Process for producing hypochlorite

Abstract

In a process for producing sodium hypochlorite in an electrolytic cell comprises forming an aqueous based chloride solution with a chloride salt; controlling the concentration of chloride within the solution to an amount comprising less than 25 g/L chloride salt; piping the salt solution to the electrolytic cell, the electrolytic cell comprising an anode and a cathode, the cathode comprising a metallic base material, a first coating on the metallic base material and a second non-conductive ceramic coating on the metallic base material. The chloride solution is then in contact with the anodes and cathodes and an electric current is sent throughout the electrolytic cell to produce hypochlorite. During this process the electric current is controlled so that the power consumption is less than 2.5 kWh per pound of hypochlorite produced and the resulting cell efficiency comprises less than 2.5 kg of chloride salt consumed for every 1 kg of hypochlorite generated.

Description

FIELD OF THE INVENTION

This invention relates generally to a process for producing hypochlorite. More specifically, this invention relates to a process of electrolytic production of hypochlorite from salt containing chlorides in an aqueous solution.

BACKGROUND OF THE INVENTION

Chlorine in the form of hypochlorite was first used for disinfecting water systems in London after an outbreak of cholera in 1850. For the past century, chlorination has become the standard way to disinfect water supplies, potable water, wastewater, and swimming pools, to eliminate epidemic waterborne diseases. The traditional way to disinfect water with chlorine was through the use of chlorine gas. Transporting bulk chlorine on crowded highways and into residential areas has become a major safety concern since the transport of chlorine gas under high pressure can be very hazardous. Also, the transport of commercial hypochlorite, which is predominantly water, is very expensive. Stringent regulation of toxic gasses and accidental releases of chlorine and higher costs have caused alternative sources for chlorine to be sought for water disinfection. Onsite production of a chlorine source, sodium hypochlorite for example, is currently the best option for obtaining a less expensive and safer source.

On-site generation has proven itself as a safe and cost efficient process for providing for the chlorine needs of water treatment facilities. On-site hypochlorite generation has been accomplished by different means in the past. The preferred on-site reaction is creating sodium hypochlorite (NaOCl) according to the following equation:
NaCl+H₂O+2e→NaOCl+H₂.

There is a great need to improve the electrolytic production of hypochlorite from chloride-containing salts dissolved in an aqueous solution. Problems that occur during the reaction affect the amount of hypochlorite produced, chlorate formation for example. Problems that occur in the market place, such as the availability and cost of salt and electrical power, affect the economy of hypochlorite production. Reducing salt and power consumption as well as making the process more efficient with improved current efficiency is desired to reduce costs. The acceptable current efficiency under prior methods for producing hypochlorite ranged from 65% to above 75%. Prior electrolytic processes have attempted to achieve such results using different methods.

Early on in the development of chlorine cells used for sodium chlorate manufacture, a film-coated cathode for the electrolysis of alkali metal halide solutions was used in the substantial absence of chromium ions. The cathode comprised a conductive substrate, such as titanium, steel, iron, or alloys thereof, coated with an adherent, porous film of a substantially nonconductive material having an average coating thickness of less that about 10³ microns. The nonconductive, film-forming material was further characterized as being chemically inert in the halite solution. According to the patent, this permitted electrolytic operation with enhanced current efficiency without the use of chromate ions in the solution.

In another method, a substrate metal, such as a valve metal as represented by titanium, is provided with a highly desirable rough surface characteristic for subsequent coating application. This can be achieved by various operations including etching to ensure a roughened surface morphology. In subsequent operations, a barrier layer is provided on the surface of enhanced morphology. This may be achieved by operations including heating, as well as including thermal decomposition of a layer precursor. Subsequent coatings provide enhanced lifetime even in the most rugged commercial environments.

Electrode assemblies and cells for electrolytic processes have been improved for the production of alkali metal hypochlorite, alkali metal chlorate, and other inorganic and organic chemical products. One disclosure taught a diaphragm-less electrolytic cell having at least one assembly of a plurality of planar, parallel, closely spaced foraminous dimensionally stable substantially horizontally disposed anodes and a plurality of parallel foraminous cathodes substantially horizontally disposed, the cathodes interleaved with the anodes in substantially face-to-face closely spaced parallel alignment. Organic chemical products, alkali metal hypochlorite and alkali metal chlorate are produced by placing the assembly of electrodes provided with a means for supplying current to the individual anodes and current from the individual cathodes, in alkali metal halide solutions, solutions of organic electrolytes and electrolyzing the solutions while maintaining operating parameters suitable for the production of alkali metal hypochlorite and alkali metal chlorate and organic chemical products.

