Variable

 

Range and levels

-α

-1

0

+1

+α

Temperature (oC)
Time (min)
Acid concentration (%)

X1
X2
X3

123.2
19.8
0.2

130
30
0.5

140
45
1.0

150
60
1.5

156.8
70.2
1.8
Table 4: Range and levels of independent process variables used in experimental design.