Fischer-Tropsch slurry reactors

In 1976 he was appointed to Associate Professor for Technical Chemistry at the University Hannover. His research group experimentally investigated the interrelation of adsorption, transfer processes and chemical reaction in bubble columns by means of various model reactions a) the formation of tertiary-butanol from isobutene in the presence of sulphuric acid as a catalyst b) the absorption and interphase mass transfer of CO2 in the presence and absence of the enzyme carboanhydrase c) chlorination of toluene d) Fischer-Tropsch synthesis. Based on these data, the processes were mathematically modelled Fluid dynamic properties in Fischer-Tropsch Slurry Reactors were evaluated and mass transfer limitation of the process was proved. In addition, the solubiHties of oxygen and CO2 in various aqueous solutions and those of chlorine in benzene and toluene were determined. Within the framework of development of a process for reconditioning of nuclear fuel wastes the kinetics of the denitration of efQuents with formic acid was investigated. 

Mass Transfer and Product Selectivity in a Mechanically Stirred Fischer—Tropsch Slurry Reactor... 

These reactors for liquids and liquids plus gases employ small particles in the range of 0.05 to 1.0 mm (0.0020 to 0.039 in), the minimum size limited by filterability. Small diameters are used to provide as large an interface as possible since the internal surface of porous pellets is poorly accessible to the liquid phase. Solids concentrations up to 10 percent by volume can be handled. In hydrogenation of oils with Ni catalyst, however, the solids content is about 0.5 percent, and in the manufacture of hydroxylamlne phosphate with Pd-Citis0.05 percent. Fischer-Tropsch slurry reactors have been tested with concentrations of 10 to 950 g catalyst/L (0.624 to 59.3 Ibm/fF) (Satterfield and Huff, Chem. Eng. Sci., 35, 195 [1980]). 

On the basis of the assumptions of model <22> and <23> the Fischer-Tropsch synthesis in a slurry phase BCR has been modeled [37, 38]. As this hydrocarbon synthesis from synthesis gas (CO + H2) is accompanied by considerable volume contraction, it is clear that gas flow variations have to be accounted for. The developed models are useful to evaluate experimental data from bench scale units and to simulate the behavior of larger scale Fischer-Tropsch slurry reactors. Though only simplified kinetic laws were applied, the predictions of the model are in reasonable agreement with data reported from 1.5 m diameter demonstration plant. Fig. 12 shows computed space-time-yields (STY) as a function of the inlet gas velocity. As the Fischer-Tropsch reaction on suspended catalyst takes place in the slow reaction regime, it is understood that STY passes through a maximum in dependence of uqo- The predicted maximum is in striking agreement with experimental observations [37]. 

Example 4 Optimum Gas Velocity for Fischer-Tropsch Slurry Reactor... 

De Swart, J.W.A., Krishna, R., Sie, S.T., 1997. Selection, design and scale up of the Fischer—Tropsch slurry reactor. Studies in Surface Sciences and Catalysis 107,... 

Saxena, S. C., Rosen, M., Smith, D. N., and Ruether, J. A., Mathematical Modeling of Fischer-Tropsch Slurry Bubble Column Reactors, Chem. Eng. Comm., 40 97 (1986)... 

Slurry reactors find many applications in chemical industry. Most of these arc heterogeneous catalytic processes with hydrogenation of edible oils as the most classic example and SASOL s novel continuous Fischer Tropsch slurry synthesis process [1], the latest impressive new development in this area. Doraiswamy and Sharma [2] identified over 50 different slurry reactor applications, and an updated list would no doubt be longer still. 

Solids play different roles in the different processes. In direct coal liquefaction, a part of the solid is dissolved in liquid (mainly in the preheater) and a part (i.e. mineral matter) may act as a catalyst for the hydrogenation reactions. In Fischer-Tropsch slurry processes, solids are catalysts. Finally, in chemical cleaning of coal, only a part of solid (i.e. sulfur) takes part in the reaction following the shrinking core diffusion/ reaction mechanism. The role of solids in the design and scaleup of the reactors for the three processes is therefore different. 

Turner JR, Mills PL. Comparison of axial dispersion and mixing cell models for design and simulation of Fischer-Tropsch slurry bubble column reactors. Chem. Eng. Sd. 1990 45 2317-2324. 

Heat Release and Reactor Stability. Highly exothermic reactions, such as with phthaHc anhydride manufacture or Fischer-Tropsch synthesis, compounded with the low thermal conductivity of catalyst peUets, make fixed-bed reactors vulnerable to temperature excursions and mnaways. The larger fixed-bed reactors are more difficult to control and thus may limit the reactions to jacketed bundles of tubes with diameters under - 5 cm. The concerns may even be sufficiently large to favor the more complex but back-mixed slurry reactors. 

