Two-step TSAR process for biogas upgrading: computational study of CO2 capture and catalytic methanation via reactive regeneration in a dual-function adsorber/reactor with conductive structured internals

This work presents a novel two-step Temperature Swing Adsorption/Reaction (TSAR) process for biogas upgrading and CO2 valorization through reactive regeneration. The proposed cycle uses a mechanical mixture of CO2 sorbent and methanation catalyst, enabling CO2 adsorption during biogas upgrading and catalytic methanation during regeneration. In the adsorption phase, CO2 is selectively removed from the biogas stream to produce high purity biomethane. For sorbent regeneration, the reactor bed is fed with hydrogen while being heated to a higher temperature, thereby facilitating in-situ methanation of the desorbed CO2. This reaction not only converts CO2 into synthetic methane but also enhances desorption by lowering the CO2 partial pressure, thus intensifying the overall regeneration step. To improve thermal management and reduce cycle time, the sorbent and catalyst pellets are packed inside a conductive Periodic Open Cellular Structure, which enhances heat transfer accelerating temperature transients and limiting the formation of hot spots in the reactor. A non-isothermal non-adiabatic, 1-D dynamic model is developed to simulate the TSAR cycle. The model is used to evaluate the influence of process conditions and operating parameters on the proposed cycle performance. Simulation results indicate that, by adopting a recycle strategy of the outlet stream from regeneration 99% of overall CO2 conversion is achieved with a process outlet stream containing 83% methane, 15% hydrogen and only 0.2% CO2, demonstrating the potential of the proposed process for sustainable biogas upgrading.