UW–Madison chemical engineers create efficient, profitable plastic recycling process 

Only about 9% of plastic in the U.S. is ever reused, often in low-value products; however, according to WisBusiness, with a new technique, University of Wisconsin–Madison chemical engineers are turning low-value waste plastic into high-value products.

The new method, described in the Aug. 11 issue of the journal Science, could increase the economic incentives for plastic recycling and open a door to recycling new types of plastic. The researchers estimate their methods could also reduce greenhouse gas emissions from the conventional production of these industrial chemicals by roughly 60%.

The new technique relies on a couple of existing chemical processing techniques. The first is pyrolysis, in which plastics are heated to high temperatures in an oxygen-free environment. The result is pyrolysis oil, a liquid mix of various compounds. Pyrolysis oil contains large amounts of olefins — a class of simple hydrocarbons that are a central building block of today’s chemicals and polymers, including various types of polyesters, surfactants, alcohols, and carboxylic acids.

In current energy-intensive processes like steam cracking, chemical manufacturers produce olefins by subjecting petroleum to extremely high heat and pressure. In this new process, the UW–Madison team recovers olefins from pyrolysis oil and uses them in a much less energy-intensive chemical process called homogenous hydroformylation catalysis.

This process converts olefins into aldehydes, which can then be further reduced into important industrial alcohols. These higher-value materials include ingredients used to make soaps and cleaners, as well as other more useful polymers.

The recycling industry could adopt the process soon; in recent years, at least 10 large chemical companies have built or announced plans for facilities to produce pyrolysis oils from waste plastics. Many of them run the pyrolysis oil through steam crackers to produce low-value compounds. The new chemical recycling technique could provide a more sustainable and lucrative way to use those oils.

The next step for the team is to fine tune the process and better understand what recycled plastics and catalyst combinations produce which final chemical products.