Ethylene Flow Rate Research Articles

Gas-jet HFCVD synthesis of diamonds from mixtures of hydrogen with ethylene and methane

The gas-jet deposition method (a modification of the Hot Filament Chemical Vapor Deposition method (HFCVD)) was used to deposit some diamond structures on a molybdenum substrate from a hydrogen-ethylene mixture activated on hot tungsten. The experiments were performed for two lengths of activation reactors at different ethylene flow rates. For comparison, some diamond structures were synthesized from a hydrogen-methane mixture under similar conditions. The resulting structures were studied with the scanning electron microscopy and Raman spectroscopy methods. The reacting mixture flow through the heated catalytic channel was simulated by solving the Navier-Stokes equations accounting for homogeneous and heterogeneous chemical reactions. The reactor (hot tungsten tube) length and diameter effects as well as carbonaceous admixture supply effects were analyzed. The main diamond precursor's formation pathways were analyzed and the reaction chains' complexity was demonstrated. The simulation results are in good agreement with the experimental data. The numerical experiments made it possible to reveal the growth process key driving parameters.

Thermogasdynamics of a Model Ethylene-Fueled Combustion Chamber in Supersonic Flow

Abstract The results of numerical investigation of thermogasdynamics of a model scramjet combustion chamber with an ethylene flameholder made in form of an asymmetric trapezoidal cavity are given. The regimes of supersonic air flow at the combustion chamber inlet are studied at the Mach number 2.2, the pressure 0.416–1 atm, and the total ethylene flow rate of the order of 10 g/(s cm) through two injectors located in the cavity. A two-dimensional computational model based on the system of time-dependent Navier–Stokes equations, the energy conservation and continuity equations for the gas mixture and individual chemical components, as well as the system of chemical kinetics, is used. The spectral and integral radiative heat fluxes towards the chamber walls were calculated using the thermal radiation transfer equation. It is shown that in the calculated cases considered the density of convective heat flux towards the combustion chamber walls can reach 20 W/cm2 and the density of integral radiative heat fluxes is of ~1 W/cm2.

Synthesis of carbon-coated silicon nanoparticles by induction thermal plasma for lithium ion battery

Synthesis of silicon nanoparticles with carbon coating by induction thermal plasma was investigated experimentally. Crystalline silicon was injected into plasma as raw material, and nanoparticles were produced through quenching process. Ethylene was chosen as carbon source for coating and injected into plasma downstream as a counter-flow with different gas flow rates to understand the effect on products. Synthesized silicon nanoparticles were successfully coated with carbon materials, and had an average diameter around 70 nm which was independent from ethylene flow rate. Obtained carbon coating was amorphous and consisted of sp2 carbons and sp3 carbons. Molar ratio of sp2 carbons to sp3 carbons, as well as the hydrogen content, decreased with higher ethylene gas flow rate. Increased concertation of hydrogen radicals was believed as the reason for those phenomenon due to etching effect on carbon coating. The above results are significant for the better performance of lithium ion batteries.

An Analysis of Increasing the Purity of Ethylene Production in the Ethylene Fractionation Column by the Genetic Algorithm

AbstractDistillation columns are among the most common fractionation systems with numerous applications in petrochemical units. Hence, the optimization of these columns is a large step in reducing energy consumption and increasing process productivity. This study was, therefore, carried out as a case study of the simulation and optimization of the parameters influencing the ethylene production of the ethylene distillation column in an olefin unit. The two defined objective functions in this research were maximum mass flow of ethylene in the upstream flow of the distillation column and the minimum energy consumption in the distillation column. The optimal operating conditions for the independent variables were estimated using the NSGAII algorithm. The sensitivity analysis of the results was, thereafter, carried out and the optimization results introduced tray no. 71 as the most suitable feed location. In addition, the optimal reflux ratio and the optimal feed flow temperature were 5.26 and −18.49 °C, respectively. In this condition, the upstream ethylene flow rate and energy consumption in the unit increased by approximately 0.74 % and 0.9 % as compared to the initial conditions, respectively.

