Sour crude is usually less competitive than lighter crude. Nowadays, in many countries there are methods to improve the quality of black gold by removing contaminants, including sulfur.
The better preparation of the oil, the higher the price. Hence the higher demand for the raw material which costs less to process. When choice exists, benchmark crude is preferred: the quality is better and the price is higher. One of the important parameters is the content of sulfur in the oil. Usually it doesn’t exceed 0.5% in benchmark crude.
To remove sulfur, sulfuric compounds must be destroyed or extracted. The extraction method is the most promising. It is a complex process, with the cost proportional to the amount of sulfur in the oil.
The idea is to bind sulfur by adding catalyst or adsorbent into the oil. In some cases, special microbes are used.
In catalytic hydrofining, sulfuric compounds are extracted from the oil by molecular attachment to hydrogen. In the final stage, hydrogen sulfide is removed and can be transformed into hydrogen and sulfur.
Another promising method is the “soft” sulfur removal (biosulfurization), selectively removing the contaminants. Other components of the crude oil remain unchanged. Some fungus can remove up to 80% of sulfur compounds.
For large industrial applications, hydropyridoxine oxidation of organic sulfur compounds is well suited. This is a selective purification method, and the process rate is quite high. Sulfur is separated in alkaline environment and requires additional processing.
The methods listed above are not the only ones. There are alternatives, each with its efficiency and certain environmental impact. They are not as widely used in crude oil refining, but can be considered by smaller refineries.