Methanol Vapor Concentration Research Articles

Encapsulation of a novel D-A phenothiazine derivative in ZIF-8 for luminescent response to organic solvents vapor

A donor-acceptor (D-A) phenothiazine derivative(PZQ) was designed and synthesized. The PZQ was characterized utilizing infrared (FTIR) and 1H/13C nuclear magnetic resonance. The fluorescence spectra of PZQ were investigated in various solvents with differing polarities to demonstrate the presence of positive solvatochromism was attributed to the intramolecular charge transfer. It was observed that the Stokes’ shifts increased proportionally with the polarity of the solvents, exhibiting a maximum value of 11420 cm−1 in the highly polar solvent (ACN). Moreover, a porous composite (PZQ@ZIF-8) was fabricated by encapsulating PZQ into the metal-organic framework (ZIF-8) to respond to the organic solvent vapors. The PZQ@ZIF-8 was characterized using infrared, X-ray diffraction (XRD). The fluorescence spectra of the PZQ@ZIF-8 displayed significant solvent-dependent emission. Most importantly, the PZQ@ZIF-8 exhibited high reusability, and a specific response to methanol vapor. The emission intensity of the PZQ@ZIF-8 was correlated with methanol vapor concentration negatively, which was essential for the practical sensing application.

Water and heat management of vapor-fed direct methanol fuel cells with a non-isothermal triple-phase mass transfer model

Direct methanol fuel cells (DMFCs) operating with methanol vapor tends to operate under higher temperature, which contributes to improve cell performance and specific energy. However, the design of vapor-fed DMFCs with high performance and adaptability are still hindered by the complex water and heat management. To provide a comprehensive understanding of the critical multiphase heat and mass transfer, we develop a two-dimensional non-isothermal triple-phase mass transfer model for a passive vapor-fed DMFC. Effects of the electrochemical reactions and related thermal effect are fully investigated. Increasing the current density raises the operating temperature, thus enhancing the generation rate of methanol vapor and reducing concentration polarization under high current densities. With the enlargement of the open area ratio (from 0.1 to 0.3), an excessive methanol supply rate may cause deteriorated methanol crossover rates and excessively high temperatures, resulting in severe dehydration of polymer electrolytes and a degraded cathode overpotential (from −0.48V to −0.54V). For the DMFC with Nafion 112 membrane, the maximum current density and peak power density are 33.3% and 36.0% greater than that of Nafion 117 membrane. The simulation work will provide an exhaustive theoretical guidance for the efficient management of water and heat in DMFCs fed with neat methanol.

A Low-Power MEMS IDE Capacitor with Integrated Microhotplate: Application as Methanol Sensor using a Metal-Organic Framework Coating as Affinity Layer.

Capacitors made of interdigitated electrodes (IDEs) as a transducer platform for the sensing of volatile organic compounds (VOCs) have advantages due to their lower power operation and fabrication using standard micro-fabrication techniques. Integrating a micro-electromechanical system (MEMS), such as a microhotplate with IDE capacitor, further allows study of the temperature-dependent sensing response of VOCs. In this paper, the design, fabrication, and characterization of a low-power MEMS microhotplate with IDE capacitor to study the temperature-dependent sensing response to methanol using Zeolitic imidazolate framework (ZIF-8), a class of metal-organic framework (MOF), is presented. A Titanium nitride (TiN) microhotplate with aluminum IDEs suspended on a silicon nitride membrane is fabricated and characterized. The power consumption of the ZIF-8 MOF-coated device at an operating temperature of 50 C is 4.5 mW and at 200 C it is 26 mW. A calibration methodology for the effects of temperature of the isolation layer between the microhotplate electrodes and the capacitor IDEs is developed. The device coated with ZIF-8 MOF shows a response to methanol in the concentration range of 500 ppm to 7000 ppm. The detection limit of the sensor for methanol vapor at 20 C is 100 ppm. In situ study of sensing properties of ZIF-8 MOF to methanol in the temperature range from 20 C to 50 C using the integrated microhotplate and IDE capacitor is presented. The kinetics of temperature-dependent adsorption and desorption of methanol by ZIF-8 MOF are fitted with double-exponential models. With the increase in temperature from 20 C to 50 C, the response time for sensing of methanol vapor concentration of 5000 ppm decreases by 28%, whereas the recovery time decreases by 70%.

