2.5 Chemical composition analysis of untreated and pretreated
biomass
The chemical composition of untreated and pretreated biomass was
analyzed in accordance with the NREL procedure.29 In
brief, 3 ml of 72% sulfuric acid and 0.3 g of biomass were mixed in a
glass tube, and the mixture was stirred for 1 h at 30 °C in a water
bath. After the 1 h reaction, the mixture was diluted with 84 ml of
distilled water and autoclaved at 121 °C for 1 h. The mixture was
filtered through medium pore-size crucible glass filters, and the
filtrate was collected to determine the content of acid-soluble lignin
and sugar. Acid-soluble lignin content was measured by a UV-vis
spectrometer at 320 nm wavelength, while the sugar composition was
analyzed by a high-performance liquid chromatography (HPLC, Agilent
Technologies 1260 Infinity) equipped with a Biorad Aminx HPX-87H column.
The crucible was dried, weighed, heated to 575 °C in a muffle furnace,
and weighed again to determine the content of acid-insoluble lignin. All
untreated and pretreated biomass were analyzed in duplicates.