Retention Of Toluene Research Articles

Transient photocatalytic oxidation of toluene vapor via nanostructured layers prepared by sol-gel on anatase particles

Gas-phase photocatalytic degradation of toluene mixed with wet oxygen was performed in a continuous reactor using anatase nanoparticles, home-prepared by the sol-gel method combined with peptization treatments. Titanium (IV) isopropoxide was used to synthesize amorphous titania precursor, partially transformed into crystalline nanoparticles by hydrothermal or thermal treatments. The main oxidation product was carbon dioxide, but traces of benzene and benzoic acid were also detected. In order to characterize the catalysts, the evolution of titanium (IV) alkoxide to form anatase nanoparticles was studied using 1H-MAS NMR, EPR, TPD, and FTIR techniques. The results indicate that the four coordinated Ti4+ cations of the alkoxide induce the formation of amorphous aggregates of polymeric layers. The organics removal by peptization originates thin nanostructured titania layers that cover anatase particles, forming TiO2 homojunction. Photoactivity runs showed that both toluene retention and mineralization occurred at the start of irradiation, both processes exhibiting a long transient. After different times, retention stopped while mineralization reached steady-state conditions. Hydrated proton structures are considered to be the origin of both processes. Under irradiation, water photodesorption from these structures favors both the interaction of nanostructured layers with anatase particles, determining hole transfer to external surfaces and the generation of hydrated hydronium cations which, depending on the water loss, are centers able to carry out toluene mineralization or retention. After the mineralization step, photocatalytic centers must be reconstituted by recovering water, a process whose rate becomes the rate-determining one.

Retention and mass transfer properties of the series of unbonded, amide-bonded, and alkylsulfobetaine-bonded ethylene bridged hybrid hydrophilic interaction liquid chromatography columns

This work investigates the link between the retentivity and the stationary phase to mobile phase mass transfer resistance of hydrophilic interaction liquid chromatography (HILIC) columns packed with the same base ethylene-bridged hybrid particles (BEH). The retention volumes, the plate heights, and the volume of the adsorbed water layer were measured for the ACQUITYTM UPLCTM BEHTM 130 Å HILIC Column (unbonded BEH), ACQUITY UPLC BEH 130 Å Amide Column (amide group attached), and AtlantisTM Premier BEH 95 Å Z-HILIC (zwitterionic group attached) Column. The method of Guo (toluene retention volumes in pure acetonitrile and in the HILIC eluent) was validated from the UNIFAC group-contribution method and applied to measure accurately the water layer volumes in these columns. A strong correlation was found between the retention volumes of most neutral polar analytes and the volume of the water layer adsorbed in the HILIC column. The fraction of the pore volume occupied by the water layer increases significantly from the BEH HILIC Column to the BEH Amide Column, and to the BEH Z-HILIC Column. This is explained by the water solvation of the attached ligands in the pore volume of the BEH Particles and to the smaller average mesopore size of the BEH Z-HILIC Particles. A second and strong correlation is also observed between the water content in the HILIC particle and the stationary phase to mobile phase mass transfer resistance of the HILIC columns at high mobile phase linear velocities. The measured intra-particle diffusivity normalized to the bulk diffusion coefficient decreased from 0.33 (BEH HILIC Column) to 0.10 (BEH Amide Column) and to only 0.03 (BEH Z-HILIC Column) for comparable retention of cytosine. These results are fully consistent with the higher viscosity of the internal eluent (higher water content) and higher internal obstruction for diffusion (smaller mesopores and internal porosity) in the BEH Z-HILIC Particles. Still, in gradient elution mode, the peak capacity was found to be 18% higher for the BEH Z-HILIC Column than that on the BEH Amide Column because the retention factors at elution were smaller when maintaining the same analysis time and starting eluent composition.

