Chemical Recycling 101

1 Chemical Recycling – An Introduction
1.1 Mass Balance
2 Technologies and their application
2.1 Purification
2.2 Depolymerisation
2.3 Feedstock Recycling
2.3.1 Pyrolysis
2.3.2 Gasification
2.3.3 Hydrothermal Treatment (HTT)
3 The Market for Chemical Recycling
3.1 Supporting a Circular Economy
4 Business Models
5 Further reading
6 Reference

1. Chemical Recycling – An Introduction

Traditionally, plastics recycling is undertaken using mechanical methods. Below we provide an overview of the non-mechanical recycling technologies that are currently under development in the new ‘chemical recycling’ sector.

Chemical recycling is the broad term used to describe a range of emerging technologies in the waste management industry which allow plastics to be recycled, that are difficult or uneconomic to recycle mechanically.

By turning plastic waste back into base chemicals and chemical feedstocks, chemical recycling processes have the potential to dramatically improve recycling rates and divert plastic waste from landfill or incineration.

Chemical recycling complements mechanical recycling processes by enabling the further extraction of value from polymers that have exhausted their economic potential for mechanical processing. Chemical recycling serves as an alternative to landfill and incineration for erstwhile hard-to-recycle plastic products such as films, multi-layered and laminated plastics. Additionally, chemical recycling supplies virgin-quality raw materials to the plastics supply chain. This enables the production of food grade plastics from post-consumer waste.

Several pilot plants demonstrating the viability of various chemical recycling processes are currently in operation at the time of writing. Commercial plants range in size from large-scale centralised plants with 30-200kt annual throughput to much smaller, modular, distributed units with capacity from 3-10kt per annum.

1.1 Mass Balance

Chemical recycling (a subset of non-mechanical or advanced recycling) offers the opportunity to process plastic waste - both fossil and non-fossil derived - that is difficult to recycle into high quality, high value recycled plastics.

Chemical recycling complements mechanical recycling by keeping plastics fully circular, using plastic waste which otherwise may have been difficult to recycle, or not suitable for certain end-uses such as food packaging or medical applications. For chemically recycled materials, a Mass Balance calculation with associated allocation must be undertaken[a].

What is the Mass Balance Approach?

Mass Balance is a particular chain of custody model, by which inputs and outputs and associated information are transferred, monitored and controlled as they move through each step in the relevant supply chain.

The choice of a chain-of-custody model and of the associated rules and principles is necessary to evaluate certain product characteristics and ensure the credibility and transparency of associated product claims, either being:

• Renewable content or origin;
• Recycled content, etc.

Mass Balance is a model in which materials or products with a set of specified characteristics are mixed according to defined criteria with materials or products without that set of characteristics, as depicted below[b]:

Application of Mass Balance to Chemical Recycling

With a Mass Balance approach, the feedstock is attributed to a product where there is market demand for more circularity. The mass balance and certification concept allows the plastics industry to use existing commercial assets to convert its products.

Where is Mass Balance Used?

Mass Balance is widely used in certification schemes in different industry sectors.

2. Technologies and their application

Chemical recycling describes any technology that utilises processes or chemical agents that directly affect the chemistry of the polymers.

The technologies fall into three distinct categories based on the position of their outputs in the plastics supply chain (Figure 1). These categories are: 

• Purification 
• Depolymerisation 
• Feedstock (thermal conversion) recycling 

Chemical recycling differs from mechanical recycling which uses operations to prepare waste polymers for reuse, without significantly changing  the chemical structure of the material. Mechanical recycling processes the separated, single-polymer stream, which is washed, granulated and then re-extruded to make recycled pellets that are ready for moulding applications. Chemical recycling processes based on depolymerisation and feedstock recycling, breaks down the long hydrocarbon chains in plastics into shorter hydrocarbon fractions or into monomers using chemical, thermal or catalytic processes. Purification, on the other hand, deals with the use of solvents for removing additives from the polymers.

