PET-Recycling – Looping the loop in Liebenau
In Interzero’s new PET recycling plant, shredded deposit bottles are now being transformed into food-grade granulate for the beverage industry.
When it comes to recycling PET beverage bottles from the deposit system, it really is a case of ‘turning old into new’. What modern systems now make possible is revealed by a look at the brandnew plant just opened by Interzero in Liebenau, Lower Saxony. Although you won’t find any empty bottles here: the material has already gone through several process steps before being delivered. After collection, the PET bottles are shredded, sorted by material and colour, and then washed at a high temperature.
1: Inbound delivery and quality control
The PET flakes are delivered to the recycling plant in one-tonne big bags. The Interzero team takes a sample from every second bag, and then tests this material sample for impurities, residual chemicals, moisture content and viscosity. The actual processing of the flakes only starts once quality control has given the go-ahead.
2: Homogenisation
The flakes are first homogenised in mixing silos, to even out any variations in the composition of the material and therefore make the subsequent processes run more smoothly. A horizontal screw conveyor then moves the material to another, even finer sorting stage, where Interzero makes use of near-infrared (NIR) technology.
3: Near-infrared separator
The NIR separator is fully automatic, separating out any impurities still present, plus unwanted colours like green, yellow or dark blue. Only light blue flakes are allowed to remain, as they positively influence the clear colour hues needed for competitive, production-grade plastic.
4: Extrusion
Now the actual extrusion stage starts, which turns the pre-treated PET flakes into high-quality granulate for manufacturing. This involves the plastic being melted at about 290 °C and fed in with another screw conveyor. This viscous mass passes through several filters before ultimately being pressed through a perforated panel for shredding by a granulator. One final processing stage is needed to make the granulate fit for use as a food contact material and this occurs in the solid state polycondensation (SSP) reactor. The material stays in the reactor for about 10 hours at roughly 180 °C, in a vacuum/nitrogen atmosphere that allows oxygen to escape and avoids any unwanted reactions with the material.
5: Back into the loop
The finished granulate is then filled back into big bags and shipped out for further processing. Interzero’s customers use the food-grade rPET to manufacture what are known as ‘preforms’. These ‘bottle blanks’ are made using injection moulding and look a little like test tubes: they can be blown up into full-size bottles and — once filled — end up back on the shelves in stores, completing the bottle-to-bottle cycle. The cycle then starts again once consumers return their bottles to collect the deposit.
Facts and figures
Bottle-to-Bottle recycling in compact form: the plant can handle a total of 12,000 tonnes per year.
Recycling operates in a vacuum, with parts of the process using a nitrogen atmosphere. This process step ensures that the material stream is free of moisture and unwanted substances that out-gas when the plastic is heated.
A key benefit for customers from the beverage industry: the plant has been accredited by the European Food Safety Authority (EFSA).
Managing Director, RDB plastics GmbH
Sustainability Magazine
Win-win – Shaping the circular economy