Cobalt precipitation catalysts

Cobalt precipitation catalysts. The development of cobalt catalysts (Fischer and Koch, 12) was similar to the development of the corresponding nickel catalysts. In the case of cobalt, however, it was easier to prevent extensive methane formation. The lOOCo 18Th02 100 kieselguhr catalyst became the so-called standard cobalt catalyst. 

Reaction of cw- 1,4-Poly butadiene and PVC. Et2AlClt-Cobalt Compound Catalyst. Commercial cw-1,4-polybutadiene prepared with a Et AlCl-cobalt compound catalyst system was freed of antioxidant by solution in benzene and precipitation with methanol. The cis-1,4,polybutadiene had an intrinsic viscosity in benzene at 25 °C of 2.4 and a greater than 96% cis-1,4 content. 

The introduction of iron-zinc catalysts led to the low pressure nthesis of liquid and solid hydrocarbons from CO/Hj in 1925 [19. 20. However, it was found that these catalysts were deactivated rapidly and thus further investigations concentrated on nickel and cobalt catalysts. They led to the introduction of a standardized cobalt-based catalyst for llic normal-pressure synthesis of mainly saturated hydrocarbons at temperatures below 200 C. In 1936, the first four commercial plants went on stream. Until 1945 the Fischer-Tropscit synthesis was carried out in nine plants in Germany, one plant in France, four plants in Japan and one plant in Manchuria. The total capacity amounted to approximately one million tons of hydrocarbons per year in 1943. The catalysts used consisted of Co (1(X) parts), ThO (5 parts). MgO (8 parts), and kieselgur (200 parts) and were prepared by precipitation of the nitrates. These catalysts were used in fixed-bed reactors at normal or medium pressures (< 10 bar) and produced mainly saturated straightproduct obtained consisted of 46% gasoline. 23% diesel oil, 3% lubricating oil and 28% waxes (3.15). 

An amorphous layer was observed on the surface of the particles (refer Fig. 5) as analysed by TEM. The possible origin of this amorphous layer can be described by the following hypothesis During the aqueous phase cobalt nitrate catalyst preparation step, the alumina support dissolves and the dissolved aluminium ions can precipitate either as boehmite or may, in combination with cobalt ions, precipitate as a cobalt aluminium hydrotalcite-like layer [16], producing a physically amorphous layer, uniformly covering the sur ce of the bulk support material [15]. It was, however, not possible to characteri2e the observed layer. 

The best catalysts were produced by thermal decomposition of nitrates in the presence of porous carriers. Fischer and Tropsch carried out experiments with precipitated catalysts too. However, the precipitation of cobalt was performed with hydroxides (NaOH, KOH, etc.) which produce catalysts of very low activity. Unknown up to that time was the outstanding behavior of kieselguhr as carrier of the catalyst, and the fact that only carbonates can be used for the production of active precipitation catalysts. 

Nickel precipitation catalysts. Fischer and Meyer (11) carried out exhaustive research work trying to develop active Ni catalysts for the synthesis of higher hydrocarbons. In spite of the failure of all previous attempts, Fischer and Meyer found two types of nickel catalysts with a behavior similar to that of the best cobalt catalysts. 

Fischer and Pichler resumed such experiments at varied pressures during the winter of 1935-1936. They used cobalt-thorium-kieselguhr precipitation catalysts for the synthesis at increased pressures and found a very interesting behavior of the catalysts at pressures of 5-20 atm. (medium pressure) ... 

In connection with their work on medium-pressure synthesis with cobalt catalysts, Fischer and Pichler began (1936-1937) some research work with iron catalysts too. The first positive results, comparable with results obtained with cobalt catalysts were achieved when an iron precipitation catalyst that had been in use at atmospheric pressure for several weeks was switched to operation at a synthesis gas pressure of 15 atm. The initial pretreatment of the catalyst at 1 atm. proved to be necessary for the successful use of the catalyst at higher pressure. The combination of proper pretreatment (reduction and carbonization) followed by synthesis at elevated pressures increased the yields of Cs+ hydrocarbons to more than double and the lifetime of the catalyst was... 

Alkali-Promoted Precipitated Cobalt-Based Catalyst ... 

From experimental work with precipitated cobalt-iron catalysts it appeared that the cobalt reacted with alumina giving cobalt spinels, which helped to form smaller iron and cobalt crystallites during reduction and to increase the surface area to make the catalyst more stable and less sensitive to oxide forming poisons. In the presence of potash, cobalt was able to decrease the reduction temperature. 

