Method for suppressing cyanide compound formation in aqueous water containing seawater

Abstract

To provide a method for suppressing cyanide compound formation capable of suppressing formation of cyanide compounds in treatment of aqueous water containing seawater, which includes a step of adding at least one compound selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent.SOLUTION: A method for suppressing cyanide compound formation in aqueous water includes adding peroxide to aqueous water containing seawater, in which the method comprises a step of adding at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agent, and bromine-based oxidizing agent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for inhibiting the formation of cyanide compounds in water systems including seawater. [Background technology]

[0002] Seawater is used in large quantities as industrial cooling water, particularly for the condensers of thermal and nuclear power plants. Seawater is also used not only as cooling water but also as process water (heat transfer medium for heating, dilution water, etc.) in various factories. In water systems containing seawater, various chemicals are added in combination to inhibit or remove the attachment and proliferation of organisms that may cause various problems.

[0003] For example, Patent Document 1 discloses a method for preventing adhesion of marine organisms that can prevent the adhesion of a wide range of marine organisms and slime, in which a chlorine-based oxidant or a bromine-based oxidant and chlorine dioxide are added to the seawater in the seawater cooling water system to prevent the adhesion of marine organisms to the seawater cooling water system.

[0004] Patent Document 2 discloses a method for inhibiting or removing the attachment or proliferation of organisms in a seawater cooling water system, the method comprising, in this order: a first step of adding monochloramine to seawater cooling water system water to which monochloramine is to be added so that the total residual chlorine concentration is 0.01 mg / L or more and 0.15 mg / L or less; and a second step of adding a thiosulfate compound to the seawater cooling water system water to which monochloramine has been added before the sea, in an amount 1 to 1.5 times the amount expected to offset the total amount of residual chlorine in the seawater cooling water system water to which monochloramine has been added. It is disclosed that this method significantly reduces or eliminates concerns about adverse effects on aquatic organisms near the discharge outlet due to the reduction in the dissolved oxygen concentration caused by the combined residual chlorine and free residual chlorine, as well as the reducing agent added to offset these, when the seawater is discharged into the sea, while reducing the amount of reducing agent required to offset the total residual chlorine, and furthermore, suppresses or eliminates the adverse effects of the combined residual chlorine and free residual chlorine. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-122292 [Patent Document 2] Patent No. 7256058 Summary of the Invention [Problem to be solved by the invention]

[0006] However, as a result of investigations by the present inventors, it was found that in conventional methods for treating seawater-containing water, adding a chlorine-based oxidizing agent such as monochloramine or a bromine-based oxidizing agent to seawater-containing water can produce cyanide compounds. For example, cyanide compound cyanogen chloride (CNCl) is a toxic, non-electrolyte substance that is easily volatile with a boiling point of 13°C.

[0007] Therefore, an object of the present invention is to provide a method for inhibiting the formation of cyanide compounds, which can inhibit the formation of cyanide compounds in the treatment of aqueous water containing seawater, the method comprising the step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent. [Means for solving the problem]

[0008] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have found that adding a peroxide to an aqueous system containing seawater can suppress the production of cyanide compounds that would occur if a chlorine-based oxidizing agent or a bromine-based oxidizing agent, such as monochloramine, were added to the aqueous system containing seawater, and have thus completed the present invention.

[0009] That is, the present invention relates to the following processing methods, although the present invention is not limited thereto. [1] A method for inhibiting the formation of cyanide compounds in aqueous water, comprising a step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent, and further comprising adding a peroxide to the aqueous water containing seawater. [2] The method for inhibiting the formation of cyanide compounds in aqueous water according to [1] above, wherein the peroxide is hydrogen peroxide. [3] The method for inhibiting the formation of cyanide compounds in aqueous water according to [1] or [2] above, wherein in the step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent, at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent is added to the aqueous water so that the residual chlorine concentration in the aqueous water is 0.01 mg / L or more. [4] A method for inhibiting the formation of cyanide compounds in aqueous water according to any one of [1] to [3] above, comprising adding peroxide so that the concentration of peroxide in the aqueous water is 0.05 to 10 mg / L in terms of hydrogen peroxide concentration. [5] The method for inhibiting the formation of cyanide compounds in aqueous water according to any one of [1] to [4] above, wherein the peroxide is added to the aqueous water before a step in which at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent is added, and / or in an aqueous system to which the aqueous water after the step reaches within 60 minutes. [6] The method for inhibiting the formation of cyanide compounds in aqueous water according to any one of [2] to [5] above, wherein at least one oxidant selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents is added to aqueous water containing seawater having a hydrogen peroxide concentration of 0.05 to 10 mg / L. [7] The method for inhibiting the formation of cyanide compounds in aqueous water according to any one of [1] to [6] above, wherein the step of adding at least one selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent is a step of adding monochloramine, and the monochloramine is generated by mixing a substance that generates hypochlorous acid with ammonium ions, or by allowing a substance that generates hypochlorous acid and ammonium ions to coexist in the aqueous water. [8] The method for inhibiting the formation of cyanide compounds in aqueous water according to any one of [1] to [6] above, wherein the step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent is a step of adding a chlorine-based oxidizing agent, and the chlorine-based oxidizing agent is at least one selected from the group consisting of sodium hypochlorite, potassium hypochlorite, seawater electrolyte, N-chlorosulfamate, and chlorine dioxide. [9] The method for inhibiting the formation of cyanide compounds in aqueous water according to any one of [1] to [6] above, wherein the step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent is a step of adding a bromine-based oxidizing agent, and the bromine-based oxidizing agent is at least one oxidizing agent selected from the group consisting of sodium hypobromite, monobromoamine, and N-bromosulfamate. [Effects of the Invention]

