Effects of Na/Ca/Fe intermetallic interactions on nitrogen transformations in high-alkali coal pyrolysis

China Xinjiang high-alkali low-rank coal has the characteristics of low ash, high sodium content and high reactivity. Developing clean and efficient conversion technology for high alkali coal into high-value chemicals will have important strategic significance for solving its resources utilization and helping to achieve the “dual carbon” goal. The mineral components Na, Ca and Fe in high-alkali coal have catalytic activity in coal pyrolysis, which has a significant influence on nitrogen transformation. There is still a lack of research on the effects of interactions between mineral components on the thermal conversion mechanisms of fuel-N. This study aims to elucidate the effects of intermetallic interactions on nitrogen transformation during pyrolysis of high-alkali coal. The results have significant implications for formulating control strategies of nitrogen distribution in gas, liquid and solid phases during the cascade utilization of high-alkali coal. Na, Ca, Fe mono-metal and poly-metals were added to deashed coal by equal volume impregnation and sequential impregnation methods, and nitrogen transformation was studied in fixed-bed pyrolysis of high-alkali coal. GC-MS, XPS and solution absorption method were used to quantitatively analyze the effects of mono-metals and polymetals on the distribution of nitrogen-containing products in coal pyrolysis, and interactions between them were analyzed by comparing the results of experiments results with theoretical calculations results. The effect of poly-metals on the pathway of N transformation in pyrolysis of high-alkali coal was studied by analyzing yield/residual rate of nitrogen-containing products. The results indicate that poly-metals usually exhibit an intermetallic antagonism on the migration of nitrogen into the gas phase, with stronger inhibition of HCN, NH₃ than monometallic. The synergistic effects of Na/Ca and Fe/Ca significantly enhance the conversion of N−6 and N−5 in char to heterocyclic nitrogen and amine-N in tar, which demonstrates stronger promotion of nitrogen-containing compound formation in tar compared to mono-metallic systems. Furthermore, Na/Fe and Na/Fe/Ca play a synergistic role for conversion of N-6 to N-Q in char though intermetallic interaction, thus promoting the fixation of nitrogen in char.