FTS Reaction Research Articles

Hydrodynamic effect of oxygenated byproduct during Fischer–Tropsch synthesis in slurry bubble column

The Fischer–Tropsch reaction was performed using a pilot-scale slurry bubble column reactor (SBCR) and a lab-scale continuous stirred tank reactor (CSTR). In contrast to the CSTR, a transitory induction period was observed in the SBCR. In this study, we investigated the catalyst performance during the induction period focusing on the hydrodynamic parameter changes inside the reactor. We measured the hydraulic pressure for the constant slurry thickness during FTS reaction. The FT wax product was regularly withdrawn using a metal filter and analyzed for density, oxygen concentration, and compositional analysis. The liquid density was affected by the dilution of the initial liquid media by fresh FT product for the whole reaction time of 180h. On the other hand, the oxygen concentration increased sharply for the initial 85h and then reached the steady state. Accordingly, the gas hold-up and CO conversion were enhanced for the same period. The increase in the gas hold-up could be explained by the coalescence inhibition effect of oxygenated compounds, which were the main byproducts when iron-based catalysts were used. The dynamic gas disengagement technique was employed to identify the coalescence inhibition effect of alcohol in the hydrocarbon system using a cylindrical acrylic bubble column.

Effect of K and CeO2 promoters on the activity of Co/SiO2 catalyst for liquid fuel production from syngas

Effect of potassium and ceria promotion on the activity and selectivity of Co/SiO2 catalyst was investigated for CO hydrogenation in a high pressure reactor. Five different SiO2 supported cobalt catalysts promoted with K and CeO2 were synthesised by sol gel followed and wet impregnation. These catalysts were characterised by BET surface area, pore volume, TGA, TPR, SEM, TEM, and chemisorptions methods. The cobalt particles were well dispersed in sol gel method in presence of complexing agent. The major phase obtained was Co3O4 and the average metal particle size as determined from the hydrogen chemisorptions and TEM studies varied from 20 to 60nm. The performance of these catalysts were compared at 250°C and 20bar pressure and at a weight hourly space time of (W/Fo) 1000kg(catalyst)s/Nm3. Incorporation of K and CeO2 significantly influenced the catalyst reducibility due to increased metal support interaction. The CO conversion and C5+ selectivity were highest for ceria doped Co/SiO2 catalyst. Both K and CeO2 promoted Co/SiO2 were found active and stable for the FTS reaction, however compared to K promoted catalyst ceria promoted catalyst notably improved the C5+ selectivity, while suppressing the CH4 and coke formation.

A UBI-QEP Microkinetic Study for Fischer-Tropsch Synthesis on Iron Catalysts

The microkinetic of gas-solid Fischer-Tropsch synthesis on Fe–Cu–K–SiO2 catalyst was studied which was consisted of different elementary steps. The operation condition was in temperature of 523K, total pressures from 0.8 to 3.2MPa, space velocity from 0.5 to 2.0 ×10-3 Nm3kg-1s-1 and H2/CO inlet ratios from 0.5 to 2mol/mol. Unity bond indexquadratic exponential (UBI-QEP) and transition state theory (TST) was used to calculate heats of adsorption and initial estimates of some of the kinetic parameters. The pre-exponential factors were calculated based on statistical thermodynamics. The accuracy of the UBI-QEP method in calculating the energetic of the elementary reactions on catalyst surface was acceptable. The calculated activation energies to produce n-alkanes and 1-alkenes were in range of 19.57 to 25.68 and 19.53 to 20.45kcal/mol respectively. These values were used to obtain the product distributions. However the application of the microkinetic study with molecular approach can provide better insight to the analysis of the FTS reaction mechanism.