Experimental study on soot formation, evolution and characteristics of diffusion ethylene/air flames in ψ-shaped mesoscale combustors

Soot formation, evolution and characteristics of diffusion ethylene/air flames in ψ-shaped mesoscale combustors of two different diameters with the variations of excess air ratio and flow rate were experimentally investigated. The variation in nanostructure and oxidation reactivity of soot was compared based on the results of high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Results demonstrated that with an increasing excess air ratio and flow rate, the unventilated flames with bifurcated shapes were observed in both types of combustors due to the deteriorated mixing process in large flow velocity. Different effects on characteristics of soot from two combustors with the same variation of flow rate were found. For the variation in ethylene flow rate of 60–100 ml/min at excess air ratio of 0.5, the oxidation reactivity of soot from the combustor with d = 4 mm first decreased and then slightly increased, while it decreased all the time as for the soot from the combustor with d = 6 mm. Moreover, the significant distinctions in soot nanostructure due to the scale effect were observed. The soot from the combustor with d = 4 mm exhibited the partial amorphous structure aggregated by a large amount of PAHs with high reactivity. Whereas among the soot from the combustor with d = 6 mm, a typical fullerene-like structure which represented the simultaneous existence of PAHs and graphitic parts was found. The soot graphitization degree and production increased notably with the enlargement of combustor size because the higher combustion temperature and longer residence time were simultaneously obtained, which both were beneficial to soot formation and growth rate. Significantly, the lower combustion efficiency was obtained in the combustor of d = 6 mm than 4 mm at α = 0.5 because of the larger soot production and more existence of unburned gas. But the higher combustion efficiency was found for the 6 mm than 4 mm at α = 1 in the case of almost no soot generation, which was due to the longer residence time.

Design and construction of a flexible laboratory-scale mixing apparatus for continuous ethylene supplementation of fresh produce

The design and construction of a laboratory-scale apparatus for generating variable concentrations and flow rates of exogenous ethylene for fresh produce supplementation during storage trials is described. A stock of compressed ethylene in nitrogen (5000 μl l −1 ) was blended into a continuous flow stream of air and diluted to the desired concentrations. The ethylene and air flow rates were controlled with calibrated mass flow control valves. An empirical mathematical model was derived for real-time variation of both the mixed concentration and flow rate during continuous flow. Validation of the model was performed using fresh sweet potato as a case study where a steady continuous ethylene concentration of 10 μl l −1 was achieved for three months. The bespoke system offers easy-to-manage ethylene supplementation for research.

Effect of Ethylene Flow Rate and CVD Process Time on Diameter Distribution of MWCNTs

To date, focus of the research activities in nanoscience was to control the chemical vapor deposition (CVD) growth of carbon nanotubes (CNTs) by changing the precursor pressure and process temperature. The effect of the precursor flow rate and process time on CNTs growth parameters has been overlooked in past studies and therefore is very little known. This study was focused on the optimization of the ethylene flow rate and CVD process time for CNTs growth over Fe2O3/Al2O3 catalyst in a fluidized bed chemical vapor deposition (FBCVD) reactor, operating at atmospheric pressure. Argon and hydrogen were considered as the carrier and supporting gases, respectively. Transmission electron microscope (TEM) and Scanning Electron Microscopy (SEM) were used to investigate the surface morphology, nanostructures, purity and yield of the grown CNTs. In-depth analysis revealed an increase in tube length, yield and the carbon concentration with ethylene flow rate in the range of 50–110 sccm. However, an inverse relationship between flow rate and tube diameter distribution was predicted in the given work. The most favorable results were obtained at an ethylene flow rate of 100 sccm and a CVD process time of 60 minutes. The dense and homogeneous growth of relatively pure nanotubes of increased tube length and narrow diameter distribution, in the range of 20–25 nm, was observed at optimized flow rate and process time.

