Research Progress on Selective Depolymerization of Waste Plastics to High-Quality Liquid Fuels
This study evaluates catalytic pyrolysis, microwave pyrolysis, and photocatalytic depolymerization for converting waste plastics into liquid fuels, with an emphasis on the efficiency, selectivity, and scalability. Catalytic pyrolysis achieved a 79.08% liquid yield from high-density polyethylene (HDP...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | zho |
| Published: |
Editorial Office of Energy Environmental Protection
2025-06-01
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| Series: | 能源环境保护 |
| Subjects: | |
| Online Access: | https://doi.org/10.20078/j.eep.20241106 |
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| Summary: | This study evaluates catalytic pyrolysis, microwave pyrolysis, and photocatalytic depolymerization for converting waste plastics into liquid fuels, with an emphasis on the efficiency, selectivity, and scalability. Catalytic pyrolysis achieved a 79.08% liquid yield from high-density polyethylene (HDPE) at 550 ℃ using Fe-HZSM-5 catalysts. Hydrocarbon selectivity was governed by catalyst acidity and pore structure. Hierarchical ZSM-5 further enhanced low-density polyethylene (LDPE) conversion (>95%) by mitigating overcracking through optimized pore architecture. The microwave pyrolysis demonstrated rapid heating kinetics, yielding a 98.78% aromatic-rich liquid fuel from polystyrene (PS) at 600 W with 60 g SiC absorbent. Monoaromatic hydrocarbons dominated the liquid fuel (93.9%), meeting aviation fuel standards. However, excessive power (>6 kW) reduced yields by 10% due to secondary decomposition. Photocatalytic depolymerization in 30% H2O2 facilitated the production of acetic acid yield of 1.1 mmol·g−1·h−1 from polyethylene (PE), utilizing hydroxyl radicals (·OH) to cleave C—C bonds, leading to an increase in PE mass loss from 50.1% to 85.4%. The key findings are as follows: (1) Fe doping in HZSM-5 boosted liquid yields by 16% via enhanced dehydrogenation activity; (2) Microwave absorber loading (e.g., SiC) nonlinearly affected cycloparaffin selectivity (65.6% at 450 W for polypropylene); (3) H2O2 increased photocatalytic PE conversion by 70% compared to pure water, where limited ·OH generation restricted CO2-to-fuel pathways (≤47.4 μg·g−1·h−1). Catalytic pyrolysis faces the challenge of rapid catalyst deactivation (resulting in a 30% activity loss after 5 cycles), while microwave systems incur high capital costs. Photocatalysis prioritizes gaseous products (e.g., H2, CH4) with liquid fuel selectivity below 15% for most polymers. To address these challenges, three actionable pathways are proposed: (1) Pilot-scale optimization: Current studies predominantly use lab-scale feeds (<100 g), necessitating trials with industrial-grade plastics containing pigments and plasticizers. Electrostatic separation pretreatment reduced PVC-derived HCl corrosion by 80% in pilot tests, while anti-fouling membranes (90% recovery) enhanced acetone purity (>98%) in continuous systems. (2) Hybrid energy systems: Integrating microwave heating (200 – 300 ℃/min) with photocatalysis may synergize rapid thermal activation and selective bond cleavage. For instance, microwave-enhanced light absorption in TiO2-MoS2 hybrids doubled charge carrier density, potentially reducing energy consumption by 30% – 40%. (3) Intelligent reactors: IoT-enabled sensors and machine learning algorithms stabilized multiphase reactions in simulated trials, minimizing yield fluctuations to ±5% versus ±15% in batch modes. Real-time monitoring of temperature gradients and microwave power enabled dynamic adjustments, improving diesel-range hydrocarbon selectivity by 25%. Economically, catalytic pyrolysis shows near-term viability with a break-even cost of 0.8 – 1.2 $/L for diesel-range fuels, while photocatalysis requires a 50% – 70% reduction in catalyst synthesis costs (e.g., replacing Pt with Fe-Ni sulfides). Environmentally, microwave pyrolysis reduces carbon intensity by 40% – 60% versus incineration, aligning with net-zero roadmaps. Lifecycle assessments revealed that hybrid systems could achieve carbon-negative profiles when coupled with renewable energy. Future work should focus on developing multifunctional catalysts (e.g., acid-base bifunctional sites for tandem cracking-isomerization), modular reactor designs, and standardized testing protocols to expedite industrial implementation. These strategies underscore the potential of tailored energy-input systems to advance plastic valorization, supporting circular economies and global decarbonization efforts. |
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| ISSN: | 2097-4183 |