Beyond Mechanical Recycling: Giving New Life to Plastic Waste

Abstract Increasing the stream of recycled plastic necessitates an approach beyond the traditional recycling via melting and re‐extrusion. Various chemical recycling processes have great potential to enhance recycling rates. In this Review, a summary of the various chemical recycling routes and assessment via life‐cycle analysis is complemented by an extensive list of processes developed by companies active in chemical recycling. We show that each of the currently available processes is applicable for specific plastic waste streams. Thus, only a combination of different technologies can address the plastic waste problem. Research should focus on more realistic, more contaminated and mixed waste streams, while collection and sorting infrastructure will need to be improved, that is, by stricter regulation. This Review aims to inspire both science and innovation for the production of higher value and quality products from plastic recycling suitable for reuse or valorization to create the necessary economic and environmental push for a circular economy.


Process: Take away messages:
A review on pyrolysis of plastic wastes [1] (March 2016) Energy Conversion and Management 1,2,3,4,5,6 Pyrolysis -fluidised bed has the greatest economic potential for pyrolysis of plastic -microwave-assisted pyrolysis offers benefits although inconsistent dielectric properties mean real waste streams are difficult to handle -measurable impact of various carrier gasses with H2 producing the least coke and Ar the most with the opposite trend in olefin production A review on tertiary recycling of high-density polyethylene to fuel [2] (May 2011)

Resources, Conservation and Recycling 2
Pyrolysis -reaction pathways are temperature dependent highlighting importance in understanding heat and mass transfer limitations -a wide variety of catalysts have been tested, each giving different product distributions Chemical recycling of plastics using sub-and supercritical fluids [3] (October 2008) The Journal of Supercritical Fluids 1,2,4,7 Solvolysis -supercritical 'solvents' allow for chemical recycling of certain crosslinked polyethylene (thermoset) without depolymerisation -supercritical conditions can allow for almost 100 % monomer recovery from PET Chemical recycling of waste plastics for new materials production [4] (June 2017) Nature Reviews Chemistry 1,2,3,4,5,6,7 Solvolysis, Pyrolysis -Hurdles to commercialization are financial incentives and catalyst effectiveness -Unique issues with each type of plastic highlighting the importance of reducing mixed polymer plastics -Progress in design for recycling of polymers will facilitate chemical recycling Current state and future prospects of plastic waste as source of fuel: A review [5] (June 2015) Renewable and Sustainable Energy Reviews 2,4,5 Pyrolysis -generally for PO pyrolysis: -thermal pyrolysis occurs through free radical mechanism -catalytic pyrolysis proceeds through carbonium mechanism -importance of pre-treatment prior to pyrolysis for high quality fuel products Developing Advanced Catalysts for the Conversion of Polyolefin Waste Plastics into Fuels and Chemicals [6] (July 2012) ACS Catalysis 2,4,5 Pyrolysis -importance of accessibility of acid sites, promoted through large pore size or increasing surface area through decreased catalyst crystal size -further study into deactivation and regeneration of catalysts need to be better understood -two-step process holds great potential decoupling impurity removal/pre-processing with catalytically sensitive product formation -large list of potential catalysts given Fuels from Waste Plastics by Thermal and Catalytic Processes: A Review [7] (October 2008) Industrial and Engineering Chemistry Research 2,3,4,5, 6 Pyrolysis -reactor type and operating mode has large influence on product distribution due to heat and mass transfer limitations -two stage processing results in better quality fuel -the use of a solvent in the reactor can alter reaction mechanism and improve product distribution -recirculation and use of pyrolysis gas as fluidising gas promotes BTX formation in 600 -800 °C Hydrocracking of virgin and waste plastics: A detailed review [8] (April 