Mass balance comparison between ammonia fiber expansion (AFEX) and dilute acid pretreatment on corn stover. (a) AFEX pretreatment and (b) dilute acid pretreatment. AFEX and dilute acid pretreatment were conducted at 62.5% and 5.0% solids loading, respectively. Washing of pretreated corn stover from both pretreatment was carried out at 5.0% solids loading based on input materials to the pretreatment. ISL = insoluble lignin (Klason lignin). aThe assay condition for the insoluble lignin measure was 4% final H2SO4 concentration, 121°C, 60 min.