Gas Concentrator Research Articles

Determining the dynamics of carbon monoxide formation during gas welding processes

This paper reports a study of the air medium where welding processes take place, with special attention paid to the evolution of carbon monoxide (CO) in the working medium in the process of gas welding. Plots were constructed and polynomial dependences were obtained to show a change in the concentration of carbon monoxide in the air of the working area during gas welding. It was confirmed experimentally that the concentration of carbon monoxide exceeds the permissible sanitary and hygienic indicators MPC (20 mg/m3) during gas welding. As a result of the experiment, the effectiveness of the use of an additional device was proven, namely an umbrella gas concentrator, in order to capture welding gases that are formed during gas welding. It was established that the MPC is exceeded under certain working conditions and welding wire. The carbon monoxide formation during gas welding was analyzed; these processes were compared with electric arc welding. The mathematical dependences derived make it possible to assess the risks of the welders’ work and conclude that the electric arc welding is characterized by a much higher rate of CO evolution from the beginning of the welding process (8.5 mg/s), that speed then decreases over 20 s by 2 times (to 4.5 mg/s). In 90 s, the speed becomes constant, to 2 mg/s. In comparison, gas welding has almost the same rate of CO formation, namely 0.3–0.9 mg/s. By changing the types of welding wires used in gas welding and taking into consideration the type of material that needs to be welded (including the period of its use), it is possible to influence the volume of CO emissions entering the working area and an employee’s respiratory area

Gas Sensor Array Using a Hybrid Structure Based on Zeolite and Oxide Semiconductors for Multiple Bio-Gas Detection.

Semiconductor-type gas sensors, composed of metal-oxide semiconductors and porous zeolite materials, are attractive devices for bio-gas detection, particularly when used as bio-gas sensors such as electronic nose application. Previous studies have shown such detection can be obtained with a separate gas concentrator and a sensor device using zeolites and oxide semiconductors of WO3 nanoparticles. By applying the gas concentrator, porous molecular structures alter both the gas sensitivity and the selectivity, and even can be used to define the sensor characteristics. Based on such a gas sensor design, we investigated the properties of an array of three sensors made of a layer of WO3 nanoparticles coated with zeolites with different interactions between gas molecule adsorption and desorption. The array was tested with four volatile organic compounds, each measured at different concentrations. The results confirm that the features of individual zeolites combined with the hybrid gas sensor behavior, along with the differences among the sensors, are sufficient for enabling the discrimination of volatile compounds when disregarding their concentration.

Gas concentrator with an activated carbon adsorbent for breath analysis

Abstract The detection of volatile organic compounds (VOCs) in respired breath is important because it can serve as a non-invasive means for obtaining information regarding an individual’s health status and for diagnosing diseases. However, it is difficult to detect respired VOCs because the concentration is very low, i.e., on the order of ppt to sub-ppm. Current commercially available small-sized VOC detectors are unable to detect sub-ppm-level VOCs; thus, large-scale analytical equipment, such as gas chromatography systems and mass spectrometers, are required for breath analysis research. To realize practical application of the breath analysis method, performance measures, such as the selectivity and sensitivity of a small-sized VOC detector, must be improved. Here, we propose a gas concentrator for breath analysis and evaluate its adsorption and desorption performance. The gas concentrator concentrates the low level of VOCs in exhaled breath to a level that is detectable by commercial VOC detectors. In this study, we also considered the practicability of our proposed device in terms of collection convenience, storability, and transportability of the exhaled sample. We experimentally demonstrated that the gas concentrator could capture gas molecules without reducing the pressure of the gas. Furthermore, we demonstrated that the process of collecting the target gas molecules from a large amount of initially injected gas and subsequently transferring it to a small volume of carrier gas increased the gas concentration by at least 25 times. Consequently, the adsorption and desorption rates of the gas concentrator were found to reach approximately 90% and 70%, respectively. It is expected that the proposed gas concentrator can be combined with a gas analyzer or detector for breath analysis-based disease diagnosis.

Biochemical Gas Sensor and Gas Concentrator for Monitoring of Ethanol in Skin Gas

A high-sensitive biochemical gas sensor (bio-sniffer) with skin gas cell and gas concentrator for monitoring of ethanol gas concentration emanated from human skin was constructed and demonstrated. This biosensor measured the concentration of ethanol according to the fluorescence intensity change of nicotinamide adenine dinucleotide (NADH), which was produced by an enzymatic reaction of alcohol dehydrogenase. By introducing a gas concentrator using liquid nitrogen, we constructed a highly sensitive system for skin gas measurements. In order to measure skin gas using the bio-sniffer, we designed a measurement system for detecting concentrated gases by connecting the sensor with a gas concentrator and introducing concentrated skin gas to the sensing surface. The monitoring of low concentration of skin ethanol gas was realized after drinking based on alcohol metabolism.

