONOHUE ETAL 3,
ELECTROLYTIC PRODUCTION OF OZONE Filed 061'.- 30, 1963 2 Sheets-Sheet 2 Fig. 2
PRODUCT, Gms/KW -Hr.
HF ELECTROLYTE WATER CONTENT, W\. K,
John A. Dona/me William A. Wilson Maw ATTORNEY INVENTORS:
United States Patent 3,256,164 ELECTROLYTIC PRODUCTION OF OZONE John A. Donohue, Chicago, IlL, and William A. Wilson, Griflith, Ind., assignors to Standard Oil Company, Chicago, 11]., a corporation or Indiana Filed Oct. 30, 1963, Ser. No. 320,057 3 Claims. (Cl. 204-129) This application is a continuation-inpart of our copending application S.N. 14 1,175, filed September 27, 1961, now abandoned. This invention relates to the electrolytic production of mixtures of ozone (O and oxygen difluoride (0P particularly where ozone is the predominant product.
We have discovered that excellent yields of ozone can be obtained from hydrogen fluoride-water solutions by electrolysis conducted in a particular manner. According to our invention, ozone is produced in high yield by carefully controlling the water concentration of the liquid electrolyte during electrolysis. 'For best results, the liquid electrolyte consists essentially of HF and about 2-7 percent water, by weight. Maximum ozone yield is obtained when the HF electrolyte contains about 46% water.
In our electrolytic method of generating ozone, anelectric current is passed through a liquid electrolyte consisting of hydrogen fluoride and not more than about weight percent of water to produce a mixture of gases containing ozone; oxygen difluoride, hydrogen and oxygen are also produced. The amount of ozone produced is substantially greater than the amount of oxygen difluoride produced when the electrolysis is carried out at a temperature of not more than about 50 C., preferably 20 C. to +20C., with the electrolyte consisting of hydrogen fluoride and 4-6 percent of water.
The electrolytic method of the invention can be carried out in any electrolytic cell wherein a liquid electrolyte can be positioned in the cell and an electric current passed therethrough; more commonly, electrodes are immersed in the liquid electrolyte and provisions are made for maintaining liquid electrolyte at the desired temperature of operation. Electrolytic cells suitable for the carrying out of a method of the invention include those now used for the electrolytic production of fluorine except that the carbon anode needs to be replaced by a metal anode. Illustrative descriptions of suitable cellsare given in Chapter 8, Flourine Chemistry, I. H. Simons, editor (Academic Press, 1950). It is to be understood that the cells will be modified by anyone of ordinary skill to mate-rials of construction suitable for use with HF solutions. It has been found that particularly suitable materials of construction for the electrodes are: anode formed of nickel and cathode formed of iron, specifically, black iron. We
have also found that the anode and cathode compartments need not be separated.
When an electric current is passed through a liquid electrolyte consisting of an HP solution containing not more than about 10 weight percent of water, gases are produced. These gases include hydrogen, molecular oxygen, oxygen difluoride (0P and ozone (0 content of the HF electrolyte is critical and must be carefully controlled. Enough water must be present to perrnit passage of the electric current through the liquid HF positioned in the cell and to furnish the oxygen for the production of the O and 0P In general, at least about 1 weight percent of water is present; that is, the electrolyte consists of 99 percent of HF and 31 percent of water. We have discovered that upon increasing the water content of the liquid electrolyte above about 1%, the-amount of ozone produced increases markedly and also increases with relative to the oxygen difluoride produced. Also, as the water content of the liquid electrolyte increases in the The water ice range of 4-6 weight percent, the yield of ozone passes through a maximum point. However, as the water content of the liquid electrolyte approaches toward 10 ,weight percent, the predominant position of ozone decreases and eventually the oxygen difluoride becomes predominant; so that the electrolyte used in the production of ozone as the desired product contains not more than about 10 weight percent of water; that is, the liquid electrolyte preferably consists of about 93-98 percent of HP and about 2-7 percent of water. The best combination of ozone content in the product gases and yield of ozone per kilowatt-hour of power consumed in the cell is'obtained when the liquid electrolyte consists of about 4-6 weight percent of water and the remainder essentially hydrogen fluoride. Since water is consumed during production of O and 0P make-up water must be added to the electrolyte to maintain the water concentration within the critical range for maximum ozone producion and yield.
