Investigation of the Phase Equilibria of CO2/CH3OH/H2O and CO2/CH3OH/H2O/H2 Mixtures

The storage of excess electricity from renewable energy sources is nowadays a crucial topic. One promising technology is the methanol (CH₃OH) synthesis from H₂/CO₂ mixtures. The achievable one‐pass conversion is limited within this exothermic equilibrium reaction. A possibility to overcome this limitation would be withdrawing CH₃OH and H₂O from the gas phase through in situ condensation under reaction conditions. In this work, the phase equilibrium for mixtures representative for different degrees of conversion was studied. A view cell was employed to determine systematically the single‐ and two‐phase regimes and obtain phase envelopes for mixtures of H₂, CO₂, CH₃OH, and H₂O from 66 to 305 °C and 61 to 233 bar. Furthermore, the densities in the single‐phase area were determined and quantified by an empirical model.     

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.     

Synthesis and mechanical wear studies of ultra smooth nanostructured diamond (USND) coatings deposited by microwave plasma chemical vapor deposition with He/H2/CH4/N2 mixtures

Ultra smooth nanostructured diamond (USND) coatings were deposited by microwave plasma chemical vapor deposition (MPCVD) technique using He/H₂/CH₄/N₂ gas mixture. The RMS surface roughness as low as 4 nm (2 micron square area) and grain size of 5–6 nm diamond coatings were achieved on medical grade titanium alloy. Previously it was demonstrated that the C₂ species in the plasma is responsible for the production of nanocrystalline diamond coatings in the Ar/H₂/CH₄ gas mixture. In this work we have found that CN species is responsible for the production of USND coatings in He/H₂/CH₄/N₂ plasma. It was found that diamond coatings deposited with higher CN species concentration (normalized by Balmer H_α line) in the plasma produced smoother and highly nanostructured diamond coatings. The correlation between CN/H_α ratios with the coating roughness and grain size were also confirmed with different set of gas flows/ plasma parameters. It is suggested that the presence of CN species could be responsible for producing nanocrystallinity in the growth of USND coatings using He/H₂/CH₄/N₂ gas mixture. The RMS roughness of 4 nm and grain size of 5–6 nm were calculated from the deposited diamond coatings using the gas mixture which produced the highest CN/H_α species in the plasma. Wear tests were performed on the OrthoPOD®, a six station pin-on-disk apparatus with ultra-high molecular weight polyethylene (UHMWPE) pins articulating on USND disks and CoCrMo alloy disk. Wear of the UHMWPE was found to be lower for the polyethylene on USND than that of polyethylene on CoCrMo alloy.     

Darstellung,Konfigurationen und NMR-Daten der Säuren CH3(SR)  CHCOOH (R  C6H5, CH2C6H5, CH2COOH)

Preparation, Configurations and N.M.R. Dates of the Acids CH₃(SR)CHCOOH (R  C₆H₅, CH₂C₆H₅, CH₂COOH) The cis and trans isomers of the acids CH₃(SR)CHCOOH (R  C₆H₅, CH₂C₆H₅, CH₂COOH) were prepared by addition of HSR to CH₃CCCOOH in alkaline water solution and by alkaline hydrolysis of CH₃C(SR)₂CH₂COOC₂H₅ (R  C₆H₅, CH₂C₆H₅, CH₂COOC₂H₅). The oxidation products CH₃C(SO₂R)  CHCOOH (R  C₆H₅, CH₂COOH) were also prepared. The n.m.r. dates of the acids were obtained and some relations between them were discussed.     

