Synthesis of Multicomponent Separation Systems

Liu, Y. A. and Williams, D. C., "Optimal Synthesis of Heat-Integrated Multicomponent Separation Systems and Their Control System Configurations," Proc. of the 1981 Summer Computer Simulation Conf., Washington, D.C., pp. 238-248, published by ISA, Research Triangle Park, NC, July (1981). 

The economics of the various methods that are employed to sequence multicomponent columns have been studied. For example, the separation of three-, four-, and five-component mixtures has been considered (44) where the heuristics (rules of thumb) developed by earlier investigators were examined and an economic analysis of various methods of sequencing the columns was made. The study of sequencing of multicomponent columns is part of a broader field, process synthesis, which attempts to formalize and develop strategies for the optimum overall process (45) (see Separation systems synthesis). 

Human CYPs are multicomponent enzyme systems, requiring at a minimum the CYP enzyme component and a reductase component to be functional. The reductase requires a reduced nicotinamide cofactor, typically NADPH, and this cofactor must be regenerated to provide a steady supply of reducing equivalents for the reductase. Regeneration is accomplished with a separate substrate and enzyme. Glucose-6-phosphate and glucose-6-phosphate dehydrogenase have been widely used for this purpose. The overall complexity of the reaction mixtures and their cost have been barriers to the widespread use of recombinant human CYPs for metabolite synthesis in the past. 

For zeotropic mixtures, the main difficulty of the solution of synthesis task consists of the large number of alternative sequences that have to be calculated and compared with each other in terms of expenditures. This number greatly increases when the number of the products into which the mixture should be separated increases. The best sequence (or several sequences with close values of expenditures) depends on the concentrations of the components in the mixture under separation and on the field of phase equilibrium coefficients of the components in the concentration simplex. To ensure the solubility of the task of synthesis for multicomponent zeotropic mixtures, it is necessary to create a program system that would include as main modules programs of automatic design... 

The theory of trajectory bundles described in Chapters 5 and 6 ensures the possi-bihty of identification of all feasible splits of multicomponent azeotropic mixtures. The software for synthesis of separation units for multicomponent azeotropic mixtures should include, besides the module of identification of feasible splits, a module of preliminary selection of these splits (i.e., choice of the most interesting splits, a module of determination of necessary recycle flow rates, a module of choice of entrainers, and also modules entering into the system of synthesis for zeotropic mixtures). 

There are two major approaches for the synthesis of crystallization-based separation. In one approach, the phase equilibrium diagram is used for the identification of separation schemes (For example Cisternas and Rudd, 1993 Berry et al., 1997). While these procedures are easy to understand, they are relatively simple to implement only for simple cases. For more complex systems, such as multicomponent systems and multiple temperatures of operation, the procedure is difficult to implement because the graphical representation is complex and because there are many alternatives to study. The second strategy is based on simultaneous optimization using mathematical programming based on a network flow model between feasible thermodynamic states (Cisternas and Swaney, 1998 Cisternas, 1999 Cisternas et al. 2001 Cisternas et al. 2003). 

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