Process for producing benzene by hydrodealkylation of a hydrocarbon fraction comprising alkyl-aromatic hydrocarbons, olefinic hydrocarbons and sulfur compounds

A process for producing benzene from a stabilized hydrocarbon fraction comprising toluene, xylene or a mixture thereof, sulfur and olefinic hydrocarbons, and having a sulfur content of at least 100 ppm by weight, a bromine number higher than 5, and a maleic anhydride value lower than 4, said process comprising the steps of:

• (a) contacting a mixture of said stabilized hydrocarbon fraction and a recycle hydrocarbon fraction from step (e), in the presence of hydrogen, with a hydrodesulfuration catalyst, under hydrodesulfuration conditions comprising a temperature of 250.degree.-400.degree. C. and a pressure of 10-150 bars, so selected as to reduce by at least 90% the sulfur content of said mixture, and to reduce its monoolefin content to such an extent that the bromine number of the resultant effluent is at most 2;
• (b) subjecting the unfractionated crude hydrodesulfuration product, containing H.sub.2 S, to hydrodealkylation conditions comprising a temperature of 600.degree.-800.degree. C. and a pressure of 5-70 bars;
• (c) subjecting the unfractionated hydrodealkylation product to catalytic hydrogenation, at a temperature of 250.degree.-400.degree. C., under a pressure of 10-150 bars, whereby thiophene is converted to other sulfur compounds;
• (d) fractionating the catalytic hydrogenation effluent, and separately recovering a gaseous fraction, a product benzene fraction, and a fraction comprising toluene, xylene or a mixture thereof, and containing sulfur, and
• (e) recycling at least a portion of said sulfur-containing fraction comprising toluene, xylene or a mixture thereof to step (a).