Slurry Phase Fischer Tropsch Synthesis Research Articles

The role of nano-sized iron particles in slurry phase Fischer–Tropsch synthesis

The slurry phase Fischer–Tropsch (F–T) activity of three α-Fe 2O 3-based materials, two unsupported nano-sized, NANOCAT (3 nm) and BASF (20–80 nm), and a supported micron-sized (32.5 μm) UCI, are compared with respect to total hydrocarbon production from synthesis gas (H 2/CO∼2/1) at 513 K. Low temperature Mössbauer spectra of the quenched slurry samples after 120 h on-line show that all three catalysts are essentially a mixture of oxide and carbide phases with magnetite (Fe 3O 4) being the dominant phase. TEM images of the quenched samples reveal unexpected particle characteristics. While both unsupported nano-sized materials essentially avoid expected agglomeration, the micron-sized UCI transforms into nano-sized material. These results suggest a crucial role of nano Fe during F–T synthesis.

Chemical Effect and Spatial Effect of New Bimodal Catalysts for Fischer-Tropsch Synthesis.

A catalyst support with both small pores and large pores, as well as a distinct bimodal pore structure, has excellent advantages in industrial solid-catalysis reactions because the large pores provide pathways for rapid molecular transportation and the small pores serve a large area of active surface. A simple preparation method of bimodal supports was developed by introducing SiO2 or ZrO2 sol into large pores of an SiO2 gel pellet directly. The pores of the obtained bimodal supports distributed distinctly as two kinds of main pores. On the other hand, the increased BET surface area and decreased pore volume, compared to those of original silica gel, indicated that the obtained bimodal support formed according to the designed route. The obtained bimodal support loaded with cobalt was applied in slurry-phase Fischer–Tropsch synthesis (FTS). The bimodal catalyst presented the best reaction performance in slurry-phase FTS with a high reaction rate and low methane selectivity, because the spatial promotional effect of the bimodal structure and the chemical effect of the porous zirconia were available inside the large pores of original silica gel.

Mesoporous metallo-silicates as a support of cobalt catalysts for slurry phase Fischer–Tropsch synthesis

A series of mesoporous metallo-silicates (M-MPS, M = Al, Mn, V, Zr, and Mo) was synthesized at ambient temperature by utilizing hexadecylpyridinium chloride as a surfactant and was used as the support of cobalt catalysts for Fischer–Tropsch synthesis in a slurry phase. The catalysts supported on M-MPS showed a higher selectivity for C5+ hydrocarbons and had a higher chain growth probability α, as well as a lower selectivity for CH4. A good correlation between the selectivity for CH4 and the standard enthalpy of formation of metal oxides incorporated into the silica framework, –ΔH0f, was obtained and the role of metals incorporated into the silica framework in Fischer–Tropsch synthesis is discussed.

Slurry phase Fischer–Tropsch synthesis over manganese-promoted iron ultrafine particle catalyst

An industrial manganese-promoted ultrafine particle (UFP) iron catalyst for slurry phase Fischer–Tropsch synthesis was examined in a 1 dm 3 stirred tank slurry reactor under various reaction conditions as a representative of industrial practice (533–573 K, 1.5–2.5 MPa, 1.0–2.5 l (STP)/g-cat h, H 2/CO=0.65–2.0). The Fe–Mn UFP catalyst showed high CO conversion and gave high yields of C 2–C 4 alkenes, partially attributed to less secondary hydrogenation of alkenes during the slurry reaction. The catalyst displayed a slow deactivation rate with time on stream. The effects of reaction conditions on the catalytic activity, hydrocarbon product distribution and the ratio of alkene/alkane were discussed.

Supported iron catalysts for slurry phase Fischer–Tropsch synthesis

The present study was undertaken to investigate reduction and catalytic behavior of silica and alumina-supported iron Fischer–Tropsch (F–T) catalysts promoted with potassium and copper. It was found that the alumina (Vista Catapal B) inhibits reduction of iron, whereas the reduction behavior of the silica (Davison Grade 952) supported catalyst was similar to that of the two precipitated iron catalysts synthesized in our laboratory. Supported and precipitated (Fe/Cu/K/SiO 2) catalysts were tested in a stirred tank slurry reactor. Initial activity of the silica-supported catalyst, measured by a value of an apparent first-order reaction rate constant, was 20–40% higher than that of the precipitated iron catalysts, whereas the activity of the alumina-supported catalyst was about 50% less than that of the silica-supported catalyst. Silica-supported catalyst had higher gaseous selectivity and lower olefin content than the alumina-supported catalyst and precipitated catalysts. These results were explained in terms of interactions between potassium with supports, resulting in reduction of the potassium promotion effectiveness.

