Catalysts monolithic

Catalyst monoliths may laos be employed as catalytic combustion chambers preceding aircraft and stationary gas turbines. As shown diagramatically in Fig. 16, a catalytic combustor comprises a preheat region, a catalyst monolith unit and a thermal region. In the preheat region, a small fuel-rich flame burner is employed to preheat the fuel-air mixture before the hot gases reach the monolith unit. Additional fuel is then injected into the hot gas stream prior to entry to the monolith where... 

Fig. 17.17 Conceptual illustration of gas-turbine engine with the combustor sections based on flow through catalyst monoliths. Because of the need for high catalyst surface area, the combustor sections are much larger than those in an ordinary gas turbine based on...

Monolith Catalyst Nalcomo 474 Catalyst Monolith Catalyst Nalcomo 474 Catalyst... 

Monolith is now one of the most widespread form of catalysts. Monoliths are formed by extrusion through special dies creating multiple channels. (A variant in monolith manufacture uses corrugated foils of the support which are joined together to create channels). 

In many applications involving gas-phase reactants and solid catalysts, monoliths are the state-of-the-art technology. In most cases, convenience and the low-pressure drop are the main drivers. 

Not all catalysts need the extended smface provided by a porous structure, however. Some are sufficiently active so that the effort required to create a porous catalyst would be wasted. For such situations one type of catalyst is the monolithic catalyst. Monolithic catalysts are normally encountered in processes where pressure drop and heat removal are major considerations. Typical examples include the platinum gauze reactor used in the ammonia oxidation portion of nitric acid manufacture and catalytic converters used to oxidize pollutants in automobile exhaust. They can be porous (honeycomb) or non-porous (wire gauze). A photograph of a automotive catalytic converter is shown in Figure CD 11-2. Platinum is a primary catalytic material in the monolith. 

Catalyst Monolith. The previous discussion in this chapter focused primarily on chemical reactions taking place in packed-bed reactors. However, when a gaseous feedstream contains significant amoimts of particulate matter, dust tends to clog the catalyst bed. To process feedstreams of this type, parallel-plate reactors (monoliths) are commonly used. Figure 11-11 shows a schematic diagram of a monolith reactor. The reacting gas mixture flows between the parallel plates, and the reaction takes place on the smface of the plates. 

This problem examines the effect on temperature in a catalyst monolith. [2nd Ed. PI0-13]... 

This phenomenon is the same for ail types of geometric shapes of catalysts, monoliths, pellets or nets, In a monolith the mass transfer, between gas bulk and the outer surface of catalyst, is not particular good since the flow, at least in the boundary layers, tends to become laminar, but the pressure drop is low. In a packed bed with pellets the mass transfer is very good in general, but the pressure drop is high. A stack of nets, however, combine good mass transfer and low pressure drop, it is in between a monolith and a packed bed. 

Manufacturers and names or codes of the commercial V-W-Ti catalysts (monoliths) used in this work were ... 

Four European research groups also provided these authors with samples of their V-W-Ti catalysts (monoliths too) ... 

Fig. 7. Performance of the improved catalyst in commercial gas engine cogeneration systems. Catalyst GEC-01 (the same as in Fig. 6b). (O, , ) Site A (1000 kw), (A) site B (460 kw), ( ) site C (100 kw). Operation conditions NO = 2500-3500 ppm, CH4 = 400-2000 ppm, CO = 2500-5000 ppm, T = 870-950 K, GHSV = ca. 30000 h. Disproportionate flow due to the clogging of catalyst monolith by dust from engine oil.

Figure 46. Arrhenius diagram for eq 13, recorded in a Berty reactor experiment with a fresh three-way catalyst (monolith catalyst with 62cellscm partial pressure CO 0.005 bar, partial pressure NO 0.005 bar, balance N2 Pt 1.1 g T, Rh 0.2 g I" ). Reprinted from ref [36] with kind permission of Elsevier Seience.

Figure 59. Influence of space velocity on gas temperature needed to reach 50% and 70% conversion of CO, HC and NOjt over a fresh and an engine aged three-way catalyst (monolith catalyst with 62 cells cm, three-way formulation with Pt 1.42gl-, Rh 0.28gl->, engine bench light-off test at lambda 1.02 for CO and HC, and at lambda 0.986 for NO engine bench aging during 200 h).

Preshaped catalysts, monolithic structures, are found to have many large-scale applications downstream from gas turbines, heaters, and in afterburners. Catalytic membranes are under development. 

Emissions data produced from a catalyst monolith are presented in Table 1. 

Chapter 9 covers the treatment of fluidized-bed reactors, based on two-phase models and new empirical correlations for the gas interchange parameter and axial diffusivity. These models are more useful at conditions typical of industrial practice than models based on theories for single bubbles. The last chapter describes some novel types of reactors including riser reactors, catalyst monoliths, wire screen reactors, and reactive distillation systems. Examples feature the use of mass and heat transfer correlations to help predict reactor performance. 

If the catalyst is deposited as a thin layer on the inside or outside of a tube, the slab model can be used if the thickness of the catalyst layer is much less than the tube radius. The slab model is also used to analyze the performance of eggshell catalysts, which have a layer of active catalyst near the outer surface of the pellet, and of catalyst monoliths, which have a thin layer of catalyst on the inside of square, triangular, or hexagonal passages. Flowever, when the catalyst layer is very thin, pore diffusion effects are... 

Catalyst monoliths are also effective in the control of air pollution from stationary sources. They have been used for many years to oxidize hydrocarbon vapors in the vent streams from chemical plants and to reduce solvent emissions from printing and cleaning processes. More recent applications include CO removal from gas turbine exhaust and the selective catalytic reduction of NO in flue gas. Performance curves for the oxidation of various compounds over a Pt/Al203 catalyst are shown in Figure 10.5, where the conversion is plotted against the feed temperature. The reactors operate adiabatically, and the exit temperature may be 10-100°F above the feed temperature. At first, the conversion increases exponentially with temperature, as expected from the Arrhenius relationship. The decrease in slope... 

---