Conversion Of Waste Plastics Research Articles

Oxidative Conversion of Polyethylene Towards Di-Carboxylic Acids: A Multi-Analytical Approach.

To reduce the pressure on the environment created by the increasing amount of plastic waste, the need to develop suitable plastic recycling methods has become more evident. However, the chemical recycling toolbox for polyethylene (PE), the most abundant type of plastic waste, remains underdeveloped. In this work, analytical methods were developed to explore the possibility to oxidatively convert PE into di-carboxylic acids as reaction products. A multi-analytical approach including gas chromatography-mass spectrometry, gas chromatography-flame ionization detection, several (2D) nuclear magnetic resonance methods as well as in-situ transmission infrared spectroscopy was used. This led to a thorough qualitative and quantitative analysis on the product mixture, which extends and clarifies the existing literature. Without a catalyst (thermally) already up to 7 mol % di-carboxylic acids can be formed. Furthermore, it was found that the majority of the oxidized functionalities are carboxylic acids, (methyl) ketones, γ-lactones, γ-ketones and esters. An intra-molecular hydrogen shift seemed key in the cleavage step and the formation of late-stage side products. In addition, crosslinking reactions due to esterification reactions seem to limit the di-carboxylic acid yield. Therefore, these two handles can be taken into account to study and design similar (catalytic) systems for the oxidative conversion of plastic waste.

Utilization of fuel energy from single-use Low-density polyethylene plastic waste on CI engine with hydrogen enrichment – An experimental study

An effective strategy to reduce global waste is to convert the waste into Energy effectively. Single-use Low-density polyethylene (LDPE) plastic waste poses an environmental challenge by slower decomposition. Pyrolysis is one of the best techniques for converting waste plastics into Waste Low-density polyethylene pyrolysis oil (WLPO), a useful energy source similar to diesel. Operating an engine directly with neat WLPO lowers the performance and increases carbon monoxide, unburnt hydrocarbons, and smoke emissions than diesel. Hence, to enhance the performance and emission characteristics of the engine operating with WLPO dual fuel mode, different flow rates of hydrogen induction from 3 to 12 lpm were studied. The results were compared with diesel and neat WLPO. 12 lpm of hydrogen induction shares 15.19 % of hydrogen energy in combustion for WLPO. Compared to neat WLPO, 12 lpm hydrogen induction has a percentage increase of 22.89 in brake thermal efficiency, 15.88 in peak pressure, 60.85 in heat release rate, and 61.46 in Nitrogen oxides, as well as a percentage decrease of 53.42 in smoke, 48.94 in carbon dioxide, 53.99 in unburnt hydrocarbons, and 86.86 in carbon monoxide. Also, these are all similar to and better than the neat diesel operation except for the NOx emission. The hydrogen induction with WLPO increases the engine performance and reduces the smoke and carbon emissions. This fuel usage with hydrogen in IC engines indirectly supports LDPE plastic waste reduction by utilization and reduces objectionable emissions.

Sosialisasi Pembuatan Mesin Pirolis Plastik Sederhana sebagai Alat Pengolah Sampah Plastik Menjadi Bahan Bakar Minyak di Desa Lopo Kabupaten Gorontalo

Garbage is something that humans throw away because it can no longer be used. An environment with a buildup of garbage can cause various problems such as hygiene, health, beauty, environmental pollution, and social issues. One of the problems regarding waste is located in Lopo Village-Gorontalo District. Garbage is thrown away and then burned, especially plastic waste. The combustion results can undoubtedly pollute the environment. This happens due to the need for more guidance and community empowerment in recycling waste into something that can be useful. One of the solutions for handling waste into something that can be useful is to convert plastic waste into fuel oil through the socialization of making a simple plastic pyrolysis machine. This socialization activity provides an understanding of waste and its impact on the environment, methods of waste management, and how to make a simple plastic pyrolysis machine. The participants were very enthusiastic about participating in this socialization because they learned how to process plastic waste into fuel and make simple plastic pyrolysis machines that can be products of high economic value

