Toluene Removal Efficiency Research Articles

Decomposition of gaseous toluene using a continuous flow discharge plasma reactor with new configurations

The destruction of gaseous toluene was carried out in a tubular multilayer dielectric barrier discharge reactor which can yield a steady state of low-temperature plasma with an array structure. The research was investigated under different relative humidities, input voltages, energy densities, energy consumption and the reactor processing capacities. The results showed that the highest removal efficiency and processing capacity (γ) were acquired using an additional dielectric with the width of 2 mm between adjacent discharge quartz tubes, and the removal efficiency of toluene reached 86.5% and γ increased to 6272 kg/s m3 at a voltage of 6 kV. The gas-phase by-products (O3, NOx, COx and intermediate organics) were also presented and the reaction mechanism was described according to the decomposition reaction tunnels.

Biofiltration performance and characteristics of high-temperature gaseous benzene, hexane and toluene

Three biofilters were developed to treat high-temperature (50°C) gaseous benzene, hexane, and toluene. The performance of the biofilters was investigated; the parameters included removal efficiencies, kinetic analysis, biomass accumulation, pressure drops, and leachate TOC content. Results showed that the removal efficiency of toluene was the highest (more than 90%), followed by benzene (more than 70%) and hexane (more than 50%). The mass distribution coefficients (Km) of benzene, hexane, and toluene were 4.99, 3.50, and 6.36, respectively. And the yield coefficients (Y) were 0.91, 1.29, and 1.50g dry biomass/g removed VOC for benzene, hexane, and toluene, respectively. A faster biomass accumulation resulted in lower flooding velocity of the biofilter treating toluene (210m/h) than that of the biofilter treating hexane (257m/h). The leachate from the biofilter treating toluene presented the highest TOC contents. Mass balance was similar among the three biofilters, suggesting that more than half of the removed VOCs were converted to CO2 and about 40% were converted to biomass.

Combination of spontaneous polarization plasma and photocatalyst for toluene oxidation

In this paper, we report toluene destruction using a spontaneous polarization plasma and photocatalyst reactor in air at atmospheric pressure and room temperature. A spontaneous polarization material (BaTiO3) and photocatalyst (TiO2) were added to the plasma system simultaneously. Three types of catalyst, i.e., TiO2, BaTiO3, or TiO2/BaTiO3, were used for toluene removal. The catalyst carrier, type, and amount were important factors in the toluene removal efficiency. The specific energy density and energy yield during the discharge process were investigated. The toluene removal efficiency increased when a spontaneous polarization plasma was combined with the photocatalyst. In terms of toluene removal efficiency, the activity order was TiO2/BaTiO3 > BaTiO3 > TiO2 > none. Large amounts of BaTiO3 in the TiO2/BaTiO3 catalyst gave slightly better conversion. The TiO2/BaTiO3 catalyst not only enhanced the toluene removal efficiency, but also saved energy, making it useful for industrial applications.

Removal of Toluene by Dielectric Barrier Discharge Combined with Modified Photocatalyst

The toluene being removed by dielectric barrier discharge (DBD) combined with modified photocatalyst was studied in the paper. Transition metal manganese was doped into crystal lattice of TiO2 in order to improve the activity of photocatalyst, and the optimal doping ratio was confirmed in the study. As one of main factors, the influence on toluene removal efficiency of gas flow rate, initial concentration and electric field intensity was analyzed in the study. Furthermore, the energy efficiency was another important index which had been compared amongγ-Al2O3, TiO2/γ-Al2O3 and Mn-TiO2/γ-Al2O3. The result of study showed that DBD combined with Mn-TiO2/γ-Al2O3 had the best buffer action against increasing of gas flow rate and initial concentration, the energy efficiency had the tendency as Mn-TiO2/γ-Al2O3 > TiO2/γ-Al2O3>γ-Al2O3, and the optimal doping ratio of manganese was 0.01.

