Volatiles reaction during pyrolysis of corn stalk – Its influence on bio-oil composition and coking behavior of volatiles.

Highlights • With increasing the volatiles residence time, bio-oil quality is improved at 600 °C and deteriorated at 440 °C. • Volatiles reaction yields THF-insoluble compounds, more on the reactor downstream wall (coke -wall) and less in bio-oil. • The amount of coke -wall increases with increasing volatiles temperature and residence time. • The average size of coke -wall may be mainly 1–2 rings at 440–600 °C. Abstract Reaction of nascent volatiles is unavoidable during biomass pyrolysis and significantly influences the product yield, bio-oil quality and coking on the reactor wall. However, experimental studies in this aspect are still very limited. This work aims to advance the knowledge in this aspect using a two-stage reactor. Volatiles were generated in-situ from pyrolysis of corn stalk at 540 °C and swept off to the second-stage reactor preheated at 440–650 °C with a residence time of 1.5–4.7 s. The bio-oil quality was evaluated using simulated distillation gas chromatography. Results show that with increasing the volatiles temperature, the bio-oil yield decreases but the quality is improved: the contents of phenols, aldehydes and monocyclic aromatics increase significantly, those of esters and alcohols increase slightly and the contents of ketones, acids and furans decreases. Effect of volatiles residence time on the bio-oil quality depends on the volatiles temperature: becoming worse at 440 °C and better at 600 °C with increasing the residence time. The volatiles reaction also generates a few tetrahydrofuran-insoluble compounds, depositing on the downstream wall of the second-stage reactor (termed coke -wall) or suspending in bio-oil (termed soot -oil). The coke -wall yield increases with increasing volatiles temperature and residence time and is generally higher than the soot -oil yield. [ABSTRACT FROM AUTHOR]