Precipitated Iron Fischer-Tropsch Catalysts Research Articles

Effect of reaction temperature and H2/CO ratio on deactivation behavior of precipitated iron Fischer-Tropsch synthesis catalyst

In this paper, a precipitated iron Fischer-Tropsch catalyst was synthesized, which is similar to commercial CNFT-1 catalyst. The effect of reaction temperature and H2/CO feeding ratio on the deactivation behavior were throughly investigated. The results revealed that deactivation rate was significantly affected by the reaction temperature, which showed 15 times of deactivation rate constant operated at 290 ℃ than that at 270 ℃. However, deactivation rate constant had less difference with different H2/CO ratio from 2 to 5. Further characterization results demonstrated that the sintering and surface oxidation of iron carbide crystallite might be the main reason responsible for the deactivation when increased the reaction temperature. An opposite effect of iron carbide oxidizing inhibition and crystallite agglomeration was observed when increasing of H2/CO feeding ratio, which would lead to the slight deactivation of the precipitated iron catalyst.

Deactivation behavior investigation on commercial precipitated iron Fischer–Tropsch catalyst for long time reaction

Deactivation behavior investigation on commercial precipitated iron Fischer–Tropsch catalyst for long time reaction

Precipitated iron Fischer–Tropsch catalyst manufacturing: impact of Hematite

This study found that promoted precipitated iron catalysts, containing large quantities of Hematite, demonstrated adequate activity, selectivity, and attrition resistance operating under commercial Fischer–Tropsch synthesis conditions in a product demonstration slurry bed reactor run over an approximately 170-day period. While small quantities of Hematite ( 0.30 cm3/g) and pore size (60–80 A) can be induced if larger quantities of about 30–40 wt % Hematite are present in the fresh calcined unreduced catalyst. The catalyst demonstrated exceptional attrition resistance.

Hydrogen reduction kinetics modeling of a precipitated iron Fischer–Tropsch catalyst

Mechanisms and kinetics for the reduction of a precipitated iron-based Fischer–Tropsch catalyst in H 2 have been investigated using in situ Mössbauer effect spectroscopy (MES) and thermogravimetric (TG) method in the temperature range of 250–350 °C. In situ MES results indicate that the reduction of paramagnetic (PM) α-Fe 2O 3 (70%) and superparamagnetic (spm) Fe 3+ (30%) in the fresh catalyst proceed via different steps. PM α-Fe 2O 3 is firstly reduced to magnetite and then to metallic iron, while the reduction of spm Fe 3+ proceeds in three consecutive steps: it is first reduced to magnetite with a significantly rapid rate, then to non-stoichiometric wüstite, and finally to metallic iron. The reduction of PM α-Fe 2O 3 to Fe 3O 4 can be described by a two-dimensional Avrami–Erofe’ ev phase change model (formation and growth of nuclei). However, the corresponding overall reduction, which includes the reduction of PM α-Fe 2O 3 and spm Fe 3+ to Fe 3O 4, can be described by a three-dimensional phase-boundary-controlled reaction model based on the overall extraction ratio of oxygen. The difference between the two models selected for the PM α-Fe 2O 3 reduction and the corresponding overall reduction is attributed to the rapid reduction of spm Fe 3+ to Fe 3O 4. For the reduction of PM magnetite to α-Fe and its corresponding overall reduction (including the reduction of PM and spm Fe 3O 4 to α-Fe), it is found that both of them follow the Avrami–Erofe’ ev phase change model (two-dimensional or three-dimensional). The value of apparent activation energy for the overall reduction has been calculated and compared with the literature data.

