Fluidized bed of catalyst

Steinfeld et al. [133] demonstrated the technical feasibility of solar decomposition of methane using a reactor with a fluidized bed of catalyst particulates. Experimentation was conducted at the Paul Scherrer Institute (PSI, Switzerland) solar furnace delivering up to 15 kW with a peak concentration ratio of 3500 sun. A quartz reactor (diameter 2 cm) with a fluidized bed of Ni (90%)/Al2O3 catalyst and alumina grains was positioned in the focus of the solar furnace. The direct irradiation of the catalyst provided effective heat transfer to the reaction zone. The temperature was maintained below 577°C to prevent rapid deactivation of the catalyst. The outlet gas composition corresponded to 40% conversion of methane to H2 in a single pass. Concentrated solar radiation was used as a source of high-temperature process heat for the production of hydrogen and filamentous... 

An equimolal mixture of octenes and hydrogen is fed to a fluidized bed of catalyst at 2 atm. Find the required weight of catalyst per unit of feed, Wc/F0, as a function of conversion in (a) plug flow (b) a completely mixed bed. 

Fluid catalytic cracking cracking in the presence of a fluidized bed of catalyst. 

Reactors batch (B), continuous stirred tank (CST), fixed bed of catalyst (FB), fluidized bed of catalyst (FL), furnace (Furn.), multitubular (MT), semicontinuous stirred tank (SCST), tower (TO), tubular (TU). 

Abbreviations reactors batch (B), continuous stirred tank (CST), fixed bed of catalyst (FB), fluidized bed of catalyst (FL), furnace (Fum.), monolith (M), multitubular (MT), semicontinuous stirred tank (SCST), tower (TO), tubular (TU). Phases liquid (L), gas (G), both (LG). Space velocities (hourly) gas (GHSV), liquid (LHSV), weight (WHSV). Not available, NA. To convert atm to kPa, multiply by 101.3. 

One such catalytic system has been pilot planted by Toyo Engineering Company (7 ). It utilizes a combination catalyst and specially designed feedstock vaporization system to process hydrocarbons as heavy as crude oil to obtain reasonable conversions to hydrogen and carbon monoxide. Another process announced by Grand Paroise uses a fluidized bed of catalyst for the reforming step (8). Heat required is introduced into the fluidized catalyst by burning fuel inside of tubes immersed in the bed. Both of these systems have been extensively tested in large pilot installations and could be included in commerical installations in the near future if justified by economic considerations. 

Fluid catalytic cracking (FCC) (Fig. 13.5) was first introduced in 1942 and uses a fluidized bed of catalyst with continuous feedstock flow. The catalyst is usually a synthetic alumina or zeolite used as a catalyst. Compared to thermal cracking, the catalytic cracking process (1) uses a lower temperature, (2) uses a lower pressure, (3) is more flexible, (4) and the reaction mechanism is controlled by the catalysts. Feedstocks for catalytic cracking include straight-run gas oil, vacuum gas oil, atmospheric residuum, deasphalted oil, and vacuum residuum. Coke inevitably builds up on the catalyst over time and the issue can be circumvented by continuous replacement of the catalyst or the feedstock pretreated before it is used by deasphalting (removes coke precursors), demetallation (removes nickel and vanadium and prevents catalyst deactivation), or by feedstock hydrotreating (that also prevents excessive coke formation). 

Opposiny-reactants mode. When immobilized with a catalyst or enzyme, the interconnected tortuous pores or the nearly straight pores of a symmetric inorganic membrane provides a relatively well controlled catalytic zone or path for the reactants in comparison with the pellets or beads in a fixed or fluidized bed of catalyst particles. This unique characteristic of a symmetric membrane, in principle, allows a novel reactor to be realized provided the reaction is sufficiently fast. The concept applies to both equilibrium and irreversible reactions and does not utilize the membrane as a separator. Consider a reaction involving two reactants, A and B ... 

