Vegetable oils are tri-glycerides. These molecules can be cracked into three long chain paraffins and a propane molecule by reacting them with hydrogen at high temperature and pressure over a catalyst. This makes a raw diesel fuel that then needs to be isomerized to lower the cloud point (basically when it begins to freeze). The end result is a drop in replacement for fossil diesel fuel that burns smoother and cleaner.
Two refineries in the SF Bay Area have converted from fossil fuel operation to manufacturing this renewable diesel.
Fun fact: over 70% of diesel sold in California is now renewable or bio diesel. Both types start with tri glycerides - either vegetable oil, waste cooking oil or animal fats.
I was blessed to have a leader who wanted us to spend a lot of time on the field, working turnarounds doing, whatever I could to be helpful, etc. to learn the business and build relationships.
Working around the refineries, especially during turnaround, was a crash course in constraint theory and economics.
Good times.
At any rate, all of that was to qualify that most people would not believe how much time and money has been wasted trying to find innovative new ways to serve and capitalize on the CA biodiesel market.
Bio fuel is what most people think of when it comes to renewable - though by way of proper refinery processes, none of the issues or perceived issues would exist especially for more modern fuel injection pumps.