Phase inert

Finally, selective hydrogenation of the olefinic bond in mesityl oxide is conducted over a fixed-bed catalyst in either the Hquid or vapor phase. In the hquid phase the reaction takes place at 150°C and 0.69 MPa, in the vapor phase the reaction can be conducted at atmospheric pressure and temperatures of 150—170°C. The reaction is highly exothermic and yields 8.37 kJ/mol (65). To prevent temperature mnaways and obtain high selectivity, the conversion per pass is limited in the Hquid phase, and in the vapor phase inert gases often are used to dilute the reactants. The catalysts employed in both vapor- and Hquid-phase processes include nickel (66—76), palladium (77—79), copper (80,81), and rhodium hydride complexes (82). Complete conversion of mesityl oxide can be obtained at selectivities of 95—98%. 

As the mobile phase (inert gas) carries the chemicals through the column, repeated partitioning of molecules takes place between the mobile and the stationary phases, and molecules of same (or similar) chemical and physical nature are separated into groups. These groups reach the end of the column at different times. This process is called elution, and it can be compared to a marathon race all runners start at the same time, but reach the finish line at different times due to the differences in their athletic ability. 

Stationary phase Inert Support Absorption solution Elution solution Temperature Flow rate... 

III. Two reacting phases with the third phase inert... 

In GC, normally thermally stable but volatile compounds are separated. Both uncoated and coated solid adsorbents as well as thin Hlms of liquids or polymers of high molecular weight are used as the stationary phase. Inert gases (He, Ar, Nj) and Hj are used as the mobile phase, which is normally inert compared with the separated compounds. Many GC detectors are therefore based on thermal decomposition or ionization processes which convert the eluted substances into ions. Detector systems which measure a physical property of the column eluent (mobile phase and/or compound) and the eluted substance alone are also frequently used [12, 13]. 

Separation of ionic soiutes what works out best - endcapped phases, inert phases, phosphate bu er or ion pairing reagents Part I... 

Separation of ionic solutes what works out best - endcapped phases, inert phases, phosphate buffer or ion pairing reagents Part I 118 Separation of ionic solutes what works out best - endcapped phases, inert phases, phosphate buffer or ion-pairing reagents Part II (see also Chapter 5 ) 120... 

In psychrometric calculations we consider thermodynamics of three phases inert gas phase, moisture vapor phase, and moisture liquid phase. Two gaseous phases form a solution (mixture) called humid gas. To determine the degree of complexity of our approach we will make the following assumptions ... 

The conditions of the calcium silicate hydrated phases formation given in Sect. 4.2.2 are of significant importance from the practical point of view. Depending on the temperature, time of theimal treatment, w/c ratio and the composition of initial mixture there are various intermediate phases produced. The reactivity of many phases, inert in relation to water, is markedly increased in the paste hydro-thermal treatment [216]. 

Ketelaar s development considers only the binary system chlorine-water. It does not recognize the influence of gas-phase inerts. In the binary system, the relative volatility and the distribution coefficient are one and the same. This is not true when inerts are present. 

Helium coolant, which is single phase, inert, has only minute reactivity effects and does not become radioactive... 

Very-high—temperature reactor (VHTR) safety (Class G) Restricted to 600 MW (thermal) huge thermal inertia of graphite structure and matrix fuel not damaged below 1600°C, single-phase inert coolant. 

The equilibrium conversion can be increased by employing one reactant in excess (or removing the water formed, or both). b. Inerts concentration. Sometimes, an inert material is present in the reactor. This might be a solvent in a liquid-phase reaction or an inert gas in a gas-phase reaction. Consider the reaction system... 

Reactor diluents and solvents. As pointed out in Sec. 2.5, an inert diluent such as steam is sometimes needed in the reactor to lower the partial pressure of reactants in the vapor phase. Diluents are normally recycled. An example is shown in Fig. 4.5. The actual configuration used depends on the order of volatilities. 

The material to be analyzed is pyrolyzed in an inert gas at 1100°C in the presence of carbon the carbon monoxide formed, if any, is either analyzed directly by chromatography or analyzed as carbon dioxide after oxidation by CuO. The CO2 is detected by infra-red spectrometry or by gas phase chromatography. 

For some materials, the most notable being silicon, heating alone sufiBces to clean the surface. Commercial Si wafers are produced with a thin layer of silicon dioxide covering the surface. This native oxide is inert to reaction with the atmosphere, and therefore keeps the underlying Si material clean. The native oxide layer is desorbed, i.e. removed into the gas phase, by heating the wafer in UHV to a temperature above approximately 1100 °C. This procedure directly fonus a clean, well ordered Si surface. 

In addition to the case of a metal in contact with its ions in solution there are other cases in which a Galvani potential difference between two phases may be found. One case is the innnersion of an inert electrode, such as platinum metal, into an electrolyte solution containing a substance S that can exist m either an oxidized or reduced fomi tlirough the loss or gain of electrons from the electrode. In the sunplest case, we have... 

