Model Volatile Organic Compounds Research Articles

Adsorption and degradation of model volatile organic compounds by a combined titania–montmorillonite–silica photocatalyst

A series of adsorptive photocatalysts, combined titania–montmorillonite–silica were synthesized. The resultant photocatalysts consisted of more and more spherically agglomerated TiO 2 particles with increasing of TiO 2 content, and anatase was the only crystalline phase with nano-scale TiO 2 particles. With increasing of the cation exchange capacity to TiO 2 molar ratio, specific surface area and pore volume increased very slightly. In a fluidized bed photocatalytic reactor by choosing toluene, ethyl acetate and ethanethiol as model pollutants, all catalysts had relatively high adsorption capacities and preferred to adsorb higher polarity pollutants. Langmuir isotherm model better described equilibrium data compared to Freundlich model. Competitive adsorptions were observed for the mixed pollutants on the catalysts, leading to decrease adsorption capacity for each pollutant. The combined titania–montmorillonite–silica photocatalyst exhibited excellent photocatalytic removal ability to model pollutants of various components. Almost 100% of degradation efficiency was achieved within 120 min for each pollutant with about 500 ppb initial concentration, though the efficiencies of multi-component compounds slightly decreased. All photocatalytic reactions followed the Langmuir–Hinshelwood model. Degradation rate constants of multi-component systems were lower than those for single systems, following the order of toluene < ethyl acetate < ethanethiol, and increased with the increase of adsorption capacities for different pollutants of various components.

Adaptation of a Constructed Wetland to Simultaneous Treatment of Monochlorobenzene and Perchloroethene

Mixed groundwater contaminations by chlorinated volatile organic compounds (VOC) cause environmental hazards if contaminated groundwater discharges into surface waters and river floodplains. Constructed wetlands (CW) or engineered natural wetlands provide a promising technology for the protection of sensitive water bodies. We adapted a constructed wetland able to treat monochlorobenzene (MCB) contaminated groundwater to a mixture of MCB and tetrachloroethene (PCE), representing low and high chlorinated model VOC. Simultaneous treatment of both compounds was efficient after an adaptation time of 2½ years. Removal of MCB was temporarily impaired by PCE addition, but after adaptation a MCB concentration decrease of up to 64% (55.3 μmol L−1) was observed. Oxygen availability in the rhizosphere was relatively low, leading to sub-optimal MCB elimination but providing also appropriate conditions for PCE dechlorination. PCE and metabolites concentration patterns indicated a very slow system adaptation. However, under steady state conditions complete removal of PCE inflow concentrations of 10–15 μmol L−1 was achieved with negligible concentrations of chlorinated metabolites in the outflow. Recovery of total dechlorination metabolite loads corresponding to 100%, and ethene loads corresponding to 30% of the PCE inflow load provided evidence for complete reductive dechlorination, corroborated by the detection of Dehalococcoides sp.

Effect of channel geometry, degree of activation, relative humidity and temperature on the performance of binderless activated carbon monoliths in the removal of dichloromethane from air

This work addresses the adsorption of dichloromethane (DCM), as a model volatile organic compound (VOC) over activated carbon monoliths (ACM). Several binderless ACM have been prepared at MAST Carbon Ltd. with different channel geometries (square and regular hexagon), cell densities and degrees of activation. The influence of relative humidity ( RH) and temperature, as most important atmospheric variables, on DCM adsorption over the ACM have been studied. The influence of the monolith geometric variables onto DCM adsorption has been experimentally proved and explained by the analysis of the mass transfer coefficients. Hexagonal channel monoliths present higher internal and external mass transfer coefficients and lower pressure drops than square ones. The influence of the degree of activation has been studied, both in equilibrium and dynamic vapour phase adsorption experiments. The variation of the degree of activation level from 23% to 40% increased the pore size of this materials leading to higher pore volumes and diffusivities, however DCM enthalpy of adsorption decreased due to confinements effects that are more important for smaller pores. RH and temperature decreased the adsorption capacities at breakthrough and saturation time. As main conclusion, hexagonal channel monoliths with low activation levels present the best properties on DCM adsorption in different atmospheric conditions.

