Abstract
The realistic numerical simulation of chemical processes, such as those occurring in catalytic reactors, is a complex undertaking, requiring knowledge of chemical thermodynamics, multi-component activated rate equations, coupled flows of material and heat, etc. A standard approach is to make use of a process simulation program package. However for a basic understanding, it may be advantageous to sacrifice some realism and to independently reproduce, in essence, the package computations. Here, we set up and numerically solve the basic equations governing the functioning of plug-flow reactors (PFR) and continuously stirred tank reactors (CSTR), and we demonstrate the procedure with simplified cases of the catalytic hydrogenation of carbon dioxide to form the synthetic fuels methanol and methane, each of which involves five chemical species undergoing three coupled chemical reactions. We show how to predict final product concentrations as a function of the catalyst system, reactor parameters, initial reactant concentrations, temperature, and pressure. Further, we use the numerical solutions to verify the “thermodynamic limit” of a PFR and a CSTR, and, for a PFR, to demonstrate the enhanced efficiency obtainable by “looping” and “sorption-enhancement”.
Highlights
We demonstrate how one may simulate the simplified operation of a catalytic reactor using basic thermodynamic data, a kinetic model for the multi-step reactions, and numerical solutions of reactor-specific differential equations describing the evolution from reactant to product chemical specCiehesm.EnWgineeerfinogc20u20s, 4o, xuFrORaPtEtEeRnRtEiVoInEWon the two archetypes of continuous-flow r2eoaf 1c7tors: the plug flow reactor (PFR) and the continuously stirred tank reactor (CSTR) [5]
We demonstrate the usefulness of this approach to reactor simulation and hopefully motivate further exploCrhaemtiEongnineerbinyg 20t2h0,e4, x;rdeoai: dFOeRrPEbERyREeVxIEaWmining the enhanwcwewd.mdepiffi.comc/ijeounrncayl/cheomfengtiwneeoringmodifications of the PFR, which effectively shift the thermodynamic equilibrium: product separation and the removal/recycling of unreacted species in a “looped” reactor [7], and product removal by selective absorption (“sorption enhancement”) [11]
Materials and Methods Equilibrium constants for the chemical reactions considered were either computed from thermodynamic data on the Gibbs free energy change [12] or taken from the literature [13,14], and the kinetic rate factors were obtained from published models of experimental data [13,14,15]
Summary
We demonstrate how one may simulate the simplified operation of a catalytic reactor using basic thermodynamic data, a kinetic model for the multi-step reactions, and numerical solutions of reactor-specific differential equations describing the evolution from reactant to product chemical specCiehesm.EnWgineeerfinogc20u20s, 4o, xuFrORaPtEtEeRnRtEiVoInEWon the two archetypes of continuous-flow r2eoaf 1c7tors: the plug flow reactor (PFR) and the continuously stirred tank reactor (CSTR) [5]. We explain how the relevant equations are set up to describe the. Tohefseeach chemical equations are numerically solved to yield the time or position-dependent concentration of each component. A series of progressively more challenging student exercises which review and develop the concepts treated in the main text is included, with answers, as an Supplementary Materials
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