RU2064978C1 - Filtering diaphragm for chlorine electrolyzer - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: filtering diaphragm is made of two layers one of which turned to cathode has, wt.-%: fibers prepared of inorganic dielectric substance 10-40; ; polymer 4-10, and asbestos fiber - the rest. Diaphragm can contain an intermediate layer. Invention can be used for chlorine and alkali production by electrochemical method. EFFECT: increased effectiveness of diaphragm. 5 tbl

Description

 The invention relates to the chemical industry and can be used in the production of chlorine and alkali by the electrochemical method in electrolytic cells with a solid cathode and a diaphragm.

 Known diaphragm (1), consisting of asbestos fibers (up to 90%) and fibers from inorganic substances that are non-conductive and corrosion resistant, including fiberglass. The diaphragm layer is fixed on two or one side with fine-mesh nets to fix the specified thickness of the filtering partition (diaphragm), since in the manufacture without nets the diaphragm thickness will vary from 2 to 6 mm. The diaphragm may also contain a polymeric substance, including polytetrafluoroethylene fibers.

This diaphragm allows you to get chlorine and alkali with a high content of the target product with a minimum interelectrode distance and with a high current density reaching 20-60 A / DM ² . However, during electrolysis with a known diaphragm, an increased energy consumption occurs, and the chlorate content in alkali reaches a concentration of sodium hydroxide of 140 g / l of 0.1-0.2 g / l. In addition, the chlorine content in chlorine gas does not exceed 98.5 vol.

 The objective of the invention is to increase the purity of the resulting chlorine and alkali products and reduce the energy consumption for electrolysis.

 The problem is solved in that the filtering diaphragm containing asbestos fibers, fibers of an inorganic non-conductive substance and a fluorine-containing polymer, is made of at least two layers, of which the layer facing the cathode (cathode) contains (wt.): Inorganic non-conductive fibers 10-40% fluorine-containing polymer 4-10% the rest is asbestos. The layer facing the anode (anode) contains (wt.): Polymer 6-12% and the rest is asbestos. The proposed diaphragm may include an intermediate layer, which contains (wt.): Fibers from non-conductive inorganic substances 1-5% fluorine-containing polymer 4-10% asbestos the rest. The mass ratio for the layers facing the anode, the intermediate layer and the layer facing the cathode is 1: (≅ 3) :( 6-10), respectively. Such a layered structure allows to obtain a diaphragm with desired properties. So, for example, with a significant intensification of the electrolysis process, such a filtering diaphragm is needed that would provide a higher permeability of the layers in combination with an increased separation ability of the diaphragm and a decrease in voltage on it. It is not possible to achieve this by directly reducing the thickness of the asbestos diaphragm, since the heterogeneity of the electrolyte filtration front through the porous septum sharply increases. The addition of non-asbestos fibers in one or several layers makes it possible to control the permeability of the porous layer and increase the separation ability of the filtering diaphragm while reducing the voltage on the electrolyzer or achieving the same voltage as on the known diaphragm, but with an interelectrode distance of 12 mm instead of 6 mm. Examples of diaphragm tests for the proposed solution are presented in tables 1-5, where, along with the voltage values on the electrolytic cells, data are presented on the quality of the electrolytic alkali and the composition of chlorine gas.

 Example 1

A two-layer diaphragm from asbestos-containing suspensions is deposited on the mesh cathode of a laboratory vertical electrolyzer. The suspension for the preparation of the first layer on the cathode side contains (wt.): 8% fluorine-containing polymer F-4MB (a) (copolymer of hexafluoropropylene with tetrafluoroethylene), hydrophilized with a wetting agent, 8% fiberglass, the rest is asbestos fiber. The suspension for the deposition of the second layer facing the anode contains (wt.): 10% polymer F-MB (a) and 90% asbestos fibers. The suspension is prepared on the basis of electrolytic alkali composition: sodium hydroxide 140 g / l, sodium chloride 170 g / l, the rest is water. The deposition of the first layer is carried out with an increase in vacuum from 0 to 400 mm Hg. during the deposition of the second layer, a vacuum of 400-450 mm RT. Art. Precipitation is carried out to a ratio of layers (anodic and cathodic) 1: 8. Then heat treatment is carried out to a temperature of no higher than 300 ^o C. The diaphragm installed in the electrolyzer is tested in a 300 g / L NaCl solution. The composition of the prepared diaphragm and the test results are presented in table 1. The tests were carried out in a laboratory electrolyzer with an interelectrode distance of 12 mm current density of 20 A / dm ² , the area of the anode, cathode and diaphragm 50 cm ² .

