Toluene In Vapor Phase Research Articles

Bimetallic Catalysts Containing Gold and Palladium for Environmentally Important Reactions

Supported bimetallic nanoparticles (SBN) are extensively used as efficient redox catalysts. This kind of catalysis particularly using SBN has attracted immense research interest compared to their parent metals due to their unique physico-chemical properties. The primary objective of this contribution is to provide comprehensive overview about SBN and their application as promising catalysts. The present review contains four sections in total. Section 1 starts with a general introduction, recent progress, and brief summary of the application of SBN as promising catalysts for different applications. Section 2 reviews the preparation and characterization methods of SBN for a wide range of catalytic reactions. Section 3 concentrates on our own results related to the application of SBN in heterogeneous catalysis. In this section, the oxidation of cyclohexane to adipic acid (an eco-friendly and novel approach) will be discussed. In addition, the application of bimetallic Pd catalysts for vapor phase toluene acetoxylation in a fixed bed reactor will also be highlighted. Acetoxylation of toluene to benzyl acetate is another green route to synthesize benzyl acetate in one step. Finally, Section 4 describes the summary of the main points and also presents an outlook on the application of SBN as promising catalysts for the production of valuable products.

Ecocompatible Halloysite/Cucurbit[8]uril Hybrid as Efficient Nanosponge for Pollutants Removal

AbstractHybrid materials based on halloysite nanotubes (HNT) and cucurbit[8]uril (CB[8]) were prepared with the aim to obtain efficient nanosponges towards hydrocarbons both in liquid and vapor phases. The loading on both HNT surfaces and the hybrid morphology were evidenced by FTIR spectroscopy, thermogravimetric analysis and scanning electron microscopy. In order to highlight the interactions in the hybrid 13C {1H} CP‐MAS NMR experiments were performed. The aqueous colloidal stability of HNT/CB[8] was highlighted through ζ potential and dynamic light scattering measurements. The HNT/CB[8] composite was employed as nanosponge to capture aromatic oils in aqueous phase as evidenced by fluorescence emission spectra of pyrene. These results were correlated with the adsorption capacity of the hybrid toward toluene in vapor phase. This paper provides an efficient way to prepare a biocompatible hybrid material that could be used as a potential multi‐pockets nano‐container for decontamination of polluted water and/or air.

Biodegradation of vapor-phase toluene in unsaturated porous media: Column experiments

Biodegradation of organic chemicals in the vapor phase of soils and vertical flow filters has gained attention as promising approach to clean up volatile organic compounds (VOC). The drivers of VOC biodegradation in unsaturated systems however still remain poorly understood. Here, we analyzed the processes controlling aerobic VOC biodegradation in a laboratory setup mimicking the unsaturated zone above a shallow aquifer. The setup allowed for diffusive vapor-phase transport and biodegradation of three VOC: non-deuterated and deuterated toluene as two compounds of highly differing biodegradability but (nearly) identical physical and chemical properties, and MTBE as (at the applied experimental conditions) non-biodegradable tracer and internal control. Our results showed for toluene an effective microbial degradation within centimeter VOC transport distances despite high gas-phase diffusivity. Degradation rates were controlled by the reactivity of the compounds while oxic conditions were found everywhere in the system. This confirms hypotheses that vadose zone biodegradation rates can be extremely high and are able to prevent the outgassing of VOC to the atmosphere within a centimeter range if compound properties and site conditions allow for sufficiently high degradation rates.

Layered Clay Aerogels by a Freeze-Drying Process for a Platinum-Supported Catalyst

We prepared a clay aerogel by freeze drying an aqueous viscous suspension of a synthetic saponite (a layered clay mineral of the smectite family). The nanostructure and texture of the resulting aerogel varied with the freezing conditions. The freeze drying resulted in microporous aerogels with well-ordered (stacked) silicate layers. A fine texture was observed after freeze drying of a starting suspension at a lower concentration. Freezing in liquid propane yielded a well-defined continuous network texture. Toluene in vapor phase was oxidatively decomposed in air flow over aerogels on which platinum was deposited by an impregnation wetness method; the decomposition was probably affected by the size distribution of micropores.

