Enriching pyrrole components in bio-oil by nitrogen-rich pyrolysis of tobacco stem employing ZIF-67/ZSM-5 dual-catalyst

Abstract

Traditional pyrrole preparation methods have challenges such as operational complexity, harsh conditions. In this study, This study proposes a strategy for the preparation of pyrrole via nitrogen-rich catalytic pyrolysis of tobacco stems (TS) using a ZIF-67/ZSM-5 dual-catalyst system. Using urea as the exogenous nitrogen source, the in-situ catalytic pyrolysis experiment was carried out in a horizontal tube furnace, the mass ratio of the reaction raw materials (tobacco stem, urea and catalyst) was 5: 3: 5, the air was purged with argon gas before the reaction, the pyrolysis temperature was set to different gradients for the experiment, and the pyrolysis time was fixed at 15 min. Experimental data revealed that, with a 60 % addition of external nitrogen (urea) and a 4:1 molar ratio of ZIF-67, the ZIF-67/ZSM-5 dual catalyst achieved a notable increase in bio-oil yield, reaching 39.6 wt% at 450 ℃. Pyrrole compounds accounted for 45.5 wt% of the total, and the selectivity of nitrogen-containing compounds was remarkably high at 68.9 %. Compared with the pyrolysis of ZIF-67 and ZSM-5 alone, the relative content of pyrrole compounds increased by 7.1 % and 10.4 %, respectively. The ZIF-67 catalyst promotes redox and coordination catalysis to enhance the production of pyrrole precursors such as furans, hydroxyacetone, and aldehydes, ultimately increasing the relative content of Pyrrole compounds. Meanwhile, Utilizing acid catalysis and sieve properties, ZSM-5 suppresses dehydrogenation and nitrile formation. Therefore, the ZIF-67/ZSM-5 dual catalyst can effectively utilize the renewable waste TS and efficiently prepare the high-value chemical pyrrole.