The viscosity and density of the methanol + n-nonane, ethanol + n-nonane, and ethanol + n-decane systems

This work presents the results obtained in measurements of the kinematic viscosity and density of the methanol-n-nonane, ethanol-n-nonane, and ethanol-n-decane systems at various temperatures and low n-alkane concentrations (within the concentration range of miscibility). The dynamic viscosities of these systems at 298.15 K were calculated according to free volume theory. The results substantiated the existence of an anomaly in the behavior of viscosity of the methanol-n-nonane system (positive Δlnη values) and its absence for the ethanol-n-alkane systems.     

Kinetics study of OH radical reactions with n-octane, n-nonane, and n-decane at 240-340 K using the relative rate/discharge flow/mass spectrometry technique

The kinetics of the reactions of hydroxyl radical with n-octane (k1), n-nonane (k2), and n-decane (k3) at 240-340 K and a total pressure of approximately 1 Torr has been studied using relative rate combined with discharge flow and mass spectrometer (RR/DF/MS) technique. The rate constant for these reactions was found to be positively dependent on temperature, with an Arrhenius expression of k1 = (2.27 +/- 0.21) x 10(-11)exp[(-296 +/- 27)/T], k2 = (4.35 +/- 0.49) x 10(-11)exp[(-411 +/- 32)/T], and k3 = (2.26 +/- 0.28) x 10(-11)exp[(-160 +/- 36)/T] cm3 molecule(-1) s(-1) (uncertainties taken as 2sigma), respectively. Our results are in good agreement with previous studies at and above room temperature using different techniques. Assuming that the reaction of alkane with hydroxyl radical is the predominant form for loss of these alkanes in the troposphere, the atmospheric lifetime for n-octane, n-nonane, and n-decane is estimated to be about 43, 35, and 28 h, respectively.     

First and second thermodynamic mixing functions of ethylbenzene+n-nonane, +n-decane,and+n-dodecane at 25 and 45°C

Isothermal compressibilities _T and isobaric thermal expansion coefficients _p have been determined for mixtures of ethylbenzene+n-nonane, +n-decane, and +n-dodecane at 25 and 45°C in the whole range of composition. The excess functions and have been obtained at each measured mole fraction. The first one is zero for ethylbenzene +n-nonane, positive for ethylbenzene +n-decane, and +n-dodecane and increases with chain length n of the n-alkane. The function is positive for the three studied systems and nearly constant with n. Both mixing functions increase slightly with temperature. From this measurement and supplementary literature data of molar heat capacities at constant pressure C _P , the isentropic compressibilities _S, the molar heat capacities at constant volume C _V and the corresponding mixing functions have been calculated at 25°C. Furthermore, the pressure dependence of excess enthalpy H ^B , at zero pressure and at 25°C has been obtained from our experimental results of and experimental literature values for excess volume V ^E .     

Diffusion coefficients in supercritical fluids: available data and graphical correlations

The methods for obtaining reliable data on diffusion coefficients at high pressure have received great attention over the last 15 years. This interest has been due to the importance that supercritical fluids have assumed in some industrial areas, mainly in emerging separative operations based on mass transfer mechanisms. This review includes all the available data of diffusion coefficients in supercritical fluids at infinite dilution. Revised literature includes references until 1998. Frequent types of graphical correlation were analyzed.     

Extended corresponding states model for fluids and fluid mixtures: II. Application to mixtures and natural gas systems

We report an extended corresponding states model optimised for accurate prediction of the thermodynamic properties and vapour–liquid equilibria of natural gases and similar mixtures. The corresponding states model uses methane as the reference fluid and employs shape factors for pure components that were reported recently [Fluid Phase Equilib. 204 (2002) 15]. The van der Waals one-fluid model is used for mixtures and, in this paper, we report two alternative temperature- and density-dependent correlations of the binary interaction parameters. Model ECSmixS1 was optimised for 19 binary systems in the wide domain 90≤T (K)≤670 with p (MPa)≤510 and is suitable for the prediction of both liquid- and gas-phase thermodynamic properties and for the solution of vapour–liquid equilibrium problems. Model ECSmixS2 was specialised for increased accuracy in the natural gas ‘custody transfer’ interval 270≤T (K)≤330 with p (MPa)≤12 and is intended for gas-phase thermodynamic properties only. For mixtures of the major components of natural gas, we obtain with Model ECSmixS1 an overall average absolute deviation (AAD) of 0.12% in calculated densities, an AAD of 0.16% in calculated speeds of sound and an AAD of 1.8% in bubble pressure. With Model ECSmixS2, we obtained improved AADs of 0.03% in density and 0.03% in speed of sound. These results compare very favourably with other commonly used mixture models. The present model may be systematically improved or extended by introducing new or improved correlations of the binary parameters.     

