Downstream the Sabatier reactor, step-wise product purification is considered. Since water is formed stoichiometrically with methane, it needs to be separated from the raw product stream, preferably in the first purification step (WS1 and WS2 in Figure ). For the SPO base case (𝑟 in = 4.7, 𝑛̇C O 2 ,in = 0.91 kmol d -1 ), the thermodynamic separation unit achieves a removal efficiency of 99.62% due to the vapor pressure of water. An additional separation step, e.g. by adsorption on a molecular sieve , would be required to lower the residual water content further.