Gas phase reactions system

Here AGr° is the Gibbs free energy change in the ideal gas phase reaction system when all the gases are in their respective standard states. The equilibrium constant Kp is given in terms of the partial pressures at equilibrium by... 

There are some common characteristics for gas-phase reaction systems that form the basis for understanding and describing the chemical behavior. In this section we will discuss some basic definitions and terms that are useful in kinetics, such as reaction order, molec-ularity, chain carriers, rate-limiting steps, steady-state and partial equilibrium approximations, and coupled/competitive reactions. 

Important parameters were varied over relatively wide ranges producing particleboards with acceptable properties i.e., properties similar to those obtained using a phenol-formaldehyde resin as the control. Conditions used in both the liquid and gas phase reaction systems gave results shown by the examples in Table II. 

Dynamics of Chemical Reactions Induced by Cluster Impact, T. Raz and R. D. Levine, Heidelberg Conference Gas-Phase Reaction Systems Experiments and Models — 100 Years after Max Bodenstein, Springer-Verlag (1995). 

Isomerization of n-paraffin, especially normal pentane to iso-pentane is essential for making high octane gasoline with low aromatics content. Isomerization of lower paraffins has been conducted in the solid catalyzed gas-phase reaction system by using noble metal-supported solid acid under hydrogen atmosphere. The most predominant reaction mechanism for the isomerization of alkane is as follows (1) the dehydrogenation of alkane to alkene on the supported metal (2) proton addition to the alkene to form carbenium ion on the acidic component (3) skeletal isomerization of the carbenium ion on the acidic component (4) deprotonation of the isoraerized carbenium ion to form alkene on the acidic component (5) hydrogenation of the alkene to alkane on the metal [1]. 

G. (1996) Die Photochemischen Bildung des Chlorwasserstoffs. Dynamics of Cl + H2 HCl + H on a New Potential Energy Surface The Photosynthesis of Hydrogen Chloride Revisited lOOYears after Max Bodenstein in J Wolfram, H-R Volpp, R Rannacher and J Wamatz (eds), Gas-Phase Reaction Systems Experiments and Models 100 Years after Max Bodenstein, Springer, Heidelberg, pp. 111-24 Manolopoulos, D. E. (1997) The dynamics of the F+H2 reaction, J. Chem. Soc. Faraday Trans. 93, 673-83 Casavecchia, P. (2000) Chemical reaction dynamics with molecular beams. Rep. Prog. Phys. 63, 355-414. 

A good example of this approach Is provided by the gas-phase reaction systems... 

Although it is almost impossible to cover all aspects of this rapidly developing research field in one book, we feel that the articles in this volume together with the list of references given, reflect the diversity and importance, as well as the exciting challenge the investigation of gas phase reaction systems still offers. 

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... 

The importance of numerical treatments, however, caimot be overemphasized in this context. Over the decades enonnous progress has been made in the numerical treatment of differential equations of complex gas-phase reactions [8, 70, 71], Complex reaction systems can also be seen in the context of nonlinear and self-organizing reactions, which are separate subjects in this encyclopedia (see chapter A3,14. chapter C3.6). 

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. 

Oxidation can also occur at the central metal atom of the phthalocyanine system (2). Mn phthalocyanine, for example, can be produced ia these different oxidation states, depending on the solvent (2,31,32). The carbon atom of the ring system and the central metal atom can be reduced (33), some reversibly, eg, ia vattiag (34—41). Phthalocyanine compounds exhibit favorable catalytic properties which makes them interesting for appHcations ia dehydrogenation, oxidation, electrocatalysis, gas-phase reactions, and fuel cells (qv) (1,2,42—49). 

Although they are termed homogeneous, most industrial gas-phase reactions take place in contact with solids, either the vessel wall or particles as heat carriers or catalysts. With catalysts, mass diffusional resistances are present with inert solids, the only complication is with heat transfer. A few of the reactions in Table 23-1 are gas-phase type, mostly catalytic. Usually a system of industrial interest is liquefiea to take advantage of the higher rates of liquid reactions, or to utihze liquid homogeneous cat ysts, or simply to keep equipment size down. In this section, some important noncatalytic gas reactions are described. 

At any instant, because gas-phase reactions are often carried out in tubular systems, the mass flowrate G and C- the concentration of i in moles per unit mass is used. The mass flowrate G does not change with position when fluid density changes as is the case with u, the volumetric flowrate (Figure 5-29). 

Explicit mechanisms attempt to include all nonmethane hydrocarbons believed present in the system with an explicit representation of their known chemical reactions. Atmospheric simulation experiments with controlled NMHC concentrations can be used to develop explicit mechanisms. Examples of these are Leone and Seinfeld (164), Hough (165) and Atkinson et al (169). Rate constants for homogeneous (gas-phase) reactions and photolytic processes are fairly well established for many NMHC. Most of the lower alkanes and alkenes have been extensively studied, and the reactions of the higher family members, although little studied, should be comparable to the lower members of the family. Terpenes and aromatic hydrocarbons, on the other hand, are still inadequately understood, in spite of considerable experimental effort. Parameterization of NMHC chemistry results when NMHC s known to be present in the atmosphere are not explicitly incorporated into the mechanism, but rather are assigned to augment the concentration of NMHC s of similar chemical nature which the... 

Rate constants for a large number of atmospheric reactions have been tabulated by Baulch et al. (1982, 1984) and Atkinson and Lloyd (1984). Reactions for the atmosphere as a whole and for cases involving aquatic systems, soils, and surface systems are often parameterized by the methods of Chapter 4. That is, the rate is taken to be a linear function or a power of some limiting reactant - often the compound of interest. As an example, the global uptake of CO2 by photosynthesis is often represented in the empirical form d[C02]/df = —fc[C02] ". Rates of reactions on solid surfaces tend to be much more complicated than gas phase reactions, but have been examined in selected cases for solids suspended in air, water, or in sediments. 

Other types of non-micro-channel, non-micro-flow micro reactors were used for catalyst development and testing [51, 52]. A computer-based micro-reactor system was described for investigating heterogeneously catalyzed gas-phase reactions [52]. The micro reactor is a Pyrex glass tube of 8 mm inner diameter and can be operated up to 500 °C and 1 bar. The reactor inner volume is 5-10 ml, the loop cycle is 0.9 ml, and the pump volume adds a further 9 ml. The reactor was used for isomerization of neopentane and n-pentane and the hydrogenolysis of isobutane, n-butane, propane, ethane, and methane at Pt with a catalyst. 

The rate of an electrochemical reaction depends, not only on given system parameters (composition of the catalyst and electrolyte, temperature, state of the catalytic electrode surface) but also on electrode potential. The latter parameter has no analog in heterogeneous catalytic gas-phase reactions. Thus, in a given system, the potential can be varied by a few tenths of a volt, while as a result, the reaction rate will change by several orders of magnitude. 

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