Evidence of dual mobility in sulfur dioxide-polyarylate system: An integral sorption analysis

Integral sorption/desorption measurements were carried out for the sulfur dioxide-glassy polyarylate polymer system at 25°C, 40°C, 55°C, and 63°C. The transport of sulfur dioxide in the glassy polyarylate polymer was governed by Fickian diffusion. The effective diffusion coefficient of sulfur dioxide increased with increasing penetrant concentration. The concentration dependence of the effective diffusion coefficient is explained on the basis of the partial-immobilization model developed by Paul and Koros. The mobility of the molecules sorbed in the Langmuir mode is shown to be significantly lower than the mobility of the molecules in Henry's law dissolution mode. The predictions of permeability values as a function of upstream gas pressure are presented. The equilibrium sorption isotherms for this system are well represented by the dualmode sorption model. The eltergetics and the temperature dependence of the dual-mode parameters are also discussed.     

Sorption of N-butane,propane, and ethane in ethylcellulose

The sorption of n-butane, propane, and ethane in ethylcellulose has been investigated between 0 and 200 mm Hg pressure over the temperature range from 30 to 70°C. Sorption isotherms of n-butane, propane, and ethane in ethylcellulose suggest that both Henry's law and the Langmuir forms of sorption, are operative. Sorption data were analyzed using the dual sorption model and sorption parameters determined. The sorption attributed to the Langmuir mode decreases as the temperature increases. This result indicates that the nonlinear Langmuir mode of sorption is more characteristic of the glassy state than sorption represented by the Henry's law mode. It was found that sorption attributed to the Henry's law and Langmuir modes decreases as the molecular size of gaseous hydrocarbon penetrants decrease. In this study, the molecular size of gaseous molecule decreased as the gases studied changed from n-butane to propane to ethane. A correlation of the Henry's law constants for the solution of n-butane, propane, and ethane in ethylcellulose with the Lennard-Jones force constants, ?/k at different temperatures was also determined. The temperature dependence of the Henry's law constants were correlated by a van't Hoff relationship and heats of sorption determined.     

Sorption and transport of benzene in poly(ethylene terephthalate)

The kinetics and equilibria of benzene sorption in poly(ethylene terephthalate) were measured at 40°C, 50°C, and 60°C, with benzene activities ranging from 0.02 to 0.3. At most experimental conditions, diffusion was found to be Fickian; however, evidence of non-Fickian transport was found at the highest activity levels. Values of the diffusion coefficient of benzene range from 10^-14 cm²/s at 40°C to 10^?12 cm²/s at 60°C in the limit of low concentrations. Nonlinear isotherms observed for benzene sorption were successfully interpreted in terms of the dual mode model for sorption in glassy polymers, whereby the sorbed penetrant exists as two populations: one sorbed according to Henry's law and the other following a Langmuir isotherm. Non-Fickian transport data were correlated with a model that superimposes diffusion of both the Henry's law and Langmuir populations (the “partial immobilization” model) upon first-order relaxation of the polymer matrix.     

A CALCULATION METHOD OF OBTAINING DESORPTION ISOTHERMS OF BEECH (FAGUSMOESL4CA) WOOD

ABSTRACT

This paper presents the specific methods to obtain sorption isotherms. Sorption isotherms were first obtained experimentally for 20°C and 100°C and then, by using the presented method, isotherms were also obtained for 50°C and 80°C. The same treatment can be applied in finding any isotherm sorption in the temperature range between 20°Cand 100°C.

The experiments were carried out on beech (Fagus moesiaca) and sample dimensions were 3×3×3cm. Based on the results of the experiment, by regression analysis, the most suitable analytic formula was proposed. It relsites temperature and air humidity with the equilibrium moisture content in wood. Experimental results were compared with psychrometric tables and Bramhall's formula for desorption curves with good agreement. This proves that the method presented in this paper is precise and efficient to decrease the lime needed to obtain sorption isotherms experimentally.     

