Hexane Vapor Research Articles

COMPARATIVE STUDY OF THE ADSORPTION-DESORPTION CYCLES OF HEXANE OVER HYPERCROSSLINKED POLYMERIC ADSORBENTS AND ACTIVATED CARBON

Abstract In this work, the behavior of n- hexane vapors in the adsorption-desorption cycles of non-functionalized polymeric adsorbents (MN 202 and MN 250) and granular activated carbon (AC 20) was studied. The adsorption experiments were performed in a fixed bed column, under dynamic conditions, at 30°C and atmospheric pressure. The inlet concentration of n- hexane in the air streams was 0.115 mg/cm 3 (32500 ppm) and the space velocity was 2.75 s -1 . Also, desorption experiments were performed in dynamic conditions by gas stripping at 120°C. It was observed that the AC 20 losses about 15% of its adsorption capacity for each cycles, while the polymeric adsorbents (MN 250 and MN 202) lose only 5% per cycle. Also, the time required for a complete regeneration of polymeric adsorbents MN 202 and MN 250 was much shorter that for activated carbon AC 20 (40, 60 and 300 minutes, respectively). Key words: VOCs, hexane, adsorption, desorption, AC20, MN 202, MN 250 ∗ Author to whom all correspondence should be addressed: E-mail: adelahaleta@ch.tuiasi.ro; haletaadela@yahoo.co.uk.

Specific features of morphology and the structure of nanocrystalline cubic silicon carbide films grown on a silicon surface

The composition, surface morphology, and crystal structure of nanocrystalline cubic silicon carbide films grown on a silicon surface through chemical conversion from hexane vapors have been studied using various methods of analysis (transmission electron microscopy, atomic-force microscopy, white light interference microscopy, electron diffraction, and X-ray diffraction). The characteristics of the 3 C-SiC films prepared on the Si(100) and the Si(111) substrates are compared. For the 3CSiC/ Si(111) heterostructures, the specific features of the shapes, sizes, and crystal structure of islands formed on the growth surface are analyzed by different methods. It is shown that the growth patterns on the surface form a close-packed nanocrystalline texture with a grain size of less than 50 nm. Electron diffraction patterns obtained from the growth patterns on the film surface demonstrate the occurrence of an additional superperiod that is related to the screw axes in the space group of the crystal symmetry elements.

Structure and ultraviolet photoluminescence of 3C-SiC films grown on Si(111)

The structure and light-emitting properties of nanocrystalline cubic silicon carbide films prepared by chemical conversion from hexane vapors are discussed. The morphology, the composition, and the crystallographic structure of the grown silicon carbide thick films are thoroughly analyzed using X-ray diffraction, electron diffraction, white light interferometry, and scanning probe and transmission electron microscopies. The excitation with the use of the third harmonic of a femtosecond laser (λexcit = 266 nm) makes it possible for the first time to reveal the luminescence line lying in the deep UV region with the wavelength λ = 340 nm in addition to the usually observed lines in the high-temperature photoluminescence spectrum. The nature of the lines observed in the photoluminescence spectrum is discussed.

Effects of variable density for film evaporation on laminar mixed convection in a vertical channel

A numerical investigation was conducted to study mixed convection in a vertical parallel-plate channel with evaporation of thin liquid films on wetted walls. Air–water vapor and air–hexane vapor mixtures, assumed as ideal gases, are considered under various boundary conditions. Steady laminar, two-dimensional flows are examined in detail for large mixture density changes between the inlet and outlet sections of the channel. Comparisons with the usual problem formulations based on the Boussinesq approximation are discussed. The elliptic flow model used allow to predict flow reversal as well as recirculation cells in the entrance region. The evaporation of water and hexane into a downward laminar stream of dry air leads to various flow structures according to the interfacial mass fraction, W v,w , and differences in the molecular weights of the species. For water evaporation, the thermal and solutal forces are opposing. In the entrance region, evaporation produces a significant increase in axial velocity at the core region in comparison with pure forced flow. For W v,w larger than ≈0.2, upward velocities may be observed in the wall regions due to solutal buoyancy forces near the wetted surfaces. For hexane evaporation, the solutal force acts downward. Mass diffusion produces both a strong flow acceleration in the boundary layers and flow recirculations at the channel center for large mass evaporation rates.

