Decomposition of ethoxyethane in the cold plasma environment

A radio frequency (RF) plasma system was used to decompose the ethoxyethane (EOE) contained gas. The reactants and final products were analyzed by using an FTIR (Fourier Transform Infrared) spectrometer. The effects of plasma operational parameters, including input power wattage (W), equivalence ratios (Φ), feeding concentration (C) of EOE and total gas flow rate (Q) for EOE decomposition were evaluated. In addition, the possible reaction pathways for EOE decomposition and the formation of final products were built up and are discussed in this paper. The mole fraction profiles of C₂H₅OC₂H₅, CH₃CHO, CH₄, C₂H₆, C₂H₄, C₂H₂, CO₂ and CO were detected and are also presented in this paper. At lower input power wattages, the creation of glow discharge is strongly dependent on the plasma production index ( PPI ). When input power wattages are smaller than 30 W, the minimum values of PPI to create glow discharge ranged between 18.2 and 19.0. The results of this study revealed that, in the RF plasma reactor, the decomposition fraction of EOE could reach 100% under most operational conditions. © 2000 Society of Chemical Industry     

Experimental data vs. 3-D model calculations of HFCVD processes: correlations and discrepancies

An existing 3-D model [Mankelevich et al. Diamond Relat. Mater. 7 (1998) 1133] has been used to explain experimentally measured spatially resolved CH₃ radical number densities in hot filament CVD reactors operating with both CH₄/H₂ and C₂H₂/H₂ process gas mixtures and to examine in detail the process of C₂↔C₁ inter-conversion in the gas phase. It has been shown that cooler regions distant from the filament need to be modelled in order to obtain the significant C₂→C₁ conversion observed in HFCVD reactors with C₂H₂/H₂ process gas mixtures. The origin and effect of the non-equilibrated H₂ molecule vibrational state population distribution are studied for the first time in the context of HFCVD reactor models.     

The effect of synthesis gas composition on the Fischer–Tropsch synthesis over Co/γ-Al2O3 and Co–Re/γ-Al2O3 catalysts

The Fischer–Tropsch synthesis over Co/γ-Al₂O₃ and Co–Re/γ-Al₂O₃ was investigated in a fixed-bed reactor at 20 bar and 483 K using feed gases with molar H₂/CO ratios of 2.1, 1.5 and 1.0 simulating synthesis gas derived from biomass. With lower H₂/CO ratios in the feed, the CO conversion and the CH₄ selectivity decreased, while the C₅₊ selectivity and olefin/paraffin ratio for C₂–C₄ increased slightly. The water–gas shift activity was low for both catalysts, resulting in high molar usage ratios of H₂/CO (close to 2.0), even at the lower inlet ratios (i.e. 1.5 and 1.0). For both catalysts, the drop in the production rate of hydrocarbons when shifting from an inlet ratio of 2.1 to 1.5 was significant mainly because the H₂/CO usage ratio did not follow the change in the inlet ratio. The hydrocarbon selectivities were rather similar for inlet H₂/CO ratios of 2.1 and 1.5, while significantly deviating from those for an inlet ratio of 1.0. With the studied catalysts, it is possible to utilize the advantages of an inlet ratio of 1.0 (higher selectivity to C₅₊, lower selectivity to CH₄, no water–gas shifting of the bio-syngas needed prior to the FT reactor) if a low syngas conversion is accepted.     

Experimental study of the structure of laminar premixed flames of ethanol/methane/oxygen/argon

The structures of three laminar premixed stoichiometric flames at low pressure (6.7 kPa): a pure methane flame, a pure ethanol flame, and a methane flame doped by 30% of ethanol, have been investigated and compared. The results consist of mole fraction profiles of CH₄, C₂H₅OH, O₂, Ar, CO, CO₂, H₂O, H₂, C₂H₆, C₂H₄, C₂H₂, C₃H₈, C₃H₆, CH₃-C CH (propyne), CH₂ C CH₂ (allene), CH₂O, and CH₃HCO, measured as a function of the height above the burner by probe sampling followed by on-line gas chromatography analyses. Flame temperature profiles have been also obtained by using a PtRh thermocouple. The similarities and differences between the three flames have been analyzed. The results show that, in these three flames, the mole fraction of the intermediates with two carbon atoms is much larger than that of the species with three carbon atoms. In general, the mole fraction of all intermediate species in the pure ethanol flame is the largest, followed by the doped flame, and finally the pure methane flame.     