Effect of carbon derivatives in sulfonated poly(etherimide)–liquid crystal polymer composite for methanol vapor sensing

A class of highly sensitive chemiresistive sensors is developed for methanol (MeOH) vapor detection in ambient atmosphere by introducing conductive nanofillers like carbon black, multi-wall carbon nanotubes, and reduced graphene oxide into sulfonated poly(etherimide) (PEI)/liquid crystal polymer (LCP) composite (sPEI-LCP). Polar composites are prepared by a sulfonation process for instantaneous enhancement in adsorption capability of the sensing films to the target analyte (MeOH). Sensing properties exhibit that polymer composite-based fabricated sensors are efficient for the detection of different concentration of methanol vapor from 300–1200 parts-per-million (ppm) at room temperature. The incorporation of nanofiller induces the dramatic change in sensing behavior of base composite film (sPEI-LCP). Thus, less mass fraction of nanofillers (i.e. 2 wt%) influences the nonlinear sensing behavior for the entire range of methanol vapor. The simple method and low fabrication cost of the prepared sensor are compelling reasons that methanol vapor sensor is suitable for environmental monitoring.

Sensor for volatile organic compounds using an interdigitated gold electrode modified with a nanocomposite made from poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) and ultra-large graphene oxide

A highly efficient gas sensor is described based on the use of a nanocomposite fabricated from poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) and ultra-large graphene oxide (UL-GO). The nanocomposite was placed by drop casting in high uniformity on interdigitated gold electrodes over a large area of silicon substrate and investigated for its response to volatile organic compounds (VOCs) at room temperature. Monolayers of UL-GOs were synthesized based on a novel solution-phase method involving pre-exfoliation of graphite flakes. The nanocomposite was optimized in terms of composition, and the resulting vapor sensor (containing 0.04 wt% of UL-GO) exhibits strong response to various VOC vapors. The improved gas-sensing performance is attributed to several effects, viz. (a) an enhanced transport of charge carriers, probably a result of the weakening of columbic attraction between PEDOT and PSS by the functional groups on the UL-GO sheets; (b) the increase in the specific surface area on adding UL-GO sheets; and (c) enhanced interactions between the sensing film and VOC molecules via the network of π-electrons. The sensitivity, response and recovery times of the PEDOT-PSS/UL-GO nanocomposite gas sensor with 0.04 wt% of UL-GO are 11.3 %, 3.2 s, and 16 s, respectively. At a methanol vapor concentration as low as 35 ppm, this is an improvement by factors of 110, 10, and 6 respectively, compared to a PEDOT-PSS reference gas sensor without UL-GO.

Pure and Iso-Butyl Methyl Ketone Treated Multi-Walled Carbon Nanotubes for Ethanol and Methanol Vapor Sensing

Multi-walled carbon nanotubes (MWCNTs) coated intensity modulated fiber optic sensor for the detection of ethanol and methanol vapors at room temperature is reported. Pure, 30 and 60 min iso-butyl methyl ketone (IBMK) treated MWCNT were coated on cladding removed polymethyl methacrylate fiber by the dip coating technique. The pure and IBMK treated MWCNT coated fibers were used as sensors. Response of the sensors was studied by measuring the change in output light intensity for different methanol and ethanol vapor concentrations in the range of 0-500 ppm. The 60 min IBMK treated MWCNT coated sensor showed 2 and 3.4 fold increase in the sensitivity for methanol and ethanol vapors at 640 and 630 nm wavelengths light, respectively, compared with the pristine MWCNT coated sensor. Fourier transform infrared spectroscopy confirmed the attachment of C=O functional group in IBMK treated MWCNT. Thermogravimetry results reveal the functionalized nanotubes decomposed at 475 °C after the elimination of attached functional groups. The pristine nanotubes start to decompose at 540 °C. The randomly oriented nanotubes layer of average thickness 1.5 μm on the cladding modified fiber is observed from scanning electron microscope images.

Calixarene Molecules Immobilized on Gold Substrates of QCM Sensors Based on Self-Assembled Monolayer Technology

Four calixarene supramolecular compounds, RCT, PCT, MRCT, and TBCA as active materials, were immobilized on gold substrates of quartz crystal microbalance (QCM) sensors by using L-cysteine self-assembled monolayer (SAM) as a linker. The RCT immobilized QCM sensor possessed the best response characteristics for methanol molecule when the assembling concentration of RCT reached 1.0 mg/mL. The frequency shift response value of the RCT immobilized QCM sensor was in direct proportion to the concentration of methanol vapor with a range of 0 ~ 6000 ppm. Comparing with a gas chromatography, the proposed QCM sensor could be well used for the determination of methanol vapor with a recovery rate of 98.01 ~ 103.9 %, and the two methods showed a well consistent examination result. Also, the sensor possessed good reproducibility and stability, showing that the RCT immobilized QCM sensor can be applied for the detection of the methanol vapor of atmospheric polutants in our living environment.

