Preparation of alkyl sulfonates

In a method for the manufacture of water-soluble petroleum sulfonates by sulfonation of an extract fraction from solvent refining of a hydrocarbon lubricating oil feedstock wherein said lubricating oil feedstock is contacted with a selective solvent for aromatic constituents of said feedstock in an extraction zone thereby forming a raffinate phase comprising non-aromatic hydrocarbons and a primary extract phase comprising aromatic hydrocarbons, said raffinate phase is separated from said primary extract phase, and at least a portion of said primary extract phase is subjected to sulfonation to produce a petroleum sulfonate, the steps comprising:

• (a) cooling said primary extract phase after separation from said raffinate phase to a temperature at least 28.degree. C. below the temperature in said extraction zone thereby forming a secondary extract phase relatively richer in multi-ring and sulfur-containing aromatic hydrocarbons and a secondary raffinate phase relatively poorer in multi-ring and sulfur-containing aromatic hydrocarbons,
• (b) separating said secondary raffinate phase from said secondary extract phase,
• (c) separating secondary raffinate from said secondary raffinate phase,
• (d) subjecting said secondary raffinate to sulfonation by reaction with sulfur trioxide effecting conversion of a portion of said secondary raffinate to petroleum sulfonates with the concomitant formation of by-product sludge,
• (e) separating sludge from the reaction product of sulfur trioxide and said secondary raffinate,
• (f) contacting the resulting sludge-free reaction product with a selective solvent consisting of water and isopropyl alcohol in a second extraction zone forming a solvent-rich phase containing water-soluble petroleum sulfonates and an oil-rich phase comprising oil-soluble petroleum sulfonates and unreacted hydrocarbon constituents of said secondary raffinate,
• (g) separating said solvent-rich phase from said oil-rich phase,
• (h) contacting said solvent-rich phase with an aqueous alkaline sodium salt solution effecting conversion of said petroleum sulfonates to the sodium form,
• (i) recovering water soluble sodium petroleum sulfonates from said solvent-rich phase from step (h), and
• (j) introducing said oil-rich phase from step (f) comprising oil-soluble sulfonates and unreacted hydrocarbon constituents of said secondary raffinate into admixture with lubricating oil feedstock to said first extraction zone.