Spectroscopic characterization of lignocellulosic biomass

This thesis focuses on characterization of organic components and inorganic elements in lignocellulosic biomass. The chosen biomass models were mostly wood from conifers and straw from rhizomatous grasses but also forest-based residues and agro-based plants. X-ray fluorescence (XRF) and near infrared (NIR) spectroscopy are techniques that can potentially be incorporated in a future biorefinery concept, where characterization of the feedstock is crucial due to the heterogeneous nature of biomass.XRF spectroscopy combined with principal component analysis (PCA) was used to classify a number of different biomass materials. Moreover, partial least squares regression calibration models were developed for several ash elements and ash content with good predictive capabilities. The capability of XRF and NIR spectroscopy to measure ash content in biomass was investigated and it was concluded that XRF spectroscopy was the superior method of the two, especially for measuring contaminated material. If the two techniques were used in conjunction, it was possible to estimate the degree of contamination. In an additional study into the potential for future separation techniques, it was shown that the 2D-NIR technique is useful for classifying wood chips, as well as identifying individual wood chips with high extractive content. Synchrotron-based X-ray absorption techniques such as X-ray absorption near edge structure (XANES) and scanning transmission X-ray microscopy (STXM) based near edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to study the effect of thermal treatment of lignocellulosic material at 300 to 800 °C and low O2 partial pressures. PCA modelling of Ca XANES spectra in combination with linear fitting of spectra from reference compounds mainly confirmed the results from calculated theoretical thermodynamic models. The results from STXM C 1s NEXAFS spectroscopy showed that thermal treatment up to 300 °C induced only minor change in plant cell walls and that the major decomposition of the carbon matrix occurred between 300 and 500 °C. Nanomapping of Ca by STXM revealed a size distribution of calcium crystals mainly within the 100 to 200 nm range, which might provide an insight into the volatile behaviour of Ca in combustion processes.