How height-related variations in hybrid poplars affect composition and pyrolytic behaviour: The key role of lignin maturity during woody-biomass pyrolysis

• Published in: Journal of analytical and applied pyrolysis 2023-01, Vol.169, p.105861, Article 105861
• Main Authors: Folgueras, M.B., Gómez-Martín, J.M., Diez, M.A.
• Format: Article
• Language: English
• Subjects: Biomass component interactions; FTIR indices; Hybrid poplars; Lignin maturity; Short Rotation Woody Coppice; Thermogravimetry
• ISSN: 0165-2370; 1873-250X
• DOI: 10.1016/j.jaap.2023.105861

This work aims to explore the height-related changes in chemical composition, calorific value, and thermochemical behavior during pyrolysis of four types of hybrid poplars (AF2, Beaupré, I214 and Monviso) and their structural components. The samples were collected from a Short Rotation Woody Coppice (SRWC) located in an abandoned opencast mine in the north of Spain. The effect of lignin and extractives (hydrophilic and hydrophobic ones) on wood pyrolysis, as well as the relationships between thermochemical properties and lignocellulosic composition, extractive content and lignin maturity, are investigated. The higher bark content of the top sections influences chemical and structural compositions. They have higher calorific values and more lignin, extractives, N and S contents, yielding more fixed carbon and ash. Additionally, the lignin of the top sections is less thermally stable. The isolation of structural components from the samples shifts the maximum volatile emission to higher temperatures for lignin and lower temperatures for holocellulose and cellulose, compared with those in the un-extracted samples. Lignin has a notable influence on wood decomposition since: (i) until its β-O-4 linkages and hemicellulose/lignin connections have been broken, cellulose devolatilization does not reach its maximum rate; and (ii) its removal reduces sample thermal stability, its effect being more significant than that of extractive removal. DRIFT spectroscopy is a valuable technique for predicting variations in chemical and thermochemical characteristics with the height of the wood sample. Several indices representing ratios of the maximum absorbance of specific signatures of lignin and cellulose could be appropriate for quick preliminary screening of woody biomass. [Display omitted] •Three sections of four genotypes of hybrid poplars from SRWC were studied.•Tree chemical properties vary with height, which conditioned the optimum process.•Top sections contain more bark and lignin, which is less thermally stable.•Lignin has a relevant impact on holocellulose and cellulose thermal stability.•FTIR indices are adequate for predicting some biomass thermal properties.