Search Results (58)

Bio-jet fuels produced from biomass-derived feedstocks represent a promising pathway for reducing the carbon intensity of aviation energy systems. However, designing supply chain networks for bio-jet fuel production requires solving large-scale mixed-integer linear programming (MILP) models that integrate facility location, feedstock allocation, material flows, and routing decisions. These models can become computationally expensive, particularly when evaluating multiple network configurations or large candidate sets of production and processing facilities. This study develops a hybrid machine learning and optimization framework to improve the computational efficiency of bio-jet fuel supply chain network design while preserving high-quality decision outcomes. The proposed iterative procedure uses supervised learning to approximate the relationship between facility location decisions and total supply chain cost. First, an initial set of supply chain configurations is generated by solving the optimization model while using randomly selected facility locations. These solutions are then used to train predictive models, including ridge regression, feed-forward neural networks, and ensemble neural networks, with facility-location configurations as inputs and total supply chain cost as the output. The trained learner is subsequently used to identify promising facility-location candidates through Thompson sampling and small-scale linear programming. These candidate solutions are evaluated by the original mixed-integer model, and the resulting observations are fed back into the learning process until convergence. Numerical experiments show that the proposed hybrid approach obtains near-optimal bio-jet fuel supply chain designs while substantially reducing computational time. For the linear case, the method achieves solutions within 0.23–0.29% of the objective function value while reducing computational time by 70.95–81.95%. For nonlinear learning models, the optimality gap decreases further to 0.13–0.15%, with computational time reductions of 45.37–60.36%. For the Texas case study and the modeling assumptions evaluated, the findings demonstrate that machine-learning-assisted optimization can reduce computational effort while preserving high-quality supply chain solutions. The extent of these benefits may vary with network size, candidate-facility structure, facility-capacity assumptions, demand characteristics, and the amount of information available to train the learning models. Full article

Co and Mo mono- and bimetallic catalysts supported on CNT-H-ZSM-5 composites were prepared and characterized using various techniques. The catalysts were evaluated for the conversion of sunflower oil (SO) into sustainable aviation fuel (SAF) hydrocarbons in the C₈–C₁₆ range. The effects of reduction temperature and metal loading were the main parameters investigated in this study. The catalyst reduced at 600 °C promoted the formation of Mo₂C species, resulting in high SO conversion (84%), complete deoxygenation, and enhanced isomerization within the C₈–C₁₆ fraction. Optimal metal loadings (2.5 wt% Co and 8 wt% Mo) and the bimetallic configuration led to superior performance compared with monometallic catalysts and physical mixtures, clearly highlighting a synergistic effect between Co and Mo species. In contrast, when waste cooking oil was used as feedstock, lower conversion and reduced selectivity toward SAF-range hydrocarbons were observed, which were attributed to the higher complexity and impurity content of this residue feedstock. Full article

Global energy demand relies heavily on fossil fuels, which produce greenhouse gas emissions. Additionally, municipal solid waste, driven by population growth, represents another source of emissions. In Mexico, organic waste contributes 61 million tons of CO₂eq annually due to inadequate disposal. In Mérida, Yucatan, over 231,000 tons of organic waste are generated yearly, including Urban Tree Pruning (UTP) from 760 public spaces—a significant, undervalued lignocellulosic resource. This study presents a comprehensive, year-round compositional characterization of Mérida’s UTP to establish its chemical profile and assess its seasonal stability as a precursor for bio-based products (i.e., bioethanol). Characterizing local and stable feedstocks, such as UTP, is a fundamental step to enabling Mexico’s compliance with biofuel policies like the 5.8% gasoline blend mandate (NOM-016-CRE) and the Alcohol-to-Jet strategy, supporting progress toward SDGs 7, 11, and 13. Based on a stratified random sampling, monthly analysis (May 2024–April 2025) revealed a consistent biochemical profile with mean annual contents of 23.32% lignin and 62.46% holocellulose. Statistical analysis (Tukey’s test) confirmed its structural homogeneity throughout the year. This uniformity is a key operational attribute, as it allows for the use of standardized industrial pretreatment parameters. Furthermore, the characterized composition supports a theoretical ethanol yield of 170 g/kg of dry biomass, a value competitive with traditional feedstocks like sugarcane bagasse. Consequently, Mérida’s UTP is characterized as a reliable and consistent biomass resource, supporting a transition from linear waste disposal to a circular bioeconomy model. Full article

