Toward valorization of lignin: characterization and fast pyrolysis of lignin recovered from hot-water extracts of electron-beam irradiated sugar maple
This paper provides an analysis of lignin-rich (> 80%) solids recovered as a byproduct of hot-water extraction (HWE) pretreatment performed on sugar maple (Acer saccharum) (autohydrolysis at 160 degrees C for 2 h). The effects of electron beam irradiation (EBI) pretreatment before HWE were assessed with regard to lignin removal during HWE and selected features of the recovered lignin. The results of catalytic fast pyrolysis - gas chromatography-mass spectrometry (Py-GCMS) are also discussed. EBI of sugar maple increased lignin removal (delignification) during subsequent HWE; however, recovery of dissolved lignin and lignin degradation products from the hot water extract was hindered. Variation of EBI energy dosages before HWE had little effect on lignin recovered from extracts, except for a slightly reduced molecular weight, as evidenced by size exclusion chromatography. The recovered lignin was hypothesized to have advantages for Py-GCMS compared with common technical lignins, such as kraft or dilute acid hydrolysis lignin, because of lower ash and sulfur content and fewer condensed structures (i.e., increased reactivity). The Py-GCMS results showed that the hot water-extracted lignin-rich samples produced less residual char than kraft and commercial dilute acid hydrolysis lignin samples; however, yields to simple phenols were reduced compared with kraft lignin results, mostly because of the high syringyl-unit content of the hardwood-derived lignin.
Application: This research could benefit a mill's research and development efforts toward developing products other than paper from lignocellulosic material.