Benzene, Toluene, Ethylbenzene And Xylene Research Articles

Exploratory analysis of the atmospheric levels of BTEX, criteria air pollutants and meteorological parameters in a tropical urban area in Northeastern Brazil

Air pollution is responsible for serious damage to the environment and to the health of the population. The objective of this study was to apply chemometric methods to determine and evaluate the relationships between the atmospheric concentrations of BTEX (benzene, toluene, ethylbenzene and xylene) compounds, criteria air pollutants and meteorological parameters, as well as to identify the type of emission source associated with these pollutants at seven sites in the city of Salvador, Bahia, Brazil during rainy and dry periods. BTEX compounds were monitored using passive samplers with a solvent desorbable adsorbent (activated charcoal) for 14 days and determined by gas chromatography with flame ionization detection. Criteria air pollutants were determined using automatic continuous analyzers and the meteorological parameters by means of multi-parameters sensors. The average data obtained were submitted to multivariate analysis, using principal component analysis (PCA) with varimax rotation and hierarchical cluster analysis (HCA). Some diagnostic ratios between the BTEX species, besides correlation analysis between the pollutants and meteorological parameters were also used to identify the origin of the emissions. The sum of average concentrations of BTEX compounds was lower in the dry period (5.90 ± 3.28 μg m−3) than in the rainy period (7.95 ± 2.95 μg m−3), probably due to higher values of temperature and solar radiation which favor photochemical reactions in the dry period, thereby increasing the rate of removal of the BTEX compounds from the atmosphere. The first three principal components together (PC1, PC2 and PC3) explain 80.1% of the total data variance, with a tendency to separate the samples into two groups, depending on the seasonal period. According to HCA, four main groups were formed with high degrees of similarity. Strong correlations were found among BTEX species, and between these compounds with CO, NO, and NO2, thus indicating a common emission source for these compounds, the vehicular fleet. Toluene/benzene (T/B), m,p-xylene/benzene (m,p-X/B) and o-xylene/benzene (o-X/B) ratios suggested that vehicular emissions constituted the main source of BTEX compounds. PCA and HCA results also confirmed these observations.

Toxicity removal by Daphinia similis assay in BTEX contaminated groundwater using nanometric TiO2/ZrO2 film and black light

In this work, a photocatalytic tubular reactor, with a nanometric TiO2/ZrO2 film, immobilized on glass substrate, was developed in order to investigate the degradation of volatile organic compounds, such as, benzene, toluene, ethylbenzene and xylene (BTEX ) in groundwater sample, under black light irradiation (365nm). The BTEX compound were determined by solid phase microextraction (SPME) technique and analyzed by Gas Chromatography - Ionization Flame Detection (CG-FID). The efficiency of photocatalytic process was evaluated by determination of BTEX removal and toxicity, using Daphnia similis as organism-test. The influence of the initial concentration of BTEX in the degradation process was investigated. The degradation process of sample groundwater contaminated with BTEX (145μg/L) from gasoline, resulted in 90% of efficiency after 120 minutes of treatment. The toxicity (EC50-48 h) of the groundwater sample to Daphnia similis was 14.1% (10.5-19.0) for untreated samples. After 30 min of treatment, the EC50-48 h was of 84.3 (71-100%). The benzene efficiency removal was reduced in function of the increase of its initial concentrations that observation was not found for the other compounds studied.

Exposure to ambient volatile organic compounds in an area with excess cancer and asthma morbidity

