Modeling of Catalytic Fixed-Bed Reactors for Fuels Production by Fischer–Tropsch Synthesis

Abstract

A comprehensive review of the various studies reported in the literature to date on the mathematical modeling of fixed-bed reactors for the production of fuels by the Fischer–Tropsch synthesis (FTS) was carried out. It is quite clear that most of the proposed models are based on a set of assumptions that allow their wide simplification by reducing the models into forms of low complexity, due to the fact that in most cases the effects of phase equilibrium are neglected, and relatively simple Fischer–Tropsch kinetics of the power law type are used. In addition, most of the proposed modeling schemes neglect the effects of resistances to gas–liquid and liquid–solid mass transfer. On the other hand, few reports consider the energy effects under the consideration of a nonisothermal operation assuming a plug-flow behavior and a gas–liquid system. A generalized model of a fixed-bed FTS reactor is proposed which takes into account all the mass and heat transfer phenomena, as well as hydrodynamics and vapor–liquid equilibrium (VLE), based on the information given in the literature. It is evident that for fixed-bed reactors for fuel production using Fischer–Tropsch technology, there is little experimental information for validation and a need to explore different types of reactor models, such as reactor models under a trickle-flow regime considering the effects of phase distribution and dispersion under transient-state conditions.

Development of a kinetic model for low temperature Fischer-Tropsch synthesis

“…Product selectivity in FT synthesis is temperature dependent due to the high exothermicity of the reactions occurring (Claeys & van Steen, 2004). The low temperature FT (LTFT) synthesis conditions of 180-260 • C and 20-30 bar (a), therefore enables syngas to be converted to long chain waxy hydrocarbons, with a high n-paraffin content (Espinoza et al, 1999;Leckel, 2005;Méndez et al, 2017). These waxy products can be subsequently upgraded allowing high quality, clean-burning liquid fuels to be obtained (Geerlings et al, 1999).…”

“…Heat transfer rates are approximately five times lower than in slurry reactors (Geerlings et al, 1999). It is, however, attractive since it operates with a concentration gradient of plug-flow, has a higher catalyst hold-up and no unique separation process is required to separate catalyst from wax (Geerlings et al, 1999;Méndez et al, 2017). This is advantageous in terms of time savings and lower operating costs.…”

“…Although the product distribution of FT synthesis is complex, it shows order with respect to the class and size of the products formed (Claeys and van Steen, 2004). Under the low temperature FT (LTFT) conditions of 180-260 • C and 20-30 bar (a), the main products are linear n-paraffins and 1-olefins, with their formation described by the overall Reactions 2.1 and 2.2 (Claeys & van Steen, 2004;Méndez et al, 2017).…”

Catalytic Technologies for CO Hydrogenation for the Production of Light Hydrocarbons and Middle Distillates

“…Computation studies are recently being advised in the field of kinetics and engineering simulations for the design of more efficient catalysts and novel reactor technologies (e.g., microchannel reactor and monolith reactor). For the FTS reaction, Mendez et al are trying to generalize the modeling scheme of the fixed-bed reactor [94]. In addition, computational studies by Jacobs et al [28] indicate that certain promoters can inhibit polymeric C formation by hindering C-C coupling.…”

Another Critical Look at Three-Phase Catalysis

“…Hydrodynamics of trickle bed reactors were studied 15,16 using transport modeling, 17 computational fluid dynamics (CFD) modeling, 18 electrical resistance tomography, 19 as well as by high pressures. 20 Due to the reliability of their operation, trickle bed reactors have won a great use in oil industry, and also found applications in SO 2 oxidation, 21 glucose hydrogenation over ruthenium catalyst, 22 hydro-treating atmospheric residue, 23 hydro-purification, 24 catalytic hydro-treatment of vegetable oils, 25 fuel production via Fischer-Tropsch synthesis, 26 hydrogen production by aqueous-phase reforming of xylitol, 27 hydrogenolysis, 28,29 continuous thermal oxidation of alkenes with nitrous oxide, 30 liquid-phase selective hydrogenation of methylacetylene and propadiene, 31 hydrogen peroxide, 32 as well as continuous operation. 33 There are two possible mechanisms in trickle bed reactors for breaking down bubble sizes and initiating dissolution of gas into liquid: (1) the interactions of liquid and gas flows, (2) through the tortoise routes that are formed by the packed catalysts, the denser the solid particles, the smaller the diameters of bubbles so formed.…”