Homogeneous Gas Phase Reactions

Homogeneous reactions are those in which the reactants, products, and any catalysts used form one continuous phase (gaseous or liquid). Homogeneous gas phase reactors are almost always operated continuously, whereas liquid phase reactors may be batch or continuous. Tubular (pipeline) reactors arc normally used for homogeneous gas phase reactions (e.g., in the thermal cracking of petroleum of dichloroethane lo vinyl chloride). Both tubular and stirred tank reactors are used for homogeneous liquid phase reactions. 

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... 

A homogeneous gas-phase reaction that follows a third-order kinetic scheme is... 

Suppose a homogeneous, gas-phase reaction occurs in a constant-volume batch reactor. Assume ideal gas behavior and suppose pure A is charged to the reactor. 

Hinshelwood and Green d Studied the homogeneous, gas-phase reaction ... 

GP 11] ]R 19] The suppression of explosive homogeneous gas-phase reactions is not due simply to thermal quenching as a result of the heat losses from a micro reactor, but rather to radical quenching [9]. The micro reactor will therefore be safe even when heat losses from the reaction micro channel are reduced by design modifications. 

Bellman et al. (1967) have considered the estimation of the two rate constants k and k2 in the Bodenstein-Linder model for the homogeneous gas phase reaction of NO with 02 ... 

Table 6.1 Data for the Homogeneous Gas Phase Reaction of NO with 02.

Table 16.20 Homogeneous Gas Phase Reaction Convergence of the Gauss-Newton Method...

Figure 16.1 Homogeneous Gas Phase Reaction Experimental data and model calculated values of the NQ2 concentration.

Physical Methods that have been Used to Monitor Reaction Kinetics. In this section some physical property measurements of general utility are discussed. One of the oldest and most useful techniques used in kinetics studies involves the measurement of the total pressure in an isothermal constant volume reactor. This technique is primarily used to follow the course of homogeneous gas phase reactions that involve a change in the total number of gaseous molecules present in the reaction vessel (e.g., the hydrogenation of propylene). 

The kinetics of the irreversible reaction A -> B + C has been studied in a laboratory scale recycle reactor. A nonporous solid catalyst is being used to obtain an appreciable reaction rate. The data reported by your technician are shown in Figure 6P.6. Each of the sets of data was recorded holding the partial pressures of the other species constant. The homogeneous gas phase reaction may be neglected. The reaction rate is expressed in terms of the... 

In the thermal zone, above the catalyst bed, further conversion occurs by homogeneous gas-phase reactions. The main reactions in the thermal zone are homogeneous gas-phase... 

For the experimental investigation of a homogeneous gas-phase reaction occurring in a CSTR,... 

For a homogeneous gas-phase reaction occurring in a plug-flow reactor, explain briefly under what circumstances tlr < 1. Consider each factor affecting this ratio separately. Give an example (chemical reaction + circumstance(s)) for illustration. Assume steady-state operation and... 

Suppose the following data were obtained for the homogeneous gas-phase reaction 2A + 2B - C + 2D carried out in a rigid 2-L vessel at 800°C. 

In a series arrangement, all changes in properties are taken into account, such as adjustment of T (without reaction) by a heat exchanger between stages (lengths). Such adjustment is more common for solid-catalyzed reactions than for homogeneous gas-phase reactions. 

For a certain homogeneous, gas-phase reaction taking place in a PFR, suppose it has been... 

In 1989, Gadalla and Sommer (252) reported that a solid-solution NiO/MgO (1 1.35) catalyst prepared by precipitation can inhibit the carbon deposition in the CO2 reforming of methane however, they obtained a low CO2 conversion (66%), a low H2 selectivity (79%), and a low CO selectivity (77%), even at the very low WHSV of 3714 cm3 (g catalyst)-1 h-1 with a CH4/CO2 (1/1, molar) feed gas and the high temperature of 1200 K. Their relatively high CH4 conversion was partly a consequence of homogeneous gas-phase reactions that occurred under their conditions. Indeed, the authors found extensive carbon deposits plugging the reactor upstream and downstream of the reaction zone. 

Baulch, D. L., Duxbury, J., Grant, S. J., and Montague, D. C., Evaluated kinetic data for high temperature reactions Homogeneous gas phase reactions of halogen and cyanide containing species, J. Phys. Chem. Ref. Data 4, 10, Supplement No. 1 (1981). 

The actual configuration of the reactor may take various forms depending on the precise requirements of the process. For example, for a high-temperature homogeneous gas-phase reaction such as naphtha cracking, the reactor may be simply a long tube in a furnace [Fig. 6(a)]. In other cases, the single tube is replaced by a number of tubes in parallel as shown in Fig. 6(b). 

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