a Reaction conditions: catalyst size of 10-20 mesh (1.34 mm used in simulation), T = 200 °C, P = 2 MPa, H2/CO = 2, GHSV = 4.8 L/gcat·h.
b Macroporosity calculated based mercury intrusion volume from 50 to 30000 nm.
c\(\eta_{\exp}=R_{CO,exp}\ /R_{CO,exp,\mathrm{(}\mathrm{\text{for\ }}\mathrm{Co/S6000)}}\).
The simulation results also indicated that the increase of macroporosity from 0.563 to 0.606 also contributed to the enhancement of mass transfer with increasing macropore size. However, the increase of Knudsen diffusion coefficient only played a slight effect, because the Knudsen diffusion was not the limiting factor as the macropore size was larger than 200 nm according to the relationship between gas phase diffusivity and pore size. (see Figure 5S in Supporting Information).
4.4 Simulation results of a 2 mm catalyst pellet
Based on our meso-macropore model with the fixed mesopore size of 8 nm, the C5+ space-time yield (\(\text{STY}_{C_{5+}}\)) in FTS was optimized by adjusting the porosity and macropore diameter over the range of 50 to 800 nm. The performance of the monodisperse catalyst pellet with the pore size of 8 nm was given as a benchmark for comparison. The simulation results at the temperature of 473, 493and 513 K are displayed in Figure 4.