But chemical recycling can turn polyester waste back into completely new, colourless PET, with other, possibly better properties than the original. Cumapol in Emmen has developed a process to do this and will soon start building a pilot plant.
Marco Brons, technical director at Cumapol, explains how it works: ‘Polyester production is a balance reaction. When you add a large quantity of one of the monomers, glycol, this disrupts the stability and the polymer will degrade. This depolymerisation results in a liquid whose viscosity is so low that it can be purified well. That is how we can remove the colour, among other things. The raw materials (monomers) are purified and introduced back into a polymerisation process, to produce pure PET. The superfluous glycol is recovered and can be used again.’
Feasibility
The process steps for chemical recycling are not new in themselves. Not enough raw materials flows used to be available in the past, so the process could not be performed on an industrial scale. ‘And that is exactly what Cumapol wants to do: first prove that it is technically feasible in the pilot plant we are building, so that we know how to convert the existing plant, where we will produce 25 Ktonnes annually in a round-the-clock process. That will make it economically viable. The reason we can do this is that more and more polyester is being collected.’
PET bottles under the deposit system have been around for a while already, but initiatives like ‘Plastic Heroes’ mean that increasingly more different plastics are entering the recycling market, such as meat trays, food packaging and synthetic textile. ‘The polyester flows are accordingly becoming larger and larger, but the food legislation prevents them from being recycled mechanically just like that. Chemical recycling, however, is permitted.’
Less critical
The purity of the raw materials is also not such a problem with chemical recycling; the process is less critical and the legislation is less strict. ‘The material does need to be properly cleaned beforehand and any sand and organic contamination removed. If a small amount of polymers other than PET is present, that is not a problem; we can remove it in the process. That would be impossible with mechanical recycling, because the polymers would simply be melted together.’
But chemical recycling is still relatively expensive. It will not replace mechanical recycling on a large scale. Brons: ‘It does not have to either, if the quality of the raw materials is steady and the contamination is kept to a minimum. Thanks to a good recycling system like the one for the bottle deposits, mechanical recycling will remain the perfect solution.’
The story changes totally if the colour of the end product is important for its usability. For example, for carpet. Cumapol is working together with DSM Niaga, for instance, on a project to produce 100% polyester carpet which incorporates no other additives or adhesives. As far as composition goes, mechanical recycling should be possible, but there are only limited possibilities of application for the resultant black granule. ‘At most, the automotive industry will be interested in it,’ according to Brons.
Cooperation
Cumapol wants to use bioglycol for the process, to make the end result of the chemical recycling as sustainable as possible. Discussions on this are underway, for example with Avantium in Delfzijl. That company is currently collaborating with partners AkzoNobel, Chemport Europe, RWE and Staatsbosbeheer (National Forest Service in the Netherlands) on the construction of a biorefinery that will convert residual flows from Dutch forests (second generation biomass) cost-effectively into pure glucose, lignin and a mixed syrup. These are used to develop new types of chemicals. ‘We evaluate their products and they examine how they can use biobased monomers to cater for our need to produce polyester specialities. That is how we keep the existing raw material flows intact and can supplement shortages with biobased material. We believe that it is only really sustainable that way.’
Cumapol also works in recycling together with other companies from the Chemport Europe area, such as BioBTX in Groningen which produces biobased terephthalic acid and Morssinkhof in Emmen which has the technical facilities for cleaning and cutting polyester waste flows so they are suitable for chemical recycling. ‘Chemport Europe is the binding factor,’ says Marco Brons. ‘It is how we know each other, trust each other and know each other’s strong points.’
This article was created in cooperation with Chemport Europe
