RU2466214C1 - Method for electrochemical obtaining of solution of magnesium and copper hypochlorites - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves electrolysis of water solution of magnesium chlorides obtained by dilution of natural bischofite, in non-flowing undivided electrolysis unit with copper electrodes to which electric current with voltage of 3-5 V is supplied, at temperature of electrolyte of 20-25°C. Pulse current with average density of 0.5-1.0 A/dm², frequency of 100-200 Hz and relative pulse duration of 2-4 is supplied to copper electrodes, at electrolyte concentration of 5-10% and pH=8-9. Electrolysis is performed during 0.25-0.5 hours.

EFFECT: increasing the yield of copper and magnesium hypochlorites and reducing the electric energy consumed for obtaining product unit by one third.

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Description

A method for the electrochemical preparation of a solution of magnesium and copper hypochlorites.

The invention relates to the field of production of hypochlorite solutions by electrolysis.

A known method of producing a solution of magnesium hypochlorites, including the electrolysis of a solution of metal chloride using an insoluble anode, the solution containing magnesium chloride in the form of bischofite, boric acid, magnesium sulfate and calcium sulfate at pH 4.5-6.0 in an electrolyzer without diaphragms with a graphite anode and a titanium cathode at a current density of 8-12 A / dm ² and a temperature of 20-50 ° C (see the description of the invention for USSR copyright certificate No. 1624057, IPC С25В 1/26, publication January 30, 1991).

The disadvantage of this method is the absence of a soluble anode. On graphite used as an anode, oxidation reactions of chloride ions occur with the generation of hypochlorite ions, which leads to an increase in current density. Otherwise, the ionic composition of the solution used remains unchanged.

The same source of information (see No. 1624057, example 10, pages 5 and 6) describes a method for producing a solution of magnesium hypochlorites, in which 0.9 l of water is taken to prepare the initial solution for electrolysis, 165 g of crystalline bischofite are dissolved in it content of 45% MgCl ₂ and get 1 l of the original solution containing 70 g / l MgCl ₂ , pH 5.3. The electrolysis is carried out in an electrolyzer without a diaphragm with a graphite anode and a titanium cathode, at a current density of 8 A / dm ² , an electrolyte temperature of 30 ° C and a voltage of 2.8-3.0 V for 4 hours 50 minutes, performing an additional continuous intensive stirring the solution.

The disadvantage of this known method is the high current densities used in the method and the lengthy implementation of the process with additional intensive mixing of the solution.

A known method of producing a solution of magnesium hypochlorite, comprising the electrolysis of an aqueous solution of magnesium chloride in the form of bischofite in an electrolytic cell with a carbon graphite anode and a steel cathode, at constant current at a current density of 0.1-1.5 A / dm ² and an electrolyte temperature of 20 ° C (see the description of the invention to the patent of the Russian Federation No. 2238348, IPC С25В 1/26, 1/18, publication October 20, 2004).

The disadvantage of this method is the use of graphite as an anode, which allows to obtain only one product, magnesium hypochlorite.

A known method of producing magnesium and copper hypochlorites, including the electrolysis of an aqueous solution of magnesium chlorides obtained by dissolving natural bischofite in a non-flow diaphragm electrolyzer with copper electrodes, to which a direct current voltage of 1-25 V, density 1-10 A / dm ² , at an electrolyte concentration is applied 0.5-2% and a temperature of 20-25 ° C, the electrolysis process is carried out for 0.5 hours (see the description of the invention to the RF patent No. 2361016, MPK С25В 1/00, publication July 10, 2009).

The disadvantage of this known method, selected as a prototype, is to carry out the process using a constant current. As a result, due to the constancy of the current mode, the electrodes are polarized. As a result of this, in order to obtain a unit of the product (magnesium and copper hypochlorites), an excessive amount of electric energy is consumed, and the current output of the resulting product decreases.

The task of the invention is to increase the efficiency of the process of producing magnesium and copper hypochlorite by reducing the consumption of electrical energy to produce a unit of production in the form of a solution of magnesium and copper hypochlorites.

The essence of the claimed invention is as follows. A method for the electrochemical preparation of a solution of magnesium and copper hypochlorites, including the electrolysis of an aqueous solution of magnesium chlorides obtained by dissolving natural bischofite in a non-flow diaphragm-free electrolyzer with copper electrodes that are supplied with an electric current of 3-5 V (depending on the magnitude of the used current density), at electrolyte temperature 22-25 ° C. The difference is that pulsed current is supplied to the copper electrodes with an average density of 0.5-1.0 A / dm ² , a frequency of 100-200 Hz and a duty cycle of 2-4 pulses at an electrolyte concentration of 5-10% and pH 8-9, the process electrolysis is carried out within 0.25-0.5 hours. This allows you to increase the current output of the product of magnesium and copper hypochlorite at current densities whose values are equal to direct current densities.

The method is as follows.

The inventive method can be implemented in an electrolytic cell with non-separated anode and cathode spaces of continuous or periodic action with a copper cathode in a solution of bischofite mineral (magnesium chloride) with a concentration of 5-10% and pH 8-9. The cell is connected to a pulse current source with a frequency of 100-200 Hz, duty cycle 2-4, with an average current density of 0.5-1.0 A / dm ² , the electrolysis process is carried out within 0.25-0.5 hours.

Examples of specific performance are presented in tables 1, 2, 3, which show the effect of density, duty cycle on the current efficiency of copper ions and active chlorine.

