Valorisation of Secondary Petrochemical Feedstocks into a Multicomponent Demulsifier: Sodium Xylenesulfonate from Pyrolysis-Derived Xylene Formulated with Alkaline-Earth Stearates and Waste Motor Oil

Stable water-in-crude-oil emulsions remain a bottleneck in the treatment of heavy Uzbek crudes, and the demulsifiers used at field level are almost entirely imported. Two local secondary streams—the xylene-rich Ustyurt pyrolysis distillate and collected waste motor oil—were converted into a multicomponent demulsifier. Xylene was sulfonated with 98 wt.% H2SO4 and neutralised to sodium xylenesulfonate (SXS), reaching 96.8% isolated yield at 110–120 °C and an acid:xylene molar ratio of 1.34:1. Fixed-time yields gave a linear Arrhenius dependence (R2 = 0.998) with an apparent activation energy of 21.7 kJ mol−1, ΔH‡ = 18.4 kJ mol−1 and ΔS‡ = −262 J mol−1 K−1, indicating a transport-influenced electrophilic substitution. FTIR confirmed the –SO3Na group, and TG/DTA showed only 5.9% mass loss below 415 °C. Of four hydrophilic–lipophilic balance estimates, only the Davies value (14.2) is compatible with the observed water solubility. The optimum formulation KS-6 (30 wt.% SXS, 50 wt.% waste oil, 18 wt.% Ca and 2 wt.% Sr stearate) gave water-separation efficiencies of 81.0, 93.7 and 98.9% at water cuts of 60, 70 and 80 vol.%, exceeding the imported reference ND-12 by factors of 1.18–1.26, and lowered the residual salt content to 125 mg dm−3.