One of the greatest differentiating powers of supercritical fluid extraction (SFE) with carbon dioxide (CO2) is the tunable selectivity of the extraction and collection process. I would direct the readers to many of the papers and books that have been written over the past decades that support this with extensive mathematics and graphs. Today I will do it with glittering generalities in which I have (again) taken (enormous) liberties with scientific theory to fit my word pictures and analogies. (Also I have taken significant liberties with the English language.)
This article illustrates how to predict the best conditions for extraction if you know the solubility of the components of botanical of interest. To illustrate this I made a fictional plant, AlphaBet, with the compounds of interest being A and B.
Overview of Generic Extraction System:
I will choose a generic extraction system that is simple in design. In addition, to make it easy for the calculations that we will look in later blogs, I will assume the extraction vessel is one liter in volume and ignore the length and width in the assumptions.
The system is best described by following the flow: it begins with a source of liquid CO2, then through a flow meter for knowing the density of CO2, and next a pump for metering the flow based on grams per minute of CO2 as measured by the flow meter. On a separate flow path there is a pump for delivering co-solvents such as food grade ethanol (provides faster extractions and automated cleaning of system fluidics). After the mixing T, an in line heat exchanger is used to preheat the CO2 before entering the 10,000 psi extraction vessel (5 ml to 10,000 ml size – today we are assuming 1,000 ml) then to a computer controlled back pressure regulator (provides ability to have automated step gradient pressure methods). While you can have a series of three collection vessels (provides ability to collect extractions at different conditions) this system shows just a single fraction collection vessel.