Heat Of Sorption Research Articles

Moisture sorption characteristics of freeze dried whey-grape beverage mix.

Moisture sorption isotherms of freeze dried whey-grape beverage powder were determined at 20, 30 and 40°C. A gravimetric static method was used under 0.11-0.85 water activity range and the sorption isotherms were found to be Type II. Various mathematical models were fitted to experimental data and it was found that Peleg model suits best in describing the equilibrium moisture content-equilibrium relative humidity relationships of instant whey-grape beverage mix over the range of temperatures studied. The net isosteric heat of sorption varied between 5.22 and 1.12KJ/mol at moisture level varying between 1 and 9% db. At moisture content below 1% (db) the isosteric heat of sorption increased sharply for freeze dried whey-grape beverage powder and value of 49.08KJ/mol was estimated.

Moisture sorption characteristics of lal peda at different storage temperatures

Moisture sorption isotherms of lal peda, a heat-desiccated traditional milk product of Indian sub-continent were determined at 10, 25 and 37°C over a water activity range of 0.113 to 0.868 using standard saturated salt solutions. The isotherms obtained were of sigmoid shape (type II) at all temperatures. Among five sorption models fitted, Guggenheim–Anderson–de Boer (GAB) model was fitted best to the sorption at three temperatures. The monolayer moisture content as calculated by the best fitted GAB model for desorption and adsorption processes at 10, 25 and 37°C were 3.852, 4.551 and 5.235 and 3.214, 4.103 and 5.253% on a dry basis, 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.

Thermodynamic Analysis of Moisture Sorption Characteristics of Cheese-PuriMix

Sorption data were determined by static gravimetric method for cheese–puri mix at 25, 35 and 45C. The Guggenheim-Anderson-deBoer (GAB), Caurie, Henderson, Oswin and Smith isotherm models were attempted to describe the experimental data and were found to describe the sorption behavior of the product adequately. The solid surface area of the product was computed based on the GAB model monolayer moisture contents of the product and was found to increase with temperature. Thermodynamic properties of the product, including the isosteric heat of sorption, sorption entropy, spreading pressure, net integral enthalpy and entropy, were determined as a function of the product moisture content. Application of the enthalpy–entropy compensation theory to the sorption data revealed that the process was enthalpy-driven. The net integral enthalpy and entropy were found to decrease with increasing moisture content and were described as a function of the equilibrium moisture content using a power model. Practical Applications Sorption isotherms are important tools for food scientists to understand the behavior of a food product, especially low-moisture foods, toward the moist air that envelopes its surroundings. They are particularly useful to predict the physical, chemical and microbial stability of the product during storage and reconstitution. Thermodynamic properties of the product provide an insight into the energy requirement associated with moisture sorption and the temperature dependence of water activity. Cheese–puri mix is a value-added convenience dairy product, and information on its sorption characteristics would be useful to monitor its quality and shelf stability.

ChemInform Abstract: MOFs for Use in Adsorption Heat Pump Processes

AbstractReview: 80 refs.

Equilibrium and kinetics analysis of carbon dioxide capture using immobilized amine on a mesoporous silica

Thermogravimetric analysis is used to study the adsorption kinetics, equilibrium, and thermodynamics of CO2 on immobilized polyethylenimine sorbent impregnated on a mesoporous silica over the range of 300–390 K and 5–100% CO2 concentration. Adsorption isotherm models were fitted to the experimental data indicating that a change in adsorption mechanism occurred near 70°C. Below this temperature, the adsorption data followed the heterogeneous isotherms, while data taken at higher‐temperatures followed isotherms for homogeneous surfaces. Heat of sorption was estimated to be 130 kJ/mole for the low‐temperature regime, but this decreased to 48 kJ/mole above 70°C. The rate of CO2 fractional uptake decreased as temperature increased. A phenomenological kinetic model was derived from the Weibull distribution function using a nucleation growth theory to describe the two‐step process. The kinetic model was used to predict the uptake at different operating conditions and resulted in good agreement with experimental data. Published 2012 American Institute of Chemical Engineers AIChE J, 2013

