WO2013019427A1

WO2013019427A1 - Method for generating biocide

Info

Publication number: WO2013019427A1
Application number: PCT/US2012/047558
Authority: WO
Inventors: Zijun Xia; Rihua Xiong; Chihyu Sui; Hai Yang; Qunjian Huang
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2011-07-29
Filing date: 2012-07-20
Publication date: 2013-02-07
Anticipated expiration: 2014-02-01
Also published as: TW201321310A; CN102897874A

Abstract

A method comprises: positioning a first capacitive electrode and a first non- capacitive electrode in a first aqueous solution comprising at least one of sodium chloride, potassium chloride, sodium bromide and potassium bromide; applying a first electrical current on the first capacitive electrode and the first non-capacitive electrode to electrolyse the first aqueous solution to generate at least one of chlorine and bromine, while the first capacitive electrode acts as cathode and the first non- capacitive electrode acts as anode; applying a second electrical current on the first capacitive electrode and the first non-capacitive electrode to electrolyse the first aqueous solution to generate hydrogen, while the first capacitive electrode acts as anode and the first non-capacitive electrode acts as cathode; and switching polarities of the first capacitive electrode and the first non-capacitive electrode before the first capacitive electrode is fully occupied.

Description

METHOD FOR GENERATING BIOCIDE

BACKGROUND

[0001] The present invention relates to methods for generating biocides, such as chlorine, hypochlorite, bromine, and hypobromide.

[0002] Bacteriostatic treatment/sterilization of water, such as those cycling in cooling devices, those to be provided in swimming pools, and those to be provided as drinking water, is usually done by introducing biocides, e.g., at least one of chlorine, hypochlorite, bromine, and hypobromide, to the water.

[0003] The chlorine, hypochlorite, bromine, and hypobromide are generated using different methods. U.S. patent No. 6,045,704 discloses a raw water purification system for purifying raw water with a first d.c. voltage applied between a conductive adsorber portion and a primary electrode in the raw water and accelerating generation of chlorine from the raw water with a second d.c. voltage higher than the first d.c. voltage. The first d.c. voltage is of a low level sufficient to capture the microorganisms and the bacteria and the second d.c. voltage is of a relatively high level capable of performing electrolysis of the raw water to generate chlorine. That is to say, in this raw water purification system, electrolysis of the raw water does not happen when the first d.c. voltage is applied and only happens when the second d.c. voltage is applied. In addition, the concentration of chlorine generated in this raw water purification system is as low as, e.g., 1 ppm.

[0004] Other existing generating technologies do not fulfill all the requirements of the world either at least partially because the biocide and the byproduct generated while preparing the biocide are usually corrosive and apt to causing explosion problem at relatively high concentration thereof. There is a need, therefore, for a new method to generate biocides (at least one of chlorine, hypochlorite, bromine, and hypobromide).

BRIEF DESCRIPTION

[0005] In one aspect, the present invention relates to a method, comprising: positioning a first capacitive electrode and a first non-capacitive electrode in a first aqueous solution comprising at least one of sodium chloride, potassium chloride, sodium bromide and potassium bromide; applying a first electrical current on the first capacitive electrode and the first non-capacitive electrode to electrolyse the first aqueous solution to generate at least one of chlorine and bromine, while the first capacitive electrode acts as cathode and the first non-capacitive electrode acts as anode; applying a second electrical current on the first capacitive electrode and the first non-capacitive electrode to electrolyse the first aqueous solution to generate hydrogen, while the first capacitive electrode acts as anode and the first non- capacitive electrode acts as cathode; and switching polarities of the first capacitive electrode and the first non-capacitive electrode before the first capacitive electrode is fully occupied.

