Fused iron catalyst

The catalyst was reformulated by Alwin Mittasch, who synthesized some 2500 different catalysts and performed more than 6500 tests. They arrived at a triply promoted catalyst consisting of a fused iron catalyst, with AI2O3 and CaO as structural promoters and potassium as an electronic promoter. The process was first commercialized by BASF, with the first plant located in Oppau in Germany producing 30 tons per day in 1913. The plant initially produced ammonium sulfate fertilizer, but when the First World War broke out it was redesigned to produce nitrates for ammunition. The plant was expanded and in 1915 it produced the equivalent of 230 tons ammonium per day. 

Some of these same experiments have been done using 10% Fe/Al203 rather than the fused iron catalyst (53). Figure 22 shows the result of a switch from H2 to 10% CO in H2 over a freshly reduced catalyst. Here a large initial rate of methane formation is observed and water does not appear until most of the initial peak has passed. The probable explanation for the presence of the CHi peak is that water produced by methanation is adsorbed on the initially dry y-Al203 support (100 m2/g). Thus the iron remains briefly in a relatively reduced state. For the CCI catalyst the AI2O3 promoter is not sufficient to prevent the water from rising quickly as shown in Fig. 19. The H/0 ratio on the surface is reduced, and carburization occurs more rapidly than methanation, as for the unsupported catalyst. 

Figure 19. Formation of major components as a function of exposure time for the reaction of 10% CO/H2 at 250°C over CCI fused iron catalyst (reduced at 450°C) (52).

To date, the best results obtained for an iron catalyst in a slurry reactor have been reported by Kolbel with a precipitated iron catalyst promoted with potassium and copper.2 Current efforts in our laboratory have been aimed at developing a catalyst with activity and productivity superior to the catalyst used by Kolbel. Most research efforts have focused on precipitated and fused iron catalysts however, promising results have been reported for... 

When cyclic ketones undergo deuterium addition on a fused iron catalyst in the temperature range of 323-483 K, the deuteriogenation proceeds via both the ketonic and enolic... 

Figure 7. High-resolution SEM images of the activated fused iron catalyst for ammonia synthesis. The anisotropic meso-structure and the high internal surface area are visible. The small probe size of a 200keV electron beam in a JEOL CX 200 instrument was used for backscattering detection of the scanning image from very thin objects.

Hall, Dieter, Hofer, and Anderson (19) studied reactions of nitrides and carbonitrides in a reduced, fused iron catalyst (Bureau of Mines number D3001). The results of these experiments were in general similar to those of Jack, and most of the differences may be explained by the differences in the type of iron employed. The major discrepancy was that in the catalyst of large surface area and small crystallite size, the <-carbonitride phase was found under conditions under which massive iron is converted to the f-phase. Since the transformation of the - to the f-phase involves only slight changes in the lattice positions of iron atoms and small changes in the x-ray pattern, it is possible either that this transformation did not occur in the catalyst or that the pattern of the f-phase could not be distinguished from that of the e-phase in the diffuse diffraction patterns. 

The reduction of nitrides of iron in pure hydrogen was very rapid, and at 200°C. nitrogen was virtually completely removed from fused iron catalysts in three hours. The hydrogenation of carbonitrides was considerably slower than that of nitrides, and the rate varied inversely with the carbon content of the carbonitride (Table III and reference 19). In... 

Fig. 7. Product from Fischer-Tropsch synthesis with nitrided fused iron catalyst. Reprinted by permission of the copyright holder, the American Chemical Society.

Bureau of Mines studies by M. D. Schlesinger, now in progress, indicate that nitrided fused iron catalysts operate successfully in the slurry process with about the same selectivity as observed in the fixed-bed tests. 

Fig. 22. Poisoning of reduced fused iron catalyst by H2S 7 = 535 K, H2/CO = 1, P = 2.16 MPa. Sulfur concentration in feed (rag S/m3) (O) 6.9, ( ) 23.0, ( ) 69.0. Reprinted with permission from Ref. 199. Copyright 1963, 1964 American Chemical Society.

