The first-order model in the simulation of essential oil extraction kinetics

Abstract The aim of the present work is to investigate the generalization possibilities of models describing the kinetics of essential oils extraction and the relevance of the adopted assumptions for their development. A database of 132 extraction kinetics was built on the basis of works reported in the literature. This data analysis showed two types of kinetics which differ by the presence or not of an inflection point. The simulations based on known and developed models indicated that simple first-order model considering only diffusion into solid phase with several simplifying assumptions provides results that are in good agreement with the experimental data in more than 80% of the studied cases. More complex models considering the presence of parallel or simultaneous kinetics proved highly successful; nevertheless, it was observed that the contribution of the term relative to kinetics other than first-order is significant only at the first stage of the process; thereafter all models show similar predictions. The application of the model, which takes into account the resistance in both solid and vapor phases, showed that, in nearly all cases, this model converged to a first order one. This result could be an argument in favor of approaches considering only solid phase resistance. However, several such models neglect the essential oil concentration in the vapor phase; this renders them unrepresentative, especially when the extraction kinetics is affected by the steam flow rate variations. Thus the simple first-order model proves an acceptable general option and allows in practice to predict with precision and robustness the yield of the extraction operations over time.