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Equilibrium Data (equilibrium + data)
Kinds of Equilibrium Data Selected AbstractsA Statistically Based Strategy for Obtaining Equilibrium Data in Xanthophylls LixiviationJOURNAL OF FOOD SCIENCE, Issue 8 2001J.L. Navarrete-Bolantos ABSTRACT: The design of many separation processes is often hindered by the lack of equilibrium data. In recent years, statistically based experimental design has been successfully used to quantify relevant factors in many biological and chemical processes. We illustrate the capabilities of one of these approaches in obtaining equilibrium data for the design of lixiviation processes. The study case involves the lixiviation of marigold flower flour for xanthophylls extraction using hexane in a multistage countercurrent system. The method leads to conditions that allow the recovery of 95.3% of the pigment in seven stages. [source] Computational study of a novel continuous solar adsorption chiller: performance prediction and adsorbent selectionINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2007Evan Voyiatzis Abstract A novel solar adsorption chiller intended for domestic use is presented. The chiller can be integrated with existing solar systems based on flat plate collectors, and, contrary to commercial chillers, it operates continuously. A detailed analysis of both the simple and the heat-integrated cycle is carried out so as to select the optimal adsorbent and operating conditions. The employed integral thermodynamic model takes into account the inert masses that limit the performance of the chiller, such as the metal frame, the thermo-fluid, and the non-adsorbed steam, by introducing heat capacity effects. Given the adsorption equilibrium data, the energy balances, the performance, and the useful thermal loads of the system can be calculated at any operating conditions. The results indicate that silica gel Type A is a more efficient adsorbent compared to silica gel Type RD or Type 3A. Furthermore, the total porosity has a slight effect on system performance, while optimal operation can be achieved when the condenser temperature is less than 326 K and the evaporator temperature greater than 280 K. Copyright © 2006 John Wiley & Sons, Ltd. [source] Equilibrium moisture content and heat of desorption of saffronINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 8 2010Hamid Reza Gazor Summary The equilibrium moisture contents of saffron (Crocus sativus L.) stigmas were determined experimentally using the standard gravimetric method at temperatures 30, 45 and 60 °C and water activity ranging from 11% to 83%. The sorption isotherm curves of saffron were sigmoidal in shape and decreased with increased temperature at constant relative humidity. Five selected isotherm models GAB, modified Henderson, modified Chung-Pfost, modified Halsaey and modified Oswin were tested to fit the experimental isotherm data. Modified Oswin and modified Henderson models were found acceptable for predicting desorption moisture isotherms and fitting to the experimental data, respectively. The isosteric heats of desorption, determined from equilibrium data using the Clausius-Clapeyron equation, were found to be a function of moisture content. The net isosteric heat of desorption of saffron varied between 1.38 and 5.38 kJ mol,1 at moisture content varying between 2% and 20% (d.b). [source] A generalized exo -anomeric effect.ISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2000Substituent, solvent effects on the conformational equilibria of 2-(arylseleno)cyclohexanones The effects of substitution and solvent on the conformational equilibria of 2-[(4-R-substituted-phenyl)seleno]cyclohexanones are described. The conformational equilibria were determined by comparison of the linewidths of the H-2 resonances in the 1H NMR spectra of the conformationally averaged systems with those of the anancomeric (highly biased) 4-isopropyl-2-substituted cyclohexanones. The substituent (R = NMe2, OMe, Me, H, F, Cl, CF3, NO2) and solvent ((CD3)2CO, CD3CN, CD2Cl2, CDCl3) effects are discussed in terms of electrostatic effects and the possible stabilizing orbital interactions. The values of Keq (axial-equatorial) increase as the substituent becomes more electron withdrawing, in agreement with the dominance of nSe , ,*C=O or ,C-Se , ,*C=O orbital interactions in the axial conformers. The increase in the proportion of the equatorial isomers in more polar solvents for a given substituent suggests a damping of the dipolar interactions in the equatorial isomers. However, the proportion of the equatorial isomers in a given solvent increases as the substituent becomes more electron withdrawing, indicating that electrostatic interactions do not dominate in controlling the conformational equilibria. Analysis of the equilibrium data by means of a dual substituent parameter approach indicates the best correlation with ,I and ,+R substituent constants in CD2Cl2 and with ,I and ,°R substituent constants in CD3CN, with similar sensitivities to the resonance and polar effects. The correlations are interpreted in terms of accommodation of effective positive charge on the selenium atom in the axial isomers in CD2Cl2, and a lesser sensitivity to the