Base-free catalytic aerobic oxidation of mercaptans for gasoline sweetening over HTLcs-derived CuZnAl catalyst

An aerobic oxidative removal of mercaptans from gasoline in the absence of liquid base has been demonstrated for gasoline sweetening over CuZnAl catalyst. This process could proceed at large WHSV of gasoline (50-70 h^-1) with <95% mercaptan conversion at 150°C (or 300°C) using an O ₂/S molar ratio of 20-40. At 150°C, dimerization of mercaptans occurred dominantly to form their disulfides. At 300°C, deep oxidation of the mercaptans to SO₂ was the dominant process in the first tens of hours, but it decreased then with prolonged time on stream and meanwhile the dimerization increased. The spent catalyst could be restored to its fresh activity level only through a calcination treatment in air. This process was also demonstrated to be effective and efficient for sweetening of a real cracking gasoline.