Catalyst wires

Reactor 19 [R 19] Catalyst-wire-in-channel Micro Reactor... 

Figure 3.24 Image of the catalyst-wire-in-channel micro reactor [82].

Reactor type Catalyst-wire-in- channel Housing a diameter thickness 50 mm 7.5 mm... 

The N20 decomposition, CO oxidation, and H2 oxidation reactions are known to exhibit concentration oscillations over noble metal catalysts. Flytzani-Stephanopoulos et al. (47) have observed oscillations for the oxidation of NH3 over Pt. The effects are dramatic and lead to large temperature cycles for the catalyst wire. Heat and mass transfer effects are important. 

There are many correlations for these geometries, both of which are important for mass transfer in chemical reactors. Tube banks could be catalyst wires or tubes in a reactor over... 

Figure 1. Vertical section of reactor. Key A, normal to catalyst wire B, reactant gas stream and C, argon stream.

Monolithic Catalysts Wire-Screen Catalysts Reactive Distillation Nomenclature Problems References... 

The anhydrous ammonia and process air used must be free from catalyst poisons, dust, and oil. Platinum catalysts can be poisoned by such elements as As, Bi, P, Pb, S, Si, and Sn. Fortunately, synthetic ammonia is normally of high purity unless it is accidentally-contami -nated. However, since air can be contaminated by dust or many other pollutants, thorough air cleaning is necessary. Location of the air intake in an area relatively free from contaminants will help. If poisoning by impure ammonia or air ould arise, deep penetration may occur, leading to the formation of inactive compounds in the catalyst wires and, perhaps, to the extent of ruining the catalyst, fri other instances, contamination by traces of Cr, Fe, or Ni may temporarily reduce conversion efficiency, but this can often be restored by treatment with hydrochloric acid or certain sails. 

A practical way to increase the efficiency of fractionation or the quality of products is to employ wire-mesh mist extractors below the points at which products are withdrawn. In the production of an asphalt bottom product and at the same time a gas-oil catalytic feedstock that is free from entrained asphalt or metal contaminants that tend to poison the catalyst, wire-mesh has resulted in phenomenal increases in capacity or in large reductions in contaminants. 

C. Fumaric acid from furfural. Place in a 1-litre three-necked flask, fitted with a reflux condenser, a mechanical stirrer and a thermometer, 112 5 g. of sodium chlorate, 250 ml. of water and 0 -5 g. of vanadium pentoxide catalyst (1), Set the stirrer in motion, heat the flask on an asbestos-centred wire gauze to 70-75°, and add 4 ml. of 50 g. (43 ml.) of technical furfural. As soon as the vigorous reaction commences (2) bvi not before, add the remainder of the furfural through a dropping funnel, inserted into the top of the condenser by means of a grooved cork, at such a rate that the vigorous reaction is maintained (25-30 minutes). Then heat the reaction mixture at 70-75° for 5-6 hours (3) and allow to stand overnight at the laboratory temperature. Filter the crystalline fumaric acid with suction, and wash it with a little cold water (4). Recrystallise the crude fumaric acid from about 300 ml. of iif-hydrochloric acid, and dry the crystals (26 g.) at 100°. The m.p. in a sealed capillary tube is 282-284°. A further recrystaUisation raises the m.p. to 286-287°. 

Chapter III. 1 Heptene (111,10) alkyl iodides (KI H3PO4 method) (111,38) alkyl fluorides (KF-ethylene glycol method) (111,41) keten (nichrome wire method) (111,90) ion exchange resin catalyst method for esters (111,102) acetamide (urea method) (111,107) ethyl a bromopropionate (111,126) acetoacetatic ester condensation using sodium triphenylmethide (111,151). 

Rates and selectivities of soHd catalyzed reactions can also be influenced by mass transport resistance in the external fluid phase. Most reactions are not influenced by external-phase transport, but the rates of some very fast reactions, eg, ammonia oxidation, are deterrnined solely by the resistance to this transport. As the resistance to mass transport within the catalyst pores is larger than that in the external fluid phase, the effectiveness factor of a porous catalyst is expected to be less than unity whenever the external-phase mass transport resistance is significant, A practical catalyst that is used under such circumstances is the ammonia oxidation catalyst. It is a nonporous metal and consists of layers of wire woven into a mesh. 

Silicon—Ca.rbon Thermoset. The Sycar resins of Hercules are sihcon—carbon thermosets cured through the hydrosilation of sihcon hydride and sihcon vinyl groups with a trace amount of platinum catalyst. The material is a fast-cure system (<15 min at 180°C) and shows low moisture absorption that outperforms conventional thermosets such as polyimides and epoxies. Furthermore, the Sycar material provides excellent mechanical and physical properties used in printed wiring board (PWB) laminates and encapsulants such as flow coatable or glob-top coating of chip-on-board type apphcations. 

Usually they are employed as porous pellets in a packed bed. Some exceptions are platinum for the oxidation of ammonia, which is in the form of several layers of fine-mesh wire gauze, and catalysts deposited on membranes. Pore surfaces can be several hundred mVg and pore diameters of the order of 100 A. The entire structure may be or catalytic material (silica or alumina, for instance, sometimes exert catalytic properties) or an active ingredient may be deposited on a porous refractory carrier as a thin film. In such cases the mass of expensive catalytic material, such as Pt or Pd, may be only a fraction of 1 percent. 

Fast catalytic reac tions that must be quenched rapidly are done in contac t with wire screens or thin layers of fine granules. Ammonia in a 10% concentration in air is oxidized by flowthrough a fine gauze catalyst made of 2 to 10% Rh in Pt, 10 to 30 layers, 0.075-mm (0.0030-in) diameter wire. Contact time is 0.0003 s at 750°C (1,382°F) and 7 atm (103 psi) followed by rapid quenching. Methanol is oxidized to formaldehyde in a thin layer of finely divided silver or a multilayer screen, with a contact time of 0.01 s at 450 to 600°C (842 to 1,112°F). 

The cross-linking stage is facilitated by the use of a cross-linking catalyst, which is typically an organo-tin compound. A number of variations of this process exist and in one of these compounding, grafting and extmsion onto wire are carried out in the same extruder. 

A device based on flame ionization measures the total concentration of hydrocarbons. By using a catalyst, such as a heated platinum wire, hydrocarbons other than methane can be removed from the sample gas. With a platinum catalyst, these hydrocarbons are oxidized at a lower temperature than methane. Hence, the total concentration of hydrocarbons, methane, and hydrocarbons other than methane can be determined. 

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