PROCESS FOR REDUCING THE CORROSIVENESS OF A BIOCIDAL COMPOSITION CONTAINING IN SITU GENERATED SODIUM HYPOCHLORITE

Abstract

A process for substantially reducing the corrosiveness of a composition containing in situ generated sodium hypochlorite in which the sodium hypochlorite is substantially converted to a haloamine.

Claims

1. A process for substantially reducing the corrosiveness of a biocidal composition containing in situ generated sodium hypochlorite, wherein the process comprises the following steps of: A. generating sodium hypochlorite in situ by passing an electric current through a first aqueous salt water composition; B. adding an ammonium-containing component to the first composition containing in situ generated sodium hypochlorite; whereby the sodium hypochlorite is substantially converted to a haloamine having biocidal properties and whereby the corrosiveness of the biocidal composition is substantially reduced as compared to the corrosiveness of the first composition containing the in situ generated sodium hypochlorite.

2. A process as defined by claim 1 wherein the haloamine is monochloramine or monobromoamine.

3. A process as defined by claim 2 wherein the bromamine is monochloramine.

4. A process as defined by claim 2 wherein the haloamine is monobromoamine.

5. A process as defined by claim 1 wherein the ammonium-containing component is an ammonium salt or aqueous ammonia.

6. A process as defined by claim 5 wherein the ammonium-containing component is aqueous ammonia.

7. A process as defined by claim 5 wherein the ammonium salt is ammonium sulfate.

8. A process as defined by claim 5 wherein the ammonium salt is ammonium phosphate.

9. A process as defined by claim 5 where the ammonium salt is ammonium chloride.

10. A process as defined by claim 1 wherein the pH is maintained at an alkaline pH.

11. A process as defined by claim 10 wherein the pH is maintained in a range from about 10 to about 11.

12. A process for substantially reducing the corrosiveness of a biocidal composition containing in situ generated sodium hypochlorite, wherein the process comprises the following steps: A. adding an ammonium-containing component to an aqueous composition containing salt water and B. passing an electric current through the aqueous composition to generate in situ sodium hypochlorite, whereby the sodium hypochlorite is substantially converted to a haloamine having biocidal properties and whereby the corrosiveness of the biocidal composition is substantially reduced as compared to the corrosiveness of the composition containing the in situ generated sodium hypochlorite.

13. A process as defined by claim 12 wherein the haloamine is monochloramine or monobromoamine.

14. A process as defined by claim 13 wherein the bromamine is monochloramine.

15. A process as defined by claim 13 wherein the haloamine is monobromoamine.

16. A process as defined by claim 12 wherein the ammonium-containing component is an ammonium salt or aqueous ammonia.

17. A process as defined by claim 16 wherein the ammonium-containing component is aqueous ammonia.

18. A process as defined by claim 16 wherein the ammonium salt is ammonium sulfate.

19. A process as defined by claim 16 wherein the ammonium salt in ammonium phosphate.

20. A process as defined by claim 16 wherein the ammonium salt is ammonium chloride.

21. A process as defined by claim 12 wherein the pH is maintained at an alkaline pH.

22. A process as defined by claim 21 wherein the pH is maintained in a range from about 10 to about 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIGS. 1 and 2 are Tables showing the biocidal properties of sodium hypochlorite and monochoramine.

[0032] FIG. 3 is a flow chart of the process described in Example 1.

[0033] FIG. 4 is a flow chart of the process described in Example 2.

DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention provides a biocidal composition which can be effectively used in situations where undesired microorganisms are present, such as in the oil and gas industry. In that industry, metal equipment is frequently used which is subject to corrosion from microorganisms. Corrosion of this equipment often results in downtime in the industry for cleaning and/or replacement of the equipment or replacement of corroded parts.

[0035] Sodium hypochlorite is a compound having known biocidal properties. However, as explained above, the use of sodium hypochlorite can cause corrosion problems, especially with equipment which is primarily made of metal or having metallic parts, such as equipment used in the oil and gas industry.

[0036] Halomines, such as monochloramine, are similarly known for their biocidal properties. The data shown in the Tables of FIGS. 1 and 2 demonstrate the biocidal properties of sodium hypochlorite and monochloramine.

[0037] The data from kill studies which is presented in FIGS. 1 and 2 was produced using the following procedures.

[0038] The kill studies were done in synthetic cooling water, pH 8.0, at room temperature. Suspensions of overnight cultures of Pseudomonas aeruginosa or Enterobacter aerogenes were added to the synthetic cooling water, followed by the biocide in the desired concentrations. The biocide concentrations were based on the active levels added to the test medium rather than the total residual chlorine. The contact time was 1.5 hours.

