Speciationof Sulfur in Biochar Produced from Pyrolysisand Gasification of Oak and Corn Stover

摘要

The effects of feedstock type and biomass conversion conditions on the speciation of sulfur in biochars are not well-known. In this study, the sulfur content and speciation in biochars generated from pyrolysis and gasification of oak and corn stover were determined. We found the primary determinant of the total sulfur content of biomass to be the feedstock from which the biochar is generated, with oak and corn stover biochars containing 160 and 600–800 ppm sulfur, respectively. In contrast, for sulfur speciation, we found the primary determinant to be the temperature combined with the thermochemical conversion method. The speciation of sulfur in biochars was determined using X-ray absorption near-edge structure (XANES), ASTM method D2492, and scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS). Biochars produced under pyrolysis conditions at 500–600 °C contain sulfate, organosulfur, and sulfide. In some cases, the sulfate contents are up to 77–100%. Biochars produced in gasification conditions at 850 °C contain 73–100%organosulfur. The increase of the organosulfur content as the temperatureof biochar production increases suggests a similar sulfur transformationmechanism as that in coal, where inorganic sulfur reacts with hydrocarbonand/or H2 to form organosulfur when the coal is heated.EDS mapping of a biochar produced from corn stover pyrolysis showsindividual sulfur-containing mineral particles in addition to thesulfur that is distributed throughout the organic matrix.