Advanced Depth Filtration

The linear plastic lifecycle is unsustainable. Mechanical recycling of mixed plastic waste remains challenging, making chemical recycling necessary. Polyolefins, the largest share of plastic waste, can be chemically recycled through thermal pyrolysis. However, the impact of the feedstock type on pyrolysis oil composition remains unclear. Only very advanced analytical techniques allow to assess the detailed composition of these oils, which is crucial to evaluate their economic potential. Therefore, in this work, the hydrocarbon and oxygenate contents of three pyrolysis oils derived from postconsumer waste polyethylene, polypropylene, mixed polyolefins, and virgin polyethylene are characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry. Both positive-ion atmospheric-pressure photoionization and negative electrospray ionization were employed to identify oxygenates and hydrocarbons. It was found that the presence of trace polymers, metals, and polymer defects in postconsumer waste oils resulted in a higher fraction of complex polycyclic aromatic hydrocarbons compared to virgin pyrolysis oils. Furthermore, clear sources of oxygenates (polymer additives, trace polymers, or organic residues) could be identified in all four samples. Suspected thermal dissociation products of polymer additives such as Irganox 1010 and diethylhexyl phthalate (DEHP) were observed, indicating the various reactions occurring upon pyrolysis of these complex blends. The fact that a variety of additive-derived contaminants were found in pyrolysis oil from virgin polyolefins further indicates that pyrolysis oil contaminants do not exclusively accumulate during the plastics’ lifetime but could potentially be limited on the manufacturing side. This unprecedented level of molecular detail in the compositional analysis of plastic pyrolysis oils will aid in the development of improved recycling strategies, which can help close the loop to a circularized lifecycle for polyolefin waste.

Assessing the feasibility of chemical recycling via steam cracking of untreated plastic waste pyrolysis oils: Feedstock impurities, product yields and coke formation

Characterization and impact of oxygenates in post-consumer plastic waste-derived pyrolysis oils on steam cracking process efficiency

Chemical recycling of complex plastic waste via pyrolysis can reduce fossil resource dependence of the plastics value chain and greenhouse gas emissions. However, economic viability is crucial for its implementation, especially considering challenging waste streams with high shares of engineering plastics that have lower pyrolysis product quality than standard thermoplastics waste. Thus, this study conducts a techno-economic assessment determining the profitability factors of pyrolysis plants for automotive plastic waste in Germany including different plant capacities and calculating cost-covering minimum sales prices for the resulting pyrolysis oil. Main findings are that due to economies of scale, the cost-covering minimum sales prices vary between 1182 €/Mg pyrolysis oil (3750 Mg input/year) and 418 €/Mg pyrolysis oil (100,000 Mg input/year). The pyrolysis technology employed must be robust and scalable to realize these economies of scale. Large plant capacities face challenges such as feedstock availability at reasonable costs, constant feedstock quality, and pyrolysis oil quality, affecting pyrolysis oil pricing. Due to the limited yield and quality of pyrolysis oil produced from these technically demanding feedstocks, policy implications are that additional revenue streams such as gate fees or subsidies that are essential to ensure a positive business case are necessary. Depending on the assessed plant capacity, additional revenues between 720 and 59 €/Mg pyrolysis oil should be realized to be competitive with the price of the reference product heavy fuel oil. Otherwise, the environmental potential of this technology cannot be exploited.

Robust downstream technologies in polystyrene waste pyrolysis: Design and prospective life-cycle assessment of pyrolysis oil reintegration pathways

Plastics are engineering marvels that have found widespread use in all aspects of modern life. However, poor waste management practices and inefficient recycling technologies, along with their extremely high durability, have caused one of the major environmental problems facing humankind: waste plastic pollution. The upcycling of waste plastics to chemical feedstock to produce virgin plastics has emerged as a viable option to mitigate the adverse effects of plastic pollution and close the gap in the circular economy of plastics. Pyrolysis is considered a chemical recycling technology to upcycle waste plastics. Yet, whether pyrolysis as a stand-alone technology can achieve true circularity or not requires further investigation. In this study, we analyzed and critically evaluated whether oil obtained from the non-catalytic pyrolysis of virgin polypropylene (PP) can be used as a feedstock for naphtha crackers to produce olefins, and subsequently polyolefins, without undermining the circular economy and resource efficiency. Two different pyrolysis oils were obtained from a pyrolysis plant and compared with light and heavy naphtha by a combination of physical and chromatographic methods, in accordance with established standards. The results demonstrate that pyrolysis oil consists of mostly cyclic olefins with a bromine number of 85 to 304, whereas light naphtha consists of mostly paraffinic hydrocarbons with a very low olefinic content and a bromine number around 1. Owing to the compositional differences, pyrolysis oil studied herein is completely different than naphtha in terms of hydrocarbon composition and cannot be used as a feedstock for commercial naphtha crackers to produce olefins. The findings are of particular importance to evaluating different chemical recycling opportunities with respect to true circularity and may serve as a benchmark to determine whether liquids obtained from different polyolefin recycling technologies are compatible with existing industrial steam crackers’ feedstock.

