Resolving steady-state multiplicities for diffusion with surface chemical reaction by invoking the Prigogine principle of minimum entropy production

The process of coupled multicomponent diffusion and surface reaction is described by combining the Maxwell–Stefan (M–S) and Langmuir–Hinshelwood (L–H) formulations. Five different systems are investigated: epoxidation of ethene C2H4+12O2⇄C2H4O, oxidation of carbon monoxide CO+12O2⇄CO2, hydrogenation of ethene H2+C2H4⇄C2H6, CO methanation CO+3H2⇄CH4+H2O, and chemical vapor deposition WF₆ + 2SiH₄ → W_(s) + 2SiHF₃ + 3H₂. For isothermal, isobaric operations under steady-state conditions, multiplicity of solutions are found for all five reaction systems. The origin of the multiplicities is traceable to the non-linear characteristics of the L–H kinetics. Application of the Prigogine principle of minimum entropy production indicates that the low-conversion steady-state is the stable one that can be realized in practice. The reported results have important consequences for modelling and design of chemical vapor deposition processes and micro-channel reaction devices consisting of thin catalyst coatings on the walls.