Transformer oils - with improved resistance to sludge formation

摘要

Transformer oils made from naphthenic distillates by hydrogenating refining under severe conditions or by acid refining, are improved by increasing the content of hydrocarbons with 4 or more condensed aromatic rings. A fraction rich in such polynuclear hydrocarbons, obtd. from the recycle oil of catalytic cracking, may be added to the refined naphthenic distillate, or the latter, contng. fully saturated polynuclear hydrocarbons, may be subjected to catalytic aromatisation. The products have a sludge-free Doble life of at least 100 hrs and are characterised by a UV absorption at 335 millimicrons of 0.04-2.5 (pref. 0.06-2.0) and a ratio of UV absorption at 335 to that at 330 m mu of not less than 1.0. Preferred fractions from catalytic cracking for addition to the naphthenic distillate have a boiling range of 316 degrees to 538 degrees C (pref. 343 to 399 degrees C). Catalytic aromatisation is carried out above 357 degrees C and below cracking temp., with a hydrogen pressure of 56 to 112 atm., a total pressure below 141 atm., using a catalyst contng. cobalt, nickel or molybdenum sulphide.