Diffusion Coefficient Of Toluene Research Articles

Molecular simulation to analyze the influence of ultrafine particles on activated carbon adsorbing low concentration toluene

Adsorption is an effective technology to remove the gaseous pollutants. In the actual implementation, the particulate matters (PMs) are firstly filtered to guarantee the adsorption performance of absorbent. However, the PMs cannot be completely removed based on the current state of the art, especially the ultrafine particles. Therefore, in this work, taking activated carbon as an example, the influence of ultrafine particles on its gaseous adsorption performance was detailed investigated. The nanoporous carbon model was proposed and the adsorption of toluene with/without NaCl particles was simulated based on the GCMC (Grand Canonical Monte Carlo) method and MD (Molecular Dynamics) method. The results showed that, with the existence of NaCl, the diffusion coefficient of toluene in the activated carbon was reduced by 27%, the amount of toluene absorbed was reduced by 20.8%–28.6%, and the van der Waals energy was varied in a relative wider range. The favorable adsorption sites were 4.4 Å away from the graphite slices of activated carbon, which was not affected by NaCl particles. This was also verified by the analysis of energy distribution. This study revealed the mechanism of gas-solid coupling mass transfer in the porous materials and would help master the actual adsorption performance of adsorbent.

The structural parameters of rigid matrix of saccharide-based gel described by short and long diffusion regime analysis

The tortuosity–porosity relation and internal structure diameters in a selected organogel are studied. The diffusion coefficient measured by pulsed field gradient NMR at short and long observation times can be used to estimate the tortuosity and the pore surface-to-volume (S/Vpore) ratio of a porous material (Latour et al. in J Magn Res A 112:83–91, 1995; Mair et al. in Magn Res Imaging 19:345–351, 2001; Mitra et al. in Phys Rev B 47(14):8565–8574, 1993; Valiullin and Skirda in J Chem Phys 114:452–458, 2001). The value of S/Vpore allows to calculate the average pore and barrier diameters. In the experiment, the time-dependent diffusion coefficient of toluene in a low molecular weight gelator methyl-4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside (Gluco-NO2) matrix was measured. The results revealed the relation between the diffusion coefficient of toluene and the concentration of gelator Gluco-NO2 in the system. With increasing Gluco-NO2 compound in the sample, the diffusion coefficient of toluene decreases. On the basis of the diffusion coefficient behaviour as a function of time and gelator concentration, the fibrous structure of the gel matrix was identified and the structural parameters of the system were investigated.

Mass transfer of trichloroethylene through the palladized iron coated reactive geomembrane

Palladized iron coated reactive geomembrane (Pd/Fe RGM) was developed to mitigate the mass transfer of chlorinated volatile organic compounds through HDPE geomembrane. It had good performance in mitigating the mass transfer of TCE at the preliminary study. This study focused on the effects of Pd/Fe coating on the mass transfer parameters and the reaction rate constant of RGM. Also, the effects of sulfide and aging on the RGM were evaluated. It was proved that the effect of Pd/Fe coating on partition and diffusion coefficients of toluene was not significant by batch immersion test results with student's t-test. The reactivity of Pd/Fe RGM had a linear correlation with an increase in the Pd/Fe loading rate on RGM. However, it was lower than the reactivity of the Pd/Fe powder by a factor of one hundred because the effective surface area of Pd/Fe was blocked partially by the geomembrane and the opportunity to contact Pd/Fe and TCE was reduced. The reactivity of Pd/Fe RGM decreased severely at 10 mM sulfide concentration and with long-term aging of RGM in the atmosphere for three years. However, the reactivity of aged RGM was recovered slightly by acid treatment, but not completely.

Determination of adsorption isotherm and diffusion coefficient of toluene on activated carbon at low concentrations

Adsorption is one of the most effective technologies for indoor gas pollutant removal. To guide the design and modeling of sorbent-based air cleaners, it is necessary to characterize a sorbent material (e.g., activated carbon) in advance. A new dynamic volumetric adsorption test method was developed in this study. The adsorption capacity of toluene on activated carbon was determined in the concentration range of 0.1–100 ppm at three relative humidity conditions (20%, 50%, and 80%). The obtained adsorption isotherm was used to evaluate the validity of Langmuir model, Freundlich model and Dubinin-Radushkevich (D-R) model, respectively. Langmuir model gave the best fit. A linear adsorption isotherm was observed when the concentration was below 1.5 ppm. The measured data was then used to determine the model parameters (partition coefficient, mass transfer coefficient and diffusion coefficient) by least-square fitting to a mechanistic numerical model. Results show that the diffusion coefficient increases with increased concentration, indicating the dominating role of surface diffusion during VOC adsorption on activated carbon.

