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Isotherms
Kinds of Isotherms Terms modified by Isotherms Selected AbstractsMOISTURE SORPTION ISOTHERM, PROPERTIES OF SORBED WATER AND HEAT OF SORPTION OF SANDESH, AN INDIAN MILK PRODUCTJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2010J.K. SAHU ABSTRACT Moisture sorption isotherm of sandesh, one of the most popular milk products in India, was determined in terms of its moisture adsorption isotherms by gravimetrical method at 20 and 30C using various saturated salt solutions in the range of 11.2 to 97.2%. The isotherms obtained were of sigmoid shape and of the Brunauer,Emmett,Teller type. Out of three sorption models fitted to the experimental data, Caurie's model was found superior in interpreting the moisture adsorption characteristics of sandesh. The monolayer moisture content as calculated from the Caurie's model at 20 and 30C were 5.89% (dry basis [d.b.]) and 5.21% (d.b.), respectively. The values of isosteric heat of sorption as calculated from Clausius,Clapeyron equation was found to increase with decreasing moisture content at lower moisture content and approached the value of heat of vaporization of free water above 17.25% (d.b.). PRACTICAL APPLICATIONS The present paper describes basically the storage stability of sandesh. The sandesh is a heat,acid coagulated product of milk in Indian subcontinent and forms the part and parcel of social life, ceremonies and festivals. It has an excellent market potential and higher profit margin compared with other milk products like table butter, cheese and milk powder. Although Indian dairy industry has made rapid strides in the last few decades, there is no proper packaging system, developed so far, for storage of sandesh. Keeping pace with the growing consumers' demand for fresh, convenient and microbiologically free foods, design of proper packaging system is the need of the hour. The data presented in the paper will be very much essential for the researchers and research and development institutions for proper designing of packaging system for sandesh. [source] Sorption Isotherm and Calorimetric Behavior of Amorphous/Crystalline Raffinose-Water SystemsJOURNAL OF FOOD SCIENCE, Issue 4 2000H.A. Iglesias ABSTRACT: The water adsorption and desorption isotherms at 27 °C of initially amorphous raffinose over a range of relative humidity of 11% to 97% have been determined. Upon adsorption, the isotherm exhibited a "quasi" plateau, and the moisture content at this plateau was found to be very close to the amount required to form the crystalline raffinose pentahydrate (R.5 H2O). Crystallization of raffinose (R.5 H2O) during water adsorption at 52% and 58% RH was indicated by differential scanning calorimetry (DSC); both thermograms showed an endothermal peak of melting corresponding to R.5H2O. The results of the crystallization kinetics at 52% and 58% RH indicated that the time to assess the stable physical state in a sugar system for a given external condition has to be properly defined and depends on the (T-Tg) value. [source] Simulation and validation of ethanol removal from water in an adsorption packed bed: Isotherm and mass transfer parameter determination in batch studiesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2010R. A. Jones Abstract Preferential adsorption of ethanol from ethanol/water mixtures in batch equilibrium and kinetic experiments were carried out on a commercially available activated carbon adsorbent Filtrasorb 600 (F-600). A model based on finite difference method was developed and employed to determine the mass transfer parameters and equilibrium behaviour for the adsorption of ethanol from simple batch systems. The estimates of the adsorption isotherm along with the mass transfer parameters were used to simulate the transient performance that could be expected in a packed bed under various operating conditions (feed flow rate, feed concentration, and particle size). The applicability of the simulation results were found to be a good match with experimental packed bed experiments over the entire range of operating conditions tested. La cinétique et l'isotherme d'adsorption de l'éthanol des mélanges eau/éthanol lors d'expériences en discontinus ont été déterminées pour un adsorbant au charbon activé disponible dans le commerce, le Filtrasorb 600 (F-600). Un modèle basé sur la méthode des différences finies a été développé et utilisé pour déterminer les paramètres de transfert de matière et étudier le comportement à l'équilibre pour l'adsorption préférentielle de l'éthanol en systèmes discontinus. Les estimations de l'isotherme d'adsorption aussi bien que les paramètres de transfert de matière ont été utilisées pour simuler la performance en régime transitoire d'un lit d'adsorbant sous diverses conditions de fonctionnement (taux d'écoulement du mélange, concentration du mélange et la taille des particules). L'applicabilité des résultats de simulation s'est avérée tout à fait concordante avec les données expérimentales sous toutes les conditions de fonctionnement examinées. [source] Molecular simulation of ammonia absorption in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N])AICHE JOURNAL, Issue 9 2009Wei Shi Isotherms for ammonia absorption