High Carrier Gas Flow Research Articles

Comparative analytical characteristics of multicapillary chromatography columns with different capillary diameters

Straight gas chromatography multicapillary columns (MCC) with 40 µm diameter capillaries (hereafter – 40 µm MCC) have been known for quite a long time and are well studied; they are used in portable gas analyzers. Some chromatographic characteristics of 25 µm MCCs, which appeared relatively recently, were also studied, while commercially available 60 and 80 µm MCCs are poorly studied. In this work the main analytical characteristics of 60 and 80 µm MCCs were determined and compared with the characteristics of 25 and 40 µm MCCs. It was shown that the maximum specific efficiency of the columns decreased with increasing column capillary diameter and is approximately 24.8, 18.2, 13.7 and 9.5 thousand theoretical plates (t.p.) per meter for 25, 40, 60 and 80 µm MCCs, respectively. It was established that the height equivalent to a theoretical plate of 60 and 80 μm MCCs was not varied significantly over a wide range of carrier gas velocities (nitrogen and helium), which allowed operating MCCs at high carrier gas flows essentially without loss of their efficiency. Moreover, for all MCCs the separation rate for peaks with a retention factor over 10 exceeded 600 t.p./s, and for peaks with a lower retention factor could be several thousand t.p./s, which is significantly higher than for conventional capillary and packed columns. It was established that it was possible to create very high carrier gas flows (up to 1000 cm3/min or more) for 60 µm MCCs and especially 80 µm MCCs at a relatively low pressure drop across the column. Therefore they can work as a part of chromatographic systems that require high carrier gas flow.

Real-time monitoring of atomic layer etching in Cl2/Ar pulsed gas, pulsed power plasmas by optical emission spectroscopy

Optical emission spectroscopy was used as a real-time monitor of the atomic layer etching (ALE) of Si in an Ar inductively coupled plasma (ICP). Pulses of Cl2 gas were repetitively injected into a continuous flow of Ar, followed by the ignition of the ICP and the application of substrate rf bias power (either continuous or rapidly modulated). Optical emissions from Si, SiCl, SiCl2, Ar, and Cl were monitored along a line parallel and close to the substrate surface as a function of time during the bias period, as well as in the ICP without bias power. From an analysis of the time dependencies of the decays of emissions during the modulated bias periods, it is argued that emissions at high Ar carrier gas flow rates are mainly from the primary products sputtered by the energetic Ar ions. Products decay with different, non-exponential time signatures. Cl and SiCl2 emissions decay to nearly undetectable levels toward the end of the bias period. SiCl emission follows a decay profile between that of Si and SiCl2. The time-integrated SiCl2 emission intensity scales linearly with time and correlates with etching rates measured by laser interferometry. The amount of Si etched per ALE cycle and the degree of self-limiting evolution of etching products is a sensitive function of the timing between the initiation and termination of Cl2 flow into the reactor and the application of ICP power. Spatially resolved optical emission is shown to be a useful in situ diagnosis, providing mechanistic insights, as well as process optimization for plasma-assisted atomic layer etching. It is also shown that the emission bands between 360 and 400 nm that are commonly observed during Si etching in a chlorine-containing plasma and are often ascribed to SiCl3 or SiCl3+ are instead most likely the A2Σ → X2Πr system of SiCl.

Highly sensitive detection of polystyrene by on-line splitless pyrolysis-gas chromatography/mass spectrometry with cryo-trapping of pyrolyzates and forced venting of carrier gas

Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) has been extensively used as a powerful tool for polymer analysis. In Py-GC/MS measurements, GC methods have usually employed split injection conditions for qualitative and quantitative analysis, but splitless injection of pyrolyzates to GC/MS has been reported to obtain higher sensitivity for small amount of analytes, since split ratio is inversely related to the amount of analyte entering the detection systems. However, the slower total carrier gas flow rate of splitless injection, which is necessary to keep the column flow rate at around a few mL/min, can increase residence time in the pyrolysis chamber, which can cause unfavorable secondary reactions of pyrolyzates such as decomposition and recombination in the pyrolyzer. In this study, we developed a new on-line splitless Py-GC/MS method called the Forced-Venting-and-Trap-Splitless (F-Splitless) method, based on cryo-trapping of pyrolyzates and forced venting of carrier gas under high carrier gas flow rate. Calibration curves measured by the F-Splitless method for polystyrene (PS) using the styrene monomer and trimer as key compounds show a good linearity over the concentration range from 0.01 ng to 100 ng. Limit of detection (LOD) and limit of quantification (LOQ) were 17 pg and 56 pg for the styrene monomer (S) based on the criterion of LOD: 3σ/a and LOQ: 10σ/a, where a is the slope of the calibration curve and σ is the standard deviation of the peak area of the minimum concentration, using the selected ion monitoring (SIM) mode. At a trace concentration level of PS, contamination from the environment was recognized. However, 100 pg of PS showed a signal to noise ratio (S/N) of 570 for S in SIM mode and 1.8 pg of PS could be quantified according to the criterion of LOQ based on signal to noise ratio (S/N), i.e., S/N = 10.

Aerosol assisted atmospheric pressure plasma jet for a high deposition rate of silica-like thin films

This paper investigated thin films deposition processes of silica-like based on the injection of liquid droplets in Atmospheric Pressure Plasma Jet–APPJ operated in open air. An aerosol of hexamethyldisilane is produced by a syringe-pump and injected in a nitrogen post-discharge for different liquid precursor and carrier gas flow rates. For high carrier gas flow, this process enables to form silica-like without addition of oxygen in the plasma phase. Furthermore, this process offers a thin film dynamic deposition rate from 500 to 1400 nm.m.min−1 depending on the carrier gas flow and the film structure departs from silica-like to organosilicon layers for the lowest flow rates. These evolutions are attributed to plasma–droplets interactions related to the transport of droplets, the evaporation of liquid and plasma polymerization.

Low chlorine oil production through fast pyrolysis of mixed plastics combined with hydrothermal dechlorination pretreatment

Fast pyrolysis of the mixed plastics (PE: PP: PS: PVC = 0.5: 0.3: 0.15: 0.05) with and without hydrothermal dechlorination pretreatment were investigated in a fixed bed reactor to determine the effects of pyrolysis parameters (temperature, carrier gas flow rate and particle size) on the distribution and the quality of the products. The results showed that high pyrolysis temperature, high carrier gas flow rate and small particle size promoted the migration of organic chlorine in condensable products to inorganic chlorine in gas products. And the optimal conditions for fast pyrolysis of mixed plastics to produce oil were the pyrolysis temperature of 500 °C, carrier gas flow rate of 40 ml/min and particle size of 0.1–0.15 mm with the maximum oil yield of 67.88 wt%. Hydrothermal pretreatment of mixed plastics has shown an excellent dechlorination efficiency of 99.9 %. Furthermore, the total yield of oil and wax was increased by 7.06 wt%, meanwhile the content of C5-C9 components in the pyrolysis oil showed an upward trend when compared with fast pyrolysis without pretreatment. Besides, the concentration of methane achieved 50.68 % due to the possible weakening effect of hydrothermal pretreatment on CC bond energy of β-position.

Pyrolysing Horse Manure via Microwave-Induced Heating for Bioenergy Recovery

Transforming waste to energy is essential in view of the need to search for greener and more sustainable energy sources. Such transformation of energy is also aligned with the aim of reducing excessive waste generation whilst creating potential biofuel pathways for power generation. In the present study, animal waste in the form of horse manure is being used as feedstock to undergo microwave-induced pyrolysis via a fixed-bed pyrolysis rig. The relationship of the pyrolysis parameters such as pyrolysis temperature of 350 and 550 ?C, carrier gas flow rate of 0.5 and 1.5 L/min and ratio of horse manure to activated carbon blend of 1:2 and 1:1, with the yield of pyrolysed products is studied. The derived pyrolysis products in the form of solid, liquid and gaseous are characterised and quantified. Result shows that the highest yield of solid, liquid and gaseous products obtained are 78.8 wt%, 24.7 wt% and 34.2 wt%. Solid yield is observed to decrease with increasing pyrolysis temperature while gaseous yield shows a reverse trend. Higher carrier gas flow rate is observed to lower the generation of gaseous and liquid yield while increasing the solid yield. Higher amount of activated carbon within the feedstock is seen to lower the solid yield but increase the gaseous and liquid yields. The liquid yield is found to contain 55.78 wt% of phenolic compounds while gaseous product consists of up to 55 vol% of syngas. The control of the operating conditions in pyrolysis rig enables the production of pyrolysis end products in different phases, generating useful bioenergy and biofertilizer products in the context of circular economy.