One improved process for the electrolysis of sea water comprised admixing sea water before electrolysis with sufficient recycled hypochlorite solution to substantially oxidized bromine, iodine and sulfur ion impurities to their elemental forms for removal. Another method for chlorine production was directed to an alkali metal chlorate cell using solid salt and a cell with higher temperatures so that a brine feed solution replaced a solid salt feed. One further process of producing sodium hypochlorite comprised electrolyzing an aqueous solution of sodium chloride. The use of at least one cooling means in or between the electrolytic cells to cool the electrolyte solution preferably between 5° C. and 45° C. was found to increase available chlorine.

It is the amount of available chlorine in the resulting solution that determines the efficiency of the hypochlorite generation process. Competing reactions, such as the reverse reaction back to NaCl and H₂O or the formation of sodium chlorates, occur in the resulting sodium hypochlorite solution produced from the initial reaction. The amount of sodium hypochlorite lost to side reactions, chlorate formation and back reactions, is proportional to greater concentrations of available chlorine and higher temperatures. The temperature of aqueous solutions used in the reaction has been found to affect the resulting amount of sodium hypochlorite produced.

DEFINITIONS/EQUATIONS

• Cell Efficiency: Cell efficiency is a ratio of the concentration of chloride salt within the aqueous brine solution fed to the electrolytic cell to concentration of hypochlorite in the effluent of the electrolytic cell. For example, in the case of an NaCl solution the cell efficiency is calculated by the following equation: $\mathrm{Cell}\mathrm{Eff}.\left[\mathrm{NaCl}/\mathrm{NaOCl}\right]=\frac{\mathrm{NaCl}g\text{/}L}{\mathrm{NaOCl}g\text{/}L}$
• Power Consumption DC: Power consumption is expressed as kWatt-Hours/NaOCl Lb. Power consumption is calculated by the following equations: $\mathrm{Amps}*\mathrm{Volts}=\mathrm{Watts}$ $\mathrm{DC}\mathrm{Amps}⨯\mathrm{DC}\mathrm{Volts}⨯\frac{k\mathrm{Watts}}{1000\mathrm{Watts}}⨯\frac{\mathrm{Day}}{\mathrm{NaOCl}\mathrm{Lb}\left(\mathrm{as}{\mathrm{Cl}}_2\right)}⨯\frac{24\mathrm{Hour}}{\mathrm{Day}}=\mathrm{Power}\mathrm{Cons}.\mathrm{DC}$
• Current Efficiency: Current efficiency is the measurement of available chlorine produced during electrolysis in relation to the power or current consumed and is based on Faraday's law. Faraday's Law states that the amount of substance (number of moles) consumed or produced at one of the electrodes in an electrolytic cell is directly proportional to the amount of electricity that passes through the cell (number of moles of electrons transferred at that electrode) Current efficiency is expressed as a percent calculation based on Faraday's law and the production of sodium hypochlorite as follows:
• First, the theoretical amount of sodium hypochlorite (g/L Theo.) that should be produced in an electrolytic cell is calculated using the following:
• Equation Terms 1-6
• 1. The amount of Current (Amps)
• 2. The amount of electric charge that flows through the cell
• 3. Faraday's Constant 96500 C/mol e.
• 4. The electron mole to Chlorine mole ratio based on the balanced equation.
  • According to the balanced equation for the reaction that occurs at the anode of this cell, one mole of chlorine for every 2 moles of electrons.
    Anode (+): 2 Cl⁻→Cl₂+2 e⁻
• 5. The atomic mass unit of Chlorine
  • (used to express the amount of Sodium Hypochlorite)
• 6. The number of cells
• The equation is below where terms 2 -5 are constants and 1 & 6 are variables: $\stackrel{1}{\mathrm{DC}\mathrm{Amps}}⨯\stackrel{2}{\frac{3600C}{\mathrm{Amp}\text{-}\mathrm{Hour}}}⨯\stackrel{3}{\frac{1\mathrm{mol}{e}^{-}}{96\text{,}500C}}⨯\stackrel{4}{\frac{1\mathrm{mol}{\mathrm{Cl}}_2}{2\mathrm{mol}{e}^{-}}}⨯\stackrel{5}{\frac{70.91g{\mathrm{Cl}}_2}{1\mathrm{mol}{\mathrm{Cl}}_2}}⨯\stackrel{6}{\mathrm{No}.\mathrm{Cells}}=g{\mathrm{Cl}}_2\text{/}\mathrm{Hour}$
• Dividing the grams of Cl₂/Hr by the flow rate results in g/L Cl2. $\frac{g{\mathrm{Cl}}_2\text{/}\mathrm{Hour}}{\mathrm{liter}\text{/}\mathrm{minutes}}⨯\frac{\mathrm{Hour}}{60\mathrm{minutes}}=g{\mathrm{Cl}}_2\text{/}\mathrm{liter}\left(g\text{/}L\mathrm{Theo}.\right)$
• Current Efficiency is then calculated by comparing the actual amount of hypochlorite produced with the theoretical amount of hypochlorite using the the following equation: $\frac{\mathrm{NaOCl}g\text{/}L\mathrm{Actual}}{\mathrm{NaOCl}g\text{/}L\mathrm{Theo}.}⨯100=\mathrm{Current}\mathrm{Eff}.\%$

