Investigation on K and Cl release and migration in micro-spatial distribution during rice straw pyrolysis

• The exact region rich in K and Cl and the morphology of K- and Cl-rich particles in rice straw.
• Visual evidence of K- and Cl-rich particles found gradually reducing or even disappearing during rice straw pyrolysis.
• The release of K and Cl is determined by both the mobility of K and Cl and the resistance along the diffusion way.

This study investigates the release and migration of potassium (K) and chlorine (Cl) in micro-spatial distribution during rice straw pyrolysis in a lab-scale reactor at temperatures from 300 °C to 900 °C. The K and Cl enrichment region and the morphology of K- and Cl-rich particles in rice straw and char obtained after pyrolysis was clearly revealed for the first time in this field of research. Scanning Electron Microscope/Energy-Dispersive Spectrometry (SEM/EDS) was used to analyze the morphology and distribution of inorganic matters in raw rice straw and water-washed rice straw, as well as the char obtained from raw rice straw pyrolysis, both upon the epidermis (outside surface) and the ground tissue (internal surface). X-ray Diffraction (XRD) was used to analyze the inorganic matters in the obtained char. The particles dispersedly distributed on the cell walls in the ground tissue were proven to be inorganic salt, rich in K and Cl. The ground tissue rather than the epidermis is the main part that decomposes and loses weight during pyrolysis. K and Cl diffuse from the ground tissue to the epidermis and they might be partly restricted to the epidermis during rice straw pyrolysis. The release of K and Cl is determined by both the mobility of K and Cl and the resistance along the diffusion way inside rice straw.