On-line gas chromatographic analysis of light Fischer-Tropsch synthesis products

Summary A simple gas chromatographic system has been developed for the rapid on-line analysis of light Fischer-Tropsch products. This involves a single chromatography fitted with two columns, a porous-layer open-tubular column coated with KCl deactivated alumina and a packed Porapak-Q column. The capillary column separates the 16 most common C₁−C₄ hydrocarbons and permits a reasonable analysis of the hydrocarbons in the C₅−C₇ range. The packed column is used for the separation of methane, carbon monoxide, carbon dioxide, water and methanol. Retention characteristics for the analysis on the capillary column are presented. The total analysis cycle is 30 minutes.     

Development and study of zeolite catalytic systems for the transformation of lower hydrocarbons into valuable chemicals

The results of studies aimed at the development of highly efficient catalysts based on zeolites of the pentasil family for synthesis of aliphatic and aromatic hydrocarbons from C₂−C₅ olefins and paraffins are summarized. Dedicated to the memory of Academician M. E. Vol'pin timed to his 75th birthday. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1071–1080, June, 1998.     

Automatic headspace gas chromatography of C1–C7 hydrocarbons in sedimentary rocks. Application in Petroleum Geochemistry

Summary The analysis of hydrocarbons (C₁–C₇ molecular range) from the water-saturated pore structure of sedimentary rocks is performed by headspace gas chromatography. Hydrocarbon yields are compared to those of dynamic gas extraction techniques (gas stripping, thermovapourization). Lowest detectable quantity is estimated as 1–10 ppb (w/w) for the C₁–C₅ molecular range. Automation of the method helps to improve its application for routine light-hydrocarbon analysis in rock samples of oil and gas exploration wells. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Gas chromatographic analysis of C2−C16 dicarboxylic acids esterified in aqueous solutions as n-propyl esters

Summary C₂−C₁₆ dicarboxylic acids were esterified in aqueous solution in the presence of sulfuric acid. Esterification in water/n-propanol mixtures with mole ratios between 0.03 and 2.21 can be utilized for the quantitative determination of dicarboxylic acids by gas chromatography. The presence of water does not interfere at water/n-propanol mole ratios below 0.45. For mole ratios above 0.45 anhydrous sodium sulfate has been used for binding the water. The mole ratio range tested was 0.12–0.99 for anhydrous sodium sulfate/water, and 0.16–2.55 for sulfuric acid/anhydrous sodium sulfate.     

Evaluation of 4-amino-2-hydroxybenzoic acid as an eluent for indirect photometric determination of uncommon anions

Summary The efficacity of 4-amino-2-hydroxybenzoic acids as an eluent for the separation and determination of uncommon anions has been evaluated. The intensely absorbing eluent (λ_max 320 nm) offers a convenient indirect photometric approach to quantitate the species of interest in ppm and sub-ppm range. In the singlecolumn ion chromatography mode at 2 mM/2 mL/min and pH=6.0, clean separations of common and uncommon anions can be realized.     

Chromatography of glycols. Regularities in the retention of C3−C6 branched glycols in gas-solid and gas-liquid chromatography

Summary Linear correlation between the major physico-chemical properties of glycols and their relative retention volumes measured by gas-solid (GSC) and gas-liquid (GLC) chromatography is shown. The coefficients of the linear regression equations describing the relationship between the relative retention volumes and the physico-chemical parameters (boiling point, density, etc.) are given. The values of the change in the free energy for the stationary phases studied are given as well as the increments of this change per −CH₂- and CH₃-group. The main factors determining the retention of branched glycols on Polysorb, Tween and poly(ethylene glycol) are shown to be the distance between the hydroxyl groups in their molecules, the presence of alkyl substituents and the type and the number of these substituents.     

A column packing for isothermal gas chromatographic analysis of C1−C5 paraffins and monoolefins and dimethyl ether

Summary An analytical GC method was developed which uses a single packed column consisting of three packings in series prepared with the following liquid phases: dimethyl sulfolane, propylene carbonate, and silver nitrate. This system provides satisfactory resolution of mixtures of C₁–C₅ hydrocarbons and dimethyl ether obtained when converting methanol to gasoline. Due to the high capacity of the column it is possible to inject larger sample amounts permitting trace analysis.     

