Reactor stirred cell

Laboratory reactors for studying gas-liquid processes can be classified as (1) reactors for which the hydrodynamics is well known or can easily be determined, i.e. reactors for which the interfacial area, a, and mass-transfer coefficients, ki and kc, are known (e.g. the laminar jet reactor, wetted wall-column, and rotating drum, see Fig. 5.4-21), and (2) those with a well-defined interfacial area and ill-determined hydrodynamics (e.g. the stirred-cell reactor, see Fig. 5.4-22). Reactors of these two types can be successfully used for studying intrinsic kinetics of gas-liquid processes. They can also be used for studying liquid-liquid and liquid-solid processes. 

If it is assumed that the values for kG, k l, and a have been measured for the commercial tower packing to be employed, the procedure for using the laboratory stirred-cell reactor is as follows ... 

Measurements of kinetic parameters of liquid-phase reactions can be performed in apparata without phase transition (rapid-mixing method [66], stopped-flow method [67], etc.) or in apparata with phase transition of the gaseous components (laminar jet absorber [68], stirred cell reactor [69], etc.). In experiments without phase transition, the studied gas is dissolved physically in a liquid and subsequently mixed with the liquid absorbent to be examined, in a way that ensures a perfect mixing. Afterwards, the reaction conversion is determined via the temperature evolution in the reactor (rapid mixing) or with an indicator (stopped flow). The reaction kinetics can then be deduced from the conversion. In experiments with phase transition, additionally, the phase equilibrium and mass transport must be taken into account as the gaseous component must penetrate into the liquid phase before it reacts. In the laminar jet absorber, a liquid jet of a very small diameter passes continuously through a chamber filled with the gas to be examined. In order to determine the reaction rate constant at a certain temperature, the jet length and diameter as well as the amount of gas absorbed per time unit must be known. 

Our own dynamic experiments for the determination of the gas-liquid-reaction kinetics have been performed in a stirred-cell reactor (Fig. 9.6). After thermodynamic equilibrium is reached inside the reactor, the gas is introduced rapidly and the pressure decrease recorded as a function of time. From this course, the reaction rate constant at the respective temperature can be obtained. 

For the studied system consisting of monoethanolamine, CO2 and water, experiments for the determination of reaction kinetics in a stirred-cell reactor have been carried out (see Section 9.4.5). These experiments yield the following Arrhenius expression for the second-order reaction (R18) (Fig. 9.18) ... 

A comprehensive discussion of the most important model parameters covers phase equilibrium, chemical equilibrium, physical properties (e.g., diffusion coefficients and viscosities), hydrodynamic and mass transport properties, and reaction kinetics. The relevant calculation methods for these parameters are explained, and a determination technique for the reaction kinetics parameters is represented. The reaction kinetics of the monoethanolamine carbamate synthesis is obtained via measurements in a stirred-cell reactor. Furthermore, the importance of the reaction kinetics with regard to axial column profiles is demonstrated using a blend of aqueous MEA and MDEA as absorbent. 

We studied these phenomena experimentally in a wetted wall column and two stirred cell reactors and evaluated the results with both a penetration and a film model description of simultaneous mass transfer accompanied by complex liquid-phase reactions [5,6], The experimental results agree well with the calculations and the existence of the third regime with its desorption against overall driving force is demonstrated in practice (forced desorption or negative enhancement factor). 

Negligible and medium interaction regimes. Experiments were carried out with an aqueous 2.0 M DIPA solution at 25 °C in a stirred-cell reactor (see ref. [1]) and a 0.010 m diameter wetted wall column (used only in negligible interaction regime, see ref. [4,5]). Gas and liquid were continuously fed to the reactors mass transfer rates were obtained from gas-phase analyses except for CO2 in the wetted wall column where due to low C02 gas-phase conversion, a liquid-phase analysis had to be used [5]. In the negligible interaction regime some 27 experiments were carried out in both reactors. The selectivity factors were calculated from the measured H2S and CO2 mole fluxes and are plotted versus k... 

Extreme interaction regime. The experimental set-up is given in figure 6. The stirred-cell reactor was operated batchwise with respect to the liquid and semi-batchwise with respect to the gas-phase which was also circulated by means of a peristaltic pump over an infrared spectrophotometer for C02 detection. 

