Ammonia synthesis composition

Remaining trace quantities of CO (which would poison the iron catalyst during ammonia synthesis) are converted back to CH4 by passing the damp gas from the scmbbers over a Ni methanation catalyst at 325° CO -t- 3H2, CRt -t- H2O. This reaction is the reverse of that occurring in the primary steam reformer. The synthesis gas now emerging has the approximate composition H2 74.3%, N2 24.7%, CH4 0.8%, Ar 0.3%, CO 1 -2ppm. It is compressed in three stages from 25 atm to 200 atm and then passed over a promoted iron catalyst at 380-450°C ... 

Table 8.6. Typical composition of the feed gas when it enters the ammonia synthesis reactor.

LEIS has been applied to study the surface composition of Co-Mo and Ni-Mo hydrodesulfurization catalysts [46-48], Fe-based Fischer-Tropsch [49] and ammonia synthesis catalysts [50], and model systems such as Pt evaporated on Ti02 [51]. The review of Horrell and Cocke [52] describes several applications. 

As example of the caculation of the equilibrium composition of a homogeneous gas reaction the ammonia synthesis reaction at 450 °C will be considered ... 

The gas composition is optimized with DOFs outside the CO2 scrubbing system with regard to inert composition (methane and argon) and hydrogen to nitrogen ratio since the levels of these components affect downstream (ammonia synthesis) reaction kinetics. Improved kinetics at lower inert levels are achieved at the expense of using more fuel or feedstock, since lower inerts can be achieved by firing the primary... 

Purification Exit Gas Composition Primary Reforming Secondary Reforming High Temperature CO ShiR Low Temperature CO Shift COj Removal Methanation MUG Ammonia Synthesis Loop... 

The present treatment of the conventional process will be based on the process diagram presented in Figure 1, which represents a steam reformer coupled with an ammonia synthesis plant [6], This is one of the two cases, which were considered in the project. The other was the use of the produced hydrogen as fuel in combined cycle gas turbines. In this chapter, the steam reforming part will be treated only, but some comments on the ammonia plant will be made, in view of the composition of the product stream leaving the steam reformer. 

Forced Composition Cycling Experiments in a Fixed-Bed Ammonia Synthesis Reactor... 

The effect of feed composition cycling on the time-average rate and temperature profile was explored in the region of integral conversion in a laboratory fixed bed ammonia synthesis reactor. Experiments were carried out at 400°C and 2.38 MPa over 40/50 US mesh catalyst particles. The effect of various cycling parameters, such as cycle-period, cycle-split, and the mean composition, on the improvement in time-average rate over the steady state were investigated. 

Some chemical operations, however, demand a supply of pure hydrogen these include ammonia synthesis and fat-hardening, and so it became necessary to find a way of altering the composition of water-gas to achieve this. Its gaseous components can be brought into equilibrium by the water-gas shift... 

Figure 6. Steady-state (curve 1) and cycle-average (curve 2) reaction rate versus feed composition. Experimental data for ammonia synthesis reaction by Jain, Silveston and Hudgins adapted from Chemical Reaction Engineering, ACS Symposium Ser, 1982, 196, 97-107.

FIGURE 5 Characterization of iron ammonia synthesis catalyst. High-resolution laboratory diffraction indicated a reversible modification of the iron (111) line profile. Under catalytic reaction conditions, a sub-nitride with x = 15-18 is present in addition to the bulk iron matrix. The fitting and assignment of the data were substantiated by observations of the line profile during step changes in the composition of the gas atmosphere. Details and references are given in the text. 

Equations for describing ammonia synthesis under industrial operating conditions must represent the influence of the temperature, the pressure, the gas composition, and the equilibrium composition. Moreover, they must also take into consideration the dependence of the ammonia formation rate on the concentration of catalyst poisons and the influence of mass-transfer resistances, which are significant in industrial ammonia synthesis. 

All steam reforming catalysts in the activated form contain metallic nickel as active component, but the composition and structure of the support and the nickel content differ considerably in the various commercial brands. Thus the theoretical picture is less uniform than for the ammonia synthesis reaction, and the number of scientific publications is much smaller. The literature on steam reforming kinetics published before 1993 is summarized by Rostrup - Nielsen [362], and a more recent review is given by K. Kochloefl [422]. There is a general agreement that the steam reforming reaction is first order with respect to methane, but for the other kinetic parameters the results from experimental investigations differ considerably for various catalysts and reaction conditions studied by a number of researchers. 

A.K. Jain. P.L. Silveston. and R.R. Hudgins, Forced composition cycling experiments in a fixed-bed ammonia synthesis reactor. Chem. Reaction. Eng. 9 97 (1982). 

As to the reaction rate, it is to be noted here that the change in adsorption with time accompanies the change in the amount and composition of the reacting gas. This should be taken into account in the calculation of the reaction rate. In Tamaru s studies of ammonia synthesis, the produced ammonia was always trapped in a liquid nitrogen trap and its amount gave the reaction rate. 

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