in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) are computed at temperatures ranging from 298 K to 348 K using osmotic ensemble Monte Carlo simulations. The results agree well with previous experimental measurements. Activity coefficients vary from 0.5 to 0.8, indicating negative deviations from Raoult's Law. The computed enthalpy of mixing ranges from ,2 to ,11 kJ/mol. Computed partial molar volumes are on the order of 25,30 cm3/mol. Energy and radial distribution analyses indicate that ammonia interacts more strongly with the cation than the anion, in contrast to observations made of other gases in ionic liquids such as CO2. The reason for this behavior is that ammonia forms a strong hydrogen bond with the ring hydrogen atoms of the cation. The simulations predict that strategies aimed at changing the solubility of ammonia should focus on altering the hydrogen bond donating ability of the cation, and that altering the anion will have more modest effects. It is shown that this hypothesis is consistent with available experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Molecular Mechanism of the Hydration of Candida antarctica Lipase B in the Gas Phase: Water Adsorption Isotherms and Molecular Dynamics SimulationsCHEMBIOCHEM, Issue 18 2009Ricardo J. F. Branco Dr. Abstract Hydration is a major determinant of activity and selectivity of enzymes in organic solvents or in gas phase. The molecular mechanism of the hydration of Candida antarctica lipase B (CALB) and its dependence on the thermodynamic activity of water (aw) was studied by molecular dynamics simulations and compared to experimentally determined water sorption isotherms. Hydration occurred in two phases. At low water activity, single water molecules bound to specific water binding sites at the protein surface. As the water activity increased, water networks gradually developed. The number of protein-bound water molecules increased linearly with aw, until at aw=0.5 a spanning water network was formed consisting of 311 water molecules, which covered the hydrophilic surface of CALB, with the exception of the hydrophobic substrate-binding site. At higher water activity, the thickness of the hydration shell increased up to 10 Å close to aw=1. Above a limit of 1600 protein-bound water molecules the hydration shell becomes unstable and the formation of pure water droplets occurs in these oversaturated simulation conditions. While the structure and the overall flexibility of CALB was independent of the hydration state, the flexibility of individual loops was sensitive to hydration: some loops, such as those part of the substrate-binding site, became more flexible, while other parts of the protein became more rigid upon hydration. However, the molecular mechanism of how flexibility is related to activity and selectivity is still elusive. [source] Design of Simulated Moving Bed Plants by Using Noncompetitive Langmuir IsothermsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2009M. Fütterer Abstract The simulated moving bed process is increasingly used for the separation of binary mixtures. To ensure proper operation, the volumetric flow rates and the time interval must be exactly adjusted. This study presents a general method for determining the control variables for a dispersion-free SMB process. For noncompetitive Langmuir isotherms, explicit equations are derived for the case of complete separation. The proposed method allows both a good estimation of the time trajectories of the concentrations at the drains and the design of new applications for optimization and control of SMB plants. [source] Improved methods for carbon adsorption studies for water and wastewater treatmentENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2006Wei-chi Ying Abstract An improved method was developed to rank activated carbon in removing organic water pollutants. The simple and standardized evaluation method uses a set of four adsorptive capacity indicators: phenol, iodine, methylene blue, and tannic acid numbers; those four indicator compounds were selected because they cover the molecular size range of most organic water pollutants. An improved microcolumn rapid breakthrough (MCRB) test method was developed from the existing HPMC (high-pressure minicolumn) and RSSCT (rapid small-scale column test) methods by simplifying the experimental procedure and using readily available low-cost pump, sampler, piping, and fittings. This method can be practiced in an ordinary environmental laboratory to select the best carbon, to verify the treatment effectiveness, and to estimate the adsorption treatment cost based on the observed capacity utilization rate for carbon in the adsorber without the problems often encountered with using small and mini traditional columns. The benefits of the four-parameter carbon selection method and the MCRB method were demonstrated by adsorption isotherm and breakthrough data for several indicator compounds and organic water pollutants. These improved methods will enable efficient carbon adsorption studies necessary for more applications of carbon adsorption technology in water and wastewater treatment. © 2006 American Institute of Chemical Engineers Environ Prog, 2006 [source] Comparison of Cd, Cu, and Zn toxic effects on four marine phytoplankton by