Figure 3. Selectivity factor S as a function of kgHts in the negligible interaction regime. Key O, stirred cell reactor +, wetted wall column, cocurrent and X. wetted wall column (countercurrent).

Figure 4a. Influence of gas phase composition in a stirred cell reactor. 

In this way, the diffusion/reaction equations are reduced to trial and error algebraic relationships which are solved at each integration step. The progress of conversion can therefore be predicted for a particular semi-batch experiment, and also the interfacial conditions of A,B and T are known along with the associated influence of the film/bulk reaction upon the overall stirred cell reactor behaviour. It is important to formulate the diffusion reaction equations incorporating depletion of B in the film, because although the reaction is close to pseudo first order initially, as B is consumed as conversion proceeds, consumption of B in the film becomes significant. 

The correct physico-chemical parameters to be used in simulations of the stirred cell reactor presents some difficulty since some parameters are susceptible to uncertainty. In particular, the influence of viscosity changes as conversion proceeds has a simultaneous effect upon the diffusion coefficients and the mixing intensity generated by the liquid phase stirrer. The simulations presented in Fig. 4(a) to 4(c) use the relationship... 

Therefore we studied the absorption of HoS and CO2 into an aqueous DIPA solution using a stirred cell reactor and the associated physico-chemical parameters and mass transfer properties were used as a starting point for calculations. 

The experimental set-up is given in figure 6. A closed reactor-detector system was used to enable detection of small mole fluxes. The stirred cell reactor is 0.10 m in diameter and was filled before each experiment with 120 ml of charged 2.0 M DIPA solution. The gas phase in the system was circulated by means of a flexible tube pump over a flow-through cell in a Perkin Elmer model 257 Infrared Grating Spectrophotometer for CO2 detection. Although spectrophotometers are not exceptionally well-suited for quantitative measurements, we preferred this type of analysis compared to gas chromatography for example because it does not influence the gas phase. 

The experiments were carried out in a stirred cell reactor. The operation was batch-wise with respect to the liquid phase. The stirred cell reactor constructed from resistant glass with interfacial area for mass transfer of 76.93 cm. The internal diameter of the reactor was 10 cm with a total volume of about 1800 cm. The gas and liquid phases were stirred separately using two stirrers. To prevent the formation of vortex, four equidistant baffles were placed inside the reactor. An infrared Rosemount model 880A CO2 analyzer was used to measure the amount of carbon dioxide at the exit of the reactor. 

The perfonnances of amine blends to absorb CO2 were evaluated for mixtures of DEA and MDEA using a laboratory stirred cell reactor. The DEA to MDEA ratios were selected so that DEA-CO2 reaction would not dominate the overall reaction rate. It was observed that the addition of small amounts of DEA to MDEA resulted in a significant increase in the CO2 absorption rates as shown in Fig.l which, can be attributed to the higher reactivity of DEA with CO2. 

The stirred cell reactor was of the DaiKkwerts type [4, page 180]. The reactor was filled with degassed (diluted) benzene and kept under its own vapour pressure. The experiment was then started by connecting the space above the liquid to a thermostrated (30°C) container, filled with degassed stabilized liquid sulfurtrioxide, which was also under its own vapour pressure. Due to the difference in partial pressure of reaction mixture and liquid SO3, the latter evaporated and flowed via a flow controller arxl a rotameter to the cell reactor where it absorbed into the liquid. 

Mass Transfer in Stirred Cell Reactor during Sulfonation. The actual k during sulfonation follows experimentally from... 

Table II. Estimated values for ges-liquid interface pyrosulfonic acid concentration rise (Cjj- C ),surface temperature rise (T.-T) and reaction rata constant (k2D ) in stirred cell reactor sulfonation experiments.

Selectivity in Stirred Cell Reactor. Observed 1 — ij is always 1. Therefore eqn. (6) is expected to be applicable though its accuracy is probably low due to the discussed interface viscosity increase. From eqn. (6)... 

Figure 4. By-product formation in sulfonation of benzene with gaseous sulfur trioxide in a stirred-cell reactor in relation to initial benzene concentration and stirrer speed. (J ) 5.3 vol % benzene in dichloroethane, T = 35°C, = 0.8 (O) 30 vol % benzene in dichloroethane, T = 25°C, i = 0.09 (O) 30 vol % benzene in dichloroethane, T = 35°C, = 0.1 (100 vol %...

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