A primary requirement of any reactor design or process development computation is knowledge of the major properties of the compounds involved. Although most of these can be obtained from the literature, there is still a need to estimate them from correlations. The main difficulty is the large number of correlations proposed for a given property and the need to select the best from among them. No single correlation works with equally high precision under all conditions. On the other hand, correlations that can be used with acceptable levels of precision over a wide range of conditions are also available for a number of properties. The slight sacrifice of accuracy is often more than compensated for by the ease and generality of application of these methods. Our emphasis here will be on such correlations. For a detailed treatment, reference should be made to books devoted exclusively to properties estimation. The book by Reid, Prausnitz, and Poling (1987), along with its earlier versions by Reid and Sherwood (1958, 1966) and Reid, Prausnitz, and Sherwood (1977), and the works of Janz (1958), Hansch and Leo (1979), and Lyman, Reehl, and Rosenblatt (1982) are noteworthy. The following methods selected for a few properties are based in part on the recommendations contained in these treatises. The two most important bases for formulating correlations for estimating the properties of organic compounds (indeed of any compound) are the law of corresponding states (LCS), and the method of group contributions (GC). LCS is based on the concept that all substances exhibit identical properties under conditions equally removed from their critical states. The “equally removed” state for any property is usually expressed as the ratio of its value at that state to the value at the critical state and is referred to as the reduced property. Thus Tr — T/TC, Pr = P/PC, Vr = V/Vc and ηr = η/ ηc are the reduced temperature, pressure, volume, and viscosity, respectively. If the simple ideal gas law PV/RgT — Z, where Z is the compressibility, can be recast in terms of reduced properties as PrVt/RgTr = Z/ZC, then the PVT behavior of all fluids can be represented as Pr versus Tr plots for different values of Zr.
Approach for the description of PvT behavior of thermoplastics at high cooling rates
