Increasing Toluene Concentration Research Articles

Nanostructured Pr-doped Ceria (PCO) thin films as sensing electrodes in solid-electrolyte type gas sensors with enhanced toluene sensitivity

Pr0.1Ce0.9O2 (PCO) films, with columnar structure containing voids, were fabricated by pulsed laser deposition (PLD) and integrated into YSZ-based potentiometric gas sensor as a sensing electrodes (SEs). Sensors with PCO film thicknesses of 550, 1100 and 2200 nm, fabricated by controlling the number of PLD shots of 750, 1500 and 3000 respectively, were examined over the temperature range of 450–600 °C. The sensor output voltage, E, of all sensors showed increasing negative change with increasing toluene concentration. The sensor with the thickest PCO SE film (thickness: 2200 nm) showed a much larger toluene response at 450 °C than the others (PCO-SE thickness: 550, 1100 nm). Because PCO is a mixed ionic and electronic conductor and the morphology of SE was porous, the electrochemical oxidation reaction is viewed as occurring at the double phase boundaries – DPBs (interfaces between PCO/gas) as well as triple phase boundaries – TPBs (interfaces of PCO/YSZ/gas). Because a fraction of the toluene is catalytically oxidized in part during gas diffusion within the SE films, especially at lower operating temperatures, the much larger toluene response can be explained by the electrochemical oxidation reaction of the partially oxidized products together with toluene at the TPBs and DPBs.

Dynamically asymmetric binary glass formers studied by dielectric and NMR spectroscopy.

We investigate the component dynamics in asymmetric binary glass formers. Focusing on the dielectric spectra of the high-Tg components m-tricresyl phosphate and quinaldine mixed with toluene as low-Tg component, the broadend spectra cannot be described by Kohlrausch or Cole-Davidson (CD) functions. Instead, we apply a generalized CD function which allows to control the width of the susceptibility independently of its high-frequency flank. The spectra show a common broadening and failure of the frequency-temperature superposition with increasing toluene concentration. This is confirmed by stimulated echo experiments showing an increased stretching of the probed orientational correlation function. In analogy to the definition of Tg, we consider "isodynamic points". For each component, a different but linear concentration dependence of 1/Tiso is revealed, indicating different time scales. Qualitativly, we do not find significant differences for the present mixtures with Tg-contrasts of 63-89K compared to those with larger Tg-contrast ( [Formula: see text] K): Whereas the high-Tg component shows relaxation features similar to those of neat glass formers, yet, with "atypical" weak relaxation broadening, the faster low-Tg component displays pronounced dynamic heterogeneities. This is supported by scrutinizing NMR relaxation data of several mixtures investigated previously as a function of concentration. A universal evolution of the dynamics of the high-Tg as well as the low-Tg component is suggested for mixtures with high [Formula: see text]Tg .

Ionic liquid modified multiwalled carbon nanotube embedded styrene butadiene rubber membranes for the selective removal of toluene from toluene/methanol mixture via pervaporation

Abstract Present work reports the fabrication of elastomeric membrane based on ionic liquid functionalized multiwalled carbon nanotubes (f-MWCNT) incorporated Styrene butadiene rubber (SBR) for the separation of azeotropic composition of toluene and methanol. The fabricated membranes were characterized by morphological analysis using transmission electron microscopy and glass transition temperature and heat capacity measurements by differential scanning calorimetry. Composite membranes demonstrate impressive separation performance with preferential selectivity towards toluene and 5 phr f-MWCNT loaded membranes was found to show the best result with respect to toluene flux and selectivity. Optimal separation performance with the permeation flux 225% of SBR control membrane and separation factor of 128 (1.6 times of SBR control membrane) is obtained for this membrane. The concurrent optimization of the physical and chemical structures of toluene permeation path on f-MWCNT surface provides the membrane with high-efficiency toluene permeation. Ionic liquid on MWCNT surface confer aromatic pi-pi interaction with toluene molecules leading to greater toluene affinity and higher repellency against methanol. Pervaporation characteristics of the membranes were also strongly influenced by the feed mixture composition. The study confirmed that increasing toluene concentration improved the toluene flux but reduced the separation factor. The experimental pervaporation fluxes were compared with the calculations based on modified Maxwell–Stefan equation. The model allows a good quantitative prediction of experimental flux values.

