sentence: Petroleum contains hydrocarbons.
sentences_after: After distillation, it still contains chemical compounds with sulfur, oxygen and  Nitrogen as well as other unwanted compounds, such as Alkalenes. For this reason, they are extracted using a process called hydrogenation. In hydrogenation, Hydrogen sulfide and ammonia gases are produced. These gases require special handling, as they are very toxic.
concept_name: petroleum
headings: Refining Petroleum
categories: Industries