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Separation process could revolutionise polyolefin sorting

A new process for separating polyolefins could bring significant benefits to plastics sorting, according to its developer.

The process (pictured) brings commercial viability to separating plastic types that are typically left mixed in current processes, according to Steve Burns, a project developer from plastic consultancy Impact Solutions.

“Traditional optical plastic separators cannot see black, which can be up to 30% of some waste streams,” he said. “That tends to be a rich source of polyolefin, but it is coming out unseparated because we cannot do anything with it under current technology.”

Impact Solutions has completed a feasibility study using a baffled oscillation reactor which is traditionally used to mix pharmaceutical liquids.

The unseparated, chipped polyolefins are fed into the reactor which is filled with water. The reactor then agitates the solution until the denser plastics are separated from those lighter than water (polypropylene and HDPE).  

The system then splits the lighter fraction into two plastic types, PP and PE. The heavier fraction sinks, giving a third output material.

Burns said that while other systems such as sink/float tanks are currently used, they are unable to separate polyolefins without the use of liquids of differing densities.

Due to the expense of these liquids, such technologies have not generally been considered commercially viable for separating polyolefins. 

Burns said the system offers a commercial advantage over current technologies because it uses water for the separation.

An additional benefit of the process is that the separated plastic at the end is relatively clean after being held in the water.

“Waste sites tend to be dirty – a lot of plastic coming out is covered in dirt and grime,” he said.

The system is currently being scaled up for commercial use where it will be able to process one tonne of polyolefin per hour. Burns said this was the feed rate requested by commercial partners.

The project is the result of four years of research, and has received additional support from Scottish Enterprise, Scottish Environmental Technology Network and Zero Waste Scotland.

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