Investigations on gas-phase reactions of ethane under SOFC conditions: An experimental and modeling study

Experiments using a model gas mixture which is chosen to represent hydrocarbon fuel from hydrothermal gasification of biomass were carried out under gas-phase conditions similar to those expected in the anode channel of a solid-oxide fuel cell (SOFC). Ethane conversion and product formation were evaluated from the measurements at various temperatures ranging from 610 °C to 860 °C and at a total pressure of 1.2 bar. The employed reactor was simulated using a plug-flow model coupled to a detailed gas-phase reaction mechanism. The measured temperature profile along the reactor was imported in the calculation routine. A satisfying agreement in both ethane conversion and product composition was reached between the model predictions and the experimental data. In order to determine which reactions were responsible for much of the observed kinetics a sensitivity analysis based on the rate of production (ROP) principle was performed. The results from the sensitivity analysis show that there are only six elementary reactions whose rates significantly affect the consumption or formation of the four species of interest, i.e. H₂, CH₄, C₂H₄ and C₂H₆.     

Preparation and C3H8/Gas Separation Properties of a Synthesized Single Layer PDMS Membrane

In this paper, a new polydimethylsiloxane (PDMS) membrane was synthesized and its ability for separation of heavier gases from lighter ones was examined. Sorption, diffusion, and permeation of H₂, N₂, O₂, CH₄, CO_2, and C₃H₈ in the synthesized membrane were investigated as a function of pressure at 35°C. PDMS was confirmed to be more permeable to more condensable gases such as C₃H₈. This result was attributed to very high solubility of larger gas molecules in hydrocarbon?based PDMS in spite of their low diffusion coefficients relative to small molecules. The synthesized membrane showed much better gas permeation performance than others reported in the literature. Increasing upstream pressure increased solubility, permeability and diffusion coefficients of C₃H₈, while these values decreased slightly or stayed constant for other gases. Local effective diffusion coefficient of C₃H₈ and CO₂ increased with increasing penetrant concentration which indicated plasticization effect of these gases over the range of penetrant concentration studied. C₃H₈/gas solubility, diffusivity and overall selectivities also increased with increasing feed pressure. Ideal selectivity values of 4, 13, 18, 20, and 36 for C₃H₈ over CO₂, CH₄, H₂, O_2, and N₂, respectively, at upstream pressure of 7 atm, confirmed the outstanding separation performance of the synthesized mebrane.     

Pyrolysis of tire powder: influence of operation variables on the composition and yields of gaseous product

The pyrolysis of tire powder was studied experimentally using a specially designed pyrolyzer with high heating rates. The composition and yield of the derived gases and distribution of the pyrolyzed product were determined at temperatures between 500 and 1000 °C under different gas phase residence times. It is found that the gas yield goes up while the char and tar yield decrease with increasing temperature. The gaseous product mainly consists of H₂, CO, CO₂, H₂S and hydrocarbons such as CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, C₄H₈ and C₄H₆ with a little other hydrocarbon gases. Its heating value is in the range of 20 to 37 MJ/Nm³. Maximum heating value is achieved at a temperature between 700 and 800 °C. The product distribution ratio of gas, tar and char is about 21:44:35 at 800 °C. The gas yield increases with increasing gas residence time when temperature of the residence zone is higher than 700 °C. The gas heating value shows the opposite trend when the temperature is higher than 800 °C. Calcined dolomite and limestone were used to explore their effect on pyrolyzed product distribution and composition of the gaseous product. It is found that both of them affect the product distribution, but the effect on tar cracking is not obvious when the temperature is lower than 900 °C. It is also found that H₂S can be absorbed effectively by using either of them. About 57% sulfur is retained in the char and 6% in the gas phase. The results indicated that high-energy recovery could not be achieved if fuel gas is the only target product. In view of this, multi-use of the pyrolyzed product is highly recommended.     

