Phases homogeneity

Propylene oxide is also produced in Hquid-phase homogeneous oxidation reactions using various molybdenum-containing catalysts (209,210), cuprous oxide (211), rhenium compounds (212), or an organomonovalent gold(I) complex (213). Whereas gas-phase oxidation of propylene on silver catalysts results primarily in propylene oxide, water, and carbon dioxide as products, the Hquid-phase oxidation of propylene results in an array of oxidation products, such as propylene oxide, acrolein, propylene glycol, acetone, acetaldehyde, and others. 

The properties of alloys are affected by their composition and structure. Not only is the crystalline structure important, but the size and texture of the individual grains also contribute to the properties of an alloy. Some metal alloys are one-phase homogeneous solutions. Examples are brass, bronze, and the gold coinage alloys. Other alloys are heterogeneous mixtures of different crystalline phases, such as tin-lead solder and the mercury-silver amalgams used to fill teeth. 

Hsieh and Plesset assumed that the two-phase homogeneous mixture can be represented as a uniform medium with physical properties synthesized from the constituent phases and weighted according to void fraction, a, and quality, X. Using such a model, they were able to show that the gas compression is essentially isothermal and the acoustic velocity can be approximated as... 

In 1906 Bodenstein and Lind (24) investigated the gas phase homogeneous reaction between molecular bromine and molecular hydrogen at pressures in the neighborhood of 1 atm. They fitted their experimental data with a rate expression of the form... 

McMurray, P. H. and J. C. Wilson, Droplet Phase (Heterogeneous) and Gas Phase (Homogeneous) Contributions to Secondary Ambient Aerosol Formation As Functions of Relative Humidity, Atmos. Environ.. 

Acetic acid can be synthesized from methane using an aqueous-phase homogeneous system comprising RhCI as catalyst, CO and 02.17 Side-products included methanol and formic acid, although yields of acetic acid increased upon addition of either Pd/C or iodide ions. The active species is thought to be a CH3-Rh(l) derivative, formed from the C-H activation of methane. The activation of ethane was also achieved, although selectivities were lower, with products including acetic and propionic acids and ethanol (Equation (9)). 

Various catalytic systems for H202- and 02-based oxidations catalyzed by POMs have been developed. Typical examples are listed in Table 13.1. The systems can be classified into four groups according to the stmctures of POMs (1) mixed-addenda POMs, (2) transition-metal-substituted POMs, (3) POMs, and (4) lacunary POMs. In this chapter, liquid-phase homogeneous oxidations by POMs with H202 and 02 are described according to the above classification. 

Ta-N The system contains the so-called 6 phase (high-temperature phase homogeneous between 40 and 50 at.% N, NaCl-type), Ta2N (21-35 at.% N, Fe2N-type) and TaN (CoSn-type). 

Figure 4.1 Schematic diagram of a general-purpose CSTR recycle system for in situ investigations of liquid-phase homogeneous catalyzed reactions. The blocks represent in-line instruments and their signals, namely, (i) sets of scalar valued measurements (sensors), (ii) sets of vector valued measurements (ID spectroscopies) and (iii) sets of matrix valued measurements (2D spectroscopies). The recycle time for the system is given by t.

Initial Times Immediately after the introduction of a reagent into a CSTR-recycle system, and for the first ca. 100 s, the compositions of the fluid elements throughout the liquid phase homogeneous catalytic system are measurably different. 

Model Dense phase Lean phase Homogeneous reactions Heterogeneous reactions Reference... 

TOPHAT-shaped 90° pulses are used in other cases as the best compromise with respect to the excitation profile, the phase homogeneity and length. Depending on the type of the detected spin-spin interaction - being either scalar or dipolar coupling - each selected spin is initially perturbed only once (ID TOCSY, ID INADEQUATE, ID C/H COSY, 2D TOCSY-COSY and 2D HMBC), or for several times (ID NOE). With each of the selected spins initially perturbed only once the inherently smaller transient NOEs would be detected in the latter case, whereas with the multiple excitation of a selected spin within the NOE build-up period the stronger steady-state NOEs are more or less approximated. 

Intermolecular forces also play an important role in determining the compatibility of two or more polymers in a polymer blend or polymer alloy. Although the distinction between a polymer blend and a polymer alloy is still the subject of some debate, we will use the convention that a polymer alloy is a single-phase, homogeneous material (much as for a metal), whereas a blend has two or more distinct phases as a result of polymer-polymer immiscibility (cf. Section 2.3.3). In general, polymers are... 

From the activation energies and the preexponential factors, the rate constants at 873 K can be calculated. They are listed in Table II. They show that for the gas-phase homogeneous reactions, the reactions of O atoms and OH radicals with ethene are very rapid and somewhat faster than their reactions with ethane. This fact would limit the maximum yield of ethene. It is well known that if the reactions of an alkane and an alkene are both first order in the hydrocarbon, then the maximum yield for the alkene of about 35% would be obtained when the rate constants, kA and kn, for the two reactions have equal values ... 

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