Hydrocarbons In Gas Phase Research Articles

Thermo-Responsive Polymer-Mediated Extraction Followed by Flotation for the Removal of Poly(aromatic hydrocarbons) from Gases

Abstract A simple and efficient gas decontamination system has been developed. The method is based on the aeration of an aqueous solution of a thermo-responsive polymer and polymer-mediated extraction followed by flotation. Polyaromatic hydrocarbons (PAHs) in gas phase were dissolved by aeration through the aqueous solution of a water-soluble polymer, poly(N-isopropylacrylamide) [PNIPAAm], containing 0.1 mol dm−3 sodium nitrate and 1% (v/v) ethanol. The efficiency of the dissolution increased with increasing PNIPAAm concentration. PAHs consisting of more than 3 aromatic rings were quantitatively collected in the polymer solution, while the collection of volatile naphthalene was insufficient. Subsequently, on heating the polymer solution to 50 °C, the polymer media incorporating PAHs formed precipitates. The precipitates were floated to the surface of water by bubbling. Hydrophobic PAHs, such as pyrene and benzo[a]pyrene, were highly concentrated into the polymer phase having a very small volume.

An Intensive Study of the Size and Composition of Submicron Atmospheric Aerosols at a Rural Site in Ontario, Canada

Atmospheric sampling was conducted at a rural site near Egbert, about 70 km north of Toronto, Ontario, Canada from March 27 to May 8, 2003 to characterize the physical and chemical properties of the ambient aerosol in near real-time. The instrumentation included a tapered element oscillating microbalance (TEOM), an ultrafine condensation particle counter (UCPC), a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), an aerosol mass spectrometer (AMS), and a particulate nitrate monitor (R&P 8400N) for aerosol measurements. Gas-phase non-methane hydrocarbon compounds (NMHCs) were measured by gas chromatograph-flame ionization detection (GC-FID). Filter samples were also collected for analysis of inorganic ions by ion chromatography (IC). Aerosol properties varied considerably depending upon meteorological conditions and airmass histories. For example, urban and industrial emissions advected from the south strongly influenced the site occasionally, resulting in higher particulate mas...

Evaluation of hydrogen chemisorption in nanostructured carbon films by near edge X-ray absorption spectroscopy

We have developed a method for the quantitative evaluation of the chemisorbed fraction of hydrogen in nanostructured carbon films using Near Edge X-ray Absorption Spectroscopy (NEXAFS). In the carbon K-edge spectrum the peak related to carbon bonded to hydrogen is assumed to be correlated with the amount of hydrogen bonded to carbon. This assumption is supported by a comparative analysis of gas-phase hydrocarbons obtained via Electron Energy Loss Spectroscopy (EELS). We applied the method to nanostructured carbon (ns-C) films synthesized by supersonic cluster beam deposition. The evaluated quantity of chemisorbed hydrogen in different samples exposed to molecular hydrogen (pressure of 0.12 MPa, for 3 hours at room temperature) is ∼1.5 wt.%.

Playing with Fire: Safety and Reaction Efficiency Research on Gas Phase Hydrocarbon Oxidation Processes: Project SAFEKINEX

Hydrocarbon oxidation is still a growing field of industrial interest and provides for our needs for a large variety of substances and materials. As soon as hydrocarbon and oxygen are brought in contact a potential combustion hazard problem arises and, on the one hand, one wishes to stay with considerable margin outside the flammable or spontaneous ignition ranges. On the other hand there is a drive to increase conversion per pass through reactors, since recycle consumes energy and causes pollution. Industrial processes usually take place at elevated conditions (up to 500°C and 50 bar) while gas explosion safety has been investigated extensively only at or close to ambient conditions. At the same time the knowledge about oxidation mechanisms is growing quickly and computer simulation of the thousands of validated reaction steps become more widely used. In the EU sponsored project SAFEKINEX (www.safekinex.org) there are dual objectives to further develop both the explosion safety knowledge and the kinetic interpretation from a fundamental standpoint. The marriage is intended to produce an important contribution for a better understanding of the phenomena that may reduce process hazards and to provide models from which tools can be developed to control the processes better or enable improved design.

