Experimental investigation on the effect of k+ions on the slow pyrolysis of xylan

Pyrolysis is a promising biomass upgrading process capable to produce solid, liquid and gaseous fuels. One of the major concerns about biomass utilization is the remarkable variety of its composition, in terms of both organic and inorganic matrices, affecting the pyrolysis characteristic temperatures and products yield. The effect of different alkali and earth alkali metals (AAEMs) on biomass and cellulose has been extensively studied, whereas only few works exist concerning the effect of AAEMs on the other two main biomass components, namely hemicellulose and lignin. Hemicelluloses, having a carbohydrate nature like cellulose, are expected to be influenced by the presence of AAEMs during the pyrolysis process. In this study, the impact of potassium ions on the slow pyrolysis of hemicellulose is assessed using xylan as a representative of hardwood hemicellulose. To this aim, slow pyrolysis tests, up to a temperature of 973 K using a heating rate of 7 K/min, were conducted for xylan samples loaded with K+ in different amounts. Commercial xylan was demineralized through a cation exchange resin to reduce the presence of inherent inorganics. Subsequently, the demineralized sample was doped with a controlled amount of K+ (0.3, 0.6 and 1.2 wt.%). The experimental results show that doped and demineralized xylan samples exhibit different pyrolytic behaviors. The initial decomposition temperature of the doped xylan is slightly anticipated with respect to the demineralized xylan. Moreover, the gas production is favored at the expense of pyrolysis liquids and the evolution of the release rate of permanent gases (mainly CO2 and CO) with the temperature is significantly affected by the presence of K+.