Search Results (60)

Microwave-assisted pyrolysis (MAP) has emerged as a revolutionary technology for converting solid waste into high-value hydrocarbons. However, conventional pyrolysis and traditional single-function catalysts often face an inevitable “performance trade-off” involving severe mass transfer resistance, poor microwave absorption, and rapid coking. This review systematically summarizes the recent evolution of catalyst design toward advanced multi-site composites. It highlights the synergistic mechanisms of integrating microwave-responsive cores, hierarchical pore networks, and metal-acid bifunctional sites to achieve ultrafast localized heat transfer, targeted bond cleavage, and in-situ coking suppression. Furthermore, this paper critically examines current bottlenecks in scaling MAP to industrial levels. To address these challenges, we discuss emerging solutions, including hydrogen-enriched co-pyrolysis, non-destructive in-situ regeneration, and the integration of machine learning frameworks for intelligent process optimization. Full article

A rapid accumulation of plastic waste has created an urgent need for efficient and sustainable recycling technologies. Among various approaches, pyrolysis stands out as promising method of thermochemical recycling of plastic waste; however, the process needs optimization and further research to make it more energy-efficient and sustainable. The conventional approaches for optimization focus on the enhancement of yield, only overlooking efficiency and system-level sustainability. In this study, a machine learning-enabled surrogate-assisted multi-objective artificial intelligence (AI) optimization framework is developed for plastic pyrolysis to maximize product recovery and minimize energy consumption. The model integrates energy return on investment (EROI) and higher heating value (HHV) into process design. A curated dataset of 312 experimental cases covering polyolefins, PET, nylon, and mixed plastics was used to train multiple machine learning algorithms, such as polynomial regression, Gaussian process regression, and Random Forest models. The Random Forest algorithm demonstrated superior predictive robustness across oil yield, HHV, char formation, and EROI. Pareto front analysis using NSGA-II revealed that moderate reaction severities (400–450 °C, 40–70 min) maximize net energy performance while minimizing solid residues. The conditional variational autoencoder as a GenAI model was incorporated to work as a generative proposal engine, which enhances the exploration of chemically feasible operating regions under uncertainty-aware active learning. The integration of techno-economic and life-cycle assessment demonstrates that energy-positive configurations outperform high-yield scenarios, achieving IRR > 15%, energy intensity < 10 MJ kg⁻¹, and CO₂ reductions up to 47% relative to incineration. The proposed framework establishes a data-driven methodology for aligning polymer pyrolysis optimization with circular economy and energy sustainability objectives. Full article

Formic acid (FA) has emerged as a promising liquid hydrogen storage material, yet efficient photothermal dehydrogenation catalysts with high activity and H₂ selectivity remain challenging. Herein, a polymetallic synergistic PdCu/M-ZNC (where M represents the co-doped In, Sn and Mo species) is fabricated by molten-salt-assisted pyrolysis of ZIF-8 precursors followed by metal incorporation. The unique molten salt environment effectively preserves the porous architecture of ZIF-8, enabling the secure anchoring of PdCu alloy nanoparticles onto the carbonaceous matrix enriched with M-N_x coordination sites. Under light irradiation, the PdCu alloy sites kinetically accelerated the overall adsorption and activation of FA molecules. Based on empirical observations and corroborated by the established literature, this alloying effect was inferred to facilitate the C-H bond cleavage and HCOO* desorption processes. Concurrently, the M-N_x sites act as efficient electron transfer channels, facilitating the rapid coupling of photogenerated electrons with protons (H⁺) to evolve H₂. Consequently, the optimal catalyst exhibits an enhancement in gaseous product yield (404.46 mmol/g/h) and H₂ selectivity (67.49%) at 75 °C. This work offers a catalyst design that aligns with several principles of green chemistry: it maximizes the atom utilization of precious Pd, incorporates synergistic non-precious metals within MOF-derived frameworks to enhance stability, and leverages solar energy to drive hydrogen production under mild conditions, presenting a more sustainable pathway for hydrogen release from liquid carriers. Full article