PRODUCTION OF PLASTIC INCORPORATED CONCRETE AND STABILIZED MUD BLOCK

Rapidly escalating plastic consumption has led to a significant surge in plastic waste, causing notable repercussions for environmental well-being due to the non-biodegradable nature of plastics. In order to mitigate the environmental impact of plastic, it is imperative to explore alternative approaches to recycling plastic. In the present day, several industries repurpose plastic waste to create a wide array of products, including domestic items, clothing, household materials, textiles, construction elements, and even convert waste plastic into fuel. Among these options, the utilization of plastic waste in the creation of building materials has garnered significant focus. This practice not only reduces the amount of plastic waste discarded as litter or sent to landfills but also diminishes the necessity for mining raw materials used in construction. This, in turn, contributes to mitigating the adverse environmental impacts associated with the construction industry. Within this endeavor, the initiative involves partially substituting plastic waste for the fine aggregate in both concrete blocks and stabilized mud blocks. A comparative analysis is conducted between the compressive strength of these integrated plastic blocks and conventional standard blocks. The outcomes unequivocally demonstrate the viability of recycling plastic waste in a constructive manner, achieved through the incorporation of waste plastics in the production of building blocks. Notably, incorporating plastic waste by approximately 3%-6% to replace fine aggregates in Fly-Ash blocks results in enhanced strength compared to regular Fly-Ash blocks

Converting Waste Plastic to Liquid Organic Hydrogen Carriers.

The accumulation of waste plastics in landfills and the environment, as well as the contribution of plastics manufacturing to global warming, call for the development of new technologies that would enable circularity for synthetic polymers. Thus far, emerging approaches for chemical recycling of plastics have largely focused on producing fuels, lubricants, and/or monomers. In a recent study, Junde Wei and colleagues demonstrated a new catalytic system capable of converting oxygen-containing aromatic plastic waste into liquid organic hydrogen carriers (LOHCs), which can be used for hydrogen storage. The authors utilized Ru-ReOx /SiO2 materials with zeolite HZSM-5 as a co-catalyst for the direct hydrodeoxygenation (HDO) of oxygen-containing aromatic plastic wastes that yield cycloalkanes as LOHCs with a theoretical hydrogen capacity of ≈5.74 wt % under mild reaction conditions. Subsequent efficiency and stability tests of cycloalkane dehydrogenation over Pt/Al2 O3 validated that the HDO products can serve as LOHCs to generate H2 gas. Overall, their approach not only opens doors to alleviating the severe burden of plastic waste globally, but also offers a way to generate clean energy and ease the challenges associated with hydrogen storage and transportation.

Mechanism insights for formation of graphene quantum dots from Styrofoam waste and its application as security ink

Plastic pollution free environment is the utmost demand of the present day, which arises due to the urgent need of transforming plastic waste into valued materials suitable for wide range of applications. In this context, a single step synthesis of graphene quantum dots (GQDs) from plastic waste might be a promising approach for bulk conversion of plastic waste into value-added high-end products. The acid/base free, cost-effective, rapid synthesis of GQDs has the potential to meet the future demands. More importantly, a crucial aspect lies in comprehending the underlying mechanism for the formation of such nanomaterials which can open new paths for optimization and functionalization, ultimately facilitating the synthesis of cutting edge materials. This study presents an investigation into the synthesis mechanism of GQDs from Styrofoam waste using the microwave pyrolysis method. The research approach combines experimental technique with simulation studies to elucidate the process. The simulation methodology demonstrated the conversion of Styrofoam into a mix of saturated and unsaturated cyclic structures. These structures subsequently interacted to form intermediate species featuring two or more units bonded together. The intermediate species then gave rise to larger graphene like structure which ultimately led to the formation of GQDs. The GQDs synthesized in this study were subsequently transformed into a printable ink formulation in order to evaluate its potential as a practical solution for addressing the concerns associated with counterfeit currencies, fake documents, and tampered or manipulated goods. The synthesis of GQDs based printable ink from nonbiodegradable plastic waste serves the dual benefit of managing plastic waste and its utilization in advanced applications. This approach holds significant promise in providing sustainable solutions for the future.