Parametric study on vapor-solid-solid growth mechanism of multiwalled carbon nanotubes

This study aimed at investigating the effect of the fluidized bed chemical vapor deposition (FBCVD) process parameters on growth mechanism, morphology and purity of the multiwalled carbon nanotubes (MWCNTs). Nanotubes were produced in a vertical FBCVD reactor by catalytic decomposition of ethylene over Al2O3 supported nano-iron catalyst buds at different flow rates. FESEM, TEM, Raman spectroscopy and TGA thermograms were used to elaborate the growth parameters of the as grown MWCNTs. As the growth process was driven by the process temperatures well below the iron-carbon eutectic temperature (1147 °C), the appearance of graphite platelets from the crystallographic faces of the catalyst particles suggested a solid form of the catalyst during CNT nucleation. A vapor-solid-solid (VSS) growth mechanism was predicted for nucleation of MWCNTs with very low activation energy. The nanotubes grown at optimized temperature and ethylene flow rate posed high graphitic symmetry, purity, narrow diameter distribution and shorter inter-layer spacing. In Raman and TGA analyses, small ID/IG ratio and residual mass revealed negligible ratios of structural defects and amorphous carbon in the product. However, several structural defects and impurity elements were spotted in the nanotubes grown under unoptimized process parameters.

Liquid Gradient Refractive Index Microlens for Dynamically Adjusting the Beam Focusing

An in-plane liquid gradient index (L-GRIN) microlens is designed for dynamically adjusting the beam focusing. The ethylene glycol solution (core liquid) withde-ionized (DI) water (cladding liquid) is co-injected into the lens chamber to form a gradient refractive index profile. The influences of the diffusion coefficient, mass fraction of ethylene glycol and flow rate of liquids on the refractive index profile of L-GRIN microlens are analyzed, and the finite element method and ray tracing method are used to simulate the convection-diffusion process and beam focusing process, which is helpful for the prediction of focusing effects and manipulation of the device. It is found that not only the focal length but the focal spot of the output beam can be adjusted by the diffusion coefficient, mass fraction and flow rate of liquids. The focal length of the microlens varies from 942 to 11 μm when the mass fraction of the ethylene glycol solution varies from 0.05 to 0.4, and the focal length changes from 127.1 to 8 μm by varying the flow rate of the core liquid from 0.5 × 103 to 5 × 103 pL/s when there is no slip between the core and cladding inlet. The multiple adjustable microlens with a simple planar microfluidic structure can be used in integrated optics and lab-on-chip systems.

Numerical and experimental study of the influence of CO2 and N2 dilution on soot formation in laminar coflow C2H4/air diffusion flames at pressures between 5 and 20 atm

The effects of fuel dilution by CO2 and N2 on soot formation and the flame structure in laminar coflow C2H4/air diffusion flames at pressures between 5 and 20atm were investigated both experimentally and numerically. Experimentally a constant ethylene flow rate and a constant dilution rate of 1:2 (fuel:diluent by mass) were maintained throughout the experiments. The flames were stable and non-smoking over the pressure range investigated. The radially-resolved soot volume fraction and temperature distributions were measured by the spectral soot emission (SSE) technique. Numerical calculations were conducted using two C2 chemistry models with formation of PAHs up to pyrene and a soot model incorporating pyrene collision as the soot inception step and hydrogen-abstraction acetylene addition mechanism and PAH condensation as the surface growth processes. The two C2 chemistry models were the ABF mechanism [Appel et al. (2000)] and the DLR mechanism [Slavinskaya and Frank (2009)]. The DLR mechanism predicted little or no chemical effect of CO2 dilution, depending on the pressure, in the present context. Numerical results are in qualitative agreement with experimental measurements. Soot volume fractions and carbon conversion are lower in the CO2-diluted flames due to the additional chemical effect of CO2. CO2 is still more effective than N2 as a diluent to suppress soot formation at elevated pressures. The primary pathway for the chemical effect of CO2 dilution is through the reverse reaction of CO+OH↔CO2+H. The chemical effect of CO2 lowers the rates of soot inception, C2H2 addition, and PAH condensation. The effectiveness of the CO2 chemical effect on soot formation suppression diminishes with increasing pressure. The diminishing effectiveness of the chemical effect of CO2 dilution with increasing pressure is due to the significant decrease in the H radical mole fraction.

