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Chemical Deconstruction & Upcycling of Polymer Waste:
08:00am - 12:00pm USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Konstantinos Alexopoulos, Organizer, Presider; Susannah Scott, Organizer, Presider; Hilal Ezgi Toraman, Organizer, Presider
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person
Division/Committee: [CATL] Division of Catalysis Science & Technology

In current paradigms, most polymers (particularly plastics) are used once and disposed, whereafter they accumulate in the environment. A better vision is that of a circular economy, wherein we reclaim carbon in waste polymers, recycle to produce virgin-quality polymers, or upcycle it to produce value-added commodities. Key steps in this sustainable approach are the deconstruction of waste polymers into basic chemical building blocks, and the conversion of those building blocks into fungible products. This symposium focuses on emerging thermochemical and catalytic technologies and the supporting research topics that enable polymer reclamation. We welcome contributions in applied and fundamental catalysis; analysis and modelling of the complex reaction networks arising in polymer deconstruction; and systems level analyses that consider the economic and environmental impacts of emerging technologies. This symposium will foster cross-pollination of knowledge used for developing polymer waste conversion processes.

Monday
3754706 - From recycling to upcycling of plastic waste with catalysis
08:00am - 08:40am USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Bert Weckhuysen, Presenter
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person
After a period with a lot of fundamental research and development aimed - started from the 1950s when both Ziegler-Natta and Phillips catalysts were discovered - at improving the production and durability of a wide variety of plastics, research has recently refocused on efficiently degrading and repurposing plastics. This invited talk focusses on breaking the chemical bonds of the most important polymers, such as polyethylene, polypropylene, polyurethane and polystyrene, with the aiml of making new molecules from it that could incentivize the chemical industry to recycle more plastic waste in the years to come. In particular, we summarize the varous catalytic routes currently available or developed. These methods are compared with each other and with traditional recycling via melting and re-extrusion. This work reveals the promise, but also the relative infancy of the field of plastic waste recycling and upcycing. While, there is much knowledge that can be transferred from the established field of catalytic conversion of crude oil and natural gas, including cataltyic cracking and hydrocracking, unique challenges arise from the sheer size of the polymer molecules and contaminations, such as metal poisons as well as plastizers, in real plastic waste streams which are different from what is found in traditional feedstocks for the chemical industry. The potential use of non-traditional chemo-catalytic routes to tackle these important issues, e.g. using less explored solvents, electro-, photo- and mechano-chemistry is discussed. Based on this knowledge, we propose a generic approach of assessing processes proposed in recent literature with respect to sustainability, economic viability and their potential to convert high volumes of plastic waste as these aspects will be essential to implement such processes.
Monday
3737112 - Selective conversion of mixed polyolefins to valuable base chemicals
08:40am - 09:00am USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Kevin Van Geem, Presenter
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person
Unprecedently high olefin yields were obtained with a phosphorous-modified conventional and mesoporous HZSM-5 zeolite. They were demonstrated to be suitable catalysts for producing valuable base chemicals from different virgin and post-consumer waste polyolefins. After steam treatment at 800 °C, the acidity of the catalysts was reduced to ~0.10-0.15 mmol NH3/g, resulting in a lower activity. However, these catalysts can be considered stable under reaction and regeneration conditions which are not expected to exceed 700 °C in the process of cracking plastics pyrolysis vapors. Varying the catalyst/feed ratio between 10 and 80 and the catalyst temperature between 500 and 700 °C affected the proportion of different monomer products. This provides great flexibility for plant operators to steer the product slate towards the highest market demand and maximize C4 olefins, ethylene, propylene, or aromatics production, all while keeping carbon losses to CH4 and coke low, below 1.5% and 0.5 %, respectively.
The yield structure obtained from a synthetic polyolefins mixture of LLDPE, LDPE, HDPE and PP matched the relative contributions of the single polymers, and an extremely high monomer yield of 84 wt. %, i.e., 79 wt. % C2-C4 olefins and 5 wt. % aromatics was obtained. When using post-consumer MPO feed, the monomer yield was slightly lower with 74 wt. % C2-C4 olefins and 9 wt. % aromatics, and this is attributed to the higher aromatics content in the feed from PS and the presence of some PET.
While parent HZSM-5 rapidly deactivated and showed a high coking propensity (27 µg of coke /m2 catalyst), HZSM-5 that was modified with 2 wt. % P and steam treated at 800 °C showed almost no deactivation during 130 runs with stable conversion of C5+ aliphatics and high C2-C4 olefins selectivity with a much lower coke deposition of 8 µg/m2.
Finally, the studied catalytic process constitutes a sustainable alternative process for plastic waste valorization since it leads to about an order of magnitude (0.3 versus 3.1 kg CO2-eq./kgplastics) lower environmental burden than the current practice of incineration.