Laser-based fabrication of superhydrophobic carbide surfaces from waste plastics

We report a procedure for fabricating superhydrophobic carbides with femtosecond laser-assisted carburization of metals, semiconductors, and oxides from waste plastics. To form a concentrated plastic dispersion, plastic is laser-ablated in toluene. Hydrogenated carbides are synthesized by applying the dispersion drop by drop onto the target surface, and then employing femtosecond laser scanning. Hydrogenated carbides of tungsten, silicon, and zirconium were syntehszied, and they depicted exceptional hydrophobic properties. Hierarchical structuring further promoted the hydrophobicity of these hydrogenated carbides. A water contact angle ∼ 168○ and roll-off angle ∼ 6○ were observed. Further, the samples retained hydrophobicity after 30 days of exposure to ambient air and 100 ○C thermal treatment. Our study holds equal significance from both environmental and technological perspectives, as it not only eliminates the use of fluorinated compounds but also contributes to environmental remediation by converting waste plastics into valuable superhydrophobic carbides.

Solar thermal reactor model for pyrolysis of waste plastic

ABSTRACT The ability to convert waste plastic into combustible liquids and gases using solar energy could help transform the problem of disposal of non-recyclable plastic into a valuable and environmentally responsible source of fuel. The purpose of this study is to propose a practical model for a compound parabolic trough solar thermal reactor for pyrolysis of waste plastic. The model integrates predictions of energy available from solar radiation (at a given location, time of day and time of year) with parabolic trough collector orientation and efficiency, a transient energy balance for an evacuated tube reactor and pyrolysis kinetics of waste plastic. The experimental setup used to test the model includes a pyranometer, a commercial solar collector consisting of a 60 cm long evacuated tube with a compound parabolic reflector and multi-channel data loggers to collect temperature, humidity and radiation data. The solar radiation sub-model was found to be in excellent agreement with clear-sky irradiance data collected using the pyranometer. Predictions of reactor temperature and reaction rate were found to be sensitive to the concentrator aperture area, solar irradiance, type of plastic (Arrhenius kinetics) and radiation properties of the evacuated tube reactor but relatively insensitive to humidity, wind velocity and terrestrial irradiance. The model shows that even on a small scale, favourable conditions for pyrolysis of waste plastic can be achieved within a solar reactor.

Process Synthesizes Janus Carbon Nanofluids From Waste Plastics for EOR

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 214799, “Novel Janus Carbon Nanofluids From Waste Plastics as Sustainable Nanoagents for Enhanced Oil Recovery: Scaleup Synthesis and Performance Evaluation,” by Wei Wang, Sehoon Chang, SPE, and Ayrat Gizzatov, SPE, Saudi Aramco, et al. The paper has not been peer reviewed. _ The complete paper describes nanomaterials—Janus carbon nanofluids—derived from waste plastics and demonstrates the potential of the nanofluids as highly effective alternative nanoagents for enhanced oil recovery (EOR) applications at reservoir conditions. A novel, sustainable, cost-effective method has been developed to scale up synthesis of Janus carbon nanoparticles (JC-NPs) from waste plastic feedstock by combined pyrolysis, chemical functionalization, and pulverization, which allows for production of the JC-NPs in mass quantities at an industrial scale. Introduction Recent research has demonstrated that nanoparticles with asymmetric surface properties (i.e., Janus nanoparticles) could achieve a much higher efficiency of oil recovery factors with very low concentrations of loading compared with homogeneous nanoparticle fluids. To date, however, major challenges facing the exploration and use of Janus nanoparticles exist, impeding scalability of synthesis, tailored chemical functionalization, and the ability to introduce a diverse set of functionalities. Therefore, new methods for production of Janus nanomaterials on an industrial scale are desired. The authors present a novel technique to convert waste plastic materials into carbon-based nanomaterials for EOR applications. Waste plastics, as a low-cost feedstock, can be converted into high-value-added carbon-based microparticles through the controlled carbonization of polymers. Furthermore, the carbon microparticles (C-MPs) can be surface-functionalized by post-chemical treatment and then their chemical symmetry reduced to nanosize by a ball-milling technique. The resulting asymmetrically surface-functionalized carbon nanoparticles (i.e., Janus C-NPs) exhibit both nanoparticulate and surfactant-like properties that can be used as new nanoagents in nanofluid flooding for EOR applications. Experimental materials and measurement methodology are detailed in the complete paper. Results and Discussion Synthesis of C-MPs From Waste Polymers. Approximately 90% of the plastics produced globally consist of six types: low-density polyethylene, high-density polyethylene, polypropylene, polyvinylchloride, polystyrene, and polyethylene terephthalate (PET). Given their widespread use, these waste polymers constitute a substantial proportion of global plastic waste. Therefore, they present an opportunity to be used as precursors in the synthesis of C-MPs. This study offers an approach for repurposing these ubiquitous waste polymers. As depicted in Fig. 1, the authors propose synthesis of C-MPs through carbonization reactions using these waste polymers as feedstock. This methodology offers dual benefits. First, it presents a practical solution to the growing environmental concern posed by plastic waste. Second, it provides a cost-effective way to produce C-MPs, an essential component in many technological applications.

