Search Results (297)

Long-chain n-alkane hydroisomerization is a key catalytic route for upgrading wax-rich, bio-derived, and synthetic hydrocarbon feedstocks into diesel fuels, sustainable aviation fuels, and lubricant base oils with improved low-temperature properties. However, selective hydroisomerization remains challenging because mismatches in the spatial proximity and relative strength of metal and acid sites can prolong the residence time of olefin/carbenium-ion intermediates, thereby promoting over-isomerization to multibranched species, deep cracking, and coke formation. This review summarizes recent advances in zeolite-based bifunctional catalysts for long-chain n-alkane hydroisomerization. The catalytic mechanisms are first discussed, including metal-catalyzed dehydrogenation/hydrogenation, acid-catalyzed skeletal rearrangement, and shape-selective pathways governed by pore-mouth and key-lock effects. Catalyst construction strategies are then outlined, with emphasis on the preparation of zeolite supports and the introduction and localization of metal sites. Subsequently, structure–performance relationships are reviewed from the perspectives of support properties, metal site characteristics, and promoter effects, followed by a concise assessment of catalyst performance with real feedstocks under industrially relevant conditions. Finally, this review provides guidance for the precise design of metal–acid bifunctional hydroisomerization catalysts by highlighting descriptor-guided optimization, spatially regulated metal–acid–pore architectures, multiscale characterization and modeling, and scalable catalyst construction under practical reaction conditions. Full article

This study investigates the integration of CO₂/H₂S separation and internal power generation in power- and biomass-to-liquid (PBtL) and fuel-assisted PBtL (FAPBtL) processes to enhance carbon efficiency and reduce external electricity demand. Four configurations (PBtL, FAPBtL-recycle, FAPBtL-purge, and Purge-to-Fuel (Purge-tF)) are evaluated through detailed mass and energy balances, thermal integration analysis, and techno-economic assessment. Reintegration of separated CO₂ eliminates carbon losses in the acid gas removal unit, increasing carbon efficiencies to approximately 98% for PBtL and Purge-tF, 97% for FAPBtL-recycle, and 79% for FAPBtL-purge. Increasing the carbon efficiency from 91% to 98%, for PBTL, comes from capturing 85% of the CO₂ downstream of the acid gas removal unit. In parallel, integration of a supercritical two-step reheat Rankine cycle with preheating enables the recovery of high-temperature process heat, increasing cycle efficiency from 42% to 55% and generating up to 61 MW of internal power. Although CO₂/H₂S separation introduces additional capital and energy requirements, the combined integration of carbon recycling and heat-to-power recovery improves overall system performance. The Purge-tF configuration achieves the lowest net production cost of 2.60 €/kg_fuel (2.11 €/L_fuel). Sensitivity analysis confirms electricity price as the dominant economic driver. The results demonstrate that strategic integration of carbon recycling and advanced heat recovery can substantially improve both the carbon utilization and economic viability of biomass-based synthetic fuel production. Full article

Decarbonizing the aviation sector remains one of the most challenging aspects of the global energy transition because commercial aviation relies on high-energy-density liquid hydrocarbon fuels that cannot be readily replaced by electrification or hydrogen in the near term. Sustainable Aviation Fuel (SAF) has emerged as a viable solution for reducing lifecycle greenhouse gas (GHG) emissions while maintaining compatibility with existing aircraft, engines, and fuel infrastructure. This review presents an assessment of renewable biomass, waste-derived feedstocks, and captured CO₂ as sustainable carbon resources for SAF production. This study compares biological, thermochemical, electrochemical, and catalytic routes. Comparative evaluation indicates that no single technology can independently satisfy future aviation fuel demand; instead, integrated, feedstock-flexible circular-carbon biorefineries combining complementary conversion technologies provide the most promising route toward large-scale SAF deployment. Finally, this review identifies key research gaps and commercialization barriers, highlighting feedstock availability, renewable hydrogen integration, standardized sustainability assessment, and integrated biorefinery development as critical priorities for advancing scalable, ASTM-compliant, low-carbon aviation fuels and supporting the transition toward net-zero aviation. Full article