The transition to sustainable energy systems has intensified the search for renewable alternatives to reduce greenhouse gas emissions and reliance on fossil fuels. In this context, microalgae have emerged as a promising third-generation feedstock for biofuel production due to their rapid development, high lipid content, and ability to grow in wastewater without competing with freshwater resources. In this study, the hydrotreatment of biocrudes derived from C. vulgaris, T. obliquus, and a mixed microalgal culture cultivated in domestic wastewater is investigated. Catalytic upgrading was applied using sulphided CoMo/Al₂O₃ (sCoMo) and Pt/Al₂O₃ catalysts. The results demonstrated that catalytic upgrading enhanced the upgraded bio-oils’ quality compared to non-catalysed reactions, confirming the crucial role of catalysts in improving bio-oil properties. Compared with the Pt catalyst, sCoMo produced higher yields of upgraded bio-oil, greater enrichment in carbon and hydrogen, and higher heating value (HHV), while effectively enhancing nitrogen and oxygen removal. However, when compared with the non-sulphided CoMo, the sulphiding treatment did not significantly improve denitrogenation and treated oil yields. The highest fraction of components within the jet fuel boiling range (37.7%) was obtained using a Pt catalyst, while the non-catalysed process yielded the lowest (26.6%). In this sense, catalytic upgrading of microalgae-based biocrude represents an important step towards the production of advanced and environmentally sustainable fuels. Full article

In this study, a techno-economic and carbon footprint (GHG, CO₂-equivalent) analysis was conducted on two alternative biofuels, green diesel and bio-jet fuel, produced from renewable lipids. The focus of the work is the comparison of various lipid feedstocks, including waste cooking oil, and four types of vegetable oils: cardoon, soybean, palm, and sunflower. Process optimization and design were performed to minimize production costs by using the process simulation software Aspen Plus^®. Green diesel and bio-jet fuel were obtained via hydrodeoxygenation and hydroisomerization/hydrocracking, respectively. Sensitivity analyses confirmed consistent results across the tested vegetable oils. Hydrodeoxygenation achieved triglyceride molar conversions exceeding 97%, with overall mass yields into the diesel fraction surpassing 79%. Conversely, hydroisomerization/hydrocracking of green diesel resulted in over 90% conversion of n-paraffins and more than 50% overall mass yield. The economic analysis showed that the primary cost factor influencing the payback selling price of the biofuels is the price of the lipid feedstocks. Biofuels are economically viable only when lipid prices are below 1000 €/ton and hydrogen prices are below 3000 €/ton. An important aspect is also represented by the combined-cycle energy recovery system, which strongly affects the overall capital cost and increases internal power generation efficiency. The carbon footprint calculated over a cradle-to-grave boundary showed shows net GHG reductions versus the fossil reference fuels for all scenarios. Net avoided emissions range from 1.74 to 3.63 kgCO₂-eq/kg green diesel and from 0.80 to 3.70 kgCO₂-eq/kg bio-jet fuel across the investigated feedstocks, approximately 40–84% and 20–95% of the respective savings relative to the fossil reference fuels under the stated background and logistics assumptions. Results are expressed per kg of produced fuel as a functional unit, using literature-derived upstream emission factors for oil supply and background inputs (hydrogen, Italian grid electricity and transport). For the bio-jet configuration, co-product burdens were partitioned by mass; the Discussion section highlights the sensitivity of the GD vs. BJF comparison to co-product handling and allocation choices. In this context, the choice of feedstock is essential in establishing the resulting GHG intensity of the two biofuels. From both economic and climate change perspectives, waste cooking oil emerges as the most promising option, particularly given its classification as waste-derived feedstock in the system boundary, unlike the virgin oil sources. Full article