2018) Renewable and Sustainable Energy Reviews 1,2,3,4,5,6,7 Hydrocracking -kinetics of hydrocracking and deactivation methods not well understood -dependence on plastic type for optimum process conditions PET Waste Management by Chemical Recycling: A Review [9] (September 2008) Journal of Polymers and the Environment 1 Solvolysis -Polyethylene terephthalate (PET) polymer is difficult to purify once formed, so recycling needs to yield a very pure monomer to allow for repolymerization -Large variety of PET available due to differing degrees of crystallinity -Risks that legislation aims at eliminating polymers that have highest potential for recycling, like PET Plastics to fuel: a review [10] (November 2015) Renewable and Sustainable Energy Reviews 2,3,4,5,6 Pyrolysis -work required to reduce costs associated with catalytic process -heating rates of plastic impact the product distribution -current legislation and economic driving forces do not create a market for plastic derived fuel oil Recycling and recovery routes of plastic solid waste (PSW): A review [11] (July 2009) Waste Management 1,2,3,4,5 Pyrolysis -various recycling methods complement each other, there is no single recycling solution at this stage Recycling of waste from polymer materials: An overview of the recent works [12] (October 2013) Polymer Degradation and Stability 1,7 Solvolysis -interesting suggestion that combining polymer types with 'compatibilizers' is the best option for mechanical recycling -how many rounds of recycling does this work for The valorisation of plastic solid waste (PSW) by primary to quaternary routes: From re-use to energy and chemicals [13] (October 2009) Progress in Energy and Combustion Science 1,2,3,4,5,6,7 Pyrolysis -important to design future plastics with recycling (mechanical or chemical) in mind -proper assessment of waste streams i.e. through LCA is vital to properly compare and develop waste processing techniques Thermal degradation of PVC: A review [14] (December 2015) Waste Management 3 -in HCl environment dechlorination is autocatalytic -additives, especially stabiliser, can have a large impact on dechlorination process Thermochemical routes for the valorisation of waste polyolefin plastics to produce fuels and chemicals. A review [15] (January 2017) Renewable and Sustainable Energy Reviews 2,4,5 Pyrolysis -Reactor design and process conditions crucial for tuning product distribution due to heat and mass transfer limitations in processing waste plastic -Importance of (acid) catalyst for reducing reaction temperatures Thermolysis of waste plastics to liquid fuel: A suitable method for plastic waste management and manufacture of value added products-A world prospective [16] (  [17] (April 2011) Waste and Biomass Valorisation 1,2,3,4,5,6 Pyrolysis -requirement for waste management legislation to keep up with waste production, processing methods and environmental targets -issues for industrialisation include, catalyst coking, fouling, HCl above 200 ppm -opportunities to crack plastic into suitable feed for industrial scale units Recycling of polyurethanes from laboratory to industry, a journey towards the sustainability [18] (April 2018) Waste Management 7 Solvolysis -single-phase glycolysis of polyurethane yields a variety of monomers that do not allow for reconstruction of flexible foams -split-phase glycolysis provides potential for recovery of monomers for flexible PU as well, although currently only developed to pilot scale due to costs of cleavage agent Catalytic pyrolysis of plastic waste: A review [19] (June 2016) Process Safety and Environmental Protection 1,2,3,4,5,6 Pyrolysis -geometrical limitations of catalysts result in wax formation on the surface of catalysts with smaller products (gasses) formed on the internal sites -pore clogging is an important factor to consider with limited trials focussing on regeneration of catalyst -deposits of impurities on the catalyst affect the activity but also remove these impurities from final product -contains a table (Table 4) with various catalysts and their effect on the pyrolysis products -investigation into cheaper and regeneration of catalysts to be investigated for industrial operation A review of polymer dissolution [20] (July 2003)