It is to be understood that the hydrogen fluoride as used herein may include regular commercial grade acid as well as high purity hydrogen fluoride itself. When utilizing commercial grade acid, the water content thereof will be calculated as part of the total desired water content of the particular liquid electrolyte present in the electrolytic cell.
The electrolyte must be in the liquid state and s'uflicient pressure must be maintained on the cell to keep the electrolyte in the liquid state at the particular temperature of operation. The temperature must not be so low that the electrolyte freezes.
The electrolytic cell is operated at any temperature which will permit the production of ozone. In general, the cell is operated at a temperature of not more than about C. and desirably at a temperature below about 50 C. When the absolute maximum of ozone production'is desired, the cell is operated at a temperature between about 20 C. to +20 C.
The product of the electrolysis comprises a mixture of hydrogen, oxygen, oxygen difluoride and ozone. The hydrogen may be readily separated from the other gaseous products by condensing these three. When it is desired to operate with a mixture of low molecular oxygen content, the oxygen may be removed by low temperature distillation from the ozone and the oxygen difluoride. The ozone and the oxygen difluoride may be separated by low temperature distillation. It has been discovered that silica gel adsorbs ozone in preference to oxygen difluoride and essentially pure ozone may be recovered from the silica gel adsorbent. Without taking any special pains to eliminate oxygen difluoride present in the spaces between silica gel particles, it has been possible to obtain desorbed ozone containing on the order of 4 mole percent of oxygen difluoride. By taking special precautions, it is entirely possible to produce ozone containing only trace amounts of oxygen difluoride ornone at all.
ILLUSTRATIONS The cell used in this work is shown schematically in, FIGURE 1. It is composed of a Kel-F cup covered by a stainless steel cap. The use of Kel-F allows the contents of the cell to be observed during the electrolysis. The cup was approximately 2" in diameter and 4 high. The diaphragm made from $5 Kel-F sheet, was solid above the liquid level to prevent mixing of anode and cathode gaseous products, but perforated below the liquid level to allow free flow of the electrolyte. The nickel anode x 1%" x 2%") and the black iron cathode (%2" x 1'78 x 3") were held in place by slots in the cup wall and a Kel-F spacer. The electrode separation was inch. Nichrome wire leads were welded to each electrode and insulated from the steel cap with Teflon. The steel cap was provided with two openings on each side of the diaphragm. The anode inlet was connected, via a calibrated Kel-F transfer buret, to an HP cylinder. The fittings were of Monel, and the gas (nitrogen or helium) used to transfer the HF was also used as anode flush gas. A copper tube conducted the flush gas to the cathode inlet. This could be easily removed and water or other materials inserted. The vents on both sides of the cell were connected separately, via copper tubing, to a reflux condenser filled with Dry Ice-acetone (78 C.). Any HF which passed the condenser was absorbed in sodium fluoride packed tubes. The HF free gases could then be passed into glass bubblers for analysis.
Current was obtained from a DC. power line and In this reported series of tests the cell was equipped with a new nickel anode, and the concentration of water was kept above about 3%. As a further precaution the tests at lower water concentration were run at lower voltages and, therefore, lower current densities. This was done to prevent formation of even small amounts of fluorine which is one possible cause of corrosion at the anode.
In the first half of this series (Tests 1-5) the results were quite good even at low current densities. At higher current densities results were slightly better. Then the cell was allowed to stand at room temperature for two weeks with the anode in contact with the HF-water elecstepped down with a variable resistance. The voltage trolyte. When the cell was started up again the ozone and amperage were measured with standard meters. 15 yield had dropped. A second test showed an ozone yield TABLE Added Testing Product Test No. Water, Volts b Amps. Opera weight on, percent a Minutes u 0 013; 0 0F; 0
2. 9 6. 9 1. 2 60 18. 0 9. 8. 8 5. 8 3. 9 ,6. 6 1. 2 G0 20. 7 12. 4 10. 1 6. 9 4. 7 6. 4 1. 2 60 24. 1 15. 0 8.6 6. 0 4. 6 7. 0 1. 6 45 26. 8 l4. 8 l0. 4 6. 7 4. 6 7. 4 2. 0 36 27. 1 14. 6 12. 9 7. 9 5. 5 8. 0 2. O 36 25. O 12. 5 14. 4 8. 1 7. 0 8. 7 2. 0 37 19. 8 9. l 16. 4 8. 5 8. 2 l1. 0 2. 0 36 6. 9 2. 6 17. 8 7. 3
Remainder of electrolyte consisted of commercial HF solution containing 99.9% mini.
mum HF.