Potential of ionic liquids for VOC absorption and biodegradation in multiphase systems

This work aims to evaluate the feasibility of using imidazolium ionic liquids (ILs) in the design of multiphase bioreactors for the removal of volatile organic compounds (VOCs). The IL affinity for three model VOCs (dimethyl sulfide, dimethyl disulfide and toluene) was evaluated by means of the dimensionless partition coefficient ( K). It was observed that ILs showed K values comparable to typical liquid solvents used in multiphase bioreactors for VOC biodegradation ( K values ranged from 0.009 to 0.011, 0.0012 to 0.0013 and 0.00061 to 0.00096 for dimethyl sulfide, dimethyl disulfide and toluene, respectively). Toxicity tests showed that both ILs at concentrations of 5% and 10% (v/v) inhibited the glucose uptake of an activated sludge during approximately 24 h. After such lag period, the microorganisms were able to recover its metabolic activity. However, VOC biodegradation experiments showed that ILs at 5% (v/v) were toxic for the activated sludge and a toxic synergistic effect of the IL–VOC combination likely occurred. After acclimation to the target VOCs, only the toluene biodegradation capacity was significantly increased in the presence of ILs. These toxic effects represent a key drawback for the potential of IL-based multiphase systems devoted to VOC biodegradation. Therefore, this study suggests that microbial acclimation only to the VOCs is not enough to get an efficient biodegradation in multiphase systems including ILs as non-aqueous phases.

Non-thermal Plasma for VOC Treatment in Flue Gases

The paper discusses non-thermal plasmas, their generation and characteristics, formation mechanisms of ozone and the treatment of volatile organic compounds (VOCs). In the experimental part, undecane (C11H24 as model VOCs) was treated with assistance of low temperature plasma at an atmospheric pressure which was generated in the so-called stack reactor. The gas composition was 13% of oxygen in nitrogen with impurities of carbon dioxide, carbon monoxide and undecane. The formation of by-products, as well as the removal efficiency, were investigated.

The effect of zirconia and niobia supports on the catalytic activity of surface VO x species in total oxidation of model volatile organic compounds

Samples of the catalysts containing 0.5, 5.0 and 40 mol.% of V 2O 5 supported on the ZrO 2 and Nb 2O 5 oxides, prepared by wet impregnation, were characterized by XRD and EPR. Their catalytic activity was tested in methanol and acetone total oxidation. Vanadium bronze samples were synthesized as a reference. Redox properties of surface oxovanadium entities were investigated by adsorption of NO probe molecule and monitored by EPR. Strong effect of the support on surface architecture of the vanadium species and their catalytic performance was observed. The highest activity in total VOC oxidation ( T 50% = 205 °C for methanol and 230 °C for acetone) was observed for zirconia-supported catalysts containing 5.0 mol.% of V 2O 5. In all cases the niobia-supported catalysts were less active than the corresponding zirconia-supported samples.

Catalytic nonthermal plasma reactor for the abatement of low concentrations of isopropanol

Oxidative decomposition of a model volatile organic compound (isopropanol, IP) has been carried out in a catalytic dielectric barrier discharge (DBD) reactor, where modified sintered metal fiber (SMF) filter was used as the inner electrode. The SMF was modified with Mn and Co oxides by impregnation, followed by calcination and the performance of the DBD reactor was tested for the oxidation of IP in the specific input energy range 160–720 J/l by varying the high voltage and frequency. It has been observed that SMF modification by MnO x and CoO x not only improved the conversion of isopropanol, but also increased the selectivity towards total oxidation. MnO x modification showed better performance than CoO x , which may be attributed to the formation of atomic oxygen by in situ decomposition of ozone. It has been demonstrated that with MnO x /SMF it is possible to completely oxidize 100 ppm of isopropanol at SIE < 200 J/l.

Characterization of methane, benzene and toluene-oxidizing consortia enriched from landfill and riparian wetland soils

The microbial oxidations of methane (M) and volatile organic compounds (VOCs) were compared with those of M and VOCs alone after enriching soil samples with M and/or VOCs. Landfill cover and riparian wetland soils from which M and VOCs were simultaneously emitted were selected as representative samples. Benzene (B) and toluene (T) were employed as the model VOCs. With the landfill soil consortia, the rate of M oxidation decreased from 4.15–5.56 to 2.26–3.42μmolg-dry soil−1h−1 in the presence of both B and T, but with the wetland soil consortia the rate of M oxidation (3.09μmolg-dry soil−1h−1) in the mixture of M as well as both B and T was similar to that of M alone (3.04μmolg-dry soil−1h−1). Compared with the methanotrophic community with M alone, the portion of type II methanotrophs was greater in the landfill consortia; whereas, the proportion in wetland consortia was less in the presence of both B and T. The oxidations of B and T were stimulated by the presence of M with both the landfill and wetland consortia. There were no correlations between the oxidation rate of M and those of B and T with the gene copy numbers of pmoA and tmoA responsible for the oxidations.

