The production of green diesel is, in many ways, no different from the production of petrol diesel. Both go through a refining process to yield a fuel at the end. In other words, producing green or petrol diesel is more about separating the components of interest from the rest of the material than about changing the fundamental properties of the feedstock. Biodiesel, on the hand, is all about chemically altering the feedstock.
There are actually several processes for producing biodiesel that include batch processing, supercritical processing, ultrasonic processing, and microprocessing. Though vastly different in application, each of these procedures has the same outcome; the transesterification of triglycerides.
Triglycerides are a type of biological molecule common in plants and animals. They are made up of three atoms, oxygen, carbon, and hydrogen. They look something like this.