Sustainable aviation fuel is among the most practical near-term routes for aviation decarbonization because it can be used in existing aircraft, engines, and airport fuel systems with limited infrastructure changes while minimizing disruption to the aviation fuel supply chain. This review examines SAF applications in aerospace propulsion systems, focusing on production pathways, aero-engine compatibility, property prediction, and fuel heat sink potential. It compares hydroprocessed esters and fatty acids (HEFA), Fischer–Tropsch (FT), alcohol-to-jet (ATJ), synthesized iso-paraffins (SIP), and power-to-liquid (PtL) fuels in terms of feedstock type, process complexity, product composition, and blending constraints. It also assesses how molecular composition governs density, cold-flow behavior, thermal stability, coking propensity, seal compatibility, and emissions. Recent advances in molecular dynamics, machine learning, spectroscopic analysis, and uncertainty quantification show a shift from empirical estimation toward composition-based prediction, prescreening, and fuel design. For high-thermal-load propulsion systems, SAF is further evaluated as a fuel heat sink in active regenerative cooling. Current evidence points to advantages in thermal stability and low coking tendency, but important gaps remain in transcritical and supercritical heat transfer, pyrolytic heat absorption, wall-material effects, coke deposition, and heat sink capacity modeling across wide operating ranges. Full article

Sustainable aviation is an ever-growing field, with feasibility, safety, and longevity being key areas of concern. Future electric aircraft will rely on multiple energy sources. Batteries can provide a fast response to changes in power demands, and fuel cells offer high energy density for prolonged operation. This work has developed an energy management strategy (EMS) aimed to minimise the overall energy consumption from these sources. The EMS is further designed to respect the operational limits of each component. It investigates three EM approaches to account for the hydrogen consumption restriction, namely the unconstrained method, the fixed-limit method, and a novel depletion-aware method. The unconstrained method assumes there is an unlimited amount of hydrogen, meaning it uses 14.81% more hydrogen than is available, whereas the fixed-limit approach applies the maximum amount of hydrogen available within the fuel tank. However, when there is no hydrogen available, the fuel cell shuts down immediately. This work introduces a novel depletion-aware approach which is conscious of reaching the hydrogen supply minimum limit and, hence, allows for greater use of the battery energy during this period. This allows for better coordination between the battery and fuel cell. The three EMSs are simulated and verified in MATLAB/SIMULINK. The simulation results are then validated using software-in-the-loop in dSPACE. The work demonstrates that the depletion-aware approach has distinct benefits compared to the other two methods as it constrains the fuel consumption and allows a smoother transition between energy storage devices and provides a scalable energy management strategy applicable to a range of all-electric and hybrid-electric aircraft. Full article

Surface congestion and taxiing delays at high-density airports increasingly constrain aviation sustainability, as ground-phase fuel consumption and emissions constitute a significant share of total airport emissions. Existing studies typically decouple air traffic flow management from ground resource scheduling, hindering coordinated optimization of punctuality, environmental benefits, and resource utilization. This paper proposes a multi-objective optimization method for runway-taxiway systems oriented toward air–ground collaborative decision-making, integrating Calculated Take-Off Time (CTOT) compliance constraints. A tri-objective mixed-integer programming model is formulated to minimize CTOT deviation, total taxiing time, and runway workload imbalance. A hybrid intelligent algorithm, SSA-SCA-NSGA-II, is designed with a bidirectional elite feedback mechanism to address this NP-hard problem. Validation uses real operational data of 58 departure flights during a peak period at Beijing Daxing International Airport. The results demonstrate that the proposed method achieves effective trade-offs on the Pareto front: CTOT compliance rate increased from 77.6% to 89.7–96.6%; total taxiing time decreased from 692 min to 551–635 min; and dual-runway utilization imbalance declined from 5.2% to 1.7–3.8%. These improvements translate into quantifiable sustainability gains: fuel consumption is reduced by 1425–3525 kg and CO₂ emissions by 4503–11,139 kg per peak hour, alongside a 19-percentage point improvement in punctuality that lowers passenger delay costs and reduces controller coordination workload. By simultaneously advancing environmental sustainability (carbon footprint reduction), economic sustainability (fuel and operational cost savings), and social sustainability (service punctuality and labor efficiency), the framework provides a measurable, monitorable, and policy-relevant decision-support tool for green airport surface operations aligned with sustainable development goals (SDGs). Full article