Preparation and VOC gas sensing properties of Sr(II)-added copper aluminate spinel composites

Abstract Pure and strontium(II)-added CuAl 2 O 4 composites prepared by sol–gel technology were investigated for their sensing properties towards volatile organic compounds (VOCs) like benzene, toluene, hexane, heptane and acetic acid. X-ray diffraction, scanning electron microscopy (SEM) and nitrogen adsorption/desorption isotherms at 77 K were employed to identify the structural phases, surface morphology and BET surface area of the composites, respectively. The results revealed that the sensitivity factor increased with an increase in temperature up to the optimum temperature at which the maximum sensitivity was obtained and thereafter progressively decreased. Among all the composites tested, CuSA5 (the Cu:Sr molar ratio was kept as 0.2:0.8) showed the highest sensitivity to all VOCs under investigation. The sensitivity factor ( S f ) data in the studied temperature range for all the vapors were employed to fit the Gaussian function. The fit parameters revealed that the data satisfactorily fitted for hexane and acetic acid vapors than the other vapors taken for the study.

Rapid chemical-vapor sensing using optofluidic ring resonators

We develop rapid chemical-vapor sensors based on optofluidic ring resonators (OFRRs). The OFRR is a glass capillary whose circular wall supports the circulating waveguide modes (WGMs). The OFRR inner surface is coated with a vapor-sensitive polymer. The analyte and polymer interaction causes the polymer refractive index to change, which is detected as a WGM spectral shift. Owing to the excellent fluidics, the OFRR exhibits subsecond detection and recovery time with a flow rate of only 1 mL/min, a few orders of magnitude lower than that in the existing optical vapor sensors. The detection limit is estimated to be 5.6 x 10(-6) refractive index units, over ten times better than other ring-resonator vapor sensors. Ethanol and hexane vapors are used as a model system, and chemical differentiation is demonstrated with different polymer coatings.

Influence of the chamber volume on the upper explosion limit for hexane–air mixtures

Fundamental hexane vapour–air explosion parameters were found by measuring the explosion pressure variation in closed chambers of 5.6 and 40 dm 3 volume. Also the explosion pressure and rate of explosion pressure rise of hexane droplets–air mixtures close to upper explosion limit were obtained for chambers of 5.6, 40, 150 and 1250 dm 3. It was found that the upper explosion limit for hexane droplets–air mixture is in the range of 1.8–5.5 kg/m 3 and is about 30–40 times higher than the stoichiometric concentration and 3–9 times higher than that for hexane vapours–air mixtures. It was stated, that rich explosion limit is increasing along with an increase of the droplets mean diameter and also along with the chamber size. 3D and large eddy simulation of the investigated process with using computer code FLUENT 6.0 was also made.

Liquid-Vapor Coexistence at a Mesoporous Substrate

The condensation of hexane vapor onto a mesoporous Si substrate with a pore radius of 3.5 nm has been studied by means of volumetry and ellipsometry. The filling fraction of the pores and the coverage of the substrate have been determined. The coverage of the regime after the completion of capillary condensation has been compared to recent theoretical work.

Rapid hydrocarbon analysis using a miniature rectilinear ion trap mass spectrometer

A miniature ion trap mass analyzer was applied to the analysis of traces of hydrocarbons and simple heteroatomics in the vapor phase and in aqueous solution. Vapors of acetone, acetic acid, acetonitrile, benzene, butanethiol, carbon disulfide, hexane, dichloromethane, naphthalene, toluene and xylenes were detected and quantified using solid sorbent trapping and, in some cases, by passage through a membrane interface. Aqueous solutions of benzene, toluene, xylenes, hexane and a petroleum naphtha distillate were examined using the membrane interface. Sampling, detection and identification of all compounds was completed in times of less than one minute. The gas-phase samples of toluene and benzene were detected at 200 ppt (limit of detection, LOD) for toluene and 600 ppt for benzene. Identification of benzene and xylene in aqueous solutions was readily achieved with LODs of 200 and 400 ppb, respectively. Quantification over a linear dynamic range of two orders of magnitude for the aqueous samples and three orders of magnitude for the vapor-phase samples was demonstrated.