Simultaneous hydrogen production and conversion of plastic wastes into valued chemicals over a Z-scheme photocatalyst

Solar-powered photoreforming of plastics provides a facile and low-energy pathway for generating green hydrogen while converting plastic wastes into valuable organic compounds. Herein, a Z-scheme photocatalyst, containing Cd0.5Zn0.5S for hydrogen production, red phosphorus (RP) for oxidizing plastics, and CoxPy as the electron mediator, was constructed. The photoreforming of polylactic acid (PLA) and polyethylene terephthalate (PET) was carried out under alkaline aqueous conditions. The photogenerated electrons from the RP recombined with the holes from Cd0.5Zn0.5S. The retained electrons in Cd0.5Zn0.5S reduced water to hydrogen, whereas the holes in the RP oxidized plastic-derived polymers into valuable organic products, such as pyruvate, acetate, and methanol. The hydrogen evolution rates from the photoreforming of PLA and PET using the optimal photocatalyst at 35 °C reached 503.9 and 74.4 μmol h−1, corresponding to the apparent quantum efficiencies of 5.84 % and 0.89 % at 420 nm.

Solving two environmental problems simultaneously：Microporous carbon derived from mixed plastic waste for CO2 capture

Conversion of plastic waste into porous carbon for CO2 capture is an attractive approach to solve the carbon emission and plastic pollution problems, simultaneously. However, the previous studies are limited to the utilization of single PET plastic. The conversion of mixed plastic waste (MPW), which is of more practical significance, is seldom reported. In this study, mixed plastic waste was converted into porous carbon materials for CO2 capture through cascading autogenic pressure carbonization (APC) and chemical activation. The carbon yield of 56% was achieved through APC of MPW. The activator (KOH) dosage had significant effects on the structure and properties of the prepared porous carbons. Porous carbon prepared with KOH/C ratio of 4 had the largest micropore area and the maximum CO2 adsorption was 2.7 mmol g−1 at 298 K and 1 bar. The experimental data were well fitted to the pesudo first-order kinetic model. The MPW derived porous carbon exhibited not only high CO2 uptake capacity, but also fast adsorption rate, good selectivity of CO2 over N2 and good cyclic stability, which could be regarded as a promising adsorbent for CO2 adsorption.

Self-assembly kieselguhr-based ZSM-5 for catalytic pyrolysis of mask waste to produce high value-added aromatics

The conversion of plastic waste to high value-added aromatics such as benzene, toluene, ethylbenzene, xylene (BTEX) through catalytic pyrolysis offers huge untapped opportunities for resource recovery and plastic pollution control. Economical equipment configuration, operation and maintenance, high safety factor, high efficiency, stability, low-cost catalyst synthesis design, high yield, high selectivity of products are the key to the practical application of catalytic pyrolysis. In present study, low-cost kieselguhr based ZSM-5 was synthesized by one-pot in situ hydrothermal method using kieselguhr as silicon-aluminum source. During the depolymerization-recrystallization process, the selective growth and self-assembly of crystals on the a, c axis formed large-grain of ZSM-5 with extended straight channels and maximized sinusoidal channels. Native transition and alkaline-earth metals were coordinated to the acidic sites of the silica-aluminum skeleton, achieving tunability of the catalyst acidity. Catalytic pyrolysis of mask waste at 550 °C in a fixed bed reactor achieved the highest pyrolysis oil yield (44.3 wt%) and BTEX selectivity (77.1 %) with p-xylene as the dominant xylene product (78.2 %). After 3 cycles of long-life experiments, the BTEX selectivity of the catalyst remained at 65.1 %, which is higher than that of commercial ZSM-5 (54.9 %), indicating the superior use stability. Molecular dynamics simulations showed that the excellent shape-selectivity of the catalyst is based on its unique pore structure, which facilitates the diffusion and transport of appropriately sized intermediates/products within the structure, resulting in products with advantageous distributions. This study proposes an efficient and feasible plastic closed-loop strategy for green upgrading of medical waste to high value-added chemicals.

