Gasoline upgrading process

摘要

Low sulfur gasoline is produced from a catalytically cracked, sulfur-containing naphtha by fractionating the naphtha feed into a number of fractions of differing boiling range and hydrodesulfurizing them by by feeding them into a hydrodesulfurization reactor at spaced locations along the length of the reactor in order of descending boiling range, with the highest boiling fraction first. Staged introduction of the feed into the hydrodesulfurization reactor in this way promotes desulfurization of the sulfur-rich, olefin poor back end of the feed while reducing the saturation of the high octane olefins in the olefin-rich, sulfur-poor front end, so preserving octane while achieving the desired desulfurization. The hydrodesulfurization is followed by treatment over an acidic catalyst, preferably an intermediate pore size zeolite such as ZSM-5. The treatment over the acidic catalyst in the second step restores octane loss which takes place as a result of the hydrogenative treatment and results in a low sulfur gasoline product with an octane number comparable to that of the feed naphtha.