TPS 671: Cardiometabolic effects of long-term air pollution exposure, Exhibition Hall, Ground floor, August 26, 2019, 3:00 PM - 4:30 PM Background: The Haifa Bay Area (HBA) has been documented to experience relatively high morbidity from asthma and cancer. Previously, association with emissions from industrial facilities in the HBA has been examined. However, ambient concentrations of fine particulate matter, nitrogen oxides and BTEX (benzene, toluene, ethylbenzene and xylene) are lower in HBA than in other districts (such as the Tel-Aviv area). It has been proposed that this discrepancy may possibly result from unmeasured concentrations of certain volatile organic compounds and/or heavy metals, which are uniquely emitted by industrial facilities and are not characteristic of traffic, such as 1,2-dichloroethane and Isoamyl alcohol. A list of such compounds was formulated by the regulatory bodies and bi-weekly measurements began in 2015. Methods: Data on 25 distinct pollutants was collected from 30 locations spread within and outside of HBA. The measurements were generally performed on a bi-weekly basis from the start of 2015 until the end of 2018. The annual mean measurements within HBA were compared to those in other regions using a Mann-Whitney U-test. Results: A preliminary analysis indicates that there are significantly lower concentrations of butadiene, benzo(a)pyrene, and trichloroethylene in HBA than in other regions. The only pollutant whose concentrations seem to be significantly higher in HBA is particulate vanadium, which is commonly emitted into the atmosphere by metallurgical industries, oil refineries and the combustion of fossil fuels. No significant differences were found in the concentrations of the remaining 21 pollutants. Conclusion: The excess morbidity in the HBA was not found to be related to ambient air pollution. Future research of this issue should perhaps focus on indoor exposures and explanatory variables rather than on ambient air pollution.

Microbial degradation of BTEX compounds in groundwater after ozonation process

BTEX (benzene, toluene, ethylbenzene, and xylene) compounds are common in a variety of water resources, including groundwater. However, the ongoing biodegradation processes are not sufficiently effective, and accumulation of these substances occurs. To enhance the biodegradability, ozonation can be used for transformation of these recalcitrant compounds to easily biodegradable organics. This paper is focused on expanding existing knowledge of degrading BTEX substances by ozonation process before biological degradation. Batch experiments were prepared from aquifer sediment with ozonated and non-ozonated groundwater contaminated by 10 mg dm−3 BTEX. The results showed that degradation efficiency of these compounds without previous ozonation was in the first 7 days 9.1% for benzene, 68.4% for toluene, 74.9% for p-xylene, and 89.4% for ethylbenzene. In this process, the complete degradation time for these substances was up to 7 days for ethylbenzene, and 14 days for toluene and p-xylene. Benzene was not degraded even after 21 days of the experiment. In comparison, the ozonation process increased the biological degradation efficiency when all these compounds were completely degraded within 7 days of the experiment. The total number of attached cells was on average 1.2 orders of magnitude higher than in the case of the non-ozonated BTEX samples.

Evaluation of dimethyl sulfoxide (DMSO) as a co-solvent for toxicity testing of hydrophobic organic compounds.

Toxicity testing of hydrophobic compounds with low aqueous solubility remains challenging. Dimethyl sulfoxide (DMSO) is widely used as a co-solvent for toxicity testing of hydrophobic chemicals, but it may modulate chemical toxicity patterns. In this study, we critically evaluated the suitability of DMSO as a co-solvent for toxicity testing of hydrophobic organic compounds in aqueous solutions. As the toxicity measure, we used growth inhibition of a natural bacterial community, and the test toxicants included phenol, BTEX (benzene, toluene, ethylbenzene and xylene) and transformation products of polycyclic aromatic hydrocarbons (PAHs). We found that dose-response curves for phenol were unaffected by DMSO concentrations up to 10% (v/v) and that DMSO (5% v/v) did not affect the degree of bacterial growth inhibition for any of the other test compounds in short-term experiments (3.5 h). By contrast, marked co-solvent effects of DMSO were observed in the long-term assay (25 and 27 h). We therefore conclude that DMSO has excellent co-solvent properties for short-term (≤3.5 h) toxicity testing of sparingly water-soluble compounds and its application provides a simple, inexpensive approach for screening of various environmentally relevant hydrophobic chemicals. Importantly, the use of DMSO allows for generation of full dose-responses that may otherwise not be attained.