Figure 1 Closing The Loop - Processes To Return Recycled Materials To The Plastics Supply Chain[1].

Feedstock recycling is a subset of chemical recycling that derives its name from the primary output that is produced, namely a petrochemical feedstock. The term ‘feedstock recycling’ is used to differentiate thermal processes that convert the waste plastic into feedstock for a petrochemical plant, from chemical processes that purify the plastic waste stream (i.e., purification) or break down the waste product into monomers (i.e., depolymerisation) for further reprocessing or repolymerisation.

 

2.1. Purification

Solvent based purification[2] is a process in which plastic is dissolved in a suitable solvent (or solvents), after which a series of purification steps are undertaken to separate the polymer from additives and contaminants. Once the polymer(s) are dissolved in the solvent(s), they can be selectively crystallized. When a solvent can dissolve either the polymer of main interest or all the other polymers except the target one, it might be used for selective dissolution. The crucial requirement for this is to have a selective solvent. The resulting output is the precipitated polymer, which ideally remains unaffected by the process and can be reformulated into plastics.

Target Feedstock

• PVC, PS, PE and PP

Products

• “Purified” plastic polymers

Technology Status

This is a new technology and efforts are underway to scale up to a commercially viable level. Generally, waste plastics are collected as mixed polymers. Therefore, the primary challenge is the separation and recycling of waste components selectively.

 

2.2. Depolymerisation

Depolymerisation[3] (sometimes referred to as chemolysis) is the reverse of polymerisation and yields either single-monomer molecules or shorter polymer fragments known as oligomers. Monomers are identical to those used in the preparation of polymers and because of this, the plastics prepared from depolymerisation are similar in quality to virgin monomers. The main disadvantage of chemical depolymerisation is that it can only be applied to ‘condensation’ polymers such as PET and polyamides. It cannot be used for the decomposition of most ‘addition’ polymers (e.g., PP, PE, PVC) which make up the majority of the plastic waste stream.

Target Feedstock

• Polycondensates, which include polyesters (PET), polyamides (PA), and polyurethanes

Products

• Monomers of the recycled polycondensates

Technology Status

A number of industrial plants carrying out PET degradation are currently in operation, based mainly on methanolysis and glycolysis treatments. Hydrolytic processes are less advanced, most of them being used at laboratory and pilot-plant scales, although several projects are being developed for commercial applications in the next few years. Ammonolysis and aminolysis-based processes are less established and well-developed treatments. Glycolysis and hydrolysis are currently the most significantly used chemolysis methods to reverse the polyurethane polymerization reaction. Chemical depolymerization of polyamides is mainly carried out by hydrolysis.

 

2.3. Feedstock Recycling

Feedstock recycling is any thermal process that converts polymers into simpler molecules, in order to form the feedstock for petrochemical-type processing. The two main processes here are pyrolysis and gasification. The outputs of feedstock recycling are basic chemicals (e.g., hydrocarbons or syngas), which need to be processed further to yield a polymer. This allows flexibility for reuse in the petrochemical industry.

2.3.1. Pyrolysis

In the pyrolysis process, plastics are broken down into a range of basic hydrocarbons by heating in the absence of oxygen, or ‘cracking’ (sometimes referred to as thermal cracking). By utilising a distillation process, the hydrocarbon vapour can then be made into products ranging from heavy wax and oils to light oils and gas. It is possible to skew the production from heavier to lighter by adjusting process time and temperature. Heavier output products can also be reintroduced into the process for additional cracking into lighter products.

Pyrolysis products can be processed in much the same way as oil, using conventional refining technologies to produce building blocks for polymers. Alternatively, they can be used directly as a fuel.

Using pyrolysis to make feedstock for polyethylene and polypropylene production could fill a large processing gap as polyethylene and polypropylene cannot be depolymerised directly into monomers. Further, the plastic produced would be virgin-quality polymers and could be used in all the same applications (e.g., food packaging).

