Benzene, Toluene And O-xylene Research Articles

Electrochemical oxidation of volatile organic compounds in all-solid cell at ambient temperature

The catalytic elimination of indoor low-concentration gaseous benzene, toluene and o-xylene (BTX) under ambient conditions remains a challenge. Here, we firstly report a facile gas-solid interface electrochemical oxidation method for the mineralization of BTX at ambient temperature. A membrane electrode assembly (MEA) was used in the all-solid cell. An antimony-doped SnO2 catalyst was coated onto the surface of a porous Ti foam to act as the anode, and reduced graphene oxide/carbon fiber paper-supported Pt (Pt/rGO/CFP) was employed as the cathode. The activity test results showed that 100% BTX conversion to CO2 (85–99%) and CO (15–1%) was achieved within 4–5 h at the optimal cell voltage of 2.0 V at relative humidity 60%. Proton-transfer-reaction time-of-flight mass spectrometry and Fourier transform infrared spectroscopy results showed that no organic byproducts could be detected in the anodic reservoir. OH generated from water vapor discharge was measured directly by laser-induced fluorescence techniques. The electrochemical behavior of the working electrode in benzene solutions with different concentrations revealed that the benzene oxidation process was mainly mediated by OH at the onset potential of OER (2.0 V vs Ag/AgCl, saturated KCl). Our findings provide evidence that the gas-solid interface electrochemical oxidation method can be a potential method for ambient VOC destruction in indoor air environments.

Adsorption-Desorption of BTX (Benzene, Toluene and O-xylene) on Fe, Fe-Al Pillared Clay

The studies are conducted in laboratory to determine the adsorption-desorption behavior of BTX (benzene, toluene and o-xylene) in gas phase on Fe, Fe-Al pillared clays adsorbents. In experimental conditions of constant atmospheric pressure, initial concentrations with an increasing volume (0.5 - 2 ml) injected benzene (2.25), toluene (1.89) and o-xylene (1.66) μmol/L at T (40℃, 60℃ and 80℃), and the adsorption increases with increase of temperature, indicating that the adsorption process would be a chemical adsorption rather than physical one. The results are shown that the BTX adsorption data fitted very well (R2 > 0.999) to the both equations Langmuire and Elovitch for the three samples: bentonite (B), Fe-bentonite () and Fe-Al/bentonite (). At 80℃, the BTX adsorption capacity increased in the following order: . The maximum adsorption capacity () at 80℃ is 175.13, 171.84 and 171.81 μg/g respectively for benzene, toluene and o-xylene for ; the last is a good adsorbent of BTX removal. The benzene diffuses faster than toluene and o-xylene. Thermodynamic parameters, such as ,and are also discussed and the results suggested that the BTX adsorption on all samples used is a spontaneous and endothermic process. Desorption studies show that BTX is very easily desorbed with .

Versatile and efficient catalysts for energy and environmental processes: Mesoporous silica containing Au, Pd and Au-Pd

We described a versatile approach for the synthesis of Au/MCM-41, Pd/MCM-41 and Au-Pd/MCM-41 by the direct incorporation of the noble metals into the MCM-41 framework. The structural, textural and chemical properties were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), N2-adsorption (BET and BJH methods), H2-chemisorption, small angle X-ray scattering (SAXS), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The nanomaterials, being comprised of Au, Pd and Au-Pd nanoparticles and possessing high surface areas were applied as versatile and efficient catalysts in benzene, toluene and o-xylene (BTX) oxidation and in the steam reforming of ethanol for hydrogen production. The results revealed that the catalytic behavior in both processes was influenced by the experimental conditions and the nature of the catalyst employed. The Au-Pd/MCM-41 catalyst was the most active in the BTX total oxidation. On the basis of characterization data, it was proposed that the close contact between Pd and Au and the higher dispersion of Pd may be responsible for the enhanced activity of the bimetallic catalyst. However, the strong interaction between the noble metals did not improve the performance of the bimetallic catalyst in ethanol steam reforming, the Pd/MCM-41 catalyst being the most active and selective for hydrogen production.

