Low Molecular Weight Alkanes Research Articles

Sensitivity and selectivity of Pt electrodes for hydrocarbon sensing in an ultra high vacuum environment

X-ray photoelectron spectroscopy (XPS) and temperature-programmed reaction (TPR) were used to investigate the suitability of polycrystalline platinum as a sensing electrode for sensitive and selective detection of hydrocarbons in a vacuum environment by electrochemical means. At 870 K, all the species investigated undergo precursor-mediated dissociative adsorption to yield graphite, though at widely different rates. It is found that polycrystalline platinum discriminates effectively between “sticky” hydrocarbons such as alkenes, aromatics and alkanes >C 5 on the one hand, and “benign” low molecular weight alkanes on the other. The proposed methodology offers a promising way forward with respect to the intended application.

Studies of Instrumental Spreading in Gel Permeation Chromatography by Coupling with a Two‐Angle Laser Light Scattering Detector

The instrumental spreading of a high temperature gel permeation chromatograph (GPC) was evaluated by coupling with a two‐angle laser light scattering (TALLS) detector, using narrow polystyrene, polyethylene, and syndiotactic polypropylene samples. The determined spreading factor increased with increasing molecular weight of polymers, and no maximum for spreading factor was observed in the studied retention volume, while the spreading factors for single low molecular weight alkanes are independent of their molecular weight. Neglecting of the spreading effect for GPC would not introduce much error in molecular weight calculation when high quality high performance columns were used, especially when equipped with a laser light scattering detector. The scaling relationship between radius of gyration and molecular weight of polymer, determined by GPC with a TALLS detector, was independent of the instrumental spreading.

Segmental dynamics in a blend of alkanes: Nuclear magnetic resonance experiments and molecular dynamics simulation

The segmental dynamics of a model miscible blend, C24H50 and C6D14, were investigated as a function of temperature and composition. The segmental dynamics of the C24H50 component were measured with C13 nuclear magnetic resonance T1 and nuclear Overhauser effect measurements, while H2 T1 measurements were utilized for the C6D14 component. Use of low molecular weight alkanes provides a monodisperse system in both components and allows differentiation of dynamics near the chain ends. From these measurements, correlation times can be calculated for the C–H and C–D bond reorientation as a function of component, position along the chain backbone, temperature, and composition. At 337 K, the segmental dynamics of both molecules change by a factor of 2 to 4 across the composition range, with the central C–H vectors of tetracosane showing a stronger composition dependence than other C–H or C–D vectors. Molecular simulations in the canonical and isobaric–isothermal ensembles were conducted with a united-atom force field that is known to reproduce the thermodynamic properties of pure alkanes and their mixtures with good accuracy. With a minor change to the torsion parameters, the correlation times for pure tetracosane are in good agreement with experiment. For pure hexane and its mixtures with tetracosane, the simulated dynamics are faster than experiment.

Effect of leucine on aroma volatiles production from Ceratocystis fimbriata grown in liquid culture

Aroma volatiles produced by Ceratocystis fimbriata on a defined liquid synthetic medium with and without the addition of leucine were identified by gas chromatography–mass spectrometry and quantified by gas chromatography-flame ionisation detection in the liquid medium as well as in the headspace. Volatiles were extracted from the liquid by simultaneous steam distillation–solvent extraction. Ceratocystis fimbriata produced a complex set of volatile intermediary metabolites, of which ethanol was the dominant compound (∼92–95% of total volatiles). Low molecular weight esters, alcohols, aldehydes, ketones, alkanes, and carboxylic acids were identified in the liquid broth. Alcohols and esters were the most abundant aroma volatiles. Leucine addition effected further growth and higher volatiles production. In the headspace, ethanol and ethyl acetate accounted for 92% of total volatiles over the synthetic medium and 89% when leucine was added. Aroma perception (fruity and banana) correlated closely with liquid and headspace total volatiles.

Perfluoroalkanes in Water: Experimental Henry's Law Coefficients for Hexafluoroethane and Computer Simulations for Tetrafluoromethane and Hexafluoroethane

The solubility of hexafluoroethane in water was determined experimentally and, together with that of tetrafluoromethane, calculated by molecular simulation. A high-precision apparatus based on an extraction method was used to measure the solubility of hexafluoroethane in water in the temperature range of 287−328 K at pressures close to atmospheric. The experimental data obtained were used to calculate Henry's law coefficients H2,1(p1sat,T), whose temperature dependence was represented by appropriate correlations. The imprecision of the results was characterized by average deviations of H2,1 from these smoothing equations and is of ±0.17%. From the temperature variation of the Henry's law coefficients, partial molar solution quantities such as the variation of the Gibbs energy, enthalpy, entropy, and heat capacity were derived. Monte Carlo simulations, associated with Widom's test particle insertion method and the finite−difference thermodynamic integration technique, were used to calculate the residual chemical potential of low molecular weight alkanes and perfluoroalkanes in water leading to Henry's law coefficients. Simulations were performed from 280 to 500 K along the saturation line of the pure solvent. The simulation method was validated by the calculation of H2,1(p1sat,T) for methane and ethane in water for which quantitative predictions were attained even at the lowest temperatures. The calculations for tetrafluoromethane and hexafluoroethane in water were compared with experimental values, when available, to test intermolecular potential models. Solute−solvent radial distribution functions were obtained from simulation at low and high temperatures.

