Feed Gas Ratio Research Articles

Nanodiamond formation by hot-filament chemical vapor deposition on carbon ions bombarded Si

Nanocrystalline diamond films were grown by a two-step process on Si(1 0 0) substrate, which was first pretreated by pure carbon ions bombardment. The bombarded Si substrate was then transformed into a hot-filament chemical vapor deposition (HFCVD) system for further growth. Using the usual CH 4/H 2 feed gas ratio for microcrystalline diamond growth, nanodiamond crystallites were obtained. The diamond nucleation density is comparable to that obtained by biasing the substrate. The uniformly distributed lattice damage is proposed to be responsible for the formation of the nanodiamond.

1-Heptene hydroformylation over phosphinated silica-anchored rhodium thiolate complexes

The rhodium (I) pentaflurophenylthiolate complexes [Rh(μ-SC 6F 5)(COD)] 2 and [Rh(μ-SC 6F 5)(CO) 2] 2 were anchored on phosphinated silica. These catalysts were tested in the hydroformylation reaction of 1-heptene in toluene at 343–393 K using a gas feed ratio of CO:H 2=1 mole. The conversion of 1-heptene versus the reaction time followed S-shaped curves in which the induction period depended on the catalyst precursor and number of cycles in the reaction. Selectivity towards linear aldehyde was high, although the extent of isomerisation to internal olefins was found to be important. The addition of free PPh 3 to the reaction medium markedly increased the yield to linear aldehyde but the rate of the reaction appeared to be retarded. The results are compared with those obtained on using these complexes in homogeneous phase under similar conditions. The effects of temperature, pressure and the phosphine/Rh mole ratio on the reaction rate and selectivity are discussed.

Epitaxial growth of AlN films on Si substrates by ECR plasma assisted MOCVD under controlled plasma conditions in afterglow region

Wurtzite-type aluminum nitride (h-AlN) films were epitaxially grown on off-axis Si (111) substrates by electron–cyclotron–resonance plasma-enhanced metalorganic chemical vapor deposition (ECRMOCVD) using trimethylalminum (TMA) and ammonia (NH 3) as source gases. Plasma space potential in the growth chamber was lowered by setting the magnetic field distribution as a mirror field. For the growth of h-AlN with excellent crystallinity on Si substrates, nitridation of the substrate surface, growth of a low-temperature (LT) buffer layer, and epitaxial growth of AlN films were performed under a mirror field condition in a growth chamber. Thermal nitridation at 1050°C prior to the epitaxial growth appreciably improved the crystallinity of AlN films. The growth of buffer layer at temperatures below 650°C was not so effective for the improvement of the crystallinity and crystal orientation of AlN epitaxial layer. The proportion of domain including stacking faults and that whose c-axis was parallel to the substrate surface was very small ( I (0002)/( I (10–10)+ I (10–11))>700), irrespective of the gas feed ratio of N source to Al source (NH 3/TMA) during the epitaxial growth process. Under a small gas feed ratio (NH 3/TMA<200), however, the diffraction peak intensities from the non-epitaxial domains became large.

Experimental Study on Ozone Synthesis via Dielectric Barrier Discharges

The characteristics of ozone generation using a dielectric barrier discharge reactor were investigated experimentally. Results indicate that ozone concentration increases with increasing applied voltage and gas residence time. In addition to applied voltage, ozone generation rate varies with reactor configuration as well. Optimum ozone generation rates can be reached at the specific gas residence time for a given applied voltage and gas composition. At the same applied voltage, the reactor with a single dielectric barrier results in a higher ozone generation rate in comparison with the reactor having double dielectric barriers. Given a constant N2/O2 ratio in the feed gas, NOx concentration increases as applied voltage and gas residence time increase. Results indicate that maximum NOx concentration is reached when the N2/O2 ratio of feed gas is 4.

95/03468 Studies on Fischer-Tropsch synthesis over Fe-Cu-K catalyst. I. Catalytic performance

The influence of reaction pressure, temperature, space velocity (GHSV), particle size of catalyst and H2/CO ratio of feed-gas on the steady-state product distribution, conversion of CO, H2 and syngas, olefin to paraffin ratio and CO2/ H2O ratio for FTS reaction were investigated using a coprecipitated copper- potassium promoted iron catalyst. The test was carried out in a fixed-bed reactor. Increasing the reaction temperature from 493. 2 to 5-13. 2 K shifted the hydrocarbon distribution toward the heavier hydrocarbons (C5-C23) and selectively increased CO conversion to CO2. The hydrocarbon distribution was found to be dependent on the H2/CO feed-gas ratio in the range from 1.23 to 2. 22. The CO2/H2O ratio in product decreased as the flow of feed-gas rate increased, which suggests that H2O is a primary product and its reaction with CO to form CO2 occurs via a secondary process. The CO conversion increased with the decrease of catalyst particle size from 10 to 60 mesh (2. 0-0. 3 mm), while the CO conversion changed very little as the particle size of the catalyst was further reduced to 60- 100 mesh (0. 3-0. 154 mm). The CO conversion increased with the increase of operating pressure. The pressure also affects CO2 selectivity and product distribution of FTS.

Growth rate studies of CVD diamond in an RF plasma torch

This paper addresses the complex chemistry in the boundary later over a substrate in a chemical vapor deposition rector at atmospheric pressure. In this study, a highspeed plasma (140m/s) was created using a radio-frequency inductively coupled plasma torch for the deposition of diamond thin films. Growth rates on the order of 50 μm/ h were obtained for well-faceted continuous films grown on molybdenum substrates positioned normal to the plasma flow. The highest growth rates were obtained at substrate temperatures of 1370 K and a feed gas ratio of 2.5% CH4 in H2. Growth rates are compared to predicted results obtained from numerical simulations, based on a one-dimensional stagnation-point flow, and are/mend to be in good agreement. Several other surface analysis techniques were used to characterize the deposited films, inchaling SEA/, Raman spectroscopy, transmission electron microscopy. Rutherfard backscattering spectroscopy, and hydrogen-forward recoil spectroscopy. Optical emission spectroscopy was used to characterize the RF plasma during the deposition process. Results from these studies form an important database for the validation and improvement of current models of the atmospheric-pressure diamond CVD environment.

