The selective cleavage of lignin aliphatic C–O linkages by solvent-assisted fast pyrolysis (SAFP)

Abstract

We report the effect of an organic solvent on the selective cleavage of individual lignin model compounds and lignin C–O linkages during the fast thermal pyrolysis of lignin. During this process, it was possible to lower the aliphatic hydroxyl contents of lignin, along with increasing the amount of single and double bonded aliphatics. It was found that the addition of solvent during fast pyrolysis of lignin lowered the molecular weight distribution of the obtained bio-oil (~ 49–52% decrease) and at the same time inhibited the formation of a high amount of char. A detailed study of the cleavage of complex model compounds using Ethanol-Assisted Fast Pyrolysis (EAFP) revealed that the aliphatic hydroxyl groups and etheric linkages are very reactive during this process. By the use of deuterated lignin model compounds and solvent, it was then possible to elucidate the mechanism for cleavage of lignin in the EAFP process that involves the formation of a transition state between solvent and oxygen bonds of lignin. This transition state involves the cleavage of etheric bonds by the in situ transfer of hydrogen from ethanol to this linkage.