Selection of optimal conversion path for willow biomass assisted by near infrared spectroscopy

Abstract

Willow (Salix sp.) is one of the most common hardwood species suitable for short-rotation coppice. It can be converted to different products, including chemicals, fuels, fibers or furniture. It may also be used in agriculture and environmental engineering. Molecular composition of biomass and its physical properties highly influence effectiveness of its chemical, thermo-chemical or mechanical-chemical conversion. Therefore, it is challenging to provide biomass feedstock with optimized properties, best suited for further downstream conversion. The goal of this research was to establish a procedure for determination of the willow biomass optimal use cultivated in four different plantations in Poland. A special attention has been paid to the application of the near infrared spectroscopy for evaluation of biomass chemical composition and its physical properties. Near infrared spectroscopy (NIR) could be an alternative to standard analytical methods supporting the research and development of biomass production technologies. Partial least squares regression models for quantitative prediction of wood chemical components (lignin, cellulose, holocellulose, hemicellulose and extractives) and high heating values were developed. The residual prediction deviation (RPD) values confirm the applicability of chemometric models for screening in breeding programmes (for lignin, cellulose and extractives content) and for research in the case of high heating value. The analysis of NIR spectra highlighted several peculiarities in the chemical composition of the investigated willow clones. Finally, a knowledge-based expert system and a prototype automatic NIR system allowing the computation of a “suitability index” based on PLS models and dedicated to selection of optimal biomass conversion path, was developed.