pulse-amplitude-modulated fluorometryENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2005Ai-Jun Miao Abstract The toxic effects of Cd, Cu, and Zn on four different marine phytoplankton, Dunaliella tertiolecta, Prorocentrum minimum, Synechococcus sp., and Thalassiosira weissflogii, were examined by comparing the cell-specific growth rate, pulse-amplitude-modulated (PAM) parameters (maximum photosystem II quantum yield ,M and operational quantum yield ,'M), chlorophyll a content, and cellular metal concentration, over a 96-h period. The calculated no-observed-effect concentration (NOEC) based on both cell-specific growth rate and two PAM parameters (,M and ,'M) were mostly identical. Thus, these PAM parameters and cell-specific growth rate were comparable in their sensitivities as the biomarkers for trace metal toxicity to marine phytoplankton. The cyanobacteria Synechococcus sp. was the most sensitive species among the four algal species tested because of its higher cell surface to volume ratio. The toxicity of the three tested metals followed the order of Cd > Cu > Zn based on the cellular metal concentration of the four algae at the NOEC. The cellular metal bioaccumulation followed the same Freundlich isotherm for each metal regardless of the algal species, indicating that the metal accumulation was a nonmetabolic process under high ambient metal concentrations and that the cell surface metal binding was comparable among the different species. For all the algae examined in our study, the bioaccumulation potentials of Cu and Zn were similar to each other, while the Cd bioaccumulation was much lower under environmentally realistic metal concentration. [source] Theoretical framework for the distribution of trace metals among the operationally defined speciation phases of a sedimentENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2001René A. Nome Abstract The use of a model based on Langmuir's isotherm to evaluate the metal associated with separate geochemical phases of a sediment is proposed and its validity tested with sediments of certified composition. The model takes into account a standard procedure for a certified reference material (CRM601), which defines, experimentally, a set of sequential extractions that divide the sediment into four operational fractions. The derived equations allow the treatment of data from sediment of Flumendosa Lake, Italy, and certified material CRM601 and also allow the computation of corrected concentrations, i.e., the metal affinities for each fraction. Experimental values for Ni show its low sensitivity and an equal distribution among different phases, which suggests a similar adsorption mechanism in all cases. In the case of Cd, the corrected concentration in the Fe/Mn oxide phase is nine times higher than for the residual fraction. For sediment of the Bèsos River, Spain, results show the percentage distribution of Ni over different fractions. Affinity values for Ni on a Flumendosa Lake sediment have also been calculated. The present model is simple to apply and shows satisfactory agreement with experimental data. [source] Effect of mass-transfer limitations on bioavailability of sorbed naphthalene in synthetic model soil matricesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2000Hendricus Mulder Abstract External and internal mass-transfer resistances influencing the bioavailability of sorbed naphthalene in a synthetic model matrix for soil aggregates were investigated in batch experiments in mixed reactors. Amberlite® adsorption resins (XAD4 and XAD7) were used as the synthetic model for soil aggregates. The effect of hydrodynamic conditions in the slurry phase on the diffusive transport across a stagnant film surrounding the model particles was studied. In addition, a mechanistic model was developed based on mass balances, diffusion equations, a nonlinear sorption isotherm, and microbial degradation kinetics. Experimental results could be explained well with this model. In the absence of external transfer limitations, intraparticle effective diffusion coefficients of (3.55 ± 0.10) × 10,9 m2/s and (5.29 ± 0.86) × 10,10 m2/s were determined for naphthalene in Amberlite XAD4 and XAD7, respectively. [source] Aligning Single-Walled Carbon Nanotubes By Means Of Langmuir,Blodgett Film Deposition: Optical, Morphological, and Photo-electrochemical StudiesADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Gabriele Giancane Abstract An alkoxy-substituted poly(phenylene thiophene) is used in order to suspend single-walled carbon nanotubes in an organic solvent. The suspension is spread on the air,water interface of a Langmuir trough and the floating film is characterized by means of Brewster angle microscopy and UV-visible reflection spectroscopy and the compression isotherm is recorded. The polymer/carbon-nanotube blend is transferred onto different substrates using the Langmuir,Blodgett technique. AFM measurements indicate the formation of globular structures for the samples transferred at low surface-pressure values and a tubular morphology for high-pressure-deposited samples. AFM analysis is repeated on a sample exposed to soft X-rays for about 5,h and a highly organized structure of bundles of carbon nanotubes rises up. Samples with different numbers of layers