I think your math is wrong. Most of modern cars do up to 150g of CO2 per 100km, there are other emissions too, but they are in way smaller numbers.
The poster child for me for this is low-GWP refrigerants. Sounds good, right? Well, think about how CO2 captured filtered and compressed compares. I'll leave everybody to argue with their-self on this. Does co2 vs r-whatever use more energy? Less? Does it somehow justify the emissions and pollution of manufacture?
My conclusion is... I don't know.
I am confused why everybody mentions emissions though. In a discussion on paper/plastic/reusable bags, in a response to a call for napkin math for a claim of "10,000 bags from the fuel needed to get to the store" (essentially the argument made)- CO2 isn't relevant: just the mass of the gas used to get to the store.
I'm not pleased with how this turned out. to be told I'm wrong? That's fine, its the internet. I'm disappointed and alarmed with how badly wrong the suggested corrections are... it's deeply frustrating for me as well.
See: https://www.sciencedirect.com/science/article/pii/S036013232...
As for a kilo of gas per 10 miles- see https://en.m.wikipedia.org/wiki/Gasoline - says 0.71-0.77g/mL, standard conversion table says 3.785L per gallon. (https://www.engineeringtoolbox.com/volume-units-converter-d_...), and finally- since we're comparing burning gas for a car vs using it in plastic: the figure of merit is petroleum usage, not greenhouse gas emission. Technically, plastic and gasoline aren't going to be 1:1. But that's not napkin math anymore unless you're a petroleum engineer/chemist.
It doesn't really make sense to be comparing plastic waste to CO2 emissions though. These aren't fungible.