Selective removal of hydrogen sulfide from gases containing hydrogen sulfide and carbon dioxide by absorption into aqueous solutions of 2-amino-2-methyl-1-propanol

Selective absorption of H 2 S from N 2 streams containing H 2 S and CO 2 into aqueous solutions of 2-amino-2-methyl-1-propanol was investigated in a 2.55×10 -2 m o.d. stainless steel wetted-wall column at atmospheric pressure and constant feed gas ratio. In the range of gas flow rates studied (90×10 -6 to 180×10 -6 m 3 /s), the effect of gas-phase resistance to mass transfer on the absorption of H 2 S was significant. The rates of absorption of H 2 S and the selectivity factor decreased with the increase in the contact time. For an increase in the concentration of the amine from 0.5 to 2.0 kmol/m 3 , the rates of absorption of both CO 2 and H 2 S increased, but to a larger extent for CO 2 resulting in a consequent decrease in the selectivity factor. In the temperature range of 290.5-301.5K the rates of absorption of CO 2 increased marginally with the increase in temperature while the rates of absorption of H 2 S and the selectivity factor decreased. The maximum value of the selectivity factor observed was 22.5

Electron trapping and chemical composition in radio frequency glow discharge a-SiN:H

The electron trapping phenomenon in a-SiN:H films deposited by radio frequency (rf) glow discharge has been studied as a function of rf power and gas feed ratio. The chemical composition of the films was determined with Fourier transform infrared spectroscopy. The nitrogen content of the films increased with rf power level if the feed ratio of silane to ammonia was sufficient, 1:10. A gas ratio of 1:5 lacked sufficient ammonia fraction to yield nitrogen rich films despite an increase in rf power level. The electrical resistivity increased and in general electron trapping decreased with increasing nitrogen content in the a-SiN:H films. There is weak experimental evidence that an electron trapping minimum is obtained at a film composition similar to stoichiometric silicon nitride. The measured coordination number of 2.4 for films at this stoichiometric ratio corresponded to the optimum coordination number for a random covalent network. This conceivably should yield the lowest trap density material. At this time, however, it is safer to conclude that electron trapping decreases with increasing nitrogen content in the material.

Simultaneous Absorption of Hydrogen Sulfide and Carbon Dioxide into di‐isopropanolamine Solution

AbstractThe simultaneous absorption of hydrogen sulfide and carbon dioxide into di‐isopropanolamine (DIPA) solution was investigated in a 183 cm long, 2.72 cm OD wetted‐wall column at atmospheric pressure. The influence of liquid flow rate, gas flow rate, temperature and liquid concentration on the absorption rate, overall gas‐phase mass transfer coefficient and selectivity factor were studied at a constant gas feed ratio. The results show that the absorption rate of CO2 increases rapidly with increasing liquid flow rate (the Reynolds number of the turbulent liquid film ranges from 2600 to 4350) but increases moderately with increasing gas flow rate (G = 18‐91 L/min), indicating that it is liquid‐phase mass transfer controlled. In contrast, the absorption rate of H2S increases very slowly with increasing liquid flow rate but increases rapidly with increasing gas flow rate, indicating that it is gas‐phase mass transfer controlled. The absorption rate of CO2 also increases with increasing temperature (26‐80°C) but H2S absorption rate decreases with increasing temperature. When the concentration of DIPA solution increases from 0.2 to 2.6 mol/L, the absorption rate of both CO2 and H2S increases but with a larger rate of increase for CO2 For selective H2S removal, it is preferable to operate at low liquid and high gas flow rates, low temperatures and low DIPA concentrations.

Selective Fischer-Tropsch synthesis on metal powder catalysts prepared by the potassium reduction of halides in THF

Metal powders such as Fe, Co, Ni, FeCo, and FeNi prepared by reducing metal iodides or bromides with potassium metal in refluxing THF were used as catalysts for Fischer-Tropsch syntheses. These metal powders contained very small particles and have large BET surface areas (28–36 m 2/g). The metal powder catalysts, such as Fe and FeCo (80:20), gave l-butene with more than 35 wt% selectivity at a rather high CO conversion of over 10 wt% at 533–553 K, while products on the Co catalyst obeyed conventional Schulz-Flory type distribution. The Ni catalyst showed little activity. Effects of reaction variables (temperature, H 2 CO feed gas ratio, and composition of FeCo) were investigated.

Fractionation of gas mixtures in a moving‐bed adsorber. I. Correlation of adsorber performance

AbstractThe design and operation of a pilot‐scale‐moving bed adsorber to separate the various components of a gas mixture using activated carbon as the preferential adsorbent are described. A binary system, methane–acetylene, and a ternary system, methane–carbon dioxide–acetylene, were studied. The performance of the unit was analyzed by means of the transfer‐unit‐height (H.T.U.) concept based on the observed changes in gas composition during tower operation. For both the binary and ternary systems the transfer‐unit height was independent of feed‐gas composition but was found to vary linearly with the ratio of feed gas to carbon flow. The over‐all transfer‐unit‐height values based on either the gas or the adsorbed phase were observed to vary from 6.5 in. at 1.39 std. cu. ft./lb. carbon to 36.9 in. at 4.81 std. cu. ft./lb. carbon.