Effective extrapolation models for ecotoxicity of benzene, toluene, ethylbenzene, and xylene (BTEX)

Benzene homologues have significant toxic effects to aquatic organisms. In this study, the acute toxicity data of benzene, toluene, ethylbenzene and xylene (BTEX) were collected and screened, and the toxicity extrapolation model of paired BTEX was established. The results showed that except the correlation between benzene and xylene was not strong due to insufficient data, the linear correlation of the other five paired BTEX was good (p < 0.01), and R2 fitted by the four out of five paired BTEX was greater than 0.85. The cross validation showed that ethylbenzene-xylene model was optimal, and for most species (81.8%), the established five BTEX models had a prediction error of less than 10%. Also, these extrapolation models were validated by experimental results of Pseudorasbora parva. The difference between the predicted and measured values of the acute toxicity of BTEX was less than 1 fold, which indicated that the extrapolation model had high accuracy.

Exposure to BTEX in buses: The influence of vehicle fuel type

Diesel-fueled buses have been replaced by Compressed Natural Gas (CNG) to minimize the high level of emissions in urban areas. However, differences in indoor exposure levels to Benzene, Toluene, Ethylbenzene and Xylene (BTEX) in those vehicles have not been investigated so far. The primary aim of this study was to determine if passengers are exposed to different BTEX levels when using buses powered by CNG or by diesel, and further explore if indoor levels are influenced by external air quality. For this purpose, BTEX air concentrations were measured in bus cabins (CNG and diesel), parking stations and in a background urban area using passive air samplers. Results showed that BTEX concentrations inside vehicles were higher than outside, but no significant differences were found between buses powered by CNG or by diesel. In CNG vehicles, high and significant positive correlation was found between benzene and the number of journeys in the same route (rs = 0.786, p < 0.05), vehicle operating time (rs = 0.738, p < 0.05), exposure time (rs = 0.714, p < 0.05) and exposure index (rs = 0.738, p < 0.05), but this was not observed for diesel vehicles. Benzene in bus cabins was found to be significantly below reference value for human health protection. However, excepting p-xylene, all other aromatic pollutants have a mean concentration significantly above the lowest effect level (p ≤ 0.002 for all comparisons). Additionally, higher BTEX levels in cabin buses than in outdoor air suggest the presence of other emission sources in indoor cabins. These findings emphasize the need for further studies to fully characterize indoor emission sources in order to minimize the negative impact of BTEX exposure to human health.

Experimental investigation on combustion and unregulated emission characteristics of butanol-isomer/gasoline blends

Effects of butanol isomers on characteristics of combustion and emission were studied on PFI SI engine. Experiments were operated under the condition of 3 and 5 bar brake mean effective pressure (BMEP) engine loads and different equivalence ratios (φ=0.83−1.25) with engine speed of 1200 r/min using blends made of 70 vol.% gasoline and 30 vol.% butanol isomers (N30, S30, I30 and T30). The results indicated that compared with gasoline, all butanol isomer blends have higher cylinder pressure. N30 has the highest and most advanced peak pressure, and T30 shows a higher brake specific fuel consumption (BSFC) and lower brake thermal efficiency (BTE). N30 presents a lower UHC emissions and I30 has slightly higher CO emissions than other blends. For unregulated emissions, compared with gasoline, butanol isomer blends have higher acetaldehyde, and N30 produces a higher emission of 1,3-butadiene than other blends. A reduction in benzene, toluene, ethylbenzene and xylene (BTEX) has been found with butanol isomer blends.

