Effect of formation conditions on biochars: Compositional and structural properties of cellulose, lignin, and pine biochars

Abstract

The application of biochar to soil has been proposed as a long-term sink for atmospheric carbon dioxide in terrestrial ecosystems while providing improved soil fertility and increased crop production. Because biochar differs from the widely documented activated carbon, initial characterization information on effects of formation conditions on physical and chemical properties of biochar is important prior to its large-scale incorporation into soils. Plant biomass is composed primarily of cellulose and lignin. As a means of predicting biochar characteristics, samples of cellulose, lignin, and pine were charred under a nitrogen atmosphere at temperatures ranging from 250 °C to 500 °C for times ranging from 1 h to 168 h. Mass loss, elemental composition (carbon, hydrogen, and oxygen), Fourier transform infrared and 13C Nuclear Magnetic Resonance (NMR) spectra of the biochars produced were compared. Mass loss combined with NMR spectrometry showed that the initial rapid loss of material is attributed to aliphatic components, which are either lost or converted to aromatic carbon early in the charring process, and oxygen was lost more rapidly than carbon. The biomass contains a labile oxygen fraction that is quickly removed or lost upon initial heating, and a recalcitrant oxygen fraction which remains fixed in the char. If biochar is to be incorporated into agricultural soils, formation conditions should be tailored to optimize desirable characteristics, such as recalcitrance to degradation, soil fertility and pollutant sequestration, and minimize less desirable characteristics of degradability or low yield (mass loss).