Isosteric Heat Of Sorption Research Articles

Effects of environmental conditions on characteristics of annatto seed by-product

Introduction The processing of annatto seeds yields a low-cost by-product known as annatto seed by-product. Due to its remarkable bixin levels, which is a natural antioxidant, the annatto seed by-product could be used in animal feed supplemen- tation. As a low-moisture product, it is important to know information about hygroscopic behavior, changes during storage, package selection and drying equip- ment design. Objectives The annatto seed by-product's hygroscopic behavior was studied at 25 °C and 35 °C by using saturated salt solutions and the static method. Methods During storage with different relative air humidity, the annatto seed by-product's isosteric heat of sorption, bixin content and instrumental color parameters were evaluated. Results The isotherms exhibited type III behavior and the Kuhn model properly fitted the annatto seed by-product's equilibrium mois- ture data. Above 75% air relative humidity, agglomeration, darkening and fungal development were observed. The isosteric heat of sorption decreased with an increase in moisture content. Conclusion Once the equilibrium was established, bixin losses (approximately 43% of the content) and color changes were more prominent at 35 °C, especially under 68% relative humidity.

Modeling Desorption Isotherms and Thermodynamic Properties of Fresh Tea Leaves (Camellia sinensis var. assamica)

Abstract Desorption isotherm of fresh tea leaves was studied using static gravimetric method of saturated salt solutions at temperatures of 15, 20, 25 and 30ºC and water activities of 0.07 to 0.97. Data were fitted to five mathematical equations. Using the best-fit mathematical model, thermodynamic properties of fresh tea leaves including net isosteric heat of sorption, differential entropy were estimated. The applicability of enthalpy – entropy compensation theory for fresh tea leaves was also evaluated. Results showed that the modified Oswin model was best fitted with the experimental data. Thermodynamics properties like net isosteric heat of sorption and differential entropy were found to decrease exponentially with the increase in moisture content. Net isosteric heat of sorption and differential entropy increased exponentially with decreasing moisture content of fresh tea leaves. Isosteric heat of sorption of fresh tea leaves was very close to heat of vaporization of pure water when the moisture content of tea leaves exceeded 40% (d.b.). The enthalpy-entropy compensation theory could be successfully applied for the moisture desorption behavior of fresh tea leaf samples and it was enthalpy driven spontaneous process.

Sorption isotherms and isosteric heats of sorption of Malaysian paddy.

Understanding the water sorption characteristics of cereal is extremely essential for optimizing the drying process and ensuring storage stability. Water relation of rough rice was studied at 20, 30, 40 and 50°C over relative humidity (RH.) between 0.113 and 0.976 using the gravimetric technique. The isotherms displayed the general sigmoid, Type II pattern and exhibited the phenomenon of hysteresis where it was more pronounced at lower temperatures. The sorption characteristics were temperature dependence where the sorption capacity of the paddy increased as the temperature was decreased at fixed (RH). Among the models assessed for their ability to fit the sorption data, Oswin equation was the best followed by the third order polynomial, GAB, Smith, Chung-Pfost, and Henderson models. The monolayer moisture content was higher for desorption than adsorption and tend to decrease with the increase in temperature. Given the temperature dependence of the sorption isotherms the isosteric heats of sorption were calculated using Claussius-Clapeyron equation. The net isosteric heats decreased as the moisture content was increased and heats of desorption were greater than that of adsorption.

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.

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.

The Hygroscopic Properties and Sorption Isosteric Heats of Different Chinese Wheat Types

The moisture sorption isotherm data of fourteen Chinese wheat varieties were determined using the static gravimetric method at five different temperatures (10, 20, 25, 30 and 35 ° C) and relative humidity ranging from 11.3 to 96%. Eight models, namely Brunauer-Emmett-Teller, CAE, Chen-Clayton, Modified-Chung-Pfost (MCPE), Modified-Henderson, Modified-Guggenheim-Anderson-deBoer, and Modified-Oswin and Strohman-Yoerger, were used to fit the sorption data. MCPE shows the best fitting results. A significant hysteresis effect was found between wheat desorption and adsorption isotherm at lower ERH, but the similar hygroscopic properties remained for different wheat types like hard vs. soft, red vs. white, and winter vs. spring, respectively. The experimental results show that the isosteric heats for both wheat adsorption and desorption, and all the sorption heats for different wheat types decrease rapidly with increasing seed moisture initially, however, after the moisture is more than 15% w.b. they decrease tardily with increasing moisture content. The isosteric heats of wheat desorption were considerably higher than those of adsorption below 17.5% m.c., but the similar sorption isosteric heats were found for wheat types like hard vs. soft, red vs. white, or winter vs. spring, respectively. It is concluded that the wheat grains from different types have similar hygroscopic properties and sorption isosteric heats and can be synchronously dealt with during physical control in storage.

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.

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.

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.

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.

Experimental Determination and Modelling of the Sorption Isotherms of Kilishi

This work was carried out in collaboration between author and National Advanced School of Engineering (University of Yaounde I). AT designed the study, performed the statistical analysis, wrote the protocol, wrote the first draft of the manuscript, managed the analyses of the study, and managed the literature searches. AT read and approved the final manuscript. ABSTRACT Sorption isotherms of kilishi have been experimentally determined at 30, 40 and 50oC by using salt method for a range of water activity from 0,064 to 0,973. His sorption capacity increases with the temperature for a given water activity. The experimental curves obtained have been simulated by the GAB model. This model enables the representation of the whole desorption isotherms, with maximum deviation of 1.2% . . The water content corresponding to monolayer saturation was estimated. The isosteric heat of sorption is deduced from experimental results and empirical correlations are proposed leading to satisfactorily representation. These results can be used to predict the potential changes in kilishi stability and later for the development of a system of suitable drying.

Sorption isotherms and thermodynamic properties of freeze‐dried colostral whey powders with different additives

SummaryMoisture adsorption isotherms of colostral whey (CW) powders with different additives (maltodextrin and sucrose) were determined using gravimetric static method at 15–35 °C in the water activity range of 0.067–0.76. The moisture adsorption isotherms obtained were typical sigmoid curves, and the modified‐Halsey and Guggenheim–Anderson–de Boer (GAB) equations gave the best fit to experimental data among five well‐known equations. Addition with maltodextrin into CW powders could effectively decrease equilibrium moisture content (EMC), whereas addition with sucrose increased EMC in the water activity of 0.43–0.76 at 15 and 25 °C and in the water activity of 0.21–0.76 at 35 °C, respectively. Thermodynamic properties including net isosteric heat of sorption and differential entropy were determined from adsorption data using Clausius–Clapeyron equation. The results showed that net isosteric heat of sorption of all the samples decreased exponentially with increasing EMC. Enthalpy–entropy compensation theory was applicable for adsorption process of all the samples, and the adsorption processes were enthalpy‐driven.