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A geometric approach for the conceptual design of polymerization reactor systems
In designing a reactor system to produce a resin, the limits of feasible molecular weights and conversions provide targets and alternatives for the design and a rapid assessment of feasibility. To find the feasibility limits for polymers a geometric method called the attainable region has been developed in terms of quantities which can be specified during production: moments of the molecular weight distribution for homopolymers and average compositions for copolymers. These quantities can be related to properties and calculated in simulations. However, the key is to find the limits of these quantities without fully specifying the reactor system. From the attainable regions for free-radical polymerizations, maximum and minimum molecular weights and the reactor systems corresponding to these limits have been determined. In particular, it is found that isothermal polymerizations can produce molecular weights an order of magnitude greater than adiabatic systems. The highest molecular weights are substantially above those typically produced, and so products with different properties than those currently made may be possible. From the feasibility limits it was determined that the highest molecular weights are produced in an isothermal continuous stirred tank reactor, and when only adiabatic reactors are considered the maximum molecular weight is produced in a plug-flow reactor. These extremes of perfect backmixing and plug-flow arise because the type of mixing which produces the highest molecular weight depends on whether molecular weight increases or decreases with conversion. For copolymers, the attainable region shows the limiting reactor systems and feasible average compositions. The results show that through a simpler method one can find the feasible copolymer compositions. These limiting compositions are bounded by the feed composition and the product of a plug-flow (or batch) reactor. Along with the attainable regions of molecular weights and copolymer compositions, other dependent variables can be determined and developed into "corresponding regions." These regions show in two dimensions the limits for dependent variables when finding the feasibility limits of an attainable region. In the case of homopolymers, corresponding regions show the polydispersities, initiator concentrations, and residence times for the associated attainable molecular weights. For copolymers the corresponding regions show the conversions, molecular weights, and residence times for attainable copolymer compositions. These regions can be used to find alternatives for reactor system designs. Thus, with these methods, one can find the feasible products, target reactor systems for achieving the limiting products, and generate alternatives for reactor systems that meet product specifications.
Smith, Raymond L, "A geometric approach for the conceptual design of polymerization reactor systems" (1998). Doctoral Dissertations Available from Proquest. AAI9909221.