Composition of the C₆+ Fraction of Natural Gas by Multiple Porous Layer Open Tubular Capillaries Maintained at Low Temperatures

As the sources of natural gas become more diverse, the trace constituents of the C₆+ fraction are of increasing interest. Analysis of fuel gas (including natural gas) for compounds with more than six carbon atoms (the C₆+ fraction) has historically been complex and expensive. Hence, this is a procedure that is used most often in troubleshooting rather than for day-to-day operations. The C₆+ fraction affects gas quality issues and safety considerations, such as anomalies associated with odorization. Recent advances in dynamic headspace vapor collection can be applied to this analysis and provide a faster, less complex alternative for compositional determination of the C₆+ fraction of natural gas. Porous layer open tubular capillaries maintained at low temperatures (PLOT-cryo) form the basis of a dynamic headspace sampling method that was developed at the National Institute of Standards and Technology (NIST) initially for explosives in 2009. This method has been recently advanced by the combining of multiple PLOT capillary traps into one “bundle” or wafer, resulting in a device that allows for the rapid trapping of relatively large amounts of analyte. In this study, natural gas analytes were collected by flowing natural gas from the laboratory (gas out of the wall) or a prepared surrogate gas flowing through a chilled wafer. The analytes were then removed from the PLOT-cryo wafer by thermal desorption and subsequent flushing of the wafer with helium. Gas chromatography (GC) with mass spectrometry (MS) was then used to identify the analytes

Vapor Pressure Measurements on Linalool Using a Rapid and Inexpensive Method Suitable for Cannabis-Associated Terpenes

Vapor pressure (psat) data are needed to assess the potential use of terpenes as breath markers of recent cannabis use. Herein, a recently introduced gas-saturation method for psat measurements, known as dynamic vapor microextraction (DVME), was used to measure psat for the terpene (±)-3,7-dimethylocta-1,6-dien-3-ol, commonly known as linalool. The DVME apparatus utilizes inexpensive and commercially available components, a low internal volume, and helium carrier gas to minimize nonideal mixture behavior. In the temperature range from 314 to 354 K, DVME-based measurements of the psat of linalool ranged from 81 to 1250 Pa. With a measurement period of 30 min, the combined standard uncertainty of these measurements ranged from 0.0358·psat to 0.0584·psat depending on temperature. The DVME-based measurements agree with a Wagner correlation of the available literature data. We demonstrate that DVME produces accurate results for values of psat that are 200 times higher than in the DVME validation study with n-eicosane (C20H42). The oxidative stability of linalool was improved by the addition of 0.2 mass % of the antioxidant tert-butylhydroquinone

Comprehensive Assessment of Composition and Thermochemical Variability by High Resolution GC/QToF-MS and the Advanced Distillation-Curve Method as a Basis of Comparison for Reference Fuel Development

Commercial and military aviation is faced with challenges that include high fuel costs, undesirable emissions, and supply chain insecurity that result from the reliance on petroleum-based feedstocks. The development of alternative gas turbine fuels from renewable resources will likely be part of addressing these issues. The United States has established a target for one billion gallons of renewable fuels to enter the supply chain by 2018. These alternative fuels will have to be very similar in properties, chemistry, and composition to existing fuels. To further this goal, the National Jet Fuel Combustion Program (a collaboration of multiple U.S. agencies under the auspices of the Federal Aviation Administration, FAA) is coordinating measurements on three reference gas turbine fuels to be used as a basis of comparison. These fuels are reference fuels with certain properties that are at the limits of experience. These fuels include a low viscosity, low flash point, high hydrogen content “best case” JP-8 (POSF 10264) fuel, a relatively high viscosity, high flash point, low hydrogen content “worst case” JP-5 (POSF 10259) fuel, and a Jet-A (POSF 10325) fuel with relatively average properties. A comprehensive speciation of these fuels is provided in this paper by use of high resolution gas chromatography/quadrupole time-of-flight–mass spectrometry (GC/QToF-MS), which affords unprecedented resolution and exact molecular formula capabilities. The volatility information as derived from the measurement of the advanced distillation curve temperatures, <i>T</i>_k and <i>T</i>_h, provides an approximation of the vapor-liquid equilibrium, and examination of the composition channels provides detailed insight into thermochemical data. A comprehensive understanding of the compositional and thermophysical data of gas turbine fuels is required not only for comparison but also for modeling of such complex mixtures, which will, in turn, aid in the development of new fuels with the goals of diversified feedstocks, decreased pollution, and increased efficiency

Application of the Advanced Distillation Curve Method to the Comparison of Diesel Fuel Oxygenates: 2,5,7,10-Tetraoxaundecane, 2,4,7,9-Tetraoxadecane, and Ethanol/Fatty Acid Methyl Ester Mixtures