Characterization of physical aging of poly(methyl methacrylate) powders by a novel high pressure sorption technique

High pressure CO₂ sorption isotherms were measured at 35°C in previously dilated PMMA microspheres, which were subsequently aged in vacuum at 35°C. The dilation was induced by preswelling with high activity methanol vapor at 13°C, or alternatively with CO₂ at a pressure of 20 atm and a temperature of 5°C. The state of the samples during long-term aging was probed by rapid and intermittent determination of complete high pressure CO₂ isotherms. The dilation increased the sorption levels observed in the sorption experiments compared to those observed in untreated samples and, as the aging time increased, the sorption level progressively decreased. The isotherms under all conditions were well described by the dual mode sorption model. The observed time dependence of the isotherms was successfully described by confining all changes in sorption capacity to a systematic decay of the Langmuir capacity parameter. The equilibrium parameters of the model, however, were essentially unaffected by the preswelling and aging histories.     

Low-pressure CO2 sorption in poly(vinyl benzoate) conditioned to high-pressure CO2

Sorption of CO₂ in poly(vinyl benzoate) was gravimetrically measured at pressures up to 1 atm. Sorption isotherms were determined above and below the glass transition temperature T_g from 5 to 85°C. The isotherms were analyzed by the dual-mode sorption model assuming that the plasticizing effect of sorbed CO₂ is negligible at this pressure range. The solubilities and Henry's law dissolution parameters were compared with those obtained by the high-pressure sorption and permeation measurements. Henry's law dissolution parameters were in good agreement with one another. However, the solubilities first determined here were smaller than those determined by the high-pressure sorption experiment at the same temperature. It was clear that the Langmuir capacity of the present specimen was smaller in spite of similar high-pressure CO₂ exposure. Relaxation of the polymer was expected to be one of the reasons. This expectation was confirmed from the observation and analysis of sorption isotherms after two kinds of treatments. After annealing above T_g, the Langmuir capacity was shown to be decreased to 1/2 or even to 1/3 from the sorption isotherms below 45°C. This means that the conditioning to the high-pressure CO₂ surely has a large effect on the nature of glassy polymer. Just after high-pressure CO₂ exposure at 25°C, increased solubility was observed. Furthermore, the slow decrease of solubility, that is, the decrease of conditioning effect, was also followed from the continual measurements at 25°C. This result reflects not only the characteristic of sorption capacity after high-pressure CO₂ exposure, but also the relaxation of polymer in glassy state.     

High-pressure sorption of carbon dioxide in solvent-cast poly(methyl methacrylate) and poly(ethyl methacrylate) films

Carbon dioxide sorption isotherms in poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) are reported for pressures up to 20 atm. Temperatures between 35 and 80°C were studied for PMMA and temperatures between 30 and 55°C were studied for PEMA. Typical dual mode sorption isotherms concave to the pressure axis were observed in all cases. The measured Langmuir sorption capacities of both polymers extrapolated to zero at the glass transition (T_g) consistent with the behavior of other glassy polymer/gas systems. Sorption enthalpies for CO₂ in the Henry's law mode for PMMA and PEMA are in the same range (?2 to ?4 kcal/mole) as has been reported for a variety of other glassy polymers such as poly(ethylene terephthalate), polycarbonate, and polyacrylonitrile. Some of the data suggest that postcasting treatment of the PEMA films left a small amount of residual solvent in the film. the presence of the trace residual solvent during quenching from the rubbery to the glassy state after annealing appears to cause a dilation of the Langmuir capacity and an alteration in the apparent Langmuir affinity constant of the PEMA film. These results suggest the possibility of tailoring physical properties of glassy polymers such as sorptivity, permeability, impact strength, and craze resistance by doping small amounts of selected residuals into polymers prior to quenching to the glassy state from the rubbery state.     

