For what it's worth, that's just not true. You're gaining energy in combustion by going from CH4/etc + O2 and producing CO2 + H2O. The added energy comes from

For what it's worth, that's just not true. You're gaining energy in combustion by going from CH4/etc + O2 and producing CO2 + H2O. The added energy comes from breaking those carbon-hydrogen bonds. You're then sequestering CO2. Not C2. You're not doing anything other than concentration. Yes it takes energy to re-concentrate it for sequestration. No, that's not necessary as much energy as you gain from combustion. It's energy positive overal from a thermodynamic perspective. Yes, practicalities make that more energy intensive and more difficult (e.g. capture after emission into the air instead of from a high concentration source), but it's not quite what folks keep articulating when claiming "thermodynamics demands that this takes at least as much energy". The original article is about those practalities and whether or not they amount to more energy than what's released during combustion. It's far from obvious whether or not they do overall, though.