[0010] According to the present invention, there is provided a method for inhibiting the formation of cyanide compounds, which can inhibit the formation of cyanide compounds in the treatment of aqueous water containing seawater, the method comprising the step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention relates to a method for inhibiting the formation of cyanide compounds in aqueous water, including seawater, which comprises a step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent, and the method comprises adding a peroxide to the aqueous water (hereinafter, also simply referred to as the "method for inhibiting the formation of cyanide compounds of the present invention").

[0012] The inventors' investigations have confirmed that adding at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents to water systems including seawater produces cyanide compounds. This is thought to be because trace amounts of nitrogen-containing organic matter in seawater react with monochloramine, chlorine-based oxidizing agents, or bromine-based oxidizing agents to produce cyanide compounds. In the method for suppressing the formation of cyanide compounds in seawater-containing aqueous solutions according to the present invention, the mechanism by which the use of peroxides suppresses the formation of cyanide compounds that occurs when at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents is added to seawater-containing aqueous solutions is unclear. However, according to the results of tests conducted by the present inventors (described below), even when monochloramine was added to seawater with a high nitrogen compound content and a sufficient reaction time was allowed to generate cyanide compounds, and then hydrogen peroxide was added, no change in the concentration of the generated cyanide compounds was observed. Therefore, the main effect of using peroxides such as hydrogen peroxide in the method for suppressing the formation of cyanide compounds in seawater-containing aqueous solutions is thought to be that the addition of peroxides to seawater suppresses the formation of cyanide compounds that occurs when at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents is added to seawater, rather than the effect of the peroxides in the water decomposing the cyanide compounds that occur when at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents is added to seawater.

[0013] The method for inhibiting the production of cyanide compounds of the present invention is carried out on an aqueous system containing seawater, and includes a step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent.

[0014] Here, monochloramine, chlorine-based oxidizing agents and / or bromine-based oxidizing agents are added for the purpose of inhibiting or removing the attachment or proliferation of marine organisms that may cause various problems in water systems including seawater.

[0015] In the present invention, at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents is preferably added to aqueous water including seawater so that the residual chlorine concentration in the aqueous water is 0.01 mg / L or more, in terms of the residual chlorine concentration in the aqueous water, because the addition of at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents can sufficiently suppress or remove the adhesion and proliferation of organisms in the aqueous system. In the present invention, the upper limit of the concentration of at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents in the aqueous water, expressed as a residual chlorine concentration, is not particularly limited, but it is preferable that the agent be added to the aqueous water containing seawater at a concentration that provides an appropriate inhibitory effect on the adhesion of marine organisms relative to the amount of agent added. When the agent added is a bromine-based oxidizing agent, the residual bromine concentration is converted and expressed as a residual chlorine concentration equivalent. In this disclosure, the residual chlorine concentration and the equivalent value of the residual chlorine concentration obtained from the residual bromine concentration are not distinguished from each other, and are shown as the concentration in terms of the residual chlorine concentration for the aqueous water. Furthermore, when an explanation applies to both the residual chlorine concentration and the residual bromine concentration, the expression "residual chlorine (bromine) concentration" is used.