Precipitated iron Fischer-Tropsch catalyst: Effect of carbidization on the morphology of iron oxyhydroxide nanoneedles

The effect of carbidization on the morphology of iron oxyhydroxide particles has been studied. Homogeneous oxidation of iron(II) sulfate results in predominantly γ-FeOOH particles which have a rod-shaped crystalline structure. Carbidization of the prepared iron oxyhydroxide particles at 270 °C and atmospheric pressure without mechanical stirring was found to produce iron carbides with spherical layered structure residing in close proximity. HRTEM, EDS and electron microdiffraction analysis revealed that carbidization alters the initial nanoneedle-type morphology and generates ultrafine carbide particles with irregular spherical shape. When carbidization was performed under severe mechanical stirring, formation of spherical carbide particles completely separated from each other was obsrved. Initial activity of iron oxyhydroxide for Fischer-Tropsch synthesis was found to be high (a CO conversion of about 84%) which declined steadily with synthesis time (26% CO conversion after 340 h of synthesis). The effect of carbidation on the morphology of iron hydroxide oxide (γ-FeOOH) particles with a three dimensional crystalline nanoneedle structure has studied. Carbidation of γ-FeOOH with CO at atmospheric pressure produced iron carbides with spherical layered structure. HRTEM and EDS analysis revealed that carbidation changes the initial nanoneedles morphology and generates ultrafine carbide particles with irregular spherical shape.

Deactivation of a precipitated iron Fischer–Tropsch catalyst—A pilot plant study

A pilot plant Fischer–Tropsch synthesis reaction was performed in a fixed bed reactor containing a precipitated iron catalyst. Sections were taken from the reactor and tested for Fischer–Tropsch activity in micro reactors. The catalyst sections were subjected to SEM, SIMS and XRD analysis and revealed catalyst deactivation due to (i) sulphur poisoning in the top portion of the reactor bed and (ii) magnetite formation and crystallite growth in the bottom portion of the reactor bed.

Novel precipitated iron Fischer–Tropsch catalysts with Fe3O4 coexisting with α-Fe2O3

The present study was undertaken to investigate the catalytic behavior of an industrial iron catalyst (Fe/Cu/K/SiO2) prepared from ferrous sulfate precursor for Fischer–Tropsch (FT) synthesis, in which different amount of Fe3O4 coexist with α-Fe2O3. The catalyst samples were characterized by BET, XRD, H2-TPR and Mossbauer effect spectroscopy (MES). The FT synthesis performance of the catalysts were carried out in a fixed bed reactor (FBR) under reaction conditions of 250 °C, 1.5 MPa, 2.0 nL/g-cat/h, and H2/CO=2/1 for 200 h. The results from XRD and MES for the catalyst samples of pre- and post-reduction indicate that more iron carbides form in the catalysts that have lower Fe3O4 contents. H2-TPR for the catalysts displays that Fe3O4 may facilitate the reduction of catalysts only when it was highly dispersed. FT reaction study in the FBR shows that the catalysts become more active with the decrease of Fe3O4 contents in the catalysts. However, the catalyst with certain amount of highly dispersed Fe3O4 exhibited high FT synthesis activity with CO conversion more than 75%. The catalyst also displayed much less olefins selectivity. A comparison of FTS performances of one of these catalysts with some known catalysts was also made in this paper.

Attrition studies with precipitated iron Fischer–Tropsch catalysts under reaction conditions

Iron Fischer–Tropsch (F–T) catalyst particles break-up during reaction in slurry phase reactors by physical attrition, and due to chemical stresses caused by phase transformations. Although “chemical” attrition is known to be important with iron (Fe) F–T catalysts, there have been no studies of attrition properties of precipitated Fe catalysts under reaction conditions. Here we report on attrition properties of three precipitated Fe catalysts (100 Fe/3–5 Cu/4–6 K/16–25 SiO2) during F–T synthesis in a stirred tank slurry reactor (STSR). Our results show that after 295–497 h of F–T synthesis with these three catalysts in the STSR, the particle size reduction by fracture was moderate, whereas erosion (generation of particles smaller than 10 μm) was small (2.3–2.7). The attrition strength of these catalysts is adequate for use in Slurry bubble column reactors (SBCRs) for F–T synthesis.

