(452c) Types of Carbon in Biochars From Slow Pyrolysis, Fast Pyrolysis and Gasification

Biochars, sustainably produced charcoals used for soil amendment and carbon sequestration applications, contain both organic (carbon) and inorganic (ash) constituents. The composition of the inorganic fraction is mostly dependent on the mineral matter present in the feedstock. The types and quantities of carbon in the organic fraction of the biochars, however, are highly dependent on processing conditions such as temperature, heating rate, reaction atmosphere (inert or oxic), and residence time. This study compares the types of carbons in biochars from the slow pyrolysis, fast pyrolysis, and gasification of switchgrass, corn stover and various hardwoods. Among the analytical techniques used to characterize the chars are CHNOS elemental analysis, proximate analysis, Fourier-transform infrared spectroscopy (FTIR), and quantitative ¹³C solid-state nuclear magnetic resonance spectroscopy (NMR) using direct polarization magic angle spinning (DP/MAS) techniques. Three biochars from the fast pyrolysis of corn stover were also used to conduct a soil incubation study to measure carbon bioavailability based on CO₂ evolution rates. Overall findings suggest that biochars can be tailored to specific applications and that not all chars created from the thermochemical conversion of biomass will be suitable for use as biochars.