Permeation of H2, N2, CH4, C2H6, and C3H8 through asymmetric polyetherimide hollow‐fiber membranes

Permeation properties of pure H₂, N₂, CH₄, C₂H₆, and C₃H₈ through asymmetric polyetherimide (PEI) hollow‐fiber membranes were studied as a function of pressure and temperature. The PEI asymmetric hollow‐fiber membrane was spun from a N‐methyl‐2‐pyrrolidone/ethanol solvent system via a dry‐wet phase‐inversion method, with water as the external coagulant and 50 wt % ethanol in water as the internal coagulant. The prepared asymmetric membrane exhibited sufficiently high selectivity (H₂/N₂ selectivity >50 at 25°C). H₂ permeation through the PEI hollow fiber was dominated by the solution‐diffusion mechanism in the nonporous part. For CH₄ and N₂, the transport mechanism for gas permeation was a combination of Knudsen flow and viscous flow in the porous part and solution diffusion in the nonporous part. In our analysis, operating pressure had little effect on the permeation of H₂, CH₄, and N₂. For C₂H₆ and C₃H₈, however, capillary condensation may have occurred at higher pressures, resulting in an increase in gas permeability. As far as the effect of operating temperature was concerned, H₂ permeability increased greatly with increasing temperature. Meanwhile, a slight permeability increment with increasing temperature was noted for N₂ and CH₄, whereas the permeability of C₂H₆ and C₃H₈ decreased with increasing temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 698–702, 2002     

Modelling of the gas phase chemistry during diamond CVD: the role of different hydrocarbon species

The chemkin suite of computer programs has been used to model the concentration profiles of different hydrocarbon species present within a hot filament CVD reactor during diamond growth, and the calculated values are compared with those obtained by direct measurements using an in situ molecular beam mass spectrometer. Different hydrocarbon gases (CH₄, C₂H₂, C₂H₄ and C₂H₆) were used as the carbon source in the input gas mixture, ensuring that the ratio of C:H₂ remained constant at 1%. Calculations for when C₂H₆ is used as the precursor gas, after reaction and thermal equilibrium is realised, yield similar CH₄:C₂H₂ mole fraction ratios in the reactor under growth conditions to those obtained using CH₄, and to those measured experimentally. However, simulations using C₂H₄ or C₂H₂ as input gases do not reproduce the experimentally observed ratio of CH₄:C₂H₂ mole fractions. This suggests that the conversion of unsaturated C₂ species to C₁ species is not a straightforward gas phase process, and there must be one or more reactions occurring within the chamber that are not present in the standard models for hydrocarbon reactions. We suggest that these neglected reaction(s) probably involve surface-catalysed hydrogenation, which in this case, is most likely occurring on the surface of the filament.     

Atmospheric Chemistry of 2-Ethyl Acrolein

The atmospheric oxidation of the unsaturated aldehyde 2-ethyl acrolein, CH₂=C(C₂H₅)CHO, has been studied in laboratory experiments involving the reaction of ozone with 2-ethyl acrolein in the dark (with cyclohexane added to scavenge the hydroxyl radical), and the sunlight irradiation of 2-ethyl acrolein with NO in air. The major carbonyl products of the 2-ethyl acrolein reaction with ozone are formaldehyde, acetaldehyde, and the dicarbonyl ethylglyoxal, CH₃CH₂COCHO. Sunlight irradiation of 2-ethyl acrolein and NO led to the formation of three carbonyls (formaldehyde, acetaldehyde, and ethylglyoxal) and three peroxyacyl nitrates, (RC(O)OONO₂), including PAN (R = CH₃), PPN (R = C₂H₅), and the unsaturated compound EPAN (R = CH₂=C(C₂H₅)). Mechanisms are outlined for the reactions of ozone and of the hydroxyl radical with 2-ethyl acrolein. These mechanisms are consistent with the observed carbonyl and peroxyacyl nitrate products. Thermal decomposition, a major atmospheric removal process for peroxyacyl nitrates, has been studied for EPAN. The decomposition rate of EPAN relative to that of PAN is 0.59–0.73 at 292–294 K and 1 atm of air. Atmospheric implications of these results are discussed.     

