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3.4. FEM-7 module, devices and technologies on its basis, RPE reactors with FEM-7 modules

• V.M. Bakhir, Yu.G. Zadorozhny, B.I. Leonov, S.A. Panicheva. Electrochemical modular cell for treatment of water solutions, a device for obtaining products of anodic oxidation of alkaline or alkaline-earth chloride solution. RF Patent # 2176989. Filed on 01.11.2000, published on 20.12.2001.

C o m m e n t s: FEM-7 flow-through electrochemical modular reactor (FEM-7 module) is meant for realizing ion-selective electrolysis with diaphragm (ISED) and can be used in the range of electrolyte solution concentration from 0.2-0.3 to 2-3 mol/l and higher. FEM-7 modules can be used in various-purpose electrochemical devices both as individual devices (FEM-7 reactor) and as a combination of FEM-7 modules connected hydraulically in parallel – RPE-07 reactor.

A distinctive feature of FEM -7 module is the chamber of inner electrode (anode) that can operate under pressure up to 2 kgf/cm 2 at a very low rate of filtrational liquid transfer through the diaphragm, and in which conditions exist for intensive internal electrolyte circulation, as well as its heat exchange with cathodic chamber electrolyte.

FEM-7 modules are manufactured by the Russian company “Laboratory of Electrotechnology” founded by the patent authors V.M. Bakhir and Yu.G. Zadorozhny, in various modifications, which guarantee the most optimal parameters of electrochemical exposure as applied to various technological processes and electrochemical systems. The main differences between FEM-7 modifications are in the type of anodic electrode coating of central electrode, as well as in the shape and configuration of connections for initial solutions' supply and electrolysis products' discharge.

The advantage of FEM-7 modules working on concentrated electrolyte solutions, over commercial diaphragm-type or membrane electrolyzers is the possibility of supplying the final consumer with required products (chlorine, chlorine dioxide, hydrochloric acid, caustic soda, sodium hypochlorite, hypochlorous acid) synthesized on-site in required quantities in compact-size economic devices, with minimal requirements to the quality of initial solutions and with minimal labor input, time and chemicals consumption.

Development of ISED technology allowed designing commercial modular compact-size devices of ECOCHLOR type for synthesis of gaseous chlorine and concentrated (150-170 g/l) sodium chloride solutions. Gaseous chlorine output of one module of ECOCHLOR device is 2.0 kg/h , with dry sodium chloride consumption being 3.4-3.5 kg/h and consumed electric power being 4.0-5.0 kW.

Another family of devices based on ISED technology includes OXYTRON-type devices producing sodium hypochlorite solution of 30 to 100 g/l concentration, and common salt consumption varying from 2.0 to 2.5 kW / h per 1 kg of active chlorine.

ISED technology is implemented not only in the processes of final product synthesis, but also permits to produce electrochemically activated antimicrobial solutions with high specific content of oxidants.

For this purpose, AQUATRON-type devices with high AN-type anolyte output have been developed. AQUATRON devices make it possible to realize most efficiently processes associated with AN anolyte application in industrial conditions, i. е ., they are capable of non-stop long-term operation with short breaks (no longer than 30 minutes a day) to clean electrochemical reactors. Fundamental distinction of AQUATRON-type devices from STEL-type devices is application in them of ISED technology for AN anolyte production. In AQUATRON devices, before coming into contact with humid gaseous oxidant mixture, water is saturated with hydrogen and simultaneously рН value changes from 7 to 11 due to mixing with catholyte, after which formed insoluble hydroxides of heavy metals, excessive amount of catholyte and hydrogen are eliminated in flotation reactor.

ISED technology also permits production of electrochemically activated antimicrobial anolyte of ANK type with high specific oxidant content in OXYMED family devices developed for the purpose, which are capable of producing large quantities of ANK anolyte (from 200 to 1000 liters per hour for one device). OXYMED devices endure continuous operation for many days, with short breaks (no longer than 30 minutes a day) to clean electrochemical reactors. Fundamental feature distinguishing OXYMED-type devices from AQUATRON- and STEL-type devices is combination in one devices of RPE-03 reactors with FEM-3 modules, and RPE-07 reactors with FEM-7 modules. RPE-03 reactors are meant for electrochemical water treatment with the purpose of modifying its structure and providing the best conditions for dissolution and stabilization of gaseous phase followed by introduction of a humid gaseous mixture of oxidants produced in RPE-07 reactor from sodium chloride solution of 50 – 150 g/l concentration.

Further development of ISED technology makes it possible to expand the scope of its application and offer for practical use cost-effective, highly-productive and safe technological processes of synthesis of pure gases: ozone, hydrogen, oxygen, chlorine dioxide, as well as concentrated solutions of sulfuric, hydrochloric, nitric acids, concentrated solutions of sodium and potassium hydroxides.