Catalytic pyrolysis of poplar sawdust over biochar of varied origin: Impact of volatile-char interactions

Abstract

Volatile-char interaction is almost unavoidable in pyrolysis, which is part of the process shaping composition of bio-oil/gases and properties of char. In this study, the influence of the char from sawdust/spinach/rice/spirulina/pig manure on pyrolysis of poplar sawdust was investigated at 500 °C, aiming to understand the impact of the char of same or varied origin on formation of volatiles/gases and change of the char catalysts themselves from the volatile-char interaction. The results suggested that the sawdust-, spinach- or rice-char catalyzed cracking of volatiles, reducing formation of heavy tar, decreasing production of bio-oil (28.6–35.5 % vs 49.4%) while enhancing gases generation (36.9–44.0 % vs 22.4%). The spirulina- and manure-char enhanced secondary condensation of volatiles, producing more heavy tar, more bio-oil, and additional oxygen-rich carbonaceous deposit with highly aliphatic nature. This reduced thermal stability, the C/O ratio of the char catalyst, and also led to coverage of char surface, especially for the manure-char catalyst. The in-situ IR techniques showed that manure-char catalyzed formation of abundant ketones and esters/lactones in intermediates, which further involved in polymerization. In comparison, the sawdust-char catalyst catalyzed cracking and aromatization of the volatiles of same origin, producing carbon- and hydrogen-rich carbonaceous solid, enhancing aromatic nature of the char catalyst, which was actually a real process for evolution of structure of biochar in pyrolysis of the sawdust.