[0016] In this specification, the residual chlorine (bromine) concentration in the aqueous water is preferably the total residual chlorine (bromine) concentration, but may be the residual free chlorine (bromine) concentration or the residual combined chlorine (bromine) concentration depending on the type of chemical agent added in the step of adding at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents. The total residual chlorine (bromine) concentration is the sum of the residual free chlorine (bromine) concentration and the residual combined chlorine (bromine) concentration. The total residual chlorine (bromine) concentration, residual free chlorine (bromine) concentration, and residual combined chlorine (bromine) concentration in water can be measured, for example, by the DPD method. In the present invention, the residual free chlorine (bromine) concentration by the DPD method is the result of a chlorine or bromine concentration measurement (mg-Cl / L (mg-Br / L)) after 30 seconds using a DPD(Free) reagent, which is a reagent for measuring free chlorine or free bromine. The residual combined chlorine (bromine) concentration is the value obtained by subtracting the chlorine (bromine) concentration measurement (mg-Cl / L (mg-Br / L)) after 30 seconds using a DPD(Free) reagent, which is a reagent for measuring free chlorine, from the chlorine or bromine concentration measurement (mg-Cl / L (mg-Br / L)) after 120 seconds using a DPD(Total) reagent, which is a reagent for measuring total chlorine or total bromine. The total residual chlorine (bromine) concentration is the result of a chlorine or bromine concentration measurement (mg-Cl / L (mg-Br / L)) after 120 seconds using a DPD(Total) reagent, which is a reagent for measuring total chlorine or total bromine.

[0017] Regardless of the type of chemical added in the step of adding at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents, the total residual chlorine (bromine) concentration may be measured as the residual chlorine (bromine) concentration in the aqueous water. For example, when hypochlorous acid or hypobromous acid is used, the residual free chlorine (bromine) concentration may be measured as the residual chlorine (bromine) concentration in the aqueous water. When monochloramine, combined chlorine, or combined bromine is used, the residual combined chlorine (bromine) concentration may be measured as the residual chlorine (bromine) concentration in the aqueous water. In this specification, the residual chlorine (bromine) concentration in the aqueous water may be a concentration that accurately indicates the residual chlorine (bromine) of the chemical added.

[0018] Monochloramine can be produced by mixing a substance that generates hypochlorous acid with ammonium ions, and can be prepared by methods described, for example, in Japanese Patent No. 4914146, JP 2017-119245 A, and JP 2017-53054 A. Alternatively, monochloramine may be produced by allowing a substance that generates hypochlorous acid and ammonium ions to coexist in aqueous water; the method for producing monochloramine is not particularly limited. The hypochlorous acid-producing substance used in the production of monochloramine can be the compounds listed in (a) and (b) of the chlorine-based oxidizing agents used in the step of adding at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents in the cyanide compound production suppression method of the present invention, as described below. Among these, hypochlorite is preferred. As the ammonium ion, known compounds can be used, for example, ammonia water and ammonium salts such as ammonium chloride, ammonium bromide, ammonium nitrate, ammonium carbonate, ammonium phosphate, ammonium sulfate, and ammonium borate, with ammonium chloride and ammonium sulfate being particularly preferred.

[0019] The term "chlorine-based oxidizing agent" as used herein means a known "chlorine-based oxidizing agent" used based on the common general technical knowledge pertaining to the technical field of the present invention, but does not include monochloramine. Examples of the "chlorine-based oxidizing agent" as used herein include: (a) Substances that generate hypochlorous acid in water, such as chlorine gas, hypochlorites (sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, etc.), chlorinated isocyanuric acid, dichloroisocyanurates (sodium dichloroisocyanurate, potassium dichloroisocyanurate, etc.), monochloroisocyanurates (sodium monochloroisocyanurate, potassium monochloroisocyanurate, etc.), trichloroisocyanurates (sodium trichloroisocyanurate, potassium trichloroisocyanurate, etc.), (b) Seawater electrolyte (an electrolyte containing hypochlorous acid obtained by electrolyzing seawater in an electrolytic cell), (c) Combined chlorine (stabilized chlorine), such as dichloramine, trichloramine, and N-chlorosulfamate; (d) Chlorine dioxide Examples of the "chlorine-based oxidizing agent" include (a) and (b) from the practical viewpoints of the effect of preventing adhesion of marine organisms, economy, ease of handling, etc., and sodium hypochlorite and potassium hypochlorite are particularly preferred from the viewpoint of industrial availability. Furthermore, among the above-mentioned (c), N-chlorosulfamate is preferred from the viewpoint of the effect of preventing adhesion of marine organisms. In the present invention, the chlorine-based oxidizing agent is more preferably at least one selected from the group consisting of sodium hypochlorite, potassium hypochlorite, seawater electrolyte, N-chlorosulfamate, and chlorine dioxide.

