Process evaluation and kinetic analysis of 3D-printed monoliths comprised of CaO and Cr/H-ZSM-5 in combined CO2 Capture-C2H6 oxidative dehydrogenation to C2H4

In this study, dual-function materials (DFMs) comprised of CaO and Cr/H-ZSM-5 were formulated in 3D-printed monolithic structures and investigated in a combined process for capture and utilization of CO2 in oxidative dehydrogenation of C2H6 to C2H4 (CO2-ODHE). Various formulation strategies were employed to fabricate these DFM structures. Two bed designs were considered: i) a layered-bed in which adsorbent (CaO) and catalyst were printed separately and stacked on top of each other, and ii) a single-layer bed where the adsorbent-catalyst materials were 3D-printed into a singular monolith and loaded into the bed as DFMs. Between these, the layered-bed displayed enhanced performance as compared to the composite DFMs, as this configuration generated a 3.73 mmol/g CO2 adsorption capacity, 42.5% C2H6 conversion, 90.6% C2H4 selectivity and 38.6% C2H4 yield compared to 2.4 mmol/g CO2 adsorption capacity, 37.9% C2H6 conversion, 89% C2H4 selectivity and 33.8% C2H4 yield in the best singular monolith configuration. The enhanced performance of this configuration was attributed to a higher degree of adsorptive site accessibility and a lesser degree of active site blockage from intraparticle binding (as evident from the textural properties). This work also assessed the effects of monolith cell density on CO2 adsorption and utilization for ODHE by varying the cells per square inch (cpsi) from 200 to 600 cpsi. These experiments revealed that increasing the cell density from 200 to 600 cpsi enhanced the overall mass transfer coefficient from 0.40 x 10(-2) to 1.01 x 10(-2) s(-1) due to a sizable enhancement in film mass transfer between the two geometric designs. Such enhancement improved the C2H4 selectivity and yield to 92 and 45.1% in the 600 cpsi sample. As such, this work also indicated that higher cell densities lead to better performance of the layered-bed configuration, where the optimum configuration is separate stacking of the adsorbent and catalyst phases. Overall, these findings provide a deeper understanding of DFM materials, bed configuration, and establish a groundwork which can be used to optimize their structures for CO2 adsorption-reaction processes.