Improvement of a cryogenic preconcentration unit for C2 - C6 hydrocarbons in ambient air at ppt levels

A previously described method for the quantitative analysis of C₂ - C₆ hydrocarbons in the ppt range based on cryogenic preconcentration has been improved further. Problems caused by condensation of O₂ and traces of water from the sample were overcome using a modified dyring procedure and a tandem preconcentration trap. In addition, the flow path through the unit was simplified further. Technical details are given. The reproducibility of both quantitative results and retention times was improved by these modifications. Typical standard deviations were in the order of 2% at the 200 ppt level.     

Efficient dichloromethylation of some aromatic hydrocarbons catalyzed by a new ionic liquid [C12minPEG800]Br under homogeneous catalysis in aqueous media

A series of new imidazolium-type ionic liquids based on polyethylene glycol have been prepared. The new recyclable temperature-dependant phase-separation system comprised of [C₁₂minPEG₈₀₀]Br and methylcyclohexane was also developed and successfully applied to the dichloromethylation of some aromatic hydrocarbons to prepare dichloromethyl-substituted hydrocarbons in excellent yields. The ionic liquid could be excellent recycled without any apparent loss of catalytic activity and little loss of weight even after 8 times recycling.     

Thermal mobilization of hydrocarbons from small-size rock samples. Application in petroleum geochemistry

Summary The quantitative analysis of hydrocarbons (C₁ to C₁₅ molecular range) from the water saturated pore structure of sedimentary rocks is performed by a combined thermal mobilization/glass capillary GC system. Organic geochemical processes, such as the generation of hydrocarbons as a function of kerogen type and maturity of sedimentary organic matter are studied.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Molecular mobility and N.M.R. relaxation in the binary system Triton X 114-water

Abstract

The proton spin lattice relaxation time T_t has been measured for several samples of the binary system Triton X 114-water in the concentration range 20-90 per cent by weight. The correlation time, the activation energy and the constant of the dipole-dipole interaction C were calculated for all samples. The results show the existence of two relaxation mechanisms connected with the mobility of the alkyl chains and the oxyethylene chains.     

Determination of molecular line parameters for acrolein (C3H4O) using infrared tunable diode laser absorption spectroscopy

Acrolein (C₃H₄O) molecular line parameters, including infrared (IR) absorption positions, strengths, and nitrogen broadened half-widths, must be determined since they are not included in the high resolution transmission (HITRAN) molecular absorption database of spectral lines. These parameters are required for developing a quantitative analytical method for measuring acrolein in a single puff of cigarette smoke using tunable diode laser absorption spectroscopy (TDLAS). The task is complex since acrolein has many highly overlapping infrared absorption lines in the room temperature spectrum and the cigarette smoke matrix contains thousands of compounds. This work describes the procedure for estimating the molecular line parameters for these overlapping absorption lines in the wavenumber range (958.7–958.9 cm⁻¹) using quantitative reference spectra taken with the infrared lead-salt TDLAS instrument at different pressures and concentrations. The nitrogen broadened half-width for acrolein is 0.0937 cm⁻¹ atm⁻¹ and to our knowledge, is the first time it has been reported in the literature.     

Selective deoxygenation of vegetable oils in the presence of Pt–Sn/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

We studied deoxygenation of individual fatty esters and fatty acid triglycerides from vegetable oils and lipid extracts from microalgae in the presence of catalysts prepared by deposition of Pt–Sn-containing compounds onto the γ-aluminum oxide surface. Using individual esters as an example, selective reduction of oxygen into water was demonstrated for the first time to proceed on a catalytic system at the 5 : 1 molar ratio of Sn and Pt active components to afford hydrocarbon components of substrates in virtually quantitative yield. Transformation of vegetable oil in the presence of this catalyst affords the C₃–C₁₈ hydrocarbon fraction in yield up to 99% at the content of C₃ and C₁₈ hydrocarbons up to 90%. The fraction of C₁ and C₂ hydrocarbons and carbon oxides is not higher than 0.5%. The possibility of carbon weight loss minimization during transformation of lipids was shown for the first time.     

Novel kinetic modelling of methanol-to-gasoline (MTG) reaction on HZSM-5 catalyst: Product distribution

A new kinetic model of MTG process on HZSM-5 catalyst, which enables us to predict the distribution of the subdivided product, has been proposed. The new model includes four reaction steps with oxygenates, C₂~C₄ unsaturated hydrocarbons, C₅₊ unsaturated hydrocarbons, C₁~C₄ saturated hydrocarbons, C₅₊ saturated hydrocarbons and aromatics as the product lumps. The kinetic parameters have been calculated using this model. The objective function has been introduced to check the availability of calculation. Based on the above kinetic parameters, a MTG fixed bed process has been simulated kinetically by using Aspen Plus.     

