(314c) Bifurcation Analysis of Oxidative Coupling of Methane in Short Monolith/Gauze/Wire-Mesh Reactors

Bifurcation analysis is a very important mathematical tool, which can help in analyzing the multiple steady states and different possible behaviors of catalytic partial and deep oxidation processes for various choices of physical parameters. Using this theory, in this work, we determine the impact of design and operating parameters such as space time, feed temperature, reactor dimensions and feed conditions on the ignition-extinction phenomena of oxidative coupling of methane (OCM).

Methodology

A two-phase ‘Short Monolith/Gauze/Wire-mesh Reactor Model’ with pore diffusion in washcoat is used in this study. This type of model is applicable to systems where the axial diffusion time scale is much smaller compared to the transverse diffusion, convection and reaction time scales. A 12 step global kinetic model comprising of 5 homogeneous and 7 catalytic reactions on La₂O₃/CaO catalyst has been considered here.

Results

As can be seen in the top row of fig. 1, at a constant inlet CH₄/O₂ mole ratio = 8 and Ï„ = 100 ms, increasing the channel hydraulic radius R_Ω from 50 µm to 1 mm decreases the maximum CH₄ conversion and C₂ selectivity while increasing the extinction temperature. However, if the transverse Peclet number, P (the ratio of transverse diffusion time to space time) at R_Ω = 250 µm and Ï„ = 100 ms is taken as the base case and R_Ω and Ï„ are changed such that P remains constant, higher CH₄ conversion and C₂ selectivity can be achieved at higher R_Ω as shown in the bottom row of fig. 1.

Conclusions

Our calculations show that using the gauze reactor model with appropriate dimensions, it is possible to achieve 80% C₂ selectivity with 20% CH₄ conversion at a feed inlet temperature of 400 K and inlet CH₄/O₂ mole ratio = 8 and with Ï„ of 0.01 to 0.1s.