High-pressure fixed-bed reactors

Figure 1. Key elements of the TAP reactor (A) and high pressure fixed bed reactor (B) experimental systems. The TAP reactor schematic shows the heated valve manifold and reactor with the elevated pressure attachment located in the main high vacuum chamber. The fixed bed reactor shows the feed system, liquid vaporizer, oxygen disperser, reactor, and waste recovery system.

In this work we have evaluated the catalytic properties of the molybdenum-phosphorus catalysts. For this purpose, we have prepared two Ni-Mo-P/AljOj samples following the impregnation sequences (Mo+P->Ni) and (P->Mo->Ni). These samples present the same chemical composition (15 wt% MoOj, 7.5 wtiK PjOj and 5.0 wt% NiO). The catalytic reaction was carried out in a high pressure fixed bed reactor using a vacuum gasoil under typical mild-hydrocracking conditions (T = 653K, P = 5 MPa, LHSV = 0.65 1/h, Hj/Hc = 600). 

The Geminox process oxidizes n-butane in air over a vanadium-phosphorous oxide catalyst in a fluid-bed reactor to maleic anhydride, which is then quenched to maleic acid by absorbing it into water. This highly acidic stream is then pumped to two high-pressure fixed-bed hydrogenation reactors containing carbon-supported catalysts to convert maleic acid to BDO. The major product of reaction, a mixture of 1,4-butanediol, tetrahydrofuran (THF), and y-butyrolactone, is then separated by fractional distillation. The yield of... 

Applications of the organic solvents in fluidized-bed reactors have also been investigated, particularly with immobilized cells (Table 5). This type of reactor has several advantages over a fixed-bed reactor, namely, reduced coalescence of the emulsion particles, lower pressure at high flow rate, and less channeling and plugging. 

The most difficult problem to solve in the design of a Fischer-Tropsch reactor is its very high exothermicity combined with a high sensitivity of product selectivity to temperature. On an industrial scale, multitubular and bubble column reactors have been widely accepted for this highly exothermic reaction.6 In case of a fixed bed reactor, it is desirable that the catalyst particles are in the millimeter size range to avoid excessive pressure drops. During Fischer-Tropsch synthesis the catalyst pores are filled with liquid FT products (mainly waxes) that may result in a fundamental decrease of the reaction rate caused by pore diffusion processes. Post et al. showed that for catalyst particle diameters in excess of only about 1 mm, the catalyst activity is seriously limited by intraparticle diffusion in both iron and cobalt catalysts.1... 

In the cobalt-catalyzed Fischer-Tropsch reaction, oxygen is mainly rejected as water and this will generate high partial pressures of water at the reactor exit for fixed-bed reactors. As a consequence of extensive back mixing in slurry reactors,... 

The first reaction is the isomerization from a zero-octane molecule to an alkane with 100 octane the second is the dehydrocyclization of heptane to toluene with 120 octane, while the third is the rmdesired formation of coke. To reduce the rate of cracking and coke formation, the reactor is run with a high partial pressure of H2 that promotes the reverse reactions, especially the coke removal reaction. Modem catalytic reforming reactors operate at 500 to 550°C in typically a 20 1 mole excess of H2 at pressures of 20-50 atm. These reactions are fairly endothermic, and interstage heating between fixed-bed reactors or periodic withdrawal and heating of feed are used to maintain the desired temperatures as reaction proceeds. These reactors are sketched in Figure 2-16. 

Ethyl Chloride. Hydrochlorination of ethylene with HC1 is carried out in either the vapor or the liquid phase, in the presence of a catalyst.182-184 Ethyl chloride or 1,2-dichloroethane containing less than 1% A1C13 is the reaction medium in the liquid-phase process operating under mild conditions (30-90°C, 3-5 atm). In new plants supported AlClj or ZnCl2 is used in the vapor phase. Equimolar amounts of the dry reagents are reacted in a fluidized- or fixed-bed reactor at elevated temperature and pressure (250-400°C, 5-15 atm). Both processes provide ethyl chloride with high (98-99%) selectivity. 

Acetic acid is formed when methane reacts with CO or C02 in aqueous solution in the presence of 02 or H202 catalyzed by vanadium complexes.327 A Rh-based FeP04 catalyst applied in a fixed-bed reactor operating at atmospheric pressure at 300-400° C was effective in producing methyl acetate in the presence of nitrous oxide.328 The high dispersion of Rh at sites surrounded by iron sites was suggested to be a key factor for the carbonylation reaction. 

By choosing a suitable solvent and suitable conditions (concentrations, temperatures, and pressures), the solvent, the substrate, the product, and the hydrogen can form a single phase. When such a single phase is fed to a fixed-bed reactor, extremely high reaction rates have been achieved for very large molecules [28 - 30]. These reaction rates, expressed on a molar basis, are the same as those achieved in gas-phase reactors for small molecules [30]. 

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