Treatment of toluene gaseous streams using packed column electro-scrubbers and cobalt mediators

• Toluene was efficiently removed from gases using the electro-scrubbers. • Low faradaic efficiencies because of low solubility of toluene in the absorbent. • Mediated electro-oxidation mechanisms promoted by the presence of cobalt. • Current density needs to be balanced according to polluted gas flowrate. An absorption system has been combined with an electrochemical cell to treat a gaseous stream polluted with toluene. Toluene retention in 3 h operation tests was higher than 87.0% in the case of treating the gaseous stream with single scrubbing, 97.0% in the case of using electro-scrubbing and over 99.0% in using cobalt-mediated electro-scrubbing. It was found that the amount of toluene that escapes from the electro-scrubber does not only depend on the flow rate but also on the current density and the presence of the metallic mediator. The higher the current densities are, the higher the amount of electrochemically degraded toluene is. In addition to the mediating effect of the metal catalyst, the results also suggest an important participation of the redox sulfate/persulfate pair in the degradation of toluene. Only methyl-cyclohexane (at very low concentrations) is observed as intermediate, despite carboxylic acids were also initially expected. The formation of this compound can be explained in terms of the hydrogenation of toluene. The very low concentrations absorbed, and the very high current densities, support the occurrence of an electrochemical cold combustion in the electro-scrubber.

The Impact of Lanthanum and Zeolite Structure on Hydrocarbon Storage

Hydrocarbon traps can be used to bridge the temperature gap from the cold start of a vehicle until the exhaust after-treatment catalyst has reached its operating temperature. In this work, we investigate the effect of zeolite structure (ZSM-5, BEA, SSZ-13) and the effect of La addition to H-BEA and H-ZSM-5 on the hydrocarbon storage capacity by temperature-programmed desorption and DRIFT spectroscopy. The results show that the presence of La has a significant effect on the adsorption characteristics of toluene on the BEA-supported La materials. A low loading of La onto zeolite BEA (2% La-BEA) improves not only the toluene adsorption capacity but also the retention of toluene. However, a higher loading of La results in a decrease in the adsorbed amount of toluene, which likely is due to partial blocking of the pore of the support. High loadings of La in BEA result in a contraction of the unit cell of the zeolite as evidenced by XRD. A synergetic effect of having simultaneously different types of hydrocarbons (toluene, propene, and propane) in the feed is found for samples containing ZSM-5, where the desorption temperature of propane increases, and the quantity that desorbed increases by a factor of four. This is found to be due to the interaction between toluene and propane inside the structure of the zeolite.

Evaluation of a linear free energy relationship for the determination of the column void volume in hydrophilic interaction chromatography

The application of a linear free energy relationship (LFER) to a variety of hydrophilic interaction chromatography columns with different bonded ligands and pore sizes was studied in order to determine their void volume Vm. The method was based on the determination of the elution volume of a series of alkylbenzene standards from C1 (toluene) to C17 (heptadecylbenzene). Results were compared with those obtained by injection of toluene alone, which has traditionally been used as a simple Vm marker. Vm was smaller when derived from the LFER plot than when measured with toluene with differences between the two methods ranging from 2.7 to 12.7 % for the columns studied. This result could be due to the small but appreciable retention of toluene due to its solubility in the water rich layer, which partially constitutes the stationary phase in HILIC. Larger pore size columns showed less difference in Vm between LFER and toluene procedures. This result may be due to size sieving effects of non-excluded solutes in the pores of the stationary phase, or to differences in phase ratio between columns of different pore size.

Computational and Experimental Investigations of the Role of Water and Alcohols in the Desorption of Heterocyclic Aromatic Compounds from Kaolinite in Toluene

Nonaqueous extraction is an attractive alternative to the currently employed warm water process for extraction of bitumen from oil sands, as it could use less energy and water. Hydroxylated cosolvents, such as alcohols, that compete for the adsorptive clay surfaces and help release bitumen components could help improve bitumen recovery. The water naturally present in oil sand also affects oil–mineral interactions. Electronic structure methods and the statistical-mechanical 3D-RISM-KH molecular theory of solvation as well as experimental desorption measurements are employed to study the effects of water and aliphatic alcohol cosolvents in toluene solvent on the desorption of fused pyridinic heterocycles (ArN) from kaolinite. The geometries of phenanthridine and acridine (representative of pyridinic heterocycles of petroleum asphaltenes) adsorbed on the kaolinite clay surface are optimized in periodic boundary conditions using density functional theory. The 3D-RISM-KH method is employed to calculate the solvation free energy and potential of mean force for adsorption of the heterocycles on kaolinite in pure and alcohol-containing toluene. The potentials of mean force show that the adsorption of the fused pyridines on kaolinite is stronger in pure toluene than in toluene mixed with aliphatic alcohol. Analysis of the mechanism of desorption of phenanthridine and acridine from kaolinite in toluene containing alcohol reveals that the alcohol stabilizes both the pyridinic moiety and kaolinite platelet by hydrogen bonding, thus disrupting the ArN···HO–Al(kaolinite) hydrogen bond. A mechanism for retention of toluene on kaolinite is also highlighted. Experimental studies of the desorption of fused pyridines from an ArN–kaolinite aggregate show that in water-saturated toluene the rate of desorption of the phenanthridine from kaolinite is twice as high as that in dry toluene. The experimental and computational results show that water and aliphatic alcohols in toluene help desorb pyridinic heterocycles from kaolinite, a clay mineral abundant in the oil sands. The presented insights are valuable for understanding the molecule-clay interactions in solution and relevant to improving the nonaqueous extraction of bitumen from oil sand.

