Packaging Matters

PET RECYCLING

PET RECYCLING

Source: Dreamstime

INTRO: An extremely brief history of PET

Nathaniel Wyeth, inventor of the PET bottle in 1986. Source: Newspapers.com

Even if you know nothing about polymers or chemistry is just a forgotten nightmare from your high school days, you have probably heard about PET, and know that it’s the plastic that most bottles are made of.

It’s quite likely you have also heard that it’s an environmental problem, and that it end up polluting the oceans.

I’m going to skip most references to polymer chemistry. Suffice to say that PET is a polyester, which technically means that it contains several ester groups.

And yes, polyester fabric is also  made from polyethylene terephthalate, or PET. PET is the most common of all the polyesters. Another- although lesser-known – polyester example is PLA, or polylactic acid, a bioplastic which already mentioned in this post.

PET synthesis

However, I said most, not all references to polymer chemistry, since some organic compounds will be mentioned lated when commenting on chemical recycling of PET.

PET can be obtained by:
a) Esterification of terephthalic acid (TPA) with ethylene glycol (EG).TPA is sometimes referred to as PTA (purified terephthalic acid). EG is sometimes call MEG ( monoethylene glycol).
b) Transesterification of dimethyl terephthalate (DMT).

In either reaction, an intermediate monomer bis(2-hydroxyethylterephthalate) (BHET) is formed. All these chemical substances will come up later, since chemical recycling is in a way reversing the polymerization reaction.

PET synthesis from Recent Developments in the Chemical Recycling of PET

PET was developed by British chemists named Rex Whinfield and James Dickson in1941 while working at a small company called Calico Printer’s Association. After a series of agreements, DuPont that had already developed an improvement in its pipeline, acquired the manufacturing rights for the USA in 1946, In 1947  ICI (now part of AkzoNobel) did the sane for the rest of the world. PET was used to manufacture synthetic fibres such as Dacron or Terylene.

PET films were developed in the late 1950s (such as DuPont’s Mylar in 1952, or Melinex). Later, PET was modified for the manufacture of injection parts (generally reinforced with fiberglass).

In 1960, Amoco introduced the production of terephthalic acid (PTA) which facilitates the production of PET. In 1965 the Hans J. Zimmer ( from the Vickers-Zimmer company) was already producing three tons per day in continuous process, and in the early 70s the first pieces were manufactured oriented three-dimensional parts were manufactured.

The first to discover how to make PET bottles for carbonated soft drinks was Nathaniel Wyeth who patented the process in 1973.

PLASTIC WASTE MANAGEMENT

PET as most plastic present two huge environmental problems:

Plastic environmental issues are basically twofold:

  • Their end-of-life problems
  • Their non-renewable origin

For more info on this specially regarding the second point,  you can go to this post.

Source: https://www.statista.com/chart/15905/the-estimated-number-of-years-for-selected-items-to-bio-degrade/

Let’s have a look at how much plastic is recycled.

https://www.bpf.co.uk/sustainability/plastics_recycling.aspx#2.2

So, it seems that some Asian countries like India and South Korea lead the way. EU countries average is around 30% (more details later), and in the US only about 9% of the plastic is recycled.

More info about US plastic recycling rates:

https://www.forbes.com/sites/niallmccarthy/2019/05/20/plastic-recycling-still-has-a-long-way-to-go-in-the-u-s-infographic/?sh=1822d65c5c6a

The previous graphics show the recycling rates of all plastics. I have searched for more specific info about plastic packaging waste:

Source:  Plastic waste and recycling in the EU: facts and figures

So we see that in Europe approximately 40% of the plastic produced is used in packaging. Let’s see the evolution of the plastic recycling rates in the EU:

Source: eurostat

Recycling facilities usually separate PET and high-density polyethylene (HDPE) containers like milk jugs. They are relatively clean and homogeneous materials, and recyclers handle enough of them to make extraction worthwhile.

If we look at the recycling rates of PET bottles by country:

PET plastic bottle recycling rates in select countries 2018
Source: https://www.statista.com/statistics/1166550/plastic-bottle-recycling-rates-in-select-countries/

We find Norway is a spectacular exception in Europe, recycling 97% of its plastic bottles. 92 percent of the bottles recycled yield such high quality material, it can be used again in drink bottles. In some cases, the system has already reused the same material over50 times. More about this later.