The Fischer-Tropsch reaction is highly exothermic. Therefore, adequate heat removal is critical. High temperatures residt in high yields of methane, as well as coking and sintering of the catalyst. Three types of reac tors (tubular fixed bed, fluidized bed, and slurry) provide good temperature control, and all three types are being used for synthesis gas conversion. The first plants used tubular or plate-type fixed-bed reactors. Later, SASOL, in South Africa, used fluidized-bed reactors, and most recently, slurry reactors have come into use. 

The catalytic hydrogenation of fatty oils, the desulfurization of liquid petroleum fractions by catalytic hydrogenation, Fischer-Tropsch-type synthesis in slurry reactors, and the manufacture of calcium bisulfite acid are familiar examples of this type of process, for which the term gas-liquid-particle process will be used in the following. 

Epoxides such as ethylene oxide and higher olefin oxides may be produced by the catalytic oxidation of olefins in gas-liquid-particle operations of the slurry type (S7). The finely divided catalyst (for example, silver oxide on silica gel carrier) is suspended in a chemically inactive liquid, such as dibutyl-phthalate. The liquid functions as a heat sink and a heat-transfer medium, as in the three-phase Fischer-Tropsch processes. It is claimed that the process, because of the superior heat-transfer properties of the slurry reactor, may be operated at high olefin concentrations in the gaseous process stream without loss with respect to yield and selectivity, and that propylene oxide and higher... 

Various methods may be used for the determination of gas holdup—for example, displacement measurements and tracer experiments. Farley and Ray (F2) have described the use of gamma-radiation absorption measurement for the determination of gas holdup in a slurry reactor for the Fischer-Tropsch synthesis. 

Calderbank et al. (C6) studied the Fischer-Tropsch reaction in slurry reactors of 2- and 10-in. diameters, at pressures of 11 and 22 atm, and at a temperature of 265°C. It was assumed that the liquid-film diffusion of hydrogen from the gas-liquid interface is a rate-determining step, whereas the mass transfer of hydrogen from the bulk liquid to the catalyst was believed to be rapid because of the high ratio between catalyst exterior surface area and bubble surface area. The experimental data were not in complete agreement with a theoretical model based on these assumptions. 

Tavasoli, A., Abbaslou, R. M. M., Trepanier, M., and Dalai, A. K. 2008. Fischer-Tropsch synthesis over cobalt catalyst supported on carbon nanotubes in a slurry reactor. Applied Catalysis A General 345 134-42. 

O Shea, V. A. D., Alvarez-Galvan, M. C., Campos-Martin, J. M., and Fierro, J. L. G. 2007. Fischer-Tropsch synthesis on mono- and bimetallic Co and Fe catalysts in fixed-bed and slurry reactors. Applied Catalysis A General 326 65-73. 

Graver, V., Zhan, X., Engman, J., Robota, H. J., Suib, S. L., and Polverejan, M. 2004. Deactivation of a Fischer-Tropsch catalyst through the formation of cobalt carbide under laboratory slurry reactor conditions. Prepr. Pap.-Am. Chem. Soc. Div. Pet. Chem. 49 192-94. 

A continuous cross-flow filtration process has been utilized to investigate the effectiveness in the separation of nano sized (3-5 nm) iron-based catalyst particles from simulated Fischer-Tropsch (FT) catalyst/wax slurry in a pilot-scale slurry bubble column reactor (SBCR). A prototype stainless steel cross-flow filtration module (nominal pore opening of 0.1 pm) was used. A series of cross-flow filtration experiments were initiated to study the effect of mono-olefins and aliphatic alcohol on the filtration flux and membrane performance. 1-hexadecene and 1-dodecanol were doped into activated iron catalyst slurry (with Polywax 500 and 655 as simulated FT wax) to evaluate the effect of their presence on filtration performance. The 1-hexadecene concentrations were varied from 5 to 25 wt% and 1-dodecanol concentrations were varied from 6 to 17 wt% to simulate a range of FT reactor slurries reported in literature. The addition of 1-dodecanol was found to decrease the permeation rate, while the addition of 1-hexadecene was found to have an insignificant or no effect on the permeation rate. 

Benham, C. B., Yakobson, D. L., and Bohn, M. S. 2000. Catalyst/wax separation device for slurry Fischer-Tropsch reactor. U.S. Patent 6068760. 

Schulz, H., and Claeys, M. 1999. Reactions of a-olefins of different chain length added during Fischer-Tropsch synthesis on a cobalt catalyst in a slurry reactor. Appl. Catal. A 186 71-90. 

Change in Fischer-Tropsch synthesis. In the 1990s the Kellogg Fe-HTFT synthesis section was decommissioned and additional Fe-LTFT synthesis capacity was added with the introduction of a slurry bed reactor.35 This modified the syncrude feed to the refinery to Fe-LTFT only. This was accompanied by a significant change in the product slate being produced. 

AGC-21 A process for converting natural gas to liquid fuels in three stages generation of syngas in a fluidized bed, Fischer-Tropsch synthesis in a slurry bubble column reactor, and hydrocracking. Piloted in 1997 and proposed for installation in Qatar. 

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,... 

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