Analysis of heteroazenotropic systems
Author(s)Tolsma, John E
Massachusetts Institute of Technology. Dept. of Chemical Engineering.
Paul I. Barton.
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Separation processes are used extensively in the chemical process industries and by far the most common of these is distillation. Although several alternative strategies have been developed, distillation will likely remain dominant particularly for the largescale separation of non-ideal liquid mixtures. A topic of particular interest in recent years has been heterogeneous azeotropic distillation or heteroazeotropic distillation. This technique is commonly employed to separate azeotropic mixtures by introducing a heterogeneous entrainer that causes liquid-liquid phase separation. Although the design and simulation of heteroazeotropic systems is far more complicated than its homogeneous counterpart, heteroazeotropic distillation is often preferred due to the ease of recovery of the entrainer and the crossing of distillation boundaries due to the liquid-liquid phase split in the decanter. The topic of this thesis is the analysis of heteroazeotropic systems. Specifically, an algorithm has been developed which, under reasonable assumptions, will compute all homogeneous and heterogeneous azeotropes present in a multicomponent mixture predicted by the phase equilibrium model employed. The approach is independent of both the particular representation of the nonideality of the mixture and the topology of the liquid-liquid region. Furthermore, the approach can be readily extended to handle any number of liquid and/or solid phases in equilibrium. Moreover, the heteroazeotrope finding algorithm can be extended to explore the phase equilibrium structure of a multicomponent mixture under system and/or property model parameter variation, including the detection of incipient homogeneous and heterogeneous azeotopes and the determination of the bifurcation values of the parameters where they appear, disappear, or switch between each other. The ability to predict the incipient homogeneous and heterogeneous azeotropes that may appear under different conditions or property parameter values can be incorporated into design algorithms to expand the number of alternative designs. Furthermore, the ability to systematically and efficiently explore the phase equilibrium structure is a valuable tool when fitting property model parameters, allowing the experimentalist to rapidly explore the capabilities and limitations of the phase equilibrium model. The techniques mentioned above are useful when analyzing heteroazetropic systems for design purposes. The second product of this thesis improves the efficiency of the actual simulation of the heteroazeotropic system (or any system for that matter). Specifically, a new class of automatic differentiation methods, known as 'subgraph reduction methods', have been developed that offer substantial improvement over existing techniques both in the increase in speed of the derivative evaluation and the reduction in memory required to store and evaluate the Jacobian matrix of a sparse system of equations. Furthermore, a variant of the subgraph reduction approach has been custom-tailored for use within an interpretive simulator architecture that dramatically increases speed and reduces memory requirements compared to other techniques commonly employed in this environment.
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1999.Includes bibliographical references (p. 305-322).
DepartmentMassachusetts Institute of Technology. Department of Chemical Engineering
Massachusetts Institute of Technology