[stcredzero]

This thread seems to suggest that the big barrier is energy. The reason why natural gas and petroleum are used as feedstocks for the manufacture of plastic on earth is precisely because using them reduces the required energy input. The thread is also a good source of a few interesting links.

http://newmars.com/forums/viewtopic.php?id=6970

In terms of having enough output from a material standpoint, the requirement is still mostly energy. It would require a lot of energy to move enough CO2 through the plant.