Determination Of Sorption Isotherms Research Articles

How accurate are automated sorption balances? An analysis of errors in wood moisture content from uncertainties in the conditioning environment

Automated sorption balances are increasingly used to determine sorption isotherms of hygroscopic materials like wood. The sorption isotherms are constructed based on a number of equilibrium states between a specimen and the surrounding conditioning environment. In recent years, the uncertainty of these equilibrium states has been thoroughly discussed related to the time at constant environmental conditions needed to reach an adequate mass stability. However, uncertainties related to the conditioning environment are rarely discussed. This study describes a framework for analyzing and quantifying the effect of these uncertainties on the error in determined equilibrium moisture content. Various effects of the conditioning environment are analyzed, and the most important effects relate to the relative humidity (RH) in the instruments, both in terms of fluctuations in RH and an offset from the target value. The moisture error for these effects was found within the range 0.001–0.01 g g−1.

Biopolymers impact on hygrothermal properties of rammed earth: from material to building scale

Three biopolymers were tested as rammed earth (RE) stabilizers, evaluating their impact on the hygrothermal behavior from material to building scale. Hygrothermal characterization included the determination of sorption isotherm, water vapor permeability, thermal conductivity at different moisture content, and specific heat capacity. The hygrothermal data were used as input for the simulation at whole-building scale considering combined heat and moisture transfer. The results were evaluated by comparing heating demand, thermal comfort during summer, and the contribution of walls for passively controlling indoor humidity. The results show that hygric properties were only slightly affected by the use of stabilizers, while the thermal conductivity was 33% higher for RE stabilized with lignin, consequently increasing the heating demand at whole-building scale. All RE walls were effective in reducing temperature oscillations in summer. In the particular case of a canicular event, the indoor temperature was reduced by up to 10° compared with the outdoor value. The indoor humidity also benefited from the passive regulation by RE walls, regardless of whether a stablizer was used.

Measurement of lead complexation by humic acids and humic acid analogues using competitive ligand exchange

In soil and water, metal complexation by humic substances has been demonstrated to have great importance in determining the bioavailability of many trace metals including lead. The binding of lead by humic acids has important implications for lead toxicity, and remediation. In this study we demonstrate the use of 4-(2-pyridylazo)-resorcinol (PAR) as a competitive ligand for the purposed of determining sorption isotherms for Pb2+ on humic acids and humic acid analogs. Equilibration rates at pH 8 were very rapid and the sorption isotherms measured were fit to the Langmuir isotherm equation and values for the stability constants (KHA) and complexing site concentrations (Lt) are reported. At a PAR concentration of 0.24 mM and humic acid concentrations of 25–200 mg/L, the mass normalized log KHA values for the humic substances ranged from 7.2 to 7.9, while the log Lt values ranged from −2.8 to −3.8. At lower PAR concentrations both KHA and Lt tended to increase in magnitude indicating the role of the PAR concentration in establishing the measurement window for the interaction of Pb2+ with humic materials.

The sorption properties, structure and shrinkage of freeze-dried multi-vegetable snack bars in the aspect of the environmental water activity

The aim of the research was to determine the water condition in freeze-dried multi-vegetable snacks, using a method based on the determination of sorption isotherms, with particular attention to the influence of storage conditions in the variable water activity of the environment on the structure and shrinkage of the snacks tested.Models to describe the course of sorption processes were well suited to the experimental data. Due to the observed differences during sorption properties, most likely resulting from the raw material (vegetable) composition of the tested freeze-dried multi-vegetable snack bars in the form of bars, the water level was analyzed based on the description of the experimental data using BET and GAB models.Due to the observed differences in the course of sorption processes, most likely resulting from the raw material composition of the tested freeze-dried multi-vegetable snacks in the form of bars, the water level was analyzed on the basis of the description of experimental data using BET and GAB models. The samples of bars with the addition of a mixture of locust bean flour and xanthan were characterized by the most porous structure typical for freeze-dried food, regardless of the vegetable ingredients used in the recipe.