Restoration of an Oil-Contaminated St. Lawrence River Shoreline: Bioremediation and Phytoremediation

ABSTRACT The purpose of this field study was to evaluate bioremediation and phytoremediation in restoring an oil-contaminated freshwater shoreline. Weathered Mesa light crude oil was released intentionally onto small plots in the upper intertidal zone of a study site located along the St. Lawrence River. Treatments were established to examine the effect of nutrient addition and the role of plants (Scirpus pungens) on the removal of oil constituents from the contaminated plots. Fertilizers under evaluation included sodium nitrate, prilled ammonium nitrate, and triple super phosphate. Composite core samples were collected after 0, 1, 2, 4, 8, 12, 16, and 21 weeks for identification of remaining oil constituents by gas chromatography-mass spectrometry (GC-MS). To account for differences because of physical washout, all oil constituents were normalized to the conservative biomarker hopane. Although bioremediation and phytoremediation treatments achieved slightly better degradation of hydrocarbons than natural attenuation, no statistically significant evidence of stimulation through addition of nutrients or biodegradation enhancement by vegetation was observed. After 21 weeks, reduction of target parent and alkyl-substituted polycyclic aromatic hydrocarbons (PAHs) averaged 32% in all treatments. Reduction of target alkanes was of similar magnitude. The pattern of disappearance of hydrocarbons was characteristic of biodegradation: namely, the lower molecular weight alkanes declined to a greater extent than the higher carbon-number alkanes, as did the lower molecular weight PAHs compared to the higher molecular weight PAHs. Since there was little evidence supporting enhancement of biodegradation by nutrient addition with and without vegetation, it was concluded that oxygen limitation most likely dominated the persistence of oil hydrocarbons on the oil-contaminated plots.

Electrolytic Reduction of Low Molecular Weight Chlorinated Aliphatic Compounds: Structural and Thermodynamic Effects on Process Kinetics

A series of chlorinated low molecular weight alkanes and alkenes was transformed electrolytically using a porous nickel cathode at potentials from −0.3 to −1.4 V (versus standard hydrogen electrode). Kinetics were first-order with respect to the concentration of the halogenated targets. The dependence of the first-order rate constants on cathode potential followed the Butler−Volmer equation, modified to account for mass transfer resistance to reaction. The mass-transfer-limited rate constant for reaction of all species was about 1.55 L m-2 min-1. Log-transformed reaction rate constants for reduction of chlorinated alkanes, derived via experiments at the same cathode potential (Ec = −1.0 or −1.2 V vs SHE), were linearly related to carbon−halogen bond enthalpies, as expected based on a physical model that was developed from transition state theory. The chlorinated ethenes reacted much faster than predicted from bond enthalpy calculations and the alkane-based correlation, suggesting that alkenes are not tran...

Removal of chlorinated and brominated alkanes from drinking water using reverse osmosis

Membrane use in water treatment has historically focused on desalination. With the development of new membrane materials, attention began to focus on reverse osmosis and pervaporation as alternatives to traditional water treatment processes. This paper addresses the use of reverse osmosis in removing one class of organic compounds, the alkanes (chlorinated and brominated hydrocarbons) from drinking water, using six membranes: a cellulose acetate, a polyamide (hollow fibre), and four different types of thin-film composites. The thin-film composite membranes removed 80–95% of the low molecular weight (100–250) alkanes tested.

The dynamical origin of non-normal energy scaling and the effect of surface temperature on the trapping of low molecular weight alkanes on Pt(111)

Molecular classical dynamical simulations of alkanes trapping on platinum surfaces were performed to examine the origin of non-normal energy scaling for molecular adsorption. Conversion of normal to parallel translational energy at normal incidence and conversion of parallel translational energy into normal translational energy at glancing angles are the primary mechanisms which produce non-normal energy scaling of alkanes trapping on cold Pt(111). In addition, a tendency to convert rotational energy gained in the first gas-surface collision into normal translational energy for collisions at glancing incidence further increases the degree of non-normal energy scaling. Increasing surface temperature is shown to have little effect on energy transfer processes in the first bounce but increasing influence on subsequent bounces. Despite difficulties in defining trapping at high surface temperatures, simulations indicate that the initial trapping probability of ethane on Pt(111) does not fall by more than a factor of two over the surface temperature range of 100–700 K.

