Desulphurization or Sweetening

Once distilled separated, and upgraded, the crude oil fractions need to be refined further in order to clean it of the impurities that contribute to air pollution. One impurity that is of great concern and found naturally in fossil fuels is sulphur. We experience sulphur as the “rotten egg” smell that can accompany well sites.

Sulphur when involved in the combustion process produces sulphur dioxide (SO2) which is the major pollutant involved in acid rain, and an important component in the formation of fine particulate matter (PM). In addition, sulphur also reduces the effectiveness of some pollution control technologies, such as catalytic converters that reduce other types of pollutants such as nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons from the combustion of gasoline and diesel in our vehicles.

Not all crude oil has the same composition. Crude oil is considered “sour” when it contains >2.5% of sulphur (by weight). Alternatively, crude oil that contains <0.5% of sulphur (by weight) is called “sweet.” Typically, fossil fuels extracted from the east coast of North America have higher concentrations of sulphur, as compared to western fuel deposits.

The process of removing sulphur from fossil fuels is called desulphurization, or sweetening, and uses a technique called hydrotreating. Hydrotreating involves a chemical reaction at high temperature and pressure to remove sulphur atoms from the oil and replace them with hydrogen.

Fuels with high sulphur content are more difficult to refine and require special equipment; however, the investment is worth its benefit to improve air quality.