buildup of positive charge in the more polar solvent CD3CN. Comparison of the IR ,CO -stretching frequencies for the axial and equatorial ArSe-substituted anancomeric systems (R = NO2, NMe2) indicates a higher stretching frequency for the NO2 -substituted isomers. In the case of the NMe2 -substituted compounds, ,CO appears at a higher frequency in the equatorial isomer, whereas in the case of the NO2 -substituted compounds, ,CO is less sensitive to the axial or equatorial orientation of the substituent. The results are consistent with the operation of nse , ,*c=0 or ,C-Se , ,*C=O orbital interactions in the axial isomers. The JC2-H2 values in the axially-substituted anancomeric isomers are of greater magnitude than those in the equatorially-substituted isomers, which is also consistent with the operation of the orbital interactions described above. There is, however, no marked substituent effect on the JC2,H2 values within the series of axial or equatorial isomers. We argue that this does not support the dominance of ,C-Se , ,*C=O orbital interactions. Examination of crystal structures reported in the literature for related compounds indicates a particular gauche orientation about the C2,Se bond, which lends further support to the operation of an nSe , ,*C=O orbital interaction. We suggest that the latter interaction is a manifestation of a generalized exo -anomeric effect. [source] A Statistically Based Strategy for Obtaining Equilibrium Data in Xanthophylls LixiviationJOURNAL OF FOOD SCIENCE, Issue 8 2001J.L. Navarrete-Bolantos ABSTRACT: The design of many separation processes is often hindered by the lack of equilibrium data. In recent years, statistically based experimental design has been successfully used to quantify relevant factors in many biological and chemical processes. We illustrate the capabilities of one of these approaches in obtaining equilibrium data for the design of lixiviation processes. The study case involves the lixiviation of marigold flower flour for xanthophylls extraction using hexane in a multistage countercurrent system. The method leads to conditions that allow the recovery of 95.3% of the pigment in seven stages. [source] The applicability of the GRIPS geobarometry in metapelitic assemblagesJOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2006C.-M. WU Abstract Although the garnet-rutile-ilmenite-plagioclase-silica (quartz) (GRIPS) geobarometer has been experimentally calibrated and widely applied, its applicability to metapelitic rocks has not yet been discussed carefully. In this paper, this barometer was recalibrated by fitting the available reversed-phase equilibrium data incorporating different combinations of activity models of garnet, plagioclase and ilmenite. The resultant GRIPS barometer formalisms reproduce the experimental pressures well within ±0.2 kbar. The GRIPS and garnet-aluminium silicate-plagioclase-quartz (GASP) barometer values are concordant within ±1 kbar for pressures above ,6 kbar for natural metapelites, but the difference of pressure determinations between these two barometers becomes larger when pressure and/or the grossular content of garnet decrease. However, the pressure difference is independent of either temperature, or almandine in garnet, or anorthite in plagioclase, or iron content in ilmenite. After testing and application of the GRIPS barometer to aluminosilicate-bearing metapelites and metapelitic assemblages within limited geographical areas as well as within contact thermal aureoles, it is concluded that this barometer may be applied to low- to high-grade, medium- to high-pressure metapelites. The application of the GRIPS barometer to metapelites is not advocated in situations where calcium is deficient in garnet ( < 0.05) or plagioclase ( < 0.17), or for pressures below ,6 kbar. [source] Chemisorption of carbon dioxide on sodium oxide promoted aluminaAICHE JOURNAL, Issue 11 2007K. B. Lee Abstract New equilibrium and column dynamic data for chemisorption of carbon dioxide from inert nitrogen at 250, 350, and 450°C were measured on a sample of sodium oxide promoted alumina, which was found to be a reversible chemisorbent for CO2. The equilibrium chemisorption isotherms were Langmuirian in the low pressure region (p <2.0 kPa) with a large gas,solid interaction parameter. The isotherms deviated from the Langmuirian behavior in the higher pressure region. A new analytical model which simultaneously accounted for Langmuirian chemisorption of CO2 on the adsorbent surface and additional reaction between the gaseous and sorbed CO2 molecules was used to describe the measured equilibrium data. The heats of CO2 chemisorption and the additional surface reaction were, respectively, 64.9 and 37.5 kJ/mol. The column breakthrough curves for CO2 sorption from inert N2 on the chemisorbent as well as the desorption of CO2 from the chemisorbent by N2 purge at 350°C could be described by the linear driving force (LDF) model in conjunction with the new sorption isotherm. The same LDF mass transfer coefficients can be used to describe both sorption and desorption processes. The CO2 mass transfer coefficients were (i) independent of feed gas CO2 concentration in the range of the data at a given temperature, and (ii) a weak function of temperature. The ratio of the mass transfer zone length to the column length was very small due to highly favorable CO2 sorption equilibrium. Several sequential cyclic CO2 sorption,desorption column dynamic tests were conducted to demonstrate the apparent stability of the material. