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The future of chemical recycling in plastic waste management

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On the 3rd & 4th November I attended a virtual conference held by AMI on Chemical Recycling. As much as my poor grade in Chemistry A level would allow me to understand it, I found it very interesting and thought-provoking. Here are my thoughts from a keen amateur.

My general impression was that the EU recycling targets could not be met with mechanical recycling alone and that chemical recycling would be a good complementary solution for difficult to recycle multi-layer and soiled plastics. 

With China refusing entry for imported plastic waste (historically the only way for many countries to achieve their targets), a solution is needed to recover and recycle as much of our own waste in-house, as we can.  The ideal system would be to add either a mini pyrolysis or gasification plant onto each MRF (Material Recovery Facility) to enable a 100% solution. 

With this in mind – and in my opinion – the development in the Chester area of the Power House Energy group, that takes difficult to recycle mixed plastics and turns them into syngas then hydrogen, is a good short/ medium term solution to our problem. Relatively low cost, it can easily be added onto our MRF’s throughout the country. And I am certain there are other equally good technologies out there. 

The common outlook at the conference was that the ultimate solution for mixed, difficult to recycle plastics is conversion back to the chemical feedstock and not fuel. But realistically, the experts felt that in the short/medium term, incineration of waste to energy, or gasification/pyrolysis into syngas for fuel, is a necessary step.

A quick summary of the Chemical Recycling Technologies

Dissolution – A particular polymer is dissolved into a solvent leaving the impurities behind to be siphoned off. The advantage of this is that it retains the polymer structure and is relatively low cost. The disadvantage is that this can only apply to single-stream plastic as the solvent used only works with a particular polymer. This technology is still at the pilot stage.

Depolymerisation –  A polymer such as PET or PS is broken down into its monomers, leaving all impurities behind. The monomers can then be built up again in polymerisation to produce virgin PET or PS.

The advantages are that this technology is good for producing new Polyester fibres out of old and it is profitable at a relatively small scale. The disadvantages are that scaling up could be a problem and it also relies on a single stream waste. Once again, this is still at the pilot stage.

Pyrolysis – The thermal decomposition of materials into an oil – in this case, mixed plastics – at elevated temperature and in an inert atmosphere.

The advantages of this method are that it can take a mixed stream of plastics (except PET or PVC) and the technology works well in collaboration with Petro-chemical companies. The disadvantages are that it does not take all plastics and the output needs purification prior to cracking and refining.

Gasification – A process that converts mixed plastics into syngas. This is achieved by reacting the materials at high temperatures without combustion and with a controlled amount of oxygen and/or steam. The resulting syngas can then be converted into oil for the refinery process.

The advantage of this process is it will take all plastics. But the technology is very expensive to install.

Both of the latter two technologies have moved beyond the pilot stage and in some cases have become industrial – albeit, in some cases, the output is being used for fuel.

To give you an idea of why we need chemical recycling, we have carried out some calculations.

Global Polymer (plastic) produce has a 100% potential to be either mechanically or chemically recycled. Unfortunately, this potential is not being tapped into.

In 2019, out of this 100%: 

  • 74% ended up as global post-consumer waste 

Out of all this post-consumer waste:

  • 61% was either incinerated or ended up on the landfill;
  • 13% was collected for recycling; 
  • 9% was mechanically recycled; 
  • 0% was chemically recycled.

Based on current efforts, out of the 100% of global polymer demand, it is predicted that by 2030:

  • 67% will end up as global post-consumer waste 

Out of this post-consumer waste, an estimated

  • 52% will either be incinerated or on the landfill;
  • 15% will be collected for recycling;
  • 11% will be mechanically recycled;
  • And only 2% will get chemically recycled.

As you can see Chemical Recycling is a slow burn, hence the need for a short-term, to a medium-term, solution. The question to my audience (if I have one at this stage) is this: is modern incineration, or any other ‘waste to energy’ scheme worse than destroying our oceans and environment?

To explore this, let’s now take a look at what a Pyrolysis plant would look like, in a bit more detail.

The feedstock would be a mixture of contaminated and multi-layer plastics which nobody wants and which are impossible to mechanically recycle. So, there would be no need to wash or separate by polymer type. 

Feedstock would enter the thermal conversion plant and be converted into 72-75% Taco Oil, 18% Syngas (used to power the plant) and 8-10% Char, which would be sold to the construction industry.  Quite an efficient process! 

The Taco oil, which is a Naphtha-like substitute, would need to be purified by the Petro Chemical Industry before it could be used in the cracking process to eventually make monomers. The Petro Chemical Industry seems very keen to help here, as it sees the regulatory system in the future demanding this and presenting an opportunity.

In Life Cycle Analysis Terms, one kilogram of mixed plastic waste gives off 0.55 kilograms of CO2 during pyrolysis. This is 65% less than during incineration. If we then convert this Taco oil into virgin plastic then one kilogram gives 0.86 kilograms of CO2. That is 55% fewer emissions than using crude oil! 

In summary, the experts at the conference felt that mechanical recycling was the best process in terms of Life Cycle Analysis. But as we now all know this process can only recycle certain polymers. 

So, to ensure that we capture all the benefits from all polymers, it is important to have a complementary technology to process the difficult to handle items. In the short term, this could be incineration or pyrolysis for energy. In the longer term true Chemical Recycling should be the answer. 

What must not happen anymore is the irresponsible disposal of plastic into our oceans and the natural environment. Each country, or group of countries, should set about recycling as much of its own plastic waste as it can and stop exporting large quantities of it around the world.

What is stopping the Department for Environment, Food and Rural Affairs (DEFRA) from attaching small scale incinerators or pyrolysis plants to our MRFs, starting tomorrow?