SUMMARY

Reducing salt and power consumption as well as making the process of hypochlorite production more efficient with improved current efficiency is desired to reduce costs. The process of this invention generates hypochlorite, either in the form of sodium hypochlorite or potassium hypochlorite, in terms of available chlorine, more efficiently, that is with a reduction of feed product consumed or energy required to produce equivalent amounts of hypochlorite as previous methods. Increased efficiency is measured by an increase in the percentage of sodium or potassium chloride converted to hypochlorite during the electrolytic process and a decrease in power consumption.

Temperature can also affect the efficiency of the process. Higher temperatures of the solution during electrolysis and increased concentrations of available chlorine enhance the probability of a shift in kinetics to form undesirable by products. The amount of available chlorine, the desired end product, is reduced. Because of these side reactions, more sodium chloride and electric current must be consumed to produce an equal amount of available chlorine. Advantageously, during the process of this invention, the amount of chloride salt consumed during the electrolysis process is reduced while maintaining both cell efficiency and current efficiency. Side reactions are reduced thereby allowing greater production of available chlorine. The current efficiency of the process can be increased so that the current efficiency is within a range of from about 70% to about 80%. Improved efficiency translates to cost savings in terms of feed product and electric power consumption.

Therefore, disclosed herein is a process for producing a hypochlorite solution in an electrolytic cell. In one embodiment, the process comprises forming an aqueous based chloride solution with a chloride salt. Preferably, the concentration of chloride within the solution is controlled to an amount comprising less than 20 g/L chloride salt. The salt solution is piped to the electrolytic cell. The electrolytic cell comprises an anode and a cathode. The cathode preferably comprises a metallic base material, a first coating on the metallic base material and a second non-conductive ceramic coating on the metallic base material. The chloride solution is allowed to contact the anode and to contact the cathode. An electric current is passed throughout the electrolytic cell to produce hypochlorite. Preferably, the electric current is controlled so that the power consumption is less than 2.3 kWh per pound of hypochlorite produced, the cell efficiency comprises less than 2.5 kg of chloride salt consumed for every 1 kg of hypochlorite generated.

In one embodiment for producing a hypochlorite solution according to the present invention the salt solution comprises sodium chloride, the amount of sodium chloride consumed during the process comprising less than 2.5 kg for every 1 kg of hypochlorite generated.

In one embodiment for producing a hypochlorite solution according to the present invention the metallic base material is selected from a group comprising titanium, iron, steel, copper and nickel alloys, and the first coating comprises an oxide of the metallic base material. The second coating can comprise a non-conductive ceramic selected from a group comprising yttria-stabilized zirconia, zirconia, titania, chromia and hastelloy. Advantageously, in this process for producing a hypochlorite solution, the current efficiency is greater than 70% even though the salt feed is decreased below 20 g/L. In another embodiment for producing a hypochlorite solution according to the present invention the temperature of the solution is maintained within a range of about 15° C. to less than 60° C.

