TG-FTIR STUDY OF THE INFLUENCE OF POTASSIUM-CHLORIDE ON WHEAT-STRAW PYROLYSIS

The interest in utilizing biomass as a Con neutral fuel bg; combustion , gasification, or pyrolysis processes is increasing due to concern ab out the emission of greenhouse gases from fossil fuel combustion. In t hermal fuel conversion, pyrolysis is an important step which determine s the split of products into char, tar, and gas. In this work, a combi nation of thermogravimetry and evolved gas analysis by Fourier transfo rm infrared analysis (TG-FTIR) has been applied to study the influence of potassium chloride (KCl) on wheat straw pyrolysis. Raw straw, wash ed straw, and washed straw impregnated with KCl have been investigated . To facilitate interpretation of the results, pyrolysis of biopolymer s (cellulose, xylan, lignin) in the presence and absence of KCl was in vestigated as well. The raw straw decomposed in a single broad feature less peak. By washing, two peaks appeared in the derivative weight los s curve, corresponding to the decomposition of hemicellulose and cellu lose components in the straw. Washing reduced the char yield from 23 w t % (daf) to 12 wt % (daf), reduced the;yields of gases, and increased the tar yield from 32 wt % (daf) to 66 wt % (daf). Adding 2 wt % (daf ) KCl to the washed straw resulted in a char yield which was close to that of the raw straw, and the yields of tar and gases were between th ose from the raw and washed straw. Furthermore, the peaks correspondin g to hemicellulose and cellulose decomposition moved to lower temperat ures, from 670 to 633 K for the cellulose peak, but did not collapse t o a single peak as in the raw straw. The influence of KCl on the peak temperature of hemicellulose and cellulose decomposition was not obser ved with the single biopolymers. This indicates that minerals in straw influence the interaction between the biopolymers in whole biomass. C ombustion of the char remaining after pyrolysis showed that char combu stion is catalyzed by the minerals present in wheat straw. Char from t he washed straw with KCl added burned with two peaks in the derivative weight loss curve corresponding to a catalyzed and noncatalyzed part, indicating that the added salt did not behave in the same way as the inherent minerals in the straw.