At the chosen base case, a CO2 conversion (Eq. ( )) of 99.89% and a selectivity (Eq. ( )) of 99.999% is achieved. The impurities entering the storage unit for the SPO base case (see Table together with RO results) are sufficiently low to fulfil the fuel Grade A of the US department of defence for the performance specification of LCH4 (liquified methane) as propellant . Thus, our results show, that the required goal in methane productivity of 0.91 kmol d -1 can be achieved by employing sufficiently high H2/CO2 feed ratios in the SPO concept without compromising the required fuel purity for applications as propellant with fewer unit operations compared to the setup proposed by Alam et al. . Further details about the stream compositions of the remaining streams are provided for the RO base case in Table (in the SI).