Treatment of Chlorobenzene-Contaminated Gas Stream in a Biotrickling Filter Inoculated with <i>Ralstonnia pickettii</i> L2

Biotrickling filter (BTF) inoculated with Ralstonniapickettii L2 was established to treat waste gas containing chlorobenzene (CB). Results revealed BTF could achieve more than 80% removal efficiency of CB under the conditions of <0.6 g·m-3inlet concentration and >30 s empty bed residence time (EBRT). The mass ratio of carbon dioxide produced to the mixture of benzene, toluene, and oxylene (BTo-X) removed was approximately 2.10, indicating that 89.5% mineralization of the incoming CB vapor. The degradation of CB in the BTF followed Michaelis-Menten kinetic model, and the maximum specific degradation rate (rmax) was 76.3g·m-3·h-1. AWCD values indicated that the microganisms in the BTF showed the high microbial metabolic activities. Real-time PCR indicated that Ralstoniapickettii L2 could still maintain its stability andactivity in the BTF under different conditions.

Benzene, toluene and o-xylene (BTX) removal from aqueous solutions through adsorptive processes

In this study, the monocomponent adsorption of benzene, toluene and o-xylene (BTX) compounds, as model contaminants present in the petrochemical wastewaters, was investigated using three types of adsorbents: activated carbon (Carbon CD 500), a polymeric resin (MN-202) and a modified clay (Claytone-40). Langmuir and Freundlich models were able to fit well the equilibrium experimental data. The BTX adsorption capacity increased in the following order: Claytone-40 < CD 500 < MN-202. The maximum uptake capacity of MN-202, given by the Langmuir fitting parameter, for benzene, toluene and o-xylene was 0.8 ± 0.1, 0.70 ± 0.08 and 0.63 ± 0.06 mmol/g at 26 °C. Desorption kinetics for polymeric resin with 50 % methanol solution were fast being able to reuse the resin in consecutive adsorption/desorption cycles without loss of sorption capacity. The adsorptive behaviour at batch system was modelled using a mass transfer kinetic model, considering that the sorption rate is controlled by a linear driving force model, which successfully predicts benzene, toluene and o-xylene concentration profiles, with homogeneous diffusivity coefficients, Dh, between 3.8 × 10−10 and 3.6 × 10−9 cm2/s. In general, benzene diffuses faster than toluene and o-xylene, which is in agreement with molecular diffusivity in water.

Dual function adsorbent-catalyst CuO-CeO2/NaX for temperature swing oxidation of benzene, toluene and xylene

Abstract A less common cyclic process of decontamination of benzene, toluene and o-xylene (BTX) using a dual function adsorbent-catalyst, referred to as the temperature swing oxidation, is introduced and discussed in this research. Preparation technique and characterization of the dual function adsorbent-catalyst CuO-CeO2/NaX are presented. The temperature swing oxidation of BTX consists of two stages: adsorption of the VOC from the stream saturating the adsorbent-catalyst at different levels and catalytic oxidation of concentrated VOC induced by raising bed temperature at different flow rates of regenerative air. The results indicate that at lower saturation levels and lower flow rates of regenerative air a complete oxidation performance is better. The highest obtained values of the overall conversion of toluene, o-xylene and benzene into CO2 and H2O were 99.3, 99.8 and 77.5%, respectively, proving that the temperature swing oxidation using a dual function adsorbent-catalyst is a promising VOC decontamination technique under properly selected operating conditions.

Mesoporous Co3O4-supported gold nanocatalysts: Highly active for the oxidation of carbon monoxide, benzene, toluene, and o-xylene

Three-dimensionally ordered mesoporous Co3O4 (meso-Co3O4) and its supported gold (xAu/meso-Co3O4, x=3.7–9.0wt%) nanocatalysts were prepared using the KIT-6-templating and polyvinyl alcohol-protected colloidal deposition methods, respectively. The meso-Co3O4 and xAu/meso-Co3O4 samples exhibited a high surface area of 91–94m2/g. The Au nanoparticles with a size of 1–5nm were uniformly deposited inside the mesoporous channels of meso-Co3O4. There were good correlations of oxygen adspecies concentration and low-temperature reducibility with catalytic activity of the sample for CO or BTX (benzene, toluene, and o-xylene) oxidation. Among meso-Co3O4 and xAu/meso-Co3O4, the 6.5Au/meso-Co3O4 sample performed the best, giving the T90% (the temperature required for achieving a CO or BTX conversion of 90%) of −45, 189, 138, and 162°C for the oxidation of CO, benzene, toluene, and o-xylene, respectively. The apparent activation energies (23 and 45–55kJ/mol) over 6.5Au/meso-Co3O4 were much lower than those (48 and 72–92kJ/mol) over bulk Co3O4 for CO and BTX oxidation, respectively. The effects of water vapor, carbon dioxide, and sulfur dioxide on the catalytic activity of the 6.5Au/meso-Co3O4 sample were also examined. It is concluded that the higher surface area and oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and meso-Co3O4 were responsible for the excellent catalytic performance of 6.5Au/meso-Co3O4.

