(200t) Heat Transfer Transients in Semi-Batch Systems: A Computational Approach to Process Intensification and Mitigating Process Hazards

Localized thermal pockets can have a significant impact on yield and quality if thermally labile compounds are present in the reaction mixture. They can also present a formidable process hazard in the form of runaway scenarios. Hence, semi-batch operations with controlled addition protocols are popular in the chemical and pharmaceutical sectors for highly reactive and/or exothermic systems.

For example, in the semi-batch operation the liquid level in the vessel keeps changing with time resulting in a continuous change of the mixing profiles and therefore changes in effective heat and mass transfer rates resulting into heat removal from the reactor.

The resulting change in relative positions of agitators with respect to the liquid surface affects the flow pattern significantly. For example, agitators rotating near the liquid surface or in the vapor phase do not contribute to mixing and heat transfer which can cause in-homogenous mixing resulting into localized thermal pockets. These effects are neither accounted by simple empirical relationships nor by standard commercial software tools.

Computational fluid dynamics (CFD) is an effective tool to design and/or troubleshoot systems as stated above. Our work using CFD is a simple and effective approach using modified CFD simulators data combining with the process design tools (Dynochem). The approach is not only computationally faster but can also provide excellent results in terms of predicting liquid phase mixing and heat/mass transfer transients. This tool has been used effectively to plan batch operation schedules and thermal profiling of reactions posing a runaway process hazard. It has also been used to intensify batch distillation/evaporation operations. Furthermore, the CFD based approach can be integrated into quality-by-design (QbD) frameworks in pharmaceutical manufacturing and scale up activities.