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Equilibrium Concentration (equilibrium + concentration)
Selected AbstractsPolycyclic aromatic hydrocarbons (PAHs) adsorption on solid surfaces applied to waste lubricant oils recovery processTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010José Lima Assunção Filho Abstract Lubricant oils undergo degradation increasing polycyclic aromatic hydrocarbons (PAHs) concentration. In this work, PAHs adsorption onto activated carbon, powder silica, and powder chitosan surfaces was estimated, with their concentrations in organic solvents (ethanol, 2-propanol, 1-butanol, and terc -butanol) monitored by UV-visible absorption. Equilibrium concentration was attained after 72,h and the isotherms presented characteristic of multilayer formation. The greater surface density was determined for the chitosan, but the system containing activated carbon and 1-butanol presented better efficiency for PAHs removal. Results indicated that the adsorption evaluated in this work can be a potential stage in the waste lubricant oils global recovery process. Les huiles de lubrification subissent une dégradation augmentant la concentration d'hydrocarbures aromatiques polycycliques (HAP). Dans ce travail, on a estimé l'adsorption de HAPs sur du carbone activé, de la silice en poudre et des surfaces de chitosane en poudre, leurs concentrations dans des solvants organiques (éthanol, 2-propanol, 1-butanol et terc -butanol) étant suivies par absorption UV et dans le domaine visible. Une concentration d'équilibre a été atteinte après 72,h et les isothermes présentaient des caractéristiques de formation de couches multiples. La densité de surface la plus importante a été déterminée pour le chitosane mais le système contenant du carbone activé et du 1-butanol présentait une meilleure efficience en matière de retrait des HAPs. Les résultats indiquaient que l'adsorption évaluée dans ce travail pourrait constituer une étape potentielle du processus global de récupération des résidus d'huiles de lubrification. [source] Effect of alkali metal hydroxides on the enantioseparation of amines using di- O -isopropylidene-keto- L -gulonic acid as the selector in NACEELECTROPHORESIS, Issue 22 2006Ylva Hedeland Dr. Abstract The present work demonstrates the importance of the ionic composition in the BGE for enantioseparation. (,)-2,3:4,6-di- O -Isopropylidene-2-keto- L -gulonic acid ((,)-DIKGA) has been used as the chiral selector in methanolic and ethanolic BGEs. The influence of added alkali metal hydroxides on the EOF and the chiral separation of amines (atenolol, isoprenaline, pindolol and propranolol) have been studied. The ion-pair formation constants in ethanol were determined by precision conductometry for the enantiomers of pindolol with (,)-DIKGA, for Li+, Na+ and Cs+ with (,)-DIKGA, and also for the corresponding alkali metal hydroxides. The effective mobilities and the enantiomeric mobility differences were affected by the type of alkali metal hydroxide (LiOH, NaOH, KOH, RbOH or CsOH) added to the BGE. The effective mobility and mobility difference were increased with decrease in solvated radius of the alkali metal cation. These differences could partly be correlated to the ion-pair formation constants of the alkali metal cations with the chiral selector, affecting the equilibrium concentration of the free selector. The electroosmosis was also affected by the alkali metal hydroxide added to the BGE. The cathodic electroosmosis decreased with decreasing solvated radius of the alkali metal cation added to the BGE. Interestingly, the cathodic EOF was even reversed, i.e. became anodic in the ethanolic BGEs containing KOH, RbOH or CsOH and the methanolic ones with RbOH and CsOH. [source] Evaluation of Noble Gas Recharge Temperatures in a Shallow Unconfined AquiferGROUND WATER, Issue 5 2009Bradley D. Cey Water table temperatures inferred from dissolved noble gas concentrations (noble gas temperatures, NGT) are useful as a quantitative proxy for air temperature change since the last glacial maximum. Despite their importance in paleoclimate research, few studies have investigated the relationship between NGT and actual recharge temperatures in field settings. This study presents dissolved noble gas data from a shallow unconfined aquifer heavily impacted by agriculture. Considering samples unaffected by degassing, NGT calculated from common physically based interpretive gas dissolution models that correct measured noble gas concentrations for "excess air" agreed with measured water table temperatures (WTT). The ability to fit data to multiple interpretive models indicates that model goodness-of-fit does not necessarily mean that the model reflects actual gas dissolution processes. Although NGT are useful in that they reflect WTT, caution is recommended when using these interpretive models. There was no measurable difference in excess air characteristics (amount and degree of fractionation) between two recharge regimes studied (higher flux recharge primarily during spring and summer vs. continuous, low flux recharge). Approximately 20% of samples had dissolved gas concentrations below equilibrium