Optimum H2/N2 ratio

Figures 8.11-8.13 shows the effect of H2/N2 ratio on the activity of ZA-5 catalysts. It is seen from the results that H2/N2 ratio has a certain effect on the catalytic activity. For given space, velocity and pressure the optimum H2/N2 ratio changes with the reaction temperature.

Fig. 8.14 Relationship between the optimum H2/N2 ratio and catalyst efficiency Dotted line calculation value of equation (8.9) Solid line the experimental data...

In contrast to the above-mentioned variables, the dependence of the converter performance on the H2/N2 ratio shows a true maximum (Fig. 81). The optimum conversion at high space velocity [SV = m3 (STP) gas h l- nrf3 catalyst] lies close to an H2/N2 ratio of 2 and approaches 3 at low space velocities. The reason is that equilibrium plays a greater role at low space velocities and has a maximum at a ratio of 3, except for small corrections [33] with regard to the behavior of real gases. Usually, the ratio is adjusted to 3, because in most plants, conversions near equilibrium are attained. 

Control of many modern ammonia plants is accomplished via gas analyzers and on-line computers to adjust conditions for optimum performance. The control strategy includes adjustments to the H2/N2 ratio, purge rate, and reformer furnace control. Heat recovery during regeneration of the catalysts also is included. 

Fig. 3 A shows the effluent NH3 concentration observed for Ru/MgO as a function of reaction temperature for three different Pn, / Phj / Paf ratios at 20 bar total pressure. It is obvious that the reaction orders for N2 and H2 have opposite signs. Fig. 3B illustrates that the reaction orders for N2 and H2 partly compensate each other in the kineticaliy controlled temperature regime. Hence an increase in total pressure with a constant Pnj / Phj 1/3 ratio does not lead to a significant increase in conversion at lower temperatures. For the plication of alkali-promoted Ru catalysts under industrial synthesis conditions, it is necessary to find a compromise between kinetics and thermodynamics by increasing the Pn, / Phj ratio. The optimum observed for Cs-Ru/MgO prepared from CS2CO3 at 50 bar is at about Pnj / Phj 40 / 60 [15]. The high NH3 concentration of about 8 % obtained with 0.138 g catalyst using a total flow of 100 Nml/min clearly shows that Ru catalysts have indeed the potential to replace Fe-based catalysts in industrial synthesis [15].

The liquid propellant rocket combination nitrogen tetroxide (N204) and IJDMII (unsymmetrical dimethyl hydrazine) has optimum performance at an oxidizer-to-fuel weight ratio of 2 at a chamber pressure of 67 atm. Assume that the products of combustion of this mixture are N2, C02, H20, CO, H2, O, H, OH, and NO. Set down the equations necessary to calculate the adiabatic combustion temperature and the actual product composition under these conditions. These equations should contain all the numerical... 

The optimum ammonia synthesis reaction rate depends on several factors including pressure, temperature, H2-to-N2 molar ratio, concentration of impurities and catalyst activity. Therefore the H2-to-N2 molar ratio is adjusted to suit the requirements in the ammonia synthesis. This adjustment occurs before the compression step. 

---