In the ARGE fixed bed process Idgh boiling fractions and waxes are mainly obtained [4J, Under the same curidiliuns, sintered iron catalysts yield mainly hydrocarbons in the gasoline and diesel range. This can be explained by their lower specific surface area, pore volume and specific activity. Of the three catalyst types, (he fused iron catalyst Is characterized by the lowest specific surface area, pore volume and activity and is thus operated at higher temperatures. 

Pischer-Tropsch catalysts undergo sign>P>cant alterations under synthe s conditions. As is shown in Figure 10, for a fused iron catalyst, the originally... 

Linear a-olefins together with linear paraffins are the main primary products. On Fe the olefin content in the fraction of linear hydrocarbons for small carbon numbers was found to be about 80% (Fig. 4), which is very close to their primary selectivity [6]. This can be due to the high potassium loading, which suppresses the secondary reactions of the olefins. With increasing CO2 content a slight increase of the olefin content is observed. This can be due to the increasing amount of water formed from the reaction with CO2 instead of CO. The effect of added water on the olefin selectivity for a potassium promoted fused iron catalyst has been reported earlier by Satterfield [7]. With increasing CO2 concentration in the reaction gas on Co no more olefins were present in the products. 

The reaction of H2 and N2 to form ammonia is a reaction for which an enormous literature exists, dating to the beginning of the century. Recent reviews are those of Boudart (309) and Ertl (310). Industrial fused iron catalysts present iron particles of 25 nm or higher, and it has not been possible to prepare well-reduced small iron particles (1-10 nm) on conventional silica and alumina supports. Dumesic et al. (311a-c) were able to prepare iron crystallites of diameters from 1.5 to 30 nm by using MgO as the support. The state of the iron was monitored by Mossbauer-effect spectroscopy. The synthesis rates were measured from 300 to 405°C at atmospheric pressure the conversion was small enough so that the reverse reaction could be neglected. It was found that the reaction showed antipathetic structure sensitivity. 

Different Precipitation Catalysts with a NH3 Type Fused Iron Catalyst). 302... 

Schwarzheide—experiments with iron catalysts (comparison of different precipitation catalysts with a Nil 3 type fused iron catalyst). In view of the favorable results obtained by the Coal Research Institute in Miilheim (Fischer Pichler, 1937), industrial companies started experiments on medium-pressure synthesis with iron catalysts. 

D. Iron catalysts for medium-pressure require pretreatment with reducing gases. A very cautious reduction of fused iron catalysts with pure dry hydrogen was necessary while active catalysts could be pretreated with synthesis gas only. 

With magnesium oxide, activated fused iron catalysts produce hydrocarbons with higher olefin content during the synthesis. The ratio of potassium to magnesium seems to be of importance. H. Kolbel (Chemische Werke Rheinpreussen) and co-workers carried out x-ray investigations as well as magnetochemical investigations on iron catalysts... 

The fact that fused iron catalysts of the synthetic ammonia type were successively used in many investigations of hydrocarbon synthesis for both fluidized and fixed catalyst bed operations is of interest in different respects. Due to this fact it is possible to make use of the valuable experience obtained during development work of the ammonia synthesis (73). This applies to the reduction, the tendency to oxidize, and the effect of promoters and poisons, and to a certain extent also to questions regarding the reaction mechanism. 

Anderson made further studies on precipitated- and fused-iron catalysts to determine the relationship between rate and operating temperature. Tests were made with varying temperatures and flows at a constant conversion of 1 Hi ICO synthesis gas. Arrhenius plots of space-time yield [voliume of Hi -f- CO converted/ (volume of catalyst) (hour)] against reciprocal of the absolute temperature were approximately linear. The over-all apparent activation energy was 20.0-20.9 kcal/g mole, and a general expression was established to include temperature... 

