Hydrocarbon Gas Mixtures Research Articles

Application of IAST in the Prediction of Multicomponent Adsorption Equilibrium of Gases in Heterogeneous Solids: Micropore Size Distribution versus Energy Distribution

This article investigates the effect of surface heterogeneity and energy-matching scheme on the prediction of adsorption equilibria on activated carbon. The ideal adsorbed solution theory (IAST) is employed to evaluate the local adsorption equilibria on each energy site while the energetic heterogeneity of the system is represented by two forms: (1) uniform energy distribution, which employs the cumulative energy scheme to match different adsorbates in the adsorbed phase; and (2) micropore size distribution, which invokes the adsorbate-pore interaction matching scheme. The adsorption equilibria of hydrocarbon gas mixtures measured on two commercial activated carbons are used to compare the two models. It is found that uniform energy distribution can be insufficient in the prediction of multicomponent adsorption equilibria. On the other hand, the model assuming micropore size distribution as adsorption energetic heterogeneity and the adsorbate-pore interaction energy-matching scheme presents relatively stable prediction results.

Multicomponent adsorption, desorption and displacement kinetics of hydrocarbons on activated carbon — dual diffusion and finite kinetics model

The adsorption kinetics of binary hydrocarbon gas mixtures onto activated carbon (AC) were studied by the heterogeneous finite kinetics (FK) model [D.D. Do, K. Wang, AIChE J. 44 (1998) 68], which assumes three mass transfer mechanisms coexisting inside AC. The bulk phase diffusion is described by the Maxwell-Stefan equation and the driving force for surface diffusion is the chemical potential gradient. The distribution of the slit-shaped micropores (MPSD) is taken as the source of surface heterogeneity, which affects the adsorption equilibria as well as kinetics via the dispersive interaction between adsorbate molecules and carbon surface. An adsorbate-pore interaction mechanism is employed to describe the matching energies between different species in the adsorbed phase in equilibria as well as kinetics processes. The adsorption, desorption and displacement kinetics of hydrocarbon gas mixtures onto a commercial activated carbon were measured on a differential adsorber bed (DAB) rig for adsorbent pellets with different sizes, geometries, and under various operating conditions. These experimental results were employed to examine the predictive capability of the model. It is demonstrated that, with the structural, equilibria and kinetics of parameters obtained from the related pure component systems, the model predictions for adsorption kinetics of multicomponent systems generally show good agreement with experimental data, except for desorption kinetics on small cylindrical pellets where some deviations have been observed. (C) 1999 Elsevier Science B.V. All rights reserved.

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.

Solubility of light hydrocarbons and their mixtures in pure water under high pressure

New solubility data of methane, ethane, n-butane and their mixtures in pure water are obtained at 344.25 K, from 2.5 to 100 MPa. The results agree well with those of the literature in the case of pure hydrocarbons in water, but differ significantly for hydrocarbon mixtures. In contrast to the conclusion reached by Amirijafari and Campbell [B. Amirijafari, J. Campbell, Solubility of gaseous hydrocarbon mixtures in water, Soc. Pet. Eng. J. (1972) 21–27.], the experimental solubility data of methane–ethane mixtures shows an ideal solution behavior, while the solubility data of methane– n-butane mixtures shows a weaker non-ideality than that observed by McKetta and Katz [J.J. McKetta, D.L. Katz, Methane– n-butane–water system in two-and three-phase regions, Ind. Eng. Chem. 40 (1948) 853–863]. The pure hydrocarbon solubility data are satisfactorily correlated using the Soreide and Whitson modification [I. Soreide, C.H. Whitson, Peng–Robinson predictions for hydrocarbons, CO2, N2, and H2S with pure water and NaCl brine, Fluid Phase Equilib. 77 (1992) 217–240] of the Peng–Robinson equation of state.