Voltages in tests 4, 7 and 8 are averages over the time.
The actual moles produced are the numbers listed multiplied by 0.0001, i.e., 10- Hydrogen and oxygen also produced.
B Grams of product produced per kilowatt-hour of power consumed in the electrolysis eel l The bubblers were filled with 200 ml. of a 2% KI solution. After each run the free iodine was titrated by the usual method using thiosulfate with starch as the indicator. The fluoride ion was also determined by the thorium chloranilate method. The amount of 0P formed can be calculated from the fluoride analysis directly. To determine ozone the iodine released by 0P is first calculated and subtracted from the analyzed iodine. The corrected value then gives the amount of ozone:
O +2KI+H 0 I +2KOH+O The following is a generalized procedure for a series of tests. The cell was assembled and pressure tested with air at 10 p.s.i.g. The diaphragm was checked by filling the cell with water and raising the liquid level on one side. The cell was then sealed and set aside overnight. If the liquid level did not equilibrate the diaphragm was considered gas tight. The cell was then emptied and a measured amount of water was added. It was next placed in ,an ice bath (0 C.) and connected to transfer lines and condensers. After the desired amount of HF was transferred to the cell, a slow flow of helium was begun on one side of the diaphragm and a slow flow of nitrogen was begun on the other side of the diaphragm. This gave a fairly constant pressure on the system, activating the KI bubblers while keeping the electrolyte level undisturbed.
For the first minutes after electrolysis was begun the products were usually vented. Then when the amperage and voltage had settled down and were fairly constant, the run was started by switching the product gases into Kl bubblers. (Average values of voltage are reported in tests where they were not constant.) The test was continued until sufficient reaction occurred in the K1 bubblers. Then electrolysis was stopped and the KI solutions were submitted for analysis. The water concentration of the cell was then increased and the series continued.
increase with time of operation. (These results are not reported here.) Increasing the water concentration in later Test 6 gave nearly complete recovery of ozone yield. Further increases in water concentration in Tests 78 caused ozone yield to drop off. The results of these Tests 1-8 are set out in the table. The critical effect of electrolyte water content on ozone and oxygen difluoride yields,based upon the power consumed in the cell, is shown in FIGURE 2.
. Several runs were made with a platinum anode. It was found that at about 3% water the platinum corroded rapidly. As soon as the current was turned on the solution blackened from corrosion products. In all the tests reported here with the nickel electrode, the solution remained clear and colorless. Any corrosion of nickel was small, or at least it adhered tightly to the anode.
In other tests, it has been observed that the presence of a diaphragm to separate anode and cathode compartments is not essential to successful operation of the cell.
Ozone itself has a considerable use in the purification of drinking water, the treatment of industrial wastes and the deodorization of air and sewage gases. The compositions containing ozone and oxygen difluoride are useful where oxidizing power is desired and there is no problem of effect on animal life. For example, the mixed composition of the invention may be used in the treatment of industrial wastes which are not disposed of directly in sources of drinking water. Also, the mixed compositions may be used in chemical reactions where the presence of combined fluorine is not detrimental to the quality of the final product; for example, in ozonolysis reactions with olefins.
Thus having described the invention, what is claimed is:
1. A method of electrolytically generating ozone which method comprises passing an electrical current at a voltage in the range of about 6.0 v. to about 11.0 v. through a liquid electrolyte positioned in an electrolytic cell said liquid electrolyte being maintained at a temperature in the range of about 20 C. to about +20 C., said liquid electrolyte consisting of hydrogen fluoride and about 2-7 weight percent of Water, and withdrawing fro said cell gases containing ozone.
2. The method of claim 1 wherein said electrolyte composition is: HF, 93-98%; and water, 27%.
3. A method of electrolytically generating ozone and oxygen difluoride, with the ozone being in the greater amount, which method comprises passing an electrical current at a voltage in the range of about 6.0 v. to about 11.0 v. between the electrodes of an electrolytic cell, said cell containing a liquid electrolyte into which said electrodes are immersed said liquid electrolyte being maintained at a temperature in the range'of about ,20 C. to about +20 C., said liquid electrolyte consisting of hydrogen fluoride and about 4-6 weight percent of Water, and withdrawing from said cell gases containing ozone and oxygen difiuoride, the amount of ozone being substantially greater than the amount of oxygen diflouride.
References Cited by the Examiner UNITED STATES PATENTS 2,034,458 3/1936 Calcott et a1 204128 X OTHER REFERENCES Chemical Abstracts I, volume 37, column 61972, 1943.
