Chloralkali diaphragm process

This hydrogen is, however, mostly used in house. Hydrogen is also produced in other petrochemical and chemical processes (synthesis of olefins, ethyne, styrene, acetone). Coke oven gas contains over 50 volume % of hydrogen, from which it can be isolated. Finally hydrogen occurs as a valuable byproduct in chloralkali-electrolysis (directly with the diaphragm process or indirectly with the amalgam process and hydrochloric acid hydrolysis) see Section 1.7.3.3. The electrolysis processes account for less than 5% of the worldwide production of hydrogen. 

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. 

Mercury is emitted from the mercury cell process from ventilation systems and by-product streams. Control techniques include (1) condensation, (2) mist elimination, (3) chemical scrubbing, (4) activated carbon adsorption, and (5) molecular sieve absorption. Several mercury cell (chloralkali) plants in Japan have been converted to diaphragm cells to eliminate the poisonous levels of methyl mercury found in fish (9). 

Any of the products of brine electrolysis, chlorine, sodium hydroxide, and hydrogen can be hazardous if released. When releases do occur, it is usually from process upsets or breakdowns, which may be minimized by the construction of fail-safe plants, proper maintenance, and by safe transport and storage practices. Probably of greater long-term concern is the mercury loss experienced through the process streams of a mercury cell chloralkali operation. These losses can also carry over to the products of the diaphragm cell, even though this does not use mercury, if a common brine well or common salt dissolver is used for both sets of 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... 

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... 

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