Preferred examples of such dispersants for use in the process according to the invention are products prepared by reacting a polyalkenyl substituted succinic acid or anhydride, such as polyisobutylene maleic anhydride, with one or more polar compounds, such as polyalcohols, e.g. pentaerythritol or tris(hydroxymethylamino)methane, and/or polyamines, e.g., polyalkyleneamines such as tetraethylenepen