RU2398618C2 - Method of concentrating electrolyte solutions and electrodialyser to this end - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to method of concentrating electrolyte solutions by processing them in electrodialyser that comprises vertical alternating cation- and anion-exchange membranes that form desalting flow chambers accommodating gaskets of frameless structure and static chambers of concentration accommodating gaskets of frame structure. Slit-like groove are made in bottom part of the latter. Electrodialyser additionally incorporates a pan tightly jointed with membrane lower edges by sealing rubber lining. Note here that said pan has one or several air feed unions or those to feed gas inert with respect to concentrated gas solution. Said unions are arranged in the pan face wall. It comprises also solution discharge union arranged at the pan bottom. Pressure equal to 30-120% of desalting chamber pressure is maintained in concentration chambers.

EFFECT: new method of electrolyte solution concentration.

1 ex, 1 tbl, 1 dwg

Description

The invention relates to techniques for electrodialysis, and in particular to a method for producing concentrated solutions and the design of an electrodialyzer for its implementation, and can be used in the chemical and nuclear industries, in hydrometallurgy, analytical chemistry, in wastewater treatment with utilization of the components contained in them, and other industries, where electrolyte concentration is required.

Known electrodialyzer, including vertically arranged alternating cation exchange and anion exchange membranes, separated by gaskets forming flowing desalination chambers and non-flowing concentration chambers. In the concentration chambers of the gasket, a frame design is made, in the lower part of which slotted grooves are located [1].

The disadvantage of this electrodialyzer is the complexity of the design of the gaskets of the concentration chambers and the possibility of deflection of the membranes in the concentration cavity, which reduces the reliability of the apparatus.

A known method of concentrating electrolyte solutions in an electrodialyzer, including alternating cation exchange and anion exchange membranes, forming flow-through desalination chambers and non-flow concentration chambers. The gaskets in the desalination chambers are made of a frameless design, the gaskets in the concentration chambers are made of a frame design, and the slotted grooves in the gaskets of the neighboring concentration chambers are offset from each other. The initial solution is not supplied to the electrodialyzer concentration chambers, and water is transferred to them as part of the solvation shells of cations and anions [2].

The disadvantage of this method is that when processing concentrated aqueous and non-aqueous solutions, the hydrodynamic permeability of ion-exchange membranes increases sharply. This leads to the fact that, due to the pressure difference, the barofiltration flow of the solvent directed from the desalination chambers to the concentration chambers increases, which reduces the maximum possible salt content of the concentrate.

The technical task of the invention is to develop a method for concentrating solutions and the design of the electrodialyzer, which can significantly increase the degree of concentration of solutions.

The technical result is achieved by the fact that in the method of concentrating electrolyte solutions by treating them in an electrodialyzer, including vertically arranged alternating cation exchange, anion exchange membranes, forming flow-through desalination chambers, in which gaskets of a frameless structure are located, and non-flowing concentration chambers in which gaskets of a frame structure are located, in the lower part of which slotted grooves are made, the concentration process is carried out in an electrodialyzer, in addition equipped with a tray, hermetically connected to the lower sides of the membranes using a rubber gasket and having one or more air inlets or inert gas in relation to the concentrated solution located in the end wall of the tray, and a solution outlet fitting located in the bottom of the tray and in the chambers concentration support pressure equal to 30-120% of the pressure in the desalination chambers.

The drawing shows a schematic representation of an electrodialyzer for concentration of solutions, including vertically arranged alternating cation exchange 1, anion exchange 2 membranes, gaskets of a frameless structure 3, gaskets of a frame structure 4, forming flowing desalination chambers 5 and non-flowing concentration chambers 6. Gaskets of a frame structure 4 have in the lower part slotted grooves 7. The electrodialyzer is additionally equipped with a pallet 8. The fitting 9 is used to discharge air by the compressor or inertly in relation to the concentrated gas solution and the creation of excess pressure. The presence of two or more fittings 9 provides a more uniform distribution of gas in the sump 8. The fitting 10 is located in the bottom of the sump 8 and serves to bypass the resulting concentrate. The tray 8 is hermetically connected to the lower sides of the cation exchange 1 and anion exchange 2 membranes using a rubber gasket 11, which does not allow the resulting concentrated solution to leave the concentration chamber 6, while the pressure in them does not compensate for the external pressure. Thus, by adjusting the pressure in the pan 8, it is possible to increase the excess pressure in the concentration chambers 6. The gas “cushion” formed in the pan 8 leads to a rupture of the liquid connection between the solution in the concentration chambers 6 and the bottom of the pan 8. The resulting concentrate is removed from the concentration chambers 6 separate drops. This ensures the breaking of current lines and increases the reliability and electrical safety of the electrodialyzer of the proposed design, while significantly increasing the degree of concentration of solutions.

