Accumulation of liquid hydrocarbons in catalyst pores during cobalt-catalyzed Fischer–Tropsch synthesis

Abstract

aIn the literature, it is widely claimed that during the initial period of Fischer-Tropsch synthesis liquid higher hydrocarbons fill catalyst pores completely, at least for temperatures of less than 250°C at a typical pressure of about 2 MPa. This leads to diffusional restrictions in the porous network for particles with a size for industrial fixed-bed operation (> 1 mm), whereby catalyst effectiveness and product selectivity are strongly affected. However, under industryally relevant reaction conditions, our experimental and theoretical investigations on the interplay of reaction and diffusion in cobalt catalyst particles reveal that the pores are only partly filled with liquid higher hydrocarbons even at a very long time on stream of months or more for a chain growth probability below about 0.8. Experiments were conducted in a magnetic suspension balance using particles of technical size (dp = 3 mm), and a mathematical model was developed describing quite accurately the formation, vaporization and accumulation of liquid products and their C-number distribution in the porous particle.

Activity and Structural Changes of Fe‐based Catalysts during CO2 Hydrogenation towards CH4 – A Mini Review

“…In line with the influence of reactor pressure, high residence time of CO x and H 2 in the catalyst bed enhances the chain growth of the hydrocarbons. Also, a slight decrease in CO 2 conversion with rising pressure is found in the range of 0.5 to 1.0 l/g/h (Figure ), which is ascribed to condensation of higher hydrocarbons in the pores of the Fe catalysts limiting the gas diffusion …”

“…Also, a slight decrease in CO 2 conversion with rising pressure is found in the range of 0.5 to 1.0 l/g/h (Figure 1), which is ascribed to condensation of higher hydrocarbons in the pores of the Fe catalysts limiting the gas diffusion. [23] Furthermore, high molar H 2 /CO 2 ratios are beneficial for pronounced CO 2 conversion as well as CH 4 yield. Excess of H 2 increases the thermodynamic CH 4 yield and accelerates the methanation.…”

Formation and Vaporization of Hydrocarbons During Cobalt‐Catalysed Fischer‐Tropsch Synthesis

“…Experiments were carried out in two magnetic suspension balances (MSB, Rubotherm) and a horizontal thermobalance (Seiko Instruments Exstar 6000). With the first MSB, which is explained in detail by Pöhlmann et al , in situ measurements of the catalyst particle weight gain due to HC accumulation during FTS are conducted, placing up to 8 technical sized particles in a stainless steel mesh basket. An electrically powered heating system enables to adjust the temperature within the measuring chamber in the range of 100 to 300 °C.…”

“…Tab. displays the intrinsic kinetic parameters for the formation of C 2+ ‐hydrocarbons, as found for the utilized cobalt‐catalyst , . …”

“…Tab. 2 displays the intrinsic kinetic parameters for the formation of C 2+ -hydrocarbons, as found for the utilized cobalt-catalyst [8,15].…”