Pyrolysis of creosote-treated railroad ties to recover creosote and produce biochar

Authors: Gonzalez, Javier; Boddu, Veera; Jackson, Michael - Mike; Moser, Bryan; RAY, PETER - The Indiana Rail Road

Submitted to: Journal of Analytical and Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2020
Publication Date: 5/11/2020
Citation: Gonzalez, J.M., Boddu, V.M., Jackson, M.A., Moser, B.R., Ray, P. 2020. Pyrolysis of creosote-treated railroad ties to recover creosote and produce biochar. Journal of Analytical and Applied Pyrolysis. 149. Article 104826. https://doi.org/10.1016/j.jaap.2020.104826.
DOI: https://doi.org/10.1016/j.jaap.2020.104826

Interpretive Summary: Creosote is used as a wood preservative used in railroad ties and utility poles. It is estimated that about 17 million railroad ties are replaced every year in the U.S., of which about 700,000 to 900,000 railroad ties may end up in landfills. Besides the environmental concerns and health issues by creosote, landfill disposal is expensive to the railroad industry. Alternative approaches are needed to recycle these creosote-railroad ties, including extraction of creosote, which can be used as a fuel. The burning of feedstock, e.g., railroad ties, at high temperatures under low oxygen conditions (pyrolysis) to recover creosote is an alternative to landfill disposal of the creosote-treated railroad ties. The pyrolysis of a feedstock also produces char-like material (biochar) and depending on its quality; it may serve as a soil amendment or as a water filter to remove pollutants. In this study, the extraction of creosote from pyrolyzed creosote-treated railroad ties at 450 and 700C were compared to the original feedstock. During the 700C pyrolysis, the fumes were condensed and analyzed for their heating value. Toxicity tests of the biochars were conducted too. The results of this study indicated that the 450 and 700C pyrolysis of creosote-treated railroad ties reduced by 98.7 and 99.9% relative to the raw creosote-treated railroad ties. The residual creosote is insignificant in the biochar from the 700C pyrolysis that qualifies as “basic” biochar for soil amendment according to the European Biochar Certificate requirements on the PAHs content; however, the biochar from the 450C pyrolysis does not qualify. No heavy metals of environmental concern were detected in neither biochar. The heating values of the condensates were high; thus, these condensates may be used as fuel or blended with other fuels. The pyrolysis at 700C of creosote-treated railroad ties may be a better alternative to the landfill disposal of these materials. Further work is needed to assess the effectiveness of the biochar from railroad ties to remove contaminants from water and wastewater streams.

Technical Abstract: Annually in the USA, about 800,000 creosote-treated railroad ties (“ties”) may end up in landfills, presenting environmental concerns. Pyrolysis of ties to recover creosote and produce biochar may be an alternative to landfill disposal. In this study, ties were pyrolyzed under different conditions at 667 and 700C at two different facilities and analyzed for residual creosote (as polyaromatic hydrocarbons, PAHs). Condensed gases from the 700C pyrolysis were collected. Toxicity and leachability tests were conducted on ties and biochars. Relative to the ties, both 667 and 700C pyrolysis reduced the extracted PAHs by 98.71 and 99.94%, respectively. Only the 700C pyrolysis biochar qualified as “basic” biochar for soil amendment according to the European Biochar Certificate PAHs requirements. The condensed gases generated a lower (high PAHs content) and upper (low PAHs content) layer. No trace metals of environmental concern were detected on the biochars using toxicity and leachability tests.