Attrition properties of precipitated iron Fischer–Tropsch catalysts

While precipitated iron catalysts provide optimal activity and selectivity for Fischer–Tropsch (F–T) synthesis with coal-derived synthesis gas, their attrition resistance under reaction conditions has been questioned. It is well known that iron oxides undergo phase transformations during activation and reaction, leading to changes in volume, which are a primary cause of catalyst break up (‘chemical attrition’). In this paper we report on attrition properties of precipitated Fe catalysts under both inert and reactive conditions in a stirred tank slurry reactor (STSR). Our results show that after 364 h of testing in the STSR, the particle size reduction due to fracture and erosion was moderate. The observed increase in fraction of particles smaller than 10 μm was small (7.8%). Catalytic performance was excellent, yielding low methane and high C 5 + selectivities of 2.6 and 82.5%, respectively, at 78.5% single pass conversion. We conclude therefore that iron catalysts used in this study have adequate attrition resistance and desirable F–T activity and selectivity for use in conversion of coal-derived syngas to liquid fuels in the slurry bubble column reactor.

Studies with a precipitated iron Fischer-Tropsch catalyst reduced by H 2 or CO

A precipitated Fe 2O 3 catalyst precursor was reduced by H 2 or CO and characterized by diffuse reflectance FT-IR with high-pressure syngas adsorption, syngas temperature-programmed desorption (TPD), XRD and BET surface area, and tested for FT synthesis from high-pressure syngas. The results show that on the H 2-reduced sample metallic iron particles are formed and on the CO-reduced sample a mixture of metallic iron and iron carbides are formed. The iron carbides on the CO-reduced sample can be decomposed to metallic iron by H 2 treatment at 300 °C, and the metallic iron on the H 2-reduced sample can be partly converted to iron carbides by CO treatment at 300 °C. Both the metallic iron and iron carbides on the reduced samples have high ability for CO dissociation. The BET surface area of the CO-reduced sample is about five times higher than that of the H 2-reduced sample. The treatment of the CO-reduced sample with H 2 and the treatment of the H 2-reduced sample with CO result in only small changes in the surface areas. During performing high-pressure FT synthesis, amorphous carbon-rich iron carbides and crystalline magnetite are formed, which have relatively weaker ability for CO dissociation than those of metallic iron and iron carbide particles on the freshly reduced samples. CO-reduced sample exhibits remarkably higher catalytic activity for FT synthesis than the H 2-reduced sample. Treatment of the CO-reduced sample with H 2 leads to an obvious decrease in the catalytic activity of the sample, and treatment of the H 2-reduced sample with CO leads to a great increase in the activity. These results clearly indicate that those iron carbides formed during CO reduction of the precipitated Fe 2O 3 sample or CO treatment of the H 2-reduced sample have played an important role in enhancing the catalytic activities of the samples.

Application of in situ Mössbauer spectroscopy to investigate the effect of precipitating agents on precipitated iron Fischer–Tropsch catalysts

The type of the precipitating agent used during the preparation of a precipitated iron-based Fischer–Tropsch (FT) catalyst affects the catalyst pore structure, crystallite size, phase composition and catalytic behavior. Catalysts prepared by using precipitating agents, that contain carbonate ions, have pores that are larger than those of catalysts prepared using precipitating agents that contain hydroxides. Precipitation at pH>8, using aqueous NH 3 solution as a precipitating agent, results in the formation of large crystallites of FeOOH, which are not observed when Na 2CO 3 and K 2CO 3 are used. Higher % CO conversion during FT synthesis was observed with the catalyst prepared by using aqueous NH 3 solution. However, this is correlated with a low selectivity for the formation of olefins. For all catalysts, in situ Mössbauer spectra recorded during FT synthesis show that the % CO conversion increases with the formation of iron carbides, viz. ε′-Fe 2.2C and χ-Fe 2.5C.