Moisture Sorption Isotherms and Net Isosteric Heats of Sorption of Green Soybean

Abstract Moisture sorption isotherms of green soybean seeds were determined by static gravimetric method and water activity ranging from 0.11to 0.94 at 20, 30 and 40°C. The optimal sorption model of green soybean was determined by using nonlinear regression method. Modified BET multilayer sorption theory model parameters at different temperatures were calculated, isosteric sorption heat was derived by the water activity sorption isosteric model. Results indicated that sorption isotherms were belong to type III behaviour, a notable hysteresis effect was observed, Green soybean monolayer saturated sorption capacity was greater in desorption process than that of adsorption. The monolayer saturated sorption capacity decreased with increasing temperature, while the number of multilayer had a reverse trend with the monolayer saturated sorption capacity, the optimal sorption isotherm model for green soybean is Halsey model, The thermodynamic parameters including net isosteric heat of adsorption and desorption calculated at 40°C were 105.2-1865.4 kJ/kg and 111.62-1939.0 kJ/kg with equilibrium moisture content between 5% and 32% (d.b.), respectively. The net isosteric heat of sorption decreased with increasing equilibrium moisture content.

Grain Sorption Equilibria of Algarroba Flour

Water vapour sorption of white and black algarroba flour obtained from Prosopis alba and Prosopis nigra was determined at 20, 30 and 40°C in the range of 0.089-0.851 water activity by mean of isopiestic method. The isotherms were adequately modelled using GAB equation. Equations based on the enthalpy-entropy compensation theory, was used to describe the temperature effect on water sorption isotherms and to obtain predicted values of the isosteric heat of sorption and its moisture content dependence. The predicted values agree with the experimental isosteric heat values calculated by means of Clausius-Clayperon equation.

Benzene sorption by a microporous coordination polymer based on a zinc carboxylate

Benzene vapor sorption by the organometallic coordination polymer [Zn2(bdc)2(dabco)] (H2bdc = benzene-1,4-dicarboxylic acid, dabco = diazabicyclo[2.2.2]octane) is reported. The [Zn2(bdc)2(dabco)] polymer has a high C6H6 sorption capacity of up to 3.8 mol of benzene per formula unit. The heat of sorption has been determined, and its dependence on the composition of the inclusion compound has been investigated. Included benzene molecules are nonequivalent in terms of the energy of their interaction with the metal-organic framework.

Thermodynamic properties of moisture adsorption of whole wheat flour. Calculation of net isosteric heat

SummaryThe moisture sorption isotherms of whole wheat flour were determined at 10, 20 and 30 °C over a relative humidity range of 10–90%. Two models were applied to the sorption experimental data: the Guggenheim–Anderson–de Boer (GAB) and the Caurie models. The goodness of fit of the mathematical models was statistically evaluated by means of the root mean square per cent error (%RMS), obtaining values between 1.44 and 1.05 for GAB, and between 2.69 and 2.57 for the Caurie model. Hence, both models provided a good fit to the experimental data. The isosteric heat of sorption was calculated using two methods: the Clausius–Clapeyron expression and the Caurie equations, showing in both cases maximum values (11.03 and 12.39 kJ mol−1, respectively) when moisture content was minimum (2.5 g H2O per 100 g dry matter), and gradually diminishing to the value of the heat of vaporisation of pure water when moisture content reached a maximum value.

Moisture Adsorption Characteristics of Solar-Dehydrated Mango and Jackfruit

The moisture adsorption isotherms of solar dehydrated mango and jackfruit were determined at temperatures ranging from 30 °C to 50 °C. The equilibrium moisture content (EMC) of mango and jackfruit increased sharply as the temperature increased at water activity (aw) above 0.6 and 0.8, respectively. However, there were no clear isothermal intersection points observed at higher aw and temperatures. The EMC of solar dehydrated jackfruit showed the isothermal characteristics between types II and III. In contrast, dehydrated mango followed the characteristic type III adsorption isotherms due to high total soluble solids content of 67.8 °Brix and total sugars of 14.21 g/100 g fresh mango. Estimated parameters and fitting ability of three isotherm models were also evaluated. The Guggenheim-Anderson-Boer (GAB) model gave the best fit to the experimental EMC data. The GAB monolayer moisture contents (mo) of mango and jackfruit ranged from 11.1–10.0 % and 4.7–3.4 %, respectively. Specific surface area of active binding sites (S) was calculated based on the mo values. The S value of dehydrated mango was 2.5 to 2.8 times larger than jackfruit. The maximum net isosteric heat (qs) of sorption of solar dehydrated mango and jackfruit were determined as 19.5 and 33 kJ mol−1, respectively, and qs decreased significantly at high moisture.