Effect of V-UV-radiation on VOCs-saturated zeolites

The combination of adsorption on zeolites and vacuum ultraviolet (V-UV) irradiation was applied to the treatment of gaseous effluents containing volatile organic compounds (VOCs). A xenon-excimer (Xe 2*) radiation source emitting at 172 nm was employed and two types of zeolites (faujasite Y (DAY) and ZMS-5 (DAZ)) were tested in adsorption/irradiation cycles of three model VOC pollutants (1-butanol, benzene and toluene). A specific diffusion cell was used in dynamic experiments for producing air streams containing each VOC at chosen and stable concentrations. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses were performed on the solids after VOC saturation and irradiation. Important changes were detected in the properties of the DAY zeolite when using toluene as a pollutant. In particular, the Si/Al ratio was modified at the surface and in the framework of the zeolite, as a consequence of a rearrangement of the Al and Si atoms in the solid. In contrast, the DAZ zeolite retained its superficial and structural properties after V-UV treatment. In the case of 1-butanol, changes in the zeolite structure were negligible, and no change was observed in the zeolite in the case of benzene. Solid state NMR analysis confirmed these results and revealed that when the DAY zeolite saturated with toluene was irradiated at 172 nm, changes in the shifts of Si and Al atoms took place, suggesting a possible interaction/reaction between the zeolite framework and the benzyl radical produced as a consequence of the toluene oxidation.

Synergistic Coupling of the Redox Properties of Supports and Cobalt Oxide Co3O4 for the Complete Oxidation of Volatile Organic Compounds

Cobalt catalysts supported on metal oxides (CeO2, TiO2 and Al2O3) were prepared to investigate the effects of the support for the complete oxidation of propene, a model volatile organic compound of hydrocarbon type. The presence of ethylenediamine during the preparation of Co/metal oxides was also studied and compared with a conventionally prepared catalyst. Addition of an aqueous solution of ethylenediamine to a cobalt nitrate solution had a promotional effect on the catalytic performance of the solids. More activated oxygen species are available for propene oxidation due to the highest cobalt dispersion obtained when ethylenediamine is used during the synthesis. But the activation of oxygen species and the reducibility of the catalyst depend on the support used. The Co/CeO2 catalysts, synthesized by two protocols, presented the highest propene oxidation activity from the series due to the highest synergistic coupling of the redox properties of CeO2 and Co3O4.

Degradation of VOC gases in liquid phase by photocatalysis at the bubble interface

Photocatalytic reactions in the gas phase have a number of disadvantages including the adverse effects of relative humidity, the emission of decomposition intermediates at the reactor exit and the deactivation of the photocatalyst surface by decomposition intermediates. In this study, these disadvantages can be overcome using a novel photocatalytic reaction system. Volatile organic compound (VOC) gases were decomposed at the bubble interface in a TiO2 suspension by using TiO2 photocatalysis in the heterogeneous liquid-bubble (LB) phase since the intermediates dissolve into water and then are continuously decomposed regardless of humidity. Toluene, p-xylene, styrene and formaldehyde were chosen as model VOC gases to investigate photocatalytic reactivity in the LB phase. The removal ratio of VOC gases in the LB phase was equal to or greater than that in the gas phase, although the reactivity in the LB phase depended on the reaction rate of OH radicals and the hydrophobicity of the VOC gases. The reaction in the LB phase also depended on the wavelength and intensity of UV light. Specifically, the removal and mineralization ratios were improved by using shorter wavelengths of UV irradiation. Finally, as a trial experiment, we applied the microbubble technique to this system. When VOC gases were introduced into the system as microbubbles, VOC gas was effectively removed and high removal ratios were obtained regardless of the wavelength and intensity UV light.

