Mineral Oils, Untreated or Mildly Treated

Mineral oils (also known as base oils, mineral base oils or lubricant base oils) are chemical substances prepared from naturally occurring crude petroleum oil. Crude oil is distilled first at atmospheric pressure and then under high vacuum to yield vacuum distillates and residual fractions that can be further refined to mineral oils. Mineral oils refined from petroleum crude oils are complex and variable mixtures of straight and branched-chain paraffinic, naphthenic (cycloparaffinic), and aromatic hydrocarbons having carbon numbers of 15 or more and boiling points in the range of 300–600°C (IARC, 1984). Mineral oils are described by several dozen generic “petroleum stream” Chemical Abstracts Service (CAS) numbers. Many mineral oils may have more than one CAS number because different refiners submitted slightly different descriptions for similar refining streams when CAS numbers were being assigned (both in the United States of America and Europe) (CONCAWE, 1997). The hydrocarbon composition and physical characteristics of a mineral oil depend on both the composition of the original crude oil and the processes used during refining (e.g. solvent extraction, hydro-treatment) (CONCAWE, 1997). Production processes of mineral oils have changed substantially over time (IARC, 1987; Tolbert, 1997). In the past, many mineral oils were only mildly refined and contained significant levels of polycyclic aromatic hydrocarbons (PAHs). Acid treatment was initially used to remove PAHs and other impurities and to improve the technical properties of the finished oils. In recent decades, acid treatment has largely been replaced by extensive refining with solvent extraction and/or hydro-treatment, which has further reduced the level of PAHs and other contaminants. Mineral oils have been produced by means of the severe hydro-treatment procedure since the 1960s (Kane et al., 1984; Mackerer et al., 2003). Regulatory pressures in the USA further encouraged the move to highly refined mineral oils in the mid-1980s (Woskie et al., 2003). There are several assays that can be used to determine if a mineral oil is highly or severely refined (Mackerer et al., 2003). Two useful MINERAL OILS, UNTREATED OR MILDLY TREATED