The Role of N 2 in Aspect‐Ratio‐Dependent Etching of SiO2

We report mechanistic study of the role of nitrogen in reducing aspect‐ratio‐dependent etching when added to a mixture of hydrocarbon and fluorocarbon gases in a magnetically enhanced reactive ion etcher. Through examination of ion and neutral transport phenomenon, reactant transport issues, and surface charging, the source of aspect‐ratio‐dependent etching was identified for the etch chemistry processes investigated. The total flow of was held constant at 30 sccm. Polymerization was found to be the primary source of aspect‐ratio‐dependent etching. The addition of nitrogen is investigated with respect to its impact on etch and deposition rates.

Hydrate-free zone for synthetic and real reservoir fluids in the presence of saline water

The application of extended-reach subsea gathering networks and transportation of unprocessed wellstreams are serious considerations for reducing field development costs. These lines will convey a mixture of gaseous and/or liquid hydrocarbons, condensed or saline water. A good knowledge of the hydrate phase boundary for the above systems is essential in the confident and economical design and operation of associated fields, pipelines and processing facilities. In this paper, experimental data for the hydrate-free zone of several pure and multicomponent systems in the presence of single and mixed electrolyte solutions are presented. The paper, which is a continuation of three previous communications, presents data on C 2, C 3, CO 2, two synthetic multicomponent gas mixtures, and a black oil sample. The comparison of results with recent literature data shows some discrepancy at high salt concentrations, where a possible source of error is identified. An in-house numerical model has been used for predicting the experimental data with good results.

Plasma‐Enhanced Chemical Vapor Deposition of Fluorocarbon Films with High Thermal Resistance and Low Dielectric Constants

Fluorocarbon films with low dielectric constants and high thermal resistance have been developed by plasma‐enhanced chemical vapor deposition (PECVD) using gas mixtures of fluorocarbons (e.g., ), hydrocarbons (e.g., ), and/or hydrogen. A conventional parallel plate electrode PECVD system was used as the reactor. We report dielectric constants lower than 2.4 with these fluorinated films. The thermal decomposition temperature was higher than 400°C and the glass transition temperature (Tg) was also higher than 450°C. This enables the use of organic films with very low dielectric constant in actual devices.

Boundaries of the diamond domain in the C - H - O diagram of carbon film deposition

Chemical vapour deposition experiments using gas mixtures of hydrocarbons with carbon dioxide can produce films of either diamond or a graphitic, amorphous form of carbon. The boundaries of the diamond growth domain in the triangular C - H - O gas composition diagram appear to be straight lines. It is shown that this is consistent with a simple model of the competition between the deposition of diamond and amorphous carbon phases. Gas phase carbonaceous fragments can attach to the surface of a growing film. Hydrogen in the gas phase etches poorly bound carbonaceous material from the surface, and also assists the incorporation of carbon into the diamond lattice. Oxygen in the gas phase forms carbon monoxide, and oxygen-bearing species also etch carbonaceous material. With these simple ingredients a rate equation approach is developed which also predicts the rate of diamond growth within the diamond domain, and indicates that oxygen can improve the efficiency of the process.

Reacting flow simulation for a large-scale ram accelerator

Computational fluid dynamics solutions of the full Navier-Stokes equations have been used to numerically simulate the reacting in-bore flowfield for the ram accelerator projectile propulsion system. In this system a projectile and obturator are injected at supersonic velocity into a stationary tube filled with a pressurized mixture of hydrocarbon, oxidizer, and inert gases. Flow stagnation on the obturator initiates combustion of the mixture, before it is discarded. A system of shock waves on the projectile, in conjunction with viscous heating, sustains combustion. The resulting energy release, which travels with the projectile, also generates high pressures that impart thrust to the projectile. Numerical simulation utilizing finite rate chemical kinetics have been used to investigate this flowfield. Numerical results are used to visualize the flowfield, predict the effects of variation in system parameters, and predict projectile in-bore velocity.

