All pretreatments were
conducted using 150 g wood chips in oven-dried (od) weight in a
1-L reactor with a liquor to wood ratio of 3:1 at 170 C for
20 min. This set of mild conditions was used to avoid over pretreatment
so that the differences in the recalcitrance among the poplars
could be shown. The pretreatment liquor was made of sulfuric acid
and sodium bisulfite. Acid concentration was 0.2% (v/v) or 1.1% on
od wood for DA pretreatment. Sodium bisulfite of 2% on od wood
was applied in addition to the application of the same amount of
sulfuric acid in SPORL pretreatment. Three, 1-L vessels were
mounted inside of a 23-L wood pulping digester (pressure vessel)
in an autoclave configuration as described elsewhere