Observation of the Graphene Surface Structure at the Early Stages of Graphene Growth on Copper

Scalable growth is essential for graphene-based applications. Recent development has enabled the achievement of the scalability by use of chemical vapor deposition (CVD) at 1000°C with copper as a catalyst and methane as a precursor gas. Here we report our observation of early stage of graphene growth based on an ethylene-based CVD method, capable of reducing the growth temperature to 800°C for monolayer graphene growth on copper films and foils. We track the early stages of slow growth under low ethylene flow rate and observe the graphene domain evolution by varying the temperature and growth time. As the physical properties of the surface also changes along with the graphene domain structure, we also investigate the surface energy of the partially grown graphene. Thus, we demonstrate that the hydrophobicity can be fine tuned by controlling the initial growth of the graphene domains.

Novel low temperature atmospheric pressure plasma jet systems for silicon dioxide and poly-ethylene thin film deposition

In this study, both low-density plasma quartz tube (QT) and high-density plasma metallic tube (MT) jet-electrodes with pulsed-type alternating-voltage (AC) generator were used to investigate the influences of the process parameters and electrode types on the microstructures and the corrosion behaviors of silicon dioxide (SiO 2) or poly-ethylene (PE, (CH 2CH 2)n ) thin films. Tetraethoxysilane (TEOS) and ethylene (C 2H 4) were used as precursors for SiO 2 and PE thin film deposition. The TEOS precursor was vaporized by an ultrasonic oscillator and introduced into the AP plasma systems by argon (Ar) carrier gas. The main plasma working gas was Ar gas mixed with or without oxygen gas. The pulsed-type AC generator, with a frequency of 30 kHz, a voltage of 10 kV and a wattage of 300 W, was used to deposit SiO 2 and PE thin films on the silicon and AISI 1005 low carbon steel substrates at the room temperature, respectively. The high-density plasma MT jet-electrode with an Ar gas flow rate of 6 slm, a precursor flow rate of 40 sccm and an oxygen flow rate of 40 sccm revealed optimal plasma dissociation and chemical reaction efficiencies to synthesize effective atomic stoichiometry of SiO 2 (in-organic films) thin films. However, the low-density plasma QT jet-electrode with an Ar gas flow rate of 6 slm and an ethylene flow rate of 15 sccm appeared optimal plasma-induced polymerization efficiency to exhibit reasonable atomic stoichiometry of PE (organic films) thin films. Moreover, the optimal SiO 2 thin films deposited by MT jet-electrode possessed better corrosion resistant integrity than the optimal PE thin films synthesized by QT jet-electrode. It was also found that SiO 2 and PE thin films synthesized by the AP plasma method possess effective corrosion barrier characteristics like other deposition techniques.

Plasma Deposited Electrocatalytic Films with Controlled Content of Pt Nanoclusters

AbstractCombining platinum sputtering with plasma polymerization in argon–ethylene plasmas, nanocomposite Pt‐hydrocarbon thin films, useful as catalytic layers for proton exchange membrane fuel cells, can be deposited. Pulsing the ethylene flow rate allowed for a fine tuning of the Pt amount in deposited films at low RF input power. The proposed deposition process seems to be an efficient strategy to control the metal content over a wide range of atomic percentages (5–80%). Deposited films were characterized in terms of their chemical, electrochemical and structural properties. The XPS spectra revealed that platinum is included in the films in metallic state. SEM and TEM analyses showed that nanosized Pt clusters (3–7 nm diameter) are uniformly distributed in a porous columnar film structure. The best electrochemical activity (202 cm2 · mg) was achieved with a 500 nm thick thin film containing 0.56 mgPt · cm−2 of catalyst. magnified image

