RU2380145C2 - Multichamber electrodialysis apparatus for deep demineralisation - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to electrodialysis equipment. The multichamber electrodialysis apparatus for deep demineralisation consists of electrode chambers, alternating cation-exchange and anion-exchange membranes which form desalting and concentration cells, in which there are granules of cation-exchange and anion-exchange resin. Granules of the cation-exchange resin are arranged into a single grain layer and touch the cation-exchange membrane. Granules of the anion-exchange resin are arranged into a single grain layer and touch the anion-exchange membrane. Between granules of the cation-exchange resin and granules of the anion-exchange resin there is a mesh pad made from non-conducting material whose threads form cells. Granules of the cation-exchange and anion-exchange resin have diametre which is greater than the dimension of the cells of the mesh pad and less than the total dimensions and diametre of the threads of the mesh pad.

EFFECT: increased degree of purity of water, including more effective removal of polysilicic acid, carbonic acid and other weakly-ionised compounds.

2 dwg, 1 tbl, 2 ex

Description

The invention relates to techniques for electrodialysis, in particular to multi-chamber electrodialyzers with an ion-exchange nozzle in desalination chambers, and can be used to produce high-quality deionized and demineralized water, in processes of concentration of trace amounts of matter, to remove weakly ionized bases and acids, etc.

Known electrodialyzer, consisting of alternating cation-exchange and anion-exchange membranes forming desalination and concentration chambers, and frames located between them, filled with a multilayer of a mixed layer of ion exchangers [1].

The disadvantage of this design of the electrodialyzer is its low productivity. This is explained by the random arrangement of granules of cation-exchange and anion-exchange resins, which leads to the appearance of both “useful” bipolar contacts between cation exchange resin and anion exchange resin, on which electrosorption takes place, and “harmful” bipolar contacts, on which ion “adsorbed” ion exchangers into the solution phase . In addition, the significant thickness of the frames filled with a polylayer of cation exchanger and anion exchanger leads to an increase in energy consumption, and existing antipolar contacts between ion exchangers and membranes lead to screening of part of the membrane surface.

Known electrodialyzer for desalination of aqueous solutions, containing a housing with electrodes located inside it, between which are placed alternating anion-exchange and cation-exchange membranes, forming concentration chambers and desalination chambers with an ion-exchange filler placed in them, equipped with permeable gaskets placed inside the chambers parallel to the membranes. The filling is made of an anion exchange filler placed between the anion exchange membrane and the permeable gasket, and a cation exchange filler placed between the cation exchange membrane and the water permeable gasket. Watertight gaskets can be equipped with differently located partitions [2].

In the specified electrodialyzer, a number of design flaws [1] are overcome due to the presence of “harmful” bipolar contacts cation exchange resin / anion exchange resin and membrane / ion exchange resin. At the same time, a significant intermembrane distance is maintained, due to the presence of organic glass frames, inside of which watertight gaskets are installed, equipped with partitions located on both sides of the latter. In the electrodialyzer of this design, a layer of a cation exchange filler located at the cation exchange membrane and an anion exchange filler at the anion exchange membrane are alternately washed. The desalination process consists of the electrosorption of salts from a solution by granular cation exchange resin and anion exchange resin and their removal through membranes to concentration chambers. Necessary and sufficient conditions for the operation of the electrodialyzer are the presence of equipolar contacts of the membranes with the corresponding granules of ion exchangers and antipolar contacts of anion exchange resin / cation exchange resin in the center of the desalination chamber. In this case, only two orderedly arranged granules of cation exchanger and anion exchanger work effectively in the direction of current flow (perpendicular to the electrodes). The multilayer granules of the ion exchanger, perpendicular to the electrodes, is only an ion transport medium and is essentially ballast. Ballast grains of ion exchanger located within the framework of an electrodialyzer increase energy consumption and reduce specific productivity.

The technical task of the invention is to develop the design of an electrodialyzer, which allows to increase the degree of water purification, including more fully remove polysilicic acid, carbonic acid and other weakly ionized compounds, as well as increase the performance of the electrodialyzer and reduce the energy consumption for the process of demineralization of water.

The technical result is achieved by the fact that in a multi-chamber electrodialyzer of deep demineralization, consisting of electrode chambers, alternating cation-exchange and anion-exchange membranes forming desalination and concentration chambers, in which granules of cation-exchange and anion-exchange resins are located, granules of cation-exchange resins are located in a layer of one grain of cation exchange membrane, the granules of the anion-exchange resin are located in a layer of one grain and are in contact with the anion-exchange membrane, between the granules mi cation exchange resin and anion exchange resin beads mesh pad is located a non-conductive material, the filaments which form the cell, wherein the cation exchange granules and of anion exchange resins have a diameter greater than the size of the mesh pad cell and a smaller cell size and the total strand diameter mesh pad.

Figure 1 presents a diagram of the proposed electrodialyzer, consisting of an anode 1, a cathode 2, alternating anion-exchange membranes 3, cation-exchange membranes 4, forming desalination chambers 5 and concentration chamber 6. Granules of cation-exchange resin 7 are located in desalination chambers 5 between the cation-exchange membrane 4 and the mesh gasket 8. Granules of anion exchange resin 9 are placed in desalination chambers 5 between the anion exchange membrane 3 and the mesh gasket 8. Granules of cation exchange resin 7 and granules of anion exchange resin 9 laid in a single grain layer and through the cells of the mesh pad 8 are in contact with each other, this eliminates unwanted contacts cation exchange membrane 4 - anion exchange resin 9 and anion exchange membrane 3 - cation exchange resin 7, and the area where water is dissociated on antipolar granules of resins 7 and 9, is shifted to the center of the desalination chambers 5.

