> but we will need to expend more energy later to put the extra carbon back where it belongs
Is this actually a given? I mean trying to make gasoline from the atmosphere would certainly require more energy than you get by burning it, a lot more.
But I thought sensible capture proposals ran on different chemistry, possibly relying on a wet/dry cycle under which the affinity for carbon is different in the two halves. And letting evaporation (i.e. solar energy) move you from wet to dry. It's not obvious that these must use more energy than you got by burning the coal in the first place.
Sure, I agree. The part I question is "more energy later". Or at least, this is not obvious from a first-principles no-perpetual-motion argument. It's a technology question.
Is this actually a given? I mean trying to make gasoline from the atmosphere would certainly require more energy than you get by burning it, a lot more.
But I thought sensible capture proposals ran on different chemistry, possibly relying on a wet/dry cycle under which the affinity for carbon is different in the two halves. And letting evaporation (i.e. solar energy) move you from wet to dry. It's not obvious that these must use more energy than you got by burning the coal in the first place.