Microbial contamination of aviation fuels is a persistent operational and safety challenge, compromising fuel quality and accelerating material degradation. The global transition toward sustainable aviation fuels (SAF) amplifies the need to reassess microbial risks across both conventional and alternative fuel systems. Here, we present the first systematic review and meta-analysis to synthesize evidence on microbial prevalence in jet fuel environments and to evaluate implications for SAF deployment. Of 2837 records screened, 37 studies fulfilled the inclusion criteria. Microorganisms were detected in up to 87% of jet fuel systems worldwide (95% CI: 76–100%); however, this pooled estimate was associated with substantial heterogeneity (I² = 96%) and should therefore be interpreted with caution as reflecting an overall trend rather than a precise global value. Taxonomic analysis identified consistently reported bacterial genera (Actinomycetes, Halomonas, Mycobacterium, Nocardioides, Rhodococcus, Stenotrophomonas) and fungal genera (Aspergillus, Alternaria, Amorphotheca, Byssochlamys, Candida, Fusarium, Saccharomyces, Schizosaccharomyces, Talaromyces, Trichocomaceae). Deteriorative organisms dominated (bacteria 57%; fungi 75%) relative to non-deteriorative taxa (12% and 32%, respectively). These findings highlight microbial spoilage as a pervasive and underrecognized threat to fuel integrity. Importantly, they suggest that risks currently documented in conventional systems are likely to extend to SAF, reinforcing the urgent need for proactive monitoring frameworks and bio-contamination mitigation strategies to ensure aviation fuel reliability. Full article

Sustainable aviation fuels (SAFs) are vitally important for aviation decarbonization. The laminar burning velocity (LBV), a key parameter reflecting the combustion behavior of fuel/oxidizer mixtures, serves as a fundamental metric for evaluating SAF performance. This paper systematically reviews and evaluates the LBV experiment method and the performance of traditional aviation fuel, SAFs produced via different pathways, and individual components (n-alkanes, iso-alkanes, cycloalkanes, and aromatic hydrocarbons, as well as the impacts of isomers and homologues) in aviation fuels. It is found that LBV values of different SAFs exhibit significant fluctuations, approaching or slightly deviating from those of conventional aviation fuels. Carbon number, branching degree, substituent types, and testing methods in the components all affect LBV performance. Specifically, increased branching in iso-alkanes reduces LBV, cyclohexane and benzene show higher LBV than their methylated counterparts (methylcyclohexane and toluene), and n-alkylcyclohexanes/benzenes with short (C1–C3) side chains demonstrate minimal LBV variation. Spherical flame methods yield more consistent (and generally lower) LBV values than stagnation flame techniques. These findings provide insights for optimizing SAF–conventional fuel blends and enhancing drop-in compatibility while ensuring operational safety and usability. Full article

The generation of fine coal particles during mining and processing presents significant environmental and logistical challenges, particularly in coal-dependent, developing countries like South Africa (SA). This review critically evaluates the technical viability of fine coal briquetting as a sustainable waste-to-energy solution within a SA context, while drawing from global best practices and comparative benchmarks. It examines abundant feedstocks that can be used for valorization strategies, including fine coal and agricultural biomass residues. Furthermore, binder types, manufacturing parameters, and quality optimization strategies that influence briquette performance are assessed. The co-densification of fine coal with biomass offers a means to enhance combustion efficiency, reduce dust emissions, and convert low-value waste into a high-calorific, manageable fuel. Attention is also given to briquette testing standards (i.e., South African Bureau of Standards, ASTM International, and International Organization of Standardization) and end-use applications across domestic, industrial, and off-grid settings. Moreover, the review explores socio-economic implications, including rural job creation, energy poverty alleviation, and the potential role of briquetting in SA’s ‘Just Energy Transition’ (JET). This paper uniquely integrates technical analysis with policy relevance, rural energy needs, and practical challenges specific to South Africa, while offering a structured framework for bio-coal briquetting adoption in developing countries. While technical and economic barriers remain, such as binder costs and feedstock variability, the integration of briquetting into circular economy frameworks represents a promising path toward cleaner, decentralized energy and coal waste valorization. Full article