BETA Zeolite Thin Films Supported on Honeycomb Monoliths with Tunable Properties as Hydrocarbon Traps under Cold‐Start Conditions

A high percentage of hydrocarbon (HC) emissions from gasoline vehicles occur during the cold-start period. Among the alternatives proposed to reduce these HC emissions, the use of zeolites before the three-way catalyst (TWC) is thought to be very effective. Zeolites are the preferred adsorbents for this application; however, to avoid high pressure drops, supported zeolites are needed. In this work, two coating methods (dip-coating and in situ crystallization) are optimized to prepare BETA zeolite thin films supported on honeycomb monoliths with tunable properties. The important effect of the density of the thin film in the final performance as a HC trap is demonstrated. A highly effective HC trap is prepared showing 100% toluene retention, accomplishing the desired performance as a HC trap, desorbing propene at temperatures close to 300 °C, and remaining stable after cycling. The use of this material before the TWC is very promising, and works towards achieving the sustainability and environmental protection goals.

Towards a Deep Desilication/Dealumination of NU‐10 Zeolite: Shape‐Selectivity Regulation

AbstractThe present work was aimed at performing alkaline desilication of different severities, in order to generate a broad range of mesopore volumes within the framework of the intermediate pore size NU‐10 zeolite and to evaluate both physicochemical and catalytic consequences. The shape‐selective sensitive o‐xylene isomerisation reaction was used as a characterisation method of zeolite pore modification. Thus, several NU‐10 samples, with preserved crystallinity, were obtained by treatment of a microporous parent NU‐10 sample with sodium hydroxide solutions of different concentrations (0.4–0.6 M), at several contact times (15, 30, 45, 60 and 120 min) and at 353 K. The characterisation by nitrogen adsorption allowed the evaluation of the micropore volumes of the samples and the mesopore volumes generated by desilication, as well as the external surface area. Toluene adsorption experiments were also performed, an important increase in the toluene adsorption capacity for increasing desilication levels being observed, except for the most severely modified samples. The sample treated at 0.6 M for 60 min revealed lower toluene retention, probably due to a higher level of extra‐framework aluminium and silicon species remaining in the internal porosity. In the case of aluminium species, they were detected by 27Al NMR spectroscopy, which is also in agreement with the pronounced increase in the number of Lewis acid sites detected for the most severely treated samples. A slight decrease in the initial o‐xylene isomerisation activity, at 673 K, was generally noticed as a consequence of desilication, and this can be related to a slight decrease in the concentration of protonated sites. Nevertheless, for intermediate‐severity‐treated samples, the activity per acid site increased significantly when compared with the parent zeolite, suggesting easier reactant accessibility. Furthermore, the para/meta‐xylene product molar ratio decreased and, therefore, the zeolite shape selectivity, thus reinforcing the hypothesis of an extra space generation consequence on the catalytic properties.

Analysis of tetramethylammonium–montmorillonite and retention of toluene from aqueous solution

Non-ionic organic contaminants , such as toluene, can be effectively absorbed by organo-montmorillionite. The tetramethylammonium (TMA)–montmorillonites were prepared by ion-exchange and used to evaluate toluene uptake from water. The TMA–montmorillonites were characterized by total organic carbon determinations, swelling index, X-ray diffraction, thermal analyses, and infrared spectroscopy . Toluene adsorption was measured by UV–visible spectrophotometry . The thermal stability of the TMA–montmorillonites decreased as TMA addition increased; the total mass loss decreased with increasing temperature up to 500 °C. The amount of carbon retained by the TMA–montmorillonites was proportional to the area of the infrared band at 1488 cm − 1 (asymmetric C–H bending vibration of –CH3 group). The retention of toluene by TMA–montmorillonites increased from 0.2 to 0.22 mg g − 1 mainly to interlayer adsorption. The adsorption of toluene influenced the OH-stretching vibration.

