Modeling Textured Enzyme Immobilizing Scaffolds in a Packed Bed Reactor

The goal of this research was to computationally analyze the impact of surface texturing on enzyme immobilizing scaffolds in packed bed reactors. Many bioreactors utilize enzyme immobilizing scaffolds to control the spatial orientation of surface bound enzymes to maximize the probability for productive collisions.^[1] This, paired with the high interfacial surface area that a typical packed bed reactor can support, allows for high conversion rates when compared with similar alternatives.^[2] For this analysis, it was hypothesized that the implementation of surface texturing would increase the overall surface area of the bed and thus improve reactor efficiency.

To study surface texturing, a comprehensive model of the packed bed was designed. To do so, an algorithm to randomly generate packed beds was utilized along with equations for transport and heterogeneous reaction kinetics. Surface texturing was modeled using an algorithm that approximates a lattice of evenly-spaced dimples on the surface of a sphere-like particle. Steady state simulations were performed on 3 bed meshes with increasing surface dimple density to analyze the change in overall conversion as a function of enzyme activation energy. Contrary to the original hypothesis, the model predicted a negative correlation between reactor conversion and surface texturing. A further analysis revealed that the decrease in fluid drag over dimpled surfaces resulted in lower residence times overall and thus poorer conversion despite the additional reactive surface area.

The resulting model is novel in its combination of coupled forms of transport and reaction kinetics within a packed bed, which has generally been avoided in the past due to its demand for computational hardware.^[3]However, with access to GPU banks and multi-threading-enabled processes ever increasing, the ability to model a complex system such as this one is becoming increasingly possible. The use of this model for future applications could lead to a better understanding of kinetics in packed bed reactors.

1. Jéssie da Natividade Schöffer et al. “Directed immobilization of CGTase: The effect of the enzyme orientation on the enzyme activity and its use in packed-bed reactor for continuous production of cyclodextrins”. In: Process Biochemistry 58 (2017), pp. 120-127
2. José AC Leite et al. “Application of an anaerobic packed-bed bioreactor for the production of hydrogen and organic acids”. In: International Journal of Hydrogen Energy 33.2 (2008), pp. 579–586.
3. Nico Jurtz, Matthias Kraume, and Gregor D Wehinger. “Advances in fixed-bed reactor modeling using particle-resolved computational fluid dynamics (CFD)”. In: Reviews in Chemical Engineering 35.2 (2019), pp. 139–190.