In an alternative embodiment, a process for producing a hypochlorite solution in an electrolytic cell comprises steps (a) thru (g). In step (a) an aqueous based chloride solution is formed with a chloride salt. In step (b) the concentration of chloride within the solution is controlled to an amount comprising less than 20 g/L chloride salt. In step (c), the salt solution from step (a) is piped to the electrolytic cell, the electrolytic cell comprising an anode and a cathode, the cathode comprising a metallic base selected from a group comprising titanium, iron, steel, copper and nickel alloys, a first coating on the metallic base comprising an oxide of the metallic base material, and a second coating on the oxide of the metallic base material comprising a non-conductive ceramic. In step (d) the chloride solution is allowed to contact the anode. In step (e) the chloride solution is allowed to contact the cathode. In step (f) an electric current is passed throughout the electrolytic cell to produce hypochlorite. Finally, in step (g) the electric current is controlled so that the power consumption is within a range of about 1.8 kWh per pound of hypochlorite produced to about 2.5 kWh per pound of hypochlorite produced, wherein the cell efficiency comprises less than 2.5 kg of chloride salt for every 1 kg of hypochlorite generated and the current efficiency is maintained at greater than 70%.

In one preferred embodiment for producing a hypochlorite solution, the chloride solution comprises less than 20 g/L chloride salt and the chloride salt can be selected from sodium chloride or potassium chloride. The cathode can comprise a titanium base for conducting electrons, a first coating on the titanium base, the first coating comprising titanium oxide, and a non-conductive yttria-stabilized zirconia second coating applied to the titanium first coating. The electric current can be controlled so that power consumption is within a range of about 1.5 kWh per pound of hypochlorite produced to about 2.0 kWh per pound of hypochlorite produced. The temperature is maintained within a range of about 15° C. to about 60° C. Cell efficiency comprises less than 2.5 kg of chloride salt consumed for every 1 kg of hypochlorite generated and the current efficiency is maintained at greater than 70%.

An alternative process for producing a hypochlorite solution in an electrolytic cell comprises forming an aqueous based chloride solution with a chloride salt, the chloride solution comprising an amount ranging from 25 g/L to 30 g/L. In another alternative embodiment, the chloride solution is greater than 30 g/L chloride salt. The salt solution is piped to the electrolytic cell, the electrolytic cell comprising an anode and a cathode, the cathode comprising a metallic base selected from a group comprising titanium, iron, steel, copper and nickel alloys, a first coating on the metallic base comprises an oxide of the metallic base material, and a second coating on the oxide of the metallic base material comprises a non-conductive ceramic. The chloride solution is allowed to contact the anode and the cathode. An electric current is passed throughout the electrolytic cell to produce hypochlorite. During the process, the power consumption is controlled within an amount comprising less than 2.0 kWh per pound of hypochlorite produced so that the cell efficiency comprises less than 3.0 kg of chloride salt consumed for every 1 kg of hypochlorite generated and the current efficiency is maintained at greater than 80%.

BRIEF DESCRIPTION OF DRAWINGS

FIGURE is a schematic of one embodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the practice of the process of this invention hypochlorite is generated more efficiently. In this instance, more efficiently means with a reduction of either feed product consumed or energy required to produce equivalent amounts of hypochlorite as previous methods. Cell efficiency is a ratio of the amount of chloride salt converted to hypochlorite during the electrolytic process. Cell efficiency indicates the amount of chloride salt consumed per unit of hypochlorite produced. The object of this invention is to decrease the amount of sodium chloride consumed thereby resulting in a decrease in the cell efficiency ratio. Current efficiency is based on a decrease in power consumption as expressed in actual hypochlorite produced divided by theoretical hypochlorite under Faraday's Law. Advantageously, the present process consumes less chloride salt without a loss of efficiency as will be shown in the examples described below and accompanying tables.

Higher temperatures of the solution used during electrolysis and increased concentrations of available chlorine enhance the probability of a shift in kinetics to form undesirable by products. The amount of available chlorine, which is the desired end product, is reduced by these side reactions. Because of the side reactions during previously known processes, more sodium chloride and electric current had to be consumed to produce an equal amount of available chlorine. Advantageously, during the process of this invention, the amount of chloride salt consumed during the electrolysis process is reduced while maintaining both cell efficiency in terms of number of kilograms of chloride salt consumed per kilogram of hypochlorite produced as well as current efficiency based on power consumption. Side reactions are reduced thereby allowing greater production of available chlorine. The current efficiency of the process can be increased so that the current efficiency is within a range of from about 70% to about 80%. Improved current efficiency translates to cost savings in electric power consumption. A decrease in cell efficiency ratio is desired because it indicates a decrease in the amount of salt consumed and therefore a decrease in cost.