A Method for Estimating Mass-Transfer Coefficients in a Biofilter from Membrane Inlet Mass Spectrometer Data

A membrane inlet mass spectrometer (MIMS) was used in combination with a developed computer model to study and improve management of a biofilter (BF) treating malodorous ventilation air from a meat rendering facility. The MIMS was used to determine percentage removal efficiencies (REs) of selected sulfur gases and to provide toluene retention profiles for the model to determine the air velocity and overall mass-transfer coefficient of toluene. The mass-transfer coefficient of toluene was used as a reference for determining the mass transfer of sulfur gases. By presenting the model to scenarios of a filter bed with a consortium of effective sulfur oxidizers, the most likely mechanism for incomplete removal of sulfur compounds from the exhaust air was elucidated. This was found to be insufficient mass transfer and not inadequate bacterial activity as anticipated by the manager of the BF. Thus, knowing the relationship between mass-transfer coefficients and air velocity for a given type of BF allows for an improved dimensioning and managing of this and similar BFs. This research demonstrates that it is possible to estimate mass-transfer coefficients and air velocity in BFs using MIMS in combination with computer modeling.

Preparation of CPB-modified FAU zeolite for the removal of tannery wastewater contaminants

The preparation of organomodified zeolites with different framework structures (FAU, LTA and MOR) using N-cetylpyridinium bromide (CPB) as tailoring agent was studied. The sorption properties of CPB-modified zeolites were evaluated in the removal of tannery contaminants from aqueous solution. The CPB-modified FAU-type zeolite presented the highest Cr(VI) retention capacity (37 mmol/kg) due to the higher Cr(VI) retention of its unmodified form (larger pore opening) and its high CPB sorption capacity. CPB-modified FAU zeolite also exhibited high thermal stability as consequence of special interactions between the CPB molecules and the zeolite surface. In addition, the intrinsic Cr(III) exchange capacity of FAU zeolite increased with CPB loading (162–527 mmol/kg), which appear to be due to an additional retention mechanism provided by the sorbed cetylpyridinium surfactant layer. On other hand, CPB-modified FAU zeolite also exhibited high toluene retention capacity (62 mmol/kg) due to of the hydrophobic character of its surfactant-modified surface and toluene adsorption on internal sorption sites of FAU zeolite. Thus, CPB-modified FAU zeolite appears as a promising adsorbent for simultaneous removal of Cr(III), Cr(VI) and toluene contaminants from aqueous solution.

Trapping of solvent by a C60 fullerene film

Mass spectrometry was used over a wide temperature range to compare processes of solvent (toluene) release and desorption of C60 fullerene molecules from a fullerite film formed from solution on an oxidized metal substrate. It is shown that toluene is strongly retained in the fullerite film and that it is almost impossible to remove the toluene from the film without damaging its structure. Quantitative characteristics of the toluene retention and trapping effect are determined.

The changes in surface free energy and surface heterogeneity of controlled-porosity glasses

The adsorption energy distribution function was calculated according to the asymptotically corrected condensation approximation method from n-octane and toluene retention data for two thermally treated and rehydroxylated controlled-porosity glasses. Similar calculations were performed for a model series of silica gels, the surfaces of which were previously covered with boron and sodium compounds. Certain differences in surface site distributions were observed. The results for toluene were then correlated with changes in the surface free energy. Such correlations are presented separately for thermally treated and subsequently rehydroxylated materials. The results are discussed in terms of the differences in surface chemistry.

Effects of stationary-phase polarity on retention in reversed bonded phase HPLC columns

Variations in retention and selectivity have been studied in cyano, phenyl and octyl reversed bonded phase HPLC columns. The retention of toluene, phenol, aniline and nitrobenzene in these columns has been measured using binary mixtures of water and methanol, acetonitrile or tetrahydrofuran mobile phases in order to determine the relative contributions of proton donor-proton acceptor and dipole-dipole interactions in the retention process. Retention and selectivity in these columns was correlated with polar group selectivities of mobile phase organic modifiers and the polarity of the bonded stationary phases. In spite of the prominent role of bonded phase volume and residual silanols in the retention process, each column exhibited some unique selectivities when used with different organic modifiers.