Fuels, Volume 6, Issue 3 (September 2025) – 5 articles

Alternative energies have become relevant in global strategies to address climate change, and third-generation biodiesel derived from the generation of lipids from microalgae represents a viable option. This process can also be coupled with wastewater treatment to remove organic matter. To determine the effects of two catalyst levels (1 and 1.5% KOH) and two molar ratios of alcohol (methanol) with oil (1:6 and 1:9) on the conversion of lipids into FAMEs and the quality of the biodiesel produced, this work suggests a method for the ultrasonication-based extraction of lipids from C. vulgaris. It also employs an experimental 2² design and three replicates. It was found that with a molar ratio of 1:9 and a 1% catalyst, the highest yield of 98.48 ± 1.13% was achieved. The FAME profile was similar to the profiles obtained in cultures with bold basal medium or INETI. The quality of the biodiesel met ASTM standards, achieving refractive indices of 1.435–1.478. The flash point (FP) was 165 ± 18 °C, and the acid number was 0.31 ± 0.17 mg KOH/g. The viscosity ranged from 4.33 to 4.87 mm²/s. However, the rheological behavior was correlated with the Ostwald–de Waele model with pseudoplastic behavior. Full article

The global energy sector is aiming to substantially reduce CO₂ emissions to meet the UN climate goals. Among the proposed strategies, underground storage solutions such as radioactive disposal, CO₂, NH₃, and underground H₂ storage (UHS) have emerged as promising options for mitigating anthropogenic emissions. These approaches require rigorous research and development (R&D), often involving laboratory-scale experiments to establish their feasibility before being scaled up to pilot plant operations. Microorganisms, which are ubiquitous in laboratory environments, can significantly influence geochemical reactions under variable experimental conditions of porous media and a salt cavern. We have selected a consortium composed of Bacillus sp., Enterobacter sp., and Cronobacter sp. bacteria, which are typically present in the laboratory environment. These microorganisms can contaminate the rock sample and develop experimental artifacts in UHS experiments. Hence, it is pivotal to sterilize the rock prior to conduct experimental research related to effects of microorganisms in the porous media and the salt cavern for the investigation of UHS. This study investigated the efficacy of various disinfection and sterilization methods, including ultraviolet irradiation, autoclaving, oven heating, ethanol treatments, and gamma irradiation, in removing the microorganisms from silica sand. Additionally, the consideration of their effects on mineral properties are reviewed. A total of 567 vials, each filled with 9 mL of acid-producing bacteria (APB) media were used to test killing efficacy of the cleaning methods. We conducted serial dilutions up to 10⁻⁸ and repeated them three times to determine whether any deviation occurred. Our findings revealed that gamma irradiation and autoclaving were the most effective techniques for eradicating microbial contaminants, achieving sterilization without significantly altering the mineral characteristics. These findings underscore the necessity of robust cleaning protocols in hydrogeochemical research to ensure reliable, reproducible data, particularly in future studies where microbial contamination could induce artifacts in laboratory research. Full article

This study presents a comprehensive characterization of oak biochar produced via downdraft gasification at 850 °C. The research employs a wide range of advanced analytical techniques to examine the biochar’s physical, chemical, and structural properties. Scanning electron microscopy (SEM) revealed a mesoporous structure, while Brunauer–Emmett–Teller (BET) analysis showed a surface area of 88.97 m²/g. Thermogravimetric analysis (TGA) demonstrated high thermal stability and carbon content (78.7%). X-ray photoelectron spectroscopy (XPS) and ultimate analysis confirmed the high degree of carbonization, with low O/C (0.178) and H/C (0.368) ratios indicating high aromaticity. Fourier transform infrared spectroscopy (FTIR) identified functional groups suggesting potential for CO₂ adsorption. The biochar exhibited a negative zeta potential (−31.5 mV), indicating colloidal stability and potential for soil amendment applications. X-ray diffraction (XRD) and Raman spectroscopy provided insights into the biochar’s crystalline structure and graphitization degree. These findings highlight the oak biochar’s suitability for diverse applications, including soil improvement, carbon sequestration, and environmental remediation. By filling knowledge gaps in oak-specific biochar research, this study underscores the benefits of optimized downdraft gasification and sets a foundation for future advancements in sustainable biochar applications. Full article

In bulk liquid or on solid surfaces, nanobubbles (NBs) are gaseous domains at the nanoscale. They stand out due to their extended (meta)stability and great potential for use in practical settings. However, due to the high energy cost of bubble generation, maintenance issues, membrane bio-fouling, and the small actual population of NBs, significant advancements in nanobubble engineering through traditional mechanical generation approaches have been impeded thus far. With the introduction of the electric field approach to NB creation, which is based on electrostrictive NB generation from an incoming population of “electro-fragmented” meso-to micro bubbles (i.e., with bubble size broken down by the applied electric field), when properly engineered with a convective-flow turbulence profile, there have been noticeable improvements in solid-state operation and energy efficiency, even allowing for solar-powered deployment. Here, these innovative methods were applied to a selection of upstream and downstream activities in the oil–water–fuels nexus: advancing core flood tests, oil–water separation, boosting the performance of produced-water treatment, and improving the thermodynamic cycle efficiency and carbon footprint of internal combustion engines. It was found that the application of electric field NBs results in a superior performance in these disparate operations from a variety of perspectives; for instance, ~20 and 7% drops in surface tension for CO₂- and air-NBs, respectively, a ~45% increase in core-flood yield for CO₂-NBs and 55% for oil–water separation efficiency for air-NBs, a rough doubling of magnesium- and calcium-carbonate formation in produced-water treatment via CO₂-NB addition, and air-NBs boosting diesel combustion efficiency by ~16%. This augurs well for NBs being a potent agent for sustainability in the oil and fuels sector (whether up-, mid-, or downstream), not least in terms of energy efficiency and environmental sustainability. Full article

This research work seeks to introduce eco-friendly, low-carbon, and high-octane biofuel gasoline production using a synergistic approach. Four types of high-octane gasoline, including SynergyFuel-92, SynergyFuel-95, SynergyFuel-98, and SynergyFuel-100, were generated, emphasizing the deliberate combination of petroleum-derived gasoline fractions using reformate, isomerate, and delayed coking (DC) naphtha with octane-boosting compounds—bio-methanol and bio-ethanol. A set of tests have been performed to examine the effects of antiknock properties, density, oxidation stability, distillation range characteristics, hydrocarbon composition, vapor pressure, and the volatility index on gasoline blends. The experimental results indicated that the gasoline blends made from biofuel (SynergyFuel-92, -95, -98, and 100) showed adherence to important fuel quality criteria in the USA, Europe, and China. These blends had good characteristics, such as low quantities of benzene and sulfur, regulated levels of olefins and aromatics, and good distillation qualities. By fulfilling these strict regulations, Synergy Fuel is positioned as a competitive and eco-friendly substitute for traditional gasoline. The results reported that SynergyFuel-100 demonstrated the strongest hot-fuel-handling qualities and resistance to vapor lock among all the mentioned Synergy Fuels. Finally, the emergence of eco-friendly, low-carbon, and high-octane biofuel gasoline production with synergistic benefits is a big step in the direction of sustainable transportation. Full article