The co-pyrolysis of Chlorella vulgaris (CV) and Eucalyptus branches (EP) offers a promising strategy to enhance bio-oil yield, improve resource utilization efficiency, and alleviate environmental pressures. In this study, the microwave-assisted co-pyrolysis of CV and EP at a mass ratio of 2:1 was investigated, focusing on the catalytic performance of Ni-X (X = Mg, Cu, Fe) bimetallic modified HZSM-5 zeolites. The effects of these catalysts on pyrolysis characteristics, product distribution, and bio-oil composition were systematically evaluated. Experimental results showed that the 15% Ni-Cu/HZSM-5 catalyst exhibited the best catalytic performance, achieving the highest bio-oil yield of 16.83%; it also elevated the R_m to 0.0687 wt.%/s and reduced T_s to 2084 s. Composition analysis revealed that Ni-Cu/HZSM-5 significantly promoted the formation of hydrocarbons, increasing their relative content from 11.59% (C2E1 Group) to 28.92%, while effectively suppressing the formation of nitrogen-containing compounds, reducing their content by 5.05%. Based on these results, a possible reaction pathway is proposed in which the Ni-Cu/HZSM-5 catalyst may enhance heteroatom removal through hydrodeoxygenation (HDO) at the Ni-Cu sites, followed by cracking and aromatization at the HZSM-5 acid sites. This effect may be complemented by preferential adsorption of oxygenated intermediates over nitrogen-containing species, which could help suppress the formation of nitrogenous heterocycles. This work provides theoretical guidance for the application of bimetallic zeolite catalysts in microalgae/lignocellulose co-pyrolysis, alongside a viable pathway for valorizing Eucalyptus by-products to produce high-quality bio-oil. Full article

Thermochemical/catalytic co-processing of biomass and solid wastes is a promising route for waste valorization, low-carbon energy recovery, and the co-production of fuels, chemicals, and carbon materials. Conventional pathways, including pyrolysis, gasification, liquefaction, and carbonization, provide the basic framework for mixed-feed conversion. Emerging routes, such as flash Joule heating, microwave-assisted conversion, plasma processing, supercritical water treatment, solar-driven systems, and machine-learning-assisted optimization, further expand opportunities for process intensification and selective upgrading. Owing to feedstock complementarity, including hydrogen donation from plastics, catalytic effects of ash minerals, and interactions among reactive intermediates, co-processing can enhance deoxygenation, hydrogen generation, aromatization, and carbon utilization. Major challenges remain, however, including feedstock heterogeneity, reactor scale-up, catalyst stability, and the limited transferability of laboratory-scale synergy to realistic waste streams. Future progress should therefore focus on continuous validation, mechanistic clarification, and integrated techno-economic, life-cycle, and data-driven assessments. Full article

Co-pyrolysis of polyolefins (LDPE, PP, PS) mixed with silicone rubber (SR) was investigated using a laboratory-scale pyrolysis apparatus to evaluate product composition, synergistic interactions, and siloxane recovery potential. Synergistic effects were assessed by comparing experimental mass balances and product distributions with calculated values derived from individual polymer pyrolysis. Co-pyrolysis resulted in a reduction in liquid yield and an increase in gaseous products and solid residue compared to calculated values, with liquid yields decreasing by up to ≈15 wt% at high SR content. This shift was accompanied by an enrichment in lighter hydrocarbons in both phases, reaching up to a ≈18% relative increase at high SR content, and by a redistribution towards smaller cyclic siloxanes. Chromatographic analysis confirmed that no new compounds were formed, but the proportion of low molecular weight species increased with silicone content. These effects are attributed to the distinct thermal behavior of the polymers, as silicone rubber does not melt but becomes brittle, allowing molten polyolefins to infiltrate surface cracks and prolong residence time, thereby promoting secondary cracking. Furthermore, recovery of hexamethylcyclotrisiloxane (D₃), the primary silicone pyrolysis product, was demonstrated from the liquid co-pyrolysis products via solvent-assisted filtration using ethanol, achieving purities above 99.5% and recovery rates up to ≈75% compared to other possible methods. These findings provide insights into co-pyrolysis behavior and offer a basis for developing strategies for the recovery of siloxane and advanced recycling of mixed polymer waste. Full article

