"non-feedstock energy [for plastic production is] (between 1.4 x 1018 J and 2.2 x 1018 J)". Non-feedstock means the stuff that doesn't turn into plastic, but just powers the product. From the same paper, adding both feedstock and non-feedstock together:

"between 2.5% and 4.0% of total U.S. primary energy consumption in 2008 was due to the energy for plastic."

Also, plastics are a fossil fuel, and a lot of waste plastic is burned for energy production, which results in significant fossil-fuel based CO2 emissions.