The growing popularity of rerefined base oils projects seems undimmed by the flat-lining of global lubricant demand, judging by the number of recent project announcements in the EU, United States and the Far East. Its interesting to stand back and examine the drivers for such projects and to understand the technical and marketing issues associated with rerefined oil production and use.
In the EU, member states have mandated used oil collection requirements – a prerequisite for providing a regular feedstock supply. However, high levels of used oil collection in specific countries do not necessarily correlate with its use in rerefined base oil production.
For example, the United Kingdom which has historically had one of the highest levels of collection of used lubes in the EU, has not until recently been noted for converting that feedstock to base oils. Rather, the United Kingdom has used the material collected largely to provide recovered fuel oil for space heaters in industrial premises and fuel for road stone coating plants.
The route to market has been affected historically by European Commission directives, either directing that collected used lubricants be specifically prioritized for base oil production (The Waste Oil Directive) or the type of fuels that can be combusted for low grade industrial heat (The Waste Incineration Directive).
EU countries with historically lower percentage used oil collection rates than the United Kingdom, such as Italy and Germany have been far more proactive in using such feedstocks for rerefined base oil production. In some cases, the use of these oils in those countries has been supported in the past by national or local subsidy to encourage their production and use. But even the United Kingdom now seems to be going the rerefined route with the recent announcement of a significant API Group II+/III project in the planning stage at the Stanlow refinery on Merseyside.
Rerefined base oils can be as good as any virgin base stock made from crude oil sources, but it is important that they are properly processed. Used oil requires a de-asphalting step to remove its significant ash content, derived mainly from metal-containing lubricant additives. The oils also require the removal of some aromatics accumulation to ensure they meet health and safety requirements. The aromatics largely derive from dilution by the heavy-end high-octane gasoline blending stock, rather than from those originally in the base oil.
Another requirement, especially if the upgrading step involves hydrotreating, is to ensure the used lube feedstock has tolerably low levels of chlorine. During hydrotreating, the chlorine may convert to hydrogen chloride, which is very corrosive to a hydrotreating base oil plant.
Today, chlorine is mainly derived from the performance additive packages, for example the ashless dispersants that contain residual chlorine from process intermediates – or even chlorinated paraffin antiwear agents. Another chlorine source in used lubricant feedstock can be contamination with polychlorinated biphenyls from very old transformer oils. PCB levels must be less than 5 parts per million to ensure used lube feedstock is not classified as hazardous waste in California.
Once we have good quality rerefined base oil, what can we do with it? For industrial lubricants, no base oil interchange requirements apply. But good blenders will probably want to satisfy themselves of the base oils performance in what are normally lightly additized industrial lubricants, as they would with any base oil, virgin or rerefined.
Provided the blender is prepared to spend the money on base oil interchange testing, there are good outlets in the crankcase lubricant market. Most OEMs are happy to use finished lubes containing rerefined oils, and there are good examples of such crankcase lubricants carrying significant OEM approvals, as well as standard API and ACEA performance claims. In the United States, the military positively requires some use of rerefined base oil in their lubricant supply contracts.
However, this has to be tempered with the fact that most rerefinery projects are single manufacturing units and sometimes lack the scale of virgin base oil plants. Therefore, the base oil slate corresponds to relatively small procurable volumes for that interchange testing outlay.
There does seem to be some resistance to use of rerefined base oils in the marine lubricants market, where certain OEMs will not endorse their use. It is probably a reflection of the requirement for shipping to pick up both fuels and lubes in regions of the world where used oil processing may be more cursory and quality less well controlled than in more developed economies.
Most rerefined base oil projects do not normally involve bright stock production but are limited to the solvent neutral 150 to 500 distillate grades. Some of the rerefined base oils currently offered meet Group II specifications, and some future projects aspire to Group III-type specifications. All this bodes well for a continuous improvement in the quality of rerefined grades being offered.