Viscosity group contribution models

The performance of many process equipment encountered in crystallization practice is often profoundly affected by the flow properties of the liquid media. Heat transfer, for example, may be severely impeded in thick sluggish liquors or magmas crystallization may occur only with difficulty, and filtration and washing of crystalline product may be impaired (Mullin, 1961). Since viscosity is a function of temperature the viscosity at the average temperature of crystallization is considered. The viscosity of the solvent can be estimated using the following group contribution model (ICAS, 2003)... 

Overall the density of ionic liquids is somewhat easier to predict as the function of temperature and pressure than the viscosity, which explains why many group contribution models are now already described into the literature within a good accuracy. However, as with other physical properties impurities can have a significant effect. It was... 

Viscosity is a difficult property to predict and flexible predictive models will require further experimental data in order to obtain a better understanding of this property. Many prediction methods are available in literature for the viscosity of pure component and their mixtures [88] most of these are generally based on group contributions (e.g., the Orrick-Erbar method [89], the Sastry-Rao method [90], and the UNIFAC-VISCO method [91]), the corresponding states concept (e.g., Przezdziecki and Sridhar [92], Chatter] ee and Vasant [93], Teja and Rice [94, 95],... 

Prediction models for ionic conductivity and viscosity of ILs using quantitative structure property relationships coupled with the descriptors of group contribution type were introduced [155], The polynomial expansion model based on the type of cation, length of side chain, and type of anion was applied to the expression of IL properties. Parameters of these polynomial expansion models were determined by means of a genetic algorithm. The reverse design of ILs was also tested [155],... 

The model of Cao et al. [26] is based on Eyring s rate theory, and has then been formulated [27] in such a way that one obtains a group contribution viscosity model for mixtures based on the UNIFAC prediction method for activity coefficients. Their expression for the dynamic viscosity of a pure liquid is ... 

Mixing rules with an excess function. Ratcliff and Khan calculate the viscosity of a mixture based on the absolute viscosities of components it is necessary to include an excess function to account for deviation from ideality. Wedlake and Ratcliff reported a model based on an excess quantity that is calculated from a structural constant, the number of groups in molecular species, and the individual group contribution of each group in the mixture. 

A major use of theoretical and computational methods is the prediction or validation of observed experimental data. New applications involving quantitative structure-property relationships (QSPR) and quantitative structure-retention relationships (QSRR) for the prediction of various physicochemical properties have also been reported. A series of allg ltributylphosphonium chloride ionic liquids has been synthesized and their experimental density and viscosity data interpreted using QSPRs and group contribution methods. A QSRR study has also been performed on a series of new phosphoramidic acid derivatives. Their retention factors Id ) were predicted using a model obtained from a set of previously-synthesized phosphoramidic acid derivatives. 

Luciani et al. (1998) critically examined the experimental methods used for the measurements of the interfacial coefficient in polymer blends as well as the theoretical models for its evaluation. A new working relation was derived that makes it possible to compute the interfacial tension from the chemical structure of two polymers. The calculations involve the determination of the dispersive, polar, and hydrogen-bonding parts of the solubility parameter from the tabulated group and bond contributions. The computed values for 46 blends were found to follow the experimental ones with a reasonable scatter of +/— 36 %. The authors mentioned also that since many experimental techniques have been developed for low-viscosity Newtonian fluids, most were irrelevant to industrial polymeric systems. For their studies, two were selected capillary breakup method and a newly developed method based on the retraction rate of deformed drop. 

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