 Example 2

 The diaphragm is manufactured and tested in accordance with Example 1, but in experiments 2-5 (items 2-5) the fiberglass content is changed in the ranges of 10-50% (wt.), And in experiments 6-10 the fiberglass concentration in the cathode layer in the intervals of 8-45% (wt.) at a polymer concentration of 10% (wt.), in experiments 11-15 at a polymer concentration of 4% (wt.). The composition of the cathode layer of the diaphragm and the test results are shown in table 1.

 Example 3

 The diaphragm is fabricated as described in Example 1, but when the glass fiber content in the cathode layer is 10 and 30% (wt.), And the polymer content is changed in the range of 2-12% (wt.) (Table 2).

 Example 4

 The diaphragms are manufactured and tested according to Example 1, but at the same time (pp. 26-30), the polymer content in the anode layer is changed in the range of 5-12.5% (wt.). The mass ratio of the anode and cathode layers is 1: 9. The cathode layer contained 5-6% (wt.) Polymer and 25-30% (wt.) Fiberglass (table 3).

 Example 5

 A three-layer diaphragm is fabricated and tested (as in Example 1), the intermediate layer being precipitated under a vacuum of 400-420 mm Hg. and the anode at 420-450 mm Hg The solution of electrolytic alkali for the preparation of the pulp of the intermediate layer is the same as in example 1. The ratio of the masses of the layers from the anode to the cathode is 1: 2: 8. The cathode layer contains 9-10% (wt.) Polymer and 20% (wt.) Fiberglass, the anode layer contains 10% (wt.) Polymer.

 In p.p. 31-35 the intermediate layer contains 6% of the polymer, and the content of glass fiber in it is changed from 0.5 to 6% (wt.). In p.p. 36-40 the intermediate layer contains 4% (wt.) Silica fiber, and the polymer content is changed in the range of 3-12 wt. (table 4).

 Example 6

 A three-layer diaphragm is manufactured, as in example 5, but by changing the mass ratios of the layers according to table 5, the cathode layer containing (wt.): 6-8% polymer, 20% glass fiber, the rest is asbestos. The intermediate layer contains (wt.): 6% polymer, 4% fiberglass, the rest is asbestos. The anode layer contains (wt.): 10% of the polymer mixed with asbestos (the rest).

 Example 7

The diaphragm is manufactured according to a known method and tested simultaneously under comparative conditions with the diaphragm of Example 1 in laboratory vertical electrolyzers. When the interelectrode distance on the electrolytic cells was 6 mm and the current density was 40 A / dm ^{2, the} voltage on the electrolytic cells was 3.75 and 3.40 V, respectively, for the known and proposed diaphragms; accordingly, the sodium chlorate content in catholyte is 0.15 and 0.05 g / l (at a concentration of sodium hydroxide in catholyte 140 g / l).

 Example 8

 The diaphragm is manufactured according to a known method and tested simultaneously under comparative conditions with the diaphragm of Example 1 in laboratory vertical electrolyzers. The diaphragm consists of a fibrilized fibrous fluoropolymer F-4 instead of asbestos fibers, the rest of the composition is the same as in example 7.

 The test results in electrolysis for the known and proposed diaphragms, respectively: the sodium chlorate content in catholyte is 0.15 and 0.05 g / l (at a concentration of sodium hydroxide in catholyte 140 g / l). The voltage across the electrolysers was 3.75 and 3.35 V, respectively, for the known and proposed diaphragms.

 The results presented in tables 1-5 and in examples 7 and 8 confirm the validity of the ranges of component concentrations and layer ratios selected for the proposed solution, since for the limited regions the optimal structures of layered diaphragms were obtained, which allow the electrolysis process to be performed with lower voltages and with higher purity target products. Since the proposed diaphragm in comparative examples 7 and 8 at an interelectrode distance is half that of examples 1-6, and twice as large as the current density shows positive results, it should be concluded about its advantage over the known diaphragm.

Claims (2)

 1. The filtering diaphragm for a chlorine electrolyzer, including asbestos fibers, fibers from non-conductive substances and fluoropolymers, characterized in that it is made of layers, of which the layer facing the cathode contains asbestos fibers, fibers from non-conductive substances and fluoropolymer in the following ratio of components, wt. Non-conductive fiber 10 40
Fluoropolymer 4 10
Asbestos fiber
and the layer facing the anode contains a fluoropolymer and asbestos fiber in the following ratio of components:
Fluoropolymer 6 12
Asbestos fiber
2. The diaphragm according to claim 1, characterized in that the ratio of the masses of the layers from the anode is 1 (6 10).  3. The diaphragm according to claim 1, characterized in that it is equipped with an additional intermediate layer, which contains fibers of non-conductive substances, asbestos fibers and a fluoropolymer in the following ratio of components, wt. Non-conductive fiber 1 5
Fluoropolymer 4 10
Asbestos fiber
4. The diaphragm according to claim 3, characterized in that the ratio of the masses of the layers from the anode is 1 (≅ 3) (6 10).

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