Flow Patterns of the Various Phases

The solid phase (catalyst/reactant) shows different behavior in different mnlti-phase reactors. In sparged reactors, there is an exponential decay of the solid concentration along the vertical axis. For stirred multiphase reactors operated at the critical speed for just suspension of the solid, N, there is a substantial variation in axial solid concentration. The speed required for achieving uniform solid concentration and the corresponding power input are relatively very high (Nienow 1969, 2000 Shaw 1992). Hence, most stirred multiphase reactors operate at rather than For venturi loop reactors, Bhutada and Pangarkar (1989) have shown that above a certain power input at which the three-phase jet reaches the reactor bottom, the solid concentration is uniform both axially and radially. In this respect, venturi loop reactor is a definitely better option (Chapter 8). 

For trickle beds or monoliths, the catalyst is fixed in space and hence, a uniform concentration is available along the reactor axis. The problem of nonuniform catalyst wetting, however, needs to be addressed to achieve the desired performance. 

TABLE 3.1 Approximate Heats of Hydrogenations of Representative Unsaturated organic Compounds  

Similarly, oxidation reactions are also highly exothermic. If the reaction selectivity is affected by temperature, temperature control must be given due importance. Most gas-dispersed multiphase reactors yield fairly high heat transfer coefficients ( 400W/ m °C). However, as the reactor is scaled up, the heat transfer area may not be sufficient and additional heat transfer area must be provided. As an example, heat transfer area per unit volume for kettle-type reactors is given by (jacket heat transfer area/volume) = (4 X or (4/7). Most large stirred reactors face this problem 

The NO absorption reaction system is extremely complex consisting of more than 40 possible reactions (Hupen and Kenig 2005). These include several gas- and liquid-phase reactions. 

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