BTEX compositions and its potential health impacts in Malaysia

This study aims to determine the composition of BTEX (benzene, toluene, ethylbenzene and xylene) and assess the risk to health at different sites in Malaysia. Continuous monitoring of BTEX in Kuala Lumpur City Centre, Kuala Terengganu, Kota Kinabalu and Fraser Hill were conducted using Online Gas Chromatograph. For comparison, BTEX at selected hotspot locations were determined by active sampling method using sorbent tubes and Thermal Desorption Gas Chromatography Mass Spectrometry. The hazard quotient (HQ) for non-carcinogenic and the life-time cancer risk (LTCR) of BTEX were calculated using the United States Environmental Protection Agency (USEPA) health risk assessment (HRA) methods. The results showed that the highest total BTEX concentrations using continuous monitoring were recorded in the Kuala Lumpur City Centre (49.56 ± 23.71 μg/m3). Toluene was the most dominant among the BTEX compounds. The average concentrations of benzene ranged from 0.69 ± 0.45 μg/m3 to 6.20 ± 3.51 μg/m3. Measurements using active sampling showed that BTEX concentrations dominated at the roadside (193.11 ± 114.57 μg/m3) in comparison to petrol station (73.08 ± 30.41 μg/m3), petrochemical industry (32.10 ± 13.13 μg/m3) and airport (25.30 ± 6.17 μg/m3). Strong correlations among BTEX compounds (p<0.01, r>0.7) at Kuala Lumpur City Centre showed that BTEX compounds originated from similar sources. The values of HQ at all stations were <1 indicating the non-carcinogenic risk are negligible and do not pose threats to human health. The LTCR value based on benzene inhalation (1.59 × 10−5) at Kuala Lumpur City Centre were between 1 × 10−4 and 1 × 10−5, representing a probable carcinogenic risk.

Application of Response Surface Methodology for Ethanol Conversion into Hydrocarbons Using ZSM-5 Zeolites

The ethanol conversion into hydrocarbons (light olefins and aromatics) using alkali-treated HZSM-5 with different SiO2/Al2O3 ratios (23, 38, and 53) zeolites was evaluated. The desilicated SAR 38 zeolite exhibited significant growth on the external surface area (61–212 m2/g) and the mesopore volume (0.07–0.37 cm3/g) without significate reduction on XRD crystallinity (93%). All catalysts were active on the ethanol conversion into hydrocarbons. At the same set of variables, the alkali-treated HZSM-5 zeolites showed a better conversion and a high selectivity to C4–C9 hydrocarbons when compared to the parent microporous zeolites. Only the parent HZSM-5 zeolite (SAR 53) was chosen for the statistical study using the standard response surface methodology in combination with the central composite design. It was found that maximum BTEX (benzene, toluene, ethylbenzene, and xylenes) and minimum ethylene production were reached for the following conditions: temperature 450 °C, pressure 20 bar, and WHSV (weight hourly space velocity) 5 h−1.

Bioelectrochemical treatment of groundwater containing BTEX in a continuous-flow system: Substrate interactions, microbial community analysis, and impact of sulfate as a co-contaminant

Microbial electrochemical technologies (MET) are increasingly being considered for in situ remediation of contaminated groundwater. However, their application potential for the simultaneous treatment of complex mixtures of organic and inorganic contaminants, has been only marginally explored. Here we have analyzed the performance of the ‘bioelectric well’, a previously developed bioelectrochemical reactor configuration, in the treatment of benzene, toluene, ethyl-benzene and xylenes (BTEX) mixtures. Although to different extents, all BTEX were found to be degraded in the bioelectrochemical system, operated using a continuous-flow of groundwater at a hydraulic retention time of 8.8 h, with the graphite anode potentiostatically controlled at +0.200 V vs. the standard hydrogen electrode. In the case of toluene and ethyl-benzene, biodegradation was further confirmed by the GC–MS identification of fumarate-addition metabolites, previously shown to be involved in the activation of these contaminants under anaerobic conditions. Degradation rates were higher for toluene (31.3 ± 1.5 mg/L d) and lower for benzene (6.1 ± 0.3 mg/L d), ethyl-benzene (3.3 ± 0.1 mg/L d), and xylenes (4.5 ± 0.2 mg/L d). BTEX degradation was linked to electric current generation, with coulombic efficiencies falling in the range 53–69%, although methanogenesis also contributed to contaminant degradation. Remarkably, the system also allowed removal of sulfate simultaneously with toluene. Sulfate removal was likely driven by the hydrogen abiotically generated at the cathode. Taken as a whole, these findings highlight the remarkable potential of this innovative reactor configuration for application in a variety of contamination scenarios.

