Valorization of lignin into phenolic compounds via fast pyrolysis: Impact of lignin structure

•The relationships between lignin structure and pyrolysis activity were evaluated.•Mild acidolysis lignin shows high purity and is representative of native lignin.•Py-GC/MS of four lignins isolated from softwood, hardwood, and herbaceous crops.•The pyrolyzed phenolic compounds varies significantly with different lignin sources.•Herbaceous grass lignin produces 4-vinylphenol as the main pyrolysis product.