Release and transformation of K and Cl during the pyrolysis of KCl-loaded cellulose

The migration of K and Cl during biomass thermal utilization can cause serious ash-related problems. Pyrolysis experiments with KCl-loaded cellulose were conducted in a fixed-bed reactor to investigate the reaction of KCl with organic functional groups. The migration pathways of K and Cl were obtained based on the analysis of char samples after pyrolysis. Results showed that the amounts of generated K2CO3 were negligible after pyrolysis at both temperature levels. After pyrolysis at 500 °C, char-Cl and char-K were generated, and the unreacted KCl existed in char as crystal particles. The released Cl amount increased first and then remained stable, whereas the Cl release ratio decreased monotonously with KCl content. Meanwhile, a small fraction of organic K was released. At 900 °C, almost all of the Cl (including KCl and char-Cl) was released, whereas a significant amount of char-K remained in char. Similar to the trend of O content, the amount of char-K increased first and then reached near-saturation with the increase in KCl content, indicating that char-K is associated with the char matrix via O. At 500 °C, during pyrolysis of cellulose with low KCl content, the formation of char-K and the release of Cl are the dominant migration pathways of K and Cl, respectively. With the increase in KCl content, unreacted KCl became the main existing form of K and Cl. The amounts of formed char-K and released Cl, as well as the formation ratio of char-Cl increased first and then reached saturation gradually.