One preferred process can generate hypochlorite by using a sodium or potassium salt as the starting product resulting in sodium hypochlorite or potassium hypochlorite, respectively. For purposes of this description, but not as a limitation, sodium chloride will be used as the feed product. Prior technology taught that commercially feasible electrolytic cells were capable of producing 8 to 10 g/L of available chlorine while consuming approximately 28-30 g/L of sodium chloride, using a power consumption of 2.3 to 2.44 kWh per pound of hypochlorite produced and comprising a cell efficiency of 3.0 to 3.5 grams of salt per gram of chlorine produced. See J. E. Bennett, Non-Daiphragm Electrolytic Hypochlorite Generators, Chemical Engineering Progress, December, 1974. Current efficiency as described in the Bennett process is within the 60% to 65% range. Advantageously, the present process for producing a hypochlorite solution uses less chloride salt without a loss of current efficiency. During the process, an aqueous based chloride solution is formed with a chloride salt by controlling the concentration of chloride within the solution to an amount comprising less than 20 g/L chloride salt while maintaining a power consumption at less than 2.3 kWh per pound of hypochlorite produced and comprising a cell efficiency of 2.5 kg or less of chloride salt consumed for every 1 kg of hypochlorite generated. Current efficiency resulting from the present process is above 70%.

Referring to the schematic of the FIGURE, solid salt within a brine tank 40 combines with water piped to the brine tank from a water softener unit 15. The solid salt can be in the form of sea salt or mined salt. Water may be treated in a water softener unit to remove calcium and magnesium. These impurities are prone to form insulating precipitates between the electrodes, which inhibit the electrolytic process. This reduces the conversion efficiency and increases maintenance costs. Salt solution 44 for the electrolysis process is piped to an electolyzer assembly 20 from the brine tank 40 through pipelines 42. In one embodiment, the cells are arranged in bipolar configuration. Brine 44 from the brine tank 40 is piped to an inlet pipe 26a of the first cell 26 in the electrolyzer assembly 20 and can be mixed with chilled water piped 32 from a chiller 30. The use of chilled water piped to each cell within an electrolytic assembly 20 is taught by Bass, U.S. Pat. No. 6,805,787 and is hereby incorporated as if fully reproduced. Both the chiller 30 and the water softener unit 15 are known in the art and readily available. The system is controlled by an operator-controlled computer. In another embodiment of the process of this invention, the process can efficiently be practiced without a chiller, wherein temperatures are maintained within a range of 15° C. to 60° C. while current efficiency remains at above 70%. These temperature ranges are important especially in geographic areas where the process will be used such as the southern hemispheres and parts of the world, the middle east or southern U.S., where ambient temperatures are high during the summertime.

After the salt solution is formed, the brine solution enters the casings of the assembly and floods the cells 26, 24, 22. A DC current impressed upon the electrolyzer converts the sodium chloride to molecular chlorine and sodium hypochlorite within the cells. Unreacted brine and hydrogen gas, a product of electrolysis, remain in the solution until the hydrogen gas is removed from the generation zone by thermal convection, passes through gas ports in the compartment partitions and is finally vented to the atmosphere. The electrolysis reaction is as follows:

The brine, electrolyte and hypochlorite pass from one compartment to the next through ports located below the solution level. In multiple cell electrolyzer assemblies 20, the brine and hypochlorite solution passes through an outlet connection from the first cell and is piped to the inlet of the next electroylyzer cell. In one embodiment, the solution can be mixed with chilled water piped from the chiller 30 as it passes from one cell to the next. In the final cell, the brine, electrolyte and sodium hypochlorite together with any remaining hydrogen gas are piped to the storage tank 60 which is designed to scavenge the hydrogen from the final product. A dosing pump 66 will pump the hypochlorite to a user system requiring disinfecting, a wastewater tank or commercial swimming pool for example.

Increased efficiency is measured by a reduction in the amount of feed product, sodium chloride for example, consumed during the process and a decrease in power consumption. The current efficiency of this method is preferably within a range of from about 70% to about 80%.

One preferred process for generating sodium hypochlorite uses an electrolyzer assembly having electrolyzer cells or tubes stacked one upon another. Each electrolyzer cell comprises compartments having anode and cathode-plates. The number of anode/cathode compartments can range from about 1 compartment to about 15 compartments depending on the length of the cell, preferably 4 to 12 compartments per cell. Alternately, the electrolyzer cell can use bipolar plates having an anode and a cathode on the same plate as is known in the industry. Each compartment comprises from 5 to 25 bipolar plates. The electrolyzer cell is manufactured and available from Severn Trent Services-Water Purification Solution Inc.