Effect of water on the solubilities and mass transfer coefficients of gases in a heavy fraction of fischer-tropsch products

The effects of water on the solubilities, C^*, and volumetric mass transfer coefficients, k_La, for CO, H₂, CH₄ and CO₂ in a heavy fraction of Fischer-Tropsch liquid were examined at elevated pressures and temperatures at different mixing power inputs. For these gases, higher solubilities were measured in the hydrocarbon mixture saturated with water than those obtained in the hydrocarbon free of water. The k_La values for the four gases were slightly affected by the presence of dissolved water in the hydrocarbon mixture; and they were strongly dependent on the power input per unit liquid volume. Two empirical correlations for k_La as a function of turbine speed and pressure are proposed.     

Oxidative coupling of methane. The effect of alkali chlorides on molybdate based catalyst leading to high selectivity in C3-product formation

LiCl-Na₂MoO₄ was found to be an active catalyst for oxidative coupling of methane at temperatures around 620 °C. In these systems, the selectivity for the formation of C₃-products exceeds the selectivity for the formation of C₂-products. While the homogeneous reaction of CH₄ and O₂ leads to C₃H₆ as C₃-product, the 50% LiCl-50% Na₂MoO₄ catalyst leads to C₃H₈ as the predominant C₃-product, indicating that in the latter case the reaction cannot be purely homogeneous. The dependency of the product distribution on temperature, gas composition, reactor dimensions, flow rate, CH₄/O₂ ratio and type of catalyst has been studied. The reaction was studied by co-feeding CH₄, O₂ and a diluent gas at atmospheric pressure continuously in a conventional flow reactor containing the catalyst. The reaction products observed were: C₂H₄, C₂H₆, C₃H₆, C₃H₈, H₂O and CO + CO₂. The two latter gases were the main oxidation products observed. Characterization of the catalysts used was carried out by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD).     

Pressure dependence of gas permeability in a rubbery polymer

The effect of pressure on gas permeability of a rubbery polymer, 1,2-polybutadiene, is investigated for 15 gases with various molecular sizes and solubilities in the ranges of pressure up to 110 atm at 25°C. The permeability for slightly soluble gases (He, Ne, H₂, N₂, O₂, and Ar) decreases with increasing pressure, and that for soluble gases (CH₄, Kr, CO₂, N₂O, C₂H₄, Xe, C₂H₆, C₃H₆, and C₃H₈) increases with increasing pressure. Logarithms of permeability coefficient versus feed-gas pressure for the slightly soluble gases, CH₄ and Kr, is linear within each pressure range, whereas such plots become convex toward the pressure axis for more soluble gases, such as CO₂, N₂O, C₂H₄, Xe, C₂H₆, C₃H₆, and C₃H₈. By analyzing the pressure dependence of permeability using sorption data of the gases, contributions of concentration and hydrostatic pressure to the gas diffusivity are estimated. © 1996 John Wiley & Sons, Inc.     

Properties of cold lake bitumen saturated with pure gases and gas mixtures

This paper presents new data for the viscosity, density and gas solubility of Cold Lake bitumen saturated with light gases and gas mixtures over a temperature range of 15 to 103°C at up to 10 MPa pressure. Specifically, the gases whose effects on the bitumen properties were measured are N₂, CH₄, CO₂ and C₂H₆, and two mixtures of CO₂ and CH₄. With CO₂ and C₂H₆, experiments were also performed in the liquid-liquid region, and the results of these experiments generally agree with the previously published predictions. The viscosity of the gas-free Cold Lake bitumen is comparable to that of a Marguerite Lake bitumen that was tested previously. Due to the large solubilities of C0₂ and C₂H₆, the reduction in gas-saturated bitumen viscosity is quite dramatic. The density of the gas-saturated bitumen decreases with increased amounts of the dissolved CH₄ and C₂H₆ gases, but no such trends are evident for the N₂ and CO₂ gases. The results of the experiments with two binary gas mixtures (i.e., CO₂ and CH₄) indicate that the bitumen properties are affected largely by the major gas constituent.     

