Viscosity of Coal-Derived Liquids. 2. Application of the Model to Coal Liquid Fractions

Abstract

The group contribution viscosity model for pure coal model liquids described in a previous paper (Energy Fuels 1995, 10, 333) has been successfully extended to binary liquid mixtures of coal model compounds, and a procedure has been developed to use the model for computation of viscosities of coal-derived liquids. It is shown that simple mixing rules, or even a pseudopure component model, is adequate to estimate mixture viscosity within reasonable accuracy for these compounds. For application of the model to coal-derived liquids, a data set on SRC-II coal liquid cuts available in the literature has been used. Sufficient chemical analysis data were available for these cuts to make the application of our model possible. The computational procedure involved transformation of the analytical data into functional group characterization of the coal liquid. Central to this procedure was the definition of types and distributions of various ring structures in multiring compounds. When compared to limited studies available in the literature, this model predicts viscosities of coal liquids with better accuracy. Overall, this is the first viscosity model that has been developed for the type of structures that exist in coal-derived liquids, and provides a reasonably accurate procedure for computation of viscosities of narrow boiling coal liquid cuts, a property that is necessary in designing efficient coal liquefaction processes.

Empirical Approach for Predicting Viscosities of Liquid Hydrocarbon Systems: Defined Compounds and Coal Liquids and Fractions

“…However, additional high temperature viscosity data of light and middle distillates of coal liquid oils are needed to evaluate the reliability of the model at high temperatures. Despite these limitations, the developed model compares favorably, in terms of its accuracy, with the method of Kabadi and Palakkal for SRC-II coal liquid fractions and the method of Sharma and Goel for seven other coal liquid oils . Figures and present the comparison of the developed method with the method of Sharma and Goel and Kabadi and Palakkal, respectively.…”

“…Despite these limitations, the developed model compares favorably, in terms of its accuracy, with the method of Kabadi and Palakkal for SRC-II coal liquid fractions and the method of Sharma and Goel for seven other coal liquid oils . Figures and present the comparison of the developed method with the method of Sharma and Goel and Kabadi and Palakkal, respectively. The temperature and pressure ranges of coal liquids used for comparing the developed method with the above-mentioned methods are shown in Table .…”

“…The temperature and pressure ranges of coal liquids used for comparing the developed method with the above-mentioned methods are shown in Table . The poor predictability of the method of Kabadi and Palakkal was attributed to the inaccuracies in estimating one of the input parameters, that is, molecular weight, while the slight inaccuracies in estimating viscosity correction factors required for the correlation may have resulted in poor prediction of some of the coal liquids by the method of Sharma and Goel …”

“…Most of the currently available methods for predicting viscosities of liquids, specifically synthetic fuels, are based on semitheoretical or empirical methods. ,− This is because there are no widely accepted theoretical methods for predicting liquid viscosities . Moreover, most of the available methods for predicting the viscosities of undefined hydrocarbon liquids require too many parameters that are not readily available and cannot be accurately estimated or cannot be applied to predict viscosities at various pressures. − ,, Moreover, Riazi and Al-Otaibi claim that a model that uses too many estimated input parameters predicts the viscosities of hydrocarbon systems with significant error …”

“…The group contribution approach proposed by Kabadi and Palakkal was applied to fifteen fractions of Solvent Refined Coal-II (SRC-II) liquid fractions compiled by Gray et al The overall AAD for all the fractions was 25.01%. Moreover, the method of Kabadi and Palakkal requires significant chemical analysis data of coal liquids as input, which are not usually available.…”