Electrolytic ammonia synthesis

Murakami, T., Nishikiori, T., Nohira, T., Ito, Y. (2005). Investigation of anodic reaction of electrolytic ammonia synthesis in molten salts imder atmospheric pressure. Journal of the Electrochemical Society, 152(5), D75—D78. 

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. 

Fig. 10.9 Schematic drawing of the principle of electrolytic ammonia synthesis from water and nitrogen gas. ...

Formally, ammonia synthesis is closely related to Fischer-Tropsch synthesis. Industrial operation involves the use of an iron catalyst promoted with calcium and potassium oxides. However, the reason we consider this process here is not directly in connection with alkali promotion of the catalyst. We are concerned with a remarkable achievement reported by Yiokari et al. [15], who use a ton-conducting electrolyte to achieve electrochemical promotion of a fully promoted ammonia synthesis catalyst operated at elevated pressure. Specifically, they make use of a fully promoted industrial catalyst that was interfaced with the proton conductor CaIno.iZro.903-a operated at 700K and 50 bar in a multipellet configuration. It was shown that under EP the catalytic rate could be increased by a factor of 13 when... 

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). 

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. 

Although electrolytic hydrogen is ideal for ammonia synthesis because of its purity it accounts for only 15 per cent of the ammonia produced by the direct synthetic ammonia process. The capital cost of a plant for the electrolysis is high, and except for a few especially favorable locations, electrical energy is more valuable for other industries. Although better results are claimed for certain cells, experience shows that the larger installations in this country have consumed... 

It was tested in several small 3 to 10 ton per day plants but was never operated intact on a large scale commercial basis. Instead the large commercial units became adaptations of the Haber process, the Cassale Process, or the Claude Process for ammonia synthesis. The American Process was originally described as using electrolytic hydrogen. This was much too expensive for commercial use in America at that time. Instead hydrogen was obtained from the reaction of steam with coal or later from the... 

Wang W B, Cao X B, Gao W J, Zhang F, Wang H T and Ma G (2010), Ammonia synthesis at atmospheric pressure using a reactor with thin solid electrolyte BaCeo,85Yo,i503 5 membrane , / Membrane Sci, 360,397-403. 

Concluding from previous works, the key factor for electrocatalytic ammonia synthesis could be the number of TPB sites at the cathode to facilitate the reaction between protons from the electrolyte, N2 from gas phase, and electrons from external power source. Therefore, the big challenge on the electrochemical synthesis of ammonia is the low formation rates thus more efficient catalysts need to be identified. 

As mentioned before, high ionic conductivity is an important requirement for electrolyte materials to be used for ammonia synthesis devices. The results from many experiments confirm that proton conductors with adequate ionic conductivity can be used as electrolytes for a membrane reactor. Some examples of materials investigated as a membrane reactor are described below. 

Typical operating temperatures of electrocatalytic ammonia synthesis devices via a ceU with a proton-conducting solid oxide electrolyte are around 400—700 °C corresponding to the working temperature of the proton conductor electrolyte. A volcano-shape dependence of ammonia formation rates on temperature is observed in most cases. The formation rate of ammonia increases with temperature until a maximum is reached due to the increase of the proton conductivity. When the temperature is further increased, the ammonia formalion rate then turns downhill, because the decomposition of ammonia becomes prominent. In addition, the water loss from the electrolyte membrane due to high temperatures may decrease proton conductivity of the electrolyte. 

Solid-state proton conductors such as perovskites, pyrochlores, fluorites, and polymers have been reviewed and discussed in detail, with particular emphasis on their application in ammonia synthesis. Ammonia synthesis using an oxide-ion electrolyte has also been presented. The possibility of ammonia synthesis from N2 and steam instead of molecular H2 using either proton or oxide-ion conducting electrolytes may offer many advantages. 

Whatever the source of electricity, the salient point to note is that ammonia synthesis is a high value end-use for hydrogen and, unless the electrolytic route can compete economically with steam reforming for this premium market, the prospects for electrolytic hydrogen entering the general fuels market are not good. 

Fig. 10.8 Schematic diagram of electrochemicai ammonia synthesis using SCY ceramic solid electrolyte...

The pressure of gas was 101.325 kPa. The ammonia synthesis rate was stable after passage of current for 2-6 min and this rate was at least three magnitudes higher than that of conventional catalytic reactor. The conversion of hydrogen was close to 100% which eliminated thermodynamic equilibrium limitation. The main problem of this method is that the conductivity of SCY ceramic is very poor at normal temperature. Even at 570°C, its conductivity is unsatisfied because the current density was smaller than 2 mA-cm and could not be further increased. This limited the efficiency of ammonia synthesis and theoretical research. The use of solid electrolyte with high proton conductivity at low temperature to replace the SCY ceramic may be favorable to decreasing the synthesis temperature and increasing the current density and production efficiency. 

We replace the electrolytic reactor with a methane burner and our ammonia synthesis process becomes ... 

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. 

Promotion We use the term promotion, or classical promotion, to denote the action of one or more substances, the promoter or promoters, which when added in relatively small quantities to a catalyst, improves the activity, selectivity or useful lifetime of the catalyst. In general a promoter may either augment a desired reaction or suppress an undesired one. For example, K or K2O is a promoter of Fe for the synthesis of ammonia. A promoter is not, in general, consumed during a catalytic reaction. If it does get consumed, however, as is often the case in electrochemical promotion utilizing O2 conducting solid electrolytes, then we will refer to this substance as a sacrificial promoter. 

Haber process (Haber-Bosch process) The catalyzed synthesis of ammonia at high pressure, half-cell One compartment of an electrochemical cell consisting of an electrode and an electrolyte, half-life (f1/2) (1) In chemical kinetics, the time needed for... 

Hexamethylenediamine (HMDA), a monomer for the synthesis of polyamide-6,6, is produced by catalytic hydrogenation of adiponitrile. Three processes, each based on a different reactant, produce the latter coimnercially. The original Du Pont process, still used in a few plants, starts with adipic acid made from cyclohexane adipic acid then reacts with ammonia to yield the dinitrile. This process has been replaced in many plants by the catalytic hydrocyanation of butadiene. A third route to adiponitrile is the electrolytic dimerization of acrylonitrile, the latter produced by the ammoxidation of propene. 

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