The development of efficient, low-cost hydrodeoxygenation (HDO) catalysts is essential for converting renewable lipids into sustainable aviation fuels. Here, we report a series of sulfided bimetallic NiFe/γ-Al₂O₃ catalysts and systematically investigate the promotional role of Fe in the HDO of methyl decanoate, a model lipid compound. Using complementary characterization together with fixed-bed reactor kinetic measurements, we elucidate the influence of the Ni/Fe ratio on catalyst structure, sulfidation behavior, electronic properties, and reaction pathway. Fe incorporation promotes Ni sulfidation and induces electron transfer from Fe to Ni, as directly evidenced by a red shift in the CO stretching frequency (from 2094 cm⁻¹ for Ni-only to 2090 cm⁻¹ for NiFe), indicating increased electron density on Ni sites and enhanced π-backdonation. Among the catalysts tested, N5F5 (Ni/Fe mass ratio = 1:1) exhibits the highest Ni sulfidation degree, the highest turnover frequency (32.1 h⁻¹), and the lowest apparent activation energy (E_a ≈ 92 kJ/mol). At 360 °C, it achieves 52.9% methyl decanoate conversion, far exceeding that of monometallic Ni and Fe catalysts. Product selectivity analysis reveals that sulfided Ni sites predominantly promote the decarboxylation/decarbonylation (DCOx) pathway, whereas Fe sites contribute only marginally to direct deoxygenation (DDO). This work provides the first direct spectroscopic evidence for Fe-to-Ni electron transfer in sulfided NiFe catalysts and establishes a clear structure-performance correlation, offering a rational design strategy for low-cost, high-performance HDO catalysts for lipid upgrading. Full article

This integrative critical review examines how biomass and bioenergy can contribute to energy diversification while accounting for constraints related to climate mitigation, energy security, resource availability, and technology readiness. The review combines a targeted literature synthesis with expert-informed insights from the international seminar Energy Transition and Biofuels held at the Federal University of Itajubá in October 2025. The seminar and COP30-related discussions were used as contextual and conceptual inputs, while peer-reviewed literature, policy documents, and technical reports provided the evidentiary basis for the analysis. The manuscript evaluates biomass and biofuels utilization, refinery integration, sustainable aviation fuels, biochar, BECCS, hydrogen synergies, life-cycle assessment, artificial intelligence, and logistics. The synthesis indicates that biomass is not a universal substitute for fossil fuels. Still, it has distinctive value in applications requiring renewable carbon, dispatchable energy, process heat, liquid fuels, carbon removal, and compatibility with existing infrastructure. The analysis also shows that these contributions are contingent on feedstock governance, land and water safeguards, logistics, fertilizer inputs, technology maturity, and verified life-cycle performance. The food–fuel discussion is therefore reframed as a context-specific problem of land-use, access, productivity, and governance rather than a simple competition between energy and food production. The study concludes that bioenergy can most credibly support the energy transition when deployed through differentiated pathways tailored to regional resources, sustainability constraints, and sector-specific decarbonization requirements. Full article