DRAWINGS

[0006] These and other features and aspects of embodiments of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0007] FIG. 1 is a schematic diagram of a cell used in one embodiment;

[0008] FIG. 2 is a schematic diagram showing the cell of FIG. 1 connects to a power supplier;

[0009] FIG. 3 is a schematic diagram showing a capacitive electrode of the cell of FIG. 2 is close to be fully occupied;

[0010] FIG. 4 is a schematic diagram showing the cell of FIG. 3 is switched in polarities thereof;

[0011] FIG. 5 is a schematic diagram of the cell of FIG. 4 after electrochemical reactions;

[0012] FIG. 6 is a schematic diagram of the cell of FIG. 5 while the capacitive electrode is close to be fully occupied; and

[0013] FIG. 7 is an image view under a scanning electron microscope of an activated carbon sheet used in the examples. DETAILED DESCRIPTION

[0014] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that is not to be limited to the specific quantity specified and could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about", is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Moreover, the suffix "(s)" as used herein is usually intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term.

[0015] Any numerical value ranges recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and corresponding higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, from 20 to 80, or from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

[0016] There may be more than one cell in the method. In some embodiments, the method for generating biocides further comprises: positioning a second capacitive electrode and a second non-capacitive electrode in a second aqueous solution comprising at least one of sodium chloride, potassium chloride, sodium bromide and potassium bromide; applying a third electrical current on the second capacitive electrode and the second non-capacitive electrode to electrolyse the second aqueous solution to generate at least one of chlorine and bromine, while the second capacitive electrode acts as cathode and the second non-capacitive electrode acts as anode; applying a fourth electrical current on the second capacitive electrode and the second non-capacitive electrode to electrolyse the second aqueous solution to generate hydrogen, while the second capacitive electrode acts anode and the second non- capacitive electrode acts as cathode; and switching polarities of the second capacitive electrode and the second non-capacitive electrode before the second capacitive electrode is fully occupied.

[0017] The first aqueous solution and the second aqueous solution may be from a same source or different sources. The first cell comprising the first non-capacitive electrode and the first capacitive electrode and the second cell comprising the second non-capacitive electrode and the second capacitive electrode may be the same or different from each other. The first and the second cells may generate the at least one of chlorine and bromine at the same time or at different times.

[0018] The first electrical current and the third electrical current may be the same as or different from the second electrical current and the fourth electrical current, respectively. If the first electrical current is higher than the second electrical current, the time to apply the first electrical current before the first capacitive electrode is fully occupied may be shorter than the time to apply the second electrical current before the first capacitive electrode is fully occupied. If the third electrical current is higher than the fourth electrical current, the time to apply the third electrical current before the second capacitive electrode is fully occupied may be shorter than the time to apply the fourth electrical current before the second capacitive electrode is fully occupied. During the time period while the capacitive and the non-capacitive electrodes are in a certain polarity, the first, the second, the third and the fourth electrical currents may be increased or decreased, respectively.

[0019] In some embodiments, the first electrical current is applied at the same time as the fourth electrical current is applied and the second electrical current is applied at the same time as the third electrical current is applied, and product streams from the two cells are mixed together. In such way, at the same time, the at least one of chlorine and bromine is generated at a place different from where hydrogen is generated and the at least one of chlorine, bromine, hypochlorite and hypobromide may be continually obtained from the combination of the two cells. [0020] When "the first" and "the second" are not used preceding cell, aqueous solution, capacitive electrode and non-capacitive electrode, the description herein thereabout is applicable to either or both of the cells, aqueous solutions, capacitive electrodes, and non-capacitive electrodes, respectively.

[0021] Referring to FIG. 1, a cell 10 used in one embodiment has an entrance 20 for receiving a raw material stream 30 which is electrolysed to generate a product stream 40 flowing out from an export 50. A non-capacitive electrode 1 and a capacitive electrode 2 of the cell 10 are positioned in an aqueous solution 3 from the raw material stream 30 in the cell 10. The at least one of sodium chloride, potassium chloride, sodium bromide and potassium bromide in the aqueous solution 3 could be expressed as MX existing in the form of ion, in which X^" is CI^" or Br^" and M⁺ is Na⁺ or K⁺.