Products and mechanisms of the oxidation of organic compounds in atmospheric air plasmas

Atmospheric plasma-based technologies are developing as a powerful means for air purification, specifically for the oxidation of organic pollutants. To achieve a better control on the emissions produced by such treatments mechanistic insight is needed in the complex reactions of volatile organic compounds (VOCs) within the plasma. An account is given here of our comparative studies of the behaviour of model VOCs in response to different corona regimes (+dc, −dc and +pulsed) implemented within the same flow reactor. Model VOCs considered include two alkanes (n-hexane and i-octane), one aromatic hydrocarbon (toluene) and two halogenated methanes, dibromomethane (CH2Br2) and dibromodifluoromethane (CF2Br2, halon 1202). Efficiency and product data are reported and discussed as well as various possible initiation reactions. A powerful diagnostic tool is ion analysis, performed by atmospheric pressure chemical ionization-mass spectrometry: it provides a map of major ions and ion–molecule reactions and a rationale for interpreting current/voltage characteristics of dc coronas. It is shown that, depending on the specific VOC and corona regime adopted, different initiation steps prevail in the VOC-oxidation process and that the presence of a VOC, albeit in small amounts (500 ppm), can greatly affect some important plasma properties (ion population, current/voltage profile, post-discharge products).

Total oxidation of benzene and chlorobenzene with MoO 3- and WO 3-promoted V 2O 5/TiO 2 catalysts prepared by a nonhydrolytic sol–gel route

Vanadia–titania oxidation catalysts are highly regarded for the abatement of persistent air pollutants including aromatics, chlorinated aromatics, furans and dioxins in gas effluents. Molybdenum and tungsten oxides are recognized as efficient promoters enhancing the efficiency of vanadia-based catalysts. Classical approaches for the preparation of promoted catalysts involve multi-step processes. Here, binary and ternary mixed oxide xerogels are formed in one step by nonhydrolytic condensation reactions of chloride precursors in non-aqueous medium. Calcination was applied to provoke the migration of active and promoting oxides toward the surface, leading to well-spread vanadium, molybdenum and tungsten oxide species on the surface of anatase particles. The resulting catalysts are mesoporous and their composition is precisely controlled, confirming the versatility and reliability of the preparation route. The samples perform well in the deep oxidation of benzene and chlorobenzene, chosen as model volatile organic compounds (VOC). The performances of ternary catalysts systematically exceed those of binary V 2O 5-TiO 2, highlighting the promoting effect of WO 3 and MoO 3.

Detection of Volatile Organic Compounds in Breath Using Thermal Desorption Electrospray Ionization-Ion Mobility-Mass Spectrometry

A thermal desorption unit has been interfaced to an electrospray ionization-ion mobility-time-of-flight mass spectrometer. The interface was evaluated using a mixture of six model volatile organic compounds which showed detection limits of <1 ng sample loaded onto a thermal desorption tube packed with Tenax, equivalent to sampled concentrations of 4 microg L(-1). Thermal desorption profiles were observed for all of the compounds, and ion mobility-mass spectrometry separations were used to resolve the probe compound responses from each other. The combination of temperature programmed thermal desorption and ion mobility improved the response of selected species against background ions. Analysis of breath samples resulted in the identification of breath metabolites, based on ion mobility and accurate mass measurement using siloxane peaks identified during the analysis as internal lockmasses.

Characterization of carbon cryogel microspheres as adsorbents for VOC

Adsorption characteristics of carbon cryogel microspheres (CC microspheres) with controlled porous structure composed of mesopores (2 nm < d p < 50 nm; d p is pore diameter) and micropores ( d p < 2 nm) were studied to examine their suitability as adsorbents for a volatile organic compound (VOC). The amount of toluene, as a model VOC, adsorbed on the CC microspheres could be changed by varying either the size of the mesopores or the volume of the micropores. The peak temperature of the temperature-programmed desorption profiles of toluene from the CC microspheres was higher than that from granular activated carbon (GAC) with numerous micropores, indicating that toluene is adsorbed more strongly on CC microspheres than on GAC. To permit the practical use of CC microspheres, the adsorption characteristic of moisture on CC microspheres and GAC were evaluated. The effect of adsorption of moisture on the gas permeation property of an adsorption module prepared from the CC microspheres was also examined.