Phase equilibria in mixtures of triglycerides with low-molecular weight alkanes

Phase equilibria of ternary ethane propane-sunflower oil mixtures were measured at 313, 333 and 353 K, and at pressures of up to 120 bar. The region of partial liquid miscibility, at high hydrocarbon concentration, was particularly explored. The Soave-Redlich-Kwong equation of state was used to fit experimental vapor-liquid and liquid-liquid equilibria of alkane-vegetable oil mixtures. The application of a quadratic mixing rule for the co-volume b with a binary interaction coefficient kb ij greatly improves the performance of the model.

95/01265 High-silica zeolites as components of catalysts for synthesis of low-molecular weight olefins by the Fischer-Tropsch method

95/01265 High-silica zeolites as components of catalysts for synthesis of low-molecular weight olefins by the Fischer-Tropsch method

Short-term weathering rates of buried oils in experimental sand columns over north-temperate temperature range.

Petroleum residues are degraded (weathered) at different rates, depending on various conditions. Degradation in slicks generally has time scales of days to weeks for loss of low molecular weight alkanes and aromatics. This largely involves physical processes of wind-driven evaporation, and dissolution into the water column. Weathering in homogeneously oiled surface sediments, not having the benefit of evaporation, has time scales of months to years. Tidal submergence and temperature can influence this significantly. For example, Prudhoe Bay crude oil in sediments placed in trays on the bottom of a near-arctic bay showed virtually no weathering. Here we report on weathering rates and qualitative changes of oils, buried within constantly submerged and irrigated sandy beach sediments for up to 11 mon. Such conditions occur when coastal stranded oil becomes buried subtidally, or becomes mixed into intertidal beach sediments below the water table. Experimental conditions included continuous sea water irrigation, indigenous microbial populations, and continuous complete submergence. For preliminary microbial incubation and weathering results, see Thorpe et al. (1986). We expected that oil degradation within sandy sediments would be comparatively slow, as organic material and nutrients are more limited, thereby limiting microbial activity. Lower temperatures and submergence also should limit the weatheringmore » process.« less

Inverse gas chromatography of lignocellulosic fibers coated with a thermosetting polymer: Use of peak maximum and conder and young methods

The Conder and Young (CY) and the peak maximum (PM) methods were used to estimate the retention time of n-alkane probes on chemithermomechanical pulp (CTMP) wood fibers treated with a low molecular weight grade phenol-formaldehyde resin (PFR). Thermodynamic functions (Δ H a o , Δ G a o , and ΔS a o ) and the London dispersive component of the surface energy were derived from these retention times. Treated wood fibers show a high energy surface due to the presence of the thermoset resin on their surface. Values of Δ H a o obtained from the CY method were higher than those obtained with the PM method at relatively high temperatures and with relatively low molecular weight alkanes. The results from the two methods were identical at low temperature (293 K) and with the relatively high molecular weight alkane n-undecane.

Peptization of asphaltene by various oil soluble amphiphiles

The dispersion of asphaltene in heptane by different oil soluble amphiphiles was investigated. Alkyl phenols show good peptizing properties and partially lose their capacity when oxyethylenic groups are incorporated into the molecule. Primary aliphatic amines also show some ability to disperse asphaltene, but long chain aliphatic alcohols and alkyl benzenes are rather inefficient. Asphaltene solutions in toluene containing alkyl phenols are less sensitive to precipitation by the addition of low molecular weight alkanes. The asphaltene adsorption onto quartz was also reduced by the addition of amphiphiles.

Manganese-oxide-supported iron Fischer-Tropsch synthesis catalysts: Physical and catalytic characterization

It has been claimed that catalysts containing iron and manganese are especially selective for production of low molecular weight olefins in the Fischer-Tropsch (FT) synthesis. In this study a new system, manganese-oxide-supported iron, Fe MnO , was prepared, subjected to various calcination and reduction treatments, and then employed as a FT catalyst. Reaction studies were run with approximately 1 1 : CO H 2 feed at 515 and 540 K and 7.8 and 14.8 bar pressure. Although low conversions were employed, the synthesis rate decreased strongly with increasing conversion. Compared to conventional Fe catalysts, the Fe MnO was more active for water-gas shift and less selective for methane and alcohols, especially at higher conversions, lower temperature, and higher pressure. Olefin selectivity was high, hydrogen chemisorption was depressed, and secondary hydrogenation was not apparent. In general it is concluded that the manganese-supported iron does promote FT selectivity for low molecular weight olefins, but at the expense of high CO 2 formation.