Hydrocarbon selectivity model for the slurry phase Fischer–Tropsch synthesis on precipitated iron catalysts

A new hydrocarbon product distribution model for Fischer–Tropsch-synthesis (FTS) reaction has been developed. The model is based on the assumption that there are two types of active sites on the catalyst surface: type-1, where growth of hydrocarbon intermediates occurs, and type-2, where reversible readsorption of 1-olefins occurs. The readsorbed 1-olefins form alkyl intermediates, C n H 2 n+1 , on the surface, which in turn can participate in several reactions: chain growth propagation, hydrogenation to n-paraffins, and dehydrogenation to 2-olefins. Chain growth is considered on the basis of methylene monomer (CH 2) insertion mechanism. Steady-state mass balances for adsorbed intermediates C 1–C 50 and equations for the product formation rates were derived. The model has been tested using results from experiments conducted over long periods of time under industrially relevant conditions in a slurry reactor. The model predictions provide information on hydrocarbon product distribution, 2-olefin content and total olefin content as a function of carbon number. The curved line for the distribution of paraffins and olefins can be fitted well with the proposed hydrocarbon selectivity model, over the entire range (C 1–C 50) of carbon numbers. The kinetic model proposed in this paper can be used for interpretation of experimental data, comparison of performance of different catalysts, and reactor modelling and simulation studies.

00/02362 Active Co/SiO 2 catalysts prepared from mixing precursors for slurry phase Fischer—Tropsch synthesis

00/02362 Active Co/SiO 2 catalysts prepared from mixing precursors for slurry phase Fischer—Tropsch synthesis

Characteristic Feature of Co/SiO2 Catalysts for Slurry Phase Fischer-Tropsch Synthesis.

Cobalt-based catalysts showing high Fischer-Tropsch reaction activity in slurry-phase semi-batch reactor are studied. CO conversion increases with increasing cobalt loading, and chain growth probability increases as well. It is found that catalytic activity shows a linear relationship with the surface cobalt amount. At high cobalt loadings, two kinds of cobalt metal crystallites, cubic and hexagonal, exist, the cubic crystallite being predominant. The effects of reaction conditions, catalyst pore sizes, calcination and reduction temperatures are studied.

00/00093 Slurry phase Fischer-Tropsch synthesis process development

Fischer-Tropsch synthesis can convert a variety of synthesis gas mixtures produced from both coal and natural gas to obtain hydrocarbons, which can be further processed to manufacture automotive fuels. As the Fischer-Tropsch reaction is highly exothermic, a slurry phase reactor offers a significant advantage over the traditional fixed bed reactor for heat management. Since 1992, Air Products and DOE have been developing the slurry phase Fischer-Tropsch synthesis process with help of a number of industrial partners. This paper discusses the evolution of the technology through four pilot plant campaigns conducted at DOE`s Alternative Fuels Development Unit in LaPorte, Texas. Key issues such as catalyst-wax separation, reactor productivity improvements, reactor temperature control, and in-situ activation are addressed.

Catalytic performances of cobalt-based ultrafine particles prepared by chemical reduction in slurry-phase Fischer–Tropsch synthesis

For the purpose of developing the catalysts for slurry phase Fischer–Tropsch synthesis, fundamental studies of catalysis by ultrafine particles (UFP) of Co were carried out using a slurry bed reactor. Co UFP prepared by the method of chemical reduction in liquid phase was more active for this reaction than a precipitated Co catalyst, due to its nonporous structure. The addition of Cr, Ti, Mn, Mo, or Zr onto Co UFP was found to be effective to enhance the catalytic activity. Among these UFP catalysts, Co–Cr UFP exhibited the highest activity. The space time yield of hydrocarbons on Co–Cr UF P prepared in the mixed solution of H 2O and CH 3OH was 14.9 g g-cat −1 h −1. The increased activity was attributed to a decrease in particle size of Co. Distribution of hydrocarbons produced was also dependent on the particle size. The selectivity for CH 4 was lowered and that for C 5 + hydrocarbons was enlarged by a decrease in particle size.