To mitigate the environmental footprint of the aviation sector, this study proposes an integrated cascading biorefinery scheme to produce Sustainable Aviation Fuel (SAF) precursor bloodstock via enzymatic transesterification of coconut oil. Utilizing a synergistic binary alcohol system (ethanol-butanol) and the liquid lipase Eversa Transform 2.0, a strategic molecular reconfiguration of fatty acid esters was achieved. Optimization through Response Surface Methodology (RSM) identified critical parameters—5% catalyst loading, total binary alcohol-to-oil molar ratio of 7:1 (specifically comprised of a 2.5:4.5:1 ethanol/butanol/coconut oil matrix), and an operation temperature of 57.5 °C—yielding a 97% conversion efficiency. A sequential vacuum fractional distillation process was implemented to partition the ethyl-butyl esters into high-value streams. Notably, the light distillate fraction, characterized by a specific carbon chain distribution (C6: 27.2%, C8: 52.5%, C10: 6%, and C12: 13.6%), perfectly aligns with the molecular window of aviation kerosene. This fraction exhibits excellent cold-flow properties, viscosity, and volatility profiles, positioning it as an ideal high-performance SAF precursor blendstock to increase the renewable content of current aviation fuels. Simultaneously, the remaining C16–C18 residue serves as a high-density energy source for internal refinery processes, while C8–C14 species are recovered as high-purity chemical feedstocks. This circular model maximizes carbon atom economy and economic viability by cogenerating high added-value biochemicals alongside jet-grade blendstocks. These findings provide a scalable, enzymatic framework for the next generation of decarbonized aviation fuels. Full article

Under the background of the green transformation and energy conservation in the aviation field, hydrogen-fueled aero-engines are the primary direction for achieving sustainable aviation power development. However, the unique thermophysical properties of hydrogen fuel induce extreme thermal load challenges to engine thermal management. Based on the requirements of energy conservation and digital-intelligent technologies, this paper reviewed the recent research progress, important challenges, and future development directions in the thermal management field for hydrogen-fueled aero-engines, and filled the gaps in existing related reviews. (1) As for the liquid hydrogen thermal properties and thermal management requirements, the unique thermal physical properties of liquid hydrogen can easily cause fluctuations in heat load, large temperature differences, and material compatibility issues such as hydrogen embrittlement during storage, transportation, and combustion. The application of thermal barrier coatings, the design of targeted cooling structures, and the regulation of heat loss in the pipeline of the hydrogen supply system require particular attention. (2) As for the technical architecture and optimization of thermal management, the optimization of the high-pressure side manifolds in the cooled cooling air heat exchanger increases the flow uniformity by 18.8% and reduces the weight by 22.5%. The intercooled recuperated engine with the optimum area ratio reduces specific fuel consumption by 5.3% compared to the baseline engine in cruise. However, the system-level optimization research of the above widely recognized solutions is relatively limited in terms of coordinating the energy flow of engines. The baseline engine employed the method of system integration optimization to achieve a 2.99% increase in thrust and a 6.78% reduction in fuel consumption. (3) As for the thermal management modeling and simulation, the intelligent optimization method based on computational fluid dynamics reduces the pressure loss coefficient of the vane-integrated heat exchanger by 36%. Nevertheless, the multiphysics coupling model confronts a contradiction between computational cost and accuracy. (4) As for the comprehensive evaluation method, the advanced configuration of the hydrogen-fueled aero-engine can approximately reduce specific fuel consumption by 68.5% and NOx emission by 12.7% under the same maximum thrust condition. The hydrogen consumption of the proton exchange membrane fuel cells system model compared with the baseline system, optimized by the multi-objective optimization algorithm, has decreased by 15%, while the thermal uniformity has improved by 20–30%. However, the current evaluation system mostly focuses on a single dimension, lacking the analysis of nonlinear coupling among multiple factors and a closed-loop mechanism for evaluation, optimization, and verification. Future research should focus on the matching model of liquid hydrogen’s thermophysical properties and full flight conditions, global multi-energy flows optimization methods, multidimensional collaborative numerical simulation, multiphysics coupling models, and multidimensional comprehensive evaluation systems, to provide closed-loop theoretical support for the efficient, intelligent, and reliable thermal management system for hydrogen-fueled aero-engines. Full article