Role of Three-Hydrocarbon-Phase Flow in a Gas-Displacement Process

Summary The objective of this work is to identify the role of three-hydrocarbon-phase flow in the displacement of a reservoir oil by light-hydrocarbon-gas mixtures (methane through n-butane). Slim-tube displacements were conducted with several hydrocarbon-gas mixtures. A compositional simulator capable of handling three nonaqueous phases was used to simulate these 1D displacements. Slim-tube experiments show that as dilution with lean gas increases, the displacements go from first-contact miscible to multicontact miscible to three-phase, 3ϕ, immiscible to two-phase, 2ϕ, immiscible. Recovery is high (> 85%) at high enrichment, but nonmonotonic with dilution. Simulation results mimic experimental slim-tube recovery and gas-breakthrough behavior qualitatively; especially the increase in oil recovery with increasing methane dilution of the solvent. High oil recoveries in the 3ϕ cases appear to be the result of condensation of solvent into the oil, resulting in (1) low oil viscosity and (2) effective displacement of oil by the second liquid phase that forms.

FT-IR in the Quantitative Analysis of Gaseous Hydrocarbon Mixtures

An FT-IR spectrometer provided with software for multi component analysis of FR spectra was used for simultaneous determination of up to 12 hydrocarbons in a gaseous mixture. The hydrocarbons, ranging from methane to n-butane, were selected to simulate reaction product mixtures obtained in the dehydrogenation of n-butane. The concentrations of the hydrocarbons in the sample were determined by fitting to the sample spectrum a set of pure calibration spectra of the gases present in the sample. In principle, the entire wavenumber range of the low-resolution IR spectrum could be utilized in the fit. The reliability of the results was checked from the residual spectrum, obtained by subtracting the fitted from the measured spectrum. The residual spetrum will be pure noise when the set of calibration spectra chosen for the analysis fits exactly with the sample spectrum. Precision of the results, expressed as average relative standard deviation, was ±4%. Concentrations of most of the hydrocarbons were determined with an error less than ±10%. The concentrations of isobutane, trans-2-butene, propane, and ethane deviated by more than 10% from the reference concentrations. The sum concentration of ethane and propane, however, deviated less than ±1% from the reference. Difficulties in determining ethane and propane accurately were due to the broad nature and small number of peaks in their IR spectra. IR spectrometry with multicomponent analysis of spectra provides a rapid and powerful method with potential for the study of catalytic reactions at a time resolution of seconds

95/01793 Treatment of gaseous hydrocarbons, hydrocarbon mixtures, hydrogen, and hydrogen compounds in tubes of a tube furnace

95/01793 Treatment of gaseous hydrocarbons, hydrocarbon mixtures, hydrogen, and hydrogen compounds in tubes of a tube furnace

Uniaxial magnetic FeC thin films sputtered onto polymer substrates

Thin films of FeC were deposited onto a polymer substrate by reactive DC magnetron sputtering, using an argon and hydrocarbon gas mixture. The polymer web is wound by a roll coater, and an individual thin film with a constant thickness is piled up by increasing a number of passes UP to a desired thickness. Uniaxial films with Hk=4000 A/m and low dispersion were obtained. The coercive force was a function of thickness; it was Hc=8 A/m for films 0.8 /spl mu/m thick. The easy axis of the uniaxial anisotropy was along the direction transverse to the rolling direction of the polymer web. The origin of the uniaxial anisotropy is the anisotropic thermal shrinkage of the polymer web is discussed by a model.

