Mixed Vapors Research Articles

Development of Automatic Adsorption Apparatus for Binary Mixture: Measurement of Individual Adsorption Isotherms of Ethanol and Water from Their Mixed Vapors by Active Carbon Fiber

The automatic adsorption apparatus has been developed to measure the individual adsorption isotherms of constituent vapor from binary mixed vapor. The present adsorption apparatus consists of a combination of gravimetry and volumetry. The weight increase due to gas adsorption was determined by the magnetic suspension vacuum balance with a sensitivity of 0.01 mg, while the pressure decrease due to adsorption was measured by a high precision pressure gauge with a sensitivity of 0.2 Pa. The adsorption data obtained from both gravimetry and volumetry make it possible to determine the individual isotherms of the constituent vapors without chemical analysis, if the molecular weights of the constituent vapors are significantly different one another. In the later part of this work, the present adsorption apparatus has been applied to measure the individual adsorption isotherms of ethanol and water by active carbon fiber from their mixed vapor. The reliability of the individual isotherms measured by the present apparatus has been considered. The adsorption data obtained in the present work clearly indicate that ethanol molecules are preferentially adsorbed into the micropores of active carbon fiber with a pore width of 0.67 nm. The present adsorption result suggests the possibility of the energy-saving separation of ethanol from the mixed vapors of ethanol and water.

Preparation and optical study of APCVD mixed metal oxide films

Mixed metal oxides based on MoO 3 and WO 3 are prepared by chemical vapor deposition (CVD) using a precursor-mixture of Mo(CO) 6 and W(CO) 6 powders. By pyrolytical decomposition of the mixed vapors at atmospheric pressure in presence of oxygen, thin films were deposited on silicon substrates at 200°C. The films were characterized by Raman, IR and Ellipsometric Spectroscopies. In as-deposited form the films are amorphous as revealed by Raman spectra. Post-deposition annealing at 200 and 300°C does not significantly change the vibrational and optical properties. Annealing at 400 and 500°C leads to predominantly amorphous structure with appearing of crystalline phase. The character of the absorption spectra and the values of the optical energy bandgap (2.57-2.66 eV) suggest that the CVD-MoO 3 -WO 3 oxide films have highly defective structure.

Modeling the removal of VOC mixtures in biotrickling filters

A mathematical model was derived for describing removal of mixed VOC vapors in biotrickling filters (BTFs). The model accounts for potential process rate limitation by the availability of oxygen as well as for potential kinetic interactions among pollutants during their biodegradation. Without using any fitted parameter, the model was found capable of predicting experimentally obtained removal rates of mono-chlorobenzene (m-CB) and ortho-dichlorobenzene (o-DCB) vapors. Experimental results reported here show that m-CB removal is better than that of o-DCB. The two compounds were known to be involved in a kinetic cross-inhibition interaction when degraded in suspended culture. However, model sensitivity studies showed that cross-inhibition does not affect BTF performance due to the low pollutant concentrations involved. For the same reason, the influence of oxygen on BTF performance was found to be minimal under the conditions tested. The model was found to predict experimentally obtained values with less than 10% error in the majority of cases. Computations with an earlier model describing VOC removal in conventional biofilters showed that, for the model mixture used in this study (m-CB/o-DCB), removal rates obtained with BTFs are one to more than two orders of magnitude higher than those obtained with conventional biofilters. This is attributed to the larger active specific biofilm surface area in BTFs, obtained through the creation of favorable growth conditions for the biomass, and better moisture control.