CoAsS, are also used as sources. The ore is roasted and Co is precipitated as the hydroxide and then reduced to Co with carbon (hep below 417 - C, cep to m.p.). The metal is silvery white and readily polished. It dissolves in dilute acids and is slowly oxidized in air. Adsorbs hydrogen strongly. The main use of cobalt is in alloys. Cobalt compounds are used in paints and varnishes, catalysts. Cobalt is an essential element in the diet. World production 1976 32 000 tonnes metal. 

Where sodium sulfite is added as a component of multifunctional or one-drum products designed for smaller boilers, no cobalt catalyst is added because of the cobalt alkaline precipitation problem. Consequently, if the FW temperature is low this type of formulation is unsuitable because the sulfite requirement will be too high and the available reaction time too short. Probably a tannin-based, one-drum product would be more suitable (although here again there may be a problem because tannin-based products, unlike sulfite cannot be mixed with amines). 

Where dry, catalyzed sodium sulfite is used as the scavenger source, the provision of 2 to 3% metabisulfite into the day-tank batch provides sufficient pH level reduction to ensure the cobalt catalyst does not precipitate. The overall oxygen scavenging reaction is as follows ... 

Proven, industrially used catalysts are mostly based on either iron or cobalt. Ruthenium is an active F-T catalyst but is too expensive for industrial use. Both Fe and Co are prepared by several techniques including both precipitation and impregnation of (e.g. alumina or silica) supports. The more noble Ni catalyst produces nearly exclusively methane and is used for the removal of trace of CO in H2. 

Co-NHC complexes receive considerably less attention than Rh-NHC complexes, despite the fact that NHCs may actually be better suited to cobalt. That is, basic phosphines work well with Co whereas less basic phosphines and phosphites provide the best Rh catalysts [2]. Van Rensburg and co-workers synthesised the dimer [Co(CO)3(lMes)]2 (25) and combined it with 1-octene and syngas (H iCO = 2 1) at 60 bar and 170°C [29, 30]. The result was a dark brown oily precipitate identified as the imidazolium salt [IMesH]+[Co(CO) ] . 

Unimmobilized Corynebacterium propinquum (CGMCC No. 0886) cells containing a cobalt-dependent NHase were employed in either batch or continuous reactions for the production of nicotinamide from 3-cyanopyridine [24]. In the continuous process, membrane filtration separated precipitated product (>5 wt%) and the microbial cell catalyst from the reaction mixture, where the catalyst was then recovered and returned to the reactor using a continuous addition of aqueous 3-cyanpyridine to maintain substrate concentration at <20% (w/v), a final conversion of >99% was obtained. 

Bezemer, G. L., Radstake, P.B., Koot, V., van Dillen, A. J., Geus, J. W., and de Jong, K. P. 2006. Preparation of Fischer-Tropsch cobalt catalysts supported on carbon nanofibers and silica using homogeneous deposition-precipitation. Journal of Catalysis 237 291-302. 

FIGURE 9.24 Molar radioactivity of the reaction products when co-feeding n-hexa-decene-(l)-(l-14C) together with the synthesis gas to FT synthesis on cobalt. Catalyst 100Co-18Th02-100Kieselguhr (by weight), precipitated, 190°C, 1 bar, H2/CO = 2, Xc0 = 70%, 0.1 vol% of hexadecene-14C in the synthesis gas. 

Sample Preparation. The preparation of the unsupported Co-Mo catalysts has been carried out using the homogeneous sulfide precipitation (HSP) method as described earlier (l8) and only few details will be given here. A hot (335 3 5 K) solution of a mixture of cobalt nitrate and ammonium heptamolybdate with a predetermined Co/Mo ratio is poured into a hot (335 3it5 K) solution of 20 ammonium sulfide under vigorous stirring. The hot slurry formed is continuously stirred until all the water has evaporated and a dry product remains. This product is finally heated in a flow of 2% H2S in H2 at 675 K and kept at this temperature for at least b hr. Catalysts with the following Co/Mo atomic ratios were prepared 0.0, 0.0625, 0.125, 0.25, 0.50, 0.75, and 1.0. 

F-T Catalysts The patent literature is replete with recipes for the production of F-T catalysts, with most formulations being based on iron, cobalt, or ruthenium, typically with the addition of some pro-moter(s). Nickel is sometimes listed as a F-T catalyst, but nickel has too much hydrogenation activity and produces mainly methane. In practice, because of the cost of ruthenium, commercial plants use either cobalt-based or iron-based catalysts. Cobalt is usually deposited on a refractory oxide support, such as alumina, silica, titania, or zirconia. Iron is typically not supported and may be prepared by precipitation. 

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