Preconcentration of Volatile Hydrocarbons as Air Pollutants by C-18 Bonded Silica used for Solid Phase Extraction

ABSTRACT

C₁₈-Silica used for Solid-Phase Extraction exhibits the same degree of adsorption of volatile hydrocarbons as compared to conventional Tenax adsorbent. The vapor pressure of the hydrocarbons and the velocity of the air sample through the sorbent are dominants of the preconcentration. Recovery of 80% for n-hexane and 98% for p-xylene at a concentration of 10 mg.m^?3 was obtained at 10 ml.g^?.min^? velocity.

C₁₈Bond Elut cartridges have been successfully used for quantitative determination of hydrocarbons as air pollutants by gas chromatography. The detection limit for p-xylene using preconcentration from 1 L air sample and a S/N ratio of 5 was 0.1 mg.m^?3. After regeneration of C₁₈Bond Elut cartridges by washing with acetonitrile and diethyl ether and drying at 85°C/15 min, their preconcentration potential remain acceptable upon reusing at least three times.     

Separation of different types of monoaromatic hydrocarbons in petroleum fractions by preparative high performance liquid chromatography on silica gel

Summary The character of preparative HPLC separation of monoaromatic hydrocarbons in light and middle petroleum fractions (containing C₁₀–C₁₇ hydrocarbons) has been studied, together with the dependence of the separation efficiency both on hydrocarbon molecular mass and the width of the distillation range of the analyzed petroleum cuts. Preparative HPLC may be advantageously used as a pre-concentration technique for detailed analyses of complex mixtures of petroleum monoaromatic hydrocarbons, owing to the fact that there are specific criteria holding for the separation of various structural types of monoaromatic hydrocarbons (the number of substituents on the aromatic ring, molecular mass, and the hydrocarbon type: benzenes-indanes).

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Trennung verschiedener Typen monoaromatischer Kohlenwasserstoffe aus Erdölfraktionen durch präparative HPLC an Silicagel

Zusammenfassung Die präparative HPLC-Trennung monoaromatischer Kohlenwasserstoffe (C₁₀–C₁₇) aus leichten und mittleren Erdölfraktionen wurde untersucht und die Abhängigkeit des Trennungseffektes von der Molekularmasse der Kohlenwasserstoffe und der Breite des Destillationsbereichs wurde geprüft. Die präparative HPLC kann vorteilhaft für die Vorkonzentrierung bei der Analyse komplexer Gemische monoaromatischer Erdölkohlenwasserstoffe eingesetzt werden, da spezifische Kriterien für die Trennung der verschiedenen Strukturtypen gelten (Anzahl der Substituenten am aromatischen Ring, Molekularmasse, KW-Typ: Benzole-Indane).

     

Chromatographic study of the organic matter from Moroccan Rif bituminous rocks

The bituminous rocks of the Upper Cretaceous in the Moroccan Rif have been assessed and characterized in detail using organic geochemical techniques and a variety of organic geochemical parameters. The organic matter from 4 sites was studied in order to determine its thermal maturity and its depositional environments. The organic extracts (bitumens) were fractionated on silica-potassium hydroxide column according to the aliphatic hydrocarbons, acid compounds and polar compounds. Aliphatic hydrocarbons were identified by gas chromatography and mass spectrometry (GC/MS).The distribution of the aliphatic hydrocarbon fractions, and the various organic geochemical parameters (pristane/phytane, isoprenoids/n-alkanes, CPI, C₂₇:C₂₈:C₂₉ regular, C₂₉20S/(20S+20R), C₂₉ββ/(ββ+αα), C₂₉/C₃₀ hopanes and Ts/Tm) showed that the studied samples were generally mature. Two of the 4 samples appeared to be derived from source rocks deposited under anoxic conditions while suboxic to oxic conditions seemed to have been dominant for the remaining two samples. Rock–Eval pyrolysis data in addition to GC results suggested types II, III and IV kerogens for the studied samples.     

Application of Computer-Assisted 13C NMR Spectrometry for Separation and Determination of Heptane Isomers in the Feed Stocks of Cyclohexane Used in Purification Process

Abstract

A computer-assisted ¹³C NMR spectrometric method for separation, identification and quantitative determination of C₇ hydrocarbons in cyclohexane has been developed. A simulated library containing chemical shift and multiplicity data of 131 compounds of C₇ hydrocarbons has been prepared. The method incorporates the unique features of quantitative and edited ¹³C NMR spectra for separation and identification of mixture of hydrocarbons. It serves as an alternative method to GC-MS for monitoring the composition of feed stocks used for cyclohexane purification process.     