Estimation of PAHs dry deposition and BaP toxic equivalency factors (TEFs) study at Urban, Industry Park and rural sampling sites in central Taiwan, Taichung

The concentrations of polycyclic aromatic hydrocarbons (PAHs) in gas phase and particle bound were measured simultaneously at industrial (INDUSTRY), urban (URBAN), and rural areas (RURAL) in Taichung, Taiwan. And the PAH concentrations, size distributions, estimated PAHs dry deposition fluxes and health risk study of PAHs in the ambient air of central Taiwan were discussed in this study. Total PAH concentrations at INDUSTRY, URBAN, and RURAL sampling sites were found to be 1650 ± 1240, 1220 ± 520, and 831 ± 427 ng/m 3, respectively. The results indicated that PAH concentrations were higher at INDUSTRY and URBAN sampling sites than the RURAL sampling sites because of the more industrial processes, traffic exhausts and human activities. The estimation dry deposition and size distribution of PAHs were also studied. The results indicated that the estimated dry deposition fluxes of total PAHs were 58.5, 48.8, and 38.6 μg/m 2/day at INDUSTRY, URBAN, and RURAL, respectively. The BaP equivalency results indicated that the health risk of gas phase PAHs were higher than the particle phase at three sampling sites of central Taiwan. However, compared with the BaP equivalency results to other studies conducted in factory, this study indicated the health risk of PAHs was acceptable in the ambient air of central Taiwan.

TiO 2 on magnesium silicate monolith: effects of different preparation techniques on the photocatalytic oxidation of chlorinated hydrocarbons

In this article, the comparative results of the photocatalytic oxidation of trichloroethylene (TCE) alone and a mixture of chlorinated hydrocarbons (trichloroethylene, perchloroethylene and chloroform) in gas phase, obtained with three different monolithic catalysts in a flat reactor frontally illuminated with a Xenon lamp are presented. The three catalysts incorporate titanium dioxide (TiO 2) as active phase on a magnesium silicate support, by means of different procedures: (i) incorporation of commercial TiO 2 powder into the silicate matrix (“massic monolith”); (ii) sol–gel coating of the silicate support; (iii) impregnation with a commercial TiO 2 aqueous suspension of the same silicate support. In the first case, the massic monolith was made from a 50:50 w/w mixture of magnesium silicate and “Titafrance G5” TiO 2 powder. In the second case, a magnesium silicate monolith was coated with several layers of an aqueous TiO 2 sol prepared from hydrolysis and condensation of titanium tetra-isopropoxide (Ti(OC 3H 7) 4) in excess of acidified water (acid catalysis). The third catalyst was prepared by impregnating the same silicate support with several layers of “Titafrance G5” TiO 2 powder water suspension. All the catalysts were thermal treated under comparable conditions in order to fix the TiO 2 active phase to the silicate support. Although the performance of the massic monolith was better than the sol–gel monolith, the latter is of great interest because this technique allows the chemical composition of the active films to be easily modified.

Polycyclic aromatic hydrocarbons in the ambient air of suburban and industrial regions of central Taiwan

The concentrations of gas-phase and particle-bound polycyclic aromatic hydrocarbons (PAHs) were measured simultaneously at an industrial area (Taichung Industrial Park) and a suburban area (Tunghai University Campus) in Taichung, Taiwan. Twenty-four hours samplings for two consecutive days were performed between August and December 2002 at both sampling sites. Ambient air particle-bound PAHs were collected on quartz filters and gas-phase PAHs were collected on glass cartridges using a PUF Sampler, respectively. Both types of samples were extracted with a DCM/ n-hexane mixture (50/50, v/v) for 24 h, then the extracts were subjected to gas chromatography–mass spectrometric (GC–MS) analysis. Total PAHs concentrations at the Taichung Industrial Park (TIP) sampling site and the Tunghai University Campus (THUC) sampling site were found to be 1232.3 ± 963.6 and 609.8 ± 356.3 ng/m 3, respectively. Stationary combustion processes were mainly responsible for PAHs sources at the TIP sampling site, while traffic vehicle exhaust was the largest contributor for PAHs sources at the THUC sampling site.

