Fischer-Tropsch synthesis operating temperature

Dr. Moeller A methanation plant does not have a problem of selectivity. Whether you operate at low or high temperature, when using a nickel catalyst you will form only methane and no higher hydrocarbon. But with the Fischer-Tropsch synthesis, you have a wide range of possible products which can be formed. If you want to have a certain product, you must keep your temperature at a certain constant value. 

The aim of this work was to apply combined temperature-programmed reduction (TPR)/x-ray absorption fine-structure (XAFS) spectroscopy to provide clear evidence regarding the manner in which common promoters (e.g., Cu and alkali, like K) operate during the activation of iron-based Fischer-Tropsch synthesis catalysts. In addition, it was of interest to compare results obtained by EXAFS with earlier ones obtained by Mossbauer spectroscopy to shed light on the possible types of iron carbides formed. To that end, model spectra were generated based on the existing crystallography literature for four carbide compounds of... 

The methanation reaction is a highly exothermic process (AH = —49.2 kcal/ mol). The high reaction heat does not cause problems in the purification of hydrogen for ammonia synthesis since only low amounts of residual CO is involved. In methanation of synthesis gas, however, specially designed reactors, cooling systems and highly diluted reactants must be applied. In adiabatic operation less than 3% of CO is allowed in the feed.214 Temperature control is also important to prevent carbon deposition and catalyst sintering. The mechanism of methanation is believed to follow the same pathway as that of Fischer-Tropsch synthesis. 

FIGURE 5 Anderson-Schulz-Flory distribution of the linear hydrocarbons, linear oxygenates (n-alcohols, n-aldehydes, and linear carboxylic acids), and methyl alkyl ketones formed in the Fischer-Tropsch synthesis on an iron-containing Fischer-Tropsch catalyst operating at a temperature of 498 K (plotted using log(lO)). 

A Slurry Bubble Column Reactor (SBCR) is a gas-liquid-solid reactor in which the finely divided solid catalyst is suspended in the liquid by the rising gas bubbles. SBCR offers many advantages over fixed-bed type reactors such as 1) improved heat transfer and mass transfer 2) isothermal temperature profile is maintained and 3) relatively low capital and operating cost. Fischer-Tropsch Synthesis (FTS) takes place in a SBCR where the synthesis gas is converted on catalysts suspended as fine particles in a liquid. The synthesis gas flows in a bubble phase through the catalyst/wax suspension. The volatile products are removed with unconverted gases, and the liquid products are separated firom the suspension. A gas distributor located in the bottom of the reactor produces the bubbles in the reactor. 

Removal of carbon monoxide and carbon dioxide by methanation is required for the protection of certain hydrogenation and ammonia synthesis catalysts against rapid deactivation. It is also necessary when the hydrogen is used in hydroprocessing operations because CO2 and CO can lead to temperature excursions and catalyst damage in the reactors. Furthermore, methanation is an essential step in the reaction systems associated with the Fischer-Tropsch synthesis and with the production of synthetic natural gas from liquid hydrocarbons and coal. Grayson (1956) presented a detailed discussion of methanation in connection with the Fischer-Tropsch process. 

Change occurred in high-temperature Fischer-Tropsch reactor technology. The circulating fluidized bed Sasol Synthol reactors were replaced by fixed fluidized bed Sasol Advanced Synthol (SAS) reactors.44 This did not meaningfully affect the Fe-HTFT syncrude composition, but it reduced the operating cost of HTFT synthesis. 

Here the chemical formula is written CH2, which is one-eighth of a typical gasoline molecule (CgHi6). The reaction is catalyzed by a number of metal-based catalysts including iron, cobalt, and nickel. The reactors in which the synthesis takes place operate within a temperature range of 225 to 365°C and at pressures from 0.5 to 4 MPa. It should also be noted that the Fischer-Tropsch reactions produce a wide spectrum of oxygenated compounds such as alcohols. 

Fischer-Tropsch Technology FTS can be carried out in several different reactor types fixed bed, fluidized bed, or slurry phase and at different temperatures. The high-temperature Fischer-Tropsch (HTFT) synthesis runs at 320°C-350°C, at which temperatures typically all products are in the gas phase [22], HTFT is operated in fluidized-bed reactors, with iron catalysts. Selectivities correspond to chain-growth probabilities in the range of 0.70-0.75 and are ideal for gasoline production, but olefins and oxygenates are formed as well and are used as chemicals. 

The Fischer-Tropsch (FT) synthesis involves catalytic reactions in which CO and H are reacted to form mainly aliphatic straight-chain hydrocarbons (C Hy). The kind of liquid obtained is determined by the process parameters (temperature, pressure), the kind of reactor, and the catalyst used. Typical operation conditions for the FT synthesis are a temperature range of 200-3 5 0 C and pressures of 15-35 bar, depending on the... 

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