where M0 is the modified severity parameter; t is the residence
time (min); C is the chemical concentration (wt%); Tr is the reaction
temperature (◦C); Tb is the base temperature (100 ◦C); n is
an arbitrary constant. This equation was adapted for application
to sodium hydroxide pretreatment by replacing the acid concentration
with the alkali concentration and calculating a different
n-value (Silverstein et al., 2007). In the present study, alkali concentration
(NaOH) (C) and pretreatment time (t) varied as per
experiments shown in Table 2, while reaction temperature (Tr)
remained constant 121 ◦C throughout the experiments. The following
equation (Eq. (4)) was used to calculate combined severity
factor:
M0 =
t
·
C
·
exp
Tr −
Tb
14.75
(4)
The relationship between % lignin reduction and standard severity
parameter and between sugar yield and standard severity
parameter was also calculated.