Development of enantioselective gas chromatographic quantitation assay for dl-threo-methylphenidate in biological fluids

An enantioselective gas chromatographic quantitation assay was developed for the enantiomers of dl-threo-methylphenidate in plasma and urine. dl-threo-Methylphenidate and the internal standard were acylated with N-heptafluorobutyryl-1-prolylchloride under Schotten-Baumann conditions prior to gas chromatographic separation on achiral mixed stationary phases. The derivatives were detected by means of a nitrogen-phosphorus detector. Linear and reproducible calibration curves were obtained over the concentration ranges 0.43-43.25 and 2.16-216.25 ng/ml enantiomer in plasma or urine, respectively. This enantioselective gas chromatographic quantitation assay was applied in a single oral dose disposition study of dl-threo-methylphenidate in a healthy adult volunteer. Stereoselective differences were observed in the plasma concentration-time profiles and cumulative urinary excretion profiles following oral doses of 20 and 40 mg of dl-threo-methylphenidate hydrochloride. Only d-threo-methylphenidate was detectable in plasma after 4 h.     

Theoretical and experimental correlations of gas dissolution, diffusion, and thermodynamic properties in determination of gas permeability and selectivity in supported ionic liquid membranes

Supported ionic liquid membranes (SILMs) has the potential to be a new technological platform for gas/organic vapour separation because of the unique non-volatile nature and discriminating gas dissolution properties of room temperature ionic liquids (ILs). This work starts with an examination of gas dissolution and transport properties in bulk imidazulium cation based ionic liquids [C(n)mim][NTf2] (n=2.4, 6, 8.10) from simple gas H(2), N(2), to polar CO(2), and C(2)H(6), leading to a further analysis of how gas dissolution and diffusion are influenced by molecular specific gas-SILMs interactions, reflected by differences in gas dissolution enthalpy and entropy. These effects were elucidated again during gas permeation studies by examining how changes in these properties and molecular specific interactions work together to cause deviations from conventional solution-diffusion theory and their impact on some remarkably contrasting gas perm-selectivity performance. The experimental perm-selectivity for all tested gases showed varied and contrasting deviation from the solution-diffusion, depending on specific gas-IL combinations. It transpires permeation for simpler non-polar gases (H(2), N(2)) is diffusion controlled, but strong molecular specific gas-ILs interactions led to a different permeation and selectivity performance for C(2)H(6) and CO(2). With exothermic dissolution enthalpy and large order disruptive entropy, C(2)H(6) displayed the fastest permeation rate at increased gas phase pressure in spite of its smallest diffusivity among the tested gases. The C(2)H(6) gas molecules "peg" on the side alkyl chain on the imidazulium cation at low concentration, and are well dispersed in the ionic liquids phase at high concentration. On the other hand strong CO(2)-ILs affinity resulted in a more prolonged "residence time" for the gas molecule, typified by reversed CO(2)/N(2) selectivity and slowest CO(2) transport despite CO(2) possess the highest solubility and comparable diffusivity in the ionic liquids. The unique transport and dissolution behaviour of CO(2) are further exploited by examining the residing state of CO(2) molecules in the ionic liquid phase, which leads to a hypothesis of a condensing and holding capacity of ILs towards CO(2), which provide an explanation to slower CO(2) transport through the SILMs. The pressure related exponential increase in permeations rate is also analysed which suggests a typical concentration dependent diffusion rate at high gas concentration under increased gas feed pressure. Finally the strong influence of discriminating and molecular specific gas-ILs interactions on gas perm-selectivity performance points to future specific design of ionic liquids for targeted gas separations.     