Enhancement of adsorptive chemical filters via titania photocatalysts to remove vapor-phase toluene and isopropanol

Adsorption-type chemical filtration is essential in many indoor purification applications. However, these chemical filters are expensive and have a limited filter life after breakthrough of contaminants. With toluene and isopropanol (IPA) as model contaminants, this study investigates the breakthrough behaviors of adsorptive chemical filters and TiO 2-enhanced chemical filters with various configurations—a chemical filter containing TiO 2-preloaded activated carbon (Scenario A), a chemical filter preceded by a TiO 2-coated non-woven sheet (Scenario B), and a chemical filter pressed against a TiO 2-coated non-woven sheet (Scenario C). The photocatalytic performance of the TiO 2-coated non-woven sheet was evaluated using several key operating parameters such as air moisture (relative humidity), TiO 2 loading density, light intensity, and challenge concentrations of model contaminants. The generation and accumulation of oxidative intermediate products from photocatalysis of toluene and IPA were also examined. Additionally, the Yoon–Nelson breakthrough model was experimentally validated and applied to generate adsorption breakthrough curves of several hypothetical challenge concentrations. The breakthrough studies indicate that the life of the filter in Scenario C was markedly longer than those of filters in scenarios A and B, even when photocatalysts were de-activated as a result of benzaldehyde accumulation from toluene decomposition. By pressing the TiO 2-coated non-woven sheet against the front face of the chemical filter, TiO 2 particles in the non-woven sheet and activated carbon granules in the chemical filter comprised a quasi-homogeneous system, yielding synergistic effects that enhance the operating lifespan of a chemical filter via photocatalysis.

A Model to Evaluate the Cytotoxicity of the Fungal Volatile Organic Compound 1-octen-3-ol in Human Embryonic Stem Cells

Microbial growth in damp indoor environments has been correlated with risks to human health. This study was aimed to determine the cytotoxicity of 1-octen-3-ol ("mushroom alcohol"), a major fungal volatile organic compound (VOC) associated with mushroom and mold odors. Using an airborne exposure technique, human embryonic stem cells were exposed for 1 h to different concentrations (0-1,000 ppm) of racemic 1-octen-3-ol and its enantiomers, (R)-(-)-1-octen-3-ol and (S)-(+)-1-octen-3-ol. Cytotoxicity was assayed using both the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay and the fluorescently tagged Calcein AM-mediated "live and dead" assay. Racemic 1-octen-3-ol and (S)-(+)-1-octen-3-ol exhibited greater cytotoxicity to the undifferentiated human cell line H1 than did (R)-(-)-1-octen-3-ol. The inhibition concentration 50 (IC(50)) values assessed by the MTS assay for racemic 1-octen-3-ol, (S)-(+)-1-octen-3-ol and (R)-(-)-1-octen-3-ol were, respectively, 109, 98, and 258 ppm. These IC(50) values were 40-80-fold lower than that of vapor phase toluene, an industrial chemical used as a positive control in this study. Our report pioneers the modeling of human embryonic stem cells as an in vitro approach to screen the potential toxicity of fungal VOCs. Human embryonic stem cells exposed to 1-octen-3-ol, and its enantiomers in the vapor phase showed more cytotoxicity than those exposed to toluene.

Effect of Fe doped over V–Sb oxide catalyst in toluene selective oxidation

Mixed oxides Fe x V 1− x SbO 4 with x = 0–1.0 were prepared by slurry method and characterized by X-ray diffraction (XRD), Mössbauer spectroscopy, and temperature-programmed reduction (TPR). The samples with x = 0, 0.4 and 1.0 were evaluated as catalyst in vapor phase toluene partial oxidation reaction. It was found by XRD that Fe, as doping, was introduced in the rutile structure of VSbO 4. The BET surface area of partially substituted solid with x = 0.4 was higher than those obtained for VSbO 4 and FeSbO 4 samples. It was shown that V is responsible of the hydrocarbon molecule activation. The catalyst with Fe x = 0.4 presented lower specific rate reaction and lower selectivity to total oxidation products than undoped solid (VSbO 4), which it would be related to a partial replace of V by Fe in the V–O–V chains. In conclusion, the solid activity and selectivity to total oxidation decrease due to a higher isolation of V sites, when V 3+ is substituted by Fe 3+ in the rutile structure.

