Effects of Alkali and Alkaline Earth Metals on N-Containing Species Release during Rice Straw Pyrolysis

Abstract: To study the effects of inherent and external alkali and alkaline earth metallic species (AAEMs, i.e., K, Ca and Mg) on the behavior of N-containing species release during rice straw (RS) pyrolysis, different pretreatments were applied in numerous experiments. Results indicate that ammonia (NH3) and hydrogen cyanide (HCN) are the major N-containing species and that the yields of isocyanic acid (HNCO) and nitric oxide (NO) are relatively low. The removal of inhert AAEMs shifts N-containing species release to a high-temperature zone according to volatile release behavior because of the increase in activation energy. The formation selectivity of NH3, HNCO, and NO increases by demineralized pretreatment, whereas HCN selectivity decreases. The formation of HNCO is mainly affected by alkaline earth metal. N-containing species release occurs in low temperatures with the addition of external AAEMs. The activation energy of samples impregnated with CaCl2 and MgCl2 sharply decreases compared to the original RS. The total yields of N-containing species are reduced significantly in the presence of KCl, CaCl2, and MgCl2 as additives. The inhibition ability of AAEMs follows the sequence MgCl2 > CaCl2 > KCl. The inhibition effect of MgCl2 can be improved by solution immersion compared with solid powder mixing. The clean biomass pyrolysis and gasification technology with low N-containing species content may be developed according to the results.