This problem
is solved by adding fresh carbon dioxide in both the extraction column
and separator. The addition of fresh carbon dioxide into the
extraction column is carried out by opening the valve connecting
the CO2 reservoir and the compressor while addition of fresh carbon
dioxide into the separator is carried out by opening the valve
connecting the buffer autoclave to the separator. In general, instabilities
in the column will disappear in a few minutes (5–10 min).
This procedure has the disadvantage that the liquid draining which
is based on a visual procedure may cause errors to close the mass
balance. It is assumed for sake of simplicity that addition of fresh
carbon dioxide does not disturb the equilibrium (dynamic) process
inside the column. After leaving the separator, the carbon dioxide
flows through a filter filled with activated carbon to remove
the remaining substances which cannot be separated by pressure
reduction in the separator and is recycle back via a coriollis type
mass flow meter, the recycle compressor, and a preheater before
been introduced atthe column bottom as shown in Fig. 2. The reflux
and solvent mass flow rate are read directly from the displays ofthe
mass flow meters. The extract and raffinate samples (condensates)
were collected in small glass tubes, sealed under inert atmosphere
(N2) in order to avoid oxidation of tocopherols, and kept into a
freezer at 268K. All the samples were analyzed twice by gas chromatography.