CHARACTERIZATION OF UNRESOLVED COMPLEX-MIXTURES OF HYDROCARBONS FROM LUBRICATING OIL FEEDSTOCKS

Lubricating oils, particularly those blended from hydrocarbon feedstocks for use as automobile lubricants, are economically important petroleum products. The hydrocarbons of waste lubricating oils are also quantitatively important sources of environmental pollution. However, both the feedstocks and the hydrocarbons found in sediments polluted with waste lube oils are very difficult to characterize by existing analytical methods and little is known, in detail, of their chemical composition. For example, the hydrocarbons often appear as unresolved complex mixtures (UCMs) when examined by techniques which are routinely successfully used to characterize other hydrocarbon mixtures such as crude oils (e.g., gas chromatography (GC) or GC-mass spectroscopy (GC-MS)). We report here our attempts to characterize UCMs from three lubricating oil hydrocarbon feedstocks by oxidative degradation followed by GC and GC-MS of the functionalized products. Oxidation with chromium trioxide produced reasonable yields (ca. 70-80%) of total recoverable products, of which ca. 90% was functionalized. Furthermore, and perhaps most importantly, in each case about 15% of the oxidation products were resolved by GC and GC-MS and were identified as n-carboxylic acids, ketones, and lactones. On the basis of these identifications and from the reported mechanism of CrO3 oxidations, potential precursor compounds for some of the hydrocarbon components of the lubricating oil UCMs are proposed. These include simple monoalkyl acyclic and monocyclic alkanes. Examples of these alkanes were synthesized and the synthetic alkanes also oxidized by the CrO3 method. Many of the products were again n-acids, ketones, and lactones which confirms the proposed UCM alkane structures. It remains to be seen whether the remaining functionalized UCM can be more easily characterized than the parent alkane UCM.