[0020] The term "bromine-based oxidizing agent" as used herein means a known "bromine-based oxidizing agent" that is used based on the common technical knowledge pertaining to the technical field of the present invention. Examples of the "bromine-based oxidizing agent" as used herein include: (e) Substances that produce hypobromous acid in water, such as sodium hypobromite, the reaction product of sodium bromide with sodium hypochlorite, and bromine water; (f) Bound bromine (stabilized bromine) such as monobromoamines, dibromoamines, tribromoamines, and N-bromosulfamates Among these, (e) is preferred from the practical viewpoints of the effect of preventing adhesion of marine organisms, economy, ease of handling, etc., and among (f), monobromoamine is preferred from the viewpoint of the effect of preventing adhesion of marine organisms, followed by N-bromosulfamate. In the present invention, the bromine-based oxidizing agent is more preferably at least one selected from the group consisting of sodium hypobromite, monobromoamine, and N-bromosulfamate.

[0021] N-chlorosulfamate and N-bromosulfamate can be prepared by known methods, such as those described in JP-T-2003-503323, JP-A-2006-022097, JP-T-11-506139, JP-T-2001-501869, JP-T-2003-507326, JP-A-2014-101251, and JP-A-2017-159276.

[0022] The monochloramine, chlorine-based oxidizing agent, and bromine-based oxidizing agent may be diluted or dissolved with seawater or freshwater to a desired concentration before addition. For example, a high-concentration monochloramine solution having a residual chlorine concentration of 500 mg / L to 10,000 mg / L may be used, diluted, and added to an aqueous system including seawater.

[0023] In the method for inhibiting the production of cyanide compounds of the present invention, the at least one oxidant selected from the group consisting of monochloramine, chlorine-based oxidants, and bromine-based oxidants added to the aqueous water containing seawater is preferably at least one oxidant selected from the group consisting of monochloramine, chlorine-based oxidants, and bromine-based oxidants having a high concentration, for example, in an amount equivalent to 500 mg / L to 10,000 mg / L in terms of residual chlorine concentration. This is because it is believed that the higher the residual chlorine concentration (converted to the residual chlorine concentration when the added chemical is a bromine-based oxidant) of the monochloramine, chlorine-based oxidant, and / or bromine-based oxidant added to the aqueous water containing seawater, the more likely cyanide compounds are produced in the aqueous water containing seawater to which at least one oxidant selected from the group consisting of monochloramine, chlorine-based oxidants, and bromine-based oxidants has been added.

[0024] In the present invention, the cyanide compounds generated by adding at least one selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent to aqueous water containing seawater include cyanogen chloride and cyanogen bromide. However, this does not mean that cyanogen chloride is generated when monochloramine or a chlorine-based oxidizing agent is added, and cyanogen bromide is generated when a bromine-based oxidizing agent is added. For example, adding monochloramine or a chlorine-based oxidizing agent to aqueous water containing seawater primarily produces cyanogen chloride. However, this reaction is not the only reaction that occurs in water. For example, when monochloramine is added to aqueous water containing seawater, the added monochloramine is replaced with bromide ions in the seawater to produce monobromoamine, monobromochloramine, etc. Furthermore, when a chlorine-based oxidizing agent is added to aqueous water containing seawater, depending on the chlorine-based oxidizing agent, hypochlorous acid is generated in the aqueous water, and this hypochlorous acid reacts with bromide ions in the seawater to produce hypobromous acid. Therefore, monobromoamine, monobromochloramine, hypobromous acid, etc., produced in water by the addition of monochloramine or chlorine-based oxidizing agents may further react in aqueous water containing seawater to produce cyanogen bromide.

[0025] In the present invention, the water system containing seawater may be water in a seawater cooling water system in a factory such as a power plant, steel mill, or petrochemical plant that uses seawater as cooling water, or may be water in a system through which seawater flows when seawater is used as dilution water, wash water, etc. in various factories, and is not particularly limited. The water system is not particularly limited as long as it is equipment that forms a flow path through which seawater flows, and examples include a seawater intake channel, piping, a water conduit, a heat exchanger, a condenser, and a drainage channel.

[0026] Examples of peroxides that can be used in the method for inhibiting the production of cyanide compounds of the present invention include hydrogen peroxide, peracetic acid, perbenzoic acid, and persulfuric acid, all of which have a hydroperoxide group in their structure. Of these, hydrogen peroxide is preferred.