Hydrate capture CO2 from shifted synthesis gas,flue gas and sour natural gas or biogas

CO₂ capture by hydrate formation is a novel gas separation technology, by which CO₂ is selectively engaged in the cages of hydrate and is separated with other gases, based on the differences of phase equilibrium for CO₂ and other gases. However, rigorous temperature and pressure, high energy cost and industrialized hydration separator dragged the development of the hydrate based CO₂ capture. In this paper, the key problems in CO₂ capture from the different sources such as shifted synthesis gas, flue gas and sour natural gas or biogas were analyzed. For shifted synthesis gas and flue gas, its high energy consumption is the barrier, and for the sour natural gas or biogas (CO₂/CH₄ system), the bottleneck is how to enhance the selectivity of CO₂ hydration. For these gases, scale-up is the main difficulty. Also, this paper explored the possibility of separating different gases by selective hydrate formation and reviewed the progress of CO₂ separation from shifted synthesis gas, flue gas and sour natural gas or biogas.     

Improved gas chromatographic method for the determination of nicotine and cotinine in biologic fluids

Improved methods have been developed for the determination of nicotine and its major metabolite, cotinine, in blood, plasma, and urine samples. These methods utilize gas chromatography with alkali flame ionization (nitrogen--phosphorus) detection and structural analogs of nicotine and cotinine as internal standards.     

Methyketene,a minor but highly reactive byproduct in the pyrolysis gas of acetone

Methylketene was identified during the pyrolysis of acetone, and proved to be much more reactive than ketene : METHYL-β-LACTAMS were the dominant cycloaddition products when imines are reacted with the pyrolysis gas of acetone at ROOM TEMPERATURE.     

Application of purge and trap extraction and gas chromatography for determination of minor esters in cider

The validation of a method based on the purge and trap technique combined with gas chromatography-mass spectrometry-flame ionization detection has been carried out in order to apply it to the analysis of ciders. Although 49 compounds were identified, our work was focused on the study of nine minor esters, obtaining recoveries ranging between 93% for ethyl decanoate and 117% for ethyl 3-methylbutyrate, and a precision (RSDs) ranging between 2.2% for hexyl acetate and ethyl decanoate and 10.9% for isopentyl acetate. To demonstrate the feasibility of the procedure, the method was applied to the analysis of commercial ciders.     

Practical method for the measurement of Alkyl mercaptans in natural gas by multi-dimensional gas chromatography, capillary flow technology, and flame ionization detection

Volatile sulfur compounds such as alkylmercaptans are undesired impurities in natural gas streams. As a result, natural gas treatment and purification services are essential in many industries that utilize natural gas either as a fuel or in a chemical process. While there are many analytical methods that can be employed for the measurement of mercaptans, a simple, practical, and easy-to-implement method is required for remote field deployment. An analytical method, based on multi-dimensional gas chromatography (MDGC), capillary flow technology and flame ionization has been successfully developed for the application described. Results based on the technique showed alkylmercaptans can be accurately measured with a minimum detection limit of 200 ppb (v/v) or better, a linear range of up to 100 ppm (v/v), and a relative standard deviation (n=10) of 1.2% or less were obtained by manual injection with a total sample-to-sample analysis time of less than 15 min.     

An improved microwave apparatus for phase behaviour measurements in lean gas condensate fluids

An apparatus based on a microwave resonant cavity has been designed and fabricated for phase behaviour measurements in lean gas condensate fluids over a wide range of temperature and pressure. The re-entrant geometry of the resonator is optimised for detecting any liquid phase present in very lean natural gases. The mode structure of the cavity has been thoroughly investigated with both analytic and finite element models. Three modes, excited by an electric field probe, are monitored when measuring a fluid contained within the resonator. The highest mode (f_vac≈6.9 GHz) is used to detect dew points while the lower modes (460 MHz and 4.3 GHz) are employed for liquid volume and dielectric constant measurements. Careful microwave circuit design ensures good signal-to-noise ratios for all modes over the operating temperature range. Simulations of the resonator containing various fluids indicate that the system is over 10⁴ times more sensitive than previous microwave systems and can detect liquid volumes as small as 5×10⁻⁶ cm³. Dew point measurements in a gas condensate fluid support this prediction.