The F-HPE methodology comprised: (i) a first step in which pine
bark was subjected to extraction with CO2 in order to remove lowpolarity
compounds, employing a 10 min static period followed by
a 360 min dynamic period; (ii) a second step in which CO2:EtOH
(90:10, %, v/v) was used to extract polar compounds, such as procyanidins,
and employing a 360 min dynamic period. Three solvent
flow rates were assayed for these fractionated extractions, varying
between
∼8
×
10−5 and
∼19
×
10−5 kg/s, corresponding to solventto-
solid ratios from 254:1 up to 645:1 (w/w, on a dry basis, d.b.).
Approximately the same flow rate was used in each step of the
same experiment. The selection of this solvent-to-solid mass ratio
interval was based on a previous work developed by the authors
[23] and taking into consideration the obtained extraction kinetics.
In order to evaluate the fractionation effect on the characteristics
of the extracts obtained with CO2 and EtOH, NF-HPE
experiments were further assayed using the same experimental
conditions of the fractionated second step (CO2:EtOH (90:10),
303 K, 20 MPa, 360 min and three levels of solvent flow rate,
Table 1). Then, the optimum flow rate at the tested conditions of
pressure and temperature was identified and was used to perform
another set of non-fractionated extractions, varying the composition
of EtOH in the solvent mixture between 30% and 90% (v/v)
(Table 1). For these assays, extraction time was reduced to 210 min,
since the diffusional period was already attained. The extraction
performed with CO2:EtOH (30:70) was quadruplicated in order to
determine the experimental error.