Researchers at Chevron and the University of Kentucky have developed a new process for converting waste plastic into lubricating oil for engines.
This is potentially environmentally important from two perspectives. First, a more stable synthetic oil (an oil with high paraffinicity and, therefore, high Viscosity Index (VI, signifying high stability to change in viscosity over a wide temperature range) and low viscosity) will extend the interval between oil drains. That in turn reduces the amount of used oil requiring disposal. According to the EPA, some 200 million gallons each year are dumped into the environment.
The other benefit of a low-viscosity oil is reduced engine friction and thereby improved fuel economy.
Second is the obvious benefit in being able to recycle a portion of the ever increasing stream of waste plastics. Plastics represent 11 wt% of municipal solid waste today, up from less than 5 wt% in 2001.
While much work has been done on the potential conversion of plastics to fuels, the researchers note,
Little has been reported on the conversion of waste plastic to higher-valued products. In this study, we investigate the conversion of waste polymers such as polyethylene (PE) to high-quality lubricant oils.
The process uses a thermal, noncatalytic, atmospheric pressure pyrolysis process that converts high-molecular-weight molecules in plastic waste to lower-molecular-weight molecules in the lube oil range, which are in turn processed through hydroisomerization to create the lube oils.
The Chevron-UKy process can also be used with Fischer-Tropsch wax—a product from the Fischer-Tropsch process that can be further processed into lube oils.
The main findings of the study, as reported in a paper to be published in the ACS journal Energy & Fuels, are:
Potential lube yields were in the 60%–70 wt % range.
The product distribution and lube quality surprisingly showed little variation, whether the feed was polyethylene, FT wax, or a combination of the two. (This opens up the interesting possibility of coprocessing waste PE and FT wax in the same plant, increasing product volume of lube and diesel, thus further improving the economics.)
The pyrolysis process could be performed at atmospheric pressure, and at a temperature and residence time that is not atypical of refinery operations. (Simplifying integration into refinery process.)
Hydrotreatment of the feed prior to the hydroisomerization step did not significantly affect lube yield or quality. Eliminating this step could benefit the overall process economics.
When 4 wt % poly(ethylene terephthalate) (PET), from used soda bottles, was added to the polyethylene, no decline in lube quality was observed. This indicates a high degree of separation of the waste plastic may not be necessary, which would reduce the feedstock cost to the process.
The paper describing the research will appear in the 20 July 2005 issue of Energy & Fuels.
“Conversion of Waste Plastic to Lubricating Base Oil” Energy & Fuels. Miller, Shah, Huffman.