Design and development of a bench scale vegetable oil based wet packed bed scrubbing system for removing producer gas tar compounds

The overall goal of this study was to design, fabricate and evaluate a vegetable oil based wet packed bed scrubbing system to study the removal of model producer gas tar compounds, i.e., benzene, toluene, and ethylbenzene. The designed column was 0.5m diameter by 1.1m tall and contained 6-mm raschig rings. Soybean and canola oils were used as solvents. These oils were not statistically (p>0.05) different in removal efficiencies of benzene, toluene and ethylbenzene. Packing specific constants of Billet and Schultes (1999) correlation (CV=0.80 and CL=2.40) were found experimentally. These constants can be used to predict height equivalent to a theoretical plate (HETP) of laboratory or pilot scale vegetable oil based wet packed bed scrubbing systems. The pressure drop across the column was in the range of 6.7 to 18.8mm of water column.

Volatile organic compounds emission control in industrial pollution source using plasma technology coupled with F-TiO2/γ-Al2O3

Volatile organic compounds’ (VOCs) effluents, which come from many industries, are triggering serious environmental problems. As an emerging technology, non-thermal plasma (NTP) technology is a potential technology for VOCs emission control. NTP coupled with F-TiO2/γ-Al2O3 is used for toluene removal from a gaseous influent at normal temperature and atmospheric pressure. NTP is generated by dielectric barrier discharge, and F-TiO2/γ-Al2O3 can be prepared by sol-gel method in the laboratory. In the experiment, the different packed materials were packed into the plasma reactor, including γ-Al2O3, TiO2/γ-Al2O3 and F-TiO2/γ-Al2O3. Through a series of characterization methods such as X-ray diffraction, scanning electronic microscopy and Brunner–Emmet–Teller measurements, the results show that the particle size distribution of F-TiO2 is relatively smaller than that of TiO2, and the pore distribution of F-TiO2 is more uniformly distributed than that of TiO2. The relationships among toluene removal efficiency, reactor input energy density, and the equivalent capacitances of air gap and dielectric barrier layer were investigated. The results show that the synergistic technology NTP with F-TiO2/γ-Al2O3 resulted in greater enhancement of toluene removal efficiency and energy efficiency. Especially, when packing with F-TiO2/γ-Al2O3 in NTP reactor, toluene removal efficiency reaches 99% and higher. Based on the data analysis of Fourier Transform Infrared Spectroscopy, the experimental results showed that NTP reactor packed with F-TiO2/γ-Al2O3 resulted in a better inhibition for by-products formation effectively in the gas exhaust.

Photocatalytic Degradation of Toluene on SiO2/TiO2 Photocatalyst in a Fluidized Bed Reactor

Silica supported titania photocatalyst, SiO2/TiO2, is prepared by the sol–gel doping method using titanium tetra isopropoxide as the precursor and nitride acid as the acid catalyst. The structure and physical properties of SiO2/TiO2 particles are characterized by SEM/EDS, XRD, and BET specific surface area measurement. When a small amount of TiO2 coated onto the silica gel surfaces, the BET specific surface area of the SiO2/TiO2 particles increases. However, when the ratio of SiO2/TiO2 precursor decreases, TiO2 fills the pores of silica gel and the BET specific surface area of SiO2/TiO2 particle decreases. The as-prepared SiO2/TiO2 particles are used as the fluidizing media in a fluidized bed photoreactor and toluene is degraded therein. The results show that the contaminated stream containing toluene with the concentration as high as 1000ppm can be continuously degraded in the fluidized bed photoreactor. The continuous toluene removal efficiency is around 30%-40% at steady state.