Hygroscopic behavior of water absorbed by capillarity and stabilization of a bio-composite building material: Clay reinforced with Chamarrops humilis fibers

The paper aims to study the hygroscopic behavior of water absorbed by capillarity of clay reinforced with Chamarrops humilis fibers as an ecologic building material strongly used in building construction in Morocco. This leads to provide a better understanding and controlling hydrothermal behavior of a building material, which integrates sorption phenomenon and its intrinsic characteristics. The static gravimetric method was used to determine sorption isotherms. Six salts were chosen so as to have a range of air relative humidity of 5.72% to 89.8%. The results showed that the water content absorbed by capillarity increases with the increasing of the air relative humidity at a given temperature, and the equilibrium water content absorbed by capillarity decreases with the increasing temperature. The sorption isotherms are of type IV, showing that the water absorption is enhanced at low humidities and a strong dominance of macropores. The differential enthalpy and entropy of sorption show that there is a strong dependence on the air relative humidity. Stabilization of clay by adding fibers indicated a strong influence on the rate of equilibrium moisture content loss, this leads to prevent cracking of earthen structures during the drying period by distributing the tensions due to shrinkage.

Binding of per- and polyfluoroalkyl substances (PFASs) by organic soil materials with different structural composition – Charge- and concentration-dependent sorption behavior

The charge- and concentration-dependent sorption behavior of a range of per- and polyfluoroalkyl substances (PFASs) was studied for three organic soil samples with different organic matter quality, one Spodosol Oe horizon (Mor Oe) and two Sphagnum peats with different degrees of decomposition (Peat Oi and Peat Oe). Sorption to the two peat materials was, on average, four times stronger compared to that onto the Mor Oe material. In particular, longer-chained PFASs were more strongly bound by the two peats as compared to the Mor Oe sample. The combined results of batch sorption experiments and 13C NMR spectroscopy suggested sorption to be positively related to the content of carbohydrates (i.e., O-alkyl carbon). Sorption of all PFAS subclasses was inversely related to the pH value in all soils, with the largest pH effects being observed for perfluoroalkyl carboxylates (PFCAs) with C10 and C11 perfluorocarbon chain lengths. Experimentally determined sorption isotherms onto the poorly humified Peat Oi did not deviate significantly from linearity for most substances, while for the Mor Oe horizon, sorption nonlinearity was generally more pronounced. This work should prove useful in assessing PFAS sorption and leaching in organic soil horizons within environmental risk assessment.

Nanopore-Level Wood-Water Interactions—A Molecular Simulation Study

The nanoscale wood-water interaction strength, accessible sorption sites, and cell wall pore sizes are important factors that drive water sorption and the hysteresis phenomenon in wood. In this work, these factors were quantitatively studied using molecular simulations based on a cell wall pore model, previously developed by the authors. Specifically, the wall-water interaction strength, the sorption sites network including their number, interaction range, strength, and spatial distributions were set at a series of theoretical values as simulation input parameters. The results revealed that most of the investigated parameters significantly affected both sorption isotherms and hysteresis. Water monolayers and clusters were observed on the simulated pore surface when the wood-water interaction and sorption site strength were set at unrealistically high values. Furthermore, multiple linear regression models suggested that wood-water interaction and sorption site parameters were coupled in determining sorption isotherms, but not in determining hysteresis.

Nanopore-Level Wood-Water Interactions—A Molecular Simulation Study

The nanoscale wood-water interaction strength, accessible sorption sites, and cell wall pore sizes are important factors that drive water sorption and the hysteresis phenomenon in wood. In this work, these factors were quantitatively studied using molecular simulations based on a cell wall pore model, previously developed by the authors. Specifically, the wall-water interaction strength, the sorption sites network including their number, interaction range, strength, and spatial distributions were set at a series of theoretical values as simulation input parameters. The results revealed that most of the investigated parameters significantly affected both sorption isotherms and hysteresis. Water monolayers and clusters were observed on the simulated pore surface when the wood-water interaction and sorption site strength were set at unrealistically high values. Furthermore, multiple linear regression models suggested that wood-water interaction and sorption site parameters were coupled in determining sorption isotherms, but not in determining hysteresis.

Sorption isotherms of ingredients and diets for poultry

This study aimed to determine sorption isotherms of ingredient and poultry diet. The samples were encapsulated in capsules and dehydrated by oven-drying in a desiccator for more than 24 hours. The samples were transferred to desiccator containing water in the base and placed in the oven, with one sample of each material being removed at incremental intervals. The sample was weighed and for determination of water activity and for dry matter. The moisture and water activity data were evaluated by eight mathematical models. The GAB mathematical model fitted the experimental data to constitute the isotherm for each material. Type II sorption isotherms were found, except for BHT: demonstrated values that did not fit the isotherm determination. The hygroscopic behavior of the ingredients in ascending order were: L- threonine, limestone, BHT, DL- methionine, L-valine, L- tryptophan, phosphate, kaolin, vitamin supplement, salt, mycotoxin deactivator, pelleted rooster diet, mash rooster diet, mash layer diet, pelleted layer diet, corn, bacitracin zinc, vitamin mineral supplement, phytase, rice bran, wheat bran, mineral supplement, soybean meal, coccidiostat, L- Lysine HCl and choline chloride. Ingredients and diets have different hygroscopic behavior: can lead to deterioration and low accuracy in nutritional values of diet, since formulation is based on as-is fed basis.

