The sources I could find say 4% is used for plastic and another 4% for the energy to make the plastic. Nowhere near 50%.

http://www.plasticoceans.net/the-facts/energy-consumption/

Only more reasons to stop using oil for energy and transportation - we need it for plastics.

I thought refining of oil was mostly separating the different hydrocarbons- or can gasoline be used to make plastic?

You can "crack" or "reform" any hydrocarbon to any other at the cost of some energy. Plastic tends to be ethane -> polyethylene, and the like. The fraction called "naptha" which is between ethane and gasoline in refining tends to be used as chemical feedstock.

this is not even remotely true

http://www.eia.gov/tools/faqs/faq.cfm?id=34&t=6