Increasing recycling rates of plastic waste is necessary to achieve a sustainable and climate-neutral chemical industry. For polyolefin waste, corresponding to 60% of plastic waste, chemical recycling via thermal pyrolysis is the most promising process. However, the hydrocarbon composition of these pyrolysis oils differs from conventional fossil-based feedstocks as they are heavier and more unsaturated. GC × GC-FID is the most prevalent characterization method for the analysis of these complex hydrocarbon mixtures but fails to discern heavy unsaturated, aromatic compounds. An up-and-coming technique to fully characterize those analytically challenging heavy fractions is ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with soft ionization techniques, such as atmospheric pressure photoionization and atmospheric pressure chemical ionization. In this work, FT-ICR MS has been employed to analyze both real PE and PP postconsumer waste pyrolysis oils, which allowed to provide additional insights into the pyrolysis reaction pathways of both polyolefin types. FT-ICR MS identifies heavy hydrocarbons, up to C85, and discerns a wide range of complex polycyclic aromatic hydrocarbons with up to seven aromatic rings. These hepta-aromatics were not found in PP, which only revealed penta-aromatics; this complies with the reaction mechanism proposed in the literature. Moreover, the polypropylene (PP) pyrolysis oil displayed clear signs of depolymerization reactions occurring during pyrolysis, both for the formation of olefins and diolefins. Here, FT-ICR MS identified heavier, unsaturated, and highly aromatic hydrocarbons, whereas GC × GC-FID quantified saturated and less complex unsaturated components. These observations highlight the added benefit of combining GC × GC-FID and FT-ICR MS data to completely characterize plastic pyrolysis oils and understand pyrolysis reaction pathways.

Mixed plastic packaging waste sorting residue (MPO323) was treated by thermal pyrolysis to utilize pyrolysis oil and char. The pyrolysis oil was found to contain aromatic and aliphatic hydrocarbons. The chlorine and bromine contents were as high as 40,000 mg/kg and 200 mg/kg, respectively. Additionally, other elements like sulfur, phosphorous, iron, aluminum, and lead were detected, which can be interpreted as impurities relating to the utilization of oils for chemical recycling. The pyrolysis char showed high contents of potentially active species like silicon, calcium, aluminum, iron, and others. To enhance the content of aromatic hydrocarbons and to reduce the level of contaminants, pyrolysis oil was reformed with the corresponding pyrolysis char to act as an active material in a fixed bed. The temperature of the reactor and the flow rate of the pyrolysis oil feed were varied to gain insights on the cracking and reforming reactions, as well as on performance with regard to decontamination.

Contaminant removal from plastic waste pyrolysis oil via depth filtration and the impact on chemical recycling: A simple solution with significant impact

The hypothesis that was tested in this task was that separation of char, with its associated mineral matter from pyrolysis vapors before condensation, will lead to improved oil quality and stability with respect to storage and transportation. The metric used to evaluate stability in this case was a 10-fold reduction in the rate of increase of viscosity as determined by ASTM D445 (the acceleratedaging test). The primary unit operation that was investigated for this purpose was hot-gas filtration. A custom-built heated candle filter system was fabricated by the Pall Corporation and furnished to NREL for this test campaign. This system consisted of a candle filter element in a containment vessel surrounded by heating elements on the external surface of the vessel. The filter element andhousing were interfaced to NREL's existing 0.5 MTD pyrolysis Process Development Unit (PDU). For these tests the pyrolysis reactor of the PDU was operated in the entrained-flow mode. The HGF test stand was installed on a slipstream from the PDU so that both hot-gas filtered oil and bio-oil that was not hot-gas filtered could be collected for purposes of comparison. Two filter elements from Pallwere tested: 1) porous stainless steel (PSS) sintered metal powder; 2) sintered ceramic powder. An extremely sophisticated bio-oil condensation and collection system was designed and fabricated at NREL and interfaced to the filter unit.