Influence of the methods of TiO 2 incorporation in monolithic catalysts for the photocatalytic destruction of chlorinated hydrocarbons in gas phase

Three different methods of fixing titanium dioxide on a monolithic, natural magnesium silicate matrix, onto-the-wall extrusion, wash-coating and sol–gel, are compared. Photo-assisted oxidation tests with chlorinated hydrocarbons, trichloroethylene (TCE) alone and in mixtures with perchloroethylene (PCE) were carried out with the monolithic photocatalysts. Results show that the use of extruded titania monoliths provides significant advantages for best stability of anatase, porosity and resistance to loss of active phase due to erosion. Catalysts obtained by the sol–gel method maybe a good option for this application, but the coating method must still be improved.

Regional groundwater focusing of nitrogen and noble gases into the Hugoton-Panhandle giant gas field, USA

The Hugoton-Panhandle giant gas field, located across SW Kansas and the Texas and Oklahoma panhandles in the USA, is the case type example of high nitrogen concentrations in a natural gas being linked with high helium concentrations. We collected 31 samples from producing wells in a north-south traverse of the 350-km-long field. The samples reflect the previously observed north-south change in 4He/N 2, with values changing from 0.020 to 0.049 respectively. 3He/ 4He, 21Ne/ 22Ne, and 40Ar/ 36Ar vary between 0.14–0.25 Ra, 0.0373–0.0508, and 818–1156 respectively, and are caused by quantifiable contributions from mantle, crustal, and atmosphere-derived sources. The atmosphere-derived 20Ne/ 36Ar ratios are indistinguishable from groundwater values. The crustal 4He/ 21Ne* and 4He/ 40Ar* ratios show a 60% excess of 4He compared to predicted production ratios in the crust and are typical of noble gases released from the shallow crust. The mantle 3He/N 2 and groundwater-recharge 36Ar/N 2 ratios enable us to rule out significant magmatic or atmosphere contributions to the gas field N 2, which is dominantly crustal in origin. Correlated 20Ne/N 2 and 4He/N 2 shows mixing between two distinct crustal N 2 components. One N 2 component (N 2*) is associated with the crustal 4He and groundwater-derived 20Ne, and the other with no resolvable noble gas contribution. Measured δ 15N N 2 values vary from +2.7‰ to +9.4‰. The N 2* and non–He-associated N 2 endmembers are inferred to have δ 15N N 2 = −3‰ and +13‰ and contribute from between 25–60% and 75–40% of the nitrogen respectively. The non–He-associated nitrogen is probably derived from relatively mature organic matter in the sedimentary column. The δ 15N N 2 * value is not compatible with a crystalline or high-grade metamorphic source and, similar to the 4He, is inferred to be from a shallow or low metamorphic-grade source rock. 4He mass balance requires a regional crustal source, its association with significant magmatic 3He pointing to a tectonically active source to the west of the Hugoton system. The volume of groundwater required to source the 20Ne in the gas field demonstrates the viability of the groundwater system in providing the collection, transport, and focusing mechanism for the 4He and N 2*. The N 2*/ 20Ne ratio shows that the N 2* transport must be in the aqueous phase, and that the degassing mechanism is probably contact between the regional groundwater system and the preexisting reservoir hydrocarbon gas phase.

Characterization of diesel particulate matter with excimer laser fragmentation fluorescence spectroscopy

Excimer laser fragmentation fluorescence spectroscopy (ELFFS) is an effective technique for monitoring diesel particulate matter in engine exhaust. Measurements were made in the exhaust of a single-cylinder, 4 kW diesel generator with several different air to exhaust dilution ratios. Light from a 193 nm ArF laser photofragments the particles and produces fluorescence from the atomic carbon fragments at 248 nm and from CH (431 nm) and C2 (468 nm) fragments. Interferences from carbon monoxide and carbon dioxide are negligible. The interference from unburned gas-phase hydrocarbons is significant when the engine is not under load, but insignificant when the engine is loaded. The gas-phase hydrocarbons can be removed by a diffusion denuder to eliminate this interference under no-load conditions. The 100-shot (1 s) detection limit for particles in the exhaust is approximately 0.2 ppb volume fraction. The single-shot detection limit of ELFFS is low enough to allow for real-time monitoring of particulate matter from diesel engines, as well as from other combustion systems. ELFFS is sensitive to both the volatile and non-volatile fraction of the particulate matter, and monitoring fluorescence from multiple fragments provides information on the chemical composition of the particles.