Toluene decomposition performance and NOx by-product formation during a DBD-catalyst process

Characteristics of toluene decomposition and formation of nitrogen oxide (NOx) by-products were investigated in a dielectric barrier discharge (DBD) reactor with/without catalyst at room temperature and atmospheric pressure. Four kinds of metal oxides, i.e., manganese oxide (MnOx), iron oxide (FeOx), cobalt oxide (CoOx) and copper oxide (CuO), supported on Al2O3/nickel foam, were used as catalysts. It was found that introducing catalysts could improve toluene removal efficiency, promote decomposition of by-product ozone and enhance CO2 selectivity. In addition, NOx was suppressed with the decrease of specific energy density (SED) and the increase of humidity, gas flow rate and toluene concentration, or catalyst introduction. Among the four kinds of catalysts, the CuO catalyst showed the best performance in NOx suppression. The MnOx catalyst exhibited the lowest concentration of O3 and highest CO2 selectivity but the highest concentration of NOx. A possible pathway for NOx production in DBD was discussed. The contributions of oxygen active species and hydroxyl radicals are dominant in NOx suppression.

Studies on the Electrical Behaviour and Removal of Toluene with a Dielectric Barrier Discharge

Abstract This contribution attempts to establish an easy-to-apply non-thermal plasma reactor for efficient toluene removal. Derived from the already established knowledge of the so called Dielectric Barrier Discharge (DBD) Stack Reactor a new model reactor was used in this work. The DBD Stack Reactor is a multi-elements reactor but in this work only one stack element was used to investigate the efficiency and efficacy of toluene removal. In case of reliable results the scalability process for industrial application is already well known. Therefore, laboratory experiments were conducted in dry and wet synthetic air with an admixture of 50 ppm toluene. Along with the toluene removal process the electrical behaviour of the discharge configuration was investigated. It was found that the electrical capacitance of the dielectric barrier changes with variations of the operating voltage. This could be due to the changes in the area of the dielectric barrier which is covered with plasma. Additionally, it was found that the power input into the plasma, at a fixed operating voltage, is proportional to the frequency, which is in agreement with the literature. Regarding the decomposition process, the total removal of toluene was achieved at specific input energy densities of 55 J L-1 under dry conditions and 110 J L-1 under wet conditions. The toluene removal was accompanied by the production of nitric acid (dry conditions) and formic acid (wet conditions). The latter suggested a combination of the plasma reactor with a water scrubber as an approach for total removal of pollutant molecules.

Experimental studies of removing typical VOCs by dielectric barrier discharge reactor of different sizes

This research conducted both lab-scale and pilot-scale tests by selecting toluene as the typical volatile organic compounds (VOCs) and by using the promising non-thermal plasma oxidation technology – dielectric barrier discharge (DBD). To develop baseline engineering data to demonstrate the feasibility of application of self-made DBD reactors, the peak voltage, gas flow speed, initial toluene concentration, discharge frequency and duty ratio were studied. The results showed that toluene removal efficiency improves with increase of electrical voltage, frequency and duty ratio, and declines with increase of polar distance, gas flow speed and toluene initial concentration. When the voltage increases, the energy efficiency rises first and then drops. The energy efficiency reaches the climax when the energy density reaches 150.8J/L and 101.7J/L in the lab-scale experiment and pilot-scale experiment respectively.

On the performance and mechanisms of toluene removal by FeOx/SBA-15-assisted non-thermal plasma at atmospheric pressure and room temperature

FeOx/SBA-15 catalysts were prepared via impregnation and utilized for toluene removal in dielectric barrier discharge (DBD) plasma at atmospheric pressure and room temperature. Toluene removal was investigated in the environment of various mixed N2/O2 plasmas, showing that toluene removal efficiency and COx selectivity were greatly increased by FeOx/SBA-15 and that the organic intermediates were greatly reduced by catalysts. In pure N2 plasma, the bulk oxygen in the catalyst was involved in the toluene oxidation, and the 3%FeOx/SBA-15 catalyst showed the optimal toluene oxidation activity. The catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), N2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR) and O2 temperature-programmed desorption (O2-TPD), showing that toluene oxidation was closely related to the highly dispersed nature of iron on the SBA-15 surface, the reduction temperature of Fe2+ and the oxygen adsorption ability of the catalyst. The pathways of toluene decomposition in the combination of FeOx/SBA-15 with a non-thermal plasma (NTP) system were proposed based on the identified intermediates.

