Essentially you're proposing capturing the CO2 emitted by fossil fuel heat engines and converting it back to hydrocarbons using the Sabatier process. There's se

Essentially you're proposing capturing the CO2 emitted by fossil fuel heat engines and converting it back to hydrocarbons using the Sabatier process. There's several barriers to this: 1. Capturing the carbon emissions. The exhaust if a gas turbine is a high temperature mix of air and C02. Separating out the CO2 requires either cooling it or a chemical process to capture the carbon dioxide. Both of these processes are every energy intensive. 2. The Sabatier process needs a source of hydrogen. Typically this is done through steam reformation, but that emits CO2. Electrolysis or thermochemical water splitting needs to be done instead, and these are both energy intensive and expensive to do. 3. The Sabatier process itself also requires energy, as it's putting the carbon in a higher energy state. It'd probably be easier to just use the hydrogen in step 2, but that's still a difficult undertaking that nobody has done cost effectively as of now.