(13b) Scale up of Stirred Batch and Semi-Batch Reactors - Gaps and Limitations of the Current Methodologies

Stirred batch and semi-batch reactors are widely used in many industrial chemical processes that involve exothermic reactions, especially in the fine chemical and pharmaceutical industries, many of these reactors are multi-purpose. The safe scale up of this type of reactor is one of the most important aspects in the process development of batch and semi-batch operations. However, this is not a straightforward task and an incorrect scale up approach can lead to undesired events, such as runaway reactions. Incidents such as T2 Laboratories (2007) and Syntron LLC. (2006), where the scale up without good understanding of the thermochemistry, for both intented and unintended reactions, resulted in undersized cooling systems. This contributed to the occurrence of accidents with catastrophic consequences, and clearly highlighted the importance of the development and utilization of a proper and reliable scale-up methodology for stirred tank reactors. Experimental and theoretical scale up methodologies for batch and semi-batch reactors can be found in the literature. However, most of them were developed for a specific reaction and many times do not take into account the combined and simultaneous effects of mixing, reaction kinetics, and heat transfer dynamics. Also many times these methodologies, due to time pressures, are based on a limited series of laboratory and pilot scale experiments that may miss the correct identification of a hazardous scenario. In this paper, a comprehensive review of the current methodologies for the scale up of batch and semi-batch stirred tank reactors will be presented along with the identified gaps, limitations and challenges encountered. The paper also will address a detailed description of the importance of considering other factors including, for example,the heat transfer dynamics and the interaction between mixing and mass transfer kinetics. Finally, the paper will discuss additional aspects of a scale up methodology with experimantal case studies.