Molecular beam mass spectrometry investigations of low temperature diamond growth using CO2/CH4 plasmas

Diamond films have been successfully deposited at substrate temperatures as low as 435°C using CO₂/CH₄ gas mixtures in a microwave plasma chemical vapour deposition (CVD) reactor. In order to understand why it is possible to grow diamond at these low temperatures using these gases, we have performed the first in situ molecular beam mass spectrometry studies to measure, simultaneously, the concentrations of the dominant gas phase species present during growth over a wide range of plasma gas mixtures (0–80% CH₄, balance CO₂). Optical emission spectroscopy has also been used to investigate gas phase species present in the microwave plasma. These experimental measurements give further evidence that CH₃ radicals may be the key growth species and suggest that CO may be of greater importance to the plasma chemistry of CO₂/CH₄ gas mixtures than previously thought.     

Synergetic thermodynamic/kinetic separation of C3H8/CH3F on carbon adsorbents for ultrapure fluoromethane electronic gas

Atomic layer etching (ALE) using the environmentally friendly electronic gas fluoromethane (CH₃F) is guided for fabricating nanoscale electronic components. The adsorptive purification of CH₃F provide a viable direction to remove trace amounts of impurities to produce highly pure CH₃F (>99.9999%) for the ALE process. Herein, to remove trace propane (~100 ppm) in CH₃F, we report synergetic thermodynamic and kinetic separation of C₃H₈/CH₃F over glucose-derived carbon molecular sieve CMS-T, (T as pyrolysis temperature). With pore size slightly larger than the kinetic diameter of C₃H₈, CMS-600 allows both strong confined adsorption of C₃H₈ and a higher diffusion rate of C₃H₈ over CH₃F, resulting in a remarkable separation factor of 51.1. Breakthrough experiment demonstrates a high dynamic production capacity of 457 L kg⁻¹ of 7 N CH₃F (<100 ppb of C₃H₈) over CMS-600 with excellent cycling stability. Adsorption purification over carbon provides a feasible approach for industrial hyperpurification of electronic gas.     

H atom production in a hot filament chemical vapour deposition reactor

Multiphoton ionisation spectroscopy of atomic hydrogen, resonance enhanced at the two photon energy by the 2s¹;²S_1/2 state, and subsequent analysis of the resulting Doppler broadened lineshapes, has been used to provide direct, spatially resolved relative H atom number densities and gas temperature profiles in the vicinity of a coiled Ta hot filament (HF) in a reactor used for diamond chemical vapour deposition. The effects of filament temperature and H₂ pressure on the relative H atom number densities and the gas temperature profiles have been investigated, as have the effects of small amounts of added CH₄. The effective activation energy for H atom production so obtained (E_a=237±22 kJ mol⁻¹) suggests that the HF provides a particularly efficient means of heating (and thus promoting the dissociation of) H₂ molecules that adsorb onto its surface.     

Characteristics of carbon-related materials deposited in electron-energy controlled CH4/H2 RF discharge plasmas

The influence of electron temperature T_e on the production of carbon-related materials was investigated in a hollow-type magnetron radio-frequency (RF) CH₄/H₂ plasma. Here, the electron temperature decreased along the plasma column. Since the dissociation of CH₄ is determined by the electron energy in plasmas, the density ratio of radicals CH₂/CH₃ can be varied by the electron temperature. Therefore, the change of the electron temperature is quite important for controlling the characteristics of carbon-related materials. In the experiment, the production of diamond microparticles in low T_e plasma was detected. On the other hand, thin carbon films consisting of graphitic carbons were observed in the high T_e plasma. Therefore, it is shown that control of the electron temperature in the plasma has a key effect on the film quality.     

Using fluorine and chlorine in the diamond CVD process

We deposited diamond films at low substrate temperatures T_sub using the halogen containing precursor gases CHF₃ and C₂H₅Cl with an abundance of hydrogen. Diamond film growth was possible down to T_sub=370 °C using a hot-filament chemical vapor deposition process. The possibility of low temperature growth of diamond could be correlated with an increase of radical density in the gas phase caused by the halogen addition. These radicals, especially atomic hydrogen, fluorine and chlorine are responsible for the creation of active surface sites on the diamond surface. Chlorine especially is able to break surface bonds even at low substrate temperatures. Recent secondary ion mass spectroscopy measurements revealed that halogens are involved in surface reactions and that fluorine and chlorine were incorporated in the deposited films especially at low T_sub. Along with the creation of active surface sites the surface diffusion is important for the diamond growth, which is strongly limited by reduction of the substrate temperature. We succeeded in good quality diamond growth on glasses and aluminium substrates at T_sub=490 °C. A further decrease of T_sub leads to a decrease of diamond film quality and a poor adhesion of the diamond films to the substrate.     