are transferred onto ITO substrates by means of the Langmuir,Blodgett method and are tested as photocathodes in a photo-electrochemical cell. A Voc of 0.18,V, an Isc of 85.8,mA, FF of 40.0%, and , of (6.23,×,10,3)% are obtained. [source] Analysis of the behaviour of the structural concrete after the fire at the Windsor Building in MadridFIRE AND MATERIALS, Issue 2 2010E. Menéndez Abstract The analysis of the concrete subjected to high temperatures is usually undertaken by means of tests specifically designed and carried out in the laboratory, or by using theoretical approaches using standardized curves for theoretical fires. An analysis by different techniques has been carried out on structural concrete to real fire of Windsor Building in Madrid, which was severally damaged by a fire in 2005. These techniques are X-ray diffraction, differential thermal and thermogravimetric analysis and backscattered electron microscopy with dispersive X-ray microanalysis. Samples of the concrete were taken from different floors in the building and analyses were carried out at different depths starting from the surface exposed to the fire itself. The analysis allows the damaged area to be limited as well as situating the 500,C isotherm in the concrete element. In accordance with the results obtained, the damage is limited to just a few centimeters from the surface exposed to the fire itself, in spite of its prolonged exposure to the fire. This would justify that the concrete has demonstrated a suitable resistant behaviour. Likewise, it can be deduced from the results obtained that the fire, to which the concrete was subjected, can be qualified as severe. Also, these results can confirm that the calculation hypothesis in the project is correct in relation to the fire resistance exigencies of the concrete. Copyright © 2009 John Wiley & Sons, Ltd. [source] Comparison between the charring rate model and the conductive model of Eurocode 5FIRE AND MATERIALS, Issue 3 2009Paulo B. Cachim Abstract Eurocode 5, Part 1,2, presents several models for the calculation of fire resistance of timber structures. These models are based on the hypothesis that for temperatures above 300°C , wood is no longer able to sustain any stress, which makes the determination of the location of the 300°C isotherm decisive for the result provided by the models. In this paper, the charring rate model and the conductive model presented in Eurocode 5, Part 1,2 are compared regarding the determination of the location of the 300°C isotherm. The main wood parameters investigated are density, moisture content and anisotropy. The almost complete independence of the charring rate model from these parameters leads to some inconsistencies between the models. To reduce these inconsistencies some proposals to improve the conductive and the charring rate models are presented. Copyright © 2008 John Wiley & Sons, Ltd. [source] Photoluminescence Detection of Biomolecules by Antibody-Functionalized Diatom BiosilicaADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Debra K. Gale Abstract Diatoms are single-celled algae that make microscale silica shells called "frustules", which possess intricate nanoscale features imbedded within periodic two-dimensional pore arrays. In this study, antibody-functionalized diatom biosilica frustules serve as a microscale biosensor platform for selective and label-free photoluminescence (PL)-based detection of immunocomplex formation. The model antibody rabbit immunoglobulin G (IgG) is covalently attached to the frustule biosilica of the disk-shaped, 10-µm diatom Cyclotella sp. by silanol amination and crosslinking steps to a surface site density of 3948,±,499 IgG molecules µm,2. Functionalization of the diatom biosilica with the nucleophilic IgG antibody amplifies the intrinsic blue PL of diatom biosilica by a factor of six. Furthermore, immunocomplex formation with the complimentary antigen anti-rabbit IgG further increases the peak PL intensity by at least a factor of three, whereas a non-complimentary antigen (goat anti-human IgG) does not. The nucleophilic immunocomplex increases the PL intensity by donating electrons to non-radiative defect sites on the photoluminescent diatom biosilica, thereby decreasing non-radiative electron decay and increasing radiative emission. This unique enhancement in PL emission is correlated to the antigen (goat anti-rabbit IgG) concentration, where immunocomplex binding follows a Langmuir isotherm with binding constant of 2.8,±,0.7,×,10,7M. [source] Biodegradation and transport of benzene, toluene, and xylenes in a simulated aquifer: comparison of modelled and experimental resultsHYDROLOGICAL PROCESSES, Issue 16 2002Jiin-Shuh Jean Abstract Both laboratory experiments and numerical modelling were conducted to study the biodegradation and transport of benzene,toluene,xylenes (BTX) in a simulated semi-confined aquifer. The factors incorporated into the numerical model include advection, hydrodynamic dispersion, adsorption, and biodegradation. The various physico-chemical parameters required by the numerical model were measured experimentally. In the experimental portion of the study, BTX compounds were introduced into the aquifer sand. After the contaminants had been transported through the system, BTX