Pyrolysis behavior of xylan-based hemicellulose in a fixed bed reactor

Investigation on the biomass components pyrolysis behaviors in a lab-scale reactor is a necessary step before its industrialization due to the poor transportability of the findings obtained from the micro-scale pyrolyzer which often neglects the heat and mass transfer effect. In present study, the pyrolysis behavior of xylan-based hemicellulose in a fixed bed reactor was investigated. The residue evolution and bio-oil composition of xylan, xylose, arabinose and glucose show the close relationship of pyrolysis characteristics between xylan and its components. It is noteworthy that the xylan and those mono-sugar units melted during pyrolysis, and many bubbles formed. Investigation of the effect of temperature, material thickness and carrier gas flow rate on the products distribution and bio-oil composition indicates that high temperature promotes the xylan conversion and increases the yield of bio-oil, however, if the temperature is too high (>500°C), violent decomposition of xylan occurs and leads to the formation of low molecular weight compounds (such as hydroxyl acetaldehyde, acetic acid and 1-hydroxyl-2-propaone etc.). And interestingly, the bio-oil yield increases monotonically with the material thickness, and thick material layer can increase the content of furfural in bio-oil. Carrier gas flow rate has a little influence on the xylan char yield, and relative high carrier gas flow rate (>2.55L/min) could decrease the secondary decomposition of primary didehydrated pentose but reduce the bio-oil yield.

Production of Syngas from Controlled Microwave-Assisted Pyrolysis of Crude Glycerol

Conversion of crude glycerol into synthesis gas was studied by using controlled microwave-assisted pyrolysis method. Pyrolysis of crude glycerol in the presence of carbonaceous catalyst was performed in a fixed bed reactor under oxygen-deficient environment using a domestic microwave. The effects of inert carrier gas flow rate and pyrolysis temperature on the product yield were investigated. Characterisation of the gaseous product showed that hydrogen, methane and carbon dioxide are the main components in the gaseous product. High temperature and low inert carrier gas flow rate are effective in pyrolysing crude glycerol due to sufficient energy and residence time for complete cracking of vapour into small gaseous molecules. Peak hydrogen yield of 35.2% by volume was obtained at the carrier gas flow rate of 100 mL/min and 600 °C.

Controlled vapour-phase deposition synthesis and growth mechanism of Bi2Te3 nanostructures

This work presents a study on the controlled growth and the growth mechanism of vapour-phase deposited two-dimensional Bi2Te3 nanostructures by investigating the influence of growth conditions on the morphology of Bi2Te3 nanostructures. The formation of a hexagonal plate geometry for Bi2Te3 nanostructures is a consequence of the large difference in growth rate between crystal facets along 〈0001〉 and 〈112¯0〉 directions. Under low Ar carrier gas flow rates (60–100 sccm), the growth of Bi2Te3 nanoplates occurs in the mass-transport limited regime, whereas under high carrier gas flow rates (130 sccm), the growth of Bi2Te3 nanoplates is in the surface-reaction limited regime. This leads to an increase in the lateral size of Bi2Te3 nanoplates with increasing the Ar carrier gas flow rate from 60 to 100 sccm, and a decrease in size for a flow rate of 130 sccm. In addition, the lateral size of Bi2Te3 nanoplates was found to increase with increasing growth time due to the kinetic characteristics of material growth. The proposed growth model provides an effective guide for achieving controlled growth of Bi2Te3 nanoplates, as well as other two dimensional nanomaterials.

