Multicomponent separation processes property models

The fundamental adsorptive properties governing the performance of the separation processes are the multicomponent equilibria, kinetics, and heat. A large volume of data, as well as models to describe them, exist in the published literature only for adsorption of pure gases and binary liquid mixtures. Binary gas adsorption data are sporadic. Multicomponent data are rare. Existence of adsorbent heterogeneity can introduce severe complexity in the multicomponent adsorption behavior. 

A better insight into composition of phases along the separation process is provided by multicomponent process simulation as it can be carried out with commercial process simulating programs, such as ASPEN-h. As usual, the process is separated into theoretical stages. Normally, ASPEN+ provides thermodynamic models and calculates thermodynamic properties such as the distribution coefficients and separation factors. As the accuracy of these results is not sufficient for a design analysis in many cases, distribution coefficients (and if necessary solubilities) can be provided by a user-defined module which uses empirical correlations for these values. 

Reliable models of reactive separation processes have to be based on a sound knowledge of the properties of the reacting fluid. Thermodynamics provides both the experimental methods and models to study and describe these properties. Different aspects of their use in RD process design are discussed, namely the question of sensitivity to inaccurate input data, predictions of properties of multicomponent mixtures from binary data, benefits of thermodynamically consistent models, and consequences of inconsistent models. These topics are addressed using examples from different esterifications and intrinsically chemically reactive systems. 

In most commercial process simulators, model parameters for pure component properties and binary parameters can be found for a large number of compounds and binary systems. However, the simulator providers repeatedly warn in their software documentations and user manuals that these default parameters should be applied only after careful examination by the company s thermodynamic experts prior to process simulation. For verification of the model parameters again, a large factual data bank like the DDE is the ideal tool. The DDE allows checking all the parameters used for the description of the pure component properties as a function of temperature and of the binary parameters of a multicomponent system by access to the experimental data stored. On the basis of the results for the different pure component properties and phase equilibria, excess enthalpies, activity coefficients at infinite dilution, separation factors, and so on, the experienced chemical engineer can decide whether all the data and parameters are sufficiently reliable for process simulation. 

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