Microbial Biodegradation of Aromatic Compounds in a Soil Contaminated with Gasohol

The studies developed in this work aimed to find alternatives to biodegradation or bioremediation of soils contaminated with gasoline or gasohol. So, the biodegradation of benzene, toluene and o-xylene (BTX) in soil samples contaminated with gasoline or gasohol by a bacterial consortium was studied. Four bacterial strains were selected for the consortium based on their growth capacity in gasoline, gasohol and BTX as sole carbon sources, and on the production of biosurfactants in mineral medium containing gasohol as the sole carbon source. The reduction of TX concentrations in soil slurries in a multi-cell bioreactor system was used as the criterion to evaluate biodegradation efficiency. BTX removal was highly stimulated by air injection and mineral nutrients, and was significantly increased by the presence of the bacterial consortium. Addition of a proprietary oxygen release compound did not stimulate the biodegradation of BTX.

Heterogeneous adsorption and catalytic oxidation of benzene, toluene and xylene over spent and chemically regenerated platinum catalyst supported on activated carbon

The heterogeneous adsorption and catalytic oxidation of benzene, toluene and o-xylene (BTX) over the spent platinum catalyst supported on activated carbon (Pt/AC) as well as the chemically treated spent catalysts were studied to understand their catalytic and adsorption activities. Sulfuric aqueous acid solution (0.1N, H 2SO 4) was used to regenerate the spent Pt/AC catalyst. The physico-chemical properties of the catalysts in the spent and chemically treated states were analyzed by using nitrogen adsorption–desorption isotherm and elemental analysis (EDX). The gravimetric adsorption and the light-off curve analysis were employed to study the BTX adsorption and oxidation on the spent catalyst and its modified Pt/AC catalysts. The experimental results indicate that the spent Pt/AC catalyst treated with the H 2SO 4 aqueous solution has a higher toluene adsorption and conversion ability than that of the spent Pt/AC catalyst. A further studies of H 2SO 4 treated Pt/AC catalyst on their catalytic and heterogeneous adsorption behaviours for BTX revealed that the activity of the H 2SO 4 treated Pt/AC catalyst follows the sequence of benzene > toluene > o-xylene. The adsorption equilibrium isotherms of BTX on the H 2SO 4 treated Pt/AC were measured at different temperatures ranging from 120 to 180 °C. To correlate the equilibrium data and evaluate their adsorption affinity for BTX, the two sites localized Langmuir (L2m) isotherm model was employed. The heterogeneous surface feature of the H 2SO 4 treated Pt/AC was described in detail with the information obtained from the results of isosteric enthalpy of adsorption and adsorption energy distributions. Furthermore, the activity of H 2SO 4 treated Pt/AC about BTX was found to be directly related to the Henry's constant, isosteric enthalpy of adsorption and adsorption energy distribution functions.

Polymeric nanofilm-coated optical fibre sensor for speciation of aromatic compounds

An optical fibre sensor has been shown to be suitable for monitoring of benzene, toluene and o-xylene (BTX) with both high selectivity and sensitivity. The sensing principle underlying this experimental device is based on the changes of the reflected optical power when BTX vapours are present in the analytical tube containing an optical fibre coated with a thin film of poly[methyl(3, 3, 3-trifluoropropyl)siloxane]. The interaction of organic vapour with the sensitive surface promotes a variation of the light power, proportional to the amount of adsorbed BTX vapour. A set of experiments concerning different operational conditions was performed in order to promote a higher analytical performance and the newly developed BTX sensor showed higher sensitivity and shorter analytical time than a method based on gas chromatography–flame ionisation detector. Furthermore, the proposed sensor also provides the basis for an inexpensive analytical technique with adequate specificity for measurements of BTX at trace levels with appropriate reversibility, repeatability, and reproducibility. Finally, the analytical performance of the developed sensor was also evaluated and found adequate for industrial air samples.

