Abstract: The doctor test often does not pass for hydrotreated FCC naphtha with 10μg/g sulfur, even lower than 5μg/g mercaptan content. Based on the data of routine doctor test, the reason was analyzed and corresponding solutions were suggested. It is found that the main reason for the failure is the newly formed trace amount of mercaptan with larger molecular weight during FCC naphtha hydrotreating. Those compounds have no influence on the properties of the gasoline. Solutions are: cancelling doctor test for hydrotreated FCC naphtha when national V/VI standard gasoline are the operation objective; increasing the blending ratio of zero-sulfur gasoline component/hydrotreated FCC naphtha; and oxidative sweetening the hydrotreatd naphtha.

Key words: FCC naphtha, hydrotreating, mercaptan, doctor test