[0039] Monochloramine (MCA) can be prepared by a standard procedure in the lab at Buckman Laboratories (Memphis, Tenn.). Sodium hypochlorite (Na Hypochlorite) was a 5.0% solution obtained from Ricca Chemical Company (Arlington, Tex.).

[0040] Tables 1 and 2 show the biocidal properties of these 2 materials.

[0041] Although commonly used in oil and gas waterfloods for biocidal properties, sodium hypochlorite can lead to problems with corrosion. Therefore, this invention has been developed to overcome the corrosive tendency and to utilize the non-biocidal properties of sodium hypochlorite, while maintaining the biocidal properties of the final composition.

[0042] The process of this invention can be performed by (1) first generating sodium hypochlorite in situ by passing an electric current through an aqueous salt water composition and (2) then adding an ammonia-containing component to the aqueous composition containing the sodium hypochlorite. The ammonia-containing component reacts with, and converts, the sodium hypochlorite to monochloramine having biocidal properties.

[0043] Alternatively, the process of this invention can be performed by (1) first adding an ammonia-containing component to an aqueous composition containing salt water and (b) then passing an electric current through the aqueous composition to generate in situ sodium hypochlorite. Again, the ammonia-containing component reacts with, and converts, the sodium hypochlorite to monochloramine having biocidal properties.

[0044] As significant advantages of either process, (a) the corrosiveness of the biocidal chloramine composition is substantially reduced as compared to the corrosiveness of the composition containing the in situ generated sodium hypochlorite and (b) the biocidal properties provided by monochloramine in the final composition are retained.

[0045] The reduced corrosiveness of the final biocidal composition prevents or at least minimizes downtime for cleaning and/or replacement of the equipment or metallic parts affected by corrosion.

[0046] The in situ generation of sodium hypochlorite by passing an electric current through an aqueous salt water composition is a known process in the art.

[0047] The ammonia-containing component can be selected from a variety of components, but preferred in this invention are aqueous ammonia, ammonium sulfate, ammonium phosphate and ammonium chloride.

[0048] The reaction of the ammonia-containing component and the in situ generated sodium hypochlorite must be carefully controlled to achieve a quantitative conversion of sodium hypochlorite to monochloramine (i.e., a reaction yield of at least about 95 percent, preferably at least about 97 percent). Careful control of the reaction is also necessary to avoid production of unwanted byproducts, such as dichloramine and nitrogen trichloride.

[0049] The most important controls to maintain in the reaction mixture are (a) an excess of ammonia, or at least no excess hypochlorite; (b) an alkaline pH, preferably at least about 10 to about 11; and (c) a concentration of monochlorine below about 1-2 percent. With these reaction controls, the conversion of sodium hypochlorite to monochloramine will be about 95 percent, preferably about 97 percent.

[0050] To confirm the conversion of sodium hypochlorate to monochloramine, there are two available tests(1) one to determine free chlorine in the reaction mixture and (2) the second to specifically determine the presence of monochloramine. The results of these 2 tests should agree, within experimental error, if the only active chlorine species in the reaction mixture is monochloramine.

[0051] The present invention is further illustrated by the following examples which are illustrative of certain embodiments designed to teach those of ordinary skill in the art how to practice this invention and to represent the best mode contemplated for carrying out this invention.

Example 1

[0052] With reference to the flow chart of FIG. 3, an aqueous solution of sodium chloride (NaCl) is passed through an electrolysis cell comprised of at least two electrodes (an anode and a cathode) connected to a power supply. As the solution flows through the cell, the chloride ion (Cl.sup.) is oxidized to hypochlorous acid (HOCl) at the anode, and water (H.sub.2O) is reduced to hydrogen gas (H.sub.2) and hydroxide ion (OH.sup.) at the cathode; as shown by:

At the Anode: Cl.sup.+H.sub.2O.fwdarw.HOCl+H.sup.++2e.sup.

At the Cathode: 2H.sub.2O+2e.sup..fwdarw.H.sub.2+2OH.sup.

Overall Reaction: Cl.sup.+2H.sub.2O.fwdarw.HOCl+H.sub.2+OH.sup.

Or: Cl.sup.+H.sub.2O.fwdarw.OCl.sup.+H.sub.2

[0053] In these reactions, two moles of electrons (e.sup.) are produced as each mole of active chlorine (hypochlorous acid, HOCl, or hypochlorite ion, OCl.sup.) is produced. The rate at which active chlorine is produced will be controlled by the electric current (measured in amperes) that passes through the cell. One ampere is defined as one coulomb of charge being transferred through the cell per second, and one mole of electrons will carry 96,485 coulombs of charge (the Faraday constant). Hence at 100% efficiency one ampere will produce 0.0163 gm of HOCl per minute.