COMPLETE OXIDATION OF VOLATILE ORGANIC COMPOUNDS OVER Ce/Cu/γ‐Al2O3 CATALYST

The effect of cerium (Ce) addition into Cu (5, 10 or 15 wt%)/γ‐Al2O3 catalysts on the catalyst properties and catalytic activity was investigated for the complete oxidation of volatile organic compounds (VOCs). X‐ray diffraction (XRD), the Brunauer Emmett Teller method (BET), temperature programmed reduction (TPR) by H2, and N2O pulse titration were used to characterize a series of supported copper catalysts modified with cerium. Cerium was observed to be an inhibitor for 5 wt% and promoter for 10 or 15 wt% Cu/γ‐Al2O3 catalyst. The results of TPR, average crystallite size and dispersion indicated that even though Ce loadings on 10 and 15 wt% Cu/γ‐Al2O3 caused a reduction in BET surface area of the catalysts, the loaded amounts of Ce enhanced the catalytic activity through the formation of highly dispersed copper clusters. Kinetic parameters were developed for individual benzene, toluene and o‐xylene (BTX) for 5 wt% Ce/10 wt% Cu/γ‐Al2O3 catalyst at temperatures ranging from 210 to 240°C. The Mars and Van Krevelen model was found to be an adequate description of the catalytic oxidation of BTX for this study. The activity sequence with respect to the BTX molecules was found to be benzene > toluene > o‐xylene under the surface‐reaction‐controlled region.

Impact of Ethanol on the Natural Attenuation of MTBE in a Normally Sulfate-Reducing Aquifer

Side-by-side experiments were conducted in an aquifer contaminated with methyl-tert-butyl ether (MTBE) at a former fuel station to evaluate the effect of ethanol release on the fate of pre-existing MTBE contamination. On one side, for approximately 9 months we injected groundwater amended with 1-3 mg/L benzene, toluene, and o-xylene (BToX). On the other side, we injected the same, adding approximately 500 mg/L ethanol. The fates of BToX in both sides ("lanes") were addressed in a prior publication. No MTBE transformation was observed in the "No Ethanol Lane." In the "With Ethanol Lane", MTBE was transformed to tert-butyl alcohol (TBA) underthe methanogenic and/or acetogenic conditions induced by the in situ biodegradation of the ethanol downgradient of the injection wells. The lag time before onset of this transformation was less than 2 months and the pseudo-first-order reaction rate estimated after 7-8 months was 0.046 d(-1). Our results imply that rapid subsurface transformation of MTBE to TBA may be expected in situations where strongly anaerobic conditions are sustained and fluxes of requisite nutrients and electron donors allow development of an active acetogenic/methanogenic zone beyond the reach of inhibitory effects such as those caused by high concentrations of ethanol.

Impact of Ethanol on the Natural Attenuation of Benzene, Toluene, and o-Xylene in a Normally Sulfate-Reducing Aquifer

Side-by-side experiments were conducted in a sulfate-reducing aquifer at a former fuel station to evaluate the effect of ethanol on biodegradation of other gasoline constituents. On one side, for approximately 9 months we injected groundwater amended with 1-3 mg/L benzene, toluene, and o-xylene (BToX). On the other side, we injected the same, adding approximately 500 mg/L ethanol. Initially the BToX plumes on both sides ("lanes") extended approximately the same distance. Thereafter, the plumes in the "No Ethanol Lane" retracted significantly, which we hypothesize to be due to an initial acclimation period followed by improvement in efficiency of biodegradation under sulfate-reducing conditions. In the "With Ethanol Lane", the BToX plumes also retracted, but more slowly and not as far. The preferential biodegradation of ethanol depleted dissolved sulfate, leading to methanogenic/acetogenic conditions. We hypothesize that BToX in the ethanol-impacted lane were biodegraded in part within the methanogenic/acetogenic zone and, in part, within sulfate-reducing zones developing along the plume fringes due to mixing with sulfate-containing groundwater surrounding the plumes due to dispersion and/or shifts in flow direction. Overall, this research confirms that ethanol may reduce rates of biodegradation of aromatic fuel components in the subsurface, in both transient and near steady-state conditions.