*2.2. Organosolv Pretreatment*

Oil palm empty fruit bunch (OPEFB), solvent ethanol 50% (v/v), and acid catalysts were added to 150 mL stainless steel tubular reactors (Swagelok, El Paso, TX, USA). The raw material and solvent were added according to the required solid loading. The reactors were sealed and placed into an oil bath (Julabo, Seelbach Germany) at specific temperature and retention time. After the desired retention time, the reactors were removed from the oil bath and quenched directly in an ice bath. The mixture was filtered using a 250 µm sieve for separation of the solid (glucan-rich) and the liquor (solvent, lignin-rich, and hemicellulosic compounds-rich) fractions after cooling down. The solid was washed using 28.3 mL of solvent/g of dry sample. The solvent was being collected and added to the liquor. To induce precipitation of lignin, 56.6 mL of water/g of dry sample was added to the liquor which was then centrifuged at 3360× *g* for 5 min to separate the lignin from the solvent and hemicellulosic compounds-rich fraction. Then, lignin-rich fraction, glucan-rich fraction, and hemicellulosic compounds-rich fractions were kept in the refrigerator at 4 ◦C until use. Series of pretreatments were carried out by varying four parameters, namely, acid type and concentration, temperature, retention time, and S/L ratio. To study the effect of catalyst, two strategies were used: (a) sulfuric acid and acetic acid were added to the solvent to reach the pH of 3; and (b) acetic acid was added in the equal amount as that of sulfuric acid added to reach the pH of 3. The pretreatment temperatures studied were 180, 210, and 220 ◦C; the retention times were 30, 60, 90, and 120 min; and the S/L ratios were 1:20, 1:10, and 1:5. The experiments were carried out using a one factor-at-time strategy.
