Selective hydrodesulfurization of catalytic cracked gasoline

Hydrodesulfurization (HDS) of catalytic cracked gasoline (CCG) over Co-Mo/gamma-Al2O3 catalyst was investigated to clarify the important factors for deep HDS of CCG containing 229 ppm sulfur and 30.4 vol% olefins. In the HDS reaction at 220 degrees C, 1.6 MPa, sulfur compounds were hydrodesulfurized, whereas thiols were formed from H2S and olefins. The reactions of thiophene HDS, isoolefin and n-olefin hydrogenation (HG) were studied to clarify the active sites on the catalyst. The effects of H2S and of Co on these three reactions were examined over catalysts with different Co/(Co + Mo) ratios. Thiophene HDS was promoted by Co, isoolefin HG was little affected, and n-olefin HG was largely retarded. Three types of active sites for thiophene HDS, isoolefin HG and n-olefin HG were proposed. Oligomers of isoolefin were found in the isoolefin hydrotreated product. The possibility of improving the HDS selectivity with carbonaceous deposit by coking pretreatment was investigated for HDS reactions of CCG and model compounds. HDS selectivity (higher activity for HDS and lower activity for olefin HG) during CCG HDS was improved. A commercial scale process of CCG HDS was designed and a simulation model was studied. To calculate the sulfur content in the hydrotreated CCG accurately, the theoretical equilibrium models for thiophene HDS, thiol formation and olefin HG were considered. The results estimated using this simulator showed good correspondence with experimental results. These investigations resulted in commercial scale plant construction. Since 2004, three plants have started operation to produce 10 ppm sulfur gasoline in Japan.