RU2151743C1 - Method of desalting of water - Google Patents

Abstract

FIELD: electrodialysis desalting of water in electrodyalizer with cation and anion exchange membranes. SUBSTANCE: water is desalted by electrodyalysis in electrodyalizer with cation and anion-exchange membranes. Process is carried out using pulse current with pulse frequency of 50-10³ Hz. EFFECT: lower electric energy consumption for water desalting process and greater purification efficiency. 1 ex, 1 tbl

Description

 The claimed invention relates to a process for electrodialysis desalination of water in an electrodialyzer with cation and anion exchange membranes.

 A known method of desalting water by electrodialysis in an electrodialyzer with ion-exchange membranes (A.S. USSR N 1398884, B 01 D 13/02, 1988).

 The disadvantage of this method is the high energy consumption of 0.53-1.9 W • h / g salt when using ion-exchange membranes.

 The closest in the greatest number of common features and the achieved result to the claimed one is a method of desalination of water by electrodialysis in an electrodialyzer with cation and anion exchange membranes (A.S. USSR N 1507413, B 01 D 13/02, 1989 - prototype).

 The disadvantage of this method is the following. It is known that the performance of the electrodialyzer is directly proportional to its current load. However, an increase in the density of alternating current is possible up to a certain limit, after which side processes begin to occur (for example, decomposition of water with the release of oxygen and hydrogen), which consumes additional energy. Moreover, the limitation of current density also limits the performance of the desalination process by reducing the intensity of the stream of extracted ions.

 The objective of the invention is to reduce the cost of electricity for the process of desalination of water and increase the productivity of the cleaning process.

The problem is solved in that in the method of desalination of water by electrodialysis in an electrodialyzer with cation and anion exchange membranes, the process is conducted on a pulsed current with a pulse frequency of 50-10 ³ Hz.

 The applicant knows the use of pulsed current (US Pat. RF N 2083268, B 01 D 13/02, 1997). In this method, the use of pulsed current of certain parameters (resonant frequency for the extracted ions, duty cycle and current density) allows the regeneration of highly concentrated (2 mol / l or more) solutions containing heavy metal polluting ions. Moreover, only one membrane is used in the electrodialyzer — the cation exchange membrane, which separates the installation into two chambers: the anodic and the cathodic one, which allows selective extraction of ions of the same charge sign, while leaving the necessary charged ones. In the proposed method, ions of both charges are extracted: both cations and anions, which allows the process of desalination of water.

The use of pulsed current reduces energy consumption due to the fact that the same values of current density J _cf on alternating asymmetric and pulsed current are achieved in the case of
J _cf = J _max / Q,
where J _max is the working current density in the pulse; Q - duty cycle of the pulse current.

 That is, the working current density in a pulse has higher values in comparison with an asymmetric alternating current, which increases the performance of the electrodialyzer. In addition, the presence of current pauses when using a pulsed current affects the reduction of energy consumption.

Example. The method is as follows: in the middle chamber of the electrodialysis cell with cation and anion exchange membranes, an aqueous solution of sodium chloride with a concentration of 0.1 mol / L is poured. In the cathode and anode chambers fill 0.1 n. HCl solution. A rectangular current pulse with a pulse frequency of 50-10 ⁴ Hz and a current density of 5-50 A / m ^{2 is} supplied to the electrodes. Thus cations Na ⁺ moved through the cation exchange membrane to the cathode and anions Cl ^{- -} through the anion exchange membrane - the side of the anode. Thus, the process of desalination of water. An increase in current density of more than 50 A / m ^{2 is} impractical in view of the increase in energy consumption for the share of transients.

 The experimental data on the desalination of a NaCl solution (0.1 mol / L) on a pulsed current and on an asymmetric alternating current (according to the prototype) are given in the table.

Таким образом, использование импульсного тока с частотой импульсов 50-10³ Гц дает наибольший эффект по снижению расхода электроэнергии и производительности процесса обессоливания.As can be seen from the table, when switching from an asymmetric to a pulsed alternating current, the energy consumption decreases by 1.2-10 times, and the ion flux through the membranes increases by more than 10 times. The value of the ion flux intensity according to the prototype (0.01 g / l • h) is defined as the ratio of the difference between the concentration of NaCl in the initial solution (200 mg / l) and the filtrate (10 mg / l) to the time of processing the solution (24 hours)

Thus, the use of pulsed current with a pulse frequency of 50-10 ³ Hz gives the greatest effect on reducing power consumption and the performance of the desalination process.

Sources of information
1. A.S. N 1398884, B 01 D 13/02, 1988.

 2. A.S. N 1507413, B 01 D 13/02, 1989.

 3. Patent 20832268, B 01 D 13/02 1997.

Claims (1)

The method of desalting water by electrodialysis in an electrodialyzer with cation and anion exchange membranes, characterized in that the process is conducted on a pulsed current with a pulse frequency of 50 - 10 ³ Hz.

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