Experimental study of soot and temperature field structure of laminar co-flow ethylene–air diffusion flames with nitrogen dilution at elevated pressures

An experimental study has been conducted to investigate soot formation in laminar co-flow ethylene–air diffusion flames with nitrogen dilution from a co-flow circular nozzle at pressures from 10 to 35 atm. Spectral soot emission (SSE) diagnostic technique was used to determine the radially resolved soot and temperature field structure. Constancy of ethylene and nitrogen flow rates were maintained and the flow rates of ethylene and nitrogen were selected such that no smoke was emitted even at the highest soot loadings. The flame height, marked by visible flame radiation, remained constant at about 5.5 mm and the cross-sectional area of the flame decreased with increasing pressure. At 10 atm, the peak soot concentration of less than 8 ppm, was measured near the flame tip. At 35 atm, the peak soot concentration of about 62 ppm, was measured near the mid-height of the flame. The conversion of carbon in the fuel to soot was strongly dependent on pressure particularly in the lower pressure range. At higher pressure this dependence was weaker. The peak carbon conversion to soot, 6.5%, was observed at 30 atm and remained constant to 35 atm. Temperatures increased along the flame axis and the peak temperature was observed near the flame tip to indicate complete soot oxidation.

One‐Step Plasma Deposition of Platinum Containing Nanocomposite Coatings

AbstractIn this paper a single step process for the synthesis of composite thin films made of platinum nanoclusters embedded in a porous hydrocarbon matrix is proposed. The process consists of a simultaneous plasma enhanced‐chemical vapour deposition of ethylene and sputtering of a platinum target. Films were characterized by means of Fourier transform‐infrared spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy and transmission electron microscopy. Optical emission spectroscopy was used to investigate the plasma phase and to find correlations with the metal content of the film. The effect of radio frequency power, deposition time, and ethylene flow rate on the chemical composition and structure of the film is presented. Results show that the platinum content in the film can be controlled by tuning the power delivered to the plasma and the monomer flow rate, and that the metal aggregates in crystalline nanoclusters uniformly distributed in the material. Film morphology is characterized by columnar structures of variable diameter and orientation depending on the deposition conditions.magnified image

Study of Growth Kinetics of Ultra-Long Carbon Nanotube Arrays through Wall Number Statistical Investigation

AbstractThe unique properties of carbon nanotubes (CNTs) strongly depend on their structures. In this study, the growth kinetics of ultra-long multi-walled CNT (MWCNT) arrays by water-assisted chemical vapor deposition (WACVD) has been investigated based on the statistical studies of CNT wall number. It was found that the kinetics of MWCNT arrays in WACVD demonstrated a lengthening and thickening growth. In the linear lengthening stage, CNT wall number remains constant and catalysts preserve the activity; while in the thickening stage, CNTs thicken substantially through the gas phase-induced thickening process and catalysts start to deactivate. The effects of ethylene and hydrogen flow rates on the MWCNT array growth have also been studied. It was found that by changing ethylene flow rate, different linear lengthening stages corresponding to different CNT wall numbers could be obtained. These findings provide experimental solutions to fabrication MWCNT arrays with both selective heights and controllable wall numbers by WACVD.

