Breakthrough in coloured PET recycling

Coloured PET is currently only recyclable to a limited extent. All colours of PET bottles can be collected, washed and shredded, but you can only reuse the granules for red, blue or green PET. While on the market there is a growing demand for pure, clear PET.
There are a number of technologies for the chemical recycling of plastics. The petrochemical industry has been familiar with most of the chemical techniques for decades. However, the application is now shifting to the recycling of plastics.

One of the options is depolymerization. This is the method Ioniqa applies. Here, a plastic, also called a polymer, is put into a solution (for example water or glycol), at a temperature of around 200 °C (Ioniqa 2019). The network of identical units (monomers) that make up a polymer is then slowly decomposed. Depolymerisation is only possible if you start with fairly pure material. For a mixture of plastics, for example with laminate film, you need a rougher method . A polymer is split up at a higher temperature (between 500 and 800 °C) and in the absence of oxygen. It is the method that multinationals Sabic and BASF want to use. In the case of pyrolysis, the polymer is broken down further than in the case of depolymerisation. This produces naphtha, an oil consisting of a mixture of carbon chains with a length of a few to around ten carbon atoms. The naphtha then enters the cracker, which breaks it down even further into, for example, ethylene and propylene, raw materials for plastics (Sabic 2019).

Although pyrolysis can handle a mix of plastics, there are limits to this. If it contains PVC, hydrochloric acid can form, which affects the metal in the installation. And with PUR, the toxic cyanide can form. In the case of chemical recycling, this type of impurity has long been a limitation, but there are now methods for removing PVC, for example, in advance.

Pyrolysis and gasification can therefore be used to process a broader mixture of plastics than depolymerisation. But they do take place at a higher temperature and cost more energy: more CO2 is released. Consultancy firm CE Delft has compared the variants of chemical recycling on this aspect with the two alternatives: incinerating plastics at waste processors, and producing plastics in the old way, via crude oil. Pyrolysis and gasification release roughly 35 percent less CO2 and depolymerization about 75 percent less (King 2019).

Ioniqa (2019). ‘Ioniqa takes first 10 kiloton PET upcycling factory into operation’ Available on: https://ioniqa.com/ioniqa-takes-first-10-kiloton-pet-upcycling-factory-into-operation/ [Accessed on 14 October 2019]

King, J. (2019). ‘Environmental problems caused by synthetic polymers’. Available on https://sciencing.com/environmental-problems-caused-by-synthetic-polymers-12732046.html [Accessed on 14 October 2019]

Sabic (2019). ‘Sabic pioneers first production of certified circular polymers’ Available on: https://www.sabic.com/en/news/17390-sabic-pioneers-first-production-of-certified-circular-polymers [Accessed on 14 October 2019]