Metal gauzes

Materials of construction C = ceramic E = expanded metal G= metal gauze S = sheet metal. 

Efficiency and pressure drop data for Siilzer BX metal gauze structured packing and for three test mixtures are shown in Fig. 14-7.5. For the ethyl benzene/styrene test mixture, the effect of operating pressure is shown. The high viscosity mixture, propylene glycoL/ethylene... 

To prevent glass fragments from flying in the event of an explosion, use should be made of metal gauzes to screen reaction flasks etc., or cages, e.g. for desiccators. Vessels of awkward size/shape may be covered with cling film. 

Thus zeolite ZSM-5 can be grown (ref. 15) onto a stainless steel metal gauze as shown in Figure 6. Presumably the zeolite crystals are chemically bonded to the (chromium-) oxide surface layer of the gauze. After template removal by calcination and ion exchange with Cu(II) a structured catalyst is obtained with excellent performance (ref. 15) in DeNOx reactions using ammonia as the reductant. 

Concerning the hydrodynamics and the dimensioning of the test reactor, some rules of thumb are a valuable aid for the experimentalist. It is important that the reactor is operated under plug-flow conditions in order to avoid axial dispersion and diffusion limitation phenomena. Again, it has to be made clear that in many cases testing of monolithic bodies such as metal gauzes, foam ceramics, or monoliths used for environmental catalysis, often needs to be performed in the laminar flow regime. 

Mass and heat transfer between the bulk fluid phase and the external catalyst surface can have an affect on reaction rates, and hence the selectivity, because of modified concentration and temperature driving forces. Such effects are unimportant for porous catalysts, but are significant for catalysis by non-porous metallic gauzes (for example, in NH3 oxidation referred to in Sect. 6.1.1). 

The catalytic bed (70 cm ), supported by a metallic gauze, is located in the reforming section. Water is fed to the reactor at the bottom of the metallic gauze. The temperature inside the reactor is monitored by four thermocouples one (Tcomb) is located on the SiC foam and the other three (T ref L, T ref M, T ref H) are located at 25, 50 and 75%, respectively, of the catalytic bed height to provide the reactor temperature axial profile. Moreover, additional thermocouples monitor... 

The modified supported powder electrodes used in the experiments hitherto described on the anodic activity of CoTAA are out of the question for practical application in fuel cells, as they do not have sufficient mechanical stability and their ohmic resistance is very high (about 1—2 ohm). For these reasons, compact electrodes with CoTAA were prepared by pressing or rolling a mixture of CoTAA, activated carbon, polyethylene, and PTFE powders in a metal gauze. The electrodes prepared in this way show different activities depending on the composition and the sintering conditions. Electrodes prepared under optimal conditions can be loaded up to about 40 mA/cm2 at a potential of 350 mV at 70 °C in 3 M HCOOH, with relatively good catalyst utilization (about 5 A/g) and adequate stability. 

Fredenhagcn and Cadenbach reacted fluorine with organic vapors within the mesh of a metal gauze. Though some of their reactions must have involved liquid films, this became a standard vapor-phase process. 

Table 7. Elimination of Fluorine from Perfluoroalkanes and -cycloalkanes Using Metal Gauze...

Substrate Metal Gauze Temp3 ( C) Product Yield3 (%) Ref... 

The flask B containing the pyridine is heated on a metal gauze or on an air-bath. The extraction is discontinued when the pyridine passes through colourless usually two hours are sufficient, but with thick or heavily felted goods, four hours may be required. In the latter case it is sometimes well, after an hour, to interrupt the extraction while the material in the tube A is rearranged. 

The nature of the charge in a desiccator, which is placed in the lower compartment below the metal gauze plate, is dependent on whether water or organic solvents are to be removed and whether acidic or basic vapours are likely to be evolved during the drying process. Suitable charges are discussed in Section 2.20. 

The appearance of gauzes is illustrated by Figures 5 and 6 (9). The use of noble metal gauzes goes back to the beginning of the 20th century for the oxidation of ammonia into NO. This work followed up work of Ostwald, who applied platinized asbestos and later a roll of corrugated strip of Pt. Probably, this was the first application of a structured reactor. 

Fig. 11. Linear correlation between activation energy and pre-exponential factor for different wavelengths (filters UG and BG) and intensities (metal gauze sieves S) of the CO oxidation on ZnO...

In 2000, U.S. Patent 6,073,467 was issued for a three-dimensional, knitted, noble metal gauze for nitric acid production. This catalyst design claims to provide elevated product yields and a stable course for the reaction. It also claims to extend catalyst service life with the smallest possible noble metal... 

In hydrogen cyanide synthesis using the Andrussow process, air, methane, and ammonia are fed over 15 to 50 layers of noble metal gauze at 1050 to 1150°C at near atmospheric pressure. 

The manufacture of nitric acid by the oxidation of ammonia on platinum-type metal gauzes uses a technology which has change little since its first introduction in 1902. Although the conversion proceeds with an efficiency in excess of 90%, the loss of... 

For many catalysts, the major component is the active material. Examples of such unsupported catalysts are the aluminosilicates and zeolites used for cracking petroleum fractions. One of the most widely used unsupported metal catalysts is the precious metal gauze as used, for example, in the oxidation of ammonia to nitric oxide in nitric acid plants. A very fast rate is needed to obtain the necessary selectivity to nitric oxide, so a low metal surface area and a short contact time are used. These gauze s are woven from fine wires (0.075 mm in diameter) of platinum alloy, usually platinum-rhodium. Several layers of these gauze s, which may be up to 3 m in diameter, are used. The methanol oxidation to formaldehyde is another process in which an unsupported metal catalyst is used, but here metallic silver is used in the form of a bed of granules. 

The silvcr based catalyst is in the fonn of a metal gauze or crystals, which may be (feposited on a support It can also be used in these two forms simultaneously. Other metals, such as copper and platinum, employed originally by Hofinann in 1868, also catalyze the inversion, but are not employed industrially. 

The key to success is to keep the pellets from rising to the top of the molten salt and floating there. Lin contrived to inject the pellets beneath a cage of metal gauze where they remain trapped—keeping them... 

---