Experimental studies of natural gas to synthesis gas converters based on permeable cavity matrices

The matrix conversion of natural gas into synthesis gas, in which the autothermal oxidation occurs in the surface combustion mode in a cavity of a closed three-dimensional matrix made of a gas-permeable material, was studied experimentally. The specific volumetric productivity of such converters considerably exceeds that of traditional types of converters and allows conversion of hydrocarbon gases of virtually any composition into synthesis gas. Prospects for practical use of the new type of converters are discussed.     

A molecular model of water based on the lattice gas model

A lattice gas model is used to describe the vapor-liquid state of water molecules. The orientationally directed interaction of the water molecules via their tetrahedral structure and dipole-dipole interaction are considered in the theory, along with the Lennard-Jones contributions to the potential of molecular interaction, which stabilize the system with dipole interaction. We studied how the radius of the molecular interaction potential affects the equilibrium characteristics of the system (the phase separation curves of the vapor-liquid system, and the relationship between the fluid density and the chemical potential value).     

New model for gas evolving electrodes based on supersaturation

A new model for gas evolving electrodes is proposed, in which the gas evolution reaction is driven by the supersaturation of dissolved gas.     

An empirical excess volume model for estimating liquefied natural gas densities

Hiza, M.J., 1978. An empirical excess volume model for estimating liquefied natural gas densities. Fluid Phase Equilibria, 2: 27–38.The mathematical model presented herein was developed to represent excess volumes at saturation for multicomponent liquid mixtures of nitrogen and the low molecular weight alkanes between 105 and 120 K. Parameters of the model were determined from experimental excess volumes for binary liquid mixtures of nitrogen, methane, ethane, propane, isobutane, and normal butane. Comparisons made with selected experimental excess volumes reported in the literature for multicomponent liquid mixtures of the above components demonstrate the predictive capability of the model in two simple forms. An extension of the model to include mixtures containing isopentane and normal pentane is also proposed. Pure component molar volumes are given at 0.5 K intervals from 105 to 116 K to facilitate the use of the present model in estimating liquefied natural gas (LNG) densities.     

ZIF-8 based polysulfone hollow fiber membranes for natural gas purification

Mixed matrix membranes (MMMs) have received worldwide attention for natural gas purification due to their superior performance in terms of permeability and selectivity. The zeolitic imidazole framework-8 (ZIF-8) blended polysulfone (PSf) membranes have been fabricated for natural gas purification. ZIF-8 was selected due to its low cost, remarkable thermal and chemical stabilities, and tunable microporous structure. The neat PSf hollow fiber membrane and mixed matrix hollow fiber membranes incorporated with the various ZIF-8 loadings up to 1.25% were fabricated. The prepared membranes were evaluated using field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and gas separation performance. The low loading of ZIF-8 nanoparticles to the MMM improved thermal stability and glass transition temperature and yielded low surface roughness. MMMs were tested using pure gases with a significant improvement of 36% in CO₂ permeability and 28% in CO₂/CH₄ selectivity compared to the neat membrane. However, the high ZIF-8 loading reduced the separation performances. Moreover, CO₂/CH₄ selectivity decreased at elevated pressure (8 and 10 bar) due to CO₂-induced plasticization. Previously, the incorporation of ZIF-8 particles has primarily been subjected to the fabrication of flat sheet membranes, whereas this work focused on hollow fiber membranes which are rarely investigated. Hence, the promising results obtained at low feed pressure in this study demonstrated the potential of ZIF-8 based hollow fiber membrane for natural gas purification.     

Towards a fundamental understanding of natural gas hydrates

Gas clathrate hydrates were first identified in 1810 by Sir Humphrey Davy. However, it is believed that other scientists, including Priestley, may have observed their existence before this date. They are solid crystalline inclusion compounds consisting of polyhedral water cavities which enclathrate small gas molecules. Natural gas hydrates are important industrially because the occurrence of these solids in subsea gas pipelines presents high economic loss and ecological risks, as well as potential safety hazards to exploration and transmission personnel. On the other hand, they also have technological importance in separation processes, fuel transportation and storage. They are also a potential fuel resource because natural deposits of predominantly methane hydrate are found in permafrost and continental margins. To progress with understanding and tackling some of the technological challenges relating to natural gas hydrate formation, inhibition and decomposition one needs to develop a fundamental understanding of the molecular mechanisms involved in these processes. This fundamental understanding is also important to the broader field of inclusion chemistry. The present article focuses on the application of a range of physico-chemical techniques and approaches for gaining a fundamental understanding of natural gas hydrate formation, decomposition and inhibition. This article is complementary to other reviews in this field, which have focused more on the applied, engineering and technological aspects of clathrate hydrates.     