concentration with respect to atmospheric pressure, indicating degassing. Geochemical and dissolved gas data indicate that saturated zone denitrification caused degassing by gas stripping. Modeling indicates that minor degassing (<10% ,Ne) may cause underestimation of ground water recharge temperature by up to 2°C. Such errors are problematic because degassing may not be apparent and degassed samples may be fit by a model with a high degree of certainty. [source] Adsorption of fulvic acids from aqueous solutions by carbon nanotubesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2007Shu-Guang Wang Abstract Carbon nanotubes (CNTs) were used as adsorbent to remove fulvic acids (FA) from aqueous solutions. The adsorption capacity of CNTs for FA can reach 24 mg g,1 at 5 °C and equilibrium concentration of 18 mg dm,3. The kinetic and thermodynamic parameters, such as rate of adsorption, standard free energy changes (,G0), standard enthalpy change (,H0) and standard entropy change (,S0), have been obtained. Acidic conditions (pH = 2,5) favor FA removal. An increase in the ionic strength or the addition of divalent cations increase the adsorption of FA dramatically (FA = 60 mg dm,3). An increase in the maximum adsorbed amount of FA was observed when treating FA in synthetic seawater. Desorption studies reveal that FA can be easily and quickly removed from CNTs by altering the pH values of the solution. Good adsorption capacity and quick desorption indicate that CNTs are a promising adsorbent to remove FA from aqueous solutions. Copyright © 2007 Society of Chemical Industry [source] Flavor Migration Out of Food Matrices: II.JOURNAL OF FOOD SCIENCE, Issue 3 2003Quantifying Flavor Migration from Dough Undergoing Isothermal Heating ABSTRACT A new approach using cold-trap, on-line sampling was applied to investigate migration rate of limonene, tert-butylbenzene, and pyrazine in a flour dough matrix. Flavor equilibrium concentration and migration rates were shown to be strong functions of initial concentration. Due to encapsulation of flavor compounds at lower moisture content, it was not possible to totally extract the flavor compounds from the matrix by solvent extraction. The cold-trap online sampling method could be satisfactorily used to generate data on flavor migration rates in dough matrices. [source] Interaction of non-ionic hydrogels with weak aromatic acidsMACROMOLECULAR SYMPOSIA, Issue 1 2003Krisztina László Abstract Measurements are reported of the swelling behaviour at 20°C of poly (N isopropylacrylamide) (PNIPA) gels in aqueous solutions of two weak aromatic acids, phenol and resorcinol. For solute concentrations below 45 mmol/l the uptake of these solutions is similar. Due to selective solvation phenol exhibits an excess equilibrium concentration inside the gel of 5% over that in the surrounding bath, while for resorcinol, the excess is found to be 12%. At 50 mmol/l solute concentration, both systems display a volume transition accompanied by expulsion of the solvent. The solubility limits in water of these aromatic compounds, which are significantly different from each other (870 mmol/l and 9080 mmol/l respectively), are far above this critical concentration. In the collapsed condition the expelled liquid spreads on the surface of the phenol treated gel, while an ordered arrangement of separate droplets is generated in the case of resorcinol. In the latter case an acute contact angle was observed. It is also shown by acid-base titration that the PNIPA/water system may exhibit a slight ion exchanging character. [source] Iron, Manganese and Copper Equilibria with Wood Fibres in Single Salt Aqueous SuspensionsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2005Robin Susilo Abstract Ions of Fe, Mn and Cu were introduced into suspensions of protonated or metal-free fibres and the equilibrium concentration of each metal in the fibre and surrounding solution was measured. The results were compared with the Donnan equilibrium model. Mn and Cu concentrations on the fibres were found to be pH dependent and in agreement with the model. An increased amount of Fe on the Kraft pulp fibres was found and attributed to iron containing precipitates trapped within the fibres. Precipitates in mechanical pulps had a very small amount (1-2 wt%) of iron. Des ions de Fe, Mn et Cu ont été introduits dans des suspensions de fibres protonatées ou « sans métaux » et la concentration d'équilibre de chaque métal dans la fibre et la solution environnante a été mesurée. Les résultats ont été comparés avec le modèle d'équilibre de Donnan. On a trouvé que les concentrations de Mn et Cu sur les fibres étaient dépendantes du pH et en accord avec le modèle. Une quantité accrue de Fe a été trouvée sur les fibres de pâte kraft et attribuée aux précipitats contenant du fer retenus dans les fibres. Les précipitats dans les pâtes mécaniques ont une très petite quantité (1-2% en poids) de fer. [source] Nanostructured Electrodes: The Role of Surface and Interface Energy on Phase Stability of Nanosized Insertion Compounds (Adv. Mater.ADVANCED MATERIALS, Issue 25-26 200926/2009) The cover shows three structures of the Li-ion