Steam explosion of Aucoumea klaineana sapwood: Membrane separation of acetylated hemicelluloses

The fractionation of the aqueous effluent of Aucoumea klaineana Pierre (Okoume) sapwood steam explosion was examined by a sequential-dilution type membrane diafiltration. The permeate and retentate fractions were characterized by HPLC-SEC, HSQC-NMR, FTIR, UV-visible and HPAE-PAD ion chromatography. Diafiltration with 10 kDa regenerated cellulose membrane has been shown to provide efficient fractionation without fouling. O-2 and/or O-3 acetylated xylans with a lower proportion of O2 and/or O-3 acetylated glucomannans were isolated in the retentate (approximate to 35% w/w and 1.08 w/w% based on initial effluent solid content and on initial dry wood respectively, including 65% w/w in the range 9-22 kDa). The molecular weights of the polysaccharides were significantly higher than those obtained by ethanolic precipitation. The permeate concentrated low molecular mass oligomers (90% w/w < 2.3 kDa, 1.88 w/w% based on initial dry wood) composed of pectic sugars, highly acetylated xylans (DS approximate to 0.9) and relatively high proportion of soluble lignin (approximate to 40% w/w) including Lignin-Carbohydrate Complexes (LCCs).