Active Co/SiO2 Catalysts Prepared from Mixing Precursors for Slurry Phase Fischer-Tropsch Synthesis

Abstract The catalysts prepared by mixing impregnation of cobalt (II) nitrate and cobalt (II) acetate displayed high activity. X-ray diffraction indicated that highly dispersed cobalt metal was the main active site on the catalyst prepared by mixing impregnation method. The metal reduced from cobalt nitrate promoted the reduction of Co2+ to metallic state in cobalt acetate by H2 spillover mechanism during catalyst reduction process.

Activity and selectivity of precipitated iron Fischer-Tropsch catalysts

Low-temperature (230°C), slurry phase Fischer-Tropsch synthesis (FTS) was conducted with precipitated iron-silicon catalysts under industrially relevant conditions (flow=3.1 Nl h −1 g-Fe −1, H 2:CO=0.7, P=1.31 MPa). The effects of activation gas (hydrogen, carbon monoxide, or syngas) and promoters (potassium and copper) on activity and selectivity were explored. Optimum potassium promotion was 4–5 at%, relative to iron. Promotion with copper lowered the reduction temperature and increased FTS activity, regardless of the activation gas used. Carbon monoxide activation gave the highest activity for a 100Fe/ 4.4Si/5.2K catalyst (atomic percent, relative to iron) while syngas activation was superior for a 100Fe/4.4Si/2.6Cu/5.2K catalyst. Selectivity of the FTS product was not affected by the activation gas employed or copper promotion; however, potassium promotion increased wax and alkene selectivity. A syngas activated 100Fe/4.4Si/2.6Cu/5.2K catalyst gave the best overall performance at 230°C. Alkene selectivity was >75% for the C 2-C 11 fraction, methane selectivity was <3 wt% and C 12 + selectivity was >70 wt%.

Attrition of precipitated iron Fischer-Tropsch catalysts

A precipitated, doubly promoted, iron oxide catalyst was studied to elucidate phenomena that may lead to catalyst attrition during slurry phase Fischer-Tropsch synthesis. The catalyst was examined by electron microscopy (SEM and TEM), electron and X-ray diffraction, sedigraph particle size analysis and BET surface area measurements. The catalyst undergoes attrition both at the micro- as well as the nano-length scales. On the micro-scale, this involves a breakup of ca. 30 μm spherical agglomerates into ca. 1 μm particles, a process that can be initiated even by the mixing that occurs in the sedigraph analyzer. On the nano-scale, we find that exposure of the catalyst to CO at increasing temperatures transforms single crystals of α-Fe 2O 3 into Fe 3O 4 and ultimately to Fe-carbide, with rounded particles as small as ca. 20 nm. The details of phase transformations and the resulting crystallite morphology and size distribution could play a major role in influencing the overall attrition resistance of precipitated iron oxide catalysts. In this paper, we describe the effects of the CO activation temperature on catalyst structure at the micro- and nano-scales.

Fischer-Tropsch synthesis: Impact of potassium and zirconium promoters on the activity and structure of an ultrafine iron oxide catalyst

Slurry phase Fischer-Tropsch synthesis was conducted with an ultrafine iron oxide catalyst promoted with either 0.5 at% K or 1.0 at% Zr or both. Pretreatment in CO yielded higher conversions and a more stable catalyst than activation in hydrogen or synthesis gas. Hydrogen pretreatment of K promoted catalysts and synthesis gas activation in general were less effective. Mossbauer spectroscopy and XRD showedχ-Fe5C2 and e′-Fe2.2C were formed during pretreatment in CO and did not depend on promoters present. Catalysts pretreated in H2 were reduced to metallic Fe and Fe3O4; promotion with K and Zr decreased the extent of reduction. Hydrogen pretreated catalysts, promoted with K, lost surface area and carbided rapidly under synthesis conditions. Activation in synthesis gas reduced all catalysts to Fe3O4. Subsequent synthesis did not affect the phase present for the unpromoted and Zr promoted catalysts while those promoted with K formed χ-Fe5C2 and e′-Fe2.2C. It is concluded that pretreatment type is more important to the catalyst activity during the early period of synthesis than the impact of promotion with K and/or Zr and that changes in the bulk composition of iron catalysts do not necessarily correlate with changes in activity.

Effects of Cr Addition on the Catalytic Properties of Ultrafine Particles of Co for Liquid Phase Fischer-Tropsch Synthesis.

