Ammonia homogeneous catalytic process

Catalytic processes today dominate the production of sulfuric acid, ammonia, methanol, and many other industrial products. The cracking of mineral oils, the hydrogenation, transformation, and synthesis of hydrocarbons are almost all centered around catalytic conversions carried out with many different catalysts including some of highly specific action. Many more catalyzed reactions are being carried out in batch processes and in continuous operations, in heterogeneous and in homogeneous systems. 

The world food production can only be maintained at its present level thanks to the use of fertilizers derived from ammonia. This explains the development of homogeneous oxidation processes, which have supplanted the catalytic process of steam reforming. This process will be described in Chapter II. 

A heterogeneous catalyst is in a different phase or state of matter than the reactants. Most commonly, the catalyst is a solid and the reactants are liquids or gases. These catalysts provide a surface for the reaction. The reactant on the surface is more reactive than the free molecule. Many times these homogeneous catalysts are finely divided metals. Chemists use an iron catalyst in the Haber process, which converts nitrogen and hydrogen gases into ammonia. The automobile catalytic converter is another example. 

The various hydrocarbon oxidation schemes discussed above were believed to proceed at the catalyst surface only. The present concepts accept the occurrence of complex heterogeneous-homogeneous reactions proceeding in part at the solid surface and in part in the gas or liquid phase. Many catalytic oxidation processes considered recently as purely heterogeneous appeared to proceed by the heterogeneous-homogeneous mechanism. Such are the oxidations of hydrogen, methane, ethane, ethylene, propene, and ammonia over platinum at elevated temperatures, as studied by Polyakov et al. (131-136). When hydrocarbons are oxidized over platinum the reaction sets in on the catalyst surface and terminates in the gas phase. 

The majority of catalysts are subject to deactivation, e.g. to changes (deterioration) of activity with operation time. The time scale of deactivation depends on the type of process and can vary from a few seconds, as in fluid catalytic cracking (FCC), to several years, as in, for instance, ammonia synthesis. Due to the industrial importance, the modelling of deactivation was mainly developed for heterogeneous catalysis. Although the reasons for deactivation (inactivation) of homogeneous and enzymes could differ from solid catalysts, the mathematical approach can sometimes be very similar. 

Among flue gas treatment methods, the selective catalytic reduction (SCR), is best proven and it is used worldwide due to its efficiency, selectivity, and economics (2,5,6). The SCR process is based on the reaction between NOx and ammonia (NH3) or urea (CO(NH2)2), injected into the flue gas stream, to produce harmless water and nitrogen. Selective noncatalytic reduction (SNCR) has also been proposed, through which NOx is selectively reduced in the homogeneous phase by ammonia (or urea), which is introduced into the upper part of the boiler. The major drawback of the SNCR process is constituted by the narrow... 

A major feature of this process is using the horizontal converter and small-particle catalyst, so that the gas flows the path shortly, its linear speed is small, the pressure drop decreases in the catalyst bed, and consequently the recycle-compress power can be saved the catalytic activity can be improved by 12%-25%. Thus the catalyst volume and the equipment size decreases, the net value of the ammonia increases, the amount of the recycle gas declines there is homogeneous distribution of the gas-flow so that gets the higher synthetic ratio, and the energy consumption is significantly reduced. 

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