Sorption characteristics of full-fatted grape seeds flour of Bulgarian origin

We were experimentally obtained the sorption characteristics of full-fatted grape seeds flour (FGSF) of different grape varieties locally grown in Bulgaria. The scientific research was investigated at temperature - 10 °C, 25 °C and 40 °C and water activity within the range from 11% to 90%. We were selected the modified Oswin and Chung-Pfost models suitable for describing the adsorption and desorption isotherms. Monolayer moisture content of FGSF is calculated – from 2.48% to 4.59%. Antioxidant capacity was proven through DPPH (578.42 ± 23.06 mM TE/g extract), ABTS (1352.12 ± 144.31 mM TE/g extract), FRAP (966.45 ± 127.31 mM TE/g extract) and CUPRAC (1789.44 ± 180.11 mM TE/g extract). The values are also shown in mM TE/g flour (578.42 ± 23.06 mM TE/g flour); (1352.12 ± 144.31 mM TE/g flour); (966.45 ± 127.31 mM TE/g flour) and (1789.44 ± 180.11 mM TE/g flour), respectively. Furthermore, we evaluated the changes in moisture content, microbiological load and particle size distribution during short-term storage study for a period of three months. FGSF were packed in plastic bags under the conditions - temperature 18 °C÷25 °C and relative air humidity 45% ÷ 55%. • Full-fatted Grape Seeds Flour of Mavrud, Cabernet Sauvignon, Syrah, Merlot, Dimyat and Sauvignon Blanc. • Antioxidant capacity proven by four different analytic methods DPPH, ABTS, FRAP and CUPRAC. • Determination of Sorption Isotherms and Monolayer Moisture Content (MMC) at 10 °C, 25 °C and 40 °C. • Three months short-term storage study of full-fatted grape seeds flour.

Preparation and Properties of Zr-Bearing Sorption Materials Based on Coal Fly Ash Microspheres

The influence of hydrothermal conditions on synthesis of analcime and a composite material ZrO2- analcime as well as zirconomolybdate coverings with ion exchange properties was studied using narrow fractions of aluminosilicate microspheres with a high content of a glass phase (91-95 wt. %). The possibility to synthesize ZrO2-analcime composites of narrow particle size distributions with maximum of about 40 μm and 6 μm under hydrothermal treatment at 150 °С was demonstrated starting from microspheres with Si/Al=2.7 and applying different regimes of a reaction mixture agitation. A microsphere material of a “core-shell” type such as ZrMo2O7(OH)2(H2O)2@(SiO2-Al2O3)glass with the nanostructured covering was prepared. Sorption properties of the materials regarding Nd3+, Sr2+ and Cs+ were studied under equilibrium conditions by means of determination of sorption isotherms and their fitting by the Langmuir model. Sorption parameters were determined including distribution coefficients which reach the values of 104−105 mL/g

Magnetic Composite Sorbents for Trapping Heavy Metals from Liquid Waste and Their Immobilization in a Mineral-Like Matrix

Magnetic sorbents were prepared by addition of ferrospheres to zirconia-silica gel followed by thermal treatment at 500 °C. The ferrosphere narrow fraction E -0.063+0.050 mm from fly ash resulted from combustion of Ekibastuz coal was used as a magnetic component. The surface of magnetic composites was additionally functionalized by grafting of – POONa and – NH2 groups. Under equilibrium conditions sorption capacities of the sorbents with respect to Се3+ used as a U4+/Th4+ simulator and Pb2+ were measured by means of determination of sorption isotherms which were fitted by the Langmuir model. It was established that extraction of Се3+ and Pb2+ from aqueous solutions is characterized by distribution coefficients of 104–106 ml/g. Temperature conditions for solid-phase crystallization of the sorbents resulting in polyphase systems with the content of zircon phase of 50 wt. % were found

The determination of isosteric heats of sorption of leather: Experimental and mathematical investigations