[0022] Referring to FIG. 2, while the non-capacitive electrode 1 acts as anode, anions (X ) move to the anode under the electric field, the following electro-chemical reaction occurs at the non-capacitive electrode 1 : 2X^"→ X2 + 2e^" so that X2 (at least one of chlorine and bromine) is generated at the surface of the non-capacitive electrode 1. At the same time, cations (M⁺) move to and are absorbed at the cathode (the capacitive electrode), electrons (e ) move along a direction shown with an arrow 5 to the cathode (the capacitive electrode 2) and no electro-chemical reaction happens on the capacitive electrode 2 before it is fully occupied.

[0023] FIG. 3 shows a status while the capacitive electrode 2 is close to fully occupied. If X2 generated on the anode is gaseous CI2, at least some of X2 leaves the solution, some flows out of the product stream 40 via the export 50, and some may be retained in the aqueous solution 3. If X2 is liquid Br₂, at least some of X2 flows out of the product stream 40 via the export 50, and some may be retained in the aqueous solution 3.

[0024] Referring to FIGS. 4 and 5, after switching the polarity of the power supplier 4, electrons (e ) move from the anode (the capacitive electrode 2) to the cathode (the non-capacitive electrode 1) along a direction shown with an arrow 6, and the following electro-chemical reaction occurs at the non-capacitive electrode 1 : 2H2O + 2e^"→ 20FF + H₂. The solubility of H₂ is low and H₂ leaves the aqueous solution 3. H₂ also can be discharged entirely from the cell 10 by an external force. The capacitive electrode 2 turns into a regeneration mode, M⁺ is released from the capacitive electrode and moves to the cathode along an arrow 7. OH^" generated at the non- capacitive electrode 1 is absorbed towards the capacitive electrode 2 along a direction shown with an arrow 8, there is still no electro-chemical reaction on the capacitive electrode 2 before it is fully occupied.

[0025] If the solution contains X₂, at least some of the MOH generated reacts with the X₂. The overall reactions in the cell are: 2MX + 2H₂0→ X₂ + 2MOH + H₂ and X₂ + 2MOH→ MOX + MX + H₂0. Therefore, X₂ (at least one of Cl₂ and Br₂) is generated in the cell, at least some of the X₂ (at least one of Cl₂ and Br₂) is further reacted into the MOX (at least one of hypochlorite and hypobromide), and the product stream from the cell comprises at least one of chlorine, bromine, hypochlorite and hypobromide. FIG. 6 shows a status while the capacitive electrode 2 is close to be fully occupied. The processes described above can be conducted circularly.

[0026] By switching the polarities before the capacitive electrode is fully occupied, electro-chemical reactions only or majorly happen on the non-capacitive electrode and H₂ and the X₂ (at least one of Cl₂ and Br₂) are generated at different times in a single cell. H₂ can be discharged rapidly from the cell. The possibility of mixing H₂ and X₂ (at least one of Cl₂ and Br₂) and the possibility of forming at least one of hydrogen chloride and hydrogen bromide, which is corrosive to the container during storage and/or transportation and is apt to explode at relatively high concentration, is eliminated/reduced.

[0027] The at least one of chlorine, bromine, hypochlorite and hypobromide generated is a biocide useful to remove microbes (microorganisms and bacteria etc.). In some embodiments, the product stream from the cell may flow into or be added into an aqueous stream comprising microbes to remove the microbes.

[0028] The cell may include other components besides the electrodes. In some embodiments, a spacer is positioned between the capacitive electrode and the non- capacitive electrode. In some embodiments, gasket, silicone rubber and enclosure plate may be used to package/support the electrodes. [0029] The capacitive electrode may be made of any materials that are suitable for capacitive electrodes used in electrochemical super capacitors. The capacitive electrode may be porous having relatively large surface area, e.g., 1000 m²/g, and capable of adsorption. In some embodiments, the capacitive electrode comprises carbon based materials, such as activated carbon. In some embodiments, the capacitive electrode comprises an activated carbon sheet and a current collector below the activated carbon sheet. In some embodiments, the current collector comprises at least one of titanium, platinum, gold and conducting polymer. The current collector may be in the form of mesh. In some embodiments, there may be a cationic exchange coating on the activated carbon sheet.

