Process for preparing an overbased metal-containing detergents

A method of manufacturing a calcium overbased detergent having a surfactant system derived from at least two surfactants, which method comprises:

• (A) treating with an overbasing agent a mixture comprising (a), (b) and (c) in the presence of water and without the use of inorganic halides or ammonium salts, wherein
• (a) is selected from the group consisting of (a1) and (a2) and mixtures thereof:
• (a1) at least two surfactants, at least one of the surfactants being a sulphurized or non-sulphurized phenol and at least one other of the surfactants being a surfactant other than a phenol surfactant, wherein the mass ratios of the components are such that the proportion of phenol surfactant in the surfactant system of the overbased detergent is at least 15 mass %;
• (a2) at least two surfactants, at least one of the surfactants being a sulphurized or non-sulphurized salicylic acid and at least one other of the surfactants being a surfactant other than a salicylic acid surfactant;
• (b) calcium hydroxide;
• and
• (c) oil, the treatment with the overbasing agent being carried out at less than 100° C.;
• (B) optionally subjecting the product of (A) to a heat-soaking step;
• (C) adding a further quantity of basic calcium compound(s) to the product of (B), and treating the mixture so obtained with an overbasing agent, the said treatment being carried out at less than 100° C.;
• and
• (D) optionally subjecting the product of (C) to a heat-soaking step:
• the mass ratios of all the components being such as to produce an overbased detergent having a TBN of at least 300.