Study of Toluene Removal by Bipolar Corona Discharge Coupled with Photocatalytic

Experimental study the degradation efficiency of toluene by bipolar corona discharge coupled with TiO2 photocatalysis. Bipolar corona discharge can degrade the toluene efficiently and rapidly, the final products are mainly carbon dioxide and water. Toluene removal efficiency reduces when the initial concentration of toluene increasing, while toluene removal quantity is increased. Removal of toluene decreases with the gas flow rate increasing, the removal quantity first increases and then decreases. Bipolar corona discharge and a photocatalytic coupling can inprove the degradation efficiency further. Increase of the applied voltage help to improve the removal of toluene, and also to improve the coupling effect of the photocatalyst. In optimized conditions, the removal efficiency of toluene can be more than 90%. The chemical reaction process of the toluene oxidation and the TiO2 catalysis mechanism are discussed. It is pointed out that the OH* produced by corona discharge has important significance for rapid oxidation of toluene.

Removal of toluene from water by photocatalytic oxidation with activated carbon supported Fe(3+)-doped TiO2 nanotubes.

In this work, activated carbon (AC)-supported TiO2 containing 1.0% (mass percent) of 1.0 at.% (atomic percent) Fe(3+)-doped TiO2 nanotubes (Fe-TNTs) were successfully synthesized. The catalyst was used to effectively decompose toluene in water under O3/UV conditions, and some properties including the morphology, X-ray photoelectron spectroscopy, X-ray diffraction patterns, specific surface area and UV-visible diffuse reflectance spectroscopy were analyzed. A removal efficiency of 90.7% was achieved in the presence of fresh AC-supported Fe-TNTs calcined at 550 °C, with a pseudo-first-order rate constant of 0.038/min. The removal efficiency of toluene was reduced when the catalysts were repeatedly used, since the amount of adsorption sites of the supporting substrates decreased. However, even after AC-supported catalyst was used four times, the removal efficiency of toluene was still sufficient in water treatment. The enhanced photocatalytic activity of AC-supported Fe-TNTs was related to the synergistic effect of AC adsorption and Fe-TNTs photocatalytic ozonation. The water from a petrochemical company in China was used to obtain the removal efficiency of the pollutants, and the toluene and total organic carbon removal efficiencies were 69.9% and 58.3%, respectively.

Plasma-Catalytic Oxidation of Toluene on MnxOy at Atmospheric Pressure and Room Temperature

MnxOy/SBA-15 catalysts were prepared via the impregnation method and utilized for toluene removal in dielectric barrier discharge plasma at atmospheric pressure and room temperature. The catalysts were characterized by X-ray diffraction, N2 adsorption–desorption, Raman spectroscopy, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, and O2 temperature-programmed desorption methods. The characterization results indicated that manganese loading did not influence the 2D-hexagonal mesoporous structure of SBA-15. The catalyst had various oxidation states of manganese (Mn2+, Mn3+, and Mn4+), with Mn3+ being the dominant oxidation state. Toluene removal was investigated in the environment of pure N2 and 80 % N2 + 20 % O2 plasma, showing that the toluene removal efficiency and CO2 selectivity were noticeably increased by MnxOy/SBA-15, especially in the presence of 5 % Mn/SBA-15. This activity was closely related to the high dispersion of 5 % Mn on SBA-15 and the lowest reduction temperature exhibited by this catalyst. Mn loading increased the yield of CO2 in the N2 plasma and promoted the deep oxidation of toluene. During toluene oxidation, oxygen exchange might follow a pathway, wherein bulk oxygen was released from the MnxOy/SBA-15 surface; gas-phase O2 subsequently filled up the vacancies created on the oxide. Each of the manganese oxidation states played an important role; Mn2O3 was considered as a bridge for oxygen exchange between the gas phase and the catalyst, and Mn3O4 mediated transfer of oxygen between the catalyst and toluene.