[0027] [hydrogen peroxide] When hydrogen peroxide is used in the method for inhibiting the generation of cyanide compounds of the present invention, the hydrogen peroxide may be at least one of commercially available hydrogen peroxide and hydrogen peroxide generators for industrial use, and in one or more embodiments, the hydrogen peroxide may be in the form of an aqueous hydrogen peroxide solution. Examples of hydrogen peroxide generators include those that generate hydrogen peroxide in a liquid such as water, and in one or more embodiments, examples thereof include peracetic acid, soluble percarbonates such as sodium percarbonate and potassium percarbonate, soluble perborates such as sodium perborate and potassium perborate, various soluble peroxy acid salts such as urea / hydrogen peroxide adducts, metasilicate / hydrogen peroxide adducts, and sodium peroxide.

[0028] In the method for inhibiting the formation of cyanide compounds of the present invention, the method for adding peroxide to the aqueous water is not particularly limited, but in one or more embodiments, the peroxide may be added by pumping it from a pipe connected to the pipe using a pump, etc. In the addition, the agent may be appropriately diluted with seawater or fresh water.

[0029] The method for inhibiting the production of cyanide compounds of the present invention preferably includes adding peroxide so that the concentration of peroxide in the aqueous water is 0.05 to 10 mg / L in terms of hydrogen peroxide concentration. The concentration of peroxide in the aqueous water can be measured by a conventionally known method (for example, titration). The peroxide is preferably added to the aqueous water so that the concentration of the peroxide in the aqueous water is 0.3 mg / L or more, calculated as hydrogen peroxide concentration, more preferably 0.5 mg / L or more, and even more preferably 1.0 mg / L or more. In addition, the concentration of peroxide in aqueous water (i.e., the concentration in terms of hydrogen peroxide concentration) means the sum of the concentrations of the added peroxides in water when multiple peroxides are added. For example, when hydrogen peroxide and peracetic acid are added to aqueous water as peroxides, the concentration of peroxide in aqueous water is the sum of the hydrogen peroxide concentration and the peracetic acid concentration in the aqueous water converted into hydrogen peroxide concentration.

[0030] In the method for inhibiting the formation of cyanide compounds of the present invention, when hydrogen peroxide is used as the peroxide, it is preferable to add hydrogen peroxide to the aqueous water containing seawater so that the concentration of hydrogen peroxide in the aqueous water is 0.05 mg / L or higher. This is because adding at least one oxidant selected from the group consisting of monochloramine, chlorine-based oxidants, and bromine-based oxidants to the aqueous water containing seawater can effectively inhibit the generation of cyanide compounds. Furthermore, the concentration of hydrogen peroxide in the aqueous water containing seawater is preferably 10 mg / L or lower. If the concentration of hydrogen peroxide in the aqueous water exceeds 10 mg / L, the amount of hydrogen peroxide added increases, making it impossible to expect a cyanide compound formation inhibition effect corresponding to the amount of hydrogen peroxide added, which is undesirable from an economic standpoint. Therefore, in the method for inhibiting the formation of cyanide compounds of the present invention, it is preferable to add hydrogen peroxide to the aqueous water containing seawater so that the concentration of hydrogen peroxide in the aqueous water containing seawater is 0.05 to 10 mg / L. The concentration of hydrogen peroxide in the aqueous water can be measured by a conventionally known method, for example, by the 4-aminoantipyrine colorimetric method using an enzyme. The hydrogen peroxide is preferably added to the aqueous water so that the concentration of hydrogen peroxide in the aqueous water is 0.3 mg / L or more, more preferably 0.5 mg / L or more, and even more preferably 1.0 mg / L or more.

[0031] In the method for inhibiting the production of cyanide compounds of the present invention, the lower and upper limits of the concentration ranges of various chemicals in water systems including seawater can be suitably combined with suitable values. Furthermore, the seawater-containing water system that is the target of the method for inhibiting the production of cyanide compounds of the present invention includes not only water containing seawater circulating within a seawater-using facility, but also seawater introduced into the seawater-using facility.

[0032] In the method for inhibiting the production of cyanide compounds of the present invention, the step of adding peroxide to aqueous water containing seawater is preferably carried out before the step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent, and / or in an aqueous system to which the aqueous water after the step reaches within 60 minutes. It is more preferable to have a step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent after adding peroxide to aqueous water containing seawater.

[0033] In the method for inhibiting the production of cyanide compounds of the present invention, it is preferable to add at least one oxidant selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents to aqueous water containing seawater, in which the concentration of peroxides in the aqueous water is 0.05 to 10 mg / L in terms of hydrogen peroxide concentration. In the method for inhibiting the production of cyanide compounds of the present invention, the seawater-containing aqueous solution to which at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent is added preferably has a peroxide concentration, calculated as hydrogen peroxide concentration, of 0.3 mg / L or more, more preferably 0.5 mg / L or more, and even more preferably 1.0 mg / L or more.

