Impacts and release characteristics of K and Mg contained in rice husk during torrefaction process

This work evaluated the catalytic effect and release characteristics of potassium (K) and magnesium (Mg) contained in rice husk during the torrefaction process. Torrefaction of rice husk samples with and without impregnating K and Mg at different torrefaction temperatures (210–270 °C) was carried out in thermogravimetric analyzer (TGA) and laboratory-scale fixed-bed apparatus. TGA studies indicated that K increased the weight loss more rapidly, while the weight losses were slightly decreased with the presence of Mg. Laboratory-scale studies also found that the solid yields of WRH, 0.1 K-WRH and 0.1 Mg-WRH were 90.2%–74.0%, 86.6%–71.8% and 90.0%–74.1% as the torrefaction temperature increased from 230 to 270 °C. K showed an obvious increase of the carbon content of solid product because of its significant catalytic deoxygenation effect. In addition, K and Mg both had the promoting effect on the formation of small molecule gas products from the catalytic conversion of the macromolecular liquid products, and K had stronger catalytic action than Mg. Besides, most K and Mg, 94.6–98.5% for K and 97.9–99.5% for Mg, were remained in the solid product while only a small amount of K and Mg were released to the volatiles during torrefaction process.