Quantification in comprehensive two-dimensional gas chromatography and a model of quantification based on selected summed modulated peaks

In common with all gas chromatography (GC) methods, comprehensive two-dimensional gas chromatography (GC x GC) has the potential to provide both qualitative and quantitative analysis. There are fundamental differences in the way one-dimensional (1D-GC) and GC x GC results are interpreted for these parameters. Since 1D-GC produces a single measured peak in the chromatogram, there is a single retention time, and associated with this a single peak response (either area or height). Peak area and height are related by peak width. GC x GC produces a series of modulated peaks at the detector. Thus, the peak metrics of retention, area and height for one component are now not simple single values for one peak, but rather are derived from the multiple peak distribution generated by the modulation process. The peak retention is interpreted in terms of two-dimensional coordinates in a retention plane. In this study, a brief background review to quantification in GC x GC is provided. Previous reviews cover aspects of quantitative GC x GC studies up to the year 2005, including different approaches to quantification, and reports of quantitative analysis with different detectors, for different compounds classes, and in different matrices. Other studies have developed chemometric approaches based on multivariate analysis to provide quantitative reporting of individual compounds. The coverage of the earlier reviews has been updated to include material that has been presented since 2005 and includes considerations of valve-based modulation. Recently the modulation ratio (M(R)) concept was proposed and intended to clarify the meaning of modulation number (n(M)) in GC x GC, which was shown to be a rather poorly defined parameter. Based on the prior studies that introduced this concept, the role of quantitative analysis is investigated here through calculation of the peak areas and peak area ratios of selected series of modulated peaks in GC x GC. The application of isotopically labelled reference compounds for polycyclic aromatic hydrocarbon (PAH) analysis is used here to develop the quantitative metric approach. It is shown that by selecting the two or three major modulated peaks for solutes and internal standards, comparing the response ratio with the sum of all modulated peaks and also with the reference non-modulated result, quantification is statistically equivalent. Thus, adequate quantitative analysis and calibration can be accomplished by using selected major modulated peaks for each compound. This may simplify quantitative interpretation of GC x GC data.     

Total synthesis approaches to natural product derivatives based on the combination of chemical synthesis and metabolic engineering

Secondary metabolites are an extremely diverse and important group of natural products with industrial and biomedical implications. Advances in metabolic engineering of both native and heterologous secondary metabolite producing organisms have allowed the directed synthesis of desired novel products by exploiting their biosynthetic potentials. Metabolic engineering utilises knowledge of cellular metabolism to alter biosynthetic pathways. An important technique that combines chemical synthesis with metabolic engineering is mutasynthesis (mutational biosynthesis; MBS), which advanced from precursor-directed biosynthesis (PDB). Both techniques are based on the cellular uptake of modified biosynthetic intermediates and their incorporation into complex secondary metabolites. Mutasynthesis utilises genetically engineered organisms in conjunction with feeding of chemically modified intermediates. From a synthetic chemist's point of view the concept of mutasynthesis is highly attractive, as the method combines chemical expertise with Nature's synthetic machinery and thus can be exploited to rapidly create small libraries of secondary metabolites. However, in each case, the method has to be critically compared with semi- and total synthesis in terms of practicability and efficiency. Recent developments in metabolic engineering promise to further broaden the scope of outsourcing chemically demanding steps to biological systems.     