Cure kinetics and swelling behaviour in polybutadiene rubber

Two polybutadiene rubbers (BR) with different 1,4- cis content were used to prepare compounds with a cure system based on sulfur and TBBS (N-t-butyl-2-benzothiazole sulfenamide). Torque curves, measured with a moving die rheometer at a temperature of 433 K, were used to characterize the vulcanization process. Vulcanization kinetics of the two BR compounds was studied using the formalism proposed by Kamal and Sourour. To vary the cure level, samples of each compound were vulcanized at 433 K at different times, according to the information obtained from the rheometer data. From swelling data, the diffusion coefficient of toluene in BR was evaluated, taking into account the influence of polymer structure and crosslink density.

Composite membranes for hydrophobic pervaporation: study with the toluene–water system

Composite membranes were utilized for hydrophobic pervaporation. Experiments were carried out with the toluene–water system using composite membranes (PERVAP ®1060 and PERVAP ®1070) and the results were analysed. The chosen membranes were characterised using a positron annihilations technique to measure free volume. In order to study solute–membrane interactions, the diffusion coefficient of toluene with in the membrane and Flory–Huggins interaction parameters (surface thermodynamic approach through contact angle measurement) were estimated. Influences of operating conditions (downstream pressure, feed toluene concentration, feed temperature) were observed on pervaporate fluxes (toluene and water) and pervaporate concentration of toluene. The selectivities of the chosen composite membranes were observed to be lower compared to known values of selectivities for dense PDMS membrane, suggesting the role played by the support layer in this regard. Individual fluxes of toluene and water increase with increase in feed temperature; however, fluxes decrease with increase in downstream pressure. Further, pervaporate concentration of toluene increases with increase in feed concentration. Similar expected trends were observed; but in case of PERVAP ®1070, the toluene flux attained a plateau with increase in feed toluene concentration. Such a trend confirmed the presence of an extra component (possibly zeolites) in the skin layer of PERVAP ®1070. A simple resistance-in-series model, along with the solution-diffusion model were employed for mathematical analysis of the results. Model predictions with experimental values showed close agreements for the PERVAP ®1060 membrane while deviations were observed for the PERVAP ®1070 membrane.

Selection of elastomeric membranes for the separation of organic compounds in acidic media

A series of elastomers were investigated, by measuring their toluene permeability and acid resistance, for their potential for use in the extraction of organics from hydrochloric acid and other membrane processes utilising acidic aqueous phases. In this study, toluene was used as a solute in aqueous solution to measure permeabilities of the elastomers, and their acid resistance was assessed after immersion in 37 wt.% hydrochloric acid by tensile-strain tests. Silicone rubber has the highest permeability among the elastomers investigated in this study, but it has poor resistance to concentrated HCl. Polyoctenamer is the best membrane material in terms of permeability and acid resistance. Other olefin based materials such as poly(ethylene-co-propylene) and poly(ethylene-co-propylene-co-diene) (EPDM) are also good candidates. The permeability generally decreases with an increase in T g for the elastomers investigated. However, for the EPDM materials with T g values grouped around −60 °C, the relationship between T g and permeabilities is not clear. A model derived from Flory–Huggins Theory and the Hildebrand and Scatchard equation was used to predict the partition coefficients of toluene between the elastomers and aqueous solution, and the predictive power found to depend critically on the value employed for the water solubility parameter. The diffusion coefficients of toluene in the elastomers can be explained by considering the polymer structure.

Transport properties of nonelectrolyte liquid mixtures. XI. Mutual diffusion coefficients for toluene + n-hexane and toluene + acetonitrile at temperatures from 273 to 348 K and at pressures up to 25 MPa

Mutual diffusion coefficients,D12, have been measured at pressures up to 25 MPa using the chromatographic peak broadening technique (Taylor dispersion method) forxtoluene+(1−x)n-hexane in the temperature range 298 to 348 K and forxtoluene+(1−x) acetonitrile in the temperature range 273 to 348 K. The estimated uncertainty is ±4%. Both systems show negative deviations from straight-line behavior. The fractional decrease inD12is about 0.8% per MPa. Hard-sphere theory is applied under limiting conditions where one of the components is present in a trace amount. It is shown that the diffusion coefficients can be estimated by the Dullien method from a knowledge of the viscosity and density under the same conditions.