Characterization, Degradation, and Reaction Pathways of Indoor Toluene over Visible-light-driven S, Zn Co-doped TiO2

Sulfur and Zinc co-doped TiO2 prepared by a sol-gel method to degrade toluene under a fluorescent lamp was investigated. The results indicate that S,Zn co-doped TiO2 photocatalysts are mainly nano-size with an anatase phase structure. The degradation reactions of toluene were performed under various operation conditions. The results show that the toluene conversion increases with increasing toluene concentration and decreasing relative humidity. Based on the results of activity test, S0.05Zn0.001/TiO2 was chosen for further studies. The main oxidation products of toluene photodegradation are CO2, H2O, benzyl alcohol, acetone, butadiene and acetic acid. Two possible mechanisms have been developed for photodegradation of toluene in a dry and a humid environment.

Bimetallic Pt-Au Nanocatalysts on ZnO/Al2O3/Monolith for Air Pollution Control.

The catalytic activity of a monolithic catalyst with nanosized Pt and Au particles on ZnO/Al2O3 (Pt-Au/ZnO/Al2O3/M) prepared by a wash-coat method was examined, specifically for toluene oxidation. Scanning electron microscopy image showed clearly the formation of a ZnO/Al2O3 layer on the monolith. Nanosized Pt-Au particles on ZnO/Al2O3/M with different sizes could be found in the Pt-Au/ZnO/Al2O3/M catalyst. The conversion of toluene decreased with increasing toluene concentration and was also largely affected by the feed flow rate. The Pt-Au/ZnO/Al2O3/M catalysts prepared in this work have almost the same activity (molecules of toluene per second) compared with a powder Pt-Au/ZnO/Al2O3 catalyst with the same loadings of Pt and Au components; thus this catalyst could be used in controlling air pollution with very low concentrations and high flow rate.

Secondary aerosol formation and oxidation capacity in photooxidation in the presence of Al2O3 seed particles and SO2

To investigate the sensitivity of secondary aerosol formation and oxidation capacity to NO x in homogeneous and heterogeneous reactions, a series of irradiated toluene/NO x /air and α-pinene/NO x /air experiments were conducted in smog chambers in the absence or presence of Al2O3 seed particles. Various concentrations of NO x and volatile organic compounds (VOCs) were designed to simulate secondary aerosol formation under different scenarios for NO x . Under “VOC-limited” conditions, the increasing NO x concentration suppressed secondary aerosol formation, while the increasing toluene concentration not only contributed to the increase in secondary aerosol formation, but also led to the elevated oxidation degree for the organic aerosol. Sulfate formation was suppressed with the increasing NO x due to a decreased oxidation capacity of the photooxidation system. Secondary organic aerosol (SOA) formation also decreased with the presence of high concentration of NO x , because organoperoxy radicals (RO2) react with NO x instead of with peroxy radicals (RO2 or HO2), resulting in the formation of volatile organic products. The increasing concentration of NO x enhanced the formation of sulfate, nitrate and SOA under “NO x -limited” conditions, in which the heterogeneous reactions played an important role. In the presence of Al2O3 seed particles, a synergetic promoting effect of mineral dust and NO x on secondary aerosol formation in heterogeneous reactions was observed in the photooxidation. This synergetic effect strengthened the positive relationship between NO x and secondary aerosol formation under “NO x -limited” conditions but weakened or even overturned the negative relationship between NO x and secondary aerosol formation under “VOC-limited” conditions. Sensitivity of secondary aerosol formation to NO x seemed different in homogeneous and heterogeneous reactions, and should be both taken into account in the sensitivity study. The sensitivity of secondary aerosol formation to NO x was further investigated under “winter-like” and NH3-rich conditions. No obvious difference for the sensitivity of secondary aerosol formation except nitrate to NO x was observed.

Adsorption and oxidation of high concentration toluene with activated carbon fibers

Many of the factors influencing the adsorption of volatile organic compounds by activated carbon fibers (ACFs) have been widely studied. However, most of them were investigated at low concentrations (500 ppm or less) and at low adsorption temperatures (lower than 100 °C). This study was to determine simultaneously the oxidation and adsorption of toluene onto activated carbon fibers (ACFs) at high concentration and high adsorption temperatures. We tested three ACFs, four inlet concentrations of toluene (700, 1,200, 1,600, and 2,000 ppm), and four adsorption temperatures (25, 50, 75, and 200 °C). The composition and morphology of the ACFs were also analyzed using BET, FTIR, EA, and FESEM. The results indicated that the best toluene adsorption capacity was for 569 mg/g ACFs at a toluene concentration of 1,200 ppm and at 25 °C. A combination of low O content and high mesopore volume was desirable for ACFs with a high toluene adsorption capacity at high toluene concentrations. Moreover, the breakthrough time decreased with increasing toluene concentration, and the adsorption capacity of toluene increased significantly when the inlet concentration of toluene increased to 1,200 ppm. The data also indicated that the breakthrough time and the adsorption capacity of toluene decreased with increasing adsorption temperature. The outlet concentration of toluene did not reach 1,200 ppm when adsorption was saturated at 200 °C, as the oxygen functional groups on the ACF surface had reacted with toluene to form other compounds.

