Most uses of fossil fuels these days are for fuel, not petrochemicals. The energy needed to get to petrochemicals (and the fraction of carbon currently coming from fossil fuels to get to petrochemicals) are relatively modest.
Citation needed. Sorry but it takes, more or less, as much energy as that which is stored within the chemical bonds of a petrochemical to make that chemical from raw materials. Also, what? Your comment doesn't seem to fit into the context of our discussion. Where is the energy and raw materials to produce the green energy materials going to come from?
When renewable energy is abundant, we will find it cheaper to synthesize the hydrocarbons we need than to pump them out of the ground, transport, refine, and transport them again.
In the meantime, the overwhelming majority of oil pumped is burned. In the nearer future, only oil that is the absolute cheapest to pump will be, mostly as feedstock for bulk chemistry, because it will not be worth the cost to refine it for fuel.
So where will energy to transition come from? Fossil fuels, which are today produced in the trillions of tons annually. As more renewables are built out, some of their output will go into producing new panels. Eventually, panels will be produced from 100% renewable energy.
You will not notice any change, except lower power bills.
The quantity of carbon in petrochemicals (rather than fuels) is small enough that it could be supplied with the carbon in waste biomass streams. This carbon is reduced; the energy cost of reducing CO2 has already been paid.