PET RECYCLING OVERVIEW

Different types of PET Recycling.

PET recycling methods can be categorized into four groups:
  • Primary recycling: Primary recycling, or re-extrusion, is just the ‘‘in-plant’’ recycling of the scrap materials that have similar features to the original products. It’s simple and cheap, but requires uncontaminated scrap,
  • Secondary recycling: Secondary recycling, also known as mechanical recycling,
  • Tertiary recycling: Tertiary recycling, more commonly known as chemical recycling,
  • Quaternary recycling:  It’s the recovery of energy content from the plastic waste by incineration. When the collection, sorting and separation of plastics waste are difficult or economically not viable, or the waste is toxic and hazardous to handle, the best waste management option is incineration to recover the chemical energy stored in plastics waste as thermal energy. However, it is thought to be ecologically unacceptable because of potential health risks from the air born toxic substances.

On this last point, I would like to comment on the use of pyrolysis for plastic waste. On this post I mentioned some initiatives to obtain oil from plastics.

Brightmark Energy has one of the largest such projects. It has started construction on a $260 million plant in the US to convert 100,000 tons per year of plastic waste into 68 million litres  of diesel and naphtha.

Ashley Plastics Renewal from Brightmark on Vimeo.

However, some experts think that material being returned to fuels or oils and being used to feed petrochemical plants should be classed as recovery and not as recycling under the waste directive, meaning it would not count towards recycling targets such as the EU’s.
Besides the aforementioned methods, direct reuse of a plastic material (i.e., PET) could be considered as a ‘‘zero-order’’ recycling technique. In many countries, it is a common practice for PET bottles to be refilled and reused. However, this should be done with great care since plastic bottles are more likely than glass to absorb contaminants that could be released back into food when the bottle is refilled.

MECHANICAL RECYCLING

Mechanical recycling was commercialized in the 1970. It involves several operations that aim to recover plastics via mechanical processes (grinding, washing, separating, drying, re-granulating and compounding), thus producing recyclates that can be converted into plastic products, substituting virgin plastics.
The polymer is separated from its associated contaminants and it can be readily reprocessed into granules by conventional melt extrusion. Mechanical recycling includes the sorting and separation of the wastes, size reduction, melt filtration, and reforming of the plastic material. The basic polymer is not altered during the process.
Here’s a graphic that shows the different steps of mechanical recycling:
Source: bluevision

And here’s a video that shows some of thesesteps (it omits the steps needed to create the pellets):

NAPCOR – PET Recovery from NAPCOR on Vimeo.

PET Mechanical Recycling Issues (and why not everybody can be like Norway)

The major issues for mechanical recycling are:

Source: Pathwater
  • PET waste is heterogeneous and highly contaminated, which makes mechanical recycling difficult. Also, small amounts of another  in the PET matrix may significantly change the properties of PET, disturbing its use in conventional applications.

Back to Norway: The Norwegian system relies on two key incentives. First, the more companies recycle, the less tax they have to pay. If they reach a collective nationwide target of more than 95 per cent, then they don’t pay any tax at all. Second, customers must pay a deposit for each bottle, about 0.03 €. There are hundreds of thousands of ‘reverse vending machines’ where bottles can be returned you begin to understand Norway’s success on this front.

Today in the US, there are only 10 states that have Container Deposit Legislation (CDL), which have resulted in recycling rates of between 65% and 95% percent, according to Plastics News. Curbside systems are less efficient with recycling rates of just 20%.

  • PET degrades each time it is recycled. Because of various factors such as temperature, ultraviolet radiation, oxygen, ozone, and mechanical stresses, leading to altered properties and reduced performance of recycled PET compared with virgin PET.
  • Color: Recycled PET is an undesirable grey color, resulting from the presence of PET waste made from the same resin. Some PET bottle resins tend to yellow more than others when recycled, especially those containing multiple layers.

CHEMICAL RECYCLING

Chemical recycling involves the transformation of the PET polymer chain (either back to its monomers or a partial depolymerization to its oligomers and other industrial chemicals).

The main chemical-recycling processes for PET are: hydrolysis, glycolysis, methanolysis, and other processes. The resulting chemical substances for each are shown below, and have been mentioned in the introduction (DMT, EG… etc.).

So chemical recycling basically consists in transforming the polymer back into its original monomers . Chemical processes are more tolerant of contamination, and they yield polymers that are identical to the originals, eliminating downcycling, and thus overcoming most of mechanical recycling issues.