Pyrolysis production can be enhanced using catalytic degradation, where a suitable catalyst is used to promote the cracking reaction. The presence of a catalyst allows reaction temperature and time to be lowered. The process results in a much narrower product distribution of carbon atom number and increases lighter hydrocarbon production. This helps to increase the proportion of the output product for use in making more plastics.

Target Feedstock

• Polyolefins [Polyethylene (PE), Polypropylene (PP), Polybutylene (PB)] 
• Polystyrene (PS)
• PMMA (poly-methymethacrylate) - acrylic glass

 While pyrolysis-based processes can be used to recycle single-polymer plastic waste, they are particularly advantageous when it comes to dealing with contaminated and mixed-polymer waste streams.

Products

• A range of basic hydrocarbon products including gases, oils, and waxes

Technology Status

Historically, pyrolysis has been commercialised in applications relating to charcoal, municipal solid waste and biomass. In the waste industry, pyrolysis of mixed plastics has been in development over the last two decades but is only now becoming a commercial reality with several commercial plants in operation and  many more industrial-scale units expected to be commissioned over the next few years.

2.3.2.  Gasification

Gasification is a process where mixed waste materials are heated to a very high temperature (~1000 - 1500' °C) in the presence of a limited amount of oxygen, which breaks the molecules down to their simplest components to produce syngas (a mix of hydrogen, carbon monoxide and some carbon dioxide). The syngas can then be used to produce a variety of chemicals (e.g., methanol, ammonia, hydrocarbons, acetic acid) for plastics production as well as fuel and fertiliser.

Gasification is generally carried out in larger process units which are designed to achieve economies of scale. In the case of pyrolysis, such units usually take a mixed waste input stream, which places less pressure on the collection and sorting system. Gasification typically requires pre-treatment to remove moisture and increase the calorific value. A very efficient gas cleaning system at the elevated process temperature is needed to meet the requirements for applying the syngas to chemical production.

Feedstock

• All plastics

Products

Gasification of waste plastics leads to the production of syngas, a stream made up of mainly hydrogen (H₂), carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄) and nitrogen (N₂). This gas can be burnt for energy or used in the production of new hydrocarbons.

Technology Status

Gasification of mixed waste has been in use for quite some time.  Gasification plants are typically built at a larger scale than pyrolysis plants.

2.3.3. Hydrothermal Treatment (HTT)

Hydrolysis[4] is a reaction in which a compound is broken down by water molecules in a super-critical condition. Generally, the temperature and pressure condition of a HTT process is around 160–240 °C with the corresponding pressure to keep the water in the liquid state. The special properties of high temperature and pressure of near-critical water make it a good medium for dissolving organic compounds. Essential reactions of HTT are hydrolysis, dehydration, decarboxylation, and depolymerization. Hydrothermal processing has been used for recycling of waste carbon fibre reinforced plastics (CFRP) and printed circuit boards (PCB) in a batch reactor. The ability of near-critical water to degrade the resins and plastics in the composite wastes is largely influenced by the presence of different additives and/or co-solvents. Hydrothermal treatment has been proposed as a solution for the separation of mixed waste (MW) into organic and inorganic substances.

Target Feedstock

• Plastic packaging waste (PET) and selected plastics, namely waste carbon fibre reinforced plastics (CFRP), printed circuit boards (PCB), polycarbonate, styrene-butadiene, poly(lactic acid), nylon 6, nylon 66

Products

• Synthetic crude oil - separation, purification, and upgrading can then be handled by standard refinery operations

Technology Status

Technology is at a development stage, with commercial operations in planning.

 

3. The Market for Chemical Recycling

According to a report by McKinsey[5] only 12% of the 260 million tonnes (Mt) of global plastic waste was recycled in 2016. The same report predicts that the amount of plastic waste is set to almost double within the next decade, reaching 460Mt by 2030. This projected growth is already putting pressure on companies across the plastics value chain to mobilise on this issue. However, the report also predicts a scenario in which 50% of plastics worldwide could be reused or recycled by 2030, representing a fourfold increase from today’s 12% global figure. Achieving this level of growth will require a significant expansion of collection infrastructure and effectiveness, implementing more and more efficient sorting and mechanical recycling , complemented by the effective roll-out of chemical recycling infrastructure.

