Catalytic hydrotreatment of alkaline lignin and its consequent influences on fast pyrolysis

The current state of lignin has been characterized by these three: (1) as one of the main components in lignocellulosic biomass with an abundant amount; (2) not be taken seriously but treated as a waste product; (3) underutilized due to a complex and stubborn structure. However, lignin can be a rich source for hydrocarbons and aromatic compounds when gives appropriate utilization. In this work, we have studied the hydrotreatment of alkaline lignin (AL) under relatively mild conditions and further investigated the characterization of hydrogenated lignin (HL), especially the behavior during fast pyrolysis. The recovery of the HL decreased with increasing reaction temperature from 60 wt.% to 41 wt.% in the range of 150-250 degrees C. The hydrotreated products were analyzed using Elemental Analysis, FTIR (for HL) and GC-MS (for bio-oil). The HL samples were found to have a higher hydrogen/carbon atomic effective ratio (H/C-eff ratio) and a higher degree of saturation than AL. Compared to the internal structure of the lignin before and after hydrotreatment, the side chain groups were removed from AL during the process. After that, from the fast pyrolysis of HL, it was observed that more light hydrocarbons and aromatic compounds were formed than that of AL. Furthermore, fast pyrolysis in the hydrogen atmosphere revealed that more volatile fractions were released compared to the Helium atmosphere. The total olefins yield was increased for HL compared AL from 1.02 wt.% to 3.1 wt.% at 250 degrees C for 7 hours. This study of HL is instructive to some extent for the industrial utilization of lignin.

Automated summary

Lignin, as a main component in lignocellulosic biomass, is currently underutilized and treated as a waste product due to its complex and stubborn structure. However, appropriate hydrotreatment can convert lignin into a rich source of hydrocarbons and aromatic compounds. The study on hydrogenated lignin (HL) showed higher hydrogen/carbon ratio and saturation compared to alkaline lignin (AL), leading to more light hydrocarbons and aromatic compounds formed during fast pyrolysis. The results of this study provide guidance for the industrial utilization of lignin.