Ammonia thermodynamic analysis

The energy consumption figures discussed so far represent a thermodynamic analysis based on the first law of thermodynamics. The combination of the first and second laws of thermodynamics leads to the concept of ideal work, also called exergy. This concept can also be used to evaluate the efficiency of ammonia plants. Excellent studies using this approach are presented in [1061], [1062], Table 39 [1061] compares the two methods. The analysis in Table 39 was based on pure methane, cooling water at 30 °C (both with required pressure at battery limits), steam/carbon ratio 2.5, synthesis at 140 bar in an indirectly cooled radial converter. 

The wet synthesis of CdS nanoparticles used in this work is based on the reaction between a dissolved cadmium salt (CdCl2) and a S-containing compound (thiourea (NH2)2CS) in an aqueous solution. Chemical deposition of CdS nanoparticles in the CdCl2 - NH3 - NaOH - (NH2)2CS - H2O bath was described elsewhere [3]. In the present work all the baths had the same composition and were prepared from solutions of cadmium chloride CdCl2 (0.005 mold-1), ammonia NH3-H2O (1.5 moll"1), sodium hydroxide NaOH (0.074 mold-1) and thiourea (NH2)2CS (0.025 mol-F1) using distilled water. The synthesis temperature was varied from 294 to 325 K. The primary concentrations of the precursors have been chosen according to the thermodynamic analysis [4]. A supersaturation of the solution with Cd(OH)2 takes place in the baths. It means that the mechanism of the cadmium sulfide formation could involve the stage of Cd(OH)2 formation. When the deposition process of CdS particles in the solution completed, the residue was filtered at an ambient pressure and dried at room temperature. 

The type of analysis discussed in the preceding paragraph with particular respect to c/ iron(ii) complexes has also been attempted for c/ palladium(ii) and gold(iii) substitutions. In the case of the reactions of [Pd(fo)L], where Hgfo is the formazan (5) and L=ammonia or pyridine, with thiocyanate, thiourea, or triphenylphosphine, a kinetic-thermodynamic analysis shows Gibbs free... 

The participation of Cd(OH)2 in the deposition of CdS (and other metal chalcogenides) has been demonstrated or suggested on many occasions. Kitaev et al. presented a theoretical thermodynamic treatment of the Cd " /ammonia/ thiourea system to show when Cd(OH)2 should be present as a solid phase in the deposition solution [36]. A graphical representation of this analysis is shown in Eigure 3.1. This graph is based on two equilibria the solubility product of Cd(OH)2 and the stability constant of the ammonia (ammine) complex of Cd. Consider first the former ... 

Classical methods of group analysis and separation take advantage of the stability of the [Ag(NH3)2]+ ion to separate silver from mercury. Treatment of a precipitate containing AgCl with dilute ammonia leads to the reaction in equation (3) bringing the silver into solution. To confirm the presence of Ag+, nitric acid must then be added to cause reprecipitation of AgQ. In aqueous ammonia, the diammine was the highest species formed, and thermodynamic data for its formation are collected in Table 3.20-23... 

Cremer, H. Thermodynamic balance and analysis of syngas and ammonia plant. ACS Symposium Series, Vol. 122, ASME Washington, DC, 1980. 

Cremer, H., "Thermodynamic Balance and Analysis of a Synthesis Gas and Ammonia Plant", Thermodynamics Second Law Analysis, A.C.S. Symposium Series, 122, 111-120, 1980. 

Thermodynamic Balance and Analysis of a Synthesis Gas and Ammonia Plant... 

Several chemical compounds (water, ammonia, nitric acid, organics, etc.) can exist in both the gas and aerosol phases in the atmosphere. Understanding the partitioning of these species between the vapor and particulate phases requires an analysis of the thermodynamic properties of aerosols. Since the most important solvent for constituents of atmospheric particles and drops is water, we will pay particular attention to the thermodynamic properties of aqueous solutions. 

It is known from analysis of the thermodynamics that the process of synthesis ammonia from H2 and N2 is hmited by the thermodynamic equilibrium, so the outlet content of ammonia obtained is below about 15% imder general industrial conditions. In order to increase the utilization ratio of H2 and N2, the un-reacted H2 and N2 should be recycled. Therefore, the product of ammonia should be separated from the mixed gas, and then the im-reacted H2 and N2 are circulated by circle-compressor for next reaction. The sjmthesis of ammonia, separation of ammonia and the recycle of unreacted H2 and N2 make up the recycle process flow for the ammonia synthesis. 

The exergy analysis can be used to calculate a thermodynamic efficiency for production of ammonia. It is simply the ratio between the exergy of product and the total feed which is ... 

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