High temperature gas chromatography for the analysis of fossil fuels: A review

For the past two or three decades geochemists have been concerned with the analyses and characterization of compounds, generally hydrocarbons, ranging from C₁? C₄₀. Significant amounts of information have resulted from these studies which have been extremely useful in many geochemical and environmental studies. However, in the past two or three years the commercial development and availability of high temperature gas chromatography columns has lead to the investigation of the occurrence and distribution of high molecular weight hydrocarbons (HMWHC), and other compounds, in the carbon number range C₄₀? C₁₀₀, present in oils, waxes, bitumens and rock extracts. The ability to study these compounds represents a major advance in organic geochemistry. In some samples these compounds may represent the bulk of the organic components but prior to development of the high temperature columns it was impossible to study their distributions. This paper will review advances that have occurred in terms of the application of high temperature gas chromatography (HTGC) to the analyses of fossil fuel samples and discuss the possible origin and significance of these compounds that have been identified. In addition, some of the potential problems involved in the analyses of these compounds will also be discussed.     

Study of the molecular tilt angle and the order parameter of a ferroelectric liquid crystal mixture using IR spectroscopy

Abstract

We report measurements of the molecular tilt angle of a ferroelectric liquid crystal mixture (ZLI 3654), using infra-red spectroscopy, and of the optical tilt angle using polarizing microscopy. The molecular tilt angle is found to be approximately the same for different molecular vibrations. The second rank orientational order parameter for the axis of molecular vibrations of different groups of the molecule for homogeneously aligned samples have been determined as a function of temperature. The order parameter depends slightly on the sample thickness and is about 8 per cent higher for a lower thickness (～ 7 μm) compared to a higher thickness (～ 12 μm). The order parameter does not change significantly at the S_C?–S_A transition. The order parameter of S_C? is found to be unaffected by the application of a constant electric field. The order parameter for the alkyl chain is found to be about three times lower than for the molecular core.     

Reactions of water vapor or molecular hydrogen with trichloroethylene in a microwave plasma reactor

The reaction of trichloroethylene (C₂HCl₃) with water vapor or molecular hydrogen has been studied in a low-pressure [ca. 5 Torr (0.67 kPa)] microwave plasma tubular flow reactor. The experimental apparatus included feed introduction systems, a microwave plasma reactor, and full product analysis by flame ionization and thermal-conductivity gas chromatography, mass spectrometry, and specific ion or pH detection for hydrogen chloride [HCl]. Conversions of C₂HCl₃ in the range 50 to almost 100% are achieved. Product analyses indicate conversion to HCl, some light hydrocarbons, nonparent chlorocarbons, and soot C_(s). For the H₂O case, carbon monoxide and trace carbon dioxide were produced in place of some light hydrocarbons and C_(s). At least 85 mole % of chlorine (Cl) from the converted parent C₂HCl₃ forms thermodynamically stable HCl at parent conversions of 80% or more. The remaining chlorine was present as nonparent chlorocarbons. Preliminary kinetic analyses were performed. The global reaction in the plasma was found to follow one-half-order kinetic dependence on each of C₂HCl₃ and H₂O or H₂. Elementary plasma reaction mechanisms are presented to account for C₂HCl₃ conversion and the observed product distribution.     

Correlation between hydrocarbon distribution and water-hydrocarbon ratio in Fischer-Tropsch synthesis

In order to shorten the evaluation cycle of cobalt catalyst before the optimized catalyst is fixed on, a mathematical method is proposed to calculate weight percentage of C5+ hydrocarbons. Based on the carbide polymerization mechanism and the main hydrocarbons being linear alkanes and α-olefins, the correlation between hydrocarbon distribution and the molecular mass ratio of water to hydrocarbons is discussed. The result shows the ratio was within the range of 1.125-1.286 and the lower the ratio, the more gaseous hydrocarbons were obtained. Moreover, a linear equation between the weight percentage of C5+ hydrocarbons and the weight ratio of C5+ hydrocarbons to the total water is established. These results are validated by corresponding experiments. The weight percentage of C5+ hydrocarbons could be immediately calculated by this linear equation without detailed gas chromatography (GC) analysis of them.     

