Equilibrium partition of rapeseed oil between supercritical CO2 and prepressed rapeseed

• Oil partition was measured by recirculating the CO2 phase up to equilibrium prior to sampling.
• Residual oil content in seed was back-estimated using mass balances for whole sorption isotherm/isobar.
• Rapeseed oil is physisorbed to the seed; heat is required to desorb and solvate it in CO2.
• Sorption isotherm/isobar data was modelled using the equation of del Valle-Urrego.
• Data uncertainties may be large for oil content in the seed, especially for low oil contents.

The equilibrium partition of a vegetable extract between supercritical (SC) CO2 (fluid phase) and a vegetable substrate (solid phase) is commonly best-fitted in the mathematical simulation of extraction curves. The aim of this study was to develop and apply an experimental methodology to measure the equilibrium partition of rapeseed oil between SC CO2 and prepressed rapeseed. We measured and modelled sorption isotherm/isobar curves using a methodology that intersperses extraction (to reduce oil content) and equilibration (by recirculation of the SC CO2 phase) steps, with oil being sampled in each step. Oil desorption was a two-stage process; when rapeseed contains more than ∼70–80 g kg−1 oil/substrate the SC CO2 phase gets saturated with oil (Cf = Csat), whereas when it contains less oil this is bound to the solid matrix in such a way that Cf dips below Csat. Increasing pressure from 22 to 28 MPa at constant temperature (40 °C) increases Cf. The effect of the increase in pressure is less pronounced when SC CO2 density is kept constant (857.1 kg/m3) by simultaneously increasing temperature from 40 to 50 °C. The heat of desorption of the oil is ∼100 kJ/mol which suggests it is bound to the prepressed seed by van der Waals interaction forces. However experimental values in this region are uncertain due to propagation of uncertainties to estimate Cs.

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