Pyrolysis of different wood species: Impacts of C/H ratio in feedstock on distribution of pyrolysis products

Highlights: • Pyrolysis of poplar with a higher C/H ratio produces more char and less tar. • Pyrolysis of pine with a lower C/H ratio produces less char while more gas and tar. • The C/H ratio also affected formation of the aromatic ring structures in tar. • TG-MS result showed that organics in tar did not reach the equilibrium. • DRIFTS study showed that different char had distinct tendencies towards aromatisation. -- Abstract: In this study, pyrolysis of the wood samples with varied C/H ratio on distribution of the products was investigated. The results show that C/H ratio in the biomass drastically affects the yields of char, tar and gas. Poplar has a higher C/H content, and consequently it produces a higher yield of char and the lower yield of tar. Pine wood has the lower C/H ratio, and the pyrolysis produces the lower char but higher gas and tar yields. Furthermore, the C/H ratio in the feedstock affects the elemental composition and the stability of the tar. The higher C/H ratio in biomass resulted in the tar with a higher stability during pyrolysis of the tar. The C/H ratio also affected the formation of the aromatic ring structures in the tar. The pyrolysis of poplar with the highest C/H content produced more aromatics with smaller ring size in the tar, while that from pine with the lowest C/H content produced more aromatics with bigger ring size. The tars produced from the feedstock with the different C/H ratio show a large similarity in terms of distribution of the functionalities but with varied intensities. The TG-MS characterisation showed that the organics in the tar did not reach the equilibrium and could continue to decompose during heating, producing CO₂ via decarboxylation, CO via decarbonylation and H₂ via dehydrogenation reactions. The DRIFTS study of heating char in inert atmosphere showed that the char originated from the different biomasses had distinct stabilities and distinct tendencies towards aromatisation.