Solid lubrication by decomposition of carbon monoxide and other gases

Extended duration high temperature (above 500°C) lubrication of silicon nitride sliding and rolling contacts was accomplished by solid carbon deposited and replenished via the decomposition of carbonaceous gas streams directed towards the tribological surfaces. Injection of carbon monoxide-hydrogen mixtures can lead to reductions in high temperature friction and wear of silicon nitride sliding contacts by factors of up to 10 × and 500 × respectively from the unlubricated case. Similar lubrication is attained by various hydrocarbon gas mixtures, while only a ten-fold reduction in wear is attained by a carbon dioxide-hydrogen mixture. Effective lubrication can be modeled as a favorable balance between carbon deposition from the gas phase and removal by wear. This model is based on the dependencies of solid lubricant deposition and removal processes on temperature, sliding speed, normal load, decomposition activation energy, gas flow rate, and tribosystem properties. The model is checked by the mapping of regions where measured friction indicates that lubrication by CO-H 2 mixtures is adequate, and the identification of a boundary representing the onset of marginally effective lubrication.

Recombination in nitrogen afterglow at low temperatures

A flowing post-discharge of N2 and N2-CH4 gas mixtures has been used to produce nitrogen and carbon atoms. New technique for qualitative and quantitative measurement of various gas phase hydrocarbon species in a flow and the apparatus for its implementation are described. The method is based on C+N chemiluminiscent reactions in flowing post-discharge of N2+hydrocarbon gas mixtures at low temperature (77 K). Detection of hydrocarbon species has been demonstrated from concentrations greater than 1010 molecules.cm−3.

Material properties and tribological performance of hydrogenated sputter carbon overcoat on rigid disk

The structure and material properties of hydrogenated carbon films were studied and related to their tribological performance. Hydrogenated carbon films containing a range of 15–50 at. % of hydrogen were fabricated by magnetron sputtering using a mixture of argon and hydrocarbon gases. Raman spectroscopy was used for determining the structure of the H–C films. For physical property of H–C films, resistance of the film was measured. Nanohardness and elastic modulus of thin H–C films were also studied by measuring the load and displacement curve. The nanohardness and elastic modulus of H–C films were found to be very close to those of diamondlike carbon films fabricated by chemical vapor deposition. The stresses of H–C films were obtained by measuring the substrate curvature before and after deposition. Thermal expansion coefficients of the H–C films were obtained by measuring the change of stress of H–C film deposited on two known substrates as a function of temperature. The accelerated drag and contact start stop tests of H–C films were performed in various gas environments and it was found that the best tribological performance was obtained from the H–C overcoat with the highest hydrogen concentration.

Diamond deposition in a permanent magnet microwave electron cyclotron resonance discharge

Diamond deposition has been investigated in a magnetoactive microwave discharge, in which a collisionally damped electron cyclotron resonance (ECR) is established by a Nd–Fe–B permanent magnet structure. Diamond crystals exhibiting a well defined 1333 cm−1 diamond Raman peak and a faceted crystal structure can be grown in hydrocarbon gas mixtures at total pressures 2.0–20 Torr, backside substrate temperatures 550–650 °C, and input microwave power levels 400–1000 W. The main effect of the magnetic field is to increase gas dissociation; optical emission spectroscopic measurements show much higher neutral radical line intensities compared to operation with no magnetic field.

Properties of sputter-deposited hydrogenated carbon films as a tribological overcoat used in rigid magnetic disks

The physical and mechanical properties of hydrogenated carbon (H-C) films used in rigid magnetic disks were studied using various techniques. The H-C films were fabricated on 65 mm Al/NiP substrates using d.c. magnetron sputtering and a mixture of argon and hydrocarbon gases. The hydrogen concentration in the H-C layer, which was analyzed by hydrogen forward scattering, ranges from 4 to 28 at. %. The structure of the H-C films was studied by Raman spectroscopy. Raman analysis indicates that the H-C films with a higher hydrogen concentration show a down-shift of the G-band peak and a decrease in the ratio of the integrated intensity of the D band to that of the G band. From the measurement of electrical resistance, it was found that an increased hydrogen concentration in the H-C films increases the electrical resistance of the film. For the mechanical properties of the H-C films, the nanohardness and elastic modulus of H-C films 350thick were measured. The nanohardness and elastic modulus of thin H-C films obtained from the load and displacement curves were found to be strongly affected by the hydrogen concentration in the films. These physical and mechanical properties of H-C films deposited by sputtering are compared with those of thin films obtained by plasma-enhanced chemical vapor deposition techniques. These physical and mechanical properties of H-C films obtained from the sputtering process could provide excellent wear resistance in magnetic disk applications.