The effect of the CH4 level on the morphology,microstructure, phase purity and electrochemical properties of carbon films deposited by microwave-assisted CVD from Ar-rich source gas mixtures

Carbon thin films were deposited on Si substrates by microwave-assisted chemical vapor deposition (CVD) using variable CH₄ levels in an Ar/H₂ (Ar-rich) source gas mixture. The relationship between the CH₄ concentration (0.5 to 3 vol.%) in the source gas and the resulting film morphology, microstructure, phase purity and electrochemical behavior was investigated. The H₂ level was maintained constant at 5% while the Ar level ranged from 92 to 94.5%. The films used in the electrochemical measurements were boron-doped with 2 ppm B₂H₆ while those used in the structural studies were undoped. Boron doping at this level had no detectable effect on the film morphology or microstructure. Relatively smooth ultrananocrystalline diamond (UNCD) thin films, with a nominal grain size of ca. 15 nm, were only formed at a CH₄ concentration of 1%. At the lower CH₄ concentration (0.5%), faceted microcrystalline diamond was the predominant phase formed with a grain size of ca. 0.5 µm. At the higher CH₄ concentration (2%), a diamond-like carbon film was produced with mixture of sp²-bonded carbon and UNCD. Finally, the film grown with 3% CH₄ was essentially nanocrystalline graphite. The characteristic voltammetric features of high quality diamond (low and featureless voltammetric background current, wide potential window, and weak molecular adsorption) were observed for the film grown with 1% CH_4, not the films' grown with higher CH₄ levels. The C₂ dimer level in the source gas was monitored using the Swan band optical emission intensity at 516 nm. The emission intensity and the film growth rate both increased with the CH₄ concentration in the source gas, consistent with the dimer being involved in the film growth. Importantly, C₂ appears to be involved in the growth of the different carbon microstructures including microcrystalline and ultrananocrystalline diamond, amorphous or diamond-like carbon, and nanocrystalline graphite. In summary, the morphology, microstructure, phase purity and electrochemical properties of the carbon films formed varied significantly over a narrow range of CH₄ concentrations in the Ar-rich source gas. The results have important implications for the formation of UNCD from Ar-rich source gas mixtures, and its application in electrochemistry. Characterization data by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), visible-Raman spectroscopy and electrochemical methods are presented.     

A Study of the NOx Selective Catalytic Reduction with Ethanol and Its By-products

The NOx selective catalytic reduction (SCR) with ethanol has been investigated over alumina supported silver catalyst with a special attention to the main involved reactions depending on the temperature test. With this aim, the possible reducers from ethanol transformations were also evaluated (C₂H₅OH, CH₃CHO, C₂H₄, CO). In addition, the contributions of the gas phase reactions and the alumina support were also pointed out. Based on the C-products and N-compounds distributions, it is assumed that at low temperature (T < 300 °C), ethanol reacts firstly with NO + O₂ to produce acetaldehyde and N₂. For higher temperatures, two reaction pathways have been proposed, supported by the CH₃CHO-SCR results: a direct reaction between NO₂ and CH₃CHO, or via –NCO species.     

Effect of co-adsorbed dopants on initial diamond growth steps: H abstraction from an adsorbed CH3

The effect induced by a neighbouring co-adsorbed dopant on H abstraction from an adsorbed CH₃ species on diamond has been investigated by using an ultra-soft pseudo-potential density functional theory (DFT) method under periodic boundary conditions. Both the (100) and (111) diamond surface orientations were considered with various types of dopants in two different hydrogenated forms; AH_x (A = N, B, S, or P; X = 0 or 1 for S; X = 1 or 2 for N, B and P, and X = 2 or 3 for C). The H abstraction by gaseous radical H was found to be energetically favoured by the presence of the dopants in all of their different hydrogenated forms. For NH₂, SH, or PH₂, this effect is induced by a destabilisation of the diamond surface by sterical repulsions between the adsorbed growth species CH₃ and the co-adsorbed dopant. For BH₂ and the dopants in their radical form, the abstraction reaction is favoured due to the formation of a new covalent bond between the dopant and the co-adsorbed CH₂ (product of the abstraction reaction), which strongly stabilises the surface after the abstraction process.     