Removal of BTEX Vapor from Waste Gases by a Trickle Bed Biofilter

ABSTRACT The system performance of a trickle bed biofilter for treating single and mixed benzene, toluene, ethylbenzene, and o-xylene (BTEX) vapors from waste gases was investigated under different gas flow rates and influent BTEX concentrations. When a single substrate was fed, removal efficiencies of greater than 90% could be achieved for the loads below 64 g benzene/m3/hr, 110 g toluene/mVhr, 53 g ethylbenzene/m3/hr, and 55 g o-xylene/m3/hr. When a mixed substrate was fed, removal efficiencies of each compound could be above 90% at BTEX loads below 96 g/m3/hr. The trickle bed biofilter appears to be an effective treatment process for removing both single and mixed BTEX vapors with low to high loads. Under similar substrate loads, BTEX vapors were preferentially bio-degraded in the order of toluene, benzene, o-xylene, and ethylbenzene. The volumetric removal rates (elimination capacities) of BTEX vapors for a single-substrate feed were higher than those for a mixed-substrate feed under similar substrate loads; these differences were enhanced at higher substrate loads and less significant for a preferred substrate.

Production and stability of silicon-doped heterofullerenes

Silicon–carbon binary clusters with various mean compositions are generated in a laser vaporization source from targets processed as mixtures of graphite and silicon powders. Their size distribution is first analyzed by time-of-flight mass spectroscopy, which shows the stability of carbon fullerenes doped with silicon atoms in substitutional sites. Further investigations on the level of silicon doping are carried out by means of the laser-induced fragmentation of selected sizes. The photoproduct size distributions give evidence for at least nine silicon atoms substituted into still stable fullerene networks. The synthesis of heterofullerenes is mainly assisted by the nucleation mechanisms from Si-C mixed atomic vapors. Just as in the case of externally doped fullerene precursors, the laser-induced annealing of stoichiometric silicon-carbide clusters appears as an alternative route to produce heterofullerenes in the gas phase.

Equilibria and dynamics for mixed vapors of BTX in an activated carbon bed

AbstractExperimental and theoretical studies were made on the adsorption of benzene, toluene, p‐xylene, and their binary and ternary mixtures by activated carbon in an isothermal condition of 303 K. Experimental isotherms for pure components were measured by two kinds of experimental techniques: the static volumetric method and breakthrough data analysis. Breakthrough data analysis shows that both the extended Langmuir equation and the ideal adsorbed solution theory could explain mixture isotherm data with good accuracy. In addition, a mathematical model was developed to simulate the column dynamics of pure and mixed‐vapor adsorption systems. To represent the mass‐transfer rate inside the adsorbent particle, the linear driving‐force approximation model was applied. By optimizing the pure‐ and the binary‐component breakthrough curve data with a dynamic model, an empirical correlation was proposed to represent the overall mass‐transfer rates for the BTX vapor‐activated carbon system. Results with this correlation, which is a function of the partial pressures for each adsorbate and interstitial bulk fluid velocities, showed that the prediction agrees well with the experimental data of ternary breakthrough curves.

An Analytical Sensor Device of Mixed Gas Based on the Cataluminescence Spectroscopy on γ -Al<sub>2</sub>O<sub>3</sub>: Dy

Cataluminescence (CTL) is a kind of chemiluminescence emitted during catalytic oxidation. A new method for analytical detection of mixed organic vapors in air is proposed using a new CTL-based gas sensor made of γ-Al2O3, catalyst doped with Dy phosphor. The CTL spectra of ethanol and acetone on γ-Al2O3 catalyst consist of two components of λL(550nm) and λs (420nm). The CTL spectra for the same sample gases on γ-Al2O3, doped with Dy have extra spectrum components peaking at λD1 (580nm) and λD2 (480nm), so that the sensor sensitivity is increased. As the CTL intensities at λD1, λs and λL show different temperature and gas concentration dependence respectively, these may result from different reaction processes. Two CTL intensities of 530 and 580 run are measured for air containing ethanol and acetone of concentrations of CE and CA. As the CTL intensities are the different single valued function of CE and CA, we can obtain the constituent concentrations of mixed organic vapor of ethanol and acetone by measuring the CTL intensities of two wavelengths of 530 and 580 nm.