Real-Time Measurement of Combustion Generated Particles with Photofragmentation-Fluorescence

Excimer laser fragmentation-fluorescence spectroscopy (ELFFS) is a viable technique for real-time monitoring of carbonaceous particles in combustion exhausts. The exhaust from a single-cylinder two-stroke engine is diluted and diverted into the laser interrogation region, resulting in a particle concentration of approximately 1 × 107/cm3. Light from a 193 nm ArF laser photofragments the particles and then produces fluorescence from the atomic carbon fragments at 248 nm, CH fragments at 431 nm, and C2 fragments at 468 nm. The atomic carbon fluorescence signal is proportional to the number concentration of particles in the laser interrogation region. The 100-shot (1 s) detection limit for particles in the exhaust is 1 mg/m3, expressed as a mass concentration of particulate matter. Interferences from carbon monoxide and carbon dioxide are negligible. The relative fluorescence yield at 248 nm is four times greater from particles than from the gas phase hydrocarbons present in the exhaust. This high yield suggests that the gas phase hydrocarbon interference would not be problematic for measurements of diesel exhaust, where the ratio of particulate carbon to gas phase hydrocarbon is high.

Membrane reactors for hydrogenation and dehydrogenation processes based on supported palladium

Membrane reactors applied to catalytic reactions are currently being studied in many places world-wide. Significant developments in membrane science and the vision of process intensification by multifunctional reactors have stimulated a lot of academic and industrial research, which is impressively demonstrated by more than 100 scientific papers on catalytic membrane reactors being published per year. Palladium as a noble metal with exceptional hydrogen permeation properties and, at the same time, broad applicability as a catalyst, first of all for hydrogenation, is part of many of these developments. This paper discusses two different membrane reactor concepts which both rely on supported palladium, on the one hand as a permselective membrane material, and on the other hand as base component of a membrane-type hydrogenation catalyst. Dense palladium composite membranes can be used for hydrogen separation from packed-bed catalysts in gas-phase hydrocarbon dehydrogenation reactions. Mesoporous membranes containing dispersed bimetallic Pd/X-clusters can be employed as so-called catalytic diffusers for liquid-phase hydrogenation, e.g. of nitrate and nitrite in water. The principles of both concepts are introduced, recently obtained experimental data are evaluated in connection with literature results, and the perspectives for further development are highlighted.

Photo-oxidation of short-chain hydrocarbons over titania

The UV-induced photo-oxidation of propene, propane, ethene, ethane, n-butane and n-hexane were studied over a TiO2 photo-catalyst at 150°C with hydrocarbon concentrations up to 4000ppm and O2 concentrations up to 20%. In the absence of O2, very little reaction was observed and rapid catalyst deactivation occurred. Increasing the O2 concentration led to increased hydrocarbon conversion. Under most conditions, the selectivity of hydrocarbon conversion to CO2 was at least 95% for propene, propane, ethene and ethane. The only exception was 50% selectivity observed for the highest propene concentration studied (4000ppm) in the presence of 12% O2.For propene and propane, the extent of photo-conversion depended on the gas-phase hydrocarbon concentration, and had maxima at 500 and 1000ppm, respectively. The observed decrease at higher concentrations was attributed to hydrocarbon blocking oxygen adsorption sites, and thereby inhibiting the production of the photo-generated reactive oxygen species responsible for hydrocarbon oxidation. Durability of the photo-oxidation reaction without catalyst deactivation was demonstrated for propene, propane, ethene and ethane. In contrast with n-butane and to a greater extent n-hexane, the deposition of stable carbonaceous species on the TiO2 surface led to catalyst deactivation.

Methylpolyynes and Small Hydrocarbons in CRL 618

We report on the detection with the Infrared Space Observatory of strong infrared absorption from NH3 and C2H4 in CRL 618. The observed NH3 and C2H4 bands arise from a region with kinetic temperatures 200 K, i.e., the dense gas in the photodissociation region associated to the dense torus surrounding the central star, as was the case for the polyynes and cyanopolyynes (see the companion Letter). Several absorption bands, probably arising from small gas-phase hydrocarbons, are observed between 5.5 and 11 μm. Two of these species have been identified with the 30 m IRAM telescope as the methylpolyynes CH3C2H and CH3C4H. However, the absorption around 6.2 μm is particularly broad and could arise from the combination of these small hydrocarbons and from the aromatic C=C stretching of polycyclic aromatic hydrocarbons of moderate size. These bands and those associated to the polyynes, cyanopolyynes, methylpolyynes, and benzene are not present in the infrared spectrum of the asymptotic giant branch star IRC +10216.

