Constant-volume batch reactor mode

The catalytic activity in decomposition of H2O-HAN (79 wt-%) mixture was followed by DTA-TGA to determine the onset of the decomposition and by means of a constant volume batch reactor using increase temperature mode or isothermal mode at 90 °C. The same catalyst to propellant ratio was used lOpL propellant and 16 mg catalyst for thermal analysis, 100 pL propellant and 160 mg catalyst for batch reactor experiments the temperature ramp was 10... 

If this reaction is to he carried out isothennally at 127°C and an initial pressure of 10 atm in a constant-volume batch mode with 90% conversion, what reactor size and cost would be required to proces.s (2.5 mol/min X 60 min/h X 24 h/day) 36fXJ mol of di-tm-buiyl peroxide per day iHinv. Recall Table 4-i.)... 

An initial charge of A (methylnaphthalene) is taken in the reactor at a concentration of [A]i, B (hydrogen peroxide solution) at a concentration of [fiJo is added, and the products are withdrawn, both continuously, at the same rate. This mode of operation is continued for a certain length of time corresponding to a fraction /sB of the total time, after which the flow of B is stopped, and the reaction is continued in the batch mode for the remaining fraction of time (1 -/sb)- This may be regarded as constant volume, semibatch operation. 

In industry, fed-batch cultivation is often used to propagate bacterial cells. This mode of operation entails feeding concentrated growth medium to a batch reactor vessel. As the cells accumulate due to growth, the rate at which medium is fed increases with time in order to keep up with the growing total mass of cells. When the aim is to sustain a constant specific growth rate ( t), the operational equations for time-dependent feed rate (F), volume (V), and cell mass concentration (X) are... 

On the other hand, an industrial process may be operated in a continuous mode, rather than in a batch mode. To achieve this, either a single or a series of interconnected vessels may be used. The required raw materials are continuously fed into this vessel or the first vessel and the reaction products continuously removed from the last so that the volume of material in the reactor(s) stays constant as the reaction proceeds. The concentrations of starting materials and products in the reactor eventually reach a steady state. One or more tanks in series may be used to conduct the continuous process. Another option for a continuous process is to use a pipe or tube reactor, in which the starting material(s) is fed into the tube at one end, and the product(s) is removed at the other. In this case, the reaction time is determined by the rate of flow of materials into the tube divided by the length of the tube. 

T o avoid or minimize the formation of mixed products, the preferred method is to operate at constant pH by using a simultaneous addition of reactants (semibatch process). However, even using this mode, mixtures are produced, albeit to a lesser degree, because the change in liquid volume in the reactor alters both the concentration of the reactants and the hydrodynamics. A further improvement, therefore, is to perform the process continuously rather than batch-wise. Even then it is important to minimize concentration gradients in the reactor through good process control. 

In Fig. 21.7 a laboratory scale PMR coupling photocatalysis with MF is shown. The PMR was applied for the removal of trichloroethylene (TCE) from water (Choo et al., 2008). The system was composed of a photocatalytic reactor (volume of 700 cm ) and a hollow fiber MF module (effective membrane surface area of 20.7 cm ). A UV-A light source was placed in the inner chamber of the photoreactor, whereas in the outer chamber the solution undergoing the photocatalytic reaction was flowing. Feed from the feed tank was pumped through the photoreactor to the membrane module. The PMR was operated either in batch or in continuous mode. In batch operations, the permeate and retentate were recycled to the photoreactor. In continuous mode, the permeate was discharged and the same volume of the solution was fed into the reactor. Thus the working volume of the photoreactor was maintained at a constant level. 

Continuous mode of operation in well-mixed stirred tanks often starts as a fed-batch process at constant feed rate under a given substrate concentration Cjo, so that D = fi until an outlet valve is opened. This is performed in order to allow the effluent to be continuously recovered from the reactor at an outlet flow rate equal to the inlet flow so that the volume of the medium in the fermenter stays constant and steady state is achieved. 

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