Waste catalyst potential for co-pyrolysis of biomass and single-use plastics: model-free isoconversional kinetics and thermodynamics

AbstractThe study aims to investigate the kinetic and thermodynamic characteristics of single and binary pyrolysis of biomass (date pits: DP) and single-use-plastics (polypropylene: PP, and polystyrene: PS), and the effect of adding natural catalysts—seashell (SS) and cuttlebone (CB) for ternary co-pyrolysis of the feeds. The activation energy (Ea) was calculated using different model-free kinetic methods, including Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (FWO), and Starink, utilizing information from the degradation at three heating rates from room temperature to 1173 K. The results showed that all three methods produced relatively similar Ea values with a high coefficient of correlation (R2), indicating a good fit for the data. The Ea values for single feeds of DP, PP, and PS using the FWO method were found to be in the range of 196–223 kJ/mol, while for binary feeds—DPPP and DPPPS—the values were found to be lower than for the individual plastics. The high Ea values of the binary plastic mixture are also reduced by ~ 40 kJ/mol in the ternary mixture due to biomass co-pyrolysis. Additionally, the study revealed that the addition of SS and CB catalysts positively affected the ternary co-pyrolysis by reducing activation energy by 28.5 and 5.8%, respectively, due to the catalytic activity of 20 wt% of CaCO3 decomposition from the seashell and cuttlebone added in situ to the feeds. The research contribution of this study lies in its comprehensive investigation of the kinetic and thermodynamic characteristics of biomass and plastic pyrolysis, including single and binary systems, as well as the introduction of natural catalysts for ternary co-pyrolysis. The findings highlight the effectiveness of the studied catalysts in reducing activation energy and provide valuable insights for the development of efficient biomass and plastic waste conversion processes.

Performance, emission and combustion characteristics of liquid fuel produced through catalytic co-pyrolysis of waste LDPE and Pongamia pinnata seeds: An experimental investigation in CI engine

As there is an urgent need to address the global problem of increasing plastic waste and decreasing petroleum-based fuels, it is possible to convert waste plastic and unused biomass seeds into fuels that can be utilized in transportation sector. The current study deals with blending pure diesel (D100) with the liquid fuel (PB2) obtained from the co-pyrolysis of Pongamia pinnata seeds and waste low-density polyethylene (LDPE) with Calcium oxide (CaO) as the catalyst. Three blends of D100, namely, PB2@10 (with 10 % blend), PB2@20 (with 20 % blend) and PB2@30 (with 30 % blend) were tested for performance, emission and combustion in an unmodified CI engine for an analytical comparative analysis using standard methods. The results showed that the BSFC was almost same (0.3 kg/kWh) at higher loads for all three blends, while the BTE was found to be equal or increased compared to D100 in the range of 27–30 % at higher loads for higher blends. NOx formation was found to decrease by 19.4 % and 13 % at the highest load for PB2@30 andPB2@30. The smoke formation also decreased for all blends (maximum 22.5 %) while the maximum difference of lambda was determined to have decreased in comparison to D100, close to 1 at higher loads. The maximum cylinder pressure and temperature were also found to have increased during combustion by approximately 1 % for PB2@10 while that of PB2@20 and PB2@30 remained quite close to D100. The obtained renewable liquid fuel could certainly be utilized in blends with pure diesel for use in vehicles.