Kinetic Modeling of Fischer-Tropsch Synthesis over Fe/Ce/Al2O3

In this experimental study, a kinetic model has been developed for Fischer-Tropsch synthesis reactions by using Fe/Ce/Al2O3 as the catalyst (80% Fe/20% Ce/5wt%Al2O3) in a fixed-bed micro reactor assuming no internal or external diffusion. Operating conditions of the reactor are as follows: reactor total pressure 6-22 atm; Temperature 543-573 K; H2/CO feed ratio 1.5-2 and space velocity 4200 hr-1. Light alkenes were successfully produced due to high activity and selectivity of the catalyst. Considering the mechanism of the process and Langmuir-Hinshelwood- Hogan-Watson (LHHW) approach, four different mechanisms, namely carbide, enol, combined carbide-enol, and parallel carbide-enol were defined for CO consumption rate equations. The rate expressions for the CO hydrogenation reactions are based on elementary reaction corresponding to the carbid-enol mechanism. The obtained rate expressions for the CO hydrogenation reactions from nonlinear regression analysis and Levenberg-Marquardt method demonstrate that the formation of monomer species (HCOs) due to CO hydrogenation reaction has controlled the FTS reaction rate. The activation energy and adsorption enthalpy were calculated as 58.38 kJ/mol and -22.26 kJ/mol, respectively. Also, the effects of temperature and pressure variation on selectivity and production rate of light products are presented.

Effect of pretreatment on precipitated Fe–Mo Fischer–Tropsch catalysts: Morphology, carburization, and catalytic performance

Unpromoted and Mo-promoted iron catalyst precursors (100Fe, 100Fe5Mo, and 100Fe10Mo) were prepared by a coprecipitation method, and were subsequently characterized by laser Raman spectroscopy, Mössbauer spectroscopy, at 298 K and 20 K, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The effect of pretreatment with H 2, CO, and H 2/CO = 0.67 at 280 and 350 °C was investigated. Specifically, the reduction/carburization behaviors and the evolution of iron phases and Mo species in the catalysts during the pretreatment and during the FTS reaction were extensively studied. During pretreatment, the catalyst structure experienced an extensive restructuring process that was strongly dependent on the pretreatment protocols and Mo promoter loading levels. The microscopic information confirmed this effect on the iron active-site dispersion and the catalytic performance.

Silicon carbide foam composite containing cobalt as a highly selective and re-usable Fischer–Tropsch synthesis catalyst

The Fischer–Tropsch synthesis was evaluated on cobalt based catalyst supported on a medium surface area SiC foam ceramic in a fixed-bed configuration. The catalytic results were compared with those obtained on a Co/Al 2O 3 foam catalyst. At medium conversion (<50%) the two catalysts display similar C 5+ selectivity indicate that the intrinsic selectivity between the two catalysts is close from each other. However, when the CO conversion was increased to 70%, a significant difference in terms of the C 5+ selectivity was observed between the two catalysts, i.e. 80% on the Co/SiC and 54% on the Co/Al 2O 3, which indicate that under severe FTS reaction conditions the SiC seems to be more suitable support than alumina. It is also worth to note that under these reaction conditions the chain length probability, α, obtained on the SiC-based catalyst was 0.91 and wax formation was especially favoured. The improvement of the C 5+ selectivity observed on the SiC catalyst was attributed to the high efficiency of the support to evacuate heat generated during the course of the reaction owing to it higher thermal conductivity and also to the presence of meso- and macro-porosity of the support. Additional catalytic test conducted on a hybrid support, i.e. Al 2O 3 coated SiC foam, again confirms the high C 5+ selectivity under a similar severe reaction conditions in the presence of a SiC structure underneath of the alumina layer which play a role of heat disperser. In addition, the high chemical inertness of the SiC material also allows one to perform an easy recovery of both the active phase and the support by a simple acid washing. The recovered SiC support was further impregnated with a fresh cobalt phase and re-tested in the FTS and the catalytic results are compared with those of the former catalyst. The same product yield was obtained which confirms the potential of SiC to be employed as a re-usable support.

Fischer–Tropsch synthesis over LaFe 1− xCo xO 3 perovskites from a simulated biosyngas feed

