Waste oil is the major part of all oil refinery wastes collected and accumulated by transport and industrial enterprises. Depending on the type of application, all waste oils are conventionally divided into groups:
- UMO – used motor oils. These include diesel, aviation, automotive, and motor oils used in hydraulic systems and transmissions;
- UIO – used industrial oils. This group includes transformer, hydraulic, compressor and turbine oil;
- UOT – used oil transmix. These include oil products, which are collected when cleaning tanks and pipelines, as well as oil products removed from wastewater treatment plants.
In accordance with the existing policies of the leading world nations, waste products should be reused as valuable material resources. Therefore, all companies and organizations whose activities are in some way related to formation of waste oils, are committed at the legislative level to collect, keep records, provide rational use and disposal of all waste oils belonging to one of the groups listed above. The final destination of waste oils is organizations and enterprises involved in regeneration and obtaining petroleum products.
The situation with transformer and industrial oils is a bit easier – they can be regenerated directly in the field. Used motor oil should be delivered to tank farms.
All methods of processing or regeneration of used motor oil can be divided into four groups: physical, physico-chemical, chemical and combined methods.
Physical methods include settling, centrifuging, filtering, light fractions recovery and vacuum distillation. This last method is the most effective one, as it allows to obtain oil with minimal ash and coke content, good color characteristics and low content of asphalt-resinous substances.
The most commonly used physico-chemical methods of motor oil treatment include coagulation, contact cleaning with bleaching clay and adsorbents, as well as purification with propane and phenol.
Chemical methods are sulfuric acid purification and alkaline purification. Sulfuric acid is an active substance in the context of its effect on the majority of contaminants and waste oil oxidation products. But this method is seriously limited by the difficulty of recycling of its by-product – acid sludge. In this regard, purification with sulfuric acid is often replaced by hydrogenation processes.
Combined methods of recovery of waste oils properties are used where there is a big diversity of contamination products.
Recycling of used motor oil using factory technology is complicated due to the presence of special additives. Some additives that turned into insoluble state, as well as part of additives, absorbed in contaminated products, can be removed by defrosting or filtration processes using a diluent and coagulants. Theoretically, a small percentage of additives can remain in the oil or its recycling product. But the situation is complicated by the need for collection and recycling of motor oils strictly according to their grades and the necessity to use an individual technology for each individual grade. It is quite difficult to implement in mass production, so in practice a different way is used. At the beginning of the treatment process, all additives are removed, including remnants of their active part.
Total losses of additives when they are removed from motor oils usually comprise no more than 3% of dehydrated material. With competent approach in case of heavily contaminated oil, you can obtain up to 70% of fully recovered product.