Surface plasmon resonance optical gas sensing of nanostructured ZnO films

Abstract The structural and optical gas sensing properties of thin nanostructured ZnO films are investigated by total attenuation surface plasmon resonance technique. Ten nanometers thick ZnO films have been prepared by sol–gel route and thermally treated at 150 °C and 400 °C. Grazing incidence X-ray diffraction studies showed that the thermal treatment promotes the increase of grain size as the annealing temperature increases. The optical properties of both films are similar being the energy gap of the films annealed at 150 °C and 400 °C equal to 3.33 ± 0.05 eV and 3.25 ± 0.05 eV, respectively, both smaller than the energy gap of the bulk ZnO (3.37 eV). The surface plasmon resonance investigations show remarkable and reversible responses to different concentrations of methanol, ethanol, isopropanol and hexane vapours in dry-air. In both films the responses to ethanol and isopropanol are similar and larger than the responses to hexane and methanol. The responses to all vapours are larger in the film annealed at 400 °C except for the methanol for which both films exhibit similar responses.

Effect of Hexanal Vapor on the Growth of Postharvest Pathogens and Fruit Decay

The effect of the natural volatile hexanal was studied as an antifungal agent on the major postharvest fungal pathogens Botrytis cinerea, Monilinia fructicola, Sclerotinia sclerotiorum, Alternaria alternata, and Colletotrichum gloeosporioides. The antifungal effect of hexanal vapor was dependent on concentration and treatment duration, but sensitivity of the pathogens varied. All spores of B. cinerea and M. fructicola were killed after exposure to 900 microL/L for 12 h at 20 degrees C, and almost all were killed after a 24-h exposure to 450 microL/L. Only moderate numbers of spores were killed at a concentration of 200 microL/L. Mycelial growth of S. sclerotiorum on agar was completely inhibited after a 12-h exposure to 900 microL/L, but only slight inhibition occurred at 450 microL/L and none at 200 microL/L. Mycelium of A. alternata and C. gloeosporioides appeared more sensitive, with strong inhibition occurring after a 12-h exposure at 450 microL/L. Similar trends in spore viability and mycelial growth were observed at 7 degrees C. The antifungal effect of hexanal vapor was further tested on raspberry fruit naturally infected with B. cinerea and on peach fruit inoculated with spores of M. fructicola. Decay was markedly reduced in raspberry and almost completely controlled in peach after exposure to 900 microL/L hexanal vapor for 24 h. The potential of hexanal for postharvest decay control is discussed.

Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors.

The development of a robust method for integrating high-performance semiconductors on flexible plastics could enable exciting avenues in fundamental research and novel applications. One area of vital relevance is chemical and biological sensing, which if implemented on biocompatible substrates, could yield breakthroughs in implantable or wearable monitoring systems. Semiconducting nanowires (and nanotubes) are particularly sensitive chemical sensors because of their high surface-to-volume ratios. Here, we present a scalable and parallel process for transferring hundreds of pre-aligned silicon nanowires onto plastic to yield highly ordered films for low-power sensor chips. The nanowires are excellent field-effect transistors, and, as sensors, exhibit parts-per-billion sensitivity to NO2, a hazardous pollutant. We also use SiO2 surface chemistries to construct a 'nano-electronic nose' library, which can distinguish acetone and hexane vapours via distributed responses. The excellent sensing performance coupled with bendable plastic could open up opportunities in portable, wearable or even implantable sensors.

Morphology of heteroepitaxial β-SiC films grown on Si(111) through high-vacuum chemical vapor deposition from hexane vapors

The characteristics of cubic silicon carbide films grown on silicon through high-vacuum chemical vapor deposition (HVCVD) from hexane vapors are investigated using scanning probe microscopy and x-ray diffraction. The surface morphology and structure of the films are analyzed as a function of the thickness of the deposited films and the nature of the substrate (silicon, sapphire). The role of different diffusion fluxes arising in the structure and the related possible mechanisms of growth of β-SiC layers on silicon substrates are discussed.