PHASE BEHAVIOR OF BRANCHED TAIL ETHOXYLATED CARBOXYLATE SURFACTANT/ELECTROLYTE/ALKANE SYSTEMS.

ABSTRACT This paper describes the effect of pH on phase behavior of branched tail EO carboxylate surfactants in electrolyte/ alkane microemulsion system3 which are of possible pertinence to enhanced oil recovery. The pH of the aqueous surfactant solutions was found to have a considerable effect on the salinity requirement for middle phase microemulsion formation. At 70 and 60°C alcohol-free optimal three phase microemulsion systems are formed with all alkanes studied over the entire pH range of 6-12. At lower temperatures and. higher pH values, liquid crystals were found to form in systems which contained lower molecular weight alkanes.

Comparative Fate of Chemically Dispersed and Beached Crude Oil in Subtidal Sediments of the Arctic Nearshore

A three-year investigation was conducted to examine the incorporation of petroleum hydrocarbons (PHC) into subtidal sediments following experimental releases of oil during the Baffin Island Oil Spill (BIOS) Project experiments. The concentrations of PHC were determined by synchronous scanning UV/Fluorescence spectroscopy, while the composition of residual saturated and aromatic hydrocarbons was determined by gas chromatography and gas chromatographic mass spectrometry. ... The eroding oil from the Bay 11 beach was compositionally quite heterogeneous, with weathered, biodegraded oil, as well as relatively unweathered oil, found on the beach and in the offshore sediments. Biodegradation of oil appeared to be restricted to the beached oil, with no significant degradation apparently occurring subtidally. After two years, the offshore oil residues still contained low molecular weight alkanes as well as alkylated naphthalenes. The situation in Bay 9, where chemically dispersed oil was discharged near the bottom, was quite different. In spite of a large water column exposure, the bottom sediments never contained more than 10 micro g/g of oil. Of this amount of oil, a significant fraction (20%) of the PHC was initially associated with the surface flocculent layer. Levels of oil in the Bay 9 sediments were on the order of 1-3 micro g/g one year after the release. Sediment PHC levels in the other less exposed bays (Bays 10 and 7) never exceeded 3 micro g/g.Key words: BIOS, experimental oil spill, petroleum hydrocarbons, arctic sediments, oil pollution

Influence of air on oil agglomeration of carbonaceous solids in aqueous suspension

Graphite or coal particles in aqueous suspension were agglomerated with various paraffinic hydrocarbons in a specially developed system which made it possible to exclude air from the system or to conduct agglomeration with controlled amounts of air present. The agglomerates were recovered by screening the suspension. Under certain conditions air was incorporated in the agglomerates which increased the recovery of carbonaceous material with a given amount of liquid hydrocarbon. Incorporation of air occurred when lower molecular weight alkanes (i.e., smaller than octane) were used as the collecting or bridging phase in limited amounts. Air had no effect on the system when higher molecular weight alkanes were employed or when larger amounts of the collecting phase were used.

Band broadening of CH2 vibrations in the Raman spectra of polymethylene chains

The isotropic and anisotropic linewidths of methylene vibrations in a homologous series of alkanes of increasing chain length have been measured in the liquid state as a function of temperature. The bandwidths of the CH2 symmetric stretching modes, which are in Fermi resonance with overtones of the CH2 bending vibrations, are temperature insensitive over a 200 K interval; this is best explained in terms of a vibrational dephasing mechanism (inhomogeneous broadening) for these modes. In contrast, for the bending and antisymmetric stretching vibrations, significant band broadening occurs over this same temperature interval. In addition, for these modes, both the absolute value of the bandwidth and the relative rate of increase of the bandwidth with increasing temperature, decrease with increasing chain length. These observations are consistent with a reorientational broadening mechanism as the principal bandwidth contribution for these vibrations. Hindered end-over-end rotation of the molecules, which contributes to the band broadening for very low molecular weight alkanes, rapidly becomes too slow to be observable on the time scale of the Raman experiment for the higher molecular weight alkanes and polyethylene. For longer chain lengths, torsional backbone motions coupled to the high frequency antisymmetric stretching modes can account for the breadth of the bands.

A systematic investigation and characterization of interfacial hydrated n-alkane films by total internal multiple reflection

We present the first systematic investigation by the technique of total internal optical reflection of a homologous series of low molecular weight alkanes adsorbed as hydrated films on a glass surface. The detected optical signals for these hydrated alkanes can be shown to depend empirically on the square of their molar refractivity times an optical depolarization scaling parameter. Relative scattering cross-section measurements between a hydrated film of methane and a water film allowed for an estimate to be made of the number of water molecules which surround the methane molecule in the ‘‘cage-like’’ hydrate structure.