[0054] Certain factors must be carefully controlled to optimize the conversion of chloride ion to hypochlorous acid and to minimize the formation of unwanted byproducts from the electrolysis reactions; such as: [0055] The rate at which HOCl is produced is limited by the electric current through the electrolysis cell, so an excess of sodium chloride must pass through the cell. [0056] A current of one ampere can convert up to 0.0182 gm of NaCl per minute, so the product of the concentration of NaCl (in gm NaCl/mL of solution) times the flow rate (in mL/minute) must exceed 0.0182. [0057] For example, if a 1% solution of NaCl is used, the flow rate through the cell must be >0.55 mL/minute for each ampere of electric current that passes through the cell. [0058] The anode potential must also be monitored to ensure that it is (a) high enough to oxidize the chloride ion but (b) not high enough to initiate other unwanted reactions (such as oxidation of water to form oxygen gas). [0059] To maintain the desired flow of electric current and the correct anode potential, the surface area of the electrodes must be in contact with enough chloride ion to support the desired current without additional reactions (e.g., the oxidation of water to form oxygen gas). [0060] In other words, the electrode area must be large enough to support the necessary current density (amperes/square meter of anode surface area) at the desired anode potential.

[0061] The sodium hypochlorite formed by this electrolysis process is then combined with a source of ammonia to form monochloramine. Three criteria must be met to ensure that a quantitative yield of monochloramine is obtained without the formation of unwanted byproducts, such as dichloroamine (NHCl.sub.2) or nitrogen trichloride (NCl.sub.3): [0062] Excess of ammonia (or at least no excess hypochlorite) at all times in the reaction mixture [0063] An alkaline pH in the reaction mixture (preferably from a pH equal to or less than about 10 to a pH equal to or less than about 11) [0064] Final concentration of monochloramine below 1-2% NH.sub.2Cl

[0065] The source of ammonia can be provided by many different ammonia-containing components. In this specific example, the ammonia source may be the Busan 1474 product, which is commercially available from Buckman Laboratories (Memphis, Tenn.) and is a blend of ammonia-containing compounds containing a total of 7.59% ammonia. The sodium hypochlorite from the electrolysis cell is combined with the Busan 1474 product so that a molar ratio of 1:1 (NH.sub.3:NaOCl) is maintained. Additional NaOH is added to the solution as needed to maintain the desired pH range.

Example 2

[0066] With reference to the flow chart of FIG. 4, an aqueous mixture of sodium chloride and ammonium chloride is passed through an electrolysis cell comprised of at least two electrodes (an anode and a cathode) connected to a power supply. As the solution flows through the cell, the chloride ion

(Cl.sup.) is oxidized to hypochlorous acid (HOCl) at the anode, which immediately reacts with the ammonium ion to form monochloramine. Water (H.sub.2O) is simultaneously reduced to hydrogen gas (H.sub.2) and hydroxide ion (OH.sup.) at the cathode;

At the Anode: Cl.sup.+NH.sub.4.sup.++2OH.sup..fwdarw.NH.sub.2Cl+2H.sub.2O+2e.sup.

At the Cathode: 2H.sub.2O+2e.sup..fwdarw.H.sub.2+2OH.sup.

Overall Reaction: Cl.sup.+NH.sub.4.sup.+.fwdarw.NH.sub.2Cl+H.sub.2

[0067] A small amount of sodium hydroxide solution may be fed to the cell along with the sodium chloride/ammonium chloride solution to ensure that the pH is in the correct range to obtain a good yield of monochloramine.

[0068] The factors described in Example 1 that are important for the efficient production of a high quality monochloramine solution are equally important in this example and, therefore, are incorporated into this example. As described above, the concentration of chloride ion in the electrolyte solution and the flow rate through the electrolysis cell must be maintained at a level that will provide an excess of chloride ion (relative to the electric current) in the cell at all times. Careful monitoring and control of the pH and of the anode potential will be even more critical to prevent oxidation of the ammonium ion in the electrolysis cell.

[0069] The process of Example 2 is simpler and less complex than the process described in Example 1.

[0070] A major advantage in both Examples 1 and 2 over the use of commercially-available bleach is the absence of sodium chlorate (NaClO.sub.3) in the resulting monochloramine solution. Regulatory agencies are beginning to take a closer look at the levels of sodium chlorate in many applications as well as in environmental situations.

[0071] Sodium chlorate is formed by a disproportionation reaction that occurs in commercially-available bleach during storage:

3NaOCl.fwdarw.2NaC+NaClO.sub.3

[0072] Since the sodium hypochlorite in both Examples 1 and 2 is converted to monochloramine immediately after it is generated, there is no storage time during which sodium chlorate will be generated. Hence there will be little or no sodium chlorate in the monochloramine solution that is fed to the treatment system.

[0073] This invention has been described with particular reference to certain embodiments, but variations and modifications can be made without departing from the spirit and scope of the invention.