Recovery of creosote from used railroad ties by thermal desorption

Abstract

Used creosote-treated wood ties were thermally treated between 250 and 350 °C to recover preservative and upgrade the wood to provide an improved quality biomass for thermochemical processes. With thermal treatments ranging from 250 to 300 °C, the amounts of creosote, mostly consisting of polycyclic aromatic hydrocarbons (PAHs), recovered were from 47 to 79 % of total creosote present in the used ties. Thermal treatment at 350 °C recovered 97 % of total PAH compounds. Larger amounts of PAHs with higher molecular weights (HMWs) and lower vapor pressures (LVP) were recovered at elevated temperatures. Temperature above 300 °C decomposed the wood matrix, with a mass loss ranging between 50 to 63 wt% and produced large amounts of light organics, anhydrosugars, and phenolic compounds that would contaminate the recovered creosote. Our study concluded that thermal treatment ranging between 275 and 300 °C would be preferred to recover preservative for recycling and improve the wood quality,

Rail road tie preservative recovery and conversion to hydrocarbon fuels: a conceptual process design and economics

“…The condensed creosote and water for the vapor are sent to a series of horizontal decanters (UOP‐205‐7) with vessel diameter and length of 1.5 m and 3 m and residence time in the dispersion zone of <5 min. The selection of decanter for creosote separation was motivated by our earlier study in which sufficient separation was observed during storage . The design specifications for the decanters assumed that creosote is the dispersed phase given its higher density relative to that of water (1075 kg m −3 ) and droplet settling dimension of 150 μm.…”

“…This classification makes energy recovery from treated wood ties as boiler fuel more challenging. As a result, an increasing volume of treated wood will be disposed of by incineration or landfill each year, resulting in revenue loss or added expenses …”

“…Over the years, various investigators have explored pyrolysis as an approach to valorize used railroad ties . We We reported recently on a two‐step thermochemical process that includes the extraction and recovery of preservatives followed by conversion of the thermally treated ties through pyrolysis . This approach recovers a high yield of preservatives with a high level of purity and permits the production of high quality bio‐oil with low amounts of water and acidic compounds and high lignin‐derived bio‐oil.…”

“…As a result, an increasing volume of treated wood will be disposed of by incineration or landfill each year, resulting in revenue loss or added expenses. 8 Over the years, various investigators have explored pyrolysis as an approach to valorize used railroad ties. 2,9,10 We We reported recently on a two-step thermochemical process that includes the extraction and recovery of pre-size, internal rate of return, and feedstock cost have the most impact on the MFSP.…”

“…© 2018 Society of Chemical Industry and John Wiley & Sons, Ltd Keywords: railroad ties; creosote; thermal desorption; pyrolysis; techno-economic analysis servatives followed by conversion of the thermally treated ties through pyrolysis. 8,10,11 This approach recovers a high yield of preservatives with a high level of purity and permits the production of high quality bio-oil with low amounts of water and acidic compounds and high ligninderived bio-oil. The threshold of toxicity for the recovered preservatives is similar to that of a conventional creosote sample.…”