Detection and Quantification of Aromatic Hydrocarbon Compounds in Water Using SH-SAW Sensors and Estimation-Theory-Based Signal Processing

This work investigates a sensor system for direct groundwater monitoring, capable of aqueous-phase measurement of aromatic hydrocarbons at low concentrations (about 100 parts per billion (ppb)). The system is designed to speciate and quantify benzene, toluene, and ethylbenzene/xylenes (BTEX) in the presence of potential interferents. The system makes use of polymer-coated shear-horizontal surface acoustic wave devices and a signal processing method based on estimation theory, specifically a bank of extended Kalman filters (EKFs). This approach permits estimation of BTEX concentrations even from noisy data, well before the sensor response reaches equilibrium. To utilize estimation theory, an analytical model for the sensor response to step-changes, starting from clean water, to mixtures of multiple analytes is first formulated that makes use of both equilibrium frequency shifts and response times (for individual analyte), the latter being specific for each combination of coated device and analyte. The model is then transformed into state-space form, and the bank of EKFs is used to estimate BTEX concentrations in the presence of interferents from transient responses prior to attainment of equilibrium. Samples used in the experiments were either manually mixed in the laboratory or taken from real monitoring sites; they contained multiple chemically similar analytes with concentrations of individual BTEX compounds in the range of 10–2000 ppb. The estimated BTEX concentrations were compared to independent gas chromatography measurements and found to be in very good agreement (within about 5–10% accuracy), even when the sample contained multiple interferents such as larger aromatic compounds or aliphatic hydrocarbons

Hydrocarbon Renewable and Synthetic Diesel Fuel Blendstocks: Composition and Properties

We examined the chemical composition and properties of several diesel fuels and blendstocks derived from Fischer–Tropsch (FT) synthesis, hydroisomerization of lipids, and fermentation of sugar via the terpenoid metabolic pathway. Comprehensive two-dimensional gas chromatographic analysis with nonpolar and polar columns, ¹³C NMR, GC-MS, and elemental analysis were used to assess fuel chemistry. Performance properties included density, heat of combustion, cetane number, and cloud point, as well as other properties. The fuels consisted almost entirely of normal and iso-paraffins. Three samples contained residual oxygen below 0.1 mass %. All of the renewable and synthetic diesel fuels have significantly lower density than is typical for a petroleum-derived diesel fuel. As a result, they have slightly higher net heat of combustion on a mass basis (2%–3% higher), but lower heat of combustion on a volume basis (3%–7% lower). Two critical diesel performance properties, cetane number and cloud point, were correlated with iso-paraffin content and chain length. The results confirm that properties of hydroisomerized fats and oils, as well as FT diesel, can be tuned by increasing the degree of isomerization to lower cloud point which also lowers the cetane number. In spite of this trade-off between cloud point, and cetane number, the cetane numbers were still over 70 for fuels with cloud points as low as −27 °C. The terpenoid biofuel exhibited a cloud point below −70 °C and a cetane number of 58

Non-Targeted Analysis of Petroleum Metabolites in Groundwater Using GC×GC–TOFMS

Groundwater at fuel release sites often contains nonpolar hydrocarbons that originate from both the fuel release and other environmental sources, as well as polar metabolites of petroleum biodegradation. These compounds, along with other polar artifacts, can be quantified as “total petroleum hydrocarbons” using USEPA Methods 3510/8015B, unless a silica gel cleanup step is used to separate nonpolar hydrocarbons from polar compounds prior to analysis. Only a limited number of these metabolites have been identified by traditional GC–MS methods, because they are difficult to resolve using single-column configurations. Additionally, the targeted use of derivatization limits the detection of many potential metabolites of interest. The objective of this research was to develop a nontargeted GC×GC–TOFMS approach to characterize petroleum metabolites in environmental samples gathered from fuel release sites. The method tentatively identified more than 760 unique polar compounds, including acids/esters, alcohols, phenols, ketones, and aldehydes, from 22 groundwater samples collected at five sites. Standards for 28 polar compounds indicate that effective limits of quantitation for most of these compounds in the groundwater samples range from 1 to 11 μg/L