Coupling aerobic biodegradation of methanol vapors with heterologous protein expression of endochitinase Ech42 from Trichoderma atroviride in Pichia pastoris

Methanol is included among the most hazardous air pollutants, and an effort of vapors biofiltration by using microbial consortiums has been reported. The aim of this work was to couple the methanol vapors biodegradation with the production of recombinant endochitinase (ech42) from Trichoderma atroviride in Pichia pastoris transformed with the pPIC-ech42 plasmid. After carrying out batch experiments at 0.5% (w/v) of methanol concentration, the recombinant P. pastoris Mut(+) strain was selected because it showed methanol biodegradation rates similar to those of wild type GS115 strain (39 g/m(3)h), but 15% higher than the transformed Mut(S) strain. In addition, the recombinant Ech42 protein production was higher in Mut(+) than Mut(S). After various methanol vapor concentrations were evaluated, the maximum recombinant protein recovery was 317 mg/l and the volumetric methanol consumption rate was 88.7 g/m(3)h at 0.5% (w/v) of methanol concentration. This research underlines the promising application of linking methanol vapors biodegradation with the production of recombinant protein with high biotechnological interests.

An ITO/Au/ITO Thin Film Gas Sensor for Methanol Detection at Room Temperature

Indium tin oxide (ITO) films with a 5 nm thick Au interlayer were prepared on glass substrates. The effects of the Au interlayer on the gas sensitivity for detecting methanol vapors were investigated at room temperature. The conductivity of the film sensor increased upon exposure to methanol vapor and the sensitivity also increased proportionally with the methanol vapor concentration. In terms of the sensitivity measurements, the ITO film sensor with an Au interlayer shows a higher sensitivity than that of the conventional ITO film sensor. This approach is promising in gaining improvement in the performance of ITO gas sensors used for the detection of methanol vapor at room temperature.

Composition of Vapor and Liquid Phases in the Potassium Hydroxide + Methanol Reaction System at 25 °C

The composition of the vapor and liquid phases of the KOH + CH3OH system has been studied by the gas chromatography (GC) method at 25 °C. It has been found that the methanol vapor concentration, and the quantity of potassium methoxide formed as a result of the acid–base reaction of potassium hydroxide with methanol, both depend on the KOH/CH3OH mole ratio. The maximum mass fraction of potassium methoxide that forms is 2.6% at the mole ratio 0.018.

Real-time, In situ Measurement of Fuel and Crossover Methanol Vapor Concentration of a Vapor-Fed Passive Direct Methanol Fuel Cell Using Laser Absorption Spectroscopy

The concentration of methanol vapor in a vapor-fed direct methanol fuel cell (DMFC) is measured using absorption spectroscopy with a 3.39 µm He–Ne laser. A noise correction method is applied to compensate for the higher noise levels associated with the He–Ne laser. Based on this, real-time, in situ measurement of the methanol vapor concentration has been performed simultaneously in a methanol vapor transport layer and on the cathode surface (air transport layer) under various DMFC operating conditions. The change in methanol vapor concentration and cell performance is measured at various galvanostatic conditions and the impact of methanol concentration in the methanol transport layer on the methanol crossover amount is analyzed. Moreover, the changes of methanol vapor concentration are measured when the fuel supply is suspended during fuel cell operation. No previous method has been able to measure the concentration of the methanol vapor in the methanol transport layer and the air transport layer in real-time with noncontact. The results from this study can contribute to the development of stable and high-power vapor-fed DMFCs.

Measuring Methanol Concentrations in a Vapor-Fed Direct Methanol Fuel Cell Using Laser Absorption Spectroscopy

Gas-phase absorption spectroscopy using a He–Ne laser enables the concentration of methanol vapor in a vapor-fed direct methanol fuel cell (DMFC) to be measured in real-time and in situ once high noise levels of the laser are corrected. The changes that methanol vapor concentrations bring to cell performance can be measured under various galvanostatic and potentiostatic conditions and analyzed with regard to methanol crossover and methanol transport capability. The absorption coefficient of +methanol vapor, , is nearly constant under the DMFC operating conditions at a wavelength of .

