Yes, Hydroprocessing units at refineries can either co-process vegetable oil with hydrocarbons or run 100% on vegetable oil after some modifications.

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.