Gas-phase Benzene Research Articles

Photodegradation of Gas Phase Benzene by SnO2 Nanoparticles by Direct Hole Oxidation Mechanism

Photodegradation of gas phase benzene by SnO2 nanoparticles has been studied in humid air, dry air and N2 by using a tubular photoreactor. The SnO2 nanoparticles are synthesized by the oxidation of anhydrous stannic chloride (SnCl4) in a propane/air turbulent flame. Direct hole oxidation and the ·OH radical mechanisms have been discussed based on experimental results. The goal of this research is to explore a viable and efficient alternative photocatalyst and photocatalytic process, in particular, for humidity-tolerant photocatalyst or photocatalytic process in environmental applications.

Tunable laser-based detection of benzene using spectrally narrow absorption features

A mid-infrared laser-based sensor for the detection of gas-phase benzene (C6H6) in ambient air is presented. It is based on the principle of tunable laser absorption spectroscopy utilizing unique fine spectral features of benzene near 3.4 µm, along with the robust design of an optical multi-pass cell. The sensor is capable of providing real-time measurement of benzene as low as 200 ppb (12 ppm m) at 2 Hz, while still being portable enough to fit in the trunk of a small car. A demonstration measurement in a moving vehicle is presented based on the data collected along Highway 101, El Camino Real, and around Stanford University campus in California, showing elevated benzene emission in several spatial regions.

Low-energy positron scattering from gas-phase benzene

In this paper we are presenting calculations of the elastic cross section of positrons with gas-phase benzene for the energy range from 0.25 eV to 9.0 eV. The calculations are done with the molecular R-matrix method for positron-scattering from poly-atomic molecules using a scaling factor to scale the electron-positron interaction. The scaling factor influences the position of the poles of the R-matrix. We adjust the scaling factor is such a way, that the position of the lowest pole is similar to the proposed binding energy of around 150 meV, given by [J.A. Young, C.M. Surko, Phys. Rev. Lett 99, 133201 (2007)]. Below the threshold for positronium formation, we calculate elastic cross section in good agreement with experimental cross sections. Above the threshold for positronium formation we use the difference between the experimental total cross section data and our computed elastic cross section to provide a first estimation of the cross section for positronium formation.Graphical abstract

The Photolysis of Aromatic Hydrocarbons Adsorbed on the Surfaces of Cosmic Dust Grains

The work is devoted to the adaptation of the results of laboratory studies of the laser-induced dissociation of molecules of benzene adsorbed on a quartz substrate to the conditions of the interstellar medium. Adsorption was performed under conditions of low temperature and deep vacuum. The difference between the photolysis of adsorbed molecules and molecules in the gas phase is identified. Significance of process of photolytic desorption in the interstellar conditions is analyzed, in particular, in the conditions of photodissociation regions. It is shown that the efficiency and dissociation channels of photolysis of adsorbed and gas phase benzene differ substantially. It is concluded that the photolysis of aromatic hydrocarbons adsorbed on the interstellar dust grains contributes a negligible fraction to the abundance of small hydrocarbons in the interstellar medium.

Equilibrium, kinetic and thermodynamic studies for dynamic adsorption of benzene in gas phase onto activated carbon produced from elaeagnus angustifolia seeds

Adsorption of pollutants onto activated carbon is very important in air purification systems. In this study, the dynamic adsorption of benzene in gas phase onto activated carbon which was produced from the elaeagnus angustifolia seeds, was investigated using a laboratory-scale continuous flow fixed-bed reactor system, under atmospheric pressure. The effects of the adsorption conditions such as activated carbon particle size (180–500 μm), nitrogen (N2) gas flow rate (0.050–0.120 L min−1) as the benzene in gas phase carrier, amount of activated carbon (0.10–0.75 g), concentration of benzene in gas phase at the inlet (9.95–14.85 ppm) and the adsorption temperature (293–323 K) on both the adsorption capacity and the adsorption efficiency were examined. Adsorption efficiency was achieved up to 100% under various adsorption conditions. Adsorption kinetics data were analyzed by using the Pseudo-First Order and Pseudo-Second Order kinetic models. Langmuir, Freundlich and Dubinin-Radushkevich models were used for the analysis of adsorption isotherms. The results showed that the Langmuir isotherm and Pseudo-Second Order models described the experimental data better when compared to other models. The maximum monolayer adsorption capacity (qmax) of activated carbon was determined to be 99.8 mg g−1 for 303 K. Thermodynamic analyzes indicated that the adsorption process of benzene in gas phase onto activated carbon was spontaneous (ΔG°<0), exothermic (ΔH°<0) and physical (ΔH°<20 kJ mol−1).

