Are plastics the new natural gas?

Yiannis Lev­endis, Dis­tin­guished Pro­fessor Mechan­ical and Indus­trial Engi­neering at North­eastern, keeps a pho­to­graph of a burning plastic foam cup tacked to the wall above his desk. Thick black smoke emanates from the recep­tacle, which, sub­se­quent pic­tures reveal, was reduced to a sooty powder by the end of the com­bus­tion process.

The photo rep­re­sents a mis­sion for Lev­endis, whose exper­tise in com­bus­tion and device design has led to the devel­op­ment of dozens of clean energy products.

Con­sider these sta­tis­tics: In 2011, global plastic pro­duc­tion reached 280 mil­lion tons. The U.S. swept aside 32 mil­lion tons as waste, and just 8 per­cent of that waste was recov­ered for recy­cling. The rest found its way into land­fills and some into the oceans, accounting for count­less seabird and marine mammal deaths.

“Instead of throwing them away,” Lev­endis won­dered, “could we make use of them in a cleaner way?” The answer, it turned out, was yes.

Burning plastic in the tra­di­tional manner cre­ates extremely pol­luting byprod­ucts, as evi­denced by the black smoke pro­duced by the cup. But this didn’t thwart Lev­endis, who noted that plastic con­tains the same amount of energy per pound as pre­mium fuel.

“We wanted to tackle the problem by pre­pro­cessing the plas­tics,” said Chuanwei Zhuo, a doc­toral can­di­date in Lev­endis’ lab. Toward that end, the team devel­oped a com­bus­tion system that adds a simple step to the burning process that allows for turning plastic into a fuel that burns just as cleanly as nat­ural gas.

Pro­fessor Yiannis Lev­endis and doc­toral can­di­date Chuanwei Zhou with their reactor. Photo by Brooks Canaday.


That simple step has a daunting name: pyrolytic gasi­fi­ca­tion. Instead of directly set­ting the cup aflame with a match in the open air, the team’s reactor heats the mate­rial to a whop­ping 800 degrees Cel­sius in a com­pletely oxygen-​​free envi­ron­ment. This causes the plastic to become a gas, which is then mixed with air before it is burned as a clean fuel.

The patent-​​pending process gave way to another sur­prising result: when the researchers intro­duced a bit of stain­less steel into the reactor, they found it acted as a cat­a­lyst for growing uni­form carbon nan­otubes. Thus, not only can our plastic waste problem be rerouted to gen­erate elec­tricity, it can also be upcy­cled to gen­erate one of the market’s most pop­ular new materials.

The researchers have also shown that the same process works for burning bio­mass, a leading alter­na­tive fuel source that is rapidly gaining trac­tion as our global energy demand reaches new heights.

“Using plastic as fuel is not a new idea,” Zhuo said. But this is the first time anyone has burned them so cleanly.


Related Faculty: Yiannis Levendis

Related Departments:Mechanical & Industrial Engineering