Assessment of CO₂/CH₄ Separation Performance of 3D-Printed Carbon Monoliths in Pressure Swing Adsorption

In recent years, the benefits of high material loading, digital tuning, and flexibility in geometric design have made three-dimensional (3D) printing an especially promising way of formulating adsorbent monoliths. However, most studies in this area have focused on material development and have failed to evaluate the performances of 3D-printed adsorbent monoliths in cyclic gas separation processes. Thus, this study evaluates the influence of adsorption pressure (3–10 bar), adsorbate superficial velocity (1.40–2.30 cm/s of 60% CH₄/40% CO₂), and adsorption time (2.5–10 min) on the pressure swing adsorption (PSA) separation performance of 3D-printed activated carbon monoliths for CO₂/CH₄ separation. The CH₄ recovery and productivity were found to both increase with the adsorbate superficial velocity and adsorption time; however, increasing these process variables yielded greater CO₂ bypass into the effluent CH₄ stream thus reducing the CH₄ purity. Meanwhile, the CH₄ purity was found to increase with pressure; however, elevating the adsorption pressure gave rise to a greater amount of CH₄ co-adsorption and longer cycle times which reduced the CH₄ recovery and productivity. As such, the PSA experiments revealed that monoliths exhibited their best performance at 3 bar pressure, 1.40 cm/s superficial velocity, and 5 min adsorption time. Under these conditions, the packed bed generated 100% CH₄ purity, 38% CH₄ recovery, and 2.3 mmol CH₄/h·g_monolith productivity, which is comparable to other benchmark materials. As another benefit, probe gas experiments from 0.44 to 8.55 cm/s also revealed that printed monoliths with 200 cells per square inch cell density can reduce pressure losses by ∼60% from 1.5 mm beads. As such, it was concluded that 3D-printed adsorbent monoliths can both reduce the energy consumptions of PSA processes compared to commercial beads while also achieving comparable light species purity, recovery, and productivity. Overall, this study further cements the promise of 3D printing as a pathway for adsorbent structuring and provides a fundamental understanding of 3D-printed adsorbent monolith process performance.