The Fischer–Tropsch synthesis reaction using a simulated gas mixture, comparable to that obtained from biomass transformation (biosyngas), was studied over LaFe 1− x Co x O 3 perovskites. The perovskites were prepared using the amorphous citrate precursor method and the FTS reaction was carried out in a stainless steel fixed bed reactor at 300 °C and 1 MPa. Nitrogen adsorption was at −196 °C. Thermal-programmed reduction (TPR), X-ray diffraction (XRD), Fourier-transform IR spectroscopy (FTIR), oxygen-temperature-programmed desorption (O 2-TPD) and scanning electron microscopy (SEM) were used as characterization methods. The perovskites were found to display two crystal systems determined by XRD patterns, orthorhombic for x Co < 0.5 and rhombohedral for x Co ≥ 0.5. The LaFe 1− x Co x O 3 perovskites, with a substitution degree x Co = 0.1, 0.2 and 1.0, displayed significant intrinsic CO conversion. This activity was probably due to the formation of Co–metal segregates on the surface, as suggested by XRD patterns. The highest CO intrinsic conversion was obtained for perovskites with a substitution degree of x Co = 0.2. The LaFe 1− x Co x O 3 perovskites presented a wide distribution of liquid hydrocarbons (C 6–C 18+) and high CH 4 formation. The liquid product distribution was related to the average size of iron particles. The increase of cobalt particle size favours the formation of hydrocarbons centred in C 8–9 chain length.

Effect of support and cobalt precursors on the activity of Co/AlPO 4 catalysts in Fischer–Tropsch synthesis

Cobalt supported on amorphous aluminum phosphate (Co/AlPO 4) catalysts were prepared by the impregnation method using three different cobalt precursors such as cobalt nitrate, acetate and chloride to elucidate the activity of Fischer–Tropsch synthesis. The use of AlPO 4 as a support for cobalt-based catalysts exhibits better catalytic performance during FTS reaction than the corresponding Co/Al 2O 3 catalyst. TPR results also suggest that the reducibility of the catalysts varies with the nature of cobalt precursors employed during the impregnation on AlPO 4 support. The Co/AlPO 4 catalyst prepared from cobalt nitrate shows higher CO conversion and C 8+ selectivity than the others due to the facile formation of homogeneous cobalt particles with proper electronic characters and high reducibility. Interestingly, all Co/AlPO 4 showed a growth of filamentous carbon initiated from the large mobile cobalt particles during the reaction. The differences in catalytic properties of Co/AlPO 4 are mainly attributed to the cobalt particle size, reducibility with different electronic states of metallic cobalt, pore diameter of AlPO 4 and formation of filamentous carbon.

A model for the dynamic behavior of a commercial scale slurry bubble column reactor applied for the Fischer–Tropch synthesis

AbstractFischer‐Tropsch synthesis (FTS) is an important chemical process for the production of liquid fuels. In the present study, a dynamic model for a commercial size slurry bubble column reactor (SBCR) operating under heterogeneous flow regime and dealing with the FTS has been developed. In such a model a detailed kinetics expressions for the FTS and water gas shift (WGS) reactions have been considered. A selectivity model combined with SBCR hydrodynamics and the multicomponent VLE scheme have been applied to estimate the distribution of olefins and paraffins in the products. In addition, the effects of catalyst deactivation on reactor performance and product distribution under transient conditions may be predicted from this model. The data calculated from the model have been correlated with the experimental results available in the literature. It seems that the present model could be applied to estimate the main characteristics of the reactor's dynamic behavior. Copyright © 2009 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Novel Three-component Zeolite Capsule Catalyst for Direct Synthesis of Isoparaffin

One zeolite capsule catalyst with core(Co/Al2O3)/shell(H-beta membrane) structure was prepared and used for isoparaffin direct synthesis via FTS reaction. Based on this core/shell zeolite capsule catalyst, a novel palladium painted zeolite capsule catalyst with three-component core (Co/Al2O3)/shell (H-beta membrane)/paint (Pd) structure was designed. In the isoparaffin synthesis on this three-component zeolite capsule catalyst, the olefins effused from the zeolite capsule catalyst were in-situ hydrogenated effectively, mostly converted to isoparaffin.