Condensation of mixed vapors and thermodynamics

AbstractA literal interface between thermodynamics and transport phenomena occurs in the steady‐state condensation/vaporization of mixed vapors/liquids in wetted‐wall towers. Unfortunately, several prominent transport texts assume that the ratio of molar fluxes is the same as the corresponding ratio of mole fractions at the interface for the phase being formed. This is shown to be true only at particular vertical positions corresponding to the first drop of condensate. The thermodynamics of the condensation/vaporization of mixtures is reviewed to understand why the ratio of pure‐component fluxes at the interface differs from that of corresponding equilibrium mole fractions. The dynamics of steady‐state condensation in wetted‐wall towers is also developed based on the film theory of Colburn and Drew. The temperature/composition diagram is used to trace both transport phenomena and thermodynamic variables at various tower heights. The Ackermann factor is corrected allowing more general use of the design equations when the vapor is nonideal. The usual neglect of liquid‐film resistance to heat transfer is examined. Numerical calculations show an unusual rise in the interfacial temperature in a parallel flow tower immediately below the onset of condensation. Possible and impossible sets of temperature and composition profiles are described.

Separation of Water and Ethanol by the Adsorption Technique: Selective Desorption of Water from Micropores of Active Carbon

The hydrophobic micropores of active carbon were filled with a mixture of water and ethanol by adsorbing their mixed vapors (H2O/EtOH = 3/1) on active carbon. The desorption isotherm of each component from the micropores has been determined simultaneously at 25°C by a combination of volumetric and gravimetric methods. A more selective desorption of water than that of ethanol was discovered from the measured isotherms. It has been clarified from the present finding that the separation of water and ethanol could be carried out by means of an adsorption technique using a hydrophobic active carbon adsorbent. The preferential desorption of water may be attributed to the weak interaction of water with the hydrophobic micropore surface in comparison with the interaction of ethanol with the micropore surface. The adsorption energy of water on the micropore surface is 17–32 kJ mol−1at low coverage, while that of ethanol on the micropore surface is 43–52 kJ mol−1. The possibility of enrichment of ethanol from its dilute aqueous solution made by fermentation was discussed on the basis of the present desorption data.

Analytical detection system of mixed odor vapors using chemiluminescence-based gas sensor

A chemiluminescence(CL)-based gas sensor made of γ-Al 2O 3 emits CL during catalytic oxidation of a combustible odor vapor. The CL intensity is proportional to the concentration of ethanol or acetone vapor in air. The algebraic sum rule is applicable to the CL intensities by the mixed gas of these two kinds of vapors, when the sensor is heated above 450°C. The CL intensities are measured in periodic temperature cycles between 650 and 450°C. The concentrations of vapor components can be detected analytically by measuring total CL intensities during the high and low temperatures for air containing mixed vapors of various concentrations of ethanol below 400 ppm and acetone below 200 ppm.

Separation of Aromatics by Vapor Permeation Through Solvent Swollen Membrane.

A vapor permeation process for aromatics separation from a hydrocarbon mixture was studied by means of the simultaneous permeation of dimethylsulfoxide vapor as an agent for membrane swelling and preferential permeation of aromatics. The separation performance of the process was demonstrated by a polyvinylalcohol membrane for mixed vapors of benzene/cyclohexane, xylene/octane and a model gasoline. The aromatic vapors preferentially permeated from these mixed vapor feeds. The separation factor was over 10. The separation mechanism of the process mainly depends on the relative solubility of the vapors between aromatics and other hydrocarbons in dimethylsulfoxide.

Mass Transfer in Binary and Ternary Distillation by a Packed Column with Structured Packing.

