1. Sweetening Processes • Presence of sulphur compounds like H2S and mercaptans makes the oil sour • Sour stocks have bad odour • The processes by which the foul smelling sour petroleum products are converted into sweet smelling or odourless products are called sweetening processes

2. Important Sweetening processes • Doctor’s sweetening process • Copper chloride sweetening process • Catalytic desulphurization • Hydrofining process

3. Doctor’s sweetening process • Mercaptans present in the petroleum products are converted into disulphide by treatment with doctor’s solution and sulphur • 2RSH + Na2PbO2 => Pb(RS)2 + 2NaOH • Pb(RS)2 + S => PbS + RSSR • PbS + 2O2 => PbSO4 • PbSO4 + 4 NaOH => Na2PbO2 + Na2SO4 + 2H2O • Temp. 65 C

4. Copper chloride sweetening process • 2CuCl2 + 2RSH => RSSR + 2HCl + Cu2Cl2 • 2Cu2Cl2 +4HCl + O2 => 4CuCl2 + 2H2O

5. Catalytic desulphurization • Catalysts e.g. bauxite can be used to convert the sulphur containing compounds to hydrogen sulphide • Used for sweetening of gasoline and kerosine • 2RSH => RSSR + H2S

6. Hydrofining process • Catalytic desulphurization in the presence of hydrogen • Molybednum oxide, cobalt oxide as catlyst • 350-450 C, 20-50 atm • Operating conditions for various feed stocks vary