Profile gas phase

Horning, E.C., Metabolic profiles Gas-phase methods for the analysis of metabolites, Clin. Chem., 17(8), 802, 1971. 

The above mostly qualitative discussion is appropriate to the case where no volume expansion takes place during ramping. It therefore applies strictly and exclusively to liquid systems with no axial profiles. Gas phase systems are quantified below. 

Figure A2.3.21 Free energy profile of the SN2 reaction Cl +CH2CI— [Cl-CHg-Cl]— CICH +Cl in the gas phase, dimethyl fonnamide and in water (from [93]).

As it has appeared in recent years that many hmdamental aspects of elementary chemical reactions in solution can be understood on the basis of the dependence of reaction rate coefficients on solvent density [2, 3, 4 and 5], increasing attention is paid to reaction kinetics in the gas-to-liquid transition range and supercritical fluids under varying pressure. In this way, the essential differences between the regime of binary collisions in the low-pressure gas phase and tliat of a dense enviromnent with typical many-body interactions become apparent. An extremely useful approach in this respect is the investigation of rate coefficients, reaction yields and concentration-time profiles of some typical model reactions over as wide a pressure range as possible, which pemiits the continuous and well controlled variation of the physical properties of the solvent. Among these the most important are density, polarity and viscosity in a contimiiim description or collision frequency. 

Fig. 5.21 The energy profile for the gas-phase Cl + MeCl reaction. (Adapted in part from Chandrasekhar J, S F Smith and PV L Jorgensen 1985. Theoretical Examination of the S 2 Reaction Involving Chloride Ion and Methyl Chloride in the Gas Phase and Aqueous Solution. Journal of the American Chemical Society 107 154-163.)...

Radial density gradients in FCC and other large-diameter pneumatic transfer risers reflect gas—soHd maldistributions and reduce product yields. Cold-flow units are used to measure the transverse catalyst profiles as functions of gas velocity, catalyst flux, and inlet design. Impacts of measured flow distributions have been evaluated using a simple four lump kinetic model and assuming dispersed catalyst clusters where all the reactions are assumed to occur coupled with a continuous gas phase. A 3 wt % conversion advantage is determined for injection feed around the riser circumference as compared with an axial injection design (28). 

Figure 14-10 illustrates the gas-film and liquid-film concentration profiles one might find in an extremely fast (gas-phase mass-transfer limited) second-order irreversible reaction system. The solid curve for reagent B represents the case in which there is a large excess of bulk-liquid reagent B. The dashed curve in Fig. 14-10 represents the case in which the bulk concentration B is not sufficiently large to prevent the depletion of B near the liquid interface and for which the equation ( ) = I -t- B /vCj is applicable. 

FIG. 14-10 Gas-ph ase aud liquid-phase soliite-couceutratiou profiles for au extremely fast (gas-phase mass-trausfer hmited) irreversible reaction system A -I-vB — products. 

FIG. 14-13 Gas-phase and liquid-phase solute-concentration profiles for a liquid-phase mass-transfer limited reaction system in which is larger than 3. 

FIG. 25-18 Biophysical model for the hiolayer. Cg is the concentration in the gas phase. The two concentration profiles shown in the hiolayer (C ) refer to (1) elimination reaction rate limited, and (2) diffusion hmited. (SOURCE Redrawn from Ref. 26.)... 

Energy Distribution Profile of Solute Molecules in the Gas Phase... 

When the solid phase 0+ at x = -f oo coexists with the gas phase 0 at X = -oo, the stationary profile of the phase field is determined so as to minimize the free energy functional F (56). The functional derivative gives... 

More recently, Rosen (R3), Spalding (S5), and Johnson and Nachbar (J4) have considered a simplified approach using the analysis of laminar-flame propagation velocities. According to these investigators, the principal exothermic reactions occur in the gas phase. Some of the heat liberated by these reactions is then transferred back to the solid surface to sustain the endothermic surface-gasification processes. Thus, the temperature profile within the reactive zone is quite similar to that of Rice and Crawford. However, gasification of the solid surface is assumed to be endothermic, while exothermic reactions were considered in the studies discussed previously. 

The basic approach taken in the analytical studies of composite-propellant combustion represents a modification of the studies of double-base propellants. For composite propellants, it has been assumed that the solid fuel and solid oxidizer decompose at the solid surface to yield gaseous fuel and oxidizing species. These gaseous species then intermix and react in the gas phase to yield the final products of combustion and to establish the flame temperature. Part of the gas-phase heat release is then transferred back to the solid phase to sustain the decomposition processes. The temperature profile is assumed to be similar to the situation associated with double-base combustion, and, in this sense, combustion is identical in the two different types of propellants. 

Figure 2.42. Relative steady-state methanation activity profiles for Ni ( ), Co (A), Fe ( ), and Ru (O) as a function of gas-phase H2S concentration. Reaction conditions 100 kPa, 400°C, 1% CO/99%H2 for Co, Fe, and Ru, 4% CO/96% H2 for Ni.131 Reprinted with permission from Academic Press.

Fig. 16. Energy profiles of the protonation and propagation reactions of ethene in the gas phase and in solution (CH2C12) starting with 4 monomer units and a free proton...

When this correction is included, the reaction energy profile diagram results for the cationation and the first three propagation steps in the gas phase and in solution (Fig. 16). 

FIGURE 10.1 Free energy profile for the gas-phase (solid line) and aqueous soltuion (dashed line) Sn2 reaction between CH3CI and Cl , from MO calculations. ... 

Ab initio molecular orbital calculations are being used to study the reactions of anionic nucleophiles with carbonyl compounds in the gas phase. A rich variety of energy surfaces is found as shown here for reactions of hydroxide ion with methyl formate and formaldehyde, chloride ion with formyl and acetyl chloride, and fluoride ion with formyl fluoride. Extension of these investigations to determine the influence of solvation on the energy profiles is also underway the statistical mechanics approach is outlined and illustrated by results from Monte Carlo simulations for the addition of hydroxide ion to formaldehyde in water. 

After gas-phase oxidation reaction finished, the reactor wall surfece was coated with a thick rough scale layer. The thickness of scale layer along axial direction was varied. The scale layer at front reactor was much thicker than that at rear. The SEM pictures were shown in Fig. 1 were scale layers stripped from the reactor wall surface. Fig. 1(a) was a cross sectional profile of scale layer collected from major scaling zone. Seen from right side of scale layer, particles-packed was loose and this side was attached to the wall surface. Its positive face was shown in Fig. 1(b). Seen from left side of scale layer, compact particles-sintered was tight and this side was faced to the reacting gases. Its local amplified top face was shown in Fig. 1(c). The XRD patterns were shown in Fig. 2(a) were the two sides of scale layer. Almost entire particles on sintered layer were characterized to be rutile phase. While, the particle packed layer was anatase phase. 

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