2.2.2. Bisulfite process
The sodium-based liquor was prepared as needed from reagent
grade sodium sulfite (NaHSO3) and sulfuric acid (H2SO4). In this
process, the EFB samples reacted with a solution of sodium bisul-
fite at 180 -
C and pH level in the range of 2–4 for 30 min in batch
operations. The pretreatment liquor to wood ratio can be as low
as 4. The pretreatment was conducted in 1 L stainless steel reac-
tors with an electrical heating system. After the pretreatment,
the spent liquor was separated from the solid (pretreated sub-
strate) via filtration and then stored for chemical analysis. The so-
lid substrate was collected, washed thoroughly with tap water,
and then stored in plastic bags for further analysis and enzymatic
hydrolysis.