Characterization of chars from biomass-derived materials: pectin chars

The effect of pyrolysis conditions on the yield and composition of char fro m pectin was studied. Pectin is a component of the carbohydrate fraction of biomass-derived materials. The pyrolysis was done at atmospheric pressure under oxidative and non-oxidative (inert) atmospheres and at temperatures r anging from 150 to 550 degreesC. The volatile product was analyzed by gas c hromatography/mass spectrometry (GC/MS). The solid product, i.e. char, was characterized by solid-state C-13 nuclear magnetic resonance (NMR) and Four ier-transform infrared (FTIR) spectroscopy. The char was also analyzed for its elemental composition and surface area. The surface morphology of char was studied by scanning electron microscopy (SEM). The results were compare d to those from chlorogenic acid (CA), a component of the phenolic fraction of biomass-derived materials. The behavior of pectin was similar to that o f CA. For both pectin and CA, the char yield decreased with increasing temp erature before leveling-off at ca. 20% of the starting substrate in non-oxi dative runs. In oxidative runs, the char yields from both substrates became negligible at 550 degreesC. NMR analysis indicated that the aromatic chara cter of char increased as the pyrolysis temperature increased. The oxygen f unctionality was progressively lost and the resonance bands corresponding t o carbonyl groups mostly disappeared above 350 degreesC. FTIR analysis also suggested the loss of hydroxyl and carbonyl groups from chars at high temp eratures. The H/C and O/C ratios of chars decreased continuously with incre asing temperature. The oxidative chars showed characteristics essentially s imilar to those of the non-oxidative chars. The surface area of char was ne gligible at low temperatures, but increased dramatically to a maximum of 70 m(2) g(-1) at 450 degreesC before decreasing at 550 degreesC. SEM analysis indicated that the pyrolysis of pectin occurred via softening and melting of the substrate followed by bubble formation. At high temperatures, surfac e etching followed by the appearance of crystal deposition on the char surf aces were also observed. The results are consistent with the analysis of th e evolved gases (C) 2001 Elsevier Science Ltd. All rights reserved.