Detection of Microscale Mass‐Transport Regimes in Supercritical Fluid Extraction

The problem of detecting supercritical fluid extraction regimes on the particle‐scale level is discussed by using a generalized multiparameter model, which includes the shrinking‐core (SC) and broken‐and‐intact‐cells (BIC) approaches as its limiting cases. The model accounts for two internal mass‐transfer resistances attributed to cell membranes and transport channels. A wide spectrum of particle‐scale extraction regimes, described by the model, agree with available up‐to‐date relatively short laboratory experiments. Simplified concepts (like SC or BIC) could only be used for available experimental data correlation, and do not allow a reliable extension to long process times. The experimental methodology was suggested to detect limiting internal mass‐transfer mechanisms. A generalized model of a particle‐scale supercritical‐fluid‐extraction process is introduced. It is demonstrated that up‐to‐date experiments only allow identification of the initial extraction rates, which decrease or remain constant with time, depending on the assumed internal extraction regime. A methodology to detect the extraction regime in the particle is suggested.