Biofiltration of toluene-contaminated air using an agro by-product-based filter bed

An innovative, coir-pith-based, filter bed for degrading vapor phase toluene in a gas biofilter over 160 days without any external nutrient supply is reported in this study. Indigenous microflora present in the coir pith as well as in the aerobic sludge added at the start-up stage metabolized the toluene, and correspondingly, CO(2) was produced in the biofilter. Inlet toluene concentration in the range of 0.75 to 2.63 g/m(3) was supplied to the biofilter in short acclimation periods. The maximum elimination capacity achieved was 96.75 g/m(3) x h at 120.72 g/m(3) x h loading where around 60% was recovered as CO(2). The filter bed maintained a stable low-pressure drop (0-4 mm H(2)O), neutral pH range (6.5-7.5), and moisture content of 60-80% (w/w) throughout the period. In addition to toluene-degrading microbial community, a grazing fauna including rotifer, bacteriovoric nematode, tardigrade, and fly larvae were also present in the filter bed. The overall performance of the biofilter bed in pollutant removal and sustainability was analyzed in this study.

Exposure and Immunological Determinants in a Murine Model for Toluene Diisocyanate (TDI) Asthma

Isocyanate-induced asthma, the most commonly reported cause of occupational asthma, has been difficult to diagnose and control, in part, because the biological mechanisms responsible for the disease and the determinants of exposure have been difficult to define. Appropriate animals models of isocyanate asthma will be instrumental to further our understanding of this disease. Previous studies have demonstrated that dermal exposure to isocyanates in mice results in systemic sensitization that leads to eosinophilic airways inflammation upon subsequent airway challenge. We hypothesized that inhalation of vapor phase toluene diisocyante (TDI) will lead to immunologic sensitization in mice and that subsequent challenge will induce pathology and immune system alterations indicative of asthma found in humans. To determine the impact of exposure dose as well as the involvement of immune (allergic) or nonimmune mechanisms, a murine model of TDI asthma was established and characterized following either low-level subchronic or high-dose acute inhalation TDI exposure. C57BL/6 J mice were exposed to TDI by inhalation either subchronically for 6 weeks (20 ppb, 4 h/day, 5 days/week) or by a 2-h acute exposure at 500 ppb. Both groups were challenged 14 days later via inhalation with 20 ppb TDI for 1 h. Mice that underwent the subchronic exposure regimen demonstrated a marked allergic response evidenced by increases in airway inflammation, eosinophilia, goblet cell metaplasia, epithelial cell alterations, airway hyperreponsiveness (AHR), T(H)1/T(H)2 cytokine expression in the lung, elevated levels of serum IgE, and TDI-specific IgG antibodies, as well as the ability to transfer these pathologies to naive mice with lymphocytes or sera from TDI exposed mice. In contrast, mice that received acute TDI exposure demonstrated increased AHR, specific IgG antibodies, and pathology in the lung consistent with asthma, but without the presence of elevated serum IgE, lung eosionophilia, or increased expression of T(H) cytokines. These results describe mouse models for TDI asthma consistent with that found in workers with occupational asthma and indicate that the pulmonary pathology associated with TDI can vary depending upon the exposure paradigm.

Critical review of methods for sampling, analysis, and monitoring of vapor-phase toluene diisocyanate.

This article is a critical review of some of the methods that have been used for the sampling, analysis, and monitoring of vapor-phase toluene diisocyanate (TDI). Only some of the methods that have received relatively widespread application have been addressed in this article. This review includes a "tutorial style" discussion of basic definitions and basic principles and procedures of quality control and metrology for sampling, analysis, and monitoring. One critical issue that is addressed: Are there methods and monitoring instruments available that are capable of sampling and analyzing or monitoring TDI vapor with sufficient speed and sensitivity to satisfy the requirements of the current ACGIH threshold limit values (TLVs) for TDI vapor?

Mite growth on fungus under various environmental conditions and its potential application to biofilters.

The effects of relative humidity, temperature, pH and vapor-phase toluene concentration on Tyrophagus putrescentiae growth on Cladophialophora sp. were tested in controlled environmental chambers. It was observed that the mites were able to reproduce readily at relative humidities between 90% and 97% as well as on porous perlite support material pre-soaked in nutrient media of pH 2.5, 4 and 7. Also, the presence of toluene at gas-phase concentrations of 500 to 2000 mg m(-3) was found to be non-toxic to the mites. The mites, however, were unable to maintain a large population when the temperature was maintained at 14 degrees C, and overpopulation of the living space led to declines in mite population over time. Overall, it was found to be relatively simple to cultivate mites that may be used for fungal biomass control measures in biofilter applications.

Quantification of toluene dioxygenase induction and kinetic modeling of TCE cometabolism by Pseudomonas putida TVA8.

