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Conceptual design of dedicated batch versus continuous processing in multireaction step processes
Typically agricultural chemicals, specialty chemicals, and pharmaceuticals production have low production rates and a number of reactions followed by solid/liquid separations; in addition, the reaction intermediates are generally not commercially available. Therefore, the complete process must be designed. A systematic procedure to synthesize flowsheets for this type of process was explored, expanding the methodology originally developed by Malone and Iribarren (Iribarren et al. 1994) and Douglas (1985, 1988) for liquid/vapor processes.^ Initially, the continuous process is considered. To better understand the interactions in and the differences between crystallization flowsheets, crystallization alternatives were examined for Itaconic Acid, a single reaction step process. The results indicate that the crystallization alternatives had similar costs.^ Subsequently, the batch process was investigated and compared to the continuous process. In the Itaconic Acid process, the major economic trade-offs were similar and the economically dominant design variables (crystal sizes) as well as the most important parameter (crystallization kinetics exponent) were the same for both types of processing. A second case study, the solid/liquid units in the production of Fenvalerate, a multireaction step process, also had similar results. In addition, the conventional rule-of-thumb for type of processing (indicating a preference for batch process at low production rates and for continuous process at high production rates) was confirmed for Itaconic Acid. However, due to the structure of the Fenvalerate process (high conversions favored), the batch process always had the lower cost.^ Finally, the merging of batch unit operations was studied. In both the Itaconic Acid and the Fenvalerate processes, the merged processes had large economy-of-scale savings compared to the batch process and the best alternative merged all possible units.^ This design methodology provides useful insights into process synthesis; identifying flowsheet alternatives, economic trade-offs, and dominant design variables and parameters in a systematic fashion. It is believed that the results obtained in these case studies by the application of this procedure are typical for low production rate, solid/liquid, multireaction step processes. These case studies indicate that the economics in this type of process are relatively insensitive to the structure of the crystallization flowsheet, but are extremely sensitive to the particulars of the crystallization (the crystal size and the crystallization kinetics). ^
Christine Barner Seymour,
"Conceptual design of dedicated batch versus continuous processing in multireaction step processes"
(January 1, 1995).
Electronic Doctoral Dissertations for UMass Amherst.