Fundamental research on supercritical fluid extraction kinetics : From on-line measurements to inverse modeling

Sammanfattning: Supercritical fluid extraction is an extraction technique suitable for lipophilic compounds from solid samples. Most commonly supercritical carbon dioxide is the main component in the extraction phase, rendering the technique relatively environmentally benign. The extraction technique is rapid due to the low viscosity and the high diffusivity of analytes in the supercritical extraction phase.The selectivity can be tuned by changing the extraction conditions of pressure, temperature and co-solvent amount. These process parameters along with flow rate and extraction time make optimization of an extraction method rather cumbersome. A fundamental understanding of the extraction process can help to make wise decisions during method development. In this work extractability, partitioning, solubility and internal and external mass transfer resistancehave been studied through inverse modeling.Methods based on in-line spectrophotometric measurements and on-line evaporative light scattering detection have been developed to efficiently acquire extraction curves, i.e., the extraction yield over time. These enable a highthroughput of extractions with high temporal resolution and good precision. The methods were applied to quantify total lipids from linseed and carotenoids, chlorophyll A, ergosterol and total lipids from microalgae. An off-line method for separating carotenoids based on supercritical fluid chromatography was also developed.Methodologies have been developed to acquire models which are calibrated using all experiments, so called complete calibration. It is shown that calibrating one model per experiment does not generate models with reliable parameters with physical meaning. The models can be used for predicting extraction curves within the investigated space of process parameters.Finally, extractability and partitioning are shown to be highly influential on the extraction process. Also, partitioning can give rise to diminishing extraction rates, which has previously believed only to be caused by intraparticlediffusion.