Thus far, mechanical recycling has demonstrated effectiveness in the recycling of PET, HDPE and PP. Demand for mechanical recycling capacity could be further driven by increasing collection rates of these polymers while expanding to other polymers such as LDPE. According to the McKinsey report, an increase in both collection and scope could help global mechanical recycling rates increase from 12% to 22% of the plastics waste market by 2030.

It is anticipated that chemical recycling will be responsible for a share of the growth forecasted by McKinsey by treating polymer streams that mechanical recyclers cannot handle. Feedstock recycling approaches have the potential to treat mixed-polymer waste streams and residual waste that has exhausted its potential for further mechanical processing. These features will be particularly relevant to building capacity in regions where the infrastructure for collecting and sorting different plastic waste is not yet in place.

The infrastructure investment required to achieve the 50% recycling rate by 2030, in the high-adoption case, is forecast as $15 billion to $20 billion per year. This is in the context of an average investment of $80 billion to $100 billion undertaken by the petrochemical and plastics industry each year over the past decade. This new landscape has the potential to radically change plastic production dynamics by enabling up to one third of production to consist of recycled plastic within a decade, offsetting virgin oil and gas feedstocks. Under this scenario, this new pool of recycled feedstocks could account for two thirds of the growth of the petrochemicals and plastics industry by 2030.

 

3.1. Supporting a Circular Economy

In a circular economy, useful plastic materials are kept in circulation as opposed to being landfilled, incinerated, or leaked into the natural environment. The EU Circular Economy Package strategy calls for a binding landfill target to reduce landfill to maximum of 10% of municipal waste by 2035 and the EU Circular Plastics Alliance has set a goal to use 10 million tonnes of recycled plastic in making  new products every year in Europe by 2025. To develop a circular system and meet these recycling and landfill reduction targets, investment in suitable collection systems and recycling facilities will be required.

Chemical recycling creates value in previously unrecyclable plastic waste by breaking down these plastics into petrochemical feedstock, which can then be reused as building blocks for new virgin-quality polymers. Chemical recycling processes create a bridge between the petrochemical and waste management industries, and may serve as an incentive for the waste management and petrochemical industries to develop relationships to create a circular value chain for plastics.

Many companies in the petrochemical sector are embracing their role in the circular economy. At the 2018 ICIS World Polyolefins Conference, Borealis explained their vision to “establish plastic waste as just another standard feedstock & as the new normal”[6] for the chemical industry.

The petrochemical sector is addressing the increasing sustainability demands of downstream market players such as retailers, brands and consumers by striving to increase the supply of plastics with recycled content and   is committed to work with partners in the plastics value chain to research and develop the use of feedstocks from plastic waste.

To achieve this coupling, cross-industry collaborations and commercial partnerships are emerging to develop the technology know-how and secure access to the supply of waste plastics.

Partnerships between the plastics recycling and petrochemical sectors

In 2017, LyondellBasell (a leading plastics, chemicals and refining company) and SUEZ (a global leader in resource management) became 50 / 50 partners in Quality Circular Polymers (QCP), a premium mechanical plastics recycling company in the Netherlands.

At the end of 2018, chemical producer BASF’s ChemCycling project first used pilot volumes of pyrolysis oil derived from plastic waste supplied by Remondis, a leading European waste management company, as a feedstock in its own production. The pilot projects were conducted with customers from various industries including electronics and packaging film producers.

In the same year, SABIC, a producer of commodity and high performance plastics, signed a memorandum of understanding with Plastic Energy, a chemical plastics recycler, for the supply of feedstock to support SABIC’s petrochemical operations in Europe. The collaboration is piloting the use of recycled feedstock to produce polymers that will be certified as having been made with recycled materials, for supply to the project’s partners - Unilever, Tupperware Brands, Vinventions and Walki Group.

