[ams6110]

What is the current process for producing "pure" CO2 gas for sale e.g. as dry ice, or for use in food/beverage or for other industrial purposes? Unlike e.g. nitrogen or oxygen, concentrating it out of the atmosphere would seem to be inefficient as it's only roughly 0.04%.

[URSpider94]

It's typically captured either from processes that make ammonia or hydrogen from methane (with CO2 being the only major byproduct), or by capturing the output from large-scale fermentation.

Source: http://www.uigi.com/carbondioxide.html

[hwillis]

Note that the gases coming out of a power plant are mostly nitrogen