[0034] In the method for inhibiting the production of cyanide compounds of the present invention, when the concentration of nitrogen compounds in the aqueous water containing seawater is 100 mg / L or less, the step of adding peroxide to the aqueous water containing seawater is preferably carried out before the step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent, and / or in an aqueous system that the aqueous water after the step reaches within 60 minutes, more preferably within 30 minutes. Furthermore, when the concentration of nitrogen compounds in the aqueous water containing seawater exceeds 100 mg / L, the step of adding peroxide to the aqueous water containing seawater is preferably carried out before the step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent. The aqueous system where the aqueous water reaches within 60 minutes after the step of adding at least one selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent may be any location from the step of adding at least one selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent to a location in the aqueous system where the aqueous water reaches after 60 minutes, and is not particularly limited.

[0035] The nitrogen compounds in water systems including seawater are preferably amino acids.

[0036] In the method for inhibiting the formation of cyanide compounds of the present invention, the location where the peroxide is added may be in a piping or conduit attached to a water intake, a heat exchanger, or a condenser, or at the inlet of the heat exchanger or the inlet of the condenser, and at least one of the water intake, the inlet of the heat exchanger, and the inlet of the condenser is preferred.

[0037] In the method for inhibiting the formation of cyanide compounds of the present invention, the location for measuring the concentration of peroxide in an aqueous system containing seawater (i.e., the equivalent hydrogen peroxide concentration) is not particularly limited, as long as the water quality of the aqueous system is measured downstream of the location of addition of each chemical agent in the present invention, and measurement is preferably carried out at at least one location of a drainage channel, a heat exchanger outlet, or a condenser outlet. Furthermore, in the method for inhibiting the formation of cyanide compounds of the present invention, if at least one oxidant selected from the group consisting of monochloramine, a chlorine-based oxidant, and a bromine-based oxidant is added to the aqueous system containing seawater after peroxide is added, it is preferable to measure the concentration of peroxide in the aqueous system upstream of the location where at least one oxidant selected from the group consisting of monochloramine, a chlorine-based oxidant, and a bromine-based oxidant is added. In the method for inhibiting the formation of cyanide compounds of the present invention, when multiple peroxides are added to an aqueous solution containing seawater, the concentrations of the added multiple peroxides may be measured at the same or different locations.

[0038] In the method for inhibiting the production of cyanide compounds of the present invention, the concentrations of components in the aqueous water containing seawater (total residual chlorine concentration, residual combined chlorine concentration, residual free chlorine concentration, peroxide concentration (i.e., hydrogen peroxide concentration equivalent value), nitrogen compound concentration, and cyanide compound concentration in the aqueous water containing seawater) can be measured by known methods.

[0039] In the method for inhibiting the generation of cyanide compounds of the present invention, the timing of adding peroxide to aqueous water containing seawater (which can also be referred to as the time period during which peroxide is added to aqueous water) is not particularly limited, but it is preferable to adjust the timing of addition to coincide with the timing of adding at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and bromine-based oxidizing agents to aqueous water containing seawater (which can also be referred to as the time period during which the above-mentioned chemical is added to aqueous water). This is because the generation of cyanide compounds caused by adding at least one selected from the group consisting of monochloramine, chlorine-based oxidizing agents, and chlorine-based oxidizing agents to aqueous water containing seawater can be effectively inhibited. [Example]

[0040] The present invention will be further described below using examples, but the present invention is not limited to the following examples.

[0041] Seawater was collected from Tokyo Bay and used as the test water.

[0042] <Comparative Examples 1 and 2> Cystine was added to a 200 mL sealed volumetric flask to the concentration shown in Table 1 below, and test water was dispensed to a total volume of 200 mL to prepare amino acid-containing test water. Next, monochloramine was added to the amino acid-containing test water to the concentration shown in Table 1 below, and the flask was shaken to ensure a uniform monochloramine concentration in the test water, sealed, and protected from light. The flask was then left to stand at room temperature for the reaction time shown in Table 1 below to obtain a reaction solution. The cyanide compound concentration of the resulting reaction solution was measured.

[0043] <Examples 1 and 2> Cystine was added to a 200 mL sealed volumetric flask to the concentration shown in Table 1 below, and test water was dispensed to a total volume of 200 mL to prepare amino acid-containing test water. Next, hydrogen peroxide solution was added to the amino acid-containing test water to the concentration shown in Table 1 below, and the flask was shaken to ensure a uniform hydrogen peroxide concentration in the test water. Monochloramine was then added to the concentration shown in Table 1 below, and the flask was shaken to ensure a uniform monochloramine concentration in the test water. The flask was then sealed, shielded from light, and allowed to stand at room temperature for 30 minutes to obtain a reaction solution. The cyanide compound concentration in the resulting reaction solution was measured.

