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Isosteric Heat (isosteric + heat)
Selected AbstractsMOISTURE SORPTION CHARACTERISTICS of STARCH GELS.JOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2004PART II: THERMODYNAMIC PROPERTIES ABSTRACT A thermodynamic approach was used to interpret the experimental adsorption and desorption isotherm data for potato starch gel. Calculation of the thermodynamic properties (differential enthalpy, integral enthalpy, differential entropy and integral entropy) provides an understanding of the properties of water and energy requirements associated with the sorption behavior. Isosteric heats (differential enthalpies) were calculated through direct use of moisture isotherms by applying the Clausius-Clapeyron equation. the differential enthalpy and entropy decreased with increasing moisture content and were adequately characterized by an exponential model. 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 net integral enthalpy increased with moisture content to a maximum value (around the monolayer moisture content) and then decreased. In a reverse manner, the net integral entropy decreased with moisture content to a minimum value and then increased. [source] Mathematical modelling of moisture sorption isotherms and determination of isosteric heat of blueberry variety O,NeilINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 10 2009Antonio Vega-Gálvez Summary The sorption isotherms of blueberry variety O'Neil were determined at 20, 40 and 60 °C, for a range of water activity of 0.10,0.95. The isotherms showed that the equilibrium moisture content increased when temperature decreased at constant water activity. The BET, GAB, Halsey, Henderson, Caurie, Smith, Oswin and Iglesias-Chirife equations were tested for modelling the sorption isotherms. The results showed that GAB, BET and Halsey models gave the best fit quality for the experimental desorption data, and BET, Oswin and Henderson for adsorption data as suggested by the statistical tests employed. The net sorption heat was calculated using the Clausius,Clapeyron equation giving 38.62 kJ mol,1 (desorption) and 30.88 kJ mol,1 (adsorption) at a moisture content of 0.01 g water (g d.m.,1). Tsami equation was applied to estimate the net isosteric heat of sorption as function of equilibrium moisture content with satisfactory results. [source] MOISTURE SORPTION ISOTHERM, PROPERTIES OF SORBED WATER AND HEAT OF SORPTION OF SANDESH, AN INDIAN MILK PRODUCTJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2010J.K. SAHU ABSTRACT Moisture sorption isotherm of sandesh, one of the most popular milk products in India, was determined in terms of its moisture adsorption isotherms by gravimetrical method at 20 and 30C using various saturated salt solutions in the range of 11.2 to 97.2%. The isotherms obtained were of sigmoid shape and of the Brunauer,Emmett,Teller type. Out of three sorption models fitted to the experimental data, Caurie's model was found superior in interpreting the moisture adsorption characteristics of sandesh. The monolayer moisture content as calculated from the Caurie's model at 20 and 30C were 5.89% (dry basis [d.b.]) and 5.21% (d.b.), respectively. The values of isosteric heat of sorption as calculated from Clausius,Clapeyron equation was found to increase with decreasing moisture content at lower moisture content and approached the value of heat of vaporization of free water above 17.25% (d.b.). PRACTICAL APPLICATIONS The present paper describes basically the storage stability of sandesh. The sandesh is a heat,acid coagulated product of milk in Indian subcontinent and forms the part and parcel of social life, ceremonies and festivals. It has an excellent market potential and higher profit margin compared with other milk products like table butter, cheese and milk powder. Although Indian dairy industry has made rapid strides in the last few decades, there is no proper packaging system, developed so far, for storage of sandesh. Keeping pace with the growing consumers' demand for fresh, convenient and microbiologically free foods, design of proper packaging system is the need of the hour. The data presented in the paper will be very much essential for the researchers and research and development institutions for proper designing of packaging system for sandesh. [source] Charged soc metal-organic framework for high-efficacy H2 adsorption and syngas purification: Atomistic simulation studyAICHE JOURNAL, Issue 9 2009Jianwen Jiang Abstract H2 adsorption and syngas purification in charged soc metal-organic framework are investigated using atomistic simulations. As experimentally observed, the extraframework NO3, ions are entrapped in carcerand-like capsule with negligible mobility. At low pressure, H2 adsorption occurs concurrently at multiple sites near the exposed indium atoms and organic components. The capsule is accessible at high pressure through the surrounding channels by restricted windows. Adsorption sites identified are remarkably consistent with inelastic neutron scattering measurements. The isotherm and isosteric heat of H2 adsorption predicted match well with experimental data. As loading rises, the isosteric heat remains nearly constant, revealing the homogeneity of adsorption sites. CO2/H2 selectivity in syngas adsorption is up to 600 and substantially higher than other nanoporous materials. With a trace of H2O, the selectivity increases slightly at low pressure due to promoted adsorption of CO2 by H2O bound proximally to the exposed indium atoms, but decreases at high pressure as a consequence of competitive adsorption of H2O over CO2. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Effects of Adsorbent Characteristics on Adiabatic Vacuum Swing Adsorption Processes for Solvent Vapor RecoveryCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2006S. A. Al-Muhtaseb Abstract The effects of the adsorbent characteristics on the performance parameters and periodic state behavior of the vacuum swing adsorption (VSA) solvent vapor recovery (SVR) processes are examined and optimized. The adsorbent characteristics studied were the adsorbent particle's porosity, density, radius and heat capacity, the packed bed void fraction, the isosteric heat of adsorption, the monolayer saturation limit of the solvent molecules on the adsorbent, the adsorbent's affinity to adsorb the solvent molecules and the mass transfer coefficient for the adsorption of the solvent molecules. It was found that the best VSA-SVR process performances can be obtained using adsorbents characterized by the minimum possible packed bed void fraction and particle porosity, with the maximum possible adsorbent heat capacity and density, adsorption monolayer saturation capacity and mass transfer coefficient, and at intermediate adsorption affinity and isosteric heat of adsorption of the solvent molecules. [source] New Microporous Materials for Acetylene Storage and C2H2/CO2 Separation: Insights from Molecular SimulationsCHEMPHYSCHEM, Issue 10 2010Michael Fischer Abstract Force-field based grand-canonical Monte Carlo simulations are used to investigate the acetylene and carbon dioxide uptake capacity, as well as the C2H2/CO2 adsorption selectivity of three novel microporous materials: Magnesium formate, Cu3(btc)2, and cucurbit[6]uril. Because no comparable computational studies of acetylene adsorption have been reported so far, the study focuses on systems for which experimental data are available to permit a thorough validation of the simulation results. The results for magnesium formate are in excellent agreement with experiment. The simulation predicts a high selectivity for acetylene over CO2, which can be understood from a detailed analysis of the structural features that determine the affinity of Mg-formate towards C2H2. For Cu3(btc)2, preliminary calculations reveal the necessity to include the interaction of the sorbate molecules with the unsaturated metal sites, which is done by means of a parameter adjustment based on ab-initio calculations. In spite of the high C2H2 storage capacity, the C2H2/CO2 selectivity of this material is very modest. The simulation results for the porous organic crystal cucurbit[6]uril show that the adsorption characteristics that have been observed experimentally, particularly the very high isosteric heat of adsorption, cannot be understood when an ideal structure is assumed. It is postulated that structural imperfections play a key role in determining the C2H2 adsorption behavior of this material, and this proposition is supported by additional calculations. [source] Preparation and sorption studies of ,-cyclodextrin/epichlorohydrin copolymersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Dawn Y. Pratt Abstract ,-Cyclodextrin (,-CD) copolymer materials were synthesized by reacting different mole ratios (1 : 15, 1 : 25 and 1 : 35) of ,-CD with epichlorohydrin (EP). The products were characterized using N2 porosimetry, Fourier Transform Infrared spectroscopy, 13C CP-MAS NMR spectroscopy, thermogravimetry analysis, elemental (C and H) analysis, and scanning electron microscopy. The sorption properties in aqueous solution were studied using p-nitrophenol (PNP) with UV,Vis spectrophotometry. Sorption isotherms were obtained at pH 4.6 and three temperatures (22, 35, and 45°C) and at pH 10.3 at 22°C. The isotherms were analyzed using the BET isotherm model and the sorption parameters provided estimates of the surface area, sorption capacity, and isosteric heats of sorption for each polymeric material. The estimated surface areas are as follows: 58.2, 52.1, and 90.1 m2/g at pH 4.6. At pH 10.3, the estimated surface areas are 44.2, 40.5, and 58.5 m2/g, respectively. The removal efficiency of PNP by the polymeric materials ranged between 4.5 and 58% for the conditions investigated whereas the isosteric heats ranged between ,24.5 and ,13.6 kJ/mol. Removal efficiencies were concluded to strongly depend on the sorption conditions such as pH, temperature, and the relative amounts of sorbent and dye in aqueous solution. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Material design using molecular modeling for hydrogen storageAICHE JOURNAL, Issue 2 2009F. Darkrim Lamari Abstract Using grand canonical Monte-Carlo simulations, the adsorption capacities and isosteric heats of hydrogen on activated carbons, graphite nanofibers, and bundles of carbon nanotubes are estimated for identical thermodynamic states. These computations allow a systematic, meaningful, and unbiased comparison of the adsorption properties of hydrogen in such porous materials. The comparison shows that the hydrogen storage capacity can be optimized, but only to a limited extent, in adjusting the material pore sizes and functionalizing a part of the adsorption sites. Therefore, at room temperature and up to 70.0 MPa, for the three models of carbonaceous adsorbents, the hydrogen maximal excess adsorption is of the order of 2% of the adsorbent mass. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Equilibrium and heat of adsorption of phosphine on CaCl2 -modified molecular sieveASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Qiongfen Yu Abstract Adsorption characteristics of the virgin and CaCl2 -immersed molecular sieves at 298 K were investigated to select the adsorbent with high adsorption capacity to phosphine. Adsorption isobars and adsorption isotherms over the phosphine partial pressure and temperature ranged 0 , 1000 Pa and 298 , 343 K were measured. The adsorption equilibrium data for phosphine at various temperatures were fitted to Langmuir and Freundlich isotherm models and their isosteric heats of adsorption were determined by the Clausius-Clapeyron equation. It was found the Freundlich was more suitable for description of phosphine adsorption process through calculating average absolute relative error, and the fitted result about Langmuir model showed the heterogeneous characteristics of modified adsorbent. The isosteric heat of adsorption was about 15 kJ/mol, which indicated adsorptive phosphine removal performance may be a dominant of physical adsorption being easy for desorption. The isosteric heat of adsorption decreased with an increase of the surface loading on CaCl2/5A, which means that CaCl2/5A molecular sieve had an energetically heterogeneous surface. The present study confirmed that the CaCl2/5A molecular sieves would be one of the candidates for separation and recycle of phosphine. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||