That is an excellent question and the primary question that I’m trying to answer in my work.
Power plant exhaust, like air, is mostly nitrogen with between 5% and 15% CO2 in it plus the trace gases (which themselves can cause problems). For transportation through pipelines, the Co2 needs to be as pure as possible.
The “capture” processes that separate the CO2 from these other gases can take different forms. The main method being used now involves using amines which react with Co2 to form a new compound. This compound can then be heated to release the purified Co2. This requires a LOT of energy. Reducing this energy cost by changing the amine, or using a different process entirely, that doesn’t need heating, for example, is very important for making cheap products from power plant CO2.