Scientists get the tiger out of PE fuel tanks

Scientists get the tiger out of PE fuel tanks
By Christopher Cundy

Researchers in Germany have devised a way of making polyethylene recycled from fuel tanks more attractive to processors.

Discarded plastic tanks have typically soaked up 3% to 5% of their weight of the fuel they once contained during their life. Recycling firms have to find ways of separating fuel from the polymer before it is reprocessed, since the combustible hydrocarbons evaporate during melting and pose a safety risk to moulders. Also, new components made from the recycled plastic give off an unpleasant smell.

Seven industrial firms are collaborating to find a cost-effective solution to the problem. Birgit Bohlmann, project manager at the Fraunhofer Institute for Chemical Technology, explained the new separation process. “The shredded fuel tanks are placed in pressurised vessels and diffused with carbon dioxide gas.

“At a specific pressure and temperature, the gas acts as a highly efficient solvent, extracting the fuel that has infiltrated the plastic. The gas is then pumped round a circuit, and the pressure is reduced releasing the fuel.”

One of the latest ideas is to combine the extraction process with extrusion. Instead of cleaning the granulate, the operation is performed on the remelted bulk plastic shortly before it is shaped. The research will also extend into plastics other than PE.

About 15,000 tonnes of such waste is collected from German scrap yards each year; new European laws on end-of-life vehicles are stimulating efforts to find better ways of recycling plastic without incineration.