Interaction between reaction/separation sections

In this section an attempt is made to construct a general scheme into which as many as possible of the conclusions reached about macrozwitterion polymerization can be fitted. It has already been pointed out that chemical reactions between electrophilic and nucleophilic molecules which yield charged products or intermediates have been studied by organic chemists for many years. For a polymerization to occur, a reaction pathway for consecutive addition of at least one molecule to the bipolar species must be available. Such reactions are properly the domain of the polymer chemist. Formation of high molecular weight polymer requires that charges be separated until there is no longer any inductive or electrostatic interaction between them. Various authors have realized that this cannot be accomplished with the enthalpy, released when monomer bonds are broken. 

The reader will recognize the two quantities i and 2 as the degree of advancement introduced by DeDonder (W) they express the two degrees of freedom or the two dimensionality of the subspace to which the composition point is confined during the course of the reaction. Thus, in addition to the constraints introduced by the conservation of mass and by irreversible steps discussed in Section IV,A,4, we have constraints introduced by the interaction between the various molecular species. Constraints may be thought of as invariants of the system they separate the entire reaction space into subspaces characterized by constant values of the invariants. No point in composition space is accessible to another point unless they have the same value for all invariants. 

It is a well-known and accepted fact that complicated interactions between chemical reaction and separation make difEcult the design and control of RD colunms. These interactions originate primarily from VLL equilibria, VL mass transfer, intra-catalyst diffusion and chemical kinetics. Moreover, they are considered to have a large influence on the design parameters of the unit e.g. size and location of (non)-reactive sections, reflux ratio, feed location and throughput) and to lead to multiple steady states (Chen et al, 2002 Jacobs and Krishna, 1993 Giittinger and Morari, 19996,a), complex dynamics (Baur et al., 2000 Taylor and Krishna, 2000) and reactive azeotropy (Doherty and Malone, 2001 Malone and Doherty, 2000). 

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