The increasing global demand for sustainable energy solutions has intensified the need to replace fossil fuels in gas turbines, particularly in aviation and power generation where alternatives to gas turbines are currently limited. This review explores the feasibility of utilizing sustainable liquid and gaseous fuels in gas turbines by evaluating their environmental impacts, performance characteristics, and technical integration potential. The study examines a broad range of alternatives, including biofuels, hydrogen, alcohols, ethers, synthetic fuels, and biogas, focusing on their production methods, combustion behavior, and compatibility with existing turbine technology. Key findings indicate that several bio-derived and synthetic fuels can serve as viable drop-in replacements for conventional jet fuels, especially under ASTM D7566 standards. Hydrogen and other gaseous alternatives show promise for industrial applications but require significant combustion system adaptations. The study concludes that a transition to sustainable fuels in gas turbines is achievable through coordinated advancements in combustion technology, fuel infrastructure, and regulatory support, thus enabling meaningful reductions in greenhouse gas emissions and advancing global decarbonization efforts. Full article

To address global climate change and the energy crisis, there is an urgent need to meet human demands through utilizing renewable energy sources. The deoxygenation of lipids to produce liquid biofuels has emerged as a promising alternative, particularly for carbon emission reduction in the aviation industry. This review critically examines recent progress in catalyst development and reaction control strategies for lipid deoxygenation. Emphasis is focused on the design of different kinds of catalysts to meet the requirements, including noble metal catalysts, non-noble metal catalysts, and non-noble metal compound catalysts, with strategies such as morphology control, utilization of metal support interactions, and constructing synergistic effects between metal acid centers and metal oxygen vacancies. The reaction networks, mechanisms, and selectivity control strategies for lipid deoxygenation, cracking, isomerization, and aromatization are comprehensively discussed. Finally, we propose that it requires focusing on the precise regulation of multiple active sites to optimizing deoxygenation performance and reusability. It is essential to integrate in situ characterization to deepen the study of structure–active relationships and explore the reaction mechanisms within complex reaction systems. Full article

In the last five years, the use of hydrogen as an energy carrier has received rising attention because it can be used in internal combustion and jet engines, and it can even generate electricity in fuel cells. The scope of this work was to critically review the methods of H₂ production from renewable and non-renewable sources, with a focus on bio-H₂ production from the perennial grass giant reed (Arundo donax L.) due to its outstanding biomass yield. This lignocellulosic biomass appears as a promising feedstock for bio-H₂ production, with a higher yield in dark fermentation than photo-fermentation (217 vs. 87 mL H₂ g⁻¹ volatile solids on average). The H₂ production can reach 202 m³ Mg⁻¹ of giant reed dry matter. Assuming the average giant reed dry biomass yield (30.3 Mg ha⁻¹ y⁻¹), the attainable H₂ yield could be 6060 m³ ha⁻¹ y⁻¹. A synthetic but comprehensive review of methods of H₂ production from non-renewable sources is first presented, and then a more detailed analysis of renewable sources is discussed with emphasis on giant reed. Perspectives and challenges of bio-H₂ production, including storage and transportation, are also discussed. Full article