Thermodynamic analysis of sorption isotherms of cassava (Manihot esculenta).

Sorption isotherms of cassava were determined experimentally using a static gravimetric method at 30, 45 and 60°C and within the range of 0.10-0.90 water activity. At a constant water activity, equilibrium moisture content decreased with increasing temperature. The equilibrium moisture content increased with increasing water activity at a given temperature. The experimental results were modelled using seven sorption models using non-linear regression technique. Results demonstrated that the GAB model adequately predicted equilibrium moisture content of cassava for the range of temperatures and water activities studied. The thermodynamic functions such as net isosteric heat of sorption, differential entropy of sorption, net integral enthalpy and entropy were evaluated to provide an understanding of the properties of water and energy requirements associated with the sorption behaviour. Net isosteric heat and differential entropy decreased with increasing equilibrium moisture content. The net integral enthalpy decreased while net integral entropy increased with increasing equilibrium moisture content. Net integral entropy was negative in value. All thermodynamic functions were adequately characterised by a power law model. The point of maximum stability was found between 0.053 and 0.154kg water/kg db for cassava.

Sorption and kinetics of CO2 and CH4 in binderless beads of 13X zeolite

The sorption equilibrium of CO2 and CH4 in binderless beads of 13X zeolite has been investigated between 313 and 373K and pressure up to 4atm. The amount adsorbed of CO2 and CH4 is around 5.2mmol/gads and 1.2mmol/gads, respectively, at 313K and 4atm. Comparing these values with the ones in literature the value of CO2 is 20% higher than in CECA 13X binder pellets. It is also found that isotherms are pronounced Type I for CO2 and almost linear for CH4. The CO2 isotherms were modeled using a simple deviation from Langmuir isotherm that takes into account interaction between adsorbed molecules at adjacent sites (Fowler model) suggesting a moderate repulsion. Henry’s constants range from 143 to 11.1mmol/gads.atm for CO2 and 0.45 to 0.27mmol/gads.atm for CH4 between 313 and 373K, respectively. The heats of sorption at zero coverage are 43.1kJ/mol for CO2 and 9.2kJ/mol for CH4.The sorption kinetics has been investigated by the Zero-Length Column technique (ZLC). Recipes to analyze ZLC desorption curves in pellets of adsorbents are reviewed and it is derived a criteria which indicates that for the sorption rate be measured macroscopically the time of the experiment (that should be above a few seconds) is directly calculated with the following expression: t0.1≥7.02×10-2rc2Dc. Based on such criteria it is shown that crystal diffusivity of CO2 in 13X can be measured macroscopically by ZLC, being the same measurement for CH4 practically impossible. The crystal diffusivity of CO2 measured experimentally is 5.8×10−15m2/s and 1.3×10−15m2/s at 373 and 313K, respectively. These values are comparable to the ones measured by a frequency response and pulse chromatography techniques reported in literature. The ZLC desorption curves for CH4 were measured under an equilibrium regime.

Relationships between the sorption behaviour of methane, carbon dioxide, nitrogen and ethane on coals

Sequestration of carbon dioxide in coal seams can reduce emissions of carbon dioxide to the atmosphere. If such sequestration simultaneously results in enhanced coal bed methane (ECBM) production, some of the sequestration costs can be recovered by the value of the methane produced. This requires knowledge of both the carbon dioxide and methane sorption behaviour of coal at high pressures. In order to elucidate the connection between them, we investigated the sorption of carbon dioxide, methane, ethane and nitrogen at 55°C at pressures up to 20MPa for a number of coals. Sorption isotherms were fitted by a modified Dubinin–Radushkevich model. The maximum sorption capacities of the coals for the different gases were found to be highly correlated. The relationship between maximum sorption capacity of a coal for a gas and its critical temperature was approximately proportional. The relationship between methane and nitrogen maximum sorption capacity was particularly close: on a volume basis, the maximum sorption capacity of all coals examined for methane was twice that of nitrogen. The ratio of maximum sorption capacity of carbon dioxide and methane decreased linearly with increasing carbon content. The ethane/methane sorption ratio also tended to decrease with increasing rank though to a smaller extent, indicating that the proportionally greater sorption at low rank coals is not unique to carbon dioxide. The heat of sorption tends to increase with increasing vitrinite reflectance; this may reflect the greater polarisability of higher rank coals (which also determines their reflectance).