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Modeling solubilities of sugars in alcohols based on original experimental dataAICHE JOURNAL, Issue 9 2007Fernando Montañés Abstract Solubility of six different carbohydrates in methanol, ethanol, 1-propanol, and 2-propanol were measured at 22, 30, and 40°C. Ketose sugars (fructose, tagatose, and lactulose) show higher solubilities than aldoses (glucose, galactose, and lactose). The binary solid,liquid equilibrium data obtained was satisfactory represented by using the A-UNIFAC model. Additionally, the capability of the model to predict the carbohydrate solubility in alcohol,alcohol and alcohol,water mixed solvents was explored. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Multicomponent mass transport model for the sorption of metal ions on bone charAICHE JOURNAL, Issue 9 2004Danny C. K. Ko Abstract The sorption of binary mixtures of copper/cadmium and copper/zinc ions onto bone char was studied in fixed beds. The effects of solution flow rate, initial dye concentration, and bone char particle size range were investigated. A mass transport model based on film-surface diffusion and the IAS model for the equilibrium relationship was used to develop theoretical fixed-bed breakthrough curves. The model incorporates the Sips isotherm for the first time in fixed-bed predictions, since this isotherm gives an excellent correlation of the experimental equilibrium data. The model was used to determine the optimum surface diffusivities as 7.37 × 10,10 and 2.73 × 10,9 cm2/s for copper and cadmium in the Cu/Cd system; and 1.61 × 10,9 and 2.43 × 10,9 cm2/s for copper and zinc in the Cu/Zn system. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2130,2141, 2004 [source] Generalized least-squares parameter estimation from multiequation implicit modelsAICHE JOURNAL, Issue 10 2003Simon L. Marshall Maximum likelihood fit of nonlinear, implicit, multiple-response models to data containing normally distributed random errors can be carried out by a combination of the Gauss-Newton generalized nonlinear least-square algorithm first described by Britt and Luecke in 1973, with a Fletcher-Reeves conjugate gradient search for initial parameter estimates. The convergence of the algorithm is further improved by adding a step-limiting procedure that ensures a reduction in the objective function for each iteration. Multiple-equation regression methods appropriate to the solution of explicit fixed-regressor models are derived from this general treatment as special cases. These include weighted nonlinear least squares (where the covariance matrix of the response is known), and uniformly weighted nonlinear least squares (where the responses are uncorrelated and characterized by a single common variance). Alternative methods for fixed-regressor fits of explicit multiequation models with an unknown covariance matrix of the responses are also considered. The moment-matrix determinant criterion appropriate in such situations is also efficiently minimized by use of the conjugate-gradient algorithm, which is considerably less sensitive to the accuracy of the initial parameter estimate than the more usual Gauss-Newton methods. The performance of the new algorithm for models defined by one, two, and three implicit functional constraints per point is illustrated by random-regressor fits of isothermal p,X and p,X,Y vapor,liquid equilibrium data, and ternary liquid,liquid equilibrium data, respectively. [source] Vacancy solution theory for binary adsorption equilibria in heterogeneous carbonAICHE JOURNAL, Issue 9 2002L. P. Ding A heterogeneous modified vacancy solution model of adsorption developed is evaluated. The new model considers the adsorption process through a mass-action law and is thermodynamically consistent, while maintaining the simplicity in calculation of multicomponent adsorption equilibria, as in the original vacancy solution theory. It incorporates the adsorbent heterogeneity through a pore-width-related potential energy, represented by Steele's 10,4,3 potential expression. The experimental data of various hydrocarbons, CO2 and SO2 on four different activated carbons,Ajax, Norit, Nuxit, and BPL,at multiple temperatures over a wide range of pressures were studied by the heterogeneous modified VST model to obtain the isotherm parameters and micropore-size distribution of carbons. The model successfully correlates the single-component adsorption equilibrium data for all compounds studied on various carbons. The fitting results for the vacancy occupancy parameter are consistent with the pressure change on different carbons, and the effect of pore heterogeneity is important in adsorption at elevated pressure. It predicts binary adsorption equilibria better than the IAST scheme, reflecting the significance of molecular size nonideality. [source] Effect of number of fractionating trays on reactive distillation performanceAICHE JOURNAL, Issue 12 2000Muhammad A. Al-Arfaj