Table 1 Factors and their levels for central composite design
From: A novel design for biodiesel production from methanol + mutton bone fat mixture
Variable | Symbol | Coded factor level | ||||
|---|---|---|---|---|---|---|
− 2 | − 1 | 0 | 1 | 2 | ||
M/O | X1 | 6 | 9 | 12 | 15 | 18 |
Catalyst amount (wt%) | X2 | 1 | 1.5 | 2 | 2.5 | 3 |
Catalyst type | X3 | NaOH | KOH | |||