Porous carbon screening for benzene sorption

Benzene is one of the aromatic hydrocarbons that are co‐absorbed with the acid gases during amine scrubbing and are carried over to the catalytic reactors in the sulfur recovery unit where they crack and deactivate the catalyst. As a solution, adsorption of benzene using porous adsorbents is being considered as a suitable process for removal. The present work considers carbon based porous adsorbents as potential adsorbents and attempts to screen the large pool of adsorbents. Preliminary screening was made using information in open literature and structural characteristics, before the adsorbents were subjected to gas phase benzene adsorption. The pool of porous carbons screened included highly acidic sulfonated carbons, ordered mesoporous carbons (OMCs) and various commercial activated carbons (ACs). Among the pool of porous carbons, mesoporous carbon identified as AC1, was found to possess the highest adsorption capacity for benzene with heat of adsorption capacity of 20–32 KJ/mol. It was found that it is possible to regenerate the benzene adsorption capacity of AC1 and a benzene adsorption capacity of about 14 mmol/g for the mesoporous carbon was found to be far superior to the adsorption capacities reported in literature. © 2018 American Institute of Chemical Engineers Environ Prog, 38: S93–S99, 2019

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 .

Performance of a thermophilic gas-phase biofilter treating high BTEX loads under steady- and transient-state operation

The performance of a thermophilic biofilter (50 °C) was evaluated to treat a mixture of gas-phase benzene, toluene, ethylbenzene, p-xylene, m-xylene, and o-xylene (BTEX), under steady- and transient-state conditions. After acclimation, steady-state total BTEX elimination capacities ranged from 6 to 360 gm−3 h−1, depending on the total BTEX loading rate applied (8–978 gm−3 h−1). CO2 production from BTEX biodegradation was found to be dependent on the total elimination capacity of the biofilter. Stratification in BTEX removal profiles along the biofilter bed height was ascertained to be a strong function of the concentrations of the individual pollutants. Under steady-state conditions, higher removal efficiencies for benzene (often 100%) was noticed in comparison to the alkylbenzene compounds at the same initial load. Furthermore, studies were carried out under shock loading and starvation conditions (transient loads) for periods of 4–6 days, showing the robustness and resilience capacity of the biofilter, as the biofilter immediately recovered its original removal efficiency when high loads were applied after the brief transient conditions.

N2- and (H2+He)-broadened cross sections of benzene (C6H6) in the 7–15 µm region for the Titan and jovian atmospheres

In support of atmospheric remote sensing of Titan and jovian planets, we measured absorption cross sections of benzene (C6H6) in the 7–15µm region at temperatures between 235K and 297K. For this, high-resolution laboratory spectra of C6H6 were obtained using two cold cells (80cm and 2.07cm path length) configured to a high resolution Fourier-transform infrared (FT-IR) spectrometer, Bruker IFS-125HR, at the Jet Propulsion Laboratory (JPL). The spectrum sets include 15 pure and 15 N2-broadened benzene spectra in the 630–1534cm−1 region, along with four additional spectra broadened by an H2(85%) and He(15%) gas mixture for the 630–740cm-1 region. From these spectra, temperature dependent benzene cross sections were obtained for gas phase benzene in the presence of N2 and (H2+He) at ambient pressures and temperatures down to 235K.In addition, we generated two independent sets of pseudolines: one of N2-broadened benzene for Titan and the other of (H2+He)-broadened benzene for jovian planets. It is shown that the benzene pseudolines can reproduce the observed features to ∼ 5% in transmittance, including the continuum-like absorption formed by numerous overlapping weak and hot band transitions. Based on the pseudoline parameters, the integrated band intensities at 296K for the three strongest bands in the region were measured to be 177.0(73), 14.0(10), 27.2(9)×10−17cm−1/(molecule·cm−2) in the region of v4 at 674cm−1, v14 at 1038.267, and v13 at 1483.985cm−1, respectively, from the combined set of pure and N2-broadened benzene spectra. For the (H2+He) mixture-broadened benzene spectra, the integrated band intensity for v4 band in the 630–735cm−1 region was measured to be 168.8(17)×10−17cm−1/(molecule·cm−2) at 296K, which is in agreement with the intensity derived from the N2-broadened benzene spectra within the combined measurement uncertainties. The results from this work show an excellent agreement (2%) with one of the latest experimental studies by Rinsland et al. (2008). Furthermore, additional characteristics carried by the pseudolines approach are discussed. Finally, we provide the two sets of pseudo line list (PLL) as electronic supplements.