Adsorption Kinetics for the Chemical Filters Used in the Make-Up Air Unit (MAU) of a Cleanroom

The adsorption of toluene onto commercially available coconut-based granular activated carbon (GAC) loaded within a piece of nonwoven fabric was investigated in a filter media at face velocities 0.076 through 0.152 m/s. The results showed that the adsorption capacity increases with increasing toluene concentration but decreases as the face velocity was increased. In order to investigate the adsorption mechanisms, three simplified kinetic models, i.e., the pseudo-first-order, second-order kinetic models, and intraparticle diffusion model were used to describe the kinetic data and the rate constants were calculated. The rate parameter, k i, of intraparticle diffusion, the rate parameter, k 2, of the pseudo-second-order and k 1, the rate parameter for the pseudo-first-order mechanism were compared. It was found that the pseudo-first-order adsorption mechanism is predominant and the overall rate of the GAC adsorption process appears to be controlled by more than one step, namely both the external mass transfer and intraparticle diffusion mechanisms.

Pervaporation separation of toluene/n-heptane mixtures using a MSE-modified membrane: Effects of operating conditions

In this work, separation of toluene/n-heptane mixtures via pervaporation using a composite membrane was investigated. Effects of operating conditions such as feed temperature, feed composition and downstream pressure on the membrane performance were studied. Experimental results were obtained at different feed compositions (10–40wt.%), operating temperatures (25–85°C) and downstream pressures (2–32mbarg). The membrane selectivity for toluene was found to be greater than that for n-heptane. According to the results, it was observed that increasing toluene concentration in the feed and operating temperature enhance the membrane swelling and increase the polymeric chain mobility. Therefore, feed concentration and temperature have the same effects on toluene selectivity and permeation flux of the membrane. Permeation flux increases and toluene selectivity decreases with increasing feed concentration and temperature. In contrary, the membrane performance enhances with decreasing downstream pressure. It was found out that for a feed with 10wt.% of toluene, at a temperature of 85°C and a downstream pressure of 2mbarg, the highest PSI value of 18.371kg/m2h (in which permeation flux=4.610kg/m2h and toluene selectivity=4.985) is achieved.

공기 중 톨루엔에 의한 고분자전해질연료전지의 성능감소

고분자전해질 연료전지에 유입되는 공기가 톨루엔에 오염되었을 때 전지 성능에 미치는 영향을 여러 톨루엔 농도와 운전 조건에서 연구하였다. 그리고 청정한 공기에 의한 전지 성능 회복과 활성탄 흡착에 의한 공기 중 톨루엔의 제거에 대해서도 연구하였다. 본 연구에서 실험한 톨루엔의 농도 범위는 0.1~5.0 ppm이었고 전지 성능감소와 회복은 일정전류에서 전압변화 측정법과 전기화학적 임피던스 측정법(EIS)에 의해 측정하였다. KOH 첨착활성탄의 톨루엔 흡착용량은 등온흡착곡선으로 구했다. 톨루엔 농도가 증가할수록, 전류밀도가 증가할수록, 공기유량이 증가할수록 톨루엔 오염에 의한 성능감소가 심했다. 그러나 상대습도가 증가할수록 톨루엔 오염에 의한 성능감소는 작았다. 가습된 청정 공기 중의 산소와 수분에 의한 톨루엔의 산화에 의해 전지의 성능이 회복되었다. 톨루엔의 백금 표면 흡착에 의한 전하 전달 저항 증가가 전지 성능을 주로 감소시킴을 EIS가 보였다. 첨착활성탄의 톨루엔 흡착 용량은 KOH 첨착량이 증가할수록 감소하였다. The contamination effect of toluene in the airstream on PEM fuel cell performance was studied with various toluene concentration under different operation conditions. And the recovery of the cell performance by applying clean air and the removal of toluene in the air by adsorption of active carbon were investigated. The toluene concentration range used in the experiments was from 0.1 ppm to 5.0 ppm. The performance degradation and recovery were measured by constant-current discharging and electrochemical impedance spectroscopy(EIS). Toluene adsorption capacity of KOH impregnated active carbon was obtained from the adsorption isotherm curve. The severity of the contamination increased with increasing toluene concentration, current density and air stoichiometry, but decrease with increasing relative humidity. The cell performance was recovered by toluene oxidation with oxygen and water in humidified neat air. EIS showed that the increase of charge transfer resistance due to toluene adsorption on Pt surface mainly reduced the performance of PEMFC. Toluene adsorption capacity of active carbon decreased as KOH weight increased in KOH impregnated active carbon.