[0044] <Comparative Examples 3 and 4> Cystine was added to a 200 mL sealed volumetric flask to the concentration shown in Table 1 below, and test water was dispensed to a total volume of 200 mL to prepare amino acid-containing test water. Next, monochloramine was added to the amino acid-containing test water to the concentration shown in Table 1 below, and the flask was shaken to ensure a uniform monochloramine concentration in the test water, sealed, protected from light, and allowed to stand at room temperature for 30 minutes. Hydrogen peroxide was then added to the concentration shown in Table 1 below, and the flask was shaken to ensure a uniform hydrogen peroxide concentration in the test water, sealed, protected from light, and allowed to stand at room temperature for 30 minutes to obtain a reaction solution. The cyanide compound concentration of the resulting reaction solution was measured.

[0045] <Measurement of cyanide compound concentration> 5-25 mL of the reaction solution was dispensed into a 50 mL sealed volumetric flask, 10 mL of the 4-PCP solution shown in JIS K0102 (2019), Section 38.3 was added, and pure water was dispensed to a total volume of 50 mL. The solution was shaken to make it uniform, and the color-developing solution was prepared. The color-developing solution was then placed in a water bath at 25°C for 30 minutes, and the absorbance of the reaction solution at 638 nm was measured. The cyanide ion (CN) solution prepared as shown in JIS K0102 (2019), Section 38.3 was used. - The cyanide ion concentration was calculated from the relationship between the amount of HCl and the absorbance, and this is shown in Table 1 below as the cyanide compound concentration.

[0046] [Table 1]

[0047] The results of Comparative Examples 1 and 2 show that when monochloramine is added to test water containing seawater, cyanide compounds are produced. The results of Examples 1 and 2 show that the production of cyanide compounds is suppressed by adding monochloramine and hydrogen peroxide to seawater. On the other hand, the results of Comparative Examples 3 and 4 show that for seawater with an amino acid content of more than 100 mg / L, the addition of hydrogen peroxide 30 minutes after adding monochloramine to the seawater did not have the effect of inhibiting the production of cyanide compounds.

[0048] Seawater was collected from Tokyo Bay and used as the test water.

[0049] <Comparative Examples 5 to 10> Cystine was added to a 200 mL sealed volumetric flask to the concentration shown in Table 2 below, and test water was dispensed to a total volume of 200 mL to prepare amino acid-containing test water. Next, monochloramine was added to the amino acid-containing test water to the concentration shown in Table 2 below, and the flask was shaken to ensure a uniform monochloramine concentration in the test water, sealed, and protected from light. The flask was then left to stand at room temperature for the reaction time shown in Table 2 below to obtain a reaction solution. The cyanide compound concentration of the resulting reaction solution was measured.

[0050] <Examples 3 to 8 and 12> Cystine was added to a 200 mL sealed volumetric flask to the concentration shown in Table 2 below, and test water was dispensed to a total volume of 200 mL to prepare amino acid-containing test water. Next, hydrogen peroxide solution was added to the amino acid-containing test water to the concentration shown in Table 2 below, and the flask was shaken to ensure a uniform hydrogen peroxide concentration in the test water. Monochloramine was then added to the concentration shown in Table 2 below, and the flask was shaken to ensure a uniform monochloramine concentration in the test water. The flask was sealed, protected from light, and left to stand at room temperature for the reaction time shown in Table 2 below to obtain a reaction solution. The cyanide compound concentration of the resulting reaction solution was measured.

[0051] <Examples 9 to 11 and Comparative Examples 11 to 13> Cystine was added to a 200 mL sealed volumetric flask to the concentration shown in Table 2 below, and test water was dispensed to a total volume of 200 mL to prepare amino acid-containing test water. Next, monochloramine was added to the amino acid-containing test water to the concentration shown in Table 2 below, and the flask was shaken to ensure a uniform monochloramine concentration in the test water, sealed and protected from light. The flask was then left to stand at room temperature for the time shown in Table 2 below. Hydrogen peroxide was then added to the concentration shown in Table 2 below, and the flask was shaken to ensure a uniform hydrogen peroxide concentration in the test water, sealed and protected from light. The flask was then left to stand at room temperature for the reaction time shown in Table 2 below to obtain a reaction solution. The cyanide compound concentration of the resulting reaction solution was measured.