Progress in Polymer Science
None specifically mentioned

Dissolution
-increased molecular weight results in decreased dissolution rate (chain disentanglement is a function of Mw) -polydisperse samples have greater dissolution rate than monodispersed samples Solvent-based separation and recycling of waste plastics: A review [21] (June 2018) Chemosphere 1,2,3,4,5,6,7 Dissolution -Gives details of strong and weak solvents for the various polymer types.
-Solvent extraction from recycled polymer can cause damage to the polymer chain due to thermal stress.
-Dissolution of mixed polymer streams results in poorer separation of the target polymer.
-Future use of hazardous solvents should be reduced Mechanical and chemical recycling of solid plastic waste [22] (August 2017) -Overview and analysis provided of various commercial projects and their status Catalytic co-pyrolysis of lignocellulosic biomass with polymers: a critical review [23] (May 2016) Green Chemistry 1,2,3,4,5,6,7 Pyrolysis -discussion of synergistic effects on the mechanism between biomass and plastics -lists provided for results of non-catalytic ( Table  2) and catalytic (Table 4) co-pyrolysis -alkali metals from the biomass have significant impact on product distribution as they can catalyse the overcracking of the polymer chains Recycling of PVC wastes [24] (April 2011) Polymer Degradation and Stability 3 Mechanical, pyrolysis -usability of mechanically recycled PVC depends on its application (bottles performed very badly whereas pipes were acceptable) -processes that chemically modify the PVC prior to recycling have been developed but are generally more expensive than mechanical recycling   Table S8. List of companies and start-ups active in chemical recycling that are referenced in the CLP report [25] . Conclusively, saperatec process produces secondary raw material with high purity which has a positive carbon dioxide and energy footprint in comparison to virgin plastic material production.
From website: "The CreaSolv® Process does not fall into the classification "Chemical or Feedstock Recycling", because the chemical structure of the polymer chains remains unchanged, whereas chemical reactions produce other substances. The dissolution of plastics is a physical process, because the substance (plastic) only changes its physical state from solid to liguid, and this can also be reversed again. It is for this reason why the CreaSolv® Process has to be classified as "Physical Recycling"." Polystyvert has developed an innovative and profitable process that allows all forms of polystyrene (PS) to be recycled. Following a unique dissolution, purification, and separation process, the regenerated polystyrene resin is of very high quality, allowing many applications to incorporate 100% recycled materials, at a lower cost than virgin resin.
Executive Summary: Nexus is an operational, commercially-scaled 50 Ton/day plant (first of many) converting waste plastics to feedstocks, which in turn are converted back to virgin plastics. (100% circular). Process is environmentally friendly (no wastewater or air issues), end-to-end business including software, frontend handling, all regulatory requirements, training, strategic pricing/positioning guided by financially-driven metrics. Versus others' Nexus is 1/3'd Capex/ton, 6x more efficient, 20% higher, quality yield, and profitable after paying for plastics, at lower crudeindex pricing. Operational and economically proven, Nexus has been shipping tanker loads of offtake and has secured sources/stockpiles of plastics. Now shifting to rapid rollout of plants in US/Globally with ability to construct multi-100 ton/day plants on a jointly owned and operated basis with large strategic partners. (These technologies are not well suited for licensing at early stages given complex, PSLoop is working on the CreaSolv® Technology which is important to know in advance is a dissolution process so we are not breaking down the polymer into monomer so it's different to chemical recycling technologies. It is a physical recycling process for the polymer chain is not broken. It was developed by CreaCycle together with Fraunhofer IVV. It was developed already some years ago. We recycle PSfoam (EPS and XPS) that comes to us in a compacted form via our members that function as a HUB/collection point. We then shred the material and add a solution that dissolves the polystyrene and allows to filter out any impurities. By addition of an anti-solvent the PS-gel is formed and the HBCD will be in the solvent. Any solvent remaining is distilled and reintroduced in the process. The PS-gel is dried and extruded. The HBCD sludge is further treated at the Bromine Recovery Unit (BRU) of ICL IP which recovers the elemental bromine and safely destroys the HBCD. We focus on the legacy resource needs) Nexus is located 20 min from Atlanta airport.
HBCD which was included as flame-retardant in PS-foam insulation applications from 1960 -2015. HBCD is today classified as persistent organic pollutant. Incineration was the only treatment possible. PSLoop now offers a sustainable solution that preserves resources and closes the loop thus contributing to the circular economy.

2) What is your business case?
Saperatec is currently transforming from technology development to a recycling service provider (waste input material processed to secondary raw materials). Saperatec will sell secondary raw materials like recycled polyethylene which are obtained out of the Saperatec process.
The CreaSolv® Process is adapted to specific plastic waste streams by Fraunhofer IVV with CreaSolv® Formulations from CreaCycle. In case of a commercialization Fraunhofer IVV will license the technology and CreaCycle will supply the licensee with CreaSolv® Formulations as specified by Fraunhofer IVV.

Technology licensing business model
Recycling fails if not economic. Nexus is not a technology, but a business focused on resolving the plastics problem technically and economically on a sustained, scaled basis. Please see one-pager attached for more detail.
Start construction end of 2019, starting operation Q1 2021. Set up as a cooperative working with the whole PS value chain with 70 companies across 18 countries in the EU only take in PS from these companies. Current geographic focus for incoming material is in NL and Germany. Funding from EU, province of Zeeland, loans and contributions by members and supporters. It is more economical for companies to provide this PS to PSLoop rather than incineration. Sell product to members to produce new PS products.

3) How close are you to break-even?
Currently, Saperatec strives for industrialization of the technology, starting operation in mid 2021.
As Chemical Recycling the CreaSolv® Process is still in pilot stage with one pilot plant running and others to be built.
Operating profitability proven.
The XPS waste is a bit a more complicated because you also have blowing agents HCFCs which makes the XPS waste a hazardous waste. We are now in a working group working on pre-treatment technologies. Based on the Montreal protocol you have to capture the HCFCs with an efficiency of 95 %. Its then more lucrative to bring the hazardous waste to us than to incineration which is very expensive.