Chemical Abstracts II, volume 42, column 4471 f, 1948.
Chemical Abstracts III, volume 54, column 13900e, 1960.
JOHN H. MACK, Primary Examiner.
5 H. M. FLOURNOY, Assistant Examiner.

Claims (1)

1. A METHOD OF ELECTROLYTICALLY GENERATING OZONE WHICH METHOD COMPRISES PASSING AN ELECTRICAL CURRENT AT A VOLTAGE IN THE RANGE OF ABOUT 6.0 V. TO ABOUT 11.0 V. THROUGH A LIQUID ELECTROLYTE POSITIONED IN AN ELECTROLYTIC CELL SAID LIQUID ELECTROLYTE BEING MAINTAINED AT A TEMPERATURE IN THE RANGE OF ABOUT -20*C. TO ABOUT +20*C., SAID LIQUID ELECTROLYTE CONSISTING OF HYDROGEN FLUORIDE AND ABOUT 2-7 WEIGHT PERCENT OF WATER, AND WITHDRAWING FROM SAID CELL GASES CONTAINING OZONE.
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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3725236A (en) * 1970-09-24 1973-04-03 Honeywell Inc Electrochemical oxygen demand apparatus
DE3003781A1 (en) * 1980-02-02 1981-09-03 Rheinisch-Westfälisches Elektrizitätswerk AG, 4300 Essen Ozone mfr. from aq. electrolyte - using electrode made of titanium and coated with cpd. contg. tetra-valent titanium ions, followed by top coating of lead di:oxide
US4316782A (en) * 1980-05-29 1982-02-23 Regents Of The University Of California Electrolytic process for the production of ozone
EP0068522A1 (en) * 1981-05-11 1983-01-05 BBC Aktiengesellschaft Brown, Boveri & Cie. Process and apparatus for the synthetic preparation of ozone by electrolysis, and its application
US4375395A (en) * 1981-05-21 1983-03-01 Foller Peter C Process for producing ozone
WO1986001542A1 (en) * 1984-09-05 1986-03-13 Dietrich Wabner Process, device and means for the production of ozone
US6022456A (en) * 1997-02-20 2000-02-08 Valdosta State University Apparatus and method for generating ozone
US20070086932A1 (en) * 2003-07-18 2007-04-19 Hallam David R Air filtration device
DE102015004101A1 (en) * 2015-03-25 2016-09-29 Condias Gmbh Process for the preparation of dilute hydrofluoric acid

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2034458A (en) * 1932-10-31 1936-03-17 Du Pont Process and apparatus

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2034458A (en) * 1932-10-31 1936-03-17 Du Pont Process and apparatus

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3725236A (en) * 1970-09-24 1973-04-03 Honeywell Inc Electrochemical oxygen demand apparatus
DE3003781A1 (en) * 1980-02-02 1981-09-03 Rheinisch-Westfälisches Elektrizitätswerk AG, 4300 Essen Ozone mfr. from aq. electrolyte - using electrode made of titanium and coated with cpd. contg. tetra-valent titanium ions, followed by top coating of lead di:oxide
US4316782A (en) * 1980-05-29 1982-02-23 Regents Of The University Of California Electrolytic process for the production of ozone
EP0068522A1 (en) * 1981-05-11 1983-01-05 BBC Aktiengesellschaft Brown, Boveri & Cie. Process and apparatus for the synthetic preparation of ozone by electrolysis, and its application
US4375395A (en) * 1981-05-21 1983-03-01 Foller Peter C Process for producing ozone
WO1986001542A1 (en) * 1984-09-05 1986-03-13 Dietrich Wabner Process, device and means for the production of ozone
US6022456A (en) * 1997-02-20 2000-02-08 Valdosta State University Apparatus and method for generating ozone
US20070086932A1 (en) * 2003-07-18 2007-04-19 Hallam David R Air filtration device
US7449053B2 (en) 2003-07-18 2008-11-11 David Richard Hallam Air filtration device
US8211374B2 (en) 2003-07-18 2012-07-03 David Richard Hallam Air cleaning device
DE102015004101A1 (en) * 2015-03-25 2016-09-29 Condias Gmbh Process for the preparation of dilute hydrofluoric acid
US11198609B2 (en) 2015-03-25 2021-12-14 Condias Gmbh Method for producing diluted hydrofluoric acid

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