If you turn 100kg of CO2 into Methane you get about 36kg. Methane is somewhere around 25x (potentially 31x) worse for global warming than CO2 by weight, so you end up with 909kg of "Carbon Dioxide equivalent", or CO2e. Let's say 2% of that leaks to atmosphere, and you burn the other 98%. Burning the 98% gets you back 98kg of CO2 (it's just the reverse process), plus 2% of that 909kg CO2e, and you end up with 116kg of CO2e, starting with 100kg. You've made global warming worse.
In fact any percentage leaking back to atmosphere (and it will) makes the numbers look pretty bad. You need a significant portion going to plastics or some other sequestered use for this to actually be a net benefit.
Thank you. This is the calculation I was looking for.
2% leakage is very conservative. The amount of additional pipeline infrastructure necessary to achieve this at scale is daunting. It will have a lot of leaks.
In fact any percentage leaking back to atmosphere (and it will) makes the numbers look pretty bad. You need a significant portion going to plastics or some other sequestered use for this to actually be a net benefit.