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  • Chemistry  (8)
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  • 1
    Digitale Medien
    Digitale Medien
    A group contribution approach to computer-aided molecular design (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 1318-1332 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A flexible and structured methodology for the computer-aided molecular design (CAMD) by the group contribution approach is presented. The proposed CAMD algorithm takes the following four steps: 1. preselect groups and target properties; 2. generate only a feasible set of compound structures in an optimal fashion; 3. predict properties for the screening of the set of feasible compound structures; and finally 4. select/design the compound. Since the success of any CAMD algorithm depends to a large extent on its ability to predict/compute the needed properties, the importance of the choice and applicability of these methods is considered along with the computational aspects related to the development of a computer program based on the proposed methodology. Finally, the scope of CAMD technology is highlighted using several practical examples.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690370905
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  • 2
    Digitale Medien
    Digitale Medien
    Miscibility of polymer blends with engineering models (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 3170-3180 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The miscibility behavior of polymer blends that do not exhibit strong specific interactions is examined. Phase equilibrium calculations are presented with the van der Waals equation of state and three group-contribution models (UNIFAC, Entropic-FV, and GC-Flory). Performance of these models is also compared. The van der Waals equation of state was recently shown to accurately correlate and predict vapor-liquid and liquid-liquid equilibria for binary polymer/solven solutions. In this work, it is demonstrated that it correlates the upper critical solution behavior of polymer blends with excellent accuracy using the usual mixing and combining rules and a single temperature- and composition-independent binary interaction parameter. This interaction parameter can be predicted via a generalized expression that uses only the pure component equation-of-state parameters. Using this generalized expression, the upper critical solution temperature can be predicted with an average error of less than 45°C. The van der Waals equation of state can correlate the lower critical solution behavior of polymer blends, using an interaction parameter that is a linear function of temperature. The UNIFAC and Entropic-FV models, in general, are able to predict qualitatively the phase behavior of polymer blends, but quantitative predictions of the critical solution temperatures are not achieved. The GC-Flory equation of state fails to predict the upper critical solution behavior in polymer blends.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690421117
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  • 3
    Digitale Medien
    Digitale Medien
    Equations of state and activity coefficient models for vapor-liquid equilibria of polymer solutions (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1711-1727 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Four noncubic equations of state, (EOS) and five activity coefficient models are applied to binary polymer and solvent solutions. Solvent activities at intermediate concentrations and equilibrium pressures are predicted with the perturbed-soft-chain theory (PSCT), group-perturbed-soft-chain theory, (GPSCT), group-contribution-lattice fluid (GCLF) EOS, GC-Flory EOS, UNIFAC-FV, entropic-FV and GK-FV models, “new” UNIFAC, and modified Flory-Huggins model. Free-volume activity coefficient models (UNIFAC-FV, entropic-FV) are simpler and, when applied to polymer solutions, more accurate than the EOS. Activity coefficient models are restricted to low-pressure calculations and require accurate values of pure-component volumes. Mixture parameters for activity coefficient models and GC-Flory EOS have been previously evaluated from experimental vapor-liquid equilibrium data for mixtures with only low-molecular-weight compounds. The GC-Flory EOS, though more complicated than activity coefficient models, provides equally good or in some cases better predictions. The application of GC-Flory EOS developed as an activity coefficient model is restricted to low-pressure calculations. On the other hand, PSCT and GCLF developed as “true” EOS provide reliable equilibrium predictions using mixture parameters evaluated solely from pure-component properties together with standard mixing and combining rules. PSCT EOS performs generally better than GCLF EOS for polymer solutions considered in this study.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690401012
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  • 4
    Digitale Medien
    Digitale Medien
    Letters to the Editor (1988)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 34 (1988), S. 171-172 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690340126
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  • 5
    Digitale Medien
    Digitale Medien
    Thermodynamic consistency using orthogonal collocation or computation of equilibrium vapor compositions at high pressures (1975)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 21 (1975), S. 49-57 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The numerical method of orthogonal collocation is used within a thermodynamically consistent framework to calculate equilibrium vapor compositions from P-T-x data for binary systems. The method may be used for isothermal or isobaric data in both the normal liquid and in the critical region, and it applies to any choice of standard states.To use the method it is necessary to have experimental or estimated values of vapor phase fugacity coefficients for both components in the mixture and liquid molar volumes (isothermal case) or heats of mixing (isobaric case). If vapor composition data are available, each set of P-T-x-y data may be checked for thermodynamic consistency by comparing y (experimental) with y (calculated). Illustrative calculations are given. The method is shown to provide an excellent procedure for obtaining Henry's constants from P-x data for systems with one noncondensable component.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690210105
