| abstract |
Heavy hydrocarbon feedstocks are subjected to a hydrogenation pre-treatment prior to pyrolysis, said hydrogenation step being so controlled as to avoid hydrocracking and being carried out at a temperature of from about 640* to about 800* F and at a pressure of from about 750 to about 1,250 psig when a significantly increased yield of mononuclear aromatics is desired and at a pressure of from about 1,250 to about 3,000 psig when a significantly increased yield of 1,3-butadiene is desired. |