Ultra-low Sulfur Diesel Classification with Near-Infrared Spectroscopy and Partial Least Squares

Abstract

Abstract : The United States Environmental Protection Agency (EPA) will have regulations in effect no later than 2010 requiring sulfur content to be no greater than 15 parts per million (ppm) for on-road, off-road, and marine diesel fuel applications. Hydrotreatment will remove sulfur, but it also removes other polar compounds that impart fuel lubricity. The rapid and accurate discrimination of ultra-low sulfur diesel (ULSD) fuels is then important for both regulation compliance and lubricity assessment. While near-infrared (NIR) spectroscopy has not yet been able to accurately predict the sulfur content of fuels, partial least-squares (PLS) models can be constructed to predict ULSD identity indirectly through the other chemical changes caused by hydrotreatment that do, in fact, affect NIR instrument responses, albeit only subtly (see the Supporting Information). Therefore, it is possible to develop relatively low-cost portable NIR field instrumentation for the rapid identification of fuels that have undergone hydrotreatment, which, by virtue of the inevitably low resulting sulfur content, are ULSD fuels. Data were collected from a set of 391 worldwide diesel fuel samples, consisting of 251 Naval distillate (NATO F-76), 129 marine gas oil (MGO), and 11 ULSD fuels from various North American sources. The non-ULSD fuels had measured sulfur contents ranging from 200 to over 9000 ppm, and the ULSD fuels contained 10 ppm or less sulfur. NIR absorbance spectra were collected from 1000-1600 nm with a fiber optic reflectance probe coupled to a custom Bruker Optics NIR spectrometer, which employed a thermoelectrically cooled 512 element GaAs detector array.