Modeling of fixed bed methanation reactor for syngas production: Operating window and performance characteristics

BIOVERT+PFOThe present work focuses on the development of phenomenological model for the bio-syngas to methane conversion process. One dimensional heterogeneous and pseudo-homogeneous model were simulated for a typical pilot plant scale fixed bed methanator processing 55 mol/h of CO (total molar flow rate of 310 mol/h) with inlet composition of H-2/CO = 3, CO2/CO = 1, CH4/CO = 0.5 at 550 K and 1 atm. Performance of the fixed bed reactor at different operating conditions like CO2/CO ratio, H-2/CO ratio, effect of H2O in the feed was studied. It was found that for feeds that were not pre-enriched with hydrogen, presence of water and water gas shift activity was found to decrease the catalyst inventory substantially. CO2 in the inlet feed stream would help to decrease the temperature due to dilution effect and more importantly, can be chosen to maximize methane yield per mole of CO converted. Further, the model was simulated to predict the performance characteristics of reactor with a mixture containing two types of catalyst, one of them being specifically added to increase H-2/CO ratio in feed through water gas shift reaction. The work also laid the importance of incorporating pore diffusion and external mass transfer locally in the computation of actual catalyst inventory and reactor volume. The work was useful in selection of operating window and assessing the various viable options for an industrial reactor. The model developed will serve in selection of operability window for commercialization of substitute natural gas synthesis (SNG) process. (c) 2013 Elsevier Ltd. All rights reserved

Fischer–Tropsch synthesis in milli-fixed bed reactor: Comparison with centimetric fixed bed and slurry stirred tank reactors

International audienceThis paper presents a comparative study of Fischer-Tropsch synthesis in single channel milli-fixed bed, conventional centimetric fixed bed and slurry stirred tank reactors. In the three reactors, the catalytic measurements were carried out with the same conventional platinum-promoted alumina supported cobalt catalyst at 493 K and 20 bar using a stoichiometric syngas ratio (H(2)/CO = 2). The single channel milli-fixed bed reactor displays a higher initial Fischer-Tropsch reaction rate than the conventional centimetric fixed bed reactor. This effect was assigned to a better temperature control and less significant catalyst deactivation during the startup of the single channel milli-fixed bed reactor. The slurry stirred tank reactor shows much lower hydrocarbon productivity than the milli- and centimetric fixed bed reactors, which is probably due to incomplete catalyst reduction. A considerable catalyst deactivation due to the uncontrolled temperature hike can occur during the reactor startup in the conventional centimetric fixed bed reactor. The slurry stirred tank and milli-fixed bed reactors show similar apparent deactivation behavior. (C) 2011 Elsevier B.V. All rights reserved

Deactivation of a Co/Al2O3 Fischer-Tropsch catalyst by water-induced sintering in slurry reactor: Modeling and experimental investigations

BIOVERT+PFOThe deactivation of cobalt based catalysts in slurry Fischer-Tropsch reactor has been modeled assuming a sintering mechanism which involves the intermediate formation of cobalt oxide layer on metallic nanoparticles. The mechanism, correlating the crystallite size growth to the water to hydrogen concentration ratio in the liquid phase, has been used to describe the activity decline with time on stream. The effect of operating conditions on the rate of sintering is considered. It is found that at the same initial conversion, sintering rate is higher for lower H-2/CO ratios, whereas higher ratios could lead to larger crystallites once operated at constant gas flow rate. The presence of water in the inlet syngas stream also accelerates sintering. The sintering model is then used to describe the deactivation in laboratory-scale slurry reactor. (C) 2013 Elsevier B.V. All rights reserved

W-SBA based materials as efficient catalysts for the ODS of model and real feeds: Improvement of their lifetime through active phase encapsulation

International audienceIncorporated W-SBA based catalysts were prepared by a direct synthesis method involving phosphotungstic acic (HPW) together with mixed structure directing agents, and by incipient wetness impregnation for comparison purpose. In the oxidative desulfurization CODS) of dibenzothiophene (DBT, 500-1500 ppmS) and of a Straight Run Gas Oil (SRGO, 2000 ppmS) in batch reactor, the impregnated solids showed higher efficiency than the incorporated ones, which was attributed to a better accessibility of the active phase present at the surface of the support in the impregnated catalysts. However, in continuous evaluation using a fixed bed reactor, the incorporated catalyst showed a stable conversion in the ODS of SRGO 2000 ppmS for 9 days while within 24 h the impregnated solid was almost completely deactivated. Higher interaction of the active phase with the support in incorporated catalysts was evidenced by Time-of-Flight Secondary Ions Mass Spectrometry (ToF-SIMS) analysis, which can be at the origin of less leaching of tungsten species during reaction and thus explain their better resistance towards deactivation. The lower efficiency of incorporated catalysts compared to impregnated ones in ODS reaction carried out in a batch reactor is clearly compensated by their resistance towards leaching of the active phase in a continuous test. These results highlight the importance of evaluating not only the catalysts performance but also their lifetime in conditions more representative of industrial ones

Effect of Different Reaction Conditions on the Deactivation of Alumina-Supported Cobalt Fischer-Tropsch Catalysts in a Milli-Fixed-Bed Reactor: Experiments and Modeling

BIOVERT+PFOThis paper focuses on the deactivation of a cobalt-based alumina-supported Fischer-Tropsch catalyst in a milli-fixed-bed reactor under different operating conditions. Different catalyst deactivation behaviors were observed at different syngas H-2/CO ratios and temperatures. The deactivation follows a two-step profile, where the initial deactivation is attributed to sintering, whereas the long-term deactivation is due to carbon deposition or cobalt oxidation on the surface. An unsteady-state semimechanistic model has been developed to represent the data at different temperatures and syngas ratios. This model takes into account cobalt sintering, coke deposition, and surface oxidation