The activities of Co-based ultrafine particles (UFP) catalysts for slurry phase Fischer-Tropsch (FT) synthesis were investigated at 270°C and 30atm. Among the catalysts tested, Co-Cr UFP catalyst exhibited the highest activity. The activity and the selectivity of Co-Cr UFP catalyst for liquidhydrocarbon production increased with increasing content of Cr, and it attained a maximum at about 2wt%. Co-Cr supported on SiO2 exhibited similar catalytic performances as those of Co-Cr UFP. There was a good relationship between catalytic activity and chemisorptive uptake of CO. Reducibility of Co was improved in the presence of Cr. Thus, we deduce that there was a maximum number of active sites due to the promoting effects of Cr on reduction of Co and on sintering of Co. Product distribution was found to be affected only by the size of Co particles.

IRON FISCHER-TROPSCH CATALYSIS — PROPERTIES OF AN ULTRAFINE IRON OXIDE CATALYST

ABSTRACT ABSTRACT Slurry phase Fischer-Tropsch synthesis has been conducted starting with an ultrafine iron oxide catalyst with an average particle size of 30A. Catalyst activity gradually increased during the first 400 hour of synthesis and then remained stable for 250 days. Potassium promotion greatly increased the initial activity of the catalyst; however, the stability decreased. The CO conversion of the unpromoted catalyst was found to vary linearly with the reciprocal of the space velocity up to 60% conversion. Alkene selectivity increased with increasing space velocity but remained constant above GHSV = 2,0. Secondary reactions are believed to account for the higher alkane content at low space velocity. Methane, ethane and alkane formation increased with increasing hydrogen partial pressure up to a H2/CO ratio of 1. CO conversion is highest at lowest CO partial pressure and likewise for hydrogen. In general it is observed that this ultrafine catalyst is not as active as precipitated catalysts and h...

Iron-based catalysts for slurry-phase Fischer-Tropsch process: Technology review

The slurry-phase reactor system is of interest in Fischer-Tropsch synthesis owing to the ability of the reactor system to efficiently remove the heat produced by the exothermic reaction. Iron-based catalysts are active for Fischer-Tropsch synthesis and for the water-gas shift reaction, and, in addition, are inexpensive. Hence, they have been examined in slurry-phase Fischer-Tropsch synthesis with CO-rich synthesis gas. The role of promoters, carbide phases, and oxide phases in iron-based catalysts is not well understood. The article reviews current knowledge of iron-based catalysts with reference to their application in slurry-phase Fischer-Tropsch synthesis. Areas of investigation requiring further research are identified.

Slurry-phase Fischer-Tropsch synthesis and kinetic studies over supported cobalt carbonyl derived catalysts

This paper reports the preparation characterization, and performance of cobalt carbonyl cluster based catalysts for use in slurry-phase Fischer--Tropsch (FT) technology investigated. Using metal carbonyls as active metal precursors allows for the control of metal particle size on the support surface, thus offering the potential for better control of activity and selectivity of the FT reaction. Silica as the support provided the highest catalyst activities. A Co{sub 2}(CO){sub 8}/Zr(OPr){sub 4}/SiO{sub 2} catalyst (3.5% cobalt, 6.6% zirconium) was developed as the most active system in the FT slurry reactor and also gave the best liquid fuel selectivity. Selectivity patterns correlated to the Schulz--Flory prediction. These catalysts exhibited low water/gas shift activity. Diesel fuel product produced by this catalyst was high quality. A kinetic expression that took water inhibition into account was verified, yielding an activation energy of 97 kJ/mol for syngas conversion ranging from 34% to 71% at 240--280{degrees} C.

Hydrogenation of Carbon Monoxide over Solid Catalysts Dispersed in the Liquid Medium. I. Slurry-Phase Fischer–Tropsch Synthesis with Supported Ruthenium Catalysts

Abstract Fischer–Tropsch synthesis on supported ruthenium catalysts were operated successfully in the slurry phase, using ethyl cyclohexane solvent, in spite of the high selectivity of waxy products. Titania, fumed silica, and Nb2O5 were found to be excellent carriers for ruthenium. A Ru/SiO2 catalyst yielded a hydrocarbon product with the rate as high as 600 mg(g-cat)−1h−1 at 240°C and 40 bar. The optimum metal loading was 2% by weight. Calcination of the catalyst precursor at 300°C or above caused a marked decrease in the metal dispersion, which was essential for the high catalytic activity and chain-growth ability. The maximum chain-growth probability obtained on a calcined Ru/Al2O3 catalyst was 0.94.