Multiple Phases

Multiphase reactors are much more prevalent in industrial practice than single-phase reactors. The behavior of multiphase systems can be very complex. It is not always straightforward to determine whether the reaction takes place in one phase, more than one phase, or at the interface between phases. However, there is one very important case where the locus of reaction is well understood. 

---

The connections between simulation and thermodynamics can be carried further. Simulations can be set up to be constant volume, pressure, temperature, and so on. Some of the most sophisticated simulations are those involving multiple phases or phase changes. These techniques are discussed further in Chapter 7. 

Reactor Internals and Unit Hardware. Requirements for mixing feed components or separating products may determine minimum pilot unit size. If reactants caimot be premixed before they are passed into the reactor, the effectiveness of the inlet distributor in mixing the reactants can markedly affect reactor performance. This is especially tme for gases, multiple phases, or Hquid streams of greatly different kinematic viscosities. 

Electrochemical systems convert chemical and electrical energy through charge-transfer reactions. These reactions occur at the interface between two phases. Consequendy, an electrochemical ceU contains multiple phases, and surface phenomena are important. Electrochemical processes are sometimes divided into two categories electrolytic, where energy is supplied to the system, eg, the electrolysis of water and the production of aluminum and galvanic, where electrical energy is obtained from the system, eg, batteries (qv) and fuel cells (qv). 

Mixing of fluids is a discipline of fluid mechanics. Fluid motion is used to accelerate the otherwise slow processes of diffusion and conduction to bring about uniformity of concentration and temperature, blend materials, facihtate chemical reactions, bring about intimate contact of multiple phases, and so on. As the subject is too broad to cover fully, only a brier introduction and some references for further information are given here. 

Multiple Phases Reaclions between gas/liquid, liquid/liquid, and fluid/solid phases are often tested in CSTRs. Other laboratoiy types are suggested by the commercial units depicted in appropriate sketches in Sec. 23. Liquids can be reacted with gases of low solubili-... 

References to mass transfer are made throughout this section wherever multiple phases are discussed. 

As we have seen, the orientation of crystallites in a thin film can vary from epitaxial (or single crystalline), to complete fiber texture, to preferred orientation (incomplete fiber texture), to randomly distributed (or powder). The degree of orientation not only influences the thin-film properties but also has important consequences on the method of measurement and on the difficulty of identifying the phases present in films having multiple phases. 

The use of inert tracer experiments to measure residence time distributions can be extended to systems with multiple inlets and outlets, multiple phases within the reactor, and species-dependent residence times. This discussion ignores these complications, but see Suggestions for Further Reading. ... 

The physical picture of emulsion polymerization is complex due to the presence of multiple phases, multiple monomers, radical species, and other ingredients, an extensive reaction and particle formation mechanism, and the possibility of many modes of reactor operation. 

Fig. 5. Multiple phases in the reduction of xanthine oxidase by xanthine at pH 8.2. Intensities of the Rapid (circles) and Slow (triangles) molybdenum EPR signals expressed as electron/mole enzyme (i-e. per 2 atom Mo) are plotted as a function of time. Note the changes in the time scale. Rapid freezing was used for reaction times (at 22°) up to 1 sec. and manual mixing for longer times (at 25°) enzyme concentrations (immediately after mixing) were 0.09 mM and 0.13 mM respectively. The enzyme had Activity/A45o 125 corresponding to 63% of active enzyme and 20 mole xanthine/mole enzyme was used. (Data from ref. 67.)...

Bell, R.G., McGregor, D.D. and Despommier, D. (1979) Trichinella spiralis . Mediation of the intestinal component of protective immunity in the rat by multiple, phase-specific, antiparasitic responses. Experimental Parasitology 47, 140-157. 

The multiplication phase the aggregates fall apart to give single strands, which now act as matrices. Complementary copying occurs, accompanied by a number of copying errors. Matrix and replication strand separate. 

Zygourakis (1990 Zygourakis and Markenscoff, 1996) developed a discretized model in which cells are assigned a degradation time, upon exposure to solvent, based on their identity as either drug, polymer, solvent, or void. The initial distribution of cells can be modeled after the microstructure of the polymer matrix and multiple phases are explicitly accounted for. The solution is found numerically. 

Alloys are classified broadly in two categories, single-phase alloys and multiple-phase alloys. A phase is characterized by having a homogeneous composition on a macroscopic scale, a uniform structure, and a distinct interface with any other phase present. The coexistence of ice, liquid water, and water vapor meets the criteria of composition and structure, but distinct boundaries exist between the states, so there are three phases present. When liquid metals are combined, there is usually some limit to the solubility of one metal in another. An exception to this is the liquid mixture of copper and nickel, which forms a solution of any composition between pure copper and pure nickel. The molten metals are completely miscible. When the mixture is cooled, a solid results that has a random distribution of both types of atoms in an fee structure. This single solid phase thus constitutes a solid solution of the two metals, so it meets the criteria for a single-phase alloy. 

Alloys of copper and zinc can be obtained by combining the molten metals. However, zinc is soluble in copper up to only about 40% (of the total). When the content of a copper/zinc alloy contains less than 40% zinc, cooling the liquid mixture results in the formation of a solid solution in which Zn and Cu atoms are uniformly distributed in an fee lattice. When the mixture contains more than 40% zinc, cooling the liquid mixture results in the formation of a compound having the composition CuZn. The solid alloy consists of two phases, one of which is the compound CuZn and the other is a solid solution that contains Cu with approximately 40% Zn dissolved in it. This type of alloy is known as a two-phase alloy, but many alloys contain more than three phases (multiple-phase alloys). 

McAuliffe, C. (1971) GC determination of solutes by multiple phase equilibration. Chem. Tech. 1, 46-51. 

Zimmerman, J.R. and Brittin, W.E. 1957. Nuclear magnetic resonance studies in multiple phase systems Lifetime of a water molecule in an absorbing phase on silica gel. J. Phys. Chem. 61, 1328-1333. 

There are multiple phases involved in the safety assessment portion of the discovery, development and marketing process. The actual conduct of the studies in each phase forms the basis of the bulk of the chapters in this book. However, unless... 

Reacting Multiple Phase Mixtures Application to the Detonation Properties of PETN. 

A similar strategy was used to develop the PFGC-MES equation of state parameters for describing the behavior of methanol hydrocarbon acid gas water systems. Multiple phase binary interaction parameters were used as required. Again, these second phase binary interaction parameters were usually not temperature dependent. 

Lower), as reported earlier, but also rises more rapidly than kp (Fig. 13 Upper). This result immediately requires a more complex kinetic scheme than that of Scheme I. Excellent self-consistent fits to the time evolution of [1] (t) are obtained with an expression that is the sum of three kinetic phases, all having a common rate constant for triplet decay, kp, but with differing values of the rate constants for the decay of 1(3000 s , 40s , 5s ). We have further seen that complexes with different Cc show similar behavior, but with the fractional contribution of these multiple phases varying with species. 

This observation indicates that the multiple phases do not arise from static non-interconverting forms of the complex, and that they can best be interpreted by a kinetic scheme that involves dynamic conformational interconversion between conformational substates within state I. The analysis indicates that the... 

Donovan, J. W. and Mapes, C. J. (1980). Multiple phase transitions of starches and Nageli amylodextrins. Starch/Stdrke 32,190-193. 

---