Numerical modeling of a four-electrode electrochemical accelerometer based on natural convection: The boussinesq flow model vs. The compressible flow model

Two-dimensional numerical simulations are conducted to study the feasibility of applying the Boussinesq approximation to the steady-state buoyancy-driven flow in a four-electrode electrochemical accelerometer. Two kinds of electrode layouts along the electrochemical cell, the anode-cathode-cathode-anode (ACCA) and the cathode-anode-anode-cathode (CAAC), are examined. The results from the model based on the Boussinesq approximation are compared to those from the compressible flow model. Though the Boussinesq flow model leads to fairly large quantitative deviations, it is capable of qualitatively estimating the output electric current when the output electric current increases linearly as the applied axial acceleration. A qualitative difference between the two models are found in the centerline density profiles in the electrochemical cell, which can be explained by the compressibility-induced acceleration/deceleration. It is found that the Boussinesq approximation is good enough for the estimation of the electric current at a single electrode while can make large deviations of the cathodic current difference, i.e., the output electric current in this study.     

Molecular simulations on volumetric properties of natural gas

We have employed Monte Carlo simulation in the NPT ensemble to determine the molar volume and the compressibility factor of naturally occurring hydrocarbon gas mixtures. The simulation results were compared to experimental data as well as to predictions based on both the Peng–Robinson and AGA 8 equations of state. The mean error of the simulation results was roughly of the same order as those of the equation of state values. For pressures higher than the retrograde dew point pressure, systematic deviations were found especially if the gases contained a high proportion of heavy components. The quality of the simulation results increased with rising temperature. In the region of retrograde condensation, we used the Gibbs ensemble technique to determine the molar volume as well as the composition of the phases. Both were in agreement with the results of flash calculations combined with the Peng–Robinson equation of state. At pressures far from the retrograde dew point pressure, the simulation results followed the experimental liquid drop out curve.     

Numerical model of a large-scale oxygen consumption fire calorimeter

The present study introduces a volumetric heat and mass source model to investigate the flow field inside the hood and duct system and optimize the sampling technique in a large scale fire calorimeter. The model was validated using experimental measurements of the oxygen depletion factor, gas temperature and heat release rate. The calculated heat release rates determined using the CFD model were in good agreement with the experiments with the maximum discrepancy between the simulations and experiments being less than 5%. A series of CFD simulations were performed to examine the effects of sampling location, and the number of sampling points on the uncertainty of the heat release calculation. Detailed flow characteristics were analyzed to understand the complicated internal duct flow.     

天然气与硫酸盐热化学还原反应的模拟实验研究

为探讨天然气中高含量硫化氢形成的化学机制，利用高温高压反应装置，对天然气与固态硫酸钙反应体系进行了热模拟实验研究。使用气相色谱仪、微库仑仪、傅里叶变换红外光谱仪和X射线衍射仪对产物进行了分析，探讨了硫酸盐热化学还原反应的热力学特征，并进行了反应动力学研究。结果表明，高温下天然气与固态硫酸钙可以发生反应，产物主要为硫化氢、二氧化碳、碳酸钙、水和炭。热力学研究表明，天然气与固态硫酸钙的反应可行，升高温度对反应有利，同一温度下长链烷烃与固态硫酸钙发生反应的可能性要比短链烷烃大。根据动力学模型得到反应活化能为96.824kJ/mol。     

Effect of natural gas usage on indoor radon levels

Effect of natural gas usage on indoor radon concentrations were investigated in dwellings in four counties of ?zmir municipality using LR-115 Type II cellulose nitrate films. The dwellings were separated two groups: natural gas user and non-user. Indoor radon levels were found higher in natural gas using dwellings. Also, indoor radon levels were evaluated in terms of concentrations and annual effective dose. Indoor radon concentrations were found between 22.8 and 707.8 Bq m^?3 and highest concentrations were determined in kitchen in third floor of Bornova dwellings. Indoor radon concentrations in kitchens were found higher than the living rooms. On the other hand, opposite results obtained for annual effective dose, because of very short occupancy period of the kitchens.     