DESORPTION ISOTHERMS AND THERMODYNAMIC PROPERTIES OF FRESH AND OSMOTIC-ULTRASONIC DEHYDRATED QUINCES

Experiments were conducted to determine the effect of pretreatment osmotic– ultrasonic dehydration on the desorption isotherms of quince by static gravimetric method at 30, 45 and 60C temperatures. The isotherms exhibited type II behavior, with the sorption capacity decreased with increasing temperature. Out of the six equilibrium sorption models that were evaluated, the Peleg equation gave the best fit to the sorption data. The Hasley equation was further used to estimate the thermodynamic functions (such as net isosteric heat, enthalpy–entropy compensation and spreading pressure) of quince. The net isosteric heat of sorption and differential entropy decreased with increasing moisture contents in an exponential function. A plot of differential heat versus entropy satisfied the enthalpy–entropy compensation theory. The spreading pressure increased with increasing water activity and decreased with increasing temperature. The value of net isosteric heat, differential entropy and spreading pressure of untreated samples are higher than that pretreated sample quince.

MOISTURE ADSORPTION ISOTHERMS AND HEAT OF SORPTION OFAGARICUS BISPORUS

ABSTRACT Moisture adsorption isotherms of Agaricus bisporus were determined at different temperatures (5, 15, 25 and 35C) using a static gravimetric method. Several saturated salt solutions were prepared to obtain different water activities in the range of 0.11–0.93. Freeze-dried A. bisporus was equilibrated with designed saturated salt solutions. For certain water activity, the equilibrium moisture contents of A. bisporus decreased with increasing temperature. Adsorption isotherms of freeze-dried A. bisporus followed type III isotherm, which is typical for polysaccharide products. Nine models were used to fit experimental data by linear regression analysis method to ascertain the best of fit. Comparisons were based on mean relative percent error (E), standard error (SE), coefficient of correlation (R2) and residual plots. Among the models tested, the Halsey model achieved the best fit. Based on Clausius–Clapeyron equation, the net isosteric adsorption heat of A. bisporus decreased from 12.12 to 0.30 kJ/mol when the moisture content increased from 8 to 50 g/100 g dry matter. PRACTICAL APPLICATIONS A. bisporus's shelf life is only 1–3 days at ambient temperature. Drying, especially freeze-drying, is one of the main preservation methods for A. bisporus. Developing moisture sorption isotherms (MSIs) for A. bisporus could provide essential information about optimizing its drying process and storage conditions. In addition, isosteric heat of sorption in dehydrated and intermediate moisture food also plays an important role in modeling of various food processing and storage. Optimization of drying process and storage conditions of dried A. bisporus could be obtained by developing its MSI.

SORPTION ENERGIES FOR ATRAZINE ONTO DEVOLATALIZED VITELLARIA PARADOXA

We utilize isotherm models in contributing to scholarly knowledge in simple terms, to measure the forces or energy defining certain adsorption phenomenon. Gas Chromatography coupled with Mass Spectrophotometer detector (GCMS) was utilized to measure equilibrium phase atrazine after adsorption onto Shea nut Shells (SS) acid derived activated carbon. Data were fitted into the D-R and Temkin isotherm relationships for energy data estimation of Sorption energy value (BD), mean free energy (ED) and heat of sorption (B). They were estimated as 0.7600mol2KJ-2, 0.8111 kjmol-1 and 0.790Jmol-1 respectively. The parameter predicting the type of adsorption was evaluated BD , B < 20kJ/mol and ED2 = 0.979 proves a better choice in explaining sorption energies. Generally, shea nut shells can be used as alternative precursors for activated carbon production via the two steps and acid treatment method..