Monday
3753175 - Application of pulse-heated analysis of solid reactions (PHASR) to promote a circular plastic economy: Intrinsic kinetics of polypropylene pyrolysis
09:00am - 09:20am USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person
Over the past several decades, there has been a rapid and continual growth in global polymer production due to the increasing demand for plastics in modern life. This growth in plastic production has resulted in billions of tons of plastic waste, the majority of which has been discarded in landfills or the environment. Accounting for almost 20% of global plastic production, polypropylene is a material of primary importance. To achieve a circular plastic economy, wherein end-of-life plastics are recycled in a closed loop recreating the original polymers with complete fidelity, a new approach to plastic waste management is needed. Pyrolysis has high potential as a technology to promote a circular plastic economy, by which polymers are thermally cracked to their constituent monomers. The mechanisms of polymer pyrolysis are highly complex and the quantification of the kinetics of pyrolysis remains a challenge. In this work, the ‘pulse-heated analysis of solid reactions’ (PHASR) method has been applied to polypropylene pyrolysis. The PHASR reactor is uniquely capable of measuring the intrinsic kinetics of polypropylene pyrolysis with millisecond scale resolution at temperatures up to 700 °C. Polypropylene pyrolysis was also studied using a Visual PHASR experimental system, which allows for direct observation of pyrolysis reactions via high speed photography. This work validates the ability of the PHASR reactor to pyrolyze polypropylene under isothermal, kinetically limited conditions, presenting yield vs. reaction time data and intrinsic lumped kinetics. In addition, visual analysis of polypropylene pyrolysis, with highlighted reaction phenomena, is shown with comparison to experimental results. These insights into polypropylene pyrolysis will help to enable the development of more efficient industrial pyrolysis reactors and ultimately a circular plastic economy.
Monday
3740921 - Single-batch, mixed plastic depolymerization by a highly efficient organocatalyst
09:20am - 09:40am USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person
Synthetic polymers have been widely used in our daily life; however, their accumulation as plastic waste and associated environmental pollution present a significant challenge to be solved. Chemical deconstruction of commodity plastics is an emerging chemical path to convert discarded plastics to fuels, refinery feedstocks, monomers, chemicals, and upcycled materials. Organocatalysts provide promising “green” routes for polymer deconstruction since the catalyzed depolymerization reactions yield highly pure small molecules that are adequate for subsequent polymerizations or other uses. However, most organocatalysts have been designed to depolymerize a specific type of polymer. Herein, we report a new organocatalyst and integrated process for depolymerization of mixed plastics to high-value chemicals. Our catalyst enabled glycolysis with more than 95% conversion to monomer within 2 hours using 1/10 of the catalyst and half of ethylene glycol compared to the conventional organocatalysts. Furthermore, this catalyst accomplished one pot, single batch selective glycolysis of diverse mixed plastic consumer products, which paves the way to increase commercial viability by eliminating costly mixed plastic sorting.
Monday
3748266 - Highly efficient and selective polyolefin upcycling by hydrogenolysis over disordered, sub-nanometer Ru structures on CeO2
09:40am - 10:00am USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person
Plastics play irreplaceable roles in a wide range of industries and are produced on a large scale. Nonetheless, the low recycle rate and resistance towards degradation of the plastic waste pose severe threats to the environment. Therefore, technologies that effectively upcycle plastics into small, valuable hydrocarbons are in urgent demand. One viable strategy is metal-catalyzed hydrogenolysis, for which Ru/CeO2 is known one of the most effective catalyst composition. In this work, we discovered that low-loading (≤ 0.25 wt%) Ru/CeO2 exhibits remarkable catalytic performance in the hydrogenolysis of polypropylene (PP), polyethylene (PE), and a model alkane n-C16H34, which is significantly superior to high-loading (≥ 0.5 wt%) Ru/CeO2. They possess high PP conversion efficiency (7-fold increase over current literature reports), low selectivity towards undesired CH4, and good isomerization ability. In the low-loading range, the intrinsic activity of Ru in PP hydrogenolysis increases as the particle size decreases, opposite of the trend in the high-loading range. Detailed characterization revealed that the abrupt changes in catalytic behaviors coincide with Ru species transitioning from well-defined to highly disordered structures in the low-loading domain. The disordered Ru species were shown to be sub-nanometer in size and cationic. Mechanistically, the regioselectivity and the rate dependence on hydrogen pressure of C−C bond cleavage are different on low- and high-loading Ru/CeO2, both explained by the higher coverage of adsorbed hydrogen (*H) on low-loading Ru/CeO2. This work uncovers the remarkable catalytic performance of highly disordered, sub-nanometer, cationic Ru species in polyolefin hydrogenolysis, opening immense opportunities to develop effective, selective, and versatile catalysts for plastic upcycling.
Monday
Intermission
10:00am - 10:20am USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person