A mass transfer correlation for distillation using a laboratory size wire-gauze structured packing was developed in terms of dimensionless diffusion flux based on experimental data for an acetone-ethanol system under total reflux conditions. The theoretical basis for mass and heat transfer in distillation that was previously developed for wetted-wall columns is shown to apply to structured packings as well. It is also demonstrated that the Sherwood number for distillation exhibited wide scattering due to the effect of convective flux, which is highly influenced by external heat effects and differences in the latent heat of vaporization of the transferring components.The model obtained from the binary system, which is based on the total area of the structured packing and corrected for the effect of condensation of mixed vapors, is shown to apply to a ternary system of acetone-methanol-ethanol. Simulation results using the correlation for a short column compared well with experimental results for longer columns for binary and ternary systems.

Heterogeneous Nucleation Characteristics of a Eutectic-Forming Vapor Mixture on a Cold Substrate

Abstract The formation of solid condensates by heterogeneous nucleation from a mixture of p-xylene and water vapor onto a cold substrate was observed by slowly cooling the substrate under reduced pressure conditions. The results from binary experiments were compared to those for the pure vapors. Two critical substrate temperatures, corresponding to the onset of nucleation, were determined experimentally at a given initial vapor pressure by observing a rapid decrease in the vapor pressure. A mixed vapor with a water content greater than 85% formed ice at the first critical point, and the critical partial vapor pressure agreed well with that for pure water. For mixed vapors in which the p-xylene content was greater than 30%, p-xylene crystals formed at the first critical point, but the critical vapor pressure tended to decrease with decreasing p-xylene content. For mixed vapors with a composition close to the eutectic, it was unclear which crystal formed at the first critical point. The relationship between the logarithm of the critical vapor pressure and the inverse of the critical temperature at the second critical point showed good linearity and was close to that at the eutectic condition. Using these experimental results, we discuss the conditions required for separating binary eutectic-forming vapors by sublimation.

Analysis of ion mobility spectra for mixed vapors using Gaussian deconvolution

A central issue in the utilization of ion mobility spectrometry for chemical analysis is the proper interpretation of ion mobility spectra and the assignment of peak identities. Ion mobility spectra for contemporary drift tubes generally produce broad peaks and simple patterns without obvious details associated with structures. These features can hinder the analyses of spectra derived from mixed vapors. However, additional information from such spectra parameters and for boundaries of operation using ion mobility spectra from binary mixtures. An ion-molecule cluster ion, not obvious in traditional spectra analysis, was disclosed by deconvolution analysis and confirmed by independent ion mobility spectrometry-mass spectrometry.

Coadsorption of organic compounds and water vapor on BPL activated carbon. 2. 1,1,2-Trichloro-1,2,2-trifluoroethane and dichloromethane

A novel volumetric apparatus is used to measure equilibria for mixed vapors of halocarbons and water coadsorbed on BPL activated carbon. Pure-component 1,1,2-trichloro-1,2,2-trifluoroethane (CFC 113) and dichloromethane (methylene chloride) isotherms are obtained at 0, 25, 50, 75, and 100 C over wide ranges of pressure. A separate isotherm measured for CFC-113 at 50 C indicates the presence of pure component hysteresis in the mesopore structure of the activated carbon at high halocarbon loadings. Mixture equilibria are measured for CFC-113/water systems at 25 and 100 C and for dichloromethane/water systems at 25 C. All components exhibit hysteresis, and the halocarbon partial pressure increases as the water loading is increased at constant halocarbon loading. Results for halocarbon/water mixtures together with previous results for hydrocarbon/water mixtures show that the apparent total pore volume filled near saturation is dependent on the adsorption temperature and the solubility of the organic compound in water.

Exposure-excretion relationship of styrene and acetone in factory workers: a comparison of a lipophilic solvent and a hydrophilic solvent.

