What happens during the pyrolysis of oil shale?

Pyrolysis is the fundamental process used to extract petroleum products from oil shale. It involves heating the rock to temperatures typically above 300 °C (about 575 °F) in an oxygen-free environment.1

During this process, the applied heat breaks the chemical bonds of kerogen macromolecules—the complex, waxy organic matter embedded in the rock. This breakdown liberates smaller molecules, resulting in the production of liquid and gaseous hydrocarbons, as well as nitrogen, sulfur, and oxygen compounds.23

Pyrolysis can be performed through various methods, including:
* Aboveground (ex situ): The rock is crushed and heated in specialized vessels called retorts, typically at higher temperatures ranging from 480–550 °C (900–1,020 °F).24
* Underground (in situ): The rock formation is heated directly, which is a slower process occurring at lower temperatures (roughly 325–400 °C) and yielding a lighter oil.2

The resulting liquid, once upgraded, creates synthetic crude oil, while the process also generates various solid by-products and gases.1