Influence of Ethylene and Hydrogen Flow Rates on the Wall Number, Crystallinity, and Length of Millimeter-Long Carbon Nanotube Array

We studied the influence of ethylene and hydrogen flow rates on the properties of carbon nanotubes (CNTs) and synthesized millimeter-long carbon nanotube arrays (CNTAs) by optimizing the ethylene and hydrogen flow rates. Our results show that the wall number, crystallinity of the graphene sheets, and length of CNTs are greatly influenced by ethylene and hydrogen flow rates. Small ethylene flow or large hydrogen flow tends to synthesize CNTs with small diameters and few walls, and even single- and double-walled CNTs can be prepared by tuning the flow rates. These results indicate that that accurate regulation of carbon source and hydrogen flow rate, which is a simple and versatile method, enables selective synthesis of various types of CNTAs. The possible mechanism of the influence of ethylene and hydrogen flow rates on CNT growth is proposed and discussed for a better understanding of these phenomena.

Maximising carbon nanofiber and hydrogen production in the catalytic decomposition of ethylene over an unsupported Ni-Cu alloy

Abstract A Ni-Cu (4:1 wt/wt) metal alloy catalyst has been studied for the catalytic decomposition of ethylene to produce hydrogen and carbon nanofibers. To maximise ethylene conversion in a horizontal tube reactor with high residence times, hydrogen yields and selectivities, the temperature, sample mass and ethylene flow rate were varied. Both high ethylene conversions (>80%) and high hydrogen selectivities (75%) were obtained at 873 and 923 K. The highest coke yield obtained after just 3 h was around 480 gC/gNi+Cu at 873 K (86% ethylene conversion) and was significantly higher than the value of 250 gC/gNi+Cu which was previously reported as the maximum coke yield for the decomposition of ethylene over Ni-Cu catalysts at this temperature. At 923 K, the optimum conditions were achieved with 50 mg of Ni-Cu, which gave ethylene conversions of 74%, a hydrogen selectivity of 71%, hydrogen yields in excess of 4000 mo l H 2 / mo l Ni + Cu and even higher coke yields of 1112 gC/gNi+Cu after 15 h with the catalyst still possessing high catalytic activity. The Ni-Cu (4:1 wt/wt) catalyst behaved similarly to a Ni-Pd (4:1 wt/wt) catalyst, which suggests that unsupported Ni-Cu alloys can replace the more expensive Ni-Pd alloys for the catalytic decomposition of hydrocarbons. In addition, there were no obvious structural differences between the carbon nanofibers obtained with the Ni-Cu and Ni-Pd alloys, which were twisted, branched and straight nanofibers composed of crystalline and amorphous carbon with diameters ranging from 30 to 300 nm.

Structural control of icicle-like carbon nanotube forest in heterogeneous catalysis growth with high voltage corona discharge

Icicle-like carbon nanotube (CNT) forest, i.e., discrete bundles of CNTs in free standing forms, can be synthesized at a tip surface of tungsten wire via heterogeneous catalysis together with corona discharge in H 2–C 2H 4 mixture at atmospheric pressure. The influences of several parameters in the synthesis condition on the product structures were investigated. It was found that there was an optimized temperature-range to synthesize the icicle-like structure,400–600 °C, and the increase of temperature caused the increase of CNT-diameter. It was observed that the discharge current affected the straightness of CNTs. It was also found that the increase of the ethylene flow rate caused the increase of the height of the CNTs bundles. The lengths of CNTs bundles were limited even when their growth process was continued due to the limited lifetime of the catalyst.

The growth of carbon nanotube stacks in the kinetics-controlled regime

A CNT stack formation technique is used for the pseudo in-situ monitoring of CNT growth in the kinetics-controlled regime. CNT stacks are fabricated by water-assisted selective etching and the cyclic introduction of ethylene into the chemical vapor deposition (CVD) reactor. By varying the growth temperature and the ethylene flow rate within growth cycles, the reaction was shown to be first order with an activation energy of 201.2 kJ/mol. This technique can be implemented to monitor the initial stage of CNT growth by deceasing the ethylene flow time in growth cycles. Within one minute, the CNT growth reaches steady state. The formation of CNT stacks could be tailored to investigate the effects of growth parameters, such as pressure, temperature, and carbon source flow rate, on the CNT growth.