Table 3. Regression Coefficients and the Corresponding 95% CI (Low and High) and Parameter Optimization.
| factor | coefficient estimate | df | standard error | 95% CI low | 95% CI high | VIF |
|---|---|---|---|---|---|---|
| intercept | 86.64 | 1 | 0.2021 | 86.19 | 87.09 | |
| A—methanol to oil molar ratio | 14.05 | 1 | 0.1341 | 13.75 | 14.35 | 1.0000 |
| B—catalyst concentration | 3.50 | 1 | 0.1341 | 3.20 | 3.79 | 1.0000 |
| C—temperature | 6.56 | 1 | 0.1341 | 6.26 | 6.85 | 1.0000 |
| AB | –0.8787 | 1 | 0.1752 | –1.27 | –0.4884 | 1.0000 |
| AC | 3.31 | 1 | 0.1752 | 2.92 | 3.70 | 1.0000 |
| BC | –0.8162 | 1 | 0.1752 | –1.21 | –0.4259 | 1.0000 |
| A2 | –9.11 | 1 | 0.1305 | –9.40 | –8.82 | 1.02 |
| B2 | –2.29 | 1 | 0.1305 | –2.58 | –2.00 | 1.02 |
| C2 | –5.31 | 1 | 0.1305 | –5.60 | –5.02 | 1.02 |
| Parameter Optimization and Validation of the Predicted
Value with the Experimental Result | ||||||
|---|---|---|---|---|---|---|
| yield of FAME (wt %) | ||||||
| parameter | constraint | optimum condition | predicted value | experimental value | ||
| methanol to oil molar ratio | 175:1–350:1 | 330.9:1 | 96.15 | 96.16 | ||
| catalyst concentration (wt %) | 3–5 | 4.09 | ||||
| temperature (°C) | 55–65 | 64 | ||||