A THERMODYNAMIC EQUILIBRIUM ANALYSIS OF GLUCOSE CONVERSION TO HYDROCARBONS

Deoxygenation, or removal of oxygen from oxygenates, is an important element in the hydrocarbon fuel production process from biorenewable substrates. A thermodynamic equilibrium analysis gives valuable insights on the theoretical limits of desired products when a substrate is reacted under a given set of conditions. Here we report the equilibrium composition of glucose-to-hydrocarbon system by minimizing the total Gibbs energy of the system. The system was treated as a mixture of 11 components comprised of C₆H₆, C₇H₈, C₈H₁₀ (ethyl benzene), C₈H₁₀ (xylenes), C₆H₅ –OH, CH₄, H₂O, C, CO₂, CO, and H₂. Equilibrium compositions of each species were analyzed between temperatures 300 and 1500 K and pressures 0–15 atm. It was observed that at high temperature, CO and H₂ dominate the equilibrium mixture with mole fractions of 0.597 and 0.587 respectively. At low temperatures the equilibrium mixture is dominated by CH₄, CO₂, H₂O, and carbon. The aromatic hydrocarbon composition observed at thermodynamic equilibrium was extremely small.     

Four-lump kinetic model for fluid catalytic cracking process

In the fluid catalytic cracking reactor heavy gas oil is cracked into more valuable lighter hydrocarbon products. The reactor input is a mixture of hydrocarbons which makes the reaction kinetics very complicated due to the involved reactions. In this paper, a four-lump model is proposed to describe the process. This model is different from others mainly in that the deposition rate of coke on catalyst can be predicted from gas oil conversion and isolated from the C₁–C₄ gas yield. This is important since coke supplies heat required for endothermic reactions occurring in the reactor. By this model we can also conclude that the C1–C4 gas yield increases with increasing reactor temperature, while production of gasoline and coke decreases.     

Comparative investigations of coal pyrolysis under inert gas and H2 at low and high heating rates and pressures up to 10 MPa

Five German hard coals of 6–36 wt% volatile matter yield (maf) were pyrolysed at pressures up to 10 MPa, using two different apparatuses, which mainly differ in the heating rates. One consists of a thermobalance where a coal sample of ≈ 1.5 g is heated at a rate of 3 K min ^?1 under a gas flow of 3 I min^?1. The other apparatus is constructed for rapid heating (10²?10³ K s^?1) of a small sample of ≈10 mg of finely-ground coal distributed as a layer between the folded halfs of a stainless-steel screen, heated by an electric current. The product gas composition was determined by quantitatively analysing for H₂, CH₄, C₂H₄, C₂H₆, CO, CO₂ and H₂O. The amounts of tar and char were measured by weighing. The heating rate, pressure and gas atmosphere were varied. Under an inert gas atmosphere, high heating rates result in slightly higher yields of liquid products, e.g. tar. The yields of light hydrocarbon gases remain the same. With increasing pressure, the thermal cracking of tar is intensified resulting in high yields of char and light hydrocarbon gases. Under H₂, pyrolysis is influenced strongly at elevated pressure. Additional amounts of highly aromatic products are released by hydrogenation of the coal itself, particularly between 500 and 700°C. This reaction is less effective at higher heating rates because of the shorter residence time and diffusion problems of H₂. The yield of light gaseous compounds CH₄ and C₂H₆ increases markedly under either heating condition owing to gasification of the reactive char.     

Experimental and modeling study of a lean premixed iso-butene/hydrogen/oxygen/argon flame

The experimental structure of a lean iso-butene/hydrogen/oxygen/argon flame (2.7% iC₄H₈, 4.5% H₂, 83.0% O₂, 9.8% Ar, ? = 0.225) has been determined by molecular beam mass spectrometry at low pressure (40 mbar). The detected species throughout the flame thickness were: H₂, CH₃, O, OH, H₂O, C₂H₂, CO, C₂H₄, CH₂O, O₂, HO₂, Ar, C₃H₄, C₃H₆, CO₂, C₂H₄O, C₄H₆, iC₄H₈, C₃H₆O, C₄H₆O and C₄H₈O. An original model, validated against premixed rich C₂H₄, has been extended by building a sub-mechanism taking into account the formation and the consumption of species involved in iso-butene combustion. This mechanism contains 520 reactions and 99 chemical species. A good agreement appears between calculated mole fraction profiles predicted by this mechanism, compared to experimental results.     