Sneesby et al. recently suggested that adding trays in the stripping and rectifying sections of a reactive distillation column can degrade performance. This effect, if true, is not only counterintuitive, but very disturbing because it suggests that the design of reactive distillation columns cannot use conservative estimates of tray numbers, that is, we cannot simply add excess trays, as in conventional distillation. The problem is compounded by the uncertainty in vapor,liquid equilibrium data and tray efficiencies. This implies that developing reactive distillation columns would require extensive experimental work at the pilot-plant and plant stages to find the numbers of stages offering the best performance. Such a scenario would mean long and expensive development programs. This article explores the effect of the number of trays in the rectifying and/or stripping sections of reactive (catalytic) distillation columns. Three reactive distillation systems are used: an ideal hypothetical system, the ETBE system, and the methyl acetate system. Contrary to the published results, it is demonstrated that additional trays do not degrade performance. Two degrees of freedom available in all cases must be carefully chosen for fair comparisons. [source] Estimation of vapour,liquid equilibrium data for binary refrigerant systems containing 1,1,1,2,3,3,3-heptafluoropropane (R227ea) by using artificial neural networksTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010M. R. Nikkholgh Abstract In this research, the ability of multilayer perceptron neural networks to estimate vapour,liquid equilibrium data have been studied. Four typical binary refrigerant systems containing R227ea have been investigated in a large range of temperatures and pressures. The systems are categorised into four groups, based on their different deviations from the Raoult's law. The networks with one hidden layer consisted of five neurons are developed as the optimal structure. For these binary systems, uncertainties in the artificial neural networks (ANNs) estimations were not more than 1.03%. In addition, the abilities of ANNs are shown by comparisons with Margules, van Laar, and some other correlations. Dans ce travail de recherche, nous avons étudié la capacité de réseaux neuraux de perceptron multicouche à estimer les données d'équilibre vapeur-liquide. Quatre systèmes typiques de réfrigérants binaires contenant du R227ea ont été étudiés sur de grands intervalles de température et de pression. Les systèmes étaient classés en quatre groupes, en fonction de leurs déviations différentes par rapport à la Loi de Raoult. Les réseaux ayant une couche cachée composée de cinq neurones sont développés comme la structure optimale. Pour ces systèmes binaires, les incertitudes dans les estimations ANN ne dépassaient pas 1,029 %. De plus, les capacités des ANN sont données en comparaison avec Margules, van Laar et certaines autres corrélations. [source] Extended NRTL model for PEG + salt based aqueous two-phase systemASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010Muthiah Perumalsamy Abstract Liquid,liquid equilibrium (LLE) data of aqueous poly(ethylene glycol) (PEG) 2000,sodium citrate systems were determined experimentally at 25°, 35° and 45 °C. Experimental techniques and analytical methods were described in the previous article (T. Murugesan, M. Perumalsamy. J. Chem. Eng. Data. 2005; 50, 1392,1395 [22]). The NRTL (nonrandom, two-liquid) model, expressed in mass fraction, was used to correlate the LLE of aqueous two-phase systems (ATPS). The interaction energy parameters of the NRTL model were adjusted using these experimental LLE data. The model described experimental equilibrium data with a good agreement. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Kinetics and mechanism of Cr(VI) adsorption onto tea-leaves wasteASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2008Md. Salatul Islam Mozumder Abstract Adsorption equilibrium and kinetic experiments have been conducted in batch mode to evaluate Cr(VI)-tea-leaves waste system. The equilibrium data followed the Langmuir adsorption isotherm and the adsorption was viewed as a physicochemical reversible process. A unified approach model was used to describe the adsorption system from both equilibrium and kinetic viewpoints. The model satisfactorily described both kinetic and equilibrium data. The adsorption and desorption rate constants were evaluated from the model fittings and were not dependent on initial concentration and adsorbent doses. pHzpc of the adsorbent was evaluated as 4.2 ± 0.1, and below that pH the adsorbent surface is positively charged. Adsorption of Cr(VI) was found highly pH-dependent, and the removal efficiency dropped sharply from 95 to 10% when pH of the system changed from 2 to 5. The surface functional groups of tea-leaves waste (before and after adsorption) were analyzed by Fourier transform infrared (FTIR) and the amine groups were found to take part in the adsorption of Cr(VI). The experimental result inferred that electrostatic attraction between the surface and the species is one of the major adsorption mechanisms for binding metal ions to the tea-leaves waste. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||