Characterization of core-shell structured Ni@GDC anode materials synthesized by ultrasonic spray pyrolysis for solid oxide fuel cells

Core-shell structured NiO@GDC powders with NiO cores and GDC shells were synthesized by ultrasonic spray pyrolysis (USP) with a four-zone furnace. The morphology of the as-synthesized powders can be modified by controlling parameters such as the precursor pH, carrier gas flow rate, and zone temperature. At high carrier gas flow rates, the as-synthesized core-shell structured NiO@GDC powders have raisin-like morphology with a rough surface; this is due to fast gas exhaustion and insufficient particle ordering. The core-shell structured Ni@GDC anode showed considerable electrochemical performance enhancement compared to the conventionally-mixed Ni-GDC anode. The polarization resistance (Rp) of conventionally-mixed Ni-GDC anodes increases gradually as a function of the operation time. Alternatively, the core-shell structured Ni@GDC anode synthesized by USP does not exhibit any significant performance degradation, even after 500h of operation. This is the case because the rigid GDC ceramic shell in the core-shell structured Ni@GDC may restrain Ni aggregation.

Growth of InAs nanowires with the morphology and crystal structure controlled by carrier gas flow rate

We report on the growth of single crystal InAs nanowires on Si/SiOx substrates by chemical vapor deposition (CVD). Both pure zincblende InAs nanowires and twin superlattice InAs nanowires are produced. We demonstrate that the morphology and crystal structure of these nanowires can be controlled by tuning the H2 carrier gas flow rate in a CVD furnace and show that highly selected growth of twin superlattice nanowires are achieved at high carrier gas flow rates. Our work provides a new route to grow and phase-engineer single crystal InAs nanowires for a wide range of potential applications.

PEMBUATAN NANOPARTIKEL SENG OKSIDA (ZNO)MENGGUNAKAN PROSES FLAME ASSISTED SPRAY PYROLYSIS (FASP)

<p>Abstract: ZnO nanoparticles have been succesfully produced using Flame Assisted Spray<br />Pyrolysis (FASP) method. Burner type was a premixed flame reactor that used LPG as a fuel<br />and air as oxidizer because of an economical point of view. Zn(NO<br />3<br />)2<br />was used as a precursor<br />source for ZnO nanoparticles production. The flow rates of carrier gas during ZnO nanoparticles<br />fabrication were 5 L/menit, 7 L/menit, and 9 L/menit. To get the information about size and<br />shape of ZnO nanoparticles was characterized using Scanning Electron Microscope (SEM) and<br />X-Ray Diffractometry (XRD). The results showed that the higher carrier gas flow rate, the bigger<br />size of ZnO nanoparticles. By using the flow rate of carrier gas at 5 L/min, the mean size of ZnO<br />nanoparticles was about 80 nm. ZnO nanoparticles at carrier gas of 5 L/min were hexagonal<br />zincite crystalline structure and XRD were about 30,62 nm<br />Keywords: Flame Assisted Spray Pyrolysis, nanoparticles, ZnO, LPG, SEM, XRD</p>

Improved GC/ECNI-MS sensitivity of decabromodiphenyl ether determination on 30 m columns by increasing the carrier gas flow after a modified gel permeation chromatographic cleanup protocol employing cyclohexane/ethyl acetate as eluent

BDE-209 is the predominant constituent of the commercial mixture decabromodiphenyl ether which is used as brominated flame retardant (BFR). Owing to difficulties associated with the high mass (thermal instability and low vapour pressure), short GC columns (≤15 m) have been suggested for its analysis while longer columns (30–50 m) are suggested for other polybrominated diphenyl ether (PBDE) congeners. To overcome this considerable expenditure in the analysis of PBDEs, we aimed at increasing the sensitivity of BDE-209 analysis by gas chromatography coupled with electron-capture negative ion mass spectrometry (GC/ECNI-MS) on a 30 m column. The chromatographic performance of BDE-209 on the 30 m GC column was improved by increasing the carrier gas flow from initially 1.2 mL min−1 to 5 or 10 mL min−1 after the last octabromo diphenyl ether (Br8DE) congener was eluted. With this high carrier gas flow, the column residence time of BDE-209 was shortened by ∼25%, the peak height was increased and, consequently, the limit of detection by GC/ECNI-MS in selected ion monitoring (SIM) mode was improved. When this high-flow GC/ECNI-MS-SIM method was applied to a sediment sample, we realized that gel permeation chromatography (GPC) – used for the removal of lipids and/or sulphur – provided low recovery rates for BDE-209. The large molecule BDE-209 eluted late and only 50% was recovered by our previous standard protocol for polyhalogenated compounds. Application of a modified GPC procedure with a longer collection time increased the recovery of BDE-209 in the GPC step to ∼90%.