Modelling Thermodynamic Properties of Banana Waste by Analytical Derivation of Desorption Isotherms

Banana is an agricultural product of great economic importance for various developing countries. The relationship between moisture content and water activity provides useful information for the processing and storage of banana waste. The water activity and moisture content of three banana (Mussa spp. Haploid AAB cv. Nanica) waste items were analyzed to determine the desorption isotherms at six different temperatures (20, 30, 40, 50, 60 and 70°C). The desorption isotherms of the peel, pedicel and pulp of overripe bananas were determined in wide ranges of moisture content (0.001–6.360 kg kg-1 d.b.) and water activity (0.02–0.907). The theoretical GAB model was used for modelling the desorption isotherms. An analytical solution of the Clausius-Clapeyron equation was proposed to compute the isosteric heat of sorption, the differential entropy and Gibbs’ free energy by way of the GAB model when the effect of temperature on the hygroscopic equilibrium was considered.

Modeling adsorption equilibria of xylene isomers in a microporous metal–organic framework

Single and multicomponent adsorption equilibria of xylene isomers: o-xylene (o-x), m-xylene (m-x), p-xylene (p-x) and ethylbenzene (eb) was investigated on the three dimensional microporous metal–organic framework Zn(BDC)(Dabco)0.5 (BDC=1,4-benzenedicarboxylate, Dabco=1,4-diazabicyclo[2.2.2]-octane), MOF 1, in the range of temperatures between 398 and 448K and partial pressures up to 0.1bar. The equilibrium data show that a significant amount (around 34g/100gads at 398K) of xylene isomers can be adsorbed in MOF 1. The affinity to the adsorbent measured by the Henry’s constants to decreases in the order o-x>m-x>eb>p-x for all temperatures. The zero coverage adsorption enthalpies are all similar and range from 77.4 (eb) to 79.8kJ/mol (o-x). The Dual-Site Langmuir model (DSL) was used for the interpretation and correlation of the experimental data. The parameters obtained from the pure component isotherms fitting were also used to predict the multicomponent equilibrium data by an extended DSL model. A good agreement was obtained between the predictions and the experimental data. It was also demonstrated that the DSL model is also capable to explain the increase in the isosteric heat of sorption with increasing coverage.

Moisture sorption isotherms and isosteric heat of sorption of leaves and stems of lemon balm (Melissa officinalis L.) established by dynamic vapor sorption

The equilibrium moisture contents (MC) of leaves and stems of lemon balm (Melissa officinalis L.) were determined separately at temperatures of 25, 35 and 45 °C over a stepwise increase of relative humidity (RH) ranging from 3 to 90% by an automatic, gravimetric analyzer (DVS system). Equilibrium was achieved within 6 h for most of the target values of relative humidity. The equilibrium moisture content of leaves was significantly higher than that of stems (p < 0.05). Differences in moisture sorption capacity between the leaves and stems can be attributed to chemical composition and structure of the tissues. Five three-parameter moisture sorption models (modifications of Chung–Pfost, GAB, Halsey, Henderson and Oswin) were tested for their effectiveness to fit the experimental sorption data. The modified Oswin equation was found to be the best model to describe the adsorption isotherms of both leaves and stems of lemon balm. The recommended MC values of leaves and stems for microbial safe storage at 25 °C were 0.124 and 0.113 kg water per kg dry solids, respectively. The net isosteric heat of sorption was computed from the predicted sorption data by applying the integrated form of the Clausius–Clapeyron equation.

Simulations of the thermo-hydro-mechanical behaviour of an annular reinforced concrete structure heated up to 200 °C

We analyze in this study the numerical thermo-hydro-mechanical response of an annular reinforced concrete structure called MAQBETH subjected to a thermal loading up to 200°C during more than 250h. This mock-up is typical of concrete structures in nuclear waste storage conditions under accidental situations. The simulations are performed with a simplified coupled model based on the mechanics of partially saturated porous media, which was previously developed in [1]. As a main contribution of this paper, we explicitly take into account the temperature effects in the water retention curves, via the introduction of the isosteric heat of sorption. These effects result in a significant reduction of the saturation degree at any given relative humidity for increasing temperatures. The numerical results of the MAQBETH simulation are then compared with experimental ones in terms of profiles of temperature, relative humidity, gas pressures and strains in the median plan at different times. This comparison shows a reasonable agreement. The effects of the temperature-dependent sorption curves are further analyzed through additional simulations carried out with a constant sorption curve. Large differences in the relative humidity and saturation degree profiles, and to a lesser extent in the gas pressure profiles, are observed between the two cases.