Environmentally Friendly Process for Recovery of Wood Preservative from Used Copper Naphthenate-Treated Railroad Ties

Haber, HL, Kim, P, Chmely, SC, Lloyd, J, Regmi, YN ORCID: https://orcid.org/0000-0001-6588-7683, Abdoulmoumine, N and Labbé, N (2017) Environmentally Friendly Process for Recovery of Wood Preservative from Used Copper Naphthenate-Treated Railroad Ties. ACS Sustainable Chemistry and Engineering, 5 (11). pp. 10806-10814. ISSN 2168-0485

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Abstract

© 2017 American Chemical Society. Removal of copper naphthenate (CN) from used wooden railroad ties was investigated to improve the commercial viability of this biomass as a fuel source and avoid alternative disposal methods such as landfilling. Bench-scale thermal desorption of organic preservative components from CN-impregnated ties was followed by extraction of the copper fraction with ethylenediaminetetraacetic acid, 1-hydroxy ethylidene-1,1-diphosphonic acid, or 2,6-pyridine dicarboxylic acid (PDA). Naphthenic acid (NA) and carrier oil were recovered at desorption temperatures between 225 and 300 °C and could potentially be recycled to treat new ties. The thermal treatment also mimicked torrefaction, improving the biomass properties for use as a thermochemical conversion feedstock. Chelation with PDA, a biodegradable chelating agent, after desorption had the highest extraction efficiency of copper and other naturally present inorganics, extracting 100% of the copper from both the raw and 225 °C-treated samples. Optimized desorbed material showed a 64% decrease in ash content when extracted with PDA; however, extraction efficiency decreased as desorption temperature increased, indicating that thermal treatment caused the inorganics to be less extractable. We concluded that the optimum desorption conditions were between 250 and 275 °C for 45 min followed by extraction with PDA when considering both NA removal and inorganic extraction efficiency.