Table 4.

Actual and coded values of independent variables.

Coded Values	Actual Values
	X1	X2	X3	X4
−1.41	0.5	10	25	5
−1	2	20	40	15
0	3.5	30	60	25
+1	5	40	75	35
+1.41	6.5	50	90	45

X₁ (Molar ratio); (water content, %); X₂ (molar ratio) and X₃ (temperature, °C); X₄ (extraction time, min).