Selective polydimethylsiloxane/polyimide blended IPN pervaporation membrane for methanol/toluene azeotrope separation

The paper describes the preparation and investigation of membranes based on new interpenetrating polymer network (IPN) of vinyl terminated poly(dimethyl siloxane) (PDMS) and aromatic polyimide (PI) with respect to their thermal and pervaporation properties. The modified membranes were prepared using simultaneous IPN (SIPN) technique by variation of polyimide loading of 5, 10 and 15wt% respectively. These membranes were characterized by different thermal, mechanical, morphological, spectroscopic and pervaporative techniques and compared with those of neat PDMS membranes. The IPN membranes exhibited synergistic improvement in the thermal stability in the range of 445–490°C in air and 410–520°C in inert atmosphere for 10% loss. Activation energies for the decomposition of polymers and their IPN's were calculated using Coats and Redfern equation. Permeation properties of PDMS and IPN blends were evaluated by water diffusion, measured by Fourier transform-attenuated total reflectance (FT-ATR) method and moisture vapour transmission rate (MVTR) as per ASTM E 96. 15wt% polyimide content in PDMS membrane slows down the water diffusion and MVTR significantly. All the IPN's form mechanically strong membrane with tensile strength up to 15.5MPa and elongation at break up to 20%. IPN membranes prepared in this work were employed in pervaporation separation of azeotrope forming toluene/methanol mixtures. The pervaporation properties could be tuned by adjusting the blend composition. All the blend membranes tested showed a decrease in flux with increasing polyimide content for methanol/toluene liquid mixtures. Toluene permeated preferentially through all tested blend membranes, and the selectivity increased with increasing polyimide content. The pervaporation characteristics of the blend membranes were also strongly influenced by the feed mixture composition. The flux increased exponentially with increasing toluene concentration in the feed mixtures, whereas the selectivities decreased for liquid mixtures. This study demonstrates that polymer IPN blends is a simple way to modulate membrane's transport properties and can achieve higher performance than the pristine polymer materials.

Development of a biofilter with water content control for research purposes

A traditional packed bed biofilter was operated as a CSTR by using internal recycle and combined with water content control. Sufficient headspace mixing eliminated interparticle gas phase concentration profiles in the compost bed. A hydrophilic membrane, hydraulically connecting the compost to a water chamber, maintained under vacuum, controlled the water content in the compost. Changing the matric potential from −20 to −300 cm H 2O decreased the elimination capacity (EC) of toluene by 50%. The reactor design allowed easy manipulation of dissolved components in the liquid phase while controlling the unsaturated water content in the compost. Nitrogen was identified as limiting the biomass growth for the particular composts tested. The addition of either ammonia or nitrate increased the steady state EC significantly (7 → 76 g m −3 h −1). The EC versus toluene concentration profile was easily generated and displayed a typical mass transfer-limited system up to a concentration between 100 and 200 ppm, followed by a biomass-limited system with increasing toluene concentration. This reactor permitted a better exploration of environmental influences on biofiltration performance than the traditional long column biofilter.

Solubility of Paracetamol in Binary and Ternary Mixtures of Water + Acetone + Toluene

The solubility of paracetamol (4-hydroxyacetanilide) in binary mixtures of acetone + water and acetone + toluene and in ternary mixtures of water + acetone + toluene is reported. The temperature range is −5 to +30 °C. In acetone + water the solubility increases to a maximum at approximately 25 mass % water before decreasing to a much lower value in pure water as compared to pure acetone. In acetone + toluene the solubility decreases monotonically with increasing toluene concentration. The water content has a strong influence also in ternary mixtures. Activity coefficients in the saturated solutions are estimated.

Energy transfer in the radiolysis of solid hydrocarbons at 77 k: Mono-olefins

When 1-pentene (or 1-hexene)-toluene mixture is irradiated by γ-rays or ns pulse X-rays, fluorescence from excited toluene is observed. Yields of excited singlet toluene in the olefin-toluene mixtures at 77 K increase remarkably with increasing toluene concentration, while G(H 2) decreases complementarily. The rapid energy transfer from mono-olefin takes place in the solid phase at 77 K. The migration distances of the energy transfer in the radiolysis of solid hydrocarbons, such as aromatics, alkane, and alkene, are proportional to the lifetimes of excited singlet state of the hydrocarbons. The energy transfer is discussed in terms of two models; an exciton transfer and a vibrational relaxation resonance transfer. The exciton transfer offers a better explanation for the energy transfer mechanism in the radiolysis of solid hydrocarbons.