Investigations into the pyrolytic behaviour of birch wood and its main components: Primary degradation mechanisms, additivity and metallic salt effects

The effect of mineral addition on biomass thermal decomposition was investigated in slow pyrolysis conditions (10 °C min−1). The tests were carried out on the biomass components, their mixtures and real wood (birch wood), using thermogravimetric analyses (TGA) and pyrolysis coupled to mass spectrometry technique (Py-MS). The main criteria chosen to study the additivity of thermal behaviour were: the mass loss of the samples (C.R %), the temperature of the maximum mass loss (Tm) and the initial degradation temperature (Ti). Furthermore, to highlight the primary reactions of thermal behaviour of the studied samples, the chemical composition of emitted vapours was analysed and the influence of some mineral salts (MgCl2, NiCl2) on pyrolysis primary mechanisms was also investigated. Considering the large data sets collected (integrated MS intensities of 19 selected ions), principal component analysis (PCA) was used to provide a tool to simplify pyrolysis data interpretation. Considering mineral effects, it is possible to favour some primary mechanisms: dehydration (inducing to char formation); ring opening (with gas and light vapours formation) and depolymerisation (with sugars, pyrans and furans formation). MgCl2 catalyses inter (or intra) molecular dehydration. However, NiCl2 does not catalyse the mentioned primary reactions but appreciably modifies the emitted gas and vapours composition. With the help of the PCA calculations, the effect of metallic salts on xylan and ternary mixtures was evidenced.

► We analyse two kinds of mineral salts on thermal degradation of biomass samples.
► MgCl2 catalyst has an important role on the promotion of the primary dehydration of cellulose.
► PCA statistical analysis is a powerful tool for the acquisition and interpretation of a large data set.