A laboratory simulation of toluene cleanup by air sparging of water-saturated sands

Laboratory air sparging experiments were performed in narrow acrylic tanks to evaluate the cleanup of toluene in water-saturated sands. Air flow channels in the sediment were identified by way of a colorimetric visualization technique, which allowed pore water samples to be collected at a known horizontal distance from an air channel. Pore water was sampled at periodic intervals during sparging experiments and analyzed by gas chromatography to yield toluene concentration vs. time data. Results indicate that channelized air flow is effective in reducing toluene concentrations in the range of 36–3 ppm, within 2 to 5 days, at least up to 185 mm from an active air channel. While relatively rapid, these toluene reduction times are longer than previously published data, from similar type experiments. The discrepancy is likely a function of air delivery flow rate and proximity of sampling sites to active air channels. Data from the current investigation were used to attempt an estimate of effective diffusion coefficients ( D*) for toluene in clean, well-characterized sands in which the concentration gradient was imposed by sparge air. Calculated D* values range from 2.98×10 −8 m 2/s to 5.74×10 −9 m 2/s, and are significantly faster than previously published values of toluene diffusion in clay soils. However, the values are also slightly greater than diffusion coefficients for toluene in aqueous solutions, indicating that the calculations more likely estimate coefficients of hydrodynamic dispersion ( D L).

Approaches to deal with the issue of plastic packages and the environment

AbstractMethods of treating the solid plastic waste are reviewed. The diffusion coefficients of toluene and benzyl alcohol in PET were determined from sorption experiments. For toluene, desorption (into water) experiments were also carried out and the diffusion coefficients were determined for various initial toluene concentrations in the polymer. The diffusion coefficients from the latter experiments were significantly lower than those determined from the sorption studies. In migration of toluene from the contaminated PET into water, a reduction of two orders of magnitude in the level of migration was achieved by sandwiching the contaminated PET between two layers of the virgin polymer. In another study, properties of Nylon 6/PE blends reprocessed at various shear rates were evaluated. The results showed that after minimum mixing of the blend obtained from a Nylon 6/PE laminate, the low oxygen permeability of the original film was preserved.

Sorption/desorption properties of ethanol, toluene, and xylene in poly(dimethylsiloxane) membranes

AbstractSorption/desorption kinetics and sorption equilibria have been determined for ethanol, toluene, and xylene vapors in a poly(dimethylsiloxane) membrane containing about 32 wt % silica resin at 25°C. Dependence of diffusion coefficient on vapor activity and sorption isotherms have been compared to identify the transport mechanisms of those penetrants in the PDMS membrane. The analysis of Zimm–Lundberg clustering functions showed that all three penetrants had a tendency to form clusters and ethanol molecules might be immobilized by the residual silanol groups within the silica resin in the membrane. The diffusion coefficient of toluene was roughly constant and that of xylene slightly decreased as increasing the vapor activity due to the competing effects of penetrant clustering and solvent swelling of polymer. The diffusion coefficient of ethanol versus activity exhibited a maximum due to the effects of ethanol immobilization and cluster formation. The freevolume effect by solvent swelling to diffusion was obscured by either penetrant clustering or immobilization for the three penetrant–polymer systems. © 1994 John Wiley & Sons, Inc.

Sorption and diffusion of toluene in blends of low-density polyethylene with polyvinylchloride

Sorption and diffusion of toluene in LDPE-PVC blends in the form of powders are prepared by elastic-strain grinding were studied by the range method. LDPE is active, PVC inactive towards toluene vapour. It was found that the first cycle of toluene vapour sorption in films of polymer blends proceeds considerably more slowly than the second and subsequent sorptions; this is caused by slow relaxation of the non-equilibrium polymer structure formed during sample preparation. The limiting values of sorption increase with increasing content of PVC in the blend, evidently owing to the growing size of microvoids. The diffusion coefficient of toluene in LDPE-PVC blends decreases with increasing content of PVC. In polymer blends toluene is sorbed in the form of clusters.

Rate constants for the termination of benzyl radicals in solution

AbstractThe rate constant for the bimolecular combination of benzyl radicals in cyclohexane and toluene is determined as a function of temperature. Further, it is studied in cyclohexane–toluene mixtures of different compositions. In the entire range covered, 9.8 × 108 ⩽ 2kt ⩽ 9.0 × 109M−1·sec−1, the data are very well described by the Smoluchowski equation for a diffusion‐controlled reaction to ground‐state products using a spin statistical factor of 1/4, a temperature‐ and solvent‐independent reaction distance, and the known diffusion coefficient of toluene.