A biofilter model for simultaneous simulation of toluene removal and bed pressure drop under varied inlet loadings

In this study, a biofiltration model including the effect of biomass accumulation and inert biomass growth is developed to simultaneously predict the Volatile Organic Compounds (VOCs) removal and filter bed pressure drop under varied inlet loadings. A laboratory-scale experimental biofilter for gaseous toluene removal was set up and operated for 100 days with inlet toluene concentration ranging from 250 to 2500 mg·m−3. According to sensitivity analysis based on the model, the VOCs removal efficiency of the biofilter is more sensitive to Henry’s constant, the specific surface area of the filter bed and the thickness of water layer, while the filter bed pressure drop is more sensitive to biomass yield coefficient and original void fraction. The calculated toluene removal efficiency and bed pressure drop satisfactorily fit the experimental data under varied inlet toluene loadings, which indicates the model in this study can be used to predict VOCs removal and bed pressure drop simultaneously. Based on the model, the effect of mass-transfer parameters on VOCs removal and the stable-run time of a biofilter are analyzed. The results demonstrate that the model can function as a good tool to evaluate the effect of biomass accumulation and optimize the design and operation of biofilters.

Simultaneous Removal of Toluene (Model Tar), NH3, and H2S, from Biomass-Generated Producer Gas Using Biochar-Based and Mixed-Metal Oxide Catalysts

Effectiveness of four catalysts (biochar, activated carbon, acidic surface activated carbon, and mixed metal oxide) was studied for simultaneous removal of toluene, NH3, and H2S from biomass-generated producer gas. NH3 (0.03%), H2S (0.015%), and toluene at a flow rate of 2 mL/h were mixed with a synthetic producer gas composition (H2: 8.5%, N2: 58%, CO: 17%, CH4: 2%, and CO2: 11%) and passed over a catalyst bed in a fixed-bed reactor tube maintained at 800 °C. Results indicate that simultaneous removal of contaminants from producer gas is feasible using biochar-based catalysts. High surface area mixed metal oxides synthesized using microwave and ultrasonication were also effective for simultaneous removal of contaminants. Among the four catalysts, acidic surface activated carbon resulted in the highest toluene removal efficiency of 97.5% and highest breakthrough time of 145 min for NH3. For H2S removal, mixed metal oxides resulted in the highest breakthrough time of 105 min. For simultaneous removal of toluene, H2S and NH3, activated carbon showed good removal capacity (91% toluene removal efficiency; NH3 adsorption capacity of 0.03g-NH3/g-activated carbon; H2S adsorption capacity of 0.008 g-H2S/g-activated carbon), whereas biochar had moderate removal capacity (86% toluene removal efficiency; NH3 adsorption capacity of 0.008 g-NH3/g-biochar; H2S adsorption capacity of 0.008 g-H2S/g-biochar).

Effect of metal-ion doping on the characteristics and photocatalytic activity of TiO2 nanotubes for the removal of toluene from water.

Toluene is an extensively used reagent that could cause water pollution and endanger human health. In this work, an O3/UV/ion-doped TiO2 nanotubes process was investigated to obtain the optimum TiO2 nanotubes for effective toluene decomposition. Photocatalytic activity is found to be influenced by the doped-ion type by affecting the ionic radius, valence state, and configuration of the dopant. The calcination temperature and doping concentration, which change the weight fractions of the anatase phase (fA), the Brunauer-Emmett-Teller surface area (SBET), and the energy band gap (Eg) of the catalyst, also affect the photocatalytic activity. When TiO2 is doped with ions, SBET decreases and Eg becomes narrower. The photocatalytic activities of TiO2 for toluene removal increase after doping with Ag(+), Al(3+), Cu(2+), Fe(3+), Mn(2+), Ni(2+), V(5+), and Zn(2+). Moreover, the 1.0% Fe(3+)-doped TiO2 nanotubes calcined at 550 °C have the highest catalytic activity, with a toluene removal efficiency of 70.7%.