An innovative mechanism of creating H1 and H3 pore types in AlSiO4 and its catalytic application to convert waste plastic into aviation fuel

ABSTRACT FeAlSiO4 -H3 and ZnAlSiO4-H1 are synthesized through the facile method without an autoclave. Tetraethylenepentamine (TEPA) is a structure-directing agent. FT-IR, XRD, BET, TPD, TGA, and TEM confirmed the framework, crystallinity, porosity, acidity, thermal stability (above 600°C), and surface morphology respectively. BET analysis revealed that two distinct pore widths (FeAlSiO4-H3: 13.79 nm, ZnAlSiO4-H1: 11.65 nm) are based on the metal ion substitution The acidity (FeAlSiO4 -H3:6.576 and ZnAlSiO4-H1:13.836 cm3/g STP). In ZnAlSiO4 – H1, 7 template molecules form a linear complex with 6 Zn2+ions which is oriented vertically to create cylindrical pores. In FeAlSiO4-H3, 8 template molecules are formed a linear complex with 7 Fe2+ which is positioned in a cross-sectional way to produce slit pores. The catalytic cracking of polypropylene has been carried out over FeAlSiO4 and ZnAlSiO4 and observed that the conversion is 100%. H3 type pore has produced higher selectivity of jet fuel (90%) than the H1 type pore (86%) at 0.5 g catalyst dosage. In addition to that, H3 type has produced diesel (3.8%) and H1 type has produced petrol (10.1%) as a minor product. The synthesized aviation fuels are equivalent to JET A-1 fuel and are characterized by FT-IR, HPLC, and GC-MS.

Polymer blends manufactured from fresh & landfill mined plastic waste: Are they composites?

Plastics are primarily single-use and are disposed of in municipal solid waste landfills at the end of their life cycle. Such plastic waste undergoes partial degradation and results in the leaching of persistent contaminants such as surfactants, plasticizers, fire retardants, micro(nano)plastics, nanomaterials, etc., which are of great concern. Hence, the recovery and utilization of landfill-mined plastic waste (LMPW) and fresh municipal plastics waste (FMPW) is mandatory. Though thermal treatment techniques are widely used, they could treat only ≈8% of the total plastic waste generated due to their demand for pollution control measures which have been proven expensive. In this context, mechanical recycling, which allows the conversion of plastic waste into composites for different engineering applications, has been investigated by adding appropriate fillers. However, before creating composites, a comprehensive understanding of mechanically recycled waste plastics alone (read as blends) is necessary. This becomes important because most plastics used in domestic and industrial activities are significantly augmented by adding organic or inorganic constituents to achieve the target properties. Hence, the perpetual question, ‘whether the recycled polymer blends obtained from FMPW and LMPW are composites’ remains unanswered. This is key to decide upon the optimal dosage of the fillers to be used for achieving the target properties of the composites. To address these issues, extensive investigations were conducted to establish the overall characteristics of different blends obtained from FMPW and LMPW. Furthermore, after removing the polymeric component, the residues obtained from these blends were extensively characterized. This exercise revealed that the residues mainly constitute CaCO3, TiO2, and SiO2, which are either intentionally added while manufacturing virgin plastics or are due to contamination. It was also observed that the mechanical properties of the blends get enhanced due to the presence of residues, which indicates that these are composites and not blends.

Performance and emission characteristics of a CI engine with post-treated plastic pyrolysis oil and diesel blend

Conversion of waste plastics into energy products is an effective waste management technique as they constitute a considerable portion of solid waste at present. In this study, distilled diesel fraction of Plastic Pyrolysis Oil (PPO) named Distilled Plastic Diesel (DPD) was hydrotreated named hydrotreated plastic diesel (HPD) and blended with commercial diesel fuel by 15:85 ratio (wt%), defined as HPD15, to experimentally investigate the performance and emission characteristics of a compression ignition (CI) engine. The experiment was done in 4-cylinder, 4-stroke diesel engine with an eddy current dynamometer testbed at full load (100 % engine load) and an engine speed of 1200–2400 rpm with 300 rpm intervals. The results are compared with neat diesel fuel data at the same operating conditions. This study found that HPD15 performed better or comparable with diesel fuel. Overall, the brake power (BP) and brake thermal efficiency (BTE) of HPD15 were higher than diesel fuel by a maximum of about 4.77 % and 3.77 %, respectively. Brake specific fuel consumption (BSFC) of HPD15 was lower at all operating speeds (by a maximum of about 4.66 %) and brake specific energy consumption (BSEC) was lower in most of the operating speeds (by a maximum of about 3.77 %). This study also revealed that CO2 at some operating speeds and NOx emission at all operating speeds for HPD15 are lower than diesel fuel. However, CO and unburnt hydrocarbon (UHC) emission are slightly higher for HPD15 than diesel at all speeds. Overall, HPD15 can be recommended as a suitable alternative for diesel fuel without any engine modification.