Improving the monitoring of methanol concentration during high cell density fermentation of Pichia pastoris

The Pichia pastoris expression system is widely used for the production of recombinant proteins. A simple and efficient experimental set-up allowing on-line monitoring of the methanol concentration during the fermentation of P. pastoris based on the detection of the methanol vapor concentration in the exhaust air from fermenter by a tin dioxide (SnO2) semiconductor sensor is described. An experimental procedure to allow precise calibration of the system and to reduce methanol sensor's interferences (>95% reduction) are also presented and discussed. Accuracy and measurement error were estimated about 0.05 g x l(-1) and 6%, respectively. The efficient monitoring of methanol will help to advanced control of recombinant protein production and process optimization.

Effect Of Combustible Vapors In Air On Extinction Of Cup Burner Flames By Hfc And Fc Fire Suppressants

HFC and FC agents were developed as replacements of halon 1301 (CF3Br), however, some fluorohydrocarbons decrease the lower flammability limits of combustible gases and vapors. To use trifluoromethane (CF3H), 1,1,1,2,3,3,3 heptafluoropropane (CF3CFHCF3), and perfluorobutane (CqF10) as the replacements safely in plants containing combustible vapors, cup-burner flame extinguishing concentrations of the agents, halon 1301, and nitrogen for nheptane flames were investigated as functions of concentration of methane or methanol vapor in air. The following conclusions have been obtained: (1) When the air contains a combustible less than the lower flammability limit, blue flame appeared around n-heptane diffusion flame by addition of the HFC and FC agents in air. Such flame did not appear through the addition of CF3Br and nitrogen. (2) Methanol vapor in air increased the flame extinguishing concentrations of all agents when increasing the vapor concentration, while methane did not affect the flame extinguishing concentrations of all the agents until the blue flame was formed. (3) If a combustible vapor is mixed in the air of a space protected by a total flooding fire extinguishing system employing the HFC or FC agenf a design concentration determined by the flame extinguishing concentration is not always sufficient to extinguish fires in the space. An inerting concentration may be desirable for the design concentration in such case.

Methanol sensors based on the conductive polymer composites from polypyrrole and poly (vinyl alcohol)

Methanol sensors based on polypyrrole-poly(vinyl alcohol) (PPy-PVA) composite films were prepared electrochemically with various charges, ranging from 0.05 to 0.20 C. The sensing abilities, including sensitivity, response time and recovery time, to various methanol-vapor concentrations, ranging from 15 to 218 mg l −1, were investigated. The methanol-sensing ability was dependent on the electropolymerization charge and was better if a lower charge was applied. A sensitivity of 9.70 mΩ mg l −1, about nine times the sensitivity of the pristine PPy sensor, was measured by the PPy-PVA sensor prepared at 50 mC.The PPy-VA composite sensors responded as quickly as 33 s in a methanol concentration of 218 mg l −1. PVA loading in the electrolytic solution showed an effect on the sensitivity of the sensor and exhibited an order of 7.5 g l −1 >5.0 g l −1 > 10.0 g l −1> 1.0g l −1> pure PPy. However, we also found that the stability of the PPy-PVA composite sensor under exposure to methanol vapor was poorer than that of the pure PPy sensor.

Transient two-dimensional fuel-concentration measurement technique

We propose a nonintrusive experimental technique, the transient fuel-concentration measurement technique (TFMT), that is capable of being used to measure two-dimensional profiles of transient fuel concentrations over an open liquid fuel surface. The TFMT is based on single-wavelength holographic interferometry; its response time is less than 1 mus and spatial resolution is 0.1 mol. %/0.1 mm. It was applied to measure both methanol vapor and n-propanol vapor concentrations. To assess the accuracy of the technique, our results were compared with steady-state methanol and n-propanol fuel-vapor concentrations measured by other researchers with a microsampling technique combined with gas chromatography. We found the TFMT to be accurate for on-line monitoring of two-dimensional profiles of fuel-vapor concentrations.

Modeling of turbulent spray diffusion flames including detailed chemistry

This investigation concerns turbulent methano/air spray diffusion flames. Standard spray and turbulence models are used to describe both nonreacting and reacting sprays in a two-dimensional, steady jet. The flames investigated lie well within the diffusion flamelet regime of the Peters diagram, and the standard flamelet model is modified to account for the fuel evaporation. Thus, the model is suitable to predict formation of both radicals and pollutants. The precalculated flamelet libraries for methanol comprise 23 species and 168 elementary reactions. A comparison with experiment shows reasonable agreement for flame characteristics except for the mass fraction of methanol vapor, which is sensitive to the spray model. In particular, the number of droplet parcel affects the Sauter mean radius of the spray, and the droplet distribution within the parcels strongly influences the width of the profile of the methanol vapor concentration. Both the experiments and the computations identify two reaction zones. The first one close to the injector or the centerline, respectively, stems, from the combustion of quickly evaporated small droplets. Gas temperature, decreases where the vaporization zone is located, and the second gas-temperature peak identifies the main reaction zone. The profiles of the combustion products follow the gas-temperature profile and peak at the stoichiometric value of the mixture fraction.