concentrations were measured at 12 equally spaced wells. Subsequently, microorganisms obtained from the activated sludge of a sewage treatment plant and cultured in BTX mixtures were introduced into the aquifer through the 12 sampling wells. The distribution data for BTX adsorption by the aquifer sand form a nonlinear isotherm. The degree of adsorption by the sand varies, depending on the composition of the solute. The degradation time, measured from the time since the bacteria were added to the aquifer until a specific contaminant was no longer detectable, was 35,42 h for BTX. The dissolved oxygen, after degradation by BTX compounds and bacteria, was consumed by about 40,60% in the entire simulated aquifer; thus the aerobic conditions were maintained. This study provides insights for the biodegradation and transport of BTX in aquifers by numerical modelling and laboratory experiments. Experimental and numerical comparisons indicate that the results by Monod degradation kinetics are more accurate than those by the first-order degradation kinetics. Copyright © 2002 John Wiley & Sons, Ltd. [source] ENSO and the South China Sea summer monsoon onsetINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2007Wen Zhou Abstract This paper investigates the relationship between the onset date of the South China Sea summer monsoon (SCSSM) and the El Niño/Southern Oscillation (ENSO). The monsoon onset date (MOD) is defined on the basis of the switch of the 850-hPa zonal winds over the South China Sea (SCS) from easterly to westerly for two consecutive pentads. The ENSO signal is represented by the ocean heat content (OHC), which is proportional to the depth of the 20 °C isotherm. It is found that, in years associated with a warm (cold) ENSO event or the year after, the monsoon tends to have a late (an early) onset and the intensity of the SCSSM also tends to be weaker (stronger). During a 2-year period prior to the onset, anomalies of OHC have an obvious eastward propagation. The 850-hPa flow east of the Philippines, specifically the strength of the subtropical high, is also found to be critical in determining the MOD. The link between these two results appears to be the propagation of cold (warm) subsurface water into the western North Pacific (WNP), which strengthens (weakens) the subtropical high, and hence a late (an early) SCSSM onset. Copyright © 2006 Royal Meteorological Society. [source] Parametric study on the silica gel,calcium chloride composite desiccant rotary wheel employing fractal BET adsorption isothermINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2005X. J. Zhang Abstract In this paper a family of new silica gel,calcium chloride composite adsorbents is presented for desiccant rotary wheel in dehumidification system. For these desiccants the water sorption equilibrium has been measured in a wide relative vapour pressure range. This experimental study shows that the vapour adsorption properties of the composites using calcium chloride as impregnated salt can be controllably modified by varying the amount of the salt inside the pores. The thermodynamic performance of such desiccant rotary wheel is analysed based on the adsorption equilibrium equations obtained through nonlinear regressions using fractal BET theory. The simulation results show that the new composite desiccants can be effectively used in a rotary wheel dehumidifier and to improve its performance, various optimum operational/system parameters have been identified. Copyright © 2005 John Wiley & Sons, Ltd. [source] Protein stabilisation of Chardonnay wine using trisacryl and bentonite: a comparative studyINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 2 2009Johannes De Bruijn Summary The stabilisation of a Chilean Chardonnay wine by SP-Trisacryl-M and bentonite was investigated, evaluating protein, polyphenol and polysaccharide adsorption, turbidity and wine quality. The wine could be stabilised by adding at least 0.3 kg m,3 of bentonite or 12 kg m,3 of trisacryl, removing 95% and 76% of the wine proteins, respectively. The protein adsorption data for bentonite and trisacryl were fitted using the Freundlich isotherm. The wine protein adsorption isotherm on trisacryl was unfavourable. Protein removal from Chardonnay by trisacryl in a packed column at continuous operation was about 50% during the first 70 bed volumes (BV) of treated wine and decreased progressively until the end of the treatment (100 BV). The adsorbents showed a higher selectivity for proteins than for polyphenols and polysaccharides. A sensorial panel could not detect statistically significant differences between the bentonite and trisacryl treatments of wine at P , 0.05. [source] Moisture sorption isotherm and xerophilic moulds associated with dried cocoyam chips in storage in NigeriaINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 5 2008J. Obeta Ugwuanyi Summary Extended storage of cocoyams (Colocasia antiquorum and Colocasia esculenta) is achieved in parts of Nigeria by processing them into smoked and dried chips. In this study, cocoyam chips were collected from parts of Nigeria at the end of drying, at various periods of storage and from markets, and analysed for moisture content, moisture sorption characteristics and xerophilic moulds. Moisture