A preferred electrolytic cell of the invention utilizes a coated cathode. The cathode comprises a metallic base material, a first coating on the metallic base material and a second non-conductive ceramic coating on the metallic base material. The metallic base material can comprise electrically conductive substrate such as titanium substrate. The term titanium as used herein is meant to include commercial titanium and titanium alloys such as grade 5 titanium. Other electrical conductive substrates which may be used include iron, steel, copper and copper-nickel alloys with titanium being preferred. The cathode substrate may be sand blasted or etched before any coatings are applied. A first coating is applied to the substrate in the form of an oxide of the metallic base material, titanium oxide for example. The oxide coating is applied prior to applying the ceramic coating to improve bonding of the coating to the substrate surface. A second coating is applied onto the oxide first coating. The second coating is a non-conductive ceramic coating. The second coating comprises a non-conductive ceramic selected from a group comprising yttria-stabilized zirconia, zirconia, titania, chromia and hastelloy. The coating may be applied by plasma spraying after the surface of the cathode substrate is suitably clean by chemical degreasing. Other methods of applying the yttria-stabilized zirconia coating may be used, including flame spraying, chemical deposition, thermal spraying and sputtering.

The sodium chloride solution, chilled or at ambient temperatures, that is from 15° C. to 60° C., is allowed to contact the anode and then the cathode. The salt concentration throughout the process is maintained at less than 25 g/L chloride salt. In one preferred embodiment, the salt concentration is maintained at less than 20 g/L. An electric current is passed throughout the electrolytic cell to produce hypochlorite. The electric current is controlled so that the power consumption is less than 2.3 kWh per pound of hypochlorite produced, preferably within a range of 1.8 to 2.3 kWh per pound of hypochlorite produced. The current efficiency with this concentration of chloride salt and this amount of power consumption is greater than 70%.

In another embodiment of this invention, the salt concentration is increased to between 25-30 g/L and the electric current is controlled so that power consumption is within a range of 1.5 kWh to 2.0 kWh per pound of hypochlorite produced. The cell efficiency of this process comprises less than 2.5 kg of chloride salt consumed for every 1 kg of hypochlorite generated. The temperature is again within a range of from 15° C. to 60° C. Current efficiency for this embodiment increases to greater than 80%.

In another aspect of this invention, electrical current required for electrolysis is sent from a power source 80 to a rectifier 82 to convert alternating current to direct current and delivered to each cell by power wiring 84. The end product, sodium hypochlorite is piped to a storage tank 60 and then to a user's system that requires disinfecting by a dosing.

The following examples illustrates the test results for sodium hypochlorite produced according to the process of this invention.

EXAMPLES

Test Procedure—Example 1

Standard Cell

A chloride brine was fed into a test electrolytic cell at a brine feed rate equivalent to 12-16 gallons per pound of product produced. This cell had no technological improvements such as coated cathodes or chilled solutions. The concentration of chloride salt within the brine solution was maintained between 28-30 grams per liter. The liquid flow rate was maintained so as to maintain the same exit hypochlorite concentration if the cell efficiency remained constant. Temperatures were ambient. In this way, any improvement in future tests for hypochlorite concentration is related to improved cell efficiency. A baseline performance profile with the above operating conditions and titanium cathodes was obtained.

Process for Producing Hypochiorite
Example I
Test	Power	Cell Inlet	Cell Outlet	NaCl	Eff. Grams	NaoCl	GPL	Current
#	Cons. DC	Temp	Temp	GPL	NaCl/NaoCl	GPL	Theo.	Eff. %
1	2.2	20	45	33	3.64	9.08	14.3	63.5
2	2.02	20	45	30	3.21	9.36	13.7	68.4
3	1.99	23	45	30	3.18	9.43	13.6	69.3
4	2.08	20	45	33	3.5	9.43	14.2	66.5
5	2.09	20	45	33	3.55	9.29	14	66.2

• The resultant current efficiency average 66.8% for example 1. The hypochlorite concentration at the exit point was approximately 9 g/L. Approximately 3.5 g/L salt were used for each g/L hypochlorite produced, and the power consumption averaged 2.01 kWh/pound hypochlorite produced.

