Symbols

Independent Variables

Coded levels

-1.68

-1

0

1

1.68

X1

T(°C)

33.2

40

50

60

66.8

X2

M

3.64

5

7

9

10.36

X3

C(%wt)

0.464

0.6

0.8

1

1.136
Table 2: Codes, ranges and levels of independent variables of temperature (T), molar ratio of methanol to oil (M) and catalyst concentration (C) in RSM design.