Fischer–Tropsch reaction–diffusion in a cobalt catalyst particle: aspects of activity and selectivity for a variable chain growth probability

Abstract

The reaction-diffusion performance for the Fischer-Tropsch reaction in a single cobalt catalyst particle is analysed, comprising the Langmuir-Hinshelwood rate expression proposed by Yates and Satterfield and a variable chain growth parameter a, dependent on temperature and syngas composition (H 2 /CO ratio). The goal is to explore regions of favourable operating conditions for maximized C 5+ productivity from the perspective of intra-particle diffusion limitations, which strongly affect the selectivity and activity. The results demonstrate the deteriorating effect of an increasing H 2 /CO ratio profile towards the centre of the catalyst particle on the local chain growth probability, arising from intrinsically unbalanced diffusivities and consumption ratios of H 2 and CO. The C 5+ space time yield, a combination of catalyst activity and selectivity, can be increased with a factor 3 (small catalyst particle, d cat = 50 mm) to 10 (large catalyst particle, d cat = 2.0 mm) by lowering the bulk H 2 /CO ratio from 2 to 1, and increasing temperature from 500 K to 530 K. For further maximization of the C 5+ space time yield under these conditions (H 2 /CO = 1, T = 530 K) it seems more effective to focus catalyst development on improving the activity rather than selectivity. Furthermore, directions for optimal reactor operation conditions are indicated.

Stabilized ordered-mesoporous Co3O4 structures using Al pillar for the superior CO hydrogenation activity to hydrocarbons

“…The I M /I Co ratios were found to be 0.0013, 0.0274, and 0.0033 on the fresh Al/meso-Co 3 a The integrated areas of metals were previously corrected using atomic sensitivity factors [29], and the intensity ratios of IM/ICo were calculated using the equation of IM/ICo = (area of metal/area of Co) × (SM/SCo), where atomic sensitivity factor (S) of SCo = 4.5, S Al = 0.11, SMn = 2.1, and S Si = 0. 17.…”

“…Therefore, the higher surface area of metallic cobalt on the Al/meso-Co 3 O 4 suggests stronger interactions between meso-Co 3 O 4 surfaces and thermally stable Al 2 O 3 particles even under the reduction and FTS reaction conditions. It may also be responsible for the stable formation of mesopore structures, resulting in a higher catalytic activity and stability on the Al/meso-Co 3 O 4 compared to other meso-Co 3 …”

“…Therefore, its use in syngas in the applications to various catalytic reactions such as oxidation reactions [15][16][17][18][19][20] or battery technologies [21,22] due to their intrinsic characteristics such as regular pore structures and active metal frameworks. However, ordered-mesoporous Co 3 O 4 has not been sufficiently investigated till now as far as we know due to its unstable structure under hydrogen-rich condition [23], especially in CO hydrogenation reactions such as the FTS reaction.…”

Breaking the Fischer–Tropsch synthesis selectivity: direct conversion of syngas to gasoline over hierarchical Co/H-ZSM-5 catalysts

“…The higher intra-particle H 2 /CO ratio contributes to an enhanced CH 4 production over the Co/H-ZSM-5 catalyst. 13 Comparison of the Co/H-ZSM-5 and Co/mesoH-ZSM-5(a) performances under iso-conversion conditions reveals that the selectivity to gasoline cut (C5-C11) is higher for the mesoporous sample and that to C1 is lower (cf. Fig.…”

Numerical optimization of a structured tubular reactor for Fischer–Tropsch synthesis

“…The modeling is based on mass-, heat-, and momentum balances, coupled with a local reaction-diffusion model by Vervloet et al [9] to capture the effects of the cobalt catalyst performance. The reaction rate is described with the kinetics published by Yates and Satterfield [10], corrected for developments in catalyst activity.…”