Skin ethanol gas measurement system with a biochemical gas sensor and gas concentrator toward monitoring of blood volatile compounds

We developed a biochemical gas sensor (bio-sniffer) using the enzymatic reaction of alcohol dehydrogenase (ADH) to target ethanol in skin gas. By introducing a gas concentrator using liquid nitrogen, we constructed a highly sensitive system for skin gas measurements. The ethanol bio-sniffer was built from an optical-fiber probe employing an ADH enzyme membrane, an UV-LED light source for excitation, and a photomultiplier tube. Ethanol was measured by detecting the autofluorescence of the coenzyme NADH due to the enzymatic reaction of ADH. We established a system for measuring concentrated gases by connecting the sensor with a gas concentrator and introducing concentrated skin gas to the sensing surface. This suppressed diffusion of the concentrated gases to achieve maximum fluorescence intensity by optimizing the measurement system. The calibration curve from obtained peak values showed ethanol gas can be measured over 1–3100 ppb, which included skin gas concentrations during alcohol consumption. Finally, when applied to measurements of ethanol in skin gas following alcohol consumption, the output was found to be dependent on concentration, similarly to using standard gases. Consecutive measurements were possible using periodic sampling with 6-min intervals for 180 min of monitoring. Skin ethanol concentrations rose from 20 min after consuming the alcohol, exhibited a peak value of 25 ppb skin gas ethanol at around 60 min, and gradually declined. Thus, the system can be used for non-invasive percutaneous evaluation of human volatile organic chemicals in blood.

Carbon isotope fingerprinting palaeo fluid inclusion gases using a crushing-trapping technique

Carbon isotope fingerprinting has been widely used to study gas origin, maturity and gas-source correlations. However, natural gas accumulation in gas reservoirs can be affected by secondary alteration processes. In contrast, palaeo gases trapped in fluid inclusions (FIs) are free of any secondary alterations that may have occurred in the reservoir. FIs are normally less than 10 um in diameter, hence the gases trapped are at trace level amounts. An online crushing-trapping system has been developed in this study which enabled carbon isotope analyses of hydrocarbon gases which are normally in low concentrations. The crushing-trapping system mainly comprises of a gas-tight crusher and a gas concentrator interface module. The micro-trap is a critical part of the gas concentrator as it collects and concentrates all the released FI gases which results in sharp chromatographic peaks. This novel design is very sensitive, making it an increased challenge to obtain an acceptable blank before running samples. A clean blank is very important for such trace-level gas analysis. System blank results show that there are no hydrocarbon gases but trace amounts of CO2 (20 mV) detected in the blank. These trace amounts of CO2 in the blank have no influence on the carbon isotope calculation. It was found that no isotope fractionation was attributable to the cryo-trapping and subsequent thermal release from the trap but there is fractionation due to re-absorption onto the freshly crushed rock matrix (quartz or calcite) powder.Compound specific carbon isotope analysis of hydrocarbon gases (C1-C5 except M-C4) and CO2 released from a FI sample from the Cooper-Eromanga Basin was achieved for the first time as a proof of concept of the technique. Preliminary research on FI gases has been carried out in the Browse Basin, Australia.

Scattering Dynamics of Nitromethane and Methyl Formate on Highly Oriented Pyrolytic Graphite (HOPG)

The gas–surface scattering dynamics of nitromethane (CH3NO2) and methyl formate (HCOOCH3) on a highly oriented pyrolytic graphite (HOPG) surface have been investigated as part of a broader effort to evaluate the efficacy of a funnel-like neutral gas concentrator that has been proposed as a mass spectrometer inlet for the characterization of tenuous planetary atmospheres or plumes. Molecular beams of CH3NO2 and HCOOCH3 with incidence energies, Ei, of 106.5 and 98.8 kJ mol–1, respectively, were directed at the surface with incidence angles, θi, of 70, 45, and 30°. A rotatable mass spectrometer, employing electron-impact ionization, was used to collect angle-resolved time-of-flight (TOF) distributions of the molecules that scattered inelastically from the surface, allowing angular distributions of the scattered product flux and translational energy distributions at a given final angle, θf, to be obtained. The TOF distributions of the scattered products detected the parent ion mass-to-charge ratios and their respective dominant ion fragments were identical, indicating that CH3NO2 and HCOOCH3 fragmented in the ionizer of the detector and not while colliding with the surface. The scattering dynamics suggested that the parallel momentum of the molecules was conserved during impact with the surface. The translational energy and angular distributions of CH3NO2 and HCOOCH3 were identical when θi = 70°. For θi = 45 and 30°, the HCOOCH3 angular distributions were shifted to a slightly larger θf than the CH3NO2 distributions. The molecules scattered from the surface through impulsive scattering (IS) and quasitrapping (QT) pathways. The IS molecules retained a large fraction of their incidence translational energy when colliding with the surface. The QT molecules transferred more energy, but they did not come completely into thermal equilibrium with the surface before scattering into the vacuum. The QT molecules had a lobular angular distribution with a maximum flux far from the surface normal, indicating that they retained some memory of their incident conditions despite losing a significant amount of energy at the surface. The results presented in this article demonstrate that for Ei near 100 kJ mol–1, these molecules would not dissociate upon impact with the surfaces of a gas concentrator constructed of HOPG. Although the observed scattering dynamics suggest that such a concentrator could perform well for a variety of molecular species, accurate concentration factors are ultimately molecule-specific and determined by the details of the molecule–surface interaction potential.