In the absence of special syimnetry, the phase mle requires a minimum of tliree components for a tricritical point to occur. Synnnetrical tricritical points do have such syimnetry, but it is easiest to illustrate such phenomena with a tme ternary system with the necessary syimnetry. A ternary system comprised of a pair of enantiomers (optically active d- and /-isomers) together with a third optically inert substance could satisfy this condition. While liquid-liquid phase separation between enantiomers has not yet been found, ternary phase diagrams like those shown in figure A2.5.30 can be imagined in these diagrams there is a necessary syimnetry around a horizontal axis that represents equal amounts of the two enantiomers. 

Electrode processes are a class of heterogeneous chemical reaction that involves the transfer of charge across the interface between a solid and an adjacent solution phase, either in equilibrium or under partial or total kinetic control. A simple type of electrode reaction involves electron transfer between an inert metal electrode and an ion or molecule in solution. Oxidation of an electroactive species corresponds to the transfer of electrons from the solution phase to the electrode (anodic), whereas electron transfer in the opposite direction results in the reduction of the species (cathodic). Electron transfer is only possible when the electroactive material is within molecular distances of the electrode surface thus for a simple electrode reaction involving solution species of the fonn... 

Figure B2.5.1 schematically illustrates a typical flow-tube set-up. In gas-phase studies, it serves mainly two purposes. On the one hand it allows highly reactive shortlived reactant species, such as radicals or atoms, to be prepared at well-defined concentrations in an inert buffer gas. On the other hand, the flow replaces the time dependence, t, of a reaction by the dependence on the distance v from the point where the reactants are mixed by the simple transfomiation with the flow velocity vy...

The action of this and other anti-bumping devices e.g., minute carborundum chips) is dependent upon the fact that the transformation of a superheated liquid into the vapour will take place immediately if a vapour phase e.g., any inert gas) is introduced. The effect may be compared with that produced by the introduction of a small quantity of a solid phaM into a supercooled liquid, e.g., of ice into supercooled water. 

Solid phase peptide synthesis (Section 27 18) Method for peptide synthesis m which the C terminal ammo acid is co valently attached to an inert solid support and successive ammo acids are attached via peptide bond formation At the completion of the synthesis the polypeptide is removed from the support... 

Increasing or decreasing the partial pressure of a gas is the same as increasing or decreasing its concentration. The effect on a reaction s equilibrium position can be analyzed as described in the preceding example for aqueous solutes. Since the concentration of a gas depends on its partial pressure, and not on the total pressure of the system, adding or removing an inert gas has no effect on the equilibrium position of a gas-phase reaction. 

In gas chromatography (GC) the sample, which may be a gas or liquid, is injected into a stream of an inert gaseous mobile phase (often called the carrier gas). The sample is carried through a packed or capillary column where the sample s components separate based on their ability to distribute themselves between the mobile and stationary phases. A schematic diagram of a typical gas chromatograph is shown in Figure 12.16. 

The most common mobile phases for GC are He, Ar, and N2, which have the advantage of being chemically inert toward both the sample and the stationary phase. The choice of which carrier gas to use is often determined by the instrument s detector. With packed columns the mobile-phase velocity is usually within the range of 25-150 mF/min, whereas flow rates for capillary columns are 1-25 mF/min. Actual flow rates are determined with a flow meter placed at the column outlet. 

The main criteria for selecting a stationary phase are that it should be chemically inert, thermally stable, of low volatility, and of an appropriate polarity for the solutes being separated. Although hundreds of stationary phases have been developed, many of which are commercially available, the majority of GLC separations are accomplished with perhaps five to ten common stationary phases. Several of... 

Diamide Chiral Separations. The first chiral stationary phase for gas chromatography was reported by GH-Av and co-workers in 1966 (113) and was based on A/-trifluoroacetyl (A/-TFA) L-isoleucine lauryl ester coated on an inert packing material. It was used to resolve the tritiuoroacetylated derivatives of amino acids. Related chiral selectors used by other workers included -dodecanoyl-L-valine-/-butylamide and... 

The choice of the solvent also has a profound influence on the observed sonochemistry. The effect of vapor pressure has already been mentioned. Other Hquid properties, such as surface tension and viscosity, wiU alter the threshold of cavitation, but this is generaUy a minor concern. The chemical reactivity of the solvent is often much more important. No solvent is inert under the high temperature conditions of cavitation (50). One may minimize this problem, however, by using robust solvents that have low vapor pressures so as to minimize their concentration in the vapor phase of the cavitation event. Alternatively, one may wish to take advantage of such secondary reactions, for example, by using halocarbons for sonochemical halogenations. With ultrasonic irradiations in water, the observed aqueous sonochemistry is dominated by secondary reactions of OH- and H- formed from the sonolysis of water vapor in the cavitation zone (51—53). 

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