Borealis, a provider of polyolefins, base chemicals and fertilizers, acquired the German plastics recycler MTM Plastics in 2018. MTM is a mechanical recycler of mixed post-consumer plastic waste and is one of Europe's largest producers of post-consumer polyolefin recyclates.

Facilitated by the Ellen MacArthur Foundation, UK-based feedstock recycling specialist Recycling Technologies Ltd led the research for ‘Project Lodestar’ in beginning in 2017, alongside 14 other companies in the value chain. Project Lodestar evaluated the economics of marrying mechanical recycling with feedstock recycling in what is termed an advanced Plastics Recycling Facility (aPRF). Compared to mechanical recycling alone, the results suggest that an aPRF offers significant uplifts in recycling rates, resulting in only 5% disposal to landfill or incineration, and could increase revenue by 25%.

In November 2019, the USA entity of oil and gas company Shell announced it had successfully used pyrolysis to produce high-end chemicals from plastic waste at its Louisiana plant using a liquid feedstock produced by Atlanta company Nexus Fuels LLC.

Meanwhile in Europe, energy company Neste announced their partnership with Remondis to develop chemical recycling of plastic waste. The partners will focus on accelerating chemical recycling and will enable other companies in the value chain to join the initiative. This follows an earlier announcement of its collaboration with ReNew ELP, who are commercialising the Licella catalytic hydro-thermal recycling process.  Additionally, in March 2020, Neste invested in Recycling Technologies to build and install its first commercial plant and also agreed an offtake contract for the output oils.

In December 2019, energy company Total announced it had joined forces with Recycling Technologies and global brands Nestlé and Mars to undertake a feasibility study to deploy a pyrolysis-based feedstock recycling plant in France. This collaboration, facilitated by CITEO, will examine the technical and economic feasibility of recycling complex plastic waste, such as small, flexible and multilayered food-grade packaging in France.

 

4. Business Models

There are several companies emerging in the chemical recycling sector at various stages of maturity. Several pilot plants across Europe are operating to demonstrate the technology and others expanding to an industrial scale.

Commercial plants will range in size from large-scale centralised plants with 30-200kt annual throughput to compact, modular distributed units with capacity from 3-10kt per annum and mobile units for <3t per annum capacity.

Companies with a larger, centralised plant tend to be operators of the plant and offer recycling as a service. In this scenario the plant will act as receiver of the waste and will retain ownership of the output product for onward sale to the chemical sector.

Companies with a distributed, smaller plant tend to offer their recycling technology solution for purchase by waste handling operators. In this case, the plant will be built remotely and distributed for installation on existing waste and material handling sites. The technology provider will earn revenue from equipment sales and maintenance agreements and the waste handler will retain ownership of the output product for onward sale to the chemical sector.

 

5. Further reading

• European Commission, A Circular Economy for Plastics – insights from research and innovation to inform policy and funding decisions (2019)
• Closed Loop Partner, Accelerating Circular Supply Chains for Plastic (2019). A landscape of transformation technologies that stop plastic waste, keep materials in play and grow markets.
• An article, Chemical recycling of waste plastics for new materials production in Nature Review describes technologies available for sorting and recycling plastic solid waste into feedstocks, as well as state‑of‑the-art techniques to chemically recycle commercial plastic. (2017)
• CE100 and Ellen MacArthur Foundation Whitepaper: Enabling a circular economy for chemicals with the mass balance approach. An important milestone on the pathway to a circular economy is the mass balance approach for the chemical industry. By publishing a whitepaper, the Ellen MacArthur Foundation’s CE100 Network, including ISCC members Eastman and UPM, propose a mass balance approach with clear and predefined rules as a key way to facilitate and encourage the use of recycled materials (2018)
• WRAP Non-Mechanical Recycling of Plastic (Oct 2019) is a high-level market study into non-mechanical recycling technologies.

 

The content for this Plastipedia entry was kindly researched and supplied by Recycling Technologies in collaboration with the BPF..

 

Reference

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