Polyamide 12-polytetramethyleneoxide block copolymer membranes with silver nanoparticles – Synthesis and water permeation properties

Polymer membranes with in situ formed silver nanoparticles were prepared by dissolving together AgBF₄ and poly(amide 12)-poly(tetramethyleneoxide) block copolymer in an organic medium then evaporating the solvent medium. UV–vis spectroscopic studies evidenced the formation in the solution of silver nanoparticles right whose content and size increase with the exposure time under the irradiation of the spectrophotometer lamp. The solid hybrid film changed its color with time under ambient conditions, indicating an evolution of the inorganic matters in the polymer matrix.The transmission electron microscopy showed nanoparticles whose size increases from 18 to 27 nm in the stabilized form in the polymer.The water vapor uptake in the membranes with different AgBF₄ contents studied by microgravimetry allowed us to determine the sorption isotherms at 25 °C. The sigmoidal BET-II type isotherms were fairly well fitted with Park’s equation, where the concave part was fitted with a Langmuir and a Henry sorption term, while the convex part was fitted with an exponential term in Park’s equation that takes into account the clustering of water molecules in the polymer matrix. We suggest that at low water activity, water molecules adsorb on Langmuir sites—probably on the nanoparticle surface—and at high activities water molecules form aggregates in the polymer matrix.     

Temperature dependence of the water‐sorption isotherms of wool

Against the background of various other theories, the well‐established D'Arcy/Watt model is applied to sorption data of wool between 20 and 100°C to determine its suitability to describe the isotherms and to systematize their temperature dependence. The model contains three components that represent two types of primary adsorption processes (Langmuir‐ and Henry‐type adsorption) and a third one, describing multilayer formation of water molecules. Sorption isotherm data, as taken from the literature, could, in all cases, be fitted extremely well by the model. The temperature dependence of the five parameters of the model, related to the continuous decrease of water regain with increasing temperature for all humidities, reveals a number of inconsistencies. Probably the most important of these is that the Langmuir capacity constant apparently becomes zero at the glass transition temperature of dry wool. This is at variance with the idea of specific molecular sites of water sorption, which is inherent to the model. Other inconsistencies relate to the small van't Hoff enthalpies and possible compensation effects for various parameters. These observations indicate that the D'Arcy/Watt theory, despite its physicochemical plausibility and empirical success, overinterprets the complexity of the mechanisms underlying the sorption behavior of wool and other α‐keratin fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1054–1061, 2001     

Effect of Heptadecane on Sorption of 2,6-di-Tert-butyl-4-Methylphenol by Polyethylene

Abstract

The sorption of vapors of 2,6-di-tert-butyl-4-methylphenol (DTP) by HDPE containing different concentrations of heptadecane has been studied using the ultraviolet spectrometry method. The isotherms of DTPh sorption at 100–200°C are presented by the Langmuir equation. The concentration of sorption of DTPh has no dependence on temperature, but depends on the concentration of heptadecane in a polymer. The heats of dissolution of DTPh in polyethylene have been determined.     

Effect of environmental conditions on the retention behaviour of Pb(II) by hematite

BACKGROUND: The retention behaviour of Pb(II) by hematite was studied as a function of various environmental parameters such as contact time, pH, ionic strength, foreign ions, humic substances and temperature under ambient conditions. RESULTS: Pb(II) sorption on hematite was rapid and the sorption could be described by a pseudo‐second‐order model very well. The sorption of Pb(II) on hematite was strongly dependent on pH and ionic strength. The presence of humic substances enhanced the sorption of Pb(II) on hematite at low pH, but reduced Pb(II) sorption at high pH. The Langmuir model fitted the sorption isotherms of Pb(II) better than the Freundlich model at three different temperatures, 293.15, 313.15 and 333.15 K. The thermodynamic parameters (ΔH°,ΔS° and ΔG°) calculated from the temperature dependent sorption isotherms indicated that the sorption process of Pb(II) on hematite was endothermic and spontaneous. CONCLUSIONS: The results indicate that hematite is a promising candidate for the treatment of heavy metal ions from large volume solution. Copyright © 2011 Society of Chemical Industry     