Monday
3729131 - Chemical recycling of waste plastics to fuels and chemicals
10:20am - 10:40am USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Leilei Dai, Presenter
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person
Plastic materials are extremely popular all over the world and used in the different walks of life due to the inherent properties of being strong, lightweight, and easily shaped. However, the vast majority of waste plastics ever produced enters into landfills or our ecosystems, creating a plastic waste crisis. Developing an effective pathway to remove waste plastics from landfill and incineration plants and create a circular economy requires a more appropriate technology beyond the conventional mechanical recycling by melting and re-molding. Pyrolysis has shown the great potential of plastic recycling for energy, fuels, chemicals, and materials production, enabling the plastic wastes to stay in the economy and out of the environment (Figure 1).
Although catalytic pyrolysis of plastics to naphtha substitute for new plastic manufacturing can contribute to the plastic circular economy, mitigating catalyst deactivation in the large-scale process is a critical challenge. Therefore, we demonstrate that catalyst lifetime during catalytic cracking can be remarkably improved (4.3× to 12.3×) without significant effects on C5-C12 aromatics selectivity by using hierarchically micro-meso-macropore high silica ZSM-5 compared with the conventional analogue at the same conditions. The lifetime improvement by using the well-developed hierarchical ZSM-5 can be rationalized based on the more open channels that promote the diffusion of reaction intermediates and the increase of Brønsted acid sites that catalyze the cracking reactions. Furthermore, the economic and life cycle assessments show that the plastic-to-naphtha route can improve the environmental benefits of plastic recycling, with a great economic potential. These outcomes highlight the potential of creating a plastic circular economy and will move the technology closer to commercial implementation.

Monday
3734787 - Metathesis, molecular redistribution of alkanes, and the chemical upgrading of low-density polyethylene
10:40am - 11:00am USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person
Catalytic alkane metathesis—comprising tandem (de)hydrogenation and olefin metathesis—is a promising technology for polyethylene (PE) upgrading due to its molecular redistribution capability. However, the use of rhenium oxide catalyst for olefin metathesis reaction in the upgrading of PE has limited the economical feasibility because rhenium oxide is costly and cannot be applied at high temperatures where reaction kinetics are most favorable due to its high volatility. Herein, a new strategy for polyethylene (PE) deconstruction via alkane metathesis is presented, in which the olefin metathesis reaction step is catalyzed by a relatively less expensive WOx/SiO2 catalyst (price ratio; rhenium/tungsten = 24). Zeolite A adsorbent acts as an essential component to protect the metathesis active sites from poisoning by in-situ-generated oxygenates in a batch reaction system. High conversion of 1-hexadecene (96%) and n-hexadecane (92%)—surrogates of long-chain molecules—demonstrate the high reactivity of WOx/SiO2 metathesis catalyst for olefin and alkane metathesis reactions, respectively, at moderate reaction temperatures of 300 °C for 2 to 3 h. Pretreatment temperature and length of the short n-alkane-chain solvent have significant effects on the metathesis reactivity and selectivity, and the effects of other parameters such as inert gas pressure, operation time, and ratio or catalysts are also investigated. Results for the deconstruction of low-density PE (LDPE) in n-decane demonstrate a remarkable potential for PE upgrading with advantages of short reaction times (3 h), low mass ratio of solvent to LDPE, and production of solid products with narrow molecular weight distributions.
Monday
3741620 - Polyolefin depolymerization over silica-alumina-based catalysts: benchmarking activity for insight gathering and rational catalyst design
11:00am - 11:20am USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Wei-Tse Lee, Presenter
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person
As versatile packaging- and textile-materials, plastics have reshaped our daily lives for our convenience. However, the sheer quantity of single-use plastic production and mismanagement of the resulting plastic waste also leads to major environmental concerns. A more sustainable future can be foreseen with a significant increase of chemical recycling for the end-of-use plastics, either into platform chemicals as energy carriers, or into their original building blocks, thereby closing the loop for plastic material circulation. The knowledge and studies upon plastic chemical recycling are key to advancing the development of catalytic processes toward sustainability.
The initial phase of our research centered around the development of efficient catalysts for polyolefin (polyethylene, PE, and polypropylene, PP) depolymerization, Ruthenium-nanoparticles immobilized on Zeolite-X was first investigated as catalysts for the deconstruction of n-dodecane (nC12), which was used as a model substrate to simulate the reactivity of polyolefin materials under a hydrogen atmosphere. This facilitated us to optimize the Ru metal loading, to trace kinetics, and to study the reaction mechanism (assisted by density-functional theory computations). The optimized catalyst was further employed to transform PE, PP and mixed plastics (PE + PP + polystyrene, PS) and afforded gas streams that are compatible with current natural gas grids.
Further studies focused on understanding the underlying C-C bond cleavage pathways of hydrocarbons (alkanes, polyolefins, etc.) through benchmarking of catalytic activity in a more systematic manner. First, precisely categorizing different catalytic C-C bond cleavage mechanisms was conducted via the deconstruction (under hydrogen) of n-hexadecane (nC16) with selected experimental parameters, i.e., types of zeolite structures, metal modifications and the reaction temperatures. Benchmarking reaction conditions for catalytic activity were then determined. A catalyst-activity diagram was then proposed to index the tested catalysts and to accommodate more data points resulting from the benchmarked nC16 deconstructions, enabling a systematic reactivity comparison across multiple variables. Such a strategy allowed us to identify parameters for the activity of interest of any zeolite-based catalyst and further fast-forward the optimization process of catalyst design.

