Study of methane upgrading using an activated carbon 3D-printed adsorbent

Although Maxsorb is a commercially available powder-form material, to be used in adsorption-based processes, its handling is easier if used with a structured geometry. Indeed, in the monolithic form, activated carbons have shown the potential to be used in adsorption-based applications. The use of additive manufacturing (AM) allows the development of structured adsorbents with adaptable geometries. In this work, Maxsorb activated carbon was 3D-printed into a monolithic structure using a polymeric binding agent, carboxymethylcellulose (CMC). The monolith was obtained through direct writing of filaments of an ink containing the adsorbent and the binding agent in a layered way, according to a pre-established pattern. The material was comprehensively characterized by N2 physisorption at 77 K and CO2 adsorption at 273 K to analyze the porous structure, SEM, and mercury porosimetry to evaluate the macrostructure porosity. To examine the affinity of CH4 and N2 with the adsorbent, pure adsorption equilibrium isotherms of these two gases on the 3D-printed monolith were measured at 303, 333, and 373 K by a gravimetric method. The adsorption capacities were compared to the ones of the original powder. The activated carbon materials showed a higher affinity to CH4. Furthermore, the adsorption equilibrium data of CO2 and Ar were also assessed. For all gases, the adsorption capacities decreased upon shaping. The monolith's CH4/N2 ideal selectivity was compared with its pristine powder (2.84 vs. 3.54). The CH4/N2 separation performance was also assessed through dynamic breakthrough tests. The experimental breakthrough curves were well predicted using a mathematical model.