Carbon-based bifunctional oxygen electrocatalysts with rationally designed architectures are essential for high-performance rechargeable zinc–air batteries (ZABs), yet the concurrent optimization of catalytic activity, durability, and mass transport remains challenging. Herein, hierarchical ZnCo carbon nanofibers/carbon nanotubes (CNFs@CNTs) are fabricated via single-nozzle electrospinning followed by melamine-assisted pyrolysis under a ZnCl₂-regulated atmosphere. During thermal treatment, Co species embedded within carbon nanofibers catalyze in situ carbon nanotube growth, while ZnCl₂ vapor modulates the carbonization process and surface chemistry, collectively generating a hierarchical CNFs@CNTs architecture with high surface area and abundant exposed active sites. As a result, ZnCo CNFs@CNTs exhibit outstanding bifunctional ORR/OER activity, surpassing Zn-free and Co-free counterparts. Combined structural and electrochemical analyses reveal that the synergistic interaction between Co active centers and Zn-assisted carbon structural regulation enhances reaction kinetics and long-term stability. When implemented as air electrodes in rechargeable ZABs, ZnCo CNFs@CNTs deliver high power density, reduced charge–discharge polarization, and excellent cycling durability, demonstrating strong practical applicability. This work presents an effective strategy for constructing hierarchical CNFs@CNTs composites via electrospinning and dual-component thermal regulation, offering new insights into the design of high-efficiency bifunctional air electrodes for advanced ZABs. Full article

To address the mounting environmental burden caused by solid waste from the food supply chain—specifically agricultural residues and plastic packaging—this study systematically investigated the synergistic mechanisms and product regulation pathways in the co-pyrolysis of four representative food processing by-products—rice husk, pine wood, corn stover, and chestnut shell—with polypropylene, a common food packaging material. A comprehensive methodology integrating thermogravimetric analysis, kinetic modeling, and product characterization was employed. The results demonstrate that incorporating polypropylene into co-pyrolysis systems, such as those involving waste oil, significantly reduces the average activation energy, indicating a catalytic effect that enhances reaction kinetics. Notably, the co-catalytic interaction between corn stover and PP led to a substantial 54.90% reduction in oxygen content, underscoring PP’s role as an effective hydrogen donor that promotes deoxygenation and free radical reactions, thereby increasing hydrocarbon production. At an optimal pyrolysis temperature of 600 °C, product distribution was effectively regulated: the hydrocarbon yield in the CP (corn stover/PP) system increased from 39.8% to a maximum of 65.6%, reflecting a targeted conversion of oxygenated compounds into high-value hydrocarbons. Furthermore, greenhouse gas (GHG) emission calculation and techno-economic analyses indicate that a natural gas-assisted co-pyrolysis process (Scenario C) can generate a net daily profit of 1835 RMB while reducing annual CO₂ emissions by 6515 tons, demonstrating both economic feasibility and environmental benefits. This study provides a theoretical foundation for the circular economy in the food industry, offering a viable technical pathway for the simultaneous treatment of organic food waste and packaging plastics, thereby supporting the sustainable development of the agri-food sector. Full article

CO₂-assisted catalytic pyrolysis presents a viable and promising approach to addressing plastic waste pollution and mitigating climate change. However, the effects of the metal–catalyst combination mode and the spatial distance between metal–acid sites on catalytic performance remain unclear. In this study, the reaction behaviors of the configurations, Fe₃O₄ and ZSM-5 in tandem catalysis (Fe₃O₄&HZ), their physical mixture (Fe₃O₄-HZ), and Fe-loaded ZSM-5 (Fe/HZ), were compared in polypropylene pyrolysis under a CO₂ atmosphere. The aromatic contents followed this order: Fe/HZ > Fe₃O₄-HZ > Fe₃O₄&HZ > ZSM-5 > Fe₃O₄. Specifically, Fe/HZ with the highest degree of metal–zeolite proximity achieved an aromatic content of 66.1%, significantly higher than the 34.2% obtained with Fe₃O₄&HZ, demonstrating that closer metal–acid proximity promoted aromatic formation. Moreover, Fe/HZ significantly reduced coke deposition. Based on characterization results from XRD, SEM, TEM, XPS, and NH₃-TPD, the enhanced spatial proximity between metal and acid sites strengthened the functional synergy between iron-based redox sites and zeolitic Brønsted acid sites. This synergy facilitated the reverse water–gas shift reaction of CO₂, which consumed hydrogen generated during aromatization and shifted the reaction equilibrium toward enhanced aromatic production. These findings would offer theoretical and strategic insights into the optimization of CO₂-assisted catalytic pyrolysis systems for the sustainable upcycling of plastic waste. Full article

