Method for routine 'naphthenic acids fraction compounds' determination in oil sands process-affected water by liquid-liquid extraction in dichloromethane and Fourier-Transform Infrared Spectroscopy

摘要

Formerly classified as naphthenic acids, "naphthenic acids fraction compounds" (NAFC) have become the subject of increasing research, in particular in view of their ubiquitous presence in the Canadian oil sands of Northern Alberta and oil sands process-affected waters (OSPW). NAFC, defined herein as the polar acid-extractable organics fraction of OSPW extractable in dichloromethane, are released into OSPW during the aqueous extraction of oil sands. A method for determining total NAFC concentration based on acidification, liquid-liquid extraction, and Fourier-Transform Infrared Spectroscopy (FT-IR) was developed by Jivraj et al. in 1995. It has become widely used in the oil sands industry for routine monitoring of NAFC. Since then, multiple variations of the method are practiced by different laboratories using different calibration materials and different extraction solvents, differences which were found to affect the results by as much as 38 and 64 percent respectively. The goal of this study was to establish a robust method for routinely quantifying NAFC that does not require complex and expensive laboratory equipment such as mass spectrometers. Described improvements include a semi-automated rolling extraction and the use of a vacuum evaporator unit to reduce the method's environmental impact. The improved FT-IR method avoids emulsions, is precise, provides good agreement with gravimetric determinations of NAFC, increases sample throughput, is inexpensive compared to MS methods, and offers a typical reporting limit of 0.1 mg kg(-1). The residue recovered by this method with minimal losses can be further analyzed by MS techniques to characterize and identify individual NAFC components if desired. (C) 2019 Elsevier Ltd. All rights reserved.