As measured by the toluene-induced bioluminescent response of Pseudomonas putida TVA8 in batch experiments, toluene dioxygenase (Tod) enzyme activities are dependent on toluene concentration between 0 and 30 mg/L. To provide a measure of the Tod activity for use in Michaelis-Menten competitive-inhibition kinetics, a correlation between toluene concentration and induced Tod activity as measured by an induced bioluminescent response of P. putida TVA8 is presented as a nondimensional Tod activity parameter. A packed-bed, radial-flow bioreactor (RFB) using the bioreporter P. putida TVA8A serves as the model system for studying the effect of the enzyme activity parameter on model predictions of vapor-phase toluene oxidation and trichloroethylene (TCE) cometabolism. Mass balances were performed on a differential section of the RFB to describe the radial transport of vapor-phase toluene and TCE through a bulk gas phase and the concomitant biological reaction in a stationary biofilm phase. The finite-element Galerkin weak-statement formulation with first-order basis functions was used to find the optimum solution to the highly nonlinear, coupled equations. For this RFB system with toluene concentrations less than 1 mg/L in the bulk gas phase, the Tod activity parameter enables accurate predictions of steady-state TCE degradation rate (0.27 microg TCE/min).

Hydrogenation of Toluene over γ-Al2O3-Supported Pt, Pd, and Pd–Pt Model Catalysts Obtained by Laser Vaporization of Bulk Metals

Pure Pd, Pt, and bimetallic Pd–Pt clusters produced by laser vaporization of bulk metals or alloys have been deposited on a high surface area alumina (γ-Al2O3). The bimetallic clusters have a perfectly well-defined stoichiometry, as demonstrated by energy-dispersive X-ray analysis experiments. Transmission electron microscopy shows that pure or bimetallic clusters have similar size distributions. The catalytic properties of Pd, Pt, Pd17Pt83, and Pd65Pt35 supported clusters have been investigated in the vapor-phase toluene hydrogenation over a wide range of reaction conditions. The activation energies are 44 ± 6 kJ/mol. The pressure dependence on toluene varies from 0 at 333 K to 0.7 at 500 K whereas this dependence on H2 increases from approximately 0.5 at 333 K up to 2.2 at 500 K. The results obtained with the pure metals corroborate those reported in the literature for catalysts prepared by chemical methods. The activities of the bimetallic catalysts do not show any synergy between Pd and Pt but rather a perfect additivity of their individual catalytic properties. Pt has been shown to have no electronic influence on the reactivity of Pd atoms. The nonlinear variation of the turnover frequency as a function of the Pd surface concentration is interpreted on the basis of an active site composed of a pair of atoms.

The measurement of toluene dioxygenase activity in biofilm culture of Pseudomonas putida F1

Toluene dioxygenase (Tod) enzyme activity can be measured by the conversion of indole to indigo. Indigo is measured spectrophotometrically at 600 nm. However, this method is inadequate to measure the whole-cell enzyme activity when interference by suspended biomass is present. Indoxyl is a highly fluorescent intermediate in the conversion of indole to indigo by Tod. A fluorescence-based assay was developed and applied to monitor Tod activity in whole cells of Pseudomonas putida F1 biofilm from a continuously operated biofilter. Suspended growth studies with pure cultures indicated that indoxyl, as measured by fluorescence, correlated with indigo production (r2=0.89) as measured by spectrophotometry. Whole-cell enzyme activity was followed during growth on a minimal medium containing toluene. The maximum normalized whole cell enzyme activity of 19±1.5×10−4 mg indigo (mg protein)−1 min−1 was reached during early stationary phase. P. putida F1 cells from a biofilm grown on vapor phase toluene had a normalized whole-cell enzyme activity of 5.0±0.2×10−4 mg indigo (mg protein)−1 min−1. The half-life of whole-cell enzyme activity was estimated to be between 5·5 and 8 h in both suspended and biofilm growth conditions.

Fiber-Optic Resonance-Enhanced Multiphoton Ionization Probe for in situ Detection of Aromatic Contamination

A simple fiber-optic probe suitable for remote analysis with the use of resonance-enhanced multiphoton ionization has been developed and demonstrated by measuring vapor-phase toluene and gasoline above aqueous solutions. An optical fiber transmits a high-power laser pulse (266 nm or 532 nm) to the sample, ionizing it, and the subsequent ions are collected with a platinum electrode mounted at the fiber tip. Measurements take approximately 100 s to perform, require no sample preparation, and have been demonstrated over a distance of five meters. The limit of detection for toluene in water with the use of this probe is 1.47 ± 0.02 ppb (wt/wt). In addition to two-photon excitation at 266 nm, the feasibility of a 2+2 excitation scheme using 532 nm has also been shown.