Energetics of gas sorption in glassy polymers

The molar enthalpy for gas sorption in glassy polymers at a fixed concentration, often called the isosteric enthalpy of sorption, exhibits a clearly discernable minimum when plotted as a function of penetrant concentration. This unexpected behaviour has been observed in several glassy polymer systems including poly(ethylene terephthalate), polyacrylonitrile and polycarbonate. The behaviour can be modelled by analysing the temperature dependence of the various equilibrium parameters comprising the so-called dual mode sorption model for gas sorption in glassy polymers. The fundamental significance of the various enthalpies describing the temperature dependence of the Henry's law solubility constant, the Langmuir affinity constant and the Langmuir capacity constant are included in the discussion. Provision is made for non-ideal vapours and gases by introduction of the compressibility factor in the expression for the isosteric enthalpy. Application of relationships for calculating both the isosteric and the isothermal enthalpies of sorption is made to the case of CO₂ in poly(ethylene terephthalate) in the temperature range 35° to 115°C. These results and analyses complement the wealth of equilibrium and transport data which are consistent with the dual mode sorption model for penetrant sorption in glassy polymers.     

Characterization of glassy state relaxations by low pressure carbon dioxide sorption in poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA) microspheres were swollen in methanol vapor, the swelling penetrant was quickly evacuated, and the subsequent relaxation of the polymer under vacuum was monitored by determination of the rate of settling of rapidly measured low pressure pseudoequilibrium CO₂ sorption isotherms. The decrease in CO₂ sorption capacity occurred very rapidly at short times, but the final stages of consolidation were protracted. In all cases, the microspheres were under vacuum between isotherm determinations. A single relaxation time is not sufficient to describe the relaxation processes characterized by the time-dependent sorption measurements. The sorption relaxation curves are similar in shape to volume relaxation curves for glassy polymers following imposition of a large pressure or temperature step change. The observed similarity between the sorption relaxation curves and classical volume relaxation curves is consistent with the notion that the excess sorption capacity introduced by methanol preswelling results from excess unrelaxed volume introduced into the glass by the quickly removed alcohol. As the excess volume relaxes, the excess sorption capacity decreases. One can, therefore, monitor the subtle process of consolidation using CO₂ as a probe of the excess volume introduced by the swelling perturbation. Subatmospheric pressure CO₂ sorption isotherms measured between 20 and 40°C for two different diameter microsphere samples (5436 Å and 1453 Å) for pressures up to 700 mm Hg were concave to the pressure axis. Such general isotherm shapes can be described by a two-term expression consisting of a Henry's law term and a Langmuir term. The Langmuir term, which arises due to unrelaxed volume in the nonequilibrium glass, is responsible for the observed concavity in the sorption isotherm. Annealing the sample, increasing the temperature of the sorption experiment closer to the T_g of the PMMA or permitting the preswollen sample to relax tends to reduce the concavity of the isotherm relative to the corresponding case for sorption in the preswollen sample measured at 25°C. This trend is presumably a consequence of the reduction in unrelaxed volume in the glass which attends either annealing, approaching the glass transition temperature of the polymer, or consolidation of excess volume following exposure to a swelling penetrant.     

Removal of copper,cadmium, and chromium from wastewater by modified wheat bran using Box–Behnken design: Kinetics and isotherm

In this work, copper, cadmium, and chromium were removed using hydrochloric acid-treated wheat bran as an adsorbent. Experiments were carried out in batch adsorption mode. Box–Behnken design of response surface methodology was used to determine the effect of initial metal concentration, pH, temperature, and adsorbent dose on removal efficiency of copper, cadmium, and chromium. Analysis of variance results are shown for all the three heavy metal, and the effect of the parameters is discussed. The optimum initial metal concentration, pH, temperature, and adsorbent dose were found to be 90.58 mg/L, 6, 35.9°C, and 2.39 g, respectively. Pseudo-second-order kinetic model was found to be the best suitable model for adsorption rate. The isotherms of adsorption data were analysed using various adsorption isotherm models such as Langmuir, Freundlich, Dubinin–Radushkevich, and Temkin isotherms. It was found that Langmuir and Temkin isotherms represent the equilibrium data for these heavy metal removals.     

