Proof-of-concept of a once-through configuration to optimize H2 conversion in CO2 methanation

Because of the high cost of green H2, its efficient conversion is of utmost importance for the deployment of any CO2 utilization process. In this work we show that it is possible to produce selectively e-methane from CO2 and H2 while approaching near complete H2 conversion. We achieve this result by leveraging a once-through configuration involving two reactors in series with intermediate water condensation working under pressure. This layout represents a flexible solution particularly useful to manage possible fluctuations in the availability of green H2. Notably, by working at the space velocity of 20 L(STP)/h/g and at the pressure of 10 barg it is possible to obtain an e-CH4 productivity of 2.8 gCH4/h/gcat, with only 0.5% of residual H2. This makes the obtained stream compliant for grid injection even in the countries with the most stringent regulations. By decreasing the GHSV, it is possible to push the H2 conversion even further, reaching residual H2 concentrations below 300 ppm. This, however, comes at the expense of a lower CH4 productivity.