Cracking, ammonia

Four hydrogen production techniques are reviewed hydrocarbon reforming ammonia cracking and two other, less common, production techniques, pyrolysis and aqueous phase reforming. 

Endothermic ammonia cracking is regarded as the reverse of the synthesis reaction, and since it is limited by heat transport, its efficiency can potentially be improved using microreactors. In industry, ammonia synthesis occurs at approximately 500 °C and 250 atm, and it is often represented by the following reaction ... 

MesoSystems is developing a 50 W portable power supply using ammonia as the fuel. The system consists of an ammonia cracking reactor, an ammonia adsorbent, a membrane, heat exchangers, and power controls. They have integrated the system with the necessary pumps, fans, and controls and tested it with fuel cells. 

The wet process for uranium(VI) fluoride manufacture is utilized in the Kerr-McGee process, in which the reduction proceeds with a H2/N2-mixture from ammonia cracking and hydrofluorination is carried out in a two stage fluidized bed. British Nuclear Fuel Ltd and Eldorado Nuclear Ltd/Canada also use wet processes. 

In principle, APT can also be directly reduced without any prior calcination step. The disadvantage of direct reduction is the formation of ammonia which has to be scrubbed, but a certain amount of ammonia cracks and dilutes the hydrogen by nitrogen. Consequently, from time to time, part of the contaminated, circulating hydrogen must be vented, thus increasing costs. 

In contrast to SCC of carbon and low-alloy steels in chloride, sulfide, and sulfuric acid environments by hydrogen-embrittlement mechanisms, cracking in several environments is attributed to passive-film cracking and/or active-corrosion-path anodic-dissolution penetration mechanisms (Ref 124). These environments include nitrates, hydroxides, ammonia, carbon-dioxide/carbonate solutions, and aqueous car-bon-monoxide/carbon-dioxide. Nitrate-bearing solutions are encountered in coal distillation and fertilizer plants hydroxide solutions in the production of NaOH and in crevices of steam boilers and ammonia cracking has occurred in tanks and distribution systems for agricultural ammonia applications. 

Ammonia can be released continuously by use of the waste heat of a fuel cell. As a result, the system efficiency is only limited by the fuel cell itself and the efficiency of the ammonia cracking reactor. The operating temperature of the fuel cell determines the choice of the base salt in the metal ammine (see Table 19.1). 

In ammonia, cracked according to Equation (11.11), there are three parts hydrogen and one part nitrogen, thus the hydrogen partial pressure in this atmosphere is 0.75 atm. Therefore, from Equation (11.14a) Equation (11.14b) is obtained ... 

The types of corrosion experienced in the chemical manufacturing industry, the petrochemical manufacturing industry, and the pharmaceutical manufacturing industry are similar in many respects. The most common types of corrosion encountered are caustic and chloride cracking, oxidation, sulfidation, corrosion under thermal insulation, ammonia cracking, and hydrogen-induced cracking. 

Figure 1.7 Microreactors with suspended tubes (over Ircatalyst) and ammonia cracking (over Pt of silicon nitride (a) tubes freely hanging in flow catalyst) for temperatures up to 900 °C. channel of chip (45 x 30 mm) for Rh-catalyzed (a) From [52], reproduced by permission of The direct partial oxidation of methane into synthesis Royal Society of Chemistry (b) reproduced gas (>600°C) (b) U-shaped tubes for from [53], with permission, Copyright2003 IEEE,...

Corrosion Problems in the Petroleum and Chemical Industries 23 2.1.3 Ammonia Cracking... 

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