[0030] The non-capacitive electrode may be made of any materials that are suitable for non-capacitive electrodes used in electrochemical cells. In some embodiments, the non-capacitive electrode comprises titanium. In some embodiments, the non- capacitive electrode comprises a coating of ruthenium oxide.

[0031] The electrolysis may be conducted at any suitable temperature and pressure such as room temperature and atmosphere pressure. The pH of the product stream from the cells may change with the change of electro-chemical reaction in the cell, e.g., in some embodiments, when the first or the fourth electrical current is applied, the product stream may be acidic while when the second or the third electrical current is applied, the product stream may be alkaline.

[0032] "Fully occupied" referred to herein means the state of the capacitive electrode being fully occupied with adsorbed materials and the point when actions at the capacitive electrode change from adsorptions to electro-chemical reactions. In some embodiments, the capacitive electrode is fully occupied when hydrogen, bromine or chlorine generated begins to be detectable. In some embodiments, "before... fully occupied" means before the concentration of hydrogen, bromine, chlorine is as high as to cause explosion problems.

EXAMPLES [0033] The following examples are included to provide additional guidance to those of ordinary skill in the art in practicing the claimed invention. Accordingly, these examples do not limit the invention as defined in the appended claims.

[0034] Each cell used in the following examples was built up by assembling a capacitive electrode and a non-capacitive electrode together. The capacitive electrode was made by pressing an activated carbon sheet on a Ti mesh having the same size as the activated carbon sheet. FIG. 7 is an image view under a scanning electron microscope of an activated carbon sheet used in the examples. The surface area of activated carbon was about 1000 m²/g. The carbon loading of the activated carbon sheet was about 0.42 g/cm³. The projection area of the electrode was 512 cm² (16 cm x 32 cm). Theoretically the activated carbon electrode area was about 53760 m². The electrode thickness was 0.25 cm. The Ti mesh was used as the current collector in the activated carbon electrode.

[0035] Another sheet of Ti mesh (16 cm x 32 cm) was used as the non-capacitive electrode and was located opposite to the capacitive electrode. An insulative spacer was positioned between the capacitive electrode and the non-capacitive electrode. A gasket, a silicone rubber sheet and an enclosure sheet was located sequentially outside each of the non-capacitive and capacitive electrodes to package the electrodes therebetween.

[0036] Electrical currents and voltages were applied to cells and recorded using a LAND® power supplier from Wuhan Landian electronics Ltd., Wuhan, China. Concentration of free chlorine was tested using a HACH DR5000 spectrophotometer with N,N-diethyl-p-phenylenediamine method and the pH was tested with a pH meter. H₂ was detected using an ATi C16 H₂ detector, the detection range of which is 0-10% voltage concentration.

Example 1

[0037] In this experiment, to separate the two electrode chambers for characterization, a cationic exchange membrane was positioned between the capacitive and the non- capacitive electrodes of the cell used. NaCl solution (52.8 g/1) was fed into the cell at a flow rate of 20 ml/min, 1.73 cm/s. Electrical current of 500 mA was charged on the electrodes and increased with time to 1,500 mA and 3,000 mA, while titanium electrode served as anode and activated carbon electrode served as cathode. There was an exit for the product stream obtained after electrolysis on the side of each electrode. When the product streams were stable, samples were randomly taken from the product streams of the electrodes at three different times during each time period when certain electrical current is applied. Concentration of free chlorine and the pH of the samples were tested, respectively.

[0038] Free chlorine was detected in the sample from the Ti electrode, that is, the anode chamber and was not detectable in the sample from the cathode chamber, the activated carbon electrode side. Except the samples taken when the electrical current of 3,000 mA was applied, the pHs of the samples from both sides kept acidic, indicating that there was no ¾ generated, since if ¾ was generated, the product stream would turn into alkaline. There was no detectable ¾ at both electrodes according to the ATi C16 ¾ detector too.