Simulações da migração de plumas dissolvidas de compostos BTEX geradas por LNAPL trapeado

O vazamento acidental de hidrocarbonetos é um cenário comum de contaminação subsuperficial. Uma vez liberado, o hidrocarboneto migra até atingir as vizinhanças da zona saturada, onde se acumula. Em razão da flutuação do nível d’água, o LNAPL (light non-aqueous phase) é redistribuído e trapeado na zona saturada. O LNAPL trapeado é responsável pela liberação de benzeno, tolueno, etilbenzeno e xilenos (BTEX) para a água, gerando plumas de fase dissolvida desses compostos. Essas plumas variam em dimensão e concentração ao longo do tempo, em resposta à depleção dos compostos BTEX na área-fonte. Para representar esta condição é proposta uma metodologia que combina o uso dos aplicativos MODFLOW, para simulações de fluxo, EXHAURIS, para simulação da transferência de massa e MT3DMS, para simulação do transporte de solutos. As simulações realizadas reproduziram o comportamento das plumas dissolvidas de benzeno e etilbenzeno geradas a partir da dissolução do querosene de aviação. Os resultados indicam que a pluma de benzeno se extingue dentro de um período de 10 anos, enquanto o etilbenzeno persiste por mais de 20 anos. Tal diferença está associada à menor fração molar e à maior solubilidade do benzeno em relação ao etilbenzeno. Os testes indicam que a metodologia proposta é uma alternativa promissora para previsões do comportamento de plumas dissolvidas ao longo do tempo, contemplando a condição de depleção da área-fonte.

Biodegradation of waste streams containing benzene, toluene, ethylbenzene and xylene (BTEX): Practical implications and brief perspectives

Biodegradation of waste streams containing benzene, toluene, ethylbenzene and xylene (BTEX): Practical implications and brief perspectives

Complex-conductivity monitoring to delineate aquifer pore clogging during nanoparticles injection

SUMMARYLaboratory and field studies have demonstrated the applicability of nanoparticles (NP) for accelerated contaminant degradation. Beside other limitations (e.g. costs, delivery, longevity, non-target specific reactions), concerns of regulators arose regarding toxicity of injected NP and particles delivered off-target (i.e. renegade particles). Renegade particles also significantly reduce the efficiency of the remediation. The delivery of particles off-target is caused, mainly, by unintended fracking, where the fractures act then as preferential flow paths changing the trajectory of the particles. Hence, the real-time monitoring of particle injection is of major importance to verify correct particle delivery and thus help to optimize the remediation strategy. However, to date NP monitoring techniques rely on the analysis of soil and water samples, which cannot provide information about clogging or the formation of fractures away of the sampling points. To overcome these limitations, in this study we investigate the applicability of complex-conductivity imaging (CCI), a geophysical electrical method, to characterize possible pore clogging and fracking during NP injections. We hypothesize that both processes are related to different electrical footprints, considering the loss of porosity during clogging and the accumulation of NP in areas away of the target after fracking. Here, we present CCI results for data collected before and during the injection of Nano-Goethite particles (NGP) applied to enhance biodegradation of a BTEX (benzene, toluene, ethylbenzene and xylene) contaminant plume. Imaging results for background data revealed consistency with the known lithology, while overall high electrical conductivity values and a negligible induced-polarization magnitude correspond with the expected response of a mature hydrocarbon plume. Monitoring images revealed a general increase (∼15 per cent) in the electrical conductivity due to the injected NGP suspension in agreement with geochemical data. Furthermore, abrupt changes in this trend, shortly before daylighting events, show the sensitivity of the method to pore clogging. Such interpretation is in line with the larger variations in CCI resolved in the unsaturated zone, clearly indicating the accumulation of renegade NGP close to the surface due to fracking. Our results demonstrate the applicability of the CCI method for the assessment of pore clogging accompanying particles injection.