Natural Gas Liquids Supply And Demand Balances In Alberta

Abstract Natural gas consists primarily of mixtures of hydrocarbon gases, predominantly methane, along with smaller amounts of natural gas liquids and non-hydrocarbons. This paper provides descriptively and quantitatively a framework for evaluating and balancing the potential sources of natural gas liquids supply and demand in the province of Alberta for the period 1988 to 2000. Introduction Natural gas consists primarily of mixtures of hydrocarbon gases, predominantly methane, along with smaller amounts of ethane, propane, butanes and pentanes plus which are called natural gas liquids (NGLs), and non-hydrocarbons such as nitrogen, oxygen, water, carbon dioxide, hydrogen sulphide, and mercaptans. Ethane is a part of natural gas which can be separated out (through application of high pressure and temperatures) at gas plants. Ethane is an important petrochemical feedstock for the production of ethylene. It is also used as a miscible agent for enhanced oil recovery. Propane and butanes are by-products of natural gas and crude oil feed to distilling, which are obtained from gas plants and refineries. Propane is used primarily as a fuel and as miscible flood for enhanced oil recovery. However, in contrast to propane, butanes are used primarily as feedstock in refineries and petrochemical plants. They are seldom used in miscible floods except when entrained in NGL mixes. Pentanes plus is a by-product of natural gas which is obtained from gas plants as well as condensate from crude oil. Pentanes plus is used as a refinery feedstock and as a diluents in reducing viscosity of bitumen and conventional heavy crude oil to allow conventional pipelining. The purpose of this paper is to describe and project supply and demand for NGLs in the province of Alberta for the period 1988 to 2000. The Gas Energy Management Model (GEMM) and Energy Requirements Model of Alberta (ERMA) are used for the projections of supply and demand for NGLs, respectively. The major assumptions used for both models are adopted from the high case of "Energy Requirements in Alberta, ERCB Report 89-A ". The high case is an optimistic pricing scenario from an upper bound forecast that assumed the plant gate price of natural gas (in 1988 constant dollars) would increase to $4.36 per GJ by the year 2000 from the 1988 level of $1.57 per GJ. Because the projections of NGLs are shown in petajoules, the approximate volume equivalent of one petajoule for each liquid is as follows: List of NGLs are shown in petajoules (Available In Full Paper) In the first section of this paper, three sources of NGL supply are described. In the second section, uses of NGLs within Alberta are identified. In the third section, the projection of supply and demand for NGLs along with the major input assumptions are described. In the last section, NGL supply and demand balances are presented. Alberta Sources of Natural Gas Liquids In Alberta, the supply sources of gas co-products (NGL and sulphur) are gas processing and reprocessing plants* and crude oil refineries. The main products of gas processing plants are propane, butanes and pentanes plus.

Selective Reactive Ion Etching of Indium‐Tin Oxide in a Hydrocarbon Gas Mixture

A new method for the reactive ion etching of a transparent conducting indium‐tin oxide (ITO) film has been investigated. With a gas mixture consisting of acetone, argon, and oxygen, high etch rate selectivities of ITO to a number of underlying materials were achieved. A useful variation on the etch process employs hydrogen chloride in a first etch step followed by the acetone‐based etch. Acetone is a source of reactive organic radicals in the plasma discharge that etch ITO films by forming volatile organometallic compounds. Selective chemical vapor deposition of carbon films on surfaces that do not etch can occur using this chemistry, but with sufficient oxygen in the plasma this is eliminated. An analysis of the plasma etch chemistry based on plasma emission spectroscopy is also presented.