Residual porosity in polymeric latex films

Solubility and diffusivity measurements of a probe gas (CO₂), which has an inherently low solubility in the polymer, have been used to characterize residual porosity in polymeric latex films. Sorption isotherms resembling those of a glassy polymer were obtained, even though the glass transition temperature of the polymer was 1°C, about 30°C below the experimental temperature. Solvent cast films of the same polymer exhibited much lower solubilities, and followed the expected Henry's law behavior. CO₂ solubility and diffusivity were found to decrease with aging time for the latex films, but did not quite reach the values of the solvent cast films, even after 75 days at room temperature. The sorption data could be described by the dual-mode sorption model, which is commonly employed in the analysis of glassy polymer sorption isotherms. Estimates of the amount of porosity were made from the sorption data, and values ranging from 0.6–0.03% were obtained for latex films aged from 62 h to 75 days, respectively. Our results suggest that permeability differences noted by others for latex and solvent cast films of the same polymer are due to the substantial solubility differences for low-solubility penetrants in these two types of films.     

Sorption and transport studies of water in Kapton polymide. I

Sorption isotherms and diffusion coefficients of water in a 0.3-mil Kapton polyimide film at 30, 45, and 60°C are reported. The data are well described by the dual mode sorption and transport models at low activities. At high penetrant activities, clustering of water is suggested by a Zimm–Lundberg analysis of the sorption data and the fact that the diffusion coefficient for water decreases with increasing external vapor activity. The effect of temperature on the diffusion coefficients at infinite dilution and the dual mode sorption parameters k_D, b, and C are presented and discussed. The magnitude of the activation energy of the diffusion coefficient at infinite dilution, 5.4 kcal/mol, is smaller than the corresponding activation energy in more flexible chain polymers, perhaps suggesting that rather small backbone motions are associated with diffusion of water through the Kapton matrix. The predictions for the isosteric enthalpy of sorption from the dual mode model are presented and compared with the values determined from graphical analysis of the sorption isotherms performed independently without reference to the dual mode sorption model.     

Moisture sorption characteristics of waste activated sludge

Nowadays the treatment of activated sludge often includes a thermal drying step. Data such as water vapour sorption isotherms and heat of sorption are required for good design and control of the drying processes. An equilibrium method was used to measure these data on domestic activated sludge, between 39 °C and 80 °C. The experimental investigation indicated that the nature of the sludge and its evolution (bulking sludge, anaerobic storage) do not affect the sorption isotherms. Experimental data were fitted to different well‐known models; the Oswin relationship gave the better fit. Based on sorption data the heat of sorption as a function of moisture content was determined. © 2001 Society of Chemical Industry     

Removal of Cr(VI) Oxy‐anions from Aqueous Solution by Sorption into Poly(Acrylamide‐Co‐Maleic Acid) Hydrogels

Abstract

The dynamic removal of hexavalent chromiuim by poly(acrylamide‐co‐maleic acid) hydrogels was studied by a batch equilibrium technique at 35°C. Various kinetic and adsorption parameters such as rate constant for sorption, intraparticle diffusion rate constant, Langmuir constant, and adsorption capacity have been evaluated. The sorption process follows the Langmuir‐type behavior and extent of sorption of Cr(VI) ions depends upon the composition of co‐polymeric gels, presence of other ions in the solution, and temperature of the system. Relatively higher temperature favors the sorption process. The activation energy was found to be ?20.369 kJ mol^?1. Finally, various thermodynamic parameters have also been calculated to elucidate the mechanism involved in the sorption process. The positive enthalpy change indicates the endothermic nature of the process. The presence of fluoride ions causes a decrease in the degree of sorption of Cr(VI). Finally, the sorption of Cr(VI) into the copolymeric sorbent has been explained on the basis of coordination between electron rich O and N atoms of sorbent molecules and the Cr(III) molecules. Moreover, H‐bonding interactions also seem to contribute to the sorption process.     

Low pressure CO2 sorption in poly(vinyl cyclohexane-carboxylate)

A gravimetric method was applied to determine the solubility of CO₂ in poly(vinyl cyclohexanecarboxylate) below 1 atm. The temperatures were varied from 5 to 85°C, above and below the glass transition temperature. The sorption isotherms were concave to the pressure axis below T_g and they were tentatively analyzed by the dual-mode sorption model. Above T_g, the isotherms were linear and described by the Henry's law. Below 75°C, the diffusion coefficients of CO₂ were also obtained from the half-time of the sorption process.