Chloralkali membrane process

The chloralkali electrolysis process is by far the most important source of electrolytically generated hydrogen because hydrogen from alkaline or membrane water electrolysis usually cannot compete with hydrogen from steam reforming followed by shift reaction and PSA purification and therefore is not performed on a large scale (62, 40). 

Production of caustic soda solution. In 1998, the worldwide production capacity was about 54 million tons per year. Ca. 96-98% of this amount is produced by chloralkali electrolysis [313). The three processes are described in detail in chapter 5 (Mercury Cell Process), chapter 6 (Diaphragm Process) and chapter 7 (Membrane process), a comparison of the relative qualities is given in chapter 9. 

A mixture of hydrogen and chlorine gas, eventually in combination with air, can be very explosive if one of the components exceeds certain limits. In chlorine production plants, based on the electrolysis of sodium chloride solutions, there is always a production of hydrogen. It is, therefore, essential to be aware of the actual hydrogen content of chlorine gas process streams at any time. There are several places in the chlorine production process where the hydrogen content in the chlorine gas can accumulate above the explosion limits. Within the chloralkali industry, mainly two types of processes are used for the production of chlorine—the mercury- and the membrane-based electrolysis of sodium chloride solutions (brine). 

This process has been used to make functionalized perlluorovinyl ethers [e.g., F2C = CF0CF2CF(CF3)0CF2CF2S02F] which are copolymerized to form fluorinated membrane materials (Nafion, Flemion), which arc important in chloralkali electrolysis. ... 

To the extent that it is discernible in the products and processes, appropriate aspects have been incorporated in the revision, for example see membrane technology in the chloralkali and hydrochloric acid electrolysis. 

F. Hine and A.J. Acioli Maciel,... the Amalgam Cell and the Membrane Cell Processes for Chloralkali Production,/. Appl. Electrochem. 22, 699-704 (1992). 

Figure 1. Basic operational process for membrane chloralkali cells.

In 2000, 45 Mt of CI2 was manufactured by the chloralkali process this represents 95% of the global supply. The main producers are the US, Western Europe and Japan. Whereas the Japanese chloralkali industry operates almost entirely with the membrane cell, the US favours use of the diaphragm cell, and just over half of the Western European industry retains use of the mercury cell. On environmental grounds, the chloralkali industry is being pressured to replace mercury and diaphragm cells by the membrane cell. This is not the only environmental concern facing the industry demand for CI2 has fallen in the pulp and paper industry and in the production of chlorofluorocarbons, the latter being phased out as a result of the Montreal Protocol for the Protection... 

Figure 9.24 The chloralkali process (a) membrane cell (b) the membrane is permeable only to Na" " ions, leading to segregation of Cr and OH in the anode and cathode compartments...

Membrane Cell Process. Less than 5% of chloralkali production in Canada is done using the membrane cell process. In this process, a cation-permeable ion-exchange membrane separates the anode from the cathode and only sodium ions and a little water can pass through the membrane. The brine is dechlorinated and recirculated, thus requiring solid salt for resaturation as in the mercury process. The chloride content in the caustic soda is similar to that in the mercury process. The chlorine gas is purified either by liquefaction or evaporation because it contains some oxygen. 

Fedkiw Jr PS. Preparing in situ electrocatalytic films in solid polymer electrolyte membranes, composite microelectrode structures produced thereby and chloralkali process utilizing the same. United States patent US 4959132. 1990 Sep 25. 

There are three major processes used for chloralkali production. They are mercury, diaphragm, and membrane and differ in the type of cell used. In the mercury cell process, the cathode is a mercury film. This process was... 

A current industrial application of ionomers is their use as permselective membranes for the chloralkali process. The ionomers used in these membranes are based on a poly(tetrafluoroethylene) backbone containing occasional ether linkages with ionic side groups. These are based upon either sulfonate or carboxylate salts. 

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