Monday
3740390 - Catalytic depolymerization and upcycling of poly(lactones) into acrylic acid and other chemical building blocks.
11:20am - 11:40am USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person
Polymer recycling has received increased attention of the past years to provide a necessary solution to solve the accumulation of post-consumer waste in the environment. For mechanical recycling, this often leads to downgraded plastics with different properties compared to the virgin plastic material. Chemical recycling on the other hand provides a viable solution to convert the polymer waste directly back into its original monomeric precursor. Biopolymers already provide a partial solution to the environmental problem. Poly(lactic acid) (PLA) is often considered to be one of the most promising solutions since it is both biobased and – in an industrial composting facility – biodegradable. Longer poly(lactones), e.g. poly(caprolactone) (PCL), recycled back into their monomeric equivalent using reversible ring-opening depolymerization. However, up until today, no clear chemical procedure has been found to convert PLA back into monomers, namely lactide.
Here, we developed a new method to convert poly(lactones) into chemical building blocks using phosphonium ionic liquids (IL) as a solvent in combination with a bromine catalyst. Depending on the reaction time and applied temperature the PLA can be converted in either Lactides or Acrylic Acid (AA). Kinetic studies showed that after dissolution of the PLA in the IL, the Br-mediator allows for fast rearrangement to the lactide dimer intermediate (>40% yield after 30 min). Under the applied reaction conditions, the lactide is converted further into AA as the final depolymerization end product. After optimization of the reaction parameters, we managed to obtain >60% AA yield directly from (post-consumer) PLA with mass balances ranging from 80-95%. Other side-products are mainly lactic acid and ethylene from rehydration and decarboxylation of the AA, respectively. In addition, poly(caprolactone) could be converted to hexenoic acids (>50% yield), which in their turn could be converted into pimelic acid as potential polyamide precursor.
With this work we provide a green solution to the recycling of plastic waste converting into interesting platform chemicals for the polymer industry. The use of green, easily recyclable ionic liquids as both the catalyst and solvent makes this one of the most promising routes towards waste stream upcycling.

Monday
3755050 - Applications of electrocatalytic functionalization of C–Halogen bonds for small molecule and macromolecule modification
11:40am - 12:00pm USA / Canada - Central - August 22, 2022 | Location: W187a (McCormick Place Convention Center)
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - In-person
Electroreductive methodologies for C-X bond functionalization have become an attractive way to form C-C bonds from a variety of aryl and alkyl electrophiles. Electrochemistry provides the ability to finely tune the redox potential of a reaction and selectively activate a desired substrate. This work describes the use of electrochemistry for the activation and functionalization of challenging C(sp3)-X bonds. While organometallic complexes that exhibit reactivity towards these electrophiles typically have extremely negative redox potentials, electrochemistry can be used to easily access the specific voltages required for catalyst activation. By doing so, alkyl radicals can be generated and subsequently coupled with a variety of radical acceptors. This methodology can be applied to larger and more complex substrates such as paraffins and polymers that currently have no efficient means of being recycled. Installing functionality onto these materials yields new structural properties that increase the recyclability and reusability of the compounds.