Surface patterns of block copolymers in thin layers after vapor treatment

A systematic study of formation of surface patterns in block copolymer thin layers after their exposure to solvent vapors was performed. The studied effect involves layers of thickness approximately equal to the ordering size of polymers – about 45 nm. Experiments were performed on three styrene – methacrylate derivative block copolymers, synthesized by living anionic polymerization: poly(4-octylstyrene)- block-poly(butyl methacrylate), poly(4-fluorostyrene)- block-poly(butyl methacrylate) and poly( p-octylstyrene)- block-poly(methyl methacrylate). The polymers were exposed to vapors of chloroform, 1,4-dioxane, hexane, acetone and tetrahydrofuran.

On the Dissolution of Vapors and Gases

The captive bubble technique in combination with axisymmetric drop shape analysis (ADSA-CB) and with micro gas chromatography is used to study the dynamics of dissolution of different gases and vapors in water in situ. The technique yields the changes in the interfacial tension and bubble volume and surface. As examples, the dissolution of methanol and hexane vapors, inhaled anesthetic vapors, and gases, that is, diethyl ether, chloroform, isoflurane, enflurane, sevoflurane, desflurane, N2O, and xenon, and as nonimmobilizers perfluoropentane and 1,1,2-trichloro-1,2,2-trifluoro-ethane (R113) were investigated. The examination of interfacial tension-time and bubble volume-time functions permits us to distinguish between water-soluble and -insoluble substances, gases, and vapors. Vapors and gases generally differ in terms of the strength of their intermolecular interactions. The main difference between dissolution processes of gases and vapors is that, during the entire process of gas dissolution, no surface tension change occurs. In contrast, during vapor dissolution the surface tension drops immediately and decreases continuously until it reaches the equilibrium surface tension of water at the end of dissolution. The results of this study show that it is possible to discriminate anesthetic vapors from anesthetic gases and nonimmobilizers by comparing their dissolution dynamics. The nonimmobilizers have extremely low or no solubility in water and change the surface tension only negligibly. By use of newly defined molecular dissolution/diffusion coefficients, a simple model for the determination of partition coefficients is developed.

Acid-catalyzed reactions of hexanal on sulfuric acid particles: Identification of reaction products

While it is well established that organics compose a large fraction of the atmospheric aerosol mass, the mechanisms through which organics are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds with carbonyl groups have recently been suggested as important pathways for transfer of volatile organics into acidic aerosols. In the present study, we use the aerodyne aerosol mass spectrometer (AMS) to probe the uptake of gas-phase hexanal into ammonium sulfate and sulfuric acid aerosols. While both deliquesced and dry non-acidic ammonium sulfate aerosols showed no organic uptake, the acidic aerosols took up substantial amounts of organic material when exposed to hexanal vapor. Further, we used 1H-NMR, Fourier transform infrared (FTIR) spectroscopy and GC–MS to identify the products of the acid-catalyzed reaction of hexanal in acidic aerosols. Both aldol condensation and hemiacetal products were identified, with the dominant reaction products dependent upon the initial acid concentration of the aerosol. The aldol condensation product was formed only at initial concentrations of 75–96 wt% sulfuric acid in water. The hemiacetal was produced at all sulfuric acid concentrations studied, 30–96 wt% sulfuric acid in water. Aerosols up to 88.4 wt% organic/11.1 wt% H 2SO 4/0.5 wt% water were produced via these two dimerization reaction pathways. The UV-VIS spectrum of the isolated aldol condensation product, 2-butyl 2-octenal, extends into the visible region, suggesting these reactions may impact aerosol optical properties as well as aerosol composition. In contrast to previous suggestions, no polymerization of hexanal or its products was observed at any sulfuric acid concentration studied, from 30 to 96 wt% in water.