A fixed-bed reactor often suffers from a substantially small effectiveness factor (e.g., 10 to 10 for a fixed-bed steam reformer according to Soliman et al. [1988]) due to severe diffusional limitations unless very small particles are used. The associated high pressure drop with the use of small particles can be prohibitive. A feasible alternative is to employ a fluidized bed of catalyst powders. The effectiveness factor in the fluidized bed configuration approaches unity. The fluidization system also provides a thermally stable operation without localized hot spots. The large solid (catalyst) surface area for gas contact promotes effective catalytic reactions. For certain reactions such as ethylbenzene dehydrogenation, however, a fluidized bed operation may not be superior to a fixed bed operation. To further improve the efficiency and compactness of a fluidized-bed reactor, a permselective membrane has been introduced by Adris et al. [1991] for steam reforming of methane and Abdalla and Elnashaie [1995] for catalytic dehydrogenation of ethylbenzene to styrene. 

Figure 249 shows the effects of these three variables on the conversion to Cr(VI) in some laboratory experiments [74], In each case, a fluidized bed of catalyst containing 1 wt% Cr(III) on silica was heated in a linear ramp up to 788 °C, and then held at 788 °C for 5 h. As shown in Figure 249 on the left, the amount of catalyst charged to the activator tube was varied, which changed the bed depth. More catalyst means more water released, and consequently lower levels of Cr(VI). Two lines are shown in the left graph, corresponding to two different values of the air flow velocity, which is the second important variable. The effect of air velocity is also evident in the middle graph of Figure 249. More air dilutes the water released and produces a higher yield of Cr(VI). The two lines in the...

A simulation model is currently applied to investigate the partial oxidation of methane in a fluidized bed of catalyst particles with some tenths of a millimeter diameter, rather than in a solid bed. This procedure is expected to provide a much better heat exchange. Total cost reduction is predicted to be about 20 %, which, however, still needs verification [72]. 

The ammoxidation of propylene is carried out by feeding the olefin, air, ammonia and steam over a fixed or fluidized bed of catalyst at between 420 and 500°C. Several binary oxide systems, Bi-Mo, U-Sb (Sohio) and Sn-Sb (BP Chemicals), form the basis of commercial catalysts. Selectivities are now about 70% on propylene, with acetonitrile and HCN as byproducts. 

Our treatment of the mathematical structure of distributed chemical reaction systems refers primarily to the porous catalyst pellet. The theory developed may be applicable, however, to other distributed systems. The catalyst pellet has been extensively investigated, experimentally and theoretically, due to its practical importance. The catalytic reactors, so common in the chemical and petrochemical industry, are devices contacting a fluid with a fixed or fluidized bed of catalyst pellets. Thus, an understanding of the properties of a single pellet is essential to the understanding of the reactor s operation. Catalytic reactions are fast and often... 

The first commercial application of truly fluidized catal)4ic cracking was in 1942 at the Standard Oil Co. of New Jersey s Baton Rouge, LA. refinery. The vaporized oil was cracked in a dense, fluidized bed of catalyst ( bed cracking ). Details of that Model I FCC are given by Avidan et al. (1989). Various hardware improvements were made to bed crackers over the ensuing 30 years, but the advent of Davison s synthetic Y zeolites signalled the demise of bed crackers as state-of-art. 

Given A flapper valve of 41 cm is submerged 1.5 m in a fluidized bed of catalyst. The existing 1 cm thick flapper plate is experiencing erosion and a proposal has been made to replace the plate with a special hardened-steel plate having double the thickness. 

If the temperature rise in an adiabatic reactor requires too many beds, the overall reaction can be made more selective and operation more economic by using a fluidized bed of catalyst at a uniform temperature. 

Reduced catalyst is then reoxidized with air, in a separate regeneration reactor, to regenerate the active form. This innovation followed the snccessful introduction of conventional fluidized bed operation by Alusuisse and other companies in 1983. Physical circulation of a fluidized bed of catalyst particles, or microspheres, is an unusual technology and has been developed commercially only for the fluid catalytic cracking of heavy gas oils and the SASOL version of the Fischer-Tropsch Synthol process. Success depends not only on an active and selective catalyst but also on the resistance of the catalyst to attrition during the transfer from the reactor to the regenerator and back agaiir... 

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