Currently, packed beds of pellets or zeolite beads are used as sorbents for CO2 in NASA CO2-removal assemblies. Inefficiency associated with packed beds are related to random packing which results in non-uniform flow, poor thermal management for CO2 desorption, and poor mechanical stability. An improved system is envisioned with a sorbent bed in the form of 3D-printed monolithic lattices. To that end, the extrusion-based additive-manufacturing technique known as robocasting was used to create prototype lattices of zeolite 13X. Formulations of zeolite 13X (with inorganic binders) were studied. A down-selected formulation was made into a zeolite paste feedstock suitable for the robocasting process and shown to be useful for creating robust structures while simultaneously retaining relatively high CO2 adsorption capacity when partially sintered at 575oC. Computer simulations and characterization of CO2 adsorption kinetics were used to guide the design of lattices with the desired size of struts potentially useful for a full-scale CO2-removal assembly. Lattices with 2mm struts were densely printed whereby 84% of the available volume was occupied by the zeolite 13X formulation while still maintaining continuous flow paths. Based on CO2 adsorption capacity and a heater design for regeneration, a new canister with a rectangular cross-section is proposed.
Cesarano et al. (Sun,) studied this question.