Short-cut model to design an efficient continuous counter-current extraction process applied to recover artemisinin from Artemisia annua

The extraction of valuable natural products from plant materials using suitable solvents is predominantly performed in batch processes. There is interest in developing and applying more efficient continuous operating modes. Rational design and process optimization require knowledge regarding several essential case specific parameters. For an evaluation of the potential of the process reduced order models are desirable. Using analogies to widely applied Chemical Reaction Engineering (CRE) concepts, we provide a theoretical framework capable to estimate the performance of continuous counter-current solid liquid extraction. The suggested short-cut model relies on a small number of simple to determine thermodynamic and kinetic parameters and captures the impact of the essential operating conditions and the equipment size. Central element of the model is the assumption that the extraction step as taking place in analogy to a homogeneous first order reversible chemical reaction. Considering a stage model and periodic switches between heterogeneous and pseudo-homogeneous situations allow efficiently implementing the counter-current movement of the two phases and deriving easy to solve and partly analytical solutions. A key quantity for designing the process is an adapted Damköhler number. The potential of the model is validated experimentally in a relevant case study considering the continuous counter-current extraction of artemisinin from leaves of Artemisia annua L. using toluene as the solvent. The short-cut model developed is considered to be broadly applicable beyond this specific case study. • exploiting analogies to chemical reaction engineering to model continuous counter-current solid liquid extraction • identification of key parameters and methods to determined them • derivation of simple solutions capable to predict extract concentrations, productivities and yields • model validation for a relevant case study (provision of artemisinin)