Minnesota Department of Transportation
The asphalt extraction solvent n-Propyl Bromide (nPB) was selected as an alternative solvent to the currently used d-Limonene and Trichloroethylene (TCE), based on a literature search, communication with asphalt technology experts, and a laboratory investigation. With proper handling techniques and training, nPB can be substituted for d-Limonene and TCE. Extractions with nPB use less solvent per extraction, take less time, and have a shorter drying times. Exposure levels to nPB for the labs were far below the EPA recommended value. The use of nPB for asphalt extraction and the implementation of nPB on-site recycling would generate only non-hazardous still bottom waste. The use of nPB would decrease the hazardous waste of laboratories and reduce annual solvent costs. Payback time for the purchase of solvent recovery units ranges from 3 months to 20 years, depending on the quantities of extraction waste generated per year. It is recommended that all Mn/DOT district laboratories change from d-Limonene or TCE extraction solvents to nPB and conduct on-site recycling with the purchase of solvent recovery systems, and that training be given to lab personnel on the proper handling techniques for nPB.
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