The granules of the cation exchange resin 7 and the granules of the anion exchange resin 9 touch each other, forming a bipolar boundary at which water is dissociated. In this case, the electromigration flows of H ⁺ and OH ^- ions are directed respectively to the cation exchange 4 and anion exchange 3 membranes, which eliminates the undesirable phenomenon of depression of electrodiffusion of salt ion flows, which reduces the value of ion flows through the membranes. In addition, proton and hydroxyl ions formed on the bipolar boundary of the granules replace salt ions in resins 7 and 9, converting them to H ⁺ and OH ^- - form, which includes an additional ion-exchange mechanism of sorption of ions from solution by resin granules.

Figure 2 schematically shows a top view of a mesh strip 8 formed by threads 10 of non-conductive material, in the cells of which are granules of cation exchange resin 7 and granules of anion exchange resin 9, which are not visible in figure 2, because located under the granules of cation exchange resin 7. The diameter of the granules of cation exchange resin 7 and the granules of anion exchange resin 9 should be larger than the mesh size of the mesh strip 8 (which excludes their contact with the antipolar membrane), but should not exceed the total cell size and the diameter of the filament 10 of the mesh strip 8 to exclude mutual technical deformation and displacement of adjacent granules of resins 7 and 9.

Example 1. The electrodialyzer of the proposed design was assembled from fifteen cation exchange membranes 4 grade MK-40 and fifteen anion exchange membranes 3 grade MA-40, an area of 4 dm ² each. A binary layer of ion-exchange resins consisting of granules of cation exchange resin 7 of grade KU-2 and granules of anion-exchange resin 9 of grade AB-17 was placed in desalination chambers 5. As a mesh strip 8, a kapron mesh of the grade 16K OST 17-46-82 with a mesh size of 0.48 mm was selected. The diameter of the filaments 10 is 0.14 mm

The particle size distribution of the cation exchange resin 7 and the granules of the anion exchange resin 9 is 0.50-0.62 mm Their volume ratio is 1: 1. The intermembrane distance in the desalination chamber 5 is 0.9 mm, in the concentration chamber 6 - 0.5 mm.

The electrodialyzer was tested in a circulating mode on partially desalinated tap water in the city of Krasnodar with a specific electrical resistance of 0.25 MΩ · cm. The recirculation rate of purified water is 110 l / h. The voltage at the electrodialyzer was kept constant and amounted to 15 V per pair chamber, the current density varied from 147 to 233 mA. The process was carried out until the maximum possible electrical resistance of water. Additionally, the content of polysilicic acids in the source and demineralized water was measured.

Example 2. Electrodialyzers with a binary layer of ion exchangers and two internal steps with a total working path length in desalination chambers of 80 cm as part of a pilot electrodialysis complex for producing ultrapure water for a power system were tested at the Armavir CHPP. The apparatus with an electrode area of 16 dm ² had 80 paired chambers, with the first section made of MK-40 and MA-40 membranes, and the second section of MK-40 and MA-41 membranes. The electrodialyzer was tested at a flow rate of desalination chambers of 380 l / h and concentration chambers of 60 l / h, a voltage of 400 V and a current strength of 0.8 A.

Partially demineralized water with a specific electrical resistance of 0.01-0.017 MΩ · cm was supplied to the electrodialyzer, which is close to the specific resistance of the water supplied for cleaning to a known electrodialyzer (prototype). The concentration of polysilicic acids was also determined in the source and purified water.

The results of the known electrodialyzer and the proposed are presented in the table.

Table The results of comparing the work of electrodialyzers (prototype and proposed) Measured parameters Prototype Proposed with gaskets without partitions with gaskets and partitions Example 1 Example 2 circulation mode direct-flow mode circulation mode direct-flow mode The achieved resistivity of demineralized water, MΩ · cm 0.24 1.39 4.0 1,2 Power consumption for desalination of 1 liter of solution to resistivity, 1.0 MΩ · cm, W · h / l 21.7 8.0 0.6 0.84 The performance of the electrodialyzer with a specific resistance of demineralized water to 1.0 MOhm · cm, l / h 2,4 7.3 BY 380 The concentration of polysilicic acids, mg / l (source water) Not determined Not determined 7.88 21.0 The concentration of polysilicic acids, mg / l (purified water) Not determined Not determined 0.5 1,6

As can be seen from the table, the proposed electrodialyzer provides an increase of 50 times the specific productivity and a decrease of more than an order of specific energy consumption. In addition, almost an order of magnitude reduction is achieved in the content of polysilicic acids.

Bibliography

1. Grebenyuk V.D., Gnusin N.P. Factory Laboratory, 1966, 32, 10.1290.

2. USSR author's certificate No. 1119708, 10.23.84, MKI B01D 13/02.

Claims (1)

A multi-chamber electrodialyzer of deep demineralization, consisting of electrode chambers, alternating cation-exchange and anion-exchange membranes, forming desalination and concentration chambers, in which granules of a cation-exchange and anion-exchange resin are located, characterized in that the granules of the cation-exchange resin are located in a layer of one grain and are in contact with the cation-exchange membrane from the cation anion-exchange resins are located in a single grain layer and are in contact with the anion-exchange membrane, between the granules of the cation-exchange cm A mesh gasket of non-conductive material, the filaments of which form cells, is located with granules and anion-exchange resins, the granules of the cation-exchange and anion-exchange resins having a diameter larger than the mesh size of the mesh gasket and smaller than the total mesh size and the diameter of the mesh gasket.

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