Catalysts reactors

Most of the world s commercial formaldehyde is manufactured from methanol and air either by a process using a silver catalyst or one using a metal oxide catalyst. Reactor feed to the former is on the methanol-rich side of a flammable mixture and virtually complete reaction of oxygen is obtained conversely, feed to the metal oxide catalyst is lean in methanol and almost complete conversion of methanol is achieved. 

Typically, reactors require some type of catalyst. Reactors with catalyst can be of the fixed-bed style for fiuid-bed types. Fixed-bed reactors are the most common. The feed often enters the reactor at an elevated temperature and pressure. The reaction mixtures are often corrosive to carbon steel and require some type of stainless steel alloy or an alloy liner for protection. If the vessel wall is less than 6 mm, the vessel is constmcted of all alloy if alloy is provided. Thicker reactor walls can be fabricated with a stainless overlay over a carbon steel or other lower alloy base steel at less cost than an all-alloy wall constmction. 

Fluidized Catalyst Reactor. Two systems have been proposed, based on large scale operation of the Fischer-Tropsch process (to produce liquid hydrocarbons) at SASOL and at Carthage Hydrocol. The SASOL system was designed by M. W. Kellogg and has been operating for about 20 years (57, 58, 59, 60). 

Ramachandran, RA. and R.V. Chaudhari, Three Phase Catalystic Reactors. 1983 Gordon and Breach. 

The flow pattern of fluids in gas-liquid-solid (catalyst) reactors is often far from ideal. Special care must be taken to avoid by-passing of the catalyst particles near the reactor walls, where the packing density of the catalyst pellets is lower than in the centre of the bed. By-passing becomes negligible if the ratio of reactor to particles diameter is larger than 10 a ratio of 20 is recommended. Flow maldistributions might be serious in the case of shallow beds. Special devices must be used to equalize the velocity over the cross-section of the reactor before reactants are introduced onto the catalyst bed. 

The regression for integral kinetic analysis is generally non-linear. Differential equations may include unobservable variables, which may produce some additional problems. For instance, heterogeneous catalytic models include concentrations of species inside particles, while these are not measured. The concentration distributions, however, can affect the overall performance of the catalyst/reactor. 

De Vos, R., Smedler, G., and Schoon, N.-H., Selectivity aspects of using the cross-flow catalyst reactor for liquid phase hydrogenations. Ind. Eng. Chem. Process Des. Dev. 25, 197-202 (1986). 

Commercially available processes for resid HCK deal with catalyst life cycle issues by the use of different catalyst/reactor/configuration arrangements. In Ref. [142], Morel et al. discuss the performance and features of these arrangements. A summary of conditions for each reaction system is collected in Table 11. 

Technology Catalyst Reactor Type Year Facility... 

Ref. Catalyst Reactor Kinetic effect Comments and additional data... 

Various reactor types have been used as the foundation for microreactor designs, including coated wall reactors, packed-bed reactors, structured catalyst reactors, and membrane reactors. 

Figure 19. Battelle s methanol specific reforming catalyst. Reactor conditions atmospheric pressure, reactant feed 50 50 by weight methanol and water mixture, 24 000— 50 000 ii GHSV. The conversion was reported as moles methanol reacted/moles methanol fed. (Reprinted with permission from ref 91. Copyright 2002 Elsevier.)...

Premixer Catalytic Post-catalyst reactor mixing... 

These experiments have made tremendous advances of in situ catalyst reactor system analysis. A discussion of all of them is outside the scope of this chapter. However, descriptions of the techniques that have contributed significantly to the rational design and analysis of catalysts are presented in the next section. It should be recognized that it is not an exhaustive list but, rather, should be considered a starting point to help in understanding the various in situ techniques both in use currently and at the forefront of development. In addition, review papers are referenced for the reader to find more information on techniques that are and are not discussed. 

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