Effect of Hexanal Vapor on Spore Viability of Penicillium expansum, Lesion Development on Whole Apples and Fruit Volatile Biosynthesis

ABSTRACT: The effects of hexanal vapor on spore viability of Penicillium expansum, lesion development on whole apple fruit, and flavor volatile biosynthesis were investigated. Spore viability was reduced by 94% after exposure to a hexanal concentration of 40 μmol/L for 24 h, compared with 50% at 18 μmol/L and 20% at 9 μmol/L. Decay on whole apple fruit inoculated with 5 × 104 spores/mL of P. expansum was reduced with exposure to hexanal vapor for 48 h. Although almost all of the fruit treated with 8 to 12 jmiol/L developed decay lesions, lesion size was reduced compared with the controls. At concentrations of 15 to 19 μmol/L, and 25 to 29 μmol/L, the incidence of fruit with lesions was 44% and 24%, respectively, compared with 100% and 98% in the inoculated control apples and lesion size was further reduced. Apples treated at 4°C with only 5 to 7 jimol/L hexanal vapor also showed a marked reduction in lesion incidence. Hexanal was rapidly converted to high levels of the aroma volatiles hexanol, hexylacetate, hexylbutanoate, and hexylhexanoate, but these decreased to levels similar to the control after 4 to 7 d of being held in air. There was no detectable hexanal after holding fruit in air for 5 h.

Preparation and characterisation of carbon-coated ceramic foams for organic vapour adsorption

Ceramic foam substrates of various porosities were coated with novolak resin, which was then subsequently carbonised and activated to develop a pore structure. The carbon forming the layer was characterised by thermal analysis, TPD and N 2, CO 2 and hexane vapour adsorption. It was found to be microporous with a high surface area (up to 1400 m 2 g −1), which made it a good adsorbent for hexane vapour at ambient temperature. The carbon–ceramic interface was examined using SEM. The coated foams displayed a reduced pressure drop compared to carbon granules and had good dynamic hexane vapour adsorption characteristics. Depending on the foam architecture, hexane breakthrough was delayed for up to 78 min.

Comparison of Solubility and Vapor Sensing Properties of Methyl‐ and Thiophene‐Terminated Alkanethiol‐Protected Gold Nanoparticle Films

Gold nanoparticles, protected by monolayers of two different lengths of methyl‐ and ω‐thienyl‐terminated alkanethiols, have been synthesized, and their solubility properties in various solvents have been evaluated by measuring the energy of the plasmon band using UV‐Vis absorbance spectroscopy and by transmission electron microscopy. Chemical sensors have been fabricated by spin‐coating films of the monolayer‐protected gold particles onto interdigitated microelectrode arrays. Exposure to chloroform, toluene, and hexane vapors causes the electrical resistance of the films to increase. A sensor based on 12‐(3‐thienyl)dodecanethiol is shown to be dramatically more sensitive to both chloroform and toluene than one based on tridecanethiol. However, in the case of hexane, these two alkanethiol‐protected gold nanoparticle sensors perform similarly. These results suggest that for very nonpolar solvents such as hexane, the functional group at the periphery of the particle is much less significant than the effect of alkanethiol chain length.

Removal of n-hexane by Fusarium solani with a gas-phase biofilter

A gas-phase biofilter inoculated with the fungus Fusarium solani, isolated from a consortium grown on hexane vapors, was used to degrade this compound. The biofilter, packed with perlite and operated with an empty bed residence time of 60 s, was supplied with hexane concentrations between 0.5 gm(-3) and 11 gm(-3). Biofilter performance was evaluated over 100 days of operation. Several strategies for supplying the nutritive mineral medium were assayed to maintain favorable conditions for the fungal growth and activity. The Fusarium system was able to sustain an average elimination capacity of 90 gm(-3)(reactor) h(-1) with a maximum of 130 gm(-3)(reactor) h(-1) . The mass transfer limitations due to high biomass development in the biofilter were confirmed in batch experiments. Bacterial contamination was observed, but experiments in the biofilter and in batch reactors using selective inhibitors and controlled pH confirmed the predominant role of the fungus. Results indicate that fungal biofilters can be an effective alternative to conventional abatement technologies for treating hydrophobic compounds.