Gas chromatographic separation of C4−C5 expoxides on a glass capillary colum coated with OV-101 methylsilicone

Summary The separation of C₄−C₅ epoxides on a glass capillary column coated with OV-101 methylsilicone liquid phase was investigated. Retention indices were determined at 70, 80 and 90°C.     

Quantitative determination of gas mixture composition by gas chromatography—New approach

Summary A new method has been developed for the quantitative determination of gas mixture composition where air penetration during gas sample collection would lead to erroneous results. It requires the use of a stationary phase that separates gas sample components and the air and involves 4–5 analyses of samples of equal volumes containing different amounts of air. By graphical extrapolation of the air peak area (S _air ) as a function of the peak areas of the individual components (S _comp ) the areas for these components in the absence of air can be obtained forS _air =0. Using calibration curves for the pure gas components the true quantitative composition of the gas mixture is estimated.     

Synthesis and electrochemical properties of nanostructured LiAl x Mn2 − x O4 − y Br y particles

Nanostructured LiAl _x Mn_2 − x O_4 − y Br _y particles were synthesized successfully by annealing the mixed precursors, which were prepared by room-temperature solid-state coordination method using lithium acetate, manganese acetate, lithium bromide, aluminum nitrate, citric acid, and polyethylene glycol 400 as starting materials. X-ray diffractometer patterns indicated that the particles of the as-synthesized samples are well-crystallized pure spinel phase. Transmission electron microscopy images showed that the LiAl _x Mn_2 − x O_4 − y Br _y samples consist of small-sized nanoparticles. The results of galvanostatic cycling tests revealed that the initial discharge capacity of LiAl_0.05Mn_1.95O_3.95Br_0.05 is 119 mAh g⁻¹; after the 100th cycle, its discharge capacity still remains at 92 mAh g⁻¹. The introduction of Al and Br in LiMn₂O₄ bring a synergetic effect and is quite effective in increasing the capacity and elevating cycling performance.     

Separation of mixtures of permanent gases and light hydrocarbons on spherical carbon molecular sieves by gas-solid chromatography

Summary Experimental results are presented on the application of Carbosieve S (Supelco) and Spherocarb (Analabs) spherical carbon molecular sieves for the gas chromatographic separation of mixtures of permanent gases and C₁–C₃ hydrocarbons using a single column or two columns in series. At a programmed temperature of 35–300°C, good separation of the sample components was obtained when using helium as the carrier gas. When hydrogen was used as the carrier gas and the analysis was carried out under isothermal conditions the elution sequence of oxygen and nitrogen reversed as the temperature was increased. This behaviour was observed within a temperature range of 35–225°C for Carbosieve S, and within a temperature range of 35–300°C for Spherocarb.     

Conversion of natural gas to C2 hydrocarbons through dielectric-barrier discharge plasma catalysis

The experiments are carried out in the system of continuous flow reactors with dielectric-barrier discharge (DBD) for studies on the conversion of natural gas to C₂ hydrocarbons through plasma catalysis under the atmosphere pressure and room temperature. The influence of discharge frequency, structure of electrode, discharge voltage, number of electrode, ratio of H₂/CH₄, flow rate and catalyst on conversion of methane and selectivity of C₂ hydrocarbons are investigated. At the same time, the reaction process is investigated. Higher conversion of methane and selectivity of C₂ hydrocarbons are achieved and deposited carbons are eliminated by proper choice of parameters. The appropriate operation parameters in dielectric-barrier discharge plasma field are that the supply voltage is 20–40 kV (8.4–40 W), the frequency of power supply is 20 kHz, the structure of (b) electrode is suitable, and the flow of methane is 20–60 mL · min⁻¹. The conversion of methane can reach 45%, the selectivity of C₂ hydrocarbons is 76%, and the total selectivity of C₂ hydrocarbons and C₃ hydrocarbons is nearly 100%. The conversion of methane increases with the increase of voltage and decreases with the flow of methane increase; the selectivity of C₂ hydrocarbons decreases with the increase of voltage and increases with the flow of methane increase. The selectivity of C₂ hydrocarbons is improved with catalyst for conversion of natural gas to C₂ hydrocarbons in plasma field. Methane molecule collision with radicals is mainly responsible for product formation.     