content of chips ranged from 7.07 ± 1.1% for freshly dried samples to 16 ± 2.2% for samples stored up to 8 months. Six mould species from four groups of the genus Aspergillus (including five xerophiles) identified as Aspergillus fumigatus, Eurotium repens, Eurotium amstelodami, Eurotium chevalieri and Aspergillus flavus and Aspergillus niger and Mucor sp. were isolated. The variety of moulds increased with storage and moisture content of samples. Moisture sorption in dried chips showed type II sigmoidal behaviour. Wood smoke significantly protected chips from mould colonization, but in cooperation with reduced water activity. Simple and inexpensive storage of freshly dried samples in airtight bags led to prolonged storage of up to 14 months without deterioration. [source] Theoretical studies of some sulphonamides as corrosion inhibitors for mild steel in acidic mediumINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 14 2010Eno E. Ebenso Abstract Density functional theory (DFT) at the B3LYP/6-31G (d,p) and BP86/CEP-31G* basis set levels and ab initio calculations using the RHF/6-31G (d,p) methods were performed on four sulfonamides (namely sulfaacetamide (SAM), sulfapyridine (SPY), sulfamerazine (SMR), and sulfathiazole (STI)) used as corrosion inhibitors for mild steel in acidic medium to determine the relationship between molecular structure and their inhibition efficiencies (%IE). The order of inhibition efficiency obtained was SMR > SPY > STI > SAM which corresponded with the order of most of the calculated quantum chemical parameters namely EHOMO (highest occupied molecular orbital energy), ELUMO (lowest unoccupied molecular orbital energy), the energy gap (,E), the Mulliken charges on the C, O, N, S atoms, hardness (,), softness (S), polarizability (,), dipole moment (,), total energy change (,ET), electrophilicity (,), electron affinity (A), ionization potential (I), the absolute electronegativity (,), and the fraction of electrons transferred (,N). Quantitative structure activity relationship (QSAR) approach has been used and a correlation of the composite index of some of the quantum chemical parameters was performed to characterize the inhibition performance of the sulfonamides studied. The results showed that the %IE of the sulfonamides was closely related to some of the quantum chemical parameters but with varying degrees/order. The calculated %IE of the sulfonamides studied was found to be close to their experimental corrosion inhibition efficiencies. The experimental data obtained fits the Langmuir adsorption isotherm. The negative sign of the EHOMO values and other thermodynamic parameters obtained indicates that the data obtained supports physical adsorption mechanism. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] In-situ small-angle neutron scattering study of pore filling and pore emptying in ordered mesoporous silicaJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2010M. Erko The capillary condensation and capillary emptying of water and perfluoropentane in ordered mesoporous SBA-15 silica is studied by in-situ small-angle neutron scattering (SANS). The SANS data can be perfectly described by a simple analytical model for spatially random pore filling (Laue scattering) for the entire range of pore-filling fractions. From this it is concluded that recently proposed pore correlations due to elastic interactions between neighbouring pores upon capillary condensation do not play a role in this system. The pores fill randomly according to their size distribution, in perfect agreement with the classical Kelvin equation. The relation between the overall pore-filling fraction as determined from the volumetric sorption isotherm, and the fraction of completely filled pores as obtained from the fit of the SANS data, allows conclusions to be drawn about the thermodynamic metastability of the adsorption process. [source] Membranes of cellulose triacetate produced from sugarcane bagasse cellulose as alternative matrices for doxycycline incorporationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009Guimes Rodrigues Filho Abstract Cellulose triacetate (CTA) membranes were prepared using polyethylene glycol, 600 g mol,1, (PEG) as additive and were utilized in essays of doxycycline (DOX) incorporation using two different procedures: (i) incorporation of the drug during the membrane preparation and (ii) incorporation of the drug to a previously prepared membrane. In the first, the produced membrane presented high compatibility between DOX and CTA, what was evidenced by analyzing the DSC curve for a CTA/PEG 50%/DOX system. Results showed that the drug is homogeneously distributed throughout the matrix, molecularly. In the second method, the drug was molecularly and superficially adsorbed, as seen through the DSC curve for the system CTA/PEG 10%/DOX, which nearly does not present alterations in relation to the original material, and through the isotherm of drug adsorption that follows the Langmuir model. Results showed that the membranes produced from sugarcane bagasse are adequate to produce matrices for drug-controlled release, both for enteric use (Method (i)) and topic use (Method (ii)). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Preparation of a heterogeneous hollow-fiber affinity membrane having a mercapto chelating resin and its recovery of Hg2+ cationsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Bing Wang Abstract A kind of heterogeneous hollow-fiber affinity filter membrane with a high chelating capacity for Hg2+ was prepared by phase separation with blends of a mercapto chelating resin and polysulfone as the membrane materials, N,N -dimethylacetamide as the solvent, and water as the extraction solvent. The adsorption isotherms of the hollow-fiber affinity filter membrane for Hg2+ were determined. The heterogeneous hollow-fiber affinity filter membrane was used for the adsorption of Hg2+ cations through the coordination of the mercapto group and Hg2+ cations, and the effects of the morphology and structure of the affinity membrane on the chelating properties were investigated. The chelating conditions, including the chelating resin grain size, pH value, concentration of the metallic ion solution, mobile phase conditions, and operating parameters, had significant effects on the chelating capacity of the hollow-fiber affinity filter membrane. The results revealed that the greatest chelating capacity of the hollow-fiber affinity filter membrane for Hg2+ was 1090 ,g/cm2 of membrane under appropriate conditions, and the adsorption isotherms of Hg2+ could be described by the Langmuir isotherm. The dynamic chelating experiments indicated that the hollow-fiber affinity membrane could be operated at a high feed flow rate and that large-scale removal of Hg2+ could be realized. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Polyethylene glycol and polyvinyl alcohol as corrosion inhibitors for aluminium in acidic mediumJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007S. A. Umoren Abstract The corrosion inhibition of aluminum in H2SO4 in the presence of polyethylene glycol (PEG) and polyvinyl alcohol (PVA) as inhibitors at 30,60 °C was studied using gravimetric, gasometric, and thermometric techniques. The inhibition efficiency (%I) increased with increase in concentration of the inhibitors. Increase in temperature increased the corrosion rate in the absence and presence of inhibitors but decreased the inhibition efficiency. Both PEG and PVA were found to obey Temkin adsorption isotherm at all concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameters obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. PEG was found to be a better inhibitor than PVA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Use of copper(II)/ethylene diamine-cotton complex for the adsorption of residual dyesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Mohamed Hassen V. Baouab Abstract The chemical modification of cotton is performed by successive reactions with thionyl chloride followed by ethylene diamine (ED) to prepare aminoalkyl amino cotton namely ED-cotton. Evidence of attaching ethylene diamine groups onto cotton is provided by nitrogen determination and thermogravimetry analysis. Because of complexation, the ethylene diamine-grafted groups immobilizes Cu(II) ions from buffered solution at pH 6. The formation of a 1/1 complex is assessed by the adsorption limit values. The binary system [Cu(II)/ED-cotton] is then tested for the adsorption of two acid dyes (Acid Blue 25 and Calmagite) as ligands in the metal-coordinating process. The adsorption of Cu(II) onto ED-cotton and of the dyes onto Cu(II)/ED-cotton is followed spectrometrically. The observed stoichiometries of the ternary-formed complex [Dye/Cu(II)/ED-cotton] are 1/1/1 with Acid Blue 25 and 0.75/1/1 with Calmagite at 20°C. The Langmuir and Freundlich isotherms constants for the adsorption of the tested dyes onto Cu(II)/ED-cotton are evaluated from the experimental data, but better agreement is obtained by using the composite isotherm of Jossens. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1389,1396, 2007 [source] A world-wide study of high altitude treeline temperaturesJOURNAL OF BIOGEOGRAPHY, Issue 5 2004Christian Körner Abstract Aim, At a coarse scale, the treelines of the world's mountains seem to follow a common isotherm, but the evidence for this has been indirect so far. Here we aim at underpinning this with facts. Location, We present the results of a data-logging campaign at 46 treeline sites between 68° N and 42° S. Methods, We measured root-zone temperatures with an hourly resolution over 1,3 years per site between 1996 and 2003. Results, Disregarding taxon-, landuse- or fire-driven tree limits, high altitude climatic treelines are associated with a seasonal mean ground temperature of 6.7 °C (±0.8 SD; 2.2 K amplitude of means for different climatic zones), a surprisingly narrow range. Temperatures are higher (7,8 °C) in the temperate and Mediterranean zone treelines, and are lower in equatorial treelines (5,6 °C) and in the subarctic and boreal zone (6,7 °C). While air temperatures are higher than soil temperatures in warm periods, and are lower than soil temperatures in cold periods, daily means of air and soil temperature are almost the same at 6,7 °C, a physics driven coincidence with the global mean temperature at treeline. The length of the growing season, thermal extremes or thermal sums have no predictive value for treeline altitude on a global scale. Some Mediterranean (Fagus