Effect of Ag/TiO2 catalyst preparation on gas-phase benzene decomposition using non-thermal plasma driven catalysis under oxygen plasma

Non-thermal plasma (NTP) driven catalytic decomposition of gas-phase benzene under oxygen plasma was carried out at room temperature over silver on titanium dioxide catalysts. Three preparation methods were investigated as well as the effect of silver loading amount. The catalysts were prepared using impregnation method (IP), deposition–precipitation method with NaOH (DPN), and deposition–precipitation method with H2O2 (DPH) with 1, 3 and 5 % silver loading by weight. The catalysts were characterized using XRD, XPS, SEM–EDS and N2 adsorption, and the catalytic activity was tested on 200 ppm benzene. Low energy treatment by NTP alone only showed insignificant change in benzene concentration but upon the addition of catalysts, IP catalysts were able to decompose the pollutant up to 20 % and with DPN and DPH catalysts up to 100 %. DPN catalysts were also able to decompose the ozone produced in the reactor. The 3 % Ag/TiO2 prepared by DPN method showed the highest energy efficiency capable of decomposing benzene at 392 g/kWh.

Photodegradation of gaseous C6H6 using CdO+CdTiO3 and TiO2 thin films obtained by sol–gel technique

Abstract In this work, TiO2 and CdO + CdTiO3 multicomponent oxide thin films growth was performed with different Ti/Cd ratios (0, 0.20, 0.49, 0.60, 0.65, 0.70 and 1) by the sol–gel route in order to degrade benzene in gas phase with an initial concentration level of 110 ± 10 ppm, under different conditions of relative humidity (RH): 25%, 50% and 80% in a batch type reactor, at room temperature. The results showed a degradation near to 100% at t = 75 min, using the CdO + CdTiO3 multicomponent oxide semiconductor with a Ti/Cd ratio of 0.65. On the other hand, the TiO2 thin films reached only a degradation of 70% in t = 240 min. A decrease of the oxidation process of benzene was observed in all films studied, as the relative humidity increased.

Isomer-Specific Spectroscopy of Benzene–(H2O)n, n = 6,7: Benzene’s Role in Reshaping Water’s Three-Dimensional Networks

The water hexamer and heptamer are the smallest sized water clusters that support three-dimensional hydrogen-bonded networks, with several competing structures that could be altered by interactions with a solute. Using infrared-ultraviolet double resonance spectroscopy, we record isomer-specific OH stretch infrared spectra of gas-phase benzene-(H2O)(6,7) clusters that demonstrate benzene's surprising role in reshaping (H2O)(6,7). The single observed isomer of benzene-(H2O)6 incorporates an inverted book structure rather than the cage or prism. The main conformer of benzene-(H2O)7 is an inserted-cubic structure in which benzene replaces one water molecule in the S4-symmetry cube of the water octamer, inserting itself into the water cluster by engaging as a π H-bond acceptor with one water and via C-H···O donor interactions with two others. The corresponding D(2d)-symmetry inserted-cube structure is not observed, consistent with the calculated energetic preference for the S4 over the D(2d) inserted cube. A reduced-dimension model that incorporates stretch-bend Fermi resonance accounts for the spectra in detail and sheds light on the hydrogen-bonding networks themselves and on the perturbations imposed on them by benzene.