battery electrode material LixFePO4 having two coexisting phases Li-rich: dark blue, Li-poor: light blue. The vertical decreasing dimension represents the downsizing of the particle size which leads to more similar Li-ion equilibrium concentrations in both phases, as indicated by the lower contrast between the blue shaded Li-ions. This result, reported by Marnix Wagemaker and co-workers on p. 2703, helps explain the changes in equilibrium properties in nanostructured insertion compounds such as Li-ion battery electrodes and H-storage materials. [source] Supercritical antisolvent micronisation of synthetic all- trans -,-carotene with tetrahydrofuran as solvent and carbon dioxide as antisolventJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2009Miguel A Tavares Cardoso Abstract BACKGROUND: Supercritical antisolvent (SAS) micronisation of synthetic trans -,-carotene was studied using tetrahydrofuran (THF) as solvent and supercritical carbon dioxide (CO2) as antisolvent, with the objective of increasing its bioavailability and facilitating its dispersion in oil and emulsion formulations as a result of its smaller particle size. The micronised powder was analysed by scanning electron microscopy and high-performance liquid chromatography. Micronisation experiments were performed in order to evaluate the effects of temperature (308.15,333.15 K), pressure (6.5,13 MPa) and concentration of the liquid solution (6,9 g L,1). The effect of the supercritical CO2/THF flow ratio in the range between 4 and 44 (on a mass basis) was also analysed. Determinations of equilibrium concentrations of ,-carotene in the CO2/THF mixture were also performed. RESULTS: The particle size obtained ranged from 1 to 500 µm, with mean particle diameters around 100 µm. Three types of morphology were found in the precipitated powder: crystalline with superficial pores and leaf-like appearance; crystalline with regular shapes and blade-like edges; and crystalline without superficial pores and leaf-like apearance. The Peng,Robinson equation of state was used to calculate the density of the CO2/THF binary mixture, and the solubility of ,-carotene in this mixture was correlated with its density. CONCLUSION: The use of the SAS technique to micronise ,-carotene proved to be efficient, and the absence of degradation in the micronised powder allows the industrial application of this technique. Copyright © 2008 Society of Chemical Industry [source] Antimicrobial peptide interactions with silica bead supported bilayers and E. coli: buforin II, magainin II, and arenicin,JOURNAL OF PEPTIDE SCIENCE, Issue 8 2009Ryan W. Davis Abstract Using the unique quantitative capabilities of hyperspectral confocal microscopy combined with multivariate curve resolution, a comparative approach was employed to gain a deeper understanding of the different types of interactions of antimicrobial peptides (AMPs) with biological membranes and cellular compartments. This approach allowed direct comparison of the dynamics and local effects of buforin II, magainin II, and arenicin with nanoporous silica bead supported bilayers and living E. coli. Correlating between experiments and comparing these responses have yielded several important discoveries for pursuing the underlying biophysics of bacteriocidal specificity and the connection between structure and function in various cellular environments. First, a novel fluorescence method for direct comparison of a model and living system is demonstrated by utilizing the membrane partitioning and environmental sensitivity of propidium iodide. Second, measurements are presented comparing the temporal dynamics and local equilibrium concentrations of the different antimicrobial agents in the membrane and internal matrix of the described systems. Finally, we discuss how the data lead to a deeper understanding of the roles of membrane penetration and permeabilization in the action of these AMPs. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd. [source] Diffusion-Influenced Reversible Trapping Problem in the Presence,of,an,External FieldCHEMISTRY - AN ASIAN JOURNAL, Issue 1-2 2006Soohyung Park Abstract We investigate the field effect on the diffusion-influenced reversible trapping problem in one dimension. The exact Green function for a particle undergoing diffusive motion between two static reversible traps with a constant external field is obtained. From the Green function, we derive the various survival probabilities. Two types of trap distribution for the many-body problem are considered, the periodic and random distributions. The mean survival probability is obtained for the crossing-forbidden case for the two types of trap distribution. For the periodic distribution it decays exponentially. For the random trap distribution, similar to the irreversible case, there exists a critical field strength at which the long time asymptotic behavior undergoes a kinetic transition from the power law to exponential behaviors. The difference between equilibrium concentrations for the two types of trap distribution due to the fluctuation effect of trap concentration vanishes as the field strength increases. [source] | |||||||||||||