Long-term stability of hydrocarbons in NIST gas standard reference material (SRM) 1800

A gas standard reference material (SRM) containing fifteen hydrocarbons in nitrogen at a nominal 5 nmol mol(-1) was issued in 1993. The certification period for SRM 1800 was assigned as 2 years, because of limited stability data. Over a period of 10 years reanalysis of the lot standard (a sample chosen from the SRM lot to which all other lot samples are compared), SRM samples remaining in stock for sale, and SRMs returned to the National Institute of Standards and Technology (NIST) for recertification, were compared with primary standards to assess the stability of the hydrocarbons. New primary standards were periodically introduced into the original primary standard suite to assess the stability and consistency of the primary standards. Over this ten-year period 11 SRM 1800 samples were reanalyzed, resulting in 210 amount-of-substance fraction (concentration) determinations performed for quality-assurance purposes. Of these measurements 209 (99.5%) agreed within the original 95% confidence interval of the +/-4% expanded uncertainty, demonstrating the stability of the standards. There was also agreement to within +/-2% of the original concentration for 204 (97%) of the measurements. This is well within the original +/-4% expanded uncertainty assigned to the hydrocarbon concentrations at the approximate 95% confidence interval demonstrating stability. These results will enable the expiry date to be increased for future restock issues of SRM 1800.     

Influence of the Lanthanide Ion and Solution Conditions on Formation of Lanthanide Wells–Dawson Polyoxotungstates

Lanthanide complexes of polyoxometalates, including the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand, have been pioneered by Michael T. Pope, to whom this paper is dedicated. Examination of the solid-state and solution behavior of lanthanide complexes of the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand are reported here to identify trends that will facilitate rational synthesis of hybrid organic lanthanide polyoxometalate complexes. Therefore, combining our data with that obtained by Pope and others a number of trends come into view. It is clear that there are two structural types for the 1:1 or 2:2 [Ln(H₂O)_X(α₂-P₂W₁₇O₆₁)]₂ ¹⁴⁻ species. The early lanthanides show a “cap to cap” structure that allows the Ln ion to be 9 coordinate and accommodates the longer bond lengths. The mid-late lanthanides show a “cap to belt” structure that allows the lanthanides to be 8 coordinate; this structural type is appropriate for the shorter bond lengths of the later lanthanides. The 1:1⇌1:2 equilibrium, that was observed by Pope for the Ce(III) analog is prevalent for the early- mid lanthanides. This equilibrium is slightly dependent on pH; however, cations have a major influence on this equilibrium. Larger, poorly hydrated cations appear to favor the 1:2 species for the early to mid lanthanides. Cations do not appear to influence the equilibrium for the later lanthanides; for all counterions, the 1:1 species was stable with no trace of the 1:2 species. Stability constants, K1 and K2, for the early to mid lanthanides were measured in this study by a competitive method and compared well with other published stability constant determinations. We suggest that the stability constants are not only dependent on the strength of interaction of the Ln with the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand, but are also significantly influenced by the medium. The medium may bias the equilibria of the early-mid lanthanides and later lanthanides. The log K₁/log K₂ ratios are very close, suggesting that it is difficult to separate the 1:1 and 1:2 Ln: α₂-P₂W₁₇O₆₁ ¹⁰⁻ species.Electronic Supplementary Material Supplementary material for this article is available at and is accessible for authorized users.This paper is dedicated to Professor Michael T. Pope in honor of his substantial and sustained contributions to polyoxometalate chemistry and his inspiration to scientists working in the field.     

Thermodynamic analysis of the structure of aqueous solutions of C<Subscript>12</Subscript>–C<Subscript>18</Subscript> hydrocarbons

Thermodynamic cycles including the increments \(\Delta G_{CH_2 }^0 , \Delta H_{CH_2 }^0 \), and \(T\Delta S_{CH_2 }^0 \) were constructed for dissolution, evaporation, hydrophobic hydration of C₅–C₉ hydrocarbons, and transfer from vapor (\(\Delta G_{CH_2 }^0 \) = ?0.7 kJ·mol^?1, \(\Delta H_{CH_2 }^0 \) = 2.9 kJ·mol^?1, \(T\Delta S_{CH_2 }^0 \) = 3.6 kJ·mol^?1) and water (\(\Delta G_{CH_2 }^0 \) = ?1.4 kJ·mol^?1, \(\Delta H_{CH_2 }^0 \) = 5.8 kJ·mol^?1, \(T\Delta S_{CH_2 }^0 \) = 7.2 kJ·mol^?1) to micelles of C₁₂–C₁₈ hydrocarbons. The formation of bistable hydrated micelles of C₁₂–C₁₈ is explained by a transition between the order-disorder states in an assembly of small (nano) systems of water. The extensive parameters of small systems and critical phenomena predicted by fluctuation theory are discussed.     

