Surface reactor

Figure 15.15 LES simulations of structures in turbulent flow in an Alfa Laval ART reactor. Surface of iso-vorticity is shown in the figure.

Attempts have also been made to obtain the radicals (CF3)3C and CeFs as products of vacuum pyrolysis of (CF3)3CI and CeFsI (Butler and Snelson, 1980b). However, only perfluoroisobutene was observed in an IR spectrum of pyrolysis products of (CF3)3CI. Thermolysis of CeFsl led to formation of CF4, CF3 and CF2 as a result of decomposition of the aromatic ring. This behaviour was explained as due to catalytic effects which take place on the platinum reactor surface. 

A Pilot Plant Reactor-Surface Analysis System for Catalyst Studies... 

Sample Introduction and Transfer System. The sample Introduction and sample transfer system is a lengthened version of the PHI Model 15-720B Introduction system which consists of a polymer bellows-covered heating and cooling probe, a transferable sample holder, an eight-port dual-axis cross, and the mlnlreactor Interface port and transfer probe (Figure 2). There Is also a transfer vessel port with the necessary transfer probe for Introduction of air sensitive samples. They are not part of the reactor/surface analysis system. The dual cross and attached hardware are supported by the probe drive mechanism which floats on a block driven vertically and transversely by two micrometers. These micrometers plus the probe drive mechanism allow X-Y-2... 

Closely related to the superheating effect under atmospheric pressure are wall effects, more specifically the elimination of wall effects caused by inverted temperature gradients (Fig. 2.6). With microwave heating, the surface of the wall is generally not heated since the energy is dissipated inside the bulk liquid. Therefore, the temperature at the inner surface of the reactor wall is lower than that of the bulk liquid. It can be assumed that while in a conventional oil-bath experiment (hot vessel surface, Fig. 2.6) temperature-sensitive species, for example catalysts, may decompose at the hot reactor surface (wall effects), the elimination of such a hot surface will increase the lifetime of the catalyst and therefore will lead to better conversions in a microwave-heated as compared to a conventionally heated process. 

Fouling of heat transfer surfaces affects the slope of the heat removal line. An increasing degree of reactor side surface fouling can change the heat removal line from the slope shown on 1 to that shown on 2, and then ultimately to that shown on 3, which is an unstable situation. Fouling of the internal reactor surface often occurs if solid particles are formed during the reaction. 

There are a number of examples of tube waU reactors, the most important being the automotive catalytic converter (ACC), which was described in the previous section. These reactors are made by coating an extruded ceramic monolith with noble metals supported on a thin wash coat of y-alumina. This reactor is used to oxidize hydrocarbons and CO to CO2 and H2O and also reduce NO to N2. The rates of these reactions are very fast after warmup, and the effectiveness factor within the porous wash coat is therefore very smaU. The reactions are also eternal mass transfer limited within the monohth after warmup. We wUl consider three limiting cases of this reactor, surface reaction limiting, external mass transfer limiting, and wash coat diffusion limiting. In each case we wiU assume a first-order irreversible reaction. 

In membrane reactors plugging is an ever-present problem because any membrane is also a good filter. In bubble, drop, emulsion, and trickle bed reactors surface-active agents can cause formidable problems with foaming. Traces of soap in liquid feeds are difficult to avoid, and their result is similar to too much detergent in a washing machine. 

Formation of products containing less than four carbon atoms is not related to the catalytic activity of the metal on the decomposition of hydroperoxides. Hence, the liquid-phase oxidation of hydrocarbons involves heterogeneous catalytic reactions of isomerization and decomposition of peroxide radicals, proceeding on the reactor surface. 

Results of these investigations demonstrate that changes of the reactor surface can be an effective method for directing chemical reactions. Thus, developing a theory of how heterogeneous factors influence liquid-phase chain reactions is one of the important lines of advancement in this area. Only a few years ago it was thought, almost a priori, that there are practically no heterogeneous factors in liquid-phase oxidation and that liquid-phase processes differ from vapor-phase processes in this respect. 

Effect of S/V Ratio. The reactor wall plays two important roles in this oxidation. First, the reactor surface promotes the initiation of radical chain (12), but if it is exceedingly large, it adversely affects the total rate of the oxidation reaction (6, 12). Second, it accelerates heterogene-... 

P. Glarborg, K. Dam-Johansen, J.A. Miller, R.J. Kee, and M.E. Coltrin. Modeling the Thermal DeNOx Process in Flow Reactors. Surface Effects and Nitrous Oxide Formation. Int. J. Chem. Kinetics, 26 421-436,1994. 

M = radiant exitance of the light source used, assuming that the irradiance at the reactor surface is equivalent to the exitance of the lamp in a given sector e = molar absorption coefficient c = concentration of the dissolved substrate... 

An assumption involving heat losses from the reactor is made in most treatments. The effect of heat transfer on the maximum reaction rates of a homogeneous reactor has been treated by DeZubay and Woodward (14). It was found that a lowering of the reactor surface temperature appreciably lowered the chemical reaction rates. Longwell and Weiss (43) found, for example, a loss equal to 5% of the maximum adiabatic heat liberated reduces the maximum heat release rate by more than 30%, while a 20% heat loss reduces the rate about 85%. One should not assume an adiabatic system without some definite knowledge of the magnitude of the heat losses. 

Fig. 2.8 (a) and (b) are thermographic pictures, recorded with the IR camera above the reactor system (Fig. 2.4) under typical reaction conditions 1% hydrocarbon in synthetic air, 375 °C and GHSV 3000 h 1. The thermogram is emissivity corrected for these conditions. The homogeneous temperature distribution of the reactor temperature (375 °C, black surface background in Fig. 2.8) is evident Each deviation from a homogeneous temperature distribution would result in colour gradients in Fig. 2.8. The result of several measurements with thermocouples around the catalyst positions of the reactor system support the finding recorded via I R-thermography on the reactor surface. The maximal temperature deviation found is below 1 °C.

The failure of latex stability,and the resultant flocculation of the latex par tides, may cause the formation of coagulum that is recovered from the latex after polymerization as well as a buildup on the reactor surfaces. Moreover, the inherent instability of the latex may also cause flocculation during storage or transportation. 

The coagulum deposited on the reactor surfaces may be the result of polymerization in large monomer drops or a separate monomer layer, or it may be the result of polymerization of the monomer in the vapor space above the latex or a surface polymerization on the walls and roof of the reactor. Polymerization in the vapor space of the reactor will form solid polymer in the form of particles which may stick to the reactor surfaces or fall into the latex in the later case, these particles serve as nuclei for the formation of coagulum. Polymerization of monomer on the reactor surfaces will form solid particles that become swollen with monomer and grow by flocculation of the latex particles. The surface polymerization can be related to the smoothness of the reactor surface the smoother the surface, the lesser the tendency for surface polymerization and formation of coagulum. 

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