Chemical recycling examples

Plastics makers are increasingly looking to partner with companies to develop chemical recycling processes.
Neste (mentioned in this post as one of the companies using pyrolisis to obtain oil from plastic) has partnered with Unilever  to test and validate systems to chemically recycle waste plastics.
Let’s look now at some companies with different approaches to chemical recycling:
Source: Chemical Recycling PET W.G. Hoenderdaal Indorama Ventures 2017
Garbo S.r.l. has developed an innovative  process, called ChemPET, capable of treating most of the PET-based waste currently not recoverable. This process uses enzymes to break down PET is transformed into an intermediate product named BHET (again these funny chemical acronyms)  which-as we have seen – is a chemical substance used for PET production.
PET based materials recoverable with the ChemPET process are:
  • Thermoforming scraps and multi-layer trays (PET / PE / EVOH / PE);
  • Scraps and films coupled with Aluminum (PET / PE / Alu / PE)
  • Opaque PET bottles (containing fillers such as TiO2, CaCO3, Silica)
  • Colored PET powders and fines
  • Black PET trays
  • PET / PP strapping
  • Non-woven fabrics, TNT
  • Polyester / Cotton blends

 

In 2019, Plastipak and Garbo announced an exclusive partnership for recycling PET on an industrial scale.

 

Gr3n technology offers a new and revolutionary approach to the chemical treatment using a microwave assisted technology able to treat R-PET in a closed loop cycle process. The core of technology is DEMETO (DEpolymerization by MicrowavE TechnolOgy), a patented technology, able to depolymerise, in continuously, a wide range of PET manufactures (e.g. colour bottles, food containers, polyester textile). DEMETO reactor is capable to overcame the drawbacks that impeded the industrial implementation thanks to the following advantages: it reduces the reaction time from 180 to 10 minutes.
Ioniqua uses “smart fluids” fluids (ionic liquids) as the solvent and/or catalyst for the glycolysis of polyester into BHET. This includes the use of (recyclable) magnetic ionic liquids for the separation step (magnetic decanter).
Carbios uses an enzymatic biorecycling process:
Loop Industries patented and proprietary process claims to be low energy consumption and transforms PET into PTA and MEG at ambient temperature and pressure in combination with readily available chemicals.
In 2020, Loop and SUEZ announced plans to build the first Infinite Loop recycling facility in Europe.

CHEMICAL OR MECHANICAL

Chemical recycling is considered to be the most sustainable option, since it leads to the formation of the raw materials (monomers) from which the polymer is originally made. In this way the environment is not surcharged and there is no need for extra resources for the production of PET.

In the past has not been cost effective to use this method because of the lower price of petrochemical feedstocks compared with the process prices for production of PET monomers or oligomers from PET waste.

Source : PR Newswire

 

Detractors list chemical recycling’s carbon and energy intensity compared to mechanical recycling, its economic viability, and low-yield as arguments against it.

Source: How plastics waste recycling could transform the chemical industry

Supporters for chemical recycling argue it has a lower environmental impact than virgin and works in tandem with mechanical recycling to treat waste volumes that would otherwise go to landfill or incineration.

Regarding the low yields and high cost, they attribute these to  the current life cycle stage of the processes, and claim they will be solved thanks to the economies of scale and future technical breakthroughs.

PET RECYCLING CONCLUSIONS (my two cents…)

The ideal sitution would be for chemical and mechanical recycling to coexist.

Hopefully, chemical recycling processes will improve and the will be more effective, less energy demanding and more profitable. Also, they should be able to use lower quality raw materials to stop competing with mechanical recycling.
However, I think there are some common issues with PET recycling in particular, and plastics recycling in general.
These issues cannot be solved by the industry or governments alone, but their solution should also involve consumers.

Under my point of view the more important issues to be improved in order to facilitate plastics recycling:

  • Cost-effective technologies recycling (specially for sorting).
  • Design for recycling: fewer materials (ideally monomaterial packaging) and fewer parts, design for disassembly.
  • Markets for recycled plastics: Assure quality, price and supply consistency.
  • Improve recycling infrastructures to make them more effective
  • Educate consumers on recycling and encourage recycling and purchasing goods containing recycled material.

     

April 2021,  Bruno Rey – The Packaging Blog –


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