Lubricant base oils are petroleum products that are predominantly derived from the vacuum distillation of crude oil. Various types of refinement can be employed during the manufacturing process, and evidence suggests that certain of the associated process streams produce skin cancer. Polycyclic aromatic compounds (PACs), some of which are considered as the causative agents, are removed, concentrated or chemically converted during the refinement process. In order to understand the effects of various types of refinement processes on carcinogenic potential, 94 oils were evaluated in the mouse epidermal cancer bioassay. This Exxon database is unique, because of the wide range of crude oils and processing histories represented. Seven processing history classifications are described, and conclusions concerning the impacts of each refinement process on dermal carcinogenicity are discussed. This research also included an evaluation of selected biological and chemical test methods for predicting carcinogenic potential. These included a modified version of the Ames test for mutagenicity, as well as analytical characterizations of the polycyclic aromatic structures in the oils. For classification purposes, a sample was considered to be carcinogenic if it resulted in the production of two or more tumor-bearing animals (in test groups of either 40 or 50 animals). The modified Ames test was considered to be positive if the mutagenicity index was > or = 2.0, and PAC analyses were similarly designated as positive or negative according to proposed guidelines. All of the alternative test methods showed similar agreement with dermal carcinogenicity bioassay data; concordance values were > or = 80%. However, each test was incorrect in ca. 10%-20% of the cases evaluated.(ABSTRACT TRUNCATED AT 250 WORDS)
Polycyclic aromatic compounds are an important component of many high-boiling petroleum products. A detailed analytical description of the polycyclic aromatic structure distribution is useful for assessing the exact effects of refining processes, such as solvent extraction and hydrotreating, that alter or remove these compounds. High-resolution, low-voltage mass spectrometry was used to characterize the clay gel aromatics fractions of a petroleum vacuum distillate and three lubricant base oils that are derived from it. Proprietary methods were used to extract and hydrotreat the distillate, and different levels of severity were employed. The measurements were made with a Kratos MS50 mass spectrometer, using Exxon proprietary computer programs for data analysis. The programs allow the determination of concentrations for as many as 5000 individual carbon number homologues and over 100 compound types. The polycyclic aromatic structure distributions of the oils are defined by the use of Z-number terminology and side-chain carbon number distributions. Structures specifically identified are the most probable ones, although other isomers cannot be totally excluded from consideration.
Ten rubber process oils were evaluated in a peroxide-cured EPDM compound. The effects of the process oil on cure-development characteristics and stress—strain properties are discussed. Certain types of molecular structures in the oil can significantly interfere with free-radical vulcanization, and analytical methods for the detection of these structures are provided. The combined effects of the process oil and the peroxide—coagent concentration are also described.
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