Detection of arsenic-containing hydrocarbons in a range of commercial fish oils by GC-ICPMS analysis

The present study describes the use of a simple solid-phase extraction procedure for the extraction of arsenic-containing hydrocarbons from fish oil followed by analysis using gas chromatography (GC) coupled to inductively coupled plasma mass spectrometry (ICPMS). The procedure permitted the analysis of a small sample amount, and the method was applied on a range of different commercial fish oils, including oils of anchovy (Engraulis ringens), Atlantic herring (Clupea harengus), sand eel (Ammodytes marinus), blue whiting (Micromesistius poutassou) and a commercial mixed fish oil (mix of oils of Atlantic herring, Atlantic cod (Gadus morhua) and saithe (Pollachius virens)). Total arsenic concentrations in the fish oils and in the extracts of the fish oils were determined by microwave-assisted acid digestion and ICPMS. The arsenic concentrations in the fish oils ranged from 5.9 to 8.7 mg kg^?1. Three dominant arsenic-containing hydrocarbons in addition to one minor unidentified compound were detected in all the oils using GC-ICPMS. The molecular structures of the arsenic-containing hydrocarbons, dimethylarsinoyl hydrocarbons (C₁₇H₃₈AsO, C₁₉H₄₂AsO, C₂₃H₃₈AsO), were verified using GC coupled to tandem mass spectrometry (MS/MS), and the accurate masses of the compounds were verified using quadrupole time-of-flight mass spectrometry (qTOF-MS). Additionally, total arsenic and the arsenic-containing hydrocarbons were studied in decontaminated and in non-decontaminated fish oils, where a reduced arsenic concentration was seen in the decontaminated fish oils. This provided an insight to how a decontamination procedure originally ascribed for the removal of persistent organic pollutants affects the level of arsenolipids present in fish oils.     

Densities against temperature of 17 organic liquids and of solid 2,2-dimethylpropane

Densities against temperature of liquids under their equilibrium vapor pressures are reported for three fluoromethanes, three aromatic hydrocarbons, four olefins, bicyclo[2,2,2]octane. 2-methyltetrahydrofuran, and {0.786(1,4-c-C₆H₈) + 0.214C₆H₆}. The volume change on melting 2,2-dimethylpropane at the triple-point temperature is 9.6 per cent. A density parameter for n-pentane by Das and coworkers (J. Chem. Eng. Data1977, 22, 3) has been corrected.     

Gaschromatographische Untersuchung der Adsorptionseigenschaften von Silicalit und ZSM-5

High silica molecular sieves (silicalite, ZSM-5) were tested as adsorbents for gas chromatographic trace analysis. Therefore the retention behaviour of low-boiling organic compounds (hydrocarbons, halogenated hydrocarbons, amines, alcohols and ethers) on these materials was investigated. The specific retention volumes at different temperatures have been determined and elution orders and peak shapes were studied. The retention data allow a simple calculation of the breakthrough volumes (dynamic adsorption capacity) and the chromatographic characterisation of the adsorbents. Both nitrogen and oxygen containing compounds could not—or at least unreproducibely—be eluated up to 300°. The elution order and the peak shape of compounds with the same number of carbon atoms but different geometric and electronic structure (e.g.n-butenes;n-hexane, cyclohexane, benzene) can be explained by the action of exclusion effects and different diffusion barriers. On the basis of calculated breakthrough volumes we conclude that silicalite should be useful in the preconcentration of both saturated C₃–C₆ hydrocarbons and C₁–C₂ chlorinated hydrocarbons from gaseous streams.     

Theoretical calculations on C30H12 bowl-shaped hydrocarbons: NMR shielding constants,stability, and aromaticity

Density Functional Theory (DFT) calculations at the B3LYP/6-31G* level have been performed on four bowl-shaped polyaromatic hydrocarbons of C₃₀H₁₂ molecular formula ( 1 – 4 ) showing C₃ ( 1 ), C_2v ( 2 and 4 ), and C_2h ( 3 ) symmetries. The geometrical and electronic properties of the compounds studied have been analyzed to explain their relative stability. NMR chemical shifts parameters for the atoms and Nucleus Independent Chemical Shifts (NICSs) for the rings were calculated using the GIAO method. The ¹³C and ¹H chemical shifts calculated are in very good agreement with the experimental data. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1412–1421, 1999     

Molecular beam sampling mass-spectrometric study of high-temperature benzene oxidation

The oxidation of benzene has been investigated with a high-temperature alumina flow reactor in the temperature range of 950–1150 K at residence times of ca. 1 ms and pressures of ca. 400 mbar. Analysis of the reaction products at various stages of the reaction was carried out by direct expansion of the reacting gas yielding a molecular beam that was analyzed by a mass spectrometer. Product identification studies were made by comparing the results from the oxidations of C₆H₆ and C₆D₆. Besides the products found in previous studies a number of new oxygenated intermediate species were identified, namely benzoquinone, cyclopentadienone, acrolein, and a C₄H₄O species. In addition, some higher hydrocarbons have been found even at high oxygen excess. The role of the intermediates within the current ideas of the reaction mechanism is discussed.