Reactor coated tube

Figure 35.6 Inner tube coating reactor with dual vacuum systems, dye tested coated tube samples are compared with that of uncoated control T top, M middle, B bottom of Im long...

However, in other cases internal diffusion limitation can be significant even with very thin washcoat thicknesses [127], when temperature is high (> 700°C). This refers, for example, to catalytic combustions, which are extremely fast. Hayes et al. [135] evaluated the extent of intraphase and interphase resistances to the catalytic conversion of low concentrations of carbon monoxide in air in a tube wall reactor (coated with a platinum-alumina deposit). Above 610 K there was strong evidence of both intraphase and interphase resistances to catalytic conversion. In Sections 8.3.2, 8.3.3, and 8.3.4, we provide a systematic analysis for prediction of the extension of external and internal diffusion limitations. 

The column made of glass with a 50-mm inner diameter was used as the reactor in order to observe the inside of the column. A transparent electrical resistant material was coated on the outer surface of the glass tube and it worked as an electrical heater. 

Porous alumina tube externally coated with a MgO/PbO dense film (in double pipe configuration), tube thickness 2.5 mm, outer diameter 4 mm, mean pore diameter 50 nm, active film-coated length 30 mm. Feed enters the reactor at shell side, oxygen at tube side. Oxidative methane coupling, PbO/MgO catalyst in thin film form (see previous column). r-750X,Pr ed 1 bar. Conversion of methane <2%. Selectivity to Cj products > 97%. Omata et al. (1989). The methane conversion is not given. Reported results are calculated from permeability data. 

There are few uses for terbium. However, terbium can be used as an activator for green phosphor in TV tubes, and some of its compounds are used to produce laser lights. It is also used to dope (coat) some forms of solid-state instruments, as a stabilizer in fuel cells so that they can operate at high temperatures, and as a metal for control rods in nuclear reactors. 

Figure 7-16 A highly simplified sketch of an automohile engine and catalytic converter with typical gas compositions indicated before and after the automotive catalytic converter. The catalytic converter is a tube wall reactor in which a noble-metal-impregnated wash coat on an extruded ceramic monolith creates surface on which reactions occur.

Figure 7-19 Sketch of a catalytic tube vrall reactor Mtii gases floMng dowi the tube and reaction occurring on the w s of the tube, which are coated with a wash coat of catalyst (dots).

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. 

This problem can be recognized as a variation of the tube wall reactor of Chapter 7, where the reactants flowing down the tube had to migrate to and into the porous catalyst on the wall to react. The only difference here is that the reactant must first migrate through the film, which coats the waU before it can enter the catalyst and react. 

Fig. 5.11. Vacuum reactor for chlorination of metals. A Reaction vessel (100 ml) B beryllia crucible containing titanium metal C silica cradle D crucible support also serving as evacuation duct, and finally sealed off at the top at E F capillary tube G duct for breaker H appendix containing liquid chlorine J fragile capillary tip K weighted glass breaker L glass-coated magnetic retainer.

Of interest in applied kinetics is the study of chemical reactions taking place in flow systems which are hydrodynamically simple, so that the kinetics effects may be properly calculated. A simple example is the flow (with flat velocity profile v0 in the z direction) of a fluid through a circular tube the fluid is an inert material S containing a small quantity of substance A. The inside of the cylindrical tube is coated with a catalyst which converts A into B according to a first-order reaction, with k as reaction-rate constant. Let it then be desired to obtain the percentage of conversion after the fluid has flowed through the reactor tube of length L and radius R. 

Wall-coated flow tube reactors have been used to study the uptake coefficients onto liquid and solid surfaces. This method is sensitive over a wide range of y (10" to 10 1). For liquids this method has the advantage that the liquid surface is constantly renewed, however if the uptake rate is fast, the liquid phase becomes saturated with the species and the process is limited by diffusion within the liquid, so that corrections must be applied [70,72,74]. Many experiments were designed to investigate the interaction of atmospheric species on solid surfaces. In this case the walls of the flow tube were cooled and thin films of substrate material were frozen on the wall. Most of the reaction probabilities were obtained from studies on flow tubes coated with water-ice, NAT or frozen sulfate. Droplet train flow tube reactors have used where liquid droplets are generated by means of a vibrating orifice [75]. The uptake of gaseous species in contact with these droplets has been measured by tunable diode laser spectroscopy [41]. 

Chlorine atoms were produced by flowing a mixture of 5 % Cl2 in helium through a quartz tube, coated with a thin film of baked phosphoric acid to inhibit Cl atom recombination, and enclosed in a 2.45 GHz microwave cavity operating at 35 W. The purity of reactants was 99.5 to 97 %, and they were frequently subjected to several freeze-pump-thaw cycles. The reactants were flowed inside the reactor neat or diluted in helium (3% mixtures). 

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