Composition cycling synthesis reactor

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. 

Our demonstration that forced composition cycling of NHj synthesis over an iron catalyst dramatically increases catalyst activity and smooths the temperature profile in fixed catalyst beds seems to call for an examination of the application of the approach to full-scale reactors. There is a major process design hurdle which must be overcome, however. Industrial reactors give relatively low conversions of NH3 per pass, so... 

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 with Rh catalysed carbonylation of MeOH, much enduring work on the mechanism of Ir catalysed carbonylation was carried out and reported by Forster at Monsanto [11], Combining data from catalytic reactions, synthesis and reactions of intermediates and IR studies of reaction solutions, three regimes or cycles, designated I, II and III, were identified, compared with the one for Rh. A key reactor composition variable determining which regime is operating is [H2O]. 

Figure 3 was calculated from steady-state measurements. Curvature of the rate vs composition relation causes the quasi steady-state rate to be well below the steady-state reactor performance. This emphasizes the very large effect of cycling frequency on the time average synthesis rate. 

The feasibility of increasing the selectivity of the Fischer-Tropsch synthesis by periodic operation is investigated. The process is modeled in a dynamic form using a CSTR reactor. The dynamic behavior of the model corresponds with in literature reported experimental results. The simulation results show a 20% increase in selectivity to Diesel range products compared to the best steady-state solution using a blockprofile. The profile has a cycle time of 1.1 O seconds and consists of a base composition of almost pure carbon monoxide and a pulse of 95% hydrogen and 5% carbon monoxide during 10.8% of the cycle time. 

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