Detection of C2 radicals in low-pressure inductively coupled plasma source for diamond chemical vapor deposition

The C₂ radical density was measured in a low-pressure, radio frequency (rf), inductively coupled plasma (ICP) employing a CH₃OH/H₂/H₂O mixture. Measurement was carried out under the conditions where predominantly diamond can be formed. At the typical growth conditions for the low-pressure, rf ICP reactor used for diamond formation, the C₂ radical density in the ICP region was of the order of 10¹³ cm⁻³. The correlation between the C₂ radical density and the quality of diamond films was investigated.     

Oxidative dimerization of CH4/CD4 mixtures: Evidence for methyl intermediate

Isotope tracer experiments prove the role of methyl in the oxidative coupling of methane and disprove a recently proposed mechanism involving methylene. The ethane product from oxidative coupling of CH₄/CD₄ mixtures over a Li/MgO catalyst consists of C₂H₆, C₂D₆ and CH₃CD₃ thus proving that ethane is formed by combination of methyl intermediates. The co-reaction of labelled CH₄ (D and¹³C) with C₂H₄ produces propylene labelled predominantly at the methyl (3) position, thus proving C₃ formation by terminal addition of methyl to ethylene rather than via a cyclic intermediate as has been proposed.     

Trapping of CH3O formed from CO + H2

Methoxy formed on Al₂O₃ from¹³CO and H₂ coadsorption on Ni/Al₂O₃ was trapped by C₂H₅OH adsorption and temperature-programmed reaction (TPR). The presence of excess C₂H₅OH significantly increases the rate of¹³CH₃OH and (¹³CH₃)₂O formation. The¹³CH₃OH forms by the reaction of C₂H₅OH with¹³CH₃O on Al₂O₃. In the absence of C₂H₅OH,TPR following¹³CO and H₂ coadsorption did not produce significant amounts of¹³CH₃OHor(¹³CH₃)₂O.     

Thermodynamic and molecular insights into the absorption of H2S,CO2, and CH4 in choline chloride plus urea mixtures

Deep eutectic solvents (DESs) are a class of promising media for gas separation. In order to examine the potential application of DESs for natural gas upgrading, the solubilities of H₂S, CO₂, and CH₄ in choline chloride (ChCl) plus urea mixtures were measured in this work. The solubility data were correlated with Henry's law equation to calculate the thermodynamic properties of gas absorption processes, such as Henry's constants and enthalpy changes. Grand-canonical Monte Carlo simulations and quantum chemistry calculations were also performed to examine the mechanism of gas absorption processes. It is found that the absorption of H₂S in ChCl + urea mixtures is governed by the hydrogen-bond interaction between Cl of ChCl and H of H₂S, whereas the absorption of CO₂ and CH₄ in ChCl+urea mixtures is governed by the free volume of solvents. Based on the different behavior of gas absorption, high H₂S/CO₂, H₂S/CH₄, and CO₂/CH₄ selectivities can be achieved by adjusting the ratio of ChCl/urea in mixtures.     

The effects of a potassium overlayer on the reaction pathway of CH2 and C2H5 on Rh(111)

The effect of potassium on the reaction pathways of adsorbed CH₂ and C₂H₅ species on Rh(111) was investigated by means of reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TDS). Hydrocarbon fragments were produced by thermal and photo-induced dissociation of the corresponding iodo compounds. Potassium adatoms markedly stabilized the adsorbed CH₂ and converted it into C₂H₄, the formation of which was not observed for K-free Rh(111). New routes of the surface reactions of C₂H₅ have been also opened in the presence of potassium, namely its transformation into butane and butene.