Focus story by Jessie Waldheim
HOUSTON (ICIS)--Oil derived from waste plastic can produce a drop-in diesel which can be blended at up to 30% in existing ultra-low sulphur diesel (ULSD), a University of Illinois researcher has found, and some companies are already producing plastic-based crude for refineries, according to the American Chemistry Council (ACC).
"Our work focuses on the utility of these oils and properties such as compatibility, stability, etc in various blends," said Brajendra Kumar Sharma, project lead and head senior research scientist at the Illinois Sustainable Technology Center.
To make the PCO, researchers used 500 grams of HDPE – 400 to 500 grocery bags – and a process called pyrolysis. About 74% of the material was converted into PCO, 17% into solid residue and 9% into gasses, but the ratio could be altered by altering the temperature and time used in the process, according to the scientific article.
Sharma said that the pyrolysis process also could work with low density PE (LDPE).
The PCO was distilled into about 10% motor gasoline, 70% diesel and 15% vacuum gas oil. Analysis showed the PCO produced a high-energy fuel which lacked oxygenated molecules such as ethers and alcohols. After the addition of antioxidants, the diesel was found to be within specifications for standard diesel fuel, the research showed.
The researchers were able to blend the PCO diesel at up to 30% with ULSD without the need for any changes. The team also speculated that the PCO could be processed in conventional refineries, Sharma said.
"It’s a much better quality crude oil than what refineries are capable of processing," Sharma said.
The research did show that properties such as oxidation stability in the PCO needed to be improved.
"One area of future work will focus on improving the storage properties using renewable sources of antioxidants," Sharma said.
Several companies are working on commercialising the processes of making oil from waste plastic feedstock. The ACC in January formed a Plastics-to-Oil Technologies Alliance in support of the developing industry.
Most commercial systems are 45 to 60 tonnes/day and scaling up the technology has not been an issue. Assuring feedstock suppliers can deliver the necessary volumes has been more problematic, ACC spokeswoman Jennifer Killinger said.
Companies using the technology have been able to produce drop-in fuels. Agilyx, a founding member of the alliance, has been able to sell crude produced from plastics directly to refineries, which have been able to create fuels and petrochemicals with it, she said.
"There is growing interest in integrated approaches to waste management and awareness of opportunities to extract value from things that were previously sent to landfill, such as plastics that cannot yet be economically recycled," Steve Russell, vice president for the ACC's plastics division.
Turning waste plastic into usable fuel could be a boon for the environment.
Only 8.3% of the 31.84m tons of plastics thrown away in 2011 were recycled. Of those plastics, 13.11m tons were HDPE or LDPE, which had a recycle rate of 9.8% and 4.9% respectively, according to figures from the US Environmental Protection Agency (EPA). It did not specify whether the plastics were measured in short tons or metric tonnes.