Rigorous Multicomponent Reactive Separations Modelling: Complete Consideration of Reaction-Diffusion Phenomena
Abstract
This paper gives the first step of the development of a rigorous multicomponent reactive
separation model. Such a model is highly essential to further the optimization of acid
gases removal plants (CO2 capture, gas treating, etc.) in terms of size and
energy consumption, since chemical solvents are conventionally used.Firstly, two main modelling approaches are presented: the equilibrium-based and the
rate-based approaches.Secondly, an extended rate-based model with rigorous modelling methodology for
diffusion-reaction phenomena is proposed. The film theory and the generalized
Maxwell-Stefan equations are used in order to characterize multicomponent interactions.
The complete chain of chemical reactions is taken into account. The reactions can be
kinetically controlled or at chemical equilibrium, and they are considered for both liquid
film and liquid bulk.Thirdly, the method of numerical resolution is described. Coupling the generalized
Maxwell-Stefan equations with chemical equilibrium equations leads to a highly non-linear
Differential-Algebraic Equations system known as DAE index 3. The set of equations is
discretized with finite-differences as its integration by Gear method is complex. The
resulting algebraic system is resolved by the Newton- Raphson method.Finally, the present model and the associated methods of numerical resolution are
validated for the example of esterification of methanol. This archetype non-electrolytic
system permits an interesting analysis of reaction impact on mass transfer, especially
near the phase interface. The numerical resolution of the model by Newton-Raphson method
gives good results in terms of calculation time and convergence. The simulations show that
the impact of reactions at chemical equilibrium and that of kinetically controlled
reactions with high kinetics on mass transfer is relatively similar. Moreover, the Fick’s
law is less adapted for multicomponent mixtures where some abnormalities such as
counter-diffusion take place.
Domains
Physics [physics]
Origin : Publication funded by an institution
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