spp.) and temperate South Hemisphere treelines (Nothofagus spp.) and the native treeline in Hawaii (Metrosideros) are located at substantially higher isotherms and represent genus-specific boundaries rather than boundaries of the life-form tree. In seasonal climates, ground temperatures in winter (absolute minima) reflect local snow pack and seem uncritical. Main conclusions, The data support the hypothesis of a common thermal threshold for forest growth at high elevation, but also reflect a moderate region and substantial taxonomic influence. [source] Sorption of copper by a highly mineralized peat in batch and packed-bed systemsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2010Marta Izquierdo Abstract BACKGROUND: The performance of peat for copper sorption was investigated in batch and fixed-bed experiments. The effect of pH was evaluated in batch experiments and the experimental data were fitted to an equilibrium model including pH dependence. Hydrodynamic axial dispersion was estimated by tracing experiments using LiCl as a tracer. Six fixed-bed experiments were carried out at copper concentrations between 1 and 60 mg dm,3 and the adsorption isotherm in dynamic mode was obtained. A mass transport model including convection,dispersion and sorption processes was applied for breakthrough curve modelling. RESULTS: Maximum uptake capacities in batch mode were 22.0, 36.4, and 43.7 mg g,1 for pH values of 4.0, 5.0, and 6.0, respectively. Uptake capacities in continuous flow systems varied from 36.5 to 43.4 mg g,1 for copper concentrations between 1 and 60 mg dm,3. Dynamic and batch isotherms showed different shapes but a similar maximum uptake capacity. Sorbent regeneration was successfully performed with HCl. A potential relationship between dispersion coefficient and velocity was obtained with dispersion coefficients between 5.00 × 10,8 and 2.95 × 10,6 m2 s,1 for water velocities ranging between 0.56 × 10,4 and 5.03 × 10,4 m s,1. The mass transport model predicted both the breakpoints and the shape of the breakthrough curves. CONCLUSIONS: High retention capacities indicate that peat can be used as an effective sorbent for the treatment of wastewater containing copper ions. Copyright © 2009 Society of Chemical Industry [source] Comparative studies of Oryza sativa L. husk and chitosan as lead adsorbentJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2006Mohamed Mohamed Daud Zulkali Abstract The adsorption capacity of two low-cost adsorbents, Oryza sativa L. husk and chitosan, was studied. Lead solution was used as the adsorbate. The effect of initial lead concentration, pH, temperature, weight of adsorbent, particle size and contact time on lead uptake was investigated. It was found that the isotherm data were well described by the Freundlich isotherm for both adsorbents. The adsorption capacities of rice husk and chitosan were 5.69 and 8.31 mg g,1, respectively. It was shown that chitosan was more effective than rice husk. Copyright © 2005 Society of Chemical Industry [source] Novel hydrogel composite for the removal of water-soluble cationic dyeJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2006Li-Ming Zhang Abstract A novel hydrogel composite was prepared by incorporating Laponite RDS clay into poly(acrylic acid- co - N -vinyl-2-pyrrolodone) hydrogel during in - situ polymerization, and investigated with respect to its adsorption kinetics and isotherm toward Crystal Violet, a widely used cationic dye. It was found that the adsorption kinetics of Crystal Violet onto the hydrogel composite was consistent with the pseudo-second-order model. Compared with pure hydrogel, the hydrogel composite is characterized by greater amounts being adsorbed at equilibrium, and a higher rate constant and initial adsorption rate. By analyzing the experimental data using the Langmuir isotherm equation, an enhanced adsorption capacity was found for the hydrogel composite. Such material is expected to be a good adsorbent for water pollutants such as cationic dyes and treatment of these organic contaminants from wastewater. Copyright © 2006 Society of Chemical Industry [source] Effect of adsorption characteristics of a modified cellulase on indigo backstainingJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2004Diomi Mamma Abstract The effect of limited proteolysis (digestion) of a commercial cellulase preparation (Ecostone® L350) on backstaining with indigo was investigated. The influence of protease (papain) concentration on limited proteolysis of cellulase preparation was studied, applying different ratios of papain/cellulase (w/w). Changes in adsorption on Avicel cellulose of the non-digested compared with the papain-digested Ecostone® L350 were examined using the Langmuir adsorption isotherm. The non-digested Ecostone® L350 exhibited stronger interaction to Avicel cellulose compared with the digested form, while the maximum efficiency of cellulase adsorption to Avicel cellulose decreased after digestion. When papain-digested Ecostone® L350 was applied on cotton fabrics during the dyeing procedure with indigo, a reduction of indigo backstaining was obtained compared with the non-digested Ecostone® L350. Copyright © 2004 Society of Chemical Industry [source] | |||||||||||||||||||||||||||||||||||||||||||