Plate-type catalyst

Uses. Nickel nitrate is an intermediate in the manufacture of nickel catalysts, especially those that are sensitive to sulfur and therefore preclude the use of the less expensive nickel sulfate. Nickel nitrate also is an intermediate in loading active mass in nickel—alkaline batteries of the sintered plate type (see Batteries, SECONDARY cells). Typically, hot nickel nitrate symp is impregnated in the porous sintered nickel positive plates. Subsequendy, the plates are soaked in potassium hydroxide solution, whereupon nickel hydroxide [12054-48-7] precipitates within the pores of the plate. 

Typical applications in the chemical field (Beaver, op. cit.) include detarring of manufactured gas, removal of acid mist and impurities in contact sulfuric acid plants, recovery of phosphoric acid mists, removal of dusts in gases from roasters, sintering machines, calciners, cement and lime Idlns, blast furnaces, carbon-black furnaces, regenerators on fluid-catalyst units, chemical-recoveiy furnaces in soda and sulfate pulp mills, and gypsum kettles. Figure 17-74 shows a vertical-flow steel-plate-type precipitator similar to a type used for catalyst-dust collection in certain fluid-catalyst plants. 

The Fischer-Tropsch reaction is highly exothermic. Therefore, adequate heat removal is critical. High temperatures residt in high yields of methane, as well as coking and sintering of the catalyst. Three types of reac tors (tubular fixed bed, fluidized bed, and slurry) provide good temperature control, and all three types are being used for synthesis gas conversion. The first plants used tubular or plate-type fixed-bed reactors. Later, SASOL, in South Africa, used fluidized-bed reactors, and most recently, slurry reactors have come into use. 

Figure 9.9 Plate-type catalyst (PTC) of Babcock-Hitachi. (Reprinted from [59].)...

Plate-type catalysts (PTCs) consist of metal sheets, metal net, or perforated metal plates with the catalytic species deposited onto, assembled in modules that are inserted into the reactor in layers [58, 59]. Several innovative structures have been reported. Figure 9.9 gives an example of a structure permitting some vibration of the individual plates, reducing possible blockage the plates are very thin, reducing the pressure drop. 

Morita, I., Ogasahara, T., and Franklin, H.N. (2002) Recent Experience with Hitachi Plate Type SCR Catalyst, The Institute of Clean Air Companies Fomm 02, Febmary 12-13. 

Plate type packing to separate the phases is discussed by Carlsson et al. (1983) and by Hatziantoniu etal. (1986). De Vos et al. (1982,1986) describe use of a monolithic porous catalyst with vertical and horizontal channels. The liquid phase flows downward through an array of parallel channels in the monolith, while gas moves in cross flow through a separate set of channels. Another approach treats the catalyst to make part of the surface hydrophobic or lyophobic (Berruti et aL, 1984). The gas phase has direct access to the surface on these unwetted portions of the surface, resulting in partial, spatial segregation of the phases. 

The process has been commercially implemented in Japan since 1977 [1] and a decade later in the U.S., Germany and Austria. The catalysts are based on a support material (titanium oxide in the anatase form), the active components (oxides of vanadium, tungsten and, in some cases, of molybdenum) and modifiers, dopants and additives to improve the performance, especially stability. The catalyst is then deposited over a structured support based on a ceramic or metallic honeycomb and plate-type structure on which a washcoat is then deposited. The honeycomb form usually is an extruded ceramic with the catalyst either incorporated throughout the stmcture (homogeneous) or coated on the substrate. In the plate geometry, the support material is generally coated with the catalyst. 

Beretta A, Orsenigo C, Tronconi E, Forzatti P, Berti F. Analysis of plate-type monolith SCR-DeNO(x) catalysts. Kinet Catal 1998 39 646-648. 

Figure 2 Types of monolithic SCR catalysts (a) honeycomb monolith (b) plate-type catalyst (c) coated metal monolith.

Honcycomb-typc catalyst Figure 4 Mechanism of erosion in plate-type and honeycomb catalysts. 

Table 2 Typical Data for Plate-Type Catalysts...

A honeycomb catalyst is shown in Fig. 8. A corrugated unit is similar in design except that the walls are thinner, thus allowing more open area. A plate-type catalyst has long, rectangular openings between the plates. 

From this catalyst performance test the lifetime of SCR catalysts may be predicted, thus providing a replacement strategy for SCR elements. Honeycomb elements or plate-type elements are placed in the oven of a bench-scale setup. With this method the integral activity of an element is obtained. 

Square-channelled monolith or plate-type vanadia on titania catalysts are commonly used in SCR units of power plants. A typical monolith block (Fig. 16) has the geometrical parameters given in Tables 7 and 10. 

The plate-type catalyst has many advantages over honeycomb systems less pressure loss higher erosion resistance less sensitivity towards fouling by dust higher mechanical and thermal stabilities [133]. 

C. Fukuhara, H. Ohkura, Y. Kamata, Y. Murakami, A. Igarashi, Catalytic properties of plate-type copper-based catalysts, for steam reforming of methanol, on an aluminum plate prepared by electroless plating, Appl. Catal. A-Gen. 273 (2004) 125. 

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