Phase transformation of unpromoted and promoted Fe catalysts and the formation of carbonaceous compounds during Fischer–Tropsch synthesis reaction

Precipitated Fe catalysts with or without additives (Zn, K, Cu) were prepared, pretreated by CO, and then time-dependent behaviors of their FTS activities were investigated at 503 K and 1.6 MPa in a fixed bed reactor. Over the catalyst without additives, CO conversion showed a maximum at ca. 8 h on stream and then decreased monotonically with increasing time on stream. When Zn, K and/or Cu were added, respectively, similar behaviors were observed. However, an increasing CO conversion was observed during on stream (29 h) when Zn, K and Cu were added simultaneously. X-ray diffraction (XRD) analysis of these catalysts showed the formation of Fe carbides (Fe 5C 2 and Fe x C) after the CO pretreatment irrespective of the catalyst composition. In the case of the catalyst without additives, these carbides were oxidized to Fe 3O 4 during on stream. The oxidation of the carbides was more significant on the catalyst charged near the outlet of the reactor. For the catalyst containing all the additives simultaneously, however, the Fe carbides were only phases detected by XRD analysis even after the long time on stream (29 h). In addition, the formation of amorphous carbonaceous compounds was observed by laser Raman spectroscopy (LRS) for the catalysts after the CO pretreatment and/or the FTS reaction. So-called a graphite-like carbonaceous compound was not observed by LRS, which was considered as one of reasons for the catalyst deactivation in the previous studies. Therefore, it is suggested that the oxidation of the Fe carbides by H 2O vapor is a main reason for the deactivation of the Fe FTS catalyst. Because the Zn, K and Cu containing catalyst showed a higher CO 2 selectivity, the combination of these additives improves the water-gas shift activity, thereby suppresses the oxidation of the Fe carbides.

Selective Synthesis of Higher Linear α-olefins over Cobalt Fischer–Tropsch Catalyst

An efficient approach for more selective synthesis of higher linear α-olefins was achieved by utilizing suitable reaction media in FTS reaction. About 41.4% average α-olefins content in C5–C25 fractions was obtained at $$\hbox{W/F}_{{({\rm CO+H_{2}})}}$$ = 5 g-cat h mol−1 in n-C10 solvent, which is markedly higher than the value (2.5%) obtained in 85% N2 + 15% n-C6.

Sulfated Zirconia as a Cocatalyst in Fischer−Tropsch Synthesis

This work deals with the direct synthesis of branched hydrocarbons from synthesis gas using a two-component catalyst: a Fischer−Tropsch synthesis catalyst (RuKY) and a sulfated zirconia (SO42-/ZrO2) strong acid catalyst. The composition of C7 hydrocarbons was used to gauge the effect of the acid catalyst on hydrocarbon product selectivity. Over RuKY alone, C7 olefins prevail in C7 hydrocarbons while the content of branched C7 paraffins is very low. The use of SO42-/ZrO2 as a cocatalyst for Fischer−Tropsch synthesis causes significant changes in the composition of hydrocarbon products, particularly in the early stages of the reaction. It increases the content of branched paraffins and decreases that of olefins. However, this catalyst suffers serious deactivation. Addition of small amounts of Pt to SO42-/ZrO2 is an effective way for stabilizing its activity under FTS reaction conditions. CO in the synthesis gas has a suppressing effect on the catalytic activity of SO42-/ZrO2 catalysts. This effect becomes ...

95/03468 Studies on Fischer-Tropsch synthesis over Fe-Cu-K catalyst. I. Catalytic performance

The influence of reaction pressure, temperature, space velocity (GHSV), particle size of catalyst and H2/CO ratio of feed-gas on the steady-state product distribution, conversion of CO, H2 and syngas, olefin to paraffin ratio and CO2/ H2O ratio for FTS reaction were investigated using a coprecipitated copper- potassium promoted iron catalyst. The test was carried out in a fixed-bed reactor. Increasing the reaction temperature from 493. 2 to 5-13. 2 K shifted the hydrocarbon distribution toward the heavier hydrocarbons (C5-C23) and selectively increased CO conversion to CO2. The hydrocarbon distribution was found to be dependent on the H2/CO feed-gas ratio in the range from 1.23 to 2. 22. The CO2/H2O ratio in product decreased as the flow of feed-gas rate increased, which suggests that H2O is a primary product and its reaction with CO to form CO2 occurs via a secondary process. The CO conversion increased with the decrease of catalyst particle size from 10 to 60 mesh (2. 0-0. 3 mm), while the CO conversion changed very little as the particle size of the catalyst was further reduced to 60- 100 mesh (0. 3-0. 154 mm). The CO conversion increased with the increase of operating pressure. The pressure also affects CO2 selectivity and product distribution of FTS.