Test Procedure—Examples 2 and 3,

Having Improved Technology and Decreased Salt Feed

The electrolytic cell was operated at a brine feed rate equivalent to 12-16 gallons per pound of product produced, with an inlet brine solution concentration of 28-30 g/L salt. Titanium cathodes were replaced with coated cathodes. The salt concentration was slowly reduced at intervals of approximately 5 g/L salt while maintaining a constant liquid flow to the cell. Target concentrations were 25, 20, and 15 g/L. All operating conditions (independent variables) were maintained constant and resulting performance parameters (dependent variables) were measured. These include; exit hypochlorite concentration, cell efficiency, current efficiency, temperature, and salt usage per pound of product. Temperatures were ambient.

Process for Producing Hypochiorite
Example 2
Test	Power	Cell Inlet	Cell Outlet	NaCl	Eff. Grams	NaoCl	GPL	Current
#	Cons.DC	Temp	Temp	GPL	NaCl/NaoCl	GPL	Theo.	Eff. %
1	1.57	21.0	48.0	21.0	2.18	9.64	11.5	84.1
2	1.57	22.0	44.0	18.0	2.05	8.79	11.2	78.7
3	1.49	23.0	48.0	27.0	2.88	9.36	11.0	84.9
4	1.88	24.0	53.0	18.4	2.13	8.65	12.0	71.9
5	1.92	23.0	53.0	18.0	2.15	8.37	11.8	71.1
6	1.90	22.0	52.5	18.0	2.15	8.37	11.5	72.7
7	1.88	24.0	53.0	18.0	2.13	8.44	11.5	73.3

Example 3
Test	Power	Cell Inlet	Cell Outlet	NaCl	Eff. Grams	NaoCl	GPL	Current
#	Cons. DC	Temp	Temp	GPL	NaCl/NaoCl	GPL	Theo.	Eff. %
1	1.87	19.0	39.0	25.5	3.27	7.80	10.3	75.9
2	1.99	19.5	39.0	26.0	3.19	8.15	11.6	70.4
3	1.80	19.5	39.0	26.5	3.40	7.80	9.8	79.2
4	1.83	19.5	39.0	25.5	3.33	7.66	9.8	77.7
5	1.90	19.5	38.0	27.0	3.49	7.73	10.4	74.5

• The resulting current efficiencies for Examples 2 and 3 were above 70%. Example 2 typically has salt feed averaging less than 20 g/L. The power consumption averaged 1.7 kWh per pound of hypochlorite produced and the cell efficiency averaged 2.23 g/L salt consumed for each g/L hypochlorite produced. Increased salt feed in Example 3 resulted in an increase in cell efficiency ratio, i.e. more feed salt used per gram of hypochlorite produced.

The foregoing description is illustrative and explanatory of preferred embodiments of the invention, and variations in the size, shape, materials and other details will become apparent to those skilled in the art. It is intended that all such variations and modifications which fall within the scope or spirit of the appended claims be embraced thereby.

Claims

1. A process for producing a hypochlorite solution in an electrolytic cell comprising:

(a) forming an aqueous based chloride solution with a chloride salt;

(b) controlling the concentration of chloride within the solution to an amount comprising less than 20 g/L chloride salt;

(c) piping the salt solution from step (a) to the electrolytic cell, the electrolytic cell comprising an anode and a cathode, the cathode comprising a metallic base material, a first coating on the metallic base material and a second non-conductive ceramic coating on the metallic base material;

(d) allowing the chloride solution to contact the anode;

(e) allowing the chloride solution to contact the cathode;

(f) passing an electric current throughout the electrolytic cell to produce hypochlorite; and

(g) controlling the electric current so that the power consumption is less than 2.3 kWh per pound of hypochlorite produced;

wherein the cell efficiency comprises less than 2.5 kg of chloride salt consumed for every 1 kg of hypochlorite generated.

2. The process for producing a hypochlorite solution of claim 1 wherein the salt solution comprises sodium chloride, the amount of sodium chloride consumed during the method comprising less than 2.5 kg for every 1 kg of hypochlorite generated.

3. The process of claim 1 wherein the metallic base material is selected from a group comprising titanium, iron, steel, copper and nickel alloys, and the first coating comprises an oxide of the metallic base material.

4. The process of claim 1 wherein the second coating comprises a non-conductive ceramic selected from a group comprising yttria-stabilized zirconia, zirconia, titania, chromia and hastelloy.

5. The process of claim 1 wherein the current efficiency is greater than 70%.

6. The process of claim 1 wherein the temperature of the solution is maintained within a range of about 15° C. to less than 60° C.