Evaluation of TiO<sub>2</sub> Films Fabricated by Aerosol Deposition

Films of titanium dioxide (TiO2) were deposited by aerosol deposition at room temperature. Anatase TiO2 powders were used. The crystal structure of these films was a mixture of the anatase and brookite TiO2 phases, while the rutile TiO2 phase was observed at high carrier gas flow rates. The TiO2 film thickness increased in proportion with the scan time and the carrier gas flow rate. Film thickness was constant at constant total deposition times. Flake-like and mesh-like surface morphologies were observed on the films. The direct-current resistivity was estimated from the dielectric constant and the loss tangent; it was found to be much smaller than that of bulk TiO2. We speculate that this low resistivity is due to reduction of TiO2 particles during room-temperature impact consolidation in a N2 atmosphere.

Hydrodeoxygenation of Guaiacol, A Surrogate of Lignin Pyrolysis Vapors, Over Iron Based Catalysts: Kinetics and Modeling of the Lignin to Aromatics Integrated Process

Biosourced aromatics (BTX (benzene, toluene, xylene) and phenols) could be produced by lignin pyrolysis coupled with catalytic hydrodeoxygenation (HDO) of uncondensed pyrolysis vapors. Guaiacol is used as a model compound to study the catalytic HDO over Fe/SiO2 catalyst. Experiments were conducted in a fixed bed reactor operated at 673 K (1 atm) with a gas mixture (guaiacol, H2, H2O, CO, CO2) that mimics the real gas composition from lignin pyrolysis. Fe/SiO2 catalyst was shown to be selective for guaiacol HDO into benzene and phenols because it does not catalyze the aromatic ring hydrogenation. Major and minor products are modeled by a semidetailed kinetic mechanism. A deactivation law is also determined. The kinetic model is then included in an Aspen Plus model of lignin to BTX process. Aspen Plus model handles (1) pyrolysis of lignin, including char, oligomers, gases and aromatic yields, (2) catalytic conversion of aromatics by the kinetic model, (3) heat exchangers, and (4) BTX vapors recovery by scrubbing with 1-methyl-naphthalene. Mass and carbon balances, heat demand, and selectivity in desired products are given for the overall process. The effect of gas dilution from pyrolysis reactor on BTX losses, heat demand, and scrubbing solvent flow rate is highlighted. High carrier gas flow rates (as required for biomass pyrolysis in fluidized bed) lead to the entrainment of fines and oligomers, dilute the products, and impact considerably the process intensification.

Vapor phase alkylation of toluene using various alcohols over H3PO4/MCM-41 catalyst: Influence of reaction parameters on Vapor phase alkylation of toluene using various alcohols over H_3PO_4/MCM-41 catalyst: influence of reaction parameters on selectivity and conversion

A mesoporous MCM-41 molecular sieve material with a molar ratio of SiO_2/Al_2O_3 = 70 and loaded with H_3PO_4 was used as a catalyst for the alkylation of toluene, using various alcohols, namely methanol, iso-propanol, and tert-butanol, as alkylating agents. Para-alkylated toluene was the predominant product, formation of which was enhanced by moderate temperature, low amounts of the alkylating agents in the feed, and high carrier gas flow rate. Time on stream was found to exert a profound effect on the selectivity and conversion to the different products.

