This is a relatively expensive way to remove all sulfur compounds from petroleum products. It is used in those cases where it is necessary to lower the total sulfur content in the product. Disadvantages of this process are high capital investment, high operating costs, loss of raw materials to cracking (1.2% - 2.5%), reduction in the octane number of light gasoline fractions. Hydrotreating is available for big refineries. For the middle size refinery hydrotreating is not economically and technologically feasible.
Often low molecular weight mercaptan are removed by caustic "wash". This method works, but the storage and disposal of toxic sulfuric-alkaline waste is costly and challenging. In addition, not all companies are able to organize a system of utilization of such wastes.
More advanced technology removal of light mercaptan from fuel involves regeneration of alkali. In such technologies low molecular weight mercaptan C1-C2 selectively oxidized to disulfides and hydrogen sulfide - to elemental sulfur by atmospheric oxygen on the catalyst. Such processes are applicable to a light oil and gas condensate. However, this process is not suitable for heavy oil and fuel oil due to the formation of persistent form of oil-water emulsion of oil and aqueous alkali. Furthermore, this process is only partially sweetening (only the lower mercaptans are removed: C1-C2 and, partially, C3).
In the world practice for sweetening light distillates are widely used MEROX process and its analogs. All caustic processes are based on mixing oil with aqueous solution. Implementation of such technology involves considerable investment in the regeneration of caustic, emulsion separation and recycling procedures.