[0052] <Measurement of cyanide compound concentration> 5-25 mL of the reaction solution was dispensed into a 50 mL sealed volumetric flask, 10 mL of the 4-PCP solution shown in JIS K0102 (2019), Section 38.3 was added, and pure water was dispensed to a total volume of 50 mL. The solution was shaken to make it uniform, and the color-developing solution was prepared. The color-developing solution was then placed in a water bath at 25°C for 30 minutes, and the absorbance of the reaction solution at 638 nm was measured. The cyanide ion (CN) solution prepared as shown in JIS K0102 (2019), Section 38.3 was used. - The cyanide ion concentration was calculated from the relationship between the amount of HCl and the absorbance, and this is shown in Table 2 below as the cyanide compound concentration.

[0053] [Table 2]

[0054] The results of Comparative Examples 5 to 8 show that even in seawater with a low amino acid content, the addition of monochloramine produces cyanide compounds. The results of Examples 3 to 5 confirm that the production of cyanide compounds is suppressed even when the amount of hydrogen peroxide added is low. The results of Comparative Examples 9 to 13 and Example 12 show that for seawater with an amino acid content exceeding 100 mg / L, the addition of monochloramine to the seawater followed by the addition of hydrogen peroxide did not have the effect of inhibiting the production of cyanide compounds. On the other hand, the results of Examples 9 to 11 show that for seawater with an amino acid content of 100 mg / L or less, the effect of inhibiting the production of cyanide compounds was achieved even when hydrogen peroxide was added 15 to 30 minutes after the addition of monochloramine. From the above, when the amino acid content in the seawater-containing aqueous solution is 100 mg / L or less, the hydrogen peroxide addition step can be provided upstream or downstream of the monochloramine, etc. addition step, whereas when the amino acid content in the seawater-containing aqueous solution exceeds 100 mg / L, it is preferable to provide the hydrogen peroxide addition step upstream of the monochloramine, etc. addition step.

Claims

1. A method for inhibiting the formation of cyanide compounds in aqueous water, comprising a step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent, and further comprising adding a peroxide to the aqueous water containing seawater.

2. 2. The method for inhibiting the formation of cyanide compounds in aqueous water according to claim 1, wherein the peroxide is hydrogen peroxide.

3. 3. The method for inhibiting the formation of cyanide compounds in aqueous water according to claim 1 or 2, wherein in the step of adding at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent, the at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent is added to the aqueous water so that the aqueous water has a residual chlorine concentration of 0.01 mg / L or more.

4. 3. The method for inhibiting the formation of cyanide compounds in aqueous water according to claim 1, comprising adding peroxide so that the concentration of peroxide in the aqueous water is 0.05 to 10 mg / L in terms of hydrogen peroxide concentration.

5. 3. The method for inhibiting the formation of cyanide compounds in aqueous water according to claim 1 or 2, wherein the addition of peroxide to the aqueous water is carried out before a step in which at least one oxidizing agent selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent is added, and / or in an aqueous system to which the aqueous water after the step reaches within 60 minutes.

6. 3. The method for inhibiting the formation of cyanide compounds in aqueous water according to claim 2, wherein at least one oxidant selected from the group consisting of monochloramine, a chlorine-based oxidant, and a bromine-based oxidant is added to aqueous water containing seawater having a hydrogen peroxide concentration of 0.05 to 10 mg / L.

7. the step of adding at least one selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent is a step of adding monochloramine, 3. The method for inhibiting the formation of cyanide compounds in aqueous water according to claim 1 or 2, wherein the monochloramine is produced by mixing a substance that generates hypochlorous acid with ammonium ions, or by allowing a substance that generates hypochlorous acid and ammonium ions to coexist in the aqueous water.

8. the step of adding at least one selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent is a step of adding a chlorine-based oxidizing agent, 3. The method for inhibiting the formation of cyanide compounds in aqueous water according to claim 1 or 2, wherein the chlorine-based oxidizing agent is at least one selected from the group consisting of sodium hypochlorite, potassium hypochlorite, seawater electrolyte, N-chlorosulfamate, and chlorine dioxide.

9. the step of adding at least one selected from the group consisting of monochloramine, a chlorine-based oxidizing agent, and a bromine-based oxidizing agent is a step of adding a bromine-based oxidizing agent, 3. The method for inhibiting the formation of cyanide compounds in aqueous water according to claim 1, wherein the bromine-based oxidizing agent is at least one selected from the group consisting of sodium hypobromite, monobromoamine, and N-bromosulfamate.

Images