Etude des systemes CaHPO4−MHPO4−H2O (M=Sr,Ba) A 50°C

The systems CaHPO₄−MHPO₄−H₂O (M=Sr, Ba) were studied at 50°C. ForM=Sr, the series of single phases, Ca_1−xSr_xHPO₄ for 0.95<X<0.75 and Ca_xSr_1−xHPO₄ for 0.4<X<1 have been prepared. These solid solution were caracterized by their infrared spectra and their crystallographic unit cell parameters. ForM=Ba a new phase Ca₂Ba(HPO₄)₃ has been determined. It was characterized by DRX, IR, ATD and chemical analyses.

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Zusammenfassung Bei 50°C wurde das System CaHPO₄−MHPO₄−H₂O (mitM=Sr, Ba) untersucht. FürM=Sr wurden Serien von Einzelphasen erhalten: Ca_1−xSr_xHPO₄ für 0.95<X< 0.75 und Ca_xSr_1−xHPO₄ für 0.4<X<1. Diese Mischkristalle wurden anhand ihrer Infrarotspektren und ihrer kristallographischen Elementarzellenparameter charakterisiert. FürM=Ba wurde die neue Phase Ca₂Ba(HPO₄)₃ ermittelt. Sie wurde mittels DRX, IR, ATD und chemischer Analyse charakterisiert.

     

Trace Analysis of Hydrocarbons in Air Using Standard Gas Chromatographic and Personal Sampling Equipment

Abstract

Unmodified standard gas chromatographs are reported to be useful for the determination of a large number of ambient hydrocarbons. Packing of standard injector glass liners with an adsorbent permits thermal desorption in the injector on to the chromatographic column. Coupling to a personal sampling pump permits exposure-related sampling. The potential of the technique is illustrated by applications with the Tenax GC adsorbent. Precautions required to avoid artifacts when working in the subnanogram range are described.     

Improved resolution and determination of ambient C5−C12 hydrocarbons by GC-coupled refocussing system

Summary A homemade cryogenic system derived from readily available material is described, illustrating its usage as an accessory for adsorption/thermal desorption chromatography. A small Chromsorb-W-HP packing (1 cm) was introduced into a deactivated precolumn as a cryofocussing, preconcentrating unit. This was able to retain the analyte which had been thermally desorpted from a Tenax TA sampling tube at a relatively higher temperature (–80°C–90°C), with the analyte also reinjected on the analytical column in a relatively narrow band. Average overall recoveries for 24 hydrocarbons tested were 97.5%. Cryofocussing enhanced sensitivity and improved resolution. Field studies at a petroleum industry site were carried out and the accessory proved to be useful for complex C₅–C₁₂ hydrocarbon analysis in ambient air.     

Heat capacity of GdBaSr(Cu<Subscript>3−x</Subscript><Emphasis Type="Italic">M</Emphasis><Subscript>x</Subscript>)O<Subscript>7−δ</Subscript> superconductor (<Emphasis Type="Italic">M</Emphasis>=Zn and Ni)

In this study, GdBaSr(Cu_3−x M _x)O_7−δ bulk samples (M=Zn and Ni; 0≤x≤0.1) were prepared via solid-state reaction. Specific heat measurement (measured with thermal relaxation technique using PPMS) shows an obvious specific heat jump around the T _c for GdBaSrCu₃O_7−δ sample as observed in most of the high temperature superconductors. It shifts towards lower temperature with increasing of both Zn and Ni doping contents, whose tendency is similar to the decreasing of T _c. Debye temperature, Θ_D (derived from specific heat measurements) calculated at around 10 K is found to be directly proportional to the T _c.     

A new method to determine reid vapour pressure for stabilized crude oils by gas chromatography

Summary A new rapid method has been developed to determine Reid Vapour Pressure (RVP) for stabilized crude oils by gas chromatography. The quantity of light hydrocarbons dissolved in crude oil was measured directly by gas chromatographic analysis, while the RVP value was computed utilizing a new correlation with this quantity at constant temperature. A variety of crude oils were investigated and the results revealed the accuracy of this method.