Sustainable production of aromatics via catalytic pyrolysis of polyolefins towards the carbon cycle for plastics

Catalytic pyrolysis has been emerging as a promising chemical recycling technology to convert plastic waste into olefins and aromatics that can be used as alternatives to petroleum-based chemicals and promote the carbon cycle for plastics. However, the above procedure typically suffers from poor selectivity of the target product. Herein, catalytic pyrolysis of polyolefin plastics was carried out in a two-stage fixed bed reactor for highly selective production of monocyclic aromatic hydrocarbons (MAHs), over Zn-P/HZSM-5 catalysts. After loading 3.0 wt% Zn and 0.5 wt% P on HZSM-5 catalyst, catalytic pyrolysis of low-density polyethylene (LDPE) at 500 °C achieved the highest liquid yield of 55.9 wt% and exhibited a remarkably high selectivity up to 87.44 % towards MAHs, especially in which the BTEX (benzene, toluene, ethylbenzene, xylene) content reached 75.16 %. The introduced Zn species decreased Brønsted acid sites while increased Lewis acid sites of HZSM-5, which in turn improved the aromatization activity. Simultaneously, the addition of P decreased the acidity strength, inhibiting the formation of coke and polycyclic aromatics hydrocarbons. Furthermore, catalytic co-pyrolysis of LDPE, high-density polyethylene (HDPE) and polypropylene (PP) were investigated to reveal the synergistic effect in terms of BTEX selectivity. Intriguingly, a high liquid yield of 55.7 wt% can be obtained at a feeding ratio of HDPE:LDPE:PP = 1:1:1, and an enhanced selectivity of MAHs up to 87.66 % was achieved, with the highest BTEX content of 79.89 %. Finally, carbon emission assessments of catalytic plastic pyrolysis indicated that it presented great potential to reduce carbon emission and facilitate carbon cycle.

Enhancing catalytic performance for waste plastic upgrading: Simultaneous regulation of pore structure and acid sites in Ga-doped desilicated HZSM-5 catalysts

Though catalytic pyrolysis through HZSM-5 has shown great potential to convert waste plastics, it is urgent to modify the catalyst to improve its catalytic performance due to the low liquid product yields and inferior selectivity to high value-added monocyclic aromatic hydrocarbons (MAHs). During the study, two main modification methods, desilication via alkali treatment and Ga metal doping, were applied on HZSM-5 to reach simultaneous regulation of pore structure and acid site. It showed that selectivity to MAHs rose from 45.37 % to 58.45 % and 59.54 %, respectively, when 0.1 M and 0.4 M NaOH solutions were used for desilication. After Ga metal doping, selectivity to MAHs further increased to 67.43 % and 67.16 %, respectively, at A 0.1 M 5 %Ga/ZSM-5 and A 0.4 M 5 %Ga/ZSM-5, with selectivity to value-added benzene, toluene, ethylbenzene and xylene (BTEX) rising to 50.86 % and 46.45 % correspondingly. After three times of recycling, the catalyst still remained active with selectivity to MAHs staying above 65 %.

Valorization of PE plastic waste into lipid cells through tandem catalytic pyrolysis and biological conversion

Worldwide plastic pollution challenges the existing recycling technologies. Upcycling approaches that can convert plastic waste into value-added products are necessary for the creation of a circular plastics economy. This study demonstrated a process concept to convert Polyethylene (PE) waste into microbial lipid through tandem catalytic pyrolysis and biological conversion by oleaginous yeast Yarrowia lipolytica. PE waste was catalytically pyrolyzed into small molecular hydrocarbons, which were further digested by oleaginous microorganism to accumulate lipid. Through catalyst selection, fermentation intensification, and strain adaptive evolution, a lipid production of 122 mg/L was obtained using pyrolysis oil as sole carbon source. Through the whole process, approximate 15 % of PE was converted into lipid cells. This upcycling process was evaluated through carbon footprint analysis. Cell production, lipid content, and electricity consumption are the main factors influencing the process carbon emission. Sensitivity analysis showed that a carbon reduction can be achieved with the improvement of these parameters. This tandem process establishes a sustainable strategy for the conversion of plastic waste into value-added products.