Physiological stress in batch cultures of Pseudomonas putida 54G during toluene degradation.

Physiological stress associated with toluene exposure in batch cultures of Pseudomonas putida 54G was investigated. P. putida 54G cells were grown using a continuous vapor phase feed stream containing 150 ppmv or 750 ppmv toluene as the sole carbon and energy source. Cells were enumerated on non-selective (R2A agar plates) and a selective minimal medium incubated in the presence of vapor phase toluene (HCMM2). Differential recovery on the two media was used to evaluate bacterial stress, culturability and loss of toluene-degrading capability. A majority of the bacteria were reversibly stressed and could resume active colony formation on selective medium after passage on non-selective medium. A small fraction of the bacterial cells suffered an irreversible loss of toluene degradation capability and were designated as Tol- variants. Numbers of stressed organisms increased with duration of toluene exposure and toluene concentration and coincided with accumulation of metabolic intermediates from incomplete toluene degradation. Respiring cell numbers in the batch cultures decreased as injury increased, indicating a possible relationship between respiring and injured cells. Rate expressions for injury, for formation of Tol- variants and for growth of Tol- variants were determined by calibrating a theoretical model to the results obtained. These rate expressions can be used to calibrate bioreactor models, and provide a basis for better design and control of bioremediation systems.

Hydrogenation of Aromatic Hydrocarbons over Supported Pt Catalysts .II. Toluene Hydrogenation

Vapor-phase toluene hydrogenation was investigated over Pt supported on SiO 2, η-Al 2O 3, SiO 2 · Al 2O 3 and TiO 2. As with benzene, activation energies and reaction orders had no dependence on the support. The E A values were 12 ± 2 kcal/mol and the partial pressure dependence on toluene was near zero, i.e. essentially the same as for benzene; however, the H 2 pressure dependence increased from less than 0.7 at 333 K to over unity at 373 K. The turnover frequencies were four times higher with the most acidic support compared to the least acidic support, i.e., at 333 K under 50 Torr toluene and 685 Torr H 2, the TOF on 0.24% Pt/SiO 2 · Al 2O 3 was 0.112 s −1, whereas it was 0.027s −1 on 0.96% Pt/SiO 2. This rate enhancement is attributed to an additional hydrogenation reaction occurring via hydrogen spilling over onto the support and reacting with aromatic molecules adsorbed on acid sites on the oxide. Deactivation was less of a problem with toluene compared to benzene.

Effects of toluene inhalation on pulmonary host defenses of mice

The potential hazards of exposure to vapor-phase toluene on pulmonary host defenses were evaluated. Mice exposed to concentrations ranging from 2.5–500 ppm, including the threshold limit value level of 100 ppm, exhibited increased susceptibility to respiratory infection with Streptococcus woepidemicus. The no-measurable-effect level for single, as well as for 5 exposures was 1 ppm. Significantly decreased pulmonary bactericidal activity was observed after single exposures to 500, 250, 100 and 2.5 ppm toluene, and after 5 daily 3-h exposures to 1.0 ppm of toluene. A 20-exposure study with toluene at 1 ppm produced no changes in either of the 2 assays.

Catalytic Oxidation of Toluene to Bibenzyl and Stilbene

A new type of benzylic oxidation of toluene in vapor-phase was described in which toluene was dehydrodimerized to bibenzyl and stilbene over Bi2O3-SnO2, catalyst in the temperature range 400∼600°C. Effects of temperature, contact time, and oxygen-to-toluene ratio were investigated in detail, and a proposal of reaction scheme was made.The results obtained show that reactions with longer contact time and higher oxygen-to-toluene ratio are favorable to the formation of stilbene, while shorter contact time and lower oxygen-to-toluene ratio favor the formation of bibenzyl. A reaction route for the formation of stilbene consistent with these data involves the following consecutive steps; toluene→benzylic intermediates→bibenzyl→stilbene. This type of benzylic oxidation is considered to be analogous to the oxidative dehydroaromatization of C3-C4 olefins.