Pyrolysis oil from used plastics and bio-based feedstocks are alternative feeds to traditional fossil feedstock. The pyrolysis oils and bio-based feeds are converted into olefins and other valuable chemical products that are used for the production of circular products. Circular and renewable polymers have identical properties to virgin-based polymers and allows plastics to be recycled repeatedly, without loss of quality. Certification via audited systems ensures that each ton of recycled or renewable feedstock is counted once only. The produced virgin polymers (PE, PP, and PC) are part of the SABIC's TRUCIRCLE™ portfolio and represent a considerable milestone on the journey toward closing the loop and creating a circular economy for plastics. This chapter describes some of the technical challenges encountered by SABIC during the implementation of the production of chemically recycled circular polymers.

On November 28, 2022, LyondellBasell and Audi announced a first-time collaboration to help close the loop for mixed automotive plastic waste. Audi is installing plastic seatbelt buckle covers in the Q8 e-tron made using LyondellBasell plastic that supports the sourcing of feedstocks from mixed automotive plastic waste. Plastic components from customer vehicles that can no longer be repaired are dismantled, shredded, and processed by chemical recycling into pyrolysis oil. The pyrolysis oil is then used as a raw material in LyondellBasell's manufacturing process for the production of new plastics, replacing virgin fossil feedstocks. The recycled content is attributed to the Audi product via a mass balance approach.

Due to the significant increasing in motorization, the long term sustainable utilization of End-of-Life Vehicles (ELV) wastes is in the focus of the waste management. In the European Union annually 8-9 Mt of ELV waste should be utilized. ELV contains mainly metals but its 15 - 20 % is plastics or rubber. According to the 2000/53/EC directive, from 1 January 2015, 95 % of the waste from vehicles have to be utilized; 85 % of the wastes by mechanical recycling and 10 % of the wastes by chemical recycling. The chemical recycling results valuable products from ELV plastic wastes, such as fuels, oil and hydrocarbon gases, which can be utilized as a feedstock for energy generation, for petrochemical processes or even in oil refinery. Mixture of real ELV waste plastic was pyrolyzed in a one-stage and a two-stage reactor in the presence of zeolite catalysts at 425 °C in the first reactor. Different modified ZSM-5 catalysts were synthesized by wet impregnation and tested in the first reactor: H/ZSM-5, Fe(III)/ZSM-5, Ni/ZSM-5 and Cu/ZSM-5. In case of two- stage pyrolysis, Ni/Mo-Al2O3 was used in the second reactor. Due to avoid the formation of harmful by- products, the pyrolysis was taken under inert nitrogen atmosphere. The composition of gases was analysed by GC. Higher yield of gaseous products was measured using catalyst in the second reactor; furthermore the hydrogen yield was also higher. Pyrolysis oil was measured by GC, HPLC or even FTIR. Regarding pyrolysis oils, they contain non-branched, branched aliphatic hydrocarbons and aromatics compounds; and significant isomerization was concluded over catalysts.

The conversion of waste plastics and tires via pyrolysis to pyrolysis oil represents one of the most promising ways of chemical recycling. Determining aromatics in pyrolysis oils from these feedstocks is crucial for their utilization as both petrochemicals and fuels. In this study, we compared three standard methods commonly available in refinery laboratories (ASTM D1319 − FIA, EN12916 − HPLC-RI, ASTM D8396 − GC × GC-FID) for analyzing aromatic content across a wide range of waste plastic pyrolysis oils, their middle distillate fractions, and hydrotreated products. Using model compounds, we explained most of the observed differences in aromatic content determined by these methods. HPLC-RI and FIA resulted in significant errors. For instance, the FIA reports some dienes and heterocompounds as aromatics. The results from HPLC-RI showed that monoaromatics are overestimated, while polyaromatics are underestimated. Among the tested methods, GC × GC-FID provided the most reliable results.

Chemical recycling of plastic waste: Bitumen, solvents, and polystyrene from pyrolysis oil