Histopathological Biomarkers of Exposure to Monocyclic Aromatic Hydrocarbons in Clarias Ggariepinus (African Catfish)

The pollution of the environment with petroleum products through spills in oil producing countries has resulted in the widespread distribution of benzene, toluene, ethylbenzene and xylene. The aim of this study was to identify histopathological alterations in Clarias gariepinus (catfish) that can be used as biological markers for detection of petroleum hydrocarbon contamination which can be included in monitoring programmes. The toxicological evaluations of benzene, toluene, ethylbenzene and xylene were carried out against Clarias gariepinus. The histopathological effects of benzene, toluene, ethylbenzene and xylene (BTEX) on different organs were investigated in C. gariepinus, Tilapia zillii, and Chrysichthys nigrodigitatus taken from the impacted areas of the Lagos Lagoon. Toxicological evaluations of the monocyclic aromatic components, benzene, toluene, ethylbenzene and xylene on Clarias gariepinus showed that ethylbenzene (0.479 ml/l) was the most toxic compound tested followed by xylene (0.519 ml/l), benzene (0.666 ml/l) and toluene (1.190 ml/l). The results from the histological study identified necrosis and deformation of the gills, inflammations in the liver, and wrinkling of the oocyte membrane in the gonads of fish, as good histopathological biomarkers of hydrocarbon related stressors. The combination of chemical analysis with these identified biomarkers can be used during environmental monitoring programmes for the protection of aquatic ecosystem.

Environmental and biological monitoring of benzene, toluene, ethylbenzene and xylene (BTEX) exposure in residents living near gas stations

ABSTRACTThe volatile organic compounds benzene, toluene, ethylbenzene, and xylene (BTEX) are emitted into the atmosphere at gas stations (GS) leading to chronic exposure of nearby residents, which raises public health concerns. This study aimes at determining the contribution of GS emissions to BTEX exposure in nearby residents. Three Control and Exposed areas to BTEX emissions from GS were defined in a medium-sized European city (Porto, Portugal). BTEX atmospheric levels were determined in Control and Exposed areas using passive samplers deployed outdoors (n = 48) and indoors (n = 36), and human exposure was estimated for 119 non-smoking residents using the first urine of the day. Results showed that median BTEX outdoor and indoor concentrations were significantly higher for Exposed than Control areas, with exception of ethylbenzene and xylene indoor concentrations, where no marked differences were found. Comparison of urinary concentrations between Exposed and Control residents demonstrated no significant differences for benzene and ethylbenzene, whereas levels of toluene and xylene were significantly higher in Exposed residents. No marked correlation was obtained between atmospheric BTEX concentrations and urinary concentrations. Data indicate the potential impact on air quality of BTEX emissions from GS, which confirms the importance of these findings in urban planning in order to minimize the impact on health and well-being of surrounding populations.

An integrated approach for produced water treatment using microemulsions modified activated carbon

In this study, the physical and chemical characterization of produced water was done followed by treatment through sand filtration coupled with activated carbon microemulsion modified activated carbon techniques. The results of characterization showed that the produced water had high chemical oxygen demand (COD), and total organic carbon (TOC) values i.e. 10,496 and 2405 mg/l respectively as well as high concentration of benzene, toluene, ethylbenzene and xylene (BTEX) and various metals. After the sand filtration, considerable reduction in TSS and COD was achieved. Furthermore, BTEX as volatile organic compounds were also removed by more than 93% except for toluene. However, sand filtration was not enough to remove most of the metals and ions. Therefore, further treatment was done through activated carbon and modified activated carbon and their treatment efficiency was compared. Both techniques were able to achieve higher removal efficiencies for BTEX, metals and ions. Thus, the treated water was free from all major pollutants of produced water and can be considered suitable for reuse at industrial or domestic level. This study aims to promote the reuse of produced water to reduce reliance on limited clean water resources.