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  • 6
    Digitale Medien
    Digitale Medien
    Group-contribution estimation of activity coefficients in nonideal liquid mixtures (1975)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 21 (1975), S. 1086-1099 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A group-contribution method is presented for the prediction of activity coefficients in nonelectrolyte liquid mixtures. The method combines the solution-of-functional-groups concept with a model for activity coefficients based on an extension of the quasi chemical theory of liquid mixtures (UNIQUAC). The resulting UNIFAC model (UNIQUAC Functional-group Activity Coefficients) contains two adjustable parameters per pair of functional groups.By using group-interaction parameters obtained from data reduction, activity coefficients in a large number of binary and multicomponent mixtures may be predicted, often with good accuracy. This is demonstrated for mixtures containing water, hydrocarbons, alcohols, chlorides, nitriles, ketones, amines, and other organic fluids in the temperature range 275° to 400°K.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690210607
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  • 7
    Digitale Medien
    Digitale Medien
    Correlation of pure component Gibbs energy. Using UNIFAC group contribution (1979)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 203-205 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The UNIFAC group contribution method has already proved highly valuable for predicting excess Gibbs energies of liquid mixtures and hence vapor-liquid equilibria. The solution of groups concept is extended to cover the total Gibbs energy of any system, pure or mixed, relative to a well-defined standard state. The result is a correlation which is capable of predicting simultaneously pure component vapor pressures and standard Gibbs energies of formation and mixture vapor-liquid equilibrium compositions. The results presented strongly support the approach and indicate that the method should be further developed.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690250130
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  • 8
    Digitale Medien
    Digitale Medien
    Eine Übersicht zur Berechnung von Phasengleichgewichten mit Hilfe der UNIFAC-Methode (1980)
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 52 (1980), S. 724-732 
    Details
    ISSN: 0009-286X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Zur Auslegung von Trennanlagen und für viele andere praktische Zwecke benötigt man die quantitative Kenntnis des Phasengleichgewichts. Dieses Phasengleichgewicht kann mit Hilfe von neueren Ansätzen für die Gibbssche Exzeßenthalpie recht gut aus den binären Konstanten berechnet werden. Da jedoch die Anzahl der technisch interessanten Systeme sehr groß ist, wird man in vielen Fällen nicht für alle beteiligten binären Systeme Phasengleichgewichtsdaten in der Literatur finden. In diesen Fällen ist es notwendig, die benötigte Information mit Hilfe allgemein anwendbarer Methoden vorauszuberechnen. Zur Zeit liefern die Inkrementenmethoden (ASOG, UNIFAC) die besten Resultate. Bei diesen Inkrementenmethoden wird die flüssige Phase wie eine Mischung von funktionellen Gruppen behandelt. Dies hat den Vorteil, daß eine große Zahl technisch interessanter Systeme mit einer relativ geringen Anzahl von Parametern, die die Wechselwirkung zwischen den Gruppen beschreiben, berechnet werden kann, da die Anzahl der verschiedenen Strukturgruppen viel kleiner ist als die Anzahl der möglichen unterschiedlichen Moleküle. In diesem Übersichtsartikel sollen die Möglichkeiten der UNIFAC-Methode zur Berechnung von Phasengleichgewichten demonstriert werden. Die UNIFAC-Methode heute für Nichtelektrolytsysteme im Temperaturbereich von 275 bis 425 K und Drücke bis 10 bar anwendbar.A survey of the calculation of phase equilibria with the aid of the UNIFAC-Methode. In the design of diffusional separation processes and for many other practical purposes one needs quantitative estimates of phase equilibrium compositions. These compositions can today be predicted with good results using modern, two-parameter models for the excess Gibbs energy. However, since the number of different multicomponent mixtures of interest in chemical technology is very large, it is in practise often not possible to find experimental data in the literature for all the possible binary combinations. In these cases it is necessary to use a predictive approach. Today, group-contribution methods such as ASOG and UNIFAC may be used with confidence to predict liquid phase excess Gibbs energies. In these methods, the mixture is assumed to consist not of molecules but of the functional groups which, when added form the parent molecules. This has the advantage that a large number of mixtures of interest in chemical technology can be described in terms of relatively few parameters characterizing the interactions between the groups. This review article demonstrates the application of the UNIFAC method to various practical problems within phase equilibria. The UNIFAC method applies to mixtures of nonelectrolytes in the temperature range of 275-425 K and at pressures up to 10 bar.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/cite.330520910
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