Researchers at the University of Wisconsin-Madison in the United States have developed a new method to recycle waste plastics into high-value alcohols, carboxylic acids, and amines. They shared their findings in “Hydroformylation of pyrolysis oils to aldehydes and alcohols from polyolefin waste,” recently published in Science.
The team recovered olefins by pyrolysing post-consumer recycled (PCR) high-density polyethylene (HDPE), as well as virgin HDPE, virgin polypropylene (PP), and virgin low-density polyethylene (LDPE) as control cases. They then used the pyrolysis oil to produce aldehydes through a chemical process called homogenous hydroformylation catalysis. The process reportedly converted more than 90% of the olefins in the pyrolysis oil into aldehydes, which were then further reduced into high-value industrial alcohols used to make soaps and cleaners, for example.
“Currently, companies [using steam cracking] don’t have a really good approach to upgrade the pyrolysis oil,” said author Houqian Li. “In this case, we can get high-value alcohols worth $1,200 to $6,000 per ton from waste plastics, which are only worth about $100 per ton. In addition, this process uses existing technology and techniques. It’s relatively easy to scale up.”
He believes that the recycling industry could soon adopt the new method. In a technoeconomic model and life cycle assessment of the process, the researchers showed that a chemical plant with 10,000 tons per year of production capacity could make an annual net profit of as much as $100 million by implementing the process, with a payback period of three years.
As for sustainability, the greenhouse gas emissions (GHGs) from recycling 1 kg of plastic waste by using the technology are 1.6 kg CO₂ equivalent. This is 60% lower than producing the same amount of chemicals via the traditional route from fossil feedstocks, and 50% lower than incinerating 1 kg of plastic. However, the carbon footprint of the technology is slightly higher than using steam cracking, which emits around 1.2 kg CO₂ equivalent.
The team said the next steps include tuning the process and better understanding what recycled plastics and catalyst combinations produce which final chemical products.
“There are so many different products and so many routes we can pursue with this platform technology,” said George Huber, a professor of chemical and biological engineering and co-author of the study. “There’s a huge market for the products we’re making. I think it really could change the plastic recycling industry.”