The design of separation processes, chemical and biochemical product design and certain other fields, e.g. material science and environmental assessment, often require thermodynamic data, especially phase equilibria. Table 1.1 summarizes the type of data needed in the design of various separation processes. The importance of thermodynamics can be appreciated as often more than 40% of the cost in many processes is related to the separation units. 1 The petroleum and chemical industries have for many years been the traditional users of thermodynamic data, though the polymer, pharmaceutical and other industrial sectors are today making use of thermodynamic tools. Moreover, thermodynamic data are important for product design and certain applications in the environmental field, e.g. estimation of the distribution of chemicals in environmental ecosystems. Already several commercial simulators have a wide spectrum of thermodynamic models to choose from and companies often use the so-called 'decision or selection trees', see Figure 1.1, for selecting models suitable for specific applications, either those developed in-house 2 or those suggested by the simulator providers. 3 Still, it is often questioned whether sufficient data and/or suitable models are available for a particular process or need. Opinions differ even within the same industrial sector and they should also be seen in relation to the time that the various statements have been made. 4,5 The needs, even within the same industrial sector, are not always the same. Dohrn and Pfohl 6 explain why, in the chemical industry, the answer to the question about the availability of thermophysical data can be almost anything from 'we have enough data', or 'we don't have enough data', to 'we have too much data'. These statements can be respectively justified based on the availability of suitable models in process simulators, the existence of difficult separations or the many databases which may be at hand. Data for multicomponent mixtures especially can be scarce and costly even for well-defined mixtures of industrial importance such as water-hydrocarbon-alcohols or glycols. Moreover, Dohrn and Pfohl 6 illustrate, using examples, how similar models may yield different designs even for rather 'simple' mixtures, e.g. in the case of ethylbenzene/styrene with the SRK equation of state. In an earlier study, Zeck 7 presents thermodynamic difficulties and needs, as seen from the chemical industry's point of view. These are summarized in Table 1.2.
As both Tables 1.1 and 1.2 illustrate, different types of phase equilibria data or calculations are needed depending on the problem, especially the separation type involved. The fundamental phase equilibria Thermodynamic Models for Industrial Applications: From Classical and Advanced Mixing Rules to Association Theories Georgios M. Kontogeorgis and Georgios K. Folas