Abstract: The light naphtha from the hydrocracking unit of PetroChina Dushanzi Petrochemical Company is used as a blending component of vehicle gasoline. At the initial stage of plant start-up, the sulfur mass fraction of the light naphtha was no more than 3.5 μg/g, with the mercaptan sulfur content less than 3 μg/g, but sometimes the doctor test failed. To solve this problem, different active sulfides in light naphtha were analyzed qualitatively and quantitatively. The results showed that the main reason for the failure of the doctor test was the synergy of trace amounts of hydrogen sulfide (no more than 0.5 μg/g) with mercaptan in samples, as long as the hydrogen sulfide was removed, the doctor test could pass. Based on this, some feasible industrial solutions were put forward, such as optimizing the operation of light naphtha fractionation system, stripping by reboiled gas instead of steam stripping in light naphtha fractionator, and using the adsorptive desulfurization or sweetening process.

Key words: hydrocracking, light naphtha, H2S, mercaptan, doctoral test