4) Do you use any patented technology?
We do not use any foreign technology which is protected by patents. In contrast, the saperatec technology is secured by patents.
Yes -our partner Fraunhofer as licensor does.
Polystyvert owns the recycling technology patents. Patent delivered in Canada and China. Notice of acceptance received for Europe, certificates will be received beginning 2020.
Nexus Intellectual Property protected by Trade Secret, not patents. Not our own, no. Pyrolysis was patented a long time ago (1960s) and patents have since expired.
CreaSolv® developed by CreaCycle and Fraunhofer. Fraunhofer is a partner of PSLoop. CreaCycle will provide the solvent for the plant.

5) Can you provide some details on your process:
From website: "On November 8, 2018 Unilever announced that the CreaSolv® Pilot plant is fully operational and they are ready to start examining the technical and commercial viability of this technology6). If successful the process will be commercialized and the technology will be made open source, available also to investors and competitors. The CreaSolv® Plant is designed for highquality polyethylene (PE) recycling, because 60% of the layers consist of this polymer. The recovered PE will be used for the production of new sachets. The energy consumption for the recycling of 6 kg PE is the same as for the production of 1 kg virgin polymer with the new technology, thus enabling a circular economy with a smaller environmental footprint. The facility currently processes approximately 3 tons sachet waste per day and Unilever invested approximately 10 Millionen Euros)."

c) by-products/ unwanted products
All fractions of the input material PE/Alu/PET will be products of the process. Most of the separation liquid will be recycled. The remaining chemical loss will be treated with state of the art and proven waste treatment technology in order to comply with all regulations.
Materials other than polystyrene; other polymers, other additives (ink, pigmentation for eg).
None. Nexus has a precycling section of the plant before conversion, to remove undesired plastics, metals. No air or water issues since the process is closed loop.
HBCD sludge, inerts, (H)CFCs from XPS (removed prior to processing ) Carbon black or graphite in the material can stain the final product but as new insulation foams are grey this is not relevant. Standardized analysis for 100 ppm HBCDrequirement for final product since there is currently no certified method for this. In some countries there is an agreement that above 1000 ppm it has to be treated through incineration or PSLoop process and in other countries its set at 100 ppm. Need to ensure that there is a market for the recycled product. Policies to stimulate the demand for recycled products in products would help. Make incineration and landfilling even less attractive.

d) type of process
policies which could lead to positive results.

9) In which country do you operate?
At the moment Germany/Europe. It is planned to move to other countries/continents after our first industrial plant is running smoothly and also extend to other application fields.
We are located in Germany but we consider our business to be global.
Demo plant in operation in Canada (Montreal, Qc). Future licensee users in Europe.
Currently US, going global. Netherlands and Germany, looking to expand across Europe following start-up of current facility. Already have contacts in France that are interested.

S3 Life Cycle Analysis of Chemical Recycling Processes
Transport related emissions from waste transport to the EoL facility is based on the Netherlands: -Municipal waste collection service: -50 km to sorting facility and municipal solid waste incineration (MSWI) -Transport by >32 tonne lorry using EURO 6 (RER) fuel: -150 km from sorting/shredding to EoL treatment plant -50 km waste from EoL treatment to MSWI -700 km to consumer Process energy consumption is estimated based on lab scale experiments (100 g) performed at TNO. The EcoInvent3 [26] database was used to estimate CO2 emissions from polymer production and packaging manufacture as well as multilayer and electronic products (Table S9-10). CO2 emissions from electricity are estimated based on a majority fossil-based electricity mix of the Netherlands. Table S10. Assumptions regarding material efficiency, product quality and energy consumption for the different EoL analysed in the life cycle analysis for the different plastic waste streams (1 tonne of plastic waste = 710 kg plastic). Process energy consumption is estimated based on lab scale experiments (100 g) performed at TNO. The EcoInvent3 [26] database was used to estimate CO2 emissions from polymer production and packaging manufacture as well as multilayer and electronic products.

S4.1 Method
For performing this particular analysis a script was developed using the programming language python (packages: json, requests, pandas, codecs, BeautifulSoup, glob, re, numpy, string, nltk). A keyword search in title abstract and author keywords '{chemical recycling} AND plastic' was performed using the Scopus application programming interface (API) yielding 369 initial results. From these initial results, keywords provided by the authors were extracted. The initial 369 research articles were filtered for reviews and the references provided in these reviews were used to extend the list of relevant research articles. For the list of research articles extended in that way, a full-text search was conducted using the Sciencedirect API with access through the network of the University of Utrecht. This way, full-texts of 474 research articles were obtained. and searched for the list of relevant keywords. The list of relevant keywords was compiled by filtering the author keywords for words ending in 'lysis' 'nation' and 'cracking' for process types. For polymer types words containing 'poly' were assembled and for polymer abbreviations words containing 'p' and being no longer than