Characterization of the near-surface gas-phase chemical environment in atmospheric-pressure plasma chemical vapor deposition of diamond

A numerical model was developed and used to study the near-surface gas-phase chemistry during atmospheric-pressure radio-frequency (RF) plasma diamond chemical vapor deposition (CVD). Model predictions of the mole fractions of CH₄, C₂H₂, C₂H₄ and C₂H₆ agree well with gas chromatograph measurements of those species over a broad range of operating conditions. The numerical model includes a two-dimensional analysis of the sampling disturbance in the thin boundary layer above the substrate, accounts for chemistry in the gas chromatography sampling line, and utilizes a reaction mechanism that is significantly revised from a previously reported version. The model is used to predict the concentrations of H, CH₃, C₂H₂ and C at the diamond growth surface. It is suggested that methyl, acetylene and atomic carbon may all contribute significantly to film deposition during atmospheric-pressure RF plasma diamond CVD. The growth mechanism used in the model is shown to predict growth rates well at moderate substrate temperatures (∼1100 to 1230 K) but less well for lower (∼1000 K) and higher (∼1300 K) temperatures. The near-surface gas-phase chemical environment in atmospheric-pressure RF plasma diamond CVD is compared with several other diamond CVD environments. Compared with these other methods the thermal plasma is predicted to produce substantially higher concentration ratios at the surface of both H/CH₃ and C₂H₂/CH₃.     

Influence of phosphine on the diamond growth mechanism: a molecular beam mass spectrometric investigation

We have used a molecular beam mass spectrometer to investigate the effects of addition of phosphine on the growth behaviour of diamond films in a hot filament chemical vapour deposition (CVD) reactor. Films were grown using gas mixtures of 1% CH₄ with increasing amounts of PH₃ (1000–5000 ppm). Gas phase species prevalent during the growth process (e.g. CH₄, CH₃, C₂H₂, PH₃ and HCP) have been monitored quantitatively and compared with the corresponding growth rates, quality and properties of the resulting films. We find that addition of up to 2000 ppm PH₃ increases the film growth rate by a factor of 2–3, and changes the crystal morphology in favour of (100). At higher PH₃ concentrations (3000–5000 ppm) the growth rate decreases again, with predominantly (111) faceted crystals. These observations are discussed in terms of a model of the gas phase chemistry during the growth process.     

Hydrogen production from coal by separating carbon dioxide during gasification

Hydrogen generation during the reaction of a coal/CaO mixture with high pressure steam was investigated using a flow-type reactor. Coal, CaO and CO reactions with steam, and CO₂ absorption by Ca(OH)₂ or CaO occurred simultaneously in the experiment. It was found that H₂ was the primary resultant gas, comprising about 85% of the reaction products. CO₂ was fixed into CaCO₃ and CO was completely converted to H₂. Pyrolysis of the coal/CaO mixture carried out in N₂ was also examined. The pyrolysis gases were compared with gases produced by general coal pyrolysis. While general coal pyrolysis produced about 14.7% H₂, 50.5% CH₄, 12.0% CO and 12.0% CO₂, the gases produced from coal/CaO mixture pyrolysis were 84.8% H₂, 9.6% CH₄, 1.6% CO₂ and 1.1% CO.     

Synthesis and gas permeation properties of a single layer PDMS membrane

In this work, a new polydimethylsiloxane (PDMS) membrane was synthesized and its sorption, diffusion, and permeation properties were investigated using H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ as a function of pressure at 35°C. PDMS, as a rubbery membrane, was confirmed to be more permeable to more condensable gases such as C₃H₈. The synthesized PDMS membrane showed much better gas permeation performance than others reported in the literature. Based on the sorption data of this study and other researchers' works, some valuable parameters such as Flory‐Huggins (FH) interaction parameters, χ, etc., were calculated and discussed. The concentration‐averaged FH interaction parameters of H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ in the synthesized PDMS membrane were estimated to be 2.196, 0.678, 0.165, 0.139, 0.418, and 0.247, respectively. Chemical similarity of O₂, CH₄, and C₃H₈ with backbone structure of PDMS led to lower χ values or more favorable interactions with polymer matrix, particularly for CH₄. Regular solution theory was applied to verify correctness of evaluated interaction parameters. Local effective diffusion coefficient of C₃H₈ and CO₂ increased with increasing penetrant concentration, which indicated the plasticization effect of these gases over the range of penetrant concentration studied. According to high C₃H₈/gas ideal selectivity values, the synthesized PDMS membrane is recommended as an efficient membrane for the separation of organic vapors from noncondensable gases. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010