The second chemical reaction approach, selective alkylation of organo-sulfur molecules, has been demonstrated at the pilot scale, but to date it has not been implemented on a large commercial scale [50]. This technology increases the molecular weight of the sulfur bearing molecules which increases their boiling point. This enables distillation approaches to remove the sulfur. This approach does not require high-pressure hydrogen, which is a potential advantage over HDS. However, the olefin content in the fuel will vary, and it may be necessary to intentionally add olefins (or alcohols) to the fuel to convert all the sulfur-bearing molecules and to achieve the desired physical
and chemical characteristics of the fuel. There is some evidence that alkylation process may occur on a limited basis in the course
of HDS operation