Tau et al. considered Scheme 2 for a promoted fused iron catalyst at about 60 percent CO conversion level ... 

Results were also obtained for the conversion of syngas containing C-labeled eth-ene or propene using a precipitated promoted iron catalyst. In addition, a fused iron catalyst was employed in a run with labeled ethene at 20 atm pressure. They found that the cracking reaction of ethene was of secondary importance with the iron catalyst, unlike the case with cobalt. The distribution of the synthesis products from C-ethene showed that about 50 percent of the transformation was to the C3 product the transformation to higher hydrocarbons decreased much quicker than for the cobalt normal pressure synthesis (Figure 33). With the addition of C-ethene the iso-paraffins had a lower activity than the normal paraffins this is consistent with the data for cobalt (Figure 34). 

The detailed isomer distribution data of Pichler, Schulz, and Kiihne (16,17) for hydrogenated hydrocarbons from a fixed-bed synthesis on a precipitated cobalt catalyst at atmospheric pressure (Co.-ThOgikieselguhr = 100 18 100) at 190°C and the entrained reactors of Sasol commercial plant in South Africa, using a reduced fused iron catalyst at 22 atm and about 320°C, were used for testing the nine chain-growth schemes in Table I in the range Co-Cg, Before the analyses, the hydrocarbons were hydrogenated under conditions that should only saturate olefins. The... 

The possible steps of Fischer-Tropsch (FT) reaction and its catalysts (Fe, Co, Ru, Ni) represent a very complicated systemThe catalysts usually need a formation or self-organisation , meaning that the full activity will only be reached after a certain period. This means that for Fe-based catalysts, a part of the initial Fe oxide is transformed into iron carbide. This was investigated as early as 1948 by the tracer method.A fused iron catalyst was carbided with The synthesis product from CO/H2 = 1 1 reactant contained 10-15% labelled molecules, almost independently of the reaction conditions, even in repeated runs, indicating the minor role of carbide incorporation into hydrocarbons. The formation of a Fe-Al-Cu catalyst at 523 K and various H2/CO ratios required 100 to 2000 minutes. The yield of retained carbon decreased gradually, while the FT yield increased more abruptly after this period. [ 1... 

Table indicates that only a fraction of the C label from ethene was incorporated into chain growth products on Co and Fe catalysts. About the same amount of C (31%) was found in FT products formed with 1[ C]-1-propene, but only 18% when l-[ C]-l-hexadecene was applied.I About 50% of radioactive ethene gave methane, and 50% chain growth products on a Co catalyst, I the specific activity of higher products being practically constant between C4 and C32. Less than 10% of C from labelled ethene was incorporated into C10-C17 products, but the incorporation from C-ethanol was 60-80 times higher on a fused iron catalyst.The difference... 

Table 10. Fischer-Tropsch Reaction in a Fluidized Bed on Promoted Fused Iron Catalyst at 320 C... 

Huff and Satterfield (1984) observed a linear decrease in the adsorption parameter a in Eq. (2) with hydrogen pressure on a fused iron catalyst and incorporated this by modifying Eq. (2) to Eq. (4) ... 

Anderson et al. (1964) studied fused iron catalysts which had either been reduced or reduced and nitrided prior to use in fixed-bed reactors, determining reaction kinetics and the effects of the extent of reduction and particle size on catalyst activity. Particle sizes ranged from 42—60 mesh to 4—6 mesh. The catalyst activity increased with smaller particle size until the diameter reached about 0.3 mm for the most active catalysts tested. Catalyst particles were modeled as an active layer of catalyst surrounding an inert core, with the depth of the active layer governed by the reduction temperature. Their calculations allowed them to estimate the effective reactant dif-fusivity, and they were also able to quantify the depth of the active layer of catalyst. Variations in catalyst activity were attributed to the diffusion of reactant through a wax-filled pore and the depth of the active layer. 

Development of fused iron catalysts for ammonia synthesis... 

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