Gas–Surface Scattering Dynamics Applied to Concentration of Gases for Mass Spectrometry in Tenuous Atmospheres

A concept for a passive neutral gas concentrator that facilitates the analysis of rarefied atmospheres using mass spectrometry on spacecraft has been developed. The efficiency of the concentrator depends strongly on gas–surface scattering dynamics between the incoming gas molecules and the concentrator surface. We conducted beam–surface scattering experiments using hyperthermal beams containing atomic and molecular oxygen with speeds of approximately 5500 m s–1, with angular and velocity resolution of the inelastically scattered O and O2, on gold thin film, SiO2, and highly oriented pyrolytic graphite (HOPG) surfaces, which were chosen as candidate concentrator surfaces. The results show clearly that atoms and molecules scattering from HOPG have the narrowest and most superspecular angular distributions with the least energy transferred to the surface. A test particle model, referred to as the Statistical Program for Aerodynamic and Radiation Pressure Coefficient Simulation, utilized the experimental resu...

Development of a test method using a VOC analyzer to measure VOC emission from adhesives for building materials

A volatile organic compound (VOC) analyzer is a portable device to measure the four main aromatic hydrocarbon gases: toluene, ethylbenzene, xylene and styrene. With the VOC analyzer, a semiconductor gas sensor eliminates the need for the carrier gas which is required for conventional gas chromatography. In addition, since the semiconductor gas sensor is supersensitive to gas components, it is not necessary to use a conventional gas concentrator or other complicated equipment. Compared with other measurement methods, the VOC analyzer is useful for measuring toluene, ethylbenzene, xylene and styrene in new buildings because of its ease in obtaining field results and repeating the test. For easy, fast and economic testing of total (TVOC) emission from adhesives used for building materials, we developed a test method using the VOC analyzer and compared its measurement of VOC emissions from building materials such as adhesives, paints and wood-based panels with that of the 20-l chamber method, which is the standardized test method in Korea. There was a good correlation between the TVOC emission concentrations determined by the VOC analyzer and the TVOC emission factor (EF) by the 20-l chamber. Based on this good correlation, the VOC analyzer is expected to gain widespread use in the manufacturing field application where a quick and easy test for VOC emission from adhesives for building materials is required. Furthermore, the VOC analyzer offers the potential to become an easier, faster and more economical technique than the currently used standard methods.

Measurement technique for inorganic chlorine gases in the marine boundary layer

A technique was developed to measure inorganic Cl gases in the marine boundary layer. The inlet inertially removed coarse aerosol (>1-μm diameter), and an in-line filter removed fine aerosol. A trace gas concentrator positioned downstream incorporated an acidic mist chamber which sampled HCl * (including HCl, NOCl, ClNO 2 , and ClNO 3 ), followed by an alkaline mist chamber which sampled Cl 2 * (including Cl - and a portion of HOCl). Mist solutions were analyzed by ion chromatography. Estimated detection limits for HCl * and Cl 2 * were 39 and 13 pptv, respectively

Chemical sensor research at the laboratory of applied physics in Linkoping

Various examples are presented to illustrate the interdisciplinary nature of chemical sensor research at the Linkoping Institute of Technology. At least three goals were followed-developing basic knowledge, developing new sensor ideas, and helping industry to solve specific sensor problems. Among examples presented are: the anaesthetic gas monitor called EMMA; a gas concentrator and separator for use in measuring very small quantities of halogenated hydrocarbons; H2-sensitive Pd-MOS structures for use in leak detection of buried cables and medical diagnostics.