Table 1.
Levels of independent variables for the CCD.
| Independent variables | Symbol | Range and levels | ||
|---|---|---|---|---|
| Low (− 1) | Central (0) | High (+ 1) | ||
| Temperature (°C) |
|
500 | 600 | 700 |
| Time (h) |
|
1.5 | 2.5 | 3.5 |
| KOH/C ratio (−) |
|
2 | 3 | 4 |
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