Modelling of Batch Reactors and CSTRs Containing Core-Shell Catalytic Pellets with Various Morphologies under Non-Isothermal Condition

Abstract

Modelling and simulation were performed for catalytic reactors containing core-shell spherical, cylindrical, and slab-type pellets, focusing on exothermic reactions. By solving material and energy balance equations simultaneously using the finite element method, the concentration and temperature of reactant inside the pellets as well as in bulk fluid could be predicted as a function of time from coupled reaction-diffusion equations. During calculations, the thickness of the inert core (x’) was adjusted to study its effect on the effectiveness factor of the core-shell pellets and reactor performance. In a batch reactor, the removal rate of the reactant was enhanced with increasing Biot number (Bi) as well as Thiele modulus (Φ0), and the decreasing rate of the reactant concentration increased in the order of sphere > cylinder > slab due to the surface to volume ratio of the pellets per unit volume of the reactor. Though the reactant concentration in the bulk fluid of CSTR at steady state decreased with decreasing x' due to the increased effective volume of the catalytic shell, a more abrupt transition with respect to x' was observed compared to the isothermal reactor. The concentration of the reactant in CSTR was affected by feed rate (Ψin), Lewis number (Le), and capacity ratio (Ω) calculated from reactant diffused through the pellets and feed stream under step input. For periodic input, the oscillating frequency of inflow temperature greatly affected the performance of CSTR, implying that the conversion of the reactant can be controlled by adjusting the inlet temperature. The performance could be also improved by connecting CSTRs in series, which can be approximated as a packed bed reactor for a sufficiently large number of reactors (N). Temperature of the reactor predicted numerically was also affected by various parameters such as x’, Bi, Le, Ψin, and Ω. As the temperaturese (ΔT) may cause evaporation and pressurization by an exothermic reaction, ΔT could be controlled by adjusting the heat transfer coefficient.

Keywords

• Effectiveness factor
• Core-shell catalyst
• Catalytic reactors
• Energy balance
• Exothermic reaction