Kinetics annular reactors

Figure 12.10 Examples of structured catalytic reactors for kinetic measurements (a) annular reactor [47, 61] (b) plate cell reactor [75].

Flat plate reactors, being very simple for construction and analysis, are often used as a tool to obtain kinetic data, later to be used in the modeling of more complex system, for example, that of an annular reactor (Mohseni and Taghipour, 2004). 

By extension, if we accept the conclusions of Ref. 3, which are based on more tenuous kinetic evidence, Equation 13 also is applicable to C4-C8 normal and isoparaffins, at least in mixtures. Unfortunately, we have very little data of good kinetic quality on other paraffins. A few runs obtained with pure n-hexane in the annular reactor exist. Conversions obtained are compared with calculated conversions in Figure 8. The agreement is fairly good. 

Homogeneous Systems. Reaction Kinetics of a Pollutant Photolysis and its Application to the Prediction of the Performance of an Annular Reactor ... 

A pilot plant scale, tubular (annular configuration) photoreactor for the direct photolysis of 2,4-D was modeled (Martin etal, 1997). A tubular germicidal lamp was placed at the reactor centerline. This reactor can be used to test, with a very different reactor geometry, the kinetic expression previously developed in the cylindrical, batch laboratory reactor irradiated from its bottom and to validate the annular reactor modeling for the 2,4-D photolysis. Note that the radiation distribution and consequently the field of reaction rates in one and the other system are very different. 

McCarty [125] used an annular reactor to evaluate kinetics of methane combustion over PdO-supported catalysts. The design of the apparatus had a small gap between cylinders (0.1-0.3 mm) and a thin coating (10 pm). Using high flow rates and dilute methane and oxygen in helium, the author claims to have measured the intrinsic rate of methane oxidation up to 900°C, without contributions from gas-phase reactions. Groppi et al. 

The suitability of the structured annular reactor for very fast catalytic combustion reactions was confirmed, since it allowed measurement of kinetic data under conditions closer to the ones in the commercial applications (at higher GHSV and temperature). Extrapolation from lab-scale results can therefore be avoided, as changes in the reaction mechanism may occur... 

Groppi G, Ibashi W, Valentini M, Forzatti P. High-temperature combustion of CH4 over Pd0/Al203 Kinetic measurements in a structured annular reactor. Chemical Engineering Science 2001 56 831-839. 

Donazzi, A., Beretta, A., Groppi, G., and Forzatti, P. (2008) Catalytic partial oxidation of methane over a 4% Rh/ a-Al20s catalyst Part 1. Kinetic study in annular reactor. /. Catal., 255 (2),... 

Vincent G, Marquaire P-M, Zahraa O (2009) Photocatalytic degradation of gaseous 1-propanol using an annular reactor kinetic modelling and pathways. J Hazard Mater 161 1173-1181... 

Computational fluid dynamics approach was utilized in the study of photocatalytic destruction of gas-phase vinyl chloride in an annular flow reactor (Mohseni and Taghipour, 2004). The kinetic data for the model was obtained from a differential glass plate reactor. The modeling results indicated significant gradient of vinyl chloride in the radial direction and nonuniform flow distributions, which resulted in reduced efficiency over the entire range of inlet concentrations. 

Some of the efforts, so far, to model such membrane bioreactors seem to not have considered the complications that may result from the presence of the biomass. Tharakan and Chau [5.101], for example, developed a model and carried out numerical simulations to describe a radial flow, hollow fiber membrane bioreactor, in which the biocatalyst consisted of a mammalian cell culture placed in the annular volume between the reactor cell and the hollow fibers. Their model utilizes the appropriate non-linear kinetics to describe the substrate consumption however, the flow patterns assumed for the model were based on those obtained with an empty reactor, and would probably be inappropriate, when the annular volume is substantially filled with microorganisms. A model to describe a hollow-fiber perfusion system utilizing mouse adrenal tumor cells as biocatalysts was developed by Cima et al [5.102]. In contrast, to the model of Tharakan and Chau [5.101], this model took into account the effect of the biomass, and the flow pattern distribution in the annular volume. These effects are of key importance for conditions encountered in long-term cell cultures, when the cell mass is very dense and small voids can completely distort the flow patterns. However, the model calculations of Cima et al. [5.102] did not take into account the dynamic evolution of the cell culture due to growth, and its influence on the permeate flow rate. Their model is appropriate for constant biocatalyst concentration. 

In these equations D represents the corresponding diffusion coefficients, and Q the permeate flow rate. The first term of each equation gives the radial dispersion and the second one corresponds to the radial convection. The authors [5.103] used in their model, a biological kinetic rate expression (cp), which was obtained by independent experiments and analysis of a batch reactor, and also made an effort to account for and correlate the permeate flow decrease with the amount of produced biomass. The simulation curves obtained matched well the experimental results in terms of permeate flow rate evolution and product concentration. One of the important aspects of the model is its ability to theoretically determine the biomass concentration profiles, and the relation between the permeate flow rate and the calculated biomass concentration in the annular volume (Fig. 5.24). Such information is important since the biomass evolution cannot be determined by any experimental methodology. 

Reactant A is converted irreversibly and exothermically to products in a 2-in.-inner-diameter tubular reactor via first-order chemical kinetics. The reactive mixture in the inner pipe is cooled using a concentric double-pipe heat exchanger. The nonreactive cooling fluid in the annular region flows countercurrently with respect to the reactive fluid. The radius ratio of the double-pipe configuration is If = Rinside/ outside = 0.5, the inlet temperature of the reactive fluid is 340 K,... 

The choice of the characteristic dimension can be nevertheless limited by other factors such as allowable pressure drop, occurrence of clogging/fouling, deviations from uniform flow distribution to individual channels, and maximization of productivity metrics based on product flow rates. For certain applications (e.g., synthesis of pharmaceuticals), larger channel diameters are also favored, since this facilitates cleaning. Beretta et al. [If] compare micropacked beds and annular microchannel reactors for intrinsic kinetic measurements at high temperature and high space velocities. The lower pressure drop and better temperature control in the coated micro-channel favored the use of the structured reactor. 

In the present work, propane-propylene mixtures with various ratios were pyrolyzed at temperatures near 900°C and at an atmospheric pressure in an annular flow reactor. Hydrogen was used as a diluent. Under these experimental conditions, it was rather difficult to maintain an uniform temperature throughout the reactor since the reaction rate was high, and consequently, thermal effects due to the heat reaction were significant. In this work, therefore, experimental data at the initial stage of decomposition were analyzed using the effective temperature method to obtain kinetic rate parameters, activation energy and frequency factor, for propane and propylene decompositions. From the relations between... 

Researchers at the Politecnico di Milano [40-44] have demonstrated the interest of this kind of reactor for the kinetic study of methane oxidation. They have shown additional advantages of this reactor configuration the small annular zone leads to short diffusion distances the gas flow is laminar and theoretically based correlations can be used to describe mass transfer and high radiation losses lead to more isothermal conditions. However, its main advantages are the direct measurement of the catalyst temperature, thus eliminating any heat... 

The Amoco annular spinning basket reactor system Is a useful tool for studying the fundamental kinetics of llquid-vapor-solid catalyzed reaction systems. We believe it is generally superior to trickle bed systems for the study of pure compound kinetics in liquid-vapor-solid catalyzed systems. A desulfurization kinetic study with dlbenzothlophene in white oil was successfully completed. The results of the study compare favorably with an earlier study performed in a trickle bed reactor by Frye and Mosby (8). 

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