Gold Nano-Structures for Transduction of Biomolecular Interactions into Micrometer Scale Movements

Microfabricated cantilevers, similar to those commonly used in scanning probe microscopies, have recently become increasingly popular as transducers in chemical and biological sensors. Surface stress changes that accompany intermolecular interactions on the cantilever surfaces offer an attractive means to develop new generations of microfabricated sensors and actuators that respond directly to chemical stimuli. In the present study, we demonstrate that interfacial molecular recognition events can be converted into mechanical responses much more efficiently when quasi 3-dimensional interfaces with nano-size features are used. Some of the particularly useful approaches to creating such interfaces are surface immobilization of gold nano-spheres and dealloying of co-evaporated Au:Ag films. Preliminary evaluation of these nanostructured surfaces was performed by measuring mechanical stresses generated by receptor modified nano-structures and smooth gold surfaces in response to gas-phase hydrocarbon compounds. The most efficient chemi-mechanical transduction was achieved when the cantilevers were modified with 50 to 75 nm thick dealloyed gold nanostrutures. Cantilevers of this type were selected for liquid phase experiments. These cantilevers were found to undergo several micron deflections upon adsorption of protein A and biotin-labeled albumin on nanostructured gold surfaces. Additional micrometer scale movements of the cantilevers were observed upon interaction of the surface bound bioreceptors with, respectively, immunoglobulin G and avidin from the aqueous phase.

Source Apportionment of Wintertime Gas-Phase and Particle-Phase Air Pollutants Using Organic Compounds as Tracers

Two chemical mass balance receptor models are developed which can determine the source contributions to atmospheric pollutant concentrations using organic compounds as tracers. The first model uses particle-phase organic compounds to apportion the primary source contributions to atmospheric fine particulate organic carbon concentrations and fine particle mass concentrations. The second receptor model simultaneously uses both volatile gas-phase hydrocarbons and particle-phase organic compounds as tracers to determine source contributions to non-methane organic gases in the atmosphere. Both models are applied to data collected in California's San Joaquin Valley during two severe wintertime air pollution episodes. Source contributions to fine particle air quality are calculated for two urban sites, Fresno and Bakersfield, and one background site, Kern Wildlife Refuge. Primary particle emissions from hardwood combustion, softwood combustion, diesel engines, meat cooking, and gasoline-powered motor vehicles contribute on average 79% of the airborne fine particle organic compound mass at the urban sites during both episodes with smaller but still measurable contributions from fine particle road dust and natural gas combustion aerosol. Anthropogenic primary particle sources contribute less than 10% of the fine particle mass concentration at the background site. The combined gas-phase and particle-phase organic compound receptor model shows that gasoline-powered motor vehicle exhaust and gasoline vapors are the largest contributors to non-methane organic gases concentrations followed by natural gas leakage. Smaller but statistically significant contributions to organic vapors from wood combustion, meat cooking, and diesel exhaust also are quantified.

Thermochemistry for Hydrocarbon Intermediates Chemisorbed on Metal Surfaces: CHn-m(CH3)m with n = 1, 2, 3 and m ≤ n on Pt, Ir, Os, Pd, Rh, and Ru

To provide insight and understanding of the thermochemistry underlying hydrocarbon rearrangements on transition metal surfaces, we report systematic studies of hydrocarbon radicals chemisorbed on metal clusters representing the closest packed surfaces of the six second and third row group VIII transition metals. Using first principles quantum mechanics [nonlocal density functional theory with exact HF exchange (B3LYP)], we find that (i) CH_(3-m)(CH_3)_m forms one bond to the surface, preferring the on-top site (η^1), (ii) CH_(2-m)(CH_3)_m forms two bonds to the surface, preferring the bridge site (η^2), and (iii) CH_(1-m)(CH_3)_m forms three bonds to the surface, preferring the 3-fold site (η^3). For all six metals, the adiabatic bond energy is nearly proportional to the number of bonds to the surface, but there are dramatic decreases in the bond energy with successive methyl substitution. Thus from CH_3 to CH_2CH_3, CH(CH_3)_2, and C(CH_3)_3, the binding energy decreases by 6, 14, and 23 kcal/mol, respectively (out of ∼50). From CH_2 to CHCH_3 and C(CH_3)_2, the binding energy decreases by 8 and 22 kcal/mol, respectively (out of ∼100). These decreases due to methyl substitution can be understood in terms of steric repulsion with the electrons of the metal surface. For CH to C(CH_3), the bond energy decreases by 13 kcal/mol (out of ∼160), which is due to electronic promotion energies. These results are cast in terms of a thermochemical group additivity framework for hydrocarbons on metal surfaces similar to the Benson scheme so useful for gas-phase hydrocarbons. This is used to predict the chemisorption energies of more complex adsorbates.