Rice husk, which accounts for approximately 22% of global rice production, is often disposed of by open field burning, causing significant greenhouse gas (GHG) emissions and air pollution. Converting rice husk into biochar via pyrolysis offers a sustainable waste management and climate mitigation pathway; however, the environmental performance of biochar production is highly sensitive to the energy source used. Hence, this study presents a gate-to-gate life cycle assessment of biochar production from rice husk via slow pyrolysis at 500 °C under three energy supply scenarios: grid electricity, biomass combustion, and photovoltaic solar energy. Using the ReCiPe 2016 methodology, environmental impacts were evaluated across four categories such as Global Warming Potential (GWP), Human Toxicity Potential (HTP), Acidification Potential (AP), and Abiotic Depletion Potential (ADP), with all process parameters held constant except the energy source. The results demonstrate that energy supply is the dominant determinant of environmental performance and the photovoltaic solar-assisted biochar production route showed superior performance across all categories, with gross production impacts for 1 ton biochar of 24.0 kg CO₂-eq (GWP), 5.6 kg 1,4-DCB-eq (HTP), 0.09 kg SO₂-eq (AP), and 259.9 MJ (ADP), representing 48-165-fold improvements over grid electricity. When accounting for carbon sequestration (2800 kg CO₂-eq per ton biochar), all scenarios achieved net negative GWP, ranging from −2776.0 kg CO₂-eq (solar PV) to −1562.5 kg CO₂-eq (grid electricity), representing 78% variation attributable to energy source. Contribution analysis revealed pyrolysis heating accounts for 95.6% of environmental impacts, with no trade-offs among impact categories. The findings recommend photovoltaic solar energy for new biochar facilities, biomass combustion for co-located agricultural operations, and avoidance of grid electricity unless grids achieve substantial decarbonization. Full article

Non-recyclable plastic waste (PSW) and residual lignocellulosic biomass (WP) represent abundant yet underused resources whose conversion can generate renewable fuels with synergistic benefits. While conventional pyrolysis remains limited by slow heat transfer and poor adaptability to heterogeneous feeds, microwave-assisted pyrolysis (MAP) offers faster volumetric heating and improved syngas quality, though it is still largely confined to the laboratory scale due to limited understanding of feedstock interactions and process behaviour. In this context, the present work provides a laboratory-scale experimental investigation of the MAP co-pyrolysis of PSW/WP blends, focusing on gas yield and syngas quality, and complements the experimental analysis with a preliminary scale-up assessment for a continuous microwave reactor. The results reveal clear synergistic effects, with gas yields exceeding those predicted by linear mixing. A 70/30 wt% PSW/WP blend produced a hydrogen-rich syngas with H₂ concentrations of approximately 42 vol% and an H₂/CO ratio of 2–3. Compared to conventional pyrolysis under analogous conditions, MAP increased hydrogen content by around 35% and reduced CO₂ concentrations by up to 40%, resulting in a cleaner and more energy-dense gas. Overall, the findings highlight the strong potential of MAP for the valorization of mixed plastic–biomass wastes. Full article

Organic-rich shale, as a significant alternative energy source, possesses abundant resources. Classified by maturity, it comprises three categories: medium-high maturity shale oil, medium-low maturity shale oil, and oil shale. Medium-high maturity shale oil faces challenges such as tight reservoirs and poor fluidity; medium-low maturity shale oil is characterized by a high proportion of retained hydrocarbons and poor mobility; and oil shale requires high-temperature conversion. Addressing the inherent characteristics of these three resource types, this paper systematically reviews the theoretical foundations and key technologies from two dimensions: “CO₂ injection for medium-high maturity shale oil extraction” and “in situ conversion of medium-low maturity shale/oil shale”. The results indicate that CO₂ injection technology for medium-high maturity shale oil utilizes its supercritical diffusion properties to reduce miscibility pressure by 40–60% compared to conventional reservoirs, efficiently displacing crude oil in nanopores while establishing a geological storage system for greenhouse gases, thereby pioneering an integrated “displacement–drive–storage” model for carbon-reduced oil production. The autothermic pyrolysis in situ conversion process for medium-low maturity shale/oil shale significantly reduces costs by leveraging the oxidation latent heat of kerogen. Under temperature and pressure conditions of 350–450 °C, the shale pore network expansion rate reaches 200–300%, with permeability increasing by two orders of magnitude. Assisted natural gas injection further optimizes the thermal field distribution within the reservoir. Future research should focus on two key directions: synergistic cost reduction and carbon sequestration through CO₂ injection, and the matching of in situ conversion with complex fracture networks. This study delineates key technological pathways for the low-carbon and efficient development of different types of organic-rich shale, contributing to energy security. Full article

