There are two broad approaches to motor oil recycling: re-refining and chemical recycling.
Re-refining aims to extend the fluid’s utility for another generation and avoid releasing it as a pollutant into the environment.
Chemical recycling breaks down plastic waste into smaller components to be used as base oils in new products.
Refining crude oil
for industrial use relies on separation processes like centrifuging and distillation to remove impurities and separate small and large hydrocarbons for use in different applications. In order to turn used oil into desirable products, plants can use similar approaches to those applied to crude oil to remove unwanted particles and sort degraded hydrocarbons from usable ones.
There are two broad approaches to motor oil recycling: re-refining and chemical recycling. Re-refining aims to extend the fluid’s utility for another generation and avoid releasing it as a pollutant into the environment, while chemical recycling starts with breaking down the hydrocarbons that gave the former oil its unique properties in order to create feedstock for a wide variety of new products. Both approaches start with removing contaminants like dirt and metal particles from the fluid. Acid treatments trap greases and gums suspended in the fluid, while separation techniques like sedimentation, filtration and decantation remove them later, along with heavier sediments and metals. Chemical recycling then goes even further to return value to the used lubricant by breaking down the hydrocarbons into simple feedstocks that can then be used as components of other products.
Large recycling services tend to focus on the spent hydrocarbon streams that produce the greatest volume of recyclable materials, partly in order to secure a place in the broader petrochemical value chain. Scott Miller, senior vice president of refinery operations at Safety-Kleen, says the company collects some 200 million gallons of used motor oil per year in the U.S. and Canada. “[Recycled] oil’s quality is directly linked to the quality of used motor oils which are collected,” explains Miller. “As OEMs have continued to progress their lubricant quality requirements, today’s engine oils begin with a minimum quality level of Group II, which increases up to Group III and PAOs.”
Each re-refining process adds a layer of complexity to the already intricate role of base oils in industrial use, making the precise environmental impact of a particular final product even more difficult to ascertain. Re-refined base oils inherently don’t qualify as environmentally acceptable lubricants (EALs), though they do have the benefit of reducing the volume of used-oil waste that returns to the earth. STLE member Douglas J. Adams, senior product development chemist at RSC Bio Solutions, says the requirements for each designation of EAL are sharply defined by the Vessel Incidental Discharge Act (VIDA), formerly the Vessel General Permit (VGP), based on their base oil types.
Base fluids that are prescribed for use in EALs are triglycerides, synthetic esters, polyalkylene glycols and PAO and related hydrocarbons. Adams explains, “Used oils are oxidized, often containing acidic compounds in addition to metals like zinc and antimony as well as biocides or other toxic components that are present in the used oils.” Additionally, Adams says, each used oil requires the addition of new components to make up for any depletion that cannot be removed by re-refining. The result? “Re-refined mineral oils can be used to successfully formulate standard mineral oil-based lubricants; however, these lubricants could not be classified as EALs,” says Adams.
Chemical recycling breaks down plastic waste into smaller components to be used as base oils in new products. In a new process called continuous microwave-assisted pyrolysis (CMAP), plastic is sealed in an oxygen-free environment and bombarded with microwaves that vaporize and decompose the organic molecules, which are then cooled for use as liquid fuel. The system is designed to convert waste streams to hydrocarbon liquids like diesel and gasoline, as well as chemical feedstocks like naphtha. A single kilogram of plastic waste typically produces between 600 and 900 mL of usable fluid through this process. “In addition, the platform produces a small amount of char, which is generally carbon black and benign carbon that has value,” says Jason Tanne, Resynergi’s cofounder and chair. “We produce some light hydrocarbon gases like methane, butane and pentane, which also have value as energy sources.”
A single kilogram of plastic waste typically produces between 600 and 900 mL of usable fluid through this process.
The type of fluid produced depends on both the source material and the preferences of whoever is operating the reactor vessel. CMAP units “can process everything from films to rigid materials,” says Tanne. “Feedstocks to make fuels with the best recovery yields are usually polyolefin plastics,” including mixtures of polypropylenes and some polyethylenes with resin codes 2, 4, 5 and 6. To make chemical feedstocks, “we tend to focus on single streams, like styrene to make monomers or a single polypropylene or polyethylene [to make] naphtha,” Tanne explains. The reactor vessels can be customized to produce different properties in the final product, resulting in final products that include paraffins, olefins, aromatics and monomers.
CMAP technology also can be deployed on an industrial scale. Typical materials recovery facilities (MRFs) wind up with tens to hundreds of tons of unrecyclable plastics daily, all of which would typically be disposed of in landfills. Larger, permanent CMAP units installed adjacent to MRFs can help reduce this reject material significantly by zapping the bulk of it into usable feedstocks. A partnership between a typical MRF and a CMAP facility can produce between 5,000 and 7,500 gallons of recycled chemical feedstocks and fuels of lower carbon intensity daily, says Tanne.
Through an efficient, low-impact oil recycling process, re-refined oil can significantly reduce the harm inherent in oil usage and limit environmental damage from discarded oils.
Advocates of oil recycling say reintroducing used oils into the manufacturing cycle has other compelling benefits for the environment. The recycling process can help reduce the volume of plastic material and fluids that would otherwise contribute to environmental destruction in landfills and waterways. Most importantly, the integration of low-impact rerefining processes into the hydrocarbon value chain can help to mitigate the effects of exploitation of petroleum reserves, a major contributor to climate change.
Lynne Peskoe-Yang is a freelance writer based in Tarrytown, N.Y. You can contact her at email@example.com