A process is disclosed for decreasing the amount of sulfur in hydrocarbon streams.
Environmentally driven regulatory standards for motor gasoline (mogas) sulfur levels will result in the widespread production of 120 ppm S mogas by the year 2004 and 30 ppm by 2006. In many cases, these sulfur levels will be achieved by hydrotreating naphtha produced from Fluid Catalytic Cracking (cat naphtha), which is the largest contributor to sulfur in the mogas pool. As a result, techniques are required that reduce the sulfur in cat naphthas without reducing beneficial properties such as octane.
Conventional fixed bed hydrotreating can reduce the sulfur level of cracked naphthas to very low levels, however, such hydrotreating also results in severe octane loss due to extensive reduction of the olefin content. Selective hydrotreating processes such as SCANfining have recently been developed to avoid massive olefin saturation and octane loss. Unfortunately, in such processes, the liberated H2S reacts with retained olefins forming mercaptan sulfur by reversion. Such processes can be conducted at severities which produce product within sulfur regulations, however, significant octane loss also occurs.
Several methods exist for removal of sulfur from hydrocarbon streams. For example, U.S. Pat. No. 3,876,532; U.S. Pat. No. 4,149,965; U.S. Pat. No. 5,423,975; and U.S. Pat. No. 5,826,373 each teach hydrotreating methods using deactivated or spent catalyst. U.S. Pat. No. 5,885,440 teaches cooling of a hydrocrackate prior to hydrotreating. U.S. Pat. No. 3,338,819 teaches hydrotreatment of a hydrocrackate over a granular catalyst bed at substantially the same conditions as used to produce the hydrocrackate.
U.S. Pat. Nos. 5,510,016; 5,308,471; 5,399,258; 5,346,609; 5,409,596; and 5,413,697 each teach hydrodesulfurization followed by treatment over an acidic catalyst to restore octane.
What is needed in the art is a process which produces sulfur levels within regulatory amounts and which minimizes loss of product octane.