Ammonia synthesis water electrolysis

There are basically three processes in usage today for the production of hydrogen or ammonia synthesis gas Steam Reforming for the conversion of light hydrocarbons from natural gas to straight run naphthas Partial Oxidation for heavy hydrocarbons and coal and Electrolysis of Water. 

The choice of process depends upon the availability of raw materials. Hydrogen for ammonia synthesis is currently rarely produced by water electrolysis, except in countries... 

When liquid air distillation is used as the source of nitrogen, the hydrogen also required for ammonia synthesis is obtained from a variety of sources. Some is obtained as the coproduct from the electrolytic production of chlorine and caustic soda (Chap. 8), some from refinery sources as a by-product of cracking processes or olefin synthesis, some from the water-gas reaction, and some is produced specifically for the purpose by the electrolysis of alkaline water (e.g., by Cominco, Trail, Eq. 11.14). 

FIGURE 11.2 Outline of the main components of an ammonia synthesis plant using reforming and secondary reforming as the principal sources of hydrogen. Electrolysis of water is used to supplement this. 

The most important product of water electrolysis is hydrogen gas, which is used as in the chemical catalytic hydrogenation of organic compounds (e.g., liquid oils that are hydrogenated to synthesize solid or semisolid fats), the refining of high-purity metals, the synthesis of ammonia, and the manufacture of semiconductors. The water-splitting route to H2 gas, however, is much more... 

Concentration of deuterium by the electrolysis of water was proposed by Washburn and Urey [Wl], used by Lewis [L4] to make the first samples of pure D2O, and employed for the first production of heavy water on a large industrial scale by the Nortic Hydro Company, at Rjukan, Norway. The Rjukan plant makes use of cheap hydroelectric power to produce electrolytic hydrogen for ammonia synthesis and by-product heavy water. 

All other plants that for primary concentration use water electrolysis (WE), steam-hydrogen exchange (SH), synthesis gas distillation (SD), hydrogen distillation (HD), or ammonia-hydrogen exchange (AH) are parasitic to a synthetic ammonia plant. Heavy water is a by-product of these plants, and its production rate is limited by the amount of deuterium in the ammonia plant feed. 

Industrial scale electrolyzers were developed early in the 20th century for the manufacture of chlorine and caustic soda from brine, and for the commercial production of hydrogen used in ammonia synthesis. Large water-electrolysis plants were constructed in Norway and Canada in the 1930 s, based on cheap hydroelectric power, and the hydrogen so produced was used in fertilizer manufacture. With the advent of natural gas and low cost petroleum, hydrogen production moved toward catalytic steam-reforming of hydrocarbons, and water electrolysis became less significant. 

Electrolytic ammonia s mthesis in a molten salt under atmospheric pressure. In 2005, Murakami et al proposed an electrolytic ammonia synthesis process from water and nitrogen gas in molten salt under atmospheric pressure and at lower temperature. In this process, water vapor and was electrolyzed via electrochemical reaction to form ammonia gas and ions in molten salt. Nitride ions were formed on metallic cathode and oxygen ions were removed from metallic anode during electrolysis. The electrolyte was alkaline metallic chloride containing The principle is showed in Fig. 10.9. 

The products of this electrolysis have a variety of uses. Chlorine is used to purify drinking water large quantities of it are consumed in making plastics such as polyvinyl chloride (PVC). Hydrogen, prepared in this and many other industrial processes, is used chiefly in the synthesis of ammonia (Chapter 12). Sodium hydroxide (lye), obtained on evaporation of the electrolyte, is used in processing pulp and paper, in the purification of aluminum ore, in the manufacture of glass and textiles, and for many other purposes. 

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