7. A process for producing a hypochlorite solution in an electrolytic cell comprising:

(a) forming an aqueous based chloride solution with a chloride salt;

(b) controlling the concentration of chloride within the solution to an amount comprising less than 20 g/L chloride salt;

(c) piping the salt solution from step (a) to the electrolytic cell, the electrolytic cell comprising an anode and a cathode, the cathode comprising a metallic base selected from a group comprising titanium, iron, steel, copper and nickel alloys, a first coating on the metallic base comprising an oxide of the metallic base material, and a second coating on the oxide of the metallic base material comprising a non-conductive ceramic;

(d) allowing the chloride solution to contact the anode;

(e) allowing the chloride solution to contact the cathode;

(f) passing an electric current throughout the electrolytic cell to produce hypochlorite; and

(g) controlling the electric current so that the power consumption is within a range of about 1.8 kWh per pound of hypochlorite produced to about 2.5 kWh per pound of hypochlorite produced;

wherein the cell efficiency comprises less than 2.5 kg of chloride salt for every 1 kg of hypochlorite generated and the current efficiency is maintained at greater than 70%.

8. The process of claim 7 wherein the chloride solution comprises less than 20 g/L chloride salt

9. The process of claim 7 wherein the chloride salt is selected from sodium chloride or potassium chloride.

10. A process for producing a hypochlorite solution in an electrolytic cell comprising:

(a) forming an aqueous based sodium chloride solution;

(b) piping the sodium chloride solution formed in step (a) to the electrolytic cell, the electrolytic cell comprising an anode and a cathode, the cathode comprising a titanium base for conducting electrons, a first coating on the titanium base, the first coating comprising titanium oxide, and a non-conductive yttria-stabilized zirconia second coating applied to the titanium first coating;

(c) allowing the chloride solution to contact the anode;

(d) allowing the chloride solution to contact the cathode;

(e) passing an electric current from the anode through the solution to the cathode to produce hypochlorite;

(f) controlling the electric current so that power consumption is within a range of about 1.5 kWh per pound of hypochlorite produced to about 2.0 kWh per pound of hypochlorite produced; and

(g) maintaining the temperature within a range of about 15° C. to about 60° C.;

wherein the cell efficiency comprises less than 2.5 kg of chloride salt consumed for every 1 kg of hypochlorite generated and the current efficiency is maintained at greater than 70%.

11. The process of claim 10 wherein the chloride solution comprises less than 25 g/L chloride salt

12. A process for producing a hypochlorite solution in an electrolytic cell comprising:

(a) forming an aqueous based chloride solution with a chloride salt, the chloride solution comprising an amount greater than 25 g/L chloride salt,

(b) piping the salt solution from step (a) to the electrolytic cell, the electrolytic cell comprising an anode and a cathode, the cathode comprising a metallic base selected from a group comprising titanium, iron, steel, copper and nickel alloys, a first coating on the metallic base comprises an oxide of the metallic base material, and a second coating on the oxide of the metallic base material comprising a non-conductive ceramic;

(c) allowing the chloride solution to contact the anode;

(d) allowing the chloride solution to contact-the cathode;

(e) passing an electric current throughout the electrolytic cell to produce hypochlorite; and

(f) controlling the power consumption within an amount comprising less than 2.0 kWh per pound of hypochlorite produced;

wherein the cell efficiency comprises less than 3.0 kg of chloride salt consumed for every 1 kg of hypochlorite generated and the current efficiency is maintained at greater than 80%.

13. A process for producing a hypochlorite solution in an electrolytic cell comprising:

(a) forming an aqueous based sodium chloride solution, the chloride solution comprising less than 20 g/L chloride salt;

(b) piping the sodium chloride solution formed in step (a) to the electrolytic cell, the electrolytic cell comprising an anode and a cathode, the cathode comprising a titanium base for conducting electrons, a first coating on the titanium base, the first coating comprising titanium oxide, and a non-conductive yttria-stabilized zirconia second coating applied to the titanium first coating;

(c) allowing the chloride solution to contact the anode;

(d) allowing the chloride solution to contact the cathode;

(e) passing an electric current from the anode through the solution to the cathode to produce hypochlorite;

(f) controlling the power consumption so that the amount of electrical power consumed comprises less than 2.0 kWh per pound of hypochlorite produced; and

(g) maintaining the temperature within a range of about 15° C. to about60° C.;

wherein the cell efficiency comprises less than 2.5 kg of chloride salt consumed for every 1 kg of hypochlorite generated and the current efficiency is maintained at greater than 70%.