[0039] The concentrations of free chlorines detected in the samples from the anode chamber and the pH of the samples from both anode chamber and cathode chamber at different electrical currents and corresponding average voltages applied are listed in table 1 below.

Table 1

[0040] There were some variations in the concentrations of free chlorine for certain electrical currents listed in table 1 possibly due to the unstability of flow rates of the sodium chloride solution.

[0041] When the cell was charged 8235 mAh, H₂ was detected at the cathode side, indicating that the activated carbon electrode was fully occupied. The pH then was about 12. The samples of while the electrical current was 3,000 mA was taken at time close to when the cell was charged 8235 mAh, so the pH of samples from the cathode chamber was close to 12.

[0042] Then the polarities of the electrodes were reversed by the power supplier to regenerate the activated carbon electrode so that titanium electrode served as the cathode and activated carbon electrode served as the anode. In this period, H₂ was continually detectable and the pH of product streams was about 12. No free chlorine was detected in samples from both chambers.

[0043] After the cell was charged 8235 mAh again, the polarities of the electrodes was reversed again. No H₂ was detected then. The electrical current was changed from 500 mA to 1,500 mA. The concentrations of free chlorines detected in the samples from the anode chamber and the pH of the samples from both anode chamber and cathode chamber at different times while each electrical current and corresponding average voltage were applied are listed in table 2 below.

Table 2

[0044] When the cell was charged 8923 mAh, H₂ was detected at the cathode side by the detector, indicating that the activated carbon electrode was fully occupied again. Then the polarities of the electrodes were reversed and the carbon electrode was regenerated, during which period H₂ was detected and the product streams were alkaline with pH of about 12.

Example 2

[0045] Two cells similar with the one used in example 1 but without cationic exchange membranes between the electrodes were used in this experiment. Each cell has one exit for the product stream therefrom. NaCl solution (52.8 g/1) was fed into the cells at a flow rate of 20 ml/min, 1.73 cm/s. One cell was charged with electrical currents listed in table 3 below to generate C¾ and the other cell was charged with electrical currents listed in table 4 below to generate ¾. Streams flowing out of the two cells were combined together to get a mixed stream. Samples were taken from streams flowing out of each cell and the mixed stream. The currents, current densities, average voltages, free chlorine concentrations, free chlorine average productivities, and pHs of samples from the cell generating C¾ are listed in table 3 below.

Table 3

[0046] The current density was calculated with the following formula: current/effective area, in examples herein the effective area was 0.16 m x 0.32 m. The productivity of chlorine was calculated using the following formula: productivity (g/m²/hr) = concentration of free chlorine (mg/1) /1000 (mg/g) x flow rate (ml/min)/ 1000 (ml/1) x 60 (min/hour)/effective area, the effective area was 0.16 m x 0.32 m in examples herein. The average productivity is the average of the three samples. [0047] It can be seen from table 3 that the average productivity of free chlorine increased with the increasing of the current densities.

[0048] Table 4 below shows the pHs of samples from the cell generating ¾ at different electrical currents and average voltages.

Table 4

[0049] It can be seen from table 4 above that the pH increased with the increasing of the current density.

[0050] The free chlorine concentrations, free chlorine average productivities, and pHs of samples of the mixed stream at different electrical currents are listed in table 5 below.

Table 5

[0051] It can be seen from table 3 and table 5 that before and after mixing, the productivity of free chlorine kept almost the same. Example 3

[0052] The experiment in example 2 was repeated. However, NaCl solution (52.8 g/1) was fed into the cells at different flow rates ranging from 20 ml/min to 80 ml/min. Electrical currents applied to the two cells was 2,000 mA and increased gradually with time to 10,000 mA. Streams flowing out of the two cells were combined together to get a mixed stream. Samples were taken from the mixed stream at different times in the time period of applying certain electrical current. The electrical currents, corresponding average voltages, flow rates of the solutoin, and corresponding free chlorine concentrations, free chlorine average productivities, and pHs of samples are shown in table 6 below.

