Table 1.

Experimental range and levels of the input variables used in the CCD model in terms of actual and coded factors.

Independent variables	Uncoded	Coded	Values of coded levels
			−2	−1	0	+1	+2
Time, min	X1	x1	10	37.5	65	92.5	120
Ethanol concentration, %	X2	x2	20	40	60	80	100
Solid-to-liquid ratio, m/v	X3	x3	1:5	1:10	1:15	1:20	1:25
Temperature, °C	X4	x4	22	36	50	64	78