A factory survey was conducted in the second half of a working week on 41 exposed male workers, who were engaged in fiber-reinforced plastics work and exposed to the mixed vapors of styrene and acetone. Nonexposed workers, 20 men, were recruited from the same factory. Styrene and acetone in respiratory zone air were monitored for a 8-h shift with carbon cloth- and water-equipped personal diffusive samplers, respectively. Blood and urine samples were collected at the shift-end. Acetone and styrene concentrations in whole blood, serum and urine were measured by head-space gas chromatography, and phenylglyoxylic acid in urine by high-performance liquid chromatography. All biological exposure indicators analyzed correlated significantly with the intensity of exposure to the corresponding solvent during the shift. The slopes of the regression lines indicate that a very small fraction of styrene absorbed will be excreted into urine as styrene per se, and that styrene is quite effectively excreted into urine after metabolic conversion. In contrast, the slopes of regression lines for acetone suggest that acetone distributes both in the blood and urine quite evenly. When the distribution of the solvent in serum was compared with that in the whole blood, it was found that almost all of styrene in blood is present in the serum, whereas acetone distributed very evenly in the cellular and noncellular fractions of the blood.

Comparison of vapor and liquid phase silylation processes of photoresists

Organosilicon groups can be incorporated into photoresists, rendering them resistant to erosion by oxygen plasmas. This process, known as silylation, can be implemented using either liquid or vapor sources. A comparison of these two methods was performed using mono-,di- and trifunctional organosilicon compounds with reactive Si-N-bonds. Among the four monofunctional compounds studied, hexamethyldisilazane is about 10 times less reactive in silylation of AZ 4110 films at normal pressure (126°C) compared to tetramethyldisilazane or dimethylaminotrimethylsilane. Mixed vapors of difunctional compounds (10% of bis/dimethylamino/methylsilane) and toluene silylate resist films at 111°C at a high rate forming crosslinked materials with an increased stability in O2 plasmas (etch rate of about 50 A/min after 2 min silylation). Trifunctional compounds (tris/dimethylamino/methylsilane) do not silylate resist films due to the formation of a crosslinked diffusion barrier on the surface. Difunctional silylating agents like bis(dimethylamino)dimethylsilane effectively silylate resist films at 80–85°C in toluene soluyion (which does not contain any diffusion promotors like NMP) without any distortions or thickness loss. The chemistry of silylation is discussed.

Condensation of Mixed Vapors—Integral vs. Differential

Abstract The heat and mass transfer processes taking place within a condenser for a mixture of vapors (total or partial condensation) will differ very significantly depending on whether integral or differential condensation is involved. It will be demonstrated that a failure to recognize this difference and thus to select an inappropriate condenser geometry can lead to the catastrophic failure of the unit to perform the anticipated duty.

Wave mixing and amplified spontaneous emission in pure potassium and mixed sodium-potassium vapors

We report observations of several wave-mixing and stimulated processes in pure potassium and mixed sodium-potassium vapors which are excited by a pulsed laser operating in the range 680–800 nm. When the laser is tuned to the potassium two-photon 4S→6S transition, we observe stimulated emission on the various cascade transitions as well as four- and six-wave mixing. When the laser is tuned over the range 747 to 753 nm, which is well away from all atomic transitions, we observe strong forward and weak backward emission at the potassium 3D3/2→4P1/2 transition wavelength (1.17 μm). However, this latter emission is only observed in the mixed sodium-potassium vapor. We present data on the excitation spectrum, forward to backward asymmetry, temporal dependence, and the laser power dependence of this emission. We speculate that twophoton photodissociation of the NaK molecule is responsible for this emission.

Selective—Area Laser Photodeposition of Transparent Conductive SnO2 Films

ABSTRACTThe deposition of SnO2 films has been demonstrated using an ArF (193-nm) excimer laser to drive the photochemical reactions of mixed SnCI4 and N2O vapors. Without any annealing, films 100 nm thick grown on room—temperature substrates have resistivities as low as 0.04 Ω—cm. The optical bandgap of 3.20 ev and transmission cutoff wavelength of 330 nm compare favorably with films obtained using alternate higher temperature techniques. The maximum temperature excursion during the 20—ns laser pulse is estimated to be 300 to 400 ºC.