Reactant in the Gas Phase

TABLE 2.1 Stability of the QM-Cytosine Conjugates Relatively to Free Reactants in the Gas Phase (AGgas) and in Aqueous Solution (AGaq). Activation Gibbs Energy for Their Decomposition into QM and Cytosine (AGjjev aq)... 

CVD [Chemical Vapor Deposition] A general term for any process for depositing a solid on a solid surface by a chemical reaction from reactants in the gas phase. To be distinguished from Physical Vapor Deposition (PVD), in which no chemical reaction takes place. (For the ten international conferences held on this between 1967 and 1987 see the reference by Stinton et al. below.)... 

A flame could begin with the reactants mixed (premixed) or reactants that might diffuse together (diffusion flame). Generally, a flame is thought of with the reactants in the gas phase. Variations in this viewpoint for a flame or fire process might occur and are defined in special terminology. Indeed, while flame applies to a gas phase reaction, fire,... 

This is a cubic equation in r with three constants and the partial pressure of the reactant in the gas phase, pg, as the variable. 

W average width of the channel perpendicular to the flight y mole fraction of ethylene (or other reactant) in the gas phase... 

Three-phase reactors are generally needed in cases where there are both volatile and nonvolatile reactants, or when a liquid solvent is necessary with all reactants in the gas-phase (Smith, 1981). Some examples are... 

Following the procedure described in Section 3.1.2, the rate per unit volume of bubble-free liquid in terms of the concentration of the reactant in the gas phase is... 

The gas energy and mass balance equations, unlike the corresponding solid balances, do not have a term for accumulation. This is because the high convective flow of gas through the channels of the monolith makes accumulation of heat or reactants in the gas phase negligible. In practice, the accumulation term in the solid mass balance could also be removed as, in general, it also tends to be small. However, it is included in our models as it enables the equations to be solved numerically more easily. 

MTBE is used on a large scale as an octane number boosting additive in unleaded gasoline. Sulfonic acid resins are applied as efficient catalysts for the industrial production of MTBE from methanol and isobutylene (222). Since 1987, investigations of the synthesis of MTBE with reactants in the gas phase have been performed with zeolites HY (223-225), H-Beta (226), HZSM-5 (224,225), and H-BZSM-5 (227) as catalysts. 

SS = the sum of the molar entropies of the reactants in the gas phase, being constant for the two reactions considered) the condition of case 3 exists ... 

These considerations can be extended to reversible processes. They also apply to single phase, liquid systems. For the case, rather common in heterogeneous catalysts, in which one reactant is in a gas phase and the others and the products are in a liquid phase, application of the principles given above is straightforward provided that there is mass transfer equilibrium between gas phase and liquid phase, i.e., the fugacity of the reactant in the gas phase is identical with its fugacity in the liquid phase. In such case, a power rate law for an irreversible reaction of the form... 

Fig. 10.2.5 Energy diagram for the activated complex and reactants in the gas phase and solution. To the left is shown the case where the stabilization of the two compounds in solution is the same, and to the right where it differs.

For these studies the NiX precursor catalyst has been impregnated with molten lithium acetate. The catalyst displayed remarkably good selectivity to octenes. A typical set of results is shown in Fig. 18, where the reactant and product concentrations are given as a function of contact time, t. The results indicate that isomerization of 1-butene to an equilibrium mixture with 2-butenes (cis and trans) occurs rapidly, followed by the slower dimerization of butenes to octenes. The reaction was carried out under mixed phase conditions with the 1-butene reactant in the gas phase and the octene products in the liquid phase (trickle-bed reactor). Under the conditions the reaction rate was found to be mass-transfer controlled. 

Before we present a survey on the adsorption of several simple gases some general aspects of the dissociative adsorption will be treated. Table 4.1 tabulates the dissociation energies of reactants in the gas phase. Table 4.2 shows some examples of the heats of formation of hydrides, nitrides, carbides and oxides. The following relevant conclusions emerge ... 

This reaction can occur in slow, fast, or instantaneous reaction regimes. In each reaction regime, the gas-phase resistance can be important, depending on the concentration of the reactant in the gas phase and the solubility of the gas in the liquid phase. The criteria for these reaction regimes are24-39... 

Reactant in the Gas Phase When A in the gas phase reacts with adsorbed B,... 

Processes with Reactants in the Gas Phase. As discussed in the preceding parts, for such processes there is hardly a problem in catalyst testing on a scale as small as that of microreactors, even with undiluted beds of catalyst of actual size. Hence, in this case testing on a larger scale than microflow reactors will seldom be neccessary. 

Experiments were conducted (see Experimental Section) in a fixed-bed reactor at isothermal conditions with reactants in the gas phase. 

The concentration of reactant in the gas phase is 0.1 mol and at the surface is 0.098 mol L . The gas-phase mass-transfer coefficient is 2 cm s . Determine the intraphase effectiveness factor. (Contributed by Prof. J. L. Hudson, Univ. of Virginia.)... 

In reactions between a solid and a gas or a solution, three steps are distinguished transport of the reactant in the gas phase or the solution to the surface of the solid reaction at the surface of the solid and transport of the reaction products into the solid, the gas phase or the solution, respectively. Reaction at the solid/gas or solid/ liquid interface comprises the following steps (a) adsorption of the reactant, (b) reaction and (c) desorption of the products, These steps are considered in more detail in the following paragraphs. 

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