Comparative Toxicokinetics of Inhaled Methanol in the Female CD-1 Mouse and Sprague-Dawley Rat

Comparative Toxicokinetics of Inhaled Methanol in the Female CD-1 Mouse and Sprague-Dawley Rat. Perkins, R. A., Ward, K. W., and Pollack, G. M. (1995). Fundam. Appl. Toxicol. 28, 245-254.Female CD-1 mice were exposed for 8 hr, both individually and in groups of eight to nine, to 2500, 5000, and 10,000 ppm methanol vapor in a flowthrough exposure chamber. The ventilation of individually exposed mice and the absorption of methanol from the chamber airstream were measured. The extraction of methanol from the airstream and the blood methanol concentration at various time points during and following exposure were determined for the group-exposed mice. The similarity of systemic kinetic parameters (volume of distribution; Michaelis-Menten elimination parameters, Vmax and KM ) between inhalation exposure and iv and po routes of administration was verified. Total 8-hr ventilation decreased slightly with increasing exposure concentration. The fraction of inhaled methanol absorbed (0.85 ± 0.14) did not vary statistically with exposure concentration. Measured ventilation, fractional absorption, and systemic kinetic parameters were combined in a semiphysiologic pharmacokinetic model that yielded accurate predictions of blood methanol concentrations during and after an 8-hr exposure. Model predictions for the mouse were compared to a previously developed inhalation toxicokinetic model for the rat. The comparison demonstrated that at similar methanol vapor concentrations, mice evidenced a two- to threefold higher blood methanol concentration than rats, despite the fact that the apparent Vmax for methanol elimination in the mouse is twofold larger than that in the rat. These data may have significant implications in understanding species differences in methanol-induced teratogenic effects.

Physiologically based pharmacokinetic model for methanol in rats, monkeys, and humans

The pharmacokinetics of methanol and formate were characterized in male Fischer-344 rats and rhesus monkeys exposed to methanol vapor concentrations between 50 and 2000 ppm for 6 hr. End-of-exposure blood methanol concentrations were not directly proportional to the atmospheric concentration. The methanol exposures did not cause an elevation in blood formate concentrations. After an intravenous dose of [ 14C]methanol in rats, metabolism, exhalation, and renal excretion contributed 96.6, 2.6, and 0.8%, respectively, to the elimination of blood methanol concentrations. These values and the calculated renal methanol extraction efficiency (0.007) are nearly identical to those for humans after low doses of methanol. A physiologically based pharmacokinetic model was developed to simulate the in vivo data. In order to simulate the observed blood methanol concentrations in the inhalation studies in rats, a double pathway for methanol metabolism to formaldehyde was used. One path used rodent catalase K m and V max values and the other used a smaller K m and V max to simulate an enzyme with a higher affinity and lower capacity. The lack of proportionality observed in end-of-exposure blood methanol concentrations may be due to saturation of an enzyme with higher affinity and lower capacity than catalase. The physiologically based pharmacokinetic model was modified to simulate the monkey data and was scaled-up for humans. In order to simulate the monkey blood methanol concentrations, the use of rodent catalase parameters for methanol metabolism was required. This finding suggests that primates and rodents may be similar in the initial step of methanol metabolism after low methanol doses. Previously published human urinary methanol excretion data was successfully simulated by the model. The models were used to predict the atmospheric methanol concentration range over which the laboratory species exhibit quantitative similarities with humans. Below 1200 ppm, all three species exhibit similar end-of-exposure blood methanol concentrations and a linear relationship between atmospheric and blood methanol concentrations. At higher atmospheric concentrations, external and internal methanol concentrations increase disparately, suggesting that delivered dose rather than exposure concentration should be used in interpreting data from high-dose studies.

The effect of methanol on the self reaction of HO2 radicals

AbstractThe rate constant for the HO2 self reaction has been determined as a function of methanol vapor concentration at 278 K and 299 K. A molecular modulation technique was used in which HO2 radicals were photochemically produced in flowing gas mixtures comprised of Cl2, CH3OH, N2 and O2 with HO2 monitored in the UV at 220 nm. A positive linear dependence of the second order rate constant on methanol concentration was found and this effect increased with decreasing temperature. The rate constant for the HO2 self reaction can be described by in nitrogen at atmospheric pressure and in the methanol concentration range 1 · 1016 to 3 · 1017 molecules cm−3.