Volatile Toluene and Xylene Removal Efficiency of Foliage Plants as Affected by Top to Root Zone Size

Phytoremediation of volatile organic compounds in indoor air involves both the plant and microbes in the media; however, removal rate is typically expressed on a leaf area basis. We determined the effect of root media volume on phytoremediation rate of volatile toluene and xylene to determine if there is a change in phytoremediation efficiency. Phytoremediation rate was calculated based on the aboveground space occupied by the plant and on the leaf area. Foliage plants of Fatsia japonica and Draceana fragrans ‘Massangeana’ were grown in different-sized pots (1, 2, 4, 6, and 12 L) that gave aerial plant to root zone volume ratios of 21:1, 21:2, 21:3, and 21:6. Total root volume and root fresh weight increased in D. fragrans with increasing media volume, whereas root density per unit of media volume decreased in both species. The efficiency of volatile toluene and xylene removal by the plants was increased as the root zone volume increased, whereas removal efficiency per unit media volume increased and then decreased. The highest volatile toluene and xylene removal efficiency was at a ratio of 21:3 (aerial plant:root zone volume) in F. japonica and 21:2 in D. fragrans. When phytoremediation efficiency was expressed on a leaf area basis, the phytoremediation rate for toluene and xylene increased progressively for both species with increasing media volume and as root volume increased. Calculating the amount of plant material needed within a home or office to obtain sufficient volatile organic compound (VOC) removal cannot be accurately predicted base solely on a leaf area (LA) or aboveground volume basis.

Synthesis and evaluation of biochar-derived catalysts for removal of toluene (model tar) from biomass-generated producer gas

Challenges in removal of contaminants, especially tars, from biomass-generated producer gas continue to hinder commercialization efforts in biomass gasification. The objectives of this study were to synthesize catalysts made from biochar, a byproduct of biomass gasification and to evaluate their performance for tar removal. The three catalysts selected for this study were original biochar, activated carbon, and acidic surface activated carbon derived from biochar. Experiments were carried out in a fixed bed tubular catalytic reactor at temperatures of 700 and 800 °C using toluene as a model tar compound to measure effectiveness of the catalysts to remove tar. Steam was supplied to promote reforming reactions of tar. Results showed that all three catalysts were effective in toluene removal with removal efficiency of 69–92%. Activated carbon catalysts resulted in higher toluene removal because of their higher surface area (∼900 m2/g compared to less than 10 m2/g of biochar), larger pore diameter (19 A° compared to 15.5 A° of biochar) and larger pore volume (0.44 cc/g compared to 0.085 cc/g of biochar). An increase in reactor temperature from 700 to 800 °C resulted in 3–10% increase in toluene removal efficiency. Activated carbons had higher toluene removal efficiency compared to biochar catalysts.

Toluene Removal from Sandy Soils via In Situ Technologies with an Emphasis on Factors Influencing Soil Vapor Extraction

The integration of bioventing (BV) and soil vapor extraction (SVE) appears to be an effective combination method for soil decontamination. This paper serves two main purposes: it evaluates the effects of soil water content (SWC) and air flow rate on SVE and it investigates the transition regime between BV and SVE for toluene removal from sandy soils. 96 hours after air injection, more than 97% removal efficiency was achieved in all five experiments (carried out for SVE) including 5, 10, and 15% for SWC and 250 and 500 mL/min for air flow rate on SVE. The highest removal efficiency (>99.5%) of toluene was obtained by the combination of BV and SVE (AIBV: Air Injection Bioventing) after 96 h of air injection at a constant flow rate of 250 mL/min. It was found that AIBV has the highest efficiency for toluene removal from sandy soils and can remediate the vadose zone effectively to meet the soil guideline values for protection of groundwater.