Development of a Micropyrolyzer for Enhanced Isotope Ratio Measurement

This paper presents design, fabrication, and testing of a microscale ceramic reactor for the pyrolysis of organic compounds. One application for this pyrolysis reactor is to convert the oxygen and hydrogen atoms in organic compounds to CO and H2 for isotope ratio measurements in a continuous flow mode. Existing commercial pyrolyzers use high carrier gas flow rates (typically 80−100 mL/min) such that >95% of the CO and H2 produced from a given sample is vented before introduction into the mass spectrometer. We describe here the fabrication and testing of a microscale pyrolysis reactor designed to be compatible with existing isotope ratio mass spectrometers. The microreactor uses carrier gas flow rates of 3−5 mL/min, decreasing the proportion of the CO and H2 lost in venting and permitting analysis of samples 20−50 times smaller than can be analyzed with conventional pyrolysis reactors. Results have shown that organic compounds, such as 1-butanol, ethanol, and ethanolamine, can be fully decomposed to desire...

Gas chromatography‐mass spectrometry with supersonic molecular beams

Gas chromatography-mass spectrometry (GC-MS) with supersonic molecular beams (SMBs) (also named Supersonic GC-MS) is based on GC and MS interface with SMBs and on the electron ionization (EI) of vibrationally cold analytes in the SMBs (cold EI) in a fly-through ion source. This ion source is inherently inert and further characterized by fast response and vacuum background filtration capability. The same ion source offers three modes of ionization including cold EI, classical EI and cluster chemical ionization (CI). Cold EI, as a main mode, provides enhanced molecular ions combined with an effective library sample identification, which is supplemented and complemented by a powerful isotope abundance analysis method and software. The range of low-volatility and thermally labile compounds amenable for analysis is significantly increased owing to the use of the contact-free, fly-through ion source and the ability to lower sample elution temperatures through the use of high column carrier gas flow rates. Effective, fast GC-MS is enabled particularly owing to the possible use of high column flow rates and improved system selectivity in view of the enhancement of the molecular ion. This fast GC-MS with SMB can be further improved via the added selectivity of MS-MS, which by itself benefits from the enhancement of the molecular ion, the most suitable parent ion for MS-MS. Supersonic GC-MS is characterized by low limits of detection (LOD), and its sensitivity is superior to that of standard GC-MS, particularly for samples that are hard for analysis. The GC separation of the Supersonic GC-MS can be improved with pulsed flow modulation (PFM) GC x GC-MS. Electron ionization LC-MS with SMB can also be combined with the Supersonic GC-MS, with fast and easy switching between these two modes of operation.

Study of Injection Angle and Carrier Gas Flow Rate Effects on Particles In-Flight Characteristics in Plasma Spray Process: Modeling and Experiments

This paper investigates the influence of particle injection angle on particle in-flight behaviors and characteristics at different primary and carrier gas flow rates through an integrated modeling and experimental approach. Particle in-flight status such as temperature, velocity, size and their distribution are analyzed to examine particle’s melting status before impact. Results from the experiments and numerical simulations both show that, when carrier gas flow rate is fixed, a small injection angle favors the particle melting and flattening. This behavior is independent of primary and secondary gas flow rates, spray distance and carrier gas flow rate. When both carrier gas flow and injection angle vary, a high carrier gas flow rate and a small injection angle are recommended for high particle temperature and velocity.

Chemical Vapor Deposition of Silicon Carbide Epitaxial Films and Their Defect Characterization

A chemical vapor deposition (CVD) system was designed and fabricated in our laboratory and SiC homo-epitaxial layers were grown in the CVD process using silicon tetrachloride and propane precursors with hydrogen as a carrier gas. The temperature field was generated using numerical modeling. Gas flow rates, temperature field, and the gradients are found to influence the growth rates of the epitaxial layers. Growth rates were found to increase as the temperature increased at high carrier gas flow rate, while at lower carrier gas flow rate, growth rates were observed to decrease as the temperature increased. Based on the equilibrium model, “thermodynamically controlled growth” accounts for the growth rate reduction. The grown epitaxial layers were characterized using various techniques. Reduction in the threading screw dislocation (SD) density in the epilayers was observed. Suitable models were developed for explaining the reduction in the SD density as well as the conversion of basal plane dislocations (BPDs) into threading edge dislocations (TEDs).