Adsorption of natural gas and its whole components on adsorbents

Adsorption of each component of natural gas on adsorbent prepared from petroleum coke was studied. At 25 °C and 3.5 MPa, adsorption capacity of the components of natural gas are as follows: C₃H₈, H₂S(0.980) > CO₂(0.691) > C₂H₆(0.160) > CH₄(0.136) > N₂(0.096) (g/g). For natural gas, adsorption capacity is 145.2 (mL/mL) and delivery capacity is 105.7 (mL/mL). One equation between adsorption capacity and boiling point of adsorbed gas was firstly generalized. The adsorption capacity of different component like O₂, N₂, CH₄, C₂H₆, CO₂, H₂S on adsorbents were predicted using the equation. The results fit well with the experimental data. The equation has significance in predicting the adsorption capacity for any component of natural gas. Charge-discharge tests were conducted 10 times, the result indicates that natural gas has significantly worse reversibility in adsorption and desorption in the adsorbent than that of CH₄. The contents of the components after 10 charge-discharge show that the adsorption capacity drop of natural gas is due to the irreversible adsorption of heavy or polar components like C₃H₈, H₂S.     

Bifurcation analysis on a reactor model with combination of quadratic and cubic steps

In this paper we give a rigorous bifurcation analysis for a reactor model with combination of quadratic and cubic steps. We extend the analysis of Satnoianu et al. in two directions. First, we impose Dirichlet boundary conditions instead of the semi-infinite domain in one space dimension. Second, we consider a variety of different bifurcation phenomena of the corresponding steady state system, focusing on their parametric sensitivity. We show that the system exhibits subcritical pitchfork bifurcation, supercritical pitchfork bifurcation and transcritical bifurcation in the different regimes of control parameters. To compare the decades old work by Auchmuty et al., we show that the spatial structures formed by the parameter p ∈ [0, 1] are richer than those formed by the purely quadratic step for p = 0 and the purely cubic step for p = 1 respectively.     

点电荷模型分析结构

用穆斯堡尔核电四极分裂的点电荷模型计算了四极裂距,计算与实测结果符合良好,利用点电荷模型可以迅速有效地对具有一定对称的穆斯堡尔原子的大量化合物的结构和化学键性质作半经验分析。本文汇总了二十八种结构形式的点电荷模型表达式,计算了一些铁、锡化合物的四极裂距,并分析其异构体、配位数、构型和构型畸变。     

Energy resolved X-ray fluorescence imaging based on a micropattern gas detector

A simple system for energy resolved X-ray fluorescence imaging using a room temperature, 2-D sensitive Micro-Hole and Strip Plate (MHSP) operating in pure xenon is proposed. The Micro-Hole and Strip Plate is an electron multiplier with two stages of avalanche production, one of them in the holes and another one in the anode strips. The X-ray interaction via photoelectron absorption in the xenon produces a number of electrons proportional to the incoming X-ray energy. The electron cloud is, then, amplified in the two amplification stages, resulting in a charge pulse that is also proportional to the detected X-ray energy. The 2-D capability is achieved in the Micro-Hole and Strip Plate by using two orthogonal resistive lines, one connecting the anode strips on the bottom face of the Micro-Hole and Strip Plate and the other one connecting the strips structured on the Micro-Hole and Strip Plate top surface. This low cost detector has an active area of 28 × 28 mm², an intrinsic position resolution of σ∼ 125 µm, an energy resolution of about 825 eV (Full Width at Half Maximum) at 5.9 keV and a count rate capability as high as 0.5 MHz. Fluorescence images were obtained by irradiating the sample with X-rays and using a pinhole placed between the sample and the detector window. Elemental map discrimination for different samples, image amplification and detector parameters, are presented.     

High-speed narrow-bore capillary gas chromatography in combination with a fast double-focusing mass spectrometer

In this work the application of high-speed narrow-bore capillary GC in combination with a fast scanning double focusing magnetic sector mass spectrometer is evaluated. Special emphasis is placed upon detection limits and scan speed in the full scan mode and in the selected ion monitoring mode (SIM). In the full scan mode, up to 20 scans per second could be obtained. The detection limits are in the low picogram range in the full scan mode and improve even to 5 to 50 fg in the SIM mode, depending on the sample complexity and mass resolving power. It will be illustrated that by increasing the resolution in the SIM mode, interferences from ions of the same nominal mass-to-charge ratio as the ions of interest are significantly reduced. Chemical background noise can therefore be largely eliminated, thus enhancing the signal-to-noise ratio.