Coupled Transport and Reaction Modeling of Sorbent Particle Size Effects in Nonisothermal Packed-Bed CO₂ Adsorption

Recent studies have shown that solid sorbents offer a promising route for post-combustion CO₂ capture. This potential remains uncertain because the influence of particle size on the capture efficiency and reactor performance has not been fully characterized. Here, we developed a two-dimensional CFD Eulerian-Eulerian model, validated it against experimental data, and applied it to simulate CO₂ capture in a packed-bed reactor filled with spherical particles of 0.5, 0.8, and 1.5 mm diameter. A carbon-based sorbent impregnated with potassium carbonate (K₂CO₃) was chosen for this study due to its relevance in industrial CO₂ capture. Under our baseline conditions of 10% CO₂, 60 °C, this sorbent follows a Langmuir isotherm with a maximum capacity of about 1.4 mmol of CO₂/g at 60 °C and achieves roughly 1.2 mmol/g uptake. Its moderate thermal conductivity of 0.25 W/m·K helps dissipate the heat released during adsorption, minimizing temperature gradients across the bed. Gas-solid interactions were modeled via a Eulerian-Eulerian framework, explicitly defining interphase forces to capture momentum exchange. We used the Syamlal-O'Brien correlation for drag. Smaller particles (0.5 mm) achieved nearly complete CO₂ removal but produced a high pressure drop of 4.2 kPa. Larger particles of 1.5 mm reduced the pressure drop (0.9 kPa) but lowered the capture efficiency to 73%. Midsized particles of 0.8 mm struck a balance, reaching about 85% capture with a moderate pressure drop of 1.7 kPa. We observed that increasing the inlet gas flow by 20% shortened the breakthrough time to 23 min but slightly reduced the capture efficiency, indicating a trade-off between the flow rate and the performance. Because CO₂ adsorption is exothermic of -145 kJ/mol, careful thermal management is required to maintain stable operation.