The co-production of BHD with other renewable fuels (i.e., using a novel process involving carbon dioxide utilization to achieve the global sustainability goal) is presented. The three configurations of BHD production from refined bleached deodorized palm oil (RBDPO), including (1) the conventional BHD process with hydrogen recovery (BHD process), (2) the BHD process coupled with the Fischer–Tropsch process (BHD-FT process), and (3) the BHD process coupled with the bio-jet fuel and methanol processes (BHD-BIOJET-MEOH process) are investigated using the process model developed in Aspen Plus. The effect of the operating parameters is studied, and the condition of each process offering the highest BHD yield is proposed. Then, the pinch analysis and heat exchanger network (HEN) design of each proposed process are performed to find the highest energy-efficient configuration. The economic and environmental analysis is later performed to investigate the sustainability performance of each configuration. The conventional BHD process requires less hydrogen and consumes less energy than the others. The BHD-BIOJET-MEOH process is the most economically feasible, offering the highest net present value (NPV) of USD 7.93 million and the shortest payback period of 3 years and 1 month. However, it offers the highest carbon footprint of 0.820 kgCO₂ eq./kg of BHD, and it presented the highest potential environmental impact (PEI) in all categories. Full article

This paper investigates how the present paths support massive manufacturing by evaluating the existing state of sustainable aviation fuel (SAF) technologies, examining technology readiness levels (TRL), fuel readiness levels (FRL), costs, economic conditions, emissions, etc. This assessment summarizes major conclusions about bio-jet replacements for conventional jet fuels. In order for SAF to play a sustainable role, a full life cycle emissions assessment, techno-economic analysis (TEA), and discussions about the sustainability of SAF materials are required. The life cycle assessment (LCA) discusses the capability of SAF in cutting down emissions, TEA argues for its economic viability, and the sustainable supply of SAF feedstock is a third critical factor determining the sustainability of the industry. With all the analyses, this overview provides recommendations for the sustainable development of the SAF industry and calls on industry stakeholders to enhance cooperation. Full article

This study presents an efficient process for producing sustainable aviation fuel (SAF) from soybean oil through hydrodeoxygenation (HDO) and hydroisomerization (HI). The research utilized a commercial nickel catalyst for the HDO step, and a newly developed platinum catalyst supported on SAPO-11 zeolite for the hydroisomerization (HI) stage. The process parameters, including temperature and pressure, were optimized to maximize conversion efficiency and meet ASTM D7566 standards. The results indicate that the HDO process using the nickel catalyst achieved a high yield of n-alkanes (97.8% ± 0.4%) with complete conversion of triglycerides. In the subsequent hydroisomerization step, the platinum catalyst demonstrated excellent selectivity for Jet-A1 fuel, yielding a bio-jet fraction of 87.5% ± 1.6% in a 200 h continuous test. This study also highlights the minimal coking phenomena and high catalyst stability throughout the process. This work suggests that soybean oil, as a readily available feedstock, could significantly contribute to the production of SAF and reduce greenhouse gas emissions in the aviation sector. Additionally, the optimization of temperature and pressure conditions is crucial for enhancing the yield and quality of the final bio-jet product. Full article

Biofuels’ induced land-use change (ILUC) emissions have been widely studied over the past 15 years. Many studies have addressed uncertainties associated with these estimates. These studies have broadly examined uncertainties associated with the choice of economic models, their assumptions and parameters, and a few bio-physical variables. However, uncertainties in land-use emission factors that represent the soil and vegetation carbon contents of various land types across the world and are used to estimate carbon fluxes due to land conversions are mostly overlooked. This paper calls attention to this important omission. It highlights some important sources of uncertainty in land-use emissions factors, explores the range in these factors from established data sources, and compares the influence of their variability on ILUC emissions for several sustainable aviation fuel (SAF) pathways. The estimated land-use changes for each pathway are taken from a well-known computable general equilibrium model, GTAP-BIO. Two well-known carbon calculator models (CCLUB and AEZ-EF) that represent two different sets of emissions factors are used to convert the GTAP-BIO estimated land-use changes to ILUC emissions. The results show that the calculated ILUC emissions obtained from these carbon calculators for each examined SAF pathway are largely different, even for the same amortization time horizon. For example, the ILUC emissions values obtained from the AEZ-EF and CCLUB models for producing jet fuel from corn ethanol for a 25-year amortization period are 24.9 gCO₂e/MJ and 15.96 gCO₂e/MJ, respectively. This represents a 60% difference between the results of these two carbon calculators for the same set of land-use changes. The results show larger differences for other pathways as well. Full article