The effect of sulfide ions on a precipitated iron Fischer–Tropsch catalyst

A new range of sulfided iron catalysts has been synthesised by adding small amounts of Na 2S (500–20 000 ppm) to precipitated iron. The new materials, after calcination (400°C, 16 h) and reduction (400°C, 16 h), were subjected to syngas (2 : 1 H 2 : CO) at 250°C at 8 bar pressure for up to 8 days. Catalysts with low sulfide concentrations were up to four times more active in the Fischer–Tropsch reaction than a sulfur-free catalyst, while catalysts with high sulfide loadings were apparently poisoned. Increased olefin/paraffin ratios were also obtained at the low sulfide loadings. The new sulfided materials were studied by a combination of BET, DRIFTS, XRD, TPR and SEM and the results indicate that the surface area and reducibility of the iron catalyst are affected by the presence of S 2− ions and that SO 4 2− acts as a promoter in the Fischer–Tropsch reaction.

Pretreatment effect studies with a precipitated iron Fischer–Tropsch catalyst in a slurry reactor

Effects of pretreatment procedures, using H 2, CO, and syngas (H 2/CO = 2/3) as reductants, on the performance (activity, selectivity and stability with time) of a precipitated iron catalyst (100 Fe/3 Cu/4 K/16 SiO 2 on a mass basis) during Fischer–Tropsch (F–T) synthesis were studied in a stirred tank slurry reactor. The catalyst reduced with hydrogen to magnetite only reached its steady state activity faster than the catalyst partially reduced to metallic iron (2 h versus 4 h). Activity of the catalyst partially reduced to metallic iron under mild reduction conditions (250°C for 4 h) was about 40% higher than that of the catalyst reduced at 280°C for 8 h. The steady state activities of the catalyst reduced to magnetite only (240°C for 2 h) and of the unreduced catalyst were the same as that of the catalyst partially reduced to metallic iron at 280°C for 8 h. Initial activity of the CO activated catalyst (280°C for 8 h) was relatively low, and increased with time, reaching a steady state level at about 50 h on stream. However, its steady state activity was the highest among all the pretreatment procedures used. Methane and gaseous hydrocarbon selectivities on the hydrogen reduced and the unreduced catalyst increased with time before reaching a steady state, whereas the opposite trend was observed on the CO and the syngas (280°C for 8 h) activated catalysts. The catalyst which was initially in an oxide form (unreduced catalyst and catalyst reduced to magnetite) had lower gaseous hydrocarbon selectivities than the catalyst partially reduced to α-Fe. The unreduced catalyst had the lowest gaseous hydrocarbon selectivity, whereas the syngas activated catalyst had the highest. Total olefin and 1-olefin contents decreased in the following order: CO activated ≈ unreduced > syngas > H 2 reduced.

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%.

97/02438 Nanoscale attrition during activation of precipitated iron Fischer-Tropsch catalysts: implications for catalyst design

97/02438 Nanoscale attrition during activation of precipitated iron Fischer-Tropsch catalysts: implications for catalyst design

97/00932 Nanoscale attrition during activation of precipitated iron Fischer-Tropsch catalysts: implications for catalyst design

97/00932 Nanoscale attrition during activation of precipitated iron Fischer-Tropsch catalysts: implications for catalyst design

96/04744 Attrition of precipitated iron Fischer-Tropsch catalysts

96/04744 Attrition of precipitated iron Fischer-Tropsch catalysts

96/04753 Roles of copper and potassium promoters on the activity and selectivity of precipitated iron Fischer-Tropsch catalysts

The goal of our work is to develop a catalyst with a high selectivity for straight α-chain olefins and wax by optimizing promoters and reaction conditions. The effects of potassium and copper promotion on the activity and selectivity of precipitade iron catalysts used in the slutrry phase Fischer Tropsch synthesis is the subject of this work

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.

95/05817 Pretreatment effect studies with a precipitated iron Fischer-Tropsch catalyst

95/05817 Pretreatment effect studies with a precipitated iron Fischer-Tropsch catalyst