Example. To confirm the achievement of the technical task, we conducted the process of concentration of a solution of lithium chloride in aqueous and aqueous-organic solutions containing dimethylacetamide and isobutyl alcohol in an electrodialyzer, including fifty-five paired concentration chambers 6 and desalination chambers 5 formed by alternating cation exchange membranes 1 of MK-40 brand and anion-exchange membranes 2 of the MA-41 brand and gaskets of the frame structure 4 and frameless structure 3.

The table shows the results of the study obtained by concentrating lithium chloride from aqueous-organic solutions (DMAA - 27.8%; IHD - 28.0%; water - 44.2%, lithium chloride - 0.85%) with a different value of compensating pressure. The pressure in the desalination chambers of 5 electrodialyzers was kept constant and amounted to 1.0 atm; the voltage on one paired chamber was 6.2 V.

Dependence of the composition of the concentrate on the compensating pressure in the pan P _comp , atm P _comp / P ₀ % LiCl,% Water% DMAA,% CHD,% η,% Q, kWh / kg 0.0 0 1.6 41.1 29.3 27.7 84.6 4.6 0.1 10 1.9 41.6 28.3 27.1 71.2 4.8 0.3 33 4.3 45.0 26.7 23.8 69.9 5.8 0.7 70 6.9 49.9 24.6 18.4 67.7 6.4 0.9 90 10.6 55.5 21.3 10.1 44.3 8.8 1.0 one hundred 12.1 61.7 19.8 6.3 30.2 12.9 1.2 120 14.2 70.1 17.3 5.1 25.1 17.3 1.5 150 No concentrate formed

where P ₀ , ATM - the average pressure in the desalination chambers;

P _comp , atm — compensating pressure in the concentration chambers;

P _comp ,% - compensating pressure in% of the pressure in the desalination chambers;

η,% - current output;

Q, kWh / kg - energy consumption per concentration of 1 kg of lithium chloride.

The table shows that with an increase in the compensating pressure, the transfer of solvent from desalination chambers 5 to concentration chambers 6 decreases with a slight decrease in electromigration transfer of salt ions (lithium chloride), which generally causes an increase in the content of lithium chloride in the concentrate. A noticeable effect is manifested at a compensating pressure of 0.3 atm, which is 33% of the average pressure in the desalination chambers 5. At a compensating pressure greater than 1 atm, the barofiltration solvent flow reverses and is directed from concentration chambers 6 to desalination chambers 5. At a pressure 1.5 atm barofiltration flow becomes larger than the electroosmotic transfer of water to the concentration chamber 6 and the concentration process stops.

In the optimal range of the compensating pressure from 33 to 120%, it is possible to increase the lithium chloride content in the concentrate by almost an order of magnitude, while the current efficiency decreases only 3 times, and the energy consumption for concentration decreases 4 times. In addition, another additional positive effect was discovered associated with an increase in the content of organic solvents DMAA and IHD in a desalted solvent. This allows you to reduce energy costs and simplify the process of obtaining pure solvents by rectification.

Literature

1. A.S. USSR No. 587960, MKI B01D 13/02.

2. A.S. USSR No. 845312, MKI B01D 13/02.

Claims (1)

The method of concentration of electrolyte solutions by processing them in an electrodialyzer, including vertically arranged alternating cation exchange, anion exchange membranes forming flow-through desalination chambers, in which there are gaskets of a frameless structure, and non-flowing concentration chambers in which gaskets of a frame structure are located, in the lower part of which slotted grooves are made characterized in that the concentration process is carried out in an electrodialyzer additionally equipped with a tray, ge metically connected to the lower sides of the membranes using a sealing rubber gasket and having one or more air inlets or gas inert with respect to the concentrated gas solution located in the end wall of the pan, and a solution outlet pipe located in the bottom of the pan, and in the concentration chambers maintain pressure equal to 30-120% of the pressure in the desalination chambers.

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