Structure and property development during solidification of VOC compliant automotive refinish clearcoats

A model volatile organic compound (VOC) compliant two component (2K) acrylic polyol refinish clearcoat was prepared and used to study the effects of a cellulose-based additive on drying, curing, rheology and stress development at room temperature. Results were compared with commercially available VOC compliant and traditional non-compliant clearcoats. Most of the drying of the low VOC coatings occurred before appreciable (20%) crosslinking. Tensile stress developed in the same timeframe as drying and then relaxed over a longer time scale. All coatings had relatively low levels of peak stress (<0.25 MPa) compared to other polymer coatings. Model low VOC coatings prepared with the additive had higher peak stresses than those without the additive. In addition, rheological data showed that the additive resulted in greater viscosity buildup after application. Both effects are attributed to the high glass transition temperature of the additive (∼70 °C).

Relationships between biomass, pressure drop, and performance in a polyurethane biofilter

In biofilters for controlling volatile organic compounds (VOCs), clogging in the filter bed due to overgrowth of biomass causes the deterioration of biofilter performance. In this study, the relationships between biofilter performance, biomass concentration ( X), and pressure drop (Δ P) was qualitatively and quantitatively evaluated in a polyurethane (PU) biofilter. Benzene was used as a model VOC. The relationship between Δ P and X at a moisture content of 80–90% was expressed as log Δ P (mm H 2O m −1) = 0.315 + 3.87 log X (g-dry cell weight (DCW) g-PU −1), 0.8 < X < 2.5. Maximum removal rate ( V m) for benzene declined with increasing biomass concentration at more than 0.8 g-DCW g-PU −1, and the following equation was obtained: V m (g m −3 h −1) = 811 − 261 X (g-DCW g-PU −1), 0.8 < X < 2.5. The quantitative relationships obtained in this study can be applied to assess and optimize PU biofilter performance for long-term operation.

VOCs absorption in rotating packed beds equipped with blade packings

Abstract This work investigated the volatile organic compounds (VOCs) removal efficiency of the RPB equipped with blade packings using absorption. Methanol, methyl ethyl ketone and methyl acetate were used as the model VOCs herein. The VOCs removal efficiency (E) was observed to increase with the rotational speed and the liquid flow rate but decrease with the gas flow rate. Moreover, methanol absorption provided the largest E values owing to that the solubility of methanol in water was the highest among three VOCs, implying that the centrifugal force induced from the RPB equipped with blade packings did not affect the thermodynamic property of VCOs. In addition, when the gas flow rate was 50 L/min, the highest E values for methanol, methyl ethyl ketone and methyl acetate absorption were 89.8, 77.6, and 68.9, respectively. Consequently, the RPB equipped with blade packings would be more applicable to the removal of more soluble VOCs from gaseous streams of huge flow rate.

Simulating accumulation of biofilms in biotrickling filter

Accumulations and spatial and dynamic variations of biofilms in the media of a biotrickling filter were simulated using mathematical models for Volatile Organic Compound (VOC) removal. Toluene was selected as the model VOC. Effects of toluene concentration and gas Empty Bed Contact Time (EBCT) on VOC removal were also investigated. Results showed that biofilm thickness increased with increased operation duration and the growth rate of biofilms increased with increased inlet toluene concentration and EBCT at a constant toluene loading. The profiles of the thickness and growth rate of biofilms along the medium depth dropped gradually at a certain time.

Design and performance of a system for blood collection of rats under whole-body inhalation exposure

In order to obtain basic risk assessment data on human health exposure to volatile organic compound (VOC) vapor by inhalation, a whole-body inhalation exposure system which allows blood collection during the exposure period was designed. The system was tested using chloroform as a model VOC. Chloroform vapor, sampled from the supply-header, animal-chambers and exhaust-header, remained constant in this system with variations in its concentration being less than 2%; flow rate of the vapor through the system was also constant. Rats were exposed to chloroform vapor and blood collected from the tail during exposure to the chloroform vapor. The chloroform concentration in the blood increased during the initial 60 min of exposure, and afterwards its concentration remained at about 2 microg/ml from 60 to 360 min. In conclusion, our design allows blood to be collected from individual rats during exposure by inhalation to test VOCs and changes in the blood concentration of the VOC during exposure to be assessed.