Evaluation of gaseous emissions from thermal conversion of a mixture of solid municipal waste and wood chips in a pilot-scale heat generator

The objective of this study was to develop a novel pilot-scale system that combines pyrolysis and combustion processes, fed by a mixture of municipal solid waste (MSW) and wood chips (WC). The pyrolysis of MSW+WC (1:1) produces char and volatiles as fuels, which just the pyrolysis gas was used in a post-combustion chamber for heat generation. The gases evaluated were carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), BTEX (benzene, toluene, ethylbenzene and xylene) and polycyclic aromatic hydrocarbon (PAHs). Initially, the pyrolysis was performed by laboratory experiments and the physicochemical characterization of MSW+WC. The MSW+WC showed a heating value of 23.93 MJ kg−1, which is higher than several bioenergy crops reported. The pyrolysis and post-combustion process were found to minimize the generation of hydrochloric acid (HCl), dioxins and furans as well as the volatile compounds. The gases concentrations emitted were (mg Nm−3): 35.83 of CO, 24.37 of SO2, 106.84 of NOx, and 4.88 × 10−3 of BTEX, with a low PAH content. These values are below the legal emission standards established by United States Environmental Protection Agency (US EPA), Danish Environmental Protection Agency (Danish EPA), German Federal Emission Control Regulations (17.BlmSchV) and National Council for the Environment of Brazil (CONAMA 316/02).

Sub-ppb Level Detection of BTEX Gaseous Mixtures with a Compact Prototype GC Equipped with a Preconcentration Unit.

In this work, a compact gas chromatograph prototype for near real-time benzene, toluene, ethylbenzene and xylenes (BTEX) detection at sub-ppb levels has been developed. The system is composed of an aluminium preconcentrator (PC) filled with Basolite C300, a 20 m long Rxi-624 capillary column and a photoionization detector. The performance of the device has been evaluated in terms of adsorption capacity, linearity and sensitivity. Initially, PC breakthrough time for an equimolar 1 ppm BTEX mixture has been determined showing a remarkable capacity of the adsorbent to quantitatively trap BTEX even at high concentrations. Then, a highly linear relationship between sample volume and peak area has been obtained for all compounds by injecting 100-ppb samples with volumes ranging from 5–80 mL. Linear plots were also observed when calibration was conducted in the range 0–100 ppb using a 20 mL sampling volume implying a total analysis time of 19 min. Corresponding detection limits of 0.20, 0.26, 0.49, 0.80 and 1.70 ppb have been determined for benzene, toluene, ethylbenzene, m/p-xylenes and o-xylene, respectively. These experimental results highlight the potential applications of our device to monitor indoor or outdoor air quality.

Investigation of BTEX Adsorption on Carbon Nanotubes Cartridges from Air Samples

The volatile organic compounds (VOCs) contribute to serious air pollution problems in Viet Nam. Many studies have investigated in air quality monitoring and treatment, in order to determine the average concentrations of Benzene, Toluene, Ethylbenzene and Xylene (BTEX). Carbon nanotubes (CNTs) have been widely used as adsorbent in environmental treatment, especially for VOCs. This paper aims to determine the adsorption capacity of multiwalled carbon nanotubes for removal of BTEX from air samples. In preliminary study, the effects of various parameters during adsorption experiments were monitored such as flow rate, temperature and BTEX concentrations in air samples. The equipment for BTEX removal was developed by our research team consisting of filter columns, air sample bags, adsorption cartridge. The air samples containing BTEX were conducted directly through a cartridge packed with adsorbent. The adsorption experiments were carried out under various operating conditions such as temperature (30 - 40°C), gas concentration (0,57 - 4,77 mg/L) and the gas flow rate (10 - 90 mL/min). In addition, isotherm studies of CNTs for BTEX removal were achieved by using Langmuir and Freundlich models. The results showed that the experimental parameters were optimized at a flow rate of 30 mL/min and an ambient temperature at 30°C. The adsorption capacity of CNTs increased proportionally with BTEX concentrations. The specific affinity of CNTs for BTEX from air samples was in order of X &gt; E &gt; T &gt; B. The experimental isotherm data were well-fit with the Langmuir model for Benzene and Xylene removal, and the Freundlich model for Toluene and Ethylbenzene adsorption. The CNTs presented highly potential application for BTEX adsorption thanks to their microporous structure and high surface area.