I hate dealing with ethanol and the only e-free gas in my area is 91 octane. I have heard mixing a bit of diesel will lower octane. How much per 10 gallons would be about right?
Zero diesel added to 10 gallons of gas will be perfect in that example.
You can remove ethanol by adding water to ethanol gas. As I recall the ratio is 15 parts gas to one part water. Add a little cheap food color to the gas to make it more visible. Mix the two and shake the container (preferably a clear plastic jug). Let it sit overnight. In the morning you'll have 2 distinct layers. One will be gasoline (on the top) without ethanol and one will be water and ethanol mixed together. Siphon the gasoline off and take the other to a haz mat disposal place in your community. Hydrogen bonding has just happened here.
Now, what will you have? Gasoline with a lower octane rating. 87 octane turns into roughly 81 or 82 octane without the ethanol so you might want to start with 91 or 92 octane before you do this. Ethanol adds octane to unleaded gas and it is added just before the fuel is delivered to the gas station (so it won't absorb water).
