Pilot scale reactor homogeneous

The holdups can play an important role in the reactor performance. For example, in a pilot-scale trickle-bed reactor, the liquid holdup can play an important role in changing the nature of the apparent kinetics of the reaction. When homogeneous and catalytic reactions occur simultaneously, the liquid holdup plays an important role in determining the relative rates of homogeneous and catalytic reactions. In a three-phase fluidized-bed reactor, the holdup of the solid phase plays an important role in the reaction rate, particularly when the solid phase is a reactant. The gas holdup, of course, always plays an important role in reactor performance when a gaseous reactant takes part in the reaction. 

Few mechanisms of liquid/liquid reactions have been established, although some related work such as on droplet sizes and power input has been done. Small contents of surface-ac tive and other impurities in reactants of commercial quality can distort a reac tor s predicted performance. Diffusivities in liquids are comparatively low, a factor of 10 less than in gases, so it is probable in most industrial examples that they are diffusion controllech One consequence is that L/L reactions may not be as temperature sensitive as ordinary chemical reactions, although the effec t of temperature rise on viscosity and droplet size can result in substantial rate increases. L/L reac tions will exhibit behavior of homogeneous reactions only when they are very slow, nonionic reactions being the most likely ones. On the whole, in the present state of the art, the design of L/L reactors must depend on scale-up from laboratoiy or pilot plant work. 

Photo-initiated AOPs are subdivided into VUV and UV oxidation that are operated in a homogeneous phase, and in photocatalysis (Fig. 5-15). The latter can be conducted in a homogeneous aqueous phase (photo-enhanced Fenton reaction) or in a heterogeneous aqueous or gaseous phase (titanium dioxide and certain other metal oxide catalysts). These techniques apply UV-A lamps or solar UV/VIS radiation and they are in pre-pilot or pilot status. According to Mukhetjee and Ray (1999) the development of a viable and practical reactor system for water treatment with heterogeneous photocatalysis on industrial scales has not yet been successfully achieved. This is mainly related to difficulties with the efficient distribution of electromagnetic radiation (UV/VIS) to the phase of the nominal catalyst. 

Reactor designs are characterized as either homogeneous or heterogeneous. Typically, homogeneous reactors are well mixed stirred tanks (either batch or continuous), but can also be tubular reactors. They are widely used in the chemical industry from pilot plant to full-scale production. Examples include decomposition of azomethane, production of ethylene glycol, and the copolymerization of styrene and butadiene. 

Tubular reactors are commonly used in laboratory, pilot plant, and commercial-scale operations. Because of their versatility, they are used for heterogeneous reactions as well as homogeneous reactions. They can be run with cocurrent or counter-current flow patterns. They can be run in isothermal or adiabatic modes and can be used alone, in series, or in parallel. Tubular reactors can be empty, packed with inert materials for mixing, or packed with catalyst for improved reactions. It is often the process that will dictate the design of the reactor, as discussed in this entry. 

Since catalytic partial oxidation seems to be appropriate for Fischer-Tropsch syntheses, it has also been proposed that the heat required for methane steam reforming could be balanced by the exothermic oxidation of methane. In this way, a quasi-homogeneous, one-dimensional model has been developed from the study of partial oxidation of methane in the presence of steam over a 5% Ru-supported on y-Al203, which according to authors can help in pilot reactor design, materials, and further scale-up. 

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