Water phase, Fischer-Tropsch

It is also interesting that if the goal is to produce H2-CO gas mixtures, for instance in the Fischer-Tropsch synthesis, one needs to suppress the WGSR operating in the vapor phase or to operate at higher concentrations of the oxygenated reactant in water or to use a catalyst on which the rate of the WGSR is slow. 

The main byproduct forming reactions in the BASF and Monsanto processes are different. In the former it is the liquid phase Fischer-Tropsch-type reaction, that leads to the formation of products such as such as alkyl acetates, methane etc. In the Monsanto process it is the homogeneous water-gas shift reaction that produces C02 and H2 as byproducts. Also note that the Monsanto process is superior in terms of selectivity, metal usage and operating conditions. 

In the design of upflow, three phase bubble column reactors, it is important that the catalyst remains well distributed throughout the bed, or reactor space time yields will suffer. The solid concentration profiles of 2.5, 50 and 100 ym silica and iron oxide particles in water and organic solutions were measured in a 12.7 cm ID bubble column to determine what conditions gave satisfactory solids suspension. These results were compared against the theoretical mean solid settling velocity and the sedimentation diffusion models. Discrepancies between the data and models are discussed. The implications for the design of the reactors for the slurry phase Fischer-Tropsch synthesis are reviewed. 

The range of operating conditions for the 276 experimental run in the 12.7 cm column and 20 experimental runs to date in the 30.5 cm column are shown in Ta ble I. Relevant physical properties of the liquids are listed in Ta ble II., and compared with estimated data for the slurry phase Fischer-Tropsch pilot plant reactor at Rheinpreussen (12). Solid densities were obtained from the literature (13). As received, the isoparaffin (lM) sample was saturated with water. However, this ppm level of water was soon removed during the initial experiments by the dry nitrogen gas. Additional isoparaffin was added when required to maintain the solid concentration weight-percent. All water based runs used humidified air. 

Bubble column reactors (BCR) are widely used in chemical process industries to carry out gas-liquid and gas--liquid-solid reactions, the solid suspended in the liquid phase being most frequently a finely divided catalyst (slurry reactor). The main advantages of BCR are their simple construction, the absence of any moving parts, ease of maintenance, good mass transfer and excellent heat transfer properties. These favorable properties have lead to their application in various fields production of various chemical intermediates, petroleum engineering, Fischer-Tropsch synthesis, fermentations and waste water treatment. 

Deactivation rates and aged catalyst properties have been investigated as a function of time on stream for iron-based Fischer-Tropsch catalysts in the presence/absence of potassium and/or silicon. There is a synergism in activity maintenance with the addition of both potassium and silicon to an iron catalyst. The addition of silicon appears to stabilize the surface area of the catalyst. Catalysts containing only iron or added silicon with or without potassium consist mainly of iron oxide at the end of the run. However, iron carbides are the dominant phase of the iron catalyst with added potassium alone. Catalyst surface areas increase slightly during synthesis. The bulk phase of the catalyst does not correlate to the catalyst activity. The partial pressure of water in the reactor is lower for potassium-containing catalysts and is not a reliable predictor of catalyst deactivation rate. 

The Fischer-Tropsch Synthesis (FTS) converts synthesis gas (a mixture of CO and H,) to hydrocarbons. Iron-based catalysts lose activity with time on stream (TOS). The rate of deactivation is dependent on the presence/absence of promoters such as potassium and/or binders such as silica [1.2]. Several possible causes of catalyst deactivation have been postulated [3] (i) Sintering, (ii) Carbon deposition, and, (iii) Phase transformations. With respect to phase transformations, there is considerable disagreement whether the active phase for the FTS is iron oxide or carbide [4,5]. In addition, certain reactor conditions, such as a high partial pressure of water, are known to cause a decline in activity [6]. 

Hydrogenation of Carbon Monoxide or Carbon Dioxide. There are two important aspects of metal carbides in CO-H2 reactions including methana-tion, Fischer-Tropsch synthesis, alcohol synthesis, and water gas shift reaction. First, metal carbides, by themselves or together with other phases, are considered as active phases in these reactions catalyzed by Fe, Co, and Ni. These carbide phases are formed in situ from the respective metals or oxides during the reaction. This aspect is not discussed here. Instead, catalysis by early transition metals intentionally prepared in a stable carbide form is the subject of this section. Molybdenum and tungsten carbides are by far the most extensively studied. 

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