Circular Logic: Sustainability of the Plastic Life Cycle

Haldor Topsoe recently announced, via press release, a partnership with Dow to turn waste plastics into circular plastics.

“Circular plastics” was a new phrase to me, so, naturally, I Googled it.

TIP: Google® what is circular plastic

One result of the search … The World's First 'Infinite' Plastic, an excellent article by Katherine Latham appearing in Future Planet, 11th May 2021.

Excerpts appear below, one of which describes the fundamental concept. Conventional recycling sorts like plastic with like plastic and creates second generation plastic from the like plastics. The problem with this approach is that the second generation plastic is a degraded form of the original. Plus, sorting the plastics in the first place is quite labor intensive.

An alternative is chemical recycling.

Quoting from the article …

“Chemical recycling is an attempt to recycle the unrecyclable. Instead of a system where some plastics are rejected because they are the wrong colour or made of composites, chemical recycling could see all types of plastic fed into an "infinite" recycling system that unmake plastics back into oil, so they can then be used to make plastic again.”

This approach has the potential to create a truly circular process … in other words, circular plastics.

///////
[ EXCERPTS ]
The world's first 'infinite' plastic
Future Planet
By Katherine Latham
11th May 2021
The way we normally recycle plastics is a downward spiral of waste and degraded materials, but there is another option – turning plastic back into the oil it was made from.
   Instead of a system where some plastics are rejected because they are the wrong colour or made of composites, chemical recycling could see all types of plastic fed into an "infinite" recycling system
This process – known as chemical recycling – has been explored as a viable alternative to conventional recycling for decades. So far, the stumbling block has been the large amount of energy it requires. This, combined with the volatile price of crude oil sometimes makes it cheaper to produce new plastic products than to recycle existing plastic.
Much of the plastic that could be recycled – such as polyethylene terephthalate (PET), which is used for bottles and other packaging – ends up in landfill. This is often due to confusion about kerbside recycling or contamination with food or other types of waste.
Other plastics – such as salad bags and other food containers – find their way to landfill because they are made up of a combination of different plastics that can't be easily split apart in a recycling plant. Litter dropped in the street and lightweight plastics left in landfill sites or illegally dumped can be carried by the wind or washed into rivers by the rain, ending up in the ocean.
Chemical recycling is an attempt to recycle the unrecyclable. Instead of a system where some plastics are rejected because they are the wrong colour or made of composites, chemical recycling could see all types of plastic fed into an "infinite" recycling system that unmake plastics back into oil, so they can then be used to make plastic again.
The way plastic is currently recycled is more of a downward spiral than an infinite loop. Plastics are usually recycled mechanically: they are sorted, cleaned, shredded, melted and remoulded. Each time plastic is recycled this way, its quality is degraded. When the plastic is melted, the polymer chains are partially broken down, decreasing its tensile strength and viscosity, making it harder to process. The new, lower grade plastic often becomes unsuitable for use in food packaging and most plastic can be recycled a very limited number of times before it is so degraded it becomes unusable.
The emerging industry of chemical recycling aims to avoid this problem by breaking plastic down into its chemical building blocks, which can then be used for fuels or to reincarnate new plastics.
   In the UK, Mura Technology has begun construction of the world's first commercial-scale plant able to recycle all kinds of plastic
The most versatile version of chemical recycling is "feedstock recycling". Also known as thermal conversion, feedstock recycling is any process that breaks polymers down into simpler molecules using heat.
The process is fairly simple – take a plastic drinks bottle. You put it out with your recycling for collection. It is taken, along with all the other waste, to a sorting facility. There, the rubbish is sorted, either mechanically or by hand, into different kinds of materials and different kinds of plastics.
Your bottle is washed, shredded and packed into a bale ready for transportation to the recycling centre – so far, the same as the conventional process. Then comes the chemical recycling: the plastic that formerly made up your bottle could be taken to a pyrolysis centre where it is melted down. Next it is fed into the pyrolysis reactor where it is heated to extreme temperatures. This process turns the plastic into a gas which is then cooled to condense into an oil-like liquid, and finally distilled into fractions that can be put to different purposes.
Chemical recycling techniques are being trialled across the world. UK-based Recycling Technologies has developed a pyrolysis machine that turns hard-to-recycle plastic such as films, bags and laminated plastics into Plaxx. This liquid hydrocarbon feedstock can be used to make new virgin quality plastic. The first commercial-scale unit was installed in Perth in Scotland in 2020.
The firm Plastic Energy has two commercial-scale pyrolysis plants in Spain and plans to expand into France, the Netherlands and the UK. These plants transform hard-to-recycle plastic waste, such as confectionery wrappers, dry pet food pouches and breakfast cereal bags into substances called "tacoil". This feedstock can be used to make food-grade plastics.
In the US, the chemical company Ineos has become the first to use a technique called depolymerisation on a commercial scale to produce recycled polyethylene, which goes into carrier bags and shrink film. Ineos also has plans to build several new pyrolysis recycling plants.
In the UK, Mura Technology has begun construction of the world's first commercial-scale plant able to recycle all kinds of plastic. The plant can handle mixed plastic, coloured plastic, plastic of all composites, all stages of decay, even plastic contaminated with food or other kinds of waste.
Mura's "hydrothermal" technique is a type of feedstock recycling using water inside the reactor chamber to spread heat evenly throughout. Heated to extreme temperatures but pressurised to prevent evaporation, water becomes "supercritical" – not a solid, liquid, nor gas. It is this use of supercritical water, avoiding the need to heat the chambers from the outside, that Mura says makes the technique inherently scalable.
Once this high-pressure system is depressurised and the waste exits the reactors, the majority of liquid flashes off as vapour. This vapour is cooled in a distillation column and the condensed liquids are separated on a boiling range to produce four hydrocarbon liquids and oils: naphtha, distillate gas oil, heavy gas oil and heavy wax residue, akin to bitumen. These products are then shipped to the petrochemical industry.
As with other feedstock techniques, there is no down-cycling as the polymer bonds can be formed anew, meaning the plastics can be infinitely recycled. With a conversion rate of more than 99%, nearly all the plastic turns into a useful product.
Yet in the past 30 years, chemical recycling has shown serious limits. It is energy-intensive, has faced technical challenges and proved difficult to scale up to industrial levels.
Full text source: https://www.bbc.com/future/article/20210510-how-to-recycle-any-plastic
///////
Google® Better!
Jean Steinhardt served as Librarian, Aramco Services, Engineering Division, for 13 years. He now heads Jean Steinhardt Consulting LLC, producing the same high quality research that he performed for Aramco.

Follow Jean’s blog at: http://desulf.blogspot.com/  for continuing tips on effective online research
Email Jean at research@jeansteinhardtconsulting.com  with questions on research, training, or anything else
Visit Jean’s Web site at http://www.jeansteinhardtconsulting.com/  to see examples of the services we can provide