The effects of weathering on the pyrolysis of low-carbon fuels: Railway ties and asphalt shingles

Abstract

Creosote-treated wooden railway ties and roofing asphalt shingles are discarded in large quantities and may be significant sources of energy; however, they may have rotted or oxidized, and the chemical changes that result from such weathering could affect their behavior as a fuel or pyrolysis feedstock. Such changes in railway tie wood, and roofing asphalt shingles were studied by identifying isothermal 250 and 550°C pyrolysis products (pyrolyzates) with pyrolysis-gas chromatography/mass spectrometry (py-GC/MS). Poplar wood pyrolysis was also studied and compared to existing literature to establish a reference scenario; identified poplar wood pyrolyzates assisted in the analysis of railway tie and asphalt shingle pyrolyzates. Poplar pyrolyzates included the products of polysaccharide ring-breaking and lignin pyrolysis, confirming one of the two competing low-temperature pyrolysis models. Railway tie pyrolyzates showed few signs of bacterial degradation or oxidation, indicating that the tie considered here did not undergo extensive weathering. Roofing asphalt pyrolyzates included many carbonyl, hydroxyl, and ether functionalized cyclic species, as well as sulfur dioxide; these pyrolyzates indicate extensive and preferential oxidation of cyclic carbon and sulfur.