Table 1.
Experimental range and levels of independent variables.
| Variables | Symbol | Code levels | ||
|---|---|---|---|---|
| −1 | 0 | 1 | ||
| Extraction time (min) | X 1 | 110 | 120 | 130 |
| Extraction pressure (MPa) | X 2 | 22 | 25 | 28 |
| Extraction temperature (°C) | X 3 | 32 | 35 | 38 |
| CO2 flow (L/h) | X 4 | 16 | 18 | 20 |
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