The safe and accurate measurement of liquid hydrogen (LH₂) tank fill levels is a critical enabling technology for the adoption of hydrogen as a sustainable aviation fuel. Although LH₂ fill level measurement techniques have been applied in industrial, automotive, and space applications, no system has yet been validated at the scale, robustness, and precision required for modern aircraft Fuel Quantity Indication Systems (FQIS). Differentialpressure sensors are commonly employed in industrial cryogenic systems and hydrogen refueling stations; however, their accuracy is strongly influenced by dynamic effects such as filling transients and liquid sloshing, rendering them unsuitable for aviation-grade FQIS requirements which call for high accuracy and reliability. While simulations and analytical studies propose alternative LH₂ level sensing concepts, experimental validation and direct comparative assessments of different sensor architectures remain scarce. Furthermore, although several manufacturers offer LH₂ fill-level sensors, the stated measurement accuracies have not been independently verified, highlighting the need for systematic experimental investigation under representative operating conditions. A complete evaluation of an ${\mathrm{LH}}_2$ FQIS requires testing under anticipated flight conditions, including accelerations, varying attitudes, vibrations, dynamic sloshing, and long-term cycling. As a preliminary investigation, this work experimentally evaluates five liquid level sensing concepts based on measurements of dielectric constant, thermal capacity, and optical absorption properties using liquid nitrogen (${\mathrm{LN}}_2$) as a representative surrogate for ${\mathrm{LH}}_2$ under quasi-static conditions. The results demonstrate that optical absorption-based sensors in the near-infrared spectrum are unsuitable for LH₂ and LN₂ liquid level measurement. In contrast, capacitive probes and resistive thermal devices (RTDs) exhibit robust and repeatable performance under cryogenic conditions, demonstrating measurement resolutions of better than $5.1\mathrm{mm}$. These findings provide experimentally grounded guidance for the development of future LH₂-compatible FQIS architectures for aviation applications. Full article

The development of low-emission and reliable propulsion systems is essential for extending the operational capability of unmanned aerial vehicles (UAVs). Although aviation decarbonization is widely recognized as an important objective, it must be considered within the broader context of limited renewable-energy availability. Recent system-level analyses of transportation decarbonization have shown that the allocation of renewable electricity and sustainable fuels should prioritize sectors where direct electrification is most efficient, while hard-to-electrify sectors require alternative pathways. Aviation is one of the most difficult transport sectors to electrify because of strict energy-density requirements, especially for long-endurance airborne platforms. Therefore, sustainable liquid fuels and hybrid propulsion systems should not be considered universal replacements for electrification, but rather complementary solutions for applications where batteries alone cannot provide the required endurance, payload capacity or operational flexibility. In this context, the present study focuses on alcohol–kerosene blends for hybrid UAV power systems, where liquid-fuel energy density and partial emission reduction remain relevant engineering requirements. This work provides one of the first systematic experimental evaluations of ethanol–, butanol– and octanol–kerosene blends in a micro-turboprop engine operating as part of a hybrid UAV power-generation architecture. Unlike previous studies focused mainly on micro-turbojet thrust response, the present work evaluates the coupled influence of alcohol chain length and blending ratio on exhaust gas temperature, gaseous emissions, electrical output and operational stability under multi-load conditions representative of UAV operation. Jet-A and nine alcohol–kerosene blends containing 10%, 20% and 30% ethanol, butanol or octanol by volume were tested over four operating regimes, from idle to 2500 W electrical load. The results show that ethanol blends provided the strongest CO reduction, with E30 reducing CO by 24.9% relative to Jet-A under R3, while E10 offered the most balanced behavior across the full operating range. Higher ethanol fractions improved CO suppression but introduced NOx and low-load stability penalties. Octanol blends, particularly O20, exhibited the most kerosene-like and stable response, supporting reliable power delivery with reduced operational variability. Butanol blends showed intermediate behavior without providing a dominant advantage. A multi-criteria evaluation combining emissions, EGT behavior, relative performance, operational stability and cost identified E10 as the best overall compromise for hybrid UAV use. The study demonstrates that alcohol chain length produces nonlinear system-level effects in hybrid micro-turboprop architectures and provides an experimental basis for fuel selection in low-emission UAV power systems. Full article

