Re-refined base oils

Based on the evidence that acceptable recycled petroleum products can be produced, there is a considerable legislative record encouraging the recycling of used oil. Starting with the Resource Conservation and Recovery Act in 1976 (20), used oil was held apart from the normal hazardous waste system because the oil was viewed as a valuable commodity. This was followed by the Used Oil Recycling Act in 1980 (33), which removed any federal requirement that lubricants containing re-refined base oil carry special labeling. 

Lubricant base oils must meet minimum performance characteristics of viscosity, viscosity index, pour point and volatility, all of which must meet required standards. When dealing with re-refined base oils, additional characteristics such as colour and odour must also be considered. These properties, of dark colour and odour, are readily perceived by customers and consumers as representing deficiencies in quality. Many examples of re-refined base oils have a definite, characteristic, oxidised or cracked odour which may be totally unacceptable in some countries and markets. Table 15.2 gives quality guidelines for the acceptance of re-refined 150 and 500 base oils. 

Due to the variety of potential sources of used lubricants, their differing histories of service use and their subsequent levels of possible contaminants, assessment of the quality of the resulting re-refined base oil is a major concern. Quality assurance must be applied both to the used lubricant feedstock and, more particularly, to the product(s) of the re-refining process. Limits to the concentration of various contaminants in the finished base oil must be set and strictly adhered to. 

Table 15.2 Guidelines for quality acceptance of re-refined base oils...

Metals Metals should not be present in re-refined base oils either as wear metals, or from previous use of metal lubricant additives, or from the clay treatment or hydrofinishing catalyst fines. Metals are measured either by determining the total sulphated ash content or as individual metals by ICP analysis. 

Water and Untreated Acid These contaminants maybe carried over from some processes. Total acid umber, TAN, and copper corrosion tests will indicate that these contaminants are present in the re-refined base oil. 

Sulphur Content This is seen as an index of inherent anti-oxidant capacity in virgin mineral base oils. For re-refined base oils, those hydrocarbons that were inherently oxidatively unstable would have been oxidised during previous use. The function of the sulphur content of a re-refined base oil is not clear and more work is required to determine the need or the concentration of sulphur required to meet minimum performance requirements. 

Health and Safety Aspects of Re-Refined Base Oils... 

The use of re-refined base oils to produce lubricants is increasingly considered on a worldwide basis. The driving force is the concept of sustainability [6], in this application, the recycling of resources to minimise their environmental impact. These considerations, whilst commendable in principle, appear to ignore the environmental costs of collection and transport. Against this, the material must be collected for disposal in any case. 

Both quality and process control should be able to produce a product of known and consistent quality, suitable for use as a lubricant base stock. In past practice, however, oils that can meet the required performance characteristics have tended not to be readily available and have historically been expensive. For these reasons, the use of re-refined oils as a lubricant base oil was not considered to represent a viable alternative to virgin mineral base oils of consistent quality when these are readily available. More recently, the quality of re-refined base oils has increased to a high level, for some cases up to Gp. II quality, and in volume quantity. In addition, the substantially increased price of crude oil, and its associated products, has made re-refining of used lubricant much more economically viable. The alternative route of using the used lubricant as a fuel directly or as a fuel extender is now much more restricted and controlled by environmental legislative authorisations and is also much less viable economically. 

Test times approximate a few minutes per test spedmen, and detectability for most elements is in the low m kg range. In addition, this test method covers a wide variety of metals in virgin and re-refined base oils. Twenty-two elements can be determined rapidly, with test times approximating several minutes per test specimen. 

The concentrations of metals in re-refined base oils can be indicative of the efficiency of the re-refining process. This test method can be used to determine if the base oil meets specifications with respect to metal content. 

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