http://www.geoengineeringmonitor.org/2018/05/direct-air-capture/
So, it will be much, much more expensive than separating out from natural gas. When I was a junior engineer at the Morgan Creek power pant in Colorado City, Tx, in 1979, a big liquid gas company, I believe it was Air Products, approached us with a proposal to separate the CO2 from the boiler stack on Unit 6, a 500 MW steam plant that went online in 1966. The CO2 was to be used in local oil fields for tertiary recovery. Texas Electric accepted, as they would pay us for the power used and a small fee for the CO2 they took out. An AE was hired and started work in late 1979. Before much more than preliminary engineering got done, mostly bid specs, and big gas strike in the upper panhandle that was high in CO2 content. I think it was about 15% on average. The project was abandoned, as it would be much much cheaper to separate it from the natural gas, which would have to be done anyway before it could be used as a fuel or feedstock.