Adsorption-Based Removal of Gas-Phase Benzene Using Granular Activated Carbon (GAC) Produced from Date Palm Pits

The Kingdom of Saudi Arabia is one of the leading countries in date fruit farming, and by-products from date palm trees can be used for several important applications, including pollution control. This study successfully employed date palm pit-based granular activated carbon (GAC) to adsorb gas-phase benzene under dynamic flow conditions. The percent carbon content (w/w) for raw date palm pits and produced GAC samples was found to be 47 and 82 %, respectively. Furthermore, the specific surface area (SSABET) of the produced GAC was 822 m2/g, and the t-Plot micropore area and t-Plot external surface area were 734.99 and 87.26 m2/g, respectively. The BJH graph for the pore size distribution also indicated a mesoporous structure. The use of date palm pit-based GAC for gas-phase benzene adsorption under dynamic continuous-flow conditions showed high efficiency with breakthrough points for different systems ranging from several hours to several days. The role of surface functional groups and their interactions with the benzene rings during the adsorption process were also explored, and surface oxygen-based groups may initiate an electron donor–acceptor mechanism with the benzene’s aromatic ring $${{\boldsymbol{\pi}}}$$ electrons. The findings confirmed that GAC produced from date palm pits can be successfully used for gas-phase benzene adsorption under various conditions. It is hoped that countries with large-scale date fruit farming, such as the Kingdom of Saudi Arabia, will be able to utilize this rich resource for environmental applications.

Real time observation of the excimer formation dynamics of a gas phase benzene dimer by picosecond pump-probe spectroscopy.

We observed the real-time excimer (EXC) formation dynamics of a gas phase benzene dimer (Bz2) cluster after photo-excitation to the S1 state by applying an ionization detected picosecond transient absorption method for probing the visible EXC absorption for the first time. The time evolution of the EXC absorption from the S1 0(0) level shows a rise that is well fitted by a single exponential function with a time constant of 18 ± 2 ps. The structure of the Bz dimer has a T-shaped structure in the ground electronic state, and that in the EXC state is a parallel sandwich (SW) structure. Thus, the observed rise time corresponds to the structural change from the T to the SW structures, which directly shows the EXC formation. On the other hand, the EXC formation after excitation of the S1 6(1) vibrational level of the stem site showed a faster rise of the time constant of 10 ± 2 ps. Supposing equilibrium between the EXC and the local excited states, it followed that the intramolecular vibrational energy redistribution rate of the 6(1) level is largely enhanced and becomes faster than the EXC formation reaction.

Sulfated perfluoropolymer–CNF composite as a gas-phase benzene nitration catalyst

Sulfated perfluoropolymers supported on carbon nanofibers are shown to be active and stable catalysts for gas-phase benzene nitration. The best catalyst exhibits 99.9% selectivity to nitrobenzene with concentration of by-products (mainly nitrophenols) less than 300ppm.

The photocatalysis and mechanism of new SrTiO3/TiO2

The SrTiO3/TiO2 was obtained via hydrothermal and sol–gel method and the optimal proportion (5wt %) was confirmed. The compounds have been characterized by XRD, UV–vis DRS, TEM and XPS. The photocatalytic degradation toward gas-phase benzene is almost 40% under UV irradiation, much better than pure TiO2 and SrTiO3. Besides, the SrTiO3/TiO2 also possessed outstanding performance toward methyl orange in liquid-phase testing. Finally, the electro-chemistry and electron spin-resonance spectroscopy (ESR) provided evidence that the improved photocatalysis is attributed to (1) the matching energy band which can transfer charge carriers efficiently and (2) enhanced generation of photo-electron and free radicals.

Intramolecular Processes Revealed Using UV-Laser-Induced IR-Fluorescence: A New Perspective on the "Channel Three" of Benzene.

Radiative relaxation in the infrared (IR) is common following nonradiative electronic relaxation processes, but it is rarely measured. We present ultraviolet laser-induced infrared fluorescence (UV-LIIRF) excitation spectroscopy and dispersed UV-LIIRF spectroscopy of gas phase benzene vibronically excited around the onset of channel 3, using a homemade spectrometer. We found that the vibrational IR fluorescence yield is clearly higher when benzene is excited above the onset than when it is excited below. Significant changes in dispersed IR emission profiles resulting from excitations below and above the onset of channel 3 were also observed. These results suggest that isomerization of benzene toward fulvene occurs efficiently below the opening of channel 3 and confirm that channel 3 involves a photophysical relaxation pathway that efficiently competes with isomerization.