Knowledge of sorption isotherms of leather products is necessary to control rehydration/dehydration and storage processes and it is valuable tool for prediction of the stability and shelf life of products but the impact of the controlled climate on moisture sorption isotherms of leather remains unclear. The aim of this work is to predict moisture desorption isotherms of leather of bovine variety. The static gravimetric method was used to determine sorption isotherms at four temperatures (30, 40, 50 and 60 °C) and the equilibrium moisture content of leather samples was measured within the range of 5–90% relative. All the curves exhibited type II behavior, according to Brunauer’s classification. Equilibrium moisture contents are observed to drop as the temperature is enhanced. Many models available in the literature were used to describe the experimental data. The agreement between experimental and calculated sorption isotherms is seen to be satisfactory (correlation coefficients from 0.93 to 0.99). Furthermore, DENT model is found to be the most appropriate for describing the relationship between the equilibrium moisture content, the water activity and temperature. On the other hand, the isosteric heats of desorption were determined from sorption isotherms and then correlated with corresponding equilibrium moisture contents. Besides, the isosteric heats of desorption decreased continuously with increasing of the equilibrium moisture content.

Glass transition of green and roasted coffee investigated by calorimetric and dielectric techniques

Solid and liquid components coexist into glassy and amorphous structures of food complex matrixes. Both states admit movements, promoting physical modifications to a more thermodynamically stable system. Green and roasted coffee beans are principally characterized by a glassy structure that slowly evolves during storage. The aim of this study was to assess calorimetric and dielectric properties in combination, as a useful multi-analytical technique to improve the understanding of the motion mechanism of localized molecules. After equilibration at different water activities (aw) for the determination of sorption isotherms of green and roasted coffee, the glass transition temperature (Tg) of the samples has been measured by using differential scanning calorimetry (DSC). Increasing the aw from 0.155 to 0.512, the Tg shifted from 48.76 (±0.04) to 34.89 (±0.02) °C for green coffee and from 45.73 (±0.05) to 40.15 (±0.10) °C for the roasted one. The spectroscopic fingerprint of the matrix has been determined by dielectric measurements in terms of “gain” spectra (related to the imaginary part of permittivity). The maximum values of the determination coefficient (R2), obtained by linear correlation between spectral data and water activity or glass transition values for a specific frequency of the whole range (1.6 GHz–2.7 GHz), were 0.999 and 0.943 for green, and 0.997 R2 and 0.925 R2 for roasted coffee respectively.

Evaluation of contaminant retention in the soil of sustainable drainage systems: methodological reflections on the determination of sorption isotherms

Abstract Runoff infiltration in Sustainable Drainage Systems enables the interception of a part of urban contaminant fluxes owing to several processes. The soil's ability to retain dissolved pollutants is generally assessed via sorption isotherms obtained from batch studies; however, the experimental points are not always in the same range as runoff concentrations. The present work (i) explores the consequences of modelling runoff–soil interactions from out-of-range equilibrium concentrations and (ii) proposes an improved method to ensure that experimental points fall within the desired range. Uncertainty analysis demonstrates that for a non-linear isotherm, using an extrapolated relationship may introduce significant biases in the ensuing estimations. Therefore, the proposed method consists of anticipating the equilibrium state of batch tests to accurately set the experimental conditions and reach appropriate concentrations. It is successfully applied to the determination of the sorption properties of copper and zinc onto three soils with different electrolyte solutions, as well as those of bisphenol A and three alkylphenols onto one soil. The contrasting affinities between the studied species and the soil materials could be related to their intrinsic properties and the soils' pedological parameters, as well as the presence of salt or dissolved organic ligands which partially inhibited metal sorption.

Investigation of hygroscopic equilibrium and modeling sorption isotherms of the argan products: A comparative study of leaves, pulps, and fruits

The aim behind this work is to demonstrate and validate a predictive experimental model of the thermophysical behaviors of the three argan products, leaves, pulps and fruits, using the experimental determination of sorption isotherms. They constitute an important information source to establish the stability of the products of argan and their conditions of conservation. The use of a suitable model for the analysis of the experimental data of sorption is a crucial step in the optimization and the design engineering setting on the scale of drying processes which are considered to be among the largest energy consumers in the chemical industry and agro-foodstuffs. The medicinal herbs are complex mixtures of chemical product that make it difficult to determine mass and heat mechanism. Digital simulations of the isotherms by the model of GAB (Guggenheim–Anderson–Boer) could not only correlate the equilibrium moisture content in food systems but also explain the different properties of sorbed water. Indeed, they are deemed of as helpful tools that allow better thermophysical valorization and lasting conservation. Net isosteric heat of sorption, total heat of wetting, differential entropy and spreading pressure were determined from the isotherms to define the energy associated with the sorption processes. The paper also investigates the impact of both the ionization (food irradiation) and the instant controlled pressure drop processes on water activity of the argan products.

