Phase reactive binary mixtures

Overview of Theoretical Studies on Phase Separation Kinetics of Nonreactive and Reactive Binary Mixtures... 

H. C. (1996) Phase segregation dynamics of a chemically reactive binary mixture. Phys. Rev. E, 54, R2212-R2215. 

N. (1995) Monte-carlo simulations of phase separation in chemically reactive binary mixtures-comment. Phys. Rev. Lett., 75, 1674 (b) see, also Carati, D. and Lefever, R. (1997) Chemical freezing of phase separation in immiscible binary mixtures. Phys. Rev. E, 56, 3127-3136. 

We emphasize that when the C component is absent (tj) = 0) the above model reduces to the well-known model for block copolymers [56-59] or reactive polymer blends [9,10]. In this case, the evolution of the reactive AB system is governed solely by Eq. (8.2) and the morphology of the mixture resembles the lamellar structure formed by micro phase-separated symmetric diblock copolymers [9]. (In the context of our work, we only consider reactive blends, and do not consider diblock copolymers.) When r+ = r = r for such reactive binary mixtures, a linear stability analysis gives the growth rate, w k), for the kth mode of the fluctuations of the order parameter around the homogeneous value cp = 0 as ... 

For process simulation, the thermodynamic properties of the quaternary mixture 1-hexanol + acetic add + hexyl acetate + water have to be known. The vapor-Uquid equilibrium model of that quaternary mixture is, as usual, parameterized based on information from the binary systems alone. There are six binary mixtures for a quaternary mixture, two of which are reactive in our example. The special challenges in the experimental determination of phase equilibria in reactive systems will be discussed later. Using typical G models, at least 12 parameters have to be adjusted to experimental binary data or estimated. Additionally, at least the... 

If studies on the electrode interface in first generation polymer electrolyte cells are scarce, they are practically non-existent in second and third generation polymer electrolyte cells, i.e. in those systems which are currently proposed as the most promising for the development of multi-purpose LPBs. However, lithium passivation in these multi-phase, multi-component cell systems is expected to be even more severe than that experienced with the cells based on the relatively simple membranes formed by binary mixtures of PEO and lithium salts. In fact, the second and third generation membranes are commonly based on liquid additives and plasticizers (e.g. propylene carbonate, see Chapter 3) which are very reactive with the lithium metal electrode... 

The phase behaviour of the binary mixtures between the potential solvents and the system components (reactants and reaction products) should be studied first later the study should be extended to the multicomponent reactive mixtures for definition of feasible operating regions. 

Reactive absorption processes occur mostly in aqueous systems, with both molecular and electrolyte species. These systems demonstrate substantially non-ideal behavior. The electrolyte components represent reaction products of absorbed gases or dissociation products of dissolved salts. There are two basic models applied for the description of electrolyte-containing mixtures, namely the Electrolyte NRTL model and the Pitzer model. The Electrolyte NRTL model [37-39] is able to estimate the activity coefficients for both ionic and molecular species in aqueous and mixed solvent electrolyte systems based on the binary pair parameters. The model reduces to the well-known NRTL model when electrolyte concentrations in the liquid phase approach zero [40]. 

Sundmacher and Qi (Chapter 5) discuss the role of chemical reaction kinetics on steady-state process behavior. First, they illustrate the importance of reaction kinetics for RD design considering ideal binary reactive mixtures. Then the feasible products of kinetically controlled catalytic distillation processes are analyzed based on residue curve maps. Ideal ternary as well as non-ideal systems are investigated including recent results on reaction systems that exhibit liquid-phase splitting. Recent results on the role of interfadal mass-transfer resistances on the attainable top and bottom products of RD processes are discussed. The third section of this contribution is dedicated to the determination and analysis of chemical reaction rates obtained with heterogeneous catalysts used in RD processes. The use of activity-based rate expressions is recommended for adequate and consistent description of reaction microkinetics. Since particles on the millimeter scale are used as catalysts, internal mass-transport resistances can play an important role in catalytic distillation processes. This is illustrated using the syntheses of the fuel ethers MTBE, TAME, and ETBE as important industrial examples. 

Formaldehyde is a low-boiling substance with a normal boiling point of approx. 254 K. It is not stable in its pure form, so it usually occurs in aqueous or methanolic solutions. Mixtures of formaldehyde and water or alcohols are not binary solutions in the usual sense, as formaldehyde reacts with both of them to a wide variety of species which are not stable as pure compounds themselves. Therefore, the standard procedure for building up a thermodynamic model by setting up the pure component properties and the binary interaction parameters fails in this case. The formaldehyde-water-methanol system is a good example freactive phase equilibrium, where a special model has to be developed. This has been done by the group of Maurer [2-6]. 

This chapter presents some important nongelling binary associating mixtures. Throughout this chapter, we assume the pairwise association of reactive groups, the strength of which can be expressed in terms of the three association constants for A-A, B-B, and A-B association. We apply the general theory presented in Chapter 5 to specific systems, such as dimerization, hnear association, side-chain association, hydration, etc. The main results are summarized in the form of phase diagrams. 

Bimolecular elementary processes involve the collisions of two molecules, which we discussed in Chapter 9. We now show that such a process obeys a second-order rate law. The collision rate in a gas is very large, typically several billion collisions per second for each molecule. If every collision in a reactive mixture led to chemical reaction, gas-phase reactions would be complete in nanoseconds. Since gas-phase reactions are almost never this rapid, it is apparent that only a small fraction of all collisions lead to chemical reaction. We make the important assumption The fraction of binary collisions... 

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