Influence of colloidal graphene oxide on photocatalytic activity of nanocrystalline TiO2 in gas-phase ethanol and benzene oxidation

Impregnation of the nanocrystalline TiO2 Degussa/Evonik P25 by colloidal graphene oxide produced by the Hummers method (H-GO) results in a 4-fold acceleration of photocatalytic gas-phase oxidation of ethanol and benzene vapors by air oxygen as a result of enhanced separation of the photogenerated charge carriers between TiO2 and H-GO. Preliminary photochemical reduction of H-GO decreases drastically its activity in ethanol photooxidation but does not affect appreciably photocatalytic oxidation of benzene. More deeply oxidized colloidal GO produced by the Brodie method (B-GO) almost does not affect the photocatalytic properties of titania in benzene photooxidation. It is concluded that the catalytic properties of GO in the photooxidation of ethanol and benzene depend on a balance between the capabilities of the GO sheets (i) to accept photoelectrons from titania nanocrystals and (ii) to bound to the TiO2 surface. The former factor depends on the aromaticity of GO particles and increases from B-GO to H-GO to photoreduced H-GO, while the latter factor depends on the density of the functional groups on GO sheets and increases in the opposite direction.

Coupling of titania with multiwall carbon nanotubes for decomposition of gas-phase pollutants under simulated indoor conditions

This study synthesized multiwall carbon nanotube (MWNT)–titania (TiO2) composites and examined their characteristics and photocatalytic performance for the cleaning of gas-phase benzene, toluene, ethyl benzene, and o-xylene (BTEX) under simulated indoor conditions. Optical and spectral surveys of the as-synthesized composite confirmed that the TiO2 nanoparticles were bound intimately to the MWNT networks. The photocatalytic performance was evaluated using an annular-type reactor inner-coated with MWNT–TiO2 or Degussa P25 TiO2. The composite revealed gas removal ability superior to that of stand-alone TiO2. This composite was also less affected by humidity during toluene decomposition compared to the previous result obtained from a stand-alone TiO2. Unlike another previous result obtained from the TiO2, the performance of the composite was not affected by changes in input concentration (IC) within a simulated indoor air quality range (0.1–1.0 ppm) but it decreased significantly when the IC was increased to 5 and 10 ppm. As the flow rate was decreased from 4.0 to 1.0 L min−1, the average efficiency for the target compounds increased to 95% or ∼100%. The MWNT–TiO2 composite could be applied effectively to the decomposition for BTEX under certain simulated indoor conditions. Implications: Unlike water applications, there are few reports of gas-phase applications of multiwall carbon nanotubes (MWCNT)–TiO2 composites. This study found that MWCNT–TiO2 composites showed performance in the removal of toxic gaseous aromatic superior to that of stand-alone TiO2. In addition, the pollutant degradation efficiency of the composite was less affected by humidity than for a stand-alone TiO2 unit within a simulated indoor relative humidity range. Moreover, unlike the TiO2 unit, the composite's performance was not affected by variations in the input concentrations within the simulated indoor air quality (IAQ) range. In addition, the decomposition efficiencies increased to 100% with decreasing flow rate.

Effect of catalyst composition and preparation conditions on catalytic properties of unsupported manganese oxides for benzene oxidation with ozone

Catalytic oxidation of benzene in gas phase with ozone was carried out at 70°C over manganese oxides and manganese-based mixed oxides to investigate the effect of catalyst composition and preparation conditions on their catalytic properties. The oxides were prepared by an evaporation-to-dryness method and a co-precipitation method from metal nitrate precursors, followed by calcination at 400–900°C. As for manganese monoxides, benzene oxidation rate normalized by catalyst surface area, product distribution and ozone/benzene decomposition ratio were almost independent of the preparation method and calcination temperature. Perovskite-type mixed oxides, LaMnO3 and La0.8Sr0.2MnO3 showed much lower activity and lower efficiency for ozone utilization in benzene oxidation than manganese monoxide and La sites promoted the accumulation of less-reactive byproduct compounds on the catalysts. In the case of manganese-based mixed oxides that contained Fe, Co, Ni, and Cu, benzene oxidation activity, CO2 selectivity and ozone/benzene decomposition ratio depended on the catalyst composition and preparation conditions. Among the mixed oxide catalysts, the Co–Mn mixed oxide prepared by the evaporation-to dryness method and calcined at 400°C was the most effective for benzene oxidation from the standpoint of CO2 selectivity and efficiency for ozone utilization.