The role of BrNO3 in marine tropospheric chemistry: A model study

Laboratory studies have shown that bromine nitrate (BrNO3) reacts on sulfuric acid and on ice particles. Here we investigate the potential role of BrNO3 in the marine boundary layer (mbl) assuming that it reacts on sea‐salt particles as well. Using the chemical box model MOCCA we find that heterogeneous reactions of BrNO3 on aerosol particles could affect the chemistry in four major ways: 1) They increase loss of NOx (=NO+NO2) from the gas phase; 2) They accelerate loss of bromide and chloride from sea‐salt aerosols. This dehalogenation occurs without the consumption of aerosol acidity; 3) The resulting loss of NOx and the increase of gas‐phase bromine species both lead to O3 destruction; 4) The resulting increase of reactive chlorine species affects gas‐phase hydrocarbons as well as S(IV) oxidation by HOCl in sea‐salt aerosols.

Manganese sulfate effect on PAH formation from polystyrene pyrolysis

Polystyrene (PS) was pyrolyzed with/without manganese sulfate addition in a 100% N 2 environment at 600, 700 and 800°C in a laboratory quartz reactor. The mole ratio of carbon (in PS) to Mn was 40/1. The gas-phase and liquid-phase polycyclic aromatic hydrocarbons (PAHs) were extracted with dichloromethane (DCM) and subsequently prepared for further analysis with an HPLC equipped with a wavelength-scanning ultraviolet (UV) detector and a fluorescence (FL) detector. Virtually no char or coke residue was observed in the reactor at the end of the pyrolysis reaction. The addition of MnSO 4 into the high-temperature pyrolysis of PS reduced PAH formation in all liquid and gas products. The transition metal-chelating oxidation mechanism previously used to explain soot reduction during combustion was not adequate for explaining the results of PAH reduction via MnSO 4 addition into the inert pyrolysis. Furthermore, it is suggested that soot reduction via manganese salt addition into oxygen-rich combustion might not result only from the well-accepted chelating oxidation mechanism; rather, it might result from the reduction of hydrocarbon species in the locally fuel-rich environment via manganese salt addition, as inferred from the reduction of PAH formation during inert pyrolysis with/without MnSO 4 addition observed in this study.

Organic emissions profile for a light-duty diesel vehicle

In this report we describe the speciated gas-phase hydrocarbon and carbonyl emissions as collected from a recent model automobile powered by a 2.5ℓ indirect injection diesel engine and outfitted with a production oxidation catalyst for exhaust after-treatment. The vehicle was run on a typical low sulfur (500 ppm S) European diesel fuel and measurements were made over the European MVEG test cycle. The diluted tailpipe emissions were sampled for light hydrocarbons (C 1C 12) using Tedlar bags and semi-volatile hydrocarbons (C 12C 20+) using Tenax cartridges. Both the light and semi-volatile hydrocarbon fractions were speciated using capillary gas chromatography. Combining the two sets of speciation data provided a profile of the gas-phase hydrocarbon emissions from a light duty diesel vehicle. Of the total gas phase non-methane hydrocarbons emitted, 80% were accounted for in the light hydrocarbon fraction, and 20% in the semi-volatile fraction. The semi-volatile fraction, which extended only to about C 15, was composed almost entirely of unburned fuel molecules, but with enrichment of the aromatic species relative to the fuel itself. n-Alkanes (paraffins) and methylnaphthalenes accounted for approximately 37% of the semi-volatile fraction. Aldehydes and ketones represented 34% of NMOG. Formaldehyde and acetaldehyde, account for 74% of the total carbonyl emissions.