Molybdenum-phosphate retention and transport in soils

Transport and retention experiments were carried out to quantify the mobility and sorption of molybdenum (Mo) and phosphate (P) in two different soils. Batch experiment was used to determine sorption isotherms over a wide range of concentrations for Mo and P. For both soils, sorption isotherms were nonlinear with higher affinity of P than Mo. Sorption of Mo was significantly reduced as the amount added P in solution increased. This was observed for both soils and is indicative of competitive sorption for available site. Miscible-displacement experiments were carried out using soil column where a pulse of Mo solution was introduced in each soil. Breakthrough curves (BTCs) indicated extensive sorption of Mo where as much as 50% of that applied was retained by a predominant kaolinatic soil. Subsequently, a pulse of mixed solution (of Mo and P) was introduced in each column. Results of BTCs for Mo indicated enhanced mobility of Mo in the presence of P for both soils. A five step sequential extraction procedure provided evidence that majority of applied Mo was strongly and/or irreversibly retained. A competitive transport model (CMRTM) based on the Sheindorf-Rebhun-Sheintuch (SRS) equation was capable of describing BTCs of Mo and to a lesser extent for P. Future research should focus on improvement of models that accounts for chemical mechanisms of competitive sorption.

NMR determination of sorption isotherms in earlywood and latewood of Douglas fir. Identification of bound water components related to their local environment

Abstract Earlywood (EW) and latewood (LW) have different hygromechanical behaviors, if subjected to relative humidity (RH) variations. To understand this effect better, the adsorption mechanisms of EW and LW of Douglas fir were studied by 2D 1H NMR relaxometry under conditions of equilibrium moisture content (EMC) at 20°C. Two bound water components were detected with relaxation times T1 and T2 indicating that they are located in distinct environments but these are similar in EW and LW. Sorption isotherms were calculated and analyzed based on the sorption model of Dent. A difference of sorption energy between the two water components is in agreement with their mobility difference observed on T1−T2 correlation spectra. Moreover, for the two bound water components, EW and LW exhibit different sorption isotherms at high RH. This may be attributed to a difference of adsorption capacity. Based on the macrofibril models provided by the literature, the following hypothesis is proposed: bound water components are located in lamellar and lenticular areas, both leading to possible deformations.

Comparative analysis of the dynamic vapor sorption (DVS) technique and the traditional method for sorption isotherms determination — Exemplified at autoclaved aerated concrete samples of four density classes

The paper assesses two research techniques for the determination of moisture sorption isotherms. On the one hand, in the time and labor-intensive traditional method the relative humidities are set in desiccators or climatic chambers by saturated water solutions of properly selected salts. On the other hand, the automated dynamic vapor sorption technique (DVS) is based on a humidity generating device. To compare both methods sorption isotherms were determined for autoclaved aerated concrete samples of four different density classes. The results obtained indicate good compatibility for all tested concretes within the humidity range from 0% to 75–85%. In the case of high humidity ranges between 75–85% and 98%, the sorption isotherms differ significantly. From the two series of experiments it can be concluded that for the materials tested the quick DVS measurement method can be used to determine sorption isotherms up to about 80% relative humidity.

Moisture Sorption Isotherms And Thermodynamic Properties Of Urtica Dioica Leaves

Urtica dioica is a Moroccon endemic plant of used for its virtues in traditional medicine. Thus, it is necessary to study the effect of preservation processes on the storage conditions of the plant. The static gravimetric method was used to determine sorption isotherms of Urtica dioica leaves at three temperatures (40, 50 and 60 °C) and in the range of water activity ( w a ) ranging from 0.0572 to 0.898. Six mathematical models were used to fit the experimental data. The Enderby and Peleg models were found to be the most suitable for describing the sorption curves. The optimal water activity for conservation of Urtica dioica leaves was determined. Isosteric heats of desorption and adsorption were calculated by applying the Clausius- Clapeyron equation to the sorption isotherms at different temperatures; it decreased with increasing moisture content. A linear relation exists between the enthalpy and entropy of the sorption reaction.