Table 1 The current density, A / DM ² The electrolyte concentration,% Current output,% Unit costs Copper hypochlorite Magnesium Hypochlorite energy, kW · h / kg 0.5 10 55.3 45.1 5.1 0.75 10 58.1 47.2 6.8 1,0 10 61.0 48,2 7.3 0.5 5 44.3 27.1 7.3 0.75 5 51.0 29.0 7.8 1,0 5 54.7 30,0 8.2

table 2 The current density, A / DM ² The electrolyte concentration,% Pulse current of 100 Hz, output but current (%) at duty cycle Copper hypochlorite Magnesium Hypochlorite Specific energy consumption, kW · h / kg 2 3 four 2 3 four 2 3 four 0.5 10 65.0 65.8 66,2 35.0 34.2 35.3 4.1 4.3 4.6 0.75 10 67.5 67.6 67.7 32,5 32,7 32.3 3.8 4.0 4.1 1,0 10 69,4 69.0 68.8 30.6 31,0 31,2 5.2 5.1 4.9 0.5 5 52,4 52.3 52,2 47.6 47.7 47.8 6.8 6.7 6.6 0.75 5 52.0 52.1 52.7 48.0 47.9 47.3 7.1 7.4 7.6 1,0 5 55.7 55.0 54.8 44.3 45.0 45,2 7.3 7.6 7.8

Table 3 The current density, A / DM ² The electrolyte concentration,% Pulse current 200 Hz, current output (%) with duty cycle Copper hypochlorite Magnesium Hypochlorite Specific energy consumption, kW · h / kg 2 3 four 2 3 four 2 3 four 0.5 10 66.1 66,4 67.2 33.9 33.6 32.8 4.3 4.6 4.9 0.75 10 67.3 67.1 67.4 32,7 32.9 32.6 3,7 4,5 4.1 1,0 10 68,2 67.9 67.8 31.8 32.1 32,2 4.2 4.6 4.9 0.5 5 53,4 52,5 52.1 46.6 47.5 47.9 6.8 6.7 6.5 0.75 5 51.0 51.7 52.1 49.0 48.3 47.9 7.9 7.1 7.3 1,0 5 53.0 53,4 53,4 47.0 46.5 46.6 7.4 7.6 7.9

The use of direct current (table 1) allows at an electrolyte concentration of 10% to obtain a current efficiency at a current density of 0.5 A / dm ² for copper hypochlorite 55.3%, magnesium hypochlorite 45.1%.

The use of a pulsed current with a frequency of 100 Hz, the same density with duty cycle 2 (table 2) increases the yield of copper hypochlorite to 65.0%. In the range of equal current densities used, an increase in the pulse current density to 1.0 A / dm ² (duty cycle 2) leads to an increase in the current output of copper hypochlorite from 61.0 for constant to 69.4% (an increase of 13.8%).

An increase in the duty cycle of a pulsed current with a frequency of 100 Hz from 2 to 3 at the same values of current densities (table 2) from electrolyte solutions of the same concentration leads to a higher output of copper hypochlorite current than when using direct current: at a density of 0.75 A / dm ² duty cycle from 2 to 3 and 4, respectively, with respect to direct current is: 2-14%, 3-16.4%, 4-16.5%.

The use of a pulsed current with a frequency of 200 Hz (table 3) at equal densities with a constant current and an electrolyte concentration of 5% also leads to a higher yield of copper hypochlorite. For example: at a current density of 0.5 A / dm ^2, an increase in the duty cycle from 2 to 4 leads to an increase in the yield of the product, compared to direct current, by percent: 2-20.5%, 3-18%, 4-17%.

The use of pulsed current with a frequency of 100 Hz with a duty cycle of 2, 3, 4 at the same current densities with constant current leads to a reduction in the cost of electric energy per unit mass of the product. For example, at a current density of 0.5 A / dm ² in an electrolyte with a concentration of 10%, the specific energy consumption is 5.1 kW · h / kg, at a pulsed current of 100 Hz and, accordingly, the wells 2, 3, 4 are: 2- 4.1 kW · h / kg (24% gain), 3-4.3 kW · h / kg (18.6% gain), 4-4.6 kW · h / kg (4.1% gain).

When using a current with a frequency of 200 Hz at the same duty cycles and a current density of 1.0 A / dm ² : 2-4.2 kWh / kg (73.8% gain), 3-4.6 kWh / kg ( 58.7% of the gain), 4-4.9 kWh / kg (48.9% of the gain).

The above examples on the influence of current density, shape, frequency and duty cycle of the pulse current in comparison with direct current of the same current density show that the current efficiency of the electrolysis product increases.

The claimed invention allows for the replacement of direct current by a pulsed current at the same current densities of 0.5-1.0 A / dm ^{2 to} increase the current output of copper hypochlorites, to reduce the consumption of electrical energy during electrolysis of a bischofite solution.

Claims (1)

A method for the electrochemical preparation of a solution of magnesium and copper hypochlorites, including the electrolysis of an aqueous solution of magnesium chlorides obtained by dissolving natural bischofite in a non-flow diaphragmless electrolyzer with copper electrodes, to which an electric current of 3-5 V is supplied, at an electrolyte temperature of 20-25 ° C, different the fact that copper electrodes are supplied with a pulsed current of medium density 0.5-1.0 A / dm ² , frequency 100-200 Hz and duty cycle 2-4, at an electrolyte concentration of 5-10% and a pH of 8-9, and the electrolysis is carried out within 0.25-0.5 hours