Although they are among the most efficient engine types, compression-ignition engines have difficulties achieving acceptable particulate emission and NO_<i>x</i> formation. Indeed, catalytic after-treatment of diesel exhaust has become common, and current efforts to reformulate diesel fuels have concentrated on the incorporation of oxygenates into the fuel. One of the best ways to characterize changes to a fuel upon the addition of oxygenates is to examine the volatility of the fuel mixture. In this work, we present the volatility, as measured by the advanced distillation curve method, of a prototype diesel fuel with novel diesel fuel oxygenates: 2,5,7,10-tetraoxaundecane (TOU), 2,4,7,9-tetraoxadecane (TOD), and ethanol/fatty acid methyl ester (FAME) mixtures. We present the results for the initial boiling behavior and the distillation curve temperatures and track the oxygenates throughout the distillations. These diesel fuel blends have several interesting thermodynamic properties that have not been seen in our previous oxygenate studies. Ethanol reduces the temperatures observed early in the distillation (near ethanol’s boiling temperature). After these early distillation points (once the ethanol has distilled out), B100 has the greatest impact on the remaining distillation curve and shifts the curve to higher temperatures than what is seen for diesel fuel/ethanol blends. In fact, for the 15% B100 mixture, most of the distillation curve reached temperatures higher than those seen with diesel fuel alone. In addition, blends with TOU and TOD also exhibited uncommon characteristics. These additives are unusual because they distill over most of the distillation curve (up to 70%). The effects of this can be seen both in histograms of oxygenate concentration in the distillate cuts and in the distillation curves. Our purpose for studying these oxygenate blends is consistent with our vision for replacing fit-for-purpose properties with fundamental properties to enable the development of equations of state that can describe the thermodynamic properties of complex mixtures, with specific attention paid to additives

Volatility of Mixtures of JP-8 with Biomass Derived Hydroprocessed Renewable Jet Fuels by the Composition Explicit Distillation Curve Method

In this paper, we apply the composition explicit distillation curve method to mixtures of JP-8 with hydroprocessed aviation fuels made from camelina (a genus within the flowering plant family Brassicaceae), from castor seed (Ricinus communis), and from waste brown grease used with the Fischer–Tropsch process. For the camelina fuel, the departures (with respect to JP-8) in volatility and in enthalpy of combustion are significant for mixtures with 25 and 50% (v/v) in JP-8. Mixtures with only 10% camelina fuel (v/v) show relatively minor departures. In all cases, the departures (with respect to JP-8) are to lower temperatures (higher volatility) and lower molar enthalpy of combustion. Mixtures of castor based fuel with JP-8 show essentially no departures in volatility or molar enthalpy of combustion up to the 40% distillate volume fraction. Subsequent to this distillate volume fraction, departures are very apparent, with mixtures showing lower volatility and higher molar enthalpy of combustion with higher volume fractions of castor based HRJ. Mixtures of the brown grease based fuel show departures to lower volatility and to higher molar enthalpy of combustion (with respect to JP-8) as the volume fraction of the brown grease SPK increases

Characterization of the Effects of Cetane Number Improvers on Diesel Fuel Volatility by Use of the Advanced Distillation Curve Method

The cetane number (CN) is a measure of the ignition quality of a fuel for compression-ignition engines according to the self-ignition delay. If the CN of a fuel is too low, chemical compounds known as CN improvers may be added to increase both the CN and performance of the fuel. The addition of CN improvers is dependent upon the detailed properties of the particular fuel. While many fuel properties are important for design, the vapor–liquid equilibrium, as described by volatility, is very sensitive to composition. In this work, we measured blends of diesel fuel with the following CN improvers: amyl nitrate, isoamyl nitrate, isoamyl nitrite, 2-ethylhexyl nitrate, and the multi-component CN improver PM-1, in diesel fuel by use of the advanced distillation curve (ADC) method to determine the amount of CN improver in the various distillate volume fractions. Tracking the CN improver throughout the volatility profile of diesel fuels provides valuable information for determining structural property relationships, and moreover, it provides the basis for the development of equations of state that can describe the thermodynamic properties of these complex mixtures, with specific attention paid to additives. We have found that the addition of CN improvers significantly decreases the temperature at which boiling begins and that the majority of the CN improver is thermolytically degraded before the first drop can be collected. These observations are supported by low-pressure ADC, where the CN improver was found in fractions up to 30%. These results have implications in the prediction of thermophysical properties of diesel fuel with CN improvers

Comparison of Diesel Fuel Oxygenate Additives to the Composition-Explicit Distillation Curve Method. Part 2: Cyclic Compounds with One to Two Oxygens

There is a great deal of interest in formulating oxygenated diesel fuels that produce low particulate emissions. The most common oxygenating additives for diesel fuels include the glycol ethers, glycol esters, alcohols, ethers, and ketones. It is important to characterize the mixture properties of diesel fuel with oxygenate additives, to assess the degree of departure of the oxygenated fuels from the base fuel. In part 1 of this series (10.1021/ef2003415), we explored a series of linear oxygenating fluids with the advanced distillation curve method to assess the mixture volatility. Here, we apply that technique to a series of cyclic molecules: 2-methyl-1,3-dioxolane, 1,4-dioxane, 1,3-dioxane, cyclohexanone, and 2-cyclohexylethanol. We find that the more volatile additives cause significant early departures from the distillation curves of diesel fuel, while the less volatile additives act more to displace the entire curve. We also note that the additive affects the curve shape and temperature profile even after being totally depleted, an observation similar to that made in earlier studies of oxygenate additive mixtures