Municipal solid waste (MSW) management is a critical challenge to advancing recycling and circular economy approaches. This review provides a comprehensive overview of MSW management, encompassing sourcing, policy frameworks, characterization techniques, separation technologies, preprocessing strategies, and utilization pathways. First, generation patterns and sourcing mechanisms are discussed in both U.S. and global contexts, with emphasis on the influence of policy frameworks on waste reduction and diversion. Second, characterization techniques are evaluated, focusing on physical and chemical analysis for material recyclability. Third, sorting technologies are critically reviewed, covering conventional methods and emerging sensor-based approaches. Preprocessing techniques are then evaluated for their role in improving downstream conversion efficiency. Finally, valorization pathways such as waste-to-syngas, waste-to-biochar, and waste-to-sustainable aviation fuel (SAF) are assessed in terms of their role in climate mitigation and the circular economy. It is anticipated that this review will provide a foundational reference for researchers, policymakers, and industry stakeholders aiming to strengthen the recyclability infrastructure and maximize the efficiency of MSW management systems in the framework of the circular economy. Full article

The aim of this paper is to give an overview of emerging technologies for the greening of aviation, how they can be applied to different classes of aircraft, and the challenges to be overcome in achieving efficiency and environmental objectives. The following steps are part of the journey towards the greening of aviation: (i) developing and maturing new technologies, including electrification and sustainable fuels; (ii) where possible, using new technologies in the current fleet to maximize short-term benefits—i.e., EU Fit for 55; (iii) when it is not possible to retrofit new technologies to current aircraft, incorporating them into new next-generation aircraft designs from 2035; and (iv) replacing existing fleets with new, cleaner aircraft to meet the ICAO Net Zero 2050 goal. These technologies of prime importance will have to be supplemented by operational, regulatory, and economic enablers to support wide deployment. There will not be one solution that meets the requirements of all aircraft classes or mission profiles, but rather a combination of electrification, hydrogen propulsion, and sustainable aviation fuels will be required. Achievement of aviation’s environmental goals will hence not solely be a function of technological progress but also certification pathways, investment in infrastructure, and integrated policy strategies. Full article

Recirculating organic byproducts like food waste, wastewater and manure efficiently and at scale in a circular bioeconomy will be critical to ensuring future food security, energy security, climate resilience, water security and environmental health. Ultimately, we will not be able to live within the safe operating space of our planetary boundaries if we do not stop our wasteful and inefficient habits. Our food, waste, energy and water sectors are starting to transform towards circularity, driven by a diverse range of drivers, from net zero emissions targets, to food waste policies, and to rising fertiliser prices and geopolitical risks. However, these sectors are often not transforming in a coordinated manner, risking unintended consequences like competition between end-uses, technology lock-in, the prevention of scalability, or failure to achieve key sustainability targets, causing rebound effects. For example, society’s organic waste is being earmarked for the production of bioenergy, sustainable aviation fuels, biomaterials, and biofertilisers; however, it is not clear if there will be a sufficient supply of organic waste to meet these diverse demands. Phosphorus flow analyses indicate that we will need to secure almost all of the nutrients in organic waste as fertiliser raw material to produce food. There are some existing pockets of innovation within sectors related to food waste, water and wastewater, fertilisers and agriculture, and bioenergy. However, many initiatives are being driven by short-term challenges, are not operating at scale, or are not sufficiently integrated across sectors. In this paper, we provide examples of innovations and challenges from around the world, including Italy, Australia, Sri Lanka, the UK, Japan, and Malawi. This paper identifies a pathway to navigate tensions to achieve co-existing sustainability goals, including key enablers and barriers, ranging from overcoming regulatory fragmentation to a lack of capital investments. Creating a truly viable circular economy for organic byproducts requires the integration of policies, markets, technologies and people. This means engaging diverse stakeholders, from local councils and private waste contractors, farmers, and fertiliser companies to energy retailers and wastewater utilities, NGOs, informal collectors, and environmental regulators and policy-makers. Full article