This study presents a techno-economic assessment of a modular, solar-assisted methane pyrolysis pilot plant designed for sustainable hydrogen production in Nigeria using concentrated solar power (CSP). Driven by the need to convert flare gas into value and reduce emissions, the work evaluates a hypothetical 100 kg/day hydrogen system by integrating a methane pyrolysis reactor with a solar heliostat–receiver field. Process modelling was carried out in DWSIM, while solar concentration behavior was represented using Tonatiuh. The mass–energy balance results show a hydrogen output of 3.95 kg/h accompanied by 12.30 kg/h of carbon black, with the reactor demanding roughly 44 kW of high-temperature heat at 900 °C. The total capital cost of the ≈50 kW pilot plant is approximately USD 1.5 million, with heliostat and receiver technologies forming the bulk of the investment. Annual operating costs are estimated at USD 69,580, alongside feedstock expenses of USD 43,566. Using annualized cost and discounted cash flow approaches, the resulting levelized cost of hydrogen (LCOH) is USD 5.87/kg, which is competitive with off-grid electrolysis in the region, though still above blue and gray hydrogen benchmarks. The results indicate that hydrogen cost is primarily driven by solar field capital expenditure and carbon by-product valorization. Financial indicators reveal a positive NPV, a 13% IRR, and a 13-year discounted payback period, highlighting the promise of solar-assisted methane pyrolysis as a transitional hydrogen pathway for Nigeria. Full article

Refuse-derived fuel (RDF) presents a viable strategy to concurrently address the challenges of municipal solid waste management and the need for alternative energy. In this context, the present review systematically synthesizes recent advances in RDF preparation, combustion behavior, and efficient utilization technologies. The study examines the full chain of RDF production—including waste selection, mechanical/optical/magnetic sorting, granulation, briquetting, and chemical modification—highlighting how pretreatment technologies influence fuel homogeneity, calorific value, and emissions. The thermochemical conversion characteristics of RDF are systematically analyzed, covering the mechanism differences among slow pyrolysis, fast pyrolysis, flash pyrolysis, pyrolysis mechanisms, catalytic pyrolysis, fragmentation behavior, volatile release patterns, and kinetic modeling using Arrhenius and model-free isoconversional methods (e.g., FWO). Special attention is given to co-firing and high-efficiency combustion technologies, including ultra-supercritical boilers, circulating fluidized beds, and rotary kilns, where fuel quality, ash fusion behavior, slagging, bed agglomeration, and particulate emissions determine operational compatibility. Integrating recent findings, this review identifies the key technical bottlenecks—feedstock variability, chlorine/sulfur release, heavy-metal contaminants, ash-related issues, and the need for standardized RDF quality control. Emerging solutions such as AI-assisted sorting, catalytic upgrading, optimized co-firing strategies, and advanced thermal conversion systems (oxy-fuel, chemical looping, supercritical steam cycles) are discussed within the broader context of carbon reduction and circular economy transitions. Overall, RDF represents a scalable, flexible, and high-value waste-to-energy pathway, and the review provides insights into future research directions, system optimization, and policy frameworks required to support its industrial deployment. Full article

Spent coffee grounds (SCG) are an abundant, carbon-rich residue that can be valorized through thermochemical conversion into biochar. Conventional CO₂ activation is typically performed in a two-step process, which is time- and energy-consuming. This study aims to evaluate whether a one-step CO₂-assisted pyrolysis can produce biochar with comparable or enhanced structural and textural properties while simplifying the process. We compare a two-step pyrolysis process followed by CO₂ activation with a one-step CO₂-assisted route for producing biochar from SCG. CO₂ treatment markedly increases surface area (from 9.8 m²∙g⁻¹ to 550.6–671.0 m²∙g⁻¹) and pore volume. FTIR and Boehm titration indicate depletion of oxygenated surface groups, while N₂ adsorption–desorption analyses and SEM reveal a more uniform micro/mesoporous texture for the one-step sample. Although fixed carbon decreases due to gasification, the one-step route delivers superior textural properties in a single thermal stage, reducing energy demand. These results highlight one-step CO₂-assisted pyrolysis as an efficient, scalable option for producing high-porosity biochar from coffee waste. Full article