Emissions Characteristics and Formations of Carbonyl Compounds from the Combustion of Biomass and Their Three Compounds at Different Temperatures

Abstract

Carbonyl compounds are important precursors of free radicals, ozone (O 3 ), and secondary organic aerosols in the atmosphere. Global biomass combustion contributes more than 30–50% to atmospheric carbonyls. To explore the formation mechanism of carbonyl compounds and the effects of temperature and fuel composition, this study performed combustion experiments using three biomass types (rice straw, pine, and poplar) and their components (cellulose, hemicellulose, and lignin) at seven different temperatures (300–900 °C, 100 °C gradient) and two oxygen concentrations (21% and 10.5%) in a quartz tube furnace. The results showed that the average emission factors (EFs) of carbonyl compounds generated from wood (pine and poplar) combustion were slightly higher than those from rice straw combustion were. Additionally, emissions of carbonyl compounds from biomass burning were mainly concentrated in the low temperature (300–500 °C) stage, with formaldehyde and acetaldehyde being the most emitted compounds. However, most carbonyls decreased rapidly, from 4208.3 ± 1023.5 to 513.6 ± 264.1 mg/kg, when the ignition temperature ranged between 600 and 900 °C, while the proportions of acetone and aromatic aldehydes increased. This indicated different formation mechanisms for acetone and aromatic aldehydes at different temperatures. Furthermore, oxygen reduction promoted the emission of carbonyl compounds. Overall, the three components of biomass combustion revealed that large amounts of formaldehyde, acetaldehyde, and unsaturated aldehyde were produced from cellulose, while acetone was mainly produced from hemicellulose and lignin. However, lignin could continuously produce aromatic aldehydes owing to its rich aromatic ring structure. This study provides data support for proving the formation mechanism of carbonyl compounds emitted from biomass combustion.

Keywords: Carbonyl compounds, biomass combustion, three components, ignition temperature, aromatic aldehydes