Table 6

38 2017.54 5.88

39 1842.11 5.85

37 1732.46 /

10,000 3.5 80 38 1710.53 161.73 /

39 1732.46 /

[0053] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

What is claimed is:

1. A method, comprising:

positioning a first capacitive electrode and a first non-capacitive electrode in a first aqueous solution comprising at least one of sodium chloride, potassium chloride, sodium bromide and potassium bromide;

applying a first electrical current on the first capacitive electrode and the first non- capacitive electrode to electrolyse the first aqueous solution to generate at least one of chlorine and bromine, while the first capacitive electrode acts as cathode and the first non-capacitive electrode acts as anode;

applying a second electrical current on the first capacitive electrode and the first non-capacitive electrode to electrolyse the first aqueous solution to generate hydrogen, while the first capacitive electrode acts as anode and the first non- capacitive electrode acts as cathode; and

switching polarities of the first capacitive electrode and the first non-capacitive electrode before the first capacitive electrode is fully occupied.

2. The method of claim 1, wherein the at least one of chlorine and bromine is generated at a different time from when hydrogen is generated.

3. The method of claim 1, wherein after electrolysis, the first aqueous solution turns into a product stream flowing into or added into an aqueous stream comprising microbes.

4. The method of claim 1, wherein the first aqueous solution comprises sodium chloride and chlorine is generated while the first capacitive electrode acts as cathode and the first non-capacitive electrode acts as anode.

5. The method of claim 1, further comprising: positioning a second capacitive electrode and a second non-capacitive electrode in a second aqueous solution comprising at least one of sodium chloride, potassium chloride, sodium bromide and potassium bromide;

applying a third electrical current on the second capacitive electrode and the second non-capacitive electrode to electrolyse the second aqueous solution to generate at least one of chlorine and bromine, while the second capacitive electrode acts as cathode and the second non-capacitive electrode acts as anode; applying a fourth electrical current on the second capacitive electrode and the second non-capacitive electrode to electrolyse the second aqueous solution to generate hydrogen, while the second capacitive electrode acts as anode and the second non- capacitive electrode acts as cathode; and

switching polarities of the second capacitive electrode and the second non- capacitive electrode before the second capacitive electrode is fully occupied.

6. The method of claim 5, wherein the first electrical current is applied at the same time as the forth electrical current is applied.

7. The method of claim 5, wherein the first aqueous solution comprises sodium chloride and turns into a first product stream when the first electrical current is applied.

8. The method of claim 7, wherein the second aqueous solution comprises sodium chloride and turns into a second product stream, when the forth electrical current is applied, to mix with the first product stream to yield a mixed stream.

9. The method of claim 5, wherein the second electrical current is applied at the same time as the third electrical current is applied.

10. The method of claim 5, wherein the second aqueous solution comprises sodium chloride.

11. The method of claim 10, wherein chlorine is generated while the second capacitive electrode acts cathode and the second non-capacitive electrode acts as anode.

12. The method of claim 5, wherein the first capacitive electrode comprises carbon based material.

13. The method of claim 5, wherein the first capacitive electrode comprises an activated carbon plate and a current collector.

14. The method of claim 13, wherein the current collector comprises at least one of titanium, platinum, gold and conducting polymer.

15. The method of claim 14, wherein the second capacitive electrode is the same as the first capacitive electrode.

16. The method of claim 5, wherein the first non-capacitive electrode comprises titanium.

17. The method of claim 16, wherein the first non-capacitive electrode comprises a coating of ruthenium oxide.

18. The method of claim 17, wherein the second non-capacitive electrode is the same as the first non-capacitive electrode.

19. The method of claim 1, wherein the first electrical current changes with time.

20. The method of claim 1, wherein the first capacitive electrode and the first non- capacitive electrode is opposite to each other and a spacer is positioned between the first capacitive electrode and the first non-capacitive electrode.